Guide to External Curing
of Concrete
Reported by ACI Committee 308
'
I
ex:
00
0
(Y)
u
<(
�
� acI •
�
American Concrete Institute
Always advancing
First Printing
May 2016
American Concrete Institute
Always advancing
ISBN: 978-1-942727-87-3
Guide to External Curing of Concrete
Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material
may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other
distribution and storage media, without the written consent of ACI.
The technical committees responsible for ACI committee reports and standards strive to avoid
ambiguities, omissions, and errors in these documents. In spite of these efforts, the users of ACI
documents occasionally find information or requirements that may be subject to more than one
interpretation or may be incomplete or incorrect. Users who have suggestions for the improvement of
ACI documents are requested to contact ACI via the errata website at http://concrete.org/Publications/
DocumentErrata.aspx. Proper use of this document includes periodically checking for errata for the most
up-to-date revisions.
ACI committee documents are intended for the use of individuals who are competent to evaluate the
significance and limitations of its content and recommendations and who will accept responsibility for
the application of the material it contains. Individuals who use this publication in any way assume all
risk and accept total responsibility for the application and use of this information.
All information in this publication is provided "as is" without warranty of any kind, either express or
implied, including but not limited to, the implied warranties of merchantability, fitness for a particular
purpose or non-infringement.
ACI and its members disclaim liability for damages of any kind, including any special, indirect, incidental,
or consequential damages, including without limitation, lost revenues or lost profits, which may result
from the use of this publication.
It is the responsibility of the user of this document to establish health and safety practices appropriate
to the specific circumstances involved with its use. ACI does not make any representations with regard
to health and safety issues and the use of this document. The user must determine the applicability of
all regulatory limitations before applying the document and must comply with all applicable laws and
regulations, including but not limited to, United States Occupational Safety and Health Administration
(OSHA) health and safety standards.
Participation by governmental representatives in the work of the American Concrete Institute and in
the development of Institute standards does not constitute governmental endorsement of ACI or the
standards that it develops.
Order information: ACI documents are available in print, by download, on CD-ROM, through electronic
subscription, or reprint and may be obtained by contacting ACI.
Most ACI standards and committee reports are gathered together in the annually revised ACI Manual of
Concrete Practice (MCP).
American Concrete Institute
38800 Country Club Drive
Farmington Hills, MI 48331
Phone: +1.248.848.3700
Fax:
+1.248.848.3701
Coovriaht American Concrete Institute
www.concrete.org
ACI 308R-16
Guide to External Curing of Concrete
Reported by ACI Committee 308
Erik Holck, Vice Chair
David M. Suchorski, Chair
Lawrence Homer Taber', Secretary
Voting Members
Dale P. Bentz
Sidney Freedman
Michael
Dianne Carey
G.
Hernandez
John C. Hukey
Jennifer K. Crisman
Jonathan E. Dongell
Cecil L. Jones
Michael Faubel
Frank A. Kozeliski
Dale Fisher
Ronald L. Kozikowski Jr.
Richard E. Van Horn
Mauricio Lopez
Darryl Manuel
Jody R. Wall
Steven F. McDonald
Daniel Webber
Mike Murray
John B. Wojakowski
John
W.
Roberts
Philip A. Smith
•chair of document subcommittee.
Consulting Members
Ralph C. Bruno
James N. Cornell
Ben E. Edwards
II
R. Doug Hooton
David E . Hoyt
Jerome H. Ford
This guide reviews and describes practices, procedures, materials,
CONTENTS
and monitoring methods for the external curing of concrete and
provides guidance for specifYing curing procedures. Current curing
techniques are presented and commonly accepted methods, proce­
dures, and materials are described. Methods are given for curing
structures and buildings, pavements and other slabs-on-ground,
and for mass concrete. Curing methods for several specific catego­
ries of cement-based products are discussed in this document.
The materials, processes, quality control measures, and inspec­
tions described in this document should be tested, monitored, or
performed as applicable only by individuals holding the appro­
priate ACI certifications or equivalent.
Keywords: cold weather construction; curing compound; hot weather
construction;
mass concrete;
reinforced
concrete;
sealer;
shotcrete;
slabs-on-ground.
ACI Committee Reports, Guides, and Commentaries are
intended for guidance in planning, designing, executing, and
inspecting construction. This document is intended for the use
of individuals who are competent to evaluate the significance
and limitations of its content and recommendations and who
will accept responsibility for the application of the material it
contains. The American Concrete Institute disclaims any and
CHAPTER 1 -INTRODUCTION, p. 2
1 . 1-Introduction, p. 2
1 .2-Curing, p. 2
1 .3-Curing and hydration of portland cement, p. 2
1 .4-Deliberate curing procedures, p. 5
1 .5-Curing-affected zone, p. 1 0
1 .6-Concrete properties influenced by curing, p. 1 1
1 .7-Effects of elevated temperature, p. 1 2
1 .8-Sustainability, p. 14
CHAPTER 2-DEFINITIONS, p. 1 5
CHAPTER 3-CURING METHODS AND
MATERIALS, p. 1 5
3 . 1 -Scope, p . 1 5
3.2-Use of water for curing concrete, p . 1 5
3.3-Initial curing methods, p . 1 5
3.4-Final curing measures, p . 1 6
3 .5-Termination of curing measures, p. 20
3.6-Cold-weather protection and curing, p. 20
3 .7-Hot-weather protection and curing, p. 2 1
all responsibility for the stated principles. The Institute shall
not be liable for any loss or damage arising therefrom.
Reference to this document shall not be made in contract
documents. If items found in this document are desired by
the Architect/Engineer to be a part of the contract documents,
they shall be restated in mandatory language for incorporation
by the Architect/Engineer.
ACI 308R- I 6 supersedes ACI 308R-0 I and was adopted and published May 2016.
Copyright© 2016, American Concrete Institute.
All rights reserved including rights of reproduction and use in any form or by any
means, including the making of copies by any photo process, or by electronic or
mechanical device, printed, written, or oral, or recording for sound or visual reproduc­
tion or for use in any knowledge or retrieval system or device, unless permission in
writing is obtained from the copyright proprietors.
Coovriaht American Concrete Institute
�-
2
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
3 .8-Accelerated curing, p. 2 1
3.9-Minimum curing requirements, p . 2 1
3 . 1 0-Temperature limits during curing, p . 22
CHAPTER 4-CURING FOR DIFFERENT TYPES OF
CONSTRUCTION, p. 23
4. 1-Pavements and other slabs on ground, p. 23
4.2-Buildings, bridges, and other structures, p. 23
4.3-Mass concrete, p. 24
4.4-Curing colored concrete floors and slabs, p. 25
4.5-Specialty constructions, p. 25
CHAPTER 5-MONITORING CURING AND CURING
EFFECTIVENESS, p. 25
5 . 1-General, p . 25
5 .2-Evaluating environmental conditions, p. 25
5 .3-Means to verify application of curing, p. 28
5.4-Impact of curing procedures on immediate environment, p. 28
5 .5-Impact of curing procedures on moisture and
temperature within concrete, p. 29
5 .6-Maturity method, p. 29
5.7-Assessing curing effectiveness, p. 29
CHAPTER 6-REFERENCES, p. 30
Authored references, p. 3 1
CHAPTER 1 -INTRODUCTION
1.1 -lntroduction
The principles and practices of external curing are appli­
cable to all types of concrete construction. This document
does not fully address curing for specialty concrete and
special construction techniques (refer to 4.5), nor does it fully
address internally cured concrete. For additional information
on internally cured concrete using preconditioned absorp­
tive lightweight aggregates, refer to ACI (308-2 1 3)R. Curing
measures, in general, are specified in ACI 308. 1 . Curing
measures directed toward the maintenance of satisfactory
concrete temperature under specific environmental condi­
tions are addressed in greater detail in ACI 305R, ACI 306R,
ACI 301 , and ACI 3 1 8.
The fundamental principles of external curing remain the
same as in the past; however, new research and methods of
curing are presented herein. Topics such as internal curing,
curing at elevated temperatures, sustainability, curing of
moisture-sensitive flooring, sensors for mass concrete
curing, and new curing monitoring techniques have been
added or enhanced in this document.
1.2-Curing
Curing is an action taken to maintain moisture and
temperature conditions in a freshly placed cementitious
mixture to allow hydraulic cement hydration and, if pozzo­
lans are used, pozzolanic reactions to occur so that the
potential properties of the mixture may develop. A mixture
is properly proportioned and adequately cured when the
properties of the in-place concrete equal or exceed the
Coovriaht Am�te Institute
Fig. 1 . 3.1 a-Unhydrated particles of portland cement­
magnification 2000x (Soroos 1994).
design properties of the concrete. The curing period begins
at placing and continues until the desired concrete proper­
ties have developed. The objectives of curing are to prevent
the loss of moisture from concrete and maintain a favorable
concrete temperature for a sufficient period of time. Proper
curing allows the cementitious material within the concrete
to properly hydrate. Hydration is the chemical reaction that
leads to changes that take place when portland cement reacts
with water. Both at depth and near the surface, curing has a
significant influence on the properties of hardened concrete,
such as strength, permeability, abrasion resistance, volume
stability, propensity for early-age cracking, and resistance to
freezing and thawing and deicing chemicals.
The term "curing" has also been used in a more general
sense to describe the process by which hydraulic cementi­
tious concrete matures and develops hardened proper­
ties over time as a result of the continued hydration of the
cementitious materials in the presence of sufficient water and
heat. While all concrete hydrates to varying levels of matu­
rity with time, the rate and extent to which this developm�nt
takes place depends on the natural environment surroundmg
the concrete and on the measures taken to modify this envi­
ronment by limiting the loss of water, heat, or both, from the
concrete; externally providing moisture and heat; or incor­
porating special materials in the mixture design.
1.3-Curing and hydration of portland cement
1.3.1 Hydration of portland cement-Portland-cement
concrete is a composite material in which aggregates are
bound in a porous matrix of hardened cement paste. At the
microscale, the hardened paste is held together by bonds t�at
develop between the products of the reaction of cement with
water and mechanically interlocks the aggregate. Similar
products are formed from the reactions between cement,
other cementitious materials, and water.
The cement-water reaction includes both chemical and
physical processes that are collectively known as the hydra­
tion of the cement (Taylor 1 997). As the hydration process
continues, the strength of the interparticle bonding increases,
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
Fig 1 .3. 1 b-Multiple particles of partially hydrated port­
,land cement-magnification 4000x (Soroos 1 994).
and the interparticle porosity decreases. Figure 1 . 3 . 1 a shows
particles of unhydrated portland cement observed through a
scanning electron microscope. In contrast, Fig. 1 .3 . 1 b shows
:the development of hydration products and interparticle
bonding in partially hydrated cement. Figure 1 .3 . 1 c shows
,a single particle of partially hydrated portland cement. The
'
surface of the particle is covered with the products ofhydra­
tion in a densely packed, randomly oriented mass known
as the cement gel. In hydration, water is required for the
chemical formation of the gel products and for filling the
micropores that develop between and within the gel prod­
ucts as they are being formed (Powers and Brownyard 1 947;
Powers 1 948). The rate and extent of hydration depend on
the availability of water. Parrott and Killoh ( 1 984) found
that as cement paste comes to equilibrium with air at succes­
sively lower relative humidity (RH), the rate of cement
hydration dropped significantly. Cement in equilibrium with
air at 80 percent RH hydrated at only 1 0 percent the rate of
companion specimens in a 1 00 percent RH curing environ­
ment. Snyder and Bentz (2004) observed that exposure to 90
percent or less RH is sufficient to suspend hydration at early
ages. Therefore, curing procedures ensure that sufficient
water is available to the cement to sustain the rate and degree
of hydration necessary to achieve the desired concrete prop­
erties at the required time.
The water consumed in the formation of the gel products is
known as the chemically bound water, or hydrate water, and
its amount varies with cement composition and the condi­
tions of hydration. A mass fraction of between 0.2 1 to 0.28
of chemically bound water is required to completely hydrate
a unit mass of cement depending on its phase composition
(Powers and Brownyard 1 947; Copeland et a!. 1 960; Mills
1 966). An average value is approximately 0.25 (Kosmatka
and Panarese 1 988; Powers 1 948). Coefficients for chemi­
cally bound water for the various clinker mineral phases are
available in Molina ( 1 992) and range between 0.2 1 for dical­
cium silicate to 0.4 for tricalcium aluminate.
As seen in Fig. 1 . 3 . 1 b and 1 .3 . 1 c, the gel that surrounds
the hydrated cement particles is a porous, randomly
Coovriaht American Concrete Institute
3
Fig 1 . 3. 1 c-Close-up ofsingleparticle ofhydrated cement­
magnification ll, OOOx (Soroos 1 994).
oriented mass. Besides the hydrate water, additional water
is adsorbed onto the surfaces and in the interlayer spaces of
the layered gel structure during the hydration process. This
is known as physically bound water, or gel water. Gel water
is typically present in all concrete in service, even under
dry ambient conditions, as its removal at atmospheric pres­
sure requires heating the hardened cement paste to 22 1 °F
( 1 05°C) (Neville 1 996). The amount of gel water adsorbed
onto the expanding surface of the hydration products and
into the gel pores is approximately equal to the amount that
is chemically combined with the cement (Powers 1 948). The
amount of gel water has been calculated more precisely to
be a mass fraction of approximately 0.20 for a unit mass of
cement (Powers 1 948; Powers and Brownyard 1 947; Cook
1 992; Taylor 1 997).
Both the hydrate water and physically adsorbed gel water
are distinct in the microstructure of the hardened cement
paste, yet both are required concurrently as portland cement
hydrates . Continued hydration of the cement is possible
only when sufficient water is available both for the chemical
reactions and for the filling of the gel pores being formed
(Neville 1 996). The amount of water consumed in the hydra­
tion of portland cement is the sum of the water incorporated
physically onto the gel surfaces plus the water incorporated
chemically into the hydrate products themselves (Neville
1 996; Powers and Brownyard 1 947; Mindess and Young
1 98 1 ; Taylor 1 997). Because hydration can proceed only
in saturated space, the total water requirement for cement
hydration is approximately 0.44 g of water per gram of
cement plus the curing water that needs to be added to keep
the capillary pores of the paste saturated (Powers 1 948).
Other sources place this approximate value at 0.42 to 0.44 g
of water for each gram of dry cement (Powers and Brown­
yard 1 947; Taylor 1 997; Neville 1 996). As long as sufficient
water is available to form the hydration products, to fill the
interlayer gel spaces and ensure that the reaction sites remain
water-filled, the cement will continue to hydrate until all of
the available pore space is filled with hydration products or
�.
4
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
60
8
ro
CL 50
::2
.£
Ol
6
40
c
�
(;) 30
Q)
In laborato
air entire time
>
·u;
(/)
.r:
i5l
c
�
4 (;)
Q)
>
·u;
(/)
� 20
a.
E
0
(.)
·u;
0..
0
0
0
2
10
�
0..
E
0
(.)
0
07 28
91
=
0
365
Age at test, days
Fig. 1.3. ld-Compressive strength of6 x 12 in. (150 x 300 mm)
cylinders as afunction ofagefor a variety ofcuring conditions
(Kosmatka and Wilson 2011).
12.5
�<J)
_c �
::::l
.
0
C\J _c
Eco
:::::'..t
Ol�
� 0
ai';
OlOl
ro ro
�
ro
Q)
_J
2.5
Non-air-entrained concrete
Specimens: 25 x 150 mm
{1 x 6 in.) mortar disks
Pressure: 140 kPa
{20 psi)
10.0
2.0
7.5
1.5
5.0
1.0
Q)
>
ro
�
::::l
0
�
�
Q)
o_
"iii
o_
ai
Ol
ro
�
�
0.5
2.5
ro
Q)
_J
0.0
0.0
0
7
14
21
28
Period of moist curing and age at test, days
Fig. 1 . 3. le-Influence of curing on water permeability of
mortar specimens (Kosmatka and Wilson 2011).
until all of the cement has hydrated. When sufficient water
is supplied, the former condition can be achieved for watercementitious materials ratios (w/cm) of approximately 0.38
and less depending on cement type, mixing, and other physical and chemical properties (Powers and Brownyard 1 947).
The key to the development of both strength and durability
in concrete, however, is not so much the degree to which the
cement has hydrated but the degree to which the pores between
the cement particles have been filled with hydration products
(Powers and Brownyard 1 947; Powers 1 948). This is evident
from the microperspective seen in Fig. 1 .3 . 1 b and from the
macrobehavior illustrated in Fig. 1.3. 1 d and 1.3. 1e, in which
the continued pore filling that accompanies sustained moistcuring leads to a denser, stronger, less-permeable concrete.
The degree to which the pores are filled, however, depends
not only on the degree to which the cement has hydrated,
but also on the initial volume of pores in the paste, thus the
combined importance of the availability of curing water and
the initial w/cm.
The pore volume between cement particles seen in Fig.
1 .3 . 1 b (darker areas of the photograph) was originally occupied in the fresh paste by the mixing water. As the volume .of
Coovriaht Am�te Institute
mixing water decreases relative to the volume of the cement,
the initial porosity of the paste decreases as well. For this
reason, pastes with lower w/cm have a lower initial porosity,
requiring a reduced degree of hydration to achieve a given
degree of pore filling. This is clearly demonstrated in Fig .
1 .3 . 1e, which shows the combined effects of the duration of
curing and w!cm. For the particular mortar specimens tested,
a leakage rate of0.5 lb/ft2/h (2.4 kg/m2/h) was achieved after
2 1 days of moist curing for a w/cm of0.80. The same level of
permeability and degree of pore-filling was reached after 1 0
days for w/cm 0.64, and 2.5 days for w/cm 0.50.
This interaction of mixing water and w!cm in developing
the microstructure of hardened cement paste is potentially
confusing. On one hand, it is important to minimize the
volume of mixing water to minimize the pore space between
cement particles. This is done by designing concrete
mixtures with a low w/cm. On the other hand, it is neces­
sary to provide the cement with sufficient water to sustain
the filling of those pores with hydration products. While a
high w!cm may provide sufficient water to promote a high
degree of hydration, the net result would be a low degree of
pore filling due to the high initial paste porosity. The more
effective way to achieve a high degree of pore filling is to
minimize initial paste porosity with a low w/cm and then to
foster hydration by preventing loss of the internal mixing
water, or externally applying curing water to promote the
maximum possible degree of hydration. The maximum
degree of hydration achievable is a function of both w/cm
and the availability of water (Mills 1 966).
1.3.2 Need for curing-Even if the amount of water
initially incorporated into the concrete as mixing water will
sustain sufficient hydration to develop the desired proper­
ties for a given concrete mixture, curing measures are still
required to ensure that this water remains in the concrete
until the desired properties are achieved. At lower initial
water contents, where advantage is being taken of lower
w!cm and lower initial porosity, it may be necessary to use
curing measures that provide additional water to sustain
hydration to the degree of pore filling required to achieve
desired concrete properties. Concrete mixtures with a w/
em less than approximately 0.50 and sealed against loss of
moisture cannot develop their full potential hydration due to
lack of water; such mixtures would therefore benefit from
externally applied curing water (Powers 1 948). Powers also
pointed out, however, that not all mixtures need to reach
their full hydration potential to perform satisfactorily, and
externally applied curing water is not always required for
mixtures with w/cm less than 0.50.
A related issue in concrete with a low w/cm is that of selfdesiccation, which is the internal drying of the concrete due to
consumption of water by hydration (Neville 1 996; Parrott et
al. 1 986; Patel et al. 1 988; Spears 1983 ; Persson and Fagerlund 1 997). As the cement hydrates, insufficient mixing water
remains to sustain further hydration. Low-w/cm mixtures,
sealed against water loss or water entry, can dry themselves
from the inside. This problem is most commonly associated with mixtures with a w/cm of approximately 0.40 or
... te ss (Powers 1 948; Mills 1 966; Cather 1 994; Meeks and
=
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
Carino 1 999) and is responsible for an almost negligible
long-term strength gain in many low-w/cm mixtures. Self­
desiccation also results in autogenous shrinkage due to the
capillary stresses existing in partially-filled pores. In low-w/
em concretes, this autogenous deformation can be a primary
cause of early-age cracking (ACI 23 1 R). Given that water
also interacts with cementitious materials such as fly ash,
slag, and silica fume, self-desiccation can also arise with
mixtures having low w/cm.
Self-desiccation can be remedied near the concrete surface
by externally providing curing water to sustain hydration.
At such low values of w!cm, however, the permeability of
the paste is normally so low that externally applied curing
water will not penetrate far beyond the surface layer (Cather
1 994; Meeks and Carino 1 999). Conversely, the low perme­
ability of low-w/cm mixtures prevents restoration of mois­
ture lost in drying at the surface by migration of moisture
from the interior. The surface of low-w/cm concrete can
therefore dry quickly, calling attention to the critical need
to rapidly provide curing water to the surface of low-w/cm
concrete (Ai'tcin 1 999). This also means that surface proper­
ties, such as abrasion resistance and scaling resistance, can
be markedly improved by wet-curing low-w!cm concrete.
Bulk properties, such as compressive strength, however, can
be considerably less sensitive to surface moisture conditions
( 1 .5 and 1 .6). Philleo ( 1 99 1 ) suggested that in satisfying the
critical need for a way to get curing water into the interior
of high-strength structural members, a partial replacement
of fine aggregate with saturated lightweight fines might be
a solution. For additional information on internally-cured
concrete using preconditioned, absorptive, lightweight
aggregates, refer to ACI (308-2 1 3)R- 1 3 .
1.3.3 Moisture and temperature control-Curing proce­
dures that address moisture control ensure that sufficient
water is available to the cement to sustain the degree of
hydration necessary to achieve the desired concrete prop­
erties. The hydration process-a series of chemical reac­
tions-is thermally dependent; the rate of reaction approxi­
mately doubles for each 1 8°F ( 1 0°C) rise in concrete
temperature. Curing procedures should also ensure that
the concrete temperature will sufficiently sustain hydra­
tion. As early-age concrete temperatures increase, however,
the rate of hydration can become so rapid as to produce
concrete with diminished strength and increased porosity,
thus requiring temperature control measures (refer to ACI
305R). At temperatures above approximately 1 58°F (70°C),
ettringite phases can become unstable, leading to poten­
tial damage due to so-called delayed ettringite formation
(Thomas 200 1 ). Curing measures directed primarily toward
the maintenance of satisfactory concrete temperature under
specific environmental conditions are addressed in greater
detail by ACI 305R, ACI 306R, ACI 301 , and ACI 3 1 8.
1.4-Deliberate curing procedures
Deliberate curing measures are required to add or retain
moisture whenever the development of desired concrete
properties will be unacceptably delayed or arrested by
insufficient water being available to the cement or cementiCoovriaht American Concrete Institute
5
tious materials. Curing measures are required as soon as
the concrete is at risk of drying and when such drying will
damage the concrete or inhibit the development of required
properties. Curing measures should be maintained until the
drying of the surface will not damage the concrete, and until
hydration has progressed so that the desired properties have
been obtained, or until it is clear that the desired properties
will develop in the absence of deliberate curing measures.
1.4.1 Natural conditions-Whether action is required to
maintain an adequate moisture content and temperature in
the concrete depends on the ambient weather conditions,
concrete mixture, and desired properties of the hardened
concrete. Under conditions that prevent excessive moisture
loss from the concrete, or when the required performance
criteria for the concrete are not compromised by early mois­
ture loss, it is entirely possible that no deliberate action needs
to be taken to protect the concrete. Guidance for predicting
the impact of ambient conditions on the behavior of fresh
concrete is found in 1 .4 and in Chapters 3 through 5 . The
best source for guidance on the impact of ambient conditions
on hardened concrete properties would be field experience
with environmental conditions and the concrete mixture in
question. Note that in most environments it is unlikely that
favorable, natural conditions will exist for the duration of the
curing period. The contractor should therefore be prepared
to initiate curing measures as soon as favorable ambient
conditions change.
