This paper evaluates the effect of discrete fibers in concrete on the pulse velocity and mechanical properties of FRC. Two different type of synthetic fibers consisting of Polypropylene and Nylon were investigated. The effect of concrete mix proportions such as types of fiber, volume fraction of fiber, water-to-cement ratio (w/c), and curing conditions were examined. An experimental program was designed and conducted on 100 mm x 200 mm cylindrical specimens to evaluate the properties of FRC. The compressive strength obtained from the Compression Test Machine (CTM) was compared to those calculated from UPV. The difference between two types of synthetic fibers on concrete properties were investigated. Results show that the highest compressive strength of Polypropylene Fiber Reinforced Concrete (PFRC) was achieved at 0.5% fiber volume fraction, whereas for Nylon Fiber Reinforced Concrete (NFRC) the highest compressive strength was obtained at 1.0% fiber volume fraction. Additionally, results show that the available equations relating UPV to compressive strength of concrete need modifications when used for different fibers. Therefore, either new or modified empirical equations are needed for better estimation of mechanical properties of FRC.
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