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The Life Cycle Assessment (LCA) of asphalt pavements are associated with significant uncertainty resulting from variability in the quantity and impact of individual components, the quality of data for each component, and variability of asphalt durability. This study presents a framework to quantify and incorporate the uncertainty of LCA and asphalt durability data into LCA of asphalt surfacings. The suggested framework includes: estimating the uncertainty of asphalt production processes by the pedigree matrix method, conducting a deterministic LCA, applying Monte Carlo Simulation (MCS) to estimate the probability density functions (PDFs) of the considered impacts using the uncertainty data, deterministic solution, and asphalt durability. This framework was applied to six asphalt mixtures; the results show that there is significant uncertainty in the processes that contribute to the environmental impacts. They also showed that considering asphalt durability and its uncertainty is critical and can significantly change the results and interpretation of LCA.

ABSTRACTThe binder content of rubberised asphalt mixtures is usually increased compared to that used in conventional asphalt. This increase is deemed important to compensate for the reduction in the actual bitumen due to the existence of rubber particles. This study presents the results of performance evaluation conducted on different rubberised Stone Mastic Asphalt (SMA) mixtures produced using different types and contents of rubberised bitumen. The energy ratio (ER) computed from Superpave Indirect Tensile (IDT) tests was used to evaluate the cracking resistance of asphalt mixtures while the rutting behaviour was evaluated using the Repeated Load Axial Test (RLAT). The indirect tensile stiffness and strength were used to evaluate the moisture susceptibility. Using the same binder content for rubberised SMA mixtures as used in the conventional mixtures can still give superior performance properties. Adding crumb rubber to softer base bitumen can produce asphalt mixtures with superior cracking and rutting resistance.

The current need to move towards more sustainable technologies in the construction sector has promoted the investigation of using alternative materials in asphalt mixtures for pavements. Biomaterials, used as biobinders, have shown their potential as partial replacement of bitumen in asphalt mixtures as solution to decreasing the demand for fossil-fuel-based binders as well as CO2emissions. However, more research is needed to increase the replacement of bitumen in asphalt mixtures. In this investigation,biobinders are used as full replacement of virgin bitumen and as recycling agent within asphalt mixtures with high Reclaimed Asphalt (RA) content. Blends of biobinders and RA binders, and bio-recycled asphalt mixtures, were produced, subjected to ageing and rheologically characterised. The results show that the rheological properties of binders’ blends seem adequate for their use, while the bio-recycled asphalt mixtures seem to have a faster ageing than conventional ones, hence their full-scale application still remains a concern.

ABSTRACTInter-laboratory experiments were designed to evaluate the impact of plastic waste blended directly in bitumen and to assess the properties, using conventional and advanced bituminous binder testing. The blends targeted 5% of plastic waste in 95% bitumen, using two types of polyethylene (PE) primary (pellets) and secondary (shreds) waste. The experiments showed that the addition of PE waste to bitumen does not alter the chemistry of the bitumen, the blending is physical. The DSR results indicate a strong dependency on the testing temperature as at low temperatures the composite material bitumen and PE behave both elastically whereas, at higher temperatures, the bitumen becomes viscoelastic. The MSCR tests indicated that the neat binder is more sensitive to permanent deformation compared to the blends with PE. The fatigue performance using the Linear Amplitude Sweep test showed a better performance in terms of stress and fatigue life for the PE blends.

The tire rubber obtained from end-of-life car and truck tires has been successfully recycled, among other applications, in the asphalt industry by providing a mean to get asphalt mixtures with superior performance. Textile fibres are another component derived from tire recycling typically disposed of in landfills or used in energetic valorisation. This paper wants to re-ignite interest in this secondary product by evaluating its use as a valuable resource in asphalt mixtures. Indirect tensile tests, dynamic modulus, fatigue resistance, and permanent deformation tests were performed on a series of AC14 asphalt mixtures manufactured with two binders, namely 50/70 and 35/50 pen, using several binder and fibre contents. The results indicate that incorporating fibres of tire recycling is not problem-free. Results have shown that can be advisable in pavement applications whenever the investigated fibre-modified mixtures allowed to incorporate at least 6.5% binder content with great benefit for pavement performance.

