Use of the Falling-Head Method to Assess Permeability of
Freshly Mixed Cementitious-Based Materials
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Joseph J. Assaad 1 and Jacques Harb 2
Abstract: The falling-head method determined using a permeameter cell is commonly used to study permeability (k) of soils and facility of
fluids to travel through a solid skeleton. A research program was undertaken to evaluate the suitability of such test for assessing permeability
of freshly mixed mortars and concrete. Validation of k values with respect to bleeding and surface settlement responses and correlations
with permeability calculated using empirical soil models are established. The falling-head method was found appropriate to assess the
effect of mixture composition (i.e., binder content, water-to-cement ratio, and chemical/mineral admixtures) on permeability variations.
Concrete incorporating coarse aggregates exhibited greater permeability levels than those determined on mortars. Despite the differences
in chemical nature between soil and mortar, the actual k values determined by testing were found to be well correlated to those calculated
by using several previously reported empirical soil models. DOI: 10.1061/(ASCE)MT.1943-5533.0000630. © 2013 American Society of
Civil Engineers.
CE Database subject headings: Mortars; Concrete; Permeability; Settlement; Soils; Cement.
Author keywords: Mortar; Concrete; Bleeding; Permeability; Settlement; Soil.
Introduction
Hydraulic conductivity or simply permeability (k) of freshly mixed
cementitious-based materials is a key indicator of hydromechanical
properties (i.e., static stability, pumping, formwork pressure, plastic
shrinkage) and their evolution with time. Several researchers reported that permeability of fresh concrete can be used to reflect
its ability to remain homogeneous during the pumping and forming
processes (Browne and Bamforth 1977; Perrot et al. 2009). Mixtures exhibiting lower levels of permeability were found to develop
better static stability including lower aggregate segregation and
bleeding, together with improved hardened properties such as
bonding to embedded reinforcement (Appleby and Wilson 1996;
Josserand et al. 2006). Moreover, permeability was reported to
largely influence lateral pressure developed by plastic concrete
on vertical formworks. Assaad et al. (2009b) found that concrete
proportioned with higher cement content and lower water-tocement ratio (w=c) reduced tendency of water to drain out of the
material, thus resulting in lower formwork pressure. In addition,
concrete permeability affects the rate of capillary pressure buildup during setting, and consequently the susceptibility against plastic shrinkage (Slowik et al. 2008).
The approach traditionally used to assess hydraulic conductivity
of fresh cementitious-based materials involves applying a given
pressure on top of the specimen and measuring the amount of
free mixing water that is squeezed out from the bottom surface.
1
Professor of Civil Engineering; R&D Manager, Holderchem Building
Chemicals, P.O. Box 40206, Lebanon (corresponding author). E-mail:
jassaad@ndu.edu.lb
2
Associate Professor and Chair, Dept. of Civil Engineering, Notre Dame
Univ., P.O. Box 72, Lebanon. E-mail: jharb@ndu.edu.lb
Note. This manuscript was submitted on October 3, 2011; approved on
June 28, 2012; published online on August 25, 2012. Discussion period
open until October 1, 2013; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil
Engineering, Vol. 25, No. 5, May 1, 2013. © ASCE, ISSN 0899-1561/
2013/5-580-588/$25.00.
The pressure may be induced by air or mechanical consolidation
using a compression machine. For example, Bolton and McKinley
(1997), Picandet et al. (2011), and Khayat et al. (2004) used air
pressures in the range of 5.1–58.4, 10–100, and 0–700 kPa, respectively, to evaluate filtration properties of cement paste and concrete
mixtures. Values of k in the order of 10−4 to 10−5 cm=s were derived from slurry mixtures made with various cement types and
w=c ranging from 0.6 to 1 (Bolton and McKinley 1997). Khayat
et al. (2004) found that the collected bleed water over a 10-min
filtration period is dependent on mixture composition and can
be directly related to permeability of fresh concrete deducted from
Darcy’s law.
Using the one-dimensional consolidation test, Uzomaka (1969)
reported that plastic concrete behaves similarly to remolded clay
soil of low compressibility. The derived k values were in the order
of 10−8 cm=s and largely influenced by the mixture composition.
Picandet et al. (2011) found that cement pastes with w=c varying
from 0.3 to 0.4 behave according to the soil consolidation theory
when tested using a displacement-controlled consolidometer.
The authors found that hydration of cement does not result in noticeable decrease in permeability of tested mixtures during the first
hour after mixing, and the k value is in the order of 10−5 to
10−6 cm=s. It is to be noted that the traditional approaches to evaluate k including the filtration and consolidation tests induce changes
in the materials porous network due to applied pressure gradients
(Picandet et al. 2011). This can result in higher effective stresses in
the lower part of the tested samples together with a decrease in the
void ratio due to forced consolidation and settlement.
Objectives of the Research Project
The notion of permeability has been mostly developed in soil mechanics to evaluate the ease with which fluid moves through the
tortuous path of a solid skeleton with interconnected voids (Das
2010). Such measurement can be used for stability analyses of earth
and retaining structures, and to estimate the quantity of underground seepage under various hydraulic conditions. The value
580 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013
J. Mater. Civ. Eng. 2013.25:580-588.
of k (cm=s) is basically deduced from the measured percolating
flow rate (Q, cm3 =s) through a specimen section (S, cm2 ) from
Darcy’s law as Q=S ¼ ki, where i denotes the vertical hydraulic
gradient (dimensionless).
Four empirical models developed by Hazen (1930), KozenyCarman (Kozeny 1927; Carman 1956), Amer and Awad (1974),
and Chapuis (2004) to estimate permeability of soils are given
in Eqs. (1)–(4), respectively.
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kðcm=sÞ ¼ CH × D210
ð1Þ
Eq. (1) is used for determining k in loose and clean sand, where
CH is a coefficient varying from 1 to 1.5, and D10 (mm) is the particle size for which 10% of the soil is finer.
