Asphalt is the sustainable material for constructing pavements. From the production of the paving material, to the placement of the pavement on the road, to rehabilitation, through recycling, asphalt pavements minimize impact on the environment. Low consumption of energy for production and construction, low emission of greenhouse gases, and conservation of natural resources help to make asphalt the environmental pavement of choice.
I. Energy and Recycling
Less energy consumed in building pavements
Asphalt pavements require about 20 percent less energy to produce and construct than other pavements.1
Less energy consumed by the traveling public
Congestion leads to unnecessary consumption of fuel and production of emissions. Reducing congestion by constructing asphalt pavements just makes sense. Asphalt pavements are faster to construct and rehabilitate. And, a new or newly rehabilitated asphalt pavement can be opened to traffic as soon as it has been compacted and cooled. There is no question of waiting for days or weeks for the material to cure.
America’s leading recycler
The asphalt industry reclaims about 65 million tons of its own product every year, and reuses or recycles about 99 percent of it. This makes it America’s number one recycler.
Other materials are routinely recycled into asphalt pavements. Some of the most common are rubber from used tires, glass, blast furnace slag, and asphalt roofing shingles.
II. Ultimate Sustainability
The road doesn’t wear out
Only asphalt can be the Perpetual Pavement. When appropriately designed and constructed, the road itself doesn’t wear out. Maintenance is simple: only the top layer is removed and replaced. This can be done quickly, even overnight, and it saves taxpayers money. The material that has been reclaimed is then recycled. The newly overlaid road surface (which may also contain recycled material) is a good-as-new pavement. Total removal and reconstruction is not needed. This is a truly sustainable construction process.
Rubblizing for sustainability
When concrete pavements reach the end of their useful life, they must undergo expensive, time-consuming rehabilitation or be completely removed and replaced. This process squanders precious natural resources—unless the pavement is rehabilitated through a sustainable process called rubblization. The worn-out concrete is “rubblized” (fractured) and becomes the base for the new asphalt road. This saves fuel that would have been used by trucks hauling the old material away; saves the virgin materials that would have been needed to build a new road base; and can give the traveling public a new Perpetual Pavement. In addition to the environmental and speed of construction advantages, cost savings can be significant.
Smooth asphalt roads give vehicle tires superior contact with the road, improving safety.
Open-graded asphalt allows rainwater to drain through the pavement surface, reducing the amount of splash and spray kicked up by vehicles.
Asphalt is the quiet pavement. Newer quiet pavement technologies include fine-graded dense pavements, open-graded surfaces, and two-layer open-graded pavements.3 Studies show that the noise-reducing properties of asphalt last for many years.4
Noise reductions of 3 to 10 dB(a) are common. Reducing noise by 3 dB(a) is about the same as doubling the distance from the road to the listener, or reducing traffic volume by 50 percent.
For more information on quiet pavement technology, visit www.quietpavement.com.
Asphalt moves traffic along
Asphalt pavements are faster to construct and rehabilitate. In crowded urban areas, where closing a road for rehabilitation or reconstruction would dump increased traffic on to neighboring routes, asphalt is the answer. Highways and roads can be milled for recycling, then overlaid, during off-peak hours. An entire freeway can be resurfaced without commuters ever being inconvenienced.
III. Water Quality
Stormwater management with porous asphalt
Porous asphalt pavement systems can replace impermeable surfaces for parking lots, roads, walking/biking paths, and other applications. Porous pavements can turn runoff into infiltration; restore the hydrology of a site, or even improve it; improve water quality; and eliminate the need for detention basins.5
Asphalt pavements do not leach
Once constructed, asphalt pavements have minimal impact on the environment. Studies show that asphalt pavements and stockpiles of reclaimed asphalt pavement do not leach.6,7
Asphalt is used to construct liners and caps for landfills. The impermeable material is an effective barrier to potential leaks.
Drinking water reservoirs are often lined with asphalt. Asphalt cement is also used to line water pipes that supply potable water to humans.
