| 1. |
- Ghafoori Roozbahany, Ehsan, 1982-, et al.
(author)
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Modelling the flow of asphalt under simulated compaction using discrete element
- 2019
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In: Construction and Building Materials. - : Elsevier Ltd. - 0950-0618 .- 1879-0526. ; 227
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Journal article (peer-reviewed)abstract
- The flow differences between the particles of asphalt mixtures compacted in the laboratory and in the field have been identified as one of the reasons for the discrepancies between laboratory and field results. In previous studies, the authors developed a simplified test method, the so-called compaction flow test (CFT), for roughly simulating the flow of particles in asphalt mixtures under compacting loads in laboratory. The CFT was used in different studies to examine its capability of revealing the differences between the flow behavior of different asphalt mixtures under various loading modes. The promising results encouraged further development of the CFT by investigating the possible impacts of simplifications and boundary conditions on the results of this test. For this reason, discrete element method (DEM) was utilized to investigate possible impacts of the mold size, geometry of the loading strip as well as the loading rate on the results of the CFT. The results of the simulation indicate that in case of wearing course layers with nominal maximum aggregate size of 11 mm, the length of the CFT mold can be increased from 150 mm to 200–250 mm for reducing flow disturbances from the mold walls. However, since the majority of the flow of asphalt mixture particles is expected to take place within the first 100–150 mm length of the mold, reasonable results can still be obtained even without changing the size of the CFT mold. Moreover, comparing results with different loading strip geometries and loading rates indicates that the current CFT setup still appears to provide consistent results.
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| 2. |
- Jelagin, Denis, et al.
(author)
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Experimental and numerical modelling of shear bonding between asphalt layers
- 2023
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In: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 24:S1, s. 176-191
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Journal article (peer-reviewed)abstract
- Interlayers in asphalt pavements are potential structural damage initiators. In order to better understand the quantitative role of interlayer parameters, such as surface roughness, binder type, binder content and loading type on interlayer shear strength, this paper focuses on the effects of particle interlock and contact conditions on interlayer strength through experimental and numerical modelling. Experimentally, interlayer shear box strength tests on a model material consisting of stiff binder blended with steel balls are performed with and without normal force confinement. A Discrete Element method model of the test is developed using measurements of the model material for calibrating the contact law and for validating the model. It is shown that this model captures adequately the measured force-displacement response of the specimens. It is thus a feasible starting point for numerically and experimentally studying the role of binder and tack coat regarding interlayer shear strength of real asphalt layers.
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| 3. |
- Olsson, Erik, 1986-, et al.
(author)
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A numerical framework for modelling settlements of railway ballast layers
- 2024
-
In: Transportation Geotechnics. - : Elsevier. - 2214-3912. ; 44
-
Journal article (peer-reviewed)abstract
- Permanent deformation in ballast layers is a major contributing factor to the railway track geometry deterioration. In spite of a considerable amount of research on understanding and predicting performance of ballast layers, accurately capturing their settlements remains a challenge. In order to contribute to solving this important issue, a new numerical method for predicting ballast settlements is presented in this paper. This method is based on the finite element (FE) method combined with a constitutive model that captures permanent deformation accumulation in unbound materials under cyclic loading. This allows predicting permanent deformations of large structures and at large number of load cycles in a computationally efficient manner.The developed constitutive model is validated based on triaxial test measurements over wide range of loading conditions. Stress state in ballast layers has been examined with a 3D FE model, for several embankment structures and traffic load magnitudes. The determined stress distributions and loading frequencies were used as an input of the constitutive model to evaluate permanent strains and settlements of ballast layer. The influence of embankment structural designs and traffic loading magnitudes on the ballast layers settlements is examined and the results obtained are compared with the existing empirical performance models.
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| 4. |
- Saliko, Denis
(author)
-
Validation of heavy vehicle loading responses and temperature predictions in flexible pavements using field data
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- It is well established that both traffic-related loading and environmental conditions influence the structural behaviour of pavements. Pavement design methods aim to consider the effect of traffic loading and environmental variables on pavement structure, foresee their changes during the lifetime of the pavement and predict the resulting distresses and pavement life. Newer models are required to further advance the development of pavement design methods. Validations using reliable and representative data are required prior to incorporating these models in pavement design methods.The impact of environmental factors such as temperature, moisture content and freeze-thaw cycles on pavement behaviour have been examined in this doctoral thesis. Furthermore, the impact of increased loading by new long heavy vehicles on low-volume roads subjected to large variations of the environmental conditions has been investigated. The findings presented in this thesis have been based on field data collected on roads that have been and currently are in day-to-day operation. The collected data on mechanical response, temperature, moisture and frost was used to validate models on mechanical behaviour and thermal behaviour, as well as the effect of their interaction in pavement structures. The models developed and validated in this study are aimed to be integrated into a new mechanistic-empirical pavement design framework that is currently under development in Sweden. The work done for this thesis is presented hereby in the form of 5 papers and a short summary part. This thesis is a continuation of a licentiate thesis previously published at KTH Royal Institute of Technology. Part of the material published in the licentiate thesis has been included in this doctoral thesis.In paper 1, air temperature data recorded over a span of 10 years from 44 meteorological stations and temperature data from built-in sensors in 49 pavement structures located in different locations throughout Sweden were analysed. The data was used to statistically correlate the freezing index, calculated using the mean daily air temperature and the frost penetration depth in the cross-section of the pavement. Comparisons were made for the results obtained for various climatic zones in the country. The output of the paper is a country-specific empirical chart obtained through exponential interpolation and nonlinear prediction limits that indicates a range of expected frost penetration depth based on historical air temperature data. Paper 2 presents a study in which the structural response of a test section was evaluated using built-in sensors. The instrumentation consisted of asphalt strain gauges (ASG) recording the tensile strain in the bottom of the asphalt layer, strain measuring units (εMU) recording the vertical strain in the granular layers, and soil pressure cells (SPC) recording the vertical stresses in the granular layers. Falling weight deflectometer (FWD) measurements were performed on the structure to backcalculate the stiffness of the layers from the measured surface deflections. The aim of the study was to evaluate the structural response of the structure under loading by three long heavy vehicles (LHV) weighing ~64 tonnes, ~68 tonnes, and ~74 tonnes and compare the resulting estimated accumulated damage from each vehicle. The main finding from the paper was that the damage caused to pavements by long heavy vehicles was slightly larger than the damage caused by shorter vehicles with fewer axles but higher axial loading and tyre pressure.Paper 3 focuses on the effect of environmental factors and their variation on the structural behaviour of a thin pavement structure. Loading by long heavy trucks was applied to a test section at four different measurement campaigns performed at different seasons over one year. The variation of temperature and moisture in the structure was monitored continuously for the entire duration for which the study was performed. Thermocouples embedded in the asphalt layer and a frost rod placed in the granular layers were used to monitor the temperature variation in the structure. The moisture variation was monitored using time-domain reflectometer (TDR) probes. The correlation of the changes in temperature and moisture to the changes in mechanical stiffness of the layers was investigated. The instrumentation used to monitor the mechanical response, temperature variation, and moisture variation in the structure was found to be reliable for collecting data over the entire duration of the study. The main finding of the study is that it is possible to model the mechanical behaviour of thin pavement structures using multilayer elastic theory (MLET) calculations modelling, using linear-elastic material models if the stiffness of the asphalt layer is adjusted based on temperature and the stiffness of the granular layers is adjusted based on moisture levels.In Paper 4, the same response testing procedure as in Paper 3 was performed for a second pavement structure with a thicker asphalt layer. Data from response testing results for 2 pavement structures on 4 different dates, with a focus on the spring thaw period, were considered in the paper. Three different strategies for material modelling were used to investigate the mechanical response of the pavement structures. The layers were initially modelled using linear material parameters and the response results were compared both to calculations in which a viscoelastic model was used for the asphalt layer and to calculations in which a nonlinear K-Theta model was used for the granular layers. Comparisons were made between the calculated response using each modelling strategy and the measured response values. It was found that the viscoelastic and nonlinear models provided only marginal improvements in the range of 1%-4% in predicting the mechanical response of the structures. Based on the results, it was concluded that the linear elastic model was sufficiently accurate in capturing the mechanical behaviour of both pavement structures, including at the critical locations.Paper 5 presents the development and validation of a one-dimensional finite control volume (FCV) model capable of predicting temperature in pavements. The model is intended to be implemented into a new mechanistic-empirical pavement design framework currently under development in Sweden. The model uses easily obtainable meteorological data for air temperature, solar radiation, and wind speed for the three main modes of heat transfer, namely conduction, convection and radiation. To validate the model and estimate its accuracy, comparisons were made between the measured temperature and the calculated temperature values, using the FCV model. Comparisons were made for the pavement surface temperature, the temperature within the asphalt layer, and the temperature in the granular layers for 4 pavements located in different climatic zones in Sweden. In general, good agreement was found between the measured and calculated temperature values. Points for future improvements include better consideration of the surface properties, including the latent heat transfer in the calculations, and coupling the model to a moisture transfer model.
