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

Abstract

The invention discloses a preparation process and application of a modified anti-segregation admixture for machine-made sand, and relates to the technical field of polymer modified materials. Modified polyoxyethylene ether and vinyltrimethoxysilane are adopted to construct a steric hindrance effect, styrene-acrylate emulsion is introduced to form an interpenetrating network structure, and nano silicon dioxide and bentonite are cooperated to construct a multi-scale enhancement system. Silane coupling agent hydrolysis and nano grafting reaction are realized through gradient heating, and the particle size distribution D90 of the emulsion is less than or equal to 5 microns by combining an ultrasonic-mechanical synergistic emulsification process. A three-dimensional network is formed by the composite thickening agent and anhydrous sodium sulfate, and after in-situ curing at 25 DEG C with RH greater than or equal to 80%, 0.1-0.5% of the additive is added, so that the slump retention value of the machine-made sand concrete is greater than 315mm (1h), the pressure bleeding rate is less than or equal to 9.7%, the 28d compressive strength is improved by 24.5-72.6 MPa, and the segregation resistance coefficient is reduced to 0.08-0.11. The technology breaks through the limitation of insufficient adaptability of traditional admixtures to machine-made sand, and is particularly suitable for long-distance pumping construction of high-stone-powder-content machine-made sand concrete.

Description

Technical Field

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

[0002] As an important aggregate in modern concrete production, manufactured sand is increasingly widely used. Especially in the context of the increasing shortage of natural sand resources, manufactured sand has gradually replaced natural sand and become one of the main raw materials in the concrete industry. Compared with natural sand, manufactured sand has the advantages of controllable source and high production efficiency. However, it also faces many challenges in the production process. Manufactured sand is usually produced by mechanically crushing rocks. Limited by the type of crushing equipment, the properties of rock raw materials, and the differences in production processes, its particle characteristics show obvious uniqueness, such as uneven particle size distribution, more angularity, higher surface roughness, and richer stone powder content. These characteristics endow manufactured sand with certain application advantages to a certain extent, but at the same time also bring significant technical problems, especially the segregation phenomenon is likely to occur during the concrete preparation process.

[0003] Segregation refers to the phenomenon that in the process of transportation, pouring or vibration of concrete mixtures, due to the density difference or inconsistent fluidity between components, coarse aggregates sink and mortar floats. This phenomenon will seriously damage the uniformity and stability of concrete, directly affecting its workability, such as fluidity, pumpability, and construction convenience. More importantly, segregation will also have a profound impact on the properties of hardened concrete, such as reducing compressive strength, impermeability, and durability, and even causing cracks or pores inside the structure, thus threatening the safety and service life of the project. For manufactured sand concrete, due to its more angular and rough particles, the friction between particles is larger, and the cohesion of the mixture is poor, the segregation problem is particularly prominent. Therefore, how to effectively solve the segregation problem of manufactured sand concrete has become a research hotspot in the current concrete technology field and a key requirement in engineering practice.

[0004] To address the segregation problem of manufactured-sand concrete, scholars and engineering technicians at home and abroad have conducted extensive research and proposed various solutions. Among them, the application of admixtures is considered an economical and efficient means to improve the performance of manufactured-sand concrete. By adjusting the rheological properties of the concrete mixture and enhancing its cohesiveness and water retention, admixtures can effectively reduce the occurrence of segregation and bleeding phenomena, thereby improving the overall quality of the concrete. Traditional concrete admixtures, such as water reducers, air-entraining agents, and thickeners, can improve the workability of manufactured-sand concrete to a certain extent. For example, polycarboxylate water reducers can alleviate some segregation problems by reducing water consumption and increasing fluidity; while thickeners can reduce the settlement of coarse aggregates by increasing the viscosity of the mixture. However, due to the significant differences in the particle shape and gradation characteristics between manufactured sand and natural sand, the effects of traditional admixtures in manufactured-sand concrete are often limited and difficult to fully meet the engineering requirements of high-performance concrete. In addition, the relatively high content of stone powder in manufactured sand will also have complex physical and chemical interactions with the admixtures, further weakening their effects. Therefore, developing special admixtures for the characteristics of manufactured sand has become an urgent technical problem to be solved.

