Organic binders and materials based on them. Binders: properties, classification, description, application Division of binders depending on the composition
Lecture 17
Binder materials(or simply binders) are called finely dispersed powdered substances or compositions of substances that form high-polymer solid materials when interacting with liquids. Substances of organic, organoelement and inorganic nature can be used as binders. As a liquid for inorganic binders, water is usually used, sometimes phosphoric acid.
Alabaster. Naturally occurring gypsum CaSO 4 2H 2 O is transferred by partial dehydration at 160 ° C to the so-called burnt gypsum - a mixture of CaSO 4 0.5H 2 O and fine CaSO 4, or alabaster:
2CaSO 4 2H 2 O \u003d CaSO 4 0.5H 2 O + CaSO 4 + 3.5H 2 O
Burnt gypsum hardens rather quickly, turning again into CaSO 4 2H 2 O. Due to this property, gypsum is used to make casting molds and casts from various objects, as well as a binder for plastering walls and ceilings. Gypsum concrete products are also obtained, containing various fillers in addition to gypsum in the material. In surgery for fractures, plaster bandages are used.
Mortar. A mixture of slaked lime with sand and water is called lime mortar and is used to hold bricks together when laying walls. Slaked lime is also used as a plaster. The hardening of lime occurs first due to the evaporation of water, and then as a result of the absorption of carbon dioxide from the air by slaked lime and the formation of calcium carbonate:
Ca (OH) 2 + CO 2 \u003d CaCO3 + H 2 O.
Due to the low content of CO 2 in the air, the hardening process is very slow, and since water is released, buildings built with lime mortar are damp for a long time. When the lime mortar hardens, the process also proceeds:
Ca (OH) 2 + SiO 2 \u003d CaSiO 3 + H 2 0.
Cement. Among the most important materials produced by the silicate industry is cement, which is consumed in large quantities during construction work.
Ordinary cement (silicate cement) is obtained by firing a mixture of clay and limestone. During the firing of the cement mixture, calcium carbonate decomposes into carbon dioxide and calcium oxide; the latter interacts with clay, and calcium silicates and aluminates are obtained.
The cement mixture is usually prepared artificially. But in some places in nature there are calcareous-argillaceous rocks - marls, which in composition just fit the cement mixture.
The chemical composition of cements is usually expressed as a percentage (mass.) of the oxides contained in them, of which the main ones are CaO, Al 2 Oz, SiO 2 and Fe 2 Oz.
When mixing silicate cement with water, a dough-like mass is obtained, after a while a hardening mass. Its transition from a doughy state to a solid state is called "seizure".
The hardening process of cement proceeds in three stages. The first stage consists in the interaction of the surface layers of cement particles with water according to the scheme:
ZCaO SiO 2 + nH 2 O \u003d 2CaO SiO 2 2H 2 O + Ca (OH) 2 + (n - 3) H 2 O.
From the solution contained in the cement test, saturated with calcium hydroxide, the latter is released in an amorphous state and, enveloping the cement grains, turns them into a bound mass. This is the second stage - the setting of the cement. Then the third stage begins - crystallization or hardening. The calcium hydroxide particles coarsen into long needle-like crystals that compact the calcium silicate mass. At the same time, the mechanical strength of the cement increases.
When cement is used as a binder, it is usually mixed with sand and water; this mixture is called cement mortar.
When mixing cement mortar with gravel or crushed stone, concrete is obtained. Concrete is an important building material: vaults, arches, bridges, swimming pools, residential buildings, etc. are built from it. Concrete structures with a base of steel beams or rods are called reinforced concrete.
In addition to silicate cement, other types of cements are produced, in particular, aluminous and acid-resistant.
aluminous cement obtained by fusing a finely ground mixture of bauxite (natural alumina) with limestone. This cement contains a percentage of more alumina than silicate cement. The main compounds that make up its composition are various calcium aluminates. Aluminous cement hardens much faster than silicate cement. In addition, it resists the action of sea water better. Aluminous cement is much more expensive than silicate cement, so it is used in construction only in special cases.
acid resistant cement is a mixture of finely ground quartz sand with an "active" siliceous substance with a highly developed surface. As such a substance, either tripol, subjected to preliminary chemical treatment, or artificially obtained silicon dioxide is used. After adding a solution of sodium silicate to this mixture, a plastic dough is obtained, which turns into a strong mass that resists all acids except hydrogen fluoride.
