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  • 51.
    Partl, Manfred
    et al.
    EMPA, Swiss Federal Laboratories for Materials Testing and Research, Road Engineering and Sealing Components, Dübendorf, Switzerland.
    Canestrari, Francesco
    Grilli, A.
    Gubler, R.
    Characterization of Water Sensitivity of Asphalt Mixtures with Coaxial Shear Test2008In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 9, no 2, p. 247-270Article in journal (Refereed)
    Abstract [en]

    The CoAxial Shear Test (CAST) performs fatigue test under simultaneous action Of dynamic loading, temperature cycles and water, and modulus test on wet or dry specimen. Both a dense graded and an open graded mixture were studied at different air void content. The water sensitivity of both mixtures was determined by comparing fatigue performance of dry and wet tests. Additionally the effects of water action, temperature and loading cycles were also investigated by comparison of modulus test before (undamaged specimen) and after (damaged specimen) each fatigue test. The introduced Water Sensitivity Index for fatigue test confirms that water damage in asphalt pavements is considerably related to air voids. Finally, the modulus test analysis allowed explaining also the different consequences of environmental factors on viscoelastic properties of asphalt mixtures by using the Standard Linear Solid model.

  • 52.
    Partl, Manfred
    et al.
    Empa, Swiss Federal Laboratories for Materials Testing and Research, Road Engineering/Sealing Components, Dübendorf, Switzerland.
    Flisch, A.
    Jönsson, M.
    KTH.
    Comparison of Laboratory Compaction Methods Using X-ray Computer Tomography2007In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 8, no 2, p. 139-164Article in journal (Refereed)
    Abstract [en]

    Changes and differences in homogeneity of asphalt concrete specimens during Marshall and Rolling-Wheel compaction are investigated by means of standard air-void content determination (AV) and X-ray Computer Tomography (CT). Following an earlier study on Gyratory compaction with the same objective and material, this study, again, focuses on expert. mental aspects serving as a basis for laboratories and producers to optimize compaction procedures and devices. The results demonstrate that X-ray CT is a powerful tool leading to a better understanding of compaction mechanisms, In this way, X-ray CT may be considered very suitable for developing improved laboratory compaction methods and procedures.

  • 53. Poulikakos, L.
    et al.
    Takahashi, S.
    Partl, Manfred
    Swiss Federal Laboratories for Materials Testing and Research (EMPA), Road Engineering/Sealing Components, Dübendorf, Switzerland.
    Coaxial Shear Test and Wheel Tracking Tests for Determining Porous Asphalt Mechanical Properties2007In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 8, no 3, p. 579-594Article in journal (Refereed)
    Abstract [en]

    Performance oriented test procedures are compared and discussed with respect to their suitability for porous asphalt optimization and for development of improved mix design. Coaxial shear tests and wheel tracking tests were carried out in order to compare the properties of both theoretically and empirically designed porous asphalt specimens. The specimens were produced using an improved theoretical mix design approach for porous asphalt. This method is based on a packing theory for aggregate grading optimization, reducing the post compaction effects on the pavement under traffic. The problems with porous asphalt arise from premature aging and therefore laboratory aging of the mix was used for the simulation of in-situ condition. As presented in this paper the test results vary significantly with aging as seen in the rutting behavior and shear modulus. The packing theory leads, in many cases, to porous asphalt mixes with superior quality as compared to traditional standard mixes provided that the influence of the binder is considered accordingly.

  • 54.
    Rahman, Mohammad Shafiqur
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    A Model for Predicting Permanent Deformation of Unbound Granular Materials2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 3, p. 653-673Article in journal (Refereed)
    Abstract [en]

    A simple model has been proposed to characterize the accumulation of permanent deformation (PD) in Unbound Granular Materials (UGMs) under cyclic loading of variable magnitudes. The model was developed based on Multi-Stage (MS) Repeated-Load Triaxial (RLT) tests. The material parameters of this model can be evaluated using an MS RLT test. The model was validated by calibrating it for a few UGMs with a range of grain size distributions, moisture contents and degrees of compaction. The calibrated model was further validated by predicting the PD behaviour of some of these UGMs for different stress conditions. Generally, quite satisfactory predictions were obtained with this model with the advantage of reduced effort required for its calibration compared to some existing models. Additionally, the sensitivity of the parameters of this model to moisture, degree of compaction and grain size distribution was investigated with the aim of incorporating them into the model in future.

