Alkali-reducing reagent suitable for ecological concrete and preparation method of alkali-reducing reagent

Abstract

The invention relates to the technical field of ecological concrete, and discloses an alkali-reducing reagent suitable for ecological concrete and a preparation method, the alkali-reducing reagent comprises the following raw materials by weight: 10-30 parts of nano alkali-resistant powder, 10-20 parts of an organic acid compound, 30-50 parts of a mineral admixture, 6-9 parts of a retarder, 4-7 parts of a dispersant, 3-4 parts of a water-retaining agent, and 0.5-2 parts of a microbial agent. The preparation method comprises the following steps: S1, uniformly mixing and stirring the nano alkali-resistant powder, the organic acid compound, the mineral admixture, the retarder, the dispersing agent, the water-retaining agent and the microbial agent in parts by weight; s2, performing granulation through a double-screw extruder; s3, drying; and S4, packaging. By adopting renewable raw materials and an environment-friendly modification process, the use of toxic and harmful substances is reduced, the green development requirement of the ecological concrete is met, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of ecological concrete, in particular to an alkali-reducing reagent suitable for ecological concrete and a preparation method thereof. Background Art

[0002] As a new building material, eco-concrete not only provides engineering protection but also provides space for plant growth, achieving the goals of ecological restoration and environmental beautification. However, during the preparation and use of eco-concrete, the hydration of cement releases a large amount of alkaline substances, causing the pH value within the concrete to increase. This excessively alkaline environment is extremely detrimental to plant growth, severely restricting the effectiveness of eco-concrete in actual engineering applications.

[0003] At present, there are some solutions to the high alkalinity problem of ecological concrete. For example, the carbonization method is used to react carbon dioxide with alkaline substances such as calcium hydroxide in cement hydration products to reduce the alkalinity of concrete. However, this method requires special carbonization equipment, and the carbonization process is time-consuming and energy-intensive, making it unsuitable for large-scale production and practical engineering applications. For another example, some acidic substances or mineral admixtures are added to concrete to neutralize the alkalinity, but these methods may have a certain negative impact on the strength and durability of concrete, or the alkali reduction effect is not long-lasting. Therefore, it is of great practical significance to develop an alkali reduction agent and preparation method that is efficient, long-lasting, and has no adverse effects on concrete performance. Summary of the Invention

[0004] (1) Technical problems solved

[0005] In view of the deficiencies in the prior art, the present invention provides an alkali-reducing agent suitable for ecological concrete and a preparation method thereof.

[0006] (2) Technical solution

[0007] To achieve the above object, the present invention provides the following technical solution: an alkali-reducing agent suitable for ecological concrete, comprising the following raw materials in parts by weight:

[0008] 10-30 parts of nano-alkali-resistant powder, 10-20 parts of organic acid compounds, 30-50 parts of mineral admixtures, 6-9 parts of retarder, 4-7 parts of dispersant, 3-4 parts of water-retaining agent, and 0.5-2 parts of microbial agent;

[0009] The nano-alkali-resistant powder comprises 15-25 parts of modified nano-titanium dioxide, 5-10 parts of modified nano-cellulose whiskers, and 3-8 parts of modified carbon nanotubes; the modified nano-titanium dioxide is dual-modified by nitrogen doping and silver loading; the modified nano-cellulose whiskers are formed by graft copolymerization of 2-(dimethylamino)ethyl methacrylate and 2-hydroxyethyl methacrylate monomers on the surface of the nano-cellulose whiskers, and cross-linking using N,N'-methylenebisacrylamide; and the modified carbon nanotubes are grafted and polymerized on the surface of the carbon nanotubes by 1-vinyl-3-butylimidazolium bromide and glycidyl methacrylate monomers.

[0010] Furthermore, the organic acid compound is one of citric acid, oxalic acid or malic acid.

[0011] Furthermore, the mineral admixture is a ternary compound system of silica fume, fly ash and slag powder, with a mass ratio of 1:2~3:1~2.

[0012] Furthermore, the retarder is a compound of sodium gluconate and sodium tripolyphosphate with a mass ratio of 1 to 2:1.

[0013] Furthermore, the dispersant is one of a polycarboxylic acid high-performance dispersant, a lignin sulfonate dispersant, and a naphthalene sulfonate dispersant.

[0014] Furthermore, the water-retaining agent is a graft copolymer of polyacrylamide and starch, with a mass ratio of 1:1~2.

[0015] Furthermore, the microbial agent is a Bacillus microbial agent.

