Adalberto Leandro Faxina

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.

Fatigue Behavior of Asphalt-rubber Binders Modified With Shale-oil Residue

This work aims at evaluating the effects of the proportions of crumb rubber and shale-oil residue on the fatigue parameter G*sinδ. Eight asphalt binders were submitted to short- and long-term aging and then tests in the oscillatory-shear mode were performed. Based on regression models, response trace plots, and contour plots were made. Both rubber and oil reduce the G*sinδ parameter, increasing the controlled-mode fatigue resistance. As the test temperature decreases, the intensity of the effects of rubber and oil on G*sinδ increases and the number of mixtures that meet the Superpave limit of 5.0 MPa reduces.

Rheological Behavior of Asphalt–Rubber Binders Modified With Shale-Oil Residue and Polyphosphoric Acid

The objective of this paper is to assess the effects of adding two modifiers of different chemical nature on the rheological behavior of asphalt–rubber binders: the shale-oil residue and the polyphosphoric acid. Four modified asphalt–rubbers were prepared: asphalt–rubber–PPA (18 % crumb rubber + 1 % PPA), asphalt–rubber–oil (18 % rubber + 10 % shale-oil residue), asphalt–rubber–oil–PPA–1 (18 % rubber + 10 % oil + 1 % PPA) and asphalt–rubber–oil–PPA–2 (9 % rubber + 5 % oil + 0.5 % PPA). A reference asphalt–rubber was prepared using 18 % crumb rubber. The samples were submitted to oscillatory-shear tests to obtain data (complex modulus, G*, and phase angle, δ) to construct master curves. Compared to the base asphalt binder, the pure asphalt–rubber improves the rutting and strain-controlled fatigue resistances. The addition of 1 % PPA enhances even more the rutting resistance and improves slightly the fatigue resistance below 20°C. The most substantial increase in fatigue resistance is obtained when 10 % oil is added to the pure asphalt–rubber, but its rutting resistance is drastically reduced. Mixtures 1 (18 % rubber + 10 % oil + 1 % PPA) and 2 (18 % rubber + 5 % oil + 0.5 % PPA) have lower rutting resistance compared to the base asphalt–rubber, but only mixture 1 has higher fatigue resistance. Compared to the base asphalt binder, all modified asphalt–rubber binders present higher G*/sinδ values (at all rutting temperatures) and lower G*·sinδ values (only below 20°C) when traffic speed reduces. Taking this evidence into account, the asphalt–rubber and the asphalt–rubber–PPA are the most appropriate. Although shale-oil residue has shown opposite results at intermediate and high pavement temperatures (enhancing the fatigue resistance and reducing the rutting resistance), it is able to reduce the viscosity of the asphalt–rubber, enhancing the workability of the HMA mixes during construction.