Modifying self-sensing cement-based composites through multiscale composition

This paper aims to develop self-sensing cement-based composites with high sensitivity through building a multiphasic and multiscale conductive network formed by hybrid super-fine stainless steel wires (SSWs) and carbon nanotubes (CNTs)/nano-TiO2 particles (NTs). Experimental results show that 0.15 vol% SSWs are already in the percolation threshold zone, and incorporating CNTs/NTs has a synergistic effect of decreasing the electrical resistivity and increasing the strain sensitivity of cement-based composites under cyclic/monotonic compressive loading. The hybrid modification effect is closely related to the dosage and conductivity of nano-fillers. The sensing mechanisms mainly include the change of capacitance, tunneling resistance between fillers and intrinsic resistivity of fillers. For cement-based composites with 0.3 vol% SSWs, the electrical resistivity and self-sensing properties are primarily dominated by the SSW network, and are barely affected by the addition of CNTs. However, the strain sensitivity corresponding to the maximum absolute value of fractional change in electrical resistivity under monotonic loading is increased by 62.8% and reaches up to 140 as NTs are added, resulting from the semiconductor and nano-core properties of NTs to form a barrier between overlapping SSW conductive networks. It can therefore be concluded that tailoring different conductive networks by incorporating hybrid multiscale and multicharacteristic fillers is an effective method of developing self-sensing cement-based composites with high sensitivity.