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Title: Atmospheric corrosion and epoxy-coated reinforcement

Abstract

Atmospheric corrosion can have a tremendous effect on the ability of epoxy-coated reinforcement to maintain its effectiveness. Corrosive conditions can result in the coating becoming brittle and more susceptible to damage from handling. Atmospheric conditions can also enhance localized corrosion at holidays on the bars. Efforts to minimize these effects will be discussed.

Authors:
 [1]
  1. Univ. of Texas, Austin, TX (United States)
Publication Date:
OSTI Identifier:
350042
Report Number(s):
CONF-980316-
TRN: IM9925%%390
Resource Type:
Conference
Resource Relation:
Conference: Corrosion `98, San Diego, CA (United States), 22-27 Mar 1998; Other Information: PBD: 1998; Related Information: Is Part Of Corrosion `98: 53. annual conference and exposition, proceedings; PB: [6600] p.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; WEATHERING; CORROSION; EPOXIDES; STEELS; REINFORCED CONCRETE; PROTECTIVE COATINGS; CORROSION PROTECTION

Citation Formats

Wheat, H.G. Atmospheric corrosion and epoxy-coated reinforcement. United States: N. p., 1998. Web.
Wheat, H.G. Atmospheric corrosion and epoxy-coated reinforcement. United States.
Wheat, H.G. 1998. "Atmospheric corrosion and epoxy-coated reinforcement". United States. doi:.
@article{osti_350042,
title = {Atmospheric corrosion and epoxy-coated reinforcement},
author = {Wheat, H.G.},
abstractNote = {Atmospheric corrosion can have a tremendous effect on the ability of epoxy-coated reinforcement to maintain its effectiveness. Corrosive conditions can result in the coating becoming brittle and more susceptible to damage from handling. Atmospheric conditions can also enhance localized corrosion at holidays on the bars. Efforts to minimize these effects will be discussed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1998,
month =
}

Conference:
Other availability
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  • This paper describes a simplified ab initio numerical model of the oxygen transport and electrochemical reaction kinetics associated with a hole in a coated reinforcement bar. The model examines the influence of area of disbandment of the coating around the hole on the corrosion rate of the exposed steel. The significance of coating disbandment is found to depend on the concrete permeability. An important conclusion is that experiments in which the coated bar is coupled to uncoated bar can be expected to give markedly different results, as the uncoated bar (assuming that it is passive) will provide a large areamore » cathode that negates many of the assumptions made in this model. It is also clear that coupling between coated and uncoated bar provides a very severe test of the coating integrity. The thin solution layers in the crevice are able to transfer the current produced by oxygen reduction efficiently to the anodic site at the holiday in the coating. It appears that for nominally dry concrete the oxygen permeability of the epoxy coating and the radius of disbandment of the coating will have an important influence on the total metal loss occurring, and it should have a low oxygen permeability and disbond as slowly as possible. The area of hole in the coating will be important when processes in and around the hole are rate-controlling, including situations when there is very widespread disbanding and/or the coating has a very high oxygen permeability. Corrosion occurring as a result of oxygen transport through the hole will be important when the coating is not disbonded and/or has a very low oxygen permeability.« less
  • Two of the most widely used corrosion protection systems for steel in reinforced concrete are epoxy-coated steel and calcium nitrite. In severe exposures to deicing or marine environments engineers often require more than one protection system, referred to as a ``Belts and Suspenders`` approach. In this work the performances of calcium nitrite and epoxy-coated reinforcing bars in combination and alone are documented after several years of accelerated testing in good quality concretes. The data show that calcium nitrite definitely improves the performance of epoxy-coated reinforcing bars, even when they are severely damaged as might occur due to poor handling ormore » concrete placement. Undamaged epoxy-coated reinforcing bars had similar performance to calcium nitrite and the combination system was an improvement.« less
  • The state of Oregon is graced with a rugged and beautiful coastline with a zone extending several miles inland that can be highly corrosive. Microclimates, which strongly affect the performance of steel, are created in this zone by precipitation, salt spray, fog, airborne salts, high winds, and solar radiation. Atmospheric corrosion measurements were conducted on one-sided panels to examine the effects of sheltering, orientation, and distance from the ocean on seven bridges, in eight coastal communities, and three inland locations. The test materials included mild steel, thermal-sprayed aluminum on mild steel sealed with moisture-cured urethane, and a three-coat bridge maintenancemore » paint system on mild steel. The surface of the coated steels was scribed from corner to corner in an X-pattern to create a damaged area that exposed the mild steel. Results indicated a wide difference in performance of the steels as a function of the coastal environment. Corrosion led to the formation of insoluble corrosion product and runoff contributed negligibly to total mass loss. Mass loss increased with decreasing distance to the ocean, increasing ''wetness'' of the location, and decreasing inclination of the surface in bold exposures. Mass loss in shelter and partially sheltered exposures were high, as much as an order of magnitude higher than bold exposures. Mild steel protected by a sealed thermal-sprayed aluminum coating exhibited no undercutting or corrosion damage. Mild steel protected by a three-coat bridge maintenance paint system exhibited increasing undercutting and damage with decreasing distance to the ocean.« less
  • New epoxy-clay nanocomposites with sub-ambient glass transition temperatures have been prepared by the reaction of epoxy resin and a polyetheramine curing agent in the presence of long chain (carbon number {>=}10) alkylammonium ion exchanged forms of montmorillonite clays. Owing to the expansion of the clay galleries upon polymer network formation, the cured composites contain nanoscopic clay plates dispersed in a rubbery polymer matrix. Both the tensile strength and the modulus of the polymer-clay nanocomposite increased with increasing clay content. Shorter chain (carbon number <10) alkylammonium ion exchanged montmorillonite was exfoliated by using hot-mold-casting methods. The structure and properties of themore » fully exfoliated nanocomposites were compared with those of the partially exfoliated epoxy-clay nanocomposites. Short chain alkylammonium exchanged clays are preferred as reinforcing agents if a fully exfoliated nanocomposite can be obtained.« less
  • Thirty-one relatively large reinforced concrete slabs were fabricated in 1980 using either non-specification epoxy-coated reinforcing steel or calcium nitrite admixture with black (uncoated) steel. Their performance is compared with uncoated steel in concrete without admixtures. The slabs were placed in two lifts: the bottom lift consisted of a bottom mat of reinforcing steel in chloride-free concrete; and a top lift consisting of the top-mat rebars in concrete contaminated with various quantities of sodium chloride. All the electrical connections between the reinforcing mats were made exterior to the slabs so that the corrosion current flow could be monitored. A worst casemore » type of research design was used by specifying poor quality concrete, nonspecification epoxy-coated rebars, and good electrical coupling between the rebar mats. After curing, the slabs were mounted above ground and exposed to the environment of the Washington, D.C. location. They were periodically subjected to additional chloride exposure while being monitored for about 1 year to determine the corrosion rate. Selected slabs were then demolished to confirm the findings of the nondestructive testing.« less