Sensing performances of hybrid steel wires and fibers reinforced ultra-high performance concrete for in-situ monitoring of infrastructures

Abstract

Steel wires (SWs) with microscale diameter and high aspect ratio can overlap each other to form the stable conductive network at a low content, thus they are the promising conductive fillers to enhance the poor conductivity and sensing capacity of ultra-high performance concrete (UHPC) containing steel fibers (SFs) for in-situ monitoring of infrastructures. In this paper, the electrical conductivity and sensing performances to flexural loading of hybrid SWs and SFs reinforced UHPC are investigated, meanwhile, the conductive and sensing mechanisms are revealed by the analysis on microstructure, equivalent circuit and cracking behavior of composites. The test results indicated that 0.4 vol% SWs are in the percolation threshold zone, and the hybrid SWs and SFs have a positive synergistic effect on the conductivity of UHPC. The optimum electrical resistivity of UHPC with SFs can be reduced from 12900 Ω cm to 1310 Ω cm due to the addition of SWs. The hybrid SWs and SFs reinforced UHPC can effectively monitor the cracking initiation and development by measuring the fractional change in resistivities (FCR) under flexure, especially it performs more stable and accurate in monitoring the initial cracking and more sensitive in monitoring residual flexural loading and cracking development compared to mono SFs reinforced UHPC. This can be attributed to the inhibition effect of SWs on microcracks and the extensively conductive network formed by both SWs and SFs. UHPC with low content of hybrid SWs and SFs can already achieve self-sensing with high stability and sensibility in terms of in-situ monitoring crack initiation and propagation under flexural loading.