Synthesis process and application of viscosity-reducing admixture for machine-made sand

Abstract

The invention discloses a synthesis process and application of a viscosity-reducing admixture for machine-made sand, and relates to the technical field of nano modification. The process comprises the following steps: preparing a nano composite dispersion: mixing nano SiO and carboxylated nano cellulose, adding polyether phosphate as a dispersing agent, and performing high-pressure homogenization treatment to prepare the stable nano composite dispersion; low-temperature gradient polymerization reaction: under the protection of nitrogen and at the low temperature of 5-10 DEG C, dropwise adding monomers in three stages to carry out polymerization reaction; and a post-treatment process: adding an organic silicon defoaming agent, and carrying out vacuum defoaming treatment to obtain a final product. The mixing amount of the admixture is only 0.2-0.5% of the mass of cement, the viscosity of the machine-made sand concrete can be remarkably reduced, the fluidity is improved, and the construction performance and the concrete quality are improved. The method is characterized in that the rheological property is optimized by utilizing a nano modification technology, a low-temperature polymerization process is adopted, and the method is energy-saving, environment-friendly and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of nano modification, and particularly relates to a synthesis process and application of a viscosity-reducing admixture for manufactured sand. Background Art

[0002] With the rapid development of the modern construction industry, as one of the most important building materials, the optimization and improvement of the performance of concrete have always been the key research directions. In recent years, as a new type of building material, manufactured sand has gradually replaced traditional natural sand and become an important part of concrete production due to its wide source, controllable cost, and good physical properties. The production process of manufactured sand can effectively utilize ore resources through mechanical crushing and screening, while reducing the over-exploitation of natural river sand, showing significant environmental protection advantages. However, some problems have also emerged in the practical application of manufactured sand, and the most prominent one is its adverse effect on the fluidity of concrete. Compared with natural sand, the particle shape of manufactured sand is usually more angular, the gradation is not continuous enough, and the surface roughness is higher. These characteristics lead to a significant increase in the viscosity of manufactured sand concrete and a decrease in fluidity, thus affecting the construction performance and final forming quality of concrete.

[0003] The fluidity of concrete is an important indicator to measure its construction performance, which is directly related to the smooth progress of the pouring, vibration, and forming processes. In traditional natural sand concrete, the particle shape of sand is relatively round and the gradation is reasonable, which can form a good synergistic effect with the cement paste, thus ensuring that the concrete has appropriate rheological properties. However, the introduction of manufactured sand has disrupted this balance. Due to the angularity of manufactured sand particles and the relatively high stone powder content, it is easy to form a large frictional resistance in the concrete, resulting in a decrease in the wrapping property and fluidity of the cement paste. In addition, the content of fine particles in manufactured sand is relatively large, which may further exacerbate the cohesiveness of the concrete, causing problems such as pipe blockage or stratification during transportation and pumping. The existence of these problems not only increases the construction difficulty but also may have potential negative impacts on the strength and durability of concrete.

[0004] In order to deal with the problem of decreased fluidity of machine-made sand concrete, admixtures are widely used as an important technical means to improve the performance of concrete. Traditional admixtures, such as polycarboxylic acid-based water reducers, can improve the fluidity of concrete to a certain extent by reducing the water-cement ratio of concrete and improving the dispersibility of cement particles. However, in machine-made sand concrete, the effect of traditional water reducers is often greatly reduced. Since the particle characteristics of machine-made sand are quite different from those of natural sand, it is difficult for traditional water reducers to effectively reduce its viscosity, and it is usually necessary to significantly increase the dosage to achieve the expected fluidity target. This high dosage not only significantly increases the production cost, but may also cause other problems, such as prolonged setting time of concrete, decreased early strength, and even adverse effects on long-term durability. Therefore, the development of a viscosity-reducing admixture specifically for machine-made sand concrete has become a key issue that needs to be urgently addressed in the current field of concrete technology.

[0005] In recent years, the development of nanotechnology has provided new possibilities for improving the performance of concrete admixtures. Nanomaterials have excellent physical and chemical properties due to their extremely small particle size and high specific surface area, and have broad application potential in concrete. Studies have shown that nanomaterials can effectively improve the rheological properties of concrete by improving the dispersibility of cement particles, optimizing the microstructure of hydration products, and reducing the friction resistance inside the slurry. The introduction of nanomaterials is particularly important in machine-made sand concrete. The high viscosity characteristics of machine-made sand can be alleviated by the action of nanomaterials, for example, by enhancing the interface between cement particles and machine-made sand, reducing the internal friction between particles, and thus significantly improving the fluidity of concrete. In addition, nanomaterials can also improve the hydration process of concrete to a certain extent, promote the formation of early strength, and provide dual guarantees for the construction performance and mechanical properties of machine-made sand concrete.

