Low-temperature early-strength water reducer and preparation method thereof

Abstract

The present invention belongs to the technical field of preparation of water reducers, and the present invention discloses a low-temperature early-strength water reducer and a preparation method thereof. The present invention obtains a polyester macromonomer by first subjecting the monomer obtained by amidation reaction and esterification reaction to Michael addition reaction, and then undergoes free radical polymerization reaction with polyether macromonomer, carboxylic acid small monomer and sulfonic acid small monomer, and then sequentially undergoes functional modification by Hofmann degradation reaction and amidation reaction, and then undergoes Thiol-ene reaction with thiolated trehalose to synthesize a low-temperature early-strength water reducer. The low-temperature early-strength water reducer prepared by the present invention has the advantage of maintaining good dispersibility under low-temperature conditions, and the synthesis process is controllable, energy-saving and environmentally friendly, and can be effectively used in the field of concrete to solve the problems of poor concrete working performance and slow early strength development under low-temperature conditions, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of water reducing agents, in particular to a low-temperature early-strength water reducing agent and a preparation method thereof. Background Art

[0002] In recent years, with the acceleration of infrastructure construction in my country and the rapid development of industries such as real estate, concrete, as the largest consumable in the building materials industry, has been widely used in many fields. In addition, with the development of reinforcement and maintenance projects, the production of precast concrete parts and the advancement of national housing industrialization, new requirements have been put forward for the early strength of concrete. Especially for cold areas, the low-temperature construction of ready-mixed concrete is a common problem faced by northern my country. During the transition period between winter construction and normal construction, temperature fluctuations will lead to great uncertainty in the development of concrete strength. Due to the low ambient temperature, traditional concrete has problems such as poor working performance and collapse resistance and slow early strength development, which seriously affect the construction progress of concrete. Therefore, there is an urgent need to develop an admixture that can effectively improve the working performance of concrete and increase its early strength in a low-temperature environment.

[0003] Currently, research is underway to improve the early strength of concrete by reducing the water-cement ratio, using high-strength cement, employing high-quality aggregates, and adding early-strength agents. Early-strength agents, with their low cost, ease of use, and effective early-strength enhancement, are considered one of the most widely used methods for improving the early strength of concrete.

[0004] There are many types of early strength agents, which can be divided into inorganic salt early strength agents, organic early strength agents, and composite early strength agents (composite of inorganic and organic substances) according to their chemical composition. Inorganic salt early strength agents mainly include chlorides (such as calcium chloride, etc.), sulfates, nitrates, nitrites, carbonates, lithium salts, nanomaterials and crystal embryos, etc. Organic early strength agents mainly include alcoholamines (such as triethanolamine and triisopropanolamine, etc.), calcium formate, urea and early strength polycarboxylic acid water reducers, etc. Composite early strength agents mainly include composites of chlorides and alcoholamines, composites of carbonates and alcoholamines, composites of inorganic salts and early strength polycarboxylic acid water reducers, etc. Although inorganic salt early strength agents can improve the early strength of concrete, the Cl contained in them - 、SO4 2- and CO3 2-It will increase concrete shrinkage, exacerbate steel corrosion, and seriously affect the durability of concrete. Organic early strength accelerators are mainly small organic molecules. Their mechanism of action is relatively simple, and their effect on improving the early strength of concrete is poor. They are also expensive. In addition, some early strength polycarboxylate water reducers, while they can improve the early strength of concrete at room temperature, cannot exert their early strength effect in low temperature environments. Therefore, the development of low-temperature early strength water reducers suitable for low-temperature curing environments, with good working performance and good early strength improvement effect, is of great practical significance for solving the problem of developing the early strength of concrete in cold regions.

[0005] The natural high-molecular-weight polymer chitosan used in the present invention contains a large number of amino groups, making the molecules highly designable. Long polymer chains containing multiple amide groups are obtained through amide reactions and Michael addition reactions. These chains are then free-radical polymerized with polyether macromonomers, olefinic acid small monomers, and sulfonic acid small monomers to obtain polymers containing imides. Finally, olefin-functionalized polymers are obtained through Hofmann degradation reactions and amidation reactions. The presence of olefins enables them to serve as junctions for Thiol-ene reactions. Therefore, if monomers containing multiple hydroxyl groups are grafted onto the olefin-functionalized polymer through the Thiol-ene reaction to form a molecular structure with multiple hydroxyl groups, the synergistic effects of carboxyl groups, sulfonic acid groups, amide groups, and hydroxyl groups are achieved, effectively lowering the freezing point of the pore solution within the concrete. This innovatively addresses the problem of poor performance and insignificant early strength enhancement of traditional early-strength polycarboxylate water-reducers in low-temperature environments.

[0006] Chinese invention patent CN117304422A (publication date: December 29, 2023) reports an early-strength polycarboxylic acid water-reducing agent and a preparation method thereof. The early-strength polycarboxylic acid water-reducing agent is copolymerized at room temperature by unsaturated sulfonic acid monomer, unsaturated esterification monomer, unsaturated carboxylic acid monomer, initiator and solvent. The invention uses epoxy silane coupling agent and double-end silicone oil to carry out dealcoholization reaction to obtain epoxy-terminated modifier, and then reacts with saturated monobasic organic acid to obtain silicon-modified esterification product containing hydroxyl group, and then reacts with allyl epoxy-terminated polyether containing an amino group and a silyl group to produce epoxy ring-opening reaction. The advantage of this invention is that the synthesized early-strength water-reducing agent has good dispersibility in cement particles, high water reduction rate and good early strength effect. However, the functional group that plays an early strength role in this invention is only the sulfonic acid group, the number of functional groups is small, and the type is relatively single, and the effect of improving the early strength of concrete under low temperature environment has not yet been carried out.

[0007] Chinese invention patent CN117126346A (publication date: November 28, 2023) reports a crystal nucleus early strength polycarboxylic acid water reducer and its preparation method. The invention uses a one-step synthesis process and adopts unsaturated carboxylic acid, unsaturated amide, ethylene glycol monovinyl polyoxyethylene ether, oxidant, reducing agent, chain transfer agent and modified crystal nucleus free radical polymerization. The advantage of this invention is that it adopts a one-pot synthesis method, which can improve the early strength of concrete, improve the discharging state of concrete, and has good dispersibility and plasticity for mortar. However, the invention does not significantly improve the early strength of concrete by relying solely on modified crystal nuclei, and whether it is effective in developing the early strength of concrete in a low temperature environment remains to be investigated.

[0008] Chinese invention patent CN116535580A (publication date: August 4, 2023) reports a polyether end-functionalized ultra-early strength polycarboxylic acid water-reducing agent and its preparation method. The invention prepares a modified polyether macromonomer with a terminal hydroxyl grafted carboxyl group by alcoholysis of a cyclic dianhydride, and then undergoes an amidation reaction with an aminosiloxane to prepare a modified polyether with a long-chain branched end group having an amino group and a silane ring structure, which is then copolymerized with an amide monomer free radical. The advantage of this invention is that the synthesis process is simple and easy to operate, and it has a certain promoting effect on the development of early strength of concrete. However, this invention does not purify the product during the alcoholysis reaction, amidation reaction and free radical polymerization reaction process. The final synthesized sample may contain some by-products, and the unknown product ratio brings greater uncertainty to subsequent applications.

