Super-long slow-release slump retaining agent suitable for low-carbon cement as well as preparation method and application of super-long slow-release slump retaining agent

Abstract

The invention provides a super-long slow-release slump retaining agent suitable for low-carbon cement as well as a preparation method and application thereof. The slump retaining agent is obtained by carrying out a Graft From grafting reaction on a prepolymer main chain and a side chain with a block structure, the main chain of the prepolymer is of a polymer structure with a plurality of modifiable hydroxyl groups, and is obtained by free radical polymerization of unsaturated enol monomers in the presence of an initiator and a chain transfer agent; the side chain is obtained by polymerization reaction of a monomer A, a monomer B, a monomer C and a monomer D; the monomer A is hydrophobic alkyl acrylate, the monomer B is unsaturated acid, the monomer C is hydroxyl ester, and the monomer D is polyoxyethylene ether. An ATRP initiator of a main chain initiates generation of a multi-branched side chain structure, a side chain contains carboxylic acid and hydroxyl ester at the same time, an ester bond between the main chain and the side chain can be hydrolyzed to release a side chain slump retaining component, and the released slump retaining component can continue to be hydrolyzed through a small monomer to gradually release adsorption groups; and the cement particles can be continuously and slowly adsorbed on the cement particles so as to prolong the slurry fluidity retention time.

Description

Technical Field

[0001] The invention relates to the technical field of concrete admixtures, and in particular to an ultra-long slow-release collapse-preventing agent suitable for low-carbon cement, and a preparation method and application thereof. Background Art

[0002] Carbon or carbon dioxide (CO2) emissions from cement production account for about 5% of current global anthropogenic emissions. These carbon emissions come from the combustion of fossil fuels in kilns, the electricity used for grinding raw materials and finished materials, and the clinkering process of major raw materials such as limestone. In recent years, in order to achieve the "dual carbon" goal, carbon emission reduction has become the only way for the construction industry to achieve green and sustainable development. At present, the development and application of high-performance auxiliary cementitious materials and the replacement of cement and clinker in large quantities are one of the important technical approaches. This new low-carbon cement material uses a large amount of recycled resources such as slag, calcined limestone, metakaolin, fly ash, and solid waste, resulting in a large difference in concrete raw materials, resulting in traditional slump retaining agents that can no longer meet the needs of modern concrete production. Improper use can easily cause concrete segregation, bleeding, poor water retention and workability, and it is easy to have a large slump loss during long-term and long-distance transportation. In addition, the complexity of concrete components, such as unreasonable particle grading of machine-made sand, high stone powder content, poor particle morphology, and diversified structures, also make it increasingly difficult to control the long-term flow performance of concrete.

[0003] In order to maintain the working performance of concrete and make it have good fluidity, one method is to increase the amount of water reducer. Although the use of some admixtures improves the local performance of concrete, it still cannot fundamentally improve the performance of concrete. Excessive use of water reducer can easily lead to segregation and bleeding of concrete, reducing the compressive strength of concrete. Another method is to solve the slump loss problem of concrete by adding appropriate retarders, such as sodium citrate, sucrose, sodium citrate, etc., but too much retarder not only cannot effectively solve the slump loss problem of concrete, but will affect the performance of water reducer and the state of concrete.

[0004] Patent CN105712651B discloses a concrete collapse-preserving agent with ultra-long-term collapse-preserving performance. It is a polycarboxylic acid collapse-preserving agent with both amide and ester groups. The ester is introduced to provide early adsorption groups, while the amide molecules provide late adsorption groups, so that there are enough adsorption groups for a long time to meet the needs of dispersing cement particles. The polymer has ultra-long-term collapse-preserving performance. In practical application engineering, it can meet the needs of long-term collapse-preserving (more than 4 hours) of concrete under high temperature and long-distance transportation conditions.

[0005] Patent CN110746549B discloses an ultra-long sustained-release polycarboxylic acid slump-preventing agent and a preparation method thereof. The slump-preventing agent molecule contains both hydroxypropyl acrylate units and maleoyloxyethyl pyrrolidone units, which hydrolyze at one fast and one slow speed in the alkaline environment of concrete, ensuring its ultra-long continuous hydrolysis, thereby continuously releasing water-reducing agent molecules to compensate for the consumption of cement hydration and achieving ultra-long-term slump maintenance.

[0006] Patent CN109790261B discloses a method for preparing a segmented slow-release concrete admixture. By introducing polyether side chains of different types and lengths into the molecular side chains, the spatial configuration and degree of stretching of the concrete admixture in the concrete multiphase system can be regulated; by introducing carboxylic acid hydroxy esters, cross-linking monomers, and amino compounds into the molecular main chain, the lubrication effect and hydrophilic state of the particles in the concrete multiphase system can be improved, thereby improving the slump retention of the concrete mixture and reducing the time loss of the concrete.

