Evaluation of adhesion strength in concrete with crack induced due to steel corrosion by nondestructive testing

Abstract

Currently, it is regarded as a problem that aged structures are rapidly increasing in maintenance of RC members. Therefore, it is desirable to integrate rational inspection and repair for aged RC members in maintenance. In other words, it is ideal to first conduct a standard investigation for a wide area in a short time and then to examine the degree of deterioration in detail at a limited range. Therefore, it is necessary to consider the corrosion of the steel bar which serves as the nucleus in the maintenance control against chloride attack, and the adhesion characteristics between the steel bar and the concrete decreased thereby. However, a quantitative and systematical estimation method has not been established for the steel corrosion in RC members. Therefore, in this study, specimens having several degrees of steel corrosion were prepared within the range where no cracks appeared on the surface. A combination of nondestructive testing was conducted to estimate the adhesion strength between steel bars and concrete. The degree of steel corrosion was estimated first by the half-cell potential, then internal cracks due to steel corrosion in concrete were visually investigated by ultrasonic tomography method. As a result of this experiment, it was possible to identify the corroded area was specified with the half-cell potential. Moreover, as corrosion progressed, it became clear that the ultrasonic velocity around the steel bar decreased, and the adhesion strength between the steel bar and the concrete decreased. Therefore, this study could develop a maintenance method combining the half-cell potential and the ultrasonic tomography method.