Preparation method of nano-protein cement foaming agent for improving durability and mechanical properties of lightweight concrete

Abstract

The present invention relates to the technical field of nano-protein cement foaming agents, and more specifically, to a method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete. The method comprises the following steps: mixing modified soy protein powder with deionized water to form a modified soy protein powder dispersion; adding graphene oxide to the deionized water and polyaspartic acid to prepare a graphene oxide suspension; and subsequently mixing the modified soy protein powder dispersion, the graphene oxide suspension, a foam stabilizer, and sodium lauryl sulfate to obtain the nano-protein cement foaming agent. The modified soy protein powder forms a three-dimensional network structure by introducing thiol groups, thereby enhancing the stability of the foam interface film; and the imidazole groups in the foam stabilizer stabilize the bubble interface through electrostatic repulsion, thereby extending the foam half-life.

Description

Technical Field

[0001] The invention relates to the technical field of nano-protein cement foaming agents, in particular to a method for preparing a nano-protein cement foaming agent capable of improving the durability and mechanical properties of lightweight concrete. Background Art

[0002] Lightweight concrete has been widely used in many engineering fields such as buildings, bridges, and roads due to its advantages such as low density, excellent thermal insulation properties, and convenient construction. For example, in building wall materials, roof insulation, and ground cushioning, lightweight concrete can effectively reduce the deadweight of buildings, improve construction efficiency, and reduce material transportation and construction costs. However, although traditional protein foaming agents (such as animal / plant proteins) can produce foam, their poor bubble stability and uneven pore size distribution limit the durability and mechanical properties of lightweight concrete. In view of this, we propose a preparation method for a nanoprotein cement foaming agent to improve the durability and mechanical properties of lightweight concrete. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, so as to solve the problem mentioned in the above background technology that although traditional protein foaming agents (such as animal / plant proteins) can produce foam, their bubble stability is poor and the pore size distribution is uneven, which limits the durability and mechanical properties of lightweight concrete.

[0004] To achieve the above object, the present invention provides a method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0005] S1.1. Weigh modified soy protein powder, graphene oxide, foam stabilizer, sodium lauryl sulfate, and polyaspartic acid by weight;

[0006] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5-8.0 with 0.05-0.1 mol / L sodium hydroxide, and ultrasonically treat the mixture in a water bath at 40-50°C at a power of 100-200 W for 20-30 min to obtain a modified soy protein powder dispersion;

[0007] S1.3. Add graphene oxide to deionized water and sonicate at a power of 400-500 W for 30-40 min. Add polyaspartic acid and adjust the pH to 9-10 with 0.05-0.1 mol / L sodium hydroxide. Stir at 400-500 rpm for 1-2 h to obtain a graphene oxide suspension.

[0008] S1.4. Mix and stir the modified soybean protein powder dispersion, graphene oxide suspension, foam stabilizer and sodium lauryl sulfate to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0009] Preferably, in S1.1, the modified soy protein powder comprises 70-80 parts by weight, graphene oxide 0.5-1 parts by weight, foam stabilizer 5-10 parts by weight, sodium lauryl sulfate 0.5-1 parts by weight and polyaspartic acid 0.05-0.1 parts by weight.

[0010] Preferably, in S1.2, the modified soy protein powder is prepared by a thiolation reaction between soy protein powder and DL-N-acetylhomocysteine ​​thiolactone, wherein the mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone is 1:1.2-1.5.

[0011] Preferably, the preparation method of the modified soy protein powder is as follows:

[0012] Mix soy protein powder and deionized water in a mass ratio of 1:10, adjust the pH to 7.5-8.5 with 0.05-0.1 mol / L sodium hydroxide, and stir at 400-500 rpm for 30-60 min at 40-50° C. to obtain a soy protein solution;

[0013] Add DL-N-acetylhomocysteine ​​thiolactone to the soy protein solution, stir at 700-800 rpm and 50-60°C for 4-6 hours, and maintain the pH at 8.0-8.5 with 0.05-0.1 mol / L sodium hydroxide;

[0014] After the reaction is completed, the mixture is cooled to 4°C and the pH is adjusted to 4.5 with 0.5-1 mol / L hydrochloric acid to precipitate the protein; the mixture is then centrifuged at 8000-10000 rpm for 15-20 min at 4°C to collect the precipitate; the precipitate is washed 2-3 times with deionized water, dialyzed with a dialysis bag with a molecular weight cutoff of 8-10 kDa for 24-48 hours, freeze-dried at -80--60°C for 24-48 hours, and crushed and sieved to obtain modified soy protein powder;

[0015] The thiol reaction increases the number of thiol groups by combining the cysteine ​​residues in the soy protein molecules with DL-N-acetylhomocysteine ​​thiolactone; thiol groups are highly reactive and can cross-link protein molecules through disulfide bonds to form a stable cross-linked network, thereby generating a more stable interfacial film during the foaming process and inhibiting bubble merging and rupture; the elongation of the modified soy protein molecular chain is increased, the hydrophobic groups are more fully exposed, and the hydrophilic functional groups (such as carboxyl and amino groups) are more evenly distributed, forming an amphiphilic structure, which significantly reduces the surface tension of the solution, making the bubble formation more uniform and the dispersion more stable; the modified protein improves the stability of the bubble wall, reduces the pore size and increases the distribution concentration through the synergistic effect of thiol cross-linking and electrostatic repulsion; in addition, polar groups (such as hydroxyl and carboxyl groups) can form hydrogen bonds and coordination bonds with cement hydration products, reducing the interface defects between the foam and the cement matrix, thereby improving the mechanical properties and impermeability of lightweight concrete.

[0016] Preferably, the soy protein powder has a purity greater than 85%;

[0017] The particle size of the modified soybean protein powder obtained by crushing and sieving is less than 100 nm.

[0018] Preferably, in S1.3, the concentration of the graphene oxide suspension is 0.1-0.3%.

