PRELIMINARY RESULTS OF THE ACCELERATED AGEING OF MODIFIED AND UNMODIFIED BITUMINOUS BINDERS USING THE PRESSURE AGEING VESSEL

The Transport Research Laboratory in collaboration with road authorities in a number of developing countries is currently developing recommendations for the use of bitumen modifiers in both hot mixed asphalt (HMA) and surface dressings. This project forms part of an extensive programme of research, funded by the Department for International Development (DFID), which has the final objective of producing a guide to design and construction of bituminous surfacings in tropical climates. A specific aim is to identify modified and unmodified bitumens which may have improved resistance to environmentally induced degradation. The effect of natural weathering on a range of modified and unmodified bitumens has been assessed in trials constructed in four tropical countries. The change in viscosity of bitumens used in these trials has been monitored over a two year period, to establish rates of hardening. Ever increasing numbers of bitumen modifiers are being introduced and it would be advantageous to have an accelerated laboratory technique for testing the effect of ageing on new products without the need for laborious field-testing. To do this a Pressure Ageing Vessel (PAV), as used during the Strategic Highway Research Programme (SHRP, 1996), has been used to simulate long-term weathering using the standard and two extended ageing procedures. Early results indicate that, under controlled laboratory conditions, the PAV can be used to estimate the rate of ageing of bitumens used for surface dressing. (A)