Hyperbranched water reducing agent for high-tensile wet joint UHPC (Ultra High Performance Concrete) as well as preparation method and application of hyperbranched water reducing agent

Abstract

The invention discloses a hyperbranched water reducing agent for high-tensile wet joint UHPC (Ultra High Performance Concrete) as well as a preparation method and application of the hyperbranched water reducing agent, and belongs to the technical field of concrete admixtures. The preparation method comprises the following steps: mixing pentaerythritol and maleic anhydride, adding a catalyst p-toluenesulfonic acid, and carrying out an esterification reaction to prepare an esterification product; carrying out amidation reaction on the esterification product, diethanol amine and a catalyst sodium ethoxide to obtain a prepolymer; acrylic acid, maleic anhydride and the prepolymer are dissolved in deionized water, an initiator ammonium persulfate is added for a free radical copolymerization reaction, and a main chain polymer is obtained; carrying out phosphorylation reaction on the main chain polymer and phosphorus pentoxide to obtain a phosphorylated main chain polymer; the phosphorylated main chain polymer, methoxypolyethylene glycol and a catalyst p-toluenesulfonic acid are subjected to an etherification reaction, a hyperbranched comb-shaped polymer water reducing agent solution is obtained and then subjected to aftertreatment, and the water reducing agent is prepared. According to the hyperbranched comb-shaped polymer water reducing agent prepared by the preparation method disclosed by the invention, the problems of poor flowability and high viscosity of ultra-high performance concrete (UHPC) are solved by combining a linear side chain of a comb-shaped structure and a three-dimensional branch of hyperbranched topology.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete admixtures, and in particular relates to a hyperbranched water reducer for high tensile strength wet joints UHPC and a preparation method and application thereof. Background Art

[0002] High-tensile UHPC (Ultra-high Performance Concrete) typically has a water-to-binder ratio of less than 0.18. The steel fibers often contain excessive amounts of these fibers, often of a special shape. This results in poor concrete fluidity, high viscosity, and significant construction difficulties. In actual production, fluidity plummets after the steel fiber content reaches 2%, while the steel fiber content for high-tensile UHPC is expected to reach 4%-8%. Excellent working properties, primarily high fluidity and low viscosity, are crucial for the smooth pouring of UHPC in areas with densely reinforced steel overlaps. Traditional polycarboxylate superplasticizers (PCs) have significant dispersibility limitations in UHPC, making it difficult to meet the required fluidity and low viscosity. Therefore, the development of a high-performance superplasticizer suitable for UHPC is of great engineering significance.

[0003] Currently, conventional comb polymers enhance dispersibility through carboxylic acid and polyether side chains, but their adsorption capacity for ultrafine powders is limited. Hyperbranched structures reduce viscosity through three-dimensional steric hindrance, but the preparation process is complex and costly. Branched functional group design enhances adsorption through phosphate groups, but this results in higher solution viscosity and a significant bridging effect.

[0004] In summary, it is urgent to research and propose a new type of hyperbranched comb polymer water reducer that combines the advantages of comb structure and hyperbranched topology to achieve high fluidity, low viscosity and excellent adsorption performance of UHPC through innovative design. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a hyperbranched water reducer for UHPC with high tensile strength wet joints, and its preparation method and application, and to prepare a hyperbranched comb polymer water reducer. By combining the linear side chains of the comb structure with the three-dimensional branches of the hyperbranched topology, the problems of poor fluidity and high viscosity of ultra-high performance concrete (UHPC) are solved.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints, comprising the following steps: S1: Pentaerythritol and maleic anhydride are mixed and then p-toluenesulfonic acid is added as a catalyst to carry out an esterification reaction to obtain an esterified product; the esterified product, diethanolamine and sodium ethoxide as a catalyst are subjected to an amidation reaction to obtain a prepolymer; S2: dissolving acrylic acid, maleic anhydride and prepolymer in deionized water, stirring evenly, adding ammonium persulfate as an initiator to carry out free radical copolymerization to obtain a main chain polymer; S3: The main chain polymer is subjected to a phosphorylation reaction with phosphorus pentoxide to obtain a phosphorylated main chain polymer; the phosphorylated main chain polymer, polyethylene glycol monomethyl ether, and a catalyst, p-toluenesulfonic acid, are subjected to an etherification reaction to obtain a hyperbranched comb polymer water reducer solution; S4: The hyperbranched comb polymer water-reducing agent solution is dialyzed, extracted, pH-adjusted, and concentrated in sequence to prepare a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints.

[0007] In one embodiment, in S1, the molar ratio of pentaerythritol to maleic anhydride is 1:4.4; the amount of the catalyst p-toluenesulfonic acid is 0.5 wt%-2 wt% of the sum of the mass of pentaerythritol and maleic anhydride; The molar ratio of the esterification product to diethanolamine is 1:4.4; the amount of the catalyst sodium ethoxide is 3 mol%-8 mol% of the amount of maleic anhydride.

[0008] In one embodiment, in S2, the molar ratio of acrylic acid, maleic anhydride and prepolymer is 6:4:1; the amount of initiator ammonium persulfate used is 0.2 wt%-4 wt% of the total mass of the monomers consisting of acrylic acid, maleic anhydride and prepolymer; The amount of deionized water used is 3-5 times the total weight of the monomers, preferably 3 times. The monomers are the sum of acrylic acid, maleic anhydride and prepolymer.

[0009] In one embodiment, in S3, the molar ratio of the main chain polymer to phosphorus pentoxide is 1:0.5-1; the molar ratio of the phosphorylated main chain polymer to polyethylene glycol monomethyl ether is 1:1-2; and the amount of the catalyst p-toluenesulfonic acid used is 0.5 wt%-2 wt% of the mass of polyethylene glycol monomethyl ether.

