RU2614865C1 - Raw mixture and method for producing raw mixture for foam and gas concrete of non-autoclave hardening - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: raw mixture for foam and gas concrete of non-autoclave hardening comprises, wt %: Portland cement 51.76-51.90, a highly concentrated suspension with the humidity of 12-22%, with the particle content of less than 5 microns 30-50%, obtained by the wet grinding of quartz sand, 12.94 -12.97, the foaming agent "Penostrom" 0.09-0.27, the aluminium blowing agent containing more than 90 wt % of active aluminium with the particle size less than 100 microns 0.01-0.09, water 34.94-35.03. In the method for producing the above-mentioned raw material mixture comprising the preparation of the nanostructured modifier, the subsequent mixing of the resulting nanostructured modifier, the aluminium blowing agent, and water in an ultrasonic disperser under the action of ultrasound, feeding the resulting suspension to foam concrete mixer, where it is mixed at low speeds of 60 rev/min with Portland cement to complet system homogeneity, with the subsequent introducing of a predetermined amount of the blowing agent and the final stirring at high speeds of 250 rev / min for 3-5 minutes until obtaining the high foam mass stability, the nanostructured modifier preparation is carried out by means of the wet grinding of quartz sand to obtain a highly concentrated suspension with the humidity of 12-22% and the content of particles less than 5 microns 30-50%.

EFFECT: increasing the compressive strength and decreasing the thermal conductivity.

2 cl, 1 dwg, 8 tbl, 1 ex

Description

The invention relates to the building materials industry and can be used for the manufacture of non-autoclave heat-insulating cellular concrete for various purposes.

Known foam concrete [patent application of the Russian Federation No.: 2003119641/03, decl. 07/03/2003., Publ. 02/10/2005, class С04В 38/10] obtained from a raw material mixture prepared by mixing in a turbulent mixer from Portland cement, an aqueous solution of a foaming agent, a siliceous component and a dispersed fiber, characterized in that microsilica is used as a siliceous component, chopped fiberglass or basalt fiber is used as a dispersed fiber , or chrysotile asbestos, and the specified fiber is pre-treated with liquid glass in an amount of 1.5-2.5 wt. % of the raw mixture, and mixing is carried out until a homogeneous colloidal solution is formed in the following ratio of components, wt.%:

Portland cement 44.11-66.64 silica fume 15.57-29.42 specified fiber 17.79-26.47 water foaming agent (taking into account mixing water in excess of 100%) 0.80-2.50

The disadvantage of this analogue is the use of a siliceous component with a relatively low specific surface area, which can serve as a serious obstacle to the occurrence of a full-fledged process of structure formation in the resulting material.

A known method of producing a binder for concrete [RF patent No. 2389711, decl. 09/22/2008. class С04В 40/00; B02C 19/18; B82B 1/00], including wet grinding of the quartz component to a grain composition corresponding to a sieve residue of 60 μm 5–25%, stabilization of the suspension, their mixing. Pre-or in conjunction with wet grinding of the quartz component, the suspension is sonicated by acoustic waves in the ultrasonic range at frequencies of 17-35 kHz, the quartz component is quartz sandstone, and mixing is carried out at the following component ratios: Portland cement 35-80%; suspension of quartzite sandstone (in dry matter) 20-65%. According to this method, Portland cement is ground. Separately, wet grinding of quartzite sand is carried out to a grain composition corresponding to a sieve residue of 60 μm 5-25%. In this case, preliminary or together with wet grinding, acoustic suspension is processed by means of sound vibrations and additionally stabilization of the quartzite sandstone suspension for 2-4 hours. Replacing sand with quartzite sandstone allows you to reduce energy costs, since the structure of quartzite sandstone has more crystalline defects, it is easier to break down when grinding to the required fractions. Ultrasonic treatment of the suspension contributes to the formation of microcracks in the crystals of quartzite sandstone and the mechanical activation of the suspension and subsequently contributes to more efficient grinding with low energy and time costs. At the same time, concretes obtained on a binder activated in a cavitation field of ultrasonic frequency: Portland cement with a suspension of quartzite sandstone, as the results show, are stronger (2-3 times) in strength and higher than those obtained on other binders in their strength properties.

