Experimental study on comparison of equivalent concrete compressive strength of cores and rebound hammer tests with in-place and standard cubes

Abstract

This study has presented a comprehensive test program that has compared the following, namely, the compressive strength of concrete cores extracted from the plinth beam (PB) of a substation, the compressive strength of both concrete cubes cast for the trial mix and those cast at the time of construction of the plinth beam, and the compressive strength of the plinth beam as assessed with a rebound hammer. Even though various techniques have been available for structural evaluation, there have been significant uncertainties in correlating the actual compressive strength of concrete. The standard procedures have been applied to a case study of a substation at Silapathar, Assam, owned by PowerGrid Corporation of India. To evaluate the quality of construction, different accepted methods suggested by various codes, such as the Indian Standard, the American Society for Testing and Materials Standard, the American Concrete Institute Standard, and the European Standard, have been employed. Experimental results have indicated that the equivalent compressive strength of concrete based on the rebound hammer has been 15.11% higher than the in-situ concrete strength. Similarly, the equivalent compressive strength of the concrete cube estimated using European and Indian codes has been 22% and 27% higher than the experimentally measured core compressive strength. The expressions proposed for estimating equivalent cylinder compressive strength have closely predicted the core compressive strength, compared with expressions for estimating cube compressive strength. This information has been useful for practising engineers not to reject concrete solely based on the acceptance criteria of the cube compressive strength of in-situ concrete, and to accept concrete based on non-destructive or semi-destructive tests.