1.4.2 Sequence and timing of curing steps for unformed
surfaces
Curing has traditionally been considered to be a
single-step process, conducted sometime after the concrete
has been placed and finished. Adequate control of moisture,
however, can require that several different procedures be
initiated in sequence, culminating in a last step that is defined
herein as final curing. This section will describe three stages
of curing procedures, defined by the techniques used and the
time at which they are initiated.
Initial curing refers to procedures implemented any time
between placement and final finishing of the concrete to
reduce moisture loss from the surface. Examples of initial
curing measures include fogging and the use of evaporation
reducers (Cordon and Thorpe 1 965). This is covered in more
detail in 3.3 .
Intermediate curing is sometimes necessary and refers to
procedures implemented when finishing is completed but
before the concrete has reached final set. During this period,
evaporation may need to be reduced, but the concrete may
not yet be able to tolerate the direct application of water or
the mechanical damage resulting from the application of
fabric or plastic coverings. Spray-applied, liquid membrane­
forming curing compounds can be used effectively to reduce
evaporation until a more substantial curing method can be
implemented, if required.
Final curing refers to procedures implemented after
final finishing and after the concrete has reached final set.
Examples of final curing measures include application of
wet coverings such as saturated burlap, ponding of water, or
the use of spray-applied, liquid membrane-forming curing
compounds.
-
�-
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
6
Bleed water
disappears
and
finishing
begins
at initial set
Finishing
complete
when
concrete
c
.Q
C>
.!:
""C
Q)
Q)
05
reaches
final set
-ro
0
a.
C1l
>
w
�
�::l
�
�::l
E
E
::l
l)
::l
l)
�
c
ro
ii)
"iii
Q)
0::
c
0
:+::>
�
Q)
c
Q)
c...
o------ Time since placing ------
Fig. 1 . 4. 2.2-Schematic illustration showing the combined
influence of bleeding characteristics and evaporation in
determining the time at which the surface ofconcrete begins
to dry.
(!)------�
Transport,
placing,
consolidation,
strike-off,
bullfloat
Time since batching
f..--+--+
Floating,
brooming,
troweling
Final
Curing
Window of
finishability
Fig. 1 . 4. 2. 1-Conventional construction operations under
ideal conditions. Initial set coincides with the cessation
of bleeding and final set coincides with the completion of
fi nishing. Finishing can be initiated immediately aft er all
bleed water has just evaporated. Final curing can begin
immediately after concrete has reached the final set.
Curing procedures and their time of application vary
depending on when the surface of the concrete begins to dry
and how far the concrete has advanced in the setting process.
Curing measures should be coordinated with the sequence
and timing of placing and finishing operations.
1.4.2.1 Timing of placing and finishing operations­
Transport, placing, consolidation, strike-off, and bull­
floating of unformed concrete surfaces, such as slabs, all
take place before the concrete reaches initial setting. Time of
initial set is also known as the vibration limit, indicating that
the concrete cannot be properly consolidated after reaching
initial set (Tuthill and Cordon 1 955 ; Dodson 1 994). Surface
texturing can begin at initial set but should be completed by
the time the concrete has reached final set. Both initial and
final set are defined on the basis of the penetration-resistance
test (ASTM C403/C403M) for mortar sieved from concrete
(Kosmatka 1 994; Dodson 1 994). This concept is illus­
trated in Fig. 1 .4.2. 1 (ACI 302 . 1 R; Suprenant and Malisch
1 998a,b,e; Abel and Hover 2000).
Surface finishing beyond bull floating should not be initi­
ated before initial set or before the bleed water has disap­
peared from the concrete surface. Before initial set, the
concrete is not stiff enough to hold a texture or support
Coovriaht Am�te Institute
the weight of a finisher or finishing machine. Further­
more, bleeding of the concrete also controls the timing of
finishing operations. Bleed water appears at the surface of
freshly cast concrete because of the settling of the denser
solid particles in response to gravity and accumulates on the
surface until it evaporates or is removed by the contractor
(refer to 1 .4.2.2.2). Bleed water is evident by the sheen on
the surface of freshly cast concrete, and its amount can be
measured by ASTM C232/C232M (Suprenant and Malisch
1 998a,e). Finishing the concrete surface before settlement
and bleeding has ended can trap the residual bleed water
below a densified surface layer, resulting in a weakened zone
just below the surface. Finishing before the bleed water fully
disappears remixes accumulated bleed water back into the
concrete surface, thus increasing the w/cm and decreasing
strength and durability in this critical near-surface region.
Remixing bleed water can also decrease air content at the
surface, further reducing durability. Proper finishing should
not start until bleeding has ceased and the bleed water has
disappeared or has been removed. In most cases, the concrete
surface is drying while it is being finished.
The presence of bleed water is detected visually. The
appearance of the concrete surface can be misleading,
however, when the rate of evaporation equals or exceeds
the rate of bleeding. In this case, the apparently dry surface
would suggest that bleeding has stopped and that finishing
can begin. In reality, finishing may yet be premature, as
bleed water is still rising to the surface. When it is necessary
to evaluate this situation more carefully, a clear plastic sheet
can be placed over a section of the concrete to block evapo­
ration and to allow observation of bleeding.
Surface finishing should be completed before the concrete
attains the level of stiffness (or penetration resistance
measured by ASTM C403/C403M) characterized by having
reached final set (Abel and Hover 2000). Attempts to texture
the concrete beyond final set usually require the addition
of water to the surface. This practice should not be allowed
because of the loss of surface strength and durability that
results from the addition of water to the concrete surface. ACI
302. 1 R refers to the term "window of finishability" to iden-
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
tify the time period between initial and final set (Fig. 1 .4.2. 1 )
(Suprenant and Malisch 1 998e; Abel and Hover 2000).
1.4.2.2 Timing of curing procedures-Curing measures
should be initiated when the concrete surface begins to
dry, which starts as soon as the accumulated bleed water
evaporates faster than it can rise to the concrete surface
(Lerch 1 957; Kosmatka 1 994; Al-Fadhala and Hover 200 1 ).
The time at which drying and the need for curing begins
depends not only on the environment and the resulting rate
of evaporation, but also on the bleeding characteristics of
the concrete, as shown schematically in Fig. 1 .4.2.2. The
figure illustrates the cumulative bleeding of three different
mixtures measured as a function of time since concrete
placeme�t. Superimposed on this diagram is the cumulative
loss of surface water due to evaporation arising from three
different environments, characterized by high, medium, and
: low evaporation rates (Rates 1 , 2, and 3). Given that surface
: drying begins as soon as cumulative evaporation catches
: up with cumulative bleeding, it can be seen that there is a
. wide divergence in the time at which curing measures are
"
: required to control such drying. For structural concrete and
: slipformed concrete, the initial bleed rate may often be less
: than the evaporation rate, giving further urgency for the
application of early curing measures (Wojakowski 1 999).
1.4.2.2.1 Evaporation-The rate of evaporation is influ­
enced by air and concrete temperatures, relative humidity,
wind speed, and radiant energy from direct sunshine. The
driving force for evaporation of water from the surface
of concrete is the pressure difference between the water
vapor at the surface and the water vapor in the air above
that surface; the greater the pressure difference, the faster
the evaporation. Vapor pressure at the concrete surface is
related to the temperature of the water, which is generally
assumed to be the same as the concrete surface temperature.
The higher the concrete surface temperature, the higher the
surface water-vapor pressure.
Because evaporation is driven by the difference between
vapor pressure at the surface and in the air, factors that lower
water-vapor pressure in the air will increase evaporation.
While low humidity in the air increases evaporation rate,
it is not as well known that low air temperature, especially
in combination with low humidity, increases evaporation.
Evaporation rate is exacerbated in hot, dry weather as the
concrete temperature rises. Wind speed becomes a factor
as well, because wind moves water vapor away from the
surface as it evaporates. In still air, evaporation slows due
to the accumulation of water vapor (increased humidity)
in the air immediately over the evaporating surface. Direct
sunlight also accelerates evaporation by heating the water
on the surface.
There have been multiple attempts to mathematically esti­
mate evaporation rate based on these factors dating back to
the early 1 800s (Dalton 1 802). The most commonly used
evaporation rate predictor in the concrete industry is that
introduced by Menzel ( 1 954) but developed from 1 950 to
1 952 by Kohler et a!. ( 1 955) for hydrological purposes, as
reported by Veihmeyer ( 1 964) and Uno ( 1 998). Most well­
known is the evaporation rate nomograph that was refor-
7
Bleed water evaporates and
surface drying begins
Begin surface finishing
Qi
en
ro
c
u:
-
,'
Coovriaht American Concrete Institute
························
·=v
I
-----t----11 Time since batching
o-
f------..
�
Initial curing required
over this time interval
Fig. 1. 4.2. 2. 3-Bleed water disappears and surface drying
commences at some time before beginning finishing. Initial
curing is required to minimize moisture loss before and
duringfinishing operations.
matted from Menzel's earlier version in 1 960 by the National
Ready Mixed Concrete Association (NRMCA 1 960) (Fig.
5 . 2 . 1 ). The use, limitations, and accuracy of this tool for esti­
mating rate of evaporation are discussed in detail in 5.2. 1 . 1 .
1.4.2.2.2 Bleeding-Both the rate and duration of bleeding
depend on the concrete mixture, the depth or thickness of
the concrete, and the method of consolidation (Kosmatka
1 994; Suprenant and Malisch 1 998a). Although water
content and w/cm are the primary compositional factors,
cement, cementitious materials, aggregates, admixtures,
and air content all influence bleeding. Thorough vibration
brings bleed water to the surface earlier, and deep members
tend to show increased bleeding compared with shallow
members (Kosmatka 1994). The rate of bleeding dimin­
ishes as setting takes place, even in the absence of surface
drying, so that surface drying will ultimately occur even
under benign evaporation conditions (Al-Fadhala and Hover
2001 ). Mixtures with a low to negligible bleeding rate are
particularly susceptible to surface drying early in the placing
and finishing process and may experience plastic shrinkage
cracking. Such concrete mixtures often incorporate silica
fume, fine cements, or other fine cementitious materials; low
w/cm ; high air contents; or water-reducing admixtures.
1.4.2.2.3 Initial curing-For mixtures with a low to zero
bleeding rate, aggressively evaporative environments,
�-
8
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
or both, surface drying can begin well before initial set
and initiation of finishing operations, as indicated in Fig.
1 .4.2.2.3 . Under such conditions, it is necessary to reduce
moisture loss by one or more initial curing techniques, such
as fogging; the use of evaporation reducers; or by modifying
the environment with sunshades, windscreens, or enclosures
(refer to 3 .3). Because finishing can involve several separate
and time-consuming operations, initial curing measures may
need to be continued or reapplied until finishing is complete.
Initial curing measures should be applied immediately after
the bleed water sheen has disappeared because the concrete
surface is protected against drying as long as it is covered
with bleed water. When finishing begins immediately after
the disappearance of the bleed water, it is unnecessary to
apply initial curing measures. When the concrete exhibits a
reduced tendency to bleed, when evaporative conditions are
severe1 or both, the concrete can begin to dry immediately
after piacing. Under such conditions, initial curing measures,
such as fog-spraying to increase the humidity of the air or the
application of a liquid-applied evaporation reducer, should
be initiated immediately after strike-off and, in some cases,
before. bull floating. Such initial curing measures should
be continuously maintained until more substantial curing
meas�es can be initiated. Excess water from a fog spray
or an evaporation reducer should be removed or allowed to
evaporate before finishing the surface (refer to ACI 302. 1R).
Application of initial curing measures is also frequently
required for concretes that exhibit low or negligible
bleeding. Such concrete mixtures often incorporate silica
fume, fine cements, or other fine cementitious materials;
low w/cm; high air contents; or water-reducing admixtures.
Initial curing measures are frequently required immediately
upon placing such concrete to minimize plastic shrinkage
cracking. Plastic shrinkage is initiated by surface drying,
which begins when the rate of evaporative water loss from
the surface exceeds the rate at which the surface is moistened
by bleed water. Refer to ACI 305R for further discussion on
plastic shrinkage, and to ACI 234R for further discussion on
curing concrete incorporating silica fume.
1.4.2.2.4 Final curing-The concrete surface should be
protected against moisture loss immediately following the
finisher or finishing machine. Significant surface drying can
occur when curing measures are delayed until the entire
slab is finished because the peak rate of evaporation from a
concrete surface often occurs immediately after the last pass of
the finishing tool, as tool pressure brings water to the surface
(Al-Fadhala and Hover 2001 ; Shaeles and Hover 1 988). This is
especially true when the finished texture has a high surface area
such as a broomed or tined surface (Shariat and Pant 1 984).
Therefore, it is necessary to control moisture loss immediately
after finishing (Transportation Research Board 1 979).
When the conclusion of finishing operations coincides
with the time of final set, as indicated in Fig. 1 .4.2 . 1 , final
curing should be applied at exactly the right time to reduce
the peak rate of moisture loss. A delay in final curing can
result in considerable water loss (Al-Fadhala and Hover
200 1 ). Under some conditions, however, applying final
curing measures immediately after completion of finishing
Coovriaht Am�te Institute
Surface finishing
completed before final set
C···································································· ··········································· ·····················
�
:;:::
-
J
J_
v�
ca
-�� �
Time since batching
1
Period of potentially
high rate of moisture loss, but
surface may not be hard
enough for final curing methods
Final
curing
Intermediate curing
required
Fig. 1 . 4. 2. 2. 5-Surface.finishing has been completed before
concrete surface has reachedfinal set.
can be deleterious. These conditions are described in the
following section.
1.4.2.2.5 Conditions under which intermediate curing is
recommended-Intermediate curing measures are performed
whenever the concrete surface has been finished and before
final curing can be initiated.
A freshly finished concrete surface is not only vulner­
able to the deleterious loss of moisture, but can be vulner­
able to damage from the early application of curing mate­
rials. The need to protect against moisture loss can conflict
with the need to prevent damage to the surface immediately
following finishing. Of particular concern is concrete that
has been surface-finished before the concrete has reached
final set, as shown in Fig. 1 .4.2.2.5.
Before reaching final set, the concrete surface is susceptible
to marring by applying wet burlap, plastic sheets, or other
curing materials. Furthermore, the bonds between the cement
particles can be easily broken and the particles displaced by
water added to the concrete surface and forced between the
cement particles, resulting in weakening normally associ­
ated with the premature addition of water. For this reason,
the earlier that water is applied as a final curing measure,
the more gently it should be applied to avoid displacement
of cement particles. Fogging is an example of a gentle appli­
cation, as long as accumulated water is not finished into the
surface. As setting progresses with an increased strength of
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
cement particle bonding, water can be applied to the surface
more aggressively. In laboratory and field tests of this prin­
ciple (Falconi 1 996), application of wet burlap to concrete
surfaces immediately after finishing reduced resistance to
deicer salt scaling. When concrete slabs of the same mixture
were lightly covered with plastic sheets immediately after
finishing, and the plastic replaced with wet burlap when the
concrete had reached final set as measured by ASTM C403/
C403M, wet curing was consistently beneficial in increasing
scaling resistance.
Intermediate curing methods can be a continuation
of initial curing measures, such as evaporation reducers
or fogging, maintained until the final curing is applied.
Membrane-forming curing compounds meeting the require­
ments ofASTM C309 or C 1 3 1 5 can be applied from a power
sprayer, making it unnecessary to walk on the concrete
surface, and can be applied immediately behind the final pass
of the finishing tool or machine. Curing compounds have
the advantage of being applicable before final set, as well as
being a frequently acceptable final curing method. Curing
compounds, therefore, can be an effective intermediate
curing method or precursor to other final curing methods,
such as water curing or protective coverings, minimizing
water loss during the last stages of the setting process.
The combination of a curing compound as an intermediate
curing method followed by water-saturated coverings as a
final curing method is more common in bridge construction
than in building construction (Krauss and Rogalla 1 996).
The curing compound can be spray-applied to the concrete
surface from the perimeter of the bridge deck immediately
behind the finishing machine or from the finishers' work
bridge. After the curing compound has dried, the wet burlap
or similar material is applied and, to keep it continuously
wet, soaker hoses or plastic sheets are installed. This is not
a dual or redundant application of two equivalent curing
methods. Curing compounds and so-called breathable
sealers meeting the requirements of ASTM C309 and C 1 3 1 5
permit moisture transmission and have a variable capacity to
retard moisture loss, depending on the quality of the product
used, field application, and field conditions. Wet curing by
ponding, sprinkling, or the application of wet burlap not
only prevents water loss but also supplies additional curing
water to sustain cement hydration, which is important for
low-w!cm mixtures that can self-desiccate (Powers 1 948 ;
Mills 1 966; Mindess and Young 1 98 1 ; Neville 1 996; Persson
1 997; Meeks and Carino 1 999).
1.4.2.3 Preparation for placing and curing-Curing
procedures have to be initiated as soon as possible when
the concrete surface begins to dry or whenever evapora­
tive conditions become more severe. The curing measures
to be used should be anticipated so that the required mate­
rials are available on site and ready to use if needed. Water
or curing chemicals, coverings, and application equipment
and accessories need to be ready, particularly when harsh
environmental conditions may require rapid action. To be
effective, sunshades or windbreaks (3 . 7) should be erected
in advance of concrete placing operations. Actions such as
dampening the subgrade, forms, or adjacent construction, or
Coovriaht American Concrete Institute
9
cooling reinforcing steel or formwork are likewise required
in advance of concrete placement. Refer to ACI 3 0 1 , 302 . 1 R,
3 05R, and 306R for additional information on preparedness.
1.4.3 Curing of formed surfaces-Moisture loss is a
concern for both formed and unformed surfaces. Forms left
in place reduce moisture loss if the forms are not water­
absorbent. Dry, absorbent forms will extract water from the
concrete surface. In addition, concrete usually shrinks from
the form near the top of the section and it is not unusual to
find dry concrete surfaces immediately after removing forms.
As soon as the forms can be loosened without damage to the
concrete, water should be applied to the top of the form and
allowed to run down the interface between the form and new
concrete until forms are fully removed. After form removal,
formed surfaces can benefit from curing. The use of perme­
able formwork in placing and curing concrete has been exten­
sively reviewed by Malone ( 1 999). Controlled permeability
formwork systems have also been presented and evaluated in
numerous reports (Price and Widdows 1 99 1 ; Basheer et al.
1 993 , 1 995 ; Long et al. 1995; Sousa-Coutinho 1 999; Price
2000). The use ofpermeable formwork can enhance the curing
process while the forms are in place; however, recommended
curing procedures for formed surfaces should be followed
after removing the permeable formwork.
1.4.4 When curing is required: cold and hot weather-The
environment dictates the need for curing and influences the
effectiveness and logistical difficulty in applying the curing
methods. For example, use of a fog spray as an initial curing
method in freezing weather is impractical and may be of
little value despite the critical need to limit surface evapora­
tion under such conditions. Similarly, in hot, arid environ­
ments, there is a critical need to prevent water loss from the
concrete surface. Such factors often influence the choice of
curing methods in hot or cold weather. This choice should
be made with consideration of not only the logistical and
economic issues, but also of the relative effectiveness of
the curing methods proposed in terms of surface strength,
resistance to abrasion or deicer scaling, surface perme­
ability, or other factors. The influence of the curing method
on achieving the desired properties of the concrete should be
given first consideration in such decisions (refer to 3 . 6 and
3 . 7 for details).
1.4.5 Duration ofcuring-The required duration of curing
depends on the composition and proportions of the concrete
mixture, the values to be achieved for desired concrete prop­
erties, the rate at which desired properties are developing
while curing measures are in place, and the rates at which
those properties will develop after curing measures are
terminated. Tests have shown that the duration of wet curing
required to bring pastes of different w!cm to an equivalent
permeability varied from 3 days for low w/cm to 1 year for
high w/em (Powers et al. 1 959). The duration ofcuring is sensi­
tive to the w/cm of the pastes because a lower w/cm results in
closer initial spacing of the cement particles, requiring less
hydration to fill interparticle spaces with hydration products.
Curing should be continued until the required concrete
properties have developed or until there is a reasonable assur­
ance that the desired concrete properties will be achieved
�.
G U IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
10
1 00 ��r----r----.--,
LIGHTWEIGHT CONCRETE
90
80
�
�
a:
90
��
NORMALWEIGHT CONCRETE
3" cover
\'�'\.''....., �/
j i
1 -3/4" cover
80 \
\ \
3/4" cover
1/4" cover
70 \ ', ' ...., _ .:: - - _
- --#:_
=: .:::: :- - ' ......
.... _ _ _ _ _
--\
....
._
----- ---=-=- - = = = = ����
5 0 �--�--�--------�------------���
60
0 28
90d
1 80d
1 yr
2 yr
Time of Drying
Fig. 1. 5-Example of variation of internal relative humidity
with depth from surface of concrete cylinder (Hanson 1968).
(Note: 1 in. 25. 4 mm.)
=
after the curing measures have been terminated and the
concrete is exposed to the natural environment. Most likely,
the continued rate of development of the concrete properties
will be slower after curing measures have been terminated.
Figure 1 .3 . 1 d shows the compressive strength of 6 x 1 2 in.
( 1 50 x 3 00 mm) cylinders for a particular concrete mixture
as a function of curing time for a variety of curing condi­
tions. The figure demonstrates that the rate of continued
strength development decreases sharply after curing proce­
dures are terminated. This post-curing rate of continued
property development should be considered in approving
the termination of curing any time before full attainment of
specified concrete properties. For example, it is common to
permit termination of curing measures when the compres­
sive strength of the concrete has reached 70 percent of the
specified strength. This is a reasonable practice if the antici­
pated post-curing conditions allow the concrete to continue
to develop to 100 percent of the specified strength within the
required time period. When post-curing conditions are not
likely to allow the required further development of concrete
properties, it may be more reasonable to require curing until
the concrete has developed the full required properties.
In determining the appropriate duration of curing, concrete
properties that are desired in addition to compressive strength
sh6uld be considered. For example, if both high compressive
st(ength and low permeability are required concrete perfor­
m�mce characteristics, then the curing needs to be long enough
to develop both properties to the specified values. The appro­
priate duration of curing will depend on the property that is
the slowest to develop. Other considerations in determining
the specified duration of curing include the cost of applying
and subsequently maintaining various curing measures, and
the risk and costs associated with not achieving the necessary
concrete properties if curing is insufficient. Refer to 3 .8 for
details on recommended duration of curing.
Coovriaht Am�te Institute
1.5-Curing-affected zone
Concrete is most sensitive to moisture loss and, therefore,
most sensitive and responsive to curing at its surface where
it is in contact with dry moving air or absorptive media such
as a dry subgrade or porous formwork. Figure 1 .5 shows
an example of how internal relative humidity (RH) varies
with depth from the surface for a 6 x 1 2 in. ( 1 50 x 3 00 mm)
concrete cylinder (Hanson 1 968). Concrete with an internal
RH of 70 percent, for example, would gain or lose no mois­
ture when placed in air at an RH of 70 percent. The cylinder
specimens had been moist cured for 7 days and then dried
at 73°F (23°C) and 50 percent RH. For the specimen cast with
normalweight aggregate, the humidity at 1/4 in. (6.4 mrn) depth
was approximately 70 percent at an age of 28 days, whereas
the humidity was approximately 95 percent at the center of the
cylinder. At 28 days, the cement in the outer 1/4 in. (6.4 mrn)
would have ceased to hydrate, whereas that in the center of the
cylinder would have continued to hydrate ( 1 .3 ).
Cather ( 1 992) defined the curing-affected zone as that
portion of the concrete most influenced by curing measures.
This zone extends from the surface to a depth varying from
approximately 1 14 to 3/4 in. (5 to 20 mm), depending on
the characteristics of the concrete mixture, such as wlcm
and permeability, and the ambient conditions (Carrier 1 983 ;
Spears 1 983). Concrete properties in the curing-affected
zone will be strongly influenced by curing effectiveness,
whereas properties further from the surface will be less
susceptible to moisture loss.
The lower the permeability of the concrete, the more
slowly moisture moves between the surface and the inte­
rior. Similarly, the lower the permeability, the less readily
water from the interior can replenish water removed from
the surface by evaporation (Pihlaj avaara 1 964, 1 965). In
such low-permeability concrete, surface drying can inhibit
the development of surface properties, whereas interior or
bulk properties may develop more fully.
