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28 June 2017

Councils Relying on Granite Dust to Prevent Road Surface Melting as Temperatures Soar

The hot weather experienced throughout the UK over recent weeks hasn’t come without its drawbacks. Sure we’ve all enjoyed relaxing in the sun and soaking up a few rays over the weekend but the heat can cause a wide variety of issues in terms of our health and the environment, affecting features both natural and man-made.

Img: Flickr/brownpau
For example, the Road Surface Treatments Association (RSTA) state that many of the nation’s roads have simply been unable to cope with the dramatic spike in temperatures, resulting in the surfaces of such roads behaving more like chocolate than tarmac, melting into a messy puddle as more and more heat is absorbed and heavy vehicles put additional strain on the now-compromised surface.

The reason for this is that high temperatures above 50°C can cause the bitumen contained within to rise to the surface as it melts. This makes the road somewhat sticky and malleable, which results in surface ridging and rutting as heavy vehicles put high pressure loads on the road. Although 50°C may seem like quite a high threshold, the ambient temperature need never rise so high for surface temperatures to exceed this limit; in fact, outside temperatures just above 20°C can be enough to raise surface temperatures beyond this upper limit as the dark asphalt absorbs high levels of heat.

The solution to this issue now being deployed by many town & city councils is the use of gritter trucks to spread fine granite dust across the road surface, which absorbs into the asphalt and thereby stabilises the surface. It also reduces its susceptibility to further melting and strengthens it against heavy pressure loads. Using this technique, the damaging effects of excess heat can be counteracted, at least to some extent.

RSTA chief executive Howard Robinson commented, “Drivers may be bemused to see the gritters out in the summer when they are usually spreading grit and salt during the winter. However, this is effective standard practice for keeping a road surface safe during extreme hot temperatures.

“Asphalt is like chocolate – it melts and softens when it’s hot, and goes hard and brittle when it’s cold – it doesn’t maintain the same strength all year round.

“Melting of some roads is not surprising during this heatwave but they can be quickly treated and revert back to normal once temperatures decline.”

It is worth noting however that some roads are performing better than others, and the key lies in their composition. Following a heatwave which occurred in 1995 and caused similar problems throughout the country, the industry introduced new specifications which included the use of polymer modified binders in asphalt mixtures. This modified form of asphalt has a higher road surface softening point, able to endure temperatures reaching as high as 80°C. However, according to Mr Robinson, such techniques are only employed on around 5% of UK roads, largely due to the high cost associated with modified asphalts.

Hopefully in the future these modified asphalts will see more widespread use and such issues can be avoided, but for now at least, granite dust seems to be the best solution on offer.

Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.