[0009] The early-strength polycarboxylate superplasticizers described in most existing patents have a certain improvement effect on the working performance of concrete and can promote the development of early strength of concrete to a certain extent. This confirms that the synthesized early-strength polycarboxylate superplasticizers with sulfonic acid groups and amide groups can significantly improve the application efficacy of polymers. However, the above-mentioned synthesis methods all have certain shortcomings. Researchers have mostly focused on modifying traditional polycarboxylate superplasticizers. It is difficult to achieve the goal of significantly improving the early strength of concrete by simply introducing groups or modifying polyether side chains. In addition, most patents only study the effect of improving the early strength of concrete under room temperature conditions. Under low-temperature curing conditions, many superplasticizers lose their activity, making it difficult to promote the development of early strength of concrete under low-temperature conditions. This limits their promotion and application in low-temperature environments. Therefore, it is urgent to develop a low-temperature early-strength water reducer with a new molecular structure. It is necessary to innovatively synthesize a water reducer containing carboxyl, sulfonic acid, amide and hydroxyl groups based on the molecular structure design concept. The molecular structure of the low-temperature early-strength water reducer can be precisely controlled through the synthesis methods of amidation, esterification, Michael addition, free radical polymerization, Hofmann degradation and Thiol-ene reaction, so that the synthesized low-temperature early-strength water reducer can not only play the role of water reduction, but also ensure that the freezing point of the concrete pore solution is lowered to promote the development of the early strength of concrete. The synthesis method is easy to control, which is conducive to industrial promotion. There are no relevant reports on this work at home and abroad. Summary of the Invention

[0010] In view of this, the present invention provides a low-temperature early-strength water reducer and a preparation method thereof, wherein the monomers obtained by amidation reaction and esterification reaction are first subjected to Michael addition reaction to obtain a polyester macromonomer, which is then subjected to free radical polymerization reaction with a polyether macromonomer, a carboxylic acid small monomer and a sulfonic acid small monomer, and then functionally modified by Hofmann degradation and amidation reaction in sequence, and then Thiol-ene reaction is carried out with thiolated trehalose to synthesize a low-temperature early-strength water reducer, so as to solve the problems existing in the prior art.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] The present invention provides a low-temperature early-strength water reducer, the structural formula of which is as follows:

[0013]

[0014] Among them, the structural formula of R' is:

[0015]

[0016] Among them, the wavy line position is the connection position, R is CH2, CH2CH2 or O(CH2CH2O)2, R1 is H, CH3, CH2CH3 or CH2COOH, R2 is H or CH3, R3 is H, OH, CH3O, Cl or Br, R4 is H, OH, CH3O or Cl, and R5 is H or Na; a, b, c, d, m, n, x and f are integers, representing the number of repeating units of each part in the polymer, a is 10 to 150, b is 3 to 40, c is 3 to 30, d is 3 to 50, m is 0 to 100, n is 10 to 150, x is 2 to 10, and f is 1 to 5.

[0017] The present invention also provides a method for preparing the low-temperature early-strength water-reducing agent, comprising the following steps:

[0018] (1) dissolving chitosan in solvent 1 to obtain mixed solution 1; activating unsaturated carboxylic acid small monomer, solvent 2 and activating agent to obtain mixed solution 2; adding mixed solution 2 to mixed solution 1 to carry out amidation reaction, followed by dialysis and vacuum drying to obtain amidated product 1;

[0019] (2) reacting poly(ethylene glycol) methacrylate, bipyridine, and solvent 3 to obtain a mixed solution 3; uniformly mixing N,N'-disuccinimidyl carbonate, a pyridine compound, and solvent 4, and adding the resultant mixture to the mixed solution 3 for esterification, followed by vacuum distillation and purification to obtain an esterified product;

[0020] (3) reacting the amidation product 1 with solvent 1 to obtain a mixed solution 4; dissolving the esterification product in solvent 5 and then adding it dropwise to the mixed solution 4 to perform a Michael addition reaction, followed by dialysis and vacuum drying to obtain a Michael addition product;

[0021] (4) The polyether macromonomer and solvent 5 are mixed to obtain a bottom liquid, an oxidant is first added to the bottom liquid and stirred evenly, and then liquid A, liquid B and liquid C are simultaneously added to the bottom liquid; wherein, liquid A is a mixture of olefinic acid small monomer, sulfonic acid small monomer and solvent 5, liquid B is a mixture of Michael addition product and solvent 5, and liquid C is a reducing agent, a chain transfer agent and Solvent 5 After the dropwise addition is completed, a free radical polymerization reaction is carried out, and a free radical polymerization product is obtained by distillation under reduced pressure;

[0022] (5) subjecting the free radical polymerization product, the catalyst, the solvent 6, and the alkaline solution to a Hofmann degradation reaction, followed by purification and vacuum drying to obtain a Hofmann degradation product;

[0023] (6) reacting the Hofmann degradation product with solvent 5 to obtain a mixture 6; dissolving the anhydride small monomer in solvent 7 and heating in a water bath to obtain a mixture 7; subjecting the mixture 6, the mixture 7, and the amine small monomer to an amidation reaction, followed by dialysis and vacuum drying to obtain an amidated product 2;

[0024] (7) Trehalose, triphenylphosphine and solvent 4 are mixed, and an amine compound is added dropwise thereto to carry out reaction 1. After reaction 1 is completed, an ester substance and an alcohol substance are added thereto in sequence to carry out reaction 2, and then extraction, washing and vacuum drying are carried out in sequence to obtain thiolated trehalose; amidation product 2 is reacted with solvent 4 to obtain mixed solution 8; thiolated trehalose is dissolved in solvent 2, and solvent 8 is added and mixed, and then added to mixed solution 8 to carry out thiol-ene reaction, and then cooled to room temperature and purified in sequence to obtain a low-temperature early-strength water reducer.

[0025] In step (1) of the present invention, solvent 1 includes acetic acid or hydrochloric acid, and the mass concentration of solvent 1 is 0.5-2%; the unsaturated carboxylic acid small monomer includes cinnamic acid, m-chlorocinnamic acid, m-bromocinnamic acid, p-chlorocinnamic acid, p-bromocinnamic acid, caffeic acid or 3,4-dimethoxycinnamic acid; solvent 2 includes phosphate buffer; the activator includes 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide. The molar ratio of imide is 1-2:1; the molar ratio of chitosan and unsaturated carboxylic acid small monomer is 1-2:1; the molar ratio of activator and unsaturated carboxylic acid small monomer is 2-4:1; the mass ratio of solvent 1, solvent 2 and chitosan is 40-60:20-40:1; the dissolution temperature is 20-30°C, and the dissolution time is 12-24 hours; the activation temperature is 20-30°C, and the activation time is 1-3 hours; the amidation reaction temperature is 30-35°C, and the amidation reaction time is 2-6 hours.

[0026] In step (2) of the present invention, solvent 3 includes water or anhydrous ethanol; the pyridine compound includes pyridine, 4-dimethylaminopyridine or 2-bromo-4-dimethylaminopyridine; solvent 4 includes one or more of N,N-dimethylformamide, N,4-dimethylformamide, and dimethyl sulfoxide; the molar ratio of poly(ethylene glycol) methacrylate, bipyridine, N,N'-disuccinimidyl carbonate and pyridine compound is 10-40:1:30-60:40-60; the mass ratio of poly(ethylene glycol) methacrylate, solvent 3 and solvent 4 is 1:30-60:40-80; the reaction is carried out under nitrogen conditions, and the reaction time is 10-30 minutes; the esterification reaction is carried out under nitrogen conditions, the esterification reaction temperature is 70-90°C, and the esterification reaction time is 4-6 hours.

[0027] In step (3) of the present invention, solvent 1 includes acetic acid or hydrochloric acid, and the mass concentration of solvent 1 is 0.5-2%; solvent 5 is water; the molar ratio of esterification product and amidation product 1 is 0.5-1:1; the mass ratio of amidation product 1, solvent 1 and solvent 5 is 1:60-120:40-80; the reaction is carried out under nitrogen conditions, the reaction temperature is 30-50°C, and the reaction time is 1-3h; the dropwise addition time is 40-80min; the Michael addition reaction is carried out under nitrogen conditions, the Michael addition reaction temperature is 50-70°C, and the Michael addition reaction time is 20-24h.

