Asphalt is the pavement of choice for sustainability. It’s 100 percent reusable and recycled at a higher rate than any other material in America — including soda cans and newspaper. In fact, more than 99 percent of asphalt reclaimed from old roads and parking lots goes back into new pavements.1
In addition, asphalt pavements are able to use waste and byproducts from other industries — reducing environmental impacts. Instead of going to landfills, materials such as rubber from used tires, glass, asphalt roofing shingles and blast furnace slag can all be put to use in asphalt pavements.2 In 2017, more than 76.2 million tons of RAP and nearly 950,000 tons of reclaimed asphalt shingles (RAS) were used in new asphalt pavement mixes in the U.S.1
Fewer Greenhouse Gases
Asphalt pavements require less energy3 to produce and their production generates less material waste4 than other paving materials, and its production emits fewer greenhouse gases than concrete pavement.5 In fact, the asphalt binder used to make asphalt pavements is a byproduct of fossil fuels that were never burned and used as energy, such as diesel fuel or gasoline. Thus, the inherent CO2 is never released into the atmosphere.
According to the U.S. Environmental Protection Agency (EPA), 99.6 percent of the carbon in asphalt binder is stored instead of contributing to greenhouse gases.6 Not only are asphalt pavements a very effective means of sequestering carbon, the production of liquid asphalt from the heaviest fraction of a barrel of oil is much less energy intensive than trying to convert it to a fuel for energy use.7
To further reduce our environmental footprint, the asphalt industry continues to make great strides in the use of warm-mix asphalt (WMA) production. WMA technologies reduce the production and placement temperature of asphalt pavement mixtures by 30°F to 120°F.8 This lowers fuel consumption further and cuts greenhouse gas emissions.
On average, contractors report energy savings of almost 25 percent during warm-mix production. When WMA is fully implemented across the industry, the U.S. will save an estimated 150 million gallons of No. 2 fuel oil per year, while also slashing carbon dioxide emissions by an equivalent of 210,000 cars annually.9
The use of warm-mix asphalt grows each year. The estimated total tonnage of asphalt pavement mixtures produced at reduced temperatures with WMA technologies for the 2017 construction season was about 147.4 million tons.1 This was a 26 percent increase from the estimated 116.8 million tons of WMA in 2016, driven largely by increased WMA tonnage in the commercial, residential, and DOT sectors.1
Full-depth porous asphalt has shown to help filter water to keep pollutants out of the environment.10,11 These pavement structures, used mostly for parking lots, allow water to drain through the pavement surface into a stone recharge bed and infiltrate into the soils below the pavement. By replenishing water tables and aquifers rather than forcing rainfall into storm sewers, porous asphalt also helps to reduce demands on storm sewer systems. In areas where storm-water impact fees are imposed by local governments, such fees may be reduced by using porous asphalt.
Reduced Fuel Consumption
A smooth roadway not only provides drivers with peace of mind, it also increases vehicle fuel efficiency. Contrary to some recent claims that pavement rigidity is a major contributing factor to vehicle fuel economy, the FHWA WesTrack Tests quantified the relationship between smooth pavements and improved fuel economy. Smoother pavements lead to lower fuel consumption — 4.5 percent lower in the WesTrack Tests.12
While manufacturers make strides to improve an automobile’s fuel economy, transportation agencies, researchers, and engineers are concurrently working to refine and build smooth roadways that do the same. All told, Americans burn 175 billion gallons of fuel driving approximately 3 trillion miles a year. If roads across the nation were smoother and maintained in good condition, approximately 4 percent of the fuel consumed could be saved, reducing annual vehicle fuel consumption by about 7 billion gallons — the equivalent of taking more than 10 million vehicles off the road every year.12
Virginia RAP Project Biggest in North America
VDOT decided to go big by rebuilding seven miles of I-64 near Williamsburg using a mix with 85 percent RAP.
