RU2427549C1 - Refractory concrete mixture - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to special-purpose concrete and can be used in production of commercial-grade refractory concrete and thermal generating unit structures subject to high temperatures and sharp temperature drop for long periods. The refractory concrete mixture contains portland cement M 400, sand and crushed stone with particle size 5-20 mm obtained by crushing scrap chamotte refractory followed by size grading, fine filler in form of a sludge obtained via combined wet-grinding of scrap chamotte and high-alumina refractory to particle size 30-200 nm with preliminary addition of liquid sodium glass with density 1.23 g/cm3 to water, with the following ratio of components in wt %: portland cement M 400 8-15, said filler from scrap chamotte refractory 8-15, said filler from scrap high-alumina refractory 3.7-5.9, said sand 24.5-26.4, said crushed stone 35-36.3, said liquid glass 0.2-0.35, water - the rest. ^ EFFECT: high density, strength, heat resistance, low shrinkage and susceptibility to cracking. ^ 2 tbl, 2 dwg

Description

The invention relates to concrete for special purposes and can be used in the manufacture of commodity heat-resistant concrete and structures of thermal units that are exposed to prolonged exposure to high temperatures and their sudden changes.

At present, heat-resistant concrete with different types of aggregates and additives with increased consumption of Portland cement is known and used in the construction of thermal industrial facilities to increase the initial strength of concrete (after drying). But Portland cement as a hydraulic binder containing hydrated clinker minerals after firing at a temperature of 800 ° C gives a sharp drop in strength, therefore, according to GOST 20910-90 [3], residual strength after firing at this temperature is allowed up to 30%.

Thus, with increased cement consumption, the strength drop can reach 70%. In this case, significant shrinkage of concrete occurs and its tendency to crack. And heat resistance at sudden changes in temperature does not exceed 10 water heat exchangers. This helps to reduce the durability of concrete with prolonged exposure to high temperatures and their sudden changes.

Known concrete mixture on aggregates from blast furnace slag [1], including, wt.%: Portland cement 16-22, alumina hydrate, sand slag pumice fr. 0-5 mm - 28-36, crushed stone slag pumice fr. 5-20 mm - 15-29, superplasticizer C-3 - 0.5-1.5, water - the rest.

The disadvantages of this mixture are: increased consumption of cement and scarce and expensive superplasticizer, which burns out during firing, reducing the density of the hardened concrete and its strength and heat resistance. During firing, clinker minerals are dehydrated, which leads to an increase in shrinkage and a tendency to crack, as well as to a drop in strength, which can reach 70% of the strength of dry samples. These disadvantages are exacerbated by the burnout of the organic superplasticizer. Alumina hydrate is expensive and scarce, requiring import from other regions. The use of slag aggregates having a lower melting point allows the use of such concrete to service temperatures of no higher than 1100 ° C.

When using chamotte aggregates and fillers, heat-resistant concrete on Portland cement can be used up to 1200 ° C, and with reduced cement consumption, up to 1300 ° C.

An object of the invention was to increase the density, strength, residual strength after firing at a temperature of 800 ° C and heat resistance of heat-resistant concrete, reducing shrinkage and tendency to crack. The solution to this problem is achieved by the fact that in the composition of the proposed heat-resistant concrete mixture on Portland cement M 400, sand and gravel fractions of 5-20 mm obtained by crushing the battle of fireclay refractories with subsequent sieving into fractions, a finely ground filler is introduced in the form of sludge obtained by joint grinding of the battle chamotte and high alumina refractories up to a particle size of 30 - 200 nm, with the preliminary introduction of sodium liquid glass into the water with a density of 1.23 g / cm, with the following ratio of components, wt.%:

Portland cement M400 8-15 filler from the battle of fireclay refractories 8-15 filler from the battle of high-alumina refractories 3.7-5.9 sand 24.5-26.4 crushed stone 35-36.3 liquid glass 0.2-0.35 water rest.

The reduction in cement consumption due to nanoscale fillers allows to reduce the strength dump of concrete and its shrinkage, and consequently, the tendency to crack under the action of high temperatures. The heat resistance of heat-resistant concrete increases under sharp temperature changes.

