Development of Scheffe’s regression model to predict compressive strength of concrete using metakaolin as partial replacement of cement

Abstract

Abstract Kaolinite clay, that Nigeria has been proven to have about 3 billion tonnes scattered across all the geo-political zone, can be used to produce Metakaolin through a simple calcinations process. Metakaolin may be used as a cement replacing material in concrete, to reduce cement consumption, to increase strength and the rate of strength gain, to decrease permeability and to improve durability. In this study, it served as a fifth component of concrete blend as it replaces between 0% to 20% of cement. The other four ingredients were water, cement, fine aggregates (sand), coarse aggregates(granite). Scheffe’s simplex theory was used for the five-mix design in a {5,2} experimental design which resulted in an additional ten mix ratios. For the purpose of testing and verification, additional fifteen mix ratios were made. The thirty concrete mix ratios were subjected to laboratory experiment to determine the 28days compressive strengths. The results of the first fifteen compressive strengths (model mixes) were used for the calibration of the model constant coefficients, while those from the second compressive strength (control mixes) were used for the model verification. A mathematical scheffe’s regression model was derived from the experimental results, which was used to predict the compressive strength of concrete. The regression model was subjected to a t-test with 5% significance, which ascertain the model to be adequate with an R2 value of 0.9417. The study reveal that Metakaolin can replace up to 20% of cement without compromising 28-day compressive strength.