The disadvantage of this invention is the low degree of mechanical activation of the siliceous component, as well as the high energy intensity and complexity of the technological design.

A known method of obtaining and the composition of a mixture of non-autoclaved aerated concrete [patent application of the Russian Federation No.: 2003124027/03, decl. 07/30/2003, publ. 12/27/2004, class C04B 38/02].

In the method for producing non-autoclaved aerated concrete, including dosing of cement, a silica component, a blowing agent, additives, water and subsequent mixing of the mixture, combined with its hydromechanical activation, additives are additionally dosed, the duration of said activation is 5-10 minutes, and the blowing agent is introduced 2-3 minutes before its completion. A mixture for the production of non-autoclaved aerated concrete, containing cement, a silica component in the form of TPP ash or fine sand, gypsum, a blowing agent, plasticizer and water, contains aluminum powder or paste as a blowing agent and an additional activating additive - alumina soda sulphate waste or another product, in which sodium sulfate predominates, in the following ratio of components, wt.%: cement 48-52, said siliceous component 10-14, water 35-37.5, said blowing agent 0.04 -0.06, building gypsum 1.2-1.4, the specified activating additive 1.2-1.4, plasticizer 0.25-0.35. The disadvantages of the known concrete is the use of technogenic raw materials of unstable chemical and mineralogical composition, which has rather limited reserves. In addition, the density of the resulting aerated concrete is high with insufficient strength.

The known composition and method of manufacturing products from foam concrete [RF patent No. 2412136, application. 09/21/2009, class С04В 38/10, С04В 40/00, В82В 1/00], namely, non-fired, autoclave-free building products based on silica-containing raw materials, including the preparation of technical foam by mechanical treatment in a foam generator-mixer of an aqueous solution of a foaming agent, mixing it with a cementless nanostructured binder - a highly concentrated suspension of silica-containing raw materials, molding from the resulting foam mass of products, hardening and drying. An additional hardening operation consists in treating the surface of the product after drying with an alkaline silicate solution with a density of 1.06-1.08 g / cm ³ , followed by final drying.

The material obtained by this method can be attributed to the group of heat-insulating and structural, but for this type of material, the products obtained by the method described above have low performance characteristics. The disadvantage of this invention is the inability to obtain by the proposed method a highly effective thermal insulation and structural cellular concrete without additional hardening operations.

A known method of manufacturing aerated concrete [RF patent No. 2253636, decl. 12/26/2003, class С04В 38/02], which consists in feeding water and cement or water, cement and sand to the mixer and mixing them, mixing is carried out in a cavitation mixer with an activator for 5-15 minutes, then a dry pore-forming mixture is introduced into the resulting solution, having the following composition , wt.%: cement 70, aluminum pigment powder 12, water-soluble aluminum powder 12, frost-resistant plasticizer 2, water 4, and subsequent mixing is carried out for 15-60 seconds.

A known method of producing aerated concrete involves the inclusion of silica in the form of natural sand. Due to the characteristics of the hardening of the mixture by this composition, the microporosity of the cement stone is relatively small. The reduced microporosity of the material of the inter-pore walls is an obstacle to the production of aerated concrete with enhanced heat-insulating properties, while aerated concrete is mainly used in building exterior structures for thermal protection.

As a prototype of the composition [RF patent No. 25006545, declared. 05/05/2009, class C04B 38/02; С04В 38/10], the composition of the raw material mixture is selected for the production of non-autoclaved cellular concrete of natural hardening, which contains wt.%: Portland cement 63.03-66.06, a synthetic foaming agent 0.15-0.21, a blowing agent containing 80% active aluminum with particle size not more than 100 nm and 20% polyethylene glycol, 0.68-0.74, water 33.04-36.07. The composition additionally contains a modifying nanocrystalline additive - corundum in an amount of 0.02-0.3 wt. % by weight of Portland cement. The method of obtaining a composition according to claim 1 includes feeding and mixing in a mixer of a mixer type, first a foaming agent with part of the water and Portland cement, and then into the resulting mass with stirring, a suspension of the specified blowing agent and part of the water. A modifying nanocrystalline additive, corundum, in an amount of 0.02-0.3 wt.% By weight of Portland cement is additionally added to the suspension.

The disadvantage of this invention is the complexity of the technological design, a rather lengthy process of hardening of the semi-finished product. A positive result is possible only with strict observance of all the claimed parameters of the method and composition.

