Influence of different types of fibers on the mechanical properties of recycled waste aggregate concrete

Substantial volumes of concrete waste are generated daily from construction and demolition activities, which, from an environmental standpoint, have become a global concern. Recycled crushed stone aggregate (RA) generated as a byproduct of construction and demolition waste can be used to replace natural crushed stone aggregate (NA). Although RA degrades various mechanical properties of concrete, incorporating fiber into the concrete mixtures may improve them. Thus, the present study investigates the influence of different fibers, such as galvanized iron (GI) fiber and polypropylene (PP) fiber, on the physical and mechanical properties of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). The GI fiber having 0.51 mm diameter with three different lengths, such as 15 mm, 26 mm, and 36 mm, and PP fiber having 0.03 mm diameter with 12 mm length were used at 0.5% by the volume of the total concrete mixture. The short and long-term compressive strength, splitting tensile strength, and flexural strength of fiber-based NAC and RAC were evaluated. Results revealed that the effect of GI fiber was more significant in compressive strength than that of PP fiber. Concrete with 15 mm long GI fiber showed the highest compressive and split tensile strengths than the other GI fiber reinforced concrete (GFRC). Approximately 42% and 13% higher split tensile strength was observed from NAC and RAC with 15 mm GI fiber. The GI fiber tended to arrest the crack formations in concrete better than PP fiber reinforced concrete. Moreover, incorporating GI fiber increased the flexural strength and toughness of the concrete compared to PP fiber. The cost sensitivity analysis revealed that approximately 18.8% of energy costs could be saved by replacing natural stone with recycled stone in GFRC. Finally, it is recommended to use 15 mm long GI fiber with an aspect ratio of 30 both in NAC and RAC.