New helicoidal spindle for mixing and viscosity measurements of tyre rubber modified binders

Abstract

The use of modified bituminous binders, in place of pure bitumen, is a common practice to enhance performance of road pavements. The measurement of rheological properties of the modified binders is often challenging due to presence of suspended solids. Phase separation during the course of measurements makes viscosity of non-homogeneous blends, such as tyre rubber modified bitumens, difficult to ascertain. In this study, a new spindle was designed and manufactured to be used with a rotational viscometer in order to adapt the viscometer as a low shear mixer and to guarantee reliable viscosity measurements of samples which contains suspended particles. This helps optimize the modification process of tyre rubber modified bitumen by having a reliable real-time viscosities measurement. Spindle geometry was optimised to create a convective like flow within the sample and so minimise phase separation. Shear rate constant is geometry dependent and a calibration exercise was carried out to ascertain investigate this. Development of prototype spindles was undertaken using a layer based manufacturing technique which allows the rapid realisation of a design intent which could not be achieved in another fashion. In this case nested features are created in a prototype to verify the design before a fully functional prototype is produced using conventional 4-axis machining. The new spindle allows the Brookfield viscometer to be used as a low shear mixer of small volumes of bitumen-rubber blends while allowing real-time reliable measurements of the viscosity.