Quality of concrete: requirements, indicators

When performing active works with building compounds, one has to learn to determine their characteristics by means of special devices or by visual signs. If necessary, the inspection of the quality of concrete can be carried out both in the liquid and in the already hardened state, when the structure is completely ready.

How to determine the parameters of a mixture in a liquid state?

Good concrete, as a rule, has a gray color. Before pouring a freshly prepared solution, you need to make sure that the technological properties are at a high level, especially if the manufacturer can not inspire confidence or the kneading was done by hand. Having made independent check, it is possible to learn a lot about qualitative characteristics of production. The parameters of the mixture in the liquid state can be determined by laboratory tests.

Control of solidified material

A more accurate assessment of the quality of concrete can be made after it has finally solidified when twenty-eight days have passed since the casting was made.

Control can be non-destructive and destructive. In the first case, testing is carried out by different instruments, the indications of which are not particularly accurate, and in the second case, the sample is taken directly.

Non-destructive methods

There are the following types:

1. Tearing disc elements involves the removal of tension produced by local destruction.
2. The cleavage of the ribs, which can allow to determine the characteristic of a linear structure in the form of columns, piles and beams. The method can not be performed if the protective layer does not exceed two centimeters.
3. Tearing off with chips is the only way of nondestructive testing, according to which everything is officially regulated, including calibration dependence. When passing the test, you can sometimes see high accuracy.
4. The rebound elasticity can provide the ability to measure the amount by which the impactor moves after being exposed to the structural surface. Tests are carried out by spring hammers.
5. The impact pulse makes it possible to record the energy of the impact that occurs when the striker contacts the surface. Such devices may differ in their compact size.
6. Plastic deformation is based on measuring the size of the left print from being hit by a steel ball.

Ultrasonic testing

To check the quality of concrete by ultrasonic method it is possible with the help of wave passes in the form of through and surface sounding. The difference is in how the sensors are located.

Destructive methods

The following types of methods are used:

• Cutting out a sample from a concrete structure is executed with special equipment URB-175, equipped with a cutting device such as diamond disks;
• Drilling is performed using drilling machines of the type IE 1806. They have a diamond or carbide drill.

Before you buy a ready-made mortar from the manufacturer, you need to find out if he has a quality passport for concrete. This is not an obligatory condition, but it gives an idea of the reliability of the company.

Features of concrete

One of the key indicators of the quality of concrete is its workability (the ability of a mortar to fill the form of a concrete product and tamp down in it under the influence of gravity or due to external mechanical action). This feature of concrete is assessed by the stiffness and mobility indicators. When concrete reinforced concrete monolithic structures are concretely used, concrete mixtures are used.

Workers of the construction company must not at least twice control the mobility of the mixture. For concrete, in which the mobility with zero cone slump, the stiffness of the mixture in the laboratory is determined in accordance with the methodology according to the applied standard. The stiffness is characterized by the period of vibration required to equalize and compact the preformed concrete cone in the stiffener.

Transportation of concrete mixture

Correctly made delivery of the mixture largely determines the quality of concrete by the time it is placed in the structure. If the rules for transporting and feeding the mixture into concreting systems are violated, the concrete mixture loses its uniformity: it breaks up: heavier components (gravel, sand, gravel) are deposited, and cement milk appears on top. Therefore, the given mobility is disrupted and the workability is reduced. The quality of concrete is achieved by regular monitoring of the transportation and supply of the mixture in the structure.

The foreman and the master of the construction site are required to regularly monitor the quality of compaction of the concrete mix. When stacking with horizontal strata, the thickness of all laid layers is kept in accordance with the requirements of the project. The duration of the vibration ensures compaction of concrete, the main properties of which are considered: the end of the settling of the mixture, the appearance of cement milk on its plane, the termination of the separation of air bubbles from it.

The resumption of concreting after a pause is permitted only if concrete is compressed with a compressive strength of at least 1.5 MPa. The duration of these intervals, as a rule, is not more than 2 hours.

For the adhesion of a new layer of mortar to the already hardened surface, it is cleaned of debris, the cement film is removed with iron brushes, then it is washed with a jet of water under pressure. Remain the remaining water from the depressions. Before laying a new layer, you must put a layer of cement mortar on the surface of the old concrete, the thickness of which is 20 mm of the same composition as in the old concrete.

What affects the quality?

The quality of concrete largely depends on the conditions in which the composition is already after the installation. The intensity of solidification is strongly influenced by the humidity and ambient temperature. The laid concrete is kept in a wet condition and protected from mechanical damage, shaking, sudden temperature changes and rapid drying.

What is used to conserve moisture?

To save moisture in concrete use diluted bitumen, bitumen and tar and other emulsions that can quickly form a waterproof film on the concrete surface.

Concrete quality indicators

The most important indicators of the quality of concrete include strength. This is one of the most important indicators. It is the ability of concrete to withstand heavy loads and makes it almost indispensable for construction work. Concrete has 3 types of strength:

• On compression, according to which the property of concrete is evaluated to withstand compressive loads;
• On stretching during bending, on which the property of concrete is determined to resist the bending load;
• On the axial extension, which determines the ability of concrete to withstand tensile stresses over the entire cross-sectional area.

Strength is determined by testing standard concrete samples on tearing machines and presses.

• Frost resistance of concrete . With the help of this indicator, the ability of concrete to retain its strength characteristics after alternating freezing and thawing is evaluated. Frost resistance is an important indicator for concrete used in places with severe climate and cold winters.
• Water resistance of concrete . This indicator assesses the ability of concrete to resist water percolation. It is used in places where there is direct contact with water.
• Corrosion resistance of concrete . With the help of this quality requirement, the ability to retain its strength characteristics after an aggressive environment is evaluated. This figure is important to take into account when there is a risk of contact with concrete during operation with aggressive chemicals.

The quality of concrete for foundation or other construction work is very important. It depends on it the life span of the building and the safety of its operation.