Web特集
May 17, 2011
Series: Focus on Paint Market in Japan
Features of heavy duty coating Surface preparation depending on circumstances is needed
The handbook, issued by Japan Road Association, for heavy duty coating on road/bridge was revised in 2004, repainting coat was recommended as method of long-lived process. It was heavy duty coating applied on the surface treated by zinc-rich paint after the peeling of old film by blast. After this publication, repainting works started with blast construction. The number has 10% shares now, but it makes big movement because there was nothing before this guideline appeared.
As for the blast method, "open blast" using grinding material such as garnet is running at many places. But recently "vacuum blast" method is highly interested, because of some advantages; compact equipment, less dust and noise, recycle of abrasive. This method finally reduces lots of industrial waste, only 2% disposal compared with current system.
"Dry-blasting association", consisting of constructors supporting vacuum blast method, mentioned the inquiry about this method in previous year was only 10, but it increases 50 this year. They gain an order from national or local government and railway companies, then operate trial and actual work. For further technology improvement and promotion, they co-work with "Public Works Research Center" (PWRC) and introduce qualification system through examine and training managed by the association in order to maintain good quality/safety of this construction method. They have already provided the qualification to 180 people. "This qualification system aims at clarifying where the responsibility lies and making credibility by the operator having good knowledge, experience and skill", chair man of the association said.
Although the blasting process is most effective as surface preparation, it cannot be approved widely because of limited budget and working condition, so flexible on-site adjustment is needed. Most of repainting work is generally designed with reference to the most damaged (corroded) portion, so even healthy part must be treated and re-coated. That leads more paint consumption against the budget reduction pressure. In order to achieve effective surface treatment, dry-blasting association proposed proper combination of suitable peeling and scraping method and blasting process especially on easily-rusted part.
For Honshu-Shikoku highway, basically base/top coat will be repainted before the primer is damaged. The objective is to prolong effectively durability of the film by regular maintenance on degraded section without recoat of the primer.
Public Works Research Center proposed sectional maintenance coating using blast method
Public Works Research Center (PWRC) recommend sectional repainting coat, ie. sectional maintenance with blast method, that makes heavy duty coating economically long-lived. Sectional maintenance coating is defined as the following process; scraping and blasting on corroded part and top coat or non-coat on healthy part. PWRC stress this is efficient method to prolong the durability of steel constructions. General repainting work overcoat even on healthy part, and it doesn't perform enough at the edge, finally it cannot slow the progression of corrosion. In 2005, PWRC tried first trial of sectional maintenance with blast method, later worked the bridge between isolated islands in NAGASAKI prefecture.
Regarding over 2 meters bridges, there are 670,000 units in Japan. 90% of them are managed under local government. Those are not mostly controlled by systematic maintenance. Lots of bridges were only painted over 20 years ago. Despite of increasing number of bridge needing maintenance, given budget is getting decreased. It could be impossible to keep healthy condition of coating on all bridges, therefore, we should select maintenance coating method applicable to limited expense for repainting work.
In 2009, Japanese ministry issued the draft of guideline regarding sectional repainting for road/bridge. It is expected to push more work, so PWRC held the seminar and plan on-site visit to propose positively sectional maintenance coating to local government staff, constructors and consulting companies. In TOHOKU, HOKURIKU, KYUSHU region, number of works is increasing, recently trial work will start in KANTO region. Development of blasting method, cost estimation, supply channel of equipment will support further promotion of sectional maintenance with blast method.
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