ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/532296
CONCRETE BRIDGE TECHNOLOGY Improving Durability Through Certification of Epoxy-coated Reinforcing Steel by Dr. David McDonald, Epoxy Interest Group In 2012, the Concrete Reinforcing Steel Institute (CRSI) was approved by the American National Standards Institute (ANSI) as a Standards Development Organization (SDO). The hallmarks of the American National Standards process include • consensus by representatives from materially affected and interested parties, • broad-based public review and comment on draft standards, • consideration of, and response to, comments from voting members as well as public review commenters, • incorporation of approved changes into a draft standard, and • right to appeal by any participant that believes that due process principles were not sufficiently respected during the standards development. History of Epoxy-coated Bars Epoxy-coated reinforcing steel was introduced in 1973, in response to significant bridge deck corrosion concerns in the 1960s. The increased use of epoxy-coated reinforcing steel was rapid and by 2014, over 82,000 bridge decks and many other structures contained epoxy-coated reinforcing steel. The early history of epoxy-coated reinforcing steel was marred by a few notable failures, including corrosion of coated reinforcing steel in piers of bridges in the Florida Keys observed in 1986. This corrosion—exacerbated by porous concrete, thin concrete cover, and inadequate manufacture and protection of the coated steel—led many research programs to question the value of the epoxy-coating system. One of these research programs involved testing of bent, coated reinforcing steel from seven manufacturers. After approximately two years of testing, five of the systems exhibited poor performance, while two of the systems exhibited excellent performance. It was concluded that the performance was based directly on the application of the coatings and manufacturing procedures. Initial Certifcation Programs In 1991, CRSI launched a voluntary epoxy-coated reinforcing steel certification program. This program required independent review of plant procedures using unannounced inspection. Improvements in epoxy-coated bar consistency between plants was dramatic. For example, prior to the certification program, certain plants were coating products that had 50 to 70% dust contamination, which was termed backside contamination. Currently, this value averages 15%. The CRSI program has worked synergistically with the ASTM specifications, leading to changes that improved product quality. Such changes to the requirements include: • Increased coating thickness • Introduction of required steel roughness prior to coating • Requirements for clean substrates (backside contamination) • No cracking allowed during bending • Improved storage and handling Cracking of the coating during bending is considered unacceptable now; however, in 1983 certain agencies permitted unrepaired hairline cracking in the coating and did not require repairs, nor did damage repair, if the damaged area was less than 25 mm^2 (0.04 in.^2).