What is cement made from? What is cement made from? What is cement clinker

The word cement is familiar to everyone. Even those who have never been involved in construction know that cement is needed for mortar when brickwork that it is the main component of reinforced concrete products. However, few people know what cement is made of.

Peculiarities

Cement is ubiquitous. It is used not only in the construction of all kinds of buildings. You can not do without it when carrying out restoration and repair work. So far, there is no substitute for cement. This justifies his demand.

The basis of the building material are astringent inorganic components. Cement is needed in the production of panel slabs. Plaster and masonry mortars are made from it. In the composition of concrete, cement is given one of the main places.

In fact, cement is a finely dispersed powder. The main feature of the powder mass is that when interacting with water, it gradually begins to harden. The process of interaction of two components (cement and water) ends with the formation of a continuous array, similar in hardness to natural stone.

A strong structure is formed with excessive moisture. The reaction occurs as outdoors, as well as in water. Cement after hardening retains strength for a long time.

Properties

The physical characteristics of cement depend on several factors.

The most significant are:

• types of additives;
• grinding degree;
• compound.

The fineness of cement grinding affects the strength and the time required for hardening. Fine grinding provides greater strength and faster setting.

The finer the powder particles, the stronger the concrete is, the faster it sets. The cost of the material also depends on the degree of grinding.

To determine the fineness of grinding, a special sieve with the smallest cells up to 80 microns is used. When preparing a mortar from too finely ground cement, more water is required. This disadvantage is eliminated by mixing particles different size: large and small. Dust particles of 80 microns are considered large, and 40 microns are considered small.

Cement has the following properties:

• strength;
• corrosion resistance;
• frost resistance;
• water demand;
• setting (hardening) time.

Strength

This figure depends on the brand. Strength properties are determined by performing compression tests. An experienced blank is kept under load for lunar month- 28 days. After testing the sample, the cement is assigned the appropriate designation. Strength is measured in MPa.

For domestic use, cement grades 300 - 600 are suitable. For products that require special strength, higher grades - 700 or even 1000 are used.

Corrosion resistance

Reinforced concrete products under the influence of water and other liquid media begin to corrode. The negative impact is eliminated in several ways. For example, you can change the composition, introduce hydroactive materials into the powder mixture. The presence of specific substances prevents the occurrence of harmful chemical reactions.

Corrosion resistance increases with the use of polymer additives. As a result, microporosity is reduced, and the durability of products is increased.

Pozzolanic cement has the highest corrosion protection. Therefore, it is used for the construction of structures operated in conditions of high humidity.

Frost resistance

One of the main indicators of the quality of cement is the ability to repeatedly freeze and thaw a concrete product.

The cement stone has micropores that contain water. When freezing, water can increase in volume by 8%.

Repeated freezing and subsequent thawing over the years leads to the destruction of the structure of the stone, to the appearance of cracks.

In construction, cement without additives is not used. Components are added to different brands that give cement the ability to resist temperature changes.

Air-entraining additives are included in the concrete manufacturing process. The smallest air bubbles are distributed evenly inside the concrete body, which solves the problem associated with the freezing of water and its expansion.

Water requirement

This is the amount of water, expressed as a percentage, that is required to produce cement mortar optimal consistency.

In a solution of nominal density of water, as much as cement can hold. For example, in Portland cement, this value is in the range of 22-28 percent.

Higher quality concrete is obtained from cement with low water demand. than the one with the highest score. In the first case, the products are resistant to temperature changes. In the second, concrete has increased porosity and is not at all suitable for construction. Such cement is used for the production of reinforced concrete fences or drainage structures.

setting time

This is the time period for a change physical properties cement mortar from the state of plasticity to the formation of a stone.

The solution is considered ideal if it does not harden too quickly, but not too slowly. The setting time is regulated by the presence of a certain amount of gypsum in the composition of the material. A larger volume of gypsum provides a high-speed setting. While a decrease in its content contributes to a longer solidification of the solution.

