Continuous fight against ALWC: an evaluation

摘要

On the grounds of a report commissioned by the EU, the Belgium authorities started action to do some research on the corrosion of steel sheet piles. This report revealed for the first time the different rates of corrosion and the preferable location of the corrosion. In the design of many structures in Belgium steel elements were used frequently, it was clear that the design life, e.g. 50 years, of those structures may be in great danger. Several protection systems were taken into consideration: cathodic protection, treatment of the piles before driving, special steel composition, protection with special marine paints after driving and the use of a tailormade solvent free coating in dry conditions. In 1985 the solvent free coating was applied as a first in situ test on sheet piles along the canal Ghent-Terneuzen. To create accessibility for inspection, maintenance, repair and treatment a special caisson adapted to the form of the steel sheet piles was developed. The SSP was sandblasted, repaired and treated with the one layer coating. Over the years this system has been applied in more then 50 locations in Belgium and abroad in different conditions. Consequently the applied solution has subsequently been adapted, ameliorated and optimised. The latest development and research concerns creeping rust. Indeed, one could fear that although the coating is practically perfect, creeping rust could repel the coating. In the case of creeping rust the corrosion is moving from the edge between the treated and the non-treated zone underneath the coating. A special investigation on applications of more than 7 years old revealed the following conclusions: 1. After 7.5 years of exposure under water, there were no significant differences as far as the steel thickness measured above and below the dividing line between protected and non-protected steel are concerned. So there is no shift of the concentrated corrosion. 2. No creeping rust was observed at the lower edge of the coating. 3. Notwithstanding the biological overgrowth, the coating remains undamaged and the coating surface is not attacked. 4. It is very difficult to remove the coating with a cutter, the adhesion strength remains very high and the layer thickness is far more than the prescribed 400μ. The vitality of the protective coating is still in very good state.