Concrete for precast concrete elements

The main direction of the precast concrete industry - production of standardized designs and details for zhilischnogo and promyshlennog of construction.

For precast concrete structures used osnovnye all types of concrete: heavy, light porous aggregates and yacheisty. Concrete is often used in conjunction with spetsialnogo use materials (thermal insulation, sound insulation, anti-corrosion and gidroizolyatsionnymi), which significantly uluchshayut performance prefabricated and increase their durability.

Because precast concrete manufacturing all parts of the building: fundamenty, basement walls, interior and exterior walls, frame and covering elements, intercommunication floors, stairs, etc. (Figure 20.5.)..

The outer walls of large buildings can be odnosloynymi of lightweight concrete and three-layer - from light or heavy concrete with internal insulation layer (of the mineral wool, foam glass, etc..).

On the intercommunication overlap in large-panel residential buildings consumes a significant portion of precast concrete (about 30%). The use of intermediate floors of lightweight concrete reduces the weight of the building, thus improving sound insulation.

The projects of industrial buildings, constructed of precast concrete. Thin prestressed plastiny length of 12-30 m, manufactured by continuous armirovaniya are used in large-span suspension constructions zdany and structures. The plates can be bend without cracking, creating a variety of these coatings.

Production of concrete and concrete prefabricated konstruktsy can be organized in two fundamentally otlichnymi ways: in-line moved in forms or peremeschaemyh pallets; bench in stationary (unmovable) forms.

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

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.

Cement mortar

Grout - this is probably the most important element in quality construction. At first glance, it seems that such a mixture to cook simple. By and large, this is the correct assumption. But for a first-class cement mortar is very careful approach to the selection of the optimal component composition and proportions. Before you learn the subtleties of receipt of such building materials, let's find out the function of each of the components in its formation. Cement-sand rastvor.S technical point of view, the foundation of the solution is water. Therefore, it is better to take a pure content without any water impurities. The filler sand acts in solution and binds together all the components of cement. During the preparation of cement mortar must be carefully approach the issue of the quality of sand. Firstly, it is necessary to ensure the absence of clay and other rocks, debris. Second, pick the right crop of sand. For example, fine sand is best used for masonry and rough sand plastering can cause more grinding or leveling.

Choosing cement must take into account some of its features. First, even with prolonged storage of unopened cement can zakamenet and become unfit for work. Therefore, it is wiser to buy cement before starting work. Secondly, the cement should be packaged only in paper. It is important to choose the correct grade of cement, depending on the type of construction work. For example, the foundation can not be used with cement brand M300 below. Consider the recommendations and standards for the preparation of cement-sand mortar, depending on the type of work. M400 brand cement used in the construction of massive whole buildings need to use M400 cement. If M400 mix cement and sand in the ratio 1: 2, the composition obtain M200. For finishing, surface preparation to the wall, it is desirable to take for a mixture of cement M400 or M500, sand and water at a ratio of 1: 3: 0.5. If we increase the relative proportion of cement in the solution, it is possible to reduce the curing time of plaster. Also, a good result is obtained with a ratio of cement, sand and lime milk 1: 5: 2 in plastering and screeds for floors - at a ratio of 1: 2-1: 6. When building is optimal ordinary buildings standing ratio from 1: 3 to 1: 6. In a life as popular proportions - 1: 3 and 1: 4.

