Use of Rice Husk Ash (RHA) as a Sustainable Cementitious Material for Concrete Construction

Abstract

Use of supplementary construction materials in concrete industries has become a great interest in recent years. Stringent guidelines of the Unites States Environmental Protection Agency (EPA) influence the use of recycled materials in construction industry. Furthermore, there is an eminent shortage of the predominately used fly ashes from local sources generated by coal plant industries in Arkansas. On the other hand, rice husk ash (RHA), a by-product of the rice milling process, has high potential of being a supplementary cementing material. The RHA generated by Riceland Foods, the largest grain processing industry in the United States located in Arkansas, is treated as waste materials. It has become a financial burden to local famers due to its ever increasing handling, storage and disposal costs. The RHA consists of non-crystalline silica, which proves it as a very reactive pozzolanic material in mortar and concrete. To this end, laboratory-based experimental study investigated the performance of a locally available RHA as a supplement of Type-I Ordinary Portland Cement (OPC). Properties of concrete with different percentages of RHA (10% and 20% by weight) were investigated in this study. Fresh concrete properties (slump, unit weight, air entrainment etc.) as well as mechanical properties (compressive, tensile, flexural strength) of hardened concrete were determined. Additionally, alkali-silica reaction (ASR) test was conducted on mortar bars to evaluate cracking and expansion of concrete while exposed to adverse weather. It was found that, RHA particles were 13 times coarser than the cement particles. Use of this bulk RHA yielded significant strength reduction of the RHA modified concrete compared to the control sample. The maximum compressive strength gained by 10% RHA-modified concrete was 56% of that of the control specimen. Tensile and flexural strengths achieved by 10% replacement level were 76% and 96%, respectively, of those of the control samples. Moreover, the ASR test revealed that the bulk RHA was very reactive. Local construction industries can use this RHA as flowable fill as an alternative of cement and fly ash.