[0028] In step (4) of the present invention, the polyether macromonomer includes methyl allyl polyoxyethylene ether, isopentanol polyoxyethylene ether or butanediol monovinyl polyoxyethylene ether, and the molecular weight of the polyether macromonomer is 2000-5000 g / mol; the solvent 5 independently includes water; the oxidant includes H2O2, ammonium persulfate, potassium persulfate or sodium persulfate; the olefinic acid small monomer includes acrylic acid, methacrylic acid, 2-ethylacrylic acid, maleic anhydride, itaconic acid, crotonic acid, crotonic anhydride, isomethacrylic acid or trans-2-pentenoic acid; the sulfonic acid small monomer includes 2-acrylamide-2-methylpropanesulfonic acid or 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt; the reducing agent includes one or more of ascorbic acid, bleaching agent and FeSO4; the chain transfer agent includes thioglycolic acid, 3-mercaptopropionic acid, sodium hypophosphite, sodium allylpropanesulfonate or sodium methacrylic acid; the polyether The molar ratio of the macromonomer to the olefinic acid small monomer is 1:4-8; the molar ratio of the oxidant, olefinic acid small monomer, sulfonic acid small monomer, Michael addition product, reducing agent and chain transfer agent is 0.03-0.1:1:0.035-0.1:0.035-0.1:0.003-0.01:0.01-0.2; during the mixing process of the polyether macromonomer and the solvent 5, the mass ratio of the polyether macromonomer to the solvent 5 is 1:20-160; the ratio of the total mass of the olefinic acid small monomer and the sulfonic acid small monomer in liquid A to the mass of the solvent 5 is 1:10-40; the mass ratio of the Michael addition product to the solvent 5 in liquid B is 1:10-20; the ratio of the total mass of the reducing agent and the chain transfer agent to the mass of the solvent 5 in liquid C is 1:10-20; the dropwise addition time is 40-80 minutes; the temperature of the free radical polymerization reaction is 20-70°C, and the free radical polymerization reaction time is 2-6 hours.

[0029] In step (5) of the present invention, the catalyst includes one or more of silver chloride, cuprous bromide, bromine, sodium chlorite, and sodium bromite; the solvent 6 includes anhydrous ethanol or water; the alkaline solution includes one or more of a NaOH aqueous solution, a KOH aqueous solution, and an NH4OH aqueous solution, and the mass concentration of the alkaline solution is 4-6%; the molar ratio of the free radical polymerization product to the catalyst is 10-20:1; the mass ratio of the free radical polymerization product, the solvent 6, and the alkaline solution is 1:30-100:20-40; the Hofmann degradation reaction includes a first-stage Hofmann degradation reaction and a second-stage Hofmann degradation reaction; the parameters of the first-stage Hofmann degradation reaction are as follows: argon gas conditions, a temperature of 20-30°C, and a time of 30-50 min; the parameters of the second-stage Hofmann degradation reaction are as follows: argon gas conditions, a temperature of 120-180°C, and a time of 4-8 h.

[0030] In step (6) of the present invention, solvent 5 is water; the anhydride small monomer includes nadic anhydride or cis-5-norbornene-exo-2,3-dicarboxylic anhydride; solvent 7 includes one or more of tetrahydrofuran, benzene, toluene, methanol, ethanol, isopropanol, and n-butanol, and the mass concentration of solvent 7 is 4-6%; the amine small monomer includes ethylenediamine, tetramethylenediamine, 1,4-butanediamine, 1,6-hexanediamine, 1,8-octanediamine or decanediamine; Hofmann degradation products and anhydrides The molar ratio of the small monomer is 1 to 4:1; the molar ratio of the Hofmann degradation product, the solvent 7 and the amine small monomer is 1:1 to 2:1 to 2; the mass ratio of the Hofmann degradation product and the solvent 5 is 1:40 to 60; the reaction temperature is 20 to 30°C, and the reaction time is 4 to 8 hours; the water bath heating temperature is 40 to 60°C, and the water bath heating time is 0.5 to 1 hour; the amidation reaction temperature is 20 to 30°C, and the amidation reaction time is 12 to 24 hours.

[0031] In step (7) of the present invention, the solvent 4 independently includes one or more of N,N-dimethylformamide, N,4-dimethylformamide, and dimethyl sulfoxide; the amine compound includes N-bromosuccinimide and / or N-hydroxysuccinimide; the ester substance includes ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, ethyl valerate or ethyl isovalerate; the alcohol substance includes DL-dithiothreitol, dithiothreitol, dithioerythritol, L-1,4-dithiothreitol, 1,2-butanedithiol, 1,4-butanedithiol, 2,3-butanedithiol, 1,6-hexanediol. Thiol, 1,2-ethanedithiol or 1,5-pentanedithiol; solvent 2 includes phosphate buffer; solvent 8 includes one or more of 240-260 mg / ml methanol, 0.01-0.03 w / v% eosin, and 0.1-0.3 v / v% triethanolamine; the molar ratio of trehalose to triphenylphosphine is 0.2-0.8:1; the molar ratio of trehalose to alcohol substances is 1:2-4; the molar ratio of triphenylphosphine, amine compounds and ester substances is 1:1-2:1-3; the molar ratio of amidated product 2 to thiolated trehalose is 2-4:1; solvent 2, solvent 8 and The mass ratio of thiolated trehalose is 20-40:5-20:1; during the mixing process of trehalose, triphenylphosphine and solvent 4, the mass ratio of solvent 4 to trehalose is 30-60:1; in the mixed solution 8, the mass ratio of solvent 4 to amidated product 2 is 10-40:1; the dropwise addition time is 1-2 hours; the temperature of reaction 1 is 20-30°C, and the reaction time is 36-48 hours; the temperature of reaction 2 is 20-30°C, and the reaction time is 12-24 hours; the reaction temperature is 20-30°C, and the reaction time is 12-24 hours; the Thiol-ene reaction includes The reactants are sequentially subjected to a first-stage Thiol-ene reaction, pH adjustment, and a second-stage Thiol-ene reaction. The parameters of the first-stage Thiol-ene reaction are as follows: nitrogen conditions, ultraviolet light irradiation, a temperature of 20-30°C, and a time of 12-24 hours. The pH adjuster used for adjusting the pH value includes one or more of phosphate buffer, oxalic acid, acetic acid, and citric acid, and the pH value is adjusted to 6-8. The parameters of the second-stage Thiol-ene reaction are as follows: nitrogen conditions, ultraviolet light irradiation, a temperature of 30-40°C, and a time of 10-30 minutes.

[0032] In steps (1) to (7) of the present invention, the dialysis is independently performed using a dialysis bag, and the dialysis time is independently 48 to 72 hours; the vacuum drying time is independently 24 to 48 hours; the temperature of the reduced pressure distillation is independently 100 to 115°C; the extraction agent used includes one or more of benzene, toluene, xylene, and chloroform; and the cleaning reagent includes anhydrous ethanol.

[0033] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. Based on molecular structure design theory, the present invention introduces unsaturated carboxylic acid small monomers and polyester macromonomers into the natural high molecular weight polymer chitosan through the "amide + esterification + Michael addition" method. The monomers are then free radical polymerized with polyether macromonomers, carboxylic acid small monomers, and sulfonic acid small monomers to obtain a polymer containing two long side chains, which increases the steric hindrance effect of the polymer. The polymer is then functionalized through an amidation reaction, and then reacted with thiolated trehalose to form a low-temperature, early-strength water reducer. The molecular structure of the low-temperature, early-strength water reducer contains a large number of carboxyl groups, sulfonic acid groups, amide groups, and hydroxyl groups. The synergistic effect of these functional groups enables the low-temperature, early-strength water reducer to exhibit excellent water-reducing effects and significantly improve the early strength of concrete in low-temperature environments. Compared with existing early-strength polycarboxylic acid water reducers on the market, the water-reducing and early-strength effects in low-temperature environments are superior. This is an innovation and breakthrough in the field of early-strength polycarboxylic acid water reducers, and it has opened up new ideas and directions for the subsequent development of low-temperature, early-strength water reducers.

[0035] 2. Based on the concept of green and environmentally friendly development, the present invention applies biomass materials, natural polymer chitosan, unsaturated carboxylic acids (such as cinnamic acid and its derivatives), trehalose and other materials to the synthesis and preparation of low-temperature early-strength water reducers, realizing the combination of biomass materials and the diversity needs of concrete admixtures. At the same time, copolymerization with traditional polyether macromonomers to form low-temperature early-strength water reducers can further enhance the water-reducing and early-strengthening effects of traditional early-strength polycarboxylate water reducers in low-temperature or even negative-temperature environments. This not only helps to solve the problems of poor concrete performance and slow early strength development in low-temperature or negative-temperature environments, but also effectively reduces the impact and damage to the ecosystem, and is also conducive to the industrial promotion and application of low-temperature early-strength water reducers.

