Ph dual response type concrete multifunctional admixture and preparation method thereof

Abstract

The application discloses a kind of PH dual-response type concrete multifunctional admixture and preparation method thereof.The concrete multifunctional admixture preparation method is as follows: first, carboxymethyl chitosan, chitosan, nano silicon dioxide, cellulose acetate, N,N'-methylene bisacrylamide, ammonium persulfate / tetramethyl ethylenediamine mixture, nano hydrated calcium silicate are added to acetic acid solution, and hybrid particles are obtained after ultrasonic continuous dispersion;Second, polycarboxylate superplasticizer, acrylamide, sodium alginate and nano halloysite particles are uniformly stirred by magnetic force to form a mixed dispersion solution;Finally, hybrid particles are added to the mixed dispersion solution to obtain a concrete multifunctional admixture.The concrete admixture can not only remain stable under polycarboxylate superplasticizer solution storage conditions, but also can not increase the viscosity of concrete after being added to concrete, so that it can maintain good mixing performance, achieve good water retention and early strength effect.

Description

Technical Field

[0001] This invention relates to the field of building materials, specifically to a pH-responsive, multifunctional concrete admixture and its preparation method. Background Technology

[0002] Polycarboxylate superplasticizers have become an extremely important admixture component in modern concrete production and application. As a high-performance water-reducing agent, they can significantly improve the workability and mechanical properties of concrete. However, in the concrete construction process, in order to meet its construction and performance requirements, it is often necessary to use it in combination with other non-water-reducing components. For example, it can be used in combination with early-strength components to improve its early strength, or with water-retaining components to reduce its bleeding rate and improve its workability, thereby solving the technical problems that arise when using polycarboxylate superplasticizers alone. When polycarboxylate superplasticizers are compounded with water-retaining components, the water-retaining components are mainly high-molecular-weight materials with high viscosity, resulting in excessively high viscosity of the compounded system. This causes difficulties in mixing and pumping, especially since substances such as cellulose ethers are prone to deterioration under long-term storage conditions after compounding with polycarboxylate superplasticizers, leading to flocculation and precipitation, which affects their performance. When polycarboxylate superplasticizers are compounded with early-strength components, the early-strength agent dissolves rapidly into the concrete system in the initial stage of dissolution and participates in the concrete hydration reaction, usually resulting in a significant shortening of the setting time and affecting construction. This inability to precisely match the hydration process with the concrete not only affects the effectiveness of the polycarboxylate superplasticizer but also leads to a decline in the later strength of the concrete. Currently, there is no integrated multifunctional admixture that can coexist stably with polycarboxylate superplasticizers for a long time and can release different functional components in an orderly manner according to changes in the alkalinity inside the concrete. Therefore, there is an urgent need for a multifunctional admixture in concrete applications that can coexist stably with polycarboxylate superplasticizers and can release different functional components in a reasonable and orderly manner according to changes in the internal environment of concrete, so as to meet the needs of concrete at different stages, improve concrete performance, and meet the application needs of diverse engineering scenarios. Summary of the Invention

