A polycarboxylate modified c-s-h nanocomposite

Abstract

This invention discloses a polycarboxylic acid-modified C-S-H nanocomposite material, its preparation method, and its applications. The composite material comprises C-S-H nanocrystal nuclei and a polycarboxylic acid dispersant. The comonomers of the polycarboxylic acid dispersant include polyether macromonomers, carboxylic acid monomers, and urea monomers with specific structures. The urea monomers are prepared via a two-step method involving the monoacylation reaction of diamine monomers and a ureolation reaction. This invention utilizes the hydrogen-bonded anchoring effect of urea groups on the surface of the C-S-H nanocrystal nuclei to replace the traditional calcium ion chelation anchoring of carboxyl groups, significantly reducing the retarding side effect of the dispersant on cement hydration. Simultaneously, the retention of an appropriate amount of carboxyl groups ensures good electrostatic dispersion. The resulting composite material has small particle size, uniform dispersion, and good storage stability. It exhibits excellent early strength performance under both standard and low-temperature curing conditions and can be widely used in the fields of low-carbon cement early strength agents, special low-carbon cement early strength agents, and rapid demolding admixtures for lightweight building materials.

Description

Technical Field

[0001] This invention relates to the field of concrete admixture technology, specifically to a polycarboxylate-modified CSH nanocomposite material. Background Technology

[0002] With my country's increasing emphasis on energy conservation, emission reduction, and low-carbon development, the cement industry, as a high-carbon-emission sector, faces immense pressure to reduce emissions. Low-carbon cement (such as alkali-activated cement and sulfoaluminate cement) has become a research hotspot in the building materials field due to its lower carbon emissions and superior mechanical properties. However, in practical applications, especially in low-temperature environments (such as shallow well bottoms in northern my country), low-carbon cement suffers from slow early strength development, making it difficult to meet the engineering requirements of rapid construction and early demolding.

[0003] Currently, a common solution is to add an accelerator to the cement paste to promote the cement hydration rate and thus improve the early strength of the cement paste. Among them, nano-CSH (calcium silicate hydrate) seed crystals, as a novel accelerator, can shorten the induction period of cement hydration by providing crystal nucleation sites, causing the hydration exothermic peak to appear earlier, thereby accelerating the setting and hardening process of the cement paste and promoting the formation of more high-density CSH, achieving the dual purpose of accelerating setting and early strength.

[0004] However, while nano-CSH seeds possess good early strength properties, their nanoscale particle size and extremely high specific surface energy make them prone to aggregation in aqueous suspensions, leading to poor dispersibility and weakening their early strength effect. To prevent CSH nano-crystal aggregation, existing technologies typically employ polycarboxylate superplasticizers (PCEs) as dispersants. Traditional anionic polycarboxylate dispersants use carboxyl groups (-COOH) as the main anchoring group, achieving adsorption and dispersion through coordination between the carboxyl groups and calcium ions on the CSH crystal nucleus surface. However, these dispersants have the following drawbacks: (1) Carboxyl groups have a strong chelating ability for calcium ions, and while dispersing CSH crystal nuclei, they will also chelate a large amount of Ca in the cement slurry phase. 2+ It poisons CSH nucleation centers, inhibiting the nucleation and growth of cement hydration products.

[0005] (2) Excessive carboxyl groups will adsorb on the surface of cement particles to form a stable solvation layer, which hinders the contact and hydration reaction between cement particles and has a significant retarding effect on cement, which is not conducive to the development of early strength.

[0006] (3) Existing polycarboxylic acid dispersants are difficult to balance between good dispersibility and low retarding. Generally, formulations with good dispersibility also have significant retarding side effects, while formulations with low retarding have insufficient dispersibility. Summary of the Invention

[0007] To address the problems existing in the prior art, the purpose of this invention is to provide a polycarboxylic acid modified CSH nanocomposite material to solve the technical problems of easy agglomeration of nano CSH seeds, strong chelating ability of carboxyl groups to calcium ions in traditional polycarboxylic acid dispersants leading to poisoning of nucleation centers and the generation of retarding side effects, which in turn affect the early strength development of cement, especially the insufficient early strength effect under low temperature conditions.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned polycarboxylic acid modified CSH nanocomposite material.

