PH-responsive concrete water-retaining agent as well as preparation method and application thereof

Abstract

The invention provides a pH response type concrete water-retaining agent as well as a preparation method and application thereof, and relates to the technical field of concrete admixtures. Specifically, the water-retaining agent is prepared from the following raw materials: an acrylic monomer, an initiator, a reducing agent, a cross-linking agent, a molecular weight regulator and a stabilizer, wherein the acrylic monomers comprise two of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methylacrylate, ethyl acrylate or propyl acrylate, and the cross-linking agent comprises at least one of allyl sucrose ether, glucose acrylate or glyceryl acrylate. The water-retaining agent disclosed by the invention has excellent adaptability to a polycarboxylic acid water reducer, has high water-retaining property in an alkaline cement slurry environment, can solve the problems of poor responsiveness, weak adaptability and the like of a traditional water-retaining agent, and provides technical support for construction and durability improvement of high-performance concrete.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete admixtures, in particular to a pH-responsive concrete water-retaining agent, a preparation method and application thereof. BACKGROUND

[0002] As one of the most widely used structural materials in modern construction engineering, the performance of concrete directly affects the safety and durability of the project. In engineering practice, concrete is prone to bleeding and segregation, which can lead to reduced workability of concrete and further problems such as voids and exposed reinforcement. To improve such defects of concrete, adding an appropriate amount of water-retaining agent can improve workability, enhance cohesiveness, and prevent bleeding. Traditional water-retaining agents are mainly cellulose ethers, polyacrylamide, dextrin, guar gum, xanthan gum, and water-soluble polymers, which have certain water-retaining ability, but generally have low solubility when compounded with polycarboxylic acid, are prone to precipitation, have poor responsiveness, and interfere with the cement hydration process. For example, cellulose ether-based water-retaining agents have reduced water-retaining efficiency in alkaline environments and can cause excessive viscosity of concrete, affecting the construction performance; polyacrylamide-based water-retaining agents have poor electrolyte resistance and insufficient long-term stability, and polyacrylamide competes with polycarboxylic acid for adsorption, affecting the effect of polycarboxylic acid and greatly reducing the workability of concrete.

[0003] In recent years, intelligent responsive polymer materials have attracted widespread attention due to their ability to adjust their structure and performance according to environmental changes such as temperature, pH, and ion strength. Among them, pH-responsive polymer materials have unique environmental response characteristics, and their molecular chain structure and performance change significantly with changes in external pH. Under acidic conditions, the molecular chains of such polymers shrink; this shrinkage enhances the interaction between polymer chain segments and makes the molecular packing more compact, resulting in better solubility in solvents; at the same time, due to the shrinkage of the molecular chain, the internal friction of the system decreases, and the viscosity of the solution is lower. When the environment changes to an alkaline condition with high pH, the ionizable groups such as carboxyl groups on the polymer chain dissociate, generating a large number of charged groups. These charged groups are repelled by electrostatic forces, causing the molecular chains to fully expand. Further, the expansion of the molecular chain not only increases the steric hindrance between the chain segments but also significantly increases the viscosity of the system. More importantly, the expanded molecular chain can strongly adsorb and retain water through hydrogen bonding, van der Waals forces, and other interactions, thereby exhibiting excellent water-retaining properties. Based on this pH-responsive swelling behavior, pH-responsive polymer materials exhibit great potential for water retention.

[0004] Such pH-responsive polymer materials with intelligent response characteristics have broad application prospects in many fields such as agricultural water-saving irrigation, biological medicine sustained release, cosmetic moisturizing, etc. However, there is no report on the pH-responsive water-retaining agent designed for the alkaline environment of concrete. In the prior art, the aqueous synthesis of carbomer polymers has been mature, but it is mainly used in the daily chemical field, and its application in concrete is limited by poor high ionic strength resistance, poor dispersibility, easy adsorption and inactivation by cement, etc.

