EVAPORATION, SETTLEMENT, TEMPERATURE EVOLUTION, AND
DEVELOPMENT OF PLASTIC SHRINKAGE CRACKS IN MORTARS
WITH SHRINKAGE-REDUCING ADMIXTURES
Pietro Lura (1), Guy B. Mazzotta (2), Farshad Rajabipour (2), and Jason Weiss (2)
(1) Technical University of Denmark, Lyngby, Denmark
(2) Purdue University, West Lafayette, IN, US
Abstract
This paper deals with the development of plastic shrinkage cracks in mortars containing a
commercially available shrinkage-reducing admixture (SRA). Mortars containing SRA show
fewer and narrower plastic shrinkage cracks than plain mortars when exposed to the same
environmental conditions. It is proposed that the lower surface tension of the pore fluid in the
SRA mixtures results in less evaporation, reduced settlement, reduced capillary pressure, and
lower crack-inducing stresses at the topmost layer of the mortar. It is hoped that by improving
the understanding about how SRA work, mixtures containing SRA can be more appropriately
designed and utilized in cases where early-age plastic cracking is a potential problem.
1.
INTRODUCTION
One of the age-old problems in concrete is cracking. In addition to being unsightly, cracks
have the potential to act as weak planes for further distress or as conduits for the accelerated
ingress of aggressive agents that may lead to reduced durability. In particular, fresh concrete
may be susceptible to plastic shrinkage cracking, which occurs between the time of placement
and the time of initial set [1]. In the literature, plastic cracks are generally attributed to four
driving forces: rapid evaporation of water that creates menisci and high tensile stresses in the
capillary water near the surface [2,3]; differential settlement, since plastic shrinkage cracks
are frequently observed above reinforcing steel or at locations where there is a sudden change
in cross-sectional thickness [1,4,5]; differential thermal dilation due to temperature gradients
and temperature development within the fresh concrete; and autogenous shrinkage that occurs
during the plastic phase [6,7]. While these factors are often addressed independently, in
reality they will act simultaneously to increase the potential for cracking.
Over the last two decades, significant research has examined the use of SRA’s in concrete.
A recent review article [8] reported that SRA mixtures generally have lower shrinkage, lower
or equal chloride penetration indexes, reduced sorptivity, and reduced cracking potential,
despite having similar or slightly lower strength, modulus of elasticity, and fracture toughness
to plain concrete. However, substantially fewer studies have been conducted on the role of
Page
1
SRA in fresh (i.e., plastic) concrete systems. Bentz et al. [9] examined the role of SRA in
pastes and mortars at early ages using x-ray absorption. Mora et al. [10] presented an
experimental study where a reduction of evaporation and of plastic shrinkage cracking was
observed in concrete with three different types of SRA.
A previous work by the current authors [11] used a theory originally developed for drying
of gels [12] to explain how SRA, by reducing the surface tension of the pore fluid, influences
the rate of evaporation, temperature evolution, capillary stresses, and cracking of mortars. In
this paper, further experimental evidence is presented to support this hypothesis. It is hoped
that by improving this understanding, SRA mixtures can be more appropriately designed and
utilized in cases where early-age plastic cracking is a potential problem.
2.
Experimental Investigation
2.1
Materials
The SRA used in this research is a commercially available product (Tetraguard® AS20).
This product belongs to a class of admixtures that are specifically designed to lower the
surface tension of the pore water.
Standard mortars were studied with a water-to-cement mass ratio of 0.50, 55% aggregate
volume, and 0%, 1%, 2% and 5% SRA (the SRA replaced an equal amount of the mixing
water to maintain a constant liquid-to-cement ratio). The cement used in this investigation
was a Type I ordinary Portland cement with a Blaine fineness of 360 m2/kg and a Bogue
phase composition of 60% C3S, 12% C2S, 12% C3A, 7% C4AF and a Na2O equivalent of
0.72%. River sand was used with a fineness modulus of 2.60 and grading consistent with the
requirements of ASTM C 33 [13].