[0003] To address the problems existing in the aforementioned background technology, this invention provides a pH-responsive, multifunctional concrete admixture and its preparation method. The concrete admixture prepared using this method remains stable under polycarboxylate superplasticizer solution storage conditions, does not increase the viscosity of concrete after addition, thus maintaining good mixture properties, and achieves good water retention and early strength even when the concrete releases alkali. Furthermore, this invention provides a preparation method for the admixture and clarifies its excellent application effects in various concrete engineering scenarios.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a pH-responsive, multifunctional concrete admixture includes the following steps: (1) Carboxymethyl chitosan, chitosan, nano silica, cellulose acetate, N,N'-methylenebisacrylamide, ammonium persulfate / tetramethylethylenediamine mixture, and nano hydrated calcium silicate were added to an acetic acid solution. After continuous ultrasonic dispersion to form an emulsion, the emulsion was added to the oil phase solution. The pH of the solution was adjusted to 6.5-7 by adding calcium hydroxide. After reacting for 6-8 hours, the precipitate was filtered, washed, and dried to constant weight to obtain hybrid particles. The hybrid particles consist of a coating layer formed by cellulose acetate, carboxymethyl chitosan, and chitosan, containing nano-silica, nano-hydrated calcium silicate particles, N,N'-methylenebisacrylamide, and ammonium persulfate / tetramethylethylenediamine. Nano-silica and nano-hydrated calcium silicate serve as solid, insoluble crystal nuclei, while carboxymethyl chitosan and chitosan adhere to their surface to grow and form the coating layer. Cellulose acetate acts as a filler and network connector. In this step, the solubility of carboxymethyl chitosan and chitosan is altered by adjusting the pH, leading to precipitation and the growth of the coating layer using silica and nano-hydrated calcium silicate as crystal nuclei. The size of the hybrid particles prepared in step (1) is controlled to be 1~10 μm; The mass fractions of each raw material component in step (1) are as follows: 20-25 parts of carboxymethyl chitosan 8-12 parts chitosan 2-3 parts of nano-silica 0.3-0.5 parts of cellulose acetate, 0.1-0.2 parts of N,N'-methylenebisacrylamide 0.2-0.3 parts of ammonium persulfate / tetramethylethylenediamine mixture 1-2 parts of nano-hydrated calcium silicate 100 parts of acetic acid solution The mass ratio of ammonium persulfate to tetramethylethylenediamine in the mixture of ammonium persulfate and tetramethylethylenediamine is 1:1. The acetic acid solution has a mass concentration of 30-50%. The carboxymethyl chitosan has a carboxylation degree of 60%~80% and its insoluble region has a pH value of 6~8; The particle size of the nano-silica particles is no greater than 100 nm. The particle size of the nano-hydrated calcium silicate particles is no greater than 100 nm. The oil phase is a non-polar oil phase such as n-hexane, cyclohexane, or mineral oil; the volume ratio of the oil phase to the emulsion is 4:1 to 3:2.

[0005] In step (1), the ultrasonic frequency is 20~25kHz and the ultrasonic dispersion time is 3~5min; The drying temperature is 40~60℃; (2) The polycarboxylate superplasticizer, acrylamide, sodium alginate and nano halloysite particles are magnetically stirred until uniform to form a stable mixed dispersion solution in the polycarboxylate superplasticizer solution; The amounts of each raw material component in step (2) are as follows: 100-150 parts of polycarboxylate superplasticizer Acrylamide 4-6 parts, 1-2 parts sodium alginate 3-5 parts of nano-haloite particles, The polycarboxylate superplasticizer, as the dispersion matrix, has a solid content of 20-40%, a water reduction rate of not less than 25%, and a pH value of 6-8. The nano-haloite particles are at the nanoscale, with a size not exceeding 100 nm. The magnetic stirring speed is 600~1000 r / min; (3) The hybrid particles obtained in step (1) are added to the mixed dispersion solution obtained in step (2), and the mixture is ultrasonically dispersed to form an emulsion, which is the pH dual-response concrete multifunctional admixture of the present invention. Step (3) The ultrasonic frequency is 20~25kHz and the ultrasonic dispersion time is 3~5min.

[0006] Among them, the hybrid particles obtained in step (1) can remain relatively stable in the acidic and neutral environments of polycarboxylate superplasticizer, and dissolve and release early strong crystal nuclei and N,N'-methylenebisacrylamide, ammonium persulfate / tetramethylethylenediamine in the alkaline environment of concrete; while the mixed dispersion solution in step (2) is a low viscosity solution in the acidic and neutral environments. In the alkaline environment of concrete, acrylamide generates a polyacrylamide network structure under the initiation and catalysis of N,N'-methylenebisacrylamide, ammonium persulfate / tetramethylethylenediamine, and sodium alginate and calcium ions react to generate calcium alginate gel. Through the synergistic effect of the two, in-situ polymerization forms a three-dimensional water-retaining gel network.

[0007] Furthermore, the present invention also provides a pH-responsive, dual-functional concrete admixture prepared by the above method.

[0008] Compared with the prior art, the present invention has the following beneficial effects: (1) In polycarboxylate superplasticizers, by preparing composite hybrid particles, it is possible to achieve stability in neutral and slightly acidic solutions, while slow release under alkaline conditions. This ensures the stability of the entire polycarboxylate superplasticizer compound system, allowing it to act as a filler in the form of microparticles during concrete mixing, improving its fluidity. It also allows for gradual and stable release under alkaline conditions as cement dissolves and increases the alkalinity of the solution, thus achieving early strength. This structural system achieves the orderly provision of functional requirements such as long-term storage, mixture improvement, and early strength, avoiding the adverse effects of early strength on mixture performance and construction time, and solving the instability of functional components under acidic conditions.

