Public Roads: A Journal of Highway Research and Development, Vol. 47 No. 1

Clear, Kenneth C.; Virmani, Yash Paul; Balmer, Glenn G.; Gallaway, Bob M.; Schlag, Bernhard; Riediger, Germot; Lever, William F. · 1983 · ROSA P / United States. Government Printing Office

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Summary

This paper presents interim findings from a Federal Highway Administration (FHWA) study initiated in 1980 to evaluate the effectiveness of epoxy-coated reinforcing steel in preventing corrosion in chloride-contaminated concrete. The research addresses the widespread deterioration of concrete bridge decks caused by chloride intrusion from deicing salts or saltwater, which facilitates the formation of expansive rust products. Specifically, the study investigates whether epoxy coating all reinforcing bars provides greater corrosion protection than coating only the top mat, and how electrical coupling between mats affects corrosion rates. The experimental design utilized outdoor concrete slabs (0.6 m x 1.5 m x 0.15 m) containing two reinforcing steel mats. To simulate a "worst-case" scenario, the study ensured 100 percent electrical contact between the top and bottom mats. The top mat concrete contained 8.9 kg/m³ of chloride ions, while the bottom mat remained chloride-free. Variables included slabs with uncoated black steel, slabs with epoxy-coated top mats only, and slabs with epoxy-coated mats in both layers. Notably, the epoxy-coated bars used did not meet standard AASHTO or ASTM specifications due to excessive holidays (pinholes) and failure in bend tests, representing non-specification quality. Some bars also had artificially created damaged areas (0.24% to 0.86% bare steel). Corrosion was monitored via macrocell current, driving voltage, and electrical resistance measurements over approximately two years. The results demonstrated that even non-specification epoxy-coated rebar significantly reduced corrosion rates compared to uncoated black steel. Slabs with only the top mat epoxy-coated reduced corrosion rates such that it would take an average of 11.5 years to consume the same amount of iron consumed in one year by uncoated steel. Slabs with both mats epoxy-coated extended this timeframe to 41 years. The primary mechanism for protection was increased electrical resistance between the mats, which limited the macroscopic corrosion cell current. Additionally, when both mats were coated, macrocathodic polarization further inhibited corrosion. Visual inspections in April 1982 confirmed these findings: uncoated slabs exhibited widespread corrosion and cracking, while epoxy-coated slabs showed little to no corrosion-induced distress, regardless of the presence of holidays or small damaged areas. The study concludes that epoxy-coated reinforcing steel offers substantial protection against corrosion-induced concrete damage in salt environments, even when the coating quality is below standard specifications. The findings reinforce the validity of strict specification requirements, as the long-term performance of substandard coatings remains uncertain. The research highlights that corrosion control in these systems is primarily driven by resistance effects and, when both mats are coated, cathodic polarization, offering a robust solution for extending the service life of highway infrastructure in corrosive environments.

Key finding

Epoxy-coated reinforcing steel reduced corrosion rates by a factor of 11.5 when only the top mat was coated and by a factor of 41 when both mats were coated compared to uncoated steel.

Methodology

field_study

Sample size: 15

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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