ACI MATERIALS JOURNAL
TECHNICAL PAPER
Title no. 106-M46
Short-Term Mechanical Properties of High-Strength
Concrete
by Andrew Logan, Wonchang Choi, Amir Mirmiran, Sami Rizkalla, and Paul Zia
A comprehensive experimental program was undertaken to determine
the short-term mechanical properties of high-strength concrete
(HSC). Modulus of rupture beams and two different sizes of
concrete cylinders with three different target compressive strengths
ranging from 10 to 18 ksi (69 to 124 MPa) were subjected to three
different curing methods and durations. Test results were combined
with data from the literature to improve predictive equations for
the elastic modulus and modulus of rupture of HSC. Of the three
different curing methods, cylinders moist-cured for 7 days exhibited
the highest compressive strengths at ages of 28 and 56 days. In
contrast, 1-day heat curing generally resulted in the lowest
compressive strength. The study shows that a Poisson’s ratio of 0.2
can be adequately used for HSC.
Keywords: compressive strength; elastic modulus; high-strength concrete;
modulus of rupture; Poisson’s ratio.
INTRODUCTION
The development of high-strength concrete (HSC) has led
to more efficient design of buildings and bridges, with shallower
members and longer spans. Although some design specifications
have addressed the use of HSC, many have implicitly or
explicitly placed restrictions on its use, primarily because
of limited research data.1 For example, the American Association
of Highway and Transportation Officials (AASHTO) LRFD
Bridge Design Specifications2 limits its applicability to
concrete compressive strength of 10 ksi (69 MPa) unless
physical tests are conducted. Furthermore, many design
provisions in both ACI 318-053 and AASHTO-LRFD2 are
based on test data obtained from specimens with compressive
strengths up to 6 ksi (41 MPa) and, therefore, do not accurately
reflect the mechanical properties of HSC.
In the late 1970s, Carrasquillo et al.4 tested specimens
from three concrete mixtures with 53-day compressive
strengths ranging from 4.6 to 11.1 ksi (31.7 to 76.5 MPa).
Some of the specimens were moist-cured for 7 days and were
then allowed to dry until tested at an age of 28 days. Others
were moist-cured for 28 days and then allowed to dry until
tested at an age of 95 days. The control group was moistcured until 2 hours prior to testing. The data suggested that
drying of HSC cylinders resulted in a lower compressive
strength and modulus of rupture, in contrast to the normalstrength concrete (NSC). The reduction in the modulus of
rupture was more significant than that of the compressive
strength. The study also revealed that the compressive
strength of 6 x 12 in. (150 x 300 mm) cylinders was, on
average, approximately 90% of that of the 4 x 8 in. (100 x
200 mm) cylinders, irrespective of the compressive strength
or the age at testing. Carrasquillo et al.4 then proposed equations
for both modulus of elasticity and modulus of rupture of HSC,
which were later included in the ACI 363R-92 report.5
The Strategic Highway Research Program (SHRP) of the
early 1990s also focused on the mechanical properties of
ACI Materials Journal/September-October 2009
high-performance concrete (HPC), with some specimens
referred to as “very high strength,” with 28-day compressive
strengths ranging from 8 to 13.4 ksi (55 to 92 MPa).6 The
study found that the ratio of the compressive strength of the
6 x 12 in. (150 x 300 mm) cylinders to that of the 4 x 8 in.
(100 x 200 mm) cylinders ranged from 0.91 to 0.98,
depending on the type of coarse aggregates used.6 The study
also determined that the proposed equation of Carrasquillo et
al.4 (and ACI 363R-925) underestimated the elastic modulus
of HSC. With regards to the modulus of rupture, the study
showed that at the design age, the ratio of the observed value
to that predicted by ACI 318-053 was 1.06 for concrete made
with fly ash and 1.15 for concrete made with silica fume.
Comparing the measured values to those predicted by
Carrasquillo et al.4 (and ACI 363R-92 5), the ratio was as
low as 0.686.
Mokhtarzadeh and French7 studied 142 concrete mixtures
with 28-day compressive strengths ranging from 8 to 18.6 ksi
(55 to 128 MPa). Their data showed the ACI 318-053 equation
to overestimate the elastic modulus of HSC, whereas the
ACI 363R-925 equation was found more favorable. Also, the
ACI 363R-925 equation for the modulus of rupture was
found acceptable for the moist-cured specimens, whereas the
modulus of rupture of the heat-cured specimens fell in
between the values predicted by the ACI 363R-925 and
ACI 318-053 equations. The study proposed a new modulus
of rupture equation with a coefficient of 9.3 to be used
instead of the 7.5 in the ACI 318-053 equation.
