Concrete grade or grade? How to classify concrete when building your own house?

Most of the developers of individual houses classify concrete using a concept such as a concrete brand. Nevertheless, this building material has one more characteristic - a class. What is the reason for such selectivity, and what is the difference between a brand and a class?

Concretes are the most common, unparalleled, building material, and second in use, after water, resource on Earth. They represent an artificially obtained stone formed as a result of the solidification of a homogeneous mass of components mixed in certain proportions, such as cement, water, fillers and / or modifying additives.

There is a fairly large number of very different concretes, differing in purpose, and in type and type of the main binder, as well as fillers - both in terms of maturation and in structure. Nevertheless, in spite of all this diversity of concretes, there are only three basic qualitative characteristics that are used in calculations for the design of future objects - strength, waterproofness and frost resistance. To determine the numerical values of these important properties of concrete , the concepts of brand and class were introduced.

For example, widely used in individual construction for the erection of various foundations, 200 grade concrete belongs to class B 15 and has frost resistance - F75-F100 and water resistance - W2-W4.

Of course, the first question begs the question of what the brand of concrete is and what is its difference from the class.

It should begin with the fact that classes and grades of concrete are extremely strength characteristics, however, having some nuance in practical application.

The brand of strength is A standardized numerical value obtained as a result of laboratory tests on compression and tension. In other words, it is a quantity that determines what maximum mechanical load the square centimeter of the surface can withstand. Since concrete is characterized by a build-up of strength with time, then the standard samples (molded cubes with a side of 10 centimeters) undergo aging at least 28 days old. Existing brands of concrete - in the range from M50 to M800 (with increasing density on the rise of the numerical index). For individual construction, concretes not higher than grade 400 are used.

However, the strength declared by the brand is precisely the laboratory value, since in practice it is affected by a number of destabilizing factors, such as violations in manufacturing technology, sand and water quality mismatch, changes in laying and setting conditions. All this leads to a decrease in strength characteristics. And this error, or coefficient of variation, is the main difference between the class of concrete and its brand. In fact, this is just the actual strength with a small (5%) deviation. In practical application, the concrete class is an important design value used (as opposed to the brand) in the design of future structures. Measured in MPa, and regulated by GOST 26633-85. In total, there are sixteen strength classes in the range from B 3.5 to B 60.

The following qualitative characteristics - water resistance and frost resistance - are classified only by grade.

A grade of concrete that characterizes frost resistance is also a laboratory value. It is the maximum numerical value of the number of tests during which the sample was subjected to alternating freezing and thawing. Frost resistance is determined by eight brands in the range from F 50 to F 500.

Another quality characteristic - a brand of concrete for watertightness. To classify by watertightness, six grades are used in the range from W2 to W12, which is the maximum value of the water pressure at which the reference samples are capable of not passing water (under the standard test conditions).