Alkali-activated foam concrete and preparation method thereof

Abstract

The invention relates to alkali-activated foam concrete and a preparation method thereof. The alkali-activated foam concrete comprises the following raw materials in parts by weight: 55-65 parts by weight of slag powder, 25-35 parts by weight of fly ash, 25-35 parts by weight of waste concrete powder, 57-67 parts by weight of a multi-element alkali activator, 6-8 parts by weight of a retarder, 5-7 parts by weight of foam and 22-26 parts by weight of water. According to the invention, industrial waste slag powder, fly ash and waste concrete powder are used as cementing materials, the source is green, the cost is low, the concept of low carbon and environmental protection of building material design is met, and the cyclic utilization of industrial waste is facilitated. The main crystalline components in the waste concrete powder are dicalcium silicate and calcium oxide, the hydration reaction of dicalcium silicate is slow, the hydration heat is small, the mold entering temperature of the foam concrete can be reduced, shrinkage cracks of the foam concrete can be reduced, and the water resistance and the long-term compressive strength after 28 days of the foam concrete can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to alkali-activated foam concrete and a preparation method thereof. Background Art

[0002] Foam concrete is a lightweight, porous building material made from raw materials such as cement, sand and stabilizers. Foam concrete has good thermal insulation, sound absorption and seismic performance, and is light and easy to process. It has been widely used in housing construction, underground engineering, tunnel lining, roadbed filling and other fields. However, in actual engineering applications, due to the high water-cement ratio, foam concrete products are prone to mold collapse, low strength and large drying shrinkage in the early stage. In addition, since traditional foam concrete uses cement and natural river sand as cementing materials, it not only has a long initial setting time, but also causes a lot of environmental pollution during the cement production process. The large amount of natural river sand consumption will also bring serious resource waste.

[0003] In addition, how to deal with the large amount of concrete construction waste generated every year due to various reasons is also an urgent problem to be solved. Traditional concrete construction waste is generally transported to the suburbs for stacking or burying, which not only occupies a large amount of land, but also pollutes the environment. Summary of the invention

[0004] The purpose of the invention is to provide an alkali-activated foamed concrete to solve the technical problems of easy mold collapse, low strength, large drying shrinkage value of the existing foamed concrete and difficulty in handling the existing concrete construction waste.

[0005] The second object of the present invention is to provide a method for preparing alkali-activated foamed concrete.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] An alkali-activated foamed concrete comprises the following raw materials in parts by weight: 55-65 parts by weight of slag powder, 25-35 parts by weight of fly ash, 25-35 parts by weight of waste concrete powder, 57-67 parts by weight of a polybasic activator, 6-8 parts by weight of a retarder, 5-7 parts by weight of foam, and 22-26 parts by weight of water.

[0008] Furthermore, the particle size of the fly ash is ≤15 μm.

[0009] Furthermore, the particle size of the waste concrete powder is ≤75 μm.

[0010] Furthermore, the slag powder includes S95 grade slag powder and ultrafine slag powder, the mass ratio of the S95 grade slag powder to the ultrafine slag powder is 75-85:15-25; the ultrafine slag powder is made by grinding the S95 grade slag powder, and the particle size of the ultrafine slag powder is ≤5μm.

[0011] Furthermore, the preparation method of the polybasic activator is: dissolving 17-22 parts by weight of solid sodium hydroxide in 17-22 parts by weight of water at 1-3°C to obtain a sodium hydroxide solution, and mixing the sodium hydroxide solution with 240-260 parts by weight of water glass to obtain the polybasic activator; the modulus of the polybasic activator is 1.4-1.8.

[0012] Furthermore, the retarder is sodium gluconate.

[0013] Furthermore, the foam is foamed by a cement foaming agent.

