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In this paper, a new and simple approach to estimate the rheological properties of Reclaimed Asphalt Pavement (RAP) binder is proposed to overcome the limitations of the conventional extraction procedure. This method is based on Dynamic Shear Rheometer tests performed on mortars composed of RAP fine fraction and virgin binder, together with a new back-calculation solution. The properties of the bituminous blends of virgin and RAP binders are obtained with a modified Nielsen model. The Voigt model is then successfully used to estimate complex modulus and phase angle of the RAP binder from the properties of the back-calculated binder blend. This procedure would prevent the need of RAP binder extractions to determine its properties, which is time-consuming and might modify the actual binder characteristics. [ABSTRACT FROM AUTHOR]

Reclaimed Asphalt (RA) has shown great potential to be reused in new asphalt mixtures, however its incorporation in top asphalt pavement layers is still very limited (10–30%). In fact, despite the advantages that its use implies, RA content in road pavement surface courses is still restricted in most countries due to mainly legislation limitations, but also some technical issues. This paper aims at being a step further to improve the latter by providing a methodology that allows producing fundamental inputs for confidently performing mix design of asphalt mixtures incorporating up to 100% RA. The methodology consists in an advanced preliminary binder's blend design that can be used with any type of RA and also in presence of rejuvenators. This procedure includes in the production of blending charts and laws that considers the uncertainties on accounting the extent of final binder content, Degree of Blending and Replaced Virgin Binder. The description of the methodology is accompanied with results of two extreme case studies consisting in the preliminary design of binders for asphalt mixtures with high content of two types of RA corresponding to extreme cases: the short-term aged RA (STA-RA), having a very soft residual binder (Pen > 20 dmm) and the long-term aged RA, having a much harder residual binder (Pen < 10 dmm). As a result, the proposed methodology allowed assessing the feasibility of using up to 90% of RA and determining whether the use of rejuvenating agents was needed. [ABSTRACT FROM AUTHOR]

• Pyrolysis and liquefaction (HTL) of biomass are compared to produce biobinders. • HTL provides a more stable product in high yield with relatively low oxygen content. • Biobinders performance depends on the biomass source and the technology applied. • Long-term performance and environmental impact studies for biobinders are missing. • Tables compiled from the literature are provided to identify suitable biobinders. Biobinders (binders manufactured from biomass) are becoming popular in asphalt engineering due to growing environmental concerns of greenhouse gas emissions from the use of fossil fuels and depleting petroleum bitumen reserves. Waste biomass products are sources of particular interest due to their widespread availability and impact on sustainability, however, they generally need to be thermochemically treated before being used as biobinders. Although biobinders can exhibit good performance in terms of resisting common distresses affecting road pavements, they are still relatively unknown and the uncertainty around them discourages their further use. In this context, this review aims at providing a link between biomass thermochemical conversion technologies and their respective products that may be used as biobinders in pavement engineering. For this purpose, firstly, a detailed insight of the biomass thermochemical conversion technologies available for the manufacture of biobinders is provided. Specifically, solvent liquefaction and pyrolysis are compared and the operating parameters affecting the production of biobinders from solvent liquefaction are explored. Secondly, the review focuses on providing an overview of current biobinder studies for asphalt mixtures with an emphasis on the feedstock utilised and their key engineering properties. The review shows that biobinders' performance highly depends on the biomass source and the technology applied to produce them. Summary tables provide researchers with a quick but insightful way of identifying potential biobinder feedstocks according to certain properties. [ABSTRACT FROM AUTHOR]

