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

Abstract

The present invention discloses a synthesis process and application of a viscosity-reducing admixture for machine-made sand, and the present invention relates to the field of nano-modification technology. The process comprises the following steps: preparation of a nano-composite dispersion: mixing nano-SiO₂ with carboxylated nano-cellulose, adding polyether phosphate as a dispersant, and preparing a stable nano-composite dispersion by high-pressure homogenization; low-temperature gradient polymerization: under nitrogen protection, at a low temperature of 5-10°C, dropping monomers in three stages to carry out polymerization reaction; post-treatment process: adding an organosilicon defoaming agent, carrying out vacuum degassing treatment, and obtaining the final product. The admixture dosage is only 0.2-0.5% of the cement mass, which can significantly reduce the viscosity of machine-made sand concrete, improve fluidity, and enhance construction performance and concrete quality. It is characterized in that it utilizes nano-modification technology to optimize rheological properties, adopts a low-temperature polymerization process, is energy-saving and environmentally friendly, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of nanotechnology, specifically to a synthesis process and application of a viscosity-reducing admixture for manufactured sand. Background Technology

[0002] With the rapid development of the modern construction industry, concrete, as one of the most important building materials, has always been a key research focus in terms of performance optimization and improvement. In recent years, manufactured sand, as a new type of building material, has gradually replaced traditional natural sand and become an important component of concrete production due to its wide availability, controllable cost, and good physical properties. The production process of manufactured sand, through mechanical crushing and screening, can effectively utilize mineral resources while reducing the over-exploitation of natural river sand, resulting in significant environmental advantages. However, manufactured sand has also revealed some problems in practical applications, the most prominent of which is its adverse effect on the fluidity of concrete. Compared to natural sand, manufactured sand particles are usually more angular, have less continuous gradation, and have higher surface roughness. These characteristics lead to a significant increase in the viscosity and a decrease in fluidity of manufactured sand concrete, thus affecting the workability and final molding quality of the concrete.

[0003] The fluidity of concrete is a crucial indicator of its workability, directly impacting the smooth progress of pouring, vibration, and molding. In traditional natural sand concrete, the sand particles are relatively rounded and well-graded, enabling good synergy with cement paste and ensuring suitable rheological properties. However, the introduction of manufactured sand disrupts this balance. Due to the angularity of manufactured sand particles and its higher stone powder content, it easily generates greater frictional resistance in concrete, leading to reduced cement paste encapsulation and fluidity. Furthermore, the higher fine particle content in manufactured sand may further exacerbate concrete cohesion, causing problems such as pipe blockage or segregation during transportation and pumping. These issues not only increase construction difficulty but may also have potential negative impacts on the strength and durability of the concrete.

[0004] To address the issue of decreased fluidity in manufactured sand concrete, admixtures have been widely used as an important technical means to improve concrete performance. Traditional admixtures, such as polycarboxylate superplasticizers, can improve concrete fluidity to some extent by reducing the water-cement ratio and improving the dispersibility of cement particles. However, in manufactured sand concrete, the effectiveness of traditional superplasticizers is often significantly reduced. Due to the significant differences in particle characteristics between manufactured sand and natural sand, traditional superplasticizers are unable to effectively reduce its viscosity, usually requiring a substantial increase in dosage to achieve the desired fluidity. This high dosage not only significantly increases production costs but may also lead to other problems, such as prolonged setting time, decreased early strength, and even adverse effects on long-term durability. Therefore, developing a viscosity-reducing admixture specifically for manufactured sand concrete has become a critical issue that urgently needs to be addressed in the field of concrete technology.

[0005] In recent years, the development of nanotechnology has provided new possibilities for improving the performance of concrete admixtures. Nanomaterials, due to their extremely small particle size and high specific surface area, exhibit excellent physical and chemical properties 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 internal frictional resistance of the paste. The introduction of nanomaterials is particularly important in manufactured sand concrete. The high viscosity of manufactured sand can be alleviated by nanomaterials, for example, by enhancing the interfacial interaction between cement particles and manufactured sand, reducing internal friction between particles, thereby significantly improving the fluidity of concrete. Furthermore, nanomaterials can also improve the hydration process of concrete to a certain extent, promoting the formation of early strength, and providing dual protection for the workability and mechanical properties of manufactured sand concrete.

