Gypsum as a material has been known since ancient times, but to this day it has not lost its popularity and demand. In addition, even the newest and most improved materials could not compete with it. Application of gypsum very wide, ranging from the porcelain industry to medicine. However, the most in demand is construction.

What is gypsum as a material?

It is made from gypsum stone. They are fired in ovens of different temperatures, and then broken until a powder mixture appears. Surfaces treated with gypsum can absorb unnecessary moisture from the air and also release it in very dry air. This material is classified as sulfates. Exists two types of gypsum: selenite and alabaster. The first is the fibers and the second is the grains.

What technical characteristics does building gypsum have?

Almost all gypsum mixtures 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 in literally 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 plaster must be diluted 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 gypsum, therefore the specific, volumetric and bulk weight have almost the same indicators.

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

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

6. Gypsum meets GOST, that is, state standards.

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

What are the different types of gypsum?

1. . The use of this type of gypsum extends to the creation of gypsum parts and slabs for plastering work. All work with it must be done in 10-20 minutes, as it hardens very quickly. It is within this period of time that the material must be completely used. Only at the initial moment of hardening does gypsum gain approximately half its strength. When hardened, no cracks 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 building mixture reduces the difficulty of work and material costs in general. It is mined by blasting gypsum-containing rock. After this, the gypsum is transported to manufacturing enterprises in the form of stones.

2. Highly durable. In its structure and composition it is practically no different from the previous type. However, the building type has smaller crystals, while the high-strength type has larger crystals, so it has less porosity and enormous strength. It is produced by heat treatment in a special device. Application of gypsum This species is quite diverse. Various solutions are made from it, and partitions are erected that do not burn. It is also worth giving preference to porcelain plumbing fixtures; they are made from high-strength gypsum. We should not forget about the fields of medicine, or rather dentistry and traumatology.

3. Polymer. This type of plaster is very popular in traumatology; bandages are made from it, which will later be used for applying bandages. The advantages of using polymer dressings include: they are several times lighter than simple plaster, they are applied without difficulty and with minimal time, they 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 plaster. It is almost the same as the polymer one, only its composition allows the bandage to be stretched in all directions and in different directions.

5. Structural or molding. The most environmentally friendly, as it does not contain any additives. Used to create molds for sculptures, various figurines, modeling, etc. also used in automotive and aircraft manufacturing activities. It is the main element of dry putty substances. 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 melts in water. When this type has completely hardened, the material is similar to simple construction material, but it is lighter. Various decorative stucco moldings are entirely due to the acrylic material. Gypsum can withstand different temperatures and has low moisture absorption, so it can also be used to create beautiful and unusual building facades. It is very easy to work with him. If you add aluminum powder or marble chips to the mixture, the plaster will respectively resemble marble or metal.

7. Polyurethane. Also used in stucco. In terms of cost, it is much more profitable than the construction type. But in terms of its indicators it is no different.

8. White plaster. He is an excellent assistant in various repair work Oh. They put everything in order. White gypsum can be combined with different building materials - this is its main advantage. It hardens in about 7 minutes.

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

10. Liquid gypsum. Made from gypsum powder. The manufacturing algorithm is as follows: 1 - prepare water, 2 - pour gypsum into it and mix, 3 - stir 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 plaster is fire intolerant, but this type is made from tongue-and-groove plaster, which can withstand extreme temperatures. Used in all areas, especially where it is necessary to increase fire resistance.

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

Can anything replace plaster?

Yes, it can. And this material is alabaster. It is also known in the construction world; it is obtained from gypsum dihydrate by processing at high temperatures. In terms of external characteristics, they do not differ from each other. It is used if there is little humidity in the room.

Differences between alabaster and plaster

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

2. If special components are not added to 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 characterized by greater strength than gypsum.

In the construction industry, gypsum is in second place after cement-sand mixtures. The unpretentiousness of the material, excellent environmental friendliness and relatively simple technology of use became the reason mass use building gypsum for the production of safe blocks, finishing elements and even interior items.

