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

In a mountainous region that endures 300 freeze/thaw cycles a year, maintaining roads is an inherent challenge. Through its ongoing search for cost-effective ways to extend pavement life, Colorado DOT (CDOT) may have discovered its ideal solution: thin whitetopping.

While asphalt has always been part of the state's pavement structure, the pliable material is susceptible to damage from the harsh climate, snow tires, and chains that road agencies use several months every year. “When you have repetitive maintenance issues, you need to compare the cost and frequency of repairs with a long-term solution that may cost more upfront but saves money in the long run.” says Pavement Design Program Manager Jay Goldbaum.

Goldbaum has learned from experience. As a CDOT employee of 23 years, he has worked on whitetopping projects since 1993 — and now serves on the national panel to develop AASHTO's mechanistic empirical pavement design guide (MEPDG) DARW-in ME software.

CDOT began considering thin white-topping as an alternative to asphalt overlays in 1990, with a test project on State Highway 68 near Fort Collins. Based on its success, the agency continued using the pavement-restoration method on highways and local roads, and added it to state specifications in 2004. To date, CDOT has placed almost 900,000 square yards of thin whitetopping.

“We base our decision to use thin whitetopping on a 40-year life-cycle cost analysis,” says Goldbaum (see above chart). In general, the agency assumes the concrete overlay will last 27 years before requiring significant rehabilitation efforts, as compared to an asphalt overlay's 12-year life span. Half of the state's thin whitetoppings have been in service for a decade or longer, and have an average annual maintenance cost of less than $400/lane-mile.

Goldbaum has also noticed an interesting economic trend — more stable asphalt costs. “In areas where we've done whitetopping, we've seen hot-mix asphalt prices stay constant or even come down.”