Water reducing agent for concrete and preparation method thereof

Abstract

The invention relates to the technical field of concrete, and relates to a water reducing agent for concrete and a preparation method thereof. The preparation method of the water reducing agent for concrete comprises the following steps: dispersing silicon dioxide in ethanol, and heating and refluxing to obtain activated silicon dioxide; then dispersing in toluene, adding a silane coupling agent for reaction, and separating to obtain silanized silicon dioxide; the preparation method comprises the following steps: dispersing silanized silicon dioxide in ethanol and water, adding vinyl phosphonic acid, polyethylene glycol methacrylate and azobis (isobutylamidine hydrochloride) for reaction, and separating to obtain first modified silicon dioxide; then dispersing in a sodium gluconate aqueous solution for oscillation adsorption, adding 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide, reacting, and separating to obtain second modified silicon dioxide; and adding the second modified silicon dioxide into the polycarboxylate superplasticizer mother liquor, and shearing and dispersing to obtain the polycarboxylate superplasticizer. According to the water reducing agent for the concrete, provided by the invention, the freezing resistance and durability of the concrete are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and in particular to a water reducing agent for concrete and a preparation method thereof. Background Art

[0002] Water-reducing agents, an important concrete admixture, possess a unique amphiphilic structure, with a hydrophilic group at one end and a hydrophobic group at the other. When added to concrete, the hydrophilic groups rapidly adsorb onto the surfaces of cement particles. This adsorption process imparts a uniform charge to the surfaces of the cement particles, generating electrostatic repulsion between them. This electrostatic repulsion effectively prevents the aggregation of cement particles, keeping them more dispersed within the concrete, thereby increasing their fluidity and improving their workability. Simultaneously, the hydrophobic groups of the water-reducing agent molecules form a stable hydration film on the surface of the cement particles. This hydration film not only further prevents direct contact between cement particles, reducing interparticle friction, but also acts as a lubricant, effectively increasing the fluidity of the concrete and facilitating construction operations.

[0003] Although water-reducing agents play a significant role in improving the strength and performance of concrete, existing water-reducing agents still have many shortcomings in improving concrete durability. For example, some water-reducing agents may increase the air content of concrete after being added. If the air entrainment in the concrete is uneven or the bubble structure is unreasonable, the bubbles will form weak links within the concrete. Under the action of freeze-thaw cycles, these weak links easily become places where water accumulates and freezes, causing stress concentration within the concrete, thereby reducing the concrete's frost resistance. In some areas with high sulfate content, concrete structures face severe sulfate attack. Sulfate reacts chemically with hydration products in concrete to produce expansive products such as ettringite and gypsum. These expansive products generate expansive stresses within the concrete. When the stress exceeds the tensile strength of the concrete, it can cause damage to the concrete structure, such as cracking and spalling, seriously affecting the service life of the concrete structure. Based on this, the present invention provides a water-reducing agent for concrete and a method for preparing it. Summary of the Invention

[0004] The present invention provides a water reducer for concrete and a preparation method thereof, which improves the problem that existing water reducers may reduce the frost resistance of concrete due to uneven air entrainment after being added to concrete; and improves the ability of existing water reducers to resist cracking, spalling and other damage to concrete caused by sulfate erosion when used in areas with high sulfate content, thereby enhancing the durability of concrete.

[0005] The technical solutions of the present invention are as follows: In a first aspect, the present invention provides a method for preparing a water reducing agent for concrete, comprising the steps of: (1) dispersing silica in ethanol and heating under reflux to obtain activated silica; dispersing the activated silica in toluene, adding a silane coupling agent to react, and separating to obtain silanized silica; (2) dispersing the silanized silica in a mixed solvent of ethanol and water, adding vinylphosphonic acid, polyethylene glycol methacrylate and azobisisobutylamidine hydrochloride to react, and separating to obtain a first modified silica; (3) dispersing the first modified silica in a sodium gluconate aqueous solution for oscillation adsorption, adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, reacting, and separating to obtain a second modified silica; (4) The second modified silica is added to the polycarboxylate water-reducing agent mother liquor, and the concrete water-reducing agent is obtained after shearing and dispersion.

