Cement ( lat. Caementum - “crushed stone, broken stone”) is an artificial inorganic hydraulic binder . One of the main building materials . When interacting with water , aqueous solutions of salts and other liquids, it forms a plastic mass, which then hardens and turns into a stone-like body. It is mainly used for the manufacture of concrete and mortar . 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.
Cement grade is a conditional value, which means that the compressive strength will not be lower than the indicated grade (200, 300, 400, 500, 600)
Cement for mortar - low - clinker composite cement intended for masonry and plaster mortars. They are made by joint grinding of Portland cement clinker, active mineral additives and fillers.
Content
Historical Information
The Romans mixed certain materials with lime to give it hydraulic properties. These were:
- pozzolans (deposits of volcanic ash of Vesuvius );
- crushed or crushed bricks ;
- tracks that they found in the Eiffel region (hardened deposits of volcanic ash).
Despite the differences, all these materials contain oxides : silicon dioxide SiO 2 ( quartz or silicic acid), aluminum oxide Al 2 O 3 ( alumina ), iron oxide Fe 2 O 3 - and cause lime to interact with them; in this case, water joins ( hydration ) with the formation, first of all, of compounds with silica. As a result, insoluble calcium hydrosilicates crystallize . In the Middle Ages, it was accidentally discovered that the products of firing clay-contaminated limestones are not inferior in water resistance to Roman pozzolanic mixtures and even surpass them.
After this, a century-long period of intensive experimentation began. In this case, the main attention was paid to the development of special deposits of limestone and clay, to the optimal ratio of these components and the addition of new ones. Only after 1844 they came to the conclusion that, in addition to the exact ratio of the components of the raw material mixture, first of all, a high firing temperature (of the order of +1450 ° C, 1700 K) is necessary to achieve a strong connection of lime with oxides. These three oxides, after sintering with lime, determine the hydraulic properties; they are called oxides, which determine the hydraulicity (factors of hydraulicity).
Portland cement is obtained by heating limestone and clay or other materials of similar gross composition and sufficient activity to a temperature of + 1450 ... + 1480 ° C. Partial melting occurs and clinker granules form. To produce cement, clinker is ground together with about 5% gypsum stone. Gypsum stone controls the setting speed; it can be partially replaced by other forms of calcium sulfate. Some specifications allow you to add other materials when grinding. A typical clinker has an approximate composition of 67% CaO, 22% SiO 2 , 5% Al 2 O 3 , 3% Fe 2 O 3 , 3% other components and usually contains four main phases called alite , belite , aluminate phase and aluminoferrite phase . Several other phases, such as alkaline sulfates and calcium oxide, are usually present in clinker in small amounts.
Alite is the most important component of all conventional cement clinkers; its content is 50–70%. This is a three-calcium silicate, Ca 3 SiO 5 , the composition and structure of which are modified due to the placement of foreign ions in the lattice, especially Mg 2+ , Al 3+ and Fe 3+ . Alite reacts relatively quickly with water and in normal cements from all phases plays the most important role in the development of strength; for 28 day strength, the contribution of this phase is especially important.
Belite content for normal cement clinkers is 15-30%. This is dicalcium silicate Ca 2 SiO 4 , modified by the introduction of foreign ions into the structure and usually completely or mostly present as a β-modification. Belite slowly reacts with water, thus slightly affecting the strength during the first 28 days, but significantly increases the strength at a later date. After a year, the strengths of pure alite and pure belite are approximately the same under comparable conditions.
The aluminate phase content is 5-10% for most normal cement clinkers. This tricalcium aluminate is abbreviated 3CaAS (composition - 3CaO * Al 2 O 3 * SiO 2 ), significantly changed in composition, and sometimes in structure, due to foreign ions, especially Si 4+ , Fe 3+ , Na + and K + . The aluminate phase reacts rapidly with water and can cause undesired quick setting if a setting control agent, usually gypsum, is not added.
The ferritic phase is 5-15% of the usual cement clinker. This is four-calcium aluminoferrite, abbr. 4СaAFS (4CaO * Al 2 O 3 * Fe 2 O 3 * SiO 2 ), 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 slightly due to differences in composition or other characteristics, but, as a rule, it is high in the initial period and is intermediate between the rates for alite and belite in late periods.
The outstanding scientist chemist Shulyachenko Alexey Romanovich is considered the father of the Russian cement industry. The Antonov shaft furnace for firing and clinker production was widely used. On the issues of cement technology and hardening of hydraulic binders, many works were carried out by Yu. M. Butt, S. M. Royak, I. F. Ponomarev , N. A. Toropov and others.
Types of Cement
According to the presence of the main mineral, cements are divided: [1]
- romance - the predominance of belita, currently not produced;
- Portland cement - the prevalence of alite, the most widespread in construction;
- alumina cement - the predominance of the aluminate phase;
- magnesia cement ( Sorel cement ) - based on magnesite, shuts with an aqueous solution of salts;
- acid-resistant cement - based on sodium hydrosilicate (Na 2 O · m SiO 2 · n H 2 O), a dry mixture of quartz sand and sodium silicofluoride , is shut with an aqueous solution of water glass .
Biocement is also known, which differs from ordinary cement in that it is produced using biotechnology .
In the vast majority of cases, cement refers to Portland cement and cement based on Portland cement clinker. At the end of the 20th century, the number of varieties of cement was about 30. [1]
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: 3 cement solution with quartz sand. Stamps are expressed in numbers M200 - M600 (usually in increments of 100 or 50) denoting compressive strength of 100-600 kg / cm2, respectively (10-60 MPa). Cement with a mark of 600 due to its strength is called "military" or "fortification" and costs significantly more than a mark of 500. It is used for the construction of military facilities, such as bunkers, missile silos, and so on.
