Launch Slideshow

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Concrete paving, Colorado style

Concrete paving, Colorado style

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    State Highway 66 runs through the foothills of the Colorado Rockies between Lyons and Longmont. CDOT repaired 27 lane-miles (244,000 square yards) of the roadway with 6-inch thin whitetopping in 2009. After two years in service, the pavement shows no signs of distress. Photo: Bill Palmer

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  • SIX-INCH THIN WHITETOPPING VS. FOUR-INCH HOT-MIX ASPHALT OVERLAYS: A COST ANALYSIS

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    CDOT has developed a cost comparison model, based on material costs for a sample project: a 1-mile road, 44-feet wide (a 12-foot lane and 10-foot shoulder in each direction), with a total area of 25,800 square yards. Based on initial construction costs, asphalt is $95,000 less expensive. Based on material costs over a 40-year period, thin whitetopping saves $160,000.

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    Thin whitetopping requires closely-spaced construction joints — a deterrent to some municipalities that favor quicker repair techniques. This 6-inch thin whitetopping project has longitudinal and transverse joints every 9 feet. Photo: Bill Palmer

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    In 1999, CDOT placed a 5-inch thin whitetopping overlay on Parker Road, a high-volume urban corridor on the southeast side of Denver. The $2.9 million project covers 12.5 lane-miles; in 12 years, repairs have been limited to minor transverse cracks. Photo: CDOT

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    In urban areas, curbs and gutters pose a challenge to thin whitetopping design. CDOT has two approaches: covering the curb face with an angled, mountable profile (Figure 1); or removing the curb face (Figure 2) to reduce the vertical profile by 4 inches before placing the overlay. Courtesy of CDOT

Techniques and methods

In 1998, guidelines for the thickness design of thin whitetopping were developed for CDOT by Construction Technology Laboratories Inc. in Skokie, Ill., with basic parameters and techniques unique to concrete overlays. The guidelines require a minimum asphalt thickness of 5 inches, after milling or grinding, for a resurfacing project to qualify for thin white-topping. A hot-mix asphalt base is required to avoid cracking, especially in areas with heavy traffic.

In urban areas, where CDOT has placed most of its thin whitetopping, the department has developed a couple of ways to overlay existing curbs and gutters. One process covers the curb face with a mountable (angled) profile; the other removes a section of the curb face before the overlay. By removing the original curb, the contractor can reduce its vertical profile by 4 inches.

Roadblocks to adoption

CDOT has overcome some of the most common barriers that can discourage states and municipalities from trying thin whitetopping.

Noise control. Transverse tining has historically been the most popular way to texture concrete overlays. Although the technique meets Federal Highway Administration safety guidelines, it often results in noise complaints. Since 2003, CDOT has tested alternatives, including tining with sinusoidal waves, burlap, and diamond grooving and grinding. The agency's preferred method is now Astro Turf: rough enough to add skid resistance but low-noise. If the pavement is designed for speeds of 50 mph or greater, it must have a macrotexture; if speeds are lower, CDOT specifications don't require texturing.