A polymer-inorganic nano-composite early strength agent, its preparation method and application

Abstract

The present invention discloses a polymer-inorganic nano composite early strength agent and its preparation method and application, belonging to the technical field of building materials. The early strength agent includes monomer A, monomer B, monomer C and a modified nano unit. The polymer-inorganic nano composite early strength agent has a weight average molecular weight of 60 to 110 kDa and a PDI of 2 to 3. By utilizing its structural characteristics, the composite early strength agent of the present invention improves the dispersibility of nano attapulgite through the charge adsorption and dispersion effect, and significantly enhances the release of the activity of nano attapulgite. The nano attapulgite is grafted onto the molecular chain of the composite early strength agent through a polymer coupling agent modified polymerization reaction, thereby further exerting its nano activity, and jointly forming a spatial cross-linked double network structure with the long-chain polyether unit, significantly improving problems such as low early strength of cement-based materials, and ultimately achieving the purpose of shortening the construction period and improving the environment.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and specifically relates to a polymer-inorganic nano composite early strength agent and a preparation method and application thereof. Background Art

[0002] In the past decade, the early strength technology of cement-based materials and products has achieved major breakthroughs in theory and practice. However, although the traditional technology of adding early strength agents, adjusting cement mineral composition, increasing cement fineness or adopting steam curing has greatly improved the early strength of concrete, it has reduced the service life of concrete components.

[0003] Based on the hydration principle of cement-based materials, the existing means to accelerate the hydration process of cement-based materials mainly include the following two: one is to rely on early-strength polycarboxylic acid admixtures, and the other is to use nanomaterials. The size of nanomaterials is at the same order of magnitude (nanoscale) as that of calcium silicate hydrate gel (CSH). Their extremely high reactivity and specific surface area can reduce the crystallization barrier of hydration products, easily induce the crystallization of hydration products, and cause a large amount of early hydration products to be generated, thereby greatly improving the early strength.

[0004] For early-strength polycarboxylic acid admixtures, they mainly rely on the preparation of reactive polyethers with ultra-long side chains. However, the molecular weight of the main reactive polyethers in China is mainly concentrated in medium and short side chains, while the price of foreign products is relatively high, which is very unfavorable for the development of ultra-early strength water reducers; for nanomaterials, compared with traditional early strength agents, their dosage is extremely low, the early strength effect is obvious and does not affect the later strength development, and they have broad development prospects. There have been relevant reports abroad, but there is currently little research investment in this area in China. In addition, the nano effect of nanomaterials is highly dependent on dispersibility. The strong alkaline and high salt environment in cement-based materials will cause nanoparticles to agglomerate, which greatly reduces the application effect of nanomaterials. Therefore, the use of polymer materials to effectively disperse inorganic nanoparticles and the organic combination of the two materials will further enhance their early strength performance, and reducing the dosage can greatly reduce the cost of use.

[0005] Patent document CN104446102B "An admixture for improving the flexural and tensile strength of cement-based materials and its preparation method" provides a silica-based hybrid admixture with a core-shell structure and its preparation method. Although the admixture can improve the flexural and tensile strength of cement-based materials, its preparation process is relatively complicated. The core-shell structure of the admixture needs to go through multiple steps and harsh conditions such as an anaerobic system, which limits its application.

[0006] The patent document CN104944824B, "An early-strength agent and an early-strength water-reducing agent for cement concrete", discloses an early-strength agent component containing nano-calcium carbonate, calcium salt and water-reducing agent, which has a relatively obvious improvement effect on the strength of concrete after 1 day, but its improvement effect before 1 day is not good.

[0007] The patent document CN105712655B, "A functional concrete admixture and its preparation method and application", provides a functional concrete admixture and its preparation method and application. The functional concrete admixture is a compound of various siloxanes and silica. This admixture can reduce the electric flux of concrete, improve the chloride salt erosion resistance of concrete, but has no obvious improvement effect on the early strength of concrete.

[0008] Basically, the above patents mostly use surfactants to chemically modify nano-materials. It can be seen that the working performance and stability of the admixtures doped with nano-materials are one of the difficulties solved in various patents.