2 3 2 1
100%
e
kðcm=sÞ ¼ 1.99 × 104 ×
× P
×
SF
½fi =DðavÞi 1þe
ð2Þ
where e = void ratio, SF = shape factor varying from 6 to 8
depending on the angularity of the individual soil particles, fi =
percent fraction of particles between two consecutive sieve sizes,
and DðavÞi = average particle size between consecutive sieves.
3 e
2.32
kðcm=sÞ ¼ 35 ×
ð3Þ
× C0.6
u × D10
1þe
Eq. (3) is used for estimating k in granular soil, where D10 is in
mm, e = void ratio, and Cu = coefficient of uniformity.
e3 0.7825
kðcm=sÞ ¼ 2.462 × D210 ×
ð4Þ
1þe
Eq. (4) is used for determining k in the range of 10−1 to
10 cm=s for natural uniform sand and gravel, but can be extended for natural silty sands without plasticity. Value of D10 is
in mm and e = void ratio.
During the dormant period of cement hydration, fresh mortars
or concrete behave as weakly bonded materials submerged in fluid
medium, and thus can be regarded as soil (Alexandridis and
Gardner 1981; Assaad and Harb 2011). Therefore, the main objective of this paper is to evaluate suitability of the permeameter test to
assess permeability of fresh mortars and concrete. Universally
available in most research centers, the permeameter test is standardized [ASTM D2434 (ASTM 2006); ASTM D5084 (ASTM
2010b)] and quite simple to be realized, thus unifying the characterization of permeability. Parameters tested included cement
content, w=c, coarse aggregate, and various concentrations of
high-range water reducer (HRWR), silica fume, calcium stearate,
and viscosity-modifying admixture (VMA). Validation and comparison of the investigated k values with theoretical models developed on soil are established. Such data are particularly useful for
researchers, concrete engineers, and contractors to standardize testing protocols and optimize the hydromechanical properties of
concrete.
−3
Experimental Program
Materials
Portland cement and silica fume conforming to ASTM C150 Type I
(ASTM 2012a) and ASTM C1240 (ASTM 2012b), respectively,
were used in this project. The surface area of the cement (Blaine)
and silica fume (BET) were 340 and 20,120 m2 =kg, respectively;
and their specific gravities were 3.14 and 2.22, respectively. The
cement had C3 S, C3 A, and Na2 Oeq . values of 60.4%, 6.6%, and
0.73%, respectively. Continuously graded ASTM C33 (ASTM
2011) crushed limestone aggregate with 20-mm nominal size
and well-graded siliceous sand with 4.75-mm nominal size were
used. The coarse aggregate and sand had fineness moduli of 6.4
and 2.5, respectively, and bulk specific gravities of 2.71 and
2.69, respectively.
A polycarboxylate-based HRWR conforming to ASTM C494
(ASTM 2012c) Type F was used; its solid content and specific
gravity were equal to 40% and 1.11, respectively. A powder welan
gum VMA was used; it was diluted in 5% mixing water before adding to mortar or concrete. A calcium stearate product intended to
impart water repellency and reduce efflorescence in cementitiousbased products was also used. It is a white powder compound of
calcium with fine mixture of solid organic acids and some fatty
acids obtained from edible sources, harmless to the environment,
having a bulk density of 0.38. Finally, a sodium gluconate-based
set-retarder was used to reduce workability loss during testing.
Mixture Proportions
As summarized in Table 1, four concrete series made with 300, 350,
400, and 450 kg=m3 of cement were investigated in this project.
The sand-to-total aggregate ratio remained fixed at 0.46. The
mortars were proportioned using the concrete-equivalent-mortar
(CEM) approach, i.e., same concrete compositions except that
the coarse aggregates were replaced by an equivalent quantity of
sand to take into consideration the amount of water that can be
absorbed onto their surfaces during mixing. More details on the
method for proportioning CEM mixtures can be seen in
Schwartzentruber and Catherine (2000) and Assaad et al. (2009a).
In each series, different combinations of w=c (0.35–0.65), silica
fume (0–10% of cement), calcium stearate (0–0.15% of cement),
and VMA (0–0.08% of cement) were tested. Unless otherwise
specified, the dosage of HRWR was adjusted to secure a concrete
slump of 180 10 mm according to ASTM C143 (ASTM 2012d)
or an equivalent CEM flow of 210 10 mm following five drops
on the flow table according to ASTM C1437 (ASTM 2007; Assaad
et al. 2009a). To minimize the effect of workability loss on permeability measurements during the first 30-min after mixing, the
set-retarder was used at dosages of 0.6% and 0.4% of the cement
weight in concrete and CEM mixtures, respectively.
Table 1. Mixture Composition of Evaluated Concrete and CEM
Series
Series
Series
Series
number 1 number 2 number 3 number 4
Type I cement (kg=m3 )
Silica fume (% of cement)
w=c
VMA (% of cement)
Calcium stearate (% of cement)
HRWR (% of cement)
Concrete mixture
Sand (0–4.75) (kg=m3 )
Coarse aggregate
(4.75–20) (kg=m3 )
Vol. sand/Vol. cement paste
Vol. coarse aggregate (L=m3 )
Sand/(sand+coarse aggregate)
Corresponding CEM mixture
Sand (0–4.75) (kg=m3 )
Vol. sand/Vol. cement paste
300
350
400
450
Varying from 0 to 10
Varying from 0.35 to 0.65
Varying from 0 to 0.08
Varying from 0 to 0.15
Various dosages to achieve
different consistencies
960
1,120
930
1,080
890
1,040
840
980
1.58
418
0.46
1.36
401
0.46
1.14
386
0.46
0.96
364
0.46
1,150
1.83
1,060
1.56
1,005
1.29
940
1.07
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Batching of Mixtures
Water standpipe,
Area a
The mixing procedure for the concrete consisted of homogenizing
the sand and coarse aggregate with half of the mixing water, then
introducing the cementitious materials gradually over 30 s. The remaining part of water along with the HRWR, prehydrated VMA,
calcium stearate, and set-retarder were then added and mixed for
1 min. After a rest period of 30 s, the concrete was remixed
for 2 additional min. The same mixing procedure was adopted
for the CEM, except that the coarse aggregates were removed from
the batch. Testing and sampling of all concrete and CEM mixtures
were made at room temperature of 23 2°C and 50% 5%
relative humidity. It is to be noted that all mortar and concrete
mixtures exhibited fresh air contents of 5.3% 0.8% and
2.3% 0.5%, respectively, which were determined according to
ASTM C231/C231M (ASTM 2010a) test method.