Surface hardness, abrasion resistance, scaling resistance,
surface permeability and absorption, modulus of rupture,
surface cracking, surface strain capacity, and similar surface­
type properties are strongly influenced by curing. Further, the
results of tests for such properties can be useful indicators of
curing effectiveness (Chapter 5). Conventional compression
tests of cores, cylinders, or cubes are useful as indicators of
concrete strength within the bulk of the specimen but are not
necessarily representative of the surface properties. Whereas
tests of compressive strength have traditionally been used
to demonstrate the effects of curing (Fig. 1 .3 . l d), such tests
are actually not as representative of curing effectiveness
as tests of the aforementioned surface properties. This is
because the curing-affected zone is not critical with regard
to the compressive strength of cylinders or cores, which
fail away from their ends. For example, drilled cores can
be misleading indicators of curing effectiveness when the
curing-affected zone includes only the top 1 12 in. ( 1 2 mm) or
so of the core sample (Montgomery et a!. 1 992). In a typical
core test, the concrete in the curing-affected zone is covered
or reinforced with neoprene caps or capping compound and
ground smooth, or cut off altogether. Core tests, therefore,
11
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
50
0
-
.
0
,_
X
0
Q)
�0
.�
40
E
....
Q)
Q.
.Q
j
e
Water pressure: 20 MPa (3000 psi)
Curing:
30
:.0
<IS
Q)
Non-air-entrained concrete
Specimens: 1 00 x 200 mm
(4 x 8 in.) cylinders
20
---
� d�y moist, 90 days
1n cur
. ... .
day� mpist, 90
days 1n cur
7
Water-cement
ratio
10
"'0
>J:
0.70
0.62
0 �---K���--�----�
0.3
0.5
0.7
0.4
0.6
0.8
O.S1�---;2!;----;!;3---:4!---i--=���­
Duration of initial water curing, days
Water-cement ratio, by mass
Fig. 1. 6a-Irifluence ofcuring on waterpermeability ofconcrete
(Kosmatka and Wilson 2011). (Note: 1 cmls 0.39 in./s.)
=
Fig 1. 6c-Surface absorption is reduced by 50 percent by
extending water curing from 1 to 4 days (Dhir et al. 1987).
(Note: 1 mL/m2/s 0. 74 lb/jrlh.)
=
8
86
N
e
...._
-
""
-....
0.. 6
W/C RATIO
oD
'52
0 0 .5
• 0.65
>-
�
:c 4
C3
43
Ql
>.
-
�
IB
e
....
Ql
Cl.
�
Ql
Cl.
ii 2
�
)(
�
>.
)(
0
0
0
3
Time cured (days )
28
0
E
E
:ij 2
"'
;:
�c. 3
Q)
0
4
5
0
2
3
4
Number of test cycles
5
Fig. 1. 6d-Sawyer (19 5 7) demonstrated effects ofcuring on
abrasion resistance by Standard DIN 51951. (Note: 1 mm
0.04 in.)
=
Fig. 1. 6b-Effect ofcuring on reducing oxygen permeability
of concrete surface (Grube and Lawrence 1984; Gowriplan
et al. 1990).
are not consistently reliable indicators of concrete perfor­
mance in the curing-affected zone, nor are core tests neces­
sarily reliable indicators of curing effectiveness as related to
surface properties and performance.
1.6-Concrete properties influenced by curing
Because curing directly affects the degree of hydration of
the cement, curing has an impact on the development of all
concrete properties. The impact of curing on a broad range
of concrete properties is illustrated by the following collec­
tion of data from various sources.
As seen previously, Fig. 1 . 3 . 1 d indicates the influence of
curing on compressive strength, and Fig. 1 .3 . 1 e and 1 .6a
indicate the influence of curing on the water permeability of
hardened concrete. Figure 1 .6b shows a 50 percent reduction
Coovriaht American Concrete Institute
in permeability achieved by extending the duration of moist
curing from 1 to 3 days and a similar improvement achieved
by further increasing the curing period to 7 days. Figure 1 .6a
shows a similar trend.
The data in Fig. 1 .6c indicate that surface absorption is
reduced by approximately 50 percent by extending water
curing from 1 to 4 days (Dhir et a!. 1 987).
Sawyer ( 1 957) demonstrated the effects of curing on abra­
sion resistance (Fig. 1 .6d) and the effects of a 24-hour delay
in curing (Fig. 1 .6e). The number of test cycles is the number
of successive applications of the abrasive wear test device.
Dhir et a!. ( 1 99 1 ) demonstrated a similar relationship between
abrasion resistance and curing, as shown in Fig. 1 .6f.
Murdock et a!. ( 199 1 ) showed a relationship between the
duration of wet curing and the resistance to freezing and
thawing of air-entrained concrete, as shown in Fig. 1 .6g. For a
w!Ciii of0:45 (ACl3l8 inaximum value for concrete exposed
�.
12
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
300
E
E
Immediate
curing
I
01
s:::
'iii
+CI ..S:::
..s::: 01
+- ·Cll
-o 3::
§ .!:
2' :;::
0
0
.s:;: 3
0..
"'
0
4
250
200
·-
N -
= a-!!
'- an
....
C\1
Curing delayed ---"
24 hours
1 50
't o
.. Cll
.!!
�
U -o
I ----�
2 ---3
�---4L-�
5o�---L
1 00
>- o
u ...
N umber of test cycles
Fig. 1. 6e-Sawyer (1957) demonstrated effects of delaying
curing on abrasion resistance. (Note: 1 mm 0. 04 in.)
.._ c..
0 0
. +0
z
50
v
-- wJc
ratio • G-45
J
I
Average
tv
�
"""'"
I
WIC ratio • 0·62
WI
W/C ratio
1
•
G-80
=
5
2.5
20
25
30
Fig. 1 . 6g-Jnjluence of duration of moist-curing time on
resistance to freezing and thawing of concrete, also as func­
tion ofw/c (Murdock et al. 1991).
2.0
E
E
z
0
iii
<
a::
ID
<
LL
0
15
10
Length of moist curing, days
1.5
1 6 r-------�
0.70
1.0
Curing
condition
0 no curing
A solvent borne resin membrane
o wax emulsion membrane
"il 3 davs water curing
by ponding
0.62
:I:
>-ll.
w
0
0.55
0.5
o.•o
(b)
(a)
1 4 7
14
28 0.4
DURATION OF MOIST CURING. davs
12
0.6
0.5
0.7
WATER/CEMENT RATIO
Fig. 1 . 6f-Dhir et al. (1991) demonstrated relationship
between abrasion resistance and curing. E1
24-hour wet
burlap followed by 2 7 days immersion curing in water at
68°F (20°C); E2 = 24-hour wet burlap followed by 6 days
immersion curing in water at 68°F (20°C) and 21 days in air
at 68°F (20°C) and 55 percent RH; E3 = 24-hour wet burlap
followed by 3 days immersion curing in water at 68°F (20°C)
and 24 days in air at 68°F (20°C) and 55 percent RH; and
E4 = 24-hour wet burlap followed by 2 7 days in air at 68°F
(20°C) and 55 percent RH. (Note: 1 mm 0. 04 in.)
=
Diameter of core 25 mm
Thickness 1 2· 5 mm
NE
:!!
I
0
X
>
t-:::;
iii
<
w
�
a:
w
0...
z
w
Cl
>
X
0
8
4
=
to freezing while moist), resistance to freezing and thawing
continues to develop over the entire 28-day curing period.
Gowriplan et a!. ( 1 990) demonstrated a relationship
between curing and oxygen permeability at various depths
from the surface. This work included comparisons of various
methods for curing (Fig. 1 .6h).
1.7--Effects of elevated temperature
While elevated temperatures may occur without applying
additional external heat, it is often applied (particularly in
precast concrete construction) to accelerate the early-age
strength gain of concrete. There is some evidence, however,
that curing for a shorter time at a higher temperature will
not be as beneficial as longer curing at a lower temperature
Coovriaht Am�te Institute
0
1 2 ·5
25
37·5
50
DEPTH FROM SUR FACE-mm
Fig. 1 . 6h-Injluence of various curing types on oxygen
permeability at various depths (Gowriplan et al. 1 990) .
(Note: 1 m m = 0.04 in.; 1 m 2 = 1 0. 76ftl.)
in terms of final strength (Fig. 1 .7a). Other work (Hanson
1 963 ; Erdogdu and Kurbetci 1 998) has indicated that little
additional benefit in terms of early-age strength is attained
as the maximum curing temperature increases above 1 50 to
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
10
20
deg C
30 4 0 50
6000
41.4
5000
34. 5
"'
0..
ca
a...
:5. 4 0 0 0
c::
�
....
Ill
�
27.6
�
..r:::.-
OJ
c::
�
300 0
20.7
· v;
Cl'l
G)
....
� 2 000
(J0
,,0"
'A
A t I day
,1:1"
1 00 0
u:;
C1>
>
'(i)
en
C1>
0.
1 3.8 0E0
69
40
60
80
1 00 1 20
Curin g temperature, deg F
Fig. 1. 7a-One-day strength increases with increasing
curing temperature but 28-day strength decreases with
increasing curing temperature (Verbeck and Helmuth 1 968).
1 5 8°F (66 to 70°C). Some research has shown that curing
at higher temperatures leads to a more porous microstruc­
ture (Verbeck and Helmuth 1 968; Kjellsen et a!. 1 99 1 ) and,
hence, a concrete with an increased permeability to fluids
(Goto and Roy 1 98 1 ) or chloride penetrability (Detwiler
et a!. 1 9 9 1 , 1 994) (refer to Fig. 1 . 7b). Other research has
shown that the permeability of heat-cured concrete with low
w!cm typically used in precast prestressed concrete is not
substantially effected by heat curing, and the w!cm has the
greatest effect on permeability, regardless of whether or not
the concrete was accelerated-cured (Pfeifer et a!. 1 996).
It has been alleged that heat-cured concrete elements
can, under certain conditions, suffer volume expansion and
cracking on subsequent exposure to moisture. This form of
deterioration has been commonly referred to in the literature
as delayed ettringite formation (DEF) (Hime 1 996; Pavoine
et a!. 2006). It has been shown that the normal early forma­
tion of ettringite that occurs in concrete cured at ambient
temperature can be broken down as a result of exposure
to excessive temperatures during manufacture. The ettrin­
gite then reforms at later ages during subsequent exposure
to moisture in service, and this delayed formation of ettrin­
gite can lead to internal expansion of the hardened concrete.
It appears that heat-cured railway ties, for example, have
been reported in the literature to be susceptible to this form
of deterioration with cases involving ties being reported in
Germany (Heinz and Ludwig 1 987), Finland (Tepponen and
Eriksson 1 987), former Czechoslovakia (Vitousova 1 99 1 ),
Canada, the United States (Mielenz et a!. 1 995), South Africa
Coovriaht American Concrete Institute
13
(Oberholster et a!. 1 992), and Australia (Shayan and Quick
1 992). In most, if not all, of the alleged cases of DEF, other
mechanisms of deterioration, especially alkali-silica reaction
and freezing-and-thawing damage, have also been implicated
and it has been difficult to determine the precise role of DEF
in the deterioration process.
The occurrence of these problems and the apparent role
of elevated-temperature curing have led many countries to
impose restrictions on the heat-curing process used during the
manufacture of precast concrete. These restrictions include
limits placed on preset times, rates of heating and cooling,
and the maximum allowable concrete or curing temperatures.
Experience with the German recommendations dates back to
1 977, and there is evidence that these and similar practices in
Europe have been successful in eliminating damage due to
DEF (Skalny and Locher 1 997; Stark et a!. 1 998).
It should be noted that the risk of damage due to DEF
is not restricted to heat-cured precast concrete elements.
Internal concrete temperatures may increase due to the heat
released during the hydration of the cementitious component
of the concrete to sufficiently high levels to promote DEF
in non-heat-cured precast concrete or in massive cast-in­
place concrete elements. Indeed, the new European practices
impose similar limits on the maximum internal concrete
temperature for both precast and cast-in-place concrete.
Reviews of laboratory studies (Day 1 992; Thomas 200 1 )
indicate that expansion due to DEF is unlikely to occur unless
mortar or concrete specimens have an elevated temperature
somewhere in excess of 1 58°F (70°C) and that the risk of
expansion increases as the maximum temperature increases
above this threshold value. For mortar or concrete that has
been exposed to temperatures above the threshold, the risk
of expansion appears to be a function of many parameters,
especially the cement composition. Taking published results
collectively (Thomas 200 1 ), it appears that cements produced
from high-reactivity clinker, such as those with high C3A,
C3S, Na20e, and fineness, which consequently have a high
S03 content, have the greatest susceptibility to DEF expan­
sion when heat cured. These parameters characterize high­
early-strength cements and Kelham ( 1 996) showed a clear
correlation between the 2-day compressive strength of mortar
and the expansion of the same mortar subsequent to heat­
curing at 1 94°F (90°C). Although studies have shown rela­
tionships between DEF expansion and various compositional
parameters of the cement, there is no single parameter that
can be used to reliably predict the performance of a particular
cement. Hence, it is not possible to impose a single limit such
as sulfate content on the cement chemistry to eliminate the
risk of expansion in concrete that may be exposed to exces­
sive temperature during curing. It is apparent from labora­
tory studies, however, that high-early-strength cements such
as ASTM C l 50/C l 50M Type III cements have the highest
propensity for expansion when heat-cured at high tempera­
tures, and that cements that generally exhibit lower early-age
strength development, such as ASTM C l 50/C l 50M Types
IV, V, and cements or ASTM C l 50/C 1 50M Type II of low or
moderate fineness, will present a much lower risk of expan­
sion (Ramlochan et a!. 2003).
�.
14
G U IDE TO EXTERNAL CURING O F CONCRETE (ACI 308R-16)
Hanson,
4500
:=-
g
4000
5 3500
3000
�
U5 2500
1 00
1 25
1 50
1 75
0
200
0
25
Goto & Roy, 1 981
Detwiler et al,
1 . E-05
1 00
1 994
20000
C T = 23
�
en
.0
C T = 50
E
-;:: 1 .E-06
� 1 5000
0
• T = 70
0
ro
�
�
•
Steam
�
:g 1 0000
�
:c 1 .E-07
Q)
ro
Q)
a..
75
50
l'v1ax. Temperature {0C}
Max. Temperature (°F}
E
Q;
0
1 hr preset - SOF/hr
c
2000
PC 32.5
5 hr preset - 60F/hr
co
OJ
PC 42.5
o
/;
�
iii
Erdogdu & Kerbetci, 1 998
40
7 hr preset - 40F/hr
.r;
.r;
1 963
E
£
1 .E-08
� 5000
.Q
.r;
()
1 . E-09
0.30
0.35
0.40
0.45
0
0.50
O PC
Water-Cement
5% SF
30% Slag
Concrete Mx
Fig. 1. 7b-Various effects ofelevated temperatures.
It has been demonstrated that the risk of expansion of heat­
cured mortars and concrete can be effectively eliminated by
the incorporation of a sufficient quantity of certain pozzo­
lans such as fly ash, metakaolin, or slag cement (Ghorab et
al. 1 980; Ramlochan et al. 2003).
1.8-Sustainability
1.8.1 General-Curing plays an important role in sustain­
ability. Predictive modeling, which assesses service life of a
cementitious product, must consider the materials' initial and
ongoing hydration. Optimizing the selection, proportioning,
and mixing of materials, as well as procedures of forming,
placing, consolidation, finishing, and curing of concrete
are essential in achieving sustainable concrete with good
strength, durability, and service-life properties. Sustain­
ability is facilitated through the tailoring of a good curing
regimen to suit a given mixture design, placement, and
environmental conditions. To facilitate sustainability in the
future, new mix:ture designs may require novel approaches
Coovriaht Am�te Institute
to curing. Sustainable curing measures and materials should
include techniques that reduce the footprint on the environ­
ment, including embodied energy and C02 emissions.
1.8.2 Predictive modeling of service life-Sustainability
includes predictive models using strength or durability
requirements for concrete in a given placement environment
and generally requires that a specified curing regimen be in
place. Service life or survivability of cementitious materials
should include defined curing measures that ensure proper
hydration achieves the required performance criteria. As
state-of-the-art methods of production criterion for durable
concrete become a benchmark, curing may become increas­
ingly tailored to specific projects.
1.8.3 Curing of sustainable materials-Sustainability,
through the use of green building materials, including pozzo­
lans, fillers, and recycled materials, may require that novel
approaches be taken to facilitate adequate hydration. As higher
volumes of these materials are incorporated into mixture
designs, traditional curing measures may need to be altered.
GU IDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
Materials that have a slower hydration rate may require an
increase in the duration of curing by misting, fogging, or
wet-cover materials to maintain high humidity levels within
the curing-affected zone until a given performance level is
attained. High-performance concrete materials may benefit
by augmenting mixing water with the use of preconditioned,
absorptive, lightweight aggregate or other absorbent materials
to supplement the hydration moisture that is available.
1.8.4 Reducing environmentalfootprint-Curing can play
an important role in reducing the concrete construction envi­
ronmental footprint. Curing can be achieved with materials
that are low-VOC, nonacidic, waterborne, environmentally
sound, or green building materials. Streamlining curing
methodologies may also limit redundancies, minimize mate­
rial usage, and reduce labor and transportation costs. The use
of on-site or remote monitoring measuring devices may also
help reduce the curing footprint.
CHAPTER 2-DEFINITIONS
ACI provides a comprehensive list of definitions through
an online resource, "ACI Concrete Terminology," https://
www.concrete.org/store/productdetail.aspx?ItemiD=CT 1 3 .
Definitions provided herein complement that resource.
curing-affected zone-portion ofthe concrete most influ­
enced by external surface curing measures.
ev apo rativity maximum rate at which the atmosphere
can vaporize water from a free water surface.
-
CHAPTER 3-CURING METHODS AND
MATERIALS
3.1 -Scope
The intent of employing materials and methods for curing
concrete is to maintain a satisfactory moisture content and
temperature so that the design properties are allowed to
develop. While there are many methods for controlling the
temperature and moisture content of freshly placed concrete,
not all of these methods are equal in price, appropriateness,
or effectiveness. The means and methods used will depend
on the demands of each set of requirements. The economics
and effectiveness of the particular method of curing selected
should be evaluated for each job. Factors to be considered
include the availability of water or other curing materials,
labor requirements, control of water runoff when wet curing
is used, expected weather conditions during the curing
period, and subsequent construction requirements such as
floor finish or application of floor coverings.
Methods of curing, as discussed in ACI 308 . 1 , involve
retention of mixture water either by maintaining high
humidity at the surface with supplied water in the form of
ponding, fogging, or water-saturated cover material, or by
imposing a physical barrier such as plastic sheeting or a liquid
membrane-forming curing compound. It is the responsibility
of the user of this guide to establish appropriate safety and
health practices and to determine the applicability of regula­
tory limitations before making use of curing materials.
Coovriaht American Concrete Institute
15
3.2-Use of water for curing concrete
The method of water curing selected should provide a
complete and continuous cover of water. The curing water
should be free of aggressive impurities that are capable of
attacking or causing deterioration of the concrete (Pierce
1 994). In general, water that is potable and satisfactory as
mixing water and meets the requirements of ASTM C94/
C94M is acceptable as curing water. Where appearance is
a factor, the water should be free of harmful amounts of
substances that will stain or discolor the concrete. Dissolved
iron or organic impurities may cause staining, and the poten­
tial staining ability of curing water can be evaluated by
means of CRD-C40 1 (U.S. Army Corps of Engineers 1 975).
The use of seawater as curing water is not recommended.
The potential effects are discussed by Eglinton ( 1 998).
Care needs to be taken to avoid thermal shock or exces­
sively steep thermal gradients due to the use of cold or hot
curing water. Curing water should not be more than 20°F
( 1 1 °C) cooler than the internal concrete temperature to
minimize stresses due to temperature gradients that could
cause cracking (Kosmatka and Wilson 20 1 1 ). A sudden drop
in concrete temperature of approximately 20°F ( 1 1 °C) can
produce a strain of approximately 1 00 millionths, which
approximates the typical strain capacity of concrete (Mather
1 987) beyond which the concrete may crack. Thermal
shrinkage cracking associated with a cooling rate of more
than 5°F (3°C) per hour is discussed in ACI 306R.
3.3-lnitial curing methods
As discussed in 1 .4, initial curing refers to procedures imple­
mented anytime between placement and finishing of concrete
to reduce the loss of moisture from the concrete surface.
3.3.1 Fogging-Fogging provides excellent protection
against surface drying when applied properly and frequently
and when the air temperature is well above freezing. Fogging
requires the use of an inexpensive but specially designed
nozzle that atomizes the water into a fog-like mist. The fog
spray should be directed above, not at, the concrete surface,
as its primary purpose is to increase the humidity of the air
and reduce the rate of evaporation. This effect lasts only as
long as the mist is suspended in the air over the slab. This
means frequent or continuous fogging is necessary, and the
frequency of application should be increased as wind velocity
increases over the concrete surface. Typically, when a visible
fog is suspended over the concrete surface, the droplets are fine
enough and the application is continuous enough. Fogging is
also useful for reducing the tendency for a crust to form on the
surface of the freshly cast concrete. Fogging can precipitate
water on the concrete surface and is not deleterious as long
as the water from the sprayer does not mar or penetrate the
surface. Water from fogging should not be worked into the
surface in subsequent finishing operations. Water from fogging
should be removed or allowed to evaporate before finishing.
3.3.2 Liquid-applied evaporation reducers-Evaporation
reducers (Cordon and Thorpe 1 965) are solutions of organic
chemicals in water that are capable of producing a film over
the bleed water layer that rises to the top surface of concrete.
If present in sufficient concentration, these chemicals form
�-
16
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
an effective film that reduces the rate of evaporation of the
bleed water from the concrete surface.
Evaporation reducers can be sprayed onto freshly placed
concrete to reduce the risk of plastic shrinkage when the evap­
oration rate equals or exceeds the bleeding rate. Evaporation
reducers should be used only in accordance with manufac­
turer's instructions and are not to be used for the purpose of
making it easier to finish concrete surfaces. Materials designed
for such purpose are often referred to as finishing aids.
3.4-Final curing measures
As discussed in 1 .4, final curing refers to procedures
implemented after final finishing and when the concrete has
reached final set. It may be necessary to use an intermediate
curing technique when the concrete surface has been finished
before the concrete reaches final set, as premature applica­
tion of final curing may damage the freshly cast concrete.
3.4.1 Final curing measures based on application ofwater
3.4.1.1 Sprinkling-Fogging or sprinkling with nozzles
or sprays provides excellent curing when the air tempera­
ture is above freezing. Lawn sprinklers are effective after
the concrete has reached final set and where water runoff
or conservation measures are not a concern. A disadvantage
of sprinkling is the cost of the water in regions where an
ample supply is not readily available. Intermittent sprin­
kling should not be used if the concrete surface is allowed
to dry between periods of wetting. Soaker hoses are useful,
especially on surfaces that are vertical or nearly so. Care
should be taken to avoid erosion of the surface and potential
contamination to surrounding soils and streams. In addition
to sprinkling or soakers hoses, the use of a water-absorbent
media in nonhorizontal surface applications can help mini­
mize the possibility of erosion or contamination by lessening
the volume of water required to provide constant surface
moisture. The use of a vapor barrier in conjunction with an
absorbent media can even further reduce the water volume
required. Adding a perforated vapor barrier may be benefi­
cial in providing ease of rewet.
3.4.1.2 Ponding or immersion-Though seldom used, the
most thorough method of water curing consists of immersion
of the finished concrete in water. Ponding is sometimes used
for slabs, such as culvert floors or bridge decks; pavements;
flat roofs; or wherever a pond of water can be created by a
ridge, dike, or other dam at the edge of the slab. Van Aardt
(1 953) documented dilution of the paste and weakening of
the surface resulting from premature application of ponding.
