Preparation method of high-performance concrete retarder

Abstract

The invention relates to the technical field of concrete admixtures, in particular to a preparation method of a high-performance concrete retarder. According to the method, graft copolymerization and supramolecular chemical modification are organically combined, firstly, straw fibers serve as a matrix and are subjected to free radical graft copolymerization with acrylic acid and acrylamide, carboxyl and amide functional groups are introduced, and nanofibers with a slow release function are formed; then constructing a dynamic network structure with sodium gluconate and zinc ions through supramolecular self-assembly (hydrogen bonds and coordinate bonds), compounding with the modified sweet potato powder, and performing swelling treatment to obtain the retarder. According to the retarder prepared by the method, the initial setting time reaches 9-10 hours, the final setting time reaches 10-11 hours, the compressive strength of 3d exceeds 45MPa, the compressive strength of 28d reaches 75MPa or above, and the retarder has good compatibility with a polycarboxylate superplasticizer and is free of the problem of condensation sensitivity. The method is suitable for the low-carbon fields of maritime work cement, light building materials and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete admixtures, and particularly relates to a preparation method of a high-performance concrete retarder. BACKGROUND

[0002] The concrete retarder is a key admixture for adjusting the cement hydration rate and prolonging the setting time, and is widely used in commercial concrete and large-volume engineering to avoid temperature difference cracks and ensure construction plasticity. At present, the commonly used retarders include sugars (such as sodium gluconate), citrate, phosphonate and inorganic salts, etc., but there are problems such as poor compatibility, great influence on strength, environmental sensitivity, etc. For example, comparative document 1 (CN112645624A) discloses a concrete retarder, which adopts a first retarder component, a second retarder component and zinc sulfate, and improves the retarding effect through particle size control (3-10:1) and swelling treatment, but its components rely on physical accumulation, the retarding time and low-temperature strength improvement are limited, and the component sensitivity problem is not solved; comparative document 2 (CN113185173B) uses sorbitol diethylenediamine hexanoate alkali metal salt and phosphonate for compounding, and delays hydration through complexation, which improves the compatibility, but the synthesis process is complex, the cost is high, and the low-temperature adaptability is insufficient.

[0003] The development of high-performance retarders needs to solve the limitations of existing technologies: first, the balance between retarding effect and mechanical strength, conventional modification often sacrifices strength for retarding time; second, environmental adaptability, such as performance decay at low temperature; third, compatibility with water reducing agents and other admixtures. The present application is based on chemical modification method, combining graft copolymerization with supramolecular chemical modification to design slow-release structure and dynamic network at the molecular level, which not only improves the retarding performance, but also enhances the mechanical strength of the material under harsh conditions, and is suitable for emerging fields such as low-carbon and marine cement. SUMMARY

[0004] The present application aims to provide a preparation method of a high-performance concrete retarder. The method combines graft copolymerization and supramolecular chemical modification, first grafts acrylic acid and acrylamide onto straw fibers as a matrix through free radical graft copolymerization to introduce carboxyl and amide functional groups, forming nano-fibers with slow-release function; then constructs a dynamic network structure through supramolecular self-assembly (hydrogen bonds and coordination bonds) with sodium gluconate and zinc ions, and further compounding with modified white potato powder, and then swelling treatment to obtain the retarder. The retarder prepared by the method has low dosage, functional groups are given to the material by graft copolymerization, and dynamic response is realized by supramolecular assembly, which synergistically improves the retarding performance and mechanical strength, and is suitable for low-carbon fields such as marine cement and lightweight building materials. A preparation method of a high-performance concrete retarder, comprising the following steps: S1: Straw fiber is grafted copolymerized with acrylic acid, acrylamide, and N-(hydroxymethyl)acrylamide under the initiation of sodium persulfate. The reaction temperature is 70-80℃ and the reaction time is 3-5 hours. The reaction is stopped when the viscosity reaches 5000 mPa·s by monitoring with a viscometer to obtain grafted copolymer nanofibers. S2: The grafted copolymer nanofibers obtained in step S1 are mixed with sodium gluconate and zinc sulfate in water and stirred at 40-60℃ for 1-2 hours to form a supramolecular self-assembled network structure through hydrogen bonds and zinc ion coordination bonds, thus obtaining a composite retarding component. S3: Mix the composite retarding component from step S2 with modified sweet potato powder at a weight ratio of 100:(5-20), swell in room temperature water for 2-5 minutes, and dry to obtain a high-performance concrete retarder.

