In this paper, the working mechanism and the measurement principle of topology-based crack sensors made of coaxial cables was briefly reviewed. Thesensitivity, spatial resolution, and ruggedness of two coaxial cable sensors, respectively made of rubber and Teflon dielectric materials, were compared and validated with laboratory testing of a 4/5-scale, T-shaped, RC beam-column specimen. Two Teflon sensors were installed on one of the soliddecks of a three-span continuous highway bridge to investigate their durability and measurement repeatability. Laboratory tests indicated that bothtypes of sensors have high sensitivity, but the Teflon-sensor has a higher spatial resolution and a negligible spillover effect of any significant cracks. At a 90° bend, however, the Teflon-sensor is more susceptible thanthe rubber-sensor to the rubbing action of the outer conductor of a coaxial cable against its dielectric layer. No cracks were observed during the field load tests of the instrumented bridge. Both sensors indicated high durability in the real-world application but a certain variation of waveforms measured over a period of five years due to the use of different instruments. As a result, future research is directed to develop an on-line calibration of crack sensors with a small portion of built-in standard cable at the end of the cable sensor.
Abstract