Influence of industrial-grade graphene oxide on macro and micro properties of ultra-high performance concrete incorporating recycled fine aggregate

In order to address the limitations of recycled aggregate concrete prepared from recycled fine aggregates (RFA), the utilization of nanomaterials has been demonstrated as an innovative and effective approach. This study aimed to enhance the performance of ultra-high performance concrete (UHPC) reinforced with recycled fine aggregates (RFA) by incorporating industrial-grade graphene oxide (GO). The effects of GO on various aspects of UHPC, including workability, mechanical properties, autogenous shrinkage, permeability, interfacial transition zone (ITZ), and microstructure, were thoroughly investigated. The results demonstrated that the addition of RFA significantly reduced the early compressive strength of UHPC and increased water permeability and chloride ion penetration. However, it effectively mitigated autogenous shrinkage, and the 7-day autogenous shrinkage was reduced by 61.07%. Moreover, increasing the GO content improved the compressive strength and transport performance of RFA-reinforced GO-UHPC. The incorporation of GO led to a substantial enhancement in the tensile strength of UHPC due to its bridging effect and changes in pore structure, thereby improving the interface bonding between steel fibers and the matrix. At a critical GO content of 0.06%, the autogenous shrinkage was further reduced by 54,85%, and the compressive and tensile strengths were improved by 8.24% and 28.39%, respectively, with an increase in the matrix density. The addition of GO promoted the formation of more calcium silicate hydrate, resulting in a more homogeneous microstructure and an increased proportion of small pores in the ITZ. Overall, this study highlights the synergistic effect of GO and RFA in UHPC as a promising approach for developing low-cost, environmentally friendly, and sustainable building materials.