[0005] More preferably, in step S1, the weight ratio of straw fiber, acrylic acid, acrylamide, and N-(hydroxymethyl)acrylamide is 100:(10-20):(5-15):(1-5), the amount of sodium persulfate added is 0.1-0.5% of the total mass, and the grafting rate is 80-90%.

[0006] More preferably, in step S2, the weight ratio of grafted copolymer nanofibers, sodium gluconate, and zinc sulfate is 10:(1-5):(0.1-1), and supramolecular self-assembly is carried out under pH 7-9 conditions with a stirring speed of 200-350 rpm.

[0007] More preferably, in step S2, the supramolecular self-assembled network structure is formed through dynamic hydrogen bonds and coordination bonds between zinc ions and carboxyl groups, wherein the zinc ions are derived from zinc sulfate.

[0008] More preferably, in step S3, the amount of water used for swelling treatment is 2-5 times the weight of the composite retarding component, and the moisture content of the material after swelling is controlled at 10-22%.

[0009] More preferably, the straw fiber is derived from corn straw, pretreated with acetic acid at a concentration of 50-60%, at a temperature of 50-60℃ for 2-4 hours, and ultrasonically dispersed at a power of 400-550W for 20-35 minutes; the average particle size of the grafted copolymer nanofiber is 5-10μm, and the specific surface area of ​​the composite retarding component is 50-100m² / g; the retarder is added to the concrete at a dosage of 0.5-1.0% of the total mass of the adhesive material, which includes cement and fly ash.

[0010] More preferably, the preparation method of the modified sweet potato flour in step S3 is as follows: sweet potato flour and 2-chloroethylphosphonic acid are mixed at a weight ratio of 100:(10-20), and an etherification reaction is carried out under alkaline conditions; the reaction pH is controlled at 10-11, the reaction temperature is 60-80℃, and the reaction time is 4-6 hours; the reaction is carried out under nitrogen protection, and the stirring speed is 200-300 rpm; after the reaction, the mixture is washed with ethanol and dried to obtain phosphonic acid-modified sweet potato flour.

[0011] In a further preferred embodiment, the alkaline conditions in the preparation method of modified sweet potato flour are achieved by adding sodium hydroxide solution, wherein the amount of sodium hydroxide added is 5-10% of the weight of sweet potato flour; the degree of substitution of the phosphonic acid-modified sweet potato flour is 0.1-0.3, and the phosphorus content is 2-5%.

[0012] The high-performance concrete retarder prepared by this invention is suitable for marine cement, lightweight building materials and special low-carbon concrete.

[0013] In a further preferred embodiment, the retarder introduces carboxyl and amide functional groups through graft copolymerization to form nanofibers with slow-release function, and constructs a dynamic network structure through supramolecular self-assembly with sodium gluconate and zinc ions. The dynamic network structure is formed through hydrogen bonds and coordination bonds between zinc ions and carboxyl groups, realizing the intelligent release of cement hydration ions, thereby prolonging the setting time and improving compressive strength. At the same time, the modified sweet potato powder is swollen and interpenetrated with the supramolecular network to optimize the pore structure and enhance the stability of the hydration microenvironment at low temperatures.

[0014] The core innovation of this invention lies in the organic combination of graft copolymerization and supramolecular chemical modification to construct a retarder structure with dynamic response and functional synergy. Graft copolymerization uses straw fiber as the matrix, introducing acrylic acid and acrylamide to form nanofibers grafted with carboxyl and amide functional groups through free radical reactions, endowing the material with slow-release capability and hydrophilicity. Supramolecular chemical modification utilizes sodium gluconate to form a self-assembled network with zinc ions through hydrogen bonds and coordination bonds, dynamically regulating the concentration of hydrated ions and delaying cement setting. The two modifications work synergistically: graft copolymerization provides functional group anchors, while supramolecular assembly enhances network stability, enabling the retarder to form an intelligent release system in the cement paste. This extends the setting time while simultaneously improving early strength through network structural support.

[0015] Furthermore, the introduction of modified sweet potato flour, through swelling treatment and interpenetration with a supramolecular network, further optimizes the pore structure and enhances the stability of the hydration microenvironment at low temperatures. This method breaks through the traditional trade-off between "retardation and strength" in retarders, achieving high performance.

