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  • 1. Birgisson, Björn
    et al.
    Soranakom, C.
    Napier, J. A. L.
    Roque, R.
    Microstructure and fracture in asphalt mixtures using a boundary element approach2004In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 16, no 2, p. 116-121Article in journal (Refereed)
    Abstract [en]

    This paper describes the use of the displacement discontinuity boundary element method to model the microstructure of asphalt mixtures. The problem of indirect tension test (IDT) was used to demonstrate the application of the method in the modeling of the cracking behavior of asphalt mixtures. An IDT sample was modeled by three sets of displacement discontinuity boundary elements based on location and function: (1) on the periphery of the specimen, (2) inside the specimen to represent the aggregate structure, and (3) internal fracture path elements inside the aggregate structure. The mastic was modeled by a nonlinear failure law. The simulation of the cracking behavior of the IDT test with this method showed a good agreement with laboratory observations. The predicted stress-strain curves matched the experimental results for both vertical compressive stress and horizontal tensile stress. Crack patterns from these simulations were also similar to the patterns observed visually in the laboratory. In summary, explicit fracture modeling has shown promise as a tool for studying the crack growth and localization of asphalt mixtures.

  • 2.
    Edvardsson, Karin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Magnusson, Rolf
    Dalarna Högskolan .
    Impact of fine materials content on the transport of dust suppressants in gravel road wearing courses2011In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 23, no 8, p. 1163-1170Article in journal (Refereed)
    Abstract [en]

    A significant problem when dust-suppressing agents are used on gravel roads is that they tend to leach during rainfall. The purpose of this study is to illustrate this problem by using laboratory studies and studies in situ. Both capillary rise and leaching of suppressants were examined by using cylinders filled with wearing course material. Chloride was more prone than lignosulphonate to transport upwards by means of capillary rise, and therefore, it showed a more effective performance over a longer period of time. Optimal percentages of fine material for minimal lignosulphonate and chloride leaching were found to be 15% by weight and 10-15% by weight, respectively. Ions of calcium chloride seemed to flocculate clay particles, which probably prevents them from leaching. To study the in situ longevity of fine material in general, calcium carbonate, mesa, was used as a marker. The fine material in gravel wearing courses must be replenished regularly. Mesa loss was up to 80% after 1 year.

  • 3.
    Karlsson, Robert
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Isacsson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Material-related aspects of asphalt recycling-state-of-the-art2006In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 18, no 1, p. 81-92Article in journal (Refereed)
    Abstract [en]

    Current knowledge on material-related aspects of asphalt recycling with focus on findings from fundamental studies is summarized. By way of introduction, a general description of different types of asphalt recycling methods is given, after which a more detailed compilation of material-related knowledge is presented. Special attention is given to the binder rejuvenation process at asphalt recycling, that is the restoration of reclaimed binder properties. Studies concerning properties of recycled mixtures are also summarized.

  • 4. Kim, Hyunwook
    et al.
    Arraigada, Martin
    Raab, Christiane
    Partl, Manfred
    Empa Swiss Fed Labs Mat Testing & Res, CH-8600 Dubendorf, Switzerland.
    Numerical and Experimental Analysis for the Interlayer Behavior of Double-Layered Asphalt Pavement Specimens2011In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 23, no 1, p. 12-20Article in journal (Refereed)
    Abstract [en]

    Bonding characteristics between pavement layers have an important influence on responses of pavement structures. This paper deals with this subject by analyzing the interlayer behavior of double-layered asphalt (DLA) specimens taken from an in-service motorway using a coaxial shear test (CAST) and a layer-parallel direct shear (LPDS) test. To analyze and model the influence of the interlayer condition, finite-element simulations of CAST DLA specimens were conducted. In the models, both idealized fully bonded and no-bonding assumptions were used to characterize the interlayer behavior of DLA specimens. Experimental results presented for CAST and LPDS tests demonstrate that there is a strong influence of temperature in the interlayer bonding mechanism. At lower temperatures, there is an increase on the bonding strength produced by the binder stiffening and aggregate interlocking. Further, it was observed that comparisons of CAST experimental and numerical results indicate that the interlayer can be close to the fully bonded condition at low temperatures below 20 degrees C while the interlayer, at higher temperatures, behaves between fully bonded and no-bonding idealized conditions.

  • 5. 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.

  • 6.
    Lundstrom, Robert
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Isacsson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Linear viscoelastic and fatigue characteristics of styrene-butadiene-styrene modified asphalt mixtures2004In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 16, no 6, p. 629-638Article in journal (Refereed)
    Abstract [en]

    Three styrene-butadiene-styrene coblock polymer modified asphalt concrete mixtures (70/100M5, 160/220M5, and 160/ 220M10) are characterized using complex modulus and fatigue testing. The compositions of the materials investigated are identical (aggregate, size distribution, binder, and void contents) and differ solely regarding binder characteristics. The modified binders are manufactured using two base bitumens (70/100 and 160/220) modified by a styrene-butadiene-styrene coblock polymer. The fatigue tests are carried out at three different temperatures (0, 10, and 20degreesC) using both stress- and strain-controlled modes. A continuum damage model is used to investigate its ability to characterize fatigue of polymer modified mixtures. The results indicate that the continuum damage model is suitable for characterizing the materials at the test conditions used (mode of loading, excitation amplitude, and testing temperature) in that visually similar material functions are obtained. Using statistical analysis, it was indicated that strain amplitude does not significantly influence the model parameters of the characteristic material functions. However, even though different loading conditions lead-to apparently similar material functions, the model parameter values were actually significantly affected by the testing temperature used. Predictions of fatigue path, including number of cycles to failure, based on the material functions indicate reasonable accuracy.

  • 7.
    Lundström, Robert
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Di Benedetto, H
    Isacsson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway and Railway Engineering (closed 20110301).
    Influence of asphalt mixture stiffness on fatigue failure2004In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 16, no 6, p. 516-525Article in journal (Refereed)
    Abstract [en]

    This paper examines the question of an appropriate failure criterion for asphalt fatigue characterization. The results presented are based on cyclic fatigue tests and obtained from three mixtures containing different penetration grade bitumens from one and the same source. The mixtures are tested at 0, 10, and 20degreesC using uniaxial testing (tension/compression) on cylindrical samples. It is found that failure can be demonstrated by studying the evolution of the strain field using three parallel extensometers (separated by 120degrees around the specimen). The failure arises from coalescence of microcracks (damage localization). The decrease in stiffness at failure is related to mixture stiffness, where stiff materials (low temperature and/or mixtures containing low pen grade binder) show comparatively small decrease. A statistical approach based on fatigue tests carried out at different temperatures is suggested, an approach which uses stiffness degradation as a measure of critical fatigue stiffness. The advantage of such a failure criterion compared to the classical failure criterion (decrease in stiffness by 50%) for different temperatures is discussed. Using the proposed criterion, higher consistency in results is achieved compared to results obtained using the classical failure criterion.

  • 8. 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.

  • 9. 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)
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