Construction gypsum get from gypsum stone. This is a soft plastic mineral belonging to the sulfate class. It has a fibrous or granular structure with a density of up to 2320 kg/m³, formed from destroyed rocks and their chemical precipitation after the evaporation of the ancient ocean. Building gypsum is obtained from a fibrous variety of gypsum stone and is called selenite, and from a granular mineral it is obtained.
Plaster stucco
Properties of gypsum
The most valuable property of gypsum is its astringent properties. Gypsum is obtained by firing gypsum stone and then grinding it. Gypsum is divided into fractions:I - coarse fraction.
II - medium grinding fraction.
III - fine grinding fraction.
Depending on the impurities of the original mineral, building gypsum differs in setting time:
A - gypsum sets in 2-15 minutes - quickly.
B - plaster sets in 6-30 minutes - normal.
B - plaster sets in 30 minutes or more - slowly.
When casting molded figures, gypsum penetrates into all details of the form, and when hardening it expands and heats up slightly. Within two hours after the gypsum dries, its strength doubles.
Gypsum has the following disadvantages: you need to work with it quickly and carefully. Its shelf life is not long; after just three months of storage, it loses about half of its qualities. Plaster products must be handled with care; they are fragile, easy to scratch, and not waterproof.
Strength and marking of gypsum
To determine the strength of gypsum, 12 grades are used, which are designated by the letter G and numbers indicating the compressive strength of gypsum at 1 MPa or 10 kg/cm2: -2, -3, -4, -5, -6, -7, -10 , -13, -16, -19, -22, -25. The strength of G-19 is 19 MPa.Depending on the brand, it is used for various purposes. Elements of gypsum decor - stucco molding is made from gypsum, starting from M-7 and above. For construction needs, gypsum is used to produce various products: plasterboard, gypsum boards for partitions.
Gypsum is one of the most common minerals in the world. It is extracted from the bowels of the earth everywhere and is widely used in industry, the construction industry, and medicine. In our article you will find detailed description and a photo of the mineral gypsum. In addition, you will learn about the main areas of its application.
Mineral gypsum: description and chemical composition
The rock, as well as the corresponding building material, came from Greek word gypsos ("chalk"). Humanity has known about gypsum since ancient times. He has not lost his popularity even today.
Gypsum is a soft mineral. By the way, it is the reference for the Mohs scale of relative hardness, adopted at the beginning of the 19th century (hardness - 1.5-2.0).
By chemical composition The mineral gypsum is aqueous calcium sulfate. Its structure includes elements such as calcium (Ca), sulfur (S) and oxygen (O). Let us describe the chemical composition of gypsum in more detail:
- sulfur trioxide, SO 3 - 46%;
- calcium oxide, CaO - 33%;
- water, H 2 O - 21%.
Genetic classification: monoclinic system. This mineral is distinguished by a layered crystalline structure and very perfect cleavage (individual thin “petals” can be easily split off from it).
Mineral gypsum: properties and distinctive features
Here are the main ones physical characteristics gypsum, by which it can be distinguished from other minerals:
- the fracture is uneven but flexible;
- gloss: from glassy to silky or matte;
- hardness: low (easily scratched with a fingernail);
- the mineral dissolves slowly in water;
- not greasy to the touch;
- leaves behind a clearly visible white line;
- color: white to gray (sometimes may be pink).
Gypsum does not react with acids, but is soluble in hydrogen chloride (HCl). It can have different transparency, although the transparent mineral gypsum is more common in nature. When heated above 107 degrees Celsius, gypsum turns into alabaster, which, in turn, hardens when wetted with water.
Gypsum is often confused with anhydrite. These two minerals can be distinguished from each other by their hardness (the second is much harder than the first).
Genesis of the mineral and its distribution in nature
Gypsum is a typical mineral of sedimentary origin. Most often it is formed from natural aqueous solutions(for example, at the bottom of drying seas and reservoirs). The mineral gypsum can also accumulate in weathering zones of native sulfur and sulfides. In this case, so-called gypsum hats are formed - loose or compacted rock masses contaminated with numerous impurities.