[0016] Furthermore, a method for preparing an alkali-reducing agent suitable for ecological concrete comprises the following steps:

[0017] S1. Add nano-alkali-resistant powder, organic acid compound, mineral admixture, retarder, dispersant, and water-retaining agent to a planetary mixer in order by weight, start the planetary mixer, stir at a speed of 800-1200 r / min for 10-15 minutes, reduce the mixer speed to 400-600 r / min, add microbial agent, and continue stirring for 3-5 minutes;

[0018] S2. The stirred mixture is pelletized through a twin-screw extruder. The pelletizing temperature is set at 40-60°C. The particle size is controlled at 0.5-1 mm by adjusting the screw speed and die aperture.

[0019] S3. Place the granulated alkali-reducing reagent in a vacuum drying oven and dry at 50-70°C for 1-2 hours;

[0020] S4. After drying, use sealed packaging materials for packaging. Select intelligent packaging materials with built-in humidity sensors and microcontrollers. When it detects that the humidity in the package exceeds the standard, the desiccant release device will automatically start to prevent the inactivation of microbial agents.

[0021] (3) Beneficial technical effects

[0022] The modified nano-titanium dioxide is doubly modified by nitrogen doping and silver loading, and has both photocatalytic acid production and antibacterial functions, which can sustainably reduce the internal pH value of concrete; after the modified nano-cellulose whiskers are grafted and copolymerized, they can exert pH response characteristics in an alkaline environment and neutralize excess alkaline substances; the modified carbon nanotubes introduce imidazole groups, epoxy groups and ester groups, which can undergo hydrolysis reactions under alkaline conditions to generate hydroxyl groups, consume hydroxyl groups and form hydrophilic structures, further neutralizing the alkalinity; the organic acid compound citric acid can react with alkaline substances. The synergistic effect of the three significantly reduces the pH value of concrete at 7 days and 28 days, effectively inhibiting the alkali-aggregate reaction and ensuring the long-term stability of concrete.

[0023] With their high specific surface area and excellent mechanical properties, modified nanomaterials, when evenly dispersed in concrete, improve the density and strength of the concrete, enhance its impermeability, and extend its service life. Silver-loaded modified nano-titanium dioxide possesses antibacterial properties, reducing microbial erosion of concrete.

[0024] The present invention adopts renewable raw materials and environmentally friendly modification technology, reduces the use of toxic and harmful substances, meets the green development needs of ecological concrete, and is suitable for large-scale industrial production. 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 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 any creative efforts shall fall within the scope of protection of the present invention.

[0026] The components of the alkalinity-reducing reagent of the present invention are all commercially available unless otherwise specified.

[0027] The parts used in the present invention are all parts by weight;

[0028] Example 1

[0029] An alkali-reducing agent suitable for ecological concrete comprises the following raw materials in parts by weight:

[0030] 10 parts of nano-alkali-resistant powder, 10 parts of organic acid compounds, 30 parts of mineral admixtures, 6 parts of retarder, 4 parts of dispersant, 3 parts of water-retaining agent, and 0.5 parts of microbial agent;

[0031] The nano-alkali-resistant powder comprises 15 parts of modified nano-titanium dioxide, 5 parts of modified nano-cellulose whiskers, and 3 parts of modified carbon nanotubes; the modified nano-titanium dioxide is dual-modified by nitrogen doping and silver loading; the modified nano-cellulose whiskers are formed by graft copolymerization of 2-(dimethylamino)ethyl methacrylate and 2-hydroxyethyl methacrylate monomers on the surface of the nano-cellulose whiskers, and cross-linking using N,N'-methylenebisacrylamide; the modified carbon nanotubes are grafted and polymerized on the surface of the carbon nanotubes by 1-vinyl-3-butylimidazole bromide and glycidyl methacrylate monomers.

[0032] The organic acid compound is citric acid.

[0033] The mineral admixture is a ternary compound system of silica fume, fly ash and slag powder with a mass ratio of 1:2:1.

[0034] The retarder is a compound of sodium gluconate and sodium tripolyphosphate, with a mass ratio of 1:1.

[0035] The dispersant is a polycarboxylic acid-based high-performance dispersant.

[0036] The water-retaining agent is a graft copolymer of polyacrylamide and starch, with a mass ratio of 1:1.

[0037] The microbial agent is a Bacillus microbial agent.

