What is cement made from? How and from what cement is made: all about the production process Building materials that include 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 of chemical reactions with cement grains, they have properties different from conventional grades.
• Mixed - obtained by joint grinding of different types of clinkers or by introducing multicomponent mineral mixtures (for example, 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.

Judging by the scale of use in the construction of mortars and concretes based on mineral binders, it seems that the history of artificial stones based on cements goes back many centuries. But a truly proven production technology and the optimal composition of cement became known less than two centuries ago.

the invention of stone

The stones of prehistoric houses were fastened in the wall with the help of clay, but they could not survive without firing, and the most ancient buildings that have come down to us were built using lime mortar. Burnt and ground limestone (calcium oxide - Ca(OH)₂) hardens after mixing with water, absorbing carbon dioxide from the air, and then turns into stone again. The main disadvantage of lime binder is low moisture resistance, so today it is used more in the manufacture of silicate bricks.

Another type of airy mineral binder (that is, gaining strength in air) is gypsum. It is obtained by heat treatment and subsequent grinding of natural gypsum stone (CaSO 4 -2H 2 O) or natural anhydride (CaSCu). Gypsum binder has a long history of use from ancient times to the present day. The most striking examples are luxurious stucco and sculptural decorations, sheet materials (GVL, GKL) for dry construction and finishing methods.

Hydraulic binders

The scope of air binders is limited to those places where the finished structures are not exposed to moisture, otherwise it is necessary to use water-repellent (water-repellent) additives or carry out waterproofing measures, so the use of hydraulic binders is more convenient and more widespread.

These include substances that form hydrated (a water molecule enters the crystal lattice as an integral part) compounds, when the transformation into a stone-like body and further strength gain can occur in a humid environment, and the impact of water during the operation of structures does not lead to their destruction.

Mortars and concretes for making water-resistant structures are prepared on the basis of hydraulic lime (from sedimentary limestone rocks of a special composition - marls) and Portland cement, and it is the latter that gives the monolithic and prefabricated elements of the building the necessary strength, and lime mortars are used where loads are minimal.

History of cement

Attempts to overcome the low water resistance of lime and gypsum compositions have been made since ancient times. Cement (caementum in Latin - crushed, broken stone) appeared by adding various mineral substances with hydrophobic properties to lime. For this, crushed remains of baked clay bricks, various volcanic rocks were used. So, the composition of cement, which was used by the builders of ancient Rome, included pozzolans - ash deposits of the famous volcano Vesuvius.

Experiments continued for many centuries, until the need for a large amount of durable and inexpensive binder forced builders to develop an optimal technology for its production. A decisive contribution to such research was made by Russian military technician Yegor Cheliev, who published a book on cement for underwater work (1825), and John Aspdin, a bricklayer from English Leeds, who received a patent for Portland cement (1824). This name comes from the English island of Portland, located in the English Channel and consisting of calcareous rocks. Stones from a quarry located on this island were considered the most prestigious building material in England. The artificial stone Aspdin received was very similar in color and strength to it.

Interestingly, Cheliev's technology is more consistent with what is now called Portland cement, and Aspdin's cement was produced without the now accepted sintering of the feedstock.

Production technology

Cement binder from different manufacturers may differ in raw materials, but the main technological operations are identical. The first stage is the preparation of the initial mineral raw materials, i.e., several stages of grinding limestone and clay, mixing these components in the required proportions. What is cement made of? Usually it is 3 parts by weight of limestone and 1 part of clay. Sometimes sedimentary rock is used - marl, where these components are contained in the desired proportion.

"Dry" and "wet" method

There are two ways to obtain the desired state of the mixture: "dry" and "wet". If the moisture content of the components is high, clay and soft limestone (chalk) dissolve in water, then water is removed from this suspension, called raw sludge, by strong heating (evaporation). It turns out a uniform finely ground mixture. A more economical method is "dry", where there is no stage of bringing the sludge to a boil, and the mixture is crushed mechanically.

Further, in rotating kilns - cylinders with a diameter of about 5 m, a length of about 200 m, having a slope for moving the raw mass during the firing process, the formation of clinker occurs - rounded granules that appear during the sintering of the mixture at a temperature of 1450 ⁰С as a result of physical and chemical interactions.

The clinker is cooled and aged for up to two weeks before the final operation - joint grinding with a certain amount of gypsum, which is added to slow down the setting process. Here, the cement composition is finally formed, at the same stage, various mineral additives are introduced, which give the binder the necessary specific properties.

