Guildford, Surrey - Sunflower oil is being used to to prevent potholes by helping to fill cracks in the road.
British roads authority Highways England is carrying out the unusual trial after sunflower oil capsules were found to make roads "self heal" when added to tar. It costs more than £88 million (R1.6 billion) a year to fill in the potholes in England’s roads, making the cooking oil - which costs around R20 a litre - a cheap solution.
The capsules work by making bitumen, a sticky black substance used in road surfacing, thinner so that it flows more easily into cracks before they form dangerous potholes. By adding them to tar, the capsules can remain in a road for many years - breaking open only when the build-up of traffic pressure reaches the point where it causes cracks.
Researchers say the oil, which "sticks" the tar back together, could increase a road’s lifespan by at least a third, from 12 to 16 years, and mean roads wouldn't have to be closed for repairs. Engineers at Nottingham University found the capsules do not make road surfaces more slippery or less durable.
Real-world test
Highways England, which funded the research, will add 18.5 litres of sunflower oil to five tons of tar along a five-metre stretch of new road and, if the test proves a success, the scheme could be rolled out across the road network within five years. Initial tests of the 2.9mm oil capsules will be on carefully selected patches of road, which would be monitored for one to two years before a second test on a longer stretch.
It would take 82 000 tones of cooking oil to cover the entire British road network.
Dr Alvaro Garcia of Nottingham University’s engineering department said: "You could use any oil - although sunflower oil is very cheap. This solution allows roads to repair their own cracks of up to half a millimetre wide in a matter of hours."
Weight of traffic
Potholes form after sunshine causes roads to swell, before night-time temperatures fall and they contract. The weight of traffic as this happens causes cracks to form, which become larger due to rainwater. Bitumen, which is found in tar, can fill these cracks - but it takes up to three days, and only works when a road has no traffic.
Sunflower oil speeds this process up to four hours by making bitumen less viscous. It is expected to do so even with traffic on the road. Dr Garcia was inspired by a Spanish cooking show that "spherified" oil.