Each year, a new set of buzzwords or cliches are used in our society and culture. A quick search of the internet lists the most popular words for 2019. Concepts such as “disruptor,” “data mining,” “agile,” and “synergy.” While all are impressive-
sounding, what do they mean?
For the transportation industry, the common buzzwords of “sustainable” and “resilient” are used, but what do these words mean concerning transportation and specifically pavements? In October 2014, FHWA published TechBrief1 (2014 TechBrief) which defined a sustainable pavement as:
“One that achieves its specific engineering goals, while, on a broader scale, (1) meets basic human needs, (2) uses resources effectively, and (3) preserves/restores surrounding ecosystems.”
As the 2014 TechBrief acknowledged, it is an “aspirational goal” and will take time to achieve.
Along with sustainable, “resilient” has been used extensively with infrastructure, particularly as the number of natural disasters seems to increase. Whether it was the hurricanes along the Atlantic and Gulf Coasts or earthquakes in Alaska, roads and bridges need to withstand the destruction or be renewed/repaired quickly to allow for the flow of emergency supplies to impacted areas.
So, how are asphalt pavements sustainable and resilient?
Asphalt – The Sustainable Choice
The 2014 TechBrief outlined pavement sustainability in terms of Pavement Life Cycle, Measuring Sustainability, and Impacts. The pavement life cycle is the “cradle to grave” concept, starting with securing the pavement materials, to design, to use, and finally end of life.
When the interstate system was established in 1956, new highways were constructed primarily as “green-field” projects. While some sections of interstates utilized existing pavements, most of the mileage was comprised of new pavements from the subgrade up. The cradle for these pavements utilized virgin aggregates and virgin asphalt binders. Early interstates did not include recycled asphalt pavements because they either did not exist or were not even considered. Today, the cradle for new pavements contains varying percentages of recycled materials along with virgin aggregates and binder.
The role model for sustainable pavement is I-64 between Williamsburg and Hampton. I-64 Segments 2 and 3 are complete reconstruction and widening of pavements built in the 1950s and 1960s. Constructed initially as jointed reinforced concrete pavement, deterioration over time lead to extensive patching and grinding to maintain a minimum level of serviceability.
New pavement designs using conventional materials were initially selected to increase traffic capacity and replace the existing pavement. However, an alternative pavement design using sustainable materials was proposed and selected. This pavement design grew from the lessons learned from the 2011 rehabilitation of I-81 and the 2012 NCAT Test Track sections. The cradle for the alternative pavement design incorporated recycled asphalt pavement (RAP), recycled concrete pavement, sub-base reclamation, and asphalt mixes containing RAP produced with warm mix asphalt technologies. In an analysis performed by Dr. Brian Diefenderfer, P.E., Principal Scientist at the Virginia Transportation Research Council, the alternative pavement sections on I-64 contained up to 80% recycled materials. This is a vast departure from the traditional approaches to designing and constructing pavements.
During the “use” phase of a highway, the 2014 TechBrief pointed out the pavement characteristics of roughness, stiffness/rigidity, and macrotexture. To varying degrees, these characteristics impact the consumption of fuel and resulting vehicle emissions. In a 2006 report prepared by James Gillespie and Kevin McGhee of Virginia Transportation Research Council2, the potential cost savings and fuel savings through smooth pavements are documented. Virginia has employed an International Roughness Index based ride spec since the late 1990s, and today the average IRI on Virginia’s interstate system is 73 inches per mile3. While most of the interstate does have an asphalt surface, some districts do maintain a concrete surface. Figure 16 of the same report shows the increased roughness experienced on concrete surfaces.
The last stage in the pavement life cycle is End of Life. The 2014 TechBrief defines this stage as “the final deposition and subsequent reuse, processing or recycling of any portion of the pavement system that has reached the end of its performance life.” For I-64, the End of Life involved the removal of concrete slabs, crushing the material and reuse as a stabilized sub-base. For most of the asphalt pavements in Virginia, the End of Life has not been reached. Even for interstate sections constructed over 50 years ago, most mileage still has the original asphalt base and intermediate layers. Where asphalt layers have been removed, the material has been recycled into new asphalt mixes.
Asphalt – The Resilient Choice
Today, highways are the lifeline for the economy—locally, nationally, and internationally. When these lifelines get impacted or severed by disasters (natural or man-made), economies suffer. Recent examples of large-scale disasters are Hurricane Maria (2017), Puerto Rico Earthquake (2019), Hurricane Michael (2018), and the Alaska Earthquake (2019). Within the state of Virginia, historic flooding has been widespread in 2018 and 2019. These floods have wiped out sections of roads and entire bridges, as well as leading to numerous landslides. When the pavement is gone, it’s imperative to replace the pavement quickly. Multiple emergency projects in 2018 and 2019 involved the placing of an aggregate fill material and base layer, then overlaid with asphalt. Once completed and the asphalt cooled, roadways were reopened.
Along with natural disasters, man-made disasters or vehicle accidents can close a highway. On Saturday, February 1, 2020, a deadly fuel truck accident and fire in Atlanta forced the closure of all northbound and southbound lanes of I-85. The highway was closed for hours while emergency responders worked to secure the scene. The fire resulted in extensive damage to the existing pavement in the northbound lanes. Once the fire was extinguished on Saturday, the damaged pavement was removed and repaved overnight to be opened for traffic on Sunday.4 The resiliency of asphalt allowed a critical interstate to be repaired and reopened before the Monday morning rush hour in Atlanta.
While most infrastructure cannot or was not designed to resist disasters, the ability to perform repairs and be constructed quickly is a crucial characteristic of asphalt pavements.
Asphalt – The Easy Choice
Nationally, over 94% of the highway mileage has an asphalt surface. In Virginia, where the department of transportation maintains nearly 129,000 lane miles, more than 98% of the interstate and primary systems have an asphalt surface, and almost 80% of the secondary system has an asphalt or asphalt-based surface. The remaining 20% is comprised of gravel or other unstabilized surfaces.3 Whether it is due to the initial construction cost, speed of construction, driveability, sustainable features, or resilient attributes, asphalt materials and pavements are a natural choice.
1. Federal Highway Administration. (October 2014). Pavement Sustainability TechBrief FHWA-HIF-10-012.
2. Gillespie, James S. and Kevin K. McGhee. Impact of a Smoothness Incentive-Disincentive on Hot-mix Asphalt Maintenance Resurfacing Costs. VTRC 06-R28. Virginia Transportation Research Council, Charlottesville, VA., 2006.
3. Virginia Department of Transportation, Maintenance Division. State of the Pavements – 2018. Richmond, VA 23219.
4. WTHR.com. Deadly Fuel Truck Crash Closes Atlanta Highway. (February 2, 2020).