Production of gypsum mass

The raw materials for the production of gypsum for construction purposes are natural deposits of gypsum stone in the form of anhydrous anhydride - calcium sulfate, its two-water modification CaSO 4 *H 2 O, as well as huge amount industrial waste from the chemical and metallurgical production sector.

The gypsum production technology consists of three sequential operations:

• Purification, fractionation and pre-grinding of raw materials;
• Heat treatment at different temperatures, from 160 o C to 1000 o C;
• Final grinding of the heat-treated gypsum mass to a powdery state, drying and packaging of the building material in hermetically sealed packaging.

The general technology for the production of gypsum divides the binder gypsum material into two categories - quickly setting, or semi-aqueous material, and slowly setting gypsum stone. The first group includes construction and high-strength molding gypsum material, the second group includes less durable anhydride cement and highly calcined stone, called estrich gypsum in the old fashioned way.

In the process of heating to 180 o C, the raw material - two-water gypsum stone breaks down into two modifications, after separation on sieves, high-strength α-gypsum is used for the manufacture of gypsum stone, blocks and forms, β-modification is divided into several categories, the most viscous, with high bending strength, used for construction purposes, the rest as decorative and auxiliary material.

Types of gypsum stone

In addition to the chemical composition, the properties and characteristics of gypsum largely depend on the structure of the raw material. For example, in addition to natural alabaster stone, which has a pronounced polycrystalline structure, a fibrous type of calcium anhydride, selenite, is used for production.

All types of gypsum, from building to decorative or architectural, are obtained by varying the content of selenite, alabaster, raw gypsum stone, finely ground waste calcium sulfate, heat-treated at different temperatures. After fractionation of the raw material according to the degree of grinding, gypsum is divided into three groups:

• A - quick-hardening or alabaster materials;
• B and C - mixtures with a hardening time of up to 15 minutes;
• G - gypsum building materials.

The finer the grain, the faster the material hardens.

Construction or high-quality gypsum

For construction work, not the most durable grades of gypsum are used; uniform hardening and relatively high water absorption, which provides the mixtures with high plasticity, are considered more important. For the production of building materials from gypsum, putties, and gypsum plaster mixtures, the β-modification of medium fineness is used.

Due to special wetting and setting-retarding additives, you can work with gypsum mortar almost like you would with a cement-sand mixture. This reduces gypsum shrinkage and the risk of cracks in the building material.

High strength gypsum stone

Finely ground α-modifications of raw gypsum are used for the manufacture of finished building finishing elements, for example, artificial facing stone, plasterboard sheets, fire partitions and slabs for laying flooring.

High-strength gypsum mixtures can be used to finish walls of frame buildings, ceilings, and interior parts. Per 100 kg of heat-treated raw material there is no more than 20% of the high-strength fraction, so the material is quite expensive and is rarely used in its pure form. Most often, high-strength building gypsum is the basis for the manufacture of fire-resistant or architectural material.

Polymer stone-gypsum

The idea of ​​adding polymer additives to the gypsum mass has been used for quite a long time. Polymer gypsum is obtained in two ways:

• Addition of water-soluble polymer compounds that improve the fluidity of gypsum and wetting of grain. A water-soluble polymer, for example, polyvinyl acetate emulsion or an aqueous solution of carboxycellulose, increases the resistance of the material to impacts and alternating loads;
• Saturation of the surface of the finished casting from building gypsum with volatile polymer compositions, most often based on polyurethane or polypropylene.

In both cases, a thin plate of building gypsum turns out to be quite elastic and at the same time light. From polymer gypsum you can easily make an inexpensive finish that imitates expensive types of wood in texture and pattern.

Cellacast gypsum material

The widespread use of gypsum material is hampered by one of its inherent disadvantages - the high fragility of gypsum. This prevents the production of thin screeds or shells from plaster. Therefore, the building material is saturated with special reinforcing microfiber, the surface of which is treated with polyurethane.

