Velocity-strength relationship of concrete by impact-echo method

This paper describes using, the impact-echo method to evaluate the early-age strength of normal- and high-strength concrete. Impact-echo and compression tests were carried out between 12 h and 28 days to measure the rod-wave velocity and compressive strength, respectively, of concrete specimens. with various water-cementitious Material-ratios (w/cms) between 0.58 and 0.27. Test results demonstrate that the velocity-strength relationship of normal-strength concrete with w/cms ranging from 0.58 to 0.35 is noticeably different from that of high-strength concrete with w/cms below 0.35. Also noted, in this study is that the velocity-strength relationship of normal-strength concrete was influenced by. the curing age of the specimen. The addition of fly ash (FA) had little influence on the velocity-strength relationship of either normal- or high-strength concrete specimens. Based on these observations, formulae to determine the,,relationship between the strength and wave velocity of concrete were proposed that incorporate the effects of the w/cm and the curing age of the specimen.