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| 5. |
- Bekele, Abiy
(author)
-
Evaluation of Low Temperature Damage in Asphalt Mixtures with Non-Contact Resonance Testing
- 2020
-
Doctoral thesis (other academic/artistic)abstract
- Thetemperature induceddamage in asphalt mixtureshas always been a major distress that requires a substantialconsiderationin the asphalt industry. One of the most important aspects of studying temperature induceddamage is developing a practical test method for evaluation of the material’s resistanceto it. Hence, there is a growing interest in developing testing methodologieswhich are more efficient, less expensive and simpler to perform than the conventional test methods. Impact resonance testing is a well-documented non-destructive testing method,and ithas been successfully appliedon asphalt mixturesto measure their elastic and viscoelastic properties. This research aims at extending the impact resonance testing methodology to characterization of temperature induced damage in asphalt mixtures and to investigate experimentally and numerically damage induced in asphalt mixtures due to thermomechanical mismatch between the masticand aggregate phases.In order to improve temperature control and thus accuracy of the resonance testing, an automated non-contact test procedure is developedwith a loudspeakerutilized as a source of excitation.The developed methodology has been evaluatedfor a range of asphalt concrete materialsand temperatures. The measurementsobtained from the new method have been verified by taking similar resonance frequency measurements usinganinstrumented impact hammer. Results from this work show that repeatable fundamental resonance frequency measurements can be performed onadisc shaped specimen in an automated manner without the need to open thethermal chamberthat is used to condition test specimens.Investigationsofmicro-damage in asphalt concrete due to differential thermal contraction during cooling cycles havebeen carried out experimentally by using the developedautomated non-contact resonance testingcombined withcyclic cooling. The results of the experimental work haveshown the initiation of low temperature micro-damage and a hysteretic behavior of stiffness modulus during thethermal cycles. Energy based micro-mechanical model is also utilized in order to characterize themicro-crackinitiation and growthin asphalt concrete due to cyclic low temperature variations.Results of this approach have indicated the initiation of micro-cracksat low temperatures as well as the decrease in their length with increase in temperature. In order to obtain a quantitative insight into the temperature induced damage formation, a micromechanical finite element model (FEM) of asphalt mixtureunder thermal loading is developed. The model is used to investigate the damage evolution during the thermal cycles as well as its effect on material’s stiffness. Four cases ofmastic-aggregate combinations aremodelledin order to investigate effects of aggregate gradation as well as of masticpropertieson the thermal damage evolution. Cohesive Zone Model (CZM) isused to define aggregate-masticinterface so that an initiation of micro-damage due to differential thermal contraction can be probedin terms of its effect on the overall stiffness modulus. It is observed numerically that during the thermal cycles, thermal damage is initiated at the aggregate-mastic interface due to the differential contraction of mastic. It is also shown that the modelling observations are in qualitative agreement with the experimental findings from the resonance testing. Accordingly, the proposed modelling approach is a viable tool for evaluation of theeffect of asphalt mixture design on its resistance to thermally induced damage.
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| 6. |
- Butt, Ali Azhar, 1984-, et al.
(author)
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The Effect of Wax Modification on the Performance of Mastic Asphalt
- 2010
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In: International Journal of Pavement Research and Technology (IJPRT). - No.300, Jhongda Rd., Jhongli City, Taoyuan County 32001, Taiwan : Chinese Society of Pavement Engineering. - 1997-1400. ; 3:2, s. 86-95
-
Journal article (peer-reviewed)abstract
- The scope of this study is to evaluate the mechanical performance of the polymer modified mastic asphalt with 4% montan wax (Asphaltan A) additive. The impact of wax modification on binder, binder/filler mixtures and mastic asphalt was investigated in the laboratory. Wax modified binder properties were determined using dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR) spectroscopy and conventional tests (softening point, penetration, elastic recovery, breaking point, viscosity and storage stability). The bending beam rheometer (BBR) was used for determining low temperature creep compliance and the tensile stress restrained specimen test (TSRST) for determining low temperature fracture. The fatigue cracking behavior of mastic asphalt was investigated using Superpave Indirect Tensile Test (IDT). Based on HMA Fracture Mechanics the influence of wax on the asphalt mixture resistance to fatigue and brittle cracking has been evaluated. The addition of wax to the polymer modified binder resulted in a viscosity reduction at higher temperatures, indicating a possible lower production and laying temperature as compared to asphalt without wax additive. DMA and BBR results showed some increase in stiffness and a more elastic response of the wax modified binder at medium and low temperatures. The TSRST fracture temperature was higher for the mastic asphalt containing wax, indicating a certain negative impact of wax modification.
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| 7. |
- Butt, Ali Azhar, 1984-, et al.
(author)
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Using Life Cycle Assessment to Optimize Pavement Crack-Mitigation
- 2012
-
In: Scarpas et al. (Eds.), 7th RILEM International Conference on Cracking in Pavements<em></em>. - Delft, The Netherlands : Springer Netherlands. ; , s. 299-306
-
Conference paper (peer-reviewed)abstract
- Cracking is very common in areas having large variations in the daily temperatures and can cause large discomfort to the users. To improve the binder properties against cracking and rutting, researchers have studied for many years the behaviour of different binder additives such as polymers. It is quite complex, however, to decide on the benefits of a more expensive solution without looking at the long term performance. Life cycle assessment (LCA) studies can help to develop this long term perspective, linking performance to minimizing the overall energy consumption, use of resources and emissions. To demonstrate this, LCA of an unmodified and polymer modified asphalt pavement using a newly developed open LCA framework has been performed. It is shown how polymer modification for improved performance affects the energy consumption and emissions during the life cycle of a road. Furthermore, it is concluded that better understanding of the binder would lead to better optimized pavement design, hence reducing the energy consumption and emissions. A limit in terms of energy and emissions for the production of the polymer was also found which could help the polymer producers to improve their manufacturing processes, making them efficient enough to be beneficial from a pavement life cycle point of view.
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| 8. |
- Celma Cervera, Carlos, et al.
(author)
-
Contact-induced deformation and damage of rocks used in pavement materials
- 2017
-
In: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 133, s. 255-265
-
Journal article (peer-reviewed)abstract
- Performance of stone-based construction materials, such as asphalt and unbound aggregate mixtures is defined to a great extent by the mechanics of the stone-to-stone interactions. Accordingly, the Discrete Element Method (DEM) is gaining popularity as a modelling tool to investigate the mechanical behavior of these materials. Contact and failure laws defining particles force-displacement relationships and the propensity of particles to break are crucial inputs for the DEM simulations. The present study aims at providing an experimental contact mechanics basis for the development of physically based stone-to-stone interaction laws. The attention is focused on investigating stone's force-displacement relationship and damage characteristics at pure normal loading for two stone materials used by the road industry. Experiments are performed at spherical contact profiles for cyclic and monotonically increasing loads. The emphasis lies on the evolution of contact compliance and accumulation of contact induced damage. The effect of surface roughness on the materials response is examined through comparative experiments performed on the specimens with different roughness values. Optical and environmental scanning electron microscopy (ESEM) observations of the contact induced damage at the material surface are presented and discussed in the context of contact mechanics. The implications of the reported experimental findings on the development of mechanics based contact and failure laws for the DEM modelling of stone-based construction materials are discussed.
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| 9. |
- Chen, Feng, 1987-, et al.
(author)
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Experimental and numerical analysis of asphalt flow in a slump test
- 2019
-
In: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 20, s. S446-S461
-
Journal article (peer-reviewed)abstract
- The mechanical behaviour of uncompacted asphalt mixtures is still not well understood,threatening directly to the pavement practices such as control of mixture’s workability andsegregation. This situation may become even worse due to the gradually increasing complexityand advances in paving materials and technologies. This study adopts a slump flow testbased on concrete technology and a Discrete Element (DE)-based numerical tool to investigatethe mechanical behaviour of uncompacted asphalt mixture from a microstructural point ofview, particularly focusing on the bituminous binder effects. The combined experimental andnumerical analysis indicates that bitumen distinctly influences the contact interactions withinthe mixture and thus its macroscopic flow, which can be physically interpreted as a combinedeffect of lubricated friction and bonding force. Additional case studies demonstrate that the DEmodel is capable of simulating the flow response of asphalt mixtures under changed particlecontact conditions and driven force.
