Preparation process and application of modified anti-segregation admixture for machine-made sand

Abstract

The present invention discloses a preparation process and application of a modified anti-segregation admixture for machine-made sand, relating to the technical field of polymer modified materials. A steric hindrance effect is established by using modified polyoxyethylene ether and vinyltrimethoxysilane, an interpenetrating network structure is formed by introducing styrene-acrylate emulsion, and a multi-scale reinforcement system is constructed in collaboration with nano-silica and bentonite. The hydrolysis and nano-grafting reaction of the silane coupling agent are achieved by gradient heating, and an ultrasonic-mechanical synergistic emulsification process is combined to achieve an emulsion particle size distribution D90 ≤ 5μm. A composite thickener forms a three-dimensional network with anhydrous sodium sulfate. After in-situ curing at 25°C / RH ≥ 80%, the addition of 0.1-0.5% of the admixture can result in a slump retention value of > 315mm (1h) for machine-made sand concrete, a pressure water bleeding rate ≤ 9.7%, an increase in the 28d compressive strength by 24.5% to 72.6MPa, and a reduction in the anti-segregation coefficient to 0.08-0.11. This technology breaks through the limitation of traditional admixtures' insufficient adaptability to manufactured sand, and is particularly suitable for long-distance pumping construction of manufactured sand concrete with high stone powder content.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer modified materials, in particular to a preparation process and application of a modified anti-segregation admixture for machine-made sand. Background Art

[0002] As a key aggregate in modern concrete production, manufactured sand is increasingly being used. In particular, with natural sand resources becoming increasingly scarce, it is gradually replacing natural sand as one of the primary raw materials in the concrete industry. Compared to natural sand, manufactured sand offers advantages such as a controllable source and high production efficiency, but it also faces numerous challenges during production. Manufactured sand is typically produced by mechanically crushing rock. Due to the type of crushing equipment, the properties of the rock raw material, and differences in production processes, its particle characteristics exhibit distinct unique characteristics, such as uneven particle grading, a high degree of angularity, a high surface roughness, and a high content of stone dust. These characteristics give manufactured sand certain application advantages, but they also present significant technical challenges, particularly the tendency for segregation to occur during concrete preparation.

[0003] Segregation refers to the phenomenon in which coarse aggregate sinks and mortar floats during the transportation, pouring or vibration of the concrete mixture due to density differences or inconsistent fluidity between the components. This phenomenon can seriously damage the uniformity and stability of the concrete, and directly affect its working performance, such as fluidity, pumpability and construction convenience. More importantly, segregation can also have a profound impact on the performance of the concrete after hardening, such as reducing compressive strength, impermeability and durability, and even causing cracks or pores to appear inside the structure, thereby threatening the safety and service life of the project. For machine-made sand concrete, the segregation problem is particularly prominent due to its angular particles, rough surface, large friction between particles, and poor cohesion of the mixture. Therefore, how to effectively solve the segregation problem of machine-made sand concrete has become a research hotspot in the current field of concrete technology and a key demand in engineering practice.

[0004] To address the segregation problem in manufactured sand concrete, scholars and engineers at home and abroad have conducted extensive research and proposed various solutions. Among them, the use of admixtures is considered an economical and effective means of improving the performance of manufactured sand concrete. Admixtures can effectively reduce segregation and bleeding by adjusting the rheological properties of the concrete mix, enhancing its cohesiveness and water retention, and thus improving the overall quality of the concrete. Traditional concrete admixtures, such as water reducers, air entraining agents, and thickeners, can improve the performance of manufactured sand concrete to a certain extent. For example, polycarboxylate water reducers can alleviate some segregation issues by reducing water consumption and improving fluidity, while thickeners increase the viscosity of the mix and reduce the settling of coarse aggregate. However, due to the significant differences in particle shape and gradation characteristics between manufactured sand and natural sand, the role of traditional admixtures in manufactured sand concrete is often limited, making it difficult to fully meet the engineering requirements for high-performance concrete. Furthermore, the high stone powder content in manufactured sand can interact with admixtures in complex physical and chemical reactions, further weakening their effectiveness. Therefore, the development of specialized admixtures tailored to the characteristics of manufactured sand has become an urgent technical challenge.

