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Study of shrinkage reducing admixture efficiency in alkali activated systems
Fojtík, Ondřej ; Koplík, Jan (referee) ; Bílek, Vlastimil (advisor)
Significant drying shrinkage is one of the major issues for the wider application of materials based on alkali-activated slag (AAS). Some shrinkage reducing admixtures (SRA) were developed for the ordinary portland cement systems. A couple of previous studies focused on the efficiency of these SRA in alkali-activated materials. The studies were mainly concentrated on the SRA based on polypropylene glycol. This thesis deals with efficiency of the SRA based on 2 methyl-2,4-pentanediol in AAS pastes and mortars. Influence of the SRA and activator (waterglass) dose on the drying shrinkage and other properties of AAS (flexural and compressive strength, autogenous shrinkage, workability, setting time and microstructure) were investigated. It was found, that at the activator dose when Na2O/slag mass ratio equals 4 or 6 %, SRA causes retardation of hydration, which leads to shrinkage reduction, however strength is reduced significantly, weight lost during the drying is increased and the coarsening of the pore structure occurs. At the activator dose when Na2O/slag mass ratio reaches 8, 10 or 12 %, in the presence of SRA the drying shrinkage is reduced, weight lost during the drying is similar to the reference, strength is increased and microstructure is unchanged against reference. It has been proved that SRA works properly in AAS only at higher activator doses.
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Construction safety and health costs
Fojtík, Ondřej ; Mikulová, Kateřina (referee) ; Nový, Martin (advisor)
Main course of this Bachelor thesis is health protection and security on a construction site. Fundamental techniques of construction project management and terminology required for orientation in security and health protection plans, are subject of the theoretical part of this thesis. Practical part is focused on creating this security plan, where is a section dedicated to overall costs of security, spent on realisation of this particular project. Reader should realise, after reading this thesis, that the security topic is necessary part of every construction project.
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Reconstruction of the pre-station area in Havířov
Fojtík, Ondřej ; Mikulová, Kateřina (referee) ; Nový, Martin (advisor)
Diploma thesis focuses on the reconstruction of the forecourt area in the city of Havířov. The theoretical part clarifies the concept of project management and its fundamental principles, addressing requirements for construction site equipment and the construction schedule. In the practical section, theoretical knowledge is applied, presenting the reconstruction project itself with a detailed description of its progression. An essential component is the proposal for construction site equipment, including cost estimation, along with the calculation of electricity and water consumption costs. The goal of the thesis is to compare real components of the project with alternative solutions, with an emphasis on potential savings in terms of finances and time.
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Preparation and optimization of piezoelectric materials based on BCZT for energy harvesting
Fojtík, Ondřej ; Holcman,, Vladimír (referee) ; Tofel, Pavel (advisor)
This thesis deals with fabrication and optimization of lead-free piezoceramics based on (Ba0,85Ca0,15Zr0,1Ti0,9)O3 (BCZT). The BCZT precursor powder was synthesized by sol-gel method. Dependence of relative density, microstructure, phase structure and piezoelectric properties on the sintering temperature in a range from 1300–1500 °C was studied on disc shaped samples, which were prepared by cold isostatic pressing (CIP) using pressure of 700 MPa. It was found, that sintering at 1300 and 1350 °C leads to ceramics with fine-grain microstructure, which exhibits poor piezoelectric properties (d*33 = 50 pC·N1 and 65 pC·N1, respectively). The highest value of piezoelectric charge coefficient was obtained by sintering at 1500 °C (d*33 = 390 pC·N1). Furthermore, BCZT thick films were prepared by tape casting. The composition of the ceramic slurry was optimized and various sintering techniques were tested to obtain completely flat films of BCZT ceramics. The correct sintering configuration has not been found. The least deformation of the films was achieved when the samples were sintered hung on the ZrO2 rod. The highest value of d*33 for BCZT films was measured when the sample was sintered at 1400 °C with the dwell time for 4 h (d*33 = 340 pC·N1).
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Construction safety and health costs
Fojtík, Ondřej ; Mikulová, Kateřina (referee) ; Nový, Martin (advisor)
Main course of this Bachelor thesis is health protection and security on a construction site. Fundamental techniques of construction project management and terminology required for orientation in security and health protection plans, are subject of the theoretical part of this thesis. Practical part is focused on creating this security plan, where is a section dedicated to overall costs of security, spent on realisation of this particular project. Reader should realise, after reading this thesis, that the security topic is necessary part of every construction project.
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Preparation and optimization of piezoelectric materials based on BCZT for energy harvesting
Fojtík, Ondřej ; Holcman,, Vladimír (referee) ; Tofel, Pavel (advisor)
This thesis deals with fabrication and optimization of lead-free piezoceramics based on (Ba0,85Ca0,15Zr0,1Ti0,9)O3 (BCZT). The BCZT precursor powder was synthesized by sol-gel method. Dependence of relative density, microstructure, phase structure and piezoelectric properties on the sintering temperature in a range from 1300–1500 °C was studied on disc shaped samples, which were prepared by cold isostatic pressing (CIP) using pressure of 700 MPa. It was found, that sintering at 1300 and 1350 °C leads to ceramics with fine-grain microstructure, which exhibits poor piezoelectric properties (d*33 = 50 pC·N1 and 65 pC·N1, respectively). The highest value of piezoelectric charge coefficient was obtained by sintering at 1500 °C (d*33 = 390 pC·N1). Furthermore, BCZT thick films were prepared by tape casting. The composition of the ceramic slurry was optimized and various sintering techniques were tested to obtain completely flat films of BCZT ceramics. The correct sintering configuration has not been found. The least deformation of the films was achieved when the samples were sintered hung on the ZrO2 rod. The highest value of d*33 for BCZT films was measured when the sample was sintered at 1400 °C with the dwell time for 4 h (d*33 = 340 pC·N1).
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Study of shrinkage reducing admixture efficiency in alkali activated systems
Fojtík, Ondřej ; Koplík, Jan (referee) ; Bílek, Vlastimil (advisor)
Significant drying shrinkage is one of the major issues for the wider application of materials based on alkali-activated slag (AAS). Some shrinkage reducing admixtures (SRA) were developed for the ordinary portland cement systems. A couple of previous studies focused on the efficiency of these SRA in alkali-activated materials. The studies were mainly concentrated on the SRA based on polypropylene glycol. This thesis deals with efficiency of the SRA based on 2 methyl-2,4-pentanediol in AAS pastes and mortars. Influence of the SRA and activator (waterglass) dose on the drying shrinkage and other properties of AAS (flexural and compressive strength, autogenous shrinkage, workability, setting time and microstructure) were investigated. It was found, that at the activator dose when Na2O/slag mass ratio equals 4 or 6 %, SRA causes retardation of hydration, which leads to shrinkage reduction, however strength is reduced significantly, weight lost during the drying is increased and the coarsening of the pore structure occurs. At the activator dose when Na2O/slag mass ratio reaches 8, 10 or 12 %, in the presence of SRA the drying shrinkage is reduced, weight lost during the drying is similar to the reference, strength is increased and microstructure is unchanged against reference. It has been proved that SRA works properly in AAS only at higher activator doses.
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