How and from what is cement made? Description and technical characteristics of building cement, its chemical composition What material is used to produce cement

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 chemical reactions with grains of cement, 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 (compound of grinding clinker and limestone and magnesia marls, not produced industrial scale), magnesia (mixed with saline solutions, characterized by a high setting speed and resistance to mechanical stress after solidification) and acid-resistant quartz-based compositions diluted with liquid glass.

The chemical composition of cements of different groups

Proportions of clinker and other components:

Name	The material composition of the dry mixture, %			Mineralogical composition of clinker, in % by weight
	Share of clinker	Gypsum share	Other additives
Regular PC	Up to 80	1,5-3,5	Mineral impurities - up to 20%	ZCaO x SiO 2 - 45-67 2CaO x SiO 2 - 13-35 ZCaO x Al 2 O 3 - 2-12 4СаО xAl 2 O 3 x Fe 2 O 3 - 8-16
Hydrophobic	Up to 90	—	Mylonaft, oleic acids - up to 0.05
Plugging		—	Active mineral supplement - up to 25 inert - up to 10 slag - up to 15 sand - up to 10 plasticizers - 0.15
Portland slag cement	40-70	Up to 3.5	Granular diatomite slag - 30-60
plasticized	Up to 90	—	plasticizers - 0.15-0.25
Fast hardening	90	1,5-3,5	Active mineral supplement - up to 10	ZCaO x SiO 2 and ZCaO x Al 2 O 3 - up to 65 2CaO x SiO 2 and 4СаО xAl 2 O 3 x Fe 2 O 3 up to 33
high strength	90	1,5-3	—	ZCaO x SiO 2 - up to 70 ZСАО x Al2O 3 - 8
Decorative (white cement)	80-85	—	Diatomaceous earth - 6 Inert mineral additive - 10-15	3CaO x SiO2 - 45-50 2CaO x SiO2 - 23-37 ZCaO x Al2O3 - up to 15 4СаОхAl 2 O 3 xFe 2 О 3 - up to 2
Pozzolanic sulfate resistant	Up to 60	Up to 3.5	Rocks of sedimentary origin - 20-35 Lava, baked clay, fuel fly ash - 25-40	ZCaO x SiO 2 - up to 50 ZCaO x Al 2 O 3 - 5 ZCaO x Al 2 O 3 and 4CaOxAl 2 O 3 xFe 2 O 3 - 22
Sulfate resistant	Up to 96	Up to 3.5	—
Aluminous	99		1	The exact proportions depend on the destination. CaO Al 2 O 3 - the predominant share 2CaO Al 2 O 3 2SiO 2
Same, expanding	Up to 70	20	Bura - 10
straining	Clinker PC - 65-70 Alumina - 13-20	6-10		Joint grinding of aluminous and Portland cement clinker

The scope and main properties of varieties are given below:

Name	Optimal area of ​​use, advantages	Limitations, possible disadvantages
Portland cement	Monolithic and prefabricated concrete and reinforced concrete structures, mortar production, road construction	Final curing after 28 days
PPC	Massive structures exposed to fresh and mineralized waters. Highly sulfate resistant	Slow hardening at the beginning, low frost resistance
Pozzolanic	Underground and underwater structures exposed to the aggressive effects of sulphate waters	Not recommended for objects with fluctuations in humidity levels, at the risk of frequent freezing or hardening of the mortar in dry conditions
Aluminous	Production of heat-resistant building mixtures, fast-hardening or emergency concrete	Not used for pouring massive structures, the maximum allowable ambient temperature for initial stage hardening is +25 °C
Straining	Production of thin-walled products, pressure reinforced concrete pipes, waterproofing coatings	Depending on the brand, there may be restrictions in the operating temperature. The only drawback is the complex production process, and as a result, the high price.

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 compressive strength, in the laboratory it is determined for products from CPR, mixed in a ratio of 1: 3 and hardened in normal conditions within 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.

Any construction or repair work are impossible without the use of a universal building material - cement of various types and brands. We are so accustomed to this product that we do not even think about the problem, but how cement is made. Is it possible to make it at home and not overpay?

