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Classification of concrete

Concrete - artificial stone obtained by molding and hardening a rationally selected mixture of binder, water and aggregates (sand and crushed stone or gravel). The mixture of these materials before hardening is called a concrete mixture.

Concrete is classified according to the following leading characteristics: by main purpose, type binder both filler and structure.

By purpose concretes are of the following types:

constructive - for concrete and reinforced concrete load-bearing structures of buildings And structures (foundations, columns, beams, slabs, floor panels, etc.);

special - heat-resistant, chemical-resistant, decorative, radiation-protective, heat-insulating, etc.,

concrete prestressing, concrete polymers, polymer concretes .

By type of binder concrete substances are: cement , made with hydraulic binders - Portland cement and its varieties; silicate - on lime binders in combination with silicate or aluminate com-ponets; plaster - using gypsum anhydrite binders and concretes on slag and special binding materials.

Concrete is produced using conventional dense fillers, on natural or artificial porous fillers; In addition, a variety is cellular concrete, which is a hardened mixture of binder, water and fine silica component. It is characterized by high porosity up to 80...90% with evenly distributed pores measuring 3 mm.

In this regard, concretes are also classified according to their structure: dense, porous, cellular Andlarge-porous.

By type of filler Concrete is distinguished: with dense aggregates, porous and special, meeting special requirements (protection from radiation, heat resistance, chemical resistance, etc.).

By strength indicators during compression, heavy concrete has grades from 100 to 800. The grade of concrete is one of the standardized values ​​of a unified type of a given concrete quality indicator, taken according to its average value. TO various types concrete requirements are established for indicators characterizing strength, average density, water resistance, resistance to various influences, elastic-plastic, thermophysical, protective, decorative and other properties of concrete.

Certain requirements are imposed on materials for preparing concrete (binders, additives, fillers), its composition and technological parameters for the manufacture of structures for their operation in specific conditions.

Based on concrete strength indicators, their guaranteed values ​​- classes - are established. According With ST SEV 1406-78 concretes intended for buildings and structures are divided into classes B, the main controlled characteristic of which is the compressive strength of cubes measuring 150XI50X150 mm and, accordingly, cylinders measuring 150X300 mm. To transfer from concrete class (MPa) with a standard coefficient of variation of 13.5%, use the formula

R avg.bet = B/0.778.

Durability concrete is assessed by the degree of frost resistance. According to this indicator, concrete is divided into grades from F15 to F1500. The quality of concrete is assessed by water resistance, which is determined by the maximum value of water pressure at which no leakage is observed through control samples manufactured and tested for water resistance in accordance with the requirements of current standards.

Materials for heavy concrete (START)!

Heavy concrete used for the manufacture of foundations, columns, beams, bridge spans and other load-bearing elements and structures of industrial and residential buildings and engineering structures must acquire a certain strength within a given curing period, and the concrete mixture must be easy to lay and economical. When used in structures not protected from the external environment, concrete must have increased density, frost resistance and corrosion resistance. Depending on the purpose and operating conditions of concrete in a structure, appropriate requirements are imposed on its constituent materials, which predetermine its composition and properties, influence the technology of production of products, their durability and efficiency.

For the preparation of heavy concrete, Portland cement, plasticized Portland cement, Portland cement with hydraulic additives, Portland slag cement, rapid-hardening Portland cement (BTC), etc. are used. Cement is selected taking into account the requirements for concrete (strength, frost resistance, chemical resistance, water resistance, etc.), as well as technology for manufacturing products, their purpose and operating conditions. The brand of cement is chosen V

depending on the designed compressive strength of concrete: For cooking concrete mixture drinking water is used, as well as any water that does not contain harmful impurities (acids, sulfates, fats,, sugar), which prevent the normal hardening of concrete. You cannot use swamp and waste water, as well as water contaminated with harmful impurities, having a pH value of less than 4 and containing sulfates calculated as SO 4 ions more than 2700 mg/l and all other salts more than 5000 mg/l. Sea and other water containing mineral salts can be used if the total amount of salts in it does not exceed 2%. The suitability of water for concrete is established by chemical analysis and comparative tests of the strength of concrete samples made with this water and with clean drinking water and tested at the age of 28 days during storage under normal conditions. Water is considered suitable if samples prepared with it have a strength no less than that of samples with clean drinking water. Additives for concrete include inorganic and organic substances or mixtures thereof, through the introduction of which in controlled quantities the properties of concrete mixtures and concretes are specifically regulated or Concrete is given special properties. The classification of concrete additives is based on the effect of their action. Based on this criterion, concrete additives are divided into the following groups:

1. Regulatory rheological properties concrete mixtures. These include plasticizers, which increase the mobility of concrete mixtures; stabilizing, preventing delamination, and water-retaining, reducing water separation.

2. Regulating the setting of concrete mixtures and concrete hardening. These include additives that retard setting, accelerate setting and hardening, and anti-frost, i.e., ensuring hardening of concrete at subzero temperatures.

3. Additives, porosity regulating concrete mixture and concrete. These include air-entraining, gas-forming and foam-forming additives, as well as compacting (air-removing or clogging concrete pores).

4. Additives, giving concrete special properties: hydrophobic, reducing wetting, increasing radiation protection, heat resistance; anti-corrosion, i.e. increasing resistance in aggressive environments; steel corrosion inhibitors that improve protective properties concrete to steel; additives that increase bactericidal and insecticidal properties.

