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    <title>Transport Research International Documentation (TRID)</title>
    <link>https://trid.trb.org/</link>
    <atom:link href="https://trid.trb.org/Record/RSS?s=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" rel="self" type="application/rss+xml" />
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    <language>en-us</language>
    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
    <image>
      <title>Transport Research International Documentation (TRID)</title>
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      <link>https://trid.trb.org/</link>
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    <item>
      <title>Effect of internal erosion on the hydraulic behavior of gap-graded coarse-fine mixtures: Experimental and mathematical investigations</title>
      <link>https://trid.trb.org/View/2492857</link>
      <description><![CDATA[Internal erosion is a phenomenon in which fine particles are removed by seepage through pore channels between coarse particles in internally unstable soil. It can lead to widespread pavement collapse or sinkholes, undesirable incidents in tunnel engineering and dike foundations, and clogging of oil wells. The erodibility of soil is influenced by critical factors such as the plasticity index (PI) and fines content (FC). However, the combined effects of these factors on internal erosion remains uncertain. For this reason, in this research a triaxial-erosion apparatus was developed to perform an experimental and mathematical investigation of erosion of sand-fines mixtures. Three different clay-sized particle types (rock powder, kaolinite or bentonite) each with three fines contents 20 %, 25 % and 30 % were used. The results indicated that while the output velocity initially rose rapidly with an increasing hydraulic gradient during the early stages of erosion, hydraulic conductivity eventually decreased due to the clogging of particles in specific areas and the blockage of flow paths. The non-Darcy flow behavior resulting from internal erosion positively impacted seepage control in tested soils. Increasing the PI and fines content enhanced the stability of the sample, as PI had a significant impact on the flow in soils with a higher FC. It was seen that rapid erosion was experienced by rock powder mixtures before stabilization, gradual erosion occurred in bentonite due to high cohesion, and uniform erosion was exhibited by kaolinite without significant flocculation. Following erosion, the granulation results of various soil layers clarified three interconnected internal erosion processes: reattachment, rearrangement, and transport. In this study, an equation is derived that describes the variation in the eroded mass with respect to the hydraulic gradient, time, PI and FC.]]></description>
      <pubDate>Thu, 06 Mar 2025 09:23:20 GMT</pubDate>
      <guid>https://trid.trb.org/View/2492857</guid>
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    <item>
      <title>Evaluation of Rapid Mix Design for Lime Treated Materials</title>
      <link>https://trid.trb.org/View/2437690</link>
      <description><![CDATA[There is a need to develop guidelines for a rapid mix design with small samples for lime-treated materials for Texas Department of Transportation (TxDOT). Thus, the objectives of this project are to: (1) conduct a literature review and summarize state-of-the practice and key findings; (2) review and summarize mix design methods currently in use for lime treated materials; (3.) conduct a comprehensive lab program comparing existing procedures with small sample methods; (4) develop a lab mix design method for lime treatment that is similar in methodology, with accelerated methods of mix design currently in use or under development for asphalt-based and cement-based treatments; (5) demonstrate the procedures for upcoming construction projects; (6) develop recommended test procedures and updates to specifications. To achieve these objectives, the research team will conduct comprehensive testing and analysis program for a set of carefully selected soils and base course, with a range of plasticity index and clay minerals, and will develop a mix design procedure that will result in a significant reduction in turnaround time and amount of materials required for mix design. The research team will evaluate and compare physical, chemical, and mechanical test properties of the samples designed according to the current method and the selected potential methods, to recommend the most optimum curing, moisture conditioning and testing methods. The research team will provide conclusions and recommendations in the form of specification updates for effective implementation.]]></description>
      <pubDate>Thu, 03 Oct 2024 10:34:32 GMT</pubDate>
