Numerical study of sorption of asphalt binders on minerals

During the production of asphalt mixes, specific functional groups of asphalt binder interact chemically with certain reactive sites on the surface of minerals forming compounds that enhance the material resistance to environmental effects. The thermodynamics of surface phenomena between various combinations of functional groups of minerals and asphalt binders has been studied for quite a long time but it remains extremely difficult to control the desired material properties in practice. In this study, the chemical thermodynamics that determine the sorption phenomena and subsequently the relative affinity of asphalt binders onto mineral particles were analysed numerically and discussed. A two-step sorption configuration is studied in a multi-physics tool including reaction-driven mass transport of free species (i.e., carboxylic acid diluted in binder) onto a reactive surface (i.e., calcium functionalized mineral). Based on this configuration, the mechanism of asphalt-mineral interaction was determined at different surface temperatures and reactivity characteristics (i.e., activation energy and reaction kinetics of adsorption). The sorption model is applicable for various scenarios of asphalt-mineral interactions, especially for functionalized surfaces, in which the reaction-driven distribution of concentrations of asphalt adsorbates on minerals can provide useful information once the energetic parameters are known.Pavement Engineerin

Durability of European Asphalt Mixtures Containing Reclaimed Asphalt and Warm-Mix Additives

This paper investigates the moisture susceptibility of European asphalt mixtures (SMA) containing reclaimed asphalt (RA) and warm mix (WMA) additives. Test sections of a typical SMA mixture have been laid, from which cylindrical samples were cored and utilized for laboratory testing. Four variants of the SMA mixture were prepared; a control HMA mixture with 0% RA, a mixture with 30% RA and no WMA additive, a mixture with 30% RA in which a WMA additive was added and a mixture with 40% RA and a WMA additive. The coring procedure and testing were carried out in two phases; first field cores were taken 24 hrs after the construction of the test section was completed and then once again 12 months later. In this way, the influence of field aging on the mechanical performance of the mixtures was considered. The samples were moisture conditioned at various combinations of water bath immersion and cyclic pore pressures by means of the Moisture Induced Sensitivity Tester (MiST). The degradation in strength due to moisture was quantified through indirect tensile strength tests. The results indicated that the use of RA in combination with WMA additives resulted to mixtures with improved durability characteristics, with respect to moisture damage, compared to the control HMA mixture. Based on the results, recommendations were made for characterizing and limiting moisture damage of asphalt pavements

Modelling of membrane bonding response: Part 1 development of an adhesive contact interface element

The adhesive bonding strength of the membrane layers between the asphalt concrete surface layers and the decks of steel bridges has a strong influence on the fatigue life of orthotropic steel deck bridges (OSDBs). The most important requirement for the application of membrane materials to orthotropic steel deck bridges is that the membrane adhesive layer is able to sufficiently bond to its surrounding material layers. The interfacial properties between the membrane and the layers bonded to it have not been extensively studied in the current orthotropic steel deck bridge system. In this paper, details of the contact interface element utilised to model the interfacial bonding properties will be discussed. Furthermore, the traction-separation material law will be chosen to describe the bonding response of the interfacial properties of the membrane to its surrounding surfacing layers on OSDBs. Some numerical examples, in which various aspects of the finite elements response of the contact interface model will be presented. Utilisation of the model in finite element analyses has enabled the investigation of the response of a 3D orthotropic steel deck bridge subjected to the different traffic loading conditions.</p

Framework for replacing steel with aluminum fibers in bituminous mixes

This research explores the incentives for replacing steel fibers with aluminum fibers in fiber modified bituminous mixes. In this work the focus is on fiber modified bituminous mixes especially designed for induction heating. Inductive fibers are heated up because eddy currents are generated - according to Joule’s law - when alternating magnetic field is applied by electro-magnetic induction coil. Aluminum fiber-type particles are proposed as an alternative solution for developing corrosion resistant and lightweight bituminous mixes capable to be induced by electro-magnetic fields. In another publication (Pavlatos et al., Inductive bituminous mortar with steel and aluminum fibers, Advances in Materials and Pavement Performance Prediction, Submitted, 2018), a finite element three-dimensional model is developed in order to determine the effective electrical conductivity of steel and aluminum fiber modified bituminous mortar, as well as to show the potential utilization of alternative particles for developing multi-functional paving materials with improved properties

Durability of European Asphalt Mixtures Containing Reclaimed Asphalt and Warm-Mix Additives

This paper investigates the moisture susceptibility of European asphalt mixtures (SMA) containing reclaimed asphalt (RA) and warm mix (WMA) additives. Test sections of a typical SMA mixture have been laid, from which cylindrical samples were cored and utilized for laboratory testing. Four variants of the SMA mixture were prepared; a control HMA mixture with 0% RA, a mixture with 30% RA and no WMA additive, a mixture with 30% RA in which a WMA additive was added and a mixture with 40% RA and a WMA additive. The coring procedure and testing were carried out in two phases; first field cores were taken 24 hrs after the construction of the test section was completed and then once again 12 months later. In this way, the influence of field aging on the mechanical performance of the mixtures was considered. The samples were moisture conditioned at various combinations of water bath immersion and cyclic pore pressures by means of the Moisture Induced Sensitivity Tester (MiST). The degradation in strength due to moisture was quantified through indirect tensile strength tests. The results indicated that the use of RA in combination with WMA additives resulted to mixtures with improved durability characteristics, with respect to moisture damage, compared to the control HMA mixture. Based on the results, recommendations were made for characterizing and limiting moisture damage of asphalt pavements.harvestPavement Engineerin