We will immediately answer the question - is it possible to make cement with your own hands? Having necessary equipment and raw materials - you can get cement at home. At the moment in Russian Federation mini-plants for the production of cement are in great demand, with a capacity of about 120,000 tons of cement per year. It is economically unprofitable to produce cement for a single construction site. It is easier and cheaper to buy this necessary construction material factory or shop.

Composition of cement

Cement is obtained by long-term crushing 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 grinding 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) to improve some properties and reduce the cost of cement.

Production of cement in factories

At the moment, cement manufacturers use three technologies for the production of a binder:

• Wet way.
• Dry way.
• Combined method.

It is worth noting that the "dry" technology is used foreign manufacturers cement: Egypt, Turkey and China. "Wet" technology is traditionally used by domestic cement plants.

Dry way

There is no need to use water here. Raw material(clay and limestone) are crushed on special equipment. Dried and ground into fine flour, mixed pneumatically and served for roasting.

The cement clinker formed as a result of firing is crushed to the appropriate degree of fraction, packaged in packaging and sent to the warehouse finished products. This method allows to reduce production costs, however, it is “capricious” to the homogeneity of the starting materials and is an environmentally hazardous option.

wet way

The undeniable advantages of this method lies in the possibility of accurate selection of the composition of the feedstock with a high heterogeneity of the initial components: rock, type of rock, etc. The feedstock (sludge) is a liquid substance containing up to forty percent moisture.

Before making cement, the composition of the sludge is adjusted in special technological pools. After holding the raw materials in the pool, annealing is carried out in special rotary kilns and subsequent grinding.

The wet method requires a greater consumption of thermal energy spent on drying the feedstock. This significantly increases the cost of cement production, however, the quality of the final product does not suffer from the possible heterogeneity of the clinker, as in the wet version.

Combined methods

This technology is based on wet look obtaining a binder. The intermediate substance is dehydrated using a special technology. Clinker is granulated with the addition of water, after which annealing and subsequent grinding to one or another brand of cement are carried out.

Among the advantages of the combined method of cement production: a high yield of "good" cement, the possibility of using waste from the metallurgical industry.

How white cement is made

The technology for the production of white cement is slightly different from the technology for the production of conventional "gray" material. Like the usual "gray" material, white cement is produced in a dry and wet way. The main difference between the technology is the firing of raw materials at a high temperature and rapid cooling in water.

White cement clinker is characterized as "low iron" and contains in its composition: mineral additives, limestone, gypsum, salts and other components. The feedstock for clinker is carbonate and clay rock (limestone, kaolin clay, tailings, quartz sand).

In the Russian Federation, white cement is produced only at one enterprise - Kholsim (Rus) SM LLC (until 2012, Shchurovsky Cement OJSC). Most white cement is supplied to the Russian market from abroad by the following companies: Holsim (Slovakia), Cimsa and Adana (Turkey), AalborgWhite (Denmark) and AalborgWhite (Egypt).

The main advantage of white cement is its unique characteristic - snow-whiteness, and the main disadvantage is many times higher cost compared to the usual "gray" material.

Conclusion

Now you know how cement is made in a factory in the general case. For information on how to make cement correctly in all details, numbers, diagrams, tables and other subtleties, see the special literature.

Whatever steps the progress takes in various branches of production and technologies, the well-known cement stably holds the leading position in construction. And although the production of cement is a labor-intensive, energy-intensive and costly process, the payback of cement plants is very high.

In order to reduce costs, these enterprises, as a rule, are located in the same place where raw materials are mined.

The main methods of cement production

The basis of cement production is the burnt mass, called "clinker". The composition of clinker can be varied, so we will talk about it later.

Whole technological process cement production can be divided into two main stages:

• obtaining clinker is the most costly and time-consuming process;
• crushing clinker to obtain a powdery mass.

Samo Clinker production is divided into four stages:

• raw materials from which clinker will be prepared are mined and delivered to the place of processing;
• raw materials are crushed;
• the raw mixture is prepared in the required proportions;
• the finished mixture is fired at high temperatures.

1.1 Methods for producing cement are divided into three main groups:

• wet;
• dry;
• combined.

The choice of one of them depends on the thermal capacity of the enterprise and the quality of raw materials.

1.2 Wet method

The main advantage of this method is that, no matter what the clinker is made of, no matter how heterogeneous raw materials are taken initially, the wet method allows you to accurately select the desired composition of the sludge.

