Polymer additives are used to improve the properties of road bitumens including their oxidative resistance. However, their usage as anti-oxidative materials remains relatively unclear. This study...

Polymer additives are widely used to improve the performance of road bitumens including their resistance to hardening during oxidation, although their oxidative inhibitor effect has not been well documented. This study aims to investigate the effect of laboratory-simulated ageing on the microstructure, and rheological properties of Polymer Modified Bitumens (PMBs) prepared with a Styrene-Butadiene-Styrene (SBS) copolymer and sulphur as a cross-linker. The laboratory ageing was conducted through the Rolling Thin Film Oven (RTFO) and the Pressure Aging Vessel (PAV) procedures. The unaged and aged binders were characterised using the Multiple Stress Creep and Recovery (MSCR) test, Gel Permeation Chromatography (GPC) and fluorescence microscopy. The MSCR test showed that the cross-linked polymer had a higher capability of mitigating the effect of bitumen hardening on the rheological response, while for the PMBs without cross-linking, the polymer effects decreased significantly after RTFOT ageing. The GPC results showed that the aromatics, resins and asphaltenes fractions of the unmodified bitumens shifted towards heavier molecules after one cycle of PAV ageing but showed limited variation with further ageing. Similar behaviour was observed for the uncross-linked polymer binders, while for the cross-linked polymer binder, the behaviour depended on the polymer concentration.

Road authorities are challenged by traffic-induced vibrations due to their detrimental effects on humans and to the damage of buildings and structures. For this reason, asphalt mixtures designed as damping layer are investigated to resist vibration and noise caused by traffic loads, while a reliable design method to optimise for the mixes needs to be developed and their damping and mechanical properties require corresponding evaluation. In this work, a novel mix-design method special for the damping layer is proposed. Two rubberised asphalt mixtures were designed by optimising their damping properties and their volumetrics were adjusted to accommodate a high content of rubberised bitumen. Tensile strength, rutting resistance, stiffness, loss factor, phase angle and damping ratio were measured to evaluate their mechanical and functional potential as thin damping interlayer in road pavements. Results show that the designed mixes have higher damping capacity than traditional rubberised asphalt mixes. Aside from this, the mixes appear to be rut resistant and show sufficient levels of tensile strength and resistance to water damage.

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.

Molecular weight distributions are widely used to evaluate the effects of aging or modifiers in bituminous binders. As with polymers, the most common techniques to obtain the distributions can be subdivided into two main groups, depending on whether or not they use a solvent. In the first group, the dimension of the molecules is evaluated in a diluted unperturbed state, while, in the second, the dimension derives from the bulk, where aggregated or interacting molecules may behave as single entities. However, the calibration curves used in the bulk are tuned in order to homogenize the results derived from the two approaches. This sort of contradiction, plus the high number of experimental uncertainties, suggest that the term “apparent” should be used for both distributions. These aspects are well known in the field of polymers but have received less attention in the case of bitumens, which are even more complex. This paper pinpoints the advantages and disadvantages of the two techniques, thus highlighting the most appropriate use. Bulk methods are preferred when evaluating properties that are strictly dependent on the microstructure, such as the level of aging and the effects of additives or modifiers. Diluted methods should be used when the molecular size matters, such as in quantifying the presence of polymers or rejuvenators. Both techniques should be used for comparative studies only.