[0014] A method for preparing alkali-activated foamed concrete comprises the following steps:

[0015] S1: Prepare materials

[0016] Slag powder: S95 grade slag powder is dried to a constant mass and then ground to a particle size of ≤5 μm to obtain ultrafine slag powder, which is then mixed with S95 grade slag powder;

[0017] Fly ash: obtained by drying Class I fly ash to a constant mass and then grinding it to a particle size of ≤15μm;

[0018] Waste concrete powder: waste concrete is calcined at 400-550°C to obtain activated waste concrete powder, and the activated waste concrete powder is ground to a particle size of ≤75 μm;

[0019] Foam: dilute the cement foaming agent and water in a mass ratio of 1:60-1:80 to obtain a foaming liquid, and foam the foaming liquid to obtain;

[0020] S2: Mixture preparation

[0021] The slag powder, fly ash, waste concrete powder and retarder in the formula are mixed and slowly stirred to obtain a mixture;

[0022] S3: Preparation of polybasic activator

[0023] Dissolve the solid sodium hydroxide in water at 1-3°C to obtain a sodium hydroxide solution, then add the water glass in the formula amount, stir evenly, and let stand to cool to room temperature to obtain a sodium hydroxide solution;

[0024] S4: Mortar preparation

[0025] Add the polybasic activator and the formulated amount of water into the mixture, and slowly stir until it is uniform;

[0026] S5: Preparation of alkali activated foamed concrete slurry

[0027] Add the foam into the mortar and stir slowly for 1-2 minutes until it is completely uniform;

[0028] S6: Preparation of alkali activated foamed concrete

[0029] The alkali-activated foamed concrete slurry is poured into a test mold, and then demoulded and cured to obtain the product.

[0030] Beneficial effects of the present invention:

[0031] The present invention uses industrial waste slag powder, fly ash and waste concrete powder as cementitious materials, which are green in source and low in cost. They conform to the concept of low-carbon and environmentally friendly design of building materials and are conducive to the recycling of industrial waste. The main crystalline components in waste concrete powder are dicalcium silicate and calcium oxide. The hydration reaction of dicalcium silicate is slow and the hydration heat is small, which can reduce the mold entry temperature of foam concrete, reduce the shrinkage cracks of foam concrete, and improve the water resistance and long-term compressive strength of foam concrete after 28 days. The alkali-activated foam concrete with a dry density grade of A07 prepared by the present invention has a 28d compressive strength of 4.2MPa, which is significantly better than traditional cement foam concrete. The alkali-activated foam concrete prepared by the present invention significantly improves the compressive strength of foam concrete on the premise that the water absorption rate and shrinkage strength meet the regulatory requirements.

[0032] The alkali-activated foamed concrete prepared by the present invention has a fast initial setting speed and can be initially solidified within 20 minutes after pouring, which can effectively avoid the early collapse of the foamed concrete. The alkali-activated foamed concrete with a dry density grade of A07 prepared by the present invention has an initial setting time of no more than 20 minutes.

[0033] The present invention produces alkali-activated foamed concrete with excellent mechanical properties, low water absorption and good shrinkage performance, which can ensure the normal construction application of the alkali-activated foamed concrete and has high durability. The raw materials of the present invention are all industrial waste products, no additional resource waste will be generated, and the environmental friendliness is excellent. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the embodiments of the present invention.

[0035] The water glass of the present invention is calculated by weight, and the substances are as follows: SiO2 accounts for 30%, Na2O accounts for 13.5%, and H2O accounts for 56.5%.

[0036] Example 1

[0037] The alkali-activated foamed concrete of this embodiment includes the following raw materials: 1200 g of slag powder, 600 g of fly ash, 600 g of waste concrete powder, 1240 g of polybasic activator, 120 g of foam, 140 g of retarder, and 480 g of water.

[0038] The average particle size of fly ash is ≤15μm; the average particle size of waste concrete powder is ≤75μm; the modulus of the polybasic activator is 1.6; the retarder is 95% pure sodium gluconate powder; the foam is produced by using YS-200 composite cement foaming agent through a foaming machine.

