THE CORROSION PERFORMANCE OF INORGANIC-, CERAMIC-, AND METALLIC-CLAD REINFORCING BARS AND SOLID METALLIC REINFORCING BARS IN ACCELERATED SCREENING TESTS

This report describes corrosion tests conducted in the first 2 years of a 5-year project on 14 inorganic-, ceramic-, and metallic-clad reinforcing bars and 10 solid metallic alloy reinforcing bars. Test results obtained from wetting and drying of bent and straight specimens in the pH 7 and pH 13 solutions are presented. These tests were conducted on bars in three different conditions: as-received, with a drill hole, and after abrasion. Test conditions were developed to be representative of concrete. From polarization resistance measurements of the bars in the wet-dry corrosion tests and visual assessment of the bars after testing, it was determined that the stainless steel reinforcing bars and the titanium rod tested in the program exhibited significantly lower corrosion rates than any of the other bars. Other bars that exhibited good performance included solid aluminum bronze and copper-clad bars. The zinc-alloy clad bars exhibited improved performance over the galvanized bars; however, little difference was observed between the corrosion rates of these bars and black bars. Some bars, such as the ceramic- and zinc-silicate-clad bars were deemed to be unsuitable due to their poor abrasion resistance which would limit their field applications. In addition to the laboratory tests, a brief review of the corrosion performance of several of the clad and solid alloy bars in concrete corrosion tests is presented. A discussion of some of the economic considerations is also presented. The report discusses corrosion rates and the time for the corrosion to cause cracking of concrete, based upon review of laboratory corrosion tests conducted by a number of other researchers. It was found that small losses in bar radius of about 0.025 mm (0.001 in.) results in a volume of corrosion by-product that can crack concrete. This ongoing FHWA study has selected 4 of the 24 types of bars for further testing under severe 2-year in-concrete corrosion tests. These coatings are: type 304 stainless steel bars, copper-clad bars, galvanized bars, and a new zinc-alloy clad bar system. The performance of these clad and solid alloy bars is being compared with the performance of three nonbendable epoxies, three bendable epoxies, and black bars. The in-concrete tests on 11 different bar types will be completed in 1998.