[0009] Another object of the present invention is to provide the application of the above-mentioned polycarboxylate-modified CSH nanocomposite material in low-carbon cement early-strength agents, special low-carbon cement early-strength agents, and fast demolding admixtures for lightweight building materials.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A polycarboxylic acid modified CSH nanocomposite material includes CSH nanocrystal nuclei and a polycarboxylic acid dispersant, wherein the comonomers of the polycarboxylic acid dispersant include polyether macromonomers, carboxylic acid monomers and urea monomers, and the molar ratio of the polyether macromonomers, carboxylic acid monomers and urea monomers is (65~75):(5~12):(18~28). The general structural formula of the urea monomer is: CH2=C(R1)-CO-NH-(CH2) n -NH-CO-NH-R2, where R1 is H or CH3; n is an integer from 2 to 4; R2 is a C2 to C6 straight-chain or branched alkyl group, preferably a C3 to C4 straight-chain or branched alkyl group.

[0011] Preferably, the polyether macromonomer is selected from one or more of methyl allyl polyoxyethylene ether (HPEG), allyl polyoxyethylene ether (APEG), or ethylene glycol monovinyl polyethylene glycol ether (EPEG); the carboxylic acid monomer is selected from one or more of acrylic acid, methacrylic acid, or maleic acid.

[0012] Preferably, the molecular weight of the polyether macromonomer is 1500-3000, more preferably 2000-2400.

[0013] Preferably, the amount of the polycarboxylic acid dispersant is 20-40 wt% of the dry CSH nanocrystal nucleus, more preferably 25-35 wt%, and the molar ratio of Ca / Si in the CSH nanocrystal nucleus is 1.5-1.8.

[0014] Preferably, the polycarboxylic acid dispersant further includes a chain transfer agent selected from one or more of mercaptoethanol, mercaptoacetic acid, thioglycerol, and isopropanol.

[0015] Preferably, the urea monomer is prepared by the following method: S1. The diamine monomer and the acyl chloride monomer are subjected to a monoacylation reaction in an inert organic solvent at a temperature of -10~10℃. The unreacted diamine monomer and solvent are removed by filtration and vacuum distillation to obtain a purified monoacylated intermediate. S2. The monoacylated intermediate and the isocyanate monomer are subjected to a ureylation reaction in an inert organic solvent at a temperature of 0-15°C to obtain the urea monomer.

[0016] Preferably, the diamine monomer is selected from one or more of ethylenediamine, 1,3-propanediamine or 1,4-butanediamine.

[0017] Preferably, the acyl chloride monomer is selected from one or more of acryloyl chloride or methacryloyl chloride.

[0018] Preferably, the molar ratio of the diamine monomer to the acyl chloride monomer is (3~10):1.

[0019] Preferably, the monoacylation reaction uses triethylamine as an acid-binding agent.

[0020] Preferably, the isocyanate monomer is a C2-C6 straight-chain or branched alkyl isocyanate, preferably ethyl isocyanate, n-propyl isocyanate, isopropyl isocyanate, n-butyl isocyanate, isobutyl isocyanate, tert-butyl isocyanate, pentyl isocyanate or hexyl isocyanate.

[0021] Preferably, the molar ratio of the monoacylated intermediate to the isocyanate monomer is 1:(1.0~1.2).

[0022] Preferably, the inert organic solvents in steps S1 and S2 are each independently selected from any one of anhydrous tetrahydrofuran, anhydrous dichloromethane, or anhydrous toluene.

[0023] Preferably, the polycarboxylic acid dispersant is prepared by free radical copolymerization. The preparation method is as follows: dissolve the polyether macromonomer in water to prepare solution A; dissolve the carboxylic acid monomer, urea monomer and chain transfer agent in water and a cosolvent system to prepare solution B; dissolve the initiator in water to prepare solution C; mix solution A and solution B in a reaction vessel, stir and heat, and introduce inert gas for protection. When the temperature reaches 50~70°C, add solution C dropwise. After the addition is complete, keep the reaction at the temperature for 2~6 hours to obtain the polycarboxylic acid dispersant.