[0006] As a further technical solution, in step (1), the solid-liquid ratio of silicon dioxide to ethanol is 1 g:10-12 mL; and the heating and reflux step comprises: refluxing under nitrogen protection at 100-110° C. for 2-3 hours.

[0007] As a further technical solution, the silane coupling agent in step (1) is γ-(methacryloyloxy)propyltrimethoxysilane, and the amount ratio of the activated silica, toluene and γ-(methacryloyloxy)propyltrimethoxysilane is 1g:10-20mL:1-2mL.

[0008] As a further technical solution, the usage ratio of silanized silica, ethanol, water, vinylphosphonic acid, polyethylene glycol methacrylate and azobisisobutylamidine hydrochloride in step (2) is 40-50 g: 200-250 mL: 200-250 mL: 25-35 g: 65-75 g: 0.8-1.2 g.

[0009] As a further technical solution, the reaction conditions in step (2) are 350-450 rpm, 65-75° C., and nitrogen protection for 7-8 hours.

[0010] As a further technical solution, in the sodium gluconate aqueous solution, the solid-liquid ratio of sodium gluconate to water is 12-15 g:100 mL; in the step (3), the weight ratio of the first modified silica, sodium gluconate, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide is 35-45:48-60:0.4-0.6:0.4-0.6.

[0011] As a further technical solution, during the oscillation adsorption in step (3), the oscillation adsorption is carried out at pH = 6.0 ± 0.1 and 35-45°C for 10-12 hours.

[0012] As a further technical solution, the reaction conditions in step (3) are to react at a temperature of 25±1°C for 2-3 hours.

[0013] As a further technical solution, the preparation method of the polycarboxylate water-reducing agent mother liquor includes: mixing isopentanol polyoxyethylene ether with water to obtain a mixed solution; mixing acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, mercaptopropionic acid and water to obtain a premixed monomer; mixing azobisisobutylamidine hydrochloride with water to obtain an initiator solution; simultaneously adding the premixed monomer and the initiator solution to the mixed solution, stirring and reacting at 60±1° C. and 200-250 rpm for 4-5 hours, cooling to 40±1° C., slowly adding 30wt% NaOH solution to adjust the pH to 6.0-6.5, and passing through a 100-mesh sieve to obtain the obtained product.

[0014] As a further technical solution, the weight ratio of the second modified silica to the polycarboxylate water-reducing agent mother liquor is 18-22:78-82.

[0015] In a second aspect, the present invention provides a water reducer for concrete, which is prepared by the preparation method of the water reducer for concrete.

[0016] The working principle and beneficial effects of the present invention are: The present invention treats the surface of activated silica with a silane coupling agent to introduce reactive double bonds. The surface of traditional silica lacks active groups, making it difficult to chemically bond with subsequent monomers, resulting in limited modification effects. The present invention uses γ-(methacryloyloxy)propyltrimethoxysilane as a silane coupling agent. The trimethoxysilane group in its molecule can undergo a hydrolysis-condensation reaction with the hydroxyl groups on the surface of silica to form a stable Si-O-Si bond, while simultaneously introducing a double-bonded methacryloyloxy group into the surface of silica. This treatment not only enhances the compatibility of silica with the organic phase, but also provides a reaction site for the subsequent copolymerization of vinylphosphonic acid and polyethylene glycol methacrylate. When the silane coupling agent does not contain a double bond, this chemical grafting cannot be achieved, resulting in a significant decrease in the dispersibility and durability of the modified silica.

[0017] Based on silanized silica, the present invention further functionalizes the silica surface through a copolymerization reaction of vinylphosphonic acid and polyethylene glycol methacrylate. The phosphonic acid groups in vinylphosphonic acid have strong chelating ability and can form stable complexes with calcium ions in concrete, thereby effectively inhibiting expansion damage caused by sulfate attack and improving the concrete's sulfate corrosion resistance. Polyethylene glycol methacrylate introduces hydrophilic polyethylene glycol segments, which significantly improve the dispersion properties of the water reducer through steric hindrance and electrostatic repulsion, increasing the water reduction rate and fluidity of the concrete. The synergistic effect of these two components is reflected in the fact that the phosphonic acid groups provide corrosion protection, while the polyethylene glycol segments ensure uniform distribution of the water reducer in the concrete. If either component is missing, the performance of the modified silica will be significantly weakened. For example, the absence of vinylphosphonic acid will lead to a significant decrease in sulfate resistance, while the absence of polyethylene glycol methacrylate will cause a sharp drop in the water reduction rate.

