Tailoring mechanical properties and microstructure of stainless steel wires-modified ultra-high performance concrete via direct electric curing

This study investigates the influence of direct electric curing with various durations on thermal, mechanical properties and microstructure of stainless steel wires (SSWs) modified ultra-high performance concrete (UHPC), meanwhile, the energy consumption and carbon emission were compared to verify the supplementary effectiveness of SSWs for incomplete network of commonly used steel fibers (SFs). 0.2 vol% SSWs with micro diameter clearly stabilizes the electrical resistivity of UHPC and enables temperature ascending rate of UHPC reach 0.7–0.9 °C/min by Joule effect. 8 h/12h-20 W direct current electric curing with surface temperature of 70–80 °C results in compressive strength of 120.3 MPa /130.7 MPa, and flexural strength of 18.7 MPa/18.2 MPa, respectively, for UHPC modified with 0.2 vol% SSWs and 1.6 vol% SFs (S02F16), accounting for 80.8 %/87.8 % and 78.6 %/76.5 % of compressive and flexural strength of composites achieved with 28 d-standard curing. The compressive strength of composites typically increases with prolonged electric curing. However, the flexural strength demonstrates decreasing trend when the duration exceeds 8 h. The flexural failure strain, absorbed energy before the occurrence of macrocracks, and multiple cracking failure characteristic of 8h-electric curing S02F16 preserved to 28 d are significantly enhanced, resulting from the refined pore structure , coarsened SSWs’ interfaces, and enhanced SFs’ interfaces under the coupling effect of elevated temperature and direct electric current, confirming an innovative finding of reinforcing effect of SSWs-controlled conductive pathway on SFs’ interface and matrix’s microstructure. Energy consumption/carbon emission for per MPa/per-increasing MPa compressive strength of electric curing is 23.2 %/36.5 % and 14.6 %/23.8 % less than that of hot water curing for S02F16 and S04F16. Furthermore, taking advantage of SSWs’ micro diameter and superior conductivity, electric curing on UHPC has potential to be carried out with green and new energy sources to further reduce carbon footprint especially for low temperature environment construction. • 0.2 vol% wires enable temperature ascending rate of concrete reach 0.7–0.9 °C/min by Joule effect. • 8h-20 W electric curing develops 80.8 % of 28 d-standard curing compressive strength of concrete. • Wires-controlled conductive pathway refines pore structure, coarsens wires’ interface, and enhances fibers’ interface. • Flexural failure toughness of concrete with wires and fibers is enhanced by 58.0 % by electric curing. • Carbon emission for per MPa-increasing compressive strength of electric curing is reduced by 36.5 % compared with hot water curing.