[0019] Preferably, in S1.4, the mixing and stirring is to first add the modified soy protein powder dispersion and the graphene oxide suspension into the reactor, and stir at 200-300 rpm at 50-60° C. for 10-15 minutes; then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 60-70° C., and continue stirring at 200-300 rpm for 15-20 minutes;

[0020] The surface of graphene oxide is rich in oxygen-containing functional groups (such as -COOH, -OH, etc.). These functional groups not only serve as nucleation sites for cement hydration reactions to promote the formation of CSH gel, but also can form a protein-graphene oxide composite network through hydrogen bonding with the sulfhydryl groups (-SH) in modified soy protein, thereby significantly improving the interfacial bonding strength and inhibiting the propagation of microcracks; in addition, the hydrophobic region (six-membered carbon ring) of graphene oxide can be anchored at the bubble interface, while the hydrophilic groups extend to the aqueous phase, forming a three-dimensional stable structure; under the synergistic effect of sodium dodecyl sulfate, the average pore size of the bubbles is reduced and the distribution is more uniform.

[0021] Preferably, in S1.4, the foam stabilizer is prepared by grafting corn starch and 1-vinyl-3-methylimidazole hydrogen sulfate, wherein the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.5-1.2.

[0022] Preferably, the specific preparation method of the foam stabilizer is as follows:

[0023] Corn starch and deionized water are mixed in a mass ratio of 1:10, and stirred at 300-400 rpm in a water bath at 85-90°C for 30-40 minutes to form a gelatinized starch solution; the temperature is lowered to 50-60°C, and the pH is adjusted to 6.5-7.0 with 0.05-0.1 mol / L sodium hydroxide; ammonium persulfate solution is added to the gelatinized starch solution, and nitrogen is passed through to deoxygenate for 15-20 minutes to obtain an activated starch solution;

[0024] Add 1-vinyl-3-methylimidazole hydrogen sulfate dropwise to the activated starch solution, and stir at 200-300 rpm under nitrogen protection at 58-62°C for 3-5 hours;

[0025] After the reaction is completed, add 2-3 times the volume of anhydrous ethanol and let it stand for 10-12 hours; centrifuge at 8000-10000 rpm for 10-15 minutes to collect the precipitate; wash the precipitate with deionized water 2-3 times, dialyze with a dialysis bag with a molecular weight cutoff of 8-10 kDa for 24-48 hours, freeze-dry at -80~-60℃ for 24-48 hours, and crush to obtain a foam stabilizer.

[0026] Corn starch is grafted with ionic liquid groups of 1-vinyl-3-methylimidazolium hydrogen sulfate to form an amphiphilic polymer structure. After gelatinization, the starch molecular chains fully unfold, exposing more hydroxyl groups (-OH), which combine with imidazole groups through a grafting reaction to form a starch / ionic liquid copolymer. This structure significantly enhances the flexibility and surface activity of the molecular chains, reduces the surface tension of the solution, and achieves a more uniform distribution of bubbles. The grafted foam stabilizer, through the directional arrangement of the molecular chains, reduces the pore size of the bubbles and increases their distribution concentration. The sulfonic acid groups of the imidazole groups can form coordination bonds with cement hydration products, reducing interfacial porosity and improving the mechanical properties and impermeability of lightweight concrete.

[0027] Preferably, the ammonium persulfate solution is prepared by dissolving 1-3% of ammonium persulfate by weight of corn starch in deionized water to obtain an ammonium persulfate solution with a concentration of 5-10%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. In this method for preparing a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete, modified soy protein powder forms a three-dimensional network structure by introducing thiol groups, thereby enhancing the stability of the foam interface film. The stretchability of the modified protein molecules is improved, and the hydrophobic / hydrophilic groups are arranged in an orderly manner, which reduces the foam pore size and makes its distribution more concentrated. In addition, the carboxyl groups on the protein surface chemically bond with cement hydration products, thereby improving the foam-cement interface bonding strength.

[0030] 2. In the preparation method of a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, the foam stabilizer forms an amphiphilic structure by introducing ionic liquid groups, which significantly reduces the surface tension of the solution; the electrostatic repulsion of the imidazole group stabilizes the bubble interface, prolongs the foam half-life, and effectively suppresses the mold collapse problem; at the same time, the thiol group in the modified soy protein powder forms a hydrogen bond network with it, enhancing the stability of the interfacial film; the sulfonic acid group bonds with the cement hydration product, reducing the matrix porosity, thereby improving the mechanical properties of the concrete. DETAILED DESCRIPTION

[0031] 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 embodiments described 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 making creative efforts are within the scope of protection of the present invention.

[0032] Example 1: A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0033] S1.1. Weigh the following raw materials in parts by weight: 70 parts by weight of modified soy protein powder, 0.5 parts by weight of graphene oxide, 5 parts by weight of foam stabilizer, 0.5 parts by weight of sodium lauryl sulfate, and 0.05 parts by weight of polyaspartic acid;

[0034] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5 with 0.05 mol / L sodium hydroxide, and ultrasonicate the mixture in a 50°C water bath at 200 W for 30 min to obtain a modified soy protein powder dispersion.

[0035] S1.3. Add graphene oxide to deionized water and sonicate at 400 W for 30 min. Add polyaspartic acid and adjust the pH to 9 with 0.05 mol / L sodium hydroxide. Stir at 500 rpm for 2 h to obtain a 0.1% graphene oxide suspension.

[0036] S1.4. Add the modified soy protein powder dispersion and graphene oxide suspension into the reactor and stir at 300 rpm at 60°C for 15 minutes. Then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 70°C, and continue stirring at 300 rpm for 20 minutes to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0037] Wherein, the preparation method of modified soy protein powder is as follows:

[0038] 90% pure soy protein powder was mixed with deionized water at a mass ratio of 1:10, the pH was adjusted to 8.0 with 0.05 mol / L sodium hydroxide, and the mixture was stirred at 500 rpm for 60 min at 50°C to obtain a soy protein solution;

[0039] DL-N-acetylhomocysteine ​​thiolactone was added to the soy protein solution, and the mixture was stirred at 800 rpm at 60°C for 6 h while maintaining the pH at 8.5 with 0.05 mol / L sodium hydroxide.