[0005] In recent years, with the rapid development of polymer materials science, modified anti-segregation admixtures have gradually attracted attention. These admixtures, by introducing high molecular weight polymers and leveraging their unique molecular structure and chemical properties, significantly improve the rheological properties and inter-particle adhesion of concrete. Polymer-modified materials can form a network structure within concrete, enhancing the cohesion and stability of the mixture, thereby effectively inhibiting segregation. Polymer materials also exhibit excellent viscosity-increasing and water-retention properties, reducing water bleeding and improving concrete uniformity. Furthermore, research has shown that polymer-modified admixtures not only enhance the workability of concrete but also improve its mechanical properties and durability after hardening, such as freeze-thaw resistance and corrosion resistance, providing technical support for the long-life design of concrete. Therefore, modified anti-segregation admixtures are considered a solution with broad application prospects.

[0006] However, most modified anti-segregation admixtures currently on the market are designed for natural sand concrete, and their formulations and performance characteristics do not fully consider the specific needs of manufactured sand. The characteristics of manufactured sand, such as angular particles, high surface roughness, and high stone powder content, require admixtures with greater adaptability and specificity. Furthermore, existing preparation processes have limitations, such as high production costs, complex processes, and insufficient batch stability. These factors restrict the widespread application of modified anti-segregation admixtures in manufactured sand concrete. To more clearly analyze the shortcomings of the existing technology, the following detailed description is provided with reference to reference documents. Several prior art studies have been conducted on modified anti-segregation admixtures. For example, patent CN108793844A discloses a method for preparing a polymer-modified anti-segregation admixture. This method combines polymers such as polyvinyl alcohol (PVA) and polyacrylamide (PAM) with inorganic materials to produce an admixture with excellent anti-segregation properties. Experimental results have shown that this admixture significantly improves the cohesiveness of concrete and reduces segregation and bleeding. However, this patent primarily focuses on natural sand concrete and fails to fully consider the particle characteristics of manufactured sand, such as its high angularity and stone dust content. This may compromise its anti-segregation effectiveness in manufactured sand concrete. Furthermore, the preparation process is complex, involving multiple chemical reactions and compounding steps, resulting in high production costs and hindering large-scale industrial application. Another related technology, patent CN110642993A, proposes a method for preparing an anti-segregation agent specifically for manufactured sand concrete. This method utilizes silicone-modified polyacrylamide as the primary ingredient and produces the anti-segregation agent via an emulsion polymerization process. Compared to traditional admixtures, this method has made some progress in improving the anti-segregation properties of manufactured sand concrete and can effectively enhance the stability of the mixture. However, its preparation requires high temperature and high pressure, resulting in high energy consumption, and the emulsion polymerization process places stringent equipment requirements, leading to increased production costs. Furthermore, this admixture suffers from insufficient long-term storage stability, prone to delamination and performance degradation, limiting its practical application. Summary of the Invention