[0005] Therefore, if a water-retaining agent with good solubility in acidic and neutral environments and good compatibility with polycarboxylate superplasticizer, excellent pH response in the alkaline environment of concrete, and good water retention, and a green and controllable preparation process can be provided, it has important engineering value and market prospect. In view of this, the present application is proposed. SUMMARY

[0006] The first object of the present application is to provide a pH-responsive concrete water-retaining agent, which aims to overcome the defects of the existing concrete water-retaining agent, such as low solubility, poor compatibility with polycarboxylate, causing high viscosity of concrete, and large interference with the cement hydration process.

[0007] The second object of the present application is to provide a preparation method of the pH-responsive concrete water-retaining agent.

[0008] The third object of the present application is to provide a concrete admixture composition.

[0009] In order to achieve the above objects of the present application, the following technical solutions are adopted: A pH-responsive concrete water-retaining agent is prepared from the following raw materials: acrylic monomers, initiators, reducing agents, crosslinking agents, molecular weight regulators, and stabilizers. The acrylic monomers include two of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, ethyl acrylate, or propyl acrylate, and the crosslinking agent includes at least one of allyl sucrose ether, glucose acrylate, or glycerol acrylate.

[0010] Preferably, the initiator includes at least one of potassium persulfate, sodium persulfate, ammonium persulfate, or hydrogen peroxide.

[0011] Preferably, the reducing agent includes at least one of ascorbic acid, sodium sulfite, or E51 reducing agent.

[0012] Preferably, the molecular weight regulator includes at least one of sodium hypophosphite, mercaptoacetic acid, mercaptoethanol, or mercaptopropionic acid.

[0013] Preferably, the stabilizer includes at least one of isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, or vinyl polyoxyethylene ether.

[0014] Preferably, the acrylic monomer comprises a combination of acrylic acid and hydroxyethyl acrylate, with a mass ratio of 2-4:1.

[0015] Preferably, the mass ratio of the crosslinking agent to the acrylic monomer is 0.3%-0.7%.

[0016] Preferably, in the polycarboxylic acid water reducer solution, when the pH of the polycarboxylic acid water reducer solution is 2-6 and the concentration of the polycarboxylic acid water reducer is ≤20wt.%, the water retaining agent is added to the polycarboxylic acid water reducer solution, and when the dosage of the water retaining agent is ≤0.5wt.%, the water retaining agent is completely dissolved in the solution and does not precipitate within 7 days.

[0017] Preferably, in the aqueous solution of the water retaining agent, when the dosage of the water retaining agent is 0.2wt.%-0.5wt.% and the pH of the aqueous solution is adjusted from 3 to 12, the volume expansion rate is >650.

[0018] A preparation method of the pH-responsive concrete water retaining agent, comprising the following steps: preparing a reaction base containing a stabilizer and an initiator; preparing a first feeding liquid containing an acrylic monomer and a crosslinking agent; preparing a second feeding liquid containing a reducing agent and a molecular weight additive; simultaneously adding the first feeding liquid and the second feeding liquid to the reaction base to perform a polymerization reaction; after the addition is completed, performing a heat curing to obtain a precursor liquid; performing a vacuum distillation treatment and a freeze-drying treatment on the precursor liquid in sequence to obtain the water retaining agent.

[0019] Preferably, the addition of the first feeding liquid and the second feeding liquid and the duration of the polymerization reaction are 4h-8h.

[0020] Preferably, the temperature of the curing is 38°C-45°C, and the duration of the curing is 1.6h-3h.

[0021] A concrete admixture composition, comprising a solute and an aqueous solvent, and the solute comprises the pH-responsive concrete water retaining agent and a polycarboxylic acid water reducer.

[0022] Preferably, the concentration of the pH-responsive concrete water retaining agent is 0.1wt.%-0.5wt.%.

