Gypsum binder: characteristics, properties, production and application. Gypsum binder: characteristics, properties, production and application of GOST 125 79 what is canceled in it

5. REPUBLICATION. October 2002

This standard applies to gypsum binders obtained by heat treatment of gypsum raw materials to calcium sulfate hemihydrate and used for the manufacture of building products of all types and during construction work, as well as for the manufacture of forms and models in porcelain, earthenware, ceramics and other industries.

The standard complies with the requirements of ST SEV 826-77 in the part specified in Appendix 2.

Requirements for medical plaster must be established by the relevant regulatory and technical document developed on the basis of ST SEV 826-77.

1. TECHNICAL REQUIREMENTS

1. TECHNICAL REQUIREMENTS

1.1. Binders must be manufactured in accordance with the requirements of this standard according to technological regulations approved in the manner established by the manufacturer's ministry.

1.2. For the production of binders, gypsum stone is used according to GOST 4013 or phosphogypsum according to current regulatory and technical documentation.

1.3. Depending on the compressive strength, the following grades of gypsum binders are distinguished: G-2, G-3, G-4, G-5, G-6, G-7, G-10, G-13, G-16, G -19, G-22, G-25.

The minimum tensile strength of each brand of binder must correspond to the values ​​given in Table 1.

Table 1

1.4. Depending on the setting time, the types of binders listed in Table 2 are distinguished.

table 2

1.5. For the porcelain-faience and ceramic industries, binders are produced with the setting times established for normal-hardening gypsum.

1.6. Depending on the degree of grinding, the types of binders listed in Table 3 are distinguished.

Table 3

1.7. For the porcelain, earthenware and ceramics industries, finely ground binders are produced with a maximum residue on a sieve with cells with a clear mesh size of 0.2 mm of no more than 1%.

1.8. The manufacturer must determine the specific surface area of ​​the finely ground binder at least once a month and indicate its value in a document of the established form.

1.9. Binders used in porcelain, earthenware, ceramics and other industries must meet the additional requirements specified in Table 4.

Table 4

1.10. Binders of the highest quality category must meet the additional requirements specified in Table 5.

Table 5

An example of a symbol for a gypsum binder with a strength of 5.2 MPa (52 kgf/cm) with setting times: beginning - 5 minutes, end - 9 minutes and residue on a sieve with a clear cell size of 0.2 mm 9%, i.e. binder grade G-5, fast-hardening, medium grinding:

G-5 A II

Note. Possible areas of application of binders are indicated in Appendix 1.

2. ACCEPTANCE RULES AND TEST METHODS

________________
* Acceptance rules - according to GOST 26871.

2.1. Delivery and acceptance of binders is carried out in batches. A batch is considered to be binder of one type and one brand.

The batch size is determined depending on the annual capacity of the enterprise in the following quantities:

Up to 200 tons - with an annual capacity of St. 150 thousand tons;

- up to 65 tons - with an annual capacity of up to 150 thousand tons.

When exporting binder to the courts, the size of the batch is determined by agreement of the parties.

2.2. The manufacturer must guarantee and confirm with a document in the established form that the properties of the binder comply with the requirements of this standard based on the results of current tests.

2.3. The consumer has the right to carry out a control check of compliance of the properties of the binder with the requirements of this standard, using the sampling procedure and test methods according to GOST 23789.

If a discrepancy is detected between the bending or compressive strength of the binder and the grade specified in the relevant document, it must be changed in accordance with the actual strength.

2.4. Sampling and testing methods for binders are carried out according to GOST 23789.

3. PACKAGING, LABELING, TRANSPORTATION AND STORAGE

________________
* Packaging, labeling, transportation and storage - according to GOST 26871.

3.1. Binders are shipped unpacked or packed in bags according to GOST 2226 and other containers.

3.2. Binders used for the porcelain, earthenware and ceramics industries, as well as for special purposes, must be shipped only packed in bags according to GOST 2226.

3.3 The manufacturer must accompany each shipped batch with a document in the prescribed form, which indicates:

- name of the organization subordinate to which the manufacturer is located;

- name and address of the manufacturer;

- batch number and date of issue of the document;

Batch weight and dispatch date;

- name and address of the recipient;

- designation of the binder according to clause 1.10 and the results of physical and mechanical tests;

- specific surface area for finely ground astringent;

- designation of this standard.

3.4. During transportation and storage, binders must be protected from moisture and contamination.

4. MANUFACTURER WARRANTY

4.1. The manufacturer must ensure that the properties of gypsum binders comply with the requirements of this standard, subject to the conditions of transportation and storage.

The guaranteed shelf life of binders is 2 months from the date of manufacture.

APPENDIX 1 (for reference). AREA OF APPLICATION OF GYPSUM BINDERS

ANNEX 1
Information

APPENDIX 2 (for reference). INFORMATION DATA ABOUT COMPLIANCE WITH GOST 125-79 ST SEV 826-77

APPENDIX 2
Information

INFORMATION DATA ABOUT COMPLIANCE WITH THIS STANDARD ST SEV 826-77

Electronic document text
prepared by Kodeks JSC and verified against:
official publication
M.: IPK Standards Publishing House, 2002

5. REPUBLICATION. October 2002

This standard applies to gypsum binders obtained by heat treatment of gypsum raw materials to calcium sulfate hemihydrate and used for the manufacture of building products of all types and during construction work, as well as for the manufacture of forms and models in porcelain, earthenware, ceramics and other industries.

The standard complies with the requirements of ST SEV 826-77 in the part specified in Appendix 2.