[0007] The existing technology suffers from the following major issues: Due to the angular shape, rough surface, and high stone dust content of manufactured sand during production, it often exhibits high friction and poor cohesion in concrete. This makes concrete prone to segregation during transportation, pouring, and vibration. While traditional admixtures such as water reducers and thickeners can alleviate this segregation problem to a certain extent, they often fail to meet the demands of high-performance concrete applications because they lack the ability to effectively modify the specific properties of manufactured sand. Most traditional admixtures are designed for natural sand concrete and fail to fully account for the angularity and surface roughness of manufactured sand particles. These admixtures are poorly adapted to manufactured sand concrete, especially in cases where the stone dust content is high. The effectiveness of these admixtures is often affected by the stone dust, preventing them from fully realizing their performance-enhancing properties. Therefore, there is an urgent need to develop admixtures specifically tailored to the characteristics of manufactured sand to address the shortcomings of traditional admixtures in manufactured sand concrete. Manufactured sand concrete typically contains a high level of stone dust, which can easily cause surface water bleeding during cement hydration, affecting the uniformity and final hardened properties of the concrete. While traditional thickeners can reduce bleeding to a certain extent, their lack of effective moisture control means the problem remains intractable, impacting key concrete properties such as strength and durability. Currently, the preparation processes for most manufactured sand admixtures on the market are complex, often involving multiple chemical reaction steps and requiring a wide variety of raw materials. This results in high production costs and low process efficiency. Furthermore, some traditional admixtures require high temperatures and pressures during production, requiring high equipment requirements and consuming large amounts of energy. This further increases production costs and hinders large-scale industrial application. Existing modified admixtures are prone to performance degradation, stratification, or precipitation during long-term storage, impacting their effectiveness. Especially in high-temperature and humid environments, admixtures exhibit poor stability and are prone to uneven distribution, resulting in unstable application in concrete. Prolonged storage of admixtures can lead to fluctuations in concrete quality, impacting the quality and safety of projects. While some admixtures have made some progress in improving the fluidity and pumpability of manufactured sand concrete, significant deficiencies remain in enhancing the mechanical properties of hardened concrete, such as compressive strength, crack resistance, and durability. Existing admixtures fail to effectively enhance concrete's toughness and crack resistance, particularly under extreme conditions such as high strain rates and dynamic loads. This limits their application in projects requiring high strength and durability. The present invention addresses these shortcomings in the prior art by providing a modified, anti-segregation admixture for manufactured sand and its preparation process.The present invention introduces a variety of polymer compounds such as modified polyoxyethylene ether, vinyl trimethoxysilane and styrene-acrylate emulsion, constructs a steric hindrance effect and an interpenetrating network structure, and combines materials such as nano-silica and bentonite to form a multi-scale reinforcement system, which effectively solves the problems of segregation and bleeding of machine-made sand concrete. By adopting advanced technologies such as gradient heating and ultrasonic-mechanical collaborative emulsification, the emulsion particle size of the admixture is accurately controlled, and the three-dimensional network structure formed by the composite thickener and anhydrous sodium sulfate can greatly improve the cohesion and stability of the concrete, thereby effectively improving the fluidity, pumpability and compressive strength of the concrete. In addition, the present invention simplifies the production process, reduces production costs, and improves the stability and adaptability of the product by optimizing the preparation process of the admixture, so that it has a wide range of application prospects, and is particularly suitable for long-distance pumping construction of machine-made sand concrete with high stone powder content.

[0008] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a process for preparing a modified anti-segregation admixture for machine-made sand, comprising the following steps: (1) gradient heating reaction: preparing modified polyoxyethylene ether, vinyltrimethoxysilane, nano-silica, anhydrous sodium sulfate, a thickener, a polycarboxylic acid water reducer and deionized water, mixing the above-mentioned components according to a proportion, first hydrolyzing them, and then carrying out a grafting reaction; (2) ultrasonic-mechanical synergistic emulsification: first ultrasonically dispersing the reaction product obtained in step (1), and then mechanically stirring it; (3) in-situ curing control: transferring the emulsified product obtained in step (2) to a constant temperature and humidity environment for curing; wherein the preparation method of modified polyoxyethylene ether is as follows: the preparation method of modified polyoxyethylene ether The method comprises: reacting polyoxyethylene ether (CAS No.: 9004-95-9) with a modifier in the presence of a catalyst, wherein the modifier is selected from one or a combination of acrylic acid (CAS No.: 79-10-7), methacrylic acid (CAS No.: 79-41-4) or maleic anhydride (CAS No.: 108-31-6), with a mass ratio of polyoxyethylene ether:modifier = 10:1-15:1; the catalyst is p-toluenesulfonic acid (CAS No.: 104-15-4) or sulfuric acid, with an amount of 0.5-1.0% of the total mass of the reactants; the reaction is carried out at 80-120°C for 3-6 hours, and after the reaction is completed, unreacted monomers are removed by reduced pressure distillation, and the grafting rate of the obtained modified polyoxyethylene ether is ≥85%.

