Polycarboxylate superplasticizer in alkali-activated slag system as well as preparation method and application thereof

Abstract

The invention discloses a polycarboxylic acid water reducer in an alkali-activated slag system as well as a preparation method and application of the polycarboxylic acid water reducer. According to the preparation method, unsaturated anion group monomers and unsaturated polyether monomers or unsaturated anion group monomers and polycarboxylic acid modified unsaturated polyether monomers are taken as raw materials, a molecular weight regulator is combined, and polymerization reaction is performed under the initiation of an initiator to obtain the polycarboxylic acid water reducer in the alkali-activated slag system. Compared with the traditional polycarboxylate superplasticizer, the alkali-activated slag superplasticizer disclosed by the invention has higher anion content, has better compatibility with an alkali activator solution, and can be well dissolved in the alkali activator solution. Meanwhile, the adsorption capacity can be enhanced due to the high acid-ether ratio, the high adsorption capacity and the good dispersion effect are achieved in an alkali-activated slag system, the flowability of newly-stirred slurry can be obviously improved, the water reducing dispersion effect is improved, bleeding is avoided, and the engineering requirement is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of concrete admixtures, and particularly relates to a polycarboxylate superplasticizer in an alkali-activated slag system and a preparation method and application thereof. BACKGROUND

[0002] For many years, ordinary Portland cement has been widely used in various infrastructure projects due to its durability and high mechanical properties as the largest consumable in the construction industry. However, with the continuous development of the economy, the cement industry has also generated a large amount of pollution and energy consumption loss. In the traditional process of producing cement, a large amount of resources and raw materials are consumed, and a large amount of carbon dioxide is discharged into the environment; in addition, the process requires calcination at an extremely high temperature of 1500 degrees Celsius, resulting in a large amount of energy waste. Therefore, with people's attention to carbon emission reduction, it is an important task for the construction industry to urgently find a low-carbon and environmentally friendly alternative material.

[0003] Alkali-activated cementitious materials (AAM) exhibit higher sustainability in economic and environmental aspects due to their lower energy consumption and carbon dioxide emissions in the manufacturing process, and are considered to be a promising cement replacement cementitious material. In addition, alkali-activated cementitious materials have many advantages, such as lower hydration heat, early development and higher mechanical properties, and better chemical resistance, which make alkali-activated cementitious materials have broad application prospects in the field of building materials. Alkali-activated cementitious materials are mainly inorganic materials obtained by mixing and hardening silico-aluminate materials with alkaline solutions, and the raw materials are mainly industrial waste, such as fly ash and slag, etc. At the same time, these two systems are the most common alkali-activated systems due to their wide source of raw materials.

[0004] Although alkali-activated cementitious materials have the above advantages, they also face some challenges in practical application, such as poor paste fluidity, too short setting time, and easy shrinkage. As an important component of concrete, different types of chemical admixtures are widely used to improve the performance of concrete. Therefore, in order to better apply alkali-activated cementitious materials, researchers use chemical admixtures to improve the performance of the system. However, since these admixtures are designed for Portland cement systems, the high pH and high ionic strength in the alkali-activated system will affect the solubility and stability of the superplasticizer molecules, so it is necessary to design a superplasticizer suitable for the alkali-activated system.

[0005] The reasons for the poor dispersion effect of polycarboxylic acid superplasticizer in alkali-activated systems were explored. The main reasons are as follows: (1) the high-efficiency superplasticizer is insoluble in the alkali activator solution and its molecular structure changes in the solution. Researchers found that the performance of polyester superplasticizer is the worst by comparing the performance of polyester superplasticizer and polyether superplasticizer. The main reason is that polyester will decompose and its structure will be destroyed in different alkali activator solutions (Cement and Concrete Research 190 (2025) 107807). (2) There is competitive adsorption between the anion groups in the alkali activator and the adsorption groups of the polycarboxylic acid superplasticizer (Cement and Concrete Research 186 (2024) 107659). (3) The conformation of the superplasticizer molecules shrinks in the alkali activator solution, resulting in reduced steric hindrance (Cement and Concrete Research 163 (2023) 107020). In view of the above problems, researchers have carried out a series of molecular structure design of polycarboxylic acid, such as using starch modification to improve the dispersion performance and prolong the setting time (Cement and Concrete Composites 165 (2026) 106358) and introducing functional monomers such as unsaturated phosphonic acid to increase the adsorption performance and thus improve the dispersion effect. The synthesis of amphoteric polycarboxylic acid superplasticizer by introducing quaternary ammonium groups can also improve the dispersion effect (patent CN115746217B). In addition, researchers have found that polycarboxylic acid with shorter side chains, higher acid-ether ratio and larger molecular weight can improve the fluidity of the slurry at very low dosage by regulating the molecular structure of comb-shaped polycarboxylic acid superplasticizer (Cement and Concrete Research 116 (2019) 95-101). Although the above research can improve the dispersion effect of the slurry in the alkali-activated system, there is a lack of targeted structure design for the commonly used polyether macromonomer methylallyl polyethylene glycol on the market. SUMMARY

