For structures and structures in varying degrees in contact with water, a special material is required that can withstand the aggressive effects of a liquid medium. For construction in such conditions, hydraulic concrete is used. It has the necessary characteristics for the safe operation of the constructed facility.
Definition
Hydraulic engineering concrete belongs to the category of heavy, it is used for the construction of embankments, bridges and other structures, parts of which are partially or completely immersed in water, or have contact with it.
A feature of the material is its ability to maintain its original characteristics in an aggressive environment without compromising on the quality and bearing capacity of the element. Some functions, such as strength, in a sludge environment increase over time, while maintaining the integrity and structure of the stone.
Classification
There is a certain set of requirements that concrete hydraulic must meet. GOST 26633-2012 “Concrete heavy and fine-grained. Technical conditions ”regulates the quality of the components of the mixture and the properties of the finished solution. The document is international in nature, it was accepted by 8 countries.
According to GOST, hydraulic concrete is divided into several groups according to the degree of immersion and exposure to the aquatic environment:
- Surface.
- Underwater.
- For an unstable water level.
By the volume of the created structure, the material is divided into:
- Massive - complex shapes and large sizes of the element, accompanied by uneven hardening with the release of heat.
- Non-massive - simple designs with small dimensions.
As the force affects the hardened object:
- For pressure systems.
- For gravity elements.
An additional classification shares the place of application of concrete:
- For internal structures (they are less susceptible to leaching, water pressure, but must withstand static influences).
- For external elements and surfaces (such are influenced by the active movement of water and an unstable chemical background).
Mixture composition
The solution must meet the requirements of GOST to obtain a stone of sufficient hardness, strength and safety. Quality control passes all the components included in the hydraulic concrete. The composition of the mixture:
- The main component is astringent. For the effect resistant to aggressive waters, sulfate-resistant cement is used. For a variable level of immersion, hydrophobic or with the inclusion of plasticizing additives are taken. In other cases, pozzolanic, slag or Portland cement is used.
- Fine aggregate - quartz sand, it increases the resistance of concrete to water. It should not contain small impurities and debris - in wet conditions, inclusions can significantly weaken the material.
- Coarse aggregate - gravel and crushed stone from sedimentary and igneous rocks. This is characterized by high hydrophobicity, frost resistance. The fraction of stones depends on the technical characteristics of the concrete mortar required for operation in specific conditions. The shape of the aggregate should be voluminous and convex, flaky gravel or gravel has less strength.
- Additives are mortar improvers. They increase the resistance of the stone to temperature changes, the aggressive effects of water, reduce heat as necessary, and prevent cracking.
The properties of all components, their parameters, the exact formulation of the solution are prescribed in GOST 26633-2012 p. 3. Compliance with the standards should be carried out in any production, the finished mixture receives a document of compliance with the standard.
Specifications
The material has many varieties. They are distinguished by composition and properties, which should have hydraulic concrete. Technical specifications depend on the brand and type of composition. The main ones include compressive strength, axial bending, tensile, frost resistance and hydrophobicity. The working solution is selected according to the totality of these indicators, since the properties of each batch may differ, which is unacceptable for this material.
Strength
The first and most important indicator is the amount of compression resistance, since most structures experience a vertical force load from the building volume above.
The strength of concrete is determined by creating a cube for testing and then testing it under presses. The prototype can withstand from 28 to 180 days for a set of strength. In the case of hydraulic material, the cube is placed in water for the time of hardening.
The tests are carried out under the action of forces until cracks appear.
According to the results of the study, concrete is awarded a class from B3.5 to B60. The most common types are B10-B40.
Tensile and bending strength
Structures that are not affected by vertical loading are subject to other influences - axial tension and bending. To understand whether concrete can withstand such deformations, it is tested in laboratory conditions. The tensile strength grade is Bt0.4 ... 4.0.
Water resistant
It is determined in laboratory conditions on sample cubes of the same age as in the first case. The essence of the test is to gradually increase the pressure of the water before it seeps through the concrete body. As a result, the stone is assigned a waterproof brand W2-20.
For aggressive conditions of sea water, high pressure, hydraulic concrete is used not lower than W4.
Frost resistance
In conditions of high humidity, special attention is paid to temperature differences with the possibility of solidification of water. As you know, during expansion, the liquid crystallizes and causes damage to building materials into which it managed to penetrate. To prevent this from happening with a responsible construction, special hydraulic additives and plasticizers are added to the mortar at the factory, which increase the concrete's resistance to solidification.
The frost resistance brand F shows how many cycles of complete alternate freezing and thawing a concrete sample withstands a strength loss of no more than 15%. For the hydraulic mixture, the tests are carried out with water, heating it and turning it into ice.
According to the results of the study, hydrophobic concrete is assigned a frost resistance grade F50-300.
Mixture improvers
Indicators of strength, water resistance and frost resistance are laid at the stage of mixing the solution at the plant. Special properties of hydraulic concrete are determined by salts of various metals and composite compounds.
Modifier additives are divided into 2 groups.
Group I reduces water absorption up to 5 times by the design strength of 28 days. Among the most used:
- Phenylethoxysiloxane 113-63 (formerly FES-50).
- Sodium Aluminomethyl Siliconate AMSR-3 (Russia).
- "PlastIL" (Russia).
- Hydroconcrete (EU).
- Addiment DM 2 (Germany).
- Liga Natriumoleat 90 (Russia).
- Sikagard-702 W-Aquahod (Switzerland).
Group II is less powerful (decrease to 2-4.8 times). Its use is possible for mixing concrete above the surface:
- Polyhydrosiloxanes 136-157M (former GKZh-94M) and 136-41 (former GKZh-94).
- KOMD-S.
- Stavinor Zn Yee Stavinor Ca PSE.
- HIDROFOB E (Slovenia).
- Cementol E (Slovenia).
- Sikalite (Switzerland).
- Sikagard-700S (Switzerland).
Group III to create hydraulic concrete is not used. Additives reduce water absorption up to 2 times.
Other properties
When choosing a working mixture, not only the main characteristics of hydraulic concrete are taken into account, but also its other parameters:
- The amount of shrinkage.
- Resistance to deformation.
- The degree of resistance to water flow and pump pressure.
There is no single recipe for hydraulic concrete: in each case, the chemical composition of water, the pressure value and other loads are taken into account. In accordance with the requirements, fillers and additives are used that can ensure reliable operation of the future stone.
Application
Laying a solution under a layer of water is a responsible and difficult matter. It is poured in large volumes to prevent uneven solidification and erosion. Due to the specifics of laying in the body of the hardening structure, thermal stresses and differences occur, which must be regulated. To avoid overheating and premature deformation of the mold, plasticizers and special types of cement are added to the solution:
- Pozzolanic.
- Slag.
- Hydrophobic.
For the construction of coastal structures, hydraulic concrete is used. Its application is widespread:
- Bridges, their supports and girders.
- Arrangement of embankments and shore-strengthening walls, ports.
- Pools, their bowls and surrounding areas.
- Walls of sewer wells and shafts.
- Tunnels of the subway.
- Technical facilities: dams, hydroelectric power stations, breakwaters.
In housebuilding, low-grade hydraulic concrete is used to fill the foundation with a high level of groundwater or its significant drops during melting snow and heavy rains.