[0038] A method for preparing an alkali-reducing reagent suitable for ecological concrete comprises the following steps:

[0039] S1. Add nano-alkali-resistant powder, organic acid compound, mineral admixture, retarder, dispersant and water-retaining agent to a planetary mixer in order by weight, start the planetary mixer, stir at 800 r / min for 10 min, reduce the mixer speed to 400 r / min, add microbial agent and continue stirring for 3 min;

[0040] S2. The stirred mixture is granulated through a twin-screw extruder. The granulation temperature is set at 40°C. The particle size is controlled at 0.5 mm by adjusting the screw speed and the die aperture.

[0041] S3. Place the granulated alkali-reducing reagent in a vacuum drying oven and dry at 50°C for 1 h;

[0042] S4. After drying, use sealed packaging materials for packaging. Select intelligent packaging materials with built-in humidity sensors and microcontrollers. When it detects that the humidity in the package exceeds the standard, the desiccant release device will automatically start to prevent the inactivation of microbial agents.

[0043] The preparation method of modified nano titanium dioxide comprises the following steps:

[0044] A1. Nano-titanium dioxide powder: Use anatase nano-titanium dioxide powder with a purity of ≥99.5% and an average particle size of 20-30 nm as the base material;

[0045] Nitrogen source: urea is used as the nitrogen source for nitrogen doping, which is of analytical grade and needs to be ground into uniform fine powder before use to ensure that it is fully mixed with nano-titanium dioxide;

[0046] Silver source: Silver nitrate was selected as the precursor for silver loading. Analytically pure silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 0.05 mol / L.

[0047] A2. Add nano-titanium dioxide powder and urea in a mass ratio of 1:0.5 into a mortar and grind thoroughly for 30 min. Transfer the mixed powder into a crucible and place it in a muffle furnace. Under nitrogen atmosphere, heat the mixture to 400°C at a heating rate of 5°C / min and hold the mixture for 2 h. The nitrogen flow rate is controlled at 100 mL / min. After the holding period, the mixture is naturally cooled to room temperature to obtain nitrogen-doped nano-titanium dioxide.

[0048] A3. Add the prepared nitrogen-doped nano-titanium dioxide powder to the silver nitrate solution prepared above, with the solid-liquid ratio of nitrogen-doped nano-titanium dioxide to silver nitrate solution being 1 g:10 mL. Stir the mixture at room temperature using a magnetic stirrer at 200 r / min for 3-4 h.

[0049] A4. Add 0.1 mol / L sodium borohydride solution as a reducing agent dropwise to the above mixed solution, with a molar ratio of silver nitrate to sodium borohydride of 1:2. Stir continuously for 1 h during the dropwise addition process. Centrifuge at 8000 r / min for 10 min. Collect the precipitate, wash alternately with deionized water and anhydrous ethanol, and vacuum dry at 60°C for 6 h to obtain nitrogen-doped and silver-loaded dual-modified nano-titanium dioxide.

[0050] The preparation method of modified nanocellulose whiskers comprises the following steps:

[0051] B1. Add 10 parts of nanocellulose whiskers to 600 parts of deionized water and disperse them ultrasonically at 200 W for 10 min. Keep the temperature ≤30°C.

[0052] B2. Transfer the dispersion to a four-necked flask equipped with a mechanical stirrer, a thermometer, and a reflux condenser, add 0.2 parts of potassium persulfate, raise the temperature to 50°C, and stir at 200 r / min for 5 minutes;

[0053] B3. Mix 10 parts of 2-(dimethylamino)ethyl methacrylate, 5 parts of 2-hydroxyethyl methacrylate, and 0.2 parts of cross-linking agent N,N'-methylenebisacrylamide to prepare a monomer mixture. Slowly add the monomer mixture dropwise to the above reaction system using a constant pressure dropping funnel at a dropping rate of 1 mL / min. After the addition is complete, add 0.2 parts of accelerator tetramethylethylenediamine and react at 50°C for 2 h with a rotation speed of 100 r / min.

[0054] B4. After the reaction is completed, the product is cooled to room temperature and filtered with a 300-mesh filter cloth. The filter cake is washed with a 0.1 mol / L dilute hydrochloric acid solution and anhydrous ethanol in sequence. The washed product is dried at 60°C and a vacuum degree of -0.06 MPa for 8 h, and crushed through a 200-mesh sieve to obtain modified nanocellulose whiskers.

