The origin of gypsum in nature. What are the technical characteristics of building gypsum? Gypsum as a binder

If you wondered what gypsum is, then you should know that it is a mineral belonging to the class of sulfates. Two varieties of this material are known, one of which is called fibrous, and the other is called granular. The latter is alabaster.

general information

Gypsum has a silky or vitreous luster, the former of which is characteristic of the fibrous variety. Cleavage is perfect in one direction. The material is split into thin sheets. Color can be:

• reddish;
• grey;
• white;
• brown;
• yellowish.

Fibrous varieties give a splintered fracture. The density of the material is 2.3 g/cm 3 . The gypsum formula is as follows: CaSO4 2H2O. The texture is massive.

Properties and varieties

The specific gravity of the material can reach 2.4 g/cm 3 . Gypsum is quite dense, it can be granular and foliated, as well as fibrous. Some of its counterparts resemble. Sometimes it is confused with anhydride, which has an average hardness.

When you study the question of what gypsum is, you will find out that when heated, the material turns into CaSO4.1 / 2.H2O. The temperature limit is 107 °C. When wetted with water, it hardens and seizes, and dissolves in hydrochloric acid.

To date, 3 varieties are known, among them:

• selenite;
• "marino glass";
• alabaster.

The first is parallel needle-shaped and has a silky sheen. Transparent thick sheet is "marino glass". Painted fine-grained may be alabaster.

Application

Selenite, which is fibrous, is used for inexpensive jewelry. But the large ones are based on alabaster, which has been used since ancient times. The raw material is churned out. As a result, you can also get interior items, including:

• inkwells;
• countertops;
• vases.

If you are interested in the question of what gypsum is, then you should know: the material is used in its raw form as a fertilizer, as well as to obtain glazes, enamels and paints in industry and the pulp and paper industry.

The fired material is used for casts and castings. It can be cornices and bas-reliefs. In medicine and construction, the material acts as a binder. More dense varieties serve as ornamental material.

More about application

Gypsum is a valuable stone and is widely used in construction. Thousands of years ago, it was noticed that when ground, it helps fight soil salinization. This mineral was mined in karst caves. From antiquity to this day, gypsum has been applied to the soil to increase crop yields.

For many nations, he was the breadwinner. Entire cities were built from plaster. Crystal blocks were sawn out of it, which went to the construction of walls. The white stone shines dazzlingly in the sun. This can be seen even today, when only ruins remained of the ancient cities.

All over the world, sculptors cannot do without this mineral. It is inexpensive, weighs little and is easy to handle. Appreciated by painters, plasterers, traumatologists and paper manufacturers.

Origin

If you are trying to understand what gypsum is, then you should also familiarize yourself with its origin. This mineral has several types, the method of formation of which is different. In some deposits, a mineral is mined, which was concentrated there in the process of accumulation of marine sediment. In other cases, gypsum was formed when various lakes dried up. The mineral could have arisen from the deposition of native sulfur and from the weathering of its compounds. Deposits in this case can be contaminated with debris rocks and clays.

Place of Birth

After reviewing the description of gypsum, you should also learn about the main deposits that are found on all continents. Russian developments are carried out mainly in the territories of the Caucasus and the Urals. The mineral is mined in the mountainous regions of America and Asia. The United States is the champion of gypsum production. There are also deposits in the foothills of the Alps.

Specifications

The described mineral has a rather dense fine-grained structure. In a loose bulk form, the density can vary from 850 to 1150 kg/cm 3 . In compacted form, this parameter reaches 1455 kg/cm 3 . Getting acquainted with the description of gypsum, you will pay attention to one of its advantages, which is expressed in rapid hardening and setting. At the fourth minute after mixing the solution, the first stage of drying begins, and after half an hour the material solidifies.

Ready gypsum mortar requires immediate consumption. To slow down the setting, water-soluble is added to the ingredients. Among the properties of gypsum, the melting point should be distinguished. The material can be heated up to 700 °C without destruction. Gypsum products are quite fire resistant. They begin to break down only 6 hours after exposure to high temperature.

The strength of gypsum is also often taken into account. During compression, this parameter can vary from 4 to 6 MPa. If we are talking about high-strength material, then it reaches 40 MPa and may even exceed this value. In well-dried samples, the strength is 3 times higher. Mineral corresponds state standards 125-79. It has a thermal conductivity, which is equal to 0.259 kcal / m * deg / hour. The temperature range in this case is equal to the limit from 15 to 45 ° C.