The closest way to prepare the raw mix for aerated concrete is a method of producing a raw mix for nanostructured autoclaved aerated concrete [RF patent No. 2448929, decl. 09/01/2010, class C04B 38/02; B82B 1/00], which includes the preparation of a lime-silica binder, subsequent mixing in a mixer of the obtained lime-silica binder, gypsum, a finely ground silica-containing component and a suspension of aluminum paste or powder, the production of calcareous-silica binder from ground brown sand and ground sand is carried out by joint to a specific surface of 900 m ² / kg, and the preparation of a finely ground silica-containing component is carried out by wet grinding of quartz sand to obtain highly concentrated suspension with a moisture content of 12-20% with a particle content of less than 5 microns 30-50% and subsequent dilution of the resulting suspension with water to a density of 1.75-1.80 kg / l, with the following ratio of components, wt.%: the specified suspension (dry substance) 62.5-72.5, the specified lime-silica binder, with a ratio of components, wt.%: quicklime 75-85 and quartz sand 15-25, 25-35, gypsum 1.5-2.5, aluminum paste or powder 0.05-0.1, water to a density of 1.75-1.80 kg / l.

The disadvantage of the presented method is the high energy and metal consumption of the technological process due to the need for autoclaving to achieve the required operational strength of the cellular composite, as well as the imperfection of the pore structure of the material due to the applied pore formation method.

Currently, an increase in the normative indicators of the heat-shielding properties of building envelopes determines the high volume of use of cellular concrete in construction. Their wide range allows achieving modern requirements for thermal insulation together with the necessary strength characteristics. Moreover, from the standpoint of economic efficiency, it is advisable to use non-autoclave cellular composites.

Along with high thermal insulation properties, non-autoclaved cellular concrete, as a rule, is characterized by a low strength of the frame and the mono-sized porous structure of the composite. It is possible to compensate for these shortcomings, on the one hand, by using active modifying components, including nanostructured ones, capable of increasing the characteristics of the composite support matrix, and, on the other, by complex system porization, which will ensure the formation of a heteroporous cellular structure of concrete with a lower density.

Today, there is a significant amount of research devoted to improving the production and use of non-autoclaved cellular concrete, the main purpose of which is to improve the performance properties of composites while maintaining their heat-shielding ability. To increase the strength properties of aerated concrete, a number of authors have proposed the use of composite binders - fine-ground cements (TMC) or a binder of low water demand (VNV), as well as modified binders, which contain active components of different composition and genesis. Improving the thermal insulation properties of cellular composites is associated with the use of modern effective foaming and gas-forming agents, as well as with their complex (joint) use.

In the works performed earlier, the feasibility of using a nanostructured modifier (NM) of a silicate composition in the production of autoclaved hardening materials is substantiated [Nelyubova V.V. Autoclaved cellular composites using a nanostructured modifier / V.V. Nelyubova, V.V. Strokova, N.I. Cmonberry // Building materials. - 2014. - No. 5. - S. 44-47]. However, the possibility of using it as a modifier of the matrix and porous structures of non-autoclave cellular foam-gas concrete based on cement in combination with activated aluminum was not considered.

Currently, a promising way to increase the efficiency of cellular concrete is the joint use of a chemical and mechanical method of porous system. The possibility of obtaining foam concrete of various grades by density and strength [Deryabin P.P. The influence of prescription and technological factors on the rheological properties of the foam-gas mixture / P.E. Deryabin, P.P. Deryabin // News of higher educational institutions. Construction. - 2006. - No. 1. - S. 32-35]. It is noted that one of the promising areas of regulating the properties of cellular concrete mixtures and reducing the average density of cellular concrete is the use of highly dispersed mineral or organo-mineral fillers and stabilizers of the structural strength of the porous mass.

Thus, increasing the efficiency of production and use of cellular concrete is possible due to the development and implementation of technological solutions that reduce the average density of the material and energy consumption of the process while improving performance. The application of cement matrix modification techniques together with the creation of multimodal porosity will increase the strength of the finished material, while reducing its density and thermal conductivity.

The objective of the invention is the creation of a highly effective heat-insulating non-autoclave foam concrete using a nanostructured modifier of silicate composition and an integrated method of porosity.

