Read an article about expansive concrete. Find out everything about the properties, where to use it and whether you can make it yourself

Expanding types of cement include a group of cementitious materials that do not shrink or increase in volume during the hardening process. The need for their use arises when it is necessary to obtain crack-resistant coatings, carry out waterproofing and repair work. The ability to expand is achieved through the introduction of a number of additives; as a rule, such compositions are more expensive and have special hardening conditions. Despite all their advantages, these brands are highly specialized; their use must be economically justified.

Description of material

These mixtures are made from aluminous slag, natural gypsum stone (dihydrous or semihydrous), quicklime, aluminum powder or similar additives. The increase in volume occurs due to the formation of microscopic bubbles or the growth of crystals in the initial minutes of solidification, exclusively under conditions of high humidity (in normal or dry air the ability to expand will not manifest itself; in extreme cases, the solution will remain non-shrinkable). The time for setting and final strength development depends on the brand: from 4-14 minutes and 14 hours and above; in general, this group of binders has an accelerated time to reach a solid state.

Types of Expandable Cement

• Gypsum-alumina (GGRC).
• Waterproof (WRC).
• Waterproof non-shrink (WBC).
• Straining (NC).
• Plasticized.
• Expanding Portland cement (EPC).

1. Gypsum-alumina.

Designed for the production of non-shrinking and expanding waterproof mortars and waterproofing plasters. It consists of 70% finely ground aluminous blast furnace slag and 30% gypsum. Characteristics:

• beginning of setting - 10 minutes;
• completion of setting - no later than 4 hours from the moment of adding water;
• tensile strength on the third day - 280 kg/cm;
• linear expansion after three days - from 0.1 to 0.7%;
• waterproof after three days - samples can withstand pressure up to 1.1 MPa;
• GHRC-based concretes can be steamed, but cannot be used at temperatures above 100°C;
• frost resistance;
• fire resistance is higher than that of PC, but lower than that of simple alumina.

To slow down the setting, add borax, acetic acid, and sulfate-yeast mash (SYB).

Applications of gypsum alumina expansive cement:

• preparation of non-shrinking and waterproof solutions;
• sealing joints of concrete and reinforced concrete structures;
• production of waterproofing plasters;
• strengthening and filling of foundations;
• sealing foundation bolts;
• caulking of seams and sockets of water supply lines;
• ensuring the waterproofness of subway tunnels;
• construction of liquid fuel storage tanks;
• as a waterproofing coating for wastewater treatment plants;
• in the construction of swimming pools, repair of showers.

2. Waterproof.

Fast-hardening binder, its composition:

• aluminous cement - 70%;
• semi-hydrous gypsum - 20%;
• ground highly basic calcium hydroaluminate - 10%.

Distinctive characteristics of the VRC:

• setting: start - 4 minutes, completion - 10 minutes;
• water resistance - complete after 1 day at a pressure of up to 0.6 MPa;
• strength grade 28 days - 500 (50 MPa);
• linear expansion - up to 1%.

Disadvantages of the VRC:

• price;
• very fast setting;
• low frost resistance - suitable only at positive air temperatures.

Application: waterproofing of locks, docks, swimming pools, pipelines and tunnels, foundations, sealing cracks in reinforced concrete structures. You can use the VRC regardless of the humidity level.

3. Waterproof and non-shrink.

Hydraulic fast-hardening binder, 85% consisting of aluminous cement, the rest - gypsum and slaked lime.

Distinctive characteristics of VBC:

• setting - from 5 minutes;
• brand strength on the third day - from 60 to 80%;
• waterproof - withstands water pressure up to 0.7 MPa.

Selected for waterproofing underground structures with a humidity level of 75% at an air temperature of +20°C. Unsuitable in rooms where dry conditions are periodically possible, as it shrinks.

4. Straining.

A binder for mortars that has high expansion energy and is capable of compressing and tensioning reinforcement in concrete. Based on the magnitude of self-stress energy, three types are distinguished:

• NTs-10 - up to 1 MPa;
• NTs-20 - up to 2;
• NTs-40 - from 4 and above.

Compound:

• Portland cement - from 65 to 75%;
• aluminous cement - from 13 to 20%;
• gypsum - from 6 to 10%.

Distinctive characteristics of NTs-20:

• strength at 28 days - 40 MPa;
• linear expansion on day 28 - 1.5%;
• setting speed: start - after 30 minutes, end - no later than 240 minutes;
• water resistance - excess water pressure up to 20 atm;
• frost resistance - up to 1500 freeze-thaw cycles;
• gas permeability - 40 lower than that of Portland cement;
• abrasion - 0.08 g/cm2.

