(The following article and photograph are reproduced, with permission, from the January/March 2001 issue (Vol. 15, No. 2) of The Bridge, a publication of the Transportation Center at Michigan Technological University in Houghton, Michigan. Our thanks to Michigan's Local Technical Assistance Program for providing electronic copies of the article and photograph.)

Rutted intersections? Washboard roads? Ultrathin Whitetopping (UTW) is one option for the rehabilitation of any area where rutting, washboarding, and shoving of asphalt is a problem. UTW is the term for paving with a thin layer (2-4 inches) of Portland Cement Concrete (PCC) over an existing bituminous pavement. The technique was developed specifically for low-volume roads, parking areas, and light-duty airports. UTW is a subcategory of whitetopping, wherein the concrete is thinner than conventional whitetopping and forms a bond with underlying asphalt, thereby creating a composite action. Short joint spacing significantly improves the overlay's performance.

The first experimental application of UTW was constructed on an access road in Louisville, Kentucky in 1991. Since then, nearly 200 UTW projects have been constructed in 28 states.

Apparent advantages of UTW

Test data on UTW indicates that, in most cases, it requires less time to construct and repairs last much longer than conventional asphalt rehabilitation techniques. In Iowa, a recent cost comparison study on conventional whitetopping showed that ". . . a 5 to 6- inch concrete overlay costs up to 50% more than a 2 or 3-inch asphalt overlay, but that the concrete pavement can last twice as long as asphalt. ¹ Likewise, UTW provides a cost-competitive, durable wear surface. UTW surfaces reflect light and street lighting costs can be reduced. Finally, UTW provides a cooler surface and its attendant environmental benefits.

Four-step UTW Construction

1. Milling and cleaning or blasting the surface with water or abrasive material prepares the surface so that it will bond the two layers.
2. Place, finish, and cure concrete overlay using conventional techniques. The concrete mix is matched to the project's traffic conditions and time line for opening the road to traffic. Many mixes include synthetic fibers used to increase post-crack integrity of the panels. Because the overlay is thin, it can lose water rapidly due to evaporation. Proper curing is critical, and curing compound is applied at twice the normal rate.
3. Cut saw joints as early as possible to control cracking.
4. Open to traffic

UTW in Michigan

Until 1999, concrete whitetopping had not been used on any Michigan trunklines, but it had been used on local and private roads:

• September 1996--an entrance drive to a steel company and concrete redi-mix plant in Traverse City.
• October 1996--a short portion of Schaefer Hwy. at the Coolidge Yard Bus Terminal in Detroit.
• October 1997--the intersection of Ann Arbor-Saline Rd. and Pleasant Lake Rd. in Washtenaw County.

Section 7-UTW Project-M-46, Sanilac County

In 1999, a rehabilitation project was constructed on M-46 in Sanilac County. The project scope includes concrete whitetopping and concrete inlay treatments, in addition to typical bituminous fixes. The project evaluation will measure the cost effectiveness of each rehabilitation treatment in similar traffic, soils, and environmental conditions.

The expected evaluation period is fifteen years, which should equate to the maximum fix life of the bituminous alternatives.

For additional information on UTW in Michigan, contact the Michigan Concrete Paving Association at (517) 347-7740 or Michael Eacker at eackerm@mdot.state.mi.us.

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