Concrete is what? What classes of concrete exist?

Concrete is an artificial stone material for construction, which is obtained as a result of molding and solidification of a properly selected mixture, including astringent, water, and also small and large fillers. All this is undergoing compulsory compaction. In some cases, special additives are used, and when it comes to asphalt concrete, water is not used at all.

Components

At its core, concrete is a mixture of cement and water, as a result of the reaction between which a cement stone is formed, which binds the fillers in a single monolith. The structure and properties of concrete depend on these substances. They change its degree of porosity, reaction to the effects of loads, the time of solidification, and also significantly reduce the deformation of concrete during its solidification. Concrete has become the main building material used in all areas due to the fact that it provides ample opportunities for obtaining mixtures with different properties with the addition of various fillers. It is these characteristics that open up such wide opportunities for application.

Concrete is a durable material with a high degree of fire resistance, its density, strength and other characteristics can be changed, giving it some specific properties. When properly processed from the mixture, it is possible to make structures of the required shape from the positions of architecture and construction mechanics.

A bit of history

As an artificial building material consisting of water, fillers and binders, concrete is known from the deepest antiquity. More than seven thousand years ago it was used by residents of the Mesopotamian River to build economic buildings and dwellings. He also used the builders of the Great Pyramids. By the ancient Romans, the construction of concrete was brought to a new level - after themselves they left not only the foundations of buildings, but entire blocks of concrete buildings. The design features of Roman roads, domes, vaults and floors from this material have not lost their significance. However, in the Middle Ages the technology of manufacturing Roman concrete was irretrievably lost.

Of course, ancient concrete is not the same as modern. The main difference is in the composition, at that time there was no cement in it. As an astringent, gypsum, lime or clay was used.

Characteristics

The strength of concrete is the most important characteristic of concrete, which has a direct impact on the operational parameters of the material. This term is commonly understood as the ability of concrete to withstand the effects of aggressive media and external mechanical forces. This value is determined by the methods of control: ultrasonic and mechanical. GOST 18105-86 specifies the rules for testing the strength of concrete for bending, stretching and compression. One of the characteristics is the coefficient of variation, which demonstrates the homogeneity of the mixture.

In accordance with GOST 10180-67, the ultimate strength of concrete is determined by compressing a control cube having a rib size of 200 millimeters at the age of 28 days. This type is called cube strength. In addition to GOSTs, SNiPs are also used to determine the strength. For example, the minimum formwork strength of concrete horizontal unloaded structures with a span length of up to 6 meters should be at least 70% of the design strength, and at a length of more than 6 meters - 80% of the design strength. In this case, strength is the most important property. Like natural stone, this material is more resistant to compression than to stretching, so it is the strength limit for this indicator that is chosen as the main criterion.

Properties

Concrete is a material for which strength is a characteristic that grows as a result of the physicochemical processes of interaction between cement and water, which passes properly in moist and warm conditions. If the material freezes or dries, this process will be completed. Previously, drying or freezing affects negatively on the final characteristics of the material.

Uniformity

Together with all other factors, the uniformity in strength depends on the quality and content of the fillers used, especially if some properties of the latter do not allow the concrete to obtain the required strength. Therefore, this parameter is associated with the previous one, although the experimental data show that such a relationship does not always take place. With increasing uniformity of concrete, there are opportunities for its more effective application.

The homogeneity index is determined as a result of the tests carried out on control samples made from working concrete with certain specified properties. For example, in the process of calculating this indicator, the results of a test of the same age and storage conditions of age-old material samples are taken into account. Uniformity in water resistance is determined by testing samples of the same thickness under the conditions of using the same methods.

Density

This characteristic of concrete is rather difficult, as it varies depending on which components are added to the mixture. To increase the density of concrete, you can use pozzolanic Portland cement, which expands, or aluminous cement, which does not form voids when it solidifies. The plasticizers additives influence this parameter, which often improve the characteristics of the ready-made mixture. If the composition of cement corresponds to GOST, then its density will be known.

Classes

At the moment there are several types. Lightweight concrete is a material whose density is 500-1800 kg / m ³ . This class includes: foam concrete, expanded clay, aerated concrete, cellular, arbolite, perlite and vermiculite concrete. In such a mixture, the bearing capacity after hardening is rather small. The usual, or heavy concrete, is characterized by a density of 1800-2500 kg / m ³ . As a filler, gravel is used here. This type is used in industrial construction, which is provided by its increased resistance to wear. An especially heavy class of concrete is a material characterized by a density of more than 2500 kg / m ³ . Such mixtures are used for the construction of nuclear power plants, since they possess the properties of protection against ionizing radiation.

Concrete grade

This is another important characteristic of this material. The compressive strength index shows the resistance to axial compression. The concrete grade with respect to stretching shows resistance to axial stretching of the control samples. The frost resistance indicator shows the number of cycles of alternating thawing and freezing. The concrete grade for waterproofness shows at what one-sided hydraulic pressure the concrete will not pass water during standard tests.

conclusions

When constructing an object of any purpose, the right decision will be the purchase of ready-made concrete, manufactured in full accordance with GOSTs, since it is difficult to achieve the desired result when making it independently and without special equipment.