Advanced NDT methods for evaluating concrete bridges and other structures

Abstract

Several advances in methods and equipment for sonic and ultrasonic non destructive testing (NDT) of concrete structures are presented, including advances for methods applicable to large structures such as bridges and dams. These new advances and methods greatly increase the speed and accuracy of many NDT investigations, and allow collection of NDT information previously not readily obtainable. The first topic presented is a brief overview of the impact echo (IE) method along with a case history on how is has been employed in testing concrete structures. The IE method is used to locate damage and determine member thickness when access is available from one side only. The next topic is a relatively new N DT method for concrete using surface waves analysis, in a method known as the spectral analysis of surface waves (SASW) technique. This allows the determination of the shear wave velocity profile versus depth for any layered system and is particularly applicable to testing pavements, slabs, tunnels, shaft liners, and massive concrete structures. For bridges and dams, the technique is particularly effective in determining the depth of weathering effects on the concrete. Included is an overview of the method and the principles behind it, as well as some case history examples. The final topic presented is an advance in the technique of ultrasonic plus velocity (UPV) testing. This advance involves the use of rapid scanning techniques to greatly increase the speed and utility of UPV testing. The U PV method uses compression wave energy which is sent through a member and the arrival time, wave amplitude, and velocity are recorded and computed. This new scanning technology allows the near-continuous acquisition of data along any given path over a structure. Included is test data collected using the scanning system to show the great increase in testing speed and utility of scanner-collected data when compared to traditional point-by-point methods.