As a result, the strength of the building material increases by 40-50%, and resistance to bending loads by 150-200%. Celacast plaster is widely used in medical institutions for applying fixing bandages for fractures and severe injuries of the extremities.

Sculptural or moldable gypsum material

Ordinary building plaster, after slight modification with polymer resins and dihydric alcohol, turns into a mass from which a model, impression, or bas-relief of any complexity can be made.

Gypsum molding material cannot be diluted with water, as is usually done for building gypsum. In the kit, a special water-alcohol based solvent is added to the white or beige-gray finely ground powder. Thanks to the use of a solvent, it is possible to achieve almost zero shrinkage of the material. Therefore, souvenirs and casts of objects with minute carvings or engravings are often made from sculptural plaster, for example, when copying rare coins, artifacts, and ancient awards.

Acrylic gypsum block

It’s easy enough to turn building plaster into a homemade version of homemade earthenware. It is enough to knead with the preliminary addition of one-component acrylic resin. The result is a light and very hard casting that can be processed by carving, grinding, and drilling. For example, make decorative stucco moldings or vases imitating antique porcelain from building plaster.

In the construction industry, mixtures of acrylic and gypsum are used to make wall cladding from gypsum blocks and to form the rough base of self-leveling self-leveling floors.

Polyurethane gypsum material

The use of non-woven polyurethane fabrics and fibers with a specially treated surface made it possible to create a fundamentally new material for the manufacture of immobilizing bandages, tourniquets and pads that fix limbs and body parts in case of severe injuries.

Unlike cellocast plaster, polyurethane gypsum material has high strength and sufficient casting flexibility to reduce discomfort from its use. Polyurethane material is obtained from construction materials using a special procedure for reseeding the ground mass and separating the largest grains of the same size. As a result of processing the rough mass of building gypsum, a casting with huge pores is obtained, providing free access air to body tissues.

White gypsum stone

Construction gypsum serves as a raw material for the production of so-called white or dental gypsum materials. White obtained through deep purification of the feedstock, sulfur oxides, sulfates of heavy metals, iron, and organic impurities, which usually color construction gypsum in a grayish-beige color, are removed.

Mixtures are made from finely ground white stone to form impressions necessary for subsequent prosthetics or treatment. White stone differs from building material in a whole bunch of additional qualities:

• The gypsum casting must not contain irritating or toxic materials;
• No shrinkage of white gypsum molds;
• Minimum water absorption;
• Rapid setting of the gypsum matrix.

For your information! White plaster generally provides very high performance imprint, which is why it is often used to make foundry molds for jewelry. Parts weighing at least 3g in size are poured into a mold made of building plaster.

Fine-grained gypsum

Reducing the grain size of building gypsum can significantly improve its two main characteristics:

• The strength of the material increases under the influence of bending loads;
• Higher flexibility for thin castings.

A casting based on finely ground α-gypsum grain can show a strength of 350-400 kg/cm 2 . The only limitation that has to be taken into account is high shrinkage, so building gypsum based on fine grains is used for repair work and the manufacture of high-strength coatings.

For your information! From fine-grained gypsum, after vacuuming and high-temperature curing of the mixture, a thin sheet can be easily produced, almost identical in appearance and properties to packaging cardboard.

Liquid gypsum material

If alcohol glycol solutions are used instead of water to mix building gypsum, the material can be stored in an unchanged state for a long time. Liquid gypsum material is used to perform repair and thermal insulation work. After adding an aqueous solution of calcium chloride and table salt Liquid gypsum can be pumped under pressure into cracks in walls or floor slabs. To repair foundations, liquid is used only in combination with polymer resins, for example, polyurethanes.

Waterproof gypsum stone

For all its advantages, ordinary building gypsum remains quite sensitive to moisture or condensation. Moisture-resistant gypsum board material is made using thermosetting polymer powders, and sometimes simply finely ground polystyrene, added to dry building gypsum at the stage of forming the slab.

After curing, the building boards are subjected to heat treatment, and the material acquires water-resistant qualities.

