Strength. Performance. Passion.
Technical Manual
Cement & Concrete
Holcim (Vietnam) Ltd.
1st edition 2013
2
3
Imprint
Copyright
C2013, Holcim (Vietnam) Ltd
All rights, including the partial re-print of parts or
entire section of the book in Vietnamese version
and/ or English version (including photo copy, micro
copy, CD-Rom, or any other way of copying and
presenting it in public), the storage in date centers
and the translation, are reserved to the authors.
Special permission must be requested in writing to
Holcim (Vietnam)
Authors
Technical consultant team
Holcim (Vietnam) Ltd
A special thank to Silvia Vieiria Mcs, PhD – Holcim
Group Support Ltd
Publication
1st edition 2013 in Vietnamese
1st edition 2013 in English
Disclaimer
Alone the complete standards referred hereto serve
as reference. They can be sourced at the respective
organizations. Holcim (Vietnam) is not liable for
misapplication and/or interpretation of the content
of this manual.
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5
About Holcim (Vietnam) Ltd.
Founded in 1912 in the tiny Swiss village of Holderbank, Holcim is
one of the world leading cement and construction materials
companies. Holcim operates in more than 70 countries across all
continents and employs around 90,000 people world-wide. Today
Holcim has become synonymous of leadership in the supply of
cement and aggregates (crushed stone, sand and gravel), as well as
readymix concrete and construction-related services.
Holcim (Vietnam), founded in 1993, has the unique network of 4
cement plants in south Vietnam at Hon Chong, Hiep Phuoc, Cat Lai,
Thi Vai, to guarantee the best supply security for each project. To
meet the requirements of every application, Holcim Vietnam has
researched and developed a wide range of cements that offer the
optimal solution for every project.
Established in 2005, Holcim Beton has developed into a leading
readymix supplier in southern Vietnam, offering its customers high
quality, innovative products and services. Over the last years,
Holcim Vietnam has worked with leading national and
international contractors and developers as the preferred partner in
projects in southern Vietnam.
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Preface
To develop Vietnam in the 21st century and to meet the requirements of modern society, many high rise
buildings and infrastructure projects, like ports, roads, bridges… are being designed and constructed by
national and international developers, designers and contractors.
These structures are expected to be in service for long time, sometimes for 100 years, with low maintenance
costs. The durability of concrete as building material is a key element for long lasting projects. This Technical
Manual offers an overview of good practices in concrete as well as an overview of relevant Vietnamese and
international standards.
A better understanding of cement/concrete standards can make it easier for designers, consultants and
contractors to choose the type of cement and concrete, suitable for their specific project. With good concrete
practice at the jobsite, the high quality building material “concrete” will be molded and transformed into
long lasting concrete structures, to build Vietnam for future generations.
As the different standards are complex to summarize and the construction industry changes quickly in
Vietnam, it is possible that there are inaccuracies in this Technical Manual. We are looking forward to any
feedback or input for improvement on technical.service-vnm@holcim.com.
Yours sincerely,
Pieter Keppens
Technical Marketing Manager
8
Index
Chapter I
Cement & Concrete
11
A. Components of concrete
1. Cement
2. Mixing water
3. Fine aggregate 4. Coarse aggregate
5. Admixtures
6. Additions
11
11
12
13
14
16
17
B. From fresh concrete to hardened concrete
1. Composition of concrete
2. Workability
3. Concrete strength
4. Special characteristics
5. Production and transport 6. Placing and compaction
7. Concreting in hot weather 8. Pumped concrete
9. Curing 10. Influence of formwork
20
20
23
27
33
37
38
41
43
45
47
Chapter II
Applications with specific requirements 49
A. Infrastructure
1. Introduction
2. Cement for infrastructure
49
49
49
B. Aggressive environments
1. Introduction 2. Sulfate resistant Portland cement
3. Sulfate resistant blended cements
50
50
50
51
C. Massive structure
1. Introduction
2. Cement for massive structures
3. Concrete for massive structures
52
52
52
53
D. High strength concrete
1. Introduction
2. Production and use of high strength concrete
54
54
55
E. Very flowable and self-compacting concrete
1. Introduction
2. Production of very flowable / self-compacting concrete
56
56
57
F. Cement treated aggregates
1. Introduction
2. Cement for treated aggregates
3. Testing procedure for cement treated aggregates
4. Optimization of cement treated aggregates
58
58
58
59
61
9
Chapter III
Causes and prevention of concrete defects
62
A. Segregation of concrete
63
B. Cracking
1. Plastic settlement cracks
2. Plastic shrinkage cracks
3. Surface crazing
4. Drying shrinkage cracks
5. Early thermal cracking
64
65
66
67
67
68
C. Carbonation and corrosion of reinforcement
69
D. Degradation in seawater environment
1. Chloride-induced corrosion of the steel reinforcement
2. Attack by sulfates from seawater
3. Preventive measures
70
70
71
71
E. Chemical attack
1. Classification
2. Preventive measures
72
72
73
F. Alkali – Aggregate Reaction
74
G. Fire Resistance
1. Concrete in fire
2. Preventive measures 75
75
75
Chapter IV
Overview of cement & concrete standards
76
A. Cement
Vietnamese standards – TCVN
American standards – ASTM
European standards – EN
77
77
83
86
B. Concrete
Vietnamese standards – TCVN
American standards – ASTM
European standards – EN
British standards – BS
89
89
91
93
95
C. Recommendation for limiting values of concrete composition
Chloride - induced corrosion in sea water
Aggressive chemical environments
97
97
97
Reference
98
10
Chapter I:
Cement & Concrete
A. Components of concrete
1. Cement
General
Cement is a hydraulic binder – a material that
hardens after being mixed with water, either in the
air or under water. The hardened cement paste is
water-resistant and possesses high strength. For
all concrete without specific requirements, the type
of cement generally used in Vietnam is a blended
Portland cement, type PCB 40, according to the
Vietnamese standard TCVN 6260. For plaster/mortar
in rural areas, PCB30, a lower strength class, is
sometimes used as well.
Several types of blending materials are used, like
limestone, puzzolan or slag, depending on the locally
available materials.
International standards, comparable to TCVN 6260,
are:
• American Standard ASTM C1157: type GU
(General Use)
• European Standard EN 197-1: CEM II/A or CEM
II/B 42.5
Other types of cement, which are used worldwide, like
• Ordinary Portland Cement OPC (TCVN 2682,
ASTM C150, EN 197-1 CEM I)
• Blast Furnace Slag cement (TCVN 4316, ASTM
C1157, EN 197-1 CEM III)
are not available in Vietnam as general use cement.
The test methods of the TCVN standard are very
close to the EN standard, with the correction of
testing temperature (27oC instead of 20oC), to take
the local climate conditions into account.
The ASTM standards use a completely different
set of testing methods and the requirements
cannot be compared to the TCVN/EN standards. In
Vietnam, several 3rd party laboratories are equipped
to test cement according to TCVN & ASTM, but not
according to the EN standard.
Holcim recommendation
For general use concrete, standard cement offers
the best supply security for any project:
• TCVN 6260:2009 – PCB 40
• ASTM C1157:2008 – GU
Testing cement quality and conformity
The quality and conformity of Vietnam cements are
assured through three types of control:
• Control of the product in the plant
• An certified quality-management system
• External monitoring
Control of the product in the plant
At each step of the cement production, from the
quarry to cement delivery, material specimens
are collected for analysis. Gap-free monitoring of
production ensures uniform, high-quality cement.
The testing methods for cement are described in
standard TCVN 6017:1995 and ISO 9597:2008.
Quality management system
Most cement plants have established a quality
management system and all are certified according
to the ISO 9001:2008 series of standards. Some
cement plants also have a testing center in series of
VILAS according to ISO 17025. This ensures that all
operational processes are standardized, traceable,
and transparent.
External monitoring
In-house testing is supplemented by external
monitoring. External monitoring is carried out by a
testing institute accredited for testing cement. In the
south part of Vietnam, the most referenced external
monitoring is Quality Assurance and Testing Center 3
(QUATEST 3). From November 2012, every cement in
Vietnam has to carry the CR quality label.
Cement storage and shelf life
If cement is stored unprotected for a long time, it
absorbs moisture, which leads to lumps and may
reduce the strength development. If lumps can be
crushed between the fingers, the loss of strength
will be negligible.
Cement can be stored for a limited time in silo or
bags. Bag cement is best stored in dry shelter. Bags
stacked temporarily outdoors must be placed on
timber sleepers for ventilation. The plastic cover
must not be allowed to contact the cement bags,
because condensation would wet the bags.
11
12
Chapter I: Cement & Concrete
A. Components of concrete
2. Mixing water
Water for mixing concrete and mortar must comply
with TCXDVN 302:2004 or ASTM C1602. Water that
meets these requirements, can be used for washing
aggregate and curing concrete sample. According to
these standards, drinking water can be used as
mixing water without testing. Water from rivers and
canals is in most cases not appropriate to make
concrete. The use of seawater in reinforced concrete
is strictly forbidden.
Requirements for mixing water
According to TCXDVN 302:2004, mixing water must
meet these following requirements:
• Does not contain oil scum and oily film
• Organic content < 15mg/l
• 4 < pH < 12.5
• Color free
• Depending on the type of concrete, sulfate and
chloride content must follow the requirements
in Table I.1 (TCXDVN 302 : 2004).
General
Mixing water is the total amount of water contained
in fresh concrete. It is the sum of:
• The water added directly to the mix
• The surface moisture of the aggregates
• The water content of the concrete admixtures
and additions, if applicable
(silica fume, pigment in suspension, etc.)
Mixing water has two functions in concrete
technology. It is required for hydration of the
cement, and for the production of a plastic concrete
that can be well compacted.
Maximum Level
(mg/l)
Purpose of mixing water
Soluble
Salt
Sulfate Ion
(SO4-2)
Chloride Ion
(Cl-)
Insoluble rest
1. Pre-stressed concrete.
2000
600
350
200
2. Reinforced concrete.
5000
2000
1000
200
3. Non-reinforced concrete.
10000
2700
3500
300
Table I.1 - Limit sulfate and chloride content in mixing water for different purpose
A. Components of concrete
3. Fine Aggregate
Grading
Fine aggregate shall consist of natural sand, crushed
sand, or a combination thereof. For concrete
production, fine aggregates must comply with TCVN
7570 : 2006 or ASTM C33 (Standard Specification for
Concrete Aggregates). In the south of Vietnam, 3
sources of fine aggregates are used in concrete (FM
= fineness modulus):
• Sand from Dong Nai river : FM = 2.40 (good – not
available in significant quantity)
• Sand from Mekong river : FM = 1.1 -1.6 (too fine)
• Manufactured (crushed) sand : FM = 4.0 (too
coarse)
Usually when the sand is very fine, the mix is
un-economical because the increase of water
demand will lead to the increase of cement. When it
is very coarse, the mix is harsh and unworkable
because there are so much voids between the grains
and the cement paste can not fill the voids.
According to ASTM C33, a reference for good sieve
curve of fine aggregates for concrete is like Fig I.1.
In the south of Vietnam, sand compliant to ASTM
C33 cannot be found. The current practice is to
combine Mekong sand with manufactured sand, to
reach the best performance.
Organic Impurities
Fine aggregate must be free of deleterious amounts
of organic impurities. Fine aggregates that contains
many organic impurities, will lead to delay in
concrete setting, loss of strength and durability of
concrete.
Fine aggregate should be tested before use on
organic impurites according to standard TCVN
7572-9 : 2006 or ASTM C40 (Standard Test Method
for Organic Impurities in Fine Aggregates for
Concrete). When a sample has a color darker than
the standard color, or Organic Plate No. 3, the fine
aggregate under test contains possible injurious
organic impurities. It is advisable to perform further
tests before approving the fine aggregate for use in
concrete.
Other Impurities
Impurities like silt, dust, clay content also have a
disavantage effect on concrete. It should be tested
before use for concrete according to standard TCVN
7572-8 : 2006 (Standard test method for silt, dust,
clay content) or ASTM C117 (Standard Test Method
for Materials Finer than 75-μm).
13
4.75
9.50
100
2.36
1.18
0.60
0.30
0.15
90
Mekong sand
80
70
Passing (%)
Chapter I: Cement & Concrete
60
Manufactured sand
50
40
30
20
10
0
10.0
Coarse limit (ASTM C33)
0.1
1.0
Sieve openings (mm)
Combination
Fine limit (ASTM C33)
Fig I.1 - Good sieve curve of fine aggregate for concrete
Akali-Silica Reaction
For concrete that is subjected to wetting, extended
exposure to humid atmosphere, or contact with
moist ground (for example, foundations, bridges,
tunnels,…), the aggregates (both fine and coarse)
shall not contain any materials that are deleteriously
reactive with the alkalies in the concrete to cause
Alkali Aggregate Reaction. This expansive reaction
can create cracks in the concrete, which reduces
both the concrete strength and the durability.
Potential Alkali-Silica Reactivity of Aggregates
should be tested according to standard TCVN 757214:2006 (Determination of alkali silica reactivity ) or
ASTM C289 (chemical method), ASTM C1260 or
ASTM C227 (mortar – bar method).
Fig I.2
Organic
impurities test
using organic
plate.
14
Chapter I: Cement & Concrete
A. Components of concrete
4. Coarse aggregate
General
Coarse aggregates form the skeletal structure of the
concrete and must comply with TCVN 7570 :2006 or
ASTM C33 (Standard Specification for Concrete
Aggregates).
Characteristics
The most important characteristics of coarse
aggregates are:
• Specific gravity
• Bulk density (unit weight) and moisture content
• Mineral composition, grain shape, and surface
texture
• Purity
• Grading (grain size distribution) and aggregate
fractions (range of sizes)
• Soundness
Table I.2
Classification of
aggregates by
specific gravity
Aggregate type
Specific Gravity (kg/m3)
Aggregate Material
Standard aggregate
2700
River or glacial deposits;
crushed stone
Reinforced and
non-reinforced concrete
Heavy aggregate
>3000
Barite (heavy spar), iron ore,
granulated steel
Concrete for radiation
protection
Lightweight aggregate
< 2000
Expanded clay, polystyrene
Insulating concrete, concrete
topping, sloped concrete
Hard aggregate
> 2500
Quartz, corundum, silicon
carbide
Hard concrete slabs,
abrasion-resistant concrete
Bulk density (unit weight) and moisture content
Bulk density is the weight of loosely poured material
per unit of volume. It is greatly influenced by
moisture content of the aggregate (Fig I.3). Thus the
two characteristics, bulk density and moisture
content, are closely related. Test method of bulk
density according to TCVN 7572-6 : 2006 or ASTM
C29 (Standard Test Method for Bulk Density and
Voids in Aggregate).
The moisture state of aggregates can change
between ovendry and wet aggregates, depending on
the situation.
Fig I.3
The moisture
state of
aggregate
Application
Specific gravity
The aggregate specific gravity is the ratio of the
weight of a given volume of aggregate to the weight
of an equal volume of water. Aggregate specific
gravity is needed to determine weight-to-volume
relationships and to calculate various volumerelated quantities such as voids in mineral
aggregate. The test standard for coarse aggregate
specific gravity and water absorption is the TCVN
7572-4 : 2006 or ASTM C127 (Determination of
apparent specific gravity, bulk specific gravity and
water absorption).
State
Ovendry
Air dry
Saturated surface dry
(SSD)
Damp or wet
Total moisture
None
Less than potential
absorption
Equal to potential
absorption
Greater than
absorption
Chapter I: Cement & Concrete
A. Components of concrete
Purity
Adhesive impurity on coarse aggregate surface, such
as dust from degraded rock, reduces concrete
quality, for example, by disturbing setting properties
and reducing the contact area between aggregate
and cement paste. It is suggested to wash coarse
aggregate before use in concrete (Fig I.4.).
15
Mineral quality, grain shape, and surface texture
Porous or overly soft aggregate (for example
degraded rock) impairs the quality of concrete. Grain
shape largely determines the compactability and
water requirement of concrete, as does grading and
surface texture (Fig I.6).
A cubical grain shape is good for concrete mix, it
decreases the water requirement and increases
workability of concrete. In contrast, non-cubical,
grain shape (elongated and flaky- aggregate
particles having a ratio of length to thickness
greater than a specified value) will increase water
demand and decreases the workability of concrete.
Non-cubical grain shape content is measured
according to TCVN 7572-13 (Determination of
elongation and flakiness index of coarse aggregate).
Fig I.4 - Screening and washing aggregate in a gravel plant
Grading
The grading and maximum size of coarse aggregate
is an important parameter in concrete mix. The
grading of aggregate is measured according to
TCVN 7572-2 or ASTM C136 (Standard Test Method
for Sieve Analysis of Fine and Coarse Aggregates)
Fig I.6
Grain shapes of
aggregate
Desirable
Grading, or the distribution of grain sizes – along
with surface texture, specific surface, and grain
shape of coarse aggregate – greatly determines the
water requirement, and thus is one of the most
important characteristics.
The maximum size of aggregate (Dmax) is the
smallest sieve size, through which at least 90% the
aggregate would pass. The maximum size of
aggregates is limited by the application. It depends
on: the distance between reinforcement, size of
elements, and pumpability of concrete. The choice
for maximum size of aggregate follows the Fig I.5.
Rounded
c
d
c
d
Angular
Less Desirable
The use of smaller aggregates increases the water
demand, increases the cement content to meet the
same strength.
I-
Irregular
Dmax < 3d/4
Dmax < 3c/4
f
II-
III-
IV-
Dmax < e/5
Dmax < f/5
e
a
For pumped concrete
Dmax < a/3
Dmax < 1/3 diameter of hose
or 37.5mm
Fig I.5 - The choice for maximum size of aggregate
Flaky
Elongated
Flaky
Elongated
16
Chapter I: Cement & Concrete
A. Components of concrete
5. Admixtures
Definition and classification
Concrete admixtures are chemical substances that
are added to concrete to change, through chemical
and/or physical action, some of its properties, such
as workability, setting, hardening.
In Vietnam, the performance requirements for
different types of admixtures comply with standards
TCVN 8826 : 2011 or ASTM C494 (Standard
Specification for Chemical Admixtures for Concrete).
Dosage
Admixtures are added to concrete mainly in liquid
form and in very small amounts. The dosage is
generally about 0.4 to 2% in relation to the weight
of cement. In certain cases the amount will be
recommended by the manufacturer. If the dosage
exceeds about 1%, the water introduced with the
admixture, must be considered as part of concrete
mixing water. Too low dosage can reduce
significantly the desired effect, and too high dosage
can produce unwanted effects such as retarded
setting or loss of compressive strength.
The most important and common types of
admixtures
According to ASTM C494, there are seven types of
admixture (from type A through type G). In Vietnam,
three types are commonly used:
a/ Water reducing and retarding admixture.
This type of admixture, based on lignosulphonate,
can be used at dosage 0.4 - 0.6% to reduce the
quantity of water required (6% - 12%).
Water reducing admixtures require less water to
make a concrete of equal slump which improves the
concrete strength, or increase the slump of concrete
at the same water content.
b/ Mid-range water reducing admixture.
This type of admixture, based on napthalene
sulfonate, can be used at dosage 0.7 – 1.2% to
decreases the water requirements by about 15
– 25%.
Mid-range water reducers allow larger water
reduction to increase strength or slump/slump
retention at jobsite. They can achieve a specific
consistency and workability at a greatly reduced
amount of water. As with most types of admixtures,
napthalenes can significantly delay the initial setting
time of concrete, depending on the admixture
formulation.
c/ High-range water reducing admixture
This type of admixture is based on polycarboxylate
base. Common dosages are between 0.8 – 1.8%,
depending on the supplier recommendation. This
type of admixture can reduce the quantity of mixing
water required (20 - 35%) to produce concrete with
high consistency, better workability and high
strength. The optimal dosage needs to be
determined based on the particular concrete mix
and specific requirements.
Other type of admixtures
Many other types of admixture for concrete are
available:
• Accelerators
• Air entrainer admixture
• Corrosion inhibitor
These specific admixtures are rarely used in
Vietnam. More information can be found from
different admixture suppliers.
Retarding admixture is useful for concrete that has
to be transported over long distances, requires a
long slump retention and to retard the setting time
of concrete when placed at high temperatures.
Fig I.7 - Admixture used in concrete.
Chapter I: Cement & Concrete
A. Components of concrete
6. Additions
Fibers
Polypropylene fibers are organic fibers, used in
concrete to prevent plastic shrinkage cracks. About
0.7kg - 1kg of fibers is required per m3 of concrete
(Fig I.8).
