Lightweight foam soil and preparation method thereof

Abstract

The invention discloses a light foamed soil and a preparation method thereof, belonging to the technical field of foamed soil preparation. The light foamed soil is prepared by mixing a slurry component and a foam component, wherein the slurry component comprises cement, fine sand, modified bentonite, a water reducer and water; and the foam component comprises a composite foaming agent, hydroxyethyl cellulose and water. The invention uses an organic modification method to modify bentonite, and the prepared modified bentonite is rich in siloxane structure. On the one hand, the siloxane structure is hydrolyzed to produce silanol, thereby improving the bonding tightness between bentonite and other raw materials such as cement, fine sand and foaming agent. On the other hand, the siloxane structure is self-condensed to produce an organic hydrophobic network, thereby improving the anti-seepage performance of the foamed soil. The invention compound the protein foaming agent with a surfactant to prepare the composite foaming agent, and finally prepare the modified foaming agent with excellent foaming performance and foam stability. The light foamed soil prepared by using the modified foaming agent has uniform compressive strength and anti-seepage performance in all directions.

Description

Technical Field

[0001] The invention belongs to the technical field of foam soil preparation, and in particular relates to lightweight foam soil and a preparation method thereof. Background Art

[0002] Lightweight foam soil is a new type of building energy-saving material that is waste-recycling, energy-saving, environmentally friendly and low-cost. The preparation principle of lightweight foam soil: add the foam into the mixed cement slurry and stir evenly. When the solidifying material binds the soil particles together, a large number of tiny pores are left in the solidified body, thereby reducing the density of the foam soil. Some admixtures can also be added to improve the corresponding mechanical properties.

[0003] With the improvement and development of foundation treatment technology, lightweight foam soil has gradually attracted the attention of the civil engineering community as a more advanced filling technology because of its advantages such as light weight, good seismic resistance and easy construction. It can reduce the lateral pressure on the retaining wall and the additional stress on the original foundation, reduce the total settlement and uneven settlement, improve the stability of the foundation and the impact of the new roadbed on the old embankment, and reduce the area occupied by the slope.

[0004] However, due to the insufficient foam stability of the foaming agent on the market, the prepared lightweight foam soil has the problems of low compressive strength and poor impermeability. After pouring, the lightweight foam soil is prone to surface cracking and water seepage due to its porous and loose structure. The poor impermeability will reduce the freeze-thaw resistance, affecting the applicability of lightweight foam soil in scenes with high freeze-thaw resistance requirements such as tunnels. Summary of the invention

[0005] The purpose of the present invention is to provide a lightweight foam soil and a preparation method thereof, and to improve the mechanical properties and anti-permeability properties of the lightweight foam soil by preparing and studying the lightweight foam soil and the preparation method thereof.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A light foam soil is prepared by mixing a slurry component and a foam component in a mass ratio of 10:3.5-4, wherein:

[0008] The slurry components include the following raw materials in parts by weight: 35-60 parts of cement, 28-35 parts of fine sand, 8-10 parts of modified bentonite, 0.2-0.3 parts of water reducing agent, and 15-25 parts of water;

[0009] The foam component comprises the following raw materials in parts by weight: 55-65 parts of a composite foaming agent, 13-15 parts of hydroxyethyl cellulose and 5-8 parts of water.

[0010] Furthermore, the preparation process of modified bentonite is as follows: bentonite is ground through a 200 mesh sieve, calcined at 300°C for 2-3h, bentonite and γ-(2,3-epoxypropoxy)propyltrimethoxysilane are added to anhydrous ethanol, stirred and mixed evenly, deionized water is added, the pH is adjusted to 8-10 with sodium hydroxide, stirring is continued for 3-4h, centrifuged to obtain a precipitate, the precipitate is washed with deionized water until neutral, and dried at 60°C to constant weight to obtain modified bentonite.

[0011] Furthermore, the usage ratio of calcined bentonite, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, anhydrous ethanol and deionized water is 20g:2g:50-80mL:350-400mL.

[0012] Furthermore, the water reducer is a polycarboxylate water reducer.

[0013] Furthermore, the composite foaming agent is prepared by mixing a protein foaming agent, a surfactant and a nano-modifier in a mass ratio of 60:10-12:0.05-0.1.