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| 10. |
- Das, Prabir, et al.
(author)
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Importance of Thermal Contraction Coefficient in Low Temperature Cracking of Asphalt Concrete
- 2016
-
In: Proceedings of the Fifty-Ninth Annual Conference of the Canadian Technical Asphalt Association (CTAA): Winnipeg, Manitoba.
-
Conference paper (peer-reviewed)abstract
- A major distress mode in asphalt pavements is low temperature cracking, which results from the contraction and expansion of the asphalt pavement under extreme temperature changes. The potential for thermal cracking involves interplay between the environment, the road structure, and importantly the properties of the asphalt mixture. In the present study, the low temperature cracking performance of asphalt mixture has been investigated numerically and experimentally. A low temperature cracking model has been utilized, which was developed by integrating fracture energy threshold into an asphalt concrete thermal fracture model considering non-linear thermal contraction coefficients. Based on the asphalt concrete mixture viscoelastic properties, this enhanced model can predict thermally-induced stresses and fracture temperatures. It was observed that the thermal contraction coefficient in asphalt concrete is non-linear in the temperature range of interest for low temperature cracking. The implications of having non-linear thermal contraction coefficient were investigated numerically. From the analysis, it was found that this enhanced model can be utilized to evaluate the low temperature cracking performance of asphalt mixtures and rank them accordingly. Interestingly, non-linear thermal contraction coefficient gave much better prediction than the linear approach.
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| 11. |
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| 12. |
- Das, Prabir Kumar, 1982-, et al.
(author)
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Evaluation of the low temperature cracking performance of asphalt mixtures utilizing HMA fracture mechanics
- 2013
-
In: Construction and Building Materials. - : Elsevier. - 0950-0618 .- 1879-0526. ; 47, s. 594-600
-
Journal article (peer-reviewed)abstract
- In the present study, the low temperature cracking performance of asphalt mixture has been investigated numerically and experimentally. To do so, the HMA thermal fracture model has extended by including fracture energy threshold and non-linear thermal contraction coefficient. This extended model is capable to predict thermally induced stress and fracture temperature, which is validated with experimental results obtained from three different types of asphalt mixtures. From the parametric study, it was observed that understanding the influence of thermal contraction coefficient, the cooling rate and the creep compliance parameters can make a significant contribution to the material's sustainability. From the analysis, it was found that this extended model can be utilized to evaluate the low temperature cracking performance of asphalt mixtures and capable to provide correct ranking. Interestingly, non-linear thermal contraction coefficient gave much better prediction than linear approach.
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| 13. |
- Das, Prabir Kumar, et al.
(author)
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Investigation of the asphalt mixture morphology influence on its ageing susceptibility
- 2015
-
In: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:4, s. 987-1000
-
Journal article (peer-reviewed)abstract
- The main objective of this study is to investigate the influence that asphalt mixture morphology aspects have on its overall ageing behavior. Since mixture morphology is controllable, having insight into how the various morphological parameters influence the mixture’s long-term behavior can be of great value to optimize its design, regardless of the individual material properties. To do so, this study is utilizing a new framework to characterize the combined effect of aggregate packing, average air void size, porosity and level of compaction on ageing for a large set of data from different sources of field compacted and laboratory produced asphalt mixtures. The paper also hypothesizes about the mechanisms that lay behind the found influences and how thus mixture design improvements can be made. From all the investigated cases, it was found that the framework can be used to optimize the durability performance of asphalt mixtures. It was also observed that prediction of ageing behavior without considering the influence of mixture morphology may lead to erroneous conclusions and non-optimal mix design.
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| 14. |
- Das, Prabir Kumar, et al.
(author)
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Micro-Mechanical Investigation of Low Temperature Fatigue Cracking Behaviour of Bitumen
- 2012
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In: 7th RILEM International Conference on Cracking in Pavements. - Dordrecht : Springer Netherlands. - 9789400745650 ; , s. 1281-1290
-
Conference paper (peer-reviewed)abstract
- In an effort to understand the effect of low temperature fatigue cracking, atomic force microscopy (AFM) was used to characterize the morphology of bitumen. In addition, thermal analysis and chemical characterization was done using differential scanning calorimetry (DSC) and thin-layer chromatography/flame ionization detection (TLC/FID), respectively. The AFM topographic and phase contrast image confirmed the existence of bee-shaped microstructure and different phases. The bitumen samples were subjected to both environmental and mechanical loading and after loading, micro-cracks appeared in the interfaces of the bitumen surface, confirming bitumen itself may also crack. It was also found that the presence of wax and wax crystallization plays a vital role in low temperature cracking performance of bitumen.
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| 15. |
- de Frias Lopez, Ricardo, et al.
(author)
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Force transmission and soil fabric of binary granular mixtures
- 2016
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In: Geotechnique. - : ICE Publishing. - 0016-8505 .- 1751-7656. ; 66:7, s. 578-583
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Journal article (peer-reviewed)abstract
- The effect of fines content on force transmission and fabric development of gap-graded mixtures under triaxial compression has been studied using the discrete-element method. Results were used to define load-bearing soil fabrics where the relative contributions of coarse and fine components are explicitly quantified in terms of force transmission. Comparison with previous findings suggests that lower particle size ratios result in higher interaction between components. A potential for instability was detected for underfilled fabrics in agreement with recent findings. It was also found that the threshold fines content provides an accurate macroscopic estimation of the transition between underfilled and overfilled fabrics.
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| 16. |
- Dinegdae, Yared H., et al.
(author)
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Mechanics-based Topdown Fatigue Cracking Initiation Prediction Framework for Asphaltic Pavements
- 2015
-
In: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 16:4
-
Journal article (peer-reviewed)abstract
- In this paper, a new mechanics-based top-down fatigue cracking analysis framework is presented for asphalt pavements. A new mixture morphology-based set of material sub-models is presented for characterising key mixture properties and their change over time. Predicting the load induced top-down fatigue crack initiation (CI) time by utilising comprehensive mixture properties creates the possibility of optimising the mixture morphology while taking into account its subsequent effect on long-term pavement performance. The new framework was calibrated and subsequently validated against a number of field pavement sections with varying traffic levels that are representative for current practices and which have a wide range in material properties. The framework accounts the change in key mixture properties due to ageing and mixture-healing effect on damage accumulation while determining the overall effect of design inputs on cracking performance. Model calibration and validation were achieved based on the healing potential of the asphalt mixture. It was found out that the CI predictions for all the sections are in general agreement with the observed performance in the field, thus giving credibility for the framework.
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| 17. |
- Etikan, M. Kaan, et al.
(author)
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Experimental and numerical analyses of crushing resistance of unbound road materials
- 2024
-
In: The international journal of pavement engineering. - : Taylor & Francis. - 1029-8436 .- 1477-268X. ; 25:1
-
Journal article (peer-reviewed)abstract
- Aggregate breakage in unbound pavement layers can lead to pavement distresses that affect their functionality and service life. Thus understanding the mechanics and clarifying the factors affecting materials breakage resistance are important for ensuring adequate performance of these layers. In this study, aggregate breakage in unbound granular materials (UGM) is investigated experimentally and numerically. Experimentally, aggregate breakage under uniaxial compression is examined for two UGMs prepared with the same aggregate type but different gradations. To capture the experimentally observed influence of gradation and load magnitude on aggregate breakage, a Discrete Element Method (DEM) model was developed, based on granular mechanics particle contact and failure laws. A simple procedure to identify the contact and failure law parameters from experiments is proposed. With those parameters, the model’s capability of capturing the effect of gradation and loading on the aggregate breakage in UGM is evaluated. Based on comparison with experimental findings, it is shown that the model can capture macro-scale properties of UGM, such as its deformation response under uniaxial compression, as well as the amount of aggregate breakage in the material.
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| 18. |
- Fadil, Hassan, et al.
(author)
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A New Viscoelastic Micromechanical Model for Bitumen-Filler Mastic
- 2020
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 253
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Journal article (peer-reviewed)abstract
- A new micromechanical model for predicting viscoelastic properties of mastic is proposed and validated with experiments. The developed model is based on the finite element method and allows predicting the viscoelastic properties of mastic by means of the fundamental mechanical and geometrical properties of its constituents. The influence of modelling parameters on the model’s accuracy is evaluated and optimal parameter combinations are identified. It is shown that the proposed model can capture the measured viscoelastic behaviour of mastics for the range of loading, temperature and material parameters examined. Accordingly, it may be a useful tool for optimizing mastics material design meeting the target viscoelastic properties.