[0009] Preferably, in step (1), the mass ratio of modified polyoxyethylene ether, vinyl trimethoxysilane (CAS No. 2768-02-7), nano-silica, anhydrous sodium sulfate, thickener, polycarboxylate water reducer and deionized water is (4.5-5.5): (1.8-2.2): (0.05-0.15): (0.5-1.5): (2.2-2.8): (8-12): (20-30); wherein the average particle size of the nano-silica is 10-20 nm, and the specific surface area is ≥200 m 2 / g; the thickener is a mixture of guar gum and maltodextrin in a mass ratio of 2:1, the viscosity of guar gum (CAS number is 9000-30-0) is 5000mPa·s, and the glucose equivalent of maltodextrin (CAS number is 9050-36-6) is 15-20.

[0010] Preferably, the hydrolysis method in step (1) is as follows: the hydrolysis reaction is carried out at a constant temperature of 50±2°C for 1-2 hours, and the stirring speed is controlled at 200-300 rpm during the hydrolysis process; the grafting reaction method in step (1) is as follows: the temperature is then raised to 65±5°C, and the grafting reaction is carried out for 1.5-3 hours. During the grafting reaction, nitrogen protection is introduced at an air flow rate of 0.1-0.2 L / min.

[0011] Preferably, the ultrasonic dispersion method in step (2) is as follows: placing in a 20-40kHz ultrasonic device for dispersion for 20-40 minutes, the ultrasonic power is 300-400W, and the temperature is controlled at 30-35°C during the dispersion process; the mechanical stirring method in step (2) is as follows: mechanical stirring is performed at a speed of 1500-2000rpm for 40-60 minutes.

[0012] Preferably, the curing temperature in step (3) is 25±2°C, the curing relative humidity is ≥80%, and the curing method is to stand for 24 hours.

[0013] The application of the admixture prepared by the preparation process described above.

[0014] Preferably, the dosage form of the admixture is an acceptable dosage form for concrete additives.

[0015] Preferably, the dosage form of the admixture is an emulsion.

[0016] Preferably, the weight of the admixture is 0.1%-0.5% of the concrete.

