Ammonium-based polycondensate water reducing agent matched with high-alumina phase admixture and preparation method thereof

Abstract

This invention relates to the field of concrete admixtures, and more particularly to an ammonium-based condensation polymer water-reducing agent adapted to high-alumina phase admixtures and its preparation method. The water-reducing agent comprises a polycarboxylic acid copolymer containing carboxyl and ammonium groups. The copolymer is prepared by free radical copolymerization of the following monomers: an allyl-containing ammonium salt monomer, methyl allyl polyoxyethylene ether, and acrylic acid; wherein the molar amount of acrylic acid is greater than the molar amount of methyl allyl polyoxyethylene ether to introduce abundant carboxyl groups into the main chain; the allyl-containing ammonium salt monomer can introduce ammonium functional groups into the main chain. This invention uses an excess of acrylic acid in the monomer molar ratio, and employs a three-way independent nitrogen pre-pass combined with a delayed initiator dripping process to effectively eliminate oxygen inhibition of polymerization. The monomer conversion rate reaches over 92%, the process conditions are mild, the cost is low, and the water-reducing rate is high. It can be directly transferred from laboratory to industrial scale, production is safe and reliable, and it has good industrialization prospects.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures, and in particular to an ammonium-based condensate water-reducing agent adapted to high-alumina phase admixtures and its preparation method. Background Technology

[0002] High-efficiency water-reducing agents for concrete are an indispensable key component of modern high-performance concrete. Their development has evolved from lignin sulfonate, naphthalene-based, and aliphatic-based to polycarboxylate-based. Currently, polycarboxylate-based water-reducing agents have become the mainstream product in the market due to their advantages such as high water reduction rate, good slump retention, and strong designability of molecular structure.

[0003] With the widespread use of industrial byproducts such as fly ash, slag, and silica fume in concrete, especially high-alumina admixtures like high-alumina fly ash, calcined coal gangue, and bauxite tailings, traditional polycarboxylate superplasticizers have revealed poor adaptability. Studies show that the tricalcium aluminate (C3A) content in cement mineral components significantly affects the effectiveness of superplasticizers. High-alumina cement or cement containing more C3A is prone to strong reactions with certain superplasticizers, reducing their effectiveness. Polycarboxylate superplasticizers exhibit the highest adsorption capacity on the surface of silicate cement. High-alumina admixtures, with their strong positive charge, readily undergo strong electrostatic adsorption with the carboxylate anions in the polycarboxylate superplasticizer molecules, leading to significant and ineffective consumption of the superplasticizer. This manifests as rapid loss of concrete fluidity, decreased water reduction rate, and insufficient slump retention. In addition, high-alumina phase admixtures such as metakaolin, activated coal gangue, and zeolite powder have a strong tendency to absorb water or a large specific surface area, which has a significant negative impact on the effect of polycarboxylate superplasticizers.

[0004] To address the aforementioned issues, researchers have conducted numerous explorations. Chinese patent CN107652405A discloses an amide / imide structured polycarboxylate superplasticizer, prepared through the amide / imide reaction of terminal amino polyethers. It possesses advantages such as high water reduction rate and good flow retention. However, this superplasticizer still belongs to the polycarboxylate molecular structure, and its anionic characteristics remain fundamentally unchanged, thus the electrostatic adsorption problem with high-alumina phase admixtures remains unresolved. Chinese patent CN108264619A discloses a method for preparing a viscosity-reducing polycarboxylate superplasticizer. The resulting product exhibits good viscosity-reducing effects, but it primarily addresses the viscosity problem of low water-cement ratio concrete and does not address compatibility improvements with high-alumina phase admixtures. Chinese patent CN108239279A discloses a method for preparing a small-molecule superplasticizer with retarding and slump-retaining properties, introducing phosphite groups through Michael addition and Mannich reaction. However, this superplasticizer has a small molecule structure, limiting its dispersibility and slump-retaining ability.