[0007] Patent CN115725035A discloses a slump-retaining superplasticizer for concrete, a preparation method and application thereof. The main chain of the superplasticizer is composed of a phenyl group connected by a phosphoric acid / phosphite group and an ester group, and the side chain is a comb-shaped polyether containing an ester group. The plasticizer of the present application introduces a small monomer containing an ester group and a comb-shaped structure monomer containing an ester group, which can be further hydrolyzed in an alkaline environment of cement to provide an adsorption group, thereby having excellent slump retention ability; the superplasticizer polymer contains a phosphoric acid group and has a strong coordination ability, which can delay cement hydration, slow down fluidity loss, and improve the slump-retaining ability of the polymer; the main chain structure of the phenyl group in the superplasticizer and the side chain of the comb-shaped structure can reduce the curling ability of the polymer molecule, increase the molecular size of the polymer, and improve the cement adaptability of the polymer.

[0008] In summary, facing the complex diversity and low adsorption of low-carbon cement materials, it is a huge challenge to maintain the workability of concrete for a long time after mixing. Existing technologies either use retarders or new hydrolyzable monomers, cross-linked structures, etc. to achieve the purpose of increasing the collapse retention time, but the technical effects are often limited, and it is difficult to achieve ultra-long-term collapse retention or the performance is poor in low-carbon cement materials. Developing a concrete collapse retaining agent with outstanding collapse retention ability and widely applicable to low-carbon cement-based materials can greatly promote the green and sustainable development of the admixture construction industry. Summary of the invention

[0009] Aiming at a series of adaptability problems of water reducers in the prior art, such as poor dispersion and rapid fluidity loss during the application of low-carbon cement, this application proposes an ultra-long slow-release collapse-preventing agent suitable for low-carbon cement, and a preparation method and application thereof.

[0010] The collapse retaining agent is obtained by a "Graft From" grafting reaction of a prepolymer main chain of an unsaturated enol structure and a side chain of a block structure; the prepolymer main chain is a polymer structure with multiple modifiable hydroxyl groups, which is obtained by free radical polymerization of unsaturated enol monomers in the presence of an initiator and a chain transfer agent.

[0011] The above side chain is obtained by polymerization reaction of A monomer, B monomer, C monomer and D monomer;

[0012] The above-mentioned A monomer is a hydrophobic alkyl acrylate, B monomer is an unsaturated acid, C monomer is a hydroxy ester, and D monomer is a polyoxyethylene ether;

[0013] The molar ratio of the above-mentioned monomer A: monomer B: monomer C: monomer D is (2-10): (2-5): (2-10): 1;

[0014] The weight average molecular weight of the main chain is 1000-10000Da. If it is too short, it will not play the role of the main chain. If it is too long, the molecular chains will be entangled with each other, affecting the grafting effect. The weight average molecular weight of the collapse retaining agent is 30000-50000Da. If the molecular weight is too long, it will cause entanglement within or between the molecular chains, which is not conducive to dispersion. If the molecular weight is too short, it will contain fewer adsorption groups, which is also not conducive to dispersion.

[0015] The main chain structure is shown in the following formula (1):

[0016]

[0017] Wherein R1 is selected from C1-C4 alkyl or -COOCH2CH2-, -COOCH2CH2CH2, -CONHCH2CH2-, -CONHCH2CH2CH2-, ph-CH2-, -OCH2CH2-, -OCH2CH2OCH2CH2-, -OCH2CH2CH2CH2- or does not exist; R2, R3, R4 are independently selected from -CH3 or -H, and m is an integer from 25 to 100.

[0018] The above-mentioned A monomer structure is shown in the following formula (2):

[0019]

[0020] Wherein R5, R6, R7 are independently selected from -CH3 or -H, and R8 is C1~C12 alkyl, ph- or ph-CH2-.

[0021] Preferably, monomer A is selected from any one of methyl acrylate, ethyl acrylate, cyclohexyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, tert-butyl acrylate, phenyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, tert-butyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and propyl methacrylate.

[0022] The unsaturated acid is selected from any one of acrylic acid, methacrylic acid, itaconic acid, citraconic acid, fumaric acid, maleic acid or maleic anhydride, methoxyacrylic acid, methallyl sulfonic acid, methoxyallyl sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, and styrene sulfonic acid.

[0023] The C monomer structure is shown in the following formula (3):

[0024]

[0025] Among them, R9, R 10 , R 11 are independently selected from -CH3 or -H, R 12 It is a C1-C5 alkyl group.

[0026] Preferably, the C monomer is selected from any one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate and hydroxybutyl methacrylate.

[0027] The structure of the D monomer is shown in the following formula (4):

[0028]

[0029] Wherein X is -CH2-, -CH2CH2- or -OCH2CH2- or -OCH2CH2OCH2CH2-, R 13 It is -CH3 or -H, a+b=20~50.

[0030] Preferably, the D monomer is selected from any one of methyl allyl polyoxyethylene ether, allyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, vinyl hydroxybutyl polyoxyethylene ether, and vinyl diethylene glycol polyoxyethylene ether.