Légeron and Paultre8 reported that curing conditions
significantly affected the measured value of the modulus of
rupture. They also compiled data from the literature and
proposed predictive equations for the minimum, average,
and maximum values of the modulus of rupture. They
suggested that the minimum values be used for service limit
states to control deflections and cracking, whereas the
maximum values should be used for the ultimate limit state
to ensure ductility of flexural members. Burg and Ost9 found
that the ratio of the moduli of rupture of moist-cured specimens
to air-cured specimens ranged from 1.54 to 2.02.
In the last few years, the AASHTO has addressed the need
to expand the applicability of its LRFD Specifications2 to HSC
with a number of research projects conducted through the
National Cooperative Highway Research Program (NCHRP).
This paper reports on one of these projects (NCHRP 12-64),
which focused on flexure and compression design provisions
ACI Materials Journal, V. 106, No. 5, September-October 2009.
MS No. M-2008-005 received January 3, 2008, and reviewed under Institute publication
policies. Copyright © 2009, American Concrete Institute. All rights reserved, including the
making of copies unless permission is obtained from the copyright proprietors. Pertinent
discussion including authors’ closure, if any, will be published in the July-August 2010
ACI Materials Journal if the discussion is received by April 1, 2010.
1
Table 1—Concrete mixture proportions
Andrew Logan works for a civil engineering firm in Leesburg, FL. He received his
BS and MS in civil engineering from the University of Florida, Gainesville, FL, and
North Carolina State University, Raleigh, NC, respectively. His research interests
include short-term mechanical properties of high-strength concrete.
Wonchang Choi received his PhD from North Carolina State University, and his BS
and MS in civil engineering from Hongik University, Seoul, Korea. His research interests
include the flexural behavior of prestressed girders using high-strength concrete.
Target compressive strengths
Cement (Type I/II), lb/yd3 (kg/m3)
3
ACI Honorary Member Paul Zia is a Distinguished University Professor Emeritus at
NC State University. He is an ACI Past President and is currently a member of the
Concrete Research Council, ACI Committee 363, High-Strength Concrete; Concrete
Research Council; and Joint ACI-ASCE Committees 423, Prestressed Concrete; and
445, Shear and Torsion.
for HSC.10 As part of this project, an effort was made to
characterize the short-term mechanical properties of HSC.
RESEARCH SIGNIFICANCE AND OBJECTIVES
The main objective of this study was to improve predictive
equations for short-term mechanical properties of HSC,
including its elastic modulus, modulus of rupture, and
Poisson’s ratio. The significance of this research is not only
to improve the predictive equations, but also to enhance the
test database for HSC with three different target compressive
strengths, different specimen sizes, and different curing
conditions. The database is especially significant because it
is based on ready mixed concrete delivered from batch
plants, and not laboratory-scale mixtures. Although not
directly the focus of this paper, it is also important to note
that the specimens for short-term mechanical properties
were made and tested side-by-side and as part of a larger test
matrix, which included reinforced concrete columns and
beams and prestressed girders.
EXPERIMENTAL PROGRAM
Materials and mixture design
Three different concrete mixtures with target compressive
strengths of 10, 14, and 18 ksi (69, 97, and 124 MPa) were
prepared using ready mixed concrete delivered from a batch
plant. The mixture proportions were selected from a large
number of trial laboratory batches and are shown in Table 1.
The mixtures for the 10 and 14 ksi (69 and 97 MPa)
compressive strengths were proportioned to exceed their
target values by 10 to 20%, assuming that there would be a
strength reduction due to the large batch size and the
increased difficulty in maintaining quality control in truckmixed batches. In both cases, however, as will be discussed
later, the compressive strengths of the truck-mixed batches were
approximately
p
y the same as those of the laboratoryy batches.
The coarse aggregates
gg g
were crushed stone qquarried in
Butner, NC, with a nominal maximum size of 3/8 in. (9.5 mm).