In the inventive composition of the raw material mixture and the method of its preparation for non-autoclaved foam concrete, the following tasks were also set:

- make the most full use of the effect of hydration hardening and structure formation in the silicate system through the use of a siliceous component - a nanostructured modifier with a high degree of reaction interaction;

- to make it possible to comprehensively porize a system implemented through the joint use of a synthetic blowing agent and activated aluminum AA-T / 7 as a blowing agent, which ensures the formation of an optimal heteroporous structure of a cellular composite;

- to obtain cellular composites with high thermal insulation properties while maintaining the necessary strength characteristics.

The invention is also aimed at increasing the competitiveness of the resulting cellular products as a result of increased strength and lower thermal conductivity compared to industrial products, improving the technology and expanding the arsenal of means for producing foam-gas concrete non-autoclave products.

These tasks are achieved by developing the composition of the raw material mixture for non-autoclaved foam concrete, including Portland cement, nanostructured modifier, Penostrom foaming agent, aluminum gasifier and water, according to the proposed solution, a highly concentrated suspension with a moisture content of 12-22% and a particle content of less than 5-22 microns is used as a nanostructured modifier 30-50% obtained by wet grinding of quartz sand, and the blowing agent contains more than 90 wt.% Active aluminum with size particles less than 100 microns with the following component ratio, wt.%:

Portland cement 51.76-51.90 nanostructured modifier 12.94-12.97 foaming agent "Penostrom" 0.09-0.27 aluminum blowing agent 0.01-0.09 water 34.94-35.03

The tasks are also achieved by a method of obtaining a molding mixture for non-autoclaved foam concrete of the claimed composition, including the preparation of a nanostructured modifier, subsequent mixing in an ultrasonic disperser under the action of ultrasound of the obtained nanostructured modifier, aluminum blowing agent and water, feeding the resulting suspension into a concrete mixer (where it is 60 rpm) with cement until complete uniformity of the system, followed by the introduction of a certain amount of foaming agent and final stirring at high speeds (250 rpm) for 3-5 minutes until foam stability appears, in which, according to the proposed solution, the preparation of a nanostructured modifier is carried out by wet grinding of quartz sand to obtain a highly concentrated suspension with a moisture content of 12-22% s a particle content of less than 5 microns 30-50%.

As raw materials for obtaining a nanostructured modifier, natural and artificial quartz sands can be used, mainly containing at least 60% SiO ₂ (table 1).

Portland cement without additives as per GOST 31108-2003 can be used as the constituent components of the raw material mixture for the production of foam concrete. Water can also be used according to GOST 23732.

As the foaming agent can be used synthetic foaming agents (table 2).

As a blowing agent - aluminum blowing agent (table 3).

Concrete example

To obtain the raw mix and test its suitability for the production of non-autoclaved foam gas concrete, a number of operations were performed in accordance with the claimed composition of the raw mix and the method for its preparation.

Natural and artificial quartz sands can be used as a siliceous feedstock to obtain a nanostructured modifier, in this case, the sand of the Razumensky deposit (Belgorod region), with a content of 93.75% SiO ₂ , the chemical composition of which is shown in table 1, was used.

To obtain a nanostructured modifier, wet grinding was carried out in a ball mill with a stepwise loading of the material, observing the basic principles of obtaining highly concentrated suspensions [Pivinsky Yu.E. Ceramic binders and ceramic concrete / Yu.E. Libyan. - M: Metallurgy, 1990. - 270 p.].

The choice of the concentration of the system at the first grinding stage was carried out taking into account the packing coefficient of the source material and its other characteristics, as well as the overall dimensions of the mill. In the first grinding stage, usually all of the liquid calculated from the final suspension concentration is introduced. The duration of this stage of the process, depending on many factors, ranges from 1 to 5 hours. In this case, the duration of this stage of the process was 3 hours. The degree of dispersion should be such that the average particle size is at least 10-20 times less than the size of the material introduced during the next loading. Optimal results, as a rule, can be obtained when dispersion is achieved at the first grinding stage, characterized by a significant (up to 20-50%) content of particles of the fraction less than 5 microns. In this case, the suspension is as if compressed, accelerating the process of subsequent grinding after the introduction of the next portion of the material.

