Adsorption type crystal nucleus early strength agent and preparation method thereof

Abstract

The invention provides an adsorption type crystal nucleus early strength agent and a preparation method thereof, and belongs to the field of concrete admixtures, and the preparation method comprises the following steps: 1, dissolving an adsorbent in a solvent according to a set proportion, and then adding an auxiliary agent under the condition of heating and stirring to form a uniform solution A; 2, putting nano silicon dioxide into a dispersing agent, and performing ultrasonic treatment to obtain a reaction base solution; 3, heating and stirring the reaction base solution, dropwise adding the solution A, and adjusting the pH value to 4-6 in the dropwise adding process; after the solution A is dropwise added, a coupling agent is added for continuous reaction, and the adsorption type crystal nucleus early strength agent is obtained.The adsorption type crystal nucleus early strength agent can accelerate the cement hydration rate and improve the early strength of a Portland cement system and has good stability.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete admixtures, and particularly relates to an adsorption-type crystal nucleus early strength agent. Background Art

[0002] Early strength agent is one of the earliest types of concrete admixtures used. Its main function is to accelerate the hydration of cement and promote the development of early strength of concrete. In winter construction or emergency repair projects, the demand for early strength agent is particularly prominent because it can significantly shorten the setting time of concrete and speed up the progress of the project.

[0003] Traditional early strength agents are mainly divided into three types: inorganic salts, organic and composite. Inorganic early strength agents, such as chlorides, sulfates, nitrates and carbonates, can improve the early strength of concrete, but they have some defects and limitations. For example, chlorides will accelerate the corrosion of steel bars, sulfates have poor early strength effects and may cause reduced concrete performance, nitrates may cause concrete dissolution, and carbonates may cause problems such as false setting of cement. Organic early strength agents, such as alcoholamines, are usually not used alone, but in combination with other inorganic early strength agents. These organic early strength agents are sensitive to dosage and may have cement adaptability problems. Improper dosage may cause severe retardation of concrete.

[0004] Composite early strength agents combine the characteristics of different types of early strength agents, aiming to improve the early strength effect and reduce the problems that may be caused by a single type of early strength agent. However, some new early strength agents mentioned in existing literature, such as crystal nucleus concrete early strength agents, may have problems such as complex processes and high costs despite their good performance, and no guidance is given on the compatibility of early strength agents with concrete; in view of the limitations of traditional early strength agents and the urgent need for early strength effects in concrete construction, the development of new early strength agents has become the research focus of concrete science and technology workers.

[0005] Nanocrystalline core early strength agent has been reported as a new early strength agent for improving the early strength of concrete. Among them, the nanocrystalline seed materials as crystal nuclei can be divided into two categories according to the mechanism of action. One category is nanocrystalline seed materials with physical effects, such as nano calcium silicate hydrate, nano TiO2, nano Fe2O3, nano ZrO2 and carbon nanotubes. Such materials mainly accelerate cement hydration by providing additional nucleation sites. They are dispersed in cement slurry, increasing the surface area of ​​cement particles in contact with water, thereby providing more nucleation points for the formation of CSH (calcium silicate hydrate) gel and other hydration products. This acceleration effect mainly relies on its own physical properties and does not involve chemical reactions. Due to its mechanism of action, it has high chemical stability and less impact on the environment. Also due to the limitation of its mechanism of action, the enhancement effect on early strength performance is limited. In addition, nanoparticles are prone to agglomeration during preparation and application, affecting the overall stability and use effect.

[0006] The other type is chemically active nano-seed materials, such as nano-SiO2, nano-Ca(OH)2, and nano-CaCO3. Such materials not only provide nucleation sites, but also promote hydration by participating in chemical reactions during cement hydration. For example, nano-SiO2 can react with Ca(OH)2 in cement to generate more CSH gel, while nano-CaCO3 may participate in the formation of calcium carbonate or other hydration products, thereby accelerating cement hydration and improving the performance of the final product. Such materials can significantly improve hydration efficiency and improve the quality of the final product by participating in chemical reactions during the cement hydration process. However, when such materials participate in chemical reactions, there may be slow or incomplete reactions. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an adsorption-type crystal nucleus early strength agent and a preparation method thereof, so that the adsorption-type crystal nucleus early strength agent can accelerate the cement hydration rate, improve the early strength of the silicate cement system, and have good stability.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a method for preparing an adsorption-type crystal nucleus early strength agent, comprising the following steps:

[0009] Step 1: dissolving the adsorbent in the solvent according to a set ratio, and then adding the additive under heating and stirring to form a uniform solution A;

[0010] Step 2: Add nano-silicon dioxide into a dispersant and use it as a reaction base liquid after ultrasonic treatment;

[0011] Step 3: Heat and stir the reaction base liquid, and add solution A dropwise at the same time, and adjust the pH value to 4-6 during the addition process; after the addition of solution A is completed, add a coupling agent to continue the reaction, and the adsorption type crystal nucleus early strength agent is obtained after the reaction is completed.