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| 19. |
- Fadil, Hassan, et al.
(author)
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A spherical indentation test for quasi-non-destructive characterisation of asphalt concrete
- 2024
-
In: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873.
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Journal article (peer-reviewed)abstract
- The indentation test is a promising technique for the viscoelastic characterisation of asphalt concrete (AC). Indentation measurements are primarily influenced by the material properties in the direct vicinity of the indenter-specimen contact point. Accordingly, it may become a useful alternative for the characterisation of thin asphalt layers as well as for a quasi-non-destructive AC characterisation in the field. In this study, the spherical indentation test is used to measure the linear viscoelastic properties of AC mixtures extracted from a road test section. The measured complex moduli are compared to those obtained by the shear box test and are found to exhibit a linear correlation. The measurements are further analysed using the Gaussian mixture model to assign each indentation test to either aggregate-dominated or mastic-dominated response. The measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and AC’s binder properties as compared to the average measurements. Accordingly, the proposed test method may provide a promising tool to measure AC viscoelastic properties and monitor the changes in AC binder phase in a non-destructive manner. A finite element micromechanical model is used to identify a representative scale for the response measured in mastic-dominated tests as well as to quantify the effect of measured properties on the AC damage propensity.
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| 20. |
- Fadil, Hassan, et al.
(author)
-
Measurement of the viscoelastic properties of asphalt mortar and its components with indentation tests
- 2019
-
In: International Journal on Road Materials and Pavement Design. - : TAYLOR & FRANCIS LTD. - 1468-0629 .- 2164-7402.
-
Journal article (peer-reviewed)abstract
- Reliable determination of material properties is a key component for modelling and performance prediction of asphalt pavements. This paper deals with the potential use of instrumented indentation tests for viscoelastic characterisation of asphalt mortar as a new alternative to existing techniques. The main focus lies on the potential of indentation tests for multi-scale measurement of the shear relaxation modulus. A three-dimensional finite element model of a rigid spherical indenter penetrating an asphalt mortar sample is developed and used to model indentation tests performed at different material scales. The asphalt mortar is modelled as an idealised fine aggregate composite with elastic spheres, suspended within a viscoelastic bitumen mastic matrix. Based on the obtained numerical results the scale-dependency of the shear relaxation modulus measured with the indentation test is investigated. It is shown that the measurement scale is effectively controlled by the size of the indenter-specimen contact area, while the effect of indentation depth is minimal. The minimum contact area size required for obtaining representative properties, measured at the mortar scale, is determined. The viscoelastic parameters obtained from the indentation model are compared to those obtained using a representative volume element (RVE) for the asphalt mortar. In this way, the paper provides a new impulse for linking the mortar and asphalt scales in the multiscale modelling of asphalt mixtures. Feasibility of the proposed testing technique is further evaluated experimentally. Viscoelastic indentation tests are performed on asphalt mastics and mortar at two different sizes of contact areas. Experimental results indicate that indentation tests allow reliable characterisation of mortars relaxation modulus on both macro-scale as well as on individual component level.
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| 21. |
- Fadil, Hassan, 1990-
(author)
-
New Experimental and Modelling Tools for Multiscale Characterization of Asphalt Mastic
- 2020
-
Licentiate thesis (other academic/artistic)abstract
- Asphalt mastics act as a binding phase in asphalt mixtures and their rheological properties strongly affect the performance of asphalt mixtures with respect to virtually all damage modes. In order to measure mastics properties, relevant for field performance, testing should be performed at size-scales representative for the morphology and material inhomogeneity of asphalt mixtures. This thesis aims to contribute to solving these important issues by developing new experimental and modelling tools for the multi-scale characterization of asphalt mastics.An instrumented indentation test for viscoelastic characterization of asphalt mastics is proposed as a new alternative to existing techniques. A methodology for spherical indentation testing of bituminous materials is developed allowing measuring their viscoelastic properties at arbitrary non-decreasing loading. The potential of indentation tests for multi-scale measurements of viscoelastic properties of binder-aggregate composites is investigated for the special case of asphalt mortar, composed of mastic and aggregates smaller than 2.36 mm. The effect of the test parameters on the measured apparent shear relaxation modulus of asphalt mortar is evaluated. Experimental and modelling results indicate that the measurement scale in the indentation tests can be controlled efficiently by testing with different indenter-specimen contact areas. Accordingly, indentation tests may be used for reliable viscoelastic characterization of binder-aggregate composites on macro-scale as well as on the mastic phase level. It may thus potentially provide a relatively simple tool for measuring viscoelastic properties of mastics in situ in asphalt mixtures. In order to establish a quantitative link between material design parameters of mastics and its rheology, a new finite element (FE) micromechanical modelling approach has been developed. It allows predicting the viscoelastic properties of bitumen-filler mastic from its volumetric, mechanical and geometrical design parameters. The influence of modelling parameters on the model’s accuracy is evaluated and optimal parameter combinations are identified. The model is validated with the measurements performed on several mastics and for a range of volumetric concentration of filler. It is shown that the proposed model can capture the measured viscoelastic behaviour of mastics for the examined range of loading, temperature and material parameters. Accordingly, it may be a useful tool for optimizing mastics material design for the target viscoelastic properties.
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| 22. |
- Fadil, Hassan, et al.
(author)
-
On the Measurement of two Independent Viscoelastic Functions with Instrumented Indentation Tests
- 2018
-
In: Experimental mechanics. - : Springer. - 0014-4851 .- 1741-2765. ; 58:2, s. 301-314
-
Journal article (peer-reviewed)abstract
- In the present paper, a methodology for complete characterization of linear isotropic viscoelastic material with spherical instrumented indentation test is proposed. The developed method allows for measuring two independent viscoelastic functions, shear relaxation modulus and time-dependent Poisson's ratio, from the indentation test data obtained at non-decreasing loading, but otherwise arbitrary. Finite element modelling (FEM) is relied upon for validating the proposed methodology and for quantifying the influence of experimental variables on the measurements accuracy. Spherical indentation experiments are performed on several viscoelastic materials: polyoxymethylene, bitumen and bitumen-filler mastics. The viscoelastic material functions obtained with the indentation tests are compared with the corresponding results from the standard mechanical tests. Numerical and experimental results presented indicate that the methodology proposed allows mitigating the machine compliance and loading rate effects on the accuracy of the viscoelastic indentation tests.
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| 23. |
- Fadil, Hassan, et al.
(author)
-
Predicting the Master Curve of Bituminous Mastics with Micromechanical Modelling
- 2022
-
In: RILEM International Symposium on Bituminous Materials. - Cham : Springer Nature. ; , s. 1473-1479
-
Conference paper (peer-reviewed)abstract
- The performance of asphalt mixtures is significantly affected by the viscoelastic properties of their mastic phase. The analytical approaches used to predict the mastic’s properties from its composition and constituents are limited in their accuracy as well as potential to handle non-linear material behaviour. An alternative micromechanical finite element modelling approach to calculate the mastic’s master curve from the binder and filler phase properties is presented in this paper. In the model, the mastic’s representative volume element is generated and it consists of a linear viscoelastic bitumen matrix and elastic spherical filler particles. In order to validate the model, shear relaxation moduli of bitumen and bitumen-filler mastics are measured at temperatures between −10 to 80 °C. For the two mastic materials characterized experimentally, micromechanical models are set-up and their capability to capture the measured response is evaluated and compared with the existing analytical solutions. The obtained results indicate that the proposed finite element modelling approach is advantageous as compared to the analytical solutions, as it both allows predicting mastic’s properties over wider temperature, frequency and material range as well as results in a better agreement with the measurements.
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| 24. |
- Fadil, Hassan, et al.
(author)
-
Predicting the master curves of bituminous mastics with micromechanical modelling
- 2021
-
In: International Journal on Road Materials and Pavement Design. - : Informa UK Limited. - 1468-0629 .- 2164-7402.
-
Journal article (peer-reviewed)abstract
- The performance of asphalt mixtures is significantly affected by the viscoelastic properties of their mastic phase. The analytical approaches used to predict the properties of mastics from their constituents’ properties are limited in their accuracy and potential to handle non-linear material behaviour. An alternative micromechanical finite element modelling approach to calculate the master curves of mastics from the binder and filler phase properties is presented, where the representative volume elements of mastics consist of linear-viscoelastic bitumen matrices and elastic spherical filler particles. For validation, shear relaxation moduli of bitumen and bitumen-filler mastics are measured at (Formula presented.) °C (Formula presented.) °C. Additionally, the model is evaluated and compared with the existing analytical solutions. The results indicate that the proposed approach is advantageous as compared to the analytical solutions, as it allows predicting the mastics’ properties over wider temperature, frequency and material ranges at better agreement with the measurements while giving insight into the micromechanical behaviour.
