Asphalt Material Types
Common Asphalt material types
Asphalt – The umbrella term used to describe the many different bituminous mixes available for use within the road & construction industry.
Bitumen, (refined from crude oil) is mixed together with aggregate, (generally crushed rock and or sand) to form a homogenous mixture which is referred to as asphalt.
These mixes may be modified to improve or alter the performance of the materials by adding fibre, polymers or indeed selecting a different bitumen grade which can affect the stiffness of the mixture and other Asphaltic properties such as softening point or penetration.
Bituminous materials are thermoplastic. This means that they are soft and workable when heat is applied but solidify when cool. As a result, this makes these materials ideally placed to install over a short period of time and therefore have an advantage over cementitious products which need to cure over several weeks.
Asphalt Concrete - AC, (previously known as macadams) as specified in BS EN 13108: 1 These are probably the most common asphalt materials used on the British road network. Materials such as AC 20 dense binder or AC 10 Close surface course achieve their structural strength from the aggregate interlock obtained from a smooth grading curve where open graded materials like AC 10 open trade the strength properties for more gap graded which can help with drainage solutions etc.
Hot Rolled Asphalt – HRA which is specified in BS EN 13108: 4 This is almost only found in the U.K. and is predominately used on high speed or major roads. HRA is a gap graded material which uses a stiffer binder in conjunction with a large amount of fine aggregate to provide a durable weather resistant mastic surfacing mixture. To achieve a good surface texture pre coated high PSV chippings may be rolled into the material before cooling.
Stone Mastic Asphalt- SMA was developed in Germany during the 1960’s and has partly replaced or become an alternative to the traditionally used HRA. As specified in BS EN 13108:5, SMA is a gap graded material which obtains its strength and impressive rutting resistance from the high binder content and usually has the addition of cellulose fibres to stop the binder from draining or fatting up.
Proprietary Mixes – These are usually variations on the aforementioned AC, HRA & SMA mixes. They are performance designed mixes which have been modified to enhance a certain property or properties. For Example. more rut resistant, higher softening point or specified texture depth level. examples of these are Viatex, Viacourse, Viamain – See CEMEX materials.