Early-strength water reducing agent as well as preparation method and application thereof

Abstract

The invention relates to an early-strength water reducing agent as well as a preparation method and application thereof. The synthesis of the early-strength water reducing agent comprises two steps of polymerization reaction of low-molecular-weight polycarboxylic acid and ring-opening esterification reaction of polyether glycidyl ether. According to the low-molecular-weight polycarboxylic acid, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and itaconic acid are used as raw materials, and the low-molecular-weight polycarboxylic acid with the molecular weight of 1000-5000 is synthesized through water-phase free radical polymerization; and then carrying out ring-opening esterification reaction on the low-molecular-weight polycarboxylic acid and polyether glycidyl ether to synthesize the ester type polycarboxylic acid water reducer with a comb-shaped molecular structure. Compared with the prior art, the early-strength water reducing agent and the preparation method thereof have the performance advantages of simple synthesis process, high esterification rate and good early-strength effect.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete admixtures, in particular to an early strength water reducing agent and a preparation method and application thereof. Background Art

[0002] Concrete, a mixture of cementitious materials, sand and gravel aggregates, water, and admixtures, is currently the world's largest and most widely used building material, widely used in various engineering and construction projects. Water reducers are the most widely used type of concrete admixture, offering advantages such as reduced water and cement usage, and improved concrete strength and durability. Since the early days of lignin sulfonate water reducers in concrete in the 1930s, they have undergone three major iterations and have now evolved into the third generation of high-performance polycarboxylate-based water reducers (Lei et al., 40 years of PCE superplasticizers - History, current state-of-the-art and an outlook[J], Cement and Concrete Research, 2022, 157:106826). The molecular structure of polycarboxylate superplasticizers is comb-shaped, with a main chain consisting of carboxylic acid adsorption groups and side chains consisting of polyether segments with a certain molecular weight. There is also the electrostatic interaction of the carboxylic acid groups and the steric hindrance of the polyether segments (Shui Liangliang et al., Research Progress on the Action Mechanism of Polycarboxylate Superplasticizers [J], Journal of Building Materials, 2020, 23(1): 64-69+76). Polycarboxylate superplasticizers have the characteristics of low dosage, high water reduction rate, and good fluidity retention. Since their introduction in Japan in the 1980s, polycarboxylate superplasticizers have developed into the most important superplasticizer product, accounting for more than 80% of concrete superplasticizers.

[0003] Early strength is one of the most important technical indicators for precast concrete components. This is especially true for precast concrete products like pipe piles, beam boxes, and building components. The molds used to form these products are expensive, necessitating increased mold turnover to reduce the number of molds needed. Consequently, manufacturers of pipe piles, beam boxes, and building components have a strong desire to improve the early strength of concrete. Traditional methods for increasing concrete strength include increasing the amount of cement in the mix; reducing the amount of water used; increasing the curing temperature to accelerate the hydration reaction of the cementitious materials in the concrete; and adding early-strength agents such as sodium sulfate and triethanolamine.

[0004] Studies have shown (Liu Ming, Study on the Effect of Polycarboxylate Water-Reducing Agent on Cement Hydration and Related Mechanisms [D], Wuhan: Wuhan University of Technology, 2015) that polycarboxylate water-reducing agents improve concrete strength mainly by reducing water consumption. Polycarboxylate water-reducing agents themselves have a certain delaying effect on cement hydration reaction. The acid-ether ratio, polyether side chain length, and adsorption group type can all affect the inhibitory effect of polycarboxylate water-reducing agents on the cement hydration reaction process to a certain extent.

[0005] Sun Zhenping et al. (Research on the performance of early-strength polycarboxylic acid water-reducing agent [J]. 2010, (5): 54-56) used methoxy polyethylene glycol methacrylate, sodium methacrylate sulfonate and methacrylic acid as raw materials, and obtained an ultra-early-strength polycarboxylic acid water-reducing agent PC-A through aqueous free radical polymerization, which has a good early-strength effect in pipe pile concrete.

[0006] Qiao Min et al. (Effect of ultra-long side chain comb-shaped polycarboxylic acid water reducer on early performance of cement paste [J]. New Building Materials, 2013, 40(01): 20-22) studied the effects of different types of polyether macromonomers such as vinyl polyether with a molecular weight of 5000 and methoxy polyethylene glycol acrylate on the early strength and dispersion properties of water reducers. The study found that the water reducer synthesized from vinyl polyether has superior dispersion properties; the water reducer synthesized from methoxy polyethylene glycol acrylate has superior early strength properties.

[0007] Ran Qianping et al. (Effect of side chain length of comb copolymer superplasticizer on early hydration of concentrated cement suspension [J]. Journal of the Chinese Ceramic Society, 2010, 38(09): 1718-1722) found that extending the length of polyether side chains can not only accelerate the early hydration rate of cement, but also change the crystal morphology of the hydration product.

