Evaluation and Permeability Modeling Of Open – Graded Friction Course Pavement

Abstract

An open-graded friction course (OGFC) is a special-purpose surface layer of hot-mix asphalt (HMA) pavement that is increasingly being used around the world. Owing to its numerous benefits, OGFC is being regularly used as a final riding surface on interstate and high-traffic expressways by different highway agencies in countries like United States of America, Japan, United Kingdom, Malaysia, Australia, New Zealand and South Africa. OGFC is more expensive per ton than conventional HMA, but the unit weight of the mix in-place is lower, which partially reduces the in-place cost. The problems hindering the widespread use of OGFC are raveling, bleeding, potholes and relatively short performance life. As the use of OGFC is increasing, research is needed on all problem areas related to OGFC. The major challenges associated with OGFC can be classified into three categories: Design, maintenance and premature failures. Research is needed to improve the service life/durability of OGFC and enhance its beneficial properties. The research described in this thesis attempts to address all above mentioned challenges. This research identifies the possible causes for premature failures and proposes methods to improve the durability of OGFC mixtures. The research forms part of a larger project to improve durability of OGFC pavements by Alabama Department of Transportation (ALDOT) “Improvement of Open-Graded Friction Course in Alabama”. The research study presented in this thesis is divided into three phases. In the first phase, five OGFC pavements situated in Alabama, state located in south eastern region of United States, was evaluated in terms of strength and durability. The testing plan was made to identify the possible causes of premature failure of OGFC pavements. The scope of this phase involved both field work and lab investigations. This part of the research showed that granite aggregate is better as compared to slag and sandstone in terms of abrasion resistance. Also, indirect tensile (IDT) strength value can be considered a criterion for performance evaluation of OGFC in earlier ages of the OGFC pavement. Distribution of air voids along the depth of OGFC pavements with age has come up as an important factor in deterioration of OGFC pavements. In the second phase, the effect of using fog and rejuvenator seals on the surface friction and durability of OGFC was assessed with the aim of recommending an optimal application rate. The scope of this phase involved both field work and lab investigations. This part of the research showed that fog and rejuvenator seals significantly affect the micro and macro texture of the OGFC surfaces in general. An application rate of 0.10-0.15 gal/sy, in case of fog and rejuvenator seal, may be suitable depending on the type of rejuvenator being applied and the type of modified binder used in the pavement. In the third phase, laboratory performance tests were also conducted to investigate the improvement in durability of OGFC mixtures. The testing plan was made to recommend optimal thickness and gradation for durable OGFC pavements. This phase also, included, developing a statistical model through multiple regression analysis to predict permeability based on mixture volumetric properties and gradation. Based on this part of the research, a coarser gradation with a thickness of 1.5 inch is recommended for OGFC pavements. The statistical model developed during course of this research successfully predicted permeability based on asphalt content, gradation and air voids. The results from this research will contribute in better understanding of causes leading to premature failure and develop better maintenance techniques of OGFC pavements. This research will be useful in enhancing durability of OGFC mixtures.