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| 25. |
- Fadil, Hassan
(author)
-
Spherical Indentation Technique for Multiscale Characterisation of Asphalt Mixtures
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- The viscoelastic properties of asphalt mixtures strongly influence the performance of flexible pavements with respect to their resistance to several common distress modes. Therefore, accurate measurement of these properties and their change during the service life is an important area of ongoing research. Despite considerable progress in this field, certain questions are still not fully resolved. In particular, commonly used experimental methods cannot be applied for the viscoelastic characterisation of thin asphalt layers and asphalt overlays. Moreover, measuring the viscoelastic properties of the downscaled sub-phases of asphalt mixtures, such as mastic or mortar, in the field remains a challenge. Understanding the viscoelastic properties of those sub-phases is crucial for gaining fundamental insight into the mixture performance. In this context, advanced and computationally efficient micromechanical models are also needed in order to establish the quantitative link between the viscoelastic properties of asphalt mixtures and of their sub-phases. This thesis aims to contribute to this important area through the development of new experimental and modelling tools for the multiscale characterisation of asphalt mixtures. In this thesis, a new micromechanical modelling approach for bitumen-aggregate composites is proposed and used to investigate the mechanical behaviour of mastic, mortar and asphalt mixtures. To achieve computational efficiency, the proposed approach is based on a simplified, computer-generated representation of materials internal structure and utilises periodic boundary conditions to reduce the representative volume element size. Based on the Dynamic Shear Rheometer (DSR) measurements, it is shown that the proposed model can capture the measured viscoelastic behaviour of mastics for the range of loading, temperature and material parameters examined. For the modelling of mortar and asphalt mixtures, the multiscale approach is applied in order to improve computational efficiency. Obtained computational results indicate that the developed approach is capable of capturing the mixtures’ macro-scale viscoelastic properties with reasonable accuracy. An instrumented indentation test for the viscoelastic characterisation of bitumen and bitumen-aggregate composites, such as mastic, mortar and asphalt mixtures is proposed in this thesis as a new alternative to existing techniques. A new methodology for the indentation testing of linear viscoelastic materials is developed, allowing their characterisation at arbitrary non-decreasing loading. In order to extend the developed method to the multiscale characterisation of bitumen-aggregate composites, the spherical indentation on different types of asphalt mixtures, such as asphalt mortar, mastic asphalt (MA) and asphalt concrete (AC), has been investigated experimentally and through micromechanical modelling. The effect of the indentation test parameters on the measured apparent viscoelastic properties of bitumen-aggregate composites has been evaluated. A particular emphasis is put on the identification of test parameters corresponding to the characterisation of binder-aggregate composites on the macroscale as well as on the individual component scale. The experimental results demonstrate that the developed indentation test can capture the macroscale properties of materials reasonably well, and the obtained results correlate linearly with the properties measured with established test methods. Furthermore, in order to gain better insight into mastic phase properties from the indentation tests performed on MA and AC, a new statistical analysis procedure has been developed for the evaluation of a series of indentation tests. The developed procedure allows identifying clusters of measurements capturing the mastic- and aggregate-dominated responses of the asphalt mixture. The indentation measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and mastic properties as compared to the mean measurements of the indentation test series. The obtained results indicate that the developed indentation test is a viable alternative to existing viscoelastic characterisation methods, in particular as the test is quasi-non-destructive and can be used to characterise thin asphalt layers. Furthermore, combined with the developed statistical analysis procedure, indentation testing is a promising tool to monitor the changes in the mastic phase of the materials due to ageing, moisture damage or fatigue from the measurements on asphalt mixtures without extracting the binder. The developed micromechanical model can also be used to quantify the effect of changing mastic properties on the asphalt mixture performance. This is particularly true for the strain localisations in the mastic phase and thus the mixture’s damage resistance.
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| 26. |
- Gullberg, David, et al.
(author)
-
Evaluation of a novel calibrated-mechanistic model to design against fracture under Swedish conditions
- 2012
-
In: International Journal on Road Materials and Pavement Design. - : Informa UK Limited. - 1468-0629 .- 2164-7402. ; 13:1, s. 49-66
-
Journal article (peer-reviewed)abstract
- Sweden has initiated the development of a new calibrated-mechanistic pavement design procedure to replace the current mechanical-empirical pavement procedure entitled “PMS Objekt.” The first phase was focused on the implementation and calibration of the vi scoelastic fracture mechanics framework entitled “HMA Fracture Mechanics”, developed at the University of Florida. This paper outlines the implementation and calibration of a new pavement design module for Sweden that is based on the HMA fracture mechanics framework. Both the developed design module, as well as the reference model used for calibration (PMS Objekt) are presented in this paper. The results in thickness design after calibration of the design module indicate that the framework is clearly applicable for common Swedish conditions and design standards.
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| 27. |
- Gullberg, David, et al.
(author)
-
Evaluation of the predictive models used in the new swedish mechanistic-empirical design module
- 2012
-
In: International Journal on Road Materials and Pavement Design. - : Informa UK Limited. - 1468-0629 .- 2164-7402. ; 13:2, s. 300-311
-
Journal article (peer-reviewed)abstract
- In order to perform thickness design of flexible pavements based on the HMA fracture mechanics framework prior to construction, the tensile strength and creep power law parameters of the mixture has to be determined. As samples are normally not available in the design stage, these properties will have to be modelled rather than determined in a laboratory. This paper evaluates material models based on the relationship between dynamic (complex) modulus and creep compliance in order to predict tensile strength and creep power law parameters for a mixture. For this evaluation, fourteen field sections from the United States have been used for verification and the results indicate that the crack resistance of a mixture can indeed be estimated without a development of extensive empirical relations between mixture properties and crack-resistance.
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| 28. |
- Hesami, Ebrahim, et al.
(author)
-
An empirical framework for determining asphalt mastic viscosity as a function of mineral filler concentration
- 2012
-
In: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 35, s. 23-29
-
Journal article (peer-reviewed)abstract
- Sufficient coating, easy paving and good compaction are desirable parameters, which are approachable with the optimum viscosity of the mastic. In many studies, models have been developed for calculating the viscosity for different types of suspensions at various particle-to-fluid ratios. Unfortunately, none of them are applicable to asphalt mastics, since this material has a much wider range of mineral filler concentration from dilute to very concentrate. To give an overview of the existing viscosity models and to evaluate their range of applicability to asphalt mastics, an extensive literature review was performed. A new empirical framework was developed that removes some of the stipulated limitations of the existing theories.
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| 29. |
- Hesami, Ebrahim, 1982-, et al.
(author)
-
Towards a New Experimental and Numerical Protocol for Determining Mastic Viscosity
- 2012
-
In: 7th RILEM International Conference on Cracking in Pavements. - Dordrecht : Springer Netherlands. - 9789400745667 ; , s. 103-113
-
Conference paper (peer-reviewed)abstract
- The rheological characteristics of mastics, or filler-bitumen mixtures, as a component of asphalt mixtures have a significant effect on the overall in-time performance of asphalt pavements such as low temperature cracking, fatigue and rutting behaviour. Viscosity is one of the rheological characteristics which is influenced by the physico-chemical filler-bitumen interaction. In this study, after reviewing some of more often used theories for calculating the viscosity of suspensions, a framework for calculating the viscosity of mastics is presented. This framework aims at covering the entire range of filler concentrations that is found in mastics. Also, a procedure for measuring viscosity mastic from dilute to high concentration mastic using a vane rotor viscometer is introduced. The paper is presenting the first experimental results and discusses the effect of the shape of the investigated fillers on the measured viscosity of the mastics.
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| 30. |
- Inozemtcev, Sergey, et al.
