Deterioration law and life prediction of aeolian sand concrete under sulfate freeze-thaw cycles

Abstract

To study the deterioration law of aeolian sand concrete (ASC) under the coupling effect of sulfate freeze-thaw, this paper uses aeolian sand as a substitute for river sand to prepare ASC with different replacement rates (0%, 20%, and 100%). Freeze-thaw cycle (FTC) tests are conducted in different salt solution environments (5% Na2SO4, 10% Na2SO4, and 5% Na2SO4 + 3.5% NaCl) to analyze the changes in physical and mechanical properties, and the mechanism of performance degradation of ASC is analyzed by SEM, XRD and NMR. The results show that incorporating aeolian sand significantly improves the salt-freeze erosion resistance of concrete, and when the content is 100%, the impact on salt-freeze erosion on macroscopic properties such as mass loss and compressive strength is minimized, signifying the salt-freeze erosion resistance is the best. During the FTCs, the relative dynamic elastic modulus of concrete initially increases and then decreases, while the trend in mass loss rate reverses. SO42- and Cl- in the salt solutions react with the hydration products to form calcium vanadate, gypsum, and Friedel salts. During the initial stages of FTCs, erosion products fill the matrix pores, increasing the compactness of the concrete, which positively affects macroscopic properties. As the FTCs progresses, ice crystals and excessive erosion products accumulate, resulting in a further expansion of internal pores and cracks in concrete. Consequently, the ratio of harmful to beneficial pores continues to increase, resulting in freeze-thaw damage. After 200 FTCs, in the 5% Na2SO4 + 3.5% NaCl erosion medium, the internal cracks in aeolian sand concrete get bigger and the holes get larger, causing the most damage and deterioration. Different degradation indices are used to predict the residual lifetime of ASC based on a Wiener random probability distribution. The Wiener stochastic process effectively predict the lifetime of ASC under the coupling effect of sulfate FTCs, with the compressive strength loss rate as the most sensitive degradation index. Among them, for ASC-0, ASC-20, and ASC-100 in the 5% Na2SO4 + 3.5% NaCl environment, the maximum FTCs, based on the compressive strength loss rate, are 198, 206, and 213 times, respectively. This study could provide a theoretical foundation for the durability design of concrete structures in cold regions and other salt-frozen regions within Northwest China.