Assessing concrete strength variability in existing structures based on the results of NDTs

One of the main factors affecting the survey of concrete strength in existing structures is the inherent material variability, which can only be fully characterized when destructive tests are performed, especially in older structures. Therefore, having a preliminary estimate of the concrete strength variability facilitates the planning of destructive testing campaigns. In light of this, the proposed study presents the development of general empirical expressions estimating the in situ concrete strength variability using non-destructive test (NDT) results. These expressions are defined by examining the correlation between statistical parameters of datasets of concrete core strength, rebound hammer and ultrasonic pulse velocity test results using several correlation models that are based on common conversion models and on a generalization of the bi-objective approach. Based on these analyses, empirical models that are able to provide a reliable estimate of concrete strength variability using NDT results are proposed.