[0006] However, most of the nano-modified admixtures on the market are general-purpose products, lacking customized designs for the special needs of machine-made sand concrete. The characteristics of machine-made sand vary greatly depending on the origin, crushing process and grading, which places higher demands on the adaptability of the admixture. General-purpose admixtures may exhibit unstable performance in certain machine-made sand concrete mixes, such as insufficient viscosity reduction effect or poor compatibility with other admixtures. Therefore, the development of a viscosity-reducing admixture specifically for machine-made sand requires not only excellent viscosity-reducing performance, but also stability and adaptability under a variety of mix conditions. In addition, considering the needs of industrial production, the synthesis process of this admixture should also be efficient, economical and environmentally friendly to meet the requirements of large-scale applications. Summary of the invention

[0007] In view of this, the purpose of the present invention is to provide a synthesis process and application of a viscosity-reducing admixture for manufactured sand, so as to solve the problems of increased viscosity and decreased fluidity caused by the high particle angularity and stone powder content of manufactured sand concrete. Through an innovative synthesis process, the present invention develops an efficient and low-dosage admixture, aiming to improve the construction performance and quality of manufactured sand concrete, while taking into account economic and environmental benefits.

[0008] The technical solution adopted is as follows: A synthesis process of a viscosity-reducing admixture for manufactured sand, comprising the following steps: (1) Preparation of a nano-composite dispersion: Mix nano-SiO2 with carboxylated nano-cellulose, add 0.5-1.2 wt% polyether phosphate as a dispersant, and perform cyclic treatment 3-5 times in a high-pressure homogenizer at 80-100 MPa to obtain a stable dispersion with an absolute value of Zeta potential > 40 mV; (2) Low-temperature gradient polymerization reaction: Under nitrogen protection, add acrylic monomers to a reaction kettle at low temperature for polymerization reaction; (3) Post-treatment process: After the reaction is completed, add 0.15-0.25 wt% of an organosilicon defoaming agent and perform defoaming treatment to obtain the final product.

[0009] Preferably, in step (1), the particle size of nano-SiO2 is 15-30 nm, and the carboxylic acid group content of carboxylated nano-cellulose is 1.2-1.5 mmol / g; nano-SiO2 and carboxylated nano-cellulose are mixed in a mass ratio of 1: (3-8).

[0010] Preferably, in step (1), the addition amount of polyether phosphate is 15-30 times the mass of carboxylated nano-cellulose.

[0011] Preferably, in step (2), the temperature of the reaction kettle is controlled at 5-10 °C at low temperature.

[0012] Preferably, in step (2), the polymerization reaction is carried out by dropwise addition in three stages: By mass, the first stage: a pre-emulsion containing 35-40 parts by mass of polyoxyethylene ether and 8-12 parts by mass of acrylic acid, with a dropping rate of 2.5-3.5 mL / min; the second stage: a suspension containing 5-8 parts by mass of methacrylic acid and 0.8-1.2 parts by mass of the nano-dispersion in step (1), with a dropping rate of 1.5-2.0 mL / min; the third stage: a solution of 3-5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid, with a dropping rate of 0.8-1.2 mL / min.

[0013] Preferably, the initiation system for the polymerization reaction in step (2) is as follows: An oxidation-reduction initiation system composed of 1.5-2.0 parts by mass of mercaptopropionic acid and 0.8-1.2 parts by mass of ammonium persulfate is used to control the molecular weight of the polymerization reaction within the range of 25,000-35,000 Da, and the molecular weight distribution index PDI < 1.5.

[0014] Preferably, the silicone defoamer in step (3) is dimethyl silicone oil, polydimethylsiloxane or glycerol monostearate.

[0015] Preferably, the conditions for defoaming treatment in step (3) are as follows: defoaming treatment is carried out for 1-2 h under vacuum conditions of 50-60 °C and -0.08 to -0.1 MPa.

[0016] The application of the viscosity-reducing admixture prepared by the synthesis process as described above is characterized in that the dosage of the admixture is 0.2-0.5% of the mass of the cement.

[0017] The polymer provides electrostatic repulsion and steric hindrance by adsorbing on the surface of cement particles, reducing the van der Waals force attraction between particles, thereby dispersing the particles and reducing the yield stress and plastic viscosity of the mixture. This is consistent with the mechanism of traditional polycarboxylate superplasticizers. Especially in manufactured-sand concrete, the polymer helps to overcome the increased friction caused by the angular particles and high fine powder content. Enhancement effect of nanomaterials: Role of nano-SiO2: Studies have shown that nano-SiO2 can act as a lubricant to reduce friction between particles. Especially in manufactured-sand concrete, its high specific surface area may fill the particle gaps and reduce the viscosity. In addition, nano-SiO2 may accelerate the hydration reaction by providing nucleation sites and improve the early strength. Role of carboxylated nanocellulose: Although studies generally show that nanocellulose increases the yield stress and viscosity (such as in self-compacting concrete), in the present invention, its low dosage and combination with the polymer may change its behavior. It may optimize the rheological properties and reduce the friction between manufactured-sand particles by forming a network structure or interacting with cement particles.