With stepwise loading of the material, as the volume concentration increases, the effective density of the grinding media decreases and the humidity increases significantly. Due to a gradual decrease in the volumetric liquid content and an increase in the friction forces, the process temperature increases, which largely determines the rheological properties of the system directly in the grinding process, as well as the properties of a highly concentrated suspension of silica-containing raw materials after grinding. So, with increasing temperature, the overall viscosity of the system decreases significantly, its fluidity increases, as well as dilatant properties, which allows the grinding process to be carried out at elevated concentrations.

After wet grinding, the resulting highly concentrated suspension of silica-containing raw materials had a moisture content of 18.2% with a particle content of less than 5 microns 45%.

Next, the raw material mixture for foam concrete was obtained by mixing the prepared nanostructured modifier of a given amount of water and a blowing agent using ultrasound in an ultrasonic disperser, the technical characteristics of which are shown in table 3.

Activated aluminum AA-T / 7 manufactured by Ekoenergotech LLC was used as an aluminum blowing agent (table 4).

To obtain a suspension of the required fine and uniform structure, the ultrasonic method is adopted [Lukuttsova, N.P. Analysis of the influence of ultrasonic dispersion parameters on the size, stability, morphology and particle composition of nanomodifier for concrete based on schungite / N.P. Lukuttsova, A.A. Pykin, E.G. Degterev [et al.] // Construction and reconstruction. - 2013. - No. 5. - S. 62-72].

The efficiency of homogenization of activated aluminum in the presence of a nanostructured modifier due to ultrasonic treatment provides an intensification of the distribution processes of dispersed modifier and gasifier of different sizes, as well as an increase in the stability of the system (absence of delamination).

Replacing a portion of cement with HM reduces the initial viscosity of the cement paste. This effect increases with an increase in the dosage of NM from 15 to 70%. According to the criterion of the effectiveness of additives (GOST 24211-2008), the optimal composition was selected with a content of NM in the amount of 20%, which contributes to an increase in strength by more than 30%. Based on the conducted comprehensive studies, it was shown that this amount of modifier helps to reduce the normal density of the modified binder; leads to a reduction in the setting time of the binder compared to the original cement by 1.9 times (table 6) under normal hardening conditions and 2 times at a temperature of 40 ° C (the temperature is due to gas evolution); reducing the initial viscosity of the binder, practically does not qualitatively and quantitatively change its rheological characteristics. These effects are prerequisites for improving the process of porous system and increasing the stability of the foam gas mass.

Next, the resulting suspension was fed into a foam mixer, the technical characteristics of which are shown in table 5.

Next, the resulting suspension in a concrete mixer was mixed at low speeds (60 rpm) for about 2 minutes until the system was completely homogeneous with the required amount of cement. Then, a predetermined amount of a foaming agent (foaming agent) was introduced into the resulting mortar mixture. Synthetic foaming agent “Penostrom” manufactured by Shield LLC (Russia), which was introduced into the mortar mixture in the form of a liquid concentrate, was used as a foaming agent (table 2).

Then, final mixing was carried out at high speeds (250 rpm) for 5 minutes until the foam became stable.

Next, the prepared raw material mixture for non-autoclaved foam-gas concrete was fed to the molding section.

Then, using mathematical design of the experiment, rational concrete compositions were developed. The optimization of properties was evaluated on the basis of compressive strength, density and coefficient of thermal conductivity of foam concrete. The number of gas and foaming agents was used as variable parameters.

According to the developed compositions, cube samples 100 × 100 × 100 mm in size were formed. Further, after the completion of the hardening process, the cube samples were tested for strength, density, sorption moisture, vapor permeability, and thermal conductivity. The test results are presented in table 7.

Based on the data obtained, compositions were selected that meet the requirements of regulatory documents, in particular GOST 25485-89 (tables 7, 8). Foam and gas concrete brand D400 has a significant margin of safety. So, the lower limit of strength for such products is class B0.5. Offered products exceed the specified value by 2 times. In the case of foam concrete of the D500 grade, the strength class is equal to the same indicator for a cellular composite of the D400 brand. Nevertheless, the value of the real strength of the composite exceeds the strength class by 1.5 times.