Steel fibers, uniformly distributed in concrete,
improve
certain
mechanical
characteristics,
particularly ductility (toughness) and tensile
strength. The efficiency of steel fibers greatly
depends on their length, diameter, and shape. The
main use of steel fibres is in industrial floors, to
replace the steel mesh in the concrete (Fig I.9).
17
Fig I.8
Polypropylene
fibers
Fig I.9
Steel Fiber
Glass fibers are used to reinforce thin prefabricated
sections. Using glass fibers is tricky; it requires the
experience of a recognized expert (Fig I.10).
Silica fume
Silica fume (Fig I.11), also known as silica dust or
microsilica, possesses a high pozzolanic activity due
to extreme fineness and very high amorphous silica
content. Silica fume dosages of 5 to 10% by weight
of cement can produce permanent improvement of
concrete characteristics:
• Reduction
of
concrete
porosity,
thus
improvement of durability; increased resistance
to salts, sulfates, and other aggressive chemicals.
• Carbonation
reinforcement
corrosion.
Fig I.10
Glass fiber, cut
and bundled
progresses
slower,
thus
is better protected against
• Contributes to concrete strength; allows the
production
of
high-strength
concrete
(80-100MPa)
Caution
Adding silica fume to a concrete mix reduces
the workability and changes the rheologic
characteristics (flow characteristics)! Adequate
workability can be achieved by adding special
superplasticizers.
As silica fume is very fine, the homogeneous
distribution into the concrete is an important
issue that requires specific attention. If the silica
fume is not well distributed into the concrete,
its efficiency in increasing strength and
durability will be reduced.
Fig I.11
Silica fume
18
Chapter I: Cement & Concrete
A. Components of concrete
Other mineral additions (puzzolan, fly ash)
In many countries, high quality fly ash, a by product
from thermo power plants, is commonly used in
concrete, as this is an active puzzolan that
contributes to the strength of the concrete.
In Vietnam, the use of both puzzolan (Fig I.12) and
fly ash (Fig I.13) is mainly limited to Roller
Compacted Concrete (RCC) in hydraulic dams. The
available fly ash is not suitable for flowable
concrete, due to its:
• High loss of ignition (= unburned coal)
Inorganic pigments
Inorganic pigments are used to dye concretes and
mortars (Fig I.14). Oxide pigments are virtually the
only ones that can meet the demanding criteria of
stability and grading. Pigments have no chemical
effect on concrete. Because of their high fineness,
they increase the concrete water demand. This can
be counteracted by adding a highrange water
reducer. Pigment dosage, usually a few percent
measured by weight of cement, depends on the
desired color intensity. Amounts are recommended
by the suppliers.
• High water demand
• Issues with admixture compatibility
• Unstable quality, with limited quality control.
Fig I.12
Puzzolan
Fig I.14 - Concrete products made using white portland
cement colored with pigments
Producing flawless colored concrete surfaces
requires great experience. Uniformly colored, bright
concrete surfaces can be achieved only with a
completely homogeneous concrete mix using white
cement and light colored sand. The color of the
gravel is not so important.
Fig I.13
Fly Ash
Any residue of colored concrete must be completely
removed from mixers, transport vehicles, and
conveyor equipment, so that subsequent batches of
concrete are not contaminated. Even the best
pigments cannot prevent the color of concrete from
fading somewhat over time.
Cement & Concrete
Concrete component
19
20
B. From fresh concrete to
hardened concrete
1. Composition of Concrete
Concrete is a composite material that consists
essentially of fine and coarse aggregates, glued
together by the cement paste. Aggregates occupy
60-75% of the concrete (measured by weight or by
volume, as Fig I.15 and they are important
constituents from a technical and economical point
of view. Aggregates play a central role in concrete
strength and durability.
Importance of the water/ cement (w/c) ratio
A central characteristics of concrete, and one that
largely determines its performance, is the water/
cement ratio, or w/c ratio (Fig I.16).
Fig I.15 - Composition of Concrete
But the picture looks a bit different when we
consider the so-called internal surface area, that is,
the combined surfaces of all the particles in
concrete. Measured in this way, the dominant
component in concrete is clearly cement and the
cement paste is fundamental in defining many
concrete characteristics.
Concrete mixing
In proportioning the constituents of concrete, or
determining the so-called concrete mix or mix
design, the producer is primarily concerned with
optimizing concrete's:
• Workability
• Strength
• Production cost
• Durability
Fig I.16 - Influence of the w/c ratio on concrete properties
The relationships between the w/c ratio and
required characteristics of concrete are well known
in practice. Thus, the designing engineer usually
specifies the w/c ratio when he specifies the type of
concrete.
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Choosing the water/cement ratio
An appropriate w/c ratio will depend primarily upon
environmental exposure and the loads the concrete
construction
will
be
carrying
(Fig
I.17).
Recommended maximum w/c for different exposure
conditions are given, for example, in the EN 206 or
in ACI 318.
21
Fig I.17
Influence of the w/c
ratio on 28-day
compressive
strength of
concrete
Minimum cement content in concrete
With sufficient cement in concrete, enough calcium
hydroxide is formed during hydration that the high
alkalinity and low porosity achieved in the concrete
will reliably protect the steel reinforcement from
rusting. On the other hand, overly large amounts of
cement in concrete increases the possibility of cracks
due to shrinkage and increased heat of hydration.
According to EN 206, reinforced concrete with a
maximum aggregate size of 32mm should normally
contain at least 300kg cement per m3 compacted
concrete. The dosage may be reduced to 250 kg/m3
only if the constructed element is permanently
protected from environmental action and other
forms of attack.
Fig I.18
Poor filling of
void spaces, high
permeability
concrete with
only one size of
aggregate
(schematic)
TCXDVN 327:2004 - Concrete and Reinforced
Concrete Structures Requirements of Protection
from Corrosion in Marine Environment requires:
Area
Minimum cement
content (kg/m3)
No direct contact
350
Direct contact
400
Table I.3 - Minimum cement content depend on
environmental exposure (TCXDVN 327)
The European standard EN206 increases the
minimum cement content to the environmental
conditions (refer chapter IV.C)
Low porosity in concrete
A well-designed aggregate mix with a smooth
grading curve produces concrete with good
workability and high cohesion, with a high
resistance to segregation. The hardened concrete
will have low permeability, which gives it good
durability (Fig I.18 and I.19).
Fig I.19
Good filling of
void spaces, low
permeability
concrete with a
smooth grading
curve (schematic)
22
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Proportioning the mix by absolute volume
In practice, the proportions of each constituent of a
concrete mix are determined by calculating their
absolute volumes. The unit volume of each
component is calculated based on 1m3 (1000l) of
compacted concrete, and obtained by dividing the
mass of each component by the specific gravity
Volume (m3)=
Mass (kg)
Specific Gravity
(kg/m3)
Example:
Specification: Cement dosage
Water/Cement ratio
Plasticizer
Assumption: Normal porosity
325 kg/m3
0.48
1% based on cement mass ( = ~ 3 kg)
1.5% entrapped air (=15 l)
Specific Gravity
(kg/m3)
Component
Mass (kg)
Cement
325
3,100
0.105 
Mixing water
156
1,000
0.156 
Plasticizer
3
~ 1,000
0.003 
-
0.015 
Entrapped air
Subtotal
484
Dry aggregate
0.721 x 2,700 = 1947 
Fresh concrete
484 + 1947 = 2431 
Unit volume (m3)
0.279 
2,700
1 - 0.279 =0.721 
2,431
1
1) Mixing water = water added + moisture of aggregates. The number  through  indicate the sequence of the
calculation.
To calculate the actual amount of aggregate
necessary, the water contained as moisture in the
aggregate (generally 4 to 6% for sand and 1 to 3 %
for gravel) must be added for each fraction.
Subtracting the moisture contained in all the
aggregates from the total mixing water gives the
necessary amount of water to be dispensed.
The unit volume of entrapped air bubbles (generally
1 to 2 %) as well as the volume of entrained air must
also be considered in proportioning the mix by
absolute volume. The example shows a method of
calculating the “dry“ aggregate amount and the
fresh concrete density.
Influence of other factors on the workability &
strength of concrete
Besides admixtures, many other factors influence
concrete workability. Changing one or more of these
factors changes not only the workability, but also
other characteristics of concrete, for example
strength. Table I.4 shows how various changes in
concrete constituents and mix affect the
consistence and 28-day compressive strength of
concrete.
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Change
Workability
23
28-day
compressive
strength
Smoother grading
More rounded aggregate
Table I.4
Effect of various
factors on
workability and
strength of
concrete
More crushed (angular) aggregate
More mixing water
Higher concrete temperature
Use of a superplasticizer
Use of an air entrainer
Use of a retarder
positive influence
negative influence
2. Workability
To achieve a high quality concrete structure, the
method of placing and compaction as well as the
shape of the concrete element and reinforcement
arrangement, should be considered to select the
workability of the concrete.
The concrete workability affects the speed of
placement and the degree of compaction of
concrete. Inadequate compaction may result in the
reduction in both strength and durability of
concrete.
Different test methods for workability are available
including slump, Vebe time, flow table, etc. The
choice of the test method depends on the concrete
workability and its application.
To get reliable results, each test method for
workability should be applied within its test range
(EN206):
• Slump
≥ 10 mm and ≤ 210 mm;
• Vebe time
≤ 30 sec and > 5 sec;
• Flow diameter
> 340 mm and ≤ 620 mm.
TCXDVN 374:2006 specifies:
• For too dry concrete: the vebe time > 50 second.
• For dry concrete: the vebe time > 5 second and <
50 second.
• For plasticized concrete: The slump from 10 to
220 (mm)
• For super-plasticized concrete: the flow from 260
– 400 (mm)
no significant influence
a. Slump test :
The slump test is the most well-known and widely
used method to characterize the workability of fresh
concrete. This simple test is used at the job sites to
quickly determine whether a concrete batch should
be accepted or rejected.
The slump test measures the ability of concrete to
flow under its own weight, without vibration. This
method is suitable for medium to high workability
concrete with slump ranging from 10 to 210 mm
(EN 206).
The test method is widely standardized throughout
the world:
• TCVN 3106
• ASTM C143
• EN 12350-2
The apparatus used in the slump test are: mold,
tamping rod, measuring equipment (Fig I.20):
Fig I.20
Apparatus to
determine slump
24
Chapter I: Cement & Concrete
-
B. From fresh concrete to hardened concrete
-
In EN and TCVN standards, the slump is the
vertical difference between the top of the mould
and that of the highest point of the slumped test
specimen.
Fig I.21 - Determine Slump conform to TCVN and EN
standard
The slump test is only valid if the concrete cone
stays visible and symmetrical (true slump). If the
concrete cone shears (shear slump), the test needs
to be done again. If it fails again, the slump test is
not applicable for the concrete (EN 12350-2)
In ASTM standard, the slump is the vertical
difference between the top of the mould and the
displaced original center of the top surface of the
specimen.
Fig I.22 - Determine Slump conform to ASTM standard
True Slump
Fig I.23 - True and shear slump shape
Table I.5
Slump range for
different
applications
Shear Slump
Depending on the application of concrete, the following slump values are recommended:
Slump Range (mm)
60-80
Application
Elements with intense vibration:
Precast elements, concrete pavement.
Concrete placed by bucket
100-160
Elements with good vibration (compaction
needles): column, slab, beams etc.
Concrete placed by bucket or pump
180-200
Elements with low vibration level:
• Bore piling
• Retaining wall
• Core wall
Concrete placed by bucket or pump
Illustrated photo
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
b. Slump flow:
The slump flow test method is used to determine
workability of very flowable concrete with a very
high slump. At this high slump > 200mm, normal
concrete has the tendency to segregate, which
impacts the concrete quality significantly. To reach a
high quality concrete at very high workability, the
mix design needs to be specially developed to avoid
segregation and achieve the required stability.
Two types of concrete can be distinguished
(see Chapter II.E):
- Very flowable concrete (slump flow: 450- 650mm)
-
25
The upright mold (same way as the slump test) is
popularly used in Vietnam. Slump flow is the
average of the largest diameter of circular spread of
the concrete and the circular spread of the concrete
at an angle approximately perpendicular to
diameter above.
Concrete with high workability is used for structure
with dense reinforced steel such as transfer beam,
core walls, pile cap, etc or for the areas that are
difficult to reach for compaction.
Fig I.25
Structure with
dense reinforce
steel
Self Consolidating Concrete (SCC), also known as
Self Compacting Concrete (slump flow > 650mm).
This test uses the same equipment as the slump
test, but the diameter of the concrete spread is
measured.
Fig I.26
Transfer beam
c. VEBE test:
For semi-dry concrete with a low workability, the use
of the Vebe test is recommended. The Vebe time is
the time needed to level and compact fresh concrete
in Vebe consistometer and ranges from 5s to 30s
(EN 206). Some typical applications are:
Fig I.24 - Determine slump flow for fresh concrete
-
Roller compacted concrete (RCC) for hydraulic
RCC dams
The test method to determine slump flow is ASTM
C1611 or EN 12350-8. In ASTM standard, there are
two ways to measure slump flow of concrete:
-
Base layers of roads, container ports
-
Precast products: concrete pipes
-
Upright mold
-
Inverted mold
26
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
The freshly mixed concrete is packed into a similar
cone used for the slump test. The cone stands within
a special container on a Vebe table, which is vibrated
at a standard rate after the cone has been lifted. The
time taken for the concrete to be compacted is
measured.
d. Flow table test:
The flow table test measures the workability of
concrete under the impact of compaction energy.
Generally, in Viet Nam, EN 12350-5 standard is used
to test flow table of fresh concrete.
Fig I.27
RCC for hydraulic
dams
General standards which are used to determine
Vebe time:
-
TCVN 3107:1993,
-
EN 12350-3,
-
ASTM C1170.
In Viet Nam, two methods have been applied: TCVN
3107 and EN 12350-3 to test Vebe time of semi-dry
concrete. Basically, both of standards are similar.
However, EN standard is more detailed than TCVN.
Rotating Arm
Moving Vertical Rod
Slump Cone
Clear Plastic Disk
Container
Vebe Table
Fig I.28 - Apparatus
to measure Vebe
time
Fig I.29 - Flow table test for fresh concrete
To perform the test, the cone mold is placed in the
center of the plate and filled in two layers, each of
which is compacted with a tamping rod. The plate is
lifted by the attached handle at a distance of 40 mm
and then dropped a total of 15 times. The horizontal
spread of the concrete is then measured.
200mm
Clip
40mm
Handle
Mold
30mm
200mm
Bottom
Plate
Top Plate
Hinge
700mm
Fig I.30 - Apparatus to determine flow table
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
3. Concrete strength
One of the most important characteristics of
concrete is the strength, as strength is an important
input parameter to the design of the concrete
structure. Concrete is a very strong material when it
is used in compression and it is however, less
resistant to tension.
There are different ways to measure the concrete
strength, such as compressive strength, flexural
strength, and tensile strength tests.
27
To obtain accurate test result with cylinder
specimens, the cylinder should be capped with a
thin layer of stiff Portland cement or sulfur paste
which is permitted to harden and cure with the
specimen in accordance with ASTM C 617.
This capping method has to be done carefully,
especially for high strength concrete.
Fig I.33
Equipment for
capping
specimen and
the specimen
after capping
and testing
a. Compressive strength:
Compressive strength is the capacity of a material or
structure to withstand axially directed pushing
forces. When the limit of compressive strength is
reached, the concrete fails and breaks.
The compressive strength of concrete is the most
common performance parameter used by the
engineer in designing building and other structures.
The compressive strength is measured in cylindrical
(150x300mm) or cubical (150mm) concrete
specimens that are casted, compacted, cured and
tested in standard conditions.
The compressive strength is conventionally
determined on specimens tested at 28 days age. For
particular applications, for example mass concrete,
RCC etc, the concrete strength can be specified at
later ages, like 56 or 90 days.
The type of specimen, as well as sampling method,
curing and testing, are specified in the following
standards:
In case early strength is required, to remove the
support frame or formwork, or to prestress the
concrete the compressive strength at earlier ages (1
day, 3 days etc) are commonly specified in addition
to the 28 days strength.
-
TCVN 3105 :1993 & TCVN 3118:1993
-
BS EN 12390-2 & EN 12390-3
-
ASTM C31 & ASTM C39
Sometimes, other specimen sizes are used – the
following correlation factors can be appied to
recalculate into the standard size specimen (cube
150mm):
Shape & size specimen (mm)
Fig I.31 - Cube and cylinder specimens
Cube
specimen
Cylinder
specimen
100x100x100
0.91
150 x 150 x 150
1,00
200 x 200 x 200
1.05
300 x 300 x 300
1.1
71,4 x 143 & 100 x 200
1.16
150 x 300
1.2
200 x 400
1.24
(source: TCXDVN 3118:1993)
Fig I.32 - Specimens in a compression-testing machine:
cube and cylinder specimens
Correlation factor
Table I.6 - The correction factor to recalculate into the
standard size specimen (cube 150mm)
28
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
In Vietnam, the concrete is classified based on grade
and class of hardened concrete.
Grade of hardened concrete (TCXDVN 239:2006)
The grade of concrete is the mean compressive
strength in MPa, tested on 150 x 150 x 150mm cube
samples, which are casted, compacted, cured and
tested according to the standard at the age of 28
days. Grade of concrete is prefixed with letter “M”.
Class of hardended concrete (TCXDVN 356:2005)
The class of concrete is the compressive strength of
concrete which the reliable probability is 0.95. Class
of concrete is prefixed with letter “B”.
B = M(1 – 1.64v)
With:
v – variable strength coefficient
b. Flexural strength
The flexural strength of concrete is measured by
loading 150x150mm concrete beams with a span
length at least three times the depth. The flexural
strength is expressed in MPa and is determined by
standard test methods ASTM C78 (four-point
loading), ASTM C293 (three-point loading) or EN
12390-1.
1/2 Load
Fig I.34 - Four point loading
Load
Accoding to the European standard EN 206, the
concrete is classified based on compressive strength
at 28 days of 150mm diameter by 300mm cylinders
(fck,cyl) or 150mm cubes (fck, cube). Example:
C30/37 is interpreted as follows:
• C stands for concrete
1/2 Load
• 30 is the characteristic strength, determined
using test cylinders (d=150mm, h=300mm),
Fig I. 35 - Three point loading
• 37 is the characteristic strength, determined
using test cubes measuring 150mm.
Flexural strength is about 10 to 20 percent of
compressive strength depending on the type, size
and volume of coarse aggregate used. However, the
best correlation for specific materials is obtained by
laboratory tests for given materials and mix design.
The flexural strength of specimens shall be prepared
and cured in accordance with ASTM C42 or Practices
C31 or C192 or EN 12350-1 and EN 12390-2.
EN 206 defines 16 concrete classes, ranging from C
8/10 to C 100/115.
In American standard system, there are two main
standards for concrete: ASTM C94 – Standard
specification for ready-mixed concrete and ACI 318 Building Code Requirements for Structural Concrete
and commentary. The ASTM/ACI standards do not
classify concrete based on compressive strength.
Pavements are normally designed to achieve a
targeted flexural strength. Therefore, laboratory mix
design based on flexural strength tests may be
required, or a cement content may be selected from
past experience to obtain the required flexural
strength. Sometimes it is used for field control and
acceptance of pavement or slab. Very few use
flexural testing for structural concrete.
Depending on actual use, it may be necessary to
specify the flexural strength at different ages such
as: 3 days, 7 days, 28 days and 56 days.
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
29
c. Assessment of compressive strength test results
Test methods for sampling & testing
General methods for the making of the concrete specimen, their curing and testing are summarized in below
table:
Characteristic
EN
TCVN
ASTM-ACI
Making
EN 12390-2
TCVN 3105:1993
ASTM C31
Curing
EN 12390-2
TCVN 3105:1993
ASTM C31
Compressive strength
EN 12390-3
TCVN 3118:1993
ASTM C39
Table I.7
Test methods for
making, curing
and sampling
concrete
specimen
The below 3 steps are very important to assure the
reliability of the result:
Fig I.36
Satisfactory
failure of cube
specimens
• The sampling of the concrete and the making of
the concrete specimens shall be done properly,
so that the concrete cubes are representative of
the concrete batch. This procedure is sometimes
neglected in some job sites, which may lead to
low strength of the concrete specimen.
