Best Asphalt Paving Materials

Hot Mix Asphalt (HMA)

• Hot Mix Asphalt (HMA) is the traditional asphalt concrete mixture used to construct roads and highways in the United States. Asphalt cement (binder) and mineral aggregates are the major materials in HMA. HMA may contain additives, Reclaimed Asphalt Parchment (RAP), and recycled asphalt roof shingles. HMA is called "hot mix" because it requires temperatures of 300 degrees Fahrenheit or more to effectively bind the asphalt cement to the mineral aggregates.

Basic HMA Materials

• Asphalt cement is derived from processing petroleum and also is found in the form of natural deposits (asphalt rock). The APAI Design Guidelines describe asphalt cement as adhesive that is waterproof, durable, and resistant to most acids, alkalies and salts.

  Mineral aggregates include sand, gravel, crushed bedrock, large stones, slag and rock dust. They are cleaned, screened, crushed and/or processed to meet gradation specifications before being mixed with asphalt cement.

Additives

• In a report published in March 2010, researchers at The Utah Department of Transportation tested two anti-stripping additives: lime and powdered Gilsonite. The additives were mixed in two separate applications of HMA and over a four-year period demonstrated a similar reduction in the amount of damage to the pavements.

  Chemical additives allow asphalt concrete to be processed at temperatures below 300 degrees Fahrenheit. This combination is called Warm-Mix Asphalt (WMA).

Warm Mix Asphalt (WMA)

• Technologies such as Aspha-Min and WMA-Foam developed in Europe, and Evotherm and Advera-WMA in the United States use a variety of mixing techniques and materials to produce WMA mixtures. The U.S. Department of Transportation, Federal Highway Administration research report indicates further research and investigation are required to confirm the environmental and cost benefits associated with the production and placement of WMA mixtures.

Recycled Asphalt

• Reclaimed Asphalt Pavement (RAP) is recycled asphalt concrete removed from roads and highways. The pavement is taken to a processing plant, where it is crushed and screened for reuse in HMA or WMA. RAP may be used as an aggregate substitute material and/or an asphalt cement supplement. Asphalt roof shingles also are recycled for use in asphalt mixtures. The shingles are sent to a processing plant, where they are crushed and screened for reuse.