Inlet water
valve
L
where a (cm2 ) = cross-sectional area of the inlet water valve
(equal to 2.01 cm2 ), A (cm2 ) = cross-sectional area of specimen,
h2
Specimen,
Area A
Datum
Outflow
Permeability Testing of Mortars and Concrete
In general, permeability of soils is measured using a permeameter
test following either the constant-head or falling-head method. The
former method is recommended for coarse-grained soils where k is
expected to be smaller than 10−5 cm=s, or when the soil contains
90% or more particles that are retained on the 75-μm sieve (Das
2010). Conversely, the falling-head test is suited for testing finegrained soils where the k value is expected to be within the range
of 10−5 to 10−8 cm=s, or when the soil contains 10% or more particles passing the 75-μm sieve. Therefore, the falling-head method
was selected in this study for testing mortar and concrete materials
containing fine particles such as cement and silica fume.
A commercially available soil permeameter apparatus was used
for testing. Different steel-made cells having diameter/height dimensions of 102=105, 152=115, and 305=230 mm=mm were used
for this purpose. Their inner surfaces were coated with a thin layer
of specially made grease to reduce eventual water leakage along the
sides of the cell (Engineers Manual 1110-2-1901 1986). To avoid
entrapment of air, the tested material was well compacted using a
tamping device in three layers of approximately similar heights.
Two filter papers were placed between the upper and lower perforated plates and the tested material to retain approximately 96% of
all particles greater than 1 μm. De-aired distilled water at room
temperature was used during testing. This is essential to minimize
the amount of air dissolved in water, which can collect fine bubbles at the solid particles/water interface and reduce permeability (Engineers Manual 1110-2-1901 1986). More details on the
falling-head method determined on soils can be seen in various geotechnical books such as Das (2010).
The permeameter stand consisted of a metal frame with water
tank adjustable in height between 1,500 and 4,500 mm. This allows
monitoring the extent of hydraulic gradient (i) applied on top of the
tested specimen to values ranging from 10 to approximately 55.
The value of i is being calculated as the ratio of total head of water
under motion to the length of tested specimen. After opening the
inlet water valve on top of the cell, outflow is observed to ensure a
continuous flow regime (i.e., indicating complete saturation of the
tested specimen) where water constantly trickles out from the outflow valve (Fig. 1). The time needed to reach such regime varied
from 4 to 10 min, depending on mixture composition. After ensuring continuous flow, the value of k was determined as follows:
a L
h
kðcm=sÞ ¼ ×
ð5Þ
× ln 1
A Δt
h2
h1
Cylinder
Fig. 1. Sketch for the permeameter test, falling-head method
L (cm) = height of specimen, and Δt (s) = time needed for the total
head to drop from clearly marked graduations h1 to h2 (Fig. 1).
Generally, Δt in the range of 2–8 min was obtained throughout
testing to drop the level of water from h1 to h2 , again depending
on the mixture composition. The maximum total time that was
needed to prepare the mix (i.e., concrete or mortar), place in the
cell, ensure a continuous flow regime, and testing permeability
was less than approximately 25 min.
Bleeding and Surface Settlement of Tested Mortars
and Concrete
In addition to permeability, bleeding and surface settlement responses of tested materials were evaluated. Bleeding was determined according to ASTM C232/C232M (ASTM 2009) test
method, which involves measuring the relative quantity of mixing
water that has bled from the freshly cast material in a container. The
percent of bleeding water was obtained by dividing the collected
water by the total mixing water in the tested mortar or concrete
specimen.
Settlement of fresh mortars was determined using a traditional oedometer apparatus commonly used for measuring onedimensional consolidation of clays and other compressible soils
(Assaad and Harb 2011). Such test was found adequate to assess
settlement of cementitious-based materials made with different
compositions. The CEM sample having 71.4-mm diameter and
20-mm height was encased between fiber glass filters placed at
its top and bottom surfaces. The displacements were recorded using
a 0.002-mm dial gage after reaching a steady-state condition following the application of 2-kg normal load. As for the plastic concrete, surface settlement was determined using a polyvinyl chloride
(PVC) column measuring 200 mm in diameter and 600 mm in
height (Assaad et al. 2004). The settlement was monitored using
a 0.002-mm dial gage fixed on top of a thin acrylic plate placed
at the upper concrete surface until a steady-state condition is
reached. Assaad and Harb (2011) reported that concrete settlements
obtained from the PVC column can be well correlated to those
determined on CEM using the oedometer test.
582 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013
J. Mater. Civ. Eng. 2013.25:580-588.
Effect of Hydration Time
In order to determine the effect of hydration time on variations of
permeability, the k values were measured at different elapsed times
following initial mixing on several mortar and concrete mixtures.
The hydraulic gradient was fixed at 25 2. The specimen remained in the permeameter cell during testing, and the inlet water
valve opened to realize the measurement at specific time intervals,
and then closed back again. In parallel, the setting time was determined on a separate specimen by penetration resistance according
to ASTM C403/C403M (ASTM 2008) test method. Typical variations of k and penetration resistance obtained on CEM made with
350 kg=m3 cement and 0.5 w=c are plotted in Fig. 3. As expected,
the k values gradually decreased as a function of time during the
initial 200 min after mixing due to the loss in mixture’s consistency
and continuous change in the pore network structure as the cement
reacts with water. Beyond approximately 250 min, which roughly
coincides with the mortar’s initial setting time, the k value sharply
dropped toward zero. This result is in agreement with the findings
of Garcia et al. (2008) who reported that initial setting time reflects
a percolation threshold affecting connectivity between solid particles and voids within the newly hardened cement paste.
