Triaxial Frequency Sweep Characterization of Asphalt-Aggregate Adhesion in Saskatchewan Asphaltic Mixes

Abstract

Antistrip additives are commonly used to mitigate loss of asphalt-aggregate adhesion, particularly when siliceous aggregates are used in asphaltic concrete mix. Although both liquid antistrip and lime antistrip additives have shown improved “visual based” laboratory results, field performance in Saskatchewan has shown the addition of lime provides improved long term climatic durability and structural performance of asphaltic mixes relative to liquid antistrip additives. As a result, improved laboratory characterization is needed to properly quantify the performance-related properties of these antistrip additives. This laboratory study employed triaxial frequency sweep characterization to determine the effect of hydrated lime antistrip and amine liquid antistrip additives on a standard Saskatchewan Type 72 dense graded asphalt mix comprised of siliceous aggregates. This research found that the addition of hydrated lime antistrip to the Saskatchewan Type 72 asphalt mix showed a considerable improvement in the mechanical behavior of the mix, including increased dynamic modulus, decreased strain, and increased phase angle. Although increased phase angle is generally not considered an improved material property in asphalt cement, an increase in phase angle in asphalt mixes may be an indication of improved strain dissipation by the asphalt binder due to more effective stress transfer from the aggregate to the asphalt matrix through improved asphalt-aggregate bonding. This improvement in laboratory mechanical behavior concurs with improved rutting and fatigue performance observed within typical Saskatchewan dense graded asphalt mixes when treated with lime antistrip.