Study on the durability and micro-mechanism of granite manufactured sand concrete under coupled alkali-silica reaction and sulfate attack

Granite manufactured sand is increasingly used as a substitute for river sand, but its potential alkali-silica reactivity may aggravate durability deterioration in sulfate-rich environments. This study investigated the coupled effect of alkali-silica reaction (ASR) and sulfate attack on granite manufactured sand concrete, and evaluated the mitigating performance of fly ash, silica fume, slag, alumina, and aluminum hydroxide by sulfate wet-dry cycling, chloride ion penetration testing, and SEM/EDS/XRD analyses. ASR accelerated sulfate-induced strength deterioration; after 100 wet-dry cycles, the concrete containing 30% fly ash maintained a corrosion resistance coefficient of about 0.79, whereas the coefficients of the other single-admixture mixtures were below 0.75. Among the blended systems, slag + alumina, slag + aluminum hydroxide, and fly ash + silica fume + slag all retained corrosion resistance coefficients above 0.75 after 100 cycles. EDS results further showed that the Ca/Si ratio decreased from 0.93 in the reference group to 0.64, 0.51, and 0.51 in the fly ash, silica fume, and slag groups, respectively, but increased to 1.43 in the alumina group, indicating clear differences in gel chemistry and sulfate-response pathways. Overall, mineral admixtures improved matrix compactness and chloride resistance, whereas aluminum-based additives alone provided weaker sulfate resistance; the combined use of mineral admixtures and aluminum-based compounds showed a synergistic benefit under coupled deterioration.