[0017] Beneficial effects

[0018] The modified anti-segregation admixture for machine-made sand and its preparation process provided by the present invention have significant technical advantages and application value, can effectively solve the segregation and bleeding problems commonly existing in machine-made sand concrete during the construction process, and at the same time improve the working performance of concrete and the mechanical properties after hardening. Specifically, the admixture of the present invention has the following beneficial effects: effectively reducing the segregation phenomenon of machine-made sand concrete: machine-made sand concrete is prone to segregation during actual construction, especially when pumped over long distances, that is, coarse aggregate sinks and mortar floats, resulting in concrete inhomogeneity and affecting its overall performance. Traditional admixtures have poor adaptability in machine-made sand concrete and cannot effectively solve the segregation problem. The present invention, by adopting the synergistic effect of modified polyoxyethylene ether and vinyltrimethoxysilane, constructs a molecular structure with a steric hindrance effect, forming an interpenetrating network structure, which can significantly improve the cohesion and stability of concrete and inhibit the occurrence of segregation. At the same time, the three-dimensional network structure formed by the composite thickener and anhydrous sodium sulfate further enhances the cohesiveness of the concrete and reduces the separation between water and solid components, thereby effectively avoiding the segregation problem of machine-made sand concrete. Improving the anti-bleeding performance of concrete: Bleeding is the phenomenon of water loss caused by the migration of water to the surface of concrete during the curing process, which usually affects the durability and strength of concrete. Traditional admixtures usually cannot effectively control the problem of bleeding while improving the fluidity and workability of concrete. The admixture of the present invention can significantly reduce the bleeding rate by enhancing the water retention and viscosity increasing properties of the mixture. In the present invention, a three-dimensional network structure is formed through the synergistic effect of the composite thickener and anhydrous sodium sulfate. This structure can form a good moisture retention effect in concrete, significantly reduce the occurrence of bleeding, and thus improve the overall quality and durability of concrete. Improving the fluidity and pumpability of concrete: Machine-made sand concrete usually has poor fluidity and poor pumping performance due to the characteristics of rough particle surface, many edges and corners, and uneven grading, which brings certain difficulties to construction. Through the application of the modified anti-segregation admixture of the present invention, the fluidity and pumpability of concrete can be significantly improved. The admixture can enhance the cohesiveness of concrete, so that sand and gravel aggregates of different particle sizes can be better distributed in the concrete, improve the overall fluidity of the concrete, and reduce the blockage and separation of the concrete during the pumping process. Specifically, after using this admixture, the slump retention time of the machine-made sand concrete can be maintained at more than 1h, and the slump retention value is greater than 315mm, which greatly improves the construction performance of the concrete and is especially suitable for long-distance pumping construction. Improve the compressive strength and durability of concrete: By adopting the modified anti-segregation admixture of the present invention, the 28d compressive strength of the machine-made sand concrete can be increased by 24.5%, reaching 72.6MPa.High strength is the basis of the bearing capacity of concrete structures, and the introduction of this admixture enables machine-made sand concrete to maintain high fluidity while improving its mechanical properties after hardening, especially in terms of compressive strength and crack resistance. In addition, the synergistic effect of modified polyoxyethylene ether and vinyltrimethoxysilane enhances the microstructure inside the concrete, improves the concrete's impermeability and corrosion resistance, and further improves its durability. This makes the admixture suitable for engineering projects such as bridges and tunnels that require high strength and durability. Simplify the preparation process and reduce production costs: The preparation process of the present invention adopts methods such as gradient heating, ultrasonic-mechanical collaborative emulsification and in-situ curing, which not only optimizes the performance of the admixture, but also makes the preparation process more efficient. Through reasonable temperature control and dispersion process, the present invention can effectively control the emulsion particle size distribution, making the distribution of the admixture in the concrete more uniform and enhancing the stability of its performance. In addition, the preparation method of modified polyoxyethylene ether further reduces production costs by simplifying the reaction steps and optimizing the use of catalysts, so that the admixture can be widely used in industrial production. Wide Applicability and Environmental Friendliness: The modified anti-segregation admixture of the present invention has wide applicability, demonstrating excellent performance in concrete containing high-stone powder content manufactured sand. Manufactured sand typically contains a high level of stone powder, which can easily cause segregation in concrete. The admixture of the present invention exhibits good adaptability to various types of manufactured sand, addressing this lack of adaptability. Furthermore, the admixture's rational composition, lack of harmful substances, and environmental friendliness meet current demands for green building materials.

[0019] In summary, the modified anti-segregation admixture of the present invention successfully solves the common problems of segregation and bleeding in the construction of machine-made sand concrete through innovative molecular structure design and optimized preparation process, and significantly improves the fluidity, pumpability, compressive strength and durability of concrete, and has broad application prospects and engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a physical picture of the admixture prepared in Example 1. DETAILED DESCRIPTION

[0021] In the examples of the present invention, parts by weight are equivalently replaced with kilograms (kg) or grams (g), and can be scaled up or down in the same proportion with minimal impact on the experimental results. The polycarboxylate superplasticizer used in this invention is KD-502PS, produced by Shandong Kundu Chemical Co., Ltd., which complies with GB8076-2008 and TB / T3257-2018 standards.

[0022] Example 1

[0023] The amounts of components are shown in Table 1 below.

