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.