|
|
Study of the influence of structure on the resistivity of silicate composites
Uher, Vojtěch ; Šteffan,, Pavel (referee) ; Drochytka, Rostislav (advisor)
Electroconductive silicate-based composites are advanced materials that allow building structures to perform several different functions simultaneously. Addressing the issues of their development and use is a suitable topic for research work. The aim of this work is to study the effect of structure on the resistivity of silicate composite. The structure of electrically conductive composites is studied on dry cement paste and mortar mixtures as well as on test bodies made of hardened cement paste and mortar after 28 days of curing. Based on the analysis of the raw materials, six suitable electroconductive fillers are selected based on particle size, resistivity, and water absorption. The parameters of dry cement paste and hardened cement paste with replacement of 4-19 wt. % cement by the selected fillers are determined. Two of the fillers are selected for use in dry and hardened mortar. Resistivity is determined for all dry mixes and hardened composites variants, and percolation thresholds are approximately determined. By studying the structure of the selected variants, it is shown that the most important parameters that have the greatest influence on the resistivity of the silicate composites are mainly the particle size and the intrinsic resistivity of the electrically conductive filler. For silicate composites in the hardened state, the volume of hydration products, especially portlandite and C-S-H gels, also has a significant influence. For both dry blends and hardened composites, it was found that the smaller the particle size of the electroconductive filler, the smaller the representation needed to reach the percolation threshold. Portlandite and C-S-H gels in the volume of the hardened composite cause its high resistivity. The resistivity of the hardened composite is always higher than that of the dry blends. Thus, the proportion of electroconductive filler needed to reach the percolation threshold is higher in hardened composites than in dry mixes. The resist
|
|
|
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.
|
|
|
Study of the influence of structure on the resistivity of silicate composites
Uher, Vojtěch ; Šteffan,, Pavel (referee) ; Drochytka, Rostislav (advisor)
Electroconductive silicate-based composites are advanced materials that allow building structures to perform several different functions simultaneously. Addressing the issues of their development and use is a suitable topic for research work. The aim of this work is to study the effect of structure on the resistivity of silicate composite. The structure of electrically conductive composites is studied on dry cement paste and mortar mixtures as well as on test bodies made of hardened cement paste and mortar after 28 days of curing. Based on the analysis of the raw materials, six suitable electroconductive fillers are selected based on particle size, resistivity, and water absorption. The parameters of dry cement paste and hardened cement paste with replacement of 4-19 wt. % cement by the selected fillers are determined. Two of the fillers are selected for use in dry and hardened mortar. Resistivity is determined for all dry mixes and hardened composites variants, and percolation thresholds are approximately determined. By studying the structure of the selected variants, it is shown that the most important parameters that have the greatest influence on the resistivity of the silicate composites are mainly the particle size and the intrinsic resistivity of the electrically conductive filler. For silicate composites in the hardened state, the volume of hydration products, especially portlandite and C-S-H gels, also has a significant influence. For both dry blends and hardened composites, it was found that the smaller the particle size of the electroconductive filler, the smaller the representation needed to reach the percolation threshold. Portlandite and C-S-H gels in the volume of the hardened composite cause its high resistivity. The resistivity of the hardened composite is always higher than that of the dry blends. Thus, the proportion of electroconductive filler needed to reach the percolation threshold is higher in hardened composites than in dry mixes. The resist
|
|
|
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.
|
|
|
Time lapse tomography of fracture progress in silicate-based composite subjected to the loading a combination with acoustic emission scanning
Kumpová, Ivana ; Kytýř, Daniel ; Fíla, Tomáš ; Veselý, V. ; Trčka, T. ; Vopálenský, Michal ; Vavřík, Daniel
The initiation and propagation of a fracture in quasi-brittle materials (such as silicatebased composite) is an increasingly discussed topic for which various methods of research have been developed/applied. As the quasi-brittle silicate-based composite compounds are very non-homogenous, the mechanism of the crack initiation and propagation can be very different even for samples with the\nidentical geometry. One possible approach to study the fracture mechanism in quasi-brittle materials is to use several different experimental techniques in a single experiment and perform detail analysis to identify generally valid fracture process phenomena. In this work, a simultaneous monitoring of fracture\nprocess zone formation and propagation by three different methods is presented and discussed. A three point bending test was performed on a notched silicate composite specimen. During the loading process, a highly accurate force displacement dependence was recorded accompanied with X-ray radiography,\nX-ray computed tomogra-phy and acoustic emission scanning.
|
guest ::
