RU2795802C1 - Raw mixture for geopolymer foam concrete and method for its production - Google Patents

Abstract

FIELD: building materials industry.

SUBSTANCE: group of inventions is related to a raw mix for geopolymer foam concrete and a method for its production. The raw mix for geopolymer foam concrete includes, in % by weight: low-calcium fly ash with a specific surface of 1850 cm²/g 50.5-52.9, kaolin with a specific surface of 10910 cm²/g 2-3.4, alkaline activator - caustic sodium NaOH 8.5-9.1, foaming agent of protein origin 0.16-0.2, the rest is water. The method for obtaining the above raw mixture includes preparation of an alkaline solution from water and caustic soda, preparation of a mixture of aluminosilicate solid-phase components - low-calcium fly ash and kaolin , preparation of a geopolymer binder suspension, preparation of foam by mixing a foaming agent and 1/10 part of an alkaline solution, followed by its adding to the geopolymer binder suspension, consisting of the remaining 9/10 parts of an alkaline solution and a mixture of aluminosilicate solid components: low-calcium fly ash and kaolin.

EFFECT: decrease in the average density and thermal conductivity of geopolymer foam concrete while maintaining the compressive strength.

2 cl, 2 tbl, 1 ex

Description

The present invention relates to lightweight foam concrete from a geopolymer binder and a method for its production and can be used in the building materials industry.

Known raw mixes and methods for producing foam concrete are close to the claimed technical essence and the achieved result [Patent No. CN 201710279623.0 A, published 2017-09-22] (P1) and [Patent WO 2012092047 A1, 2012-07-05] (P2) .

The raw material mixture and the method for preparing the foam concrete mixture according to (P1) is to mix dry material such as steelmaking slag powder, modified red mud, modified metakaolin, ground slag powder; adding an alkaline activator and water to a mixture of solid components and mixing them until a suspension is formed; in parallel with this: preparation of foam by mixing the foaming agent and water in a ratio of 1:15 using a homogenizer; adding the resulting foam to the suspension and mixing them for 2.5-3 minutes until the foam is evenly distributed in the suspension.

The disadvantages of the known raw material mixture and the method according to (P1) are the multicomponent solid phase component, consisting mainly of industrial waste. This greatly complicates the technological process of selecting compositions, and also increases the risk of variation in performance due to the instability of the properties of raw materials. To ensure the declared performance characteristics, a long curing time is required - within 28 days, which significantly increases the production process. The main disadvantage of the known raw mixture of the method is the relatively high average density and thermal conductivity with a relatively low compressive strength of the final cellular composite.

With an average foam concrete density value of 550 kg/m ³ and a thermal conductivity coefficient of 0.107 W/(m·K), the compressive strength is not more than 2.8 MPa.

The raw material mixture and the method for preparing the foam concrete mixture according to (P2) consists in mixing the following components: class C (high calcium) and class F (low calcium) fly ash and mixtures thereof, alkali metal salts and citric acid, alkali metal silicates, foaming agents and, preferably, , a foam stabilizer such as polyvinyl alcohol. Class F fly ash formulations may additionally contain Type III Portland cement. Production method: sodium silicate and sodium citrate and a foaming agent are mixed with water to form a solution, followed by its addition to a solid phase component or a mixture of solid phase components, followed by mixing until a homogeneous mixture.

The disadvantages of the known raw mixture and the method according to (P2) is also multicomponent, both in terms of solid-phase components and activating agents. In addition, an additional component is introduced - a foam stabilizer. This contributes to the emergence of additional controlled factors, which greatly complicates the process. In addition, a large amount of industrial waste as raw materials increases the risk of expanding the range of dispersion in the performance properties of foam concrete due to the instability of the properties of raw materials.

The main disadvantage of the known raw mix and method is the relatively high average density and thermal conductivity at a relatively low compressive strength of the final cellular composite. With a minimum average density of 957 kg/m ³ a compressive strength of 3.3 MPa is provided.

In both cases (P1) and (P2), an additional component is used - a foam stabilizer.

The technical solution closest to the proposed invention, taken as a prototype, is a raw mix and a method for manufacturing a cellular geopolymer mixture (Cong M., Zhang Sh., Sun D., Zhou K. Optimization of Preparation of Foamed Concrete Based on Orthogonal Experiment and Range Analysis Frontiers in Materials, Vol. a foam and water stabilizer and obtained in the following sequence: a complex of alkaline activating agents is mixed with water until an aqueous alkaline solution is formed; then dry components are mixed: kaolin, slag and fly ash, to a homogeneous mass for ≈ 3 min; then, the prepared aqueous alkaline solution is gradually poured into a uniformly mixed mixture of solid components with continuous stirring for ≈ 1 min until a geopolymer suspension is formed; in parallel, foam is prepared by mixing a foaming agent and water and a foam stabilizer; the resulting foam is placed in a mixer filled with a geopolymer slurry and mixed rapidly for about 45 seconds until a pasty foam concrete is formed.

The disadvantages of the known prototype is also a multicomponent raw mixture and a relatively high average density and thermal conductivity with a relatively low compressive strength of the final cellular composite. When the value of the average density of foam concrete 510-570 kg/m ³ and the coefficient of thermal conductivity of 0.075-0.082 W/(m·K), the compressive strength is not more than 1.36-1.73 MPa.