Requirements for medical plaster must be established by the relevant regulatory and technical document developed on the basis of ST SEV 826-77.

1. TECHNICAL REQUIREMENTS

1. TECHNICAL REQUIREMENTS

1.1. Binders must be manufactured in accordance with the requirements of this standard according to technological regulations approved in the manner established by the manufacturer's ministry.

1.2. For the production of binders, gypsum stone is used in accordance with GOST 4013 or phosphogypsum in accordance with the current regulatory and technical documentation.

1.3. Depending on the compressive strength, the following grades of gypsum binders are distinguished: G-2, G-3, G-4, G-5, G-6, G-7, G-10, G-13, G-16, G -19, G-22, G-25.

The minimum tensile strength of each brand of binder must correspond to the values ​​given in Table 1.

Table 1

1.4. Depending on the setting time, the types of binders listed in Table 2 are distinguished.

table 2

1.5. For the porcelain-faience and ceramic industries, binders are produced with the setting times established for normal-hardening gypsum.

1.6. Depending on the degree of grinding, the types of binders listed in Table 3 are distinguished.

Table 3

1.7. For the porcelain, earthenware and ceramics industries, finely ground binders are produced with a maximum residue on a sieve with cells with a clear mesh size of 0.2 mm of no more than 1%.

1.8. The manufacturer must determine the specific surface area of ​​the finely ground binder at least once a month and indicate its value in a document of the established form.

1.9. Binders used in porcelain, earthenware, ceramics and other industries must meet the additional requirements specified in Table 4.

Table 4

1.10. Binders of the highest quality category must meet the additional requirements specified in Table 5.

Table 5

An example of a symbol for a gypsum binder with a strength of 5.2 MPa (52 kgf/cm) with setting times: beginning - 5 minutes, end - 9 minutes and residue on a sieve with a clear cell size of 0.2 mm 9%, i.e. binder grade G-5, fast-hardening, medium grinding:

G-5 A II

Note. Possible areas of application of binders are indicated in Appendix 1.

2. ACCEPTANCE RULES AND TEST METHODS

________________
* Acceptance rules - according to GOST 26871.

2.1. Delivery and acceptance of binders is carried out in batches. A batch is considered to be binder of one type and one brand.

The batch size is determined depending on the annual capacity of the enterprise in the following quantities:

Up to 200 tons - with an annual capacity of St. 150 thousand tons;

- up to 65 tons - with an annual capacity of up to 150 thousand tons.

When shipping binders in courts, the size of the batch is determined by agreement of the parties.

2.2. The manufacturer must guarantee and confirm with a document in the established form that the properties of the binder comply with the requirements of this standard based on the results of current tests.

2.3. The consumer has the right to carry out a control check of compliance of the properties of the binder with the requirements of this standard, using the sampling procedure and test methods in accordance with GOST 23789.

If a discrepancy is detected between the bending or compressive strength of the binder and the grade specified in the relevant document, it must be changed in accordance with the actual strength.

2.4. Sampling and testing methods for binders are carried out in accordance with GOST 23789.

3. PACKAGING, LABELING, TRANSPORTATION AND STORAGE

________________
* Packaging, labeling, transportation and storage - according to GOST 26871.

3.1. Binders are shipped unpacked or packed in bags in accordance with GOST 2226 and other containers.

3.2. Binders used for the porcelain-faience and ceramic industries, as well as for special purposes, must be shipped only packed in bags in accordance with GOST 2226.

3.3 The manufacturer must accompany each shipped batch with a document in the prescribed form, which indicates:

- name of the organization subordinate to which the manufacturer is located;

- name and address of the manufacturer;

- batch number and date of issue of the document;

Batch weight and dispatch date;

- name and address of the recipient;

- designation of the binder according to clause 1.10 and the results of physical and mechanical tests;

- specific surface area for finely ground astringent;

- designation of this standard.

3.4. During transportation and storage, binders must be protected from moisture and contamination.

4. MANUFACTURER WARRANTY

4.1. The manufacturer must ensure that the properties of gypsum binders comply with the requirements of this standard, subject to the conditions of transportation and storage.

The guaranteed shelf life of binders is 2 months from the date of manufacture.

APPENDIX 1 (for reference). AREA OF APPLICATION OF GYPSUM BINDERS

ANNEX 1
Information

APPENDIX 2 (for reference). INFORMATION DATA ABOUT COMPLIANCE WITH GOST 125-79 ST SEV 826-77

APPENDIX 2
Information

INFORMATION DATA ABOUT COMPLIANCE WITH THIS STANDARD ST SEV 826-77

Electronic document text
prepared by Kodeks JSC and verified against:
official publication
M.: IPK Standards Publishing House, 2002

Construction and other materials made from gypsum are used in various sectors of the national economy. They won't surprise anyone for a long time. But few people think about what gypsum binder actually is, what its raw materials are and how it is obtained. But for the production of all building materials (plasters, masonry mortars, plaster sheets) and other parts, you must first prepare the raw materials. After all, the characteristics of the finished material largely depend on the quality of the raw materials used.

Concept and composition

Gypsum binder is an airy material that consists primarily of gypsum dihydrate. The composition of gypsum is also supplemented by natural anhydride and certain industrial wastes, which include calcium sulfide.

This group also includes combined substances. They contain semi-hydrous gypsum, lime, cement.

The raw materials for production are rocks containing sulfates. GOST determines that for the production of gypsum binder only gypsum stone (meeting all the requirements imposed on it by GOST 4013) or phosphogypsum, which also meets the requirements of regulatory documents, can be used.

