Effect of Fly Ash Content and Aggregate Type on Concrete Mechanical, Durability, and Environmental Performance

This study investigates the influence of fly ash (FA) content and aggregate type on the mechanical performance and environmental efficiency of concrete. Twelve concrete mixtures were prepared using limestone and basalt aggregates, with FA replacement levels of 0%, 15%, and 35% and water-to-binder (w/b) ratios of 0.4 and 0.7. Compressive strength (CS), the modulus of elasticity (MoE), water absorption, and freeze–thaw resistance were measured. Basalt aggregates enhanced the CS and MoE while reducing water absorption and freeze–thaw deterioration compared to limestone. Although a higher FA content lowered early-age strength and stiffness, it contributed to long-term improvements and greater eco-efficiency. A new MoE prediction model incorporating CS, unit weight, aggregate type, and FA content demonstrated better accuracy than current standards. Assessment of binder usage and CO2 intensity confirmed that all mixtures remained below the average literature values. The optimal combination was achieved with basalt aggregates, a high FA content, a low w/b ratio, and extended curing, highlighting strategies for sustainable concrete production.