Multifunctional Super-Fine Stainless Wires Reinforced UHPC for Smart Prefabricated Structures

Owing to their excellent mechanical, electrical, thermal, electromagnetic characteristics, micro diameter and high aspect ratio, super-fine stainless wires (SSWs) can form widely-distributed reinforcing and conductive network in ultra-high performance concrete (UHPC) at low dosage, thus endowing UHPC with multifunctional properties including enhanced mechanical performances and durability as well as smart property. In this paper, the mechanical, electrically conductive, and self-sensing performances of SSWs reinforced UHPC were investigated. The modification mechanisms of SSWs to UHPC were revealed by microstructure, electrochemical impedance spectroscopy and intrinsically electrical conductivity analysis. The results show that the 1.5 vol. % of SSWs can increase the flexural strength, flexural toughness of UHPC unnotched beams and equivalent flexural strength of UHPC notched beams by 103.2%, 146.5% and 80.0% respectively. Meanwhile, the dynamic impact toughness and dissipate energy of SSWs reinforced UHPC with the strain rate ranging from 94 /s to 926 /s are increased by 43.5% and 58.2%, respectively. The electrical resistivity is reduced by six orders of magnitudes and the electrochemical impedance spectroscopy only shows small flat arcs in the first quadrant in UHPC containing 0.5 vol.% of SSWs in diameter of 20 μm. The gauge factor of UHPC reinforced with SSWs in diameter of 8 μm can reach up to 22.5, 94.9 and 43.6 under cyclic compression, monotonic compression and flexure, respectively. The microstructure analysis indicates that the modification effect of SSWs on UHPC results from the extensive network of SSWs in UHPC, the inhibition on micro-cracks propagation and the pull-out and stripping of SSWs under loading. SSWs reinforced UHPC has great potential for developing pre-cast structural elements or cast-in-place joints for prefabricated structures, which will achieve the monitoring for structural key positions and can be efficiently used for health monitoring and safety assessment of prefabricated structures driven by the sensing information of multifunctional concrete. This will further avoid the issue concerning high cost of large scale application of multifunctional concrete. In addition, the smart pre-cast structural elements can be reusable and replaceable. Therefore, developing SSWs reinforced UHPC for prefabricated structures can make infrastructures safer, more durable and sustainable.