Cement

of these articles describes the building material cement; for other one, derived meanings see cement (term clarifying).
Silhouette eines Zementwerks in Beckum/Westf. mit Vorwärmerturm (Mitte), Silos und Förderbandbrücken
Silhouette of a cement plant in Beckum/Westf. with preheater tower (center), silo and conveyor bridges

cement (v. lat.: caementum = break stone, component) is a hydraulic, artificially manufactured bonding agent for the building materials mortars and concrete. It is a usually grey powder, which in largely industriellen processes of the raw materials limestone, clay/tone, sand and iron ore are made. Due to its high firmness and the durability of concrete cement is world-wide one of the most important bonding agents. “Caementum” was already used by the Romans, from whose names the word cement is derived. This building material consisted of burned lime, water and sand. 1835 it by the Ulmer pharmacist Dr. became. Ernst Gustav Leube rediscovers.

Table of contents

production process

Schema eines Zementwerkes (nicht maßstabsgetreu)
pattern of a cement plant (not true to scale)
cement is made today in modern cement plants during a continuous process of predominantly natural raw materials. The plants reach an output of 3000 to 10,000 tons of clinkers per day.

The raw materials (usually limestone, clay/tone, sand and iron ore) are diminished in quarries, before-cut up in crushers and carried into the cement plant. In a raw mill all raw materials are dried at the same time together to grind and. The raw meal developing thereby becomes then in a rotary kiln at temperatures of approx. 1450 °C to so-called clinker burned, which is then down-cooled in a radiator on a temperature of under 200 °C. The developing grey-brown Granalien becomes afterwards in a ball mill as well as gypsum or anhydrite the finished product, which cement, to grind. The Englishman Joseph Aspdin in its patent of 1824 Portland Cement called these cement places. The designation leaned against the haven land stone, a limestone, which was diminished on the peninsula (haven country) at the English channel coast as Werkstein and which from portland cement was coloured similar to manufactured art products.

By the Zumahlung of different additives such as granulated blast-furnace slag, Puzzolan, fly ash and limestone cements with different chemical and physical characteristics can be manufactured.

hydraulic characteristics

cement is, contrary to Kalkmörtel, a hydraulic bonding agent. As hydraulic materials are regarded, which confirm both at air and under water and are also steady. Cement fulfills these characteristics. It confirmed not like lime under admission of carbon dioxide from air, but reacts with water under education of insoluble, stable compounds. These connections, which form calcium silicate hydrates, fine needle-shaped crystals out, which tooth themselves among themselves and lead in such a way to the high firmness of a cement. These characteristics make cement a bonding agent, which corresponds to the high requirements within the building range.

composition and characteristics

Strength classes and identification colour codes according to DIN 1164
firmness
class
pressure strength
[N/mm ²]
identification colour code
after 2 D after 28 D bag bag
print
32.5 - ≥32,5 light brown black
32.5 R ≥10 ≥32,5 light brown red
42.5 ≥10 ≥42,5 green black
42.5 R ≥20 ≥42,5 green red
52.5 ≥20 ≥52,5 red black
52.5 R ≥30 ≥52,5 red knows

portland cement, manufactured by the grinding of clinker and gypsum and/or. Anhydrite, consists chemically seen of about 58 to 66% calcium oxide (CaO), 18 to 26% silicon dioxide (SiO 2), 4 to 10% alumina (aluminium 2 O 3) and 2 to 5% ferric oxide (Fe 2 O 3). With the fuel process in the rotary kiln minerals from these main parts , which are for the special characteristics of cement of crucial importance, form. The most important these connections are the tri calcium silicate (3 CaO × SiO 2), the Dicalciumsilikat (2 CaO × SiO 2), tri calcium aluminate (3 CaO × aluminium 2 O 3) and the Tetracalciumaluminatferrit (4 CaO × aluminium 2 O 3 × Fe 2 O 3).

Except the chemical and mineralogical composition also the refinement of a cement is decisive for its characteristics. In principle it can be said that a cement with higher refinement develops also a higher firmness. The specific surface (also called Blaine) serves as measure for the refinement and normally lies between 2500 and 5000 cm ² /g. The standard for cements , the EN 197, valid in Europe, differentiates between three different strength classes (32.5, 42.5 and 52.5 N/mm ²), which are divided again into slow and fast-hardening (r = rapidly) cements, and five different kinds (CEM I = portland cement, CEM II = Portlandkompositzement, CEM III = blastfurnace cement, CEM IV = Puzzolanzement, CEM V = Kompositzement).

In order to prevent confounding in particular on the building site, in Germany identification colour codes are assigned to the cements with the paper of the cement bags and the print.

