PERFORMANCE EVALUATION OF NDTS IN PREDICTING COMPRESSIVE STRENGTH OF CONCRETE

Abstract

Accurate prediction of concrete compressive strength is imperative for investigating the in-situ concrete quality. To avoid destructive testing, developing reliable predictive models for concrete compressive strength using nondestructive tests (NDTs) is an active area of research. However, many of the developed models are dependent on calibration and/or concrete past history (e.g. mixture proportion, curing history, concrete mechanical properties, etc.), which limits their utility for in-situ predictions. The main objective of the study to establish a relationship between NDT test results with the compressive strength of the structures. This study developed predictive models for concrete compressive strength. In this study, concrete cylinders were casted with strength varied from 15 to 60 MPa. Ultrasonic pulse velocity (UPV) and rebound hammer (RH) tests were performed on 90 concrete cylindrical samples and 90 concrete core cylindrical samples. After that, compressive strengths were determined using destructive testing on 90 cylinders and 90 core cylinders. The rebound number at 7 days shows the concrete quality varied from fair to good for C15 to C60 grade of Concrete for both cylinder and core cylinder. For similar grade of concretes, the rebound number at 28 and 90 days shows the concrete quality varied from good to excellent. The UPV test results show that the concrete quality varied from very good to excellent for both cylinder and core cylinder. It is found that the strength obtained from rebound hammer and core cutting is well comparable with cylinder crushing strength. RH strength is found lower than the cylinder compressive strength for all grade of concrete by an amount of about 3% to 8%. Whereas, core strength is found lower than the cylinder compressive strength by an amount of about 8% to 11% for all grade of concrete. Finally, predictive equations were developed at 7, 28 and 90 days age of concrete cylinder and concrete core based on NDT results.