[0009] (2) By preparing a stable dispersion based on polycarboxylate superplasticizer, the low viscosity and stability of the entire polycarboxylate superplasticizer compound system are guaranteed, so that it can be stored for a long time without deterioration, and is easy to pump and meter; when applied in concrete, the low viscosity small molecule substances can be polymerized and ion crosslinked when the cement is dissolved to a certain alkalinity, so as to quickly build a water-retaining network structure and solve the problem of bleeding after pouring.

[0010] (3) In summary, through the synergistic effect of the above two measures, a pH-sensitive composite hybrid particle and dispersion system is formed in the polycarboxylate superplasticizer system. The composite hybrid particles are stable in polycarboxylate, while the dispersion system is in a dissolved state, ensuring the stability and low viscosity of the entire system, making it convenient for application. During application, as it is incorporated into concrete, the cement in the concrete gradually dissolves, increasing the alkalinity and calcium ion concentration of the system. When a certain alkalinity is reached, the structure of the hybrid particles is destroyed, dissolving and releasing early-strength components. The dispersion begins to polymerize and generate ionic crosslinking, forming a water-retaining network structure, improving water retention, and reducing bleeding and pressure bleeding rates.

[0011] (4) In this invention, the formation and release of functional components are controlled by controlling the dosage of different components and the synthesis conditions, so as to achieve the orderly production and effect of functional components and the synergistic improvement of concrete performance. This invention successfully combines water reduction, water retention and early strength functions, simplifies the application process, and cleverly uses pH changes to achieve the aggregation and disintegration of hybrid particles and dispersion systems, so as to achieve the orderly control of functional components.

[0012] (5) The admixture described in this invention is particularly suitable for precast components requiring early strength demolding and concrete with high apparent quality requirements, and has significant economic and environmental benefits. Detailed Implementation

[0013] The present invention will be further illustrated by specific embodiments below, but the scope of protection of the present invention is not limited thereto.

[0014] A method for preparing a pH-responsive, multifunctional concrete admixture includes the following steps: (1) Carboxymethyl chitosan, chitosan, nano silica, cellulose acetate, N,N'-methylenebisacrylamide, ammonium persulfate / tetramethylethylenediamine mixture, and nano hydrated calcium silicate were added to an acetic acid solution. After continuous ultrasonic dispersion to form an emulsion, the emulsion was added to the oil phase solution. The pH of the solution was adjusted to 6.5-7 by adding calcium hydroxide. After 6-8 hours, the precipitate was filtered, washed, and dried to constant weight to obtain hybrid particles. The hybrid particles prepared in step (1) have a size of 1~10 μm; The mass fractions of each raw material component in step (1) are as follows: 20-25 parts of carboxymethyl chitosan 8-12 parts chitosan 2-3 parts of nano-silica 0.3-0.5 parts of cellulose acetate, 0.1-0.2 parts of N,N'-methylenebisacrylamide 0.2-0.3 parts of ammonium persulfate / tetramethylethylenediamine mixture 1-2 parts of nano-hydrated calcium silicate 100 parts of acetic acid solution The mass ratio of ammonium persulfate to tetramethylethylenediamine in the mixture of ammonium persulfate and tetramethylethylenediamine is 1:1. The acetic acid solution has a mass concentration of 30-50%. The carboxymethyl chitosan has a carboxylation degree of 60%~80% and an insoluble region pH of 6~8; The particle size of the nano-silica particles is no greater than 100 nm. The particle size of the nano-hydrated calcium silicate particles is no greater than 100 nm. The oil phase is a non-polar oil phase such as n-hexane, cyclohexane, or mineral oil; the volume ratio of the oil phase to the emulsion is 4:1 to 3:2.