[0008] The above research shows that extending the length of the polyether side chain can significantly improve the early strength performance of polycarboxylic acid-based water reducers. Ester-type polyether monomers with the same molecular weight can produce even better early strength results in water reducers. Currently, the preparation of ester-type polyether monomers mainly utilizes a water-carrying esterification process, using methoxy polyethylene glycol and methacrylic acid or acrylic acid as raw materials, and toluene as a water-carrying agent to remove the water generated in the reaction system and increase the esterification rate of the methoxy polyethylene glycol. However, as the molecular weight of the methoxy polyethylene glycol increases, the esterification reaction activity decreases rapidly, making it difficult to achieve a monomer esterification rate of more than 90%, which has a significant adverse effect on the subsequent synthesis and application performance of early-strength polycarboxylic acid-based water reducers.

[0009] Based on this, there is a need for an early-strengthening water-reducing agent with a high monomer esterification rate, a simple synthesis process, and good early-strengthening effect, and a preparation method thereof. Summary of the Invention

[0010] The present invention aims to address the above-mentioned problems by providing an early-strength water-reducing agent, its preparation method, and its application. The synthesis of the early-strength water-reducing agent comprises two steps: a polymerization reaction of a low-molecular-weight polycarboxylic acid and a ring-opening esterification reaction of a polyether-based glycidyl ether. The low-molecular-weight polycarboxylic acid is synthesized from unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid via aqueous free radical polymerization to form a low-molecular-weight polycarboxylic acid with a molecular weight of 1000-5000. The low-molecular-weight polycarboxylic acid then undergoes a ring-opening esterification reaction with a polyether-based glycidyl ether to synthesize an ester-type polycarboxylic acid-based water-reducing agent with a comb-shaped molecular structure. The resulting early-strength water-reducing agent exhibits the advantages of a simple synthesis process, a high esterification rate, and excellent early-strength effect.

[0011] The purpose of the present invention is achieved through the following technical solutions:

[0012] The first object of the present invention is to provide an early strength water reducer, the molecular structure of the early strength water reducer is comb-shaped, the main chain has one or more of monocarboxylic acid groups and dicarboxylic acid groups, the polyether side chains are grafted onto the main chain through carboxylate groups, and the polyether side chains are also connected to secondary hydroxyl groups.

[0013] Furthermore, the main chain has monocarboxylic acid groups and dicarboxylic acid groups.

[0014] Furthermore, the polyether side chain of the early strength water-reducing agent is synthesized from polyether glycidyl ether through a ring-opening esterification reaction.

[0015] Furthermore, the polyether glycidyl ether has the following structural formula (C):

[0016]

[0017] Wherein, R is one of a linear alkane group, a branched alkane group, a cyclic alkane group, etc. between C1-C15, m is the number of ethylene oxide structural units, which is a positive integer between 100-200, and n is a positive integer between 0-20.

[0018] Furthermore, the early strength water-reducing agent is synthesized by a ring-opening esterification reaction of polyether glycidyl ether with a carboxylic acid group in a low molecular weight polycarboxylic acid.

[0019] Furthermore, the weight average molecular weight of the low molecular weight polycarboxylic acid is 1000-5000.

[0020] Furthermore, the low molecular weight polycarboxylic acid has the following structural formula (B):

[0021]

[0022] Wherein, a, b, c, and d represent the number of structural units of the propionic acid monomer, which are integers ≥ 0, and a, b, c, and d are not 0 at the same time.

[0023] Optionally, the early strength water reducing agent has the following structural formula (A):

[0024]

[0025] Wherein, a, b, c, and d respectively represent the number of structural units of the propionic acid monomer, which are integers ≥ 0, and a, b, c, and d are not 0 at the same time; R is one of a linear alkane group, a branched alkane group, a cyclic alkane group, etc. between C1-C15; m is the number of ethylene oxide structural units, which is a positive integer between 100 and 200; and n is a positive integer between 0 and 20.

[0026] Furthermore, R is selected from one of the structures such as methyl, ethyl, isopropyl, butyl, cyclohexyl, phenyl, naphthyl, 4-nonylphenyl and the like.

[0027] Furthermore, the weight average molecular weight of the early strength water reducer is between 15,000 and 50,000, and the molecular weight distribution index is ≤2.0.

[0028] A second object of the present invention is to provide a method for preparing an early strength water-reducing agent, the method comprising the following steps:

[0029] (1) Using acrylic monomers as raw materials, a low molecular weight polycarboxylic acid with a weight average molecular weight of 1000-5000 is synthesized by an aqueous phase free radical polymerization method;

[0030] (2) Using low molecular weight polycarboxylic acid and polyether glycidyl ether as raw materials, under the action of a catalyst, the carboxylic acid group in the low molecular weight polycarboxylic acid reacts with the polyether glycidyl ether to undergo a ring-opening esterification reaction to synthesize the early strength water reducing agent.

[0031] In step (1), the aqueous phase free radical polymerization method includes the following process:

[0032] With water as the primer, acrylic acid monomer prepared into an aqueous solution as the dropping liquid A, oxidant prepared into an aqueous solution as the dropping liquid B, chain transfer agent prepared into an aqueous solution as the dropping liquid C, reducing agent prepared into an aqueous solution as the dropping liquid D, under certain reaction temperature and time conditions, the dropping liquid A, dropping liquid B, dropping liquid C, and dropping liquid D are respectively and continuously added dropwise to the primer, and after the addition is completed, the temperature is kept for reaction to obtain a low molecular weight polycarboxylic acid.

