Gypsum today has not lost popularity, although it has been known since antiquity. Many modern materials to this day can not compete with him. It is used in ceramic, porcelain and earthenware, oil industry, construction and medicine. Gypsum is in demand in sculpting, in the production of decorative stone and is divided into different grades depending on the strength obtained.
Definition
Gypsum has a grayish or white color. The grinding of the material is thin, it is obtained from gypsum stone. After processing, natural gypsum is fired at temperatures up to 190 ° C. The substance quickly sets, is a fast-hardening binder. It is used for plastering, in the manufacture of gypsum building objects, gypsum concrete, castings, and also as an additive to binders such as cement and lime.
The material is fired in rotary kilns, after which the raw material is ground to a powder. To date, two varieties of gypsum are known - fibrous and granular. The first is called selenite, the second - alabaster.
Specifications
If you want to use gypsum, brands and their characteristics should interest you. There are a total of 12. The characteristics of all gypsum mixtures are very similar. Among the main features of building gypsum should be highlighted density, which varies from 2.60 to 2.76 g / cm 2 . The material has a dense fine-grained structure. In loose bulk form, the density varies from 850 to 1150 kg / m 2 .
If the material is presented in a compacted form, then this parameter varies from 1245 to 1455 kg / m 2 . A rather important feature is the drying time. Among the main advantages should be highlighted quick hardening and setting. In the 4th minute after mixing, the gypsum begins to harden, after 30 minutes it sets completely. In this regard, the finished solution must be consumed immediately.
About melting point and bulk density
To slow down setting, water-soluble animal glue is added to the gypsum . It is important to mention also the specific gravity, which is the ratio of the mass to the volume occupied by it. Volumetric and bulk density are approximately the same. Quite often, consumers are also interested in what temperature gypsum undergoes. This characteristic is also called the melting point. Heating can occur up to 700 ° C without destruction. Fire resistance is quite high. Destruction occurs only 8 hours after exposure to high temperature.
If you want to purchase the described material, then you should be interested in the brands of gypsum for strength. For example, a building material in compression has a strength parameter of 4 to 6 MPa. If you have high-strength gypsum in front of you, then this parameter varies from 15 to 40 MPa. In dried samples, the strength can be three times higher. The material also complies with state standards 125-79 (ST SEV 826-77).
Thermal Conductivity and Solubility
Among the characteristics should be highlighted the ability to conduct heat. Plaster has a bad deal with this. Thermal conductivity is 0.259 kcal / m deg / h, which is true for temperatures from 15 to 45 ° C. The solubility in one liter reaches 2.256 g. These figures are correct at 0 ° C. If the temperature increases to 15 ° C, the solubility is 2.534 g. At a temperature of 35 ° C, the solubility increases to 2.684 g. If heating continues, the solubility decreases.
additional characteristics
Studying the brands of gypsum for artificial stone, you can note that it is not always convenient that the material sets so quickly. When working with solutions, you must consider that the hardening dough sets and rejuvenates with stirring. But if such a solution is applied to the surface, it will no longer have the required strength, and when dried, the material will begin to collapse, become covered with cracks. Therefore, gypsum-based solutions should be prepared in small volumes, which you can use in a few minutes.
In order to reduce hardenability, clay or lime mortar should be added. For this purpose, a special moderator from a solution of borax is used. All these mixtures are prepared in water. Hardened gypsum is characterized by high strength and low density, which varies in the range of 1200-1500 kg / m 3 , such a material is almost two times lighter than cement. This suggests that the composition is less heat conductive.
Stamps
Marks of gypsum, as mentioned above, 12. They include some varieties of gypsum, among them are:
- building;
- technical; modified;
- molding.
The first is marked as G4 or G5 and is used for plastering and the manufacture of various building elements. The technical variety is marked G5 and is a molding model material. When considering grades of gypsum, you should pay attention to the modified variety, which is labeled as G16 and is used to seal joints, grout primers and putties.
Molding gypsum is marked as follows: G10, G18. It is used in the ceramic, aviation and automotive industries. Among the main areas of application, it is worth highlighting the manufacture of molds for casting alloys and non-ferrous metals. Molding gypsum was widely used in the manufacture of sculptural models.
