RU2770944C1 - Composition of the dry mixture for gunniting coal seams - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to the field of chemistry, in particular to substances used for the gunniting coal seams. The composition of the dry mixture for gunniting coal seams includes cement, sand of a dry fraction of 0-0.63 mm, calcium formate, superplasticizer, a redispersible polymer powder, a water-retaining additive, a shrinkage compensator, a hydrophobic additive at the following ratio, wt. %: cement 38.50 – 42.48, sand 46.60–52.74, calcium formate 3.50–5.47, superplasticizer 1.2–3.8, redispersible polymer powder 3.50–8.00, water-retaining additive 0.14–0.52, shrinkage compensator 0.33–0.50, hydrophobic additive 0.09–0.50.EFFECT: ensuring air tightness and improved adhesion of concrete to coal seams.7 cl, 1 tbl

Description

The claimed technical solution relates to the field of chemistry, in particular, to substances used for gunning coal seams.

According to statistics, the largest number of accidents in coal mines are endogenous fires, which can later be the cause of methane explosions. Due to the fact that endogenous fires are difficult to predict and predict, their study is relevant for scientists from leading research institutes of the mining industry.

Studies have shown that spontaneous combustion of coal occurs in the marginal parts of the workings, bordering on the coal massif. In the stage of intensive oxidation (ignition), coal is characterized by a decrease in natural moisture content to 30–40%.

During the destruction of the mountainous part of the seam, the temperature of the coal is 25–35°C higher in comparison with the collapsed rocks and the main coal massif. Oxidation of coals occurs when they come into contact with oxygen entering the mine workings during their ventilation. The chemical activity of the extracted rocks and the geological features of their deposits are natural factors in the occurrence of endogenous fires. When air enters, self-heating of coal occurs, which causes the formation of a fire in the area of the part of the seam that has undergone mechanical destruction. Oxidation reactions are exothermic, in connection with this, heating occurs first, the temperature in the centers of local overheating can reach 80 - 100 ° C, and then, in the absence of thermal equilibrium, spontaneous combustion of coal. Oxidative processes developing under the action of gaseous oxygen, and especially oxygen dissolved in adsorption films of water on the surface of coal, have a strong aggressive effect. The intensity of hydrolytic processes increases with an increase in the stage of coal oxidation due to the fact that oxygen-containing groups accumulate in coal at this time, activating this process.

The methane explosion is the cause of the subsequent ignition, since the fire and methane fall into the coal dust located in the adjacent workings, which causes the ignition of the coal masses.

Spontaneous combustion of coal causes great damage to both human lives and material property. People working in the mine may be exposed to high temperatures or poisonous gases. Due to the vastness and depth of the burning layers, an underground fire is difficult, and sometimes simply impossible to eliminate.

Known raw mix for the manufacture of foam-gypsum concrete composites, including gypsum binder, filler, reinforcing fiber, Portland cement, foaming agent and water, characterized in that it contains as a filler volcanic ash Zayukovsky field with a maximum grain size of 1.25 mm, which is simultaneously active mineral additive, and as a reinforcing material and a blowing agent - basalt fiber produced by PJSC Ivotsteklo, grade RNB-9-1200-4 s. Patent of the Russian Federation No. 2660675, published on 07/09/2018.

Known antifreeze additive for concrete, including superplasticizer polycarboxylate-based Melflux 2651F, defoamer Troykyd D128 and sodium thiosulfate and silica gel. RF patent 2728023, published on 07/28/2020.

Known mixtures do not prevent fire, in particular due to the lack of the ability to eliminate coal dust.

The technical result of the claimed technical solution is to provide airtightness and improved adhesion of concrete to coal seams.

The claimed technical result is achieved by the fact that the composition of the dry mix for shotcrete of coal seams includes cement, sand of a dry fraction of 0 - 0.63 mm, calcium formate, superplasticizer, redispersible polymer powder, water-retaining additive, shrinkage compensator, hydrophobic additive in the following ratio, wt. %: cement 38.50 - 42.48; sand 46.60 -52.74; calcium formate 3.50 - 5.47; superplasticizer 1.2 - 3.8; redispersible polymer powder 3.50 - 8.00; water-retaining additive 0.14 - 0.52; shrinkage compensator 0.33 - 0.50; hydrophobic additive 0.09 - 0.50.