[0016] The role of modified sweet potato flour in this invention: Phosphonic acid-modified sweet potato flour enhances the crosslinking density and stability of the dynamic network by introducing phosphonic acid groups that form stable coordination bonds with zinc ions in the supramolecular network. During the swelling process, this modified sweet potato flour more readily interpenetrates with grafted copolymer nanofibers and sodium gluconate, forming a denser ion-releasing system. The phosphonic acid groups chelate with calcium ions in the cement paste, delaying the formation of hydration products and significantly extending the setting time. Simultaneously, its dynamic coordination bonds provide support in the early stages of cement hydration, improving the microstructure and enhancing early strength and durability. Compared to unmodified sweet potato flour, the modified retarder exhibits a more uniform retarding effect, further improved compatibility with polycarboxylate superplasticizers, increased paste fluidity, and improved low-temperature compressive strength retention, making it suitable for harsh environments such as marine cement. Overall, the modified sweet potato flour, through the synergistic effect of chemical bonding and supramolecular assembly, overcomes the limitations of traditional retarders in the retarding-strength trade-off, achieving high performance.

[0017] The following is the chemical formula for preparing modified sweet potato flour: Starch-OH+Cl-CH2-CH2-PO(OH)2+NaOH→Starch-O-CH2-CH2-PO(OH)2+NaCl+H2O; Starch-OH represents the hydroxyl group in sweet potato flour, and an ethyl phosphonate group (-O-CH2-CH2-PO(OH)2) is introduced after the reaction.

[0018] Beneficial technical effects of the present invention 1. High efficiency in retarding setting: At a dosage of 0.5%, the initial setting time reaches 9-10 hours and the final setting time is 10-11 hours, with no problem of setting sensitivity.

[0019] 2. Excellent mechanical strength: 3-day compressive strength exceeds 45MPa, and 28-day strength reaches over 75MPa, solving the problem of strength decay at low temperatures.

[0020] 3. Good compatibility: When compounded with polycarboxylate superplasticizer, the paste has good fluidity (mm) and is suitable for various engineering environments.

[0021] 4. Low carbon and environmentally friendly: Utilizing biomass raw materials such as straw fiber and sweet potato flour reduces the carbon footprint and meets the requirements for marine cement and lightweight building materials. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation process of the high-performance concrete retarder of the present invention, including graft copolymerization, supramolecular assembly and swelling treatment steps. Detailed Implementation

[0023] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0024] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or identical to those described in the embodiments of this invention may be used to implement this invention.

[0025] Unless otherwise stated, the test methods, detection methods and preparation methods disclosed in this invention all adopt conventional techniques in this technical field.

[0026] Example 1 Using corn stalks (commercially available, moisture content ≤10%, particle size ≤1mm) as raw material, pre-treatment was performed by soaking in 55% acetic acid solution at 60℃ for 3 hours to remove lignin and hemicellulose. After drying, the stalks were pulverized to obtain straw fiber. 100g of this straw fiber was mixed with 2000ml of deionized water and treated in an ultrasonic disperser (500W) for 30 minutes to form a uniform suspension as the first raw material. Subsequently, 10g of sodium hydroxide was dissolved in 100ml of deionized water, and 15g of acrylic acid was slowly added for neutralization reaction, with the temperature controlled below 40℃, to generate sodium acrylate solution as the second raw material. Separately, 10g of acrylamide and 3g of N-(hydroxymethyl)acrylamide were dissolved in 130ml of deionized water and stirred until completely dissolved as the third raw material. The first, second, and third raw materials were mixed and poured into a reaction vessel, and the temperature was raised to 75℃ within 5 hours, with 0.3g of persulfate added. Sodium-initiated free radical graft copolymerization reaction was carried out at a stirring speed of 200 rpm for 4 hours. The reaction was stopped when the viscosity reached 5000 mPa·s, yielding graft copolymer nanofibers with an average particle size of 8 μm and a BET specific surface area of ​​85 m² / g, as measured by a laser particle size analyzer. Then, 10 g of the nanofibers were mixed with 3 g of sodium gluconate and 0.5 g of zinc sulfate in 500 mL of deionized water. The pH was adjusted to 8.0 with 1 mol / L sodium hydroxide solution, and the mixture was stirred at 300 rpm for 1.5 hours in a 50 °C water bath to form a supramolecular self-assembled network structure, resulting in a composite retarder. Finally, the composite component was mixed with 2 g of modified sweet potato flour, and 30 mL of deionized water was added. The mixture was swelled at 25 °C for 3 minutes to allow the water to penetrate evenly to a moisture content of 18%. The mixture was then dried in a 60 °C oven to constant weight and pulverized through a 200-mesh sieve to obtain a high-performance concrete retarder.

