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Highlights • We study some asphalt rubbers with different crumb rubber types and base asphalts. • We assess the asphalt rubbers performance-related characteristics. • We analyse the asphalt rubber surface through scanning electron microscopy images. • We assess the asphalt rubbers mechanical performance. • We conclude about the effect of prolonged digestion time of asphalt rubber performance. Abstract This study wants to provide fundamental understanding of prolonged storage time on asphalt rubber binder properties by performing an investigation on the variation of conventional properties, rheology and morphology of four asphalt rubbers maintained at 180 °C in low shear for different digestion/storage times up to 48 h. The analysed asphalt rubbers were manufactured by combining two different asphalt binder grades, pen 35/50 and pen 50/70, with both cryogenic and ambient crumb rubber. Results have shown that keeping asphalt rubber agitated at the above mentioned processing conditions, up to 48 h, is significantly detrimental when an ambient crumb rubber is used, while it seems not to negatively affect the asphalt rubber produced with cryogenic rubber crumbs. Instead, no remarkable change is recorded when asphalt rubbers are produced with the same rubber type and by changing the base asphalt binders, namely pen 35/50 and pen 50/70. [ABSTRACT FROM AUTHOR]

• The use of waste polyethylene as a sustainable additive to asphalt binder was experimentally investigated with the DSR. • Plastic-type, source, and experimental condition have limited influence on the measured scattered results. • Three different rheological behaviors were observed and identified by using the Black Diagram. • The Glover-Rowe parameter is a sensitive tool to discriminate the rheological behaviors of plastic modified binders. • Analysis of variance and Shapiro-Wilk Test were used to evaluate the results statistically. Significant volumes of waste materials such as plastics is generated every year worldwide with a potentially harmful impact on the environment. At the same time, the demand for asphalt modifiers has seen an increase over the year with consequent higher costs for these types of additives. Therefore, combining large amounts of available waste plastics with asphalt binder as an extender or modifier would potentially improve the paving material properties while limiting the disposed waste. While several rheological studies have been performed in the past, they were restricted to single research efforts hindering a consistent comparison among the valuable results of these investigations. For this reason, the Task Group 1 of the RILEM Technical Committee 279-WMR established a research activity with 11 international institutions to conduct interlaboratory research to evaluate the possibility of using waste polyethylene (PE) as an additive in asphalt binder. The study addressed the combined impact of PE materials and experimental conditions on the rheological properties of asphalt binder. For this purpose, conventional tests (penetration value, softening point temperature, and Fraass breaking point temperature) and the linear viscoelastic characterization using the Dynamic Shear Rheometer (DSR) were adopted. An unaged pen grade 70/100 neat binder was selected as the reference binder; PE-pellets and PE-shreds, produced from the recycled waste polyethylene materials, were used as the polymer additives. A single content (5%) of PE-pellets and PE-shreds was used to blend the PE material with the reference binder (95%) and prepare the two PE modified binders. Results indicate that the use of plastic modifiers leads to an overall higher complex shear modulus and softening point temperature while decreasing the penetration value. Higher dispersion in the results, especially in phase angles, was observed for blended binders at high temperatures. The PE modified binders exhibited poor reproducibility among laboratories and a low level of repeatability. Such a scatter in the data could result from an uneven dispersion of plastic material at high temperatures. In contrast, plastic shapes and batches appeared to have a limited impact. Three different rheological behaviors, neat binder, modified binder, and complex modified binder, were visually identified among the interlaboratory results and based on a simple statistical analysis of variance. Further analysis of the data suggested that the Glover Rowe (G-R) parameter can be used as a sensitive tool to classify the rheological behaviors of PE modified binders. Further experimental evaluation on specific testing conditions, such as measurement gaps of DSR at high temperatures, is recommended to advance the understanding of their influence on the rheological behavior of PE modified binders. [ABSTRACT FROM AUTHOR]

The measurement of rheological properties of the tyre rubber bitumen blends is often challenging due to presence of suspended tyre rubber's crumbs. Furthermore, the phase separation during the course of measurements makes the viscosity of these non-homogeneous blends difficult to ascertain. In this study, a new dual helical impeller was designed and manufactured to be used with a rotational viscometer in order to have a real-time control of the viscosity while performing a laboratory mixing of the blends. Layer based manufacturing techniques showed to be a convenient method to produce complex shaped impeller prototypes before manufacturing the more expensive stainless steel assembly. Impeller geometry was optimised to create a convective like flow within the sample and so minimise phase separation. Shear rate constant is geometry dependent and a calibration exercise was carried out to ascertain this. Results of both calibration and validation phases showed that the new impeller provides reliable viscosity measurements of homogenous fluids such as neat bitumen. With regards to complex fluids the new impeller showed a more stable and realistic trend than that obtained by using a standard spindle. In fact, it was demonstrated that the new impeller significantly decreases phase separation within the blend and in turns provides a more realistic measurement of the viscosity. This system represents a feasible and improved solution for optimising the laboratory modification process of tyre rubber bitumen blends by adapting the rotational viscometer as a low-shear mixer. [ABSTRACT FROM AUTHOR]

Ageing of bituminous materials can result in loss of the durability of a flexible pavement. Using rubberised bitumens can enhance pavement performance while at the same time it solves a serious waste disposal problem. Combining Warm Mix Asphalt (WMA) additives with rubberised bitumens reduces the difficulties associated with the production of asphalt mixtures using this modified binder. This work was conducted to study the effect of ageing using fundamental parameters based on performance, i.e., CTOD and Glover-Rowe parameters have been related to pavement cracking. Different unmodified bitumens and rubberised bitumens were short-term aged using the Thin Film Oven Test (TFOT) and long-term aged using the Pressure Ageing Vessel (PAV). The rheological and fracture properties of the binders were studied before and after laboratory ageing. The results indicated that rubberized bitumens are more resistant to laboratory ageing. However, the pre-treatment with Sasobit® seemed to be detrimental when the materials were evaluated based on their fracture properties. The results also showed that base bitumen properties can affect the ageing mechanism of rubberised bitumens. Using softer bitumen could produce rubberised bitumens with superior anti-ageing properties when the analysis is based on linear viscoelastic properties using the Glover-Rowe parameter. However, these improvements were significantly reduced after ageing when the analysis is based on fracture properties. [ABSTRACT FROM AUTHOR]