This document reviews the use of recycled fine aggregate (RFA) in concrete as an alternative to natural river sand. It finds that RFA has higher water absorption and fineness modulus than natural sand, resulting in a need for a lower water-cement ratio in RFA concrete. However, RFA concrete can achieve comparable strength to natural sand concrete when nano-materials are added, since they help form additional calcium-silicate-hydrate gel. The document concludes that using RFA is an environmentally friendly way to address the shortage of natural construction sand, and nano-materials can improve the strength of concrete with high RFA content.