Evaluation of Corrosion Protection Methods for Reinforced Concrete Highway Structures

Abstract

Since the 1970s, research projects and field studies have been conducted on different methods for protecting reinforced concrete bridges from corrosion damage. The methods include alternative reinforcement and slab design, barrier methods, electrochemical methods, and corrosion inhibitors. Each method and its underlying principles are described, performance results of laboratory and/or field trials are reviewed, and systems are evaluated based on the results of the trials. Using performance results from the studies and costs obtained from transportation agencies, an economic analysis is used to estimate the cost of each system over a 75 year economic life using discount rates of 2, 4, and 6%. Epoxy-coated reinforcing steel is the most common corrosion protection method used in the United States today. Although controversial in many areas, epoxy-coated reinforcement has performed well in many states, including Kansas, since it was introduced in the early 1970s and is a low-cost backup to many other corrosion protection options. Research on stainless steel reinforcement indicates that it may remain free of corrosion in chloride contaminated concrete for more than 75 years. At a low discount rate (2%), solid stainless steel reinforcement is a cost-effective option compared to other options, but at higher discount rates (4%+), the present value cost of a deck with solid stainless steel is significantly higher than that of an unprotected deck. Stainless steel clad reinforcement is much less expensive than solid stainless steel reinforcement. The performance of stainless steel-clad reinforcement will be similar to that of solid stainless steel bars if the stainless steel coating is continuous and if the black steel core, exposed at the bar ends, is protected so that it does not come into contact with concrete pore solution. The present value of the cost of a bridge deck built with stainless steel-clad reinforcement is significantly lower than the present value for the cost of any other corrosion protection system. This method should be considered for experimental use. Solid stainless steel should be considered, as well, if a low discount rate (around 2%) is used. Hot rubberized asphalt membranes are the least expensive option, other than stainless steel-clad reinforcement. Hot rubberized asphalt and spray-applied liquid membranes should be considered for use on future projects. In laboratory tests, corrosion inhibitors have been shown to provide protection to steel in chloride contaminated concrete, but information on their performance in the field is limited. Both calcium nitrite and organic corrosion inhibitors have the potential to be cost-effective, if they perform as well in the field as they have in the laboratory, and should be considered for experimental use.