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Evaluation of Thin Asphalt Overlays for Pavement Preservation in Nevada
AdvisorHajj, Elie Y.
Civil and Environmental Engineering
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Over the last 35 years, state highway agencies changed their emphasis from the construction of new roads to the maintenance and rehabilitation of existing infrastructures. As a routine pavement maintenance and preservation tool, thin asphalt overlays have seen importance and were classified as extremely useful for flexible and composite pavements since 1999. Defined as simple surface lifts or part of mill-and-fill strategies typically placed at no more than 1.5 in. (38 mm) thick on a well prepared surface, their essential function is not to strengthen the existing pavement capacity, but primarily to address issues related to pavement functional performance. The overall objective of this study was to assess the use of locally available materials in Nevada for the development of a durable fine-graded thin hot-mix asphalt (HMA) overlay mixture for pavement preservation. A comprehensive laboratory evaluation using typical materials in Nevada was conducted. The investigation considered establishing two mix designs using typical local materials for the northern and southern part of the state. An optimal asphalt binder content (OBC) was selected for each mixture based on the volumetric properties and following the Nevada department of transportation (NDOT) volumetric requirements. For each mixture, the optimal binder content was varied within the allowable tolerances to simulate the potential variation in asphalt binder content during plant production. The performance of the two thin HMA mixtures were then evaluated at the various asphalt binder contents in terms of their resistance to moisture damage using indirect tensile strength (TS), resistance to surface raveling and abrasion, dynamic modulus (|E*|) property, resistance to rutting using the flow number (FN) test, resistance to reflective cracking using the Texas Transportation Institute (TTI) overlay tester, workability and compactability using the pressure distributor analyzer (PDA), and the developed interlayer bond strength using the Louisiana Interlayer Shear Strength Tester (LISST). Overall, both designed fine-graded mixtures showed a very good performance and are expected to perform well when used as a thin hot-mix asphalt overlay. In particular, good stability, very good resistance to surface raveling and abrasion, and excellent resistance to reflective cracking were observed for both thin HMA overlay mixtures at all evaluated asphalt binder contents. Thin asphalt overlay mixtures behaved as ordinary mixture and are expected to last longer than chip seals for a lower net present worth costs. Based on the findings from this study, it was recommended to construct field test sections in various parts of the state to evaluate the field performance of the developed thin HMA overlay mixtures in Nevada.