[0010] In one embodiment, in S1, the reaction conditions of the esterification reaction are as follows: reaction temperature 110-130° C., reaction time 4-6 hours; The amidation reaction process is as follows: half of the diethanolamine is added to the esterification product, and the temperature is raised to 100-200° C. under nitrogen protection, and the reaction is carried out for 1-3 hours. After the reaction is carried out until no water is distilled out, the remaining diethanolamine and the catalyst sodium ethoxide are added, and the reaction is continued at 40-110° C. for 1-5 hours to obtain a prepolymer.

[0011] In one embodiment, in S2, the reaction conditions of the free radical copolymerization reaction are as follows: reaction temperature 60-90° C., reaction time 4-12 hours; In S3, the reaction conditions of the phosphorylation reaction are as follows: reaction temperature 60-80° C., reaction time 2-4 hours; the reaction conditions of the etherification reaction are as follows: reaction temperature 80-100° C., reaction time 3-6 hours.

[0012] In one embodiment, in S4, the pH of the hyperbranched comb-shaped polymer water-reducing agent solution is 8-9 after pH adjustment; and the solid content of the hyperbranched comb-shaped polymer water-reducing agent solution is greater than 20% after concentration.

[0013] Another aspect of the present invention further provides a hyperbranched water-reducing agent for UHPC with high tensile strength and wet joints, prepared by the above-mentioned method for preparing a hyperbranched water-reducing agent for UHPC with high tensile strength and wet joints. The general structural formula of the hyperbranched water-reducing agent for UHPC with high tensile strength and wet joints is as follows: Main chain: -[CH2-CH(COOM)] m -[CH2-CH(COO-PO3H2)] n - Side chain: -O-(CH2-CH2-O) p -R Hyperbranched unit: -C(CH2OH)4-(CO-NH-CH2-CH2-OH) q Among them, the main chain connects the hyperbranched units through ester bonds or amide bonds, and connects the side chains through ether bonds; Wherein: m is the number of acrylic acid units, accounting for 70%-90%; n is the number of phosphorylated maleic anhydride units, accounting for 10%-30%; p is the length of the polyether chain, which is 8-114 repeating units; q is the number of branches of the hyperbranched unit, which is 3-4.

[0014] M is a monovalent cation selected from Na + , K + or NH4 + ; R is preferably methyl (-CH3).

[0015] The main chain of the hyperbranched comb polymer is connected to the hyperbranched units through ester bonds or amide bonds, and is connected to the polyether side chains and the phosphorylated side chains through ether bonds.

[0016] In one embodiment, the main chain molecular weight of the hyperbranched water-reducing agent for high tensile strength wet joints of UHPC is Mw=20,000-50,000.

[0017] In another aspect, the present invention further provides a use of a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints prepared by the method for preparing a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints in UHPC with high tensile strength wet joints.

[0018] Compared with the prior art, the present invention has the following beneficial effects: On one hand, the present invention provides a method for preparing a hyperbranched water-reducing agent for high-tensile-resistance wet joints in UHPC. The method includes three main steps: prepolymer synthesis, main chain polymerization, and side chain grafting. The prepolymer synthesis is the core structure of a hyperbranched comb polymer, which is prepared by esterification and amidation reactions. The main chain polymer is prepared by free radical copolymerization, combining prepolymer, acrylic acid, and maleic anhydride. The main chain is the backbone of the polymer and is responsible for providing charge density and adsorption sites. The side chain grafting includes phosphorylation and etherification reactions, respectively introducing phosphate groups and polyether side chains. The side chain is the functional part of the polymer and is responsible for providing steric hindrance and dispersibility. The hyperbranched unit is the core topological structure of the polymer and is responsible for reducing solution viscosity and weakening the bridging effect.

[0019] Another aspect of the present invention provides a hyperbranched comb-shaped polymer water reducer produced using the above-mentioned preparation method. The main chain is a copolymer of acrylic acid and maleic anhydride, with polyether and phosphate side chains as side chains. The hyperbranched units utilize pentaerythritol as the core, forming a three-dimensional topological structure. By combining the linear side chains of the comb-shaped structure with the three-dimensional branches of the hyperbranched topology, this invention addresses the poor fluidity and high viscosity issues of ultra-high-performance concrete (UHPC). Urgent technical solutions include enhancing adsorption capacity, reducing viscosity, and improving fluidity. Specifically, the phosphate groups and polyol amine side chains enhance adsorption performance for ultrafine powders such as cement and silica fume, thereby increasing adsorption capacity. The hyperbranched structure reduces the bridging effect between polymer chains, reducing the viscosity of the UHPC slurry. The polyether side chains provide steric hindrance, improving the fluidity of the concrete and enhancing its flowability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart of a method for preparing a hyperbranched water-reducing agent for high tensile strength wet joints of UHPC. DETAILED DESCRIPTION

[0021] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0022] The present invention provides a hyperbranched water reducer for high tensile strength wet joints UHPC, and a preparation method and application thereof.

[0023] like Figure 1As shown, the present invention provides a method for preparing a hyperbranched water-reducing agent for high-tensile-strength wet joints in UHPC. Specifically, the preparation method of this technical solution consists of three main steps: prepolymer synthesis, main chain polymerization, and side chain grafting. The following is a detailed preparation process and process parameters.

[0024] S1: Prepolymer synthesis. The prepolymer is the core structure of the hyperbranched comb polymer and is prepared through esterification and amidation reactions.

[0025] (1) Esterification reaction Raw materials: pentaerythritol (C(CH2OH)4): 0.2 mol; maleic anhydride (HOOC-CH=CH-COOH): 0.88 mol; catalyst: p-toluenesulfonic acid (0.5 wt%-2 wt%, based on the mass of the reaction substrate, i.e., the mixture of pentaerythritol and maleic anhydride).

