Are we going to change the type of asphalt on the streets because of climate change?
Jean Pellerin
Yes, but in Canada, this may not be enough to avoid roads that are more potholed than before.
“With climate change, we must have bitumens that resist higher temperatures, but we must maintain resistance to the coldest temperatures,” explains Alan Carter, an asphalt engineer at the École de Technologie Supérieure ( ETS). “So the asphalt is going to have to withstand a wider range of temperatures. It will easily be 20% to 30% more expensive. »
As we saw last winter, climate change will also be accompanied by sudden warming in winter.
PHOTO TAKEN FROM THE ETS SITE
Alan Carter, asphalt engineer at ETS
We’re going to have more freeze and thaw cycles. It affects the durability of the asphalt. And at the moment, we don’t have tools to quantify durability based on the number of freeze-thaw cycles.
Alan Carter, asphalt engineer at ETS
Asphalt is made up of 95% stone granules and 5% bitumen, a heavy residue from petroleum. “Rocks don’t care about climate change,” says Mr. Carter. They get hotter, colder, that’s all. The temperature affects the glue, the bitumen. »
Asphalt is characterized by a “performance index” (PG) which indicates the maximum and minimum temperature it can withstand. In southern Quebec, you need PG 58-34, which means it can withstand temperatures ranging from -34 to 58 degrees Celsius.
PHOTO FROM INDIANA DEPARTMENT OF TRANSPORTATION SITE
Rutting caused by exceeding the maximum temperature of the asphalt performance index.
Thermal tank
“The ground is a thermal reservoir,” explains the ETS engineer. So, it will heat up more on the surface than the air, because it cools less during the night. And in winter, the heat from deep in the ground will temper the surface temperature of the asphalt. »
When it’s hot, asphalt expands and when it’s cold, it contracts. This creates a movement which can create cracks if the PG is exceeded. “And there is a limit to the number of hot-cold thermal cycles that asphalt can withstand. Afterwards, it becomes less elastic and cracks appear during too sudden temperature changes. »
As there are more sudden increases and drops in temperature, particularly in winter, work is being done to develop an index that would measure the ability to withstand more or fewer temperature cycles.
Alan Carter, asphalt engineer at ETS
These winter temperature changes explain why our roads are more cracked than in France, for example, according to Mr. Carter. “Climate change will bring winters that are less harsh on average, but with more temperature changes. So ultimately, it’s going to be harder on the asphalt. »
Exceeding the maximum PG temperature creates ruts. For temperatures below the PG minimum, thermal cracks appear perpendicular to the direction of circulation. They occur at intervals corresponding to the width of the street. For a 1 kilometer street that is 20 meters wide, there will therefore be 50 cracks separated by 20 meters each.
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- 77.4%
- Proportion of roadways under provincial responsibility in Quebec that were in good condition in 2022. In 2006, this proportion was 63.2%.
SOURCE: Transport and Sustainable Mobility Quebec