Impact of lime on the mechanical and mechanistic performance of hot mixed asphalt mixtures

The purpose of this research was to evaluate the impact of hydrated lime on the mechanical and mechanistic performances of typical hot mixed asphalt (HMA) mixture. This research differed from previous studies in several respects. First, since lime is used in HMA primarily for anti-stripping benefits, previous studies rarely quantified lime's other performance benefits. Second, because testing is typically performed on only the HMA mixture being considered for a project, and only as necessary to satisfy specifications, typical studies do not capture the full range of failure modes and environmental stresses. Furthermore, once specifications are met, test results are rarely translated into pavement performance characteristics. This research, by contrast, evaluated two typical HMA mixtures from the northern part of Nevada and two HMA mixtures from the southern part of Nevada used by Nevada Department of Transportation with the most widely accepted laboratory tests. The Hveem mix design method was used for all eight mixtures. The mixtures were evaluated at the unconditioned (i.e. 0 freeze–thaw (F–T) cycles) and conditioned (i.e. 6 F–T cycles) stages. The moisture damage was evaluated through the dynamic modulus test at various temperatures and frequencies. The repeated load triaxial test was used to evaluate the permanent deformation of the mixtures. The flexural beam fatigue test was used to assess the fatigue resistance and the thermal stress restrained specimen test was conducted to evaluate thermal cracking resistance. This was followed by a comprehensive mechanistic analysis using the Pavement-ME design software, previously named MEPDG, in order to quantify the impact of lime on the long-term performance of asphalt pavements. Overall, the laboratory test results as well as the mechanistic analysis showed significant improvement in Nevada's mixtures performance when hydrated lime was utilised.