Browsing by Author "Habermehl-Cwirzen, Karin"

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    Bond Strength between Glass Fiber Fabrics and Low Water-to-Binder Ratio Mortar: Experimental Characterization
    (2018-09-02) Böhling, Daniel; Cwirzen, Andrzej; Habermehl-Cwirzen, Karin; Department of Civil Engineering; Aalto University; Luleå University of Technology
    Full utilization of mechanical properties of glass fiber fabric-reinforced cement composites is very limited due to a low bond strength between fibers and the binder matrix. An experimental setup was developed and evaluated to correlate the mortar penetration depth with several key parameters. The studied parameters included fresh mortar properties, compressive and flexural strengths of mortar, the fabric/mortar bond strength, fabric pullout strength, and a single-lap shear strength. Results showed that an average penetration of mortar did not exceed 100 mu m even at a higher water-to-binder ratio. The maximum particle size of the used fillers should be below an average spacing of single glass fibers, which in this case was less than 20 mu m to avoid the sieving effect, preventing effective penetration. The pullout strength was strongly affected by the penetration depth, while the single-lap shear strength was also additionally affected by the mechanical properties of the mortar.
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    An insight : studies of atomic and molecular adsorption on Co(0001)
    (Helsinki University of Technology, 2006-03-17) Habermehl-Cwirzen, Karin; Department of Engineering Physics and Mathematics; Teknillisen fysiikan ja matematiikan osasto; Laboratory of Physics; Fysiikan laboratorio
    This thesis deals with the adsorption of selected atoms and molecules on a well defined single crystal cobalt surface. X-ray photoelectron spectroscopy has been used to identify different adsorption sites and coverages. Work function measurements have been utilized to monitor the strength of the interaction between adsorbed species and cobalt substrate. Thermal desorption spectroscopy has identified the desorption products and has given information on the activation energies for desorption. By means of low energy electron diffraction measurements the adsorbate unit cell and, by utilizing I-V curve analysis, the atomic positions have been determined. Adsorption processes are important, e.g. in catalytic reactions, therefore studying adsorption and desorption of atoms and molecules on a well-defined surface can give useful insight information on reactions and how these reactions might be influenced. We have studied a selection of important atoms and molecules on a Co(0001) surface. Deuterium has been extensively studied as single adsorbate as well as in coadsorption with carbon monoxide and sulfur. Methanol adsorption and O-H bond scission has been an important topic of this thesis. Benzene adsorption has been determined at length, as a single component including I-V curve analysis and DFT calculations, as well as coadsorbed with carbon monoxide. Sulfur, a common unwanted component in a variety of processes like, e.g. crude oil refinery, was investigated as single adsorbate as well as coadsorbed with carbon monoxide.
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    Internal curing of concrete
    (2015-05-18) Kyllästinen, Karri; Habermehl-Cwirzen, Karin; Insinööritieteiden korkeakoulu; Cwirzen, Andrzej
    Internal curing was used already in the Roman times, for example the famous Pantheon building is done partly with internally cured concrete. The external curing of concrete such as fogging the surface only achieves the surface of the concrete, with internal curing the whole 3-dimensional microstructure of the concrete could be cured. The objective of this thesis was to study the impact of internal curing on compressive strength, tensile/flexural strength and drying shrinkage. The goal was also to determine which grain sizes lightweight aggregates will be the best in internal curing use. In this thesis the internal curing is done with lightweight aggregates. The calculated amount of normal weight aggregate is replaced with lightweight aggregate, which is prewetted in the water for 24h before it was added to the concrete mix. Before it was added to the mix, the surface moisture of it was removed. Prewetted lightweight aggregate released its internal water to the concrete mix which improved the hydration process. The used research methods include; literature review, definition of research program and experimental studies. The obtained tests results showed that the best grain size of lightweight aggregates for internal curing are 0-2 mm and 2-4 mm. The usage of these sizes enabled to produce concrete having similar mechanical properties to normal concretes but significantly reduced drying shrinkage.
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    A novel cement-based hybrid material
    (IOP Publishing, 2009) Nasibulin, Albert G; Shandakov, Sergey D; Nasibulina, Larisa I; Cwirzen, Andrzej; Mudimela, Prasantha R; Habermehl-Cwirzen, Karin; Grishin, Dmitrii A; Gavrilov, Yuriy V; Malm, Jari E M; Tapper, Unto; Tian, Ying; Penttala, Vesa; Karppinen, Maarit; Kauppinen, Esko I; Kemian laitos; Department of Chemistry; Kemian tekniikan korkeakoulu; School of Chemical Technology
    Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance structural and multi-functional composite materials. However, one of the largest obstacles to creating strong, electrically or thermally conductive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of purification and functionalization of the carbon nanomaterial are required. We propose a new approach to grow CNTs/CNFs directly on the surface of matrix particles. As the matrix we selected cement, the most important construction material. We synthesized in a simple one-step process a novel cement hybrid material (CHM), wherein CNTs and CNFs are attached to the cement particles. The CHM has been proven to increase 2 times the compressive strength and 40 times the electrical conductivity of the hardened paste, i.e. concrete without sand.
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    Synthesis of Carbon Nanotubes and Nanofibers on Silica and Cement Matrix Materials
    (Hindawi Publishing Corporation, 2009) Mudimela, Prasantha R.; Nasibulina, Larisa I.; Nasibulin, Albert G.; Cwirzen, Andrzej; Valkeapää, Markus; Habermehl-Cwirzen, Karin; Malm, Jari E. M.; Karppinen, Maarit; Penttala, Vesa; Koltsova, Tatiana S.; Tolochko, Oleg V.; Kauppinen, Esko I.; Kemian laitos; Department of Chemistry; Kemian tekniikan korkeakoulu; School of Chemical Technology
    In order to create strong composite materials, a good dispersion of carbon nanotubes (CNTs) and nanofibers (CNFs) in a matrix material must be obtained. We proposed a simple method of growing the desirable carbon nanomaterial directly on the surface of matrix particles. CNTs and CNFs were synthesised on the surface of model object, silica fume particles impregnated by iron salt, and directly on pristine cement particles, naturally containing iron oxide. Acetylene was successfully utilised as a carbon source in the temperature range from 550 to 750 C. 5–10 walled CNTs with diameters of 10–15 nm at 600 C and 12–20 nm at 750 C were synthesised on silica particles. In case of cement particles, mainly CNFs with a diameter of around 30 nm were grown. It was shown that high temperatures caused chemical and physical transformation of cement particles.