The introduction of a nanosized filler from the battle of high alumina refractories eliminates the use of scarce and expensive imported alumina hydrate and at the same time increases the content of the alumina component, which increases the fire resistance and heat resistance of concrete. Nanoscale fillers from the battle of chamotte and high-alumina refractories mixed with cement have increased activity, creating a complex filled binder due to the interaction of amorphous oxides SiO ₂ and Al ₂ O ₃ from refractories with Ca (OH) ₂ , which is released during the mixing and hardening of cement stone with the formation of insoluble low basic calcium silicates, filling the pores in it and increasing the density of the cement stone. Nanoscale fillers do not push apart the grains of a large aggregate, but only fill the surface pores in it and increase the adhesion of the binder to the fillers. In addition, such fillers increase the ductility and workability of the concrete mixture, which eliminates the use of burnable scarce and expensive S-3 superplasticizer. The introduction of sodium liquid glass thinner into the composition of concrete, which simultaneously increases the mobility and workability of the concrete mixture at a lower water consumption and at the same time does not fade at high concrete service temperatures, allows to increase the density, strength and fire properties of hardened concrete.

As small and large aggregates, it is recommended to use the battle of fireclay refractories obtained during repairs of the linings of thermal units and cleaned of impurities of slag and metal. These materials are waste from the metallurgical industry, inexpensive and not scarce. Their use in compositions of heat-resistant concrete contributes to the improvement of the environment of the industrial zone of these industries.

In the proposed composition, in comparison with the known compositions of heat-resistant concrete based on chamotte aggregates, the reduced sand content ensures the filling of voids in a large aggregate without the expansion of gravel grains. This helps to ensure the most dense packing of grains of the mineral mixture, increase the density of hardened concrete and does not require increased cement consumption for enveloping small grains of sand.

The compositions of the investigated concrete according to the invention, according to the known invention [1] and according to the prototype [2] are presented in table 1.

Table 1 The compositions of the investigated concrete. Name of source materials Consumption of materials, wt.% / In kg per 1 m ⁵ concrete mix In the proposed compositions In a known composition According to the prototype one 2 3 four Portland cement M400 8/176 9/198 12/264 15/330 22/484 19.2 / 422 TMD chamotn., 30-200 nm 15/330 14/308 11/242 8/176 - - The same fr. <0.14 mm - - - - - - The same from blast furnace slag - - - - - 5.8 / 125 The same from the battle high clay. refractory. Fr. 30-200 nm 3.7 / 81 4/88 4.8 / 106 5.9 / 130 - - Clay hydrate. FR. <0.14 mm - - - - 20/440 - Sand fr. 0-5 mm fireclay 26.4 / 581 26.2 / 577 25.6 / 563 24.5 / 539 - 30.8 / 679 The same of blast furnace slag - - - - 30/660 - Crushed stone fr. 5-20 mm from the battle of fireclay refractories. 36.3 / 800 36.0 / 792 35.4 / 779 35.0 / 770 - 30.8 / 679 The same from the slag domain - - - - 15/330 - Plasticizer S-3 - - - - 1,5 / 33 - Sodium Liquid Glass 0.2 / 4.3 0.3 / 6.5 0.3 / 6.5 0.35 / 7.7 - - Water 10.4 / 228.8 10.5 / 231 10.9 / 240 11.25 / 247.3 11.5 / 253 13.4 / 295 Wed density bet. mixture, kg / m ³ 2201 2201 2201 2201 2200 2200

To determine the properties of heat-resistant concrete of the proposed compositions, crushing and sieving of the battle of refined chamotte refractories were preliminarily carried out to obtain the specified sizes of sand and gravel fractions. And to obtain fillers with nanoscale particles up to 200 nm, a joint wet grinding of the screenings of the fireclay and high-alumina refractories, taken in the ratio indicated in Table 1, was carried out. A thinner — liquid glass — was added to the water for wet grinding, which made it possible to reduce the amount of water to 15% of the mass of dry materials without decreasing the fluidity of the sludge. After grinding, the sludge was drained through a 0.063 mm sieve, which made it possible to separate particles larger than 200 nm and return them to the mill for re-grinding. Due to the increased fluidity of the sludge, it was possible to reduce the workability of the concrete mixture at a lower water content.

The sizes of the filler nanoparticles were determined using a Solver NT-MDT scanning probe microscope manufactured by the Zelenograd Institute of Physics and Technology of Nanotechnology and Microscopy. The shape and size of the particles of fillers from the battle of chamotte and high-alumina refractories after joint wet grinding under a microscope are presented in figures 1 and 2.