[0031] A method for preparing an ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement comprises the following steps: (1) preparing a prepolymer mixed solution: dissolving an unsaturated ene alcohol, an initiator and a chain transfer agent in an anhydrous solvent, and obtaining a prepolymer mixed solution after a free radical polymerization reaction; (2) preparing an intermediate: dissolving an ATRP initiator in an anhydrous solvent and slowly dropping it into the cooled prepolymer mixed solution, and purifying the intermediate after the reaction is completed; (3) preparing a collapse-preventing agent: freezing and thawing the intermediate, A monomer, a transition metal catalyst and an anhydrous solvent for three times, adding a ligand and then freezing and thawing twice, reacting at 45-120° C. for 1-24 hours, and quenching free radicals in an ice-water bath after the reaction is completed; then adding B monomer, C monomer and D monomer for three times of freezing and thawing, reacting at 45-120° C. for 1-24 hours, and obtaining a collapse-preventing agent after purification.

[0032] The chain transfer agent in the above step (1) is an aliphatic mercaptan, and the amount used is 0.2-2 mol% of the total molar amount of the unsaturated enol; the initiator in the above step (1) is an azo compound or a peroxide or a composite initiator system, and the amount used is 0.1 mol%-1 mol% of the total molar amount of the unsaturated enol.

[0033] The aliphatic mercaptan is selected from at least one of isopropyl mercaptan, n-butyl mercaptan, tert-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, lauryl mercaptan and tert-dodecyl mercaptan; the azo compound is any one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate initiators; the peroxide is any one of hydrogen peroxide, benzoyl peroxide, tert-butyl benzoyl peroxide and methyl ethyl ketone peroxide; the composite initiation system is selected from any one of azobisisobutyronitrile and azobisisoheptanenitrile composite initiation system and dibenzoyl peroxide and tert-butyl perbenzoate composite initiation system.

[0034] The ATRP initiator in the above step (2) is any one of 2-bromoisobutyryl chloride, 2-bromoisobutyryl bromide, 2-bromopropionyl bromide and 2-chloropropionyl chloride; the molar ratio of the amount to the unsaturated enol is (1-1.05):1.

[0035] The above transition metal catalyst is at least one of cuprous bromide, cuprous chloride, and cuprous iodide; the above ligand is at least one of 2,2'-bipyridine, pentamethyldiethylenetriamine, hexamethyltriethylenetetramine, tetrakis[(2-pyridyl)methyl]ethylenediamine, tris[2-(dimethylamino)ethyl]amine, and tris(2-pyridylmethyl)amine; and the molar ratio of the above ATRP initiator:transition metal catalyst:ligand is 1:(1-0.1):(1-0.1).

[0036] The anhydrous solvent used in the above preparation method is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, methylpyrrolidone and toluene; the above step (1) controls the total mass concentration of the reaction system to be 30-60wt%, and the above step (2) controls the total mass concentration of the reaction system to be 10-50wt%.

[0037] The free radical polymerization reaction conditions of the above step (2) are a temperature of 50 to 90°C and a stirring time of 1 to 24 hours; the cooling temperature of the prepolymer mixed solution in the above step (2) is 0 to 10°C; the reaction conditions of the above step (2) are first reacting at 0 to 15°C for 1 to 12 hours, and then transferring to 25°C for reaction for 1 to 12 hours; the above steps (2) and (3) are both carried out in an oxygen-free environment to avoid free radical quenching, and inert gases such as nitrogen (N2) or argon (Ar) can be used to expel oxygen from the system.

[0038] The purification method in the above preparation method is to filter out the metal salt, distill or distill under reduced pressure to remove most of the solvent, precipitate in a precipitant, centrifuge and then dry; the precipitant is any one of ether, n-hexane and petroleum ether, and the amount used is 1 to 3 times the total mass of the substance.

[0039] The amount of the collapse-preventing agent is 1 to 5‰ of the total mass of the cementitious material; it can be used in combination with commonly used commercial retarders, early strength agents, air-entraining agents, defoaming agents, expansion agents, etc.

[0040] Compared with the prior art, this application has the following advantages:

[0041] (1) The present application discloses an ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement, which specifically comprises a gradient hydrolysis group consisting of monomer A, monomer C and a connecting ester bond of a main chain and a side chain, wherein the hydrolysis rate of monomer A is much lower than that of monomer C, so as to ensure an ultra-long dispersion effect of the collapse-preventing agent; in addition, the hydrophobic block segments composed of monomer A undergo hydrophobic association in the solution, which can protect the ester bonds of the main chain and the side chain from being easily hydrolyzed;

[0042] (2) The ATRP initiator of the main chain generates a multi-branched side chain structure, and the side chain contains both carboxylic acid and hydroxy ester. The ester bond between the main chain and the side chain can be hydrolyzed to release the side chain collapse-preserving component. The released collapse-preserving component can continue to release the adsorption group gradually through the hydrolysis of small monomers, so as to achieve continuous and slow adsorption on cement particles to improve the fluidity retention time of the slurry;

[0043] (3) The block structure composed of hydrophobic monomers forms hydrophobic micro-regions, which can effectively slow down the hydrolysis rate of ester bonds and achieve ultra-long fluidity retention time;

[0044] The present application can also simultaneously control the hydrolysis rate by adjusting the main chain length, side chain length, side chain sequence structure and other multiple methods to obtain collapse-preserving agents with different collapse-preserving times, effectively meeting the low-carbon cement environment and the dispersion system of complex cementitious materials. DETAILED DESCRIPTION

[0045] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The amounts described in the various embodiments and comparative examples are based on mass.

