Effects of recycled aggregate replacement modes and binder systems on concrete mechanical properties: an evidence based review of raw indicators

This review analyzes how replacement modes and binder systems affect recycled aggregate concrete using raw 28-day indicators. Two summary tables compile original values of compressive strength, splitting tensile strength, elastic modulus, and slump. In ordinary Portland cement systems, replacing natural coarse aggregate by 50 to 70 % reduces strength and stiffness while keeping slump in a workable range. Powder blends with fly ash and slag around 30 % partly recover stiffness. Higher water to binder ratios lower all indicators. Mixed recycled coarse aggregates that include waste brick show larger losses. In geopolymer systems, increasing recycled coarse aggregate from zero to full replacement decreases strength and stiffness, with only a modest drop in slump. The evidence supports a practical window of 50 to 60 % coarse replacement for structural use in ordinary Portland cement, with targeted mix design required beyond that level.