Enhancing early-age strength of alkali-activated slag cement with high- and low-calcium fly ash: Impact of water-to-slag ratio under steam curing

This study investigates the influence of high-calcium fly ash (HCFA), low-calcium fly ash (LCFA), and water-to-slag cement (W/SC) ratios on the early-age strength and workability of alkali-activated slag cement (AASC) under steam curing. AASC, recognized as a sustainable alternative to Ordinary Portland Cement (OPC), was prepared using slag cement as the primary binder, with HCFA and LCFA incorporated as partial substitutes for fine aggregate. Experimental results demonstrated that HCFA accelerates early-age strength development due to its higher calcium content, whereas LCFA enhances long-term durability. Lower W/SC ratios (45% and 50%) led to higher early strength but reduced workability, while higher W/SC ratios (55%) improved flowability but compromised strength. Steam curing significantly enhanced the early-age mechanical performance, particularly in HCFA-based mixtures. These findings emphasize the importance of optimizing fly ash type and W/SC ratio for achieving a balance between workability, strength, and durability in sustainable construction applications.