|
|
Study of the influence of fillers and external conditions on the resistivity of cement composites
Kejda, Dalibor ; Melichar, Jindřich (referee) ; Černý, Vít (advisor)
The progress of new materials is important for the construction industry. Modern materials include cement composites with reduced resistivity. This is achieved by adding suitable electrically conductive fillers. If there is enough of these fillers, the so-called percolation threshold occurs. Suitable fillers (Condufit C4 and Supragraphite C300) have been proposed. Recipes have been designed to be before and after the percolation threshold. The tests were performed on beams measuring 40x40x160 mm with built-in electrodes for measuring their resistivity. The aim of the work was the research of influencing external conditions on cement composites. The effect of temperature was verified. The lowest values of resistivity were evaluated at temperatures of 50 ° C and the resistivity increased with decreasing temperature. The effect of humidity on the resistivity was then verified. Reference samples and samples with a smaller proportion of graphite powder showed larger differences in resistivities with increasing humidity. The samples above the percolation threshold were not much affected by increasing humidity. Finally, the effect of loading on the resistivity of the samples was verified. Almost all samples with increasing compressive stress showed an increasing value of resistivity.
|
|
|
New possibilities of using superabsorbent polymers in cement composites
Holubová, Petra ; Melichar, Jindřich (referee) ; Černý, Vít (advisor)
The work deals with the influence of superabsorbent polymers (SAP) on the structure and properties of cement composites. SAPs excel in their unique ability to hold large amounts of water. This property can be used in hydration processes for internal curing of concrete. Two types of mixtures were tested in cement paste, which were further modified by two types of SAP. SAPs were always used in two dosing modes (dry, in suspension). The samples were then stored for 28 days in a laboratory conditions, respectively. in an conditions with a temperature of 30 °C. Physical and mechanical properties, such as compressive strength, flexural tensile strength and bulk density, were determined. The addition of SAP to the mixture resulted in an increase in tensile strength of almost twofold. It can therefore be concluded that SAP helped with hydration processes.
|
|
| |
|
| |
|
|
Advanced material based on secondary raw materials for construction of subgrade layer
Hrubý, Jakub ; Luňáček,, Martin (referee) ; Černý, Vít (advisor)
The diploma thesis deals with the development of a new material for the establishment of a layer of the ground body of a railway undercarriage purely on the basis of secondary raw materials. The theoretical part presents the characteristics of structural layers, materials used for bonded substrates, including their requirements. The following are the general conditions for the creation of base layers from purely secondary raw materials and previous experience with the issue. The introduction of the experimental part of the thesis sets out the basic parameters of secondary raw materials (construction recyclates, waste from railway bed cleaning, dust from cement plant) and energy by-products (fly ash, coal slag and municipal waste incinerator), which together form the raw material base. Grain size, absorbency, moisture, bulk density, chemical analysis and pollutant content were determined on the raw materials. Bulk densities and compressive strengths of the bonded mixtures were determined. The optimum humidity of all mixtures was determined by the Proctor standard test. Experimental verification was performed on testing of bonded mixtures in order to verify the effect of cement dose, when the original dose of 8% was optimized for construction recycled and slag from municipal waste incinerator to 4%, due to high strengths ranging from 4.5 to 6.0 MPa. Further optimization also included the addition of an energy by-product in a proportion of 10% of the weight of the secondary raw material. At the end of the experimental part, two optimal recipes were selected (recycled concrete with 4% cement and 10% fluid fly ash; slag from a municipal waste incinerator with 3% cement and 10% fluid fly ash), which underwent advanced testing in the form of frost resistance and resistance to water and a functional sample was designed. The final functional sample is recycled concrete with cement and 10% addition of fluid fly ash, which is suitable for core layers without frost loading.
|
|
|
Proposition of conductive silicate composite for heating
Surovcová, Jana ; Černý, Vít (referee) ; Drochytka, Rostislav (advisor)
The bachelor's thesis deals with the development of electrically conductive silicate composite with the self heating value designed for surfaces in the exterior, on which an ice layer can form during the winter. The developed silicate composite should replace the defrosting of surfaces with chemical defrosting substances, which could have an adverse impact on the environment and are usually applied with a delay when a sudden change of weather appears. The theoretical part of this thesis summarizes the theory of electric field and electric current conduction, approached the issue of silicate binders, various types of electrically conductive phases and presents the current state of knowledge in the field of research of self heated composites. The practical part contains an assessment of selected effects of the exposure environment, based on which the requirements for the developed composite are formulated. Furthermore, the practical part is devoted to the analysis of necessary materials for producing self heated composite, so the focus is on conductive fillers. Selected fillers with the low level of the impedance are then used in the proposed recipes and the production of test specimens for the comparison of real parameters and the required ones. The work succeeded in proving the ability of heating the silicate composite with a conductive filler by means of an electric current, while the required mechanical parameters were not achieved. The bachelor thesis serves as a suitable basis for further research linked to the issue of electrically conductive self heated silicate composites.