[0039] The preparation method of alkali-activated foamed concrete of Example 1 comprises the following steps:

[0040] S1: Prepare materials

[0041] Slag powder: 80% of S95 grade slag powder and 20% of ultrafine slag powder are mixed; the ultrafine slag powder is prepared by drying the S95 grade slag powder at 60°C to a constant mass and then grinding it to an average particle size of ≤5μm using an ultrafine tube mill technology;

[0042] Fly ash: After drying Class I fly ash at 60°C to a constant mass, grind it to an average particle size of ≤15μm using superheated steam kinetic energy grinding technology;

[0043] Waste concrete powder: waste concrete is calcined at 550℃ to obtain activated waste concrete powder, and the activated waste concrete powder is ultra-finely ground to an average particle size of ≤75μm;

[0044] Foaming liquid: dilute YS-200 composite cement foaming agent and water at a mass ratio of 1:60 to form a foaming liquid.

[0045] S2: Mixture preparation

[0046] Slag powder, fly ash, waste concrete powder and retarder are mixed according to the formula, put into a mixer and slowly stirred until a uniform mixture is obtained.

[0047] S3: Preparation of polybasic activator

[0048] 80 g of solid sodium hydroxide was dissolved in 80 g of water at 1° C. to obtain a sodium hydroxide aqueous solution with a mass fraction of 50%. The obtained sodium hydroxide aqueous solution was mixed with 1080 g of water glass and stirred evenly, and then allowed to stand and cool to room temperature.

[0049] S4: Preparation of mortar

[0050] Add the polybasic activator and the formulated amount of water into the mixture in S2, and slowly stir until it is uniform to obtain mortar.

[0051] S5: Preparation of alkali activated foamed concrete slurry

[0052] Use a foaming agent to physically foam the foaming liquid in S1 to obtain foam, add the foam to the mortar in S4, and slowly stir for 1-2 minutes until it is completely uniform.

[0053] S6: Preparation of alkali activated foamed concrete

[0054] Pour the alkali-activated foamed concrete slurry in S5 into a test mold of required specifications, demould after 1 day, and cure to the specified age.

[0055] Comparative Example 1

[0056] The cement-fly ash foamed concrete of Comparative Example 1 includes the following raw materials: 1200 g of cement, 1200 g of fly ash, 960 g of water, and 120 g of foam.

[0057] The cement used is ordinary Portland cement of grade PO42.5 specified in GB / T1596-2017 "Fly ash used in cement and concrete";

[0058] The fly ash adopts the Class I ground fly ash specified in GB / T1596-2017 "Fly ash used in cement and concrete"; the foam is made by using YS-200 composite cement foaming agent through a foaming machine.

[0059] The preparation method of the cement-fly ash foamed concrete of Comparative Example 1 is as follows:

[0060] S1: Mix the formulated amount of cement and fly ash and put them into a mixer and slowly stir until they are uniform;

[0061] S2: Add the formulated amount of water into a blender and mix well to form a slurry;

[0062] S3: diluting the foaming agent and water in a mass ratio of 1:60 to form a desired foaming liquid, and using a foaming machine to foam to obtain foam;

[0063] S4: Add foam into the slurry, stir slowly for 3 minutes and then pour.

[0064] Comparative Example 2

[0065] The raw materials of the alkali-activated foamed concrete of Comparative Example 2 and the alkali-activated foamed concrete of Example 1 are substantially the same. The difference between the alkali-activated foamed concrete of Comparative Example 2 and the alkali-activated foamed concrete of Example 1 is that Comparative Example 2 contains 1680 g of slag powder, 360 g of fly ash, and 360 g of waste concrete powder.

[0066] The preparation method of the alkali-activated foamed concrete of Comparative Example 2 is the same as that of Example 1.

[0067] Comparative Example 3

[0068] The raw materials of the alkali-activated foamed concrete of Comparative Example 3 and the alkali-activated foamed concrete of Example 1 are substantially the same, and the difference between the alkali-activated foamed concrete of Comparative Example 3 and the alkali-activated foamed concrete of Example 1 is that Comparative Example 3 contains 720 g of slag powder, 840 g of fly ash, and 840 g of waste concrete powder.

[0069] The preparation method of the alkali-activated foamed concrete of Comparative Example 3 is the same as that of Example 1.

[0070] Comparative Example 4

[0071] The alkali-activated foamed concrete of Comparative Example 4 includes the following raw materials: 1200 g of slag powder, 600 g of fly ash, 600 g of waste concrete powder, 1240 g of polybasic activator, 120 g of foam, 140 g of retarder, and 480 g of water.

