Executive Summary : | The wearing course and binder course in a bituminous pavement consist of aggregates of varying sizes and proportions bound by a bituminous binder at the interface. The manner in which various distresses such as rutting (permanent deformation) and fatigue (load-induced cracking) are resisted is strongly dependent on the aggregate interlock in the bituminous mixtures. Such an aggregate interlock is facilitated during production and evolves as the material densifies during the service period. As of now, it is assumed that the viscosity of the binder during the mixture production plays a critical role in facilitating a uniform coating on the aggregate particles, and assuming Newtonian behaviour during mixture production and construction, appropriate temperatures are prescribed for the construction operation. As the bituminous technology expanded in the use of warm mix binders, modified binders, and reclaimed bituminous mixtures, the simplistic notion of a mixing and compaction temperature corresponding to the Newtonian response of the binders is no longer valid due to many reasons. Firstly, the modified binders are non-Newtonian at such temperatures, which means the viscosity will vary drastically as a function of shear rate. Secondly, the ease of working even with reduced mixing and compaction temperature, as seen in warm mix binders, is more due to the reduced interfacial friction (increased lubricity) between the aggregates and binder. Thirdly, in hot mix recycling, the interaction of aged binders with the rejuvenator in the presence of virgin binder is exceedingly complex. Hence, in addition to the Newtonian/non-Newtonian viscosity of the mixture of these binders, the interfacial friction and the surface energy between the binder and aggregates need quantification. Finally, in cold-mix recycling, in emulsion with reclaimed bituminous mixtures, an additional factor is the emulsion breaking kinetics and the concomitant reduction in the ease of workability. The binder rheology, the interfacial friction between the binder and the aggregate particles, the surface tension of the binder and the surface free energy between the aggregate and the binder play a vital role in the workability of the mixtures. This proposal aims to investigate these factors in detail. Experimental data corresponding to Newtonian – non – Newtonian transition, interfacial friction through mapping the various regimes of a Stribeck curve, surface tension, and surface free energy are proposed to be measured, analysed and quantified for a variety of bituminous binder and mixture systems. In addition, all these measures captured at different scales and constituent levels will be related to the gross measure of the workability of the different bituminous mixtures. It is expected that such an exercise will help better understand the physics of mixing a variety of bituminous binders and mixtures and lead to an optimized mixture production process. |