[0015] In step (1), the ultrasonic frequency is 20~25kHz and the ultrasonic dispersion time is 3~5min; The drying temperature is 40~60℃; (2) The polycarboxylate superplasticizer, acrylamide, sodium alginate and nano halloysite particles are magnetically stirred until uniform to form a stable mixed dispersion solution in the polycarboxylate solution; The amounts of each raw material component in step (2) are as follows: 100-150 parts of polycarboxylate superplasticizer Acrylamide 4-6 parts, 1-2 parts sodium alginate 3-5 parts of nano-haloite particles, The polycarboxylate superplasticizer, as the dispersion matrix, has a solid content of 20-40%, a water reduction rate of not less than 25%, and a pH value of 6-8. The nano-haloite particles are at the nanoscale, with a size not exceeding 100 nm. The magnetic stirring speed is 600~1000 r / min; (3) The hybrid particles obtained in step (1) are added to the mixed dispersion solution obtained in step (2), and the mixture is ultrasonically dispersed to form an emulsion, which is the pH dual-response concrete multifunctional admixture of the present invention. Step (3) The ultrasonic frequency is 20~25kHz and the ultrasonic dispersion time is 3~5min.

[0016] Furthermore, the present invention also provides a pH-responsive, dual-functional concrete admixture prepared by the above method.

[0017] Example 1 A method for preparing a pH-responsive, multifunctional concrete admixture includes the following steps: (1) 20 parts of carboxymethyl chitosan, 12 parts of chitosan, 2 parts of nano silica, 0.5 parts of cellulose acetate, 0.1 parts of N,N'-methylenebisacrylamide, 0.3 parts of ammonium persulfate / tetramethylethylenediamine mixture (the mass ratio of ammonium persulfate to tetramethylethylenediamine is 1:1), and 1 part of nano hydrated calcium silicate were added to 100 parts of acetic acid solution with a concentration of 50%. The mixture was continuously dispersed by ultrasonication at 20 kHz for 5 min to form an emulsion. Then, the emulsion was added to the hexane oil phase (the volume ratio of oil phase to emulsion is 4:1). Then, calcium hydroxide was added to adjust the pH of the solution to 6.5. After 8 h, the precipitate was filtered, washed, and dried at 40 °C to obtain hybrid particles. The carboxymethyl chitosan has a carboxylation degree of 80% and an insoluble region pH of approximately 6.5. The nano-silica particles have a particle size of 20 nm. The nano-hydrated calcium silicate particles have a particle size of 96 nm. The prepared hybrid particles have a size of 1 μm; (2) Mix 150 parts of polycarboxylate superplasticizer, 4 parts of acrylamide, 2 parts of sodium alginate, and 3 parts of nano halloysite particles (size 28nm) with magnetic stirring (magnetic stirring speed of 600r / min) until completely clear to form a mixed dispersion solution; The polycarboxylate superplasticizer, used as a dispersion matrix, has a solid content of 40%, a water reduction rate of 25%, and a pH of 6.5. (3) Add the hybrid particles prepared in step (1) to the mixed dispersion solution prepared in step (2) and disperse them by ultrasonication at 20 kHz for 5 min to form an emulsion.

[0018] Example 2 A method for preparing a pH-responsive, multifunctional concrete admixture includes the following steps: (1) 25 parts of carboxymethyl chitosan, 8 parts of chitosan, 3 parts of nano silica, 0.3 parts of cellulose acetate, 0.2 parts of N,N'-methylenebisacrylamide, 0.2 parts of ammonium persulfate / tetramethylethylenediamine mixture (the mass ratio of ammonium persulfate to tetramethylethylenediamine is 1:1), and 2 parts of nano hydrated calcium silicate were added to 100 parts of acetic acid solution with a concentration of 30%. The mixture was continuously dispersed by ultrasonication at 25 kHz for 3 min to form an emulsion. Then, it was added to the cyclohexane oil phase (the volume ratio of oil phase to emulsion is 3:2). Then, calcium hydroxide was added to adjust the pH of the solution to 7. After 6 h, the precipitate was filtered, washed, and dried at 60 °C to obtain hybrid particles. The carboxymethyl chitosan has a carboxylation degree of 80% and an insoluble region pH of 7. The nano-silica particles have a particle size of 100 nm. The nano-hydrated calcium silicate particles have a particle size of 12 nm. The prepared hybrid particles have a size of 10 μm; (2) Mix 100 parts of polycarboxylate superplasticizer, 6 parts of acrylamide, 1 part of sodium alginate and 5 parts of nano halloysite particles (size 68nm) with magnetic stirring (magnetic stirring speed of 800r / min) until completely clear to form a mixed dispersion solution; The polycarboxylate superplasticizer, used as a dispersion matrix, has a solid content of 20%, a water reduction rate of 32%, and a pH of 6.9. (3) Add the hybrid particles prepared in step (1) to the mixed dispersion solution prepared in step (2) and disperse it by ultrasonication at 25 kHz for 3 min to form an emulsion.

