Comparative evaluation of high- and low-calcium fly ash in alkali-activated slag composites under steam curing conditions

This study explores the feasibility of utilizing sustainable composites made from alkali-activated slag-fly ash as an eco-friendly alternative to traditional Portland cement. It further evaluates the influence of high-calcium fly ash (HCFA) and low-calcium fly ash (LCFA) on the fresh and hardened properties of alkali-activated slag cement (AASC) composites under steam curing conditions. The fresh properties examination indicates that increasing fly ash (FA) content reduces workability, with HCFA exhibiting a more pronounced slump flow reduction than LCFA. Compressive strength results reveal that HCFA enhances early-age strength due to accelerated hydration, whereas LCFA contributes to long-term strength through sustained pozzolanic activity. The most significant strength gain occurs between days 1 and 7, followed by a gradual increase up to 28 days. These findings underscore the potential of FA as a sustainable alternative material in cementitious composites, optimizing both early-age and long-term performance for construction applications.