The invention is aimed at reducing the multicomponent nature of the raw mix, as well as reducing the average density and thermal conductivity of the final foam concrete composite while maintaining the compressive strength. This is achieved by increasing the stability of the foam mass without an additional stabilizing agent during the preparation and further hardening of the cellular composite. Increasing the stability of the foam mass makes it possible to provide a more regular shape of the pores and their more uniform distribution in the structure of the foam mass and the structure of the final (hardened) geopolymer foam concrete without burdening the raw mixture with additional components.

This is achieved by the fact that the raw mix for geopolymer foam concrete includes an aluminosilicate component of low-calcium fly ash and kaolin, an alkaline activator - sodium hydroxide NaOH, a foaming agent and water, while using low-calcium fly ash with a specific surface of 1850 cm ² /g, kaolin is used with a specific surface of 10910 cm ² /g, a foaming agent of protein origin is used in the following ratio of components, wt.%:

- low-calcium fly ash - 50.5–52.9;

– kaolin – 2–3.4;

- caustic soda NaOH - 8.5–9.1;

- foaming agent of protein origin - 0.16–0.2;

- water - the rest.

The method for producing a raw mix for geopolymer foam concrete includes preparing an alkaline solution from water and caustic soda, preparing a mixture of aluminosilicate solid-phase components - low-calcium fly ash and kaolin, preparing a geopolymer binder suspension, preparing foam by mixing a foaming agent and 1/10 part of an alkaline solution, followed by by adding it to a geopolymer binder suspension consisting of the remaining 9/10 parts of an alkaline solution and a mixture of aluminosilicate solid components: low-calcium fly ash and kaolin.

Characteristics of the materials used.

1. Fly ash is a finely dispersed coal fuel combustion residue from its mineral impurities contained in the flue gas in suspension with a specific surface area of 1850 cm ² /g (the chemical composition is presented in Table 1).

2. Kaolin is a monomineral clay aluminosilicate rock with a specific surface area of 10910 cm ² /g (the chemical composition is presented in Table 1).

3. Water GOST 23732-2011 “Water for concrete and mortar. Specifications".

4. Alkaline activator - sodium hydroxide NaOH, GOST R 55064-2012. “Technical caustic soda. Specifications".

5. Foaming agent of protein origin, for example, Biofoam (manufactured by BioFomm LLC).

Table 1

Chemical composition of low-calcium fly ash and kaolin

Component The content of oxides, wt.%: Σ _{SiO2 Al2O3 _ Fe2O3 _ TiO2 K2O} MgO CaO _{P2O5 _ N2O} p.p.p. fly ash 56.98 25.29 4.63 0.97 0.65 1 3.74 0.36 0.63 6.07 99.75 Kaolin 53.8 43.4 1.02 0.58 0.56 0.21 0.01 0.06 - 0.03 99.64

table 2

Characteristics of the proposed compositions of geopolymer foam concrete and prototype

Lineups Component composition, wt.%: Compressive strength, MPa Medium
density,
kg / m ³ Thermal conductivity coefficient, W / m ² ∙ ^o С fly ash kaolin sodium hydroxide NaOH blowing agent
protein
origin water 1 50.5 3.4 9.1 0.16 36.84 1.67 506 0.068 2 51.6 2.8 8.8 0.18 36.62 1.85 488 0.056 3 52.9 2 8.5 0.2 36.4 1.99 514 0.074 Prototype - 1.73 570 0.082

The use of this method for the preparation of geopolymer foam mass at the specified ratio of components makes it possible to increase the stability of the foam mass. This leads to the formation of a more regular shape of the pores and their more uniform distribution in the structure of the final (hardened) geopolymer foam concrete without burdening the raw mix with additional components. As a result, the formation of the correct pore structure allows to reduce the density of foam concrete from 10 to 14% compared to the prototype, while maintaining the compressive strength unchanged.

Example (table No. 2, composition No. 2).

At the first stage, an alkaline solution was prepared by mixing 547 kg of water and 131.7 kg of alkali until the solid component was completely dissolved. Separately prepared 70.6 kg of foam in an alkaline medium by mixing 2.69 kg of foaming agent and 1/10 of the alkaline solution (ie 67.9 kg); preparation of a mixture of solid-phase components: 772 kg of low-calcium fly ash and 71.9 kg of kaolin by mixing them for 1-1.5 minutes; preparation of a binder geopolymer suspension by mixing the remaining 9/10 of the alkaline solution (i.e. 610.8 kg) and a mixture of solid components - low-calcium fly ash and kaolin for 2-3 minutes until a homogeneous mass; introduction of foam into the binder geopolymer suspension with stirring for 4-5 minutes until a homogeneous foam mass is formed.

Claims (3)

1. Raw mixture for geopolymer foam concrete, including an aluminosilicate component from low-calcium fly ash and kaolin, an alkaline activator - sodium hydroxide NaOH, a foaming agent and water, characterized in that low-calcium fly ash with a specific surface area of 1850 cm ² /g is used, kaolin is used with a specific surface of 10910 cm ² /g, a foaming agent of protein origin is used in the following ratio of components, wt.%: fly ash low calcium 50.5-52.9 kaolin 2-3.4 sodium hydroxide NaOH 8.5-9.1 protein foaming agent origin 0.16-0.2 water rest 2. A method for producing a raw mix for geopolymer foam concrete according to claim 1, including preparing an alkaline solution from water and caustic soda, preparing a mixture of aluminosilicate solid phase components - low-calcium fly ash and kaolin, preparing a geopolymer binder suspension, preparing foam by mixing a foaming agent and 1 /10 parts of an alkaline solution, followed by its addition to a geopolymer binder suspension consisting of the remaining 9/10 parts of an alkaline solution and a mixture of aluminosilicate solid components: low-calcium fly ash and kaolin.