Mechanical and Bond Behavior of a Hybrid Steel-Basalt-Polypropylene Fiber-Reinforced High-Performance Concrete with Steel, GFRP or CFRP Bars.

This study addresses the limited availability of unified experimental datasets comparing ribbed steel and smooth FRP bars embedded in the same hybrid-fiber high-performance concrete (HPC) matrix under identical conditions. It investigates the mechanical and bond behavior of a triple-fiber HPC combining hooked-end steel (ST), basalt (BA), and polypropylene (PP) fibers and reinforced with steel, GFRP, and CFRP bars of identical diameter and embedment. Under a uniform curing regime, the HFRC reached a compressive strength of approximately 82 MPa and exhibited a high fracture energy Gf approximately 3.7 kJ/m2 with a stable post-peak response in a notched-beam test, demonstrating effective multi-scale crack bridging within a dense hybrid fiber network. Pull-out tests on 200 mm embedment revealed distinct interfacial mechanisms: ribbed steel developed a pronounced peak bond stress (τmax = 13.05 MPa) and the largest bond energy (Gb = 146 N/mm) due to mechanical interlock, whereas smooth GFRP and CFRP showed low τmax (=1.46 and 0.78 MPa) and smoothly decaying τ-s governed by adhesion-friction with Gb = 3-4 N/mm. A consistent experimental framework enabled direct mechanistic comparison of bond-slip behavior across reinforcement types without confounding matrix or curing variables. Simple constitutive laws calibrated to the experimental τ-s curves (ramp-softening for steel and ramp-plateau or exponential for FRP) captured the stiffness, strength, and energy hierarchy with low error. The main contribution of this study lies in providing a configuration-consistent reference dataset and calibrated bond-slip descriptions for hybrid-fiber HPC members reinforced with both steel and FRP bars. The results highlight the role of the hybrid fiber network in improving crack stability and provide design-oriented parameters for anchorage assessment and nonlinear bond-slip modeling. Although the results are based on a limited experimental program, they establish a mechanistically coherent basis for further optimization of hybrid HPC matrices and development of performance-based anchorage formulations in high-performance structural applications.