  • 55.
    Salour, Farhad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Erlingsson, Sigurdur
    Investigation of a pavement structural behaviour during spring thaw using falling weight deflectometer2013In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no 1, p. 141-158Article in journal (Refereed)
    Abstract [en]

    The response of an instrumented flexible pavement structure in southern Sweden, subjected to seasonal freezethaw cycles, was investigated during the spring thaw and the recovery periods in 2010. The pavement environmental condition was continuously monitored by measuring subsurface temperature and moisture contents. The mechanical behaviour of the pavement structure was investigated by conducting frequent falling weight deflectometer (FWD) measurements throughout the study period. Considerable decrease in the pavement-bearing capacity was observed as thaw penetrated the pavement structure and consequently moisture content increased in all pavement unbound layers. Highest annual moisture content in the subgrade upper section was registered as thaw penetrated the subgrade and pavement exhibited its weakest structural condition. The analyses of the deflection basin indices and back-calculated unbound layer stiffness from the FWD measurements exhibited a clear correlation with the measured subsurface moisture content. Furthermore, the dissipated energy measured from the FWD timehistory data was calculated, exhibiting its highest annual value during the thawing period. Using the back-calculated layer stiffness and moisture measurements in unbound layers, a degree of saturation-based moisture-stiffness model was developed for the granular layer and the subgrade. This model fell on a unique curve showing promising agreement with the laboratory-based model proposed by Mechanistic-Empirical Pavement Design Guide that analytically predicts changes in modulus due to changes in moisture.

  • 56.
    Salour, Farhad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute, VTI, Sweden .
    Erlingsson, Sigurdur
    University of Iceland.
    Resilient modulus modelling of unsaturated subgrade soils: laboratory investigation of silty sand subgrade2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 3, p. 553-568Article in journal (Refereed)
    Abstract [en]

    In flexible pavement structures, stiffness of unbound granular layers and subgrade soil significantly contribute to the overall performance of the pavement system. The stiffness of pavement unbound materials is widely characterised by the resilient modulus, M-r, which is obtained from repeated load triaxial (RLT) tests. Although pavement unbound materials are usually in partially saturated conditions and experience seasonal moisture content and therefore suction variations in the field, their stiffness is conventionally characterised using the total stress approach in which the effect of soil suction is not taken into account. Thus, an enhanced approach in predicting the stiffness of subgrade soils has to account for the partially saturated conditions and incorporate soil suction (i.e. matric suction) in the M-r constitutive models. In this study, several M-r prediction models that take into account the effect of pore suction were investigated. The M-r data set from an experimental investigation of two silty sand subgrade soils that was conducted using a suction-controlled RLT testing apparatus was used to optimise the parameter of these models. The capability of the M-r predictive models in capturing the resilient modulus behaviour of the silty sand subgrade soils and its variation due to seasonal changes in the moisture content (soil suction) were evaluated. It was observed that the M-r models that combine the three fundamental stress state variables (confining stress, deviator stress and matric suction) performed better in capturing the resilient modulus behaviour of the subgrade materials.

  • 57.
    Vieira, Tiago
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. VTI.
    Sandberg, Ulf
    VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. VTI.
    Negative texture, positive for the environment: effects of horizontal grinding of asphalt pavements2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, p. 1-22Article in journal (Refereed)
    Abstract [en]

    A pavement surface having deflections from a plane mostly directed downwards in valleys is said to have a “negative texture”, in contrast to a “positive texture” dominated by peaks. Negative textures are typical of porous asphalt pavements, but another way to achieve this feature is to grind off the peaks of the surface. This paper explores the effects of grinding off texture peaks in the horizontal plane on a number of Swedish asphalt pavements in order to reduce noise and rolling resistance. Noise measurements were made to evaluate the ground-off surfaces versus the original surfaces, and, in most cases, also rolling resistance, texture and friction were also evaluated. It was found that grinding led to a more negative texture, tyre/road noise reductions up to 3 dB and tyre/road rolling resistance reductions up to 15%. It is concluded that horizontal grinding provides a maintenance operation with a significant potential for reduction of noise and rolling resistance, without sacrificing friction, though with limited longevity.

