United States Department of Transportation
i
Effects of Wet Mat Curing Time and Earlier Loading on Long-term Durability of Bridge Decks: Rapid Chloride Permeability Tests and Ponding Tests
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2009-01-01
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[PDF-2.21 MB]
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Edition:Final Report 04/07/99 - 08/31/04
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Abstract:This research report is one of several published from a six-year study sponsored by the Texas Department of Transportation (TxDOT) that investigated the impact of wet-mat curing duration on bridge deck concrete durability. This report presents findings related to chloride permeability of several widely used TxDOT bridge deck concrete mixes. The Rapid Chloride Permeability Test (RCPT) and the Ponding Test (AASHTO T259) were selected and seven mix designs were tested; four were evaluated using cores taken from field-cast model bridge decks and the other three from laboratory-cast specimens. Mix designs were selected based on their extent of use around the State, with differences in terms of type of cement, coarse aggregate type, supplementary cementitious material (SCM) type and SCM content. Wet-mat curing durations of 0, 2, 4, 8, 10 and 14 days were evaluated for each mix. The chloride permeability of each mix was found to be sensitive to the wet-mat curing duration and each mix appeared to provide increases in resistance to permeability up to 4 or 8 days depending on the mix, beyond which the marginal benefits appeared to diminish. Both tests, the RCPT in particular, showed sensitivity to mixes that contained SCMs. Mixes that contained siliceous gravel coarse aggregate and Type I cement showed some of the highest permeability values among all mixes tested. They displayed moderate water soluble integral chloride (ponding) and electric charge (RCPT) values. It was also found that permeability of concrete decreased as percentage of fly ash (either class F or class C) increased from around 20% to around 30%. For the seven mixes evaluated, the ponding test results showed that steel reinforcement can be put at a depth 1.25” when compared with threshold chloride contents commonly used in the literature. A comparison of results obtained from the two test methods showed a correlation between their results for some mixes. This may indicate that RCPT does not correlate well with actual long-term chloride penetration for all mixes. Further research is needed to either develop a new test or evaluate an alternative test method that can provide a quick direct measurement of the chloride ion concentration rather than an indirect process where electrical conductivity is used.
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