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Laboratory scale mechanical performances on six plant produced mixtures; three semi-dense surface courses and three dense binder courses modified with engineered crumb rubber (ECR) using the dry process are presented. The two types of mixtures produced and investigated fulfilled for the most part, the requirements of the Swiss and/or US standards regarding volumetric properties, water sensitivity and rutting. In advanced testing where no requirements exist, the dense ECR mixtures performed similar to the reference polymer modified mixtures and slightly worse for semi-dense mixtures in high temperature tests, where the binder becomes viscous in the rubber-binder composite and its ability to transfer loads is reduced. The ECR mixtures performed similarly or better than the reference in low temperature tests. Across the advanced testing data set, all obtained results were well within acceptable values for both ECR and reference polymer mixtures indicating that crumb rubber can effectively replace polymer in asphalt mixtures. [ABSTRACT FROM AUTHOR] more...

The fracture performance of rubberised bitumen in addition to one pre-treated with a Warm Mix Additive (Sasobit ® ) was investigated using different test methods measuring different damage mechanisms. Two Recycled Tyre Rubber (RTR) modifiers together with two base binders were blended in the laboratory to produce various combinations of Recycled Tyre Rubber Modified Bitumens (RTR-MBs). The first RTR is a standard recycled polymer derived from discarded truck and passenger car tyres by ambient grinding. The second RTR consists of 100% recycled truck tyres derived by cryogenic grinding and pre-treated with special oil and WMA to allow further decrease of asphalt mixture production temperatures. A fracture mechanics testing approach was used for evaluating the binder fatigue resistance; consisting of the double-edge-notched tension (DENT) test. The critical tip opening displacement (CTOD) obtained from the DENT test was used for fracture characterization of the binders within the ductile failure region. The study applied the partitioning concept of the total energy of bituminous binders to have a more reliable parameter that could be independent of the stress state of the ligament. The results show that generally the addition of RTR improves the fracture properties of binders indicating better fatigue performance. Pre-treatment with Sasobit® makes the materials more brittle and hence more susceptible to fracture. [ABSTRACT FROM AUTHOR] more...

The addition of recycled tyre rubber as a modifier to enhance the mechanical properties of bitumen has proven to provide asphalt mixtures with better mechanical performance. However the rubberised bitumen presents the limitation of requiring higher manufacturing and compaction temperatures. This could be solved by subjecting the tyre rubber to sort of pre-treatments such as: Adding warm-mix additives and/or using partial devulcanisation. These solutions have the potential of lowering the overall environmental impact of the asphalt pavement, however it is still not clear whether these can be detrimental for the rubberized asphalt binder mechanical properties. This paper investigates the effect on fatigue and healing properties of rubberized bitumen blended with pre-treated crumb rubber. An innovative combined fatigue and healing analysis will be presented and used to compare the several rubberised binders with a neat bitumen. The analysis consists in conducting time sweep tests by means of dynamic shear rheometer, by applying repeated cycles of stress or strain loading at selected temperatures and loading frequency. The healing potential of binders was evaluated by introducing short rest periods after a certain number of load pulses. At last, the unique energy parameter obtained using the Ratio of Dissipated Energy Change approach, was applied to obtain a unique index that could provide combined information for both fatigue binder damage and healing phenomenon. The results showed that the analysed rubberised bitumens show having better fatigue and healing performance when compared to the straight-run bitumen. [ABSTRACT FROM AUTHOR] more...

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] more...

Highlights: [•] Introducing the Recycled Tyre Rubber (RTR) material as environmental problem as well as engineering resource. [•] Introducing the wet process technology. [•] Describing in details the existing products associated to the wet process high viscosity technology. [•] Describing in details the wet process No Agitation technology. [•] Comparing the described technologies and providing justifications and suggestions toward a widespread use of RTR-MBs. [Copyright &y& Elsevier] more...

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] more...

Railway ballast degradation under dynamic loads progressively leads to loss of mechanical performance and geometry of the track, so that maintenance interventions are frequently needed. In order to systematically avoid this issue, recently solutions have been proposed to reinforce track-bed by using polyurethane and/or resins as well as asphalt layers among others. Nonetheless, their main limitations are related to the high initial cost and low productivity. To cope with these limitations, in this study, bitumen stabilized ballast (BSB) is proposed as a new solution for ballast stabilization. This method aims at improving durability and reducing settlement by modifying both stiffness and the ability of energy dissipation of the layer. The paper introduces the potential of this technology as material to be used in railway track-beds by presenting the results of a laboratory-based investigation using the Precision Unbound Material Analyser (PUMA). Different variables such as ballast grading, bitumen emulsion dosage, compaction method and stress levels are considered. Results showed a significant decrease in permanent deformation and deformation rate associated with modified stiffness and energy dissipation properties of BSB, which suggest the potential for improving long-term performance and sustainability of ballasted track. [ABSTRACT FROM AUTHOR] more...