Stone Mastic Asphalt (SMA) has been broadly used on heavily trafficked roads and motorways in the UK due to its known stability and durability. In this study, several sets of SMA mixtures were produced using different rubberised bitumens, including a Fischer–Tropsch wax pre-treated rubberised bitumen. Properties associated with rutting were evaluated using both linear and nonlinear viscoelastic analyses, using different test methods such as the Strategic Highway Research Programme (SHRP), Shenoy rutting parameter, zero shear viscosity (ZSV) and multiple stress creep recovery (MSCR) tests. The rutting resistance of the resulting SMA mixtures was assessed using the Repeated Load Axial Test (RLAT). The addition of rubber was expected to enhance rutting resistance of these materials. The results indicated that among the binder rutting parameters assessed, the non-recoverable creep compliance (Jnr) computed from the MSCR test, showed the best correlation with the rutting resistance of the corresponding asphalt mixtures. Finally, a more fundamental analysis was provided by assessing the conditions of binder films that would be experienced in the mixtures.HighlightsRutting resistance of binders and mixtures are well correlated when the realistic strain conditions are taken into accountSMA produced using rubberised bitumens resulted in highly rut resistant mixturesMSCR test can measure the rutting resistance of binders

ABSTRACTLaboratory 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.

The performance of cold bitumen emulsion (CBE) mixtures is strongly linked to an optimised design of the binder blends and mastics. Types and dosages of bitumen, mineral additions and the workability must be characterised and optimised. This study aims at providing an approach for the fundamental characterisation of CBE materials using rotational viscometry. Firstly, a procedure for measuring the viscosity of CBE slurries using the Brookfield viscometer was investigated by comparing results obtained by using a traditional spindle geometry and a novel impeller engineered to avoid phase separation: the dual helical ribbon (DHR). Afterwards, the effect of mineral additions and bitumen emulsions types was measured and modelled, also considering the influence of their concentration. The Krieger-Dougherty model proved to be a powerful tool to fit results and provide fundamental parameters for improved CBE materials engineering characterisation. Overall, the DHR was found a promising tool for CBE slurries rheological characterisation.

An experimental study was conducted to evaluate the effectiveness of two bio-additives as rejuvenators on the properties of asphalt mixtures containing 50% RAP and their binder constituents containing 37% RAP binder. Before mixing, the rejuvenators were blended with fresh bitumen and the extracted and recovered RAP bitumen, and changes in the rheological properties of the binders were assessed using performance grading (PG) criteria. The results showed that both rejuvenators could improve the low-temperature performance of the aged RAP binder and restore its low-temperature properties. Master curves for the unaged, RTFO-aged, and PAV aged blends were constructed using both the Christensen-Anderson-Marasteanu (CAM) model and the Sigmoidal models. A comparative statistical analysis conducted on the models indicated no significant difference between the measured and predicted complex modulus values at any aging conditions. The pairwise statistical comparison between the two models showed that at unaged conditions, they can perfectly overlap as the p-values were greater than the level of significance. However, for the PAV-aged binders, this behaviour appears to weaken due to the brittle behaviour of the binders. Further statistical analyses revealed no significant differences between the two models at unaged conditions, however, as the binders where subjected to aging, significant differences between the two models began to appear. Mixing was performed in two locations: lab and plant, while compaction was performed only in the lab. After mixing and compaction, mixtures were evaluated for their stiffness characteristics through dynamic modulus testing. Compared to the control mixture, rejuvenated mixtures showed lower dynamic modulus values specially at high temperatures. A statistical comparison between the lab-produced, lab-compacted mixtures and plant-produced, lab compacted mixtures showed that both the rejuvenation and the location of mixing were significant factors in the stiffness measurements.

Using Reclaimed Asphalt (RA) in new asphalt mixtures can reduce the amount of new material required thereby saving money and natural resources. In addition, asphalt mixtures with RA have shown comparable properties and performance to that generally associated with asphalt mixtures made with 100% virgin material. However, RA content in pavement surface layers is still limited due to specification and technical limitations. For higher contents, the aged RA binder must be analysed to accurately determine the requirements for virgin binders and additives while the degree of blending (DOB) between the RA binder and the virgin binder also needs to be quantified. This is not a simple process and generally designers assume one of two opposing theories associated with 100% (full blending) or 0% (“Black Rock”) DOB. This paper proposes a new approach to estimate a unique property of the RA known as the Degree of Binder Activity (DoA) as a function of the processing temperatures of the RA. The study showed positive results and indicated that this DoA approach can be used as a tool to better understand RA in order to improve the binder/blend design for recycled asphalt mixtures.

