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  • 101.
    Khavassefat, Parisa
    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.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    A computational framework for viscoelastic analysis of flexible pavements under moving loads2012In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 45, no 11, p. 1655-1671Article in journal (Refereed)
    Abstract [en]

    A general quasi-static computational procedure is established to evaluate stresses and strainsinduced in the viscoelastic flexible pavement bymoving traffic. The procedure is based on superposition principle and is computationally favourable, as itrequires only reduced incremental problem to besolved numerically. The impact of traffic speed anddensity on the mechanical response of flexible pavement is examined numerically. Results relevant fortwo major modes of pavement’s distress, i.e. crackingand rutting, are reported. It is shown that the state-ofpractice layered elastic analysis used in pavementdesign is unable to capture several important qualitative and quantitative aspects of pavements response.

  • 102.
    Khavassefat, Parisa
    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.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Dynamic Response of Flexible Pavements at Vehicle-Road Interaction2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 2, p. 256-276Article in journal (Refereed)
    Abstract [en]

    In the present paper a robust and general computational framework that captures the dynamic response of flexible pavements to a moving vehicle is presented. A finite element method is relied upon in order to establish the response function for a linear viscoelastic pavement structure with dynamic effects taken into account. In order to characterise the dynamic loads induced on the pavement by moving traffic, a quarter car model combined with measured road profiles is used. Once both the traffic loads and pavement response functions are known, the stresses and strains induced in the pavement can be obtained in the frequency-wavenumber domain through the convolution procedure. The computational procedure developed is applied in the present study to evaluate the effect of the pavement surface roughness on the pavement structure response to truck traffic loading. Stress field parameters governing fracture initiation in asphalt layers are reported for two measured road roughness profiles. It is shown that the dynamic effects at vehicle-road interaction may have a profound influence on the stresses induced in flexible pavements; therefore, these effects need to be taken into account for the accurate estimation of the road resistance to cracking.

  • 103.
    Khavassefat, Parisa
    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.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Impact of Long and Heavy Vehicles on Pavement Damage2013Conference paper (Refereed)
    Abstract [en]

    In the present paper the effect of vehicle configuration and traffic characteristics on the damage induced in pavements by traffic is investigated numerically. A three dimensional time-dependent pavement-vehicle interaction analysis is performed in order to study the impact of the parameters mentioned above on the mechanical response of flexible pavements. The analysis is based on a fast and robust computational procedure, developed by the authors. The numerical algorithm utilizes the three-dimensional finite element solution of the reduced problem of one tyre pavement interface loaded with tyre pressure. Afterwards, a superposition procedure based on fast Fourier transform techniques is applied to find the pavement response to moving loads. The method is general and capable of capturing the stress-strain response to any arbitrary loading history.One particular area of study with employing the current procedure is the analysis of long and heavy vehicle impact on pavement damage. Two major modes of distress, i.e. cracking and rutting have been discussed for 6 different truck types with 2 speeds. It is shown that an accurate numerical model provides a more accurate explanation of different distress modes. Moreover the conventional analysis and design methods with layered linear elastic behaviour assumption for asphalt layer are unable to capture several important aspects of pavement response.

  • 104.
    Khavassefat, Parisa
    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.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Non-stationary Response of Flexible pavements to Moving Vehicles2016In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 17, no 5, p. 458-470Article in journal (Refereed)
    Abstract [en]

    In this paper the pavement surface deterioration is investigated based on field measurements of surface roughness profiles obtained in Sweden. A predictive function for surface deterioration, based on average gradient of yearly measurements of the road surface profile in Swedish road network, is proposed. In order to characterise the dynamic loads induced on the pavement by moving traffic a quarter car model is used. Afterwards a non-stationary stochastic approach is used to obtain the yearly response of the pavement to moving loads. The solution is in frequency-wavenumber domain and is given for a non-stationary random case as the pavement surface deteriorates in pavement service life influencing thus the magnitude of the dynamic loads induced by the vehicles. The effect of pavement surface evolution on the stress state induced in the pavement by moving traffic is examined for a specific case of quarter car model and pavement structure. The results showed approximately a 100% increase in the dynamic component of stresses induced in the pavement.

  • 105.
    Khavassefat, Parisa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mirzadeh, Iman
    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.
    A Life Cycle Cost Approach on Minimization of Roughness-Related Damages on Flexible PavementsManuscript (preprint) (Other academic)
  • 106. Kim, B
    et al.
    Roque, R
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Laboratory Evaluation of the Effect of SBS Modifier on Cracking Resistance of Asphalt Mixtures2003In: Transportation Research Record, Vol. 1829Article in journal (Refereed)
  • 107. Kim, J.
    et al.
    Roque, R.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Integration of thermal fracture in the HMA fracture model2008In: Journal of Asphalt Paving Technologists, ISSN 0270-2932, Vol. 77, p. 631-661Article in journal (Refereed)
    Abstract [en]

