Flexural performance and tension-stiffening evaluation of reinforced concrete beam incorporating recycled aggregate and fly ash

Abstract

This paper presents the effect of fly ash in recycled aggregate concrete (RAC with 100% recycled coarse aggregates) on the flexural performance of reinforced concrete (RC) beam. Particle packing method (PPM) of mixture proportioning is used in a novel way for the flexure study. This method by principle accounts for the excess adhered mortar present on the outer surface of recycled coarse aggregates (RCA) while calculating maximum packing density and consequently minimize the requirement of fresh mortar. The parameters such as materials (aggregate type and fly ash), mix design method and reinforcement percentages are considered for evaluation of moment carrying capacity, deflection, and failure pattern. Based on experimental results, the constitutive relation for cracked RAC and natural aggregate concrete (NAC) is evaluated numerically showing tension stiffening effect. The results conclude mostly comparable moment carrying capacity of RAC incorporating fly ash beams and NAC beams at ultimate limit state. The maximum mid-span deflection has been observed to be higher, but the variation is not substantial at service load due to the effect of fly ash and PPM in RAC. The reduced tension-stiffening effect, as observed from the derived stress–strain relation of cracked concrete justifies the higher mid-span deflection in RAC. The applicability of existing code provisions for NAC beam is assessed for RAC with fly ash beams. The results suggest the potential application of 100% recycled coarse aggregates and up to 30% fly ash in a reinforced concrete beam without compromising its flexure performance.