Not as dramatically as gypsum, other factors affect setting. In particular, the volume of water in the solution and the ambient temperature in the working area are important.

According to the standard, under normal conditions, Portland cement begins to set after three quarters of an hour. The hardening process should be completed after 10 hours.

Compound

Cement is produced at specialized enterprises. Cement plants are built in close proximity to the places of extraction of raw materials.

Raw materials for its production are obtained from natural rocks:

• fossils of the carbonate type;
• clay materials.

Carbonates have an amorphous or crystalline structure, which determines the effectiveness of the interaction of the material with other constituents during the firing process.

Carbonate rocks include:

• marl (marl limestone);
• limestones, including shell rocks;
• rocks of the dolomite type.

Clay materials are sedimentary rocks. Having a mineral base, they are endowed with plasticity, and with excessive moisture they can increase in volume. Clay materials are used in the dry method of manufacture.

Clay rocks include:

• clay;
• loams;
• clay-based shales;
• loess.

In addition to raw materials, corrective additives are used in the production of cement.

They are obtained from fossils, which include:

• apatite;
• alumina;
• fluorspar;
• silica.

Additives introduced according to a certain technology improve the quality of the described material.

The composition of cement depends on the required characteristics, which are determined by the grade assigned to the material.

The most popular Portland cement consists of:

• 60% lime;
• 25% silicon dioxide;
• 10% iron oxides and gypsum;
• 5% aluminum (alumina).

In different brands, the percentage of starting materials is different, as is the composition itself. For example, Portland slag cement contains slag. Quantitative proportions can also change with the features of the chosen technology for the manufacture of building material.

For any brand of cement and for any method of its production, limestone and clay remain unchanged. Moreover, limestone is always three times more than clay. This ratio contributes to the production of high-quality clinker, from which cement is made.

In the industry for the production of cement, the following components are used:

• clinker;
• gypsum;
• special additives.

Clinker is the most significant component of cement. It determines the strength properties of the final material. The clinker enters the production process in the form of granules. The diameter of the granules varies between 10-60 mm. The heat treatment of the component is carried out at a temperature of about one and a half thousand degrees.

The amount of gypsum is determined by the established hardening period. In the basic version, gypsum in the form of a powder is included in the cement in a volume of 6%.

Additives allow you to enhance specific characteristics. With their help, cement receives additional properties, which significantly expands its capabilities.

Production stages of cement production

First, limestone is mixed with clay in a ratio of 3/1. The mixture is then fired at high temperature. As a result, the source material for the production of cement is formed. It's called a clinker. Granulated clinker is sent for grinding in ball mills.

There are three ways to get cement.

Depending on the manufacturing technology, it can be:

• wet;
• dry;
• combined.

The differences are in the methods of preparation of the feedstock.

In accordance with wet technology not lime is used, but chalk. Its mixing with clay and other ingredients occurs with the addition of water. The result is a mixture with a moisture content of 30 to 50 percent. The charge is converted into clinker balls during firing.

According to the dry technology, the manufacturing process is shortened, since two operations (drying and grinding) are combined into one. The resulting mixture becomes powdery.

In different enterprises, the combined method is used in different ways. In some cases, a dry mixture is first obtained, and then it is moistened. In others, not wet, but semi-dry method with low humidity, not exceeding 18%, is used. Roasting is performed in both cases.

Kinds

There are many different types of cement. The most famous is Portland cement.

Other material options are also quite popular:

• slag;
• pozzolanic;
• aluminous;
• expanding.

Portland cement is available in several grades: 400, 500, 550, 600. Mortars are made from M400 cement.

Higher grades are in demand in the manufacture of reinforced concrete structures, as well as in the creation of high-strength concrete products.

White Portland cement is characterized by fine grinding. The composition includes low-iron clinker, gypsum and dolomite additives. Differs in the high durability and resistance to an atmospheric precipitation. Products made of white Portland cement have an aesthetic appearance. Used in the manufacture of self-leveling floors, decorative elements as well as in road construction. It is the basis for colored cements.

