Mechanical performance and eco-strength efficiency of sustainable concrete incorporating supplementary cementitious materials (SCMs), glass powder, and recycled plastic

This study evaluates the performance and environmental sustainability of concrete incorporating supplementary cementitious materials (SCMs): fly ash (FA), silica fume (SF), and bottom ash (BA) as partial cement replacements, and waste glass powder (GP) and recycled plastic (RP) as partial fine aggregate replacements. Eight mixes with varying replacement levels were tested for workability, fresh density, compressive and indirect tensile strength, dry density, void ratio, and water absorption at 14 and 28 days. The mix with 10% FA and 15% GP (Mix 1) performed best, increasing compressive strength by 7.9% and 9.2% and indirect tensile strength by 48% and 42.3% at 14 and 28 days, respectively, versus the control. Mixes with high RP or combined high replacement levels (e.g., 50% RP in Mix 7) showed severe strength loss, with compressive strength reductions above 95% in extreme cases. A sustainability assessment using embodied carbon (EC) and eco-strength efficiency (ESE) showed that high SCM contents cut CO₂ emissions by up to 37.5% at 45% cement replacement. Mix 1 achieved the highest ESE, 18.4% above the control. Thus, very high replacement levels can drastically reduce mechanical properties, but well-optimized SCM and waste combinations, particularly FA with GP, can enhance mechanical performance while reducing environmental impact. The study is novel in its multi-material simultaneous substitution approach and its use of the ESE index to systematically identify mixes that balance strength and embodied carbon reduction.