Hot Mix Asphalt (HMA) is one of the most common roadway materials used today. HMA is a versatile and essential building material that has been used to surface ninety-four percent of the more than 2 million miles of paved roads and highways in the U.S. It is also commonly used to surface parking lots, bike paths and tennis courts.
Typically, asphalt is placed in three distinct layers to create a flexible pavement structure. These layers consist of a base course, an intermediate or binder course, and a surface or wearing course. These layers vary in thicknesses of 3”-6” for base mix, 2”-4” for intermediate mix and 1”-2” for surface mix.
The components of HMA consist of ninety-four percent aggregate and 6 percent asphalt cement a petroleum based product, to serve as the binder. The ingredients are then metered, mixed and brought up to a temperature in excess of 300 degrees Fahrenheit before being placed in a truck and delivered to the jobsite for final placement.
Asphalt pavement is 100 percent recyclable and reusable and is the most reused and recycled pavement material in the U.S. Reclaimed Asphalt Pavement (RAP) can be incorporated into the new pavement at replacement rates in excess of thirty percent depending upon the mix and the application of the product.
The use of Warm Mix Asphalt (WMA) or “green” asphalt is becoming increasingly popular. The immediate benefit to producing WMA is the reduction in energy consumption required by burning fuels to heat traditional hot mix asphalt (HMA) to temperatures in excess of 300° F at the production plant. These high production temperatures are needed to allow the asphalt binder to become viscous enough to completely coat the aggregate in the HMA, have good workability during laying and compaction, and durability during traffic exposure. WMA can reduce the temperature by 50 to 100 degrees Fahrenheit. With the decreased production temperature comes the additional benefit of reduced emissions from burning fuels, fumes, and odors generated at the plant and the paving site.
Asphalt consumption in the U.S. is of between 500 to 550 million tons per year and is produced out of over 4,000 asphalt plants with a total value in excess of $30 billion.