OPTIMIZING THE STRUCTURAL AND DURABILITY PERFORMANCE OF CONCRETE USING RECYCLED AGGREGATES AND SUPPLEMENTARY CEMENTITIOUS MATERIALS

Abstract

Background: The construction industry generates approximately 1.3 billion tonnes of waste aggregate annually, while cement production accounts for nearly 8% of global CO₂ emissions. Integrating recycled coarse aggregates (RCA) and supplementary cementitious materials (SCMs) into concrete mix design offers a dual pathway to reduce environmental impact and manage construction waste streams. Objectives: This study systematically investigates the combined influence of varying RCA replacement levels (0–100%) and three SCM types—fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF)—on the structural performance and durability characteristics of concrete. Methods: Seven concrete mix designs were experimentally evaluated through 28-day compressive strength, splitting tensile strength, modulus of elasticity, water absorption, rapid chloride permeability (RCPT), and accelerated carbonation tests on 126 specimens following EN 12390 and ASTM C1202 protocols. Results: Silica fume at 10% replacement substantially mitigated strength losses associated with high RCA content, maintaining compressive strength above 40 MPa at 50% RCA. Chloride permeability increased with RA content but was effectively controlled in SCM-modified mixes. The M7 control mix with 100% RCA and no SCM exhibited the poorest durability, with chloride permeability of 4920 Coulombs and carbonation depth of 11.4 mm. Conclusion: Strategic SCM incorporation can compensate for the inherent quality limitations of recycled aggregate concrete, enabling structural-grade performance with substantially improved sustainability credentials.