Performance-driven utilization of industrial wastes as fine aggregates in ambient-cured alkali activated concrete

Rapid urbanization and the growing demand for sustainable construction materials have encouraged the development of low-carbon alkali-activated concrete (AAC). This study investigates the utilization of finely burnt clay brick dust (BD) and waste foundry sand (WFS) as alternative fine aggregates in ambient-cured cement-free AAC. Natural river sand was replaced from 25 to 100% using BD and WFS to evaluate their influence on fresh, mechanical, and durability properties. The binder system consisted of Class-F fly ash and ground granulated blast furnace slag, activated using an 8 M sodium-based alkaline solution with a constant solution-to-binder ratio of 0.50. Results indicated that incorporation of BD reduced compressive strength due to its porous structure and higher water absorption, with reductions of 18.3% and 24.2% at 28 and 90 days, respectively, at full replacement. In contrast, WFS significantly enhanced the performance of AAC because of its micro-filler effect and improved particle packing. The optimum performance was achieved at 50% WFS replacement, where compressive strength increased by 41.5% and 21.5% at 28 and 90 days, respectively, while split tensile and flexural strengths also improved considerably. Durability performance was substantially enhanced at the optimum WFS level, with reductions of 60.9% in chloride penetrability, 62.7% in carbonation depth, 45.7% in water permeability, and 42% in sorptivity compared to the control mix. Furthermore, the 50WFS mix exhibited superior resistance against acidic and sulfate environments. The findings demonstrate that WFS can effectively replace natural sand up to 50% in ambient-cured AAC, producing a sustainable and durable construction material, while BD can be utilized at moderate replacement levels for effective waste valorization.