Ultrasonic Tomography as Non Destructive Measuring Technique for Concrete Pavement Evaluation

Ultrasonic tomography is a non-destructive method to evaluate different characteristics of the pavement such as thickness, position of reinforcement, presence of cracks and impurities, strength evolution. This technique can be used for control and follow-up of new pavements but also for non-destructive analysis of existing pavements in order to determine the cause and extent of distresses on these pavements. This technique has first been applied on concrete pavements by researchers at the University of Minnesota, USA. With their help, the E34, a Belgian highway constructed with a double layered continuously reinforced concrete pavement, was analysed. This pavement exhibited early punch-out at the surface, due to the existence of horizontal cracks located at the height of the reinforcement and which could be detected by the ultrasonic tomograph. Extreme shrinkage probably laid at the basis of the observed damage. Since the beginning of 2013 the BRRC has invested in an ultrasonic tomography device. First calibrations have been done on a test slab with various thicknesses and reinforcement bars. Subsequently, measurements on different pavements have shown that ultrasonic tomography is indeed a suitable method for the evaluation of concrete roads. This paper presents the ultrasonic tomography method and its possible applications. The accuracy of the measuring technique is demonstrated, based on the calibration measurements done in the laboratory and in-situ. The usefulness of this method for pavement management is shown by some particular measuring campaigns carried out in Belgium.