The Met Office has confirmed the heatwave that started on 7 August 2020 broke records in terms of maximum temperatures reached and duration. One striking effect was that some roads melted like chocolate, resulting in ridges, ruts and other permanent damage.
Roads will generally stay solid up to about 50C, which sounds sufficient as the air temperature never rises that high. However, the dark road surface absorbs sunlight and gradually heats up during the afternoon. A sunny day in the high 20Cs can be enough to soften tarmac but this depends very much on the exact angle to the sun and the wind conditions.
When roads did melt, some local authorities responded by sending out gritters. While these might be a surprising sight in summer, they were loaded with granite dust to make the soft bitumen less sticky and more stable.
The industry introduced a new standard for surface material, adding polymer modified binders to the hot asphalt, in response to the 1995 heatwave. These additives help the material resist temperatures up to 80C. However, they are expensive and are used only on the busiest roads.
One simpler solution may be a dressing of polymer binders added to the surface of vulnerable roads to help prevent future melting.