5. Additives multifunctional action, simultaneously regulating various properties of concrete mixtures and concretes: plasticizing-air-entraining; plasticizing, increasing the strength of concrete, and gas-forming-plasticizing.

6. Mineral powders - cement substitutes. The brand of cement is chosen This group includes finely ground materials introduced into concrete

amount 5...20%. These are ash, ground slag, stone crushing waste, etc., which give concrete special properties (heat resistance, electrical conductivity, color, etc.).

Surfactants (surfactants) are the most widely used plasticizing additives. TO , cement hardening accelerators increasing the strength increase of concrete, especially in early dates

, include calcium chloride, sodium sulfate, nitrite-nitrate-calcium chloride, etc. Antifreeze additives

- potash, sodium chloride, calcium chloride, etc. - lower the freezing point of water, which contributes to the hardening of concrete at subzero temperatures. For setting retardation

Sugar syrup and additives SDB, GKZh-10 and GKZh-94 are used. Sand - a loose mixture of grains with a particle size of 0.16...5 mm, formed as a result of the natural destruction of massive rocks

(natural sands). Natural sands according to their mineralogical composition are divided into quartz, feldspathic, limestone, and dolomite. Of the natural sands, quartz sands are most widely used for heavy concrete.

Sands of increased coarseness are used as fine aggregates, coarse, medium and fine - natural and enriched; sands from crushing screenings and enriched sands from crushing screenings. The grain composition of sand is of particular importance for obtaining high-quality concrete. Sand for concrete should consist of grains of various sizes (0.16...5 mm) so that the volume of voids in it is minimal; The smaller the volume of voids in the sand, the less cement is required to obtain dense concrete. The grain composition of sand is determined by sifting dry sand through a standard set of sieves with hole sizes (from top to bottom) 10; 5; 2.5; 0.63; 0.315; 0.16 mm. A sand sample dried to a constant weight is sifted through sieves with round holes with a diameter of 10 and 5 mm. The residues on these sieves are weighed and calculated to the nearest 0.1%.

CONTINUATION!

Materials for heavy concrete (END)!

From a sample of sand that has passed through the above sieves, weigh 1000 g (G) of sand and sift it sequentially through a set of sieves with holes of size 2.5; 1.25; 0.63; 0.315 and 0.16 mm. The residues on each sieve are weighed (G,) and calculated:

the partial residue on each sieve - as the ratio of the mass of the residue on a given sieve to the mass of the sieved sample (a;) - is calculated with an accuracy of 0.1%:

the total residue (L) on each sieve - as the sum of partial residues on all sieves with large openings plus the residue on a given sieve - is calculated with an accuracy of 0.1%:

Ai = a2.5 + a1.25 + ... + ai,

where a2.5, a1.25, ... are partial residues on sieves with large openings starting from a sieve with openings of 2.5 mm, %; a, - partial residue on a given sieve, %.

The sand fineness modulus Mk (without gravel fractions with grain sizes larger than 5 mm) is determined as the quotient of the sum of total residues on all sieves divided by 100, starting with a sieve with a hole size of 2.5 mm and ending with a sieve with a hole size of 0.16 mm ;

sand fineness modulus is calculated with an accuracy of 0.1%:

Mk = (A 2 ,5 +A 1, 25 + A ABOUT .63 + A0.315+Ao,16)/100.

According to the size of the fineness modulus, sand is divided into increased fineness M To - W...3.5, large with M To > 2.5, average M To = 2.5...2.0, small Mk = 2.0...1.5 and very small M To = 1,5...1,0;

the total residues on sieve No. 063 (% by weight) are respectively equal to: 65...75, 45...65, 30...45, 10...30 and less than 10.

The grain composition of the fine aggregate must correspond to that indicated on the graph (Fig. 6.1). In this case, only grains passing through a sieve with round holes with a diameter of 5 mm are taken into account.

AS A LARGE aggregate used for heavy concrete gravel and crushed stone from rocks or crushed stone from gravel with a grain size of 5...70 mm.

Gravel- grains of a rounded shape and a smooth surface with a size of 5...70 mm, formed as a result of the natural destruction of rocks. The quality of gravel is characterized by: grain composition and grain shape, strength, grain content of weak rocks, the presence of dust and clay impurities, petrographic characteristics, density, porosity, voids and water absorption. For concrete, the most suitable form of grains is low-rounded (crushed stone), ovoid (rounded) is worse, lamellar and needle-shaped, which reduce the strength of concrete, are even worse.

Often gravel occurs along with sand. When the sand content in gravel is 25...40%, the material is called a sand-gravel mixture. Gravel, like sand, may contain harmful impurities of dust, silt, clay, organic acids...

The strength of gravel is assessed by testing for crushability in a cylinder. The latter is determined by crushing a gravel sample in a cylinder with a static load. After this, the sample is sifted through a sieve with a hole size corresponding to the smallest grain size in the original gravel sample, and the amount of weight loss is determined. Depending on this value, gravel is divided into grades: Dr8 (with a loss in weight of up to 8%), Dr12 (over 8 to 12%), Dr16 (over 12 to 16%) and Dr24 (over 16 to 24%).

For the construction of industrial and civil buildings, the strength of gravel grains should be more than 1.5...2 times higher than the strength of concrete.

