S20 / CONCRETE PROGRESS www.ROADSBRIDGES.com Kamil E. Kaloush, Ph.D., P.E., and Maria Carolina Rodezno I I n the past few years, the Arizona Department of Trans- portation (AzDOT) together with Arizona State University (ASU) and the local concrete industry constructed and tested several thin whitetopping (TWT) pavement sec- tions to evaluate their laboratory and field performance. Earlier projects included a major intersection in the city of Cottonwood in Yavapai County and a highway ramp on the Casa Grande- Tucson I-10 in Pinal County. Both projects utilized glass fibers, polypropylene fibers and crumb rubber as additives to the con- crete. The fibers were added at the normal dosage rate of 3 lb/ cu yd. The crumb rubber was added at 50 lb/cu yd to provide additional ductility to the concrete. The fiber-reinforced concrete plays a major role in increas- ing the ductility of TWT concrete pavement structures. It allows ultrathin and thin sections, normally 2 to 5 in., supported by the existing asphalt concrete layer, to act as a structural load-bear- ing system. Cracks or microcracks are intersected by random fibers that provide for the energy absorption and toughening. This effect is normally measured in the laboratory by evaluat- ing the post-peak region of the load-deformation responses. While all of the aforementioned test sections performed reasonably well, the polypropylene test sections performed the best in the laboratory testing program and the field. A third recent project was constructed on a very busy highway ramp of the Kingman-Seligman I-40 and was dedicated exclusively to evaluating the effects and benefits of utilizing different dos- ages of the polypropylene fibers in the TWT mix. Four differ- ent mixtures were evaluated in this third study: a control mix with no fibers and three mixtures with 3, 5 and 8 lb/cu yd of polypropylene fibers. For each mix, field samples during con- struction were collected and subjected to a laboratory testing program that included compression, three-point bending and round-panel tests. Divine intervention The study project is located in the Kingman-Seligman, Andy Divine interchange off the I-40 highway. The project included milling 5 in. of the existing asphalt surface and placing three TWT sections with the variable fiber dosages. A full-depth sec- tion with a control (no fiber) mix was constructed adjacent to the TWT sections. Approximately 413 sq yd of pavement was paved using these concrete sections. TWT pavement thicknesses were 5 in. for the fiber-reinforced sections. The section poured with the control mix had a 10-in. thickness after the complete removal of the original AC material. An approximate total of 70 cu yd of concrete were placed. All laboratory specimens were cast on the jobsite. The next day, the samples were transferred to a curing room at AzDOT facilities and kept for 28 days. The samples were then brought to ASU for testing at the structural laboratory. Several load frames, ranging from load capacities of 20 to 110 kps, equipped with servohydraulic closed-loop testing controllers, were used. Closed-loop testing allows monitoring and control of the response of a system during the test. Deflections were measured using linear variable differential transducers. Additives give concrete whitetopping strength Additives give concrete whitetopping strength
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S20 / CONCRETE PROGRESS www.ROADSBRIDGES.com
Kamil E. Kaloush, Ph.D., P.E., and Maria Carolina Rodezno
II n the past few years, the Arizona Department of Trans-
portation (AzDOT) together with Arizona State University
(ASU) and the local concrete industry constructed and
tested several thin whitetopping (TWT) pavement sec-
tions to evaluate their laboratory and fi eld performance. Earlier
projects included a major intersection in the city of Cottonwood
in Yavapai County and a highway ramp on the Casa Grande-
Tucson I-10 in Pinal County. Both projects utilized glass fi bers,
polypropylene fi bers and crumb rubber as additives to the con-
crete. The fi bers were added at the normal dosage rate of 3 lb/
cu yd. The crumb rubber was added at 50 lb/cu yd to provide
additional ductility to the concrete.
The fi ber-reinforced concrete plays a major role in increas-
ing the ductility of TWT concrete pavement structures. It allows
ultrathin and thin sections, normally 2 to 5 in., supported by the
existing asphalt concrete layer, to act as a structural load-bear-
ing system. Cracks or microcracks are intersected by random
fi bers that provide for the energy absorption and toughening.
This effect is normally measured in the laboratory by evaluat-
ing the post-peak region of the load-deformation responses.
