Properties of refractory concrete, its composition and preparation

Heat- and fire-resistant cement mixtures are used to prepare concrete elements of stoves, fireplaces, heating elements, and also in production facilities of metallurgical and chemical plants. They are able to withstand severe thermal exposure. The properties that refractory concrete must have are achieved by adding a number of components to its composition.

Types of refractory aluminas

For different operating conditions, heat-resistant cement is produced in several types. The packaging is marked with the following symbols:

1. GC. Aluminous cement, capable of setting and gaining grade strength in air and water (without access to oxygen). Material with a high content of Al₂O₃ (aluminum oxide). The powder has a shade from dark brown to gray-green.
2. GC40 – GC60. These compounds are used in the fuel, energy, industrial and road construction sectors. Widely used in the creation of special mortars and dry heat-resistant mixtures, monoliths. Indispensable for concreting at low temperatures.
3. VGTs 70 – VGTs 75, VGTSI – VGTsIII. Designation of high-alumina grades with enhanced characteristics. They do not “gas” when heated strongly. Intended for the production of construction quick-hardening concrete or mortar. In relation to GC, their cost is higher.

VGKTs-70-1 is used in ferrous and non-ferrous metallurgy, oil refining, chemical industries, production of refractories, lining of firing furnaces (glass, cement, ceramics). It is used to make stones and substrates due to its combination of heat resistance and strength.

How to prepare fireproof material yourself?

Heat-resistant properties in private construction will be required for cement for the stove, chimneys, base and firebox. It can be chosen as an additive during concreting if the air temperature at the work site has dropped to -10°C. The fireproof characteristics of PC-based concrete can be enhanced by including asbestos powder, liquid glass, alumina, periclase or barium binder in its recipe.

Mixing of the composition with the inclusion of liquid glass is carried out with the addition of granulated blast furnace slag, sodium silicofluoride, and nepheline sludge. With the participation of periclase material, an aqueous solution of magnesium sulfate must be used.

In addition to special cements, it is advisable to use a certain filler. It imparts rigidity to the frozen mass, is a heat insulator and retains its shape, having a low coefficient of expansion, in the area of ​​high temperatures.

At home, you can buy and add the following types of fireproof fillers, differing in particle size:

• expanded clay;
• broken fireclay bricks;
• lump fireclay;
• fly ash;
• vermiculite;
• granulated blast furnace slag;
• broken magnesite brick;
• Cemyanka;
• perlite;
• pumice;
• andesite;
• chromite ore;
• loess loam;
• break of diatomaceous brick.

The components are mixed in proportions 3:2:2:0.5, where gravel is 3 parts, 2 refractory binders, 2 sand, 0.5 slaked lime. The amount of prepared composition should not affect the ratio of ingredients in the recipe. Portland cement can be used for work on areas of chimneys, supporting and decorative structures that are remote from the combustion zone and where there are significant temperature changes.

It will be cheaper to buy a high-quality fire-resistant dry mix in winter than in summer. But in any case, it must have a manufacturer’s certificate.

Brand	Manufacturer country)	Quantity, kg	Price, rubles
GORKAL 40	Poland	50	1300
GC-40	Ukraine	50	1300
ISIDAS 40	Türkiye	25	625
LAKKA TULENKESTAVA	Finland	25	1300
VGTs-50	Novosibirsk, Russia)	20	1800
GC-40	Russia (LLC Construction Materials Plant)	1000	23040
GC-40	Russia (Pashinsky PMCP)	50	37/1 kg
VGTs-2-25	Russia (Ogneuporkomplekt LLC)	1	99
VGMC-I-1700	Russia (TECHNOCENTER LLC)	1	127
VGC-2	Russia (Own production)	50	3900

Raw firing technology

Scheme of firing bricks in an industrial kiln.

It is necessary to lay the brick in the barrel, ensuring small gaps for high-quality heating. Due to the fact that you do not have an industrial furnace, such work can be done using an ordinary barrel, the volume of which should be 250 liters.

Initially, you need to prepare a pit for a fire, the depth of which is 50 cm. The barrel must be deprived of the bottom, placing it on the fire on legs, the length of which is limited to 20 cm. This will make it more comfortable to maintain and regulate the fire, while the heating of the clay brick will be uniform.

After laying clay-based bricks in a barrel, it must be covered with a steel sheet, for which it is permissible to use the extracted bottom. This stage will take a period of 18-20 hours, during which time the fire must be maintained. Afterwards, the barrel should be left to cool; there is no need to open the lid. The fire should be reduced gradually. 5 hours after the barrel and bricks have cooled, the finished products can be removed.

