Inhibition of sulfate attack on cement-based materials under stray currents and low temperatures by mineral materials

Metro tunnel structures frequently suffer from sulfate attack under stray current conditions at low temperatures, which accelerates concrete degradation through physico-chemical processes. This study investigates the resistance of cement-based materials to such combined degradation, focusing on the effects of mineral admixtures and limestone powder characteristics. Comprehensive experimental methods combining macroscopic testing and microstructural characterization revealed the degradation mechanisms among different cementitious materials. A 6 % silica fume addition lowered the overall porosity from 33.1 % to 27.9 %; combined with its pozzolanic reactivity, this contributed to improved sulfate resistance. By contrast, metakaolin accelerated the formation of expansive products (25.2 % ettringite and 10.0 % thaumasite by mass of the dried degraded sample), resulting in more severe degradation. Increasing limestone powder fineness (387–811 m²/kg) significantly accelerated degradation, particularly in metakaolin-containing systems, leading to 64 % higher strength loss. A correlation between electrical resistivity evolution and phase transformation was established, providing new insights for durability monitoring. These findings advance the understanding of degradation mechanisms and suggest optimal material combinations for enhanced durability in underground metro environments.