Influence of Corrosion and Cracking on Bond Behavior and Strength of Reinforced Concrete Members

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Title: Influence of Corrosion and Cracking on Bond Behavior and Strength of Reinforced Concrete Members

Author(s): G. J. Al-Sulaimani, M. Kaleemullah, I. A. Basunbul, and Rasheeduzzafar

Publication: Structural Journal

Volume: 87

Issue: 2

Appears on pages(s): 220-231

Keywords: beams (supports); bond (concrete to reinforcement); concrete durability; corrosion; cover; cracking (fracturing); deterioration; fiber reinforced concretes; pullout tests; reinforced concrete; slippage; reinforcing steels; strength; tests; Structural Rese

Date: 3/1/1990

Abstract:
Pullout and beam tests have been conducted to study the influence of reinforcing bar corrosion and cracking on bond behavior and bond strength of reinforced concrete members. Pullout tests are used to simulate severe local corrosion, and beam tests to simulate relatively uniform corrosion, along the reinforcing bar surface. Bond behavior is studied at different stages of reinforcing bar corrosion: noncorrosion, precracking, cracking, and postcracking levels. These stages of corrosion have been achieved by impressing direct current for increasing periods on the reinforcing bar embedded in the pullout or beam specimen located in water; the current is so arranged that the reinforcing bar serves as the anode while a stainless steel plate is located in the water to act as cathode. The bond strength increases with corrosion up to a certain amount. However, with progressive increase in corrosion, the bond strength decreases rapidly for pullout tests but at a slower rate for beams; for pullout tests, bond strength becomes negligible at 7.5 percent corrosion for 14-mm bars, while it is about 1.5 times the permissible bond stress delineated in ACI 318-83, even after a 5 percent corrosion for beam tests. The initial increase in bond is due to the increased toughness of the reinforcing bar surface with the growth of a firm layer of corrosion. However, with further progress in corrosion, especially in the case of severe localized corrosion, the bond behavior is influenced by the severely deteriorated reinforcing bar ribs, by the lubricating effect of the flaky corroded metal on the reinforcing bar surface, and by the reduced confinement of the reinforcing bar due to the widening of the longitudinal crack resulting from corrosion. It has been found that the induction of 0.2 percent polypropylene fibers by volume into concrete improves the bond resistance of concrete, especially at postcracking levels of corrosion; this is due to reduced level of damage at the concrete-steel interface and to an intrinsic contribution in improving the confining and holding capacity of the surrounding concrete for the reinforcing bar.