A RHEOLOGICAL STUDY ON MODIFIED BINDERS

Abstract

Bitumen as a binder plays an important role in the performance of the bituminous pavements. In order to increase the life of bituminous pavements, quality of bitumen needs to be enhanced. To achieve the improvement of binder, it is. necessary to add some modifier to the bitumen. By adding small amount of modifiers, the 'properties of bitumen can be enhanced considerably and the life span of the road pavement can be increased. Pavements constructed with modified binders exhibits greater resistance to rutting and thermal cracking, and decreased fatigue damage, stripping and temperature susceptibility. Modified binders have been used with success at locations of high stress, such as intersections of busy streets, airports, vehicle weigh stations, and race tracks. Polymers that have been used to modify bitumen include Styrene Butadiene Styrene (SBS), Styrene Butadiene Rubber (SBR), Natural Rubber, Crumb Rubber, Ethyl Vinyl Acetate (EVA), Polyethylene etc. Other chemicals consist of Sulphur, Fly ash, Carbon Black, Gilsonite etc. Desirable characteristics of modified binders include greater elastic recovery, a higher softening point, greater viscosity, greater cohesive strength and greater ductility. As the bitumen is so important for the flexible pavements, so its Theological properties should be ascertained to have a thorough knowledge about the behaviour of the bituminous binders. In India, the Theological characterisation of bituminous binders is till now based on the properties such as penetration, softening point, ductility and viscosity, which are usually inadequate to characterise the bituminous binders. Dynamic Mechanical Analysis (DMA) is the method already in use in developed countries to study the Theological properties of bituminous binders. In the present study two polymers i.e. Ethyl Vinyl Acetate (EVA), a plastomer and Styrene Butadiene Styrene (SBS), an elastomer are taken. In addition to these two polymers a non-polymer chemical, Sulphur is taken, to modify the VG 30 bitumen. The changes in the conventional and Theological properties of VG 30 modified with different percentages of EVA, SBS and Sulphur (1% to 6%) are studied. The Theological properties of the bituminous binders in terms of their complex modulus (G*) which depicts the stiffness and overall resistance to deformation, storage modulus (G) which indicates binder elasticity, loss modulus (G") which indicates viscous behaviour and phase angle (°) indicator of viscoelastic behaviour are measured by using Dynamic Shear Rheometer (Physica Smartpave Asphalt Rheometer). Temperature sweep test is performed at temperature ranging from 45°C to 90°C at a frequency