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Questions & Answers
Q: What is asphalt pavement?
Asphalt pavement a high-quality, thoroughly controlled, engineered material made from aggregates (stone, sand or gravel) using asphalt cement as a binder.
Q. How environmentally safe are asphalt plants?
Asphalt plants must meet rigorous standards established by the EPA and other agencies, but often the individual plants set their own standards that are even more demanding. Recent improvements in asphalt production have made the industry even more environmentally friendly. In fact, after a six-year study, the EPA announced in 2002 that asphalt plants are no longer on its list of industries considered major sources of hazardous air pollutants.
Q: Can asphalt pavement be recycled?
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, both in terms of tonnage (73 million tons, more than any other material) and in terms of percentage (80 percent of reclaimed asphalt pavement is recycled, a higher percentage than any other substance). 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 uses the following recycled materials: slag from the steel-making process, roofing shingles, sand from metal-casting foundries, and rubber from old tires.
- In a joint report to Congress, the Federal Highway Administration and the Environmental Protection Agency estimated that more than 73 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 more than $300 million each year.
Q: How is asphalt pavement made?
Asphalt pavement is made by heating asphalt cement and mixing it with aggregates and mineral fillers. The asphalt paving mixture is loaded immediately onto trucks for delivery to construction sites or kept in storage silos.
Q. What is asphalt cement?
A derivative of crude oil refining that is the binder or "glue" in the asphalt pavement mixture.
Q: Is asphalt pavement a safe driving surface?
Yes! Asphalt pavements can be designed and constructed for maximum skid resistance. Research has shown that asphalt roads tend to be quieter than concrete roads, leading to less driver fatigue. 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 with "open-graded" surfaces that allow water to drain through the surface layer of the pavement, thus reducing splash and tire spray, and increasing tire-road contact during wet weather.
Q. Is asphalt a sustainable material?
Clearly, it is. In addition to its recyclability, which conserves precious natural resources, asphalt provides long-life solutions for pavement construction. Some asphalt pavements reduce noise pollution and alleviate other environmental concerns. And, while annual production of asphalt paving material has increased by more than 250 percent over the past 40 years, emissions from asphalt plants have dropped by 97 percent or more. Some additional points to consider:
- Asphalt is not soluble or harmful in a water environment. It has been used successfully for many years in fish hatcheries, reservoirs of drinking water for human consumption, and other environmental protection applications.
- Asphalt 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. Asphalt pavements are effective liners and caps for landfills.
- Many states have tested discarded asphalt pavement and determined that it should be categorized as clean fill.
Q. Why are so many asphalt plants necessary?
Asphalt pavement material begins to cool as soon as it is mixed. In order to maintain workability at the paving site, and for the highest quality of the finished pavement, the mixing facility (asphalt plant) must be near the paving site.
Q. Is asphalt pavement used only for roads?
No. Asphalt has a variety of uses, including:
- Paving running tracks, airport runways, greenway trails, bicycle and golf cart paths, basketball and tennis courts.
- Paving cattle feed lots, poultry house floors, barn floors and greenhouse floors.
- Lining surfaces from fish hatcheries to industrial retention ponds.
- Laying railbeds for transit systems.
- Creating 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.
Q. Is paving asphalt the same as roofing asphalt?
No. While both paving and roofing asphalts are derived from the petroleum refining process, they are used in very different ways. Asphalt used in roofing is typically a harder grade of asphalt that is heated to much higher temperatures than those used in paving operations.
Q. How have asphalt plants changed over time?
In the early 20th century, asphalt plants were on railroad cars. Pavers would go from town to town, pave all the roads and move on to the next town. Today, many modern asphalt plants are a permanent part of communities. The plants need to be near where roads are built, because the paving material must be delivered to the paving site while it is still hot. Portable asphalt plants are used in more remote areas.
Q. Are asphalt pavements quieter than other types of pavement?
Yes, there is considerable research that shows that asphalt pavements tend to be quieter than concrete pavements.
Q. How durable is asphalt pavement?
Well-designed, well-built asphalt pavements last many years. For instance, the asphalt portions of Interstate 90 in Washington State have been in place since their original construction more than 35 years ago with no rehabilitation for structural reasons. The entire New Jersey Turnpike is asphalt. Built in 1951, it has never had a failure in the pavement structure. The chief engineer for the turnpike expects it to last another 50 years.
Called the "perpetual pavement," asphalt pavements can last a lifetime because it's possible to maintain them with only periodic replacement of the surface layer. And with the newer heavy-duty surface pavements, it is possible for overlays to last more than 15 to 20 years.
Q. Is asphalt considered to be less expensive than concrete?
Numerous studies in the U.S. and Europe have shown that asphalt pavements generally have a lower life cycle cost. The initial cost of asphalt pavement is usually less than concrete. In addition, an increasingly important factor is the traffic delay cost during construction or rehabilitation. You can't close down a busy road and spend weeks repairing it without costing businesses and individuals money – potentially millions of dollars. With asphalt, you can usually perform construction and rehabilitation operations at night and reopen the road to traffic the next morning.
Q. How is an asphalt pavement built?
The pavement is built in layers. The first step is to remove topsoil and compact the earth. Then, a base that will help to carry the load is placed and compacted. (The base may be constructed solely of stone, or it may include both stone and asphalt.) Then, two or more layers of hot mix asphalt are placed and compacted.
Q. How thick does the asphalt need to be for a road?
That’s an engineering decision, based on what kind of stresses the pavement must withstand (trucks vs. cars) and other factors such as soil conditions and climate. It also depends on what materials will be used in the asphalt and what materials might be present in the lower layers of the pavement.
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