Evaluation of Corrosion Inhibitors for Concrete Bridge Deck Patches and Overlays

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This report presents the results to date of a national pooled fund study initiated in August 1996 to evaluate the long-term performance of bridges and outdoor exposure slabs damaged by chloride-induced corrosion that have concrete containing corrosion inhibiting admixtures and that had topical applications of inhibitors prior to being patched and overlaid. The study includes 156 exposure slabs, 4 bridge decks with overlays, and 1 patched bridge substructure. A total of 136 exposure slabs were constructed to simulate overlay and patch repairs, and 20 full-depth slabs were constructed to simulate new construction. Each repaired slab was constructed with one of four levels of chloride to cause corrosion. The new slabs were ponded to cause corrosion. Previous reports provide details on the construction and initial condition of the exposure slabs and the construction and initial condition of the repaired bridges. The results presented here are based on quarterly nondestructive measurements between September 1997 and June 2001, visual inspections of the exposure slabs, and tensile bond test results and visual inspections of reinforcement removed from the exposure slabs that were patched and overlaid. Overlays cracked and delaminated on exposure slabs that were fabricated with 15 lb./yd3 of chloride ion because of corrosion of the top mat of reinforcement. There was no difference in the performance of overlays constructed with and without inhibitors and topical treatments. Overlays and patches with and without inhibitor treatments placed on and in slabs with 3, 6, and 10 lb/yd3 of chloride are performing satisfactorily. However, results do not show reductions in the tendency for corrosion that can be attributed to the inhibitors. Overlays and patches with and without inhibitor treatments on and in the five bridges indicate mixed results. Corrosion is occurring in the majority of the repairs done with and without inhibitor treatments. The corrosion-inhibiting treatments do not seem to be reducing corrosion in the bridges and, in fact, may be increasing corrosion. It is not obvious that corrosion is occurring in the full-depth slabs constructed with and without inhibitors to represent new construction. The slabs do not show signs of corrosion-induced cracking after 5 years of ponding. Topical applications of inhibitors did not affect the bond strength of the overlays. Overlays containing Rheocrete 222+ and 7 percent silica fume had lower bond strengths. Overlays on base concretes with the higher chloride content had lower bond strengths. In summary, this project does not show any benefit from the use of the corrosion inhibiting admixtures and the topical applications made to the chloride-contaminated concrete surfaces prior to placement of the patches and overlays. Additional years of monitoring of the exposure slabs and bridges may provide useful results.

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