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Concrete Pavement Technology Update

August 2008

In This Update:

Concrete Overlays—An Established Technology With New Applications

The need for optimizing preservation and rehabilitation strategies used to maintain the Nation’s highway pavements has never been greater. Concrete overlays have a long history of use to preserve and rehabilitate concrete and asphalt pavements, and many of the practices are well established. However, of recent origin are techniques that use thinner concrete overlays with shorter joint spacing. Field experience over more than 15 years with the thinner concrete overlays under a range of traffic and site conditions has demonstrated their viability as a cost-effective solution to extend the service life of deteriorated asphalt and concrete pavements.

The Federal Highway Administration (FHWA) has initiated several activities to support technology transfer related to concrete overlays. These activities include reviews, on a regional or statewide basis, of current applications of concrete overlays, identification of gaps in technology, and assistance in developing a program—jointly with State departments of transportation (DOTs) and industry—for technology transfer and demonstration projects. FHWA is assisting with organization of meetings at the State and regional levels to help coordinate concrete overlay technology transfer activities.

Overview of Concrete Overlays

Concrete overlays offer a broad range of applications for preserving and rehabilitating asphalt, concrete, and composite pavements. Concrete overlays can be designed for a range of traffic loading to provide long performance lives, 15 to 40+ years, to meet specific needs. Well-designed and well-constructed concrete overlays require low maintenance and can have low life-cycle costs. Applications include the following:

  • Over existing asphalt pavements
    • Bonded overlay of asphalt pavements
    • Unbonded (directly placed) overlay of asphalt pavements
  • Over existing concrete pavements
    • Bonded overlay of concrete pavements
    • Unbonded (separated) overlay of concrete pavements
  • Over existing composite pavements
    • Bonded overlay of composite pavements
    • Unbonded (directly placed) overlay of composite pavements

Bonded overlays are typically thin, 2 to 6 in. (50 to 150 mm) in thickness. When bonded to a milled asphalt surface, the overlay panels are typically 6 by 6 ft (1.8 by 1.8 m) or less in dimension.

When bonded to a prepared concrete surface, the overlay jointing pattern matches the jointing pattern of the existing jointed concrete pavement. In the case of continuously reinforced concrete pavement, transverse jointing is not provided.

Unbonded overlays are of two types:

  • Conventionally thick overlays, 6 in. (150 mm) or thicker, are full-width and have transverse joint spacing of 12 to 15 ft (3.7 to 4.6 m).
  • Thinner overlays are 4 to 6 in. (100 to 150 mm) thick, and the overlay panels are typically 6 by 6 ft (1.8 by 1.8 m) or less in dimensions.

Irrespective of thickness, unbonded overlays are always placed over an asphalt concrete surface—whether an asphalt pavement or an asphalt interlayer/resurfacing placed over a concrete pavement.

Regional Meetings

A keystone activity of FHWA’s concrete overlay program is meeting with highway agency senior management to assist with reviewing their agency’s application of concrete overlays, identifying gaps in technology, and developing a program, jointly with FHWA, highway agencies, and industry, for technology transfer activities. In November 2007, a meeting was held in Springfield, Virginia, among FHWA; senior management from highway agencies in Delaware, District of Columbia, Maryland, Virginia, and West Virginia; and the American Concrete Pavement Association (ACPA) Virginia Chapter. The mid-Atlantic experience with concrete overlays was reviewed, and the successful experiences of Colorado and Michigan with concrete overlays were discussed. Meetings were also held with the Louisiana DOT staff in Baton Rouge in April 2008 and the South Dakota DOT staff in Pierre in July 2008, where the North Dakota DOT staff participated as well. Local concrete overlay experience was reviewed and assistance discussed.

Concrete Overlays Guide

The Guide to Concrete Overlay Solutions (National Concrete Pavement Technology Center, January 2007) is available at www.cptechcenter.org/publications/overlays/. Print copies are available from ACPA (800-868-7633).

Rough sketches show bonded and unbonded concrete overlays used in three ways: over asphalt, concrete, and composite pavement. The unbonded overlays are shown as thicker than the bonded overlays, and for the unbonded overlay over concrete a thin layer of asphalt is sandwiched between the two layers of concrete.

With support from FHWA, the National Concrete Pavement Technology Center (NCPTC) at Iowa State University developed a best practices Guide to Concrete Overlay Solutions. Prepared by a joint industry/State DOT Task Force on Concrete Overlays, the guide presents an overview of concrete overlay systems for resurfacing or rehabilitating pavements and includes detailed guidelines for overlay use:

  • Evaluating existing pavements to determine whether they are good candidates for concrete overlays.
  • Selecting the appropriate overlay system for a specific pavement condition.
  • Managing concrete overlay construction work zones under traffic.
  • Accelerating construction of concrete overlays when appropriate.

Best Practices Workshop

Under FHWA’s Concrete Pavement Technology Program (CPTP), a 6-hour workshop based on the Guide to Concrete Overlay Solutions has been developed and is available to highway agencies. The concrete overlay workshop covers the following topics:

  1. Pavement fundamentals for overlay applications
  2. Existing pavement evaluation
  3. Technical discussion of concrete overlay design, construction, and materials
  4. Special considerations—geometrics, transitions, shoulders
  5. Concrete overlay case studies
  6. Maintenance of traffic
  7. Overlay performance and life-cycle cost considerations
  8. FHWA/NCPTC Concrete Overlay Field Applications Program

The overlay workshop has been presented to State DOT staff from Pennsylvania, Louisana, North and South Dakota, and Washington State.

Construction of an unbonded concrete overlay on concrete pavement, I-44, Missouri.

A stretch of highway where unbonded concrete overlay has been applied to a concrete pavement.

Field Applications Program

To advance the use of concrete overlays as cost-effective solutions for a wide variety of pavement conditions, FHWA and NCPTC are implementing the Field Applications Program. The overall objective of this 2-year program is to increase awareness and knowledge related to concrete overlay applications among State DOTs, cities, counties, contractors, and engineering consultants by demonstrating and documenting various concrete overlay applications. At least six States from diverse regions will participate in the selection, design, and construction of concrete overlay demonstration projects.

The Field Applications Program includes the following components:

  • A workshop based on the Guide to Concrete Overlay Solutions through CPTP.
  • Site visits to select candidate concrete overlay demonstration projects.
  • Meetings with an expert team managed by NCPTC for guidance on design and construction of the projects.
  • Access to Iowa State University’s mobile concrete testing laboratory to document quality control at the project sites.
  • Documentation of the design and construction processes.
  • Development of recommendations for updating concrete overlay practices.

The Louisiana and South Dakota DOTs have agreed to participate in the FHWA/NCPTC Concrete Overlays Field Applications Program, have hosted the Best Practices workshops, and are in the process of identifying candidate projects.

FHWA, South Dakota, and consultant staff visit a candidate concrete overlay site.

Seven men (FHWA, South Dakota Department of Transportation, consultants) stand by a stretch of highway in a field visit.

For more information:

Field Applications Program:

CPTP Concrete Overlay Workshop:

Article prepared by Shiraz Tayabji, CPTP Implementation Team.

August 2008
FHWA-IF-08-015

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Updated: 04/07/2011
 

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