Avaliação da influência da cinza de casca de arroz no comportamento de concretos com agregado reciclado de concreto em relação a propriedades mecânicas e de durabilidade, com ênfase no transporte de íons cloreto

Abstract

The durability of building materials is emphasized when it searches to maintain the useful life of the construction design or extend it. Corrosion reinforcement in concrete is among one major problem that affects the constructions throughout the world. Chloride ion is one of the agents that can induce the corrosion reinforcement in concrete. For this reason, research about the durability of construction materials in severe environments gained space in the scientific community. The use of recycled concrete aggregate as replacement of natural aggregate has been studied to solve the question about non-renewable raw materials. But, these recycled waste as aggregate can increase the concrete porosity and reduce its durability. The rice husk ash has been employed as supplementary material in Portland cement concrete to get a more sustainable concrete and improve its durability, mainly related to chloride ingress. The aim of this research was to study the influence of rice husk ash on the chloride penetration in concrete made with recycled concrete aggregate. The natural coarse aggregates were replaced by recycled concrete aggregates in amounts of 0; 25 and 50%. The rice husk ash was employed as replacement of Portland cement in 0; 10 and 20%. Three water/binder ratios were used in concrete production: 0.42, 0.53 and 0.64. The compressive strength tests were conducted at 7, 28, 63 and 91 days age. The concrete resistance to chloride ingress was tested by the ASTM C1202 test method and by the NT Build 492 test method. The results of all studied properties showed that the use of rice husk ash can improve the concrete resistance against chloride ingress in concrete made with recycled concrete aggregate. This behavior can be attributed to the reduction of the porosity of recycled concrete aggregate due to interaction of rice husk ash with the calcium hydroxide of this aggregate as well as due to micro filler effect. The best performance was obtained in concrete with 50% of recycled concrete aggregate and 20% of rice husk ash. The resistance against chloride ingress in relation to the same concrete without rice husk ash was increased 91% in average when tested by ASTM C1202, and 64% when tested by NT Build 492.