Materials and testing
The mixture of materials has considerable internal friction properties as well as viscous flow properties which again are dependent on the temperature. If the material is produced by crushing, a considerable degree of control of the shape is possible. The best guide to the temperature at which a bituminous material should be laid is the viscosity of the binder in the mix. The quality of a bituminous road material is mainly determined at the mixing plant, there is close control of aggregates and of the binder – one of the more important points being the mixing temperature. The material in the heap, from which the sample is to be taken, is passed through a riffle box of a suitable size. Traditionally, mastic asphalt was a fluid, hand floated material, unsuitable for machine laying. Laid material will cool to the setting temperature in a very few minutes, thus limiting the time available for compaction.