Multi-scale performance, life-cycle and economic assessment of blended concrete using recycled coarse aggregates

The construction industry confronts dual challenges of natural resource depletion and construction waste accumulation, necessitating sustainable alternatives to conventional concrete production. This investigation evaluated mechanical properties, microstructural characteristics, environmental impacts, and economic feasibility of concrete incorporating recycled coarse aggregate (RCA) at varying replacement levels (0%, 12.5%, 25%, 50%, 65%) with ground granulated blast furnace slag (GGBS) supplementation (20%, 25%). Mechanical testing revealed optimal performance at 12.5% RA replacement, achieving 55.43 MPa, compressive strength at 28 days, representing 13% improvement over control specimens. Higher replacement ratios demonstrated progressive strength deterioration, with 65% replacement yielding 48% reduction in compressive strength. Microstructural analysis through SEM-EDS confirmed enhanced interfacial transition zone densification in RA12.5%+GGBS mixes, correlating with superior mechanical performance. Life cycle assessment following ISO 14040:2006 demonstrated 27% reduction in carbon emissions (282.2 vs. 386.7 kg CO₂-eq/m³) for RA12.5%+GGBS25% configuration, with manufacturing processes contributing 46.5% of total environmental burden. Environmental impact categories showed consistent improvements, particularly resource depletion (28.2% reduction) and terrestrial acidification (24.2% reduction). Economic analysis revealed 30.6% lifecycle cost savings (₹13,550/m³) over 50-year service period despite modest 5.3% initial cost reduction, with 2.1-year payback period and favorable sensitivity to carbon pricing mechanisms (-3.8% per ₹100/ton CO₂). Sensitivity analysis identified cement price volatility as primary economic risk factor (± 6.8% impact). The convergence of optimal mechanical, environmental, and economic performance at 12.5% RCA with 20–25% GGBS substitution challenges conventional assumptions regarding linear sustainability benefits, establishing critical thresholds for sustainable concrete design in infrastructure applications.