According to the degree of frost resistance, gravel is divided into grades F 15, 25, 50, 100, 150, 200 and 300. Frost resistance of gravel is determined by direct freezing or testing in a solution of sodium sulfate. Gravel is considered frost-resistant if, in a water-saturated state, it can withstand repeated (15 cycles or more) alternating freezing at a temperature of -17°C and thawing without destruction. In this case, the loss in mass after testing is more than 5%. For grades F 15 and 25, a weight loss of 10% is allowed

A good grain composition of gravel is considered to be one in which there are grains of different sizes, which creates the least voids. The grain composition of gravel is determined by sifting 10 kg of dry sample through a standard set of sieves with opening sizes of 70, 40, 20, 10 and 5 mm. The grain composition of each fraction or mixture of several fractions of gravel must be within the limits indicated in the graph in Fig. 6.3. The largest size of gravel grains, Dmax, is taken to be the size of the sieve openings, on which the total residue does not exceed 10% of the sample, and the smallest gravel size, Dmax, is the size of the opening of one of the upper sieves, through which no more than 5% of the sifted sample passes. Below are the values ​​of total residues on control sieves when sifting gravel (cold) fractions from 5 (3) to 10 mm, over 10 to 20; over 20 to 40 and over 40 to 70 mm.

Crushed stone is produced by crushing massive rocks, gravel, boulders or artificial stones into pieces measuring 5...120 mm. To prepare concrete, crushed stone is usually used, obtained by crushing dense rocks, gravel, blast furnace and open-hearth slag. Crushing is carried out in stone crushers. In this case, not only crushed stone grains are obtained, but also small fractions related in size to sand and dust. The crushed stone grains have an irregular shape. The best shape is considered to be one that approaches the cube and tetrahedron. Due to the rough surface, crushed stone grains adhere better to the cement stone in concrete than gravel, but the concrete mixture with crushed stone is less mobile.

In terms of crushability, frost resistance, grain composition, and wear, crushed stone has the same requirements as gravel.

Depending on the shape of the grains, GOST 8267-82 establishes three groups of crushed stone from natural stone: cuboid, improved and ordinary. The content of lamellar (flaky) and needle-shaped grains in them does not exceed 15, 25 and 35% by weight, respectively. Lamellar and needle-shaped grains include those in which their thickness or width is 3 times or more less than their length.

Properties of concrete mixture

Heavy concrete must acquire design strength by a certain date and have other qualities corresponding to the purpose of the structure being manufactured (water resistance, frost resistance, density, etc.). In addition, a certain degree of mobility of the concrete mixture is required, which would correspond to the accepted methods of laying it.

Concrete mixture is a complex multicomponent system consisting of new formations formed during the interaction of binder with water, unreacted clinker particles, filler, water, introduced special additives and entrained air. Due to the presence of interaction forces between dispersed particles of the solid phase and water, this system becomes connected and can be considered as a single physical body with certain rheological, physical and mechanical properties.

The determining influence on these properties will be exerted by the quantity and quality of cement paste, which, being a dispersed system, has a highly developed interface between the solid and liquid phases, which contributes to the development of molecular adhesion forces and increased cohesion of the system.

Workability is the ability to fill a mold with a given type of compaction. Har-sya mobility, rigidity and coherence.

Mobility of concrete mixture- its ability to spread under its own weight. To determine under. For visibility, a cone is used (Fig. 6.4), which is filled layer by layer in three steps with concrete mixture, compacted by bayonet. After compacting the latter, the mold is removed. The resulting cone of concrete mixture settles under the influence of its own mass. The amount of cone settlement (cm) serves as an estimate of the mobility of the concrete mixture. Based on this indicator, a distinction is made between flexible (plastic) mixtures with a cone settlement of 1...12 cm or more, and rigid mixtures, which practically do not give a cone settlement, but when exposed to vibration, the latter have different molding properties. To assess the hardness of these mixtures, they use their own methods.

Hardness index concrete mixture is determined using a special device (Fig. 6. 5), which consists of a cylindrical vessel with an internal diameter of 240 mm and a height of 200 mm with a device attached to it for measuring the slump of the concrete mixture in the form of a guide stand, a rod and a metal rod and six holes. The device is installed on a vibration platform and tightly attached to it. Then a metal cone mold with a nozzle is placed in the vessel, which is fixed in the device using a special holder ring and filled with three layers of concrete mixture. Then the cone shape is removed by turning the tripod, a disc is placed on the surface of the concrete mixture and the vibrating platform is turned on. Vibration with an amplitude of 0.5 mm is continued until the release of cement paste from two holes of the disk begins. The vibration time (s) determines the hardness of the concrete mixture. The classification of concrete mixtures according to the degree of their rigidity (workability) is given in Table. 6.2.

Table 6.2.Classification of concrete mixtures

The mobility of a concrete mixture is influenced by a number of factors: type of cement, water and cement paste content, aggregate size, grain shape, sand content.

The introduction of a surfactant, such as SDB, into the concrete mixture increases the mobility of the concrete mixture and reduces its water demand. Superplasticizers (S-3, 10-03, 40-03, etc.) have a positive effect on the mobility of the mixture. Their efficiency is higher in mobile mixtures; they can reduce the water requirement of the mixture by 20...25%.

At the same time, it should be taken into account that the mobility of the mixture decreases over time due to the physicochemical interaction of cement with water.

Connectedness- characterizes the homogeneity of the concrete structure.

