Assessment of durability and thermal stability in cementitious composites with Coal Washery Rejects

The current study is designed to evaluate the durability, microstructural behaviour, and economic feasibility of incorporating Coal Washery Rejects (CWR) as a partial coarse aggregate replacement in concrete. Four mixes (0%, 25%, 50%, and 75% CWR) were assessed for water absorption, drying shrinkage, chloride permeability, sulphate resistance, and compressive strength. Results showed that water absorption increased from 1.22% to 1.70% and chloride permeability from 1755 to 2315 Coulombs as CWR content rose. Microstructural analysis confirmed the inert nature of CWR via XRD (dominant phases: Quartz, Alumina, Hematite), and SEM revealed increased porosity and weaker ITZ in higher CWR mixes, particularly M50. Despite minor reductions in durability, economic analysis indicated net savings of ₹850/m³ for M50 and over ₹1000/m³ for M75, along with up to 23.8% reduction in embodied CO₂. The M50 mix achieved the best balance between performance and sustainability, validating the potential of CWR as a sustainable, cost-effective alternative for low to moderate strength applications.