Frequently Asked Questions
Q: What is asphalt?
Asphalt, also known as hot mix asphalt (HMA), is made from dried crushed rock and asphalt cement, which is a mixture of petroleum compounds produced by oil refineries.
Q: How is asphalt made?
Asphalt cement is heated and combined with crushed rock. The asphalt is then mixed and loaded immediately onto trucks for delivery to construction sites or kept in storage silos.
Q: What makes asphalt pavement so safe for driving?
Safety is largely a function of maintaining tire contact with the pavement surface and skid resistance of the surfacing. Asphalt has microtexture, which aids in skid resistance. Asphalt roads also are quieter than concrete roads because they don’t have expansion joints to create noise. Other safety features of asphalt:
- Asphalt is impervious to de-icing salts and chemicals and is unaffected by winter road safety maintenance.
- Asphalt pavements can be designed so that water drains through the surface layer of the pavement, thus reducing
splash and tire spray, and increasing tire-road contact during wet weather.
- Asphalt retains heat better than other materials, so ice doesn't form as quickly and melts faster.
Q: Is asphalt environmentally sound?
Yes! Asphalt pavement is 100 percent recyclable and can be made to perform better the second or even third time around. In fact, it is the most recycled product in the United States at 80 percent. That compares to significantly lower percentages for aluminum cans, newsprint, plastic and glass beverage containers, and magazines. Asphalt roads are removed, recrushed, mixed with additional aggregate and fresh asphalt cement, remixed and placed back on the road. The hot mix asphalt industry also accepts the following recycled materials: rubber from used tires; slag from the steel-making process; roofing shingles; and sand from metal-casting foundries.
- In a report to Congress, the Federal Highway Administration estimated that over 70 million tons of asphalt paving material was recycled in 1992.
- Recycling roads not only conserves natural resources and decreases construction time, it saves American taxpayers over $300 million each year.
- Asphalt is not soluble or harmful in a water environment.
- Asphalt also prevents pollution from getting into water supplies and protects against disease from waste materials. It can be combined with aggregate to form a voidless and impermeable layer.
- Many states have tested discarded asphalt pavement and determined that it should be categorized as clean fill.
Q. How environmentally safe are asphalt plants?
Asphalt plants in North Carolina must meet rigorous standards. The North Carolina Division of Air Quality (DAQ) regulations for air toxins are not only more rigorous than those of many states, they’re also more rigorous than those of the EPA. These regulations are based on the recommendations of a panel of scientists and health experts who spent more than five years studying air pollutants. CAPA members are dedicated to meeting the demands of those regulations.
Q. Why are so many asphalt plants necessary?
North Carolina has the second largest state-maintained highway system in the United States, with 78,000 miles of roads. These roads are resurfaced every 12 to 15 years, which means 4,400 miles of roads are repaved annually requiring approximately 3 million tons of asphalt. In addition, asphalt plants are located throughout the state near road construction sites to ensure the mixture maintains the required temperature of at least 300 degrees.
Q. Is asphalt used only for roads?
No. Asphalt has a variety of uses, including:
- In paving running tracks, airport runways, greenway trails, bicycle and golf cart paths, in addition to basketball and tennis courts.
- In paving cattle feed lots, poultry house floors, barn floors, and greenhouse floors.
- In lining surfaces from fish hatcheries to industrial retention ponds. In railbeds for transit systems.
- In sea walls, dikes and groins to control beach erosion. Its strength, waterproofing capability and inertness to seawater helps prevent the eroding action of tides and waves.
Sources: National Asphalt Pavement Association, N.C. Department of Environment and Natural Resources, North Carolina State University