Sulphate-resistant portland cement is used in the manufacture of piles, supports for bridges, hydraulic structures, wherever there is repeated wetting and drying of structures, where structures are subjected to freezing and thawing.

The main purpose of slag cements is the creation of concrete products for structures located underground and under water.

Pozzolanic cements are needed in the construction of dams, river hydraulic structures, various underground utilities, as they are endowed with resistance to fresh water.

Alumina are not afraid of sea waters, therefore they are part of reinforced concrete products that come into contact with mineralized waters. Can be used for urgent plugging of wells, including oil wells; when concreting in winter time; for fixing cracks in rocks.

The beauty of expanding cements is that when they set, they do not shrink, but, on the contrary, expand in volume. The increase in volume is from 0.2 to 2 percent.

How to do it yourself?

It is possible to prepare cement at home if it is possible to reach a high temperature for firing. Perhaps the most that can be obtained in an artisanal way is cement grade M 200. Chalk and kaolin will be required in a ratio of 3 to 1. About 5% of gypsum powder must be added to the burned and crushed substance - and the cement is ready.

For home production appropriate knowledge, suitable raw materials, special equipment and precise execution of the technological process will be required.

Even when there is everything you need, it is hardly worth doing cement production on their own. Before starting work, answer yourself the question of the expediency of the process. It is unlikely that your work and the costs incurred will pay off. Most likely, it is more profitable to simply buy a bag of ready-made cement.

When choosing cement for certain needs, remember that there are many varieties. The right choice for initial stage work will guarantee the durability of the building. You should not always give the choice to higher and more expensive brands. The strength of the product will not increase from this, and the costs will not be justified.

The process of obtaining cement, see the video below.

Cement (Latin caementum - “crushed stone, broken stone”) is an artificial inorganic binder, usually hydraulic, one of the main building materials. When mixed with water, aqueous solutions of salts and other liquids, it forms a plastic mass, which then hardens and turns into a stone-like body. Mainly used for making concrete and mortar.

Cement is fundamentally different from other mineral binders (gypsum, air and hydraulic lime), which harden only in air.

Cement is obtained by heating slaked lime and clay or other materials of similar gross composition and sufficient activity to a temperature of 1450 ° C. Partial melting occurs and clinker granules are formed. To obtain cement, clinker is mixed with a few percent of gypsum and finely ground. Gypsum controls setting speed; it can be partly replaced by other forms of calcium sulfate. Some specifications allow the addition of other materials when grinding. A typical clinker has an approximate composition of 67% CaO, 22% SiO2, 5% Al2O3, 3% Fe2O3 and 3% other components and usually contains four main phases called alite, belite, aluminate phase and ferritic phase. In clinker, several other phases are usually present in small amounts, such as alkali sulfates and calcium oxide.

Alite is the most important constituent of all conventional cement clinkers; its content is 50-70%. It is a tricalcium silicate, Ca3SiO5, whose composition and structure are modified by the placement of foreign ions in the lattice, especially Mg2+, Al3+ and Fe3+. Alite reacts relatively quickly with water and in normal cements of all phases plays the most important role in the development of strength; for the 28-day strength, the contribution of this phase is especially important.

The content of belite for normal cement clinkers is 15-30%. This is a dicalcium silicate Ca2SiO4 modified by the introduction of foreign ions into the structure and usually completely or for the most part present as a β-modification. Belite slowly reacts with water, thus having little effect on strength during the first 28 days, but significantly increasing strength in later periods. After a year, the strengths of pure alite and pure belite under comparable conditions are approximately the same.

The content of the aluminate phase is 5-10% for most normal cement clinkers. This is tricalcium aluminate Ca3Al2O6, significantly changed in composition, and sometimes in structure, due to foreign ions, especially Si4, Fe3+, Na+ and K+. The aluminate phase reacts rapidly with water and can cause an undesirably rapid setting unless a setting controlling agent, typically gypsum, is added.