[0006] To solve the defects and deficiencies of the prior art, the primary purpose of the present application is to provide a preparation method of polycarboxylic acid superplasticizer in alkali-activated slag systems, which solves the problem of poor dispersion of traditional superplasticizers.

[0007] Another purpose of the present application is to provide a polycarboxylic acid superplasticizer in alkali-activated slag systems obtained by the above preparation method.

[0008] Still another purpose of the present application is to provide the application of the above-mentioned polycarboxylic acid superplasticizer in alkali-activated slag systems in the field of concrete.

[0009] To achieve the purpose of the present application, the following technical solutions are adopted:

[0010] In a first aspect, the present application provides a method for preparing a polycarboxylic acid water reducer in an alkali-activated slag system, comprising the following steps:

[0011] (1) mixing an unsaturated anionic monomer and a molecular weight regulator in water to obtain a mixed solution;

[0012] (2) esterifying an unsaturated polyether monomer and a polycarboxylic acid under the protection of an inert gas and the action of a catalyst to obtain a modified unsaturated polyether monomer;

[0013] (3) simultaneously dropping the initiator solution and the mixed solution of step (1) into the unsaturated polyether monomer solution or the modified unsaturated polyether monomer solution, and then performing a heat preservation reaction, cooling to room temperature, adjusting the pH of the system to neutral, and obtaining the polycarboxylic acid water reducer in the alkali-activated slag system.

[0014] Preferably, the unsaturated anionic monomer in step (1) comprises at least one of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate, and maleic anhydride; more preferably, the unsaturated anionic monomer is acrylic acid.

[0015] Preferably, the molecular weight regulator in step (1) comprises at least one of 3-mercaptopropionic acid, mercaptoethanol, mercaptoacetic acid, and sodium hypophosphite.

[0016] Preferably, the amount of the molecular weight regulator in step (1) is 0.3-0.8% of the total mass of the unsaturated anionic monomer in step (1) and the unsaturated polyether monomer in step (2), or 0.3-0.8% of the total mass of the unsaturated anionic monomer in step (1) and the modified unsaturated polyether monomer in step (3).

[0017] Preferably, the mass ratio of the unsaturated anionic monomer in step (1) to water is (40-122):100.

[0018] Preferably, the unsaturated polyether monomer in steps (2) and (3) comprises at least one of methyl allyl polyoxyethylene ether (HPEG), iso-pentenyl polyoxyethylene ether (TPEG), and ethylene glycol monovinyl polyethylene glycol ether (EPEG); the molecular weight of the unsaturated polyether monomer is 500-4000 Da; more preferably, the unsaturated polyether monomer is methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da.

[0019] Preferably, the polycarboxylic acid in step (2) comprises at least one of citric acid, nitrilotriacetic acid, and tricarballylic acid; more preferably, the polycarboxylic acid is tricarballylic acid.

[0020] Preferably, the molar ratio of the unsaturated polyether monomer to the polycarboxylic acid in step (2) is 1:(0-5), wherein the polycarboxylic acid is not 0; more preferably, the molar ratio is 1:3.

[0021] Preferably, the inert gas in step (2) comprises at least one of nitrogen, argon and helium.

[0022] Preferably, the catalyst in step (2) comprises at least one of 4-dimethylamino pyridine, 4-pyrrolidinyl pyridine and triethylamine; more preferably, 4-dimethylamino pyridine.

[0023] Preferably, the catalyst in step (2) is used in an amount of 0-5wt% and not 0, more preferably 1.5wt%, based on the total mass of the unsaturated polyether monomer and the polycarboxylic acid.