Tools for making bricks: 1 – pound, 2 – flooring, 3 – sand with a shovel, 4 – clay with a shovel, 5 – a hammer, 6 – a staple or scraper.

Clay products may contain ingredients added and mixed in different proportions. Thus, to obtain adobe, you must first prepare a large container that has low sides. This container is convenient for mixing the mixture. To mix, you need to use a combination of two types of clay, one of which is lean, the other is fat. The composition should also contain straw, the final proportion is as follows - 1:1:5. You need to add water to the mentioned components, and then mix with a shovel. If you decide to use the specified recipe for bricks, then before starting work the straw will have to be crushed. If this requirement is neglected, the lumps will cause a decrease in the strength characteristics of the brick. It is preferable to use wheat stalks that have undergone high-quality drying.

If desired, when producing independently, products based on clay can be given dimensions that differ from the standard dimensions.

The waterproof characteristics of bricks, which contain unfired clay, are not too high, for this reason, if the products form the basis of external walls, they must be protected from moisture. To do this, the length of the roof overhangs should not be less than 60 cm, in addition, the seams must be carefully bandaged. Openings should be located no closer than 1.5 m from the corners. Once the walls are in place and the house is settled, the surface of the walls will need to be plastered, and siding can be used as an alternative solution for protection.

Scheme for checking the quality of bricks by splitting them.

If you decide to make bricks, the composition of which is devoid of straw, then instead of it you need to add a small amount of sand to the solution. The proportion remains the same. It is preferable to use fine-grained pure quartz sand for this.

After firing, you need to analyze the size and correctness of the shape of the brick, as well as its quality. To analyze the quality characteristics, one product needs to be split with a hammer. With good firing, the color of the product will be the same, which also applies to the structure along the entire fault. The brick test is not over yet. The battle still needs to be filled with water and left for a while. If the material is well fired, then the color and structure will be the same over the entire surface.

Thus, ceramic bricks can be made independently, without having a press or other complex industrial equipment.

Do-it-yourself heat-resistant concrete based on alumina cement

Making cinder blocks with your own hands: instructions for making them at home
To make fire-resistant concrete on a base at home, you need to prepare the following components:

1. Water.
2. Binding and heat-resistant additives.

The technological process contains a lot of nuances. First of all, you should take care of the cleanliness of all components, and also prevent the possibility of contamination of refractory components with sand, granite or limestone.

Experts recommend choosing the first option, since ready-made dry mixtures have the required performance characteristics and are produced using a factory process. Therefore, the user is provided with premium quality cement, which only needs to be diluted with water or solvent.

When starting to make your own mixture, it is important to provide for the following additives:

1. Chromite ore.
2. Magnesite cement.
3. Andesite.
4. Fireclay fight.

If you choose the right ingredients, the final design will be reliable and durable.

All components are transferred to a concrete mixer and thoroughly mixed in a ratio of 1:4 (cement and sand). When you get a homogeneous mixture, you can add liquid to it until a dough-like consistency appears. In this case, the mixture will receive the required degree of viscosity and quickly become solid.

When diluting it with water, it is important to adhere to the recommendations of specialists and not deviate from the recipe

The finished composition is placed in molds and poured into formwork or used for brickwork

When using aluminous fillers, it is important to dilute them with water in time to prevent excessively rapid setting. After completing all actions, it is necessary to clean the equipment and get rid of the frozen material with the tool

If you want to make a small amount of Portland cement-based mortar, mixing the components can be done without a concrete mixer. Wide containers and hand tools are used for this purpose.

After completing all the steps, it is necessary to clean the equipment and get rid of the frozen material with the tool. If you want to make a small amount of Portland cement-based mortar, mixing the components can be done without a concrete mixer. For this purpose, wide containers and hand tools are used.

Cooking features

If you want to make fireproof concrete yourself, you can assemble the ingredients yourself. Or purchase a finished product at a hardware store. Preparation instructions are placed on the original packaging, which must be strictly followed. If the components are purchased separately, the preparation is carried out in two stages:

• mixing the cement base;
• filling of fillers and mixing of refractory.

The readiness of the material for work can be determined by this criterion. If you take a lump of mortar in your hand and it does not crumble or spread, you can begin construction.

Note! During the preparation of concrete mortar, the solution should be mixed until smooth. And after using the material in the construction of the structure, you need to accurately maintain the drying regime.

Practice shows that it is better to do the mixing not in a barrel or concrete mixer, but in an ordinary construction tray using a shovel. During drying, monitor the moisture distribution in the structure. For uniform drying, a constant influx and outflow of fresh air is necessary. It is better to cover the structure itself to slow down the drying process and ensure uniform release of moisture. It is advisable to periodically wet the surfaces. Heat or exposure to fire is permissible only after complete drying.