[0018] This invention further optimizes the performance of modified silica through a coupling reaction with sodium gluconate. The gluconic acid groups in the sodium gluconate molecule have excellent corrosion inhibition properties and can be adsorbed on the surface of concrete pores, forming a protective film that inhibits the penetration of moisture and salt, thereby improving the concrete's frost resistance. More importantly, the present invention uses the catalytic action of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to covalently couple sodium gluconate to the modified silica surface, rather than simply physically adsorbing it. This chemical bonding ensures the long-term stability of the gluconic acid groups and avoids the problem of shedding caused by physical adsorption. If the coupling step is skipped, the sodium gluconate will only adhere to the silica surface through physical adsorption, significantly reducing its corrosion resistance and affecting its frost resistance.

[0019] The present invention achieves a comprehensive improvement in the performance of the water reducer through a three-step synergistic treatment of silanization, copolymerization and coupling. The silanization treatment provides active sites for subsequent reactions, the copolymerization reaction constructs a functionalized surface, and the coupling reaction further enhances the frost resistance and durability. These three steps are indispensable, and the absence or replacement of any link will lead to a significant decrease in performance. For example, the direct use of unmodified original silica has poor compatibility with polycarboxylic acid water reducer, dispersion failure, and a significant reduction in water reduction rate; while ordinary water reducers on the market lack silica reinforcement and phosphonic acid / gluconic acid composite protection, and their durability is much lower than the embodiments of the present invention. This multi-step synergistic effect optimizes the structure of the water reducer at the molecular level, thereby significantly improving the water reduction rate, mechanical properties and durability of concrete at the macro level. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0021] In the present invention, polyethylene glycol methacrylate (Mn=950), CAS No.: 26915-72-0, was purchased from Shanghai Hansi Chemical Co., Ltd.; azobisisobutylamidine hydrochloride (V-50), CAS: 2997-92-4, was purchased from Zhongshan Dixin Chemical Co., Ltd.; isopentanol polyoxyethylene ether, TPEG-2400, was purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd.

[0022] Example 1 This embodiment provides a method for preparing a water reducing agent for concrete, comprising the following steps: (1) 50 g of silica was dispersed in 550 mL of ethanol and refluxed at 105 °C for 2.5 h under nitrogen protection to obtain activated silica; 50 g of activated silica was dispersed in 750 mL of toluene, 80 mL of γ-(methacryloyloxy)propyltrimethoxysilane was added to react, and then separated to obtain silanized silica; (2) 45 g of silanized silica was dispersed in a mixed solvent of 225 mL of ethanol and 225 mL of water, 30 g of vinylphosphonic acid, 70 g of polyethylene glycol methacrylate and 1 g of azobisisobutylamidine hydrochloride V-50 were added, and the mixture was reacted at 400 rpm, 70 ° C, and nitrogen protection for 7.5 h. The mixture was centrifuged at 5000 rpm for 10 min, washed with deionized water, and dried in vacuum at 60 ° C to obtain the first modified silica; (3) 40 g of the first modified silica was dispersed in a sodium gluconate aqueous solution with a solid-liquid ratio of sodium gluconate to water of 54 g:400 mL, and adsorbed under oscillation at pH = 6.0 and 40 ° C for 11 h. 0.5 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 0.5 g of N-hydroxysuccinimide were added, and the mixture was reacted at a temperature of 25 ° C for 2.5 h. The mixture was centrifuged at 5000 rpm for 10 min, washed with deionized water, and dried in vacuum at 60 ° C to obtain the second modified silica. (4) 480 g of isopentanol polyoxyethylene ether was mixed with 500 g of water, and nitrogen was bubbled at 60 ° C and 300 rpm for 35 min to deoxygenate to obtain a mixed solution; 108 g of acrylic acid, 41 g of 2-acrylamide-2-methylpropanesulfonic acid, 6.3 g of mercaptopropionic acid and 52 g of water were mixed to obtain a premixed monomer; 12.6 g of azobisisobutylamidine hydrochloride V-50 and 50 g of water were mixed to obtain an initiator solution; the premixed monomer was added to the mixed solution at a rate of 2.0 mL / min and the initiator solution was added to the mixed solution at a rate of 0.5 mL / min, and the mixture was stirred at 60 ° C and 225 rpm for 4.5 h. The mixture was cooled to 40 ° C, and a 30 wt% NaOH aqueous solution was slowly added to adjust the pH to 6.2. The mixture was passed through a 100 mesh sieve to obtain a polycarboxylic acid water reducer mother liquor; (5) The second modified silica and the polycarboxylic acid water reducer mother liquor were mixed in a weight ratio of 20:80, and the water reducer for concrete was obtained after high-speed shear dispersion at 3000 rpm for 35 minutes.

