Materials selection for concrete overlays : the final report Page: 68
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4.4.4 Modulus of Elasticity
The modulus of elasticity was determined in accordance with ASTM C469.- 10
"Standard Test Method for Static Modulus of Elasticity." The modulus of elasticity was
measured at seven-day and 28-day using specimens later tested for compressive strength. One of
the three 4-in. by 8-in. concrete cylinders was loaded to 40% of its ultimate load. The other two
cylinders were strain gauged and tested up to failure.
4.4.5 Average Residual Strength (ARS)
One of the benefits of incorporating fibers into concrete is their ability to bridge and carry
load after the concrete cracks. The distributed fibers act as tensile-load carrying elements and
their quantifiable after-crack strength is called residual strength.
The average residual strengths (ARS) were determined in accordance with ASTM C1399
- 10 "Standard Test Method for Obtaining Average Residual-Strength of Fiber-Reinforced
Concrete" with a modification to the apparatus and procedure using four-point bending. For
each type of fibers tested, five 4-in. by 4-in. by 14-in. specimens were made using cast-in-place
method. It was made sure that the specimens were in 100% humidity until the specimens were
ready for testing at 7 days. The test was performed at TxDOT Materials Lab using their
modified test setup, as shown in Figure 4.8.
r' 1E
Figure 4.8. TxDOT ARS setup
The specimen was loaded until a TxDOT-specified 0.020-in. deflection was reached
instead of 0.008 in. as specified according to ASTM C1399. The reason for the modification in
procedure was that a majority of the specimens did not crack when a 0.008-in. deflection was
reached. Based on previous experience, the first crack occurred before reaching 0.020-in.
deflection on a majority of the specimens tested.
After the first crack, the specimen was unloaded, and the steel plate was removed. The
specimen was then reloaded and measured for ARS at 0.020, 0.030, 0.040, 0.050-in. deflection
increments. TxDOT developed a computer program that captured the data. After each test, the
dimensions of the specimen were measured and input into the program to get the final result. A68
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Kim, Dong H.; Fowler, David W.; Ferron, Raissa P.; Trevino, Manuel M. & Whitney, David P. Materials selection for concrete overlays : the final report, report, July 2012; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth303706/m1/88/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.