[0047] Example 1

[0048] (1) dissolving 100 parts of ethylene glycol monovinyl ether, 0.13 parts of azobisisobutyronitrile and 1.3 parts of n-butyl mercaptan in 200 parts of N,N-dimethylformamide, heating to 50° C., stirring and reacting for 24 hours, and obtaining a prepolymer mixed solution after the reaction is completed for standby use;

[0049] (2) Under Ar gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 5°C; 21 parts of 2-bromoisobutyryl chloride were dissolved in 20 parts of N,N-dimethylformamide, and slowly added to the prepolymer mixed solution at 5°C for 1 hour, and then the temperature was raised to 25°C and reacted for 1 hour to obtain an intermediate for standby use;

[0050] (3) Under Ar gas atmosphere, 10 parts of the intermediate obtained in step (2), 5.5 parts of methyl acrylate, 0.19 parts of CuBr, and 140 parts of N,N-dimethylformamide were mixed evenly, and then frozen-thawed for three times. 0.22 parts of PMDETA were added and then frozen-thawed for two more times. The mixture was reacted at 65° C. for 16 h. After the reaction was completed, the free radicals were quenched in an ice water bath. Then, 4.8 parts of acrylic acid, 22 parts of hydroxyethyl acrylate, and 60 parts of methyl allyl polyoxyethylene ether (M w =1000) freeze-thaw cycle three times, react at 65°C for 16 hours, filter to remove metal salts, distill or distill under reduced pressure to remove most of the solvent, precipitate in ether, centrifuge and dry for 24 hours to obtain an ultra-long slow-release collapse-preventing agent SRA-1 suitable for low-carbon cement;

[0051] Example 2

[0052] (1) 100 parts of 2-butenol, 0.68 parts of azobisisoheptanenitrile (ABVN) and 1.25 parts of n-butyl mercaptan are dissolved in 70 parts of N,N-dimethylformamide, the temperature is raised to 60° C., and the mixture is stirred for reaction for 10 hours. After the reaction is completed, a prepolymer mixed solution is obtained for standby use;

[0053] (2) Under N2 gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 5°C; 95 parts of 2-bromoisobutyryl bromide were dissolved in 270 parts of N,N-dimethylformamide, and slowly added to the prepolymer mixed solution at 5°C for 3 hours, and then the temperature was raised to 25°C and reacted for 8 hours to obtain an intermediate for standby use;

[0054] (3) Under N2 gas atmosphere, 10 parts of the intermediate obtained in step (2), 5.2 parts of ethyl acrylate, 0.8 parts of CuCl, and 300 parts of N,N-dimethylformamide were mixed evenly and then frozen-thawed for three times, 1.85 parts of HMTETA were added and then frozen-thawed for two more times, and the mixture was reacted at 65°C for 24 hours. After the reaction was completed, the free radicals were quenched in an ice water bath; 9.0 parts of methacrylic acid, 30 parts of hydroxypropyl acrylate, and 100 parts of allyl polyoxyethylene ether (M w =2000) freeze-thaw cycle three times, react at 65°C for 24 hours, filter to remove metal salts, distill or distill under reduced pressure to remove most of the solvent, precipitate in ether, centrifuge and dry for 24 hours to obtain an ultra-long slow-release collapse-preventing agent SRA-2 suitable for low-carbon cement;

[0055] Example 3

[0056] (1) Dissolve 100 parts of 2-allyl alcohol, 3.3 parts of benzoyl peroxide (BPO) and 3.6 parts of n-octyl mercaptan in 150 parts of N,N-diethylformamide, heat to 90° C., stir and react for 4 hours, and after the reaction is completed, obtain a prepolymer mixed solution for standby use;

[0057] (2) Under Ar gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 0°C; 75 parts of 2-bromopropionyl bromide were dissolved in 65 parts of N,N-dimethylacetamide, and slowly added to the prepolymer mixed solution at 0°C for 4 hours, and then the temperature was raised to 25°C and reacted for 1 hour to obtain an intermediate for standby use;

[0058] (3) Under Ar gas atmosphere, 10 parts of the intermediate obtained in step (2), 23 parts of tert-butyl acrylate, 1 part of CuBr, and 500 parts of N,N-dimethylacetamide were mixed evenly, and then frozen-thawed for three times, 3.2 parts of TPEN were added, and then frozen-thawed for two more times, and reacted at 120° C. for 1 hour. After the reaction was completed, the free radicals were quenched in an ice water bath; 50 parts of vinyl sulfonic acid, 230 parts of hydroxybutyl acrylate, and 260 parts of isopentyl polyoxyethylene ether (M w =1000) freeze-thaw cycle three times, react at 120°C for 1 hour, filter to remove metal salts, distill or distill under reduced pressure to remove most of the solvent, precipitate in ether, centrifuge and dry for 24 hours to obtain an ultra-long slow-release collapse-preventing agent SRA-3 suitable for low-carbon cement;

