Multi-indicator decision modelling for sustainable high-performance concrete with full RCA substitution

Concrete’s reliance on cement and virgin aggregates drives greenhouse gas emissions and resource depletion. This study evaluates full replacement of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA, 0%–100%), partial cement substitution by silica fume (SF, 5%–10%) and nylon waste fibres (NWF, 0.1%–0.25%) on mechanical performance and cradle-to-gate focusing on global warming potential (GWP). A probabilistic life cycle assessment with 10,000 Monte Carlo draws (±10% input uncertainty) characterised GWP distributions. Comparative simulations (10 000 triangular draws) quantified mean reductions and probability of outperforming a virgin-aggregate reference. A multi-indicator matrix visualised per cent changes, and a tiered global sensitivity analysis (Spearman ρ) identified cement energy and transport as primary drivers. Finally, a multi-criteria decision analysis synthesised GWP into scores under Balanced, Climate-Focus and Health-Focus weightings. Results show SF and NWF reduce GWP variability by up to 3% and 2%, respectively, while 100% RCA with 10% SF and 0.1% NWF yields the lowest GWP score with >80% probability of outperformance. Compressive strength, splitting tensile strength and water absorption tests confirm 0.1% NWF and 10% SF mitigate strength losses from RCA. These findings establish optimal RCA–SF–NWF formulations balancing carbon savings, uncertainty reduction and structural performance.