4
k × 10-5, cm/s
Effect of Hydraulic Gradient (i)
Permeability computed on the basis of Darcy’s law is limited to the
condition of complete saturation of specimen and laminar flow
characterized by straight and parallel flow lines (Engineers Manual
1110-2-1901 1986). Therefore, for example, for highly plastic clays
of low permeability, Darcy’s law may not hold as the flow rate is so
small and the soil considered being impervious. In contrast, at high
i values, the flow becomes turbulent with fluctuations in fluid
velocity in both parallel and transverse directions. This can result
in significant changes in the specimen structure due to washing out
of the finest particles and dissolution/precipitation of ions toward
the bottom of the sample (leaching effect).
To evaluate the validity of Darcy’s law, permeability measurements were conducted at different i values ranging from 10 to 55 on
various mortar and concrete mixtures. As can be seen in Fig. 2, the
variations in k due to different hydraulic gradients did not exceed
5% from the mean value, indicating that permeability is independent from i. Therefore, k of fresh mortars and concrete determined
using the falling-head method can be regarded as valid when computed with respect to Darcy’s law.
20
Beginning of
setting time
Permeability
3
15
Setting time
2
10
Mortar with 350 kg/m³
cement and 0.5 w/c
1
5
Initial set at
3.5 MPa
0
0
50
100
150
200
Time, min
250
300
350
0
400
Fig. 3. Effect of hydration time on k and penetration resistance (cell of
102-mm diameter was used for testing at i ¼ 25 2)
Effect of Specimen’s Volume
Generally speaking, higher permeability values were measured
when increasing the specimen’s volume. For example, as can be
seen in Fig. 4, the k value increased from 4.9 to 5.1 and
8.3 × 10−5 cm=s for the CEM tested using the 102, 152, and
305 mm diameter cells, respectively. The increase in permeability
was particularly important in concrete, as the k value has almost
doubled when the cell diameter increased from 102 to 305 mm
(Fig. 4). In geotechnical engineering, the increase in permeability
when increasing sample’s volume is attributed to increased relative
voids and hydraulic defects such as cracks, fissures, sand lenses,
which have statistically bigger chance of being present in a large
sample compared with a small one (Boynton and Daniel 1985). In
fresh mortars and concrete, the increase in k may be related to an
increase in the relative void ratio along with higher cement/sand/
aggregate surface interfaces present in the larger cell that can increase easiness of water percolation.
Repeatability of Testing
Several mortar and concrete mixtures made with different compositions were repeated five to seven times to evaluate repeatability of
the falling-head method. The 102-mm diameter cell was used, and a
constant hydraulic gradient of 30 3 was applied. The standard
deviation among various measurements was found to range from
0.05 to 1.3 × 10−5 cm=s, with the resulting coefficient of variation
(COV) varying from 1.3% to 6.5%. The COV is taken as the ratio
between standard deviation and mean values, multiplied by 100.
Compared with other testing methods, a COV less than 6.5% obtained from the permeameter test can be considered as quite acceptable. For instance, COV values of 8.1% and 12% were reported for
the surface settlement determined on mortars using the oedometer
10
16
8
14
Mixtures with 350 kg/m³
cement content
6
4
2
0
CEM
Concrete
12
k × 10-5, cm/s
k × 10-5, cm/s
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Phase I: Validity of the Falling-head Method to Assess
Permeability of Fresh Mortars and Concrete
25
Penetration resistance, MPa
5
Test Results and Discussion
Mortar: w/c = 0.55
Concrete: w/c = 0.55
Concrete: w/c = 0.4
Mortar: w/c = 0.4
10
8.8
8
6
14.5
Mixtures with 300
kg/m³ cement and
0.45 w/c
8.3
6.9
4.9
5.1
4
2
0
10
20
30
40
Hydraulic gradient (i ) value
50
60
Fig. 2. Effect of hydraulic gradient on k values (cells of 102- or
152-mm diameter were used for testing CEM or concrete, respectively)
0
102 / 105
152 / 115
305 / 230
Cell diameter / height dimensions, mm
Fig. 4. Effect of sample dimensions on k values
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013 / 583
J. Mater. Civ. Eng. 2013.25:580-588.
The use of higher cement content resulted in decreased k
(Fig. 6); a value of 1.6 × 10−5 cm=s was obtained for the mortar
made with 450 kg=m3 cement and 0.5 w=c. This can be attributed
to higher compaction rates which hinders water movement. Furthermore, mixtures containing higher cement contents require
lower HRWR demand to achieve the needed flowability, which
may increase cohesiveness (Assaad et al. 2004) and result in lower
permeability.
Effect of Silica Fume. The fine silica fume particles are known
by their ability to improve compaction and reduce bleeding of
freshly mixed mortars and concrete, thus leading to reduced permeability (Table 2). For example, k decreased from 1.6 to
0.85 × 10−5 cm=s for the CEM made with 450 kg=m3 cement
and 0.5 w=c with the addition of 8% silica fume. Such decrease
was from 3.1 to 1.6 × 10−5 cm=s for the equivalent concrete
mixtures.
test and on concrete using the 600-mm PVC column, respectively
(Assaad and Harb 2011).
Phase II: Permeability of Freshly Mixed Mortars and
Concrete
Effect of Mixture Composition on k Values
Effect of Coarse Aggregates. Good relationship with high correlation coefficient (R2 ) of 0.95 is obtained between k values
determined on CEM and those determined on concrete (Fig. 5).
However, concrete incorporating coarse aggregates exhibited k
of 40–120% greater than the one determined on mortar. Just like
in soils where k is affected by the particle size (Das 2010), this
indicates that water percolates easily in cementitious-based materials containing coarse aggregates.
Effect of w=c and Cement Content. Typical variations of k
for CEM made with various w=c and cement contents are illustrated in Fig. 6. Mixtures made with reduced w=c are shown to
yield lower permeability. For example, k decreased from 8.6 to
4.9 × 10−5 cm=s for CEM prepared with 300 kg=m3 cement and
w=c of either 0.65 or 0.45, respectively. In newly mixed cementitious materials, Picandet et al. (2011) reported that the void volume
representing the degree of porosity through which water percolates
can be assumed equal to the water volume, and thus expressed as
a function of w=c. Therefore, mixtures prepared with lower w=c
are expected to possess lower porosity that can slow down water
percolation in the tested specimen.