Manufactured sand made from the same type
yp of rock was used
because the lab mixtures had clearlyy
as fine aggregates
gg g
shown that it would increase the compressive
p
strength
g of
concrete. The cement was Type I/II. Additional details on
2
703 (417) 703 (417) 935 (555)
3
Densified microsilica fume, lb/yd (kg/m ) 75 (44)
Amir Mirmiran, FACI, is Professor and Interim Dean of the College of Engineering
and Computing at Florida International University, Miami, FL. He is a member of
ACI Committees 440, Fiber Reinforced Polymer Reinforcement, and E803, Faculty
Network Coordinating Committee, and Joint ACI-ASCE Committee 343, Concrete
Bridge Design. His research interests include high-strength concrete and advanced
composite materials for bridge applications.
Sami Rizkalla, FACI, is Distinguished Professor of Civil Engineering and Construction at
North Carolina State University. He serves as Director of the Constructed Facilities
Laboratory as well as the NSF I/UCR Center on Repair of Structures and Bridges at
NC State. He is a member of ACI Committees 440, Fiber Reinforced Polymer Reinforcement,
and E803, Faculty Network Coordinating Committee, and Joint ASI-ASCE Committees
423, Prestressed Concrete, and 550, Precast Concrete Structures.
10 ksi
14 ksi
18 ksi
(69 MPa) (97 MPa) (124 MPa)
Materials
75 (44)
75 (44)
Fly ash, lb/yd3 (kg/m3)
192 (114) 192 (114)
50 (30)
Sand, lb/yd3 (kg/m3)
1055 (625) 1315 (780) 1240 (736)
Rock (diabase 78M), lb/yd3 (kg/m3)
1830
(1085)
1830
(1085)
1830
(1085)
Water, lb/yd3 (kg/m3)
292 (173) 250 (148) 267 (158)
High-range water-reducing admixture
(HRWRA), oz/100 lb (mL/100 kg)*
17 (1110) 24 (1565) 36 (2345)
Retarding agent, oz/100 lb (mL/100 kg)* 3 (195)
3 (195)
3 (195)
w/cm
0.30
0.26
0.25
Average 28-day compressive strength of
laboratory batch, ksi (MPa)
11.45
(78.9)
14.37
(99.1)
17.09
(117.8)
*
Ounces per 100 lb of cementitious materials (mL per 100 kg cementitious materials).
the trial batches and the selected mixture proportions can be
found elsewhere.111
Specimen preparation and curing procedures
Concrete was batched in a ready mixed concrete plant
using commercial production procedures. The 4 x 8 in.
(100 x 200 mm) and 6 x 12 in. (150 x 300 mm) cylinders
were used for the compressive strength and elastic modulus
of concrete, and 6 x 6 x 20 in. (150 x 150 x 510 mm) beams
were used for the modulus of rupture. Cylinders were cast in
plastic molds, and the beams were cast in steel molds. The specimens were made according to AASHTO T23 (ASTM C31)
(ACI 363.2R-9812). Table 2 shows the test matrix. Testing ages
were 1, 7, 14, 28, and 56 days. On each testing day, two of the
4 x 8 in. (100 x 200 mm) cylinders were used to determine the
elastic modulus before being tested to failure.
The specimens were subjected to one of the three
following curing conditions: 1) 7-day moist curing to represent
typical curing procedures for reinforced concrete members;
2) 1-day heat curing similar to that used in precast concrete
plants for prestressed structural members; and 3) continual
moist curing until the day of testing according to the ASTM
standards used for the purposes of quality control and certifying
the compressive strength of concrete in the industry.12 The heatcured specimens were placed in a chamber with a heating
regime ramping up to a constant temperature of 150 to 160° F
(66 to 71°C), and back to room temperature in 24 hours.
Testing procedures and instrumentations
The cylinders were ground at both ends before testing to
remove any surface irregularity and to also ensure that the
ends would be perpendicular to the sides of the specimen.
Compression tests were performed using a Universal testing
machine for both the 4 x 8 in. (100 x 200 mm) and the 6 x 12 in.
(150 x 300 mm) cylinders. Tests followed ASHTO T22
(ASTM C39) at a loading rate of approximately 0.04 ksi/s
(0.28 MPa/s). The loading rate was selected at the higher end
of the standard range to avoid prolonged loading, which could
possibly cause extensive microcracking in concrete cylinders.
The elastic modulus was determined using the 4 x 8 in.
