Abstract: The underground environment where cable tunnels are located is complex, leading to severe performance degradation of the tunnel's concrete support structure due to corrosion. However, the insufficient performance of traditional repair materials often results in repeated cracking and water leakage in cable tunnels, and this degradation phenomenon is particularly pronounced in aged cable tunnels. Additionally, traditional copper-plated micro-fine steel fibers exhibit poor high-temperature resistance and corrosion resistance, making them unsuitable for complex underground environments. Therefore, this study adopted basalt fiber bar (BFB) to replace copper-plated micro-fine steel fibers and designed a basalt fiber bar reinforced ultra-high performance cementitious composite (BFB-UHPCC) repair material. The material's performance was investigated through mechanical tests and CT technology. The results show that the incorporation of BFB significantly enhances the material's mechanical properties, with compressive strength reaching 123.7 MPa and flexural strength reaching 20.0 MPa under steam curing. The combination of 1.5% (volume fraction) BFB and curing agent treatment yields the best toughness. Although an increase in BFB volume fraction slightly raises porosity and the number of pores, the excellent performance of BFB still greatly improves the material's mechanical properties, making it suitable for repair in complex underground environments.

Key words: basalt fiber bar, cable tunnel, toughness, microstructure, pore structure, concrete support structure