Fireproof block

Heat-resistant or even fire-resistant gypsum block on an industrial scale is made on the basis of ordinary building gypsum and fire-resistant additives. Such material can even be made with your own hands using the following recipe:

• 30% of the weight of high-quality building gypsum and the same amount of water;
• 15% ground ash or fireclay dust;
• 4% aluminum oxide, you can take washed skinny white clay;
• 2% each of quicklime and ground iron dioxide.

For your information! If building gypsum is required for fire safety class G1, then the complex composition can be replaced with finely ground quartz sand, however, such gypsum stone will not withstand heating above 600°C.

Architectural

Most often, building gypsum for architectural work means ordinary molding gypsum modified with polyurethane fibers or polystyrene. This is a relatively soft material, and you can use it to make a model or cast simple stucco elements without any problems.

Real architectural gypsum for construction work is made on the basis of gypsum stone, fired at a temperature of 800-1000 o C. The result is a very hard, viscous building gypsum that does not absorb water well. If you follow the mixing technology, you will get a plaster casting with a very hard and at the same time wear-resistant surface.

Unlike polystyrene architectural plaster, from which craftsmen currently like to assemble finishing XVII style century, real stucco for external walls was cast from high-fired building plaster. The difference is impressive. Polystyrene stone lasts at most 10 years; old hardened plaster lasted almost two hundred years in the climate of St. Petersburg.

Brands of gypsum mixtures

During the production process, the heat-treated mass after grinding is fractionated according to density and particle size. In accordance with GOST No. 125-79, the material is divided into four groups or twelve grades.

The first group includes ordinary gypsum materials G2-G7, with a strength of 20-70 kg/cm2, the second group includes low-shrinkage mixtures G10, G13-16. The third group is high-strength G22-25, the fourth group includes gypsum mixtures with special properties, for example, fire-resistant or highly porous blocks and stones.

Properties of building gypsum

A typical gypsum block used for construction purposes is a highly porous mass; the volume of air channels can reach 50-55%. The density of building gypsum stone is 2.6-2.75 g/cm 3 , for a bulk mass of 900-1000 kg/m 3 in a pressed but uncured state, the building mixture can be compacted to 1400 kg/m 3 .

Dry hard gypsum stone can easily withstand heating up to 450-500 o C; 100-120 minutes after the start of thermal exposure, the surface begins to peel off until gradual destruction. The thermal conductivity of gypsum block is 0.259 kcal/m deg/hour at room temperature.

Grinding degree

The raw building gypsum obtained during treatment with superheated steam under a pressure of 1.5-2.5 Atm is conventionally divided into three grades

• The first grade of material corresponds to the fraction that leaves 918 units on a sieve with a hole density of 918 units. per cm 2 no more than 15% of the initial volume. This is the most active and durable fraction of building gypsum;
• To the second grade include more viscous masses with residual moisture of no more than 0.1% of the mass; after passing the sieve test, no more than 25% should remain on the mesh;
• The third grade, especially finely ground building gypsum, leaves no more than 2% of the mass on the sieve.

It is clear that the finer the grain of calcium anhydride, the faster water absorption occurs and the more hydraulic bonds are formed between individual grains of building gypsum, the stronger and harder the gypsum stone becomes.

Compressive and bending strength

The tensile strength for building gypsum of the first category is determined as 55 kg/cm 2. The second category, after completion of the hardening process, must withstand a static load of 40 kg/cm2. After about four hours, the hardened building stone after drying should withstand up to 200 kg/cm2.

The flexural strength for dried stone is 30% of the static compression for unreinforced material and 65% for reinforced mass. An increase in stone moisture content by just 15% can reduce strength by 40-60%.

Normal density, water requirement or water-gypsum ratio

The amount of water required to form internal bonds between grains depends on chemical composition. For α-gypsum based on hemihydrate, 35-38% of water by weight of building gypsum stone is required, for weaker viscous β-hemihydrate, from which the bulk of building gypsum material is produced, 50-60% of an aqueous solvent is required.