[0040] After the reaction, the mixture was cooled to 4°C and the pH was adjusted to 4.5 with 1 mol / L hydrochloric acid to precipitate the protein. The mixture was then centrifuged at 10,000 rpm for 15 minutes at 4°C to collect the precipitate. The precipitate was washed three times with deionized water, dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10 kDa, freeze-dried at -60°C for 48 hours, and crushed and sieved to obtain a modified soy protein powder with a particle size of 80 nm. The mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone was 1:1.2.

[0041] The specific preparation method of the foam stabilizer is as follows:

[0042] Corn starch and deionized water were mixed in a mass ratio of 1:10 and stirred at 400 rpm in an 85°C water bath for 40 minutes to form a gelatinized starch solution. The solution was cooled to 60°C and the pH was adjusted to 7.0 with 0.05 mol / L sodium hydroxide.

[0043] Dissolve 2% of the mass of corn starch in deionized water to obtain an 8% ammonium persulfate solution; add the ammonium persulfate solution to the gelatinized starch solution, and deoxygenate with nitrogen for 15 minutes to obtain an activated starch solution;

[0044] 1-vinyl-3-methylimidazole hydrogen sulfate was added dropwise to the activated starch solution, and the mixture was stirred at 300 rpm at 60°C for 5 h under nitrogen protection.

[0045] After the reaction is completed, 3 volumes of anhydrous ethanol are added and the mixture is allowed to stand for 12 hours; the mixture is centrifuged at 8000 rpm for 15 minutes to collect the precipitate; the precipitate is washed 3 times with deionized water, dialyzed with a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed to obtain a foam stabilizer; wherein the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.5.

[0046] Example 2: A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0047] S1.1. Weigh the following raw materials in parts by weight: 75 parts by weight of modified soy protein powder, 0.7 parts by weight of graphene oxide, 7 parts by weight of foam stabilizer, 0.7 parts by weight of sodium lauryl sulfate, and 0.07 parts by weight of polyaspartic acid;

[0048] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5 with 0.05 mol / L sodium hydroxide, and ultrasonicate the mixture in a 50°C water bath at 200 W for 30 min to obtain a modified soy protein powder dispersion.

[0049] S1.3. Add graphene oxide to deionized water and sonicate at 400 W for 30 min. Add polyaspartic acid and adjust the pH to 9 with 0.05 mol / L sodium hydroxide. Stir at 500 rpm for 2 h to obtain a 0.1% graphene oxide suspension.

[0050] S1.4. Add the modified soy protein powder dispersion and graphene oxide suspension to a reactor and stir at 300 rpm at 60°C for 15 minutes. Then, add a foam stabilizer and sodium lauryl sulfate, raise the temperature to 70°C, and continue stirring at 300 rpm for 20 minutes to obtain a nanoprotein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0051] Wherein, the preparation method of modified soy protein powder is as follows:

[0052] 90% pure soy protein powder was mixed with deionized water at a mass ratio of 1:10, the pH was adjusted to 8.0 with 0.05 mol / L sodium hydroxide, and the mixture was stirred at 500 rpm for 60 min at 50°C to obtain a soy protein solution;

[0053] DL-N-acetylhomocysteine ​​thiolactone was added to the soy protein solution, and the mixture was stirred at 800 rpm at 60°C for 6 h while maintaining the pH at 8.5 with 0.05 mol / L sodium hydroxide.

[0054] After the reaction, the mixture was cooled to 4°C and the pH was adjusted to 4.5 with 1 mol / L hydrochloric acid to precipitate the protein. The mixture was then centrifuged at 10,000 rpm for 15 minutes at 4°C to collect the precipitate. The precipitate was washed three times with deionized water, dialyzed using a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed and sieved to obtain a modified soy protein powder with a particle size of 80 nm. The mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone was 1:1.3.

[0055] The specific preparation method of the foam stabilizer is as follows:

[0056] Corn starch and deionized water were mixed in a mass ratio of 1:10 and stirred at 400 rpm in an 85°C water bath for 40 minutes to form a gelatinized starch solution. The solution was cooled to 60°C and the pH was adjusted to 7.0 with 0.05 mol / L sodium hydroxide.

[0057] Dissolve 2% of the mass of corn starch in deionized water to obtain an 8% ammonium persulfate solution; add the ammonium persulfate solution to the gelatinized starch solution, and deoxygenate with nitrogen for 15 minutes to obtain an activated starch solution;

[0058] 1-vinyl-3-methylimidazole hydrogen sulfate was added dropwise to the activated starch solution, and the mixture was stirred at 300 rpm at 60°C for 5 h under nitrogen protection.

[0059] After the reaction is completed, 3 volumes of anhydrous ethanol are added and the mixture is allowed to stand for 12 hours; the mixture is centrifuged at 8000 rpm for 15 minutes to collect the precipitate; the precipitate is washed 3 times with deionized water, dialyzed using a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed to obtain a foam stabilizer; the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.8.

[0060] Example 3: A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0061] S1.1. Weigh the following raw materials in parts by weight: 80 parts by weight of modified soy protein powder, 1 part by weight of graphene oxide, 10 parts by weight of a foam stabilizer, 1 part by weight of sodium lauryl sulfate, and 0.1 part by weight of polyaspartic acid;

[0062] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5 with 0.05 mol / L sodium hydroxide, and ultrasonicate the mixture in a 50°C water bath at 200 W for 30 min to obtain a modified soy protein powder dispersion.

[0063] S1.3. Add graphene oxide to deionized water and sonicate at 400 W for 30 min. Add polyaspartic acid and adjust the pH to 9 with 0.05 mol / L sodium hydroxide. Stir at 500 rpm for 2 h to obtain a 0.1% graphene oxide suspension.

