Effect of Subtropical Natural Exposure on the Bond Behavior of FRP-Concrete Interface

Abstract

Subtropical natural exposure may significantly affect the bonding behavior of fiber reinforced polymer (FRP) externally bonded to concrete. To study the effect of subtropical natural climates on the FRP-concrete interface, natural exposure tests and an analytical approach were carried out on specimens externally bonded with carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP). The bilinear bond stress-slip relationships for different exposure periods were derived from the experimental results of the strengthened reinforced concrete (RC) beams. Based on these bond-slip relationships, the full-range behavior of shear stress along the bond length and debonding load can be obtained through the analytical solution. The testing and numerical results showed that subtropical natural exposure can greatly affect the bond behavior of CFRP-concrete and BFRP-concrete interfaces in the early exposure period. In the late exposure period, the bond behavior was basically stable. With the increase of exposure time, the position of maximum shear stress tended to move backward, which indicated that the behavior of the FRP-concrete interface was weakened by natural exposure. Compared to the CFRP-concrete interface, subtropical natural exposure has greater influence on the bond behavior of the BFRP-concrete interface.Polymers 2020, 12, 967 2 of 21 cycles. Under moisture cyclic condition, weakening in bond strength was observed. Cromwell [4] carried out experiments considering water exposure which showed that higher temperatures (above 60 • C) may affect the bond properties, and proposed that exposure time should exceed 10,000 h. Wan [5] found that the bond behavior of the CFRP-concrete interface degraded when the CFRP bonded specimens were submerged in water for eight weeks. Ren [6] studied the bond strength between concrete and FRP after the specimens were subjected to 98% humidity at 40 • C for 1000 h. The influence of the wet-thermal environment on the CFRP-concrete interface was significant. Ramani [7] designed a series of cyclic moisture environments including 50 • C and 100% RH, and 23 • C and 35% RH, room conditions to study the effect of moisture environments on the CFRP-concrete bond. The shear joints were exposed for five weeks before testing, and the results showed that the behavior of the CFRP-concrete bond declined by 28%. Benzarti [8] carried out pull-off tests under an accelerated aging condition (40 • C, RH 95%). It was found that moisture caused a progressive decrease in the strength of the bonded interface. Zheng [9] kept the specimens in an environmental chamber for 14 days; the RH and temperature condition were set as 95% and 60 • C, respectively. The failure mode and behavior of the CFRP-concrete interface changed compared to specimens without environmental impact.From the above literature review, it can be seen that many studies involving the interfacial durability caused by hydrothermal environment focused on the accelerated aging method [10][11][12]. However, many researchers found ...

Flexural Behavior of Damaged Hollow RC Box Girders Repaired with Prestressed CFRP

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“…For RC girders strengthened with prestressed CFRP, the main failure modes include CFRP fracture at the bottom of the midspan, concrete crushing at the top of the RC girders, yielding of the main reinforcement steel bars, and CFRP-concrete interfacial debonding failure [7]. Many studies [7,27,35] have shown that CFRP-concrete interfacial debonding failure and CFRP fracture frequently occur with increasing prestress levels. So far, most concrete specimens used for prestressed CFRP strengthening experiments have had rectangular or T-shaped cross-sections, and there have been few studies describing the failure modes of hollow box girders strengthened with prestressed CFRP.…”

Durability of CFRP strengthened RC beam after six years exposure to natural hygrothermal environment with sustained loads

“…After 12 months of exposure, the interfacial bond behavior was stable. In precious work [40], the effect of natural subtropical exposure on CFRP-concrete interface was studied.…”