Concrete composition design

The design of the composition has the goal of establishing such a consumption of materials per 1 m 3 of concrete mixture, which most economically ensures the production of a workable concrete mixture and the specified strength of concrete, and in some cases the necessary frost resistance, water resistance and special properties of concrete.

The composition of the concrete mixture is expressed as a ratio by mass (less often by volume) between the amounts of cement, sand and crushed stone (or gravel), indicating the water-cement ratio. The amount of cement is taken as one. Therefore in general view The composition of the concrete mixture is expressed by the ratio cement: sand: crushed stone = 1: x:y at W/C = z (for example, 1:2.4:4.5 at W/C = 0.45).

There are two compositions of concrete: nominal(laboratory), accepted for materials in a dry state, and production(field) - for materials with natural humidity.

By the time of calculating the composition of the concrete mixture, it is necessary to determine the quality of the starting materials: cement, water, sand and crushed stone (gravel) - in accordance with the requirements of GOSTs.

Depending on the conditions in which the concrete will be located in a building or structure, other requirements may also be imposed on it, for example, the degree of frost resistance, resistance to aggressive water, and water resistance. The high frost resistance and impermeability of densely laid concrete are regulated by W/C and binder consumption, hence the need to standardize W/C in hydraulic, road and other special concretes.

The calculation of the concrete composition is carried out in the following order: the cement-water ratio is determined, ensuring the production of concrete of a given strength and water consumption; calculate the required consumption of cement, and then crushed stone (or gravel) and sand; check the mobility (rigidity) of the concrete mixture if these indicators deviate from the design; make adjustments to the composition of the concrete mixture; prepare samples to determine strength and test them within specified periods; recalculate the nominal composition of the concrete mixture to the production composition.

Determination of cement-water ratio produced according to the following formulas:

for concrete with C/V = 2.5

Water flow determination. The optimal amount of water in the concrete mixture (water content, l/m3) should provide the necessary mobility (or rigidity) of the concrete mixture. The amount of water for hardening 1 m 3 of concrete mixture for all calculations in accordance with ONTP 07-85 is taken equal to 200 l, regardless of the type, hardness and mobility of the concrete mixtures.

Determination of cement consumption. With the C/V value determined from the formula and the accepted water demand of concrete mixture B, the approximate cement consumption is calculated, kg/m3 of concrete:

Cement consumption per 1 m 3 of concrete should be no less than the minimum. If the cement consumption per 1 m 3 of concrete is below the permissible level, then it is necessary to bring it up to ■ the norm or introduce a finely ground additive.

Determination of aggregate consumption(sand and crushed stone or gravel) per 1 m 3 of concrete. To determine the consumption of sand and crushed stone (gravel), two conditions are specified:

1) the sum of the absolute volumes of all components of concrete (l) is equal to 1 m 3 (1000 l) of compacted concrete mixture:

where C, V, P, Sh - the content of cement, water, sand and crushed stone (gravel)< кг/м 3 ; q u , q b , g n , Q m - плотности этих материалов,кг/м 3 ;

2) cement-sand mortar will fill the voids in the coarse aggregate with some spreading of the grains:

where Vost.sh(g) is the voidness of crushed stone or gravel in a standard loose state (substituted into the formula as a relative value); a is the coefficient of expansion of crushed stone grains (or excess solution); for rigid mixtures a= 1.05...1.20, for flexible mixtures a= 1.2...1.4 and more; q h .

u (G > - bulk density of crushed stone (gravel), kg/l; Q m (g > - density of crushed stone (gravel), kg/l.

Coefficient a determines the ratio between sand and crushed stone in concrete.

After determining the consumption of crushed stone or gravel, calculate the consumption of sand (kg/m3) as the difference between the design volume of the concrete mixture and the sum of the absolute volumes of coarse aggregate, cement and water:

If gravel or crushed stone is made up of several fractions, then it is necessary to establish in advance the optimal ratio between them, using a graph of the best grain composition or selecting a mixture with a minimum amount of voids. Checking the mobility of the concrete mixture

. After a preliminary calculation of the concrete composition, a test batch is made and the cone settlement or rigidity is determined. If the concrete mixture turns out to be less mobile than required, then increase the amount of cement and water without changing the cement-water ratio. If the mobility is greater than required, then sand and coarse aggregate are added in small portions, keeping their ratios constant. In this way, the specified mobility of the concrete mixture is achieved. Experimental batches of concrete are produced at three values ​​of the water-cement ratio, of which one is taken as calculated, and the other two are 10...20% more or less. The amount of cement, water, sand and crushed stone (gravel) for concrete with a water-cement ratio not equal to the design one is determined using the above method. From each prepared mixture, three cube samples measuring 20X20X20 cm are prepared, which are kept under normal conditions and tested at the age of 28 days to determine the class of concrete (or at other times). Based on the test results, a graph is drawn up of the dependence of concrete strength on the cement-water ratio, with the help of which a C/V is selected that ensures the production of concrete of a given strength.

During trial batches, the mobility or rigidity of the concrete mixture is also checked (it must satisfy the design one), its density is determined and, based on the test results of trial batches, appropriate adjustments are made to the calculated composition of concrete. When changing the content of sand and crushed stone (gravel), their moisture content is taken into account.

Properties of concrete

Strength of concrete. In the structures of buildings and structures, concrete can be exposed to various operating conditions, experiencing compression, tension, bending, and spalling. The compressive strength of concrete depends on the activity of the cement, the water-cement ratio, the quality of the aggregates, the degree of compaction of the concrete mixture and the hardening conditions. The main factors in this case are the activity of cement and the water-cement ratio.