[0064] S1.4. Add the modified soy protein powder dispersion and graphene oxide suspension into the reactor and stir at 300 rpm at 60°C for 15 minutes. Then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 70°C, and continue stirring at 300 rpm for 20 minutes to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0065] Wherein, the preparation method of modified soy protein powder is as follows:

[0066] 90% pure soy protein powder was mixed with deionized water at a mass ratio of 1:10, the pH was adjusted to 8.0 with 0.05 mol / L sodium hydroxide, and the mixture was stirred at 500 rpm for 60 min at 50°C to obtain a soy protein solution;

[0067] DL-N-acetylhomocysteine ​​thiolactone was added to the soy protein solution, and the mixture was stirred at 800 rpm at 60°C for 6 h while maintaining the pH at 8.5 with 0.05 mol / L sodium hydroxide.

[0068] After the reaction, the mixture was cooled to 4°C and the pH was adjusted to 4.5 with 1 mol / L hydrochloric acid to precipitate the protein. The mixture was then centrifuged at 10,000 rpm for 15 minutes at 4°C to collect the precipitate. The precipitate was washed three times with deionized water, dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10 kDa, freeze-dried at -60°C for 48 hours, and crushed and sieved to obtain a modified soy protein powder with a particle size of 80 nm. The mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone was 1:1.5.

[0069] The specific preparation method of the foam stabilizer is as follows:

[0070] Corn starch and deionized water were mixed in a mass ratio of 1:10 and stirred at 400 rpm in an 85°C water bath for 40 minutes to form a gelatinized starch solution. The solution was cooled to 60°C and the pH was adjusted to 7.0 with 0.05 mol / L sodium hydroxide.

[0071] Dissolve 2% of the mass of corn starch in deionized water to obtain an 8% ammonium persulfate solution; add the ammonium persulfate solution to the gelatinized starch solution, and deoxygenate with nitrogen for 15 minutes to obtain an activated starch solution;

[0072] 1-vinyl-3-methylimidazole hydrogen sulfate was added dropwise to the activated starch solution, and the mixture was stirred at 300 rpm at 60°C for 5 h under nitrogen protection.

[0073] After the reaction is completed, 3 volumes of anhydrous ethanol are added and the mixture is allowed to stand for 12 hours; the mixture is centrifuged at 8000 rpm for 15 minutes to collect the precipitate; the precipitate is washed 3 times with deionized water, dialyzed using a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed to obtain a foam stabilizer; wherein the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:1.2.

[0074] Example 4: A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0075] S1.1. Weigh the following raw materials in parts by weight: 65 parts by weight of modified soy protein powder, 0.7 parts by weight of graphene oxide, 7 parts by weight of foam stabilizer, 0.7 parts by weight of sodium lauryl sulfate, and 0.07 parts by weight of polyaspartic acid;

[0076] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5 with 0.05 mol / L sodium hydroxide, and ultrasonicate the mixture in a 50°C water bath at 200 W for 30 min to obtain a modified soy protein powder dispersion.

[0077] S1.3. Add graphene oxide to deionized water and sonicate at 400 W for 30 min. Add polyaspartic acid and adjust the pH to 9 with 0.05 mol / L sodium hydroxide. Stir at 500 rpm for 2 h to obtain a 0.1% graphene oxide suspension.

[0078] S1.4. Add the modified soy protein powder dispersion and graphene oxide suspension into the reactor and stir at 300 rpm at 60°C for 15 minutes. Then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 70°C, and continue stirring at 300 rpm for 20 minutes to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0079] Wherein, the preparation method of modified soy protein powder is as follows:

[0080] 90% pure soy protein powder was mixed with deionized water at a mass ratio of 1:10, the pH was adjusted to 8.0 with 0.05 mol / L sodium hydroxide, and the mixture was stirred at 500 rpm for 60 min at 50°C to obtain a soy protein solution;

[0081] DL-N-acetylhomocysteine ​​thiolactone was added to the soy protein solution, and the mixture was stirred at 800 rpm at 60°C for 6 h while maintaining the pH at 8.5 with 0.05 mol / L sodium hydroxide.

[0082] After the reaction, the mixture was cooled to 4°C and the pH was adjusted to 4.5 with 1 mol / L hydrochloric acid to precipitate the protein. The mixture was then centrifuged at 10,000 rpm for 15 minutes at 4°C to collect the precipitate. The precipitate was washed three times with deionized water, dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10 kDa, freeze-dried at -60°C for 48 hours, and crushed and sieved to obtain a modified soy protein powder with a particle size of 80 nm. The mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone was 1:1.3.

[0083] The specific preparation method of the foam stabilizer is as follows:

[0084] Corn starch and deionized water were mixed in a mass ratio of 1:10 and stirred at 400 rpm in an 85°C water bath for 40 minutes to form a gelatinized starch solution. The solution was cooled to 60°C and the pH was adjusted to 7.0 with 0.05 mol / L sodium hydroxide.

[0085] Dissolve 2% of the mass of corn starch in deionized water to obtain an 8% ammonium persulfate solution; add the ammonium persulfate solution to the gelatinized starch solution, and deoxygenate with nitrogen for 15 minutes to obtain an activated starch solution;

[0086] 1-vinyl-3-methylimidazole hydrogen sulfate was added dropwise to the activated starch solution, and the mixture was stirred at 300 rpm at 60°C for 5 h under nitrogen protection.

[0087] After the reaction is completed, 3 volumes of anhydrous ethanol are added and the mixture is allowed to stand for 12 hours; the mixture is centrifuged at 8000 rpm for 15 minutes to collect the precipitate; the precipitate is washed 3 times with deionized water, dialyzed using a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed to obtain a foam stabilizer; the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.8.