[0026] Steps: Add pentaerythritol and maleic anhydride to a four-necked flask, along with p-toluenesulfonic acid as a catalyst. While stirring, heat to 110-130°C and allow to react for 4-6 hours. Remove generated water through a water separator until no more water remains. After the reaction, cool to room temperature to obtain the esterified product (hyperbranched core).

[0027] Reaction equation: C(CH2OH)4+4HOOC-CH=CH-COOH→C(CH2O-CO-CH=CH-COOH)4+4H2O During the above preparation process, the anhydride ring may partially hydrolyze to maleic acid at 110-130°C. However, high-temperature dehydration conditions drive the reaction toward esterification, so the maleic anhydride directly participates in the reaction as an unhydrolyzed anhydride. The generated water is removed through a water separator during the reaction to promote esterification equilibrium.

[0028] The esterification product retains the double bond structure ( 1 There is a CH=CH proton peak at δ 6.0-7.0 ppm in H NMR and 1640 cm in FTIR. -1 There is a C=C stretching vibration peak at ).

[0029] The reaction temperature is controlled at 110-130°C, and especially avoid exceeding 130°C to prevent double bond polymerization, because the maleic anhydride double bond may polymerize under high temperature conditions.

[0030] (2) Amidation reaction Raw materials: esterification product: 0.2 mol; diethanolamine (HN(CH2CH2OH)2): 0.88 mol; catalyst: sodium ethoxide (3 mol%-8 mol%, based on the amount of maleic anhydride used) Procedure: Add the esterified product to a four-necked flask and add 50% diethanolamine (0.44 mol). Under nitrogen, raise the temperature to 100-200°C and react for 1-3 hours. After the reaction is complete and no water is distilled off, add the remaining diethanolamine and the catalyst, sodium ethoxide. Continue the reaction at 40-110°C for 1-5 hours to obtain a prepolymer.

[0031] Reaction equation: C(CH2O-CO-CH=CH-COOH)4+4HN(CH2CH2OH)2→C(CH2O-CO-CH=CH-CO-NH-CH2CH2OH)4 S2: Main chain polymerization, the main chain polymer is prepared by free radical copolymerization, combining prepolymer, acrylic acid and maleic anhydride.

[0032] Raw materials: Acrylic acid (CH2=CH-COOH): 0.6 mol. Maleic anhydride (HOOC-CH=CH-COOH): 0.4 mol. Prepolymer: 0.1 mol. Initiator: Ammonium persulfate (APS, 0.2 wt%-4 wt% based on the total monomer weight). Solvent: Deionized water. The amount of deionized water used is 3-5 times the total monomer weight, preferably 3 times. Monomers: The sum of acrylic acid, maleic anhydride, and prepolymer.

[0033] Steps: Dissolve acrylic acid, maleic anhydride, and prepolymer in deionized water and stir until uniform. Add the initiator, ammonium persulfate, and heat to 60-90°C. Under nitrogen, react for 4-12 hours until the monomers are fully converted. After the reaction, cool to room temperature to obtain a main-chain polymer solution.

[0034] nCH2=CH-COOH+mHOOC-CH=CH-COOH+prepolymer→main chain polymer S3: Side chain grafting. Side chain grafting includes phosphorylation reaction and etherification reaction, which introduce phosphoric acid groups and polyether side chains respectively.

[0035] (1) Phosphorylation reaction Raw materials: Main chain polymer: 1 mol. Phosphorus pentoxide (P2O5): 0.5-1.0 mol. Solvent: deionized water.

[0036] Steps: Add the backbone polymer solution (10%-30% solids content) to a reactor and add phosphorus pentoxide. Stir and react at 60-80°C for 2-4 hours. After the reaction is complete, cool to room temperature to obtain the phosphorylated backbone polymer.

[0037] Reaction equation: -CH2-CH2-OH+P2O5→-CH2-CH2-O-PO3H2 (2) Etherification reaction Raw materials: Phosphorylated backbone polymer: 1 mol. Polyethylene glycol monomethyl ether (MPEG, CH3O-(CH2CH2O)pH): 1-2 mol. Catalyst: p-toluenesulfonic acid (0.5 wt%-2 wt%, based on MPEG mass). Steps: Add the phosphorylated backbone polymer solution to a reactor, along with MPEG and a catalyst. Stir and react at 80-100°C for 3-6 hours. After the reaction is complete, cool to room temperature and remove the catalyst by dialysis (deionized water, 24 hours) or ion exchange resin. Unreacted MPEG is then removed by vacuum distillation (60°C, -0.1 MPa) to yield the final hyperbranched comb polymer water reducer.

[0038] Reaction equation: -CH2-CH2-OH+CH3O-(CH2CH2O) p -H→-CH2-CH2-O-(CH2CH2O) p -CH3 Among them, a semipermeable membrane is used to remove small molecule catalysts, the solvent is deionized water itself, and the dialysis time is more than 24 hours.

[0039] S4: Dialysis and extraction to remove unreacted monomers and excess diethanolamine.

[0040] Specific methods of dialysis: The reaction solution was placed in a dialysis bag (molecular weight cutoff 1000 Da) and dialyzed in deionized water for 24 h, changing the water every 6 h until the dialysate conductivity was <10 μS / cm.

[0041] Specific extraction method: The aqueous phase was extracted three times with ethyl acetate (volume ratio 1:1), and the organic phases were combined and the solvent was removed by rotary evaporation to separate the excess diethanolamine.

[0042] S5: Adjust the pH value and concentrate. The dialysate is adjusted to pH 8-9 with NaOH solution and concentrated under reduced pressure at 60°C to a solid content of >20% to obtain the target water reducer.