Abstract: Bearing in mind the need to answer one of the most frequent needs for civil construction, in general, and major project such as road infrastructures in particular, this paper presents the results of a laboratory experimental study in order to evaluate the performance improvement that is possible to achieve when modifying road bitumen with CRM (Crumb Rubber Modifier) from discarded tire rubber (TR), using a Wet Process. The environmental advantage is double, since the aim of the research is to obtain high performance road bitumen thanks to the re-use of a discarded material, such as the rubber tires, which otherwise would be dumped in scrap-yard. In particular, this experimental study aimed to define a laboratory optimization protocol that allowed to discriminate amongst the different asphalt–rubber blends, in relation to the different content of rubber, as well as to the blending times, with the possibility of carefully controlling the production temperature throughout the production process. In order to do this, simple and widespread laboratory equipments and procedures have been adopted, such as the Brookfield rotational viscometer, capable of ensuring the representativeness of the final product to be tested. After the optimization study, a comparison was made between the conventional and rheological properties of the optimized rubber–asphalt blend with those of two commercially available PMBs, modified with synthetic rubber type Styrene–Butadiene–Styrene, with two different level of modification: a medium and a high level of polymer, respectively termed as “Medium” and “High” in this study. This comparison allows one to appreciate to what extent control of the modification process is able to affect the properties of the final product and shows that the preliminary optimization of the mixing parameters carried out with the proposed protocol allows one to obtain a rubber–bitumen blend with improved performances, above all reduced temperature susceptibility, as proved by an increase in the Superpave™ high temperature performance grading, up to a two grade jump, which it is possible to obtain only for SBS modified bitumen with high content of polymer. Therefore, this study proves that, thanks to the appropriate re-use of crumb rubber form scrap tires, with the proposed optimization protocol it is possible obtain improved bitumen with high content of recycled materials that, with respect to specific needs of regions with warm climates such as the Mediterranean area, can be considered as “high-performance blends”. [Copyright &y& Elsevier] more...

• Cost effective optimisation of modified bitumen with liquid rubber for pavements and roofing membranes is presented. • Design optimisation technique allowed producing superior bituminous binders. • LR improves the flexibility at low in-service temperatures (using up to 50% contents), while EBS improves stiffness at high in-service temperatures. • The Response Surface Methodology was successfully used to optimise the final blends also in terms of cost. • Analytical functions amongst the design parameters have been derived and here provided for future design exercises. • The final properties were comparable to Polymer Modified Binders. Polymer Modified Bitumens (PMBs) are largely used for pavement and roofing membranes applications with Styrene-Butadiene-Styrene Block copolymer (SBS) playing a major role in both markets despite its constantly increasing price due to the rising demand for quality bitumen modifiers. On the other hand, there is an increasing trend of recycling end of life tyres generating Recycled Tyre Rubber (RTR) at affordable price. This investigation aims at engineering a modified bitumen with a combination of Liquid Rubber (LR), a homogeneous blend of 50–70% RTR pre-processed in combination with heavy oils, and a wax denominated Ethylene Bis Stearamide (EBS). In the first phase, the effect of LR and EBS was independently characterised and compared to PMBs. Next, the Response Surface Methodology (RSM) was used to predict the response of different combinations of LR and EBS in terms of low and high temperature properties and cost, to then be optimised targeting conventional and rheological properties of PMBs currently used in asphalt mixtures and roofing membranes in UK. As a result, an optimum combination of LR and EBS was found leading to a cost-effective modified bitumen comparable to PMBs. The work provided also analytical functions that could be of use in further design exercises. [ABSTRACT FROM AUTHOR] more...

• Previously used methods for determining DoA, DoAv and DoB are shown. • Investigation methods for determining DoA, DoAv and DoB are classified. • Advantages and disadvantages of the investigation methods and techniques are shown. • The literature review which may help in quantifying DoA, DoAv and DoB is given. The lack of understanding the mechanisms governing the interaction between reclaimed asphalt binder (RAb) 1 1 RAb – Reclaimed Asphalt binder. and recycling agents is one of the technical issues that still need to be resolved when high amount of reclaimed asphalt (RA) 2 2 RA – Reclaimed Asphalt. is used in a new recycled asphalt mixture (RAM). Due to important role of RAb in that interaction and increased used of RA, it becomes necessary to have a way to classify RA, as any other material used in asphalt mixture production. It is very important to determine how much RAb is active by itself (DoA) 3 3 DoA – Degree of binder Activity. , but also to determine how much RAb can be considered available for a mix design of RAM (DoAv) 4 4 DoAv – Degree of binder Availability. when a recycling agent is used. Finally, since that RAM's properties are strongly dependent on the degree of blending between RAb and recycling agent (DoB) 5 5 DoB – Degree of Blending. , it should evaluate to what extent RAb contributes to the final properties of RAM. These blending parameters (DoA, DoAv and DoB) are so crucial that identifying suitable methodologies for their assessment would be extremely important in performing a proper mix design due to dangerous of having a lack of active bitumen in RAM. This paper presents a literature review of methods which have been used for the evaluation and assessment of mentioned parameters, grouped in four macro-areas: mechanical, chemical, visualization and mechanistic approaches. Furthermore, summarized review of used methods was prepared together with their critical review, all with aim to find appropriate methods for determining these parameters. [ABSTRACT FROM AUTHOR] more...