Use of refractory

Advantages

Making molds for concrete casting

Refractory grades of cement have the following advantages:

• ability to withstand open fire;
• resistance to short-term heating above 3000 ℃;
• high mechanical strength;
• increased adhesion compared to all other types of mixtures;
• high speed of complete solidification of the mass;
• inertia in relation to the aggressive influence of the external environment.

Heat-resistant cement is finely ground, after which the homogeneous powder is sifted through sieve No. 008, obtaining 90% of the material. The fraction with larger grains is no more than 10%. Cement mixture with normal alumina content is colored gray or light brown; with an increased concentration of a heat-resistant component - in white or light steel colors. The density of the refractory powder is different: its minimum is 2.8 g/cm2, the maximum is 3.2 g/cm2.

A product with improved refractory properties is prepared using standard technology, using the usual amount of sand and water. In this case, you have to wait from 1 to 3 days for Portland cement to harden, while fire-resistant grades harden completely in 10 hours, even in a humid environment.

Among the negative aspects characterizing heat-resistant cement, they note an increased price compared to other varieties, which is quite understandable. Some authors talk about the harmful effects of alkalis on refractory materials. It is possible that concentrated alkalis under some conditions can react with a certain part of the refractory raw material, but in practice, alkaline effects of this kind cannot occur under any circumstances.

GOST requirements

Gosstandart 52541-2006 has been put into circulation in Russia since 2007. It mainly focuses on testing methods, performing calculations and generating reports. GOST is based on several standards. The only term that defines the standard is consistency. The following tools and equipment are recommended for testing:

• scales with weights;
• measuring cylinder;
• polyethylene film;
• thermometer;
• gas or electric oven;
• mechanical mixer;
• calipers;
• spherical cup;
• latex gloves;
• spatula or trowel;
• water;
• steel sheet plate;
• drying cabinet;
• vibration platform;
• humidification chamber;
• form with a coating that protects against corrosion;
• stopwatch.

Attention! Samples are prepared in a certain order: selection, consistency analysis, preparing the mass for research, creating a mold, determining the density of the samples, drying, firing. After firing, samples can be stored for no more than 3 days before testing. If research is carried out on unfired samples, then the work is carried out immediately after drying. Such products cannot be stored.

Based on the test results, a protocol must be drawn up, which must reflect the following information:

• the State Standard according to which the research was carried out is indicated;
• the organization that performed the work is indicated;
• the date when the research was carried out is indicated;
• the grade of material is determined according to the standard;
• apparent density indicators of selected samples;
• dimensions and configurations of samples;
• storage time from removal from the kiln to the start of testing;
• test parameters: heating rate, maximum temperature, duration of exposure;
• volumes of water used;
• stirring time, the interval from stirring to completion of research;
• height of the form;
• for dense materials, the spreadability index is indicated;
• for thermal insulating concrete refractories - full research time.

You can watch tests of refractory concrete in this video:

Developments for critical temperature conditions

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In practice, conventional concrete mixtures do not tolerate high temperatures well. Even those options that are considered one of the highest quality and most expensive cannot guarantee safety at temperatures exceeding 150 degrees. The material begins to crumble and lose shape, as a result of which the entire structure suffers.

That is why experts have developed special compositions that retain properties at elevated temperatures. Today, there are so-called highly refractory concretes, used in conditions where temperatures exceed 1770 degrees, fireproof options that work with temperatures from 1580 to 1770 degrees, and heat-resistant ones, their limit is 1580 degrees.

Any heat-resistant concrete consists of a base and a filler; in the manufacture of such material, specific elements are used: liquid glass, aluminum cement, expanded clay, etc.

Let's summarize

On the Internet you can find many recipes for preparing refractory concrete and how to make it yourself. But when working independently, the master will not have guarantees that the material meets the parameters necessary for the object. It is better to buy certified solutions from the manufacturer. Factory prepared materials will have a higher price, but they have guarantees and recommendations for storage and use. Most often they are indicated on the packaging. Having correctly maintained the technology, the user will receive concrete with the required technical parameters.

DETERMINATION OF LIQUID GLASS MODULE BY ACCELERATED METHOD

The average sample for analysis is taken from the upper settled layer of liquid glass without stirring, after first removing the surface film, then proceed to determine the content of sodium oxide in it. To do this, liquid glass is diluted with water to a density of 1.38 g/cm3. Then a sample of liquid glass weighing about 1 g is washed off with hot distilled water into a beaker with a volume of 250-300 ml, mixed thoroughly, covered with a watch glass and boiled for 10 minutes.