    Field observations indicate that both traffic and thermal stresses affect top-down cracking performance of flexible pavements. Further evaluation of these observations will require the development and use of cracking models that can consider the effect of temperature. A rigorous analytical model was developed to assess the effect of thermal loading conditions and mixture properties on dissipated creep strain energy (DCSE) and cracking. Accumulation of DCSE in a mixture subjected to thermal stresses is much less straightforward than for load-induced stresses, and performance may be affected by the rheological aspects of the mixture other than creep. Appropriate equations were developed to calculate thermal stress development and DCSE accumulation for an asphalt mixture subjected to thermal loading cycles. Calculations performed with the resulting model showed that although top-down cracking performance in Florida was most strongly affected by traffic loading, thermal effects also affected performance. A combined system that incorporates the effect of both load- and temperature-induced damages on top-down cracking was developed and resulted in better correlation between predicted and observed top-down cracking performances.

  • 108. Kim, J.
    et al.
    Roque, R.
    Birgisson, Björn
    Interpreting dissipated energy from complex modulus data2006In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 7, no 2, p. 223-245Article in journal (Refereed)
    Abstract [en]

    An asphalt mixture's ability to absorb energy without fracturing is directly related to cracking performance of asphalt pavement. The dissipated energy per load cycle is commonly determined as the area of the hysteresis loop developed during cyclic loading of asphalt mixture. However, it is unclear whether all dissipated energy determined in this manner is irreversible and associated with damage, or whether it is at least partially reversible and not fully associated with damage. Therefore, this study was undertaken to evaluate the nature of the dissipated energy determined from the area of the hysteresis loop developed during cyclic loading of asphalt mixture. Dissipated energies determined experimentally from cyclic load tests were compared to dissipated energies predicted using rheological parameters determined from static creep tests. For a range of asphalt mixtures, the area of the hysteresis loop appeared to be strongly affected by the delayed elastic behavior of the mixture, even when cyclic response had reached steady-state conditions. Therefore, it appears that the area of the hysteresis loop is not fully associated with damage and very probably overestimates the rate of dissipated energy and damage development during cyclic load testing of asphalt mixture. Furthermore, it is generally not possible to reliably separate reversible from irreversible dissipated energy in the hysteresis loop using conventional complex modulus data. Consequently, it is recommended that irreversible dissipated energy be determined using rheological parameters obtained from static creep test data. The key is to have parameters in the rheological model that properly separate the elastic (immediate and delayed) from the viscous response, since only the viscous response is irreversible and contributes to damage.

  • 109. Kim, J
    et al.
    Roque, R
    Birgisson, Björn
    Univ Florida, Dept Civil & Coastal Engn, Gainesville, FL 32611 USA .
    Obtaining Creep Compliance Parameters Accurately From Static or Cyclic Creep Tests2005In: Performance Tests for Hot Mix Asphalt (HMA) Including Fundamental and Empirical Procedures  , 2005, Vol. 2, p. 177-197Conference paper (Refereed)
    Abstract [en]

    Obtaining creep compliance parameters that accurately represent the creep response of asphalt mixtures is critical for proper evaluation of the thermal cracking performance, as well as load induced cracking performance of asphalt pavements. A power law, which uses three parameters to describe the creep compliance curve, is commonly used for asphalt mixtures. However, the specific values of the parameters obtained can depend on both the testing and the data interpretation methods used. Different testing methods (for example, static versus cyclic creep) offer different advantages and disadvantages related to complexity in testing, as well as in the sensitivity of the data obtained from each test to the compliance parameters of interest. In general, cyclic creep tests provide greater sensitivity and accuracy at shorter loading times, while static creep tests are more accurate and reliable for the determination of the long-term creep response..

  • 110. Kim, K
    et al.
    Roque, R
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Kim, J
    Laboratory Test Methods to Uniquely Characterize the Presence and Contribution of SBS Modifiers on the Cracking Performance of Asphalt Mixtures2004In: Proceedings, Fifth International RILEM Conference on Cracking in Pavements – Mitigation, Risk Assessment and Prevention, Limoges, France, 2004Conference paper (Refereed)
  • 111. Kim, Sungho
    et al.
    Guarin, Alvaro
    Roque, Reynaldo
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Laboratory evaluation for rutting performance based on the DASR porosity of asphalt mixture2008In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 9, no 3, p. 421-440Article in journal (Refereed)
    Abstract [en]

    Research has shown that gradation characteristics determine whether the aggregate structure in asphalt mixture results in good performance. A recent study indicated that large enough aggregates should engage dominantly to form an aggregate structure that can resist deformation; also, a new approach identified the porosity of the Dominant Aggregate Size Range (DASR) as the key parameter that determines whether or not a particular gradation results in a suitable aggregate structure. This paper presents a laboratory experiment to evaluate the DASR porosity in terms of its ability to identify unsuitable aggregate structures. Fight dense-graded Superpave mixtures were designed using two aggregate types (limestone and granite). For each aggregate hype, mixtures with varying DASR porosity were produced and tested to evaluate laboratory rutting resistance. Test results indicated that the new approach successfully, separated mixtures according to their observed laboratory rutting performance, indicating that DASR porosity can serve as an effective parameter to evaluate aggregate structure.

