<b>MODELLING AND OPTIMISATION OF COMPRESSIVE STRENGTH OF RICE HUSK ASH (RHA) CONCRETE USING SCHEFFE’S THEORY</b>

The study covered the development of model for predicting the compressive strength of rice husk ash (RHA) concrete at 28 days curing age for materials sourced from Afikpo-North Local Government Area of Ebonyi State, Nigeria using Scheffe’s (5, 2) simplex lattice design theory to enhance the usage of rice husk ash in order to reduce the cost of cement and concrete production. A total of 30 mix ratios were used to produce 90 concrete cubes of 150mm x 150mm x 150mm size to develop the model and test adequacy using Fisher’s test at 95 percent confidence level. The Scheffe’s regression model was used to generate the mathematical equation= 28.27X₁ + 23.13X₂+ 21.35X₃ + 20.56X₄ + 19.38X₅+ 7.64X₁X₂– 1.84X₁X₃ – 2.90X₁X₄– 9.26X₁X₅+ 0.04X₂X₃ – 2.10X₂X₄ – 2.42X₂X₅– 1.78X₃X₄– 1.70X₃X₅– 2.04X₄X₅that gave the highest compressive strength of 28.27 N/mm² corresponding to a mix ratio of 0.50:0.95:2.00:4.00:0.05 for w/c ratio, cement, sand, granite and RHA respectively and the minimum compressive strength of 19.38N/mm²corresponding to mix ratio of 0.70:0.75:1.70:3.70:0.25 for w/c ratio, cement, sand, granite and RHA respectively. The study recommended that the rice husk ash used as partial replacement of cement for the model developed should not exceed 17.5% in order to achieve grade C20 concrete. This paper has first appeared in <i>Afrisophia: Journal of African Experiment, Thought and Experience</i> which is published by Academia Africa..