[0023] Example 2 This embodiment provides a method for preparing a water reducing agent for concrete, comprising the following steps: (1) 50 g of silica was dispersed in 500 mL of ethanol and refluxed at 100 °C for 2 h under nitrogen protection to obtain activated silica; 50 g of activated silica was dispersed in 500 mL of toluene, 50 mL of γ-(methacryloyloxy)propyltrimethoxysilane was added to react, and then separated to obtain silanized silica; (2) 40 g of silanized silica was dispersed in a mixed solvent of 200 mL of ethanol and 200 mL of water, 25 g of vinylphosphonic acid, 65 g of polyethylene glycol methacrylate and 0.8 g of azobisisobutylamidine hydrochloride V-50 were added, and the mixture was reacted at 350 rpm, 65 ° C, and nitrogen protection for 7 h. The mixture was centrifuged at 5000 rpm for 10 min, washed with deionized water, and dried in vacuum at 60 ° C to obtain the first modified silica; (3) 35 g of the first modified silica was dispersed in a sodium gluconate aqueous solution with a solid-liquid ratio of sodium gluconate to water of 48 g:400 mL, and adsorbed by shaking at pH = 6.0 and 35 ° C for 10 h. 0.4 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 0.4 g of N-hydroxysuccinimide were added, and the mixture was reacted at a temperature of 25 ° C for 2 h. The mixture was centrifuged at 5000 rpm for 10 min, washed with deionized water, and dried in vacuum at 60 ° C to obtain the second modified silica. (4) 480 g of isopentanol polyoxyethylene ether was mixed with 500 g of water, and nitrogen was bubbled at 55 ° C and 250 rpm for 30 min to deoxygenate to obtain a mixed solution; 108 g of acrylic acid, 41 g of 2-acrylamide-2-methylpropanesulfonic acid, 6.3 g of mercaptopropionic acid and 52 g of water were mixed to obtain a premixed monomer; 12.6 g of azobisisobutylamidine hydrochloride V-50 and 50 g of water were mixed to obtain an initiator solution; the premixed monomer was added to the mixed solution at a rate of 2.0 mL / min and the initiator solution was added to the mixed solution at a rate of 0.5 mL / min, and the mixture was stirred at 60 ° C and 200 rpm for 4 h. The mixture was cooled to 40 ° C, and a 30 wt% NaOH aqueous solution was slowly added to adjust the pH to 6.0. The mixture was passed through a 100 mesh sieve to obtain a polycarboxylic acid water reducer mother liquor; (5) The second modified silica and the polycarboxylic acid water-reducing agent mother liquor were mixed in a weight ratio of 18:82, and the water-reducing agent for concrete was obtained after high-speed shear dispersion at 2500 rpm for 30 minutes.

