Grades and classes of concrete and cement mortars, fields of application

Concrete  is a man-made stone. Mixing of four components - cement, fillers (crushed stone, building sand) and water. Concrete is a composite material - the result of molding and hardening. The main component is cement of a certain brand, thanks to the cement, the mixture after hardening acquires properties that are not inferior to natural stone.

The brand and (or) class of concrete is the most important indicator characterizing the strength of concrete.

Axial compressive strength - the ability of a concrete mixture to resist destruction from external loads.

Depending on the axial compressive strength index, concretes are subdivided into classes. The class is designated by the letter "B" and numbers indicating the withstand pressure in megapascals (MPa).

Along with the classes, the strength of concrete is also set by the marks designated by the letter "M" and the numbers 50-1000, showing the ultimate compressive strength in kgf / cm2, and the higher this figure, the heavier the concrete.

CORRESPONDENCE BETWEEN CLASSES AND BRANDS

CONCRETE М100 B7.5

М100 B7.5 is the worst concrete grade. Main application: preparatory concrete work, laying a thin layer on compacted soil or sand cushion.

In construction, concrete M100 B7.5 is used quite often, but as an unloaded layer - preparation for monolithic supporting structures, floors concreted on the ground.

When carrying out preparatory work, M100 B7.5 is cast on compacted soil or a layer of sand. The purpose of the preparation from concrete M100 B7.5 is to prevent the leakage of cement laitance from the monolithic bearing structures into the ground and, accordingly, the ingress of moisture from the outside so that the concrete of the main structure retains its strength characteristics.

Used concrete M100 B7.5 and in road construction as a preparation for the main roadbed. M100 B7.5 concrete is used as a grout for fixing curbs, installing small architectural forms and in other irresponsible structures.

CONCRETE М150 B12.5

Ready-mix concrete М150 B12.5 is used as a preparatory material for screed floors and concrete sidewalks, pouring strip foundations, monolithic slabs.

Concrete M150 B12.5 has sufficient strength, which makes it the main brand used for laying concrete paths and slabs.

CONCRETE М200 B15

M200 B15 concrete is used in the manufacture of concrete screeds for floors, foundations, blind areas, paths. The strength of M200 B15 is sufficient for solving most of the tasks of individual construction: foundations (tape, slab, pile-grillage), production of concrete stairs, platforms.

In road construction, concrete M200 B15 is used to create a monolithic cushion for the main road pavement.

CONCRETE М250 B20

M250 grade is used mainly for the manufacture of monolithic foundations, including strip, slab, pile-grillage, lightly loaded floor slabs, fences, stairs, retaining walls.

CONCRETE М300 B22.5

The most frequently ordered concrete grade (this also applies to M200 B15). The combination of technological qualities and a relatively low price of concrete of this brand makes its use universal for almost any construction needs. M300 B22.5 is suitable for a monolithic or strip foundation for almost any house, including a country cottage.

CONCRETE М350 B25

The main application of М350: production of load-bearing walls, floor slabs, beams, columns, reinforced concrete structures and products, casting of monolithic foundations.

CONCRETE М400 B30

The main application of the M400 is: pouring pool bowls, cross beams, hydraulic structures, retaining walls, bridge structures, basements of monolithic buildings.

CONCRETE М450 B35

М450 is used for bridge structures, hydraulic structures, bank vaults, in the metro construction.

Cement mortar 

Cement mortar  - does not contain coarse filler, it has three components - water, cement and sand. The cement slurry is greatly influenced by additives and plasticizers, which are introduced into the mixture during mixing. The additives increase the quality characteristics of the solidified solution - water resistance, frost resistance, additional strength, etc.

In accordance with GOST 28013-98, cement slurries differ in compression strength grades.

Table of applications depending on the strength grade of the cement mortar

1. Simple solutions.

Mixed on the basis of one binder ( cement , gypsum, lime, water glass, clay).

2. Complex solutions.

Made with the addition of mixed powder materials. Mixtures can be lime-gypsum, cement-lime, cement-clay.

By composition, cement mortars are divided into the following types:

1. Cement-sandy. The mortar is mixed with the addition of sand, which is a component that forms a crystalline structure and prevents shrinkage and cracking. Used sand of medium fractions. Cement mortars are used for masonry and plastering walls. Cement plaster is durable, vapor permeable and resistant to mold and mildew. It can be applied to all types of coatings, including decorative tiles, as well as to decorate the exterior walls of buildings.
2. Cement-lime. Cement-lime plaster combines two binders, of which cement is a water-hardening binder, and lime is air. Slaked lime reduces the cost of the mortar, and also works as a plasticizer, increasing its mobility. Cement-lime plaster can be used for finishing any premises, including wet ones, as well as building facades. Its advantages are plasticity, strength, layering capabilities, moisture resistance, resistance to mold, mildew, availability and cost-effectiveness
3. Cement-gypsum mortar - the advantage is fast hardening, percentage, the disadvantages are fragility, and the incompatibility of the components - gypsum is acidic, while cement is alkaline. It is also possible the appearance of  ettringitis or cement bacillus -  calcium hydrosulfoaluminate - ettringite. Formed in the cement stone, in the presence of increased dosages of gypsum, this substance greatly increases in volume and literally breaks the cement stone into powder. calcium hydrosulfoaluminate - ettringite - is a good and useful thing for the strength of concrete. But within reasonable limits! The degree of this rationality is controlled even at the cement plant, by adjusting the amount of gypsum introduced during grinding, depending on the specific raw material base for the production of clinker.
4. Cement-clay mortar. Clay is used in masonry mortars due to its cheapness, plasticity and durability. Among other things, it has quite good adhesion, but it does not resist water well and hardens for a long time. Cement-clay mortar is characterized by plasticity, thanks to clay, and frost-resistant, and, thanks to cement, it withstands moisture well. Suitable for almost any work with stone and ceramics. Used for masonry

Difference between grout and concrete.

The main difference between concrete and cement mortar is that concrete contains a large aggregate - gravel or crushed stone. But the cement mortar contains only building sand as a filler.

Another difference follows from this - the use of building mixtures. Parts of supporting structures are made of concrete, and cement mortar is used to fill joints, plaster and to treat other surfaces.

Concrete has a wider scope of application in construction work, because it is stronger than cement mortars. But it cannot be used as a decorative coating for finishing individual elements of the structure. Cement mortars, in comparison with concrete mix, age quickly, become covered with cracks, and then crumble.