Development and Experimental Performance Evaluation of Sustainable Concrete Incorporating Industrial Waste and Recycled Construction Materials for Low-Carbon Infrastructure

Abstract

Concrete production is a major source of anthropogenic carbon emissions, and the reuse of construction and demolition waste together with industrial by-products offers a practical route to reduce this burden. This study reports an experimental programme on seven concrete mixtures designed at a fixed water-to-binder ratio of 0.45 and a fixed total binder content of 380 kg/m³. Natural coarse aggregate was replaced by mass with 0%, 25%, and 50% recycled concrete aggregate (RCA), 30% of the Portland cement was replaced by a binary blend of 20% ground granulated blast-furnace slag (GGBS) and 10% fly ash, and in one mixture a further 5% of the binder mass, taken from the Portland cement, was replaced by silica fume, which gave a total cement replacement of 35%. Slump, compressive strength at 7, 28, and 90 days, splitting tensile and flexural strength, ultrasonic pulse velocity (UPV), water absorption, and rapid chloride penetration test (RCPT) charge passed were measured, and an itemised raw-material embodied carbon inventory was prepared for every mixture. Among the investigated mixtures, R50S30SF5 (50% RCA and 35% cement replacement) showed the best combination of properties, although no formal optimization procedure was applied. Its compressive strength was 43.8 MPa at 28 days and 47.9 MPa at 90 days, which is 6.4% and 2.0% below the control, its RCPT charge passed was 37% lower than that of the control (1980 C compared with 3150 C), and its calculated embodied carbon was 247.3 kg CO₂-eq/m³ compared with 356.9 kg CO₂-eq/m³ for the control, a reduction of 30.7%. At 28 days, the binary binder alone did not offset the strength loss caused by 50% RCA, and its benefit appeared mainly at 90 days and in combination with silica fume. The results show that these waste streams can be combined into concrete with mean strengths of about 44 to 48 MPa and a lower embodied carbon, but characteristic strength, chloride transport coefficients, and a wider life cycle boundary must be established before structural use.