How is the asphalt of our highways has been tested

Comment l’asphalte de nos autoroutes a été testé

Félix Séguin

Our Office of investigation has been the analysis of samples of new asphalt applied last summer on two of the most important motorways of the Quebec autoroute 20 in Sainte-Madeleine, Montérégie, and highway 10 in Bromont, Cantons-de-l’est. We also analyze a piece of asphalt to the entrance of a residential building in Saint-Lambert, on Montreal’s South Shore, to see if the product laid on a highway is really more resistant. The experts of the École de technologie supérieure in Montreal have determined that the asphalt from the two motorways was of acceptable quality.

The analysis by the experts

Using a needle, Francis Bilodeau, École de technologie supérieure, calculates the rate of penetration of the bitumen heated to 25 °C.

The technician Sylvain Bibeau shows one of the sieve used to calculate the size of the aggregates contained in the asphalt mix.

1. The sample of road is first broken up into large pieces.

2. It is then placed in an oven at 540 °C (1004 °F).

3. It is clear of stones, bitumen has been completely burned. It is thus that one can know the percentage of bitumen.


  • % of bitumen in the asphalt : bitumen binds the aggregates (rocks) between them in the mixture of asphalt mix. If there is a lack of bitumen, the asphalt crumbles more quickly. Conversely, if there is too much, it may cause rutting on the pavement.
  • Granulometry : Size of the rocks (aggregate) in the mixture. A certain variety of sizes of rocks is necessary for it to perform correctly. The percentage represents the amount of rocks that passes through different types of sieves.
  • Shear on asphalt : the Higher the temperature is, the higher the mix is going to withstand temperatures hot enough before you warp or crack.
  • % penetration at 25 °C : Number of millimeters that a needle penetrates into the bitumen heated to 25 °C. If the needle sinks too much, this may suggest issues of sustainability.

The results

Highway 20 : meets the standards

▶ % of bitumen in the asphalt mix : 5,40 %

▶ Size : 8,6 % to 0.08 mm, 57 % at 5 mm, and 92 % at 10 mm

▶ Shear on bitumen : 93,2 °C

▶ % of penetration at 25 degrees °C : 26 mm

Highway 10 : meets the standards

▶ % of bitumen in the asphalt mix : 5,62 %

▶ Size : 8.7% to 0.08 mm, 47 % at 5 mm, 95% at 10 mm

▶ Shear on bitumen : 81,7 °C

▶ % of penetration at 25 °C : 48 mm


The asphalt installed on the entrance to a building of condos is less resistant than that imposed on the two highways. The logic is respected, because it is not designed to support a volume of traffic too high.

▶ % of bitumen in the asphalt mix : 5,62 %

▶ Size : 6.6 per cent to 0.08 mm, 66 % at 5 mm, 98 % at 10 mm

▶ Shear on bitumen : 66,6 °C

▶ % of penetration at 25 °C : 74 mm

Some ways to improve our roads

Our Bureau of investigation has asked three questions to professor Alan Carter about the state of our roads. Here are his comments.

What is the problem with our roads in Quebec ?

The climate does not explain all the problems of the roads, as many argue. Some pavements have been constructed for a period of 15 years, but it’s been over 50 years that they are being used. It is therefore normal that they are in a poor state. In redoing completely the route, including the infrastructure underneath it, there’s a way to make roads that will last a long time.

The recycled asphalt pavement, a good idea or a bad idea ?

The asphalt can be recycled as many times as you want. It all depends on the government or the city with which we are working. The ministry of Transport, we are talking about a maximum of 20 % in the base layer. It has even been shown that 40 % of asphalt is recycled, it had been coated were better than a wrapped normal nine. The one thing you must be careful with the coated recycled, it is the thermal cracking, that is to say the low temperature. Just take a new bitumen which is soft and which will compensate for the stiffness of the bitumen to be recycled.

Is this normal to have potholes, including on highways ?

The potholes should not exist. A pothole, it is a terminal phase. To be made to the pothole, there must have been a cracking caused by too much traffic, the traffic is too heavy, too many cycles of freezing and thawing, poor accounting between the bitumen and the aggregate, a wrong formula or a wrong set up. There are plenty of possible reasons. If it has potholes, is that we have not done the maintenance work that we would have had to do.

– Éric Yvan Lemay

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