[0088] Example 5: A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0089] S1.1. Weigh the following raw materials in parts by weight: 75 parts by weight of modified soy protein powder, 0.7 parts by weight of graphene oxide, 1 part by weight of a foam stabilizer, 0.7 parts by weight of sodium lauryl sulfate, and 0.07 parts by weight of polyaspartic acid;

[0090] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5 with 0.05 mol / L sodium hydroxide, and ultrasonicate the mixture in a 50°C water bath at 200 W for 30 min to obtain a modified soy protein powder dispersion.

[0091] S1.3. Add graphene oxide to deionized water and sonicate at 400 W for 30 min. Add polyaspartic acid and adjust the pH to 9 with 0.05 mol / L sodium hydroxide. Stir at 500 rpm for 2 h to obtain a 0.1% graphene oxide suspension.

[0092] S1.4. Add the modified soy protein powder dispersion and graphene oxide suspension into the reactor and stir at 300 rpm at 60°C for 15 minutes. Then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 70°C, and continue stirring at 300 rpm for 20 minutes to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0093] Wherein, the preparation method of modified soy protein powder is as follows:

[0094] 90% pure soy protein powder was mixed with deionized water at a mass ratio of 1:10, the pH was adjusted to 8.0 with 0.05 mol / L sodium hydroxide, and the mixture was stirred at 500 rpm for 60 min at 50°C to obtain a soy protein solution;

[0095] DL-N-acetylhomocysteine ​​thiolactone was added to the soy protein solution, and the mixture was stirred at 800 rpm at 60°C for 6 h while maintaining the pH at 8.5 with 0.05 mol / L sodium hydroxide.

[0096] After the reaction, the mixture was cooled to 4°C and the pH was adjusted to 4.5 with 1 mol / L hydrochloric acid to precipitate the protein. The mixture was then centrifuged at 10,000 rpm for 15 minutes at 4°C to collect the precipitate. The precipitate was washed three times with deionized water, dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10 kDa, freeze-dried at -60°C for 48 hours, and crushed and sieved to obtain a modified soy protein powder with a particle size of 80 nm. The mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone was 1:1.3.

[0097] The specific preparation method of the foam stabilizer is as follows:

[0098] Corn starch and deionized water were mixed in a mass ratio of 1:10 and stirred at 400 rpm in an 85°C water bath for 40 minutes to form a gelatinized starch solution. The solution was cooled to 60°C and the pH was adjusted to 7.0 with 0.05 mol / L sodium hydroxide.

[0099] Dissolve 2% of the mass of corn starch in deionized water to obtain an 8% ammonium persulfate solution; add the ammonium persulfate solution to the gelatinized starch solution, and deoxygenate with nitrogen for 15 minutes to obtain an activated starch solution;

[0100] 1-vinyl-3-methylimidazole hydrogen sulfate was added dropwise to the activated starch solution, and the mixture was stirred at 300 rpm at 60°C for 5 h under nitrogen protection.

[0101] After the reaction is completed, 3 volumes of anhydrous ethanol are added and the mixture is allowed to stand for 12 hours; the mixture is centrifuged at 8000 rpm for 15 minutes to collect the precipitate; the precipitate is washed 3 times with deionized water, dialyzed using a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed to obtain a foam stabilizer; the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.8.

[0102] Example 6: A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0103] S1.1. Weigh the following raw materials in parts by weight: 75 parts by weight of modified soy protein powder, 0.7 parts by weight of graphene oxide, 7 parts by weight of foam stabilizer, 0.7 parts by weight of sodium lauryl sulfate, and 0.07 parts by weight of polyaspartic acid;

[0104] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5 with 0.05 mol / L sodium hydroxide, and ultrasonicate the mixture in a 50°C water bath at 200 W for 30 min to obtain a modified soy protein powder dispersion.

[0105] S1.3. Add graphene oxide to deionized water and sonicate at 400 W for 30 min. Add polyaspartic acid and adjust the pH to 9 with 0.05 mol / L sodium hydroxide. Stir at 500 rpm for 2 h to obtain a 0.1% graphene oxide suspension.

[0106] S1.4. Add the modified soy protein powder dispersion and graphene oxide suspension into the reactor and stir at 300 rpm at 60°C for 15 minutes. Then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 70°C, and continue stirring at 300 rpm for 20 minutes to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0107] Wherein, the preparation method of modified soy protein powder is as follows:

[0108] 90% pure soy protein powder was mixed with deionized water at a mass ratio of 1:10, the pH was adjusted to 8.0 with 0.05 mol / L sodium hydroxide, and the mixture was stirred at 500 rpm for 60 min at 50°C to obtain a soy protein solution;

[0109] DL-N-acetylhomocysteine ​​thiolactone was added to the soy protein solution, and the mixture was stirred at 800 rpm at 60°C for 6 h while maintaining the pH at 8.5 with 0.05 mol / L sodium hydroxide.

[0110] After the reaction, the mixture was cooled to 4°C and the pH was adjusted to 4.5 with 1 mol / L hydrochloric acid to precipitate the protein. The mixture was then centrifuged at 10,000 rpm for 15 minutes at 4°C to collect the precipitate. The precipitate was washed three times with deionized water, dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10 kDa, freeze-dried at -60°C for 48 hours, and crushed and sieved to obtain a modified soy protein powder with a particle size of 80 nm. The mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone was 1:1.

[0111] The specific preparation method of the foam stabilizer is as follows:

[0112] Corn starch and deionized water were mixed in a mass ratio of 1:10 and stirred at 400 rpm in an 85°C water bath for 40 minutes to form a gelatinized starch solution. The solution was cooled to 60°C and the pH was adjusted to 7.0 with 0.05 mol / L sodium hydroxide.

[0113] Dissolve 2% of the mass of corn starch in deionized water to obtain an 8% ammonium persulfate solution; add the ammonium persulfate solution to the gelatinized starch solution, and deoxygenate with nitrogen for 15 minutes to obtain an activated starch solution;

[0114] 1-vinyl-3-methylimidazole hydrogen sulfate was added dropwise to the activated starch solution, and the mixture was stirred at 300 rpm at 60°C for 5 h under nitrogen protection.