(author)
-
Experimental and numerical study on SMA modified with an encapsulated polymeric healing agent
- 2022
-
In: Materials and Structures. - : Springer Nature. - 1359-5997 .- 1871-6873. ; 55:9
-
Journal article (peer-reviewed)abstract
- The present study aims at experimentally and numerically investigating the effect an encapsulated healing agent on the mechanical characteristics of a stone mastic asphalt (SMA). As a healing agent a thiol-containing urethane AR-polymer is used in this study. In order to gain a numerical insight into mechanical behavior of the capsules in SMA, a micromechanical finite element modeling is employed. The developed model allows capturing the stresses induced in the capsules at different load cases applied to the SMA on macro-scale. Particular attention is paid presently to the numerical evaluation of the local stress state that arises around capsules during compaction, operation, and also during crack initiation. SMA mixtures with various volumetric contents of healing capsules were manufactured and the capsules survival during mixture production was evaluated based on X-Ray Computed Tomography measurements. The effect of capsules on the self-healing properties of asphalt mixtures has furthermore been examined with repeated compressive strength tests. The obtained experimental results indicate that the absolute majority of capsules survive mixture production, and that their addition increases the SMA strength recovery during the healing period. The experimental and numerical results concerning capsules breakage are found to be in reasonable agreement. The developed micromechanical model may thus potentially provide a useful tool for optimization of capsules mechanical properties in order to improve their survival during mixture production as well as their timely activation.
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| 31. |
- Jelagin, Denis, Docent, 1979-, et al.
(author)
-
Asphalt layer rutting performance prediction tools
- 2018
-
Reports (other academic/artistic)abstract
- Flexible pavement rutting due to permanent deformation accumulation in asphalt layers is one of the most common modes of road failures. In addition to creating high maintenance costs, rutting is a major concern for traffic safety, as the rut development increases the risk of hydroplaning and introduce difficulties in vehicle steering. In this context, accurate methodologies for pavement rutting performance prediction are crucial for decision support in pavement design and rehabilitation. In particular, better rutting performance models are needed to evaluate, new asphalt materials as well as to evaluate the impact of different vehicle types on roads’ service life.The main goal of this report is to present a summary of the existing asphalt rutting performance prediction tools. The present review is limited to available and/or frequently referred to tests and models with an established link to field rutting performance. Accordingly, models focusing solely on permanent deformation on the material level are beyond the framework of the present study.Road structure and its materials, heavy vehicle parameters and climate affecting rutting accumulation in the field are identified. Their significance has been evaluated based on the experimental and numerical findings reported in the literature. Several rutting performance prediction models recently proposed in the literature are summarized along with the material characterization tests used in the models. The reviewed models’ capability to quantify the influence of various structural, material and traffic parameters on the pavement’s rutting performance is examined.It is concluded that implementation of rutting performance models incorporating experimentally measured viscoelastic and permanent deformation properties of asphalt mixtures is a promising way to improve the accuracy of pavement performance predictions. In particular since they allow the effect of novel materials, e.g. polymer-modified, on the pavement’s rutting performance to be quantified.
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| 32. |
- Jelagin, Denis, 1979-
(author)
-
Frictional Effects on Hertzian Contact and Fracture
- 2007
-
Doctoral thesis (other academic/artistic)abstract
- This thesis addresses normal axisymmetric contact of dissimilar elastic solids at finite interfacial friction. It is shown that in the case of smooth and convex but otherwise arbitrary contact profiles and monotonically increasing loading a single stick-slip contour evolves being independent of loading and profile geometry. This allows developing an incremental procedure based on a reduced problem corresponding to frictional rigid flat punch indentation of an elastic half-space. The reduced problem, being independent of loading and contact region, was solved by a finite element method based on a stationary contact contour and characterized by high accuracy. Subsequently, a tailored cumulative superposition procedure was developed to resolve the original problem to determine global and local field values for two practically important geometries: flat and conical profiles with rounded edges and apices. Results are given for relations between force, depth and contact contours together with surface stress distributions and maximum von Mises effective stress, in particular to predict initiation of fracture and plastic flow. It is also observed that the presence of friction radically reduces the magnitude of the maximum surface tensile stress, thus retarding brittle fracture initiation.Hertzian fracture through indentation of flat float glass specimens by steel balls has been examined experimentally for a full load cycle. It has been observed that if the specimen survived during loading to a maximum level it frequently failed at decreasing load. It has been proposed by Johnson et al. (1973) that the underlying physical cause of Hertzian fracture initiation during load removal is that at unloading frictional tractions reverse their sign over part of the contact region. Guided by these considerations a robust computational procedure has been developed to determine global and local field values in particular at unloading at finite friction. In contrast to the situation at monotonically increasing loading, at unloading invariance properties are lost and stick-slip regions proved to be severely history dependent and in particular with an opposed frictional shear stress at the contact boundary region. This causes an increase of the maximum tensile stress at the contour under progressive unloading. It is shown that the experimental observations concerning Hertzian fracture initiation at unloading are at least in qualitative correlation with the effect friction has on the maximum surface tensile stress.A contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been further investigated analytically and numerically for a wider range of material parameters and contact geometries. With the issue of Hertzian fracture initiation in mind, results concerning the influence of the friction coefficient and compliance parameters on the absolute maximum surface tensile stress during a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation.Fracture loads are measured with steel and tungsten carbide spherical indenters in contact with float glass specimens at monotonically increasing loading and during a load cycle. Computational predictions concerning the fracture loads are given based on Hertz and frictional contact theories combined with a critical stress fracture criterion. The computational results obtained for frictional contact are shown to be in better agreement with experimental findings as compared to the predictions based on the Hertz theory. The remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen’s surface. In order to account for the influence of the random distribution of these defects on the fracture loads at monotonic loading, Weibull statistics was introduced. The predicted critical loads corresponding to 50% failure probability were found to be in close agreement with experimentally observed ones.
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| 33. |
- Jelagin, Denis, et al.
(author)
-
Hertzian Fracture at Finite Friction : A Parametric Study
- 2008
-
In: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 265:5-6, s. 840-848
-
Journal article (peer-reviewed)abstract
- Friction has a profound influence on Hertzian fracture initiation when dissimilar materials are involved. Experimental studies show that the presence of friction results in higher fracture loads and fracture radii as compared to the frictionless case. It has also been shown recently that the experimental observations concerning Hertzian fracture initiation at unloading may be explained by the effect friction has on a surface tensile stress distribution. Presently a contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been investigated numerically for a wide range of material parameters and contact geometries. Emphasis has been given to the surface tensile stress distribution which is assumed to be a governing parameter for Hertzian fracture initiation. In particular it was found that during loading the contact region divides into invariant stick and inward slip regions and the presence of outward frictional shear tractions reduces the maximum surface tensile stress and shifts it away from the contact contour as compared to the frictionless case. At unloading, the distributions of stick-slip zones were found to be severely history- and geometry-dependent and shear tractions reversed their direction over part of the contact area. Consequently, tensile stresses were found to grow at unloading. Results concerning the influence of the friction coefficient, Dundur's parameter and the specimen's Poisson's ratio on the absolute maximum surface tensile stress obtained at a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation.
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| 34. |
- Jelagin, Denis, et al.
(author)
-
Measurement of the Viscoelastic Properties of Bitumen Using Instrumented Spherical Indentation
- 2013
-
In: Experimental mechanics. - : Springer Science and Business Media LLC. - 0014-4851 .- 1741-2765. ; 53:7, s. 1233-1244
-
Journal article (peer-reviewed)abstract
- Indentation testing as a tool for determination of the viscoelastic mechanical properties of bitumen is examined in some detail using theoretical, numerical as well as experimental methods. In particular Brinell indentation is analysed and simple but rigorous formulae for a complete characterization of linear viscoelastic materials are presented. Numerical methods (finite element methods) are used in order to verify and substantiate these relations for an experimental situation. Indentation experiments are then performed on bitumen and special efforts are made in order to avoid size effects, i. e. anomalous results due to the fact that the indented specimens are too small and as a result, far field boundary conditions will influence the interpretation of the experimental output. The mechanical properties determined experimentally by indentation are compared with corresponding results from standard mechanical tests, and the results are encouraging considering the fact that non-linear effects are also influencing the outcome of the experiments.
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| 35. |
- Jelagin, Denis, et al.
(author)
-
Mechanical Characterization of Granite Rock Materials : On the Influence from Pre-Existing Defects
- 2018
-
In: Journal of Testing and Evaluation. - : ASTM International. - 0090-3973 .- 1945-7553. ; 46:2, s. 540-548
-
Journal article (peer-reviewed)abstract
- The length, orientation, and population of pre-existing cracks play an important role in the mechanical response of quasi-brittle materials, such as granite. Specifically, Bohus granite rock is at issue in the present investigation. The aims of this study are (1) to demonstrate the existence and characteristics of pre-existing defects (cracks) in granite rock specimens, and (2) to determine the influence from these defects at characterization of such materials. In doing so, X-ray tomography was the method used to visualize the cracking of three-point bending specimens in the context of pre-existing defects. It was also the intention to relate the experimentally determined effect of these cracks at three-point bending testing with corresponding results from numerical methods and specifically finite-element calculations. In the latter case, the location of these cracks was of primary interest and it was shown that this feature can be of considerable importance at material characterization.
