Empirical Modelling of Mechanical Properties of Concrete Using Bida Natural Gravel as Coarse Aggregate

Abstract

Strength performance remains the most important property of structural concrete, from engineering point of view. Compressive, flexural, tensile strengths and elastic modulus of concrete are of great importance in structural engineering. The determination of compressive strength of concrete is easier to carry out in the field when compared to flexural tensile strengths and elastic modulus. It is therefore, customary to determine the compressive strength and correlate it to other strength properties. In this study, empirical relationships have been developed to relate the compressive strength to the flexural, splitting tensile strengths and elastic modulus of concrete using Bida gravel as coarse aggregate. Extensive experimental work was conducted using 400 specimens for compressive strength, 400 for flexural strength, 400 for splitting tensile strength and 400 for elastic modulus (1,600 in all). Central composite design was used for the factor setting with the following range of values; W/C= 0.4, 0.5, 0.6, CA/TA= 0.55, 0.615, 0.68, TA/C= 3.0, 4.5 and 6.0. The specimens were produced and cured for 7, 14, 21 and 28 days. The compressive, flexural and splitting tensile strengths of concrete samples from these mixes were determined at 7, 14, 21 and 28 days of age. From the strength data obtained at 28 days, regression equations were developed that relate the strength properties with the aid of regression analysis tool in Microsoft Excel. The empirical models developed to predict the flexural, splitting tensile strengths and elastic modulus of concrete from the compressive strength recorded R² values of 0.99, 0.99 and 1, P-values of 2.41 × 10⁻⁹, 1.6× 10⁻⁹, and 6.7× 10⁻¹⁰ standard errors of 0.684, 0.19 and1.42respectively. Furthermore, residuals from the values of predicted strength properties show that there is very slight deviation between the experimental and predicted values. It was concluded that the empirical equations developed are significant, have high predictive capabilities and can be used in predicting the flexural, splitting tensile strengths and elastic modulus of concrete.