[0055] The preparation method of modified carbon nanotubes comprises the following steps:

[0056] C1. Add 10 parts of carbon nanotubes to 50 parts of concentrated nitric acid (65%), reflux and stir for 2 h, then wash with deionized water until neutral, and dry in vacuum at 60 °C for 6 h;

[0057] C2. Add the pretreated carbon nanotubes to 60 parts of anhydrous ethanol and ultrasonically disperse them for 10 minutes to form a uniform dispersion. Add 2 parts of 2-hydroxy-2-methyl-1-phenylacetone to the dispersion and stir evenly. Place the reaction vessel under an ultraviolet lamp with a wavelength of 365 nm, keep the light source 10 cm away from the reaction liquid surface, and react for 2 hours. After the reaction is completed, separate the product by centrifugation, wash with anhydrous ethanol to remove unreacted photoinitiator, and dry the product in vacuum at 60°C for 6 hours to obtain photoinitiated modified carbon nanotubes.

[0058] C3. Disperse the photoinduced modified carbon nanotubes in 1000 parts of anhydrous ethanol to prepare a suspension, disperse under ultrasonication at room temperature for 10 min, add 0.5 parts of cuprous bromide and 2 parts of 2,2'-bipyridine, and heat to 50°C with stirring for 10 min;

[0059] C4. Add 20 parts of 1-vinyl-3-butylimidazolium bromide and 10 parts of glycidyl methacrylate to anhydrous ethanol to prepare a monomer solution with a total concentration of 0.4 mol / L, and slowly add it dropwise to the above reaction system. Continue stirring at 50°C for 8 h. After the reaction is completed, wash the product with acetone and deionized water in sequence, and dry it in vacuum at 60°C for 3 h to obtain modified carbon nanotubes.

[0060] Example 2

[0061] An alkali-reducing agent suitable for ecological concrete comprises the following raw materials in parts by weight:

[0062] 20 parts of nano-alkali-resistant powder, 15 parts of organic acid compounds, 40 parts of mineral admixtures, 8 parts of retarder, 6 parts of dispersant, 4 parts of water-retaining agent, and 1 part of microbial agent;

[0063] The nano-alkali-resistant powder comprises 20 parts of modified nano-titanium dioxide, 6 parts of modified nano-cellulose whiskers, and 5 parts of modified carbon nanotubes; the modified nano-titanium dioxide is dual-modified by nitrogen doping and silver loading; the modified nano-cellulose whiskers are formed by graft copolymerization of 2-(dimethylamino)ethyl methacrylate and 2-hydroxyethyl methacrylate monomers on the surface of the nano-cellulose whiskers, and cross-linking using N,N'-methylenebisacrylamide; the modified carbon nanotubes are grafted and polymerized on the surface of the carbon nanotubes by 1-vinyl-3-butylimidazole bromide and glycidyl methacrylate monomers.

[0064] The organic acid compound is oxalic acid.

[0065] The mineral admixture is a ternary compound system of silica fume, fly ash and slag powder with a mass ratio of 1:2.5:1.5.

[0066] The retarder is a compound of sodium gluconate and sodium tripolyphosphate with a mass ratio of 1.5:1.

[0067] The dispersant is lignin sulfonate dispersant.

[0068] The water-retaining agent is a graft copolymer of polyacrylamide and starch, with a mass ratio of 1:1.5.

[0069] The microbial agent is a Bacillus microbial agent.

[0070] A method for preparing an alkali-reducing reagent suitable for ecological concrete comprises the following steps:

[0071] S1. Add nano-alkali-resistant powder, organic acid compound, mineral admixture, retarder, dispersant and water-retaining agent to a planetary mixer in order by weight, start the planetary mixer, stir at a speed of 1000 r / min for 15 min, reduce the mixer speed to 500 r / min, add microbial agent, and continue stirring for 4 min;

[0072] S2. The stirred mixture is pelletized through a twin-screw extruder. The pelletizing temperature is set at 50°C. The particle size is controlled at 1 mm by adjusting the screw speed and the die aperture.

[0073] S3, placing the granulated alkali-reducing reagent in a vacuum drying oven and drying at 60°C for 1.5 h;

[0074] S4. After drying, use sealed packaging materials for packaging. Select intelligent packaging materials with built-in humidity sensors and microcontrollers. When it detects that the humidity in the package exceeds the standard, the desiccant release device will automatically start to prevent the inactivation of microbial agents.

