U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Summary of FHWA International Scanning Program For Pavement Preservation France, South Africa and Australia July 6 22, 2001
Traditionally, highway agencies have allowed the ride quality and structural condition of their pavements to deteriorate to fair or poor condition before taking steps to rehabilitate the pavements. The aim of rehabilitation is to repair structural damage and restore measurable pavement conditions such as ride, rutting and cracking. This is a costly and time consuming activity with associated traffic disruptions and inconvenience to adjacent businesses and residences. In recent years, an increasing number of highway agencies have found that applying a series of low-cost pavement preservation treatments can extend the service lives of their pavements. This translates into a better investment and increased customer satisfaction and support.
France, South Africa and Australia were identified as nations that have innovative programs as well as new treatments for pavement preservation.
OBJECTIVES and PANEL COMPOSITION
The objective of this scanning tour was to review and document innovative techniques, materials, procedures and equipment utilized in the host countries relative to pavement preservation and to evaluate these elements for potential application in the United States. To this end, the panel had meetings with government agencies and private sector organizations involved with pavement preservation, and also participated in site visits to observe the results of pavement preservation techniques and strategies.
The Federal Highway Administration (FHWA), an agency of the U.S. Department of Transportation, and the American Association of State Highway and Transportation Officials (AASHTO), jointly sponsored the Pavement Preservation International Scanning Tour. The delegation included members representing state departments of transportation in Georgia, Michigan, Pennsylvania, and Texas; National Association of County Engineers (NACE); FHWA; National Parks Service; American Public Works Association (APWA); and, from the private sector, Koch Materials Company and Kristen Betty and Associates.
The countries visited were very thorough in their preparations for the scanning teams visit and were very generous in sharing their experience and expertise. Based on discussions with the host countries, the team recorded many general observations and documented what the team called Key Findings actions taken that have a marked impact on pavement preservation activities and program success. The Key Findings were categorized in the same topic areas as the amplifying questions sent to the hosting
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agencies prior to the teams visit. The teams Key Findings are outlined below by topic area and country.
Management Perspective and Policies
All the countries visited have made a commitment to design and build long lasting structural pavement sections on their national roadway networks. This decision has caused all of these nations to focus maintenance activities on surface courses in order to preserve the large investment in the underlying layers. This, in turn, promotes the use of relatively low cost seals and thin overlays as the primary maintenance techniques, instead of more costly types of rehabilitation.
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authorities to better manage their systems. Secondly, it provides a means to demonstrate to management the importance of and needs for additional funding for their road assets.
Resource Commitment and Cost-Effectiveness
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Treatments, Techniques, and Performance
All three countries use only quality materials for both bitumen and aggregate. Generally, crushed granite and proven polymer-modified asphalt binders are used. This is ensured through the use of very rigorous specifications. Materials sources are specified and there is no inhibition to using sources a great distance away from the project site.
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Innovative Methods, Practices, and Procedures
sophisticated and superior to currently available vehicles. Funding is currently being sought to develop and market this vehicle.
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The scan team was provided with a wealth information at the formal presentations, during informal discussions and gatherings, and in written documents and materials. Throughout the tour, the team members discussed their perceptions of what they were learning in the context of what techniques and strategies in use by the host countries could be practically and successfully put into place in the United States. The team members met at the end of the tour to review their findings and developed the following recommendations that may have a potential for implementation in the United States.
Deep Subbase, Deep Base, and Extended Pavement Design Life
Recommendation: Demonstration projects with deep subbase and deep base designs be initiated in different regions of the United States to determine the effectiveness of this design strategy.
As a first step, a seminar presenting the experience of South Africa and Australia with these design concepts would be of value. A second step would be to develop a pool fund study to design and construct these demonstration sections with a companion NCHRP project to monitor the long-term performance. These sections should also be integrated with other recommendations in this report for thin surface treatments, including chip seals. Treatments outlined in the Chip Sealing section should be incorporated into these demonstration projects.
The countries visited had made decisions to develop pavement sections that included long-lived pavements. These pavements consist of deep subbase and deep base sections with a thin, high-quality wearing course, to provide a good riding surface and moisture protection for the base. Pavement maintenance activities mainly consist of periodic thin surface treatments to renew the ride quality and reestablish an impervious layer. This allows for the maintenance investment to be directed to less expensive surface treatments and not toward costly rehabilitation activities.
In addition, for major sections of the interstate highway system beyond the 20-year design life, it is recommended that consideration be given to design utilizing deep subbase and deep base sections, to provide 30 and 40-year design life.
The following innovative procedures and applications have a high probability of improving performance of chip seals in the US.
Although chip seals are commonly used in the US, two of the countries visited (South Africa and Australia) have developed innovative design procedures and application techniques that are not commonly used in the US. Performance lives up to 15 years are being achieved on sections with up to 60,000 vehicles per day. This outstanding performance is due in part to the deep-strength pavement designs employed.
Recommendation: Agencies include pre-coating of chips in their chip seal specifications.
Pre-coating of aggregates will improve the adhesion of chips to the binder. The South Africans use this technique on their highest volume roads with good success.