The ferritic phase is 5-15% of conventional cement clinker. This is a tetracalcium aluminoferrite Ca2AlFeO5, the composition of which changes significantly with a change in the Al/Fe ratio and the placement of foreign ions in the structure. The rate at which the ferritic phase reacts with water may vary somewhat due to differences in composition or other characteristics, but is generally high early on and intermediate between alite and belite later in life.

The most widely used is Portland cement.

What are cements?

Over the years that have passed since the advent of Portland cement, scientists have come up with, and industrialists have introduced a huge number of new modifications of it. The family of Portland cements has grown and, in order not to get confused in their diversity, a special nomenclature has been developed. It is set out in the state standard of Ukraine DSTU B V.2.7-46-96 “Cements for general construction purposes. Specifications". All cements included in this document are united by the mandatory content of ground Portland cement clinker. Although its content can be quite low - in some cements it is only 20%, but it is a basic, structure-forming component.

The classification of Portland cement and its "relatives" is based on two key parameters: type and amount of additive (or additives) and grade strength.

Depending on the additives contained, cements are divided into five types:

I Actually, Portland cement. Without additives or with a minimum amount (up to 5%). Designated PC I.

II Portland cement with additives: slag, pozzolana, fly ash, limestone. His index is PC II. To make it clear which additive is included in the composition, the corresponding letter is indicated to the right of the type designation (for slag - W, for pozzolana - P, for fly ash - Z). In addition, the designation includes another letter indicating the maximum content of clinker. If it is "A" - at least 80% clinker, if "B" - at least 65%.

Composite Portland cement is also referred to this type. It may include several of the above additives at once. To distinguish it from Portland cement with additives, the designation was supplemented with the letter "K". It turned out: PC II / A-C or PC II / B-C.

III Slag portland cement. As the name suggests, the material contains granulated blast-furnace slag. And since the slag itself has astringent properties, cement can "accommodate" it much more than other additives. Accordingly, the clinker content in Portland slag cement is low: ShPTs III with the letter “A” may contain only 35% slag, and with the letter “B” - even less: 20%.

IV Pozzolanic cement (may contain both pozzolana and fly ash). Designated PTSTS IV ("A" and "B").

V Composite cement KTs V ("A" and "B"). This cement, like composite Portland cement, may contain several additives, with the exception of limestone. The permissible minimum content of clinker in it is lower than in composite Portland cement, and is at least 40% for the letter "A" and at least 20% for the letter "B".

In terms of strength, DSTU B V.2.7-46-96 regulates grades 300, 400, 500, 550 and 600 for type I and II cements, and 300, 400 and 500 for other types.

In addition to the above symbolism, symbol may contain additional information about the special properties of the cement. For plasticized cements, the index PL is introduced into the designation, for hydrophobized - GF, for cements with high early strength - R.

For example, plasticized Portland slag cement grade 500, containing 40% slag and characterized by high early strength, will be designated as follows: ShPTs III / A-500R-PL DSTU B V.2.7-46-96.

Cement is included in many compositions: concrete, reinforced concrete, plaster, putty, masonry mortar. It is used in the construction complex structures, in underwater, underground construction, for autoclave materials.

Speaking of such a popular building material, a homogeneous loose mixture immediately comes to mind. gray color. However, the definition will be inaccurate if not supplemented - this is an artificially obtained, inorganic binder. When interacting with water, it is converted into a rather plastic mass, which subsequently hardens and becomes stone-like. For the ability to gain strength under wet conditions, it is classified as a hydraulic substance.

The brand of cement is the main indicator of its strength. There are many classes: M100, 150, 200, 250, 300 and even M600. But grades from M350 to 500 are in the greatest demand. The numerical value indicates what load 1 cm2 of the hardened composition can withstand. For example, the ultimate strength of M400 for bending and compression is 400 kg / cm2.

What is the material made from?