[0024] Example 3 This embodiment provides a method for preparing a water reducing agent for concrete, comprising the following steps: (1) 50 g of silica was dispersed in 600 mL of ethanol and refluxed at 110 °C for 3 h under nitrogen protection to obtain activated silica; 50 g of activated silica was dispersed in 1000 mL of toluene, 100 mL of γ-(methacryloyloxy)propyltrimethoxysilane was added to react, and then separated to obtain silanized silica; (2) 50 g of silanized silica was dispersed in a mixed solvent of 250 mL of ethanol and 250 mL of water, 35 g of vinylphosphonic acid, 75 g of polyethylene glycol methacrylate and 1.2 g of azobisisobutylamidine hydrochloride V-50 were added, and the mixture was reacted at 450 rpm, 75 ° C, and nitrogen protection for 8 h. The mixture was centrifuged at 5000 rpm for 10 min, washed with deionized water, and dried in vacuum at 60 ° C to obtain the first modified silica; (3) 45 g of the first modified silica was dispersed in a sodium gluconate aqueous solution with a solid-liquid ratio of sodium gluconate to water of 60 g:400 mL, and adsorbed by shaking at pH = 6.0 and 45 ° C for 12 h. 0.6 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 0.6 g of N-hydroxysuccinimide were added, and the mixture was reacted at a temperature of 25 ° C for 3 h. The mixture was centrifuged at 5000 rpm for 10 min, washed with deionized water, and dried in vacuum at 60 ° C to obtain the second modified silica. (4) 480 g of isopentanol polyoxyethylene ether was mixed with 500 g of water, and nitrogen was bubbled at 65 ° C and 350 rpm for 40 min to deoxygenate to obtain a mixed solution; 108 g of acrylic acid, 41 g of 2-acrylamide-2-methylpropanesulfonic acid, 6.3 g of mercaptopropionic acid and 52 g of water were mixed to obtain a premixed monomer; 12.6 g of azobisisobutylamidine hydrochloride V-50 and 50 g of water were mixed to obtain an initiator solution; the premixed monomer was added to the mixed solution at a rate of 2.0 mL / min and the initiator solution was added to the mixed solution at a rate of 0.5 mL / min, and the mixture was stirred at 60 ° C and 250 rpm for 5 h, cooled to 40 ° C, and 30 wt% NaOH aqueous solution was slowly added to adjust the pH to 6.5. After passing through a 100 mesh sieve, a polycarboxylic acid water reducer mother liquor was obtained; (5) The second modified silica and the polycarboxylic acid water reducer mother liquor were mixed in a weight ratio of 22:78, and the water reducer for concrete was obtained after high-speed shear dispersion at 3500 rpm for 40 minutes.

[0025] Comparative Example 1 Adjustments were made based on Example 1. The difference from Example 1 was that the γ-(methacryloyloxy)propyltrimethoxysilane in Comparative Example 1 was replaced with an equal amount of silane coupling agent KH560.

[0026] Comparative Example 2 Adjustments were made based on Example 1. Unlike Example 1, the step of treating with γ-(methacryloyloxy)propyltrimethoxysilane was skipped in Comparative Example 2. The preparation steps of the water reducer included: dispersing 50 g of silica in 550 mL of ethanol, refluxing at 105° C. for 2.5 h under nitrogen protection to obtain activated silica, and performing step (2) using the activated silica instead of the silanized silica. Steps (3) to (5) were consistent with those in Example 1.

[0027] Comparative Example 3 Adjustments were made based on Example 1. Unlike Example 1, step (2) of preparing the water reducer in Comparative Example 3 was replaced by dispersing 45 g of silanized silica in a mixed solvent of 225 mL of ethanol and 225 mL of water, adding 0 g of vinylphosphonic acid, 70 g of polyethylene glycol methacrylate and 1 g of azobisisobutylamidine hydrochloride V-50 to react. Other conditions remained unchanged, and steps (3) to (5) were consistent with those in Example 1.

[0028] Comparative Example 4 Adjustments were made based on Example 1. Unlike Example 1, step (2) of preparing the water reducer in Comparative Example 4 was replaced by dispersing 45 g of silanized silica in a mixed solvent of 225 mL of ethanol and 225 mL of water, adding 30 g of vinylphosphonic acid, 0 g of polyethylene glycol methacrylate and 1 g of azobisisobutylamidine hydrochloride V-50 to react. Other conditions remained unchanged, and steps (3) to (5) were consistent with those in Example 1.

