Sustainable green concrete: multi-criteria optimization of bentonite–fly ash–silica fume ternary systems integrating life cycle assessment and mechanical performance analysis

Global CO₂ emissions from the cement sector account for approximately 8% of anthropogenic greenhouse gas emissions, underscoring the urgent need for sustainable concrete alternatives based on supplementary cementitious materials (SCMs). This study evaluates the mechanical performance, durability, and environmental impacts of green concrete mixtures incorporating bentonite, either alone or in combination with fly ash and silica fume as partial replacements for ordinary Portland cement (OPC). An experimental program encompassing 22 mixtures assessed workability, compressive strength at multiple ages, and resistance to seawater sulfate attack. A comprehensive life cycle assessment (LCA) was conducted using One Click LCA(tm) software to quantify environmental-mechanical trade-offs, with a case study application to the Damietta University Hospital project in Egypt. The results demonstrate that cement contributes 83-95% of the global warming potential (GWP) across all mixtures, confirming it as the dominant driver of environmental impact. Mixtures containing 50% fly ash achieved a GWP reduction of up to 50.1%. Mix 20 (4% bentonite + 15% silica fume) exhibited the highest compressive strength (49.0 MPa at 28 days, 54.27 MPa at 56 days) and superior seawater sulfate resistance, emerging as the structural optimum. In contrast, Mix 12 delivered the best environmental performance. Crucially, no single mixture simultaneously optimized both mechanical and environmental indicators, underscoring the need for context-dependent mixture selection guided by the Pareto frontier framework developed in this study.