[0023] The application provides a pH-responsive concrete water-retaining agent with a three-dimensional network structure, which has the characteristics of high solubility, good compatibility, increased concrete workability, reduced concrete bleeding rate and low influence rate on the cement hydration process in a polycarboxylate superplasticizer. The application also provides a green and efficient preparation method and application scheme, which can be widely applied to high-performance concrete, self-compacting concrete, sprayed concrete and concrete engineering in extreme environments, and effectively improves the workability, homogeneity and durability of concrete. Compared with the prior art, the beneficial effects of the application mainly include the following aspects: (1) The water-retaining agent of the application has good solubility and polycarboxylate compatibility in an acidic to neutral liquid phase environment of a polycarboxylate superplasticizer solution, and can be stored for a long time without precipitation.

[0024] (2) When the water-retaining agent is mixed with a polycarboxylate superplasticizer as an admixture composition, the carboxyl group in the water-retaining agent molecule ionizes when added to the cement paste of concrete in a strong alkaline environment, and the molecular chain is extremely expanded due to the mutual repulsion of negative charges, forming a high-viscosity transparent gel to lock the excess free water, thereby achieving good water-retaining effect.

[0025] (3) When the concrete admixture composition of the application is used, the water-retaining agent can have excellent salt resistance and high mechanical strength in a high-salt ion environment of cement paste, thereby having stable water-retaining effect.

[0026] (4) When the concrete admixture composition of the application is used, in the later stage of concrete hydration, the water-retaining agent releases its bound water to continue to participate in the hydration process of concrete as the water in the environment decreases, thereby realizing dynamic adjustment of water-retaining performance.

[0027] (5) The application optimizes the raw materials and preparation process of the water-retaining agent to ensure the environmental protection, cost controllability and compatibility with cement-based materials. DETAILED DESCRIPTION

[0028] The technical solutions of the application will be described clearly and completely in combination with specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the application, not all the embodiments, and are only used to illustrate the application, and should not be regarded as limiting the scope of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market. In addition, the terms "first", "second", "third" are only used for description purposes, and cannot be understood as indicating or implying relative importance.

[0029] The first aspect of the present application is to provide a pH-responsive concrete water-retaining agent, which is mainly prepared from the following raw materials: acrylic monomers, initiators, reducing agents, cross-linking agents, molecular weight regulators and stabilizers; wherein the acrylic monomers include two of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, ethyl acrylate or propyl acrylate, and the cross-linking agent includes at least one of allyl sucrose ether, glucose acrylate or glycerol acrylate.

[0030] In the present application, the acrylic monomers serve as the backbone monomers of the water-retaining agent polymer, providing carboxyl or hydroxyl functional groups to impart hydrophilicity and pH responsiveness to the polymer. In some embodiments, the acrylic monomers can be selected from one of the above-listed types or a combination of two types, such as a combination of acrylic acid and hydroxyethyl acrylate to balance hydrophilicity and mechanical strength.

[0031] In the present application, the cross-linking agent is used to form a three-dimensional network structure of the water-retaining agent polymer; by selecting the type of cross-linking agent, the water absorption and expansion ratio and mechanical stability of the water-retaining agent can be improved.

[0032] As a preferred embodiment, the initiator includes at least one of potassium persulfate, sodium persulfate, ammonium persulfate or hydrogen peroxide; in the present application, free radicals are generated by thermal decomposition or redox system of the initiator to initiate polymerization of the monomers.

[0033] As a preferred embodiment, the reducing agent includes at least one of ascorbic acid, sodium sulfite or E51 reducing agent; in the present application, the reducing agent forms an oxidation-reduction effect with the initiator to initiate the polymerization reaction at a lower temperature.

[0034] As a preferred embodiment, the molecular weight regulator includes, but is not limited to, at least one of sodium hypophosphite, mercaptoacetic acid, mercaptoethanol or mercaptopropionic acid; in the present application, the molecular weight regulator is used to control the molecular weight distribution of the polymer by chain transfer to avoid solubility problems caused by excessive cross-linking or excessively large molecular weight.