  • 112. Kim, Sungho
    et al.
    Roque, Reynaldo
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Guarin, Alvaro
    Porosity of the Dominant Aggregate Size Range to Evaluate Coarse Aggregate Structure of Asphalt Mixtures2009In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 21, no 1, p. 32-39Article in journal (Refereed)
    Abstract [en]

    This paper presents the results from an evaluation of a new gradation-based framework developed for identifying and assessing the coarse aggregate structure of dense-graded mixtures for resistance to rutting. A theoretical packing-based analysis procedure was used to evaluate the coarse aggregate structure for hot mix asphalt mixtures. This procedure was applied to an extensive range of mixtures. A key feature of this new framework is the concept of the existence of a dominant aggregate size range (DASR). The porosity of the DASR is calculated based on an interaction diagram to evaluate the degree of particle-to-particle interaction of coarse aggregates between contiguous sieve sizes. In addition, an interaction diagram-based criteria for dense-graded Superpave mixtures are determined, as well as criteria for the porosity of the DASR. Based on the field and laboratory-based rutting performance of the mixtures evaluated in this paper, it was concluded that DASR along with the porosity of the DASR may provide a framework for evaluating the gradation of dense graded mixtures for their likely rutting potential.

  • 113. Kim, Sungho
    et al.
    Roque, Reynaldo
    Guarin, Alvaro
    Birgisson, Björn
    Univ Florida, Dept Civil & Coastal Engn, Gainesville, FL 32611 USA.
    Identification and Assessment of the Dominant Aggregate Size Range (DASR) of Asphalt Mixture2006In: Journal of Asphalt Paving Technologists, ISSN 0270-2932, Vol. 75, p. 789-814Article in journal (Refereed)
    Abstract [en]

    Coarse aggregate structure or interlock is critical for resistance to rutting, and recent work has shown that it can also play a significant role in resistance to damage and fracture. Therefore, large enough aggregates should engage dominantly in the structure for good mixture performance. This study focused on the development of a conceptual and theoretical approach to evaluate coarse aggregate structure based on gradation.In soil mechanics, it has been well established that the porosity of granular materials in the loose state is approximately constant between 45% and 50%, regardless of size or gradation. This implies that one can use porosity as a criterion to assure contact between large enough particles within the mixture to provide suitable resistance to deformation and fracture. Calculations performed for gradations associated with typical dense graded mixtures indicated that the porosity of particles retained on any single sieve was significantly greater than 50%, even for gradations associated with the maximum density line. Since many dense graded mixtures are known to provide suitable resistance to deformation and fracture, then there must be a range of contiguous coarse aggregate particle sizes that form a network of interactive particles with a porosity of less than 50%.A theoretical analysis procedure was developed to calculate the center to center spacing between specific size particles within a compacted assemblage of particles of known gradation. Calculations performed with this procedure indicated that the relative proportion of two contiguous size particles, as defined by the standard arrangement of Superpave sieves, can be no greater than 70/30 in order to form an interactive network. Thus, the 70/30 proportion can be used to determine whether particles on contiguous Superpave sieves can form an interactive network of particles in continuous contact with each other. The range of particle sizes determined to be interactive was referred to as the dominant aggregate size range (DASR) and its porosity must be no more than 50% for the particles to be in contact with each other.It was concluded that porosity of the DASR may provide a good criterion for determining the suitability of gradation for dense-graded asphalt mixture.

  • 114. Kuo, C
    et al.
    McVay, M
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Calibration of Resistance Factors for LRFD Drilled Shaft Design2002In: Transportation Research Record, Vol. 1808Article in journal (Refereed)
  • 115.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Redelius, Per
    Nynas Bitumen, Nynäs AB, Nynäshamn, Sweden.
    Interaction forces between mineral aggregates and bitumen Calculated using the Hamaker constant2010In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 11, p. 305-323Article in journal (Refereed)
    Abstract [en]

    Moisture damages to bituminous pavements leads to costly repairs. The most serious outcome of the influence of water is the loss of adhesion between binders and aggregates. This is often described as stripping. Adhesion is the ability at a molecular level of materials to stick steadfastly to one another. An alternative way of explaining the adhesion of bitumen to aggregates is presented in this paper using the Hamaker constant, a measure of the van der Waals attraction forces between two materials. The Hamaker constant is significantly lower for water as the intervening medium than for air. For the aggregates and minerals studied, the Lifshitz-van der Waals interactions contribute 65-78 percent of the 'work of adhesion' calculated by the acid-base method. The performance of the aggregates and minerals correlates well to A(total) where resistance to stripping data is available.

