Concrete mixture, as you know, is a moving and plastic material. It is very convenient to lay such solutions in the formwork. However, previously used concrete mixes required compulsory compaction. Moreover, the more thoroughly this procedure was carried out, the better the concrete structure subsequently turned out to be. Today a new variety of cement mixes has appeared on sale . They are called self-sealing and do not require tamping during installation.
Main advantages
When pouring mixtures of this type fill all parts of the formwork equally quickly and without voids. That is, self-compacting concrete can be used not only in the construction, for example, of residential buildings, but also in complex architectural structures. In addition, such mixtures are simply ideal for pouring heavily reinforced structures. Near the frame elements, no air bubbles form in their thickness, and the layer itself is obtained as homogeneous as possible.
Another indisputable advantage of self-compacting concrete is that the structures poured from it have absolutely smooth surfaces. It is not required to carry out any actions to correct them at the final stage. For example, when pouring ceilings from such concrete, there is no need to use leveling material before installing the finishing floor.
Builders who use such concrete in their work, of course, consider it to be a great advantage that there is no need to purchase expensive vibration equipment. Such concrete is compacted just under its own weight. Therefore, pouring all kinds of structures with its use turns into a very simple procedure.
Vibration equipment is known to have a high degree of noise. Since it is not necessary to use such aggregates when laying self-compacting concrete, work with this material can also be done at night.
Self-compacting mixtures are, of course, more expensive than regular cement ones. However, due to the lack of need for the use of vibration equipment, designs from them are often even cheaper.
In terms of performance, these two types of solutions are similar. Mixtures of heavy and self-compacting concrete allow the construction of equally strong and durable structures. Sometimes structures constructed using solutions of the latter type are distinguished by even better operational characteristics.
Composition of self-compacting concrete
In appearance, this material is practically no different from ordinary cement. The same goes for its composition. In the preparation of such mixtures, in principle, the same materials are used as when mixing conventional heavy construction cement mortars. The difference between these two types of materials lies only in the fact that for self-sealing initial components are carefully selected according to particle size distribution. Compared to conventional solutions, such compositions 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 solutions is partly associated with 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;
fine gravel;
chemical modifiers;
plasticizers;
water.
Various types of substances that increase their anticorrosion properties can also be mixed in such solutions. As an additive for self-compacting concrete, often also means that reduce its ability to crack.
What are the characteristics
When choosing a cement mixture of any kind, builders first of all, of course, pay attention to such an indicator as compressive strength. Concrete is not very resistant to rupture, and any structures made of it are erected in such a way that this material is subjected to this type of load as little as possible.
The compressive strength of self-compacting mixtures 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;
the content of air bubbles is not more than 6%;
water resistant - from W62.
If we talk about technical characteristics, then self-compacting mixtures, in comparison with conventional ones, also have the advantage that they do not exfoliate even if they are transported for a long time.
What varieties exist
In Appendix A of GOST 25192-2012, in paragraph 3.7., The concrete of self-compacting type is given the exact name and definition. They call it so, according to the standards, the material "made of concrete mixture, capable of compacting under the influence of its own weight."
Currently, the industry produces mainly two varieties of such mixtures:
finely divided;
stabilizing.
The mixtures of the first type are primarily distinguished by the fact that they contain a much larger amount of finely dispersed materials than conventional solutions. Such fillers primarily increase the stability of the composition to delamination. As additives for self-compacting finely dispersed concrete can be used, for example:
fly ash;
siliceous entrainment.
Sometimes ordinary limestone powders are added to such mixtures. A good type of fine aggregate for self-compacting concrete is also granular blast furnace slag.
The second type of material is manufactured using special stabilizers. Such additives can achieve optimal viscosity of the mixture and provide the perfect balance between their mobility and resistance to delamination.
Classification
Before acquiring a self-sealing composition, of course, you should pay attention to its brand. By class, such mixtures are currently distributed as follows:
Of course, when buying, developers, among other things, should pay attention to such an indicator as the viscosity of self-compacting concrete. For the quality of surfaces of finished structures, this is, for example, of great importance. Check the finished mixture of this type for the degree of viscosity can using two technologies. In this regard, classes of self-sealing mixtures are distinguished:
There are also workability classes for self-compacting concrete - SF1 – SF3.
