Performance degradation mechanism and strength prediction of silica fume concrete under sulfate dry–wet cycles

Extensive saline soil regions are found throughout the country, where durability issues caused by sulfate attack have become increasingly prominent. In this study, a dry–wet cycling environment in 5 % Na 2 SO 4 solution was simulated, and a multi-scale experimental approach—including mechanical testing, NMR, SEM, and TG-DSC—was employed to quantitatively assess the synchronicity between macroscopic mechanical degradation and microstructural evolution. The results demonstrate that concrete with 10 % silica fume exhibited the highest resistance to sulfate-induced deterioration, retaining 79.08 % of its compressive strength after 150 cycles and showing the lowest macropore proportion. In contrast, specimens without silica fume experienced pore structure degradation prior to strength loss. A moderate silica fume content significantly increased the proportion of gel pores and inhibited pore coarsening, thereby promoting a more synchronized evolution of pore structure and strength degradation. This effect is attributed to the pozzolanic reaction between silica fume and Ca(OH) 2 , which produces dense C–S–H gel, suppresses the accumulation of corrosion products, and significantly enhances structural stability and sulfate resistance. Furthermore, a support vector regression model based on genetic algorithm optimization was constructed, with an R 2 value as high as 0.984 and an error controlled within ±6 %. SHAP analysis identified the number of dry–wet cycles, transition pore ratio, and silica fume content as the primary influencing factors. The experimental and predicted results showed strong agreement. This work offers valuable insights for the development of sulfate-resistant concrete and its service life prediction, with potential applications in hydraulic engineering, bridge structures, and other civil infrastructure.