Usage:

• production of mixtures for waterproofing foundations, cellars, basements, tunnels, roofs;
• installation of prefabricated and monolithic tank and underground structures, floors in industrial premises, road and airfield surfaces;
• production of reinforced concrete products and structures with prestressed reinforcement;
• production of pressure and non-pressure pipes;
• construction of radioactive waste storage facilities.

If NC is used for waterproofing, then no additional means are required.

5. Expanding PC.

It consists of Portland cement clinker and sulfoaluminate additive, which imparts special properties. You can purchase one of its types: ROC-10 and ROC-20. Both are intended for the preparation of non-shrinking mortars, which are used primarily for waterproofing.

Comparative characteristics:

Parameter	ROC-10	ROC-20
Linear expansion, %	0,1 — 1	0,2 — 1,5
Self-stress, MPa	1	1,9
Waterproof class	W10	W12 - W20
Compressive strength at 28 days, MPa	40	49
Application	Underground tank structures, swimming pools, basements, underground garages, roll-free roofs, tunnels, floors of non-residential buildings, crack-resistant waterproof joints, repair and strengthening of structures	Same as ROC-10 plus: private construction (all types of premises), sports facilities (swimming pools, stadium stands, skating rinks, hockey rinks, running tracks), waterproofing of premises with high humidity or prone to mold, above-ground and underwater tanks , foundations for equipment, road and airfield pavements, radioactive waste storage facilities, treatment facilities

RPC-20 ensures complete elimination of shrinkage and the deformations caused by it, and is characterized by increased resistance in aggressive environments. Setting time: start - 30 minutes, completion - about 8 hours. During the hardening process, be sure to maintain humidity. Frost resistance - 300 freeze-thaw cycles.

6. Plasticized.

A type of expanding non-shrinking cement is plasticized MACFLOW brand from the world's largest chemical concern BASF. It consists of PC and a complex additive, which imparts expanding and plasticizing properties. Advantages:

• obtaining concrete of high early and final strength;
• achieving a level of workability without additional plasticizer additives;
• obtaining injection non-shrinking solutions with high fluidity.

Characteristics of MACFLOW cement:

• strength at the age of 28 days - three classes: 42.5; 52.5; 62.5 MPa;
• linear expansion 1 day - 0.5%;
• water resistance - 8 atm;
• frost resistance - 300 freeze-thaw cycles.

Usage:

• repair and construction of road and airfield pavements, bridge structures and civil structures;
• installation of anchors in concrete, soil and rocks;
• as cement for sealing cracks (by injection method) in concrete and stone buildings;
• filling channels containing prestressed reinforcement or anchors under mechanical tension;
• soil injections;
• installation of equipment and metal structures;
• sealing joints.

Self-expanding cements - special building mixtures

The main binding materials in construction are cements. The most widespread are compositions based on Portland cement. Despite their wide popularity, sometimes their use is undesirable - defects in the form of micro- and macrocracks cause deformation and shrinkage of the structure. Self-expanding cements belong to a special type of binder mixtures that do not have such negative qualities.

Classification and properties

Normal shrinkage of Portland cement (reduction in linear dimensions) reaches up to 2 mm/m of product. While the mixture is wet, its dimensions increase due to absorbed water. Direct shrinkage occurs when the cement mortar dries in air during the third week of hardening.

Depending on the composition and required characteristics, the material is divided into the following types:

1. non-shrinking cements - expansion is equal to subsequent shrinkage, which leads to constant dimensions;
2. expanding cements – dry shrinkage is less than the initial expansion by 5-6 mm/m of the finished product;
3. Tensile cement is an expanding variety that is used in the production of reinforced concrete structures.

The operating principle of prestressing cement is based on the mechanical interaction of concrete mortar and metal reinforcement. The reinforced concrete frame is subject to tension when pouring the expanding mixture. The strength of the reinforcement prevents further tension and stops the expansion of the cement mixture.

This interaction leads to simultaneous stretching of the metal frame and stopping the expansion. The reinforcement tends to shrink, and the concrete tends to expand. This keeps the entire structure in tension and increases strength by 1.5-2 times. A comparison of the shrinkage dynamics of conventional, non-shrinkable and expanding cement is shown in Figure 1.

Rice. 1. Dynamics of cement shrinkage. Designations: “1” - ordinary Portland cement; “2” - non-shrink cement; “3” - expanding cement:

Composition and production

Various areas of application determine the construction and operational parameters of materials. To achieve them, various compositional production schemes are used, including a wide range of components. Let us consider the fundamental compositions of self-expanding cements.

Compositions based on Portland cement

There are compositions for the production of conventional self-expanding and tensile cements.

