Fracture monitoring within concrete structure by time domain reflectometry

Abstract Time Domain Reflectometry (TDR) is an electromagnetic pluse testing technique using Radar theory. Electrical engineers use it to locate breaks in power transmission lines. Recently, this technique has been applied to monitor rock movement induced by underground mining. Coaxial cables are grouted into the rock mass which is expected to move. Rock movement deforms the cable and produces changes in the TDR reflection signature. These changes can be quantitatively related to the location and magnitude of rock mass movement. While the coaxial cable is embedded in a concrete structure, the fracture or damage within the structure could be detected by sending an electromagnetic pulse down the cable. Observation of the reflected pulse on the oscilloscope would show the change. This forms a very good tool, and could be used to detect and monitor fracture or damage within a large concrete structure. Experimental data will be presented to demonstrate the applicability of this technique. Results show positive. Fracture and relative block movement can be measured quantitatively. This technique can be applied in building warning and monitoring systems for the safety of large concrete structures.