[0036] 3. The present invention is based on the water-reducing and early-strengthening action principle of low-temperature early-strengthening water-reducing agent. After copolymerizing unsaturated carboxylic acid small monomers with polyether macromonomers, sulfonic acid small monomers and polyester macromonomers, a thiolated trehalose containing a large number of hydroxyl groups is introduced to synthesize a low-temperature early-strengthening water-reducing agent. The presence of a large number of carboxyl groups can improve its adsorption capacity for cement particles as a whole, thereby achieving an excellent water-reducing effect. The presence of sulfonic acid groups can improve the dispersion performance of cement paste and promote the hydration of C3A in cement to achieve an early-strengthening effect. The presence of a large number of hydroxyl groups can generate a hydrogen bond network that destroys the hydrogen bond network that causes water to freeze in a low-temperature environment, thereby improving the early strength of concrete in a low-temperature or even negative-temperature environment. At the same time, the polyether side chains and polyester side chains can produce a strong steric hindrance, causing the cement particles to repel each other and disperse, so that the prepared low-temperature early-strengthening water-reducing agent has an excellent water-reducing and dispersing effect.

[0037] 4. Compared with traditional early-strength polycarboxylate water-reducers, the present invention introduces biomass materials, reduces the use of petroleum-based polyether macromonomers, and significantly reduces the preparation cost of low-temperature early-strength water-reducers. The raw materials are green, environmentally friendly, non-toxic and harmless, avoiding the harm to the environment and human body caused by excessive use of toxic materials. The low-temperature early-strength water-reducer prepared by the present invention has a more significant water-reducing and early-strengthening effect than the early-strength polycarboxylate water-reducers with a single functional group through the synergistic effect of multiple functional groups. At the same time, the reaction steps such as amidation, esterification, Michael addition, free radical copolymerization, Hofmann degradation, and Thiol-ene used in the present invention belong to common preparation processes, do not require special equipment conditions and process flows, are conducive to the industrial production of products, and have broad application prospects.

[0038] 5. From the perspective of engineering application, the low-temperature early-strength water-reducing agent prepared by the present invention has good stability, and no stratification, deterioration or precipitation occurs during long-term storage. At the same time, it has the characteristics and performance advantages of high water reduction rate and excellent early-strength effect. It has good working performance and collapse resistance when applied to concrete in low temperature or even negative temperature environment, and can meet the requirements of long-distance transportation. At the same time, the early strength develops rapidly, the construction quality is high, and the turnover rate of the formwork is improved, which solves the problems of normal construction in low temperature environment or even negative temperature environment, severe concrete freezing damage, and slow development of early strength of concrete. It has significant economic benefits, performance advantages and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0040] Figure 1 This is the infrared spectrum test chart of the low-temperature early-strength water-reducing agent obtained in Example 1. DETAILED DESCRIPTION

[0041] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] (1) Amidation reaction: Chitosan was dissolved in 1% acetic acid solution and stirred at 20°C for 24 hours. Cinnamic acid was then dissolved in phosphate buffer, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added. After stirring and activating at 25°C for 1 hour, the mixture was added to the chitosan solution and stirred at 30°C for 4 hours. The unreacted solvent and small molecules were removed by dialysis using a dialysis bag for 48 hours, and the mixture was vacuum dried for 48 hours to obtain an amidation product. (The molar ratio of chitosan, cinnamic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide was 2:1:2:2, and the mass ratio of acetic acid, phosphate buffer, and chitosan was 60:40:1.)

[0044] (2) Esterification reaction: Add poly(ethylene glycol) methacrylate, bipyridine and anhydrous ethanol to a reactor, introduce N2, and stir for 10 minutes. Add N,N'-disuccinimidyl carbonate and 4-dimethylaminopyridine to N,N-dimethylformamide, stir evenly, and then add to the reactor. Continue to introduce N2, stir and react at 90°C for 4 hours, and distill under reduced pressure at 100°C for purification to obtain an esterification product. (Wherein, the molar ratio of poly(ethylene glycol) methacrylate, bipyridine, N,N'-disuccinimidyl carbonate, and 4-dimethylaminopyridine is 40:1:40:40, and the mass ratio of anhydrous ethanol, N,N-dimethylformamide, and poly(ethylene glycol) methacrylate is 40:60:1)

[0045] (3) Michael addition reaction: The amidation product obtained in step (1) and 1% acetic acid were added to a reactor, N2 was introduced, and the mixture was stirred and reacted at 30°C for 1 hour. Subsequently, the esterification product obtained in step (2) was dissolved in deionized water and added dropwise to the reactor within 50 minutes. The mixture was then stirred and reacted at 50°C under N2 for 24 hours, dialyzed for 48 hours, and vacuum dried for 48 hours to obtain a Michael addition product. (Wherein, the ratio of esterification product to amidation product is 0.5:1, and the mass ratio of acetic acid, deionized water, and amidation product is 60:40:1.)

[0046] (4) Free radical polymerization reaction: Methyl allyl polyoxyethylene ether with a molecular weight of 2400 g / mol and deionized water are added to the reactor and stirred evenly to obtain a bottom liquid. H2O2 is first added to the bottom liquid and stirred evenly, and then liquid A, liquid B and liquid C are simultaneously added dropwise to the bottom liquid within 50 minutes; wherein, liquid A is a mixture of acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and water, liquid B is a mixture of Michael addition product and water, and liquid C is a mixture of bleaching powder, FeSO4, 3-mercaptopropionic acid and water; after the addition is completed, the mixture is stirred and reacted at 65°C for 2 hours, and the solvent and by-products are removed by reduced pressure distillation to obtain a free radical polymerization product. (Wherein, the molar ratio of methyl allyl polyoxyethylene ether, H2O2, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, Michael addition product, bleaching agent, FeSO4, and 3-mercaptopropionic acid is 1:0.3:5:0.175:0.2:0.02:0.015:0.1, the mass ratio of deionized water and methyl allyl polyoxyethylene ether is 80:1, the mass ratio of the total mass of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid in liquid A to water is 1:20, the mass ratio of Michael addition product to water in liquid B is 1:10, and the mass ratio of the total mass of bleaching agent, FeSO4, and 3-mercaptopropionic acid to water in liquid C is 1:10)

[0047] (5) Hofmann degradation reaction: The free radical polymerization product obtained in step (4), sodium chlorite, anhydrous ethanol, and a 5% NaOH aqueous solution were added to a reactor, purged with argon, and stirred at 20°C for 45 minutes. The mixture was then heated to 150°C and stirred for 5 hours. The mixture was purified and vacuum dried for 48 hours to obtain a Hofmann degradation product. (The molar ratio of the free radical polymerization product to sodium chlorite was 10:1, and the mass ratio of anhydrous ethanol to the NaOH solution to the free radical polymerization product was 50:30:1.)

[0048] (6) Amidation reaction: The Hofmann degradation product obtained in step (5) and deionized water were added to a reactor and stirred at 20°C for 4 hours. Then, nadic anhydride was dissolved in 5% tetrahydrofuran, heated in a constant temperature water bath at 40°C for 0.5 hours, and then added to the reactor. Ethylenediamine was added and stirred at 20°C for 18 hours. The mixture was dialyzed for 48 hours and vacuum dried for 48 hours to obtain an amidation product. (The molar ratio of Hofmann degradation product, nadic anhydride, tetrahydrofuran, and ethylenediamine was 2:1:2:2, and the mass ratio of deionized water to Hofmann degradation product was 50:1.)

