Evaluation of corrosion resistance of different steel reinforcement types
The corrosion of steel reinforcement in an aging highway infrastructure is a major problem currently facing the transportation engineering community, in particular bridge engineers. Further, the use of deicing salts has resulted in steady deterioration of bridge decks due to corrosion. In the United States, maintenance and replacement costs of deficient bridges are measured in billions of dollars. These concerns have initiated continual development of protective measures. Application of corrosion-resistant steel reinforcement as an alternate reinforcement for existing mild steel reinforced concrete bridge decks has great potential due to the inherent corrosion resistant properties associated with the materials. To investigate corrosion prevention through the use of corrosion-resistant alloys, the performance of corrosion resistance for MMFX Microcomposite steel reinforcement, a high-strength, high chromium steel reinforcement, is evaluated. The study presented herein presents the separate field and laboratory studies of ongoing research at Iowa State University to determine if in fact MMFX reinforcement provides superior corrosion resistance to epoxy-coated mild steel reinforcement in bridge decks. However, as definitive field evidence of the corrosion resistance of MMFX reinforcement may require several years of monitoring, attention transferred to investigate the reinforcement under accelerated conditions in a laboratory. In the laboratory investigation, the evaluation process was based on using ASTM and Rapid Macrocell accelerated corrosion tests. After 40 weeks of testing, the associated ASTM ACT corrosion potentials indicate corrosion has not initiated for either MMFX or as-delivered epoxy-coated reinforcement. However, the uncoated mild steel underwent corrosion within the fifth week, while epoxy-coated reinforcement with holidays underwent corrosion between 15 and 30 weeks. For the study presented herein, concrete powder specimens were collected at the top reinforcement depth at the first indication of corrosion initiation. While the limited results from 40 weeks of laboratory testing do not constitute a prediction of life expectancy and lifecycle cost, a procedure is presented to determine the life expectancy and lifecycle cost once definitive evidence is attained. The life expectancy of bridge decks constructed with different steel reinforcing systems is estimated by the two-stage, diffusion-spalling model (i.e., the time required for corrosion initiation and the subsequent time period required to cause spalling due to corrosion).