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  • 1.
    Chen, Feng
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. KTH Royal Institute of Technology.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Vibration-induced aggregate segregation in asphalt mixtures2020In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 53, no 27Article in journal (Refereed)
    Abstract [en]

    Aggregate segregation in asphalt mixture is a bothersome engineering issue during pavement construction. The practitioners have some measures to mitigate the segregation potential based on experiences which, however, can only reduce the risk to a certain extent. In this research, the authors aim to contribute to the discussion in a rational non-empirical way, by using novel experimental and numerical techniques. A case study is carried out to investigate the vibration-induced segregation in asphalt mixtures, corresponding to the circumstance arising during material transportation to the construction site. A novel experimental test is conducted for evaluating the segregation characteristics of asphalt mixtures under vertical vibration in laboratory conditions. A numerical investigation based on discrete element method is further performed to study the phenomenon from a micromechanical point of view. The obtained experimental and numerical results indicate that vibratory loading induces aggregate size segregation in asphalt mixtures, and the degree of segregation is influenced profoundly by the adhesive properties of bituminous binders and the aggregate gradation.

  • 2.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    A contact model for the normal force between viscoelastic particles in discrete element simulations2019In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 342, p. 985-991Article in journal (Refereed)
    Abstract [en]

    DEM modeling of granular materials composed of viscoelastic particles can provide valuable insights into the mechanical behavior of a wide range of engineering materials. In this paper, a new model for calculating the normal contact force between visoelastic spheres is presented based on contact mechanics that takes the mechanical behavior of the DEM particles into account. The model relies on an application of the viscoelastic correspondence principle to elastic Hertz contact. A viscoelastic relaxation function for the contact is defined and a generalized Maxwell material is used for describing this function. An analytical expression for the increment in contact force given an increment in overlap is derived leading to a computationally efficient model. The proposed model provides the analytical small deformation solution upon loading but provides an approximate solution at unloading. Comparisons are made with FEM simulations of contact between spheres of different sizes of equal and dissimilar materials. An excellent agreement is found between the model and the FEM simulations for almost all cases except at cyclic loading where the characteristic times of the viscoelastic behavior and the loading are similar.

  • 3.
    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.
    Acoustical performance of winter tyres on in-service road surfaces2019In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 153, p. 30-47Article in journal (Refereed)
    Abstract [en]

    Exposure to excessively high noise levels is a relevant health problem in Europe and road traffic noise is the most widespread noise source. When considering cold climate countries, the available scientific literature on noise emission properties of winter tyres is still very limited. In order to contribute into filling this knowledge gap, this paper investigates the acoustical performance of different types of tyres, with focus on winter tyres, on different road surfaces, at different speeds, and with different states of wear. The results indicate that studded winter tyres have, indeed, an increased noise level at frequencies between 315 Hz and 10 kHz, having a significantly different response especially at frequencies higher than 4 kHz. The acoustical response also depends on the tyre type when comparing different road surfaces, as a result of conflicting vibrational and aerodynamic noise generation mechanisms. Additionally, the relationship between labelled and measured values was explored, however, no statistically significant relationship was found between them (and labelling is not applied for studded tyres). A frequency spectrum correction was attempted based on previous measurements on an ISO track, which reduced the difference between measured and labelled values, however, further investigation is still required to properly understand differences between label and road measurements, where the label is determined on a test track with a special, smooth surface.

  • 4.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Forquin, P. A.
    Computational framework for analysis of contact-induced damage in brittle rocks2019In: International Journal of Solids and StructuresArticle in journal (Refereed)
    Abstract [en]

    This paper presents a numerical approach for predicting damage in rock materials caused by contact loading. The rock material is modelled using a constitutive description that combines pressure dependent plasticity, for capturing shear deformation under high confining pressure, with an anisotropic damage model for capturing mode I cracking in tension. Material parameters for the model are taken from a recently performed investigation on a granite material. The model has been used to simulate two types of contact loading experiments from the literature, cyclic loading and monotonic loading up to fracture. In order to achieve accurate predictions, the model has been extended to account for small loaded volumes which occur at contact loading. The results show that the main damage mechanism at cyclic loading is crack propagation due to Hertzian stresses whereas in the monotonic experiments sub-surface cracks could initiate. All features measured in the contact loading experiments are captured by the model and hence, the modelling framework is judged to be able to capture contact damage if real stone geometries are studied in FEM.

  • 5.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. EMPA–Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Switzerland.
    Experimental and numerical analysis of asphalt flow in a slump test2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 20, p. S446-S461Article in journal (Refereed)
    Abstract [en]

    The mechanical behaviour of uncompacted asphalt mixtures is still not well understood,threatening directly to the pavement practices such as control of mixture’s workability andsegregation. This situation may become even worse due to the gradually increasing complexityand advances in paving materials and technologies. This study adopts a slump flow testbased on concrete technology and a Discrete Element (DE)-based numerical tool to investigatethe mechanical behaviour of uncompacted asphalt mixture from a microstructural point ofview, particularly focusing on the bituminous binder effects. The combined experimental andnumerical analysis indicates that bitumen distinctly influences the contact interactions withinthe mixture and thus its macroscopic flow, which can be physically interpreted as a combinedeffect of lubricated friction and bonding force. Additional case studies demonstrate that the DEmodel is capable of simulating the flow response of asphalt mixtures under changed particlecontact conditions and driven force.

  • 6.
    Ghafoori Roozbahany, Ehsan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Investigation of asphalt joint compaction using discrete element simulation2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    Constructing high quality asphalt joints plays a vital role in preventing premature failures of pavements. Previous studies suggested that many construction parameters directly and indirectly influence the quality of asphalt joints. Due to uncertainties about the influence of each parameter on the quality of the finalised joints, closer and more detailed studies are still needed for achieving further improvements in this field. This study investigates the possible impacts of thickness, bottom layer roughness, joint interface geometries and compaction techniques on the particle flow of a coarse structured mixture during compaction. Therefore, discrete element method (DEM) was utilised to evaluate the influence of each construction parameter on the interlock between the cold and the hot side of an asphalt pavement joint. The results helped to explain earlier experimental findings about the joints and revealed potential for further laboratory and field investigations.

  • 7.
    Sun, Guoqiang
    et al.
    Tongji Univ, Minist Educ, Key Lab Rd & Traff Engn, Shanghai 200092, Peoples R China..
    Sun, Daquan
    Tongji Univ, Minist Educ, Key Lab Rd & Traff Engn, Shanghai 200092, Peoples R China..
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Ma, Jianmin
    Tongji Univ, Minist Educ, Key Lab Rd & Traff Engn, Shanghai 200092, Peoples R China..
    Chen, Feng
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Ghafooriroozbahany, Ehsan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Low temperature self-healing character of asphalt mixtures under different fatigue damage degrees2019In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 223, p. 870-882Article in journal (Refereed)
    Abstract [en]

    The primary objective of this study is to advance the understanding of the low temperature self-healing character of asphalt mixtures under different damage degrees, thus to determine the effective strategy of asphalt pavement maintenance. Firstly, three kinds of asphalt mixtures are selected to conduct the indirect tensile (IDT) fatigue test to a certain fatigue damage degree at low temperatures, and then the resilient modulus (Mr) at different rest time is measured to quantify the healing potential. Next, the fatigue loading with different intermittent time (0 s, 1 s and 3 s) is applied to determine the impact of intermittent time on healing potential. The results indicate that the descending order of healing potential of asphalt mixtures is: SMA-11 > AC-8 > AC-11 at 5 degrees C and -5 degrees C. The loading intermittent time has an obvious effect on the fatigue damage state of asphalt mixtures, while the longer the intermittent time, the less the effect on fatigue damage healing. Besides, the fatigue damage state has great influence on its healing potential of asphalt mixture. Under the low damage conditions, the initial healing rate is greater than the long term healing rate. However, the low temperature (-5 degrees C) dramatically reduces the healing rate of asphalt mixtures, and causes their long-term healing rate to stabilize gradually to a very low level. Especially under the high fatigue damage conditions, the healing potential of asphalt mixtures will almost disappear at -5 degrees C. Furthermore, together with meso-scale Computed Tomography (CT) scanning technique, it is found that the intemal crack distribution characteristics of different graded asphalt mixtures are different even under the same damage degree, which may explain the differences in the healing potential of asphalt mixtures. The use of a fast two-dimensional (2D) scanning technology further confirms that the crack zones inside the asphalt mixture are gradually shrinking after a period of high temperature healing. Finally, the Grey relational analysis reveals that the healing time has the most significant influence on the healing potential of asphalt mixtures. The gradation type and temperature have the similar influence level on the healing potential. The correlation degree between the fatigue damage degree and healing potential is the smallest compared with the other three factors. All rights reserved.

