Study on the advancement process of surface slurry argillisation layer corrosion caused by concrete sulfate attack

Sulfate attack significantly compromises the durability of cement-based materials, yet the quantitative evolution of eroded layers remains inadequately understood. The degradation mechanisms of cement pastes with water/cement ratios (w/c) of 0.4 and 0.6 under long-term sodium sulfate immersion were investigated in this study. A multi-scale approach – combining microhardness profiling, elemental analysis (energy-dispersive spectroscopy and X-ray fluorescence) and three-dimensional pore characterisation based on micro-computed tomography (μ-XCT) – was employed to quantify the deterioration process. The results indicated that sulfate attack initiates with a prolonged incubation period, followed by non-uniform, layer-by-layer degradation. The eroded region can be spatially categorised into wetting, yellowing and argillised zones, leading to progressive surface disintegration. Notably, the w/c = 0.6 specimens exhibited a sharp increase in penetration depth from negligible levels at 10 months to 3.9 mm at 30 months, whereas the penetration depths of the w/c = 0.4 specimens remained below 1.0 mm. Microhardness analysis revealed mechanical stratification, with surface zones retaining only 50% of the core hardness. μ-XCT data suggest that sulfate ingress is primarily governed by surface-open pores rather than isolated internal voids. The transition of the paste into an argillised state exposes new substrate surfaces, creating a feedback loop that accelerates inward chemical penetration and structural decay.