[0059] Example 4

[0060] (1) Dissolve 100 parts of 3-methyl-3-butene-1-ol, 0.57 parts of azobisisobutyronitrile (AIBN) and 0.62 parts of tert-butyl mercaptan in 100 parts of N,N-diethylformamide, heat to 60° C., stir and react for 6 hours, and after the reaction is completed, obtain a prepolymer mixed solution for standby use;

[0061] (2) Under N2 gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 0°C; 37 parts of 2-chloropropionyl chloride were dissolved in 110 parts of N,N-dimethylacetamide, and slowly added to the prepolymer mixed solution at 0°C for 6 hours, and then the temperature was raised to 25°C and reacted for 6 hours to obtain an intermediate for standby use;

[0062] (3) Under N2 gas atmosphere, 10 parts of the intermediate obtained in step (2), 33 parts of ethyl methacrylate, 1.25 parts of CuCl, and 750 parts of N,N-dimethylacetamide were mixed evenly and then frozen-thawed for three times, 3.0 parts of Me6TREN were added and then frozen-thawed for two more times, and the mixture was reacted at 90°C for 12 hours. After the reaction was completed, the free radicals were quenched in an ice water bath; 110 parts of methoxyacrylic acid, 190 parts of hydroxyethyl methacrylate, and 225 parts of vinyl hydroxybutyl polyoxyethylene ether (M w =1500) freeze-thaw cycle three times, react at 90°C for 12h, filter to remove metal salts, distill or distill under reduced pressure to remove most of the solvent, precipitate in n-hexane, centrifuge and dry for 24h to obtain an ultra-long slow-release collapse-preventing agent SRA-4 suitable for low-carbon cement;

[0063] Example 5

[0064] (1) dissolving 100 parts of N-hydroxyethyl acrylamide, 0.86 parts of azobisisoheptanenitrile (ABVN) and 0.89 parts of lauryl mercaptan in 100 parts of toluene, heating to 70° C., stirring and reacting for 12 hours, and obtaining a prepolymer mixed solution after the reaction is completed for standby use;

[0065] (2) Under Ar gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 10° C.; 50 parts of 2-bromoisobutyryl bromide were dissolved in 650 parts of toluene, and the mixture was slowly added dropwise to the prepolymer mixed solution at 10° C. for 10 h, and then the mixture was heated to 25° C. and reacted for 12 h to obtain an intermediate for standby use;

[0066] (3) Under Ar gas atmosphere, 10 parts of the intermediate obtained in step (2), 2.8 parts of ethyl acrylate, 0.1 parts of CuBr, and 600 parts of toluene were mixed evenly, and then frozen-thawed for three times, 0.1 parts of bpy was added, and then frozen-thawed for two more times, and reacted at 85° C. for 8 h. After the reaction was completed, the free radicals were quenched in an ice water bath; 10 parts of acrylic acid, 30 parts of hydroxyethyl acrylate, and 58 parts of vinyl diethylene glycol polyoxyethylene ether (M w =1000) freeze-thaw cycle three times, react at 85°C for 8h, filter to remove metal salts, distill or distill under reduced pressure to remove most of the solvent, precipitate in n-hexane, centrifuge and dry for 24h to obtain an ultra-long slow-release collapse-preventing agent SRA-5 suitable for low-carbon cement;

[0067] Example 6

[0068] (1) Dissolve 100 parts of 2-methylallyl alcohol, 3.36 parts of benzoyl peroxide (BPO) and 0.57 parts of tert-dodecyl mercaptan in 150 parts of toluene, heat to 75° C., stir and react for 8 hours, and after the reaction is completed, obtain a prepolymer mixed solution for standby use;

[0069] (2) Under Ar gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 10° C.; 60 parts of 2-bromopropionyl bromide were dissolved in 250 parts of toluene, and the mixture was slowly added dropwise to the prepolymer mixed solution at 10° C. for 12 hours, and then the mixture was heated to 25° C. and reacted for 5 hours to obtain an intermediate for standby use;

[0070] (3) Under Ar gas atmosphere, 10 parts of the intermediate obtained in step (2), 13 parts of benzyl methacrylate, 0.4 parts of CuCl, and 750 parts of toluene were mixed evenly, and then frozen-thawed for three times. 0.7 parts of PMDETA was added and then frozen-thawed for two more times. The mixture was reacted at 80° C. for 8 h. After the reaction was completed, the free radicals were quenched in an ice water bath. Then, 25 parts of methacrylic acid, 85 parts of hydroxypropyl acrylate, and 85 parts of methallyl polyoxyethylene ether (M w =2000) freeze-thaw cycle three times, react at 80°C for 8h, filter to remove metal salts, distill or distill under reduced pressure to remove most of the solvent, precipitate in ether, centrifuge and dry for 24h to obtain an ultra-long slow-release collapse-preventing agent SRA-6 suitable for low-carbon cement;

