Compaction Sensitivity of Saskatchewan SPS-9A Asphalt Mixes

Saskatchewan Ministry of Highways and Infrastructure (SMHI) currently use the Marshall compaction method for laboratory hot-mix asphalt (HMA) design and placement quality control / quality assurance. Unfortunately, Saskatchewan has witnessed premature rutting in some pavements due to significant reduction in air voids under traffic loading. As a result, it is hypothesized that laboratory compaction during the design process may not be accurately predicting in-service air voids of typical Saskatchewan asphalt mixes. This research characterized the effect of varied laboratory compaction energy on the volumetric and mechanistic mix properties of laboratory compacted hot-mix asphalt mixes. The volumetric and mechanistic mix properties of four Radisson SPS-9A asphalt mixes are summarized and presented in this paper. One of the four asphalt mixes considered in this research is designed and constructed to meet conventional Saskatchewan Marshall Type-71 mix design protocol, two of the research mixes were designed and constructed to meet SuperpaveTM Level I mix design criteria. One of the research mixes was designed and constructed to meet the SuperpaveTM recycle mix design criteria. This research found that laboratory volumetric properties are sensitive to varying Marshall and gyratory compaction energies. With regards to Saskatchewan air voids criterion, 50-blow Marshall compaction satisfied air voids criterion. However, at 75-blow Marshall compaction effort, the conventional SMHI Type-71 asphaltic mixes yielded air voids below the minimum allowable air voids. Air voids was sensitive to increased gyratory compaction energy. In terms of gyratory compaction, the conventional SMHI Type-71 mixes met air voids criterion at 1.25°, but not 2.00° and 2.75° gyratory angle. Triaxial frequency sweep characterization of the Radisson SPS-9A mixes proved that increasing gyratory compaction energy significantly increased the mechanistic dynamic modulus mix properties of the Radisson SPS-9A mixes across deviatoric stress.