Aluminous cement: what is it, its features and properties, composition and characteristics

What is aluminous cement called?

One of the most important building materials in conditions of high humidity is alumina cement.

Rapidly hardening in air and water, this substance with high strength properties is indispensable in construction as a component of high-temperature and waterproofing mortars and concretes.

The common name “alumina Portland cement” is not correct, since alumina cement and Portland cement are different materials.

There are two types of aluminate cement in demand in industry - alumina cement (HA) (35% Al2O3) and high alumina cement (HAC) (60-80% Al2O3).

Differences between aluminous and Portland cement

Although aluminate mixture and Portland cement have a common purpose, due to the difference in mineral composition, the properties of the materials differ significantly.

A short list of differences:

the strength gain of the GC proceeds as an exothermic reaction, which can take up to a day;
the density of the GC monolith significantly exceeds that of Portland cement;
the water resistance of the GC monolith is an order of magnitude higher than that of classical cement;
GCs reach their design strength after three days, Portland cement reaches the same strength indicator after twenty-eight days;
a monolith made of aluminate cement is more susceptible to the destructive effects of an alkaline environment than standard material.

Portland cement concretes in a humid environment quickly lose their qualities - penetrating into the pores, moisture causes corrosion of the reinforcement, and soluble salts destroy the structure of the monolith.

Aluminous compositions do not have these disadvantages.

The production of aluminate material is less than 1% of the total volume of cement produced. The reason is the shortage of raw materials and the high cost of GC.

Specifications

The technical characteristics of alumina cement vary depending on which brand it belongs to. According to GOST 969-91, developed back in the 70s, based on strength, such cement is divided into GC-40, GC-50 and GC-60. Also, the proportions of certain substances in the composition depend on what properties need to be achieved and in what area the cement will be used. It makes no sense to give here the chemical formulas of the substances that make up cement, but for comparison it is worth saying that ordinary aluminous cement contains from 35% to 55% bauxite, while high-alumina refractory cement contains from 75% to 82%. As you can see, the difference is significant.

As for technical properties, although aluminous cement is a fast-hardening option, this should not affect its setting speed. According to the rules and regulations, it should be at least 30 minutes, with full setting occurring after 12 hours after application (maximum). Since the material has a special crystalline structure (all the crystals in the substance are large), it is little susceptible to deformation changes, and therefore we can confidently speak about its non-shrinkability and relatively small mass.

Options differ in characteristics and depending on the method of their production. In total, only two methods are presented: melting and sintering.

Each of them has its own specifics.

Scientifically, the first method is called the raw material mixture melting method. It involves several stages, each of which deserves close attention. First you need to prepare the raw materials. After this, the cement raw material mixture is melted and gradually cooled, carefully monitoring the temperature to ensure the best strength characteristics. Finally, the resulting high-strength slag is crushed and ground to produce aluminous cement.

With the sintering method, everything happens the other way around: first, the raw materials are crushed and crushed, and only then they are fired. This is fraught with the fact that the cement obtained in this way is not as strong as with the first production method, but the second option is less labor-intensive.

The technical parameters of the aluminous cement composition can vary within fairly wide limits (this also applies to the chemical formulas of the substance), but this should not significantly affect its main characteristics, such as speed of hardening, strength, moisture resistance, and resistance to deformation. If the manufacturing technology was not followed and some of the listed characteristics are lost, then the material is considered defective and is not subject to further use.

Manufacturing technology

Limestones CaCO3 and bauxites with the general formula Al2O3*nH2O are used as raw materials for the production of GC.

Bauxite is heterogeneous in its composition and contains oxides of aluminum (Al2O3), silicon (SiO2), iron (Fe2O3) and others.

In the production of GC, bauxite is used with a silicon modulus (quality factor), which is calculated as the Al2O3/SiO2% ratio and is at least 2%.

Due to the shortage of bauxite in Russia, bauxite iron ore is used, to which limestone and scrap iron are added. Granulated blast furnace slags are used as clinkers.

The use of these materials as raw materials can significantly reduce the cost of aluminate compositions.

There are two main methods for producing high alumina cement.

Melting at t-1400° C

At a temperature in special drums, the mixture is melted. Allow the resulting product to cool and grind to a fine powder.

Sintering at t-1300° C

The raw materials are ground to powder and fired in ovens. After the resulting granules have cooled, they are ground into a fine powder.