The influence of boundary conditions on the healing of bitumen

Damage in pavements is known to reduce over time when the material is left to rest, this phenomenon is identified as healing. It has been shown that healing has a large influence on pavement performance. However, as the healing mechanism is not fully understood, there is currently no accepted method available to assess the healing performance of an asphalt binder. Healing of cracks can be seen as the sum of two processes, cracked surfaces coming into contact (wetting) and strength gain of the contact area (intrinsic healing). This paper aims to increase the understanding of the process of two surfaces coming into contact. Healing of bitumen is assessed using a novel test method, which allows for controlled variation of the stress state during healing. This method consists of bringing two pieces of bitumen together and allowing them to heal under controlled conditions. The extent of healing is then assessed by testing the healed specimens in direct tension. The results, presented in this paper, show that the stress state at assembly and during healing has a significant impact on the extent of healing.Pavement Engineerin

Direct Tensile Test to Assess Healing in Asphalt

Asphalt concrete has the advantageous ability to heal. During restperiods, damage present In the material is restored to a certain extent.Healing of the material can be observed in iis regaining of strengthand stiffness after rest periods. In this paper, a new test method is presented.It was developed to increase the understanding of the healingphenomenon. The test method focused on asphalt as it v/ss assumed tobe the driver of the healing performance. The test method assessedthe heaUng performance of asphalt In stiffness and strength by testingthe bond strength In tensile mode of two pieces of asphalt that wereassembled under controlled temperature and stress conditions. Withthe test method, healing tests ^yere performed on one type of binder;the load level during healing and the healing tune were varied. The tesiresults showed that after a short healing time of only 6 min, a significantamount of healing could be detected. That finding indicates the importanceof adhesion between two crack surfaces v/hen the healing capacityis assessed. It v/as also found that the maximum tensile stress reached aplateau value after 24 h of healing; the finding indicates thatfull healingcan be realized in short time periods for pure, unaged, soft binders. Itv/as also shov/n that the load level perpendicular to the damage duringheaUng had a significant effect on the observed healing.Pavement Engineerin

Mechanisms in Healing of Bitumen and the Impact of Normal Force

Damage in pavements is known to reduce over time when the material is left to rest, this phenomenon is known as healing. It has been shown that healing is an important influence factor in pavement performance. However, an accepted method to assess the healing capability of a pavement is currently not available. Healing of cracks is assumed to be the sum of two processes, cracked surfaces coming into contact (wetting) and strength gain of surfaces in contact (intrinsic healing). The paper describes influencing parameters of these two processes. The healing potential of bitumen is assessed using a novel test method. In this method two pieces of bitumen are brought together and left to heal under controlled condi-tions. After healing the amount of healing is assessed by testing the specimens us-ing a direct tensile test. From the results it can be seen that normal force has a sig-nificant impact on the observed healing, indicating that the process of two surfaces coming into contact (wetting) has a significant impact on healing behavior of the bitumen.Pavement Engineerin

Framework for replacing steel with aluminum fibers in bituminous mixes

This research explores the incentives for replacing steel fibers with aluminum fibers in fiber modified bituminous mixes. In this work the focus is on fiber modified bituminous mixes especially designed for induction heating. Inductive fibers are heated up because eddy currents are generated - according to Joule’s law - when alternating magnetic field is applied by electro-magnetic induction coil. Aluminum fiber-type particles are proposed as an alternative solution for developing corrosion resistant and lightweight bituminous mixes capable to be induced by electro-magnetic fields. In another publication (Pavlatos et al., Inductive bituminous mortar with steel and aluminum fibers, Advances in Materials and Pavement Performance Prediction, Submitted, 2018), a finite element three-dimensional model is developed in order to determine the effective electrical conductivity of steel and aluminum fiber modified bituminous mortar, as well as to show the potential utilization of alternative particles for developing multi-functional paving materials with improved properties.Pavement Engineerin

Study of Asphalt Binders Fatigue with a New Dynamic Shear Rheometer Geometry

With the effort to predict precisely the lifetime of asphalt binders and subsequently optimize their utilization in a more economical way, the objective of this study was to introduce a new methodology to improve the fatigue characterization of asphalt binders through a new dynamic shear rheometer (DSR) sample testing geometry. Initially, numerical analyses were performed to study the geometry-related issues of standard DSR sample on time sweep tests and assisted on the effort to increase the understanding of DSR damage phenomena of asphalt samples. On the basis of these numerical analyses, a new testing geometry, the parallel hollow plate, was developed and its test results compared with the standard sample testing geometry. A single type of asphalt binder was assessed using amplitude sweep tests. The obtained results demonstrated a significant difference between the fatigue of the two sets of DSR sample geometries. On the basis of these, time sweep tests were conducted for the same sample geometries and the results demonstrated that the new testing geometry yields material response consistency under different loading conditions. The lifetime prediction of the standard parallel plates showed a significant difference with the newly developed DSR sample testing geometry by overestimating the total number of cycles until asphalt binder failure. The new testing geometry allowed the insolation of the damage area of asphalt binder by localizing the shear stresses in the samples’ periphery