[0024] Table 1

[0025]

[0026] The preparation process is as follows: gradient heating reaction: hydrolysis at 50°C for 1.5 hours (250 rpm) → grafting at 65°C for 2 hours (nitrogen flow rate 0.15 L / min); ultrasonic emulsification: 35kHz ultrasonic wave for 30 minutes (power 350W, temperature 32°C); mechanical stirring: stirring at 1800 rpm for 50 minutes; curing conditions: 25°C / RH85% for 24 hours. Figure 1 shown.

[0027] Performance test: Taking C30 concrete as an example, when the admixture dosage is 0.3% (i.e., 3kg of admixture is added per cubic meter of concrete). Slump retention test: Specimen preparation: Prepare fresh concrete specimens according to the "Standard for Test Methods for Properties of Ordinary Concrete Mixtures" (GB / T50080), controlling the initial slump to 320±10mm. Curing: After the concrete in the slump cone has been allowed to stand for 1 hour, re-measure the slump value according to the standard method. Measure the difference between the slump cone height (300mm) and the highest point after the specimen collapses, accurate to 1mm. Slump retention value = 300 - slump height. Pressure Bleeding Rate Determination: Using a pressure brine analyzer specified in T0531-2020, set the pressure at 3.5 MPa, place 500g of concrete into the test mold. After 10 seconds of static pressure application, apply pressure. Continue pressurizing for 140 seconds, collecting the brine volume V1. At the end of pressurization, collect V2. Pressure Bleeding Rate = (V2 - V1) / Concrete Mass × 100%. 28-day Compressive Strength Test: 150mm cubic specimens were produced according to the "Standard Test Method for Estimating Early Strength of Ready-Mixed Concrete." Standard curing was performed for 28 days. A microcomputer-controlled press was used, maintaining a loading rate of 0.5 MPa / s. The arithmetic mean of the strength values ​​of the three specimens was taken. When the maximum / minimum ratio was greater than 1.15, the median value was used. Anti-segregation coefficient test: Use a 5mm standard sieve to let a 10kg concrete sample stand for 15 minutes before sieving. Weigh the mass m of the coarse aggregate on the sieve. Anti-segregation coefficient = (m-initial coarse aggregate mass) / initial coarse aggregate mass. When the coefficient is <0.15, it is judged to be qualified for anti-segregation.

[0028] The test results are as follows: slump retention value (1h): 322mm; pressure water seepage rate: 9.2%; 28d compressive strength: 73.1MPa; anti-segregation coefficient: 0.09.

[0029] Examples 2-6

[0030] By adjusting the ratio of key components and process parameters, a series of preferred solutions are formed. The ratio of components or process parameters not listed are the same as those in Example 1, as shown in Table 2.

[0031] Table 2

[0032]

[0033] It should be noted that, for the component ratios and process parameters not listed in Table 2, their performance parameters are close to 80%-90% of the performance of Example 1.

[0034] Comparative Examples 1-10

[0035] The test was carried out based on Example 1.

[0036] Comparative Example 1: When preparing the admixture, ordinary polyoxyethylene ether was substituted for the modified polyoxyethylene ether, while other components and process steps remained unchanged. Test results: Slump retention (1h): 290mm, pressure bleeding rate: 12.5%, 28-day compressive strength: 60.2MPa, anti-segregation coefficient: 0.18. Ordinary polyoxyethylene ether lacks the steric hindrance effect brought about by the modification, resulting in insufficient cohesiveness of the concrete, exacerbated segregation and bleeding problems, and a decrease in strength.

[0037] Comparative Example 2: Vinyltrimethoxysilane was omitted from the admixture preparation, while other components and process steps remained unchanged. Test results: Slump retention (1h): 305 mm, pressure water bleeding rate: 11.8%, 28-day compressive strength: 62.5 MPa, and anti-segregation coefficient: 0.16. The lack of vinyltrimethoxysilane prevented the formation of an effective interpenetrating network structure, resulting in reduced cohesion and stability of the concrete.

