Evaluation of compressive strength of concrete durability degradation in dry and wet environments using destructive and non-destructive testing

Abstract

To develop an effective non-destructive testing (NDT) method to assess the strength of concrete in dry and wet cyclic environments, concrete compressive strengths were evaluated of six different mix ratios in this study using ultrasonic method, rebound method and quasi-static compression tests indoors. Firstly, the results of concrete indoor quasi-static compressive strength tests were compared with the NDT results and the optimum NDT methods applicable to different concrete strength classes were determined. Subsequently, an in-situ NDT evaluation of concrete gates exposed to dry and wet environments for a long-term period was carried out based on the results of the laboratory indoor tests, and the degradation mechanism of concrete strength under dry and wet cyclic conditions was revealed by rebound method testing, borehole coring, and industrial computerized tomography (CT) scanning. The results show that the concrete strength obtained by the ultrasonic rebound method is closer to the actual value when the initial strength of concrete is less than 30 MPa; When the initial strength of concrete is between 30 and 40 MPa, the concrete strength obtained by the rebound method is closer to the actual value; When the initial strength of concrete is greater than 40 MPa, the concrete strength obtained by the rebound and ultrasonic rebound methods differ greatly from the quasi-static compressive strength. In addition, the compressive strength of concrete increases and then decreases with the number of dry and wet cycles increases. In the early stage of the dry and wet cycle, the main reason for the increase of the concrete strength is that the filling of the pores by the hydration products reduces the porosity of the concrete; As the number of dry and wet cycles increases, the hydration products absorb water to expand and lose water to shrinkage, which leads to microcracks, and this is the main reason for the decrease of the concrete strength in the late stage of the dry and wet cycle.