Recycling has evolved and offers a number of benefits in terms of saving materials and minimizing costs. In the construction industry, there are many different recycling solutions. On road construction projects, one solution is asphalt recycling.
In the U.S., one-fifth (70 million tons) of the approximately 350 million tons of asphalt mix produced and used to pave roads is recycled asphalt. This saves a lot of space in landfills and there are environmental and financial benefits of those recycling efforts.
Recycling can result in an estimated $2.3 billion in savings annually compared to the cost of purchasing raw materials; the conservation of 22 billion tons of asphalt binder and 68 million tons of aggregate; and the reduced associated costs of producing, processing and trucking of those materials.
The FHWA (Federal Highway Administration) has been encouraging the use of recycled materials for a number of years, and the use of RAP (reclaimed asphalt pavement) has increased from 15% in 2009 to 21% currently.
The basics of asphalt recycling
There are five categories to describe the various asphalt recycling methods. These categories are CP (cold planing), hot recycling, HIR (hot in-place recycling), CR (cold recycling) and FDR (full depth reclamation). In addition, asphalt recycling methods can be used in conjunction with one another on some projects.
CP is the controlled removal of an existing pavement to a desired depth, longitudinal profile and cross-slope using specially designed equipment. The resulting textured surface can be immediately used as a driving surface, can be further treated with one of the other asphalt recycling methods or once cleaned and tack coated overlaid with HMA or recycled mix.
There are many advantages to using CP. Some of the bigger ones are correction of longitudinal profile and cross-slope, removal of crack sealant or seal coats prior to HMA overlays, improvement of friction numbers, removal of built-up pavement at curbs to restore reveal height, energy conservation compared to other reconstruction methods and higher productivity with less disruption to the public.
Hot recycling is the process of combining RAP with new aggregates, new asphalt binder and/or recycling agents in a central plant to produce a recycled mix. HR uses the heat-transfer method to soften the RAP to permit mixing with the virgin aggregates and asphalt binder and/or recycling agent. HR of RAP currently is the most widely used asphalt recycling method in the world.
There are many advantages to using HR: conservation of non-renewable resources, energy conservation compared to other reconstruction methods and economic savings are realized.
Hot in-place recycling
With HIR, 100% of the existing asphalt pavement is recycled on-site. The process consists of heating and softening the existing asphalt pavement, which allows it to be scarified or hot rotary-milled to the specified depth. The scarified or loosened asphalt pavement is then thoroughly mixed and subsequently placed and compacted with conventional HMA paving equipment.
Advantages to using HIR are conservation of non-renewable resources, energy conservation compared to other reconstruction methods, reduced truck hauling compared with other rehabilitation methods, treatment of complete roadway width or only the driving lanes, reduced traffic disruptions and user inconvenience, roadways opened to traffic at end of day with little or no edge drop off and economic savings.
Full depth reclamation
FDR is the rehabilitation technique in which the full thickness of the asphalt pavement and a predetermined portion of the underlying materials (base, subbase and/or subgrade) is uniformly pulverized and blended to provide an upgraded, homogenous base material. FDR is performed on the roadway without the addition of heat, similar to CIR.
Advantages of full depth reclamation are conservation of non-renewable resources, energy conservation compared to other reconstruction methods, few pieces of equipment are required, in-place construction and high production rates that improve safety by reducing traffic disruptions and user inconvenience, and economic savings.
CR consists of recycling asphalt pavement without the application of heat during the recycling process to produce a rehabilitated pavement. Two subcategories within CR are used to further define CR based on the process used. These processes are CIR (cold in-place recycling) and CCPR (cold central plant recycling).
Advantages of cold recycling are conservation of non-renewable resources, energy conservation compared to other reconstruction methods, significant structural treatment and improved ride quality, in-place construction and high production rates improve safety by reducing traffic disruptions and user inconvenience and economic savings.
Asphalt recycling & reclamation
innovation moves forward
With so many options for asphalt recycling and reclamation, there are some advantages and disadvantages to using the methods and the technology surrounding them. Steve Cross, technical director for the Asphalt Recycling & Reclaiming Association, highlighted some of the challenges agencies are facing.
“Agencies are faced in many cases with dwindling resources, increased construction cost and road networks that need attention. In order to maintain and/or improve the condition of their road networks, agencies are going to have to do more with less. That is where new and innovative techniques, such as in-place recycling, comes into play,” Cross said.
Even though it seems asphalt recycling would be happening everywhere and all the time, that is not necessarily the case. When adopting these new technologies and practices, there can be pushback.
“There is always a hesitancy to try something new. We often hear there is a lack of performance data, specifications and available contractors. There has been a tremendous amount of work in these areas. Excellent performance and engineering information is available from the work by the National Center for Asphalt Technology and others. Test sections of the in-place recycling techniques at NCAT on the test track have all shown excellent performance as well as the I-91 project in Virginia. ARRA has developed guidelines for mix design, construction, and quality control,” Cross stated.
Still, even with hesitancy to try something new, there are a number of benefits to leveraging the new innovation.
Victor Gallivan, CEO of Gallivan Consulting, said there are numerous advantages. “It is very cost effective when using recyclable asphalt. Knowing which method suits your needs best is helpful. HIR goes around one inch down in the pavement, CIP can go four inches and full-depth reclamation can go from eight to 12 inches down. It depends upon the severity of the cracks and the road damage,” Gallivan explained. “A lot of equipment now uses GPS to be more efficient.”
The real interest expands beyond just cost effectiveness. In fact, according to Cross, the benefits of in-place recycling fall in three categories: engineering, economics and environment.
“The techniques are a proven engineering technology. The processes, because we can recycle 100% of the existing materials in-place, greatly reduce haul costs and typically have high production rates, which are quite economical. Finally, the processes are environmentally friendly. Reusing the existing materials results in the need for less new binder aggregates and because most of the processes are performed cold, considerably less energy is used,” Cross said.
Taking all of this into consideration, Cross has an optimistic outlook for the industry. “This is an exciting time for in-place recycling. There has been an increased interest all across the country in these technologies with plenty of growth opportunities,” he said.
At the same time, the market is starting to be driven by government efforts to improve processes on road construction projects.
“This market is a bit more agency-driven. The city, county and state governments handing out the specs for the project need to be the ones who call for the recycled asphalt. They need to call for the sustainability in the materials for the industry to grow,” Gallivan said.
Asphalt paving technology advances
In terms of technology that needs to be more widely adopted in the construction industry in the future, Gallivan points to intelligent compaction. “Intelligent compaction is the number one construction activity to ensure a better performance of the pavement and roadway,” he noted.
Asphalt recycling and reclamation will continue to grow and become a more widely adopted practice. As the population grows and more infrastructure is needed, so will roads. As long as there are vehicles driving down a road, there will be need for roads and road repairs using asphalt recycling and reclamation