[0043] Specific method for pH adjustment: add 10% NaOH solution until the system pH is 8-9, stir for 30 minutes, and terminate the adjustment after the pH is stable.

[0044] Specific measures for concentration: concentrate the solution under reduced pressure at 60° C. to a solid content of more than 20%, filter out insoluble matter, and obtain a hyperbranched comb polymer water reducer.

[0045] The important parameters in the above preparation process are summarized in Table 1 below.

[0046] Table 1

[0047] Another aspect of the present invention provides a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints prepared by the above-mentioned preparation method. The general structural formula of the hyperbranched water-reducing agent for UHPC with high tensile strength wet joints is as follows: Main chain: -[CH2-CH(COOM)] m -[CH2-CH(COO-PO3H2)] n - Side chain: -O-(CH2-CH2-O) p -R Hyperbranched unit: -C(CH2OH)4-(CO-NH-CH2-CH2-OH) q Where: m is the number of acrylic acid units, accounting for 70%-90%. n is the number of phosphorylated maleic anhydride units, accounting for 10%-30%.

[0048] The ratio of m to n directly reflects the ratio of carboxylic acid to phosphoric acid groups in the main chain; p: polyether chain length (8-114 repeating units); q: number of branches in the hyperbranched unit (usually 3-4). M is a monovalent cation, selected from Na + , K + or NH4 + ; R is methyl.

[0049] The main chain of the hyperbranched comb polymer is connected to the hyperbranched units through ester bonds or amide bonds, and the polyether side chains and the phosphorylated side chains are connected through ether bonds.

[0050] M is a monovalent cation selected from Na + , K + or NH4 + , formed by neutralization of carboxylic acid groups by alkaline reagents during pH adjustment.

[0051] In the final stage of preparation (after product purification), the pH needs to be adjusted to 8-9, at which point the carboxylic acid groups (-COOH) are neutralized to carboxylate salts (-COOM).

[0052] The specific process of pH adjustment, for example, when using NaOH for adjustment: after the reaction is completed, alkaline solution (such as 10% NaOH) is added dropwise to the polymer solution, and the pH is detected during the process until it reaches the target range.

[0053] The materials used are MPEG-350, MPEG-500, or MPEG-5000. MPEG-350 has an average molecular weight of 350, corresponding to a degree of polymerization (p) of approximately 8, which is suitable for high adsorption. MPEG-500 has a p of approximately 11, while MPEG-5000 has a p of approximately 115, which indicates particularly high fluidity (extremely low adsorption and high steric hindrance).

[0054] The structural design principle of the hyperbranched water-reducing agent for high tensile strength wet joint UHPC is as follows: 1) Main chain design: The main chain is the backbone of the polymer, responsible for providing charge density and adsorption sites.

[0055] The backbone is composed of a copolymer of acrylic acid (AA) and maleic anhydride (MA). Acrylic acid provides a high charge density, enhancing electrostatic adsorption to cement particles. Maleic anhydride provides double bonds and carboxylic acid groups, participating in free radical copolymerization and increasing the backbone charge density. The molar ratio of acrylic acid to maleic anhydride is 3:1, ensuring sufficient carboxylic acid groups in the backbone.

[0056] The main chain is copolymerized via aqueous free radical random copolymerization. The main chain structure is regulated by the molar ratio of AA to MA (3:1) and the amount of initiator used, ultimately forming a copolymer backbone with both high charge density (AA) and functional sites (MA). This design is the core foundation of the water reducer's performance (adsorption and dispersibility).

[0057] Through phosphorylation, phosphate groups (-PO3H2) are grafted onto the main chain to enhance adsorption of ultrafine powders such as silica fume. The proportion of phosphate groups is 10%-20% (based on the total amount of main chain monomers).

[0058] 2) Side chain design: Side chains are the functional parts of polymers, responsible for providing steric hindrance and dispersion capabilities. Polyether side chains and phosphorylated side chains are suitable.

[0059] The polyether side chain uses polyethylene glycol monomethyl ether (MPEG) to provide a long-chain polyether structure and enhance the steric hindrance effect; the phosphorylated side chain is a phosphate group formed by grafting polyol amine groups (such as diethanolamine) onto the main chain through a phosphorylation reagent (such as phosphorus pentoxide), thereby enhancing the adsorption capacity.

[0060] 3) Hyperbranched unit design. The hyperbranched unit is the core topological structure of the polymer, responsible for reducing the solution viscosity and weakening the bridging effect.

[0061] Pentaerythritol (C(CH2OH)4) was chosen as the hyperbranching monomer, which provides four hydroxyl groups as the hyperbranching core. Each pentaerythritol core is connected to 3-4 branches, forming a three-dimensional topological structure.

[0062] The branch structure includes esterification branches and amidation branches. The esterification branch is formed by connecting maleic anhydride to the hydroxyl group of pentaerythritol through an esterification reaction. The amidation branch is formed by connecting diethanolamine to the esterification branch through an amidation reaction, forming a polyol amine side chain.

[0063] 4) Structural terminal optimization.

[0064] Molecular weight control: By adjusting the amount of initiator, the molecular weight of the main chain polymer (Mw=20,000-50,000) can be controlled.

[0065] Side chain length adjustment: Optimize the steric hindrance effect by selecting MPEG with different polymerization degrees (p=8-114).

[0066] The number of hyperbranched units: The number of branches in the hyperbranched unit can be controlled by adjusting the ratio of pentaerythritol to maleic anhydride.

[0067] Experimental verification To verify the performance of a hyperbranched comb polymer water reducer, we designed the following experimental protocol, including molecular weight testing, adsorption testing, flowability testing, and viscosity testing. The following is a detailed analysis of the experimental steps, methods, and results.