To obtain a workable concrete mixture, the ratio of water to cement is usually taken as W/C = 0.4...,0.7, while the chemical interaction of cement with water requires no more than 20% of water by weight of cement. Excess water that has not entered into a chemical interaction with cement evaporates from the concrete, forming pores in it, which leads to a decrease in the density and, accordingly, the strength of concrete. Based on this, the strength of concrete can be increased by reducing the water-cement ratio and increasing compaction.

Along with the activity and quality of cement, the water-cement ratio and the quality of aggregates, the strength of concrete is significantly influenced by the degree of compaction of the concrete mixture, the duration and conditions of concrete hardening.

Concrete is an artificial stone material obtained as a result of hardening of a properly selected, thoroughly mixed and compacted mixture of binder, water, fillers and, if necessary, special additives. Concrete mix- this is a mixture of the above components before hardening begins.

Concrete is classified according to the following main characteristics: purpose, average density, type of binder, type of fillers, structure and hardening conditions.

The following concretes are distinguished by purpose: ordinary concrete, hydraulic concrete, concrete for transport construction, road concrete, heat-resistant concrete, structural thermal insulating concrete, corrosion-resistant concrete.

• Ordinary, or general construction, called concrete, to which no special requirements are imposed.
• To hydraulic engineering include concrete used for the construction of hydraulic structures (dams, water control, water intake and other structures).
• Concrete for transport construction designed for the construction of bridges, viaducts, overpasses, overpasses, culverts and regulatory structures on railways and roads.
• Road refers to concrete used in road surfaces, airfields and other similar structures.
• Heat-resistant concrete is used for the manufacture of structures that, under operating conditions, are exposed to constant or periodic exposure to temperatures above 200 °C.
• Structural and thermal insulation concretes are intended for reinforced concrete structures, which are subject to requirements, as per bearing capacity, and in terms of thermal insulation properties.
• Corrosion resistant are called concretes that can withstand the action of aggressive environments under operating conditions.

Depending on the average density, a distinction is made between extra-heavy, heavy, light and extra-light concrete.

• Extra heavy concrete with an average density of more than 2500 kg/m 3 are manufactured using especially heavy aggregates (magnetite, limonite, barite, cast iron shot, steel scraps). These concretes are used for the manufacture of special structures, for example in the construction of buildings nuclear power plants, for protection against radioactive radiation.
• Heavy concrete with an average density of 2000-2500 kg/m 3 are made on dense sand and coarse aggregate from dense rocks and are used in all load-bearing structures.
• Lightweight concrete with an average density of 500-2000 kg/m 3 are manufactured using porous coarse aggregate and porous or dense fine aggregate. They are used mainly for the production of fencing or load-bearing structures.
• Extra-light concrete (cellular) with an average density of less than 500 kg/m3, they are made on the basis of a binder and a blowing agent. Used as thermal insulation material in the form of slabs, shells and other products.

Based on the type of binder, concrete is divided into cement, lime binders, gypsum, slag-alkaline, and polymer.

• Cement concrete made using Portland cement and its varieties, and aluminous cement. They have universal properties. They are used for load-bearing and enclosing structures of buildings and structures.
• Concrete on lime binders made from lime, quartz sand, slag, ash, and active mineral additives. Concretes based on lime and silica component, hardening at autoclave processing, are called silicate. The most common are silicate concretes based on quartz sand. They are used in industry and civil construction: for the manufacture of wall blocks, panels, facing slabs; cellular concrete In addition, they are used for thermal insulation.
• Gypsum concrete are made on the basis of gypsum binders: construction, high-strength (technical), high-firing. These concretes have low water resistance. They are used mainly for the manufacture of partition slabs and panels used in dry environments. Concrete made with gypsum-cement-pozzolanic binder, which is used for the manufacture of sanitary cabins and even for external walls, is more water-resistant.
• Slag-alkaline concrete made from slag-alkaline binders - granulated blast furnace or electrothermophosphorus basic slag and alkaline components - soda, potash, liquid glass etc. They are used for the manufacture of any structures.
• Polymer concrete They are made using polymer binders - polyester, epoxy and other resins. They are used for operation in aggressive environments. Concrete with a mixed binder is called polymer-cement; concrete impregnated with polymers - concrete polymers.

Depending on the type of aggregates used in concrete, they can be dense, porous and special aggregates.

• Concrete on dense aggregates made using aggregates from rocks or industrial waste with an average density of more than 2000 kg/m 3. For example, granite crushed stone, metallurgical slag,
• Concrete on porous aggregates made using aggregates with an average density of less than 2000 kg/m 3 . These are specially manufactured aggregates - expanded clay gravel and sand, agloporite crushed stone and sand, etc., or obtained from porous rocks - tuff, limestone, etc. This also includes concrete with porous large and dense fine aggregates, concrete with organic aggregates (arbolite).
• Concrete with special aggregates are made with aggregates obtained from materials that impart certain properties to concrete. Thus, aggregates made from iron ores limonite and hemotite, which have increased density, absorb radioactive rays. They are used in concrete for protection against radioactive radiation. Heat-resistant concrete is made using crushed ceramic products, fireclay crushed stone and sand.

Based on the size of the aggregate grains, fine-grained and coarse-grained concretes are distinguished.