The thickness of the gypsum mixture in the first minutes corresponds to wallpaper glue, after 10 minutes. This is already thick sour cream, and after another 5 minutes. - viscous, crumbling mass. By introducing additives based on FFA, alum gels or even lime, the density can be stabilized and the overall water consumption of the building material can be reduced by 10%.

Reinforcement of gypsum boards and blocks

Despite the internal homogeneity of the hardened gypsum mass, the bending strength of blocks and slabs is considered insufficient. It is especially difficult to work with thin slabs and sheets. Often, the fall of building gypsum cladding from a wall to the floor means destruction and puncture of the material.

Building gypsum blocks are reinforced with chopped polyester fiber, thin-sheet panels are strengthened by the introduction of fiberglass and fluff pulp.

Gypsum as a binding material

Dry gypsum mixture has a high water absorption capacity, for example, hemihydrate α-gypsum has a surface area of ​​up to 6000 cm 2 /g, and the weaker β-modification has twice as much. A small amount of 3-5% gypsum mixture added to lime or cement mortar can increase viscosity by 15%.

Relatively simple and effective way correction of the viscosity of any mortar, but it is worth considering that the water absorption process develops progressively, so the residual viscosity of the mixture will be formed no earlier than 15 minutes after adding the material.

Plaster setting

High-quality gypsum has a high hardening speed; in practice, for freshly fired building material of the first category, the setting process should begin within 4 minutes after dilution with water. For gypsum material of the second category, the curing process according to the standard should begin no earlier than after 6 minutes. It is clear that due to the absorption of water vapor from the air, gypsum, even when carefully packaged in a waterproof shell, loses activity, therefore, the standards for gypsum material limit the start time of hardening to 30 minutes. Anything more than that is already considered unusable. Total time setting from the beginning of mixing to the transition to a solid state should not exceed 12 minutes.

The setting time of building gypsum is limited to a period of 3 hours. An exception is anhydrite cement, for which the setting limit is set at 24 hours. If a building gypsum block gains full strength after 3-4 hours, depending on the temperature and mixing conditions, then for an anhydrite gypsum masonry mortar the limit is set, as for cement -sand mixtures, 28 days. A sample of hardened anhydrite gypsum binder must withstand a compressive load of 50-150 kgcm2.

Hardening of gypsum

The process of binding water and gaining strength with building gypsum can be accompanied by expansion of the hardening mass. The more anhydride in soluble form in the chemical composition, the greater the degree of expansion. For example, hemihydrate can increase the size by 0.5%, and for β-modification the casting material increases by 0.8%.

This leads to self-strengthening of the building mass, but it is not very convenient if you need to maintain maximum accuracy of the cast, so the effect is combated by adding 1% lime or Pomazkov materials. During the drying process, building gypsum shrinks, so stone masses of great thickness are always loaded with internal stresses.

Construction gypsum: application

A high degree of versatility and very simple preparation technology have become the reason for the enormous popularity of gypsum stone. The material is perfectly processed, cut, drilled, and glued. At the same time, in the mass of building stone there are practically no aging and degradation processes, like in plastic or polymer-mineral boards.

Gypsum blocks and plasterboard sheets have become one of the most popular options for wall cladding in residential premises. Firstly, the high porosity of gypsum makes it possible to regulate humidity naturally. Secondly, building gypsum has good sound insulation and low thermal conductivity.

The material is easy to paint and plaster; if necessary, using wax mastic, the walls can be made moisture-proof to water and condensation, but relatively transparent to water vapor.

Preparing the mixture

The process of preparing a gypsum solution begins with sifting the dry mixture through a sieve, it is best to use DK0355, this is approximately 400 holes per square centimeter. Next, the required amount of water is heated to 40 o C and poured into the mixer container. Gypsum is added in small portions to the water, and then a thin film formed on the water surface is immediately broken with a trowel.

In theory, the strength of a cast gypsum block depends on the consistency of the mix. The thicker the solution, the smaller the size of the pores and anhydride crystals. When there is an excess of water, the crystals quickly increase in size, which leads to intense pore formation.

