Evolution of Impedance Spectra during Debonding and Pullout of Single Steel Fibers from Cement

Impedance measurements were made during the debonding and pullout of a fully embedded, crack-bridging single steel fiber from a cement matrix. Nyquist plots gave evidence of two bulk arcs, and the "cusp" between them proved to be sensitive to both debonding and pullout of the embedded fiber. Physical simulations that used a steel wire in tap water were applied to interpret the debonding and pull-out results. The cusp resistance from impedance spectroscopy provided quantitative information about the extent of pullout and, at least qualitatively, correlated with the debond length before pullout. Impedance measurements on both sides of the matrix crack showed that crack deflection and debonding occurred on both sides symmetrically.