[0024] Preferably, the esterification reaction in step (2) is carried out at a temperature of 100-120℃, more preferably 110-115℃, for a time of 4-6 hours.

[0025] Preferably, after the esterification reaction in step (2) is completed, the purified modified unsaturated polyether monomer is obtained through extraction and rotary evaporation.

[0026] Preferably, the initiator in step (3) comprises at least one of hydrogen peroxide, ammonium persulfate and sodium perborate; more preferably, ammonium persulfate.

[0027] Preferably, the concentration of the initiator solution in step (3) is 2.6-3.4wt%, and the solvent is water.

[0028] Preferably, the concentration of the unsaturated polyether monomer solution or the modified unsaturated polyether monomer solution in step (3) is 20-60wt%, and the solvent is water.

[0029] Preferably, in step (3), the molar ratio of the unsaturated anionic group monomer to the unsaturated polyether monomer is (5-15):1.

[0030] Preferably, in step (3), the molar ratio of the unsaturated anionic group monomer to the modified unsaturated polyether monomer is (4-9):1.

[0031] Preferably, in step (3), the amount of initiator used is 0.3-2% of the total mass of the unsaturated anionic group monomer in step (1) and the unsaturated polyether monomer in step (3), or 0.3-2% of the total mass of the unsaturated anionic group monomer in step (1) and the modified unsaturated polyether monomer in step (3).

[0032] Preferably, the temperature of the incubation reaction in step (3) is 75-85℃, and the time is 1.5-3h.

[0033] Preferably, the pH adjusting agent used to adjust the pH in step (3) comprises a sodium hydroxide solution with a concentration of 35-45wt%.

[0034] Secondly, the present invention provides a polycarboxylate superplasticizer in an alkali-activated slag system prepared by the above preparation method.

[0035] Thirdly, the present invention provides the application of polycarboxylate superplasticizer in the above-mentioned alkali-activated slag system.

[0036] Preferably, the amount of polycarboxylate superplasticizer added to the alkali-activated slag system is 0.1-2 wt%, more preferably 0.5 wt%.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] This invention discloses two alkali-activated cementitious material water-reducing agents and their applications. Water-reducing agents suitable for alkali-activated slag materials were prepared through molecular design. Compared with traditional polycarboxylate water-reducing agents, the first alkali-activated slag water-reducing agent, CPCE, disclosed in this invention has a higher anion content, exhibits better compatibility with alkali activator solutions, and can dissolve well in the alkali activator solution. Simultaneously, the higher acid-ether ratio enhances its adsorption capacity, resulting in higher adsorption capacity and better dispersion in alkali-activated slag systems.

[0039] The second alkali-activated slag water-reducing agent, PCETA, disclosed in this invention mainly addresses the insolubility of long side chains of water-reducing agents in alkali activator solutions. Compared to traditional PEO side chains, high ionic strength environments cause PEO side chains to salt out and become insoluble. By introducing water-soluble groups, not only can the solubility of PEO be increased, but the steric hindrance effect can also be further increased, preventing the coiling and collapse of the side chain conformation, thereby obtaining a better dispersion effect. This allows the water-reducing agent to dissolve well in strongly alkaline activator solutions, significantly improving the fluidity of freshly mixed slurry. It has an improved water-reducing and dispersion effect without bleeding, meeting engineering requirements.

[0040] In the alkali-activated slag system disclosed in this invention, only water-soluble polymer is added as a water-reducing agent to achieve excellent dispersion effect. No other additives were added in the performance tests of the subsequent embodiments.

[0041] In the alkali-activated slag system disclosed in this invention, the dosage of water-reducing agent in the dispersion system is 0.1-2 wt%, preferably 0.5 wt%, which has the advantages of excellent dispersion performance and low dosage. Attached Figure Description

[0042] Figure 1 The molecular structure diagram of CPCE is shown (a:b=4~15).

[0043] Figure 2 This is a schematic diagram of the synthesis process of HPEGTA.

[0044] Figure 3 The fluidity of the paste in Comparative Example 1 and Examples 1-5 is shown.

[0045] Figure 4 The fluidity of the paste in Comparative Example 1 and Examples 3, 6-7 is shown.

[0046] Figure 5 The fluidity of the paste in cement systems and alkali-activated slag systems in Examples 3, 5 and 7.