[0075] The preparation method of modified nano titanium dioxide comprises the following steps:

[0076] A1. Nano-titanium dioxide powder: Use anatase nano-titanium dioxide powder with a purity of ≥99.5% and an average particle size of 20-30 nm as the base material;

[0077] Nitrogen source: urea is used as the nitrogen source for nitrogen doping, which is of analytical grade and needs to be ground into uniform fine powder before use to ensure that it is fully mixed with nano-titanium dioxide;

[0078] Silver source: Silver nitrate was selected as the precursor for silver loading. Analytically pure silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 0.08 mol / L.

[0079] A2. Add nano-titanium dioxide powder and urea in a mass ratio of 1:0.7 into a mortar and grind thoroughly for 40 min. Transfer the mixed powder into a crucible and place it in a muffle furnace. Under nitrogen atmosphere, heat the crucible to 450°C at a heating rate of 10°C / min and hold the temperature for 2.5 h. The nitrogen flow rate is controlled at 150 mL / min. After the holding period, cool the crucible naturally to room temperature to obtain nitrogen-doped nano-titanium dioxide.

[0080] A3. Add the prepared nitrogen-doped nano-titanium dioxide powder to the silver nitrate solution prepared above, with the solid-liquid ratio of nitrogen-doped nano-titanium dioxide to silver nitrate solution being 1 g:15 mL. Stir the mixture at room temperature using a magnetic stirrer at 250 r / min for 3.5 h.

[0081] A4. Add 0.1 mol / L sodium borohydride solution as a reducing agent dropwise to the above mixed solution, with a molar ratio of silver nitrate to sodium borohydride of 1:2.5. Stir continuously for 1.5 h during the dropwise addition process. Centrifuge at 9000 r / min for 10 min. Collect the precipitate, wash alternately with deionized water and anhydrous ethanol, and vacuum dry at 70°C for 7 h to obtain nitrogen-doped and silver-loaded dual-modified nano-titanium dioxide.

[0082] The preparation method of modified nanocellulose whiskers comprises the following steps:

[0083] B1. Add 15 parts of nanocellulose whiskers to 700 parts of deionized water and disperse them ultrasonically at 300 W for 15 minutes while controlling the temperature to ≤30°C.

[0084] B2. Transfer the dispersion to a four-necked flask equipped with a mechanical stirrer, a thermometer, and a reflux condenser, add 0.4 parts of potassium persulfate, raise the temperature to 60°C, and stir at 250 r / min for 10 min.

[0085] B3. Mix 15 parts of 2-(dimethylamino)ethyl methacrylate, 8 parts of 2-hydroxyethyl methacrylate, and 0.3 parts of a cross-linking agent, N,N'-methylenebisacrylamide, to form a monomer mixture. Slowly add the monomer mixture dropwise to the above reaction system using a constant pressure dropping funnel at a dropping rate of 1 mL / min. After the addition is complete, add 0.4 parts of a accelerator, tetramethylethylenediamine, and react at 60°C for 3 h at a rotation speed of 200 r / min.

[0086] B4. After the reaction is completed, the product is cooled to room temperature and filtered with a 300-mesh filter cloth. The filter cake is washed with a 0.1 mol / L dilute hydrochloric acid solution and anhydrous ethanol in sequence. The washed product is dried at 70°C and a vacuum degree of -0.08 MPa for 9 h, and crushed through a 200-mesh sieve to obtain modified nanocellulose whiskers.

[0087] The preparation method of modified carbon nanotubes comprises the following steps:

[0088] C1. Add 15 parts of carbon nanotubes to 80 parts of concentrated nitric acid (65%), reflux and stir for 3 h, then wash with deionized water until neutral, and vacuum dry at 70 °C for 10 h;

[0089] C2. Add the pretreated carbon nanotubes to 80 parts of anhydrous ethanol and ultrasonically disperse them for 15 minutes to form a uniform dispersion. Add 4 parts of 2-hydroxy-2-methyl-1-phenylacetone to the dispersion and stir evenly. Place the reaction vessel under an ultraviolet lamp with a wavelength of 365 nm, keep the light source 10 cm away from the reaction liquid surface, and react for 3 hours. After the reaction is completed, separate the product by centrifugation, wash with anhydrous ethanol to remove unreacted photoinitiator, and dry the product in vacuum at 65°C for 7 hours to obtain photoinitiated modified carbon nanotubes.

