Strength Optimisation of concrete based on Scheffe’s model using Bida gravel as partial replacement for crushed granite

Abstract

Abstract In Nigeria, the need to source for cheap and locally available materials like Bida gravel as a replaceable substitute for granite without necessarily compromising the structural integrity of the concrete arise due to the rapid rise in the cost of crushed granite (which is an important ingredient in concrete). This research work relates Scheffe’s statistical model to obtain the response function for the optimisation of compressive strength of a five-component concrete made with water, cement, sand, granite and Bida gravel. A total of ninety standard 150mm x 150mm x 150 mm cubes were cast, consisting of three cubes per mix ratio and for a total of thirty mix ratios. The first fifteen was used to determine the coefficients of the model, while the other fifteen were used to validate the model. The maximum compressive strength predicted by this model was 29.93N/mm2 corresponding to mix ratio of 0.45:1:1:1.9:0.1 for water: cement: sand: granite: Bida gravel. A MATLAB program was used to ease the use of the model. The output of the statistical model compared favorably with the corresponding experimental results and the predictions from the response function were tested with statistical Fischer test and found to be adequate at 95% accuracy level. The model delivered in this study can be used for optimising and predicting the future 28th days compressive strength of concrete made from water, cement, sand, granite and Bida gravel as partial replacement for granite when the mix proportions of the concrete is known and vice versa.