PERFORMANCE EVALUATION OF A COAT-TYPE PEELABLE MATERIAL FOR REDUCING RESIDUAL SALT ON BLAST-TREATED CORRODED STEEL

Abstract

 To extend the service life of aging bridges, particularly those over 50 years old, the long-term durability of anticorrosive coatings is crucial. A significant challenge is the premature degradation of paint films on bridges with severe corrosion, caused by airborne salt and deicing agents, as salt often remains after conventional blast cleaning, making it difficult to achieve expected durability. Existing salt treatment methods like blasting are insufficient, while water washing is often impractical due to operational complexities and environmental concerns. This paper reports on the development and performance evaluation of a novel coat-type peelable material designed to mitigate this issue, which acts as a salt-reducing agent. This material, a water-based paint-like agent containing a thixotropic thickener, traps dissolved salt within a film formed upon water evaporation, which can then be peeled off by hand. Laboratory tests on corroded steel plates demonstrated that the agent effectively reduces both surface and inherent salt quantities, comparable to or exceeding water washing. Applying the agent showed no adverse effects on the adhesion of subsequent paint layers to various existing coatings. Furthermore, it contributed to improved paint film durability by altering the distribution of residual salt. Field tests on actual steel bridges confirmed its salt-reducing effectiveness, even on surfaces prepared by power tools. While its general workability was good, issues like sagging on vertical surfaces and difficult peeling from heavily corroded areas were identified, suggesting areas for further material improvement.