[0035] As a preferred embodiment, the stabilizer is a non-ionic surfactant, including but not limited to at least one of isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether or vinyl polyoxyethylene ether; in the present application, the stabilizer is used to stabilize the reaction emulsion system to prevent gel agglomeration, ensure uniform dispersion of the product, and help improve the compatibility of the water-retaining agent with polycarboxylic acid and the salt tolerance of the water-retaining agent in subsequent application processes.

[0036] In a preferred embodiment, the dosage relationship of each raw material component in this invention has one or more of the following characteristics, and is calculated based on the dosage of the acrylic monomers (or, when multiple acrylic monomers are present, the sum of the dosages of the monomers used): The mass ratio of the initiator to the acrylic monomer is 1.0% to 3.0%. The mass ratio of the reducing agent to the acrylic monomer is 0.5% to 2.0%. The mass ratio of the crosslinking agent to the acrylic monomer is 0.3% to 0.7%. The mass ratio of the molecular weight regulator to the acrylic monomer is 0.2% to 0.6%. The mass ratio of the stabilizer to the acrylic monomer is 10% to 40%.

[0037] In a preferred embodiment, the water-retaining agent maintains high solubility and high solubility stability in polycarboxylate superplasticizer solution over a long period. Simultaneously, in the strongly alkaline cement slurry environment of the concrete precursor, the carboxyl groups of the water-retaining agent ionize, causing the molecular chains to expand dramatically due to mutual repulsion of negative charges, forming a high-viscosity transparent gel that locks in free water, achieving a high water retention effect. This enables the water-retaining agent to exhibit pH responsiveness. The technical effect is characterized by the following features: (a) In a polycarboxylate superplasticizer solution, when the pH of the polycarboxylate superplasticizer solution is 2 to 6 and the concentration of the polycarboxylate superplasticizer is ≤20 wt.%, when the amount of the water-retaining agent is ≤0.5 wt.%, the water-retaining agent is completely dissolved in the solution and there is no precipitation within 7 days; It should be further explained that the term "polycarboxylate superplasticizer" can refer to any existing polycarboxylate superplasticizer that conforms to the definition in this field. It can be any commercially available product or one that is prepared in-house. (b) In the aqueous solution of the water-retaining agent, the dosage of the water-retaining agent is 0.2 wt.% to 0.5 wt.%. When pH=3, the viscosity of the aqueous solution is ≤80 mPa·s; when pH=12, the aqueous solution is converted into a gel with a viscosity ≥14000 mPa·s; in some embodiments, when the pH of the aqueous solution is adjusted from 3 to 12, it is converted from a solution state to a gel state with a volume expansion rate >650.

[0038] A second aspect of the present invention is to provide a method for preparing a water-retaining agent as described in the first aspect, which mainly includes the following steps: Prepare a reaction base containing stabilizers and initiators; prepare a first feed solution containing acrylic monomers and crosslinking agents; prepare a second feed solution containing reducing agents and molecular weight additives; The first feed solution and the second feed solution are simultaneously added dropwise to the reaction substrate to carry out a polymerization reaction; after the addition is completed, the mixture is kept at a certain temperature for curing to obtain a precursor solution. The precursor liquid was subjected to vacuum distillation and freeze-drying in sequence to obtain a water-retaining agent.

[0039] In a preferred embodiment, the solvent for the reaction substrate includes tert-butanol and deionized water; the solvent for the first feed solution includes tert-butanol and deionized water; and the solvent for the second feed solution includes deionized water. In this invention, tert-butanol is used as a co-solvent, which is miscible with water in any proportion, thereby improving monomer solubility, adjusting the polarity of the reaction system, and enhancing the polymerization rate and product stability. At the same time, its low boiling point facilitates subsequent freeze-drying, thereby increasing the yield.

[0040] In a more preferred embodiment, the mass ratio of tert-butanol to deionized water in the solvent for the reaction substrate and the first feed solution is 3~6:1, more preferably 4:1.

[0041] As an optional implementation, the preparation of the reaction substrate, the first feed liquid, and the second feed liquid can be assisted by independently selecting methods such as oscillation, stirring, shaking, centrifugation, ultrasound, and heating, which helps to accelerate dispersion and obtain a relatively uniform dispersion system. In some implementations, bubbling treatment is also performed to remove oxygen from the reaction liquid and prevent free radical quenching.

