Significant Findings from Full-Scale Accelerated Pavement Testing (2004)

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SIGNIFICANT FINDINGS FROM FULL-SCALE ACCELERATED PAVEMENT TESTING SUMMARY A large volume of knowledge exists globally in the field of accelerated pavement testing (APT). The focus of this study was to tap this source of knowledge for application to re- search and practice. In particular, the focus was on programs operational during the past 20 years. A number of the APT programs are featured prominently because they have been op- erational for extended periods of time. For this report, accelerated pavement testing was de- fined as the controlled application of wheel loading to pavement structures for the purpose of simulating the effects of long-term in-service loading conditions in a compressed time pe- riod. This included programs of the Council for Scientific and Industrial Research in South Africa, France’s Roads and Bridges Research Center (Laboratoire Central des Ponts et Chaussees), the Australian Road Research Board, and, more recently, the APT program in California in the United States. In NCHRP Synthesis of Highway Practice 235, published in 1996, Metcalf presented a comprehensive overview of APT programs with details about the extensive range of APT facilities in existence at that time. A wide variety of APT programs are operational in the world today. Twenty-eight such programs were reported as being currently active, with 15 of these in the United States. Most of these tests are being conducted at fixed sites. However, there are still programs that focus on field studies in the belief that this results in improved vehicle–pavement–environment interaction. Of the new facilities, the National Airport Pavement Testing Facility is unique. That it can simulate full-scale landing gear (undercarriages) of aircraft is indicative of its sheer size. The other facilities are conventional linear trafficking test devices that have, in most cases, been customized to suit specific needs. It is notable that the latest generation of test devices either has partial or full environmental control. The test track at the National Center for Asphalt Technology at Auburn University, Auburn, Alabama, is similar to the WesTrack test facility at Reno (Nevada), except that the former is in a different climatic zone and the trucks have drivers instead of being remotely controlled. The information used for this study was obtained through a questionnaire distributed in- ternationally. The respondents to the questionnaire added considerable value to the synthesis through their detailed answers. The information was not only relevant but of a quantitative and qualitative nature difficult to obtain cost-effectively through any other means. This in- formation was supplemented by a detailed study of the extensive bibliography that is avail- able on APT. The international APT conference that was held in Reno in 1999 provided the most recent comprehensive update on APT information. An important aspect of APT is the Co-operative Science and Technology study program of the European Community (COST). This organization is currently working in parallel with the current synthesis toward establishing a knowledge base on APT in Europe. There is some overlap; however, both efforts should benefit from the understanding that was reached between the TRB A2B09 committee on APT and the COST 347 committee. According to this agreement there will be as much exchange of information as possible. The agreement

2 paved the way for the European APT programs to share their knowledge by participating in the survey conducted as part of this project. The analysis for this synthesis was done by reviewing the available information in terms of elements of a pavement system. The results were then synthesized and the significant findings were categorized relative to the different pavement elements. Summaries of views of the respondents were compiled relative to the following topics: • Evaluation, Validation, and Improvement of Structural Designs; • Vehicle–Pavement–Environment Interaction; • Evaluation of Materials and Tests; • Enhancement of Modeling in Pavement Engineering; • Development and Validation of Rehabilitation, Construction, and Maintenance Strategies; • Pavement Engineering Applications and Issues; and • Improvement of Pavement Economics and Management Through APT Applications. These views were considered to be important, because they are related to the direct ex- perience of the users and their application and use of significant findings. The questionnaire responses also contained categorized references, which were used to compile an annotated topical bibliography that is provided at the end of this report. The extensive list of applications that were collated as a product of the synthesis was primarily generated by the delegates themselves. It provides examples of what can be achieved if APT is used prudently in a systematic manner. The following overview presents the generic core of significant findings in terms of applications. APT has been instrumental in validating and refining agency structural design guidelines. Improvements in structural design have also been brought about by the insight gained on the effect of a number of factors on pavement performance, including • The influence of water on performance and related failure mechanisms, • The importance of bond between layers and the quantification of the effect, • The interaction between structural composition and material characteristics, • The influence of concrete slab configuration, and • The influence of support under concrete slabs. The scope of APT studies is very large, which was evident from the analysis of the ques- tionnaire responses that were received from APT programs worldwide. This analysis and the many case studies that were taken from the bibliography have made it possible to access the large number of applications in a logical manner, depending on the needs of the reader. These were included as integral parts of the various chapters, covering specific fields of pavement engineering, and related appendixes. This synthesis is constructed such that the details of the various aspects of APT that were reviewed have been captured and embedded in a number of locations for subsequent re- trieval by researchers and practitioners who are active in APT or in using the results of APT. An index is provided that should prove useful in this regard. More particularly, the following findings are noteworthy: • Unique, unconventional pavement structures have been tested and evaluated through APT.

