(Quebec) “Why are there not more viaducts aluminum on our roads or over streams? To my knowledge, the only road bridge aluminum that exists in Quebec is located in Arvida (Saguenay) and it is an arch structure, like that of the Three Rivers Bridge. However, aluminum is resistant to corrosion, is lighter, so requires less work on the abutments, and we produced in Quebec, so it should be cheaper to buy than steel, “Luc Côté request , Quebec.
It is true that aluminum has undeniable advantages over steel. It is actually lighter: 2700 kg / m 3, it is three times lighter than steel, about 8000kg / m 3. Ductility (ability to deform without leaving break under tension) and malleability (ability to compress leave without yielding) make it easy to work, and as it naturally forms a thin stable layer of aluminum oxide to its surface, it actually is highly resistant to corrosion. It is also a particularly critical aspect in Quebec, since road salt accelerate the onset of rust, making our infrastructure age prematurely. This applies to steel structures, of course, but also for reinforced concrete structures (that is to say, reinforced by steel rods inside). Concrete, indeed, is not impervious material, contrary to what is spontaneously led to believe. It is let soak with water, and thus by the salts it transports, making rust its metal reinforcement.
In short, all kinds of steel throughout, especially in our latitudes. But then – and the crux of the problem is in part here – the aluminum is not less expensive than steel, far from it, says civil engineering professor at the University Laval Mario Fafard, a specialist structural steel. According sites following the commodity prices, the aluminum currently sells for around $ 2000-2200 per ton, against 500 to $ 600 per ton for steel …
“Aluminum is used in many aircraft because in that area, it is the weight that has the primary importance, says Fafard. The price account for much less. […] In Quebec, there is only one bridge aluminum, the bridge Arvida. He has more than 50 years, and [the time of its construction] the steel price was high, it was just after the war. But steel prices went down later and became more advantageous than aluminum, although it is heavier. ”
That said, however, the price of materials is only one aspect, though partial, what cost infrastructure. Thus, a structure that was not designed for easy maintenance can be relatively cheap to build, but prove to be a money pit later – we just dream to be convinced, at the eternal question of painting the Quebec Bridge. Similarly, a material may well be twice cheaper than its competitor, if it lasts three or four times as long, it becomes more expensive in the long run.
“We see it with concrete structures that degrade dramatically, it is necessary to put nets to prevent pieces of concrete falling. But at the time we designed for the cheapest possible [to buy], “says Fafard.
Fortunately, this approach has changed, he says. Both provincial and federal departments of transportation are now choosing projects based on construction costs and maintenance. This will certainly make aluminum more competitive.
For example, illustrates Mr. Fafard, “when designing a bridge for 75 years, we know we will redo the concrete slab once or twice, and we also know that the paving on the concrete will be to repeat most often only that; while an apron [the surface on which the cars roll] aluminum will survive 75 years without intervention. ”
We should therefore expect to see more and more “aluminum” in our infrastructure, said Mr. Fafard – and it’s already started.
The bridge deck of Saint-Ambroise, Saguenay-Lac-St-Jean, was rebuilt entirely in aluminum in 2013. “The advantage is that it’s light, so the steel beams [who support aluminum deck] may be smaller. It is more durable, too, and it’s pretty tight. Even if you put water on, there is little or no will flow underneath, so the steel beams are less rust, “says Fafard.
Moreover, he continues, “the government launched [this summer] an aluminum development strategy in which the MTQ must look at the use of aluminum in the field of bridges”. That of St. Ambrose also serve as a test bed.
However, it will be patient until the proper taxpayer enjoys widespread virtues of aluminum, warns the researcher in engineering for some reason every beast “Civil engineers do not know how to design with aluminum. I myself work in a civil engineering department, and I can tell you that our students learn to design with steel, they are taught to design with concrete, and we also design courses in lumber, even if it is minimal for now. But no teaching on aluminum. […] The only course of civil engineering on aluminum tray that I know is given at UQAC, and it is optional. Here at the UL, we hope to be able to give an optional shortly [there is already one for students at the master’s and doctoral]. But now, the way to go for this knowledge then for engineers is continuing education. ”