Why Asphalt?
In the UK asphalt is the generic name for all road construction and maintenance materials which are produced by mixing bitumen with various aggregates. The adhesive and waterproofing properties of bitumen, which is refined from crude oil, make it ideal for binding the aggregate together to produce the strong, flexible and durable material needed to construct and maintain modern roads.
Roads have been built with asphalt since the 1870s. The fact that over 95 per cent of all UK roads are asphalt testifies to the material's inherent qualities of flexibility, efficiency of construction, riding comfort, ease of maintenance and value for money.
The structure of a road comprises several layers and asphalt is widely used to form the structural layers or courses.
Different mixes of bitumen and aggregate are used to produce the main types of asphalt - bitumen macadams, thin surfacings, hot rolled asphalt, stone mastic asphalt, and cold-mix macadams used in road surfacing and basecourses.
KINDS OF ASPHALT
According to the Transport Research Laboratory (TRL) road surfacing materials should be:
- of an even, smooth profile for comfort and low operating costs
- able to provide sufficient skid resistance at all speeds and in all weather conditions
- quiet, glare-free and spray-free
- durable
- economical to lay and maintain
- capable of being re-used or recycled
- Asphalt surfacings meet all these criteria.
There is a wide variety of proprietary asphalts available in the UK each designed to provide specific benefits. Modified asphalts are developed to meet the specific needs of individual locations or uses. The main generic categories of asphalt are:
Hot Rolled Asphalt (HRA)
Hot rolled asphalt has been used in the UK for nearly 100 years and is the most common surface on the country's road network. With high polished-stone-value pre-coated chippings applied, it has helped to make the UK network the safest in the EU.
Stone Mastic Asphalt (SMA)
Developed in Germany and Scandinavia, stone mastic asphalt is now widely used in
the UK. It has a high resistance to rutting and is extremely durable. SMA has good spray
and traffic-noise-reducing properties.
Thin Surfacings
Thin surfacings represent one of the most significant developments in asphalt in recent years. As their name suggests, they are thin layers, usually between 20-40mm, compared
with traditional wearing course thicknesses of around 30-50mm, and provide good surface
texture and high-quality riding surfaces. They have important cost benefits as they are quick to lay, thus cutting maintenance programme times. In addition, they contribute significantly to the reduction of spray and traffic noise.