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 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.
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.
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 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.
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.
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.
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.
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.
Material on this issue is presented in the article Linear thermal expansion and moisture expansion .
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.
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.
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.
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.
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%).
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.
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.
Material on this issue is presented in the article Frost resistance .
Slip resistance is determined by the kinetic and dynamic conditions of motion of the body interacting with the surface. When it comes to flooring, it is obvious how the degree of slip is related to the safety of using the surface. Knowledge of surface properties is essential for the cladding designer, tiler, retailer and end user, as well as the safety inspector. Please mark the correct conclusions in your opinion:
According to the DIN 51097 method, in rooms where floors are often wet and where people walk on them barefoot (for example, swimming pool sides, children's pools, common shower rooms, saunas, etc.), the classification contains groups: A; B (A+B); C (A+B+C). Where A is the slipperiest tile.
According to the DIN 51130 method, floors in production facilities or work areas where there is a high risk of slipping are classified into the following groups (according to the average inclination angle): NC; R9; R10; R11; R12; R13. Where R13 is the slipperiest tile.
Ceramic tiles, characterized by their smoothness and shine, form the most intimate contact between the surface and the sole, thereby increasing the coefficient of friction. While rough, uneven surfaces tend to allow water or other liquids to accumulate on them, as well as dirt, grease and other substances that act as lubricants. In addition, the area of contact with the sole, in this case, is limited by the protruding edges of the surface, which also reduces slip resistance. This factor must be taken into account when choosing tiles.
The DIN 51130 and DIN 51097 methods, also called "incline plane methods", consist of a person walking back and forth on a platform covered with the tiles being tested. The inclination of the test section increases at a constant rate until an angle is reached at which the person begins to feel unsure when walking, that is, begins to slide.
Friction coefficient is a parameter characterizing the degree of surface sliding. It is proportional to the force parallel to the interaction surface that must be applied in order to create relative motion between two bodies. The higher its characteristics such as smoothness and shine, the lower the coefficient of friction for floor surfaces, since this contributes to the appearance of a thin, continuous layer of water (as well as grease, dirt, etc.), which acts as a lubricant between the sole and the floor. Ceramic tiles, while smooth and shiny, create a slippery surface and increase the risk of falls and accidents.
Material on this issue is presented in the article Slip resistance on dry and wet surfaces .
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.
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.
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”.
Information on this issue is presented in the article Abrasion resistance, wear resistance .
