RU2278841C1 - Raw material mixture for making gypsum articles and method of making such articles - Google Patents

Abstract

FIELD: manufacture of building materials; manufacture of wall structural materials.

SUBSTANCE: raw material mixture for production of gypsum articles contains ground technogenious calcium sulfate dihydrate, lime and water; technogenious gypsum is used at specific surfaces of 3000 and 9000 cm²/g; used as lime and water is saturated solution of slaked lime at the following ratio of components, mass-%: gypsum at specific surface of 3000 cm²/g, 37.6-41.6; gypsum at specific surface of 9000 cm²/g, 46.4-50.4; saturated solution to content: slaked lime, 0.0135-0.019; the remainder being water. Proposed method of production of gypsum articles includes preparation of raw material mixture by mixing the ground technogenious calcium sulfate dihydrate with lime and water and molding; molding is performed in two stages: at first stage by loading with specific pressure equal to 1/3 of terminal pressure, holding at this pressure for 45-60 s and relieving the pressure to zero; at final stage, by loading with pressure of 30-40 Mpa, holding at this pressure for 2.5-3 min and relieving pressure to zero.

EFFECT: enhanced strength of gypsum articles.

3 cl, 1 tbl, 3 ex

Description

The invention relates to the production technology of building materials and can be used to obtain wall structural material.

Known raw mix for building materials, including wood, gypsum, an additive and water, and it contains as an additive trivalent metal sulfate and optionally quicklime ground in the following ratio, wt.%: Crushed wood (absolutely dry) - 35- 40; gypsum - 25-28; ferric metal sulfate - 7-8; ground quicklime - 10-12; the rest is water (see patent No. 1804454, IPC: C 04 B 28/14, B.I. 311 -1990 year).

The disadvantage of this technical solution is the use of expensive components.

The closest technical solution to the claimed is a raw material mixture for the manufacture of building material, including two-water gypsum, gypsum binder, lime and water to obtain a composition containing, wt.%:

Two-water gypsum - 50-70

Plaster binder - 5-20

Lime is 15-40, and mixing water is removed until a water-binding ratio of 0.22-0.30 is obtained (see USSR author's certificate No. 1132485, С 04 В 28/14, 1983).

The disadvantages of this technical solution are the low strength of the obtained products, the high cost of the process, energy consumption. A known method, including the preparation of the raw material mixture, pressing while removing excess water of mixing, excluding exposure under a layer of water. The raw material mixture is prepared by mixing two-water gypsum from the group: ground natural gypsum, phosphogypsum, borogypsum, citrogypsum, cryogypsum with water until a water-hard ratio of 0.25-0.3 is obtained, followed by the introduction of a lime suspension with W / T 2.0-4.0 and gypsum binder, obtaining a composition containing, wt.%:

Two-water gypsum - 50-70

Plaster binder - 5-20

Lime - 15-40,

and mixing water is removed until a water-binding ratio of 0.22-0.30 is obtained (see USSR author's certificate No. 1132485, С 04 В 28/14, 1983).

The disadvantages of the method of producing gypsum binders and products based on them are the low strength of the obtained products, the high cost of the process, energy consumption.

The closest in technical essence is a method of manufacturing gypsum products by preparing a raw mixture, pressing while removing excess mixing water, while the raw mixture is prepared by mixing wet two-water gypsum from the group: lump natural gypsum, citrogypsum with concentrated sulfuric acid, followed by dry quicklime to obtain a composition containing, wt.%:

Two-water gypsum - 50-70

H ₂ SO ₄ - 10-20

CaO - 20-30

Mixing water - until a test of normal density is obtained, and mixing water is removed until a water-binding ratio of 0.3-0.35 is obtained (see RU 2132310, C1, June 27, 1999). The disadvantage of this method is the duration and complexity of the manufacturing process, the danger to human health in the manufacturing process.

The purpose of the invention is the creation of a new mixture for the production of gypsum products and the development of a new method for the manufacture of gypsum products with increased strength and water resistance.

The technical effect consists in a denser packing of the grains of the two-part mixture due to the application of increased pressure.