The gypsum is often found accompanied by sand, rock salt, anhydrite, sulfur, limestone and iron. The proximity to the latter, as a rule, gives it a brownish tint.
In nature, gypsum occurs in the form of elongated and prismatic crystals. It also often forms dense scaly, fibrous, or “tablet-like” aggregates. Often gypsum is presented in the form of so-called roses or swallowtails.
Main varieties of mineral
Geologists identify several dozen varieties of gypsum. The mineral can be fibrous, satiny, dense, foamy, fine-grained, boney, cubic, etc.
The main types of gypsum include:
- selenite;
- alabaster;
- "Maryino glass"
Selenite is a translucent mineral with a silky sheen. The name comes from the Greek word selena - "moon". This mineral actually has a slightly bluish tint. Selenite is used as an ornamental stone in the manufacture of budget jewelry.
Alabaster is a soft, easily destructible white material, a product of gypsum dehydration. Widely used in the production of garden sculptures, vases, table tops, stucco moldings and other interior items.
“Maryino glass” (girl’s or lady’s ice) is another type of gypsum, a transparent mineral with a pearlescent or colored tint. Features a unique structure crystal lattice. In the old days, “Maryino glass” was widely used in the design of icons and holy images.
Main deposits of gypsum
The mineral gypsum is common in earth's crust everywhere. Its deposits are found in sediments of almost all periods of the geological history of the planet - from the Cambrian to the Quaternary. Deposits of gypsum (as well as its accompanying anhydrite) in sedimentary rocks have the shape of lenses or layers with a thickness of 20-30 meters.
Every year, over 100 million tons of gypsum are extracted from the bowels of the earth. The world's largest producers of valuable building materials are the USA, Iran, Canada, Türkiye and Spain.
In Russia, the main deposits of this rock are concentrated on the western slopes of the Ural Mountains, in the Volga and Kama regions, Tatarstan and Krasnodar region. The main gypsum deposits in the country are Pavlovskoye, Novomoskovskoye, Skuratovskoye, Baskunchakskoye, Lazinskoye and Bolokhovskoye.
Areas of application of gypsum
The scope of gypsum is extremely wide: construction, medicine, repair and finishing, agriculture, chemical industry.
Since ancient times, sculptures and sculptures have been carved from this mineral. various items interior - vases, tabletops, balustrades, bas-reliefs, etc. Cornices are often made from it, wall blocks and slabs (so-called drywall). In its “raw” form, gypsum is also used in agriculture as a fertilizer. It is scattered on fields and lands to normalize soil acidity.
Where else is gypsum used? The mineral is widely used in the paper and chemical industries to produce cement, sulfuric acid, paints and glazes. In addition, anyone who has ever broken a leg or arm is familiar with another area of its application - medicine.
Gypsum as a building material
The building material gypsum is obtained from the rock. For this, the rock is fired in special furnaces and then ground into a fine powder. Subsequently, the resulting raw materials are widely used in construction and finishing.
The industrial industry has its own classification of gypsum - technical. So, the following varieties are distinguished:
- high-strength gypsum (used in medicine and dentistry; it is also used to produce various building mixtures and molds for the porcelain and earthenware industry);
- polymer (used exclusively in traumatology for applying fixing bandages for fractures);
- sculptural (the name speaks for itself - this is the main component putty mixtures, various figurines and souvenirs);
- acrylic (lightweight gypsum used for finishing building facades);
- fireproof from which is often produced plasterboard sheets and wall blocks).
In addition, there is a separate marking of gypsum for strength. According to it, 12 grades of gypsum are distinguished - from G2 to G25.
Alabaster is also widely used in construction and finishing works. Compared to gypsum, it is stronger and easier to process. True, without special additives, alabaster is practically unsuitable, since it dries instantly.