[0090] C3. Disperse the photoinduced modified carbon nanotubes in 1100 parts of anhydrous ethanol to prepare a suspension, perform ultrasonic dispersion at room temperature for 10 min, add 0.8 parts of cuprous bromide and 4 parts of 2,2'-bipyridine, and heat to 55°C with stirring for 20 min;

[0091] C4. Add 25 parts of 1-vinyl-3-butylimidazolium bromide and 12 parts of glycidyl methacrylate to anhydrous ethanol to prepare a monomer solution with a total concentration of 0.5 mol / L, and slowly add it dropwise to the above reaction system. Continue stirring and react at 55°C for 10 hours. After the reaction, wash the product with acetone and deionized water in sequence, and vacuum dry it at 70°C for 4 hours to obtain modified carbon nanotubes.

[0092] Example 3

[0093] An alkali-reducing agent suitable for ecological concrete comprises the following raw materials in parts by weight:

[0094] 30 parts of nano-alkali-resistant powder, 20 parts of organic acid compounds, 50 parts of mineral admixtures, 9 parts of retarder, 7 parts of dispersant, 4 parts of water-retaining agent, and 2 parts of microbial agent;

[0095] The nano-alkali-resistant powder comprises 25 parts of modified nano-titanium dioxide, 10 parts of modified nano-cellulose whiskers, and 8 parts of modified carbon nanotubes; the modified nano-titanium dioxide is dual-modified by nitrogen doping and silver loading; the modified nano-cellulose whiskers are formed by graft copolymerization of 2-(dimethylamino)ethyl methacrylate and 2-hydroxyethyl methacrylate monomers on the surface of the nano-cellulose whiskers, and cross-linking using N,N'-methylenebisacrylamide; the modified carbon nanotubes are grafted and polymerized on the surface of the carbon nanotubes by 1-vinyl-3-butylimidazole bromide and glycidyl methacrylate monomers.

[0096] The organic acid compound is malic acid.

[0097] The mineral admixture is a ternary compound system of silica fume, fly ash and slag powder with a mass ratio of 1:3:2.

[0098] The retarder is a compound of sodium gluconate and sodium tripolyphosphate with a mass ratio of 2:1.

[0099] The dispersant is a naphthalene sulfonate dispersant.

[0100] The water-retaining agent is a graft copolymer of polyacrylamide and starch, with a mass ratio of 1:2.

[0101] The microbial agent is a Bacillus microbial agent.

[0102] A method for preparing an alkali-reducing reagent suitable for ecological concrete comprises the following steps:

[0103] S1. Add nano-alkali-resistant powder, organic acid compound, mineral admixture, retarder, dispersant and water-retaining agent to a planetary mixer in order by weight, start the planetary mixer, stir at a speed of 1200 r / min for 15 min, reduce the mixer speed to 600 r / min, add microbial agent, and continue stirring for 5 min;

[0104] S2. The stirred mixture was pelletized through a twin-screw extruder. The pelletizing temperature was set at 60°C. The particle size was controlled to 1 mm by adjusting the screw speed and die aperture.

[0105] S3, placing the granulated alkalinity-reducing reagent in a vacuum drying oven and drying at 70°C for 2 h;

[0106] S4. After drying, use sealed packaging materials for packaging. Select intelligent packaging materials with built-in humidity sensors and microcontrollers. When it detects that the humidity in the package exceeds the standard, the desiccant release device will automatically start to prevent the inactivation of microbial agents.

[0107] The preparation method of modified nano titanium dioxide comprises the following steps:

[0108] A1. Nano-titanium dioxide powder: Use anatase nano-titanium dioxide powder with a purity of ≥99.5% and an average particle size of 20-30 nm as the base material;

[0109] Nitrogen source: urea is used as the nitrogen source for nitrogen doping, which is of analytical grade and needs to be ground into uniform fine powder before use to ensure that it is fully mixed with nano-titanium dioxide;

[0110] Silver source: Silver nitrate of analytical grade was selected as the precursor for silver loading and dissolved in deionized water to prepare a silver nitrate solution with a concentration of 0.1 mol / L for later use.

[0111] A2. Add nano-titanium dioxide powder and urea in a mass ratio of 1:1 into a mortar and grind thoroughly for 45 min. Transfer the mixed powder into a crucible and place it in a muffle furnace. Under nitrogen atmosphere, heat the mixture to 500°C at a heating rate of 10°C / min and hold the temperature for 3 h. The nitrogen flow rate is controlled at 200 mL / min. After the holding period, cool the mixture naturally to room temperature to obtain nitrogen-doped nano-titanium dioxide.

[0112] A3. Add the prepared nitrogen-doped nano-titanium dioxide powder to the silver nitrate solution prepared above, with the solid-liquid ratio of nitrogen-doped nano-titanium dioxide to silver nitrate solution being 1 g:20 mL. Stir the mixture at room temperature using a magnetic stirrer at 300 r / min for 4 h.

