Garrity, John

Warm mix asphalt (WMA) is a general term describing the use of any additive or technology that allows for lower asphalt plant mixing temperatures. Developed in Europe, WMA was brought to the United States in 2004 and has since gained widespread use around the country. Environmental benefits experienced with WMA include reduced emissions, fumes, and odors. With a cooler work environment enabled by WMA technology, reduced production temperatures add up to energy savings. The Minnesota Department of Transportation (MnDOT) saw the promise in this technology, especially the anticipated benefit of reduced low temperature and reflective cracking because of the reduced binder aging at the plant.

Expansion and maintenance of roadway infrastructure creates a demand for high quality paving aggregates. Taconite industry rock and tailings are a potential source of virgin paving aggregates. Currently there is limited information available for implementing these products in construction design specifications. Preliminary information of product performance within current design constraints is valuable to both state design engineers and to future pooled-fund studies. This information can identify the potential for using these products in surface courses or possibly for use in rich-bottom leveling layers. This study examined the viability of utilizing these products in the Minnesota Department of Transportation (Mn/DOT) Superpave bituminous mixture design specifications. As part of the study 40 laboratory specimens were produced from 11 asphalt mixtures and then evaluated for asphalt content, air voids, and aggregate gradation. This report summarizes the results of the laboratory mixture evaluation.

This report summarizes efforts of using the disk-shaped compact tension (DCT) test to measure thermal fracture properties of asphalt mixtures on five asphalt paving projects in Minnesota during the 2013 construction season. Five construction projects throughout the state were chosen by a team of researchers at the Minnesota Department of Transportation (MnDOT) and University of Minnesota Duluth (UMD) representing differing climatic conditions, construction practices, and asphalt PG binder grades. Contractors from these varying projects provided UMD with mix design and production pills and MnDOT with loose production mix and raw materials for specimen fabrication. Testing was done to verify mixes met the required fracture energy value of 400 J/m2. If DCT results did not meet this requirement, mix adjustment recommendations were made by the research team. When recommendations were accepted, test sections with adjusted mix were paved. DCT testing was conducted on both adjusted and unadjusted production mix. Results of these efforts showed a drop in fracture energy between mix design and production for each project. The cause is not known at this time, but will be investigated in future research. Preliminary distress surveys indicated projects with mill and overlay experienced higher amounts of cracking compared to projects with reclaim or new construction. It should be noted distress surveys were conducted 9 months after initial paving, with the roadways subjected to only one season of freezing conditions. Condition of underlying pavement structure was not investigated before paving began in the cases of mill and overlays