What is concrete? — it is the strong construction mix consisting of a filler (sand, gravel, crushed stone, etc.), binding substance (cement) and water, and also various additives improving quality of mix, such as frost resistance, water tightness, durability, plasticity.
Concrete happen usual — for building of individual constructions and industrial buildings, and also special — for pavings, hydraulic engineering constructions. Distinguish still the heat-resistant concrete resistant to chemical influences, sound-absorbing, the concrete used for nuclear objects and others. Also concrete distinguish on volume weight — heavy to 2500 kg/m3, especially heavy — from 2500 kg/m3, the easy 1800-2200 kg/m3 facilitated to 1800 kg/m3.
Concrete durability on compression is among basic parameters of concrete. Till 1986 at design of designs from concrete the term "Concrete Brand" was used. The brand is designated by a letter "M" with number which displays an average value of durability of a sample of concrete on compression in kgf/cm2.
The brands of commodity concrete applied in construction: M50, M75, M100, M150, M200, M250, M350, M400, M450, M550, M600, M6OO, M700, M800.
Now, after acceptance the Construction Norms and Regulations 20301-84 when performing calculations of concrete and reinforced concrete constructions are used not brand of concrete, but durability class at compression or stretching. The marked indicator is displayed by a letter B with a digital combination, kakovy indicates the guaranteed durability in MPa, that is on durability reached in the majority of tests (in 95% of cases).
The concrete classes applied in construction: B1; B1,5; B2; B2,5; B3,5; B5; B7,5; B10; B12,5; B15; B20; B25; B30; B40; B45; B50; B55; B60.
Concrete is everywhere used in modern construction, both individual structures, and industrial facilities.