Cement is the main component in the composition of the dry mix for shotcrete and acts as a binder. The content of cement in the composition of the dry mixture is 38.50 - 42.48% of the mass. With a cement content of less than 38.50%, the required design strength of concrete will not be achieved. With a cement content of more than 42.48%, the mixture will be too thick, which will complicate its application, and an increased value of modifying additives will be required to give it the necessary properties.

Preferably, the cement is Portland cement grade M500 D0 CEM I 42.5H to achieve the required design strength and consistency of the composition, as well as for better interaction with modifying additives.

Sand of dry fraction 0 - 0.63 mm is necessary to create a monolithic concrete structure. The content of sand in the composition of the dry mixture is 46.60 -52.74 wt. %. With a sand content of less than 46.6%, the required mix structure and subsequently the required concrete structure will not be achieved, which is important for all design characteristics. With a sand content of more than 54.5%, the design strength of concrete decreases.

Calcium formate is an accelerator for curing the resulting concrete. The content of calcium formate is 3.50 - 5.47 wt. %. When the content of calcium formate is less than 3.5%, the effect of accelerating strength development will not be fully manifested. When the content of calcium formate is more than 5.47%, the curing stops accelerating, and the design strength can be reduced.

The superplasticizer helps to reduce the water-to-solid ratio of the mixture, thereby making the mixture more dense, and reduces its porosity, and also increases the strength of the finished concrete. The content of the superplasticizer is 1.2 - 3.8 wt. %. When the content of the superplasticizer is less than 1.2%, the decrease in the water-solid ratio of the mixture is insignificant. With a superplasticizer content of more than 3.8%, the mixture becomes too fluid, which makes it difficult to apply, and curing may also slow down.

Preferably, the superplasticizer is a Melflux 2651F brand superplasticizer because it is a modified polyester carboxylate superplasticizer and has a better effect than, for example, melamine based plasticizers.

The redispersible polymer powder provides high adhesion of ready-mixed concrete to coal seams. The content of the redispersible powder is 3.50 - 8.00 wt. %. When the content of redispersible polymer powder is less than 3.5%, the adhesion of concrete to coal seams is unsatisfactory. When the content of redispersible polymer powder is more than 8%, there is a negative impact on the design strength.

Preferably, the redispersible polymer powder is an ORP 7085 HM grade powder prepared by drying a Vinyl Acetate/Acrylic copolymer emulsion with PVA as the protective colloid. The specific chemical composition of the polymer ensures that the redispersible polymer coalesces at low temperatures and provides good adhesion to various substrates.

The water-retaining additive is necessary to prevent the evaporation of moisture necessary for the hydration reaction of the binder with a large air supply to the mine workings. The content of the water-retaining additive is 0.14 - 0.52 wt. %. When the content of the water-retaining additive is less than 0.14%, the effect of water retention is insignificant, there is a risk of incomplete hydration of the cement. With a water-retaining additive content of more than 0.52%, an increase in the water-to-solid ratio of the mixture occurs, which can lead to a decrease in the design strength of concrete.

Preferably, the water-retaining additive is Culminal C 9115 powder, which is chemically based on methylhydroxyethyl cellulose (MHEC) and has a viscosity in the range of 62,000 to 75,000 mPa*s (2% solution on a dry basis; Brookfield RVT; 20 rpm; 20 °C), which provides a high degree of water retention, as well as good slip resistance.

The shrinkage compensator allows, by reducing the shrinkage of concrete, to prevent a decrease in the volume of concrete and the formation of cracks. The content of the shrinkage compensator is 0.33 - 0.50 wt.%. If the content of the shrinkage compensator is less than 0.33%, the concrete shrinkage reducing effect will not be sufficient to prevent shrinkage cracks and volume loss . With a shrinkage compensator content of more than 0.50%, a decrease in the design strength of concrete and a slowdown in strength development may occur.