[0047] Figure 6 This represents the variation of slurry shear stress with shear rate.

[0048] Figure 7 This represents the change in apparent viscosity (the ratio of shear stress to rate at a constant rate) over time.

[0049] Figure 8 The graphs show the transmittance of the water-reducing agent solutions in Examples 1-7 and Comparative Example 1 as a function of sodium hydroxide content.

[0050] Figure 9 The diagram shows the anion content of the water-reducing agent solutions in Examples 1-7 and Comparative Example 1. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0052] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0053] Comparative Example 1

[0054] 30 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80 °C with stirring at 250 rpm. Then, solution A, containing 3.90 g of acrylic acid (AA) and 0.1695 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.3390 g of ammonium persulfate (APS) (1 wt% of the total monomer mass), was dissolved in 13 mL of deionized water. Solutions A and B were added to the three-necked flask over 2.5 h and 3 h respectively using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 h, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, named CPCE4:1.

[0055] Example 1

[0056] 30 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80 °C with stirring at 250 rpm. Then, solution A, containing 4.88 g of acrylic acid (AA) and 0.1744 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.3488 g of ammonium persulfate (APS) (1 wt% of the total monomer mass), was dissolved in 13 mL of deionized water. Solutions A and B were added to the three-necked flask over 2.5 h and 3 h respectively using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 h, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, named CPCE5:1.

[0057] Example 2

[0058] 30 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80 °C with stirring at 250 rpm. Then, solution A, containing 6.83 g of acrylic acid (AA) and 0.1841 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.3683 g of ammonium persulfate (APS) (1 wt% of the total monomer mass), was dissolved in 13 mL of deionized water. Solutions A and B were added to the three-necked flask over 2.5 h and 3 h respectively using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 h, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, named CPCE7:1.

[0059] Example 3

[0060] 30 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80 °C with stirring at 250 rpm. Then, solution A, containing 8.78 g of acrylic acid (AA) and 0.1939 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.3878 g of ammonium persulfate (APS) (1 wt% of the total monomer mass), was dissolved in 13 mL of deionized water. Solutions A and B were added to the three-necked flask over 2.5 h and 3 h respectively using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 h, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, named CPCE9:1.

[0061] Example 4

[0062] 30 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80 °C with stirring at 250 rpm. Then, solution A, containing 10.73 g of acrylic acid (AA) and 0.2036 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.4073 g of ammonium persulfate (APS) (1 wt% of the total monomer mass), was dissolved in 13 mL of deionized water. Solutions A and B were added to the three-necked flask over 2.5 h and 3 h respectively using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 h, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, named CPCE11:1.

[0063] Example 5

[0064] 30 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80 °C with stirring at 250 rpm. Then, solution A, containing 14.63 g of acrylic acid (AA) and 0.2231 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.4463 g of ammonium persulfate (APS) (1 wt% of the total monomer mass), was dissolved in 13 mL of deionized water. Solutions A and B were added to the three-necked flask over 2.5 h and 3 h, respectively, using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 h, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, which was named CPCE15:1.

[0065] Example 6

[0066] First, nitrogen gas was introduced into a three-necked flask in an oil bath for 15 minutes to ensure an oxygen-free environment and protect the double bonds. Then, 100 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 22.02 g of tricornioic acid (TA) were placed in the oil bath and heated to 110°C. 1.8303 g of 4-dimethylaminopyridine was added as a catalyst, and a reflux condenser was connected. The reaction was carried out under a nitrogen atmosphere for 6 hours to obtain the modified unsaturated polyether macromonomer HPEGTA. The crude product was extracted multiple times using water and dichloromethane as solvents and extractants, respectively, to remove excess tricornioic acid. Finally, dichloromethane was removed by rotary evaporation to obtain purified HPEGTA. Next, 30 g of the modified polyether macromonomer HPEGTA and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80°C at a stirring speed of 250 rpm. Then, solution A, containing 3.90 g of acrylic acid (AA) and 0.1695 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.3390 g of ammonium persulfate (APS), was dissolved in 13 mL of deionized water. Solutions A and B were added to three-necked flasks over 2.5 hours and 3 hours, respectively, using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 hours, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, which was named PCETA4:1.