The differences lie in the composition, which determines the setting parameters:

• 65-75% Portland cement, 6-10% gypsum, 15-25% high-alumina slag. The high content of the expanding binder helps to increase the setting speed (start - after 30 minutes, end - 4-6 hours after preparing the solution). The rapid increase in mechanical stress allows the use of such compositions for the production of tensile cements. As the gypsum content increases, the setting speed decreases. This makes it possible to use mixtures for domestic purposes (coating joints, plastering, etc.);
• 94-95% Portland cement, 0.1-0.2% polymer additive, 5-6% quicklime. The principle of operation is the formation of tiny gas bubbles that accompany the slaking of lime when water is added. The initial expansion of such cement will be high, but subsequent shrinkage returns the volume to its original state. A similar composition is used for non-shrinking mortars used to seal joints between slabs of reinforced concrete structures. Another direction is the “silent explosion” method (see below), used in the extraction of stones;
• options for mixtures of Portland cement, gypsum and other mineral additives. Alunite, a mixed basic sulfate of calcium and aluminum, can be used as a replacement for high-alumina slag. An additional component that increases expansion is quicklime.

Compositions based on alumina cement

These include bi-, tri- and more component mixtures, necessarily containing aluminous cement (a product of firing and grinding bauxite and limestone) and watered calcium sulfate (gypsum).

A distinctive feature of this cement is its very high setting speed (start - from 10 minutes, completion - 1 hour after preparing the mixture). To regulate the rate of hardening, the addition of borax or acetic acid is used.

Gypsum-alumina cements are used to treat joints and porous surfaces, providing high water resistance. Selected non-shrink compositions can be used for coating pipe joints, withstanding water pressure up to 10 atm. The advantage of such mixtures over Portland cement is their higher (10-20 times) adhesion to the old construction mortar.

The production of expanding cements involves mixing components crushed to a dusty state or crushing their mixture together. In the household production of self-expanding compounds, a mixture of Portland cement, gypsum and quicklime is used. The resulting composition is used for waterproofing joints between building blocks.

Requirements for cements and quality control methods are established by GOST 30515-97. A number of specific parameters can be regulated by industry regulations and technical specifications.

The bulk of self-expanding cements are grades 400, 500 and 600, withstanding pressures of at least 40, 50 and 60 MPa/cm2, respectively. Tensile cements are the strongest (grade 600).

Restoring a wall using self-expanding cement

Technical characteristics and types

All types of expanding building materials are made on the basis of alumina-type cement or cement mixtures that contain an alumina component. But depending on the leading additive, expanding cement comes in 5 types.

1. Expanding Portland cement (EPC). It is produced with the addition of blast furnace slag, which gives the composition increased strength. Most often used for the construction of monolithic buildings. Not suitable for plastering and facing work due to uneven linear expansion and uneven geometric surface. When immersing in water or simply watering the laid mortar, expansion will not be achieved. Changes in volume occur only with a single short steaming. The composition hardens within 30-80 hours.
2. Gypsum-alumina cement (GGRC). The mixture consists of 30% gypsum, which ensures rapid setting and hardening of the solution. Although gypsum cement is capable of maintaining volume even after hardening, it cannot be called absolutely non-shrinking. When the mixture hardens in air, it sags slightly and is only capable of growing in an aqueous environment. For work in winter and in the off-season, gypsum-alumina cement is better than others. It is resistant to frost (down to minus 25 ° C), retains its beneficial properties even with frequent temperature fluctuations.

In the heat and high humidity, the gypsum-alumina type of cement “works” poorly, losing some of its characteristics.

1. Plasticizing (PPS). The basis of this composition is Portland cement with the addition of a plasticizer and sulfite liquor as an expanding component. Its strength qualities are higher than other types of cement, and its linear expansion is predictable. This means that the solution creates a flat surface and can be used where strict geometry of shapes and planes is needed. This cement is considered beneficial - the developer does not need to use pure plasticizer. It can be successfully replaced by a plasticizing type RC.
2. Waterproof (WRC). It is produced by mixing aluminous cement, semihydrous gypsum and highly basic calcium aluminate. The mixture is characterized by rapid hardening properties - setting of the mass is observed within 3 minutes after preparing the solution. The mass completely hardens after 25-28 hours, and its expansion occurs only at a humidity of at least 70%. It is possible to reduce the rate of hardening of the solution by adding borax or acetic acid to the composition.
3. Straining (NC). It consists of Portland cement, gypsum and blast furnace slag, and is characterized by increased gas and moisture resistance. When used, the mass first hardens and then expands, stressing the building structure. The material copes well with cracks and defects and is suitable for repairing concrete and reinforced concrete structures. The mixture sets in the first 4 hours, and finally hardens after 70-75 hours.

