Microstructural design of concrete reinforcing bars for improved corrosionperformance

Corrosion of steel in concrete is a complex phenomenon. The corrosion perfo rmance of reinforcing steel embedded in concrete is dependent on many varia bles. These variables include differences in materials constituents, micros tructure, processing procedures, concrete mixture proportions, structural d esign, construction methods, loadings, cracks, and environmental conditions . Reinforced concrete structures are often expected to have relatively long service lives under severe loading and exposure conditions. Often, the pri mary governing factor affecting the service life of the structure is the co rrosion performance of the steel reinforcement. For many systems, concrete is often the only protective cover that prevents the ingress of aggressive ions and eventual corrosion of the reinforcing steel. Significant advances in state of the practice have been exhibited with the use of high-performan ce concrete materials. Due to the high cost associated with deteriorating r einforced concrete structures, however, other approaches need to be investi gated to ensure long-term serviceability of these structures. A complementa ry approach to improving the quality and corrosion performance of reinforce d concrete structures is to utilize reinforcement that has been microstruct urally designed to resist corrosion. This approach can increase the redunda ncy of the protective system, decrease corrosion activity, and increase the service life of reinforced concrete structures. To properly evaluate the corrosion performance and to better predict the se rvice life of reinforced concrete structures, it is necessary to evaluate t he characteristics of the bulk concrete, the steel-concrete interface, the steel mill scale, the passive film, and the steel microstructure. This rese arch program investigated the performance of microstructurally designed rei nforcing steel for improved corrosion resistance when embedded in concrete and exposed to accelerated chloride environments. Reinforced concrete speci mens containing ASTM A 615 and controlled rolled dual-phase ferritic marten sitic (DFM) reinforcing steels were embedded in concrete and subjected to c hloride solutions. Samples were then evaluated for mass loss and macrocell current flow for a period of approximately 1 year. The results from the mac rocell and mass loss testing indicate that the controlled rolled DFM reinfo rcing steel exhibited less mass loss due to corrosion than the ASTM A 615 r einforcing steel.