Impact of bridge deck cracking on durability
Date
1998
Authors
Pape, Jeff Jonathon
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Fanous, Fouad
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Abstract
Since the late 1970's, the Iowa Department of Transportation has used epoxy-coated reinforcement in all bridge decks. Although the performance of epoxy-coated rebars in resisting corrosion is thought to be superior to black steel rebars, large cracks and the presence of chloridein bridge decks have caused some concern as to the condition of these bars. This work represents a part of an ongoing investigation to determine the impact of cracking on the durability of bridge decks in Iowa. The objective of this research was to be accomplished in two phases. Phase I, which the work presented herein encompasses, consisted of field and laboratory studies to determine the extent of corrosion of epoxy-coated rebars in 38 bridge decks across the State. The field evaluation consisted of collecting four core samples from each bridge deck. Two of each were taken from cracked and uncracked locations.
In addition, concrete powder samples were drilled at two different depths in five locations across each deck. In the laboratory, the powder samples taken from the bridge decks and others taken directly from the cores were analyzed for chloride content. Coating hardness, coating bond, epoxy coating thickness, crack widths, and the general condition of epoxy-coated rebar samples were further analyzed and documented. Additionally, the laboratory analysis involved evaluating a core cross section and a few rebars utilizing a scanning electron microscope. The analysis revealed that the chloride content at the rebar level in most cases was higher than the corrosion threshold of bare steel. The laboratory evaluation also showed that the rebar samples with surface corrosion undercutting the epoxy coating came from cores that were taken from cracked locations.
Although some of the rebar samples had significant corrosion on the steel surface, a large buildup of corrosion by-product was not seen. Of the bridges analyzed, it was found that significant corrosion on the steel surface had only occurred on bridges built in 1986 or before. Additionally, no delaminations or spalls were evident on any of the decks evaluated in this study.
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