Experimental investigation of bond behavior of steel, GFRP, and CFRP reinforcement in self-compacting and fiber-reinforced concrete using RILEM beam tests.

Bond behavior critically governs the structural performance of FRP-reinforced concrete; however, a comprehensive experimental assessment of the coupled effects of concrete type, fiber reinforcement, and confinement mechanisms is limited. This study presents a thorough investigation of bond behavior between ribbed steel, glass FRP (GFRP), and carbon FRP (CFRP) rebars embedded in self-compacting concrete (SCC) and multiple fiber-reinforced concrete (FRC) systems. A total of 52 RILEM beam tests were conducted under consistent conditions to systematically evaluate the influence of concrete compressive strength, transverse reinforcement, fiber type, and fiber volume fraction. The results demonstrate that higher concrete strength, transverse reinforcement, and fiber incorporation significantly enhance bond performance, with the magnitude of improvement strongly dependent on rebar type. GFRP rebars exhibited pronounced sensitivity to confinement and fiber-induced crack control, while CFRP rebars showed lower sensitivity due to their higher stiffness. Among the fibers investigated, steel fibers provided the most substantial bond enhancement, followed by glass fibers, while polypropylene fibers showed limited effectiveness. This study provides new experimental evidence that fiber reinforcement can partially substitute conventional confinement, particularly in FRP-reinforced SCC, contributing valuable insights for improved bond modeling and rational design of FRP-reinforced concrete systems.