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

75CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS7.1 CONCLUSIONSThe results of this study demonstrate varied differentials between the mixes and associatedrutting potential of mixes prepared with the Marshall and Superpave mix design methods. Forthe mixes evaluated, there were some cases where the Marshall mixes performed better andother cases where Superpave mixes performed better. The net result was that a statisticallysignificant difference was not identified for mixes prepared for the same design situation.The evaluation of the effect of sand on the mix was inline with industry expectations, sand has adetrimental effect on the rutting potential of asphalt concrete. However, for the Superpavemixes, the rutting potential of mixes with 100 percent limestone and 13 percent natural sandwere not statistically significantly different. On the other hand the Marshall mix with 13 percentsand showed greater rutting potential than the 100 percent limestone mix. The Superpavemixes for low traffic roads designed with high sand contents displayed very high ruttingpotential. Due to the experimental plan used in the research, the percent sand and FineAggregate Angularity factors were confounded, hence, conclusions drawn concerning theperformance of the mix relative to sand content could also be associated with Fine AggregateAngularity. The Superpave method totally relaxes the Fine Aggregate Angularity for low volumeroad design. The results produced in this research demonstrate that this will produce a mix withhigh rutting potential when high sand contents are used. However, low volume roads may notexperience sufficient traffic to develop sever rutting.The differences in the asphalt contents between the two mix design methods ranged from 0.2 to0.8 percent. While this is an appreciable difference, there was no apparent trend with respectto the mix design method. For the 100 percent limestone mixes, the asphalt contents werehigher for the Superpave mixes. For the mixes with 13 percent natural sand, the Marshall mixesrequired more asphalt. Not enough data were collected during the research to determine if thisis a consistent trend.7.2 RECOMMENDATIONSThe results of this research indicate that the performance of Marshall and Superpave mixes iscomparable with respect to rutting performance. This demonstrates that correctly applying themethodology and criteria of a mix design method may be more important than which mix designmethod is used. At this time, there does not appear to be a pavement performance reason touse one mix design method over the other.