[0006] However, most nano-modified admixtures currently on the market are general-purpose products, lacking customized designs specifically for the needs of manufactured sand concrete. The properties of manufactured sand vary significantly depending on its origin, crushing process, and gradation, placing higher demands on the adaptability of admixtures. General-purpose admixtures may exhibit unstable performance in certain manufactured sand concrete mix proportions, such as insufficient viscosity reduction or poor compatibility with other admixtures. Therefore, developing a viscosity-reducing admixture specifically for manufactured sand requires not only excellent viscosity-reducing properties but also ensuring its stability and adaptability under various mix proportions. Furthermore, 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 application. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose a synthesis process and application of a viscosity-reducing admixture for manufactured sand, in order to solve the problems of increased viscosity and decreased fluidity caused by the angularity of particles and high stone powder content in manufactured sand concrete. This invention, through an innovative synthesis process, develops a high-efficiency, low-dosage admixture, aiming to improve the workability and quality of manufactured sand concrete while taking into account both economic and environmental benefits.

[0008] The technical solution adopted is: a process for synthesizing a viscosity-reducing admixture for manufactured sand, including the following steps: (1) Preparation of nanocomposite dispersion: mix nano-SiO2 with carboxylated nanocellulose, add 0.5-1.2wt% polyether phosphate as a dispersant, and cycle it 3-5 times in an 80-100MPa high-pressure homogenizer to obtain a stable dispersion with an absolute value of Zeta potential >40mV; (2) Low-temperature gradient polymerization reaction: under nitrogen protection, add acrylic monomers to the reactor at low temperature for polymerization reaction; (3) Post-treatment process: after the reaction is completed, add 0.15-0.25wt% organosilicon defoamer for 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 content of carboxylated nanocellulose is 1.2-1.5 mmol / g; nano-SiO2 and carboxylated nanocellulose are mixed at a mass ratio of 1:(3-8).

[0010] Preferably, the amount of polyether phosphate added in step (1) is 15 to 30 times the mass of carboxylated nanocellulose.

[0011] Preferably, in step (2), the temperature of the reactor is controlled at 5-10℃ at low temperature.

[0012] Preferably, the polymerization reaction in step (2) is carried out by dropping in three stages: by mass, the first stage is 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 is a suspension containing 5-8 parts by mass of methacrylic acid and 0.8-1.2 parts by mass of the nano-dispersion from step (1), with a dropping rate of 1.5-2.0 mL / min; the third stage is 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: 1.5-2.0 parts by mass of mercaptopropionic acid and 0.8-1.2 parts by mass of ammonium persulfate are used to form a redox initiation system, and the molecular weight of the polymerization reaction is controlled within the range of 25000-35000 Da, with a molecular weight distribution index PDI < 1.5.

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

[0015] Preferably, the degassing treatment conditions in step (3) are as follows: degassing treatment at 50-60℃ and -0.08 to -0.1MPa vacuum for 1-2 hours.

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

[0017] The polymer, by adsorbing onto the surface of cement particles, provides electrostatic repulsion and steric hindrance, reducing van der Waals attraction between particles, thereby dispersing the particles and lowering the yield stress and plastic viscosity of the mixture. This is consistent with the mechanism of traditional polycarboxylate superplasticizers, especially in manufactured sand concrete, where the polymer helps overcome increased friction caused by sharp particle edges and high fine powder content. The reinforcing effect of nanomaterials: The role of nano-SiO2: Studies have shown that nano-SiO2 can act as a lubricant, reducing interparticle friction, especially in manufactured sand concrete, where its high specific surface area may fill interparticle gaps and reduce viscosity. Furthermore, nano-SiO2 may improve early strength by providing nucleation sites to accelerate hydration reactions. The role of carboxylated nanocellulose: Although studies generally show that nanocellulose increases yield stress and viscosity (e.g., in self-compacting concrete), in this invention, its low dosage and binding with polymers may alter its behavior. It may optimize rheological properties and reduce interparticle friction in manufactured sand by forming network structures or interacting with cement particles.