  • 8.
    Fadil, Hassan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Measurement of the viscoelastic properties of asphalt mortar and its components with indentation tests2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    Reliable determination of material properties is a key component for modelling and performance prediction of asphalt pavements. This paper deals with the potential use of instrumented indentation tests for viscoelastic characterisation of asphalt mortar as a new alternative to existing techniques. The main focus lies on the potential of indentation tests for multi-scale measurement of the shear relaxation modulus. A three-dimensional finite element model of a rigid spherical indenter penetrating an asphalt mortar sample is developed and used to model indentation tests performed at different material scales. The asphalt mortar is modelled as an idealised fine aggregate composite with elastic spheres, suspended within a viscoelastic bitumen mastic matrix. Based on the obtained numerical results the scale-dependency of the shear relaxation modulus measured with the indentation test is investigated. It is shown that the measurement scale is effectively controlled by the size of the indenter-specimen contact area, while the effect of indentation depth is minimal. The minimum contact area size required for obtaining representative properties, measured at the mortar scale, is determined. The viscoelastic parameters obtained from the indentation model are compared to those obtained using a representative volume element (RVE) for the asphalt mortar. In this way, the paper provides a new impulse for linking the mortar and asphalt scales in the multiscale modelling of asphalt mixtures. Feasibility of the proposed testing technique is further evaluated experimentally. Viscoelastic indentation tests are performed on asphalt mastics and mortar at two different sizes of contact areas. Experimental results indicate that indentation tests allow reliable characterisation of mortars relaxation modulus on both macro-scale as well as on individual component level.

  • 9.
    Ghafoori Roozbahany, Ehsan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. VTI Swedish National road and transport research institute, Olaus Magnus väg 35, Linköping, 583 30, Sweden.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Elaguine, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Modelling the flow of asphalt under simulated compaction using discrete element2019In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 227, article id 116432Article in journal (Refereed)
    Abstract [en]

    The flow differences between the particles of asphalt mixtures compacted in the laboratory and in the field have been identified as one of the reasons for the discrepancies between laboratory and field results. In previous studies, the authors developed a simplified test method, the so-called compaction flow test (CFT), for roughly simulating the flow of particles in asphalt mixtures under compacting loads in laboratory. The CFT was used in different studies to examine its capability of revealing the differences between the flow behavior of different asphalt mixtures under various loading modes. The promising results encouraged further development of the CFT by investigating the possible impacts of simplifications and boundary conditions on the results of this test. For this reason, discrete element method (DEM) was utilized to investigate possible impacts of the mold size, geometry of the loading strip as well as the loading rate on the results of the CFT. The results of the simulation indicate that in case of wearing course layers with nominal maximum aggregate size of 11 mm, the length of the CFT mold can be increased from 150 mm to 200–250 mm for reducing flow disturbances from the mold walls. However, since the majority of the flow of asphalt mixture particles is expected to take place within the first 100–150 mm length of the mold, reasonable results can still be obtained even without changing the size of the CFT mold. Moreover, comparing results with different loading strip geometries and loading rates indicates that the current CFT setup still appears to provide consistent results.

  • 10.
    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.

  • 11.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Jelagin, Denis
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    New discrete element framework for modelling asphalt compaction2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    During asphalt mixture compaction, loads in the material are mainly transferred through contact between the stones and the interaction between the stones and the binder. The behaviour of such materials is suitable to model using the Discrete Element Method (DEM). In this study, a new DEM modelling approach has been developed for studying the asphalt compaction process, incorporating contact and damage laws based on granular mechanics. In the simulations, aggregate fracture is handled by a recently developed method of incorporating particle fracture in DEM, based on previously performed fracture experiments on granite specimens. The binder phase is modelled by adding a viscoelastic film around each DEM particle. This surface layer has a thickness that obtains the correct volume of the binder phase and has mechanical properties representative for the binder at different temperatures. The ability of the model to capture the influence of mixture parameters on the compactability and the eventual stone damage during compaction is examined for the cases of compaction flow test and gyratory compaction. Explicitly, the influence of different aggregate gradations, mixture temperatures and binder properties are studied. The results show that the proposed DEM approach is able to capture qualitatively and quantitatively responses in both cases and also provide predictions of aggregate damage. One large benefit with the developed modelling approach is that the influence of different asphalt mixture parameters could be studied without re-calibration of model parameters. Furthermore, based on comparative DEM simulations, it is shown that the proposed approach provides more realistic force distribution networks in the material.

  • 12.
    Francart, Nicolas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Sustainability Assessment and Management.
    Erlandsson, Martin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Malmqvist, Tove
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Sustainability Assessment and Management.
    Larsson, Mathias
    Florell, Josefin
    Requirements set by Swedish municipalities to promote construction with low climate change impact2019In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 208, p. 117-131Article in journal (Refereed)
    Abstract [en]

    This study investigates how Swedish municipalities work to reduce the climate change impact of building construction. It focuses on current practices related to promoting the use of sustainable construction materials and on barriers to environmental requirements in construction, in particular environmental performance requirements based on LCA procedures. Municipalities were surveyed about the existence of municipal policies dealing with environmental issues in construction, the knowledge level about these issues, and the measures and requirements used to promote materials with low climate change impact. The survey was followed by semi-structured interviews about current practices and barriers to environmental requirements in construction. Results show that large municipalities are more likely to have dedicated policies and implement more measures than their smaller counterparts. However, willingness to implement future measures and knowledge of sustainable construction do not vary significantly with municipality population. Efforts are often limited to procurement, municipal construction projects and discussions with stakeholders. When requirements are set, they are almost always based on prescribing a technical solution (e.g. use of timber) rather than assessing environmental performance (e.g. calculating greenhouse gases emissions with a LCA tool). Measures that municipalities can take as public authorities are restricted by the law, which remains ambiguous as to the legality of environmental performance requirements. Legal issues, limited knowledge and resources appear to be the main barriers to environmental performance requirements in construction. A strategy is proposed to o​v​e​r​

  • 13.
    Penaloza, Diego
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Royne, Frida
    RISE Res Inst Sweden, Gothenburg, Sweden..
    Sandin, Gustav
    RISE Res Inst Sweden, Gothenburg, Sweden..
    Svanstrom, Magdalena
    Chalmers Univ Technol, Div Environm Syst Anal, Gothenburg, Sweden..
    Erlandsson, Martin
    IVL Swedish Environm Res Inst, Stockholm, Sweden..
    The influence of system boundaries and baseline in climate impact assessment of forest products2019In: The International Journal of Life Cycle Assessment, ISSN 0948-3349, E-ISSN 1614-7502, Vol. 24, no 1, p. 160-176Article in journal (Refereed)
    Abstract [en]

    PurposeThis article aims to explore how different assumptions about system boundaries and setting of baselines for forest growth affect the outcome of climate impact assessments of forest products using life cycle assessment (LCA), regarding the potential for climate impact mitigation from replacing non-forest benchmarks. This article attempts to explore how several assumptions interact and influence results for different products with different service life lengths.MethodsFour products made from forest biomass were analysed and compared to non-forest benchmarks using dynamic LCA with time horizons between 0 and 300years. The studied products have different service lives: butanol automotive fuel (0years), viscose textile fibres (2years), a cross-laminated timber building structure (50years) and methanol used to produce short-lived (0years) and long-lived (20years) products. Five calculation setups were tested featuring different assumptions about how to account for the carbon uptake during forest growth or regrowth. These assumptions relate to the timing of the uptake (before or after harvest), the spatial system boundaries (national, landscape or single stand) and the land-use baseline (zero baseline or natural regeneration).Results and discussionThe implications of using different assumptions depend on the type of product. The choice of time horizon for dynamic LCA and the timing of forest carbon uptake are important for all products, especially long-lived ones where end-of-life biogenic emissions take place in the relatively distant future. The choice of time horizon is less influential when using landscape- or national-level system boundaries than when using stand-level system boundaries and has greater influence on the results for long-lived products. Short-lived products perform worse than their benchmarks with short time horizons whatever spatial system boundaries are chosen, while long-lived products outperform their benchmarks with all methods tested. The approach and data used to model the forest carbon uptake can significantly influence the outcome of the assessment for all products.ConclusionsThe choices of spatial system boundaries, temporal system boundaries and land-use baseline have a large influence on the results, and this influence decreases for longer time horizons. Short-lived products are more sensitive to the choice of time horizon than long-lived products. Recommendations are given for LCA practitioners: to be aware of the influence of method choice when carrying out studies, to use case-specific data (for the forest growth) and to communicate clearly how results can be used.