  • 116.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Collin, Måns
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Obstacles to Measuring Bitumen Surface Energy as it Pertains to Adhesion in AsphaltManuscript (preprint) (Other academic)
  • 117.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Krivosheeva, Olga
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Adhesion between bitumen and aggregate: implementation of spectroscopic ellipsometry characterisation and estimation of Hamaker's constant2013In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 46, no 10, p. 1737-1745Article in journal (Refereed)
    Abstract [en]

    Refractive indices of seven bitumen samples and three aggregates (typical components in flexible asphalt pavement) were determined by ellipsometry in order to predict bitumen-aggregate adhesion and bitumen-bitumen cohesion using Hamaker’s constant.

    Hamaker’s constant according to Lifshitz was introduced to the asphalt field by two of the authors to describe and estimate van der Waal’s interaction and bitumen–aggregate adhesion. Lifshitz used the refractive index to estimate the dispersive non-polar van der Waal’s interaction component of adhesion, the predominant component in adhesion between minerals and bituminous binder. The impact of an intervening thin medium such as air or water on the adhesion can be estimated using Hamaker’s coefficient, which in turn can be related to stripping potential.

    The bitumen binders studied were delivered as a paving grade 70/100 according to EN 12591:2009 and came from different bitumen suppliers. The three aggregates studied were two types of granite and one diabase.

    It is concluded from the measurement of refractive indices and calculations of the Hamaker’s constant that there was a larger spread in refractive index among the three aggregate samples studied than among the seven bitumen samples.

  • 118.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Redelius, Per
    Nynas AB, Stockholm, Sweden.
    Collin, Måns
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Characterization of stripping properties of stone material in asphalt2013In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 46, no 1-2, p. 47-61Article in journal (Refereed)
    Abstract [en]

    Aggregates and bitumen together form a composite called asphalt concrete pavement. Moisture damage to asphalt concrete pavement can occur as stripping, and is a common problem that can lead to costly repairs. There is therefore a need to understand which stone aggregates adhere best to bituminous binder and result in a minimum of stripping. Lifshitz used the refractive index to estimate the dispersive non-polar van der Waal's interaction component of adhesion, the predominant component in adhesion between minerals and bituminous binder. The impact of an intervening thin medium such as air or water on the adhesion can be estimated using Hamaker's coefficient, which in turn can be related to stripping potential. Aggregates consist of minerals and minerals consist of different elements. The objective of this study was to investigate variation in the dispersive component of minerals via their refractive indices using data from mineral data sheets. The influence of the position of elements in the periodic table and chemical composition on refractive index of minerals was examined in order to classify mineral aggregates for asphalt road building with regard to dispersive adhesive properties and expected resistance to stripping. It is clear from this study that the elemental composition of a mineral will affect its refractive index and hence its dispersive adhesion to bitumen. Aggregates and minerals have been classified according to degree of stripping in the literature. In this study it was shown that aggregates and minerals that have a refractive index higher than approximately 1.6 are expected to be less susceptible to stripping. Also, minerals containing alkali metals are sensitive to stripping since they are partially soluble in water.

  • 119.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Redelius, Per
    Nynas Bitumen, Nynäs AB, Nynäshamn, Sweden.
    Collin, Måns
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    The mechanism of adhesion between aggregates and bitumen in asphaltIn: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873Article in journal (Refereed)
  • 120.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jäverberg, Nadejda
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Low Frequency Dielectric Spectroscopy of Bitumen Binders.Manuscript (preprint) (Other academic)
  • 121.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Wallqvist, V.
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Claesson, Per
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Surface wrinkling: The phenomenon causing bees in bitumen2013In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 20, p. 6970-6976Article in journal (Refereed)
    Abstract [en]

    The so called "bee phenomenon" in bitumen has been investigated by means of AFM quantitative nanomechanical property mapping. Bees are a phenomenon that can be observed by topography measurements using AFM. The characteristic "bee" appearance comes from regions with alternating higher and lower bands in the surface topography of bitumen, which are surrounded by a flat area. The proposed mechanism for bee formation is phase separation and differential contraction during cooling from melt temperatures leading to wrinkling due to differences in the elastic modulus of the material phases. Using a laminate wrinkling model, the thickness of the bee laminate was calculated from the wavelengths and Young's moduli of the bee laminate and the matrix. It was found to vary between 70 and 140 nm for the five bitumen samples that contained significant amounts of wax.