[0071] Comparative Example 1

[0072] (1) dissolving 100 parts of ethylene glycol monovinyl ether, 0.13 parts of azobisisobutyronitrile and 1.3 parts of n-butyl mercaptan in 200 parts of N,N-dimethylformamide, heating to 50° C., stirring and reacting for 24 hours, and obtaining a prepolymer mixed solution after the reaction is completed for standby use;

[0073] (2) Under Ar gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 5°C; 21 parts of 2-bromoisobutyryl chloride were dissolved in 20 parts of N,N-dimethylformamide, and slowly added to the prepolymer mixed solution at 5°C for 1 hour, and then the temperature was raised to 25°C and reacted for 1 hour to obtain an intermediate for standby use;

[0074] (3) Under Ar gas atmosphere, 10 parts of the intermediate obtained in step (2) were added with 4.8 parts of acrylic acid, 22 parts of hydroxyethyl acrylate, and 60 parts of methyl allyl polyoxyethylene ether (M w =1000), 0.19 parts of CuBr, and 140 parts of N,N-dimethylformamide were mixed evenly, and then freeze-thawed for three times, and reacted at 65°C for 16 hours. After the reaction was completed, the free radicals were quenched in an ice-water bath; the metal salt was filtered out, and most of the solvent was removed by distillation or reduced pressure distillation. After precipitation in ether, centrifugation and drying for 24 hours, REF-1 was obtained;

[0075] Comparative Example 2

[0076] (1) dissolving 100 parts of ethylene glycol monovinyl ether, 0.13 parts of azobisisobutyronitrile and 1.3 parts of n-butyl mercaptan in 200 parts of N,N-dimethylformamide, heating to 50° C., stirring and reacting for 24 hours, and obtaining a prepolymer mixed solution after the reaction is completed for standby use;

[0077] (2) Under Ar gas atmosphere, 50 parts of the prepolymer mixed solution were cooled to 5°C; 21 parts of 2-bromoisobutyryl chloride were dissolved in 20 parts of N,N-dimethylformamide, and slowly added to the prepolymer mixed solution at 5°C for 1 hour, and then the temperature was raised to 25°C and reacted for 1 hour to obtain an intermediate for standby use;

[0078] (3) Under Ar gas atmosphere, 10 parts of the intermediate obtained in step (2), 5.5 parts of methyl acrylate, 0.19 parts of CuBr, and 140 parts of N,N-dimethylformamide were mixed evenly, and then freeze-thawed for three times. 0.22 parts of PMDETA were added and then freeze-thawed for two more times. The mixture was reacted at 65°C for 16 hours. After the reaction was completed, the metal salt was filtered out, and most of the solvent was removed by distillation or reduced pressure distillation. After precipitation in ether, the mixture was centrifuged and dried for 24 hours to obtain REF-2.

[0079] The following test examples use homemade limestone calcined clay cement (LC3) for relevant tests. The specific preparation method refers to invention patents CN111875268B, CN115959870A, and CN116018328A, wherein the proportion of LC3 cement is 50% P·I 42.5 silicate cement, 30% calcined clay, 15% limestone, and 5% gypsum;

[0080] Test Example 1: Cement paste fluidity test

[0081] The fluidity of the pure paste was tested according to GBT8077-2012, the admixture dosage was 0.12% water reducer and 0.12% slump retainer, the water-cement ratio was 0.29, and the water reducer was a commercially available polycarboxylate water reducer. The results are shown in Table 1 (unit: mm)

[0082] Table 1

[0083] Admixtures Initial fluidity 1h fluidity 2h fluidity 3h fluidity 4h fluidity Collapse Retention Agent SRA-1 225 270 266 256 226 Slump Retention Agent SRA-2 219 260 262 256 231 Slump Retention Agent SRA-3 224 264 272 254 222 Slump Retention Agent SRA-4 222 263 261 255 233 Collapse Retention Agent SRA-5 224 269 270 257 232 Slump Retention Agent SRA-6 229 266 274 265 220 Collapse Retention Agent REF-1 215 274 235 172 152 Slump Retention Agent REF-2 175 208 225 215 205 Commercially available anti-slump agent 210 242 205 165 No flow

[0084] From the data of LC3 cement in Table 1, it can be seen that, except for REF-2, the initial fluidity of the pure paste of all other samples is relatively close, and all show a significant increase after 1 hour. Compared with the commercial slump retaining agent, the fluidity increase of Examples SRA-1 to 6 is more obvious, and its fluidity does not lose significantly after 4 hours, and the fluidity of the pure paste can be maintained for at least 4 hours; while the commercial slump retaining agent only begins to show a significant loss of fluidity after 2 hours, and the pure paste does not have obvious fluidity after 4 hours; compared with the comparative example REF-1, the difference is that there is no alkyl acrylate segment structure. The results show that REF-1 has a good release rate of fluidity in the early stage, but poor fluidity retention in the later stage, and fluidity begins to lose at 2 hours, proving that the introduction of alkyl acrylate segments plays a decisive role in mid- and late-stage slump retention. Compared with the comparative example REF-2, the difference is that REF-2 only has alkyl acrylate segments, and its initial dispersion ability of the pure paste is seriously insufficient, and the loss rate in the later stage is acceptable, indicating that the block structure described in the invention has excellent dispersion and dispersion retention ability in low-carbon LC3 cement.