[0019] Example 3 A method for preparing a pH-responsive, multifunctional concrete admixture includes the following steps: (1) 24 parts of carboxymethyl chitosan, 10 parts of chitosan, 2.5 parts of nano silica, 0.4 parts of cellulose acetate, 0.15 parts of N,N'-methylenebisacrylamide, 0.25 parts of ammonium persulfate / tetramethylethylenediamine mixture (the mass ratio of ammonium persulfate to tetramethylethylenediamine is 1:1), and 1.8 parts of nano hydrated calcium silicate were added to 100 parts of acetic acid solution with a concentration of 40%. After continuous dispersion by ultrasonication at 24 kHz for 4 min, an emulsion was formed. Then, hexane oil phase was added (the volume ratio of oil phase to emulsion was 7:3). Then calcium hydroxide was added to adjust the pH of the solution to 6.8. After 7 h, the precipitate was filtered, washed, and dried at 50 °C to obtain hybrid particles. The carboxymethyl chitosan has a carboxylation degree of 85% and an insoluble region pH of approximately 8. The nano-silica particles have a particle size of 50 nm. The nano-hydrated calcium silicate particles have a particle size of 64 nm. The hybrid particles prepared have a size of 2 μm.

[0020] (2) Mix 120 parts of polycarboxylate superplasticizer, 5 parts of acrylamide, 1.5 parts of sodium alginate, and 4 parts of nano halloysite particles (size 46nm) with magnetic stirring (magnetic stirring speed of 1000r / min) until completely clear to form a mixed solution; The polycarboxylate superplasticizer, used as a dispersion matrix, has a solid content of 30%, a water reduction rate of 30%, and a pH of 7.8. (3) Add the hybrid particles prepared in step (1) to the mixed dispersion solution prepared in step (2) and disperse it by ultrasonication at 24 kHz for 4 min to form an emulsion.

[0021] Example 4 The admixture prepared in Example 3 was stored at room temperature for 6 months for future use.

[0022] Comparative Example 1 Compared to Example 3, the above substances were directly mixed into the polycarboxylate superplasticizer solution to form a mixed solution. (That is, all components in steps (1) and (2) were weighed in the same amount and added to the polycarboxylate superplasticizer, without performing the process steps in steps (1) and (2).) Comparative Example 2 Compared to Example 3, only 34 parts of carboxymethyl chitosan were used, and no chitosan was added.

[0023] Comparative Example 3 Compared to Example 3, only 34 parts of chitosan were used, without the addition of carboxymethyl chitosan.

[0024] Comparative Example 4 The difference from Example 3 is that cellulose acetate is not added.

[0025] Comparative Example 5 The difference from Example 3 is that halloysite is not added.

[0026] Comparative Example 6 The difference from Example 3 is that N,N'-methylenebisacrylamide and the mixture of ammonium persulfate / tetramethylethylenediamine are not added.

[0027] Comparative Example 7 The difference from Example 3 is that step (1) does not contain acetic acid solution and calcium hydroxide.

[0028] The slump, 2-hour slump loss, setting time (final setting), and compressive strength of concrete were tested according to national standards GB / T 50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" and GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The reference mix proportions for concrete were: 330 kg / m³ of ordinary Portland cement P.O42.5, 860 kg / m³ of river sand, 1050 kg / m³ of 5~20mm graded crushed stone, and 149 kg / m³ of water. Admixtures were added to the concrete in all examples and comparative examples, with an admixture dosage of 2.0% of the cementitious material mass. The reference concrete contained an equal amount of polycarboxylate superplasticizer. The concrete performance indicators are shown in Table 1.

[0029] Table 1 Concrete Properties The results in Table 1 show that: The results of Comparative Example 1 show that when the mixed solution of Comparative Example 1 is added to concrete, the slump of the concrete decreases and the slump loss after 2 hours increases. It has a certain water retention capacity, but because the admixture is too viscous and difficult to disperse evenly, the water retention capacity decreases, the pressure bleeding rate increases, and the setting time is advanced, but the early strength improvement effect is limited.