[0012] As a preferred embodiment of the present invention, the mass fraction of the adsorbent in the solvent is 1% to 10%; the mass fraction of the auxiliary agent in the solvent is 0.5% to 5%.

[0013] As a preferred embodiment of the present invention, in step 1: the adsorbent is any one of carboxymethyl modified chitosan, hydroxypropyl modified chitosan, methyl modified chitosan, acylated modified chitosan, glycolic acid copolymer modified chitosan and ultrasonically modified chitosan;

[0014] The solvent is any one of acetic acid, hydrochloric acid and sulfuric acid.

[0015] The auxiliary agent is any one of dodecyl ammonium sulfate, hexadecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium chloride, dodecyl dimethyl benzyl ammonium bromide, didecyl dimethyl ammonium chloride, dioctyl dimethyl ammonium chloride and octadecyl ammonium sulfate.

[0016] As a preferred embodiment of the present invention, in step 2: the mass fraction in the dispersant is 1% to 7%; the dispersant is a polycarboxylate water reducer with a molecular weight of 5000 to 100000; and the mass fraction of nano-silicon dioxide in the dispersant is 1% to 10%.

[0017] As a preferred embodiment of the present invention, in step 3: the heating temperature is 20-80° C.; the stirring speed is 200-1500 rpm; the solution A is added dropwise for 20-30 min, and the coupling agent is added and the reaction is continued for 3-16 h.

[0018] As a preferred embodiment of the present invention, in step three: the mass ratio of the coupling agent to the nano-silica is 1: (10-100); the coupling agent is any one of 3-(triethoxysilyl)-1-propanethiol, 3-aminotriethoxysilane, 3-(2-aminoethylamino)-propyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-(carboxypropyl)trimethoxysilane, 3-(vinyl)trimethoxysilane, 3-(methyl methacrylate)propyltrimethoxysilane and 3-(carboxypropyl)triethoxysilane.

[0019] The present invention also discloses an adsorption type crystal nucleus early strength agent prepared by the preparation method of the above-mentioned adsorption type crystal nucleus early strength agent, comprising a composite surface layer with calcium ion adsorption ability and a nano-silicon dioxide core wrapped by a coupling agent; the composite surface layer with calcium ion adsorption ability and the nano-silicon dioxide core wrapped by a coupling agent are connected through different reactions with the same coupling agent.

[0020] As a preferred embodiment of the present invention, the composite surface layer with calcium ion adsorption capacity is the product of amidation reaction between amino groups on the surface of the modified adsorbent and a coupling agent; the nano-silica core wrapped by the coupling agent is the combination product of nano-silica and ethoxy groups in the coupling agent.

[0021] Compared with the prior art, the crystal nucleus early strength agent of the present invention has the following beneficial technical effects:

[0022] The adsorption-type crystal nucleus early strength agent of the present invention can effectively adsorb calcium ions in the cement system and use them as nucleation sites to promote the transition from "small nuclei" to "large nuclei" and from "passive induction" to "active adsorption". It can quickly build a more developed crystal nucleus system, significantly accelerate the hydration process of cement, and thus improve the early strength of the silicate cement system. Due to its unique spatial structure, the early strength agent exhibits excellent stability.

[0023] The present invention not only provides more nucleation sites to accelerate cement hydration, but also participates in the chemical reaction of cement hydration process through chemical action, reducing the situation of slow reaction speed or incomplete reaction. This effect is due to the special structure of the early strength agent:

[0024] (1) The adsorption structure of the early strength agent is that the surface amino groups of the modified chitosan and the coupling agent form a composite shell through an amidation reaction, which produces an amide bond, thereby enhancing the stability of the overall structure of the material. The modified chitosan has abundant functional groups, which provide it with active sites for reacting with calcium ions in cement. At the same time, the large specific surface area and porosity of the modified chitosan further improve its adsorption activity, allowing the material to more effectively adsorb calcium ions in cement, thereby playing a positive role in the cement hydration process.