[0005] Traditional condensation-type water-reducing agents, such as naphthalene-based and aliphatic-based agents, have relatively fewer anionic groups such as sulfonic acid groups or carbonyl groups in their molecular structure, resulting in weaker electrostatic adsorption of high-alumina phase admixtures compared to polycarboxylate-based agents, thus exhibiting certain adaptability. However, naphthalene-based water-reducing agents have a low water reduction rate (typically 15%–25%), while aliphatic-based water-reducing agents have poor slump retention. Both are insufficient to meet the construction requirements of high-strength, high-performance concrete for water reduction rate (≥30%) and slump retention capacity (≤20mm slump loss after 2 hours).

[0006] Therefore, developing a new type of high-efficiency water-reducing agent that has good compatibility with condensation-type water-reducing agents and high-alumina phase admixtures, as well as high water reduction rate and excellent slump retention performance, has important engineering application value and market prospects. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide an ammonium-based condensation polymer water-reducing agent compatible with high-alumina phase admixtures and its preparation method. The method involves free radical copolymerization of an allyl-containing ammonium salt monomer, methyl allyl polyoxyethylene ether, and acrylic acid, with an excess of acrylic acid to ensure dense carboxyl groups in the main chain. Through triple deoxygenation, slow dropwise addition, and precise proportioning of chain transfer agent / initiator, a polycarboxylate-based water-reducing agent containing both carboxyl and ammonium groups is obtained. This water-reducing agent has low cost, high water reduction rate, excellent slump retention, and good compatibility with high-alumina phase admixtures.

[0008] The technical solution adopted is as follows: An ammonium-based condensate water-reducing agent suitable for high-alumina phase admixtures, the water-reducing agent comprising a polycarboxylic acid copolymer containing carboxyl and ammonium groups, the copolymer being prepared by free radical copolymerization of the following monomers: Allyl-containing ammonium salt monomers, methyl allyl polyoxyethylene ether (HPEG), and acrylic acid (AA); The molar amount of acrylic acid is greater than that of methyl allyl polyoxyethylene ether, so as to introduce abundant carboxyl groups into the main chain; the allyl-containing ammonium salt monomer can introduce ammonium functional groups into the main chain.

[0009] Preferably, the allyl-containing ammonium salt monomer is allylamine hydrochloride (N1) or N,N-dimethylallylamine (N2); The molar ratio of the allyl-containing ammonium salt monomer, methyl allyl polyoxyethylene ether, and acrylic acid is 1:1:6.

[0010] Preferably, the number average molecular weight of the methyl allyl polyoxyethylene ether is 1000 to 3000, and more preferably, the number average molecular weight is 2400.

[0011] This invention also provides a method for preparing an ammonium-based condensate water-reducing agent adapted to high-alumina phase admixtures, comprising the following steps: (1) Prepare monomer solution and initiator solution respectively; the monomer solution contains methyl allyl polyoxyethylene ether, acrylic acid, allyl-containing ammonium salt monomer and chain transfer agent; the initiator solution contains initiator; (2) Add deionized water to a reaction vessel equipped with a stirrer, a reflux condenser and an inert gas inlet, heat and stir, and simultaneously add the monomer solution and the initiator solution to the reaction vessel at a constant rate, controlling the addition time to carry out the free radical copolymerization reaction; wherein, the time when the initiator solution is added is later than the time when the monomer solution is added. (3) After the reaction is complete, the temperature is lowered and the pH is adjusted to neutral or weakly alkaline to obtain the ammonium-based condensate water-reducing agent.

[0012] Preferably, the amount of chain transfer agent used is 1 / 15 of the total molar amount of methyl allyl polyoxyethylene ether, allyl-containing ammonium salt monomer and acrylic acid; The amount of the initiator is 1 / 30 of the total molar amount of methyl allyl polyoxyethylene ether, allyl-containing ammonium salt monomer and acrylic acid.

