Materials Performance

SEP 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 48 of 128

SEPTEMBER 2018 W W W.MATERIALSPERFORMANCE.COM W W W.MATERIALSPERFORMANCE.COM SEPTEMBER 2018 (Left) Corrosion of the reinforcing steel in a bridge beam on a jetty led to extensive repairs and ICCP. (Right) During the jetty's repairs, MMO-coated titanium expanded ribbon anodes were installed in the soffit. Photos courtesy of John P. Broomfield, FNACE. Corrosion of reinforcing steel that surrounds a poor-quality patch repair due to the ring anode, halo, or incipient anode effect. Photo courtesy of John P. Broomfield, FNACE. Mitigating Corrosion of Steel in Concrete with Impressed Current Cathodic Protection John P. Broomfield, FNACE United Kingdom The whole field of our understanding, investigating, and treating corrosion of steel in concrete has come into being and developed radically in the past 74 years. I remember being told by a leading state materials engineer that when he was a young engineer fresh out of college, his state bridge engineer supervisor told him to "go out and investigate the potholes on the bridges and prove that it was down to bad construction by the contractors." His supervisor did not be- lieve all that "rubbish" about deicing salts causing corrosion. Prior to that, it was believed by some that corrosion of steel in concrete only occurred due to stray current corrosion from direct current-powered streetcar traction systems. and marine conditions. The development by Jack Bennett and others at Eltech of the mixed metal oxide (MMO)-coated titanium mesh anode for reinforced concrete transformed the industry. 4 MMO anodes now come as rolls of mesh, ribbons, and tubes of various sizes and capacities that enable us to apply CP to the most complex steel reinforcement cages. ICCP is now applied in many countries throughout the world based on NACE SP0290 (formerly RP0290), "Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures," and ISO 12696, "Cathodic Protection of Steel in Concrete." The next major development was in galvanic CP. Early trials suggested that concrete resistivity was too high for galvanic CP to be effective. However, pioneering work by the Florida Department of Transportation showed, first, that sheets of perforated or expanded mesh zinc could be used on columns in marine environments; and, second, that thermal-sprayed zinc also could be successfully ap- plied to concrete and act as a galvanic anode. 5 Meanwhile, in the United Kingdom, Page and colleagues at the University of Aston were looking at suppressing the ring anode effect by installing zinc anodes in a special activating mortar in repairs. 6 These innovations have now led to a wide range of galvanic anodes for corrosion control of steel reinforcement in concrete. Most recently, hybrid anodes have become available. These galvanic anodes are given an initial impressed current "boost" when first installed, as described by Glass, et al. 7 We will see if this lat- est innovation takes off or becomes a niche application like some other innovations, such as electrochemical chloride extraction and realkalization. 8 Over the past 75 years, the concrete repair industry has been transformed from an annoyance to state departments of transpor- tation to a worldwide activity. Many other innovations have been skipped over in this brief commentary, but these are perhaps some of the major milestones in its development. n John P. Broomfield, FNACE, of Broomfield Consultants (Surrey, United Kingdom) is a leading international specialist in corrosion of rein- forced concrete structures, its investigation, and treatment. He chairs several NACE task groups and is past chair of the committee for the European and ISO standards for CP of steel in concrete and for realka- lization and chloride extraction. Broomfield has published several books and over 100 papers on the corrosion control of buildings, monuments, and civil engineering structures. His projects include the National War Memorial in Wellington, New Zealand; Philip Island Bridge in Melbourne, Australia; Churchill College in Cambridge, United Kingdom; Louvre Abu Dhabi in Abu Dhabi, United Arab Emirates; and the Battersea Power Station, School of Oriental and African Studies, Selfridges Department Store, and various residential towers and housing estate in London, United Kingdom. He has a D.Phil. degree from Linacre College, Oxford University, is past chair of the NACE Publications Activities Commit- tee, and is a Fellow of NACE, the Institute of Corrosion, The Concrete Society, and the Institute of Materials Mining and Metallurgy. Broomfield is also a Chartered Engineer and a Chartered Scientist. He received the 2018 Paul McIntyre Award from the Institute of Corrosion. In 1974 Dick Stratfull, with the California Department of Transportation (Caltrans), published the latest results of his trials of impressed current CP (ICCP) of reinforced concrete bridge decks and substructures, recently republished as a classic article in Materials Performance. 2 Shortly afterwards, J.R. Van Daveer of the U.S. Federal Highway Administration published the results of his investigation of the use of reference electrode (half-cell) surveys of corroding bridge decks. 3 This led to the development of ASTM C876, "Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete," which standardized the practice that is now used worldwide to determine the corrosion risk of steel in concrete exposed to chlorides. These innovations led to the creation of entirely new industries for researching, investigating, assessing, and repairing corrosion of steel reinforcement in concrete, as well as investigating the long- term durability of steel-reinforced concrete structures. It became apparent that conventional patch repairs of spalling concrete did not cure the reinforcement corrosion problem due to what is known as the ring anode, halo, or incipient anode effect that occurs unless all chloride-contaminated concrete is removed during the repair— which is usually structurally and financially unacceptable. The problem is that corrosion breaks out around the repairs because the steel in sound concrete is "cathodically protected" by the corroding steel in the area to be repaired, but once the repair area is refilled with uncontaminated, chloride-free concrete, the steel that acted as the anode then becomes a cathode, and steel in unrepaired areas with chloride at the surface has no anode to protect it. The development of ICCP to control corrosion across the whole chloride-contaminated area and the half-cell survey to identify areas of high corrosion risk gave the concrete repair industry the tools it needed to address corrosion in structures exposed to deicing salts A28 A28

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