Steel bridges account for about 50% of the total length of bridges in Japan, and almost all of them are coated to prevent corrosion, and most of them are coated with durable coatings with a lifespan of 30 years or more. However, the coating film at the end of the skeleton and at the joints is prone to corrosion and thinning, and corrosion occurs in less than 30 years. In order to enhance the corrosion resistance of these corrosion-prone areas by coating them with titanium foil, the technicians investigated a method that would give the coating a longer service life than that of the coating alone.
By applying this method to ends and joints that are prone to deterioration after painting, not only can localised corrosion deterioration be reduced, but also the frequency of repairs to painted buildings and cycle life costs can be reduced.
Japanese scholar Ganaha Yasuhiko introduced the weak parts of the bridge steel skeleton coating of titanium foil coating construction steps, in general: ① the surface of the steel substrate to be coated with titanium foil.
① Clean the surface of the steel substrate; ② Apply a zinc-resistant coating.
(ii) Apply zinc-containing corrosion- and heat-resistant paint.
③Adjustment of the unevenness or bumpy areas.
④Attach the titanium foil and adhesive tape together to the object, taking care not to float or wrinkle the titanium foil; ⑤Apply the titanium foil to the object if it is not suitable for use.
⑤Paint the areas where titanium foil is not suitable with normal paint.
(6) Apply intermediate coatings to the suitable and unsuitable parts of the titanium foil; (7) Final coating.
(vii) Final coating.
The economy of painting is generally evaluated in terms of life cycle cost. The design life of a coated bridge (C-5 coating system) is 30 years along the coast with high salt content (more than 20 g/m2-a-1), and the weak parts of the coating film need to be re-coated 10-15 years earlier than the design life, so the weak parts are often coated with a thick film in multiple processes in the actual construction. The use of titanium foil eliminates the need for such multi-process thick film coating of weak areas and maintains long-term corrosion resistance without the maintenance cost of re-coating. Therefore, the use of titanium foil can reduce life cycle costs.
The study compares the results of the titanium foil corrosion protection method with those of the painted corrosion protection (C-5 coating system) and shows that after 3,000 h of corrosion testing, no corrosion occurred in the titanium foil method, whereas corrosion occurred in the painted corrosion protection method, demonstrating the superiority of the titanium foil method of corrosion protection.
In addition, several typical application examples are presented at the end of the study.
In the first case, the titanium foil method was applied to the end of the lower edge of a bridge skeleton, and after 10 years, no change in the surface was observed, while the painted end showed rust colour; in the second case, the titanium foil method was applied to the end of the lower edge of a bridge skeleton.
In the second case, the titanium foil method was applied to the articulation part of the bridge skeleton, and after 23 years, the bonding strength and the titanium foil were still intact; in the third case, the titanium foil method was applied to the lower edge of the steel trestle.
In the third case, the titanium foil method was applied to the end of a steel trestle bridge, which showed that its life span had been extended.
In the fourth case, the steel lighthouse was covered with titanium foil except for the riveted joints, which shows that titanium foil can be used to achieve good corrosion protection for complex shapes such as overlapping steel plates with a step difference and protruding window frames as long as the uneven parts are carefully constructed.
