Asphalt

Asphalt (known in the industry as Hot Mix Asphalt, or HMA), is a combination of aggregates (usually crushed stone and some sand), filler (cement, hydrated lime or stone dust) and a bituminous binder called "asphalt cement". Additives are sometimes used (e.g. rubber from old car tires) . Reclaimed "asphalt" from old roads, called RAP (recycled asphalt pavement), is also, increasingly, being used.

When hot, HMA is pliable and can be rolled flat to create a smooth, durable, water proof substrate.

Standards

Hot Mix Asphalts are defined by the gradation of the aggregate. This includes the maximum size of crushed stone present in the mix. Most asphalt specifications state what mix type to use for various projects and give the range of particle size that the aggregate gradation must fall within.

Asphalt mix types are referred to by the gradation limits. Each state, city or municipality has their own designation for asphalt mixes suitable for use in their jurisdiction. For example Florida DOT refers to S1 mixes while Texas DOT uses Type A, B C or D mixes.

To adopt a national standard for HMA all States are moving to the SuperPave method of describing asphalt mixes.