Maintaining High Performance Levels

Follow the correct course of action to assure a high-performance, quality HMA pavement

Asphalt Article December 28, 2000
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Hot-mix asphalt (HMA) pavements are essential to America’s transportation system. The performance of HMA must be maintained at its highest possible level to ensure the safety and mobility of the motorist. Getting optimum performance from the pavement minimizes the frequency of disruption to the traveling public.

Improve product performance

In this key issue, there is only one element. Agencies, the Federal Highway Administration (FHWA) and the industry must do everything possible throughout the construction process to improve the performance of the pavement. By getting longer life out of the pavement placed, the frequency of inconvenience to the traveling public will be reduced.

Performance-based specifications move the construction process to higher performance standards, thereby “raising the bar” for product acceptance. Performance specifications will require the contractor to develop greater understanding of the effect construction practices have on performance, thereby allowing the selection of mix types and construction processes, which optimize performance of the pavement.

In order for this to take place, an ability to quantify and measure performance of materials must be developed.

Extending pavement life

The life of the pavement can be made longer through more efficient use of equipment and materials. If the life of the pavement is increased, maintenance cycles can be increased and the disruption to the motorist is reduced. Efficient use of equipment and materials can positively impact the life of the pavement. Specifications should be developed to demand the highest level of performance commensurate with the level of service of the facility. These specifications should be performance-based rather than prescriptive requirements.

The type of mix used for the specific pavement must be selected to ensure appropriate performance. The mix must be handled and placed in such a manner that segregation does not occur. Further, the mix must be compacted to achieve the appropriate density, including joint density, to ensure performance. Both segregation and compaction are equipment-related issues upon which emphasis must be placed. Control of the entire construction process is critical to achieve a high-performance HMA pavement.

Use of non-destructive testing techniques for evaluating existing pavements can provide good guidance on appropriate rehabilitation techniques. It is necessary to identify and develop improved procedures and equipment to evaluate structural capability of existing pavements. Falling Weight Deflectometer (FWD) testing of the pavement may provide the best data, but data analysis techniques need to be advanced. An essential element of this issue is to ensure that a pavement design is constructable.

Efforts must be undertaken to ensure that pavement drainage systems are properly designed and maintained. New maintenance techniques and equipment may be required to accomplish this. This activity alone could have a significant impact on the performance of pavement structures.

Course of action

Through all appropriate channels, pursue equipment and materials opportunities which can improve HMA performance.
In particular, develop heightened awareness for technology which already exists but may not be universally is use. Specific examples of this are:

Specify the use of the Reed tachometer to verify the correct dynamic input of vibratory compaction equipment. This technology has been widely available for many years, but is not widely used to verify the number of vibrations per minute of the compactor. This is a simple technology which can improve the achievement of specified density in the HMA, thereby improving the life of the pavement.

Develop guidelines for the use of specific mix types relating to the pavement level of service. Use of an appropriate mix will ensure that longevity in the pavement can be achieved. This activity can be accomplished through joint discussions with AASHTO and the industry.

Guidelines have been developed for the elimination of segregation. Information is available which describes best practices, but the
concepts may not always be followed. Equipment and training must be available for the contractor’s personnel to ensure best practices are being used. Non-destructive technology to measure segregation will aid in identifying and reducing segregation.

Through FHWA and National Cooperative Highway Research Program (NCHRP) channels, develop a plan for the evaluation of analysis techniques using FHWA data.

Establish a working group to promote new techniques and equipment for the inspection and maintenance of drainage systems. the FHWA has a demonstration project on pavement drainage inspection. This group should include equipment manufacturers, agency and industry personnel.

Performance, quality, innovation

In order to stimulate superior performance, quality and innovation, contracting procedures must be jointly developed using performance-based specifications. In order for this to occur, measurement criteria for quality must be quantified and appropriate rewards for quality must be established. Continued joint support of the National Quality Initiative should be an integral part of the process.

Course of action

Convene a joint industry/agency group to continue the development and incorporation of performance-based specifications into contracting procedures. Coordinate with FHWA and NCHRP activities currently underway to identify measurement criteria for quality. Work with the AASHTO subcommittees on materials, maintenance and construction.

Accelerated test methods

Accelerated testing procedures that measure product performance must be established. Identify and develop accelerated test methods for QC/QA that directly reflect product performance and then validate the use of tests that offer promise to predict performance. After the developmental process is completed, AASHTO approval must be achieved along with acceptance by the industry.

Course of action

Develop a synthesis of accelerated testing procedures that measure product performance. Significant work elements by FHWA and NCHRP are underway on this subject. This is a critical element for the industry to move ahead with innovative technology. As part of this process, testing procedures that impede construction progress should be identified and eliminated.

Longer product life, higher performance

In order to develop construction practices that provide longer lasting products and higher performance, testing and inspection of pre-existing conditions should be required prior to placement of HMA. Techniques must be established to accomplish this expeditiously, allowing the condition to be appropriately treated prior to the placement of the new pavement.

Evaluation techniques must be developed which will allow the evaluation of new products in a reasonable time frame against performance-based criteria.

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