(100 x 200 mm) concrete cylinders and in accordance with
ASTM C469. Deflections were measured using potentiometers
ACI Materials Journal/September-October 2009
Table 2—Description of test specimens for each target strength
Testing age (days)
Specimen
Test type
4 x 8 in. (100 x 200 mm) cylinders
Axial compression
Curing method
1
7
14
28
56
Total
7-day moist curing
3
3
3
3
3
15
1-day heat curing
3
3
3
3
3
15
3
3
Continual moist curing
Total number of 4 x 8 in. (100 x 200 mm) cylinders
6 x 12 in. (150 x 300 mm) cylinders
Axial compression
7-day moist curing
3
3
6
1-day heat curing
3
3
6
Continual moist curing
3
3
Total number of 6 x 12 in. (150 x 300 mm) cylinders
6 x 6 x 20 in. (150 x 150 x 510 mm) beams
Modulus of rupture
6
36
6
18
7-day moist curing
3
3
3
3
3
15
1-day heat curing
3
3
3
3
3
15
Continual moist curing
Total number of 6 x 6 x 12 in. (150 x 150 x 510 mm) beams
3
3
33
Fig. 1—Fully instrumented 4 x 8 in. (100 x 200 mm)
cylindrical specimen.
Fig. 3—Compressive strength of 4 x 8 in. (100 x 200 mm)
cylinders at 28 days.
Fig. 2—Modulus of rupture test setup.
attached to two fixed rings (Fig. 1). Four vertical potentiometers
measured axial deflections, while two horizontal potentiometers
attached at midheight measured lateral dilation of concrete.
The apparatus consisted of two aluminum rings with screws
for attachment to the specimen. Prior to attaching the apparatus
to the specimen, the rings were joined by three aluminum bars.
The spacing between the screws on the top ring and the
screws on the bottom ring when the aluminum bars were
attached was 5 in. (127 mm), which served as a gauge length
for calculating axial strains from the measured deformations.
The modulus of rupture beams were placed in the testing
frame, oriented in such a way that the specimen was turned
on its side with respect to its molded position, as specified in
ASTM C78 (Fig. 2). The load was applied using a hand
pump. The loading rate was controlled such that the stress at
the extreme bottom fiber of the beam would increase at a rate
of 0.15 ksi/s (1.03 MPa/s).
ACI Materials Journal/September-October 2009
TEST RESULTS AND DISCUSSIONS
Compressive strength
The compressive strengths for the first two concrete
mixtures exceeded their target values, whereas the third
batch failed to reach its target value (Table 1). The tests,
however, still provided useful information for expanding and
adding to the knowledge base on mechanical properties of HSC.
The effects of curing procedures on the compressive
strength measured from the 4 x 8 in. (100 x 200 mm) cylinders
at 28 days are illustrated in Fig. 3. The 7-day moist-cured
specimens showed the highest compressive strengths at 28 days
in each of the three batches. The 1-day heat curing increased
strength gain at an early age, but weakened it at later ages. This
behavior was attributed to rapid hydration, which causes the
structure of the cement paste to be more porous than when
cement paste hydrates slowly. The higher porosity, in turn,
leads to decreased strength. Although the majority of the
strength gain in heat-cured specimens occurred within the
first few days, their strength continued to increase until 56 days,
albeit at a slow rate. The average 28-day strength of the 7-day
moist-cured specimens were 1.17, 1.10, and 1.16 times those
of the heat-cured specimens for the 10, 14, and 18 ksi
(69, 97, and 124 MPa) target strengths, respectively. The
continually moist-cured specimens exhibited a slightly
lower strength, with failure closer to the surface, primarily
because of the remaining moisture in the capillary pores.
3
Fig. 4—Strength gain over time expressed as percentage
of 28-day strength.
Fig. 5—Elastic modulus versus compressive strength. (Data
from References 4 and 13 to 18).
The strength gain of concrete over time is depicted in Fig. 4.
For the 10 and 14 ksi (69 and 97 MPa) target strengths, the heatcured specimens reached approximately 90% of their 28-day
strength during the first day of curing. The specimens made
from the 18 ksi (124 MPa) target strength concrete also
gained the majority of their 28-day strength in the first day,
but at a lower rate. This was attributed to: 1) higher heat of
hydration resulting from the larger cement content in the
mixture; and 2) the larger dose of high-range water-reducing
admixture in the mixture.
Elastic modulus
The current code equation in ACI 318-053 and the
AASHTO-LRFD2 for estimating the elastic modulus of
concrete is as follows
E c = 33w c
1.5
E c = 0.043w c
1.5
f cc psi
(1)
where w is the unit weight of concrete, and fcc is the 28-day
compressive strength. ACI 363R-925 suggests the following
alternative equation
Ec = (40,000(fcc )0.5 + 106)(wc /145)1.5 (psi)
4
Fig. 7—Statistical comparisons for modulus of elasticity.
