The assessment of concrete subjected to preloading using non destructive testing methods

Different non-destructive tests are in use for the structural health monitoring. Test variables affecting non destructive behavior of concrete were discussed by some researchers, including the effect of instantaneous loading during testing for ultrasonic pulse velocity (UPV). This study aimed at determining rebound number (RN) using Schmidt hammer and UPV of concrete subjected to short term and continuous loadings. Tests were carried out on concrete cubes and cylinders to study the effect of short term loading, while to apply a continuous loading, reinforced concrete beams were loaded inside a rigid steel frame. Reduction of RN and UPV for concrete subjected to 80% compressive loading was found to be 8.1% and 10% respectively. There is some effect of loading cycle at high loading level especially for lower strength concrete. Also, RN was found to reduce with increasing tensile short term loading, in which for lower strength concrete reached 5%. There is a continuous reduction in UPV percentage with increasing tensile loading level, especially for lower strength concrete but the effect of tensile loading was found to be smaller than that of compressive loading. Analysis of data was made and equations were presented to calculate the changes take place due to short term loading effects. It is concluded that for concrete under continuous tensile stress, equations for UPV-compressive strength relationship should be modified with a reduction factor of 0.87 or calculated from an equation proposed in this study.