[0067] Example 7

[0068] First, nitrogen gas was introduced into a three-necked flask in an oil bath for 15 minutes to ensure an oxygen-free environment and protect the double bonds. Then, 100 g of methyl allyl polyoxyethylene ether (HPEG) with a molecular weight of 2400 Da and 22.02 g of tricornioic acid (TA) were placed in the oil bath and heated to 110°C. 1.8303 g of 4-dimethylaminopyridine was added as a catalyst, and a reflux condenser was connected. The reaction was carried out under a nitrogen atmosphere for 6 hours to obtain the modified unsaturated polyether macromonomer HPEGTA. The crude product was extracted multiple times using water and dichloromethane as solvents and extractants, respectively, to remove excess tricornioic acid. Finally, dichloromethane was removed by rotary evaporation to obtain purified HPEGTA. Next, 30 g of the modified polyether macromonomer HPEGTA and 50 g of deionized water were placed in a three-necked round-bottom flask equipped with a stirrer, and the mixture was heated to 80°C at a stirring speed of 250 rpm. Then, solution A, containing 8.78 g of acrylic acid (AA) and 0.1939 g (0.5 wt% of the total monomer mass) of 3-mercaptopropionic acid (MPA), was dissolved in 12 mL of deionized water; solution B, containing 0.3878 g of ammonium persulfate (APS), was dissolved in 13 mL of deionized water. Solutions A and B were added to three-necked flasks over 2.5 hours and 3 hours, respectively, using a peristaltic pump. After the addition was complete, the reaction was continued at 80 °C for 2 hours, then cooled to room temperature, and the pH of the system was adjusted to neutral by adding a 40 wt% sodium hydroxide solution to obtain the final product, which was named PCETA9:1.

[0069] The monomers and their dosages used in the alkali-activated cementitious water-reducing agents in Examples 1 to 7 are shown in Table 1 below.

[0070] Table 1. Raw material ratios of alkali-activated cementitious water-reducing agents in Examples 1-7.

[0071]

[0072] Performance of neat pulp fluidity test:

[0073] Alkali-activated slag material without any admixtures (see slag proportions in Table 2 below) was used as a comparison. Alkali-activated cementitious material with added water-reducing agents prepared in Examples 1-7 was used as a comparative example, along with conventional water-reducing agents as a control. Referring to GB / T "Test Method for Homogeneity of Concrete Admixtures", the initial fluidity of the neat cement paste in Comparative Example 1 and Examples 1-7 was measured under the conditions of a water-cement ratio of 0.5, an alkali activator concentration of 2 mol / L, and a water-reducing agent dosage of 0.5 wt%. The results are as follows: Figure 3 and Figure 4 As shown.

[0074] passFigure 3 It can be seen that, compared with the alkali-activated slag system without any additives, the addition of admixtures is beneficial to the dispersion of the alkali-activated slag system. However, CPCE4:1 (Comparative Example 1), which is conventionally applicable to traditional silicate cement systems, has almost no fluidity in this system, indicating that even at higher water-cement ratios and dosages, admixtures for cement systems do not bring beneficial effects to the flow and dispersion of the alkali-activated system. Figure 3 It can be seen that as the acid-ether ratio increases, the water-reducing agents used all increase the initial fluidity of the alkali-activated slag system with a concentration of 2 mol / L alkali activator. Even when the acid-ether ratio increases to 15:1 and the side chain density is relatively low, the initial fluidity can reach 316 mm, which is completely opposite to the traditional silicate cement system. This indicates that increasing the content of adsorption groups is beneficial to improving the dispersion effect. Figure 4 It can be seen that, compared with conventional water-reducing agents, the samples 6 and 7 modified with water-soluble carboxyl groups can improve the fluidity of the alkali-activated slag system. Even when the adsorption capacity is insufficient due to a low acid-ether ratio (4:1), the initial fluidity of Example 6 is still 13.40% higher than that of Comparative Example 1. When the adsorption capacity is further increased (the acid-ether ratio is increased to 9:1), this effect will be greatly increased. That is, compared with Example 3, the fluidity of Example 7 is significantly improved to 310 mm. Therefore, the water-soluble group-modified water-reducing agent designed to address the insolubility of the alkali-activated slag system is beneficial to improving the fluidity of freshly mixed slurry and has a good water-reducing and dispersing effect.