Figure 5 shows test results from this research project as
compared to the ACI 318-053 (AASHTO-LRFD2) and the
ACI 363R-925 equations. In the same figure, data by
others4,13-18 are also shown for comparison. The measured
values are generally in agreement with the predicted values
calculated using the ACI 363R-925 equation, regardless of
the curing method. The data also support the statement in
ACI 363R-925 that the ACI 318-053 (AASHTO-LRFD2) equation consistently overestimates the elastic modulus for HSC.
A total of 4388 test data for elastic modulus, with concrete
strengths between 3.7 to 24 ksi and unit weight between
90 to 176 lbf, were collected from the literature19 (see
Reference 20 for details). Based on the collected data, the
following equation for the elastic modulus of concrete with
compressive strength up to 18 ksi (124 MPa) is proposed20
Ec (ksi) = 310,000K1[wc(kip/ft3)]2.5 × [fcc (ksi)]0.33
f cc MPa
Ec = (3320( fcc )0.5 + 6900)(wc /2320)1.5 (MPa)
Fig. 6—Predictions of over 4400 data points using proposed
equation.
(2)
Ec (MPa) = 0.000035K1[wc(kg/m3)]2.5 × [fcc (MPa)]0.33 (3)
where K1 is the correction factor to account for the source of
aggregates, which may be taken as 1.0 unless determined by
physical tests. The collected data, including results from this
study, are compared with the proposed equation in Fig. 6.
The figure indicates that the collected data are still scattered,
however, with an improved R2 = 0.76. Figure 7 shows the
probability distribution of the modulus of elasticity data as a
function of the predicted over the measured value for the
ACI Materials Journal/September-October 2009
Fig. 8—Poisson’s ratio for various concrete strengths.
three different equations using statistical analysis. The
figure shows that the ACI 318-053 (AASHTO-LRFD2)
equation overestimates the elastic modulus. Although
the ACI 363R-92 5 equation has the lowest standard deviation
among the three predictions, its predictions are slightly
conservative. The proposed equation, on the other hand,
has the best normal distribution, although its standard deviation
is slightly higher than that of the ACI 363R-925 equation.
Poisson’s ratio
Following ASTM C469,12 Poisson’s ratio was determined
using the measured lateral and axial strains of the cylinders
tested in compression, based on two points on the stressstrain curve. The lower point was defined by an axial strain
value of 0.00005, while the upper point was defined by an
axial stress value of 40% of the peak stress. The measured
Poisson’s ratios for concrete had large variations, as shown
in Fig. 8. Test results do not show an apparent correlation
between the Poisson’s ratio and the measured compressive
strength. In addition, it was observed that curing procedures
and age of concrete had little or no effect on the Poisson’s
ratio. The average Poisson’s ratio for all tested cylinders is
0.17 with a standard deviation of 0.07. The generally
accepted range for the Poisson’s ratio of NSC is between
0.15 and 0.25, while it is generally assumed to be 0.2 for
analysis.21 Test data from this project suggest that it is
reasonable to use 0.2 as Poisson’s ratio for HSC up to
compressive strength of 18 ksi (124 MPa).
Modulus of rupture
Effect of curing methods on the modulus of rupture for the
three different target strengths are shown in Fig. 9. Test
results suggest that the modulus of rupture is significantly
affected by curing conditions for all target strengths. The
trend indicates that removal of the beam specimen after 7 days
from the curing tank causes a significant reduction of the
modulus of rupture. Similarly, the 1-day heat-cured beams
showed low values of the modulus of rupture due to the
dryness after removal from the molds, which had prevented
moisture loss during the first day of curing. In both cases, the
reduced modulus of rupture is attributed to the microcracks
initiated by drying shrinkage. The low permeability of the
HSC is expected to cause differential shrinkage strains
across the depth of the specimen due to the fact that the
moisture trapped in the interior part of the specimens
ACI Materials Journal/September-October 2009
Fig. 9—Effect of curing process on modulus of rupture for
concrete compressive strength: modulus of rupture versus
time for (a) 19 ksi (69 MPa) target strength; (b) 14 ksi (97 MPa
target strength; and (c) 18 ksi (124 MPa) target strength.
cannot evaporate as quickly as the surface moisture. This
relative shrinkage difference causes microcracking of
concrete. Therefore, the specimens that were moist-cured up
to the day of testing showed much higher modulus of rupture
than those cured differently.
