Requirements for Successful Asphalt Pavement Recycling

As the world population grows, so does the amount and type of waste being generated. Much of the waste produced today will remain in the environment for hundreds, perhaps thousands, of years. The creation of nondecaying waste materials, combined with a growing population, has resulted in a waste disposal crisis. One solution to this crisis lies in recycling waste into useful products.

Research into new and innovative uses of waste materials is continually advancing. Many highway agencies, private organizations, and individuals have completed or are in the process of completing a wide variety of studies and research projects concerning the feasibility, environmental suitability, and performance of using recycled products in highway construction. The solutions try to match society's need for safe and economic disposal of waste materials with the highway industry's need for better and more cost-effective construction materials.

According to the EPA (Environmental Protection Agency), environmental stewardship is the responsibility for environmental quality shared by all those whose actions affect the environment. Meanwhile, the FHWA (Federal Highway Admin.) supports and promotes the use of recycled highway materials in pavement construction in an effort to preserve the natural environment, reduce waste, and provide a cost effective material for constructing highways. The primary objective is to encourage the use of recycled materials in the construction of highways.

As part of the FHWA recycled materials policy, the FHWA actively promotes asphalt pavement recycling and technology. Contractors need to know these policies and be prepared to do asphalt pavement recycling on road projects.

Top Three Requirements

There are three key requirements that must be satisfied for asphalt pavement recycling to be successful. Recycled asphalt pavements must be cost effective, be environmentally responsible, and perform well. There are many ways to encourage asphalt pavement recycling.

The use of recycled material in the construction of highways is encouraged. The use of RAP (reclaimed asphalt pavement) can have the greatest economical, environmental, and engineering impact in pavement recycling. The FHWA makes it as easy as possible to use RAP and to do asphalt pavement recycling.

By using fundamental engineering principles in the design of mixtures, the performance and reduced impact on the natural environment can be optimized using a high concentration of recycled asphalt mixtures.

There are some challenges in using high amounts of RAP. A primary concern is the performance of high RAP mixtures in cold climates. The addition of high amounts of RAP to an HMA mixture usually increases the mixtures stiffness. In cold climates, this may contribute to the occurrence of low-temperature cracking. Another concern is due to the uncertainty of what occurs between the virgin and the RAP binder during mixing in a HMA plant.

There are several types of asphalt recycling methods. Victor Gallivan, CEO, Gallivan Consulting Inc, explains that in place recycling technology is advancing all over the country.

There are several types of it. Hot in-place recycling, which removes the top inch of the road, has been around since the 90s. Cold in-place recycling removes three to four inches of the road with a train of equipment, but it is half the cost of hot in-place and the materials are 100 percent recycled. There also are no emissions with this method.

The cold central plant recycling method is identical to cold in-place. This one takes the top three to five inches off the top of the road to a plant off site where it is mixed and brought back to the site and put down. There are some additional costs, but it’s 100 percent recycled. Cold depth recycling goes the deepest, 12-14 inches down on the road, mixes it up and puts it back on the road as a new. Most states do this form of asphalt recycling.

Even though the methods have been around for a while, the market is evolving with new technology. “New RAP machines have made the process easier. Ones have been used on projects in Fort Wayne, Ind., and Los Angeles, Calif., for 100 percent recycling of the asphalt,” Gallivan says.

Overcoming Obstacles

Mike Marshall, director recycling products, Wirtgen America, knows about the challenges of promoting asphalt recycling. “In North America, there are three recycling methods. With traditional RAP around 25-35 percent of the asphalt that goes back on the road is recycled. In-place recycling uses 100 percent of the asphalt when the road is replaced. The constant challenge has been to take the option to the road owners, to get them to adopt the recycling option instead of traditional methods,” Marshall says.

Even with road owners and contractors willing to use RAP, issues with adopting the practice occur. Marshall says the history of in-place recycling has been on less busy roads in more rural, less populated areas. The technology has grown and gotten better so it has moved to more populated areas. San Jose has done 100 miles of road with cold-in place recycling in the last three years. The equipment has evolved, which has helped the growth of the methods.

“If you reconstruct a road, it’s an extensive job, its labor intensive, time consuming, and has a big impact on the traveling public and adjacent roads. With a recycling method, you aren’t bringing in new materials, the impact on the traveling public is less, and you can have the new road ready sometimes in a day. The surrounding roads won’t get affected by materials being transported. This all leads to dollar savings. Road owners are looking at the performance of the road, will it work, and will the method save money,” Marshall says.

Most contractors have a pulse on the market. Marshall says the contractors in North America are very good and they know what they have to achieve to satisfy the road owners. They have it nailed down. When contractors work with partners who can tell them what is new in the market that is very useful to them.

With the goal of using RAP and asphalt recycling techniques in road projects, contractors and administrators need to come together and be on the same page. Then the road owners will be more than willing to use these methods on their streets.

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