The recent drive to find ways to increase sustainability and decrease costs in asphalt paving has led researchers to find innovative ways to incorporate more recycled materials and bio-derived binders into mixes with varying success. A new novel bio-derived binder made from refined pine chemistry stabilised with a polymer can increase the sustainability of asphalt mixes while maintaining pavement performance. Laboratory performance testing was conducted on asphalt mixes containing 50% Reclaimed Asphalt Pavement (RAP) by mix weight and the novel bio-derived binder. Results show that the bio-derived binder outperforms the conventional 50/70 pen grade binder mixes with respect to resistance to thermal cracking and adequately passes all requirements for pavements with 20-year design loadings of less than 30 million ESALs. This research shows that asphalt mixes containing 50% RAP and a bio-derived binder can be designed to pass performance criteria at low, intermediate, and high temperatures without the need of neat bitumen.

Polymer additives are widely used to improve the performance of road bitumens including their resistance to hardening during oxidation, although their oxidative inhibitor effect has not been well documented. This study aims to investigate the effect of laboratory-simulated ageing on the microstructure, and rheological properties of Polymer Modified Bitumens (PMBs) prepared with a Styrene-Butadiene-Styrene (SBS) copolymer and sulphur as a cross-linker. The laboratory ageing was conducted through the Rolling Thin Film Oven (RTFO) and the Pressure Aging Vessel (PAV) procedures. The unaged and aged binders were characterised using the Multiple Stress Creep and Recovery (MSCR) test, Gel Permeation Chromatography (GPC) and fluorescence microscopy. The MSCR test showed that the cross-linked polymer had a higher capability of mitigating the effect of bitumen hardening on the rheological response, while for the PMBs without cross-linking, the polymer effects decreased significantly after RTFOT ageing. The GPC results showed that the aromatics, resins and asphaltenes fractions of the unmodified bitumens shifted towards heavier molecules after one cycle of PAV ageing but showed limited variation with further ageing. Similar behaviour was observed for the uncross-linked polymer binders, while for the cross-linked polymer binder, the behaviour depended on the polymer concentration.

It is common practice to assume full blending of the aged binder of reclaimed asphalt (RA) within the design of new asphalt mixtures. Although being practical, this assumption has often led designers to asphalt mixtures lacking binder. Hence, going towards recycled asphalt mixtures (RAM) there is a need to have a better understanding of the blending phenomena, to have a general agreement on terminology and finally adapting RA classification and mix design procedures accordingly. This manuscript aims at being both a reference and stimulus for the scientific community to work in this direction and on this basis provides a nomenclature and a theoretical framework of the blending phenomena. The study is built upon a literature review on definitions, methods and influencing factors related with the blending phenomena and as a result, an intrinsic property of RA, the Degree of binder Activity (DoA), is introduced for the sake of improving RA classification. Furthermore, the two well-known concepts of the Degree of Blending (DoB) and the Degree of binder Availability (DoAv) are redefined, within the proposed framework, together with practical suggestions to introduce them in mix design procedures.

Modified bituminous binders allow asphalt technologists to design asphalt mixtures with superior performance. However, several recent studies highlighted that due to the complexity of these material, their characterisation can be challenging since common procedures used to characterise neat bitumen might not be adequate. For instance, during high temperature rotational viscosity testing of recycled tyre rubber modified binders (RTR-MB), a number of changes may occur to the sample leading to the here-defined sample stability which in turn provides misleading results. In this study the authors want to first provide a deeper understanding of this phenomenon by a numerical analysis using a bespoke Computational Fluid Dynamics (CFD) model to simulate the laboratory tests and use innovative visual aids to monitor the sample stability of heterogeneous bituminous binders during the rotational test. The numerical analysis was complemented by a laboratory campaign aiming at proving the occurring of sample stability during viscosity measurement of heterogeneous bituminous binders with a standard testing setup (SC-27). Furthermore, a dual helical ribbon (DHR) is here introduced as a solution to overcome the issue. Hence, laboratory tests were undertaken also with DHR and differences in viscosity measurements of neat bitumen, SBS-MB and RTR-MB were recorded. Results of this combined numerical and empirical approach proved that the standard setup for rotational viscosity measurements seems not be adequate for RTR-MB and depending on the level of modification and test temperatures, might not be best suited for SBS-MB either. The DHR seems to solve the issue and authors strongly recommend the adoption of this testing geometry to obtain more realistic high-temperature viscosity measurement of heterogeneous bituminous binders.

