Mechanical performance enhancement of UHPC via ITZ improvement using graphene oxide-coated steel fibers

By virtue of its superior strength, high toughness, and low porosity, ultra-high-performance concrete (UHPC) has a wide range of application prospects in construction engineering. However, the interfacial transition zone (ITZ) formed between the cementitious matrix and steel fiber seriously restricts the steel fiber's strength utilization rate in UHPC. Hence, in this work, graphene oxide (GO) is employed to be coated on the steel fiber surface to strengthen the UHPC. The results demonstrate that through a three-step GO coating approach, the roughness and hydrophilicity of the steel fiber surface can be enhanced by about 280.6 % and 40.6 % compared with plain steel fiber. The coated GO can provide pore-infilling and nucleation effects during the hydration processes of the UHPC, thus decreasing the porosity by 37.5 % compared with non-GO reinforcement. After the three-step coating treatment, the compressive and bending strength of the coated-GO reinforced UHPC is enhanced by 33.7 % and 26.2 %, respectively. The molecular dynamic simulation results further reveal that benefiting from the crackbridging effects of the coated GO, the interface between the steel fiber surface and cement matrix is prone to a ductile failure, with the failure energy of the C-S-H composites increasing by about 320%-1340 %. The findings advanced by this work can enhance the understanding of nano-cement technology and promote the potential application of the GO-coated fiber to generate high-performance UHPC.