Characteristics of gypsum binders

The gypsum solution must be used until it has completely hardened. You cannot stir it after the crystallization process has already begun. Stirring causes the destruction of the formed bonds between the crystals of the framework. Because of this, the solution loses its astringent abilities.

Products made from gypsum are not waterproof. But material manufacturers have found a way out of this situation. Scientists have determined that various additions of gypsum binders can increase this figure. Therefore, various substances are added to the material: lime, crushed blast furnace slag, organic liquids that contain silicon.

The use of gypsum materials does not require the use of additional fillers. They do not shrink and cracks will not appear on the treated surface. Gypsum binders, on the contrary, increase in volume after complete hardening. In some situations, sawdust, firewood, pumice, expanded clay and other materials are added.

Another feature is that gypsum materials accelerate the corrosion process of ferrous metals (nails, fittings, wire, etc.). This process occurs even faster in humid conditions.

Gypsum binders quickly absorb moisture and lose their activity. Therefore, during storage and transportation it is necessary to follow some rules. The material can only be stored in a dry place. Even if this rule is followed, after three months of storage the material will lose approximately thirty percent of its activity. The material is transported in bulk or packed in containers. It is important to protect it from debris and moisture.

Production

For this process, the following processes must be completed:

• crushing natural gypsum substance;
• drying of raw materials;
• influence of temperature.

It is fed into a hopper, from where it enters the crusher. There it is crushed into pieces whose size does not exceed four centimeters. After crushing, the material is sent through the elevator to the supply hopper. From there it goes into the mill in equal parts. There it is dried and crushed to a smaller fraction. Drying at this stage is necessary to speed up and facilitate the process of crushing the material.

In the mill the powder is heated to ninety degrees. In this state, it is transported to the gypsum boiler. This is where water is released from the substance during the firing process. This process begins with low temperatures (about eighty degrees). But water leaves the material best at a temperature range from one hundred ten to one hundred eighty degrees.

The entire temperature treatment process is divided into two stages. First, the material is kept in a digester for three hours. There the water is removed and the dihydrous gypsum turns into semi-hydrous. All this time, the gypsum is stirred to ensure uniform heating. At the end of the specified time, the substance in a heated state is sent to the so-called simmering bunker. It no longer heats up. But due to the high temperature of the substance itself, the dehydration process continues there. This takes about another forty minutes. After this, the binding materials are considered ready. And they are sent to the finished goods warehouse.

Hardening of the material

Hardening of gypsum binders occurs when the powder is mixed with water. In this case, a plastic mass is formed, which hardens within a few minutes. From a chemical point of view, the opposite process occurs to what occurred during the production process. It just happens much faster. That is, semi-aqueous gypsum adds water, resulting in the formation of a dihydrate gypsum substance. This whole process can be divided into three stages.

In the first stage, the semi-aqueous gypsum substance is dissolved in water to form a saturated solution of gypsum dihydrate. The dihydrate has a high solubility index. Due to this, the process of supersaturation of the solution occurs very quickly. As a result, a precipitate forms, which is a dihydrate. These fallen particles stick together, thereby starting the setting process.

The next stage is crystallization. As individual crystals of the substance grow, they begin to connect and form a strong frame. As it dries (moisture is removed), the bonds between the crystals become stronger.

Changing the setting speed

The setting process can be accelerated or, conversely, slowed down as necessary. This is done with the help of additives that are introduced into gypsum binders.

Types of additives that speed up the setting process:

• substances that increase the solubility of the hemihydrate: sodium or potassium sulfate, table salt and others;

• substances that will be the center of crystallization in the reaction: salts of phosphoric acid, crushed natural gypsum, and so on.

Most often, crushed gypsum stone is used. Its particles serve as crystallization centers around which the crystal will grow in the future. “Recycled” gypsum is characterized by greater efficiency. It is understood as gypsum, which is already going through the stage of setting and hardening of calcium sulfide. This type includes broken and crushed products.

The following substances slow down the setting process:

• increasing the plasticity of the dough: a solution of wood glue in water, pine infusion, lime-glue emulsion, LST, and so on;

• The growth of crystals is prevented by a film that forms on grains of semi-aqueous gypsum under the influence of substances such as borax, ammonia, keratin retarder, alkali metal phosphates and borates, lilac alcohol and others.

It is worth noting that the introduction of additives accelerating the process negatively affects the strength of gypsum. Therefore, they must be used with caution and added in small quantities.

The setting (hardening) time largely depends on the quality of the starting material, time and storage conditions, the temperature at which the process of combining the material with water occurs, and even the time of mixing the solution.

Too short a setting time is usually associated with the presence of dihydrate particles in the material that remain there after firing. The setting time will also increase if the gypsum substance is heated to approximately forty-five degrees. If the temperature of the material is increased even more, the process, on the contrary, will slow down. Prolonged stirring of the gypsum mixture will speed up the setting process.

Differences between theory and practice

A feature of the hardening process is that gypsum, unlike other binders, increases in volume when hardening (up to one percent). Due to this, to hydrate a semi-aqueous substance, approximately four times more water is needed than should be in theory. In theory, water requires approximately 18.6% of the mass of the material. In practice, water is taken to obtain a solution of normal thickness in an amount of up to seventy percent. To determine the water requirement of a material, determine the volume of water as a percentage of the mass of the material itself, which must be added to obtain a solution of normal thickness (cake diameter 180 + 5 millimeters).

Another difference in practice is that when excess water is removed during drying, pores form in the material. Due to this, the gypsum stone loses its strength. This issue can be eliminated by additional drying. Gypsum products are dried at a temperature not exceeding seventy degrees. If the temperature is increased further, the dehydration reaction of the substance will begin.

