Comparison of Marshall and SUPERPAVE Level I Mix Design for Asphalt Mixes MLR-95-01, August 1994

(1994) Comparison of Marshall and SUPERPAVE Level I Mix Design for Asphalt Mixes MLR-95-01, August 1994. Transportation, Department of

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Abstract

Mix designs were conducted on 20 different mixtures categorized as: (a) conventional, (b) wet process asphalt rubber (manufacturer preblended), (c) dry process rubber asphalt, (d) polymer modified mixes, and (e) wet-process asphalt rubber (plant-blended). These designs were developed using both the Marshall procedure and the Superpave gyratory Level I procedure. A comparison between the design asphalt contents results obtained by the two procedures is presented. The Superpave designs were conducted at a traffic level compared to traffic for the 75-blow Marshall procedure and for three climatic regions representative of cool to warm conditions. Major problems were encountered with the Syperpave gyratory approach for five mixtures within the dry-process rubber asphalt groups. These problems appear to be related to the high resiliency of the rubber aggregate during the gyratory compaction process coupled with time-dependent swell of these mixtures directly after compaction. It is concluded that the Superpave Level I mix design approach is not applicable to those mixtures. For the other four groups of mixtures studied, differences between the binder contents from the Marshall and Superpave were found to be a function of the group type. Differences in design content obtained from the Superpave gyratory were found to be about 1.0% more asphalt as the climatic regions went from warm to cool conditions. This finding was true for all types of mixtures studied. In general, the conventional mixtures and manufacturer-preblended rubber asphalts gave similar design values between the Marshall and "warm" Superpave climatic region and the converse is true for the plant-blended rubber asphalt. In contrast, 0.5% to 0.8% less asphalt was found for the Superpave design, in warm conditions, compared to the Marshall design for the polymer modified asphalts investigated.