Combined NDT methods to determine the variations in compressive strength throughout concrete structures

Compressive strength is an essential characteristic of reinforced concrete structures. Standards and codes of practice give rules for the assessment of the structural compressive strength of hardened concrete in situ, which are to be compared with the strength class used in design. In this paper, Non-Destructive Testing (NDT) methods were used to map the compressive strength variations of a concrete mock-up wall. A combination of Ultrasonic Pulse Velocity (UPV) and Rebound (Schmidt) Hammer were used to estimate the in-situ compressive strength of concrete. Compressive strength estimation models were generated using NDT methods with a minimal number of drilled concrete cores in order to calibrate the NDT methods. Reliability of the estimated compressive strength values was a challenge when assessing the in-situ strength of the mock-up wall. The factors affecting the compressive strength estimation models include the number of test location for cores used to identify the model, quality of measurements, the type of NDT technique, the use of single or combined NDT techniques, and the model identification approach. This article presents the on-site evaluation of concrete compressive strength using combined NDT techniques. The investigation was carried out on a thick-walled reinforced concrete mock-up wall. The test results show some variation in the compressive strength when applying the combined NDT techniques. The prediction of compressive strength carried out shows how the use of known destructive methodologies associated with a combined non-destructive method improves the accuracy of the estimation of the concrete compressive strength if the NDT methods are calibrated using enough test samples.