White gypsum dissolves in water in small quantities:

• At 0 °C, 2.256 g can dissolve in one liter.
• If the temperature is raised to 15 °C, the solubility increases to 2.534 g.
• This value rises to 2.684 g at 35°C.

If further heating occurs, the solubility decreases.

Description, scope and properties of building gypsum

If we compare gypsum with other binders, then the first one has a wider area of ​​​​use. With it, you can save on other components. The construction variety is used in the manufacture of gypsum parts, during plastering works and formation of partition plates.

It is necessary to work with gypsum mortar very quickly. The polymerization start time can be from 8 to 25 minutes after mixing the solution. The final value depends on the variety. At the moment of the beginning of hardening, the mineral gains about 40% of the final strength. In this process, white gypsum is not covered with cracks, so it is possible to refuse various aggregates when mixing the solution with a lime composition. The construction variety reduces the complexity and cost of work.

Scope of use and properties of high-strength and polymer gypsum

By chemical composition the high-strength variety is similar to the construction one. However, the latter has smaller crystals. High-strength has coarse particles, therefore it has less porosity and high strength. This material is obtained from heat treatment under sealed conditions.

The area of ​​​​use is the manufacture of building mixtures and the construction of fireproof partitions. From a high-strength mineral, molds are made for the production of faience and porcelain products. Polymer look also called synthetic and more familiar to orthopedic traumatologists. Based on it, they are made for applying bandages for fractures. But the scope of gypsum is not the only advantage, among others it should be highlighted:

• easy overlay;
• moisture resistance;
• lighter weight compared to conventional plaster casts.

Finally

The formula of gypsum should be known to you if you are interested in this mineral. It is important to take an interest in other properties, as well as varieties. Among others, it is necessary to single out molding, sculptural and cellacast.

The latter is used to make bandages, and the structure allows the material to be stretched in all directions. The most high-strength is sculptural gypsum, which does not contain impurities. Among the properties of gypsum white color one can distinguish its impeccable whiteness.

Sulfate class, CaSO 4 .2H 2 O. In its pure form it contains 32.56% CaO, 46.51% SO 3 and 20.93% H 2 O. Mechanical impurities are mainly in the form of organic and clay substances, sulfides, etc. Crystallizes in monoclinic. The crystal structure is based on double layers of anionic groups (SO 4) 2- bound by Ca 2+ cations. The crystals are tabular or prismatic, form twins, the so-called dovetail. very perfect. Aggregates: granular, foliose, powdery, concretions, fibrous veinlets, radial-acicular. Pure gypsum is colorless and transparent, in the presence of impurities it has a gray, yellowish, pinkish, brown to black color. Glass luster. 1.5-2. 2300 kg / m 3. Let's noticeably dissolve in (2,05 g/l at 20 °C). Mainly chemogenic in origin. It precipitates at t 63.5°C, and in solutions saturated with NaCl, at a temperature of 30°C. With a significant increase in salinity in drying sea lagoons and salt lakes, instead of gypsum, anhydrous calcium sulfate begins to fall out -, the same way anhydrite occurs when gypsum dehydrates. Also known is hydrothermal gypsum, which is formed in low-temperature sulfide deposits. Varieties: - translucent fibrous aggregates, cast in reflected light with a beautiful silky sheen; gypsum spar - lamellar gypsum in the form of transparent crystals of a layered structure, etc.

The use of gypsum

Gypsum is used in raw and burnt form. 50-52% of gypsum stone mined is used to produce gypsum binders for various purposes (GOST 195-79), obtained by roasting natural gypsum, 44% of gypsum is used in the production of Portland cement, where gypsum is used as an additive (3-5%) to regulate the timing cement setting, as well as for the production of special cements: gypsum-aluminous expanding cement, tension cement, etc. 2.5% of gypsum consumes Agriculture in the production of nitrogen fertilizers (ammonium sulfate) and for gypsuming saline soils; in non-ferrous metallurgy, gypsum is used as a flux, mainly in smelting; in paper production - as a filler, mainly in higher grades writing papers. In some countries (, etc.), gypsum is used for the production of sulfuric acid and cement. The ability of gypsum to work easily, accept polish well, and generally high decorative properties allow it to be used as a simulator in the production of facing slabs for interior decoration buildings and as a material for various crafts.