• The curing in water tanks – specific attention
needs to be given to the transport of concrete
cubes at early age. A careless handling can
impact their final strength.
• Finally, the compressive strength of the concrete
specimen is determined in the laboratory.
Experience shows that the skill of laboratory
staff can have a significant impact on the final
test result. Special attention is required for the
loading speed of the concrete specimen.
1
2
3
4
5
6
7
8
9
Fig I.37
Unsatisfactory
failure of cube
specimens
Fig I.38
Satisfactory
failure of
cylinder
specimens
EN 12390 – 3: 2002 defines the shape of satisfactory
and unsatisfactory specimens (cube and cylinder)
after the compressive strength test as shown beside:
Fig I.39
Unsatisfactory
failure of
cylinder
specimens
When the specimen shows an unsatisfactory failure,
the obtained result will not represent the true
compressive strength of the concrete.
A
B
C
D
E
F
G
H
I
J
K
30
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Following causes can lead to unsatisfactory failure of the specimen:
Table I.8
Posible causes of
unsatisfactory
failures
Specimens
Cause
• The surface of the cube is not flat and parallel
Cube
• The cube is not positioned centrally in the test machine
• The fresh concrete has segregated during compaction
• The capping method is not suitable or well-done
Cylinder
• The cylinder is not positioned centrally in the test machine
• The fresh concrete has segregated during compaction
• The compression plates are not flat
Compressive machine
• Excentric loading of the test machine
• Inappropriate measuring range (20-80 max load)
Assessment of test results
The test results from cube or cylinder specimen are
primarily used to determine that the delivered
concrete mix meets the strength requirements
specified in the technical specification.
Strength test results may be used for quality control,
acceptance of concrete, or for estimating the
strength in a structure for scheduling construction
Table I.9
Asessment of
test result
operations such as formwork removal or for
evaluating the adequacy of curing and protection
provided to the structure.
The test results on concrete specimen, to meet the
required grade of concrete according to a specific
standard, are evaluated as follows:
TCXDVN 356:2005
TCXDVN 374:2006
ASTM C94:2005
BS 5328:1990
EN 206-1:2000
Cylinder 300x150mm
Cube 150mm
Cube 150mm
For a strength test, at
least two standard test
specimens shall be made
from a composite sample
secured
1 set = 2 specimens
Cylinder
300x150mm
TCVN 4453:1995
Type of
sample
Cube 150mm
1 set = 3 specimens
1 set = 3 specimens
Chapter I: Cement & Concrete
Method of
Sampling
Foundation: 1set/100m3
Foundation under
machinery: 1set/50m3
B. From fresh concrete to hardened concrete
Not less than 1 set for each
115m3
Frame and thin structure:
1set /20m3
31
number of set required:
First 50m3: 3 set
V ≤ 40m3: 1 / 10m3
Then 1 set / 150m3
V ≤ 80m3: 1 / 20m3
Take 2 or more
specimens per set.
V ≤ 200m3: 1 / 50m3
Base and sub-base:
1set/200m3
Mass pour:
• V < 1000m3: 1set/250m3
• V ≥ 1000m3: 1set/
500m3
Testing
fmin : lowest strength
specimen
f’c : the specified
compressive strength.
fmin: lowest strength
specimen
fmed: median strength
specimen
f’cr : the average
compressive strength.
fmax: highest strength
specimen
fmax: highest strength
specimen
fcm = (fmax + fmin) / 2
Measure
compressive strength
of the specimens.
fmin: strength of
the specimen with
lowest strength
fmax: strength of
the specimen with
highest strength
∆1 = fmax - fmed ;
∆2 = fmed - fmin
fcm = average
strength of all
specimens
Compliance
checking
• If (fmax – fmin) / fcm > 15%
then the sample was
invalid.
•If ∆1 and ∆2 are both
less than 15% of fmed,
then
favg = (fmin + fmed + fmax)/3
• Otherwise, f = fcm
• If either ∆1 or ∆2 is
larger than 15% of fmed,
then favg = fmed
Compressive
strength
assessment
favg ≥ fck
fmin ≥ 85% x fck
The average of 3
consecutive strength tests
shall be equal to or greater
than specific strength-f'c
• If f'c ≤ 35 MPa:
individual strength test
≥ f‘c - 3.5(MPa)
favg = average strength of all
valid sample.
For C20 or above
Criteria 1 (Rolling average):
First 2 samples: favg ≥ fck +1
First 3 samples: favg ≥ fck +2
Any consecutive 4 samples:
• If f'c > 35 MPa: individual favg ≥ fck + 3
strength test ≥ 0.9f 'c
Criteria 2 (Individual sample):
When meeting failure case, All valid samples: f ≥ fck - 3
refer to section 19 ASTM
C94-2005.
For C7.5 to C15
Criteria 1 (Rolling average):
First 2 samples: favg ≥ fck
First 3 samples: favg ≥ fck+1
Any consecutive 4 samples:
favg ≥ fck + 2
Criteria 2 (Individual):
All valid samples: f ≥ fck - 2
• If (fmax – fmin) /
fcm > 15% then
the sample was
invalid.
• Otherwise, f = fcm
favg = average
strength of all valid
samples
Criteria 1 (Rolling
average):
favg ≥ fck + 4
Criteria 2 (Individual
sample):
All valid samples:
f ≥ fck - 4
32
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
d. Comparison of strength between different
standards:
Every standard has its own system to evaluate the
compliance of the test result to the requirement of
the standard.
It is very difficult to compare the standards. In
principle, it is not recommended to translate one
Table I.10
Comparison of
strength between
different standards
in terms of cube
sample
TCVN
BS
EN 206
M300
C30
C25/30
M350
C35
standard into a different standard. To assure the
compliance to the design, the concrete should be
tested according the standard set (TCVN, ASTM, EN,
BS), used for the design.
The following graph provides an indication how
TCVN, EN and BS are related in terms of cube
strength (not to scale).
M400
C40
C30/37
M450
C45
C35/45
M500
C50
C40/50
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
4. Special characteristics
a. Concrete density
The density of both fresh and hardened concrete is
of interest to the engineers for different reasons
including structural design and impact on
compressive strength.
By choosing suitable aggregates and mix design, the
density of concrete can be increased significantly
(heavy concrete) or reduced (light-weight concrete).
For fresh concrete:
The density plays an important role in controlling
concrete yield (compared to the mix design) at
readymix batching plant. Typical readymix concrete
density varies from 2200 – 2500kg/m3 (TCXDVN
374:2006), depending on the aggregate type and
mix design.
Based on the density of compacted fresh concrete,
plant operators are able to check if the mix design is
over- or under yielding: this means that the mix
design gives more or less than 1m3 concrete after
compaction. Fresh concrete density test method
complies with ASTM C138; EN 12350 – 6; TCVN
3108:1993.
For hardened concrete:
Before testing the compressive strength, the density
of concrete samples (cube, cylinder) should be
checked and compared with the mix design to
confirm the sampling, compaction, presence of
entrained air.
b. Air content
Air content of concrete is also an important
characteristic to indirectly assess the quality of
concrete.
Fresh concrete always contains a significant amount
of air bubbles. One of the main reasons to compact
the concrete is to remove them. If the concrete is
not well compacted, some air will remain in the
concrete, reducing the strength significantly.
Normally, a typical compacted concrete will have air
percentage varies from 0.5 – 2.5%. Concrete with
high slump usually has lower air content than low
slump concrete. Besides, the plasticizer/super
plasticizer admixture can increase the air content in
concrete, which may lead to lower strength.
A rule of thumb
1% excessive air
reduces the concrete strength by 4-5%.
In some cases, the air content in the concrete is
increased with an air-entraining admixture up to
4-6%, to improve the resistance of the concrete
against deterioration caused by freeze-thaw. For the
tropical climate in southern Vietnam, air entrained
concrete is normally not used for this purpose.
Air content test method is complied with ASTM
C231, TCVN 3111:1993
Pump
Main air valve
Petcock B
Pressure gage
Air bleeder valve
Petcock A
Example: A mix design shows that the density of
concrete is 2450 kg/m3; however, the hardened
concrete sample only measures 2370 kg/m3 .The
strength of this sample will be much lower than the
design strength. Hardened concrete density is
determined either by simple dimensional checks,
followed by weighing and calculation or by weight in
air/water buoyancy methods (comply with EN
12390-7).
33
Air chamber
Clamping device
Extension
tubing for
calibration
checks
Bowl
Fig I.40
illustration of the
pressure method
for air content
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
c. Bleeding
Bleeding is a particular form of segregation, in
which the water from the concrete appears on the
surface of the concrete. Bleeding is predominantly
seen in very wet mixes with high workability.
Excessive bleeding can have a negative impact on
the quality of the concrete:
• Dusty surface, linked to cement particles that are
carried to the top of the concrete layer
• Discolorations of the concrete surface
• Reduction of the bond between large aggregates
/ steel bars and mortar.
Not all bleeding is harmful for the concrete. A
limited amount of bleeding protects the concrete
surface against plastic shrinkage, in hot and windy
weather.
d. Setting time of concrete
After cement and water are mixed, they react
chemically, the concrete sets and changes to the
hardened state. Concrete setting time is defined as
the time taken for the concrete to change from the
fresh to the hardened state. Setting time of concrete
is defined by 2 two parameters: (ASTM C403 – Test
method for setting time of concrete):
• Initial set: the period time from mixing until the
penetration resistance of equals 500psi (3.5
MPa).
• Final set: the period time from mixing until the
penetration resistance equals 4000psi (27.6 MPa).
Fig I.43
Apparatus to
determine the
setting time of
concrete
For concrete floors, the bleeding of concrete is a very
important characteristic:
• A limited bleeding reduces the risk of early
cracking
• Too much bleeding water delays the finishing of
the concrete floor and can lead to delamination
problems
The bleeding of concrete can be reduced by:
• Lowering the water/cement ratio
• Intense and uniform mixing
• Adapting the sand fraction of the concrete
• Increasing the cement content in the mix
5000
Fig I.41 - Bleeding of fresh concrete (good and bad)
Bleeding of concrete test method is specified in
ASTM C232 (or TCVN 3109:1993). Bleeding of
concrete is determined by the percentage of water
coming out the concrete.
Fig I.42
Concrete
bleeding meter
Penetration Resistance, psi
34
4000
Final Setting
3000
2000
1000
0
Initial Setting
Outlier
180 210 240 270 300 330 360 390 420
Elapsed Time, min
Fig I.44 - Diagram to determine the setting time of concrete
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
The setting time of concrete should not be confused
with the slump retention or early strength of the
concrete. These three characteristics are very
different properties of concrete, even if they
sometimes move in similar directions.
The setting time is heavily influenced by the type of
admixture, as some plasticizers act as a retarder for
concrete.
Thus, for specific application with different setting
time requirement, the admixture (compatible with
cement, dosage) and concrete workability (slump,
flowability, mixing water) should be controlled very
carefully.
Warning
The overdosage of admixture may delay the
setting time of concrete up to 1 day or even
longer.
35
e. Permeability
To determine the durability of concrete, the concrete
permeability is more important than the
compressive strength.
There are two types of concrete permeability,
frequently used in Vietnam:
• Water permeability – for water-tightness of concrete
• Chloride permeability – for concrete in aggressive
environment (seawater, brackish water)
Permeability to Water:
For specific structures which directly get in contact
with water such as : basement for high rise building,
dams, dikes…, the water tightness of concrete is
required, in addition to strength.
The concrete to permeability to water is classified
into 6 levels: B2, B4, B6, B8, B10 and B12 and the
testing method is specified in TCVN 3116:1993.
The level for permeability to water is the maximum
water pressure for which water has not gone
through 4 in 6 test samples.
Fig I.45
The test method
to determine the
water
permeability of
concrete
3
6
1
5
2
4
4
4
4
4
4
4
4
In general, concrete with a higher strength will have
a lower water permeability. So from the grade of
concrete, the level of permeability to water can be
estimated.
Fig I.46 - Water permeability test machine
Concrete Grade
Estimated Level of Water
Permeability
30
B6
35
B8
40
B10
45 - 50
B12
Table I.11
Estimation of
water permeability
base on concrete
grade
36
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Permeability to chlorides
The permeability of concrete to chloride ions is an
important indicator to measure the durability of
concrete in aggressive environment. At a low
chloride permeability, the steel reinforcement will
be protected against the chloride-linked pitting
corrosion and the durability of concrete will be
increased.
The method to measure the rapid chloride
permeability of concrete is specified in ASTM C1202
or TCXDVN 360:2005.
The test method consists of monitoring the amount
of electrical current which passes through 51 mm
thick slices of 102 mm nominal diameter cores or
cylinders during a 6 hours period. The total charge
passed, in coulombs, has been found to be related to
the resistance of the specimen to chloride ion
penetration.
Fig I.47
The rapid
chloride
permeability test
equipment
As the ASTM C1202 specification, the rapid chloride
penetration ability of concrete is classified into 5
levels:
Charge passed
(coulombs)
Chloride Ion
penetrability
> 4000
High
2000 – 4000
Moderate
1000 – 2000
Low
100 – 1000
Very low
< 100
Negligible
Table I.12: Classification of the rapid chloride penetration
ability of concrete
The chloride permeability of concrete can be
improved by:
• Using blended cements, with a high percentage
of blended material
• Reduction of water/cement ratio, to make a
more compact concrete
• Efficient compaction and curing
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Fig I.48
Homogeneity of
the mix as a
function of
mixing duration
5. Production and Transport
Dosage of the components
The production of concrete is closely linked to the
technology and equipment used. The task of dosage
is to dispense the components of the concrete mix –
aggregate, cement, additions, mixing water,
admixtures – in controlled amounts, to produce the
specified mix proportions with great accuracy. Two
systems are used, dosage by volume and dosage by
mass. Dosage by mass gives more accurate results.
Every batching plant must establish sequencing for
adding the material through systematic pretests.
Sequencing is critical for:
•
•
•
•
•
The dispersion
The mixing effect
The optimal effect of admixtures
Plant efficiency
Mechanical wear
Mixing the components
The mixer must blend the separate components into
a homogeneous mix. The mixer must also satisfy the
following requirements and tasks:
• High mixing intensity
• Short mixing duration
• Dispersion of the cement and the additions
• Optimal coating of the aggregates with fines
mortar (fines paste)
• Fast discharging
• Low wear
At ready-mix plants the paddle mixer is the most
common type, used discontinuously for mixing
single batches. Each type of mixer requires a
minimum batch size, below which the quality of the
fresh concrete is reduced.
Mixing duration
The duration of mixing depends on the type of
mixer (drum or paddle mixer). Mixing duration
should be determined by testing.
Definition:
Mixing duration = “Wet-mixing duration”
starts when all components are in the mixer.
If a small additional dosage of water is necessary
during mixing to achieve the specified concrete
consistence, the mixing duration must be
appropriately extended. Plotting homogeneity of the
mix as a function of mixing duration gives a curve that
increases rapidly at first and asymptotically
approaches the ideal line as mixing advances (Fig I.48)
37
Readymix concrete should be brought to the
construction site immediately after production at
the concrete plant and placed without delay in order
to preserve quality. There is a certain danger of
segregation during transport, so truck mixers are
used when the concrete is of highly plastic
consistence, for long hauls, or when traffic
conditions are poor.
During the trip, concrete must be protected from
rain, exposure to sun, wind blast, and the like.
Depending on the prevailing weather conditions on
the day of concreting, suitable measures should be
taken (covering the concrete, reducing the
temperature of fresh concrete, etc.).
For delivery by truck mixer, the concrete should be
mixed an additional one to two minutes after arrival
on site and immediately before pouring. Adding
more water should be avoided, because such
additions are uncontrolled and the water cannot be
mixed in thoroughly. If the delay becomes too long,
the concrete may be used only for less critical
applications (fill, lean concrete, etc.).
38
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
6. Placing and Compaction
Conveying and depositing
In Vietnam there are three main means of conveying used: chute, bucket and pump. Depend on local
circumstances, kind of structure, workability of fresh concrete, economy and progress of project , the method
of conveying will be chosen. Show in table I.13
Table I.13
Method of
conveying
Structure
Workability of concrete
(Slump)
Picture
Some small structures like
foundation, ground slab, floor...
8 -10 cm
Fig I.49
Bore piling
> 18 cm
Fig I.50
Method of conveying
Chute
Fig I. 49
Fig I.50
Bucket
Column, beam and floor… in
highrise building
8 - 14 cm
Fig I.51
Pump
Floor slab, foundation...
12 - 18 cm
Fig I.52
Fig I.51
Fig I.52
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
39
Delivery volume and placing capacity must be
coordinated. Concrete should be deposited at a
constant rate, in horizontal layers of uniform
thickness. To prevent segregation, the concrete
should not be dropped more than 50 to 70 cm. Drop
heights greater than 1,5 m require the use of a drop
chute or feed hose.
Fig I.53 - Segregate concrete because of too high drop
Compaction
Good compaction is the prerequisite for durable
concrete. The advantages of well-compacted
concrete are:
• Higher density
• Improved durability
• Good compressive strength
• Better bond between reinforcement and concrete
Fig I.55
The structure
with good
compaction
Method of compaction
Selecting the best method of compaction will
depend on the workability of the concrete and the
reinforcement density/rebar spacing of the element.
The most common effective method of compaction
is vibrating. Vibrating is most often done with
internal vibrators (poker-type vibrators) or external
vibrators (form vibrators or surface finishers with
surface vibrators).
Vibration almost completely overcomes the internal
friction between the aggregates. The separate
particles move closer together, and entrapped air
escapes to the surface in the form of air bubbles
(the content of entrapped air after compaction is
about 1.5 % by volume). The voids become filled
with fines paste and the fresh concrete is
consolidated under its own weight.
Effective range of electrical high-frequency vibrator
heads (Table I.14).
Diameter of
vibrator head
(mm)
Effective range
diameter
(mm)
Spacing
between
inserrtion
points (cm)
< 40
30
25
40 bis 60
50
40
> 60
80
70
Experience shows that a frequency of about 12,000
CPM is best for normal concrete. The vibration
frequency should be increased (up to 18,000 CPM)
for fine-aggregate concretes.
Fig I.54 - Honeycomb on concrete
Table I.14
Reference values
for the effective
range diameter
and spacing of
insertion points
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Rules for good compaction
• The vibrator head should be quickly immersed in
the concrete, held briefly at the lowest point and
slowly extracted. The concrete surface must
close behind. If the surface no longer closes,
either the consistence is too stiff, the concrete
has already begun to set, or the duration of
vibration has been insufficient. Spacing between
the insertion points should be uniform.
• The vibrator head should not be used to
distribute the concrete.
• Vibration should be stopped when a thin film of
fine mortar forms on the surface and larger air
bubbles surface only occasionally.
• The insertion points should be spaced close
enough that the effective range diameters of the
vibrator overlap.
• If concrete is deposited in several layers “fresh on
fresh“, the vibrator head should extend through
the layer to be compacted and about 10 to 15 cm
into the underlying layer of fresh concrete. This
ensures a good bond between the two layers
(Fig I.56).
Rule of thumb
Spacing between insertion points =
8 to 10 times the diameter of the vibrator head
Fig I.57
Spacing between
insertion points,
depositing “fresh
on fresh“
300-400 mm
Fig I.56 - Concrete compaction by vibrating method
Right
1-2xD
Wrong
insertion point
II
I
III
150 mm
40
8-10 D
8-10 D
I
II
III
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
7. Concreting in hot weather
Vietnam is a country located in hot climates, it
effects directly to the placing and quality of
concrete.
• With hot weather, the workability of fresh
concrete drops faster so the placing of concrete
becomes harder. In spite of warnings not to add
extra water to the mix on the construction site,
this pratice is still often used to improve
consistence. Water addition at the jobsite
increases the w/c ratio, lowers the strength and
durability of the concrete. It can lead to strength
failures at the project.
Rule of thumb
10 liters of extra mixing water per m3 concrete
causes a 10-percent drop in 28-day strength.
• To keep the drop in concrete strength due to hot
weather within narrow limits, the temperature
of fresh concrete should be controlled carefully.
Some projects in Vietnam require the temperature of fresh concrete from 30 to 32oC.
In addition to the decrease in strength and
durability, higher concrete temperatures produce
other negative effects:
41
Methods of controlling the temperature of concrete
• The temperature t of fresh concrete can be
roughly estimated using the formula:
tconcrete = 0,7 · taggregate + 0,2 · t water + 0,1 · t cement
• Base on this formula, controlling the
temperature of aggregate and water has the
highest impact on the temperature of concrete.
