When performing active work with building mixtures, one has to learn to determine their characteristics using special instruments or by visual signs. If necessary, the quality check of concrete can be carried out both in a liquid state and in an 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 in 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 cannot inspire confidence or the batch was made by hand. Having made an independent check, you can learn a lot about the quality characteristics of products. The parameters of the mixture in the liquid state can be found in laboratory studies.
Hardened Material Control
A more accurate assessment of the quality of concrete can be made after it has completely hardened, when twenty-eight days have passed from the moment it was poured.
Control can be non-destructive and destructive. In the first case, testing is carried out with different devices, the readings of which are not very accurate, and in the second, a sample is taken directly.
Non-destructive methods
The following types are distinguished:
- Tearing off disc elements involves stress relief produced by local failure.
- Cleavage of ribs, which can make it possible to define the characteristic of a 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 a chip is the only method of non-destructive testing, according to which everything is officially regulated, including the calibration dependence. When passing the test, you can sometimes see high accuracy.
- Rebound resilience can provide a measure of how much a striker will move after impacting a structural surface. Tests are carried out with spring hammers.
- Impact impulse allows you to register the energy of the completed impact, formed when the striker comes into contact with the surface. Such devices may be compact in size.
- Plastic deformation is based on measuring the size of the imprint left by a steel ball impact.
Ultrasound test
You can check the quality of concrete by ultrasonic method using wave passages in the form of through and surface sounding. Differenceis how the sensors are positioned.
Destructive methods
The following kinds 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 performed using drilling machines type IE 1806. They have a diamond or carbide drill.
Before you purchase a ready-made solution from the manufacturer, you need to find out if he has a quality certificate for concrete. This is not a requirement, 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 the mortar to fill the form of the concrete product and compact it under the influence of gravity or due to external mechanical influence). This feature of concrete is evaluated by indicators of stiffness and mobility. When concreting reinforced concrete monolithic structures, concrete mixtures are most often used.
Employees of the construction company are obliged to control the mobility of the mixture at least twice. For concrete with zero slump mobility, the building laboratory determines the stiffness of the mixture in accordance with the methodology of the applicable standard. Rigidity is characterized by the period of vibration required to level and compact the preformedcone of concrete in the stiffness tester.
Transportation of concrete mix
Properly executed delivery of the mixture largely determines the quality of the concrete by the time it is placed in the structure. If the rules for transporting and supplying the mixture to the concreted systems are violated, the concrete mixture loses its uniformity - it delaminates: the heavier components (gravel, sand, crushed stone) settle, and cement milk appears on top of the surface. Therefore, the given mobility is violated and the workability decreases. The quality of concrete is achieved by regular monitoring of the transportation and supply of the mixture in the structure.
The foreman and foreman of the construction site are required to regularly monitor the quality of the compaction of the concrete mixture. When laying in horizontal layers, ensure that the thickness of all laid layers is consistent with the requirements of the project. The duration of vibration ensures the compaction of concrete, the main properties of which are: the end of the settling of the mixture, the appearance of cement laitance on its plane, the cessation of the separation of air bubbles from it.
Resumption of concreting after a pause is allowed only when the concrete gains a compressive strength of at least 1.5 MPa. The duration of these intervals, as a rule, is no more than 2 hours.
For the strength of adhesion of the new layer of the mortar with the already hardened one, its surface is cleaned of debris, the cement film is removed with iron brushes, then washed with a jet of water under pressure. The remaining water from the recesses is eliminated. In front ofwhen laying a 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 the old concrete.
What affects quality?
The quality of concrete largely depends on the conditions in which the composition is already after its laying. The intensity of hardening is greatly influenced by humidity and ambient temperature. Laid concrete is kept in a wet state and protected from mechanical damage, shaking, sudden changes in temperature and rapid drying.
What is used to conserve moisture?
To save moisture in concrete, liquefied bitumen, bituminous and tar and other emulsions are used that can quickly form a film impervious to water on the concrete surface.
Concrete quality indicators
The most important indicators of the quality of concrete is strength. This is one of the most important indicators. It is the ability of concrete to withstand heavy loads that makes it practically indispensable in construction work. Concrete has 3 strength types:
- for compression, which evaluates the property of concrete to withstand compressive loads;
- in tension in bending, which determines the property of concrete to withstand a bending load;
- on axial tension, which determines the ability of concrete to withstand tensile loads over the entire cross-sectional area.
Strength is determined by testing standard samples of concrete for tensilemachines and presses.
- Frost resistance of concrete. With the help of this indicator, the ability of concrete to maintain its strength characteristics after alternate freezing and thawing is evaluated. Frost resistance is an important indicator for concrete used in places with harsh climates and cold winters.
- Waterproofing of concrete. This indicator evaluates the ability of concrete to resist water infiltration. 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 maintain its strength characteristics after exposure to an aggressive environment is evaluated. This indicator is important to consider if there is a risk of concrete contact during operation with aggressive chemicals.
The quality of concrete for foundations or other construction work is very important. It is on him that the life expectancy of the building and the safety of its operation depend.