The technical effect is also to increase safety by eliminating the work with sulfuric acid.

The technical effect of increasing the strength of gypsum products is achieved by finer grinding of gypsum raw materials and pressing them at high pressure. With increasing dispersion, solubility increases. In a polydisperse system, the concentration of the solution at the surface of particles of different diameters will be different, it will be greater at the surface with a smaller radius.

In the raw mix for the manufacture of gypsum products containing crushed technogenic two-water gypsum, lime and water, technogenic gypsum is used with specific surfaces of 3000 and 9000 cm ² / g, as lime and water, a saturated solution of hydrated lime in the following ratio, wt.% :

the specified gypsum with a specific surface of 3000 cm ² / g - 37.6-41.6, the specified gypsum with a specific surface of 9000 cm ² / g - 46.4-50.4,

the specified saturated solution to the content: slaked lime 0.0135-0.019, water - the rest. In the method of manufacturing gypsum products, including the preparation of a raw material mixture by mixing ground man-made gypsum gypsum with lime and water and pressing, using the specified raw material mixture, pressing is carried out in two stages: in the first by loading with a specific pressure equal to 1/3 of the final pressure, keeping under pressure 45-60 seconds and dropping the pressure to zero on the final way by loading with a specific pressure of 30-40 MPa, keeping it under pressure for 2.5-3 minutes and dropping it to zero.

If during compression such particles come together, conditions are created under which a large particle is in a supersaturated solution. As a result, the process of condensation of the dissolved substance on its surface will begin. This process will most actively occur in the places of particle contacts, where the curvature is maximum. Condensation of the substance will lead to the formation of phase contact between the particles in question.

The contact area will depend on the level of supersaturation, and therefore on the ratio of diameters. The strength of the system depends not only on the strength of the contact, but also on their number per unit area. It is important to create the maximum number of contacts between particles in the pressed raw material mixture by technological methods. The number of contacts between particles in a polydisperse system depends on the ratio of their diameters. Thus, in a polydisperse system of the optimal composition of crushed calcium sulfate hemihydrate, the formation of crystallization contacts occurs due to its own resources, without additional introduction of an additive with greater solubility than hemihydrate.

The kinetics of structure formation is greatly influenced by the introduction of lime. Lime introduced into the system affects the solubility of gypsum, participates in the process of hardening of crystals, forming metastable compounds on the surface of gypsum crystals. For pressed material with the addition of lime, crystal defects are characteristic. In this regard, fusion occurs in the system more actively and begins earlier than in materials without the addition of lime.

A saturated solution of lime is proposed as the most appropriate in this case. The concentration of the solution is quite sufficient for the formation of a solid structure, therefore, the introduction of lime in the form of a dry substance is not required.

The two-water gypsum gypsum indicated in this case is gypsum raw material based on industrial wastes that are close in chemical composition to those indicated in table 1.

Table The chemical composition of man-made two-water gypsum obtained from a gypsum binder of the Peshelansky deposit SiO ₂ Al ₂ O ₃ TiO ₂ Fe ₂ About ₃ CaO MgO SO ₄ Na ₂ O K ₂ O P ₂ O ₅ F 0.8 traces traces - 37.52 0.10 53.78 0.05 0.007 - -

Holding the material under pressure in the first stage for more than 1 minute is impractical, since it increases the energy intensity of the operation without a significant change in the structural characteristics of the material. Reducing the exposure time to 45 seconds or less leads to the fact that the formation of primary contacts of the gypsum crystals does not have time to occur, which entails a decrease in the strength characteristics of the material. Pressure release after the specified time is necessary for the release of pressed air enclosed between the gypsum particles during the pressing process.

The final pressing pressure should not be less than 30 MPa, since in this case the pressure is not enough to bring the gypsum crystals closer together. The increase in pressure above 40 MPa is impractical, since the properties of the material change slightly, and the energy intensity of the process increases. At the same time, it is necessary to withstand under pressure no more than 3 minutes, which is also just an extra waste of energy, but not less than 2.5 minutes, which is necessary for the initial structure formation.

