Effect of Steel–Basalt Hybrid Fibers on the Mechanical, Durability, and Bonding Performance of Ultrahigh-Performance Concrete for Steel Deck Pavement Applications

Mixing steel fiber (SF) into ultrahigh-performance concrete (UHPC) boosts strength and fracture energy but faces issues like poor dispersion, self-shrinkage, and corrosion. This study substituted SF with resin twisted basalt fiber (BF) for improved dispersion and a ribbed surface. The microstructure of hybrid fiber UHPC was analyzed by using scanning electron microscopy while investigating the changes in mechanical and durability properties. This study also evaluated the bonding performance of UHPC with asphalt mastic crushed stone (SMA), which needs attention in bridge deck pavement. BF enhanced UHPC’s mechanical properties and early compressive strength, with the hybrid fiber–reinforced UHPC achieving 80% of its 28 day strength within just three days. The flexural strength attained its peak with a 25% substitution of BF, reaching 42.3 MPa. The synergy between SF and BF enhanced impact resistance, resulting in the greatest number of initial and final cracks at a 25% BF replacement. Adding BF reduced drying shrinkage by 52.9% at a 50% replacement rate, enhancing frost resistance with the highest dynamic modulus of elasticity at the same rate. BF improved pore structure, increased C-S-H gel, and densified the microstructure, reducing water absorption. The interlayer shear strength with SMA varied with asphalt spread, with the optimal SBS-modified asphalt dose at 1.0 kg/m2, increasing bonding strength by 27.6% compared with 0.5 kg/m2. UHPC reinforced with steel–basalt hybrid fibers can be effectively utilized in bridge deck pavement, addressing the issue of bonding failure between asphalt and the base layer.