A Canadian civil engineer and researcher who works and lives in Indiana made the case for that state’s implementation of Superpave5 asphalt during the Ontario Asphalt Pavement Council’s (OAPC) recent fall seminar.
One of two keynote speakers, Heritage Research Group associate director of research Gerald Huber said this latest version of asphalt can extend pavement life.
“Superpave5 increases density, reduces permeability and requires no additional materials in the production or the use of different heavy equipment.”
Consequently, there is less impact on the environment in terms of reduced material extraction and energy consumption in the production and installation, said Huber, who made a short reference to Canada’s 2050 Carbon Neutral objectives.
The basic strategy of Superpave5 is to make the mix more compactable so that five per cent in-place air voids can be achieved. That produces a mix on the road with lower permeability and slower aging. It also includes changing the mix design process to allow the higher levels of compaction, he said.
Viewers watching the webinar-delivered seminar were given a snapshot of the Indiana Department of Transportation (IDOT) figurative and literal long road to the use of Superpave5 asphalt.
The Heritage Research Group is an Indianapolis-based technical and research firm that originally proposed the concept which became Superpave5 and served as a technical resource for a research study conducted by Purdue University for the department.
That research led to three trial projects, one each in 2013, 2014 and 2016. There were follow up evaluations and reviews. Based on those reviews, the IDOT conducted 10 more test projects in 2018 contrasting Superpave5 to Superpave4. A major finding was that the Superpave5 sections achieved an almost 95 per cent (94.6) compaction compared to 93.2 per cent with Superpave4, Huber said.
“It (the test study) demonstrated that the industry could design the Superpave5 mixtures and achieve the compaction desired.”
In 2019 the IDOT offered an opted-in no-cost change order allowing existing contracts to be converted to Superpave5 from Superpave 4. In September of that year it became mandatory for all new projects, said Huber.
Replying to emailed questions following the seminar, Huber said some other American states have expressed an interest in Superpave5. But there are a lot of factors to consider and transportation agencies have to understand its principles. One state conducted a test section but wasn’t able to achieve the 95-per-cent compaction rate.
Also on the seminar agenda was a talk from a second stateside-based asphalt specialist.
David Newcomb is the materials and pavements division head for Texas A&M Transportation Institute. He has been a guest speaker at previous OAPC seminars. At this year’s event he provided a perspective on Percent Within Limits specifications which rewards high quality and low variability and penalizes low quality and high variability in roadbuilding projects.
The basic thrust of his message was the need to be cognizant of all the factors that can lead to too much variability, be it in the mineral extraction process or the sampling and testing procedures.
Noting there is an element of risk for both transportation departments and contractor in any project, he said that: “A good specification has a reasonable level of risk for both parties.”