| 1. |
- Jelagin, Denis, et al.
(författare)
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Experimental and numerical modelling of shear bonding between asphalt layers
- 2023
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Ingår i: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 24:S1, s. 176-191
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Olsson, Erik, 1986-, et al.
(författare)
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A numerical framework for modelling settlements of railway ballast layers
- 2024
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Ingår i: Transportation Geotechnics. - : Elsevier. - 2214-3912. ; 44
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Saliko, Denis
(författare)
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Validation of heavy vehicle loading responses and temperature predictions in flexible pavements using field data
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 4. |
- Bekele, Abiy
(författare)
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Evaluation of Low Temperature Damage in Asphalt Mixtures with Non-Contact Resonance Testing
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 5. |
- Etikan, M. Kaan, et al.
(författare)
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Experimental and numerical analyses of crushing resistance of unbound road materials
- 2024
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Ingår i: The international journal of pavement engineering. - : Taylor & Francis. - 1029-8436 .- 1477-268X. ; 25:1
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Fadil, Hassan, et al.
(författare)
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A New Viscoelastic Micromechanical Model for Bitumen-Filler Mastic
- 2020
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 253
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Fadil, Hassan, et al.
(författare)
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A spherical indentation test for quasi-non-destructive characterisation of asphalt concrete
- 2024
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Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873.
-
Tidskriftsartikel (refereegranskat)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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| 8. |
- Fadil, Hassan, 1990-
(författare)
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New Experimental and Modelling Tools for Multiscale Characterization of Asphalt Mastic
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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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| 9. |
- Fadil, Hassan, et al.
(författare)
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Predicting the Master Curve of Bituminous Mastics with Micromechanical Modelling
- 2022
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Ingår i: RILEM International Symposium on Bituminous Materials. - Cham : Springer Nature. ; , s. 1473-1479
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Konferensbidrag (refereegranskat)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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| 10. |
- Fadil, Hassan, et al.
(författare)
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Predicting the master curves of bituminous mastics with micromechanical modelling
- 2021
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Ingår i: International Journal on Road Materials and Pavement Design. - : Informa UK Limited. - 1468-0629 .- 2164-7402.
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Fadil, Hassan
(författare)
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Spherical Indentation Technique for Multiscale Characterisation of Asphalt Mixtures
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 12. |
- Inozemtcev, Sergey, et al.
(författare)
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Experimental and numerical study on SMA modified with an encapsulated polymeric healing agent
- 2022
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Ingår i: Materials and Structures. - : Springer Nature. - 1359-5997 .- 1871-6873. ; 55:9
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Tidskriftsartikel (refereegranskat)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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| 13. |
- Ling, Senlin, et al.
(författare)
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Experimental and numerical analyses on the fracture characteristics of cement-asphalt mastic-aggregate interface
- 2023
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 401
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Tidskriftsartikel (refereegranskat)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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| 14. |
- Ma, Ziye, et al.
(författare)
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Optimal design of fresh sand fog seal mortar using response surface methodology (RSM) : Towards to its workability and rheological properties
- 2022
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 340
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Tidskriftsartikel (refereegranskat)abstract
- As a popular preventive maintenance material, sand fog seal (SFS) could fill the micro-cracks and improve the skid-resistance and wear-resistance of road surface, but little research has been conducted to explain how the components of fresh SFS mortar affect its workability and rheological behavior. In this paper, an improved workability evaluation system is established for fresh SFS mortar based on self-developed devices, including the basic indexes such as dynamic uniformity DUt,s, slump flow X, and seepage velocity V-s. There is a negative correlation between the fluidity index (slump flow and seepage velocity) and the uniformity index (dynamic uniformity), and both of them are important bases for the performance balance design of fresh SFS mortar. Then, the effects of water, filler and sand on the workability are evaluated using response surface methodology (RSM) with I-optimal design method. The results show that water mainly regulates the consistency of the SFS mortar, which in turn affects its flowability. The sodium bentonite filler could alter the suspension capacity of the fog seal paste and determine the state of dispersion of sand in the paste. Besides, the addition of sand plays a negative role in the fluidity of fresh SFS mortar. Meanwhile, three design intervals for fresh SFS mortar are proposed based on its workability, (1) Easy-to-separate interval: DUt,s < 0.8; (2) Hard-to-flow interval: X <= 54.9 mm and V-s = 0. (3) Recommended interval: DUt,s > 0.8, V-s > 0, and X > 54.9 mm, where the fresh SFS mortar can balance stability and fluidity well. Hence, to maximize the balance between uniformity and fluidity of fresh SFS mortar, a formulation design optimization guideline is proposed based on desirability optimization methodology (DOM). The formulation has the widest distribution of high desirability when the sand content is 25%. Finally, the results of rheological test show that fresh SFS mortar is a typical shear-thinning pseudoplastic fluid, which can fit the "Herschel-Bulkley" model well. Yield stress and plastic viscosity can be used as the important rheological indexes to predict the workability of fresh SFS mortar. In general, based on the approach proposed herein, an optimized fresh SFS mortar with both good uniformity and fluidity could be produced.