After cooling, add 3-4 drops of 0.2% methyl orange solution to the solution and titrate with 0.1 normal HCl solution until the color of the liquid changes from yellow to pale pink.

The modulus of liquid glass is determined by the formula

Msg = 162dι- 2.5,

where d is a sample of liquid glass, ι is the volume of 0.1 HCl solution consumed during titration, ml; 162 and 2.5 are empirical coefficients.

CHECKING THE QUALITY OF THE HARDENER

To check the quality of the hardener (except for sodium silicofluoride), a sample of about 5 kg is taken from each batch from several places, but not less than three, and reduced to 0.5-1 kg using the quartering method. Next, the material is dried to constant weight at a temperature of 100-110 ° C and the grinding fineness and chemical composition are determined. To control the grinding fineness, take a sample of the material weighing 100 g and sift it through sieve No. 008. The chemical composition of all hardeners (except sodium silicofluoride) is determined according to GOST 2642.0-86.

To check the quality of the hardener - sodium silicofluoride, an average sample is taken, dried to a constant weight at a temperature of 100-110 ° C and crushed in a mortar.

A sample of the material weighing about 1 g is dissolved in 100 ml of hot water, free of carbon dioxide, and titrated with a 0.5 normal NaOH solution containing two to three drops of phenolphthalein until a faint pink color appears. The solution is then heated to boiling and titrated again until the color no longer discolors. A slight pink color upon boiling indicates the end of the titration. The percentage of sodium silicofluoride in a technical product is calculated using the approximate formula

m = 0.0235/K V 100,

where 0.0235 is the amount of Na2SiF6 corresponding to 1 ml of 0.5 normal NaOH solution; V

— volume of 0.5 N NaOH solution used for titration, ml;
K
- weighed portion of technical sodium silicofluoride, g.

To determine the activity of hardeners, mix 200 g of finely ground chamotte and 100 g of a hardener (nepheline sludge, self-disintegrating slag, phosphorus slag) or 30 g of a hardener (sodium silicofluoride), mix with liquid glass until a dough of normal thickness is obtained, a cake is made from the resulting mixture, which is immediately wrapped in plastic wrap. After keeping the cake in the film at a temperature not lower than 20 ° C for 24 hours, it is removed and broken.

A high-quality hardener ensures good hardening and strength of the cake over its entire cross-section.

Main characteristics

Concrete refractories are divided into several groups according to their parameters, the materials of each of them differ in their technical parameters:

• Heat resistant. Concrete stably withstands heating up to +700 degrees C, and short-term excesses up to 1500 degrees C. For mixing, slag-portlant cements or Portland cements are used.
• Refractory. The material is intended for the construction of objects that heat up to +1000 degrees C. A temporary increase is possible - up to 1800 degrees C. Liquid glass and alumina components are often added to them for resistance to corrosion processes.
• Highly fire-resistant. This refractory will be required for facilities that operate at extremely high temperatures - over 1800 degrees C. Crushed fireclay bricks, Portland cements, diatomaceous earth, alumina and other components are added to them.

Main settings

Classification of refractory concrete

Fire-resistant concrete is classified according to various criteria:

1. maximum operating temperature;
2. purpose of the material;
3. type of filler;
4. type of binder component.

Scope of application

The scope of use of the material is not limited to the manufacture of thermally resistant structures: combustion chambers, home or industrial furnaces, collectors and foundations. Due to the inclusion of specific ingredients in the composition, the material is widely used in the production of building materials, the chemical industry, and the energy sector.

Heat-resistant concrete is also used for the construction of floating structures, floors, bridges - in structures that require high strength of the material with low weight. The relatively small mass of concrete is due to the addition of porous fillers.

Heavy heat-resistant concrete: application and composition

Heavy heat-resistant mixtures are in demand for lining units operated at high temperatures, at chemical industry enterprises, and during the construction of chimneys. The specific area of ​​application is determined by the components of the mixture.

Portland cement and Portland slag cement with microadditives

This material is stable in neutral and alkali-containing environments. This is the most popular group of heat-resistant concretes. The popularity is explained by the relatively low cost of raw materials, proven manufacturing technology, and good performance characteristics of the finished product. Such concrete mixtures are in demand in the construction of heating units, pipes of nuclear power plants and other objects operated at elevated temperatures.