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| 36. |
- Jelagin, Denis, et al.
(author)
-
Nonlocal Frictional Effects at Indentation of Elastic Materials
- 2013
-
In: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 51:3, s. 397-407
-
Journal article (peer-reviewed)abstract
- Indentation of elastic materials is investigated numerically using the finite element method. Large deformation theory is relied upon for accuracy. The study focuses on nonlocal frictional effects on relevant indentation quantities in the microindentation regime. The indentation quantities investigated include both local and global ones. It is shown that nonlocal frictional effects are small when global quantities are at issue, as is the case when conventional (Coulomb) theory of friction is used, also when these features are introduced at the ridges of a Vickers indenter where stress gradients are substantial. These effects are, however, shown to be of importance for particular indenter geometries as far as local field variables are concerned.
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| 37. |
|
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| 38. |
- Jelagin, Denis, et al.
(author)
-
On indentation and initiation of fracture in glass
- 2008
-
In: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 45:10, s. 2993-3008
-
Journal article (peer-reviewed)abstract
- The influence of indenter elasticity on Hertzian fracture initiation at frictional dissimilar elastic contact has been examined experimentally and numerically. In flat float glass specimens initiation of cone cracks has been observed and fracture loads measured with steel and tungsten carbide indenters at monotonically increasing loading and during a load cycle. The observed effect of indenter elasticity on fracture loads was found to be qualitatively different from the one predicted by the Hertz contact theory. This discrepancy may be explained by the presence of interfacial friction. The friction coefficient between the indenters and the specimen was measured and a contact cycle at finite Coulomb friction has been analyzed numerically. The influence of the indenter elasticity and the friction coefficient on the surface maximum tensile stress has been investigated and the results concerning the influence of these parameters on the fracture loads as given based on a critical stress fracture criterion. The obtained computational results were found to be in better agreement with experimental findings as compared to the predictions based on the frictionless contact theory. A remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen's surface. In order to account for the influence of the random distribution of these defects a Weibull statistics was introduced. The predicted critical loads corresponding to the 50% failure probability were found to be in close agreement with experimentally observed ones.
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| 39. |
- Jelagin, Denis, et al.
(author)
-
On Indenter Boundary Effects at Elastic Contact
- 2012
-
In: Journal of Mechanics of Materials and Structures. - : Mathematical Sciences Publishers. - 1559-3959 .- 2157-5428. ; 7:2, s. 165-182
-
Journal article (peer-reviewed)abstract
- Axisymmetric contact problems at finite Coulomb friction and rounded profiles are examined for linear elastic solids. In previous analytical/numerical approaches to this problem often incremental procedures have been developed resulting in a reduced incremental problem corresponding to a rigid flat indentation of an elastic half-space. The reduced problem, being independent of loading and contact region, can be solved by a finite element method based on a stationary contact contour and characterized by high accuracy. Subsequently, with cumulative superposition procedures it is then possible to resolve the original problem in order to determine global and local field values. Such a procedure, when applied to for example to flat and conical profiles with rounded edges and apices, is exact save for the influence from boundaries close to the contact region. This influence could be exemplified by the indenter boundaries of a flat deformable profile with rounded edges indenting a linear elastic half-space. In the present analysis such effects are investigated qualitatively and quantitatively. In doing so, the results derived using previously discussed analytical/numerical approaches are compared with corresponding ones from full-field finite element calculations. Both local as well as global quantities are included in the comparison in order to arrive at a complete understanding of the boundary effects at elastic contact.
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| 40. |
- Khavassefat, Parisa, 1984-, et al.
(author)
-
A computational framework for viscoelastic analysis of flexible pavements under moving loads
- 2012
-
In: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 45:11, s. 1655-1671
-
Journal article (peer-reviewed)abstract
- A general quasi-static computational procedure is established to evaluate stresses and strainsinduced in the viscoelastic flexible pavement bymoving traffic. The procedure is based on superposition principle and is computationally favourable, as itrequires only reduced incremental problem to besolved numerically. The impact of traffic speed anddensity on the mechanical response of flexible pavement is examined numerically. Results relevant fortwo major modes of pavement’s distress, i.e. crackingand rutting, are reported. It is shown that the state-ofpractice layered elastic analysis used in pavementdesign is unable to capture several important qualitative and quantitative aspects of pavements response.
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| 41. |
- Khavassefat, Parisa, 1984-, et al.
(author)
-
Dynamic Response of Flexible Pavements at Vehicle-Road Interaction
- 2015
-
In: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 16:2, s. 256-276
-
Journal article (peer-reviewed)abstract
- In the present paper a robust and general computational framework that captures the dynamic response of flexible pavements to a moving vehicle is presented. A finite element method is relied upon in order to establish the response function for a linear viscoelastic pavement structure with dynamic effects taken into account. In order to characterise the dynamic loads induced on the pavement by moving traffic, a quarter car model combined with measured road profiles is used. Once both the traffic loads and pavement response functions are known, the stresses and strains induced in the pavement can be obtained in the frequency-wavenumber domain through the convolution procedure. The computational procedure developed is applied in the present study to evaluate the effect of the pavement surface roughness on the pavement structure response to truck traffic loading. Stress field parameters governing fracture initiation in asphalt layers are reported for two measured road roughness profiles. It is shown that the dynamic effects at vehicle-road interaction may have a profound influence on the stresses induced in flexible pavements; therefore, these effects need to be taken into account for the accurate estimation of the road resistance to cracking.
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| 42. |
- Khavassefat, Parisa, 1984-, et al.
(author)
-
Impact of Long and Heavy Vehicles on Pavement Damage
- 2013
-
Conference paper (peer-reviewed)abstract
- In the present paper the effect of vehicle configuration and traffic characteristics on the damage induced in pavements by traffic is investigated numerically. A three dimensional time-dependent pavement-vehicle interaction analysis is performed in order to study the impact of the parameters mentioned above on the mechanical response of flexible pavements. The analysis is based on a fast and robust computational procedure, developed by the authors. The numerical algorithm utilizes the three-dimensional finite element solution of the reduced problem of one tyre pavement interface loaded with tyre pressure. Afterwards, a superposition procedure based on fast Fourier transform techniques is applied to find the pavement response to moving loads. The method is general and capable of capturing the stress-strain response to any arbitrary loading history.One particular area of study with employing the current procedure is the analysis of long and heavy vehicle impact on pavement damage. Two major modes of distress, i.e. cracking and rutting have been discussed for 6 different truck types with 2 speeds. It is shown that an accurate numerical model provides a more accurate explanation of different distress modes. Moreover the conventional analysis and design methods with layered linear elastic behaviour assumption for asphalt layer are unable to capture several important aspects of pavement response.
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| 43. |
- Khavassefat, Parisa, 1984-, et al.
(author)
-
Non-stationary Response of Flexible pavements to Moving Vehicles
- 2016
-
In: The international journal of pavement engineering. - : Taylor & Francis. - 1029-8436 .- 1477-268X. ; 17:5, s. 458-470
-
Journal article (peer-reviewed)abstract
- In this paper the pavement surface deterioration is investigated based on field measurements of surface roughness profiles obtained in Sweden. A predictive function for surface deterioration, based on average gradient of yearly measurements of the road surface profile in Swedish road network, is proposed. In order to characterise the dynamic loads induced on the pavement by moving traffic a quarter car model is used. Afterwards a non-stationary stochastic approach is used to obtain the yearly response of the pavement to moving loads. The solution is in frequency-wavenumber domain and is given for a non-stationary random case as the pavement surface deteriorates in pavement service life influencing thus the magnitude of the dynamic loads induced by the vehicles. The effect of pavement surface evolution on the stress state induced in the pavement by moving traffic is examined for a specific case of quarter car model and pavement structure. The results showed approximately a 100% increase in the dynamic component of stresses induced in the pavement.
