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

59were made, the samples were removed from the retaining molds and discarded. This processwas repeated for twelve APA runs and data recorded for all test runs.5.3.3 APA Testing ResultsRut depths were measured and recorded for each sample of every mix design tested. The fourrut depths per sample were averaged and these values for the triplicate samples were alsoaveraged to get one average rut depth for each mix design. Standard deviation was alsocalculated over the sample set of data points consisting of the individual rut depths on eachsample. Table 5.6 contains these results and data on average percent air voids for each sample.These results show that the hypothesis of mixes that contain natural sands would exhibitgreater rut depths than mixes that contain all limestone was correct, however, some interestingand contradicting results were also observed. One interesting result was that the Superpavemedium 13% natural sand mix incurred an average rut depth of 9.43mm while the heavy designof the same natural sand content had an average rut depth of 10.35mm. In theory, a heavy mixdesign should be less likely to rut than a medium traffic design of the same gradation. Anotherunexpected result was that both Superpave light 100% limestone sand mixtures performedbetter than all the other mixes, with the exception of the 100% limestone sand Marshalldesigns. This is especially interesting in that the Superpave light 100% limestone sand designwas passed through the restricted zone. By doing this, the mixture should have exhibited thecharacteristics of a tender mix (i.e. high rut depths).As expected the designs containing very high percentages of natural sand exhibited very high rutdepths. This was particularly true with the Superpave light 40% natural sand and 68% naturalsand mixtures. These mixes resulted in the deepest rut depths of all the mix designs. It shouldbe noted that most of the samples tested failed the Georgia DOT requirement if a maximum of7.5mm rut depth. However, well performing mixtures designed for the WVDOH typically exhibitaverage rut depths greater than 7.5mm. This shows that the maximum rut depth requirementwould need reexamined if this test was ever implemented in West Virginia. Rut depth data,along with all other test results and data developed during this research, will be further analyzedin the next chapter.