Experimental study and piezoresistive mechanism of electrostatic self-assembly of carbon nanotubes–carbon black/epoxy nanocomposites for structural health monitoring

Since electrostatic self-assembly carbon nanotubes–carbon black (CNTs–CB) composite fillers have good electrical conductivity and an easy dispersion process, they were incorporated into epoxy matrix to fabricate the CNTs–CB/epoxy nanocomposites. The mechanical properties, electrical conductivity, piezoresistivity, as well as microstructure characterization of the CNTs–CB/epoxy nanocomposites were experimentally investigated. The piezoresistive mechanisms of the CNTs–CB/epoxy nanocomposites were also established based on tunneling conduction and contacting conduction. The significant improvements in compressive yielding strength and elastic modulus of the nanocomposites could be attributed to the stable interfacial interaction. A moderate percolation threshold was obtained at 0.41 vol% for the CNTs–CB/epoxy nanocomposites in comparison with that of the nanocomposites filled with only CNTs or CB particles. In monotonic compressive loading, the CNTs-CB/epoxy nanocomposites exhibited highly sensitive and remarkably non-monotonic piezoresistive responses, which could be divided into three stages and showed dependence on the distinct evolution of hybrid conductive networks under compression. Moreover, the experimental results of cyclic loadings confirmed the stability, repeatability, and recoverability in piezoresistive responses of the nanocomposites. Overall, the highly sensitive and steadily piezoresistive responses demonstrate that the CNTs–CB/epoxy nanocomposites are attractive to be used as compressive strain sensors for structural health monitoring in civil infrastructures.