[0068] 1. Molecular weight test 1.1 Test method The molecular weight and distribution of polycarboxylate superplasticizers were determined by gel permeation chromatography (GPC). An Agilent 1100 chromatography system was used, equipped with two PL aquagel-OH MIXED 8 μm columns (7.5 × 300 mm) connected in series, a RID detector, and a column oven. The eluent was 0.1 mol / L phosphate buffer solution, the flow rate was set at 1 ml / min, and the column temperature was controlled at 30°C.

[0069] In this experiment, a series of polyacrylic acid samples with varying molecular weights and narrow molecular weight distributions were used as reference materials. Under identical experimental conditions, the GPC elution volumes of the reference samples were measured and the natural logarithm molecular weight (lnM) of polyacrylic acid was plotted against the elution volume (Ve). This generated a calibration curve between molecular weight and elution volume, and a calibration equation was derived. Under the same experimental conditions, the GPC elution volume of the polycarboxylate superplasticizer to be tested was measured, and its molecular weight was calculated using the calibration equation, ultimately yielding a molecular weight and distribution curve.

[0070] (1) Test equipment and conditions Equipment: Gel Permeation Chromatography (GPC / SEC). Column: Use a gel column suitable for water-soluble polymers (e.g., TSKgel GMPWXL). Mobile Phase: 0.1 M NaNO₃ aqueous solution (or phosphate buffer, pH 7.0). Flow Rate: 1.0 mL / min. Detector: Refractive Index (RI) or Multi-Angle Laser Light Scattering (MALS). Standards: Polyethylene glycol (PEG) or polyacrylic acid (PAA) standards for molecular weight calibration.

[0071] (2) Sample preparation Dissolve the sample: Dissolve the hyperbranched comb polymer water reducer sample in the mobile phase to prepare a solution with a concentration of 2-5 mg / mL.

[0072] Filtration: Filter the sample through a 0.22 μm microporous membrane to remove insoluble impurities.

[0073] Injection: Take 100 μL of filtered sample solution and inject it into the GPC system.

[0074] (3) Test steps System calibration: Use PEG or PAA standards to calibrate the system and establish a curve between molecular weight and retention time.

[0075] Sample testing: Inject the sample to be tested into the GPC system and record the chromatogram.

[0076] Data analysis: The number average molecular weight (Mn), weight average molecular weight (Mw) and molecular weight dispersion index (PDI) of the polymer were calculated from the chromatogram.

[0077] 1.2 Test results and analysis When 100 μl was injected, the molecular weight (Mw) and distribution index (PDI) were calculated.

[0078] Target molecular weight: Mw = 38,500 g / mol, PDI = 1.25.

[0079] The calculated test results showed a weight-average molecular weight (Mw) of 38,200 g / mol, a number-average molecular weight (Mn) of 30,500 g / mol, and a molecular weight dispersion index (PDI) of 1.25.

[0080] The narrow molecular weight distribution (PDI=1.25) indicates good polymerization reaction control and uniform molecular weight distribution. The weight-average molecular weight is close to the target value (38,500 g / mol), indicating that the polymerization conditions were properly optimized. This narrow molecular weight distribution and moderate molecular weight facilitate good polymer dispersion and water reduction in UHPC.

[0081] 2. Adsorption performance test Adsorption performance is a key indicator for evaluating the effectiveness of hyperbranched comb polymer water reducers in cementitious materials. Adsorption testing can assess the polymer's adsorption capacity on cement particle surfaces and, in turn, analyze its impact on concrete flowability, viscosity, and dispersion properties. The quality of adsorption directly determines the effectiveness of the water reducer in ultra-high-performance concrete (UHPC).

[0082] 2.1 Test Principle Adsorption performance testing mainly evaluates the adsorption capacity of cement by measuring the amount of polymer adsorbed on the surface of cement particles. Commonly used testing methods include: (1) Total organic carbon (TOC) analysis method: The adsorption amount is calculated by measuring the change in polymer concentration in the solution.

[0083] (2) Zeta potential test: By measuring the changes in the surface potential of cement particles, the adsorption effect of the polymer is indirectly reflected.

[0084] (3) Ultraviolet-visible spectrophotometry (UV-Vis): Applicable to polymers containing specific chromophores, the adsorption amount is calculated by the change in absorbance.

[0085] This proposal intends to use a combination of Zeta potential test and TOC analysis to comprehensively evaluate the adsorption performance of hyperbranched comb polymer water reducer.

[0086] 2.2 Test methods (1) Test equipment and conditions Equipment: Zeta potential analyzer (such as Malvern Zetasizer Nano ZS), Total Organic Carbon Analyzer (TOCAnalyzer), Centrifuge (for separating cement particles from solution).

[0087] Conditions: Temperature: 25 ± 1°C. Cement sample: Ordinary Portland cement (OPC). Superplasticizer concentration: 0.1%-0.5% (based on cement mass). Water-cement ratio (W / C): 0.35.

[0088] (2) Sample preparation Preparation of cement paste: Mix cement and water-reducing agent solution in appropriate proportions and stir evenly. Let it stand for 5 minutes to allow the polymer to fully absorb onto the surface of cement particles.

[0089] Centrifugation: The cement paste was centrifuged at 5000 rpm for 10 minutes to separate the supernatant and precipitate. The supernatant was collected for TOC analysis.

[0090] Zeta potential test sample: Dilute the cement paste to an appropriate concentration (0.1%-0.2%) for Zeta potential testing.

[0091] (3) Test steps Sample loading: Inject the diluted cement paste into the sample cell of the Zeta potential analyzer.

[0092] Test parameter settings: Temperature: 25℃.

[0093] Electric field strength: Set according to instrument requirements.

[0094] Data collection: Record the zeta potential value of the cement particle surface. Each group of samples was tested three times and the average value was taken.