3 • Diagnostic studies of failure mechanisms provided a basis for understanding and coun- teracting distress mechanisms. • A wide range of structural design packages has been evaluated or developed and this has greatly enhanced implementation. • Systematic investigation of the vehicle–pavement–environment interaction is feasible through APT, but it will require a dedicated collaborative effort and commitment to overcome the constraints owing to the extended nature of such a study. • The large number of APT tests relating to pavement materials is indicative of the po- tential of APT to provide sound answers about pavement materials. More particularly, it has been shown to be useful for answering questions relating to the use of new mate- rials, composite materials, and materials with complex physical characteristics. • APT is a tool for the confirmation and validation of laboratory test procedures. • APT has become an important tool for developing and evaluating models. • APT is an important means of answering questions related to rehabilitation, construc- tion, and maintenance. Answering those questions would be more difficult and take far longer without APT experiments. This synthesis provides ample evidence of the economic and management benefits that have been generated by APT. More particularly • The economic gains as a result of APT are measurable. Details are given as to what has been achieved in terms of benefit-cost ratios, savings on capital expenditure, and the use of new and recycled materials and new pavement structures. Benefit-cost ratios varying from 1:1 to greater than 20:1 have been reported. • Many ancillary artifacts have been developed in APT-related technologies in support of programs throughout the world. These have had considerable impact on the ability to understand pavement response and performance. A variety of examples are dis- cussed. An important example is the improved understanding of tire–pavement interac- tion and its effect on performance. • APT has provided a quantitative basis for communicating with decision makers about pavement performance. However, it will be necessary to upgrade APT systems to be able to account for environmental effects on a quantifiable basis. • APT has attributes that supplement many aspects of pavement management systems and in-service pavement evaluation. If the identified gaps in the system are addressed, it may lead to rapid advances in pavement engineering and ultimately to long-life pavements with reduced maintenance costs. The growth of APT in the United States may stimulate advances in the field of pavement engineering. This could gain additional momentum as the COST study program of the Euro- pean Community (OECD COST 347) achieves its goals in Europe. Several items were identified where further research could be undertaken to advance the practice. • As a matter of course, the performance of in-service pavements that have been tested in APT programs could be tracked for future comparative performance studies. This would enhance continued improvement in the understanding and development of per- formance models. • APT programs could, where possible, have closer association with in-service pavement evaluations, formal long-term pavement performance studies, and related pavement management systems to validate and evaluate APT results.

4 • Vehicle–pavement–environment interaction could be further explored to enhance the ability to do quantitative performance prediction of different pavement structures un- der specific conditions, which would probably be best achieved through a comprehen- sive collaborative APT program. APT programs could advance pavement knowledge more rapidly by the prudent use of the available information and collaborative research efforts. This could include some planned replication to improve on the reliability of findings and to establish confidence limits. The wide range of pavement types and configurations that have been tested through APT provide a broad foundation of knowledge on pavement engineering. A new generation of re- searchers has entered the APT field in the United States. This synthesis should assist them in their quest to become acquainted with all aspects of APT. Internationally, the situation is somewhat different because many facilities have reached maturity and services are being rendered in an environment of privatization. Clients are now often road agencies and projects are being conducted on the basis of design, build, and oper- ate. This in turn is leading to partnering and the use of APT in support of warranty contracts and improved management of pavement infrastructure. With globalization it would seem prudent to anticipate similar wide-ranging changes in the United States. It is therefore particularly fortunate that the APT programs in the United States have entered a phase of development that should provide tools, technology, and APT practices that enable them to be well prepared for the challenge. This development also has a negative aspect that needs to be considered. With the trend towards privatization and partnering, the results of APT studies are by default no longer in the public domain. This does not necessarily eliminate access to the information, but often it slows down the technology transfer through conferences and publications, although increasing use of the Internet may change all of that dramatically. APT activities throughout the world have become interlinked and this is greatly enhancing exchange of data and information.