      <guid>https://trid.trb.org/View/2437690</guid>
    </item>
    <item>
      <title>Evaluating the Influence of Soil Plasticity on the Vibratory Roller—Soil Interaction for Intelligent Compaction</title>
      <link>https://trid.trb.org/View/2113214</link>
      <description><![CDATA[Use of intelligent compaction (IC) is a growing technique for compaction in the field of construction. It provides an efficient way of evaluating the soil compaction level with a higher degree of certainty than traditional quality control methods. IC involves the interpretation of measured values received through the accelerometer and other sensors attached to the roller. The key objective of this paper is to analyze the dynamic roller–soil interaction via a three-dimensional nonlinear finite element model, capturing soil nonlinear response and damping in both small and large strain ranges as a result of dynamic load applied via the vibratory roller. In particular, the impact of soil plasticity index (PI) on the response of a typical vibratory roller is assessed. Indeed, the soil plasticity impacts stiffness degradation with shear strain influencing the soil stiffness during compaction and the roller response. The numerical predictions exhibit that the soil plasticity can significantly influence the response of the roller and the ground settlement level; hence, practicing engineers can consider the soil plasticity index as an influencing factor to interpret the intelligent compaction results and optimize the compaction process.]]></description>
      <pubDate>Mon, 10 Apr 2023 11:58:13 GMT</pubDate>
      <guid>https://trid.trb.org/View/2113214</guid>
    </item>
    <item>
      <title>Soil damping calculation of the offshore wind turbine supported by wide-shallow bucket foundation</title>
      <link>https://trid.trb.org/View/1851217</link>
      <description><![CDATA[The soil damping, which shows an obvious relationship with the foundation type and soil parameters, has a very important effect on the dynamic response and fatigue characteristics of Offshore Wind Turbine (OWT) structure. Known as a novel type of foundation, the Wide-Shallow Bucket Foundation (WSBF) has been gradually applied in a few Offshore Wind Farms (OWF) of China during the past five years. Due to the shallow bucket skirt and the more contact area between soil and foundation, the soil damping of the OWTs supported by WSBF may reflect different foundation-soil interaction characteristics compared with monopile and jacket foundation. There, the calculation of soil damping for the OWTs supported by WSBF was focused on and discussed in this paper. Firstly, the rotation and swing theoretical model of OWT supported by WSBF was established and then the theoretical model of natural frequency calculation was also presented based on the transfer matrix method. Further, one new theoretical calculation method of soil damping for the OWT supported by WSBF was proposed considering soil hysteresis characteristics. Secondly, taking an OWT of one actual OWF as the research object, accurate theoretical estimation of soil damping for WSBF was achieved combined prototype observation, modal frequency identification and Genetic Algorithm (GA) with a value around 0.120%. Then, three different geological conditions and soil parameters of another actual OWF were selected to complete the comparison between the results obtained from the proposed theoretical calculation method and numerical simulation method, and verify the general applicability of the new model and method based on the engineering error within 5%. Finally, the influence on the soil damping of OWT structure considering different factors (compression modulus and Plasticity Index (PI)) was discussed by using the new theoretical calculation method. It is concluded that the soil damping rises with the increase of the compression modulus, while it decreases as the PI increases.]]></description>
      <pubDate>Thu, 24 Jun 2021 16:40:51 GMT</pubDate>
      <guid>https://trid.trb.org/View/1851217</guid>
    </item>
    <item>
      <title>Properties of aggregate fines influencing modulus and deformation behaviour of unbound aggregates</title>
      <link>https://trid.trb.org/View/1777969</link>