• Asphalt mixtures with 20% crumb rubber are manufactured at 150 and 130 °C. • High penetration bitumen and two additives are used to reduce viscosity. • Asphalt mixtures are designed and mechanically characterised. • Rubberised asphalt mixtures could be adequately manufactured at 130 °C. • Their mechanical performance was not adversely affected. The construction and maintenance of road pavements need to be undertaken to ensure proper economic and social growth. Considering the high environmental impact that the production of asphalt mixtures for road pavements entails, in terms of energy consumption and greenhouse gas (GHG) emissions, these operations must follow the global transition towards more sustainable development practices. In response to this, previous research has been focused on the development of manufacturing low temperature asphalt mixtures and the use of recycled modifiers such as tire crumb rubber to improve their durability. However, the use of high dosages of the latter reduces mixture workability, thus requiring high manufacturing temperatures to reduce the viscosity of the binder, and therefore limiting the advancement towards more sustainable mixtures. In this regard, further knowledge is needed on this topic to promote the combination of such techniques to maximise their advantages. This study aims to check the viability of producing asphalt mixtures with high crumb rubber contents at reduced temperatures, testing their workability, stiffness, cohesion, resistance to permanent deformations and resistance to moisture damage. Results show that it is possible to manufacture viable, warm, rubberised asphalt mixtures at 150 °C using a high penetration bitumen and reduce this temperature to 130 °C (45 °C less than conventional rubberised asphalt mixtures) by including warm additives, without compromising their mechanical performance. [ABSTRACT FROM AUTHOR]

• 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]

The addition of crumb rubber particles as bitumen modifier can be currently considered as a well-established alternative to conventional polymers for bitumen modification. However, Recycle Tyre Rubber (RTR) modified binders still present drawbacks such as poor mix workability and hot storage stability. Within this study the authors try unlocking the full potential of devulcanised tyre rubber-heavy oils blend, named Liquid Rubber (LR), by exploring the possibility of tailoring recycled polymer modified bitumen with unconventional high-content of RTR and designed to overcome the above mentioned technological problems of RTR modified bitumen while keeping its advantages. Results show that LR-bitumen blends incorporating up to 30% RTR in weight of total binder clearly improves useful temperature interval of base bitumen by maintaining solubility values allowing them to be considered stable at hot-storage temperature. Furthermore, the LR modifier allows reducing usual manufacture temperatures up to 30 °C by providing superior low and intermediate temperature rheology, however high service temperature properties are improved only at low strain. [ABSTRACT FROM AUTHOR]

The use of tire crumb rubber in road engineering as a modifier of bituminous mixes constitutes one of the revalorization techniques for this waste. The main objective of this research consists of analysing the possible fatigue cracking improvements in the performance of bituminous mixtures containing crumb rubber in comparison to bituminous mixtures manufactured with conventional bitumen and bitumen modified with SBS polymers. For this purpose, four different types of mixes with the same mineral skeleton but different bitumens were studied. The test used to evaluate their behaviour was the UGR-FACT with an additional system for taking pictures, which allows controlling the propagation of the cracks at every moment. The results show that the addition of crumb rubber retards the appearance of cracks; however, once it begins, the damage propagation is faster. Therefore, the fatigue cracking life of mixes with crumb rubber seems considerably longer than the fatigue cracking life of those with conventional bitumens. Moreover, in the mixes with crumb rubber added by the dry process, cracks are thinner and less ramified than in the other ones. [ABSTRACT FROM AUTHOR]

In order to achieve current sustainability and circular economy targets, the use of cleaner practices is required. Therefore, for the abatement of emissions in a cost-effective way, the use of waste materials, reduced manufacturing temperatures, and the increased use of bio-based materials should be explored in the asphalt pavement sector. In response to this need, this study carried out a carbon footprint and economic analysis for the three aforementioned strategies. To fully understand the potential of these pathways, the use of reclaimed asphalt (RAP) and crumb rubber (CR) in different quantities, the use of hot-, warm- and half-warm-mix asphalts, and the use of bio-based binders were considered both at the cradle-to-laid and 40-year life cycle level. The results of this study indicate high quantities of RAP and producing mixtures below 100 °C would provide the greatest environmental and cost benefits. At lower amounts of RAP, the use of CR was found to be more viable; especially with a higher durability. Bio-based materials also provide a large GHG saving potential, but would require commercialisation to be viable. The results of this study serve as a primer for researchers, industry and local authorities to better explore and combine climate mitigation and cost-effective strategies. Future work will cover the use of these results for their implementation in a decision-making system, including the novel indicator defined. • Three GHG and cost saving strategies were analysed across their life-cycle. • A novel indicator was defined to clearly interpret its viability. • High reclaimed asphalt at lower manufacturing temperatures was the most viable. • At low reclaimed asphalt quantities, crumb rubber was more viable. • Bio-materials have a large abatement potential when biogenic carbon is considered. [ABSTRACT FROM AUTHOR]