Accelerated exposure tests as evaluation tool for estimating life of organic coatings on steel bridges

Abstract

The present study performed accelerated exposure tests on 5 types of painting systems, which are commonly used for steel bridges in Japan, and discussed corrosion degradation from initial defects on the paintings. The structural steel plates were surface treated and painted conforming to the ‘Japanese painting manual’, and circular defects with 0·2, 1·0 and 2·0 mm in diameters reaching the steel substrate were created on each of the painted plate. The painted steels were exposed into an environmental testing chamber controlled by the S6 cycle test condition, which is a laboratory cyclic accelerated exposure test condition of spraying/wetting/drying, for up to 600 days. The corrosion degradation curve of the each painting system was evaluated based on rusting area from the circular defects, which was measured by using laser focus measuring instrument at 250 μm intervals. The proposed degradation curves were applied to evaluating remaining lifetime of the painted steels with initial defects to the future conditions. The evaluation procedure for field environments was also presented based on the acceleration coefficient of the S6 cycle tests and the amount of flying salt.