[0072] Among them, 100% of the slag powder is S95 grade slag powder;

[0073] The fly ash adopts Class I fly ash;

[0074] Waste concrete powder is obtained by calcining waste concrete at 550℃;

[0075] The modulus of the polybasic activator was adjusted to 1.6;

[0076] The retarder is 95% pure sodium gluconate powder;

[0077] The foam is produced by using YS-200 composite cement foaming agent through a foaming machine.

[0078] The preparation method of the alkali-activated foamed concrete of Comparative Example 4 comprises the following steps:

[0079] S1: Prepare materials

[0080] Slag powder: Dry the S95 grade slag powder at 60°C to a constant mass;

[0081] Fly ash: Dry Class I fly ash at 60°C to a constant mass;

[0082] Waste concrete powder: Calcine the waste concrete at 550℃ to obtain activated waste concrete powder;

[0083] Foaming liquid: dilute YS-200 composite cement foaming agent and water in a mass ratio of 1:60 to form the required foaming liquid for use.

[0084] S2: Mixture preparation

[0085] Slag powder, fly ash, waste concrete powder and retarder are mixed according to the formula ratio, put into a mixer and slowly stirred until uniform to obtain a mixture.

[0086] S3: Preparation of polybasic activator

[0087] 80 g of solid sodium hydroxide was dissolved in 80 g of water at 1° C. to prepare a 50% NaOH aqueous solution by mass. The obtained NaOH aqueous solution was mixed with 1080 g of water glass and stirred evenly, and then allowed to stand and cool to room temperature.

[0088] S4: Mortar preparation

[0089] Add the polybasic activator and water to the mixture prepared in S2, and slowly stir until it is uniform to obtain mortar.

[0090] S5: Preparation of alkali activated foamed concrete slurry

[0091] The foaming liquid obtained in S1 is physically foamed using a foaming machine to obtain foam, and the foam is added to the mortar obtained in S4, and slowly stirred for 1-2 minutes until it is completely uniform, thereby obtaining an alkali-activated foamed concrete slurry.

[0092] S6: Preparation of alkali activated foamed concrete

[0093] The alkali-activated foamed concrete slurry prepared in S5 is poured into a test mold of the required size, demolded after 1 day, and cured to the specified age.

[0094] Experimental Example 1

[0095] Basic performance test of foam concrete

[0096] The basic properties of the foamed concrete of Example 1 and Comparative Examples 1-4 were tested, and the test items included the dry density, initial setting time, compressive strength, water absorption and drying shrinkage of the foamed concrete. The test methods for dry density, 28d compressive strength and water absorption refer to "Foamed Concrete" (JG / T266-2011), and the test method for drying shrinkage refers to the specification "Test Methods for Performance of Autoclaved Aerated Concrete" (GB / T 11969-2020).

[0097] The test results are shown in Table 1:

[0098] Table 1 Basic performance test results of foamed concrete of Example 1 and Comparative Examples 1-4

[0099]

[0100] From Table 1, we can see that:

[0101] The initial setting time of the alkali-activated foamed concrete prepared in Example 1, Comparative Example 2 and Comparative Example 3 is greatly improved compared with the initial setting time of the traditional cement-fly ash foamed concrete prepared in Comparative Example 1.

[0102] The compressive strength of Example 1 is better than that of Comparative Example 1, which indicates that the alkali-activated foamed concrete prepared by the present invention is superior to the traditional cement-fly ash foamed concrete in terms of mechanical properties.

[0103] In Comparative Example 2, Example 1 and Comparative Example 3, the amount of fly ash and waste concrete powder gradually increased, the compressive strength first increased and then decreased, and the drying shrinkage value gradually decreased, which shows that the addition of fly ash and waste concrete powder can effectively improve the drying shrinkage performance of alkali slag-fly ash foamed concrete, but will greatly weaken the mechanical properties. This is mainly because the activity of fly ash and waste concrete powder is much lower than that of slag powder, resulting in less hydration products generated in a shorter initial setting time, which is not conducive to the formation of compressive strength. However, due to the low activity of fly ash and waste concrete powder, the foamed concrete is still undergoing hydration reaction in the late stage of slurry coagulation. At this time, the early pore wall has sufficient strength to resist the capillary tension caused by water loss. At this time, the hydration product can play a role in filling the pores in the system and optimizing the pore structure. In addition, the fine particles in the fly ash play a micro-aggregate effect and can be filled in the pores inside the system, which can also play the same role, which is conducive to inhibiting the drying shrinkage of the foamed concrete.

