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  • 1.
    Dinegdae, Yared H.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Onifade, Ibrahim
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mechanics-based Topdown Fatigue Cracking Initiation Prediction Framework for Asphaltic Pavements2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 4Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Onifade, Ibrahim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Continuum Plasticity Mechanics (CPM) - An energy-based plasticity model - Application to asphalt concrete mixtures.In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146Article in journal (Refereed)
    Abstract [en]

    A new generalized energy-based elasto-plastic constitutive model for both pressure-sensitive and pressure insensitive materials is developed and presented in this paper. The model is developed with the energy formulation which inherently captures the rate-sensitivity and can be used to model a wide range of materials ranging from rate-dependent materials such as polymers and asphalt concrete to rate-independent materials such as steel. No additional rate-dependency parameters is required to model rate dependent behaviour at different strain-rates. The new energy-based plasticity formulation takes a similar form as the conceptsused in continuum damage mechanics with the plastic strain transformed into a plasticity variable whichenters into the formulation to obtain the corresponding stress and strain due to the applied or subjected load conditions. The new energy-based plasticity formulation fits nicely into the thermodynamics framework thereby providing a true unifying framework for coupling damage and plasticity

  • 3.
    Onifade, Ibrahim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Damage and Fracture Characterization of Asphalt Concrete Mixtures using the Equivalent Micro-crack Stress ApproacIn: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526Article in journal (Refereed)
    Abstract [en]

    In this paper, a new parameter termed ”equivalent micro-crack stress” (σmc) is proposed for characterizingthe cracking performance of asphalt mixtures. The ”equivalent micro-crack stress” (σmc) is a function ofthe material stiffness and a critical micro-crack initiation threshold (MCIT). The ”equivalent micro-crackstress” (σmc) takes a similar form as the failure stress obtained from the Griffith energy balance equation.The MCIT incorporates the influence of the fracture work and the size and spatial distribution of the airvoids in the determination of the material cracking performance. Experimental tests are carried out toobtain the (σmc) to characterize the cracking performance of unmodified and wax modified mixtures usingthe Superpave IDT tests at low temperature range (i.e. -20oC, -10oC and 0oC). The result shows that the ”equivalent micro-crack stress” (σmc) gives a good indication of the material cracking performance ofthe unmodified and wax modified mixtures. The result of numerical simulations of the fatigue behaviouralso shows that the relationship between the number of cycles to micro-crack formation (Nmc) and σmc can be used to distinguish the wax modified mixtures from the unmodified mixture.

  • 4.
    Onifade, Ibrahim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Development of a Morphology-based Analysis Framework for Asphalt Pavements2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The morphology of asphalt mixtures plays a vital role in their properties and behaviour. The work in this thesis is aimed at developing a fundamental understanding of the effect of the asphalt morphology on the strength properties and deformation mechanisms for development of morphology-based analysis framework for long-term response prediction. Experimental and computational methods are used to establish the relationship between the mixture morphology and response. Micromechanical modeling is employed to understand the complex interplay between the asphalt mixture constituents resulting in strain localization and stress concentrations which are precursors to damage initiation and accumulation. Based on data from actual asphalt field cores, morphology-based material models which considers the influence of the morphology on the long-term material properties with respect to damage resistance, healing and ageing are developed. The morphology-based material models are implemented in a hot-mix asphalt (HMA) fracture mechanics framework for pavement performance prediction. The framework is able to predict top-down cracking initiation to a reasonable extent considering the variability of the input parameters. A thermodynamic based model for damage and fracture is proposed. The results from the study show that the morphology is an important factor which should be taken into consideration for determining the short- and long-term response of asphalt mixtures. Further understanding of the influence of the morphology will lead to the development of fundamental analytical techniques in design to establish the material properties and response to loads. This will reduce the empiricism associated with pavement design, reduce need for extensive calibration and validation, increase the prediction capability of pavement design tools, and advance pavement design to a new level science and engineering.

  • 5.
    Onifade, Ibrahim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Development of Energy-based Damage and Plasticity Models for Asphalt Concrete Mixtures2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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. The result shows that the energy-based damage and plastic deformation models are capable of predicting the behaviour of asphalt concrete mixtures under varying stress-states and strain-rate conditions. The work in this thesis provides the basis for the development of more fundamental understanding of the asphalt concrete material response and the application of sound and solid mechanics principles in the analysis and design of pavement structures.