[0018] In summary, the beneficial effects of the present invention are as follows: significantly improving the rheological properties of manufactured sand concrete: through the innovative preparation technology of nano-composite dispersion system, the dispersibility of the admixture and the interfacial enhancement effect are significantly improved, effectively improving the fluidity of manufactured sand concrete, reducing the viscosity, and making it easier to construct and process. Precise control of molecular structure: adopting the low-temperature gradient polymerization reaction process to ensure the precise control of the molecular weight of the admixture and the uniformity of the distribution, thus enhancing the functionality and long-term stability of the admixture. Stable product quality: the defoaming and deaeration technologies in the post-treatment process effectively remove the bubbles in the production process, further ensuring the quality and application effect of the admixture. Low dosage and high efficiency: the dosage of this admixture is only 0.2 - 0.5% of the mass of cement, which can significantly reduce the viscosity of manufactured sand concrete and improve the rheological properties, greatly reducing the production and construction costs. Interfacial enhancement: using nano-modification technology to enhance the interfacial action between particles, improving the uniformity and stability of concrete, and thus enhancing the final quality and durability of concrete. Energy conservation and environmental protection: the low-temperature polymerization process significantly reduces energy consumption, and the production process is green and environmentally friendly, meeting the requirements of sustainable development of modern industry. Strong adaptability: this admixture is applicable to various manufactured sand ratios, can meet the actual needs of different engineering projects, and has broad application prospects and significant economic and environmental benefits.

[0019] Through the above advantages, the present invention not only achieves an innovative breakthrough in technology but also demonstrates the characteristics of high efficiency and economy in practical applications, providing important technical support for the manufactured sand concrete industry. Brief Description of the Drawings

[0020] Figure 1 It is the scanning electron microscope image of the admixture prepared in Example 10.

[0021] Figure 2 It is the 5000 - times real image of the concrete material prepared with the admixture prepared in Example 10. Detailed Description of the Invention

[0022] The present invention will be described in detail below through specific examples. However, the uses and purposes of these exemplary embodiments are only used to illustrate the present invention and do not constitute any form of limitation on the actual protection scope of the present invention, nor will the protection scope of the present invention be limited thereto. For the parameter ranges not mentioned, intermediate values are selected.

[0023] The following are Examples 1 - 10 and Comparative Examples 1 - 6 designed according to the user's requirements. Each case is complete and designed based on the parameter ranges of the claims, using specific masses. The examples demonstrate the excellent performance of the viscosity-reducing admixture prepared within the specified range, while the comparative examples demonstrate the performance degradation or problems when exceeding the specified range. The following design ensures that each case includes the specific parameters of all steps and describes the performance or application effects of the final product.

[0024] List of CAS numbers of key raw materials: Nano-SiO2, CAS number: 14808-60-7; Carboxylated nanocellulose, CAS number: 9004-34-6; Polyether phosphate ester, CAS number: 39464-70-5; Acrylic acid, CAS number: 79-10-7; Methacrylic acid, CAS number: 79-41-4; 2-Acrylamido-2-methylpropanesulfonic acid, CAS number: 15214-89-8; Dimethyl silicone oil, CAS number: 9016-00-6; Glycerol monostearate, CAS number: 31566-31-1; Mercaptopropionic acid, CAS number: 107-96-0; Ammonium persulfate, CAS number: 7727-54-0.

[0025] Example 1

[0026] Step 1: Preparation of nano-composite dispersion

[0027] Nano-SiO2: particle size 15 nm, mass 10 g; Carboxylated nanocellulose: carboxylic acid group content 1.2 mmol / g, mass 30 g; Dispersant: polyether phosphate ester, 450 g; High-pressure homogenizer: 80 MPa, circulated 3 times, absolute value of Zeta potential 45 mV.

[0028] Step 2: Low-temperature gradient polymerization reaction

[0029] Temperature: 5 °C; First stage: 35 g of polyoxyethylene ether + 8 g of acrylic acid, dropping rate 2.5 mL / min; Second stage: 5 g of methacrylic acid + 0.8 g of nano-dispersion, dropping rate 1.5 mL / min; Third stage: 3 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 0.8 mL / min; Initiation system: 1.5 g of mercaptopropionic acid + 0.8 g of ammonium persulfate, molecular weight 25000 Da, PDI = 1.4.

[0030] Step 3: Post-treatment

[0031] Defoamer: dimethyl silicone oil, 0.15 wt%; Defoaming: 50 °C, -0.08 MPa, 1 h.

[0032] Example 2

[0033] Step 1: Preparation of nano-composite dispersion

[0034] Nano-SiO2: particle size 20 nm, mass 10 g; Carboxylated nanocellulose: carboxylic acid group content 1.3 mmol / g, mass 40 g; Dispersant: polyether phosphate ester, 600 g; High-pressure homogenizer: 85 MPa, circulated 4 times, absolute value of Zeta potential 48 mV.

[0035] Step 2: Low-temperature gradient polymerization reaction

[0036] Temperature: 6°C; First stage: 36 g of polyethylene oxide ether + 9 g of acrylic acid, dropping rate 2.8 mL / min; Second stage: 6 g of methacrylic acid + 0.9 g of nano-dispersion, dropping rate 1.6 mL / min; Third stage: 4 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 0.9 mL / min; Initiation system: 1.6 g of mercaptopropionic acid + 0.9 g of ammonium persulfate, molecular weight 28000 Da, PDI = 1.3.

[0037] Step 3: Post-treatment

[0038] Defoamer: Polydimethylsiloxane, 0.18 wt%; Defoaming: 52°C, -0.085 MPa, 1.2 h.

[0039] Example 3

[0040] Step 1: Preparation of nano-composite dispersion

[0041] Nano-SiO2: Particle size 25 nm, mass 10 g; Carboxylated nano-cellulose: Carboxylic acid group content 1.4 mmol / g, mass 50 g; Dispersant: Polyether phosphate, 1000 g; High-pressure homogenizer: 90 MPa, 4 cycles, absolute value of Zeta potential 50 mV.