[0027] Preparation of the modified sweet potato flour: Sweet potato flour was etherified with 2-chloroethylphosphonic acid under alkaline conditions to introduce phosphonic acid ethyl groups. The specific steps included: taking 100 parts by weight of dried sweet potato flour (commercially available, passed through a 100-mesh sieve) and dispersing it in 300 parts by weight of deionized water to form a suspension; adding 15 parts by weight of 2-chloroethylphosphonic acid (chemically pure, content ≥95%), and slowly adding 8 parts by weight of sodium hydroxide solution (concentration 15%) to adjust the pH to 10.5. Under nitrogen protection, the temperature was raised to 70℃, and the reaction was stirred at 250 rpm for 5 hours. After the reaction was completed, the mixture was cooled to room temperature, the precipitate was washed three times with ethanol to remove unreacted material, and then dried in a 60℃ oven to constant weight to obtain phosphonic acid-modified sweet potato flour.

[0028] Example 2 Example 2 optimized the graft copolymerization parameters to enhance network density based on Example 1: In the pretreatment stage, 100g of corn stalks were treated with 55% acetic acid to obtain stalk fibers, which were then ultrasonically dispersed with 2000ml of deionized water; in the preparation of the second raw material, the amount of sodium hydroxide was increased to 12g, which was reacted with 20g of acrylic acid at 35°C to generate sodium acrylate solution; in the third raw material, the amount of acrylamide was adjusted to 12g, and N-(hydroxymethyl)acrylamide was increased to 4g, which was dissolved in 140ml of deionized water; after mixing the raw materials, the temperature was increased to 80°C in the reactor using a programmed temperature rise method within 2 hours, 0.4g of sodium persulfate initiator was added, and the reaction was maintained at a stirring speed of 250rpm for 3 hours. The results were determined by gel permeation chromatography (GPC). The grafting rate reached 85%, yielding grafted copolymer nanofibers with an average particle size of 10 μm and a BET specific surface area of ​​78 m² / g. In the supramolecular assembly stage, 10 g of the nanofibers were mixed with 4 g of sodium gluconate and 0.8 g of zinc sulfate in 600 mL of deionized water. The pH was adjusted to 8.5 with sodium hydroxide, and the mixture was stirred at 350 rpm for 2 hours in a 60°C water bath. During the swelling treatment, the composite component was mixed with 15 g of modified sweet potato flour, and 45 mL of deionized water was added to swell for 4 minutes until the moisture content reached 20%. The mixture was then dried at 55°C until the moisture content reached 12%. The higher grafting density and assembly temperature enhanced the supramolecular network stability, extending the retardation time but slightly reducing the fluidity, making it suitable for marine cement environments with higher retardation requirements.

[0029] The preparation method for modified sweet potato flour is the same as above.

[0030] Example 3 Example 3 optimizes dynamic response performance by adjusting the supramolecular assembly ratio: The graft copolymerization step is the same as in Example 1, yielding nanofibers with an average particle size of 8 μm; in supramolecular assembly, 10 g of nanofibers are mixed with 5 g of sodium gluconate and 1 g of zinc sulfate in 500 ml of deionized water, and the pH is precisely adjusted to 7.5 with hydrochloric acid and sodium hydroxide. The mixture is stirred at 280 rpm for 1 hour in a 55°C water bath. During the swelling treatment, the composite component is mixed with 10 g of modified sweet potato flour, and 40 ml of deionized water is added to swell for 5 minutes. The moisture content is controlled to 22%, and the mixture is dried at 65°C to a moisture content of 10%. This retarder, due to the optimized molar ratio of sodium gluconate to zinc ions to 5:1, forms a more efficient ion-release system, significantly improving early strength while maintaining a long retarding time. The improved fluidity stems from balanced intermolecular forces, making it suitable for high-fluidity concrete in lightweight building materials.

[0031] The preparation method for modified sweet potato flour is the same as above.

[0032] Comparative Example 1 Comparative Example 1 aims to verify the importance of the graft copolymerization step. Comparative Example 1 omitted graft copolymerization and directly used unmodified straw fiber. The results showed that the lack of carboxyl and amide functional groups prevented the formation of a sustained-release carrier, leading to shortened coagulation time, decreased strength, and poor compatibility. This highlights the necessity of graft copolymerization for introducing functional groups and constructing sustained-release structures. Comparative Example 1 omitted the graft copolymerization step and directly used unmodified straw fiber: 100g of corn straw was pretreated with 55% acetic acid and then crushed. It was then physically mixed with 3g of sodium gluconate and 0.5g of zinc sulfate in 500ml of deionized water. There was no supramolecular assembly process, and it was only stirred at 200rpm for 30 minutes. Then it was mixed with 2g of modified sweet potato flour, and 30ml of water was added to swell for 3 minutes. After drying, a retarder was obtained. Due to the lack of grafted functional groups, the straw fiber could not form a slow-release carrier. The accelerated hydration led to a shortened coagulation time. Moreover, without supramolecular network support, the strength was significantly reduced, and the poor compatibility was manifested as low fluidity.

