RU2378228C1 - Cellular concrete of autoclave hardening - Google Patents

Abstract

FIELD: construction. ^ SUBSTANCE: invention is related to production of construction materials and may be used to make heat insulation cellular concretes of autoclave hardening for civil and industrial construction. Cellular concrete of autoclave hardening is made of raw mix, which contains flue ash of TPP of electric filter extraction with content of SiO2 50-65%, Al2O3 18-30%, Fe2O3 2-15%, CaO not more than 10%, MgO not more than 3% and SO3 not more than 2% and free CaO of less than 1% and specific surface, which corresponds to residue on sieve 008 of not more than 20%, cement, lime-ash mix LAM with ratio of lime and ash 1:1, gasifier on the basis of aluminium powder and sludge made of cellular concrete production wastes, characterised with density of 1200-1500 kg/m3 and temperature of 20-40C, at the following ratio of components, wt %: cement 24-27, specified LAM 14-21, specified flue ash 34-40, specified sludge 16-21, specified gasifier 0.07-0.09, and also over 100 wt % water in amount that corresponds to water-solid ratio W/S=0.6-0.7. ^ EFFECT: method is suggested to production of construction materials and may be used to make heat insulation cellular concretes of autoclave hardening for civil and industrial construction. ^ 3 cl, 3 tbl

Description

FIELD OF THE INVENTION

The invention relates to the production of building materials and can be used for the manufacture of insulating cellular concrete autoclaved for civil and industrial construction.

State of the art

Known autoclaved aerated concrete produced by JSC "Zabudova" Belarus, containing cement, quicklime, sand, crushed gypsum stone (anhydrite), crumb of aerated concrete products (production waste), a gasifier based on aluminum powder and water (http://www.stromros.ru ) The aforementioned aerated concrete is characterized by high strength up to 2.5 MPa (B2.5) and a fairly low coefficient of thermal conductivity. Among the shortcomings of the aforementioned aerated concrete, low frost resistance can be noted: thus, insulating concrete with a density of 400-500 kg / m ³ withstands only 15-25 cycles according to the data of the journal "Energy Saving" No. 10, 2005, Yu.G. Granik. Thermal insulation of residential and civil buildings (or: http://wwvv.stroinauka.ru). The disadvantages include the use of quite expensive and popular natural raw materials and high energy consumption due to the need for grinding quartz sand.

The use of production waste, in particular ash or ash and slag materials, can significantly reduce the cost of production of cellular concrete, helps to solve the problem of waste disposal and at the same time reduces the consumption of binder, shrinkage of concrete and improves the quality of cellular concrete.

Autoclave ash foam is known (see patent No. 2256632, IPC: С04В 38/10, publ. 2005.07.20), containing cement, lime, sand and ash from burning sewage sludge, foaming additive and water in equal parts. Autoclave hardening of ash foam is carried out for 12 hours at T = 175 ° C and a pressure of 8 atm. Ash foam is characterized by increased thermal insulation characteristics.

Among the drawbacks of the mentioned solution, it can be noted: the use of sand as part of a silica-containing component, as well as lower strength and higher shrinkage in comparison with aerated concrete.

As the closest analogue for the proposed solution, autoclaved aerated concrete produced by the Stupinsky cellular concrete plant was used, in the production of which quartz sand is not used, and ash obtained as a result of burning brown coal of the Moscow Region basin was used as a silica-containing component (see the book by M.Yu. Leshchinsky Concrete and mortar with the use of TPP ash. Construction and scientific and technological progress 11/1988 series. M.: Knowledge, 1988, pp. 26-27). The heat-insulating aerated concrete (with a density of 400 kg / m ³ ) according to the source contains a lime-ash binder obtained by co-grinding ash and lime, ground ash and a gasifier based on aluminum powder with the addition of sulfanol. The composition of the mixture to obtain structural heat-insulating aerated concrete additionally contains agloporite aggregate, gypsum.

The disadvantages of the known aerated concrete include low frost resistance, because even using as an additive to the aforementioned cement composition in an amount of 100 kg per 1 m ^{3 of} concrete allows to increase the frost resistance of products only to the F50 grade.

Disclosure of invention

The objective of the invention is to improve the quality indicators of aerated concrete autoclaved on the basis of ash - waste from the production of thermal power plants, in particular - increase its frost resistance.

The problem is solved due to the fact that the raw material mixture for the preparation of aerated concrete autoclaved, containing ash, cement, lime-ash mixture, a gasifier based on aluminum powder and water, according to the claimed invention contains ashes fly ash of a thermal power plant of electrostatic precipitation, characterized SiO ₂ content _of 50-65%, Al ₂ O ₃ 18-30%, Fe ₂ O ₃ 2-15%, CaO not more than 10%, MgO not more than 3% and SO ₃ not more than 2% and free CaO less than 1% and the specific surface corresponding to the residue on sieve 008 no more than 20%, the ratio of lime and ash in the lime-ash mixture is 1: 1, while the raw mixture additionally contains sludge prepared from waste products of cellular concrete, characterized by a density of 1200-1500 kg / m ³ and a temperature of 20-40 ° C, in the following ratio of components, wt. %:

Cement 24-27 Lime-ash mixture (IZS)  14-21 Fly ash  34-40 Specified Sludge  16-21 blowing agent  0.07-0.09

and water (in excess of 100% dry components) in an amount corresponding to a water-solid ratio W / T = 0.6-0.7.

