The long-spanned bridges of the Honshu-Shikoku Linking Project have been constructed above the sea, so they have been exposed to severe natural conditions like saline corrosion environment. Basically, inorganic zinc-enriched paint has been utilized as the first layer of the paint system for steel plate structure, in spite of its surface layer of changing from chloroplane rubber paint and polyurethane paint to fluoropolimer paint. The first step of maintenance work of long spanned bridges is to check health diagnosis of the structure. In order to look closely and touch by fingers, some footways and inspection cars are prepared for the bridge girders. As for paint maintenance, local damage of point stain, layer separation and so on should be repaired as soon as possible. And paint inspection sections for each bridge are marked off to plan paint repairing as a whole bridge. Dry air injection system, as well as wire galvanization, has been adopted against corrosion of cables of Honshu-Shikoku suspension bridges. Some other developed maintenance facilities are also introduced.
The recent trends for long span bridges and their using steels are reviewed. The newly developed structural steels, that is high performance steels for bridge construction, are also reviewed in this paper. As the span length increases, higher strength steel, increasing weldability for decreasing weld fabrication cost and bare use of weathering steel for decreasing maintenance cost are required. To meet these requirements, high strength steel, steel allowing low-temperature preheating, steel for cold bending, weathering steel for coastal region, longitudinally-profiled (LP) steel plate and high-strength steel wire for bridge cables have been developed. Especially newly developed weathering steel and its surface treatment for minimum maintenance cost are reviewed in detail.
Seto Ohashi Bridge was opened to traffic as one of the national constructing projects in April 10, 1988. The construction of the bridge was the epoch-making project in terms of construction period and its lifetime. It was spent over 10 years to build and is expected to be over 100 years of usage. The coating system of the bridge, which is a combination of zinc rich primer, epoxy resin primer and polyurethane top-coat, was established through long term durability tests of various Heavy Duty Coating (HDC) systems under civil institute. The concept of the coating system became a good guideline for steel constructions under severe environmental conditions. Kansai International Airport Bridge, Tokyo Bay Crossing Bridge and other steel constructions such as, sea-front objects, oil tanks and plants followed the same system. Akashi Kaikyo Ohashi Bridge, which is the world largest cable stayed bridge took also the same anti-corrosion system. The key technology of providing ultimate anti-corrosive property onto steel constructions is named as composite anti-corrosion method, which is a combination of sacrifical cathode effect of zinc power and interception effect of epoxy based film. The environmental condition is strictly severe in Japan, where long span bridges are put over the sea, therefore the concept of coating method is to protect steels firmly under such conditions. It has an advantage of extending maintenance cycle leading to long-term economy and environmetal friendly in term of number of coatings. The following is the report of coating system of Honshu Shikoku Bridges, which is the most important work among long span bridges in Japan.
Concrete structures have in general shown excellent performance in various environments. Recently, however, several cases have come to light where structures have shown signs of premature deterioration on account of severe environmental conditions, improper choice of condstruction materials, and lack of proper workmanship and quality control. At the same time, the movement in the world economy towards better utilization of resources is putting sustained pressure on concrete engineers to develop tools for construction of economical and more durable structures. This papaer presents a summary of the main causes for deterioration in concrete structures and provides a brief review of the mechanism of deterioration on account of chloride induced reinforcement corrosion, as a typical example. It may be noted that is one of the most important causes of rapid deterioration in our country. The paper also introduces the concepts on durability design, maintenance planning and rehabilitation methods in concrete structures.
Ternary copolymers composed of acrylic acid, acrylamide and sodium stylene sulfonate [P (AA/AAm/NaSS)] were synthesized and these inhibition effects on corrosion of mild steel in cooling water system were investigated by physicochemical methods. P (AA/AAm/NaSS) acted as an adsorption-type inhibitor in solutions with low concentrations of ionic species and suppressed mainly the anodic reaction during corrosion of mild steel. In solutions with high concentrations of ionic species, the corrosion of mild steel was inhibited by the formation of the film mixed with scale and P (AA/AAm/NaSS) on the steel when 25mg/l or less of the copolymer was containded. By contrast, the adsorption of P(AA/AAm/NaSS) on the steel surface inhibited the corrosion when 75mg/l or more of the copolymer was contained.
Effects of carbon content and microstructure on corrosion rate of 13% chromium steel were investigated in wet CO2 environments. First, corrosion rates of ferrite, martensite and tempered martensite were different from each other in 13% chromium steel. Corrosion rate of tempered martensite was the highest and that of martensite was the lowest. Second, corrosion rate of 13% chromium steel was indicated as the summation of the product of corrosion rate for each microstructure by its areal fraction.
Pitting corrosion of copper coiled tubes has been experienced in the air conditioning system having the open heat storage water tank. Although the morphology of the pitting was similar to type 1 pitting corrosion in plumbing copper tubes, the quality of circulating water in the system was different from those in plumbing system and the inner surface of corroded tubes was fully covered with corrosion product occurred for galvanized steel tubes using main plumbing in the air conditioning system. The factor of the pitting corrosion has been investigated by field test in above actual air conditioning system. The circulating water was more corrosive and contained the fine corrosion-product particles of galvanized steel. The presence of both carbon film and corrosion product of galvanized steel on the copper tubes caused the pitting corrosion. As the pitting corrosion was much influenced by fine corrosion-product particles of galvanized steel rather than carbon film on inner surface of copper tube, pitting corrosion was reduced by entrapping the fine corrosion-product particles of galvanized steel in the circulating water with fine mesh filter.
The sealing in alkali earth metal ion solutions was effective to increase the resistance to pitting of the aluminum anodized in a sulfuric acid solution. After sealing, formation of crystalline BaSO4 in the anodic oxide film was confirmed by XRD and EPMA. The formation of sulfate and/or carbonate of Ca (II) and Sr (II) was suggested, though no direct evidence was obtained except for Ca 2p XPS spectrum. The resistance depended on the composition of sealing solution and increased in the order of doubly distilled water<Ba (II) solution<Sr (II) solution<Ca (II) solution. This is in reverse order of the insolubility of each sulfate, so that the effect cannot be explained simply by the formation of insoluble sulfate by sealing. Less increment of resistance with Ba (II) was due to the formation of crystalline BaSO4 in the anodic oxide film during sealing, which eventually comes off the film, leading to the formation of large defects in the film. The best results were obtained with Ca (II) but the reason is not clearly explained so far.