Attention! The product obtained by melting is an order of magnitude superior in quality to the GC obtained by sintering.

Russian manufacturers of aluminate mixtures mainly produce GC by melting.

Specifications

When producing aluminous mixtures, manufacturers are guided by GOST requirements:

GOST 11052-74 regulates gypsum-alumina expanding cement. The technical characteristics of this material depend on the proportion of bauxite, in this case - up to 55%;
Conventional aluminous compositions of grades 40, 50 and 60, as well as high-alumina cement, are produced on the basis of GOST 969-91. The bauxite content ranges from 35% for standard types of material and up to 82% for cements with a high bauxite content in the mixture formula.

Depending on the brand of cement, the material must meet the following parameters:

Properties, advantages and disadvantages

Aluminous cements are a dark, finely dispersed powder, which in air and aqueous environments, when mixed with water, forms binders that harden in a short time.

Compositions based on them have a number of unique qualities:

high setting speed and rapid development of design strength;
the ability to work with solutions at low temperatures;
the ability to form a high-strength monolith with fire-resistant properties;
indifferent attitude towards aggressive environments (except alkaline ones).

Product advantages:

in terms of setting speed and time of strength development, it is an order of magnitude superior to the best indicators of Portland cement;
increased frost resistance;
lack of corrosion and insensitivity to aggressive environments;
high fire resistance values of products;
excellent protection of the reinforcing mesh of concrete products from external influences;
High-alumina and expanding types of GC are used in works of high complexity that cannot be performed with other materials.

Disadvantages of the product:

high cost of GC associated with the peculiarities of production;
cannot be used for filling large areas - due to the release of thermal energy during strength development, setting is uneven, which leads to destruction;
due to heat generation, the product cannot be used at temperatures above 30° C;
are destroyed by alkaline media.

Note! The quality of the aluminous material directly depends on the degree of dispersion - the finer the grind, the better the setting and the higher the strength characteristics.

Structure and types

Depending on the volume of impurities in the substance, cement of this type is divided into two main types: regular composition and high-alumina. Determination of the cement grade is carried out after 72 hours. The composition is usually imported to Moscow and the region, other regions in small volumes, sold in special bags or containers of 40-50 kilograms. Depending on the volume of iron in the overall composition and the oxidation rate of the components, aluminous cement can be green, yellow, brown, or black in color.

Products are marked with GOST. There are three main types of aluminous cement, which differ in their ability to withstand compressive loads: grades GC-40, GC-50 and GC-60. After 72 hours after pouring, the GC-40 mixture gains strength from 22.5 (MPa after 24 hours) to 40 MPa. This is the most popular brand, relevant for various construction works. The strength indicator of GC-50 reaches 50 MPa; accordingly, cement is used in the field of fuel and energy. The strength of GC-60 reaches 60 MPa; this mixture is used in the defense sector and metallurgy.

Aluminous cement is a material that requires proper operation. It is advisable to entrust the work with the mixture to specialists. Cement has a high viscosity, it is more difficult and longer to mix (when compared with ordinary Portland cement, for example), but the homogeneity and durability of concrete depend on the correct mixing.

The mixture is usually prepared in small portions, since it will not be possible to slow down the hardening process, and it is almost impossible to quickly use large volumes of concrete. When the composition begins to set immediately after preparation, it is very difficult to work with it, and this can also affect the quality of the final structure.

Aluminous cement is often used to prepare various types of expanding mixtures and quick-hardening compounds. For any such solution, the ratio of components and composition are calculated separately. Typically, the mixture expands in volume as it hardens, balancing shrinkage, and also self-compacts. To obtain these mixtures, aluminous cement is mixed with various additives.

Special types of GC:

with gypsum and crushed slag - sets quickly and expands in water.
A waterproof mixture with minimal shrinkage - gypsum hemihydrate and slaked lime are added to cement, which makes it possible to obtain a material suitable for use in waterproofing work.
Expanding waterproof cement - quickly gains strength, used for waterproofing shipping locks, tunnels, pipelines, swimming pools, etc.

https://youtube.com/watch?v=iiiJ3BWPxnE

Application of aluminous materials

Although GC has a number of advantages over traditional cement, it has not found widespread use. The reason for the limited scope of use of the product is the high price - it is 3-5 times more expensive than standard cement.

Therefore, aluminous mixtures are used only where the use of a more expensive material is justified by its specific properties.

