B2 - Asphalt Concrete
Asphalt concrete has the characteristics of the mixtures that used to be known as bitumen macadam.
Bituminous mixtures have four components — coarse aggregate, fine aggregate, filler and bitumen. The difference between the many bituminous mixtures produced in the UK is based on the proportions of these four components.
In general terms, just over half of an asphalt concrete mixture is coarse aggregate — the aggregate retained on a 4mm size test sieve. Slightly less than half is fine aggregate passing a 4mm size test sieve. The remainder of the mixture consists of small and almost equal percentages of filler and bitumen.
Mixtures with the largest coarse aggregate size have a lowest proportion of bitumen. The maximum size of the coarse aggregate varies according to the intended use of the mixture: 32mm is the largest size, 4mm is the smallest.
Asphalt concretes are continuously-graded mixtures. There is a proportion of every aggregate fraction within the mixture.
Full details are given in:
- BS Guidance: PD 6691, Asphalt - Guidance on the use of BS EN 13108 Bituminous Mixtures, Material specifications
- Standard: BS EN 13108-1, Bituminous mixtures – material specifications. Part 1: Asphalt concrete
BS EN 13108-1 replaced:
- BS 4987-1 Coated macadam (asphalt concrete) for roads and other paved areas. Part 1: Specification for constituent materials and asphalt mixtures
The BS EN 13108 Standards present a menu of specification requirements from which individual specifications can be selected. Not all of the requirements in the Standard are appropriate to UK applications. The guidance in PD 6691 is important.
