clay was also applied as an admixture. In addition, the Vuppor organic admixture 6 was used to modify the pore H igh f rost resistance is one of the signs of good quality structure of test specimens. in clay roo ng tile products. T he present paper deals with the question of whether the water absorption of clay roo ng tiles aVects f rost resistance. T he results PREPARATION OF SPECIMENSshow that clay roo ng tiles with high water absorption Mineral admixtures were added to the brick clay in doses can be just as f rost proof as tiles with lower absorption.of 1 or 10 wt-% referred to the weight of dried clay, along M edian pore radius is found to be an important factor with Vuppor admixture at a constant dose of 1 wt-% of in determining f rost resistance: increasing the median dried admixture to dried clay. Test specimens (100Ö pore radius increases frost resistance. BCT /561 50Ö 20 mm) were manufactured from a plastic mass (upsetting height 24 mm according to PfeVerkorn test), held T he author is in the Department of Materials for 48 h at laboratory temperature (20°C), and then dried Engineering, Faculty of Civil Engineering, Slovak at 110°C to constant weight. Specimens were red in an University of T echnology, R adlinského 11, SK -813 68 electric laboratory furnace at 900°C with a dwell time of 1 h. Bratislava, Slovak R epublic ( sveda@svf.stuba.sk). M anuscript absorption N V (wt-%) is de ned as 100(m n m s )/m s , where the Institute of M aterials, M inerals and M ining.m n is the saturated weight of the specimen after 4 h submersion in boiling water and m s is the dry weight of the specimen.
The aim of the article is to find the optimal fluxing agent for porcelain body regarding to the possibility of the lowest firing temperature. Sintering behaviour of dry pressed test samples made from the mixture of kaolin and three different types of industrially milled feldspar rocks, bone ash and quartz sand with similar granulometry as dependence of water absorption on the firing temperature was investigated. The most intensive fluxing agent for the sintering is bone ash-the mixture containing bone ash (20wt.%) showed sintering temperature 1200 • C. That is about 50 • C lower compared with the most intensive feldspar based fluxing agent-potassium feldspar rock containing 75% of pure microcline.
T he present paper extends previous findings already published where the relationships among total porosity, bulk density, compressive strength, and thermal conductivity were analysed. T he paper brings more accuracy into some original mathematical relationships and takes into account two additional physical properties (pore volume and the median pore radius). It has been found that the relationships between physical properties and a dose of any admixture added to brick clay could be better described using a quadratic function. T he relationships between pairs of physical characteristics can be described by three types of mathematical function (linear, exponential, and power). T he amount of admixture used, the firing temperature, and type of clay aVect the value of the coeYcients but not the type of functions.BCT /371
This study investigated the effects of three pore-forming agents on the properties of the fired clay body applied in the production of lightweight bricks for the building envelopes. Test samples were made from clay raw material already containing two combustible pore-forming agents (sawdust and cellulose sludge). A part of this research was focused on studying the influence of adding two combustible pore-forming agents (molasses and cornstarch) and a chemical additive Vuppor to the claw raw material. Testing of the material properties showed that although the three samples had almost the same pore volume, their thermal conductivities varied. These findings led to an important conclusion. The pore size of 1–200 µm (filled with not only air but also biomass ash) reduced the thermal conductivity, and conversely, an increase in the small pore size less than 1 µm increased the thermal conductivity of the fired clay body.
A plan to reduce CO2 emissions is a priority these days. Brick industry contributes to the increase of these emissions mainly through the use of combustible pore-forming agents such as sawdust, cellulose, and coal sludge. These agents are used to improve the thermal insulation properties of brick products, and the suppliers regularly increase the prices of these agents based on their high consumption. Therefore, in an effort to reduce raw material expenses and CO2 emissions, brick manufacturers are looking for new possibilities while maintaining the quality of their products. This article discusses the possibility of using industrially manufactured product Vuppor as an additive as a replacement for combustible poreforming agents. The presence of this additive in the fired clay body increases the proportion of pores, especially with a size range between 0.1 and 5 µm, having a positive impact on the reduction of its thermal conductivity. With a 0.5 wt.% dose of Vuppor additive, the brick production costs and thermal conductivity can be reduced by 20 % and 12 %, respectively, while also achieving reductions in CO2 emissions over 60 %. Consequently, the combustible pore-forming agents can be used in a more environmentally friendly manner, for example in the furniture industry, the biogas production, and the like.
The paper deals with the monitoring of brick body in the process of volumetric freezing and thawing. The samples were fired at temperatures of 900, 1000 and 1060 °C. Attention is focused on monitoring of the irreversible expansion, water absorption and pore structure of a brick body. We found that in all cases the endpoints take place continuously, where the amount firing temperature plays a crucial role. The greatest influence of freeze/thaw cycles on the change of the pore structure was also observed at the lowest temperature. The change of the pore system during the freeze-thaw cycles occurs in such a way, that the pore volume of small pores further decreases and conversely, the pore volume of large pores increases. The knowledge gained can be used not only in the production of new but also in predicting the remaining durability of older clay roofing tiles.
Influence of limestone sludge (generated during the washing process of limestone crushed aggregates) with high content of CaO in the form of calcite on the properties of brick body made from non-calcareous sludge (from the washing process of quartz sand) as a basic plastic brick clay was determined. Presence of calcite very distinctly influenced the firing process and properties of fired body. Limestone sludge decreases firing shrinkage, bulk density and coefficient of thermal conductivity of the brick body after the firing in the range of 850 – 950 °C. Higher modulus of rupture and water absorption is typical for fired bodies with limestone sludge addition. Most of these improvement are caused by the formation of anorthite only in the bodies based on the limestone sludge.
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