Concrete Diffusion Coefficients and Existing Chloride Exposure in North Carolina

摘要

The present project focused on the diffusion coefficients of ten concrete mixes used in North Carolina bridge structures, and on the chloride loading rates present in the different climatic and environmental regions of the state with respect to the mitigation policies and structural condition of bridges in North Carolina. In order to determine the diffusion coefficients of the selected mixes, ponding tests were performed for 12 months. These results were then correlated with rapid chloride permeability tests, and later with bulk diffusion and rapid migration test results. Furthermore, as a possible alternative to the potentiometric titration, a rapid chloride test kit was also evaluated to determine the chloride content of concrete powder samples. A survey was sent out to highway and bridge maintenance personnel in the six geographic regions considered (Coastal, Manteo, Triad, Triangle, Piedmont and Mountain regions), requesting information with regards to deicing material type and frequency/quantity of application on bridges/roads. To supplement this information, 28 bridges were sampled, focusing on bridge decks and pier caps/abutments for inland bridges; and footings, columns and decks for coastal bridges. An attempt was also made to develop a corrosion model using chloride surface concentrations, estimated diffusion coefficients, and age of structure. This model was also calibrated using historic data developed for a few coastal bridges.