At temperatures between 85°C (185°F) and 150°C (300°F), the asphalt binder is fluid enough to act as a lubricant in the compaction process aiding movement of the mix aggregates into a dense configuration. As it cools below this temperature range, asphalt becomes very stiff and sticky making further mix densification extremely difficult. Therefore, compaction must be completed before the mix cools to 85°C (185°F).
==Definitions==
'''Asphalt cement''' or "binder" is a complex hydrocarbon found as a natural deposit or as a residue from distilling crude oil to remove petroleum, motor oils, naphtha and kerosene. Asphalt cement is dark brown or black in color and at normal temperature is a solid but as the temperature is increased it becomes sticky and then oily. Asphalt cement makes up about 5% of the volume of the mix and is used to hold together (or cement or glue) the aggregate particles together in the HMA.
'''Aggregates''' are crushed stone, [[sand]] and fine ground rock, mixed in a predetermined proportion to obtain desired properties in the HMA. Aggregates and fillers make up about 90% of the volume of the mix.
'''Filler''' is a fine dust used to harden the asphalt cement, and improve adhesion of the asphalt cement to the aggregates.
'''Aggregate gradation''' HMA is graded by the percentages of different-size aggregate particles it contains. Aggregate gradation is a way of describing the proportions of the various sizes of crushed stone, sand and filler, by passing the aggregate through a set of sieves and measuring the weight retained on each sieve.
'''Compaction''' this is the process of densifying the HMA while it is in a hot, pliable state, to pack the aggregate particles together and to remove as much of the air voids as possible. Compaction gives the mix strength, resistance to rutting (the additional densification under the action of vehicular traffic), it seals the surface from the ingress of water and gives a smooth riding surface.
'''SuperPave''' is a method of [[design|designing]] Hot Mix Asphalt.
==References==