0000000000010988
AUTHOR
Gordon Airey
Effect of ageing on the morphology and creep and recovery of polymer-modified bitumens
Polymer additives are used to improve the properties of road bitumens including their oxidative resistance. However, their usage as anti-oxidative materials remains relatively unclear. This study aims to investigate the changes in the morphology and the rheological response of polymer modified bitumens used in road pavement construction caused by ageing. An elastomer (radial styrene butadiene styrene, SBS) and a plastomer (ethyl vinyl acetate, EVA) polymer were mixed with one base bitumen at three polymer concentrations. The bitumens were RTFO and PAV aged. The morphology of the bitumens was captured by fluorescence microscopy while the rheological properties were measured by means of the m…
Toward more realistic viscosity measurements of tyre rubber–bitumen blends
AbstractThe 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…
Rubberised bitumen manufacturing assisted by rheological measurements
This paper investigates the effect of processing temperature and time on the rheological proper- ties 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 …
New simplified approach for obtaining a reliable plateau value in fatigue analysis of bituminous materials
The Plateau Value (PV) based on the Ratio of Dissipated Energy Change (RDEC) approach has been proven to provide a unique relationship with the fatigue life, N-f, independent of loading mode, temperature and frequency. In this paper, a new simplified approach is proposed to compute the unique energy parameter PV. The results of this study show that applying the proposed method allows a unique fatigue power law to be produced and eliminates the ambiguity and variability in calculating PV. However, the study also shows that the PV-N-f fatigue curves for bituminous materials are dependent on material type which is contradictory to other studies dealing with PV. The study also highlights the im…
Thermo-rheological analysis of WMA-additive modified binders
AbstractThermo-rheological characteristics of unmodified and modified bitumen have significant impacts on the mechanical response of asphalt. This study investigates the impacts of an organic and a chemical Warm Mix Asphalt additive on bitumen thermo-rheological and mechanical characteristics. Modified binders with different concentrations of each additive were studied and analysed comparatively to a 40/60 penetration grade bitumen. Frequency sweep tests were performed at different ageing levels to characterise the Linear Viscoelastic properties. The multiple stress creep and recovery, linear amplitude sweep (LAS) and low temperature creep stiffness tests, together with the Glover–Rowe (G–R…
An investigation of the mechanical properties of rubber modified asphalt mixtures using a modified dry process
Incorporating recycling tyres into asphalt mixtures contributes to solving a serious environmental problem as well as the potential of improving the mechanical performance of asphalt mixtures. The recycled tyre rubber is added by two technologies known as the dry process (when rubber particles are treated as an aggregate modifier) and the wet process (when rubber particles are treated as a binder modifier). Although, the dry process is easier and requires minimal or no modification in the asphalt plant, the inconsistency in field performance makes the dry process not widely used. The main reason for this is believed to be the lack of interaction between the rubber particles and binder. In o…
Data Compression Approach for Long-Term Monitoring of Pavement Structures
Pavement structures are designed to withstand continuous damage during their design life. Damage starts as soon as the pavement is open to traffic and increases with time. If maintenance activities are not considered in the initial design or considered but not applied during the service life, damage will grow to a point where rehabilitation may be the only and most expensive option left. In order to monitor the evolution of damage and its severity in pavement structures, a novel data compression approach based on cumulative measurements from a piezoelectric sensor is presented in this paper. Specifically, the piezoelectric sensor uses a thin film of polyvinylidene fluoride to sense the ener…
Intrinsic adhesive and cohesive assessment of the moisture sensitivity of bio-rejuvenated recycled asphalt 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 certai…
An investigation on using pre-treated tyre rubber as a replacement of synthetic polymers for bitumen modification
Rubberized bitumen obtained through a swelling process, has widely proven 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 needs the adoption of costly special equipment. Firstly, significant high value of High Temperature Viscosity (HTV) which imposes mixing and compaction difficulties and 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-MBs) with improved storage st…
Fatigue resistance: is it possible having a unique response?