The quality and composition of a cement are today constantly supervised in the laboratory. In addition in regular intervals samples are taken automatically out of current production and examined with modern analysis methods regarding their characteristics. Thus it is ensured that also with varying raw material characteristics a constantly constant product can be manufactured.

special cements

the high requirements of the building industry to the building material concrete - and thus also to the bonding agent cement - make it necessary to manufacture cements with special chemical and physical characteristics. This is done via the Zumahlung of different materials such as granulated blast-furnace slags, Puzzolan, fly ash or limestone in differently large quantities. These cements with special characteristics affect the hydration speed (cement with low heat of hydration (size)), the stability against chemical materials (cement with high sulfate resistance (HS)) or cement with low effective alkali content (WELL)) or also the workability and firmness of the cement.

Except normal grey cements there are also white cements. These are made of very iron-poor raw materials (Fe 2 O 3 - content < 0.1%) and mainly used for Terrazzo , Sichtbeton and finery. White cement is suitable not only for lightcolored preparing, but can with Farbpigmenten more easily be dyed than usual grey portland cement. This one takes advantage of in particular with the production of colored Terrazzoplatten.

aspects of environmental protection

into the 1960er years were considered cement plants as “dirt centrifuges”, which led a large quantity of dust and exhaust gases into the environment. Today this picture improved to favour of the environment. The dust mission was drastically lowered by more modern filtering units. Likewise by the advancement of the rotary kilns and the firing technology the output by harmful exhaust gases such as sulfur dioxide (SO 2), carbon dioxide (CO 2) and nitrogen oxides (NO x) were lowered. The latters are removed by so-called DENOX procedures from the exhaust gases. For the saving of fossil fuels such as coal, natural gas and oil partially so-called secondary fuels are used. These alternative fuels such as domestic refuse (in Switzerland one does not use), motor-car tire or waste oil become in the cement plant due to the extremely high temperatures in the furnace (flame temperature > 2000°C) without the emergence of harmful exhaust gases burned. In Switzerland the portion of these alternative fuels is more than 50%. Since a majority of the cements produced today so-called Kompositzemente is, in which clinker is replaced by other Zumahlstoffe, the natural raw materials is preserved. In addition it acts with this Zumahlstoffen for example with the granulated blast-furnace slag and the fly ash, around waste materials out of other branches of industry. Also the heat energy balance improved by the intensive use of waste heat from the rotary kiln, for example for meal drying process and for preheating the raw meal, enormously. Environmental protection guidelines and the associated legal emission limit values led to the fact that modern cement plants consider these factors increasingly.

Itself a problem aggravating with increasing greenhouse effect is however the high output of carbon dioxide. World-wide annually 1.4 billion tons cement are manufactured, which contains on the average about 60% CaO. Thus in the case of optimal processing an output of at least a billion ton of CO 2 or 4% of the annual CO 2 results - output.

consumer

the largest need of cement has the People's Republic of China. There approximately 45% of world-wide production are blocked.

Yearly cement consumption per head of the population an interesting characteristic is economical. In countries such as Indonesia become only approx. 15 to 20 kg per inhabitant annually needs; in countries such as Singapore or the Arab countries consumption can be more than 2,000 kg per inhabitants and year. Consumption in Germany has values around approximately 350 kg per inhabitants and year. The annual consumption at cement is so an important characteristic for the intensity of building activity in a region.

list of the largest cement producers

in the following table the largest producers of cement are specified (in million tons).

Country struggled 1970 1980 1990 2000 2002
1. VR China 10.000 79.860 209.712 583.404 725.000
2. India 14.000 17.700 45.720 102.084 108.144
3. The USA 67.700 67.884 70.944 87.846 91.266
4. Japan 57.200 87.957 84.444 81.070 72.012
5. South Korea 8.200 15.636 33.912 51.420 56.820
6. Spain 16.700 28.008 28.092 38.115 42.336
7. Brazil 9.000 27.192 25.848 39.564 42.192
8. Italy 33.100 41.333 40.548 39.588 42.048
9. Russia 29.600 38.745 42.640 32.389 39.672
10. Mexico 7.300 16.260 24.504 33.876 33.348
11. Turkey 6.400 12.876 24.636 35.796 32.508
12. Thailand 5.300 6.732 25.500 32.004 32.244
13. Indonesia 6.200 7.800 14.748 22.789 31.200
14. Germany 46.300 46.991 37.632 36.635 30.972
15. France 29.000 29.100 26.508 20.191 20.004
16. Taiwan 2.900 3.700 21.800 17.572 19.363
17. Egypt 3.700 3.012 13.284 15.600 16.500
18. Greece 4.800 12.672 13.944 14.500 15.500
19. Malaysia 3.100 3.900 7.400 11.445 14.328
20. Canada 7.300 10.349 11.808 12.612 13,200
World 569.800 867.700 1,140, 000 1,660, 000 1,800, 000


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