One of the major tasks in any transportation agency pavement management system is to select the appropriate alternative for rehabilitation and maintenance. There is a need to understand how preventive maintenance improves the performance of the existing pavements, to develop new techniques, and to determine the optimal timing for the application of these treatments. Perhaps the main reason to apply a preventive maintenance treatment to an HMA pavement is to reduce the aging of the asphalt binder and therefore maintain a higher level of pavement performance. Some research has documented the aging of asphalt through traffic loadings. However, the mechanisms that cause environmental aging are not well understood. This research aims to better understand the mechanisms behind aging and therefore apply the right surface treatment at the right time. This research requires a mixture of fundamental analyses based on laboratory experiments and field investigations. The timing of the surface treatment is related to the aging and distresses that develop in asphalt pavements over time. Ideally, a surface treatment should be applied at the proper time to provide a balance between maximum life and minimum cost. The progression of the asphalt pavement surface condition is mostly related to the aging characteristics of the asphalt binder and to the evolution of the mechanical properties of the binder with aging. An ongoing project at the University of Minnesota is investigating some of the issues related to the application of surface treatments, including environmental (climatic) modeling and mixture and binder testing to determine when preventive maintenance activities should be done. Related studies include: . TPF-5(112): Midwest States Pooled Fund Pavement Preservation Partnership (Michigan) . NCHRP 14-14: Guide for Optimal Timing of Pavement Preventive Maintenance Treatment Applications (Applied Pavement Technology, Inc.) . NCHRP 14-17: Manual for Emulsion-Based Chip Seals for Pavement Preservation . NCHRP 9-36: Improved Procedure for Laboratory Aging of Asphalt Binders in Pavements (Dr. David Anderson) . TPF-5(045): Performance Guidelines for the Selection of Hot-Pour Crack Sealants (Imad Al Qadi) . TRB HPR-PL-1(43)371: Maintenance Cost Effectiveness Study (Larry Scofield/Dr. Nazarian) . SPR-3(073): Micro-Surface Mix Design Procedure (Caltrans) . LRRB 803, 817: Determination of Optimum Time for the Application of Surface Treatments to Asphalt Concrete Pavements ¿ Phase I & II (University of Minnesota) The research proposed in this pooled fund study aims to fill several gaps in current research projects. Few if any studies have examined the pavement performance after placing a preventive maintenance treatment immediately after construction (year 0), but this could be accomplished in this study. Many of the existing studies monitor pavements under live traffic loadings. This study hopes to examine strictly environmental aging by either leaving pavement sections without traffic or by studying shoulders for their performance under various preventive maintenance treatments. MnROAD has the potential to be only the second site in the country that would apply surface treatments to a pavement with known properties at various times to study the effects of the surface treatments on aging. Finally, MnROAD provides a unique opportunity to study pavements with detailed weather information and known traffic applications in a safe and controlled work environment. The ability to divert traffic allows researchers to monitor and sample test sections in a safe manner, and it encourages researchers to push the envelope and try something new without causing a major disruption to the traveling public if it fails prematurely. The results of this study should lead to recommended guidelines on the timing and value of preventive maintenance applications to HMA pavements.

The goal of this study is to determine the proper timing of preventive maintenance treatments in order to optimize life cycle costs and pavement performance. Environmental aging of the asphalt binder in the underlying pavement is not well understood, and this project will seek to better understand the aging mechanism and how it can be reduced through pavement preservation. This pooled fund study is strictly to perform the preventive maintenance research on newly built test sections at MnROAD, and its funding will come from Mn/DOT and other participating states. The funding for initial construction of the test sections will be obtained separately from Mn/DOT and other partners.

This project is expected to consist of the following activities: . Work Plan: The work plan for this pooled fund study will be developed by the participating organizations. . Instrumentation Design: Thermocouples, strain gages, etc. . Surface Treatment Application: Determine the parameters to include in designing and applying surface treatments to HMA pavements and/or shoulders at MnROAD. Preventive maintenance treatments (i.e., chip seal, fog seal, rejuvenator, flexible slurry, etc.) will be applied to successive sub-sections at various times throughout the pavement life (from immediately behind the paver to successive years). Consideration will be given to the type of binder in the surface treatment (modified vs. neat). . General Testing & Monitoring: Monitor the pavement performance over this time on each of the sub-sections. Monitoring activities will include distress surveys, ride measurements, friction, and analysis of pavement sensor data. . Special Testing & Monitoring: Obtain field cores from each sub-section every year to determine material properties, especially related to aging. The pooled fund panel will recommend the proper laboratory tests to evaluate the pavement (especially binder) performance under certain surface treatments at certain times during the pavement life, from the refinery through various stages of pavement construction and service life. The testing and monitoring activities will compare untreated vs. treated pavements. . Pooled Fund Travel: Money for each state to travel to discuss the progress of the study. . Data Analysis & Report: Work done under a research contract will develop interim and final reports that document the findings of this study.

Mn/DOT along with other participating states are asked to contribute $15,000 per year for 5 years to fund the research proposed in this pooled fund study. The Minnesota Department of Transportation (as the lead agency) along with other partners will provide approximately $200,000 in initial construction funding outside of this pooled fund study to construct the pavement sections.