  • 58.
    Yideti, Tatek Fekadu
    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.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Influence of aggregate packing structure on California bearing ratio values of unbound granular materials2014In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 15, no 1, p. 102-113Article in journal (Refereed)
    Abstract [en]

    Over the past several decades, California bearing ratio (CBR) value has been used in many countries for empirical pavement designs and still many countries are using it for unbound granular materials strength measurement and as input to their pavement design chart. Furthermore, CBR value of unbound granular material is frequently correlated with its fundamental mechanical properties such as resilient modulus, which in turn is often used as an input to a mechanistic pavement design procedure. In the present study, the effect the aggregate packing has on the CBR values of unbound materials is investigated. A packing theory-based framework that allows to identify the load-carrying part of the aggregate skeleton is presented. Aggregate packing parameters controlling the CBR performance of the unbound materials are introduced and evaluated with the experimentally measured CBR values of 20 unbound granular materials found in the literature. It is shown that the CBR values of granular materials are to a great extent controlled by the packing characteristics of their load-carrying skeleton.

  • 59.
    Zhu, Jiqing
    et al.
    Swedish Natl Rd & Transport Res Inst VTI, Linkoping, Sweden..
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Wang, Haopeng
    Delft Univ Technol, Fac Civil Engn & Geosci, Sect Pavement Engn, Delft, Netherlands..
    The use of solubility parameters and free energy theory for phase behaviour of polymer-modified bitumen: a review2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    Advances related to the use of solubility parameters and free energy theory for the phase behaviour study of polymer-modified bitumen (PMB) are reviewed in this paper. The origin and effects of PMB phase behaviour are criticised with a focus on PMB storage stability, morphology and swelling ratio. An overview of the solubility approach for studying PMB is given regarding the historical and future developments. Free energy expressions for PMB systems are analysed, including the free energy of mixing, elastic free energy and gradient energy. The kinetic aspects are discussed with respect to the diffusion and flow processes. It is indicated that the solubility bodies in the three-dimensional Hansen space and their degree of intersection can be useful for analysing the PMB thermodynamic equilibrium and thus storage stability. But they give no indication by themselves on the PMB morphology. With solubility parameters linked to the PMB free energy, however, an integrated thermodynamic approach can assist in understanding both PMB storage stability and morphology comprehensively. Due to the chemical complexity of bitumen and certain modifiers, the solubility body centres and radiuses should be both considered for a proper expression of the polymer-bitumen interaction in PMB. A hypothetical dilution process can simplify this process, but with limitations. The introduction of elastic free energy may lead to a new and more realistic expression of free energy for PMB system. With this overview, it is expected that a preliminary foundation is established towards a comprehensive and realistic thermodynamic framework for interpreting and predicting PMB phase behaviour.

  • 60.
    Zhu, Jiqing
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kringos, Niki
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Towards the development of a viscoelastic model for phase separation in polymer-modified bitumen2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no S1, p. 39-49Article in journal (Refereed)
    Abstract [en]

    The development of a viscoelastic model for phase separation in polymer-modified bitumen (PMB) is proposed in this paper. PMB is considered as a pseudo-binary blend. Equilibrium thermodynamics and phase separation dynamics of PMB are discussed. The effects of dynamic asymmetry on phase separation in PMB are analysed with related theories and some image data. Based on the discussion in this paper, it is concluded that the effects of dynamic asymmetry between bitumen and polymer should be taken into consideration when studying phase separation in PMB. By analysing related literature and image data, it is found that some features of viscoelastic phase separation are shown during the phase separation process in some PMBs. It is possible to develop a viscoelastic model for PMB to describe its phase separation behaviour. The stress-diffusion coupling would play a key role in the model by introducing composition-dependant mobility, shear and bulk stress.

12 51 - 60 of 60
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