Properties of Sustainable Concrete Mixtures Incorporating Waste Concrete and Silica-Based Binders

Rapid urbanization and intensive construction activities have significantly increased concrete demand, imposing substantial environmental burdens due to resource depletion and waste generation. Recycling construction and demolition waste into recycled concrete aggregate (RCA) addresses sustainability, but reduces concrete performance due to the inherent porosity and weakened interfacial bonds of RCA. This study investigated the effectiveness of silica fume (SF) and silica fume slurry (SFS) at dosages of 0%, 5%, 7.5%, and 10% in improving mechanical and durability properties of recycled aggregate concrete (RAC). Results indicated that RCA incorporation reduced compressive strength, splitting tensile strength, modulus of elasticity, and increased water absorption compared to natural aggregate concrete (NAC). At 10% SFS, RAC achieved up to 39% improvement in compressive strength and 55% reduction in water absorption. These enhancements were attributed to refined pore structure and a strengthened interfacial transition zone, making silica fume an effective strategy for producing durable and high-performance recycled concretes.