  • 14.
    Sjökvist, Tinh
    et al.
    Linnaeus Univ, Dept Forestry & Wood Technol, SE-35195 Vaxjo, Sweden.
    Blom, Åsa
    Linnaeus Univ, Dept Forestry & Wood Technol, SE-35195 Vaxjo, Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    The infuence of heartwood, sapwood and density on moisture fuctuations and crack formations of coated Norway spruce in outdoor exposure2019In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 65, no 45Article in journal (Refereed)
    Abstract [en]

    The moisture sorption behaviour of wood strongly influences the durability of exterior-coated wood. Wood characteristics are known to influence the water sorption of uncoated wood. Despite this, the majority of the research on coated wood has been focused on the coating properties. This study aims to investigate the impact of heartwood, sapwood and density on the moisture content (MC) and crack formation of coated Norway spruce (Picea abies (L.) Karst.). Boards with film-forming coatings or a non-film-forming coating were exposed outdoors during 3 years. Crack development and the mass of the boards were recorded during this period. Heartwood and sapwood samples showed no differences in MC. Thus, a coating seems to reduce the differences in water sorption behaviour that is present in uncoated heartwood and sapwood spruce. The reduction is probably related to wetting properties and different sorption mechanisms, involving free and bond water diffusion. However, the low-density samples had significantly higher MC levels than the high-density samples. The high-density samples with a non-film-forming coating showed a higher number of cracks than those with lower density. Furthermore, sapwood samples had a remarkably high number of cracks when compared to the corresponding heartwood samples, despite a similar density and MC.

  • 15.
    Lillqvist, Kristiina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Lahti Univ Appl Sci, Fac Technol, Mukkulankatu 19, Lahti 15101, Finland.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Altgen, Michael
    Aalto Univ, Dept Bioprod & Biosyst, POB 16300, Aalto 00076, Finland.
    Belt, Tiina
    Aalto Univ, Dept Bioprod & Biosyst, POB 16300, Aalto 00076, Finland.
    Rautkari, Lauri
    Aalto Univ, Dept Bioprod & Biosyst, POB 16300, Aalto 00076, Finland.
    Water vapour sorption properties of thermally modified and pressurised hot-water-extracted wood powder2019In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 12, p. 1059-1068Article in journal (Refereed)
    Abstract [en]

    The objective of the study was to investigate the water vapour sorption behaviour of thermally modified (TM) wood powder, e.g. ground wood prepared from waste streams of TM solid wood, and wood powder that was extracted in pressurised hot water. Solid spruce wood was TM in steam conditions (210°C for 3 h), milled and hot-water-extracted (HWE) at elevated pressure (140°C for 1 h). The results evidence that the hot-water extraction reduced the water sorption and the accessible hydroxyl group concentration by the removal of amorphous carbohydrates. In contrast, the enhanced cross-linking of the cell wall matrix and the annealing of amorphous matrix polymers during thermal modification reduced the sorption behaviour of wood additionally, without further reducing the hydroxyl accessibility. These additional effects of thermal modification were at least partially cancelled by hot-water extraction. The results bring novel insights into the mechanisms that reduce the water vapour sorption of wood by compositional and structural changes induced by heating.

  • 16.
    Lundberg, Joacim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Swedish Natl Rd & Transport Res Inst VTI, S-58195 Linköping, Sweden..
    Blomqvist, Göran
    Swedish Natl Rd & Transport Res Inst VTI, S-58195 Linköping, Sweden..
    Gustafsson, Mats
    Swedish Natl Rd & Transport Res Inst VTI, S-58195 Linköping, Sweden..
    Janhall, Sara
    RISE Res Inst Sweden, Borås, Sweden..
    Jarlskog, Ida
    Swedish Natl Rd & Transport Res Inst VTI, S-58195 Linköping, Sweden..
    Wet Dust Sampler-a Sampling Method for Road Dust Quantification and Analyses2019In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 230, no 8, article id 180Article in journal (Refereed)
    Abstract [en]

    In northern countries, the climate, and consequently the use of studded tyres and winter traction sanding, causes accumulation of road dust over winter and spring, resulting in high PM10 concentrations during springtime dusting events. To quantify the dust at the road surface, a method-the wet dust sampler (WDS)-was developed allowing repeatable sampling also under wet and snowy conditions. The principle of operation is flushing high-pressurised water over a defined surface area and transferring the dust laden water into a container for further analyses. The WDS has been used for some time and is presented in detail to the international scientific community as reported by Jonsson et al. (2008) and Gustafsson et al. (2019), and in this paper, the latest version is presented together with an evaluation of its performance. To evaluate the WDS, the ejected water amount was measured, as well as water losses in different parts of the sampling system, together with indicative dust measurement using turbidity as a proxy for dust concentration. The results show that the WDS, when accounting for all losses, have a predictable and repeatable water performance, with no impact on performance based on the variety of asphalt surface types included in this study, given undamaged surfaces. The largest loss was found to be water retained on the surface, and the dust measurements imply that this might not have as large impact on the sampled dust as could be expected. A theoretical particle mass balance shows small particle losses, while field measurements show higher losses. Several tests are suggested to validate and improve on the mass balances. Finally, the WDS is found to perform well and is able to contribute to further knowledge regarding road dust implications for air pollution.

  • 17.
    Peñaloza, Diego
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. RISE - Research Institutes of Sweden.
    Erlandsson, Martin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Pousette, Anna
    Climate impacts from road bridges: effects of introducing concrete carbonation and biogenic carbon storage in wood2018In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 14, no 1, p. 56-67Article in journal (Refereed)
    Abstract [en]

    The construction sector faces the challenge of mitigating climate change with urgency. Life cycle assessment(LCA), a widely used tool to assess the climate impacts of buildings, is seldom used for bridges. Materialspecificphenomena such as concrete carbonation and biogenic carbon storage are usually unaccountedfor when assessing the climate impacts from infrastructure. The purpose of this article is to explore theeffects these phenomena could have on climate impact assessment of road bridges and comparisonsbetween bridge designs. For this, a case study is used of two functionally equivalent design alternativesfor a small road bridge in Sweden. Dynamic LCA is used to calculate the effects of biogenic carbon storage,while the Lagerblad method and literature values are used to estimate concrete carbonation. The resultsshow that the climate impact of the bridge is influenced by both phenomena, and that the gap betweenthe impacts from both designs increases if the phenomena are accounted for. The outcome is influencedby the time occurrence assumed for the forest carbon uptake and the end-of-life scenario for the concrete.An equilibrium or 50/50 approach for accounting for the forest carbon uptake is proposed as a middlevalue compromise to handle this issue.