[0005] In recent years, with the rapid development of polymer materials science, modified anti-segregation admixtures have gradually attracted attention. By introducing polymer polymers, these admixtures utilize their unique molecular structures and chemical characteristics to significantly improve the rheological properties of concrete and the bonding force between particles. The polymer modified materials can form a network structure in the concrete, enhancing the internal cohesion and stability of the mixture, thereby effectively inhibiting the occurrence of segregation phenomena. At the same time, polymer materials also have excellent viscosity-increasing and water retention properties, which can reduce bleeding and improve the uniformity of the concrete. In addition, research shows that polymer modified admixtures can not only improve the construction performance 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 of the modified anti-segregation admixtures on the current market are designed for natural sand concrete, and their formulations and properties do not fully consider the special requirements of manufactured sand. The characteristics of manufactured sand, such as more angular particles, higher surface roughness, and larger stone powder content, require the admixture to have stronger adaptability and pertinence. In addition, there are also certain limitations in the existing preparation processes, such as high production costs, complex processes, and insufficient product batch stability, which all limit the popularization and application of modified anti-segregation admixtures in manufactured sand concrete. To more intuitively analyze the deficiencies of the existing technology, the following will be specifically described in combination with the comparative documents. In the existing technology, there have been some research results on modified anti-segregation admixtures. For example, Patent CN108793844A discloses a preparation method of a polymer-modified anti-segregation agent. This method prepares an admixture with excellent anti-segregation performance by compounding polymer polymers such as polyvinyl alcohol (PVA) and polyacrylamide (PAM) with inorganic materials. Experiments show that this admixture can significantly improve the cohesiveness of concrete and reduce segregation and bleeding phenomena. However, the research object of this patent is mainly natural sand concrete, and it does not fully consider the particle characteristics of manufactured sand, such as higher angularity and stone powder content, which may lead to a discounted anti-segregation effect in manufactured sand concrete. In addition, the preparation process of this method is relatively complex, involving multiple chemical reactions and compounding processes, and the production cost is relatively high, which is not conducive to large-scale industrial application. Another related technology, Patent CN110642993A, proposes a preparation method of an anti-segregation agent specifically for manufactured sand concrete. This method uses organosilicon-modified polyacrylamide as the main component and prepares the anti-segregation agent through an emulsion polymerization process. Compared with traditional admixtures, this method has made certain progress in improving the anti-segregation performance of manufactured sand concrete and can effectively enhance the stability of the mixture. However, its preparation process needs to be carried out under high temperature and high pressure conditions, with high energy consumption, and the emulsion polymerization process has strict requirements on equipment, resulting in an increase in production costs. In addition, the long-term storage stability of this admixture is insufficient, and problems such as delamination or performance degradation are likely to occur, which limits its application in actual projects. Summary of the Invention

[0007] The existing technology has the following main problems: Due to the factors such as the angular shape of the particles of machine-made sand, rough surface, and high stone powder content during the production process, it often has high friction and poor cohesion in concrete, which makes it easy for concrete to segregate during transportation, pouring, vibration, etc. Although traditional admixtures such as water reducers and thickeners can alleviate the segregation problem to a certain extent, they are often difficult to meet the needs of high-performance concrete in practical applications because they cannot effectively modify the special properties of machine-made sand. Most of the traditional admixtures are designed for natural sand concrete, and the angularity and surface roughness of machine-made sand particles are not fully considered. These admixtures have poor adaptability to machine-made sand concrete, especially in machine-made sand containing high stone powder. The effect of the admixture is often affected by the stone powder, resulting in the admixture being unable to fully play its role in improving performance. Therefore, it is urgent to develop admixtures specifically for the characteristics of machine-made sand to solve the shortcomings of traditional admixtures in machine-made sand concrete. Machine-made sand concrete usually contains a high amount of stone powder, which easily causes water seepage on the concrete surface during cement hydration, affecting the uniformity of the concrete and the performance after final hardening. Although traditional thickeners can reduce bleeding to a certain extent, the bleeding problem cannot be completely solved due to the lack of efficient moisture control ability, which affects the key properties of concrete such as strength and durability. At present, the preparation process of most admixtures for machine-made sand on the market is relatively complicated, often involving multiple chemical reaction steps, and the required raw materials are of various types, resulting in high production costs and low process efficiency. In addition, some traditional admixtures require high temperature and high pressure conditions during the production process, high equipment requirements, and high energy consumption, which further increases the production cost and is not conducive to large-scale industrial application. Existing modified admixtures are prone to performance degradation, stratification or precipitation during long-term storage, affecting their use effect. Especially under high temperature and humid environmental conditions, the stability of the admixture is poor, and it is easy to have uneven distribution, resulting in unstable application effect in concrete. Long-term storage of admixtures may cause fluctuations in concrete quality, thereby affecting the quality and safety of the project. Although some admixtures have made certain progress in improving the working performance of machine-made sand concrete such as fluidity and pumpability, there are still obvious deficiencies in improving the mechanical properties of concrete after hardening, such as compressive strength, crack resistance and durability. Especially in the face of extreme working conditions such as high strain rate and dynamic load, the existing admixtures fail to effectively improve the toughness and crack resistance of concrete, limiting its application in projects requiring high strength and high durability. The present invention aims to solve the above-mentioned deficiencies in the prior art and provide a modified anti-segregation admixture for machine-made sand and its preparation process.The present invention effectively solves the problems of segregation and bleeding of manufactured sand concrete by introducing various polymer compounds such as modified polyoxyethylene ether, vinyltrimethoxysilane, and styrene-acrylate emulsion, constructing a steric hindrance effect and an interpenetrating network structure, and combining materials such as nano-silica and bentonite to form a multi-scale reinforcement system. By adopting advanced technologies such as gradient heating and ultrasonic-mechanical synergistic emulsification, the emulsion particle size of the admixture is precisely controlled, and the three-dimensional network structure formed by the composite thickener and anhydrous sodium sulfate can greatly improve the cohesiveness and stability of the concrete, thereby effectively improving the fluidity, pumpability, and compressive strength of the concrete. In addition, by optimizing the preparation process of the admixture, the production process is simplified, the production cost is reduced, and the stability and adaptability of the product are improved, so that it has a wide range of application prospects, and is particularly suitable for the long-distance pumping construction of manufactured sand concrete with a high stone powder content.