Plaster

Plaster - finishing layer formed by the hardened mortar, as well as the mixture itself. Classification: Plaster can be categorized by purpose: Ordinary plaster - designed to align the walls (creating a flat, level surface for subsequent application of a thin layer of decorative coatings) and the protection of the external walls of buildings from environmental sredy.Spetsialnye plaster - are used as insulating layers and filmed (. sound-absorbing, heat-saving, X-ray, etc.) Decorative plaster - used for finishing walls, ceilings and structures to enhance their aesthetic vyrazitelnosti.Dekorativnye plaster, in turn, are subdivided into the following types: - colored plaster, which is ideal for interior walls, door and window openings. - Stone plaster that their appearance resembles natural stone. - Venetian plaster. This type of plaster in appearance resembles a real mramor.Terrazitovaya plaster. This type is suitable for interior walls and plaster fasadov.Shёlkovaya - intended for interior use. Non-flammable, does not accumulate static electricity. The material consists of natural or synthetic fibers, mineral fillers and different decorative additives. Apply a plastic spatula on plastered and coated with a primer or oil paint surface. It has a variety of color and texture solutions, has no odor, is obtained by applying a seamless coating, the material is flexible and will not crack when "shrinkage" of the walls. The main disadvantage - poor moisture resistance, but when processing a moisture varnish can be used in rooms with high humidity (kitchen, bathroom, etc.) The most common conventional plasters are: mortar, cement-sand mortar, plaster smesi.Izvestkovye solutions. mainly used in outdoor applications, as well as the inner workings and the main advantages of this material are its speed and ease of use of the substrate, as well as maximum environmental friendliness. Among the shortcomings noted relatively low strength compared with other materials. The material consists of slaked lime and river sand in the ratio 1: 4, is used with the addition of tsementa.Tsementno-sand solutions are used both in domestic and outdoor applications. The popularity is due to the cheapness of the finishing materials. They are a little more complex in application, but the coating is much stronger than when working with lime or plaster solution. The material consists of sand and cement in a ratio of 1: 4, for small amounts in ductility added lime or PVA glue. Subject to the application of technology, the life of the finished coating exceeds several decades. Cement-sand solutions allow to align the strengths flaws poverhnosti.Gipsovye mix - intended for interior use. Using plaster mixes can obtain a smooth white coating. The main disadvantages of the material are its higher cost compared with other materials, insufficient moisture resistance, poor water vapor transmission rate and low strength. Also, in the pursuit of a consumer wishing to save on finishing thin layer mixture in the gypsum plaster is often added to asbestos and other adverse human health chemical additives that give the white surface. However, gypsum plasters can significantly simplify the process of finishing the cycle and reduce the time spent on alignment of the walls, which affects the popularity of data materialov.Magnezialnye mix - intended for interior use. Non-combustible, high-strength, non-dusting compositions for plastering interior walls of buildings for painting, tile, wallpaper, and so on. N. They belong to the category of non-dusting and non-combustible materials

Cementing deep wells

In principle, all portland cement the well borehole. They differ from conventional standard cements requirement that they should be produced without the addition of recycled fuel and distillate. They can not even be used intensify the additive. Cements are usually manufactured in a batch mode with fineness of 3000 cm2 / g Blaine, i.e. they are relatively coarse. Today Base uses two class G cement and Class H. Tampon Their technical properties controlled can be adjusted with suitable retardants for use in almost any desired downhole temperature to 250 ° C and thus, they are universal cements. According to API standard mortar class G is tested with W / C ratio is 0.44, Class H cement tested at the W / C ratio is 0.38. These indicators are only slightly deflected by praktike.Skvazhinnoe pressure increases the temperature and results in faster hardening of Portland cement and, therefore, accelerates well cementing accelerates hydration product formation. As a result, at a temperature of about 110 ° C C-S-H gel forms a highly-S2SH crystallinity and, thus, most of the hydration products becomes denser. This conversion process requires a strong shrinkage and partial loss of strength of the hardened cement paste, with devastating consequences for the well density. In a class of standardized G- slurries reduction in compressive strength may be 80%, and 100-fold increase in permeability (typically 0.1 mDarsy) is observed at 230 ° C. This is "the power of regression." The marked technical problem is solved by reducing the ratio CaO: SiO2 - solution ratio is about 1. For this purpose, for oil wells, operating at temperatures above 110 ° C, prepared slurries containing 30-40% quartz flour. Under these conditions, it is obtained as the preferred phase C-S-H - tobermoritopodobny (C5S6H5) mineral which is not formed at normal temperature and elevated temperature.Pri calcium aluminates and others in hydrated form products. It turns C3A at a temperature of about 80 ° C instead of hexagonal C2AH8 cubic C3AH6 (Kato). Ettringite at about 110 ° C becomes unstable and decomposes with the formation of C-A-N phase CaSO4.Burovoy hemihydrate and cement, in particular, two basic Class G Cement and Class H iz-za fit their well-defined composition and preparation method as for manufacturing of complex building structures is responsible oil and gas wells. Their purity and quality make them particularly interesting for research.