  • 18. Jeoffroy, E.
    et al.
    Bouville, F.
    Bueno, M.
    Studart, A. R.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Swiss Federal Laboratories for Materials Science and Technology, Switzerland.
    Iron-based particles for the magnetically-triggered crack healing of bituminous materials2018In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 164, p. 775-782Article in journal (Refereed)
    Abstract [en]

    Bituminous road pavements may suffer from cracking over the years due to repeated stresses. In this study, we compare the effect of different sizes and chemical compositions of magnetically-responsive iron-based particles used as additives to heat up road pavements and thus to close cracks. By applying an alternating magnetic field (AMF), we found that there is an optimal size depending on the particle electrical conductivity at which the temperature on the surface of asphalt samples is the highest. Even when particles are well-distributed after mixing, we found that asphalt samples containing larger particles display inhomogeneous heating during the exposure to the AMF. The mechanical recovery of samples during a double torsion test before and after the exposure to the AMF confirmed the healing capability of asphalt materials containing iron-based particles. Based on these results we provide guidelines for the design of magnetically-responsive asphalts for road pavements of enhanced durability.

  • 19.
    Sjökvist, T.
    et al.
    Linnaeus Univ, Dept Forestry & Wood Technol, SE-35195 Vaxjo, Sweden..
    Wålinder, Magnus E.P.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Blom, A.
    Linnaeus Univ, Dept Forestry & Wood Technol, SE-35195 Vaxjo, Sweden..
    Liquid sorption characterisation of Norway spruce heartwood and sapwood using a muiticycle Wilhelmy plate method2018In: International Wood Products Journal, ISSN 2042-6445, E-ISSN 2042-6453, Vol. 9, no 2, p. 58-65Article in journal (Refereed)
    Abstract [en]

    A multicycle Wilhelmy plate method was applied to study the water and octane sorption behaviour of small Norway spruce veneers. Dry heart- and sapwood samples of varying density were investigated. The results showed a correlation between the porosity and the sorption of octane for all samples, i.e. a higher wood porosity resulted in higher octane sorption. However, no difference in octane sorption was found between heart- and sapwood samples of similar density. The water sorption behaviour was difficult to interpret, probably due to the influence of surface-active wood extractives. It is suggested that the presence of such extractives, particularly in the sapwood samples, increases the sorption of water due to a significant decrease in its apparent surface tension. Hence, the results indicate that the liquid water sorption of spruce heart- and sapwood is strongly influenced by variations in the extractives content rather than by the micromorphology.

  • 20.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Moghaddam, Maziar Sedighi
    Wålinder, Magnus E. P.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Liquid sorption, swelling and surface energy properties of unmodified and thermally modified Scots pine heartwood after extraction2018In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 3, p. 251-258Article in journal (Refereed)
    Abstract [en]

    The effect of extractives removal on liquid sorption, swelling and surface energy properties of unmodified wood (UW) and thermally modified Scots pine heartwood (hW) (TMW) was studied. The extraction was performed by a Soxtec procedure with a series of solvents and the results were observed by the multicycle Wilhelmy plate method, inverse gas chromatography (IGC) and Fourier transform infrared (FTIR) spectroscopy. A significantly lower rate of water uptake was found for the extracted UW, compared with the unextracted one. This is due to a contamination effect in the latter case from water-soluble extractives increasing the capillary flow into the wood voids, proven by the decreased water surface tension. The swelling in water increased after extraction 1.7 and 3 times in the cases of UW and TMW, respectively. The dispersive part of the surface energy was lower for the extracted TMW compared to the other sample groups, indicating an almost complete removal of the extractives. The FTIR spectra of the extracts showed the presence of phenolic compounds but also resin acids and aliphatic compounds.

  • 21.
    Jelagin, Denis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Saadati, Mahdi
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). Atlas Copco, Sweden.
    Jerjen, I.
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Mechanical Characterization of Granite Rock Materials: On the Influence from Pre-Existing Defects2018In: Journal of Testing and Evaluation, ISSN 0090-3973, E-ISSN 1945-7553, Vol. 46, no 2, p. 540-548Article in journal (Refereed)
    Abstract [en]

    The length, orientation, and population of pre-existing cracks play an important role in the mechanical response of quasi-brittle materials, such as granite. Specifically, Bohus granite rock is at issue in the present investigation. The aims of this study are (1) to demonstrate the existence and characteristics of pre-existing defects (cracks) in granite rock specimens, and (2) to determine the influence from these defects at characterization of such materials. In doing so, X-ray tomography was the method used to visualize the cracking of three-point bending specimens in the context of pre-existing defects. It was also the intention to relate the experimentally determined effect of these cracks at three-point bending testing with corresponding results from numerical methods and specifically finite-element calculations. In the latter case, the location of these cracks was of primary interest and it was shown that this feature can be of considerable importance at material characterization.

  • 22.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Altgen, Michael
    Georg August Univ Gottingen, Wood Biol & Wood Prod, DE-37077 Gottingen, Germany.;Aalto Univ, Dept Bioprod & Biosyst, FI-00076 Aalto, Finland..
    Militz, Holger
    Georg August Univ Gottingen, Wood Biol & Wood Prod, DE-37077 Gottingen, Germany..
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Sorption and surface energy properties of thermally modified spruce wood components2018In: Wood and Fiber Science, ISSN 0735-6161, Vol. 50, no 3, p. 346-357Article in journal (Refereed)
    Abstract [en]

    The objective of this work is to study the water vapor sorption and surface energy properties of thermally modified wood (TMW) components, ie wood processing residuals in the form of sawdust. The thermal modification was performed on spruce wood components using a steam-pressurized laboratoryscale reactor at two different temperature (T) and relative humidity (RH) conditions, T = 150 degrees C and RH = 100% (TMW150), and T = 180 degrees C and RH = 46% (TMW180). A dynamic vapor sorption (DVS) technique was used to determine water vapor sorption isotherms of the samples for three adsorption-desorption cycles at varying RH between 0% and 95%. Inverse gas chromatography (IGC) was used to study the surface energy properties of the samples, including dispersive and polar characteristics. The DVS results showed that the EMC was reduced by 30-50% for the TMW samples compared with control samples of unmodified wood (UW) components. A lower reduction was, however, observed for the second and third adsorption cycles compared with that of the first cycle. Ratios between EMC of TMW and that of UW samples were lower for the TMW180 compared with the TMW150 samples, and an overall decrease in such EMC ratios was observed at higher RH for both TMW samples. The IGC results showed that the dispersive contribution to the surface energy was higher at lower surface coverages, ie representing the higher energy sites, for the TMW compared with the UW samples. In addition, an analysis of the acid-base properties indicated a higher KB than KA number, ie a higher basic than acidic contribution to the surface energy, for all the samples. A higher KB number was also observed for the TMW compared with the UW samples, suggested to relate to the presence of ether bonds from increased lignin and/or extractives content at the surface. The KB was lower for TMW180 compared with TMW150, as a result of higher modification temperature of the first, leading to cleavage of these ether bonds.

  • 23.
    Larsson, Magnus
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Falk, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Teleodynamic timber façades2018In: Frontiers in Built Environment, ISSN 2297-3362, Vol. 4, article id 37Article in journal (Refereed)
    Abstract [en]

    This paper investigates ways in which weathering-related site conditions can be allowed to inform the design process in order to improve a building's geometry and performance. Providing a building design with the capacity to remember past experiences and anticipate future events can provide substantial gains to the architectural configuration and engineering of a timber façade. A new theory of architecture is outlined based on recent “teleodynamic” theories—a hypothesis about the way far-from-equilibrium systems interact and combine to produce emergent patterns. The proposed explanation considers nested levels of thermodynamic systems applied to an architectural context: “homeodynamic” operations that involve equilibration and dissipation of constraint combine to produce self-organising “morphodynamic” procedures that amplify and regularise site-specific constraining data streams. A teleodynamic design reconstitutes itself by combining morphodynamic processes so as to optimise its relationship to the past, present, and future. A novel teleodynamic design tool called Contextual Optimisation Workspace (COW) is assembled within the Grasshopper visual programming environment. The tool is used to carry out four experiments that combine to produce the teleodynamic design of an urban wooden façade, exemplifying an alternative framework for the design of wood-based structures. The first experiment investigates a variegated grid combining two distinct subdivision methods (an orthogonal grid and a Voronoi tessellation), transmuting one system into another. The second and third experiments focus on durability aspects of a wooden façade and devise strategies for how the effects of photochemical degradation and wetting due to driving rain might be minimised using the COW tool. The fourth experiment optimises the building for daylight based on an illuminance simulation. Using simulation and anticipation to add the advantages of site- and time-specific data streams as a design strategy can effectively suspend an algorithm-driven design iteration in time and space in order to allow it to be parametrically influenced by past or future events such as unique site and project conditions. The COW tool can be used to produce such teleodynamic designs.