14
k of concrete × 10-5, cm/s
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More than 50 mixture combinations were tested in this project.
Table 2 summarizes typical permeability, bleeding, and surface
settlement responses obtained on CEM and concrete. Permeability
cells of 102-mm or 152-mm diameter were used for testing CEM or
concrete, respectively, at i values of 20 2.
12
y = 1.54 x
R ² = 0.95
10
8
6
CEM tested in cell φ = 102 mm
Concrete tested in cell φ = 152 mm
i = 20 ± 2
0.05 < St. deviation < 1.21 x 10-5 cm/s
1.3% < COV < 6.5%
4
2
0
0
1
2
3
4
5
6
k of CEM × 10-5, cm/s
7
8
10
9
Fig. 5. Relationship between k determined on CEM and concrete
mixtures
Table 2. Typical Results of k, Surface Settlement, and Bleeding Determined on CEM and Concrete Mixtures
Cement
content
(kg=m3 )
300
350
400
450
Silica fume
(% of
cement)
—
—
—
—
—
—
—
—
—
—
7
—
—
—
4
—
—
10
—
—
2
—
—
8
CEM properties
Concrete properties
w=c
VMA
(% of
cement)
Calcium
stearate
(% of cement)
kðCEMÞ × 10−5
(cm=s)
SettleðCEMÞ
(mm)
BleedðCEMÞ
(%)
kðConcÞ × 10−5
(cm=s)
SettleðConcÞ
(mm)
BleedðConcÞ
(%)
0.45
0.45
0.45
0.52
0.52
0.65
0.4
0.4
0.55
0.55
0.55
0.55
0.42
0.46
0.46
0.46
0.51
0.51
0.35
0.35
0.35
0.5
0.5
0.5
—
0.03
—
—
0.05
—
—
0.015
—
0.06
—
—
0.01
—
—
0.05
—
—
—
0.02
—
—
0.08
—
—
—
0.1
—
—
—
—
—
—
0.05
—
0.12
—
—
—
—
—
0.08
—
0.05
—
—
—
—
4.9
2
4.8
6.2
5
8.6
3.8
2.7
5
1.9
3.6
3.9
2.1
3.3
2.8
1.7
4.2
1
0.9
0.045
0.74
1.6
0.28
0.85
1.39
1.24
1.62
2.54
1.84
3.2
1.55
1.32
2.15
1.51
2.06
1.82
1.12
1.5
1.37
1.28
1.88
0.75
0.45
0.27
0.85
1.4
0.42
1.03
3.9
3.4
3.58
4.26
2.85
5.15
2.2
1.74
3.82
2.6
3.5
3.26
1.44
2.3
1.98
1.24
2.66
0.98
1.42
0.41
1.29
1.15
0.76
1.12
6.9
—
—
8.8
—
12.5
5.4
—
8.2
2.6
—
7.1
—
6.1
5.4
3.7
—
1.8
2
—
—
3.1
0.63
1.6
—
—
—
2.52
—
4.14
2.28
—
3.72
2.46
—
3.18
—
1.7
1.62
1.21
—
—
—
—
—
1.56
0.66
1.08
—
—
—
7.2
—
8.4
5.1
—
7.5
6.2
—
6.4
—
4.4
3.1
3.4
—
—
—
—
—
2.5
1.8
2.3
Note: Permeability cells of 102- or 152-mm diameter were used for testing CEM or concrete, respectively, at i values of 20 2. The COV for kðCEMÞ and
kðConcÞ is less than 6.5%. HRWR is adjusted to achieve concrete slump of 180 10 mm and CEM flow of 210 10 mm. Fixed dosages of set-retarder of 0.6%
or 0.4% of cement weight were used in concrete and CEM mixtures, respectively.
584 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013
J. Mater. Civ. Eng. 2013.25:580-588.
10
CEM mixtures
(COV < 3.3%)
8.6
k × 10-5, cm/s
8
6.2
6
5
4.9
4.2
4
1.6
0
Cement,
kg/m³
w/c
300
300
300
350
400
450
0.45
0.52
0.65
0.55
0.51
0.5
Fig. 6. Effect of cement content and w=c on k values (cell of 102-mm
diameter was used for testing at i ¼ 20 2)
Effect of VMA. All CEM and concrete incorporating VMA exhibited a decrease in k, particularly when such agent is added at
high concentration (Table 2). For example, the k value decreased
from 1.6 to 0.28 × 10−5 cm=s when the VMA was added at 0.08%
of cement weight in the mortar made with 450 kg=m3 and 0.5 w=c.
This can be attributed to the mode of function of the VMA that
binds part of the water (either mixing water or the one being circulated from the falling-head method), thus improving the overall
thixotropy and stability of the mixture (Assaad et al. 2004).
Effect of Calcium Stearate. The addition of calcium stearate
led to reduced permeability levels in the tested mixtures (Table 2);
a decrease from 5 to 3.9 × 10−5 cm=s was noted when the calcium
stearate was incorporated at 0.12% of cement weight in the CEM
prepared with 350 kg=m3 cement and 0.55 w=c. Such decrease
was from 8.2 to 7.1 × 10−5 cm=s in the corresponding concrete
mixtures. This can be related to the fact that the calcium stearate
imparts water repellency when added to cementitious-based materials, thus interfering with the free movement of water in the
specimen.
Effect of Consistency. Typical variations of k determined on
mixtures possessing different levels of consistency obtained by
adjusting the dosage of HRWR are plotted in Fig. 7. Clearly, a
considerable increase in k was obtained for mixtures having higher
consistency levels, mainly due to a decrease in the mixture’s cohesiveness and stability that allow water to permeate easily in the matrix. For example, such increase was from 3.7 to 12.8 × 10−5 cm=s
when concrete slump increased from 140 to 245 mm, respectively.
