Concrete mixture, as you know, is a mobile and plastic material. It is very convenient to lay such solutions in the formwork. However, the previously used concrete mixtures required mandatory compaction. Moreover, the more carefully such a procedure was carried out, the better the concrete structure subsequently turned out. Today, a new type of cement mixtures has appeared on sale. They are called self-compacting and do not require tamping when laying.
Key Benefits
When pouring mixtures of this type, all parts of the formwork are filled equally quickly and without voids. That is, self-compacting concrete can be used not only in the construction of, for example, residential buildings, but also in complex architectural structures. In addition, such mixtures are simply ideal for pouring densely reinforced structures. Near the frame elements, no air is formed in their thickness.bubbles, and the layer itself is as homogeneous as possible.
Another indisputable advantage of self-compacting concrete is that structures poured from it have absolutely flat surfaces. It is not required to perform any actions to correct them at the final stage. For example, when pouring floors from such concrete, there is no need to use leveling material before installing the finished floor.
Builders who use such concrete in their work, of course, consider it a great advantage that there is no need to purchase expensive vibration equipment. Such concrete is compacted simply under its own weight. Therefore, filling various kinds of structures with its use turns into a very simple procedure.
Vibrating equipment is known to be very noisy. Since it is not necessary to use such aggregates when laying self-compacting concrete, it is possible to work with this material, including at night.
Self-compacting mixtures are, of course, more expensive than ordinary cement ones. However, due to the absence of the need to use vibration equipment, structures made from them are often even cheaper.
The performance characteristics of these two types of solutions are similar. Mixes of heavy and self-compacting concrete allow the construction of equally strong and durable structures. Sometimes structures built using mortars of the latter type are distinguished by even the bestoperating characteristics.
Composition of self-compacting concrete
In appearance, this material is practically no different from ordinary cement. The same applies to its composition. In the preparation of such mixtures, in principle, the same materials are used as in the mixing of conventional heavy building cement mortars. The difference between these two types of materials lies only in the fact that for self-compacting, the initial components are carefully selected according to granulometry. Compared to conventional solutions, such formulations have a much more uniform structure.
Also, in the manufacture of self-compacting mixtures, slightly different plasticizers can be used. The ability to fill the formwork with an absolutely uniform layer in all its parts of such mortars is partly related to this.
Currently, there are many varieties of such material on sale. But in most cases, the composition of self-compacting concrete has the following:
- portland cement;
- sand;
- crushed stone of fine fraction;
- chemical modifiers;
- plasticizers;
- water.
Also, various substances can be mixed into such solutions that increase their anti-corrosion properties. As an additive for self-compacting concrete, agents that reduce its ability to crack are also often used.
What characteristicsdifferent
When choosing a cement mixture of any kind, builders in the first place, of course, pay attention to such an indicator as compressive strength. Concrete, as you know, is not very resistant to rupture, and any structures made of it are built in such a way that such material is subjected to this type of load as little as possible.
Compressive strength of self-compacting compounds is very good. Depending on the composition and additives used, this indicator for such concrete can be 30-90 MPa. The self-sealing material also has the following characteristics:
- workability index - 70%;
- modulus of elasticity - 30-36 GPa;
- mobility - P5;
- frost resistance - F400;
- air bubble content - no more than 6%;
- water resistant - from W62.
If we talk about technical characteristics, then self-compacting mixtures, compared to conventional ones, also have the advantage that they do not delaminate even under long-term transportation.
What are the varieties
In Appendix A GOST 25192-2012, in paragraph 3.7., Self-compacting concrete is given the exact name and definition. They call it, according to the regulations, a material “made from a concrete mixture capable of compacting under its own weight.”
At the moment, the industry produces mainly two varietiessimilar mixes:
- fine;
- stabilizing.
Mixtures of the first type differ primarily in that they contain a much larger amount of finely dispersed materials than conventional solutions. Such fillers primarily increase the resistance of the composition to delamination. As additives for fine self-compacting concrete can be used, for example:
- fly ash;
- siliceous drifts.
Sometimes ordinary limestone powders are added to such mixtures. A good type of fine aggregate for self-compacting concrete is also granulated blast-furnace slag.
The second type of material is made using special stabilizers. These additives achieve the optimum viscosity of the mixture and provide the perfect balance between their fluidity and resistance to delamination.
Classification
Before purchasing a self-sealing compound, of course, you should pay attention to its brand. By class, such mixtures are currently distributed as follows:
- pass obstacles if possible - PA1–RA2;
- for peel resistance - SR1–SR2.
Of course, when buying, developers, among other things, should pay attention to such an indicator as the viscosity of self-compacting concrete. For the surface quality of finished structures, for example, this is of great importance. Check the finished mixture of this type for the degreeviscosity can by two technologies. In this regard, classes of self-compacting mixtures are distinguished:
- for 500 mm cone - VS1–VS2;
- when checking in a V-shaped funnel - VF1–VF2.
There are also workability classes for self-compacting concrete - SF1–SF3.
