Performance degradation and damage model of rice husk ash concrete under dry–wet cycles of sulfate environment

Rice husk ash concrete (RHAC) is a new type of concrete that has been rapidly gaining acceptance in recent years. In this paper, the improvement effect of rice husk ash (RHA) on the sulfate erosion performance of concrete was confirmed. The ratio of rice husk ash concrete (RHAC) was optimized and compared with ordinary concrete (OC). The performance degradation of 9%RHAC (rice husk ash at 9% by weight of cement) and OC within 135 times erosion dry–wet cycles solution with Na₂SO₄ at 5% by weight of solution were studied, including the change of apparent phenomena, compressive strength, tensile strength, effective porosity, and dynamic elastic modulus. The microstructure changes of samples before and after sulfate dry–wet cycle were observed by using a scanning electron microscope (SEM). The results show that with the increase of sulfate dry–wet cycle times, the concrete specimen gradually peels off and expands in volume. The compressive strength and tensile strength increase first and then drop sharply, the effective porosity decreases first and then increases, and the relative dynamic elastic modulus increases and then decreases. The reason is that the ettringite and gypsum are formed by the reaction of sulfate intrusion and hydration products under wetting treatment. After drying treatment, ettringite and free water combine to form sodium sulfate. In the early of circulation, ettringite, gypsum, and sodium sulfate fill the internal pores of the concrete and improve the density. As the number of sulfate dry–wet cycles increases, expansion products accumulate, causing structural expansion damage and deterioration of mechanical performance. However, the hydrated calcium silicate hydrate gel was produced by mixing rice husk ash with concrete to improve the material strength and corrosion resistance. The deterioration degree of the 9%RHAC is better than that of OC at all stages. Finally, the damage constitutive models were established, and the accuracy is higher compared with the measured value.