3.4.1.3 Absorbent materials, burlap, and cotton mats­
Absorbent material coverings can hold water on horizontal
or vertical surfaces. Some effective materials have an inte­
gral vapor barrier to help prevent dehydration of the absor­
bent wicking media and possess adequate absorbent and
retention properties to provide sufficient curing moisture to
the concrete (Hover 2002). All curing materials should be
free of harmful substances such as sugar, fertilizer, tannins,
carryover salts, or other substances that may discolor the
concrete. Care should also be taken to prevent the growth
of molds or other fungus that may be harmful. Specifically
when using burlap, thoroughly rinse in water to remove .
Coovriaht Am�te Institute
soluble substances before placing it on the concrete. Burlap
that has been treated to resist rot and fire is preferred for
use in curing concrete. Burlap intended for reuse should also
be thoroughly cleaned and dried to prevent carryover salt
buildup and mildew when it is to be stored between jobs.
Higher basis weight absorbent materials and those made from
nonwoven natural materials typically hold more water, lay
flatter, are less prone to the effects of wind, and need rewet­
ting with much less frequency than those that are of light
weight and low absorbent construction. For mass concrete
placements, multiple thicknesses or more highly absorbent
natural nonwovens may be used advantageously. This is also
true when the mixture design requires more curing water
than is in the initial mixture (Hover 2002), such as some
high-performance concrete or shrinkage-compensating
concrete. Lapping the strips by half-widths when placing
will give greater moisture retention and aid in preventing
displacement during high wind or heavy rain. A continuous
supply of moisture is required when high temperature, low
humidity, or windy conditions prevail. For proper curing, the
concrete surface must remain moist throughout the curing
period. When the curing material is permitted to dry, it can
draw moisture from the surface of the concrete and allow
dissolved salts from the curing process to precipitate out of
the curing water on to the slab, thereby causing discolor­
ation. Permitting the curing material to dry can also cause
it to adhere to the concrete surface in areas where curing
moisture is insufficient. To further aid in the prevention
of drying, the curing material should be placed flat on the
surface without wrinkles and the presence of entrapped air
so as to prevent efflorescence. Any wrinkles or entrapped air
should be squeegeed to the nearest unlapped edge without
removing the water.
Heavier absorbent mats such as those made of cotton or
similar fibers can be applied much the same as lighter mats
except that, due to their greater weight, application to a
freshly finished surface should be delayed until the concrete
has hardened to a greater degree than for burlap.
Whenever concrete slabs are so large that the workers have
to walk on the freshly placed concrete to install the curing
materials, it will be necessary to wait until the concrete has
sufficiently hardened to permit such operations without
marring the surface. In no case should curing be delayed to the
detriment ofthe concrete; the curing option that best promotes
the quality of the concrete should always be selected.
Sheet curing materials typically fall into two categories:
reusable and single-use. The media of reusable materials
is typically composed of less-absorbent and very durable
synthetics that give good life and use when properly cared
for so as to prevent contamination. It is at times beneficial
that these materials be provided in rolls versus bundles to
eliminate creases from folding that prevent the material
from lying flat. Having the sheet material lay flat decreases
the chance of displacement from wind and greatly reduces
discoloration from wrinkles and entrapped air. Properly roll
reusable blankets after being thoroughly cleaned and dried
to minimize creases and wrinkles.
17
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
--
CLEAR PLASTIC
--- BLACK PLASTIC
- - - - - WHITE P LASTIC
40
0
30
(.)
0
Cl)
PERCENT
SUNSHINE
20
II..
::::J
-
('Q
II..
Cl)
a.
E
{!!.
MAX AIR
10
MIN AIR
0
--
-10
-9.4
�---
-9.4
- 1 3 .9
-20
L---�---L--�----L---�--�
1 5:00 03:00 1 5:00 03:00 1 5:00 03:00 1 5:00 03:00 1 5:00 03:00 1 5:00 03:00 1 5:00
1 2-28-98
12-29-98
1 2-30-98
12-31-9S
01-01-99
01·02-99
01 -03-99
Time, hours
Fig. 3.4. 2. 1-Temperature variations under clear, black, and white plastic (Wojakowski
1999).
Single-use materials offer economy of use and labor as
the cost of labor involved in proper cleaning, storage, and
care of the reusable materials is eliminated. Natural-fiber,
single-use materials offer ease of use, good absorbency, and
reduction of surface discoloration. The increasing number
of single-use materials available allows the user to pick a
specific product from a variety of materials that are designed
to satisfy the water retention requirements for the curing
duration required. Specific to slab-on-ground applications,
the water-absorbent nature of natural-fiber, single-use mate­
rial can reduce the amount of post-cure surface densifier
required by increasing the amount of hydrated cement parti­
cles on the concrete surface. In high wind conditions, care
should be taken to secure curing materials.
3.4.1.4 Sand curing-Wet, clean sand can be used for
curing, provided it is kept saturated throughout the curing
period. The sand layer should be thick enough to hold water
uniformly over the entire surface to be cured. Sand should
meet ASTM C33/C33M or similar requirements for dele­
terious materials in fine aggregate to minimize the risk of
damage to the concrete surface from deleterious materials
such as clay materials, coal, and lignites.
3.4.1.5 Straw or hay-Wet straw or hay has been used for
wet-curing small areas, but there is the danger that wind might
displace it unless it is held down with screen wire, burlap, or
other means. There is also the danger of fire if the straw or hay
is allowed to become dry. Such materials may discolor the
surface for several months after removal. If these materials are
used, the wetted layer should be at least 6 in. ( 1 5 0 mm) deep
and kept wet throughout the curing period.
3.4.2 Final curing methods based on retention of water­
Curing materials a.r� .. sl;l�<;ts. or .liq,t,liq_ .membrane-forming
Coovriaht American Concrete Institute
compounds placed on concrete to reduce evaporative water
loss from the concrete surface.
These materials can have several advantages:
a) They do not need to be kept wet to ensure that they do
not absorb moisture from the concrete.
b) They can be easier to handle than burlap, sand, straw
or hay.
c) They can often be applied earlier than water-curing
methods.
As discussed in 1 .4.2.2.5, curing materials can be applied
immediately after finishing without the need to wait for final
setting of the concrete.
3.4.2.1 Plastic film-Plastic film has a low mass per unit
area and is available in clear, white, or black sheets. Plastic
film should meet the requirements of ASTM C 1 7 1 , which
specifies a minimum thickness of 0.004 in. (0. 1 0 mm).
White film minimizes heat gain caused by absorption of
solar radiation. Clear and black sheeting have advantages in
cold weather by absorption of solar radiation but should be
avoided during warm weather except for shaded areas. The
general effect of the color of plastic sheeting on concrete
surface temperature is shown in Fig. 3 .4.2. 1 . Wojakowski
( 1 999) placed clear, black, and white plastic over a hardened
concrete surface and measured the temperature over a period
of 1 week during winter in Kansas. Within the week, four
separate periods were evaluated for minimum and maximum
air temperature and for percentage of the period in which the
sun was shining. Sunshine varied from 0 to 93 percent, and
the outside air temperatures varied over the time periods as
shown by the pairs of horizontal lines indicating maximum
and minimum values (Fig. 3.4.2. 1). The concrete under clear
plastic was as much as 45°F (25°C) warmer than the air, and
�-
18
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
the temperature under black plastic was approximately 27°F
( 1 5°C) warmer than under clear plastic and almost 36°F
(20°C) warmer than under white plastic during daylight hours.
The temperature difference was negligible in the absence of
sunshine. When plastic covers freshly cast concrete, heat is
also provided from the hydration of the cement.
Care should be taken to avoid tearing or otherwise inter­
rupting the continuity of the film. Plastic film reinforced
with glass or other fibers is more durable and less likely to
be torn.
Where the as-cast appearance is important, concrete
should be cured by means other than moisture-retaining
methods because the use of smooth plastic film often results
in a mottled appearance due to variations in temperature,
moisture content, or both (Greening and Landgren 1 966).
For curing methods requiring the application of water
(Hover 2002), it may be necessary to occasionally flood
under the film, which can also minimize mottling. A plastic
film bonded to absorbent fabric as described in 3.4. 1 .3 can
help to retain and more evenly distribute moisture between
the plastic film and the concrete surface. These materials
have been shown to be effective in reducing mottling.
Plastic film should be placed over the surface of the fresh
concrete as soon as possible after final finishing without
marring the surface and should cover all exposed surfaces
of the concrete. Joints in the film should be taped or lapped
sufficiently to avoid localized higher evaporation rates. It
should be placed and weighted so that it remains in contact
with or in very close proximity to the concrete during the
specified duration of curing. On flat surfaces such as pave­
ments, the film should extend beyond the edges of the slab
at least twice the thickness of the slab. The film should be
placed flat on the concrete surface, avoiding wrinkles, to
minimize mottling. Windrows of sand or earth or pieces of
lumber should be placed along all edges and joints in the
film to retain moisture and prevent wind from getting under
the film and displacing it. Alternatively, it is acceptable and
generally more economical to use a narrow strip of plastic
film along the vertical edges, placing it over the sheet on the
horizontal surface and securing all edges with windrows or
strips of wood. To remove the covering after curing, the strip
can be pulled away easily, leaving the horizontal sheet to be
rolled up without damage from tears or creases.
3.4.2.2 Reinforced paper-Composed of two layers of
kraft paper cemented together with a bituminous adhesive
and reinforced with fiber, reinforced paper should comply
with ASTM C 1 7 1 . Most papers used for curing have been
treated to increase tear resistance when wetted and dried.
Paper sheets with one white surface to give reflectance and
red\Jce absorption of solar radiation are available. A reflec­
tance requirement is included in ASTM C 1 7 1 . Reinforced
paper is applied in the same manner as plastic film (3 .4 .2 . 1 ).
Reinforced paper can be reused as long as it is effective in
retaining moisture on the concrete surface. Holes and tears
should be repaired with a patch of paper cemented with a
suitable glue or bituminous cement. Pin holes, resulting
froin walking on the paper or from deterioration of the paper
through repeated use, are evident if the paper is held up
Coovriaht Am�te Institute
to the light. When the paper no longer retains moisture, it
should be discarded or used in double thickness.
3.4.2.3 Liquid membranejorming compounds-Liquid
membrane-forming compounds for curing concrete should
comply with the requirements of ASTM C309 or C 1 3 1 5
when tested at the rate of coverage to be used on the job.
Compounds formulated to meet the requirements of ASTM
C309 include Type 1 , clear; Type l D, clear with fugitive dye;
Type 2, white pigmented; Class A, unrestricted composition,
which is usually used to designate wax-based products; and
Class B, resin-based compositions. Silicate solutions are
chemically reactive rather than membrane-forming (ASTM
C309). ASTM C 1 5 6 is the test method used to evaluate water­
retention capability of liquid membrane-forming compounds.
Membrane-forming curing compounds that meet the
requirements of ASTM C309 permit the loss of some mois­
ture and have a variable capacity to reduce moisture loss
from the surface, depending on field application and ambient
conditions (Mather 1 987, 1 990; Shariat and Pant 1 984;
Senbetta 1 988).
Compounds formulated to meet the requirements of
ASTM C 1 3 1 5 have special properties such as alkali resis­
tance, acid resistance, adhesion-promoting qualities, and
resistance to degradation by ultraviolet light, in addition to
their moisture-retention capability as measured by ASTM
C 1 56. Curing compounds are classified according to their
tendency to yellow or change color with age and exposure
and by whether they are clear or pigmented. When products
meeting the requirements of ASTM C 1 3 1 5 are tested in
accordance withASTM C 1 56, the allowable moisture loss is
0.08 lb/ft2 (0.40 kg/m2) in 72 hours when applied at a curing
compound coverage rate of 300 ft2/gal. (7.4 m2/L) for Type
I or Type II compounds. When performing the ASTM C 1 56
test in a laboratory to verify compliance with either ASTM
C309 or C 1 3 1 5 , the surface of the test specimen is relatively
smooth, and the laboratory-applied coverage rates specified
in the test method can be readily obtained. Achieving the
same coverage, and therefore achieving the same moisture­
retention effectiveness in the field, is more difficult given
the variable surface texture and the need to evenly cover
the concrete. ASTM C 1 3 1 5 notes that agencies can require
a substantially greater application rate on deeply textured
surfaces. Further, the specified evaporative environment for
the ASTM C 1 56 test corresponds to an evaporation rate from
a free water surface varying between approximately 0. 1 to
0.2 lb/ft2/h ( 1 12 to 1 kg/m2/h), which may be less severe than
encountered in a given construction environment. For these
reasons, the water loss experienced by concrete in the field
may vary from the values specified by ASTM for compli­
ance with the requirements of ASTM C309 or C 1 3 1 5 .
Curing materials can b e composed o f wax or other organic
material thinned with a solvent or carried in water in emulsion
form. The solvents can make the use of the curing compound
subject to various volatile organic compounds (VOCs) and
safety regulations that govern the transport, storage, or use
of hazardous materials. When appropriate, adequate ventila­
tion should be provided and other safety precautions should
be taken when using solvent-based compounds. Emulsion-
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
based products have replaced those in solvents in many
applications due to pressures of environmental regulations.
When overlays, coatings, paints, sealers, or any topping is
to be applied to concrete or where vehicular, pedestrian,
or aircraft traffic will traverse over the concrete, the use
of curing compounds that are wax-free are recommended.
When the concrete surface is to receive paint, finishes, or
toppings that require positive bond to the concrete, it is
critical that the curing procedures and subsequent coatings,
finishes, or toppings be compatible to achieve the neces­
sary bond. Curing compounds meeting the requirements of
ASTM C l 3 1 5 have been formulated to promote such adhe­
sion, and ASTM C l 3 1 5 includes references to test methods
for evaluating the bonding of tile and other floor cover­
ings (refer to 4. 1 .4(b )). Testing to establish compatibility
among the curing compound, subsequent surface treatments,
concrete moisture content, and the actual finished surface
texture of the concrete is recommended when performance
is critical. Such testing is beyond the scope of this document,
but useful references include Suprenant and Malisch ( 1 998d,
1 999a,b).
Alternatives to ensuring compatibility of the curing
compound with subsequent surface treatments include delib­
erate removal of the curing compound in accordance with
manufacturer's recommendations, the use of an alternative
water-retention curing method, or water curing.
Some organic resin-based curing compounds will degrade
over time with exposure to ultraviolet light from direct
sunlight. Dissipation is accelerated in the presence of water.
A self-dissipating resin compound is expected to break
down some time after application and can be used on trow­
eled or floated surfaces receiving subsequent finishes. Some
of these products may not dissipate fast enough in interior
or shaded locations and are not recommended if dissipa­
tion is the expected method of removal. Mechanical or
chemical removal should be specified when self-dissipating
compounds are used in interior applications.
For floors and slabs designed for high wear resistance,
optimum top surface strength development, durability, and
minimal cracking, the curing compound should meet or
exceed the moisture retention requirements ofASTM C l 3 1 5 .
In accordance with the manufacturer's recommendations,
liquid membrane-forming curing compounds should be
stirred or agitated before use and applied uniformly at the
manufacturer's recommended rate. The curing compound
should be applied in two applications at right angles to each
other to ensure uniform and more complete coverage. On
very deeply textured surfaces, the surface area to be treated
can be at least twice the surface area of a troweled or floated
surface (Shariat and Pant 1 984). In such cases, two separate
applications may be needed, each at 200 ft2/gal. (5 m2/L)
or greater if specified by the manufacturer to achieve the
desired moisture retention rate, with the first being allowed
, to become tacky before the second is applied. A curing
compound can be applied by hand or power sprayer using
: appropriate wands and nozzles with pressure usually in the
range of 25 to 100 psi (0.2 to 0.7 MPa). If the job size is
:large, application by power sprayer is preferred because of
CoovriahtAmerican Co�crete Institute
19
speed and uniformity of distribution. For very small areas
such as repairs, the compound can be applied with a wide,
soft-bristled brush or paint roller. Application rates are most
readily verified by recording the number of containers of
compound used, or the number of sprayer tanks or buckets
of compound applied to the surface.
For maximum beneficial effect, liquid membrane­
forming compounds should be applied immediately after
the disappearance of the surface water sheen following final
finishing. Delayed application of these materials not only
allows drying of the surface during the period of peak water
loss, but also increases the likelihood that the liquid curing
compound will be absorbed into the concrete and, hence, not
form a membrane.
When the evaporation rate exceeds the rate of bleeding
of the concrete, the surface will appear dry even though
bleeding is still occurring. Under such conditions, finishing
the concrete, the application of curing compound, or both,
can be detrimental because bleed water can be consequently
trapped just below the concrete surface. Clearly identifying
this condition in the field is difficult, and it is always risky to
delay finishing and curing. In such cases where it is important
to diagnose this problem, an approximately 1 8 in. (450 mm)
square transparent plastic sheet can be placed over the unfin­
ished, uncured concrete to shield the test area from evapora­
tion, and any bleed water can be seen accumulating under
the plastic.
Another consequence of applying curing compound to a
freshly cast concrete surface that appears dry is that evap­
oration will be temporarily stopped, but bleeding might
continue, resulting in map cracking of the membrane film
with the subsequent reduction in moisture-retention capa­
bility. This situation would require reapplication of the
curing compound.
When using curing compounds to reduce moisture loss
from formed surfaces, the exposed surface should be wetted
immediately after form removal and kept moist until the
curing compound is applied. The concrete should be allowed
to reach a uniformly damp appearance with no free water on
the surface, and then application of the compound should
begin at once. As with flatwork, dampening the concrete
prevents absorption of the curing compound, which would
prevent the formation of a membrane.
3.4.2.4 Linseed-oil-based curing compounds-Various
linseed oil emulsions have been successfully used as curing
compounds by some highway agencies (Sedgwick County
1 998 ; Minnesota Department of Transportation 1 998).
Although not strictly a membrane-forming compound, these
products should meet the requirements of ASTM C309 with
the exception ofthe 4-hour maximum drying time requirement.
These products are used as an ASTM C309 Type A curing
compound for retaining moisture in freshly cast concrete and
in some cases are used as a surface treatment to increase the
durability of hardened concrete. This latter use is beyond the
scope of this document. When used as a curing compound,
however, linseed-oil-based compounds are intended for
application directly after final texturing. Some retardation of
setting time may result from the use of these products.
�-
20
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
3.5-Termination of curing measures
At the end of the required wet-curing period, cover mate­
rials should be allowed to dry thoroughly before removal
to provide uniform, slow drying of the concrete surface.
Controlled and gradual termination of wet or moist curing
is particularly critical in cold weather when there is a risk
of freezing the freshly exposed water-saturated surface.
ACI 306R and ACI 301 contain recommendations for
gradual termination of curing and protection. Cessation of
wet curing on slabs and horizontal surfaces can increase the
potential for curling due to the sudden change from saturated
to rapid drying (Suprenant 2002). Methods for controlled
drying should be used to reduce the rate of drying following
wet curing methods. Application of a curing membrane after
cessation of wet curing is one possible method.
3.6-Cold-weather protection and curing
Cold weather puts immature concrete at risk in at least four
ways. First, the rate of evaporation of water from the surface
of concrete can be higher in cold weather than in warm
weather, particularly when the concrete is warm and the
humidity is low. Second, if the concrete temperature greatly
decreases, pore water can freeze, leading to frost damage.
Third, a cold concrete temperature slows the rate of hydra­
tion of the cement, slowing the rate at which all concrete
properties develop. Fourth, when protection is removed at
the end of the curing period, there is a risk of rapid drying,
and a rapid drop in temperature can crack the concrete. In
cold weather, control of moisture should be accompanied by
control of temperature. Wet-curing in freezing weather is as
beneficial to the long-term serviceability of the concrete as
it is in warm weather, but only if the moist concrete is kept
from freezing.
.Water curing in cold weather can require the construction
of a heated, temporary enclosure. For these reasons, cold­
weather curing procedures frequently include evaporation
reducers as an initial curing, followed by membrane-forming
curing compounds, by covering with dry plastic sheets or
similar coverings, or both. These techniques may or may
not produce the equivalent concrete surface properties as
provided by the application of water, but the risk of freezing
damage to the concrete surface is reduced. As discussed
in ACI 306R, enclosures heated with combustion heaters
should be well vented to avoid high concentrations of carbon
monoxide as well as damage from carbonation. Combustion
heaters should not directly heat or dry the concrete.
Cold-weather curing further requires that water supplies,
the water distribution system, and the runoff water also
should be kept from freezing. ACI 306. 1 provides specifi­
cation requirements for cold-weather concreting, and addi­
tional information is found in ACI 306R.
3.6.1 Protection against rapid drying in cold weather­
The rate of evaporation from a freshly placed concrete
surface can be greater in cold weather than in hot weather,
especially when the concrete has been heated by the addi­
tion of hot water that evaporates into cold, dry air. Further,
cold weather is often accompanied by faster average wind
speeds. Senbetta and Brury ( 1 99 1 ) discussed the likelihood
Coovriaht Am�te Institute
of developing plastic shrinkage cracking in cold weather. To
minimize plastic shrinkage cracking and to sustain hydration
of the cement, concrete placed in cold weather should be
maintained at a high moisture content at the surface.
3.6.2 Protection againstfrost damage Maintenance of a
high moisture content at the surface when the air temperature
may drop below freezing increases the risk of frost damage,
scaling, and aggregate pop-outs. If freezing and thawing is
anticipated at any time during construction or in service,
when either the cement paste or the aggregates are criti­
cally saturated near the surface of the concrete, air-entrained
concrete should be used. For such conditions, properly
air-entrained concrete containing the air contents required
by ACI 3 1 8 or ACI 3 0 1 or recommended by ACI 20 1 .2R
should be used. Damage from freezing at early ages should
be prevented by protecting the concrete from freezing, and
by curing without the addition of external water until a
compressive strength of at least 500 psi (3 . 5 MPa) is devel­
oped. If it is likely that the concrete will be critically satu­
rated when subsequently exposed to freezing and thawing
temperatures, protection and curing should be continued until
a compressive strength of approximately 4000 psi (28 MPa)
is reached. For resistance to deicer scaling, a compressive
strength of 4500 psi (3 1 MPa) should be attained before such
exposure is permitted (Klieger 1956; Powers 1 962; Mather
1 990). These general rules may not apply for concretes
incorporating special cements or other special ingredients,
or for concrete that is cured at high temperature (Pfeifer and
Marusin 1 982; Heinz and Ludwig 1 987; Kelham 1 996).
3.6.3 Rate of concrete strength development in cold
weather-When added-water curing is required in freezing
weather, ACI 306 . 1 and ACI 3 1 8 require that the temperature
of the moist concrete be kept above 50°F ( 1 0°C). Although
concrete continuously maintained at a curing temperature of
50°F ( 1 0°C) in the field will be protected against freezing,
such concrete will develop compressive strength at approxi­
mately two-thirds the rate of a companion cylinder cured in
the lab at 73°F (23°C) when measured at 3 days (Kosmatka
and Wilson 20 1 1 ). This reduced rate of strength gain can
have significant impact on construction operations such as
form and shore removal or the introduction of construc­
tion or service loads. When rate of strength development
is critical in cold weather, it may be necessary to increase
the curing temperature on the basis of tests with the specific
concrete mixture. In-place tests may be necessary.
3.6.4 Removal of cold-weather protection-When water
curing is used, either by retention or application of water,
and the ambient air temperature is or will be below freezing,
the concrete surface should be allowed to dry for at least
24 hours before discontinuing or removing the temperature
protection to minimize the likelihood of a nearly saturated
surface condition when the concrete is exposed to freezing
temperatures. Otherwise, a moist and perhaps warm concrete
surface can be rapidly cooled and dried, resulting in freezing
and, in some cases, cracking. Therefore, cold-weather curing
coverings should be removed in stages to slow the rates of
cooling and drying.
-
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
21
3.7-Hot-weather protection and curing
3.8-Accelerated curing
Hot weather includes warm, humid environments like
summer along the Gulf of Mexico or within large river
valleys that can be relatively benign in regard to concrete
curing, or the more hostile warm and dry environments like
arid regions of the west or southwest United States. In any
dry environment, it is critical to maintain adequate mois­
ture content in the concrete, and under such conditions,
added curing water can evaporate so quickly that it requires
constant replacement.
