Avaliação do emprego da cinza da casca de arroz ao concreto frente ao ataque por sulfato de sódio

In the execution of structures in sewage treatment plants it is extremely important to utilize the Portland cement concrete, however, this one is easily degraded due to the aggressive conditions of this environment. The aggressive agents present in this environment are sulfates, which directly affect Portland cement concrete. Two alternatives are widespread in the literature to mitigate these effects: the use of lower water / agglomerate ratios and the use of pozzolanic additions. In this work, the performance of concrete with partial replacement of CP II F 40 cement by rice husk ash (CCA) at 0%, 5%, 10% and 15% was compared to the performance of concrete with CP V ARI RS cement as for resistance to sodium sulfate attack. The procedures were conducted according to the American Standard ASTM C1012 / C1012M 18a, being evaluated the dimensional variation, the flexural tensile strength, the compressive strength, the pH change and the mass change of mortar bars immersed in sodium sulfate solution. The partial replacement of cement by CCA was efficient to mitigating the expansion of mortars exposed to sulfated solution. Mortar with 10% CCA presented the smallest expansion reaching 0.011% at 15 weeks. It was observed an increase in the resistance of mortars exposed to sulfated solution when compared to mortars that remained immersed in lime-saturated water, and the mortar with 15% CCA showed the highest tensile and compressive strengths. It was noted that the sulfate solution was not able to change the pH along the cross-sectional depth of the bars and an increase in mass in the mortar bars that were immersed in the sulfated solution.