Investigation into the effects of Rice Husks Ash on properties of Soil-cement fill.

Abstract

Rice husk ash (RHA) is an agricultural residue which is produced from the burning process of rice husks. Considering the increasing rice production in Uganda hence increase in rice husks waste which is a nuisance to the environment, there is a need for an alternative use for these husks. The higher percentage of silica (SiO2) present in RHA determines its highly reactive pozzolanic property hence making it an established supplementary cementitious material. The cost of cement is on high increase in some developing countries like Uganda. In addition, producing cement increases CO2 emission which creates environmental issues. In relation to carbon footprint associated to cement production, many researchers studied the use of RHA as a partial replacement of cement in concrete reporting a significant increase in compressive strength especially at 10% replacement of the cement with RHA. However, not much research has been carried out on replacement of cement with rice husk ash in soil-cement fill (flowable fill). This study involved an investigation into the effect of rice husk ash (RHA) as a partial replacement for cement on the flow consistency and compressive strength of flowable fill. CEM 1 Portland cement, well graded, sandy gravel and RHA (passing the 150µm sieve) were used in this study. The RHA was used in different replacement levels, namely 0%, 5%, 10%, 15% and 20% by weight of cement. Test results show a general decrease in the spread(flowability) of the wet mixes with increasing RHA content. However, the spread values were still in the specified range of between 20 and 30cm according to ASTM D 6103 – 04 for all mixes up to 20% replacement. There was an increase in the compressive strength of all the mixes with curing age. There was also a decrease in the compressive strength of the hardened mixes with increasing RHA content in comparison with the control mix with 0% RHA. The mix with up to 10% cement replacement with RHA had an average spread of 23cm with a compressive strength of 360 kPa and 395 kPa after 7 and 28 days of curing respectively. This mix gave a percentage decrease of only 4.8% in strength with comparison to the control sample(0% RHA). Its spread and compressive strength values were within the specified range according to ASTM D 6103 – 04 and ASTM D 4832-02 respectively hence making it sufficient.