Application of Rice Husk Ash in Flowable Fill Concrete

Rice husk ash (RHA) has been considered as an agricultural by-product in the United States as well as all over the world. The chemical composition of the RHA particle makes it a potential supplementary cementitious material. This study investigates the potential uses of RHA as a supplementary cementitious material (SCM) in the preparation of flowable fill concrete (FFC). Flowable fill is defined as a self-compacting material, which has been used for different aspects such as backfilling, utility trenches, bridge abutments, pile excavations, and retaining walls. In this study, two different types of RHA samples (600-RHA: 600 μm, and 150-RHA: 150 μm) with two different particle sizes were utilized to evaluate their application in producing low strength FFC. The evaluation process of RHA modified FFC mixtures includes determination of strength, flowability, unit weight, and air content of modified FFC mixtures through different laboratory experiments. Fresh FFC test result showed that RHA modified FFC mixtures required higher amounts of water to maintain a desired level of consistency. Laboratory experiments on hardened FFC mixtures prepared using coarse RHA particles resulted in lower strength properties compared to the regular FFC where medium-fine RHA particles in FFC mixers were found to be effective in increasing the strength properties. Two field demonstrations have been conducted to evaluate the workability, placement, and in-service performance of RHA modified FFC in field conditions. The findings of this study are expected to help the transportation and construction agencies in finding an alternative construction material.