[0025] (2) The main part of the early strength agent is nano-silica, which itself has a certain nucleus induction effect and can promote the formation of nuclei during cement hydration. Under acidic conditions, the hydroxyl groups on the surface of nano-silica react with silanol (Si-OH) generated by the hydrolysis of the coupling agent to form a stable silicon-oxygen bond (Si-O-Si). This process effectively fixes the nano-silica particles in the material matrix and significantly enhances the interfacial bonding between the nanoparticles and the matrix. At the same time, the composite surface layer with calcium ion adsorption capacity is combined with the coupling agent through another reaction site. This dual reaction not only further enhances the interfacial bonding of the material, but also provides more nucleation points for cement hydration by expanding the nucleus sites, thereby improving the early strength and performance of the overall material.

[0026] (3) When the material enters the cement hydration system, the adsorption structure on the surface actively captures the calcium ions generated during the hydration process, using them as nucleation sites to promote the transition from "small nuclei" to "large nuclei" and from "passive induction" to "active adsorption". A more developed crystal nucleus system is quickly constructed to promote the hydration process and improve early strength. In addition, the polymer dispersant generates sufficient steric hindrance on the particle surface to prevent particle aggregation, thereby improving the stability of the dispersion system. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] The method for preparing the adsorption type crystal nucleus early strengthening agent in this example comprises the following steps:

[0030] 1. Dissolve carboxymethyl chitosan in 0.1M hydrochloric acid solution, then stir at 500rpm at 40°C, and gradually add hexadecyl trimethyl ammonium chloride until mixed evenly to obtain solution A for later use. The mass ratio of carboxymethyl chitosan, 0.1M hydrochloric acid solution, and hexadecyl trimethyl ammonium chloride in solution A is 1.5:20:1.

[0031] 2. Mix nano-silica and 3% polycarboxylate water reducer in a ratio of 1:10, and after ultrasonic treatment for 10 minutes, use it as the reaction base liquid for later use.

[0032] 3. First, heat the reaction base liquid to 60°C. Then, at a stirring speed of 800rpm, add solution A to the reaction base liquid while stirring, and the dropping process lasts for 30min. During this process, use 0.1M hydrochloric acid solution or 0.1M sodium hydroxide solution to adjust the pH value of the reaction system to about 4. After the dropwise addition is completed, add 3-aminotriethoxysilane (the mass ratio of 3-aminotriethoxysilane to nano-silicon dioxide is 1:10) to the reaction system, and then continue to react at 60°C and 800rpm for 5h. After the reaction is completed, the adsorption-type crystal nucleus early strength agent is obtained.

[0033] Example 2

[0034] The method for preparing the adsorption type crystal nucleus early strengthening agent in this example comprises the following steps:

[0035] Dissolve carboxymethyl chitosan in 0.1M hydrochloric acid solution, then stir at 500 rpm at 40°C, and gradually add ammonium dodecyl sulfate until mixed evenly to obtain solution A for later use. The mass ratio of carboxymethyl chitosan, 0.1M hydrochloric acid solution, and ammonium dodecyl sulfate in solution A is 1.5:20:1.

[0036] 2. Mix nano-silica and 3% polycarboxylate water reducer in a ratio of 1:20, and treat with ultrasound for 10 minutes before use as the reaction base liquid.

[0037] 3. First, heat the reaction base liquid to 50°C. Then, at a stirring speed of 1000rpm, add solution A to the reaction base liquid while stirring, and the dropping process lasts for 30min. During this process, use 0.1M hydrochloric acid solution or 0.1M sodium hydroxide solution to adjust the pH value of the reaction system to about 5. After the dropwise addition is completed, add 3-(carboxypropyl)trimethoxysilane (the mass ratio of it to nano-silica is 1:20) to the reaction system, and then continue to react at 50°C and 1000rpm for 5h. After the reaction is completed, the adsorption-type crystal nucleus early strength agent is obtained.

[0038] Example 3

[0039] The method for preparing the adsorption type crystal nucleus early strengthening agent in this example comprises the following steps:

[0040] Dissolve carboxymethyl chitosan in 0.1M hydrochloric acid solution, then stir at 500 rpm at 40°C, and gradually add dodecyl dimethyl benzyl ammonium bromide until the mixture is evenly mixed to obtain solution A for later use. The mass ratio of carboxymethyl chitosan, 0.1M hydrochloric acid solution, and dodecyl dimethyl benzyl ammonium bromide in solution A is 1:20:1.5.

[0041] 2. Mix nano-silica and 3% polycarboxylate water reducer in a ratio of 1:30, and after ultrasonic treatment for 10 minutes, use it as the reaction base liquid for later use.