Preferably, the shrinkage compensator is a Pentamix EX3 brand additive that reduces plastic and hydraulic shrinkage by chemically acting on the surface tension mechanism that occurs in the composition before the end of setting and during curing, and thus does not cause excessive expansion and expansion of the concrete.

The hydrophobic additive ensures the water resistance of the finished concrete. The content of the hydrophobic additive is 0.09 - 0.50 wt.%. When the content of the hydrophobic additive is less than 0.09%, the waterproofing effect is not manifested. When the content of the hydrophobic additive is more than 0.50%, it can affect the time of hardening and curing of concrete, namely, to lengthen them.

Preferably, Ligaphob N90, which is a stabilized sodium oleate, is used as the hydrophobic additive. Due to its composition, the product gives good long-term results and gives the already hardened concrete excellent water resistance even with spurting water currents.

Examples of concrete mix manufacturing are shown in Table 1.

Table 1

Component Component consumption, % wt. Composition 1 Composition 2 Composition 3 cement 42.04 42.48 37.5 sand 46.60 46.7 54.50 calcium formate 3.50 3.6 2.28 superplasticizer 3.8 1.3 1.2 redispersible polymer powder 3.50 5.23 3.00 Water retention additive 0.14 0.16 0.52 shrinkage compensator 0.33 0.42 0.50 hydrophobic additive 0.09 0.11 0.50

Portland cement grade M500 D0 CEM I 42.5H, CEM I 52.5N, PC 400 D0 can be used as cement.

Superplasticizers of the brand Melflux 2651F, Melflux 5581F, Pentaflow AC 6, Pentaflow AC 7 can be used as a superplasticizer.

As a redispersible polymer powder, powders of the brand ORP 7085 HM, ORP 7090 RD, ORP 7099 RD, HW5111 can be used.

Powders of the brand Culminal C 9115, Mecellose Ema 70 U, TS R6200S, Culminal C 4053 can be used as a water-retaining additive.

Additives of the brand Pentamix EX3, Pentamix EX5, Sitren PSR 100 can be used as a shrinkage compensator.

Ligaphob N90, Pentaproof 20p, Pentaproof 50P can be used as a hydrophobic additive.

The components of the mixture are mixed and diluted with water in the required proportion. By the method of dry gunning, the resulting solution is applied to coal seams during coal mining and construction of capital mine workings passing through the coal seam.

In finished form, thanks to a complex of chemical active additives, the concrete obtained from this mixture has airtightness and good adhesion to coal seams. These properties prevent the flow of air to the coal seam, thereby increasing the fire safety of work. In addition, the use of this material is possible in the event of a hotbed of coal self-heating to eliminate it.

Claims (8)

1. The composition of the dry mix for shotcrete of coal seams, including cement, sand of a dry fraction of 0–0.63 mm, calcium formate, superplasticizer, redispersible polymer powder, water-retaining additive, shrinkage compensator, hydrophobic additive in the following ratio, wt. %: cement 38.50–42.48 sand 46.60–52.74 calcium formate 3.50–5.47 superplasticizer 1.2–3.8 redispersible polymer powder 3.50–8.00 water-retaining additive 0.14–0.52 shrinkage compensator 0.33–0.50 hydrophobic additive 0.09–0.50 2. The composition of the dry mix for shotcrete of coal seams according to claim 1, characterized in that the cement is a Portland cement grade CEM I 42.5H. 3. The composition of the dry mix for shotcreting coal seams according to claim 1, characterized in that the superplasticizer is a superplasticizer of the Melflux 2651F brand. 4. The composition of the dry mix for shotcreting of coal seams according to claim 1, characterized in that the redispersible polymer powder is a powder of the ORP 7085 HM brand. 5. The composition of the dry mix for shotcreting of coal seams according to claim 1, characterized in that the water-retaining additive is a powder of the Culminal C 9115 brand. 6. The composition of the dry mix for shotcreting of coal seams according to claim 1, characterized in that the shrinkage compensator is an additive of the Pentamix EX3 brand. 7. The composition of the dry mix for shotcreting of coal seams according to claim 1, characterized in that the hydrophobic additive is an additive of the brand Ligaphob N 90.