[0042] In a preferred embodiment, the addition of the first and second feed solutions and the duration of the polymerization reaction are 4 to 8 hours, and the feed solutions are added at a uniform rate within the above-mentioned duration.

[0043] In a preferred embodiment, the temperature of the dropwise addition and the polymerization reaction is 25°C to 35°C.

[0044] In a preferred embodiment, the curing temperature is 38℃~45℃, and the curing time is 1.6h~3h.

[0045] In a preferred embodiment, the purpose of the vacuum distillation treatment is to remove tert-butanol. The pressure, temperature, and other parameters used can be adjusted conventionally to ensure that all tert-butanol is discharged. Similarly, in the freeze-drying treatment, the time, temperature, and other parameters used can be adjusted conventionally to ensure complete separation of water. The process of this invention operates entirely in a mixed aqueous phase, and the organic solvent can be recycled, which conforms to the principles of green chemistry. The process design of using room temperature followed by vacuum distillation to remove the solvent balances initiation efficiency and product structural uniformity, making it suitable for industrial-scale production.

[0046] In a preferred embodiment, the freeze-drying process is carried out at a temperature of -60℃ to -40℃, a vacuum degree of ≤10Pa, and a drying time of 24h to 48h.

[0047] A third aspect of the present invention is to provide a concrete admixture composition comprising a pH-responsive concrete water-retaining agent as described in the first aspect, and a polycarboxylate superplasticizer.

[0048] In a preferred embodiment, the method of applying the concrete admixture composition includes: preparing an aqueous solution containing the concrete admixture composition, wherein the amount of the water-retaining agent is 0.1 wt.% to 0.5 wt.%, and the concentration of the polycarboxylate superplasticizer is 15 wt.% to 30 wt.%; adding the aqueous solution of the concrete admixture composition to the concrete paste at a ratio of 1 wt.% of the cementitious material, until it is uniformly stirred with cement, coarse aggregate, fine aggregate, and other components.

[0049] Regarding its application, the specific mechanisms of action are as follows: First, in the polycarboxylic acid solution stage: Under acidic conditions, the carboxylic acid groups of the water-retaining molecular chains remain in a protonated state (—COOH), the molecular chains exhibit a tightly coiled state, and the molecular groups are relatively small, enabling them to be uniformly and stably distributed in the polycarboxylic acid solution. Second, in the concrete addition stage: the carboxyl groups of the water-retaining agent ionize (—COOH is converted to —COO). - and H + The negative charge is distributed along the polymer backbone, and the repulsive force between like charges overcomes the attractive force of intramolecular hydrogen bonds, causing the coiled molecular chains to gradually extend. After the molecular chains extend, the volume can increase by about 700 times, forming a highly swollen three-dimensional network structure that absorbs water and expands to form a gel state, locking in free water and inhibiting water evaporation and segregation. Thirdly, in the middle stage of concrete hydration: as cement hydration consumes water, the internal temperature of the concrete rises, the water-retaining agent partially shrinks, slowly releases water, and continuously supplies the water required for the hydration reaction. Fourthly, in the hardening stage: the water-retaining agent completely releases water, participates in the formation of a dense cement stone structure, reduces porosity, and improves durability.

[0050] Example 1 S1. Add 300g of distilled water and 50g of tert-butanol to a four-necked flask, add 10g of isopentenyl polyoxyethylene ether and 1.5g of ammonium persulfate, stir to dissolve, and purge with nitrogen for 20 min to remove oxygen.

[0051] Dissolve 70g acrylic acid (AA), 30g hydroxyethyl acrylate (HEA), and 0.5g allyl sucrose ether in a mixture of 50g tert-butanol and 50g distilled water as additive a.

[0052] Dissolve 0.8g of vitamin C and 0.4g of mercaptoethanol in 50g of distilled water as additive b.