      <description><![CDATA[Unbound aggregate base and subbase layers distribute traffic induced wheel loads in a pavement and protect the weak subgrade. In this study, effects of plasticity index (PI), fines content (FC) (per cent passing No. 200 sieve size) and dust ratio (DR) (ratio of per cent passing No. 200 sieve to per cent passing No. 40 sieve) of unbound aggregates on the base/subbase layer modulus and deformation characteristics are investigated. Repeated load triaxial tests were conducted on crushed gravel and limestone specimens prepared at optimum moisture contents for two Illinois dense-graded gradations, i.e. CA 6 and CA 2, to determine the resilient modulus and deformational behaviour. Samples with 9% PI showed lower resilient moduli and greater deformations than samples with 5% PI. The effects of FC on the modulus and deformation behaviour depend on the DR. Increasing DR from 0.4 to 0.6 and eventually to 1.0 increased deformations and decreased resilient moduli at the FC of 5%. An opposite trend was observed when the DR increased from 0.4 to 0.6 and eventually to 1.0 at 12% FC. The test results were used to develop improved resilient modulus and deformation prediction models, which capture important effects of aggregate FC, PI and DR.]]></description>
      <pubDate>Mon, 05 Apr 2021 17:08:29 GMT</pubDate>
      <guid>https://trid.trb.org/View/1777969</guid>
    </item>
    <item>
      <title>Improvement of Material Criteria for Highway Embankment Construction</title>
      <link>https://trid.trb.org/View/1841357</link>
      <description><![CDATA[Performance of the highway embankments has been investigated based on two main concerns; slope stability and deformation. To examine embankment performance, parameters obtained from both total stress analysis (TSA) and effective stress analysis (ESA) have been considered, that is stability and deformation have been each investigated under two states of TSA and ESA. This also necessitates that soil strength properties are obtained at both TSA and ESA conditions. The scope considers only failures and settlements related to compacted embankment and not due to poor foundation soil conditions. A set of unconsolidated-undrained (UU) triaxial tests has been used to obtain total stress soil strength properties, and a set of consolidated-undrained (CU) triaxial tests with pore pressure measurements has been considered to achieve effective stress soil strength properties. Sixteen embankment geometric sections have been considered in total. For the highway embankment deformation analysis, two-dimensional plane strain conditions were assumed. Among all cases, not even one case showed TSA factor of safety (FS) lower than the minimum value of 1.3. In many of these cases FS is well above the minimum value. Results of the stability analysis based on ESA parameters were completely different from those of obtained using TSA parameters, as in the effective stress stability analyses many cases were found having FS lower than 1.3. For the effective stress slope stability analysis, shallow failure must be checked as it is a case with high possibility. There are some findings that might give grounds to the idea that soils with higher plasticity index (PI) such as Soil 2 Lee an A-7-6 American Association of State Highway and Transportation Officials (AASHTO) class perform slightly better under rain-induced inundation conditions. This is in opposition to the criterion of limiting material PI as material selection criteria which is currently used by the NC state standard. This might at least cast doubt on the North Carolina Department of Transportation (NCDOT) material selection specification of limiting PI to 15% in the North Carolina coastal area. Providing suitable vegetation cover (to reduce infiltration and promote runoff) as well as drainage measures for the highway embankments could be very helpful to avoid detrimental effects of presence of water in the body of embankment.]]></description>
      <pubDate>Mon, 29 Mar 2021 12:05:41 GMT</pubDate>
      <guid>https://trid.trb.org/View/1841357</guid>
    </item>
    <item>
      <title>Effects of quantity and plasticity of fine particles on the workability and resilient behaviour of aggregate-soil mixtures for granular pavement layers</title>
      <link>https://trid.trb.org/View/1765065</link>
      <description><![CDATA[The paper presents the results of a laboratory investigation seeking to quantify the effects of fine quantity and type on the workability and resilient response of aggregate-fine soil mixtures for subbase formation. Laboratory devices were used to simulate in-field conditions and compact samples and evaluate their resilient response under pulsing loads. Four different types of fines passing through a 63 µm sieve (one non-plastic silt and three silty-clays exhibiting plastic behaviour) in three different quantities (5.4, 10.8 and 16.2%) were combined with coarser aggregates while maintaining the same grading distribution. A variant of the generalized model proposed in the Mechanistic Empirical Pavement Design Guide was calibrated to distinguish the contribution of fine type to resilient modulus from that of moisture content and suction. The results evidenced an improvement in mixture workability during the compaction process when using plastic fines instead of non-plastic ones. However, the quantity of plastic fines should be limited (lower than 10.8% within the aggregate skeleton) in order to achieve a high compaction level and to attain a hardening resilient behaviour rather than the softening one observed in the case of granular materials containing non-plastic fines.]]></description>