Prior to mixing, the constituent materials were conditioned in a sealed container in an
environmental chamber (30±1°C) for 12 hours. After preconditioning, the materials were
mixed in a 0.05-m3 rotary pan mixer in accordance with ASTM C 305 [14]. During mortar
placement, external vibration was applied using a standard vibration table. The specimens
were screeded perpendicular to the stress riser before a smooth steel trowel finish was applied.
Fifteen minutes after water was added to the mixer, all of the prepared specimens were
transferred into the environmental chamber where testing took place.
Setting time was measured on the mortars at 23±1°C according to ASTM C 403/C 403M
[15]. The addition of SRA delayed both initial and final set of the mortars. Initial and final
setting times varied from 3.7 and 5.4 hours in the plain mortar to 4.7 and 6.8 hours in the
mortar with 5% SRA.
2.2
Experimental methods
The du Noüy Ring Method was used to measure the surface tension of solutions of SRA
and deionized water at a temperature of 23±1°C. The method is based on determining the
force required to detach a ring from the surface of a solution. Measurements were taken using
a tensiometer with a platinum-iridium alloy ring, in accordance with ASTM D 971 [16]. The
tensiometer was calibrated using deionized water at 23°C, which has a surface tension of
0.072 N/m.
All mortar samples were tested in a chamber, where environmental conditions were
maintained constant throughout the investigation: temperature 30±1°C, relative humidity
Page
2
90 mm
280 mm
560 mm
12.7 mm
32 mm
25 mm
68º
68º
63.5 mm
18 gage steel
355 mm
100 mm
160 mm
50±2%, and wind velocity 24±2 km/h. Immediately after mixing, all mortar specimens were
placed in the chamber and exposed to the environment to accelerate evaporation.
An electronic balance, equipped with data acquisition at 30-second intervals, measured the
weight loss of cylindrical samples of mortar (75 mm depth and 100 mm diameter). Three
specimens were tested for each mixture. In addition, evaporation of SRA-deionized water
solutions was also measured using identical cylindrical molds.
Copper-Constantan thermocouples were used to measure the temperature profile in
identical cylindrical specimens during the evaporation process. Thermocouples were placed
into the mortar at depths of 2, 4, 6, 9, 12 and 20 mm and automated temperature readings
were taken at 30-second intervals until 6 hours.
Settlement of mortars was measured with a non-contact laser system [17, 18]. The vertical
displacement of the surface of mortars was measured every 30 seconds from the time of
placement (15 minutes after water was added during mixing) until an age of six hours. Mortar
samples were cast in the same molds used in the evaporation and temperature measurements.
The non-contact laser measurement devices consisted of a laser beam projected at a small
angle from the vertical direction toward the specimen surface. The distance from the laser
head to the surface is calculated by measuring the horizontal displacement of the reflected
beam. It was observed that a film of bleed water present on the surface of the samples did not
substantially influence these measurements.
To study the plastic shrinkage cracking, a setup similar to the one proposed by Berke and
Dalliare [19] was adopted. However, the dimensions of the slab were slightly varied, as
described in Qi et al. [20, 21] (Figure 1). In particular, the cover above the stress riser was
reduced. This geometry provided a base restraint, while a stress riser placed in the centre of
the slab significantly reduced the slab depth and provided a preferential location for cracking.
Stress Riser Geometry
Side View
Top View
Figure 1: Geometry of the plastic shrinkage cracking form
After 6 hours, the environmental chamber was turned off and the specimens were stored
there for an additional 18 hours at 23±1°C and 50±2% RH. At an age of 24 hours, the slab
was ready for image acquisition. The crack width was measured using an automated image
analysis approach that takes approximately 300 measurements for each specimen, thereby
providing statistically valid information about crack width and its variability [21]. The
automated image processing and analysis procedures used in this study are described in
reference [20].
Page
3
3.