[0095] Standard curve drawing: prepare water reducer solutions of different concentrations (0.01%-0.1%).

[0096] The organic carbon content of each concentration solution was determined using a TOC analyzer, and a standard curve was drawn.

[0097] Supernatant test: The supernatant after centrifugation is injected into the TOC analyzer to determine the organic carbon content.

[0098] Calculation of adsorption capacity: The adsorption amount was calculated based on the difference between the initial concentration and the supernatant concentration.

[0099] Adsorption capacity (mg / g) = (C0- C1) × V / m C0: initial concentration (mg / L).

[0100] C1: supernatant concentration (mg / L).

[0101] V: volume of solution (L).

[0102] m: cement mass (g).

[0103] 2.3 Test results and analysis (1) Zeta potential test results Target value: -45 mV (significantly higher than the -30 mV of conventional water reducers).

[0104] Test results: Hyperbranched comb polymer water reducer: -44.5 mV. Conventional water reducer: -30.2 mV.

[0105] Hyperbranched comb polymer water reducers significantly increase the negative charge on the cement particle surface, indicating a stronger adsorption capacity. The high negative charge contributes to electrostatic repulsion between cement particles, improving dispersibility and flowability.

[0106] (2) TOC analysis results Target adsorption capacity: 8-12 mg / g (based on cement mass).

[0107] Test results: Hyperbranched comb polymer water reducer: 10.2 mg / g. Conventional water reducer: 6.5 mg / g.

[0108] The adsorption capacity of the hyperbranched comb polymer superplasticizer was significantly higher than that of conventional superplasticizers, indicating that its phosphate groups and polyol amine side chains have a stronger adsorption capacity for cement particles. This high adsorption capacity helps the polymer form a dense adsorption layer on the surface of cement particles, providing better dispersion.

[0109] 3. Flowability test The fluidity test evaluated the effectiveness of a novel hyperbranched comb polymer superplasticizer on improving the fluidity of ultra-high performance concrete (UHPC) pastes. By measuring the fluidity of the paste, the role of the hyperbranched structure and polyether side chains in enhancing UHPC fluidity was verified and compared with that of a traditional superplasticizer.

[0110] 3.1 Test method (1) Sample preparation: Prepare UHPC slurry with a water-to-binder ratio of 0.17. Add the new hyperbranched comb polymer water reducer and the traditional water reducer at an amount of 1.5% of the mass of the cementitious material. Use a forced mixer to fully stir the slurry to ensure uniform dispersion.

[0111] (2) Test apparatus: Table jump tester: in accordance with GB / T 2419-2005, with a jump frequency of 1 beat / second and a jump height of 10 mm. Test mold: a cylindrical mold with an inner diameter of 30 mm and a height of 50 mm. Glass plate: 400 mm × 400 mm in size, with a smooth and level surface.

[0112] (3) Test conditions: Temperature: 25°C (constant temperature laboratory environment). Humidity: 50% ± 5% relative humidity. Test time: Test within 5 minutes after slurry preparation.

[0113] (4) Test steps: Place the glass plate horizontally and ensure that the base of the table jumper is stable. Wipe the glass plate and the inner wall of the mold with a damp cloth to prevent the slurry from sticking. Place the test mold in the center of the glass plate. Pour the prepared UHPC slurry into the mold at one time to avoid bubbles. Use a scraper to smooth the slurry surface and ensure that it is flush with the top of the mold. Lift the mold vertically and slowly to allow the slurry to spread naturally. Start the table jumper and set the number of jumps to 15 times. After the jump is completed, use a vernier caliper to measure the maximum diffusion diameter of the slurry on the glass plate (unit: mm) and take the average of the two vertical directions. Repeat the test three times for each group of samples and take the average value.

[0114] 3.2 Test results and analysis Fluidity: The UHPC slurry with the new hyperbranched comb polymer water reducer had a fluidity of 280 mm. The UHPC slurry with the traditional water reducer had a fluidity of 220 mm. The new water reducer increased the fluidity of the UHPC slurry by 27.3% compared to the traditional water reducer, significantly improving the fluidity of the UHPC slurry. The synergistic effect of the hyperbranched structure and polyether side chains effectively enhanced the flow properties of the slurry. The slurry with the new water reducer exhibited improved uniformity and self-leveling properties, with smooth diffusion edges and no noticeable bleeding or segregation. The slurry with the traditional water reducer had acceptable fluidity, but the diffusion edges were uneven, with slight bleeding in some areas.

[0115] Analysis suggests that the three-dimensional topological properties of the hyperbranched structure reduce entanglement between polymer chains, lowering internal resistance in the paste and thus improving fluidity. The number of branches in the hyperbranched units (q = 3-4) optimizes the steric hindrance effect, further improving the paste's flow properties. The polyether side chains (MPEG) provide effective steric hindrance, dispersing cement particles and reducing inter-particle interactions, thereby enhancing the paste's fluidity. The length of the polyether side chains (p = 8-114) further optimizes the paste's fluidity by regulating the steric hindrance effect. The phosphate groups enhance the water reducer's adsorption capacity for cement particles, reducing free water consumption and further improving the paste's fluidity. The synergistic effect of the phosphate groups and the polyol amine side chains enhances the water reducer's dispersion efficiency, resulting in more uniform paste flow.

[0116] 4. Viscosity test The viscosity test was designed to evaluate the effect of a hyperbranched comb polymer superplasticizer on the viscosity of ultra-high performance concrete (UHPC) paste. By measuring viscosity at different shear rates, the effectiveness of the hyperbranched structure in reducing the viscosity of the UHPC paste was verified and compared with that of a conventional superplasticizer.

[0117] 4.1 Test method (1) Sample preparation: Prepare a UHPC slurry with a water-to-binder ratio of 0.17. Add the new hyperbranched comb polymer water reducer and a conventional water reducer at a rate of 1.5% of the mass of the cementitious material. Stir the slurry thoroughly to ensure uniform dispersion.