Alumina cement is indispensable when performing the following work:

during repair work to restore elements of hydraulic structures, including waterproofing treatment facilities;
as a waterproofing material when plugging oil wells;
in shipping to eliminate hull holes;
waterproofing emergency leaks of sewer and water supply networks;
when repairing shower rooms and swimming pools;
to obtain a solution that can harden and gain strength in a short time - 1, 2 or 7 days;
for producing waterproofing plaster;
during the construction of structures, during the operation of which contact with aggressive environments is required (excluding alkaline ones);
for anti-corrosion protection of reinforcement mesh;
in the manufacture of individual products and concrete with fire resistance up to 1700° C.

Due to its properties, GC is used in construction as a component of expanding, fire-resistant, rapid-hardening, prestressing and other special compositions.

Due to their fire resistance, aluminate compositions are widely used in metallurgy as a component of heat-resistant dry mixtures and concrete.

Where is it used?

The properties of the material determine the scope of its application - the construction of buildings and structures operating in water or high humidity conditions. Waterproof cement is required for the construction of the following objects:

dams;
underground tanks, bunkers, tunnels;
sewer systems;
docks;
bridge supports;
berths and other structures of river ports.

Pozzolanic Portland cement is also recommended for use in the construction of objects exposed to mineralized groundwater. These can be both residential and industrial buildings that are continuously exposed to an aggressive environment. The material is used for the construction of water supply lines and drainage systems: sluices, irrigation canals, drainage systems.

Pozzolanic cement is suitable for creating concrete using steaming technology. This creates durable, corrosion-resistant structures.

Aluminous cement and cements based on it

The appearance of aluminous cement dates back to the beginning of the 20th century.
and France is considered its homeland. During the First World War, the property of this cement to quickly harden in any conditions (water and air) allowed it to harden within 1 day. erect concrete and reinforced concrete defensive structures. Aluminous cement is produced by fusion or sintering (the latter method is rarely used). The raw material after firing should provide the aluminous cement with a predominant content of low-basic calcium aluminates CaO·Al2O3; CaO 2Al2O3; bCaO-ZAl2O3. In aluminous cement, the main mineral that determines the hardening rate is the mineral CaO • Al203. To produce aluminous cement, bauxite containing a significant amount of alumina (AI2O3) and limestone or lime are used. A number of other compounds may be present in bauxite; for example, Ural bauxites contain iron oxide up to 28%, iron in the form of hematite - alkalis, phosphorus anhydride, chromium oxide, sulfur in various compounds, etc. The structure of bauxites is different. All this complicates the development of a unified method for selecting the composition of raw materials.

In the production of aluminous cement, the components are assigned based on the practice of using various raw materials. Chemical composition of aluminous cements: 30-50% Al203; 35-40% CaO; 5-15% Si02; 5-10% Fe203; about 1% MgO, and Ti02, SO3, R20 may also be present. The mineralogical composition includes CA, C5A3, C2S, C2AS, etc.

According to GOST 969-66, alumina cement is tested for mechanical strength after 24 hours and 3 days. The grade is considered to be the strength of cement in 1:3 solutions of mixtures of plastic consistency in prisms (40X40X160 mm). Cement is produced in three grades: 400, 500 and 600, the tensile strength of which after 24 hours is respectively: 200, 275 and 350 kg/cm2 (10-1 MPa). From these data it is clear that after 24 hours, high strengths can be obtained with such cements, reaching 60% of the brand name. For this reason, alumina cement is called a fast-hardening hydraulic binder.

GOST standardizes the setting time, the uniformity of volume changes and the fineness of cement grinding. Experience shows that in a number of cases, using standard aluminous cement, it is not possible to obtain rapid hardening of concrete or concrete of the designed strength in periods significantly exceeding 28 days. An analysis of the operation of a number of concrete structures using alumina cement abroad shows that destructive processes occur in concrete. For this reason, GOST 969-66 contains an indication that the compressive strength of control samples - cubes of standard solution after 28 days of storage (although it is not standardized) should be no less than the tensile strength for the brand test period (after 3 days) .

Aluminous cement, unlike other types of cement, is divided into batches of 100 tons (and not 500 tons according to GOST 10178-62).

