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.
Unglazed ceramic tiles are relatively hard, and scratches only affect the aesthetic properties of the cladding, without damaging its functional qualities.
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.
Glazed ceramic tiles are relatively hard, and scratches affect the aesthetic properties of the cladding, while also damaging its functional qualities.
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.
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.
Material on this issue is presented in the article Surface hardness .
Abrasion resistance is a mechanical characteristic of a lined surface. Indicates the surface’s resistance to wear due to exposure to rubbing objects, surfaces, and materials. Which expressions do you think are correct?
Abrasion resistance also affects other functional characteristics of the ceramic tile surface, such as chemical and stain resistance and ease of maintenance. Naturally, this aspect is equally important for glazed and unglazed tiles, because... abrasion leads to a weakening of the tile structure itself, the appearance of pores and microcracks invisible to the naked eye, into which dirt, etc. gets clogged.
The wear resistance requirements for unglazed ceramic tiles and slabs are set by EN 14411 and depend on water absorption and the method of their manufacture.
According to the test method EN ISO 10545-7:1998, glazed tiles are divided into wear resistance classes, from "0" to "5". Where fifth class tiles are least resistant to abrasion.
The important point is that unlike other quality tests on tiles, durability testing does not determine the value of the tile. The results of the study divide the tiles into classes, each of which corresponds to a specific purpose of the tile, and in no way to divide the tiles into “bad” and “good”.
Abrasion resistance is a property characteristic only of glazed ceramic tiles. Since intense and prolonged exposure to the surface over time can lead to partial loss of the glazed layer, and this, in turn, will lead to exposure of the ceramic mass and, as a consequence, to the loss of not only the aesthetic, but also the functional qualities of the facing surface. Damage to unglazed tiles is almost invisible, since abrasion of the top layer leads to exposure of the ceramic mass, which in unglazed tiles is no different from the top layer.
Information on this issue is presented in the article Abrasion resistance, wear resistance .
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.
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.
The lower the degree of water absorption, the more resistant the tile will be to intense mechanical and hydrothermal influences.
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.
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.
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.
Material on this issue is presented in the article Water absorption .
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:
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.
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.
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.
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.
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.
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.
Material on this issue is presented in the article Flexural strength .
Linear thermal expansion is expressed by dimensional changes in any material, including ceramics, due to changes in temperature. Almost all known materials expand as temperature increases and contract as temperature decreases. Moisture expansion refers to the expansion of the tile due to the absorption of moisture. The consequences of such swelling are similar to the expansion of tiles due to an increase in temperature (linear thermal expansion) and are due to the porous structure of the material.
Methods for determining moisture expansion and temperature coefficient of linear expansion are given in the standards EN ISO 10545-10 and EN ISO 10545-8, respectively.
A moisture expansion test is required for tiles with a water absorption value greater than 6%.
The thermal coefficient of linear expansion α for ceramic tiles is calculated with an accuracy of 0.1•10 -6 °C -1 using the formula: α = dL/(L 0 •dT), where L 0 is the length of the test sample at room temperature; dL is the linear expansion of the test sample during the period of temperature change from room temperature to 100 °C; dT – temperature increase.
The coefficient of thermal expansion for floor and wall ceramic tiles varies from 4.1•10 -6 °C -1 to 8.1•10 -6 °C -1 . This means that elongation ranges from 40 to 80 thousandths of a millimeter per meter of ceramic tile and per degree rise in temperature.
The recommended upper limit for moisture expansion of ceramic tiles and slabs is 0.06% when testing according to ISO 10545-10 is applied. This means that the upper limit of moisture expansion of ceramic tiles and slabs should not exceed 6 mm/m.
Material on this issue is presented in the article Linear thermal expansion and moisture expansion .