      <pubDate>Tue, 23 Mar 2021 11:13:05 GMT</pubDate>
      <guid>https://trid.trb.org/View/1765065</guid>
    </item>
    <item>
      <title>Investigation of Calcium Carbide Residue as a Stabilizer for Tropical Sand Used as Pavement Material</title>
      <link>https://trid.trb.org/View/1725586</link>
      <description><![CDATA[Wastes that have cementitious properties can become a useful source of cheap materials for soil improvement, thereby reducing the cost of construction projects on sites that have unsuitable soils. This research work investigated the effects of the application of calcium carbide residue (CCR) to a tropical soil on its geotechnical properties in order to assess the suitability of the stabilized soil for use as a road pavement material. Tests to determine the grain size distribution, specific gravity, liquid and plastic limits, compaction, California bearing ratio (CBR) and unconfined compressive strength (UCS) of the natural soil and its stabilization with varying percentages of CCR were carried out. The outcome showed that increasing application of CCR generally reduced the soil’s specific gravity, plasticity index and maximum dry unit weight. A direct proportionality was also found between the CCR content and each of the liquid and plastic limits, optimum moisture content, CBR and UCS. Thus, the soil became more workable and its strength properties were improved by stabilization with CCR. Consequently, the subgrade characteristics of the soil for use as earthwork materials for road construction was improved. Based on strength properties of the stabilized soil, an optimal application of 4% CCR was found suitable for the stabilization of the sand with similar properties as those studied. The use of CCR for stabilizing sand for road construction is recommended as a cheap and sustainable approach for developing countries.]]></description>
      <pubDate>Thu, 27 Aug 2020 15:11:27 GMT</pubDate>
      <guid>https://trid.trb.org/View/1725586</guid>
    </item>
    <item>
      <title>Best-fit models for predicting the geotechnical properties of FA–stabilised problematic soils used as materials for earth structures</title>
      <link>https://trid.trb.org/View/1708292</link>
      <description><![CDATA[The effect of fly ash (FA) on geotechnical properties of high plasticity clayey soils (known as problematic soils) has been investigated by several researchers. However, few studies have been developed to predict the geotechnical properties of FA–stabilised problematic soils. This study was undertaken in order to develop best-fit models for predicting the Atterberg limits [liquid limit (LL) and plasticity index (PI)], unconfined compressive strength (UCS), free swell index (FS), optimum moisture content (OMC) and maximum dry density (MDD) of FA-stabilised high plasticity clayey soils. For this purpose, many data sources were collected from several laboratory studies published in the literature over the past. All the developed models were validated and found to have a good ability where they can be used as a reliable tool to predict all the LL, PI, UCS, FS, MDD and OMC of FA-stabilised high plasticity clayey soils. In addition, the suggested models showed that the accurate prediction of all the studied physico-mechanical properties was highly beneficial for the engineering construction enabling it to avoid the cumbersome tests in the laboratory. From these results, the obtained equations may be useful in practices of civil engineering projects and in designing earth structures such as roadway subgrades, road embankments, trench backfills, landfill liners and earth dams.]]></description>
      <pubDate>Mon, 08 Jun 2020 15:34:05 GMT</pubDate>
      <guid>https://trid.trb.org/View/1708292</guid>
    </item>
    <item>
      <title>Impact of wetting—drying cycles on the mechanical properties of lime-stabilized soils</title>
      <link>https://trid.trb.org/View/1672840</link>