Let's consider some issues related to the technology for producing alumina cement. Several methods for producing aluminous cement have been developed in the USSR. In particular, from high-alumina slag, a by-product of the blast furnace process, using blast furnace smelting. To obtain high-alumina slags (in blast furnace smelting of special types of cast iron), ferrous bauxite, limestone, coke, and metal scrap are used. The melting temperature of high-alumina slag (1700° C) is significantly higher than the firing temperature of Portland cement clinker.

Depending on the methods of firing the alumina alloy, its temperature also changes, as can be judged by the temperatures in the units (from 1500-1600 ° C of molten metallic iron when fired in cupola furnaces with water cooling to 2000 ° C in electric furnaces). From the above it is clear that the firing of alumina alloy is carried out in vertical units with relatively low productivity compared to rotary kilns. For this reason, the production of aluminous cement is limited.

To prepare aluminous cement by sintering, significantly lower firing temperatures are required (about 1200-1400°C). However, in this case, in a high-alumina melt, some of the compounds (calcium aluminates) are obtained in a crystalline modification, and the mineral helenite C2As is obtained in the form of glass. It has been established that non-crystalline calcium aluminates lose their ability to quickly harden, while crystallized gehlenite is an inert mineral, and gehlenite in a glassy state is an active calcination product. The process of formation of mineral phases should be organized so that each component acquires the properties of a binder. Research organizations are currently working on solving this problem.

To assess the quality of aluminous cement, just like for any other, structural analysis methods should be considered reliable and fast: petrography and fluoroscopy. Calculation of the mineralogical composition from the chemical composition, as is done for Portland cement clinker, cannot be made due to the previously stated provisions. In the first hours, the hardening process of aluminous cement (with a high exothermic effect during hardening) should occur at a temperature no higher than 20 ° C. An increase in temperature leads to a decrease in strength (up to 50-60%). After the first 6 hours of hardening at a temperature of 20° C, a subsequent increase in the temperature of the concrete does not cause destruction of cement stone on aluminous cement. The main reason for this decrease in strength is considered to be the occurrence of recrystallization of new formations resulting from the hydration of aluminates and, in particular, calcium hydroaluminates CaO-Al2O 10H2O - loss of stability of the resulting structure.

Compounds similar to those formed during the hydration of the mineral C3A in Portland cement are formed from hexagonal pyscobasic calcium hydroaluminates, with crystals of a cubic, more stable form - its hydrate compounds C3AH6. It is believed that unbound water released from crystalline hydrates also participates in the destruction of cement stone. The same process, apparently, can occur in hot climates for a long period of time.

However, if the reasons for the destruction of cement stone are known, then there is not sufficient data on the reasons for the destruction of structures built decades ago. For example, it is unknown under what temperature conditions the first period of cement hydration occurred following its hardening and what cement compositions were used. It is necessary to keep in mind other features of this cement, without which it should not be used. For example, the timing of the loss of plasticity of the concrete mixture (which, naturally, is associated with the setting time of cements) is of particular importance for the performance of work. It is known that regulation of the setting time of Portland cement is achieved with the help of gypsum, and of aluminous cement with the help of other additives. Some of them not only lengthen the setting time, but also slow down and, within certain limits, stop hardening (for example, 1% sugar). Available set retarders include hydrochloric acid and its salts (NaCl, KCl, etc.). Portland cement, lime, sulfuric acid, its salts, etc. speed up the setting time. For this reason, aluminous cement cannot be stored in the same warehouse with Portland cement.

Due to changes in the strength of aluminous cements during hardening after mixing at temperatures above 20 ° C, steaming and electrical heating of concrete on such cements cannot be used. Winter work conditions are also becoming more difficult. Indeed, at negative temperatures it is impossible to heat up water, since due to the high exotherm of cement, much higher than that of Portland cement, the hardening condition will be violated in the first 6 hours. Concreting massive structures with alumina cement is also unacceptable for this reason.

Concretes based on alumina cements have increased chemical resistance in soft water, in water saturated with sodium, calcium, magnesium, aluminum sulfates, in sea water, in mineralized and swamp waters (acidic, containing carbon dioxide) and other aquatic environments. Concrete based on alumina cement, subject to the rules of rational design, has high frost resistance, calculated in thousands of cycles, high water resistance and low creep.

