Low-Carbon Concrete Comprising High-volume Pozzolan and Recycled Aggregate: Evaluating Mechanical Performance, Microstructure, Environmental Impact, and Cost Efficiency

Conventional concrete, the most extensively used construction material in the world today, heavily relies on natural resources and significantly contributes to environmental degradation due to its high carbon footprint. To address these issues, this study aims to design and evaluate the performance of low-carbon concrete mixes prepared through a collaborative effect of pozzolans (such as volcanic ash (VA), pulverized fuel ash (PFA), glass powder (GP), and ground granulated blast furnace slag (GGBS)) and recycled concrete aggregate (RCA). For this motive, various tests were performed to assess the mechanical properties, microstructural characteristics, environmental impact, and production cost of low-carbon concrete mixes with respect to OPC-based concrete. Test results revealed that the inclusion of 20% RCA reduced the compressive, splitting tensile, and flexural strengths by 12%, 9%, and 16%, respectively. However, the inclusion of 30–45% pozzolanic materials significantly enhanced the mechanical properties of recycled concrete, with the 10GP-30GGBS combination demonstrating the highest enhancements. Ultrasonic pulse velocity (UPV) tests revealed about 5–11%, 9–11%, and 11–14% improvements for the samples comprising GP-VA, GP-PFA, and GP-GGBS, respectively. The water absorption progressively reduced from 4.9% to 3.6% for GP-VA combinations, from 4.6% to 3.3% for GP-PFA combinations, and from 4.0% to 2.9% for GP-GGBS combinations. From the microstructure observation and EDX analysis, notable improvements were found at the micro level together with the presence of higher silica content in pozzolan-based mixes, which contributed to the additional formation of CSH and CASH gels. Furthermore, environmental impact and cost analysis of modified mixes revealed significant reductions in carbon emissions (up to 39%) and overall cost (up to 16%) in comparison to the reference sample. Overall, it can be inferred that the combined use of GP-VA, GP-PFA, and GP-GGBS as replacements for OPC in low-carbon concrete mixes effectively enhances mechanical properties, reduces environmental impact, and lowers production costs, making it a viable approach for sustainable concrete production.