A new approach for the accelerated ageing of porous asphalt mixtures

Age hardening is related to progressive oxidation of all bituminous bound layers in flexible pavements. Excessive age hardening is of particular relevance to surface courses where it can cause premature breakdown; it is of major importance to engineers and scientists involved in the design, construction and maintenance of such pavements. This paper discusses the development of a new method for the accelerated ageing of bituminous mixtures, based on the use of a forced draft approach, to reproduce field-ageing effects in the laboratory. The applicability of the method to ageing of porous asphalt mixtures is investigated using four bitumens: a 100 pen conventional and three polymer modified binders, including Styrene Butadiene Styrene (SBS) and Ethylene Vinyl Acetate (EVA) copolymers. The new method is shown to be capable of ranking the mixtures in a reasonable order, emphasising the improved properties of polymer modified mixtures. A useful correlation has been established between the ageing resistance of mixtures and that of their recovered binders. Stiffness moduli evaluated in the Nottingham asphalt tester were used to characterise the unaged and aged mixtures, whereas the binders were characterised through their rheological properties measured in the dynamic shear rheometer. Mixture ageing results obtained from the developed laboratory method were compared with those of samples exposed to environmental ageing conditions sustained on a building rooftop for 18 months.