The sludge, in this case, is a watery, jelly-like mass containing up to 40% water. Its composition is corrected in special pools and then fired in rotary kilns at temperatures above 1000ºC.

The wet method requires more thermal energy, but allows the production of cement of the highest quality, due to the absence of the effect of sludge heterogeneity on the final product.

2 Dry method

The dry process requires that any raw material be processed without the use of water. In this case, clay, limestone and other components are crushed, then ground to a state of dust and mixed with air in closed boxes.

In the manufacture of cement by the dry method, ready-made raw materials get into the kiln for firing, without having, moreover, water vapor. Therefore, after heat treatment, we get ready-made cement that does not require crushing.

The dry method significantly reduces the cost of time, heat energy and other resources. It is very advantageous and effective with high slurry homogeneity.

2.1 Combined

The production can be based on the wet method and supplemented with dry, or dry, supplemented with wet.

In cases where the wet method is based, the raw materials are dehydrated after mixing with special filter dryers and sent to the kiln almost dry. This allows you to reduce the cost of thermal energy, as it significantly reduces evaporation during the firing process. If the production of clinker is based on a dry method, the finished mixture is granulated with the addition of water.

In both cases, the clinker enters the kiln with a moisture content of 10 to 18%.

2.2 Clinker-free production

In addition to the above traditional ways, the production of cement can take place without clinker. In this case, the raw material is a blast furnace or hydraulic slag, which is combined with additional components and activators. The output is a slag-alkaline mixture, which is crushed and ground to the desired consistency.

Clinker-free cement production technology has the following positive qualities:

• the final product is resistant to any environmental conditions;
• the cost of thermal energy and other energy costs are significantly reduced;
• waste from the metallurgical industry is used as a raw material for high-quality cement production, which positively affects the cleanliness of the environment;
• makes it possible to produce a final product with different properties and in different colors without changing the production method.

2.3 Cement production (video)

2.4 Equipment for the production of cement

Since the entire production process is divided into stages that are inherently very different from each other, equipment for the production of cement requires a variety of profiles. It can be divided into the following subgroups:

• equipment for the extraction and transportation of raw materials;
• for crushing and storage;
• kilns for roasting;
• machines for grinding and mixing clinker;
• machines for packing finished cement.

Because the production of cement is different ways, and raw materials are used differently, equipment in factories can also be different.

AT recent times private mini-plants for the production of cement are very popular. Sometimes it is even made at home, but we will talk about this later.

The thing is that the equipment for such plants is not very expensive, they can be installed in relatively small areas, and they pay for themselves amazingly quickly.

In addition, assembly, disassembly and transportation of the production line does not cause difficulties. Therefore, it is possible to install a private plant at any unpromising raw material deposit, and, having worked it out, transport it to another place. This option will free the manufacturer from the task of transporting raw materials, which will result in significant savings.

2.5 What does the production line consist of?

1. Screw crushers. Designed for coarse crushing and grinding of raw materials.
2. Hammer crushers.
3. Screens or vibrating sieve. Necessary for screening crushed material.
4. Material feeder for the first stage.
5. Transporters. Perform the function of supplying raw materials to the next stage.
6. Sorting machine.
7. Threshing and threshing-dosing machines.
8. Mill with millstones.
9. Sludge mixing machine.
10. Rotary drum kiln.
11. Drying plant.
12. Refrigeration unit.
13. Mill for clinker.
14. Bucket elevator with feed screws.
15. Weighing and packing equipment.

3 Making quality cement at home

In some cases, when you need to make a concrete screed, and go far for cement, craftsmen undertake to make cement at home. We note right away that the process of making cement at home is a very laborious process and requires serious equipment and skills.

Do not expect that you will get a quality product the first time. Before you get real cement, you will have to spoil more than a dozen kilograms of material.

Cement is called a binder that hardens in water and in air, obtained by joint fine grinding of clinker and the required amount of gypsum and additives. Clinker is obtained as a result of firing before sintering a raw mixture consisting of limestone and clay or some other materials (marl, nepheline sludge, blast-furnace slag), taken in a ratio that ensures the formation of calcium silicates, aluminate and alumino-ferrite phases in the clinker. Clinker is one of the most important components of cement; the main properties of cement obtained on its basis depend on its composition.