[0013] Preferably, the chain transfer agent is 3-mercaptopropionic acid, and the initiator is sodium persulfate; When preparing the monomer solution, add methyl allyl polyoxyethylene ether, acrylic acid, allyl-containing ammonium salt monomer, and chain transfer agent to deionized water and stir until homogeneous. Add deionized water as needed, generally adding a portion first, and then adding more according to the final volume requirement after adding the raw materials, precisely adjusting the volume of the monomer solution (and similarly the initiator solution) to the required volume.

[0014] Preferably, the volume of the initiator solution is greater than the volume of the monomer solution. As a further preferred embodiment, the volume ratio of the monomer solution to the initiator solution is 4:5. The monomer solution is added over a period of 3 to 5 hours, and the initiator solution is added over a period of 4 to 6 hours; the initiator solution is added at a time 0.5 to 1 hour later than the monomer solution.

[0015] Preferably, the monomer solution is added over 4 hours, and the initiator solution is added over 5 hours; after the addition is complete, the mixture is stirred at the reaction temperature for another 0.5 to 1.5 hours.

[0016] Preferably, the reaction temperature in step (1) is 75–85°C; In step (3), the pH is adjusted to 6-7 using an alkaline solution; wherein the alkaline solution is any one of sodium hydroxide, potassium hydroxide, or ammonia water, and the pH adjustment begins when the temperature drops to 40°C.

[0017] Preferably, before the free radical copolymerization reaction, nitrogen gas is introduced into the monomer solution, the initiator solution and the reaction vessel for deoxygenation treatment, and the nitrogen gas introduction time is generally 20 to 50 minutes.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses an excess of acrylic acid monomer molar ratio (such as a density comb structure of 1:1:3), introduces dense carboxyl groups on the main chain, provides strong initial electrostatic repulsion, and neutralizes at a low temperature of 40°C, avoiding ester bond hydrolysis, thereby increasing the water reduction rate to more than 45%, the slump loss rate after 2 hours to less than 10%, and extending the storage stability to more than 6 months. It also maintains excellent dispersion performance under harsh conditions of high mud content (5%) or high alumina phase admixture (30%).

[0019] (2) The present invention effectively eliminates oxygen inhibition by combining three independent nitrogen pre-passing with initiator delayed dripping process, the monomer conversion rate reaches more than 92%, and the batch performance deviation is less than 3%, which is significantly better than the wide distribution, low conversion rate and poor reproducibility of traditional methods.

[0020] (3) By introducing allyl-containing ammonium salt monomers (such as allyl amino hydrochloride), the polymer backbone has an ammonium functional group (-NH3⁺). This ammonium group can generate specific coordination adsorption or electrostatic interaction with the aluminum sites on the surface of high-alumina phase admixtures (metakaolin, high-alumina cement, fly ash, slag, etc.), effectively inhibiting the intercalation or consumption of water-reducing agent molecules in the high-alumina system, thereby significantly delaying slump loss.

[0021] (4) The monomers used in this invention are all conventional industrial raw materials in the field of polycarboxylate superplasticizers (HPEG, acrylic acid, allyl amine hydrochloride), requiring no expensive functional monomers or special solvents. Simultaneously, by employing a precise chain transfer agent / initiator ratio (total monomer / 15, total monomer / 30) and an optimized dripping process, the monomer conversion rate is high (>92%), with less residual monomer, reducing raw material waste and post-processing costs. Overall, the cost of the mother liquor of the superplasticizer of this invention is approximately RMB 4100–4300 / ton, which is about 10%–15% lower than that of commercially available similar highly adaptable polycarboxylate mother liquors (typically RMB 4500–5000 / ton), demonstrating significant economic advantages.

[0022] (5) The process conditions of this invention are mild, with an aqueous solution at 80°C and normal pressure. It can be directly transferred from the laboratory to the industrial scale, making production safe and reliable. It has good industrialization prospects and is especially suitable for concrete systems containing high-alumina phase admixtures (such as large amounts of fly ash, slag, metakaolin, high-alumina cement, etc.). It solves the technical problem of "decreased water reduction rate and rapid slump loss" of traditional polycarboxylate superplasticizers in such systems, and has outstanding substantial progress and industrial practical value. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing an ammonium-based condensation polymer water-reducing agent adapted to a high-alumina phase admixture in Example 1 of the present invention.

