|Content Type||Conference Paper|
|Title||Improving the Damage Tolerance, and Extending the Service Life of Fusion-Bonded Epoxy Coatings|
|Authors||D.G. Enos, C.R. Guilbert and J. Alan Kehr, 3M Austin Center|
|Source||CORROSION 2001, March 11 - 16, 2001 , Houston, Tx|
|Copyright||2001. NACE International|
|Keywords||Fusion-Bonded Epoxy, FBE, ECR, FBECR, Corrosion, Concrete, Rebar, Steel, Microencapsulation, Inhibitor|
Today, the traditional fusion-bonded epoxy (FBE) coatings used to protect carbon steel reinforcing bar (rebar) and pipe are being placed under increased scrutiny. Concerns have been raised which question the ability of such coatings to abate corrosion in the long term. Researchers have argued that a damaged, FBE coated rebar exhibits poorer corrosion performance than a comparable uncoated, black steel rebar. This reduced corrosion performance and corresponding service life is likely the result of local anodic sites which develop along the coated rebar or pipe in areas where the FBE coating has been removed due to impact or abrasion.
A novel coating design has been developed, the implementation of which significantly improves the damage tolerance of epoxy coated components in a variety of high chloride environments, such as an aging concrete bridge deck. In this study, the coating was successfully applied using conventional electrostatic-spray equipment at a commercial applicator. The resulting coated rebar was able to exceed the performance requirements of a coat-after-fabrication application in terms of cathodic delamination. This paper details the results achieved to date, as well as outlining the in-concrete test program currently underway.
Corrosion of steel in concrete is one of the most costly problems in the United States. ~ Approximately half of the nearly six hundred thousand bridges in the US Federal Aid Highway system have structural deficiencies or are functionally outmoded. According to FHWA estimates, a quarter of US bridge decks are badly deteriorated. With the advent of the widespread application of road-salt, expensive repairs are often required within five to ten years.
It's a worldwide problem. Research indicates that the service life of buildings in the Arabian Gulf may be as short as five to fifteen years due to premature rebar corrosion. In some cases, rebar corrosion problems occur before construction is complete. In Japan, reinforced concrete bridges near the seashore show rapid deterioration within ten years of construction. Eleven viaducts in the UK built in 1972 began to decay within two years of construction due to the application of road deicing salts. 2 Parking structures are the most vulnerable of all because automobiles bring in salt, but the deck is not rinsed by rain. 3
The corrosion problems discussed above are caused primarily by chloride-induced corrosion of steel in concrete. Chloride penetrates the concrete from sources such as road de-icing salts or sea exposure. It can also be built in through the use of salt-contaminated aggregate, seawater in the concrete, or chloride- based admixtures. Upon achieving a sufficiently large concentration, the chloride causes the depassivation and subsequent rapid corrosion of the steel. The resulting corrosion products occupy a much greater volume than the iron that they replace, and, as such, cause tremendous internal pressure within the concrete. This internal pressure, in turn, causes the concrete to crack and spall, allowing greater access of corrodents to the steel, further accelerating the deterioration of the structure. 2
In recent years, FBE has seen widespread use in steel reinforced concrete structures as a solution to the aforementioned corrosion problems. An FBE coating works by acting as a protective barrier, preventing both chloride and moisture from reaching the surface of the steel. Its greatest advantage lies in its applicability to existing designs without changes in load capacity or section size, the only change is in the modification of development length.l Over one-hundred-thousand structures utilizing FBE coated rebar (ECR
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