The influence of temperature on the resulting substance

To obtain gypsum binder, gypsum stone is subjected to high temperatures. Depending on the value of this temperature, the gypsum substance can be of two types:

• Low-firing, for the production of which the processing of raw materials occurs under the influence of temperatures from one hundred twenty to one hundred eighty degrees. The raw material in this case is most often semi-aqueous gypsum. The main difference of this material is the high speed of hardening.

• High-firing (anhydrite), which are formed as a result of high temperature (over two hundred degrees). This material takes longer to harden. It also takes longer to set.

Each of these groups, in turn, has several different materials included in it.

Types of low-burning binders

Gypsum binder of this category includes the following materials:

• Construction gypsum. To manufacture it, it is necessary to select the right raw materials. The production of gypsum for construction work is permissible using as a raw material a binder grade of grade five and above, the remainder of which on the sieve is no more than twelve percent. For the manufacture of construction products, binders of grades two to seven are suitable, regardless of setting time and degree of grinding. Decorative elements are made from the same types of materials. With the exception of coarse and slow-setting substances. Gypsum plaster mixtures are made from substances of grade 2-25, except for coarse and quick-hardening binders.

• High-strength gypsum can be characterized by one of several grades (with indices from 200 to 500). The strength of this material is about 15-25 MPa, which is significantly higher than that of other types.

• Molding gypsum has a high water requirement and high strength in the hardened state. It is used to produce gypsum products: ceramic forms, porcelain and earthenware elements, and so on.

Anhydrite materials

This type, in turn, forms two substances:

• anhydrite cement, obtained by processing at temperatures up to seven hundred degrees;

• Estrich-gypsum, formed under the influence of temperatures above 900 degrees on calcium sulfate.

The composition of anhydrite gypsum includes: from two to five percent lime, a mixture of sulfate with vitriol (copper or iron) up to one percent, from three to eight percent dolomite, from ten to fifteen percent blast furnace slag.

Anhydrite cement has a slow setting (from thirty minutes to a day). Depending on the strength, it is divided into the following grades: M50, M100, M 150, M200. This type of cement is widely used in construction. It is used for:

• production of adhesive, plaster or masonry mortar;

• concrete production;

• production of decorative elements;

• production of thermal insulation materials.

Estrich gypsum has the following characteristics:

1. Slow setting.
2. Durability up to twenty megapascals.
3. Low thermal conductivity.
4. Good sound insulation.
5. Resistant to moisture.
6. Frost resistance.
7. Slight degree of deformation.

These are the main, but not all, advantages that estrich gypsum has. Its application is based on these indicators. It is used for plastering walls, producing artificial marble, constructing mosaic floors, and so on.

Division of binder into types

The properties of gypsum binders make it possible to divide them into several different groups. Several classifications are used for this.

Based on setting time, the following groups are distinguished:

• Group "A". It contains binders that set quickly. This takes from two to fifteen minutes.

• Group "B". Binding materials of this group set in a time of six to thirty minutes. They are called normally setting substances.

• Group “B”, which includes slow-setting binders. It takes more than twenty minutes to set. The upper limit is not standardized.

The grinding fineness is determined by the particles remaining on the sieve. This is due to the fact that gypsum binders always remain on a sieve with a mesh size of 0.2 millimeters. GOST indicates the following groups:

• A coarse grind or first group indicates that up to twenty-three percent of the material remains on the sieve.

• Medium grinding (second group), if no more than fourteen percent of the binder remains on the sieve.

• Fine grinding (third group) means that the remaining substance on the sieve does not exceed two percent.

The material is tested for strength in bending and compression. To do this, bars with dimensions of 40 x 40 x 160 millimeters are prepared from gypsum mortar. Two hours after manufacture, when the crystallization and hydration processes are completed, testing begins. Gypsum binders (GOST 125-79) are divided into twelve grades based on strength. They have indexes from two to twenty-five. The tensile strength values, depending on the brand, are collected in special tables. It can be seen even in GOST itself.

The main parameters and types of material can be found out by its marking. It looks something like this: G-6-A-11. This inscription will mean the following:

• G-gypsum binder.
• 6 - grade of material (means that the strength is more than six megapascals).
• A - determines the type based on the setting time (that is, quick-hardening).
• 11 - indicates the degree of grinding (in this case, medium).

Scope of application of gypsum substances

The technology of gypsum binders makes it possible to obtain materials suitable for use in various fields. Gypsum is most widely used in construction. The scale of its use can be compared with the use of cement. Gypsum binder has some advantages over cement. For example, its production requires almost four times less fuel. It is hygienic, resistant to fire, has porosity ranging from thirty to sixty percent, and low density (up to one and a half thousand kilograms per cubic meter). These characteristics determined the scope of the material.

Gypsum is widely used. Its use does not depend on the grade of material. A binder with fine and medium grinding of particles is used, which sets normally and slowly. Gypsum is added to limestone and sand plaster. This improves the strength of the solution after drying. And the layer of plaster on the surface becomes smooth and light, suitable for further finishing.

Gypsum substances belonging to grades G-2 to G-7 are used for the manufacture of partition panels, sheets of so-called dry plaster and other gypsum concrete products. They are added to solutions to obtain compositions for interior work.

Ceramic, porcelain and earthenware products and parts are made with the addition of gypsum binder, belonging to grades from G-5 to G-25. The binder must belong to the category of normally setting and finely ground substances.

Gypsum binder is used to prepare a solution that is used for caulking windows, doors, and partitions. Lower grades of material are suitable for this purpose.