The effect of cement temperature to fresh
concrete temperature is relatively small.
Methods of lowering the temperature of fresh
concrete:
• Cooling the aggregate by shading or spraying
with water (*)
• Cooling the mixing water with ice or water
chiller (*)
• Cooling the concrete mix with liquid nitrogen
(*) The amount of mixing water is to be reduced
accordingly.
Fig I.58
Aggregate
shading
• Faster hydration of the cement causes faster
setting of the concrete – or even premature
setting – greatly impairing workability, to the
point of making the concrete unworkable.
• The concrete, specifically the surface layer, dries
out faster – especially under strong winds,
intensive sun, and low relative humidity.
Water loss must be prevented by curing. If water is
lost, plastic shrinkage will occur cracks (see Chapter
III.B). Additionally, cement hydration will remain
incomplete. This further reduces final strength in
the prematurely dehydrated outer layer, which
further impairs durability.
Fig I.59
Cooling concrete
by liquid
nitrogen
42
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Concreting in hot weather requires good planning
and preparation
• The delivery of fresh concrete must be well
coordinated with the concreting work so that it
can be poured without delay.
• Sufficient equipment and personnel must be
planned so that the concrete can be placed and
compacted without delay.
• The contractor’s personnel should be
familiarized with the special aspects and
requirements of concreting at high
temperatures.
• The substrate and forms must not extract water
from the fresh concrete. Forms should be
moistened before pouring the concrete (Fig I.60).
But excessive soaking of forms and substrate
should be avoided; no puddles should form.
• If sudden stops cannot be avoided, any concrete
in the truck and in the delivery equipment must
be protected from the effects of direct wind and
sun. Truck mixers can be hosed down on the
outside with water.
• If the conditions for successful concreting at
high temperatures cannot be achieved for any
reason, concrete work must be rescheduled to a
cooler hour of the day, for example at night.
• Adding extra water on the construction site is to
be strictly prohibited. Compliance with this rule
must be checked.
• Retarders can be used to largely eliminate the
disadvantages of fast cement hydration, but they
do little against premature setting of concrete.
Retarders also require extended curing times, as
they increase the risk of plastic shrinkage cracks.
Fig I.60
Wetting the forms
Placing and compaction
• The shortest waiting time and fastest possible
placement of fresh concrete are the cardinal
rules.
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
43
8. Pumped concrete
Application Range
The use of pumps is recognized as a modern and
efficient method of transport and placing concrete.
Pumped concrete can be used for practically any
construction task, and is particularly useful when
high performance in placing is required or when the
pouring location is poorly accessible. In general,
there are two types of concrete pumps: stationary
and mobile.
• Admixtures
The rules that apply to using admixtures in concrete
also apply to pumped concrete. It should be kept in
mind when using air entrainers, that fresh concrete
with an air content greater than 4% can reduce the
delivery capacity of concrete pumps.
• Consistence
Pumped concrete must have a plastic to soft
workability.
Fig I.61 - Pump concrete by mobile pump
Requirements for pumped concrete
Pumped concrete is “pushed“ like a “plug“ through a
pipeline. The key is to keep the concrete from
segregating under the forces acting upon it.
• Cement
Practically any standard cement is suitable for use in
pumped concrete. A fresh concrete that can be
efficiently moved through a pipeline should have a
cement content of at least 320 kg/m3.
• Aggregate mix
Experience shows that increasing the fines
(≤ 0.125mm, including cement) to about 400 kg/m3
considerably
improves
pumpability
without
compromising durability of the hardened concrete.
Thanks to improvements in pump design, the grain
shape of coarse aggregate has only a minor
influence on pumpability.
The required workability can depend greatly on the
characteristics of the sand, and must be adjusted
when necessary as indicated by pretests.
Fig I.62
Casting a large
concrete floor
slab. Mobile
pump fed by a
truck mixer
44
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Tips for pumping concrete
• A smooth process must be ensured by good
planning between the concrete pump operator,
the building contractor, and the concrete
supplier.
• The setup and operation of the pumps is the
responsibility of the pump operator.
• The rate of delivery and the delivery rating of the
concrete pumps should be suited to the working
capacity of the crew placing the concrete.
• The concrete should be delivered to the concrete
pump with truck mixers to prevent any
segregation. Hopper trucks or silo trucks may be
used for short hauls.
• The construction contractor is responsible for the
proper placement and curing of the concrete.
• About 0.5–2.0m3 of a cement-rich mortar serves
as a lubricating mix to prime the pumping
system. This material may not be used as
structural concrete.
Safety aspects of using concrete pumps
Delivering and placing pumped concrete can
be dangerous.
The following must be ensured:
• Formwork for walls and columns must be
strong enough to handle the increased
pressure of pumped concrete.
• No overhead power lines should be in the
working area.
• The load-bearing capacity of the pump
platform must be adequate. Directives of
the pump personnel must be strictly
followed.
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
45
Fig I.63
9. Curing
Purpose and objectives
The purpose of curing is to protect concrete from
water loss and harmful influences during the early
hardening period. Compressive strength alone does
not guarantee durability; the concrete must also be
dense. Especially in the surface layer, hardened
cement paste with high density and low-as-possible
permeability is very important.
This gives better resistance to carbonation and other
types of attack. Curing includes all the measures
taken to protect freshly placed, young concrete
while it develops adequate strength. The chief
objectives of curing is to protect the concrete from:
Fig I.64
• Evaporation due to wind, sun, dry cold
• Extreme temperatures (cold or heat) and rapid
temperature change
• Heavy rain
• Early influences of foreign substances (oil etc.)
Premature drying
Protection against premature moisture loss is
especially important. Protective measures must be
taken immediately after concrete is placed.
The consequences of premature water loss in the
surface layers are:
• Heavy plastic-shrinkage cracking (see Chapter III)
• Low strength
• Tendency to surface dusting
• Lower density and durability
• Faster corrosion of steel reinforcement
• Lower abrasion resistance
Preventive measures
• Leaving forms in place
• Covering with a membrane (Fig I.63)
• Wrapping with insulating material (Fig I.64)
• Covering with water-retaining
(burlap, geotextiles)
fabrics
• Application of a liquid curing compound
(Fig I.65)
• Continuous spraying with water
• Keep under water
• A combination of these measures
Fig I.65
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Rate of drying
The rate of drying depends on:
Typical effects of these factors are shown in Fig I.66
and Fig I.67 and Fig I.68 shows the correlations
among the factors mentioned. The chart can be used
to estimate the rate of drying.
• air temperature
• concrete temperature
• relative humidity
• wind speed
kept constantly
moist
40
Plastic shrinkage [mm/m]
Compressive strength [N/mm2]
46
kept moist
for 7 days
30
20
not
kept moist
3
unprotected concrete,
wind speed 10 km/h
2
concrete protected
with a curing compound
1
10
0
unprotected concrete,
wind speed 20 km/h
4
1
3
7
0
28
90
Testing age [days]
Fig I.66 - Influence of water retention on strength
development in the surface layer of concrete
Fig I.68 - Chart for calculating the rate
of drying of exposed concrete
surfaces. Example illustrated: air
temperature: 28°C relative humidity:
50% concrete temperature: 28°C wind
speed: 5m/sec. result: rate of drying =
0.8 kg/m2 hr.
0
6
12
18
24
Time [hours]
Fig I.67 - shows the correlations among the factors
mentioned. The chart can be used to estimate the rate of
drying.
relative humidity
concrete temperature
%
'C
100
80
40
60
35
30
40
20
0
10
20
ambient temperature
15
10
20
25
30
(0C)
4
wind speed
10
m/sec
8
3
rate of drying
(kg/m2 hr.)
6
2
1
4
2
0
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
10. Influence of Formwork
Formwork plays an important role in a successful
construction project. It gives the concrete surface its
form, texture, and color. It gives the concrete
structure, correct dimensions, and the proper form.
Formwork often does not receive the attention it
deserves.
Selection of forms
The construction contractor usually selects forms
based on the following criteria:
• Building structure / construction task
• Specified surface quality of the concrete
47
Fig I.69
Results of a leaky
form
Fig I.70
Peeled-off
concrete skin
• Number of potential reuses
• Labor required for erection
• Thermal insulation characteristics
• Price
Common facing materials for forms
• Raw, rough-cut wooden boards treated wooden
sheets
• Plastic-laminated forms (polyester, polystyrene,
linoleum, elastomers, etc.)
Fig I.71
Concrete skin
adhered to
wooden forms
• Steel, aluminium
Requirements for forms
• Dimensional accuracy
• Watertightness (Fig I.69)
• Stiffness, no deformation
• Cleanness
• Low adhesion to hardened concrete
(Fig I.70 and Fig I.71)
• Attractive surface texture (Fig I.72)
Form types
Absorptive forms usually produce a smooth, closed
concrete surface, because they absorb surplus water
and air bubbles. The face of wooden forms should
include only boards which have been used for an
equal number of times, because the absorption
capacity of the wood decreases with each use, which
has an effect on the color of the concrete surface.
Raw wooden boards should be coated with cement
paste before initial use to remove the wood sugar
that disturbs hydration of cement. This coating also
evens out any variations in absorbency of the boards
(Fig I.73).
Fig I.72
Example of a
successful
textured
concrete surface
Fig I.73
Non-uniform
absorbency of
wood used in
forms affects the
concrete surface
48
Chapter I: Cement & Concrete
B. From fresh concrete to hardened concrete
Non-absorptive, water-repellant forms promote the
partial accumulation of mortar paste. This leads to
irregularities in the color of the concrete surface
(clouding). Strong surface segregation can lead to
reduced durability (see Chapter III.A “Segregation of
Concrete“). Thus for exposed surfaces it is
advantageous to use absorptive forms or waterconducting form liners of polypropylene fibers, etc
Form-release agents
Form-release agents make it easier to loosen the
form faces from the concrete surface. At the same
time, they protect and preserve the form material.
They are to be applied thinly and uniformly,
normally before the reinforcement is put in place.
Surplus chemical should be wiped away with a cloth
(Fig I.74). Staining, and irregular gray color of the
concrete surface, can frequently be traced to
improper application of a form-release agent.
Fig I.74
Effect of form-release agents on the concrete surface:
- Left: surplus form-release agent removed with a cloth
- Right: excessive form-release agent used
Applications with
specific requirements
Chapter II:
A. Infrastructure
1. Introduction
2. Cement for infrastructure
To support the growth of the economy in Vietnam,
both public and private funds invest important
amounts of capital into infrastructure projects, like
roads, bridges, dams, ports, tunnels, power plants…
In south Vietnam, the cement, used for
infrastructure, is Blended Portland Cement (PCB40),
compliant to TCVN6260, ASTM C1157 with low
alkali content (Na2O-eq < 0.60%) to prevent alkali
aggregate reaction.
As this infrastructure is the backbone of the
economy, the design life of these projects is
significantly longer than normal buildings (houses,
schools). With proper maintenance, a bridge should
be used for at least 50 years up to 100 years and
even longer!
To meet this long service life, the concrete for
infrastructure projects requires special attention for
durability, with careful selection of the concrete
components.
The alkali-aggregate reaction – or “concrete cancer”
in laymen’s terms – is a reaction between
aggregates, the alkali in the concrete and water to
form an expansive gel that creates cracks in the
concrete. This reaction is a very slow process over
years, but can become visible in 5 to 10 years after
construction.
In case of aggressive environment (presence of
chlorides,
sulphates,
seawater,…),
additional
precautions have to be taken (see chapter II.B).
Holcim recommendation
Cement PCB 40 according to TCVN 6260:2009
or ASTM C1157 - GU, with low alkali content
(Na2O-eq M 0.60%)
49
50
B. Aggressive environments
(sulfate, seawater ...)
1. Introduction
To assure the long life of the construction in
aggressive environments, special care has to be
taken for the concrete: cement choice, mix design,
placing and compacting, and last but not least,
curing.
A key element is the choice of cement, as concrete
can be exposed to different aggressions:
• Sulfates in the environment attack the cement
matrix (C3A cement mineral) and create cracks in
concrete
• Chlorides penetrate into the concrete pores and
can lead to the dangerous pitting corrosion of
steel reinforcement of the structure
• Other aggressive elements (low pH, acids,..) can
attack the cement matrix, by dissolving its
constituents
For aggressive environments, 2 main types of
cement are generally specified:
• Sulfate resistant portland cement (only for
sulfate attack)
• Sulfate resistant blended portland cement
2. Sulfate resistant Portland
cement
Main characteristic of sulfate resistant Portland
cement is a lower C3A content, a specific cement
mineral, as this component will react with sulfates
in the environment to ettringite, that expands in the
concrete pores to create tensions and cracks in the
concrete.
The C3A-content of cement can only be measured on
Ordinary Portland Cement (OPC). For blended
cement, the addition materials will change the
chemistry of cement and the calculated C3A –
content (based on the Bogue formula C3A = 2,65
Al2O3 – 1,692 Fe2O3) is not valid any more.
This type of cement complies to following standards:
• TCVN 6067
• ASTM C150 – Type II (Medium Sulfate MS) or
type V (High Sulfate HS)
• BS 4027
The maximum value of C3A depends on the standard
used:
Normal Cement
Attention
Durability of concrete is a lot more complex
than the use of sulfate resistance cement.
To improve concrete durability, the ‘Four C’ can
be used as a rule of thumb:
• Cement choice,
adapted to the aggressive environment
• Water/cement ratio,
to reduce pore space
• Concrete cover,
to protect steel reinforcement
• Curing of concrete,
for high quality concrete cover
TCVN
ASTM
Type II (MS)
ASTM
Type V (HS)
BS 4027
3.5
5
7
8
9
% C 3A
Note: According TCVN 6067, OPC type II (comply with ASTM
C150) does not classify as sulfate resistance cement
Fig II.1 - The maximum value of C3A depends on the
standard used
By limiting the C3A mineral, sulfate resistant
Portland cement offers protection to sulfate attack
from the environment only. It does not offer
additional protection to chloride penetration or
other aggressive elements (low pH, acids…),
compared to a concrete with general use cement
PCB40.
Chapter II: Applications with specific requirements
B. Aggressive environments (sulfate, seawater ...)
3. Sulfate resistant blended
cements
With specific additions in cement, the concrete has a
more dense structure, with a lower permeability to
water
and
chloride,
which
protects
the
reinforcement steel to corrosion and increases the
service life of the construction.
This type of cement complies to following standards:
• TCVN 7711:2007
The lower permeability of the concrete can be
measured by the rapid chloride permeability test
(ASTM C1202 or TCXDVN 306:2005), on the specific
concrete mix, to be used on the project.
The rapid chloride permeability test measures how
fast the chloride-ions can penetrate into the
concrete, to attack the steel reinforcement.
The results are classified into 4 categories:
VERY LOW
• ASTM C1157 – type HS
• EN : CEM III/ CEM IV - type SR
The ASTM standard verifies the sulfate resistance
with a performance test on mortar samples. During
6 months, a mortar bar is exposed to a sulfate
environment (ASTM C1012). The swelling is
measured and determine the percentage expansion
at 6 and 12 months of the mortar bar which is
immerged in the sulfate solution.
51
0
1000
LOW
MODERATE
2000
3000
HIGH
4000
Chloride Permeability
Fig II.3
The rapid
chloride
permeability test
equipment
0.3
0.25
0.2
0.15
0.1
0.05
0
7d
14d
21d
28d
56d
91d
105d
112d
180d
Limit of Moderate Sulfate Resistance
Normal Cement
Limit of High Sulfate Resistance
Holcim Extra Durable (HS) cement
Indicative reference values for 35-40MPa concrete:
• Normal cement PCB40 : > 5000 Coulomb (high)
• Sulphate resistant blended cement : 1000 – 1500
Coulomb (low)
The use of waterproofing admixture does not reduce
significantly the chloride permeability of concrete,
as chloride ions move within the water-saturated
pores.
Holcim recommendation
Fig II.2: Test method to determine the expansion of the
mortar bar in sulfate solution
According the EN 197-1:2011 standard, specific
types of blended cement are considered to be
sulfate resistance, based on long-term experience
with these cements.
Coulomb
For concrete in aggressive environments
(seawater, brackish water, waste water,..),
Holcim recommends to use a sulfate resistant
blended cement, type TCVN 7711:2007
or ASTM C1157- HS, as it offers several
advantages:
• Better protection of steel
reinforcement against corrosion
• High sulfate resistance of concrete
• Higher resistance against other
aggressive elements (acids, low pH etc)
C. Massive structure
52
1. Introduction
In massive concrete elements, the heat of hydration
of cement will increase the concrete temperature at
the center of the mass element significantly. During
the hardening phase, the temperature can rise up to
85 – 100oC for thick elements, with general use
concrete. When the hardened concrete in the center
then cools down, the thermal shortening of the
concrete creates stresses in the element, which can
lead to thermal cracking.
Fig II.4
Heat of
hydration
development
inside mass
concrete can lead
to thermal
cracking
To reduce these risks, specific measures have to be
taken, for example:
• Limit the maximum temperature difference
ΔT < 200C or limit the maximum temperature
gradient between two points ΔT/m < 500C
(TCVN 305:2004)
• Limit the maximum temperature in the core Tmax
< 700C
• Insulation formwork is often used to warm the
concrete surface and reduce temperature
difference. It should stay in place for several days
until ΔT < 200C. Removing it too soon can cause
the surface to cool quickly and crack.
These measures should be considered when the
concrete thickness > 1.5m.
For specific concrete structures, these requirements
can be imposed from thickness > 1m, when the
consequence of cracks can lead to significant
damages (example: tunnel elements, gas storage
tanks…)
2. Cement for massive
structures
The high concrete temperature in the center has a
significant impact on the structure:
• Above 700C, there is a risk for Delayed Ettringite
Formation (DEF) in the concrete, which can lead
to long-term cracking in the concrete.
• High concrete temperature reduces the concrete
strength at 28 days, especially above 700C.
Temperature rise, 0C
80
Tmax < 700C
70
Inside
60
To manage the heat development in massive
concrete elements, specific cements are available
with a low heat of hydration:
• TCVN 7712 : 2007
• ASTM C1157 – type Low Heat (LH)
• BS-EN – type Low Heat
The EN standard uses a different test method from
the ASTM standard – the EN method is not available
in Vietnam.
ΔT > 200C (surface cracking)
Surface
40
Form
removal
20
ΔT > 200C
no cracking
Unprotected surface
cools fast
0
0
1
2
3
Days
4
5
6
7
8
Fig II.5
Timing of
formwork removal
impacts the risk of
thermal cracks
Chapter II: Applications with specific requirements
C. Massive structure
3. Concrete for massive
structures
To meet the temperature limits on the concrete
structure, additional measures on concrete are
required, as many parameters play a role in the final
results:
• Heat of hydration of the cement
• Design strength of concrete, which decides the
mix design (include cement content)
• Thickness of the concrete element
The mix design of the concrete can be optimized as
follows:
• Optimize cement content, by using more
advanced admixtures
• Use larger size aggregates
• Compressive strength requirement at 56 days
instead of 28 days.
The fresh concrete temperature should be as low as
technically possible. In South Vietnam, maximum
temperature of 30 – 320C can be obtained using
standard practices:
• Cover aggregates to reduce their temperature
• Sprinkle coarse aggregates regularly
• Use of chilled water and ice.
Before the start of the concrete pour, a mock-up with
the casting thickness is strongly recommended to
check the compliance to the specifications. This
mock-up is insulated on the sides (5cm minimum) to
simulate the real dimensions of the pour.
polystyrene
1T
5M
4M
3T
2T
2M
1M
3M
5B
4B
1B
2B
3B
Fig II.6 - Trial mock-up
After execution of the concrete pour, suitable curing
with insulation material (5cm minimum) is very
important to reduce the temperature difference
between surface and core. Water curing should not
be used as it cools down the surface. For the same
reason, the slab has to be protected from heavy rain,
as this will cool down the surface suddenly and
increases the risk of thermal cracks.
During the hardening phase, the temperature of the
concrete is measured every two hour for at least 3
days. For this purpose, thermo-couples are placed on
different locations in the concrete element.
Holcim recommendation
To reduce the risk of cracks in
massive elements, a combination of
several measures is required:
• Low heat cement compliant with TCVN
7712:2007 or ASTM C1157 type LH
to reduce risk of thermal cracks.