[0033] The preparation method for modified sweet potato flour is the same as above.

[0034] Comparative Example 2 Comparative Example 2 aimed to verify the importance of zinc ion coordination bonds in supramolecular assembly. Zinc sulfate (zinc ions) was omitted in Comparative Example 2, and assembly relied solely on hydrogen bonds. The results showed that the lack of zinc ion coordination bonds led to an incomplete dynamic network, excessively rapid release of sodium gluconate, weakened retarding effect, and low low-temperature strength retention, highlighting the role of zinc ions in enhancing network stability and dynamic response.

[0035] Comparative Example 2 omits zinc ion coordination in supramolecular assembly: The graft copolymerization steps are the same as in Example 1, yielding 8 μm nanofibers; however, zinc sulfate is omitted, and 10 g of nanofibers are physically mixed with 3 g of sodium gluconate in 500 mL of water without pH adjustment, and stirred at 200 rpm for 1 hour; subsequently, 2 g of modified sweet potato powder is added to swell for 3 minutes and then dried; due to the lack of zinc ion coordination bonds, the supramolecular network is incomplete, sodium gluconate is released too quickly, the retarding effect is weakened, and the insufficient network dynamics result in low strength retention at low temperatures.

[0036] The preparation method for modified sweet potato flour is the same as above.

[0037] Comparative Example 3 Comparative Example 3 aimed to verify the importance of swelling treatment. Swelling treatment was omitted in Comparative Example 3, and the modified sweet potato flour was directly dry-mixed. The results showed that the modified sweet potato flour did not fully interpenetrate with the supramolecular network, resulting in uneven component dispersion and limited slow-release function. This led to a decrease in retarding time and strength, highlighting the crucial role of swelling treatment in optimizing pore structure and enhancing performance.

[0038] Comparative Example 3 omitted the swelling treatment: the graft copolymerization and supramolecular assembly steps were the same as in Example 1, and a composite retarding component was obtained; however, it was directly dry-mixed with 2 grams of modified sweet potato powder without the water swelling process, and only mechanically mixed and then dried; due to the lack of swelling, the modified sweet potato powder did not fully interpenetrate with the supramolecular network, the component was unevenly dispersed, the slow-release function was limited, and the retarding time and strength were lower than those in Example 1.

[0039] The preparation method for modified sweet potato flour is the same as above.

[0040] Comparative Example 4 Comparative Example 4 aims to verify the differences between this invention and Chinese Invention Patent CN112645624A. Referring to Chinese Invention Patent CN112645624A, Comparative Example 4 relies on physical stacking and swelling, but lacks a supramolecular dynamic network. The results show poor retarding effect and strength, especially insufficient low-temperature adaptability, highlighting the superiority of the supramolecular assembly of this invention.

[0041] Comparative Example 4 was prepared according to Chinese Invention Patent CN112645624A: The raw materials for the first and second retarding components were nanofibers and sodium gluconate in a weight ratio of 100:7. They were prepared by the method of Example 1, but the particle size was controlled. The average particle size of the first component was 7 mm, and that of the second component was 1 mm. The second component was swollen in room temperature water for 2 minutes, and then mixed with the first component and zinc sulfate in a weight ratio of 10:3:1. Although the retarding was improved by physical stacking and swelling, it lacked a molecular dynamic network, had poor low-temperature adaptability, and was highly sensitive to components.

[0042] Comparative Example 5 Comparative Example 5 aims to verify the differences between this invention and Chinese Invention Patent CN113185173B. Referring to Chinese Invention Patent CN113185173B, Comparative Example 5 uses a complex synthesis process and static complexation without a dynamic network. The results show that the retarding time is short, the strength is low, and the cost is high, highlighting the simple process and superior performance of this invention.

