Self-heating curing and its influence on self-sensing properties of ultra-high performance concrete with hybrid stainless steel wires and steel fibers

This study aims to develop ultra-high performance concrete (UHPC) with self-heating curing and self-sensing properties by incorporating hybrid stainless steel wires (SSWs) and steel fibers (SFs) to advance the safety, function/intelligence, and resilience of infrastructures. 0.2 vol% SSWs with micro diameter can already form overlapped conductive network inside UHPC together with SFs to decrease the electrical resistivity and enhance high-efficiency conversion rate from electric energy to Joule heat. As 20 W input power is applied and sustained, the electrical resistivity of UHPC with hybrid 0.2 vol% SSWs and 1.6 vol% SFs (W02F16) first decreases from 45.1 Omega center dot cm to 8.3 Omega center dot cm and then to 7.88 Omega center dot cm due to the field emission effect and the microscopic thermal expansion of SSWs. The surface temperature of W02F16 specimens reaches 78.6 degree celsius for 73 minutes self-heating with an average heating rate of 0.821 degree celsius/min and a temperature difference lower than 11.6 degree celsius. Meanwhile, the fractional change in electrical resistivity and sensitivity corresponding to peak flexural stress of W02F16 after 8 h self-heating curing can reach 58.3 % and 3.22 %/MPa, higher 2.1 and 3.6 times than that after 28 d standard curing. Furthermore, self-heating curing UHPC composites at 28 d possesses more stable and sensitive self- sensing performance especially within pre-peak flexural stress period, resulting from the coarsening effect of direct current on SSWs' interface to regulate and control of conductive pathway in concrete. This is the innovative demonstration that self-heating curing process can endow hybrid SSWs and SFs reinforced UHPC with stable/high self-sensing sensitivity to rapidly fabricate multifunctional/smart infrastructures with the abilities of structural health monitoring, snow and ice self-melting, and indoor heating.