Combined Use of Copper Slag as a Supplementary Cementitious Material and an Artificial Fine Aggregate for Sustainable Mortar Production

Incorporating supplementary cementitious materials (SCMs) and alternative aggregates promotes cleaner production of cement-based materials; however, optimizing their coupled effects on mechanical and environmental performance remains a key challenge. This study assesses the valorization of copper slag (CS), a massive industrial mining by-product, simultaneously as an SCM and an artificial fine aggregate (AFA) in the development of mortar mixtures with better performance and lower embodied carbon. Specifically, CS partially replaced Portland cement (PC) at 0% and 15% by volume, while natural fine aggregate (NFA) was substituted with AFA at volumetric replacement levels of 0%, 20%, 40%, and 60%. Mortar performance was systematically evaluated in the fresh state via workability and in the hardened state through water absorption, alongside short- and long-term compressive and flexural strength development. Furthermore, a cradle-to-gate life cycle assessment (LCA), expressed in terms of embodied carbon (EC) emissions, was executed to assess the environmental performance of the mixtures. The results indicate that incorporating CS as both SCM and AFA improved mortar workability by up to 30.9% compared to the reference mortar mixture (100% PC and 100% NFA). At 7 days, compressive strength decreased by 4% to 20% relative to the reference mortar. However, long-term performance improved substantially; at 330 days, mixtures with 15% CS–0% AFA and 15% CS–60% AFA achieved average compressive strengths of 42.9 MPa and 53.1 MPa, respectively, outperforming the reference mortar (42.1 MPa) by up to 26%. The cradle-to-gate embodied-carbon assessment showed that CS incorporation reduced product-stage emissions, although outcomes depended on transport distance and strength development. EC ranged from 369.8 to 438.0 kg CO2e/m3. When transport was included, EC decreased by approximately 14%, while 330-day strength-normalized EC decreased by 29.6–32.1% relative to the reference mixture. Overall, CS-based mortars improved fresh-state properties, enhanced long-term mechanical performance, and reduced product-stage embodied carbon, demonstrating their potential for cleaner production.