5T
4T
Fig II.7 - Mock-up at jobsite
• Fresh concrete temperature
should be < 300C
• Protect the concrete element
with insulation (5cm minimum)
against heat loss
Before execution of the pour, a suitable
mock-up of the concrete pour verifies the
compliance to the temperature requirements.
• Maximum concrete temperature < 700C
• Maximum temperature difference < 200C
53
D. High strength concrete
54
1. Introduction
High strength concrete offers significantly higher
strength and stiffness (higher E modulus) than the
conventional concrete. A concrete is considered to
be high strength concrete from 60MPa to 100MPa.
Above 100MPa, the concrete is classified as ultra
high strength concrete.
High strength concrete is mainly used for elements
in compression, like columns and core walls in high
rise buildings. Other applications are prestressed
beams for bridges.
Because of its high strength, the column size can be
reduced up to 45%, compared to standard concrete.
This gives a number of benefits:
During construction:
• Savings in steel & reduced cost /m column
• Reduced weight and savings on foundation
For the building:
• Thinner columns, more architecturally pleasing
• More available floor space
Reduction of column section
6000
100%
Section area (m2)
4000
3000
2000
1000
0
B40
B60
B80
Concrete grade
B100
80%
70%
60%
50%
40%
30%
20%
10%
0%
Section area (%)
90%
5000
Source: BCA Pillars on Safe Built Environment (Singapore)
Fig II.8 - The correlation of concrete grade and column size
reduction
Fig II.9 - Slender columns in high rise buildings
Chapter II: Applications with specific requirements
D. High strength concrete
2. Production and use of high
strength concrete
Some recommendations to maintain the quality:
In general, high strength concrete is produced with
specially selected high quality components:
• Automatic dosing system for silica fume, to
control and track the quantity
• High quality cement at dosage 450-500kg/m3
• Low water/cement-ratio < 0,35
• Optimized aggregate grading, with selected
aggregates
• Use of very fine filler (silica fume, ultrafine slag)
to optimize fine fraction
• Use of last
admixture
generation
super
plasticizer
High strength concrete has a very high fines content
with a low water/cement ratio, and has the
tendency to be sticky. To be able to pump and place
this concrete, a high workability with slump >
180mm is normally used.
For thick elements (>1m), special care is required to
reduce the heat development in the concrete during
hardening. In that case, the mix design needs to be
adapted in a similar way as for massive concrete
structures.
For the concrete supplier, the main challenge of high
strength concrete is to maintain the quality over
time – every single concrete truck - and avoid
strength failures on the project.
• Control of moisture in the aggregates, especially
sand (moisture probe)
• Comprehensive quality management system, to
assure the regularity of the supplied concrete
and to reduce the risk of strength failures.
• The internal laboratory has been assessed and
found to conform with the requirements of ISO/
IEC 17025. The reliability of the internal quality
tests is very important to assure a stable
concrete quality at the project
Because of its low water/cement ratio, high strength
concrete has a higher tendency to cracks than
normal concrete. So curing is very important:
• At initial phase, use curing compound for
exposed surfaces
• As soon as possible, curing with wet cloth at
least 7 days
Holcim recommendation
High strength concrete (60MPa – 100MPa)
• Strength class: B45-B80 (TCXDVN 356:2005)
or C50/60 – C80/95 (EN 206)
• Slump : > 180mm
To control the quality of the concrete, the
readymix plant is equipped with:
• Moisture probe in sand bin
• Automatic dosing system for silica fume
• Comprehensive quality management system
• The internal laboratory has been assessed and found
conform with requirements of ISO/IEC 17025
55
56
E. Very flowable and
self compacting concrete
1. Introduction
Very flowable and self compacting concrete offers a
significantly higher workability than traditional
concrete, which allows a fast and easy concreting of
thin walls, columns and beams, with better surface
finishing.
The benefits of very flowable and self-compacting
concrete are diverse:
a/ Saves construction time and costs
• Faster placing with less labor
• Easier to pump over higher and greater distances
• Easier to finishing surface
• Less to no compaction required – no noise
• Complex elements can be concreted in one time
• Avoid loss of time and cost to repair concrete
defects
b/ Increased construction quality
• Homogeneous concreting of zones with dense
steel reinforcement
• Perfect bond
reinforcement
Fig II.10 - Determine flow of self compacting concrete
between
concrete
and
steel
• No repairs for concrete voids and honeycombs
needed
• Smooth surface finishing
Very flowable concrete and self compacting concrete
can be differentiated from normal concrete through
its workability (flow) and need for vibration to
compact the concrete :
Concrete
Flow
Applications
Self compacting
concrete
660
– 850mm
No vibration
required during
casting
Very flowable
concrete
450
– 650mm
Easy casting for
structures with
high density of
rebars.
(limited vibration)
Normal concrete
<450mm
Compaction is
required
Table II.1 - Flow range with different types of concrete
Fig II.11 - Placing self compacting concrete
Within self compacting concrete, different classes
can be distinguished (see European Guide on Self
Compacting Concrete)
• 550 – 650mm (SF1) : slabs with limited
reinforcement
• 660 – 750mm (SF2) : columns, walls
• 760 – 850mm (SF3) : complex shapes, filling
under formwork
Chapter II: Applications with specific requirements
E. Very flowable and self compacting concrete
2. Production of very flowable
/ self compacting concrete
When using very flowable or self compacting
concrete, special attention has to be given to the
formwork:
Generally speaking, this high performance concrete
is produced with specially selected high quality
components:
• The formwork should be completely tight, to
avoid mortar loss
• High quality cement, with stable quality
• Optimized aggregate grading, with selected
aggregates
• The concrete pressure is higher than
conventional concrete, especially for vertical
elements. The formwork should be designed
specifically to resist this hydrostatic pressure.
• Use of filler (limestone filler or other) to increase
the fines content
• Use of last
admixture
generation
super
plasticizer
• Addition of a Viscosity Modifying Agent (VMA)
When designing the mix, special attention has to be
given to the stability of the mix:
• Impact of small changes in water content
• Presence of segregation
resistance (sieve test)
&
segregation
• Passing ability through reinforcement (L Box - for
self compacting concrete)
For thick elements (> 1.5m), special care is required
to reduce the heat development in the concrete
during hardening. In that case, the mix design needs
to be adapted in a similar way as for massive
concrete structures.
For the concrete supplier, the main challenge of very
flowable / self compacting concrete, is to maintain
the quality over time – every single concrete truck and avoid segregation / honey combs in the finished
element.
Some recommendations to maintain the quality:
• Control of moisture in the aggregates, especially
sand (moisture probe)
• Comprehensive quality management system, to
assure the regularity of the supplied concrete
and to reduce the risk of strength failures.
• The internal laboratory has been assessed and
found to conform with the requirements of ISO/
IEC 17025:2005.
The reliability of the internal quality tests is very
important to assure a stable concrete quality at the
project.
Fig II.12 - L-box and J-ring test for self compacting concrete
Holcim recommendation
Very flowable concrete / self compacting
concrete
• Strength class: B25-B45 (TCXDVN
356:2005) as required for the construction
• Flow: as required by application +/- 50mm
To control the quality of the concrete,
the readymix plant is equipped with:
• Moisture probe in sand bin
• Comprehensive quality
management system
• The internal Laboratory has been assessed
and found conform with
requirements of ISO/IEC 17025
57
58
F. Cement treated aggregates
1. Introduction
Cement treated aggregates can be used in different
applications:
• Base layer for roads and highways
There are 2 main types of cement treated
aggregates:
• sand/cement - without any coarse aggregates
• cement treated aggregates 0/25
• Heavily loaded storage industrial platforms,
container ports etc
• Load distribution layer on top of CDM columns
(CDM: cement deep mixing as soil improvement
method)
Pavement
Base course
Loading
Road
structure
Fig II.15 - Sand/ cement layer
Subbase
Soil
Soil
stabilized
by CDM
Fig II.13 - Typical road structure
When aggregates are treated with a small quantity
of cement, the bearing capacity and the stiffness
(E-modulus) of the layer increases resulting in a
longer service life of the structure.
For the same bearing capacity, the addition of
cement to aggregates will reduce the required
thickness of the aggregate layer, which reduces the
use of natural resources and expensive aggregates.
Fig II.16 - Cement treated aggregates
2. Cement for treated
aggregates
The cement used for the treated aggregate layer
must ensure a high efficiency to develop strength as
well as a long workability of the mix. The
optimization tests in the laboratory will determine
the compatibility of the cement and the aggregates.
In general, the cement complies to:
• TCVN 6260 : 2009, type PCB40
or
• TCVN 4316 : 2007, type PCBBFS40
Fig II.14 - Compaction of road base layer
Chapter II: Applications with specific requirements
F. Cement treated aggregates
3. Testing procedure for
cement treated aggregates
or
o 22TCN 333-06
o ASSHTO T180 - ASSHTO T99
Vary the moisture of mixture (Aggregate + Cement)
until the dry density of mixture reach highest value.
The moisture which gives the maximum dry density
would be the optimal moisture (Fig II.18)
2.16
2.14
Dry Density (g/cm3)
Cement treated aggregates are tested as following:
• Determine optimal moisture and max dry
density by proctor method, according to:
59
2.12
2.10
2.08
2.06
2.04
2.02
2.00
Optimal moisture
5%
6%
7%
8%
9%
10%
Moisture
11%
12%
13%
14%
Fig II.19 - The correlation between moisture and dry density
• In function of the aggregate size, the mould can
be choosen as follows:
o Coarse aggregates
22TCN 246/ASTM D558
or
o Fine aggregate (pass 4.75mm)
ASTM D1632
Fig II.17 - Apparatus to determine optimal moisture
Sample 22TCN 246 - ASTM D558
Sample ASTM D1632
101.6 x 116.4 mm
71 x 142 mm
Fig II.20 - Different sample size to determine compressive
strength
Note: When a different standard/test method is
applied, the measured strength will be different for
the same mix design. ASTM D1633 recommends a
correlation factor between different mould size.
Fig II.18 - Determine optimal moisture by proctor method
Ratio of Length to
Diameter (L/D)
Strength Correction
Factor
2.0
1.0
1.75
0.98
1.50
0.96
1.25
0.93
1.00
0.87
Table II.2
Strength
correlation factor
for different
sample size
60
Chapter II: Applications with specific requirements
F. Cement treated aggregates
• Curing
o The specimens are cured in the moulds in
moisture room for 12h
o The specimens are removed from the moulds
by the extruder
o The specimens are returned to moist room
o At the end of the moist–cure period, the
specimens are immersed in water for 4 hours
• Unconfined compressive strength is than tested
according to the standard ASTM D1633
o A screw power testing machine, with the
moving head operating at approximately
0.05 in. (1 mm)/min when the machine is
running idle, may be used
o With hydraulic machines, adjust the loading
to a constant rate within the limits of (140 ±
70 kPa/s)
• Workability period of cement treated aggregates
o Just like normal concrete, cement treated
aggregates have a workability period, during
which the material has to be transported,
placed, leveled and compacted.
o The workability period will depend strongly
of the type of cement and aggregates, the
mix design and the temperature of the mix.
It can range from 2-3 hours up to 10 hours
and even more.
• The workability is specified in accordance with
the standard EN 13286-45
o The bulk density of the mix is determined
immediately after mixing (p(0)) and after
defined intervals of waiting time (for
example 30min)
o The workability period is the time which
corresponds to the dry bulk density p(t) equal
to 98% of p(0)
p (t)
p (0)
0,98p (0)
0
fs
f
Wpc
Fig II.21 - The diagram to determine workability period for
cement treated aggregate layer
Said differently, the standard allows a maximum
loss of 2% density after compaction, which will
already reduce the strength of the layer. After the
workability period, the loss of density will increase,
which reduces the compressive strength further.
The aggregate/cement mix, with a longer initial
setting time, allows more time for transport,
leveling and compaction and assures a better quality
of the compacted layer.
Chapter II: Applications with specific requirements
4. Optimization of cement
treated aggregates
In South of Vietnam, there are many types of sand
with variable quality so the selection of sand is very
important, as well as the choice of cement that
offers a good compatibility with the selected
aggregate.
To optimise the cement content, laboratory tests are
required at different dosages e.g: 3%, 5% and 7%
(ratio of cement to aggregate on dry weight).
Based on project requirements for a targeted
strength, the optimal cement dosage can be
determined through regression analysis.
Additionally, an in-situ test at the project needs to
be conducted to confirm the laboratory tests with
the real mixing and compaction equipment, before
execution.
After compaction of the layer, a suitable curing layer
(sprayed bitumen + sand) is recommended to:
F. Cement treated aggregates
MPa
61
Mix Crushed + Sand (50:50)
6.00
5.52
5.00
4.00
2.57
3.00
2.00
1.50
1.00
0.00
1.83
1.19
1.02
3.03
1.43
0.67
3%
3.6%
4%
5%
7 Days
28 Days
7%
Cement dosage
Required strength
This experiment was carried out as follows :
Optimal moisture
AASHTO T180
Sample moulding ASTM D558
Compressive strength test ASTM D1633
Fig II.23 - Relation between cement dosage and strength
• Avoid early dehydration of the layer and loss of
strength
• Reduce damage from rainfall, especially within
hours of compaction
Holcim recommendation
For cement treated aggregates, Holcim recommends to use
cement PCB40 according to TCVN 6260:2009 or TCVN 4316:2007.
Before execution of the project, a laboratory study is required to
optimize the mix design:
• Determine optimal water content and optimal density of
the mix
• Test the compressive strength of at least 3 different cement
dosages
• By regression, determine the optimum cement dosage, to
reach the design strength
Fig II.22 - Laying and compaction sand/ cement layer
62
Causes and
prevention of concrete
defects
Chapter III:
Concrete in the construction can show different types of defects:
• Segregation of concrete
• Different type of cracks
• Carbonatation and corrosion of reinforcement
• Degradation in seawater environment
• Attack by chemical component in ground water or soil
• Attack by fire
A correct identification of the defect and its root cause will allow the user to take
appropriate measures to avoid them in future and improve the quality and durability of
the construction.
A. Segregation of Concrete
Various types of segregation can occur when
concrete is transported, conveyed, poured and
compacted. Segregation impairs the quality and /or
appearance of concrete to varying degrees.
Causes and remedial actions:
The most important causes of concrete segregation
(which also point to the remedies) are:
Segregation can occur:
• Excessive dosage of a superplasticizer
• between different aggregate fractions
• between aggregate and cement paste
• between fines and water
In practice these types of segregation cannot be
clearly distinguished.
The most important forms of segregation:
• Stone pockets, or concentrations of coarse
aggregate in the concrete (honey-comb)
• Local concentrations of surplus water with fine
cement and aggregate particles at vertical
surfaces of forms
• Bleeding or surplus mixing water that rises to
the surface of the concrete. Bleeding causes
irregular, powdery porous surfaces.
• Micro-segregation or separation of cement and
sand/ fines. This blemishes the appearance of
concrete surfaces
Fig III.1 - Honey comb on concrete
• Too high consistency of the fresh concrete
• Improper placement or compaction of the
concrete (failure to use vertical pipes for
excessive drop heights, concrete deposit points
spaced too far apart, excessive vibrating)
• Unsuitable concrete composition (poor grading,
insufficient cement dosage)
• Maximum aggregate size too large for section
poured
• Mixing time too short
• Leaky forms, allowing cement paste to escape
(sieve effect)
• Reinforcement too dense (sieve effect)
Fig III.2 - Stone pockets formed by segregation due to excessive
drop height and/or reinforcement that is too dense
63
64
B. Cracking
Control of Cracking
Why control the cracks in concrete? A fundamental
requirement of any concrete structure is its
performance over its intended design life. Concrete
must be able to withstand wear and deterioration
given the environment and maintenance regime for
which it was designed. If a concrete structure meets
its intended design life when exposed to its
anticipated environment, then it can be described as
being durable.
Cracks Classification
There are many types of cracks in a concrete
structure, but they can be classified into 5 main
types: plastic settlement, plastic shrinkage, early
thermal, drying shrinkage, surface crazing (Fig III.3).
4
9
4
13
8
2
8
10
6
3
The most common form of concrete defect is
cracking. It becomes more vulnerable to the
penetration of damaging elements and is more
prone to spalling, wear and abrasive damage.
Therefore, through the control of the cracks, the
servicelife of concrete structures can be improved,
saving cost for repair and replacement.
11
5
5
12
1
14
8
7
8
Fig III.3 - Cracking location in concrete structure:
Allowed crack width
For reinforced concrete sections without
specific requirements, a maximum crack width
up to 0.3mm is allowed in ACI 224R and BS
8110. Bigger crack width must be repaired by
epoxy injection.
a. Plastic settlement : 4, 5, 6, 13
b.Plastic shrinkage : 1, 2 , 3
c. Early thermal : 11, 12
d.Drying shrinkage : 8
e. Surface crazing : 9, 10
Each type of those cracks occurs in concrete at
different moments from placing to hardening of the
elements (Fig III.4)
Hours
Days
Weeks Months Years
Plastics Settlement
Plastics Shrinkage
Early thermal
Drying Shrinkage
Fig III.4 – Time period of cracking occurrence
Chapter III: Causes and prevention of concrete defects
B. Cracking
1. Plastic settlement cracks
In plastic concrete, bleed water surfaces due to
gravity. If the accompanying settlement is restricted
by form work or reinforcement, cracking may occur.
The cracks occur while the concrete is plastic and
frequently while bleed water is still rising and covers
the surface. They tend to roughly follow the
restraining element, for example reinforcing bars, or
changes in the concrete section. They can be quite
wide at the surface, tend to extend only to the
reinforcement or other restraining element and
taper in width to that location (Fig III.5). In exposed
situations, this may increase the risk of corrosion of
the reinforcement and pose a threat to durability.
65
Preventive measures
• More cohesive mix, with enough fines and
low tendency to segregation
• Increase the ratio of cover to reinforcing
bar diameter, by increasing the cover or
decreasing the size of the bars.
• Set all formwork accurately and rigidly.
• Good compaction of the concrete
• Cure the concrete promptly and properly.
Cracks may develop further, due to subsequent
drying shrinkage, leading to possible cracking
through the full depth of the concrete member. This
type of cracking is often caused by insufficient
consolidation (vibration) and high slump (overly wet
concrete).
Typical plastic settlement is approximately 6-8mm
per meter depth of the concrete element
(corresponding to a typical bleeding rate of 6-8 liters
per cubic meter). Common elements that often
crack, are deep sections, top of column, suspended
floor…
Settlement cracks
Reinforcing
bar
Differential settlement cracks
Large aggregate
particles
SECTION A-A
A
Fig III.5
Plastic
settlement
cracking
direction in
concrete
structure
SECTION A-A
A
Settlement
cracks
(a)
A
Differential
settlement
cracks
(b)
A
66
Chapter III: Causes and prevention of concrete defects
B. Cracking
2. Plastic shrinkage cracks
Plastic shrinkage cracks occur on the surface of
freshly placed concrete during finishing or soon
afterwards (but before final set of concrete). This
type of cracks is normally random, without a clear
orientation.
Cracks due to plastic shrinkage are caused by rapid
loss of mixing water once the concrete is in place.
This can be due to excessive water evaporation or
excessive water absorption by the formwork or
earth. This causes the concrete to shrink locally,
while other areas without water loss, hardly shrink
at all. This induces tensile stresses within the
concrete. If the stresses exceed the tensile strength
of the concrete (naturally very low at the beginning)
cracks will form (Fig III.6). They can exceed 1mm.
Horizontal concrete slabs can be particularly
susceptible to plastic shrinkage (Fig III.7)
Fig III.6 – Surface cracks caused by plastic shrinkage due to
excessive water loss in the surface layer of the concrete
Preventive measures
• Use of anti-evaporation curing agent after
screed or floating and before finishing
• Avoid the windiest and/or driest part of the
day
• Start curing as soon as possible after
finishing
• Dampen formwork,
reinforcement
sub
grade
and
• Cover with plastic sheet prior to finishing
• Use of polypropylene fibers in the concrete
Fig III.7 – Extensive plastic shrinkage cracking in concrete
Chapter III: Causes and prevention of concrete defects
B. Cracking
3. Surface Crazing
4. Drying Shrinkage cracks
Crazing is the development of a dense network of
fine random cracks on the surface of concrete
caused by shrinkage of the surface layer. They are
more likely to occur on steel trowelled surfaces.
These cracks rarely compromise structural integrity
of the concrete.