[0038] Comparative Example 3: Nanosilica was omitted from the admixture preparation, while other components and process steps remained unchanged. Test results: Slump retention (1 hour): 300 mm, pressure water bleeding rate: 10.5%, 28-day compressive strength: 65.0 MPa, and anti-segregation coefficient: 0.14. The absence of nanosilica resulted in an incomplete multi-scale reinforcement system, insufficiently optimized concrete microstructure, and reduced strength and anti-segregation properties.

[0039] Comparative Example 4: In the preparation of the admixture, only guar gum was used as the thickener, replacing the composite thickener. All other components and process steps remained unchanged. Test results: Slump retention (1h): 310 mm, pressure water bleeding rate: 10.2%, 28-day compressive strength: 67.3 MPa, anti-segregation coefficient: 0.13. The synergistic effect of the composite thickener was weakened, resulting in a slight decrease in the concrete's cohesiveness and water retention.

[0040] Comparative Example 5: When preparing the admixture, the gradient heating step was omitted. All materials were mixed directly at room temperature (25°C), with all other components remaining unchanged. Test results: Slump retention (1h): 295mm, pressure water bleeding rate: 13.0%, 28-day compressive strength: 61.8MPa, anti-segregation coefficient: 0.19. The omission of the gradient heating step resulted in incomplete hydrolysis and grafting reactions of the silane coupling agent, resulting in reduced admixture performance.

[0041] Comparative Example 6: In the preparation of the admixture, only mechanical stirring was used, omitting the ultrasonic dispersion step. All other components and processes remained unchanged. Test results: Slump retention (1h): 308mm, pressure water bleeding rate: 11.0%, 28-day compressive strength: 64.5MPa, anti-segregation coefficient: 0.15. Ultrasonic dispersion promotes uniform particle size distribution in the emulsion, while mechanical stirring alone is insufficient, resulting in uneven dispersion of the admixture and reduced performance.

[0042] Comparative Example 7: After the admixture was prepared, it was cured at 40°C, with all other components and process steps remaining unchanged. Test results: Slump retention (1 hour): 312 mm, pressure water bleeding rate: 10.8%, 28-day compressive strength: 66.0 MPa, anti-segregation coefficient: 0.12. Warm curing may cause instability in certain components of the admixture, affecting its performance.

[0043] Comparative Example 8: After the admixture was prepared, it was cured at a relative humidity of 50%, with all other components and process steps remaining unchanged. Test results showed: slump retention (1 hour): 305 mm, pressure water bleeding rate: 11.5%, 28-day compressive strength: 63.2 MPa, and anti-segregation coefficient: 0.16. Low-humidity curing affected the stability and uniformity of the admixture, resulting in decreased performance.

[0044] Comparative Example 9: The admixture content in the concrete was reduced to 0.05%, while other components and process steps remained unchanged. Test results: Slump retention (1h): 285mm, pressure water bleeding rate: 14.0%, 28d compressive strength: 58.5MPa, anti-segregation coefficient: 0.20. The insufficient admixture content prevented the full modifier effect from being realized, resulting in poor concrete performance.

[0045] Comparative Example 10: The admixture content in the concrete was increased to 1.0%, while other components and process steps remained unchanged. Test results: Slump retention (1h): 330mm, pressure water bleeding rate: 8.5%, 28d compressive strength: 70.0MPa, anti-segregation coefficient: 0.07. While a higher admixture content improves some properties, it increases costs and has limited improvement in compressive strength.

[0046] The test results of Comparative Examples 1-10 above demonstrate the degradation of concrete performance when key components (such as modified polyoxyethylene ether, vinyltrimethoxysilane, and nanosilica) are missing or process parameters (such as gradient heating, ultrasonic dispersion, and curing conditions) are altered. These results demonstrate the importance of key components and process steps in the present invention. Compared with the inventive examples, the comparative examples exhibit varying degrees of inferiority in slump retention, pressure bleeding rate, compressive strength, and anti-segregation coefficient.

[0047] The above describes in detail the preferred embodiments of this patent, but this patent is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of this patent.