[0053] S2. Heat the four-necked flask to 30°C and begin to add material a and material b simultaneously over a period of 4 hours. After the addition is complete, raise the temperature to 40°C and maintain the temperature for 2 hours.

[0054] S3. Heat to 65℃ and recover tert-butanol by vacuum distillation; then freeze-dry the resulting viscous liquid (-50℃, vacuum degree ≤10 Pa, 48h) to obtain a white fluffy powder.

[0055] Example 2 S1. Add 350g of distilled water and 70g of tert-butanol to a four-necked flask, add 40g of methyl allyl polyoxyethylene ether and 2g of potassium persulfate, stir to dissolve, and purge with nitrogen for 20 min to remove oxygen.

[0056] Dissolve 60g of methacrylic acid (MAA), 40g of ethyl acrylate (EA), and 0.8g of glucose acrylate in a mixture of 50g of tert-butanol and 50g of distilled water, and use this mixture as additive a.

[0057] Dissolve 1g of sodium formaldehyde sulfoxylate and 0.3g of mercaptopropionic acid in 50g of distilled water as additive b.

[0058] S2. Heat the four-necked flask to 30°C and begin simultaneously adding material a and material b, controlling the adding time to 6 hours. After the addition is complete, raise the temperature to 45°C and maintain the temperature for 2 hours to mature.

[0059] S3. Heat to 65℃ and recover tert-butanol by vacuum distillation; then freeze-dry the resulting viscous liquid (-50℃, vacuum degree ≤10 Pa, 48h) to obtain a white fluffy powder.

[0060] Example 3 S1. Add 350g of distilled water and 70g of tert-butanol to a four-necked flask, add 40g of methyl allyl polyoxyethylene ether and 2g of potassium persulfate, stir to dissolve, and purge with nitrogen for 20 min to remove oxygen.

[0061] Dissolve 50g of acrylic acid, 50g of propyl acrylate, and 0.8g of glyceryl acrylate in a mixture of 50g of tert-butanol and 50g of distilled water, and use this mixture as additive a.

[0062] Dissolve 1g of sodium formaldehyde sulfoxylate and 0.3g of mercaptoethanol in 50g of distilled water as additive b.

[0063] S2. Heat the four-necked flask to 30°C and begin simultaneously adding material a and material b, controlling the adding time to 8 hours. After the addition is complete, raise the temperature to 45°C and maintain the temperature for 2 hours to ripen.

[0064] S3. Heat to 65℃ and recover tert-butanol by vacuum distillation; then freeze-dry the resulting viscous liquid (-50℃, vacuum degree ≤10 Pa, 48h) to obtain a white fluffy powder.

[0065] Comparative Example 1 It is basically the same as Example 1, except that 70g of acrylic acid and 30g of hydroxyethyl acrylate in S1 are replaced with 100g of acrylic acid.

[0066] Comparative Example 2 The example is basically the same as Example 2, except that 60g of methacrylic acid and 40g of ethyl acrylate in S1 are replaced with 100g of methacrylic acid.

[0067] Comparative Example 3 It is basically the same as Example 1, except that the amount of 0.5g allyl sucrose ether in S1 is replaced with 0.2g.

[0068] Comparative Example 4 It is basically the same as Example 1, except that the amount of 0.5g allyl sucrose ether in S1 is replaced with 0.8g.

[0069] Comparative Example 5 It is basically the same as Example 1, except that the amount of 0.4g mercaptoethanol in S1 is replaced with 0.1g.

[0070] Comparative Example 6 It is basically the same as Example 1, except that the amount of 0.4g mercaptoethanol in S1 is replaced with 0.5g.

[0071] Comparative Example 7 It is basically the same as Example 1, except that the amount of 0.4g mercaptoethanol in S1 is replaced with 0.7g.

[0072] Comparative Example 8 It is basically the same as Example 1, except that the addition of isopentenyl polyoxyethylene ether is omitted in S1.