Each of these types of cement differs in technical characteristics for a number of indicators:

• beginning of setting - 4 minutes for VRC, 20 minutes for GGRC, 30 minutes for RPC, 2.5 hours for NC;
• the final strength gain is greatest for GGRTs and ROC (up to 80 hours), least for VRC (about 25 hours);
• compressive strength - up to 500 kgf/cm2 for VRTs and GGRTs, 400-600 kgf/cm2 for RPC and NTs;
• relative linear expansion - 0.02-1% (VRC), 0.3-1% (RPC), up to 3% (NC), 0.3-1% (GGRC).

All types of expanding cement mortar are placed in high compaction formwork. To gain volume and strength characteristics, the mass must be provided with the recommended temperature and humidity.

Coarse and fine aggregates help improve the technical characteristics of expanding cement mortars. For this purpose, fine-grained quartz sand, gravel and crushed stone of fractions from 5 to 70 mm are used. Fillers increase the strength of the solution, restrain its deformation, reduce creep values ​​and partially compensate for shrinkage.

Features of the material

Expanding cement is a cement mass that increases in size as the mortar hardens. This effect is observed only in conditions of high humidity. Under normal conditions and dry weather, such material does not shrink during hardening.

The main property of the composition is the expandable volume of alumina-type cement with the introduction of a special additive with fairly rapid hardening of the mass.

Graph of strength growth during water storage of expanding cement.

The composition expansion mechanism is used to fill all (even microscopic) voids in the material, which ensures strength, solidity and high waterproofing properties of the structure. Expanding cement has found application in the construction of monolithic reinforced concrete systems, since during expansion it ensures the filling of all voids in the frame. In general, its purpose is quite specific: filling cracked concrete; production of structures operating in water or high humidity; gluing reinforced concrete structures; plastering complex surfaces (for example, shell rock).

Due to its ability to fill all air formations in concrete, expanding cement acquires unique water resistance. Due to expansion, the composition has increased adhesion to almost any material, which makes it possible to cladding walls of unusual designs. Important advantages include fairly high durability and resistance to aggressive influences.

The main disadvantage of such cement is its high price, which somewhat limits its use in private construction. It should be used for its intended purpose: in structural elements that are located in water or exposed to prolonged exposure to high humidity (basements, some foundations and plinths, floor screeds; walls of swimming pools, wells, tanks, etc.).

What is this building material?

Expanding cement is a mineral powdered binder that can expand in volume as the solution dries. Expanding, the cement mixture fills all the voids, seams and cracks of the building structure, and forms its pre-stress.

Such properties are achieved through the inclusion of expanding components, the content of which ranges from 5% to 20%. Upon contact with water, chemical bonds are destroyed, which causes an increase in the volume of the original composition and the formation of crystal lattices.

The following are used as expanding additives:

• aluminum sulfate;
• calcium chloride sulfate;
• magnesium hydroxide;
• calcium hydrosulfoaluminate;
• sulfite liquor;
• aluminum powder;
• alum stone.

Expansion properties in some cases are achieved using another technology - damping. During this process, a large number of small bubbles are formed inside the mixture, increasing its volume.

Unlike cellular concrete, which can lose strength during foaming, mortars with expanding cement retain their strength characteristics.

The expansion effect is observed only in conditions of high humidity, while in dry weather no shrinkage is observed. Self-stressing of a reinforced concrete structure occurs regardless of the location and direction of the reinforcement bars. The result is biaxial volumetric self-stress, which increases the strength and stability of the structure.

Advantages of the composition:

• high adhesion - ensures a tight fit of the mixture to the surfaces of the structure;
• waterproofing properties - suitable for sealing cracks, micropores and seams through which water can leak;
• resistance to temperature changes - maintains technical characteristics and elasticity even at low temperatures;
• accelerated strength gain - depending on the brand, the solution reaches 80% strength in the first 24 hours.

Waterproof composition

Waterproof expanding cement is designed to waterproof a structure. Concrete based on it can even be used in the construction of dams and dams. At the same time, compared to other types of such compositions, it has the lowest volumetric expansion. This property should be used when preparing plaster solutions for covering walls located in difficult wet conditions.

Scheme of cement production using dry and wet methods.

Waterproof cement is a dry mixture of aluminous cement, semi-hydrous gypsum and highly basic calcium aluminate. The additive in the form of aluminate is obtained by thermal exposure (up to 150°) for 6 hours to a mixture of aluminous cement with lime (in equal proportions) and water. The binder and additive are thoroughly mixed and ground dry.

When water is added to cement, a reaction occurs with the appearance of an expanding volume. The mixture tends to harden quickly, so within 3 minutes the process of setting the mass begins, which is completed after 10 minutes. If there is a need to slow down the hardening of the solution, then borax or acetic acid is added.

