Elongational rheology of bitumen film samples as a fingerprinting technique

Abstract

The development of improved test methods for modified bituminous binders is currently being pursued at the Council for Scientific and Industrial Research (CSIR). The ductility test laid the initial ground work for all extensional testing of asphalt bitumen in South Africa. However, with time, critical challenges of using this test as a performance indicator for bitumen were identified. As a result, it was withdrawn and equivalent tests, namely the Force Ductility (FD) test, the Binder Yield Energy Test (BYET) and more recently, the Double-Edge-Notched Tension (DENT) test, were brought to South Africa. Depending on the investigated elongational rheological property, each of these tests has their own significance. A major drawback of all the tests is the amount of material needed to determine test properties. This poses a major challenge during forensic investigations into premature failures of asphalt pavements, where extraction and recovery of the in-situ asphalt binder often results in insufficient quantity of bitumen for comprehensive characterisation. This paper presents a preliminary study towards overcoming this challenge through extensional methods, whereby thin bituminous films are tested with the Dynamic Shear Rheometer (DSR). Studies in the behaviour of bitumen as a thin film tends to be more representative of the in-situ conditions of the binder within an asphalt pavement. Limited results to date have enabled the ranking of different binders according to their transient extensional viscosity as well as differentiated modified from unmodified binders based on the strain hardening effect. Therefore this approach has the potential for improving and replacing current extensional methods in the South African asphalt pavement industry.