Degradation mechanism of cement paste buried in sulfate-rich saline soil

A deep understanding of the deterioration mechanisms of saline soils enriched with corrosive ions is essential for accurately predicting the durability degradation of cement-based materials in saline soil environments. This study investigates the corrosion mechanisms through X-ray computed tomography (X-CT), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Zeta potential analysis, to quantitatively evaluate the macro- and micro-scale deterioration effects on cement paste fully immersed in sulfate-rich saline soils or sodium sulfate (Na₂SO₄) solutions of comparable concentration. The findings indicate that sulfate-rich saline soils induce significantly greater degradation of cement paste compared to Na₂SO₄ solutions of equivalent concentration, with SS1 exhibiting the strongest corrosion effect, followed by SS2. However, this enhanced degradation is not attributed to changes in the primary internal corrosion products, as ettringite and gypsum remain the predominant phases. Instead, the observed differences arise from the physical properties of the soil, including particle gradation, microstructure, and surface charge characteristics. Larger particle sizes and higher negative surface charges in the soil exacerbate the corrosion boundary conditions by promoting ion exchange and altering ion transport pathways. Collectively, these factors amplify the accumulation of expansive corrosion products, including gypsum and ettringite, ultimately resulting in more severe corrosion effects.