Mechanical performance, durability, and hydration characteristics of binary and ternary blended mortars incorporating waste glass powder and Ethiopian scoria

The utilization of supplementary cementitious materials has become a key strategy for improving the sustainability and performance of cement-based materials. This study investigated the mechanical, durability, and hydration characteristics of mortars incorporating scoria powder (SP) and Glass–scoria powder blends (GPSP), representing a ternary blend system consisting of cement, scoria powder, and glass powder with different proportions. Mortar specimens containing 0–25% SP and GPSP blends at a total replacement level of 30% were evaluated at curing ages of 3, 7, 28, 56, and 90 days. The results showed that both SP and GPSP satisfied the requirements of ASTM C618, with GPSP exhibiting a higher strength activity index than SP. Workability decreased with increasing replacement level, with SP25 and GP25SP75 showing the largest reductions in mortar flow of 20.27% and 16.31%, respectively. Despite lower early-age strength, binary mixtures containing 10% and 15% SP exhibited improved long-term performance, with SP10 achieving increases in compressive strength of approximately 5.8%, 12.1%, and 12.7% compared with the control mixture at 28, 56, and 90 days, respectively. UPV and water absorption results suggest improved matrix densification in SP10 and SP15 mixtures, which was associated with enhanced hydration and C–S–H development. Under sulfate exposure, the control mixture exhibited a strength loss of 6% after 90 days, whereas SP25 and GPSP mixtures showed lower strength losses, indicating improved resistance to strength deterioration under the investigated sulfate conditions. FT-IR and TGA-DTA analyses indicated changes associated with portlandite consumption and progressive formation of hydration products with curing age, while GP50SP50 and SP25 exhibited greater mass loss than the control, indicating differences in hydration product formation. Overall, SP replacement levels of 10–15% provided the most balanced combination of workability, strength development, and physical performance, whereas higher replacement levels and GPSP blends demonstrated improved compressive-strength retention under sulfate exposure.