Cement is an inorganic substance of artificial origin that serves to combine materials in construction. As a rule, under the cement now mean Portland cement and cement from Portland cement clinker. Cement is a part of plastering, masonry mortars and concrete. An important feature of cement, distinguishing it from air lime and gypsum, is that it is able to harden in a moist environment.
What is cement produced from?
The cement includes carbonate mineral rocks (limestone, marl, chalk, other carbonate-clay, limestone or dolomite rocks) and clay (clay, shale, loam, loess and loess-like loam) groups, as well as mineral additives. As a rule, cements produced in different regions differ from each other in composition. This is due to the fact that the production of cement is usually located at the place of extraction of rocks.
The choice of rock for cement production is mainly dictated by its physical properties and structure.So, avoid the use of crystalline rocks, due to the fact that they are worse to interact with other components of the cement.
- Chalk - one of the most widely used for the production of cement rock, due to its softness and brittleness.
- Marl is a rock intermediate between limestone and clay. Its structure and properties are different and depend on the content of clay impurities.
- Clay - a mixture of various minerals, with plasticity in a moist state.
- In addition to clay loam contains a significant amount of sand particles and dust.
- Shale is a hard rock with less moisture than clay, which has the ability to delaminate into thin layers.
- Less is a porous rock made of clay, quartz, feldspar and other silicates.
- Loess loam is a transitional material from loam to loess.
These are important components of cement that serve to improve its properties (elasticity, solidification rate, etc.). As a rule, silica, aluminous, clay-containing additives and fluorspar are used.
About cement chemistry
To improve the properties of cement, various oxides are introduced into its composition.
- Aluminum oxide causes the refractory properties of cement. Good cement contains 60% alumina.
- Calcium oxide is responsible for the strength of cement. According to the content of this oxide, the cements are divided into high limestone (from 40% calcium oxide) and low limestone (up to 40% calcium oxide).
- Iron oxide is contained in cement in small quantities (up to 25%), because adversely affect the refractoriness of the material.
- Magnesium Oxide (up to 2%)
- Silicon oxide (up to 10%)
Avoid inclusion in the chemical composition of cement chromium oxide, which reduces the chemical reactivity of the material.
Types of cement
Consider the classification and main types of cement. According to the main mineral included in the composition, cements are divided into:
- Portland cement is the most popular type in construction, and alit and portland cement clinker prevail in composition.
- Romancement - today rare, not made cement, the composition is predominantly white.
- Magnesia, otherwise known as Sorel cement, cement is made from magnesite and mixed with an aqueous solution of various salts.
- Aluminous cement - Al prevails in its composition2O3.
- Acid-resistant cement - made from sodium silicofluoride and silica sand, kneaded with a solution of liquid glass.
- Mixed cements are obtained from the above types, which are combined with other mineral, astringent additives and slags.
For strength properties distinguish brand cement. Such a test is used for the gradation: the halves of the prismatic samples from the cement solution with quartz sand are compressed in a ratio of 1: 3 of size 40x40x160 mm and the tensile strength of such a sample is measured.
Cement strength grades are numbers from M100 to M600 in increments of 50 or 100, indicating cement strength in kg / cm2. M100-M300 today is no longer produced. M600 is also known as “fortification” or “military” cement, it is especially valued for its high strength properties and is therefore much more expensive than the M500. It finds a use in the construction of bunkers, rocket mines and other defense facilities.
Additionally, the strength of all cements are divided into classes. Cement strength class is a number from 30 to 60, denoting compressive strength in MPa. Belonging to a certain strength class of cement means that 95 out of 100 samples of this cement correspond to this class. At the end of the 20th century there were about 30 varieties of cement.
In this article, we examined in detail what the cement consists of and found out what to pay special attention to when choosing cement for various construction works. Now you are all about this.