Cement is made from 2 main elements: gypsum and clinker. The latter should be understood as the product of uniform firing of the raw mass, consisting of clay and limestone of a certain composition, before sintering. Sometimes the clinker may additionally contain marl, nepheline sludge, blast-furnace slag. With the introduction of mineral additives (up to 15-20% by weight), the properties change somewhat. The most common modifier impurities are: bauxites, pyrite cinders, sands, flue dust. If the content of additives exceeds 20%, a pozzolanic cement is obtained, which is not afraid of interaction with sulfate and fresh waters.

The composition of the binder product is determined by the firing of the raw mixture. Calcium oxides are formed from limestone at certain temperatures, which, upon further heating, enter into a complex reaction with clay components. As a result, compounds are formed that, after fine grinding and mixing with water, harden and turn into a stone-like body.

Chemical composition:

1. CaO - calcium oxide 67%;
2. SiO 2 - silicon dioxide 22%;
3. Al 2 O 3 - amphoteric aluminum oxide 5%;
4. Fe 2 O 3 - iron oxide 3%;
5. foreign elements 3%.

Varieties of cement

Characteristics largely depend on the content of mineral compositions and the proportions of the components. In industrial and private construction, the most popular compositions are:

1. Portland cement.

It is a mixture of finely ground gypsum, cement clinker and corrective additives (tripoli, flasks, pyrite cinders) with a predominant proportion of calcium silicates (up to 80%). The greater its mechanical strength, and the sooner it is achieved, the better the material is considered. In this regard, PC, which is characterized by a high increase in strength, is called fast-hardening. It is called superstrong when maintaining the maximum load on compression and bending. These characteristics are reflected in the marking. It is used in almost all areas, from building cladding to mass production of precast concrete/reinforced concrete structures. Read about such an indicator as cement density.

2. Portland slag cement.

It is created by grinding a certain amount of gypsum, clinker and granulated slag (usually blast furnace - a product obtained by smelting iron in a furnace). The manufacturing technology of the binder implies the mandatory drying of waste from metallurgical production to a moisture content not exceeding 1%. At the end, the material does not come out as frost-resistant as ordinary cement, and it hardens more slowly. However, low cost and excellent resistance to sulfates make it popular.

Scope of use: cooking concrete mixtures, wall blocks, various construction solutions. It can be used to create not only ground structures, but also underground ones that are exposed to mineralized / fresh waters.

3. Aluminous.

They are made according to a proven technology: the initial components are enriched with alumina - pure limestones and bauxites. The latter should be understood as rocks whose content is based on hydrates and impurities. The predominance of monocalcium aluminate in the clinker composition is inherent. This determines the main characteristics: to set quickly, to be resistant to moisture, thermal influences, in particular, open fire.

Due to the water resistance, it is often used in winter. And due to the high speed of hardening, it is indispensable for operational emergency work. Another area is the production of various heat-resistant concretes on its basis.

4. Magnesian.

The key difference is that magnesium oxide acts as the active ingredient here. To obtain it, finely dispersed magnesite (or dolomite) is taken, which is subsequently subjected to calcination. By itself, the mineral, when dissolved with water, almost does not reveal astringent properties. But after dilution with magnesium salts (sulfide / chloride), the final mixture acquires the necessary parameters and is quite suitable for construction work.

Renowned for good adhesion to various fillers, including those of organic origin, strength, low thermal conductivity. Due to such unique qualities, it can be used in the production of facing slabs, stairs, partitions, thermal insulation products (foam, gas magnesites). But the main area is the arrangement of seamless monolithic floors.

5. Pozzolanic.

The production technology is based on the use of clinker, active additives (pozzolana - a mixture of volcanic ash, tuff, pumice; burnt shale; fly ash; microsilica), the share of the total mass of which is 20-40%. Auxiliary additives may be included. Gypsum is poured in the amount necessary to regulate the setting time.