[0075] Table 2 Formulations for cement systems and alkali-activated slag systems

[0076]

[0077] Two water-reducing agents, high acid-to-ether ratio polycarboxylic acid and carboxyl-modified polycarboxylic acid, were tested for the fluidity of cement paste in a cement system (Table 2) (water-reducing agent dosage was 0.5 wt%). The results are shown in Table 2. Figure 5 It can be observed that the dispersibility in the cement system is reduced compared to the alkali-activated slag system. This is because a higher acid-ether ratio means a lower side chain density, which leads to a severe lack of steric hindrance in the long side chains of polyoxyethylene ether. At the same time, the formation of a large amount of polyacrylic acid results in a dominant electrostatic repulsion effect, leading to poor dispersion. Although the dispersibility of carboxyl-modified polycarboxylic acid is improved compared to unmodified polycarboxylic acid with a high acid-ether ratio, the contribution of this end modification is limited for lower side chain densities.

[0078] Rheological properties:

[0079] A slurry with a flowability of approximately (200±5) mm was prepared and poured into the coaxial cylinder of the rheometer within 1 min. The rheological program was set as follows: (1) the shear rate increased from 0 s⁻¹ to 0 s⁻¹ within 1 min. -1Increase to 100 s -1 (2) At a constant shear rate of 100 s -1 Shear for 1 min; (3) Decelerate to 0 within 1 min. Finally, the change of slurry shear stress with shear rate is obtained from the descent curve, and the change of apparent viscosity is obtained by the ratio of shear stress to rate at constant rate. The results are as follows: Figure 6 and Figure 7 As shown.

[0080] Figure 6 and Figure 7 The figures show the changes in shear stress versus rate and apparent viscosity versus time for Examples 1-7 and Comparative Example 1, respectively. Figure 6 It can be seen that as the acid-ether ratio increases, the adsorption capacity improves, and the shear stress at the same shear rate gradually decreases, indicating that the flow resistance of the slurry during dispersion gradually decreases, and its trend is consistent with the fluidity. Moreover, compared with the traditional water-reducing agent (CPCE), the shear stress of the carboxyl group modified PCETA (Example 6) is much lower than that of CPCE at the same rate. However, as the acid-ether ratio of the carboxyl group modified water-reducing agent increases, the decreasing trend of shear stress in Example 7 is gradually smaller than that in Example 3. Figure 7 This describes the change in apparent viscosity of different water-reducing agents in an alkali-activated slag system with a concentration of 2 mol / L alkali activator. Figure 7 As can be seen, for conventional water-reducing agent CPCE, the apparent viscosity remains relatively stable over time as the acid-to-ether ratio increases, and the apparent viscosity of the slurry containing a high acid-to-ether ratio water-reducing agent is significantly lower than that containing a traditional water-reducing agent. However, if the initial dispersion of the slurry is poor (i.e., low initial fluidity), increasing the stirring time can further reduce the viscosity and improve the fluidity of the slurry for the same water-reducing agent. For example, the viscosity of CPCE 4:1 and CPCE 5:1 slurries gradually decreases over time, indicating that increasing the stirring time at the same temperature is beneficial for dispersion. Figure 7 As can be seen from b, the apparent viscosity of the carboxyl group-modified water-reducing agent PCETA is much lower than that of the traditional water-reducing agent CPCE. This indicates that the carboxyl group-modified water-reducing agent reduces the viscosity of the alkali-activated slag system, thereby improving the dispersion effect.

[0081] Table 3. Concentrations of different water-reducing agents reaching the "cloud point" in alkali-activated solutions at room temperature.

[0082]

[0083] Table 3 shows that for the water-reducing agent in Comparative Example 1, which is suitable for cement systems, the sodium hydroxide concentration at room temperature when it reaches turbidity is much lower than 2 mol / L, indicating that its insolubility in this system leads to poor dispersion. However, as the acid-ether ratio of conventional water-reducing agents increases further, the sodium hydroxide concentration at which the water-reducing agent reaches turbidity in the alkali activator solution varies. Specifically, to maintain excellent dispersion in the alkali-activated slag system, the concentration of the water-reducing agent in the alkali activator solution needs to exceed the sodium hydroxide concentration of 2 mol / L in the alkali-activated slag system. Compared to traditional water-reducing agents, the carboxyl-modified water-reducing agent (Example 6) still reaches a turbidity point concentration greater than 2 mol / L even at a low acid-ether ratio (4:1), indicating that carboxyl-modification improves dispersion by increasing the solubility of the water-reducing agent molecules in the alkali activator solution. When the acid-ether ratio increases further, the turbidity point concentration in Example 7 further increases compared to Example 3, indicating that increasing the acid-ether ratio can further improve the solubility of the carboxyl-modified water-reducing agent.