The lime-ash mixture was obtained by co-grinding crushed lime and ash in a ball mill to a specific surface of 4000 ± 200 cm ² / g.

Fly ash is a material formed as a result of burning coal in furnaces and deposited from flue gases of ash collecting devices. For the proposed solution, it is important that they use fly ash of electrostatic precipitation, i.e. deposited on electrostatic precipitators, or electrostatic ash, characterized by a specific particle size distribution, determined by the residue on sieve No. 008 (with a hole size of 0.08 mm) not more than 20%, and a high content of silicon and aluminum oxides.

The above set of essential features allows you to get a new positive result, namely: significantly increase the frost resistance of products from autoclaved aerated concrete, while maintaining high strength and heat-shielding characteristics. So the frost resistance of the blocks obtained on the basis of the inventive autoclaved aerated concrete corresponds to 150 cycles (see the following examples of implementation).

Frost resistance depends on the pore structure of concrete: uniform distribution of pores, the absence of capillary porosity, and the structure of inter-pore partitions.

Products obtained on the basis of the proposed solution are characterized by a finely porous structure with evenly distributed closed pores, which is largely determined by the use of a combination of binders in the form of cement and a lime-ash mixture, as well as quality indicators of the silica-containing component used - ash, characterized by certain chemical and particle size distributions.

The rate of concrete curing also has a significant effect on pore formation - the rate of initial strength gain, which is largely determined by the amount of cement used.

The material of the walls that form the pores consists of cement stone or a hydrosilicate frame close to it. Thus, the structure of inter-pore partitions, which determines the index of frost resistance, also depends on the type and amount of binder used.

For the inventive mixture, cement (mainly Portland cement M400) is used in an amount of 24-27% and a lime-ash mixture (IZS), characterized by a ratio of ash and lime of 1: 1 and a specific surface of 4000 ± 200 cm ² / g, in an amount of 14-21 %

Used silica component related to acidic ash, waste from the combustion of coal, is 34-40% of the total mixture.

Another significant component of the mixture is sludge prepared from waste cutting aerated concrete and used in an amount of 16-21 wt.%.

The use of sludge, on the one hand, allows you to get waste-free production, and on the other hand, sludge is an essential component of the mixture, acting as both part of the binder and as part of the aggregate.

As a result of dispersion by mechanical influences and mixing with water, a slurry (the so-called reverse slurry) is obtained, which is characterized by increased alkalinity due to the hydration of its unreacted grains of cement and lime. The high alkalinity and dispersion of the particles of the reverse sludge contribute, as is known, to accelerate the course of reactions in the hardening concrete mixture, and to more quickly set the initial (stripping) strength. The temperature of the slurry 20-40 ° C and its density of 1200-1500 kg / m ³ provide optimal conditions for the occurrence of the above reactions.

The amount of mixing water affects the strength of the material of the pore walls, their structure. Excess water contributes to the formation of capillary porosity, which reduces the frost resistance of products. Thus, the amount of water characterized by the water-solid ratio (W / T) is also a significant factor influencing the frost resistance of the resulting products. W / T = 0.6-0.7 with respect to the claimed composition of the mixture, is optimal, allowing to achieve a high degree of frost resistance. With an increase in W / T> 0.7, the frost resistance and strength of aerated concrete decrease.

Based on the foregoing, we can conclude that it is the set of essential features of the proposed solution: the composition of the mixture and the quantitative ratio of the components, the type and quality characteristics of the used ash and other components of the mixture, provide a synergistic effect in the form of increased frost resistance of aerated concrete products. So tests of an independent laboratory confirmed that the cellular concrete obtained according to the inventive mixture has a frost resistance of 150 cycles (F150).

However, the inventive cellular concrete is characterized by high rates of initial strength, high strength and heat-shielding performance.

The implementation of the invention

For the manufacture of cellular concrete using:

- Portland cement M400,

- lump lime, crushed in a rotary crusher to a size of 5-10 mm,

- coal fly ash of the Omsk TPP, characterized by a SiO ₂ content _of 50-64%, Al ₂ O ₃ 18-30%, Fe ₂ O ₃ 4-15%, CaO 2-10%, MgO 0.5-2.5% and SO ₃ <2%, free CaO <1% and a particle size distribution corresponding to a residue on sieve 008 of not more than 20%,

- aluminum powder, for example PAP -1 or PAP-2.

Cement and lime, ash and aluminum powder are delivered by road or rail and stored in a warehouse. The lime-ash mixture and aluminum suspension are prepared at the production site.

To prepare the lime-ash mixture, ash and crushed lime are dosed using, for example, hopper strain gauges in equal parts (1: 1) and subjected to joint dry grinding in a ball mill to a specific surface of 4500 ± 200 cm ² / g. From the mill, the lime-ash mixture is fed into the feed silo of the concrete mixing department, where it is subjected to intensive aeration with compressed air.