[0018] In summary, the beneficial effects of this invention are as follows: Significantly improved rheological properties of manufactured sand concrete: Through innovative nanocomposite dispersion preparation technology, the dispersibility and interfacial reinforcement effect of the admixture are significantly improved, effectively improving the fluidity of manufactured sand concrete, reducing viscosity, and making it easier to construct and process. Precise control of molecular structure: The low-temperature gradient polymerization process ensures precise control of the molecular weight and uniform distribution of the admixture, thereby improving its functionality and long-term stability. Stable product quality: The defoaming and degassing technology in the post-processing effectively removes air bubbles from the production process, further ensuring the quality and application effect of the admixture. Low dosage and high efficiency: The admixture dosage is only 0.2-0.5% of the cement mass, which can significantly reduce the viscosity of manufactured sand concrete and improve rheological properties, greatly reducing production and construction costs. Interfacial reinforcement: The nano-modification technology enhances the interfacial interaction between particles, improving the uniformity and stability of concrete, thereby improving the final quality and durability of concrete. Energy saving 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 modern industrial sustainable development. Strong adaptability: This admixture is suitable for various manufactured sand proportions, can meet the actual needs of different engineering projects, and has broad application prospects and significant economic and environmental benefits.

[0019] With the above advantages, this invention not only achieves innovative breakthroughs in technology, but also demonstrates high efficiency and economy in practical applications, providing important technical support for the manufactured sand concrete industry. Attached Figure Description

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

[0021] Figure 2 This is a 5000x magnified image of the concrete material prepared with the admixture prepared in Example 10. Detailed Implementation

[0022] The present invention will now be described in detail through specific embodiments. However, these exemplary embodiments are for illustrative purposes only and are not intended to limit the actual scope of protection of the present invention in any way, nor are they intended to restrict the scope of protection of the present invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected.

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

[0024] List of key raw materials CAS numbers: Nano SiO2, CAS No.: 14808-60-7; Carboxylated nanocellulose, CAS No.: 9004-34-6; Polyether phosphate, CAS No.: 39464-70-5; Acrylic acid, CAS No.: 79-10-7; Methacrylic acid, CAS No.: 79-41-4; 2-Acrylamide-2-methylpropanesulfonic acid, CAS No.: 15214-89-8; Dimethyl silicone oil, CAS No.: 9016-00-6; Glyceryl monostearate, CAS No.: 31566-31-1; Mercaptopropionic acid, CAS No.: 107-96-0; Ammonium persulfate, CAS No.: 7727-54-0.

[0025] Example 1

[0026] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0030] Step 3: Post-processing

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

[0032] Example 2

[0033] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0037] Step 3: Post-processing

[0038] Defoamer: polydimethylsiloxane, 0.18wt%; Defoaming: 52℃, -0.085MPa, 1.2h.

[0039] Example 3

[0040] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0044] Step 3: Post-processing

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

[0046] Example 4

[0047] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0051] Step 3: Post-processing

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

[0053] Example 5

[0054] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0058] Step 3: Post-processing

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

[0060] Example 6

[0061] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0065] Step 3: Post-processing

[0066] Defoamer: Glyceryl monostearate, 0.19wt%; Defoaming: 53℃, -0.088MPa, 1.3h.

[0067] Example 7

[0068] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0072] Step 3: Post-processing

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

[0074] Example 8

[0075] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0079] Step 3: Post-processing

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

[0081] Example 9

[0082] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0086] Step 3: Post-processing

[0087] Defoamer: Glyceryl monostearate, 0.20wt%; Defoaming: 54℃, -0.089MPa, 1.4h.

[0088] Example 10

[0089] Step 1: Preparation of nanocomposite dispersion

[0090] Nano SiO2: particle size 29nm, mass 10g; Carboxylated nanocellulose: carboxylic acid group content 1.48mmol / g, mass 58g; Dispersant: polyether phosphate, 1740g; High-pressure homogenizer: 98MPa, 5 cycles, absolute value of Zeta potential 53mV.

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

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

[0093] Step 3: Post-processing

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

[0095] The microstructure of the admixture prepared in this embodiment is shown in the figure below. Figure 1 As shown.

[0096] Comparative Example 1

[0097] Step 1: Preparation of nanocomposite dispersion

[0098] Nano SiO2: Particle size 10nm (out of range), mass 10g; Carboxylated nanocellulose: Carboxylic acid group content 1.2mmol / g, mass 30g; Dispersant: Polyether phosphate, 450g; High-pressure homogenizer: 80MPa, 3 cycles, absolute value of Zeta potential 35mV (insufficient stability).