It is important to note that even with modern, so high level The development of science and industry has not yet found a worthy replacement for gypsum.
Healing and magical properties of the stone
There is a reason why gypsum is used in medicine. It promotes the fusion of bone tissue, eliminates excessive sweating, and cures spinal tuberculosis. Gypsum is also used in cosmetology - as one of the components of tonic masks.
Since ancient times, this mineral was considered a kind of “cure” for human pride, arrogance and excessive self-confidence. In magic it is believed that plaster is able to tell a person what he needs to do in a given situation. It promises good luck and material well-being. Astrologers advise people born under the signs of Capricorn, Aries and Leo to wear plaster amulets.
“Desert Rose” - what is it?
So beautiful name called a mineral aggregate, one of the varieties of gypsum. It really does look like flower buds. The aggregates consist of crystalline lens-shaped intergrowths-petals characteristic appearance. The color of the “desert rose” can be very diverse. It is determined by the color of the soil or sand in which it was formed.
The mechanism of formation of these “roses” is quite interesting. They are formed in particularly dry climatic conditions. When rain occasionally falls in the desert, the sand instantly absorbs the moisture. Water interacts with gypsum particles, which are washed away along with it. Later, the water evaporates, and the gypsum crystallizes in the sand mass, creating the most unexpected and bizarre shapes.
“Desert Rose” is well known to the nomadic tribes of the African Sahara. Some cultures in this region have a tradition of giving these stone flowers to your loved ones on Valentine's Day.
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, found as massive deposits in sedimentary rocks together with limestones and slates. 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.
Gypsum has been known since ancient times, but has not yet lost its popularity, even many modern materials cannot compete with him. It is used in construction, porcelain, ceramic, oil industry and in medicine.
Description of building material
Gypsum is produced from gypsum stone. To obtain gypsum powder, the stone is fired in rotary kilns and then ground to form a powder. Gypsum is most common in construction.
Walls, plastered gypsum mortar, capable of absorbing excess moisture and give it away when the air is too dry.
Gypsum formula
The name gypsum comes from the Greek word gipsos. This material belongs to the class of sulfates. His chemical formula CaSO4?2H2O.
There are two types of gypsum:
- Fibrous - selenite;
- Grainy - alabaster.
Photos of gypsum varieties
Selenite Alabaster
Technical characteristics and properties
Everyone has gypsum mixtures technical specifications have great similarities, let’s focus on the properties and features building gypsum.
These include:
- Density. Gypsum has a dense, fine-grained structure. The true density is 2.60-2.76 g/cm?. When loosely poured, it has a density of 850-1150 kg/m2, and when compacted, the density is 1245-1455 kg/m2.
- How long does it take to dry? The advantages of gypsum include rapid setting and hardening. The gypsum sets in the fourth minute after mixing the solution, and after half an hour it completely hardens. Therefore, the finished gypsum solution must be used immediately. To slow down the setting, water-soluble animal glue is added to the plaster.
- Specific gravity. Is the specific gravity of gypsum measured in kg/m? in the MKGSS system. Since the ratio of mass is equal to the volume it occupies, the specific, volumetric and bulk weight of gypsum is approximately the same.
- What temperature can it withstand? t melting). Gypsum can be heated to 600-700°C without destruction. The fire resistance of gypsum products is high. Their destruction occurs only six to eight hours after exposure to high temperature.
- Strength. Construction gypsum has a compressive strength of 4-6 MPa, high-strength - from 15 to 40 MPa or more. Well-dried samples have two to three times higher strength.
- GOST State standard of gypsum 125-79 (ST SEV 826-77).
- Thermal conductivity. Gypsum is a poor conductor of heat. Its thermal conductivity is 0.259 kcal/m deg/hour in the range from 15 to 45°C.
- Solubility in water. R dissolves in small quantities: 2.256 g dissolves in 1 liter of water at 0°, 2.534 g at 15°, 2.684 g at 35°; with further heating, the solubility decreases again.