[0115] After the reaction is completed, 3 volumes of anhydrous ethanol are added and the mixture is allowed to stand for 12 hours; the mixture is centrifuged at 8000 rpm for 15 minutes to collect the precipitate; the precipitate is washed 3 times with deionized water, dialyzed using a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed to obtain a foam stabilizer; the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.8.

[0116] Example 7: A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, comprising the following steps:

[0117] S1.1. Weigh the following raw materials in parts by weight: 75 parts by weight of modified soy protein powder, 0.7 parts by weight of graphene oxide, 7 parts by weight of foam stabilizer, 0.7 parts by weight of sodium lauryl sulfate, and 0.07 parts by weight of polyaspartic acid;

[0118] S1.2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5 with 0.05 mol / L sodium hydroxide, and ultrasonicate the mixture in a 50°C water bath at 200 W for 30 min to obtain a modified soy protein powder dispersion.

[0119] S1.3. Add graphene oxide to deionized water and sonicate at 400 W for 30 min. Add polyaspartic acid and adjust the pH to 9 with 0.05 mol / L sodium hydroxide. Stir at 500 rpm for 2 h to obtain a 0.1% graphene oxide suspension.

[0120] S1.4. Add the modified soy protein powder dispersion and graphene oxide suspension into the reactor and stir at 300 rpm at 60°C for 15 minutes. Then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 70°C, and continue stirring at 300 rpm for 20 minutes to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete.

[0121] Wherein, the preparation method of modified soy protein powder is as follows:

[0122] 90% pure soy protein powder was mixed with deionized water at a mass ratio of 1:10, the pH was adjusted to 8.0 with 0.05 mol / L sodium hydroxide, and the mixture was stirred at 500 rpm for 60 min at 50°C to obtain a soy protein solution;

[0123] DL-N-acetylhomocysteine ​​thiolactone was added to the soy protein solution, and the mixture was stirred at 800 rpm at 60°C for 6 h while maintaining the pH at 8.5 with 0.05 mol / L sodium hydroxide.

[0124] After the reaction, the mixture was cooled to 4°C and the pH was adjusted to 4.5 with 1 mol / L hydrochloric acid to precipitate the protein. The mixture was then centrifuged at 10,000 rpm for 15 minutes at 4°C to collect the precipitate. The precipitate was washed three times with deionized water, dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10 kDa, freeze-dried at -60°C for 48 hours, and crushed and sieved to obtain a modified soy protein powder with a particle size of 80 nm. The mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone was 1:1.3.

[0125] The specific preparation method of the foam stabilizer is as follows:

[0126] Corn starch and deionized water were mixed in a mass ratio of 1:10 and stirred at 400 rpm in an 85°C water bath for 40 minutes to form a gelatinized starch solution. The solution was cooled to 60°C and the pH was adjusted to 7.0 with 0.05 mol / L sodium hydroxide.

[0127] Dissolve 2% of the mass of corn starch in deionized water to obtain an 8% ammonium persulfate solution; add the ammonium persulfate solution to the gelatinized starch solution, and deoxygenate with nitrogen for 15 minutes to obtain an activated starch solution;

[0128] 1-vinyl-3-methylimidazole hydrogen sulfate was added dropwise to the activated starch solution, and the mixture was stirred at 300 rpm at 60°C for 5 h under nitrogen protection.

[0129] After the reaction is completed, 3 volumes of anhydrous ethanol are added and the mixture is allowed to stand for 12 hours; the mixture is centrifuged at 8000 rpm for 15 minutes to collect the precipitate; the precipitate is washed 3 times with deionized water, dialyzed using a dialysis bag with a molecular weight cutoff of 10 kDa for 48 hours, freeze-dried at -60°C for 48 hours, and crushed to obtain a foam stabilizer; wherein the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.1.

[0130] Comparative Example 1: The method of Example 2 was adopted to prepare a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, but modified soy protein powder was not used and soy protein powder was directly used.

[0131] Comparative Example 2: Using the method of Example 2, polyacrylamide was used instead of the foam stabilizer in a method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete.

[0132] Comparative Example 3: The method of Example 2 was adopted, but graphene oxide was not added in the preparation method of a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete.

[0133] By adding modified soy protein powder and a foam stabilizer to a preparation method of a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, the performance index test items and test standards of the obtained nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete are as follows:

[0134] When determining the foaming multiple according to the JC / T2199-2013 standard "Foaming Agents for Foamed Concrete", the foaming agent should be dissolved or diluted at the maximum dilution multiple and stirred evenly while preparing the cement slurry. When using an air compression foaming machine to prepare the foam, the outlet of the foaming tube should be placed near the bottom of the container during sampling. The pressure of the foam flow should be used to fill the container with foam and slightly above the container mouth. The entire process should be completed within 30 seconds. After scraping the foam flat, its mass should be weighed and the foaming multiple should be calculated using the formula. A higher foaming multiple indicates that the foaming agent can efficiently produce a large number of uniform bubbles, significantly reducing the dry density of the concrete.

[0135] When measuring the 1-hour water bleeding rate according to the JC / T2199-2013 "Foaming Agent for Foam Concrete" standard, place the sample into the container within 30 seconds and scrape the foam surface flat. Then, gently place a float on the foam and start timing. After 1 hour, open the tap under the glass tube, pour the exuded water into a measuring cylinder and weigh its mass. Finally, calculate the 1-hour water bleeding rate using the formula. A lower 1-hour water bleeding rate indicates that the foam is evenly distributed in the cement paste and has strong stability.

