Bridges are important traffic routes and landmarks that need regular maintenance in order to remain safe to use. As Finland’s bridge infrastructure is aging, the need for extensive renovations has increased. But how have the ways in which bridges are renovated changed over time? In what kinds of projects has FSP been involved? The renovation of Ounaskoski road-rail bridge was a massive undertaking that was completed in October 2018, on schedule, to serve traffic in the Rovaniemi area. This year, we have taken part in the refurbishment of the Opastinsilta bridge in Pasila.
Each year, up to 150 bridges on Finland’s public roads undergo a major overhaul, while around 400 bridges are maintained through smaller repairs. Also, between 150–200 new bridges are being built on an annual basis. These figures are based on information from Väylä, the Finnish Transport Infrastructure Agency (FTIA), until 2019 called the Finnish Transport Agency. This governmental agency is responsible for the development and maintenance of Finland’s road, rail and waterway systems.
LONG TRADITION OF PROTECTING STEEL BRIDGES
Steel bridges are among the most challenging structures for surface treatment, and their corrosion protection has long traditions. The protection of steel bridges started in the 1890s. Already in the early stages, the significance of pre-treatment of coated surfaces was also understood. In the 1930s, the priming of steel surfaces was advised to be done as soon as possible after the cleaning process. Although sand blasting was at that time already known as a pre-treatment method, it was not taken into use in bridge projects until the early 1960s.
During the following decades, major steps were taken in both the surface treatment methods and coating systems towards safer and more sustainable practices. A significant milestone was reached in the 1990s when the easily chalking and cracking alkydpaint systems and chlorinated rubber paints used as surface paints were replaced with zinc epoxy primers and polyurethane surface paints, which are more durable and dry faster.
During the last 30 years, to complement the solvent- borne epoxy-polyurethane paint systems, new combinations have been developed with low solvent content and high solids. These are durable but at the same time more environmentally friendly than the traditional solvent-borne paint systems.
As the quality of the surface treatment process is almost impossible to assess based on the finished coating film alone, each work phase and inspection must be carefully prepared.
WELL PLANNED IS HALF DONE
Good planning is crucial for a corrosion prevention coating that is executed technically well and cost-efficiently.
A surface treatment plan should address all the factors that have an impact on the final coating result and its durability. The shape of the structure, environmental and special strains, surface cleaning, pre-treatment, coating time and place, working conditions as well as supervision and maintenance coating must all be considered already in the planning of corrosion prevention coating.
Besides surface treatment, the corrosion of steel bridges can effectively be prevented with right structural solutions. Sharp edges are usually avoided as their protection with a coating film thick enough is a challenge. Moreover, structures where water or ice are easily accumulated will put a strain on the coating film, developing corrosion.
GUIDELINES AND STANDARDS TO HELP WORK PLANNING AND EXECUTION
Guidelines and standards play a pivotal role in the surface treatment of demanding steel structures, such as steel bridges. To guide the planning and execution of bridge renovations, Väylä (FTIA) and the SILKO committee have approved a set of guidelines called the SILKO Bridge Repair directives. These directives are divided into three parts: general quality requirements, work-specific quality requirements and the list of valid SILKO products.
The corrosion prevention standards for steel structures used in Finland are based on the international ISO 12944 Standard. Other standards often referred to in this context include ISO 8501, 8502 and 8503. The aspects related to structural design are examined in part 3 of the standard (ISO 12944-3), while part 4 (ISO 12944-4) is focused on surface types of steel structures, defining the pre-treatment classification of the surfaces.
Published in 2019, the standard’s updated part 5 (ISO 12944-5:2019) includes guidelines for protective paint systems for corrosivity categories C1–C5 and immersion categories lm1–lm3. Part 2 (ISO 12944-2) defines a new environmental strain category CX Extreme and immersion category lm4. Part 7 is concerned with the execution and supervision of painting work. Durability categories and projected lifespan of coatings are defined in standard 12944-1, important in designing a maintenance plan. It is worth noting, however, that durability category does not equal warranty period.
REPAIR OF THE OUNASKOSKI ROAD-RAIL BRIDGE IS A TEXTBOOK EXAMPLE OF SUCCESSFUL RENOVATION OF AN OLD BRIDGE
As our bridge infrastructure is ageing, there is more need for repairs. Refurbishment of old steel bridges, however, is challenging due to the varying structural solutions, old paint coat and weather circumstances. In all repair work done, it is also important to ensure employee safety and issues related to environmental protection.
Repairing of the Ounaskoski road-rail bridge, with is unique structural features, was a major overhaul, presenting a textbook example of a successful renovation of an old bridge. The reconstruction of the bridge was overseen by the infrastructure and construction service company Destia Rail, while FSP was responsible for surface treatment. The work was assigned by the city or Rovaniemi and Finnish Transport Agency. This was one of the largest bridge repair projects in Finland in 2018.
Renovation of the steel structures started in March 2018, preceded by the construction of new walkways on both sides of the bridge by Destia. The old protruding steel supports of the walkways were taken down on both sides of the bridge and replaced by new ones. The driveway blacktop and lighting of the bridge were also renewed. The railway, running on top of the road section of the bridge, received new rails and a new layer of crushed stone. The joints of the bridge’s five piers were renewed and the stonepillars received new lighting.
The execution of the repair work followed SILKO directives and the SILKO 3.351 approved LIVI B.1+ painting system, defined in the repair plan of the bridge.
Ramboll Oy monitored the quality of the surface treatment work, with appropriate documentation of each work phase.
The surface treatment started with shot blasting the steel structures to remove rust, old coating and other impurities. Dispersion of dust and paint from sand blasting into the water system and the environment was prevented by a protective cover on the bridge. All in all, the surface treatment took eight months, spanning over all four seasons of Lapland. The protective cover sheltered the structures being coated from the winter’s severe frosts as well as the direct sunlight in the peak of the summer. In freezing temperatures, the steel had to warmed to degrees above zero to prevent water from condensing on its surface during the surface treatment process.
Protective paint system:
LIVI B.1+; EPPUR 300/4-FeSa21⁄2 (Sa2); C5-M (H)
On the truss-structured bridge almost 400 metres long, there was a total of 23,000 m2 (248,000 sq.ft) of painted surface. The bridge had to be closed
from traffic for the entire duration of the repair, emphasizing the importance of keeping on schedule. In summer, work was done in two shifts, 12 hours per day on every weekday.
The original bridge crossing the beautiful Kemijoki river, completed in 1934, was entirely destroyed in the Lapland War in 1944. The current Ounaskoski bridge has been an important landmark and traffic route for Rovaniemi residents and visitors alike for almost 70 years. The previous maintenance of the Ounaskoski bridge took place in the 1970s. A work well done will stand the test of time, and the repaired bridge is expected to be in service for many decades.
OUNASKOSKI SILTA
- A two-decked, truss-structured road-rail bridge crossing the Ounaskoski rapids on Kemijoki river in Rovaniemi
- Nearly 400 metres in length
- One of Finland’s largest bridge repair projects in 2018
- Renovation ordered by City of Rovaniemi and the Finnish Transport Agency (since 2019 Väylä)
- Project was overseen by Destia Rail
- Surface treatment was done by FSP For Surface Protection Oy
- Painted surface totalled nearly 23,000 m2 (248,000 sq.ft)
- Quality of surface treatment was monitored and documented by Ramboll Oy
