Influence of recycled fine aggregate on microstructure and hardened properties of concrete

The objective of this work was to investigate the effect of commercially produced recycled fine aggregate (RFA) on the compressive, tensile and microstructural behaviour of recycled aggregate concrete (RAC). The effect of RFA as a substitute for natural sand at various volume replacement levels (0, 25, 50, 75 and 100%) on the compressive strength, splitting tensile strength and flexural strength of RAC was studied. For 100% replacement of natural fine aggregate (NFA) by RFA, the compressive, splitting tensile and flexural strengths were found to decrease by 13·51, 6·46 and 22·62% respectively. Microstructures of a control concrete and concrete made with RFA (RFAC) were compared, and scanning electron microscopy observations showed that the RFAC contained more unhydrated cement particles and more voids, and its calcium silicate hydrate gel was less dense than that observed in the concrete made with NFA.