Bond Strength

Corrosion plays a devastating role in reducing the structural capacity of unconfined flexural mem­bers. CFRP confinement of the bond zone in bond-beam specimens serves to maintain steel-concrete bond interaction. The effect of CFRP on the confinement of corrosion-damaged members varies de­pending on whether the member has adequate bond or is bond deficient. For those members with in­adequate bond length, the added CFRP confinement improved the performance of bond-deficient cor­roded members allowing them to outperform the unconfined specimen (Figure 3). It is important to understand the nature of failure of the CFRP confined specimens. Since no cracks were visible with the CFRP wrap in place, there are no indications of failures. Even under conditions of high ultimate bond stresses, the presence of low slip initiation bond stresses indicates that failure could potentially occur prematurely by bond pullout in the case of sustained loading or creep. Confinement was found to be more effective when applied prior to excessive corrosion of the specimens. Typically, small amounts of post-repair corrosion were found to have no effect or in some instances helped increase bond strength as a result of increased confining pressures. However, as the post-repair corrosion lev­els increased, the bond strength deteriorated. The overall structural performance of beams wrapped with CFRP was enhanced. However, caution and engineering judgement must be used in the applica­tion of this repair method since abrupt failure of the member due to bond pullout failure could occur without warning if repair is performed at high corrosion levels or if members were initially designed with inadequate bond. The confining wrap may increase the bond strength, but as with all repairs, this should not be used as a band-aid solution, and the cause of deterioration must be addressed to prevent further corrosion and deterioration.

Figure 3. Bond strength vs. mass loss