Table of compositions of heat-resistant concrete based on Portland cement and Portland slag cement

Material consumption, t/m3	Finely ground additive	Fillers	Maximum operating temperature, °C
Cement	Finely ground additive	Fillers
Small	Large
0,35	0,12	0,5-0,9	0,6-1,0	Fly ash, pumice, clay brick, granulated blast furnace slag	Andesite, basalt, diorite, diabase, tuff, blast furnace slag	700
0,35	0,12	0,5	0,6	Fuel slag	Fuel slag	800
0,35	0,12	0,5	0,6	Clay brick fight	Clay brick fight	900
0,35	0,12	0,65	0,6	Fly ash, fireclay class B	Fireclay class B	1000-1100
0,35	0,7	0,65	0,65-0,75	Fireclay class B	Fireclay class B	1100-1200

Material with finely ground fireclay components has the highest strength characteristics.

Aluminate, alumina and high alumina cement

Mixtures based on them are used in carbon, hydrogen and phosphorus environments. Heat resistance classes – I8-18. Heat-resistant structures based on aluminate cement are resistant to temperatures up to +1300°C without special additives, and up to +1700°C with additives.

Structures made from alumina and high-alumina heat-resistant concrete are characterized by:

• good mechanical properties;
• stability of characteristics under sudden temperature changes;
• low thermal shrinkage;
• small linear expansion;
• low thermal conductivity coefficient.

Liquid glass

Demanded for concrete mixtures resistant to acidic gaseous media. For the production of fire-resistant concrete intended for operation at temperatures of +800...+1600°C, potassium or soda glass is used.

Maximum application temperature, °C, permissible with one-sided heating	Finely ground additive	Fine and coarse aggregates	Composition, t/m3
Liquid glass	Mineral supplement	Sand	Crushed stone
+1400	Magnesite	Broken magnesite brick	0,35	0,6	0,6	1,15
+1000	Chromite	Chromite	0,3	0,7	0,8	1,25
+900	Chamotte	Chamotte	0,4	0,5	0,5	0,75
+600	Chamotte, andesite, diabase	Diabase, andesite, basalt	0,35	0,5	0,7	0,9

Hardening of silicate mixtures is a slow process. To increase its intensity, sodium silicofluoride and alkali metal fluorosilicates are added to the composition. These hardeners initiate the release of silicic acid, which helps compact and strengthen the concrete. The following can accelerate the hardening of a concrete mixture: nepheline sludge, ferromanganese and ferrochrome slags.

This is interesting: Characteristics of heat-resistant concrete - consider carefully

What is better to use – crushed stone or gravel?

Aggregates are of great importance in the composition of construction concrete. What is better to use crushed stone or gravel can be found out by comparing the physical properties. The external similarity of the substances is noted; both were obtained by artificial and natural crushing of rocks.

Crushed stone is a fraction of stone, 5-6 mm in size. Gravel, fragments of rock, can be glacial, marine, river or lake in origin. Gravel has loamy additives, so crushed stone is better suited for making a strong concrete mixture.

Its uneven surface, shape, ability to spread evenly and bind to cement make it the best aggregate. Suitable size 20mm. Using crushed stone of different sizes will reduce voids in the finished product.

Composition and characteristics

Classification of concrete is carried out according to GOST 25192-2012.

• The most common types are the following:
• heavy structural;
• light and cellular;
• hydraulic engineering;
• road;
• heat resistant;
• acid-resistant.

Structural ones are used in the manufacture of columns, walls, beams and trusses, and floor slabs. They are made on the basis of a cement binder with the addition of a large amount of high-strength coarse aggregate, sand and special additives that improve the properties of the concrete mixture.

Lightweight cellular materials are used for the manufacture of enclosing structures in frame buildings. In low-rise buildings, walls and columns can be constructed from this material. Light cellular concrete includes aerated concrete and foam concrete. They can only be manufactured in production and delivered to the place of use in the form of block forms. Lightweight concrete products also include expanded clay concrete blocks, in which expanded clay crushed stone is used as a coarse aggregate.

Hydraulic concrete is used for the construction of structures or some of their structures that are constantly or periodically in contact with water - dams, dams, swimming pools, wastewater treatment plants. Such materials must have a high density, ensuring water resistance and good frost-resistant properties. Special plasticizers are introduced into the composition to facilitate compaction of the mixture and eliminate the appearance of numerous pores.

Road concrete is used to make pavements for highways and airfields. Such materials must be durable and also must withstand the effects of a large number of freezing and thawing cycles. In addition, they must be resistant to various oils and other aggressive liquids.

Acid-resistant ones are used, as the name implies, for structures operating under the influence of acidic environments. They are made from quartz sand, soluble glass, and acid-resistant filler.

Separation by composition

The composition of refractory concrete differs from conventional concrete in its high concentration of porous and finely dispersed substances. They ensure the process of concrete hydration, preventing its dehydration.

Binders are a dispersion system of fine-grained cement and a chemical binder.