The aluminum suspension is prepared from aluminum powder and surfactants, which are usually used as sulfanol or a low-foaming washing powder (for example, Pemos). In order to avoid separation or sedimentation of the powder particles in the pipeline or mixer, the suspension is circulated by a closed-loop pneumatic pump. Use a suspension at T = 15-30 ° C.

Waste from cutting the slabs and cutting the masses is collected in the tank of the reverse sludge, mixed with water, dispersed to a density of 1200-1500 kg / m ³ , transported using a centrifugal pump to the slurry tank of the concrete mixing department. In this case, continuous mixing of the sludge with a stirrer and circulation are carried out. The temperature of the slurry is maintained within 30 ± 5 ° C.

The components of the cellular concrete mixture are dosed into the mixer according to a given formulation. Table 1 shows the basic compositions for the preparation of aerated concrete mix (in the percentage of mass parts). Water is added in an amount providing a water-solid ratio of the mixture B / T = 0.6. Table 2 shows the consumption of components in kg to obtain 1 m ³ concrete for the same compositions.

Table 1 The composition of the mixture No. The components of the mixture, wt.% Cement ISS Ash Reverse sludge Aluminum paste one 27 twenty 36 16,014 0,086 2 26 fifteen 40 18,022 0,078 3 24.5 20,4 34.7 20,326 0,074

table 2 The composition of the mixture No. Consumption of mixture components per 1 m ^{3 of} aerated concrete, kg Cement ISS Ash Reverse sludge Aluminum paste one 140 105 191 89 0.45 2 138 78 211 one hundred 0.41 3 133 111 189 111 0.41

The dosed components are sequentially loaded into the mixer in the following order: sludge with water, ash, then cement and a lime-ash mixture, aluminum suspension last.

As soon as aluminum mixes well with the rest of the components, the cellular concrete mixture is poured into the mold. The raw material mixture poured into the mold is subjected to vibration for 40 s.

The hardening mass is subjected to exposure in the preliminary hardening chambers for 120-180 minutes until the formwork strength is set to 200-400 g / cm ² , cutting and subsequent autoclaving at a pressure of 12 bar and a temperature of 190 ° C, the cycle of which is 12 hours.

Cutting waste is collected in a tank for reverse sludge, crushed and mixed with water, providing a density of 1200-1500 kg / m ³ and a temperature of 30 ± 5 ° C. Ready sludge is subjected to constant mixing. The return sludge is fed through a “density determination loop” for weighing.

The physicomechanical properties of cellular concrete obtained in accordance with the claimed solution were tested for compliance with the requirements of the current standards by an independent laboratory of the testing center OmskstroyTSNIL LLC certification system. Table 3 shows the results of these tests.

Table 3 The composition of the mixture No. Density, kg / m ³ Strength class Humidity, not more than,% Heat conductivity coefficient, W / m · ° С Brand for frost resistance one 500 B2.5 25-30 0.12 F 150 2 500 B2.5 25-30 0.12 F 150 3 500 B2.5 25-30 0.12 F 150

According to the table, the obtained insulating concrete with a density of 500 kg / m ³ corresponds to strength class B2.5, has a moisture content of not more than 25-30% and a thermal conductivity of 0.12 W / m · ° C, which meets the requirements of the standards. Moreover, frost resistance for all three compositions corresponds to the F 150 brand, and the vapor permeability coefficient is 0.06 mg / m · h · Pa, which is very high.

Claims (3)

1. Autoclaved aerated concrete made of a raw material mixture containing ash, cement, lime-ash mixture, a gas blower based on aluminum powder and water, characterized in that the raw material mixture contains fly ash from a thermal power plant of electrostatic precipitation, characterized by SiO content ₂ 50-65%, Al ₂ O ₃ 18-30%, Fe ₂ O ₃ 2-15%, CaO not more than 10%, MgO not more than 3% and SO ₃ not more than 2% and free CaO less than 1% and specific the surface corresponding to the residue on sieve 008 no more than 20%, the ratio of lime and ash in the lime-ash mixture is 1: 1, while the raw material mixture additionally contains sludge prepared from waste products of cellular concrete, characterized by a density of 1200-1500 kg / m ³ and a temperature of 20-40 ° C, in the following ratio of components, wt.%:
cement 24-27 lime-ash mixture (ISS) 14-21 fly ash 34-40 specified slurry 16-21 blowing agent 0.07-0.09
and water (in excess of 100% dry components) in an amount corresponding to a water-solid ratio B / T = 0.6-0.7. 2. Aerated concrete according to claim 1, characterized in that the calcareous mixture is obtained by co-grinding crushed lime and ash in a ball mill to a specific surface of 4000 ± 200 cm ² / g. 3. Aerated concrete according to claim 1, characterized in that it is obtained by molding using a vibrating action on a raw material mixture poured into a mold for 40 s, followed by exposure for 120-180 minutes in preliminary hardening and autoclaving chambers for 12 h at T = 190 ° C and a pressure of 12 bar.