National Repository of Grey Literature 47 records found  1 - 10nextend  jump to record: Search took 0.05 seconds. 
X-Ray CT inspection of subsurface areas of concretes exposed to fast flowing liquids
Sitek, Libor ; Hlaváček, Petr ; Souček, Kamil ; Bodnárová, L. ; Foldyna, Josef ; Zajícová, Vendula ; Berčáková, Andrea ; Foldyna, Vladimír
Concrete structures affected for a long time by flowing liquids are exposed to gradual erosion in surface layers caused by a combination of several degradation processes: abrasion, cavitation and chemical or bacterial impacts. Due to the complex phenomena and difficult-to-define initial and boundary conditions, the whole process cannot be easily simulated using the conventional computing tools. Laboratory experimental research is thus the most appropriate approach for the investigation of a suitable composition of concrete resistant to the flowing liquids. However, the methods used are often very time consuming and last even several years. High-speed water flows can be elegantly used for the acceleration of the mechanical simulation of a real situation. Several experiments on the effects of the high-speed water flows on concrete surfaces have been carried out. Using the X-Ray CT methods, subsurface structures of concretes exposed to the accelerated mechanical simulation of the erosion wear caused by fast flowing liquids were investigated and presented in the article. It has been shown that the simulation does not cause initiation of new fractures or cracks in the original concrete structure. The pure water flow mainly removes the hardened cement paste and reveals the aggregate grains. The water flow with abrasive particles disintegrates in greater depths and washes out entire aggregate grains, eventually amputates them and finally smoothens entire surface.
Evaluation of fracture response of Silesian granite specimens via Effective Crack Model approach and finite element analysis
Malíková, L. ; Vavro, Leona ; Vavro, Martin ; Keršner, Z.
The paper is focused on the advanced evaluation of fracture tests of selected rock specimens. Assessment of fracture response of chevron notch cylindrical specimens of Silesian granite subjected to three-point bending test was performed. The effective crack model is used and academic software chevroncylinder (author Petr Frantík) based on the finite element method is applied for the analyses. Based on the described procedures, estimation of maximum values of the effective fracture toughness are established and discussed.
Thermal behaviour of organically modified smectites
Plevová, Eva ; Vaculíková, Lenka ; Valovičová, Věra ; Simha Martynková, G.
The smectites were modified with different types of alkylammonium cations. The X-ray powder diffraction was used to calculate the values of the basal space of the modified smectites to confirm the intercalation of cations into the structure. The montmorillonites were also characterized by means of FTIR spectroscopy, which proved sorption or intercalation of the alkylammonium cations too. Thermal behaviour of the smectites was investigated by simultaneous thermogravimetry and differential thermal analysis. The temperatures of dehydratation and dehydroxylation and the temperatures related to total melting and recrystallization generally changed. Study of temperatures changes together with determination of kinetic parameters helped to obtained a comprehensive assessment of smectite thermal stability.
Characterization of fine-grained montmorillonite fractions suitable for composite preparation
Valovičová, Věra ; Vaculíková, Lenka ; Plevová, Eva ; Dolinská, S. ; Znamenáčková, I. ; Danková, Z.
The aim of this experimental study was to characterize a fine-grained fraction of montmorillonites (SAz-2, STx-1, SWy-2 and Kunipia-F). It was investigated in order to provide more precise information of used montmorillonites than could be obtained by analysis of the unfractioned montmorillonites. At first, the fine fraction of montmorillonites were prepared by sedimentation and activation by means of Na2CO3. The prepared clay materials were characterized by the X-ray diffraction analysis and FTIR spectroscopy. The thermal behaviour of the studied samples was determinated according to the characteristic temperatures obtained from TG/DTA curves. The temperatures of dehydratation and dehydroxylation were evaluated and kinetic parameters were also calculated. The porosity and surface properties of the studied samples were gained by the nitrogen adsorption measurements. The obtained results confirmed that the fine fraction of montmorillonites could be a suitable material for subsequent preparation of composites with enhanced sorption properties, especially montmorillonite/MnO2 composite.
Application of bentonite-manganese oxide composites in removal of heavy metals
Dolinská, S. ; Znamenáčková, I. ; Tomčová, J. ; Valovičová, Věra ; Vaculíková, Lenka ; Plevová, Eva
The paper is aimed on the using of non-homogeneous bentonites coated by manganese oxides for the removal of heavy metal cations from the water solutions. In the first stage Slovak natural bentonite was converted to sodium form using by Na2CO3 as the activating agent. After that the manganese oxides were precipitated on the surface of natural and sodium activated bentonite, respectively. The structural changes before and after the modifications of bentonites were characterized by X-ray diffraction analyses and X-ray photoelectron spectroscopy. To compare the sorption properties of the natural bentonite and modified bentonites, sorption experiments of Cd2+ from aqueous solutions were done.