The video talks about building gypsum and how you can improve its properties by giving additional strength:
Types of gypsum
Gypsum has the greatest variety of uses among other binding materials. It allows you to save on other materials. There are many varieties of gypsum.
Building
It is used for the production of gypsum parts, partition boards for plastering works. Work with gypsum mortar must be carried out very quickly short time– from 8 to 25 minutes, it depends on the type of plaster. During this time it must be completely used up. When hardening begins, gypsum already gains about 40% of its final strength.
Since cracks do not form on the gypsum during hardening, when mixing the solution with lime mortar, which gives it plasticity, you don’t have to add various fillers. Due to short terms setting retarders are added to gypsum. Construction gypsum reduces labor intensity and construction costs.
In deposits by blasting gypsum-containing rock. The ore is then transported to factories in the form of gypsum stones.
High strength
The chemical composition of high-strength gypsum is similar to building gypsum. But building gypsum has smaller crystals, while high-strength gypsum has large crystals, so it has less porosity and very high strength.
High-strength gypsum is produced by heat treatment in a sealed apparatus into which gypsum stone is placed.
The scope of application of high-strength gypsum is extensive. Various building mixtures are prepared from it and fireproof partitions are built. It is also made from various shapes for the production of porcelain and earthenware sanitary products. High-strength gypsum is used in traumatology and dentistry.
Polymeric
Orthopedic traumatologists are more familiar with synthetic polymer plaster; plaster bandages are produced on its basis for applying bandages for fractures.
Advantages of polymer plaster casts:
- three times lighter than conventional plaster;
- easy to apply;
- allow the skin to breathe, as they have good permeability;
- resistant to moisture;
- allow you to control bone fusion, as they are permeable to x-rays.
Cellacast
Bandages are also made from this plaster; their structure allows the bandage to be stretched in all directions, so very complex bandages can be made from it. Cellacast has all the properties of a polymer bandage.
Sculpted or molded
This is the most highly durable gypsum, it does not contain any impurities, it has high natural whiteness. It is used for making molds for sculptures, plaster figurines, sculpting souvenirs, in the porcelain and earthenware, aviation and automotive industries.
This is the main component of dry putty mixtures. Molding gypsum is obtained from building gypsum; for this, it is additionally sifted and ground.
Known for several centuries, it still remains relevant in our time. The most common rosettes are gypsum, they are easy to make with your own hands.
Acrylic
Acrylic plaster is made from water-soluble acrylic resin. After hardening, it looks similar to regular plaster, but is much lighter. Ceiling stucco and other decorative details are made from it.
Acrylic gypsum is frost-resistant and has little moisture absorption, so it can be used to decorate building facades, creating interesting design solutions.
Working with acrylic plaster is very simple. If you add a little marble chips or aluminum powder or other inert fillers to the solution, acrylic plaster products will closely resemble marble or metal ones.
This is what acrylic plaster looks like
Polyurethane
Gypsum stucco can also be made from polyurethane or polystyrene gypsum. It costs much less than ordinary gypsum, and its qualities are almost no different from it.
White
By using white plaster seal seams, cracks, make stucco molding and carry out other types of construction and repair work. It is compatible with various types building materials. White gypsum hardening time 10 minutes.
Fine grain
Fine-grained gypsum is also called translucent. It is used to fill seams, joints in slabs, etc.
Liquid
Liquid gypsum is prepared from gypsum powder.
It is prepared using the following technology:
- Pour water in the required quantity.
- Pour in gypsum and mix immediately.
- The density of the solution can be varied. A liquid solution is made to fill the molds
Waterproof (moisture resistant)
Waterproof gypsum is obtained by processing raw materials according to special technology. To improve the properties of gypsum, stillage, a waste product from the production of ethyl alcohol, is added to it.
Refractory
Gypsum is a non-flammable material and is not flammable, but plasterboard sheets made from it are quite flammable. To give them fire resistance, tongue-and-groove gypsum is used. It is used wherever it is required to increase fire resistance.