Material storage

The only one reliable way To properly store dry gypsum material, use glass jars with a sealed lid. Dry calcined gypsum can be used to drain containers or floors, but to restore its original qualities, the material must be deoxidized with an aqueous solution of sulfuric acid, remove water by calcination and re-grind into dust to a grain size of 0.01-0.003 mm. Industrial polyethylene packaging provides reliable storage of the dry mixture only for the first two months. Dry plasters based on gypsum material in paper bags after opening must be used within 3 days.

Plaster substitute

The only material that can replace building gypsum is considered to be alabaster, both in its pure form and with the addition of lime or polymer emulsions. Dry lime in an amount of up to 1% must be added at the stage of preparing the building mixture for mixing. The material is intensively ground on a metal or stone surface to make the batch as homogeneous as possible. If it is necessary to prepare a casting mold, then white clay and flake graphite can be added to alabaster at the rate of 2% and 1%, respectively.

What is the difference between plaster and alabaster?

Both materials are a product of calcination of natural sulfuric anhydride, but due to large quantity impurities of iron oxide and aluminum oxide, the alabaster material is obtained with a slight reddish tint. Unlike gypsum, alabaster sets in 3-5 minutes, so any castings made from alabaster stone have high surface hardness. Alabaster takes mechanical loads worse and gives a high degree of expansion followed by shrinkage.

Properties of gypsum

Gypsum(hydrous calcium sulfate) is the most common mineral belonging to the sulfate group. Its name comes from the Greek word gypsos. Plaster can be scratched with a fingernail and can be easily cut with a knife. Several are known varieties of gypsum, used as collection stones, in particular fine-grained alabaster. Silky spar, fiber gypsum And white plaster They have a silky sheen and are often cut into cabochons and polished to produce a cat's eye effect.

Soft selenite, which is colorless and transparent, is also sometimes cut. Beautiful desert roses, twin dovetail crystals and star shapes are popular among collectors.

Application of gypsum

Gypsum is used in the production of plaster, fertilizers, Portland cement, paper, paints and pencils. It is the most common evaporite - the sediment remaining after water evaporates. Gypsum occurs as massive deposits in sedimentary rocks along with limestones and shale. It is formed by the hydration of the mineral anhydrite.

Gypsum is accompanied by calcite, sulfur, quartz, dolomite, halite and clay. Sometimes gypsum is deposited as a result of the evaporation of salt water or forms soft translucent crystals in place of dry lakes. It also occurs as crystals in clay, as the lining of salt domes, and in volcanic areas. Alabaster, both dense and fine-grained, is used to create statues and moldings.

However, due to the extreme softness of alabaster, products made from it are easily broken and quickly destroyed. As a rule, alabaster is translucent and colored white, pinkish or brownish. Basic gypsum deposits and alabaster are found in Italy and England. Pink alabaster is mined in Wales.

Origin of gypsum

There are deposits of alabaster in Spain, Iran and Pakistan. “Alabaster,” which was supposedly used to make vases, tombstones, etc. in Ancient Egypt and Ancient Rome, is actually marble (calcium carbonate). There are rich deposits of gypsum in the USA (Arizona, California, Utah, Colorado, Oklahoma, New Mexico, Ohio, Michigan, Virginia and New York), Canada and France.

A mineral derived from calcium is its hydrous sulfate, which is called gypsum. It has many synonymous names: Montmartite, desert rose, gypsum spar(crystalline and leaf forms). The fibrous structure is selenite, the granular one is alabaster. We will talk about the varieties and properties of this stone, its prevalence throughout the country and its use in construction, medicine and other areas of the economy.

Historical background

As a result of the evaporation of the seas that occurred 20–30 million years ago, gypsum was formed - a mineral that ancient civilizations began to use. Stone is still in great demand today, despite the emergence of many modern materials.