The properties of cements obtained both on the basis of aluminous cements, expanding, tensile, etc., and on Portland cement, can be changed in the desired direction by introducing additives. Construction requires a variety of binders, including those that, when hardened in air, will expand and create stress in the reinforcement. Non-shrinkage and expanding cements can be made from high-aluminate Portland cements containing a large amount of gypsum (close to equivalent) with C3A. The properties of hydrosulfoaluminates were studied in the development of formulations for expanding and tensile cements. It was necessary to create highly basic hydrosulfoaluminates in cement stone that were stable under the specific operating conditions of the concrete (mortar). The process of expansion of the reaction products must take place within the prescribed time frame, and the stresses arising during this process are extinguished by constructive techniques (the walls of parts or parts of the structure, the seams between which are filled with expanding mortar or reinforcement). A type of waterproof expanding cement VRC is a quick-setting and fast-hardening binder, widely used when caulking seams between lining elements of subway tunnels. Such cement consists of approximately 70-75% aluminous cement, 10-11% highly basic calcium hydroaluminate and 20-22% semi-aqueous gypsum (CaSO4-0.5H2O).

The standards provide: 1) during air hardening of cement paste of normal density, after 24 hours the linear expansion is at least 0.05%, and after 28 days. — not less than 0.02%; 2) during water hardening (1 hour after manufacture, the sample is placed in water) after 24 hours, linear expansion is not less than 0.2 and not more than 1%; over the next 3 days. the value of further expansion compared to the daily value should be no more than 20%. Tests of expanding cement are carried out using a special technique that takes into account its specific properties and rather narrow area of use. Indeed, the setting time of such cement is less than 10 minutes (the beginning of setting occurs after 4 minutes, therefore, the setting period interval is about 6 minutes). The strength of expanding cement is determined not only on samples of prisms from mortar plastic mixtures of composition 1: 2 measuring 31.5 × 31.5 × 100 mm, but also on cubes measuring 20x20xx20 mm, made from pure cement paste. The molds are removed from the samples 30 minutes after mixing with water. Hardening of the cubes 1 hour after production occurs in water at a temperature of 20±3°C.

When testing for water resistance, samples of cement stone at the VRC after 24 hours of hardening at a pressure of up to 6 atm (10-1 MPa) should not allow water to pass through. The following types of expanding cements are known: gypsum-alumina cement GGRTs from a thoroughly mixed mixture of high-alumina slag (I.V. Kravchenko) no more than 30% and gypsum dihydrate; Portland cement RGShch from a thoroughly mixed mixture of Portland cement with a small amount of high-alumina slag powder, gypsum and an active mineral additive for binding lime, released during the hydrolysis of the alite mineral in Portland cement; cement (proposed by P. P. Budnikov) from a mixture of Portland cement, 15% expanding additive - kaolin, lime or gypsum calcined at 800 ° C; gypsum silicate expanding Portland cement, consisting of finely ground Portland cement with a high content of the mineral C3A and gypsum dihydrate, added in an equimolecular amount relative to C3A, in this cement the aluminate is completely bound into a highly basic hydrosulfoaluminate.

In gypsum silicate cement, the role of gypsum, which reacts with tricalcium aluminate, is very indicative. Thus, from low-aluminate clinker (calculated mineralogical composition: 60% C3S, 13% C2S, 3.1% C3A, 19.4% C4AF and 4% gypsum) cubes of composition 1: 0 (from cement paste) were prepared at a ratio of B/ C = 0.3. Gypsum was ground to different finenesses to prove the effect of different rates of hydrosulfoaluminate formation.

An attempt to simultaneously immerse cubes in water after 24 hours of hardening in humid conditions showed that samples No. 3 and 4 did not lose their shape, but samples No. 1 and 2 (on coarser ground gypsum) disintegrated. Consequently, the hardening process cannot be judged only by the amount of gypsum introduced. This experiment showed that the same cement, even with a minimum content of the mineral C3A, due to changes in the dispersion of gypsum, changes the cohesion of its new formations, which is not always characterized by a change in the tensile strength. As can be seen from the above, the properties of cements of this type are the result of the organization of the directed formation of the structure of the cement stone, in which a stressed state is created due to the formation of a highly basic hydrosulfoaluminate 3CaO-Al2O3-3CaSO4 31H2O in an environment with a high lime content - in a liquid phase saturated with lime; this ensures their stability (impossibility of subsequent dissolution in the liquid phase) and rapid growth of crystalline formations. With the formation of calcium hydrosulfoaluminate at a low concentration of lime and the dissolution of low-basic calcium hydroaluminates, the volume of the samples increases slightly, therefore this cement is not used when filling monolith cavities of highly waterproof structures.

