Influence of core sampling choices and non-destructive testing methods on calibrated empirical laws for concrete strength assessment

Abstract This paper investigates the impact of technicians’ decisions during the planning experimental tests for assessing the concrete compressive strength of existing buildings. In detail, the attention is devoted to the estimation of concrete strength using Non-Destructive (ND) testing techniques and to the effects of varying the number and location of drilled cores, as well as the type of adopted ND tests, on the calibration of empirical correlation laws. An extensive experimental campaign has been performed on two existing buildings involving destructive tests on drilled cores, Rebound Hammer (RH) tests and Ultrasonic Pulse Velocity (UPV) tests. The results of destructive and ND tests have been collected into three distinct databases, each one correspondent to a different testing scenario: the non-destructive results of RH tests combined with core tests, UPV tests combined with core tests, and the SONREB method, which integrates the results of both ND techniques, with core strength values. The resulting databases have been elaborated to investigate the influence of the experimental choices - namely the type and the position of ND tests and the number m of drilled cores used for calibration - on the parameters of the conversion models. For each investigated scenario, empirical relationships linking the parameters of the calibrated conversion models are proposed. The results show that, although different experimental configurations may lead to significantly different calibrated models, consistent relationships between their parameters can be identified, providing useful support for assessing the reliability of conversion laws in practical applications.