  • 24.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Towards improved testing of modern asphalt pavements2018In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 51, no 6, article id 166Article in journal (Refereed)
    Abstract [en]

    During the last 50 years, Rilem was continuously active in pre-standardization efforts aiming at gradually improving scientific and technological testing and analysis methods for refined understanding and characterization of bituminous binders and asphalt, both under well-defined laboratory and performance driven in-field conditions. This paper intends to highlight and provide a short overview on the international activities of Rilem’s to date 18 technical committees (TC) on asphalt and bituminous binders. After some general background information, underlining the specific complexity of asphalt pavement materials in terms of rheological behavior and basic structural functioning, it is shown that these activities resulted in numerous recommendations, state of the art reports and conference proceedings, all produced on a voluntary basis by scientific and technical commitment of individual experts. This wealth of results was created by the TCs following an own systematic methodology for many years which, at the end of the day, allowed building up activities through the new TCs of today in a much more specialized but at the same time also more diverse way. In view of this new flexibility and keeping in mind the previous success story of Rilem towards improved testing of asphalt pavements, future developments, challenges and interdisciplinary issues regarding bituminous road materials are outlined as potential starting point for future TC initiatives.

  • 25.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Jerjen, I.
    Griffa, M.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Swiss Federal Laboratories for Material Science and Technology, Duebendorf, Switzerland .
    A closer scientific look at foam bitumen2017In: Road Materials and Pavement Design, ISSN 1468-0629, Vol. 18, no 2, p. 362-375Article in journal (Refereed)
    Abstract [en]

    In the asphalt industry, a substantial interest is observed to find possibilities to reduce the production temperature of asphalt mixtures. In the context of this research, new methods for the visualisation of unstable bitumen foam, such as dynamic X-ray radiography, computed tomography (CT) and high-speed camera investigations, have been developed. Moreover, characterisation with empirical methods such as expansion ratio and half-life was determined accurately using ultrasonic measurements. This opens new possibilities to characterise bitumen foam (foaming process) for practical applications. Examination of the foam bitumen stream using a high-speed camera revealed that the foam bitumen contains fragmented pieces of bitumen, which resemble more a liquid than foam. This indicates that the foam is formed afterwards and not, as assumed, within the expansion chamber of the foam generator. In situ thermal imagery of the surface, during the hot foaming process, showed that the temperature distribution depends on the foaming water content (W.C.) and bubble size distribution. Higher W.C. results in more inhomogeneous temperature distribution as compared to lower W.C. (<2 wt%). The dynamic X-radiography results indicated that as the foam decays, the bubble size distribution becomes progressively larger with time for 160°C bitumen temperature. Furthermore, at the beginning of the foam formation, majority of the bubbles is small in cross-section size (0.2–10 mm2). At a later stage, the bubbles become polydisperse. Moreover, theoretical investigations based on the 3D X-ray CT scan data set of bubble merging show that the disjoining pressure increases as the foam film gets thinner with time and finally undergoes rupture. The speed of the bubbles also increases with time when the bubbles are getting closer to each other.

  • 26. Joffre, Thomas
    et al.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Persson, Cecilia
    Bardage, Stig L.
    Hendriks, Cris L. Luengo
    Isaksson, Per
    Characterization of interfacial stress transfer ability in acetylation-treated wood fibre composites using, X-ray microtomography2017In: INDUSTRIAL CROPS AND PRODUCTS, ISSN 0926-6690, Vol. 95, p. 43-49Article in journal (Refereed)
    Abstract [en]

    The properties of the fibre/matrix interface contribute to stiffness, strength and fracture behaviour of fibre-reinforced composites. In cellulosic composites, the limited affinity between the hydrophilic fibres and the hydrophobic thermoplastic matrix remains a challenge, and the reinforcing capability of the fibres is hence not fully utilized. A direct characterisation of the stress transfer ability through pull-out tests on single fibres is extremely cumbersome due to the small dimension of the wood fibres. Here a novel approach is proposed: the length distribution of the fibres sticking out of the matrix at the fracture surface is approximated using X-ray microtomography and is used as an estimate of the adhesion between the fibres and the matrix. When a crack grows in the material, the fibres will either break or be pulled-out of the matrix depending on their adhesion to the matrix: good adhesion between the fibres and the matrix should result in more fibre breakage and less pull-out of the fibres than poor adhesion. The effect of acetylation on the adhesion between the wood fibres and the PLA matrix was evaluated at different moisture contents using the proposed method. By using an acetylation treatment of the fibres it was possible to improve the strength of the composite samples soaked in the water by more than 30%.

  • 27.
    Celma Cervera, Carlos
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. bEMPA Swiss Federal Laboratories for Materials Testing and Research, Switzerland.
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Contact-induced deformation and damage of rocks used in pavement materials2017In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 133, p. 255-265Article in journal (Refereed)
    Abstract [en]

    Performance of stone-based construction materials, such as asphalt and unbound aggregate mixtures is defined to a great extent by the mechanics of the stone-to-stone interactions. Accordingly, the Discrete Element Method (DEM) is gaining popularity as a modelling tool to investigate the mechanical behavior of these materials. Contact and failure laws defining particles force-displacement relationships and the propensity of particles to break are crucial inputs for the DEM simulations. The present study aims at providing an experimental contact mechanics basis for the development of physically based stone-to-stone interaction laws. The attention is focused on investigating stone's force-displacement relationship and damage characteristics at pure normal loading for two stone materials used by the road industry. Experiments are performed at spherical contact profiles for cyclic and monotonically increasing loads. The emphasis lies on the evolution of contact compliance and accumulation of contact induced damage. The effect of surface roughness on the materials response is examined through comparative experiments performed on the specimens with different roughness values. Optical and environmental scanning electron microscopy (ESEM) observations of the contact induced damage at the material surface are presented and discussed in the context of contact mechanics. The implications of the reported experimental findings on the development of mechanics based contact and failure laws for the DEM modelling of stone-based construction materials are discussed.

  • 28.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, B.
    Damage and fracture characterization of asphalt concrete mixtures using the equivalent micro-crack stress approach2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 148, p. 521-530Article in journal (Refereed)
    Abstract [en]

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

  • 29.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Carleton University, Canada.
    Editorial2017In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 18, p. 1-1Article in journal (Refereed)
  • 30. Li, T.
    et al.
    Cai, J. -B
    Avramidis, S.
    Cheng, D. -L
    Wålinder, Magnus E.P.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Zhou, D. -G
    Effect of conditioning history on the characterization of hardness of thermo-mechanical densified and heat treated poplar wood2017In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 71, no 6, p. 515-520Article in journal (Refereed)
    Abstract [en]

    Poplar wood was modified by a combination of thermo-mechanical densification (TMD) and heat treatment (HT) process at five temperatures ranging from 170 to 210°C. A new two-step conditioning method (CM) is suggested, in the course of which the modified wood is submitted to 50°C/99% RH→25°C/65% RH, where RH means relative humidity in the climate chamber. The traditional one-step CM (25°C/65% RH) served as reference. The effects of conditioning history on hardness were observed and analyzed along with the change of dimensional stability. The hardness of the modified wood was lower in the case of the proposed CM due to more set-recovery release, but the extent of that decreased with the HT temperature. For a good hardness, HT200°C should be selected with the proposed CM, which is different from the optimization output of 180°C obtained from the traditional CM. In conclusion, a specific assessment method for the performance characterization of this type of modified wood would be beneficial for the combined TMD and HT processes.

  • 31.
    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.