• Fine-grained Concrete in which the grain size of coarse aggregate is no larger than 10 mm is considered.
• IN coarse-grained in concrete, the grain sizes of coarse aggregate are more than 10 mm.

Depending on the nature of the structure, there are the following types concrete.

• Concrete of dense (fused) structure, in which the space between the aggregate grains is completely occupied by hardened binder. The permissible volume of intergranular voids in a compacted concrete mixture does not exceed 6%.
• Large-porous concrete (sandless or low-sand), in which a significant part of the volume of intergranular voids remains unoccupied by fine aggregate and hardened binder.
• Porous concrete, in which the space between the grains of aggregates is occupied by a binder, porous with foaming or gas-forming additives.
• Cellular concrete— concrete with artificially created pore cells, consisting of a mixture of binder, current-dispersed silica component and rock-forming additive.

According to hardening conditions, concrete is divided into:

• natural hardening concretes, hardening at a temperature of 15-20 ° C and atmospheric pressure;
• concrete subjected to heat treatment to accelerate hardening(70-90 °C) at atmospheric pressure;
• concretes cured in autoclaves at a temperature of 175-200 °C and a steam pressure of 0.9-1.6 MPa.

Types of concrete and their classification

Before hardening, this mixture is called concrete mixture .

One of the main properties of concrete is high resistance to compressive loads and low tensile loads: Rcom is 10 - 12 times higher than Rsol.

To increase tensile strength in concrete structures reinforcement is laid, which mainly absorbs tensile forces. Reinforced concrete is called reinforced concrete – it resists both compression and tension well.

Widely used in construction practice prestressed concrete . The essence of prestressing is that the area of ​​concrete subject to tension is compressed by tensioned reinforcement. As a result, tensile forces are absorbed by the reinforcement, reducing the compressive stress in the concrete. This technique ensures high crack resistance of concrete. Prestressed reinforced concrete structures are more economical compared to conventional reinforced concrete structures, since as a result effective use high-strength materials (steel and concrete), the consumption of reinforcing steel is reduced.

Concrete is classified according to a number of characteristics.

A.) By average density concretes are divided into:

Particularly heavy over 2500 kg/m 3 ;

Heavy 1800 – 2500 kg/m 3 ;

Lightweight 500 – 1800 kg/m 3 ;

Particularly light less than 500 kg/m 3 .

For cooking especially heavy heavy aggregates from stone ore-containing rocks (magnetite, hematite) are used for concrete; in the form of steel filings or shavings, cast iron shot, scale, etc. Such concretes are used for radiation protection during the construction of nuclear power plants, and as cement concrete for filling excavations.

Heavy concrete has received the greatest application in construction practice for the construction of underground and above-ground load-bearing structures and structures (foundations, walls, columns, beams, trusses, covering and floor slabs, etc.). Crushed stone of dense rocks (granite, limestone, diabase, etc.) is used as a coarse aggregate for such concrete.

To the group lungs includes concrete with porous aggregates of natural or artificial origin, as well as cellular concrete (without aggregates) with a significant number of artificially created closed pores in the concrete body. This also includes concrete on porous aggregates in combination with porous cement stone. Used as a heat-insulating and structural material.

Extra light (thermal insulating) - these are predominantly cellular concrete with a high degree of porosity (sandless) and on light porous aggregates. Such concretes have low thermal conductivity and are used as an effective thermal insulation material.

B.) By structure Concrete comes with a dense, porous, cellular and large-porous structure.

Dense structure – when the ratio of components is selected so that no concrete remains in the body free space(absolute volume method). Concrete consists of coarse and fine aggregates (or only fine aggregates) and dense cement paste (or other hardened binder) between the aggregate particles.

Porous – when the space between the grains of inert components (large and small or one of them) is filled with a binder that has hardened in a porous state.

Cellular – without fillers, with a significant number of artificially created pores in the concrete body in the form of closed cells filled with air.

High-porous concrete – with only coarse aggregate, without sand at all (sandless) or with a very small content of it.

B.) By type of binder There are different types of concrete: cement, silicate, gypsum, slag-alkaline, polymer concrete, polymer cement and special concrete.

Cement – concretes based on clinker cements, mainly Portland cement and its varieties, Portland slag cement and pozzolanic cement.

Silicate Concrete is made using lime binder. To ensure the hardening process of such concrete, autoclaves are used, where the concrete is subjected to heat treatment under pressure.

Plaster Concrete has low water resistance, so structures inside the building are made from it ( dropped ceilings, partitions).

Slag-alkali Concrete (binder - ground slag and alkaline solutions) have high strength and resistance to aggressive environments.

Polymer concrete (binder - epoxy, polyester, furan and other resins) highly resistant to aggressive environments, used in the construction of copper smelting and chemical industry, enterprises for processing agricultural products (sugar factories and breweries), acid storage tanks, mineral waters and etc.

Polymer-cement concretes are made with the addition of aqueous dispersions of various polymers, which are introduced into the mixture along with mixing water. Polymers are deposited as a film on the surface of the aggregate, increasing the adhesion between the elements of the concrete structure. Such concretes have good tensile strength, increased frost resistance, water resistance and chemical resistance.

D.) By area of ​​application and for appropriate purposes technical specifications The following types of concrete differ.

Structural – general purpose, used in structures that perceive external force influences (loads). The defining properties of such concrete are strength and deformation characteristics, as well as frost resistance when structures operate under conditions of alternating temperatures. These are foundations, columns, beam structures, covering and floor slabs, etc.

