Predictive equations for compressive strength of concrete based on Schmidt hammer rebound and ultrasonic pulse velocity data

Abstract

The compressive strength of concrete is assessed to ensure uniformity of the placed concrete and adequacy of the strength. Non-destructive test (NDT) techniques of ultrasonic pulse velocity and Schmidt rebound hammer tests are commonly used to estimate concrete strength, but the applicability is dependent on correlation of the data with the compressive strength of concrete, the equipment calibration and interpretation of the data. Twenty four standard concrete cubes were cast respectively from 3 concrete mixes, and tested after 28 days of curing by ultrasonic velocity, rebound hammer and crushing tests. The data were analysed by regression methods to obta-in equations for predicting the compressive strength of concrete based on the ultrasonic pulse velocity and rebo-und number. Accurate prediction of the strength of concrete was made when the ultrasonic pulse velocity and the rebound hammer data were combined than when used separately, as the standard error was least. Comparis-on of the calibration curves of the prediction equations with published plots showed very good agreement.