PREDICTION OF THE FLEXURAL STRENGTHS OF LIGHTWEIGHT PERIWINKLE SHELL - RIVER GRAVEL CONCRETE

This research work puts into application the regression equation derived by Ibearugbulem for a four component mixture of concrete to develop a model for the easy forecast of 28 th day flexural strengths. To ensure an accurate forecast, the mix ratios to be predicted must fall within the boundaries defined for a four component simplex latex str ucture. The materials used in the laboratory experiment include; water, Ordinary Portland Cement, river sand, river gravel, and periwinkle shells. River gravel and periwinkle shells were combined at a volumetric mix ratio of 1:1 thereby reducing the number of material components from five to four. Manual mixing operation was adopted while all concrete ingredients except for the coarse aggregates were batched by weight. A total of 30 mix ratios were utilised in the concreting operation. While the first 15 mi x ratios were used in the formulation of the model, the last 15 mix ratios were used in the validation of the formulated model using fisher’s statistical test. Three concrete beams were cast for each mix ratio of which a total of 90 prototype beams measuri ng 150x150x600mm were produced and cured for 28 days in an open curing tank filled with potable water. From the statistical analysis, the calculated f - value 1.05 was less than the allowable f - value of 2.48 obtained from statistical table at 95% confidence level. This shows that the difference between the laboratory and model flexural strength results is not significant. Therefore, the formulated model is adequate and reliable for predicting the 28 th day flexural strengths of periwinkle shell - river gravel co ncrete when given mix ratios.