Once the concrete has set, drying shrinkage
continues for weeks and months before finally
coming to a virtual end (Fig III.9). Drying shrinkage
(also called hydraulic shrinkage) is caused by:
Crazing occurs when good concrete practice is not
followed, for example poor curing, wet mixes, rapid
surface drying or when concrete is finished too early
while bleed water is still present. This phenomenon
often occurs on “fair-faced” concrete element (Fig.
III.8) and can be recognized as:
• A network of fine random cracks on the surface
• Rarely more than 2mm depth
• Typically form hexagonal shaped areas no more
than 40mm across
• hydration of the cement, which binds part of the
mixing water
• evaporation of mixing water from the concrete
surface
• initial adjustment of the temperature of the
concrete to that of the environment
Drying shrinkage of concrete occurs at a rate of 0.3 –
1.0 mm/m, depending on mix design, aggregate
type, w/c ratio and the degree of drying out. If the
humidity of concrete increases, due to exposure to
rain for example, the concrete section will expand a
bit, meaning that drying shrinkage will be
somewhat set back. After further drying, shrinkage
will return to the previous level.
Drying shrinkage leads to cracking because the
concrete section is typically unable to contract as
shrinkage would dictate. Contraction may be
prevented by the reinforcement, by the substrate, or
by a concrete section being fixed in some way to
other members (restrained shrinkage cracks).
Fig III.8 – Surface crazing on concrete
Preventive measures
• Avoid mortar-rich concrete mix (lower
sand/aggregate ratio)
• Use coarse sand, avoid very fine sand, if
possible
• Keep setting time of concrete under control
• Cure the concrete as soon as possible.
• Don’t finish concrete while bleed water
exists
• Never sprinkle or trowel dry cement or a
mixture of cement and fine sand to absorb
bleeding water
• Avoid overcompaction of concrete
Fig III.9 – Typical drying-shrinkage cracks in a concrete slab
67
68
Chapter III: Causes and prevention of concrete defects
B. Cracking
Typical examples are long slabs and walls (Fig III.10).
5. Early Thermal Cracking
Cracks can form due to thermal shrinkage if a
significant temperature differential exists within a
concrete body. Temperature differences can arise
due to the relatively low thermal conductivity of
concrete. Such differences develop frequently in
massive sections when the heat of hydration is
released and the core temperature increases
significantly. When temperature equalization within
the concrete section occurs, internal stresses will be
induced, because high-temperature areas contract
more than low-temperature areas. If the stresses
exceed the tensile strength of the concrete, cracks
will form (Fig III.11).
The thermal cracks can occur on pile caps,
foundation blocks, massive columns.
Fig III.10 – Restrained drying shrinkage in a wall
Preventive measures
At least for reinforced concrete and larger
concrete sections, there is no way to allow the
concrete to freely shrink – cracking is
unavoidable. But by taking suitable measures,
relatively wide cracks, the damaging cracks,
can be avoided, and in their place numerous,
harmless, barely visible hairline cracks will
form. The preventive measures:
• Proper installation of shrinkage reinforcement
• Installing contraction joints in large
horizontal slabs or long walls at every 6-9m
length according to TCXDVN 313:2004
• Optimize the w/c ratio within the range
0.40 – 0.50
• Reduce the paste volume, use larger size
aggregates
Fig III.11 - Early thermal cracking on concrete
Preventive measures
See chapter II.C – Mass Concrete structures
C. Carbonation and corrosion
of reinforcement
69
How does carbonation phenomenon occur?
Carbonation is a chemical reaction between the
carbon dioxide (CO2) from the air with calcium
hydroxide (Ca(OH)2) in the concrete. The process
begins on the surface of concrete and progresses
slowly toward the interior. Carbonation has a
positive influence on the concrete itself, making it
more compact.
Fig III.13 - Concrete cover over reinforcement spalled due to
carbonation and rusting
The rate at which the carbonation front penetrates
concrete is proportional to the permeability of the
concrete. The rate decreases gradually with the time
(Fig III.14). The rate of carbonation, and thus the
depth are also influenced by number of other factors
such as cement content, concrete strength, curing
time and exposure to moisture, which may be
permanent, alternating or totally lacking.
Chiềuofsâu
cacbonat hóa(mm)
(mm)
Depth
carbonation
Effects of carbonation on reinforced concrete
On the other hand, carbonation of concrete can
result in serious damage of steel reinforcement. In
non-carbonated concrete, the high alkalinity (pH >
12) protects the steel from corrosion. Carbonation
reduces the alkalinity (pH < 9), so corrosion starts as
soon as the carbonation front (Fig III.12) reaches the
reinforcement. Corrosion causes the steel to expand,
which leads to scaling of the concrete covering the
reinforcement (Fig III.13). This greatly accelerates
further corrosion of the reinforcing steel, and the
concrete rapidly loses its load-bearing capacity and
serviceability.
ThờiTime
gian (năm)
(years)
Fig III.14 - The depth of carbonation varies widely as a
function of time, depending on other influencing factors
Preventive measures
Fig III.12 - Carbonation front made visible by a
phenolphthalein test on a cut into the concrete. The
concrete dyed violet by phenolphthalein has not yet been
carbonated.
To prevent corrosion of reinforcement by
carbonation, the carbonation front must be
prevented from reaching the reinforcement.
This is achieved by:
• Sufficient concrete cover all around the
reinforcement, generally at least 30 mm.
• Good curing of the concrete, so that after
removal of formwork, the surface concrete
hydrates well and the rate of carbonation is
minimized
70
D.Degradation in seawater
environment
In seawater, concrete can be degraded by two main
attack mechanisms:
• Chloride-induced corrosion of the steel
reinforcement
• Sulphate attack of the cement matrix
In general, the degradation from chloride-induced
corrosion advances significantly faster than the
sulphate attack of the cement matrix, and is the
biggest threat for concrete structures in contact
with seawater.
For this reason, Ordinary Portland Cement OPC with
a low C3A-content (sulfate resistant OPC according
TCVN 6067 or C150 – OPC type V) is not
recommended for seawater environment, as it has a
lower chloride resistance, compared to standard
cement PCB40 (Refer Chapter 4 of ACI 201.2R-01).
In presence of chlorides in the concrete, steel
reinforcement can corrode locally, even when the
concrete pH is still high (pH>12). This mechanism is
called “pitting corrosion” (Fig III.16), which is very
different from the distributed corrosion, linked to
carbonation of concrete. This process can be
described according to the reaction:
Fe2+ + 2Cl- ---> FeCl2
The effects of chloride attack are:
• Significant and fast reduction of the steel section
(locally)
• Risk for failure of construction
• Does not create significant cracks in concrete, so
it is less visible
Submerged wetting and drying of concrete, for
example in the tidal zone, accelerates the
degradation of concrete in sea water.
1. Chloride-induced corrosion
of the steel reinforcement
Concrete in contact with sea water or close to the
sea can be damaged by attack by the chloride ions in
sea water (Fig III.15). Chloride ions can also be
introduced into concrete by the mixing water, by
contaminated aggregates (for example: marine
aggregates) or chloride-based accelerators (which
are forbidden in most countries).
Concrete carbonation
(distributed corrosion)
Chloride corrosion
(concentrated pitting corrosion)
Fig III.16 – Mechanism of attack reinforcement steel by
chloride and CO2
Fig III.15
– Corrosion of
steel
reinforcement in
concrete in sea
water
Chapter III: Causes and prevention of concrete defects
2. Attack by sulfates from
seawater
In seawater, sulfate attack can occur at the surface
of the concrete, with the same mechanism as
mentioned in the chapter on chemical attack
(see chapter III.E)
As this reaction is slower than choride-induced
corrosion, it mainly appears as secondary reaction:
first the concrete is degraded by the corrosion of the
reinforcement, then additional damage is done by
sulfate attack.
D. Degradation in seawater environment
3. Preventive measures
Refer chapter II.B (Application for aggressive
environment)
71
72
E. Chemical attack
1. Classification
The durability of concrete does not only depend on the mix design but as well on the environment where the
concrete is exposed. An in-depth analysis on the aggressive environment is crucial to guarantee a long life
time of the concrete structure. According to standard EN 206, we can classify three levels of aggression
chemical environment following sign XA1, XA2 and XA3 (Table III.1 - Limiting value for exposure class for
chemical attack from natural soil and ground water)
Chemical
Characteristic
Reference
test method
XA1
XA2
XA3
SO4 -2 (mg/l)
EN 196-2
≥ 200 and ≤ 600
>600 and ≤3000
> 3000 and ≤ 6000
pH
ISO 4316
≤ 6,5 and ≥ 5,5
< 5,5 and ≤ 4,5
< 4,5 and ≥ 4,0
CO2
(mg/l aggressive)
Pr EN 13577 :
1999
> 15 and ≤ 40
> 40 and < 100
> 100 up to
saturation
NH4 (mg/l)
ISO 7150-1 or
ISO 7150-2
> 15 and < 30
> 30 and < 60
> 60 and < 100
Mg (mg/l)
ISO 7980
≥ 300 and ≤ 1000
> 1000 and < 3000
> 3000 up to
saturation
SO4 -2 (mg/kg total)
EN 196-2
≥ 2000 and
> 3000(*) and
≤ 12000
> 12000 and
≤ 24000
Acidity (ml/kg)
DIN 4030-2
Ground water
+
Soil
≤ 3000(*)
> 200 Baumann
Gully
Not encountered in practice
XA1 : Slightly aggressive chemical environment; XA2 : Moderately aggressive chemical environment
XA3 : Highly aggressive chemical environment
(*) : The 3000mg/kg limit shall be reduced to 2000mg/kg, where there is a risk of accumulation of sulfate ions in the
concrete due to drying and wetting cycles or capillary section
Table III.1 - Limiting value for exposure class for chemical attack from natural soil and ground water
according to standard EN-206 (attack from seawater is discussed separately)
Depending on the type of chemical attack, concrete
can either remain stable or degrade more or less
rapidly. There are two basic types of damage:
a. Chemical decomposition:
Chemical decomposition of concrete is characterized
by the degrading of one or more constituents of
the hardened cement by external chemicals (Fig
III.17). The decomposed constituent is leached out of
the concrete. The concrete becomes gradually more
porous, loses strength, and loses protection of the
reinforcement against corrosion. The process always
begins at the interface between concrete and the
aggressive chemical, and progresses (usually slowly)
toward the concrete interior.
acid attack
Fig III.17 - Cement mortar prism attacked by acid
Chapter II: Applications with specific requirements
b. Swelling due to chemical reaction
The second type of chemical attack is caused by the
reaction of a chemical with one or more
constituents of the hardened cement in the
presence of capillary water. If the reaction produces
a solid compound with a greater volume than the
component solids, the concrete will swell. The
stresses produced will soon exceed the tensile
strength of the concrete, and cracks will form,
expanding slowly but steadily.
An example is sulfate attack - sulfates in soil or
groundwater can attack hardened concrete. Sulfates
combine with tricalcium aluminate (C3A) in cement
to form the compound ettringite. This reaction
involves a significant increase in volume and
degradation of the concrete.
E. Chemical attack
73
2. Preventive measures
Protecting concrete from external chemical attack
requires a dense concrete:
• Suitable cement choice
• Low porosity, with a maximum w/c ratio
For external chemical attack, blended cements offer
significant benefits over Ordinary Portland Cement
OPC, as the blending materials (for example slag) will
reduce the pore size of the concrete and improve the
resistance to chemical attack.
If attack by dissolved sulfates is expected, these
measures must be combined with the use of cement
with high sulfate resistance.
Additional measures include:
• Increased concrete cover over reinforcement
(“sacrificial layer”)
• Special attention to curing
Concrete is relatively resistant to weak acids (XA1) only.
Moderately strong acids and strong acids can attack
concrete to the point of unserviceableness. In case of
strong acids or when no degradation is allowed,
additional acid-resistant coating (synthetic resin,
ceramic, etc.) should be considered by the designer.
Fig III.18
Prefabricated
jacking pipe
elements for
waste water
tunnel
F. Alkali – Aggregate Reaction
74
Alkali-aggregate reaction is a slowly progressing
chemical reaction between certain so-called reactive
aggregate and alkalis that are present in the
concrete or that penetrate into the concrete from
the environment. This reaction involves swelling of
the concrete, leading ultimately to heavy cracking
and significant loss of strength.
Alkali-aggregate reaction is known in many
countries. It is difficult to recognize the reaction
with certainty, partially because the processes
involved can extend over a period of time from one
year up to fourty years (Fig III.19)
Conditions that induce alkali-aggregate reaction
Alkali-aggregate reaction can occur only when all
of these conditions are simultaneously met:
• Presence of reactive aggregate
• Sufficient moisture in the concrete
(almost always the case)
• Sufficient alkali in the concrete
Fig III.19
Heavy cracking
due to swelling
of concrete
caused by
alkali-aggregate
reaction
Preventive measures
• Use a cement with low alkali content (%
Na2O eq = % (Na2O + 0.658xK2O) < 0.6%)
• Determination of the potential reaction of
these aggregate, through various tests
(chapter I). This should be done extensively
for different layers of the quarry, used at
the project.
G. Fire Resistance
1. Concrete in fire
Concrete has a high resistance against fire. Even
when exposed to extremely high temperatures,
concrete emits no smoke or toxic gases. Rather,
concrete prevents fire from spreading. When fire
impacts concrete, the temperature of the concrete
increases slowly. Therefore concrete offers excellent
protection against the spread of fire, without
requiring any fire-resistance treatment. Only after
long and intensive exposure to fire, portions of the
concrete may delaminate or spall off (Fig III.20).
Fig III.21 - Penetration depth of the critical temperature
(300°C) in concrete exposed to 1000°C heat.
2. Preventive measures
Concrete offers excellent intrinsic protection against
fire and high temperatures.
In most buildings, no additional precautions or
coatings are required to resist fire.
In specific cases, the protection can be enhanced by
increasing the reinforcement cover.
Fig III.20 – Steel reinforcement exposed after the concrete
cover was spalled off in a fire. The load-bearing capacity of
the concrete structure is undiminished.
Critical temperature:
Reinforced and non-reinforced concrete can
withstand temperatures up to 300°C without
damage. This critical temperature of concrete is
reached only very slowly with exposure to fire.
Studies show that it takes one hour for the critical
temperature of 300°C to penetrate 2 cm into the
concrete when the surface is exposed to a flame
temperature of 1000°C (Fig III.21). This temperature
roughly corresponds to that of a blazing wood fire or
gas flame. Under these test conditions, the critical
temperature reaches a depth of 5 cm after 2 hours.
For high strength concrete, the addition of
polypropylene fibres may be required to avoid
excessive spalling.
75
76
Overview of cement
and concrete standards
Chapter IV:
To understand quickly the requirements of each standard, this chapter gives an overview of the main
referenced standards in this manual. For the complete details of each standard, please refer to the official
standard itself.
As worldwide there are many standards available, this overview only lists the standards that are currently
used in Vietnam.
A. Cement
VIETNAMESE STANDARDS – TCVN
• Portland Blended Cement – Specifications
TCVN 6260 : 2009
• Portland Cement – Specifications
TCVN 2682 : 2009
• Portland Blast Furnace Slag Cement
TCVN 4316 : 2007
• Sulfate Resistant Portland Cement
TCVN 6067 : 2004
• Sulfate Resistant Blended Portland Cement
TCVN 7711 : 2007
• Low Heat Blended Portland Cement
TCVN 7712 : 2007
B. Concrete
VIETNAMESE STANDARDS – TCVN
• TCXDVN 374:2006
AMERICAN STANDARDS – ASTM
• ASTM C94
EUROPEAN STANDARDS – EN
• EN 206-1:2000
BRITISH STANDARDS – BS
• BS 5328
AMERICAN STANDARDS - ASTM
• Standard Performance Specification For
Hydraulic Cement
ASTM C1157 : 2008
• Ordinary Portland cement – Specifications
ASTM C150 : 2011
C. Recommendation for
limiting values of concrete
composition
• Chloride - induced corrosion in sea water
(EN 206-1:2000)
EUROPEAN STANDARDS - BS-EN
• Composition, Specifications and Conformity
Criteria for Common Cement
EN 197-1: 2011
• Aggressive chemical environments
(EN 206-1:2000)
A. Cement
77
VIETNAMESE STANDARD - TCVN
PORTLAND BLENDED CEMENT – SPECIFICATIONS
TCVN 6260 : 2009 (Old version: TCVN 6260 : 1997)
1. Composition
Portland blended cement is produced by
• Grinding portland clinker with a necessary
gypsum content and mineral additives. Grinding
aid can be used in the grinding process if
necessary.
2. Classification
Portland blended cement consists of 3 grades:
PCB30, PCB40 and PCB50 with
• PCB is defined sign of portland blended cement
• 30, 40 and 50 is the minimum compressive
strength of standard mortar sample at 28 days in
MPa, testing method complies with TCVN 6016 :
1995 (ISO 679 : 1989)
3. Physical Specification
No
1
2
Characteristics
Compressive Strength
- 3 days
- 28 days
Setting time
- Initial set
Unit
Requirement
Test Method
PCB30
PCB40
PCB50
MPa
min
min
TCVN 6016:1995
14
30
18
40
22
50
minute
- Final set
3
Fineness
- Retained content on
sieve 0.09mm
- Specific surface - Blaine
4
Soundness
5
Autoclave (1) Expansion
(1)
min
max
45
TCVN 6017:1995
420
%
max
(cm2/g)
min
mm
max
TCVN 6017:1995
10
%
max
TCVN 7711:2007
0.8
Unit
Requirement
Test Method
10
TCVN 4030:2003
2800
Apply when customers require
4. Chemical Specification
No
Characteristics
PCB30
PCB40
1
Grinding Aid Content
%
max
-
1.0
2
- Mineral additives
Content
- Filler Content (in
mineral additives)
%
%
max
max
-
40
20
3
MgO Content in Clinker
%
max
TCVN 141:2008
5.0
4
SO3 content
%
max
TCVN 141:2008
3.5
PCB50
78
Chapter IV: Overview of cement & concrete standards
A. Cement/ Vietnamese standard - TCVN
ORDINARY PORTLAND CEMENT – SPECIFICATIONS
TCVN 2682 : 2009 (Old version: TCVN 2682 : 1999)
1. Composition
Portland cement is produced by grinding portland
clinker with a necessary gypsum content (comply
with TCVN 5438 : 2007). Grinding aid can be used in
the grinding process if necessary.
