Hydrated lime is often used as a mineral filler or antistripping additive in hot-mix asphalt (HMA). Many agencies across North America require the use of lime in all HMA mixtures being placed on high-volume roadways. Despite this wide use of lime, its effects on the HMA mixture dynamic modulus (E*) stiffness have rarely been evaluated. The new mechanistic-empirical (M-E) pavement design guide, "Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures," developed under NCHRP Project 1-37A uses E* as the primary material property of asphalt mixtures for the HMA characterization. A comprehensive study was completed at Arizona State University to assess the effect of lime addition on the E* stiffness of HMA mixtures. The study demonstrated that the standard test and design methodologies of the new M-E pavement design guide could be used effectively for lime-modified HMA mixes. With these methodologies, hydrated lime was found to increase the E* of HMA mixtures by 17% to 65% across the range of mixtures, lime contents, and temperature, with an overall average of 25% increase found from 17 mixture-lime percentage combinations across six different HMA mixes. This paper also outlines a provisional protocol for evaluating the E* master curve for lime-modified HMA mixtures using any of the three hierarchical levels found in the new NCHRP Project 1-37A pavement design guide.
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