Pozzolanic differs from the classical composition in that it has a higher resistance to corrosion and sulfate waters. Sufficiently frost-resistant, shows minimal heat release during the hardening process. Due to the addition of light mineral additives, it has a lower specific gravity, but the same additives contribute to an increase in the yield of cement slurry. Most often used for the preparation of concrete / reinforced concrete products in underground / underwater structures. If we are talking about ground buildings in a dry climate, it is inappropriate to use it, since it will be much inferior to Portland cement.

Rarely used materials are romancement (a combination of clinker with dolomitic marl and gypsum) and acid-resistant products based on quartz/diabase, whose mixing is not carried out with water, but liquid glass. White and colored compositions, on the contrary, are in demand, but only in the field of architectural and finishing works.

Production technology

To obtain cement, refer to the following steps:

1. heating a mixture of slaked lime and clay to temperature marks + 1450-1480̊ С; at the end of this process, the desired clinker granules are formed;
2. the connection of the intermediate product (clinker) with gypsum and their further grinding until acquiring a powder state;
3. the introduction of additives and additives (if necessary), which will positively affect the properties.

In the manufacture of the binder composition, not only production processes are strictly observed, but also preparatory measures, the ratio of components. After the cement gets its finished look, it is transported to warehouses, where it waits for shipment to the consumer.

The cost of different brands

Many factors influence the formation of the final price:

1. packaging - it is more profitable to purchase in large volumes, so it is not surprising that a bag weighing 0.05 tons will cost less per 1 kg than a 5-kilogram package;
2. seasonality (activity of the period) - spring / summer, part of autumn - the time when construction and repairs are in full swing, and, therefore, the rise in the cost of binders is not unreasonable;
3. territorial pricing policy;
4. prestige of the manufacturer;
5. strength characteristics are the main aspect in determining the cost: the higher the compressive strength limit of cement, the better it will be, and its price is higher.

With aqueous solutions of salts and other liquids, it forms a plastic mass, which then hardens and turns into a stone-like body. Mainly used for making concrete and mortars. Cement is a hydraulic binder and has the ability to gain strength in wet conditions, which is fundamentally different from some other mineral binders - (gypsum, air lime), which harden only in air.

Mortar Cement- low-clinker composite cement intended for masonry and plaster mortars. It is produced by joint grinding of Portland cement clinker, active mineral additives and fillers.

Historical information

• romancement - the predominance of belite, currently not produced;
• portland cement - the predominance of alite, the most widespread in construction;
• aluminous cement - the predominance of the aluminate phase;
• magnesia cement (Sorel Cement) - based on magnesite, mixed with an aqueous solution of salts;
• mixed cements - cements obtained by mixing the above cements with air binders, mineral additives and slags with astringent properties.
• acid-resistant cement - based on sodium hydrosilicate (Na 2 O mSiO 2 nH 2 O), a dry mixture of quartz sand and sodium silicofluoride, is closed with an aqueous solution of liquid glass.

In the vast majority of cases, cement refers to Portland cement and cements based on Portland cement clinker. At the end of the twentieth century, the number of varieties of cement was about 30.

In terms of strength, cement is divided into grades, which are mainly determined by the compressive strength of halves of prism samples 40 * 40 * 160 mm in size, made from a 1 to 3 cement mortar with quartz sand. Grades are expressed in numbers M100 - M600 (usually in increments of 100 or 50) indicating compressive strength of 100-600 kg / cm2 (10-60 MPa), respectively. At present, cement grade M300 and less is not produced. Cement with grade 600 is called “military” or “fortification” due to its strength and costs significantly more than grade 500. It is used for the construction of military facilities such as bunkers, missile silos, etc.

Also, cement is currently divided into classes according to strength. The main difference between classes and grades is that strength is not derived as an average, but requires at least 95% security (that is, 95 samples out of 100 must correspond to the declared class). The class is expressed in numbers 30-60, which indicate the compressive strength (in MPa).

Production

Cement is obtained by fine grinding of clinker and gypsum. Clinker is a product of uniform firing to sintering of a homogeneous raw material mixture consisting of limestone and clay of a certain composition, ensuring the predominance of calcium silicates.