As you can see, the characteristics of gypsum binder allow the material to be used for various purposes and in various fields of activity. It is durable, frost-resistant, hygienic, environmentally friendly. Its quality characteristics are determined by belonging to a certain group of materials on one or another basis.

GOST 23789-79

(ST SEV 826-77 regarding test methods)

Group W19

STATE STANDARD OF THE USSR UNION

GYPSUM BINDERS

Test methods

Gypsum binders.

Test methods

Date of introduction 1980-07-01

INTRODUCED by Decree of the USSR State Committee for Construction Affairs dated July 19, 1979 N 123

REISSUE. September 1986.

This standard applies to gypsum binders obtained by heat treatment of gypsum raw materials to calcium sulfate hemihydrate, and establishes methods for their testing.

This standard corresponds to the standard ST SEV 826-77 in the part specified in the reference appendix.

1. General instructions

1.1. The room in which the tests are carried out, as well as the materials, samples and instruments being tested must have a temperature of (293±3) K (20±3) °C. The relative humidity in the room should be (65±10)%.

1.2. The room temperature and humidity are recorded daily in the work log.

The analysis results are calculated with an accuracy of 0.15%.

2. Sampling and preparation

2.1. The essence of the selection method is to prepare an average sample for testing.

2.2. From each batch of binder to be tested, a sample weighing from 10 to 15 kg is taken. At the manufacturer's routine inspection, individual samples should be taken primarily from the material flow before it is packaged or shipped in bulk. When the binder is supplied without packaging, the sample is taken directly from the vehicles in equal parts in four places. When delivering binder packed in bags, a sample is taken from 10 bags; a sample weighing from 1.0 to 1.5 kg is taken from the middle of each bag.

2.3. The selected sample is thoroughly mixed, then by quartering a final sample weighing from 5 to 7 kg is taken from it for testing, which is divided into two equal parts and stored in closed containers.

2.4. One of the final samples is used for testing, the second is stored as an arbitration sample at a temperature of (293±3) K (20±3) °C.

2.5. The marking of containers with samples, as well as the sampling protocol, must include: the name of the manufacturer or its trademark, the symbol of the binder, the batch number, the date of shipment, the place and date of sampling.

3. Determination of fineness (degree) of grinding

3.1. The essence of the method is to determine the mass of gypsum binder remaining after sifting on a sieve with cells with a clear mesh size of 0.2 mm.

3.2. To determine the fineness of grinding, use:

drying cabinet;

technical scales in accordance with GOST 24104-80 with a weighing error of no more than 0.05 g;

sieve with cells with a clear size of 0.2 mm according to GOST 3584-73;

thermometer with a scale up to 373 K (100 °C);

installation for mechanical sifting.

3.3. A binder sample weighing 50 g, weighed with an error of no more than 0.1 g and pre-dried in an oven for 1 hour at a temperature of (323 ± 5) K (50 ± 5) ° C, is poured onto a sieve and sifted manually or by mechanical installation.

Sifting is considered complete if no more than 0.05 g of binder passes through the sieve within 1 minute during manual sifting.

The grinding fineness of an individual sample is determined as a percentage with an error of no more than 0.1% as the ratio of the mass remaining on the sieve to the mass of the initial sample. The arithmetic mean of the results of two tests is taken as the grinding fineness value.

3.4. During arbitration tests, manual sifting is used as a basis.

4. Determination of the setting time of gypsum dough

standard consistency (normal thickness)

4.1. Standard consistency (normal thickness) is characterized by the diameter of the gypsum dough spread flowing out of the cylinder when it is lifted. The diameter of the spread should be equal to (180±5) mm. The amount of water is the main criterion for determining the properties of gypsum binder: setting time and tensile strength. The amount of water is expressed as a percentage as the ratio of the mass of water required to obtain a gypsum mixture of standard consistency to the mass of gypsum binder in grams.

4.2. To determine the standard consistency, use:

a cup made of corrosion-resistant material with a capacity of more than 500 cm3;

a hand mixer with more than three loops of wire with a diameter of 1-2 mm (Fig. 1);

glass with a diameter of more than 240 mm;

a series of concentric circles with a diameter of 150-220 mm are applied to the glass every 10 mm, and circles with a diameter from 170 to 190 mm - every 5 mm;

circles can be drawn on a sheet of white paper and placed between two sheets of glass;

a stainless metal cylinder with a polished inner surface (Fig. 2);

a ruler 250 mm long with a division value of 1 mm;

stopwatch;

drinking water according to GOST 2874-82.

4.3. Water is poured into a clean cup, previously wiped with a cloth, the mass of which depends on the properties of the gypsum binder. Then 300 to 350 g of gypsum binder is poured into the water within 2-5 s. The mass is stirred with a hand mixer for 30 s, starting the countdown from the beginning of pouring the gypsum binder into the water. After mixing is completed, the cylinder installed in the center of the glass is filled with gypsum dough, the excess of which is cut off with a ruler. The cylinder and glass are pre-wiped with a cloth. After 45 seconds, counting from the beginning of pouring the gypsum binder into the water, or 15 seconds after the end of mixing, the cylinder is very quickly raised vertically to a height of 15-20 cm and moved to the side. The diameter of the spread is measured immediately after lifting the cylinder with a ruler in two perpendicular directions with an error of no more than 5 mm and the arithmetic mean is calculated. If the diameter of the dough spread does not correspond to (180 ± 5) mm, the test is repeated with a changed mass of water.

4.4 To determine the setting time, use gypsum dough of standard consistency. The essence of the method is to determine the time from the beginning of contact of the gypsum binder with water to the beginning and end of setting of the dough.