EXPERIMENTAL RESULTS
3.1
Surface tension of solutions
The addition of SRA significantly decreases the surface tension of the deionized waterSRA solutions. The surface tension decreases rapidly until a plateau is reached at
approximately 15% SRA replacement by mass. A semi-empirical expression describing the
surface tension of dilute aqueous solutions of organic substances [22] has been used to fit the
surface tension of SRA solutions measured in the experiments [23]:
⎧
⎡
⎛ C
⎞⎤
if 0.1% ≤ CSRA < 15%
⎪γ SOL = γ Water ⎢1 - 0.0795 ln⎜ SRA ⎟⎥
(1)
⎨
⎝ 0.0164 ⎠⎦
⎣
⎪
γ SOL = 0.033 N/m
if CSRA ≥ 15%
⎩
where CSRA is the SRA content by mass of solution expressed as percentage (i.e., for 1% SRA,
CSRA = 1). These measurements compare reasonably well to others previously reported [9,24].
Specific Change in Mass (kg/m2)
3.2
Evaporation of solutions and mortars
Figure 2 shows the mass change due to evaporation for samples of deionized water and
SRA-deionized water solutions (where SRA content is defined by mass of water). The mass
change is normalized to the surface area of the specimen. It is noticed that the addition of
SRA to water appears to have little influence on the evaporation rate of deionized water in the
first few hours.
0.00
-1.00
-2.00
-3.00
Deionized water
-4.00
1% SRA Solution
5% SRA Solution
-5.00
0
1
2
3
4
5
6
Time of Drying (hours)
Figure 2: Mass change due to evaporation of solutions at 30°C, 50% RH, and 24 km/h
While these environmental conditions correspond directly to the environmental conditions
of the plastic shrinkage test, it became clear through the course of this investigation that the
need existed to understand how the evaporation rate influenced the behaviour of the
specimens during the first few hours. As a result a testing apparatus has been recently
developed to measure the evaporation rate of solutions and mortars, shown in Figure 3. The
measurement device consists of two scales on base vibration pads that are connected to a
computer for continuous data acquisition. Above the scales, a frame supports two acrylic
chambers (one over each specimen) that are designed to enable a fan to pass a very constant
Page
4
wind across the surface of the specimens. The entire apparatus is placed inside a chamber
with the ability to control the relative humidity and temperature.
Support
Frame
Fan
Acrylic
Tunnel
Solution
Container
Scales
Vibration Isolation
Figure 3: Illustration of the chambers designed to measure evaporation rates
Evaporation Rate of Solution
Evaporation Rate of Water
Figure 4 shows the rate of mass change due to evaporation over a 20 hour period for two
75 mm thick samples of deionized water and SRA-deionized water solutions at 30°C and 30%
RH. To more clearly illustrate if a difference exists between the evaporation rate of a SRA
solution and water, the evaporation rate of each solution was normalized by the evaporation
rate of pure deionized water. The solutions are preconditioned to the same temperature of the
chamber before being stirred and placed in the evaporation dishes. The results shown in
Figure 4 confirm that indeed there is little or no influence of the SRA content (other than
possibly at the beginning of the test) on the rate of evaporation of the solution, up to a SRA
content of 7.5% by mass of water. Measurements on pure SRA show no evaporation.
1.50
2% SRA
5% SRA
7.5% SRA
1.25
1.00
0.75
0
5
10
15
20
Time of Drying (hours)
Figure 4: Rate of mass change due to evaporation of solutions at 30°C and 30% RH
Page
5
Specific Change in Mass (kg/m2)
It should be noted, however, that for the specimens shown in Figure 4 the size of the water
reservoir is relatively large and as a result the concentration of the solution is not significantly
altered at the early stages of drying. Additional measurements are being performed on
solutions to further investigate the influence of the concentration of solutions containing SRA
and their rate of evaporation. This is intended to better correspond with the conditions that
may be expected in a mortar where the overall volume of the solution is more limited.
0.00
-1.00
-2.00
Mortar 5% SRA
-3.00
Mortar 1% SRA
-4.00
Plain Mortar
Deionized water
-5.00
0
1
2
3
4
5
6
Time of Drying (hours)
Figure 5: Mass change due to evaporation of mortars at 30°C, 50% RH, and 24 km/h
In addition to measuring the evaporation rate in solutions, the mass change due to
evaporation was measured for mortars, as shown in Figure 5. The rate of evaporation in the
first minutes appears similar to that of pure water for all mortars. After about 1 hour, the rate
of evaporation began decreasing in all mortars. The rate of evaporation was first reduced in
the 5% SRA mortar, followed by the 1% SRA mortar and by the plain mortar in the following
hours. The evaporation rate decreased steadily over time.