[0030] Compared with Example 3, Comparative Example 2 shows a significant decrease in slump loss over 2 hours. This is because the addition of carboxymethyl chitosan alone leads to faster hydrolysis and degradation under alkaline conditions, releasing the acrylamide catalyst and early-strength components earlier, increasing the viscosity of the slurry, and thus significantly reducing slump loss over time.

[0031] Compared to Example 3, Comparative Example 3 shows insufficient water retention and increased pressure bleeding rate. This is because chitosan alone undergoes slow hydrolysis and degradation under alkaline conditions, resulting in a slower release of the acrylamide catalyst and early-strength component, leading to slower formation of the water-retaining component and bleeding under prolonged pressure. Therefore, controlling the ratio of the two is crucial. Thus, Comparative Examples 3 and 4 demonstrate that a proper blend of chitosan and carboxymethyl chitosan can effectively control their reaction rate in concrete, more effectively coordinating the release and polymerization of functional components.

[0032] Comparing Comparative Example 4 with Example 3 reveals a decrease in slump, with significant slump loss over 2 hours, increased pressure bleeding, and earlier setting time. Cellulose acetate, being fibrous, facilitates the agglomeration and cementation of hybrid particles. A lack of cellulose acetate results in insufficient stability of the hybrid particles, leading to premature release of early-strength components and the catalytic components of acrylamide, thus degrading their performance.

[0033] In summary, comparing Comparative Examples 3-4, the synergistic effect of chitosan, carboxymethyl chitosan, and cellulose acetate allows for the slow release of early-strength functional components while also restraining the slow release of N,N'-methylenebisacrylamide and ammonium persulfate / tetramethylethylenediamine. This prevents the rapid formation of polyacrylamide structures from acrylamide in the catalytic dispersion, which would affect the workability of the concrete paste. Acrylamide partially hydrolyzes under alkaline conditions to generate acrylate groups, which can form strong hydrogen bonds with the amide groups on the unhydrolyzed acrylamide chains. This physical cross-linked network formed by hydrogen bonds can form a physical gel at high concentrations. However, this gel typically has low strength and is sensitive to temperature and ionic strength. It has some water retention but weak binding properties, and its adverse effect on concrete viscosity is relatively small. The release of N,N'-methylenebisacrylamide and ammonium persulfate / tetramethylethylenediamine from the hybrid particles catalyzes the formation of an irreversible and stable polyacrylamide network structure, significantly improving water retention while also increasing the paste concentration. Therefore, by controlling its slow release, it is possible to ensure water retention in the early stage while reducing the adverse effects that lead to increased concrete viscosity, and to generate a polyacrylamide network structure through catalysis in the later stage, thereby enhancing the overall performance of the concrete.

[0034] Comparing Comparative Example 5 with Example 3 reveals a decrease in slump, with significant slump loss over 2 hours, increased pressure bleeding rate, and decreased later-stage strength. Halloysite primarily functions to stably disperse under weakly acidic polycarboxylate superplasticizer conditions. Under highly alkaline conditions in concrete, it degrades, generating active substances and promoting hydration product formation. However, when added to concrete, it forms a stable dispersion system with the admixture. During the polymerization of acrylamide and sodium alginate, its fibrous nanotubes act as skeletal particles, ensuring structural stability. This contributes to the stability of its water-retention properties before the acrylamide initiator and crosslinking agent are released. When the alkalinity is too high, acrylamide transforms into polyacrylamide, forming a stable network structure. Halloysite then completely disintegrates, generating active substances that induced hydration products within the polyacrylamide network structure. This increased the direct composite and adhesiveness between the network structure and cement hydration products, improving overall bond strength. Therefore, when halloysite is lacking in the early stages of concrete reaction, the stability of the gel system formed by the dispersion system is insufficient, leading to decreased water retention, bleeding, poor slump, and increased slump loss. In the later stages of reaction, the lack of halloysite in the formation of hydration products within the polyacrylamide network structure results in poor binding between the hydration products and polyacrylamide, which is detrimental to strength.