[0029] Comparative Example 5 Adjustments were made based on Example 1. Unlike Example 1, in Comparative Example 5, step (3) of dispersing the first modified silica in a sodium gluconate aqueous solution for adsorption was skipped, and 40 g of the first modified silica was directly dispersed in 400 mL of water, adsorbed at pH = 6.0 and 40° C. for 11 h, 0.5 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 0.5 g of N-hydroxysuccinimide were added, and the mixture was reacted at 25° C. for 2.5 h. The mixture was centrifuged at 5000 rpm for 10 min, washed with deionized water, and then dried in vacuo at 60° C. to obtain a second modified silica. Steps (3) to (5) were consistent with those in Example 1.

[0030] Comparative Example 6 Adjustments were made based on Example 1. Unlike Example 1, in step (3) of Comparative Example 6, 40 g of the first modified silica was dispersed in an aqueous solution of sodium gluconate with a solid-liquid ratio of 54 g:400 mL, and adsorbed under oscillation at pH = 6.0 and 40°C for 11 h. The mixture was directly centrifuged at 5000 rpm for 10 min, washed with deionized water, and then vacuum dried at 60°C to obtain the second modified silica. The 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide treatment steps were skipped, and steps (3) to (5) were consistent with Example 1.

[0031] Comparative Example 7 Based on Example 1, adjustments were made. Unlike Example 1, steps (1) to (3) were skipped in Comparative Example 7. The original silica and polycarboxylate superplasticizer mother liquor were mixed in a weight ratio of 20:80 and dispersed at 3000 rpm for 35 minutes. The polycarboxylate superplasticizer mother liquor was prepared using the same method as in Step 4 of Example 1.

[0032] Comparative Example 8 The commercially available water reducing agent PC-1 was purchased from Shanghai Kaiyin Chemical, with the brand name RHEOPLUS412.

[0033] Test Example: The water reducers prepared in Examples 1-3 and Comparative Examples 1-8 were tested as follows: The water-reducing agent precast concrete samples prepared by Examples 1-3 and Comparative Examples 1-8 contain 200 parts of cement, 80 parts of fly ash, 280 parts of fine aggregate, 600 parts of crushed stone, 90 parts of water, and 3.2 parts of water-reducing agent; the cement model is Conch brand ordinary silicate PO42.5 cement; the fly ash is Grade II fly ash, the fine aggregate is purchased from Shouyang Yongxing Stone Factory, and the crushed stone particle size is 10-20 mm.

[0034] Water reduction rate and water bleeding rate: Tested in accordance with GB 8076-2008 "Concrete Admixtures"; Compressive strength: Standard test blocks were prepared in accordance with GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the compressive strength of the standard test blocks was measured after 7 days and 28 days of curing; Frost resistance: Tested in accordance with GB / T 50082-2024 "Test methods for long-term performance and durability of ordinary concrete"; slow freezing method is used for evaluation based on the maximum number of freeze-thaw cycles; Sulfate corrosion resistance: Tested in accordance with GB / T 749-2008, Test Method for Sulfate Corrosion Resistance of Cement; specimens were immersed in a 5wt% Na2SO4 solution for 16 hours, dried at 80°C for 1 hour, and cooled for 1 hour, with one cycle per day. The mass loss rate after 28 cycles and the compressive strength corrosion resistance coefficient were measured: K = (strength after corrosion / strength before corrosion) × 100%; The results are shown in Table 1 below: Table 1

[0035] Combined with the above content, it can be seen that the water reducer obtained in Examples 1-3 has excellent performance, with a water reduction rate of 31.8%-32.5%, which is significantly higher than that of the comparative example, a very low water bleeding rate of 8.1%-8.5%, good water retention, mechanical properties of 7d compressive strength ≥41.9 MPa, 28d ≥57.5 MPa, outstanding durability with frost resistance ≥320 cycles, and sulfate corrosion resistance coefficient ≥92.1%, indicating that step 1 silanization, step 2 vinylphosphonic acid / polyethylene glycol methacrylate copolymerization, and step 3 sodium gluconate coupling synergistically improve the water reduction rate, strength and durability. The absence / replacement of any link leads to a significant decrease in performance, especially frost resistance and sulfate resistance.

