Comparative Life Cycle Assessment of Portland Cement-Based and Blast Furnace Slag-Based Alkali-Activated Mortars with Similar Mechanical Properties

In this study, the mechanical properties and environmental performance of Portland cement-based and blast furnace slag-based alkali-activated mortars produced using two different activator systems were compared. Portland cement-based mortar (PC-Ref), sodium metasilicate-activated blast furnace slag mortar (AA-1), and blast furnace slag mortar activated with sodium silicate solution and 10 M NaOH (AA-2) were designed to achieve similar mechanical properties. The mixtures were characterized by unit weight, ultrasonic pulse velocity, flexural strength, and compressive strength tests. Environmental performance was evaluated through a cradle-to-gate life cycle assessment covering 11 impact categories using the CML-IA method. The compressive strengths of AA-1, AA-2, and PC-Ref were 47.48, 47.25, and 46.95 MPa, respectively, demonstrating comparable mechanical performance. Regarding global warming potential (GWP), AA-1 and AA-2 exhibited 39.2% and 27.5% lower impacts than PC-Ref, respectively. AA-1 showed the lowest impacts in abiotic depletion–fossil fuels, photochemical oxidation, acidification, and eutrophication, whereas AA-2 exhibited the highest burdens in AD, ODP, and toxicity-related categories. A transportation sensitivity analysis assuming local sourcing of all activators over 7 km further reduced the environmental impacts of AA-1 and AA-2, with their GWP decreasing to 418 and 556 kg CO₂ eq, respectively. However, the relative environmental ranking remained unchanged. These findings demonstrate that activator selection significantly influences the sustainability of alkali-activated mortars and that the environmental advantage of AA-1 over AA-2 is not solely attributable to transportation distance. Overall, AA-1 exhibited the most balanced environmental performance while maintaining mechanical performance comparable to PC-Ref.