Rheology of polymer modified bitumen : a comparative study of three binders and three binder/filter systems

Abstract

Paper presented at the 20th Annual South African Transport Conference 16 - 20 July 2001 "Meeting the transport challenges in Southern Africa", CSIR International Convention Centre, Pretoria, South Africa.

Polymer modified bitumen (PMB)is used extensively in thin asphalt surfacings and seals. PMB has to be characterised differently from penetration grade bitumen and the improved performance properties are difficult to demonstrate with conventional empirical rheological tests. This paper gives an overview of a test programme that was followed to characterise bitumen-rubber and SBS modified bitumen using conventional as well as non-conventional methods. The effect that filler addition has on binder properties was also investigated. The characterisation was done through fundamental rheological tests. This paper focuses on the testing that was done using a state of the art dynamic shear rheometer at Natref ’s laboratory in Sasolburg. In this study three binders were compared: •60/70 penetration grade bitumen •SBS modified 60/70 bitumen •Bitumen-Rubber A mineral filler prevalent to the Western Cape was used with the binders in binder/filler mixes. The binder/filler ratio in all cases was 50/50 by %volume. The dynamic shear rheometer was used to perform frequency sweeps on the binders and binder/filler systems in the temperature range of 5 °C to 75 °C. The results of the frequency sweeps were used to construct Master Curves and Black Diagrams. From the two types of curves, the influence of both rubber addition and filler addition was determined. The high temperature behaviour of the binders was also studied. The conclusions that could be drawn based on the results of this study include: - Bitumen-Rubber and SBS binders show very different behaviour compared to the 60/70 bitumen in the Black Diagram: from the Black Diagram it is clear that PMB has better performance, especially when high temperatures/low frequencies are considered. - The high temperature behaviour of SBS modified binders differs from normal penetration grade bitumen: the SBS exhibits shear thinning behaviour while the 60/70 exhibits normal Newtonian behaviour. Thus, the shear rate during mixing and compaction is very important when PMB is used.