[0008] To achieve the above object, the present invention provides the following technical solution: A preparation process for a modified anti-segregation admixture for manufactured sand, comprising the following steps: (1) Gradient heating reaction: Prepare modified polyoxyethylene ether, vinyltrimethoxysilane, nano-silica, anhydrous sodium sulfate, thickener, polycarboxylate water reducer, and deionized water. After mixing the above components according to the ratio, first carry out hydrolysis, and then carry out grafting reaction; (2) Ultrasonic-mechanical synergistic emulsification: Ultrasonically disperse the reaction product obtained in step (1), and then carry out mechanical stirring; (3) In-situ curing control: Transfer 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 includes: reacting polyoxyethylene ether (CAS No.: 9004-95-9) with a modifier under the action of a catalyst. The modifier is selected from one or a combination of acrylic acid (CAS No. is 79-10-7), methacrylic acid (CAS No. is 79-41-4), or maleic anhydride (CAS No. is 108-31-6), and the mass ratio of polyoxyethylene ether: modifier = 10:1 - 15:1; The catalyst is p-toluenesulfonic acid (CAS No. is 104-15-4) or sulfuric acid, and the dosage is 0.5 - 1.0% of the total mass of the reactants; The reaction is carried out at 80 - 120 °C, and the reaction time is 3 - 6 h. After the reaction, unreacted monomers are removed by vacuum distillation, and the grafting rate of the obtained modified polyoxyethylene ether is ≥85%.

[0009] Preferably, the mass ratio of the modified polyoxyethylene ether, vinyltrimethoxysilane (CAS No. 2768-02-7), nano-silica, anhydrous sodium sulfate, thickener, polycarboxylate water reducer and deionized water in step (1) 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); the average particle size of the nano-silica is 10 - 20 nm, and the specific surface area ≥ 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 No. 9000-30-0) is 5000 mPa·s, and the dextrose equivalent of maltodextrin (CAS No. 9050-36-6) is 15 - 20.

[0010] Preferably, the hydrolysis method in step (1) is as follows: carry out the hydrolysis reaction for 1 - 2 h under the constant temperature condition of 50 ± 2 °C, and control the stirring speed at 200 - 300 rpm during the hydrolysis process; the grafting reaction method in step (1) is as follows: then raise the temperature to 65 ± 5 °C, carry out the grafting reaction for 1.5 - 3 h, and introduce nitrogen protection during the grafting reaction, and the gas flow rate is 0.1 - 0.2 L / min.

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

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

[0013] Application of the admixture prepared by the preparation process as described above.