  • 32.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Dinegdae, Yared H.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Birgisson, Björn
    Hierarchical approach for fatigue cracking performance evaluation in asphalt pavements2017In: Frontiers of Structural and Civil Engineering, ISSN 2095-2430, E-ISSN 2095-2449, Vol. 11, no 3, p. 257-269Article in journal (Refereed)
    Abstract [en]

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

  • 33. Arm, Maria
    et al.
    Wik, Ola
    Engelsen, Christian J.
    Erlandsson, Martin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Hjelmar, Ole
    Wahlström, Margareta
    How Does the European Recovery Target for Construction & Demolition Waste Affect Resource Management?2017In: Waste and Biomass Valorization, ISSN 1877-2641, E-ISSN 1877-265X, Vol. 8, no 5, p. 1491-1504Article in journal (Refereed)
    Abstract [en]

    The revised EU Waste Framework Directive (WFD) includes a 70 % target for recovery of construction and demolition (C&D) waste. In order to study the potential change in the resource management of the main C&D waste fractions, as a consequence of fulfilling the WFD target, a Nordic project (ENCORT-CDW) has been performed. Waste fractions studied included asphalt, concrete, bricks, track ballast, gypsum-based construction materials and wood. Recovery scenarios were identified and estimations were made regarding expected savings of primary materials, impact on transport, and pollution and emissions. For wood waste, the main differences between re-use, material recycling and energy recovery were evaluated in a carbon footprint screening based on life cycle assessment methodology. The study concluded that the EU recovery target does not ensure a resource efficient and environmentally sustainable waste recovery in its present form since: It is very sensitive to how the legal definitions of waste and recovery are interpreted in the Member States. This means that certain construction material cycles might not count in the implementation reports while other, less efficient and environmentally safe, recovery processes of the same material will count. It is weight-based and consequently favours large and heavy waste streams. The result is that smaller flows with equal or larger resource efficiency and environmental benefit will be insignificant for reaching the target. It does not distinguish between the various recovery processes, meaning that resource efficient and environmentally safe recovery cannot be given priority. Improved knowledge on C&D waste generation and handling, as well as on content and emissions of dangerous substances, is required to achieve a sustainable recovery.

  • 34.
    Ghafoori Roozbahany, Ehsan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Introducing a new method for studying the field compaction2017In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 18, p. 26-38Article in journal (Refereed)
    Abstract [en]

    The flow of particles during compaction may have a prominent influence on the difference of field and laboratory results as recently demonstrated by the authors with their newly developed compaction flow test (CFT). This test with a simple compaction simulator was used for studying the flow behaviour and rearrangement of particles for mixtures with different structures and thicknesses. However, validating the CFT results for practical purposes requires field measurements that provide more insight into the compaction process and eventually allowing to adjust the CFT for further use as an evaluating in-site tool. This study presents a new method for conducting such measurements during field compaction. In this method, some representative particles are tracked inside asphalt specimens and the accuracy of the results is examined by X-ray computed tomography. The results of the feasibility tests show that this method has potential for further use in the field and for building up a comprehensive basis of knowledge on field compaction towards closing the gap between the field and laboratory results.

  • 35.
    Sedighi Moghaddam, Maziar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Tech Res Inst Sweden Chem Mat & Surfaces, Sweden.
    Van den Bulcke, Jan
    Wålinder, Magnus E. P.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Van Acker, Joris
    Swerin, Agne
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Microstructure of chemically modified wood using X-ray computed tomography in relation to wetting properties2017In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 71, no 2, p. 119-128Article in journal (Refereed)
    Abstract [en]

    X-ray computed tomography (XCT) was utilized to visualize and quantify the 2D and 3D microstructure of acetylated southern yellow pine (pine) and maple, as well as furfurylated pine samples. The total porosity and the porosity of different cell types, as well as cell wall thickness and maximum opening of tracheid lumens were evaluated. The wetting properties (swelling and capillary uptake) were related to these microstructural characteristics. The data show significant changes in the wood structure for furfurylated pine sapwood samples, including a change in tracheid shape and filling of tracheids by furan polymer. In contrast, no such changes were noted for the acetylated pine samples at the high resolution of 0.8 mu m. The XCT images obtained for the furfurylated maple samples demonstrated that all ray cells and some vessel elements were filled with furan polymer while the fibers largely remained unchanged. Furfurylation significantly decreased the total porosity of both the maple and pine samples. Furthermore, this was observed in both earlywood (EW) and latewood (LW) regions in the pine samples. In contrast, the total porosity of pine samples was hardly affected by acetylation. These findings are in line with wetting results demonstrating that furfurylation reduces both swelling and capillary uptake in contrast to acetylation which reduces mostly swelling. Furfurylation significantly increased the cell wall thickness of both the maple and pine samples, especially at higher levels of furfurylation.

  • 36. Li, Tao
    et al.
    Cheng, Da-li
    Avramidis, Stavros
    Wålinder, Magnus E. P.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Zhou, Ding-guo
    Response of hygroscopicity to heat treatment and its relation to durability of thermally modified wood2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 144, p. 671-676Article in journal (Refereed)
    Abstract [en]

    In an attempt to study the effect of heat treatment on hygroscopicity and durability of wood, Poplar (Populus spp.) wood was thermally modified using five different temperatures between 170 degrees C and 210 degrees C, for a fixed duration of 3 h. Moisture adsorption behavior and the resistance to soft rot fungi were investigated thereafter. Based on the Hailwood-Horrobin sorption model, the amount of available sorption sites within specimens for the different groups of Poplar wood were calculated from the model's m(0) parameter. Chemical analysis of the changes in wood components induced by heat treatment allows for a comparison between the easily obtained m(0) and the results of time-consuming wood decay tests. The proposed m(0)-based method for highly efficient evaluation and prediction of durability of thermally modified wood could optimize future research on the mechanisms of heat treatment processes.

  • 37. Kymalainen, M.
    et al.
    Hautamaki, S.
    Lillqvist, Kristiina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, L.
    Surface modification of solid wood by charring2017In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, no 10, p. 6111-6119Article in journal (Refereed)
    Abstract [en]

    Most wooden structures for outdoor applications require repetitive maintenance operations to protect the surfaces from adverse effects of weathering. One-sided surface modification of boards with a relatively fast charring process has the potential to increase the durability and service life of wooden claddings. To assess some weathering-related effects on surface charred wood, spruce and pine sapwood were subjected to a series of long charring processes (30-120 min) at a moderate temperature of 250 A degrees C and to a short one (30 s) at a high temperature of 400 A degrees C. The wettability and contact angles of treated samples were investigated, and the heat transfer was measured along with the micromorphological changes taking place in the material. The result revealed an increased moisture resistance of charred spruce sapwood and an increased water uptake of pine sapwood. The contact angles of both wood species improved compared to references. Heat conduction measurement revealed that only a thin section of the wood was thermally modified. Some micromorphological changes were recorded, especially on the inside walls of the lumina. The results show that spruce sapwood has an improved resistance towards moisture-induced weathering, but more studies are needed to unlock the potential of surface charred wood.

  • 38. Vahtikari, Katja
    et al.
    Rautkari, Lauri
    Noponen, Tuula
    Lillqvist (nee Laine), Kristiina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Hughes, Mark
    The influence of extractives on the sorption characteristics of Scots pine (Pinus sylvestris L.)2017In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, no 18, p. 10840-10852Article in journal (Refereed)
    Abstract [en]

    The sorption behaviour of extracted and un-extracted Scots pine (Pinus sylvestris L.) heartwood was analysed using dynamic vapour sorption apparatus. In addition to the sorption isotherm and hysteresis, the moisture increments and decrements were determined as well as the rate of sorption. Parallel exponential kinetics model was used for further analysis. The effect of cyclic humidity loading on the sorption characteristics was studied by exposing samples to ten repeated sorption cycles and by determining the amount of accessible hydroxyl (OH) groups before and after the cyclic humidity loading. Removal of extractives led to an increase in EMC both in adsorption and in desorption. Hysteresis decreased due to the removal of extractives. Cyclic humidity loading reduced the sorptive capacity of wood material for both extracted and un-extracted wood, but was more pronounced in un-extracted wood. However, despite the decrease in the sorptive capacity, the amount of accessible OH groups increased after ten repeated dry-humid cycles.

