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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MATERIALS PERFORMANCE: VOL. 57, NO. 9 SEPTEMBER 2018 A31 A31 SEPTEMBER 2018 MATERIALS PERFORMANCE: VOL. 57, NO. 9 Roundtable Panelists Share Historical Milestones in Corrosion Control Technological Advances in the Patch Repair and Protection of Reinforced Concrete Warren Green Australia In Australia, one of the most significant advancements in terms of concrete durabil- ity in the last 75 years regarding applica- tions, structure types, exposure, etc., is the development of the Durability Series by the Concrete Institute of Australia (North Sydney, New South Wales, Australia). This is a set of recommended practices based on standard input parameters for design life, reliability, and exposure that satisfies requirements applicable to all concrete structure types. The Series includes details on project planning and implementation that, if followed, will increase the likelihood that the specification, design detailing, and construction will be optimal for achieving the developer's and community's expectations regarding the long-term performance of concrete structures. Also included are methods to model degradation over time and design for crack control. The Durability Series goes a long way toward providing the necessary tools to design and construct durable structures and buildings based on the latest understanding of exposure, materials, and deterioration processes. l Anti-carbonation and chloride-resistant protective surface treat- ments and coatings, including some with elastic properties to bridge moving cracks. Coating types include acrylic, acrylates, vinyl esters, epoxy, polyurethane, and co-polymers. Penetrant systems for pro- tection against water and chloride ingress include silane, siloxane, silicone, and blends thereof. l Textured coatings, including fine and high-build (trowel applied) with some also providing anti-carbonation and chloride-resistance performance, as well as high bond strength and weathering resistance. l Relatively recent developments include cementitious mortars and shotcretes containing migratory corrosion inhibitors; silane pen- etrant treatments in cream form; more prevalence of water-borne systems; and high-build, epoxy-modified cementitious coatings. In the mid-1970s, concrete CP started in Australia with the galvanic CP of buried precast concrete pipes. The first above - ground reinforced concrete structure to receive CP was in 1985 and involved the trial of an impressed current conductive paint system to the soffit of a wharf in Fremantle, Western Australia. In 1987, an ICCP trial was undertaken on an ore pier in Port Hedland, Western Australia, which involved an oxide-coated titanium mesh anode cast into concrete repairs. The first full-scale CP installation to an aboveground reinforced concrete structure was in 1988 to a Cement Works building in Perth, Western Australia. This system uti- lized a conductive paint anode as well as an oxide-coated titanium mesh/cementitious overlay anode system. The application of ICCP steadily increased through the 1990s to the point now where it is an accepted cost-effective rehabilitation technology for long-term protection of reinforced and prestressed concrete structures. Anode systems changed from titanium mesh/ overlay systems and conductive paint systems in the early 1990s, to titanium mesh ribbon in slots and discrete anodes in holes that are now commonly used. Transformer/rectifier units have changed in terms of size, design (modular), and improved reliability. Distributed and networked CP systems are now possible, as well as remote monitoring and control systems with various levels of sophistication and means of communication. Galvanic anodes based on electric arc sprayed, pure Zn (>99% purity) metallized coatings have been applied to a limited extent to structures in Australia since the mid-1990s, with metallized coatings based on Al-Zn-In being used to a limited extent since 2000. Gal- vanic CP systems for concrete based on embedded Zn anodes or Zn sheet anodes are a more recent development in Australia. The embedded Zn anodes are typically encased in a medium formulated to maintain the electrochemical activity of the Zn. Within the last 10 years, hybrid anode systems have emerged in Australia. These systems, which involve an array of embedded Zn anodes, are initially operated in ICCP mode for a number of weeks and then switched to galvanic CP mode. More recently, within the The sewer aqueducts constructed at Johnstons and Whites Creek in 1895 in Annandale, Sydney were Australia's first major reinforced concrete structures. Photo courtesy of Cement Concrete & Aggregates Australia. Corrosion of steel reinforcement induced deterioration of concrete. Photo courtesy of Warren Green. Continued on p. A32 When reinforced with steel, concrete enables the design and construction of a plethora of buildings, bridges, tunnels, wharves, jetties, mining structures, offshore structures, and industrial plants. There are, however, several degradative processes that affect some reinforced concrete structures and buildings and lead to loss of functionality, unplanned maintenance/remediation/replacement, and in the worst cases, loss of structural integrity and safety risks. Amongst these, the most common cause of deterioration is corro- sion of reinforcing steel. Patch repair and protection of concrete suffering from steel reinforcement corrosion have advanced in Australia in the last 75 years—particularly over the last 40 years— not just from the materials point of view but also in terms of equip- ment and workmanship. These advances include: l Development of preblended, prepackaged, ready-to-use, polymer-modified cementitious repair mortars with a wide range of properties: lightweight for overhead use; cohesive, flowable, or pourable; structural grade/high strength; fairing, thin-build, level- ling; and fast-setting. Some have additional specialist performance properties such as chloride resistance, carbonation resistance, low shrinkage, high bond strength, and high electrical resistivity. l Sprayed mortars (shotcrete or gunite) for use with wet or dry spray techniques with varying strength properties and special- ized performance such as chloride resistance, high bond strength, low shrinkage, high electrical resistivity, and fiber (steel or plastic) reinforcement. l Reinforcement coatings such as zinc-rich epoxy, epoxy, resin- modified cementitious; bonding agents such as acrylic, styrene butadiene rubber, epoxy, and polymer-modified cementitious; and a range of curing compounds/agents.

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