[0043] Comparative Example 5 was prepared according to Chinese Invention Patent CN113185173B: Sodium sorbitol diethylenediamine hexaacetate was first synthesized, and dibromosorbate was obtained by reacting sorbitol and hydrogen bromide in a molar ratio of 1:2. Then, it was reacted with ethylenediamine in a molar ratio of 1:2.2 to generate sorbitol diethylenediamine. Finally, it was reacted with sodium chloroacetate in a molar ratio of 1:6.3 at 70°C with potassium bromide catalysis for 6 hours. 15 parts of this product were taken and stirred with 10 parts of 2-phosphonobutane-1,2,4-tricarboxylic acid, 6 parts of aminotrimethylphosphonic acid, 4 parts of potassium tetraborate, and 50 parts of water at 40°C for 30 minutes to obtain a retarder. Because it relies on static complexation and has no dynamic response network, the retarding time is short, and the synthesis steps are cumbersome and costly, making it unsuitable for low-carbon requirements.

[0044] Comparative Example 6 Comparative Example 6 aims to verify the effect of modified sweet potato flour on the technical effect of this invention.

[0045] Compared with Example 1, unmodified sweet potato flour was used, while other steps, quantities, reaction conditions, etc. were the same as in Example 1.

[0046] Performance testing To further illustrate the beneficial technical effects of the novel concrete retarder involved in the embodiments of the present invention, the retarders prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests. The specific test method was to add the test samples to ordinary concrete at 40°C and test the initial setting time, final setting time, and compressive strength of the concrete at 3 days and 28 days (see Table 1 below).

[0047] The initial setting time and final setting time were tested according to GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The retarder dosage was 0.5% of the binder (as is known in the industry, binder refers to cement and fly ash). The compressive strength of concrete was tested according to the method specified in GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0048] Concrete mix proportion (kg / m³) 3 Parameters: Cement 420, Fly ash 80, Manufactured sand 715, Aggregate 1100, Water 155; Table 1 Product Performance Evaluation Table To further illustrate the good compatibility of the novel concrete retarder with admixtures involved in the embodiments of the present invention, the novel concrete retarders prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to cement paste fluidity tests. The specific test methods followed the cement paste fluidity test method in GB / T8077-2012 "Standard for Homogeneous Test Methods of Concrete Admixtures". The test data are shown in Table 2.

[0049] Table 2 Experimental data of cement paste As can be seen from Tables 1 and 2 above, the following reasonable inferences can be made by analyzing Examples 1-3 and Comparative Examples 1-6: Possible reasons for the differences in test results in Examples 1-3: The differences in the test results of Examples 1-3 mainly stemmed from adjustments to the graft copolymerization parameters and supramolecular assembly ratio, leading to subtle changes in network structure and sustained-release performance. Example 1, using standard parameters (graft copolymerization reaction temperature 75℃, time 4 hours, supramolecular assembly pH 8.0, sodium gluconate to zinc ion ratio 6:1), formed a balanced dynamic network with an initial setting time of 10:10, a final setting time of 11:10, and a 3-day compressive strength of 55.6 MPa, exhibiting the best performance. Example 2 increased the grafting density (acrylic acid increased to 20 g, N-(hydroxymethyl)acrylamide increased to 4 g) and the assembly temperature (60℃), resulting in a denser network and a slightly longer retarding time (initial setting time 10:01, final setting time 10:45), but the strength decreased slightly (3-day strength 51.2 MPa), as the increased network rigidity may have limited the ion release rate. Example 3 optimized the supramolecular assembly ratio (sodium gluconate to zinc ion ratio 5:1, pH 7.5), enhancing dynamic responsiveness and slightly shortening the retardation time (initial setting 9:50, final setting 10:30). The increased zinc ion coordination sites facilitated more intelligent ion regulation. These adjustments demonstrate that by controlling the grafting rate and assembly conditions, the release kinetics and mechanical properties of the retarder can be finely tuned to meet different engineering needs (such as long retardation for marine cement and high early strength for lightweight materials).

[0050] The difference between the test results of the examples and Comparative Example 1 mainly stems from the fact that Comparative Example 1 omitted the graft copolymerization step and directly used unmodified straw fibers, resulting in the inability to form an effective slow-release structure and dynamic network. Graft copolymerization is crucial; it introduces carboxyl and amide functional groups. These functional groups not only endow the nanofibers with hydrophilicity and slow-release function but also provide anchor points for supramolecular assembly. In Comparative Example 1, the unmodified straw fibers only bind with sodium gluconate and zinc ions through physical mixing, lacking chemical bonding. Therefore, a stable dynamic network cannot be constructed, sodium gluconate is released too quickly, hydration is accelerated, and the setting time is significantly shortened. Simultaneously, the lack of graft functional groups leads to poor compatibility between the fibers and cement paste, reduced paste fluidity, and a lack of network support strength, resulting in decreased compressive strength. This indicates that graft copolymerization is essential for achieving functionalization, slow-release function, and network stability; its absence directly weakens the overall performance of the retarder.

