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Different supplementary cementitious materials are often blended with cement to produce sustainable concrete. More often than not, the strength of blended concrete is compromised, if the constituent materials are not carefully selected. In this study, optimization of strength properties of blended cement-rice husk ash (RHA) was carried out to determine the best mix ratio that produced binary blended concrete of high strength. Different mix ratios of cement and RHA were studied at a water cement ratio of 0.4 to produce concrete specimens. RHA was produced by burning 700 ℃ for an hour and its chemical composition was determined using the X-Ray Fluoresce (XRF) technique. RHA produced was used to replace cement at replacement levels of 2.5, 5, 7.5, and 10 %, and was used as binder. The compressive strength of each concrete mix was determined at 7, 28, and 56 days. Approximately 250 concrete cubes were tested and the results were subjected to statistical analysis. The results showed that compressive strength and internal structure varied with RHA as a replacement for cement. Optimal strength was achieved for a concrete mixture, prepared at a water: cement: aggregate ratio of 1:1.5:3, respectively, and a RHA replacement ratio of 5 %. HIGHLIGHTS Cement is the most utilized construction material. The energy-intensive processes that are involved in its production contribute up to 10 % of total global CO2emissions, with potentially adverse environmental implications. It is however possible, that energy and cost efficiency can be achieved by reducing on the amount of clinker, and in its place utilising supplementary cementitious materials (SCMs) or pozzolans Currently, most sustainable concrete uses either GGBS (slag) or PFA (fly ash) to reduce the quantity of cement used in construction and highways applications. GGBS and PFA come from industries (steel and coal waste respectively) which are in decline that should not be relied upon in the long term. Therefore, for long term sustainability it is imperative to focus attention on other alternative pozzolans This report shows that cement in concrete can also be replaced with rice husk ash (RHA) which actually enhances the mechanical properties. Findings show the usage of up to 5 % rice husk ash as a partial cement replacement can enhance the strength of concrete whilst reducing the embodied CO2 GRAPHICAL ABSTRACT |