  • 122.
    Laurell Lyne, Åsa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Wallqvist, Viveca
    SP Technical Research Institute of Sweden, Box 5607, SE-114 86 Stockholm, Sweden .
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Adhesive surface characteristics of bitumen binders investigated by Atomic Force Microscopy2013In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 113, p. 248-256Article in journal (Refereed)
    Abstract [en]

    Bitumen is a complex hydrocarbon whose composition-structure-property relationship is not well-understood. In this paper, microphase-separated topographic morphologies of unaged penetration grade 70/100 bitumen binders have been visualized by means of AFM QNM, and the relationship to local mechanical properties has been demonstrated. AFM QNM is a surface force mapping technique which measures parameters such as topography, adhesion and elastic modulus simultaneously. The resulting data can then be presented as images representing individual or overlaid parameters, e. g. topographic images with an adhesion overlay or topographic images with a modulus overlay. AFM QNM results show that the adhesive forces measured in the region surrounding (peri phase) the periodic topographic features resembling 'bees' (catana phase) and the region in the 'bee' areas are lower than the adhesive force measured in the smooth matrix (para phase). Likewise it was observed that Young's moduli in the region surrounding (peri phase) the 'bees' (catana phase) and in the 'bees' are higher than Young's modulus of the smooth matrix (para phase).

  • 123.
    Lira, Bernardita
    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.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Binder distribution model for asphalt mixtures based on packing of the primary structure2015In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 16, no 2, p. 144-156Article in journal (Refereed)
    Abstract [en]

    Film thickness describes the coating around aggregate particles on asphalt mixtures. The standard method of calculating film thickness has proven to present several limitations, such as assuming an average thickness independent of particle size, being completely independent to the porosity of the mixture and considering only one mineral type. In this paper, a binder distribution model is developed for aggregates according to size and role in the structure. The aggregates are separated into two different structures: primary structure, the load bearing one, and secondary structure, smaller material that provides stability to the skeleton. A coating thickness for these two structures is calculated from a geometrical consideration that includes the packing arrangement of particles and the effect of overlapping as the film grows. The results were compared with known rutting performance of field mixtures and moisture conditioned laboratory mixtures, showing a good correlation between film thickness and resistance to failure.

  • 124.
    Lira, Bernardita
    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.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Gradation-based framework for asphalt mixture2013In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 46, no 8, p. 1401-1414Article in journal (Refereed)
    Abstract [en]

    Aggregates are the major component of asphalt mixtures, greatly influencing the mixtures resistance to failure. The structure that is formed by the aggregates will depend mostly on the size distribution, shape and mineral composition. Coarse aggregate have a strong influence on the resistance to rutting, while fines provide stability to the mixture. In the present study a generalized framework is developed to identify the range of aggregate sizes which form the load carrying structure in hot mix asphalt and determine its quality. The method has been developed as a numerical procedure based on packing theory. Parameters like porosity and coordination number have been used to evaluate the quality of the load carrying structure and relate it to resistance to rutting. The framework has been evaluated on several field and laboratory mixtures and related to their rutting performance. The gradation analysis of the mixtures has compared favorably with the performances reported from the field and laboratory testing. The developed gradation analysis framework has proven to be a tool to identify those mixtures with a poor rutting performance based on the gradation of the aggregates.

  • 125. Masad, E.
    et al.
    Birgisson, Björn
    Al-Omari, A.
    Cooley, A.
    Analytical derivation of permeability and numerical simulation of fluid flow in hot-mix asphalt2004In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 16, no 5, p. 487-496Article in journal (Refereed)
    Abstract [en]

    Permeability is an important property that influences the performance of hot-mix asphalt (HMA). It is a function of compaction effort, and several properties of HMA such as asphalt content, and the shape and size distribution of aggregates. Due to the different laboratory and field methods for measuring permeability, and the interaction among the factors that influence its value, it would be difficult to develop an analytical equation that accurately relates permeability to all factors contributing to HMA permeability. This paper presents a simple equation for approximating the permeability of asphalt mixes. It utilizes the percent air voids and surface area of aggregates. The equation is empirical but it is derived based on the well-known Kozeny-Carman equation for calculating the permeability of granular materials. The developed equation was used successfully to fit permeability data collected from several studies that carried field and laboratory measurements of HMA permeability. A finite element model was developed to investigate the influence of the gradient of percent air voids in HMA on water flow patterns. The x-ray computed tomography was used to measure the percent air void gradients among sublayers of the asphalt mix. The permeability of these sublayers was calculated using the developed equation, and used as an input to the finite element model. The simulation results show that air void gradients in HMA encourage lateral flow in the horizontal direction and reduce the flow in the vertical direction.

  • 126. Masad, E.
    et al.
    Castelblanco, A.
    Birgisson, Björn
    Effects of air void size distribution, pore pressure, and bond energy on moisture damage2006In: Journal of Testing and Evaluation, ISSN 0090-3973, E-ISSN 1945-7553, Vol. 34, no 1, p. 15-23Article in journal (Refereed)
    Abstract [en]

    The relationship between hot mix asphalt moisture damage, air void structure, pore pressure, and cohesive and adhesive bond energies was investigated in this study using mixes with two different aggregate types (limestone and granite). Each of the mixes was designed with varying gradations to obtain different air void distributions among specimens. Moisture damage was evaluated using parameters derived based on the principles of fracture mechanics. Air void distribution was analyzed using a probabilistic approach with the assistance of X-ray computed tomography and image analysis techniques. The cohesive and adhesive bond energies of the mix were calculated using experimental measurements of aggregate and asphalt surface energies. Permeability, which controls the ability of the water to infiltrate into and drain out of the mix, was expressed as a function of statistical parameters of the air void distribution. Ranges of air void distributions and permeability were identified for each of the limestone and granite mixes at which moisture damage was maximum. The difference in moisture damage between the granite and limestone mixes was explained based on air void distribution and cohesive and adhesive bond energies.