How and where is it made
In some cases, such material, like conventional cement, can be supplied to the market in bags in the form of a dry mix. To prepare a solution, such compositions are simply diluted with water in the proportions indicated by the manufacturer. But in this form, mixtures of this type are still extremely rare. Mostly produced dry materials of this variety are intended for pouring only thin leveling surfaces.
Basically, today a similar composition is sold in the form of a ready-made concrete solution. The mixing of such material for pouring critical loaded structures requires highly qualified specialists performing this procedure. Ready-made solutions, of course, are more expensive than dry ones. After all, their transportation is quite a costly business. But such material is most convenient to use. The mortar structure is poured in one step by supplying the last one from the hose. For private developers, for example, the purchase of such material can be just the perfect solution for the construction of ceilings and slab foundations.
Some builders are also interested in those who are developing regulations for laying self-compacting concrete. According to the legislation in force in Russia, the manufacturer must prepare such a technological document, as well as approve it. At the same time, when developing the regulations, the specialists of such a company must necessarily adhere to the requirements of GOST, taking into account the supply contract.
Where it can be used
Of course, sometimes self-sealing mixtures can be used for pouring various kinds of structures and in private housing construction. But today, such concrete is used in most cases by construction organizations.
This material is still quite new for Russia. At the moment, even a domestic classification of such a tool has not yet been developed. Builders in the Russian Federation are guided by European standards when using self-compacting concrete. However, some documents regulating the use of this material, and GOSTs regarding it, have already been created in our country today.
This applies, for example, to the scope of self-compacting concrete. According to the SNiP standards, in industrial construction such mixtures are allowed and recommended to be used:
- in the production of precast concrete structures;
- during the construction of hydraulic structures;
- when pouring structures with special strength requirements;
- for pouring complex architectural objects;
- in the production of Lego bricks;
- for the construction of structures with a small thickness (fences, walls, etc.).
Also, such mixtures are very often used for pouring durable screeds in the event that they will subsequently be subjected to serious loads (in workshops with heavy machinery and equipment, in special equipment garages, etc.).
Very often self-compacting concrete is also used in restoration work. It is used in this case, for example, when shotcrete.
Kneading requirements
When preparing mortars from dry self-compacting mixtures, among other things, it is necessary:
- extremely accurately dispense materials into the mixer;
- Carefully control the moisture content of all types of aggregates.
Transportation of such mixtures to the construction site is allowed only by certified vehicles.
How to style correctly
In order to ultimately get the most durable and durable construction, you should, of course, follow all the required technologies when pouring such mixtures. When performing such work, it is first necessary to ensure the continuity of the supply of material to the construction site.
The self-compacting mixture should be fed into the formwork until it is completely filled. It is allowed to take technical breaks in production when pouring structures using such material. However, the total downtime should not exceed half an hour. Otherwise, the mixture may lose its self-compacting properties.
Beforeat the beginning of the pour itself, you should make sure that there is no rainwater in the formwork, for example. If present, subsequently poured self-compacting concrete will definitely delaminate.
A feature of this type of mortar is, among other things, the fact that before actually laying in the formwork, its flow must pass a certain distance. This ensures that air bubbles are removed from the mixture. Like conventional cement mortar, self-compacting is pumped into the formwork through large-section hoses. So that there are no bubbles left in such a mixture, according to the standards, sufficiently long sleeves are supposed to be used for its supply. However, this indicator according to SNiP still should not exceed 200 m.
Special occasion rules
Concreting walls with self-compacting concrete (or, for example, ceilings) is a relatively simple procedure. However, as already mentioned, such compositions are often used for the construction of structures of complex architectural form. Therefore, sometimes they have to be poured into formwork with difficult natural air removal. An example of such fixtures is molds for tall columns.
When pouring self-compacting mixtures into such formwork, certain rules must be observed. For example, in this case, the mixture is not allowed to be thrown down. When pouring columns, the sleeve is usually lowered inside the formwork and raised as the latter is filled.
What are the disadvantages
The benefits of using self-compacting concrete mixes thusthere are many. There are practically no drawbacks to such compositions. The builders consider its rather high cost to be the only disadvantage of this material.
Unlike usual, such mixes are characterized by rather high degree of ductility. In some cases, this can make them difficult to install. This builders, of course, also refer to the minor shortcomings of the material of this variety.
Mix Reviews
Working with such material, according to builders, is actually quite convenient in most cases. Self-sealing mixtures have earned good reviews from builders and for their high quality, as well as the pleasant appearance of structures poured from them.
The opinion of the builders about such concretes is thus not bad. However, many consumers note the fact that in Russia at the moment, unfortunately, mixtures of this type are often sold that do not meet the high requirements of modern construction.
This is primarily due to the fact that almost every manufacturer in the Russian Federation today produces such solutions according to its own recipe. Sometimes, in the manufacture of such material, companies do not even comply with GOST. Self-compacting concrete produced in violation of the technology may not differ in the required degree of uniformity, plasticity and strength.
To everything else, in our country today, according to some consumers, there are no materials suitable for the production of such compositions. This applies, for example, to rubble. In most cases, whenIn the manufacture of self-compacting mixtures in Russia today, material of this type is not very well suited (by the absence of impurities) for them.