By Chuck MacDonald
Pavement experts estimate that approximately 10 million tons of recycled asphalt pavement (RAP) is stored by various contractors in Virginia. “I once estimated that the amount of RAP in the state is sufficient to build a highway from my office in Charlottesville to Las Vegas,” said Brian Diefenderfer, Ph.D. P.E., a pavements researcher at the Virginia Transportation Research Council, the research division for the Virginia Department of Transportation (VDOT). Based on experience gained from using pavement recycling techniques on a 3.7-mile reconstruction of I-81 in 2011 and testing on sections built at the National Center for Asphalt Technology (NCAT) Test Track in 2012, VDOT decided to go big by rebuilding seven miles of I-64 near Williamsburg using a mix with 85 percent RAP.
“It is the biggest recycling project in North America,” said Diefenderfer.
“We estimated that using RAP on this highway saved $10 million and produced 50 percent fewer greenhouse gases than a job done using a non-recycling approach.”
The undertaking highlighted the sustainability of asphalt, America’s most recycled product.
The contractor who took on the job, Allan Myers, has approximately one million tons of RAP stored on its property. The company was interested in the innovative design but knew the job would not be easy. The paving used cold central plant recycling materials (CCPRM) and produced about 165,000 tons for the project.
“We knew we would have lots of challenges, including producing the mix that would meet the required quality control standards,” said Craig Rayfield, Quality Control Manager for Allan Myers. “We selected from four to five different piles of RAP we had collected from all over Virginia. There were extra costs to process, crush, and screen the RAP.”
Allan Myers had numerous conversations with VDOT, with both sides committed to making the project a win-win for the state and the taxpayers. The company purchased a new mobile CCPR plant for proper processing of the RAP-heavy mix.
“We tested the mix by paving on our grounds and also did some night paving,” said Ben Bushey, Construction Manager. “We trained our people how to work with this mix, which did not require any other specialized paving equipment. We also noted that the mix was temperature sensitive, so we did not make any mix or pave when the temperature was less than 50 degrees.”
"We used emulsion to seal and protect the CCPRM after compaction, which helped the curing process and allowed us to protect the material from weather and construction traffic," said Bushey. "Proper compaction and curing were vital for the CCPRM to achieve the best performance."
Most of the construction was done during 2018 as the Allan Myers team built a 12-inch-thick subbase using recycled materials in an FDR process. The next level was a 2-inch open-graded-drainage course, followed by 6 inches of the CCPRM, followed by a 2-inch SMA-19 material. The final course was a 2-imch SMA-12.5.
The CCPRM paving used cold materials plus foamed asphalt as a recycling agent. The asphalt binder was heated, but the mixture went into the paver at ambient temperatures. The contractor placed the CCPR on a new layer produced from crushed concrete and stabilized with cement using full-depth reclamation (FDR) to form a stiff subbase.
The finished interstate includes three lanes in each direction, widened from the original two lanes, and shoulders. VDOT has placed sensors in the pavement to document the performance of the RAP-heavy CCPR mix.
“This was an innovative job,” said Rayfield. “We wanted to be a part of it to see if it was possible to build a quality highway using a high amount of recycled materials. It was definitely a green project.”
Writer bio: Chuck MacDonald is a writer living in Annapolis, Md. He has been a frequent contributor to projects for NAPA and other organizations.
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NAPA (2008). Warm-Mix Asphalt (PS-30). National Asphalt Pavement Association. Lanham, Maryland.
Roseen, R.M., T.P. Ballestero, J.J. Houle, J.F. Briggs, and K.M. Houle (2012). Water Quality and Hydrologic Performance of a Porous Asphalt Pavement as a Storm-Water Treatment Strategy in a Cold Climate. Journal of Environmental Engineering, Vol. 138, No. 1, pp. 81–89.
Zhao, Y. and C. Zhao (2014). Lead and Zinc Removal With Storage Period in Porous Asphalt Pavement. WaterSA, Vol. 40, No. 1, pp. 65–72.
Sime, M., S.C. Ashmore, and S. Alavi (2000). Tech Brief: WesTrack Track Roughness, Fuel Consumption, and Maintenance Costs (FHWA-RD-00-052). Federal Highway Administration, McLean, Virginia.