[0136] The nano-protein cement foaming agents for improving the durability and mechanical properties of lightweight concrete prepared in Examples 1-7 and Comparative Examples 1-3 were tested using the above standards. The obtained data are shown in Table 1:

[0137] Table 1 Performance data of nano-protein cement foaming agent of Examples 1-7 and Comparative Examples 1-3

[0138]

[0139] It can be seen from Examples 1-3 and 4 that: when the other components in the nano-protein cement foaming agent remain unchanged and the weight of the modified soy protein powder continues to increase, the foaming multiple of the nano-protein cement foaming agent continues to increase and the 1-h water secretion rate continues to decrease; the modified soy protein powder introduces sulfhydryl groups (-SH) through a thiol reaction, significantly improving the surface activity; as the dosage increases, the concentration of surfactant molecules in the solution increases, which can more effectively reduce the gas-liquid interfacial tension, making it easier for the gas to disperse to form tiny bubbles, thereby improving the foaming efficiency; the protein molecules form a dense cross-linked film (by disulfide bonds and hydrogen bonds) at the bubble interface, inhibiting the merging of bubbles; the hydrophilic groups (-COOH, -NH2) of the modified protein combine with water molecules to form a hydration layer, reducing the proportion of free water; the viscosity of the high-concentration protein dispersion increases, slowing down the migration rate of water.

[0140] Furthermore, by comparing Examples 1-3 with Example 5, it can be seen that when the other components in the nano-protein cement foaming agent remain unchanged and the weight of the foam stabilizer is continuously increased, the foaming multiple of the nano-protein cement foaming agent is continuously improved and the 1h water secretion rate is continuously reduced; the imidazole group (-N + ) and the thiol (-SH) in soy protein. As the amount of foam stabilizer added increases, the density of cross-linking points per unit volume increases linearly, thus forming a three-dimensional network structure; this three-dimensional network reduces the gas diffusion resistance and further improves the foaming multiple; the ionic liquid groups in the foam stabilizer (such as 1-vinyl-3-methylimidazole hydrogen sulfate) are adsorbed on the surface of the liquid film to form a directional molecular layer; when the amount of foam stabilizer increases, the surface viscosity of the liquid film increases accordingly, the water secretion rate decreases, and the foam structure is further stabilized.

[0141] By comparing Example 2 and Example 6, it can be seen that: as the mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone increases, the foaming multiple of the nano-protein cement foaming agent continues to increase and the 1-hour water exudation rate continues to decrease; after the soy protein powder is combined with the DL-N-acetylhomocysteine ​​thiolactone molecules, the density of active thiol groups (-SH) on the protein surface is significantly increased through sufficient thiol reaction; the high-density thiol groups form a dense disulfide bond cross-linked network under oxidative conditions, thereby enhancing the thickness and shear strength of the bubble interface film; in the modified soy protein molecules, the exposure of the hydrophobic region (such as the α-helical structure) is increased, and the hydrophilic groups (such as carboxyl and amino groups) are more evenly distributed, forming a stable micelle structure of "hydrophobic core-hydrophilic shell"; this structure can lock water in the micelle gap and significantly reduce the water exudation rate.

[0142] By comparing Example 2 and Example 7, it can be seen that as the mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate increases, the foaming multiple of the nano-protein cement foaming agent continues to increase and the 1h water secretion rate continues to decrease; under the action of ammonium persulfate initiator, the grafting rate of the ionic liquid monomer increases, and more positively charged imidazole groups (-N + The grafted copolymer forms a ternary amphiphilic structure of "hydrophilic starch backbone-hydrophobic alkyl chains-charged imidazole groups," further reducing surface tension and promoting gas dispersion to form fine bubbles. Electrostatic repulsion inhibits bubble merging, reducing the average bubble diameter and increasing the foaming multiple. The highly grafted starch molecular chains exhibit enhanced extensibility in aqueous solution, forming a three-dimensional network structure that reduces water migration paths and increases the 1-hour water secretion rate.

[0143] According to the above test experiments, embodiment 2 is taken as the optimal embodiment;

[0144] By comparing Example 2 with Comparative Example 1, it can be seen that when modified soy protein powder is used directly without using it, the 1-hour water secretion rate of the nano-protein cement foaming agent is significantly improved; the unmodified protein cannot form a stable interfacial film due to the lack of a thiol cross-linking network introduced by thiolation, resulting in a decrease in the mechanical strength of the foam liquid film and rapid precipitation of the liquid, thereby destroying the internal pore structure of the concrete; natural soy protein has a large molecular weight, and the molecules are mainly bound by van der Waals forces and hydrogen bonds. It is prone to irreversible denaturation and aggregation in the alkaline environment of cement, which accelerates the drainage rate of the liquid film; the modified protein bonds with the oxygen-containing groups of graphene oxide through thiol (-SH) to form a "protein-graphene" composite reinforcement layer, thereby achieving a synergistic effect; this structure not only enhances the stability of the interfacial film, but also improves the stability of the bubbles and slows down the bubble merging rate; in contrast, the unmodified protein cannot achieve this synergistic effect, resulting in an increased bubble merging rate and reduced foam stability.

[0145] By comparing Example 2 with Comparative Example 2, it can be seen that when polyacrylamide is used instead of the foam stabilizer, the foaming multiple of the nano-protein cement foaming agent is significantly reduced; the foam stabilizer (such as grafted modified starch) constructs an ordered electrostatic repulsion layer on the bubble surface by forming an "ionic liquid-starch" composite structure, thereby effectively inhibiting the merging of bubbles; however, polyacrylamide, as a linear polymer, mainly functions to delay bubble bursting by increasing the viscosity of the solution, but cannot prevent further merging of bubbles, which leads to a significant decrease in the foaming multiple; in addition, the imidazole group in the foam stabilizer can synergistically act with the sulfhydryl group (-SH) in the modified soy protein, thereby enhancing the adsorption capacity of the foaming agent molecules at the gas-liquid interface and forming a stable film layer; in contrast, polyacrylamide, due to the lack of such active groups, reduces the bubble generation efficiency in the initial stage of foaming.