[0014] Furthermore, the protein foaming agent is a FH-200 protein foaming agent.

[0015] Furthermore, the surfactant is one of sodium α-olefin sulfonate, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate.

[0016] The above-mentioned sodium α-olefin sulfonate, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate are all anionic surfactant foaming agents. Anionic surfactant foaming agents generally have excellent foaming ability. The foaming volume of foaming agents with appropriate concentrations can reach more than 800 mL, especially sodium dodecyl sulfate and sodium dodecylbenzene sulfonate, which have particularly significant foaming performance. However, the foam stability of anionic surfactant foaming agents is poor.

[0017] Furthermore, the nano modifier is one of nano silicon dioxide, nano graphene, and nano calcium carbonate, among which nano silicon dioxide.

[0018] Furthermore, the method for preparing the lightweight foam soil comprises the following steps:

[0019] A1. Prepare foam: Add foaming agent and foam stabilizer to water for mechanical foaming, and control the foam density to 45-55kg / m 3 ;

[0020] A2. Prepare slurry: Add cement, fine sand and water reducing agent into water and stir until uniform to obtain slurry;

[0021] A3. Mixing: Add foam to the slurry, stir at a speed of 60-120r / min to form a uniform slurry, pour the slurry into a mold, cover with plastic film and cure for 48 hours, take out, and obtain lightweight foam soil.

[0022] Beneficial effects of the present invention:

[0023] First, the present invention utilizes an organic modification method to modify bentonite, and the prepared modified bentonite is rich in siloxane structure. On the one hand, the siloxane structure is hydrolyzed to produce silanol, which improves the bonding tightness between bentonite and other raw materials such as cement, fine sand and foaming agent. On the other hand, the siloxane structure self-condenses to produce an organic hydrophobic network of Si-O-Si, which improves the anti-seepage performance of the foamed soil. Then, bentonite can undergo a curing reaction with the hydration products of materials such as cement and fine sand to form hydrated calcium silicate, further enhancing the mechanical compressive strength of the foamed soil. Finally, bentonite absorbs the leaked free water through water absorption expansion, and offsets the frost heave and thaw shrinkage effect through water loss shrinkage, thereby improving the anti-freeze and thaw performance of the foamed soil.

[0024] The present invention compounds a protein foaming agent with a surfactant. The active substance in the protein foaming agent has a large molecular weight, strong intermolecular interaction, high liquid film strength, and good foam stability. However, due to the strong intermolecular interaction in the protein foaming agent, its foaming performance is poor. The present invention utilizes the dispersing effect of the surfactant to unfold the macromolecular chains of the protein, thereby reducing the surface tension of the protein foaming agent, and finally prepares a modified foaming agent with excellent foaming performance and foam stability. The lightweight foam soil prepared by using the modified foaming agent has uniform compressive strength and anti-seepage performance in all directions. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] Preparation of modified bentonite:

[0028] The bentonite was ground through a 200 mesh sieve and calcined at 300°C for 2h. The bentonite and γ-(2,3-epoxypropoxy)propyltrimethoxysilane were added to anhydrous ethanol, stirred and mixed evenly, and deionized water was added. The pH was adjusted to 8 with sodium hydroxide, and stirring was continued for 3h. The precipitate was obtained by centrifugation. The precipitate was washed with deionized water until neutral, and dried at 60°C to constant weight to obtain modified bentonite, wherein the amount ratio of calcined bentonite, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, anhydrous ethanol, and deionized water was 20g:2g:50mL:350mL.

[0029] Example 2

[0030] Preparation of modified bentonite:

[0031] The bentonite was ground through a 200 mesh sieve and calcined at 300°C for 3h. The bentonite and γ-(2,3-epoxypropoxy)propyltrimethoxysilane were added to anhydrous ethanol, stirred and mixed evenly, and deionized water was added. The pH was adjusted to 9 with sodium hydroxide, and stirring was continued for 4h. The precipitate was obtained by centrifugation. The precipitate was washed with deionized water until neutral, and dried at 60°C to constant weight to obtain modified bentonite, wherein the amount ratio of calcined bentonite, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, anhydrous ethanol, and deionized water was 20g:2g:70mL:380mL.