Structural and thermal insulation – used in enclosing structures (external walls, coverings). Such concretes must provide not only the load-bearing capacity of structures, but also their heat-shielding properties.

Thermal insulation – their purpose is to provide the necessary thermal resistance enclosing structures with a relatively small layer thickness, while the load-bearing capacity of the structures is provided by ordinary concrete (in two- and three-layer structures).

Hydraulic , which, along with the necessary strength and deformation characteristics, must have increased density, water resistance, frost resistance, and resistance to aggressive influence environment- water.

Road – for top surfaces of roads, airfield runways. They must have increased strength, high wear resistance, and have good resistance to alternating effects of temperature and moisture.

Chemical resistant – salt-, acid- and alkali-resistant. Along with the necessary indicators technical properties must be able to withstand the effects of concentrated solutions of salts, acids and alkalis and their vapors for a long period without destruction or reduction in performance. Such concretes are used as the main material of structures, or for protective coatings structures made of ordinary concrete.

Heat resistant – maintaining within specified limits their physical and mechanical properties with prolonged exposure high temperatures. Suitable for industrial units and building structures subjected to heating to high temperatures during operation.

Decorative – for finishing layers with textured processing on front surfaces construction products. Such concretes (mortars) must meet the requirements regarding color, texture, and have sufficiently high weather resistance.

The types of concrete discussed above, despite significant differences in certain properties and their indicators, are subject to general patterns, which follow from the common principles of the formation of their structure and structure.

Concrete is one of the most common and popular building materials, widely used throughout the world. There is probably not a single building whose structure could be constructed without a concrete mixture. Even at home from wooden beam are built on a foundation made of concrete blocks.

What does a novice builder need to know about this material? IN modern construction it is customary to subdivide this type building material for use on regular and special concrete. Moreover, each of the subspecies has its own unique characteristics and spectrum of specific purposes.

Characteristics and application of ordinary concrete in construction

The scope of application of conventional concrete is extensive. This is almost every house: from a small cottage to a huge multi-story high-rise building. These are curbs on sidewalks, lamp posts, bridge spans, airfield runways. Can not imagine modern world without concrete.

Concrete is classified according to three main indicators: strength, frost resistance and resistance to water permeability.

Each type is assigned a specific label:

1. Strength. Designated English letter B and numbers from 1 to 60.
2. Frost resistance (frost resistance). Denoted by the letter F and a numerical value from 50 to 500.
3. Waterproof. Marked with the letter W and numbers from 2 to 12.

In addition to these indicators, concrete can also be divided into light, heavy and extra heavy. Extra heavy concrete belongs to the line of special concretes and has a narrow profile use.

The difference between concrete categories in terms of density is achieved due to the fillers of the mixture. For example, in lightweight concrete Expanded clay, pumice or expanded slag are used. This type of concrete is suitable for construction wall panels, fencing structures and for the production of lightweight bricks used in private housing construction.

Heavy concrete is obtained by using granite chips or crushed stone as filler. This type of building mixture is the most widely used. It is used to create reinforced concrete products, monolithic houses, floor slabs and so on. This type is divided by grade (depending on the cement used).

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Marking of ordinary concrete

Concrete using M100 grade cement is intended to create a preparatory base for a poured floor or cushions for load-bearing blocks. In a word, the use of material of this brand is permissible only in structures that do not require responsibility.

The next grade of concrete is M150. It is widely used as a preparatory platform for concrete sidewalks and for the production of precast concrete products such as blocks strip foundations and curb stone.

Types of concrete grade M200 are often used in private housing construction. This type of concrete is loved by builders due to its remarkable density characteristics and fairly low cost. It is used to fill foundations, and it is used to create road slabs, curbs and wall blocks.

Concrete grade M250 is used for the production of flights of stairs, fences and small bridge forms.

The leader in the construction market among conventional concretes is the M300 brand mixture. This popularity was made possible due to the increased properties of strength, frost resistance and thermal conductivity. Widely used in all areas of construction: from foundations to monolithic retaining systems.

The M350 grade is used in multi-story construction to create beams, columns, load-bearing wall structures and monolithic foundations.

Types of concrete marked M400, M450, M500 and M550 are usually used for the production of special structures where increased strength is required.

M400 is used in the construction of bridges, swimming pools, bank vaults and ground floors buildings.

The M450 has found application in the construction of large bridges, tunnels and various hydraulic structures. IN low-rise construction the use of the M450 type is unprofitable.

M500 class concrete is made with the addition of special plasticizers and is used exclusively to create high-strength structures such as metro stations, dams, dams and railway tunnels.

The density of concrete M550 is mainly used only for creating structures, long time subjected to heavy loads. Using this type of mixture is very difficult due to its rapid hardening. Therefore, concrete grade M550 is made with the addition of plasticizers and hardening retarders.

Concrete grade M600 opens up the types of especially durable concrete. However, its use is very limited.

Besides cement types, there are still such forms construction mixture, such as silicate, gypsum, slag-alkaline and polymer-cement. But their production and use are not widespread and are quite highly specialized.

Concrete is an artificial stone material obtained as a result of hardening of a properly selected, thoroughly mixed and compacted mixture of binder, water, fillers and, if necessary, special additives. Concrete mix- this is a mixture of the above components before hardening begins.

Concrete is classified according to the following main characteristics: purpose, average density, type of binder, type of fillers, structure and hardening conditions.

