HRA design mixtures give better resistance to deformation where queuing of heavy traffic is likely to occur, and may also be more economical to lay.
Type C mixtures use fine aggregate of a coarser grading than Type F mixtures – usually associated with the use of crushed rock fines. Such mixtures tend to be stiffer and are less well suited to the reinstatement of small openings.
Surface course mixtures
The advantage of using chipped HRA 30/10F 40/60 is that the mixture can be used in footways, footpaths, cycle tracks and the carriageway. The other HRA options are limited in application.
Special care should be taken when using high stone content HRA (HRA 55/14 and HRA 50/10) to comply with texture depths.
The use of HRA 30/10 F surf is especially convenient when the reinstatement extends into road types 3 or 4, as the same material can be used for the whole surface.
Figure NGA2.1 shows examples of good/bad rate of chippings.