Research is underway in the field of obtaining expansive cements with a normalized linear expansion value, which allows the stress from tensile concrete to be transferred to the reinforcement, regardless of its placement. Consequently, it becomes possible to produce some prefabricated stress-reinforced structures without resorting to tensioning the reinforcement using mechanical, thermal or combined thermomechanical methods. Due to the complexity of determination, the magnitude of the stress of the reinforcement is not measured; it is judged by the magnitude of the expansion. This tensile cement consists of 65-75% Portland cement, 13-20% aluminous cement and construction (CaSO4-O.5H2O) or natural gypsum (CaS04 • 2H20).

Aluminous cement can be replaced with alunite, a rock that contains the main salt of aluminum and potassium sulfate. The increase in stress is caused by hydrothermal treatment of products (steaming), while the strength of concrete after processing of products systematically increases. In the USA, prestressing cements are used for the construction of concrete floors of buildings and in road construction. The stresses of these cements must be accurately calculated by applying advanced cement preparation technology in compliance with the compositions of the specified materials and mortar mixtures. Cement consumption is significant and reaches 800 kg/m3. The setting time of prestressing cements is regulated by the content of CaSO4-0.5H20 (according to technical conditions, the beginning of setting is more than 2 minutes, and the end is less than 6 minutes) and CaSO42H20 (8 and 25 minutes, respectively). In particular, in the manufacture of self-stressed reinforced concrete pipes, the mortar mixture is applied to the metal core by gunning. In some cases, mixed aluminous cements are prepared by analogy with special Portland cements. Tensile cements were proposed and studied by V. V. Mikhailov and his colleagues.

Mixed alumina cements can be made with various mineral additives, which are introduced to regulate properties. Anhydrite-alumina cement containing 25-30% anhydrite CaS04 (proposed by P.P. Budnikov) acquires high strength when hardened at any temperature. Such cement has high corrosion resistance in mineralized waters and allows one to obtain, during steaming, higher strength than when hardening under standard conditions, low water requirement (normal dough thickness with approximately 20% water); Setting times are close to standard for Portland cement.

To improve the quality of aluminous cement, in order to prevent the formation of the inert mineral gehlenite C2AS during clinker firing, gypsum is introduced into the raw material, which is simpler than using only bauxite with a reduced silica content, which binds part of the alumina. In such cement, a hydraulically active compound 3(CaO-Al2O3)CaS04 is formed. If in the raw mixture the ratio of Al2O3 and SiO2 oxides is less than three (when substandard bauxite is used), such cement, called belite-alumina, contains an increased amount of belite and quickly hardens. For various reasons, it is necessary to add powders from ordinary slag and other inert mineral powders to cement, then it becomes less durable and generates less heat.

Both Portland cement with mineral additives and aluminous cement with additives are mixed. The elastic modulus varies depending on the W/C, mortar and cement compositions at the same initial strength. And in this case, it cannot be assumed that there is a direct relationship between the strength and elastic modulus of the material for mortar (concrete) of all compositions (the strength index of aluminous cement with a composition of 1:3 after 3 days is 490, after 7 days - 501 and 28 days. - 500 kg/cm2 (10-1 MPa), and for alumina with sand, all figures will be less according to the amount of mineral additive introduced). An increase in W/C from 0.38 and 0.36 to 0.46 and 0.44 for any cement affects the indicator of mechanical strength (its decrease), as well as the value of the elastic modulus. The material has become more porous due to an increase in the amount of freely evaporating water in the cement stone and, as it were, more elastic. In fatty mortar compositions with a cement to sand ratio of 1:1, the elastic moduli of the samples at close W/C values (0.38 and 0.36; 0.46 and 0.44) can be considered very close within the experimental accuracy. Consequently, the composition of the cement is not revealed due to the large amount of cement in the samples on both types of cement, ensuring for each of them the filling of all voids in the compacted sand. Reducing the amount of cement to 1:2 immediately affects the change in the elastic modulus. Increasing the sand content in alumina cement samples makes them less deformable and more rigid, changing the modulus.

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Scope of use

Aluminous cement is used when performing work related to industrial construction, as well as in other industries. The material is characterized by its ability to withstand temperatures elevated to 1300 degrees Celsius, while maintaining strength properties and resistance to aggressive factors.