  • 6.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Birgisson, B.
    Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model2016In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, p. 1-19Article in journal (Refereed)
    Abstract [en]

    This paper presents a new interpretation for the Superpave IDT strength test based on a viscoelastic-damage framework. The framework is based on continuum damage mechanics and the thermodynamics of irreversible processes with an anisotropic damage representation. The new approach introduces considerations for the viscoelastic effects and the damage accumulation that accompanies the fracture process in the interpretation of the Superpave IDT strength test for the identification of the Dissipated Creep Strain Energy (DCSE) limit from the test result. The viscoelastic model is implemented in a Finite Element Method (FEM) program for the simulation of the Superpave IDT strength test. The DCSE values obtained using the new approach is compared with the values obtained using the conventional approach to evaluate the validity of the assumptions made in the conventional interpretation of the test results. The result shows that the conventional approach over-estimates the DCSE value with increasing estimation error at higher deformation rates.

  • 7.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, B.
    Damage and fracture characterization of asphalt concrete mixtures using the equivalent micro-crack stress approach2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 148, p. 521-530Article in journal (Refereed)
    Abstract [en]

    In this paper, a new parameter termed “equivalent micro-crack stress” (σmc) is proposed for the evaluation of the cracking performance of asphalt mixtures with respect to their resistance to the initiation of micro-crack. The “equivalent micro-crack stress” (σmc) is a function of the material stiffness and the “micro-crack initiation threshold” (MCIT). The MCIT is a critical strain energy density at the instance of initiation of micro-crack. Experimental testing is carried out for the evaluation of the cracking performance of unmodified and wax modified asphalt mixtures using the Superpave IDT tests at −20 °C, −10 °C and 0 °C. The low temperature range is used in the study to minimize the effect of viscoplastic dissipation on the material cracking behaviour. The result shows that the “equivalent micro-crack stress” (σmc) gives a good indication of the material cracking performance of the unmodified and wax modified mixtures. A Finite Element Analysis is performed to assess the validity of the proposed approach under cyclic loading condition in the controlled-stress mode. The result shows that there is a good agreement between the material cracking performance in both monotonic and cyclic loading conditions using the proposed approach. The higher the “effective micro-crack stress” (σmc), the better the fracture performance of the mixture.

  • 8.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE). Aston University, UK .
    Investigation of Energy-Based Crack Initiation Threshold from Meso-Scale Asphalt Concrete Response2016In: 8th RILEM International Conference on Mechanisms of Cracking and Debonding in Pavements, Springer Netherlands, 2016, p. 679-685Conference paper (Refereed)
    Abstract [en]

    The existence of a fundamental energy threshold for meso-scale crackinitiation is investigated using micromechanical modeling techniques. X-rayComputed Tomography (CT) is used to acquire the internal structure of an asphaltconcrete mixture while Digital Image Processing (DIP) techniques is used to segment and analyze the different phases present in the mixture. Finite Element (FE)modeling is used to simulate a tensile loading condition to establish a critical micromechanical criterion for meso-scale crack initiation. The meso-scale asphaltconcrete mixture is subjected to different loading rates to obtain the global strainenergy density at the instance when the critical micromechanical crack-initiationcriterion threshold is attained at different deformation rates. The result from thestudy shows that there exists a fundamental global strain energy density thresholdthat is invariant of the rate of loading at the instance of meso-scale crack initiation.The result of this study also shows the potential of the use of X-Ray computedtomography in understanding the cracking phenomenon in asphalt mixture.

  • 9.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, Björn
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Energy-Based Damage and Fracture Framework for Viscoelastic Asphalt Concrete2015In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 145, p. 67-85Article in journal (Refereed)
    Abstract [en]

    A framework based on the continuum damage mechanics and thermodynamics of irreversible processes using internal state variables is used to characterize the distributed damage in viscoelastic asphalt materials in the form of micro-crack initiation and accumulation. At low temperatures and high deformation rates, micro-cracking is considered as the source of nonlinearity and thus the cause of deviation from linear viscoelastic response. Using a non-associated damage evolution law, the proposed model shows the ability to describe the temperature-dependent processes of micro-crack initiation, evolution and macro-crack formation with good comparison to the material response in the Superpave indirect tensile (IDT) strength test.

