United States Department of Transportation
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Strategies to Increase the service life of concrete bridge decks : final report.
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2017-03-01
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[PDF-7.40 MB]
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Alternative Title:Strategies to Increase the service life of concrete bridge decks.
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Abstract:Corrosion of the steel in reinforced concrete bridge decks is a critical issue for structures that are exposed to chloride containing de-icing chemicals or marine salts. Oregon Department of Transportation (ODOT) has a large number of bridges that are vulnerable to this form of deterioration. An obvious indicator of a corrosion problem is visible damage; unfortunately, if corrosion damage is visible, the window for preventive action is likely closed. Pre-emptive actions and early detection of potential problems are more cost effective than repair or replacement of bridge decks that have already experienced corrosion. In recent years, electrical-based methods have emerged as durability-related performance indicators for reinforced concrete structures. Several investigations have shown the existence of relationships between electrical resistivity (or formation factor) of concrete and other durability-related parameters such as corrosion rate of steel reinforcement and transport properties of concrete. The main motivation of this research is to provide ODOT with a protocol to select bridges for its ongoing bridge deck treatment operations using quantitative tools that are practical and quick. Although rapid surface resistivity measurements are highly correlated with water and chloride transport properties of concrete, they do not directly provide the actual chloride depth profiling. However, transport properties that are revealed by surface resistivity measurements can be used in chloride ingress models that can be used to predict chloride profiles in concrete. The accuracy of the predictions improves with additional easily accessible quantitative information such as concrete mixture design properties (e.g. water-to-cement ratio), environmental data (e.g. temperature and relative humidity), and salt exposure histories. Most of these additional quantitative data are readily available for most locations in Oregon. These predictions, coupled with surface resistivity data, will also indicate if additional chloride profiling is necessary, and if so, at which locations on the deck it should be conducted. To achieve the project goals, the following tasks have been performed: (1) An experimental investigation was conducted to establish the relationship between electrical properties of concrete (e.g. SR or formation factor), environmental data (e.g. temperature and relative humidity), and chloride ingress in reduced-size reinforced concrete slabs simulating bridge decks commonly used in Oregon. (2) The effect of freeze-and-thaw action on the observed relationship was investigated. (3) A comprehensive modeling framework that relates the electrical properties of concrete, environmental data and chloride ingress was developed, verified, and validated. (4) A virtual test bed using the validated modeling framework was developed to conduct statistically significant number of virtual experiments to obtain closed-form relationships between electrical properties of concrete, environmental data and chloride ingress for bridge decks in different geographical areas in Oregon. (5) A demonstration case study was performed to show the development of a closed-form equation and how it can be used in a bridge-deck evaluation-protocol that can be used by ODOT in practice.
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