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Electrical Impedance Spectra to Monitor Damage During Tensile Loading of Cement Composites.


pdf icon Electrical Impedance Spectra to Monitor Damage During Tensile Loading of Cement Composites. (3661 K)
Peled, A.; Torrents, J. M.; Mason, T. O.; Shah, S. P.; Garboczi, E. J.

Title No. 98-M34;

ACI Materials Journal, Vol. 98, No. 4, 313-322, July/August 2001.

Keywords:

cements; carbon fibers; cement composites; impedance; fracture process; electrical properties; spectroscopy; bridging area

Abstract:

Use of conductive fibers can reinforce concrete and monitor damage leading to the development of a smart material. This work studied the correlation between the electrical (DC and AC) and mechanical properties of cement composites reinforced with conductive carbon fibers. The tensile behavior and impedance behavior of extruded and notched composites with a fiber volume fraction of 0.5% or 3% were examined, with the mechanical load and electrical field applied longitudinally (in the direction of extrusion). The crack growth of these composites during loading was observed and analyzed by Digital Image Correlation (DIC). A good correlation between the electrical and mechanical properties 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 fiber-reinforced composites, impedance values measured during the fracture process were used to distinguish and calculate three different areas at the crack front: uncracked area, bridging area, and open area. The bridging area is the zone where the fibers bridge the propagating crack. A greater bridging area was found for the 0.5% fiber composite, compared to the 3% fiber composite. This can be explained based on differences in the final length of the carbon fibers in the two composites.