[0024] The initiator is selected from one or more of azobisisobutylammonium hydrochloride (V-50), ammonium persulfate, potassium persulfate, or hydrogen peroxide; the co-solvent is selected from one or more of isopropanol, ethanol, or n-propanol.

[0025] A method for preparing the polycarboxylate-modified CSH nanocomposite material as described above includes the following steps: A silicon source was dissolved in deionized water to prepare solution A, and a calcium source was dissolved in deionized water to prepare solution B. Under room temperature conditions, solutions A and B were simultaneously added dropwise to a polycarboxylic acid dispersant solution, and after stirring and reacting, polycarboxylic acid modified CSH nanocomposite material was obtained.

[0026] Preferably, the silicon source is sodium silicate nonahydrate and the calcium source is calcium nitrate tetrahydrate; the reaction temperature is maintained at 25~35℃ during the dropwise addition process, and the reaction is stirred for 2~4 hours after the dropwise addition is completed.

[0027] Beneficial effects

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces a urea-based functional monomer with a specific structure into a polycarboxylic acid dispersant. The amide and urea groups in the urea group can be anchored to the surface of CSH nanocrystal nuclei through multiple hydrogen bonds, forming a stable adsorption layer, thereby achieving a good steric hindrance dispersion effect. At the same time, the chelating ability of the urea group for calcium ions is much lower than that of the carboxyl group, and it will not consume a large amount of Ca in the liquid phase. 2+ This avoids the problem of poisoning nucleation centers and significantly reduces the retarding side effect on cement hydration. Compared with common hydrogen-bonded groups such as carboxyl, amide, hydroxyl, and amino groups, the urea group is the only group that simultaneously possesses two donors and one acceptor with the donor / acceptor spatially arranged in a linear and coplanar manner. The two NH groups can simultaneously form hydrogen bonds with two adjacent Si-OH groups on the CSH surface, and the C=O group can act as an acceptor to coordinate with Ca-OH water molecules to form a closed hydrogen bond ring. The anchoring energy is 2 to 3 times that of a single amide. Moreover, the combination of urea and amide bonds does not hydrolyze, ionize, or precipitate in the strongly alkaline environment of cement, and the anchoring life is perfectly matched with the cement hydration cycle. The hydrophobic alkyl group at the end of the urea monomer can insert into the hydrophobic water space between CSH layers, expand the interlayer spacing, and prevent the layers from overlapping and agglomerating. The hydrogen bond anchor head of the urea-alkyl group and the hydrophobic intercalation tail structure together achieve triple stability of anchoring, intercalation, and steric hindrance.

[0029] (2) This invention optimizes the ternary copolymerization molar ratio of polyether macromonomer, carboxylic acid monomer, and urea monomer to (65~75):(5~12):(18~28). This ensures the dispersant has an appropriate amount of carboxyl groups to provide electrostatic repulsion, while using urea groups as the main anchoring group, achieving the best balance between dispersion performance and early strength performance. Too low a carboxyl content results in insufficient dispersion, while too high a content leads to significant retardation. Too low a urea content results in weak anchoring, while too high a content may affect the water solubility of the copolymer. Within this ratio range, the composite material exhibits excellent dispersion stability.

[0030] (3) The polycarboxylate-modified CSH nanocomposite material of the present invention has a smaller particle size and a narrower particle size distribution, good suspension stability, and is not prone to settling after long-term storage, making it easy to store and use on site. The composite material exhibits excellent early strength effect in cement mortar. Under standard curing conditions (20±1℃), when the admixture is only 1.0% of the cement mass, the compressive strength is significantly improved after 10 hours, and the compressive strength after 1 day and 3 days is significantly improved. Under low-temperature curing conditions (15±1℃), it can still maintain excellent early strength performance, effectively solving the problem of slow strength development of low-carbon cement under low-temperature environment.

