RHEOLOGICAL PERFORMANCE OF AGED POLYMER MODIFIED BITUMENS

The rheological and chemical changes associated with laboratory short term and long term aging of modified, penetration grade, bitumens are well know and understood. However, these changes are not fully understood for polymer modified bitumens (PMB's). The rheological changes that occurred after aging for three base bitumens and fifteen PMB's using conventional binder specification tests (Penetration, Softening Point and viscosity) and a dynamic mechanical test (Dynamic Shear Rheometer) were measured. The conventional tests were able to describe the effect of aging on the rheological responses to aging compared with the penetration grade bitumens. The Dynamic Shear Rheometer results indicated that the changes that occur after aging for EVA modified PMB's can be linked to a chemical change in the semi-crystalline copolymer with a shifting of the rheological characteristics of the aged PMB towards that of an unmodified bitumen. The rheological changes associated with the SBS modified PMB's can be linked to a breakdown of the molecular structure of the copolymer to form a lower molecular weight polymer substructure.