[0051] The difference between the test results of Example 1 and Comparative Example 2 mainly stems from the fact that Comparative Example 2 omitted the zinc ion coordination bonds in the supramolecular assembly, relying solely on hydrogen bonds for self-assembly, resulting in an incomplete dynamic network and limited functionality. The coordination bonds between zinc ions and carboxyl groups are a core component of the supramolecular network, enhancing its stability and dynamic responsiveness. Through reversible bonding, it regulates the concentration of hydrated ions, achieving intelligent release. In Comparative Example 2, the absence of zinc ion coordination bonds meant the network relied solely on hydrogen bonds for maintenance, resulting in insufficient strength and susceptibility to damage. This led to an accelerated release rate of sodium gluconate and a weakened retarding effect. Furthermore, the reduced network dynamism resulted in poor low-temperature adaptability, low strength retention, and decreased pulp fluidity, as the network could not effectively regulate pulp flowability. This demonstrates that zinc ion coordination bonds are indispensable for constructing a dynamic network, extending retarding time, and improving environmental adaptability.

[0052] The difference between the test results of the examples and Comparative Example 3 mainly stems from the fact that Comparative Example 3 omitted the swelling treatment and directly dry-mixed the modified sweet potato flour. This resulted in the modified sweet potato flour not being able to fully interpenetrate with the supramolecular network, affecting the dispersibility and functional synergy of the components. The swelling treatment causes the modified sweet potato flour to absorb water and swell, forming an interpenetrating structure with the supramolecular network, optimizing pore distribution, and enhancing the slow-release function and low-temperature stability. In Comparative Example 3, the dry-mixing method led to uneven distribution of the modified sweet potato flour, which could not effectively fill the network pores, limiting the slow-release function and shortening the setting time. Simultaneously, the lack of a swollen interpenetrating structure weakened the network's support for the hydration microenvironment, significantly reducing compressive strength and decreasing the fluidity of the slurry, as component agglomeration affected the slurry uniformity. This indicates that the swelling treatment is crucial for achieving the synergistic effect between the modified sweet potato flour and the network, optimizing the microstructure, and improving performance.

[0053] The difference between the test results of the examples and Comparative Example 4 mainly stems from the fact that Comparative Example 4, referencing Chinese Invention Patent CN112645624A, relies on physical stacking and swelling, but lacks a supramolecular dynamic network, resulting in insufficient retarding effect and strength. Chinese Invention Patent CN112645624A improves retarding through particle size control and swelling treatment, but this method is based on physical barriers and cannot achieve intelligent release at the molecular level. In Comparative Example 4, the lack of graft copolymerization and supramolecular assembly leads to a lack of network dynamism, uncontrollable sodium gluconate release, short setting time, and the inability of physical stacking to effectively support cement hydration, resulting in low compressive strength. Simultaneously, it exhibits high component sensitivity and poor paste fluidity, especially with significant performance degradation at low temperatures. This indicates that the supramolecular dynamic network of the present invention provides more precise ion regulation and environmental adaptability, overcoming the limitations of physical methods.

[0054] The difference between the test results of the examples and Comparative Example 5 mainly stems from the fact that Comparative Example 5, based on Chinese Invention Patent CN113185173B, uses a complex synthesis process and static complexation without a dynamic network, resulting in short setting time, low strength, and high cost. Chinese Invention Patent CN113185173B relies on the static complexation of sorbitol derivatives and phosphonic acids, which can delay hydration, but the fixed complexation effect cannot dynamically respond to environmental changes, thus limiting the retarding effect. In Comparative Example 5, the synthesis steps are cumbersome (multi-step reactions and catalysis), introducing impurities and uncertainties, resulting in lower compressive strength and generally poor pulp fluidity, as static complexation cannot optimize pulp rheology. Furthermore, the high-cost raw materials and process do not meet low-carbon requirements. In contrast, the graft copolymerization and supramolecular assembly of this invention simplify the process, achieving intelligent release through a dynamic network, thus improving performance and environmental friendliness.

