The presence of voids is a serious problem in grouted posttensioned bridges because voids greatly reduce the corrosion-protective capabilities of the grout. Current methods for void detection suffer several significant drawbacks. A new method utilizing time domain reflectometry (TDR) is discussed. TDR is a well-developed method for detecting discontinuities in electrical transmission lines. A recent study has indicated that TDR can be used as an effective nondestructive damage detection method for concrete bridges. A void changes the electrical properties of transmission lines and therefore introduces electrical discontinuities. It can be detected and analyzed by TDR. Experiments on short specimens that are used to model grouted posttensioning ducts with built-in voids have been conducted and demonstrate the potential of TDR as a void detection method.
Abstract