[0031] (4) The urea monomer described in this invention is prepared by a two-step method: first, a low-temperature monoacylation reaction is used to control the diamine monomer to participate in the reaction with only one amino group; then, an alkyl urea group is introduced through a ureylation reaction. The reaction conditions are mild, the selectivity is high, the product purity is high, and it is easy to scale up production. The preparation process of the polycarboxylic acid dispersant and composite material is simple, the raw materials are readily available, the reaction conditions are mild, and it is easy to industrialize, showing good application prospects. Attached Figure Description

[0032] Figure 1 The synthetic route for urea monomer 1 is shown below. Figure 2 The infrared spectrum of the polycarboxylic acid dispersant in Example 1 is shown. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0035] The raw materials used in the examples and comparative examples are described below: Polyether macromonomer 1: Methyl allyl polyoxyethylene ether, molecular weight 2000, Guangdong Wengjiang Chemical Reagent Co., Ltd.; Polyether macromonomer 2: methyl allyl polyoxyethylene ether, molecular weight 2400, Guangdong Wengjiang Chemical Reagent Co., Ltd.; Carboxylic acid monomer 1: Methacrylic acid, 99% purity, with 200ppm MEHQ added as a polymerization inhibitor, Shandong Chuangying Chemical Co., Ltd. Carboxylic acid monomer 2: Acrylic acid, 99% purity, with 200ppm MEHQ added as a polymerization inhibitor, Jiangsu Yulong Chemical Co., Ltd. Chain transfer agent: mercaptoacetic acid, 95% purity, Shanghai Aladdin Biochemical Technology Co., Ltd.; Initiator: Azobisisobutylamidine hydrochloride (V-50), 97% purity, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0036] Urea monomer 1: N-n-butyl-N'-(3-methacrylamidopropyl)urea, prepared in-house, preparation method as follows: S1. Equip a 250mL three-necked flask with a mechanical stirrer, a constant-pressure dropping funnel, an N2 inlet tube, and a drying tube containing CaCl2. Dry all glassware at 120℃ for 2 hours, assemble while hot, and cool with N2. Dissolve 0.5mol of 1,3-propanediamine and 0.1mol of triethylamine (TEA) in 80mL of anhydrous tetrahydrofuran (THF), and replace with N2 for 30 minutes. Cool the system to -5~0℃ using an ice-water bath-ethanol system. Dissolve 0.1mol of methacrylamide (TEA) in 30mL of anhydrous THF and slowly add it dropwise to the reaction flask through a constant-pressure funnel, controlling the dropping rate to keep the internal temperature <5℃, and the dropping time 1.0~1.5 hours. Observe the system gradually becoming turbid (forming a white precipitate of TEA·HCl hydrochloride). After the addition is complete, continue stirring at -5~0℃ for 1 hour, then raise the temperature to room temperature (20~25℃) and react for 2 hours. After the reaction was complete, the white precipitate of TEA·HCl was removed by vacuum filtration. The filtrate was a crude solution of N-(aminopropyl)methacrylamide containing excess 1,3-propanediamine. THF was removed by rotary evaporation at 35°C and 5 mbar. Subsequently, the temperature was raised to 60°C and vacuum distillation was carried out to recover excess 1,3-propanediamine (which could be reused). The residue was dissolved in 50 mL of ethyl acetate and washed twice with 30 mL of saturated NaCl solution to remove residual amine salts. The solution was dried over anhydrous Na₂SO₄, filtered, and rotary evaporated at 35°C and 20 mbar to obtain N-(aminopropyl)methacrylamide in 86.8% yield. The structure of the product was confirmed by ¹H NMR (CDCl3, 400 MHz): δ6.9 (br, 1H, CONH), 5.66 (s, 2H, =CH2), 3.35 (m, 2H, CH2NHCO), 2.78 (t, 2H, CH2NH2), 1.95 (s, 3H, CH3), 1.75 (m, 2H, CH2CH2CH2), 1.43 (br, 1H, NH2).