[0042] 3. First, heat the reaction base liquid to 60°C. Then, at a stirring speed of 1000rpm, add solution A to the reaction base liquid while stirring, and the dropping process lasts for 30min. During this process, use 0.1M hydrochloric acid solution or 0.1M sodium hydroxide solution to adjust the pH value of the reaction system to about 5. After the dropwise addition is completed, add 3-(carboxypropyl)triethoxysilane (the mass ratio of it to nano-silica is 1:60) to the reaction system, and then continue to react at 60°C and 1000rpm for 8h. After the reaction is completed, the adsorption-type crystal nucleus early strength agent is obtained.

[0043] Example 4

[0044] The method for preparing the adsorption type crystal nucleus early strengthening agent in this example comprises the following steps:

[0045] Dissolve carboxymethyl chitosan in 0.1M hydrochloric acid solution, then stir at 40°C at a speed of 500rpm, and gradually add hexadecyl trimethyl ammonium bromide until the mixture is evenly mixed to obtain solution A for later use. The mass ratio of carboxymethyl chitosan, 0.1M hydrochloric acid solution, and hexadecyl trimethyl ammonium bromide in solution A is 1:20:0.5.

[0046] 2. Mix nano-silica and 3% polycarboxylate water reducer in a ratio of 1:40, and after ultrasonic treatment for 10 minutes, use it as the reaction base liquid for later use.

[0047] 3. First, heat the reaction base liquid to 80°C. Then, at a stirring speed of 1200rpm, add solution A to the reaction base liquid while stirring, and the dropping process lasts for 30min. During this process, use 0.1M hydrochloric acid solution or 0.1M sodium hydroxide solution to adjust the pH value of the reaction system to about 4. After the dropwise addition is completed, add 3-(carboxypropyl)triethoxysilane (the mass ratio of it to nano-silica is 1:80) to the reaction system, and then continue to react at 80°C and 1200rpm for 8h. After the reaction is completed, the adsorption-type crystal nucleus early strength agent is obtained.

[0048] Example 5

[0049] The method for preparing the adsorption type crystal nucleus early strengthening agent in this example comprises the following steps:

[0050] Dissolve carboxymethyl chitosan in 0.1M hydrochloric acid solution, then stir at 500 rpm at 40°C, and gradually add octadecyl ammonium sulfate until the mixture is evenly mixed to obtain solution A for later use. The mass ratio of carboxymethyl chitosan, 0.1M hydrochloric acid solution, and octadecyl ammonium sulfate in solution A is 1:30:0.6.

[0051] 2. Mix nano-silica and 3% polycarboxylate water reducer in a ratio of 1:60, and after ultrasonic treatment for 10 minutes, use it as the reaction base liquid for later use.

[0052] 3. First, heat the reaction base liquid to 80°C. Then, at a stirring speed of 1000rpm, add solution A dropwise to the reaction base liquid while stirring, and the dropping process lasts for 30 minutes. During this process, use 0.1M hydrochloric acid solution or 0.1M sodium hydroxide solution to adjust the pH value of the reaction system to about 6. After the dropwise addition is completed, add 3-(methyl methacrylate)propyltrimethoxysilane (the mass ratio of which to nano-silica is 1:90) to the reaction system, and then continue the reaction at 80°C and 1000rpm for 12 hours. After the reaction is completed, the adsorption-type crystal nucleus early strength agent is obtained.

[0053] Example 6

[0054] The preparation method of Example 6 is basically the same as that of Example 4, except that the carboxymethyl chitosan is replaced by ultrasonically modified chitosan.

[0055] Example 7

[0056] The preparation method of Example 7 is basically the same as that of Example 4, except that carboxymethyl chitosan is replaced by glycolic acid copolymer-modified chitosan.

[0057] Comparative Example

[0058] Compressive strength ratio determination, this experiment is based on the mix ratio in Table 1, with triethanolamine, a common traditional early strength agent on the market, as comparative example 1, sodium sulfate as comparative example 2, and a commercially available crystal nucleus early strength agent as comparative example 3, and the performance test is carried out with the above 7 embodiments. The volume of the experimental test block is 100×100×100mm 3 Concrete specimens. Refer to GB / T 50080-2016 "Standard for Test Methods for Performance of Ordinary Concrete Mixtures" to test the initial and final setting time of concrete. Refer to GB 50081-2002 "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" to test the compressive strength at 12h, 18h, 24h, 28d, and 90d, and calculate the compressive strength ratio and strength retention value.

