Is it surprising that we are urgently closing a metro station?
It doesn’t surprise me any more if they saw that the condition of the beams was deteriorated. An assessment must be done before people can be readmitted. It must be understood that these are reinforced concrete structures and that there are two components: the concrete and the reinforcements. Without the steel reinforcement, the concrete has almost no strength to act as a beam. They play a vital role. They are what provide most of the resistance.
When de-icing salt, water and air enter, they act as a catalyst to initiate and promote corrosion of the reinforcement. Depending on the level of corrosion, the safety of the beam, or its ability to carry loads, may be reduced significantly, so it may pose a greater risk of collapse than is acceptable.
It is well known that de-icing salt damages structures…
Yes ! Look at the Champlain Bridge, which lasted barely 50 years and which was dismantled. It’s the same problem: there was de-icing salt, there wasn’t even a protective membrane, and it got into the concrete. It went to attack the frames. It was in the 1990s that we started to install membranes and think more about lifespan in relation to corrosion.
Are all metro stations at risk?
I would not say that all stations are at risk, but measures must be taken to avoid deterioration. Right now, they must be checking to what extent the structures have been degraded. [à la station Saint-Michel]. Normally there are regular inspections, like bridges. These metro stations are like buried bridges. They hold the ground and all the installations above it. The blue line was built in the 1980s, so over time, even if there were means of protection, water ends up entering.
Is it visible to the naked eye?
I don’t know about this specific situation, but if these were visible parts, it would have been noticed. Rust shows up. These are probably hidden parts. This is why this kind of structure, when you design them, you organize yourself so that the sensitive parts are easy to inspect.
Are there any alternatives to de-icing salt?
[En riant] We’re having a bit of a harsh winter! There is research, alternative products that we are trying to develop to replace salt and which would be more gentle on corrosion. But there is no cheap enough substitute. This is a big problem also for garage structures, where cars come with snow and salt.
For modern structures, we take measures to delay and prevent corrosion: we install waterproofing membranes, we drain the water quickly. We will also put more concrete coating around the reinforcements to delay the moment when they are attacked. We even have models to calculate the lifespan of a structure, to calculate how long it takes for the steel to start to corrode. The more modern the structure, the better it is designed.
Could we say that it is easier to maintain the metro in a milder climate than ours?
Quite. In places like Greece and Italy, structures can last longer. They do not have the same constraints.
The remarks in this interview have been edited for brevity.
De-icing salt often blamed
It is not only the Saint-Michel metro station that has suffered damage caused by de-icing salt over the years. The most infamous example is undoubtedly the Champlain Bridge, which, built at the turn of the 1960s, gave up the ghost in particular because of the de-icing salt which caused the steel frames to rust. In 2015, hundreds of residents in the Villeray–Saint-Michel–Parc-Extension district were flooded after the rupture of a pipe passing under Pie-IX Boulevard. De-icing salt was then singled out, just as it was in part last August, when the rupture of a huge water pipe created an impressive geyser at the foot of the Jacques-Cartier Bridge. , in Montreal.