Features of the use of cement "NTs"

In the construction of both high-rise buildings and small buildings, the use of concrete mortar is an important component of correct and competent work. Without it, it is impossible to lay the foundation and floor screed. Concrete contains cement. It is not resistant to aggressive environments, does not tolerate cold temperatures, and also has poor water resistance. In addition, the cement shrinks strongly.

Stress cement ("NTs") has become widespread, since its application solves the above problems, the material can be stacked in difficult conditions. The main difference between stress cement is that when the concrete mixture hardens, it begins to expand. Due to this, low temperatures and shrinkage process do not harm the structure.

Portland cement, which is part of concrete, contains gypsum and fine cement clinker. On average, ordinary Portland cement shrinks around 2 mm / m. The full effect can be seen after 2 weeks of using the mixture, when the composition has hardened. There is a risk of cracking in the 3rd week.

Stress cement gives much faster expansion, which can be observed already 3 days after applying the mixture. That is, in this case, the concrete will harden much faster, which will give additional strength and help to preserve it during the "dangerous" period.

The composition of self-expanding cements contains a variety of additives, due to which a similar effect is achieved. The more such impurities there are, the faster the mixture expands, that is, the composition will harden in a shorter time. However, with too many additives, the hardening time can be reduced to 4-5 minutes, which will create additional difficulties in working with the material.

Self-expanding compositions are divided into four types - stress cement (NC), waterproof expanding cement (VRC), alumina expanding cement (GGRC / GC) and expanding portland cement (ROC). Stressing cement is most often used in construction work. It is a binder mixture and contains about 70 percent Portland cement clinker, up to 10 percent gypsum and up to 20 percent alumina slag.

Its main characteristics are fast setting and high strength. When diluted with water, the mixture sets in a short time. After this, the expansion process takes place. In 24 hours after laying, the composition gains a strength of about 300 kg / cm3.

In this regard, the material expands, and there is a load on reinforced concrete structures. It is important to understand that the characteristics of a mixture can vary, depending on its constituents.

By analogy with the conventional formulation, the stress cement has a longer service life due to the large number of positive properties. Even currently used modifying fillers cannot always compete with it. Due to this, the use of this mixture is characterized by good reviews of its use.

As for the technical characteristics, they can be seen on the back of the package. The initial setting time of the solution is mandatory. It takes about 30 minutes.Then comes the flexural strength after 48 hours and after 4 weeks - 3.8 MPa and 5.9 MPa, respectively, and the compressive strength at the same time will be 14 MPa and 49 MPa.

The packaging also indicates that work with the composition can be carried out at temperatures from +5 to +35 degrees. Stressing cement is packed in paper bags of 25 and 45 kilograms.

The time it takes for the cement to harden, as well as what technical characteristics it will have, depends mainly on the proportions of the main constituents of the material. In order for these points to be fixed and spelled out, the document GOST 31108-2003 appeared. It regulates the proportions of the components, which helps to avoid problems and misunderstandings during all construction work.

GOST 31108-2003 divides self-expanding compositions into 3 types:

• Non-shrinking compositions are marked with NTs 10 marking;
• NTs 20 are considered to be compositions with medium expansion;
• Cement with maximum expansion rates is used under the NTs 60 brand.

The use of NTs 20 helps to achieve a high level of concrete strength. Expansion and tensile strengths are higher than conventional Portland cement based mortars. The water pressure withstand by concrete with the addition of NTs 20 can reach 20 atmospheres, frost resistance - up to 1500 cycles.

All of these characteristics make this type of stress cement especially in demand in various types of construction work.

Due to the positive characteristics of the stress cement, the scope of its application is quite wide. Its use is relevant in the construction of swimming pools and the arrangement of treatment facilities. Given its resistance to adverse environments, it can be used to create structures subject to significant dynamic loads, as well as objects intended for the storage of toxic materials. Due to its waterproof properties and good adhesion properties to the previous concrete base, this self-expanding compound is often used in the repair of buildings that are prone to flooding, as well as in the manufacture of pipelines.

When arranging private houses for the creation of fireplaces and heating stoves, cement of the NT 20 brand is often used. In the construction of a bath, garage, underground premises, this composition will also become an indispensable assistant. For any work requiring resistance to temperature extremes, waterproofing, it is also advisable to use stress cement. Indispensable for filling cracks and seams, increases the strength of the bases.

To obtain the greatest effect when using stress cement, the entire area in which it will be used must be carefully prepared. Joints and surfaces must be thoroughly rinsed and degreased, and the walls of the formwork must be moistened.

The list of items required when using the composition is quite voluminous. It is necessary to prepare special clothing in which the work will be carried out. You will also need: a container in which the mortar will be mixed, a shovel, rags, high-frequency vibrators for concrete and a triangular trowel for applying cement.

To begin with, the composition itself is being prepared. Sifted river sand is mixed with cement in a 2: 1 ratio and filled with water to about 40 percent of the powder mass.After the composition is thoroughly mixed to a homogeneous consistency, it is poured into the formwork or used to seal seams, cracks and joints. After the composition has been applied, it must be properly compacted and left for 24 hours. After that, the surface is moistened for another week.

All types of cement are marked without fail. This is done so that it is clear what composition and for what purpose it can be used. Includes numbers and letters.

Until 2003, GOST 101785 was used. Its designations included the type of mixture, its strength, and the presence of mineral additives, which was indicated as a percentage. At the end, additional properties were noted.

According to the currently valid GOST 31108, the labeling has changed slightly, but for the convenience of buyers, both options are still mostly used on the packaging. In the new labeling, the first is the composition (I - with no additives, II - with additives). Mixtures with additives are divided by their quantity, the letter "A" denotes the presence of 6 to 20 percent of impurities, the letter "B" - from 21 to 35 percent. Roman numerals indicate what type of additive is used in the mixture.

Further, the numbers indicate the strength limits - from 22.5 to 52.5 MPa, and the norms of material compression, which range from 2 to 7 days and are designated by letters: "H" - normally hardening, "C" - medium hardening, "B" - fast hardening composition. The most actively used, given its properties, is 32.5N grade cement. The M500 is suitable for specialized facilities, as it is particularly reliable and has a longer service life.

According to the experience of professionals, stress cement has many more advantages than disadvantages.

• For example, it is not subject to shrinkage, which has a beneficial effect on the strength of objects, quickly sets, is resistant to the influence of a negative environment and external pressure, has properties such as waterproofing, resistance to low temperatures, fire safety, waterproofing.
• The operating time of objects when using this mixture in operation increases several times.

There are also negative aspects.

• One of them is the rather high cost of this material. But this is more than pays off with the durability of the buildings.
• In addition, at too low temperatures, often acting on concrete, the stress cement may lose some of its properties. It will also be useful to check the certificate of conformity of the purchased product in order to avoid possible fakes.

How to mix the cement mortar correctly, you can learn from the following video.