[0024] Figure 2 This is a schematic diagram of the free radical copolymerization reaction in Example 1 of the present invention.

[0025] Figure 3 This is a schematic diagram of the free radical copolymerization reaction in Example 2 of the present invention.

[0026] Figure 4 The figures show a comparison of the properties of the products obtained in Examples 1-4 and Comparative Example 1, in mm; where a represents the comparison of flowability, b represents the comparison of flexural strength, and c represents the comparison of compressive strength. Detailed Implementation

[0027] The accompanying drawings are for illustrative purposes only. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] It should be understood that "Solution I" and "Solution II" are only for differentiation and do not represent any technical feature.

[0029] Example 1 An ammonium-based condensate water-reducing agent suitable for high-alumina phase admixtures, the water-reducing agent comprising a polycarboxylic acid copolymer containing carboxyl and ammonium groups, the copolymer being prepared by free radical copolymerization of the following monomers: Allyl amino hydrochloride (N1), methyl allyl polyoxyethylene ether (HPEG) and acrylic acid (AA); The molar amount of acrylic acid is greater than that of methyl allyl polyoxyethylene ether, so as to introduce abundant carboxyl groups into the main chain; the allyl amino hydrochloride can introduce ammonium functional groups into the main chain.

[0030] The molar ratio of allyl amino hydrochloride, methyl allyl polyoxyethylene ether, and acrylic acid is 1:1:6. The number average molecular weight of the methyl allyl polyoxyethylene ether is 2400.

[0031] like Figure 1 As shown, a method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture includes the following steps: (1) Prepare monomer solution (solution I) and initiator solution (solution II) respectively; Solution I includes deionized water (100 mL), HPEG macromonomer (0.02 mol × 2400 = 48 g), acrylic acid (0.02 mol × 6 × 72 = 8.64 g), allyl amino hydrochloride (0.02 mol × 93.56 = 1.87 g) and 3-mercaptopropionic acid (1 / 15 of the total molar amount of methyl allyl polyoxyethylene ether, allyl ammonium salt monomer and acrylic acid, i.e. 0.011 mol × 106.14 = 1.13 g); Solution II contains deionized water (120 mL) and sodium persulfate (1 / 30 of the total molar amount of methyl allyl polyoxyethylene ether, allyl ammonium salt monomer and acrylic acid, i.e. 0.0053 mol × 238.1 = 1.27 g). Except for deionized water, the mass of each reagent should be prepared according to 120 ml of solution I and 150 ml of solution II. The total amount of solution should be adjusted according to the required amount in the experiment.

[0032] (2) Prepare the reaction vessel, which is a three-necked round-bottom flask equipped with a stirrer, a reflux condenser and a nitrogen inlet. Purge nitrogen into solution I, solution II and the three-necked round-bottom flask for 30 minutes to remove oxygen from the solution.

[0033] 80 mL of deionized water was added to the reaction vessel and heated to 80 °C with stirring. Both solutions were then added to the flask at a constant rate using a peristaltic pump, with solutions I and II added at a rate of 1.5 mL / min, and the final excess of solution II added at a rate of 1 mL / min. Solution I was added over 4 hours, while solution II was pumped in over 5 hours to initiate the free radical copolymerization reaction. After the additions were complete, the mixture was stirred at 80 °C for another hour.

[0034] like Figure 2 In this context, R1 represents CH3NH2. + .

[0035] The high-efficiency water-reducing agent of ammonium-based condensation polymer is synthesized according to a molar ratio of 1:1:6. Under this molar ratio, the excess of acrylic acid can ensure that the main chain contains dense carboxyl groups, thereby providing a strong initial electrostatic repulsion force and ensuring a high water reduction rate.

