What is asphalt?

Asphalt is a mixture of aggregates (crushed rock, sand, gravel or slag), binder and filler materials, which is used for constructing and maintaining roads as well as car parks, pavements, runways, play areas and so on.

Is asphalt black because it contains tar?

Tar is a potentially hazardous material and hasn’t been used in asphalt production since the 1980s. Today’s choice is bitumen, an inert material derived from crude oil that allows asphalt to be recycled or reused at the end of its life.

What are the benefits of using Warm Mix Asphalts (WMAs)?

WMAs are manufactured and laid at lower temperatures than traditional asphalts, using less energy to deliver carbon savings without compromising performance. Their use can reduce the CO2 emissions associated with asphalt production for road laying, maintenance and construction by up to 15 per cent.

WMAs also offer workforce health and safety benefits over traditional hot mix asphalts and help to deliver time and cost savings as less time is required to cool to trafficking temperatures. This allows works to be completed sooner and carriageways to re-open earlier, minimising disruption for road users while increasing productivity. A full report on WMA can be found here.

Why don’t we use concrete to surface our roads in the UK?

Over 95% of roads in the UK – and indeed the majority of the world’s roads – are surfaced with asphalt.  It is the number one choice as it offers good performance, even under the most heavily trafficked conditions and it is smooth, durable, safe and quiet.

Is asphalt sustainable?

Yes, absolutely. Asphalt itself is 100% recyclable and the industry is working hard to incorporate more recycled material into new asphalts as well as developing technologies to cut the carbon emissions associated with production.

What is surface dressing?

Surface dressing involves spraying bitumen onto a road surface and applying chippings, which are then rolled in. It doesn’t add any strength to the road but restores skid resistance and seals the road surface to prevent water ingress and, potentially, the formation of potholes.

Why do potholes form?

The primary cause of potholes is water and the changing meteorological conditions we are experiencing are set to make the issue worse.

Water penetrates cracks and crevices within the road surface and, in time, this undermines the entire structure of the road. The risk is particularly acute during the winter months. Standing water – and water within the road surface – freezes and expands as temperatures drop, causing the road surface to rupture and potholes to form rapidly as traffic drives over the weakened areas.

This is a particular issue for poorly maintained roads, which are less resilient and cannot withstand the combination of severe weather and increased traffic. The most efficient way to deal with the problem of failing roads is to fix them properly and stop potholes forming in the first place.

How much does it cost to fill a pothole?

The cost varies across the country and also depends on whether the pothole is filled as part of a planned programme of carriageway repairs or as a reactive repair. The results of the 2022 ALARM survey demonstrated a considerable disparity in costs, with planned works costing an average of 35% less than reactive repairs in England (£46 planned; £71 reactive); 57% less in Wales (£45 planned; £105 reactive) and 37% less in London (£55 planned; £87 reactive). When looking for an average cost, £63 per pothole is an acceptable average across England and Wales.

Why, in periods of prolonged hot weather, do roads appear to melt?

During period of prolonged hot weather the bitumen binder used in asphalt can soften and appear to ‘melt’. This is because bitumen is a very complex material and can show both solid and liquid behaviour at the same time, depending on the temperature and type of traffic it is exposed to. The higher the temperature and the slower and heavier the traffic, the more the liquid behaviour will tend to take charge. Conversely, the lower the temperature and the faster the traffic, the more the solid type of behaviour will take over.

Engineers will specify bitumen grades known to perform across the expected temperature and traffic range. However, each grade has its limitations and these can occasionally be exceeded in extreme conditions.

Innovation has led to the development of polymer modified products that bring extra resilience to extremes of weather and traffic capacity.