Regular preventative maintenance programs on bridges involve projects with many facets, including paint stripping, de-rusting, painting, expansion joint cleaning and graffiti removal. Looking for innovative and cost-effective ways to advance its preventive maintenance program, the administration team for the International Bridge at Sault Ste. Marie enlisted Unimanix and its new all-in-one cleaning solution.
About the Sault Ste. Marie International Bridge
The International Bridge spans the St. Mary’s River between the United States and Canada, connecting Sault Ste. Marie, Ontario with Sault Ste. Marie, Michigan. It is the only crossing for vehicles going between Michigan and Ontario within a 600-mile distance. The bridge was officially opened in 1962 and is 1.9 miles (3.0 km) in length. It is a continuous span steel bridge with two truss arches which span the U.S. and Canadian lock approaches, a double arch span on the U.S. side and a single arch span on the Canadian side. The bridge deck and piers are concrete.
Sault Ste. Marie International Bridge. pHOTO: © istock.com / rruntsch
Daily operations are managed by the International Bridge Administration (IBA). The IBA team had made the decision to implement preventive maintenance projects in-house by integrating new or alternate technologies.
One of the major projects to be undertaken was the painting of the steel floor girders under U.S. bridge spans 1 and 2 at the south bridge abutment. The IBA bridge engineer specified a cost-effective one-coat paint system that provided enhanced corrosion resistance. Steel surface preparation for the paint system was performed with high-pressure water cleaning as opposed to sand blasting.
The IBA team decided on this approach after learning that, in recent years, high-pressure washer cleaning (up to 10,000 psi) has grown in popularity as an alternative to water blasting (over 10,000 psi) and abrasive blasting for surface preparation. High-pressure washer cleaning is available as an economical and environmentally friendly way to prepare a surface for coating application with only pressurized water.
To prepare the steel members for coating, the team chose the Unimanix pressure-washing system, UNI 7060, a new-generation solution that evolved from the manufacturer’s field experience on several bridge projects. It provides up to 7,000 psi and 6 gallons per minute to deliver the precise impact required. The UNI 7060 has a built-in additive storage and injection system to remove non-visible contaminants, using a soluble salt remover, integrated abrasive blasting capabilities to remove black oxide, and an automated low-water-level shut-off to prevent on-site breakdown due to unexpected water supply disruptions.
During their trial runs with the UNI 7060, the IBA team found that:
The hot water and chemical combination offered by the system was highly effective in removing not only the unwanted loose paint but all other chemical residue that had accumulated over the years.
The 7,000-psi at 6 gpm delivered the right amount of impact to expose crevices while leaving behind only the paint that still adhered well to the substrate.
The equipment’s adjustable-length wand was effective in cleaning hard-to-reach corners.
The use of hot water resulted in the evaporation of much of the water, thus reducing the waste stream. The small amount of collected water was then recycled, which lowered the associated water disposal costs.
Due to this evaporation, the length of time the substrate stayed wet was reduced. Subsequently, there was less flash rust, an oxidation product that forms when a wetted carbon steel substrate dries. This type of rust occurs from the time the waterjetting process starts to the time the water used for the waterjetting process dries. With less flash rust, the team was able to proceed quickly with the application of the coating.
The UNI 7060 was successful in removing water-soluble salts, and as a result, there has been no occurrence of “rust back,” which would have jeopardized the painting process.
The team met its maintenance goals, and use of the all-in-one system achieved the following:
Lowered cost for surface preparation
Reduced time for the surface to become ready for a new one-coat paint system
Less of the negative environmental impact typically caused by older paint-stripping methods
Because the water pressure can easily be adjusted, the UNI 7060 can be used for other applications, including graffiti removal, wooden bridge cleaning, and the cleaning and clearing of expansion joints. With a wider variety of applications, the return on investment may be seen more quickly.