[0033] Furthermore, in step (1), the conditions of the aqueous phase free radical polymerization method include:

[0034] The reaction was carried out under nitrogen protection, with a reaction temperature of 40-90°C and a reaction pressure of normal pressure; the dropping time of the droplet A and the droplet B was 1-3 hours; the droplet A, the droplet B and the droplet C and the droplet D were added simultaneously, and the droplet C and the droplet D were added for 0.1-0.5 hours longer than the droplet A; after the addition was completed, the reaction was kept warm for 1 hour.

[0035] Furthermore, the acrylic monomer includes one or more of highly active acrylic acid and methacrylic acid and less active itaconic acid and maleic acid.

[0036] Furthermore, in step (1), the sum of the mass of acrylic acid and methacrylic acid in the acrylic monomers accounts for ≥80%; that is, the acrylic monomers must include one or both of acrylic acid and methacrylic acid.

[0037] Furthermore, in step (1), the acrylic acid monomer is prepared into a 50% (mass fraction) aqueous solution as the dropping liquid A.

[0038] Furthermore, in step (1), the oxidant is selected from one or more of hydrogen peroxide (H2O2, mass fraction 27.5%), persulfate (such as one or more of sodium persulfate, ammonium persulfate, etc.), and the amount used is 1%-5% of the mass of the acrylic acid monomer, and is prepared into a 50% aqueous solution as the dropping liquid B.

[0039] Furthermore, in step (1), the chain transfer agent is one or more of hypophosphite, methyl allyl sulfonate, and allyl sulfonate, and the amount used is 3%-10% of the mass of the acrylic monomer, and is prepared into a 50% aqueous solution as the dropping liquid C.

[0040] Furthermore, in step (1), the chain transfer agent is one or more of sodium hypophosphite, sodium methyl allyl sulfonate, and sodium allyl sulfonate.

[0041] Furthermore, in step (1), the reducing agent is one of vitamin C (Vc), bleaching powder, and E51 (Brüggemann E51), and the amount used is 0.2%-1.0% of the mass of the acrylic monomer, and is prepared into a 1% aqueous solution as the dropping liquid D.

[0042] Furthermore, in step (1), the primer water is desalted water or distilled water, and the amount used is 1.5-2.0 times the mass of the acrylic acid monomer;

[0043] Furthermore, the polyether glycidyl ether is synthesized by reacting alkoxy polyethylene glycol and epichlorohydrin as raw materials, using liquid caustic soda as a catalyst, at 100°C and under normal pressure reflux conditions. The synthesis process is well known to those skilled in the art and will not be described in detail here. The structural formula of the alkoxy polyethylene glycol is as follows:

[0044]

[0045] Wherein, R is one of a linear alkane group, a branched alkane group, a cyclic alkane group, etc. between C1-C15, m is the number of ethylene oxide structural units, which is a positive integer between 100-200, and n is a positive integer between 0-20.

[0046] Furthermore, in step (2), the ring-opening esterification reaction includes the following process:

[0047] A low molecular weight polycarboxylic acid and a catalyst are used as a primer, and an aqueous solution of polyether glycidyl ether is prepared as a dropping liquid E. Under certain temperature and time conditions, the dropping liquid E is continuously added dropwise to the primer, and the low molecular weight polycarboxylic acid and the polyether glycidyl ether undergo a ring-opening esterification reaction. After the addition is completed, the reaction is kept warm to obtain an early strength water-reducing agent.

[0048] Furthermore, in step (2), the solid-based amount of the low molecular weight polycarboxylic acid is 5%-15% of the mass of the polyether glycidyl ether.

[0049] Furthermore, in step (2), the catalyst is a tertiary amine catalyst, and the amount of the catalyst is 0.05%-0.15% of the mass of the polyether glycidyl ether.

[0050] Furthermore, the tertiary amine catalyst includes one or more of triethanolamine (TEA), triisopropanolamine (TIPA), monoethanoldiisopropanolamine (DIPEA), and diethanolmonoisopropanolamine (DEIPA). The tertiary amine complexes with the carboxylic acid groups in the low molecular weight polycarboxylic acid to form a salt to form a catalytically active species, thereby enhancing the ring-opening esterification reaction activity of the carboxylic acid groups on the three-membered heterocyclic ring of the polyether glycidyl ether.

[0051] Furthermore, the polyether glycidyl ether is added with water to prepare a 40% aqueous solution as the dropping solution D.

[0052] Furthermore, in step (2), the conditions of the ring-opening esterification reaction include:

[0053] The reaction temperature of the ring-opening esterification reaction is 30-50° C., the reaction pressure is normal pressure, the dropping time of the dropwise addition liquid D is 1.0-3.0 h, and after the dropping is completed, the heat preservation reaction time is 3.0-10.0 h.

[0054] Furthermore, in step (2), the ring-opening esterification reaction rate of the polyether glycidyl ether is ≥90%.

[0055] The third object of the present invention is to provide an application of an early strength water reducing agent, wherein the early strength water reducing agent is used as a concrete admixture.

[0056] Furthermore, the early strength water reducer has good water-reducing performance and time-retaining collapse performance in concrete. The initial setting and final setting times of concrete mixed with the early strength water reducer are short, the water reducer has a low delay effect on the cement hydration process, and has a significant early strength effect.