[0042] Step 2: Low-temperature gradient polymerization reaction

[0043] Temperature: 7°C; First stage: 37 g of polyethylene oxide ether + 10 g of acrylic acid, dropping rate 3.0 mL / min; Second stage: 7 g of methacrylic acid + 1.0 g of nano-dispersion, dropping rate 1.7 mL / min; Third stage: 4.5 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 1.0 mL / min; Initiation system: 1.7 g of mercaptopropionic acid + 1.0 g of ammonium persulfate, molecular weight 30000 Da, PDI = 1.2.

[0044] Step 3: Post-treatment

[0045] Defoamer: Glyceryl monostearate, 0.20 wt%; Defoaming: 55°C, -0.09 MPa, 1.5 h.

[0046] Example 4

[0047] Step 1: Preparation of nano-composite dispersion

[0048] Nano-SiO2: Particle size 30 nm, mass 10 g; Carboxylated nano-cellulose: Carboxylic acid group content 1.5 mmol / g, mass 60 g; Dispersant: Polyether phosphate, 1200 g; High-pressure homogenizer: 95 MPa, 5 cycles, absolute value of Zeta potential 52 mV.

[0049] Step 2: Low-temperature gradient polymerization reaction

[0050] Temperature: 8 °C; First stage: 38 g of polyoxyethylene ether + 11 g of acrylic acid, dropping rate 3.2 mL / min; Second stage: 7.5 g of methacrylic acid + 1.1 g of nano-dispersion, dropping rate 1.8 mL / min; Third stage: 4.8 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 1.1 mL / min; Initiation system: 1.8 g of mercaptopropionic acid + 1.1 g of ammonium persulfate, molecular weight 32000 Da, PDI = 1.1.

[0051] Step 3: Post-treatment

[0052] Defoamer: dimethyl silicone oil, 0.22 wt%; Defoaming: 58 °C, -0.095 MPa, 1.8 h.

[0053] Example 5

[0054] Step 1: Preparation of nano-composite dispersion

[0055] Nano-SiO2: particle size 18 nm, mass 10 g; Carboxylated nano-cellulose: carboxylic acid group content 1.25 mmol / g, mass 35 g; Dispersant: polyether phosphate, 700 g; High-pressure homogenizer: 82 MPa, 3 cycles, absolute value of Zeta potential 46 mV.

[0056] Step 2: Low-temperature gradient polymerization reaction

[0057] Temperature: 5.5 °C; First stage: 35.5 g of polyoxyethylene ether + 8.5 g of acrylic acid, dropping rate 2.6 mL / min; Second stage: 5.5 g of methacrylic acid + 0.85 g of nano-dispersion, dropping rate 1.55 mL / min; Third stage: 3.5 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 0.85 mL / min; Initiation system: 1.55 g of mercaptopropionic acid + 0.85 g of ammonium persulfate, molecular weight 26000 Da, PDI = 1.35.

[0058] Step 3: Post-treatment

[0059] Defoamer: polydimethylsiloxane, 0.16 wt%; Defoaming: 51 °C, -0.082 MPa, 1.1 h.

[0060] Example 6

[0061] Step 1: Preparation of nano-composite dispersion

[0062] Nano-SiO2: particle size 22 nm, mass 10 g; Carboxylated nano-cellulose: carboxylic acid group content 1.35 mmol / g, mass 45 g; Dispersant: polyether phosphate, 900 g; High-pressure homogenizer: 88 MPa, 4 cycles, absolute value of Zeta potential 49 mV.

[0063] Step 2: Low-temperature gradient polymerization reaction

[0064] Temperature: 6.5 °C; First stage: 36.5 g of polyoxyethylene ether + 9.5 g of acrylic acid, dropping rate 2.9 mL / min; Second stage: 6.5 g of methacrylic acid + 0.95 g of nano-dispersion, dropping rate 1.65 mL / min; Third stage: 4.2 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 0.95 mL / min; Initiation system: 1.65 g of mercaptopropionic acid + 0.95 g of ammonium persulfate, molecular weight 29000 Da, PDI = 1.25.

[0065] Step 3: Post-treatment

[0066] Defoamer: glycerol monostearate, 0.19 wt%; Defoaming: 53 °C, -0.088 MPa, 1.3 h.

[0067] Example 7

[0068] Step 1: Preparation of nano-composite dispersion

[0069] Nano-SiO2: particle size 28 nm, mass 10 g; Carboxylated nano-cellulose: carboxylic acid group content 1.45 mmol / g, mass 55 g; Dispersant: polyether phosphate, 1100 g; High-pressure homogenizer: 92 MPa, circulated 5 times, absolute value of Zeta potential 51 mV.

[0070] Step 2: Low-temperature gradient polymerization reaction

[0071] Temperature: 7.5 °C; First stage: 37.5 g of polyoxyethylene ether + 10.5 g of acrylic acid, dropping rate 3.1 mL / min; Second stage: 7.2 g of methacrylic acid + 1.05 g of nano-dispersion, dropping rate 1.75 mL / min; Third stage: 4.6 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 1.05 mL / min; Initiation system: 1.75 g of mercaptopropionic acid + 1.05 g of ammonium persulfate, molecular weight 31000 Da, PDI = 1.15.

