TOPS News:
March 2023 |
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Oklahoma uses a “self-healing” pavement mixture to reduce cracks
Oklahoma asphalt pavement engineers are excited about the results they see with binder-rich intermediate layers, also known as crack attenuating mixture (CAM). Oklahoma Asphalt Paving Association Executive Director Larry Patrick calls it a self-healing mix. “You’ve got two types of cracking—top-down and bottom-up,” said Patrick. “CAM’s flexibility can help prevent a crack from coming up through to the surface.”
CAM is one of several asphalt products promoted as part of the Federal Highway Administration’s Every Day Counts (EDC) initiative—Targeted Overlay Pavement Solutions (TOPS). The Oklahoma Department of Transportation (ODOT) first tried CAM with PG76-28E, ODOT’s highly modified asphalt binder, as an intermediate layer in a 2012 project on I-40 in Caddo County. Eleven years later, the two-mile stretch of I-40 has an International Roughness Index that averages 50 inches per mile, which is smooth enough to result in ride quality bonuses for new construction in some states. The project was recently nominated for an Asphalt Pavement Alliance Perpetual Pavement by Conversion Award.
 Crack attenuating mixture with highly modified asphalt will be used to rehabilitate this seven-mile section of I-40 in Oklahoma. (Source: Trenton January)
ODOT plans to use CAM on an adjacent 7-mile section of I-40 in Canadian County. The project will include milling 7 inches of the existing asphalt, placing a CAM layer using PG76-28E, followed by Superpave and stone matrix asphalt, which is also an EDC TOPS initiative. ODOT awarded the project in February 2023.
“We’re super excited about it because right now, we must go out there daily to make repairs,” said ODOT District Engineer Trenton January. “We have to close down a lane, mill out a section, add new asphalt, and then five feet ahead of that, do it again. This project will give us good pavement that we’re not out there every day trying to maintain.”
I-40 traffic is estimated at 37,200 vehicles per day, and 37 percent is truck traffic. The $24 million dollar investment is expected to provide a smooth surface for at least 15 years.
Since the original I-40 project, ODOT has used CAM on roadways ranging from Interstate highways to county roads across the entire State. It has proven to be a practical, effective, and economical approach to delaying or preventing reflection cracking. Oklahoma Department of Transportation Standard Specifications section 411 describes the criteria for ODOT’s CAM or binder-rich intermediate layer.
FHWA Offers Asphalt and Concrete Workshops
The Federal Highway Administration (FHWA) is offering workshops for asphalt and concrete Targeted Overlay Pavement Solutions (TOPS) to State Highway Agencies starting in March 2023.
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Asphalt Products
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Concrete Products
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Asphalt Rubber Gap-Graded
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Bonded Concrete on Asphalt
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Crack Attenuating Mixture
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Bonded Concrete on Concrete
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Highly Modified Asphalt
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Unbonded Concrete on Asphalt
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High-Performance Thin Overlay
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Unbonded Concrete on Concrete
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Open-Graded Friction Course
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Stone Matrix Asphalt
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Ultra-Thin Bonded Wearing Course
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The one-day in-person workshops will cover the following:
- Project selection
- Specifications and acceptance
- Mixture design
- Laboratory testing, construction, and deployment strategies
The overall goal of each workshop is to provide practical technical instructions for the planning, design, and construction of TOPS asphalt and concrete overlays.
Contact TOPS co-team lead Tim Aschenbrener (asphalt) or Robert Conway (concrete) to request a workshop.
Check out a TOPS Webinar
The TOPS team has hosted four webinars in recent months including:
Concrete over Concrete Unbonded Overlays
Learn about the latest COC-U advancements, benefits, specifications, and construction considerations.
Stone Matrix Asphalt and Highly Modified Asphalt Webinar
Learn about SMA and HiMA and hear presentations from Georgia and Florida.
High-Performance Thin Overlays and Crack Attenuating Mixture Webinar
Learn about HPTO and CAM and hear presentations from New Jersey and Texas.
An Overview of Concrete Overlays Webinar
Get an introduction to concrete overlays, understand the challenges and value proposition, learn how to get started, and more.
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