Bond Strength and Slip Mechanism between FRP Bars and Concrete Matrix

Subject Areas : Advanced Materials in Structural Engineering

Ali Alemi ^{1 *}

1 - ندارم

Received: 2025-10-29 Accepted : 2025-12-06 Published : 2025-11-15

Keywords: FRP Rebar- Bond Strength-Slip Mechanism-Concrete Matrix- (GFRP- CFRP) ACI 440.1R 15- Pull Out Test- Adhesion, Debonding, Interface Modeling, Development Length.,

Abstract :

The bond interaction between Fiber‑Reinforced Polymer (FRP) bars and the surrounding concrete significantly governs the structural performance of FRP‑Reinforced Concrete (FRP‑RC) members. Unlike steel, FRP bars exhibit a distinct failure mechanism dominated by fiber‑matrix debonding and resin shear rupture at the interface, primarily because of the absence of yielding and different surface profiles.This paper examines experimental pull‑out tests, analytical bond–slip models, and microscopic interfacial behavior in GFRP and CFRP bars embedded in ordinary and high‑strength concrete. A comparative evaluation against ACI 440.1R‑15 recommendations demonstrates typical bond‑strength reduction factors between 0.60–0.75 of equivalent steel reinforcement, while slip initiation is governed by local shear failure of the resin coating. Bond strength and slip behavior dictate the stress transfer between internal reinforcement and concrete. For FRP, the absence of yielding and the polymeric interface produce different failure modes than steel. Accurate characterization of the bond–slip law is essential for predicting crack spacing, deflection, and development/anchorage length. Distinctive attributes of FRP bars compared with steel include: (i) anisotropic stiffness-high axial stiffness governed by fiber volume fraction and low transverse stiffness controlled by the resin; (ii) surface textures-sand‑coated, helically wrapped, or ribbed rather than steel deformations; and (iii) brittle interfacial failure-governed by adhesion loss, local resin shear, and frictional pull‑out rather than ductile bearing.

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