[0032] Example 3

[0033] Preparation of modified bentonite:

[0034] The bentonite was ground through a 200 mesh sieve and calcined at 300°C for 3h. The bentonite and γ-(2,3-epoxypropoxy)propyltrimethoxysilane were added to anhydrous ethanol, stirred and mixed evenly, and deionized water was added. The pH was adjusted to 10 with sodium hydroxide, and stirring was continued for 4h. The precipitate was obtained by centrifugation. The precipitate was washed with deionized water until neutral, and dried at 60°C to constant weight to obtain modified bentonite, wherein the amount ratio of calcined bentonite, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, anhydrous ethanol, and deionized water was 20g:2g:80mL:400mL.

[0035] Example 4

[0036] Preparation of lightweight foam soil:

[0037] Preparation: Lightweight foam soil is prepared by mixing a slurry component and a foam component in a mass ratio of 10:3.5, wherein the slurry component includes the following raw materials in parts by weight: 35 parts of cement, 28 parts of fine sand, 8 parts of modified bentonite prepared in Example 1, 0.2 parts of water reducer, and 15 parts of water; the foam component includes the following raw materials in parts by weight: 55 parts of composite foaming agent, 13 parts of hydroxyethyl cellulose, and 5 parts of water, wherein:

[0038] The water reducer is a polycarboxylate water reducer (commercially available polycarboxylate water reducer, brand name ZY-HS);

[0039] The composite foaming agent is a mixture of a protein foaming agent, a surfactant and a nano-modifier in a mass ratio of 60:10:0.05. The protein foaming agent is a FH-200 protein foaming agent (developed by Beijing Guanghui Company); the surfactant is sodium α-olefin sulfonate;

[0040] The nano modifier is nano silicon dioxide (brand A200, particle size 12 nm).

[0041] A method for preparing lightweight foam soil comprises the following steps:

[0042] A1. Prepare foam: Add foaming agent and foam stabilizer to water for mechanical foaming, and control the foam density to 45kg / m 3 , use a 1L container to calibrate and measure the density of the foam to determine whether the foam density meets 50±5kg / m 3 If it is unqualified, it is necessary to adjust the speed of the mechanical foaming (foaming machine) and prepare new foam again until the released foam is qualified;

[0043] A2. Prepare slurry: Add cement, fine sand and water reducing agent into water and stir until uniform to obtain slurry;

[0044] A3. Mixing: Add foam to the slurry and stir at a speed of 60r / min to form a uniform slurry. Pour the slurry into a mold, cover it with plastic film and cure it for 48 hours. Take it out to obtain lightweight foam soil. Since lightweight foam soil has a low density and a high water content, a certain depression will appear in the slurry during the natural hardening process. In order to obtain a sample of standard size, an additional depression height must be reserved during pouring so that the foam lightweight concrete slurry is 1-2cm higher than the mold. During the pouring process, the mold can be slightly vibrated to help the slurry be more evenly distributed in the mold and eliminate any large bubbles that may exist.

[0045] Example 5

[0046] Preparation of lightweight foam soil:

[0047] Preparation: Lightweight foam soil is prepared by mixing a slurry component and a foam component in a mass ratio of 10:3.8, wherein the slurry component includes the following raw materials in parts by weight: 55 parts of cement, 30 parts of fine sand, 10 parts of modified bentonite prepared in Example 2, 0.3 parts of water reducer, and 20 parts of water; the foam component includes the following raw materials in parts by weight: 60 parts of composite foaming agent, 14 parts of hydroxyethyl cellulose, and 7 parts of water, wherein:

[0048] The water reducer is a polycarboxylate water reducer (commercially available polycarboxylate water reducer, brand name ZY-HS);

[0049] The composite foaming agent is a mixture of a protein foaming agent, a surfactant and a nano-modifier in a mass ratio of 60:11:0.081. The protein foaming agent is a FH-200 protein foaming agent (developed by Beijing Guanghui Company); the surfactant is sodium dodecyl sulfate;

[0050] The nano-modifier is nano-graphene.

