Bond behavior of FRP reinforcing bars - The-state-of-the-art

Bond constitutes a critical aspect of structural behavior of all types of reinforcing materials including the steel and FRP reinforcing bars. Owing to their strength, lightweight, and noncorrosive properties, the FRP bars have evolved as promising and desirable reinforcing material, to enhance the durability of concrete structures. The strength and performance of these structures depend on the bar strength as well as on the development of adequate bond between the bars, and concrete. Thus, a good understanding of bond behavior of FRP bars with concrete is essential to harness its full potential. Several theoretical and experimental studies conducted to evaluate the bond characteristics and strength of FRP bars have indicated their dependence on many variables. These variables include size, shape, surface configuration (e.g., ribs) and surface roughness of bars, position of bars in the concrete element and the confinement pressure, compressive strength of concrete, emebdment length, environmental conditions, service/operating temperatures, temperature change, moisture absorption, mechanical interlock of bars against the concrete, chemical adhesion, and hydrostatic pressure against the FRP bars due to shrinkage of hardened concrete. It has been amply recognized that the bond behavior of FRP bars cannot be modeled after the bond behavior of steel reinforcing bars because of the fundamental differences between the physical and mechanical properties of two materials and their interaction with concrete. This paper presents the state-of-the-art of the bond behavior of FRP reinforcing bars in concrete environment, based on experimental data in addition to. discussing theoretical and experimental relationships. Finally, future course of action in terms of bond behavior is suggested.