[0073] Experimental Example 1 The water-retaining agent powders obtained in various embodiments of the present invention were subjected to the following performance tests: (1) Solubility test: The water-retaining agent powder was added to a polycarboxylate superplasticizer solution with pH=3 at a concentration of 0.3wt.% (the polycarboxylate superplasticizer used was Dr. Shi DS-J1 superplasticizer, and the concentration in the solution was 20wt.%). The solutions corresponding to each example could be completely dissolved within 30 min of stirring. After standing at room temperature and pressure for 7 days, no precipitation was observed.

[0074] (2) pH response test: The water-retaining agent solutions prepared in step (1) above were adjusted from pH=3 to pH=12 (adjusted with 5mol / L sodium hydroxide). The initial viscosity of the water-retaining agent solution and the viscosity of the water-retaining agent gel after pH adjustment were recorded for each example. The volume expansion rate (the ratio of the volume of the water-retaining agent gel to the volume of the water-retaining agent solution after pH adjustment) was calculated and recorded in Table 1.

[0075] (3) Prepare C30 concrete (380 kg / m³ of cement) 3 Water 175kg / m 3 720kg / m³ of sand 3 1125 kg / m³ of gravel 3 The concrete admixture composition prepared in step (1) above was added, with a dosage of 1 wt.% of the cementitious material; the concrete slump, bleeding rate and 28-day compressive strength improvement rate were tested and recorded in Table 1.

[0076] Table 1

[0077] Furthermore, the solubility test in step (1) and the concrete performance test in step (3) were carried out in each of the comparative examples 1 to 2, and the results are recorded in Table 2.

[0078] Table 2

[0079] As shown in Table 2, in Example 1, AA is highly hydrophilic, and HEA's hydroxyl groups enhance hydrogen bonding and compatibility, forming an elastic water-holding network in a synergistic combination. In Example 2, MAA provides responsiveness and rigidity, and EA enhances toughness and salt resistance, making the combination suitable for harsh environments. In contrast, in Comparative Example 1, AA is highly hydrophilic and has high swelling, but the gel is soft and has slightly weaker long-term water retention. In Comparative Example 2, MAA has high rigidity, slow dissolution, low swelling ratio, and average initial water-locking efficiency.

[0080] Furthermore, pH response tests were conducted in step (2) above for each of the comparative examples 3 to 4, and the gel state at pH=12 was recorded. At the same time, concrete performance tests were conducted in step (3), and the results are recorded in Table 3.

[0081] Table 3

[0082] As shown in Table 3, in Example 1, the amount of crosslinking agent was appropriate, the network density was moderate, the water-holding capacity was strong and stable, and the water release rate was reasonable. In contrast, in Comparative Example 3, the amount of crosslinking agent was too small, the network was too sparse, the water-holding capacity was poor, and it was easily damaged; in Comparative Example 4, the amount of crosslinking agent was too high, the network was too dense, which inhibited swelling, reduced the total water absorption, and resulted in slow water release. Furthermore, if the amount of crosslinking agent is too low, the concrete will not hold enough water; if it is too high, it will inhibit swelling and water release.

[0083] Furthermore, the solubility test in step (1) and the concrete performance test in step (3) were carried out in each of the comparative examples 5 to 7, and the results are recorded in Table 4.

[0084] Table 4

[0085] As shown in Table 4, molecular weight regulators control the polymer chain length and distribution. For example, when the amount of molecular weight regulator used in Example 1 and Comparative Example 6 is appropriate, the resulting water-retaining polymer has a moderate molecular weight. However, if the molecular weight is too large and uneven, the solubility and dispersion will be poor, leading to the failure of the water-retaining network and a high rate of water leakage. A reasonable dosage can obtain a product with excellent solubility and dispersibility, ensuring a uniform and efficient water-retaining network.