[0036] By slowly adding the monomer, initiator solution, and chain transfer agent solution dropwise, the concentrations of free radicals and monomers in the reaction system can be maintained at a steady state, avoiding explosive polymerization or uneven local reactions caused by one-time mixing. Extending the initiator addition time ensures that all monomers fully polymerize, significantly improving the monomer conversion rate and reducing the interference of residual monomers on concrete performance.

[0037] (3) After the reaction is completed, the temperature is lowered to 40°C, and NaOH solution is added to adjust the pH to 7 (to neutralize the carboxyl group) to obtain a light yellow transparent liquid product, which is the ammonium-based condensation polymer water-reducing agent.

[0038] The prepared ammonium-modified condensate water-reducing agent was subjected to performance tests, and the results are shown in Table 1 and 2. Figure 4 As shown.

[0039] Example 2 The difference between this embodiment and Example 1 is that allyl amino hydrochloride (N1) is replaced with N,N-dimethylallylamino (N2), so that the functional groups introduced into the main chain of the water-reducing agent have a different number of methyl groups.

[0040] Other areas not mentioned are the same as in Example 1.

[0041] See reaction formula Figure 3 As shown. Where R2 represents CH3NHCH3 + .

[0042] The prepared ammonium-modified condensate water-reducing agent was subjected to performance tests, and the results are shown in Table 1 and 2. Figure 4 As shown.

[0043] Example 3 The difference between this embodiment and Example 1 is that the number-average molecular weight of methyl allyl polyoxyethylene ether is changed to 1000, the side chain length of the water-reducing agent is shortened, the steric hindrance effect is reduced, thereby controlling the dispersibility of cement particles and the fluidity of the paste, but there is an optimal side chain length.

[0044] Other areas not mentioned are the same as in Example 1.

[0045] The prepared ammonium-modified condensate water-reducing agent was subjected to performance tests, and the results are shown in Table 1 and 2. Figure 4 As shown.

[0046] Example 4 The difference between Example 4 and Example 1 is that the number-average molecular weight of methyl allyl polyoxyethylene ether is changed to 3000, and the length of the water-reducing agent side chain is increased to enhance the steric hindrance effect, thereby improving the dispersibility of cement particles and the fluidity of the paste. However, if the length is too long, it may lead to adsorption obstruction or fluidity saturation or even decrease. There is an optimal side chain length within the length range of the examples.

[0047] Other areas not mentioned are the same as in Example 1.

[0048] The prepared ammonium-modified condensate water-reducing agent was subjected to performance tests, and the results are shown in Table 1 and 2. Figure 4 As shown.

[0049] Comparative Example 1 A method for preparing an ammonium-based polycondensation superplasticizer, wherein the monomer ratio is HPEG(2400):AA = 1:6 (without adding any ammonium structure). The prepared polycarboxylate superplasticizer was subjected to performance testing, and the results are shown in Table 1. Figure 4 As shown.

[0050] Other areas not mentioned are the same as in Example 1.

[0051] The products prepared in Examples 1-4 and Comparative Example 1 were subjected to performance tests, and the results are shown in Table 1.

[0052] Table 1. Performance comparison of the products prepared in Examples 1-4 and Comparative Example 1. As shown in Table 1, Example 1 demonstrates superior performance in both slump retention and flowability, significantly outperforming other examples and comparative examples. This indicates that it is most effective in maintaining the workability of concrete under harsh conditions such as long-term transportation or high-temperature construction. Furthermore, Example 1 exhibits the lowest batch performance deviation (RSD) of only 2.2%, indicating the best process stability and consistent quality among all samples. In summary, Example 1 demonstrates the best performance across all aspects.