This happened almost 10 thousand years ago. Evidence that in ancient Egypt The Assyrian, Greek and Roman states that used gypsum are:

In England and France, starting from the 16th century, wooden buildings began to be covered with plaster, protecting them from fires. The year 1700 is considered the beginning of the use of the mineral as a fertilizer. To create architectural forms in Russia in the 17th-18th centuries. gypsum decor was widely used, and in 1855 the Russian surgeon N.I.

During the Crimean War, Pirogov invented and began to use a plaster cast fixing the limbs to treat the wounded. This saved many soldiers from losing an arm or a leg.

Description of the mineral

A mineral from the sulfate class arising from sedimentary rocks is called gypsum. Its chemical formula looks like this: CaSO4 2H2O. In appearance, a non-metallic luster is noted: silky, pearlescent, glassy or matte. The stone is colorless or colored in white, pink, gray, yellowish, blue and red shades. Description of other indicators:

• density 2.2–2.4 t/m3;
• Mohs hardness 2.0;
• cleavage is perfect, thin plates are easily separated from the crystals of the layered structure;
• the line drawn on the stone is white.

This is what gypsum consists of: calcium oxide CaO - 33%, water H2O - 21%, sulfur trioxide SO 3 - 46%. There are usually no impurities.

If we consider the stone as a rock, then the composition contains calcite, dolomite, iron hydroxides, anhydrite, sulfur and gypsum itself. The origin is sedimentary; according to the conditions of creation, primary forms are distinguished, which were formed by chemical precipitation in salty reservoirs, or secondary derivatives - they arose as a result of the hydration of anhydrite. It can accumulate in zones of native sulfur and sulfides: gypsum hats contaminated with impurities are formed from wind erosion.

The quality of raw materials for the production of gypsum depends on the content of dihydrate calcium sulfate CaSO4 2H2O - it varies in the range of 70–90%. The final form for use is mineral powder; it is obtained by grinding gypsum stone burned in rotary kilns.

Properties and Application

In nature, the physical features of the structure consist of a variety of forms: dense and granular, earthy, leafy and fibrous, nodules and dusty masses. In voids they are found in the form of drusen crystals. The solubility of gypsum in water increases with temperature to 37–38ºС, then decreases, and upon reaching 107ºС the mineral passes into the state of CaSO4·½H2O hemihydrate. By adding a small amount of sulfuric acid to water, solubility improves. l reacts weakly to NS.

In ready-made building mixtures, the properties of gypsum are transferred to the powder itself. Products acquire the qualities of a basic substance with the following characteristics:

• bulk density 850–1150 kg/m3, smaller values for finer grinding;
• fire resistance is high: alabaster has a melting point of 1450ºC;
• setting - start after 4-7 minutes, end after half an hour, to slow down hardening add animal glue, soluble in water;
• the compressive strength of ordinary samples is 4–6 MPa, high-strength 15–40.

Poor thermal conductivity - at the brick level (about 0.14 W/(m deg)) allows the use of gypsum-based products in fire-hazardous structures. The first examples of the use of stone in this capacity were found in Syria - they are more than 9 thousand years old.

Natural views

Geologists have identified several dozen varieties of gypsum, but there are three main ones. These include:

Few people know about other varieties: gypsum spar (coarse-crystalline and sheet), intestinal or snake stone, gray in color with white, worm-like curved veins. Another little-known form is earthen gypsum.

Varieties for practical use

The use of aqueous calcium sulfate together with other binders allows for significant savings on more expensive materials. Alabaster that has passed the processing stage is divided into the following classes:

There are other varieties, but in practice they use a limited list. An analogue is fine grayish-white dust - alabaster powder, which is obtained from gypsum by heat treatment.

Other uses

In its raw form, stone is used as an additive in the production of Portland cement, sculptures and crafts. List of additional directions:

Non-traditional direction - magic. It is believed that gypsum attracts prosperity and good luck, and suggests a person’s actions in a difficult situation. Astrologers recommend amulets made from this mineral to people born under the signs of Leo, Aries and Capricorn.