[0036] In comparative example 1, γ-(methacryloyloxy)propyltrimethoxysilane was replaced with KH560. KH560 lacked double bonds and could not copolymerize with subsequent monomers, resulting in a decrease in the grafting rate on the silica surface, and a decrease in dispersibility and durability. In comparative example 2, the silanization step was skipped and no reactive double bonds were introduced. The monomer in step 2 could not be grafted, and the modification failed. In comparative example 3, vinylphosphonic acid was not added in step 2, and the phosphonic acid group was missing, which weakened the sulfate resistance and the corrosion resistance coefficient was only 72.8%. In comparative example 4, polyethylene glycol methacrylate was not added in step 2, and the polyethylene glycol hydrophilic segment was missing, and the water reduction rate was The results show that the decomposition coefficient of the modified silica was 0.0447 W / m, which was 0.033 W / m, and the decomposition coefficient of the modified silica was 0.083 W / m, which was 0.063 W / m, which was 0.067 ...

[0037] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a water reducing agent for concrete, characterized in that the steps include: (1) dispersing silica in ethanol and heating under reflux to obtain activated silica; dispersing the activated silica in toluene, adding a silane coupling agent to react, and separating to obtain silanized silica; (2) dispersing the silanized silica in a mixed solvent of ethanol and water, adding vinylphosphonic acid, polyethylene glycol methacrylate and azobisisobutylamidine hydrochloride to react, and separating to obtain a first modified silica; (3) dispersing the first modified silica in a sodium gluconate aqueous solution and performing oscillation adsorption, adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, reacting, and separating to obtain a second modified silica; (4) Adding the second modified silica to the polycarboxylate water-reducing agent mother liquor, and shearing and dispersing the mixture to obtain the concrete water-reducing agent.

2. A water reducing agent for concrete according to claim 1, characterized in that: In the step (1), the solid-liquid ratio of silicon dioxide to ethanol is 1 g:10-12 mL; and the heating and reflux step comprises: refluxing under nitrogen protection at 100-110° C. for 2-3 hours.

3. A water reducing agent for concrete according to claim 1, characterized in that: In the step (1), the silane coupling agent is γ-(methacryloyloxy)propyltrimethoxysilane, and the amount ratio of the activated silica, toluene and γ-(methacryloyloxy)propyltrimethoxysilane is 1g:10-20mL:1-2mL.

4. A water reducing agent for concrete according to claim 1, characterized in that: In the step (2), the usage ratio of silanized silica, ethanol, water, vinylphosphonic acid, polyethylene glycol methacrylate and azobisisobutylamidine hydrochloride is 40-50 g: 200-250 mL: 200-250 mL: 25-35 g: 65-75 g: 0.8-1.2 g.

5. A water reducing agent for concrete according to claim 1, characterized in that: The reaction conditions in step (2) are 350-450 rpm, 65-75° C., and nitrogen protection for 7-8 hours.

6. A water reducing agent for concrete according to claim 1, characterized in that: In the sodium gluconate aqueous solution, the solid-liquid ratio of sodium gluconate to water is 12-15 g:100 mL; in the step (3), the weight ratio of the first modified silica, sodium gluconate, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide is 35-45:48-60:0.4-0.6:0.4-0.

6.

7. A water reducing agent for concrete according to claim 1, characterized in that: During the oscillation adsorption in step (3), the oscillation adsorption is carried out at pH = 6.0 ± 0.1 and 35-45° C. for 10-12 hours.

8. A water reducing agent for concrete according to claim 1, characterized in that: The reaction conditions in step (3) are to react at a temperature of 25±1°C for 2-3 hours.

9. The water reducing agent for concrete according to claim 1, characterized in that: The preparation method of the polycarboxylate water-reducing agent mother liquor comprises: mixing isopentanol polyoxyethylene ether with water to obtain a mixed solution; mixing acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, mercaptopropionic acid and water to obtain a premixed monomer; mixing azobisisobutylamidine hydrochloride with water to obtain an initiator solution; simultaneously adding the premixed monomer and the initiator solution to the mixed solution, stirring and reacting at 60±1° C. and 200-250 rpm for 4-5 hours, cooling to 40±1° C., adding 30wt% NaOH solution to adjust the pH to 6.0-6.5, and passing through a 100-mesh sieve to obtain the obtained product.

10. A water reducing agent for concrete, characterized in that: The concrete water reducer is prepared by the preparation method of any one of claims 1 to 9.

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