[0037] S2. Dissolve 0.1 mol N-(aminopropyl)methacrylamide and 0.005 g MEHQ in 40 mL of anhydrous THF, replace with N2 for 30 min, and cool to 0–5 °C in an ice-water bath. Dissolve 0.11 mol n-butyl isocyanate in 20 mL of anhydrous THF and add slowly dropwise, controlling the internal temperature <10 °C, for 30–40 min. After the addition is complete, stir at 0–5 °C for 1 h, then react at room temperature for 2–3 h. After the reaction is complete, remove THF by rotary evaporation at 35 °C and 20 mbar to obtain N-n-butyl-N'-(3-methacrylamidopropyl)urea, with a yield of 95.6%. The synthetic route is as follows: Figure 1 As shown, the product structure was confirmed by ¹H NMR spectroscopy: ¹H NMR (CDCl3, 400 MHz): δ7.37 (br, 1H, -CO-NH-), 5.97 (br, 1H, -NH-CO-NH-, urea NH group attached to propyl group), 5.88 (br, 1H, -NH-CO-NH-, urea NH group attached to butyl group), 5.65 (s, 2H, =CH2), 3.32 (t, 2H, -CO-NH-CH2CH2) CH 2 ), 3.16(t, 2H, -CO-NH- CH 2 CH2CH2-), 3.06 (t, 2H, -NH-CO-NH- CH 2 CH2CH2CH3), 1.96 (s, 3H,=C-CH3), 1.67 (m, 2H, -CO-NH-CH2 CH 2 CH2), 1.40 (m, 2H, -NH-CO-NH-CH2 CH 2 CH2CH3),1.35 (m, 2H, -NH-CO-NH-CH2CH 2 CH 2 CH3), 0.88 (t, 3H, -CH2CH2CH2 CH 3 ).

[0038] Urea monomer 2: Compared with urea monomer 1, the difference is that 1,3-propanediamine is replaced with ethylenediamine, and the amount added is 1.0 mol, and n-butyl isocyanate is replaced with ethyl isocyanate.

[0039] Urea monomer 3: Compared with urea monomer 1, the difference is that 1,3-propanediamine is replaced with 1,4-butanediamine in an amount of 0.3 mol, methacryloyl chloride is replaced with acryloyl chloride, and n-butyl isocyanate is replaced with hexyl isocyanate.

[0040] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0041] Example 1

[0042] A polycarboxylic acid modified CSH nanocomposite material is prepared by the following method: Preparation of polycarboxylic acid dispersant: 0.07 mol of polyether macromonomer 1 was dissolved in 140 g of deionized water and dissolved in a water bath at 50 °C until clear to obtain solution A; 0.01 mol of carboxylic acid monomer 1 and 0.02 mol of urea monomer 1 were added to 30 g of deionized water, 10 g of isopropanol was added as a cosolvent and 0.5 g of mercaptoethanol was added as a chain transfer agent, and stirred in a water bath at 50 °C until completely dissolved to obtain solution B; 0.8 g of initiator azobisisobutylamidine hydrochloride was dissolved in 20 g of deionized water to prepare solution C.

[0043] Mix solutions A and B in a three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a constant-pressure dropping funnel. Stir at 200 rpm and purge with nitrogen for 30 min to remove oxygen. Heat to 60°C and slowly add solution C dropwise, controlling the dropping rate to ensure uniform addition of solution C over 3.5–4.0 h. Continuously purge with nitrogen for protection throughout the entire dropping process. After the addition is complete, add 0.3 g of initiator (dissolved in 5 g of deionized water) and heat to 65°C for 2.0 h. The temperature was then lowered to 40-50℃, and 30% NaOH solution was added dropwise to adjust the pH to 7.0-8.0. The mixture was stirred for 30 minutes, and deionized water was added to adjust the solid content to 40 wt%, yielding a polycarboxylate dispersant mother liquor. This mother liquor was first precipitated with acetone and then washed repeatedly with acetone. The white precipitate was vacuum dried at 60℃ to constant weight, ground and compressed into tablets with potassium bromide, and measured using an infrared spectrometer with a scanning range of 4000-500 cm⁻¹. -1 4 cm resolution -1 The scan was performed 32 times, and the results are as follows: Figure 2 As shown.