[0009] Nano-attapulgite (NAT) is a natural hydrated magnesium-aluminum silicate mineral, belonging to the sepiolite group. It has a layer-chain crystal structure and fibrous and rod-shaped crystal forms. It is rich in reserves, low in price and widely used, and is known as the "king of thousands of soils". Research has found that NAT has good adsorption, colloidality, filling and pozzolanic effects, and can effectively improve the performance of cement-based materials. The main reason is the existence of more rod-shaped attapulgite crystals in the interfacial transition zone. In addition, after chemical modification, the surface charge of nano-attapulgite changes from negative to positive, and the absolute value of the surface potential is also increased, thereby increasing the electrostatic repulsion between NAT powder particles. Moreover, the polymer can also provide more effective steric repulsion, thus improving the dispersion stability problem of NAT and laying a foundation for the application of NAT in cement-based materials. According to the characteristics of currently commonly used early-strength admixtures and the structure and activity effects of NAT itself, the present invention attempts to solve the above problems from the idea of synthesizing polymer-inorganic nano-composite materials and then improve the early strength of concrete. Summary of the Invention

[0010] Technical problems to be solved: Aiming at the above technical problems, the present invention provides a polymer-inorganic nano-composite early-strength agent and its preparation method and application. It is only a single polymer-inorganic hybrid material, and the preparation process is relatively simple, which can give full play to the activity of NAT, solve the dispersion stability problem of NAT, and then solve the defects of high energy consumption and short service life existing in traditional early-strength processes and technologies, and make contributions to energy conservation and emission reduction in the construction industry.

[0011] Technical solution: In the first aspect, the present invention provides a polymer-inorganic nano composite early strength agent, which includes monomer A, monomer B, monomer C and a modified nano unit. The weight-average molecular weight of the polymer-inorganic nano composite early strength agent is 60-110 kDa, and the PDI is 2-3;

[0012] The structural formula of the monomer A is shown in the following formula (Ⅰ):

[0013] ,

[0014] In formula (Ⅰ), R1 is H or CH3, and R2 is H or an alkali metal ion;

[0015] The structural formula of the monomer B is shown in the following formula (Ⅱ):

[0016] ,

[0017] In formula (Ⅱ), the value of n is an integer from 45 to 95;

[0018] The structural formula of the monomer C is shown in the following formula (Ⅲ):

[0019] ,

[0020] In formula (Ⅲ), R3 is H or CH3;

[0021] The modified nano unit is modified nano attapulgite.

[0022] Preferably, the monomer A is an unsaturated carboxylic acid.

[0023] Preferably, the monomer B is isopentenyl alcohol polyoxyethylene ether.

[0024] Preferably, the monomer C is methylacryloylpropyltrimethylammonium chloride or acryloylpropyltrimethylammonium chloride.

[0025] In the second aspect, the present invention provides a preparation method of the polymer-inorganic nano composite early strength agent described in the first aspect, including the following steps:

[0026] (1) Nano attapulgite modification reaction:

[0027] First, under normal temperature conditions, add nano-attapulgite powder to deionized water and stir to obtain suspension I with a mass fraction of 3% - 6%. Adjust the temperature of suspension I to 60 - 80 °C, add monomer C to obtain suspension II. Keep the reaction temperature unchanged, stir again, then add γ-methacryloxypropyltrimethoxysilane and continue stirring. During the reaction, the stirring rate, temperature, and time for each stage remain unchanged. The stirring speed is 600 - 1000 r / min, and the stirring time is 2 - 4 h to obtain modified nano-attapulgite. The added mass of monomer C is 3% of suspension I, and the added mass of γ-methacryloxypropyltrimethoxysilane is 5% of suspension II.

[0028] (2) Copolymerization reaction:

[0029] When the system temperature of the modified nano-attapulgite obtained in step (1) drops to 35 - 55 °C and stabilizes, mix and add monomer A, monomer B, monomer C, an oxidant, and a reductant, and react at a temperature of 35 - 55 °C for 3 - 6 hours to carry out free radical copolymerization. Among them, the free radical copolymerization is a free radical copolymerization reaction in an aqueous system, and the polymerization concentration of the free radical copolymerization is 25% - 30%.

[0030] Preferably, the mass ratio of the total amount of monomer A, monomer B, and monomer C input is 15 - 25:1 - 3:2.

[0031] Preferably, the oxidant is water-soluble ammonium persulfate, sodium persulfate, or potassium persulfate, and the dosage of the oxidant is 0.12% - 0.6% of the total mass of monomer A, monomer B, and monomer C.