12.8
Determination of the Void Ratio, e
The determination of the void ratio is based on a study carried out
by Picandet et al. (2011) to assess permeability of fresh cementitious materials using an oedometer compression test. Such materials are considered fully saturated after mixing, and thus the void
CEM
(COV < 3.3%)
6.1
6
3.7
5.7
3.3
2.4
1.12
2
140
180
210
245
Concrete slump, mm
130
Bleeding, %
Surface settlement, mm
5
8.5
8
0
Mixtures with 400
kg/m³ cement and
0.46 w/c
Concrete
(COV < 5.4%)
10
4
An attempt was made to evaluate applicability of empirical soil
models described earlier in Eqs. (1)–(4) to predict permeability
of fresh mortars. Twelve mixtures made with different w=c, cement,
and silica fume contents were tested using the 102-mm diameter cell. The determination of the various parameters used in
Eqs. (1)–(4) including e, D10 , D60 , and Cu is presented in the following sections. It is to be noted that the powder VMA or calcium
stearate was not added to the tested mortars, given that their percentages are quite small to be detected by the mixture particle-size
distribution curves (i.e., D10 and D60 ) whereas their effects on permeability are highly significant.
CEM properties
12
Phase III: Use of Empirical Soil Models to Estimate
Permeability of Fresh Mortars
6
14
k × 10-5, cm/s
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2
Validation of k Using Bleeding and Surface Settlement
Responses
The bleeding and surface settlement properties determined either
on mortar or concrete mixtures are well related within each other
(R2 > 0.7). The bleeding phenomenon reflects the upward migration of interstitial solution toward the upper material’s surface
(Josserand et al. 2006). It is normally coupled with a higher level
of consolidation, which would lead to greater surface settlement
(Assaad et al. 2004). Generally, the increase in cement content, decrease in w=c, and incorporation of silica fume, VMA, or calcium
stearate were found to reduce bleeding and surface settlement responses (Table 2). Additional discussion regarding the effect of
mixture composition on such parameters can be seen in Assaad
et al. (2004) and Khayat et al. (2004).
The relationships between bleeding measured according to
ASTM C232/C232M (ASTM 2009), surface settlement determined
using the one-dimensional oedometer test, and k values determined
using the falling-head method on CEM mixtures are plotted in
Fig. 8. As can be seen, the increase in k value is associated with
an increase in bleeding and surface settlement with R2 greater than
0.82. Similar relationships were obtained among such properties
determined on concrete, with R2 greater than 0.71. This suggests
that the k value determined using falling-head method constitutes a
suitable index to reflect hydromechanical properties (including
bleeding and surface settlement) of freshly mixed mortars and
concrete.
y = 0.55 x + 0.73
R ² = 0.82
4
3
2
y = 0.29 x + 0.55
R ² = 0.85
1
175
210
0
240
0
CEM flow, mm
Fig. 7. Effect of consistency on k values (cells of 102- or 152-mm
diameter were used for testing CEM or concrete, respectively, at
i ¼ 20 2)
1
2
3
4
5
6
k of CEM × 10-5, cm/s
7
8
9
10
Fig. 8. Relationships between k determined on CEM with respect to
bleeding according to ASTM C232/C232M (ASTM 2009) and surface
settlement (oedometer test)
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013 / 585
J. Mater. Civ. Eng. 2013.25:580-588.
Table 3. Values of e, D10 , D60 , Cu , and k Calculated Using Different Empirical Soil Models
Cement
content
(kg=m3 )
300
350
450
w=c
0
18
0
35
0
0
0
0
45
0
0
0
0.35
0.4
0.65
0.35
0.45
0.65
0.35
0.65
0.35
0.35
0.5
0.65
e
D10
(mm)
D60
(mm)
0.301
0.315
0.575
0.303
0.425
0.607
0.340
0.624
0.317
0.341
0.546
0.684
0.052
0.05
0.052
0.047
0.048
0.048
0.045
0.045
0.038
0.04
0.04
0.04
0.19
0.18
0.19
0.16
0.18
0.18
0.14
0.14
0.12
0.13
0.13
0.13
Cu
Eq. (1)
Hazen
Eq. (2)
Kozeny-Carman
Eq. (3) Amer
and Awad
Eq. (4)
Chapuis
Actual k obtained by
testing × 10−5
(cm=s)
3.65
3.60
3.65
3.40
3.75
3.75
3.11
3.11
3.16
3.25
3.25
3.25
270
250
270
221
230
230
203
203
144
160
160
160
104
94.8
319
71.2
157
406
59.2
343
16.2
78.6
213
266
168
172
965
129
364
938
153
775
85.3
120
428
772
117
122
460
101
216
454
122
434
79.9
102
275
436
3.9
3.45
8.6
1.9
4.15
6.7
0.98
5.1
0.22
0.9
1.6
3.96
Note: In Eq. (1), the Hazen’s constant (CH ) is taken to be equal to 1. In Eq. (2), the shape factor (SF) is taken to be equal to 7.5.
e¼
W γs
S γw
ð6Þ
During oedometer testing, the mortar’s height (h) is always
lower than its initial height (h0 ) due to consolidation, which
squeezes out part of the mixing water initially contained in the
material. Assuming that the dry solid mass of the specimen (S)
is constant (i.e., only the fluid phase can flow through the filter
cake), a variation Δh in the mortar’s initial height induces W=S
variation with a corresponding void ratio variation (Δe) as follows:
Δh
Δe ¼ e − e0 ¼
ð1 þ e0 Þ
h0
ð7Þ
Hence, for example, to determine Δe in the mortar made with
300 kg=m3 cement and 0.65 w=c, the actual 3.2-mm settlement
measured using the oedometer (Table 2) is divided by the mortar’s
initial height of 20 mm, and the result multiplied by (1 þ e0 ). The e
values obtained in this study varied from approximately 0.3 to 0.7
(Table 3); note that typical e values reported in the literature for
loose or dense sand and silty sand are in the range of 0.4–0.8
(Das 2010).
