Research on the pore distribution characteristics and strength degradation of cement-based materials under sulfate attack

To investigate the influence of sulfate erosion on the performance of cement-based materials, this study designed cement paste, mortar and concrete specimens with a water-to-cement ratio of 0.35. The study examined the changes in performance over 30 days, 60 days, 90 days, 120 days, and 150 days of sulfate erosion, and the findings showed that: as the duration of sulfate erosion increased, the mass change and compressive strength of cement-based materials generally showed an increasing trend first and then decreasing trend. The mass change of cement paste, mortar and concrete specimens was 0.64%, 0.274%, and 0.16%, respectively, after 150 days of sulfate erosion. The compressive strength of the 150-day cement paste, mortar, and concrete decreased by 56.86%, 14.29%, and 19.34% respectively.The porosity of cement paste, mortar and concrete specimens showed that the porosity of cement paste was greater than that of concrete, which was greater than that of mortar specimens.When employing the Mercury Intrusion Porosimetry (MIP) test, the porosity of mortar specimens decreased initially and then increased with prolonged sulfate exposure. The porosity of mortar specimens reached 12.57% after 30 days of sulfate erosion and 18.27% after 150 days of sulfate erosion.When Nuclear Magnetic Resonance (NMR) testing was adopted, the variation law of porosity after sulfate attack was basically consistent with that of MIP testing, but there were differences in porosity. The porosity was 7.60% after 30 days of erosion and 14.42% after 150 days of erosion. A comprehensive comparison of the two testing methods revealed numerical differences, but it could provide a more comprehensive understanding of the influence mechanism of pore structure on the performance of cement-based materials, and offer important references for optimizing material ratios and improving material performance.