Temperature (oC)
35
0% SRA
1% SRA
Chamber
32
Chamber
29
Depth
(mm)
0
2
4
6
9
12
20
Depth
(mm)
0
2
4
6
9
12
20
26
23
20
0
1
2
2% SRA
Chamber
3
4
5
6
Time of Drying (hours)
0
1
2
3
4
5
Depth
(mm)
0
2
4
6
9
12
20
6
Time of Drying (hours)
0
1
2
3
4
5
6
Time of Drying (hours)
Figure 6: Temperature measurements during evaporation in mortar specimens
Page
6
3.3
Temperature measurements on mortars
Figure 6 shows results of temperature measurements on mortars with 0%, 1%, and 2%
SRA. It should be noted here that the temperature readings were taken with uncalibrated
thermocouples and this explains some scatter in results. Immediately after placing the samples
in the environmental chamber, a drop in temperature occurred due to evaporative cooling. In
all mortars, the temperature dropped to approximately 23°C, or the wet-bulb temperature. In
the plain mortar, the temperature started increasing at 2 hours and equilibrated with the
external temperature at about 6 hours. In the mortars containing SRA, the temperature started
increasing earlier, before 1 hour, and eventually became higher than the chamber temperature
around 3 to 4 hours after placing, depending on the SRA content. The earlier rise in
temperature of the specimens containing SRA is consistent with the reduction in evaporation
rate demonstrated in Figure 5.
3.4
Settlement of mortars
Results of settlement vs. mass loss are shown in Figure 7. Initially, all curves are linear
with similar slope, followed by a sudden decrease and a plateau. In mortars with SRA,
settlement stopped at 1.5 hours after time of placement, while in the plain mortar settlement
stopped at about 2 hours, at a final value about 50% higher than in mortars with SRA.
0.0
Settlement (mm)
Plain mortar
-0.5
Mortar 1%
Mortar 5%
-1.0
1.5 hours
-1.5
2 hours
-2.0
-2.5
0
-1
-2
-3
2
-4
-5
Mass loss (kg/m )
Figure 7: Settlement of mortars exposed to evaporation vs. mass loss
3.4
Plastic shrinkage cracks
The cracks in the mortars were first observed above the central stress riser at approximately
90 minutes after placement. Figure 8 shows the average (of three specimens) crack width
distribution in mortars with different SRA content measured after 24 hours. The addition of
SRA results in a slight decrease in the frequency of plastic cracks and a more substantial
reduction in the width of the plastic shrinkage cracks.
Page
7
Cumulative Distribution
of Measured Cracks (%)
100
80
60
40
1% SRA
20
5% SRA
2%
SRA
Plain
0
0
0.4
0.8
1.2
1.6
2.0
Crack Width (mm)
Figure 8: Influence of SRA on the width of the plastic shrinkage cracks
4.
DISCUSSION
In the following paragraph a global description of the process leading to formation of
plastic shrinkage cracks in mortars is briefly discussed, highlighting the benefits of SRA. A
more detailed analysis of the phenomenon is presented in [11].
Initially, the solid particles in the mortars sink, causing the mixture to densify and the
bleed water to be transported to the surface. Initial evaporation of fresh mortars proceeds from
a layer of bleed water spread across the whole surface of the sample; in fact the initial rate of
evaporation of mortars is close to that of bulk water at the same temperature (Figure 5).
Furthermore, it was shown [11] that the initial rate of evaporation from mortars is independent
of SRA content, until the layer of bleed water is consumed (Figure 5).
During the first minutes of drying, the temperature of the specimen drops to the wet-bulb
temperature and remains almost constant for a period of time (Figure 6). It is also interesting
to note that temperature reduction was almost constant through the 75 mm depth of the
specimens. The temperature increased after approximately 1 hour from casting in the plain
mortar, while mortars with 1% and 2% SRA showed an earlier temperature rise (Figure 6).