The mechanical characterisation of the asphalt concrete in terms of both the fatigue resistance and the stiffness modulus is necessary to use any design method of the flexible road pavements. Different kinds of test are usually used in experimental work such as bending tests, uniaxial tests, etc., but sometimes they do not give the same answer. In this paper mechanical characterization was carried out by means of fatigue tests undertaken with two most used testing machines for asphalt material: two point bending (2PB) test at IFSTTAR in Nantes (France) and four point bending (4PB) test at University of Palermo, in Palermo (Italy). Different strain controlled tests were undertaken for the sa…
Evaluation of the fracture performance of different rubberised bitumens based on the essential work of fracture
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.…
Tyre rubber-modified bitumens development: the effect of varying processing conditions
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 b…
Experimental Investigation on Water Loss and Stiffness of CBTM Using Different RA Sources
Cold recycling of reclaimed asphalt (RA) is a promising technique to build or to maintain roads, combining performance and environmental advantages. Although this technique has been extensively used worldwide, there is no unique and internationally-shared method to characterize cold recycled mixtures. The previous work of the RILEM TC 237-SIB TG6 successfully attempted to characterize different RA sources with both traditional parameters (gradation, bitumen content and geometrical properties) and non-conventional properties (fragmentation and strength testing). The current RILEM TC 264-RAP TG1 mainly focuses on the influence of different RA sources on physical and mechanical characteristics…
Rutting analysis of different rubberised stone mastic asphalt mixtures: from binders to mixtures
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 (R…
Rheological characterisation of cold bitumen emulsion slurries
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 emulsion…
Mechanical characterization of dry asphalt rubber concrete for base layers by means of the four bending points tests
The mechanical characterisation of the asphalt concrete in terms of both the fatigue resistance and the stiffness modulus is necessary to use any design method of the flexible road pavements. Even more the determination of these mechanical properties is necessary if the asphalt concrete investigated is an innovative material as a dry asphalt rubber concrete DARC (i.e. a bituminous mixture with rubber via dry process). Such material is less known and investigated than the asphalt rubber concrete via wet process, even if its application implies peculiar economical and environmental advantages such as no specialized equipment or significant plant modifications and large quantity of recycled wa…
Linear viscoelastic properties of high reclaimed asphalt content mixes with biobinders
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…
Laboratory mix design of asphalt mixture containing reclaimed material
This paper presents a study on the production of asphalt test specimens in the laboratory containing reclaimed asphalt. The mixtures considered were stone mastic asphalt concrete mixtures containing up to 30% of reclaimed asphalt. Specimens were compacted to the reference density obtained from the Marshall mix design. Gyration compaction method was used for preparing specimens for the experimental programme, while coring and cutting methods and X-ray computed tomography (CT) were used to investigate the change in properties within the specimens and to validate the selected methodology. The study concluded that gyratory compaction is suitable to produce homogeneous test specimens also for mi…
Monitoring road pavement performance through a novel data processing approach, accelerated pavement test results
This research presents a novel performance-based interpretation method for continuous monitoring of pavement condition through the use of piezoelectric sensors. The objective of this study is to validate the compressed cumulative loading event approach, implemented in a previously developed piezoelectric sensor, for detecting subsurface fatigue cracking through full-scale accelerated pavement testing. A piezo-electric film of polyvinylidene fluoride is used to harvest the microstrain energy induced by the traffic loading at the surface. Epoxy is used to protect the sensor following a H-shape packaging. Piezoelectric sensors were exposed to approximately 1.0 million load repetitions between …
Towards 100 % recycling of reclaimed asphalt in road surface courses: binder design methodology and case studies
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 (10e30%). In fact, despite the advan- tages 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 a…
Microstructure and rheological response of laboratory-aged SBS-modified bitumens
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 Permeati…
The effects of laboratory ageing on rheological and fracture characteristics of different rubberised bitumens
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…
Binder design of high RAP content hot and warm asphalt mixture wearing courses
Reclaimed Asphalt Pavement (RAP) has shown great potential for being used in the construction or maintenance of roads. However, RAP is usually downgraded to lower pavement layers and the percentage of RAP used in wearing courses is still moderate (≤30%). The research and results contained in this paper focus on the definition of binder recipes aimed at increasing the percentage of RAP in hot and warm mix asphalt wearing courses. A review of current internationally used blend design methodologies is presented followed by case studies aimed at defining binder recipes for high RAP content asphalt mixture wearing courses to be further used for mix design and production in asphalt plants. Binder…
Binder and Mixture Fatigue Performance of Plant-Produced Road Surface Course Asphalt Mixtures with High Contents of Reclaimed Asphalt
The aged properties of Reclaimed Asphalt (RA) binders are one of the main factors working against their utilisation in high-RA content (>
Uncertainty analysis of life cycle assessment of asphalt surfacings
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,…
Linear and nonlinear fractional hereditary constitutive laws of asphalt mixtures
The aim of this paper is to propose a fractional viscoelastic and viscoplastic model of asphalt mixtures using experimental data of several tests such as creep and creep recovery performed at different temperatures and at different stress levels. From a best fitting procedure it is shown that both the creep one and recovery curve follow a power law model. It is shown that the suitable model for asphalt mixtures is a dashpot and a fractional element arranged in series. The proposed model is also available outside of the linear domain but in this case the parameters of the model depend on the stress level.
A practical approach to estimate the degree of binder activity of reclaimed asphalt materials
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 g…
Reclaimed asphalt test specimen preparation assisted by image analysis
This paper presents a laboratory investigation aimed at establishing a protocol for the production of homogeneous asphalt mixtures test specimens, incorporating reclaimed asphalt by using a gyratory compactor with coring and trimming works. Stone mastic asphalt specimens were compacted at the previously identified target densities with the final aim of obtaining specimens with a fixed and homogeneous air void distribution. A microstructural study was conducted to characterize the homogeneity in the air void distribution using X-ray computed tomography (CT) combined with image analysis techniques. The study concluded that the gyratory compactor is suitable for producing homogeneous test spec…
Fundamental characterisation of reclaimed asphalts: The importance of testing homogeneous specimens
This study highlights the importance of defining appropriate specimen manufacturing procedures when assessing the fundamental properties of reclaimed asphalt (RA) mixes for further modelling purposes. Two gyratory compactor procedures were used: the first leading to specimens with a non-uniform air voids distribution and the second tailored to obtain homogeneous specimens. The study was performed by using three stone mastic asphalts incorporating up to 30% of RA but designed to have identical properties. A detailed characterisation of the loose mixes and binders, an X-ray computer tomography micro-structural study of the manufactured specimens and a further mechanical characterisation showe…
Rubberised stone mastic asphalt mixtures: a performance-related evaluation
The 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 …