[0104] The alkali-activated foamed concrete materials and qualities of Example 1 and Comparative Example 4 are exactly the same, but the compressive strength, water absorption rate and drying shrinkage value of Example 1 are better than those of Comparative Example 4, indicating that when preparing alkali-activated foamed concrete, ultrafine tube grinding of S95 grade slag powder, superheated steam kinetic grinding of Class I fly ash, and ultrafine grinding of activated waste concrete powder can improve the interface structure between foamed concrete aggregates, thereby improving the strength, impermeability and drying shrinkage performance of foamed concrete.

[0105] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. An alkali-activated foamed concrete, characterized in that: The invention comprises the following raw materials in parts by weight: 55-65 parts by weight of slag powder, 25-35 parts by weight of fly ash, 25-35 parts by weight of waste concrete powder, 57-67 parts by weight of polybasic activator, 6-8 parts by weight of retarder, 5-7 parts by weight of foam and 22-26 parts by weight of water.

2. The alkali-activated foamed concrete according to claim 1, characterized in that: The particle size of the fly ash is ≤15 μm.

3. The alkali-activated foamed concrete according to claim 1, characterized in that: The particle size of the waste concrete powder is ≤75 μm.

4. The alkali-activated foamed concrete according to claim 1, characterized in that: The slag powder includes S95 grade slag powder and ultrafine slag powder, and the mass ratio of the S95 grade slag powder to the ultrafine slag powder is 75-85:15-25; the ultrafine slag powder is made by grinding the S95 grade slag powder, and the particle size of the ultrafine slag powder is ≤5μm.

5. The alkali-activated foamed concrete according to claim 1, characterized in that: The preparation method of the polybasic activator is as follows: 17-22 parts by weight of solid sodium hydroxide is dissolved in 17-22 parts by weight of water at 1-3° C. to obtain a sodium hydroxide solution, and the sodium hydroxide solution is mixed with 240-260 parts by weight of water glass to obtain the polybasic activator; the modulus of the polybasic activator is 1.4-1.

8.

6. The alkali-activated foamed concrete according to claim 1, characterized in that: The retarder is sodium gluconate.

7. The alkali-activated foamed concrete according to claim 1, characterized in that: The foam is foamed by a cement foaming agent.

8. A method for preparing alkali-activated foamed concrete according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: Prepare materials Slag powder: S95 grade slag powder is dried to a constant mass and then ground to a particle size of ≤5 μm to obtain ultrafine slag powder, which is then mixed with S95 grade slag powder; Fly ash: obtained by drying Class I fly ash to a constant mass and then grinding it to a particle size of ≤15μm; Waste concrete powder: waste concrete is calcined at 400-550°C to obtain activated waste concrete powder, and the activated waste concrete powder is ground to a particle size of ≤75 μm; Foam: dilute the cement foaming agent and water in a mass ratio of 1:60-80 to obtain a foaming liquid, and foam the foaming liquid to obtain; S2: Mixture preparation The slag powder, fly ash, waste concrete powder and retarder in the formula are mixed and slowly stirred to obtain a mixture; S3: Preparation of polybasic activator Dissolve the solid sodium hydroxide in water at 1-3°C to obtain a sodium hydroxide solution, then add the water glass in the formula amount, stir evenly, and let stand to cool to room temperature to obtain a sodium hydroxide solution; S4: Mortar preparation Add the polybasic activator and the formulated amount of water into the mixture, and slowly stir until it is uniform; S5: Preparation of alkali activated foamed concrete slurry Add the foam into the mortar and stir slowly for 1-2 minutes until it is completely uniform; S6: Preparation of alkali activated foamed concrete The alkali-activated foamed concrete slurry is poured into a test mold, and then demoulded and cured to obtain the product.

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