[0113] A4. A 0.2 mol / L sodium borohydride solution was added dropwise to the above mixed solution as a reducing agent, with a molar ratio of silver nitrate to sodium borohydride of 1:3. Stirring was continued for 2 h during the dropwise addition process. The mixture was centrifuged at 10,000 r / min for 15 min. The precipitate was collected and washed alternately with deionized water and anhydrous ethanol. The precipitate was vacuum dried at 80°C for 8 h to obtain nitrogen-doped and silver-loaded dual-modified nano-titanium dioxide.

[0114] The preparation method of modified nanocellulose whiskers comprises the following steps:

[0115] B1. Add 20 parts of nanocellulose whiskers to 800 parts of deionized water and disperse them ultrasonically at 400 W for 15 min. Keep the temperature ≤30°C.

[0116] B2. Transfer the dispersion to a four-necked flask equipped with a mechanical stirrer, a thermometer, and a reflux condenser, add 0.5 parts of potassium persulfate, raise the temperature to 70°C, and stir at 300 r / min for 10 min;

[0117] B3. Mix 20 parts of 2-(dimethylamino)ethyl methacrylate, 10 parts of 2-hydroxyethyl methacrylate, and 0.5 parts of a cross-linking agent, N,N'-methylenebisacrylamide, to form a monomer mixture. Slowly add the monomer mixture dropwise to the above reaction system using a constant pressure dropping funnel at a dropping rate of 2 mL / min. After the addition is complete, add 0.6 parts of a accelerator, tetramethylethylenediamine, and react at 70°C for 4 h at a rotation speed of 300 r / min.

[0118] B4. After the reaction is completed, the product is cooled to room temperature and filtered with a 300-mesh filter cloth. The filter cake is washed with a 0.1 mol / L dilute hydrochloric acid solution and anhydrous ethanol in sequence. The washed product is dried at 80°C and a vacuum degree of -0.09 MPa for 10 h, and crushed through a 200-mesh sieve to obtain modified nanocellulose whiskers.

[0119] The preparation method of modified carbon nanotubes comprises the following steps:

[0120] C1. Add 20 parts of carbon nanotubes to 100 parts of concentrated nitric acid (65%), reflux and stir for 4 h, then wash with deionized water until neutral, and vacuum dry at 80 °C for 12 h;

[0121] C2. Add the pretreated carbon nanotubes to 100 parts of anhydrous ethanol and ultrasonically disperse for 20 minutes to form a uniform dispersion. Add 6 parts of 2-hydroxy-2-methyl-1-phenylacetone to the dispersion and stir evenly. Place the reaction vessel under an ultraviolet lamp with a wavelength of 365 nm, keep the light source 15 cm away from the reaction liquid surface, and react for 4 hours. After the reaction is completed, separate the product by centrifugation, wash with anhydrous ethanol to remove unreacted photoinitiator, and dry the product in vacuum at 70°C for 8 hours to obtain photoinitiated modified carbon nanotubes.

[0122] C3. Disperse the photoinduced modified carbon nanotubes in 1200 parts of anhydrous ethanol to prepare a suspension, perform ultrasonic dispersion at room temperature for 15 min, add 1 part of cuprous bromide and 5 parts of 2,2'-bipyridine, heat to 60°C and stir for 30 min;

[0123] C4. Add 30 parts of 1-vinyl-3-butylimidazolium bromide and 15 parts of glycidyl methacrylate to anhydrous ethanol to prepare a monomer solution with a total concentration of 0.6 mol / L, and slowly add it dropwise to the above reaction system. Stir and react at 60°C for 12 h. After the reaction, wash the product with acetone and deionized water in sequence, and dry it in vacuum at 80°C for 6 h to obtain modified carbon nanotubes.

[0124] Comparative Example 1: No modified nano-titanium dioxide was added, and the rest of the process was the same as in Example 1.

[0125] Comparative Example 2: No modified nanocellulose whiskers were added, and the remaining processes were the same as in Example 1.

[0126] Comparative Example 3: No modified carbon nanotubes were added, and the remaining processes were the same as in Example 1.

[0127] Test example:

[0128] The alkali-reducing agents prepared in Examples 1-3 and Comparative Examples 1-3 were used in concrete production. The concrete formulation included PS-A32.5 ordinary Portland cement with a dry density of 3.10 g / cm³; single, continuously graded stone with a particle size of 5-10 mm as the coarse aggregate; and water. The alkali-reducing agent was added in an amount of 5% of the total concrete mass. The test results are shown in the table below.

