Long-term effects of chloride on concrete
The FHWA-testing the long-term effects of corrosive elements on rebar in concrete-subjected several test slabs to years of exposure. The above chart shows the estimated chloride accumulation at a depth of 1 inch over time.
The Concrete Reinforcing Steel Institute (CRSI), Schaumburg, I11., has announced the release of a Federal Highway Administration (FHWA) study titled Long-Term Performance of Epoxy-Coated Reinforcing Steel in Heavy Self-Contaminated Concrete. The report describes the long-term corrosion test results from slabs left over from a five-year FHWA-funded corrosion study. After the initial round of testing ended in 1998, 31 specimen slabs were placed outside to weather naturally until December 2002, when they were autopsied.
The test samples contained uncoated steel, stainless steel, and epoxy-coated steel rebar in a two-mat arrangement, similar to a bridge deck. The test results showed a significant decrease of corrosion when the top mat of reinforcing used epoxy-coated bars and the bottom mat used uncoated bars (compared to uncoated bars in both mats). The test samples that used epoxy-coated bars in both the top and bottom mats approached the corrosion-resistance level of a high-grade stainless steel rebar (ASTM A316), even though 2% of the coating area was intentionally damaged.
Also, the results showed that negligible macrocell current between the top and bottom mats of steel bars was due to bars with few signs of corrosion throughout the nine years of exposure to chlorides. Conversely, samples with high macrocell current between the mats were indicative of steel bars with a high degree of corrosion. This test and the one completed in 1998 also indicate that adhesion of the coating is a poor indicator of long-term performance, because there is no direct relationship between coating adhesion and corrosion resistance of the coating. The conclusions of the report are in direct conflict with many presumptions concerning corrosion and epoxy-coated steel rebar. The full report is available at www.crsi.org.