Performance Evaluation of 20.6 Mpa Concrete with 50% Recycled Coarse Aggregate Incorporating Silica Fume and Glass Powder

Abstract

Recycled coarse aggregate (RCA) often reduces concrete strength due to its higher porosity and the presence of adhered mortar, limiting its structural application. This study investigates the use of silica fume (SF) and glass powder (GP) as supplementary cementitious materials to enhance a concrete mixture designed for f’c = 20.6 MPa with 50% RCA replacement (by mass) of natural coarse aggregate. Three modified mixtures were produced using 10% SF, 15% GP, and a binary blend of 10% SF + 10% GP (as partial cement replacements) and were compared against (i) a natural- aggregate control and (ii) a 50% RCA mixture without additions. Compressive strength was evaluated at 7, 21, and 28 days, while splitting tensile strength was measured at 28 days. In addition, CO₂ emissions were estimated per cubic metre of concrete based on material-specific emission factors. Results indicate that the 50% RCA mixture without additions exhibited a 10.6% reduction in 28-day compressive strength compared to the natural-aggregate control. The incorporation of supplementary cementitious materials significantly improved mechanical performance, with the binary mixture achieving the highest values: 32.98 MPa compressive strength and 2.39 MPa splitting tensile strength at 28 days. From an environmental perspective, the optimized binary mixture reduced CO₂ emissions by approximately 19% relative to the reference concrete. These findings demonstrate that the combined use of SF and GP can effectively compensate for the mechanical limitations of RCA while simultaneously reducing the carbon footprint of concrete with high recycled content.