The complete hardening process of the solution inside ends after 25-28 hours, depending on the temperature. Volumetric expansion of the mass occurs only at high humidity (at least 70%). The degree of expansion of the standard solution is standardized: the linear expansion of cement after 24 hours should be within 0.2-1% (no more and no less). The expanded cement mass increases with increasing humidity.

Internal expansion, which continues for quite a long time, leads to a gradual increase in the strength of the composition. 3 days after application, the cement must meet the parameters of grade M300, and after 28 days - M500.

MANUFACTURER WARRANTY

5.1. The manufacturer guarantees the compliance of cement with the requirements of this standard provided that the consumer complies with the transportation and storage conditions established by the standard.

5.2. The warranty period is 2 months from the date of shipment.

To remove the cement film and traces of the sealing compound, the end surfaces of the samples must be thoroughly cleaned with a steel brush before testing.

After completing the preparation of samples for testing and before the start of testing, the forms with samples must be covered with a damp cloth.

The samples are tested on a device of any design that provides the ability to supply water to the lower end surface of the samples at an increasing pressure of up to 1 MPa (10 ati), as well as measure the water pressure and the ability to monitor the condition of the upper end surface of the samples.

The temperature of the room in which the test is carried out must be 20 ± 2 °C, the relative air humidity must be at least 60%.

The tests begin at a water pressure of 1 ati (0.1 MPa), then after 2 hours the pressure is increased to 2 ati (0.2 MPa) and then every 4 hours the pressure is increased in steps of 2 ati (0.2 MPa).

The samples are considered to have passed the tests if, after 2 hours of exposure at a pressure of 10 ati (1.0 MPa), none of them shows signs of water seepage.

Gypsum-alumina composition

Expanding type gypsum-alumina cement is very similar in properties to the waterproof cement considered; its main purpose is waterproofing concrete structures. Its binder composition is a mixture of aluminous clinker or slag with natural gypsum of the dihydrate class. This cement is especially good for sealing joints in structures operating in water.

A coating made of gypsum-alumina mortar, after hardening, has greater compressive strength. The process of complete hardening takes 70-80 hours. The price of this material is somewhat more expensive than waterproof cement.

Areas of use

1. Road construction. This material is suitable for creating coatings on stadiums, roads, road bridges, runways, and airfields.
2. Expanding cements for use in domestic buildings. The building materials in question are often used for flooring in utility rooms, sheds, basements, and to create paths.
3. Application in industry. Expandable ones are often used for arranging industrial premises (factories, plugging oil and gas wells, enclosing structures, subways).
4. Arrangement of hydraulic structures.
5. Leveling brick and concrete boxes and eliminating cracks and cavities using expandable cements.

The degree of expansion depends on various factors, including the type of original cement, its mineral and chemical composition, the type of expanding additive, as well as the ratio of these elements in the composition, the degree of grinding and environmental conditions (humidity, temperature) under which the expanding cement hardens.

vote

Article rating

Alumina type cement

The basic definition for aluminous cement is that it is a fast-hardening material in an aqueous environment and a very high-strength binder in air. Aluminous cement is obtained by firing until almost sintering or complete melting of the material (alumina, calcium oxide). Unlike the standard type of Portland cement, where the clinker consists of calcium silicates, the aluminous type of Portland cement consists solely of low-basic calcium aluminate. The cost of aluminous Portland cement is much more expensive. The use of the material is advisable only in cases where it is necessary to speed up the work process, and not wait until the end of the hardening period of the structure. Economically, the material justifies itself only when the use of alumina cement is an urgent need for construction and production work.

• The main areas where it is recommended to use aluminous Portland cement:
• For the construction industry, when it is necessary to apply quick solutions for the construction of structures
• To eliminate the consequences of technological accidents, when it is necessary to use quick solutions to eliminate the consequences
• For the defense industry, for the creation of military transport hubs
• For structures that are used exclusively in low-temperature operating conditions
• For structures that are constantly located in a mineralized environment and exposed to sulfur dioxide gases
• For the manufacture of high-strength concrete refractory units and structures (concrete and mortar)

Expanding gypsum-alumina cement GOST 11052 74 – varieties

Specialized stores offer various modifications of this cement:

• waterproof. It is used as a waterproofing composition when carrying out restoration measures, repairing various structures exposed to a humid environment - tanks, underground systems, tunnels;

Expanding cement is one type of material that is quickly gaining its place in the construction industry.