In the southern regions of the USSR in national economy clay gypsum is used with CaSO 4 .2H 2 O content from 40 to 90%. Loose rock, consisting of gypsum, and is called earthy gypsum, and in Transcaucasia and Central Asia- "Gazha" or "ganch". These rocks in their raw form are used for gypsuming of soils, in burned form - for plastering, as an astringent.

Gypsum deposit

In the USSR, the most large deposits located in, Tula, Kuibyshev, Perm regions RSFSR, in the Caucasus and Central Asia. At 150 deposits of gypsum and 22 deposits of clay-gypsum, drywall and ganch, reserves of 4.2 billion tons have been explored by industrial categories (1981). There are 11 deposits, the reserves of gypsum in which exceed 50 million tons (including Novomoskovsk - 857.4 million tons).

Gypsum is developed by quarries (Shedoksky, Saurieshsky combines, etc.) and mines ("Novomoskovsky", "Artyomovsky", "Kamskoe Ustye", etc.). In the USSR, 42 deposits of gypsum and anhydrite and 6 deposits of gypsum-bearing rocks are exploited with an annual production of about 14 million tons (1981), of which 60.2% are in the territory

Gypsum has been known since ancient times and is still popular both in construction and in other industries, as well as in medicine. The formula of natural (dihydrate) gypsum CaSO4 x2H2O. Even many modern materials do not surpass it in some technical characteristics. If we talk about construction, then most often gypsum is used in the form of a powder, which is obtained by roasting and grinding gypsum stone. It is used as a binder for the preparation of various mortars, as well as various decorative elements. To work with gypsum, it must be diluted in a certain proportion with water, if necessary, add a filler, after which it will turn into a plastic composition, and you can proceed directly to work with it.

Properties and application of building gypsum.

A distinctive feature of building gypsum from other binders (cement, lime paste) is its ability to expand during the hardening process. The setting process is quite fast - from 5 to 30 minutes, which, in some cases, is not very convenient. The setting time of gypsum depends on various components: the properties of raw materials, manufacturing technology, storage time, the amount of water introduced, the temperature of the binder and water, mixing conditions, the presence of additives, etc. To control the setting time, various additives are introduced into gypsum when mixing with water. . For example, to slow down the setting, SDB, lime-glue and keratin retarders are added to the gypsum mortar in an amount not exceeding 0.1-0.5% (in terms of dry matter) by weight of the gypsum. For small volumes of work, for example, during repairs, skin glue or gelatin is also used as a retarder. These additives are known as plasticizers and gypsum set retarders.
To accelerate the setting (which is necessary, for example, for faster removal of the cast product from the mold) of gypsum, gypsum dihydrate is most often used, table salt and sodium sulfate, introducing them in an amount of 0.2 to 3% by weight.
By strength, gypsum is divided into 12 grades. In construction and repair, mainly grades from G2 to G7 are used. The letter stands for the word "gypsum", and the figure indicates the compressive strength of this material. For example, the G7 gypsum grade has a compressive strength of 7 MPa or 70 kg/cm2. This is enough high strength at a density of 1200 ÷ 1500 kg / m 3.
Of the minuses, one can single out its rather low hygroscopicity, so its use is applicable only in rooms with low humidity.

Plaster work.

In practice, when working with gypsum, a solution of pure gypsum is mainly used, less often with a filler. Depending on the type of work, the gypsum mortar may have a different degree of density: liquid, medium or normal or thick. To prepare a liquid solution for 1 kg of gypsum, approximately 0.7 l of water will be required, an average or normal solution - for 1.5 kg of gypsum 1 l of water and for a thick solution - for 2 kg of gypsum 1 l of water.
The solution is prepared as follows: first pour into the prepared container required amount water and it are gradually covered with gypsum with constant thorough mixing. with this method of preparation, a homogeneous mass is obtained without impurities of lumps of unmixed gypsum. Do not mix the gypsum mortar that has already begun to set, as in this case the gypsum begins to rejuvenate and practically loses its strength qualities.
When working with gypsum, fast setting should be taken into account. gypsum mortar and cook in small batches. To slow down the setting time of the gypsum mortar, setting retarders are used, which have already been mentioned above. When using an adhesive solution as a moderator, it is poured into the water prepared for mixing, thoroughly mixed, and gypsum is closed in this water. The adhesive solution should be prepared with the expectation of one day of work.