      <description><![CDATA[This article addresses the results of an experimental study on the behavior of soil; this soil was exposed to long-term treatment with lime and numerous wetting-drying cycles. This research investigated the effect of a wide range of lime contents on the soil volume, soil water content evolution and durability (unconfined compressive strength (UCS), plasticity index (PI) and cation exchange capacity (CEC)) for stabilized soil in contact with water. This experimental study was performed on soil treated with lime (varying from no lime to 8%) corresponding to three levels of improvement: soil improvement only, stabilization and insensitivity to water, and long-term stabilization during wetting-drying cycles. The results indicated that the UCS increases, PI and CEC decreases with the lime level. For lime levels above 4%, the behavior of the treated soil under wetting-drying was satisfactory. Mineralogical analyses indicated that the formation of calcium silicate hydrate C-S-H, ettringite C-S-A-H is responsible for the increased or decreased strength of the treated soil. CaO, SiO₂ and Al₂O₃ were three important minerals responsible for the increase or decrease in soil sample stabilization. Simple model executed in JMP statistical software was proposed and validated. The authors note that CaO and SiO₂ have the most influential effects by very low values of probability for the responses studied, which confirms the hypothesis that these models can be used to model UCS and PI in curing time and wetting-drying cycles.]]></description>
      <pubDate>Sat, 21 Dec 2019 12:03:41 GMT</pubDate>
      <guid>https://trid.trb.org/View/1672840</guid>
    </item>
    <item>
      <title>Effect of calcium and chloride based stabilizer on plastic properties of fine grained soil</title>
      <link>https://trid.trb.org/View/1657987</link>
      <description><![CDATA[In soil mechanics, water is an important constituent of soil. Hence, presence of water may alter the properties of soils significantly. Geotechnical properties of fine-grained soils are very closely related to consistency limits. The present study was aimed to investigate the effect of calcium and chloride based stabilizers, i.e. eggshell powder (ESP) and sodium chloride (NaCl), on plastic properties of randomly distributed polypropylene fiber (PPF) reinforced fine grained soil. A statistical method namely, the Taguchi technique was applied to produce trial conditions for experiments and optimization. A series of consistency limits tests was conducted on parent and treated soil in laboratory. ESP (3%-9%), NaCl (2%-6%) and PPF (0.05%-0.15%) by total dry weight of solid mixture were taken for the preparation of specimens and air entraining admixture (AEA) was also used in the experiments. Series A (W+0% AEA), Series B (W+0.05% AEA) and Series C (W+0.15% AEA) were used as the mixture liquid. Experimental results showed that the most effective material to decrease the plasticity index of the samples were PPF, ESP and NaCl for series A, series B and series C respectively. The values of plasticity index for series A, series B and series C in optimized conditions were found 1%, 3% and 1% respectively.]]></description>
      <pubDate>Tue, 29 Oct 2019 11:29:10 GMT</pubDate>
      <guid>https://trid.trb.org/View/1657987</guid>
    </item>
    <item>
      <title>Modelling of cyclic and viscous behaviour of thermomechanically loaded pearlitic steels :application to tread braked railway wheels</title>
      <link>https://trid.trb.org/View/1652374</link>
      <description><![CDATA[In service, railway wheel and rail materials are subjected to high stresses and, in some cases, elevated temperatures. The high stresses are caused by the rolling contact between wheel and rail. Furthermore, heat generated from tread braking and/or sliding between wheel and rail gives additional stress due to constrained thermal expansion. The main goal of this thesis is to improve modelling of the temperature dependent cyclic and viscous behaviour of pearlitic wheel and rail steels subjected to thermomechanical loadings. Finite element (FE) analyses are carried out of generic heavy haul wheel designs subjected to thermal loading from high power drag braking. In these analyses, the results from using a plasticity and a viscoplasticity model are compared. Both models are calibrated against results from cyclic strain controlled (low strain rate) experiments with hold-time of ER7 wheel steel at different elevated temperatures. The comparison shows an increasing influence of the choice of material model with power of the drag braking. Also, a methodology to simulate full scale brake rig tests is developed. It includes an axisymmetric thermal analysis, a 3D structural wheel-rail contact analysis and a 3D structural analysis with a traversing contact load. The wheel material behaviour is modelled by a plasticity model calibrated against cyclic strain controlled (low strain rate) experiments of ER7 steel. In addition, the infuence of important operational parameters such as axle load, maximum vehicle speed and block material is investigated with respect to the ratchetting life of the wheel tread. To improve the modelling of the behaviour of ER7 steel for a wider range of loading rates and