  • 127. Masad, Eyad
    et al.
    Birgisson, Björn
    KTH, Superseded Departments, Civil and Architectural Engineering.
    Omari, Aal
    Cooley, A.
    Analysis of Permeability and Fluid Flow in Asphalt Mixes2004In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 16, no 5Article in journal (Refereed)
  • 128. McVay, M.
    et al.
    Birgisson, Björn
    University of Florida.
    Lee, S.
    Influence of Sample Size, Testing and Pile/Shaft Model Variability on LRFD Resistance Factors2004In: Geotechnical Special Publication, ISSN 0895-0563, Vol. 2Article in journal (Refereed)
  • 129. McVay, M
    et al.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Nguyen, T
    Kuo, C
    Uncertainty in LRFD phi, Factors for Driven Prestressed Concrete Piles2002In: Transportation Research Record, Vol. 1808Article in journal (Refereed)
  • 130. McVay, M. C.
    et al.
    Birgisson, Björn
    Zhang, L. M.
    Perez, A.
    Putcha, S.
    Load and resistance factor design (LRFD) for driven piles using dynamic methods - A Florida perspective2000In: ASTM geotechnical testing journal, ISSN 0149-6115, E-ISSN 1945-7545, Vol. 23, no 1, p. 55-66Article in journal (Refereed)
    Abstract [en]

    The parameters for load and resistance factor design (LRFD) of driven piles using dynamic methods are presented based on a database of 218 pile cases in Florida. Eight dynamic methods were studied: ENR, modified ENR, FDOT, and Gates driving formulas, Case Analysis with Wave Analysis Program (CAPWAP), Case Method for Pile Driving Analyzer (PDA), Paikowsky's energy method, and Sakai's energy method. It was demonstrated that the modern methods based on wave mechanics, such as CAPWAP, PDA, and Paikowsky's energy methods, are roughly twice as cost effective to reach the target reliability indices of 2.0 to 2.5 (failure probability = 0.62 to 2.5%) as the ENR and modified ENR driving formulas. The Gates formula, when used separately on piles with Davisson capacities smaller or larger than 1779 kN, has an accuracy comparable to the modem methods. The utilizable measured Davisson capacity, defined as phi/lambda (ratio of resistance/mean capacity) obtained from testing at beginning of redrive (BOR), is only slightly larger than the end of drive (EOD) values. Furthermore, past practice with driving formulas reveals the existence of a large redundancy in pile groups against failure. The latter suggests the use of a lower relatively reliability target index, B-T = 2.0 (p(f) = 2.5%) for single pile design. Also, the utilizable measured Davisson capacity, phi/lambda, for all the dynamic methods studied, is quite similar to published values (Lai et al. 1995; Sid; 1985) for static estimates from in situ tests.

  • 131. McVay, M
    et al.
    Ellis, R
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Consolazio, G
    Putcha, S
    Lee, S
    Use of LRFD, Cost and Risk: Designing a Drilled-Shaft Load Test Program in Florida Limestone2003In: Transportation Research Record, Vol. 1849Article in journal (Refereed)
  • 132. Mehta, Y
    et al.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Choubane, B
    Rubblization Over Soft Soils - The Florida Experience2002In: International Journal of Road Materials and Pavement Design, Vol. 3Article in journal (Refereed)
  • 133.
    Mirzadeh, Iman
    et al.
    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.
    Accommodating Energy Price Volatility in Life Cycle Cost Analysis of Asphalt PavementsIn: Journal of Civil Engineering and Management, ISSN 1392-3730, E-ISSN 1822-3605Article in journal (Refereed)
  • 134.
    Mirzadeh, Iman
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Butt, Ali Azhar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Toller, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies (moved 20130630).
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    A Life Cycle Cost Approach based on the Calibrated Mechanistic Asphalt Pavement Design Model2012Conference paper (Refereed)
    Abstract [en]

    Life Cycle Cost Analysis (LCCA) provides cost estimation over the life time of a project and thereby helps road administrations, designers, and contractors with choosing an economical design. Calculation of the costs can be based on a pavement design model, such as the Calibrated Mechanistic model (CM), in order to capture the mechanical behaviour of the asphalt pavement. This study aimed to develop an approach for performing comparative LCCA in order to find the most economical design alternative in terms of the total cost for the pavement design life. The integrated LCCA-CM approach was used to evaluate different design alternatives with different rehabilitation intervals for asphalt pavements. 

