Developing Index Parameters for Cracking in Asphalt Pavements Through Black Space and Viscoelastic Continuum Damage Principles

Cracking is a major distress for asphalt concrete pavements and presents significant challenges to effective design and maintenance. Fatigue and thermal cracking decrease ride quality of the pavement and allow water to penetrate into underlying layers, which can result in major damage if left unchecked. The primary obstacle in predicting field performance for cracking in asphalt pavements is related to the interaction of material, structural, and environmental components. The major objective of this work is to develop index parameters to relate material and structural parameters, identifying whether a mixture is prone to fatigue or thermal cracking. A Simplified Viscoelastic Continuum Damage (S-VECD) model, which relates material integrity and damage growth under repeated loading, is used in this project. The structural response is evaluated using layered elastic analysis principles in order to establish a material-structure space, where the pass/fail determination is based. This pass/fail index parameter is operationally efficient and easy to implement at a contractor or owner agency with capacity to test materials in the S-VECD configuration. A thermal cracking parameter is developed for mixtures through a relation to laboratory and field performances in terms of Black Space. Since Black Space diagrams are able to capture changes in stiffness and relaxation, where separation would be indicative of poorly performing materials, these parameters provide insight into relationships among pavement structures and mixture designs. The results also lend themselves to the formation of performance-related specifications, where agencies can require a certain parameter value based on experimental and field observations. Opportunities exist to extend the parameter definitions among length scales, to further examine the effects of each on cracking performance. The capabilities of the parameter will influence design and funding decisions, resulting in cost savings at the owner agency and contractor levels through enhanced performance and a reduced testing framework

Shock Wave Attenuation Using Foam Obstacles: Does Geometry Matter?

A shock wave impact study on open and closed cell foam obstacles was completed to assess attenuation effects with respect to different front face geometries of the foam obstacles. Five different types of geometries were investigated, while keeping the mass of the foam obstacle constant. The front face, i.e., the side where the incident shock wave impacts, were cut in geometries with one, two, three or four convergent shapes, and the results were compared to a foam block with a flat front face. Results were obtained by pressure sensors located upstream and downstream of the foam obstacle, in addition to high-speed schlieren photography. Results from the experiments show no significant difference between the five geometries, nor the two types of foam