Lenka Nevřivová

Study on the Properties of Geocement Based Thermal Insulating Materials for High Temperature Technical Appliances

Three different types ofgeocement thermal insulation materials for energy storage unit were selected after preliminary test. Perlite and vermiculite were added as thermal insulation fillers during mixing process. The produced materials were subjected to heat treatment before determining their properties. The materials produced are characterized by low density (321–376 kg/m3) and thermal conductivity (0.0727 – 0.0766 W/mK). These materials ensure the minimum heat losses of the energy storage unit if the temperature of the medium is 318–923 K and the thickness of thermal insulation layer is 153–160 mm.

Thermal Bridges in Insulation Systems

The article points out and describes in detail the basic thermal bridges in contact thermal insulation systems and in ventilated facades. Thermal bridges are illustrated by means of thermal images of spot thermal bridges and the calculation of spot heat transfer coefficients.

Thermal Insulating Materials for Energy Storage Application

In this paper various thermal energy storage mechanisms are overviewed. Furthermore, the effectiveness of three insulating materials based on alkali activated and prepared with different expanded perlite filler contents was investigated. The results showed that the developed materials could be used to insulate a thermal energy storage facility, operating in the temperature range of 650-800 °C.

Effect of Humidity on the Properties of Cement Mortars with a Crystalline Additive

The paper focuses on examining the properties of mortars in which secondary crystallization (crystalline additive) was used. Laboratory tests have found that the effect of secondary crystallization is influenced by conditions in which specimens have been stored during the first 28 days. The investigation focused on the physical-mechanical properties and microstructure of mortar specimens containing a crystalline additive and polypropylene fibres stored at different levels of humidity for 28 days. The influence of crystalline additive on strength was studied as well and the results show that crystalline additives improves the 28-day strength of the mortars.

Use of Undersize Fractions of Refractory Claystone for Grog Manufacturing in Shaft Kilns

Refractory aluminosilicate grogs are made by firing refractory clays and claystones. They are fired predominantly in rotary or shaft kilns. Prior to firing in shaft kilns, particles of claystone smaller than 35 mm are separated These fine fractions cannot be processed in a shaft kiln, since they lower the quality and homogeneity of firing. However, these claystones can be briquetted into larger pieces (5 – 6 cm), which can be easily fired in shaft kilns. It is possible to modify the raw material by adding correcting materials or other types of clay. This method can then be used for making special grogs. The paper discusses the possibilities of manufacturing grog with an increased Al2O3 content with undersize fractions of claystone mined in Březinka. The research focused on the influence of raw material water content and compacting pressure on the final properties of fireclay grog, and determining the influence of firing temperature on the properties of the grog.

The Effect of Temperature on the Fundamental Characteristics of Self-Compacting No-Cement Refractory Castable

In this research, the impact of firing temperature and MgO addition on mechanical and physical properties of self–compacting no-cement castables were investigated. For this propose up to 3.3 wt % of MgO was added to the corundum castable compositions and the specimens were fired at 600 °C, 800 °C, 1000°C, 1200°C and 1500°C. The mixtures were made so that the consistency of each one was the same. There were only minimal differences in the mixtures water content. The mineral composition of the input raw materials for manufacturing of the refractory castables was determined. The physical and mechanical properties of castable compositions such as self-flow values, bulk density, apparent porosity, cold crushing strength and flexural strength were examined. Also, the X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDX) techniques were used for detection the ceramic phase formation. The corrosion resistance was determined by means of the crucible test according to ČSN P CEN/TS 15418 (726022) Method of test for dense refractory products – Guidelines for testing the corrosion resistance of refractories caused by liquids. The study follows up on research, the results of which were published last year [1], but the study is focused to self-compacting refractory castable.

Influence of a Crystalline Additive on the Porosity of Cement Mortars

The pore structure of a material radically infuences its properties, such as strength, freeze-thaw resistance, capillarity or resistance to elevated temperatures. The character of the pore structure is also limiting for the intrusion of aggressive oxides into the material, which affects its service life. The paper describes how a crystalline additive influences the pore structure of cement mortars. It describes the effect of secondary crystallisation and the influence of the additon of PP fibers on the apparent porosity and the internal structure of the mortar. It also discusses the influence of aggressive conditions on the mortar’s pore structure.

Durability of Cement Based Mortars Containing Crystalline Additives

The paper focuses on the study of the durability of cement mortars made with secondary crystallization additives. It investigates the influence of the crystalline additives on the degradation process of cement mortars exposed to gaseous CO2 and freezing cycles. The specimens with were tested for compressive and flexural strength at the following ages and after being treated by the following curing techniques: 28 days, 180 days and 25 freezing cycles, 28 days and 180 days in gaseous CO2. In order to explain the obtained results and to gain new information about the microstructure of the cement mortars being studied, the SEM sampling and RDA analysis were performed. The research results confirm an improvement in the resistance of cement based mortars using crystalline additives against cyclic freezing as well as gaseous CO2. An important parameter that influences the effectiveness of the crystalline additive is the curing conditions during the first 28 days of ageing.

The Impact of In Situ-Formed Spinel on the Porosity of No-Cement Refractory Castables

The paper focuses on the determination of how in-situ formed magnesia-alumina spinel (MA spinel) content in corundum refractory castables influences the final properties and pore size distribution of no-cement refractory castables. The motivation for this research was the continued pressure on increasing the utility properties of refractory castables, namely their corrosion resistance to blast-furnace slag. The influence of MA spinel content was observed in vibration-compacted refractory castables (three mixtures). The corrosion test was performed to determine the dependence of the size of the slag-penetrated area on MA spinel content in the specimen. The pore structure of a slag-penetrated NCC and an unaffected castable was described.

History, Present State and Future of Czech Silica Bricks

This article discusses the history and progress of silica materials production in the Czech Republic over the last 30 years, including descriptions of production capacity, characteristics and quality of individual product types as well as technological changes in the production of silica-based material. Current operational conditions and material applications are summarized. The last chapter of the article focuses on development of new kinds of silica materials and their possible utilization by customers, especially in the field of glass production.