Figure 10 shows test data from material study tested in
this program along with the data collected from the litera5
•
•
Fig. 10—Modulus of rupture versus compressive strength.
ture.1,7,13,16,19 Two equations for modulus of rupture given
in Section 5.4.2.6 of the current AASHTO-LRFD2 are also
shown in the figure. Some of the tests results correspond
better to the current upper bound of the AASHTO-LRFD.2
This is mainly due to the curing condition and moisture
content of the specimens. Test results suggest that the
current lower bound of the AASHTO-LRFD2 overestimates
the modulus of rupture for HSC. A better predictive equation,
which is the lower bound of the test data, fr = 0.19 f c c ksi (fr
= 0.5 f cc MPa ), is proposed for HSC up to 18 ksi (124 MPa).
CONCLUSIONS AND RECOMMENDATIONS
A total of thirty-six 4 x 8 in. (100 x 200 mm) cylinders,
eighteen 6 x 12 in. (150 x 300 mm) cylinders, and thirtythree 6 x 6 x 20 in. (150 x 150 x 510 mm) beams were
prepared with three different target compressive strengths of
10, 14, and 18 ksi (69, 97, and 124 MPa) using ready mixed
concrete delivered from a batch plant. Three different curing
regimes were used; 1-day heat curing, 7-day moist curing,
and continuous moist curing until the day of testing. The
specimens were tested to determine short-term mechanical
properties of HSC. Based on the test data from this research
combined with those from the literature, the following
conclusions can be drawn:
• Of the three different curing methods, cylinders with 7-day
moist curing exhibited the highest compressive strengths at
ages of 28 and 56 days. In contrast, 1-day heat curing
generally resulted in the lowest strength. Cylinders
moist-cured up to the day of testing resulted in strengths
slightly lower strengths than their counterparts with 7-day
moist-curing. The reduction in the strength may be
attributed to the differences in the internal moisture
conditions of the concrete at the time of testing.
• Comparisons of the strength gain under various curing
regimes showed that moist curing of HSC beyond 7 days
would not result in any significant increase in strength.
This is believed to be due to the low permeability of HSC
and the short time required for the capillary pores of HSC
to be blocked.
• The equation specified by the AASHTO-LRFD2 overestimated the elastic modulus for all specimens. Based on the
tests’ results and the collected data in the literature, a new
equation for the elastic modulus of concrete with compressive strength up to 18 ksi (124 MPa) was proposed.
• A Poisson’s ratio of 0.2 specified by the AASHTOLRFD2 can adequately be used for HSC up to 18 ksi
6
(124 MPa).
The modulus of rupture was reduced significantly for
specimens removed from their sealed or moist environments
and allowed to dry. The continuously moist-cured
specimens developed modulus of rupture values, in
some cases twice as much as those obtained from the
7-day moist-cured specimens.
The upper bound equation specified by the AASHTOLRFD2 provided a good estimate of the modulus of
rupture for the continuously moist-cured specimens,
but overestimated the modulus of rupture for the 1-day
heat-cured and 7-day moist-cured specimens. The
lower bound equation specified by the AASHTOLRFD2 overestimated the measured modulus of rupture
for 1-day heat-cured and 7-day moist-cured specimens.
Based on the test results, a better predictive equation,
lower bound of the test data, was proposed for HSC up
to 18 ksi (124 MPa).
ACKNOWLEDGMENTS
This study was sponsored by the American Association of State Highway
and Transportation Officials in cooperation with the Federal Highway
Administration, and was conducted as part of the National Cooperative
Highway Research Program Project 12-64, which is administered by the
Transportation Research Board of the National Research Council, Senior
Program Officer D. Beal. The experiments were carried out at the
Constructed Facilities Laboratory at North Carolina State University. The
contributions of consultants—H. Russell of Henry Russell, Inc. and R. Mast
of Berger/ABAM Engineers, Inc.—are greatly acknowledged. The assistance of
Ready Mixed Concrete, Boral Material Technologies, Degussa Admixtures,
Roanoke Cement, Carolina SunRock , and Elkem are also greatly appreciated.
Z. Wu, S. Kim, and H. C. Mertol provided significant assistance during all
aspects of this research program. The findings and opinions expressed in
this paper, however, are those of the authors alone and not necessarily the
views of the sponsoring agency.
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