As the mercury rises this summer, you wouldn't be the only one surprised to see winter gritters out on the roads, and wonder what on earth is going on.
In fact, summer surface gritting is more common than you might think - they're busy spreading grit over very hot tarmac, as this keeps roads safe and stops the tarmac melting in summer!
Road Tarmac Melts!
When the sun is out, the tar on the roads becomes much softer than usual, which alters the way drivers use our roads and has safety implications for motorists.
The outside temperature only needs to be in the high 20s - this can be enough for the roads to reach 50C, since dark asphalt absorbs heat and will steadily rise in temperature throughout the day.
This then also results in roads becoming sticky and more vulnerable to pressure from heavy vehicles, as well as the tarmac eventually brittling up and possibly leading to potholes.
The image above shows what happened in a UK village road in early summer 2020, with the mercury at only 28 degrees.
Surface Gritting Road Tarmac
Hot road tarmac is typically surface gritted using one of two methods, salt or crushed rock.
Gritting salt works by attracting the moisture from the air which cools the asphalt of the road surface.
Gritting salt also removes excess moisture from the asphalt itself making it less sticky.
The disadvantage of gritting salt however, is that it can have a bad effect on older vehicles, as the salt granules can chip into the paint.
the other option is to surface grit roads in summer using a dust layer of ground stone.
The dust layer ends up absorbed into the soft bitumen, which stabilizes the surface of the road and ensures that motorists can drive safely.
Different councils and countries adopt different methods: European countries and various councils use salt, but most British operators tend to spread a crushed rock dust layer to help protect cars.
Monitoring Road Temperatures
The GRITIT weather centre monitors road temperatures throughout the nation 24/7.
We've observed that road temperatures often reach the critical mark when proactive summer gritting is beneficial to the motorists using the roads.
In our laboratory tests, some road surface material can withstand temperatures of up to 40 degrees Celsius, but during a period of heat the temperature can go as high as 55 degrees Celsius, which is when tarmac plasticization can occur.
Road and asphalt technology is continuously evolving however, and as the future with a hotter climate beckons, there is much to be learned and adopted from countries in hotter parts of the world.
Recent Summer Surface Gritting
In the record-breaking summer of 2018, summer surface gritters were out in Scotland, Cumbria, Lancashire, Doncaster and Hampshire together with many parts of the continent, notably The Netherlands.
In 2019, the scorcher month of July brought out the gritters again.
According to RAC Breakdown spokesman Rod Dennis:
"The sweltering heat will lead to some softer road surfaces over the next few days. If you see some blacker patches of road or pavement, that's how you can tell it's starting to melt. It also means that drivers might start to see something that they’d normally only associate with the depths of winter – gritting trucks. Salt can help improve the grip on roads that are starting melt."
Dave Rigby, chief technical officer at the RSTA (Road Surface Treatments Association), said:
"During very hot weather roads could reach 50C at the surface and at these temperatures can start to soften. Dark asphalt on the road surfaces absorbs a lot of heat and is like chocolate, it melts when it is hot and goes brittle when it cools down. I would not be surprised to see gritters out over the next couple of days, they are used to spread dust and sand which absorbs the soft bitumen stabilising the road surface and making it less sticky."
The 2020 summer season is underway, and even a few hot days have already brought out the surface gritters in the villages of Surrey!
In summary, gritting isn't just a sight that you can expect in winter, but as temperatures increase due to climate change, the sight of gritters working the UK summer might not be such an unusual scene.