There are a few different ways to produce asphalt, but they all share the same basic principles when being created. Crushed aggregate (stones, sand, and gravel) is mixed with asphalt/bitumen, at either hot or cold temperatures, depending on your application.

Hot Mix

The stone, sand, or gravel aggregate is bound together by asphalt cement, a product of crude oil at a hot mix asphalt (HMA) plant. Prior to mixing, the asphalt binder is heated to decrease its viscosity, and the aggregate is dried to remove moisture. Mixing is generally performed with the aggregate at about 300 °F for virgin asphalt and 330 °F for polymer modified asphalt (PMA), and the asphalt aggregate at 200 °F (to remove moisture). Once mixed it is kept at temperature to avoid early solidifying. Once delivered on site it is then applied to the proper areas for compacting using a heavy roller. This is the most commonly used mix due to durability and longevity.

Warm Mix

Warm mix asphalt is a relatively new formulation. It is produced by adding either zeolites, waxes, asphalt emulsions, or sometimes even water to the asphalt binder prior to mixing with aggregate. By doing so, it allows lower temperatures to bind the aggregate and asphalt together decreasing the amount of fossil fuels used and the amount of carbon dioxide released in the production of it. It also requires less time to cool and set, allowing for faster use of the surface. Nearly 25% of asphalt produced in 2012 was warm mix, a 416% increase since 2009.

Cold Mix

Cold mix, commonly called “Cold Patching” is fast, do-it-yourself way to temporarily fill in pot holes of a reasonable size. It is created by mixing the asphalt with water at lower temperature with anti-stripping agents before adding it to the aggregate. It’s easier to work with, but is never intended on heavily traveled services. The binding is not as strong and will break up overtime with weather and wear.