Each year the Asphalt Pavement Alliance (APA) recognizes state agencies and owners of pavements that had the foresight to build according to perpetual pavement principles. Since 2001, the APA’s Perpetual Pavement Award program has recognized 156 long-life pavements in 31 U.S. states and one Canadian province.
The winning pavements range in age from 35 years to 91 years, and the pavements average 46.37 years old at the time of recognition. Roads are at least 35 years old when honored and had never experienced a structural failure. Also, a road could not have had more than 4 inches of new material added over the previous 35 years, and it could not have been resurfaced more frequently than once every 13 years.
As stated by APA, even though the Perpetual Pavement concept was not articulated until 2000, many pavement owners have recognized the benefits of building long-lasting pavements. This is certainly true for much of Interstate 81 in Virginia. Many of the original pavement designers and constructors recognized the need to have robust pavement designs, built from the subgrade up, as critical to a long-lasting pavement. For example, Arthur Barnhart, retired Virginia Department of Transportation district materials engineer, was present during much of the construction of I-81 in the Salem District. He states, “We recognized much of the subgrade through the area was extremely weak. As such, we knew something needed to be done to ensure a long-lasting pavement. We were fortunate that many of the roadway cuts were rock and, as such, utilized this material to build a strong subbase.”
The award winner for 2020 is a pavement section located on southbound I-81 in Roanoke County from Mile Point 133.63 to 136.14. It was opened to traffic in 1964 and currently carries approximately 23,000 directional ADT, 22% of that being tractor-
trailers and a total loading to date of nearly 100 million ESALs. As already noted, this area of the Salem District is known for weak clayey, silty subgrade soils. Furthermore, local weather conditions average 41 inches of rainfall and 20 inches of snowfall each year, in addition to many freeze-thaw cycles. Despite the poor subgrade and weather conditions, this section of I-81 has withstood over 56 years of heavy truck loading with minimal maintenance.
Maintenance averaged 18.7 years between treatments, with the most prolonged period being 30 years between maintenance activities. The grade was increased approximately 1.8 inches over the roadway’s lifespan, including a 1.4 inch Surface Mix Asphalt overlay (1994) and a 0.375 inch thick Latex-Modified Slurry Seal (2020). There was also a mill-and-replace of 1.5 inch SMA Surface Mix Asphalt in 2011.
Looking at the performance of this roadway section, one can see the factors that played a role in its success. First, crushing and pugmill operations were primarily on-site for much of the construction of I-81 in the area, making these materials readily available. Travis Higgs, PE, present district materials engineer and pavement designer for many of the new sections of I-81 in the area, states, “Clearly one significant factor in the performance of this roadway section was daylighting the subbase stone from edge to edge beyond the shoulders during original construction. This undoubtedly helped get water away from the weak in situ subgrade soils and formed a strong foundation for the pavement.”
Another distinct factor in the performance of this roadway section was the targeted installation of cross drains (CD). These drains were placed at all cut/fill sections and bridge structure interfaces to ensure proper subsurface drainage throughout the mountainous terrain. Forensics associated with these drains have repeatedly highlighted this system’s effectiveness, which is continued in modern designs today.
Lastly, it is important to emphasize that the traffic levels seen today on Interstate 81 are significantly greater than the designers ever envisioned back in the 1950s. Traffic volumes have exponentially increased over the years, particularly since the deregulation of the trucking industry following the Motor Carrier Act of 1980, clearly something that the original designers could not have envisioned. Yet, the pavement still performs well today due to the decisions made during design and the steps put in place during construction.
Fortunately for VDOT, much of Interstate 81 benefits from these and other design and construction methodologies that have assisted in its pavement structures’ long-term/perpetual performance. This is evidenced by VDOT’s winning two Perpetual Pavement Awards; both have come from I-81 (the last being in 2006 for a section in Frederick County).
As we continue building new infrastructure and rebuilding our existing pavements, we must pull out all the stops to ensure a sustainable pavement system. Recognizing that sustainability and long-term pavement performance go hand in hand is critical. “One of the keys to sustainability is long life,” said Amy Miller, PE, national director of the APA. “Asphalt roads can be engineered to last indefinitely with only routine maintenance and periodic surface renewal (1).”
- Asphalt Pavement Alliance (APA) website https://www.driveasphalt.org/awards/perpetual-by-performance