Multifunctional ultra-high performance fibre-reinforced concrete with integrated self-sensing and repair capabilities towards in-situ structure monitoring.

Achieving continuous in-situ monitoring of repaired concrete structures has always been a great challenge. Ultra-high performance fibre-reinforced concrete (UHPFRC), featuring superior mechanical capacity, excellent erosion resistance, and long-life cycle, is expected to realize durable, cost-effective, and aesthetically pleasing repairs and possesses tremendous potential for intrinsic self-sensing. This paper presents the multifunctionality of UHPFRC with integrated self-sensing and repair capabilities using multi-walled carbon nanotube (MWCNT). An experimental evaluation on the bond performance and self-sensing properties, including the bond strength and failure patterns by the three-point bending, splitting tensile, and slant shear tests, electrical properties via alternating current impedance spectroscopy test, and electromechanical properties under three-point bending, was conducted through the designed composite layer between concrete substrate and UHPFRC. The microstructure of the interfacial zone was analysed to reveal the bonding mechanism. Results indicate that the addition of MWCNT improved the bond strength between concrete substrate and UHPFRC as MWCNT can enhance the adhesion and cohesion of the interfacial zone through inactive filling effect, as well as the frictional and mechanical interlocks through increased mechanical properties of repair UHPFRC. Moreover, the repair UHPFRC showed remarkable sensing capabilities for the initial cracking, deflection hardening or softening, and fibre pull-out and debonding processes of the composite layers. The optimal content of steel fibre and MWCNT in multifunctional UHPFRC should be 2 vol.% and 0.2 wt.%, respectively, considering the synergistic damage sensing and bonding properties. [ABSTRACT FROM AUTHOR]