multiaxial loading, a viscoplasticity model is adopted and calibrated against test data of ER7 steel at different temperatures for slow cyclic strain controlled tests with hold-time, ratchetting tests with rapid cycles and cyclic biaxial tests. A simulation of a brake rig experiment is used to highlight the importance of using the viscoplasticity model in the prediction of the ratchetting fatigue life. Finally, a cyclic plasticity model incorporating phase transformations is developed to examine what phases and residual stresses that are obtained in a railway wheel after repeated short term local heating followed by rolling contact. This model can be used to study thermal damage mechanisms in rail and/or wheel steels that may lead to initiation of cracks (e.g. squats (studs) in rails and crack clusters in wheels).]]></description>
      <pubDate>Tue, 17 Sep 2019 10:34:36 GMT</pubDate>
      <guid>https://trid.trb.org/View/1652374</guid>
    </item>
    <item>
      <title>Towards simulation-based optimisation of materials in railway crossings</title>
      <link>https://trid.trb.org/View/1652362</link>
      <description><![CDATA[Railway crossings are subjected to an intense load environment caused by the rail discontinuities needed to accommodate the passage of wheel flanges in intersecting traffic directions. This gives rise to high costs associated with repair and maintenance. For given traffic conditions, several approaches can be undertaken to mitigate the material degradation and hence reduce the life cycle cost. In the present thesis, the option of selecting a more suitable crossing material is explored.  To obtain a guideline for material selection, the in-track performance of different materials during the life of a crossing needs to be predicted. In this work, an existing simulation methodology is extended to improve robustness and computational efficiency. The methodology is able to account for the dynamic vehicle-track interaction, resolve the elasto-plastic wheel-rail contact, and account for the main damage mechanisms related to the running surface of a crossing.  In this thesis, the methodology is updated with a metamodel for plastic wheel-rail normal contact that is introduced to meet the computational challenge of a large number of finite element simulations. The metamodel is inspired by the contact theory of Hertz, and for a given material it computes the size of the contact patch and the maximum contact pressure as a function of the normal force and the local curvatures of the bodies in contact. The model is calibrated based on finite element simulations with an elasto-plastic material model. It is shown that the metamodel can yield accurate results while accounting for the inelastic material behaviour.]]></description>
      <pubDate>Tue, 17 Sep 2019 10:34:19 GMT</pubDate>
      <guid>https://trid.trb.org/View/1652362</guid>
    </item>
    <item>
      <title>Modeling and experimental characterization of pearlitic rail steels subjected to large biaxial strains /</title>
      <link>https://trid.trb.org/View/1652319</link>
      <description><![CDATA[Large shear strains develop in the near-surface region under the running band of railway rails. Rolling Contact Fatigue (RCF) cracks often initiate in this region, causing major problems for the railway industry. However, characterization of the constitutive and fatigue behavior of this region is difficult due to the large gradient of properties. In the present thesis, the deformed microstructure in this region is characterized. An axial-torsion test rig is used to predeform cylindrical low-cycle fatigue specimens in order to obtain material properties similar to those of the near-surface region in rails. These specimens are more suitable for further mechanical testing, compared to those resulting from many of the other predeformation methods described in the literature. The obtained material is compared to field samples in terms of the material hardness and microstructure. The microstructure is evaluated with both optical microscopy and scanning electron microscopy. This comparison shows that the predeformed material state closely resembles what is found in some used rails at a depth between 50 and 100 µm. In order to describe the behavior of the material during the large shear deformations, a sound framework for finite strain metal plasticity is needed. Several options are available in the literature, but in this thesis two frameworks for hyperelasto-plasticity with kinematic hardening are investigated. It is shown that for appropriate choices of Helmholtz' free energy these frameworks are equivalent. Furthermore, several material models formulated within this framework are evaluated in terms of their abilities to predict the mechanical response during the predeformation. Particular emphasis is put on the role of the kinematic hardening laws and how these influence the response during the biaxial loading. It is found that by combining different models from the literature, the predeformation process can be modeled accurately.]]></description>