Building materials based on gypsum.

Probably the most famous and widely used gypsum building products are drywall sheets . They are usually used for finishing walls, ceilings and partitions in rooms and buildings with dry, normal and even wet conditions. Drywall sheets are produced various sizes and are divided into two types rectangular shape: with straight longitudinal edges or with thin edges on the front side.
Another type of building material based on gypsum are gypsum fiber extrusion decorative boards. This material is widely used in interior decoration, as it has a noble and attractive appearance. In addition, the use of decorative plates reduces labor intensity. finishing works, as they exclude putty and plaster work. The front side of the plates has low water absorption and a denser structure.
In addition to products based on gypsum, widely used bulk materials. This different kind dry mixes(plasters, putties, etc.). Use of dry plaster mixes allows you to mechanize the application of the plaster layer and significantly reduce the drying time of the finished surfaces.

Along with gypsum-based finishing materials, such construction material, how gypsum concrete. And, although, due to the rather long drying time of structures, gypsum concrete is rarely used for building walls, he found quite wide application during the construction of partition walls.
The undoubted advantage of gypsum concrete is its low thermal conductivity compared to traditional concrete, as well as its heat and sound insulation properties, which significantly reduces the cost of construction and provides sound insulation for each individual residential area.

Gypsum- mineral, aqueous calcium sulfate. Synonyms: gypsum stone, mirror stone, montmartite, sand rose, desert rose, gypsum spar.

Chemical composition. Calcium oxide (CaO) 32.6%, sulfur trioxide (SO 3) 46.5%, water (H 2 O) 20.9%. Thin crystals and cleavage bending plates

The crystal structure is layered; two sheets of 2- anionic groups, closely associated with Ca2+ ions, form double layers oriented along the (010) plane. H2O molecules occupy spaces between these double layers. This easily explains the very perfect cleavage characteristic of gypsum. Each calcium ion is surrounded by six oxygen ions belonging to the SO4 groups and two water molecules. Each water molecule binds a Ca ion to one oxygen ion in the same double layer and to another oxygen ion in the adjacent layer.

Varieties of the mineral

Deposits of the mineral Gypsum

• Ulyanovsk region
• Gaurdak
• Kerch, city
• Pinega
• Kazakhstan
• Nizhny Novgorod Region
• Mexico
• Moldova
• Russia
• Ukraine
• Turkmenistan
• Arhangelsk region
• Republic of Crimea
• Uzbekistan
• Chelyabinsk region
• Algeria
• Kopey coal dumps
• Belarus
• Poland
• Kyrgyzstan
• Naryn region

Gypsum as a material has been known since ancient times, but it has not lost its popularity and demand to this day. In addition, even the newest and most advanced materials could not compete with him. The use of gypsum very wide, ranging from the porcelain field of activity and ending with medicine. However, the most demanded is construction.

What is gypsum as a material?

It is made from gypsum stone. They are fired in furnaces of different temperatures, and then they are broken until a powder mixture appears. Gypsum-treated surfaces can absorb unwanted moisture from the air and release it when the air is very dry. Attribute given material to sulfates. Exists two types of plaster: selenite and alabaster. The first is fibers and the second is grains.

What are the technical characteristics of building gypsum?

Almost all gypsum mixes have similar characteristics. These include:

1. Density. The building material is a fine-grained structure. On average, the density varies from 2.6 to 2.8 g per cm.

2. Drying period. It sets up in just a matter of minutes. Experience shows that in the fourth minute after mixing it, the solution sets, and after 30 minutes it completely hardens. It is for this reason that it is necessary to dilute gypsum in small portions, otherwise it will harden, and nothing can be done with it. However, there is a way to slow down this process. Water-soluble animal glue is added to the solution. Its use will not affect the quality of the gypsum in any way.

3. Specific gravity. The weight ratio is equal to the volume occupied by the gypsum, so the specific, volumetric and bulk weight are almost the same.