Alternative binders not derived from fossil fuels, known as biobinders, are opening new paths for multiple applications in road infrastructure. Biobinders, usually produced from bio-oils obtained from the processing of biomass and industry by-products, are tuneable materials whose properties can be adjusted to meet specific targets. For this reason, an interesting approach is to couple biobinders with Reclaimed Asphalt (RA) by taking advantage of their rejuvenating properties to design bio-asphalt mixtures with high-content RA and no additional virgin bitumen. Recent research has proven the feasibility of this approach through validation at full-scale (BioRePavation project). However certain aspects related to the durability of bio-asphalt mixtures still require further research, one of these being their resistance to moisture damage. This study aims at filling some of these current gaps by conducting an initial investigation of the moisture sensitivity of selected biobinders and bio-rejuvenated asphalt binders. In order to do this, the intrinsic adhesion and cohesion properties of an extracted RA binder, two biobinders, their blends and two types of aggregates were characterised by means of Surface Free Energy (SFE), individually and as a system. The binders/blends-aggregate systems were further tested by means of the Pneumatic Adhesion Tensile Test Instrument (PATTI) to determine their pull-off tensile strength (POTS). The results show that the bio-rejuvenated asphalt binders present equivalent cohesive and adhesive properties to a conventional bitumen and superior performance when compared to the RA binder. Hence, the combination of biobinders and RA has great potential to guarantee resistance to moisture damage of bio-recycled asphalt mixtures with high-content RA and no additional bitumen.

Three innovative environmentally friendly pavement materials, designed with 50% of Reclaimed Asphalt and three different biomaterials (2 bio-additivated bitumens and 1 bio-binder), were produced in an industrial plant. These mixes were tested in lab and also at full scale using an Accelerated Pavement Test facility. The asphalt mix viscoelastic properties were measured in lab and their intrinsic viscoelastic response were simulated. These rheological models are used to simulate the pavement mechanical response using both elastic and viscoelastic multilayer codes. Hence, full scale measurement performed during the full scale test at an early stage (without damages) can be compared with these simulations. The overall prediction accuracy, when all the signals are considered, is between 4% and 8% for all materials. It can be concluded that material characterisation in lab as well as the selected models are well adapted to simulate actual loading state under a moving load, even for these non-conventional mixes. For temperatures lower than 25°C, elastic modelling appears to be sufficient for pavement structural design with the innovative materials tested here.

The use of high Reclaimed Asphalt (RA) content mixtures together with binders produced from renewable resources (biobinders) is one of the current challenges in pavement engineering research. On the one hand, RA has been used for decades, but there are still some concerns about its performance, especially when high contents are used (>30%). On the other hand, biobinders are relatively new materials, which have to be deeply characterised and studied in order to develop good practices for their use. In this paper, linear viscoelastic properties of biobinders and bio-mixtures manufactured with high RA content and biobinders are analysed and discussed. High-modulus mixtures with 50% RA were selected for the mix design. Binders and mixtures were tested over a wide range of asphalt service temperatures and frequencies by means of Dynamic Shear Rheometer and two-point bending tests, respectively. Results show that biobinders have an important effect on mixtures behaviour. However, no direct links between their linear viscoelastic properties were found. Bio-asphalt mixtures still need further development for commercial exploitation; however, the take-away fact of this investigation is that it is possible to manufacture asphalt-like mixtures with acceptable viscoelastic properties while being composed only of RA and non-petroleum-based binders.

