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  • 1.
    Ghasemi, Yahya
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Rajczakowska, Magdalena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Emborg, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Shape-dependent calculation of specific surface area of aggregates versus X-ray microtomography2018In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763XArticle in journal (Refereed)
    Abstract [en]

    The specific surface area (SSA) of constituents in a concrete mixture has a significant effect on its workability in fresh state. Excess layer theories relate the SSA to the flow behaviour of mixtures and can be used as part of an approach to mix design. However, measurement of SSA is complex and includes several issues, and thus is commonly replaced by mathematical estimation of the parameter. The mathematical approximation of surface area is based on the assumption of a spherical shape for the particles, which leads to failure of taking into account the effect of shape and the square–cube law. The article explores the possibility of replacing the assumption of a spherical shape with that of Platonic solids as the representative shape to account for the angularity of aggregates. The calculation was conducted based on information on the particle size distribution (PSD) obtained from dry sieving method. A calculated surface area on the assumption of a dodecahedron shape for natural aggregates and a cubical shape for crushed aggregates showed good agreement with SSA measurements conducted by X-ray microtomography. Furthermore, the effect of changes in PSD on the accuracy of the approach was also studied. It was found that the estimated value of SSA was improved in comparison with the traditional way of calculation on the assumption of a spherical shape.

  • 2.
    Sobótka, Maciej
    et al.
    Faculty of Civil Engineering, Wrocław University of Science and Technology.
    Pachnicz, Michał
    Faculty of Civil Engineering, Wrocław University of Science and Technology.
    Rajczakowska, Magdalena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Induced Crack Network Evolution in Geomaterials: µct Examination and Mathematical Morphology Based Analysis2018In: Proceedings of China-Europe Conference on Geotechnical Engineering, Cham: Springer, 2018, Vol. 1, p. 216-219Conference paper (Refereed)
    Abstract [en]

    Fracture parameters of the rock material are known to change due to applied loading, having effect on, e.g. the rock permeability coefficient which can be estimated based on the geometrical descriptors of the crack space. In this paper, a method of crack network evolution analysis is proposed for the rock samples subjected to uniaxial compression. Fracture development is investigated using ex-situ time-lapse micro-computed tomography (µCT). The sets of images are acquired for each specimen at three damage levels: before loading, at approximately 50% of compressive strength and, finally, after reaching micro-dilatancy threshold (or compressive strength). The reconstructed and segmented 3D crack network is examined at each loading stage. The analysis consists of image processing and determination of the selected morphological parameters, i.e. volume fraction of the crack, spatial distribution of the fracture aperture, tortuosity as well as the structure model index (SMI).

  • 3.
    Tole, Ilda
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Rajczakowska, Magdalena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Activation of a Raw Clay by Mechanochemical Process: Effects of Various Parameters on the Process Efficiency and Cementitious Properties2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 10, article id 1860Article in journal (Refereed)
    Abstract [en]

    The efficiency of the mechanochemical activation (MCA) is influenced by various process parameters as well as by the properties of the treated material. The main objective of this research was to optimize the MCA process, gaining enhancement of the chemical reactivity of a Swedish raw clay, which is going to be used as an alkali-activated cementitious binder. The effects of the amount of water, the filling ratio, the rotation speed, and the grinding duration on the amorphization degree were evaluated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Generally, wet and dry processes showed an extensive amorphization of both kaolinite and muscovite minerals present in the studied clay. On the contrary, quartz was amorphized mainly by the wet grinding process. The efficiency of both dry and wet grinding processes was enhanced by the increased number of grinding media versus the amount of the activated material. However, longer processing times caused significant agglomeration while a higher rotational speed enhanced the amorphization. Preliminary tests have shown that alkali activation of the processed clays produced hardened samples. Furthermore, the increased amorphization corresponded to the increased compressive strength values.

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