  • 39. Bressi, S.
    et al.
    Dumont, A. G.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Carleton University, Ottawa, Canada; Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
    A new laboratory methodology for optimization of mixture design of asphalt concrete containing reclaimed asphalt pavement material2016In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 49, no 12, p. 4975-4990Article in journal (Refereed)
    Abstract [en]

    The reduction of virgin bitumen added to asphalt mixtures containing Reclaimed Asphalt Pavement (RAP) is based on the typical assumption that all the aged binder function in the same way as the virgin binder. However, recent studies conducted by the authors for a specific case show that a blend or mobilization of RAP binder are negligible. The aged bitumen becomes softer acting as glue facilitating cluster formation between small-size RAP particles. The reduction of small-size particles causes changes in the target grading curve and in the voids-fill, affecting the compactability of RAP mixtures. Therefore the target grading curve of RAP mixtures needs to be readjusted, using different proportions of virgin aggregates and taking into account the cluster phenomenon. The objective of this paper is to develop a new mix design approach for RAP mixtures, taking into account the cluster phenomenon and the contribution of the aged bitumen in the compactability. The virgin aggregates, filler and RAP are investigated and individually included in the calculation. 3D images of the virgin aggregates allowed the determination of new surface area factors; the concept of critical filler concentration led to the definition of the minimum bitumen quantity required to maintain the mastic in a diluted state and fill the voids. A RAP clustering model was introduced to predict the agglomeration of small-size RAP particles. The readjustment of the target grading curve was analytically calculated, allowing the correct estimation of the amount of virgin bitumen to be added to asphalt mixtures. Finally, a first verification of the entire process was carried out performing laboratory tests. These promising results enable the challenge of a new mix design optimization for HMA with high RAP content to be addressed.

  • 40.
    Ghafoori Roozbahany, Ehsan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    A new test to study the flow of mixtures at early stages of compaction2016In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 49, no 9, p. 3547-3558Article in journal (Refereed)
    Abstract [en]

    Workability is one of the most commonly used indicators for the capability of asphalt mixtures tobe placed and compacted on the roads with long lasting quality and minimum maintenancethroughout its service life. Despite of valuable previous efforts for measuring and characterizingworkability, none of them has proven successful in representing the field conditions of roadconstructions. This paper is an attempt towards developing a systematic workability test methodfocusing on compaction, the so-called Compaction Flow Test (CFT), by simulating fieldcompaction at early stages and at laboratory scale with the main focus on mixture flow. The CFTwas applied for different mixtures in order to identify the parameters with highest impact on theasphalt particle movements under compaction forces. A new setting inside X-ray ComputationalTomography (CT) allowed tracing asphalt particles during the CFT and acquiring CT imagesunderlining the reliability of the CFT results. In addition, simple Discrete Element Models (DEM)were successfully generated to justify some of the CFT results.

  • 41. Bressi, Sara
    et al.
    Dumont, A. G.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Carleton Univ, Ottawa, Canada.
    An advanced methodology for the mix design optimization of hot mix asphalt2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 98, p. 174-185Article in journal (Refereed)
    Abstract [en]

    The bitumen quantity to add to asphalt mixtures depends on the surfaces of aggregates and filler to be coated. The formulas currently available in the literature have limitations such as considering all the fillers with the same specific surface or the aggregates with spherical or cubical shapes. This paper aims to define an analytical approach for the determination of the optimal dosage of bitumen in HMA proposing new methodologies to go a step further in the resolution of the above mentioned approximations. Indeed, new surface area factors were calculated to determine the aggregates surface considering their real shapes and volumes. Afterwards, the authors proposed a detailed characterization of two types of fillers and the critical filler concentration, introduced by Faheem and Bahia, was used to calculate the minimum amount of bitumen for maintaining the mastic in a diluted state and filling the voids in the mixtures. Finally, a verification of the formula developed was carried out with specific laboratory tests. These results allow the challenge of revising the method of calculating the specific surface of the aggregates and filler to be addressed with the final goal to include them in a new mix design optimization for HMA. 

  • 42. Royne, Frida
    et al.
    Penaloza, Diego
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden, Sweden.
    Sandin, Gustav
    Berlin, Johanna
    Svanström, Magdalena
    Climate impact assessment in life cycle assessments of forest products: implications of method choice for results and decision making2016In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 116, p. 90-99Article in journal (Refereed)
    Abstract [en]

    As life cycle assessments are often conducted to provide decision support, it is important that impact assessment methodology is consistent with the intended decision context. The currently most used climate impact assessment metric, the global warming potential, and how it is applied in life cycle assessments, has for example been criticised for insufficiently accounting for carbon sequestration, carbon stored in long-lived products and timing of emission. The aim of this study is to evaluate how practitioners assess the climate impact of forest products and the implications of method choice for results and decision-making. To identify current common practices, we reviewed climate impact assessment practices in 101 life cycle assessments of forest products. We then applied identified common practices in case studies comparing the climate impact of a forest-based and a non-forest-based fuel and building, respectively, and compared the outcomes with outcomes of applying alternative, non-established practices. Results indicate that current common practices exclude most of the dynamic features of carbon uptake and storage as well as the climate impact from indirect land use change, aerosols and changed albedo. The case studies demonstrate that the inclusion of such aspects could influence results considerably, both positively and negatively. Ignoring aspects could thus have important implications for the decision support. The product life cycle stages with greatest climate impact reduction potential might not be identified, product comparisons might favour the less preferable product and policy instruments might support the development and use of inefficient climate impact reduction strategies.

  • 43.
    Peñaloza, Diego
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Erlandsson, Martin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Falk, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Exploring the climate impact effects of increased use of bio-based materials in buildings2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 125, p. 219-226Article in journal (Refereed)
    Abstract [en]

    Whenever Life Cycle Assessment (LCA) is used to assess the climate impact of buildings, those with high content of biobased materials result with the lowest impact. Traditional approaches to LCA fail to capture aspects such as biogenic carbon exchanges, their timing and the effects from carbon storage. This paper explores a prospective increase of biobased materials in Swedish buildings, using traditional and dynamic LCA to assess the climate impact effects of this increase. Three alternative designs are analysed; one without biobased material content, a CLT building and an alternative timber design with “increased bio”. Different scenario setups explore the sensitivity to key assumptions such as the building's service life, end-of-life scenario, setting of forest sequestration before (growth) or after (regrowth) harvesting and time horizon of the dynamic LCA. Results show that increasing the biobased material content in a building reduces its climate impact when biogenic sequestration and emissions are accounted for using traditional or dynamic LCA in all the scenarios explored. The extent of these reductions is significantly sensitive to the end-of-life scenario assumed, the timing of the forest growth or regrowth and the time horizon of the integrated global warming impact in a dynamic LCA. A time horizon longer than one hundred years is necessary if biogenic flows from forest carbon sequestration and the building's life cycle are accounted for. Further climate impact reductions can be obtained by keeping the biogenic carbon dioxide stored after end-of-life or by extending the building's service life, but the time horizon and impact allocation among different life cycles must be properly addressed.

  • 44.
    de Frias Lopez, Ricardo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Jelagin, Denis
    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), Civil and Architectural Engineering, Highway Engineering Laboratory. School of Engineering and Applied Science, Aston University, Birmingham, UK.
    Force transmission and soil fabric of binary granular mixtures2016In: Geotechnique, ISSN 0016-8505, E-ISSN 1751-7656, Vol. 66, no 7, p. 578-583Article in journal (Refereed)
    Abstract [en]

    The effect of fines content on force transmission and fabric development of gap-graded mixtures under triaxial compression has been studied using the discrete-element method. Results were used to define load-bearing soil fabrics where the relative contributions of coarse and fine components are explicitly quantified in terms of force transmission. Comparison with previous findings suggests that lower particle size ratios result in higher interaction between components. A potential for instability was detected for underfilled fabrics in agreement with recent findings. It was also found that the threshold fines content provides an accurate macroscopic estimation of the transition between underfilled and overfilled fabrics.

