Electrical impedance spectra to monitor damage during tensile loading of cement composites

Conductive fibers can reinforce concrete and monitor damage leading to the development of smart material. This work studied the correlation between th e electrical (DC and AC) and mechanical properties of cement composites rei nforced with conductive carbon fibers. The tensile behavior and impedance b ehavior of extruded and notched composites with a fiber volume fraction of 0.5 and 3% were examined; mechanical load and electrical field were applied longitudinally (in the direction of extrusion). The crack growth of these composites during loading was observed and analyzed by digital image correl ation (DIC). A good correlation between the electrical and mechanical prope rties was found, in that when a sudden growth in the crack was observed, a dramatic change was also noticed in the impedance values. Taking advantage of the special frequency-dependent electrical properties of conductive fibe r-reinforced composites, impedance values measured during the fracture proc ess were used to distinguish and calculate three different areas at the cra ck front: uncracked area, bridging area, and open area. The bridging area i s the zone where the fibers bridge the propagating crack. A greater bridgin g area was found for the 0.5% fiber composite, compared to the 3% fiber com posite. This can be explained based on differences in the final length of t he carbon fibers in the two composites.