[0084] Figure 8 This is a graph showing the transmittance of the water-reducing agent solutions in Examples 1-7 and the comparative example as a function of sodium hydroxide content. According to... Figure 8 It can be seen that as the concentration of sodium hydroxide increases to a certain extent, the transmittance initially remains constant. However, when the sodium hydroxide content increases to a certain level, the solution begins to become turbid, and its transmittance decreases continuously with increasing sodium hydroxide concentration. Figure 8 It can be seen that the transmittance of Comparative Example 1 gradually decreased with increasing sodium hydroxide concentration, while for the water-reducing agent with a higher acid-to-ether ratio (15:1) and the carboxyl-modified water-reducing agent PCETA (Examples 6 and 7), approximately 90% transmittance was observed at all sodium hydroxide concentrations (the instrument's maximum limit is 90%). This indicates that the NaOH concentration (2 mol / L) used in the flowability experiment has no effect on the solubility of high acid-to-ether ratio PCEs and PCETA in aqueous solution. That is, PCES with lower side chain density and water-soluble group modification at the side chain ends have good solubility in NaOH solution.

[0085] Figure 9 The graph shows the anion content of the water-reducing agent solutions in Examples 1-7 and Comparative Example 1. Since changing the acid-ether ratio increases the carboxyl group content of the PCEs backbone to some extent, it is necessary to test the effect of this molecular structure design on the change in anion content. Figure 9 As shown in 'a', with the increase of acid-ether ratio, the fluidity of the slurry increases, and its anion content also gradually increases. In particular, compared with traditional water-reducing agents, the anion content of the high acid-ether ratio water-reducing agent is significantly increased (5.16 mmol / gPCE), which is more than twice as high. This is why high acid-ether ratio PCE can significantly improve the fluidity of alkali-activated slag. According to Figure 9As can be seen from b, the carboxyl-modified group PCETA (Examples 6 and 7) can also increase the anion content compared to Example 3 and Comparative Example 1. The reason may be that the introduction of charged anionic groups into the polyether macromonomer can further extend the PEO side chain in the alkaline activator solution due to electrostatic repulsion, thereby exposing the adsorption groups on the main chain. This is beneficial for the adsorption of PCEs in the alkaline activated slag system, thereby improving the fluidity of the slurry.

[0086] Table 4 Compressive strength of Examples 1-7 at different times (1d, 3d, and 7d)

[0087]

[0088] Examples 1-7 were tested for compressive strength of the mortar according to the national standard GB / T 17671-2021. Table 4 shows that as the acid-ether ratio increases, the early strength of PCEs with a high acid-ether ratio decreases compared to those with a low acid-ether ratio (CPCE 5:1). This is mainly due to the carboxyl groups (-COO)... - It will strongly complex with the Ca released during cement hydration. 2+ The formation of complexes covering the cement mineral surface significantly delays early hydration, hindering early strength development. However, this also results in a certain retarding effect for high acid-ether ratio superplasticizers. This retarding effect makes hydration more complete and orderly, leading to a denser and more uniform microstructure of the hydration products. For carboxyl-modified PCETA, compared to traditional superplasticizers (CPCE5:1), its early strength (1d and 3d) is slightly lower, but the 7d compressive strength decreases more significantly. This is presumably because the lower side chain density delays the hydration reaction. Simultaneously, the increased carboxyl modification increases inter-chain repulsion, further increasing the density of carboxyl sites available for chelating calcium ions, thus giving PCETA a retarding effect. However, compared to unmodified high acid-ether ratio polycarboxylate superplasticizers, PCETA shows an increase in compressive strength, indicating that PCETA can avoid the problem of "excessive retarding" leading to insufficient compressive strength development while ensuring good dispersion.

