Hot Mix Asphalt is a proportioned mixture of dried aggregate and liquid asphaltic concrete cement used as roadway paving material. Aggregate is a graded mixture of crushed stone, sand and recycled asphalt paving. Liquid asphaltic concrete cement is a mixture of hundreds of organic compounds which remain after crude oil refining.
There are 158 asphalt plants in North Carolina with DAQ Air Quality Permit.
How does an Asphalt Plant work?
There are two types of asphalt plants, batch mix and drum mix. In a drum mix facility, undried aggregate and heated asphalt are placed directly into the rotary drum dryer, where they are mixed. The asphalt produced can be stored on site in heated storage silos or loaded directly into a truck and transported off-site. In a batch mix facility, the aggregate is dried separately in a rotary drum dryer and stored in heated bins. Heated aggregate measured per batch in a weigh box and a proportional amount of heated asphalt are mixed in a pugmill mixer and either stored on-site in heated storage silos or loaded directly into a truck for transport off-site.
How are asphalt plants regulated by DAQ?
Why are there are so many asphalt plants? *
North Carolina has the second largest state-maintained highway system in the United States. The state has about 80,0001 miles of roads, with more under construction every year. In addition, roads generally need resurfacing every 12 to 15 years, so about 4,400 miles of roads are repaved each year. Paving is difficult at lower temperatures, and highway contractors must reject asphalt that is not hot enough (at least 250oF). That means asphalt plants must be located fairly close to road construction sites.
What TAPs do asphalt plants emit?
Toxic air pollutants compounds emitted from asphalt plants include polycyclic aromatic compounds, volatile organic compounds, metals and hydrogen sulfide.
|Toxic air pollutants (TAPs) emitted from asphalt plant2|
|Toxic Air Pollutant||Emitted from |
drum dryer and
hot oil heater
|Emitted from |
|Trichlorofluoromethane (CFC 111)||no||yes|
|Methyl ethyl ketone||yes||yes|
|Soluble Chromate Compounds, as Chromium (VI)||yes||no|
|Manganese & compounds||yes||no|
|Nickel & Compounds||yes||no|
|Arsenic & Compounds||yes||no|
|Hydrogen Chloride (hydrochloric acid)||yes||no|
Who controls where asphalt plants are located? *
In reviewing air quality permits for asphalt plants, the Division of Air Quality must ensure that applicants comply with local zoning, and each permit contains a condition stating that the plant must meet these requirements. In North Carolina, local governments are responsible for regulating such land use matters, and they have the final authority over the construction of new plants through the issuance of building permits. However, many counties and municipalities, particularly in rural areas, have not adopted zoning or land use controls. The DAQ must base its permitting decisions on whether plants can meet air quality regulations, not on whether there is local opposition.