Comparison of DestruCtive methoDs to appraise the meChaniCal integrity of a ConCrete surfaCe

Depending on the technique being used, the concrete removal operation prior to repair can be harmful to the residual concrete skin left on the structure. Whenever a tight bond between the repair and the old concrete is required, the soundness of the prepared surface should thus be assessed. Although this is widely recognized, there is no standard method intended to characterize the integrity of a concrete substrate after concrete removal. This paper presents the results of an investigation intended to assess and compare quantitatively different test methods, namely the Schmidt rebound hammer, the Capo and Accelerated cohesion pullout tests, and the pull off test, to evaluate superficial mechanical integrity of a substrate after concrete removal operations. Although it does not yield a precise evaluation of compressive strength, the Schmidt rebound hammer test is recognized as a useful tool for performing quick surveys to assess concrete uniformity. The pull off test is very well correlated with the splitting-tensile test, but it is not suited for vertical and overhead surfaces. The Capo pullout test has limited interest for surface preparation, as it is applicable to flat surfaces only. Conversely, the Accelerated cohesion test showed interesting potential as a simple tool for assessing the mechanical integrity of a concrete surface prior to repair for any type of concrete surface. More work is required to refine the procedures and develop statistically based acceptance criteria. Nevertheless, it appears from the results generated in this study that the combination Schmidt hammer / pull off tests could fulfill the needs for the evaluation of horizontal surfaces after concrete removal, while the combination Schmidt hammer / Accelerated cohesion tests could be used effectively on any surface, irrespective of its orientation.