Chemical base

The necessary properties of the most popular binder are determined by the chemical composition of the cement. As a result of technological processing of raw materials, clinker becomes a combination of various chemicals in the form of four main minerals:

1. Alite - tricalcium silicate - makes up most of the clinker - 50-60%. The presence of manganese, aluminum and iron ions in the molecular lattice determines the strength of the finished mortar or concrete mixture, which is collected during the first 28 days.
2. Belit - dicalcium silicate - makes up 15-30%, and it is the basis of the strength gained by the structure at a later date.
3. Aluminate phase - tricalcium aluminate - 5-10%. The rapid reaction of aluminate with water and the possible too rapid setting require the introduction of gypsum, which slows down this process.
4. Ferrite phase - tetracalcium aluminoferrite - 5-15%

By changing the percentage composition of these phases, introducing additional components, it is possible to produce cement, the composition and properties of which will best suit the specific situation during construction.

Types of cement

Portland slag cement is obtained by adding granular slag, a by-product of iron smelting in blast furnaces, to Portland cement clinker. The use of slag reduces the cost, and the composition of cement produced using this technology gives structures based on it an increased resistance to water with a saturated mineral composition, for example, sea water.

Fast-hardening is a cement with a predominance of alite and aluminate phase in the clinker, it is distinguished by a particularly fine grinding - all this accelerates curing.

Sulfate-resistant Portland cement is used for hydraulic structures, the underwater parts of which are constantly exposed to substances that cause sulfate corrosion. What does cement intended for such critical structures consist of? In the clinker raw material, the presence of tricalcium aluminate and belite is reduced to a minimum.

Portland cement with reduced heat at curing is necessary for the manufacture of structures of large mass and volume, when the heat generated by the exothermic curing reaction can lead to the formation of cracks. The composition of such cement is similar to sulfate-resistant.

white cement

Products made using white cement have enhanced aesthetic qualities. The presence of iron oxide and manganese oxide in the feedstock gives the finished powder a characteristic gray-green color, respectively, the composition of white cement implies the minimum presence of such salts and the use of light, kaolin clay grades for the feedstock.

There are many more types of cement binder with special properties: hydrophobic, aluminous, waterproof expanding, straining, plasticized, sandy, etc.

Composition and strength

The most important indicator of the quality of cement is the strength of products made on its basis. GOST established the necessary indicators, which are indicated by a special marking. The number indicates the ultimate flexural and compressive strength in laboratory tests of standard samples, the resistance to loads of which is also affected by the composition of the cement. M400 means that the samples withstood a load of 400 kg / cm² (or 40 MPa).

Studies show that the mineral composition of the feedstock is the most important factor affecting the strength of cement mortars and concretes. The correct selection of components allows you to find the right proportion between the rate of curing and the final value of resistance to loads, which only increases over time. The composition of M500 cement allows you to create beams and slabs that can withstand enormous loads.

Today, the world produces a huge amount of cement of various qualities. The choice of raw materials for it is often determined by economic factors, and with the right attitude to the construction process, one should know what the cement that will be used consists of in order to make the right choice and be sure of the strength and durability of the future home.

The material is used very widely. It is used as an independent product and is introduced into solutions. All this is due to the property of the dry mixture - it can become plastic when water is added and after a while harden, turning into. Its characteristics vary somewhat depending on the composition, so it is important to know what cement is made of.

It always contains five main ingredients. Let's analyze them using the example of Portland cement, one of the most popular varieties:

• calcium oxide - not less than 61%;
• silicon dioxide - not less than 20%;
• alumina about 4%;
• iron oxide - not less than 2%;
• magnesium oxide - not less than 1%.

The necessary minerals are mined in an open way, these are:

• Carbonate rocks: dolomite, marl, shell rock, chalk and other limestones.
• Clay rocks: loess, loams, shales.

Apatite, fluorspar, silica, alumina, etc. are used as additives.

Portland cement

Cures in air and water. There are no mineral additives. It is widely used for the construction of diverse monolithic structures.

Sulfate resistant

Its feature is increased resistance to chemical aggressive environments. It is characterized by a low saturation coefficient. This allows the use of sulfate-resistant cement for the construction of hydraulic engineering, etc.

Pozzolanic

Aluminous

acid resistant

The composition includes quartz sand and sodium silicofluoride. It is mixed not with water, but with liquid glass. Used to obtain acid-resistant coatings. Does not withstand constant exposure to water.

plasticized

It is made with special additives that give frost resistance and increased mobility to mortars prepared on this cement. They acquire greater strength, better resist corrosion and are characterized by increased water resistance.

slag cement

His recipe includes slag, the percentage of which can vary from 20% to 80% by weight of the product. This reduces the cost of the material, slows down the rate of its hardening and increases heat resistance. It is used for the construction of ground, underwater and underground facilities.