Determination of D10 , D60 , and Cu of Dry Mortars
The particle-size distribution curves for the various combinations of
tested materials were determined by ordinary sieve analysis. The
sand was oven-dried before use, and then mixed with the cement
and silica fume according to the ratios given in Table 1. Typical
gradation for the dry mortar made with 300 kg=m3 cement is plotted in Fig. 9, along with the determination of D10 , D60 , and Cu . The
results obtained for tested dry mortars are given in Table 3.
Calculated k Using Empirical Soil Models versus
Determined k by Testing
The determined e, D10 , D60 , Cu , and particle-size distribution are
used to calculate four kinds of k according to Eqs. (1)–(4) (Table 3).
Similar k values were abnormally obtained when applying Hazen’s
empirical model [Eq. (1)] on mortars prepared with a given cement
content but different w=c, and consequently different e values. For
example, a value of 270 × 10−5 cm=s was obtained for the mix
made with 300 kg=m3 cement despite the change in w=c from
0.35 to 0.65 (Table 3). This indicates that Hazen’s model is of
limited use and thus is not adapted to estimate permeability of cementitious materials as it does not take the w=c into consideration.
The relationships between calculated k values using Eqs. (2)–(4)
with respect to those determined by testing using the permeameter
cell are plotted in Fig. 10 (the relationships were forced to intercept
the graph’s origin). On average, the calculated k was 48–120 times
greater than the actual k determined by testing. This can be related
to the fact that the empirical equations were originally developed
100
D10 = 0.052 mm
Passing percentage (by mass)
volume (i.e., void-to-solid volume ratio) can be assumed equal to
the water or liquid volume. It can be written as a function of the
water-to-solid mass ratio (W=S) and the specific unit weights of the
solids (γ s ) and water (γ w ) as follows:
Dry mortar
with 300 kg/m³
cement
D60 = 0.19 mm
80
Cu = D60 / D10 = 3.65
60
40
Natural
sand
Portland
cement
20
0
0.001
0.01
D10 0.1 D60
Sieve size (mm)
1
10
Fig. 9. Typical determination of D10 , D60 , and Cu for dry mortar made
with 300 kg=m3 cement
1.2×10-2
Calculated k using models, cm/s
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400
k calculated by models × 10−5 (cm=s)
Silica
fume
(kg=m3 )
Eq. (3):
y = 120 x
R ² = 0.72
Eq. (2): Kozeny–Carman
1.0×10-2
8.0×10-3
Eq. (3): Amer and Awad
Eq. (4): Chapuis
Eq. (4):
y = 63.8 x
R ² = 0.56
6.0×10-3
4.0×10-3
2.0×10-3
0.0×100
0×100
Eq. (2):
y = 48.2 x
R ² = 0.65
2×10-5
4×10-5
6×10-5
8×10-5
Actual k determined by testing, cm/s
1×10-4
Fig. 10. Relationships between actual k determined by testing with
respect to those calculated using different empirical soil models
586 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013
J. Mater. Civ. Eng. 2013.25:580-588.
0.8
Commonly used empirical models in soil mechanics were found
useful to predict permeability of fresh mortars made with different
w=c and contents of cement or silica fume. However, the calculated
k was 48–120 times greater than the actual k determined by testing.
The model proposed by Amer and Awad yielded the best linear
fitting with respect to actual k determined by testing, followed
by the Kozeny-Carman and Chapuis models. Linear relationships
were obtained between void ratio and logarithm of calculated k
values.
Eq. (2): Kozeny–Carman
Void ratio, e
0.7
0.6
Eq. (3): Amer and Awad
Eq. (4): Chapuis
0.5
0.4
R ² > 0.86
0.3
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0.2
1×10–4
1×10–3
Logarithm of k, cm/s
1×10–2
Fig. 11. Relationships between mortars void ratios and logarithm of k
calculated using different empirical soil models
Acknowledgments
The authors wish to acknowledge the financial support of the
National Council for Scientific Research (CNRS), Lebanon.
References
for soil where no or little chemical activity occurs in presence of
moisture. In case of mortars, hydration reactions take place as soon
as the cement particles are in contact with water to form a semirigid, interlocking, and polycrystalline solid network that can slow
down the rate of water percolation and reduce permeability (Bolton
and McKinley 1997).
Keeping in mind the differences in chemical nature between soil
and mortar, the correlations plotted in Fig. 10 between calculated
and actual k values can be considered as acceptable. The highest R2
of 0.72 resulted from Amer and Awad empirical model [Eq. (3)],
suggesting that e, D10 , and Cu parameters present in this model are
all relevant to properly estimate permeability of fresh mortars. The
Kozeny-Carman model [Eq. (2)], which takes into consideration
the fraction of particles between two consecutive sieve sizes and
e yielded a moderate R2 of 0.65. The decrease in R2 to 0.56 with
Eq. (4) (Chapuis) may be related to the fact that this model was
developed for uniform sand and gravel with expected k in the range
of 10−1 to 10−3 cm=s.
In soil mechanics, it is common to observe linear relationships
between void ratio and logarithm of k (Das 2010). Such observations are confirmed when plotting e versus log of calculated k using
empirical models for the tested mortars (Fig. 11). High R2 exceeding 0.86 are obtained, indicating applicability of soil permeability
theories and concepts to freshly mixed mortars.
Summary and Conclusions
The falling-head method realized using a soil permeameter is suitable to assess permeability of freshly mixed mortars and concrete.
This method is independent of the hydraulic gradient (i), thus making valid the computation of k using Darcy’s law. Permeability
measurements gradually decreased as a function of time after mixing until the mixture reaches initial setting, whereby k dropped
sharply toward zero. Higher permeability values were obtained
when increasing specimen’s volume.
Permeability of fresh mortars and concrete is directly affected by
the mixture composition. For example, mixtures prepared with
higher cement content, lower w=c, lower consistency, and increased
concentrations of silica fume, VMA, and calcium stearate were
found to reduce k. Concrete incorporating coarse aggregates exhibited k values 40–120% greater than those determined on CEM, indicating that permeability increases with the increase in particle
size. Good correlations with R2 greater than 0.82 were obtained
between actual k determined using the falling-head method with
respect to bleeding and surface settlement responses.
