Title: Interface of Ultra-High-Performance Concrete with Steel, Glass Fiber-Reinforced Polymer, and Basalt Fiber- Reinforced Polymer Reinforcing Bars
Author(s): Yail J. Kim and Jun Wang
Publication: Structural Journal
Appears on pages(s): 3-15
Keywords: bond; fiber-reinforced polymer (FRP); interface; ultra-high performance concrete (UHPC)
This paper presents the bond behavior of ultra-high-performance concrete (UHPC) interfaced with conventional and nonconventional reinforcing bars: deformed steel, glass fiber-reinforced polymer (GFRP), and basalt fiber-reinforced polymer (BFRP). Various UHPC mixtures are used with steel fibers (0 and 2.3% by volume) as well as with silica fume-cement ratios (S/C) varying from 20 to 40%, leading to 30 UHPC cylinders and 54 pushout interface specimens. Ancillary tests are conducted to understand the fundamental bond-resisting mechanism of the UHPC reinforcement interface, including kinetic friction, surface topography, microscopic failure analysis, and gray-level co-occurrence matrix assessments. The steel bar possesses a higher roughness than its GFRP and BFRP counterparts. The presence of the steel fibers in UHPC increases the friction coefficient of the barsubstrate contact and the compressive strength of the concrete. Regardless of bar type, the S/C of 30% results in higher interfacial capacities than the ratios of 20 and 40%. The stress-slip behavior of the steel and GFRP interfaces exhibits an abrupt stress drop immediately after bond failure; however, that of the BFRP specimens shows a gradual transition between the pre- and post-peak responses. The isotropic and orthotropic material properties of the steel and GFRP/BFRP bars, respectively, influence energy dissipation characteristics along the interface.