[0049] (7) Thiol-ene reaction: trehalose, triphenylphosphine and N,N-dimethylformamide were added to the reactor, N-bromosuccinimide was added dropwise for 1 hour, stirred and reacted at 20°C for 40 hours, ethyl acetate and DL-dithiothreitol were added in sequence, stirred and reacted at 20°C for 12 hours, extracted with toluene, washed with anhydrous ethanol, and vacuum dried for 48 hours to obtain thiolated trehalose; subsequently, the amidated product obtained in step (6) and N,N-dimethylformamide were added to the reactor, stirred and reacted at 20°C for 12 hours, thiolated trehalose was dissolved in phosphate buffer, and 250 mg / ml methanol solution was added, stirred and added to the reactor, N2 was introduced, stirred and reacted at 20°C under ultraviolet light for 12 hours, phosphate buffer was added, the pH value of the solution was adjusted to 6-8, stirred and reacted at 30°C for 20 minutes, cooled to room temperature, purified, and obtained a low-temperature early strength water reducer. (Wherein, the molar ratio of trehalose, triphenylphosphine, N-bromosuccinimide, ethyl acetate, and DL-dithiothreitol is 0.4:1:1:2:2, the mass ratio of N,N-dimethylformamide and trehalose is 50:1; the molar ratio of amidation product and thiolated trehalose is 2:1, and the mass ratio of anhydrous dimethylformamide, phosphate buffer, methanol, and sulfated trehalose is 50:40:15:1).

[0050] Example 2

[0051] (1) Amidation reaction: Chitosan was dissolved in a 1.5% hydrochloric acid solution and stirred at a constant temperature of 25°C for 16 hours. Caffeic acid was then dissolved in a phosphate buffer solution, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added. After stirring and activating at 25°C for 2 hours, the mixture was added to the chitosan solution and stirred at 30°C for 4 hours. The unreacted solvent and small molecules were removed by dialysis using a dialysis bag for 48 hours, and the mixture was vacuum dried for 48 hours to obtain an amidation product. (The molar ratio of chitosan, caffeic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide was 2:1:3:3, and the mass ratio of hydrochloric acid, phosphate buffer, and chitosan was 50:40:1.)

[0052] (2) Esterification reaction: Add poly(ethylene glycol) methacrylate, bipyridine and deionized water to a reactor, introduce N2, and stir for 20 minutes. Add N,N'-disuccinimidyl carbonate and pyridine to N,N-dimethylformamide, stir evenly, and then add to the reactor. Continue to introduce N2, stir and react at 80°C for 6 hours, and distill under reduced pressure at 110°C for purification to obtain an esterified product. (Wherein, the molar ratio of poly(ethylene glycol) methacrylate, bipyridine, N,N'-disuccinimidyl carbonate, and pyridine is 30:1:35:40, and the mass ratio of deionized water, N,N-dimethylformamide, and poly(ethylene glycol) methacrylate is 50:50:1)

[0053] (3) Michael addition reaction: The amidation product obtained in step (1) and 1% hydrochloric acid were added to a reactor, N2 was introduced, and the mixture was stirred and reacted at 40°C for 2 hours. Subsequently, the esterification product obtained in step (2) was dissolved in deionized water and added dropwise to the reactor within 45 minutes. The mixture was then stirred and reacted at 60°C under N2 for 24 hours, dialyzed for 48 hours, and vacuum dried for 48 hours to obtain a Michael addition product. (Wherein, the ratio of esterification product to amidation product is 0.8:1, and the mass ratio of hydrochloric acid, deionized water, and amidation product is 70:40:1.)

[0054] (4) Free radical polymerization reaction: add isopentanol polyethoxylate ether with a molecular weight of 2400 g / mol and deionized water into a reactor and stir evenly to obtain a bottom liquid, first add ammonium persulfate into the bottom liquid, and then add liquid A, liquid B and liquid C to the bottom liquid at the same time within 55 minutes; wherein, liquid A is a mixture of itaconic acid, 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt and water, liquid B is a mixture of Michael addition product and water, and liquid C is a mixture of ascorbic acid, thioglycolic acid and water; after the addition is completed, stir the reaction at 50°C for 5 hours, and remove the solvent and by-products by vacuum distillation to obtain a free radical polymerization product. (Wherein, the molar ratio of prenol polyethoxylate, ammonium persulfate, itaconic acid, 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, Michael addition product, ascorbic acid, and thioglycolic acid is 1:0.3:6:0.24:0.3:0.024:0.3; the mass ratio of deionized water and prenol polyethoxylate is 100:1; the mass ratio of the total mass of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in solution A to water is 1:20; the mass ratio of the Michael addition product to water in solution B is 1:10; and the mass ratio of the total mass of ascorbic acid and thioglycolic acid to water in solution C is 1:15)

[0055] (5) Hofmann degradation reaction: The free radical polymerization product obtained in step (4), cuprous bromide, deionized water, and a 5% aqueous NaOH solution were added to a reactor, purged with argon, and stirred at 25°C for 40 minutes. The mixture was then heated to 140°C and stirred for 6 hours. The mixture was purified and vacuum dried for 48 hours to obtain a Hofmann degradation product. (The molar ratio of the free radical polymerization product to cuprous bromide was 15:1, and the mass ratio of deionized water to NaOH solution to the free radical polymerization product was 60:35:1.)

[0056] (6) Amidation reaction: The Hofmann degradation product obtained in step (5) and deionized water were added to a reactor and stirred at 25° C. for 5 h. Then, cis-5-norbornene-exo-2,3-dicarboxylic anhydride was dissolved in a 5% methanol solution, heated in a constant temperature water bath at 45° C. for 0.5 h, and then added to the reactor. Tetramethylenediamine was added, stirred at 25° C. for 15 h, dialyzed for 48 h, and vacuum dried for 48 h to obtain an amidation product. (The molar ratio of the Hofmann degradation product, cis-5-norbornene-exo-2,3-dicarboxylic anhydride, methanol, and tetramethylenediamine was 3:1:4.5:3, and the mass ratio of deionized water to the Hofmann degradation product was 60:1.)

[0057] (7) Thiol-ene reaction: trehalose, triphenylphosphine and N,N-dimethylformamide were added to a reactor, N-hydroxysuccinimide was added dropwise for 1.5 hours, and the mixture was stirred at 25°C for 36 hours. Ethyl butyrate and dithiothreitol were added in sequence, and the mixture was stirred at 25°C for 12 hours. The mixture was extracted with toluene, washed with anhydrous ethanol, and vacuum dried for 48 hours to obtain thiolated trehalose. Subsequently, the amidated product obtained in step (6) and N,N-dimethylformamide were added to a reactor, and the mixture was stirred at 25°C for 12 hours. The thiolated trehalose was dissolved in phosphate buffer, and 0.02 w / v% eosin solution was added. After stirring, the mixture was added to the reactor, N2 was introduced, and the mixture was stirred at 25°C under ultraviolet light for 16 hours. Phosphate buffer was added to adjust the pH value of the solution to 6-8, and the mixture was stirred at 35°C for 25 minutes. The mixture was cooled to room temperature and purified to obtain a low-temperature early-strength water reducer. (Wherein, the molar ratio of trehalose, triphenylphosphine, N-hydroxysuccinimide, ethyl butyrate, and dithiothreitol is 0.5:1:2:2:3, the mass ratio of N,N-dimethylformamide and trehalose is 50:1; the molar ratio of amidation product and thiolated trehalose is 2.5:1, and the mass ratio of N,N-dimethylformamide, phosphate buffer, eosin, and sulfated trehalose is 60:40:20:1).

[0058] Example 3

[0059] (1) Amidation reaction: Chitosan was dissolved in a 1% hydrochloric acid solution and stirred at 30°C for 12 hours. 3,4-dimethoxycinnamic acid was then dissolved in a phosphate buffer solution, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added. After stirring and activating at 25°C for 1.5 hours, the mixture was added to the chitosan solution and stirred at 30°C for 5 hours. The mixture was dialyzed using a dialysis bag for 48 hours to remove unreacted solvent and small molecules, and vacuum dried for 48 hours to obtain an amidation product. (The molar ratio of chitosan, 3,4-dimethoxycinnamic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide was 2:1.5:2:2, and the mass ratio of hydrochloric acid, phosphate buffer, and chitosan was 55:40:1.)

