Strain-Sensing Characteristics of Carbon Fiber-Reinforced Cement

The ability of a structural material to sense its own strain (without attached or embedded sensors) is a positive attribute of smart structures. Specific applications include structural vibration control, traffic monitoring, weighting, room occupancy monitoring, and building security. This article reports on a study of strain sensing in carbon fiber reinforced cement, as enabled by piezoresistivity. This type of strain sensing is characterized by the gauge factor, which is defined as the fractional change in electrical resistance per unit strain. This study involved simultaneous measurement of the piezoresistive behavior in the longitudinal and transverse directions for each specimen. Results showed that, under uniaxial compression, the gauge factor in both longitudinal and transverse directions decrease in magnitude with increasing specimen size from 13 to 51 mm, due to a slight decrease in the degree of preferred orientation of the 5 mm-long fibers. The gauge factor in both directions also decreases in magnitude as the fiber content increases beyond the percolation threshold.