Matheus David Inocente Domingos

Rheological behaviour of bitumens modified with PE and PPA at different MSCR creep–recovery times

The main objective of the present study was to determine the effects of longer loading–unloading times on the per cent recoveries (R) and the non-recoverable compliances (Jnr) of bitumens modified with polyethylene (PE), polyphosphoric acid (PPA) and both additives (PE+PPA). These effects were quantified by means of ratios of R values and Jnr values at one test condition to another test condition, and the best formulations were reported. The base bitumen is graded as PG 64-xx and the modified bitumens have the same high PG grade (PG 76-xx). All the materials showed lower R values and higher Jnr values with increasing creep and recovery times from 1/9 s to 2/18 s, which indicates that they are more susceptible to permanent deformation when both times are longer. These higher Jnr values at 2/18 s and the high PG grade can be mainly attributed to the increase in the viscous portion of the viscoelastic response of the bitumen.

Accelerated short-term ageing effects on the rheological properties of modified bitumens with similar high PG grades

The main purpose of the study was to evaluate the effects of rolling thin-film oven (RTFO) ageing on some rheological properties of modified bitumens. They are graded as PG 76-xx and were obtained from a 50/70 bitumen graded as PG 64-xx. Three types of polymers – polyethylene (PE), styrene–butadiene–styrene (SBS) copolymer and ethylene butylacrylate glycidylmethacrylate (Elvaloy®) terpolymer – and polyphosphoric acid (PPA) were selected. Ageing mainly increased the complex modulus (G*) and decreased the phase angle (δ) of the bitumens, thereby increasing their stiffness and elasticity. The existence of plateau regions in the master curves of δ for the bitumen+Elvaloy+PPA and the bitumen+SBS can be explained by the distinctive characteristics of the modifiers, since these plateaus were not observed for the other bitumens. The bitumen+SBS and the bitumen+PE showed very high sensitivity to ageing from the point of view of G* and δ, and the opposite is observed for the conventional properties.