[0051] A method for preparing lightweight foam soil comprises the following steps:

[0052] A1. Prepare foam: Add foaming agent and foam stabilizer to water for mechanical foaming, and control the foam density to 50kg / m 3 ;

[0053] A2. Prepare slurry: Add cement, fine sand and water reducing agent into water and stir until uniform to obtain slurry;

[0054] A3. Mixing: Add foam to the slurry, stir at a speed of 80r / min to form a uniform slurry, pour the slurry into a mold, cover with plastic film and cure for 48 hours, take out, and obtain lightweight foam soil.

[0055] Example 6

[0056] Preparation of lightweight foam soil:

[0057] Preparation: Lightweight foam soil is prepared by mixing a slurry component and a foam component in a mass ratio of 10:4, wherein the slurry component includes the following raw materials in parts by weight: 60 parts of cement, 35 parts of fine sand, 10 parts of modified bentonite prepared in Example 3, 0.3 parts of water reducer, and 25 parts of water; the foam component includes the following raw materials in parts by weight: 65 parts of composite foaming agent, 15 parts of hydroxyethyl cellulose, and 8 parts of water, wherein:

[0058] The water reducer is a polycarboxylate water reducer (commercially available polycarboxylate water reducer, brand name ZY-HS);

[0059] The composite foaming agent is a mixture of a protein foaming agent, a surfactant and a nano-modifier in a mass ratio of 60:12:0.1. The protein foaming agent is a FH-200 protein foaming agent (developed by Beijing Guanghui Company); the surfactant is sodium dodecylbenzene sulfonate;

[0060] The nano modifier is nano calcium carbonate.

[0061] A method for preparing lightweight foam soil comprises the following steps:

[0062] A1. Prepare foam: Add foaming agent and foam stabilizer to water for mechanical foaming, and control the foam density to 55kg / m 3 ;

[0063] A2. Prepare slurry: Add cement, fine sand and water reducing agent into water and stir until uniform to obtain slurry;

[0064] A3. Mixing: Add foam to the slurry, stir at a speed of 120r / min to form a uniform slurry, pour the slurry into a mold, cover with plastic film and cure for 48 hours, take out, and obtain lightweight foam soil.

[0065] Comparative Example 1

[0066] Comparative Example 1 is a control experiment of Example 4, in which the modified bentonite prepared in Example 1 of the slurry component in Example 4 is removed, and the other raw materials and the preparation process remain unchanged, thereby obtaining a lightweight foam soil.

[0067] Comparative Example 2

[0068] Comparative Example 2 is a control experiment of Example 5, in which the nano-modifier used in the preparation process of the composite foaming agent in the foam component of Example 5 is removed, and the other raw materials and the preparation process remain unchanged, thereby obtaining a lightweight foam soil.

[0069] Comparative Example 3

[0070] Comparative Example 2 is a control experiment of Example 6, in which the composite foaming agent in the foam component of Example 6 is replaced with a single small molecule surfactant sodium dodecylbenzene sulfonate, and the other raw materials and preparation process remain unchanged, thereby obtaining a lightweight foam soil.

[0071] The performance of the lightweight foamed soil prepared in Examples 4 to 6 and Comparative Examples 1 to 3 was tested according to the following test standards. The test results are shown in Table 1:

[0072] The dry density, compressive strength and water absorption were determined according to Foamed Concrete (JG / T266-2011), where the sample size of lightweight foamed soil was 100 mm × 100 mm × 100 mm. Specifically:

[0073] Dry density: Take three lightweight foam soil samples as a group, measure the length values ​​in three directions one by one, and measure the length value in each direction once at both ends and in the middle of the parallel surface in this direction, and measure 6 times in total, accurate to 1mm, and take the average value as the length value in this direction. Finally, calculate the volume of each sample, recorded as V, and dry this group of samples in a drying oven at a temperature of 60±5℃ until the difference in mass between the two times separated by 4 hours is no more than 1g, and take the last weighing result as its constant mass, then put the sample in a dryer to cool, and weigh the dried mass of the sample after it reaches room temperature, recorded as M, accurate to 1g;

[0074] Dry density (kg / m 3 ) is calculated as follows: ρ = M / V × 10 -6 ;

