Durability characteristics of sustainable concrete with high-volume circulating fluidized bed fly ash and solid alkali activator using response surface methodology

This study developed a C30-grade alkali-activated concrete using high-volume circulating fluidized bed fly ash, supplemented with granulated blast furnace slag and silica fume, and activated with solid NaOH. The mixture was optimized via Response Surface Methodology based on slump, initial setting time, and 28-day compressive strength. Multi-objective optimization yielded an optimal ratio, which was validated with close agreement between predictions and experimental results. The resulting concrete exhibited excellent durability, including over P12 impermeability, D200 freeze-thaw resistance, very low chloride permeability, and KS90-grade sulfate resistance. Its drying shrinkage was lower than that of ordinary Portland cement concrete, though carbonation resistance was relatively higher. Microstructural analysis revealed that prolonged curing promoted continued hydration, increasing the formation of N, C-(A)-S-H gels, densifying the interfacial transition zone, and reducing crystallinity, thereby enhancing the macro-properties and durability. The carbon emissions and cost per unit volume were reduced by 46.97% and 55.11%, respectively. This work presents a practical and sustainable alternative for boosting industrial waste recycling and reducing the carbon footprint of concrete.