[0035] Comparing Comparative Example 6 with Example 3 reveals a significant increase in slump loss over 2 hours, increased pressure bleeding rate, and a decrease in strength. This indicates that the lack of initiation and cross-linking effects from substances such as N,N'-methylenebisacrylamide and ammonium persulfate / tetramethylethylenediamine results in poor stability of the acrylamide polymerization product, making it difficult to maintain long-term water retention. This leads to increased bleeding rate and water loss over time, and the product fails to provide network support and bonding after hardening, ultimately resulting in a decrease in strength.

[0036] Comparing Comparative Example 7 and Example 3 reveals that the concrete slump, slump retention, and pressure bleeding rate all deteriorated, setting time was advanced, and strength decreased. This indicates that without the addition of acetic acid solution and calcium hydroxide in step (1), the solubility and products of each component in the entire step cannot be adjusted by pH, and a good structure containing nano-silica, nano-hydrated calcium silicate particles, N,N'-methylenebisacrylamide, and ammonium persulfate / tetramethylethylenediamine cannot be formed. The sequential function of water retention, thickening, and early strength is lost. This further illustrates the necessity and effectiveness of using acetic acid and calcium hydroxide to adjust pH for admixture formation.

Claims

1. A method for preparing a pH-responsive, multifunctional concrete admixture, characterized in that, Includes the following steps: (1) Carboxymethyl chitosan, chitosan, nano silica, cellulose acetate, N,N'-methylenebisacrylamide, ammonium persulfate / tetramethylethylenediamine mixture, and nano hydrated calcium silicate were added to an acetic acid solution. After continuous ultrasonic dispersion to form an emulsion, the emulsion was added to the oil phase solution. The pH of the solution was adjusted to 6.5-7 by adding calcium hydroxide. After 6-8 hours, the precipitate was filtered, washed, and dried to constant weight to obtain hybrid particles. (2) The polycarboxylate superplasticizer, acrylamide, sodium alginate and nano halloysite particles are magnetically stirred until uniform to form a stable mixed dispersion solution in acidic solution; (3) The hybrid particles obtained in step (1) are added to the mixed dispersion solution obtained in step (2), and the mixture is ultrasonically dispersed to form an emulsion, which is the pH dual-response concrete multifunctional admixture of the present invention.

2. The preparation method according to claim 1, characterized in that, The mass fractions of each raw material component in each step are as follows: 20-25 parts of carboxymethyl chitosan 8-12 parts chitosan 2-3 parts of nano-silica 0.3-0.5 parts of cellulose acetate, 0.1-0.2 parts of N,N'-methylenebisacrylamide 0.2-0.3 parts of ammonium persulfate / tetramethylethylenediamine mixture 1-2 parts of nano-hydrated calcium silicate 100 parts of acetic acid solution, 100-150 parts of polycarboxylate superplasticizer Acrylamide 4-6 parts, 1-2 parts sodium alginate 3-5 parts of nano-haloite particles, The mass ratio of ammonium persulfate to tetramethylethylenediamine in the mixture of ammonium persulfate and tetramethylethylenediamine is 1:

1. The acetic acid solution has a mass concentration of 30-50%. The polycarboxylate superplasticizer serves as the dispersion matrix, with a solid content of 20-40% and a water reduction rate of not less than 25%.

3. The preparation method according to claim 1, characterized in that, The hybrid particles prepared in step (1) have a size of 1~10 μm.

4. The preparation method according to claim 1, characterized in that, The carboxymethyl chitosan in step (1) has a carboxylation degree of 60%~80% and a pH value of 6~8 in its insoluble region. The particle size of the nano-silica particles is no greater than 100 nm. The particle size of the nano-hydrated calcium silicate particles is no greater than 100 nm. The nano-haloite particles mentioned in step (2) are at the nanoscale, with a size not exceeding 100 nm.

5. The preparation method according to claim 1, characterized in that, In step (1), the ultrasonic frequency is 20~25kHz and the ultrasonic dispersion time is 3~5min; The drying temperature is 40~60℃; The magnetic stirring speed in step (2) is 600~1000 r / min; Step (3) The ultrasonic frequency is 20~25kHz and the ultrasonic dispersion time is 3~5min.

6. A pH-responsive, multifunctional concrete admixture prepared by the preparation method according to any one of claims 1 to 5.

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