Aluminous cement is a strong binder used for heat-resistant and mortars, characterized by rapid hardening in air and water.

The composition is used to perform the following tasks:

construction of transport highways, bridges with limited time for construction work, when the strength characteristics of concrete must be achieved in 2-3 days;
emergency restoration work related to eliminating the consequences of accidents, restoration of construction sites and structures;
construction of defensive structures, transport structures of a strategic nature;
carrying out activities related to the construction and repair of hydraulic structures (dams, dikes, embankments, ports) regularly exposed to aggressive water environments;
carrying out work in winter related to the construction of concrete and reinforced concrete structures, which is due to increased heat generation and accelerated hardening at negative temperatures;
accelerated construction of sites for equipment and foundations;
prompt implementation of installation and repair activities;
accelerated fixation of anchor fastening elements;
sealing wells and cavities associated with increased pressure of the liquid medium;
production of heat-resistant concrete, the temperature characteristics of which allow operation at temperatures up to 1.7 thousand degrees Celsius;
sealing holes in sea vessels.

The wide range of uses of aluminous cement makes it indispensable in industrial construction, mining, mine construction, construction chemicals, bridge construction, and the defense industry.

Active mineral additives for pozzolanic cements

Active mineral additives are finely ground substances that, when mixed with lime, give it the ability, after pre-hardening in moist air, to then harden in water. The same additives, introduced into the composition of ordinary Portland cement, bind free calcium hydroxide released during cement hardening, convert it into insoluble calcium silicate and thus increase the resistance of cement to the action of fresh and mineralized waters. Active additives (mainly siliceous) that are ground and mixed with water do not harden on their own and this differs from other additives of blast furnace basic slag. In ancient times, the simplest active additive to lime, ground brick, was used in our country.

In ancient Roman construction, pozzolana, a volcanic rock, was used for marine structures by adding it to lime. This is where the name for the active additives came from: pozzolanic, and for cements with these additives - “pozzolanic”.

In Rome, crushed brick was also used. Much later in Western Europe they began to use another natural additive for pistes. In pre-revolutionary Russia, additives such as crushed brick, blast furnace slag and imported additives (pozzolans) were used in limited quantities.

Active mineral supplements are widely used. Most additives are cheap and do not require firing, they improve the resistance of cement in aggressive waters. In terms of chemical composition and properties, these additives are classified as acidic, since they are dominated by SiO2 and Al2O3 compounds. Their composition (in%) satisfies the following condition: CaO+MgO: SiO2+Al2O3 less than 1

Part of the silica and alumina contained in the additives dissolves in alkalis and absorbs lime, increasing in volume; this part of silica (alumina) is called soluble or active silica (alumina).

Additives are divided into natural (natural) and artificial.

Natural (natural) additives for pozzolanic cements

Natural additives are of sedimentary and volcanic origin. Additives of sedimentary origin consist mainly of amorphous silica. These include the rocks diatomite and tripoli.

The solid variety of tripoli is called opoka. There are many deposits of diatomite and tripoli used by the cement industry (in Bryansk, Moscow, Saratov and other regions).

Additives of volcanic origin are obtained by grinding traces, tuff, pumice and ashes. Volcanic additives contain less soluble silica than sedimentary additives. The trails are dense, rock-like rocks rich in silica. The most famous is the Karadag route in Crimea.

Artificial additives for pozzolanic cements

Artificial active additives include:

1. Clay materials ground into fine powder:

a) temyanki, i.e. broken bricks or broken clay products; these materials have low activity and are currently little used;
b) clay clay, fired at a temperature that determines the strongest manifestation of its active properties, and ground; Usually the optimal firing temperature is 650-800°.

Cemyanka and clayite do not make Portland cement resistant to the action of mineralized waters. Therefore, they can only be used in cement intended for concrete structures in fresh water.

2. Acid blast furnace slag

3. Siliceous waste (outdated name - sishtof), rich in active silica, is obtained by extracting alumina from clay in the production of aluminum sulfate. This is one of the most active additives if it is not contaminated with impurities

4. Acid ash from the ash of certain types of fuel, which is dominated by silica and alumina: brown coal ash; peat ash, oil shale ash

5. Burnt rocks resulting from underground burning of coal seams (the so-called gliezh) or burnt mine rocks in coal mine dumps.