How cement is made

Manufacturing technology consists in obtaining and subsequent grinding. This is the name of the granules, which are an intermediate product of production. Their composition is always the same. It is limestone and clay mixed in a ratio of 3:1. In nature, there is a mineral that is completely identical in composition to clinker. It's called marl. However, its reserves are limited and cannot meet the needs of production.

Therefore, the factories use an artificial analogue of marl. To obtain it, the necessary ingredients are thoroughly mixed in large containers with special drums. The mass prepared in this way is fed into, where it is fired for about four hours. The process temperature is in the order of 1500°C. Under these conditions, the powder begins to sinter into small granules. After cooling, the clinker grains are sent for grinding. They are crushed in large drums with ball sieves and screens. At this stage, it is important to grind the granules and obtain a powder product of a certain size. Grinding is determined by the size of the sieve cells. The resulting powder is mixed with the necessary additives that determine the brand and properties of the product.

Despite the general technology, three methods can be used to produce the composition, depending on the properties of the raw material.

Dry way

This method can significantly reduce the time and cost of producing a cement mixture. It involves several steps:

1. The raw material is crushed to obtain fine grains.
2. The prepared granules are dried until the desired moisture content is reached. This is done to facilitate subsequent operations.
3. The ingredients are mixed in certain proportions. Then they are crushed to get flour.
4. The powder is fed into a rotating one, where it is fired, but not sintered into granules.

After cooling, the finished product is sent to the warehouse or to the packing area.

The dry method is considered the least energy-consuming, and therefore very beneficial for manufacturers. Unfortunately, it is not applicable to all categories of raw materials.

wet way

In some cases, it is necessary to moisten the material prepared for production. In such cases, the wet method is used. For the preparation of clinker, which consists of limestone and clay, a mixture of the main components is kneaded with the addition of water. The result is a viscous mass, which is called sludge.

It is placed in a kiln where it is fired. In this process, granules are formed from the sludge, which, after cooling, are sent for grinding.

Combined method

It is used to reduce the cost of finished products. It is a kind of symbiosis of dry and wet technology. Sludge is initially mixed, which is subsequently dehydrated. This is how clinker is made. It enters the dry technology furnace. Further, if necessary, mixing with fillers is carried out, and the product is ready. The process is shown in more detail in the video.

The quality of cement largely depends on the raw materials from which it is produced, and the accuracy of compliance with all technological stages. Considering that the characteristics of those made from it are determined by the quality of the mixture, it is worth paying close attention to it.

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 assumed to be 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 mobility (plasticity, fluidity), which ensures its density 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.

It is difficult to imagine an area of ​​construction where cement would not be used. It is necessary at all stages of any construction process, from the arrangement of the foundation to the interior decoration. Until now, analogues of this building material have not yet been found, which indicates the unique properties of cement.

What is cement made of, description

Cement is a crushed clinker powder in which modifying additives and fillers are introduced. In dry form, it is a free-flowing homogeneous mass of gray color. When diluted with water, a paste-like binder is obtained, which is easily applied to any rough surfaces.

After the cement hardens, a strong connection is formed, which is not inferior in its density to the stone. No wonder artificial stones are made from cement.

Chemical composition and formula

When limestone and clay are heated to a temperature of about 1450 degrees, the structure of these materials changes, resulting in the formation of clinker granules. These granules are mixed with gypsum and ground to a powder. The chemical formula of the finished cement is as follows: 67% calcium oxide (CaO), 22% silicon dioxide (SiO2), 5% aluminum oxide (Al2O3), 3% iron oxide (Fe2O3) and 3% other components.

quite complex and labor intensive. It requires special equipment and compliance with technological norms and conditions.

Specifications

The main technical characteristic is brand of cement. It is designated by the letter "M" and a digital indicator. The numbers indicate the maximum load in kilograms for a certain volume of hardened cement, i.e. its compressive strength.

In practice, this means the weight that the cement can support without breaking. For example, if it can withstand a weight of 200 kg, then the cement is assigned the M200 grade.

On the package, in addition to the brand, the percentage is also indicated composition of additives. It is denoted by the letter "D" and shows what this type of cement consists of. For example, the symbols "D10" mean that 10% of additives have been added to the dry mix.

Such additives are introduced to improve water resistance, corrosion resistance, frost resistance and other qualities of cement. Consider also other characteristics of cement, which should be paid attention to in the production of construction work.

M400. Its strength is 400 kg/cm2. This is the most popular brand of cement, used everywhere for all types of construction and finishing works. This is the construction of buildings, monolithic construction, the manufacture of concrete slabs, blocks, stair structures, foundations, well reinforced concrete rings, paving slabs and a number of other products.