Hot weather is defined as any combination of high air
temperature, low relative humidity, and wind velocity that
impairs the quality of fresh or hardened concrete or other­
wise results in undesirable concrete properties. Because
hot weather can lead to rapid drying of concrete, protection
and curing are critical. Additional information about curing
concrete in hot weather is contained in ACI 305R.
Hot-weather curing starts before the concrete is placed,
with steps taken to ensure that the subgrade, adjacent
concrete, or formwork do not absorb water from the freshly
placed concrete. Spraying the formwork, existing concrete,
reinforcement, and subgrade with water before placement
can minimize this problem. This step can also lower the
temperature of those surfaces. Quality-control measures
should be used to avoid standing or ponded water on these
surfaces while placing the concrete.
During hot weather, initial curing methods should be
used immediately after placing, and before and during the
finishing process. Steps for initial curing should be taken to
slow the evaporation of the bleed water or to replenish the
bleed water. Windscreens or sunscreens that block wind and
radiant energy reduce evaporation rates, and fogging raises
the humidity of the air above the concrete, thus preventing
water loss by evaporation from the concrete. Fogging should
not be used as a finishing aid by adding water to the surface.
Training, judgment, and quality-control measures are
required to replace the evaporated bleed water. At no time is
it proper to mix surface water with the top layer of cement
paste in subsequent finishing operations. Mixing of water
into the paste increases the w!cm at the surface, reducing
strength and durability in this critical portion ofthe concrete.
When high temperatures with wind, low humidity, or both,
prevail, an evaporation-reducing film may need to be applied
one or more times during the finishing operation to reduce
the risk of plastic shrinkage cracking and crusting (3 . 3 .2).
Again, the evaporation-reducing film is not to be used as a
finishing aid.
Final curing methods can be used once the concrete surface
will not be damaged by the application of curing materials
or water. The need for continuous curing is greatest during
the first few days after placement of the concrete in hot
weather. During hot weather, provided that favorable mois­
ture conditions are continuously maintained, concrete can
attain a high degree of maturity in a short time. Water curing,
if used, should be continuous to avoid volume changes due
to alternate wetting and drying. Liquid membrane-forming
compounds with white (ASTM C309 Type II, Class A)
pigments should be used to reflect solar radiation.
A variety of proprietary products and specialized curing
procedures have been developed to rapidly cure concrete prod­
ucts. These include insulating the concrete to accelerate curing
by retaining heat of hydration or the addition of heat via steam
or other methods. Such procedures, alone or in combination,
are used to reduce the total time required for the concrete to
achieve sufficient strength to permit handling or use. Elevated
curing temperatures can cause durability problems ( 1 .7 and
3 . 1 0). It is recommended, however, that the internal temper­
ature of the concrete not exceed 1 5 8°F (70°C) (Pfeifer and
Marusin 1 982; Heinz and Ludwig 1 987; Kelham 1 996).
Coovriaht American Concrete Institute
3.9-Minimum curing requirements
3.9.1 General-Curing should be continued long enough
to ensure that 1 00 percent of the specified value for concrete
properties will be developed in a reasonable time period after
deliberate curing measures have been terminated, especially
for mechanical properties such as strength or modulus of
elasticity, and for durability-related properties, such as low
permeability, abrasion, or scaling resistance; initial surface
absorption; or resistance to freezing and thawing. After curing
measures are terminated and the concrete is fully exposed
to the natural environment, the rate at which mechanical­
or durability-related properties continue to develop could
be reduced significantly. In the case of concrete proper­
ties in the curing-affected zone, further development may
cease altogether upon drying of the near-surface. For these
reasons, it is always best to maintain deliberate curing until
the desired in-place properties have been achieved. Termina­
tion of deliberate curing at some time short of full develop­
ment of desired properties may be reasonable when based
on experience with a given concrete mixture in a given envi­
ronment. Thus, when strength is the essential performance
criterion, it is common to maintain curing measures until a
minimum of 70 percent of the specified 28-day strength };!
has been achieved (ACI 3 0 1 ). When the structure's perfor­
mance requires that the in-place strength or other concrete
property reaches 1 00 percent of the specified value, curing
should be extended until tests prove that the specified prop­
erty has been reached. The temperature and moisture content
of small, field-cured cylinders, however, can differ signifi­
cantly from that of the larger concrete placement that they are
meant to represent. The in-place strength can be verified by
tests such as penetration resistance (ASTM C803/C803M),
pullout tests (ASTM C900), maturity measurement (ASTM
C 1 074), or tests of cast-in-place cylinder specimens (ASTM
C873/C873M). Also refer to ACI 228 . 1 R for procedures to
implement these in-place tests.
When performance criteria, such as surface hardness, abra­
sion resistance, resistance to freezing and thawing, surface
absorption, or permeability are required, curing may need to
be extended until the required values for such properties are
achieved. It may be necessary to perform laboratory tests to
evaluate the effect of curing on various concrete properties.
Useful standard tests for this purpose may include ASTM
C666/C666M, C642, C 1 202, C944/C944M, C4 1 8, C779/
C779M, and C 1 1 3 8M (also refer to Liu [ 1 994]). In-place
�.
22
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
tests for surface penetrability are discussed in ACI 228.2R
and in Chapter 5 of this document.
3.9.2 Factors influencing required duration of curing­
The duration of curing required to achieve the desired levels
of strength, durability, or both, depends on the chemical compo­
sition and fineness of the cementitious materials, w/cm, mixture
proportions, aggregate characteristics, chemical and mineral
admixtures, temperature of the concrete, and effectiveness of
the curing method in retaining moisture in the concrete. This
complex set of factors makes it difficult to confidently state
the minimum curing time required to achieve the desired
level of performance with the particular mixture in ques­
tion. For concrete with and without pozzolans and chemical
admixtures, a 7-day minimum duration of curing will often
be sufficient to attain approximately 70 percent of the speci­
fied compressive strength (Kosmatka and Wilson 20 1 1 ). It
is not necessarily true, however, that durability characteris­
tics, such as abrasion resistance or surface absorption, will
reach satisfactory levels in the same minimum time. Certain
cement and admixture combinations and high temperatures
are likely to reduce the time required to less than 7 days,
whereas other combinations of materials, cooler concrete
temperatures, or both, will extend the time required.
Table 3.9.2-Recommended minimum duration of
curing for concrete mixtures*
Minimum curing
period
ASTM C l 50/C l 50M Type I
7 days
ASTM C 1 50/C 1 50M Type II, Type II (MH)
1 0 days
ASTM C 1 50/C 1 50M Type III or when accelerators
are used to achieve results demonstrated by test
3 days
to be comparable to those achieved using ASTM
C 1 50/C 1 50M Type
III
cement
1 4 days
ASTM C 1 50/C 1 50M Type IV or Type V cement
Blended cement, combinations of cement and other
cementitious materials of various types in various
In general, when the development of a given strength
or durability is critical to the performance of the concrete
during construction or in service, the minimum duration
of curing should be established on the basis of tests of the
required properties performed with the concrete mixture in
question. It is the responsibility of the designer and specifier
to determine which properties are critical to the performance
of the concrete under the intended service conditions and to
develop a testing program to verify that the curing has been
maintained long enough so that such properties have been
achieved.
When natural weather conditions of temperature, humidity,
and precipitation combine to cause zero net evaporation from
the surface of the concrete, no curing measures are required
to maintain adequate moisture content for as long as those
natural conditions remain. In most climates, however, such
conditions can change hourly or daily, and rarely persist for the
time required to foster development of the required concrete
properties. It is therefore necessary to take steps to protect the
concrete against loss of moisture. When no data are available
from experience, values are not specified for concrete strength
or durability, and when testing is not performed to verify
in-place strength, concrete should be maintained above 50°F
( 1 0°C) and kept moist for the minimum curing periods shown
in Table 3 .9.2. Table 3 .9.2 is not intended to apply to acceler­
ated curing under high temperature, high pressure, or both.
3.10-Temperature limits during curing
To minimize the risk of durability problems associated
with exposure to elevated temperatures during curing,
the maximum internal temperature of concrete should be
controlled such that it does not exceed 1 58°F (70°C) at any
time during curing. If an excursion to a higher temperature
(in the range of 1 5 8 to 1 85°F [70 to 85°C]) is anticipated,
then the measures indicated in Table 3 . 1 0 should be adopted.
These recommendations apply to precast and cast-in-place
concrete whether or not heat is deliberately applied to raise
the temperature of the concrete during curing.
Variable
proportions in accordance with ASTM C595/
C595M, C845/C845M, and C l l 57/C l l 5 7M
·with various cement types when no testing is performed and no concrete properties
are specified.
Table 3.1 0-Recommended measures to minimize risk of durability problems associated with exposure to
elevated temperatures during curing
Maximum concrete temperature
T�
T
Level of prevention required
1 58°F (70°C)
No prevention required
Use one of the following approaches to minimize the risk of expansion:
I.
Use portland cement that meets the requirements of ASTM C l 50/C l 50M for Type II, IV, or Type V
cement and has a fineness value
� 400 m2/kg
2. Use portland cement with a ! -day mortar strength (ASTM C 1 09/C l09M)
�
2905 psi (20 MPa)
3. Use the following proportions of pozzolan or slag in combination with ASTM C l 50/C l 50M portland
1 5 8°F (70°C) <
T�
1 85°F (85°C)
cement or cements meeting ASTM C595/C595M or ASTM C 1 1 57/C ! 1 57M
�25 percent fly ash meeting the requirements ofASTM C 6 1 8 for Class F fly ash
�35 percent fly ash meeting the requirements of ASTM C6 1 8 for Class C fly ash
�35 percent slag meeting the requirements of ASTM C989/C989M
�5 percent silica fume (meeting ASTM C 1 240) in combination with at least 25 percent slag
� 1 0 percent metakaolin meeting ASTM C6 1 8
T>
Coovriaht Am�te Institute
1 85°F (85°C)
The internal concrete temperature should not exceed 1 85°F (85°C) under any circumstances.
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
CHAPTER 4-CURING FOR DIFFERENT TYPES OF
CONSTRUCTION
4.1 -Pavements and other slabs on ground
4.1.1 General-Slabs-on-ground include highway pave­
ments, airfield pavements, canal linings, parking lots,
driveways, walkways, and floors. Slabs have a high ratio of
exposed surface area to volume of concrete. Without preven­
tive measures, the early loss of moisture due to evaporation
from the concrete surface could be so large and rapid as to
result in plastic shrinkage cracking. Continued loss of mois­
ture and the accompanying decrease in the degree of hydra­
tion would have a deleterious effect on strength, abrasion
resistance, and durability. When moisture loss is predomi­
nantly at the top surface of the concrete, the gradient in
moisture content leads to greater shrinkage at the top than
at the bottom, which in tum leads to an upward curling of
the slab (Ytterberg 1 987a,b,c). Alternatively, moisture can
be lost from the bottom surface due to absorption into a dry
subgrade, causing the opposite moisture gradient if the top
surface is kept moist. This also leads to distortion of the slab.
To minimize the development of such gradients in moisture
content, both the top and bottom of slabs-on-ground should
be uniformly moist. Uniformly moist conditions are usually
required if the properties of the concrete surface are impor­
tant for the performance or appearance of the slab. This is
achieved by prewetting the subgrade and minimizing mois­
ture loss at the top surface through initial, intermediate, and
final curing as described in Chapter 1 . Similarly, when an
impervious membrane or vapor barrier is installed below
the slab, maintaining the top surface in a moist condition is
imperative to minimize curling. Placement of a 4 in. ( 1 00
mm) compacted, drainable fill on top of membranes and
vapor retarders helps to dry the bottom of the slab so that
curling is reduced while both the top and bottom surfaces
dry (ACI 302 . 1 R). If the compacted fill becomes wet and
is not allowed to dry prior to slab placement, it can form
a water reservoir and delay slab drying (ACI 302.2R). The
final tendency for distortion of the slab due to differen­
tial volume change, however, will depend on the moisture
gradient after curing measures have been terminated. The
decision whether the vapor membrane is directly below the
slab or below a layer of compacted, drainable fill should be
decided on a case-by-case basis. (Suprenant and Malisch
1 998c). Refer to ACI 302.2R for additional guidance.
4.1.2 Curing procedures-To maintain a satisfactory
moisture content and temperature, the entire surface of the
newly placed concrete should be treated in accordance with
one of the water-curing methods (3 .2), one of the curing
material methods (3 .4.2), or a combination thereof, begin­
ning as soon as possible after finishing operations without
marring the surface.
To avoid plastic shrinkage cracks, protective measures
such as sun shields, wind breaks, evaporation reducers,
or fog spraying should be initiated immediately to reduce
evaporation. Exposed surfaces of the slab should be entirely
covered and kept wet until the required concrete properties
have developed to. the. desired level.
Coovriaht American Concrete Institute
23
Mats used for curing can either be left in place and kept
saturated for completion of the curing, or can be subsequently
replaced by a liquid membrane-forming curing compound,
plastic sheeting, reinforced paper, straw, or water. If the
concrete has been kept continuously moist since casting
and finishing, drying of the concrete with its accompanying
shrinkage can begin only when the curing procedures are
discontinued. Therefore, the surface should be protected
against rapid loss of moisture upon the termination of curing
by replacing wet burlap with plastic sheets until the surface
has dried under the sheets.
4.1.3 Duration of curing-When the average ambient
daily temperature, which is computed as the average of the
highest and lowest temperature from midnight to midnight,
is above 40°F (5°C), the recommended minimum period of
maintenance of moisture and temperature for all procedures
is as shown in Table 3 .9.2 or it is the time necessary to attain
an in-place strength of the concrete of at least 70 percent of
the specified compressive or flexural strength. If testing is
not performed to verify in-place strength, concrete should
be maintained above 50°F ( 1 0°C) and kept moist for the
time periods shown in Table 3.9.2, unless otherwise directed
in the specifications. Longer curing periods will delay slab
drying (ACI 302.2R) and only delay, rather than decrease,
slab curling (ACI 3 60R). Strength-based criteria should be
replaced or augmented with durability-related criteria when
appropriate. When concrete is placed at an average daily
temperature of 40°F (5°C) or lower, precautions should be
taken to prevent damage by freezing as recommended in ACI
306R. These general-purpose recommendations can be insuf­
ficient if durability-related surface properties are required.
4.1.4 Moisture sensitiveflooring-Floors that will receive
moisture-sensitive flooring should receive special attention.
Using a curing compound that meets the criteria in ASTM
C 1 3 1 5 is not enough (Hukey 2008). Techniques recom­
mended by ACI 302.2R include:
a) Slabs should not be cured by adding water using
ponding or wet burlap measures, for example. Adding water
to the slab may significantly extend drying time.
b) Curing compounds or cure-and-seal materials should
not be used unless such use is approved in writing by the
adhesive and flooring manufacturer. The curing product
manufacturers' conformance to ASTM C 1 3 1 5 is not a
substitute for the adhesive and flooring manufacturers'
approval. Using a curing compound will slow the initial
drying, resulting in longer drying times, and the compound
will typically have to be removed before the covering adhe­
sive can be placed.
c) The slab should be cured by being covered with water­
proof paper, plastic sheets, or a combination of the two for
3 to 7 days.
4.2-Buildings, bridges, and other structures
4.2.1 General-Concrete in structures and buildings
includes cast-in-place walls, columns, slabs, beams, and all
other portions of buildings except slabs-on-ground, which
are covered in 4. 1 . It also includes small footings, piers,
retaining walls, tunnel linings, and conduits. Not included
�.
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
24
is mass concrete (4.3), precast concrete, and other construc­
tions as discussed in 4.5 .
4.2.2 Curingprocedures-Under usual placing conditions,
curing should be accomplished by one or more methods
discussed in Chapters 1 and 3 . For floors that will receive
moisture-sensitive flooring, refer to 4 . 1 .4.
Additional curing should be provided after the removal
of forms when the surface strength or durability of under­
side surfaces is deemed important, or when it is necessary
to minimize dusting. Additional curing is done by either
applying a liquid membrane-forming curing compound or
by promptly applying sufficient water to keep the surface
continuously moist. Water curing of vertical surfaces can be
done by using wet burlap covered with polyethylene. Water
curing of the bottom of slabs and beams is usually desirable
but is not often done, as it is difficult to effectively accom­
plish. Form removal at these locations should be done when
curing has been sufficient.
After the concrete has hardened and while the forms are
still in place on vertical and other formed surfaces, form
ties may be loosened when damage to the concrete will
not occur and water applied to run down on the inside of
the form to keep the concrete wet. Care should be taken to
prevent thermal shock and cracks when using water that is
significantly cooler than the concrete surface. Curing water
should not be more than approximately 20°F ( 1 1 oq cooler
than the concrete; refer to 3 .2. Immediately following form
removal, the surfaces should be kept continuously wet by a
water spray or water-saturated fabric or until the membrane­
forming curing compound is applied. Curing measures
should include treatment of top surfaces.
4.2.3 Duration of curing When the daily mean ambient
temperature is above 40°F (5°C), curing should be contin­
uous for the time periods shown in Table 3.9.2, or for the
time necessary to attain a minimum of 70 percent of speci­
fied compressive strength, or flexural strength if appro­
priate, whichever period is longer. If concrete is placed with
daily mean ambient temperatures at 40°F (5°C) or lower,
precautions should be taken as recommended in ACI 306R.
Strength-based criteria should be replaced or augmented
with durability-related criteria when appropriate (3 . 9 . 1 and
Chapter 5).
-
4.3-Mass concrete
4.3.1 General Mass concrete is most frequently encoun­
-
tered in piers, abutments, dams, heavy footings, and similar
massive construction, although the impact of tempera­
ture rise and thermal gradients should be considered in all
concrete, whether the concrete is reinforced or not. Such
problems are exacerbated where high-strength and high­
cementitious-materials contents are required. Recommenda­
tions for the control of temperature and thermal gradients
in mass concrete are found in ACI 207 . 1 R and ACI 207.2R.
If the maximum internal concrete temperature is likely to
exceed 1 5 8°F (70°C) during curing, then suitable precau­
tions should be taken to minimize the risk of durability prob­
lems (3 . 1 0).
Coovriaht Am�te Institute
4.3.2 Methods and duration of curing-Mass concrete is
often cured with water for the additional cooling benefit in
warm weather; however, this can be counterproductive when
the temperature gradient between the warmer interior core
and the cooler surface generates stress in the concrete. Sensors
may be used to monitor the temperature differential between
the interior core and the surface of the concrete. Because the
surface must be maintained at a relatively small tempera­
ture differential, a surface temperature of 1 20 to 1 50°F (49
to 66°C) is common. To avoid having to apply scalding hot
water, curing blankets can be used to protect the concrete
from rapid moisture loss once formwork is removed. The
blankets will help maintain both moisture and temperature
as the concrete gains strength and, therefore, tensile strength
resistance to thermal shock. Horizontal or sloping unformed
surfaces of mass concrete can be maintained continuously
wet by water spraying, wet sand, or water-saturated fabrics.
For vertical and other formed surfaces, after the concrete
has hardened and the forms are still in place, the form ties
may be loosened and water supplied to run down the inside
of the form to keep the concrete wet (4.2.2). Immediately
following form removal, the surfaces can be kept continu­
ously wet by a water spray or water-saturated fabric. Curing
water should not be more than approximately 20°F ( 1 1 °C)
cooler than the concrete because induced surface strains may
cause cracking (ACI 302. 1 R).
Liquid membrane-forming curing compounds may be the
best alternative in some instances. During cold weather, after
the initial protection period from freezing, the application of
a liquid membrane-forming curing compound, in place of
spraying surfaces with water, will adequately reduce drying
and provide satisfactory curing conditions without icing
problems. The use of curing compounds may be permitted
if the surface is not a construction joint or if the membrane
is removed before placing adjacent concrete. A self-dissi­
pating membrane-forming curing compound can be used
on concrete surfaces that are to receive an additional layer
of concrete or other bonded surface treatment. The surface
should be cleaned before the new concrete is placed. Use
of the membrane-forming curing compound, however, may
alter the appearance of the concrete surface.
Curing should start as soon as the concrete has hardened
sufficiently to prevent surface damage. For unreinforced
massive sections not containing slag cement or pozzolans,
curing should be continued for not less than 2 weeks. Where
slag cement or pozzolans are included in the concrete, the
minimum time for curing should be not less than 3 weeks.
For reinforced mass concrete, curing should be continuous
for a minimum of 7 days or until 70 percent of the speci­
fied compressive strength is obtained, if strength is the key
concrete performance criterion. For construction joints,
curing should be continued until resumption of concrete
placement or until the required curing period is completed.
4.3.3 Form removal and curingformed suifaces-Forms
for mass concrete can be removed as soon as removal
operations can be safely performed without damage to the
concrete or impairment to the serviceability of the struc­
ture. During cold weather, the protection afforded by forms
25
GUIDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
can make it advantageous to leave the forms in place until
the end of the minimum protection period, or even longer.
When forms are removed and protection is discontinued, the
concrete should be cooled gradually to ambient temperature
at rates not exceeding 20°F ( 1 1 °C) in 24 hours. The concrete
can be cooled gradually by replacing the forms with cover­
ings that retain less heat when the forms are removed. When
the temperature differential between the concrete surface
and the ambient air is less than 20°F ( 1 1 °C), forms can be
removed and protection discontinued without the need for
gradual cooling (ACI 3 0 1 ).
4.4-Curing colored concrete floors and slabs
Colored or decorative concrete has specialized curing
requirements that emphasize the protection of the aesthetics
of the finish. For example, concrete can be colored by
applying a dry-shake hardener or using integral coloring
pigments. The goal is normally to obtain a colored surface
with minimal variations. It is imperative that the curing
process be prompt, continuous, and uniform. The following
methods have been used successfully to provide satisfactory
moisture retention, adequate strength development for the
wearing surface, and to minimize cracking:
a) Application of a clear membrane-forming curing
and sealing compound meeting ASTM C 1 3 1 5, Type I,
Class A. Note that non-yellowing curing compounds can
discolor over time. For colored industrial floors subjected
to moderate or heavy traffic, the curing compound should
limit moisture loss to 0.008 lb/ft2 (0.040 kg/m2) at a
coverage rate of 300 ft2/gal. (7.4 m2/L).
b) Application of a matching pigmented membrane­
forming curing compound. Note that a significant color
difference can be expected when the curing compound
wears off.
c) Application of a removable curing compound. The
removal process should be thoroughly discussed before
applying these materials. The timing of the removal process
is affected by many factors, such as the rate of top surface
strength development.
d) Application of an approved nonstaining sheet membrane
per ASTM C 1 7 1 . This membrane has plastic on the outer
surface and felt or similar absorptive, nonstaining material
on the inner surface. This membrane should be placed flat on
the concrete surface to minimize mottling due to differential
moisture loss. The use of polyethylene alone is not recom­
mended because the contact between the polyethylene and
the surface of the concrete is variable, resulting in a mottled
appearance.
e) Application of ponding or other equivalent moist-curing
or water-retention methods. The surface should be kept
continuously moist for 7 days or longer without periodic
drying. Ponding can affect the appearance of the colored
concrete. Check the water source for minerals or compounds
that can stain or modify the color of the concrete. Also check
any water-retention coverings that can discolor the concrete.
Placement of a test slab is recommended to visually assess
the appearance achieved by the combination of concrete
coloring and curing methods. The test slab should be larger
Coovriaht American Concrete Institute
Table 4.5-Curing for specialty concrete
Specialty concrete
ACI
committee document
Insulating concrete
523. 1 R
Shrinkage-compensating concrete
223R
Roller-compacted concrete
207.5R
Self-consolidating concrete
237R
Floor and slab construction
302. 1 R
Slabs that receive moisture sensitive flooring material
302.2R
Architectural concrete
303R
Decorative concrete
3 1 0R
Vertical slipform construction
313
High-strength concrete
363R; 363.2R
Shotcrete
506.2
Pervious concrete
522R
Fiber-reinforced concrete
544.3R
Latex-modified concrete
548 . 1 R
than 1 00 ft2 ( 1 0 m2) and should b e prepared using the concrete
mixture and finishing and curing techniques planned for the
project. The environmental conditions should be the same
or similar to those expected for the project. Several different
curing methods can be used on the test slab(s).
4.5-Specialty constructions
Previous chapters and sections have addressed curing
for normal cast-in-place concrete. Further information on
curing specialty concrete and special construction tech­
niques is referenced in Table 4.5. Curing of cementitious
repairs, either concrete or mortar, should be in accordance
with manufacturer's instructions for proprietary materials.
Repairs are often smaller or thinner in scale; thus, curing can
be more important. Shrinkage and bond of the repair to the
substrate may also be affected by the curing measures used.
CHAPTER 5-MONITORING CURING AND CURING
EFFECTIVENESS
5.1 -General
Most specifications for curing freshly placed concrete
prescribe a recommended curing method or acceptable alter­
natives combined with a specified duration over which the
methods must be used. Monitoring the effectiveness of the
curing methods used or evaluating the environment in which
the concrete has been placed is of value for assuring speci­
fied performance.
5.2-Evaluating environmental conditions
The need for moisture control in freshly placed concrete
depends on the rate of moisture loss from that concrete.
Moisture loss depends on the water content, the ease with
which water can move through the fresh concrete, the rate of
bleeding, the rate of absorption into forms or subgrade, and
the rate of evaporation of water from the exposed surfaces of
�.
26
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
the fresh concrete. The rate of evaporation from the surface
of concrete depends on many factors, including the tempera­
ture and other properties of the mixture, construction opera­
tions, surface texture, whether the surface is directly exposed
to the air or is covered with bleed water, curing water or
chemical treatments, or surface coverings. Evaporation also
depends on a variety of environmental factors, including the
temperature of the concrete, the temperature of the water
on the surface of the concrete, the temperature and relative
humidity (RH) of the air above the surface of the concrete,
the wind speed close to the concrete surface ( 1 .4.2.2 . 1 ), and
surface texture.
5.2.1 Estimating evaporation rate-ACI 305R describes,
and should be referred to for, the current methods for esti­
mating the evaporation rate. The discussion that follows
is for additional information. Approximate methods for
estimating the rate of evaporation of water from a water­
covered surface have been proposed since the early 1 800s
(Brutsaert 1 987; Veihmeyer 1 964; Uno 1 998). Each of these
methods estimates the rate of evaporation on the basis of
measurements of air temperature and relative humidity,
water temperature, and wind speed. The most common of
these approximate methods used by the concrete industry
is the relationship adopted from hydrological applications
(Menzel 1 954; Veihmeyer 1 964; Uno 1 998). This method
was subsequently reformatted by the National Ready Mixed
Concrete Association (NRMCA 1 960) to produce the nomo­
graph shown in Fig. 5.2. 1 .
The nomograph is most commonly used to estimate
evaporation rates for the purpose of evaluating the risk of
plastic shrinkage cracking (Lerch 1 95 7; NRMCA 1 960).
This is based on the supposition that the surface begins to
dry when the evaporation rate exceeds the bleeding rate.
Because bleeding rates vary for different mixtures from 0 to
over O.+ lb/ft2/h ( 1 .0 kg/m2fh), vary over time after casting,
and are. not normally measured in the field, a value is most
often a�sumed for the bleeding rate that then becomes an
implicitly assumed value for critical rate of evaporation. The
most commonly quoted value is 0.2 lb/ft2/h ( 1 .0 kg/m2/h)
based qn work originally reported by Menzel ( 1 954) and
Lerch ( 1 95 7). Experience with high-performance bridge
deck oV'erlays containing silica fume that exhibited a sharply
reduced bleeding rate has led to specified maximum allow­
able evaporation rates of only 0.05 lb/ft2/h (0.25 kg/m2/h)
for such overlays (Virginia Department of Transportation
1 997). Other specifications reflecting a reduced bleeding
rate with modern concretes vary from 0. 10 to 0 . 1 5 lb/ft2/h
(0.50 to 0.75 kg/m2fh) (Krauss and Rogalla 1 996). When the
concrete mixture has a zero bleeding rate, the critical evapo­
ration rate above which the surface will dry is zero. Zero
bleeding rates are characteristic of dense mixtures incorpo­
rating fly ash, silica fume, slag cement or other pozzolans,
high cement contents, low w!cm, fine cements, or high air
contents. Further, all concrete mixtures exhibit a dimin­
ishing bleeding rate during setting with an eventual bleeding
rate of zero.
5.2.1.1 The Menzel/NRMCA nomograph-The nomo­
graph (Fig. 5.2. 1 ) and its underlying equations characterize
Coovriaht Am�te Institute
the evaporative environment and are not intended to esti­
mate the actual rate at which water is being lost from the
concrete surface. Figure 5.2. 1 provides an estimate of evap­
orativity (Jalota and Prihar 1 998; Uno 1 998). The nomo­
graph is therefore most useful as a means of approximately
characterizing the environment into which the concrete is
being placed. This can be helpful for forecasting the need for
curing and protection measures, and for estimating the likely
effects of changes in air or concrete temperature, humidity,
or wind speed on evaporation.
5.2.1.1.1 Limitations and accuracy-Because the nomo­
graph was derived from an experimental fit of actual evapo­
ration rates with measurements of wind speed, temperature,
and humidity, environmental measurements in the field
should be taken as in the original experiments as follows.
a) The air temperature is to be taken 4 to 6 ft ( 1 .2 to 1 .8 m)
above the evaporating surface in the shade.
b) The temperature of the water being evaporated at the
surface is equal to the temperature of the concrete.
c) The relative humidity should be measured in the shade,
on the windward side (upwind) of, and 4 to 6 ft ( 1 .2 to 1 .8
m) above, the evaporating surface.
d) The wind speed should be measured at a height of 20
in. (0.5 m) above the surface of the concrete. It is further
assumed that the wind velocity profile, which is the variation
of wind speed with height above the evaporating surface, is
identical to that which prevailed in the experiments that led
to development of the equation.
These measurement conditions were defined in the orig­
inal work by Menzel ( 1 954) but were inadvertently deleted
from the nomograph in 1 960 (NRMCA 1 960) and in all
subsequent versions.
Uno ( 1 998), Hover ( 1 992), Shaeles and Hover ( 1 988),
and Al-Fadhala and Hover (200 1 ) have discussed the accu­
racy of the nomograph and its sensitivity to the measuring
protocols. In wind-tunnel testing under controlled condi­
tions, Al-Fadhala and Hover (200 1 ) demonstrated that when
measurements were taken as originally defined in Menzel's
paper ( 1 954), estimates based on the nomograph were within
±25 percent of actual evaporation rates up to 0.2 lb/ft2/h
( 1 .0 kg/m2/h). At higher evaporation rates, the nomograph
consistently overestimated the actual rate by up to 50 percent
at 0.36 lb/ft2/h ( 1 .8 kg/m2fh).
The most common error in using the nomograph is to
measure wind speed at other than 20 in. (0.5 m) above the
evaporating surface in question. Because the surface air
speed defines the evaporative environment and is highly
variable based on ground clutter and the prevailing wind
velocity profile, measurements taken from nearby weather
stations at heights varying from 6 to 36 ft (2 to 1 2 m) will
almost always lead to overestimates of evaporation rate.
Furthermore, because wind speed fluctuates widely over
even a short period of time, the average evaporation rate
over the time required to cast a concrete slab, for example, is
related to an average wind speed over that period. Therefore,
a spot measurement of wind speed can be misleading in esti­
mating evaporation rate.
27
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
Air temperature, oc
5
40
25
15
50
60
70
35
80
Air temperature, oF
0.8
To use this chart:
1 . Enter with air
temperature,
move Jm to
relative humidity.
2 . Move right to
concrete
temperature.
3 . Move down to
wind velocity.
4. Move left; read
approximate rate
0.7
,E
N
....
0.6
3.0
�
N
�
E
OJ
0
c0
-"'
c 0.5
�
0
0..
t1l
>
OJ
0
2
t1l
n:::
0.4
2.0
0.3
0.2
1 .0
�
0
0..
t1l
>
OJ
0
2
C1l
0::
of evaporation.
Fig. 5.2. 1-Nomograph for estimating maximum potential rate of evaporation of environ­
ment, assuming water-covered surface in which water temperature is equal to concrete
temperature (Menzel 1 954; NRMCA 1960).
Because the output of the nomograph is the rate of water
loss from a water-covered surface under the same environ­
mental conditions, such as a lake, reservoir, or a water-filled
evaporation pan, the computed result approximates the water
loss from concrete only when the concrete surface is covered
with bleed water. Al-Fadhala and Hover (200 1 ) showed that
for the short time that concrete specimens were covered with
bleed water, the rate of evaporation from the concrete was
fairly well-approximated by the value obtained from the
nomogn1I'� : !�� actl1aJ ��t� <lJ water loss from the concrete
Coovriaht American Concrete Institute
surface decreased to approximately 50 percent of the free­
water evaporation rate at 3 hours after hatching, diminishing
to 1 0 percent at approximately 8 hours. This is similar to
the results obtained by Berhane ( 1 984) and is due to the
reduction of paste porosity that accompanies hydration of
the cement, which in tum hinders the movement of water
out of the concrete. No standardized technique is available
to estimate the rate of evaporation from a concrete surface
not covered with water (Berhane 1 984, 1 985; Mather 1 984;
Shaeles and Hover 1 988; Al-Fadhala and Hover 200 1 ) .
�.
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
28
Given the inherent variability in fluctuating environmental
conditions and the empirical nature of the nomograph itself,
this method is primarily useful for characterizing the envi­
ronment in an approximate manner. The method correctly
identifies the factors controlling evaporation and allows
the user to predict how the various factors interact to either
increase or decrease the severity of the evaporative environ­
ment. When field measurements are taken, the nomograph
produces an estimate that is likely to be within 25 percent
of the actual evaporativity of the construction environ­
ment. Alternative evaporation predictors are available in the
hydrologic literature. Several methods for estimating evapo­
ration rate are reviewed by Uno ( 1 998), Brutsaert ( 1 987),
and Shaeles and Hover ( 1 988).
5.2.1.2 Alternative technologies for estimating evapora­
tion rate-Remote sensing devices have been developed for
agricultural applications to estimate the rate of evaporation
from the surface of field crops. In limited tests, one such
instrument based on the horticultural work of Idso ( 1 968)
and Idso et a!. ( 1 969) was useful for estimating the rate of
evaporation from the surface of concrete.
More accurate estimates of the actual rate of evaporation
at the surface of the concrete can be made by typical agri­
cultural or meteorological methods of evaporation pans and
recording devices. A modification of these methods was used
in which containers of the concrete mixture were exposed to
evaporative conditions and periodically weighed to estimate
the rate of evaporation from the concrete surface (Shaeles
and Hover 1 988; Al-Fadhala and Hover 200 1 ; Krauss and
Rogalla 1 996).
It has been pointed out that evaporation from a fresh
concrete surface depends also on the development of heat
in the concrete. A device called a curing meter has been
developed to provide an integrated measure of evaporation
loss rather than estimating the loss rate from instantaneous
measurement of temperature, relative humidity (RH), and
air velocity (Jensen 2006). Placed on a freely evaporating
wet concrete surface, the 0.6 x 2.6 in. ( 1 5 x 65 mm) curing
meter is calibrated to provide a cumulative evaporative loss
reading in lb/ft2 (kg/m2). Presumably, if the observed rate
is high, immediate measures to reduce water loss from the
concrete may be taken.
Regardless of the method used to estimate evaporative
conditions, the key requirement is to recognize that the rate
of evaporation can vary considerably over a given local­
ized area, and that the most significant evaporation rate is
that measured at the concrete surface at the time of concrete
placing, finishing, and curing. Data obtained from nearby
weather stations, airports, or furnished by a local news
service are questionable when estimating the conditions at a
particular jobsite or over a particular concrete surface on that
site, and can lead to significant errors in calculating the rate
of evaporation (Falconi 1 996).
5.2.2 Curing compound evaluation protocol-A proce­
dure for evaluating the effectiveness of curing compounds
involving measuring and evaluating the effects of all envi­
ronmental parameters has been developed by Ye et a!.
(2009, 20 1 0J.u
.•
Coovriaht Am�te Institute
5.3-Means to verify application of curing
When a particular curing process is specified, one can
assess the application of curing in accordance with those
specifications. For example, if the specifications require a
3-day water cure, one can monitor the duration over which
the concrete surfaces were continuously exposed to water.
Similarly, if covering with plastic or other materials is
required, one simply observes whether this was done or not,
and whether the concrete surface remained continuously
covered without any tearing or piercing of the materials .
O n the other hand, when a liquid-applied curing membrane
is used and a particular rate of application is required either
directly by the specifications or by reference to manufac­
turer 's instructions, an average rate of application can be
determined by monitoring the volume ofliquid applied over
a measured area. While this can be done by counting empty
drums of curing material at the conclusion of several concrete
placements, more reliable estimates are made by first-hand
observation of the application of the material. When power
spray equipment is used, it is sometimes possible to monitor
the flow rate from the hose or nozzle. Verification of curing­
compound coverage rate, however, is more difficult for
deeply textured surfaces, where the contact surface area can
be more than twice the proj ected horizontal area of a slab
(Shariat and Pant 1 984). This is not only true for slabs, but
also for architecturally formed surfaces with bold relief.
To develop a sense for the degree of saturation or coverage
corresponding to the required rate of application, apply the
material in question to a small measured trial area. For
example, at heavy rates of application, the liquid-applied
curing material often forms a visible sheen over the surface
and will sometimes stand in puddles at low spots. Once it is
determined that this is the appropriate appearance for a suffi­
ciently heavy application, it would become obvious that a
light coating that is barely visible would not comply with the
applicable specification. For white-pigmented compounds,
this is especially obvious.
5.4-lmpact of curing procedures on immediate
environment
Some curing procedures, such as using a fog spray,
erecting wind screens, or heating the air around the concrete
being cast, modify the immediate environment. The effec­
tiveness of such procedures can be directly monitored by
temperature, humidity, or wind speed measurements (Woja­
kowski et a!. 2004) . A detailed analysis of the interaction
between the atmosphere and concrete bridge decks during
curing has been provided by Wojcik (200 1 ).
The effect of curing procedures on the rate of evaporation
can be assessed either by estimating evaporative conditions
before and after the application of curing, or by other indi­
rect methods. Indirect assessment of evaporation rate comes
from recognition of the impact of evaporative cooling on
the surface temperature of concrete. Thus, a drop in surface
temperature can be the result of an increase in the rate of
cooling from evaporation. In the absence of other factors
causing a change in concrete surface temperature, Folliard
and Hover ( 1 989) observed that the application of a high-
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
solids curing compound immediately reduced the evaporation
rate and resulted in a rapid increase in surface temperature.
This experiment was performed indoors without sunlight.
5.5-lmpact of curing procedures on moisture and
temperature within concrete
Curing reduces the loss of internal and surface moisture,
and controls the temperature of concrete to permit suffi­
cient hydration of the cementitious materials. Therefore,
monitoring the effectiveness of the curing procedures can
be performed by monitoring either the degree to which
the temperature and internal moisture content have been
controlled, or the degree to which hydration has progressed
and developed improved concrete properties.
Direct measurements of concrete temperature are readily
performed by a variety of techniques. Typical insertion ther­
mometers used to measure the temperature of fresh concrete
are of little value after setting, whereas embedded thermo­
couples are an inexpensive means of monitoring multiple
locations and various depths in both fresh and hardened
concrete (ACI 306R). Specially designed surface thermom­
eters are useful. Pyrometers and infrared devices can be used
to measure surface temperature remotely (Burlingame et a!.
2004). Recently, radio frequency identification technology
has also been successfully applied to the remote monitoring
of internal concrete temperatures.
Internal moisture content or internal relative humidity
(RH) can be measured with instruments of a variety of
levels of sophistication. Relatively inexpensive embeddable
moisture gauges are available, as are electronic moisture
and humidity gauges. Refer to 5 . 7 for references on use of
gauges and interpretation of results.
Through the use of such devices, one can comply with a
performance specification for curing that requires that the
concrete remain within a particular range of temperature and
internal moisture content for a specified period of time.
Such instrumentation may also be valuable in assessing
the tendency for undesirable phenomena such as shrinkage,
cracking, and curling. Such phenomena are related to
mixture composition and proportions, internal temperature
and moisture content, and thermal and moisture gradients
within the concrete.
5.6-Maturity method
The maturity method has been developed as a means of
estimating the cumulative effect of time and temperature
during curing on the development of concrete properties.
The method is based on the influence of temperature on the
rate of the reaction between cement and water, and assumes
that the higher the concrete temperature, the more rapidly
the cement hydrates and, therefore, the more rapid the devel­
opment of strength and related properties. Concrete matures
as the degree of hydration increases.
Application of the maturity method requires monitoring
the in-place concrete temperature in a structure over time and
computation of the effect of that time-temperature history on
the maturity of the in-place concrete. Accompanying labora­
tory work on the same concrete mixture correlates maturity
Coovriaht American Concrete Institute
29
to strength or other properties of interest by testing standard
specimens after exposure to various curing temperatures for
varying lengths of time. In-place strength in the structure is
inferred from the level of maturity determined in the field
and from the strength-maturity relationship developed in the
lab. Throughout this process, it is necessary to make sure
that the concrete mixture used in the structure is the same
as that used in the laboratory specimens for developing the
correlation between maturity and strength, and that there
is sufficient water for hydration. The maturity method is
described in detail in ASTM C 1 074, ACI 306R, ACI 228 . 1 R,
and Carino ( 1 99 1 ).
The temperature record required for maturity calculations
directly indicates the effectiveness of curing measures for
controlling concrete temperature. Moisture control is not
recorded in most current applications of maturity because it
is assumed that the moisture condition of the structure and
that of the test specimens is the same, such that tempera­
ture differences alone control the relative rates of hydration.
An error can be introduced into the maturity approach when
an inadequate supply of moisture inhibits hydration of the
cement. As such, a strength-maturity relationship devel­
oped on the basis of wet-cured test specimens would lead
to an overestimate of strength for in-place concrete that was
allowed to dry even though it was kept warm. Future devel­
opments in the maturity theory would allow for the quantita­
tive evaluation of the effects of both temperature and mois­
ture on the development of concrete properties and would
direct a new interest in comprehensively monitoring curing
effectiveness.
5.7-Assessing curing effectiveness
Because the ultimate goal of proper curing is the develop­
ment of appropriate concrete properties, the final test of the
effectiveness of curing is whether those properties are devel­
oped (Wainwright et a!. 1 990). While virtually all concrete
properties are sensitive to curing, the adequacy of curing is
most readily observed in the properties of concrete at the
curing-affected zone.
The curing-affected zone (Cather 1 992) will vary in thick­
ness depending on the properties of the concrete, the severity
of the ambient conditions, and the curing time involved.
For example, in low-w/cm concrete with a specified 28-day
cylinder compressive strength of 8000 psi (55.2 MPa), the
resulting curing-affected zone was observed to extend from
1/4 to 3/8 in. (6 to 10 mm) from the surface after a period
of 1 year of continuous wet curing (Hover 1 984). In more
conventional concretes, this zone may be 3/8 to 1/2 in. ( 1 0
t o 1 3 mm) deep at a n age o f 28 days (Hover 1 984; Cather
1 992; Dhir et a!. 1986, 1 987, 1 989a,b,c, 1 99 1 ). Regardless
of the shallowness of the zone, however, the concrete prop­
erties in this zone are most frequently those that determine
the durability and serviceability of the concrete. In the case
of an industrial floor, for example, the top 1 14 in. (6 mm) is
the most critical part of the entire concrete installation and
is vital to satisfactory performance. Unfortunately, standard­
ized test methods for correlating the properties of interest to
curing effectiveness do not yet exist.
�.
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
30
Table 5.7-Concrete characteristics in curing­
affected zone
Near-surface property affected by curing
Reference
Degree of hydration
Wainwright et al. 1 990
Pore size distribution mercury-intrusion
porosimetry
Wainwright et al. 1 990
Wainwright et al. 1990
Ballim 1 993
Given the shallowness of the curing-affected zone, test
techniques that evaluate the properties of the concrete at
depth, such as measuring the compressive strength of drilled
cores, have a limited sensitivity to the effectiveness of
curing. Concrete characteristics in the curing-affected zone
that are likely to be more sensitive to curing effectiveness,
along with a listing of references for test methods for these
properties, are shown in Table 5.7.
Kollek 1 989
Nolan et al. 1 997
CHAPTER 6-REFERENCES
Basheer et al. 1990
Committee documents are listed first by document number
and year of publication followed by authored documents
listed alphabetically.