[0118] (2) Test instrument: Use a Brookfield rotational viscometer (such as Brookfield DV2T) to perform viscosity testing.

[0119] (3) Test conditions: Temperature: 25°C. Speed ​​range: 10 rpm to 100 rpm. Focus on the viscosity value at 60 rpm.

[0120] (4) Pour the prepared UHPC slurry into the test container, ensuring that the slurry height covers the rotor mark. Insert the rotor vertically into the slurry to avoid air bubbles. Start the viscometer and gradually increase the speed from a low speed (10 rpm) to the target speed (60 rpm). Record the viscosity value after stabilization (unit: mPa·s). Repeat the test three times for each sample group and take the average value.

[0121] 4.2 Test results and discussion At 60 rpm, the viscosity of the UHPC slurry containing the novel hyperbranched comb polymer water reducer was 1217 mPa·s. Under the same conditions, the viscosity of the UHPC slurry containing the traditional water reducer was 1791 mPa·s.

[0122] The new superplasticizer exhibited a 32.0% lower viscosity than conventional superplasticizers, significantly improving the fluidity of the UHPC slurry. The hyperbranched structure effectively weakened the bridging effect between polymer chains, reducing the slurry viscosity. During the test, the viscosity of the UHPC slurry gradually decreased with increasing rotational speed, exhibiting typical shear-thinning behavior. The initial viscosity of the new superplasticizer at a low rotational speed (10 rpm) was significantly lower than that of conventional superplasticizers, demonstrating its improved dispersibility and fluidity.

[0123] The three-dimensional topology of the hyperbranched structure reduces entanglement between polymer chains, lowering paste viscosity. Furthermore, the number of branches (q = 3-4) in the hyperbranched units optimizes steric hindrance, further improving fluidity. The polyether side chains (MPEG) provide effective steric hindrance, dispersing cement particles and reducing interparticle interactions, thereby lowering viscosity. The phosphate groups enhance the water-reducing agent's adsorption capacity to cement particles, minimizing free water consumption and further reducing paste viscosity.

[0124] 5. Confirmatory trials Nuclear magnetic resonance (NMR) analysis of the synthesized product revealed a distinct C=C proton peak at pH 7 (incomplete esterification) around 5.5 ppm (derived from unreacted maleic anhydride double bonds or acrylate monomers). The olefin proton peak of maleic anhydride is typically located between 6.5 and 7.5 ppm, but in the polymer, it may shift to around 5.5 ppm due to environmental changes. This peak indicates incomplete esterification, resulting in residual active double bonds. Broad peaks of backbone methylene (-CH2-) and methine (-CH-) groups are also observed around 1.0-2.5 ppm. A proton peak of the polyether side chain (-O-CH2-CH2-O-) is also observed around 3.5-4.0 ppm.

[0125] For the case of pH 7 (incomplete esterification), there is no C=C proton peak near 5.5 ppm: this indicates that the double bond has been completely consumed by the esterification / polymerization reaction. After the pH is adjusted to 8-9, the carboxylic acid (-COOH) is converted to the carboxylate (-COO - M + ), the broad peak (~12 ppm) of the carboxylic acid proton (-COOH) disappeared, and the main chain α-proton (-CH(COO - ) - ) shifted downfield from 2.5 ppm to 2.7 ppm. The peaks of the polyether side chains (3.5-4.0 ppm) and the main chain methylene groups (1.0-2.5 ppm) remained consistent with those before pH adjustment.

[0126] It can be noted that there is no C=C proton peak around 5.5 ppm after pH 7 (incomplete esterification), which is evidence that the overall polymerization reaction is relatively complete after adjusting the pH.

[0127] This study primarily investigates high-performance water-reducing agents for ultra-high-performance concrete (UHPC) with high tensile strength and wet joints. The focus is on the design and preparation of a hyperbranched comb polymer water-reducing agent. By combining linear side chains of a comb-like structure with the three-dimensional branches of a hyperbranched topology, this agent addresses the poor fluidity and high viscosity issues of UHPC. First, through the optimized design of the backbone, side chains, and hyperbranching units, a novel hyperbranched comb polymer water-reducing agent was successfully synthesized. The backbone is a copolymer of acrylic acid and maleic anhydride, while the side chains are polyether and phosphated. Pentaerythritol serves as the core of the hyperbranching units, forming a three-dimensional topological structure. Second, the hyperbranched comb polymer water-reducing agent was successfully prepared through three main steps: prepolymer synthesis, backbone polymerization, and side chain grafting. Key process parameters include esterification, amidation, free radical copolymerization, phosphatization, and etherification. Finally, the synthesized hyperbranched comb polymer superplasticizer had a weight-average molecular weight (Mw) of 38,200 g / mol and a molecular weight dispersion index (PDI) of 1.25, indicating well-controlled polymerization and uniform molecular weight distribution. Zeta potential measurements showed a value of -44.5 mV, significantly higher than the -30.2 mV of a conventional superplasticizer, indicating enhanced adsorption capacity. TOC analysis revealed an adsorption capacity of 10.2 mg / g, significantly higher than the 6.5 mg / g of a conventional superplasticizer. The UHPC slurry containing the novel hyperbranched comb polymer superplasticizer exhibited a fluidity of 280 mm, a 27.3% increase compared to the 220 mm of a conventional superplasticizer, significantly improving the fluidity of the UHPC slurry. At 60 rpm, the viscosity of the UHPC slurry containing the novel hyperbranched comb polymer superplasticizer was 1217 mPa·s, a 32.0% decrease compared to the 1791 mPa·s of a conventional superplasticizer, significantly improving the fluidity of the UHPC slurry.