  • 10.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Dinegdae, Yared H.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Birgisson, Björn
    Hierarchical approach for fatigue cracking performance evaluation in asphalt pavements2017In: Frontiers of Structural and Civil Engineering, ISSN 2095-2430, E-ISSN 2095-2449, Vol. 11, no 3, p. 257-269Article in journal (Refereed)
    Abstract [en]

    In this paper, a hierarchical approach is proposed for the evaluation of fatigue cracking in asphalt concrete pavements considering three different levels of complexities in the representation of the material behaviour, design parameters characterization and the determination of the pavement response as well as damage computation. Based on the developed hierarchical approach, three damage computation levels are identified and proposed. The levels of fatigue damage analysis provides pavement engineers a variety of tools that can be used for pavement analysis depending on the availability of data, required level of prediction accuracy and computational power at their disposal. The hierarchical approach also provides a systematic approach for the understanding of the fundamental mechanisms of pavement deterioration, the elimination of the empiricism associated with pavement design today and the transition towards the use of sound principles of mechanics in pavement analysis and design.

  • 11.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, Björn
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Towards Asphalt Mixture Morphology Evaluation with the Virtual Specimen Approach2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    The morphology of asphalt mixture can be defined as a set of parameters describing the geo-metrical characteristics of its constituent materials, their relative proportions as well as spatialarrangement in the mixture. The present study is carried out to investigate the effect of themorphology on its meso- and macro-mechanical response. An analysis approach is used forthe meso-structural characterisation based on the X-ray computed tomography (CT) data.Image processing techniques are used to systematically vary the internal structure to obtaindifferent morphology structures. A morphology framework is used to characterise the aver-age mastic coating thickness around the main load carrying structure in the structures. Theuniaxial tension simulation shows that the mixtures with the lowest coating thickness exhibitbetter inter-particle interaction with more continuous load distribution chains between adja-cent aggregate particles, less stress concentrations and less strain localisation in the masticphase.

  • 12.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Asphalt Internal Structure Characterization with X-Ray Computed Tomography and Digital Image Processing2013In: Multi-Scale Modeling and Characterization of Infrastructure Materials: Proceedings of the International RILEM Symposium Stockholm, June 2013, Springer Netherlands, 2013, p. 139-158Conference paper (Refereed)
    Abstract [en]

    In this paper, detailed study is carried out to develop a new workflow from image acquisition to numerical simulation for the asphalt concrete microstructures. High resolution computed tomography scanned images are acquired and the image quality is improved using digital image processing techniques. Nonuniform illumination is corrected by applying an illumination profile to correct the background and flat-fields in the image. Distance map based watershed segmentation are used to segment the phases and separate the aggregates. Quantitative analysis of the micro-structure is used to determine the phase volumetric relationship and aggregates characteristics. The result of the quantitative analysis showed a very high level of reliability. Finite Element simulations were carried out with the developed micro-mechanical meshes to capture the strength and deformation mechanisms of the asphalt concrete micro-structure. From the micro-mechanical investigation the load transfer chains, higher strength characteristics and high stress localization at the mastic interface between adjacent aggregates was shown.

  • 13.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Effect of micro-scale morphological parameters on meso-scale response of Asphalt Concrete2014In: Asphalt Pavements - Proceedings of the International Conference on Asphalt Pavements, ISAP 2014, CRC Press, 2014, p. 1775-1784Conference paper (Refereed)
    Abstract [en]

    With recent advancement in the use of X-Ray Computed Tomography to capture the internal structure of Asphalt Concrete (AC), results have shown several possibilities to account for the distribution of the different phases in the mix and quantify them in a reliable way. The morphology of asphalt mixtures which includes the aggregate size gradation and the distribution of the air-voids and bitumen phase are captured in a single morphological parameter called the Primary Structure (PS) coating thickness-(Tps). In this study, the effect of variations in the morphological micro-structural property on the mesoscale response of three (3) AC samples is examined using the 3D Finite Element Method (FEM). The AC internal geometry is acquired using X-Ray Computed Tomography (CT); the distribution of the aggregates, mastic and air-voids phase is considered and obtained using Digital Imaging Processing (DIP) techniques. Using a surface-based cohesive behavior and assuming a predominant adhesive failure at the interface between the mastic and aggregate, a maximum traction criterion is used to obtain the damage propensity of the different mixtures. The result of the analysis shows that the microstructural morphological parameter Tps adequately captures the meso-scale response of the mixtures; there exist an inverse relationship between mixture strength characterization and the morphological parameter Tps.

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