[0085] Test Example 2: Mortar fluidity test at different temperatures

[0086] Temperature will affect cement hydration, hydrolysis rate of ester bond of slump retaining agent, adsorption rate, etc. The following verifies the performance of the ultra-long slow-release slump retaining agent for low-carbon cement described in the present invention on mortar fluidity at different temperatures. The experiment uses 1350g of ISO standard sand, 700g of LC3 cement, a water-cement ratio of 0.33, and an admixture dosage of 0.12% water reducer and 0.12% slump retaining agent. The water reducer is a commercially available polycarboxylate water reducer. The results are shown in Table 2 (unit: mm)

[0087] Table 2

[0088]

[0089]

[0090] The above mortar data show that the fluidity of all sample mortars can maintain fluidity for 2 to 3 hours at a normal temperature of 25°C, while at a high temperature of 40°C, the 2-hour fluidity retention performance decreases significantly; especially compared with the commercially available collapse retaining agent, the commercially available collapse retaining agent at a high temperature of 40°C has a 3-hour mortar fluidity of only 58% of the initial fluidity, while the fluidity of Examples SRA-1 to SRA-6 can be maintained at about 90% and the fluidity at 4 hours is maintained at about 80%; at the same time, the performance of REF-1 and REF-2 is compared, which is basically consistent with the dispersion results in the neat slurry, indicating that the ultra-long sustained-release collapse retaining agent suitable for low-carbon cement described in the present invention has a special alkyl acrylate block side chain structure and exhibits good sustained-release and dispersion retention performance in the low-carbon cement system.

[0091] Test Example 3: Concrete Performance Test

[0092] The slump and expansion of concrete were tested according to the "Test Method for Homogeneity of Concrete Admixtures" - GBT8077-2012; the 3d and 28d compressive strength of concrete were tested according to the "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T50081-2019); the test concrete mix ratio was LC3 cement 380kg / m 3 , river sand 750kg / m 3 , crushed stone 1100kg / m 3 , water-binder ratio 0.4, admixture dosage is 0.12% water reducer compound 0.1% slump retainer, water reducer is commercially available polycarboxylate water reducer. The results are shown in Table 3.

[0093] Table 3

[0094]

[0095] The concrete data also compares the differences in dispersion retention capabilities of Examples SRA-1 to 6, REF-1 to 2, and commercially available collapse agents. The results show that SRA-1 to 6 can maintain the fluidity of concrete for more than 4 hours, and the expansion of concrete in 4 hours has not decreased significantly. Compared with commercially available collapse agents, the expansion in 4 hours is only about 67% of the initial expansion, and REF-2 has no fluidity at all. At the same time, attention is paid to the 3d and 28d strengths. Due to the good dispersibility and mixing performance brought by Examples SRA-1 to 6, the concrete vibration density is higher, and the 3d and 28d strengths are relatively higher than REF-1 to 2 and commercially available collapse agents.

[0096] In summary, the ultra-long slow-release collapse-preventing agent suitable for low-carbon cement described in the invention shows good slow-release and long-term collapse-preventing capabilities in low-carbon cementitious materials. Its fluidity can be maintained for at least 4 hours in the neat paste of low-carbon LC3 cement or C30 concrete, which is better than the level of commercially available collapse-preventing agents.

[0097] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement, characterized in that: The collapse-preserving agent is obtained by a "Graft From" grafting reaction of a prepolymer main chain of an unsaturated enol structure and a side chain of a block structure; The side chain is obtained by polymerization reaction of monomer A, monomer B, monomer C and monomer D; The A monomer is a hydrophobic alkyl acrylate, the B monomer is an unsaturated acid, the C monomer is a hydroxy ester, and the D monomer is a polyoxyethylene ether; The molar ratio of the A monomer: the B monomer: the C monomer: the D monomer is (2-10): (2-5): (2-10): 1; The weight average molecular weight of the main chain is 1000-10000Da, and the weight average molecular weight of the collapse retaining agent is 30000-50000Da.

2. The ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement according to claim 1, characterized in that: The main chain structure is shown in the following formula (1): Wherein R1 is selected from C1-C4 alkyl or -COOCH2CH2-, -COOCH2CH2CH2, -CONHCH2CH2-, -CONHCH2CH2CH2-, ph-CH2-, -OCH2CH2-, -OCH2CH2OCH2CH2-, -OCH2CH2CH2CH2- or does not exist; R2, R3, R4 are independently selected from -CH3 or -H, and m is an integer from 25 to 100.

