Aluminum road bridges are more durable than concrete ones. However, Canada has only two: in Arvida and Saint-Ambroise. In order to demonstrate the enviable properties of steel beams and aluminum running surfaces, a bridge will soon be tested in the Montmorency forest for two years.
The forest is perfect for the occasion: altitude, temperatures that can reach -40 degrees Celsius, five to six meters of snow in winter, high humidity. “We are going to take thermal expansion measurements, because all material contracts when cold and expands when hot,” explains Mario Fafard, consultant at the Aluminum Center of Expertise and Innovation. Since aluminum shrinks twice as much as steel, we want to make sure that doesn’t cause a problem. »
As the decking (running surface) will be made of multiple welded aluminum extrusions and welding decreases the strength of the aluminum, measures will be taken on this as well. “We will run vehicles at low and high speeds, at different temperatures, to assess the behaviors of the bridge,” he says.
These tests are necessary even though Arvida’s aluminum bridge is already 72 years old. “Its decking is made of assembled plates. It’s a different technology. »
Why not before?
The first iron bridge was designed in 1779. Almost 60 years passed before a concrete bridge was created. Aluminum became accessible at the end of the 19th century.e century, but at a high price. “Engineers are trained to design road bridges that combine concrete and steel,” underlines Mr. Fafard.
Struggling with aluminum surpluses after the Second World War, the American company Alcoa and the Canadian Alcan (today in the bosom of Rio Tinto) eyed the infrastructures. Alcoa designed a railway bridge in 1946, which is still in operation. Alcan designed a road bridge in Arvida in 1950.
Since then, there has been no breakage. That tells us that aluminum is durable.
Mario Fafard, consultant at the Aluminum Expertise and Innovation Center
For steel-concrete bridges, the Canadian standard provides for a minimum duration of 75 years. “We must intervene at least 10 times on the slab during the first 50 years and then replace it. »
At year zero, steel-concrete bridges cost less than steel-aluminum ones. However, studies show that they will cost three times less since they require little maintenance.
So why favor the steel-concrete alloy? “The Ministry of Transport is careful with the choice of materials, because it must ensure that the structure does not endanger anyone. It takes time to confirm some things. We must give confidence to the Ministry, cities and engineers to encourage them to design structures with aluminum. »
In addition to accumulating data thanks to the Montmorency Forest bridge, aluminum supporters will have to demonstrate the ability to supply extrusions and the presence of qualified manufacturers to weld them. “Within two or three years, we should see in the habits and customs of the Ministère des Transports calls for tenders including aluminum. »