Composition of cement
Cement is an inorganic substanceof artificial origin, which serves to connect materials in construction. As a rule, cement now means Portland cement and cement from Portland cement clinker. Cement is a part of plaster, masonry mortars and concrete. An important feature of cement, distinguishing it from air lime and gypsum, is that it is able to solidify in a moist environment.
What is cement produced from?
The composition of cement includes mineral rockscarbonate (limestone, marl, chalk, other rocks of carbonate-argillaceous, limestone or dolomite composition) and clay (clay, clayey shale, loam, loess and loess-like loam) groups, and mineral additives. As a rule, cements produced in different regions differ in composition from one another. This is due to the fact that cement production is usually located at the site of mining.
The choice of rock for the production of cement is mainlyis dictated by its physical properties and structure. Thus, the use of crystalline rocks is avoided, because they are less likely to interact with other components of the cement.
- Chalk - one of the most widely used for cement production, due to its softness and fragility.
- Mergel is a rock, intermediate between limestone and clayey. Its structure and properties are different and depend on the content of clay impurities.
- Clay - a mixture of various minerals, which has plasticity in a moistened state.
- The loam besides clay contains a considerable amount of particles of sand and dust.
- Clay slate is a solid rock that is less damp than clay and has the ability to stratify into thin layers.
- Less - a porous rock from clay, quartz, feldspar and other silicates.
- Loess-like loam is a material transitional from loam to timber.
These are important components of cement, serving forimprovement of its properties (elasticity, speed of solidification and others). As a rule, siliceous, aluminous, clay-containing additives and fluorspar are used.
About chemistry of cement
To improve the properties of cement in its composition, various oxides are introduced.
- Aluminum oxide determines the refractory properties of cement. In good cement, 60% of aluminum oxide is found.
- Calcium oxide is responsible for the strength of cement. According to the content of this oxide cements are divided into highly limy (from 40% calcium oxide) and little-lime (up to 40% calcium oxide).
- Iron oxide is contained in cement in a small amount (up to 25%), tk. adversely affects the fireproofness of the material.
- Magnesium oxide (up to 2%)
- Silicon oxide (up to 10%)
Avoid including in the chemical composition of cement chromium oxide, which reduces the chemical reactivity of the material.
Types of cement
Consider the classification and the main types of cement. According to the basic mineral, which is a part of the cement, the cements are divided into:
- Portland cement is the most popular type in construction, with alit and portland cement clinker prevailing.
- Romantsement - today rare, not produced cement, the composition prevails belit.
- Magnesian, otherwise known as Sorel's cement, cement is made from magnesite and mixed with an aqueous solution of various salts.
- Alumina cement - in its composition Al prevails2O3.
- Acid-resistant cement - is made from silica and quartz sand, mixed with a solution of liquid glass.
- Mixed cements are obtained from the above species, which are combined with other mineral, astringent additives and slags.
On strength properties, cement marks are distinguished. For graduation, apply this test: compress the halves of prismatic samples from a solution of cement with quartz sand in a ratio of 1: 3 of 40x40x160 mm and measure the tensile strength of such a sample.
Cement strength grades are numbers from M100 to M600 in increments of 50 or 100, denoting the cement strength in kg / cm2. M100-M300 for today is no longerare produced. M600 is also known as "fortification" or "military" cement, it is especially appreciated for high strength indicators and therefore costs much more than the M500. It finds its use in the construction of bunkers, missile silos and other defense facilities.
In addition to strength all the cements are divided intoclasses. The strength class of cement is a number from 30 to 60, denoting the compressive strength in MPa. The affiliation of cement to a certain class of strength means that 95 out of 100 samples from 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,of which cement is made, and found out what should be paid special attention when choosing cement for various construction works. Now you are all about it.