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

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

[0101] Step 3: Post-processing

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

[0103] Comparative Example 2

[0104] Step 1: Preparation of nanocomposite dispersion

[0105] Nano SiO2: particle size 20nm, mass 10g; Carboxylated nanocellulose: carboxylic acid group content 1.0mmol / g (below range), mass 40g; Dispersant: polyether phosphate, 600g; High-pressure homogenizer: 85MPa, 4 cycles, absolute value of Zeta potential 38mV (insufficient stability).

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

[0107] Temperature: 6℃; First stage: 36g polyoxyethylene ether + 9g acrylic acid, dropping rate 2.8mL / min; Second stage: 6g methacrylic acid + 0.9g nano-dispersion, dropping rate 1.6mL / min; Third stage: 4g 2-acrylamide-2-methylpropanesulfonic acid, dropping rate 0.9mL / min; Initiation system: 1.6g mercaptopropionic acid + 0.9g ammonium persulfate, molecular weight 22000Da, PDI=1.7.

[0108] Step 3: Post-processing

[0109] Defoamer: polydimethylsiloxane, 0.18wt%; Defoaming: 52℃, -0.085MPa, 1.2h.

[0110] Comparative Example 3

[0111] Step 1: Preparation of nanocomposite dispersion

[0112] Nano SiO2: particle size 25nm, mass 10g; Carboxylated nanocellulose: carboxylic acid group content 1.4mmol / g, mass 20g (below range); Dispersant: polyether phosphate, 300g; High-pressure homogenizer: 90MPa, 4 cycles, absolute value of Zeta potential 42mV.

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

[0114] Temperature: 7℃; First stage: 37g polyoxyethylene ether + 10g acrylic acid, dropping rate 3.0mL / min; Second stage: 7g methacrylic acid + 1.0g nano-dispersion, dropping rate 1.7mL / min; Third stage: 4.5g 2-acrylamide-2-methylpropanesulfonic acid, dropping rate 1.0mL / min; Initiation system: 1.7g mercaptopropionic acid + 1.0g ammonium persulfate, molecular weight 30000Da, PDI=1.2.

[0115] Step 3: Post-processing

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

[0117] Comparative Example 4

[0118] Step 1: Preparation of nanocomposite dispersion

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

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

[0121] Temperature: 8℃; First stage: 38g polyoxyethylene ether + 11g acrylic acid, dropping rate 3.2mL / min; Second stage: 7.5g methacrylic acid + 1.1g nano-dispersion, dropping rate 1.8mL / min; Third stage: 4.8g 2-acrylamide-2-methylpropanesulfonic acid, dropping rate 1.1mL / min; Initiation system: 1.8g mercaptopropionic acid + 1.1g ammonium persulfate, molecular weight 32000Da, PDI=1.1.

[0122] Step 3: Post-processing

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

[0124] Comparative Example 5

[0125] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0129] Step 3: Post-processing

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

[0131] Comparative Example 6

[0132] Step 1: Preparation of nanocomposite dispersion

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

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

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

[0136] Step 3: Post-processing

[0137] Defoamer: Glyceryl monostearate, 0.20wt%; Defoaming: 55℃, -0.09MPa, 1.5h.

[0138] Manufactured sand, due to its sharp-edged particles and high stone powder content, often leads to increased concrete viscosity and decreased fluidity, affecting workability. Viscosity-reducing admixtures, through nanotechnology modification, optimize the rheological properties of concrete. At a dosage of 0.5% of the cement mass, they can significantly reduce viscosity, improve fluidity, and simultaneously maintain or improve the strength and durability of concrete. This test plan aims to verify its performance using standard testing methods and supplement it with special tests related to nanotechnology.

[0139] The testing plan includes the following core components: Flowability testing: Primarily slump testing to evaluate the improvement of concrete workability by admixtures. Strength testing: Compressive strength testing to ensure that admixtures do not impair the mechanical properties of concrete. Other performance tests: Including setting time, bleeding rate, and air content, to comprehensively evaluate the impact of admixtures. Nanotechnology-related tests: Supplementary tests to address the dispersibility and microstructure effects of nanomaterials. Testing is conducted according to GB8076-2008, with parameters adjusted based on actual engineering needs.