• gypsum-alumina. Maintains volume during expansion, can be used at negative temperatures. Demanded for the preparation of non-shrinking solutions. Designed for sealing joints to ensure their waterproofness and preparing moisture-resistant plasters;
• Portland cement. It quickly gains operational strength only when steamed. Used in the construction of hydraulic structures, as well as tanks intended for storing various liquids;
• straining. Produced for the restoration of structures made of reinforced concrete. The material hardens and then increases in volume. Thanks to this feature, the stress required for reinforced concrete is created;
• plasticized. It is made by mixing Portland cement with modifying additives. The material is characterized by increased strength characteristics and is plastic. Used in road and industrial construction.

The choice of a specific type of material depends on the tasks at hand.

Application

Aluminous RC is used when carrying out the following construction work:

• Repair of concrete and reinforced concrete structures, hydraulic structures, reconstruction of buildings. The material allows you to fill microscopic voids, cracks, crevices, thereby preventing further destruction of the structure.
• Urgent construction in conditions of low temperatures or high humidity. In these cases, it is better to use gypsum-alumina cement.
• Arrangement of structures where it is necessary to achieve a flat surface - road construction, laying running tracks, ice skating rinks, hockey fields, stadiums, bridges, airfields. Expanding cement with plasticizers is perfect here.
• Manufacturing of prefabricated and monolithic tanks - swimming pools, water pumping facilities, wastewater treatment plants, sewage pumping stations. Thanks to the waterproofing properties of cement, the containers are sealed and waterproof.
• Creation of moisture-resistant decorative plaster mixtures. Applied on top of shell rock and foam concrete, the solution retains the thermal insulation and strength properties of porous building materials.
• Repair, construction of underground channels and communications - metro construction, crossings, mine penetrations.
• Bonding of reinforced concrete materials during the construction of high-rise buildings. Cement with an expansion effect ensures a strong connection between floors and walls, prevents destruction, and extends the service life of the structure.

Expanding cement mixtures are used to prepare all types of non-shrink concrete. The material has one drawback - its high cost, which limits its scope of use in private households. It is suitable for forming flooring in cellars, sheds, for the construction of bathhouses, garages, arranging paths on a personal plot, for restoring the walls of residential or utility buildings.

Plasticized cement

Plasticized expanding compound is a recent development in this field. It is not yet available in Russia. Foreign companies offer a material based on Portland cement with plasticizers and an expanding ingredient in the form of sulfite-alcohol stillage. Due to its increased plasticity, such a solution is used to cover large areas (floors, roads, etc.).

When preparing expanding cement mortars, the following tools should be used:

• construction mixer;
• construction hair dryer;
• scales;
• measuring bucket;
• shovel;
• putty knife;
• Master OK;
• knife;
• file;
• sandpaper.

Expanding cements make up a number of modern high-quality building materials. Their use is somewhat limited by price, but their waterproofing and strength properties inspire confidence in them.

Non-shrink

Non-shrinking waterproof cement is created using aluminate in a small volume. A crystalline cement stone is created, strengthening and compacting the structure. Composition of the mixture: aluminous Portland cement (about 85% of the volume), asbestos (up to 5%), semi-hydrous gypsum and calcium aluminate (up to 10%).

Within an hour after hardening of reinforced concrete structures, the concrete gains 75% strength, the full cycle takes place in the usual 28 days. The mass must harden in a humid environment (minimum 70% humidity), otherwise the shrinkage process cannot be avoided.

The material is used for the construction of structures that are constantly exposed to water. Therefore, a mixture of calcium nitrate, aluminum powder and ferrosilicon is often added to the solution for an anti-corrosion effect and to protect the reinforcement from moisture.

Fillers

The proportion of large and small aggregates in concrete can reach 80% of the total volume of the mixture, and have a significant impact on the physical and chemical properties of the product. Optimal selection of the composition of these components can significantly reduce the use of cement, the price of which significantly affects the cost of the product.

Coarse and fine aggregates
In addition, aggregates, along with binders, can improve the technical characteristics of structures:

• increase strength and inhibit deformation;
• reduce creep value;
• take on the effects of linear stresses and partially compensate for shrinkage.

To prepare expanding solutions, gravel and crushed stone of fractions 5–70 mm act as coarse aggregates. The requirements for this material are the same as for traditional heavy concrete (GOST 10268-80).

The strength of aggregates is determined by the strength values ​​of the rocks from which they are made. According to GOST requirements, the average density of coarse aggregates should be 2000–3000 kg/m3. Recommended brand of coarse aggregates

Technical characteristics of some aggregates example

As a fine aggregate, quartz sand of fine fractions (GOST 8736-93) with a density of 2000–2800 kg/m3 is most often used, and the smaller the fraction, the higher the density of concrete.

Linear temperature deformation

Linear extensions

Linear expansion is volumetric transformations that occur in the structure of a material under the influence of internal or external temperature factors.