2. Classification
Portland cement consists of 3 grades: PC30, PC40
and PC50 with
• PC is defined sign of portland cement
• 30, 40 and 50 is the minimum compressive
strength of standard mortar sample at 28 days in
MPa, testing method complies with TCVN 6016 :
1995 (ISO 679 : 1989)
3. Physical Specification
No
Characteristics
Unit
Requirement
Test Method
PC30
PC40
PC50
MPa
min
min
TCVN 6016:1995
16
30
21
40
25
50
1
Compressive Strength
- 3 days
- 28 days
2
Setting time
- Initial set
- Final set
minute
min
max
TCVN 6017:1995
45
375
3
Fineness
- Retained content on
sieve 0.09mm
- Specific surface - Blaine
%
(cm2/g)
max
min
TCVN 4030:2003
10
2800
4
Soundness (mm)
mm
max
TCVN 6017:1995
10
Unit
Requirement
Test Method
4. Chemical Specification
No
Characteristics
PC30
PC40
1
Grinding Aid Content
%
max
-
1.0
2
SO3 content
%
max
TCVN 141:2008
3.5
3
MgO Content
%
max
TCVN 141:2008
5.0
4
Loss of ignition
%
max
TCVN 141:2008
3.0
5
Insoluble rest
%
max
TCVN 141:2008
1.5
6
Alkali content
%Na2O eq = %Na2O +
0.658%K2O
%
max
TCVN 141:2008
0.6
(1)
(1)
Define for Portland Cement when using with aggregate which may cause alkali-silica reaction
PC50
Chapter IV: Overview of cement & concrete standards
A. Cement/ Vietnamese standard - TCVN
79
PORTLAND BLAST FURNACE SLAG CEMENT
TCVN 4316 : 2007 (Old version: TCVN 4316 : 2006)
1. Composition
Portland blast furnace slag cement is produced by
• Grinding clinker portland cement with a
necessary gypsum content and Blast Furnace
Slag (comply with TCVN 4315 : 2007)
• Or well mixing ground blast furnace slag with
Portland Cement
2. Classification
Portland blast furnace slag cement is classified into
2 types:
• Type I: slag content is from 40 % to 60% - signed
PCBBFSI
• Type II: slag content is from 60 % to 70% - signed
PCBBFSII
3. Physical Specification
Type I
No
Characteristics
Unit
Requirement
Test
Method
1
Compressive
Strength
- 3 days
- 28 days
MPa
min
min
TCVN
6016:1995
2
Setting time
- Initial
- Final
minute
min
max
TCVN
6017:1995
45
10
3
Fineness
- Specific
surface -Blaine
(cm2/g)
min
TCVN
4030:2003
3300
4
Soundness
mm
max
TCVN
6017:1995
10
PCBBFS
30
14
30
PCBBFS
40
PCBBFS
50
PCBBFS
30
18
40
22
50
12
30
Type II
PCBBFS PCBBFS
40
50
16
40
4. Chemical Specification
No
Characteristics
Unit
Requirement
Test Method
PCBBFS
1
SO3 content
%
max
TCVN 141:2008
3.5
2
MgO Content
%
max
TCVN 141:2008
6.0
3
Loss of ignition
%
max
TCVN 141:2008
3.0
20
50
80
Chapter IV: Overview of cement & concrete standards
A. Cement/ Vietnamese standard - TCVN
SULFATE RESISTANT PORTLAND CEMENT
TCVN 6067 : 2004 (Old version: TCVN 6067 : 1995)
1. Composition
Sulfate resistant portland cement is produced by
grinding sulfate resistant portland clinker with a
necessary gypsum content
• PCSR is defined sign of sulfate resistant portland
cement
• 30, 40 and 50 is the minimum compressive
strength of standard mortar sample at 28 days in
MPa (testing method complies with TCVN 6016 :
1995)
3. Physical Specification
No
2. Classification
Portland cement consists of 3 grades: PCSR30, PCSR40
and PCSR50 with
Characteristics
Unit
Requirement
Test Method
PCSR30
PCSR40
PCSR50
1
Compressive Strength
- 3 days
- 28 days
MPa
min
min
TCVN 6016:1995
12
30
16
40
20
50
2
Setting time
- Initial set
- Final set
minute
min
max
TCVN 6017:1995
3
Fineness
- Retained content on sieve
0.08mm
- Specific surface - Blaine
%
(cm2/g)
max
min
TCVN 4030:2003
4
Soundness
mm
max
TCVN 6017:1995
10
5
Sulfate Expansion at 14 days
%
max
TCVN 6068:2004
0.04(1)
45
375
12
2800
10
3000
8
3200
4. Chemical Specification
No
Characteristics
Unit
Requirement
Test Method
PCSR30
PCSR40
1
SO3 content
%
max
TCVN 141:2008
2.5
2
MgO Content
%
max
TCVN 141:2008
5
3
Loss of ignition
%
max
TCVN 141:2008
3
4
C3A content
%
max
see Note 1
3.5 (2)
5
(C4AF + 2C3A) content
%
max
see Note 2
25
6
Alkali content
%Na2O eq = %Na2O +
0.658%K2O
%
max
TCVN 141:2008
(2)
0.6
7
Residue insoluble
%
max
TCVN 141:2008
1
8
BaO content
%
max
TCVN 141:2008
1.5 – 2.5 (3)
Note 1 : (C3A) = (2.650 x %Al2O3) - (1.692 x %Fe2O3)
Note 2 : (C4AF + 2C3A) = (3.043 x %Fe2O3) + 2C3A
Note:
• Only require (1) or (2)
• (3) only require for sulfate resistant portland cement consist of BaO
PCSR50
Chapter IV: Overview of cement & concrete standards
A. Cement/ Vietnamese standard - TCVN
81
SULFATE RESISTANT BLENDED PORTLAND CEMENT
TCVN 7711 : 2007
1. Composition
Sulfate resistant blended portland cement is
produced by grinding portland cement clinker with a
necessary gypsum content and:
2. Classification
Sulfate resistant blended portland cement is
classified into 2 types: PCBMSR30, PCBMSR40, PCBMSR50,
PCBHSR30, PCBHSR40, PCBHSR50.
• Blast furnace slag (comply with TCVN 4315 :
2007)
• PCBMSR is defined sign of moderate sulfate
resistant blended portland cement
• Other mineral additives (comply with TCVN 6882
: 2001)
• PCBHSR is defined sign of high sulfate resistant
blended portland cement
• 30, 40 and 50 is the minimum compressive
strength of standard mortar sample at 28 days in
MPa (testing method complies with TCVN 6016)
3. Physical Specification
Level
No
Characteristics
1
Compressive Strength
- 3 days
- 28 days
2
Setting time
- Initial set
- Final set
3
Fineness
- Retained content on
sieve 0.08mm
- Specific surface-Blaine
4
Unit
Requirement
Test
Method
MPa
min
min
TCVN
6016:1995
minute
min
max
TCVN
6017:1995
%
max
cm2/g
min
Sulfate durability
(Defined by the
expansion of mortar
bar in sulfate
solution):
PCBMSR
PCBHSR
30
40
50
30
40
50
18
30
20
40
22
50
16
30
18
40
20
50
45
375
10
TCVN
4030 :2003
2800
TCVN
7713 :2007
- 6 months
- 12 months
%
max
max
0.10
-
0.05
0.10
5
The expansion of
mortar bar in water
after 14 days
%
max
TCVN
6068 :2004
0.02
6
The expansion by
autoclave method
%
max
TCVN
7711 :2007
0.8
82
Chapter IV: Overview of cement & concrete standards
A. Cement/ Vietnamese standard - TCVN
LOW HEAT BLENDED PORTLAND CEMENT
TCVN 7712 : 2007
1. Composition
Low heat blended portland cement is produced by
grinding portland clinker with a necessary gypsum
content and:
• Blast furnace slag
(comply with TCVN 4315 : 2007)
• Other mineral additives
(comply with TCVN 6882 : 2001)
2. Classification
Low heat blended portland cement is classified into
2 types: PCBMH, PCBLH
• PCBMH is defined sign of moderate heat of
hydration blended portland cement, it consists:
PCBMH30, PCBMH40
• PCBLH is defined sign of Low heat of hydration
blended portland cement, it consists: PCBLH30,
PCBLH40
• 30 and 40 is the minimum compressive strength
of standard mortar sample at 28 days in MPa
(testing method complies with TCVN 6016)
3. Physical Specification
Level
No
Characteristics
Unit
Requirement
Test method
30
1
Heat of hydration
- 7 days
- 28 days
2
Compressive strength
-7 days
-28 days
3
Setting time
- Initial set
- Final set
4
5
kJ/kg
(cal/g)
max
max
TCVN
6070:2005
MPa
min
min
TCVN
6016:1995
minute
min
max
TCVN
6017:1995
Fineness
- Retained content on
sieve 0.08mm
%
max
- Specific surface-Blaine
cm2/g
min
%
max
The expansion by
autoclave method
TCVN
4030 :2003
Low heat
PCBLH
Moderate heat
PCBMH
40
30
290 (70)
335 (80)
18
30
250 (60)
290 (70)
24
40
18
30
45
375
10
2800
TCVN
7711 :2007
40
0.8
24
40
Chapter IV: Overview of cement & concrete standards
A. Cement/ American standard - ASTM
83
AMERICAN STANDARD – ASTM
STANDARD PERFORMANCE SPECIFICATION FOR HYDRAULIC CEMENT
ASTM C1157: 2008 (Old version: ASTM C1157: 2002)
1. Composition
Blended hydraulic cement – a hydraulic cement consisting of two or more inorganic ingredients which
contribute to the strength-gaining properties of the cement, which or without other ingredients, processing
additions, and functional additions
2. Classification
No
Type of Cement
1
Type GU
Hydraulic cement for general construction.
Use when one or more of the special types are not required
2
Type HE
High early strength
3
Type MS
Moderate sulfate resistant
4
Type HS
High sulfate resistant
5
Type MH
Moderate heat of hydration
6
Type LH
Low heat of hydration
3. Physical Specification
No
Cement type
Unit
Requirement
Test methods
GU
HE
MPa
min
ASTM C109/
C109M
13
-
10
20
-
MS
HS
MH
LH
-
-
11
11
-
290
250
0.05
-
-
Strength range
1
- 1 day
- 3 days
- 7 days
2
3
- 28 days
Autoclave length
change
Time of setting,
Vicat test
- Initial
28
%
max
ASTM C151
minute
min
max
ASTM C191
max
ASTM C186
max
ASTM C1038
- Initial
4
Heat of hydration
- 7 days
5
6
- 28 days
Mortar bar
expansion 14 days
Sulfate expansion
(sulfate resistant)
- 6 months
- 1 year
“-” : Not required
kJ/kg
%
max
max
-
11
11
-
-
25
18
18
5
-
-
21
0.8
45
420
max
%
-
17
-
-
ASTM C1012
-
-
-
-
-
-
290
0.02
-
-
-
-
0.1
-
0.1
-
-
84
Chapter IV: Overview of cement & concrete standards
A. Cement/ American standard - ASTM
PORTLAND CEMENT – SPECIFICATIONS
ASTM C150: 2011 (Old version: ASTM C150: 2007)
1. Classification
• Portland cement – a hydraulic cement produced by pulverizing clinker consisting essentially of hydraulic
calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground
addition.
• There are five types of portland cement in this specification.
No
Type of cement
1
Type I
For use when the special properties specified for any other type are not required
2
Type II
For general use, more especially when moderate sulfate resistant
or moderate heat of hydration is desired
3
Type III
For use when high early strength is desired
4
Type IV
For use when a low heat of hydration is desired
5
Type V
For use when high sulfate resistance is desired
When air-entraining is desired, cement type IA, IIA and IIIA are specified
2. Physical specification
No
1
Characteristics
Air content of mortar,
volume
Fineness, specific surface
2
Unit
Requirement
Test methods
I
II
III
IV
V
%
max
ASTM C185
12
12
12
12
12
-
-
-
-
-
150
150
-
150
150
min
m /kg
2
min
- Turbidiameter test
max
min
- Air permeability test
3
245
ASTM C204
Autoclave expansion
%
Compressive strength
MPa
max
- 7 days
ASTM C151
- 28 days
5
-
260
260
0.8
0.8
0.8
0.8
0.8
-
-
12
-
-
12
10
24
-
8
19
17
-
7
15
-
-
-
17
21
45
45
45
45
45
375
375
375
375
375
minute
- Vicat test
- Time of setting
min
- Time of setting
max
“-” : Not required
260
430
ASTM
C109/C109M
- 3 days
Time of setting
260
max
- 1 day
4
ASTM C115
ASTM C191
Chapter IV: Overview of cement & concrete standards
A. Cement/ American standard - ASTM
85
3. Chemical specification
No
Characteristics
Unit
Requirement
Test methods
I
II
III
IV
V
1
Aluminum Oxide (Al2O3)
%
max
ASTM C114
-
6.0
-
-
-
2
Ferric oxide (Fe2O3)
%
max
ASTM C114
-
6.0
-
6.5
-
3
Magnesium oxide (MgO)
%
max
ASTM C114
%
max
ASTM C563
6.0
Sulfur trioxide (SO3)
4
- When (C3A) is 8% or less
- When (C3A) is more than 8%
3.0
3.0
3.5
2.3
2.3
3.5
-
4.5
-
-
3.0
3.0
3.0
2.5
3.0
5
Loss on ignition
%
max
ASTM C114
6
Insoluble residue
%
max
ASTM C114
7
Tricalcium silicate (C3S)
%
max
ASTM C114
-
-
-
35
-
8
Dicalcium silicate (C2S)
%
min
ASTM C114
-
-
-
40
-
9
Tricalcium aluminate (C3A)
%
max
ASTM C114
-
8
15
7
5
10
(C4AF+2(C3A))content or
(C4AF+C2F), as applicable
%
max
ASTM C114
-
-
-
-
25
0.75
86
Chapter IV: Overview of cement & concrete standards
A. Cement/ European standard - EN
EUROPEAN STANDARD – EN
COMPOSITION, SPECIFICATIONS AND CONFORMITY CRITERIA
FOR COMMON CEMENTS
EN 197-1: 2011 (Old version EN 197-1:2000)
2. Classification:
Standard strength : 1. Composition
Depend on type of cement, which cement comply
with EN standard can consist of different main
constituents as:
• Portland cement clinker
• Blast furnace slag
• Pozzolan
• Fly ash
• Burnt shale
• Limestone
• Silica fume
Beside the minor additional constituents can be
used to improve the physical properties of the
cement.
• There are 3 classes of standard strength at 28
days: class 32,5 class 42,5 and class 52,5.
• Three early strength classes are provided for
each class of standard strength.
- Class with ordinary early strength, indicated by N.
- Class with high early strength, indicated by R.
- Class with low early strength, indicated by L.
3. Physical Specification
No
Characteristics
Early strength
(MPa)
1
Standard
strength (MPa)
Test
methods
Cement
Type (1)
2
days
7
days
EN 196-1
All
28
days
Requirements
Strength class
32.5N
32.5R
32.5L*
42.5N
42.5R
42.5L*
52.5N
52.5R
52.5L*
-
≥ 10.0
-
≥ 10.0
≥ 20.0
-
≥ 20.0
≥ 30.0
≥ 10.0
≥ 16.0
-
≥ 12.0
-
-
≥ 16.0
-
-
-
≥ 32.5
≥ 42.5
≥ 52.5
≤ 52.5
≤ 62.5
-
2
Initial setting time
(min)
EN 196-3
All
3
Soundness /Expansion
(mm)
EN 196-3
All
≤ 10
LH
≤ 270
4
Heat of hydration(J/g)
EN 196-8
at 7 days
EN 196-9
at 41 h
≥ 75
≥ 45
(1): Types of cement were given below about the composition of each of the 27 products in the family of common cements
(*): Strength class only defined for CEM III cements.
Chapter IV: Overview of cement & concrete standards
A. Cement/ European standard - EN
87
4. Chemical Specification
No
Characteristics
Test reference
Cement
type
Requirements
Strength class
32.5N
32.5R
42.5N
42.5R
1
Loss on ignition
(% by mass)
EN 196-2
CEM I
CEM III
≤ 5%
2
Insoluble residue
(% by mass)
EN 196-2
CEM I
CEM III
≤ 5%
3
4
5
Sulfate content
(as %SO3 by mass)
Chloride content
(% by mass)
Pozzolanicity
EN 196-2
CEM I
CEM II (1)
CEM IV
CEM V
≤ 3.5%
52.5N
52.5R
≤ 4.0%
CEM III (2)
≤ 4.0%
EN 196-2
All (3)
≤ 0.1% (4)
EN 196-5
CEM IV
Satisfies the test
Cement type CEM II/B-T may containt up to 4.5 % sulfate for all strength classes.
Cement type CEM III/C may containt up to 4.5% sulfate.
(3)
Cement type CEM III may containt more than 0.1 % chloride but in that case the maximum chloride content
shall be stated on the packaging and/or the delivery note.
(4)
For pre-stressing applications cements may be produced according to a lower requirement. If so, the value
of 0.1% shall be replaced by this lower value which shall be stated in the delivery note.
(1)
(2)
Chapter IV: Overview of cement & concrete standards
A. Cement/ European standard - EN
The composition of each of the 27 products in the family of common cements
The 27 products in family of common cements
Composition [percentage by mass (a)]
CEM I
Main types
Main constituents
(types of common cement)
Portland
cement
Portland-slag
cement
Portlandsilicafume
cement
CEM II
Portlandpozzolana
cement
Portland-fly
ash cement
Portland
-burnt shale
cement
Portland
limestone
cement
CEM III
Blast furnace
cement
CEM IV
Portlandcomposite
cement (c)
Pozzolanic
cement (c)
Composite
cement (c)
Clinker
Slag
Silica
fume
Pozzolana
(b)
Natural
Natural
calcined
Fly ash
Burnt shale
Limestone
Siliceous Calcareous
Minor additional
constituents
Notation of the 27 products
CEM V
88
K
S
DM
P
Q
V
W
T
L
LL
CEM I
95-100
-
-
-
-
-
-
-
-
-
0-5
CEM II/A-S
80-94
6-20
-
-
-
-
-
-
-
-
0-5
CEM II/B-S
65-79
21-35
-
-
-
-
-
-
-
-
0-5
CEM II/A-D
90-94
-
6-10
-
-
-
-
-
-
-
0-5
CEM II/A-P
8 -94
-
-
6-20
-
-
-
-
-
-
0-5
CEM II/B-P
65-79
-
-
21-35
-
-
-
-
-
-
0-5
CEM II/A-Q
80-94
-
-
-
6-20
-
-
-
-
-
0-5
CEM II/B-Q
65-79
-
-
-
21-35
-
-
-
-
-
0-5
CEM II/A-V
80-94
-
-
-
6-20
-
-
-
-
0-5
CEM II/B-V
65-79
-
-
-
-
21-35
-
-
-
-
0-5
CEM II/A-W
80-94
-
-
-
-
-
6-20
-
-
-
0-5
CEM II/B-W
65-79
-
-
-
-
-
21-35
-
-
-
0-5
CEM II/A-T
80-94
-
-
-
-
-
-
6-20
-
-
0-5
CEM II/B-T
65-79
-
-
-
-
-
-
21-35
-
-
0-5
CEM II/A-L
80-94
-
-
-
-
-
-
-
6-20
-
0-5
CEM II/B-L
65-79
-
-
-
-
-
-
-
21-35
-
0-5
CEM II/A-LL
80-94
-
-
-
-
-
-
-
-
6-20
0-5
CEM II/B-LL
65-79
-
-
-
-
-
-
-
-
21-35
0-5
CEM II/A-M
80-88
<------------------------------ 12-20 ------------------------------>
0-5
CEM II/B-M
65-79
<------------------------------ 21-35 ------------------------------>
0-5
CEM III/A
35-64
36-65
-
-
-
-
-
-
-
-
0-5
CEM III/B
20-34
66-80
-
-
-
-
-
-
-
-
0-5
CEM III/C
5-19
81-95
-
-
-
-
-
-
-
-
0-5
CEM IV/A
65-89
-
<------------------ 11-35 ----------------->
-
-
-
0-5
CEM IV/B
45-64
-
<------------------ 36-55 ----------------->
-
-
-
0-5
CEM V/A
40-64
18-30
-
<---------- 18-30 ---------->
-
-
-
-
0-5
CEM V/B
20-38
31-50
-
<---------- 31-49 ---------->
-
-
-
-
0-5
:The values in the table refer to the sum of the main and minor additional constituents.
:The proportion of silica fume is limited to 10 %
(c)
:In portland-composite cement CEM II/A-M and CEM II/B-M, in pozzolanic cement CEM IV/A and CEM IV/B and in composite cements CEM
V/A and CEM V/B the main constituents other than clinker shall be declared by designation of the cement.
(a)
(b)
B. Concrete
89
VIETNAMESE STANDARD - TCVN
I. Workability
1. Classification (TCXDVN 374:2006)
Method of testing workability
Grade of fresh concrete
in workability
Plasticity (mm)
Vebe (second)
TCVN 3107 : 1993
Slump test (mm)
TCVN 3106 : 1993
Flow test (mm)
TCVN 3106 : 1993
Super dry concrete
SC
> 50
-
-
Dry concrete
C4
31-50
-
-
C3
21-30
-
-
C2
11-20
-
-
C1
5-10
-
-
Plastic concrete
D1
≤4
10-40
-
D2
-
50-90
-
D3
-
100-150
-
D4
-
160-220
260-400
2. Specification requirement (TCXDVN 374:2006)
Acceptable deviation for workability of fresh concrete
Grade of fresh concrete in
workability
Maximum acceptable deviation compared to required value
Lower limit
Upper limit
SC
- 20 seconds
-
C4
- 15 seconds
+ 10 seconds
C3 – C1
- 10 seconds
+ 5 seconds
D1 – D2
- 10mm
+ 20mm
D3 – D4
- 20mm
+ 30mm
90
Chapter IV: Overview of cement & concrete standards
B. Concrete/ Vietnamese standard - TCVN 374:2006
II. Compressive strength
Concrete with density (from 1800 – 2500 kg/m3)
1. Grade of hardened concrete
• Definition (TCXDVN 239:2006)
The grade of concrete in compressive strength is the mean compressive strength in MPa, tested on 150 x
150 x 150mm cube samples, which are casted, compacted, cured and tested complying with the standard
at the age of 28 days. Grade of concrete is prefixed with letter “M”.