[0044] Preparation of polycarboxylic acid modified CSH nanocomposite materials: 28.43 g of sodium silicate nonahydrate was dissolved in 66.3 g of deionized water to prepare solution A. 41.33 g of calcium nitrate tetrahydrate was dissolved in 96.4 g of deionized water to prepare solution B. A polycarboxylic acid dispersant stock solution containing 5.0 g of polycarboxylic acid was weighed and diluted with 30 g of deionized water to prepare a polycarboxylic acid base solution. The polycarboxylic acid base solution was placed in a four-necked flask equipped with a mechanical stirrer, two constant-pressure dropping funnels, and a pH meter. Stirring was started at 300 rpm, and the temperature was raised to 30°C. Solutions A and B were simultaneously added dropwise to the polycarboxylic acid dispersant base solution using constant-pressure funnels, controlling the dropping rate to ensure simultaneous addition of both solutions within 3.0 h. During the dropping process, the reaction temperature was maintained at 30 ± 2°C, and the pH of the reaction solution was monitored and kept within the range of 10.0–12.0 (fine-tuned with dilute NaOH or dilute HNO3). After the addition was complete, the mixture was stirred at 30±2℃ for 3.0 h to obtain a milky white suspension, which is a suspension of polycarboxylic acid modified CSH nanocomposite material.

[0045] Example 2

[0046] Compared with Example 1, the difference is that polyether macromonomer 1 is replaced with polyether macromonomer 2, carboxylic acid monomer 1 is replaced with carboxylic acid monomer 2, and urea monomer 1 is replaced with urea monomer 2.

[0047] Example 3

[0048] Compared with Example 1, the difference is that urea monomer 1 is replaced with urea monomer 3.

[0049] Example 4

[0050] Compared with Example 1, the difference is that the amount of polyether macromonomer 1 added is 0.075 mol, the amount of carboxylic acid monomer 1 added is 0.005 mol, and other aspects remain the same.

[0051] Example 5

[0052] Compared with Example 1, the difference is that the amount of polyether macromonomer 1 added is 0.065 mol, the amount of urea monomer 1 added is 0.025 mol, and other aspects remain the same.

[0053] Comparative Example 1 Compared with Example 1, the difference is that the amount of polyether macromonomer 1 added is 0.075 mol, the amount of carboxylic acid monomer 1 added is 0.015 mol, and the amount of urea monomer 1 added is 0.01 mol.

[0054] Comparative Example 2 Compared with Example 1, the difference is that the amount of polyether macromonomer 1 added is 0.08 mol, the amount of carboxylic acid monomer 1 added is 0.020 mol, and urea monomer 1 is not added.

[0055] Comparative Example 3 Compared with Example 1, the difference is that the amount of polyether macromonomer 1 added is 0.075 mol, the amount of urea monomer 1 added is 0.025 mol, and carboxylic acid monomer 1 is not added.

[0056] Performance testing The polycarboxylic acid dispersant and polycarboxylic acid modified CSH nanocomposites prepared in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 1.

[0057] (1) Molecular weight and polydispersity index of polycarboxylate dispersant: The mother liquor of polycarboxylate dispersant prepared in the examples and comparative examples was first precipitated with acetone and then washed with acetone several times. The white precipitate was dried under vacuum at 60°C to constant weight, and then dissolved in 0.1 mol / L NaNO3 to prepare a solution with a concentration of 2.5 mg / mL and passed through a 0.45 μm filter. The weight-average molecular weight (Mw) and polydispersity index (PDI) of the sample were determined using a PL-GPC50 (Agilent Technologies, UK) gel permeation chromatograph at 30°C and a flow rate of 1.00 mL / min.

[0058] (2) Particle size test: The polycarboxylate modified CSH nanocomposite suspensions prepared in the examples and comparative examples were prepared into a suspension of 0.2 g / L. After ultrasonic dispersion for 20 min, the grain size distribution of different samples was tested using a Malvern Zetasizer ZS900c dynamic light scattering instrument.

