For structures and structures that come into contact with water to varying degrees, a special material is needed that can withstand the aggressive effects of a liquid medium. For construction in such conditions, hydrotechnical concrete is used. It has the necessary characteristics for the safe operation of the erected facility.
Definition
Hydrotechnical concrete belongs to the category of heavy, it is used for the construction of embankments, bridges and other structures, parts of the structures of which in places are either completely submerged 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 the quality and bearing capacity of the element. Some functions, such as strength, in the air environment increase over time, provided that the integrity and structure of the stone is preserved.
Classification
There is a certain set of requirements that must beconform to concrete hydraulic engineering. GOST 26633-2012 “Heavy and fine-grained concrete. Specifications” regulates the quality of the components that make up the mixture and the properties of the finished solution. The document is international in nature, it was adopted 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 fluctuating water levels.
According to the volume of the structure being created, the material is divided into:
- Massive - complex shapes and large sizes of the element, accompanied by uneven curing with heat release.
- Non-massive - simple designs with small dimensions.
As force is applied to the hardened object:
- For pressurized systems.
- For non-pressure elements.
Additional classification share the place of application of concrete:
- For internal structures (they are less prone to washout, water pressure, but must withstand static effects).
- For external elements and surfaces (such are affected by the active movement of water and a changeable chemical background).
Composition of the mixture
The solution must meet the requirements of GOST to obtain a stone of sufficient hardness, strength and safety. All components included in hydrotechnical concrete undergo quality control. Mix Composition:
- The main component is the binder. Foreffect resistant to aggressive waters, sulfate-resistant cement is used. For a variable level of immersion, a hydrophobic one or with the inclusion of plasticizing additives is 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, switching on 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 solution required for operation in specific conditions. The shape of the aggregate should be voluminous and convex, crushed stone or gravel has less strength.
- Additives - improvers properties of the solution. They increase the resistance of the stone to temperature extremes, aggressive effects of water, reduce heat release as needed, and prevent cracks.
The properties of all components, their parameters, the exact formulation of the solution are prescribed in GOST 26633-2012 p.3. Compliance must 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 the composition and properties that hydraulic engineering concrete should have. Specifications depend on the brand and type of composition. The main ones are compressive strength, axial bending, tension, frost resistance andhydrophobicity. The working solution is chosen according to the totality of these indicators, since each batch of properties may differ, which is unacceptable for this material.
Strength
The first and most important indicator is the amount of compressive strength, since most structures experience a force vertical load from the volume of the building above.
The strength of concrete is determined by creating a test cube and then testing it under pressure. The prototype is kept from 28 to 180 days to gain strength. In the case of hydraulic engineering material, the cube is placed in water during hardening.
Testing is 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 forces such as axial tension and bending. To understand whether concrete can withstand such deformations, it is tested in the laboratory. Tensile strength grade – Bt0, 4…4, 0.
Water resistant
Determined under laboratory conditions on sample cubes of the same age as in the first case. The essence of the test is to gradually increase the water pressure until it seeps through the concrete body. As a result, the stone is assigned a W2-20 water resistance mark.
For aggressiveconditions of sea water, high pressure use hydraulic concrete not lower than W4.
Frost resistance
In conditions of high humidity, special attention is paid to temperature changes with the possibility of water solidification. As you know, when expanding, the liquid crystallizes and damages the building materials into which it managed to penetrate. To prevent this from happening with a critical structure, special hydraulic additives and plasticizers are added to the solution at the production site, which increase the resistance of concrete to hardening.
Frost resistance grade F shows how many cycles of complete alternate freezing and thawing a concrete sample can withstand with a loss of strength of no more than 15%. For a hydraulic mixture, tests are carried out on water with its heating and turning into ice.
According to the results of the study, hydrophobic concrete is assigned a frost resistance grade of F50-300.
Mix improvers
Indicators of strength, water resistance and frost resistance are laid at the stage of mixing the solution at the factory. The special properties of hydraulic concrete are determined by s alts of various metals and composite compounds.
Additive modifiers are divided into 2 groups.
I group reduces water absorption up to 5 times by the term of the design curing of 28 days. Among the most used:
- Phenylethoxysiloxane 113-63 (formerly FES-50).
- Sodium aluminomethylsiliconate AMSR-3 (Russia).
- "Plastil" (Russia).
- Hydroconcrete (EU).
- Addiment DM 2 (Germany).
- Liga Natriumoleat 90 (Russia).
- Sikagard-702 W-Aquahod (Switzerland).
II group is less powerful (down to 2-4.8 times). Its application is possible for mixing surface concrete:
- Polyhydrosiloxanes 136-157M (former GKZH-94M) and 136-41 (former GKZH-94).
- "KOMD-S".
- Stavinor Zn Eu Stavinor Ca PSE.
- HIDROFOB E (Slovenia).
- Cementol E (Slovenia).
- Sikalite (Switzerland).
- Sikagard-700S (Switzerland).
III group is not used to create hydraulic concrete. Additives reduce water absorption by 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:
- Shrinkage amount.
- Resistance to deformation.
- Degree of resistance to water flow and pumping pressure.
There is no single recipe for hydrotechnical concrete: in each case, the chemical composition of water, the magnitude of the head and other loads are taken into account. In accordance with the requirements, fillers and additives are used that can ensure the reliable operation of the future stone.
Application
Laying the solution under the water layer is a responsible and difficult task. It is poured in large volumes to prevent uneven solidification and blurring. Due to the specifics of laying in the body of the hardening structure, thermal stresses and drops occur, whichneeds to 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 use is widespread:
- Bridges, their supports and girders.
- Arrangement of embankments and walls strengthening the coast, ports.
- Pools, their bowls and surrounding areas.
- Walls of sewer wells and shafts.
- Metro tunnels.
- Technical structures: dams, hydroelectric power stations, breakwaters.
In house building, hydrotechnical concrete of low grades is used to pour the foundation at a high level of groundwater or its significant differences during snowmelt and heavy rains.
