Today it is difficult to imagine a construction field in which cement is not needed. It is used absolutely at all stages of the construction and interior decoration of any structure. Despite the development of technology, so far no material has been found that could show itself better than cement. In this article we will learn more about what cement is. Indeed, many people know how it looks and where it is used, but they don’t imagine what is hidden behind this gray powder, which hardens upon drying. We will also deal with the question of how to put stress in the word cement.
History
Before you figure out what cement is, let's take a look at history. This material has been known to mankind since ancient times, but before its discovery, people also built it. They used lime, gypsum, clay and even egg whites to fasten stone blocks. All of these materials slowly hardened and were not reliable enough. Then the builders began to mix the components: clay, crushed stone and volcanic ash were added to the lime. In combination with water, this mixture gave the desired effect. It was used in ancient Rome.
In the Middle Ages, builders also used lime mixed with clay. But the mixture began to pre-burn. This was the first cement. The word, translated from Latin, means “broken stone”. In fact, it is, because the frozen mixture is really as solid as stone. The correct stress in the word cement is placed on the second letter "e", and nothing else. The experiments on this material continued for quite some time. As a result, in the 19th century, the ideal proportion of components was found to maximize reliability. The optimum temperature for calcining limestone and clay was also established, at which the compound of lime with oxides is the most durable. She was 1450 degrees. Since then, cement has entered the construction industry very tightly.
What is cement: composition
Modern cement is a clinker powder, into which fillers and modifying additives are introduced. In dry form, it is a loose homogeneous mass of gray. When water is added, an astringent paste-like composition is obtained, which is well applied to rough surfaces. After the mixture hardens, a strong compound is obtained, which in density can be compared with a stone. That is why artificial stones are made of cement.
Now consider in more detail the composition of cement. When clay and limestone are heated to a temperature of about 1450 degrees, their structure changes. As a result, clinker granules are formed. Gypsum is added to them and the mixture is ground to a loose state. From the point of view of chemistry, the composition of the finished cement is as follows: 67% CaO (calcium oxide); 22% SiO 2 (silicon dioxide); 5% Al 2 O 3 (alumina); 3% Fe 2 O 3 (iron oxide); and 3% of related substances. Cement production is a very complex and time-consuming process that requires special equipment and specific technological conditions.
Mark
We have already learned what cement is and how to emphasize the word cement, now we will get acquainted with the main characteristics of this miraculous material. The main characteristic of this product is its brand. It is indicated by the letter "M", and the corresponding digital indicator. The figure shows the maximum load (in kilograms) that 1 cm 2 of cement can withstand. In simple words, it means the weight that cement can withstand without destruction. For example, if this weight is 400 kilograms, then the material receives the M400 brand. We will analyze the main brands of cement.
M400 . As you already understood, the strength of such cement is 400 kg / cm 2 . This is the most common and universal brand. It is used in all types of construction and finishing works. This may be: the construction of buildings, monolithic construction, the production of concrete slabs and blocks, as well as the manufacture of staircases, reinforced concrete rings, and other products.
M500 . Such cement has a strength of 500 kg / cm 2 . It is characterized by quick solidification and high strength. This brand is used in the monolithic construction of high-rise structures, for the manufacture of load-bearing elements and other cases where increased strength is required.
The compressive strength of cement is also called activity. Based on its measurements, the material is assigned the appropriate grade. The activity of cement depends on: the strength of clinker granules, the degree of grinding, and the presence of additives.
Types and additives
What is cement and what brands does it happen, we already know, but how else is it classified? In addition to grades, cements are also divided into types, each of which is distinguished by a special combination of individual components (additives). For example: quick-hardening, sulfate-resistant, grouting, and so on. Each of the types is designed for specific work. For example, cement for laying a brick is not suitable for building a pool.
The composition of the additives is indicated on the packaging along with the brand. It is indicated by the letter “D”, followed by the percentage of additives. For example, if the package says "D10", then this type of cement contains 10% of additives. Further there are symbols denoting the properties of these additives. Ultimately, cement labeling looks something like this: "M400D10PTs." In this case, “PC” refers to ordinary Portland cement. Consider what other characteristics determine the quality of cement.
Density
The lowest density is observed in freshly prepared cement. Its individual particles are repelled from each other by the action of electrostatic forces. In the process of transportation and storage, these forces weaken, the material is caked and compacted. The density is also affected by the degree of clinker grinding. In the calculations, they are set by the average density of the material, which is equal to 1300 kg / m 3 . However, in practice, this indicator depends on the storage conditions of the cement.
Specific and volumetric weight
The specific gravity (in construction practice) is, in fact, the same density. This concept is used to compile the correct proportion of cement mortar. Depending on the state of the mixture, the specific gravity may vary. Fresh cement powder has a density of about 1000 kg / m 3 , and the density of caked can reach 1500 kg / m 3 .
Volumetric weight is another identical concept of density. It is used to calculate how much cement is obtained from one kilogram. For example, a bag weighing 50 kg contains 0.04 cubic meters of material if its density is 1300 kg / m 3 .
Shelf life
Despite the fact that cement is an inorganic material, its shelf life has a clear framework. Under normal conditions, in an unpressurized packaging, cement is stored for only 2 months. If you place it in a sealed package, you can extend this figure to a year. Of course, old cement can be used, but its strength characteristics will not be the same.
Moreover, the higher the grade of cement, the faster it loses its properties. For example, the material of the M500 brand, after a month of storage in conditions of high humidity, will have the properties of the M400 brand, and so on.
Cement bags are recommended to be stored in dense plastic bags, at a height of at least 0.3 meters from the floor. In special bags, the material is stored much longer than in loose form.
Solidification time
A properly prepared solution sets and hardens within a few hours. In the summer, it takes only 2-3 hours to completely harden the cement, and in winter it will take much more time. At zero temperature, it can take up to 20 hours to harden the solution. To speed up or slow down the hardening process, special additives are introduced into the solution.
Fineness of grinding
The higher the degree of grinding of the particles, the faster the solution will harden, and the more reliable it will serve in the future. The fineness of grinding depends on the quality and characteristics of the equipment used in cement plants. The optimal particle size is considered to be 40-80 microns.
Strength class
In regulatory documents, a term such as “cement grade” is transformed into a “strength class”. Material testing for compliance with its strength of a particular class is carried out in factory laboratories. At the same time, modern equipment and advanced analysis methods are used.
In the laboratory, the fineness of grinding, the density of the aqueous solution and the setting time of the cement are measured. The hardened specimens also determine the side-by-side bending and compression strength.
Certification
Certification of cement was previously carried out in accordance with GOST 10178085, 30515 97. However, recently, most large enterprises have already switched to GOST 31108-2003, which was adopted in 2004. The document spells out more stringent requirements for the quality of cement and the criteria for its testing. These standards are fully consistent with European quality standards.
Cement and concrete
Consider another problem that arises as often as improper stress in the word cement. What is the correct name for the material, we have already figured out, and how does it differ from concrete? Many people think that these are identical concepts. In reality, of course not. Concrete is called hardened cement mortar. It includes cement, fillers and water. As a filler, sand is most often used. Sometimes also used: gravel, screenings, slag, expanded clay and so on. Until the moment of hardening, the cement mortar is a mobile mixture. In order not to cause sellers of construction stores to be perplexed and tempted to deceive you, remember what emphasis in the word cement is correct and how this material differs from concrete.
Conclusion
So, we figured out what cement is. The value of this material in modern construction is difficult to overestimate. Nevertheless, many people who are far from this industry do not even know what this useful material consists of and blush when children ask them about it. Now we know what cement is and how to put emphasis in the word cement.