Specifications

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Question 1

Bending strength is an important mechanical property of ceramic tiles, according to which its quality is controlled. In this case, the resistance of the material is measured in relation to the maximum specific load, with constantly increasing pressure on the surface. Flexural strength is measured in Newtons per square millimeter (N/mm2). In order to fully appreciate the significance of this tile property and correctly apply the test results, you must first check your own understanding of this issue. Please indicate the correct conclusions in your opinion:

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The bending strength is determined by an equation that includes such variables as: breaking force, distance between support rods, width of the tested sample and the smallest thickness of the tested samples along the fracture line.

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Flexural strength is a characteristic that determines the load-bearing capacity of a tile. In addition to the density of the material, it is also affected by the linear dimensions of the tile: length, width and thickness. So, for example, if one tile is twice as thick as another, and they are made of the same material, then its bending strength will be twice as high.

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Flexural strength is a property of the material, not the tile. This indicator is used to measure the internal cohesive properties of the material that form the tile, rather than to measure a specific mechanical characteristic of the tile itself. In other words, if we take two tiles from the same material, but of different shapes and sizes, for example, one tile is twice as thick as the other, their bending strength will be the same, although the tensile strength will be different. Thus, the characteristics of the tiles differ, despite the fact that they have the same flexural strength.

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Bending strength is an indicator that does not require additional calculations. It is measured in KG (maximum load leading to destruction of the sample), per surface area (in mm2) to which the force was applied.

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In the applied aspect, the tensile strength of the tile, measured in accordance with the standards, is somewhat overestimated relative to the real load-bearing capacity of the tile as part of a multilayer structure, i.e. after installation. This is due to an increase in the area under pressure.

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The tensile strength of the tile, measured in accordance with the standards, in fact, as a rule, is inferior to the real load-bearing capacity of the tile as part of a multilayer structure, i.e. after installation.

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Material on this issue is presented in the article Flexural strength .

Question 2

The term craquelure itself refers to the crevices and cracks that form on the surface of the glaze. The pattern of these cracks is often circular, although they may be scattered across the surface of the glaze. The reason for the appearance of craquelure is either a difference in the coefficient of thermal expansion of the shard and the glaze, or deformation of the tile due to the impact of mechanical load on it.

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Glazed tiles with an "immediate crackle effect" are not considered defective, although manufacturers sometimes deliberately create collections of tiles with a "craquelure effect" for aesthetic purposes.

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When craquelure appears on polished ceramic tiles and slabs, the term "polished craquelure" is used.

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“Late craquelure” occurs under the influence of the external environment during operation. The reasons for its appearance are: thermal shock, insufficient drying of the cement base, excessive cement content in the layer, excessive thickness of the mortar layer.

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This defect can appear immediately after the end of the production cycle (in this case they speak of “immediate craquelure”) or some time after laying the tiles (in this case they speak of “late craquelure”).

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The test method for determining the resistance to cracking of glazes (craquelure) of ceramic tiles and slabs is given in the EN ISO 10545-18 standard. To determine the resistance to cracking of glazes, tiles and slabs are subjected to high pressure steam in an autoclave. Then the tiles and slabs, after applying the dye to the glazed surfaces, are examined for the presence of cracks in the glaze.

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The material on this issue is presented in the article “ Resistance to craquelure ” and “ Cracking of craquelure glaze ”.

Question 3

The surface hardness of ceramic tiles is the ability of the cladding surface to withstand the mechanical stress of other materials. For ceramic facing materials or natural stones, this property is usually indicated in accordance with the mineralogical scale of hardness, the so-called Mohs scale, named after the German mineralogist Friedrich Mohs, who proposed his test method in 1811. Please indicate the correct statements in your opinion.

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Unglazed ceramic tiles are relatively hard, and scratches only affect the aesthetic properties of the cladding, without damaging its functional qualities.

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The Mohs scale (mineralogical hardness scale) is a set of reference minerals for determining relative hardness using the scratching method. 10 minerals, arranged in order of increasing hardness, were taken as standards.

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Mohs scale - determined by which of ten standard minerals scratches the material being tested, and which of ten standard minerals scratches the material being tested.