[0060] (2) Esterification reaction: Poly(ethylene glycol) methacrylate, bipyridine and deionized water were added to a reactor, nitrogen was introduced, and the mixture was stirred for 25 minutes. N,N'-disuccinimidyl carbonate and 2-bromo-4-dimethylaminopyridine were added to dimethyl sulfoxide, stirred evenly, and then added to the reactor. N2 was continuously introduced, and the mixture was stirred at 85°C for 4 hours. The mixture was purified by vacuum distillation at 105°C to obtain an esterified product. (The molar ratio of poly(ethylene glycol) methacrylate, bipyridine, N,N'-disuccinimidyl carbonate and 2-bromo-4-dimethylaminopyridine was 45:1:40:40, and the mass ratio of deionized water, dimethyl sulfoxide and poly(ethylene glycol) methacrylate was 55:60:1)

[0061] (3) Michael addition reaction: The amidation product obtained in step (1) and 1% acetic acid were added to a reactor, N2 was introduced, and the reaction was stirred at 45°C for 1.5 hours. Subsequently, the esterification product obtained in step (2) was dissolved in deionized water and added dropwise to the reactor within 60 minutes. The reaction was then stirred at 65°C under N2 for 20 hours, dialyzed for 72 hours, and vacuum dried for 48 hours to obtain the Michael addition product. (Wherein, the ratio of esterification product to amidation product is 0.8:1, and the mass ratio of acetic acid, deionized water, and amidation product is 80:60:1.)

[0062] (4) Free radical polymerization reaction: Butanediol monovinyl polyoxyethylene ether with a molecular weight of 5000 g / mol and deionized water are added to the reactor and stirred evenly to obtain a bottom liquid. Potassium persulfate is first added to the bottom liquid, and then liquid A, liquid B and liquid C are simultaneously added dropwise to the bottom liquid within 60 minutes; wherein, liquid A is a mixture of methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and water, liquid B is a mixture of Michael addition product and water, and liquid C is a mixture of ascorbic acid, sodium allylpropanesulfonate and water; after the addition is completed, the mixture is stirred and reacted at 20°C for 5 hours, and the solvent and by-products are removed by vacuum distillation to obtain a free radical polymerization product. (Wherein, the molar ratio of butanediol monovinyl polyoxyethylene ether, potassium persulfate, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, Michael addition product, ascorbic acid, and sodium allyl formate is 1:0.42:7:0.315:0.315:0.03:0.28; the mass ratio of deionized water to butanediol monovinyl polyoxyethylene ether is 120:1; the mass ratio of the total mass of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in solution A to water is 1:15; the mass ratio of the Michael addition product to water in solution B is 1:15; and the mass ratio of the total mass of ascorbic acid and sodium allyl formate to water in solution C is 1:10)

[0063] (5) Hofmann degradation reaction: The free radical polymerization product obtained in step (4), sodium bromite, deionized water, and a 5% aqueous NaOH solution were added to a reactor, purged with argon, and stirred at 30°C for 35 minutes. The mixture was then heated to 150°C and stirred for 4 hours. The mixture was purified and vacuum dried for 48 hours to obtain a Hofmann degradation product. (The molar ratio of the free radical polymerization product to sodium bromite was 18:1, and the mass ratio of deionized water to NaOH solution to the free radical polymerization product was 80:30:1.)

[0064] (6) Amidation reaction: The Hofmann degradation product obtained in step (5) and deionized water were added to a reactor and stirred at 30°C for 4 hours. Then, nadic anhydride was dissolved in a 5% ethanol solution, heated in a constant temperature water bath at 50°C for 1 hour, and then added to the reactor. 1,6-hexanediamine was added, stirred at 30°C for 12 hours, dialyzed for 48 hours, and vacuum dried for 48 hours to obtain an amidation product. (The molar ratio of Hofmann degradation product, nadic anhydride, ethanol, and 1,6-hexanediamine was 2:1:3.5:3.5, and the mass ratio of deionized water to Hofmann degradation product was 50:1.)

[0065] (7) Thiol-ene reaction: trehalose, triphenylphosphine and dimethyl sulfoxide were added to a reactor, N-bromosuccinimide was added dropwise for 2 hours, and the mixture was stirred and reacted at 30°C for 40 hours. Ethyl propionate and dithioerythritol were added in sequence, and the mixture was stirred and reacted at 30°C for 12 hours. The mixture was extracted with xylene, washed with anhydrous ethanol, and vacuum dried for 48 hours to obtain thiolated trehalose. Subsequently, the amidated product obtained in step (6) and dimethyl sulfoxide were added to a reactor, and the mixture was stirred and reacted at 30°C for 12 hours. The thiolated trehalose was dissolved in phosphate buffer, and 0.2 v / v% triethanolamine was added. After stirring, the mixture was added to the reactor, N2 was introduced, and the mixture was stirred and reacted at 30°C under ultraviolet light for 15 hours. Phosphate buffer was added to adjust the pH value of the solution to 6-8, and the mixture was stirred and reacted at 30°C for 20 minutes. The mixture was cooled to room temperature and purified to obtain a low-temperature early-strength water reducer. (Wherein, the molar ratio of trehalose, triphenylphosphine, N-bromosuccinimide, ethyl propionate, and dithioerythritol is 0.6:1:1.5:2:4, the mass ratio of dimethyl sulfoxide to trehalose is 55:1; the molar ratio of amidated product to thiolated trehalose is 3:1, and the mass ratio of dimethyl sulfoxide, phosphate buffer, triethanolamine, and sulfated trehalose is 55:35:20:1)

[0066] Comparative Example 1

[0067] ViscoCrete-W early-strength polycarboxylate water-reducing agent commercially available from Sika Company was used as comparative example 1.

[0068] Comparative Example 2

[0069] The KS-4 early-strength polycarboxylate water-reducing agent commercially available from Guangdong Shuangta New Materials Co., Ltd. was used as comparative example 2.

[0070] Comparative Example 3

[0071] The YB-513 early-strength polycarboxylate water-reducing agent commercially available from Shaanxi Youbang New Material Technology Co., Ltd. was used as comparative example 3.

[0072] Effect and performance testing:

[0073] 1. Fluidity of cement paste:

[0074] To investigate the effect of the low-temperature, early-strength water reducer synthesized in the present invention on the fluidity of cement paste, the fluidity of cement pastes incorporating the low-temperature, early-strength water reducer prepared in Examples 1-3 and the early-strength polycarboxylate water reducer prepared in Comparative Examples 1-3 was tested in accordance with GB / T 8077, at the same water-cement ratio and water-to-binder ratio. In the tests, the W / C ratio was 0.29:1, and the water reducer dosage was 0.15% of the cement mass (solids ratio). The examples used were cement pastes incorporating the low-temperature, early-strength water reducer synthesized in Examples 1-3 of the present invention, and the comparative examples were cement pastes incorporating the early-strength polycarboxylate water reducer prepared in Comparative Examples 1-3. The cement paste fluidity test results are shown in Table 1.

[0075] Table 1 Cement paste fluidity test results

[0076]

[0077]

[0078] As can be seen from Table 1, compared with the early-strength polycarboxylate water-reducers of comparative examples 1 to 3, the low-temperature early-strength water-reducers prepared in Examples 1 to 3 can significantly improve the fluidity of the cement paste, and after 1 hour and 2 hours of time loss, the fluidity retention performance of the cement paste added with the low-temperature early-strength polycarboxylate water-reducers prepared in Examples 1 to 3 is better than the fluidity retention performance of the cement paste added with the early-strength polycarboxylate water-reducers of comparative examples 1 to 3, indicating that the low-temperature early-strength water-reducers exhibit excellent dispersibility and cement adaptability.

[0079] 2. Concrete properties:

[0080] In this test, concrete with a strength grade of C30 was selected, and its mix proportions are shown in Table 2. The cement used was Chengde Jinyu P·O 42.5 cement, the sand was Zone II continuously graded natural medium sand with a fineness modulus of 2.8 and a mud content of less than 2.1%, and the gravel was 5-20 mm continuously graded crushed stone. The low-temperature, early-strength water reducer was added in an amount of 0.2% (in terms of solids) of the mass of the cementitious material. The concrete specimens were formed and cured in accordance with GB / T 50081. The examples used were concretes incorporating the low-temperature, early-strength water reducers synthesized in Examples 1-3 of the present invention, and the comparative examples used were concretes incorporating the early-strength polycarboxylate water reducers of Comparative Examples 1-3.

