Effect of Treatment and Incineration Temperature on Extraction of Silica from Rice Husk for Cement Replacement in Concrete

Abstract

Utilization of rice husk ash (RHA) as a pozzolanic material is a viable solution for reducing air pollution that is caused by open incineration of rice husk. Treatment of the rice husk with high-concentration acid and subsequently subjecting the treated rice husk to controlled incineration at high temperature can produce RHA that contains silica of a high purity, which can contribute to a high pozzolanic reactivity of concrete. However, the dependence of high-concentration acid and high incineration temperature will have an adverse effect on the environment. Therefore, in the present study, effect of treatment and incineration temperature on extraction of silica from RHA was investigated by conducting analytical and compressive strength tests on concrete samples. Raw and treated rice husks were incinerated for an hour at 400, 500 and 600°C to produce untreated and treated RHA, respectively. Hydrothermal synthesis was performed to execute gelation of silica from the RHA. The silica gel was converted into powder and then incorporated into concrete mixes for preparation of samples. The samples comprise the control sample, which does not contain any of the silica extracted from the RHA, and those that contain 5% silica from the untreated and treated RHA. Findings indicate that the treatment was necessary to produce concrete with adequate compressive strength relative to that of conventional concrete. Incorporation of 5% silica from treated RHA at the incineration temperature of 600°C resulted in the highest compressive strength of 6.44 MPa, which is an increase of 8.5% from that of the conventional concrete.