Circular valorization of boron processing wastes as alternative activators in one-part alkali-activated mortars: Mechanical performance, reaction mechanism and life cycle assessment

The sustainable valorization of industrial wastes is an effective strategy for reducing the environmental impacts of construction materials while supporting circular economy principles. Although boron compounds have been investigated in alkali-activated systems, the direct utilization of boron processing wastes as alternative activator components remains limited. This study investigates the feasibility of using colemanite waste, tincal waste, and borogypsum as partial replacements for sodium metasilicate in one-part slag-based alkali-activated mortars. Sodium metasilicate was replaced at levels of 10–40% under two activator dosages. The mortars were evaluated in terms of workability, unit weight, water absorption, porosity, ultrasonic pulse velocity, flexural and compressive strength, isothermal calorimetry, FESEM, elemental mapping, XRD, TGA, ICP-MS, and life cycle assessment. The results showed that moderate replacement levels (10–20%) maintained or improved the engineering performance of the mortars, whereas higher replacement ratios were associated with increased porosity and reduced strength development. Among the investigated wastes, tincal waste exhibited the best overall performance. Microstructural and elemental analyses indicated the presence of Ca–Si–Al-rich reaction products and boron-associated reaction regions, with tincal waste producing the densest and most homogeneous microstructure. Furthermore, LCA showed that the slag-based Ref-8N mixture reduced GWP by 39.7% compared with Portland cement, while boron-waste substitution provided an additional 5.5-21.0% reduction. These findings confirm the environmental potential of boron-processing wastes as partial activator substitutes in one-part alkali-activated mortars.