Most builders of individual houses classify concrete, using such a concept as concrete grade. However, this building material has another characteristic - class. What is the reason for such selectivity, and what is the difference between brand and class?
Concrete is the most widespread, unparalleled building material and the second most consumed resource on Earth after water. They are artificially obtained stone, formed as a result of hardening 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 both in purpose, and in the type and type of the main binder, as well as fillers - both in terms of maturation and in their structure. Nevertheless, despite all this variety of concretes, there are only three main qualitative characteristics that are used in calculations when designing futureobjects - strength, water resistance and frost resistance. To determine the numerical indicators of these important properties of concrete, the concepts of brand and class were introduced.
For example, widely used in individual construction for the construction of various foundations, concrete grade 200 belongs to class B 15 and has frost resistance - F75-F100 and water resistance - W2-W4.
Of course, the first question that arises is what is a brand of concrete and how does it differ from a class.
We should start with the fact that classes and grades of concrete are exclusively strength characteristics, however, having some nuance in practical application.
The strength grade is
standardized numerical value obtained from laboratory compression and tensile tests. In other words, this is a value that determines what maximum mechanical load a square centimeter of the surface can withstand. Since concretes tend to increase in strength over time, reference samples (cast cubes with a side of 10 centimeters) are tested at a maturation age of at least 28 days. Existing grades of concrete - in the range from M50 to M800 (with an increase in density as the numerical index increases). For individual construction, concrete not higher than grade 400 is used.
However, the strength declared by the brand is precisely a laboratory value, since in practice it is affected by a number of destabilizing factors, such as violations in technologymanufacturing, discrepancies in the quality of sand and water, changes in laying and setting conditions. All this leads to a decrease in strength characteristics. And this error, or the coefficient of variation, is the main difference between the class of concrete and its brand.
Essentially it's just the actual strength with a slight (5%) deviation. In practical application, the class of concrete is an important design value used (unlike the brand) in the design of future structures. It is measured in MPa, and is regulated by GOST 26633-85. There are sixteen strength classes in total ranging from B 3.5 to B 60.
The following quality characteristics - water resistance and frost resistance - are classified by brand only.
The brand of concrete, which characterizes frost resistance, is also a laboratory value. Represents the maximum numerical value of the number of tests during which the sample was subjected to alternate freezing and thawing. Frost resistance is determined by eight grades in the range from F 50 to F 500.
Another quality characteristic is the brand of concrete for water resistance. For water resistance classification, six grades are used ranging from W2 to W 12, which represent the maximum water pressure at which the reference samples are able to keep water out (under standard test conditions).