M500. The strength is 500 kg/cm2. This brand of cement is characterized by rapid hardening and high strength. Cement is used for the monolithic construction of high-rise structures, the manufacture of load-bearing elements, floor slabs, prefabricated structures made of reinforced concrete, beams, as well as in other cases that require increased strength and durability of structures.

In addition to brands, classes, types and degrees of grinding, which differ from each other by a combination of individual components and composition.

According to GOST. The production of general construction cements should be based on the requirements of GOST 31108-2003. The standard regulates the ratio of the necessary components in the composition of the dry mix and the cement manufacturing technology. This does not include special formulations.

Activity. This is the compressive strength of a single sample of cement mortar. The obtained indicators of activity are compared by specialists with the standards and appropriate brand is assigned to this cement. The activity indicator depends on several factors: the activity of the clinker granules, the grinding intensity, the presence of additives. For example, active additives will significantly increase the activity of the cement itself.

Application of an automatic cement activity meter CEMENT-PROGNOZ:

Density. The lowest density is fixed in freshly prepared cement. Electrostatic forces act on its individual particles, repelling particles from their counterparts. Then, during transportation and storage, the mixture is caked and compacted.

The density also depends on the degree of grinding of the clinker granules. When making calculations, the indicator of the average density of cement is taken equal to 1300 kg per cubic meter. But in practice, the density depends on the storage conditions of the material.

Specific and volumetric weight. The specific gravity of cement is determined by the ratio of its weight to the volume it occupies. This concept is necessary for the correct compilation of the proportions of cement mortars. The specific gravity of cement can vary considerably depending on the state of the mixture. So, a fresh powder can have a specific gravity of about 1000 kg/cubic meter, and a caked mixture - 1500 kg/cubic meter.

Volume weight calculated from the average cement density. The average density is approximately 1300 kg / cu. Therefore, a bag weighing 50 kg will have about 0.04 cubic meters. Bulk density increases when cement is caking or transported.

Best before date. Cement is characterized by a limited shelf life. Manufacturers guarantee its safety under normal conditions for 2 months. If sealed storage conditions are provided, the cement can lie without problems for a year.

It should be borne in mind that the higher the brand of stored cement, the faster it can lose some of its properties. So, cement M500, after being in a warehouse with high humidity, in a month will correspond in quality to cement M400, and after 2 months - M300.

Bulk density. This is the ratio of the mass of loose cement to its volume. That is, it is practically the same as the specific gravity, if we take a loose mixture. It is determined by experience. Cement is poured into a measuring container from a certain height. After filling the container, weighing is carried out. Knowing the weight of the empty container, determine the value of the bulk density. For fresh mixtures, this figure is about 1200 kg / cu. In compacted cement, the bulk density is about 1500 kg / cu.

Freeze time. The prepared cement mortar sets and hardens in a few hours. In summer, this process can occur in 2-3 hours. In cold weather, the setting process is delayed up to 10 hours. So, at a temperature of 0 degrees, the solution can harden only after 20 hours. Additives introduced into the solution can speed up or slow down the solidification process.

With the help of cement, they equip the foundation, plaster the walls, make the floor screed. Each of these operations requires, which in any case must be prepared with high quality.

Grinding fineness. The smaller the size of the crushed cement particles, the faster the mortar hardens, and the more reliable it will be in the solidified state. The fineness of grinding directly depends on the equipment used for this. The recommended particle size should be between 40 and 80 µm.

Certificate of conformity

Certification of cement in Russia is carried out according to GOST 10178-85, 30515 97, but more often according to GOST 31108-2003. All major Russian enterprises have already switched to the new GOST 31108-2003, which was adopted in 2004. It spelled out more stringent criteria for the quality of cement, as well as its testing. The new requirements fully comply with European quality standards.

What is the difference between cement and concrete

Cement is a dry mix that is used specifically for the preparation of concrete mortar. Concrete is a hardened artificial stone, consisting of cement, water and fillers. Gravel, sand, screenings, slag, expanded clay and other materials are usually used as fillers. Until the moment of solidification, concrete is a mobile concrete mix.

Not only in construction and repair work. If you want to make something solid and strong, cement is indispensable.

Strength class of cement and strength test methods

According to GOST 31108-2003, such a term as "cement grade" is transformed into the term "strength class". Therefore, the digital marking of cement means its strength class.

Strength tests of cement are carried out in factory laboratory conditions using modern equipment and advanced analysis methods. At the same time, the fineness of grinding, the density of the cement paste diluted with water, the setting time of the cement mortar are determined. The compressive or bending strength of the hardened samples is also determined.

Determination of the normal density of cement paste in a virtual laboratory: