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In October 2010 village engineers, representatives from the consulting firms that helped design and build the project, and the Illinois Chapter of American Concrete Pavement Association presented a live demonstration of the ultra-thin whitetopping process.

Credit: Photo: Village of Lombard

OVERVIEW:

OWNER: Lombard (Ill.) Department of Public Works
PROJECT: Restoring 6,600 linear feet of asphalt pavement
GENERAL CONTRACTOR: Plote Construction Inc.
DESIGN ENGINEER: Civiltech Engineering Inc.
CONSTRUCTION ENGINEER: Baxter & Woodman Consulting Engineers
GEOTECHNICAL/CONSTRUCTION MATERIAL ENGINEER: SEECO Consultants Inc.
CONSTRUCTION: July 2010 – Spring 2011
ORIGINAL ESTIMATE: $13 million
FINAL COST: $2.5 million

Given unlimited time and resources, engineers would always completely replace the heavily abused streets that wind through industrial parks. But with an estimated price tag of $13 million over four years, that wasn't an option for the 40-year-old asphalt in Lombard's North Industrial Park.

Though it would allow businesses to continue operating during construction, a mill and overlay wouldn't sufficiently withstand the park's truck traffic over time. Public works needed a more affordable, longer-lasting solution.

Village Civil Engineer Ray Schwab found one that's rarely been used in urban settings: ultra-thin whitetopping, also known as bonded concrete overlays of asphalt pavements. Typically used on asphalt roads that are in fair condition structurally (meaning there's little more than surface distresses such as rutting and cracking), a layer of concrete 2 to 4 inches thick bonds to the existing hot-mixed asphalt to perform as one monolithic pavement.

Though installation is no different from traditional concrete paving and involves the same equipment, the technique is specified much less frequently in urban areas. This is partly because asphalt mill and overlays take less time, making proposed repairs more palatable to motorists and elected officials. But it's also because the product is assumed to be less durable. In fact, ultra-thin whitetopping wasn't an Illinois DOT-approved rehabilitation method until 2010.

So until recently the technique's been used mainly in low-volume rural areas with divided highways.