Defining Asphalt’s Future

Benjamin F. Bowers, Ph.D., PE, Auburn University

Resilience is a term we’re hearing used more frequently in committee meetings, infrastructure bill discussions and amongst our peers in the industry and agency realms. But what is resilience? And is this just another way to say sustainability? Hint: It isn’t. Resilience and sustainability are two separate things, but they are intrinsically linked.

Sustainability is established upon what is known as the triple bottom line: economy, social and environmental health. In Policy Statement 418, the American Society of Civil Engineers (ASCE) states that sustainability is a set of conditions that “all of society has the capacity and opportunity to maintain and improve its quality of life indefinitely, without degrading the quantity, quality or the availability of economic, environmental and social resources” (ASCE, 2021). The asphalt industry has been at the forefront of many sustainable practices, such as using recycled materials in mixtures, reducing emissions through warm mix technology, managing and filtering stormwater with porous pavements and implementing technologies such as cold central plant recycling. Is there more we can do? Absolutely, but we’ll speak to that later in this article.

Resilience, as defined by FHWA Order 5520, is “the ability to anticipate, prepare for and adapt to changing conditions and withstand, respond to and recover rapidly from disruptions” (FHWA, 2014). So, in essence, resilience is our ability to bounce back. To make a sports analogy, the Philadelphia Eagles showed resilience after their star quarterback, Carson Wentz, went down with a torn ACL in 2018. At that point, my apparent celebrity doppelganger, Nick Foles, stepped in and ultimately led the Eagles to their first Super Bowl Championship. Note: As a life-long Carolina Panthers fan, I was pulling for the Eagles due to my disdain for their opponent (and because I kept getting texts from people who were convinced Foles and I were related).

Another example that may hit closer to home is the COVID-19 pandemic. The world ground to a halt, but slowly and surely, we found ways to adapt by wearing masks, social distancing and Zooming so we could get back to work. Academics like myself taught online and managed to keep labs cleaner than ever. Meanwhile, agencies and the paving industry found ways to safely keep building our critical infrastructure, in some cases ahead of schedule. While in no way do I want to make light of this catastrophic tragedy; I do want to point out that we, as people, as road builders and as researchers, are resilient.

So, where does resilience fit into the context of sustainability? As I noted before, they are related. One could argue that to be sustainable would require one also to be resilient, especially since we consider performance as it relates to environmental, social and economic factors. But, our methods of adapting our pavements can be resilient but not sustainable, and vice versa.

This Venn diagram (figure 1) shows sustainable practices or attributes, resilient practices or attributes and sustainable + resilient practices or attributes. For example, using recycled materials may be sustainable, but it isn’t always a resilient solution. Likewise, using novel materials that help strengthen the pavement system to withstand disruptions without knowing the environmental or safety risks may enhance resilience, but that doesn’t mean it’s sustainable. What you will notice, however, is that most resilient options are also sustainable options, such as using warm mix asphalt to both lower emissions (sustainable) and to increase haul distances if a local asphalt plant is taken offline due to disruption and the roadway needs rapid repair (resilient).

Resilient to What?

The National Oceanic and Atmospheric Administration (NOAA) tracks annual “Billion-Dollar Weather and Climate Disasters.” As of October 8, the year 2021 has had 18 different billion-dollar weather/climate disasters such as hurricanes, wildfires, drought and flooding, to name a few. The year 2020 had the most billion-dollar climate disasters ever at 22 (NOAA 2021). As hurricanes inundate our coastal roadways, floods from rapid snowmelt drown midwestern highways, drought followed by heavy precipitation causes highway failures over expansive clays from Texas through Alabama and beyond, we have found ourselves with a unique challenge. Drawing on ASCE’s 2021 Infrastructure Report Card, the roads in the U.S. were given a grade of “D” (ASCE 2021). The report card cites a $435 billion backlog of repair needs to existing roadways. How will we revitalize our pavements while making them more resilient to these disruptions?

