The Ultimate Asphalt Guide

Asphalt is a composite material which is predominantly made up of aggregates and bitumen.

The aggregates comprise crushed stone, sand and gravel that is bound together with bitumen at high temperatures to form asphalt.

There are up to three layers of asphalt in the typical construction of a pavement. The lower layer is the base which sits on top of a sub-base and provides the main load-bearing for the road.

The layer above is binder course, approximately 50-90mm thick, which is a load bearing layer designed to distribute the load from the surfacing into the base course thus avoiding deformation. It is also used as a levelling course.

The uppermost layer is the surface course, which is approximately 25-50mm thick and provides an even, skid-resistant and waterproof surface.

Typically, the aggregate size decreases as you move up through the construction from the base to the surface course, whilst the bitumen content increases.

As we collectively move towards Net Zero, the production of asphalt has evolved to adopt greener techniques for production.

Asphalt is one of the most sustainable construction materials, as we can use construction waste and recycled asphalt planing (known as RAP – whereby the recycled road surface is put back into the production process) as replacement aggregates.

This is effectively put into practice throughout the road construction industry. We also optimise the use of RAP in new cold asphalt innovations.

We can also adapt the manufacturing method to reduce the carbon footprint of the product, and therefore the entire project. There are three key production methods:

Hot Mix Asphalt (HMA)
HMA is traditionally made at a high temperature ranging between 140-190⁰C.

Warm Mix Asphalt (WMA)
Mixed at temperatures 20° to 40°C lower than HMA, Warm Mix Asphalt is the greener choice as it requires significantly less energy during manufacturing and therefore releases less emissions.

WMA is also considered safer for construction crews as the temperature of the material is lower and it thereby emits minimal odour and steam.

All of our WMA are tested to meet industry specifications and are suitable for the same applications as HMAs, without compromising performance.

Cold Mix Asphalt (CMA)
Most useful for repairs and maintenance of small cracks, potholes or patching of existing pavements, Cold Mix Asphalt is produced without any heat and, instead, water is used for emulsification.

To go one step further, we’ve also developed other ways to reduce embodied carbon during the manufacturing process and have launched our SuperLow-Carbon range, which includes a biogenic substitution within the bitumen that effectively locks carbon within the asphalt.

Essentially asphalt and tarmac are the same product.

Back in time when tar was produced as a bi-product of coke production, tar was the primary binding agent for asphalt mixtures.

Since the association of tar as a potential carcinogenic substance, bitumen derived from oil distillation has become the default binder type and they have very similar appearance and properties.

Since the late 1980s and early 1990s, tar has ceased to be used in the production of asphalt, as it is considered hazardous.

Asphalt is cost-effective, low maintenance and extremely durable, making it an ideal road surfacing material. It is a popular choice because:

• It is fast to construct
• It can withstand significant weight and temperature fluctuations
• It is easy to maintain and repair
• It produces a smooth surface for maximum tire grip
• It reduces noise pollution
• It rapidly disperses surface water, reducing spray, the risk of aquaplaning and improving visibility for drivers
• It increases the visibility of road markings

Concrete is a stiffer mix with less flexibility, but it is more prone to cracking than asphalt.

Asphalt is also more flexible, skid resistant, quiet, cost-effective and quicker to install, but all depends on the intended application.

Yes, coloured asphalt is used frequently, from creating playground surfaces for children, demarcation for cycleways, bus lanes and residential roads, to places requiring additional safety, i.e. nearby to schools.