Comparison of Marshall and Superpave Gyratory Volumetric Properties of Saskatchewan Asphalt Concrete Mixes

Saskatchewan Highways and Transportation is investigating adding higher percentages of fractured coarse aggregate to asphalt concrete pavements to improve rutting performance. Higher percentages of fractured coarse aggregate are more costly to use, as aggregate is obtained from increasingly scarce glacial gravel deposits in Saskatchewan. The objective of this research was to investigate the influence of coarse aggregate fracture on rutting performance of typical Saskatchewan dense-graded mixes. Three Marshall mixes were compacted with varying percentages of fractured coarse aggregate. The asphalt content and gradation of the mixes were held constant, as was the asphalt cement. Seventy-five blow Marshall specimens and modified Superpave gyratory compacted (SGC) samples of the test mixes were manufactured. Analysis of the volumetric properties between types of samples showed a difference between 75- blow Marshall and SGC samples of the same test mix. Duncan’s pairwise comparison statistical analysis found that the 65 percent fracture mix and the 85 percent fracture mix were similar, but the 45 percent fracture mix was different across the Marshall specimens. The same analysis across the SGC samples found that the 85 percent fracture mix was different, where the 45 percent and 65 percent fracture mixes grouped together. Several rut performance predictors were investigated for these test mixes; however, the volumetric investigation of the SGC samples was the only analysis to show a benefit to having 85 percent fracture in asphalt mixes. Subsequent analysis of the SGC samples shows differences in compaction slopes and densities at initial and design gyration levels between test mixes.