[0059] Table 1C30 concrete mix ratio (kg / m 3 )

[0060]

[0061] Table 2 Compressive strength ratio test results of the examples

[0062]

[0063]

[0064] From the test data shown in Table 2, the use of the adsorption-type crystal nucleus early strength agent of the present invention can significantly accelerate the hydration process of cement, quickly improve the early strength of concrete, and show good strength maintenance ability. In addition, the early strength agent can also effectively shorten the initial setting and final setting time of concrete. These results show that the patented technology has obvious benefits.

Claims

1. A method for preparing an adsorption-type crystal nucleus early strength agent, characterized in that: The steps include: Step 1: dissolving the adsorbent in the solvent according to a set ratio, and then adding the additive under heating and stirring to form a uniform solution A; Step 2: Add nano-silicon dioxide into a dispersant and use it as a reaction base liquid after ultrasonic treatment; Step 3: Heat and stir the reaction base liquid, and add solution A dropwise at the same time, and adjust the pH value to 4-6 during the addition process; after the addition of solution A is completed, add a coupling agent to continue the reaction, and the adsorption type crystal nucleus early strength agent is obtained after the reaction is completed.

2. The method for preparing an adsorption-type crystal nucleation early strengthening agent according to claim 1, characterized in that: In the step 1, the mass fraction of the adsorbent in the solvent is 1% to 10%; the mass fraction of the auxiliary agent in the solvent is 0.5% to 5%.

3. The method for preparing an adsorption-type crystal nucleus early strengthening agent according to claim 1, characterized in that: In the step 1, the adsorbent is any one of carboxymethyl modified chitosan, hydroxypropyl modified chitosan, methyl modified chitosan, acylated modified chitosan, glycolic acid copolymer modified chitosan and ultrasonically modified chitosan; and the solvent is any one of acetic acid, hydrochloric acid and sulfuric acid.

4. The method for preparing an adsorption-type crystal nucleation early strength agent according to claim 1, characterized in that: In the step 1, the auxiliary agent is any one of dodecyl ammonium sulfate, hexadecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium chloride, dodecyl dimethyl benzyl ammonium bromide, didecyl dimethyl ammonium chloride, dioctyl dimethyl ammonium chloride and octadecyl ammonium sulfate.

5. The method for preparing an adsorption-type crystal nucleus early strengthening agent according to claim 1, characterized in that: In the step 2, the mass fraction of the nano-silicon dioxide in the dispersant is 1% to 7%; the dispersant is a polycarboxylic acid water reducer with a molecular weight of 5000 to 100000; and the mass fraction of the nano-silicon dioxide in the dispersant is 1% to 10%.

6. The method for preparing an adsorption-type crystal nucleus early strength agent according to claim 1, characterized in that: In the step 3, the heating temperature is 20-80° C.; the stirring speed is 200-1500 rpm; the dropwise addition time of solution A is 20-30 min, and the coupling agent is added and the reaction time is 3-16 h.

7. The method for preparing an adsorption-type crystal nucleus early strengthening agent according to claim 1, characterized in that: In the step three: the mass ratio of the coupling agent to the nano-silicon dioxide is 1:(10-100).

8. The method for preparing an adsorption-type crystal nucleus early strengthening agent according to claim 1, characterized in that: In the step three, the coupling agent is any one of 3-(triethoxysilyl)-1-propanethiol, 3-aminotriethoxysilane, 3-(2-aminoethylamino)-propyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-(carboxypropyl)trimethoxysilane, 3-(vinyl)trimethoxysilane, 3-(methyl methacrylate)propyltrimethoxysilane and 3-(carboxypropyl)triethoxysilane.

9. An adsorption type crystal nucleus early strength agent prepared by the preparation method of the adsorption type crystal nucleus early strength agent according to any one of claims 1 to 8, characterized in that: It comprises a composite surface layer with calcium ion adsorption capability and a nano silicon dioxide core wrapped by a coupling agent; the composite surface layer with calcium ion adsorption capability and the nano silicon dioxide core wrapped by a coupling agent are connected through different reactions with the same coupling agent.

10. The adsorption-type crystal nucleus early strength agent according to claim 9, characterized in that: The composite surface layer with calcium ion adsorption capacity is the product of amidation reaction between amino groups on the surface of the modified adsorbent and a coupling agent; the nano silicon dioxide core wrapped by the coupling agent is the combination product of nano silicon dioxide and ethoxy groups in the coupling agent.

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