[0140] Material Requirements: Cement: Meets the requirements of Appendix A of GB8076-2008. Manufactured Sand: Meets the requirements of GB / T14684 "Sand for Construction", with a fineness modulus of 2.6~2.9 and a mud content of <1%. Aggregate: Meets the requirements of GB / T14685 "Gravel and Crushed Stone for Construction", with a particle size of 5mm~20mm (510mm accounting for 40%, 1020mm accounting for 60%), a needle-like / flaky content of <10%, a porosity of <47%, and a mud content of <0.5%. Water: Meets the requirements of JGJ63 "Standard for Water Used in Concrete". Viscosity-reducing admixture: The dosage is 0.5% of the cement mass.

[0141] Mix design: Based on JGJ55 "Specification for Mix Design of Ordinary Concrete". Cement dosage: 360 kg / m³ for high-performance water-reducing agents / pumping agents, 330 kg / m³ for other types. Sand ratio: 43%~47% for high-performance / pumping agents, 36%~40% for other types. Water dosage: Including water in liquid admixtures, slump is controlled at 210±10 mm for high-performance / pumping agents, and 80±10 mm for other types.

[0142] Mixing equipment: Use a 60L single-shaft forced mixer, with a mixing volume of ≥20L and ≤45L per batch. Mixing process: First, dry mix cement, sand, and aggregate, then add water and admixtures, mix for 2 minutes, and control the temperature at 20±3°C.

[0143] Specimen preparation

[0144] According to GB / T50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures".

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

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

[0147] Table 1

[0148] Test Project Method details Relevant parameters Remark Slump and 1-hour loss According to GB / T50080, two layers of filling are used, with each layer compacted 15 times, and the initial slump is 210±10mm. Loss calculation: ΔSl = Sl0 - Sl1h, discard if the maximum / minimum difference > 10mm. Accurate to 5mm Water reduction rate Formula: R = (W0 - W1) / W0 × 100 Averaged 3 times, the median value is taken if the difference between the maximum and minimum values ​​is greater than 15%, and rounded to 0.1%. The final result is accurate to 1%. bleeding rate Formula: R = Bt / Bc × 100, 5L cylinder vibrates for 20 seconds, measurements are taken every 10 minutes for the first hour, and every 20 minutes thereafter, with the total amount accurate to 1g. If the average number of tests is 3 and the maximum / minimum difference is greater than 15%, discard the result; rounded to 1%. - Gas content and 1-hour loss According to GB / T50080, after 15~20s of vibration, the loss ΔA=A0-A1h Values ​​with a maximum-to-minimum difference greater than 0.5% are discarded; accuracy should be rounded to 0.1%. - Condensation time difference Formula: ΔT = Tt - Tc, penetration resistance method, initial setting pressure 3.5 MPa, final setting pressure 28 MPa On average, 3 tests were conducted; if the difference between the maximum and minimum values ​​exceeded 30 minutes, the test was discarded; the time should be accurate to 5 minutes. - compressive strength ratio Formula: R=ft / fc×100, according to GB / T50081, vibration for 15~20s, curing temperature 20±3°C Tests were conducted at 3 days, 7 days, and 28 days of age, with an average of 3 tests. Tests were discarded if the maximum / minimum difference exceeded 15%, accurate to 1%. -

[0149] The testing procedures are as follows: Slump test: The concrete mixture is poured into a slump cone in two layers, each layer is compacted 15 times, and the slump is measured after lifting the cone. The initial value and the value after 1 hour are recorded. Compressive strength test: Standard test blocks are prepared and tested at 3 days, 7 days, and 28 days of age, and the strength ratio is calculated. Other tests: Perform each item according to the requirements in Table 1, record the data, and compare them with the control group (without admixtures).

[0150] The results of Examples 1-10 are analyzed as follows: Slump: ranged from 215-223 mm, all meeting the 210±10 mm standard; 1-hour loss was controlled at 5-10 mm, indicating good slump retention. Water reduction rate: 25.0%-28.5%, showing significant water-saving effect. Bleeding rate: 20%-30%, with minimal bleeding. Air content: 3.5%-3.8%, with a 1-hour loss of only 0.1%-0.3%, demonstrating excellent stability. Setting time difference: +7 to +15 min, meeting construction requirements. Compressive strength ratio: 104%-111% at 3 days, 109%-119% at 7 days, and 114%-123% at 28 days, all exceeding standard requirements. Shrinkage ratio: 75%-86%, indicating low cracking risk. Relative durability: 89%-95%, far exceeding the 80% standard. Conclusion: The examples demonstrated excellent flowability, strength, and durability within the specified parameter range, fully showcasing the technical advantages of the admixture. Meanwhile, as... Figure 2 As shown, the concrete structure is relatively compact, with very few air pockets.

