Eco-optimized ternary mortars incorporating industrial waste: Mechanical performance, statistical, microstructure, and life cycle impact

This study investigates the formulation of high-performance, low-carbon mortars by partially substituting 30 % of Portland cement with a ternary combination of blast furnace slag (BFS), brick waste powder (BWP), and marble waste powder (MWP). Ten mortar compositions were developed using a statistical mixture design to evaluate the influence of industrial by-products on mechanical properties, microstructure, and environmental performance. Results indicate that formulations containing 33–66 % BFS and 33–50 % BWP achieved significant improvements in long-term strength, with compressive strength increasing from 17.5 to 55.1 MPa and flexural strength from 7.52 to 12.6 MPa at 180 days. A maximum density of 2.33 g/cm³ was observed, indicating enhanced matrix densification and binder hydration. SEM-EDX analysis confirmed reduced porosity and synergistic pozzolanic interaction, primarily attributed to BFS reactivity and the filler role of BWP. Predictive models derived from the ternary mixture design exhibited high accuracy (R² = 0.95–0.99), enabling efficient mix optimization. The optimal formulation, comprising 63 % BWP and 37 % BFS, exhibited superior mechanical and environmental performance, while MWP was excluded due to its limited reactivity. At 180 days, the compressive strength of other mixes, including M3 (66.7 % BFS, 16.7 % BWP, and 16.7 % MWP), M5 (33.3 % BFS, BWP, and MWP), and M6 (63 % BWP and 37 % BFS), also surpassed 50 MPa, demonstrating the synergistic effect of BFS and BWP. Microstructural analysis revealed that BWP acted both as a reactive aluminosilicate and a micro-filler, while MWP behaved as an inert filler. Ternary contour plots showed stable strength plateaus, indicating robustness to mix proportion variations. Life Cycle Assessment (LCA) and cost analysis showed that formulations with BFS and BWP reduced CO₂ emissions by up to 35 % and energy consumption by 30 %, while remaining cost-effective. This research establishes an integrated framework combining materials science, statistical modelling, and life cycle analysis that supports the adoption of circular economy strategies in the construction sector.