Recycled fine aggregates (RFA) are derived from crushed waste concrete and other construction materials smaller than 4.75 mm in size. The process of creating RFA involves the collection of concrete waste, its subsequent crushing, screening, and sometimes additional processing to remove impurities and improve quality. The primary characteristic that distinguishes RFA from virgin fine aggregates is the presence of old cement paste, which remains attached to the aggregate. This residual paste affects the aggregate’s surface texture, porosity, and particle shape, influencing how the RFA interacts with new cementitious materials in concrete mixes. These interactions are critical in determining the workability, strength, and durability of the resulting concrete.