Once the layer of bleed water at the surface is consumed by evaporation, air-liquid menisci
are formed in the liquid between the solid particles on the surface [2]. These menisci cause
tensile stress to develop in the pore fluid, leading to shrinkage. The viscous nature of the
material at these early ages causes the majority of the shrinkage to occur in the vertical
direction. As the system shrinks, the pore fluid is brought to the surface and evaporates.
When menisci form at the surface, the pore fluid is subjected to tensile stresses. The
capillary pressure caused by the menisci can be calculated as:
2γ ⋅ cos θ
(2)
P=−
r
where γ in N/m is the surface tension of the pore fluid, θ (rad) is the contact angle between
pore fluid and solids, and r (in meters) is the radius of the menisci. In mortars with SRA, the
surface tension of the pore fluid is substantially reduced, even to about half the value for pure
water in the case of the 5% SRA addition. Since the capillary pressure is proportional to the
Page
8
surface tension (Equation (2)), a proportional reduction of the capillary pressure developing
upon drying is expected in mortars with SRA.
The capillary pressure produced by the menisci on the surface compresses the mortar,
whose solid skeleton consolidates under the growing pressure. As a consequence, the pore
fluid is drawn to the upper surface of the mortar. The higher the capillary pressure, the more
fluid is forced out of the porous network and this water becomes available for evaporation. In
the SRA mortars, a lower capillary pressure develops, thereby explaining why their rate of
evaporation is lower than the one of plain mortar (Figure 5) after the first hour of drying.
Shrinkage of the mortar under the effect of the capillary pressure is resisted in part by the
modulus of the solid network, but much greater resistance is caused by friction between the
pore fluid and the network [12]. As a consequence, a pressure gradient builds up between the
surface and the interior of the drying body. The permeability of the network gradually
decreases as the network is drained and consolidated under the capillary pressure.
The higher the evaporation, the more the porous body is consolidated, and the steeper is
the pressure gradient at the surface. In Figure 7 the initial rate of the settlement versus mass
loss curves is the same for all mortars regardless of the SRA content. Moreover, in the first
period, 1 mm of settlement corresponds to the evaporation of 1 mm of water from the surface.
This confirms that no empty pores are created in the mortars in the first phase of evaporation.
The final settlement is considerably lower in mortars with SRA, as a consequence of lower
surface tension which results in lower consolidation. Consequently, the addition of SRA may
reduce the risk of plastic shrinkage cracking due to differential settlement.
As evaporation progresses, under the increasing consolidation pressure, the network of the
solid particles becomes progressively stiffer and the slope of the settlement-capillary pressure
curve decreases accordingly [2]. A critical point is reached, where the vertical deformation of
the mortar stops, because the capillary pressure is no longer able to compress the solid
skeleton of the mortar and draw water to the surface. At this point, the menisci reach a
breakthrough radius and recede into the interior of the sample [12].
The minimum radius of the menisci in a fresh cementitious material, before a pore
structure has formed, is related to the dimension of the cement particles. The cement used in
this investigation had an average cement particle diameter of about 20-30 μm. Considering
different packing arrangements of monosize spheres, the radius of the menisci will be about 5
to 7 times smaller than the particle size [12]. With these assumptions, a maximum capillary
pressure of -30 kPa is calculated with Equation (2) when the pore fluid is water. This value
compares well with -20 kPa measured on cement paste by Wittmann [2]. If a paste with 5%
SRA addition is considered, the surface tension is reduced from 0.072 to 0.039 N/m and the
calculated maximum capillary pressure would be reduced to -16 kPa. According to these
calculations, the capillary pressure in the surface of the mortars at the critical point is lowered
by SRA addition. Mortars containing SRA are subjected to lower internal stress and are
therefore less consolidated when the critical point is reached. As a consequence of being less
consolidated, mortars with SRA have higher permeability at the critical point, and the gradient
of the capillary pressure at the surface is less steep than in plain mortars.
It has been observed that cracking of cementitious materials happens at the critical point,
when the maximum pressure is reached and the settlement-pressure curve shows a plateau [2].
