Recycled concrete aggregate (RCA) is produced by breaking down concrete reclaimed from demolished structures and using it as aggregate in new concrete. The recycling mechanism involves several steps: demolition, collection of concrete waste, crushing, sorting, and sometimes treatment to improve quality by reducing contaminants like old mortar and rebar. RCA differs from virgin aggregate in several aspects, including higher porosity, lower density, and varied particle size distribution, all of which stem from the residual mortar remaining on the aggregate. These characteristics affect the water absorption and chemical properties of RCA, influencing how it interacts with new cement paste in concrete mixes.