When performing active work with building mixtures, one has to learn to determine their characteristics using special devices or by visual signs. If necessary, quality control of concrete can be carried out both in liquid and in already hardened state, when the structure is completely ready.
How to determine the parameters of a mixture in a liquid state?
Good concrete is usually gray. 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 batch was made by hand. By doing an independent check, you can learn a lot about the quality characteristics of the products. The parameters of the mixture in a liquid state can be found in laboratory tests.
Hardened material control
A more accurate assessment of the quality of concrete can be made after it finally hardens, when twenty-eight days have passed from the moment the pouring was made.
Control can be non-destructive and destructive. In the first case, testing is carried out with different instruments, the readings of which are not particularly accurate, and in the second case, a sample is taken directly.
Nondestructive methods
The following types are distinguished:
- Tearing off disk elements involves stress relieving produced by local failure.
- Chipped ribs, which can allow to determine the characteristic linear structure in the form of columns, piles and beams. The method cannot be performed if the protective layer does not exceed two centimeters.
- Tearing off with chips is the only non-destructive testing method by which everything is officially regulated, including calibration dependence. When passing the test, you can sometimes see high accuracy.
- The elasticity of the rebound may provide the ability to measure the magnitude by which the projectile will move after impact on the structural surface. The tests are carried out with spring hammers.
- The shock pulse allows you to record the energy of the strike, formed when the striker comes in contact with the surface. Such devices may be compact in size.
- Plastic deformation is based on measuring the size of the impression left by a steel ball impact.
Ultrasound check
It is possible to check the quality of concrete by the ultrasonic method using wave passes in the form of through and surface sounding. The difference is how the sensors are arranged.
Destructive methods
The following types of methods are used:
- cutting a sample from a concrete structure is performed by special equipment URB-175, equipped with a cutting device such as diamond discs;
- drilling is carried out using drilling machines of the type IE 1806. They have a diamond or carbide drill.
Before purchasing a ready-made mortar from the manufacturer, you need to find out if he has a quality certificate for concrete. This is not a prerequisite, but it gives an idea of the reliability of the company.
Concrete features
One of the key indicators of concrete quality is considered to be its workability (the ability of a solution to fill the form of a concrete product and be rammed in it under the influence of gravity or due to external mechanical stress). This feature of concrete is evaluated by indicators of rigidity and mobility. When concreting reinforced concrete monolithic structures, concrete mixtures are most often used.
Employees of the construction company are required to at least twice to monitor the mobility of the mixture. For concrete with mobility with a zero draft of cone, the stiffness of the mixture is determined in the building laboratory in accordance with the methodology used by the applicable standard. Rigidity is characterized by the period of vibration required to level and compact the preformed concrete cone in the device for determining stiffness.
Concrete mixture transportation
A correctly executed mixture delivery largely determines the quality of concrete by the time it is laid in the structure. In case of violation of the rules of transportation and supply of the mixture to the concrete systems, the concrete mixture loses its homogeneity - it exfoliates: the heavier components (gravel, sand, crushed stone) settle, and cement milk appears on top of the surface. Therefore, the specified mobility is violated and workability is reduced. Concrete quality is achieved by regularly monitoring the transportation and delivery of the mixture to the structure.
The foreman and the construction site master are required to regularly monitor the quality of the concrete mix. When laying with horizontal layers, the thickness of all laid layers is monitored according to the requirements of the project. The duration of the vibration ensures the compaction of concrete, the main properties of which are considered to be: the end of 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 when the concrete gains compressive strength of at least 1.5 MPa. The duration of these intervals is usually no more than 2 hours.
For the adhesion of a new layer of the solution to the already solidified surface, it is cleaned of debris, the cement film is removed with iron brushes, then it is washed with a stream of water under pressure. The remaining water from the recesses is eliminated. Before laying the new layer, it is necessary to 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 old concrete.
What affects the quality?
The quality of concrete largely depends on the conditions in which the composition is already after its laying. The hardening intensity is greatly influenced by humidity and ambient temperature. The laid concrete is kept in a wet state and protected from mechanical damage, shaking, sudden changes in temperature and quick drying.
What is used to save moisture?
To save moisture in concrete, liquefied bitumen, bitumen and tar and other emulsions are used that can quickly form a water-impermeable film on the surface of the concrete.
Concrete Quality Indicators
The most important indicators of concrete quality are strength. This is one of the most important indicators. It is the ability of concrete to withstand heavy loads and makes it almost indispensable in construction work. Concrete has 3 types of strength:
- compression, which assesses the ability of concrete to withstand compressive loads;
- tensile bending, which determines the property of concrete to withstand bending loads;
- axial tension, 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 tensile testing machines and presses.
- Frost resistance of concrete . Using this indicator, the ability of concrete to maintain its strength characteristics after alternating freezing and thawing is evaluated. Frost resistance is an important indicator for concrete used in places with harsh climates and cold winters.
- Water resistant concrete . This indicator assesses the ability of concrete to resist water seepage. It is used in places where there is direct contact with water.
- Corrosion resistance of concrete . Using this quality requirement, the ability to maintain its strength characteristics after exposure to an aggressive environment is evaluated. This indicator is important to consider when there is a risk of contact of concrete during operation with aggressive chemicals.
Concrete quality for foundation or other construction work is very important. It depends on him the life expectancy of the building and the safety of its operation.