When crushing clinker, additives are introduced: CaSO 4 ∙ 2H 2 O gypsum to control the setting time, up to 15% active mineral additives (pyrite cinders, flue dust, bauxites, sands, flasks, tripoli) to improve some properties and reduce the cost of cement.

Roasting of the raw mix is ​​carried out at a temperature of 1470°C for 2-4 hours in long rotary kilns (3.6x127 m, 4x150 m and 4.5x170 m) with internal heat exchangers to simplify the synthesis of the necessary cement clinker minerals. Complex physical and chemical processes take place in the fired material. The rotary kiln can be conditionally divided into zones:

• heating (200 ... 650 ° C - organic impurities burn out and the processes of dehydration and decomposition of the clay component begin). For example, the decomposition of kaolinite occurs according to the following formula: Al 2 O 3 ∙2SiO 2 ∙2H 2 O → Al 2 O 3 ∙2SiO 2 + 2H 2 O; further, at temperatures of 600…1000 °C, aluminosilicates decompose into oxides and metaproducts.
• decarbonization (900…1200 °C) decarbonization of the limestone component takes place: CaCO 3 → CaO + CO 2, at the same time, the decomposition of clay minerals into oxides continues. As a result of the interaction of basic (CaO, MgO) and acid oxides (Al 2 O 3, SiO 2), processes of solid-phase synthesis of new compounds begin in the same zone (CaO ∙ Al 2 O 3 - abbreviated notation SA, which at more high temperatures reacts with CaO and at the end of the liquid-phase synthesis, C 3 A) is formed, proceeding in steps;
• exothermic reactions (1200 ... 1350 ° C), the process of solid-phase sintering of materials is completed, here the process of formation of such minerals as C 3 A, C 4 AF (F - Fe 2 O 3) and C 2 S (S - SiO 2) - 3 is completely completed from 4 main clinker minerals;
• sintering (1300→1470→1300 °C) partial melting of the material, clinker minerals except C 2 S pass into the melt, which, interacting with CaO remaining in the melt, forms the mineral ALIT (C 3 S);
• cooling (1300…1000 °C), the temperature drops slowly. Part of the liquid phase crystallizes with the release of crystals of clinker minerals, and part solidifies in the form of glass.

World cement production

In 2002, world cement production reached 1.8 billion tons. The top three producers were China (704 million tons), India (100 million tons), and the USA (91 million tons).

The price of cement on European exchanges is about $100 per ton. Cement prices in China are about $40 per ton. Most exchange transactions with cement in Russia in 2010 are carried out on the Moscow Stock Exchange.

Sources

Reichel W., Konrad D. Concrete: In 2 hours. Part 1. Properties. Design. Trial. - M.: M.: Stroyizdat, 1979. S. 33. Per. from German / Ed. V. B. Ratinova.

• Dvorkin L.I., Dvorkin O.L. Reference book on building materials science. - M .: Infra-Engineering, 2010.

see also

Notes

Links

Wikimedia Foundation. 2010 .

See what "Cement" is in other dictionaries:

cement- a, m. ciment m., German. Zement, Cement, goal. cement lat. caementum is a broken stone. 1. Walls in sluices on the outside, only one and a half arshin or less, are lined with hewn stone and smeared with cement, and then field stones with lime are laid. 1725. Tatishchev ... Historical dictionary gallicisms of the Russian language

The quality of any artificial binder is determined by its manufacturing method and the percentage of raw materials. Cement is no exception, of all types it is one of the most difficult. This substance is obtained by grinding gypsum and burnt homogeneous multicomponent clinker to a powder state and combining them with special additives. As a result, the properties and scope of the binder depend on the ratio of these substances to each other, the processing temperature and the fineness of grinding.