[0014] Preferably, the dosage form of the admixture is a dosage form acceptable 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 manufactured sand provided by the present invention and its preparation process have significant technical advantages and application values. They can effectively solve the problems of segregation and bleeding commonly existing in the construction process of manufactured sand concrete, while improving the workability of the 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 manufactured sand concrete: During the actual construction process of manufactured sand concrete, especially during long-distance pumping, segregation is likely to occur, that is, coarse aggregates sink and mortar floats, resulting in the non-uniformity of the concrete and affecting its overall performance. Traditional admixtures have poor adaptability in manufactured sand concrete and cannot effectively solve the segregation problem. However, the present invention constructs a molecular structure with steric hindrance effect and forms an interpenetrating network structure through the synergistic effect of modified polyoxyethylene ether and vinyltrimethoxysilane. This structure can significantly improve the cohesion and stability of the 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, reduces the separation between water and solid components, and thus effectively avoids the segregation problem of manufactured sand concrete. Improving the water bleeding resistance of the concrete: Water bleeding is a phenomenon of water loss caused by the migration of water to the surface during the curing process of the concrete, which usually affects the durability and strength of the concrete. Traditional admixtures usually cannot effectively control the water bleeding problem while improving the fluidity and workability of the concrete. However, the admixture of the present invention can significantly reduce the bleeding rate by enhancing the water retention and thickening properties of the mixture. In the present invention, through the synergistic effect of the composite thickener and anhydrous sodium sulfate, a three-dimensional network structure is formed. This structure can form a good water retention effect in the concrete, significantly reduce the occurrence of water bleeding, and thus improve the overall quality and durability of the concrete. Improving the fluidity and pumpability of the concrete: Manufactured sand concrete usually has poor fluidity and pumpability due to characteristics such as rough particle surfaces, many sharp corners, and uneven gradation, which brings certain difficulties to construction. Through the application of the modified anti-segregation admixture of the present invention, the fluidity and pumpability of the concrete can be significantly improved. The admixture can enhance the cohesiveness of the concrete, enabling sand and gravel aggregates of different particle sizes to be better distributed in the concrete, improving the overall fluidity of the concrete, and reducing the blockage and separation phenomena during the pumping process. Specifically, after using this admixture, the slump retention time of manufactured sand concrete can be maintained above 1 h, and the slump retention value > 315 mm, greatly improving the construction performance of the concrete, especially suitable for long-distance pumping construction. Improving the compressive strength and durability of the concrete: By using the modified anti-segregation admixture of the present invention, the 28-day compressive strength of manufactured sand concrete can be increased by 24.5% and reach 72.6 MPa.High strength is the foundation of the bearing capacity of concrete structures. The introduction of this admixture enables manufactured sand concrete to maintain high fluidity while improving the mechanical properties after hardening, especially showing outstanding performance in aspects such as compressive strength and crack resistance. In addition, the synergistic effect of modified polyoxyethylene ether and vinyltrimethoxysilane enhances the internal microstructure of concrete, improves the impermeability and corrosion resistance of concrete, and further enhances its durability. This enables the admixture to be applicable to engineering projects with high strength and durability requirements such as bridges and tunnels. Simplify the preparation process and reduce production costs: The preparation process of the present invention adopts methods such as gradient heating, ultrasonic-mechanical synergistic emulsification, and in-situ curing, which not only optimize the performance of the admixture but also make the preparation process more efficient. Through reasonable temperature control and dispersion process, the present invention can effectively control the emulsion particle size distribution, make the distribution of the admixture in concrete more uniform, and enhance the stability of its performance. In addition, the preparation method of modified polyoxyethylene ether further reduces the production cost by simplifying the reaction steps and optimizing the use of catalysts, enabling the admixture to be widely used in industrial production. Wide applicability and environmental friendliness: The modified anti-segregation admixture of the present invention has wide applicability, especially showing excellent performance in concrete with manufactured sand containing high stone powder content. Manufactured sand usually contains a high amount of stone powder, which is prone to segregation problems in concrete. However, the admixture of the present invention can show good adaptability in different types of manufactured sand and solve the problem of insufficient adaptability. In addition, the composition of the admixture is reasonably selected and does not contain harmful substances, having a certain degree of environmental friendliness and meeting the requirements of current green building materials.

