Mark and class of concrete for strength
Class and brand are the main parameters by which to choose concrete. In fact, these indicators indicate how concrete becomes solid when hardened. As a rule, this occurs on day 28 after the mixture is laid. It is then that it acquires its basic characteristics. The brand of concrete is denoted by the letter "M" and numbers from 50 to 800. For example, the M50 has a strength of 46 kgf / cm2, and the M800 has 786 kgf / cm2( high-strength concrete).The most popular are the M100( 98 kgf / cm2), M150( 131 kgf / cm2), M250( 262 kgf / cm2), M350( 327 kgf / cm2), M400( 393 kgf / cm2), M550( 524 kgf / cm2).
The class of concrete is usually denoted by the letter "B" and the figure from 3.5 to 80. Each class means the strength of concrete in MPa( when compressed).For example, B7.5 in 95% of cases can withstand a pressure of 100 MPa. The higher the class, the higher the compressive strength of concrete. As a rule, on the package all these data are in the form of a separate table. If suddenly there is no such parameter, then it can be determined only on the 28th day the solidification field of the mixture. To check the strength of concrete on day 7 is simply useless, since its characteristics improve only over time.
How to choose concrete?
Choose one or another type of brand and class in accordance with the design of the building or structure. In the event that the project does not have a design, you will have to deal with it yourself. As already mentioned, the brand reflects the solidification index. That is, in fact, the brands M100, M300 show what is the ultimate strength of concrete during compression, measured in kgf / cm2 for 28 days. The higher the brand, the higher its solidification parameter and the higher the cost of the mixture. Do not always choose the most expensive compounds and use them.
Yes, they have excellent quality, but they are more difficult to work with. In addition, they dry up much faster. Therefore, when building a concrete structure, it is important to find a certain balance. Let us give an example. Thus, M100 and M150 are often chosen for preparatory work. M200 is great for building a foundation, a blind area, tracks, floor screeds.
M350 - one of the most popular brands, as it is ideal for any responsible structures. More often it is used in commercial construction for the erection of walls, slabs, beams, etc.
Less commonly used are brands such as M400, M450.They are highly durable and therefore suitable for the construction of hydraulic structures and bridges. Well, the M500 and M550 for household purposes are not used at all. They are needed in the construction of dams, dams, metro and in many other cases where special conditions are necessary.
A few words about the quality of the
brewed mixture. If concrete is mixed in typical field conditions, then its quality can be determined by a number of external characteristics. First, the properly selected composition after mixing does not have gravel( gravel) grains that are not coated with the solution. Secondly, if a plastic compound is made, then it should not be followed by cement milk. Otherwise, it can be considered incorrectly selected.
Thirdly, when a rigid composition is assumed, then in appearance it resembles a moist soil. Fourth, determine the quality with the help of a cone. When the form is removed, the entire mass contained inside should not fall apart. That is, it completely sits down and does not emit cement water. Also, it should not be visible individual large grains( they must all be filled with a solution).