How and where are they made?
In some cases, a material such as regular cement may be delivered in bags as a dry mixture to the market. To prepare the 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. Basically, the dry materials produced in this variety are intended for pouring only leveling surfaces of small thickness.
Basically today, a similar composition is sold in the form of a ready-made concrete mortar. Mixing such material for pouring critical loaded structures requires high qualification of the specialists who perform this procedure. Ready-made solutions, of course, are more expensive than dry ones. After all, their transportation is quite expensive. But such material is most convenient to use. The solution structure is poured in one step by supplying the latter from the hose. For private developers, for example, the purchase of such material may be just the perfect solution for the construction of floors and slab foundations.
Some builders are interested in including 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 adhere to the requirements of GOST, taking into account the supply contract.
Where can be used
Of course, sometimes self-compacting mixtures can be used for pouring all kinds of structures in private housing construction. But today, such concrete is used in most cases by construction companies.
This material is still quite new for Russia. At the moment, even the domestic classification of such a tool has not yet been developed. Builders in the Russian Federation are guided when applying self-compacting concrete to euronorms. However, some documents governing the use of this material, and GOSTs in relation to it, have been created in our country today.
This applies, for example, to the field of application of self-compacting concrete. According to the norms of SNiP, in industrial construction such mixtures are allowed and it is recommended to use:
in the production of prefabricated reinforced concrete structures;
in the construction of hydraulic structures;
when pouring structures, the strength of which is subject to special requirements;
for pouring objects of complex architectural form;
in the production of lego bricks;
for the construction of structures having a small thickness (fences, piers, etc.).
Also, such mixtures are very often used for pouring durable seamless floors in the event that they will subsequently be subjected to severe loads (in workshops with heavy machines and equipment, in garages of special equipment, etc.).
Very often self-compacting concrete is also used in restoration work. Apply it in this case, for example, with shotcrete.
Kneading Requirements
When preparing solutions from dry self-compacting mixtures, among other things, it is necessary to:
Transporting such mixtures to the construction site is allowed exclusively by certified vehicles.
How to stack
In the final analysis, in order to obtain the most solid and durable construction, of course, all the required technologies must be observed when pouring such mixtures. When performing such work, it is first of all 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-sealing properties.
Before starting the filling itself, make sure that the formwork does not have, for example, rainwater. If available, subsequently poured self-compacting concrete will necessarily delaminate.
Among other things, the peculiarity of this type of solution is that its flow must pass some distance before actually laying into the formwork. This ensures the removal of air bubbles from the mixture. Like regular cement mortar, self-compacting is pumped into the formwork through large-section hoses. In order to avoid bubbles in such a mixture, it is supposed to use rather long sleeves for its supply according to the standards. However, this indicator according to SNiP should not exceed 200 m.
Special Occasion Rules
Concreting walls with self-compacting concrete (or, for example, ceilings) - the procedure is relatively simple. 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. As an example of such devices, forms for tall columns can be cited.
When pouring self-compacting mixtures into such formwork, certain rules should be followed. For example, in this case, the mixture is not allowed to be dropped down. When pouring the columns, the sleeve is usually lowered into the formwork and lifted as the latter is filled.
What are the disadvantages
The advantages of using self-compacting concrete mixes are thus many. The drawbacks of such formulations are practically nonexistent. The only drawback of this material, builders consider it a rather high cost.
Unlike conventional, such mixtures are characterized by a fairly high degree of ductility. In some cases, this may make them difficult to install. This builders, of course, are also attributed to minor flaws in the material of this variety.
Mix Reviews
To work with such material, according to builders, in fact, in most cases it is quite convenient. Self-sealing mixtures have earned good reviews from builders for their high quality and the pleasant appearance of the structures poured from them.
The builders' opinion on such concrete has developed, therefore, is 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 due primarily to the fact that almost every manufacturer in the Russian Federation today produces such solutions according to their 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, ductility and strength.
In addition, in our country today, according to some consumers, there are no materials suitable for the production of such compositions. This concerns, for example, gravel. In most cases, in the manufacture of self-compacting mixtures in Russia today, this type of material is not very suitable (due to the absence of impurities).