Interfacial Evaluation and Self-Sensing of Single Micro-Carbon Fiber/CNF-Brittle-Cement Composites using Electro-Micromechanical Tests and Acoustic Emission

Abstract

Interfacial evaluation and self-sensing were investigated for single carbon fiber/carbon nanofiber (CNF)-brittle-cement composites by electro-micromechanical techniques and acoustic emission (AE) under cyclic loading/subsequent unloading. During the curing process, the volumetric resistivity decreased dramatically, during the initial stage, due to increased contact points between the cement matrix and the CNF. The apparent modulus and electrical contact resistivity of micro-carbon fiber/CNF-cement composites were also evaluated as a function of CNF concentration. As the CNF concentration increased, the maximum stress increased, whereas the change in resistance Delta rho decreased gradually and the contact resistivity sensitivity increased as well. Micro-damage sensing of micro-carbon fiber/CNF-cement composites was also investigated by electrical resistivity and AE. When the first fracture of micro-carbon fiber occurred, the electrical resistivity increased 'infinitely' with increasing lower CNF concentrations. For high 5 wt% CNF, however, the fracture of micro-carbon fiber could be detected just in one large step increment change in the electrical resistivity as well as consistent AE events. The percolation structure of CNF is not well formed in the cement matrix due to relatively-low electrical conductivity. The chosen CNF-cement composites are not suitable for conductive and sensing applications because of their many vertical microcracks. (C) Koninklijke Brill NV, Leiden, 2011