[0089] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a polycarboxylate superplasticizer in an alkali-activated slag system, characterized in that, Includes the following steps: (1) Unsaturated anionic monomers and molecular weight regulators are added to water and mixed evenly to obtain a mixed solution; (2) The unsaturated polyether monomer and the polycarboxylic acid were esterified under the protection of an inert gas and the action of a catalyst to obtain the modified unsaturated polyether monomer; (3) The initiator solution and the mixed solution of step (1) are simultaneously added dropwise to the unsaturated polyether monomer solution or the modified unsaturated polyether monomer solution. After the reaction is kept at a constant temperature, the solution is cooled to room temperature and the pH of the system is adjusted to neutral to obtain the polycarboxylate superplasticizer in the alkali-activated slag system.

2. The preparation method according to claim 1, characterized in that, The polycarboxylic acid in step (2) includes at least one of citric acid, hypotriacetic acid, and triglyceride; more preferably, triglyceride. And / or, the molar ratio of the unsaturated polyether monomer and the polycarboxylic acid in step (2) is 1:(0-5), wherein the polycarboxylic acid is not 0; And / or, the unsaturated polyether monomers in steps (2) and (3) include at least one of methyl allyl polyoxyethylene ether, isopentenyl polyoxyethylene ether and ethylene glycol monovinyl polyethylene glycol ether; And / or, the molecular weight of the unsaturated polyether monomer in steps (2) and (3) is 500 to 4000 Da.

3. The preparation method according to claim 1 or 2, characterized in that, In step (3), the molar ratio of unsaturated anionic monomer to unsaturated polyether monomer is (5-15):1; And / or, in step (3), the molar ratio of unsaturated anionic monomer to modified unsaturated polyether monomer is (4-9):1; And / or, the initiator in step (3) includes at least one of hydrogen peroxide, ammonium persulfate and sodium perborate; And / or, in step (3), the amount of initiator is 0.3 to 2% of the total mass of the unsaturated anionic monomer in step (1) and the unsaturated polyether monomer in step (3), or 0.3 to 2% of the total mass of the unsaturated anionic monomer in step (1) and the modified unsaturated polyether monomer in step (3).

4. The preparation method according to claim 1 or 2, characterized in that, The unsaturated anionic monomer in step (1) includes at least one of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate, and maleic anhydride; And / or, the molecular weight regulator in step (1) includes at least one of 3-mercaptopropionic acid, mercaptoethanol, mercaptoacetic acid and sodium hypophosphite; And / or, the amount of the molecular weight regulator in step (1) is 0.3 to 0.8% of the total mass of the unsaturated anionic monomer in step (1) and the unsaturated polyether monomer in step (3), or 0.3 to 0.8% of the total mass of the unsaturated anionic monomer in step (1) and the modified unsaturated polyether monomer in step (3).

5. The preparation method according to claim 1 or 2, characterized in that, The inert gas in step (2) includes at least one of nitrogen, argon and helium; And / or, the catalyst in step (2) comprises at least one of 4-dimethylaminopyridine, 4-pyrrolidinylpyridine and triethylamine; And / or, the amount of catalyst used in step (2) is 0 to 5 wt% of the total mass of the unsaturated polyether monomer and polycarboxylic acid, and is not 0, more preferably 1.5 wt%; And / or, the temperature of the esterification reaction in step (2) is 100-120 °C, more preferably 110-115 °C; and the time is 4-6 hours.

6. The preparation method according to claim 1 or 2, characterized in that, The temperature of the heat preservation reaction in step (3) is 75-85℃ and the time is 1.5-3 h.

7. The preparation method according to claim 1 or 2, characterized in that, In step (1), the mass ratio of the unsaturated anionic monomer to water is (40-122):100; And / or, the concentration of the initiator solution in step (3) is 2.6 to 3.4 wt%, and the solvent is water; And / or, the concentration of the unsaturated polyether monomer solution or the modified unsaturated polyether monomer solution in step (3) is 20-60 wt%, and the solvent is water; And / or, the pH adjuster used in step (3) to adjust the pH of the system includes a sodium hydroxide solution with a concentration of 35 to 45 wt%.

8. A polycarboxylate superplasticizer in an alkali-activated slag system prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the polycarboxylate superplasticizer in the alkali-activated slag system as described in claim 8.

10. The application according to claim 9, characterized in that, The amount of polycarboxylate superplasticizer added to the alkali-activated slag system is 0.1-2 wt%, more preferably 0.5 wt%.

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