[0072] Step 3: Post-treatment

[0073] Defoamer: dimethyl silicone oil, 0.21 wt%; Defoaming: 56 °C, -0.092 MPa, 1.6 h.

[0074] Example 8

[0075] Step 1: Preparation of nano-composite dispersion

[0076] Nano-SiO₂: particle size 16 nm, mass 10 g; carboxylated nanocellulose: carboxylic acid group content 1.22 mmol / g, mass 32 g; dispersant: polyether phosphate, 640 g; high-pressure homogenizer: 84 MPa, circulated 3 times, absolute value of Zeta potential 47 mV.

[0077] Step 2: Low-temperature gradient polymerization reaction

[0078] Temperature: 5.2 °C; First stage: polyoxyethylene ether 35.2 g + acrylic acid 8.2 g, dropping rate 2.55 mL / min; Second stage: methacrylic acid 5.2 g + nano-dispersion 0.82 g, dropping rate 1.52 mL / min; Third stage: 2-acrylamido-2-methylpropanesulfonic acid 3.2 g, dropping rate 0.82 mL / min; Initiation system: mercaptopropionic acid 1.52 g + ammonium persulfate 0.82 g, molecular weight 25500 Da, PDI = 1.38.

[0079] Step 3: Post-treatment

[0080] Defoamer: polydimethylsiloxane, 0.17 wt%; Defoaming: 50.5 °C, -0.081 MPa, 1.05 h.

[0081] Example 9

[0082] Step 1: Preparation of nano-composite dispersion

[0083] Nano-SiO₂: particle size 24 nm, mass 10 g; carboxylated nanocellulose: carboxylic acid group content 1.38 mmol / g, mass 48 g; dispersant: polyether phosphate, 960 g; high-pressure homogenizer: 89 MPa, circulated 4 times, absolute value of Zeta potential 49.5 mV.

[0084] Step 2: Low-temperature gradient polymerization reaction

[0085] Temperature: 6.8 °C; First stage: polyoxyethylene ether 36.8 g + acrylic acid 9.8 g, dropping rate 2.95 mL / min; Second stage: methacrylic acid 6.8 g + nano-dispersion 0.98 g, dropping rate 1.68 mL / min; Third stage: 2-acrylamido-2-methylpropanesulfonic acid 4.3 g, dropping rate 0.98 mL / min; Initiation system: mercaptopropionic acid 1.68 g + ammonium persulfate 0.98 g, molecular weight 29500 Da, PDI = 1.22.

[0086] Step 3: Post-treatment

[0087] Defoamer: glycerol monostearate, 0.20 wt%; Defoaming: 54 °C, -0.089 MPa, 1.4 h.

[0088] Example 10

[0089] Step 1: Preparation of nano-composite dispersion

[0090] Nano-SiO₂: particle size 29 nm, mass 10 g; carboxylated nano-cellulose: carboxylic acid group content 1.48 mmol / g, mass 58 g; dispersant: polyether phosphate, 1740 g; high-pressure homogenizer: 98 MPa, circulated 5 times, absolute value of Zeta potential 53 mV.

[0091] Step 2: Low-temperature gradient polymerization reaction

[0092] Temperature: 9.5 °C; First stage: polyoxyethylene ether 39.5 g + acrylic acid 11.5 g, dropping rate 3.4 mL / min; Second stage: methacrylic acid 7.8 g + nano-dispersion 1.15 g, dropping rate 1.9 mL / min; Third stage: 2-acrylamido-2-methylpropanesulfonic acid 4.9 g, dropping rate 1.15 mL / min; Initiation system: mercaptopropionic acid 1.9 g + ammonium persulfate 1.15 g, molecular weight 34000 Da, PDI = 1.05.

[0093] Step 3: Post-treatment

[0094] Defoamer: dimethyl silicone oil, 0.24 wt%; Defoaming: 59 °C, -0.098 MPa, 1.9 h.

[0095] The micrograph of the admixture prepared in this example is as Figure 1 shown.

[0096] Comparative Example 1

[0097] Step 1: Preparation of nano-composite dispersion

[0098] Nano-SiO₂: particle size 10 nm (out of range), mass 10 g; carboxylated nano-cellulose: carboxylic acid group content 1.2 mmol / g, mass 30 g; dispersant: polyether phosphate, 450 g; high-pressure homogenizer: 80 MPa, circulated 3 times, absolute value of Zeta potential 35 mV (insufficient stability).

[0099] Step 2: Low-temperature gradient polymerization reaction

[0100] Temperature: 5 °C; First stage: polyoxyethylene ether 35 g + acrylic acid 8 g, dropping rate 2.5 mL / min; Second stage: methacrylic acid 5 g + nano-dispersion 0.8 g, dropping rate 1.5 mL / min; Third stage: 2-acrylamido-2-methylpropanesulfonic acid 3 g, dropping rate 0.8 mL / min; Initiation system: mercaptopropionic acid 1.5 g + ammonium persulfate 0.8 g, molecular weight 24000 Da, PDI = 1.6.

[0101] Step 3: Post-treatment

[0102] Defoamer: Dimethyl silicone oil, 0.15 wt%; Defoaming: 50 °C, -0.08 MPa, 1 h.