Dhir et al. 1 995
Oxygen or air permeability
Ben-Othman and Buenfeld
1 990
Parrott 1 995
Dinku and Reinhardt 1997
Figg 1 973
Tang and Nilson 1986
Lampacher and Blight 1 998
:
Montgomery et al. 1 992
'
BS 1 88 1 -5 : 1 970, BS 1 88 1 1 22 : 1 983, BS 1 88 1 -208 : 1 996
Senbetta and Scholer 1 984
Hooton et al. 1 993
Initial surface absorption
DeSouza et al. 1 997
DeSouza et al. 1 998
DeSouza et al. 2000
Wilson et al. 1998
Nokken and Hooton 2002
Nolan et al. 1 997
Basheer et al. 1 990
McCarter et al. 1 996
Balayssac et al. 1 993
Ballim 1 993
Surface permeability/absorption test
devices
Figg 1 973
The Concrete Society
I 988
Dhir et al. 1 987
McCarter et al. 1 995
Price and Bam forth 1 993
Sabir et al. 1 998
Ba1ayssac et al. 1 998
Montgomery et al. 1 992
Parrott 1 995
Internal moisture content
McCarter et al. 1 996
Nolan et al. 1 997
Persson 1 997
Tension strength of surface concrete pulloff testing
Nolan et al. 1 997
Long and Murray 1 984
Montgomery et al. 1 992
Dinku and Reinhardt 1 997
RILEM Recommendations
Depth of carbonation
CPC- 1 8 1 988
Nolan et al. 1 997
Balayssac et al. 1993, 1998
Bier 1987
Abrasion resistance
Chloride ingress
Montgomery et al. 1 992
Sawyer 1 95 7
Hooton et al. 2002
Electrical conductivity, moisture content,
sorptivity, degree of hydration, strength,
and permeability
Coovriaht Am�te Institute
Wang et al. 2003
American Concrete Institute
ACI 20 1 .2R-08-Guide to Durable Concrete
ACI 207. 1 R-05( 1 2)-Guide to Mass Concrete
ACI 207.2R-07-Report on Thermal and Volume Change
Effects on Cracking of Mass Concrete
ACI 207.5R- l l-Report on Roller-Compacted Mass
Concrete
ACI 223R- 1 0-Guide for the Use of Shrinkage-Compen­
sating Concrete
ACI 228 . 1 R-03-In-Place Methods to Estimate Concrete
Strength
ACI 228.2R- 1 3-Report on Nondestructive Test Methods
for Evaluation of Concrete in Structures
ACI 23 1 R- 1 0-Report on Early-Age Cracking: Causes,
Measurement, and Mitigation
ACI 234R-06(1 2)-Guide for the Use of Silica Fume in
Concrete
ACI 237R-07-Self-Consolidating Concrete
ACI 30 1 - 1 6-Specifications for Structural Concrete
ACI 302. 1 R- 1 5-Guide to Concrete Floor and Slab
Construction
ACI 302.2R-06-Guide for Concrete Slabs that Receive
Moisture-Sensitive Flooring Materials
ACI 303R- 1 2-Guide to Cast-in-Place Architectural
Concrete Practice
ACI 305R- l 0-Guide to Hot Weather Concreting
ACI 306R-1 0-Guide to Cold Weather Concreting
ACI 306 . 1 -90(02)-Standard Specification for Cold
Weather Concreting
ACI 308. 1 - 1 1-Specification for Curing Concrete
ACI (308-2 1 3)R- 13-Report on Internally-Cured Concrete
Using Prewetted Absorptive Lightweight Aggregate
ACI 3 1 0R- 1 3-Guide to Decorative Concrete
ACI 3 1 3 - 1 6-Standard Practice for Design and Construc­
tion of Concrete Silos and Stacking Tubes for Storing Gran­
ular Material
ACI 3 1 8-1 4---Building Code Requirements for Structural
Concrete and Commentary
ACI 360R- l 0-Guide to Design of Slabs-on-Ground
ACI 363R- 1 0-Report on High-Strength Concrete
ACI 3 63 .2R- l l-Guide to Quality Control and Assurance
of High-Strength Concrete
ACI 506.2- 1 3-Specification for Shotcrete
ACI 522R- 1 0( 1 1 )-Report on Pervious Concrete
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
ACI 523 . 1 R-06-Guide for Cast-in-Place Low-Density
Cellular Concrete
ACI 544.3R-08-Guide for Specifying, Proportioning,
and Production of Fiber-Reinforced Concrete
ACI 548. 1 R-09-Guide for the Use of Polymers in Concrete
ASTM International
ASTM C33/C33M- 1 1 -Standard Specification for Concrete
Aggregates
ASTM C94/C94M- 1 5-Standard Specification for
Ready-Mixed Concrete
ASTM C l 09/C l 09M- 1 6-Standard Test Method for
Compressive Strength of Hydraulic Cement Mortars (Using
2 in. or [50 mm] Cube Specimens)
ASTM C l 50/C l 50M- 1 5-Standard Specification for
Portland Cement
ASTM C l 56- l l -Test Method for Water Loss [from a
Mortar Specimen] Through Liquid Membrane-Forming
Curing Compounds for Concrete
ASTM C 1 7 1 -07-Standard Specification for Sheet Mate­
rials for Curing Concrete
ASTM C232/C232M- 14-Standard Test Methods for
Bleeding of Concrete
,' ASTM
C309- l l-Standard Specification for Liquid
Membrane-Forming Compounds for Curing Concrete
•· ASTM C403/C403M-08-Standard Test Method for Time
of Setting of Concrete Mixtures by Penetration Resistance
ASTM C4 1 8- 1 2-Standard Test Method for Abrasion
Resistance of Concrete by Sandblasting
: ASTM C595/C595M- 1 5-Standard Specification for
Blended Hydraulic Cements
ASTM C6 1 8- 1 5-Standard Specification for Coal Fly Ash
and Raw or Calcined Natural Pozzolan for Use in Concrete
ASTM C642-1 3-Standard Test Method for Density,
Absorption, and Voids in Hardened Concrete
ASTM C666/C666M-1 5-Standard Test Method for
Resistance of Concrete to Rapid Freezing and Thawing
ASTM C779/C779M-1 2-Standard Test Method for
Abrasion Resistance of Horizontal Concrete Surfaces
ASTM C803/C803M-03(20 1 2)-Standard Test Method
for Penetration Resistance of Hardened Concrete
ASTM C845/C845M- 1 2-Standard Specification for
Expansive Hydraulic Cement
ASTM C873/C873M-1 5-Standard Test Method for
Compressive Strength of Concrete Cylinders Cast in Place
in Cylindrical Molds
ASTM C900-1 5-Standard Test Method for Pullout
Strength of Hardened Concrete
ASTM C944/C944M- 1 2-Standard Test Method for
Abrasion Resistance of Concrete or Mortar Surfaces by the
Rotating-Cutter Method
ASTM C989/C989M- 1 4-Standard Specification for
Slag Cement for Use in Concrete and Mortars
ASTM C l 074- l l -Standard Practice for Estimating
Concrete Strength by the Maturity Method
ASTM C l l 3 8M- 1 2-Standard Test Method for Abrasion
Resistance of Concrete (Underwater Method)
.·
Coovriaht American Concrete Institute
31
ASTM C l l 5 7/C l l 5 7M- l l -Standard Performance Spec­
ification for Hydraulic Cement
ASTM C l 202- 1 2-Standard Test Method for Electrical Indi­
cation of Concrete's Ability to Resist Chloride Ion Penetration
ASTM C l 240- 1 5-Standard Specification for Silica
Fume Used in Cementitious Mixtures
ASTM C 1 3 1 5- 1 1-Standard Specification for Liquid
Membrane-Forming Compounds Having Special Properties
for Curing and Sealing Concrete
British Standards Institution
BS 1 88 1 -5 : 1 970-Testing Concrete-Methods of Testing
Hardened Concrete For Other Than Strength
BS 1 88 1 - 1 22 : 1 983-Testing Concrete-Method for
Determination of Water Absorption
BS 1 88 1 -208 : 1 996-Testing Concrete-Recommenda­
tions for the Determination of the Initial Surface Absorption
of Concrete
Authored references
Abel, J. D., and Hover, K. C., 2000, "Field Study of the
Setting Behavior of Fresh Concrete," Cement, Concrete and
Aggregates, V. 22, No. 2, Dec., pp. 95- 1 02. doi: 1 0. 1 520/
CCA1 0469J
Ai"tcin, P.-C., 1 999, "Does Concrete Shrink or Does it Swell?"
Concrete International, V. 2 1 , No. 1 2, Dec., pp. 77-80.
Al-Fadhala, M., and Hover, K. C., 200 1 , "Rapid Evapora­
tion from Freshly Cast Concrete and the Gulf Environment,"
Construction & Building Materials, V. 1 5, No. 1 , Jan., pp.
1 -7. doi: 1 0. 1 0 1 6/S0950-061 8(00)00064-7
Balayssac, J. P. ; Detriche, C. H.; and Diafat, N., 1 998,
"Effect of Wet Curing Duration upon Cover Concrete Char­
acteristics," Materials and Structures, V. 3 1 , No. 5, June, pp.
325-328. doi: 1 0. 1 007/BF02480674
Balayssac, J.-P.; Detriche, C.-H.; and Grandet, J., 1 993,
"Validity of the Water Absorption Test for Characterizing
Cover Concrete," Materials and Structures, V. 26, No. 4,
May, pp. 226-230. doi: 1 0 . 1 007/BF024726 1 5
Ballim, Y. , 1 993, "Curing and the Durability of OPC, Fly
Ash, and Blast-Furnace Slag Concretes," Materials and
Structures, V. 26, No. 4, May, pp. 23 8-244. doi: 1 0. 1 007/
BF024726 1 7
Basheer, P. A . M.; Montgomery, F. R.; Long, A. E.;
and Batayneh, M., 1 990, "Durability of Surface Treated
Concrete," Protection of Concrete, Proceedings of the
International Conference, R. K. Dhir and J. W. Green, eds.,
E&FN Spon, London, pp. 2 1 1-22 1 .
Basheer, P. A. M.; Sha'at, A. A.; and Long, A. E., 1 995,
"Controlled Permeability Formwork: Influence on Carbon­
ation and Chloride Ingress in Concrete," Proceedings
of Concrete under Severe Conditions, Environment and
loading, V. 2, K. Sakai, N. Banthia, and 0. E. Gjorv, eds. ,
E&FN Spon, pp. 1 205- 1 2 1 5 .
Basheer, P. A. M.; Sha'at, A . A.; Long, A . E . ; and Mont­
gomery, F. R., 1993, "Influence of Controlled Permeability
Formwork on the Durability of Concrete," Proceedings of
the International Conference, Concrete 2000, Economic
�.
32
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
and Durable Construction through Excellence, V. 1, E&FN
Spon, London, pp. 737-748.
Ben-Othman, B., and Buenfeld, N. R., 1 990, "Oxygen
Permeability of Structural Lightweight Aggregate Concrete,"
Protection of Concrete, Proceedings of the International
Conference, R. K. Dhir and J. W. Green, eds., E&FN Spon,
London, pp. 725-736.
Berhane, Z., 1 984, "Evaporation of Water from Fresh
Mortar and Concrete at Different Environmental Condi­
tions," ACI Journal Proceedings, V. 8 1 , No. 6, Nov.-Dec.,
pp. 560-564.
Berhane, Z., 1 985, closure to discussion on paper, "Evapo­
ration of Water from Fresh Mortar and Concrete at Different
Environmental Conditions," ACI Journal Proceedings V. 82,
No. 6, Nov.-Dec., pp. 930-933 .
Bier, T. A., 1 987, "Influence o f Type of Cement and
Curing on Carbonation Progress and Pore Structure of
Hydrated Cement Paste," Materials Research Society
Symposium, V. 85, pp. 1 23 - 1 34.
Brutsaert, W., 1 987, Evaporation into the Atmosphere:
Theory, History and Application, D. Reidel Publishing Co.,
Boston, MA, 299 pp.
Burlingame, S.; Lautz, C.; and Hover, K. C., 2004, "Oppor­
tunities and Challenges in Concrete with Thermal Imaging,"
Concrete International, V. 26, No. 1 2, Dec, pp. 23-27.
Carino, N. J., 1 99 1 , "The Maturity Method," CRC
Handbook on Nondestructive Testing of Concrete, V. M.
Malhotra and N. J. Carino, ed., CRC Press, Boca Raton,
FL, pp. 1 0 1 - 1 46 .
Carrier, R . E . , 1 983, "Concrete Curing Tests," Concrete
_
biternational, V. 5, No. 4, Apr., pp. 23-26.
_C ather, R., 1 992, ""How to Get Better Curing," Concrete,"
The Journal of the Concrete Society, London, V. 26, No. 5,
Sept.-Oct., pp. 22-25.
Cather, R., 1 994, "Curing: The True Story?" Magazine of
Concrete Research, V. 46, No. 1 68, Sept., pp. 1 57- 1 6 1 . doi:
1 0 . 1 680/macr. l 994.46 . 1 68. 1 57
Cook, R. A., 1 992, "A Generalized Form of the Powers
Model of Cement Microstructure and its Evaluation via
Mercury Porosimetry," PhD dissertation, Cornell Univer­
sity, Ithaca, NY.
Copeland, L. E.; Kantro, D. L.; and Verbeck, G., 1 960,
"Chemistry of Hydration of Portland Cement," Proceedings
of the Fourth International Symposium on the Chemistry of
Cement, Washington, DC.
Cordon, W. A., and Thorpe, J. D., 1 965, "Control of Rapid
Drying of Fresh Concrete by Evaporation Control," A CI
Journal Proceedings, V. 62, No. 8, Aug., pp. 977-985 .
Dalton, J . , 1 802, "Experimental Essays o n Evaporation,"
Proceedings, V. 5, Manchester Literary and Philosophical
Society, pp. 536-602.
Day, R. L., 1 992, "The Effect of Secondary Ettringite
Formation on the Durability of Concrete: A Literature Anal­
ysis," Research and Development Bulletin RDI08T, Port­
land Cement Association, Skokie, IL.
DeSouza, S. J.; Hooton, R. D.; and Bickley, J. A., 1 997,
"Evaluation of Laboratory Drying Procedures Relevant to
Field Conditions for Concrete Sorptivity Measurements,"
Coovriaht Am�te Institute
Cement, Concrete and Aggregates, V. 1 9, No. 2, Dec., pp.
59-63. doi: 1 0 . 1 520/CCA 1 03 1 5 J
DeSouza, S. J . ; Hooton, R . D.; and Bickley, J. A., 1 998, "A
Field Test for Evaluating High Performance Concrete Cover­
crete Quality," Canadian Journal of Civil Engineering, V.
25, No. 3 , June, pp. 5 5 1-556. doi: 1 0. 1 1 39/197- 1 1 0
DeSouza, S. J.; Hooton, R. D.; and Bickley, J. A., 2000,
"Practical Quality Control Test Programs for High-Perfor­
mance Concrete in Precast Concrete Tunnel Liners," Water­
Cement Ratio and Other Durability Parameters: Techniques
for Determination, SP- 1 9 1 , M. S. Khan, ed., American
Concrete Institute, Farmington Hills, MI, pp. 99- 1 14.
Detwiler, R. J.; Fapohunda, C. A.; and Natale, J., 1 994,
"Use of Supplementary Cementing Materials to Increase the
Resistance to Chloride Ion Penetration of Concretes Cured
at Elevated Temperatures," A CI Materials Journal, V. 9 1 ,
No. 1 , Jan.-Feb., pp. 63-66.
Detwiler, R. J. ; Kjellsen, K. 0.; and Gjorv, 0. E., 1 99 1 ,
"Resistance to Chloride Ion Intrusion of Concrete Cured at
Different Temperatures," ACI Materials Journal, V. 88, No.
1, Jan.-Feb., pp. 1 9-24.
Dhir, R. K.; Hewlett, P. C.; Byars, E. A.; and Shaaban, I.
G., 1 995, "A New Technique for Measuring the Air Perme­
ability of Near-Surface Concrete," Magazine of Concrete
Research, V. 47, No. 1 7 1 , June, pp. 1 67 - 1 76. doi: 1 0. 1 680/
macr. 1 995.47. 1 7 1 . 1 67
Dhir, R. K.; Hewlett, P. C.; and Chan, Y. N., 1 986, "Near
Surface Characteristics of Concrete: An Initial Appraisal,"
Magazine of Concrete Research, V. 38, pp. 54-56.
Dhir, R. K. ; Hewlett, P. C.; and Chan, Y. N., 1 987, "Near
Surface Characteristics of Concrete: Assessment and Devel­
opment of In Situ Test Methods," Magazine of Concrete
Research, V. 39, No. 1 4 1 , Dec., pp. 1 83 - 1 95 . doi: 1 0. 1 680/
macr. 1 987.39. 1 4 1 . 1 83
Dhir, R. K.; Hewlett, P. C.; and Chan, Y. N., 1 989a, "Near
Surface Characteristics of Concrete: Intrinsic Permeability,"
Magazine of Concrete Research, V. 4 1 , No. 14 7, Sept., pp.
87-97. doi: 10. 1 680/macr. l 989.4 1 . 147.87
Dhir, R. K.; Hewlett, P. C.; and Chan, Y. N., 1 989b, "Near
Surface Characteristics of Concrete: Prediction of Carbon­
ation Resistance," Magazine ofConcrete Research, V. 4 1 , No.
148, Sept., pp. 1 3 7- 1 43 . doi: 1 0 . 1 680/macr. l 989.4 1 . 1 48. 1 37
Dhir, R. K.; Levitt, M.; and Wang, J., 1 989c, "Membrane
Curing of Concrete: Water Vapour Permeability of Curing
Membranes," Magazine of Concrete Research, V. 4 1 , No.
149, Dec, pp. 22 1 -228. doi: 1 0. 1 680/macr. 1 989.4 1 . 1 49.22 1
Dhir, R. K.; Hewlett, P. C.; and Chan, Y. N., 1 99 1 , "Near
Surface Characteristics of Concrete: Abrasion Resistance,"
Materials and Structures, V. 24, No. 2, Mar, pp. 1 22- 1 28.
doi: 1 0 . 1 007/BF02472473
Dinku, A., and Reinhardt, H. W., 1 997, "Gas Permeability
Coefficient of Cover Concrete as a Performance Control,"
Materials and Structures, V. 30, No. 7, Sept, pp. 387-393.
doi: 1 0 . 1 007/BF02498560
Dodson, V. H., 1 994, "Time of Setting, Significance ofTests
and Properties of Concrete and Concrete-Making Materials,"
ASTM STP 1 69C, P. Klieger and J. Lamond, eds., ASTM
International, West Conshohocken, PA, pp. 77-87.
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
Eglinton, M., 1 998, "Resistance of Concrete to Destruc­
tive Agencies," Lea s Chemistry of Cement and Concrete,
fourth edition, P. C. Hewlett, ed., Arnold Press, London, pp.
299-340.
Erdogdu, S., and Kurbetci, S., 1 998, "Optimum Heat
Treatment Cycle for Cements of Different Type and Compo­
sition," Cement and Concrete Research, V. 28, No. 1 1 , pp.
1 595- 1 604. doi: 1 0. 1 0 1 6/S0008-8846(98)001 34-3
Falconi, M. 1., 1 996, "An Investigation of the Scaling
Resistance and Other Properties of Slag-Cement Concrete,"
Master's thesis, Cornell University, Ithaca, NY.
Figg, J. W., 1 973, "Methods of Measuring the Air and
Water Permeability of Concrete," Magazine of Concrete
Research, V. 25, No. 85, Dec., pp. 2 1 3-2 1 9. doi: 1 0. 1 680/
macr. l 973.25.85 .2 1 3
Folliard, K., and Hover, K. C., 1 989, "National Science
Foundation Research for Undergraduates Program, Cornell
University (NSFREU)," Report ofActivities, Aug., 1989.
Ghorab, H. Y. ; Heinz, D.; Ludwig, U.; Meskendahl, T.;
and Wolter, A., 1 980, "On the Stability of Calcium Alumi­
nate Sulphate Hydrates in Pure Systems and in Cements,"
Proceedings ofthe 7th International Congress on the Chem­
istry of Cement, V. 4, pp. 496-503.
Goto, S., and Roy, D. M., 1 98 1 , "The Effect of w/c Ratio
and Curing Temperature on the Permeability of Hardened
Cement Paste," Cement and Concrete Research, V. 1 1 , No.
4, pp. 575-579. doi: 1 0 . 1 0 1 6/0008-8846(8 1 )90087-9
Gowriplan, N.; Cabrera, J. G.; Cusens, A. R.; and Wain­
wright, P. J., 1 990, "Effect of Curing on Durability," Concrete
International, V. 1 2 , No. 2, Feb., pp. 47-54.
Greening, N. R., and Landgren, R., 1 966, "Surface Discol­
oration of Concrete Flatwork," Journal ofthe PCA Research
and Development Laboratory, V. 8, No. 3, Sept., pp. 34-50.
Grube, H., and Lawrence, C. D., 1 984, "Permeability of
Concrete to Oxygen," Proceedings, RILEM Seminar on the
Durability of Concrete under Normal Outdoor Exposure,
Hanover University, Mar., pp. 68-79.
Hanson, J. A., 1 963, "Optimum Steam Curing Procedure
in Precasting Plants," ACI Journal Proceedings, V. 60, No.
1, Jan., pp. 75- 1 00.
Hanson, J. A., 1 968, "Effects of Curing and Drying Envi­
ronments on the Splitting Tensile Strength of Concrete,"
PCA Development Bulletin D 141.
Heinz, D., and Ludwig, U., 1 987, "Mechanism of
Secondary Ettringite Formation in Mortars and Concretes
Subjected to Heat Treatment," Concrete Durability: Katha­
rine and Bryant Mather International Conference, SP- 1 00,
J. Scanlon, ed. , American Concrete Institute, Farmington
Hills, MI, pp. 2059-207 1 .
Hime, W. G., 1 996, "Delayed Ettringite Formation: A
Concern for Precast Concrete," PC! Journal, V. 4 1 , No. 4,
pp. 26-30. doi: 1 0. 1 55 54/pcij .070 1 1 996.26.30
Hooton, R. D.; Geiker, M. R.; and Bentz, E. C., 2002,
"Effects of Curing on Chloride Ingress and Implications for
Service Life," ACI Materials Journal, V. 99, No. 2, Mar.­
Apr. , pp. 20 1 -206.
Hooton, R. D.; Mesic, T.; and Beal, D. L., 1 993, "Sorp­
tivity Testing of Concrete as an Indicator of Concrete DuraCoovriaht American Concrete Institute
33
bility and Curing Efficiency," Proceedings of the Third
Canadian Symposium on Cement and Concrete, Aug.
Hover, K. C., 1984, "The Influence of Moisture on the
Physical Properties of Hardened Concrete and Mortar," PhD
dissertation, Cornell University, Ithaca, NY, Aug.
Hover, K. C., 1 992, "Evaporation of Surface Moisture: A
Problem in Concrete Technology and Human Physiology,"
Concrete in Hot Climates: Proceedings of the Third Interna­
tional RILEM Conference on Concrete in Hot Climates, M.
J. Walker, ed., E&FN Spon, London, pp. 1 3-24.
Hover, K. C., 2002, "Curing and Hydration: Two Half
Truths Don't Make a Whole," Concrete News: LMCC,
Summer, pp. 1 -2 .
Hukey, J . C . , 2008, "Specifying Conformance with ASTM
C 1 3 1 5 : What Assurance does it Really Provide?" Concrete
International, V. 30, No. 3, Mar., pp. 5 1 -5 3 .
Idso, S. B., 1 968, Analysis of Environment-Plant Rela­
tionships, St. Paul Agricultural Experiment Station, MN.
Idso, S. B.; Jackson, R. D.; Ehrler, W. L.; and Mitchell,
S. T., 1969, "A Method for Determination of lnfrared Emit­
tance of Leaves," Ecology, V. 50, No.5, May, pp. 899-902.
doi: 1 0 .23071 1 933705
Jalota, S . K., and Prihar, S . S., 1 998, Reducing Soil Water
Evaporation with Tillage and Straw Mulching, Iowa State
University Press, Ames, IA, 142 pp.
Jensen, 0. M., 2006, "Monitoring Water Loss from Fresh
Concrete," Concrete Durability and Service Life Planning,
Proceedings of the International RILEM-JCI Seminar, Ein­
Bokek, Israel, pp. 1 97-202.
Kelham, S., 1 996, "The Effect of Cement Composition and
Fineness on Expansion Associated with Delayed Ettringite
Formation," Cement and Concrete Composites, V. 1 8 , No.
3, June, pp. 1 7 1 - 1 79. doi: 1 0. 1 0 1 6/0958-9465(95)000 1 3-5
Kjellsen, K. 0.; Detwiler, R. J.; and Gjorv, 0. E., 1 99 1 ,
"Development of Microstructures in Plain Cement
Pastes Hydrated at Different Temperatures," Cement
and Concrete Research, V. 2 1 , No. 1 , pp. 1 79-1 89. doi:
1 0 . 1 0 1 6/0008-8846(9 1 )90044-I
Klieger, P., 1 956, "Curing Requirements for Scale Resis­
tance of Concrete," Bulletin No. 1 50, Highway Research
Board, Jan.
Kohler, M. A.; Nordenson, T. J.; and Fox, W. E., 1 955,
"Evaporation from Pans and Lakes," Research Paper No.
38, U.S. Department of Commerce, Washington, DC, May.
Kollek, J. J., 1 989, "The Determination of the Permea­
bility of Concrete to Oxygen by the Cembureau Method-a
Recommendation," Materials and Structures, V. 22, No. 3,
pp. 225-230. doi: 1 0 . 1 007/BF02472 1 92
Kosmatka, S. H., 1 994, "Bleeding," Significance of Tests
and Properties ofConcrete and Concrete-Making Materials,
ASTM STP 1 69C, P. Klieger and J. Lamond, eds., ASTM,
West Conshohocken, PA, pp. 88- 1 1 1 .
Kosmatka, S . H., and Panarese, W. C., 1 988, Design &
Control of Concrete Mixtures, thirteenth edition, Portland
Cement Association, Skokie IL.
Kosmatka, S . H., and Wilson, M. L., 20 1 1 , Design &
Control of Concrete Mixtures, fifteenth edition, Portland
Cement Association, Skokie IL.
�.
34
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
Krauss, P. D., and Rogalla, E. A., 1 996, "Transverse
Cracking in Newly Constructed Bridge Decks," NCHRP
Report 380, National Cooperative Highway Research
Program, Transportation Research Board, National Academy
Press, Washington, DC, 1 26 pp.
Lampacher, B. J., and Blight, G. E., 1 998, "Permeability
and Sorption Properties of Mature Near-Surface Concrete,"
Journal ofMaterials in Civil Engineering, V. 1 0, No. 1 , pp.
2 1 -2 5 .
Lerch, W., 1 957, "Plastic Shrinkage," A CI Journal
Proceedings, V. 53, Feb, pp. 797-802.
Liu, T. C., 1 994, "Abrasion Resistance," Significance
of Tests and Properties of Concrete and Concrete-Making
Materials, ASTM STP 1 69C, P. Klieger and J. Lamond, eds.,
ASTM International, West Conshohocken, PA, pp. 1 82- 1 9 1 .