[0151] The results of Comparative Examples 1-6 are analyzed as follows: Comparative Example 1: Slump 205mm (low), 20mm loss in 1 hour, water reduction rate only 22.0%, compressive strength ratio insufficient (95%-105%), bleed rate as high as 40%. Comparative Example 2: Slump 208mm (low), 18mm loss in 1 hour, compressive strength ratio low (98%-108%), bleed rate 38%. Comparative Example 3: Slump 210mm, strength slightly low (100%-110%), bleed rate 35%, performance not optimal. Comparative Example 4: Slump 225mm (high), strength slightly low (102%-112%), bleed rate 32%. Comparative Example 5: Slump 207mm (low), 22mm loss in 1 hour, water reduction rate only 21.5%, strength insufficient (93%-103%), bleed rate 42%. Comparative Example 6: Slump 230mm (too high), 25mm loss in 1 hour, water reduction rate only 20.0%, severely insufficient strength (90%-100%), bleeding rate 45%, durability only 80%. Conclusion: The comparative example, due to parameters exceeding the specified range, resulted in insufficient fluidity, decreased strength, or worsened stability, verifying the rationality of the invention parameter settings.

[0152] Examples 1-10: Within the specified parameter range of the admixture, it exhibits excellent viscosity reduction, fluidity, and slump retention, while maintaining the strength and durability of the concrete, meeting all standard requirements. Comparative Examples 1-6: Deviations from the specified parameter range lead to a significant decrease in performance, specifically manifested as abnormal slump, insufficient strength, or poor durability, demonstrating the necessity and superiority of the invented technical parameters.

[0153] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for synthesizing a viscosity-reducing admixture for manufactured sand, characterized in that, Includes the following steps: (1) Preparation of nanocomposite dispersion: Nano-SiO2 and carboxylated nanocellulose are mixed, and 0.5-1.2wt% polyether phosphate is added as a dispersant. The mixture is circulated 3-5 times in a high-pressure homogenizer of 80-100MPa to obtain a stable dispersion with an absolute value of Zeta potential >40mV; (2) Low-temperature gradient polymerization reaction: Under nitrogen protection, acrylic monomers are added to the reactor at low temperature for polymerization reaction; in step (2), the reactor temperature is controlled at 5-10℃; in step (2), the polymerization reaction is carried out by dropping 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 2.5-3.5mL / min; the second stage: The suspension of the nano-dispersion in step (1) contains 5-8 parts by mass of methacrylic acid and 0.8-1.2 parts by mass, with a dropping rate of 1.5-2.0 mL / min; the third stage: 3-5 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid solution, with a dropping rate of 0.8-1.2 mL / min; the initiation system for the polymerization reaction in step (2) is as follows: 1.5-2.0 parts by mass of mercaptopropionic acid and 0.8-1.2 parts by mass of ammonium persulfate are used to form a redox initiation system, and the molecular weight of the polymerization reaction is controlled within the range of 25000-35000 Da, and the molecular weight distribution index PDI < 1.5; (3) post-processing: after the reaction is completed, 0.15-0.25 wt% of organosilicon defoamer is added for defoaming treatment to obtain the final product.

2. The synthesis 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 15-30nm, and the carboxylic acid content of carboxylated nanocellulose is 1.2-1.5mmol / g; nano-SiO2 and carboxylated nanocellulose are mixed at a mass ratio of 1:(3-8).

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

4. The synthesis 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 glyceryl monostearate.

5. The synthesis process of the viscosity-reducing admixture for manufactured sand according to claim 1, characterized in that, The degassing conditions in step (3) are as follows: degassing treatment at 50-60℃ and -0.08 to -0.1MPa vacuum for 1-2 hours.

6. The application of the viscosity-reducing admixture prepared by the synthesis process described in claim 1, characterized in that, The dosage of the admixture is 0.2-0.5% of the cement mass.

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