Application of Scheffe’s Model in Optimization of Compressive cube Strength of River Stone Aggregate Concrete

Abstract

Concrete mix designs are usually obtained using either empirical methods or statistical-experimental methods. It has been observed that empirical methods are prone to trial and error, which leads to material wastage whenever they are used. This paper reports an exploratory study on the adoption of the statistical-experimental method using Scheffe’s simplex model in optimizing the compressive strength of river stone aggregate concrete. The model was used to optimize the compressive strength of concrete made from river stone aggregate, river sand, cement, and water based on Scheffe’s four component second degree polynomial simplex lattice design. A total of 60 concrete cubes were cast, comprising three cubes for each mix ratio and a total of 20 mix ratios. The first ten ratios were used to determine the coefficients of the model, while the other ten were used to validate the model. The optimum compressive strength of concrete at 28 days was found to be 37.62 N/mm² and the corresponding mix ratio was 0.5: 1.0: 2.4: 3.6. Visual BASIC program was used to ease the use of the model and computer model accuracy was tested using the Fisher F-test. The model was found to be adequate for prescribing concrete mix ratios, when the desired compressive strength is known and vice versa.

Keywords:Compressive cube strength, river stone aggregate, concrete, Scheffe’s model

International Journal of Natural and Applied Sciences, 5(4): 303-308, 2009