While all of the aforementioned test sections performed
reasonably well, the polypropylene test sections performed
the best in the laboratory testing program and the fi eld. A third
recent project was constructed on a very busy highway ramp
of the Kingman-Seligman I-40 and was dedicated exclusively
to evaluating the effects and benefi ts of utilizing different dos-
ages of the polypropylene fi bers in the TWT mix. Four differ-
ent mixtures were evaluated in this third study: a control mix
with no fi bers and three mixtures with 3, 5 and 8 lb/cu yd of
polypropylene fi bers. For each mix, fi eld samples during con-
struction were collected and subjected to a laboratory testing
program that included compression, three-point bending and
round-panel tests.
Divine interventionThe study project is located in the Kingman-Seligman, Andy
Divine interchange off the I-40 highway. The project included
milling 5 in. of the existing asphalt surface and placing three
TWT sections with the variable fi ber dosages. A full-depth sec-
tion with a control (no fi ber) mix was constructed adjacent to
the TWT sections.
Approximately 413 sq yd of pavement was paved using
these concrete sections. TWT pavement thicknesses were 5
in. for the fi ber-reinforced sections. The section poured with the
control mix had a 10-in. thickness after the complete removal
of the original AC material. An approximate total of 70 cu yd of
concrete were placed.
All laboratory specimens were cast on the jobsite. The
next day, the samples were transferred to a curing room at
AzDOT facilities and kept for 28 days. The samples were then
brought to ASU for testing at the structural laboratory. Several
load frames, ranging from load capacities of 20 to 110 kps,
equipped with servohydraulic closed-loop testing controllers,
were used. Closed-loop testing allows monitoring and control
of the response of a system during the test. Defl ections were
measured using linear variable differential transducers.
Additives give concrete whitetopping strengthAdditives give concrete whitetopping strength
Prismatic specimens, 4 x 4 x 18 in., (width, depth, length)
were used for the three-point bending (fl exural) tests. The de-
formation across the tensile cracks was measured and used as
the feedback signal to the test machine. Cylindrical specimens,
3 in. in diameter and 6 in. long, were used for the compression
test. The round-panel test specimens were 24 in. in diameter
and 3 in. thick. The test yields a load-defl ection record and the
energy absorbed.
Test results were as follows:
Compression testBoth simple compression and closed-
loop tests were conducted on the vari-
ous mixes. Axial and radial deformations
were recorded during the test. The con-
trol mixture showed the highest strength
in both compression tests. The difference
within the fi ber-reinforced mixtures was
insignifi cant and was confi rmed by sta-
tistical analysis.
Flexural testThe tests also were performed under
simple and closed-loop control with ten-
sile displacement as the controlled vari-
able. The defl ection of the specimen was
measured to compute the energy absorbed throughout the test.
The cyclic test provides the post-peak response, which allows
the calculation of the material toughness. For the control mix,
no cyclic loading could be obtained, because the specimens
failed quickly after a peak load was reached. This failure was
attributed to the brittleness of the material. The peak responses
for the fi brous mixtures were very similar, but when the tough-
ness values are compared, it can be observed that toughness
increased as the fi ber content increased.
Round-panel testThe ASTM C1550-03a Standard Test Method for Flexural
Toughness of Fiber Reinforced Concrete Using Centrally Load-
ed Round Panel test method also was utilized in this study. All
mixes reached a very similar average peak load value. How-
ever, it was clear that the toughness values increased with the
increase of the fi ber. The mix with 8 lb/cu yd of fi bers had the
highest energy absorption capacity.
A residual strength analysis was conducted on both the
fl exural and round-panel tests. The fl exural test strength incre-
ments were modest of 9.5, 11.5 and 13% for the mixes with 3,
5 and 8 lb/cu yd, respectively. However, the round-panel test
results showed increments of 23, 37 and 42% for the 3, 5 and 8
lb/cu yd mixes, respectively. These results better show the ben-
efi ts of the fi bers added to the concrete mix. The increments
between the mixes (23, 14 and 5%) also suggest that there is a
14% increase in value between the 3 and 5 lb/cu yd mixes and
a 5% increase in value between the 5 and 8 lb/cu yd mixes.
Based on these percentages, it was determined that a 5 lb/cu
yd fi ber dosage has the best value-added benefi t to the mix.
CONCRETE PROGRESS / S21
Almost two years after their construction, a fi eld survey of
the test sections showed that they are all performing very well
with no signs of cracking or any other distress.
Thin air conditioningThere are several thermophysical properties that affect the
pavement maximum and minimum temperatures. These in-