For the first time, they started talking about concrete in past distant centuries. However, over this time period, this material, like other construction products, has gone through a long transformation path.
The very first concrete was discovered by archaeologists on the banks of the Danube in Yugoslavia in 5600 BC. At that time, this building material was made of gravel and local red lime.
Today, concrete should be understood as stone material of artificial origin, which is formed by hardening a well-mixed mixture with water, as well as coarse and fine aggregate, which are taken in view of a certain proportion.
Concrete strength
The most important characteristic for concrete is its strength. The strength gain of concrete depends on many factors. The hydration process itself consists of two stages:
- Grasping. This stage lasts about a day. Much depends on temperature. So, for example, at a temperature of more than 20 degrees, concrete needs three hours to set. If the temperature is zero, then this stage will last 15-20 hours.
- Hardening. This stage begins immediately after the previous action and lasts several years.
In any case, it should be noted that the set of concrete strength takes place only if there is moisture. The strength of concrete and the structure itself as a whole increases due to the interaction of this material with water.
It is also necessary to take into account the fact that the set of concrete strength is suspended both in hot and in cold weather. That is why, at high temperature, it is recommended to cover the freshly poured concrete with a wet burlap to prevent evaporation of water. Negative temperature indicators lead to freezing of water, which is part of the concrete mix. In the case of positive temperatures, the hydration process continues, however, by this time, the characteristics of this design are deteriorating, including the strength of concrete. For this reason, experts recommend adding a special substance during the preparation of concrete mortar.
Concrete strength classes
The main indicators of concrete include:
- Concrete strength class in case of axial compression.
- Strength class of concrete in case of axial tension.
There are several classes of concrete composition, the main of which are:
- Brand of concrete mortar depending on frost resistance. This mixture is used in the construction of structures that are alternately subjected to freezing and thawing.
- Brand of concrete mortar depending on water resistance. This composition is used in the construction of hydroelectric power stations, pools, canals and so on.
Concrete application
Depending on the technical and economic indicators, for the construction of each structure, the selection of the desired class and brand of concrete mixture is carried out individually. The strength of concrete in this case plays an important role. Experts recommend using concrete of a class of at least B-15 for reinforced concrete rod-type compressed elements. For arches and columns, it is best to use concrete of class B-20-B-30. For floor slabs and beams, concrete of class B-15 is suitable.