Groups of cements by composition

The main components are oxides of aluminum, calcium and silicon, when mixed with water, they form chemical compounds that harden when solidified in a humid environment. General requirements are regulated by GOST 30515-2013, according to this interstate standard, all cements are classified into groups that differ in the type of clinker into Portland cement, alumina and mixed (PC and sulfate aluminates). In the first case, a typical composition contains CaO (67%), SiO 2 (22%), Al 2 O 3 (5%), Fe 2 O 2 (3%) and up to 3% foreign matter.

For the production of aluminous and high alumina cements, bauxites and limestones are used as raw materials (the share of low-basic calcium aluminates prevails, the percentage of Al 2 O 3 increases to 50%). The ratios of the remaining components in them depend on the intended purpose and vary within the following limits: CaO - 35-45%; A1 2 O 3 - 30-50%; Fe 2 O 3 - 0-15%; SiO 2 - 5-15%. For the manufacture of sulfate-containing mixtures, clinkers based on calcium ferrites are used.

Depending on the proportions of the components and the material composition, the following groups are in demand in private and industrial construction:

• Portland cements are the most popular variety, representing a mixture of finely ground clinker with a predominant proportion of highly basic calcium silicates and gypsum. The raw materials are limestone (up to 78%) and clay (up to 25%).
• Aluminous, made by grinding raw materials from bauxite and limestone, burned or melted to a homogeneous state. These types are characterized by a high hardening rate, they are used both as an independent binder and for the production of special grades: waterproof, expanding, straining. Due to the increased hardness of the clinker, they lose to Portland cement in terms of energy consumption and cost.
• Portland slag cements - with a share of blast-furnace, electrothermophosphorus or fuel slags from 36 to 65%.
• Pozzolanic, with the addition of active mineral additives to the grinding products of PC clinker. Their proportion reaches 40%, due to the formation of chemical reactions with cement grains, they have properties different from conventional grades.
• Mixed - obtained by joint grinding of clinkers different types or by introducing multi-component mineral mixtures (eg slag and fly ash).

Less commonly used types include romancement (a compound of grinding PC clinker and limestone and magnesia marls, not produced on an industrial scale), magnesia (mixed with salt solutions, characterized by a high setting speed and resistance to mechanical stress after solidification) and acid-resistant compositions based on quartz, diluted with liquid glass.

The chemical composition of cements of different groups

Proportions of clinker and other components:

The scope and main properties of varieties are given below:

Main brands

The type of binder selected determines the proportions and properties of building mixtures. It is important to check in advance what the cement consists of, its water demand, grain size and setting time. The main quality criterion is the compressive strength, in the laboratory it is determined for products from CPR, mixed in a ratio of 1: 3 and hardened under normal conditions for 28 days. Depending on the withstand pressure, groups are distinguished from 100 to 600 kg / cm 2. Of these, brands from M300 to M500 are most in demand in private construction, but there are exceptions.

The next factor is the percentage of additives to clinker, in standard types the maximum is 20%. The marking of this indicator is indicated by the letter "D", the number following it characterizes the proportion of mineral impurities (example: PC M400 D0 is indicated for Portland cement with a compressive strength of at least 400 kg / cm 2 without additives). The given marking corresponds to GOST 10178-85, in addition to the above, it includes information on additional properties (marked only if available), also depending on the composition of the clinker and the additives introduced. Of these, the most in demand:

• H - normalized;
• B - fast hardening;
• SS - sulfate-resistant;
• VRTs - expanding waterproof;
• PL - with plasticizers;
• BC - white (decorative) cement.

Since 2003, GOST 31108 (corresponding to European standards) has come into force, according to which the composition is indicated first with a note on the presence or absence of additives (II or I). All options with mineral impurities are divided into two groups: A - with a percentage of 6 to 60%, B - from 21 to 35%. The type of additive is indicated by Roman numerals. The last are the strength class and the compression rate of the material. The standard range for general construction mixtures varies from 22.5 to 52.5 (corresponds to the brand from M300 to M600). To avoid errors, GOST is always indicated next to the marking, the introduction of cement is carried out with strict observance of proportions.