On the Road Again

In 1980, Willie Nelson’s classic song “On the Road Again” reached no. 1 on the Billboard Country Music charts. Since that date, the song has been remade and recycled by several musicians and bands that can relate to Nelson’s lyrics about life on tour.

In the construction and demolition recycling world, ‘on the road again’ does not so much describe the return of a tour bus to the highway as much as the return of recycled concrete and asphalt material to those highways on which the bus may travel. Boosted by research and funding from government agencies, with increasing frequency, asphalt and concrete debris recovered from road demolition applications are being reused as a base material or  mixed with virgin material for use in the construction of new roads.

Among the current trends observed in the road building industry are an increasing acceptance of recycled asphalt pavement (RAP) in hot mix asphalt (HMA) and a push to use more concrete material as an alternative to HMA.

RISING RAP
According to the Federal Highway Administration (FWHA) and the United States Environmental Protection Agency (EPA), there are no rules or regulations in place to require the use of recycled aggregate material in road building applications. However, that’s not to say these government bodies do not support the use of recycled materials. They are both actively involved in funding research projects examining the benefits of using RAP and recycled concrete aggregate (RCA).

“We have been working in partnership with industry, highway agencies and academia to promote and encourage the use of recycled materials rather than requiring the use through any authority we may have been given under federal statutes,” says Peter J. Stephanos, the director of the Office of Pavement Technology for the FWHA. Within the FWHA’s recycling program, Stephanos says there are emphasis areas including efforts to maximize the use of RAP, and RCA in high-end applications where virgin mineral aggregates are typically be required.

Tom Baker, materials engineer for the state of Washington’s Department of Transportation, says that the stimulus plan that went into action last year also did not contain specific language encouraging the use of recycled aggregates in road building, although he notes that the stimulus plan has boosted road construction in his state.

From his perspective, the federal government funds the research to support the use of recycled aggregates, while the free market encourages their use in road building applications.

“One of the things we try to do in Washington, is we try to let the market be as efficient as possible; so we don’t mandate a recycled percentage, because in certain situations it might not make sense,” Baker says. He adds that for a paving company without a stockpile of removed pavement, a recycling percentage mandate would require them to haul in RAP, which would be costly and inefficient.

Baker notes that in the state of Washington, after the federal government funded research that demonstrated RAP could be effective as a material in HMA, contractors began reusing the material in HMA as a cost savings. “If it costs $70 per ton for new asphalt and a $10 to $15 per ton tipping fee to haul [the old asphalt] to a landfill, contractors are pretty smart in that equation,” he says.

Contractors in other states have also taken notice. According to Stephanos, surveys that were conducted by AASHTO (the American Association of State Highway and Transportation Officials) in 2007 and 2009 to assess the degree to which RAP is allowed and used in HMA indicate a trend toward sustainability.

“The results of these surveys indicate that the number of states that use an average of 20 percent RAP in all layers of asphalt increased from two to eight,” Stephanos says. “During this same two-year period, 17 states have modified their specifications to allow for greater amounts of RAP in HMA.” According to Stephanos, the eight states that use an average of 20 percent RAP are Alabama, Georgia, Hawaii, Kansas, Minnesota, Oregon, South Dakota and Texas.

That 20 percent RAP figure is a significant one for state transportation agencies, according to Jeffrey Melton, outreach director of the FWHA-supported Recycled Materials Resource Center (RMRC), jointly based at the University of New Hampshire and the University of Wisconsin. Melton says that 20 percent is the upper limit on RAP mixtures that states have experience with, and also is the limit in which they have confidence that the HMA will perform as expected.

Melton also says that it is well established that using RAP in HMA is environmentally and economically beneficial. “Using RAP reduces the need to mine for more aggregate, and in some places the aggregate in the RAP is better than what is currently available, so using RAP puts the best aggregate back in the road,” he says. “Using RAP also reduces permanent deformation in HMA pavements. The issue people are trying understand now is how RAP affects pavement cracking.” 

Melton notes that current research is being done by the RMRC to determine how well old roads utilizing 10-20 percent RAP have held up in comparison to surfaces using 100 percent virgin material.

Given that the average life span of a road is about 20 years or more, Melton says early RAP demonstration pavements studying how they actually performed are just now reaching the end of their service life.

CONCRETE ANSWERS
Another trend affecting the industry is the increasing acceptance of (RCA) recycled concrete aggregate in road building applications.

According to information found on the FHWA Web site, 41 of the 50 states use RCA as a material for road building. while 38 specify that it is used as a base material. Consequently, only 11 states utilize RCA in portland cement concrete and eight states use it in HMA. In response to these figures, the FWHA has drawn the following conclusions:

• concrete is routinely being recycled into the U.S. highway environment;

• the principal application of RCA in the U.S. is as a base material; and

• using RCA as an aggregate in HMA and new concrete is not as widely accepted in the U.S.

Additionally, concrete is becoming more accepted because of the efforts of AASHTO, which has been considering and approving standards for recycled materials. Melton says the group has passed standards for the use of crushed concrete as a base course and in new portland cement concrete applications.

While RCA is gaining traction as a base material, typically states are only using RCA generated from state road destruction or repairs, Melton says. “While transportation uses a significant amount of DOT-generated reclaimed concrete, there is still a resistance to using building-derived aggregates in higher value applications such as embankments and structural fill, or as aggregate in new portland concrete cement,” he adds.

According to Melton, the presence of soil, wood and debris in RCA resulting from construction and demolition activities may make state DOTs hesitant to use the material on their roads. However, if this material is properly screened and processed, he believes that may alleviate some of their concerns.

In the near future, the use of concrete in road building applications may soon increase because of changes in the asphalt supply chain, Melton says. As he explains it, asphalt is formed as a residue byproduct of the petroleum refining process. However, due to advancing technology, the byproduct of petroleum refining operations is moving from asphalt to coke (dry carbon). Melton says, this is affecting the available supply of asphalt in the U.S. 

Because of its large dependence on oil, Melton says asphalt can also be susceptible to dramatic price shifts. “The spike in oil prices a few years back showed that asphalt is susceptible to large price changes,” he says. “As conventional sources of asphalt become unavailable, there will probably be a continued climb in price.”
Melton adds that concrete is not as dramatically affected by changes in oil price due to the ability to use alternative fuel sources such as tires or solid waste at cement binder plants.

“We should prioritize where HMA is needed most and where concrete pavement provides the best value,” Melton says. “In order to do this, there needs to be more life cycle assessment that considers the economic, engineering and environmental and safety aspects of using one material over another.”

Melton adds, “I think there is a place for more concrete pavement, but I don’t think one can make a blanket statement that concrete should replace HMA.”