By Rob Roy, Corrpro Canada Inc.
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| Illustration showing condition of the structure prior to a failure on August 29, 1907. When completed in 1919, it became the longest cantilever, steel railway bridge in the world. |
By Rob Roy, Corrpro Canada Inc.
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| Illustration showing condition of the structure prior to a failure on August 29, 1907. When completed in 1919, it became the longest cantilever, steel railway bridge in the world. |
Unique among the world's bridges, the Québec Bridge is located at Mile 2.70, Bridge Subdivision, Québec City. Considered the "Eighth Wonder of The World" when completed in 1919, it was the longest cantilever, steel railway bridge in the world. Its 'sister' bridge, of similar design and construction, is the famed Firth of Forth Bridge, in Scotland.
The Québec Bridge is a rivetted steel structure with 8,000,000 square feet of painted structural steel. The overall length is 3,239 feet, and the width is 94 feet. The bridge is 340 feet high, from the top of the cantilever to the water below. Each cantilever span is 540 feet long. The bridge currently accommodates one rail line, three lanes of automotive traffic, and two pedestrian walkways. In 1987, it was declared a historic monument by both the Canadian and American Society of Civil Engineers, and was declared a National Historic Site in 1996, by the Department of Canadian Heritage.
The restoration of this famous bridge is scheduled to run from 1998 to 2007, and is broken up into one and two year projects for steel repairs, lead removal and application of a new coating system, and the installation of a lighting system. Team participants for the lead removal and overcoat portion include CN North America (the owner), Corrpro Canada (coatings and environmental consultants), and CH Heist (the contractor/applicator).
Environment and containment are the two main concerns of owners when considering the removal of lead-based coatings. Both imply increased costs. In addition, the bridge is over both a heavily used arterial roadway and the St. Lawrence River. The original proposal called for total removal of all old coatings by sandblasting. Original cost estimates ranged from $120 to $180 million dollars. Structural design constraints limited the amount of area which could be contained at any one time. Original costing was not within the budget available to the owner, which meant an alternative, innovative approach was required.
Waterjetting and selective watercleaning, coupled with innovative containment systems and an overcoat paint system of calcium sulfonate alkyd, were used to reduce these costs. CN North America, the Government of Canada, and the Province of Québec, have set aside $60,000,000 as the reclamation budget.
The Québec Bridge posed some unique challenges for scaffold designers. Windload restrictions made it difficult to use traditional containment materials and construction methods. Waterjetting allowed an easing of these restrictions so 'negative pressure' containment was no longer required. The lower level of environmental control required for waterjetting operations, reduced cost, and created a safer work environment for all personnel.
Environmental controls were comprised of light platforms, geotextile fabrics for water filtration and paint chip collection, lightweight solid and flow through tarps. Another design parameter was that, in the event of high winds, the containment must be able to be dropped quickly, to protect the structure from excessive wind loads. This type of flexibility is not possible with traditional negative pressure containment, as environmental constraints demand immediate removal of lead dust and abrasives.
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| Old paint is effectively removed with waterjetting. Photo - A. Beaulieu |
Waterjetting Equipment
The bridge has been divided into 'zones', requiring different levels of surface preparation. Basically, the entire upper portion of the structure will be watercleaned using water pressures of between 5,000 to 10,000 psi. These pressures are adequate to remove loose coatings, rust and other loose debris. The coating system selected is 'surface tolerant' and CN's consultants have determined that this level of surface preparation will meet their requirements. The lower surfaces of the bridge, where salt contamination has resulted in severe corrosion, are waterjetted using ultra high pressures (30,000+ psi). This level of pressure easily removes rust scale and all coatings.
As the intent of the specification was to leave tightly adhered coatings in place and to overcoat, the waterjetting removal technique is used to determine whether existing old coatings are tight or loose.
Waste Wash Water
A common misconception regarding the use of water is that it does not have to be collected or filtered. CN, Corrpro and CH Heist have worked closely with Environment Canada, to ensure there will be no damage to the adjacent Marine Aquarium, and the St. Lawrence River below.
Current Canadian regulations require that all waste wash water be captured and tested, lead and other heavy metals removed, and pH adjusted, prior to its release into the river system. The LC 50 Test Protocol, otherwise known as 'Reference Method For Determining Acute Lethality of Effluents to Rainbow Trout', requires that trout fingerlings be placed in a sample of waste wash water for a specified amount of time (96 hours). A mortality rate of less than 50% is required. A control sample is run concurrently.
In addition, CH Heist recycles and reuses its wash water, ensuring less demand on the local water supply. All platforms have been constructed so as to totally trap and contain waste wash water and debris. A containment basin under the bridge is the repository for all wash water and paint chips. Wash water is separated, filtered, and reused. Debris is separated, manifested as hazardous waste, and trucked to a disposal centre.
CN, Canadian Coast Guard and Environment Canada regulations require absolutely no waste wash water leakage.
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| Removal of lead-based coatings requires strict containment procedures to ensure environmental protection. Photo - Rob Roy |
Environmental Monitoring and Health and Safety
CH Heist took air, soil and water samples prior to start-up. Monitoring continues on a regular basis. All appropriate agencies were advised before project start-up.
In addition, all workers on site may be exposed to the hazards of lead, or other heavy metals contained in the old coating. Workers' blood lead levels are tested every two months. Lead wipes are used to check employee lunch rooms. A "Decontamination Trailer" provides workers with daily showers prior to leaving the site. A continuously monitored Health and Safety program of all workers, ensures the protection of all employees on site.
In addition to current Canadian Regulations for Worker Health and Safety, CN has decided the jobsite work environment must conform to US regulatory requirements as well. The SSPC (Society For Protective Coatings) QP1/QP2 Program is also enforced.
QP1 is a Quality Control Program. The history, the stability of staff, and financial capabilities of the contractor are assessed by an independent third party auditor. A site audit of an active job is a part of this program.
Certification to QP2 qualifies the contractor to work on US lead removal projects. The QP2 component assesses the contractor's abilities and experience in the removal and treatment of hazardous materials. This also includes an annual audit of an active lead removal project.
Corrpro is responsible for monitoring all aspects of the Quality Control, Lead Health and Safety, and Environmental aspects of the contract. Daily Quality Control checks are performed. Site inspections confirm compliance with all regulatory requirements. Weekly and monthly summaries are forwarded to CN. This documentation is reviewed by CN, to confirm compliance, but also to verify that the method of lead removal and the coating system will meet their 25-year goal.
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