      <pubDate>Tue, 17 Sep 2019 10:33:16 GMT</pubDate>
      <guid>https://trid.trb.org/View/1652319</guid>
    </item>
    <item>
      <title>Development of energy-based damage and plasticity models for asphalt concrete mixtures</title>
      <link>https://trid.trb.org/View/1652290</link>
      <description><![CDATA[Characterizing the full range of damage and plastic behaviour of asphalt mixtures under varying strain-rates and stress states is a complex and challenging task. One reason for this is partly due to the strain rate and temperature dependent nature of the material as well as the variation in the properties of the constituent materials that make up the composite asphalt mixture. Existing stress-based models for asphalt concrete materials are developed based on mechanics principles, but these models are, however, limited in their application for actual pavement analysis and design since rate dependency parameters are needed in the constitutive model to account for the influence of the strain rate on the stress-based yield and evolution criteria. Till date, we are yet to arrive at simple and comprehensive constitutive models that can be used to model the behaviour of asphalt mixture over a wide range of strain-rate which is experienced in the actual pavement sections. The aim of this thesis is to develop an increased understanding of the strength and deformation mechanism of asphalt mixtures through multi-scale modeling and to develop simple and comprehensive continuum models to characterize the non-linear behaviour of the material under varying stress-states and conditions. An analysis framework is developed for the evaluation of the influence of asphalt mixture morphology on its mechanical properties and response using X-Ray CT and digital image processing techniques. The procedure developed in the analysis framework is then used to investigate the existence of an invariant critical energy threshold for meso-crack initiation which serves as the basis for the development of a theory for the development of energy-based damage and plastic deformation models for asphalt mixtures. A new energy-based viscoelastic damage model is developed and proposed based on continuum damage mechanics (CDM) and the thermodynamics of irreversible processes. A second order damage variable tensor is introduced to account for the distributed damage in the material in the different principal damage directions. In this way, the material response in tension and compression can be decoupled and the effects of both tension- and compression stress states on the material behaviour can be accounted for adequately. Based on the finding from the energy-based damage model, an equivalent micro-crack stress approach is developed and proposed for the damage and fracture characterization of asphalt mixtures. The effective micro-crack stress approach takes account of the material stiffness and a critical energy threshold for micro-crack initiation in the characterization of damage and fracture properties of the mixture. The effective micro-crack stress approach is developed based on fundamental mechanics principles and it reduces to the Griffith's energy balance criterion when purely elastic materials are considered without the need for the consideration of the surface energy and a crack size in the determination of the fracture stress. A new Continuum Plasticity Mechanics (CPM) model is developed within the framework of thermodynamics to describe the plastic behaviour of asphalt concrete material with energy-based criteria derived for the initiation and evolution of plastic deformation. An internal state variable termed the "plasticity variable" is introduced to described the distributed dislocation movement in the microstructure. The CPM model unifies aspects of existing elasto-plastic and visco-plastic theories in one theory and shows particular strength in the modeling of rate-dependent plastic behaviour of materials without the need for the consideration of rate dependency parameters in the constitutive relationships. The CPM model is further extended to consider the reduction in the stiffness properties with incremental loading and to develop a unified energy-based damage and plasticity model. The models are implemented in a Finite Element (FE) analysis program for the validation of the models.]]></description>
      <pubDate>Tue, 17 Sep 2019 10:32:35 GMT</pubDate>
      <guid>https://trid.trb.org/View/1652290</guid>
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