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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.
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Usability of hig speed water jet in civil engineering
Boucníková, Veronika ; Sitek,, Libor (referee) ; Bodnárová, Lenka (advisor)
The bachelor thesis deals with possibilities of using high-speed water jet in construction industry. In the theoretical part, water jet technology was generally described and a research for use in the construction industry with an emphasis on the application of concrete structures redevelopment and the process of interaction of water jet with concrete was done. Furthermore, the safety risks during work with high-speed water jet and the possibilities of recycling of waste generated by the use of this technology were evaluated. In the experimental part were prepared concrete samples with dispersed concrete reinforcement. The characteristics of the concrete samples were determined and the depth and appearance of the cross-section after interaction with the high-speed water jet was evaluated.
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Water Jet 2017 - Research, Development, Applications. Proceedings of the Conference on Water Jetting Technology
Klichová, Dagmar ; Sitek, Libor
Conference Water Jet 2017 – Research, Development, Applications coincides\nwith major changes in key technologies and economy which recently started to\nincrease pace.\nUpcoming electric mobility will strongly influence production technology in\nthe automotive industry leading probably to declining content of water jetting\nprocesses.\nThe continuing trend for automation will have an extreme impact on water jet\nbusiness. Merging robotic and data control systems with smart water jet tools will\nbe a demanding future task.\nThe need for energy saving remains unchanged and directs scientific focus on\nhigh efficient jetting, cutting and cleaning processes as well as tools. This is\nthe only way to gain substantial savings as efficiency of state of the art pump\nsystems is already on a very high level.\nTraditional technologies are moving towards marine applications. Subsea\nexploration becomes more and more important for basic raw material supply. Both\nmaintenance and decommissioning of vessels and offshore structures is already\na growing domain for special water jetting applications. Aquafarming substantially\ncontributes to supply a constantly growing human population with sea food\nwhereat water jet cleaning helps to keep high quality farming standards.\nAll these changes are linked up with associated HSE requirements. High\nefficiency, safe, ergonomic and reliable equipment as well as water treatment are\nkey factors for future developments.\nA strong scientific and engineering effort is required to meet these current and\nfollowing challenges. Water Jet 2017 Conference is organized by the Department of\nMaterial Disintegration of the Institute of Geonics.
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Erosion capability of ultra-high-speed continuous waterjet and pulsating waterjet: the comparison
Sitek, Libor ; Hlaváček, Petr ; Klichová, Dagmar ; Trieb, F. ; Pude, F.
Advantages and possibilities of continuous ultra-high-speed waterjets (with\npressures of 600 MPa and more) when cutting metals are well known to\nthe professional public both from scientific studies and from practice. In addition\nto efficiency increased as water pressure increases and reduced water\nconsumption, abrasive consumption can also be reduced in the case of abrasive\nwaterjet. Ultra-high-speed waterjet technology allows not only to cut metal sheets\nwith pure water, but also allows cutting of harder materials such as ceramics.\nDespite the initial suspicion and technical problems associated with the reliability\nand sealing of some hyperpressure elements, high-pressure devices generating\nwater pressures around 600 MPa are now commercially available. However, no\ncomparison has been made so far concerning the efficiency of these jets with\nacoustically modulated high-speed pulsating waterjets using relatively low\npressures and higher water flow rates when eroding metallic materials.\nThe article compares cuts made by pure ultra-high-speed waterjet generated at\nhyperpressures (from 500 to 800 MPa) with erosive capabilities of pulsating\nwaterjets generated on the contrary at water pressures in the order of tens of MPa\non three metallic materials (stainless steel, mild steel and copper) using the same\njet hydraulic power.
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Properties and characteristics of recycled garnet abrasives for AWJ
Martinec, Petr ; Hlaváček, Petr ; Ruppenthalová, Lucie ; Sitek, Libor
The use of recycled garnet abrasive from sludge after cutting materials is a current\nproblem. The behavior of individual garnet abrasives in the AWJ process depends\non the geological origin of the garnets, which also affects all the material\ncharacteristics of the garnet recyclate. The parameters of the BARTON HPX80 and\nGMA 80 abrasive inputs and their recycled products were compared: mineralogical\ntype, apparent density, granularity, grain shape and mineralogical purity,\nmicrohardness data and the degree of damage to the garnet grains. All individual\nparameters of abrasives and their recyclates are reflected in the index of cutting\nefficiency of abrasive. The effect of abrasive material properties on cuttability of\nabrasives is synergistic. The new parameters in the evaluation of abrasives are\nmicro-hardness (brittleness criterion), specific surface and pore size distribution\n(internal grain damage criterion).
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Application of high speed water jet technology for concrete repair
Bodnárová, L. ; Sitek, Libor ; Foldyna, Josef ; Jarolím, T.
This article brings selected knowledge from the long-term cooperation between\nthe Brno University of Technology, the Faculty of Civil Engineering, the Institute of\nTechnology of Building Materials and Components, and the Academy of Sciences of\nthe Czech Republic, v.v.i., Institute of Geonics, Ostrava – Poruba in the field of\nthe interaction of high-speed water jets and concrete, especially with regard to\nthe use of high-speed water jet technology for the removal of surface layers of\nconcrete during repair of concrete.
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Studying the behavior of concrete at high temperatures
Čonka, Ladislav ; Sitek,, Libor (referee) ; Bodnárová, Lenka (advisor)
The thesis is focused on the current issues of concrete resistance to high temperatures. The theoretical part has been processed the changes taking place in the individual components of concrete and changes affecting the physical - mechanical properties of concrete and color-changing effects manifesting high. In the experimental part of the load was, carried concrete test samples to a temperature of 400 ° C, 600 ° C and 800 ° C. After the thermal load, has been on test samples tested changes in physico - mechanical properties, especially concrete compressive strength, water absorption but also a visual assessment of the concrete surface
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Study of the properties of cement concrete at high temperatures
Žák, Michal ; Sitek,, Libor (referee) ; Bodnárová, Lenka (advisor)
This diploma thesis is focused on behavior of cement concrete at high temperatures. The theoretical part describes processes, which take place in concrete at thermal loading and effect of this thermal load to mechanical and physical properties of concrete. Also there was described recommendation for testing physical and mechanical of concrete at high temperatures according to RILEM TC. In experimental part mixes were made with greywacke aggregate, amphibolite aggregate and with the addition of polypropylene fibers or cellulose fibers. In these mixes was determined the effect of high temperatures on the density of concrete, compressive strength of concrete and thermal strain of concrete. Further there was tested addition of 2 kg/m3 polypropylene fibers to concrete with basalt aggregate and siliceous aggregate and influence of these fibers to density of concrete, compressive strength of concrete and dynamic modulus of elasticity.
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