Sustainability. What a buzzword. We know that sustainability considerations are continuing to grow worldwide. As the highway trust fund continues to be in limbo, the transportation sector is seeking more and more sustainable solutions for pavement infrastructure, yet there seems to be limited guidance currently available to them.
The Federal Highway Administration (FHWA) launched its Sustainable Pavements Program in 2010 to advance the knowledge and practice of sustainability related to pavements. The overall objective is to establish a program that considers asphalt, concrete, granular and other materials in pavement systems including new and emerging materials. A critical outcome of the program is to increase the awareness, visibility and the body of knowledge of sustainability considerations in all the life cycle phases of pavement systems.
According to the FHWA’s guide, Toward Sustainable Pavement Systems: A Reference Document, there are things that can be done at every stage of the pavement life cycle that can help contractors improve their sustainability efforts and add to the life of the pavement, thus saving money. The program all begins with the pavement life cycle which consists of six steps:
- Raw Material Acquisition
- Material Processing
- Pavement Design
- Construction, Maintenance and Preservation
- The Use Phase
- End of Life
One of the most influential elements in determining this life cycle is the pavement design stage which influences everything from materials selection, service life and maintenance.
A Life Cycle Assessment (LCA) can then be done to examine the environmental flows occurring at each stage of the road building effort. There are opportunities at each stage of the road building effort to assess and improve on the carbon footprint of the process. Here are the considerations at each stage from the FHWA to improve sustainability.
For aggregates, there are several strategies:
- Reduce amount of virgin aggregate used
- Reduce impact of virgin aggregate acquisition and processing
- Reduce impact of transporting aggregate
- Reduce virgin binder content (increase RAP, RAS and GTR)
- Reduce energy consumed and emissions generated during production
- Extend service life (compaction, polymers, improved designs)
- Use locally available materials
Pavement design considerations
There are several strategies to consider when it comes to pavement design to improve sustainability. Consider robust pavement design for optimization, long-life designs, enhanced pavement smoothness over the life cycle of the pavement, noise reducing surfaces and pervious pavements to name a few.
Construction considerations would include equipment operation and quality of construction. For asphalt construction, items such as effective construction planning and sequencing, achieving target density, preventing segregation, proper construction of longitudinal joints and achieving initial smoothness all lend themselves to a more sustainable pavement.
Use phase considerations
Vehicle-pavement interaction, tire-pavement noise, stormwater management, urban heat island, safety and lighting all fall under the "use phase" of a pavement's life. Some general strategies to optimize sustainability during this phase include:
- Maintain smoothness
- Avoid utility cuts
- Effective surface textures for noise control
- Pervious pavements for stormwater runoff
- Surface friction for safety
Pavement maintenance & preservation considerations
When it comes to the pavement maintenance and preservation stage, there are several items to consider. These include limited new material use, thinner cross sections, maintaining a high level of smoothness, an increased construction quality, and lower life cycle costs correlated with lower environmental burden, which is affected by treatment, materials, and timing of the maintenance and preservation.
End of life considerations
When it comes time to replace the pavement, where possible, one should work with the pavement in-place, such as in-place recycling with HMA or on-site recycling with PCC. Other considerations for the end-of-life phase include increasing the use of recycled materials (RAP, RAS, RCA) and reducing the use of virgin materials.
No single activity makes a pavement more sustainable. Some of these best practices however can result in large changes in environmental, social and economic impact factors. In general, most organizational approaches to sustainability involve rethinking priorities and ultimately placing more emphasis on the social and especially the environmental components of sustainability.
However, an increasing number of agencies, companies, organizations, institutes, and governing bodies are embracing principles of sustainability in managing their activities and conducting business. Whether it’s with legislation or through public opinion, sustainable efforts are going to become the norm. It’s a good idea to familiarize yourself with the FHWA Sustainable Pavements Program now and be a step ahead of your competition for when it’s a requirement and not just a consideration.
For full information on the program, visit www.fhwa.dot.gov/pavement/sustainability