Optimization of the life cycle environmental impact of shell powder and slag concrete using response surface methodology

The growing environmental concerns associated with the high carbon emissions of ordinary Portland cement (OPC) production, and the accumulation of industrial and marine waste materials, necessitate innovative solutions in the construction industry. This study evaluates the environmental feasibility of recycling industrial byproduct slag (BFS) and waste oyster shell powder (OSP) as alternative materials for traditional cement. The first to comprehensively evaluate the environmental impacts of concrete mixtures incorporating waste oyster shell powder (OSP) and blast furnace slag (BFS) using a combined Response Surface Methodology (RSM) and Life Cycle Assessment (LCA) approach. First, the RSM was used to design mixture ratios to balance performance with low environmental impact. Then, LCA was used to assess the environmental benefits from a "cradle-to-grave" perspective. The results indicate that adding OSP and BFS significantly reduces the global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP) of the mixtures. Specifically, when the incorporation levels of OSP and BFS increased, the reductions in GWP, AP and EP were 8.24–48.52 %, 7.37–36.42 %, and 6.45–31.11 %, respectively. However, the addition of OSP and BFS negatively impacted the ozone depletion potential (ODP) and photochemical ozone creation potential (POCP), since it increased the ODP and POCP by 16.89–48.27 % and 8.63–28.52 %, respectively. Additionally, the compressive strength of the mixtures was 29.78–47.67 MPa, which showed a general declining trend with increased substitution of cement with OSP and BFS. Thus, an optimization analysis of environmental impacts guided by compressive strength was conducted to optimize the balance between environmental impact and structural performance. For a compressive strength requirement of 35 MPa, the incorporation rates of OSP and BFS were relatively high (8.71 % and 37.78 %, respectively), and the environmental impact was relatively low. When the compressive strength requirement increased, the substitution rates of OSP and BFS gradually decreased, and the environmental impact increased. When the compressive strength requirement reached 45 MPa, the addition rates of OSP and BFS decreased to 4.49 % and 11.17 %, respectively. This research highlights the potential of using waste materials as functional substitutes in mixtures and contributes to sustainable construction practices while maintaining material performance.