Silicate type of concrete

Depending on the type of binder, there are:

1. hydration concrete, hardening by adding water to refractory cement;
2. silicate - in them the binder is not water, but silicic acid compounds with alkaline additives;
3. phosphate, in which aqueous solutions of orthophosphoric acid salts are used for binding;
4. sulfate-chloride - a mixture of magnesium cements and Mg, Fe, Al salts;
5. organic, where resins or their distillation products act as binders.

To improve the characteristics of refractory concrete, reinforcing additives from glass, asbestos, and steel are introduced into its composition. Ready-made dry mixtures containing all the necessary components are available on the market.

Classification

There are several types of heat-resistant concrete, which is also called fire-resistant or heat-resistant. The material contains special fire-resistant additives. The main binding component in the production of heat-resistant concrete is Portland cement. The following can be used as fillers: blast furnace slag, rock screenings (diabase, andesite, porous rocks of volcanic origin, diorite, artificial fillers), blast furnace slag.

The material is divided into separate classes according to:

1. Structure (heavy, light, porous).
2. Purpose (thermal insulation, structural).
3. The nature of the fillers.
4. The binder components used.

Specifications

Fire-resistant concrete prepared using Portland cement as a binder has a classic strength index. When conducting a compression test, the limit values ​​are in the range from 200 to 600 MPa/cm2.

Manifestations of thermal stability are observed when temperatures reach no more than 500 °C. Prolonged exposure to an open flame or prolonged contact with hot surfaces significantly reduces the strength properties of cement and often causes defects.

The most fire-resistant concretes prepared on the basis of alumina are able to withstand any household temperatures. Aluminous coatings saturated in composition are characterized by thermal stability of about 1600 °C and higher. A gradual increase in temperature leads in this case to an increase in heat resistance, since the cement mass is converted into a ceramic state.

However, despite its high resistance to elevated temperatures, aluminous refractory concrete has relatively low strength. The material made using such components can withstand mechanical pressure of up to 25-35 MPa/cm2.

Main types of heavy fire-resistant concrete

The composition of refractory concrete can be different, depending on the desired characteristics, the materials used and their proportions. There are several types of heavy concrete, the main ones are discussed below.

Concrete based on Portland cement and Portland slag cement

This is the most common type of heat-resistant concrete, characterized by low cost, proven technology of preparation and use, and good strength. Typically, such concrete is chosen for the construction of chimneys, thermal units, creating fire-resistant structures for nuclear power plants, etc.

The strength class should be in the range B15-B40. Cement M400 and higher is used in the preparation; only active minerals are added (fuel ash, fireclay, blast furnace slag, etc.). The most durable concrete is obtained with the inclusion of finely ground fireclay additives in the composition.

Portland slag cement technology provides for the addition of metallurgical blast furnace slag, so the mixture can be used for mixing concrete with expected exposure to temperatures not exceeding +700C.

On alumina aluminate cement

Concrete with a heat resistance class in the range I8-I18 is prepared from these substances. The main mineral component of such cement is calcium monoaluminate, and high-alumina cement is calcium dialuminate. If you do not add any additional additives to the composition, the concrete will withstand a maximum of +1300C; if you include corundum and aluminum oxide filler, you can increase the temperature to +1650C or more.

Main properties of structures made from aluminous cements:

• Minimal thermal shrinkage, slight linear expansion during heating
• High mechanical strength
• Maintaining a stable state during sudden temperature changes
• Thermal conductivity is minimal
• Within a day after pouring, the structures can be used

Liquid glass as a binder for heat-resistant concrete

Before preparing heat-resistant concrete from liquid glass, it is necessary to carefully study the composition of the mixture. Potassium/sodium compounds are used, thanks to which refractory concrete can be used at temperatures of +800-1600C.

In terms of structure, liquid glass can be high-modulus (indicated by the letter B), medium-modulus (B) and low-modulus (letter A).

What is important to know about liquid glass:

• The best performance of soda glass as a binder for a refractory mixture is with a silicate module of 2.0-3.5, potassium - 2.5-4.0.
• Liquid glass hardens for a long time, so various hardeners are added to the mixture (sodium silicon fluoride compound, alkali metal fluorosilicate). In addition to rapid hardening, these substances help increase the strength and density of the solution. You can also add ferrochrome, ferromanganese slag, and nepheline sludge to accelerate hardening.
• It is worth noting that various plasticizers, finely ground additives, regulators, and additives can be added to the mixtures for better workability.
• Per cubic meter of concrete you need approximately 250-400 kg/m3 of binder, hardener - 0.1-0.2 parts of the weight of the binder. The filler will need about 0.12-0.3 the weight of liquid glass.
• The solution based on liquid glass is mixed on site, since the mixture must be poured within half an hour. Laying is carried out at a temperature of at least +15C, humidity should be a maximum of 70%.