• Linear expansion coefficient of reinforced concrete (α). This is a relative increase in the linear dimensions of structures with an increase in temperature by 1 K under standard conditions.
• Coefficient of thermal expansion of concrete. Its value depends on the temperature and relative humidity of the environment. This parameter is inextricably linked with the thermal conductivity of the material.

Note: The last value represents the product’s ability to accumulate or conduct heat through its structure. The higher the density, the higher this parameter.

• Coefficient of linear expansion of concrete. Equal to 0.00001 (°C)-1 - that is, when the temperature rises to +50°C, the linear expansion will have a value of 0.5 mm/m.
• Expansion coefficient of concrete. It also depends on the brand of cement and the composition of aggregates.

Aggregate and cement stone have different coefficients of thermal expansion. Therefore, when temperature conditions change, these components behave differently, resulting in volumetric stresses in the structure of the product, which contribute to the formation of cracks both on the surface and inside the material.

To prevent cracking, thermal expansion and shrinkage deformations in modern construction, a whole range of measures is provided:

• expansion joints in concrete (expansion or temperature);
• increasing the frequency of reinforcement of structures;
• division of monolithic surfaces into separate autonomous blocks, etc.

Expansion joint

However, all these methods significantly increase the cost of construction and are not always effective in improving performance characteristics. The most effective way to eliminate the above-described disadvantages is to use expanding and tension binders.

Knitting

Expanding cements are mixtures consisting of Portland cement or aluminous cement with special additives that increase the volume of the cement stone structure at the initial stage of hardening.

The additives usually include:

• gypsum;
• aluminous slags;
• calcium hydroaluminates.

In the process of hydration of cement stone, calcium hydrosulfoaluminate compounds are formed, at the moment of their formation the effect of expanding the structure occurs, compensating for shrinkage phenomena.

The most common types of cements are:

1. Waterproof expansive cements (WECs), obtained by mixing aluminous cements (70%), calcium hydroaluminate (10%) and finely ground gypsum (20%).

Cement VRC

1. Waterproof non-shrinking cements (WBC), consisting of the same components as (WRC), but taken in other proportions and in other volumetric ratios. These cements are capable of forming highly waterproof cement stone that can withstand water pressure up to 0.70 MPa.

Waterproof non-shrinking VBC binders

1. Expanding cement (ECC), obtained by finely grinding and mixing Portland cement (60%), high-alumina blast furnace slag (5–7%), gypsum (7–10%) and mineral additive (20–25%).

Expanding cement ROC

1. Gypsum-alumina expanding cements (GAEC), consisting of a mixture of finely ground aluminous blast furnace slag (70%) and ground gypsum (30%).

Gypsum alumina expanding cement

1. Prestressing cements (NC) are produced on the basis of Portland cement (60–70%), aluminous cement (18–20%) and gypsum dihydrate, crushed together to a specific surface area of ​​at least 3500 cm2/g (see photo).

Tensile cement

Expanding solution

The modern building materials market is constantly developing, offering consumers more and more new products with wide functionality. The most interesting in terms of properties and performance characteristics is a unique solution called expanding cement among builders and repairmen. Used in repair and restoration work to fill voids, damaged areas, in concrete structures, brickwork and cement layers.

Expanding mortar is a special type of cement that increases in volume when certain components are added. The construction of monolithic reinforced concrete structures, the construction of underground structures is far from a complete list of tasks that this composition can easily cope with. Despite the high price, it is optimal as a restoration material, the use of which significantly reduces the costs of other means.

The versatility of this product makes it an ideal material for any major or cosmetic repairs, hydro and thermal insulation.

What does it contain and how does it work?

The material is based on aluminous materials with expanding components: aluminum and calcium chloride sulfates, calcium hydrosulfolumipate, magnesium oxide hydrate and other elements that provide the strength characteristics of the solution.

The mechanism of action of the material is as follows: complex chemical compounds under the influence of moisture enter into a decomposition reaction, due to which the solution increases in volume. Thus, the powder turns into a building material capable of:

• qualitatively fill cracks of different sizes;
• used as a finishing plaster that increases adhesion;
• withstand atmospheric changes and chemical exposure.

The main advantage of an expanding solution is that it dries without shrinking. It is this property that makes it possible to apply a layer up to 10 cm thick, which will set and dry within 24 hours. A feature of the material is a gradual internal expansion, which continues for quite a long time, leading to an increase in the strength of the composition. The dried layer becomes resistant to significant temperature changes, provides excellent adhesion and is able to withstand significant weight loads.

Despite the large number of advantages, self-expanding mortar has disadvantages in the form of high cost, the dominance of counterfeits in the modern building materials market and the narrow profile of the material used.

Where is it used?

• gluing reinforced concrete elements;
• filling micro and macro cracks;
• production of external plaster for walls.