|
|
|
Electrically conductive composites based on secondary raw materials
Baránek, Šimon ; Šteffan,, Pavel (referee) ; Černý, Vít (advisor)
Electroconductive composites are modern materials that are commonly used in many industries such as the construction industry among others. For example these materials can be useful as sensors for monitoring changes in constructions. The aim of this thesis is the research of electrically conductive silicate composite based on secondary raw materials. The design of this composite is based on the development of its own mixtures and experimental verification of the effect of the structure. The introduction part consists of a detailed analysis of 15 materials. Samples of the 5 fine and 2 coarse electrically conductive fillers were tested. Composite with filler Condufit C4 was selected as representative for type of fine fillers. Composite with filler Supragraphite C300 was selected as representative for type of coarse fillers. The selection of the composites was based on the impedance of the fabricated composites with these fillers. Subsequently, the individual components of the primary mixture were substituted. The cement was replaced by high-temperature fly ash in the amount of 20, 30, and 40 %, the aggregate of a similar fraction was replaced by steel sawdust, and the primary electrically conductive fillers were replaced by secondary ones in the amount of 30 and 50 %. All proposed replacements reduced the impedance of the composite. The most effective replacement for impedance reduction was replacement with waste graphite (up to 92 % reduction), which also slightly improved the mechanical properties of the composite. The result of this thesis is an optimized electrically conductive composite based on secondary raw materials with a fine type of filler with 30 % replacement by waste graphite "odpad vysavač"which achieves an impedance of 5 ohms. The partial goal of this thesis is a verification of the influence of moisture on the impedance of composites. Results are significantly affected by moisture when using the coarse type of filler, when using the fine type are not.
|
|
|
The usability of secondary raw materials in the design of liquefied suspensions based on soil
Hrubý, Jakub ; Kulísek, Karel (referee) ; Černý, Vít (advisor)
The bachelor's thesis deals with the usability of secondary raw materials in the design of liquefied suspensions based on soils in the form of self-compacting grouts. The soil treated in this way can be used as a substitute for backfill material for excavations of engineering networks. The theoretical part deals with the classification and description of soils. Furthermore, the types of soil stabilization using lime, cement, including their liquefaction, are mentioned. A wide range of potentially suitable secondary raw materials and liquefaction mechanization is presented. In the practical part, the basic soil F6-Cl is selected on the basis of a set of available soils. The basic reference mixture consists of soil, lime, cement and liquefier. A proposal for the concept of experimental verification is presented. Part of the concept is the automated calculation of input raw materials. The effect of the action of the superabsorbent polymer and the accelerating additive is verified. Based on optimization selections, functional secondary raw materials are selected. The basic recipe with the optimal amount of accelerating ingredient achieves the best results. Recycled concrete and brick generally improve the resulting parameters. Bed ash achieves the highest strength with the lowest shrinkage.
|
|
|
Proposition of new type of injection material with electrically conductive function
Uher, Vojtěch ; Černý, Vít (referee) ; Drochytka, Rostislav (advisor)
The bachelor thesis deals with the design of a new type of grouting material with electrically conductive function suitable for connecting cracks and gaps in building protection systems against lightning strikes and surges. The theoretical part summarizes the important knowledge about the grouting and grouting materials, introduces the current state of knowledge in the field of lightning and surge protection of buildings and also the preconditions of electrical conductivity of cement-based composite materials. In the practical part are summarized selected properties, which the electrically conductive grouting material should have and the relevant standards tests for experimental verification of selected properties are described. A wide range of primary and secondary fillers are studied and the most suitable ones are chosen to achieve a low electrical resistivity value. At the end of the thesis, there are recipes based on amassed knowledge and using secondary fillers to reduce the environmental impact of the developed materials during mass production. Reduced resistivity has been demonstrated in recipes using waste carbon and chopped carbon fibers, but has failed to fully meet standard requirements. The result of the work are new recipes and knowledge that can serve as a basis for further research.
|
|
| |
guest ::
RSS feed.