[0057] Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

[0058] 1) The present invention provides an early strength water reducer, a preparation method thereof, and an application thereof, and provides a preparation method of an early strength water reducer with a high monomer esterification rate, a simple synthesis process, and good early strength effect.

[0059] 2) The present invention provides an early strength water reducer, a preparation method and an application thereof. The early strength water reducer is synthesized by ring-opening esterification of polyether glycidyl ether using an acidic low molecular weight polycarboxylic acid. The preparation method has the characteristics of low ring-opening reaction temperature, high esterification rate and simple synthesis process, and avoids the hydrolysis side reaction of the carboxylate group under high temperature conditions. Furthermore, compared with the traditional toluene water esterification method and the vacuum dehydration method, the method of the present invention does not use an organic solvent and the reaction temperature is not high, which has the effects of green environmental protection, energy saving and emission reduction.

[0060] 3) The present invention provides an early strength water reducing agent and its preparation method and application, which avoids the high molecular weight alkoxy polyethylene glycol (M n ≥2000) has a low esterification reaction activity of carboxylic acids, resulting in a low esterification rate. The hydroxyl groups at the ends of the alkoxy polyethylene glycol are first capped with epichlorohydrin to synthesize polyether glycidyl ether with high acidic ring-opening reaction activity, thereby inhibiting or eliminating the adverse effect of the molecular weight of the alkoxy polyethylene glycol on the monomer esterification rate.

[0061] 4) The present invention provides an early strength water reducer, a preparation method thereof, and an application thereof. The weight average molecular weight of the early strength water reducer is between 15,000 and 50,000, and the molecular weight distribution index is ≤2.0. Compared with some existing water reducers, the early strength water reducer of the present invention has better water-reducing performance and time-retaining collapse performance in concrete. The initial setting and final setting times of concrete mixed with the early strength water reducer are shorter, the water reducer has a lower delay effect on the cement hydration process, and has a significant early strength effect.

[0062] 5) The present invention provides an early strength water reducer, a preparation method thereof, and an application thereof. Using tertiary amine substances such as triethanolamine and triisopropanolamine as catalysts, not only can the reaction activity of polyether glycidyl ether and carboxylic acid groups be enhanced, but triethanolamine and triisopropanolamine themselves have the effect of promoting cement hydration reaction, thereby further enhancing the early strength performance of the early strength water reducer.

[0063] 6) The present invention provides an early strength water reducer, a preparation method thereof, and an application thereof. First, a low molecular weight polycarboxylic acid is prepared, and highly active acrylic acid or methacrylic acid is used to copolymerize with itaconic acid and maleic acid of relatively low activity to increase the monomer conversion rate of itaconic acid and maleic acid. A dicarboxylic acid group with strong sulfate resistance, viscosity reduction, and adsorption capacity is introduced into the polycarboxylic acid to improve the use effect of the early strength water reducer of the present invention under low water-binder ratio and poor material working conditions. DETAILED DESCRIPTION

[0064] The present invention is described in detail below with reference to specific embodiments, but is by no means intended to limit the present invention. Any features, such as preparation methods, materials, structures, or composition ratios, that are not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0065] These embodiments are merely illustrative and are not intended to limit the scope of the present invention. Based on the disclosure herein, those skilled in the art will be able to modify the chemical reagents, processes, and reaction equipment within the scope of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be within the scope of protection of the present invention.

[0066] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0067] In the embodiment of the present invention, the conversion rate of the polyether glycidyl ether synthesis was determined by HPLC high performance liquid chromatography (differential refractive index detector, C 18 The reverse phase chromatography column was used, the mobile phase and sample preparation solvent were methanol-water solution (methanol / water volume ratio 4:1), the sample was prepared to a mass concentration of 1%, the injection volume was 200 μL, the mobile phase flow rate was 1.0 mL / min, and the column oven was 35°C. The conversion rate of alkoxy polyethylene glycol was calculated based on the peak area ratio of alkoxy polyethylene glycol and polyether glycidyl ether.

[0068] The weight-average molecular weight, molecular weight distribution (PDI), and monomer conversion of the low-molecular-weight polycarboxylic acid and early-strength water-reducing admixture were determined using a Wyatt Technology Corporation gel permeation chromatography instrument. (Mobile phase: 0.1 mol / L aqueous NaNO₃ solution; mobile phase rate: 1 ml / min; injection volume: 20 μl; sample preparation concentration: 0.5% (g sample / g mobile phase); detector: Shodex RI-71 differential refractive index detector; standard: polyethylene glycol GPC standards (Sigma-Aldrich, molecular weights: 1,010,000, 478,000, 263,000, 118,000, 44,700, 18,600, 6,690, 1,960, 628, 232).

[0069] Example

[0070] The present invention provides an early strength water-reducing agent and a method for preparing the same. The present invention is divided into two parts: the synthesis of low molecular weight polyacrylic acid and the preparation of the early strength water-reducing agent. The parts mentioned in the examples are specifically parts by mass; the amounts of other materials added are all converted to parts by mass.

[0071] (1) Synthesis of low molecular weight polyacrylic acid

[0072] The raw material ratios for the synthesis of low molecular weight polypropylene are shown in Table 1.