4.5. To determine the setting time, use:

stopwatch;

conical ring made of corrosion-resistant material (Fig. 3);

Vicat device with a mass of the moving part (300±2) g. The dimensions of the needle are shown in Fig. 4. The needle should be made of solid stainless steel wire with a polished surface and should not have any bending;

a polished plate made of corrosion-resistant material measuring at least 100x100 mm.

4.6. Before starting the test, check whether the rod of the Vicat device lowers freely, as well as the zero position of the moving part.

The ring, previously wiped and lubricated with mineral oil and installed on a polished plate, is filled with dough. To remove air trapped in the dough, the ring with the plate is shaken 4-5 times by raising and lowering one side of the plate by about 10 mm. After this, the excess dough is cut off with a ruler and the filled form is placed on the plate on the base of the Vicat device.

The movable part of the device with the needle is placed in a position in which the end of the needle touches the surface of the gypsum dough, and then the needle is freely lowered into the ring with the dough. The dive is performed once every 30 s, starting from a whole number of minutes. After each immersion, the needle is thoroughly wiped, and the plate along with the ring is moved so that the needle lands in a different place on the surface of the dough during a new immersion.

The beginning of setting is determined by the number of minutes elapsed from the moment the binder is added to the water until the moment when the freely lowered needle, after immersion in the dough, does not reach the surface of the plate for the first time, and the end of setting is when the freely lowered needle is immersed to a depth of no more than 1 mm. The start and end times of setting are expressed in minutes.

5. Determination of compressive strength

5.1. The essence of the method is to determine the minimum loads that destroy the sample.

5.2. To carry out the test use:

a cup made of corrosion-resistant material;

ruler 250 mm long;

hand mixer (Fig. 1);

measuring cylinder with a capacity of 1 liter according to GOST 1770-74;

scales in accordance with GOST 24104-80 with a weighing error of no more than 1 g;

a mold made of corrosion-resistant material for the production of sample beams with dimensions of 40x40x160 mm (Fig. 5).

The longitudinal and transverse walls of the molds must be sanded at the top and bottom and lie tightly on the base. The angle between the sides and the bottom of the mold should be (90±0.5)°. Mold dimensions should be checked at least once every six months. If the dimensions of the molds deviate from the nominal dimensions by more than 0.5 mm in length and 0.2 mm in width and height, then the molds must be replaced;

it is allowed to use forms for beam samples in accordance with GOST 310.4-81;

a device for determining compressive strength, consisting of two metal pressure plates (Fig. 6) with a Rockwell hardness of at least 61; the curvature of the plates should not exceed 0.05 mm;

press for determining the ultimate compressive strength of samples with a maximum load of up to 10-20 tf.

5.3. Determination of the strength of samples made from gypsum dough of standard consistency is carried out 2 hours after contact of the gypsum binder with water.

5.4. To make samples, a sample of gypsum binder weighing from 1.0 to 1.6 kg is taken. The gypsum binder is poured into a cup of water within 5-20 s, taken in the amount necessary to obtain a dough of standard consistency. After adding the binder, the mixture is intensively mixed with a hand mixer for 60 s until a homogeneous dough is obtained, which is poured into the mold. First, the inner surface of the metal molds is lightly lubricated with medium-viscosity mineral oil. The mold compartments are filled simultaneously by moving the cup with plaster dough evenly over the mold. To remove entrained air after pouring, the mold is shaken 5 times, for which it is lifted by the end side to a height of 8 to 10 mm and lowered. After the onset of setting, excess gypsum dough is removed with a ruler, moving it along the upper edges of the mold perpendicular to the surface of the samples. After (15±5) minutes after the end of setting, the samples are removed from the mold, marked and stored in the testing room.

5.5. The six beam halves obtained after the bending test are immediately subjected to a compression test. The samples are placed between two plates in such a way that the side faces, which during manufacturing were adjacent to the longitudinal walls of the molds, are on the planes of the plates, and the stops of the plates fit snugly against the smooth end wall of the sample (Fig. 7). The sample together with the plates is subjected to compression in a press. The time from the beginning of uniform loading of the sample until its destruction should be from 5 to 30 s, the average rate of load increase during testing should be (10 ± 5) kgf/cm per second.

1-upper press plate; 2- plates; 3-half sample; 4- bottom plate of the press.

Damn.7

The compressive strength of one sample is determined as the quotient of the breaking load divided by the working area of ​​the plate equal to 25 cm. The compressive strength is calculated as the arithmetic mean of the results of six tests without the highest and lowest results.

6. Determination of tensile strength in bending

6.1. The essence of the method is to determine the minimum loads that destroy the sample.

6.2. To carry out the tests, the sample is placed on the supports of the bending test device in accordance with GOST 310.4-81 in such a way that those edges of it that were horizontal during manufacture are in a vertical position. The layout of the sample on the support rollers is shown in Figure 8.

The tensile strength is calculated using the formula

0.0234 MPa (~ 0.234 kgf/cm ),

The bending strength is calculated as the arithmetic mean of the results of three tests.

Damn.8

7. Determination of hydrate water content

A weighed sample of gypsum of about 1 g is placed in a calcined weighed porcelain crucible and heated in a muffle furnace to 673 K (400 °C) for 2 hours. Calcination is repeated until a constant mass is obtained. The crucible with the sample is cooled in a hermetically sealed desiccator and weighed. The percentage of hydrate water is calculated using the formula

where is the difference in the mass of the crucible with the sample before and after calcination, in g;

Weight of gypsum sample, g.