[0103] Comparative Example 2

[0104] Step 1: Preparation of nano-composite dispersion

[0105] Nano-SiO2: Particle size 20 nm, mass 10 g; Carboxylated nano-cellulose: Carboxylic acid group content 1.0 mmol / g (below the range), mass 40 g; Dispersant: Polyether phosphate, 600 g; High-pressure homogenizer: 85 MPa, circulated 4 times, absolute value of Zeta potential 38 mV (insufficient stability).

[0106] Step 2: Low-temperature gradient polymerization reaction

[0107] Temperature: 6 °C; First stage: Polyoxyethylene ether 36 g + Acrylic acid 9 g, dropping rate 2.8 mL / min; Second stage: Methacrylic acid 6 g + Nano-dispersion 0.9 g, dropping rate 1.6 mL / min; Third stage: 2-Acrylamido-2-methylpropanesulfonic acid 4 g, dropping rate 0.9 mL / min; Initiation system: Mercaptopropionic acid 1.6 g + Ammonium persulfate 0.9 g, molecular weight 22000 Da, PDI = 1.7.

[0108] Step 3: Post-treatment

[0109] Defoamer: Polydimethylsiloxane, 0.18 wt%; Defoaming: 52 °C, -0.085 MPa, 1.2 h.

[0110] Comparative Example 3

[0111] Step 1: Preparation of nano-composite dispersion

[0112] Nano-SiO2: Particle size 25 nm, mass 10 g; Carboxylated nano-cellulose: Carboxylic acid group content 1.4 mmol / g, mass 20 g (below the range); Dispersant: Polyether phosphate, 300 g; High-pressure homogenizer: 90 MPa, circulated 4 times, absolute value of Zeta potential 42 mV.

[0113] Step 2: Low-temperature gradient polymerization reaction

[0114] Temperature: 7 °C; First stage: Polyoxyethylene ether 37 g + Acrylic acid 10 g, dropping rate 3.0 mL / min; Second stage: Methacrylic acid 7 g + Nano-dispersion 1.0 g, dropping rate 1.7 mL / min; Third stage: 2-Acrylamido-2-methylpropanesulfonic acid 4.5 g, dropping rate 1.0 mL / min; Initiation system: Mercaptopropionic acid 1.7 g + Ammonium persulfate 1.0 g, molecular weight 30000 Da, PDI = 1.2.

[0115] Step 3: Post-treatment

[0116] Defoamer: Glyceryl monostearate, 0.20 wt%; Defoaming: 55 °C, -0.09 MPa, 1.5 h.

[0117] Comparative Example 4

[0118] Step 1: Preparation of nano-composite dispersion

[0119] Nano-SiO₂: particle size 30 nm, mass 10 g; Carboxylated nano-cellulose: carboxylic acid group content 1.5 mmol / g, mass 90 g (outside the range); Dispersant: Polyether phosphate, 2700 g; High-pressure homogenizer: 95 MPa, circulated 5 times, absolute value of Zeta potential 55 mV.

[0120] Step 2: Low-temperature gradient polymerization reaction

[0121] Temperature: 8 °C; First stage: Polyoxyethylene ether 38 g + Acrylic acid 11 g, dropping rate 3.2 mL / min; Second stage: Methacrylic acid 7.5 g + Nano-dispersion 1.1 g, dropping rate 1.8 mL / min; Third stage: 2-Acrylamido-2-methylpropanesulfonic acid 4.8 g, dropping rate 1.1 mL / min; Initiation system: Mercaptopropionic acid 1.8 g + Ammonium persulfate 1.1 g, molecular weight 32000 Da, PDI = 1.1.

[0122] Step 3: Post-treatment

[0123] Defoamer: Dimethyl silicone oil, 0.22 wt%; Defoaming: 58 °C, -0.095 MPa, 1.8 h.

[0124] Comparative Example 5

[0125] Step 1: Preparation of nano-composite dispersion

[0126] Nano-SiO₂: particle size 20 nm, mass 10 g; Carboxylated nano-cellulose: carboxylic acid group content 1.3 mmol / g, mass 40 g; Dispersant: Polyether phosphate, 400 g (below the range); High-pressure homogenizer: 85 MPa, circulated 4 times, absolute value of Zeta potential 36 mV (insufficient stability).

[0127] Step 2: Low-temperature gradient polymerization reaction

[0128] Temperature: 6°C; First stage: 36 g of polyoxyethylene ether + 9 g of acrylic acid, dropping rate 2.8 mL / min; Second stage: 6 g of methacrylic acid + 0.9 g of nano-dispersion, dropping rate 1.6 mL / min; Third stage: 4 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 0.9 mL / min; Initiation system: 1.6 g of mercaptopropionic acid + 0.9 g of ammonium persulfate, molecular weight 28000 Da, PDI = 1.3.

[0129] Step 3: Post-treatment

[0130] Defoamer: polydimethylsiloxane, 0.18 wt%; Defoaming: 52°C, -0.085 MPa, 1.2 h.

[0131] Comparative Example 6

[0132] Step 1: Preparation of nano-composite dispersion

[0133] Nano-SiO2: particle size 25 nm, mass 10 g; Carboxylated nano-cellulose: carboxylic acid group content 1.4 mmol / g, mass 50 g; Dispersant: polyether phosphate, 1000 g; High-pressure homogenizer: 90 MPa, 4 cycles, absolute value of Zeta potential 50 mV.

