Nondestructive and Destructive Evaluation of Concrete Compression Strength

The evaluation of structural performance of existing concrete structures, built according to standards and materials quite different to those available today, requires procedures and methods able to cover lack of data about mechanical material properties and reinforcement detailing. This issue is more relevant when seismic zones are concerned and structural strengthening needs to prevent failures due to earthquakes. Recent seismic codes give relevance to procedure and methods to establish the performance levels of existing structures. To this end detailed inspections and test on materials are required. As a consequence tests on drilled cores are required; on the other end, it is stated that non-destructive testing (NDT) cannot be used as the only mean to get structural information, but can be used in conjunction with destructive testing (DT) by a representative correlation between DT and NDT. The poor reliability of rebound hammer and ultrasonic pulse velocity due to different aspects could be partially contrasted by using both methods together. One of the most employed NDT combined methods in practice is the SonReb method, described in RILEM 7 NDT and 43 CND. This technique achieves an improvement of the accuracy by the use of various correction factors taking into account the influence of different concrete mixture proportion. Some of the most reliable and employed formulations available in literature are considered. The aim of this study is to verify the accuracy of some formulas of correlation available in literature between measured parameters, i.e. rebound index, ultrasonic pulse velocity and compressive strength (SonReb Method). To this end a relevant number of DT tests and NDT tests has been performed on many buildings. The above relationships have been assessed comparing ND test results to strength of core drilled in adjacent locations.