[0019] In summary, through innovative molecular structure design and optimized preparation process, the modified anti-segregation admixture of the present invention has successfully solved common problems such as segregation and bleeding in the construction of manufactured sand concrete, and significantly improved the fluidity, pumpability, compressive strength and durability of concrete, having broad application prospects and engineering value. Brief Description of the Drawings

[0020] Figure 1 It is a physical picture of the admixture prepared in Example 1. Detailed Description of the Invention

[0021] For the embodiments of the present invention, weight parts can be equivalently replaced with kilograms (Kg) or grams (g), and can be scaled up or down in the same proportion with little impact on the experimental results. At the same time, the polycarboxylate superplasticizer used in the present invention is KD-502PS produced by Shandong Kunduo Chemical Co., Ltd., which meets the standards of GB8076-2008 and TB / T3257-2018.

[0022] Example 1

[0023] The component dosages are shown in Table 1 below.

[0024] Table 1

[0025]

[0026] The preparation process is as follows: gradient heating reaction: 50℃ hydrolysis for 1.5h (250rpm) → 65℃ grafting for 2h (nitrogen flow rate 0.15L / min); ultrasonic emulsification: 35kHz ultrasound for 30min (power 350W, temperature 32℃); mechanical stirring: 1800rpm stirring for 50min; curing conditions: 25℃ / RH85% standing for 24h. At the same time, the prepared admixture, its physical picture, as shown Figure 1 shown.

[0027] Performance test: Take C30 concrete as an example, when the admixture dosage is 0.3% (that is, 3kg of admixture is added per cubic meter of concrete). Slump retention value test: Specimen preparation: Prepare fresh concrete specimens according to the "Standard for Test Methods for Performance of Ordinary Concrete Mixtures" (GB / T50080), and control the initial slump at 320±10mm. Static curing: After the concrete in the slump cone is left to stand for 1 hour, re-measure the slump value according to the standard method, and measure the height 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 water seepage rate determination: Use the pressure water seepage meter specified in T0531-2020, set the pressure to 3.5MPa, put 500g of concrete into the test mold, let it stand for 10s, then apply pressure, continue pressurizing until 140s, collect the water seepage V1, and collect V2 at the end of pressurization. Pressure water seepage rate = (V2-V1) / concrete mass × 100%. 28d compressive strength test: Specimen molding is carried out according to the "Standard Test Method for Early Strength Estimation of Ready-mixed Concrete". Standard curing is carried out until 28d. A microcomputer-controlled press is used, and the loading rate is maintained at 0.5MPa / s. The arithmetic mean of the strength values ​​of the three specimens is taken. When the maximum / minimum value is >1.15, the middle value is taken. 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 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] Embodiment 2-6

[0030] By adjusting the proportions of key components and process parameters, a series of optimized solutions are formed. For component proportions or process parameters not listed, they 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 proportions 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] Taking Example 1 as the basis for testing.

[0036] Comparative Example 1: When preparing the admixture, ordinary polyoxyethylene ether is used to replace the modified polyoxyethylene ether, and other components and process steps remain unchanged. Test results: Slump retention value (1h): 290 mm, pressure bleeding rate: 12.5%, 28d compressive strength: 60.2 MPa, anti-segregation coefficient: 0.18. The lack of the steric hindrance effect brought by modification in ordinary polyoxyethylene ether leads to insufficient cohesiveness of the concrete, aggravated segregation and bleeding problems, and a decrease in strength.

[0037] Comparative Example 2: When preparing the admixture, vinyltrimethoxysilane is not added, and other components and process steps remain unchanged. Test results: Slump retention value (1h): 305 mm, pressure bleeding rate: 11.8%, 28d compressive strength: 62.5 MPa, anti-segregation coefficient: 0.16. The lack of vinyltrimethoxysilane makes it impossible to form an effective interpenetrating network structure, resulting in a decrease in the internal cohesion and stability of the concrete.

[0038] Comparative Example 3: When preparing the admixture, nano-silica is not added, and other components and process steps remain unchanged. Test results: Slump retention value (1h): 300 mm, pressure bleeding rate: 10.5%, 28d compressive strength: 65.0 MPa, anti-segregation coefficient: 0.14. The absence of nano-silica leads to an incomplete multi-scale reinforcement system and insufficient optimization of the concrete microstructure, resulting in a decrease in strength and anti-segregation performance.

[0039] Comparative Example 4: When preparing the admixture, only guar gum is used as the thickener to replace the composite thickener, and other components and process steps remain unchanged. Test results: Slump retention value (1h): 310 mm, pressure bleeding rate: 10.2%, 28d compressive strength: 67.3 MPa, anti-segregation coefficient: 0.13. The synergistic effect of the composite thickener is weakened, resulting in a slight decrease in the cohesiveness and water retention of the concrete.

