Effect of type and volume fraction of recycled-tire steel fiber on durability and mechanical properties of concrete

Tire-bead steel wires derived from the pyrolysis of waste-tires can be converted into the discrete reinforcement for fiber-reinforced concrete (FRC). This study for the first time presents the information about selecting the optimum dosage of recycled steel-fibers (RSF) in FRC application. Therefore, two most common types of RSF i.e., plain RSF (PRSF) and twisted RSF (TRSF) were incorporated in a high strength plain concrete (PC) at seven different volume fractions i.e., 0%, 0.25%, 0.5%, 0.75%, 1%, 1.5% and 2%. Both physical and mechanical properties of FRCs were studied including density, compressive strength-f(CU), modulus of rupture-f(R), splitting-tensile strength-f(SP), ultra-sonic pulse velocity-UPV, and water absorption-WA. The results revealed that TRSF performed better than PRSF in overall mechanical performance. Maximum compressive strength-f(CU), 9-12% higher than PC, was achieved with a 0.75% volume fraction of PRSF or TRSF. TRSF was extremely useful in upgrading the f(SP) and f(R) by more than 82% and 109%, respectively, at a 1.5% volume fraction w.r.t PC. PRSF-FRC showed lower permeability than TRSF-FRC at the same volume fraction. Lower volume fractions i.e., 0.25-0.5% RSF reduced the permeability of FRC, while higher volume fractions were detrimental to WA and RCP resistance. Experimental values of mechanical (i.e., f(SP) and f(R)) and permeability properties (i.e., WA and RCP) were accurately related to predicting RSF-FRC as a function of strength class of PC and reinforcement index.