Hydrotechnical concrete: properties, characteristics,

The purpose of hydraulic concrete is clear from the very name, but for a correct understanding of this material this understanding is not enough. Therefore, we want to consider the technical characteristics of hydraulic concrete - the composition, strength, water resistance and other parameters that determine the properties and characteristics of this type of concrete.

Concrete for hydraulic structures

Introduction

It is incorrect to speak about hydraulic engineering concrete as a separate building material, since it belongs to one of the varieties of a wider class of materials called concretes, therefore, the terms, classification, general concepts for this entire class will be the same.

To introduce the reader to the topic, we briefly recall the basic concepts and terms that are used to characterize and describe concrete products and mortars.

Note! All methods of labeling, classifications, all terminology and test methods are standardized and strictly defined, therefore, are considered the only reliable and generally accepted set of characteristics that can be used in serious design and large-scale construction works.

Concrete is called the stone of artificial origin, obtained by mixing with water or other solvent a dry mixture of binders, fillers and additives. Also this name is often used to refer to a solution that has already been mixed with water and prepared for laying.

There are a large variety of concrete mixes, so they are classified according to several parameters:

1. According to the purpose of the finished structure. Here are two main groups: ordinary and special. The usual group includes materials for the construction of civil and industrial objects, and a special collection of materials for the construction of hydraulic structures, roads, nuclear power plants, bridges, as well as special-purpose solutions - heat-resistant, sound-absorbing, resistant to aggressive chemical environments, etc .;
2. By type of binder used there are asphalt, slag alkaline, gypsum, cement, polymer and silicate concretes. We are talking about cement composition, since it is Portland cement that is most often used for the construction of hydraulic structures;
3. By type of filler there are compositions on porous, dense and special aggregates. In our case we are talking about dense materials - gravel and granite;
4. Also distinguish materials on the structure. Allocate porous, dense, large-pore and cellular concrete. We will talk about a dense variety;
5. Another important indicator is the hardening conditions.. There are solutions of natural hardening, as well as those that require heat and moisture treatment under atmospheric or elevated pressure (autoclaved hardening). In our case, it will be a solution of natural hardening;
6. By volume there are especially heavy (more than 2500 kg / cub. m), heavy (2200 - 2500 kg / cub. m), lightweight (1800 - 2200 kg / cub. m), light (500 - 1800 kg / cub. m) and especially lungs (less than 500 kg / cubic meter). We are dealing with heavy concrete;
7. By aggregate size There are fine-grained and coarse-grained species.

You can also add separation according to the method of preparation and composition, where there are lean, fatty and salable varieties of solutions. In lean mixtures, the cement content is lowered and the amount of coarse aggregate is increased, in fatty mixtures, on the contrary, there is more cement and less gravel, and the marketable ones are the optimal ratio of components prepared in accordance with the standard proven recipe.

Note! For the construction of hydraulic structures using only ready-mixed concrete, prepared according to standard or specially selected recipe, taking into account all the operating conditions of these structures.

In addition, regardless of the previous classification, hydraulic concrete according to GOST 26633-91 must meet a number of requirements for strength, water resistance, frost resistance and readiness. Also, depending on the casting conditions, a solution of a certain mobility and workability may be needed, which are also standardized.

To indicate the strength of the material consider the compressive strength, tensile and bending.

В нашем случае используют классы по прочности на сжатие: В3.5, В5, В7.5, В10, в12.5, <…>, В60, В65, В70, В75, В80.

Also used brands from M50 to M1000, where the number indicates the maximum effect of force on a square centimeter of the surface, which is able to withstand the material.

To determine the axial tensile strength, the classes Bt0.4 to Bt4 are used in increments of 0.2. Bending strength is characterized by classes from Btb0.4 to Btb8 with the same step.

If you meet the designation “hydraulic concrete class B25 M350”, then this means that we have before us heavy concrete of special purpose, strength class B25. Brand 350 is indicated for convenience, as it was previously adopted just such a marking.

In addition to these basic parameters, such factors as heat of hardening, deformability, resistance to abrasion by streams of water and sediment and other characteristics are taken into account when preparing a solution and determining its composition.

Note! When determining class membership, strength, frost resistance, water resistance and other material parameters, only an empirical approach is used and a specific brand or class is assigned only on the basis of tests.