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Recommendation: Geotextile-reinforced chip seals be tested and evaluated in both freeze and no-freeze environments.
Throughout Australia, a treatment called geotextile-reinforced sprayed seals has been very successful. The treatment, which involves tack coating the existing pavement, spreading a geotextile, and capping with a chip seal, is used on roadways with moderate cracking. This treatment has proven to retard reflective cracking in Australias wet and dry no-freeze climates. In addition to the geotextile, it is believed that modified binders, including crumb rubber, aid in the retardation of reflective cracking. (See Technical Bulletin 38 for specifications, geotextile type and thickness, type of tack coat, additives, etc.).
This treatment has also been used directly on subgrade and has been very successful in retarding damage to this material, provided no traffic is allowed during saturated conditions.
Recommendation: Agencies that do not use modified binders for chip seals should be encouraged to do so.
Quality chip seals exhibiting long service life use bitumen modified with a variety of products. The predominate modifiers are SBS (extensively) and crumb rubber (to a lesser degree). A unique application used in France and Australia that deserves evaluation is the use of fibers applied directly on the bitumen before the application of the cover aggregate. The fibers enhance both aggregate retention and treatment performance.
Recommendation: Encourage agencies to review their specifications and upgrade them where appropriate so that superior aggregates are used and improved service life is accomplished.
The success of chip seals in all the countries visited is due in large part to the high quality of the aggregate and the emphasis placed on design. High quality aggregate (clean, <0.05% passing the 200; low LA abrasion (<15); low micro-duval (<20)) of a single size is routinely used. In many instances, aggregate is hauled great distances (>500 km). In addition, application rates are optimized for the type of aggregate and bitumen used.
Recommendation: Encourage agencies to review their design practices for chip seals and consider placing them on base or subbase courses to prevent moisture infiltration.
To prevent moisture infiltration and capillary action, the Australians often place a chip seal on the base or subbase prior to placing the asphalt surface. This technique is especially useful on highly moisture susceptible bases and subbases. The Australians also perform designs to optimize application rates for the type and gradation/grade of aggregates and bitumen used.
Timely Preventive Maintenance
Recommendation: Chip seals should be applied earlier in the distress cycle.
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All countries visited tried to detect cracking in the 1-3 mm range, at which time a chip seal would be applied. The typical US treatment is to wait for a visible cracks to appear (4 mm or greater) before applying a crack seal. Often, only after several years of crack sealing is a chip seal applied in the US. Applying a chip seal earlier in the distress cycle would prevent water infiltration into the base and thus deter premature pavement failure. This approach may extend the life of roadway pavement structures and reduce the need for expensive rehabilitation projects.
Recommendation: The successful practice in New South Wales of placing thin (40-60 mm) asphalt overlays on PCC should be investigated.
Placing thin overlays on PCC pavement has not been very successful in the United States. The Australians have designed a system specifically for this application that may provide additional preservation options for PCC pavements in the United States. In Australia, the PCC is cured with a hydrocarbon compound followed by the application of a tack coat in the normal manner.
Innovative Methods, Practices and Procedures
Recommendation: AASHTO and FHWA should develop a mechanism to evaluate and implement new and innovative products and processes.
A new, national, institutional process needs to be established in order to foster and manage innovation. This process needs to include proprietary products that private sector investment has developed and should also consider the concept of risk sharing as exemplified by the French Charter of Innovation system. This would encourage innovation by giving contractors/suppliers greater opportunities to market new technology.
Recommendation: AASHTO and/or FHWA should conduct a seminar to share best practices and also investigate the possibility of demonstration projects in the United
States using long-term maintenance contracts.
Contracting or outsourcing maintenance activities has moved to long-term contracts of 3 to 10-year periods for various types of total maintenance. These contracts are monitored for performance by means of various asset management techniques.
Additional evaluation of the associated benefits for such long-term contracts regarding pavement preservation is needed.
Pavement Condition Survey Equipment
Recommendation: An investigation of Road Crack? and similar vehicles be conducted to fully evaluate the potential for use by transportation agencies. And, if warranted, a pilot program be developed for a side-by-side field evaluation of these vehicles
Early and accurate detection of pavement distresses is essential for an effective pavement preventive maintenance program. Transportation agencies in the US invest significant amounts of resources in the collection of road condition information.
Transportation agencies are in constant search of more efficient and cost-effective ways
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of collecting this information. In the State of New South Wales, the team was made aware of a high-speed pavement condition survey vehicle capable of detecting pavement cracks as small as one mm in width. The Road Transportation Authority (RTA) of New South Wales has developed the Road Crack? vehicle that meets this need. This vehicle has the potential of saving significant resources in transportation agencies throughout the US and other countries.
A small group of the scanning team members has been formed to develop a technology implementation plan that will outline a series of activities to document, showcase, apply and evaluate the innovative pavement preservation techniques, processes, materials and equipment utilized in the tour hosting nations. These activities will be directed to educate and demonstrate to the United States highway community the effectiveness and value of these innovative technologies.