[0055] The difference between the test results of Example 1 and Comparative Example 6 is mainly due to the fact that Comparative Example 6 used unmodified sweet potato flour, while Example 1 used phosphonic acid-modified sweet potato flour. Unmodified sweet potato flour lacks the introduced phosphonic acid groups, making it unable to form stable coordination bonds with zinc ions in the supramolecular network. This results in insufficient cross-linking density and decreased stability of the dynamic network, excessively rapid release of sodium gluconate, weakened retarding effect, and shortened setting time. Simultaneously, the absence of phosphonic acid groups weakens the chelation effect with calcium ions in the cement paste, reducing hydration retardation capacity, decreasing compressive strength, and causing uneven component dispersion, poor compatibility with polycarboxylate superplasticizer, and reduced paste fluidity. This indicates that modified sweet potato flour, through chemical bonding, enhances network synergy, which is crucial for optimizing retarding performance and mechanical strength.

[0056] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high performance concrete retarder, characterized by, The method comprises the following steps: S1: free radical graft copolymerization of straw fiber, acrylic acid, acrylamide and N-(hydroxymethyl) acrylamide is carried out under sodium persulfate initiation, the reaction temperature is 70-80 DEG C, the reaction time is 3-5 hours, the reaction is stopped when the viscosity reaches 5000 mPa s by monitoring with a viscometer, and grafted copolymerization nanofibers are obtained; S2: the grafted copolymerization nanofibers obtained in step S1 are mixed with sodium gluconate and zinc sulfate in water, stirred at 40-60 DEG C for 1-2 hours, and a supramolecular self-assembly network structure is formed through hydrogen bonds and zinc ion coordination bonds, so that a composite retarding component is obtained; S3: the composite retarding component of step S2 is mixed with modified white potato powder at a weight ratio of 100:(5-20), swells in normal temperature water for 2-5 minutes, and after drying, a high-performance concrete retarder is obtained.

2. The method for preparing the high-performance concrete retarder as described in claim 1, characterized in that: In the step S1, the weight ratio of straw fiber, acrylic acid, acrylamide and N-(hydroxymethyl) acrylamide is 100:(10-20):(5-15):(1-5), the addition amount of sodium persulfate is 0.1-0.5% of the total mass, and the grafting rate is 80-90%.

3. The preparation method of the high-performance concrete retarder as described in claim 1, characterized in that: In the step S2, the weight ratio of grafted copolymerization nanofibers, sodium gluconate and zinc sulfate is 10:(1-5):(0.1-1), the molar ratio of sodium gluconate to zinc ion is (4-6):1, and the supramolecular self-assembly is carried out under the condition of pH 7-9, and the stirring speed is 200-350 rpm.

4. The method for preparing the high-performance concrete retarder as described in claim 1, characterized in that: In the step S2, the supramolecular self-assembly network structure is formed through dynamic hydrogen bonds and zinc ion coordination bonds with carboxyl groups, and the zinc ion is derived from zinc sulfate.

5. The method for preparing the high-performance concrete retarder as described in claim 1, characterized in that: In the step S3, the amount of water used for swelling treatment is 2-5 times the weight of the composite retarding component, and the water content of the swollen material is controlled to be 10-22%.

6. The method for preparing the high-performance concrete retarder as described in claim 1, characterized in that: The straw fiber is derived from corn stalks, pretreated with acetic acid, the acetic acid concentration is 50-60%, the treatment temperature is 50-60 DEG C, the time is 2-4 hours, the ultrasonic dispersion power is 400-550 W, and the time is 20-35 minutes; the average particle size of the grafted copolymerization nanofibers is 5-10 μm, the specific surface area of the composite retarding component is 50-100 m² / g; and the dosage of the retarder in concrete is 0.5-1.0% of the total mass of the binder, which includes cement and fly ash.

7. The method for preparing the high-performance concrete retarder as described in claim 1, characterized in that, In the step S3, the preparation method of the modified white potato powder is as follows: white potato powder is mixed with 2-chloroethyl phosphonic acid at a weight ratio of 100:(10-20) under alkaline conditions to carry out etherification reaction; the reaction pH is controlled at 10-11, the reaction temperature is 60-80 DEG C, and the reaction time is 4-6 hours; the reaction is carried out under nitrogen protection, and the stirring speed is 200-300 rpm; after the reaction, ethanol washing and drying are carried out to obtain phosphonic acid group modified white potato powder.

8. The method for preparing the high-performance concrete retarder as described in claim 7, characterized in that, In the preparation method of the modified white potato powder: the alkaline condition is realized by adding sodium hydroxide solution, and the addition amount of sodium hydroxide is 5-10% of the weight of the white potato powder; the degree of substitution of the phosphonic acid group modified white potato powder is 0.1-0.3, and the phosphorus content is 2-5%.

9. The high performance concrete retarder prepared by the method of any one of claims 1-8, which is suitable for marine cement, light building material and special low-carbon concrete.

Images