Asphalt mixture evaluation using performance space diagrams, digital image correlation, and discrete element modeling

The use of asphalt modifiers and recycled asphalt materials in asphalt concrete has generated a need for greater laboratory evaluation. Asphalt modifiers, such as styrene butadiene styrene (SBS) polymer, bio-modifiers, and warm mix asphalt processes, and recycled asphalt materials, such as recycled asphalt pavement (RAP) and shingles (RAS), have limited long term field performance data. As a result, traditional and enhanced laboratory performance tests are necessary to determine their potential use in asphalt concrete applications. The characterization of asphalt concrete has evolved with technological advancements in optics, computing power and speed, and mechanical testing systems. This evolution has increased the number of tests available and used to evaluate distresses in the laboratory and field. Data output from laboratory tests has improved with the use of high speed cameras for digital image correlation (DIC) measurements, and has been complemented with heterogeneous numerical simulations via modeling tools such as the discrete element method (DEM). However, there has not been an analysis method developed using traditional high and low temperature laboratory mixture test data to identify shifts in performance. Furthermore, little research has been completed using DIC strain fields throughout low temperature asphalt concrete fracture tests. Finally, there is a need for improved heterogeneous DEM fracture modeling methods to remove trial-and-error evaluation of optimal mastic fracture properties and to add viscoelastic cohesive contacts and RAP particles. The goal of this study was to enhance asphalt mixture evaluation through performance tests, DIC imaging, and DEM numerical modeling. The present work evaluated the high and low temperatures properties of SBS polymer, bio-, and WMA modified mixtures. In addition, RAP and RAS asphalt mixtures were tested at high and low temperatures to evaluate their laboratory performance properties. The Performance Space Diagram was developed to incorporate low temperature DC(T) fracture energy and high temperature Hamburg rut depth on a single chart akin to the failure assessment diagram in metals. DIC strain fields were evaluated using the proposed DIC fracture process zone (FPZ) size measurement to determine the average strain localization radius generated in front of a crack tip. Finally, this study evaluated heterogeneous DEM simulations by virtue of: employing a DEM-DIC displacement optimization tool to determine DEM mastic fracture properties, developing a viscoelastic cohesive contact model, and introducing a four phase model to include RAP particles. Several significant outcomes were found in the course of this study. First, the Performance Space Diagram is a graphical tool capable of identifying performance shifts and balanced mixture designs. FPZ size measurements of the localized strain fields in DIC imagery are capable of delineating asphalt mixture variables. These variables include: mixture aging, polymer modification, RAP and RAS use, specimen geometry, and the brittle transition temperature for asphalt mastic. The use of a viscoelastic cohesive contact and a DEM-DIC optimization method improve heterogeneous DEM simulations of low temperature asphalt concrete fracture. Finally, the RAP randomization method used in this study provides the first functioning four phase heterogeneous DEM fracture model of mixtures containing RAP.U of I OnlyRequested through the Graduate College Extension Form for 2 year