Currently, cement is divided into strength classes. The main difference between classes and brands is that strength is not displayed as an average, but requires at least 95% coverage (that is, 95 out of 100 samples must correspond to the declared class). The class is expressed in numbers 30-60, which denote the compressive strength (in MPa).
Production
Cement is obtained by fine grinding of clinker and gypsum . Clinker is a product of uniform firing prior to sintering of a homogeneous raw mixture consisting of limestone and clay of a certain composition, which ensures the predominance of calcium silicates.
When grinding clinker, additives are added: gypsum CaSO 4 · 2H 2 O to regulate the setting time, up to 15% of active mineral additives (pyrite cinder, blast furnace dust, bauxite, sand) to improve some properties and reduce the cost of cement.
The raw material mixture is fired at a temperature of + 1450 ... + 1480 ° C for 2-4 hours in long rotary kilns (3.6 × 127 m, 4 × 150 m and 4.5 × 170 m) with internal heat exchangers, to simplify synthesis of the necessary minerals of cement clinker. Complicated physicochemical processes take place in the calcined material. A 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, aluminum silicates decompose into oxides and meta-products.
- decarbonization (+ 900 ... + 1200 ° C) there is a decarbonization of the limestone component: CaCO 3 → CaO + CO 2 , while 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 ) in the same zone, solid-phase synthesis of new compounds begins (CaO · Al 2 O 3 is an abbreviated record of SA, which reacts with higher temperatures CaO and at the end of liquid-phase synthesis C 3 A) is formed, proceeding stepwise;
- exothermic reactions (+ 1200 ... + 1350 ° C) the process of solid phase sintering of materials is completed, the formation of minerals such as C 3 A, C 4 AF (F - Fe 2 O 3 ) and C 2 S (S - SiO 2 ) is completely completed - 3 of 4 main clinker minerals;
- sintering (+1300 → +1480 → +1300 ° C) partial melting of the material, clinker minerals pass to the melt except for C 2 S, which, interacting with the CaO remaining in the melt, forms the alite mineral (C 3 S is a solid solution of tricalcium silicate and a small amounts (2-4%) of MgO, Al 2 O 3 , P 2 O 5 , Cr 2 O 3 and others);
- cooling (+ 1300 ... + 1000 ° C) the temperature drops slowly. Part of the liquid phase crystallizes with the release of crystals of clinker minerals, and part freezes in the form of glass.
World cement production
In 2010, world cement production reached 3.325 billion tons. The three largest producers included China (1.8 billion tons), India (220 million tons), and the United States (63.5 million tons). According to the Federal State Statistics Service, production in Russia of Portland cement, alumina cement, slag cement and similar hydraulic cements in 2012 amounted to 61.5 million tons.
The largest cement producers in the world for 2011 [2] :
- Holcim - Switzerland - 136.7 Mt
- Lafarge - France - 150.6 Mt
- Heidelberg Group - Germany −176 mln tons (as of July 1, 2016)
- Cemex - Mexico - 74.0 Mt
- Italcementi - Italy - 54.4 million tons
- Anhui Conch Cement - China - 41.5 Mt
- Taiheiyo Cement - Japan - 38.0 Mt
- Votorantim Cimentos - Brazil - 31.8 Mt
- Buzzi Unicem + Dyckerhoff - Italy-Germany - 26.6 Mt
- Cimpor - Portugal - 28.3 Mt
- Vicat - France - 19.8 Mt [3]
- Eurocement group - Russia - 18.4 million tons
Cement Production in Russia
Ten leading cement producers in Russia for 2013 (volume in million tons / market share in%) [4] :
- Eurocement Group - 21.649 / 32.6
- Novoroscement - 5.772 / 8.7
- Mordovcement - 4.717 / 7.1
- Siberian Cement - 4.307 / 6.5
- Heidelberg Cement - 3.654 / 5.5
- Holcim - 3.658 / 5.5
- Dyckerhoff - 3.257 / 4.9
- “ Sebryakovcement ” - 3.167 / 4.8
- Lafarge - 2.416 / 3.6
- Vostokcement - 2,037 / 3,1
The design capacity of the plants in 2014 (million tons per year):
- Eurocement Group - 33.1
- Mordovcement - 7.2
- Novoroscement - 6.9
- Siberian cement - 6.7
- Heidelberg Cement - 4.9
- Holcim - 4.6
- Vostokcement - 4.3
- Dyckerhoff - 3.7
- “ Sebryakovcement ” - 3.4
- Baselcement - 3.2
In December 2014, Mordovcement enterprises came under the control of the Eurocement Group. [5] :
Sources
- Reichel W., Conrad D. Concrete. In 2 hours. Part 1. Properties. Design. Test. - M.: Stroyizdat, 1979.P. 33. Per. with him. / Ed. V. B. Ratinova.
- Dvorkin L.I., Dvorkin O. L. Handbook of building materials science. - M .: Infra-Engineering, 2010.
See also
- List of countries producing cement
- Arbolite
- Cement crisis
- Concrete
Notes
- ↑ 1 2 Building materials science: a manual for construction specials. universities / I. A. Rybiev. - M .: Higher. school., 2003 .-- 701 s.
- ↑ Vladimir Kondratyev - [World Cement Industry], “Perspectives” Portal, 2011
- ↑ Vicat Group by the numbers .
- ↑ Top 10 largest cement producers in Russia , Kommersant , April 8, 2014.
- ↑ Independent building portal. Top 10 cement manufacturers in Russia. 02/25/2015 .
Literature
- Egorov, K.N. , Mendeleev D.I. Cements // Encyclopedic Dictionary of Brockhaus and Efron : 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.