Acid-resistant cement is used as a binder when lining chemical equipment with acid-resistant tiles. In some cases, they are replaced by more expensive lead.
Magnesia cement. A technical product obtained by mixing magnesium oxide calcined at 800°C with a 30% (wt.) aqueous solution of magnesium chloride is called magnesia cement (Sorel cement). Such a mixture after a while hardens, turning into a dense white, easily polished mass. Solidification can be explained by the fact that the basic salt, initially formed according to the equation
MgO + MgCl 2 + H 2 O \u003d 2MgCl (OH),
then it polymerizes in a chain of the type - Mg - O ----- Mg - O - Mg -, at the ends of which there are chlorine atoms or hydroxyl groups.
Magnesia cement as a binder is used in the manufacture of millstones, grindstones, and various plates. Its mixture with sawdust (xylolite) is used for flooring.
Metal phosphate binders. Binder materials based on oxides of various metals and orthophosphonic acid (or its salts) are widely used. The features of the substances obtained on their basis are increased adhesion to various materials, heat resistance and heat resistance.
For the first time, phosphate binders were used in dental practice (they, like magnesian cement, are called Sorel cement) based on zinc hydrophosphate and zinc hydroxophosphate. This cement is obtained from oxides of zinc, magnesium, silicon and bismuth. The mixture after firing is ground into powder and treated with phosphoric acid. The resulting plastic mass sets in 1-2 minutes.
Solutions of zinc phosphate and aluminophosphate binders with a molar ratio of zinc and aluminum oxides to phosphorus (V) oxide of 1:5 after application to wood create a thin layer (less than 1 mm thick) coating, transfer wood to the category of slow-burning materials.
Production aluminum chromium phosphate binder is reduced to obtaining a mixture of chromium compounds (+3), aluminum hydroxide and phosphoric acid. The resulting viscous transparent green solution corresponds to the composition Al 2 Oz 0.8Cr 2 O 3 3P 2 O 5 . On the basis of phosphate binders, anticorrosive, fire-retardant and decorative coatings and paints, heat-resistant concretes, coatings, adhesives and ceramic refractory, heat-insulating and structural materials have been developed.
Organic binders
bitumen- These are binders, consisting of various hydrocarbons and oxygen organic compounds of nitrogen and sulfur. They are soluble in organic solvents and are divided into natural and petroleum. bitumen- complex organic binders, which are colloidal systems in which oils and resins are the dispersion medium, and the dispersed phase - asphaltenes. Oil fractions of bitumen consist of hydrocarbons with an average molecular weight of 600 amu. In resins, it is about 800 amu. Sulfur, oxygen and nitrogen are part of the active groups OH, NH, SH, COOH. Bitumens contain hydrocarbons of the methane, naphthenic and benzene series and represent over several hundred thousand compounds.
Bitumen properties are evaluated by softening point, hardness and extensibility, which characterize their plasticity and ability to bind mineral materials. Paraffins worsen the properties of bitumen, increasing brittleness at low temperatures. Over time, there is a slow change in the properties of bitumen - their aging. The brittleness and hardness of bitumen increases.
Asphalt- a mixture of bitumen and finely divided mineral materials, which give them strength with temperature changes. Varieties of natural asphalts are mountain resins, asphaltides, asphalt rocks. Mineral substances such as limestones and sandstones predominate in asphalt rocks (up to 70-80%). Asphalt is also obtained artificially by mixing powdered limestone with bitumen, the amount of which ranges from 13 to 60%.
asphaltenes- the most high-molecular substances of natural oil, the mass weight of which ranges from 600-6000 amu. Depending on the chemical composition of the oil, they can be in the form of true or colloidal solutions. Asphaltenes mainly consist of C (80-86%), O (1-9%), N (lj 2%), S (0-9%), the amount of which depends on the composition of the oil. Asphaltenes are considered as condensation products of petroleum resins. These are dark brown powders, easily soluble in benzene, chloroform, carbon disulfide, which is used for separation from oil and oil products.
asphalt solutions prepared from a mixture of petroleum bitumen with finely dispersed mineral additives (limestone, slag, quartz sand, etc.). Their inclusion in bitumen increases the hardness and softening point of the solution. Asphalt mortars are water-tight, weather-resistant, strong enough and are used for pavement coating, waterproofing and corrosion protection.