[0081] Table 2C30 concrete mix ratio (kg / m 3 )

[0082] cement fly ash sand gravel water 290 60 760 1150 150

[0083] (1) Concrete slump and expansion:

[0084] In order to investigate the effect of the low-temperature early-strength water-reducing agent synthesized by the present invention on the working performance of concrete, the proportions of the various components of the concrete were controlled to be the same, and the slump, spread, and slump / spread loss over time of the concretes added with different examples and comparative examples were tested in accordance with GB 8076. The test results are shown in Table 3.

[0085] Table 3 Concrete slump and expansion test results

[0086]

[0087]

[0088] As can be seen from Table 3, compared with the early-strength polycarboxylate water-reducers of Comparative Examples 1 to 3, the low-temperature early-strength water-reducers prepared according to Examples 1 to 3 can significantly increase the slump and expansion of concrete, improve the flow properties of concrete, and after 0.5h and 1h of time loss, the slump and expansion retention performance of the concrete synthesized by the low-temperature early-strength water-reducers of Examples 1 to 3 are significantly better than the slump and expansion retention performance of the concrete mixed with the early-strength polycarboxylate water-reducers of Comparative Examples 1 to 3.

[0089] (2) Compressive strength of concrete at different curing temperatures:

[0090] In order to investigate the effect of the low-temperature early-strength water-reducing agent synthesized in the present invention on the early strength development of concrete under low temperature and negative temperature environments, the proportions of the various components of the concrete were controlled to be the same. Concrete specimens were formed according to GB / T 50081. After the molds were set, the surfaces were immediately covered with a waterproof film. The specimens were then placed at -10 to -5°C, -5 to 0°C, and 0 to 5°C for 24 hours. After the molds were removed, the compressive strength of the concrete specimens was tested at 1 day. The remaining concrete specimens were continued to be placed at -10 to -5°C, -5 to 0°C, and 0 to 5°C for curing to the specified age. The compressive strength of the concrete specimens was tested at 3 days and 28 days. The test results are shown in Table 4.

[0091] Table 4 Concrete compressive strength test results (MPa)

[0092]

[0093]

[0094] As can be seen from Table 4, at different curing temperatures, the compressive strength of the concrete specimens mixed with the low-temperature, early-strength polycarboxylate water-reducing agent prepared in Examples 1 to 3 at different curing ages is significantly higher than the compressive strength of the concrete specimens mixed with the early-strength polycarboxylate water-reducing agent prepared in Comparative Examples 1 to 3, and the early strength and late strength of the concrete specimens are significantly improved, indicating that the low-temperature, early-strength polycarboxylate water-reducing agent prepared in the present invention can promote the development of the early strength of concrete under low-temperature and negative-temperature curing environments.

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A low-temperature early-strength water reducer, characterized in that: The structural formula of the low-temperature early-strength water reducer is as follows: Among them, the structural formula of R' is: Among them, the wavy line position is the connection position, R is CH2, CH2CH2 or O(CH2CH2O)2, R1 is H, CH3, CH2CH3 or CH2COOH, R2 is H or CH3, R3 is H, OH, CH3O, Cl or Br, R4 is H, OH, CH3O or Cl, and R5 is H or Na; a, b, c, d, n, x and f are integers, representing the number of repeating units of each part in the polymer, a is 10 to 150, b is 3 to 40, c is 3 to 30, d is 3 to 50, m is 100, n is 10 to 150, x is 2 to 10, and f is 1 to 5.

2. The method for preparing the low-temperature early-strength water reducer according to claim 1, characterized in that: The steps include: (1) dissolving chitosan in solvent 1 to obtain mixed solution 1; activating unsaturated carboxylic acid small monomer, solvent 2 and activating agent to obtain mixed solution 2; adding mixed solution 2 to mixed solution 1 to carry out amidation reaction, followed by dialysis and vacuum drying to obtain amidated product 1; (2) reacting poly(ethylene glycol) methacrylate, bipyridine, and solvent 3 to obtain a mixed solution 3; uniformly mixing N,N'-disuccinimidyl carbonate, a pyridine compound, and solvent 4, and adding the resultant mixture to the mixed solution 3 for esterification, followed by vacuum distillation and purification to obtain an esterified product; (3) reacting the amidation product 1 with solvent 1 to obtain a mixed solution 4; dissolving the esterification product in solvent 5 and then adding it dropwise to the mixed solution 4 to perform a Michael addition reaction, followed by dialysis and vacuum drying to obtain a Michael addition product; (4) mixing the polyether macromonomer and solvent 5 to obtain a bottom liquid, first adding an oxidant to the bottom liquid and stirring uniformly, and then simultaneously adding liquid A, liquid B and liquid C to the bottom liquid; wherein liquid A is a mixture of an olefinic acid small monomer, a sulfonic acid small monomer and solvent 5, liquid B is a mixture of a Michael addition product and solvent 5, and liquid C is a mixture of a reducing agent, a chain transfer agent and solvent 5; after the dropwise addition is completed, a free radical polymerization reaction is carried out, and a free radical polymerization product is obtained by distillation under reduced pressure; (5) subjecting the free radical polymerization product, the catalyst, the solvent 6, and the alkaline solution to a Hofmann degradation reaction, followed by purification and vacuum drying to obtain a Hofmann degradation product; (6) reacting the Hofmann degradation product with solvent 5 to obtain a mixture 6; dissolving the anhydride small monomer in solvent 7 and heating in a water bath to obtain a mixture 7; subjecting the mixture 6, the mixture 7, and the amine small monomer to an amidation reaction, followed by dialysis and vacuum drying to obtain an amidated product 2; (7) Trehalose, triphenylphosphine and solvent 4 are mixed, and an amine compound is added dropwise thereto to carry out reaction 1. After reaction 1 is completed, an ester substance and an alcohol substance are added thereto in sequence to carry out reaction 2, and then extraction, washing and vacuum drying are carried out in sequence to obtain thiolated trehalose; amidation product 2 is reacted with solvent 4 to obtain mixed solution 8; thiolated trehalose is dissolved in solvent 2, and solvent 8 is added and mixed, and then added to mixed solution 8 to carry out thiol-ene reaction, and then cooled to room temperature and purified in sequence to obtain a low-temperature early-strength water reducer.

3. The method for preparing the low-temperature early-strength water reducer according to claim 2, wherein: In the step (1), solvent 1 includes acetic acid or hydrochloric acid, and the mass concentration of solvent 1 is 0.5-2%; the unsaturated carboxylic acid small monomer includes cinnamic acid, m-chlorocinnamic acid, m-bromocinnamic acid, p-chlorocinnamic acid, p-bromocinnamic acid, caffeic acid or 3,4-dimethoxycinnamic acid; solvent 2 includes phosphate buffer; the activator includes 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide. The molar ratio of amine is 1-2:1; the molar ratio of chitosan and unsaturated carboxylic acid small monomer is 1-2:1; the molar ratio of activator and unsaturated carboxylic acid small monomer is 2-4:1; the mass ratio of solvent 1, solvent 2 and chitosan is 40-60:20-40:1; the dissolution temperature is 20-30°C, and the dissolution time is 12-24 hours; the activation temperature is 20-30°C, and the activation time is 1-3 hours; the amidation reaction temperature is 30-35°C, and the amidation reaction time is 2-6 hours.

4. The method for preparing the low-temperature early-strength water reducer according to claim 2 or 3, wherein: In the step (2), solvent 3 includes water or anhydrous ethanol; the pyridine compound includes pyridine, 4-dimethylaminopyridine or 2-bromo-4-dimethylaminopyridine; solvent 4 includes one or more of N,N-dimethylformamide, N,4-dimethylformamide, and dimethyl sulfoxide; the molar ratio of poly(ethylene glycol) methacrylate, bipyridine, N,N'-disuccinimidyl carbonate and pyridine compound is 10-40:1:30-60:40-60; the mass ratio of poly(ethylene glycol) methacrylate, solvent 3 and solvent 4 is 1:30-60:40-80; the reaction is carried out under nitrogen conditions, and the reaction time is 10-30 minutes; the esterification reaction is carried out under nitrogen conditions, the esterification reaction temperature is 70-90°C, and the esterification reaction time is 4-6 hours.

