2nd International Symposium on Advances in Concrete through Science and Engineering 11-13 September 2006, Quebec City, Canada ANALYSIS OF STRESS WAVE PROPAGATION IN REPAIR SYSTEMS USING WAVELET APPROACH Andrzej Garbacz (1) , Tomasz Piotrowski (1) and Luc Courard (2) (1) DBME, Warsaw University of Technology, Poland (2) Geomac, University of Liege, Belgium Abstract Impact echo method is treated as one of the most promising methods for a quality control of repair efficiency. In this method, an analysis of frequency spectrum based on the fast Fourier transform - is used to detect various types of disbonds. Recently, a new tool for signal analysis – wavelet transform - is being implemented in NDT assessment, also in the case of concrete structures. It is a multiresolution time-scale methods. The aim of this paper is to analyze the effect of a bond quality on stress wave propagation in repair systems characterized by Fourier and wavelet transforms of impact-echo signal. Three types of concretes and four types of surface preparation have been combined in order to obtain twelve different repair systems. In each case, a polymer modified cement mortar has been applied as a repair material. A quality of concrete substrates has been characterized according different destructive and non destructive techniques: impact-echo, compressive strength, superficial cohesion (pull-off test), surface roughness measurement (sand patch test) and cracking quantification (microscopical observation). The bond quality has been characterized with impact-echo measurement and pull-off test. For each repair system the wavelet analysis of impact-echo signals was performed. The relationships between parameters describing surface quality (roughness, cracking), adhesion strength and stress wave propagation have been analysed. 1. INTRODUCTION Recently it is noted growing interest in application of non-destructive techniques (NDT) for evaluation of concrete structures [1,2]. This has resulted from an increase of quality requirements for concrete in new construction. On the other hand, the percentage of repair and rehabilitation in the total building market has increased [3]. In this case, there is a need for quality control of repair efficiency and its monitoring during repaired structure service as well. The European Standard EN 1504-10 [4] and ACI Concrete Repair Manual [5] give some guidelines for repair efficiency evaluation. According to those documents, the bond strength