EVALUATING CORROSIVE SITE PERFORMANCE AND POLICY WITH CONCRETE ADMIXTURES
The coastline of North Carolina (NC) is home to a large number of state-owned concrete structures such as bridges that can be adversely affected by the aggressive, chloride-rich environments in which they are constructed. To delay the corrosion-related deterioration of structural concrete in these environments, the North Carolina Department of Transportation (NCDOT) Structures Management Unit (SMU) created a Design Manual in 2003 that includes multiple corrosion prevention specifications such as the creation of corrosive boundaries, increased concrete cover, epoxy coated steel, and the addition of pozzolans and corrosion inhibitors. As of 2018, there have been more than 200 structures newly constructed or replaced within these zones. The specifications presented within the Design Manual vary based on which corrosive boundary the structure is constructed within (highly corrosive zone or corrosive zone). The highly corrosive zone is the easternmost region and considered the most chloride-rich environment. The corrosive zone is located immediately to the west and is considered the second most chloride-rich environment. Structures constructed within the highly corrosive zone are required to apply the NCDOT corrosion prevention specifications to all elements while structures constructed within the corrosive zone are required to apply the NCDOT corrosion prevention specifications only to elements located within 15 feet of the mean high tide line. The primary objective of this research was to determine the effectiveness of the NCDOT corrosion policy as currently written. To achieve this, the project was divided into three investigations which included a field study of eight structures constructed under the policy, analysis of potentially corrosion-related damages using NCDOT maintenance records, and the creation of deterioration models using National Bridge Inventory (NBI) condition rating data. These investigations aimed to answer whether the corrosive zone boundary lines are in the most effective location, whether the corrosion prevention methods are working to extend the service lives of structures located in chloride-rich environments, and whether structures constructed using these specifications are outperforming structures constructed before the policy was created. Given the research and results collected across the three investigations, it was concluded that the corrosion policy as currently written is conservative and it seems under certain circumstances (such as locations further from the coast, elements high above brackish water, and unsubmerged elements), the policy is likely overly conservative. Additionally, as there were multiple investigations from different sources (field investigation, NCDOT database, and NBI database) suggesting the same result, the following was concluded: the current location of the corrosive boundary lines and specifications for each zone are adequate to delay the onset of corrosion. From this, it was recommended that no changes be made to the current location of the corrosive boundary lines or to the current specifications. Future work intended to further investigate the efficacy of the NCDOT corrosion policy is recommended within. The work suggested is based on hypotheses that were unable to be definitively concluded upon based on the work performed in this thesis and could lead to refinement and enhancement of the policy or further confirm its adequacy as currently written.