The Road to Optimizing Asphalt Pavement Recycling
Wes Sullens and Jim Vallette - March 29, 2017
Today the Healthy Building Network and StopWaste released the sixth and final report in our Optimizing Recycling initiative: Reclaimed Asphalt Pavement (RAP) in Building & Construction.
Reclaiming and reusing asphalt has many benefits, including waste prevention, reduction of greenhouse gas emissions, and lower lifecycle impacts compared to virgin asphalt material use.
Tremendous life cycle benefits come from maximizing the use of reclaimed asphalt pavement and minimizing the use of virgin asphalt. Cold-in-Place recycling, the rarest form of asphalt pavement recycling, can reduce carbon dioxide emissions by as much as 95 percent per lane mile and save a lot of money ---- as much as 40 percent compared to conventional techniques. More common warm mix asphalt can reduce carbon dioxide emissions by 15 percent compared to conventional paving, and increase proportions of RAP used. In our report, we provide sources for these figures, as well as recommendations to greatly increase the recycling of asphalt.
The many variations of asphalt can complicate recycling efforts. Numerous virgin mix formulations and different types of aggregate (which can range from rocks to roofing shingles) add further variables. Sometimes pavement is sealed ---- especially parking lots and driveways ---- with a highly toxic substance called coal tar sealer. Even without sealants, during its use, pavement is contaminated by traffic paint that might contain lead, fluids from leaking gas tanks, exhaust from passing tailpipes, and myriad products used to patch and repair asphalt. Over time the binder in pavement degrades, and some of those materials run off and end up in waterways and the environment.
These variables lead to wildly inconsistent recycled asphalt feedstock, which suppresses the amount of reclaimed asphalt pavement that can be incorporated into new roads and products.
Although asphalt pavement is quite a different material than other feedstocks we've examined, like polyurethane foam and glass cullet, the contamination issues and the solutions thereto are now familiar to those following our Optimizing Recycling series. Keys to greatly increasing the recycling of asphalt and its attendant environmental benefits include simplifying the designs of asphalt mixes, reducing toxic additives in production, tracking materials from production through use and recycling, testing incoming materials for contaminants, and avoiding the addition of cutback solvents and other toxic rejuvenating agents to recycled pavement.
Two years ago, we began our Optimizing Recycling initiative with a simple but challenging question: are all recycled content materials created equal? As we expected, the answer was 'no,' that it was time to rethink recycling, to follow a road less traveled. We created a new analytical framework, and through painstaking research, we identified pathways for improving the condition of recycled feedstocks. Along the way, we have appreciated robust discussions with recycling authorities, health and environmental researchers, recycling workers, green chemists, product designers, building owners, and product manufacturers. Some have already implemented our recommendations. We are encouraged that many companies and circular economy advocates now embrace efforts to identify and eliminate contaminants.
This is the surest way to reducing dependencies on virgin resources and maximizing the benefits of recycling.
Jim Vallette is Research Director of the Healthy Building Network.
Wes Sullens, formerly of StopWaste, is now the Director of Codes Technical Development for the US Green Building Council. Note: The report on asphalt was written while Wes was still at StopWaste.
The Optimizing Recycling series of reports was a collaboration between StopWaste of Alameda County, California, and the Healthy Building Network, with support from San Francisco Environment and the BlueGreen Alliance. This initiative examined the hazards, supply chains, and economic impacts of recycled feedstock streams in building products. It is available online at: http://healthybuilding.net/content/optimize-recycling.