Architectural
Architectural gypsum does not contain toxic components, it is very plastic. Its acidity is similar to that of human skin. Classic modeling from architectural plaster is very popular among designers; there is a very high demand for it.
It requires certain knowledge, so you should first carefully study the features of such work, and only then proceed to practice.
Stamps
Plaster marking is carried out after testing standard samples of sticks for bending and compression two hours after they are molded. According to GOST 129-79, twelve grades of gypsum are established, with strength indicators from G2 to G25.
Plaster substitute
An analogue of gypsum is a finely dispersed grayish-white powder - alabaster. It is also popular in construction. Alabaster is obtained from natural gypsum dihydrate by heat treatment at temperatures from 150 to 180? C. Externally, alabaster and gypsum are no different from each other.
Alabaster is used to plaster walls and ceilings at low indoor humidity. Gypsum panels are produced from it.
What is the difference between plaster and alabaster?
Gypsum and alabaster have the following differences:
- Alabaster is more limited in application, as it is used only in the construction industry. Gypsum is also used in medicine.
- Alabaster dries instantly, so it is not suitable without the addition of special substances.
- Gypsum is safer for environment and human health.
- Alabaster has greater hardness than gypsum.
Composition, properties, application different varieties gypsum
One of the most used materials is gypsum. It is used at almost all stages of the manufacture of dentures and devices. The vast majority of working and auxiliary models are prepared from plaster - a positive reflection of the tissues of the prosthetic bed. There are several types of gypsum: construction, molding, high-strength, anhydride, medical. In medicine, hemihydrous gypsum is used, which can be alpha and beta hemihydrate. The last heating for the purpose of dehydration to a temperature of 170 degrees. And keep it for 12 hours. The result is a powder with increased (60-65%) water requirement.
Alpha hemihydrate is formed when heated to 125-130 degrees under a pressure of 1.3 atm in special autoclaves. Such gypsum is called high-strength, autoclaved, super gypsum. When kneading, it absorbs 40-45% of water, due to which it has increased strength.
In case of overheating, complete loss of water may occur and non-setting “dead” plaster may form.
When mixing gypsum, pour into a rubber flask required quantity water and gradually add gypsum at the rate of one part water to two parts gypsum powder. In practice, this ratio is obtained by pouring so much powder into the flask that there is no free water left near its walls. After letting the powder soak up a little water, the mixture is stirred with a spatula until it has a homogeneous consistency. From 4 minutes after mixing, crystallization begins and the formation of dihydrate occurs; In about 7-10 minutes, all the powder combines with water, crystals form, and first the gypsum is partially dissolved, then each molecule eagerly adds one and a half molecules of water. Hardening is accompanied by the release of heat. When solidifying, the crystals are pulled in different directions, the crystalline aggregates coalesce, and a single mass is obtained. Dried gypsum dihydrate is a solid, porous mass. When hardening, gypsum expands up to 1%.
The setting speed of gypsum depends on a number of factors: firing mode, powder dispersion, water temperature, intensity of stirring and additives. Increasing the water temperature from room temperature to 37 degrees accelerates the setting of gypsum; from 37 to 50 degrees it has virtually no effect; above 50 degrees – the speed drops. There are accelerators (catalysts) and retarders (inhibitors) of solidification. A 3-4% solution can be used as accelerators table salt or potassium nitrate, and as moderators - wood glue, 2-3% borax solution (salt boric acid) and 5% solution of sugar or wine alcohol.
The strength of gypsum depends on the ratio of water and powder. How less water(within reasonable limits) the stronger the gypsum.
For particularly durable models, autoclave plaster is used. Sometimes they do combined models, strengthening the most critical areas with supergypsum, and the base of the model is made of ordinary medical plaster.
To obtain fire-resistant models that can withstand temperatures up to 1000 degrees, gypsum is mixed with quartz (river) sand, and if it needs to be heated to 1500 degrees, special refractory masses from kits (sklamil, chrystosil, etc.)