Study on the advancement process of alkali loss and deterioration of concrete under MgSO4 erosion

To clarify the damage mechanism of the layer erosion argillization of concrete eroded by sulfate attack, this study investigates the compressive strength decay characteristics of eroded concrete. It employs ultrasonic velocity, SO 4 2− content, and microhardness testing methods to comprehensively evaluate the lamination and deterioration processes of concrete at different erosion ages. Additionally, nano-indentation and XRD are utilized to examine the alkali dissipation and deterioration mechanisms of concrete under sulfate attack. The results reveal that sulfate attack in concrete is not a uniform infiltration process but rather a progressive layered erosion that advances inward over time. As the erosion age increases, the C–S–H gel in the affected concrete transitions from a high-density state to a low-density state. The continuous consumption of Ca(OH) 2 by MgSO 4 induced erosion is identified as the primary driver of alkali depletion and subsequent deterioration. When the alkalinity of the cement matrix can no longer stabilize the C–S–H gel, the external C–S–H gel between cement particles begins to decompose, ultimately leading to the fracturing and disintegration of the cement matrix structure.