[0059] (3) Setting time: The standard consistency water content of cement was used to form neat cement paste specimens according to GB / T 1346-2011 "Test Method for Standard Consistency Water Content, Setting Time and Soundness of Cement", and the initial setting and final setting times were tested using a Vicat apparatus.

[0060] (4) Cement mortar strength test: Referring to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", a mortar-to-mortar ratio of 1:3 and a water-cement ratio of 0.5 were used to test the early strength effect of the polycarboxylate-modified CSH nanocomposite materials in the examples and comparative examples. The cement mortar was molded in a 4cm×4cm×16cm triple mold and then cured in a standard curing chamber at a temperature of (20±1)℃ and a relative humidity greater than 95%. The strength was tested at 10h, 1d, and 3d. During the preparation of the cement mortar, the polycarboxylate-modified CSH nanocomposite materials were incorporated in the form of a suspension, with the effective component accounting for 1.0% of the cement mass.

[0061] (5) Low-temperature strength: Referring to the "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T17671-2021), a mortar-to-mortar ratio of 1 / 3 and a water-cement ratio of 0.5 were used to test the early strength effect of the polycarboxylate-modified CSH nanocomposites in the examples and comparative examples. Cement mortar was formed in a 4cm×4cm×16cm triple mold and then cured in a standard curing chamber at a temperature of (15±1)℃ and a relative humidity greater than 95%. Strength was tested at 10h, 1d, and 3d. During the preparation of the cement mortar, the polycarboxylate-modified CSH nanocomposites were incorporated in suspension at a percentage of the cement mass, with an incorporation amount of 1.0% of the cement mass.

[0062] Table 1. Performance test results of the examples and comparative examples.

[0063] The data from the examples and comparative examples show that Examples 1-5 can all achieve effective dispersion of CSH nanocrystals, no significant extension of solidification time, and excellent early strength effect. Among them, Example 1 has the best overall performance. Although Example 2 has the smallest particle size due to the long side chain of HPEG-2400, the short hydrophobic chain of the urea monomer weakens the anchoring strength of the urea group, resulting in a slightly lower strength than Example 1. This indicates that there is an upper limit to the length of the urea end chain, rather than the shorter the better. In Example 3, due to the longer n=4 spacer arm and C6 hydrophobic chain, the hydrophobic association tendency is enhanced, the particle size and molecular weight distribution increase, and the early strength effect decreases. This confirms that the urea structure needs to balance anchoring strength and steric hindrance. In Example 4, the carboxylic acid monomer is reduced to the 5% limit, and the retarding side effect is minimized. However, the marginal weakening of electrostatic assisted dispersion slightly reduces the early strength. In Example 5, the urea monomer is increased to 25%. The increase in hydrophobic microregions leads to a wider molecular weight distribution and larger particle size, but it is still better than the comparative example.

[0064] Comparative Example 1, with its excessive carboxylic acid monomers, exhibited significant retardation and particle size deterioration. Comparative Example 2, lacking urea monomers, showed strong CSH dispersion ability, but this conflicted with its early strength function and retardation effect, resulting in the largest particle size and severely delayed setting. Comparative Example 3, without carboxylic acid monomers, lacked retardation, but the pure hydrogen-bonded steric hindrance system exhibited insufficient dispersion stability in high ionic strength cement paste, thus failing to maximize the early strength effect. In summary, only the ternary synergy of urea hydrogen bond-dominated anchoring, appropriate carboxyl electrostatic assistance, and PEO steric hindrance can achieve the optimal balance between low retardation and high early strength.

[0065] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A polycarboxylic acid modified CSH nanocomposite material, characterized in that, The product includes CSH nanocrystal nuclei and a polycarboxylic acid dispersant. The comonomers of the polycarboxylic acid dispersant include polyether macromonomers, carboxylic acid monomers, and urea monomers, with a molar ratio of (65~75):(5~12):(18~28). The general structural formula of the urea monomer is CH2=C(R1)-CO-NH-(CH2). n -NH-CO-NH-R2, where R1 is H or CH3; n is an integer from 2 to 4; and R2 is a C2 to C6 straight-chain or branched alkyl group.