Stone deposits

The distribution of gypsum in the earth's crust is observed everywhere, mainly in layers of sedimentary rocks with a thickness of 20–30 m. World production is about 110 million tons of stone per year. The largest producers are Türkiye, Canada, USA, Spain and Iran. One of the unique ones is the thermal caves of Naica Mine in Mexico, where druses of giant gypsum crystals 11 m long were found.

Numerous deposits of the Upper Jurassic period are located on the territory of neighboring countries: North Caucasus, Central Asian republics. There are 86 industrial deposits in Russia, but 90% of production comes from 19 fields, of which 9 largest can be distinguished: Baskunchakskoye, Bolokhovskoye, Lazinskoye, Novomoskovskoye, Obolenskoye, Pavlovskoye, Pletnevskoye, Poretskoye, Skuratovskoye. Their share in production is 75% of the all-Russian total. Most deposits are represented by a mixture of gypsum and anhydrite in a ratio of 9:1. In Russia, 6 million tons are mined annually, which is 5.5% of the world volume.

Gypsum is a mineral from the sulfate group: hydrated calcium sulfate. Also the rock of the same name, consisting mainly of this mineral. The name of the mineral has Greek roots and was used to refer to fired gypsum products. Chemical formula: CaSO 4 2H 2 O.

The luster is glassy, ​​pearlescent, silky or matte. Hardness 1.5-2. Specific gravity 2.2-2.4 g/cm3. Colorless, white, grayish, yellowish, pink, red, blue. The line is white. The cleavage of leafy varieties is very perfect. Solid granular, dense, earthy, leafy, fibrous, also individual crystals, dovetail-like doubles, drusen (resemble the surface of a brain or a rose in appearance). Monoclinic system. The crystals are ingrown. The leaves are flexible, but not elastic.

Distinctive features . It has a non-metallic luster, slight hardness (gypsum is soft), a white line, low density, and not greasy to the touch. May be confused with anhydrite. Differs in hardness. Anhydrite has medium hardness.

Chemical properties. When heated to 107⁰С, it turns into CaSO 4 1/2 H 2 O, which, when wetted with water, hardens (“sets”). Dissolves in hydrochloric acid.

Varieties:

1. WITHElenite– parallel-needle-shaped. The shine is silky.
2. Maryino glass– thick-sheet transparent plaster.
3. Alabaster– fine-grained, variously colored gypsum.

Gypsum desert rose Selenite Maryino glass Alabaster

Origin

Gypsum is formed on the surface of the Earth (representing lagoonal and lacustrine chemical sediment) or by hydration of anhydrite of sedimentary origin under the influence of cold groundwater (vadose water).

Satellites. In sedimentary rocks: rock salt, anhydrite, sulfur, calcite.

Application of gypsum

Gypsum is used in architecture and sculpture, in the paper industry, in medicine, as a fertilizer in agriculture, in the production of sulfuric acid, cement, enamels, glazes and paints. Maryino glass is used in the optical industry. Due to its excellent sound insulation and ability to quickly set, alabaster is often used in construction during finishing work.

Selenite is an ornamental stone. Selenite and gypsum are used to make decorative tabletop sculptures of small forms (figurines, boxes, vases, etc.). Construction parts are made from gypsum: cornices, slabs, blocks, bas-reliefs.

Sulfur is obtained from gypsum and anhydrite: when heated, CaSO 4 transforms into calcium sulfide CaS, which upon contact with water forms hydrogen sulfide. When H 2 S is burned with a small amount of oxygen, sulfur and water are formed.

Deposits

Gypsum deposits are located on the western slope of the Urals, in the Volga region, Donbass (Artemovskoye), Prikamye, Fergana (Shorsu), near Murom on the river. Oka, in Tula, Ryazan, Kaluga, Arkhangelsk, Nizhny Novgorod regions, in Crimea, Karelia and Tatarstan. Selenite deposits are located near the Kungur Ice Cave. Widely distributed in other countries: USA, Iran, Canada, Spain.