8. Determination of volumetric expansion

8.1. Equipment

The GOI (State Optical Institute) device (Fig. 9) consists of a tripod on which the indicator is mounted, and a detachable metal cylinder, fastened with rings during assembly. The inner diameter of the cylinder is 50 mm, the outer diameter is 56 mm, the height is 100 mm.

Duralumin cover with a diameter of 56 mm, a thickness of 1 mm.

Glass plate.

8.2. Carrying out the test

GOI device

1 - indicator; 2 - stand; 3 - bracket; 4 - rail; 5 - gear; 6 - axis; 7 - screw;

8 - cover; 9 - ring; 10 - cylinder; 11 - glass; 12 - base.

Damn.9

The device is installed on a rigid base, eliminating the possibility of vibration. The cylinder of the device is placed on a glass plate, filled with gypsum dough of normal thickness, closed with a lid and installed on a base plate.

The time for mixing the gypsum binder with water and filling the cylinder with it should not exceed 2 minutes.

By turning the screw, the indicator rod is brought into contact with the recess in the cylinder cover. Additionally, they make another turn of the screw to set the indicator to zero and begin to fix the movement of the arrow caused by the expansion of the gypsum solution as it hardens.

The beginning of the expansion count should be considered the moment of the appearance of positive deformations, the end of the definition is the moment the pointer stops moving, which occurs approximately 1 hour after filling the cylinder with the solution.

The amount of volumetric expansion in percentage is numerically equal to the amount of deformation in mm.

9. Determination of water absorption

9.1. Equipment

Drying cabinet.

Scales in accordance with GOST 24104-80 with a weighing error of no more than 0.01 g.

9.2. Carrying out the test

The water absorption of gypsum is determined on three samples (half-beams), previously dried to constant weight at a temperature of 318-328 K (45-55 ° C). The samples are weighed, placed horizontally in a bath and filled halfway with water. After 2 hours, they are completely filled with water and kept for another 2 hours. After this, the samples are removed from the water, wiped with a damp cloth and weighed.

The water absorption of gypsum as a percentage is determined by the formula

where is the initial mass of the sample;

Mass of the sample after saturation with water.

The value of water absorption is determined as the arithmetic mean of the results of three determinations.

10. Determination of insoluble residue content

10.1. Reagents and equipment

Hydrochloric acid according to GOST 3118-77 with a density of 1.9 g/cm (200 ml diluted with water to 1 l).

Silver nitrate according to GOST 1277-75 1% solution.

Muffle furnace.

10.2. Carrying out the test

A sample of 1 g of binder, weighed with an error of no more than 0.0002 g, is placed in a glass with a capacity of 200 ml and treated with 100 ml of hydrochloric acid. The contents of the glass are brought to a boil with constant stirring. After boiling for 5 minutes, the liquid is filtered through a loose ashless filter. The precipitate is washed with hot water until the reaction to the chlorine ion disappears (test with a solution of silver nitrate acidified with nitric acid).

11.1. Equipment

Horseshoe-shaped permanent magnet made of YN 13 DK24 alloy according to GOST 17809-72 with a magnetic induction of at least 120 mT (Fig. 10).

Plexiglas attachment (Fig. 11) for fitting onto the ends of the magnet.

Damn.10

Damn.11

Board with sides measuring 1000x500 mm covered with plexiglass or glass.

Scales according to GOST 23676-79 and GOST 24104-80.

Spatula for mixing and leveling the product.

Watch glass.

11.2. Carrying out the test

From the total sample, take a sample weighing 1 kg, which is poured onto a board and leveled with a spatula in a layer no more than 0.5 cm thick.

Using a magnet with a nozzle attached to it, slowly move it along and across the boards with gypsum in the very thickness of the binder.

Particles of metal impurities with adhering binder are periodically removed from the magnet by removing the nozzle and poured onto a sheet of white paper.

The separation of metal impurities is repeated six times. Before each isolation, the test binder is mixed and leveled into a thin layer.

Metal impurities are separated from the adhering binder by moving a magnet along the back side of the paper on which the separated material is located. After concentrating metal impurities in one place, they are transferred to a watch glass.

The metal impurity collected on the watch glass is weighed on an analytical balance with an error of no more than 0.0002 g.

The impurity content is expressed in milligrams per 1 kg of binder.

12. Determination of specific surface area

12. 1. Carrying out the test

The essence of the method is based on measuring air resistance through a layer of binder of a specified thickness and cross-sectional area in accordance with the instructions attached to the ADP-1 (PSKH-2) device.

To carry out calculations, take the density value:

for gypsum raw materials - 2.3 g/cm;

for construction, molding gypsum - 2.65 g/cm;

for technical gypsum - 2.75 g/cm.

Application

Information

Information data on compliance with GOST 23789-79 ST SEV 826-77

Clause 1.1 of GOST 23789-79 corresponds to clause 3.1.2 of ST SEV 826-77.

Section 2 of GOST 23789-79 corresponds to section 3.2 of ST SEV 826-77.

Section 3 of GOST 23789-79 corresponds to section 3.3 of ST SEV 826-77.

Section 4 of GOST 23789-79 corresponds to section 3.4 of ST SEV 826-77.

Section 5 of GOST 23789-79 corresponds to section 3.5 of ST SEV 826-77.

Section 6 of GOST 23789-79 corresponds to section 3.6 of ST SEV 826-77.

