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.
Warm Mix Asphalt (WMA)
Warm-mix asphalt is another way the asphalt industry is working to reduce environmental impacts. Typically, asphalt paving temperatures are in the range of 290 to 320°F. Warm-mix technologies, which include plant “foaming” kits or production stream additives, offer ways to lower these temperatures by 20°F or more, saving fuel and reducing production plant emissions. Working in cooperation with the Federal Highway Administration, state Departments of Transportation, and other key stakeholders, implementation of warm-mix asphalt technologies has rapidly gained ground across the country. The Washington State Dept. of Transportation (WSDOT) fully supports of the use WMA “as equal” to hot mix asphalt (HMA) and WMA is the preferred asphalt pavement technology for City of Seattle public works installations.
LEED and Green Construction
The U.S. Green Building Council’s LEED (Leadership in Energy and Environmental Design) Green Building Rating System serves as a scorecard for the design, construction, and operation of green buildings. It was designed to encourage the adoption of sustainable building and development practices. Sustainable development tries to balance the needs of people, nature, and the economy.
Pavement type selection (concrete vs. asphalt), on its own, directly contributes to only a few LEED credits. Credits can be earned in these ways:
- Porous asphalt systems earn credits for stormwater management.
- 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.
- Light-colored asphalt pavements earn credits for urban heat island mitigation.
- 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.
There is no better way to reduce road noise than to treat the problem at its source. By paving roads and highways with hot mix asphalt the noise inside homes and businesses can be significantly reduced.
Research in the U.S. and Europe shows that a Stone Matrix Asphalt (SMA) or Open-Graded FrictionCourse (OGFC) asphalt pavement mix will reduce highway noise by 3 to 5 dB(A). To the average person, this reduction is the same as doubling the distance between the source of the noise and their location.
When comparing the noise reduction that is possible by choosing HMA pavement-up to 7 dB(A) -we see how much more practical pavement surface selection is than construction of noise barrier walls.
To learn more about quiet pavement visit http://www.asphaltroads.org/why-asphalt/environment/quiet-pavement.
Recycling and Energy
About 100 million tons of asphalt pavement is reclaimed each year, and over 95 percent of that total is reused or recycled.
When asphalt pavement is reused in a new asphalt mix, the old asphalt cement is rejuvenated so that it becomes an active part of the glue that holds the pavement together, just like the old aggregate becomes part of the aggregate content of the new mix. These singular properties make asphalt a uniquely renewable pavement. The same material can be recycled again and again; it never loses its value.
While reclaimed asphalt pavement (RAP) is the material most often used in asphalt recycling, materials from other industries are routinely recycled into asphalt pavements instead of going into landfills. Some of the most common are rubber from used tires, glass, asphalt roofing shingles, and blast furnace slag.
Asphalt plants also recycle the fine mineral particles that are generated in the process of producing asphalt pavement material. This routine recycling of co-generated material helps to conserve natural resources.
Porous asphalt pavements allow for land development plans that are more thoughtful, harmonious with natural processes, and sustainable. They conserve water, reduce runoff, promote infiltration which cleanses stormwater, replenish aquifers, and protect streams.
A typical porous pavement has an open-graded surface over an underlying stone recharge bed.2 The water drains through the porous asphalt and into the stone bed, then, slowly, infiltrates into the soil. If contaminants were on the surface at the time of the storm, they are swept along with the rainfall through the stone bed. From there they infiltrate into the sub-base so that they are subjected to the natural processes that cleanse water.
A complete suite of porous asphalt pavement specifications can be found within the Washington State Department of Transportation (WSDOT) website at the American Public Works Association of Washington (APWA-WA) General Special Provisions site: Local Agency GSPs – Divisions 2-9
These porous asphalt paving specifications have been fully vetted by the FHWA and are approved for use on local government agency work. The specifications are denoted by the sections marked as “PHMA/PWMA/PConcrete”.
One of the powerful alternate porous paving materials included in the specifications is Asphalt Treated Permeable Base (ATPB, Specification 4-SA2). ATPB can be used very effectively to reduce the complication of working over permeable ballast. It’s use eliminates the need for a crushed surfacing choker course and provides a stable platform for staged construction. In many applications, the total cost of the porous asphalt pavement system can be reduced by replacing much of the permeable ballast and all of the choker course with a layer of ATPB.