3. The ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement according to claim 1, characterized in that: The A monomer structure is shown in the following formula (2): Wherein R5, R6, R7 are independently selected from -CH3 or -H, and R8 is C1-C12 alkyl, ph- or ph-CH2-.

4. The ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement according to claim 1, characterized in that: The unsaturated acid is selected from any one of acrylic acid, methacrylic acid, itaconic acid, citraconic acid, fumaric acid, maleic acid or maleic anhydride, methoxyacrylic acid, methyl allyl sulfonic acid, methoxy allyl sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, and styrene sulfonic acid.

5. The ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement according to claim 1, characterized in that: The C monomer structure is shown in the following formula (3): Among them, R9, R 10 , R 11 are independently selected from -CH3 or -H, R 12 It is a C1-C5 alkyl group.

6. The ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement according to claim 1, characterized in that: The D monomer structure is shown in the following formula (4): Wherein X is -CH2-, -CH2CH2- or -OCH2CH2- or -OCH2CH2OCH2CH2-, R 13 It is -CH3 or -H, a+b=20~50.

7. A method for preparing an ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Preparation of prepolymer mixed solution: unsaturated ene alcohol, initiator and chain transfer agent are dissolved in anhydrous solvent, and a prepolymer mixed solution is obtained after free radical polymerization reaction; (2) Preparation of intermediate: ATRP initiator is dissolved in anhydrous solvent and slowly added dropwise to the cooled prepolymer mixed solution, and the intermediate is purified after the reaction is completed; (3) Preparation of collapse retaining agent: the intermediate, A monomer, transition metal catalyst and anhydrous solvent are freeze-thawed for three times, and the ligand is added and frozen-thawed for two times, and the reaction is carried out at 45-120°C for 1-24h. After the reaction is completed, the free radicals are quenched in an ice water bath; then B monomer, C monomer and D monomer are added and frozen-thawed for three times, and the reaction is carried out at 45-120°C for 1-24h, and the collapse retaining agent is obtained after purification.

8. The preparation method according to claim 7, characterized in that: The chain transfer agent in step (1) is an aliphatic mercaptan, and the amount used is 0.2 to 2 mol% of the total molar amount of the unsaturated enol; the initiator in step (1) is an azo compound or a peroxide or a composite initiator system, and the amount used is 0.1 to 1 mol% of the total molar amount of the unsaturated enol.

9. The preparation method according to claim 8, characterized in that: The aliphatic mercaptan is selected from at least one of isopropyl mercaptan, n-butyl mercaptan, tert-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, lauryl mercaptan and tert-dodecyl mercaptan; the azo compound is any one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate initiators; the peroxide is any one of hydrogen peroxide, benzoyl peroxide, tert-butyl benzoyl peroxide and methyl ethyl ketone peroxide; the composite initiation system is selected from any one of azobisisobutyronitrile and azobisisoheptanenitrile composite initiation system and dibenzoyl peroxide and tert-butyl perbenzoate composite initiation system.

10. The preparation method according to claim 7, characterized in that: The ATRP initiator in step (2) is any one of 2-bromoisobutyryl chloride, 2-bromoisobutyryl bromide, 2-bromopropionyl bromide and 2-chloropropionyl chloride; The molar ratio of the dosage to the unsaturated enol is (1-1.05):

1.

11. The preparation method according to claim 7, characterized in that: The transition metal catalyst is at least one of cuprous bromide, cuprous chloride, and cuprous iodide; the ligand is at least one of 2,2'-bipyridine, pentamethyldiethylenetriamine, hexamethyltriethylenetetramine, tetrakis[(2-pyridyl)methyl]ethylenediamine, tris[2-(dimethylamino)ethyl]amine, and tris(2-pyridylmethyl)amine; and the molar ratio of the ATRP initiator:transition metal catalyst:ligand is 1:(1-0.1):(1-0.1).

12. The preparation method according to claim 7, characterized in that: The anhydrous solvent used in the preparation method is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, methylpyrrolidone and toluene; the total mass concentration of the reaction system in step (1) is controlled to be 30-60wt%, and the total mass concentration of the reaction system in step (2) is controlled to be 10-50wt%.

13. The preparation method according to claim 7, characterized in that: The free radical polymerization reaction conditions of step (2) are a temperature of 50 to 90° C. and a stirring time of 1 to 24 hours; the cooling temperature of the prepolymer mixed solution of step (2) is 0 to 10° C.; the reaction conditions of step (2) are first reacting at 0 to 15° C. for 1 to 12 hours, and then transferring to 25° C. for reaction for 1 to 12 hours; both steps (2) and (3) are carried out in an anaerobic environment.

14. An application of an ultra-long sustained-release collapse-preventing agent suitable for low-carbon cement, characterized in that: The amount of the collapse-preventing agent is 1 to 5‰ of the total mass of the cementitious material; the collapse-preventing agent is the collapse-preventing agent described in any one of claims 1 to 6 or the collapse-preventing agent obtained by the preparation method described in any one of claims 7 to 13.

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