[0075] Compression strength: In addition to meeting the corresponding technical requirements in the "General Technical Requirements for Testing Machines" (GB / T2611-2007), the pressure testing machine should have a measurement accuracy of ±1%. The sample failure load of lightweight foam soil, denoted as F, should be no less than 20% of the maximum load of the press and less than 80% of the maximum load of the press. Before testing, the sample should be placed in a drying oven at a temperature of 60±5℃ and dried until the mass difference between the two measurements 4 hours apart is no more than 1g. The length and width of the sample's compression surface should be measured three times in each direction of the surface, accurate to 1mm, and the average value should be taken to calculate the sample's compression area, denoted as A;

[0076] The calculation formula of compressive strength (MPa): f = F / A;

[0077] Water absorption rate: Before testing, place the sample in an electric blast drying oven to dry. The sample should be dried at 60±5℃ until the mass difference between two weighings with an interval of 4 hours is less than 1g, and the last weighing result is used as its constant mass, recorded as M1. When the sample cools to room temperature, first place it in a constant temperature water bath, then add water to 1 / 3 of the sample height, and maintain the water temperature at 20±5℃. After soaking for 24 hours, add water to 2 / 3 of the sample height. After 24 hours, add water until the water surface is more than 30mm higher than the sample, and continue to maintain for 24 hours. After soaking, take the sample out of the water, wipe off the surface moisture with a damp cloth, and immediately weigh the mass of each piece, recorded as M2, accurate to 1g;

[0078] The calculation formula for water absorption (%) is: W = M2-M1 / M1×100.

[0079] Table 1

[0080]

[0081] It can be seen from Table 1 that the modified bentonite prepared by the present invention can significantly reduce the water absorption rate of lightweight foam soil and improve the compressive strength of lightweight foam soil; the composite foaming agent prepared by the present invention can improve the comprehensive performance of lightweight foam soil.

[0082] It should be noted that, in this article, terms such as "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or equipment that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment.

[0083] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lightweight foam soil, characterized in that: The slurry component and the foam component are mixed and stirred in a mass ratio of 10:3.5-4, wherein: The slurry components include the following raw materials in parts by weight: 35-60 parts of cement, 28-35 parts of fine sand, 8-10 parts of modified bentonite, 0.2-0.3 parts of water reducing agent, and 15-25 parts of water; The foam component comprises the following raw materials in parts by weight: 55-65 parts of composite foaming agent, 13-15 parts of hydroxyethyl cellulose, and 5-8 parts of water; The preparation process of the modified bentonite is as follows: the bentonite is ground through a 200-mesh sieve, calcined at 300° C. for 2-3 hours, the calcined bentonite and γ-(2,3-epoxypropoxy)propyltrimethoxysilane are added to anhydrous ethanol, the mixture is stirred and mixed evenly, deionized water is added, the pH is adjusted to 8-10 with sodium hydroxide, stirring is continued for 3-4 hours, centrifugation is performed to obtain a precipitate, the precipitate is washed with deionized water until it is neutral, and dried at 60° C. to a constant weight to obtain the modified bentonite; The usage ratio of the bentonite, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, anhydrous ethanol and deionized water is 20g:2g:50-80mL:350-400mL; The composite foaming agent is prepared by mixing a protein foaming agent, a surfactant and a nano modifier in a mass ratio of 60:10-12:0.05-0.

1.

2. A lightweight foam soil according to claim 1, characterized in that: The water reducer is a polycarboxylate water reducer.

3. The lightweight foam soil according to claim 1, characterized in that: The protein foaming agent is a FH-200 protein foaming agent.

4. The lightweight foam soil according to claim 1, characterized in that: The surfactant is one of sodium α-olefin sulfonate, sodium dodecyl sulfate and sodium dodecylbenzene sulfonate.

5. The lightweight foam soil according to claim 1, characterized in that: The nano modifier is one of nano silicon dioxide, nano graphene and nano calcium carbonate.

6. The method for preparing a lightweight foam soil according to claim 1, characterized in that: The following steps are involved: A1. Prepare foam: Add composite foaming agent and hydroxyethyl cellulose to water for mechanical foaming, and control the foam density to 45-55kg / m 3 ; A2. Prepare slurry: Add cement and water reducing agent into water and stir until uniform to obtain slurry; A3. Mixing: Add foam to the slurry and stir until a uniform slurry is formed. Pour the slurry into a mold, cover it with plastic film and cure it for 48 hours. Take it out to obtain lightweight foam soil.

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