Alexandridis, A., and Gardner, N. J. (1981). “Mechanical behavior of fresh
concrete.” Cem. Concr. Res., 11(3), 323–339.
Amer, A. M., and Awad, A. A. (1974). “Permeability of cohesionless soils.”
J. Geotech. Eng., 100(12), 1309–1316.
Appleby, S., and Wilson, A. (1996). “Permeability and suction in setting
cement.” Chem. Eng. Sci., 51(2), 251–267.
Assaad, J., and Harb, J. (2011). “Surface settlement of cementitious-based
materials determined by oedometer testing.” Mater. Struct. (Dordrecht,
Neth.), 44(4), 845–855.
Assaad, J., Harb, J., and Chakar, E. (2009a). “Relationships between key
ASTM test methods determined on concrete and concrete-equivalentmortar mixtures.” J. ASTM Int., 6(3), 1–14.
Assaad, J., Harb, J., and Khayat, K. (2009b). “Use of triaxial compression
test on mortars to evaluate formwork pressure of SCC.” ACI Mater. J.,
106(5), 439–447.
Assaad, J., Khayat, K. H., and Daczko, J. (2004). “Evaluation of static
stability of self-consolidating concrete.” ACI Mater. J., 101(3),
168–176.
ASTM. (2006). “Standard test method for permeability of granular soils
(constant head).” D2434, Philadelphia.
ASTM. (2007). “Standard test method for flow of hydraulic cement
mortar.” C1437, Philadelphia.
ASTM. (2008). “Standard test method for time of setting of concrete mixtures by penetration resistance.” C403/C403M, Philadelphia.
ASTM. (2009). “Standard test methods for bleeding of concrete.” C232/
C232M, Philadelphia.
ASTM. (2010a). “Standard test method for air content of freshly mixed
concrete by the pressure method.” C231/C231M, Philadelphia.
ASTM. (2010b). “Standard test methods for measurement of hydraulic conductivity of saturated porous materials using a flexible wall permeameter.” D5084, Philadelphia.
ASTM. (2011). “Standard specification for concrete aggregates.” C33/
C33M, Philadelphia.
ASTM. (2012a). “Standard specification for Portland cement.” C150/C150,
Philadelphia.
ASTM. (2012b). “Standard specification for silica fume used in cementitious mixtures.” C1240, Philadelphia.
ASTM. (2012c). “Standard specification for chemical admixtures for concrete.” C494/C494M, Philadelphia.
ASTM. (2012d). “Standard test method for slump of hydraulic-cement concrete.” C143/C143M, Philadelphia.
Bolton, M. D., and McKinley, J. D. (1997). “Geotechnical properties
of fresh cement grout: Pressure filtration and consolidation tests.”
Geotechnique, 47(2), 347–352.
Boynton, S. S., and Daniel, D. E. (1985). “Hydraulic conductivity tests on
compacted clay.” J. Geotech. Eng., 111(4), 465–478.
Browne, R. D., and Bamforth, P. B. (1977). “Tests to establish concrete
pumpability.” ACI Struct. J., 74(5), 193–203.
Carman, P. C. (1956). Flow of gases through porous media, Butterworths
Scientific, London.
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013 / 587
J. Mater. Civ. Eng. 2013.25:580-588.
Downloaded from ascelibrary.org by UNIVERSITY OF PITTSBURGH on 08/01/13. Copyright ASCE. For personal use only; all rights reserved.
Chapuis, R. P. (2004). “Predicting the saturated hydraulic conductivity of
sand and gravel using effective diameter and void ratio.” Can. Geotech.
J., 41(5), 787–795.
Das, B. M. (2010). Principles of geotechnical engineering. 7th Ed.,
Cengage Learning.
Engineers Manual. (1986). “Determination of permeability of soil and
chemical composition of water.” EM 1110-2-1901, US Army Corps
of Engineers, Washington, DC.
Garcia, A., Castro-Fresno, D., and Polanco, J. A. (2008). “Evolution of
penetration resistance in fresh concrete.” Cem. Concr. Res., 38(5),
649–659.
Hazen, A. (1930). “Water supply.” American Civil Engineering Handbook,
Wiley, New York.
Josserand, L., Coussy, L. O., and De Larrard, F. (2006). “Bleeding of concrete as an ageing consolidation process.” Cem. Concr. Res., 36(9),
1603–1608.
Khayat, K. H., Assaad, J., and Daczko, J. (2004). “Comparison of fieldoriented test methods to assess dynamic stability of self-consolidating
concrete.” ACI Mater. J., 101(2), 168–176.
Kozeny, J. (1927). “Ueber kapillare leitung des wassers in boden.”
Sitzungsber. Akad. Wiss. Wien Math.-Naturwiss. Kl. Abt. 2A,
136(2a), 271–273.
Perrot, A., Rangeard, D., Melinge, Y., Estelle, P., and Lanos, C. (2009).
“Extrusion criterion for firm cement based materials.” Appl. Rheol.,
19(5), 530–542.
Picandet, V., Rangeard, D., Perrot, A., and Lecompte, T. (2011). “Permeability measurement of fresh cement paste.” Cem. Concr. Res.,
41(3), 330–338.
Schwartzentruber, A., and Catherine, C. (2000). “Method of the concrete equivalent mortar (CEM)—A new tool to design concrete
containing admixture.” Mater. Struct. (Dordrecht, Neth.), 33(8),
475–482.
Slowik, V., Schmidta, M., and Fritzsch, R. (2008). “Capillary pressure in
fresh cement-based materials and identification of the air entry value.”
Cem. Concr. Res., 30(7), 557–565.
Uzomaka, O. J. (1969). “Some fundamental engineering properties of
plastic concrete.” Ph.D. thesis, Univ. of Newcastle, Tyne and Wear, UK.
588 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2013
J. Mater. Civ. Eng. 2013.25:580-588.