2. The polycarboxylate-modified CSH nanocomposite material as described in claim 1, characterized in that, The polyether macromonomer is selected from one or more of methyl allyl polyoxyethylene ether, allyl polyoxyethylene ether, or ethylene glycol monovinyl polyethylene glycol ether; the carboxylic acid monomer is selected from one or more of acrylic acid, methacrylic acid, or maleic acid.

3. The polycarboxylate-modified CSH nanocomposite material as described in claim 1, characterized in that, The molecular weight of the polyether macromonomer is 1500~3000.

4. The polycarboxylate-modified CSH nanocomposite material as described in claim 1, characterized in that, The amount of the polycarboxylic acid dispersant is 20-40 wt% of the dry CSH nanocrystal nucleus, and the molar ratio of Ca / Si in the CSH nanocrystal nucleus is 1.5-1.

8.

5. The polycarboxylate-modified CSH nanocomposite material as described in claim 1, characterized in that, The polycarboxylic acid dispersant also includes a chain transfer agent, which is selected from one or more of mercaptoethanol, mercaptoacetic acid, thioglycerol, and isopropanol.

6. The polycarboxylate-modified CSH nanocomposite material as described in claim 1, characterized in that, The method for preparing the urea monomer includes the following steps: S1. The diamine monomer and the acyl chloride monomer are subjected to a monoacylation reaction in an inert organic solvent at a temperature of -10~10℃. The unreacted diamine monomer and solvent are removed by filtration and vacuum distillation to obtain a purified monoacylated intermediate. S2. The monoacylated intermediate and the isocyanate monomer are subjected to a ureylation reaction in an inert organic solvent at a temperature of 0-15°C to obtain the urea monomer.

7. The polycarboxylate-modified CSH nanocomposite material as described in claim 6, characterized in that, The diamine monomer is selected from one or more of ethylenediamine, 1,3-propanediamine, or 1,4-butanediamine; the acyl chloride monomer is selected from one or more of acryloyl chloride or methacryloyl chloride; the molar ratio of the diamine monomer to the acyl chloride monomer is (3~10):1; the monoacylation reaction uses triethylamine as an acid-binding agent; the isocyanate monomer is a C2~C6 straight-chain or branched alkyl isocyanate; the molar ratio of the monoacylation intermediate to the isocyanate monomer is 1:(1.0~1.2); the inert organic solvents in steps S1 and S2 are each independently selected from any one of anhydrous tetrahydrofuran, anhydrous dichloromethane, or anhydrous toluene.

8. The polycarboxylate-modified CSH nanocomposite material as described in claim 5, characterized in that, The polycarboxylic acid dispersant is prepared by free radical copolymerization. The preparation method is as follows: dissolve the polyether macromonomer in water to prepare solution A; dissolve the carboxylic acid monomer, urea monomer and chain transfer agent in water and cosolvent system to prepare solution B; dissolve the initiator in water to prepare solution C; mix solution A and solution B in a reaction vessel, stir and heat, and introduce inert gas for protection. When heated to 50~70℃, add solution C dropwise. After the addition is complete, keep the reaction at the temperature for 2~6 hours to obtain the polycarboxylic acid dispersant.

9. The method for preparing polycarboxylate-modified CSH nanocomposite materials according to any one of claims 1 to 8, characterized in that, Includes the following steps: A silicon source was dissolved in deionized water to prepare solution A, and a calcium source was dissolved in deionized water to prepare solution B. At room temperature, solutions A and B were simultaneously added dropwise to a polycarboxylic acid dispersant solution, and after stirring and reacting, polycarboxylic acid modified CSH nanocomposite material was obtained.

10. The application of the polycarboxylate-modified CSH nanocomposite material as described in any one of claims 1 to 8 in low-carbon cement early-strength agents, special low-carbon cement early-strength agents, and rapid demolding admixtures for lightweight building materials.

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