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Glazed ceramic tiles are relatively hard, and scratches affect the aesthetic properties of the cladding, while also damaging its functional qualities.

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The Mohs scale is a method of rough comparative assessment of the hardness of materials according to the “harder - softer” system, where the material being tested is scratched by a reference mineral and its surface hardness on the Mohs scale is lower, or it is scratched by a reference mineral and its hardness is higher. Thus, the values ​​of the Mohs scale can be considered indicators of the absolute hardness of minerals.

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Material on this issue is presented in the article Surface hardness .

Question 4

Water absorption is a parameter that determines the porosity of ceramic tiles. It is measured by the amount of water that ceramic tiles absorb under certain laboratory conditions, and is expressed as a percentage of the dry weight of the tiles.

Mark the true statements.

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The lower the degree of water absorption, the more resistant the tile will be to intense mechanical and hydrothermal influences.

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According to EN ISO 10545-3, the penetration of water into the open pores of samples is determined using two methods: boiling and water saturation in a vacuum. When boiling, water saturation occurs only in easily filled open pores; with the vacuum method, almost all open pores are filled.

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A low water absorption coefficient indicates that the structure of the tile is porous, and a high coefficient indicates that the structure of the material is more dense.

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According to the EN 14411 standard, ceramic tiles and slabs are divided into three main groups based on water absorption. Where the third group corresponds to the lowest water absorption rates.

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According to EN ISO 10545-3, the penetration of water into the open pores of samples is determined exclusively using the water saturation method in a vacuum. The boiling method, as a test that does not allow determining open porosity and bulk density, is considered obsolete.

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Material on this issue is presented in the article Water absorption .

Question 5

Frost resistance - the ability of ceramic tiles to withstand freezing in a humid environment and at temperatures below 0 degrees Celsius. The freezing mechanism is divided into two stages. The first stage is the penetration of water from the environment into the pores of the tile. The second stage is the hardening (freezing) of water inside the pores. As is known, the transition of water from a liquid to a solid state is accompanied by an increase in volume, since the density of ice is less than the density of water. Thus, when water freezes inside the pores, the tile is subjected to mechanical stress, which can lead to cracks or chipping of part of the material.

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Frost resistance also prevents ice from forming on the face of the tile. This is due to the fact that water, without getting inside the material through the pores of the top layer, seems to “roll off” from the surface.

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Based on the mechanisms described above, the frost resistance of a material is determined by two parameters:
1) The presence and number of pores that allow water to penetrate into the material;
2) The shape and size of the pores, the volume of voids of which, allows you to distribute the loads of the changing state of water.
It follows from this that frost resistance is directly related to water absorption: the lower the water absorption, the greater the likelihood that the material is frost-resistant. However, there are also highly porous materials (with a high rate of water absorption) that are characterized by frost resistance. Frost resistance in this case is due to the shape and size of the pores, allowing moisture to penetrate into the material without destroying it as a result of hydrothermal loads.

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According to EN ISO 10545-12:1997, tests confirming frost resistance properties are carried out as follows: ceramic tiles or slabs, after being saturated with water, are subjected to alternate temperatures of +5 ° C and minus 5 ° C. They are then completely frozen for at least 100 freeze-thaw cycles. After 100 freeze/thaw cycles, the faces and edges of ceramic tiles or slabs are examined for damage.

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According to EN ISO 10545-12:1997, tests confirming frost resistance properties are not carried out as such. A material is considered frost-resistant if it falls into group 1 of materials according to the degree of water absorption (<3%).

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Based on the mechanisms described above, the frost resistance of a material is determined by the possibility of water penetration into the material, in other words, the degree of water absorption. Thus, if a material does not absorb water, it is frost-resistant, but if it does, it is not.

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The frost resistance property of ceramic tiles is not guaranteed in extremely low temperature zones (below -40 °C). This is due to the test conditions of EN ISO 10545-12:1997, as they are carried out at temperatures between +5°C and -5°C. In this regard, manufacturers mark materials suitable for use in such an environment with a special EXTRA°C sign, which in turn indicates testing in the temperature range from -50 °C to +100 °C.

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Material on this issue is presented in the article Frost resistance .

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