[0146] By comparing Example 2 with Comparative Example 3, it can be seen that: when graphene oxide is not added, the 1-hour water secretion rate of the nano-protein cement foaming agent is significantly improved; graphene oxide, due to its two-dimensional lamellar structure and high specific surface area, can be adsorbed on the surface of bubbles, and through surface oxygen-containing functional groups (such as carboxyl, epoxy and hydroxyl groups), it forms hydrogen bonds and covalent bonds with the sulfhydryl (-SH) in the modified soy protein, thereby significantly improving the mechanical strength and toughness of the interfacial film; in the absence of graphene oxide, the cross-linking network between protein molecules is relatively weak, resulting in an accelerated bubble merging rate, easy collapse of the foam structure, and rapid precipitation of water; the nanosheet layer of graphene oxide can form a physical barrier network in the foam liquid phase, delaying water migration; and its absence will reduce the liquid phase flow resistance, making it easier for water to seep through the foam gap.

[0147] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete, characterized in that: The following steps are involved: S1.

1. Weigh modified soy protein powder, graphene oxide, foam stabilizer, sodium lauryl sulfate, and polyaspartic acid by weight; S1.

2. Mix the modified soy protein powder with deionized water in a mass ratio of 1:8, adjust the pH to 7.5-8.0 with 0.05-0.1 mol / L sodium hydroxide, and ultrasonically treat the mixture in a water bath at 40-50°C at a power of 100-200 W for 20-30 min to obtain a modified soy protein powder dispersion; The modified soy protein powder is prepared by a thiolation reaction between soy protein powder and DL-N-acetylhomocysteine ​​thiolactone, wherein the mass ratio of soy protein powder to DL-N-acetylhomocysteine ​​thiolactone is 1:1.2-1.5; S1.

3. Add graphene oxide to deionized water and sonicate at a power of 400-500 W for 30-40 min. Add polyaspartic acid and adjust the pH to 9-10 with 0.05-0.1 mol / L sodium hydroxide. Stir at 400-500 rpm for 1-2 h to obtain a graphene oxide suspension. S1.

4. Mixing a modified soy protein powder dispersion, a graphene oxide suspension, a foam stabilizer, and sodium lauryl sulfate to obtain a nano-protein cement foaming agent that improves the durability and mechanical properties of lightweight concrete; The specific preparation method of the foam stabilizer is as follows: corn starch and deionized water are mixed in a mass ratio of 1:10, and stirred at 300-400 rpm in a water bath at 85-90°C for 30-40 minutes to form a gelatinized starch solution; the temperature is lowered to 50-60°C, and the pH is adjusted to 6.5-7.0 with sodium hydroxide having a concentration of 0.05-0.1 mol / L; ammonium persulfate solution is added to the gelatinized starch solution, and nitrogen is passed through to deoxygenate for 15-20 minutes to obtain an activated starch solution; Add 1-vinyl-3-methylimidazole hydrogen sulfate dropwise to the activated starch solution, and stir at 200-300 rpm under nitrogen for 3-5 hours at 58-62°C. The mass ratio of corn starch to 1-vinyl-3-methylimidazole hydrogen sulfate is 1:0.5-1.

2. After the reaction is completed, add 2-3 times the volume of anhydrous ethanol and let it stand for 10-12 hours; centrifuge at 8000-10000 rpm for 10-15 minutes to collect the precipitate; wash the precipitate with deionized water 2-3 times, dialyze it with a dialysis bag with a molecular weight cutoff of 8-10 kDa for 24-48 hours, freeze-dry it at -80~-60℃ for 24-48 hours, and crush it to obtain a foam stabilizer; The ammonium persulfate solution is prepared by dissolving 1-3% of ammonium persulfate by weight of corn starch in deionized water to obtain an ammonium persulfate solution with a concentration of 5-10%.

2. The method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete according to claim 1, wherein: In the S1.1, the modified soy protein powder is 70-80 parts by weight, the graphene oxide is 0.5-1 parts by weight, the foam stabilizer is 5-10 parts by weight, the sodium lauryl sulfate is 0.5-1 parts by weight and the polyaspartic acid is 0.05-0.1 parts by weight.

3. The method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete according to claim 1, wherein: The preparation method of the modified soy protein powder is as follows: Mix soy protein powder and deionized water in a mass ratio of 1:10, adjust the pH to 7.5-8.5 with 0.05-0.1 mol / L sodium hydroxide, and stir at 400-500 rpm for 30-60 min at 40-50° C. to obtain a soy protein solution; Add DL-N-acetylhomocysteine ​​thiolactone to the soy protein solution, stir at 700-800 rpm and 50-60°C for 4-6 hours, and maintain the pH at 8.0-8.5 with 0.05-0.1 mol / L sodium hydroxide; After the reaction is completed, the mixture is cooled to 4°C and the pH is adjusted to 4.5 with 0.5-1 mol / L hydrochloric acid to precipitate the protein; the mixture is then centrifuged at 8000-10000 rpm for 15-20 minutes at 4°C to collect the precipitate; the precipitate is washed 2-3 times with deionized water, dialyzed with a dialysis bag with a molecular weight cutoff of 8-10 kDa for 24-48 hours, freeze-dried at -80~-60°C for 24-48 hours, and crushed and sieved to obtain modified soy protein powder.

4. The method for preparing a nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete according to claim 3, wherein: The soy protein powder has a purity greater than 85%; The particle size of the modified soybean protein powder obtained by crushing and sieving is less than 100 nm.

5. The method for preparing the nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete according to claim 1, characterized in that: In S1.3, the concentration of the graphene oxide suspension is 0.1-0.3%.

6. The method for preparing the nano-protein cement foaming agent for improving the durability and mechanical properties of lightweight concrete according to claim 1, characterized in that: In the S1.4, the mixing and stirring is to first add the modified soy protein powder dispersion and the graphene oxide suspension into the reactor, and stir at a speed of 200-300 rpm at 50-60°C for 10-15 minutes; then add the foam stabilizer and sodium lauryl sulfate, raise the temperature to 60-70°C, and continue stirring at a speed of 200-300 rpm for 15-20 minutes.

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