Effects of ageing on the damage tolerance of polymer modified bitumens investigated through the LAS test and fluorescence microscopy

The effects of polymer modification on the durability of Polymer Modified Bitumens (PMBs) still remain relatively unclear due to partial understanding of the combined effects of ageing and loading on damage accumulation. This paper investigates the effects of laboratory ageing on the damage tolerance of cross-linked SBS and EVA modified bitumens measured using the Linear Amplitude Sweep (LAS) test and corroborated with the morphology of the PMBs. The PMBs were prepared with three polymer concentrations (i.e. 2%, 4% and 6%). In general, ageing affects the capacity of bitumens to maintain integrity to damage and reduces their time-temperature susceptibility. The damage tolerance is derived from the combination of the two mechanisms as a function of the bitumen’s strain level. At low strain levels, typical of thick pavements, ageing enhances the damage tolerance. Contrarily, at higher strain levels, it provides the opposite effect. SBS improves the damage tolerance of the base bitumen as a function of polymer concentration and dispersion. However, the polymer chain undergoes oxidative degradation and its effect reduces with ageing. EVA forms a polymer network with a low oxidative susceptibility that contributes, at low strain, to maintaining or improving the damage tolerance with ageing as a function of the polymer concentration.