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Making heat-resistant concrete based on alumina cement

The exact proportions of material consumption for preparing the concrete mixture are determined by the work project or by construction laboratory specialists. But the typical composition for the production of 1 m3 of heat-resistant concrete is as follows:

• aluminous cement – ​​300 kg;
• chromite or fireclay crushed stone – 1200 kg;
• chromite or fireclay sand – 750 kg;
• water - approximately 170 l.

The concrete mixture should be prepared in such portions that it can be processed in a short time. To do this, we use a mobile concrete mixer, or improvised means: a trough or bunker, a construction mixer or a hammer drill with an attachment in the form of a mixer. As a last resort, you can mix the composition with a bayonet shovel.

First, load the calculated amount of dry ingredients into the container or drum of the concrete mixer and mix them. Without ceasing to stir, gradually add water in the amount needed to obtain the mixture of the desired plasticity.

From the resulting composition, you can make blocks for the construction of a stove or fireplace, for which we move it into a previously prepared equipment, compact it, and level the upper surface. Cover the molded products with film and leave for two to three days, periodically sprinkling them with water. We store the finished blocks on racks in a ventilated area and store them until fully ripe for 20-25 days.

Supplements

Many people use salt as an additive when mixing the solution with their own hands. But the familiar stove masonry solution does not contain it. If you nevertheless decide to take on a complex mixture, for ten kilograms of clay you should adhere to the following proportions: 150 g of salt, 1 kg of cement. Accordingly, clay – 2 buckets, sand – 2 buckets. This solution is designed for laying no more than one hundred bricks.

Subsequence:

1. Pour clay into a prepared, reliable container, gradually fill it with water (in small quantities) and wait for it to soak from six hours to two days.
2. In the process of soaking the clay, it must be mixed. You can do this with your own feet, wearing rubber boots.
3. Add pre-sifted sand and mix with a shovel. A sign of a properly prepared mixture is when it slowly slides off the shovel.

In order to determine the plasticity of the resulting mixture of stove masonry, you can make a rope 1.5 cm thick and 20 cm long, connect it into a circle along a piece of wood with a diameter of 5 cm. The rope must be positioned evenly. If our tourniquet breaks, its ends must be sharp. When multiple breaks occur, this means that the solution is thin, and if no cracks have formed on the bend, the solution is greasy. In the first case, to rehabilitate the mixture, you need to add clay, in the second, sand. You should end up with a few small cracks on the fold of the ring.

Scope of application

The production of refractory concrete began during the emergence of blast furnaces. They were used for lining air heaters and the front walls of open hearths.

Their production was carried out mainly at metallurgical enterprises, but over time it became a separate industry with a wide scope of application.

Application of refractory concrete in metallurgy

The advantages of the material are:

1. availability of constituent components;
2. high thermal insulation properties;
3. resistance to sudden temperature changes;
4. enhancing strength characteristics during operation;
5. no need for firing after pouring.

Products made from refractory concrete are used in all areas where high temperature loads are possible:

• when creating load-bearing structures for industrial furnaces at metallurgical plants;
• in organic synthesis processes during hydrocarbon processing;
• brick kilns;
• in the construction of fireplaces and hearths in private cottages;
• for internal lining of boilers;
• thermal insulation of objects under construction;
• construction of floating structures that require low weight but high strength.

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Directions for use

Refractory types of cement can be used for all construction work.
Given economic considerations, it is most often used in situations where the structure is constantly exposed to high heat. Demand for refractory cement products arises in industry and private property. The main areas of application of refractory high-alumina cement are as follows:

• lining of heated space in heating complexes and units;
• production of heat-resistant structures from reinforced concrete;
• production of fire-resistant panels, bricks, blocks, mortars;
• preparation of adhesive compositions for oil and chemical installations;
• production of furnaces for melting glass products;
• production of structures in the thermal power industry;
• construction of chimneys, home stoves, fireplaces.

Refractory types of cement are in demand in the mining and metallurgical industries, as well as in the construction of tunnels and substrates for powerful thermal installations in any field.

Materials and tools

To produce refractory concrete blocks, you will need to prepare the following tools:

• wheelbarrow;
• concrete mixer;
• hose;
• formwork;
• Master OK;
• vibrating tools (for example, a hammer drill);
• spray;
• sheet of plastic;
• refractory cement;
• slaked lime;
• gravel.

It is also not superfluous to use additives:

• asbestos;
• barium cement;
• liquid glass.

These additives will give concrete all the necessary characteristics that allow it to be used in the construction of structures that will be operated at high temperatures.

