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The development of ultra-high strength (UHPC) and reactive powder (RPC) composites
Rundt, Lukáš ; Hela,, Vlastimil (referee) ; Hela, Rudolf (advisor)
Bachelor’s thesis studies ultra-high strength concrete and reactive powder composites. In theoretical part there are researched and described properties of raw materials used for their production, mainly additions. Design methodology, processing and types of curing are also studied. Psychical mechanic and durability properties of fresh and hardened concrete are described. In practical part 4 mixtures were designed and prepared and their rheological properties, strengths after 7 and 90 days in case of UHPC and strengths after 7, 28 and 60 days in case of RPC were tested.
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Influence of anticorrosive surface treatment of steel reinforcement fibers on the properties of ultrahigh-performace cement composite
Bocian, Luboš ; Ptáček, Petr (referee) ; Novotný, Radoslav (advisor)
This thesis characterized surface layer of brass on commercially available steel microfibers. Subsequently, it was studied how to remove this surface layer of brass off these microfibers. Additionally, this thesis investigated influence of removal of brass surface layer on mechanical and ballistic properties of RPC composites. It was also studied how previously mentioned surface layer of brass influences interface between steel microfibers and matrix. It was found out that the surface layer of brass on commercially available steel microfibers is uneven and that the brass fills scratches present on steel underneath the surface layer of brass. It was also found out that conc. HNO3 and mixture of NH3 and H2O2 in volume proportion of 3 : 1 can be used to remove the surface layer of brass. The only thing to consider is that steel microfibers from conc. HNO3 corrode. Flexural strength of composite made with fibers from mixture of NH3 and H2O2 is higher than flexural strength of composite made with commercially available steel microfibers with surface layer of brass after 28 and 95 days. Compression strength wasn’t significantly affected in any composite used in this thesis after 28 and 95 days. Composite made with fibers from mixture od NH3 and H2O2 showed slightly better ballistic resistance than composite made with commercially available steel microfibers with surface layer of brass. In terms of SEM analysis of interface between matrix and steel fibers of certain composite, it was found out that there was no evidence of infiltration of components of brass into matrix.
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The methodology of survey and diagnostic methods for the assessment of the state of timber structure
Kostečka, Jan ; Anton, Ondřej (referee) ; Heřmánková, Věra (advisor)
This bachelor thesis is focused on diagnostic of wood in the timber structures, The first chapter summarizes the wood matter, including its main characteristics, composition and construction. In the section on wood diagnostic methods, we have focused on the properties of wood, which influence these methods on the diagnostic methods themselves, their description, the necessary equipment and the resulting results. In the second, practical part are given the specific measured values, which were obtained by measuring on the selected wooden element and subsequent comparison and evaluation. The text is supplemented by illustrations, graphs and cuts.
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Influence of anticorrosive surface treatment of steel reinforcement fibers on the properties of ultrahigh-performace cement composite
Bocian, Luboš ; Ptáček, Petr (referee) ; Novotný, Radoslav (advisor)
This thesis characterized surface layer of brass on commercially available steel microfibers. Subsequently, it was studied how to remove this surface layer of brass off these microfibers. Additionally, this thesis investigated influence of removal of brass surface layer on mechanical and ballistic properties of RPC composites. It was also studied how previously mentioned surface layer of brass influences interface between steel microfibers and matrix. It was found out that the surface layer of brass on commercially available steel microfibers is uneven and that the brass fills scratches present on steel underneath the surface layer of brass. It was also found out that conc. HNO3 and mixture of NH3 and H2O2 in volume proportion of 3 : 1 can be used to remove the surface layer of brass. The only thing to consider is that steel microfibers from conc. HNO3 corrode. Flexural strength of composite made with fibers from mixture of NH3 and H2O2 is higher than flexural strength of composite made with commercially available steel microfibers with surface layer of brass after 28 and 95 days. Compression strength wasn’t significantly affected in any composite used in this thesis after 28 and 95 days. Composite made with fibers from mixture od NH3 and H2O2 showed slightly better ballistic resistance than composite made with commercially available steel microfibers with surface layer of brass. In terms of SEM analysis of interface between matrix and steel fibers of certain composite, it was found out that there was no evidence of infiltration of components of brass into matrix.