An analysis of the data of these figures allows us to conclude that, after wet grinding, the mixtures of chamotte and high alumina refractories of the sludge grain have dimensions not exceeding 200 nm specified in the application. The surface of the particles and the height of the relief also does not exceed the indicated dimensions. This shape and size of the fillers contribute to the achievement of the goal: to reduce the consumption of cement binder and at the same time increase the physicomechanical and fire properties of heat-resistant concrete on Portland cement. At the same time, the issues of metallurgical waste disposal are also being addressed.

After a weighted dosage of all components from heat-resistant concrete mixtures, Portland cement was pre-mixed with filler and water, then aggregates were introduced, mixed until homogeneous, and cube samples 100 × 100 × 100 mm and 70 × 70 × 70 mm in size were prepared. The moisture contained in the wet milling fillers was taken into account when dosing the water taken to mix the concrete mix of each composition. Sodium water glass, introduced with a filler, increased the mobility and workability of the concrete mixture with less water consumption. The consumption of water glass with a density of 1.23 g / cm ^{3 was} calculated as a percentage of the mass of dry materials loaded into the mill. Water consumption was 15% by weight of dry materials. In this case, the fluidity of the sludge was sufficient for pumping it and pumping it through the pipeline.

Compaction of the cubic samples was carried out on a vibrating platform with a frequency of 3000 rpm and an amplitude of 0.3 mm until a cohesive state was reached (1-1.5 min). Hardening of the samples occurred during steaming according to the mode of 3 + 6 + 3 hours, followed by drying to constant weight. Heat-resistant concrete according to GOST 20910-90 [3] under such hardening conditions gain 100% strength.

The test results of the investigated compounds are summarized in table 2.

table 2 Properties of heat-resistant concrete Name of properties The values of the properties in the compositions one 2 3 four known prototype Average density, kg / m ³ , dry concrete 2050 2070 2085 2100 2060 1970 The same annealed at 800 ° C, kg / m ³ 1990 2000 2010 2025 1980 1760 The compressive strength of dry concrete, MPa 41,4 42.0 43,2 45.8 37,4 25.7 The same annealed at 800 ° C, MPa 30.6 30.7 30.7 31.1 24.7 8.87 Residual strength,% 73.9 73.1 71.1 67.9 66 34.5 Heat resistance, number of water heat exchangers 27 25 24 22 21 10

An analysis of the results of this table led to the following conclusions.

1. The proposed compositions of heat-resistant concrete, in spite of the reduced cement consumption by more than 2 times, in comparison with the known compositions, are not inferior to or even superior to them in compressive strength both in dry and burnt condition at a temperature of 800 ° С. It should be noted that with a decrease in cement consumption, the residual strength of concrete increases.

2. The average density of the proposed compositions is significantly higher than the known composition on chamotte aggregates, which indicates a denser packing of grains, which helps to reduce shrinkage in firing and increase heat resistance. Almost the same density of the known composition on slag aggregates was achieved only due to heavier slag aggregates and cannot serve as proof of the most dense packing of grains.

3. Compared with the known composition on chamotte aggregates, the residual strength after firing at a temperature of 800 ° C for the proposed compositions is more than 2 times higher, which indicates a greater durability of concrete with prolonged exposure to high temperatures.

4. The heat resistance of the concrete of the proposed compositions is also 2 times higher than the known composition on chamotte aggregates, which indicates their greater resistance to sudden changes in temperature. Almost the same thermal stability of concrete on slag aggregates is explained by a higher coefficient of thermal expansion of slag aggregates compared to chamotte aggregates, and not by achieving the most dense packing of grains in concrete.

Used sources

1. Patent RU 2272013, С04В 38/08, С04В 28/04, published on March 20, 2006, BI No. 8.

2. Reference manual to SNiP 3.09.01-85 Manufacturing technology of heat-resistant concrete. M .: Stroyizdat, 1991. Appendix 6.

3. GOST 20910-90. Concrete is heat-resistant. Technical conditions

Claims (1)

Heat-resistant concrete mixture, including Portland cement M 400, sand and gravel fractions of 5-20 mm, obtained by crushing the battle of fireclay refractories with subsequent sieving into fractions, fine-ground filler - in the form of sludge obtained by joint wet grinding of fireclay and high-alumina refractories to a particle size of 30 -200 nm with the preliminary introduction into the water of sodium liquid glass with a density of 1.23 g / cm ³ in the following ratio of components, wt.%:
Portland cement M 400 8-15 specified filler from the battle of fireclay refractories 8-15 specified filler from the battle high alumina refractories 3.7-5.9 specified sand 24.5-26.4 specified crushed stone 35-36.3 specified liquid glass 0.2-0.35 water rest

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