The text of the document is verified according to:

official publication

Gosstroy USSR -

M.: IPK Standards Publishing House, 1987

Construction Materials. GOST 125-79 - Gypsum binders. Technical conditions. OKS: Building materials and construction, Construction materials. GOST standards. Gypsum binders. Technical conditions. class=text>

GOST 125-79

Gypsum binders. Specifications

GOST 125-79
Group Zh12

INTERSTATE STANDARD

GYPSUM BINDERS
Specifications
Gypsum binders. Specifications

OKP 57 4431

Date of introduction 1980-07-01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of Construction Materials Industry of the USSR

2. APPROVED AND ENTERED INTO EFFECT by Resolution of the USSR State Committee for Construction Affairs dated July 19, 1979 N 123.

3. INSTEAD GOST 125-70, GOST 5.1845-73

4. REFERENCE REGULATIVE AND TECHNICAL DOCUMENTS

5. REPUBLICATION. October 2002

This standard applies to gypsum binders obtained by heat treatment of gypsum raw materials to calcium sulfate hemihydrate and used for the manufacture of building products of all types and during construction work, as well as for the manufacture of forms and models in porcelain, earthenware, ceramics and other industries.
The standard complies with the requirements of ST SEV 826-77 in the part specified in Appendix 2.
Requirements for medical plaster must be established by the relevant regulatory and technical document developed on the basis of ST SEV 826-77.

1. TECHNICAL REQUIREMENTS

1. TECHNICAL REQUIREMENTS

1.1. Binders must be manufactured in accordance with the requirements of this standard according to technological regulations approved in the manner established by the manufacturer's ministry.

1.2. For the production of binders, gypsum stone is used in accordance with GOST 4013 or phosphogypsum in accordance with the current regulatory and technical documentation.

1.3. Depending on the compressive strength, the following grades of gypsum binders are distinguished: G-2, G-3, G-4, G-5, G-6, G-7, G-10, G-13, G-16, G -19, G-22, G-25.
The minimum tensile strength of each brand of binder must correspond to the values ​​given in Table 1.

Table 1

1.4. Depending on the setting time, the types of binders listed in Table 2 are distinguished.

table 2

1.5. For the porcelain-faience and ceramic industries, binders are produced with the setting times established for normal-hardening gypsum.

1.6. Depending on the degree of grinding, the types of binders listed in Table 3 are distinguished.

Table 3

1.7. For the porcelain, earthenware and ceramics industries, finely ground binders are produced with a maximum residue on a sieve with cells with a clear mesh size of 0.2 mm of no more than 1%.

1.8. The manufacturer must determine the specific surface area of ​​the finely ground binder at least once a month and indicate its value in a document of the established form.

1.9. Binders used in porcelain, earthenware, ceramics and other industries must meet the additional requirements specified in Table 4.

Table 4

1.10. Binders of the highest quality category must meet the additional requirements specified in Table 5.

Table 5

An example of a symbol for a gypsum binder with a strength of 5.2 MPa (52 kgf/cm) with setting times: beginning - 5 minutes, end - 9 minutes and residue on a sieve with a clear cell size of 0.2 mm 9%, i.e. binder grade G-5, fast-hardening, medium grinding:

G-5 A II

Note. Possible areas of application of binders are indicated in Appendix 1.

2. ACCEPTANCE RULES AND TEST METHODS

________________
* Acceptance rules - according to GOST 26871.

2.1. Delivery and acceptance of binders is carried out in batches. A batch is considered to be binder of one type and one brand.
The batch size is determined depending on the annual capacity of the enterprise in the following quantities:

Up to 200 tons - with an annual capacity of St. 150 thousand tons;
- up to 65 tons - with an annual capacity of up to 150 thousand tons.
When exporting binder to the courts, the size of the batch is determined by agreement of the parties.

2.2. The manufacturer must guarantee and confirm with a document in the established form that the properties of the binder comply with the requirements of this standard based on the results of current tests.

2.3. The consumer has the right to carry out a control check of compliance of the properties of the binder with the requirements of this standard, using the sampling procedure and test methods in accordance with GOST 23789.
If a discrepancy is detected between the bending or compressive strength of the binder and the grade specified in the relevant document, it must be changed in accordance with the actual strength.

2.4. Sampling and testing methods for binders are carried out in accordance with GOST 23789.

3. PACKAGING, LABELING, TRANSPORTATION AND STORAGE

________________
* Packaging, labeling, transportation and storage - in accordance with GOST 26871.

3.1. Binders are shipped unpacked or packed in bags in accordance with GOST 2226 and other containers.

3.2. Binders used for the porcelain-faience and ceramic industries, as well as for special purposes, must be shipped only packed in bags in accordance with GOST 2226.

3.3 The manufacturer must accompany each shipped batch with a document in the prescribed form, which indicates:
- name of the organization subordinate to which the manufacturer is located;
- name and address of the manufacturer;
- batch number and date of issue of the document;

Batch weight and dispatch date;
- name and address of the recipient;
- designation of the binder according to clause 1.10 and the results of physical and mechanical tests;
- specific surface area for finely ground astringent;
- designation of this standard.

3.4. During transportation and storage, binders must be protected from moisture and contamination.

4. MANUFACTURER WARRANTY

4.1. The manufacturer must ensure that the properties of gypsum binders comply with the requirements of this standard, subject to the conditions of transportation and storage.
The guaranteed shelf life of binders is 2 months from the date of manufacture.

APPENDIX 1 (for reference). AREA OF APPLICATION OF GYPSUM BINDERS

ANNEX 1
Information

APPENDIX 2 (for reference). INFORMATION DATA ABOUT COMPLIANCE WITH GOST 125-79 ST SEV 826-77

APPENDIX 2
Information

INFORMATION DATA ABOUT COMPLIANCE WITH THIS STANDARD ST SEV 826-77