Hot Mix Asphalt Design to Optimize Construction and Rutting Performance Properties

The first part of this dissertation is focused on comparing the mechanisms and fundamental properties that control the performance of asphalt mixtures during the uniaxial flow number testing. It is shown that aggregate packing, as measured using an image analysis method, is the key property affecting the failure and deformation characteristics in uniaxial testing. Additionally, it is shown that the main cause of tertiary flow of mixtures in the flow number test is structural instability and bulging (dilation) of aggregate skeleton. It is observed that dense graded mixtures with better aggregate packing showed a better rutting performance due to two principal mechanisms: first, lower stress level within the binder phase during loading due to aggregate skeleton serving as the main stress path, and second, the aggregates in proximity or contact showed a supporting structure (higher aggregate particle stability), which delays the tertiary flow in material, and reduces the rate of permanent deformation. The second part of this dissertation is focused on the mechanisms and factors controlling aggregate mobility and structure formation during compaction and their application for optimization of the construction process and for the development of a performance based mix design methodology. It is shown that for sufficient packing of aggregates during compaction, the viscosity of mastic should be low enough for lubrication, but high enough to prevent dry contacts of aggregates before the required aggregate packing is obtained. Depending on the stress state at the proximity zone of aggregates, there is a minimum mastic viscosity that is required to provide sufficient film thickness to prevent locking of the mixture at the early stage of compaction. A set of recommendations are proposed to estimate the optimum conditions for effective packing of aggregates. Based on the recommendations it is shown that packing of mixtures (as measured by total proximity zone length between aggregates) is a function of mastic viscosity, aggregate gradation, and compaction effort. The levels of these factors can be selected in order to achieve the required packing characteristic that is suitable for the design traffic loading.