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

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91 CHAPTER NINE CONCLUSIONS Based on the survey and the extensive literature resources that were available it is clear that a high level of knowl- edge and information has been built up in the field of ac- celerated pavement testing (APT). The scope of APT stud- ies is indeed very large, which was evident from the analysis of the questionnaire responses (Appendixes B–D) and case studies that were derived from the subject bibliog- raphy. These were included as integral parts of the various chapters and related Appendixes G and H. The nature of this synthesis is such that the details of the various aspects of APT that were reviewed are pre- sented in a number of locations for subsequent retrieval 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. Overall, it was concluded that APT had served as a means of improving performance and economics of pave- ments. It has improved the understanding of the factors that affect pavement performance through the ability to • Explore a wide variety of structural compositions and configurations; • Simulate mechanisms, conditions, and processes through loading and environment; • Test and characterize materials; and • Analyze and understand response and performance. The acquired knowledge is being widely applied and it has enhanced innovation in pavement engineering. The following general conclusions were drawn relative to the generic core of significant findings in terms of applications. On the topic of design, construction, maintenance, and rehabilitation the survey and literature showed that • Unique, unconventional pavement structures could be tested and evaluated through APT. • Failure mechanisms could be meticulously evaluated so that it became possible to cost-effectively counter- act distress mechanisms. • A wide range of structural design packages have been evaluated or developed and this has greatly enhanced their implementation. • Systematic investigation of the vehicle–pavement– environment interaction has been made possible and feasible through APT, although much still remains to be done on this subject. • A large number of APT tests were related to pave- ment materials. This is indicative of the potential of APT to provide sound answers about pavement mate- rials. More particularly, it has been shown to be use- ful for answering questions relating to the use of new materials, composite materials, and materials with complex physical characteristics. • APT is a tool for confirmation and validation of laboratory test procedures. • APT has become a useful tool for systematically de- veloping and evaluating performance models. • APT is a means of answering questions related to re- habilitation, construction, and maintenance in the field. Answering those questions would be more dif- ficult and take far longer without APT experiments. This synthesis provides evidence of the economic and management benefits that have been generated by APT. More particularly • The economic gains as a result of APT are measur- able. Details were given as to what has been achieved in terms of benefit-cost ratios, savings on capitol ex- penditure, and the use of recycled and new materials and new pavement structures. Benefit-cost ratios ap- pear to vary from 1:1 to more than 20:1. • APT has provided a quantitative basis for communi- cating with decision makers about pavement per- formance. 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 (PMS) and in-service pavement evaluation. If the identified gaps in the sys- tem are addressed, it may lead to rapid advances in pavement engineering and ultimately to long-life pavements with reduced maintenance costs. • 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 perform- ance. A variety of examples were discussed. A good example is the improved understanding of tire– pavement interaction and its effect on performance. The growth of APT in the United States may stimulate advances in the field. This might gain even further momen- tum as OECD COST 347 achieves its goals in Europe.

92 It was apparent that APT programs in general, and in the United States in particular, have a number of common ob- jectives. This became clear from the synthesis of the results of the survey questionnaire. By prudent use of the avail- able information and collaborative research efforts, APT programs could advance pavement knowledge more rap- idly. This could include some planned replication to im- prove on the reliability of findings and to establish confi- dence limits. A number of issues that require collective input or collaborative efforts were evident from the synthesis. • There was an apparent lack of feedback on the extent to which APT performance predictions had been validated. This applies to components of the system as well as complete and comprehensive design sys- tems. Consideration should therefore be given to tracking the performance of in-service pavements that have been tested in APT programs, as a matter of course, where and when possible. This will enable comparative performance studies to be conducted. • In line with international trends, APT programs should, where possible, have closer association with in-service pavement evaluation and formal long-term pavement performance and related PMS programs. • There is an urgent need to improve on the quantifica- tion of environmental impact on APT performance. Progress in this regard could improve the credibility of APT among other professional decision makers in the field of pavement infrastructure. This would require a well-structured, strategic plan to address all aspects of the vehicle–pavement–environment interaction. • The advancement in the understanding of vehicle– pavement interaction during the last decade provides a basis for further studies that could enhance pave- ment performance prediction. The stimulus that is being provided by the strong growth of APT in the United States is likely to lead to ma- jor advances in the field. This may gain even further mo- mentum as OECD COST 347 achieves its goals in Europe. The wide range of pavement types and configurations that have been tested through APT provide a heritage of knowledge on pavement engineering. This synthesis is the link to this knowledge. It has served to create an awareness of the benefits that are to be gained from prudent use of the information through collaborative efforts. One of the rea- sons for the collaborative approach lies in the vast number of possible test parameters that can be tested for different structural configurations. This trend is growing; for exam- ple, the COST 347 project and the pooled fund studies in the United States. It is recognized that a new generation of researchers have entered the APT field. This synthesis, to- gether with NCHRP Synthesis of Highway Practice 235, should assist these researchers in their quest to become ac- quainted with all aspects of APT. Internationally, the situation is somewhat different where facilities have reached maturity and services are be- ing rendered in an environment of privatization. Clients are now often road agencies, and industry and projects are be- ing completed on the basis of Design, Build, and Operate. This is leading to partnering and the use of APT in support of warranty contracts and improved management of pave- ment 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 the tools, technology, and APT practices that will enable them to be well prepared for the challenge. This development also has a negative aspect that needs to be considered. With the trend toward privatization and partnering, the results of APT studies are no longer natu- rally in the public domain. This does not necessarily re- strict access to the information; however, it often slows down the technology transfer through conferences and publications, although the Internet may change all of that dramatically. APT activities throughout the world have be- come linked and this is greatly enhancing exchange of data and information.