Figure 1: Venn Diagram of Sustainable, Resilient and Resilient + Sustainable Practices and Attributes for Asphalt Pavements (Courtesy of the National Asphalt Pavement Association [Bowers and Gu 2021]).
We Have a Full Toolbox

The good news is we already have many tools in our toolbox, and many live in the part of the Venn diagram that overlaps sustainable and resilient. An inherent attribute of asphalt pavements is that they can be rapidly constructed. If an earthquake occurs—like the one that struck Anchorage, Alaska in 2018, causing slope stability failures that lead to pavement failure—asphalt pavements can be rapidly reconstructed in days or as little as hours to get the roadway operational again (Bowers and Gu 2021). Asphalt is also designed to be climate adaptable, like the Binder Performance Grading system, along with the ability to use polymers, fibers and other additives. Mixes can be designed to withstand extremely high and low temperatures and even temperature swings. As previously mentioned, warm mix additives can increase haul distances when local asphalt plants have been compromised. Porous asphalt is specifically designed to manage stormwater, making it a tool that can be used to handle heavy precipitation.

Pavements can also be designed to be perpetual or long-life, as was done in Iowa after the 2018 floods destroyed sections of the interstate (Bowers and Gu, 2021). When flooding occurs, it can cause a lowering in base stiffness, leading to premature failure or triggering undermining of the roadway. In either case, using a perpetual pavement can help mitigate these issues. These are just a few of the tools the asphalt industry already has that can be used to increase the resilience of pavements.

Hurricane Michael damaged SR-30 (US-98) in Franklin County, Florida.
Photo Courtesy of Kevin Wall.

Where Do We Go From Here?

I believe that we need to find ways to adapt our infrastructure that make it both more resilient and more sustainable. Take, for example, techniques like full-depth reclamation (FDR). If a coastal highway is undergoing regular flooding and loss of base stiffness, FDR can be used to stabilize 14+ inches of the existing pavement and base, 100% recycling what’s in place with minimal hauling. An asphalt overlay can then be placed on top to add structure and serve as the wearing surface. If correctly designed, a perpetual pavement structure can be built that uses a significant amount of recycled material, reduces cost for an equivalent structure, reduces greenhouse gas emissions (because mixing is done at ambient temperatures), creates a more resilient pavement and is still an asphalt roadway that can be easily repaired, replaced or further adapted as needed due to varying disruptions.

Hurricane Michael damage on SR-30 (US-98) in Franklin County, Florida. Photo Courtesy of Kevin Wall.

Further, if material supply chains are disrupted, and highways need to be rebuilt, we can rebuild them using the circular nature of asphalt pavement components: Binder used as binder and aggregate used as aggregate. Increasing recycled contents in hot or warm mix asphalt, or using cold in-place recycling or cold central plant recycling technique to rebuild the roadway using 100% recycled asphalt pavement.

Work still needs to be done to help agencies make decisions about which roads to make more resilient. Not every roadway needs to be adapted, and in some cases, it may make more sense to allow the roadway to fail and have a plan to reconstruct it rapidly. Mix producers also need to consider how to make their plants more resilient to disruptions. If a hurricane is pending, methods to protect the plant should be put in place so that the plant can be fired up to help with the recovery process once the storm has passed. Communication between the agency and the producers and contractors needs to be emphasized as well. It is best to put in place contracts, rapid contracting methods and plans for potential disruptions to reduce the time the roadway is down.

Our highways are our lifeline—they connect people, emergency services and our economy—so we must think critically about enhancing their resilience.


References:

  1. ASCE (2010). Policy Statement 418 – The Role of the Civil Engineer in Sustainable Development. https://www.asce.org/advocacy/policy-statements/ps418—the-role-of-the-civil-engineer-in-sustainable-development
  2. ASCE (2021). 2021 Report Card for America’s Infrastructure. https://infrastructurereportcard.org/cat-item/roads/
  3. Bowers and Gu (2021). Resilient Asphalt Pavements: Industry Solutions for the Resilience Goal. National Asphalt Pavement Association, Sustainability In Practice 105. https://member.asphaltpavement.org/Shop/Product-Catalog/Product-Details?productid={6399F00E-2392-EB11-B1AC-000D3A9A6645}
  4. Bowers and Gu (2021). Asphalt Pavement: A Critically Important Aspect of Infrastructure Resiliency. National Center for Asphalt Technology, NCAT Report 21-02. https://www.eng.auburn.edu/research/centers/ncat/files/technical-reports/rep21-02.pdf
  5. NOAA (2021). Billion-Dollar Weather and Climate Disasters: Overview. https://www.ncdc.noaa.gov/billions/
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