Timely Preservation Improves Performance and Longevity of Concrete Overlay on Asphalt Pavement
By Kristin Dispenza, AOE
A five-year research project in Minnesota will determine the efficacy of one type of preservation treatment for thin concrete overlay pavements. Less than one year into the study, reports on the successes of diamond grinding a faulted concrete overlay are confirming its value as a pres - ervation method.
A concrete overlay can extend the life of existing concrete, asphalt, or composite pavements. Properly constructed, the overlay will deliver the durability and excellent ride quality associated with concrete con- struction, lasting 15-35 years or more with little required maintenance. When an overlay is less than or equal to six inches thick, it is generally referred to as a “thin” overlay. Joint spacing on thin overlays is closer than on traditional pavement, with panels typically measuring six feet long by six feet wide. Thin overlays can be designed and constructed to be bonded or unbonded to the underlying pavement; in unbonded conditions, some degree of movement between the overlay and exist- ing pavement may be designed in or an interface layer may be placed between the existing pavement and the overlay. Bonded solutions utilize the underlying layer to share stresses with the concrete overlay, and are therefore better suited to applications where the underlying pavement is in reasonable condition prior to the overlay. For an overlay to function optimally during its service life, road own - ers must thoroughly evaluate the structural integrity of existing pave- ment prior to commencement of a project. During the design phase, careful consideration must be given to the various options for overlay thickness, panel dimensions and bonding conditions. Once an overlay is in place, it should be regularly inspected and maintained in order to fully reap the benefits of its longevity. Preservation of Thin Concrete Overlay on Asphalt in Minnesota Minnesota’s Washington County Public Works department wanted to ensure the continued success of a concrete overlay on an asphalt section of County State Aid Highway (CSAH) 16, known locally as Valley Creek Road. The overlay was originally installed in response to distresses in the existing asphalt pavement that had manifested by 2011. Average daily traffic levels on the road at the time averaged 25,200 vehicles per day and the pavement was in need of significant repair. The Washington County Public Works department performed
a life-cycle cost analysis and chose a concrete overlay in preference to traditional bituminous pavement rehabilitation methods such as remove-and-replace and full-depth reclamation. The analysis showed that a concrete overlay would offer high durability for comparatively little maintenance. The longer frequency between maintenance proj - ects, which permitted less overall disruption for the driving public and the neighborhoods served by Valley Creek Road, was a deciding factor in favor of concrete for the Public Works department. “After completing the cost analysis, we felt that the concrete overlay was the most cost-effective alternative to resurface the roadway while reducing future disturbances to the traveling public,” said Andrew Gie - sen, Engineer, Washington County Public Works. In all, 8,300 cubic yards of concrete was installed on a 1.42-mile stretch of CSAH 16, using a proprietary blend of ready-mix concrete that cured within 12 hours. Of this 1.42-mile stretch, 1.02 miles re - ceived a concrete overlay placed on a milled asphalt layer, while the other 0.40 miles received a full-depth concrete reconstruction. The overlay was five inches thick, with panels sized at six feet long by six feet wide, placed over the four-inch-thick remaining asphalt that had been in place since 1970. This stretch of pavement is a four-lane divided highway that includes turn lanes. The project cost was $3.268 million, with the concrete overlay expected to have a service life of 30 years. Heavy traffic and its associated vehicular weight, however, pose a risk of breaking the bond between a concrete overlay and underlying asphalt. To guard against this, the Washington County Public Works department monitors the overlay’s rideability, because rough pavement is known to exacerbate vehicular “bounce,” increasing impact loading and intensifying the risk of bond damage. By 2020, while the over - all condition of the overlay was very good, roughness had increased between the intersections of Radio Drive and Bielenberg Drive, with
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csengineermag.com
August 2022
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