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.