A two stage procedure for assessment of in situ concrete strength using combined non-destructive testing

Test resuls of two different non-destructive test methods, the ultrasonic pulse velocity and Schmidt hammer, were used in conjuction with concrete mix proportions and density, to develop mathematical relationships using multiple linear regressions to obtain a first stage estimate of concrete compressive strength. These regressions covered both wet and air-dry concrete conditions. In each part of the work, a total number of 103 different mixes were tested at ages ranging between 7–90 days.