In many sectors, including the asphalt pavement industry, sustainable materials are coming into play and are at the top of everyone’s agenda. Recycled asphalt pavement and shingles (RAP/RAS), waste tire rubber (WTR), plastics, glass – many scrap products find viable end uses in pavements. But focusing on materials alone is not enough to achieve truly sustainable pavements. It’s also about design and process. 

With SigmaBond — a truly liquefied rubber asphalt using patented Rapid Digestion Process™ — Polyco is eager to pave toward a new era for the industry, where mix producers, paving contractors and agencies can realize complete sustainability in their road and highway projects. 

Eco-consciousness, long-term performance, efficient production and construction, and cost savings are the hallmarks of a sustainable pavement — and, by marrying new innovations with tried-and-true methods, there are ways to achieve them all in a single project.

Perpetual Pavements: Built to last

One potential solution to achieving pavement sustainability is Perpetual Pavements. The Asphalt Pavement Alliance (APA) defines Perpetual Pavement as “an asphalt pavement designed and built to last longer than 50 years without requiring major structural rehabilitation or reconstruction and needing only periodic surface renewal in response to distresses confined to the top of the pavement.”¹

According to research, Perpetual Pavements have a variety of positive attributes. They eliminate reconstruction costs at the end of a pavement’s structural capacity, lower rehabilitation-induced user-delay costs, reduce excessive use of non-renewable resources, such as aggregates and asphalt binder; diminish energy costs while the pavement is in use, and reduce the life-cycle costs of the pavement network.²

However, as with any design approach, there are challenges. First, the upfront costs incurred by intense subgrade work and soil stabilization, longer periods of traffic interruption during the initial build, and the amount of material needed for what is typically a 25 to 30 percent thicker pavement than the standard.  

In addition, Perpetual Pavements are limited in how much recycled materials they can utilize. For example, states only allow WTR in the wearing course, or top layer, of a Perpetual Pavement. Fortunately, innovations like SigmaBond asphalt binder are showing that contractors can achieve dense compaction with the use of more recycled materials, such as WTR, in the base and intermediate pavement layers. 

At the NCAT Test Track, structural test research is underway on sections where recycled plastics, WTR, and synthetic fiber are utilized in different mixes. The test sections will be subjected to accelerated traffic loading over a two-year period, and the structural response and pavement performance of those sections will be monitored.³

Striking the Balance

Balanced mix design (BMD) is also trailblazing as a sustainable solution. A volumetric mix design that’s keen on performance, BMD gives contractors more leeway in the types of materials they use – as long as the final result is a balance of performance between rutting and cracking.  

With BMD, contractors are finding they can save money and maintain quality by using more recycled materials. Workability and density are further improved when technologies such as SigmaBond are incorporated into a BMD. 

While there are cost savings with regard to materials and long-term maintenance, there is the expense of the design work and laboratory testing. With BMD, you are essentially creating a custom mix from scratch. Mix designers have to assess local materials, binders, and additives and the combinations thereof to forecast expected resistance to distresses at the lowest cost.⁴

Methodologies for Determining Pavement Sustainability

Many agencies are turning to life-cycle cost analysis (LCCA) for evaluating the long-term economic viability of pavement designs. In addition to initial construction costs, “an LCCA also considers future costs such as maintenance, rehabilitation and sometimes user costs, all of which are converted into present dollars (called net present value or cost).”⁵

Often confused with LCCA, a Life-Cycle Assessment (LCA) is different in that it specifically quantifies the environmental impacts over the pavement’s full life cycle, including impacts that occur throughout the supply chain.⁶ To encourage consistency and adoption of pavement LCAs, the Federal Highway Administration has developed an LCA framework specific to pavements which provides technical guidance on the approach.

Used together, LCAs and LCCAs can truly vet a pavement for the long haul and illuminate the best project overall approach to a roadway project. 

We at Polyco look forward to being part of the long haul in the asphalt pavement industry, especially with forward-thinking products such as SigmaBond, the environmental benefits of which we will explore in our next post. 

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1.  https://www.driveasphalt.org/uploads/documents/Perpetual_Pavement_Synthesis.pdf ↩︎
2.  Timm, D.H., & D.E. Newcomb (2006). Perpetual Pavement Design for Flexible Pavements in the US. International Journal of Pavement Engineering, Vol. 7, No. 2, pp. 111–119. doi:10.1080/10298430600619182 ↩︎
3.  https://eng.auburn.edu/research/centers/ncat/research/newsletters/spring2022.pdf ↩︎
4.  https://www.eng.auburn.edu/research/centers/ncat/education/bmd.html ↩︎
5.  https://www.eng.auburn.edu/research/centers/ncat/newsroom/2021-spring/lcca.html#:~:text=An%20LCCA%20is%20a%20process,the%20best%20long%2Dterm%20value. ↩︎
6.  https://www.fhwa.dot.gov/pavement/sustainability/how.cfm ↩︎