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| 44. |
- Khavassefat, Parisa, 1984-
(author)
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Pavement Response to Moving Loads
- 2014
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Licentiate thesis (other academic/artistic)abstract
- The response of flexible pavements at vehicle-road interaction has been studied in this thesis. A quasi-static and a dynamic framework for analysing the pavement structure under moving load has been developed. Both frameworks are general, robust and computationally efficient.The quasi-static procedure is based on superposition principle and is computationally favourable, as it requires only reduced incremental problem to be solved numerically. Using the developed framework the effect of vehicle configuration and traffic characteristics on the damage induced in pavements is investigated numerically. It is shown that the developed numerical model provides a more accurate explanation of different distress modes. Moreover the conventional analysis and design methods with layered linear elastic behaviour assumption for asphalt layer are unable to capture several important aspects of pavement response.In the dynamic analysis approach the pavement roughness and vehicle suspension system is linked to a dynamic pavement model in order to account for the dynamic effects at vehicle-road interaction on pavement response. A finite element method is relied upon in order to establish the response function for a linear viscoelastic pavement structure with dynamic effects taken into account. The computational procedure developed is applied to evaluate the effect of the pavement surface roughness on the pavement structure response to truck traffic loading. Stress field parameters governing fracture initiation in asphalt layers are reported for two measured road roughness profiles. It is shown that the dynamic effects at vehicle-road interaction may have a profound influence on the stresses induced in flexible pavements; therefore these effects need to be taken into account for accurate prediction of the road performance in the field.
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| 45. |
- Khavassefat, Parisa, et al.
(author)
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The effect of road surface deterioration on pavement service life
- 2014
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In: Expanding horizons: 13th International Symposium on Heavy Vehicle Transport Technology, San Luis, Argentina, 27-31 October 2014.
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Conference paper (peer-reviewed)abstract
- The effect of pavement surface deterioration on pavement service life has been studied for a set of case studies. The Swedish mechanistic empirical design method is used in order to analyse the pavement performance under dynamic moving loads while the longitudinal profile unevenness is updated on yearly basis. The surface evolution assumed in the case scenarios are chosen in relevance with the general trend of surface deterioration in Swedish road network. Results from the case studies indicate that the pavement service life is highly affected by pavement surface deterioration, especially for pavement segments with high traffic. Moreover predictive maintenance for high traffic road segments might be beneficial as it increases pavement service life and decreases the user related costs, e.g. vehicle fuel consumption.
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| 46. |
- Khavassefat, Parisa, 1984-
(author)
-
Vehicle-Pavement Interaction
- 2014
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Doctoral thesis (other academic/artistic)abstract
- Several aspects of vehicle-pavement interaction have been studied and discussed in this thesis. Initially the pavement response is studied through a quasi-static and a dynamic computationally efficient framework under moving traffic loads. Subsequently, a non-stationary stochastic solution has been developed in order to account for the effect of pavement surface deterioration on pavement service life.The quasi-static procedure is based on a superposition principle and is computationally favourable, as it requires only a reduced incremental problem to be solved numerically. Using the developed framework, the effect of vehicle configuration and traffic characteristics on the damage induced in pavements is investigated numerically. It is shown that the developed numerical model provides a more accurate explanation of different distress modes.In the dynamic approach the pavement roughness and vehicle suspension system are linked to a dynamic pavement model in order to account for the dynamic effects of vehicle-pavement interaction on pavement response. A finite element method is employed in order to establish the response function for a linear viscoelastic pavement structure with dynamic effects taken into account. The developed computational procedure is applied to evaluate the effect of the pavement surface roughness on the pavement structure response to truck traffic loadings.Furthermore, the deterioration trends for the flexible pavement surface have been investigated based on field measurements of longitudinal profiles in Sweden. A predictive function is proposed for surface deterioration that is based on the average gradient of yearly measurements of the road surface profiles in Swedish road network. The developed dynamic framework is further elaborated to a non-stationary stochastic approach. The response of the flexible pavement is given for a non-stationary random case as the pavement surface deteriorates in pavement service life, thus influencing the magnitude of the dynamic loads induced by the vehicles. The effect of pavement surface evolution on the stress state induced in the pavement by moving traffic is examined numerically.Finally the effect of surface deterioration on pavement service life has been investigated and discussed in the thesis by incorporating the proposed prognostic surface deterioration model into a ME design framework. The results are discussed for different case studies with different traffic regimes. It was indicated that the predicted pavement service life decreases considerably when the extra dynamic loads, as a result of pavement surface deterioration, has been taken into account. Furthermore, the effect of performing a predictive rehabilitation process (i.e. resurfacing) has been studied by employing a LCC framework. The application of preventive maintenance was shown to be effective, especially when the deterioration rate is high.
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| 47. |
- Lindskog, P, et al.
(author)
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Optimization as a tool for characterization of advanced constitutive models describing powder compaction
- 2007
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In: Proceedings of the Euro PM 2007 Congress and Exhibition. - Shrewsbury : European Powder Metallurgy Association. ; , s. 381-386
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Conference paper (peer-reviewed)abstract
- The applicability of optimization procedures used in combination with advanced constitutive models, describing dry pressing powder compaction, is investigated by aid of standard finite ele- ment and optimization commercial packages. It is found that, at fairly general conditions, this can be expected to be a very advantageous approach at material characterization
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| 48. |
- Ling, Senlin, et al.
(author)
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Experimental and numerical analyses on the fracture characteristics of cement-asphalt mastic-aggregate interface
- 2023
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 401
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Journal article (peer-reviewed)abstract
- The stiffness and failure properties of cement-asphalt mastic-aggregate (C-AM-A) interface are among the most important factors affecting the performance of pouring semi-flexible pavement materials (SFP). Therefore, determining the characteristics of C-AM-A interface are essential for guiding the design of SFP from the perspective of interface enhancement. In this study, the failure characteristics of C-AM-A interfaces are examined experimentally and numerically. Firstly, the effects of temperature and the proportion of cement substituting limestone filler on the bonding strength of C-AM-A interface are analyzed via pull-off tests. Then, an innovative test method based on a three-point bending test of C-AM-A beam is proposed to investigate the influence of test temperature and asphalt mastic type on the fracture characteristics of the C-AM-A interface. Finally, based on the cohesive surface techniques, numerical modeling of C-AM-A beam under three-point bending was applied to study the effect of cohesive parameters on the interfacial fracture characteristics. The results show that the interface bonding strength decreased significantly with the increase of temperature. Using cement as a filler improves the bonding strength, fracture strength, stiffness and fracture energy of C-AM-A interface as compared to the case when limestone filler is used. As the temperature increases from -10 degrees C to 20 degrees C, the failure mode of the C-AM-A interface first alters from adhesive failure to mixed failure mode, and then to cohesive failure. It suggests that enhancing the adhesion of C-AM-A interface is more advantageous for improving the fracture resistance at low temperatures, while increasing the interface cohesion is more important at relatively high temperatures. The laboratory test methods, the numerical model and methodology developed in this study are useful to study the failure behavior of C-AM-A interface and optimize the performance of SFP from the perspective of interface enhancement.
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| 49. |
- Lira, Bernardita, et al.
(author)
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Binder distribution model for asphalt mixtures based on packing of the primary structure
- 2015
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In: The international journal of pavement engineering. - : Informa UK Limited. - 1029-8436 .- 1477-268X. ; 16:2, s. 144-156
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Journal article (peer-reviewed)abstract
- Film thickness describes the coating around aggregate particles on asphalt mixtures. The standard method of calculating film thickness has proven to present several limitations, such as assuming an average thickness independent of particle size, being completely independent to the porosity of the mixture and considering only one mineral type. In this paper, a binder distribution model is developed for aggregates according to size and role in the structure. The aggregates are separated into two different structures: primary structure, the load bearing one, and secondary structure, smaller material that provides stability to the skeleton. A coating thickness for these two structures is calculated from a geometrical consideration that includes the packing arrangement of particles and the effect of overlapping as the film grows. The results were compared with known rutting performance of field mixtures and moisture conditioned laboratory mixtures, showing a good correlation between film thickness and resistance to failure.
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| 50. |
- Lira, Bernardita, et al.
(author)
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Gradation-based framework for asphalt mixture
- 2013
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In: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 46:8, s. 1401-1414
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Journal article (peer-reviewed)abstract
- Aggregates are the major component of asphalt mixtures, greatly influencing the mixtures resistance to failure. The structure that is formed by the aggregates will depend mostly on the size distribution, shape and mineral composition. Coarse aggregate have a strong influence on the resistance to rutting, while fines provide stability to the mixture. In the present study a generalized framework is developed to identify the range of aggregate sizes which form the load carrying structure in hot mix asphalt and determine its quality. The method has been developed as a numerical procedure based on packing theory. Parameters like porosity and coordination number have been used to evaluate the quality of the load carrying structure and relate it to resistance to rutting. The framework has been evaluated on several field and laboratory mixtures and related to their rutting performance. The gradation analysis of the mixtures has compared favorably with the performances reported from the field and laboratory testing. The developed gradation analysis framework has proven to be a tool to identify those mixtures with a poor rutting performance based on the gradation of the aggregates.
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