[0073] Table 1 Raw material ratios for the synthesis of low molecular weight polypropylene (unit: parts by mass)

[0074]

[0075]

[0076] The synthesis process parameters of low molecular weight polycarboxylic acid are shown in Table 2.

[0077] Table 2 Synthesis process parameters of low molecular weight polycarboxylic acid

[0078] sample Temperature / ℃ Drop solution A Dropping solution B Dropping solution C Drop solution D Holding time / h PAA-1 40 1.0 1.0 1.1 1.1 1.0 PAA-2 50 1.5 1.5 2.0 2.0 1.0 PAA-3 60 2.0 2.0 2.4 2.4 1.0 PAA-4 70 2.5 2.5 2.7 2.7 1.0 PAA-5 80 3.0 3.0 3.5 3.5 1.0 PAA-6 90 2.0 2.0 2.5 2.5 1.0 PAA-7 60 3.0 3.0 3.3 3.3 1.0

[0079] The synthesis steps for low molecular weight polycarboxylic acids are as follows: According to the material ratios in Table 1, weigh the primer water (deionized water in this example) and add it to the reaction apparatus. Stirring was initiated and nitrogen purged to an oxygen content of <0.5%. An acrylic acid monomer was weighed and prepared into a 50% aqueous solution as dropwise addition solution A; an oxidizing agent was weighed and prepared into a 50% aqueous solution as dropwise addition solution B; a chain transfer agent was weighed and prepared into a 50% aqueous solution as dropwise addition solution C; and a reducing agent was weighed and prepared into a 1% aqueous solution as dropwise addition solution D. According to the process parameters in Table 2, the addition times for dropwise addition solutions A, B, C, and D were set respectively. Under nitrogen protection, once the set starting temperature was reached, the dropwise addition into the reaction apparatus began, with the temperature controlled within ±5°C of the set temperature. After the addition was completed, the reaction was maintained at this temperature for 1.0 h and then diluted with water to a 40% solids content to obtain low molecular weight polycarboxylic acids, namely PAA-1 to PAA-7.

[0080] The synthesized low molecular weight polycarboxylic acid sample was characterized by gel permeation chromatography (GPC), and the test data are shown in Table 3.

[0081] Table 3 GPC test of low molecular weight polycarboxylic acid

[0082] sample <![CDATA[M n ]]> <![CDATA[M w ]]> PDI Monomer conversion rate / % PAA-1 3048 3413.76 1.12 95.83 PAA-2 4212 4548.96 1.08 95.72 PAA-3 4745 5361.85 1.13 98.16 PAA-4 3282 3610.2 1.10 96.42 PAA-5 3494 3878.34 1.11 97.50 PAA-6 4379 4773.11 1.09 96.38 PAA-7 3793 4210.23 1.11 95.81

[0083] (2) Preparation of early strength water reducing agent

[0084] The molecular structure and code of polyether glycidyl ether are shown in Table 4.

[0085] Table 4 Molecular structure and code of polyether glycidyl ether

[0086]

[0087]

[0088] The synthesis steps for polyether glycidyl ether are as follows: Weigh 100 parts of methoxypolyethylene glycol and add it to a reaction apparatus equipped with a reflux condenser. Weigh 3.6 parts of NaOH (32% sodium hydroxide solution) and 0.5 parts of octadecyltrimethylammonium chloride (phase transfer catalyst) and add them to the reaction apparatus. Stirring is initiated and the temperature is raised to 100±5°C. Weigh 2.3 parts of epichlorohydrin and add it to a constant pressure titrator. Set the titration time for epichlorohydrin and add it dropwise to the reaction apparatus under atmospheric reflux. During the addition, control the reaction temperature at 105±5°C. After the addition is complete, continue the reaction at this temperature for 5.0-10.0 hours. Samples are taken and HPLC analysis shows a conversion rate of 97.49% for the methoxypolyethylene glycol, which is PEGE-1.

[0089] According to the same steps and methods, polyether glycidyl ethers PEGE-2 to PEGE-7 were synthesized. The monomer conversion rates and molecular weights are shown in Table 4.

[0090] The raw material ratio for the preparation of early strength water reducing agent is shown in Table 5.

[0091] Table 5 Raw material ratio and process parameters for the preparation of early strength water reducing agent (unit: mass parts)

[0092]

[0093]

[0094] Synthesis steps for the early strength water reducer: Follow the material ratios in Table 5. Weigh low molecular weight polyacrylic acid (40%) and add it to the reaction apparatus; weigh a catalyst and add it to the reaction apparatus; start stirring to thoroughly mix the base reaction materials. Weigh 100 parts of polyether glycidyl ether and dilute it with water to 40% solids, which serves as Dropping Solution E. Heat the reaction apparatus to the set temperature and set the addition time for Dropping Solution E. During the addition process, maintain the reaction temperature within ±2°C of the set temperature. After the addition is complete, continue the reaction at this temperature for the set time to obtain the early strength water reducers, namely ZQPCE-1 to ZQPCE-7.

[0095] The synthesized early strength water-reducing admixture samples were characterized by gel permeation chromatography (GPC), and the test data are shown in Table 6.