[0053] like Figure 4 As shown, the cement fluidity test results of different embodiments of the present invention show significant differences. Specifically, the fluidity value of Example 1 is 470, significantly higher than the reference value of 290 for Comparative Example 1; the fluidity value of Example 4 is 410, also significantly better than Comparative Example 1; the fluidity value of Example 2 is 292, basically the same as Comparative Example 1; while the fluidity value of Example 3 is only 240, lower than the reference level of Comparative Example 1. In summary, Examples 1 and 4 have the most significant effect on improving cement fluidity, Example 2's effect is comparable to the reference example, while Example 3 shows a certain degree of fluidity reduction. These results indicate that bifunctional polymers can improve processability, but excessive or unbalanced functionalization can lead to performance loss.

[0054] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An ammonium-based condensate water-reducing agent suitable for high-alumina phase admixtures, characterized in that, The water-reducing agent comprises a polycarboxylic acid copolymer containing carboxyl and ammonium groups, the copolymer being prepared by free radical copolymerization of the following monomers: Allyl-containing ammonium salt monomers, methyl allyl polyoxyethylene ether, and acrylic acid; The molar amount of acrylic acid is greater than that of methyl allyl polyoxyethylene ether, so as to introduce abundant carboxyl groups into the main chain; the allyl-containing ammonium salt monomer can introduce ammonium functional groups into the main chain.

2. The ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 1, characterized in that, The allyl-containing ammonium salt monomer is allylamine hydrochloride or N,N-dimethylallylamine; The molar ratio of the allyl-containing ammonium salt monomer, methyl allyl polyoxyethylene ether, and acrylic acid is 1:1:

6.

3. The ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 1, characterized in that, The number average molecular weight of the methyl allyl polyoxyethylene ether is 1000 to 3000.

4. A method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Prepare monomer solution and initiator solution respectively; the monomer solution contains methyl allyl polyoxyethylene ether, acrylic acid, allyl-containing ammonium salt monomer and chain transfer agent; the initiator solution contains initiator; (2) Add deionized water to a reaction vessel equipped with a stirrer, a reflux condenser and an inert gas inlet, heat and stir, and simultaneously add the monomer solution and the initiator solution to the reaction vessel at a constant rate, controlling the addition time to carry out the free radical copolymerization reaction; wherein, the time when the initiator solution is added is later than the time when the monomer solution is added. (3) After the reaction is complete, the temperature is lowered and the pH is adjusted to neutral or weakly alkaline to obtain the ammonium-based condensate water-reducing agent.

5. The method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 4, characterized in that, The amount of the chain transfer agent is 1 / 15 of the total molar amount of methyl allyl polyoxyethylene ether, allyl-containing ammonium salt monomer and acrylic acid. The amount of the initiator is 1 / 30 of the total molar amount of methyl allyl polyoxyethylene ether, allyl-containing ammonium salt monomer and acrylic acid.

6. The method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 4, characterized in that, The chain transfer agent is 3-mercaptopropionic acid, and the initiator is sodium persulfate; When preparing the monomer solution, add methyl allyl polyoxyethylene ether, acrylic acid, allyl-containing ammonium salt monomer and chain transfer agent to deionized water and stir until homogeneous.

7. The method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 4, characterized in that, The volume ratio of the monomer solution to the initiator solution is 4:5; The monomer solution is added over a period of 3 to 5 hours, and the initiator solution is added over a period of 4 to 6 hours; the initiator solution is added at a time 0.5 to 1 hour later than the monomer solution.

8. The method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 4, characterized in that, The monomer solution was added over a period of 4 hours, and the initiator solution was added over a period of 5 hours. After the addition is complete, stir the mixture at the reaction temperature for another 0.5 to 1.5 hours.

9. The method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 4, characterized in that, In step (1), the reaction temperature is 75–85°C; In step (3), the pH is adjusted to 6-7 using an alkaline solution; wherein the alkaline solution is any one of sodium hydroxide, potassium hydroxide, or ammonia, and the pH adjustment begins when the temperature drops to 40°C.

10. The method for preparing an ammonium-based condensate water-reducing agent adapted to a high-alumina phase admixture according to claim 4, characterized in that, Before the free radical copolymerization reaction, nitrogen gas is introduced into the monomer solution, the initiator solution and the reaction vessel to remove oxygen.

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