An example of a specific implementation of the method.

Pre-dried, within one day, gypsum forms-waste Konakovo faience plant is subjected to crushing in a laboratory jaw crusher. We make gypsum grinding in a ball mill with grinding bodies - celbeps. For this, we load 1.5 kg of crushed gypsum raw materials into the mill and grind to a specific surface of 3000 and 9000 cm ² / g.

Lump lime in an amount of 1 kg is subjected to crushing on a laboratory jaw crusher. Then shut with 3 liters of water heated to 60 ° C. The mixture is constantly stirred for 2 hours. The prepared composition is kept for a day, and then the settled part of the saturated lime solution is drained, which is used in the experiments.

The specified amount of ground gypsum with a specific surface of 3000 and 9000 cm ² / g, respectively, is weighed out, a saturated solution of lime is measured.

The resulting composition is stirred for 1-1.5 minutes, poured into the prepared mold and begin pressing. Pressing is carried out in two stages according to the technology described above.

Hardening is carried out in a desiccator at a humidity of at least 95% and a temperature of 20 ° C for 28 days.

Example 1. Weigh the components in an amount, wt.%:

man-made two-water gypsum with a specific surface of 3000 cm ² / g - 37.6 (103.8 g)

man-made two-water gypsum with a specific surface of 9000 cm ² / g - 50.4 (139.1 g) saturated solution to the content of:

slaked lime - 0.0135 wt.%

water - 11.9865

Samples are prepared according to the method described above — moreover, at the first stage, the pressing pressure is 10 MPa, holding for 65 s and depressurizing to 0, at the final stage, the pressure is 30 MPa, holding for 2.5 min, depressurizing to 0.

Example 2. Weigh the components in an amount, wt.%:

man-made two-water gypsum with a specific surface of 3000 cm ² / g - 39.6 (109.3 g)

man-made two-water gypsum with a specific surface of 9000 cm ² / g - 48.4 (133.6 g)

saturated solution to content

slaked lime - 0.0162 (0.045 g),

water 11.9838

Samples are prepared according to the method described above, and in the first stage, the pressing pressure is 13.33 MPa, holding 40 s and depressurizing to 0, at the final stage, pressure 40 MPa, holding 3 min and depressurizing to 0.

Example 3 (composition). Weigh the components in the amount, wt.%:

man-made two-water gypsum with a specific surface of 3000 cm ² / g - 41.6 (114.8 g)

man-made two-water gypsum with a specific surface of 9,000 si ² / g - 46.4 (128.0 g)

saturated solution to content:

slaked lime - 0.019 (0.052 g) -

water - 11.981

Samples are prepared according to the method described in example 2.

Experimental laboratory tests were carried out in the laboratory of the department "Production of building products and structures" of Tver State Technical University. The following results were obtained: compressive strength - 28.4 MPa and a softening coefficient of 0.6, which corresponds to gypsum materials of the brand G-25. In the production of this material, there is a decrease in energy consumption through the use of non-calcined two-water man-made gypsum.

Claims (2)

1. The raw material mixture for the manufacture of gypsum products containing crushed technogenic two-water gypsum, lime and water, characterized in that the specified technogenic gypsum is used with specific surfaces of 3000 and 9000 cm ² / g, as lime and water - a saturated solution of slaked lime in the following the ratio of components, wt.%: The specified gypsum with a specific surface area of 3000 cm ² / g 37.6-41.6 The specified gypsum with a specific surface area of 9000 cm ² / g 46.4-50.4 The specified saturated solution to the content: Slaked lime 0.0135-0.019 Water Rest 2. A method of manufacturing gypsum products, comprising preparing a raw mixture by mixing ground man-made gypsum gypsum with lime and water and pressing, characterized in that when using the raw material mixture according to claim 1, pressing is carried out in two stages: in the first stage by loading with a specific pressure equal to 1/3 of the final pressure, keeping it under pressure for 45-60 s and relieving the pressure to zero, at the final stage by loading with a specific pressure of 30-40 MPa, keeping it under pressure 2.5-3 min and dropping of zero.