If you are interested in the brands of building gypsum, you should pay attention to the markings from G-2 to G-7. These materials belong to group B, and their compressive strength varies from 0.2 to 0.7 MPa, which is the limit from 2 to 7 kgf / cm 2 . In this case, the start of setting takes place in the sixth minute. Grasping ends no later than half an hour. The brand of building gypsum is called alabaster. This binder is the only one that expands and increases in volume up to 1% in the hardening process, but cement and lime dough shrink.
More about brands: construction
The building mark of gypsum is used for the manufacture of parts, plastering and the formation of partition walls. Work with such a solution must be carried out in a short time - from 8 to 25 minutes. The final value will depend on the particular brand. At the beginning of hardening, the material gains about 40% of the final strength.
For the reason that cracks do not form during hardening when kneading a solution with a calcareous composition, which is necessary to obtain ductility, it is possible not to use different aggregates. The setting time in this case will be reduced due to hardening retarders.
High strength polymer grades
In composition, the high-strength brand is similar to the construction one, but the latter has smaller crystals, while the high-strength one has coarse-grained ones, so it has less porosity and high strength. Such gypsum is made by heat treatment in equipment in a tight environment where gypsum stone is placed.
Considering the definition of the brand of gypsum, you can understand that the scope of its use is quite extensive. Building mixtures are made from raw materials and fireproof partitions are formed. From gypsum, various forms are made for porcelain and earthenware sanitary products. High-strength variety is used in dentistry and traumatology. But orthopedic traumatologists are more familiar with polymer synthetic gypsum, on the basis of which gypsum bandages are made for dressings for fractures. Among the main advantages of the polymer brand are the following:
- "easy overlay";
- moisture resistance;
- ease;
- the ability to control bone fusion.
The material allows the skin to breathe, because it has good permeability.
Brand definition
If you are interested in how to determine the brand of gypsum, then you should know that marking is carried out according to some indicators, among them it should be highlighted:
- strength;
- fineness of grinding; setting speed.
The brand can be determined by bending and compressing standard samples. They have the following dimensions: 4 x 4 x 16 cm. Tests are carried out 2 hours after molding. First, bending strength is determined, after - compressive strength. During this time, crystallization and hydration are completed.
According to GOST 129-79, 12 grades of material for strength are established. The number after the letter indicates the lower compressive strength. For a gypsum binder, an important factor is the beginning and end of setting. According to these parameters, the material is divided into three groups - A, B, C. According to the fineness of grinding, which is determined by the remainder of the sample during sieving, the binder is divided into three groups: coarse, medium, thin. Density can be true and bulk. The 1st varies from 2650 - 2750 kg / m 3 , the 2nd - from 800 - 1100 kg / m 3 .
Characteristics of gypsum G5
This brand of building gypsum has a compressive strength of 5. When bending, this parameter is 2.5. Using this composition, you can repair surfaces, repair cracks, grooves, potholes and mount wiring products. Gypsum allows you to mount beacons and profiles for plastering.
Another area of use of such gypsum is the manufacture of dry building mixtures for facing work. The degree of grinding is 14% when sifting through a sieve with cells with a size of 0.2 mm. The compressive strength of samples is 5 MPa. The setting time varies from 6 to 30 minutes. Considering the characteristics of gypsum brand G 5, you should pay attention to the tensile strength in bending, which is 25 kg / cm 2 .
Characteristics of gypsum G10
This gypsum is a high-strength, finely ground white powder. In its pure form, it is transparent and colorless, and in the presence of impurities it has a yellowish, gray, brown or pink tint. Gypsum brand G 10 is a fire-resistant non-combustible material that does not have toxic components. Its acidity is similar to that of human skin.
The compressive strength is 100 kgf / cm 2 . The normal hardening variety begins to polymerize in the sixth minute, the end of curing is reached in the 9th minute. It is possible to use the material in sculptural works, in the ceramic industry, in the aviation and automobile spheres, as well as for high-quality finishing works. This gypsum is also used in the production of decorative stone.
Finally
Gypsum has been known to man for a long time, but today they are finding more and more extensive areas of use. It is used not only in industry, but also for private purposes. It becomes part of fireproof partitions and products for various purposes.