  • 135.
    Mirzadeh, Iman
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Butt, Ali Azhar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Toller, Susanna
    Swedish Transport Administration, Sweden.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Life cycle cost analysis based on the fundamental cost contributors for asphalt pavements2014In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 10, no 12, p. 1638-1647Article in journal (Refereed)
    Abstract [en]

    A life cycle costing system should include the key variables that drive future costs in order to provide a framework for reducing the risk of under- or overestimating the future costs for maintenance and rehabilitation activities. In Sweden, price of oil products is mostly affected by the global economy rather than by the national economy. Whereas the price index of oil products has had a high fluctuation in different time periods, the cost fluctuation related to labour and equipment has been steady and followed the consumer price index (CPI). Contribution of the oil products was shown to be more than 50% of the total costs regarding construction and rehabilitation of asphalt pavements in Sweden. Consequently, it was observed that neither Swedish road construction price index (Vagindex) nor CPI has properly reflected the price trend regarding the asphalt pavement construction at the project level. Therefore, in this study, a framework is suggested in which energy- and time-related costs are treated with different inflation indices in order to perform a better financial risk assessment regarding future costs.

  • 136. Montepara, Antonio
    et al.
    Romeo, Elena
    Birgisson, Bjorn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering.
    Tebaldi, Gabriele
    Strain Localization and Damage Distribution in SBS Polymer Modified Asphalt Mixtures2010In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 11, no 4, p. 899-915Article in journal (Refereed)
    Abstract [en]

    A laboratory investigation was conducted to estimate the macroscopic cracking response of Styrene Butadiene Styrene (SBS) polymer modified asphalt mixtures by analyzing the localized strain distribution within the material microstructure. Five asphalt mixtures composed by the same aggregate gradation but different SBS modified asphalt binders were produced in the laboratory. An in-house developed Digital Image Correlation (DIC)-based system was employed to obtain 2D full-field strain maps of the specimens during tensile loading. Strain distributions were observed from three different test configurations, namely the Indirect Tensile Test (IDT), the Semi-Circular Bending (SCB) test and the Three-Point Bending (3PB) test. The cracking performances of the mixtures were evaluated using a viscoelastic fracture mechanics-based model entitled HMA Fracture Mechanics. The results clearly show the beneficial effect of SBS polymer modifier in redistributing the stress within the mastic.

  • 137. Myers, L
    et al.
    Roque, R
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Propagation Mechanisms for Surface-Initiated Longitudinal Wheel Path Cracks2001In: Transportation Research Record, Vol. 1778Article in journal (Refereed)
  • 138.
    Namutebi, May
    et al.
    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.
    Bagampadde, Umaru
    Development of a gyratory compaction procedure for laterite gravels treated with foamed bitumen2013In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 14, no 3, p. 256-264Article in journal (Refereed)
    Abstract [en]

    Determining of the optimum density of the compacted foamed bitumen-treated materials is an important part of determining the field placement conditions. Laterite gravels tend to be highly susceptible to breakdown during laboratory compaction with the standard Proctor hammer, which may not be representative of field conditions. In this paper, a new method is presented for determining the optimal compaction characteristics of laterite gravels-foamed bitumen mixes. A gyratory compactor was used for compaction. The modified locking point concept was used to determine the number of gyrations to compact mixes of laterite gravels and foamed bitumen. The optimal compaction moisture content was subsequently established at this point. The average number of gyrations that gave the locking point was 44; optimum moisture content (OMC) for compaction varied from 86% to 92% for gravels only. The modified locking point seems to be suitable for determining the optimal compaction characteristics of these mixes.

  • 139.
    Namutebi, May
    et al.
    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.
    Bagampadde, Umaru
    Department of Civil Engineering, Makerere University, Kampala, Uganda.
    Foamed bitumen in bituminous paving technology : state-of-the-artManuscript (preprint) (Other academic)
  • 140.
    Namutebi, May
    et al.
    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.
    Bagampadde, Umaru
    Department of Civil Engineering, Makerere University, Kampala, Uganda.
    Foaming Effects on Binder Chemistry and Aggregate Coatability using Foamed Bitumen2011In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 12, no 4, p. 821-847Article in journal (Refereed)
    Abstract [en]

    Foaming effects on binder chemistry were investigated using two bitumens from different sources with similar grades. Infrared spectroscopy techniques were done on neat and foamed bitumen samples. Aggregate particle coating with foamed bitumen was studied using Rice density and surface energy concepts. Infrared spectra results showed that foaming does not change the bitumen chemistry. Rice density tests showed that the aggregate size mainly influenced binder coating of aggregate particles, bitumen was mostly concentrated within the fine fraction where foamed bitumen was used. Surface energy results revealed that foamed bitumen possesses higher coating attributes than neat bitumen. Film thickness results implied that aggregate size and surface area, expansion ratio and binder viscosity influences binder thickness.