The introduction of up to 15% active mineral additives into the composition of cement, provided for by the standard, affects its properties to a relatively small extent. If you introduce more such additives (above 20%), the properties of the resulting product will already differ markedly from the properties of cement. This product is called pozzolanic cement. The standard gap in the dosage of hydraulic additives from 15 to 20% is made in order to more clearly distinguish between cement and pozzolanic cement.

The specific gravity of Portland cement ranges from 3.0-3.2. The volumetric weight of cement in a loosely poured state is 900-1300 kg/m3, and in a compacted state it is 1400-2000 kg/m3. When calculating the capacity of warehouses, the volumetric weight is taken equal to 1200 kg/m 3 , and with the volumetric dosage of materials for the preparation of concrete mix 1300 kg/m 3 .

Cement (GOST 10178-76) produced without additives or active mineral additives that meet the requirements of OST 21-9-74. The main properties of cement include: strength (activity), setting time, uniformity of volume change, fineness of grinding, density, water demand, water separation, frost resistance, heat generation, adhesion to steel reinforcement.

Water requirement of cement paste. Water added to cement during mixing is necessary for the normal course of chemical processes that occur during cement hardening, and to give freshly prepared cement mortar or concrete of mobility (plasticity, fluidity), which ensures the density of its laying in a form or formwork. It is possible to reduce water demand and increase the plasticity of cement by introducing plasticizing organic and inorganic surfactants, for example, sulfite-yeast mash.
Read more - water demand and binding capacity of cement paste.

Building materials appeared at the moment when, at the dawn of our civilization, the first people began building houses and fortifications. Over time, mankind has been looking for materials that have great strength and availability in any place of residence. After long searches and experiments, it was found that finely crushed limestone and gypsum, when mixed with water and minerals, acquires special astringent properties.

After hardening, it forms a monolithic joint having the characteristics of a hard stone. From that moment, cement began to be produced in large quantities and use in the construction of large and small structures. Passing once again past a building made of stone and metal, we often ask ourselves the question: “So how is cement made?”

Interesting fact: during the construction of the Egyptian pyramids, the pharaohs used a technology similar to the production of concrete. A mixture of crushed limestone and stone chips was poured with water and turned into monolithic stone blocks.

What is cement made from?

The first stage of production begins in a limestone quarry, when the components of the future cement are removed from the soil with the help of mining machines. In order for the building material to have the required strength, limestone is chosen for production, which lies close to the surface. In its composition, in large numbers, silicon, iron and aluminum oxide are present. If you dig deeper, the rock will be cleaner, but with a high content of calcium carbonate. The mined stone, if necessary, is sorted and sent to production, where the proportions are changed to obtain cement of different grades.

Related materials:

How and from what are chips made?

limestone processing

At the plant for the production of cement, the rock is unloaded into the apparatus for the primary crushing of stones. Large boulders, under the influence of a pressing force of several tons, are gradually crushed to the size of a tennis ball and fed to the conveyor. Small and large stones are sent to secondary crushing, where they are reduced to the size of a golf ball and into a fine powder. Limestone, with different percentages of calcium carbonate, is processed separately.

Scheme of the line for crushing and drying limestone: 1 - belt feeder PL-650; 2 – magnetic separator; 3 – drying complex; 4 - elevator; 5 - supply hopper with a sliding head; 6 – belt feeder PL‑500; 7 – mill МЦВ-3; 8 – rotary jet mill MRS-2/770; 9 - cyclone-bunker TsB-4.5; 10 – dust collector II ПЦ-2.0 with a bunker; 11 – bag filter FRI-60; 12 – sector feeder PS-1V; 13 – VVD fan; 14 – medium pressure fan; 15 - slide gates; 16 - compressor.

This is necessary for their further mixing in different proportions and according to a certain technology in order to produce cement of different grades.

Sorting and grinding

Fine limestone, with the help of a sorting loader, is placed in dry warehouses, protected from moisture and temperature changes. Heaps are formed from the raw mix, of different composition, ready for the grinding stage. On the conveyor, the crushed stone enters the grinding machine - roller mill, in which limestone dust is formed.