Impact of record-breaking heat on road surfaces

Asphalt Industry alliance explains why, on a hot day, it can appear that the road surface is melting

ON the day of the highest-ever recorded temperatures in the UK [19 July], many have been left wondering why, on a hot day, does it appear that the road surface is melting?

Rick Green, chair of the Asphalt Industry Alliance (AIA), explained: ‘In order to perform well across all seasons, an asphalt road must be able to cope with the extremes of road surface temperature we might see, which, in the UK, can range from +60°C to –20°C; a significant challenge for design engineers.

‘In extremely high temperatures the road surface doesn’t ‘melt’ but the bitumen in it can soften and the material particles become more ‘mobile’. The effect is most exaggerated on south-facing gradients but is usually limited to the top surface and doesn’t generally affect the structural integrity of the road. However, in prolonged periods of hot weather where the road is exposed to slow-moving or stationary heavy traffic, the risk of permanent deformation of the surface increases.

‘Ongoing research in modern road-building materials is continuing to build both resilience and flexibility into the network, improving their performance across a wider temperature range. But in a climate of increasing costs, as well as temperatures, and against a backdrop of constrained or reducing budgets, highway authorities face even more challenges to future-proof their assets.’