[0096] Table 6 GPC test of early strength water reducing agent

[0097]

[0098]

[0099] Comparative Example 1

[0100] This comparative example provides an ether-type early strength water-reducing agent and a synthesis method thereof.

[0101] Weigh ethylene glycol monovinyl polyethylene glycol ether EPEG5000 (M n =5000) 100 parts of polyether monomer were added to the reaction apparatus and diluted with water to a 50% solids aqueous solution. Stirring was initiated and thoroughly mixed until completely dissolved. The contents of the reaction apparatus were cooled to 5°C. 0.6 parts of ammonium persulfate were weighed and added to the reaction apparatus, stirring was continued for 5 minutes and thoroughly mixed. 0.01 parts of catalyst were weighed and added to the reaction apparatus, stirring was continued for 5 minutes and thoroughly mixed. 12 parts of acrylic acid were weighed and prepared into a 50% solids aqueous solution as Dropping Solution A; 0.67 parts of mercaptopropionic acid were weighed and prepared into a 50% solids aqueous solution as Dropping Solution B; 0.21 parts of E51 were weighed and prepared into a 1% solids aqueous solution as Dropping Solution C. The contents of the reaction apparatus were maintained at a temperature of 10°C. The addition times of Solutions A, B, and C were set to 60, 70, and 70 minutes, respectively. During the additions, the temperature of the reaction apparatus was maintained at ≤35°C. After the addition was completed, the reaction was continued for 120 minutes, and water was added to dilute the mixture to a 40% solid content aqueous solution to obtain an ether-type early strength water-reducing agent. n =33881,M w =61324, PDI=1.81, monomer conversion=91.45%.

[0102] Comparative Example 2

[0103] This comparative example provides an ester-type early strength water-reducing agent and a synthesis method thereof by esterification followed by polymerization.

[0104] Weigh methoxy polyethylene glycol (MPEG5000, M n=5000), 100 parts of p-toluenesulfonic acid, 3.5 parts of p-toluenesulfonic acid, and 0.35 parts of hydroquinone were added to the reaction apparatus and mixed thoroughly. 8.65 parts of acrylic acid were weighed and added to the reaction apparatus and mixed thoroughly. 30 parts of toluene, a water-carrying agent, were weighed and added to the reaction apparatus and mixed thoroughly. A tubular reflux condenser and a water separator were connected, and the reaction apparatus was replaced with nitrogen until the oxygen content was <0.5%. Stirring and heating were initiated, and the reaction apparatus was heated to 130°C under normal pressure and kept at this temperature for 15 hours. The toluene volatilized the water from the reaction system. After condensation in the condenser and separation in the water separator, the toluene was returned to the reaction apparatus and continued to volatilize the water generated in the reaction system. After completion of the reaction, a brown esterified macromonomer was obtained. HPLC analysis showed that the ratio of the peak area of methoxy polyethylene glycol acrylate to the peak area of methoxy polyethylene glycol indicated an esterification rate of 85% for methoxy polyethylene glycol, which was named MPEGAA.

[0105] Weigh 50 parts of primer water and add it to the reaction device, start stirring and heating, and raise the temperature of the primer water to 80°C. Prepare MPEGAA into a 50% aqueous solution as dropwise addition liquid A; weigh 0.98 parts of sodium persulfate and prepare it into a 5% aqueous solution as dropwise addition liquid B; weigh 1.2 parts of sodium bisulfite and prepare it into a 5% aqueous solution as dropwise addition liquid C. Set the addition time of A, B, and C to 1.5h, 2.0h, and 2.0h respectively. During the addition process, control the temperature in the reaction device to 80±2°C. After the addition is completed, continue to keep warm for 1.0h, add 32% liquid alkali to neutralize to pH=7, and obtain an ester-type early strength water-reducing agent. According to GPC test, M n =320942,M w =38742, PDI=1.85, monomer conversion=82.93%.

[0106] Comparative Example 3

[0107] This comparative example provides an ester-type early strength water-reducing agent and a synthesis method thereof.

[0108] Weigh 50 parts of primer water and add it to the reaction device. Weigh 8.0 parts of H2O2 (27.5%) and add it to the reaction device. Weigh 50 parts of methacrylic acid and 50 parts of acrylic acid, prepare a 50% aqueous solution as the dropping liquid A; weigh 4.0 parts of chain transfer agent mercaptopropionic acid, prepare a 50% aqueous solution as the dropping liquid B; weigh 0.2 parts of reducing agent E51, prepare a 1% aqueous solution as the dropping liquid C. Control the temperature of the primer water to 20°C. Set the dropping time of the dropping liquids A, B, and C to 3.5h, 4.0h, and 4.0h respectively. The temperature of the dropping process is controlled within the range of ±5°C of the set temperature. After the addition is completed, keep the reaction warm for 1.0h, add water to dilute to 40% solid content, and obtain a low molecular weight polycarboxylic acid. After GPC test, M n =10478,Mw =21061, PDI=2.01, monomer conversion=91.45%.

