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Evaluation of New and Existing Test Methods to Assess Recycled Asphalt Pavement Properties for Mix Design
AdvisorHajj, Elie Y.
Civil and Environmental Engineering
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The use of reclaimed asphalt pavement (RAP) in flexible pavement surface layer has been a major sensitive issue in the construction industry. Due to limited space available in landfills, the decline in the amount of high quality virgin aggregate, and the high price of oil, the use of RAP in new asphalt concrete mixtures has become very attractive. In general, the RAP-percentage used by the various highway agencies is limited to less than 25%. Even many highway agencies have realized the benefits of using RAP, the incorporation of high percentage of RAP (more than 25%) in HMA mixtures, especially in the asphalt surface layer, has been relatively low compared to the possible supply of RAP. Preliminary concerns with HMA mixtures with high RAP content have been the assurance of adequate resistance fatigue and thermal cracking and moisture sensitivity. Therefore, there is a need for the development of design methods and analysis of the properties of HMA mixtures with high RAP contents.This dissertation focused on two main objectives:* To develop systems to evaluate the properties of the aggregates in the RAP materials, and* To develop a system to evaluate the properties of RAP binders.The properties of the virgin aggregates (i.e. gradation and specific gravities) were compared to those of aggregates extracted from laboratory-produced (simulated) recycled asphalt pavement (RAP) from four different aggregate sources. Additionally, the extracted asphalt binder contents were compared to their corresponding true binder contents. The study also looked on how the extraction methods influenced the likelihood of a mix designer overestimating or underestimating a given mix design property. The test results were further examined to determine the impact of the RAP aggregate properties on the voids in mineral aggregate (VMA) for mixtures incorporating different percentages of RAP. As a result, recommendations were made to select the most appropriate method for estimating the RAP aggregate specific gravity based on an acceptable level of error in the VMA calculation of mixtures containing varying levels of RAP.The determination of the RAP-binder properties is one of the most important steps in designing RAP-containing mixtures. Five methodologies were used to determine the RAP-binder properties:* Blending charts according to AASHTO T 323* Direct measurements from extracted and recovered asphalt binders using the dynamic shear rheometer. Two methods were used:o Master-master curve (MMC) using the CAM (Christensen-Anderson-Mastereanu) model.o Master-master curve using the CAS (Christensen-Anderson-Sharrock) model.* Mortar method developed by the University of Wisconsin-Madison researchers* Backcalculation of the RAP-binder properties using the Hirsch model, and* Backcalculation of the RAP-binder properties using the Huet-sayegh model.Finally, two methodologies were proposed to design RAP-containing mixtures: A system to evaluate the properties of RAP-aggregates and a system to determine the properties of RAP-binders.