Prediction of compressive strength of concrete: final report

Abstract

This report presents a method of predicting compressive strength of concrete. The approach is based on experimental investigation of compressive strength development of grade 20, 25, 30 and 50 concrete with three different brands of cement. The criterion used for the prediction of strength involves the determination of equivalent age of concrete, which depends on curing temperature and age of concrete. It was found that the compressive strength of concrete varies linearly with respect to the logarithmic value of the equivalent age. Furthermore, it was observed that the rate of change of strength with respect to logarithmic value of equivalent age varies non-linearly with respect to w/c ratio. This variation was not the same for all brands of cement tested. Expressions were derived for compressive strength for each brand of cement with respect to w/c ratio, age and curing temperature. Based on these expressions, a chart was developed to establish the relationship between strength and w/c ratio for a range of strength grades. This chart can be used in mix design of concrete using local materials. Since it was not possible to develop a unique expression for the prediction of compressive strength of concrete in terms of mix design parameters like w/c for any cement brand, the identified behavior of the strength development of concrete with respect to equivalent age was used in predicting strength of concrete. In the proposed method, the 28-day strength can be predicted with strength results at two ages such as 1-day and 3-day strengths. A good agreement with the predicted and experimental results have been obtained not only for test results obtained under this study but also for other published test data.