Bond Behavior of Fiber Reinforced Polymer Bars under Direct Pullout Conditions

TLDR

This study investigates Eurocrete FRP bars (glass, carbon, aramid, hybrid) in concrete under direct pullout, examining how embedment length, bar type, shape, surface, diameter, and concrete strength influence bond behavior. Over 130 cube specimens were tested in direct pullout without splitting, with the testing arrangement and wedging effect affecting bond strength, and parameters such as embedment length, bar characteristics, and concrete strength were systematically varied. FRP bars exhibit a distinct bond‑failure mode from deformed steel due to resin surface damage, with carbon and glass FRP bond strengths similar but slightly below steel, and load‑slip curves revealing fundamental differences between steel and FRP.

Abstract

This paper examines the behavior of Eurocrete fiber-reinforced polymer (FRP) bars (glass, carbon, aramid, and hybrid) in concrete under direct pullout conditions. More than 130 cube specimens were tested in direct pullout where no splitting was allowed to develop. In normal concrete, the mode of bond failure of FRP bars was found to differ substantially from that of deformed steel bars because of damage to the resin rich surface of the bar when pullout takes place. Bond strengths developed by carbon fiber-reinforced polymer and glass fiber-reinforced polymer bars appear to be very similar and just below what is expected from deformed steel bars under similar experimental conditions. The load slip curves highlight some of the fundamental differences between steel and FRP materials. This paper reports in detail on the influence of various parameters that affect bond strength and development such as the embedment length, type, shape, surface characteristics, and diameter of the bar as well as concrete strength. The testing arrangement is also shown to influence bond strength because of the “wedging effect” of the bars.