Effect of hoop restraint on the degradation behavior of cement paste exposed to sodium sulfate solution

Abstract

Concrete filled steel tube (CFST) is an effective method to alleviate sulfate attack in saline soil environments. In this study, the effect of hoop restraint on the degradation behavior due to sulfate attack in ordinary Portland cement (OPC) paste and sulfate-resistance Portland cement (SRPC) pastes is studied. The cracking behavior and mass variation are determined to investigate deterioration process of the pastes. EPMA-WDS, nanoindentation and SEM-EDS are performed to analyse the deterioration mechanism of the cement paste under hoop restraint condition. As the results shown: The deterioration behaviors of cement pastes is strongly affected by hoop restraint. Specifically, the hoop restraint inhibited crack formation of the specimens and formation of sulfate products. The average effective sulfate diffusion coefficient is reduced by 30.26% and 5.81% for OPC and SRPC paste during 365 days of exposure, respectively, compared with the reference group. Moreover, the mechanism of deterioration of cement paste under hoop restraint condition is proposed based on change in chemical component of C–S–H phase. The hoop restraint from steel tube can effectively inhibit the sulfate attack on cement composite with important engineering significance