If coarse aggregate is introduced into the asphalt solution, then we get asphalt concrete, which are then laid hot when covering roads. On the basis of bitumen and latex, rubemast, glass bit, fiberglass, bitumen-polymer elabit are produced, which have high elasticity in the cold with high mechanical strength.
A new rolled waterproofing material foil roofing material is made from aluminum foil, bituminous binder and cardboard. It is used to protect and insulate pipelines at temperatures from -40 to +70 ° C. Bituminous tiles of various colors are also produced, resistant to harsh climatic conditions.
Astringents quite widely used in construction in the process of preparing concretes and mortars of various compositions, for the manufacture of building structures and products.
Astringents are usually divided into two groups:
1. Organic group.
2. Inorganic group.
Inorganic binders are characterized by the following features:
1. Hydrophilicity.
2. The ability, when mixed with water, to form an easily shaped pasty plastic mass.
3. The ability to pass into a solid state from a pasty (plastic) state.
Inorganic binders
Inorganic binders include air, hydraulic and autoclaved binders.
Mineral binders widely used in construction are divided into three main groups depending on their main properties of hardening and long-term resistance to various climatic factors:
1. Air binders.
2. Hydraulic binders.
3. Acid-resistant binders.
Air binders
Air binders are able, when interacting with water, to harden and gradually turn into a stone-like solid body, capable of maintaining its strength in the air for a long time. If you systematically moisten products and building structures made on the basis of air binders, they quickly lose their strength and collapse. Air binders include magnesia and gypsum binders, air lime and clay.
According to the chemical composition, air air binders are divided into four groups:
◊ Lime binders, consisting mainly of calcium oxide CaO;
◊ Magnesia binders containing caustic magnesite MgO;
◊ Gypsum binders based on calcium sulfate;
◊ Liquid glass - sodium or potassium silicate (in the form of an aqueous solution).
Hydraulic binders
Hydraulic binders harden and retain strength for a long time (or even increase it) not only in air but also in water. According to their chemical composition, hydraulic binders are a complex system consisting mainly of compounds of four oxides: CaO-SiO2-Al2O3-Fe2O3 .
These compounds form three main groups of hydraulic binders:
〉 Silicate cements consisting predominantly (75%) of calcium silicates. These include its varieties, the main binders of modern construction.
〈 Aluminate cements, the binder base of which is calcium aluminates, the main of which is aluminous cement and its varieties.
3. Building gypsum (GOST 125-79).
Gypsum is sold in bags and comes in many brands. From brand g-25 to brand g-5, which means compressive strength. The larger the brand, the greater the strength, for example, gypsum marked g-25 can withstand compressive strength up to 25 kgf / cm. Its disadvantage is that it has a high water absorption while actively losing strength.
Various curly shapes are cast from gypsum to decorate the interiors of houses. It is also used for the manufacture of various blocks and slabs used in the laying of partitions and ventilation shafts. It is stored in bags or in bulk in dry rooms. Gypsum cannot be stored for a long time, because it loses its strength and becomes unusable. A feature of gypsum is its ability to quickly set.
Hydraulic binders
♣ Organic binders
These include various bitumen and tar dark brown and black. Used for waterproofing works. organic binders are waterproof, water-resistant, elastic and weather-resistant. When heated, binders are able to soften (thinn) and when cooled, they become more viscous and even hard.
First of all, this group can be divided into natural bitumen and bitumen products of oil refining. According to the chemical composition, bitumens are high-molecular compounds of hydrogen, oxygen, nitrogen and sulfur. Natural bitumen can be formed in natural conditions as a result of the separation of light and medium fractions (parts) from oil.
But for the needs of construction, mainly solid, semi-solid and liquid petroleum bitumen (BN) are used, which are divided into road, construction and roofing.
1. Oil construction bitumen is used for various types of construction work and is produced in the following grades:
BN-50/50, BN-70/30, BN-90/10. The first number indicates the softening temperature and the second indicates the penetration of the needle into the bitumen.
2. Oil roofing bitumens are used as impregnating compositions for the manufacture of roofing material and various coating mastics. Widely used mainly for the production of roofing. three grades are produced: BNK-90/180 impregnating, BNK-90/40 and BNK-90/30 coverslips.
Impregnating bitumens have a softening point of 40-50°C, while coating bitumen has a softening point of 85-90°C.
Bitumen grades BN-50/50, BN-70/30, BN-90/10 correspond to bitumen of previously produced grades BN-III, BN-IV, BN-V. Guaranteed shelf life of roofing oil bitumen is one year from the date of manufacture.
2. Coal tar pitch is a black solid and viscous substance. It is a product of the distillation of coal tar and has a different melting point:
soft-45-50°C, medium-65-75°C, and hard-75-90°C. It is believed that the more anthracene oil in pitch, the softer it is, and vice versa, the less it is, the harder it is. In construction, pitch is used in a mixture with heavy oil for roofing impregnation, for the preparation of tar mastics and for other purposes. When working with pitch, be careful, because if it gets on the skin, its smallest particles cause burns. The best time to work with pitch is twilight or cloudy weather.
3. Coal tar (coal tar) is a black oily liquid with a pungent odor. Coal tar is obtained at coking plants as a by-product of coal coking. They are widely used in road construction and for the preparation of simple roofing mastics.
***** WE RECOMMEND reposting the article on social networks!TECHNOLOGIES OF PRODUCTION AND APPLICATION OF BINDING MATERIALS.
Building binders are powdered materials that, when mixed with water, form a plastic, workable mass, which eventually hardens into a strong stone-like body. This definition refers to inorganic binders, which are discussed in this book, and not to organic binders (bitumens, tars, adhesives and similar materials).
Astringents, depending on the composition, basic properties and scope, are divided into groups.
The most extensive group of hydraulic binders, which, after mixing with water, are capable of hardening both in air and in water. After preliminary hardening in air, they continue to harden in water, maintaining and increasing their strength for a long time. Hydraulic binders can be used in aboveground, underground and hydraulic structures exposed to water.
The group of hydraulic binders includes cement, aluminous cement, pozzolanic cements, slag cements, cements with fillers, expanding cements, hydraulic lime, romancement. A number of varieties of these binders are known. So, depending on the composition, cements are distinguished: ordinary, alite, belite, aluminoferritic, ferritic, magnesian. In accordance with special properties, such types of cements are distinguished as fast-hardening, especially fast-hardening, plasticized, hydrophobic, sulfate-resistant, with moderate exotherm, white and colored, plugging, road, for asbestos-cement products, magnesian. Varieties of aluminous cement are anhydrite-aluminous and gypsum-aluminous cements.
Construction air lime.
One of the main components of some finishing materials are the so-called binders, which are generally divided into two large groups: aqueous and non-aqueous. The first group, in turn, is divided into mineral and organic.
Minerals include cement, lime and liquid glass.
Organic adhesives include a variety of adhesives of plant, animal and synthetic origin.
Cement
It gives concrete high strength. Thanks to him, the concrete sets quickly and is less in the formwork. As a rule, cement is made from substances such as alumina or calcium silicate, which are carefully ground, fired to sinter.
As a result of firing, cement clinker is obtained, which is well ground. The quality of cement depends on the fineness of grinding and the composition of raw materials.
Cement is used for the preparation of mortars, concrete mixtures, for the manufacture of concrete and reinforced concrete products. Cements are subdivided according to composition, hardening strength, hardening speed, etc.
Cement has the ability to set well not only in air, but also in water, so it must be stored in a dry place.
In construction, Portland cement (silicate cement), Portland slag cement (Portland cement with slag added to it) and alumina cement, which is obtained from alumina and lime fused at a temperature of 1400 ° C, are most often used.
The resulting mass is crushed into pieces, which, in turn, are ground into powder in tube mills. Grade strength (aluminous cement produced grades 400, 500, 600) cement gains after 3 days.
Portland cement is a gray-green powder. It is obtained by firing clay and chalk at a temperature of 1500 ° C. After that, cement clinker (this is the name of the resulting mass) is ground in special mills, while adding various active and inactive (inert) additives to it: slag, gypsum, quartz sand.
If the cement is dissolved with water, then after a short time it hardens, turning into a solid substance like a stone. Portland cement is produced in grades 400, 500, 600 and 700.
Compared to binders such as clay and lime, cement sets much faster.
Setting occurs already after 35-40 minutes, and the final setting - no later than 12 hours, depending on the brand of cement. You can speed up the hardening process by adding warm water to the cement.
Conversely, the use of cold water delays the setting of the diluted cement for some time.
The brand of cement depends on the fineness of grinding. In the event that the brand of cement is unknown or there are some doubts, it can be roughly determined by the density of the cement. It decreases during long-term storage: for 6 months - by 25%, for 1 year - by 40%, for 2 years - by 50%.
Portland cement
This is a hydraulic binder, a product of fine grinding of clinker with the addition of gypsum (from 3 to 5%), which regulates the setting time of cement. According to the composition, Portland cement is distinguished without additives, with mineral additives, Portland slag cement, etc.
The beginning of the setting of Portland cement at a water temperature in the solution of 20 ° C should occur no earlier than 45 minutes from the moment the solution was prepared and end no later than 10 hours later.
If water at temperatures above 40 °C is used in the preparation of the mortar, setting may occur too quickly.
The strength of Portland cement is characterized by grades 400, 500, 550 and 600. In order to bring Russian standards closer to European ones, cement is divided into classes: 22.5; 32.5; 42.5; 55.5 MPa.
Fast setting Portland cement
This is Portland cement with mineral additives, which is characterized by increased strength. It reaches more than half of the planned strength after 3 days of curing.
Fast-hardening cement is produced in grades 400 and 500.
Extra fast hardening high-strength Portland cement
They are used in the production of prefabricated reinforced concrete structures and during winter concrete work. 600 stamps are produced.
white portland cement
They produce two types - white Portland cement and white Portland cement with mineral additives. According to the degree of whiteness, white cements are divided into 3 grades (in descending order). The beginning of the setting of white Portland cement should occur no earlier than 45 minutes, the end - no later than 12 hours after the preparation of the solution.
colored portland cement
It comes in red, yellow, green, blue, brown and black. It is used for the manufacture of colored concretes and mortars, finishing mixtures and cement paints.
They produce grades 300, 400 and 500.
Slag Portland cement
It consists of blast-furnace slag and natural gypsum, added to regulate the setting time of the solution.
Available in 300, 400 and 500 grades.
Fast-hardening slag Portland cement
Differs in the increased durability in 3 days of hardening.
Issue 400 stamps.
Gypsum alumina cement
It is obtained by mixing high alumina slags and natural gypsum. The beginning of the setting of gypsum-aluminous cement should occur no earlier than 10 minutes, the end - no later than 4 hours after the preparation of the solution.
Lime
This material is mainly used when working with stone and for the preparation of a plaster mixture. There are three types of lime: hydraulic, high-hydraulic, air. They differ in the way they harden. Airborne lime hardens in air. Its main drawback is non-water resistance.
Hydraulic is able to harden in air and in water, its hardening process is faster than that of air, and its strength is much higher. High-hydraulic lime is characterized by high strength and hardening speed.
When buying lime, you need to pay attention to the presence of instructions for the preparation and storage of the solution.
Lime is quenched by treating quicklime with water. Depending on the amount of water needed for quenching, hydrated lime (fluff), lime paste and lime milk are obtained.
Powder hydrated lime is obtained if the volume of water is 60-70%. As a result of quenching, the volume of lime increases by 2-3 times. Hydrated lime is a white powder consisting of the smallest particles of calcium oxide hydrate with a density of 400 kg/m3 (in a loose state) to 500-700 kg/m3 (in a compacted state).
To obtain lime dough, when quenching water, they take 3-4 times more than lime. The volume of the resulting dough is 2-3 times higher than the volume of lime taken for its preparation.
Lime dough is a white plastic mass with a density of up to 1400 kg/m3.
Lime that has been quenched well, having increased in volume by at least 3 times, is called fatty lime, which has increased in volume by less than 2.5 times - lean.
According to the ability to harden, it is divided into hydraulic and air. In the first case, lime hardens both in water and in air, and in the second, as the name implies, only in air.
Lime is produced by burning limestone in shaft kilns. After roasting, quicklime is obtained - boiled lime, or lump lime. To extinguish lime, it is poured with water at the rate of 35 liters of water per 10 kg of lime. In the process of quenching, lime begins to “boil”, crumbling into small pieces, after which it noticeably increases in volume. According to the quenching time, quick-extinguishing (about 8 minutes), medium-extinguishing (about 25 minutes) and slow-extinguishing (more than 30 minutes) lime are distinguished.
Hydrated lime is called fluff. In order for all lime particles to be extinguished, it must be kept for about 2-3 weeks under a closed lid.
After the specified period, a finely dispersed mass remains with a water content of not more than 50%.
Air lime is quicklime and slaked (hydrated). Lime without additives is divided into 3 grades (1st, 2nd, 3rd), lime with additives - into two (1st, 2nd). Hydrated powdered lime (fluff), with and without additives, is of two grades (1st, 2nd).
The field of application of air lime is the preparation of lime-sand and mixed mortars, which are used in masonry and when plastering surfaces, as well as for whitewashing and in the production of silicate products.
Hydraulic lime is weakly hydraulic and strongly hydraulic. It is used for the preparation of masonry and plaster mortars, as well as low-grade concretes intended for hardening both in air and in conditions of high humidity.
They are divided into lime-slag with the addition of granulated slag, lime-pozzolanic with the addition of sedimentary or volcanic active rocks, lime-ash with the addition of ashes of some types of fuel. Lime-containing substances are involved in the preparation of low-grade concretes and mortars, which are used in underground structures.
Gypsum binders
It is obtained by roasting and grinding from sedimentary rock, which includes gypsum dihydrate. Gypsum binders have the ability to quickly set and harden. Depending on the temperature of heat treatment of raw materials, two groups of gypsum binders are distinguished: low-firing (moulding building and high-strength gypsum) and high-firing (anhydrite cement, extrich gypsum).
By compressive strength, 12 grades of gypsum binders are distinguished - from low-strength G-2 to high-strength G-25. According to the setting time, they are divided into fast-hardening (A), normal-hardening (B) and low-hardening (C).
According to the degree of grinding, gypsum binders are also divided into three groups: I, II, III.
Grades from G-2 to G-7 (groups A, B, C and I, II, III) are used for the manufacture of a variety of gypsum building products. Grades from G-2 to G-7 (groups A, B and II, III) are used for the manufacture of thin-walled building products and decorative details. Grades from G-2 to G-25 (B, C and II, III) are used in plastering, for sealing joints and for special purposes.
To increase strength and speed up the setting time, gypsum binders are added to lime-sand mortars. They also give greater smoothness and whiteness to the plaster layer, they are used as the main substance in mastics.
Clay
Clay is oily, bold (medium fat) and lean (loam). This division is due to the degree of sand content in the clay.
Clay is used as a binder in the manufacture of oven and plaster mortars, added to cement mortars intended for laying structures in conditions of normal air humidity.
Dense clay that does not contain impurities is an excellent building material. Bricks are made from it.
If clay is used in the construction of a house, its quality can be checked as follows. To do this, put 1 kg of material in a bucket and pour 4 liters of water into it, mix everything well and leave for 24 hours. Thanks to the water, the clay will become soft and the sand will separate from the loam. Then the contents of the bucket are thoroughly mixed again and the water is drained with the silty loam contained in it so that only clay and sand are at the bottom of the bucket. Clay and sand are weighed and their mass is subtracted from 1 kg - this way you can find out how much loam was in the material under study.
The quality of clay depends on its plasticity, and it can be checked by touch. Oily clay resembles a piece of moistened soap or a slice of lard. The quality of clay can be determined in another way. Having made a flagellum 15 cm long and 2 cm thick out of clay, you need to pull it at both ends at the same time.
Skinny clay does not stretch well, and jagged edges form at the place where the flagellum breaks. A flagellum made of plastic clay, gradually stretching out, gradually becomes thinner and eventually breaks, forming sharp teeth at the point of rupture.
The color of the clay depends on what impurities are included in the composition of the clay. Clay with an admixture of iron oxide and manganese oxide is colored red, yellow and brown, and black with organic impurities.
Silty loam can be added to clay concrete to increase its strength and ability to retain its desired shape after drying.
- Drywall, aggregates and stone finishing materials
- Mortars: choice of brand and composition of the mortar
And also don't forget
Acceptance of an apartment in a new building: what to look for?
Astringent materials (mineral binders) are powdery substances that, after mixing with water, are able to change from a viscous (dough-like) state to a stone-like state. The abundance of mineral raw materials in our country, the relatively simple production technology and high construction and technical properties of mineral binders provide them with unlimited use in finishing work for the preparation of plasters and other types of work.
Depending on the ability to harden in air and in water, binders are divided into two groups: air and hydraulic. If the binder can harden, retain its strength for a long time, or increase it only in air, then it is called an air-hardening binder. A binder capable of hardening, maintaining and increasing its strength not only in air, but even better in water or in humid conditions, is called a hydraulic hardening binder.
Clay- the cheapest and most common binder material. Volume weight - 1500-1700 kg/m. Clay was formed as a result of weathering of rocks. Depending on the impurities, clay is divided into fatty, medium and lean. The less impurities, the fatter it is. The main mineralogical composition is kaolinite. Clay is used to prepare pure clay mortars and as an additive to cement mortars for better plasticity and workability. If the clay is heavily contaminated, it is filtered and elutriated. In this case, large particles settle in the process of mixing clay with water, the water is drained, and the creamy mass (clay dough) is used in construction work.
Building lime There are several varieties:
Ground quicklime;
lime dough;
Hydrated lime (fluff).
The starting material for the listed varieties of lime is lump quicklime (), which is formed as a result of heat treatment of limestone rocks ():
When ground into a fine powder, ground quicklime is obtained. When lump lime is slaked with excess water, lime dough is obtained, and when lump lime is slaked with a limited amount of water, hydrated lime is obtained in the form of a thin white powder (fluffy lime).
The lime slaking process is exothermic, i.e. heat is released:
This reaction is very violent. Hence the name - boiling water.
The term "fluff" arose due to the fact that a very porous lump of lime, under the influence of a certain amount of water, crumbles into a fine powder. The calcium oxide hydrate separated from the solution envelops the quicklime particles, and the slaking process is suspended. Therefore, continuous mixing is necessary for complete slaking of lime. Located in the plaster layer reacts with carbon dioxide gas surrounding air:
The process of formation of calcium carbonate () occurs only in air, proceeds slowly and is accompanied by the release of water. Thus, as a result of a series of chemical and technological transformations, limestone is again formed in the form of a layer of plaster of a given shape and texture.
Building plaster. The natural raw material for the production of building gypsum is limestone sulphate. Gypsum stone (limestone sulphate) dehydrates when heated. It releases water easily and does not require as much heat as lime. When heated to a temperature of 800 "C, calcined gypsum is obtained, which quickly sets. The setting (hardening) process is determined by the fact that the substance to be mixed has a greater solubility than the product formed as a result of the interaction of the binder and water. Therefore, a new amount of semi-aqueous gypsum passes into the solution, again a supersaturated solution is formed, from which gypsum crystals stand out:
The process of curing binders is the following sequence: dissolution - hydration - colloidation - crystallization.
Hydraulic hardening binders(cements) - a product of fine grinding of pre-fired natural raw materials - marl or a mixture of limestone and clay in a ratio of 1: 3. They have the ability, after mixing with water, under the influence of physicochemical processes, to move from a pasty state to a very strong stone-like state.
The main binder for hydraulic hardening is Portland cement. This binder has a complex polymineral structure, consisting mainly of compounds of four oxides:
The material formed after firing at a temperature of 1450 ° C is called clinker. After firing, the clinker is kept in special warehouses for two to three weeks to redeem free lime and then ground in special ball mills. Thus obtained fine green powder with a bulk density of 1200-1400 kg/m2 is Portland cement. The strength (grade) of Portland cement is determined by compression until the destruction of a sample-cube of standard preparation after 28 days. from the time the sample was made, in kilograms per square centimeter (kg/cm) or megapascals (MPa). Portland cement grades: 200 (20 MPa); 300 (30 MPa); 400 (40 MPa); 500 (50 MPa); 600 (60 MPa); 700 (70 MPa). For plastering, cements of low grades are used.
Pozzolanic Portland cement is obtained by joint fine grinding of Portland cement clinker, gypsum and active mineral additives (tripoli, pumice, tuff, trass, pozzolans). Pozzolanic Portland cement has grades 200, 250, 300, 400, 500. In addition to the above, cements are produced: slag Portland cement, colored, expanding, hydrophobic, acid-resistant, etc.
