DETERIORATION ENVELOPES FOR PREDICTING CONCRETE BRIDGE DECK DETERIORATION DUE TO CHLORIDE EXPOSURE
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Abstract
While bridge decks serve as the primary interface between vehicular loads and the underlying structural system, they are particularly susceptible to deterioration caused by environmental factors—most notably, chloride ingress from deicing salts, freeze-thaw cycles driven by temperature fluctuations, and repeated wetting and drying events due to precipitation and other water-related exposure to the base concrete material. Existing concrete deterioration models often fall short in capturing and predicting the effects of chloride exposure over time due to these evolving conditions, frequently treating concrete as a static material. This study, rather, focuses on the development of a revised, data-driven modeling approach that more accurately predicts the decrease in compressive strength and long-term material integrity based on extensive laboratory testing of concrete cylinder specimens and bridge deck cores extracted from bridges in Delaware.
The overarching objective is to strengthen the predictive accuracy of deterioration models from experimental and in-situ data to better predict deterioration rates. The research draws upon three primary data sources that were generated: (1) controlled, accelerated laboratory testing, (2) core samples extracted from operational Delaware bridges provided by the Delaware Department of Transportation (DelDOT), and (3) climate-sensitive predictive modeling techniques through data collection from the National Oceanic and Atmospheric Administration (NOAA) and Federal Highway Administration (FHWA) InfoBridge™ database. Laboratory samples (n=300) were fabricated using mix designs representative of Delaware bridge construction practices from the 1970s and 1980s and testing using protocols from ASTM and ACI standards. These specimens were subjected to environmental conditioning protocols—including wet-dry and freeze-thaw cycling—at three levels of chloride concentration (low, medium, and high corresponding to 0, 3%, and 15% salt concentrations) to simulate field exposure from de-icing salts and sea spray. The laboratory specimens were designed to replicate multiple years of service-life deterioration within a condensed time frame, allowing for the observation of trends and prediction of long-term performance of degradation. Physical and mechanical parameters such as compressive strength, modulus of elasticity, resonance frequency, and chloride penetration. A comprehensive analysis of chloride-induced degradation mechanisms in concrete bridge decks was conducted to integrate the accelerated laboratory test results, in-situ field sampling, and historical inspection data to determine a representative durability index for new concrete deterioration envelopes that forecast the long-term response in terms of material degradation due to varying levels of chloride exposure. The experimental results reveal a gradual yet linear decline in both compressive strength and resonance frequency over time, accompanied by a corresponding increase in chloride content for up to 160 cycles, which corresponds to approximately 2-5 years. Resonance frequency emerged as the most sensitive and reliable indicator of internal concrete for damage, which showed a consistent decline across all chloride exposure conditions and served as a good predictor of material degradation. Overall, these findings emphasize the importance of combined in-situ and laboratory testing to better characterize material degradation of concrete that otherwise may not be fully captured by surface-based, visual bridge inspection methods alone.