• Designed Grade: M100, M150, M200, M250, M300, M400, M500, M600 (if higher strength of construction
is required, higher design grade (Ex: M700, M800) is accepted.)
2. Class of hardened concrete
• Definition (TCXDVN 356:2005 & TCXDVN 239:2006)
Class of Concrete in compressive strength is the compressive strength of concrete which the reliable
probability is 0.95. Class of concrete is prefixed with letter “B”.
B = M (1 – 1.64v)
With:
v – Standard deviation
When the variable strength coefficient can not be determined and the quality of concrete is accepted at
medium level, v = 0.135 (TCXDVN 356:2006), then B = 0.778M. Correlation between B and M comply with
TCXDVN 356:2006:
Class of
concrete
Average compressive
strength of standard
sample, MPa
Grade of
concrete
Class of
concrete
Average compressive
strength of standard
sample, MPa
Grade of
concrete
B3.5
B5
B7.5
B10
B12.5
B15
B20
B22.5
B25
B27.5
B30
4.50
6.42
9.63
12.84
16.05
19.27
25.69
28.90
32.11
35.32
38.53
M50
M75
M100
M150
M150
M200
M250
M300
M350
M350
M400
B35
B40
B45
B50
B55
B60
B65
B70
B75
B80
44.95
51.37
57.80
64.22
70.64
77.06
83.48
89.90
96.33
102.75
M450
M500
M600
M700
M700
M800
M900
M900
M1000
M1000
3. Assessment
Concrete which is considered to meet the required grade of concrete (M) must satisfy 2 below conditions:
• The mean compressive strength of one set (3 samples) is not less than designed grade of concrete
• Strength of each sample in set is not less than 85% designed grade of concrete
•
•
Concrete which is considered to meet the required class of concrete (B) must satisfy 2 below conditions
at once:
• With the initial period or without standard deviation:
- The mean compressive strength of one set (3 samples) is not less than 1.3 times designed
class of concrete (MPa)
- Strength of each sample in set is not less than 1.1 times designed class of concrete (MPa)
• In case standard deviation (v) is able to be determined:
- The mean compressive strength of one set (3 samples) is not less than:
B
MPa
1 - 1,64v
- Strength of each sample in set is not less than:
0.85
B
MPa
1 - 1,64v
Chapter IV: Overview of cement & concrete standards
B. Concrete/ American standard - ASTM C94
AMERICAN STANDARD – ASTM
I. Workability (ASTM C94)
Tolerances in slump
Specified slump
If 75 mm or less
If more than 75mm
Plus tolerance
0
0
Minus tolerance
40mm
65mm
Tolerances for normal slumps
For specified slump of
Tolerance
50mm and less
+/- 15 mm
More than 50 to 100mm
+/- 25 mm
More than 100 mm
+/- 40 mm
II. Compressive strength
1. Requirement of design compressive strength
The strength is determined by a test on cylinder specimens (150x300 mm) at 28 days after sampling, curing
according to ASTM C31.
Due to variations in materials, operations, and testing, the average strength necessary to meet these
requirements will be substantially higher than the specified strength. This higher strength amount depends
upon the standard deviation of the test results and the accuracy with which that value can be estimated
from prior data as explained in ACI 318 and ACI 301.
Appendix part of this standard give the guide to calculate the average strength, necessary to meet the
specification:
A. When historical statistical data are available
Specified strength
f ‘c, MPa
f ‘c equal to
or less than 35
Greater than 35
Required average strength
f ‘cr, MPa (use the larger from 2 formulas)
f ‘cr = f ‘c + 1.34s
(*)
f ‘cr = f ‘c + 2.33s – 3.45 (**)
f’cr = f ‘c + 1.34s
f ‘cr = 0.90f ‘c + 2.33s
(*)
(***)
With:
• f ‘c = the specified compressive strength
• f ‘cr = the required average compressive strength
• s = the standard deviation
(*): Formula to achieve the satisfactory average of three consecutive strength tests.
(**), (***): Formulas for the minimum strength test result of an individual strength test (average of two
cylinders test) result.
91
92
Chapter IV: Overview of cement & concrete standards
B. Concrete/ American standard - ASTM C94
B. When a new mix design or strength level and no standard deviation data is available. Required average
strength for mix design
Specified strength
f ‘c, MPa
Required average strength
f ‘cr, MPa
Less than 21
f ‘cr = f ‘c + 7
21 to 35
f’cr = f ‘c + 8.5
Greater than 35
f’cr = 1.1f ‘c + 5
C. When having selected standard deviations and specified strength levels
f’c, MPa
specified
strength
Less than 21
21.0
35.0
50.0
60.0
75.0
90.0
100.0
120.0
Standard deviation from fields data, MPa
2.0
3.5
5.0
6.0
7.5
No SD data
unknown
35
49
62
71
85
100
110
130
f’c + 7
29.5
43.5
60.0
71.0
87.5
105.0
115.0
137.0
f’cr, required average strength, MPa
24
38
53
63
78
93
108
128
26
40
55
65
80
95
105
125
29
43
57
67
82
97
107
127
32
46
59
68
83
98
108
128
Bold numbers identify levels of specified strength where the standard deviation should be considered
unusual or inappropriate.
2. Strength assessment (ASTM C94)
Assess compressive strength
The average of 3 consecutive strength tests shall be equal to or greater than specific strength – f 'c
- If f 'c < 35 MPa: individual strength test ( average of two cylinder tests) ≥ f'c-3.5(MPa)
- If f 'c > 35 MPa: individual strength test (average of two cylinder tests) ≥ 0.9f 'c
Chapter IV: Overview of cement & concrete standards
B. Concrete/ European standard - EN 206-1:2000
93
EUROPEAN STANDARD – EN 206-1:2000
I. Workability
Workability
Test methods
Requirement
Slump
EN 12350-2
≥ 10 mm and ≤ 210mm
Vebe
EN 12350-3
≤ 30 sec and > 5sec
Degree of compactability
EN 12350-4
≥ 1.04 and < 1.46
Flow table
EN 12350-5
> 340mm and ≤ 620mm
The consistence of concrete is classified, Tables 1,2,3 or 4 apply.
Note: the classes of consistence in Tables 1 to 4 are not directly related. In special cases, consistence may also be
specified by target value. For earth moist concrete, i.e concrete with low water content designed to be
compacted in special processes, the consistence is not classified.
Table 1:
Slump classes
Table 2:
Vebe classes
Table 3:
Compaction classes
Table 4:
Flow diameter in mm
Class
Flow diameter
in mm
Class
Slump in mm
Class
Vebe time in
seconds
Class
Degree of
compactability
F1
≤ 340
S1
10 to 40
V0
≥ 31
C0
≥ 1.46
F2
350 to 410
S2
50 to 90
V1
30 to 21
C1
1.45 to 1.26
F3
420 to 480
S3
100 to 150
V2
20 to 11
C2
1.25 to 1.11
F4
490 to 550
S4
160 to 210
V3
10 to 6
C3
1.10 to 1.04
F5
560 to 620
S5
≥ 220
V4
5 to 3
F6
≥ 630
The consistence may be specified either by reference to a consistence class according to table 1, 2,3 and 4 or,
in special cases, by a target value. For target values, the related tolerances are given in table 5.
Table 5: Tolerances for target values of consistence
Slump
Target value in mm
≤ 40
50 to 90
≥ 100
Tolerance in mm
± 10
± 20
± 30
Target value in sec
≥ 11
10 to 6
≤5
Tolerance in sec
±3
±2
±1
Target value
≥ 1.26
1.25 to 1.11
≤ 1.10
Tolerance
± 0.10
± 0.08
± 0.05
Vebe time
Degree of compact ability
Flow diameter
Target value in mm
Tolerance in mm
All values
± 30
94
Chapter IV: Overview of cement & concrete standards
B. Concrete/ European standard - EN 206-1:2000
II. Compressive strength
The strength is to be determined on test carried out either 150 mm cubes or 150/300 mm cylinders
conforming to EN 12390-1 and made and cured in accordance with EN 12390-2 from samples taken in
accordance with EN 12350-1.
The compressive strength is determined on specimens tested at 28 days. For particular uses, it may be
necessary to specify the compressive strength at ages earlier or later than 28 days or after storage under
special conditions.
The characteristic strength of concrete shall be equal to or greater than the minimum characteristic
compressive strength for the specified compressive strength class, see tables below.
Compressive strength class for normal-weight and heavy-weight concrete
Compressive
strength class
Minimum characteristic cylinder
strength
fck, cylinder
(N/mm2)
Minimum characteristic cube
strength
fck, cube
(N/mm2)
C8/10
8
10
C12/15
12
15
C16/20
16
20
C20/25
20
25
C25/30
25
30
C30/37
30
37
C35/45
35
45
C40/50
40
50
C45/55
45
55
C50/60
50
60
C55/67
55
67
C60/75
60
75
C70/85
70
85
C80/95
80
95
C90/105
90
105
C100/115
100
115
• Strength assessment
Assess compressive strength
- Criteria 1 (rolling average)
:
favg ≥ fck + 4
- Criteria 2: (individual sample) :
f ≥ fck - 4
With:
fck: specific strength of concrete.
favg: The average strength of all valid samples.
f: Any individual test result.
Chapter IV: Overview of cement & concrete standards
B. Concrete/ British standard - BS 5328
95
BRITISH STANDARD – BS 5328
From December 2003, the standards BS-EN 206-1 and BS 8500 replace the BS 5328 series of standards.
However, some projects in Vietnam still refer to BS 5328, to specify concrete.
I. Workability
• Guidance on the workability appropriate to different uses
Workability suitable for different uses of concrete
Use of concrete
Form of compaction
Pavement placed by power operated
machines
Heavy vibration
Kerb bedding and backing
Floors and pavements not placed by
power-operated machinery
Workability
Nominal Slump (1)
mm
Very low
See NOTE 1
Low
50
Medium
75
High
125
Very high
See NOTE 2
Tamping
Poker or beam vibration
Strip footings
Mass concrete foundations
Blinding
Normal reinforced concrete in slabs,
Poker or beam vibration
beam, walls and columns
and/ or tamping
Sliding formwork construction
Pumped concrete
Vacuum processed concrete
Domestic general purpose concrete
Trench fill
In situ piling
Self-weight compaction
Concrete sections containing
congested reinforcement
Poker
Diaphragm walling
self-levelling super plasticized
concrete
Self-levelling
(1) Cohesive mixes may give adequate place ability at lower values of slump than those given here.
NOTE 1. In the "very low" category of workability where strict control is necessary, e.g. pavement quality
concrete placed by "trains", measurement of workability by determination of compacting factor or Vebe
time (see BS 1881:parts 103 and 104) will be more appropriate than slump.
NOTE2. In the "very high" category of workability, measurement and control of workability by
determination of flow is appropriate (see BS 1881: part 105).
96
Chapter IV: Overview of cement & concrete standards
B. Concrete/ British standard - BS 5328
II. Compressive strength
Compressive strength grade of hardened concrete:
The strength is tested with cube specimens at 28 days made to the requirement of BS 1881. The strength
grade of concrete should be selected from table below as appropriate. Minimum grades for particular types
of work such as reinforced concrete, pre-stressed concrete and for durability under particular environmental
conditions are given in the appropriate code of practice.
Grade of hardened concrete
Grade
Characteristic compressive strength at 28 days
MPa
C7.5
7.5
C10
10
C15
15
C20
20
C25
25
C30
30
C35
35
C40
40
C45
45
C50
50
C55
55
C60
60
• Strength assessment
Assess compressive strength
Criteria 1
Criteria 2
Average strength of
samples,
favg (MPa)
Any individual test
result, f (MPa)
C20 to above
First 2 samples
First 3 samples
Any 4 consecutive
samples
favg ≥ fck + 1
favg ≥ fck + 2
favg ≥ fck + 3
f ≥ fck - 3
f ≥ fck - 3
f ≥ fck - 3
C7.5 to C15
First 2 samples
First 3 samples
Any 4 consecutive
samples
favg ≥ fck
favg ≥ fck + 1
favg ≥ fck + 2
f ≥ fck - 2
f ≥ fck - 2
f ≥ fck - 2
Specified grade
Group of samples
fck : specific strength of concrete.
C. Recommendation for limiting
values of concrete composition
These two table provide recommendations for the choice of the limiting values of concrete composition and
properties in relation to exposure classes. The values recommended below, are based on the assumption of
an intended working of the structure of 50 years.
CHLORIDE - INDUCED CORROSION IN SEA WATER
(EN 206-1:2000)
Exposure Classes of Chloride – induced corrosion in sea water
Maximum w/c
Minimum Strength Class
Minimum cement
content (kg/m3)
XS1
XS2
XS3
0.50
0.45
0.45
C30/37
C35/45
C35/45
300
320
340
XS1 - Exposure to airborne salt but not in direct contact with sea water
XS2 - Permanently submerged
XS3 - Tidal, splash and spray zones
AGGRESSIVE CHEMICAL ENVIRONMENTS
(EN 206-1:2000)
Exposure Classes – Aggressive chemical environments
Maximum w/c
Minimum Strength Class
Minimum cement
content (kg/m3)
XA1
XA2
XA3
0.55
0.50
0.45
C30/37
C35/45
C35/45
300
320
360
Other requirements
Sulfate-resisting cement *
XA1 - Slightly aggressive chemical environment
XA2 - Moderately aggressive chemical environment
XA3 - Highly aggressive chemical environment
* When SO2 leads to exposure classes XA2 and XA3, it is essential to use sulfate-resisting cement. Where
4
cement is classified with respect to sulfate resistance, moderate or high sulfate-resisting cement should be
used in exposure class XA2 (and exposure class XA1 when applicable) and high sulfate-resisting cement should
be use in exposure class XA3.
97
98
Reference
A. Components of concrete:
Cement
Specific requirement
Cement Type
Vietnamese standard
American Standard
European Standard
Portland Cement
TCVN 2682: 2009
ASTM C150
EN 197
Portland Blended cement
TCVN 6260: 2009
ASTM C1157
EN 197
Sulfate resistance Portland Cement
TCVN 6067: 2004
ASTM C150
BS 4027
Sulfate resistance Blended Portland Cement
TCVN 7711:2007
ASTM C1157
EN 197
Low Heat Blended Portland Cement
TCVN 7712: 2007
ASTM C1157
-
Blast Furnace Slag Portland Cement
TCVN 4316: 2007
-
EN 197
Characteristic
Vietnamese Standard
American Standard
European Standard
Compressive strength
TCVN 6016:1995
ASTM C109
EN 196-1
Setting time
TCVN 6017:1995
ASTM C191
EN 196-3
Fineness
TCVN 4030:2003
ASTM C115
ASTM C204
Soundness
TCVN 6017:1995
Autoclave expansion
TCVN 7711:2007
Test methods of physical characteristics
EN 196-3
ASTM C151
The expansion of mortar in sulfate solution after
TCVN 7713:2007
6 months and 1 year
ASTM C1012
-
The expansion of mortar bar in water after 14
days
TCVN 6068: 2004
ASTM C1038
-
Heat of hydration
TCVN 6070: 2005
ASTM C186
EN 196-8
EN 196-9
Chemical analysis
TCVN 141: 2008
ASTM C114
EN 196-2
Vietnamese Standard
American Standard
Grading
TCVN 7572-2:2006
ASTM C136
Organic impurities
TCVN 7572-9: 2006
ASTM C40
Material finer than 75 μm
TCVN 7572-8: 2006
ASTM C117
Potential Alkali Reactivity
TCVN 7275-14:2006
ASTM C227
ASTM C289
ASTM C1260
Grading
TCVN 7572-2:2006
ASTM C136
Specific gravity
TCVN 7572-4:2006
ASTM C127
Bulk density and moisture content
TCVN 7572-6:2006
ASTM C29
Elongation and flakiness index
TCVN 7572-13:2006
-
Water
Specific requirement: TCXDVN 302:2004, ASTM C1602
Admixture
Specific requirement: TCVN 8826:2011, ASTM C494
Aggregate
Specific requirement: TCVN 7570: 2006, ASTM C33
Test methods
Characteristic
Fine aggregate
Coarse aggregate
Cement & Concrete
Reference
99
B. Concrete
Specification for ready-mix concrete: TCXDVN 374:2006, ASTM C94, EN 206-1:2000
Test Methods
Characteristic
Vietnamese Standard
American Standard
European Standard
Slump
TCVN 3106:1993
ASTM C143
EN 12350-2
Slump flow
-
ASTM C1611
EN 12350-8
Vebe Test
TCVN 3107:1993
ASTM C1170
EN 12350-3
Density
TCVN 3108:1993
ASTM C138
EN 12350-6
Air content
TCVN 3111:1993
ASTM C231
-
Setting time
-
ASTM C403
-
Making and curing sample
TCVN 3105:1993
ASTM C31
EN 12390-2
Compressive strength
TCVN 3118:1993
ASTM C39
EN 12390-3
Bleeding
TCVN 3109:1993
ASTM C232
-
Permeability to water
TCVN 3116:1993
-
-
Permeability to Chlorides
TCXDVN 306:2005
ASTM C1202
-
Fresh concrete
Hardened concrete
Other standards for concrete
Specification for mass concrete
TCXDVN 305: 2004
Concrete and reinforced concrete structureDesign standard
TCXDVN 306:2005
BS 8110
C. Cement treated aggregate
Specific requirement: 22 TCN 245, 22TCN 246
Test Methods
Characteristic
Vietnamese Standard
American Standard
European Standard
22 TCN 333-06
ASSHTO T180
ASSHTO T99
-
22 TCN 246
ASTM D1632
ASTM D55
-
Workability period
-
-
EN 13286-45
Unconfined strength
-
ASTM D1633
-
Optimal moisture& max dry density
Making compressive strength sample
D. Other relevant sources
Concrete Practice: Holcim (Schweiz) AG
Concrete Practice: Holcim Sri Lanka
100
Cement & Concrete
Reference
E. Source of figures
Figure number
Source
Figure: Fig I.1, Fig I.2, Fig I.3, Fig I.5, Fig I.6, Fig I.7, Fig I.9, Fig I.11, Fig I.12, Fig I.13,
Fig I.15, Fig I.16, Fig I.21, Fig I.22, Fig I.23, Fig I.24, Fig I.25, Fig I.26, Fig I.27, Fig I.30,
Fig I.31, Fig I.32, Fig I.33, Fig I.34, Fig I.35, Fig I.36, Fig I.37, Fig I.38, Fig I.39, Fig I.40,
Fig I.41, Fig I.42, Fig I.43,Fig I.44, Fig I.45, Fig I.46, Fig I.47, Fig I.48, Fig I.49, Fig I.50,
Fig I.51, Fig I.52, Fig I.53, Fig I.55, Fig I.56, Fig I.58, Fig I.60, Fig I.61, Fig I.62, Fig II.1,
Fig II.2, Fig II.3, Fig II.4, Fig II.5, Fig II.6, Fig II.7, Fig II.8, Fig II.9, Fig II.10, Fig II.11, Fig II.12,
Fig II.13, Fig II.14, Fig II.15, Fig II.16, Fig II.17, Fig II.18, Fig II.19, Fig II.20, Fig II.21, Fig II.22,
Fig II.23, Fig III.1, Fig III.3, Fig III.4, Fig III.5, Fig III.6, Fig III.7, Fig III.8, Fig III.9, Fig III.10,
Fig III.11, Fig III.14, Fig III.15, Fig III.16, Fig III.18
Holcim Vietnam
Fig I.4, Fig I.8, Fig I.10, Fig I.65, Fig III.17
Holcim Swiss
Fig I.14, Fig I.17, Fig I.18, Fig I.19, Fig I.20, Fig I.28, Fig I.29, Fig I.63, Fig I.64, Fig I.66, Fig
I.67, Fig I.68, Fig I.69, Fig I.70, Fig I.71, Fig I.72, Fig I.73, Fig I.74, Fig III.2, Fig III.12, Fig
III.13, Fig III.20, Fig III.21
Holcim Sri Lanka
Fig I.54, Fig III.19
Antoine Carnot
Fig I.57, Fig I.59
Lubica Pistanska
101
102
Holcim (Vietnam) Ltd.
Fideco Tower, 9th & 10th Floors
81 - 85 Ham Nghi Street, District 1
Ho Chi Minh City, Vietnam
Phone: +84 8 39149000
Fax: +84 8 39149001
Email: technical.service-vnm@holcim.com
Website: www.holcim.com.vn
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