[0109] Weigh methoxy polyethylene glycol (MPEG6000, M n =6000) 100 parts were added to the reaction apparatus; 40 parts of low molecular weight polycarboxylic acid (40%) were weighed and added to the reaction apparatus; 5.0 parts of concentrated sulfuric acid as a catalyst were weighed and added to the reaction apparatus. The reaction apparatus was heated to 150°C and the water in the reaction system and the water generated by the esterification reaction were distilled off under reduced pressure at -0.1 MPa for 15.0 hours. The reaction system was then cooled to 80°C and neutralized to pH 7 by adding 32% liquid caustic soda. The mixture was diluted with water to a solid content of 40% to obtain an ester-type early strength water-reducing agent. GPC test showed that M n =35472,M w =63495, PDI=1.79, monomer conversion=85.45%.

[0110] The amount of hydrogen peroxide synthesized from the low-molecular-weight polycarboxylic acid was excessive and served as a primer. The amount of reducing agent E51 was insufficient. The reaction initial dropwise addition temperature was 20°C, and the addition time of the dropwise addition solutions A, B, and C exceeded the set time. The molecular weights of the low-molecular-weight polycarboxylic acid and ester-type early-strength water-reducing agent exceeded the specified limits.

[0111] Application Example 1

[0112] The fluidity test of cement paste was conducted in accordance with GB / T8077-2023, "Test Method for Homogeneity of Concrete Admixtures." The water-reducing agent was diluted to a 10% solids content. Conch PO 42.5 cement was used with a water-cement ratio of 0.29 and a water-reducing agent dosage of 0.13% of the cement content. The fluidity of the cement paste was measured on a flat glass plate. The setting time of a blank cement paste and a cement paste containing a water-reducing agent was tested in accordance with GB / T1346-2011, "Test Method for Water Consumption, Setting Time, and Soundness of Cement at Standard Consistency." Commercially available early-strength polycarboxylate water-reducers PCE-1 and PCE-2 were used as comparison samples. The test results for the cement paste are shown in Table 7.

[0113] Table 7 Cement paste fluidity test

[0114]

[0115] The data in Table 7 demonstrate that the early-strength water-reducing agent of the present invention exhibits excellent water-reducing performance and time-dependent slump-retention properties. Furthermore, the early-strength water-reducing agent of the present invention significantly reduces the delayed effect of the water-reducing agent on cement hydration, resulting in superior early-strength performance compared to Comparative Examples 1-3 and commercially available PCE-1 and PCE-2, with significantly advanced initial and final setting times.

[0116] Application Example 2

[0117] The performance of the polycarboxylic acid water-reducing agent of the present invention was tested using a concrete test. Reference was made to the test methods for concrete slump, expansion and setting time specified in the national standard GB / T 8076-2008 "Concrete Admixtures". Reference was made to the concrete specimen forming, curing and compressive strength test methods specified in the national standard GB / T50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The cement used was Conch P.O42.5 cement, and the fly ash was secondary ash; the sand was medium sand with a fineness modulus Mx=2.6, and the water content of the sand was 5%; the gravel was continuously graded crushed stone with a particle size of 5 to 20 mm, and the water content of the gravel was 2%. The dosage of water-reducing agent (solid content 10%) was 1.5%. The bulk density of C30 strength grade concrete is 2326Kg / m 3 The raw material proportions of concrete test are shown in Table 8.

[0118] Table 8 Concrete raw material ratio

[0119]

[0120] The concrete test data of polycarboxylate water reducer are shown in Table 9.

[0121] Table 9 Concrete test of polycarboxylate water reducer

[0122]

[0123] As shown in Table 9, the early-strength water-reducing agent of the present invention exhibits excellent water-reducing and time-slump-retaining properties in concrete, significantly outperforming Comparative Examples 1-3 and commercially available PCE1 and PCE-2. Furthermore, the initial and final setting times of concrete mixed with the early-strength water-reducing agent of the present invention are significantly shorter than those of Comparative Examples 1-3 and commercially available PCE1 and PCE2, significantly reducing the delay caused by the water-reducing agent on the cement hydration process and demonstrating a significant early-strength effect.

[0124] The strength test data of the concrete specimens are shown in Table 10.

[0125] Table 10 Concrete compressive strength test

[0126]

[0127] As shown in Table 10, concrete blocks mixed with the early-strength water-reducing agent of the present invention exhibited significantly higher 3d and 7d compressive strengths than those of Comparative Examples 1-3 and commercially available PCE1 and PCE2, and slightly higher 28d compressive strengths than those of Comparative Examples 1-3, commercially available PCE1, and PCE2. These compressive strength test results of the concrete blocks demonstrate that the early-strength water-reducing agent of the present invention significantly enhances the early strength of concrete, consistent with the concrete setting time test results in Table 9.

[0128] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. An early strength water reducing agent, characterized in that: The molecular structure of the early strength water-reducing agent is comb-shaped, the main chain has one or more of monocarboxylic acid groups and dicarboxylic acid groups, the polyether side chains are grafted onto the main chain through carboxylate groups, and the polyether side chains are also connected to secondary hydroxyl groups; The polyether side chain of the early strength water-reducing agent is synthesized from polyether glycidyl ether through a ring-opening esterification reaction; The polyether glycidyl ether has the following structural formula (C): Wherein, R is one of a linear alkane group, a branched alkane group, and a cyclic alkane group between C1-C15, m is a positive integer between 100-200, and n is a positive integer between 0-20.

