Performance degradation and damage model of concrete incorporating rice husk ash under sulfate attack

To prove the improvement of rice husk ash (RHA) on sulfate erosion performance of concrete, the ratio of RHA concrete was optimized and compared with normal concrete (NC). The performance degradation progresses of concrete specimens within 270 days under solution attack with 5wt%Na₂SO₄ were studied, which included changes of apparent phenomenon, compressive strength, tensile strength, effective porosity and dynamic elasticity modulus. The micro-structure changes of concrete specimens under sulfate attack were observed by SEM. The results show that the concrete specimens gradually appear local spalling and expansion with the increase of corrosion time. The compressive and tensile strength increase and then decrease sharply, the effective porosity decreases and then increases, and the relative dynamic elasticity modulus increases and then decreases. Microscopic analysis shows that the ettringite and gypsum are formed from the hydration products of concrete react with the corrosive medium, which fill pores of concrete. Whereas, with the increase of corrosion time, the expansion of the ettringite and gypsum exceeds the internal tensile strength, resulting structural expansion failure and deterioration of mechanical properties. However, RHA mixing with concrete can produce calcium silicate hydrate, which improves the strength and sulfate resistance of concrete. In each stage, the deterioration degree of RHA concrete is better than that of NC. Finally, the damage constitutive models are established, and have higher accuracy compared with the measured value.