[0129] Table 1 Concrete pH test results

[0130] Group pH value of concrete after 7 days pH value of concrete after 28 days Example 1 8.2 8.0 Example 2 8.2 8.0 Example 3 8.1 7.9 Comparative Example 1 8.5 8.3 Comparative Example 2 8.4 8.2 Comparative Example 3 8.3 8.1

[0131] Table 2 Mechanical, anti-permeability and antibacterial performance test results

[0132] Group Compressive strength (28d) Impermeability grade Antibacterial rate (Escherichia coli) Example 1 55MPa P10 85% Example 2 55MPa P10 85% Example 3 56MPa P10 85% Comparative Example 1 48 MPa P9 65% Comparative Example 2 50MPa P9 82% Comparative Example 3 52MPa P9.5 61%

[0133] It can be seen from the table that modified nano-titanium dioxide, modified nano-cellulose whiskers and modified carbon nanomaterials can effectively improve the alkali-reducing performance of alkali-reducing agents, and at the same time are beneficial to the compressive strength, impermeability and antibacterial properties of concrete.

[0134] While 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 these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A alkali-reducing agent suitable for ecological concrete, characterized in that: It includes the following raw materials in parts by weight: 10-30 parts of nano-alkali-resistant powder, 10-20 parts of organic acid compounds, 30-50 parts of mineral admixtures, 6-9 parts of retarder, 4-7 parts of dispersant, 3-4 parts of water-retaining agent, and 0.5-2 parts of microbial agent; The nano-alkali-resistant powder comprises 15-25 parts of modified nano-titanium dioxide, 5-10 parts of modified nano-cellulose whiskers, and 3-8 parts of modified carbon nanotubes; the modified nano-titanium dioxide is dual-modified by nitrogen doping and silver loading; the modified nano-cellulose whiskers are formed by graft copolymerization of 2-(dimethylamino)ethyl methacrylate and 2-hydroxyethyl methacrylate monomers on the surface of the nano-cellulose whiskers, and cross-linking using N,N'-methylenebisacrylamide; and the modified carbon nanotubes are grafted and polymerized on the surface of the carbon nanotubes by 1-vinyl-3-butylimidazolium bromide and glycidyl methacrylate monomers.

2. A alkali-reducing agent suitable for ecological concrete according to claim 1, characterized in that, The organic acid compound is one of citric acid, oxalic acid or malic acid.

3. A alkali-reducing agent suitable for ecological concrete according to claim 1, characterized in that, The mineral admixture is a ternary compound system of silica fume, fly ash and slag powder, with a mass ratio of 1:2~3:1~2.

4. A alkali-reducing agent suitable for ecological concrete according to claim 1, characterized in that, The retarder is a compound of sodium gluconate and sodium tripolyphosphate, with a mass ratio of 1~2:

1.

5. A alkali-reducing agent suitable for ecological concrete according to claim 1, characterized in that, The dispersant is one of a polycarboxylic acid high-performance dispersant, a lignin sulfonate dispersant, and a naphthalene sulfonate dispersant.

6. A alkali-reducing agent suitable for ecological concrete according to claim 1, characterized in that, The water-retaining agent is a graft copolymer of polyacrylamide and starch, with a mass ratio of 1:1~2.

7. The alkali-reducing agent suitable for ecological concrete according to claim 1, characterized in that: The microbial agent is a Bacillus microbial agent.

8. A method for preparing an alkali-reducing agent suitable for ecological concrete according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Add nano-alkali-resistant powder, organic acid compound, mineral admixture, retarder, dispersant, and water-retaining agent to a planetary mixer in order by weight, start the planetary mixer, stir at a speed of 800-1200 r / min for 10-15 minutes, reduce the mixer speed to 400-600 r / min, add microbial agent, and continue stirring for 3-5 minutes; S2. The stirred mixture is pelletized through a twin-screw extruder. The pelletizing temperature is set at 40-60°C. The particle size is controlled at 0.5-1 mm by adjusting the screw speed and die aperture. S3. Place the granulated alkali-reducing reagent in a vacuum drying oven and dry at 50-70°C for 1-2 hours; S4. After drying, use sealed packaging materials for packaging. Select intelligent packaging materials with built-in humidity sensors and microcontrollers. When it detects that the humidity in the package exceeds the standard, the desiccant release device will automatically start to prevent the inactivation of microbial agents.