Possessing excellent surface adhesion properties, the expanding cement composition is instantly absorbed into the base material, filling the pores of the structure from the inside.

When working with the material, no special skills are required. Ordinary water is used as a catalyst, and the mixture itself hardens within 24 hours. The scope of application of such material mainly extends to industrial facilities: reservoirs (dams, dams, pools, wells) and water pressure elements, as well as floor screeds, foundations, plinths and basements, where working with conventional materials is impossible due to high humidity.

Possessing a high waterproofing coefficient, the expanding composition is used for the construction of monolithic structures.

Preparing the mixture

The expanding solution of Quellmörtel Extra is diluted with water at the rate of 25 kg of powder per 4 liters of water, mixed to obtain a uniform plastic consistency and applied to the prepared base. The “lifetime” of the mixture is 30 minutes, so you should work quickly, because at 45 minutes the solution begins to harden, after which any manipulations are useless. The operating temperature in the room should be no less than +5 and no more than +30 degrees, and the base should not be wet, but slightly moistened.

Advantages and disadvantages

• products made from this material are not subject to corrosion and have excellent resistance to aggressive environments;
• the material has increased frost resistance;
• the speed of setting and full strength gain significantly exceeds the same indicators for ordinary Portland cement;
• excellent adhesion to metal, which allows you to effectively protect reinforcing mesh in concrete products and secure embedded parts or anchors in concrete elements;
• excellent resistance to high temperatures and open fire;
• Varieties of aluminous cements (high alumina and expanding) are used to perform complex work that cannot be performed by other means.

• increased requirements for the equipment used to produce this material and the process of obtaining raw materials itself, which is reflected in the high price of aluminous cements;
• the peculiarity of this material, when gaining strength, to release thermal energy does not allow the use of solutions for pouring large volumes - when trying to fill a large area, uneven setting of the material occurs, which leads to destruction of its integrity;
• Another limitation in the use of alumina compositions is associated with the process of heat release - the solution cannot be used at temperatures above +30°C;
• products made from this cement cannot resist the effects of an alkaline environment and are destroyed.

Expanding concrete: material composition

Expanding concrete (GOST 32803-2014) is a material containing prestressing cement or special expanding additives to form prestressing structures during the curing period of the mixtures.

As a result of such setting conditions for the solution, it is possible to obtain expanding concrete that has increased density, water resistance and durability (see video in this article).

Expanding and tensile concrete

Comparative characteristics of binders

Prestressing concretes are mixtures based on prestressing cements that are capable of increasing in volume in the initial hardening phase and stretching the reinforcement in direct contact, which as a result of such processes receives the effect of self-stressing (compression).

• Moreover, reinforcing bars stretch regardless of their direction and arrangement in the structure of the product, which contributes to obtaining biaxial volumetric self-stress of structures.
• The mechanism of action of expanding materials is based on the creation of controlled directional crystal formation during the hardening of cement stone, which helps regulate the process of volumetric deformations in the plastic structure of the product.
• The use of expanding fast-hardening concrete, thanks to controlled linear expansion, can significantly compensate for the effects of shrinkage deformations, increase crack resistance and service life of buildings and structures.

Expanding cement for sealing cracks

Features of sealing cracks include different formats for preparing the repair solution, depending on the size of the damage.

• A solution for sealing thin cracks 0.2-0.3 mm wide. Proportions: 1 part expanding cement to 1 part finely ground sand, dolomite or limestone flour (aggregate), water 35-40% by weight of cement. The principle applies is that the size of the filler particles should be 3-4 times less than the smaller thickness of the crack.
• Mortar for sealing cracks 0.5-3 mm wide. Proportions: 1 part cement, 2 parts sand with a particle size modulus of 1.0, water 35-40% of the weight of cement.
• Mortar for sealing damage over 3 mm thick. Proportions: 1 part cement, 3 parts quarry or river sand with a particle size modulus of 1.5, amount of water as in previous options.

Repairing concrete with expanding cement

The treated substrates are pre-cleaned from dirt, dust, stains and deposits. The surface and all reinforced parts are watered. Expanding type cement is mixed with sand in a 1:2 ratio, water is added until a homogeneous mixture is obtained. The composition is applied with construction syringes using pneumatic installations. Afterwards, the surface is covered with cellophane and the humidity is maintained for at least 7 days.

Injecting cracks in concrete

All concretes exhibit slight shrinkage, although expanding grades exhibit only the most minimal amount of shrinkage. The reason for shrinkage is the escape of air and sagging of the material under its own weight. To reduce the risk of shrinkage, use vibration if possible. Expanding concrete has a minimal tendency to shrink, so vibration is not necessary.