United States Department of Transportation
i
Development of a 4.75-mm Asphalt Mixture Design
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2024-12-01
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Edition:Final Report December 2024
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Abstract:The Louisiana Department of Transportation and Development (DOTD) and other agencies continually identify techniques to reduce roadway maintenance and construction costs. One common approach to this task is the introduction of asphalt mixtures with a smaller nominal maximum aggregate size (NMAS) for utilization in roadways. Excessive stockpiles of unused, smaller aggregates create an economically competitive resource that should be considered for asphalt mixtures. The objective of this study was to evaluate the economic viability of the recently developed mixture design criteria for 4.75-mm NMAS mixtures to be used in Louisiana. The 4.75-mm mixtures were prepared with four aggregate types and two binder types. A comprehensive performance evaluation was conducted through volumetric and mechanistic testing. Performance testing consisted of the Hamburg loaded wheel tracking (LWT) test to determine rutting resistance, the semi-circular bend (SCB) test to determine cracking potential, the dynamic modulus (E*) test to determine stiffness at different temperatures, and a friction test to evaluate the friction resistance of the proposed mixtures. Additionally, an economic analysis was conducted to determine the viability of 4.75-mm mixtures through life-cycle cost analysis (LCCA) of pavement sections designed with 4.75-mm mixture overlays compared to sections designed with 9.5-mm and 12.5-mm mixtures. The Pavement Mechanistic-Empirical (ME) design software was used for the LCCA. As expected, asphalt binder grade, aggregate type, and mixture composition affected the performance of the mixtures. The gravel mixtures were susceptible to cracking, whereas the limestone mixtures were susceptible to rutting. The 4.75-mm mixtures were found to be costeffective compared to conventional 9.5-mm and 12.5-mm NMAS mixtures.
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