Long, A . E., and Murray, A . M., 1 984, "The Pull-Off
Partially Destructive Test for Concrete," In-Situ/Nondestruc­
tive Testing of Concrete, SP-82, V. M. Malhotra, ed., Amer­
ican Concrete Institute, Farmington Hills, MI, pp. 327-350.
Long, A. E.; Sha' at, A. A.; and Basheer, P. A. M., 1 995,
"The Influence of Controlled Permeability Formwork on
the Durability and Transport Properties of Near Surface
Concrete," Advances in Concrete Technology, Proceedings
of the Second CANMET/ACI International Symposium,
SP- 1 54, V. M. Malhotra, ed., American Concrete Institute,
Farmington Hills, MI, pp. 4 1 -54.
Malone, P. G., 1 999, "Use of Permeable Formwork in
Placing and Curing Concrete," Technical Report SL-99-12,
U.S. Army Corps of Engineers, Vicksburg, MS, Oct., 50 pp.
Mather, B., 1 984, "discussion on a paper by Z . Berhane,
"Evaporation of Water from Fresh Mortar and Concrete at
Different Environmental Conditions," A CI Journal Proceed­
ings, V. 8 1 , No. 6, Nov.-Dec., pp. 930-933.
Mather, B., 1 987, "Curing of Concrete," Lewis H. Tuthill
International Symposium on Concrete and Concrete
Construction, SP- 1 04, G. T. Halvorsen, ed. , American
Concrete Institute, Farmington Hills, MI, pp. 145-1 59.
Mather, B., 1 990, "Curing Compounds," Concrete Inter­
national, V. 1 2 , No. 2, Feb., pp. 40-4 1 .
McCarter, W. J.; Emerson, M.; and Ezirim, H., 1 995,
"Properties of Concrete in the Cover Zone: Develop­
ments in Monitoring Techniques," Magazine of Concrete
Research, V. 47, No. 1 72, pp. 243-25 1 . doi: 1 0 . 1 680/
macr. 1 995.47. 1 72 .243
McCarter, W. J.; Ezirim, H.; and Emerson, M., 1 996,
"Properties of Concrete in the Cover Zone: Water Penetra­
tion, Sorptivity and Ionic Ingress," Magazine of Concrete
Research, V. 48, No. 1 76, pp. 1 49- 1 56. doi: 10. 1 680/
macr. 1 996.48. 1 76. 149
Meeks, K. W. , and Carino, N. J., 1 999, Curing of High
Performance Concrete: Report of the State-ofthe-Art,
NISTR 6295 , National Institute of Standards and Tech­
nology, Building and Fire Research Laboratory, Gaithers­
burg, MD, Mar., 1 9 1 pp.
Menzel, C. A., 1 954, "Causes and Prevention of Crack
Development in Plastic Concrete," Proceedings, Portland
Cement Association Annual Meeting, pp. 1 30- 1 36.
Coovriaht Am�te Institute
Mielenz, R. C.; Marusin, S.; Hime, W. G.; and Zugovic,
Z. T., 1 995, "Prestressed Concrete Railway Tie Distress:
Alkali-Silica Reaction or Delayed Ettringite Formation,"
Concrete International, V. 1 7, No. 1 2, Dec., pp. 62-68.
Mills, R. H., 1 966, "Factors Influencing the Cessation of
Hydration in Water Cured Pastes," Symposium on Struc­
ture of Portland Cement Paste and Concrete, HRB SR 90,
Highway Research Board, Washington, DC, pp. 406-424.
Mindess, S., and Young, J. F., 1 98 1 , Concrete, Prentice
Hall, Englewood Cliffs, NJ, 67 1 pp.
Minnesota Department of Transportation, 1 998, "Standard
Specifications for Road and Bridge Construction," Extreme
Service Membrane Curing Compound, St. Paul, MN.
Molina, L., 1 992, "On Predicting the Influence of Curing
Conditions on the Degree of Hydration," CBI Report
5 :92, Swedish Cement and Concrete Research Institute,
Stockholm.
Montgomery, F. R.; Basheer, P. A. M.; and Long, A. E.,
1 992, "Influence of Curing Conditions on the Durability
Related Properties of Near Surface Concrete and Cement
Mortars," Durability of Concrete: G. M. !darn International
Symposium, SP- 1 3 1 , J. Holm and M. Geiker, eds., American
Concrete Institute, Farmington Hills, MI, pp. 1 27 - 1 3 8 .
Murdock, L. J . ; Brook, K. M.; and Dewar, J. D . , 1 99 1 ,
Concrete Materials and Practice, sixth edition, Edward
Arnold Press, London, 470 pp.
National Ready Mixed Concrete Association, 1 960,
"Plastic Cracking of Concrete," Engineering Information,
NRMCA, Silver Spring, MD, July, 2 pp.
Neville, A. M., 1 996, Properties of Concrete, fourth
edition, Wiley, 844 pp.
Nokken, M., and Hooton, R. D., 2002, "Dependence of
Rate of Absorption on Degree of Saturation of Concrete,"
Cement, Concrete and Aggregates, V. 24, No. 1 , pp. 20-24.
doi: 1 0 . 1 520/CCA 1 0487J
Nolan, E.; Ali, M. A.; Basheer, P. A. M . ; and Marsh, B. K.,
1 997, "Testing the Effectiveness of Commonly-Used Site
Curing Regimes," Materials and Structures, V. 30, No. 1 ,
Jan., pp. 53-60. doi: 1 0 . 1 007/BF02498740
Oberholster, R. E.; Maree, H.; and Brand, J. H. B., 1 992,
"Cracked Prestressed Concrete Railway Sleepers: Alkali­
Silica Reaction or Delayed Ettringite Formation," Proceed­
ings of the 9th International Conference on Alkali-Aggregate
Reaction in Concrete, London, UK, pp. 739-749.
Parrott, L. J., 1 995, "Influence of Cement Type and Curing
on the Drying and Air Permeability of Cover Concrete,"
Magazine ofConcrete Research, V. 47, No. 1 7 1 , pp. 1 03- 1 1 1 .
doi: 1 0 . 1 680/macr. 1 995.47. 1 7 1 . 1 03
Parrott, L. J., and Killoh, D. C., 1 984, Proceedings of the
British Ceramic Society, No. 35, pp. 4 1 -53.
Parrott, L. J.; Killoh, D. C.; and Patel, R. G., 1 986,
"Cement Hydration under Partially Saturated Conditions,"
Proceedings of the 8th Congress on Chemistry of Cement,
v. 3, pp. 46-50.
Patel, R. G.; Killoh, D. C.; Parrott, L. J.; and Gutteridge,
W. A., 1 988, "Influence of Curing at Different Relative
Humidities upon Compound Reactions and Porosity in Port-
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
land Cement Paste," Materials and Structures, V. 2 1 , No. 3,
May, pp. 1 92- 1 97. doi: 10. 1 007/BF02473055
Pavoine,A.; Divet, L.; andFenouillet, S., 2006, "A Concrete
Performance Test for Delayed Ettringite Formation: Part 1
Optimization," Cement and Concrete Research, V. 36, No.
12, pp. 2 1 3 8-2 143 . doi: 1 0. 1 0 1 6/j .cemconres.2006.09.009
Persson, B., 1 997, "Self-Desiccation and its Importance in
Concrete Technology," Materials and Structures, V. 30, No.
5, June, pp. 293-305. doi: 1 0. 1 007/BF02486354
Persson, B., and Fagerlund, G., 1 997, " 1 st International
Research Seminar on Self-Desiccation and its Importance in
Concrete Technology," Report TVBM-3075, Lund Univer­
sity, Lund, Sweden.
Pfeifer, D., and Marusin, S., 1 982, "Energy Efficient
Accelerated Curing of Concrete: A State of the Art Review,"
Prestressed Concrete Institute Technical Report No. 1 ,
Chicago, IL.
Pfeifer, D. W. ; McDonald, D. B.; and Sherman, M. R.,
1 996, "Durability Aspects of Precast Prestressed Concrete,
Part 1 : Historical Review, PC! Journal, July-Aug., pp. 62-74.
Philleo, R., 1 99 1 , "Concrete Science and Reality," Mate­
rials Science of Concrete II, J. P. Skalny and S. Mindess,
eds., American Ceramic Society, Westerville, OH, pp. 1 -8.
Pierce, J. S., 1 994, "Mixing and Curing Water for
Concrete," Significance of Tests and Properties of Concrete
and Concrete-Making Materials, STP 1 69C, P. Klieger and
J. Lamond, eds., ASTM International, West Conshohocken,
PA, pp. 473-477.
Pihlajavaara, S. E., 1 964, "On the Interrelation of the
Moisture Content and the Strength of Mature Concrete and
its Reversibility," Report Series III, State Institute for Tech­
nical Research, Finland.
Pihlajavaara, S. E., 1 965, "Estimation of the Drying of
Concrete," Proceedings of the RILEM Symposium on the
Problem ofMoisture in Buildings, Helsinki, Finland, Aug.
Powers, T. C., 1 948, "A Discussion of Cement Hydration
in Relation to the Curing of Concrete," Proceedings of the
Highway Research Board, V. 27, pp. 1 78-1 88.
Powers, T. C., 1 962, "Prevention ofFrost Damage to Green
Concrete," Bulletin No. 14, RILEM, Mar. , pp. 120- 1 24.
Powers, T. C., and Brownyard, T. L., 1 947, "Studies of the
Physical Properties of Hardened Portland Cement Paste,"
Research Laboratories of the Portland Cement Association,
Bulletin 22, Mar., 992 pp.
Powers, T. C.; Copeland, L. E.; and Mann, H. M., 1 959,
"Capillary Continuity or Discontinuity in Cement Pastes,"
Journal of the Portland Cement Association Research and
Development Laboratories, V. 1 , No. 2, May, pp. 38-48.
Price, W. F., 2000, "Controlled Permeability Formwork,"
Publication C511, Construction Industry Research and
Information Association (CIRIA), London.
Price, W. F., and Bamforth, P. B., 1 993, "Initial Surface
Absorption of Concrete: Examination of Modified Test
Apparatus for Obtaining Uniaxial Flow," Magazine of
Concrete Research, V. 45, No. 1 62, Jan., pp. 1 7-24. doi:
10. 1 680/macr. 1 993.45 . 1 62. 1 7
Price, W. F., and Widdows, S . J., 1 99 1 , "The Effects
of Permeable Formwork on the Surface Properties of
CoovriahtAmerican Concrete Institute
35
Concrete," Magazine of Concrete Research, V. 43, No. 1 55 ,
June, p p . 93- 1 04. doi: 1 0 . 1 680/macr. l 99 1 .43. 1 5 5 .93
Ramlochan, T.; Zacarias, P.; Thomas, M. D. A.; and
Hooton, R. D., 2003, "The Effect of Pozzolans and Slag
on the Expansion of Mortars Cured at Elevated Tempera­
ture: Part I: Expansive Behaviour," Cement and Concrete
Research, V. 33, No. 6, June, pp. 807-8 14. doi: 1 0 . 1 0 1 6/
S0008-8846(02)0 1 066-9
RILEM Recommendations CPC- 1 8, 1 998, "Measurement
of Hardened Concrete Carbonation Depth," Materials and
Structures, V. 2 1 , No. 1 26, pp. 453-455.
Sabir, B . B . ; Wild, S.; and O'Farrell, M., 1 998, "A Water
Sorptivity Test for Mortar and Concrete," Materials and
Structures, V. 3 1 , No. 8, Oct, pp. 5 68-574. doi: 1 0. 1 007/
BF0248 1 540
Sawyer, J. L., 1957, "Wear Test on Concrete Using the
German Standard Method of Test Machine," Proceedings,
ASTM, V. 57, July, pp. 1 1 45- 1 1 5 3 .
Sedgwick County, Kansas, 1 998, "Special Provision,
Linseed Oil Emulsion Treatment," Standard Specifications
for Road and Bridge Construction.
Senbetta, E., 1988, "Concrete Curing Practices in the
United States," Concrete International, V. 1 0, No. 1 1 , Nov. ,
pp. 64-67.
Senbetta, E., and Brury, M. A., 1 99 1 , "Control of Plastic
Shrinkage Cracking in Cold Weather," Concrete Interna­
tional, V. 1 3, No. 3, Mar., pp. 49-53.
Senbetta, E., and Scholer, C. F., 1984, "A New Approach
for Testing Concrete Curing Efficiency," A CI Journal
Proceedings, V. 8 1 , No. 1 , Jan.-Feb., pp. 82-86.
Shaeles, C. A., and Hover, K. C., 1 988, "The Influence of
Construction Operations on the Plastic Shrinkage Cracking
of Thin Slabs," A CI Materials Journal, V. 85, No. 6, Nov.­
Dec., pp. 495-504.
Shariat, S . M. S., and Pant, P. D., 1 984, "Curing and Mois­
ture Loss of Grooved Concrete Surfaces," Transportation
Research Record, No. 986, pp. 4-8.
Shayan, A., and Quick, G. W., 1 992, "Microscopic Features
of Cracked and Uncracked Concrete Railway Sleepers," A CI
Materials Journal, V. 89, No. 4, July-Aug., pp. 348-36 1 .
Skalny, J., and Locher, F. W., 1 997, "Curing Practices
and Internal Sulfate Attack-The European Experience,"
Cement, Concrete and Aggregates, V. 2 1 , No. 1 , pp. 59-63 .
Snyder, K. A., and Bentz, D. P., 2004, "Suspended
Hydration and Loss of Freezable Water in Cement Pastes
Exposed to 90% Relative Humidity," Cement and Concrete
Research, V. 34, No. 1 1 , pp. 2045-2056. doi: 1 0. 1 0 1 6/j .
cemconres.2004.03.007
Soroos, E., 1 994, "Scanning Electron Microscope
Images," JSM 135 SEM, School of Materials Science and
Engineering, Cornell University, Ithaca, NY, May.
Sousa-Coutinho, J., 1 999, "Durable Concrete through Skin
Treatment with CPF," Durability of Building Materials and
Components 8, V. 1, M. A. Lacasse and D. J. Vanier, eds.,
National Research Council, Ottawa, ON, Canada, pp. 453-462.
Spears, R. E., 1 983, "The 80% Solution to Inadequate
Curing Problems," Concrete International, V. 5, No. 4, Apr.,
pp. 1 5- iS :
..
.
..
...
- - . . . . . . . ---
�.
36
G U I D E TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)
Stark, J.; Bollman, K.; and Seyfarth, K., 1 998, "Ettringite­
Cause of Damage, Damage intensifier, or uninvolved third
party?" Zement-Kalk-Gips International, V. 5 1 , pp. 280-292.
Suprenant, B . , 2002, "Why Slabs Curl (Part II: Factors
Affecting the Amount of Curling)," Concrete International,
V. 24, No. 4, Apr., pp. 59-64.
Suprenant, B . , and Malisch, W., 1 998a, "Diagnosing Slab
Delaminations (Part II)," Concrete Construction, Feb., pp.
1 69- 1 75 .
Suprenant, B . , and Malisch, W. , 1 998b, "Diagnosing
Slab Delaminations (Part III)," Concrete Construction,
Mar., pp. 1 69- 1 7 5 .
Suprenant, B., and Malisch, W., 1 998c, "Where Should
You Place the Vapor Retarder?" Concrete Construction,
May, pp. 427-433 .
Suprenant, B . , and Malisch, W., 1 998d, "Are Your Slabs
Dry ,Enough for Floor Coverings?" Concrete Construction,
Aug; , pp. 67 1 -677.
S�prenant, B., and Malisch, W. , 1 998e, "The True Window
of F inishability," Concrete Construction, Oct., pp. 859-863.
Suprenant, B., and Malisch, W., 1 999a, "Effect of Water
Vapor Emissions on Floor Covering Adhesives," Concrete
Con�truction, Jan., pp. 27-32.
Suprenant, B., and Malisch, W. , 1 999b, "Why Won't the
Con6rete Dry?" Concrete Construction, July, pp. 29-33.
Tang, L., and Nilson, L. 0., 1 986, "Effect of Drying at an
Early Age on Moisture Distributions in Concrete Specimens
Used for Air Permeability Tests," Nordic Concrete Research
Establishment Report, Watford, UK, 1 9 pp.
Taylor, H. F. W., 1 997, Cement Chemistry, second edition,
Thomas Telford, London, 459 pp.
Tepponen, P., and Eriksson, B., 1 987, "Damages in
Concrete Railway Sleepers in Finland," Nordic Concrete
Research, No. 6, pp. 1 99-209.
The Concrete Society, 1 988, "Permeability of Concrete­
A Review of Testing and Experience," Technical Report 3 I ,
London, 95 pp.
Thomas, M. D. A., 200 1 , "Delayed Ettringite Formation
in Concrete: Recent Developments and Future Directions,"
Materials Science of Concrete, V. VI, American Ceramics
Society, Westerville, OH.
Transportation Research Board, 1 979, "Curing of
Concrete Pavements," Transportation Research Circular,
No. 208, June, 13 pp.
Tuthill, L. H., and Cordon, W. A., 1 955, "Properties and
Uses oflnitially Retarded Concrete," ACI Journal Proceed­
ings, V. 52, No. 1 1 , Nov. , pp. 273-286.
Uno, P. J., 1 998, "Plastic Shrinkage Cracking and Evapo­
ration Formulas," ACI Materials Journal, V. 95, No. 4, July­
Aug., pp. 365-375.
U.S. Army Corps of Engineers, 1975, "Method of Test for
the Staining Properties of Water," Handbook for Concrete
and Cement, CRD-C 40 1 , Vicksburg, MS.
Van Aardt, J. H. P., 1 953, discussion on "The Physical
Structure of Cement Products and its Effect on Durability,"
by F. E. Jones, Proceedings of the Third International
Symposium on the Chemistry of Cement, London, pp. 433.
Coovriaht Am�te Institute
Veihmeyer, F. J., 1 964, "Evapotranspiration," Handbook
of Applied Hydrology, V. T. Chow, ed. , McGraw Hill, pp.
1 1 - 1 to 1 1 -38.
Verbeck, G. J., and Helmuth, R. H., 1 968, "Structures and
Physical Properties of Cement Paste," Proceedings of the
Vth International Symposium on the Chemistry of Cement,
V. III, Tokyo, pp. 1 -32.
Virginia Department of Transportation, 1 997, "Specifica­
tions for Highway and Bridge Construction," VDOT, Rich­
mond, VA.
Vitousova, L., 1 99 1 , "Concrete Sleepers in CSD Tracks,"
International Symposium on Precast Concrete Sleepers,
pp. 253-264.
Wainwright, P. J.; Cabrera, J. G.; and Gowriplan, N., 1 990,
"Assessment of the Efficiency of Chemical Membranes to
Cure Concrete, Protection of Concrete," Proceedings of the
International Conference, Dundee, Scotland, R. K. Dhir and
J. W. Green, eds., E&FN Span, London, pp. 907-920.
Wang, K.; Cable, J. K.; and Ge, Z., 2003, "Investigation
into Pavement Curing Materials, Application Techniques,
and Assessment Methods," Proceedings of the 2003 Mid­
Continent Transportation Research Symposium, Ames, lA,
pp. 1 - 1 1 .
Wilson, M. A.; Taylor, S. C.; and Hoff, W. D., 1 998,
"The Initial Surface Absorption Test (ISAT): An Analytical
Approach," Magazine of Concrete Research, V. 50, No. 2,
pp. 1 7 9- 1 85 . doi: 1 0. 1 680/macr. l 998.50.2 . 1 79
Wojakowski, J., 1999, "Report to ACI Committee 308
on Effect of Plastic Covering on Variations in Concrete
Surface Temperature," Kansas Department of Transporta­
tion, Topeka, KS, Nov.
Wojakowski, J.; Meggers, D.; Distlehorst, J. A.; and
Hobson, C., 2004, "Concrete Curing: Plastic Shrinkage
Cracking, Bleeding, Evaporation, and Temperature," Kansas
Department of Transportation Library, Topeka, KS.
Wojcik, G. S., 200 1 , "The Interaction between the Atmo­
sphere and Curing Concrete Bridge Decks," PhD thesis,
University at Albany, State University of New York.
Ye, D.; Mukhopadhyay, A. K.; and Zollinger, D. G.,
2009, "Laboratory and Field Evaluation of Concrete Pave­
ment Construction Curing Effectiveness," Research Report
0-5 1 06-3, Texas Transportation Institute, The Texas A&M
University System, College Station, TX, Sept.
Ye, D.; Shan, C.-S.; Mukhopadhyay, A. K.; and Zollinger,
D. G., 20 1 0, "New Performance-Based Approach to Ensure
Quality Curing During Construction," Journal of Mate­
rials in Civil Engineering, V. 22, No. 7, pp. 687-695. doi:
1 0. 1 06 1 /(ASCE)MT. l 943-5533 .0000068
Ytterberg, R., 1 987a, "Shrinkage and Curling of Slabs on
Grade (Part 1)," Concrete International, V. 9, No. 4, Apr. ,
pp. 22-3 1 .
Ytterberg, R., 1 987b, "Shrinkage and Curling of Slabs on
Grade (Part II)," Concrete International, V. 9, No. 5, May,
pp. 54-6 1 .
Ytterberg, R., 1 987c, "Shrinkage and Curling of Slabs on
Grade (Part III)," Concrete International, V. 9, No. 6, June,
pp. 72-8 1 .
American Concrete Institute
Always advancing
As ACI begins its second century of advancing concrete knowledge, its original chartered purpose
remains "to provide a comradeship in finding the best ways to do concrete work of all kinds and in
spreading knowledge." In keeping with this purpose, ACI supports the following activities:
Technical committees that produce consensus reports, guides, specifications, and codes.
Spring and fall conventions to facilitate the work of its committees.
Educational seminars that disseminate reliable information on concrete.
Certification programs for personnel employed within the concrete industry.
Student programs such as scholarships, internships, and competitions.
Sponsoring and co-sponsoring international conferences and symposia.
Formal coordination with several international concrete related societies.
Periodicals: the ACI Structural Journal, Materials Journal, and Concrete International.
Benefits of membership include a subscription to Concrete International and to an ACI Journal. ACI
members receive discounts of up to 40% on all ACI products and services, including documents, seminars
and convention registration fees.
As a member of ACI, you join thousands of practitioners and professionals worldwide who share
a commitment to maintain the highest industry standards for concrete technology, construction,
and practices. In addition, ACI chapters provide opportunities for interaction of professionals and
practitioners at a local level.
,American Concrete Institute
'
38800 Country Club Drive
Farmington Hills, MI 48331
Phone: +1.248.848.3700
Fax:
+1.248.848.3701
Coovriaht American Concrete Institute
www.concrete.org
American Concrete Institute
Always advancing
38800 Country C l u b Drive
Farmington H i l l s , Ml 48331 USA
+1 . 248.848.3700
www.con crete.org
The A m e r i c a n C o n c rete I n stitute (AC I ) is a l e a d i n g a utho rity a n d resou rce
worldwide for the deve l o p m e nt a n d d i stri bution of c o n s e n s u s-based
sta n d a rd s a n d tec h n i c a l reso u rces, ed ucati o n a l pro g r a m s , and certifi cati o n s
for i n d ivid u a l s a n d o rga n i zati o n s i nvo lved i n c o n c rete d es i g n , c o n st r u ct i o n ,
a n d materia l s , w h o s h a re a co m m itment to p u rs u i n g the best u s e o f c o n crete.
I n d ivi d u a l s i nterested in the a ctivities of ACI a re e n c o u ra g e d to explore the
ACI website fo r m e m b e rs h i p o p p o rtu n ities, c o m m ittee activities, and a wide
va ri ety of c o n crete reso u rces. As a vo l u nteer m e m be r-d riven o rg a n izati o n ,
ACI i nvites p a rt n e rs h i p s a n d w e l c o m e s a l l con crete p rofess i o n a l s w h o w i s h to
be p a rt of a res pecte d , c o n n ecte d , soc i a l g ro u p t h at p rovides a n op portu n ity
for p rofessi o n a l g rowth, n etwo r k i n g a n d e nj oy m e nt.
9
Coovriaht American Concrete Institute
1 1 1 11 11 1 11 1 1
781942
727873