Also cracking of gels occurs at the same point [12]. Both in gels and in cementitious
materials, the probability of cracking is related to the rate of drying and cracking can be
avoided by slowing down the evaporation rate [3,12].
Page 9
According to Scherer [25], the stress acting on the solid network at the surface of a drying
body can be calculated as:
~
1 − 2ν
σx =
⋅ P − P −φ ⋅ P
(3)
1 −ν
where ν is Poisson’s ratio for the solid network, P (Pa) is the capillary pressure at the surface
of the drying body, P (Pa) is the volume-weighted average of the capillary pressure in the
pore fluid, and φ is the volume fraction of fluid. If the pressure at the surface is close to the
average pressure in the body (i.e., the pressure gradient at the surface is not high), the stress at
(
)
~
the surface σ x is compressive, and cracking does not occur. When the pressure gradient at the
~
surface is high, the global stress σ x acting on the surface of the mortar becomes tensile. If
flaws, such as large pores, are present on the surface of the mortar, their edges would be
pulled apart by the global tensile stress, generating and propagating larger cracks [25]. A high
rate of evaporation causes a steep gradient of the capillary pressure at the surface and
therefore a high tensile stress at the surface (Eq. (3)), which would induce plastic shrinkage
cracks. The lower rate of evaporation obtained by addition of SRA (Figure 5) should therefore
reduce the tensile stress at the surface and ultimately reduce the probability of plastic
shrinkage cracking. This is indeed confirmed by the experimental results shown in Figure 8.
5.
CONCLUSIONS
Addition of SRA reduces the width of plastic cracks, evaporation and settlement in mortars
exposed to evaporation immediately after casting. By reducing the surface tension in the pore
fluid, SRA’s seem to be advantageous in several ways: 1) they reduce evaporation; 2) they
reduce settlement; and 3) they reduce the stresses that develop at the surface of the mortar.
Each of these benefits of SRA reduces the potential for the development of plastic shrinkage
cracks.
ACKNOWLEDGEMENTS
Financial support from Degussa Chemical Corporation is gratefully acknowledged. In
addition, this work was performed in the Materials Sensing and Simulation Laboratory and as
such the authors gratefully acknowledge the support that has made that lab possible.
REFERENCES
[1] Powers, T.C., 'The Properties of Fresh Concrete', (John Wiley & Sons, New York, 1968).
[2] Wittmann, F.H., 'On the Action of Capillary Pressure on Fresh Concrete', Cem. Concr. Res. 6 (1)
(1976) 49-56.
[3] Cohen, M.D., Olek, J. and Dolch, W.L., 'Mechanisms of Plastic Shrinkage Cracking in Portland
Cement and Portland Cement-Silica Fume Paste and Mortar', Cem. Concr. Res. 20 (1) (1990) 103119.
[4] Weyers, R.E., Conway, J.C. and Cady, P.D., 'Photoelastic Analysis of Rigid Inclusions in Fresh
Concrete', Cem. Concr. Res. 12 (4) (1982) 475-484.
[5] Qi, C., Weiss, W. J. and Olek, J., 'Image Analysis of Plastic Shrinkage Cracking in High Strength
Concrete Containing Hybrid Fiber Reinforcement', Role of Concrete in Sustainable Development:
Proc. Int. Sym. Dedicated to Surendra Shah, ed. R.K. Dhir, M.D. Newlands, and K.A. Paine, Sept.
2003, 209-218.
Page 10
[6] Bjøntegaard, Ø, Hammer, T.A. and Sellevold, E.J., 'Cracking in High Performance Concrete
Before Setting', Int. Symp. on High Performance and Reactive Powder Concrete, Sherbrooke,
Canada, V. 1, Aug. 16-20, 1998, 332-348.
[7] Pease B.J., Hossain, A.B. and Weiss, W.J., 'Quantifying Volume Change, Stress Development,
and Cracking Due to Self-Desiccation', Autogenous Deformation of Concrete, SP-220, O.M.
Jensen, D.P. Bentz & P. Lura, eds., ACI, Farmington Hills, Mich., 2004, 23-39.
