Towards the enhanced applicability of cold mix asphalt: : An experimental study focusing on surface free energies and the breaking and coalescence of bitumen emulsions

Sammanfattning: The environmental, social and economic sustainability of our infrastructure network is clearly of paramount importance to the road-engineering sector as well to society at large. Sustainable road materials and reduced transport of those materials therefore play a significant role. Cold mix asphalt (CMA) emulsion technology could be one of the better options for the road industry to explore more thoroughly. Given its lower start-up and equipment installation costs, lower energy consumption and reduced environmental impact, CMA should offer a reliable alternative to some of the Hot Mix Asphalt (HMA) or Warm Mix Asphalt (WMA) options. As CMA is not a new technology, there are many reasons why this material is not currently being used as extensively as it might be. Though risk adverseness of the market may be partly to blame for this, a number of technical challenges and uncertainties related to material behavior are certainly responsible. This thesis has addressed some of the important technical challenges, aiming to provide more guidance in material selection and design, and prediction of the behavior of emulsion-based CMAs. To do so, this research has focused on aspects of the correct formulation of the bitumen emulsions, how to select the correct combinations of material components, and how to control the breaking and coalescence processes in bitumen emulsions better, resulting in usable and predictable adhesive and cohesive bond strengths. Though most of the laboratory and modeling choices that were made in this thesis are based on theoretical considerations, the main contribution is the test protocol development. The systematic surface free energy measurements of the material components, combined with the test set-up to monitor controllably the breaking and coalescence behavior of bitumen droplets in an emulsified environment, gives a new way to approach the design of CMA. It is recommended that future research is focused on taking the developed protocols as a basis for enhanced mix design and making a direct link to validated long-term mechanical properties on the asphalt mixture scale.