Predicting Compressive Strength of Concrete

Abstract

This paper deals with development of regression models for prediction of compressive strength of concrete. The compressive strength of concrete is predicted using four variables, namely, water-binder ratio, fine aggregate-binder ratio, coarse aggregate-binder ratio and binder content. Linear regression models have been developed for variations in fly ash replacements (0 and 15 percent), Zones of aggregates (A, B and C) and curing ages (28, 56 and 91 days). An effort has also been made to modify the linear models using a two step approach. First step is to develop quadratic models (termed as full models) by identifying the suitable combinations of the four variables described above. The second step is to select the best minimal subset of the predictors in full models using Mallow's Cp statistic. The proposed quadratic regression models yielded coefficient of determination R 2 ≥ 0.99 in almost every case except for concrete with Zones A and B of aggregates without fly ash for 91 days curing period and for concrete with Zone C of aggregates without fly ash for 56 days curing period. Concrete is a strong building material composed of sand, gravel, cement and water. Additional admixtures are also added sometimes to enhance certain properties of fresh or hardened concrete. In the construction industry, among the various properties of the concrete determination of compressive strength has received a large amount of attention because concrete is primarily meant to withstand compressive stresses. The compressive strength of concrete is controlled by proportioning of cement, coarse and fine aggregates, water and various admixtures. Prediction of concrete compressive strength has been an active area of research and a considerable number of studies have been carried out in this direction. Many attempts have been made to develop a suitable mathematical model which is capable of predicting compressive strength of concrete at various ages with acceptable accuracy. Multiple regression models have been used by researchers to improve accuracy of predictions of concrete compressive strength. Nipatsat and Tangtermsirikul (1) developed equations for estimating compressive strength of concrete containing fly ash with curing ages from 3 days up to 1 year. Kazberuk and Lelusz (2) proposed regression models to predict compressive strength of concrete with fly ash replacement percentages up to 30%. Namyong et al. (3) proposed the regression equations for predicting compressive strength of in-situ concrete. They have selected