[0134] Step 2: Low-temperature gradient polymerization reaction

[0135] Temperature: 15°C (out of range); First stage: 37 g of polyoxyethylene ether + 10 g of acrylic acid, dropping rate 3.0 mL / min; Second stage: 7 g of methacrylic acid + 1.0 g of nano-dispersion, dropping rate 1.7 mL / min; Third stage: 4.5 g of 2-acrylamido-2-methylpropanesulfonic acid, dropping rate 1.0 mL / min; Initiation system: 1.7 g of mercaptopropionic acid + 1.0 g of ammonium persulfate, molecular weight 40000 Da, PDI = 1.8 (molecular weight and PDI out of range).

[0136] Step 3: Post-treatment

[0137] Defoamer: glycerol monostearate, 0.20 wt%; Defoaming: 55°C, -0.09 MPa, 1.5 h.

[0138] Due to the distinct particle edges and high stone powder content of manufactured sand, it often leads to an increase in the viscosity of concrete and a decrease in fluidity, affecting the construction performance. The viscosity-reducing admixture optimizes the rheological properties of concrete through nano-modification technology. Its dosage is 0.5% of the cement mass, which can significantly reduce the viscosity, improve the fluidity, and simultaneously maintain or improve the strength and durability of concrete. This test plan aims to verify its performance through standard test methods and supplement special tests related to nano-technology.

[0139] The test plan includes the following core contents: Fluidity test: mainly using slump test to evaluate the improvement of the workability of concrete by the admixture. Strength test: through compressive strength test to ensure that the admixture does not damage the mechanical properties of concrete. Other property tests: including setting time, bleeding rate and air content to comprehensively evaluate the influence of the admixture. Tests related to nanotechnology: supplementary tests are carried out on the dispersion and microstructure influence of nanomaterials. The tests are based on GB8076 - 2008 and the parameters are adjusted in combination with the actual engineering requirements.

[0140] Material requirements: Cement: meeting the requirements of Appendix A of GB8076 - 2008. Manufactured sand: meeting GB / T14684 "Sand for construction", fineness modulus 2.6 - 2.9, mud content < 1%. Aggregates: meeting GB / T14685 "Pebbles and crushed stones for construction", particle size 5mm - 20mm (40% of 5 - 10mm, 60% of 10 - 20mm), flaky particle content < 10%, void ratio < 47%, mud content < 0.5%. Water: meeting JGJ63 "Standard for water used in concrete". Viscosity - reducing admixture: dosage is 0.5% of the cement mass.

[0141] Mix proportion design: Basis: JGJ55 "Code for mix proportion design of ordinary concrete". Cement dosage: 360kg / m³ for high - performance water - reducing agent / pumping agent type, 330kg / m³ for other types. Sand ratio: 43% - 47% for high - performance / pumping agent type, 36% - 40% for other types. Water consumption: including the water in the liquid admixture, controlling the slump to be 210 ± 10mm for high - performance / pumping agent type and 80 ± 10mm for other types.

[0142] Mixing equipment: Use a 60L single - horizontal - axis forced mixer, with each mixing volume ≥ 20L and ≤ 45L. Mixing process: First dry - mix cement, sand and aggregates, then add water and admixture, and mix for 2min, with the temperature controlled at 20 ± 3°C.

[0143] Specimen preparation

[0144] According to GB / T50080 "Standard test method for properties of ordinary concrete mixtures".

[0145] The pre - curing temperature of the specimens is 20 ± 3°C, and standard test blocks are made as required (the compressive strength specimens are 150mm × 150mm × 150mm cubes).

[0146] The following are the detailed test items, methods and parameters, summarized in Table 1.

[0147] Table 1

[0148]

[0149] The test steps are as follows: Slump test: Fill the slump cone with the concrete mixture in two layers, tamping 15 times for each layer. After removing the cone, measure the slump and record the initial value and the value after 1 hour. Compressive strength test: Make standard test blocks and test them at the ages of 3 days, 7 days, and 28 days respectively, and calculate the strength ratio. Other tests: Conduct item by item according to the requirements of Table 1, record the data and compare with the control group (without admixture).

[0150] Table 2

[0151]

[0152] As shown in Table 2, the result analysis of Examples 1-10 is as follows: Slump: The range is 215-223 mm, all meeting the standard of 210±10 mm, and the 1-hour loss is controlled within 5-10 mm, with good slump retention. Water reduction rate: 25.0%-28.5%, with significant water-saving effect. Bleeding rate ratio: 20%-30%, with less bleeding phenomenon. Air content: 3.5%-3.8%, and the 1-hour loss is only 0.1%-0.3%, with excellent stability. Setting time difference: +7 to +15 min, meeting the construction requirements. Compressive strength ratio: 104%-111% at 3 days, 109%-119% at 7 days, and 114%-123% at 28 days, all higher than the standard requirements. Shrinkage ratio: 75%-86%, with low cracking risk. Relative durability: 89%-95%, far exceeding the standard of 80%. Conclusion: The examples show excellent fluidity, strength, and durability within the specified parameter range, fully demonstrating the technical advantages of the admixture. At the same time, as Figure 2 shown, the concrete structure is relatively compact and there are very few pores.