This paper investigates the effect of processing temperature and time on the rheological properties of recycled tyre rubber-modified bitumens (RTR-MBs) produced using two different base binders and an ambient ground crumb rubber modifier (CRM). The production of the RTR-MBs was accomplished by means of a standard Brookfield rotational viscometer together with a modified impeller, dual helical impeller, to allow mixing as well as real-time viscosity measurements of the produced RTR-MBs. The rheological properties of the final RTR-MBs were determined by means of standard dynamic mechanical analysis oscillatory and multiple stress creep recovery testing using a dynamic shear rheometer. The results indicate that the low processing conditions (160°C and 60 min) are not appropriate for developing RTR-MBs with enhanced physical and rheological properties. However, allowing the crumb rubber to interact with the base binder for longer mixing times (140 min) led to the development of an enhanced rubber (polymer) network structure within the blend (i.e. swelling of the CRM particles) and superior rheological properties. At the other extreme, using high-processing conditions (200°C and 140 min) led to RTR-MBs in which the rubber network had been subjected to devulcanisation and depolymerisation with a subsequent reduction in modification.

Rubberised bitumen obtained through a swelling process, has widely proved to be a successful technology for asphalt pavement applications and a solution to reduce the dismantling of tyre rubber on landfills. However, this technology presents two main operative issues which need the adoption of costly special equipment. First, significant high value of high-temperature viscosity (HTV), which imposes mixing and compaction difficulties, leads to increased energy consumption and emissions. Furthermore, during the hot storage period, phase separation between rubber particles and the base bitumen could occur. Developing recycled tyre rubber-modified bitumen (RTR-MB) with improved storage stability and reduced values of HTV could allow using this technology in standard asphalt plants, resulting in an environmental-friendly and cost-effective option of standard polymer-modified bitumen. In this study, two different pre-treated and one straight ambient recycled rubbers were used to produce RTR-MB. The first RTR was pre-treated by special oil and warm-mix additives and the second was partly de-vulcanised. Also, two base binders were selected with large differences in mechanical properties in order to identify the effect of base binder. The HTV was successfully reduced by using pre-treated RTR. The use of RTR together with Fischer–Tropsch wax (Sasobit®) in bitumen technology offered superior high in-service temperature properties and reduced value of HTV, and thus can be the preferred option over styrene–butadiene–styrene modification.

Tyre rubber-modified binders (TR-MBs), produced through McDonald's wet process and used worldwide (e.g. asphalt rubber), have been demonstrated to provide various benefits to pavements and, moreover, they represent a good opportunity for recycling tyre rubber (TR). However, this technology is still struggling to be fully adopted in Europe, mainly because of their poor stability during high temperatures storage, which leads to high initial costs in modifying existing asphalt plants. Storage stable TR-MBs are proving to be a great option and their development could be the key to spread the recycling of TR within paving applications in Europe. This paper aims to enrich this field of research by presenting the results of a study focused on the optimisation of laboratory procedures to better understand the effect of varying processing conditions on the rheology of TR-MBs. The experimental programme has been carried out by a preliminary selection of materials, followed by the production of the TR-MBs, via practical laboratory protocols. A continuous comparison between two commercially used styrene–butadiene–styrene (SBS)-MBs, with high and medium levels of modification, and the produced TR-MBs helped to understand the effect of varying the selected processing conditions on binder properties. Results have shown that TR-MBs are a very effective alternative to commercially used SBS-MB. Nevertheless, the rheology of TR-MBs is very sensitive to the variation of the processing conditions, so appropriate selection of materials and a superior binder design are mandatory to achieve the desired level of modification.

In this paper mixing of reclaimed material with virgin asphalt material has been studied non-destructively. Specimens prepared with virgin asphalt mix and with asphalt mix containing reclaimed material were scanned in X-ray Computed tomography (CT). The obtained Images were analysed for particles and pores (air voids) distribution. All the specimens were also tested in compression test and X-ray scanned while testing. It was found that distribution of reclaimed is not uniform through the samples. There is no considerable effect of increasing the mixing time on particles’ distribution. Similar trend of increase in air voids (cracks) with the increase in load was found for both virgin mix and for asphalt mix containing reclaimed material. Only at failure the increase in voids was found higher for specimens containing reclaimed material.

No-agitation Tyre Rubber Modified Bitumens (TR-MBs), also known as “terminal blends” or “field-blends”, are quite new technologies leading to bituminous binders similar to polymer modified bitumens in terms of both rheology and needed efforts during paving operations. Their manufacturing, as well as other TR-MBs, is strongly dependent on the selected processing variables as well as on the chosen materials. This study presents a literature review to provide an overview of the TR-MB technologies which focuses on the influence of processing conditions on the modification process, storage stability and overall properties of the final bitumen - tyre rubber blends.