Effects of abrasives during accelerated simulation of mechanical corrosion of cement composites using abrasive water flow
Hlaváček, Petr ; Sitek, Libor ; Klichová, Dagmar ; Bodnárová, L.
The paper deals with the use of the abrasive water flow technology in an accelerated simulation of the process of mechanical degradation of surface layers of cement-based composites by flowing liquids. Effects of the abrasive particle size and the mass flow rate of abrasives in an abrasive water flow impacting on the surface of concrete samples have been studied. In addition, suitability of the application of the abrasive water flow for the simulation of real situation of the surface wear by flowing liquids has been evaluated.
Possibilities of using 3D laser scanning in geotechnical practise
Kukutsch, Radovan ; Kajzar, Vlastimil ; Šňupárek, Richard ; Waclawik, Petr
We are experiencing the penetration of modern and smart technologies in all sectors of human activity, including mining and geotechnics. One of these technologies is 3D laser scanning, which has seen significant technological advancements over the last decade and has become an integral part of underground construction monitoring as a tool to enable comprehensive, accurate and unbiased capture of the spatial situation in digital form. This development was behind the fact that since 2013, 3D laser scanner has been used by the Institute of Geonics of the Czech Academy of Sciences as a necessary part of the geotechnical monitoring of mine works, when it is possible to precisely detect and quantify the time-space changes caused by man's intervention in the rock mass compared to the traditional established measuring methods. A leading project of recent years was the monitoring of the strain stress state of the rock massif during the 30th seam extraction during the trial operation of the Room and Pillar extraction method in the CSM Mine shaft safety pillar where, besides many other measuring instruments, 3D laser scanning was used for the convergence measuring of roadways, especially for capturing any deformation changes on the permanent pillars. A complementary function was the comparative evaluation with the results of other tools, e.g. with data measured by horizontal extensometers. The subject of the article will be a general description of the possibilities of using 3D laser scanning in geotechnical practice on spatial data acquired during the monitoring lasting almost 3.5 years, when important phenomena were detected in the movement of the pillar walls and the floor heave in the CSM Mine in the tens of cm, sometimes up to 100 cm.
Possibilities of using 3D laser scanning in geotechnical practise
Kukutsch, Radovan ; Kajzar, Vlastimil ; Šňupárek, Richard ; Waclawik, Petr
We are experiencing the penetration of modern and smart technologies in all sectors of human activity, including mining and geotechnics. One of these technologies is 3D laser scanning, which has seen significant technological advancements over the last decade and has become an integral part of underground construction monitoring as a tool to enable comprehensive, accurate and unbiased capture of the spatial situation in digital form. This development was behind the fact that since 2013, 3D laser scanner has been used by the Institute of Geonics of the Czech Academy of Sciences as a necessary part of the geotechnical monitoring of mine works, when it is possible to precisely detect and quantify the time-space changes caused by man's intervention in the rock mass compared to the traditional established measuring methods. A leading project of recent years was the monitoring of the strain stress state of the rock massif during the 30th seam extraction during the trial operation of the Room and Pillar extraction method in the CSM Mine shaft safety pillar where, besides many other measuring instruments, 3D laser scanning was used for the convergence measuring of roadways, especially for capturing any deformation changes on the permanent pillars. A complementary function was the comparative evaluation with the results of other tools, e.g. with data measured by horizontal extensometers. The subject of the article will be a general description of the possibilities of using 3D laser scanning in geotechnical practice on spatial data acquired during the monitoring lasting almost 3.5 years, when important phenomena were detected in the movement of the pillar walls and the floor heave in the CSM Mine in the tens of cm, sometimes up to 100 cm.
Roadways stability within coal excavation by room and pillar mining method at the great depths
Šňupárek, Richard ; Waclawik, Petr ; Kukutsch, Radovan
In order to verify the stress-strain state of mining using the room and pillar method at a depth of up to 900 m below the surface, an extensive system of geotechnical monitoring and observation of deformations and surface movement was implemented. Based on the results of the stress-strain monitoring, detailed analysis of roadway stability from the point of view of the convergence, deformation behavior of the surrounding rock mass and the function of the reinforcement used in the two monitored areas with different geological and operational conditions was carried out.
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Stability of corridors in the coal-pillar excavation process at deep depths
Šňupárek, Richard ; Waclawik, Petr ; Kukutsch, Radovan
In order to verify the stress-strain manifestations of the corridor-pillar excavation at a depth of up to 900 m below the surface, an extensive system of geotechnical monitoring and observation of deformations and surface movement was implemented. Based on the results of the stress-strain monitoring, detailed analysis of corridor stability from the point of view of the convergence, deformation behavior of the surrounding rock mass and the function of the reinforcement used in the two monitored areas with different geological and operational conditions was carried out.
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