[0040] Comparative Example 5: When preparing the admixture, the gradient heating step was cancelled, and all materials were directly mixed at room temperature (25°C), while other components remained unchanged. Test results: Slump retention value (1h): 295 mm, pressure bleeding rate: 13.0%, 28-day compressive strength: 61.8 MPa, segregation resistance coefficient: 0.19. The lack of gradient heating led to insufficient hydrolysis and grafting reactions of the silane coupling agent, resulting in a decline in the performance of the admixture.

[0041] Comparative Example 6: When preparing the admixture, only mechanical stirring was used, and the ultrasonic dispersion step was omitted, while other components and processes remained unchanged. Test results: Slump retention value (1h): 308 mm, pressure bleeding rate: 11.0%, 28-day compressive strength: 64.5 MPa, segregation resistance coefficient: 0.15. Ultrasonic dispersion helps the uniform distribution of emulsion particle sizes. The effect of simple mechanical stirring is insufficient, leading to uneven dispersion of the admixture and a decline in performance.

[0042] Comparative Example 7: After the admixture was prepared, it was cured at a high temperature of 40°C, while other components and process steps remained unchanged. Test results: Slump retention value (1h): 312 mm, pressure bleeding rate: 10.8%, 28-day compressive strength: 66.0 MPa, segregation resistance coefficient: 0.12. Warm curing may cause some components in the admixture to be unstable, affecting its performance.

[0043] Comparative Example 8: After the admixture was prepared, it was cured under the condition of a relative humidity of 50%, while other components and process steps remained unchanged. Test results: Slump retention value (1h): 305 mm, pressure bleeding rate: 11.5%, 28-day compressive strength: 63.2 MPa, segregation resistance coefficient: 0.16. Curing at low humidity affects the stability and uniformity of the admixture, resulting in a decline in performance.

[0044] Comparative Example 9: The dosage of the admixture in the concrete was reduced to 0.05%, while other components and process steps remained unchanged. Test results: Slump retention value (1h): 285 mm, pressure bleeding rate: 14.0%, 28-day compressive strength: 58.5 MPa, segregation resistance coefficient: 0.20. Insufficient dosage cannot fully exert the modification effect of the admixture, and the performance of the concrete is poor.

[0045] Comparative Example 10: The dosage of the admixture in the concrete was increased to 1.0%, while other components and process steps remained unchanged. Test results: Slump retention value (1h): 330 mm, pressure bleeding rate: 8.5%, 28-day compressive strength: 70.0 MPa, segregation resistance coefficient: 0.07. Although increasing the dosage improves some properties, it increases the cost and has limited improvement in compressive strength.

[0046] The test results of Comparative Examples 1-10 above demonstrate the decline in concrete performance in the absence of key components (such as modified polyoxyethylene ether, vinyltrimethoxysilane, nano-silica) or when process parameters are changed (such as gradient heating, ultrasonic dispersion, curing conditions). These results verify the importance of the key components and process steps in the invention. Compared with the examples of the invention, the comparative examples show varying degrees of disadvantages in terms of slump retention value, pressure bleeding rate, compressive strength, and segregation resistance coefficient.

[0047] The preferred embodiments of this patent have been described in detail above, but this patent is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist 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, thickener, polycarboxylic acid water reducer and deionized water, mixing the above components according to a proportion, first hydrolyzing 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; (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 the polyoxyethylene ether with a modifier under the action of a catalyst, the modifier being selected from one or a combination of acrylic acid, methacrylic acid or maleic anhydride, and the mass ratio of polyoxyethylene ether: modifier = 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, the reaction time is 3-6h, and after the reaction is completed, the 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: In step (1), the mass ratio of modified polyoxyethylene ether, vinyl trimethoxysilane, nano-silica, anhydrous sodium sulfate, thickener, polycarboxylic acid 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 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. During the grafting reaction, nitrogen protection is introduced, and the air flow rate is 0.1-0.2 L / min.

4. The process for preparing the modified anti-segregation admixture for machine-made sand according to claim 1, characterized in that: The method of ultrasonic dispersion in step (2) is as follows: disperse in a 20-40kHz ultrasonic device for 20-40 minutes, the ultrasonic power is 300-400W, and the temperature is controlled at 30-35°C during the dispersion process; the method of mechanical stirring in step (2) is as follows: mechanical stirring is performed at a rotation 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 relative humidity is ≥80%, and the curing method is to stand for 24 hours.

6. Use of an admixture obtained by the preparation process as claimed in 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 additive 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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