HMA should not degrade substantially from moisture penetration into the mix. HMA durability is related to air voids as well as the asphalt binder film thickness around each aggregate particle. HMA should not age excessivly during production and service life. Low temperature cracking is primarily a function of the asphalt binder low temperature stiffness. HMA should not crack when subjected to low ambient temperatures. HMA fatigue cracking is related to asphalt binder content and stiffness. HMA should not crack when subjected to repeated loads over time.

HMA deformation is related to aggregate surface and abrasion characteristics, aggregate gradation, asphalt binder content and asphalt binder viscosity at high temperatures. HMA should not distort (rut) or deform (shove) under traffic loading. Because of the wide differences in aggregate specific gravity, the proportion of asphalt binder expressed as a percentage of total weight can vary widely even though the volume of asphalt binder as a percentage of total volume remains quite constant.īy manipulating the variables of aggregate, asphalt binder and the ratio between the two, mix design seeks to achieve the following qualities in the final HMA product (Roberts et al.

Usually expressed in terms of percent asphalt binder by total weight of HMA, this ratio has a profound effect on HMA pavement performance.

The ratio of asphalt binder to aggregate.

Items such as type, durability, rheology, purity as well as additional modifying agents can be measured, judged and altered to some degree. Items such as type (source), gradation and size, toughness and abrasion resistance, durability and soundness, shape and texture as well as cleanliness can be measured, judged and altered to some degree. In order to meet these demands, the mix designer can manipulate all of three variables: It must resist deformation and cracking, be durable over time, resist water damage, provide a good tractive surface, and yet be inexpensive, readily made and easily placed. HMA is a complex material upon which many different, and sometimes conflicting, performance demands are placed. Each method has been proven to produce quality HMA from which long-lasting pavements can be constructed. Some agencies and private laboratories use the Marshall method. WSDOT uses the Superpave mix design methods.

Job mix formula