TOPS News:
April 2023 |
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North Carolina Uses Unbonded Concrete Overlay to Improve Decades-Old Pavement
In North Carolina, along interstate highway 85, transportation engineers turned a challenge of rehabilitating a pavement that was significantly past its design life into an opportunity for innovation and improvement when addressing segments of pavement constructed as early as 1960.
“There was terrible pavement out there, the worst interstate pavement in the state,” said Clark Morrison, state pavement design engineer for the North Carolina Department of Transportation (NCDOT). “We had a lot of just about every kind of distress. A really rough-riding pavement. It needed something done to it.”
To address these issues, NCDOT oversaw a project in 2007 replacing the worst of the pavement’s slabs with asphalt slabs and an ultra-thin bonded wearing course overlay to provide a uniform surface and to reduce roughness of the existing roadway.
While this “band-aid” project initially improved pavement condition, the international roughness index quickly worsened. By 2013, Morrison and NCDOT were challenged with how to address the patches.
 A paver installs a COC-U overlay in North Carolina. (Source: North Carolina Department of Transportation)
When NCDOT reached out to the Federal Highway Administration (FHWA) for guidance, FHWA set up NCDOT with its concrete overlay technical assistance program. This led to a project review and workshop involving FHWA and the National Concrete Pavement Technology Center.
Recommendations from the workshop included leaving the asphalt patches in place – unless there was severe and apparent distress – and using a concrete over concrete unbonded (COC-U) overlay.
COC-U, a concrete overlay product featured in the FHWA Targeted Overlay Pavement Solutions (TOPS) Every Day Counts (EDC) initiative, uses thicker overlays than bonded concrete overlays. These overlays are intentionally debonded from the underlying pavement through a separation layer. The resulting benefit to using COC-U is that it can often address more problems in the pavement with less concern for distresses, such as cracking of the existing pavement reflecting through to the new overlay.
“Before these unbonded overlay projects, [I-85] was probably one of the worst stretches of interstate pavement in North Carolina. Now we have a 40-mile stretch of interstate pavement that is in very good condition and is a low-maintenance pavement,” said Morrison. “The project was really a success. The unbonded concrete overlays have performed well on the I-85 corridor and are a cost-effective pavement choice.”
Visit the TOPS concrete resources to learn more about COC-U and other EDC concrete overlay products.
Concrete Overlay Feasibility Strategies Webinar
Join the FHWA Targeted Overlay Pavement Solutions (TOPS) Every Day Counts team for a “Concrete Overlay Feasibility Strategies” webinar on April 26 from 1:00-2:30 ET. Webinar topics will include:
- Value points of concrete overlay solutions
- How to evaluate existing pavement and select concrete overlay solutions
- Strategies for managing work zones and maintenance of traffic
- How to get started and plan for concrete overlays
FHWA’s Robert Conway will introduce the Every Day Counts TOPS innovation, and pavement consultant Jerry Voigt will present concrete overlay feasibility strategies, followed by a moderated questions and answers session.
 (Source: Jerry Voigt, Square One Pavement Consulting)
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 five webinars in recent months including:
Open-Graded Friction Course and Ultra-Thin Bonded Wearing Course
Learn about OGFC and UTBWC and hear presentations from South Carolina and Minnesota.
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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