Corrosion Research

Accelerated Testing for Concrete Reinforcing Bar Corrosion Protection Systems

The corrosion of reinforcing steel in highway structures results in maintenance and replacement costs in the United States that are measured in billions of dollars. The problem, due principally to chlorides in deicing salts and sea water, is the main durability concern in most transportation structures. As a result, methods that can significantly reduce or halt chloride induced corrosion have been aggressively pursued for well over thirty years. In spite of the progress that has been made during this period, the costs to implement corrosion protection techniques differ markedly, with ratios as large six to one. In addition, there is little evidence of a quantitative correlation between the performance of the techniques in the laboratory and in the field, increasing the difficulties in developing and selecting new systems. The lack of a direct correlation between laboratory and field performance is due largely to the evolving nature of the laboratory tests and the need to innovate in practice without waiting for the development of a correlation or, in some cases, waiting for lab results that may take several years. The goal of the current study is to development a detailed correlation between accelerated laboratory tests and field performance for a broad range of corrosion protection systems. The study, which is sponsored by the National Science Foundation and the Kansas Department of Transportation and carried out in partnership with the manufacturers of corrosion protection systems, takes advantage of ongoing state and university surveys in northeast Kansas evaluating the performance of bridge decks. The study includes the evaluation and modification of laboratory test procedures to establish those that provide the best match with the corrosion behavior of reinforced concrete bridge decks subjected to normal and accelerated exposure. The corrosion evaluation techniques address the protection provided by epoxy-coated bars, corrosion inhibiting admixtures, corrosion-resistant steel, the effects of different deicers, and modifications in concrete mix proportions. Corrosion performance is compared using five existing bridges selected from a group of 80 evaluated under one prior and one current study at the University of Kansas, five bridges scheduled for construction during the period of the proposed work, and field test specimens constructed in conjunction with the five new bridges. The principal laboratory techniques include the Southern Exposure, cracked beam, ASTM G 109, rapid corrosion potential, and rapid macrocell tests. In addition to "standard" versions of these tests, specimens are modified to obtain polarization resistance and electrochemical impedance measurements. Field tests involve the detailed evaluation of five existing bridges based on material properties, construction history, crack profiles, overall condition, half-cell potentials, and polarization resistance measurements. The corrosion behavior of the bridges is compared with closely matched laboratory specimens. The five newly constructed bridges are instrumented with preinstalled electrical connections to obtain corrosion measurements and constructed with different corrosion protection systems. The performance of the newly constructed decks is compared with matching laboratory test specimens, fabricated with the same materials, and 1.3 x 2.6 m (4 x 8 ft) field test platforms fabricated using the same geometry, reinforcing steel, concrete, and corrosion protection systems as used in the decks. The field test platforms are subjected to corrosion environments matching those of the bridge and to aggressive corrosion environments matching those obtained in the laboratory. Direct correlation of corrosion performance will allow more effective and rational evaluation techniques to be instituted. The final result will be more efficient selection procedures, more rapid movement of corrosion technology into practice, the extension of structure service life, and the overall reduction in the repair and rehabilitation costs associated with chloride induced corrosion in reinforced concrete structures.