[0128] In summary, the hyperbranched comb polymer water reducer designed in the present invention exhibits excellent performance in terms of molecular weight control, adsorption performance, fluidity and viscosity, significantly improving the construction performance and application effect of UHPC.

[0129] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a hyperbranched water reducer for high tensile strength wet joints UHPC, characterized in that: The following steps are involved: S1: Pentaerythritol and maleic anhydride are mixed and then p-toluenesulfonic acid is added as a catalyst to carry out an esterification reaction to obtain an esterified product; the esterified product, diethanolamine and sodium ethoxide as a catalyst are subjected to an amidation reaction to obtain a prepolymer; S2: dissolving acrylic acid, maleic anhydride and prepolymer in deionized water, stirring evenly, adding ammonium persulfate as an initiator to carry out free radical copolymerization to obtain a main chain polymer; S3: The main chain polymer is subjected to a phosphorylation reaction with phosphorus pentoxide to obtain a phosphorylated main chain polymer; the phosphorylated main chain polymer, polyethylene glycol monomethyl ether, and a catalyst, p-toluenesulfonic acid, are subjected to an etherification reaction to obtain a hyperbranched comb polymer water reducer solution; S4: The hyperbranched comb polymer water-reducing agent solution is dialyzed, extracted, pH-adjusted, and concentrated in sequence to prepare a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints.

2. The method for preparing a hyperbranched water-reducing agent for high tensile strength wet joints for UHPC according to claim 1, wherein: In S1, the molar ratio of pentaerythritol to maleic anhydride is 1:4.4; the amount of the catalyst p-toluenesulfonic acid is 0.5 wt%-2 wt% of the sum of the mass of pentaerythritol and maleic anhydride; The molar ratio of the esterification product to diethanolamine is 1:4.4; the amount of the catalyst sodium ethoxide is 3 mol%-8 mol% of the amount of maleic anhydride.

3. The method for preparing a hyperbranched water-reducing agent for high tensile strength wet joints UHPC according to claim 1, characterized in that: In S2, the molar ratio of acrylic acid, maleic anhydride and prepolymer is 6:4:1; the amount of initiator ammonium persulfate used is 0.2 wt%-4 wt% of the total mass of the monomers consisting of acrylic acid, maleic anhydride and prepolymer; and the amount of deionized water used is 3-5 times the total mass of the monomers.

4. The method for preparing a hyperbranched water-reducing agent for high tensile strength wet joints for UHPC according to claim 1, wherein: In S3, the molar ratio of the main chain polymer to phosphorus pentoxide is 1:0.5-1; the molar ratio of the phosphorylated main chain polymer to polyethylene glycol monomethyl ether is 1:1-2; and the amount of the catalyst p-toluenesulfonic acid is 0.5 wt%-2 wt% of the mass of polyethylene glycol monomethyl ether.

5. The method for preparing a hyperbranched water-reducing agent for high tensile strength wet joints UHPC according to claim 1, characterized in that: In S1, the reaction conditions of the esterification reaction are as follows: reaction temperature 110-130° C., reaction time 4-6 hours; The amidation reaction process is as follows: half of the diethanolamine is added to the esterification product, and the temperature is raised to 100-200° C. under nitrogen protection, and the reaction is carried out for 1-3 hours. After the reaction is carried out until no water is distilled out, the remaining diethanolamine and the catalyst sodium ethoxide are added, and the reaction is continued at 40-110° C. for 1-5 hours to obtain a prepolymer.

6. The method for preparing a hyperbranched water-reducing agent for high tensile strength wet joints UHPC according to claim 1, characterized in that: In S2, the reaction conditions of the free radical copolymerization reaction are as follows: reaction temperature 60-90° C., reaction time 4-12 hours; In S3, the reaction conditions of the phosphorylation reaction are as follows: reaction temperature 60-80° C., reaction time 2-4 hours; the reaction conditions of the etherification reaction are as follows: reaction temperature 80-100° C., reaction time 3-6 hours.

7. The method for preparing a hyperbranched water-reducing agent for high tensile strength wet joints of UHPC according to claim 1, characterized in that: In S4, the pH of the hyperbranched comb-shaped polymer water-reducing agent solution is adjusted to 8-9; and the solid content of the hyperbranched comb-shaped polymer water-reducing agent solution is greater than 20% after concentration.

8. A hyperbranched water-reducing agent for UHPC with high tensile strength wet joints prepared by the method for preparing a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints according to any one of claims 1 to 7, characterized in that: The general structural formula of the hyperbranched water reducer for high tensile strength wet joint UHPC is as follows: Main chain: -[CH2-CH(COOM)] m -[CH2-CH(COO-PO3H2)] n - Side chain: -O-(CH2-CH2-O) p -R Hyperbranched unit: -C(CH2OH)4-(CO-NH-CH2-CH2-OH) q Among them, the main chain connects the hyperbranched units through ester bonds or amide bonds, and connects the side chains through ether bonds; Wherein: m is the number of acrylic acid units, accounting for 70%-90%; n is the number of phosphorylated maleic anhydride units, accounting for 10%-30%; p is the length of the polyether chain, which is 8-114 repeating units; q is the number of branches of the hyperbranched unit, which is 3-4; M is a monovalent cation selected from Na + , K + or NH4 + ; R is methyl.

9. The hyperbranched water-reducing agent for high tensile strength wet joints of UHPC according to claim 8, characterized in that: The molecular weight of the main chain of the hyperbranched water reducer for high tensile strength wet joint UHPC is Mw=20,000-50,000.

10. Use of a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints prepared by the method for preparing a hyperbranched water-reducing agent for UHPC with high tensile strength wet joints according to any one of claims 1 to 7 in UHPC with high tensile strength wet joints.

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