Concrete

The construction of extensive use of concrete, made of cement or other inorganic binders. These concretes are usually shuts water. Cement and water are the active components of the concrete result of the reaction between the cement stone formed, cementing grains aggregate into a single monolith. Between cement and aggregate are usually not the case of chemical interaction (with the exception of silicate concretes obtained autoclaving), so fillers are often called inert materials. However, they significantly influence the structure and properties by changing its porosity, terms of solidification behavior under the influence of load and environment. Rigid greatly reduce the strain of concrete in hardening and thus provides more dimensional products and designs. As the aggregates are used mostly local rocks and waste (slag, etc.). Application of these cheap fillers reduces the cost of concrete, as aggregates and water are 85 ... 90%, and cement - 10 ... 15% of the mass of concrete. In recent years, widely used in the construction of lightweight concrete, produced by artificial porous aggregates. Porous fillers reduce the density of concrete, improve its thermal properties. To control the properties of concrete and concrete in their composition is introduced various chemical additives that accelerate or retard setting of concrete mix, make it more plastic and workable, accelerate hardening of concrete, increase its strength and frost resistance, and if necessary change, and other properties of concrete. Concrete on mineral binders are capillary-porous bodies on the structure and properties of which have significant influence both internal processes of interaction between the components of concrete, and the impact of the environment. For a long time in the concrete of a change in the pore structure, there is a course of structure, and sometimes destructive processes and as a result - changing the properties of the material. With increasing age of concrete increases its strength, density, resistance to the environment. Properties of concrete is determined not only by its composition and quality of raw materials, but also the technology of preparation and laying of concrete in construction, the conditions of concrete hardening. All of these factors into account when designing and manufacturing of concrete structures based on it. On organic binders (bitumen, synthetic resins, etc.), concrete mix obtained without the introduction of water, which provides high density and impermeability of concrete. The variety of binders, fillers, additives and processing methods allows to obtain concrete with a variety of properties. Concrete is a brittle material: its compressive strength is several times higher than a few times higher tensile strength. For the perception of concrete tensile stresses are reinforced with steel rods, obtaining concrete. In reinforced concrete rebar have so that she felt the tensile stresses and compressive stresses transmitted to the concrete. Collaboration reinforcement and concrete is due to good adhesion between them and about the same temperature coefficients of linear expansion. Concrete protects the rebar from corrosion. Concrete and reinforced concrete structures are made either on-site construction - reinforced concrete and reinforced concrete, or in the factories and test sites in the subsequent assembly at the construction site - a prefabricated concrete and reinforced concrete. Classification of concrete currently used in the construction of various types of concrete. To understand their diversity helps the classification of concrete. Concretes are classified according to the average density, type of binder and purpose. Many of the properties of concrete depend on its density, the value of which affect the density of the cement, the type of aggregate and concrete structure. The density of concrete is divided into very heavy with a density of 2500 kg / cubic meter. pm; heavy - 1800 ... 2500; lungs -500 ... 1800; very light - less than 500 kg / cubic meter, m especially heavy concrete is prepared for heavy fillers - steel filings or shavings (reinforced concrete), iron ore (magnetite limonitovy and concrete) or barite (barite concrete). Heavy concrete with a density of 2100 ... 2500 kg / cubic meter. am prepared to dense aggregates of rocks (granite, limestone, diabase). Lightweight concrete with a density of 1800 ... 2000 kg / m? get on the rubble of rocks with a density of 1600 ... 1900 kg / cubic meter, m lightweight concrete manufactured by porous aggregates (expanded clay, agloporit, expanded slag, pumice, tuff). By special lightweight concrete include cellular concrete (aerated concrete, foam), which receive bulging binder, finely additives and water with the help of special methods and macroporous lightweight aggregate concrete. The main component of concrete, which largely determines its properties, is a binder, which are distinguished by type of concrete cement, silicate, gypsum, shlakoschelochnye, and special polymer. Cement concrete is prepared in various cements and most widely used in construction. Among these products is dominated by concrete on cement (Portland) and its variants (about 65% of total production), was successfully used for slag cement concretes (20 ... 25%) and pozzolan cement. The varieties of cement concrete are: decorative concrete, (white and colored cement), concrete for samonapryazhennyh designs (on bend cement), concrete for special purposes (for alumina and non-shrinking cement). Silicate concretes prepared on the basis of lime. For manufacturing products in this case, the method of autoclave curing. Gypsum concrete is ready, based on gypsum. Gypsum concrete is used for interior walls, ceilings and decor elements of buildings. These are the kind of concrete sheetrock - pozzolanic concretes having high water resistance. Application-volume blocks of toilets, construction of low-rise buildings. Shlakoschelochnye concrete make for crushed slag, mixing with alkaline solutions. These concretes are just beginning to be used in construction. Polymer manufactured by different types of polymer matrix, which is based resins (polyester, epoxy, urea) or monomers (furfurolatsetonovy) solidified in concrete with special additives. These concretes are more suitable for service in aggressive environments and specific conditions of exposure (abrasion, cavitation). Polymer concretes receive a mixed binder consisting of cement and polymeric substances (water-soluble resin and latex). Special concretes prepared with the use of special binders. For acid-and heat-resistant concretes used liquid glass with fluorosilicate sodium phosphate binder. As a special binders used slag, nepheline and stekloschelochnye obtained from industrial wastes. Concrete is used for various kinds of structures, as produced in the factories of precast concrete, so erected directly on site (in hydraulic engineering, road construction). Depending on the application are distinguished: conventional concrete for reinforced concrete structures (foundations, columns, beams, slabs and bridge structures); hydraulic concrete for dams, locks, canal lining, water supply and sanitation facilities is concrete for enclosing structures (lightweight) concrete for floors, sidewalks, road and airfield pavement concrete for special purposes (heat-resistant, acid, for radiation protection). General requirements for all concrete and concrete mix should be: to hardening of the concrete mixture should be easily mixed, transported, packed (have mobility and workability), not to delaminate, concrete must have a certain rate of curing in accordance with specified terms of stripping and putting into operation construction; consumption Cement and concrete costs should be minimal.