Freeze-thaw damage and life prediction model of seawater and sea sand concrete (SWSSC)

The freeze-thaw damage behavior of seawater sea sand concrete (SWSSC) under two freeze-thaw media, freshwater and seawater, was investigated through rapid freeze-thaw tests. By analyzing changes in microstructure and reaction products, the reasons for the more severe damage of SWSSC compared to ordinary concrete (OC), and the influence of freeze-thaw media on the damage mechanism were explored. Based on the fatigue cumulative damage theory, a freeze-thaw damage and life prediction model for SWSSC in both freshwater and seawater freeze-thaw environments was proposed, using the relative dynamic elastic modulus as the damage variable. The results indicate that chloride ions and sulfate ions within SWSSC react with cement hydration products to form non-cementitious Friedel's salt, expansive columnar gypsum, and needle-like ettringite crystals, which damage the pore structure and significantly reduce the compactness of the SWSSC microstructure. Compared to freeze-thaw in freshwater, the intrusion of more Cl- and SO4 2- during seawater freeze-thaw accelerates the damage process of SWSSC. After 60 freeze-thaw cycles in freshwater, the mass loss rate of SWSSC reached 4.08 %, and the relative dynamic elastic modulus decreased to 61 % of its initial value. In seawater, the mass loss rate increased to 7.02 %, and the relative dynamic elastic modulus dropped to 48 % of its initial value. The freeze-thaw life of SWSSC in freshwater and seawater was 348.9 years and 84.5 years, respectively, while that of OC was 395.3 years and 94.8 years, respectively. Under the same freeze-thaw medium, the freeze-thaw life of SWSSC is shorter than that of OC, and the influence of the freeze-thaw medium on freeze-thaw cycles is far greater than that of the concrete material itself. SWSSC meets the durability requirements of Chinese standards in freshwater environments, but in seawater environments, additional anti-freezing measures (such as adding airentraining agents) are required to meet durability requirements. The freeze-thaw damage and life prediction model proposed in this study provides a theoretical reference for the application of SWSSC in freshwater and seawater freeze-thaw environments.