Superpave for low volume roads and base mixtures

This study evaluated the Virginia Department of Transportation's Marshall designed Subdivision surface mixture, SM-1, and base mixture, BM-2 using Superpave criteria. Twenty-four production samples were collected of four SM-1 mixture designs and nine production samples of eight BM-2 mixture designs. Samples were tested for binder content, gradation, Superpave and Marshall volumetric properties. When sufficient material was available, rut testing was performed on the SM-1 mixtures using the Asphalt Pavement Analyzer. Various SGC compaction levels were used, including stopping at both N-design and N-max. Superpave criteria for the SM-1 mixtures were generally found to be acceptable. The exceptions were the width of the gradation band and fines to effective binder content. A non-standard compaction level was recommended for SM-1 type mixtures to be compacted to N-design. Rut testing indicates that SM-1 mixtures are generally very rut resistant. This indicates VDOT could allow even lower compaction levels than those traditionally used for low volume Virginia roads in order to promote durability. The BM-2 mixtures that were tested all fell on the fine side of the maximum density line for a Superpave 25.0 mm (1 in.) nominal maximum size mixture. Compaction levels for mixtures with less than 1 million equivalent single axle loads were evaluated for VDOT's base mixture. Even at these low compaction levels, a decrease in design binder content is anticipated. Historically, these mixtures have suffered from moisture damage and not rutting.