Vickers hardness distribution and prediction model of cement pastes corroded by sulfate under the coexistence of electric field and chloride

Abstract

The durability of reinforced concrete structures in subway engineering is a continuing concern due to the long-term complications associated with the coexistence of sulfate, chloride and electric field. However, there remain challenges towards better characterizing the changes in the mechanical and durability of the influenced structures. In this study, the micro-Vickers hardness was measured to reflect the changes in the local mechanical properties of the cement pastes before and after sulfate erosion under the combined treatment of an electric field and chloride. The effect of the water-to-cement ratio, sulfate concentration, chloride concentration and current intensity on the Vickers hardness of cement paste was explored under the coupling effect of sulfate, chloride and electric field. Moreover, a Vickers hardness prediction model taking into account multiple factors was established by modifying the Logistic function. The results showed that increasing the water-cement ratio, the sulfate concentration and the current strength all led to a decrease in the Vickers hardness of the cement paste. Interestingly, an increase in the chloride concentration alleviated the sulfate-induced decrease in the Vickers hardness, indicating that the existence of chloride delayed the sulfate attack, which was substantiated by the XRD results. There was a good correlation between the Vickers hardness prediction model and the experimental data. Therefore, the developed model is able to predict the changes in the Vickers hardness of the cement paste under the changes in the above mentioned factors with a high confidence.