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Analysis of mini-jack technique for in situ measurement of strength
Kloiber, Michal ; Tippner, J. ; Kunecký, Jiří ; Sebera, V. ; Milch, J. ; Hrivnák, Jaroslav
The paper presents a recently developed diagnostic technique for in situ determination of modulus of deformability (MODL) and conventional strength (CSL) parallel to the grain using the mini-jack inserted in bored hole. The mini-jack compression technique simulates the standard compression test, it is compared to that to examine its prediction strength (correlation coefficients). The paper shows an influence of moisture content of wood on experimental measurements using this technique. The measurement was carried out at spruce samples at three moisture contents of 12, 18 and 24%. The results of the tests prove a very good correlation of the strength determined by the proposed technique and wood density and strength determined at universal testing machine in compression parallel to the grain. The effect of the moisture content on the measurement by the mini-jack technique was proved to be significant. Beside that, the newly-developed instrument was also studied using digital image correlation (DIC) technique to analyze induced strains around the bored hole. This was studied on halved spruce samples. The DIC revealed symmetric character of the loading and significant differences between strains induced in tangential and longitudinal directions.
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The methodology of survey and diagnostic methods for the assessment of the state of timber structure
Kostečka, Jan ; Anton, Ondřej (referee) ; Heřmánková, Věra (advisor)
This bachelor thesis is focused on diagnostic of wood in the timber structures, The first chapter summarizes the wood matter, including its main characteristics, composition and construction. In the section on wood diagnostic methods, we have focused on the properties of wood, which influence these methods on the diagnostic methods themselves, their description, the necessary equipment and the resulting results. In the second, practical part are given the specific measured values, which were obtained by measuring on the selected wooden element and subsequent comparison and evaluation. The text is supplemented by illustrations, graphs and cuts.
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The development of ultra-high strength (UHPC) and reactive powder (RPC) composites
Rundt, Lukáš ; Hela,, Vlastimil (referee) ; Hela, Rudolf (advisor)
Bachelor’s thesis studies ultra-high strength concrete and reactive powder composites. In theoretical part there are researched and described properties of raw materials used for their production, mainly additions. Design methodology, processing and types of curing are also studied. Psychical mechanic and durability properties of fresh and hardened concrete are described. In practical part 4 mixtures were designed and prepared and their rheological properties, strengths after 7 and 90 days in case of UHPC and strengths after 7, 28 and 60 days in case of RPC were tested.
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A new device for determining the mechanical properties of wood
Kloiber, Michal ; Drdácký, Miloš
The paper presents a novel concept of a diagnostic tool for "in-situ" assessment of the mechanical characteristics of wood in a prepared 12 mm hole. The device enables direct determination of conventional strength and modul of deformation in arbitrary depth along timber profile .The aim was to verify the measurement results of the new device with measurements on already tested devices according to european standards. Experimental tests show above all a very good correlation between conventional strength by means of the new device and standard samples strength in pressure along the fibers. This semi-destructive method causes a very gentle damage and can be used for the assessmen of historic timber structures.
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Analysis of wood behaviour in the surroundings of a pin being pushed for the diagnostics of constructional elements of buildings
Kloiber, Michal ; Tippner, J. ; Hrivnák, J. ; Vichrová, Gábina ; Valach, Jaroslav
The technical solution of this diagnostic device for in-situ and laboratory measuring of conventional strength and the module of deformation by opening clamps in a drilled hole belongs to the field of quality and material property testing, especially concerning timber. In dependence on the specific technical solution, the device can be used for an establishment of conventional strength and the module of deformation of any material by opening clamps in a drilled hole in the examined volume. It also finds application in the situations when resistance drilling cannot be used and the mechanical properties of timber need to be established through the entire section of the examined element. Its main advantages are its speed and simple operation without a need for power distribution network.
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