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BASIC TERMS

Concrete

Material obtained by mixing a cement, coarse-grained and fine-grained aggregates and water, with or without the inclusion of chemical additives, mineral additives or fibers, which improve its properties in hydration of the cement.

Concrete composition

The composition of concrete and composite materials of design and prescribed concrete should be selected so as to satisfy the requirements, specified for concrete mixtures and hardened concrete, including consistency, density, strength and durability, taking into account production processes and the intended method of execution of concrete work.
When the specification of the concrete does not include detailed types and classes of constituent materials, the manufacturer should choose them from those with suitability for specific environmental conditions, set out in regulations, applicable at the place of use.
In the case of prescribed concrete its composition is determined by the given values.

Choice of cement

The cement shall have an established suitability, taking into account:

  • the manner of carrying out the works;
  • the intended use of concrete;
  • the aging conditions (e.g. heat treatment);
  • the dimensions of the structure (exothermic reaction);
  • environmental conditions to which the structure will be exposed;
  • potential reactivity of aggregates to the alkalis of the constituent materials.

Selection of aggregates

General provisions

The type and categories of aggregates, such as grain size, content of flat grains, resistance to freeze / thaw, abrasion resistance, content of fine particles are selected taking into account:

  • the manner of carrying out the works;
  • the intended use of concrete;
  • environmental conditions to which the structure will be exposed;
  • all requirements for exposed surfaces of aggregate or for mechanical performance of the finishing works of the concrete.

Use of chemical additives

The total quantity of chemical additives must not exceed the maximum dose, recommended by their manufacturer, and should not exceed 50 g of chemical additive (in the form in which supplied) per kg cement, unless found and taken into account the impact of greater dose on the characteristics and durability of the concrete.

Chemical additives used in quantities of less than 2 g / kg of cement must be dispersed in a part of the water for the concrete, with the exception of cases, where the homogeneous dispersion is not possible (for example, when a gel is forming). In this case can be used other methods for adding them into the concrete.

If the total quantity of liquids exceeds 3 l / m3 of concrete, in determining the water-cement ratio should be taken into account their water content.

When using more than one supplement, their compatibility must be verified by initial tests.

The use of water for concrete mixture

Recycled water from the manufacture of concrete by itself or in combination with potable, or underground water can be used as water for the preparation of concrete mixtures for constructions with or without reinforcement, or concreted metal parts, and also for prestressing elements, only under the condition of requirements of EN 1008.

Compressive strength

When determining the strength of the concrete, it must be done by samples, taken in accordance with EN 12350-1 and results shall be based on the testing of cylinders with dimensions 150/300 mm, or cubes with a size of the side of 150 mm, in accordance with EN 12390-1 and prepared and aged according to EN 12390-2.

Density

According to the density in an oven-dried condition concrete is defined as regular or normal, lightweight and hardened concrete. The density of the normal concrete in an oven-dried condition should be greater than 2 000 kg / m3 and does not exceed 2600 kg / m3. The density of lightweight concrete in an oven-dried condition should be in density limits, prescribed for this class. The density of the hardened concrete in an oven-dried condition should be greater than 2600 kg / m3.

When the density is defined as the set value, applies a tolerance of ± 100 kg / m3, unless otherwise required.

Response to fire

A concrete composed of natural aggregates, cement, chemical additives, mineral supplements, fibers or other inorganic composite material is classified as Euro Class A1 and does not require testing. According to BDS EN 206: 2014 / NA: 2015

Temperature to the concrete at work in winter conditions

If a temperature of the air during application of the concrete mixture is between -3° C and +5° C, the temperature of the concrete mixture must not be lower than +5° C. However, when using low thermal cement, or the quantity of a cement in the concrete composition is less than 240 kg / m3, the temperature of the concrete mixture must not be lower than +10° C, or the temperature prescribed in the project.

If a temperature to the air during application of the concrete mixture is less than -3 ° C, the temperature of the concrete mixture must not be lower than +10 ° C, or the temperature prescribed in the project. If a temperature to the air during application of the concrete mixture is less than -8 ° C, the temperature of the concrete mixture must not be lower than +15 ° C, or the temperature prescribed in the project.

Temperature to the concrete at work in summer conditions

For the production to the concrete mixture in summer conditions with an air temperature of over 30 ° C is necessary to take measures to prevent the temperature of the concrete mixture to exceed 30 ° C.

Note: The temperature of the concrete mixture shall be measured by an immersion thermometer to a depth of not less than 100 mm. The scope of the thermometer should be in the range of -5 ° C to +50 ° C, or wider.

Environmental impacts are those chemical and physical exposures that are not considered as loads in the construction project, but on which influence concrete is exposed, and which influencing the concrete or reinforcement, or metal components inputted.

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