An Experimental Study of Shear Resistance for Multisize Polypropylene Fiber Concrete Beams

To study the influence of polypropylene fibers with different thicknesses on concrete beams, inclined section shear tests of polypropylene fiber concrete beams were carried out. The cracking load, ultimate load, midspan deflection, reinforcement, and strain of polypropylene fiber concrete beams and conventional reinforced-concrete beams under shear were compared and analyzed. The load-bearing capacity of the rectangular beams was improved significantly by polypropylene fiber addition. Compared with conventional reinforced-concrete beams, the limit shear load of concrete beams with polypropylene fibers and multisize polypropylene concrete beams that were reinforced with three types of fibers increased by 8.67% and 17.07%, respectively. By mixing polypropylene fibers into concrete beams, the initial crack shear force of the beam was improved, the number of cracks was increased and the crack width was reduced, which can increase the beam ductility, inhibit crack formation and increase the strength. The computational formula of the shear ultimate bearing capacity of polypropylene fiber–concrete beams was revised according to composite material theory, and the calculated results were consistent with the test values.