Comparison of 9.5 mm SuperPave and Marshall Wearing I Mixes in ...

47was acceptable for both Marshall and Superpave mix designs at both medium and heavy trafficlevels.Asphalt contents were calculated for these mixtures using Equations 2.12 to 2.16. The asphaltcontent estimates calculated from these equations were consistently too high. Usingexperience gained after completing a few mix evaluations achieved better estimates than wereproduced with the equations.5.1.3 Specimen Fabrication and TestingAs prescribed under Marshall mix design, test specimens were prepared over a range ofdifferent asphalt percentages to determine the optimum asphalt content. This range consists of½ percent increments with two asphalt contents above and two below the estimated asphaltcontent. Also duplicate samples of each asphalt content were made. Two maximum specificgravity, or Rice, samples were also required at the estimated asphalt content according toAASHTO T209, making the total number of samples needed, 12 per mix design. Maximumspecific gravity test samples were not needed for all asphalt contents since the Marshall methodallows for estimation of the maximum specific gravity of the other asphalt contents from theone measured value. Equations 2.1 to 2.10 are used for this analysis.Once the aggregates for the mixtures had been combined for correct weight, they were heatedto the mixing temperature of 162 C. A sufficient amount of PG 64-22 asphalt binder was alsoheated to this temperature shortly before the mixing process. The mixing bowl and mixingwand were also heated to the compaction temperature. Mixing temperature was indicated inthe binder evaluation data from the Citgo Asphalt Data Sheet. This evaluation sheet alsoindicated that the compaction temperature was 149 C. In a separate oven, the compactionmolds were heated to the compaction temperature and the Marshall hammer was placed on ahotplate.The heated aggregate mixture was then placed into the mixing bowl and the required amount ofasphalt binder was added. This was immediately placed in the tabletop mixer and mixed untilthe aggregate and binder was thoroughly mixed. After mixing, the entire specimen was placedin the mold, spaded 25 times with a spatula, and placed on the compaction pedestal. Theretaining ring was placed over the mold, the compaction hammer placed in the mold andattached to the automatic lifting device. The lifting device was then activated to apply theapplicable number of blows to the specimen. The correct number of blows per side for Marshallmedium and heavy mixtures is 50 and 75, respectively. After the compaction to one side of thespecimen was complete, the mold was then flipped over and the compaction process repeatedfor the same amount of blows. Once the compaction process was complete, the sample andmold were removed and placed into the specimen extraction device. The specimen wasremoved from the mold and allowed to cool. This entire process was repeated for the tenspecimens used for determining the optimum asphalt content.