5. The method for preparing the low-temperature early-strength water reducer according to claim 4, wherein: In the step (3), solvent 1 includes acetic acid or hydrochloric acid, and the mass concentration of solvent 1 is 0.5-2%; solvent 5 is water; the molar ratio of esterification product and amidation product 1 is 0.5-1:1; the mass ratio of amidation product 1, solvent 1 and solvent 5 is 1:60-120:40-80; the reaction is carried out under nitrogen conditions, the reaction temperature is 30-50°C, and the reaction time is 1-3 hours; the dropwise addition time is 40-80 minutes; the Michael addition reaction is carried out under nitrogen conditions, the Michael addition reaction temperature is 50-70°C, and the Michael addition reaction time is 20-24 hours.

6. The method for preparing the low-temperature early-strength water-reducing agent according to claim 5, characterized in that: In the step (4), the polyether macromonomer includes methyl allyl polyoxyethylene ether, isopentanol polyoxyethylene ether or butanediol monovinyl polyoxyethylene ether, and the molecular weight of the polyether macromonomer is 2000-5000 g / mol; the solvent 5 is water; the oxidant includes H2O2, ammonium persulfate, potassium persulfate or sodium persulfate; the olefinic acid small monomer includes acrylic acid, methacrylic acid, 2-ethylacrylic acid, maleic anhydride, itaconic acid, crotonic acid, crotonic anhydride, isomethacrylic acid or trans-2-pentenoic acid; the sulfonic acid small monomer includes 2-acrylamide-2-methylpropanesulfonic acid or 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt; the reducing agent includes one or more of ascorbic acid, bleaching powder and FeSO4; the chain transfer agent includes thioglycolic acid, 3-mercaptopropionic acid, sodium hypophosphite, sodium allylpropanesulfonate or sodium methacrylic acid; the polyether macromonomer and The molar ratio of the olefinic acid small monomer is 1:4-8; the molar ratio of the oxidant, olefinic acid small monomer, sulfonic acid small monomer, Michael addition product, reducing agent and chain transfer agent is 0.03-0.1:1:0.035-0.1:0.035-0.1:0.003-0.01:0.01-0.2; during the mixing process of the polyether macromonomer and the solvent 5, the mass ratio of the polyether macromonomer to the solvent 5 is 1:20-160; the ratio of the total mass of the olefinic acid small monomer and the sulfonic acid small monomer in liquid A to the mass of the solvent 5 is 1:10-40; the mass ratio of the Michael addition product to the solvent 5 in liquid B is 1:10-20; the ratio of the total mass of the reducing agent and the chain transfer agent to the mass of the solvent 5 in liquid C is 1:10-20; the dropwise addition time is 40-80 minutes; the temperature of the free radical polymerization reaction is 20-70°C, and the free radical polymerization reaction time is 2-6 hours.

7. The method for preparing the low-temperature early-strength water reducer according to claim 6, wherein: In the step (5), the catalyst includes one or more of silver chloride, cuprous bromide, bromine, sodium chlorite, and sodium bromite; the solvent 6 includes anhydrous ethanol or water; the alkaline solution includes one or more of a NaOH aqueous solution, a KOH aqueous solution, and an NH4OH aqueous solution, and the mass concentration of the alkaline solution is 4-6%; the molar ratio of the free radical polymerization product to the catalyst is 10-20:1; the mass ratio of the free radical polymerization product, the solvent 6, and the alkaline solution is 1:30-100:20-40; the Hofmann degradation reaction includes a first-stage Hofmann degradation reaction and a second-stage Hofmann degradation reaction; the parameters of the first-stage Hofmann degradation reaction are as follows: argon gas condition, temperature of 20-30°C, and time of 30-50 min; the parameters of the second-stage Hofmann degradation reaction are as follows: argon gas condition, temperature of 120-180°C, and time of 4-8 h.

8. The method for preparing the low-temperature early-strength water-reducing agent according to claim 6 or 7, characterized in that: In the step (6), the solvent 5 is water; the anhydride small monomer includes nadic anhydride or cis-5-norbornene-exo-2,3-dicarboxylic anhydride; the solvent 7 includes one or more of tetrahydrofuran, benzene, toluene, methanol, ethanol, isopropanol, and n-butanol, and the mass concentration of the solvent 7 is 4-6%; the amine small monomer includes ethylenediamine, tetramethylenediamine, 1,4-butanediamine, 1,6-hexanediamine, 1,8-octanediamine or decanediamine; Hofmann degradation products and anhydride small monomers The molar ratio of the monomers is 1-4:1; the molar ratio of the Hofmann degradation product, the solvent 7 and the amine small monomer is 1:1-2:1-2; the mass ratio of the Hofmann degradation product and the solvent 5 is 1:40-60; the reaction temperature is 20-30°C, and the reaction time is 4-8 hours; the water bath heating temperature is 40-60°C, and the water bath heating time is 0.5-1 hour; the amidation reaction temperature is 20-30°C, and the amidation reaction time is 12-24 hours.

9. The method for preparing the low-temperature early-strength water-reducing agent according to claim 8, characterized in that: In the step (7), the solvent 4 independently includes one or more of N,N-dimethylformamide, N,4-dimethylformamide, and dimethyl sulfoxide; the amine compound includes N-bromosuccinimide and / or N-hydroxysuccinimide; the ester substance includes ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, ethyl valerate or ethyl isovalerate; the alcohol substance includes DL-dithiothreitol, dithiothreitol, dithioerythritol, L-1,4-dithiothreitol, 1,2-butanedithiol, 1,4-butanedithiol, 2,3-butanedithiol, 1,6-hexanedithiol, 1,2-ethanedithiol or 1,5-pentanedithiol; solvent 2 includes phosphate buffer; solvent 8 includes one or more of 240-260 mg / ml methanol, 0.01-0.03 w / v% eosin, and 0.1-0.3 v / v% triethanolamine; the molar ratio of trehalose to triphenylphosphine is 0.2-0.8:1; the molar ratio of trehalose to alcohol substances is 1:2-4; the molar ratio of triphenylphosphine, amine compounds, and ester substances is 1:1-2:1-3; the molar ratio of amidated product 2 to thiolated trehalose is 2-4:1; solvent 2, solvent 8, and thiol The mass ratio of trehalose to triphenylphosphine is 20-40:5-20:1; during the mixing process of trehalose, triphenylphosphine and solvent 4, the mass ratio of solvent 4 to trehalose is 30-60:1; in the mixed solution 8, the mass ratio of solvent 4 to amidated product 2 is 10-40:1; the time of dropwise addition is 1-2 hours; the temperature of reaction 1 is 20-30°C, and the time of reaction 1 is 36-48 hours; the temperature of reaction 2 is 20-30°C, and the time of reaction 2 is 12-24 hours; the temperature of the reaction is 20-30°C, and the time of reaction 2 is 12-24 hours; the reaction temperature is 20-30°C, and the reaction time is 12-24 hours; the Thiol-ene reaction includes the reaction of The reaction mixture is subjected to a first-stage Thiol-ene reaction, pH adjustment, and a second-stage Thiol-ene reaction in sequence. The parameters of the first-stage Thiol-ene reaction are as follows: nitrogen atmosphere, ultraviolet irradiation, temperature of 20-30°C, and reaction time of 12-24 hours. The pH adjusting agent used for adjusting the pH value includes one or more of phosphate buffer, oxalic acid, acetic acid, and citric acid, and the pH value is adjusted to 6-8. The parameters of the second-stage Thiol-ene reaction are as follows: nitrogen atmosphere, ultraviolet irradiation, temperature of 30-40°C, and reaction time of 10-30 minutes.

10. The method for preparing the low-temperature early-strength water reducer according to claim 9, characterized in that: In the steps (1) to (7), the dialysis is independently performed using a dialysis bag, and the dialysis time is independently 48 to 72 hours; the vacuum drying time is independently 24 to 48 hours; the temperature of the reduced pressure distillation is independently 100 to 115° C.; the extraction agent used includes one or more of benzene, toluene, xylene, and chloroform; and the cleaning reagent includes anhydrous ethanol.

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