Masanori Nagai

Additions to Contingency Plan for Enhancing Secureness of Weathering Steel Structures

Japanese Specification for Highway Bridges [1] revised in 2002, which first stated that degradation of bridge members, including those of weathering steels, to occur in prolonged period of time must be taken into account, invoked wide scope of discussions. The final goal of these activities is to realize ultra long term durability of steel infrastructures with minimized maintenance costs. For this value creation, one should take risks which can be controlled without difficulties. Note that risk is different from crisis or failure: To take risks with adequate assessment means to enhance secureness of the structures. To reduce riskiness of anomalous rusting to occur on weathering steel, the author et.al. developed a computerized corrosion prediction system [2,3], which is now used as a corrosion controlling tool on the planning and designing stages of weathering steel structures [4]. Visual as well as instrumental rust monitoring methods and their criteria were already established as reported elsewhere [4, 5]. Unlike organic or inorganic materials, weathering steels do not deteriorate internally. Therefore, all corrosion risks can be monitored by inspections of steel member surfaces. A management system for secureness enhancement for weathering steel bridges is already available as listed in references [6, 7]. Applying these recently advanced methods according Secureness Enhancing System (SES) as depicted in Fig.1 to various stages servicing, riskiness in terms of damage due to anomalous corrosion on weathering steel bridges became much lower than ever: i.e. Weathering steel now became low risk-high return material. However, riskiness cannot be zero due to uncertainty in terms of unpredictable environmental change, breakage of upper concrete deck, human error in designing stage, etc., which might cause water leak from upper part of structures. Also, attachment of large amount of air born salt by stormy weather happened during fabrication and/or transportation might cause anomalous rusting of unpainted weathering steel parts. To cope with such risks, one must carry out corrosion monitoring using above mentioned methods [4, 5, 6]. Although anomalous state is detected, it is neither failure nor end-of-life for the weathering steel structure. Based on accurate cause analyses, one can take an appropriate maintenance. Since it has been pointed out that adherent thick rust on weathering steel is very difficult to remove, the authors have created a novel power tool and high performance zinc rich paint as additions to our contingency plan. In Fig.2, the developed stainless rotor covered with numerous diamonds [8] is shown as an example, which facilitates otherwise inefficient and ineffective surface preparation processes. This method is useful to treat such surfaces as in a place where one cannot operate a blasting machine, which generates large amount of dust influencing onto surrounding environment.

Anticorrosive Performance of Moisture Cured Polyurethane Paint after Low Temperature Curing

試験後の防食性も良好であることが判明した。 A moisture cured one-component polyurethane resin is cured by the reaction of its isocyanate group with moisture in the air or adsorbed water on the substrate. This curing system was contrived in Germany. And, it had good protective performance of this coating system for more than 20 years demonstrated through practical applications. From our studies on curing mechanism and protective performance, we found that the coating film dried at a temperature as low as 5°C and at a humidity as low as 50% RH showed excellent protective performance. Protective performance of the coating film after low temperature impact resistance test was also proved to be good because of its flexibility. 永井 昌憲 Masanori NAGAI 山本 基弘 Motohiro YAMAMOTO 3 技術報文-1 湿気硬化形ポリウレタン樹脂塗料の低温乾燥後の防食性評価