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Publication Number:  FHWA-HRT-11-060    Date:  November 2011
Publication Number: FHWA-HRT-11-060
Date: November 2011

 

Multiple Corrosion-Protection Systems for Reinforced Concrete Bridge Components

CHAPTER 1. INTRODUCTION

There are nearly 600,000 bridges in the United States, and more than 6 percent are structurally deficient due to corrosion-related damage.(1,2) The estimated direct annual cost of corrosion is $8.3 billion, and the estimated indirect cost to users due to traffic delays and lost productivity is equal to about 10 times this amount.(2) Bridge decks represent a special problem because cracks directly over and parallel to reinforcing steel provide an avenue for deicing salts to rapidly reach the reinforcement. Chloride analysis from bridge decks indicates that the chloride content in concrete around cracks can exceed the critical chloride corrosion threshold of conventional steel reinforcement within the first year.(3) Thus, the reinforcing steel in these structures must be protected against corrosion at the time of construction.

For more than 35 years, the corrosion-protection system used in most reinforced concrete structures has been epoxy-coated reinforcement (ECR) combined with increased concrete cover. This system has provided significant improvement over uncoated bars in the corrosion performance of reinforcing steel.(4,5) It has, however, not been without its critics.(6-8) Problems include the poor performance of ECR when the concrete remains saturated, such as in bridge piers in salt water, and the observation that the epoxy tends to lose its adhesion to the steel over time. (See references 4, 6, 7, and 9-11.) This reduction in adhesion, or disbondment, while the epoxy coating is still intact on the reinforcement is accelerated when the concrete remains wet.

Despite observations that portions of ECR have rusted, the corrosion of epoxy-coated steel has not resulted in the need for repairs when used in structures such as bridge decks, which allow the concrete to occasionally dry, except in the case of a few well-documented nonstandard applications.(4,5,8) Because ECR is a good, but not perfect, corrosion-protection system, there is strong impetus to develop methods to improve its performance.

The objective of this research was to evaluate a number of techniques for making ECR more corrosion-resistant by using multiple corrosion-protection strategies for ECR in bridge decks as well as in bridge members in marine environments where salt, moisture, and high temperatures (tropical weather) are prevalent.

This report describes the results for systems including chemical pretreatments and epoxy formulations that increase the adhesion of the epoxy coating to the reinforcing steel, conventional uncoated steel and conventional ECR with inorganic and organic corrosion inhibitors added to the concrete, reinforcement with a primer containing a microencapsulated corrosion inhibitor under a conventional epoxy coating, and bars coated with 98 percent zinc and 2 percent aluminum prior to epoxy application.

 

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