Particle flow during compaction of asphalt model materials

• A lab-scale Flow Test (FT) was introduced to study flow of loose mixtures.
• It was initially used on model materials and the results demonstrated its efficiency.
• The FT results on real mixtures also showed internal particle rearrangements.
• Such findings can help for developing a field-based method for testing workability.

Compaction is one of the key phases of the pavement construction and has been subject of research for a long time. However, very little is known regarding what really happens during compaction and how the pavement structure and the aggregate skeleton of the asphaltic layer are formed. Studies on that matter are of special practical importance since they may contribute to reduce the possibility of over-compaction and aggregate crushing. In this study, a new test method (Flow Test) was developed to simulate the material flow during compaction. Initially, asphalt materials were substituted by model materials to lower the level of complexity for checking the feasibility of the new test method as well as modeling purposes. Geometrically simple materials with densest possible combinations were tested for both dry and coated mixtures. X-ray radiography images were used for evaluating the material flow during compaction for different model mixtures. Results showed the capability of the test method to clearly distinguish mixtures with different properties from one another and also the potential of such a method to be used as an evaluating tool in the field. In addition, a simple discrete element model was applied for better understanding the flow of the model material during compaction as a basis for further improvement when moving from the asphalt model material to real mixtures. Therefore, real mixtures were prepared and tested under the same test configuration as for the model materials. The overall results of the real mixtures were found to support the model material test results.