[0086] Furthermore, the products of Example 1 and Comparative Example 8 were subjected to appearance inspection, and the solubility test in step (1) and the concrete performance test in step (3) were also performed as described above. The results showed that the polymer product powder in Example 1 was stable, uniform, and fluffy; while Comparative Example 8, due to the lack of stabilizer, had uneven viscosity, contained colloids, and the powder clumped. Moreover, Comparative Example 8 showed poor stability when compounded with polycarboxylic acid, and flocculation occurred after 24 hours of compounding, with a concrete bleeding rate of 4.15%. It can be seen that the stabilizer ensures the uniformity of the synthesized product and its compatibility with polycarboxylic acid; the lack of stabilizer will lead to uneven product and flocculation during compounding, forming failure points in concrete and destroying the continuity of the water-retaining network.

[0087] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A pH-responsive concrete water-retaining agent, characterized in that, It is prepared from the following raw materials: acrylic monomers, initiators, reducing agents, crosslinking agents, molecular weight regulators, and stabilizers; The acrylic monomers include two of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, ethyl acrylate, or propyl acrylate, and the crosslinking agent includes at least one of allyl sucrose ether, glucose acrylate, or glyceryl acrylate.

2. The pH-responsive concrete water-retaining agent according to claim 1, characterized in that, The initiator includes at least one of potassium persulfate, sodium persulfate, ammonium persulfate, or hydrogen peroxide; And / or, the reducing agent includes at least one of ascorbic acid, sodium formaldehyde sulfoxylate, or E51 reducing agent; And / or, the molecular weight regulator includes at least one of sodium hypophosphite, mercaptoacetic acid, mercaptoethanol, or mercaptopropionic acid; And / or, the stabilizer includes at least one of isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, or vinyl polyoxyethylene ether.

3. The pH-responsive concrete water-retaining agent according to claim 1, characterized in that, The acrylic monomers include a combination of acrylic acid and hydroxyethyl acrylate, with a mass ratio of 2 to 4:

1.

4. The pH-responsive concrete water-retaining agent according to claim 1, characterized in that, The mass ratio of the crosslinking agent to the acrylic monomer is 0.3% to 0.7%.

5. The pH-responsive concrete water-retaining agent according to claim 1, characterized in that, In a polycarboxylate superplasticizer solution, when the pH of the polycarboxylate superplasticizer solution is 2-6 and the concentration of the polycarboxylate superplasticizer is ≤20wt.%, the water-retaining agent is added to the polycarboxylate superplasticizer solution. When the dosage of the water-retaining agent is ≤0.5wt.%, the water-retaining agent is completely dissolved in the solution and no precipitation occurs within 7 days.

6. The pH-responsive concrete water-retaining agent according to claim 1, characterized in that, In the aqueous solution of the water-retaining agent, the dosage of the water-retaining agent is set to 0.2 wt.%~0.5 wt.%, and when the pH of the aqueous solution is adjusted from 3 to 12, the volume expansion rate is >650.

7. A method for preparing a pH-responsive concrete water-retaining agent as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Prepare a reaction base containing stabilizers and initiators; prepare a first feed solution containing acrylic monomers and crosslinking agents; prepare a second feed solution containing reducing agents and molecular weight additives; The first feed solution and the second feed solution are simultaneously added dropwise to the reaction substrate to carry out a polymerization reaction; after the addition is completed, the mixture is kept at a certain temperature for curing to obtain a precursor solution. The precursor liquid was subjected to vacuum distillation and freeze-drying in sequence to obtain a water-retaining agent.

8. The preparation method according to claim 7, characterized in that, The addition of the first and second feed solutions and the duration of the polymerization reaction are 4 to 8 hours. And / or, the curing temperature is 38℃~45℃, and the curing time is 1.6h~3h.

9. A concrete admixture composition, characterized in that, The concrete admixture composition comprises a solute and a water solvent, wherein the solute comprises a pH-responsive concrete water-retaining agent as described in any one of claims 1 to 6, and a polycarboxylate superplasticizer.

10. The concrete admixture composition according to claim 9, characterized in that, The concentration of the pH-responsive concrete water-retaining agent is 0.1 wt.% to 0.5 wt.%.

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