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:
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.
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.
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.
Material on this issue is presented in the article Flexural strength .
Thermal resistance is the ability of ceramic tiles to withstand without damage the stress caused by dimensional deformations due to sudden changes in temperature, especially if such changes are repeated frequently. Which statements do you think are correct?
“Resistance to thermal shock” is a property characteristic only of refractory materials, the scope of which is the metallurgical, glass, chemical industries, as well as all other industries where work takes place using blast furnaces, shaft and rotary furnaces.
The test method described in GOST 27180-2001 is as follows: samples are subjected to 10 rapid cycles of temperature changes from 15 °C to 145 °C. The maximum temperature is achieved by placing the samples in an oven for at least 20 minutes, the minimum by completely immersing them in water at a temperature of 15°C. At the end of 10 cycles, samples are inspected for visible defects.
Thermal resistance is an important physical property of ceramic tiles. Let's imagine, for example, the tiled surface of a kitchen countertop on which a hot pan is placed. The surface of the tile heats up sharply and, as a result, expands, and the lower layers become colder and less expanded as they move away from it. In this state of thermal inhomogeneity, the tile, which does not have the property of heat resistance, could be deformed and, being an inherently rigid material, could crack.
If we compare the thermal resistance testing methods of the EN ISO 10545-9 standard and GOST 27180-2001, we can conclude that the test requirements of the EN ISO 10545-9 standard are somewhat stricter than the requirements of GOST 27180-2001.
Thermal resistance is the ability of a material to resist the transfer of energy (heat exchange) from more heated parts of the body to less heated bodies, carried out by chaotically moving body particles (atoms, molecules, electrons, etc.).
Material on this issue is presented in the article Thermal resistance .
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 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.
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 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.
Material on this issue is presented in the article Linear thermal expansion and moisture expansion .
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.
When craquelure appears on polished ceramic tiles and slabs, the term "polished craquelure" is used.
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.
“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.
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.
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”).
The material on this issue is presented in the article “ Resistance to craquelure ” and “ Cracking of craquelure glaze ”.
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.
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.
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.
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.
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.
Material on this issue is presented in the article Water absorption .
