Rice husk (RH) is an agricultural waste transformed to produce secondary by-products and is widely accepted as a substitution of cement or concrete mixtures. This paper deals with the optimal level of SiO2 content due to various incineration conditions of rice husk grown in Perlis, Malaysia. RH was burnt in a controlled environment with a targeted temperature of 650, 750 and 850 °C at various incineration period between 1 and 6 h. All the ashes were assessed for visual inspection and physiochemical and mineralogical properties using X-ray fluorescence (XRF) and X-ray diffraction (XRD). From the analysis, a significant amount of SiO2 in the range of 89–93 wt % was successfully obtained with the preferable properties of supplementary cementitious materials: amorphous silica with high reactivity, ultrafine size, and large surface area. Contrary, the burning temperature of 850 °C greater than 4 h incineration period is not advisable to be used as it transformed into a crystalline phase. No obvious color changes were observed for the ashes as the amount oxide compound of K2O causes carbon entrapped in surface melting. To sum up, 650 °C incineration for 1 h shows an optimum result, and the RH is bearable to reduce the negative impact on the environment.
Cement industry is a major carbon dioxide emission contributor, which could be reduced by implementing supplementary cementitious materials. Rice husk ash (RHA) exhibits high pozzolanic characteristics when properly produced using controlled incineration. In this study, rice husk (RH) collected from rice milling industry in Perlis, Malaysia was burned at 650 °C for 1 hour. The completed burning process produced dark-grey 78 μm sized amorphous ash particles containing almost 89% silica content. To understand the compressive strength in early age mortar, varying composition of RHA between 5 to 20% was purposely replaced with OPC. It was found that replacing RHA at 5% produced the highest strength followed by RHA replacement up to 15% in relation to the conventional OPC mortar. However, adding up to 20 % results in a steep decrease in the compressive strength due to the densification and space ratio factors in the mortar. In addition, the environmental performance of 20% RHA mixture were unsatisfactory as it is associated with the control mixture. In conclusion, mortar containing 5% RHA replacement shows acceptable properties similar to conventional cement mortar. Further analysis needs to be carried out to understand the hydration mechanism that affected their performance.
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