2. An early strength water reducing agent according to claim 1, characterized in that: The early strength water-reducing agent is synthesized by the ring-opening esterification reaction of the carboxylic acid groups in the low molecular weight polycarboxylic acid with the polyether glycidyl ether; The weight average molecular weight of the low molecular weight polycarboxylic acid is 1000-5000; The low molecular weight polycarboxylic acid has the following structural formula (B): Wherein, a, b, c, and d are integers ≥ 0, and a, b, c, and d are not all 0 at the same time.

3. The early strength water reducing agent according to claim 1, characterized in that: The early strength water reducing agent has the following structural formula (A): wherein a, b, c, and d are integers ≥ 0, and a, b, c, and d are not all 0 at the same time; R is a linear alkane group, a branched alkane group, or a cyclic alkane group between C1 and C15; m is a positive integer between 100 and 200, and n is a positive integer between 0 and 20.

4. The early strength water reducing agent according to claim 1, characterized in that: The weight average molecular weight of the early strength water reducer is between 15,000 and 50,000, and the molecular weight distribution index is ≤2.

0.

5. A method for preparing the early strength water reducing agent according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) Using acrylic monomers as raw materials, a low molecular weight polycarboxylic acid with a weight average molecular weight of 1000-5000 is synthesized by an aqueous phase free radical polymerization method; (2) using low molecular weight polycarboxylic acid and polyether glycidyl ether as raw materials, and under the action of a catalyst, the carboxylic acid groups in the low molecular weight polycarboxylic acid react with the polyether glycidyl ether to undergo a ring-opening esterification reaction to synthesize the early strength water-reducing agent; The acrylic acid monomer includes one or more of acrylic acid, methacrylic acid, itaconic acid, and maleic acid.

6. The method for preparing an early strength water reducing agent according to claim 5, characterized in that: In step (1), the sum of the mass of acrylic acid and methacrylic acid in the acrylic monomers accounts for ≥80%; In step (1), the oxidant is selected from one or more of hydrogen peroxide and persulfate, and the amount used is 1%-5% of the mass of the acrylic monomer; In step (1), the chain transfer agent is one or more of hypophosphite, methyl allyl sulfonate, and allyl sulfonate, and the amount used is 3%-10% of the mass of the acrylic monomer. In step (1), the reducing agent is one of vitamin C, bleaching agent, and E51, and the amount used is 0.2%-1.0% of the mass of the acrylic acid monomer; In step (1), the primer water is desalted water or distilled water, and the amount used is 1.5-2.0 times the mass of the acrylic acid monomer; In step (1), the aqueous phase free radical polymerization method includes the following process: Water is used as a primer, an acrylic acid monomer is prepared into an aqueous solution as a dropping liquid A, an oxidant is prepared into an aqueous solution as a dropping liquid B, a chain transfer agent is prepared into an aqueous solution as a dropping liquid C, and a reducing agent is prepared into an aqueous solution as a dropping liquid D. Under certain reaction temperature and time conditions, the dropping liquids A, B, C, and D are continuously added dropwise to the primer, respectively. After the addition is completed, the temperature is kept for reaction to obtain a low molecular weight polycarboxylic acid.

7. The method for preparing an early strength water reducing agent according to claim 6, characterized in that: In step (1), the conditions of the aqueous phase free radical polymerization method include: The reaction was carried out under nitrogen protection, with a temperature of 40-90°C and a normal pressure. The dropping time of the dropwise addition liquid A and the dropwise addition liquid B was 1-3 hours. The dropping time of the dropwise addition liquid C and the dropwise addition liquid D was 0.1-0.5 hours longer than that of the dropwise addition liquid A. After the addition was completed, the reaction was kept warm for 1 hour.

8. The method for preparing an early strength water reducing agent according to claim 5, characterized in that: In step (2), the solid-to-solid amount of the low molecular weight polycarboxylic acid is 5% to 15% of the mass of the polyether glycidyl ether; In step (2), the catalyst is a tertiary amine catalyst, and the amount of the catalyst is 0.05% to 0.15% of the mass of the polyether glycidyl ether; In step (2), the ring-opening esterification reaction includes the following process: A low molecular weight polycarboxylic acid and a catalyst are used as a primer, and an aqueous solution of polyether glycidyl ether is prepared as a dropping liquid E. Under certain temperature and time conditions, the dropping liquid E is continuously added dropwise to the primer, and the low molecular weight polycarboxylic acid and the polyether glycidyl ether undergo a ring-opening esterification reaction. After the addition is completed, the reaction is kept warm to obtain an early strength water-reducing agent.

9. The method for preparing an early strength water reducing agent according to claim 8, characterized in that: In step (2), the conditions for the ring-opening esterification reaction include: The reaction temperature of the ring-opening esterification reaction is 30-50°C, the reaction pressure is normal pressure, the addition time of the dropwise addition liquid D is 1.0-3.0h, and after the addition is completed, the heat preservation reaction time is 3.0-10.0h; In step (2), the ring-opening esterification reaction rate of the polyether glycidyl ether is ≥90%.

10. A use of the early strength water reducing agent according to any one of claims 1 to 4, characterized in that: The early strength water reducing agent is used as a concrete admixture.

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