PREDICTION OF COMPRESSIVE STRENGTH OF CEMENT BLENDED FLY ASH-PERIWINKLE SHELL ASH SANDCRETE BLOCKS

This study centred on the development of a mathematical model for the prediction of the compressive strength of cement blended Fly Ash-Periwinkle shell ash sandcrete blocks using Scheffe’s simplex lattice. A total of ninety (90) fly ash-PSA solid sandcrete blocks of dimensions 450 x 125 x 225 mm were cast, consisting of three (3) blocks per mix ratio and for a total of thirty (30) mix ratios, comprising of fifteen (15) mix ratios each for both trial and control mixes. The first fifteen (15) mixes were used to develop the model while the other fifteen (15) were used to validate the model. The blocks were cured for 28 days by sprinkling of water. A computer program was written for Scheffe’s model using Visual Basic 6.0. The program was used to predict the compressive strength for a given mix ratio and vice versa. The mathematical model results compared favourably with the experimental results. The model predictions were tested using statistical Students t-Test at 95% confidence level, and were found to be adequate. The optimum compressive strength of the blended sandcrete after 28 days of curing was found to be 3.9175 N/mm2 which gave a corresponding mix ratio of 0.675, 1.19, 0.0375, 0.0225, 6.25 for water, cement, periwinkle shell ash, fly ash, and sand respectively.