Heat-resistant concrete is made by hand as follows:

1. Cement and sand are poured into a concrete mixer in a ratio of 1:4.
2. While stirring, water (preferably filtered) and finely ground ingredients are gradually poured into the mixture until a dough-like consistency is obtained.

Healthy! To improve the result, it is recommended to use ingredients at room temperature - 15-20 ° C.

Pouring the mixture

The prepared concrete mixture must be poured into formwork or molds pre-lubricated with grease or silicone to prevent moisture loss and simplify removal of the frozen block.

The work must be done quickly, since the solution is highly dense and hardens quickly. The solution is laid with a shovel with a small reserve, and the excess is removed with a trowel.

Seal

The concrete mixture is compacted using various tamping mechanisms: submersible or surface vibrators. The working part of the tool is placed in a mold filled with the mixture and the solution shrinks within a minute.

The main purpose of compaction is to eliminate air bubbles that negatively affect the characteristics of the material, as well as reducing its quality and performance properties.

Exposure and hydration

Once compaction is complete, the mortar is left to harden. During natural hardening, moisture evaporates from the mixture, which can lead to cracking of the blocks. Therefore, the solution must be periodically moistened by spraying it with water.

During the first 48 hours, the hardening blocks are covered with plastic film. After two days, the film is removed, the blocks are removed from the molds and transferred to a warm room for 28 days, which is required for the final strength gain.

At the final stage of manufacturing the material, you should wash the equipment used and remove any remaining mixture from it. It is better to clean tools immediately after using them to prevent the cement mortar from drying out.

Components

A mixture of four main components, each of them has its own tasks. Sometimes additives are present. Let's study them to figure out how to make concrete correctly.

Binders

Cement and water are the main reagents that bind all components into a single monolith. The grade of concrete directly depends on the brand and amount of cement. Even after accidental interaction with water, the cement sets and hardens into stone. It would seem that the result has been achieved. However, the technical characteristics are far from desirable. They are significantly increased by the use of fillers.

Fillers

Ideally, in a concrete mixture, a large filler - crushed stone - is supplemented with a medium - smaller size. And the free space between them is filled with fine filler - sand. This is an optimal structure that can reduce shrinkage, increase strength many times over, but at the same time significantly reduce the cost of the final product, for example, the foundation of a house. Since we are talking about the conditions for large-scale work, the proportions of concrete for the foundation in buckets is the most easy-to-understand formulation.

For an improved result, it is desirable that the strength of the filler is approximately 2 times higher than the design strength of concrete. After all, it accumulates after 28 days and grows over time. At the same time, the strength of the filler itself remains the same. And this approach more or less equalizes the difference between it and the binder. This results in a safety margin at an optimal cost.

Main types of crushed stone:

• Limestone. With some types it is possible to obtain fairly strong concrete. But low moisture resistance and frost resistance limits the scope of application. It feels good in a space protected from precipitation, and even better in heated rooms. On the street, such material deteriorates relatively quickly.
• Gravel. The most popular filler in individual construction. Its strength is more than sufficient, it is much easier to work with, and the cost is low. Therefore, there is a rather controversial opinion that the most correct do-it-yourself concrete is based on gravel.
• Granite. Durable filler with low water absorption and high frost resistance.

Chemical additives

Specific properties necessary for certain conditions are given to concrete by additives - plasticizers and modifiers:

• The plasticizing additive increases the mobility of the mixture, so you need a little less water for mixing. Consequently, the design strength is achieved with less cement - this is a saving. However, additives affect the hardening time and initial strength development.
• Antifreeze additives are not cheap. The price of a dosage that allows working down to -20 °C is comparable to the price of concrete itself. At sub-zero temperatures, after 28 days it must gain at least 30% of its design strength. The rest will pick up quickly enough at above-zero temperatures.

Important: how to mix concrete correctly without expensive chemical additives? In everyday life, any concentrated soap solution works well as a plasticizer. PVA glue increases strength, and liquid glass waterproofing properties. If concreting at a slight negative temperature is vital, you can add table salt

But this is “at your own peril and risk”, a small volume in an inappropriate place. Having prepared mentally and understanding that we will lose some of our strength. A high-quality alternative is a heating device.

If concreting at a slightly negative temperature is vital, you can add table salt. But this is “at your own peril and risk”, a small volume in an inappropriate place. Having prepared mentally and understanding that we will lose some of our strength. A high-quality alternative is a heating device.

Under normal conditions - 15-20 °C, in 3 days the concrete will strengthen by approximately 30% of the design strength, in 7 days - by 70%, after 28 days it will be 100%. As the temperature decreases, the dynamics of strength gain decreases. Of course, he will gain full strength, but this period will drag on.