20 February 2025

Bitu­minous bleed­ing during winter – what can be done?

Fluctuations in weather, with alternating freezes and thaws, and heavy traffic, not least heavy goods vehicles, are considered the main causes of winter bleeding. Moisture and wetness accumulate in the subgrade during these temperature fluctuations while the lower layers of the road structure are still frozen. When the load from vehicle tires on the pavement in these conditions, the water that has accumulated in the subgrade has no other way to escape than up through the pavement.

When the water is forced up through the pavement, it takes the bitumen from the pavement with it, which then sticks to the tires. The bitumen is sticky and also absorbs anti-slip agents that may be on the road surface, such as salt, and loose gravel that is on the road. This increases the volume significantly and forms large bitumen blocks that spread across the road surface.

Old subgrades that have lost their bearing capacity are very rich in fines and do not contain antifreeze material. This means that these old subgrades are much more likely to collect water than new ones, and thus are more likely to experience winter bleeding.

Minor winter bleeding is a known problem on paved roads, but extensive winter bleeding has fortunately not been common over time, but it is serious when it does occur. Serious damage can occur to vehicles and accidents to people in the worst cases, but fortunately most damage is in the form of cleaning tires and vehicle chassis, but it is recommended to seek advice from professionals in this regard.

About six thousand kilometers of the Icelandic Road Administration’s almost 13 thousand kilometers of road network have a paved surface. About 90 percent of the paved surface is pavement and 10 percent asphalt, but it would need to be much more considering the load on the roads. It should be noted that asphalt is about five times more expensive than pavement.

When winter snowmelt begins, attempts are made to minimize damage by:​

• Limiting axle loads when conditions are considered to be likely to cause snowmelt​
• Temporarily reducing the maximum permitted speed while the condition in question lasts​
• Temporarily diverting traffic to bypass routes​
• Closing roads

When there is a risk of winter snowmelt, the likelihood of damage can be reduced by:​

• Limiting axle loads when conditions are considered to be likely to cause snowmelt​
• Temporarily diverting traffic to bypass routes​

Preventive methods to combat winter bleeding:

• Strengthen the road’s subgrade
• Milling/attaching older pavement layers to reduce the total amount of bitumen in the cross-section.
• Asphalting roads rather than covering them

What is the difference between winter and summer bleeding?

Winter bleeding is of a different nature than so-called summer bleeding. The problem is that the excess pavement on roads heats up a lot on sunny summer days, when the temperature can reach 50-60 degrees. Under these conditions, the stones of the pavement, which are usually on top, can sink into the bitumen under the pressure of traffic. The bitumen will therefore remain on the surface of the pavement and settle on tires.

What is surfacing and why is it used?

Surfacing is a bonded pavement that is much cheaper than asphalt. It is quick to lay and does not require a mixing plant. During laying, minerals are spread on top of the binder, which is diluted bitumen with solvent, water and bio-oil. After the surfacing is laid on the road, it is swept after a certain time. Surfacing can withstand up to 2-3 thousand cars ÁDU (traffic per day) and is economical when it is well managed. Surfacing is less suitable for higher traffic volumes, especially if there is a lot of heavy traffic.

What is asphalt?

Asphalt is a mixture of minerals, bitumen and sometimes other materials. The weight ratio is 94-95% minerals and about 5-6% bitumen. Asphalt is mixed at mixing stations. The minerals are dried at a temperature of about 150-160°C and hot, thin-flowing bitumen is mixed in with additives. The mixture is transported hot and laid in a layer about 35-55 mm thick with a special paving machine. It is then rolled over until the required compaction is achieved. Asphalt roads can withstand much more and heavier traffic than paved roads, but asphalt is five times more expensive than paved roads, as stated above.