The use of complex porosity of aerated concrete mixture in conjunction with the introduction of an active modifying component that structures all the elements of the molding mixture (foam, a suspension of a blowing agent, cement matrix), contributes to a significant increase in the volume growth of the finished aerated concrete mixture (by 30%) and, as a result, a decrease in the density of finished products .

The decrease in the density of products is caused, on the one hand, by the use of a complex of pore agents, which leads to the formation of a heteroporous composite structure (Fig. 1) due to the presence of large gas pores surrounded by finely dispersed foams and a decrease in the thickness of inter-pore partitions between gas and foam foams. On the other hand, this is due to the replacement of part of the cement with a nanostructured modifier, characterized by a lower density, which contributes to a decrease in the average density of the matrix structure, i.e. interstitial septum.

Thus, rational compositions of non-autoclaved foam gas concrete have been determined using activated aluminum AA-T / 7 and a nanostructured modifier of silicate composition, allowing to obtain products with a density of 422 and 481 kg / m ³ (grades in density D400, D500); a compressive strength of 1.19 and 1.58 MPa (compression strength class B1); thermal conductivity of 0.08 and 0.085 W / (m⋅ ° С); vapor permeability of 0.231 and 0.211 mg / (m⋅h⋅Pa); sorption humidity of 7.1 and 7.5%.

Due to the significant margin of safety of products, there are prerequisites for studying the possibility of producing foam and gas concrete of low grades in density, which will significantly expand the field of use of products.

Taking into account the conducted research, it should be concluded that non-autoclaved foam gas-concrete is highly technological and promising.

Table 3

Aluminum gas blower

Name Specific surface m2 / kg The average particle size, microns Volume of gas evolved, ml Total reaction time, s Activated Aluminum AA-T / 7 865 2.6 155 279

Table 7

The compositions of foam gas using NM

Composition number Composition per 1m ³ ,% Portland cement Nanostructured binder W / T Gas generator AA-T / 7 Foaming agent
"Penostrom" one 51.90 12.97 35.03 0.01 0.09 2 51.80 12.96 34.96 0.01 0.27 3 51.85 12.97 35.00 0.09 0.09 four 51.76 12.94 34.94 0.09 0.27 5 51.83 12.96 34.98 0.05 0.18 6 51.81 12.95 34.97 0.09 0.18 7 51.85 12.97 34,99 0.01 0.18 8 51.78 12.95 34.95 0.05 0.27 9 51.88 12.97 35.01 0.05 0.09

Table 8

Properties of foam gas using NM

Plan point number The limit of compressive strength, MPa Density, kg / m ³ Thermal Conductivity, W / (m⋅ ° С) one 1.9 592 0.114 2 1.32 459 0,089 3 1.13 448 0,081 four 1,58 481 0,085 5 1.19 422 0.08 6 one 429 0,083 7 1,03 515 0.0105 8 0.96 411 0,079 9 1.12 464 0,079

Claims (3)

1. The raw material mixture for non-autoclaved foam concrete, including Portland cement, a nanostructured modifier, a foaming agent "Penostrom", an aluminum gasifier and water, characterized in that a highly concentrated suspension with a moisture content of 12-22% and a particle content of less than 5 microns 30- is used as a nanostructured modifier 50% obtained by wet grinding of quartz sand, and the blowing agent contains more than 90 wt.% Active aluminum with a particle size of not more than 100 microns in the following ratio of components in, wt.%: Portland cement 51.76-51.90 nanostructured modifier 12.94-12.97 foaming agent "Penostrom" 0.09-0.27 aluminum blowing agent 0.01-0.09 water 34.94-35.03 2. A method of producing a raw material mixture for non-autoclaved foam concrete according to claim 1, comprising preparing a nanostructured modifier, subsequent mixing in an ultrasonic disperser, using ultrasound, the obtained nanostructured modifier, aluminum blowing agent and water, feeding the resulting suspension into a foam mixer, where it is mixed at low speeds 60 rpm with cement until the system is completely homogeneous, followed by the introduction of a predetermined amount of blowing agent and finish stirring at high speeds of 250 rpm for 3-5 minutes until the foam becomes stable, characterized in that the nanostructured modifier is prepared by wet grinding quartz sand to obtain a highly concentrated suspension with a moisture content of 12-22% with a particle content of less than 5 microns 30- fifty%.

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