4. Melting point. This material can be heated up to 700 degrees Celsius! And it will not change its form or quality. Its destruction will begin only after 6 hours of continuous exposure to high temperature.

5. Strength. When compressed, it is 5 MPa, and high-strength material is from 10 to 50 MPa.

6. Gypsum meets GOST i.e. government regulations.

7. Thermal conductivity and solubility. It is a very weak conductor of heat. And practically does not dissolve.

What are the types of gypsum?

one. . The use of this type of gypsum extends to the creation of gypsum parts and slabs for plaster work. All work with it must be done in 10-20 minutes, as it freezes very quickly. It is during this period of time that the material must be fully used. Only at the initial moment of hardening, gypsum gains approximately half of its strength. When hardened, cracks do not appear on it, so there is simply no need to add any special components. But this does not apply to substances that slow down hardening. This mortar reduces the difficulty of work and material costs generally. It is mined by blasting gypsum-containing rocks. After that, the gypsum is transported to manufacturing enterprises in the form of stones.

2. High strength. In its structure and composition, it practically does not differ from the previous species. However, in the building type, the crystals are smaller, and in the high-strength type, they are larger, so it has less porosity and great strength. It is produced by heat treatment in a special device. The use of gypsum of this species is quite diverse. Various solutions are made from it, partitions are erected that do not burn. It is also worth giving preference to porcelain plumbing fixtures, they are made of high-strength gypsum. Do not forget about the fields of medicine, and more specifically about dentistry and traumatology.

3. Polymer. This type of gypsum is very popular in traumatology; bandages are made on its basis, which will later be used to apply bandages. The advantages of using polymer dressings include: they are several times lighter than simple plaster ones, they are applied without difficulty and with minimal cost time, allow the skin to breathe, because they have excellent permeability, do not absorb moisture, with their help you can observe the process of bone fusion.

4. Cellacast gypsum. It is almost the same as polymer, only its composition allows you to stretch the bandage in all directions and in different directions.

5. Structural or molding. The most environmentally friendly, as it does not contain any additives. They are used to create molds for sculptures, various figurines, sculpting, etc. also used in automotive and aircraft construction activities. It is the main element of dry putties. This type of gypsum is obtained from building gypsum by sifting and grinding it. They even make sockets out of it!

6. Acrylic. Made from acrylic resin that dissolves in water. When this type completely hardens, the material is similar to simple building material, but it is lighter. Various decorative moldings - full credit acrylic material. Gypsum withstands different temperature, has a small moisture absorption, so it can also be used to create beautiful and unusual facades building. It is very easy to work with him. If aluminum powder is added to the mixture or marble chips, then the gypsum will accordingly resemble marble or metal.

7. Polyurethane. Also used in stucco. In terms of cost, it is much more profitable than the building type. But in terms of performance, there is no difference.

8. White plaster. It is a great help in various repair work. They put everything in order. White gypsum can be combined with different building materials - this is its main advantage. Freezes for about 7 minutes.

9. Fine-grained or translucent. They fill the seams.

10. Liquid gypsum. Made from gypsum powder. The manufacturing algorithm is as follows: 1 - water is prepared, 2 - gypsum is poured into it and mixed, 3 - stirred until a liquid substance is obtained.

11. Waterproof or moisture resistant. Obtained by processing the material according to a special algorithm. To improve its qualities, bard is added to it.

12. Fireproof. All gypsum is fire resistant, but this type is made from tongue-and-groove gypsum, which can withstand extreme temperatures. Used in all areas, especially where it is necessary to increase the fire resistance.

13. Architectural. It is very plastic, and does not contain toxic elements. The acidity of gypsum of this type is the same as the acidity of human skin. Modeling from this gypsum is very popular, and therefore the demand for it is high.

Can something replace gypsum?

Yes maybe. And that material is alabaster. It is also known in the construction world, it is obtained from two-water gypsum by processing at high temperatures. According to external characteristics, they do not differ from each other. It is used if there is little humidity in the room.

Differences between alabaster and gypsum

1. Gypsum is used in many fields, without limitation, alabaster is known only in the construction field.

2. If special components are not added to the alabaster, then 1 - it will dry out very quickly, 2 - it will simply be unusable.

3. Gypsum is more environmentally friendly than alabaster.

4. Alabaster is more durable than gypsum.