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| 15. |
- Said, Safwat, 1951-, et al.
(författare)
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Prediction of rutting in asphalt concrete pavements : the PEDRO model
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)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 high maintenance costs, rutting is a major concern for traffic safety, as the rut growth increases the risk for hydroplaning and difficulties in vehicle steering. In this context, accurate methodologies for pavement rutting performance prediction are crucial for decision support in pavement design and rehabilitation. More rational rutting performance models are needed to enable the implementation of new and more sustainable and environmentally friendly asphalt materials as well as to evaluate the impact of high capacity traffic (HCT) vehicle types on bituminous layers.The main goal of this work is to implement and disseminate an asphalt rutting performance prediction tool called PEDRO (PErmanent Deformation of asphalt concrete layers for ROads). It focuses solely on the permanent deformation of asphalt concrete materials in the pavement structure. The PEDRO tool is a viscoelastic model for the calculation of permanent vertical strain under moving wheel loads over a viscoelastic half-space. The analysis is performed for the entire rutting zone and the permanent deformation of each layer or sub-layer, depending on its location in the pavement structure, is then integrated over the whole asphalt concrete depth.
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| 16. |
- Tan, Zhifei, et al.
(författare)
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Multiscale characterization and modeling of aggregate contact effects on asphalt concrete's tension–compression asymmetry
- 2023
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- Asphalt concrete (AC) exhibits significant tension–compression (TC) asymmetry and aggregate contacts can be one of the critical contributors to this behavior. Nevertheless, the underlying mechanisms are still unclear, and there has been no study to quantify this behavior. To fill the research gap, multiscale characterization and modeling on AC were performed in this study. At the microscale level, nanoindentation tests were conducted to characterize the aggregate contact characteristics in the contact region (CR). The CR was found to have a sandwich-like structure consisting of two interfacial layers, large filler particles, and asphalt mastic. Accordingly, micromechanical models of CR were developed to predict its mechanical behavior in tension and compresison (T&C). The modeling results showed that aggregate contacts significantly increase the compressive modulus, leading to the substantial TC asymmetry of CR. The predicted viscoelastic properties of CR were further applied to the developed mesostructural model of AC. The predicted master curves in T&C showed significant asymmetry and quantitatively agreed with the experimental ones, demonstrating the effectiveness of the adopted modeling approaches. This study is the first study to quantify the asymmetric performance of AC. The outcomes can be applied to evaluate AC's TC asymmetry effects on pavement performance.
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| 17. |
- Yang, Yang, et al.
(författare)
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Numerical analysis concerning the skid resistance of rubber-contaminated runway grooves
- 2021
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 163
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Tidskriftsartikel (refereegranskat)abstract
- Runway grooves are essential for water drainage and skid resistance; although the skid resistance of runway grooves has been studied, research on the frictional properties of runway grooves remains limited. This study presents a numerical method for analyzing the skid resistance of runway grooves. A aircraft tire model was developed with rubber and belt layer materials. A grooved runway sample was obtained by simulating the grooves on a runway surface specimen. A numerical algorithm was employed on the runway sample to simulate groove closure caused by rubber deposits; the degree of closure was defined as the percentage of closed grooves resulting from rubber deposits. An interaction model was developed according to the power spectrum density of a grooved runway and the viscoelastic properties of tread rubber. The numerical simulation results were verified using a runway skid resistance field test. The effects of groove closure due to rubber deposit contamination and groove geometry were analyzed. Friction increased as groove depth and width increased, but friction decreased as groove spacing and degree of closure increased.
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| 18. |
- Yang, Yang, et al.
(författare)
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Numerical analysis of hydroplaning and veer-off risk of dual-tyre on a wet runway
- 2023
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Ingår i: The international journal of pavement engineering. - : Informa UK Limited. - 1029-8436 .- 1477-268X. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of hydroplaning poses a risk when landing an aircraft on a wet runway. This study developed a finite element (FE) framework comprising a dual-tyre model, water film models, a runway model, and an interaction model to investigate wet runway landings. The dual-tyre model was created with a geometric description and material properties. Water film models for even and uneven water depths were constructed based on a coupled Eulerian-Lagrangian algorithm. The runway model was obtained through surface scanning and 3D reconstruction. The interaction model was calculated using the power spectrum density and viscoelastic property of rubber. Based on the FE approach, the effect of the slip ratio on the hydroplaning phenomenon was discussed. The results indicated that hydroplaning speed generally increases with the slip ratio. Furthermore, single- and dual-tyre wet runway landings with an even water film depth were simulated, and the results revealed similar accuracy between the two landing types. Next, the study of dual-tyre landings indicated that landings in varying depths of water face the risks of hydroplaning and veering off simultaneously. The FE approach was further used to analyse dual-tyre landings on runways with a yaw angle.
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