Y. K. Choi

Visco-Elastic Analysis of the Elastomeric Binder Shear Resistance in Relation to Asphalt Rutting

ABSTRACT This paper presents a study into a simple laboratory assessment method of the binder shear resistance (as a key property on asphalt rutting). Based on a binder testing instrument called an “Elastometer” and a simple visco-elastic (Kelvin-Voigt) model, very different behaviours of bitumens and polymer modified binders were analysed. A range of binders comprising bitumens and modified binders (with a range of different polymer modifiers) were used to produce asphalt slabs and then tested in a wheel tracking device. A comprehensive correlation study was carried out and it was found that the shear resistance at low strains was closely related to the rut resistance. This suggested that a viscous property was a more important contributor to asphalt rut resistance. However, it was thought that, for highly modified elastic binders, the elastic property also contributed to the asphalt rut resistance. The Elastometer parameters were compared to parameters from other test methods with which non-Elastometer users are familiar. Of particular importance was the comparison of Elastometer and Dynamic Shear Rheometer (DSR) parameters which were derived from the same visco-elastic model. Satisfactory correlations were observed between corresponding parameters. This demonstrated that the use of the Elastometer for the rheological testing of binders (and the application of the rheological model) was a reasonable approach.

Rheological and fracture characteristics of low penetration grade bitumen

ABSTRACT Interest in the rheological and fracture characteristics of low penetration grade bitumens has increased in recent times due to greater use of progressively stiffer base materials and the growing concern over the durability of these extremely hard, high stiffness modulus materials. This paper investigates the high and low temperature rheological characteristics, tensile fracture modes and cohesive properties of a series of semi-blown, polymer modified and straight-run (direct distillation) low (15) penetration grade bitumens using a Brookfield (rotational) viscometer, Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), Direct Tension Tester (DTT) and Vialit Pendulum Cohesion apparatus. The binders have been tested in their virgin (unaged) condition and after short-term, Rolling Thin Film Oven Test (RTFOT) and long-term, High Pressure Ageing Test (HiPAT) ageing. The results show considerable differences in the high and low temperature rheological and fracture properties of the 15 penetration grade bitumens as a function of their production method especially after ageing, although only minor differences in terms of their cohesive properties. In general the semi-blown 15 pen bitumen showed a higher susceptibility to ageing than the polymer modified and direct distillation 15 pen bitumens and an increased elastic “brittle” response to loading in terms of DSR, BBR and DTT test data.

Development of the saturation ageing tensile stiffness (SATS) test

This paper describes the development of a combined ageing/moisture sensitivity laboratory test to evaluate the performance of coated macadam binder course and base mixtures with relatively low binder contents and relatively high air void contents. The test is known as the saturation ageing tensile stiffness (SATS) test, and consists of initial saturation prior to placing compacted asphalt core samples in a high-temperature and high-pressure environment in the presence of moisture for an extended period of time. The stiffness modulus measured after the test divided by the stiffness modulus measured before the test (retained stiffness modulus), and the specimen saturation after the test (retained saturation), are used as an indication of the sensitivity of the compacted mixture to combined ageing/moisture effects. The test was used to reproduce in the laboratory the loss of stiffness modulus observed on a trial site where high modulus base (HMB) had been used. Two different aggregate types (basic and acidic...