Standard asphalt mixtures used in pavement layers

All asphalts used in the UK have basic requirements for composition and constituent materials (i.e. aggregate types and gradings, and bitumen types and contents). Where these requirements form the essence of the specifications, they are described as recipe-type specifications. Some asphalts have additional performance-related requirements that require laboratory tests, and these asphalts are referred to as having design-based specifications. However, both the recipe-type and design-based specifications are empirical specifications based on observation and experience.

The discussion in this chapter is focused on describing the specifications of standard mixes. (The concepts relating to the design of bituminous mixes are described in Chapter 13.) Before discussing the standard mixtures, the advantages and disadvantages of recipe mixtures, and some related characteristics of the aggregates used in bituminous mixes are discussed. At the end of the chapter, there are brief discussions on how the mixtures are made, laid and compacted, and on the means by which an asphalt manufacturer is encouraged to comply with specifications.