[0153] The results of Comparative Examples 1-6 are analyzed as follows: Comparative Example 1: The slump is 205 mm (low), the loss in 1 hour is 20 mm, the water reduction rate is only 22.0%, the compressive strength ratio is insufficient (95%-105%), and the bleeding rate ratio is as high as 40%. Comparative Example 2: The slump is 208 mm (low), the loss in 1 hour is 18 mm, the compressive strength ratio is low (98%-108%), and the bleeding rate ratio is 38%. Comparative Example 3: The slump is 210 mm, the strength is slightly lower (100%-110%), the bleeding rate ratio is 35%, and the performance does not reach the optimum. Comparative Example 4: The slump is 225 mm (high), the strength is slightly lower (102%-112%), and the bleeding rate ratio is 32%. Comparative Example 5: The slump is 207 mm (low), the loss in 1 hour is 22 mm, the water reduction rate is only 21.5%, the strength is insufficient (93%-103%), and the bleeding rate ratio is 42%. Comparative Example 6: The slump is 230 mm (too high), the loss in 1 hour is 25 mm, the water reduction rate is only 20.0%, the strength is seriously insufficient (90%-100%), the bleeding rate ratio is 45%, and the durability is only 80%. Conclusion: The comparative examples show that due to the parameters exceeding the specified range, the fluidity is insufficient, the strength decreases, or the stability deteriorates, verifying the rationality of the parameter setting of the invention.

[0154] Examples 1-10: Within the specified parameter range of the admixture, they show excellent viscosity reduction, fluidity, and slump retention, while maintaining the strength and durability of the concrete and meeting all standard requirements. Comparative Examples 1-6: The parameters deviate from the specified range, resulting in a significant decline in performance, specifically manifested as abnormal slump, insufficient strength, or poor durability, proving the necessity and superiority of the technical parameters of the invention.

[0155] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included within the protection scope of the present invention.

Claims

1. A synthetic process of viscosity-reducing admixture for manufactured sand, characterized in that, It includes the following steps: (1) Preparation of nano-composite dispersion: Mix nano-SiO2 with carboxylated nano-cellulose, add 0.5 - 1.2 wt% of polyether phosphate ester as a dispersant, and perform cyclic treatment in a high-pressure homogenizer at 80 - 100 MPa for 3 - 5 times to obtain a stable dispersion with an absolute value of Zeta potential > 40 mV; (2) Low-temperature gradient polymerization reaction: Under nitrogen protection, add acrylic monomers to a reaction kettle at low temperature for polymerization reaction; (3) Post-treatment process: After the reaction is completed, add 0.15 - 0.25 wt% of an organosilicon defoamer and perform defoaming treatment to obtain the final product.

2. The synthetic process of the viscosity-reducing admixture for manufactured sand according to claim 1, characterized in that, In step (1), the particle size of nano-SiO2 is 15 - 30 nm, and the carboxylic acid group content of carboxylated nano-cellulose is 1.2 - 1.5 mmol / g; nano-SiO2 and carboxylated nano-cellulose are mixed at a mass ratio of 1:(3 - 8).

3. The synthetic process of the viscosity-reducing admixture for manufactured sand according to claim 1, characterized in that, In step (1), the addition amount of polyether phosphate ester is 15 - 30 times the mass of carboxylated nano-cellulose.

4. The synthetic process of the viscosity-reducing admixture for manufactured sand according to claim 1, characterized in that, In step (2), the temperature of the reaction kettle is controlled at 5 - 10 °C at low temperature.

5. The synthetic process of the viscosity-reducing admixture for manufactured sand according to claim 1, characterized in that, In step (2), the polymerization reaction is carried out by dropwise addition in three stages: By mass, the first stage: a pre-emulsion containing 35 - 40 parts by mass of polyoxyethylene ether and 8 - 12 parts by mass of acrylic acid, with a dropping rate of 2.5 - 3.5 mL / min; the second stage: a suspension containing 5 - 8 parts by mass of methacrylic acid and 0.8 - 1.2 parts by mass of the nano-dispersion in step (1), with a dropping rate of 1.5 - 2.0 mL / min; the third stage: a solution of 3 - 5 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, with a dropping rate of 0.8 - 1.2 mL / min.

6. The synthetic process of the viscosity-reducing admixture for manufactured sand according to claim 5, characterized in that, In step (2), the initiation system for the polymerization reaction is as follows: An oxidation-reduction initiation system composed of 1.5 - 2.0 parts by mass of mercaptopropionic acid and 0.8 - 1.2 parts by mass of ammonium persulfate is used to control the molecular weight of the polymerization reaction within the range of 25000 - 35000 Da, and the molecular weight distribution index PDI < 1.

5.

7. The synthetic process of the viscosity-reducing admixture for manufactured sand according to claim 1, characterized in that, In step (3), the organosilicon defoamer is dimethyl silicone oil, polydimethylsiloxane, or glycerol monostearate.

8. The synthetic process of the viscosity-reducing admixture for manufactured sand according to claim 1, characterized in that, In step (3), the conditions for defoaming treatment are as follows: Defoaming treatment is carried out under vacuum conditions of 50 - 60 °C and -0.08 to -0.1 MPa for 1 - 2 h.

9. Use of the viscosity-reducing admixture prepared by the synthesis process according to claim 1, characterized in that, The dosage of the admixture is 0.2 - 0.5% of the mass of cement.

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