The following concretes are distinguished by purpose: ordinary concrete, hydraulic concrete, concrete for transport construction, road concrete, heat-resistant concrete, structural thermal insulating concrete, corrosion-resistant concrete.

Ordinary, or general construction, called concrete, to which no special requirements are imposed.

To hydraulic engineering include concrete used for the construction of hydraulic structures (dams, water control, water intake and other structures).

Concrete for transport construction designed for the construction of bridges, viaducts, overpasses, overpasses, culverts and regulatory structures on railways and highways.

Road refers to concrete used in road surfaces, airfields and other similar structures.

Heat-resistant concrete is used for the manufacture of structures that, under operating conditions, are exposed to constant or periodic exposure to temperatures above 200 °C.

Structural and thermal insulation concretes are intended for reinforced concrete structures, which are subject to requirements both for load-bearing capacity and thermal insulation properties.

Corrosion resistant are called concretes that can withstand the action of aggressive environments under operating conditions.

Depending on the average density, a distinction is made between extra-heavy, heavy, light and extra-light concrete.

Extra heavy concrete with an average density of more than 2500 kg/m 3 are manufactured using especially heavy aggregates (magnetite, limonite, barite, cast iron shot, steel scraps). These concretes are used for the manufacture of special structures, for example, in the construction of nuclear power plant buildings, for protection against radioactive radiation.

Heavy concrete with an average density of 2000-2500 kg/m 3 are made on dense sand and coarse aggregate from dense rocks and are used in all load-bearing structures.

Lightweight concrete with an average density of 500-2000 kg/m 3 are manufactured using porous coarse aggregate and porous or dense fine aggregate. They are used mainly for the production of enclosing or load-bearing structures.

Extra-light concrete (cellular) with an average density of less than 500 kg/m3, they are made on the basis of a binder and a blowing agent. Used as a heat-insulating material in the form of slabs, shells and other products.

Based on the type of binder, concrete is divided into cement, lime binders, gypsum, slag-alkaline, and polymer.

Cement concrete made using Portland cement and its varieties, and aluminous cement. They have universal properties. They are used for load-bearing and enclosing structures of buildings and structures.

Concrete on lime binders made from lime, quartz sand, slag, ash, and active mineral additives. Concretes based on lime and siliceous components, hardening during autoclave treatment, are called silicate. The most common are silicate concretes based on quartz sand. They are used in industry and civil construction: for the manufacture of wall blocks, panels, facing slabs; Cellular concrete is also used for thermal insulation.

Gypsum concrete are made on the basis of gypsum binders: construction, high-strength (technical), high-firing. These concretes have low water resistance. They are used mainly for the manufacture of partition slabs and panels used in dry environments. Concrete made with gypsum-cement-pozzolanic binder, which is used for the manufacture of sanitary cabins and even for external walls, is more water-resistant.

Slag-alkaline concrete They are made using slag-alkaline binders - granulated blast furnace or electrothermophosphorus basic slag and an alkaline component - soda, potash, liquid glass, etc. They are used for the manufacture of any structures.

Polymer concrete They are made using polymer binders - polyester, epoxy and other resins. They are used for operation in aggressive environments. Concrete with a mixed binder is called polymer-cement; concrete impregnated with polymers - concrete polymers.

Depending on the type of aggregates used in concrete, they can be dense, porous and special aggregates.

Concrete on dense aggregates made using aggregates from rocks or industrial waste with an average density of more than 2000 kg/m 3. For example, granite crushed stone, metallurgical slag,

Concrete on porous aggregates made using aggregates with an average density of less than 2000 kg/m 3 . These are specially manufactured aggregates - expanded clay gravel and sand, agloporite crushed stone and sand, etc., or obtained from porous rocks - tuff, limestone, etc. This also includes concrete with porous large and dense fine aggregates, concrete with organic aggregates (arbolite).

Concrete with special aggregates are made with aggregates obtained from materials that impart certain properties to concrete. Thus, aggregates made from iron ores limonite and hemotite, which have increased density, absorb radioactive rays. They are used in concrete for protection against radioactive radiation. Heat-resistant concrete is made using broken ceramic products, fireclay crushed stone and sand.

Based on the size of the aggregate grains, fine-grained and coarse-grained concretes are distinguished.

Fine-grained Concrete in which the grain size of coarse aggregate is no larger than 10 mm is considered.

IN coarse-grained in concrete, the grain sizes of coarse aggregate are more than 10 mm.

Depending on the nature of the structure, the following types of concrete are distinguished.

Concrete of dense (fused) structure, in which the space between the aggregate grains is completely occupied by hardened binder. The permissible volume of intergranular voids in a compacted concrete mixture does not exceed 6%.

Large-porous concrete (sandless or low-sand), in which a significant part of the volume of intergranular voids remains unoccupied by fine aggregate and hardened binder.

Porous concrete, in which the space between the grains of aggregates is occupied by a binder, porous with foaming or gas-forming additives.

Cellular concrete— concrete with artificially created pore cells, consisting of a mixture of binder, current-dispersed silica component and rock-forming additive.

According to hardening conditions, concrete is divided into:

natural hardening concretes, hardening at a temperature of 15-20 ° C and atmospheric pressure;

concrete subjected to heat treatment to accelerate hardening(70-90 °C) at atmospheric pressure;

concretes cured in autoclaves at a temperature of 175-200 °C and a steam pressure of 0.9-1.6 MPa.