Oregon and Washington state fish and wildlife agencies use asphalt pavement to line their fish rearing ponds.8
IV. Cleaner Air and Cool Cities
Asphalt plants are environmentally sound
Emissions from asphalt plants, including greenhouse gases, are very low and well-controlled. Between 1970 and 1999, the asphalt industry decreased total emissions by 97 percent while increasing production by 250 percent.9 Emissions from asphalt plants are so low, the EPA considers them as only minor sources of industrial pollution.10
The urban heat island effect is not a black and white issue.11 Porous asphalt pavements have been shown to lower nighttime surface temperatures as compared to impervious pavements. In at least one city, the hottest heat signature is at the airport, with its thick, dense, impervious runways.
When cars and trucks are mired in congestion, they consume fuel and produce greenhouse gases. Asphalt’s speed of construction allows planners and managers a way to fix congestion hot spots and bottlenecks, quickly and cost-effectively.
V. LEED and Green Construction
The LEED Green Building Rating System serves as a scorecard for the design, construction, and operation of green buildings. Pavement type selection (concrete vs. asphalt), on its own, can contribute directly to some LEED credits. Credits can be earned in these ways:
- Porous asphalt systems earn credit for stormwater management.
- Light-colored asphalt helps to mitigate the urban heat island effect.
- The ability to recycle asphalt pavement and the use of asphalt with high percentages of RAP (reclaimed asphalt pavement) make asphalt eligible for credits under the materials and resources heading.
- The fact that asphalt pavement material is produced locally can earn credits for materials and resources.
- Warm-mix asphalt offers several advantages which support sustainable development.
When all these factors are considered, asphalt pavements can contribute more LEED credits than other pavement types.
1. Gambatese, John A. and Sathyanarayanan Rajendran, “Sustainable Roadway Construction: Energy Consumption and Material Waste Generation of Roadways,” American Society of Civil Engineers, Reston, VA. Proceedings of 2005 Construction Research Congress. (http://tinyurl.com/yyapyts)
2. A Study of the Use of Recycled Paving Material: Report to Congress, June 1993, Federal Highway Administration and United States Environmental Protection Agency, Washington, DC. FHWA-RD-93-147 and EPA/600/R-93/095.
3. Newcomb, Dave, and Larry Scofield, “Quiet Pavements Raise the Roof in Europe,” Hot Mix Asphalt Technology, National Asphalt Pavement Association, Lanham, MD, September/October 2004.
4. Reyff, James, et al., I-80 Davis OGAC Pavement Noise Study: Traffic Noise Levels Associated With an Open Grade Asphalt Concrete Overlay. Prepared for California Department of Transportation by Illingworth & Rodkin, Inc., Sacramento, CA, December 1, 2002.
5. Jackson, Newt, Design, Construction and Maintenance Guide for Porous Asphalt Pavements (IS-131), National Asphalt Pavement Association, Lanham, MD, 2003.
6. Kriech, AJ, et. al. “Determination of polycyclic aromatic compounds in asphalt and in corresponding leachate water.” Polycyclic Aromatic Compounds, Taylor & Francis Group, Philadelphia, PA. Volume 22, Numbers 3-4, pp. 517-535. 2002.
7. Townsend, Timothy, and Allen Brantley. Leaching Characteristics of Asphalt Road Waste. University of Florida, 1998. (http://www.hinkleycenter.com/publications/townsend_98-2.pdf, accessed September 1, 2006)
8. Environmental Applications for Hot Mix Asphalt (PR-1). Asphalt Institute, Lexington, KY. Undated.
9. Report to Members 2001, National Asphalt Pavement Association, Lanham, MD. 2002.
10. Federal Register, February 12, 2002, pp. 6521 ff.
(http://frwebgate.access.gpo.gov/cgi-bin/getpage.cgi?dbname=2002_register&position=all&page=6521, accessed September 7, 2006.) Also, Federal Register, November 8, 2002, pp. 68124 ff.
(http://frwebgate.access.gpo.gov/cgi-bin/getpage.cgi?dbname=2002_register&position=all&page=68124, accessed September 7, 2006.)
11. Golden, Jay, and Kamil Kaloush, “A Hot Night in the Big City: How to Mitigate the Urban Heat Island,” Public Works, December 2005. (http://www.pwmag.com/industry-news.asp?sectionID=770&articleID=268116, accessed September 5, 2006)