  • 45.
    Sedighi Moghaddam, Maziar
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
    Heydarihamedani, Golrokh
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Tuominen, Mikko
    SP Technical Research Institute of Sweden.
    Fielden, Matthew
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haapanen, Janne
    TUT Tampere University of Technology, Aerosol Physics Laboratory, Department of Physics.
    Mäkelä, Jyrki M.
    TUT Tampere University of Technology, Aerosol Physics Laboratory, Department of Physics.
    Wålinder, E.P. Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Claessson, M. Per
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Swerin, Agne
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
    Hydrophobisation of wood surfaces by combining liquid flame spray (LFS)and plasma treatment: dynamic wetting properties2016In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 6, p. 527-537Article in journal (Refereed)
    Abstract [en]

    The hydrophilic nature of wood surfaces is a major cause for water uptake and subsequent biological degradation and dimensional changes. In the present paper, a thin transparent superhydrophobic layer on pine veneer surfaces has been created for controlling surface wettability and water repellency. This effect was achieved by means of the liquid flame spray (LFS) technique, in the course of which nanoparticulate titanium dioxide (TiO2) was brought to the surface, followed by plasma polymerisation. Plasma polymerised perfluorohexane (PFH) or hexamethyldisiloxane (HMDSO) were then deposited onto the LFS-treated wood surfaces. The same treatment systems were applied to silicon wafers so as to have well-defined reference surfaces. The dynamic wettability was studied by the multicycle Wilhelmy plate method, resulting in advancing and receding contact angles as well as sorption behaviour of the samples during repeated wetting cycles in water. Atomic force microscopy (AFM) and Xray photoelectron spectroscopy (XPS) were employed to characterise the topography and surface chemical compositions and to elucidate the question how the morphology of the nanoparticles and plasma affect the wetting behaviour. A multi-scale roughness (micro-nano roughness) was found and this enhanced the forced wetting durability via a superhydrophobic effect on the surface, which was stable even after repeated wetting cycles. The hydrophobic effect of this approach was higher compared to that of plasma modified surfaces with their micro-scale modification.

  • 46.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Birgisson, B.
    Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model2016In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, p. 1-19Article in journal (Refereed)
    Abstract [en]

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

  • 47. Jeoffroy, E.
    et al.
    Koulialias, D.
    Yoon, S.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Swiss Federal Laboratories for Materials Science and Technology, Switzerland.
    Studart, A. R.
    Iron oxide nanoparticles for magnetically-triggered healing of bituminous materials2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 112, p. 497-505Article in journal (Refereed)
    Abstract [en]

    Healing of micro-cracks is crucial for recovering the mechanical properties and extending the service time of bituminous materials. However, crack closure is often challenged by the efficiency and repeatability of the healing process or its technical and economic feasibility for large-scale applications. Here, we propose an innovative method to close micro-cracks in bituminous materials by using magnetically-triggered iron oxide nanoparticles as heating agents. Heating is generated through the so-called hyperthermia effect upon exposure of the nanoparticles to an external oscillating magnetic field. When mixed in a low volume fraction of 1% within bitumen, the nanoparticles generate enough heat to decrease the viscosity of the surrounding material and thus promote crack closure. Oleic acid is used to coat the iron oxide nanoparticles and enable their homogeneous distribution in the bitumen. Because of high hysteresis losses, γ-Fe2O3 nanoparticles with a mean crystallite size of 50 nm exhibited specific absorption rates (SAR) as high as 285 W/g when subjected to a magnetic field of 30 mT at 285 kHz. In contrast to the relatively slow heating of electrically-conductive additives, we find that iron oxide nanoparticles pre-embedded in bitumen allows for crack closure in a few seconds when subjected to similar magnetic field conditions. This represents a new efficient way to heal damage in thermoplastic road pavements in the presence of mineral aggregates.

  • 48.
    Tuominen, M
    et al.
    SP Technical Research Institute of Sweden.
    Teisala, Hannu
    Tampere University of Technology.
    Haapanen, Janne
    Tampere University of Technology.
    Mäkelä, Jyrki M.
    Tampere University of Technology.
    Honkanen, Mari
    Tampere University of Technology.
    Vippola, Minnamari
    Tampere University of Technology.
    Bardage, Stig
    SP Technical Research Institute of Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Swerin, Agne
    SP Technical Research Institute of Sweden.
    Superamphiphobic overhang structured coating on a biobased material2016In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 389, p. 135-143Article in journal (Refereed)
    Abstract [en]

    A superamphiphobic coating on a biobased material shows extreme liquid repellency with static contact angles (CA) greater than 150° and roll-off angles less than 10° against water, ethylene glycol, diiodomethane and olive oil, and a CA for hexadecane greater than 130°. The coating consisting of titania nanoparticles deposited by liquid flame spray (LFS) and hydrophobized using plasma-polymerized perfluorohexane was applied to a birch hardwood. Scanning electron microscopy (SEM) imaging after sample preparation by UV laser ablation of coated areas revealed that capped structures were formed and this, together with the geometrically homogeneous wood structure, fulfilled the criteria for overhang structures to occur. The coating showed high hydrophobic durability by still being non-wetted after 500 000 water drop impacts, and this is discussed in relation to geometrical factors and wetting forces. The coating was semi-transparent with no significant coloration. A self-cleaning effect was demonstrated with both water and oil droplets. A self-cleanable, durable and highly transparent superamphiphobic coating based on a capped overhang structure has a great potential for commercial feasibility in a variety of applications, here exemplified for a biobased material.

  • 49.
    Laine, Kristiina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Tech Res Inst Sweden, Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, L.
    Hughes, M.
    Lankveld, C.
    Surface densification of acetylated wood2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 6, p. 829-835Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of wood can be improved by compressing its porous structure between heated metal plates. By adjusting the process parameters it is possible to target the densification only in the surface region of wood where the property improvements are mostly needed in applications, such as flooring. The compressed form is, however, sensitive to moisture and will recover to some extent in high humidity. In this study, therefore, acetylated radiata pine was utilised in the surface densification process in order to both reduce the set-recovery of densified wood and to improve the hardness of the acetylated wood. Pre-acetylation was found to significantly reduce the set-recovery of surface densified wood. However, after the second cycle the increase in set-recovery of acetylated wood was relatively higher than the un-acetylated wood. The acetylated samples were compressed by only 1 mm (instead of the target 2 mm), yet, the hardness and hardness recovery of the acetylated samples significantly increased as a result of densification. It was also discovered that rough (un-planed) surfaces may be surface densified, however, even if the surface became smooth to the touch, the appearance remained uneven.

  • 50. Čermák, Petr
    et al.
    Vahtikari, Katja
    Rautkari, Lauri
    Laine, Kristiina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Horáček, Petr
    Baar, Jan
    The effect of wetting cycles on moisture behaviour of thermally modified Scots pine (Pinus sylvestris L.) wood2016In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 51, no 3, p. 1504-1511Article in journal (Refereed)
    Abstract [en]

    The moisture behaviour of thermally modified Scots pine (Pinus sylvestris L.) exposed to cyclic conditions was analysed. Specimens of dimensions 15 × 15 × 5 mm3 were thermally modified at 180 °C (TM1) and 220 °C (TM2) using atmospheric pressure and superheated steam. Radial, tangential, volumetric swelling and anti-swelling efficiency (ASE) were calculated during six consecutive drying–soaking cycles. Afterwards, additional specimens were exposed to ten relative humidity cycles (0 and 95 %) at temperature 25 and 40 °C in order to analyse its influence on sorption behaviour. Application of thermal modification led to significant reduction of swelling from original 18.4–13.3 % for TM1 and to 10.5 % for TM2. However, after exposure to six consecutive soaking–drying cycles, the swelling of control specimens slightly decreased, whereas the swelling of thermally modified specimens increased. Due to the increased swelling after repeated cycles, the original ASE (28.6 and 42.7 %) decreased to 22.5 % for TM1 and to 36.88 % for TM2. The presence of leachable compounds and release of internal stresses are mainly attributed to that phenomenon. The EMC of the reference specimens decreases over the repeated humidity cycles for approximately 1 %–units. Same trend was found for the mild thermal modification TM1, but decreasing only in the range of 0.5 %–units. However, the EMC of the TM2 specimens during humidity cycles behaved differently. The results provide a better insight into details of thermal modification of wood and its behaviour under cyclic conditions.

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