[8] Weiss, W.J. and Berke, N.S., 'Chapter 7.5: Admixtures for Reduction of Shrinkage and
Cracking', Early Age Cracking In Cementitious Systems: Report to RILEM Tech. Comm. 181EAS, A. Bentur, ed., RILEM Report 25, Bagneux, France, 2003, 323-338.
[9] Bentz, D.P., Geiker, M.R. and Hansen, K.K., 'Shrinkage-Reducing Admixtures and Early Age
Desiccation in Cement Pastes and Mortars', Cem. Concr. Res. 31 (7) (2001) 1075-1085.
[10] Mora, I., Aguado, A. and Gettu, R., 'The influence of shrinkage reducing admixtures on plastic
shrinkage', Materiales de Construccion 53 (271-72) (2003) 71-80.
[11] Lura, P., Pease, B.J., Mazzotta, G.B., Rajabipour, F. and Weiss, W.J., 'Influence of shrinkagereducing admixtures on the development of plastic shrinkage cracks', sub. to ACI Mat. J, 2005.
[12] Brinker, C.J. and Scherer, G.W., 'Sol-gel Science', (Academic Press, New York, 1990).
[13] ASTM C 33, Standard Specification for Concrete Aggregates, The American Society of Testing
and Materials, Philadelphia, USA, V. 4.08, 2000.
[14] ASTM C 305, Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars
of Plastic Consistency, The American Society of Testing and Materials, Philadelphia, USA, 1999.
[15] ASTM C 403/C 403M, Test Method for Time of Setting of Concrete Mixtures by Penetration
Resistance, The American Society of Testing and Materials, Philadelphia, USA, 2004.
[16] ASTM D 971, Standard test method for interfacial tension of oil against water by the ring method,
The American Society of Testing and Materials, Philadelphia, USA, V. 10.03, 1994, pp. 103-105.
[17] Kayir, H. and Weiss, W.J., 'A fundamental look at settlement in fresh systems: role of mixing
time and high-range water reducers', First North American Conference on Self-Consolidating
Concrete, Chicago, IL, November, 2002, 27-32.
[18] Qi, C., Weiss, W. J., and Olek, J., 'Assessing the settlement of fresh concrete using a non-contact
laser profiling approach', International Conference on Construction Materials: ConMat'05,
Vancouver, Canada, August, 2005 (CD ROM)
[19] Berke, N.S., and Dalliare, M.P., 'The Effect of Low Addition Rate of Polypropylene Fibers on
Plastic Shrinkage Cracking and Mechanical Properties of Concrete', Fiber Reinforced Concrete:
Development and Innovations, SP-142-2, ACI, Farmington Hills, Mich., 1994, 19-41.
[20] Qi, C., Weiss, W. J., and Olek, J., 'Characterization of Plastic Shrinkage Cracking in Fiber
Reinforced Concrete Using Semi-Automated Image Analysis', Concr. Science Eng. 36 (260)
(2003) 386-395.
[21] Qi, C., Weiss, W. J. and Olek, J., 'The Statistical Significance of the Restrained Slab Test to
Quantify Plastic Shrinkage Cracking in Fiber Reinforced Concrete', ASTM Int. J. 2 (7) (2005).
[22] Adamson, A.W., 'Physical Chemistry of Surfaces', 5th Ed. (John Wiley and Sons, New York
1990) 71, 777.
[23] Pease, B. J., Shah, H. R., and Weiss, W. J., 'Shrinkage Behavior and Residual Stress Development
in Mortar Containing Shrinkage Reducing Admixture (SRA's)', Shrinkage and Creep of Concrete,
ACI SP 227, ed. Gardner, J., and Weiss, W. J., Farmington Hills, MI, 2005
[24] Ai, H., and Young, J.F., 'Mechanisms of Shrinkage Reduction Using a Chemical Admixture',
Proceedings of the 10th Int. Con. on the Chemistry of Cement, ed. Justnes, H., Gothenburg,
Sweden, Vol. 3, 1997.
[25] Scherer, G.W., 'Crack-tip stress in gels', J. Non-Cryst. Sol. 144 (2-3) (1992) 210-216.
Page 11