  • 141.
    Namutebi, May
    et al.
    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.
    Bagampadde, Umaru
    Department of Civil Engineering, Makerere University, Kampala, Uganda.
    Proposed gyratory compaction procedure for determining the optimal compaction characteristics of laterite gravels treated with foamed bitumenArticle in journal (Other academic)
  • 142.
    Namutebi, May
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Bagampadde, Umaru
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    A review of some aspects for foamed bitumen technologyManuscript (preprint) (Other academic)
  • 143.
    Namutebi, May
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Makerere University, Uganda.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Guarin, Alvaro
    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.
    Exploratory study on bitumen content determination for foamed bitumen mixes based on porosity and indirect tensile strength2017In: International journal of traffic and transportation engineering, ISSN 2325-0062, E-ISSN 2325-0070, Vol. 4, no 2, p. 131-144Article in journal (Refereed)
    Abstract [en]

    Optimum bitumen content determination is one of the major aims for foamed bitumen mix design. However, mix design procedures for foamed bitumen mixes are still under development. In this paper a method to determine the optimum bitumen content for given foamed bitumen mix based on primary aggregate structure porosity and indirect tensile strength criterion is proposed. Using packing theory concepts, the aggregate gradation is divided into three aggregate structures which are oversize, primary and secondary structures. Porosity for the primary aggregate structure is determined for given bitumen contents. A maximum value for porosity of 50% for the primary aggregate structure is used to choose initial bitumen content. Furthermore, a minimum indirect tensile strength criteria is suggested to refine this bitumen content. This method enables a bitumen content value to be chosen prior to the start of experimental work, as porosity is expressed in terms of physical parameters such as aggregate and binder specific gravity, and aggregate gradation which are known before the mix design process. The bitumen content is then later refined when the indirect tensile strength is determined in the laboratory. This method would reduce resources such as time and materials that may be required during the mix design procedure.

  • 144. Novak, M
    et al.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    McVay, M
    Effects of Vehicle Speed and Permeability on Pore Pressures in Hot Mix Asphalt Pavements2003In: Proceedings, 2nd MIT Conference on Computational Fluid and Solid Mechanics, June 17-20, Massachusetts Institute of Technology, Cambridge, MA, Elsevier Science Ltd., Boston , 2003, Vol. 1Conference paper (Refereed)
  • 145. Novak, M.
    et al.
    Birgisson, Björn
    Roque, R.
    Near-surface stress states in flexible pavements using measured radial tire contact stresses and ADINA2003In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 81, no 11-aug, p. 859-870Article in journal (Refereed)
    Abstract [en]

    The finite element code ADINA was used to identify the three-dimensional stress states in a typical flexible pavement configuration, resulting from measured radial tire contact stresses. The predictions show that measured radial tire contact stresses result in stress states being both larger in magnitude and more focused near the surface than those obtained from traditional uniform vertical loading conditions. In terms of effects of possible pavement damage mechanisms, predicted high near-surface shear stresses may be a part of an explanation for near-surface rutting failure modes, as supported by near-surface slip planes seen in the field.

  • 146. Novak, M
    et al.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Roque, R
    Three-Dimensional Finite Element Analysis of Measured Tire Contact Stresses and Their Effects on Instability Rutting of Asphalt Mixture Pavements2003In: Transportation Research Record, Vol. 1853Article in journal (Refereed)
  • 147. Novak, M.
    et al.
    Birgisson, Björn
    Dept. of Civ. and Coast. Engineering, University of Florida.
    Roque, R.
    Choubane, B.
    One-way and two-way directional heavy-vehicle simulator loading effects on rutting in hot-mix asphalt pavements2004In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 1896, p. 208-214Article in journal (Refereed)
    Abstract [en]

    Instability rutting generally occurs within the top 5 cm (2 in.) of the asphalt layer when the structural properties of the asphalt concrete are inadequate to resist the stresses imposed on it. It is generally believed that near-surface transverse shear stresses perpetuate instability rutting. Field observations of heavy-vehicle simulator testing noted greater rutting in one-way directional loading than with two-way directional loading, even at lower temperatures and with longer rest periods between load applications. An analysis of stress states in the asphalt pavement layer using the three-dimensional finite element commercial code ADINA showed that longitudinal stress path patterns varied between the different directional loadings. A hypothesis was developed that the differences in longitudinal plane stress path patterns between one-way and two-way directional loading could be attributed to the different levels of rutting. A viscoelastic model with load applications simulating the different directional loadings was constructed and used to test this hypothesis. The viscoelastic model results indicated qualitatively that even with greater relaxation times, one-way directional loading produces greater strains.

  • 148. Nukunya, B
    et al.
    Roque, R
    Tia, M
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Evaluation of VMA and Other Volumetric Properties as Criteria for the Design and Acceptance of Superpave Mixtures2001In: Journal of Asphalt Paving Technologists, Vol. 70Article in journal (Refereed)
  • 149.
    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.

  • 150.
    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.

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