DCT Low Temperature Fracture Testing Pilot Project

Abstract

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.