121. Self-compacting concrete

SCC is a material which is able to be compacted under its own weight, completely filling the shape even in gustoarmirovannyh structures. It is becoming more widely used. It is promising to use it for the production of precast concrete, high-strength monolithic device screed, torkretbetonirovaniya, restoration and strengthening of structures.

Special high-strength concretes modified with additives super-plasticizers, began to be used in the late 60's - early 70-ies of the last century. In particular, in 1970, a concrete was used by Norwegian and British experts for the construction of oil platforms in the North Sea. Experience in the use of such material has shown the advantages of the introduction of superplasticizers in the concrete mix, but was seen by a number of restrictions in dealing with them. Firstly, most superplasticizers, particularly at high doses, can slow the setting of the concrete mixture. Secondly, during transportation for 60-90 minutes, the effect of the additive is reduced, i.e. reduced mobility. Thirdly, the feed mixture through the pipeline to the place of installation at a distance of over 200-250 meters stimulates bundle and creates nonuniformity in the final product. As a result, the execution of concreting works increases, deteriorating the quality of the surface of products, reduced strength.

The emergence of new ambitious projects in the construction industry (extended suspension bridges in Japan and China, large hydraulic systems and transport facilities in the Netherlands and a number of others) increased requirements for special high-strength concrete. With the construction of such structures was necessary to use casting mixes in bulk and concreting sections were often at a great distance from the place of production of concrete, and even at a considerable distance from the coast (on the water). Furthermore, another necessity was to reduce the time and effort to seal the concrete mix, as well as increased strength development at early stages.

The solution of these problems contributed to the theoretical study and practical implementation to:

• Use multifraktsionnogo filler for high-strength concrete;

• the introduction of micro- and ultrafine filler to improve strength, corrosion resistance and fracture toughness of the material;

• control the rheology of high-mobility concrete mixes;

• the creation of new types of chemical modifiers, regulators properties of

122. Building mortar

Mortars called material obtained as a result of hardening of the mixture of binder (cement), fine aggregate (sand), a mixing (water) and, where appropriate, special additives.

The following types of mortars: limestone, clay, clay, lime, lime-plaster and clay-cement. Prior to the addition of clay in the mortar, it must be carefully sifted through a fine sieve.

One of the main requirements for a mortar is long it is necessary to stir odnorodnost.smes tools so that the ingredients in the mass can not be distinguished. It is of great importance and the proportion of components. Depending on the purpose (plaster, masonry, sealing of cracks, etc.) change the composition of the solution.

For large content of the binder, mortar obtained bold. As a result, cracks are formed in the plaster after drying. If the total mass of sand prevails, such solutions are called lean. Of these, it turns unstable and poor plaster.

Determine which solution is obtained by simply kneading. If the mass is strongly stick to the instrument, the solution turned out in bold. If it does not stick, then the mortar turned postnym.pravilno made solution should slightly stick to the instrument.

Preparation of lime mortar.

On a solid surface is poured sand, leveled. Then the top is poured the required amount of lime. The layers are first mixed with a shovel, and then carefully mixed using a hoe. In the middle of the resulting mixture is a crater, which is filled with water.

The mixture was stirred so that the crater is gradually filled with a mixture, but it must be above the edge of the solution to avoid the possibility of overflow. Correctly made solution is a homogeneous thick mixture.

Preparation of the clay mortar.

Clay mortar used in secondary or auxiliary constructions for plaster and masonry. It makes this solution as well as limestone, clay solution but not so strong. To increase the strength of the solution added into it cement, lime or gypsum. To prepare the clay-cement mortar materials are taken in the following proportions: 1 part clay accounted 0.15-0.2 part cement and 3-5 parts of sand.

To prepare the clay-lime mortar 1 part clay is necessary to take 0.3-0.4 parts hydrated lime and 3-6 parts of sand. The amount required depends on the sand mortar destination. In order to make gypsum-clay solution to 1 part of clay should take 0.25 parts of gypsum and 5.3 parts of sand.

Preparation grout construction.

Cement is one of the main materials in the construction. The cement consists of a mixture of limestone and clay. This mixture is first sintered and then ground to a gray powder, which consists of CaO, Al2O3 and SiO2. If the mixture to add water and stir into the dough, the resulting mass over time hardens. When added to cement, sand and crushed concrete obtained. In the case where the product is placed inside the concrete reinforcement (frame made of iron bars or meshes) to obtain a solid material which is called reinforced concrete. Rastvorotlichaetsya cementitious binders from the rest so that after it is mixed with water hardens, and in the solid state it is stable to water. In order to make a quality material should 24-28% water. In the case of a larger or smaller amount of added water decreases the quality of the solution.

The cement slurry starts to harden in about an hour after it is mixed with water. After about 12 hours the mortar loses its plasticity and harden stops. At higher temperatures, the cement hardens quickly, so in the warmer months, the cement mortar hardens quickly. In order to accelerate the drying process for preparing the mix certain additives can be used.