Claims

1. A process for preparing a modified anti-segregation admixture for machine-made sand, characterized in that: The method comprises the following steps: (1) gradient heating reaction: preparing modified polyoxyethylene ether, vinyl trimethoxysilane, nano-silica, anhydrous sodium sulfate, a thickener, a polycarboxylic acid water reducer and deionized water, mixing the above components according to a proportion, first hydrolyzing them, and then carrying out a grafting reaction; (2) ultrasonic-mechanical synergistic emulsification: first ultrasonically dispersing the reaction product obtained in step (1), and then mechanically stirring it; (3) in-situ curing control: transferring the emulsified product obtained in step (2) to a constant temperature and humidity environment for curing; The preparation method of the modified polyoxyethylene ether is as follows: the preparation method of the modified polyoxyethylene ether comprises: reacting polyoxyethylene ether with a modifier under the action of a catalyst, wherein the modifier is selected from one or a combination of acrylic acid, methacrylic acid or maleic anhydride, and the mass ratio of polyoxyethylene ether:modifier is 10:1-15:1; the catalyst is p-toluenesulfonic acid or sulfuric acid, and the amount used is 0.5-1.0% of the total mass of the reactants; the reaction is carried out at 80-120°C for 3-6 hours, and after the reaction is completed, unreacted monomers are removed by reduced pressure distillation, and the grafting rate of the obtained modified polyoxyethylene ether is ≥85%.

2. The process for preparing a modified anti-segregation admixture for machine-made sand according to claim 1, characterized in that: The mass ratios of modified polyoxyethylene ether, vinyl trimethoxysilane, nano-silica, anhydrous sodium sulfate, thickener, polycarboxylic acid water reducer and deionized water in step (1) are (4.5-5.5): (1.8-2.2): (0.05-0.15): (0.5-1.5): (2.2-2.8): (8-12): (20-30); wherein the average particle size of the nano-silica is 10-20 nm and the specific surface area is ≥200 m 2 / g; the thickener is a mixture of guar gum and maltodextrin in a mass ratio of 2:1, the viscosity of guar gum is 5000mPa·s, and the glucose equivalent of maltodextrin is 15-20.

3. The process for preparing the modified anti-segregation admixture for machine-made sand according to claim 1, characterized in that: The method for hydrolysis in step (1) is as follows: the hydrolysis reaction is carried out at a constant temperature of 50±2°C for 1-2 hours, and the stirring speed is controlled at 200-300 rpm during the hydrolysis process; the method for grafting reaction in step (1) is as follows: the temperature is then raised to 65±5°C, and the grafting reaction is carried out for 1.5-3 hours. Nitrogen protection is introduced during the grafting reaction, and the air flow rate is 0.1-0.2 L / min.

4. The process for preparing a modified anti-segregation admixture for machine-made sand according to claim 1, characterized in that: The ultrasonic dispersion method in step (2) is as follows: place it in a 20-40kHz ultrasonic device for dispersion for 20-40 minutes, the ultrasonic power is 300-400W, and the temperature is controlled at 30-35°C during the dispersion process; the mechanical stirring method in step (2) is as follows: mechanical stirring is performed at a speed of 1500-2000rpm for 40-60 minutes.

5. The process for preparing the modified anti-segregation admixture for machine-made sand according to claim 1, characterized in that: The curing temperature in step (3) is 25±2°C, the curing relative humidity is ≥80%, and the curing method is to stand for 24 hours.

6. Use of an admixture obtained by the preparation process according to any one of claims 1 to 5.

7. The use of the admixture obtained by the preparation process according to claim 6, characterized in that: The dosage form of the admixture is an acceptable dosage form for concrete additives.

8. The use of the admixture obtained by the preparation process according to claim 7, characterized in that: The dosage form of the admixture is emulsion.

9. The use of the admixture obtained by the preparation process according to claim 8, characterized in that: The weight of the admixture is 0.1%-0.5% of the concrete.

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