Effect of Rice Husk Ash on the Carbonation Depth of Concrete under Different Curing Ages and Humidity Levels

Abstract

Alternative materials are becoming the substances of choice for designers over conventional materials due to cost and availability constraints. The sustainability and maintenance of the supply of conventional construction materials often becomes a limiting factor. This calls for the utilization of industrial refuse and agricultural by-products. Recycling of this waste can be an effective tool to decrease the levels of pollution and enhance the economy. Different materials like rice husk ash (RHA), fly ash (FA), silica fume (SF), and slag can be substituted in cement owing to their pozzolainic behavior. However, their use may make the concrete more prone to carbonation than ordinary portland cement (OPC) concrete. This research is aimed at knowing the influence of RHA on carbonation at distinct conditions. Concrete samples with varied fractions of RHA (0%–20%) with interval of 5% under three different relative humidity levels (30%, 45%, and 60%) were made to undergo accelerated carbonation tests at 5% CO2 content after being cured for 7, 14, and 28 days. It was found that there was no carbonation observed in relative humidity level of 30%. However, the depth of carbonation was directly proportional to the RHA replacement level for humidity levels of 45% and 60% and the increase was nearly the same corresponding to 15% and 20% replacement for curing age of 28 days. Hence, without compromising the carbonation resistance, greater RHA fractions can be used with a longer curing period. Besides, the results also revealed that the depth of carbonation decreased with an increase in relative humidity levels from 45% to 60%. The effect of compressive strength on carbonation depth of RHA concrete was also studied and it was found that the carbonation depth decreased as the compressive strength of concrete increased.