Requirements

It should be understood that such a detailed classification was introduced for a reason. The fact is that hydraulic engineering varieties of concrete are used for the construction of complex and very important structures, such as dams, dams, bridge supports, piers, breakwaters, moorings, etc. Of course, for such purposes, the materials are not prepared with their own hands "by eye", but adhere to a specific recipe in the conditions of plants.

It is also important to note that the listed facilities are built on the basis of serious calculations taken into account in the project, where, among other things, the requirements for strength, water resistance and other concrete parameters are necessarily listed. To make it easier to present these requirements to the manufacturer of the solution, use a detailed classification and labeling.

The measure of responsibility imposed on designers, architects and builders is enormous. Judge for yourself what are the consequences of the destruction of a bridge, dam, hydroelectric station or dam? Therefore, the choice of materials here has to be especially careful and serious.

The most frequently considered requirements for indicators such as water resistance, frost resistance and strength. We talked about the strength in detail in the previous section, here we just note that the most common strength classes are B10 - B40.

Frost resistance is determined by the number of freeze-thaw cycles that the material is capable of transferring without significant loss in strength and other indicators.

Для определения морозостойкости используют специальные климатические камеры, где образцы подвергают замораживанию и оттаиванию, а количество таких циклов фиксируют. В результате материалу присваивают класс, где указано количество перенесенных им без потерь циклов: F50, F75, F100, <…>, F600, F800, F1000.

As a rule, such brands of frost resistance as F50, F100, F200 and F300 are used in construction. For more cycles than 400, special additives are used, but such materials are rarely used when working in harsh and ultra-high conditions.

As you know, there are three main types of hydroconcrete on the operating conditions:

1. Underwater, which is constantly in the water column and is in direct contact with pressure fluid;
2. Staying in a zone of periodically changing water level, that is, the material is not constantly affected by pressure fluid;
3. Periodically washed with water, but above its level. The impact of pressure fluid is not experiencing.

It is obvious that all three varieties somehow come into contact with water, therefore water resistance is an extremely important indicator for hydroconcrete. To determine it, a material at the age of 180 days is subjected to hydrostatic pressure exposure to water.

Во время испытания бетонный куб со стороной 150 мм помещают в специальную камеру, где на него оказывают воздействие напором воды. Если материал выдерживает тот или иной напор, ему присваивают класс W2, W4, W6, <…>, W16, W18, W20. Число обозначает значение того давления, которое способен выдержать образец, измеряемое в кгс/кв. см. Наиболее часто встречаются гидробетоны четырех групп: W2, W4, W6, W8.

Especially important for water resistance is the water-cement ratio of the solution. The lower it is, the lower the porosity of the structure and the higher the water resistance. Also, this indicator is influenced by the presence of special plasticizer additives, which reduce the water consumption of the mixture.

Also impermeability to water increases the use of pozzolanic additives, as well as alumina, tense, expanding and high-strength cements. In addition, the use of concrete compaction additives of aluminum sulfate and iron, calcium nitrate, as well as mechanical compaction by centrifugation, vibration, pressing and vacuuming.

Composition

The composition of hydrotechnical concrete has the most significant effect on all subsequent properties and characteristics of structures. The selection takes into account not only the technical side of the issue, but also the price of the mixture obtained, the economic feasibility of its use in comparison with other options and other indicators.

For the preparation of concrete hydraulic engineering use components such as Portland cement, sand, gravel and water. In addition to these main ingredients, plasticizers, water repellents, air-entraining additives, seals and other substances that increase these or other indicators of the solution are added. To increase water resistance, pozzolanic slag cement and sulphate-resistant cement are also used.

Cement consumption per cubic meter of mortar should not exceed 350 - 400 kg. Use only high-quality material of high marks, produced by a proven factory with a good reputation.

The sand is best added quartz, washed from clay and dust particles, mined in natural deposits. Gravel and granite are used as coarse aggregate, which meets the requirements of fractional composition and flakiness. It is allowed to add crushed stone with a grain size of 150 mm and above to massive structures.

Note! Cutting reinforced concrete with diamond circles and diamond drilling of holes in concrete is difficult in our case and requires the use of professional tools and high-quality cutting materials.

Conclusion

We considered hydraulic concrete - class B15 M200, B25 M350 and learned to read the marking. We also determined the basic requirements and composition of this material. For more clarity and new information, see the video in this article.