Electrical properties of ultra-high-performance concrete with various reinforcing fibers

Abstract

Understanding the electrical properties of ultra-high-performance concrete (UHPC) is of paramount importance in the realm of smart concrete as it unlocks the potential for creating advanced, intelligent, and resilient infrastructure systems. This study focused on systematically assessing the electrical behaviors of UHPC with two commonly-used reinforcing conductive fillers, i.e. carbon fibers (CFs) and steel fibers (SFs). The effects of fiber type, fiber length, fiber content, and curing age on the alternating current (AC) resistivities and AC electrochemical impedance spectroscopy (AC-EIS) spectra of fiber-reinforced UHPC were investigated, and the equivalent circuit models of fiber-reinforced UHPC were established. Experimental results showed that the AC resistivities of UHPC with CFs and with SFs both exhibited a faster growth rate during the 14–28 d of curing, but subsequently decelerated after the completion of hydration, and stabilized at 90–120 d. Compared with the control sample, the addition of both CFs and SFs resulted in a reduction of the electrical resistivity of UHPC, with a more pronounced decrease observed with higher fiber content. In particular, the addition of SFs demonstrated a more significant reduction in UHPC’s AC resistivity in relative to CFs, with the addition of 4 vol.% copper-plated end-hook SFs remarkably lowering the resistivity by up to 87.5%. Furthermore, the introduction of different types of fibers caused remarkably different AC-EIS topologies of UHPC. The proposed equivalent circuit models reveal that compared to the control sample, the introduction of fibers can provide the fiber-fiber conductive paths and fiber-wrapped hydration products (Q F R F) within UHPC matrix. The role of UHPC matrix (Q 1 (R 1 W 1) in the conductive path of SFs-reinforced UHPC is weakened compared to that of CFs-reinforced UHPC as reflected by the differences in the impedance values of Nyquist plots.