[0032] Preferably, the reductant is one or two of sodium metabisulfite, sodium sulfite, sodium bisulfite, sodium dithionite, sodium thiosulfate, and ferrous sulfate, and the mass ratio of the dosage of the reductant to the oxidant is 1:2.

[0033] Thirdly, the present invention provides the application of the polymer-inorganic nano composite early strength agent described in the first aspect in the preparation of cement-based materials.

[0034] Preferably, the dosage of the polymer-inorganic nano composite early strength agent is 0.2% - 0.5% of the dosage of the gel material in the cement-based material.

[0035] The principle of the present invention is as follows:

[0036] The positively charged structural unit (monomer C) existing in the early strength agent of the present invention can replace Mg of NAT through ion exchange 2+ 、Al 3+Inorganic cations such as NAT are adsorbed onto the surface of organic particles through charge interactions, enabling effective dispersion of NAT, thus improving its dispersibility and further enhancing its activity. In addition, due to the large number of polar silanol groups on the surface of NAT, modification with silane coupling agents grafts NAT onto the molecular chain of the early strength agent through Si-O chemical bonds. The introduction of NAT lengthens the molecular chain of the early strength agent and increases the relative molecular weight, thereby enhancing the steric hindrance effect of the early strength agent molecules on cement particles and improving the dispersing ability of the early strength agent for cement particles. On the other hand, when NAT is grafted onto the molecular chain of the early strength agent, it can fully exert its nano-crystalline nucleus effect, pozzolanic effect, and filling effect in cement-based materials, increasing the formation of CaCO3 and Ca(OH)2 and further improving the mechanical properties of cement-based materials. At the same time, the carboxylic acid units present in the early strength agent can form adsorption sites with cement-based materials, thereby producing a dispersing effect and enhancing the water-reducing effect of the early strength agent. The long side-chain polyether units present in the early strength agent are water-soluble and extend in the medium, forming steric hindrance and a thick enough adsorption layer, making it difficult for NAT to agglomerate and further improving its stability and dispersibility.

[0037] Beneficial effects: The present invention utilizes the structural characteristics of the polymer-inorganic nano-composite early strength agent. Through charge adsorption, the dispersibility of nano-attapulgite is improved, significantly enhancing the release of the activity of NAT. Through modification with coupling agents, NAT is grafted onto the molecular chain of the early strength agent through Si-O chemical bonds, fully exerting the activity of NAT. By grafting long chains of polyether units to form a spatial network structure, the deficiencies of the prior art are overcome, and the dual functions of water reduction and early strength are realized. The carboxyl groups are used to form adsorption sites, fully exerting the water-reducing effect. In addition, the significant spatial effect of the long side-chain polyethers and the nano-structure of NAT present in the early strength agent of the present invention form a spatial cross-linked double network structure, creating a large steric hindrance and a thick enough adsorption layer, further enhancing the dispersing ability of the early strength agent for cement particles, and ultimately achieving the growth of the early strength of cement-based materials. Description of the Drawings

[0038] Figure 1 It is the infrared spectrum diagram of the polymer-inorganic nano-composite early strength agent in Example 3. Detailed Embodiments

[0039] The present invention will be described in detail below with reference to the drawings and specific embodiments:

[0040] In the examples, the weight-average molecular weight of the polymer-inorganic nano-composite early-strength agent was measured using a Shimadzu LC-20A high-performance gel permeation chromatograph (GPC). The chromatographic column used was the TSK G4000PWXL series, the column temperature was 25 °C, the eluent was 0.1 M aqueous sodium acetate solution, the flow rate was 0.5 mL / min, the injection volume was 15 μL of a 1‰ aqueous solution of the sample, and the standard curve was prepared using dextran standard (Sigma-Aldrich).

[0041] The raw material compositions of each example are shown in Table 1 below, where the feeding ratio is the feeding mass ratio of monomer A, monomer B, and monomer C:

[0042] Table 1 Raw material ratios of each example

[0043]

[0044] The process parameters of each example are shown in Table 2 below, where the dosages of the oxidant and the reducing agent are percentages of the total mass of the monomers:

[0045] Table 2 Process parameters of each example

[0046]

[0047] Among them, the infrared spectrum of the polymer-inorganic nano-composite early-strength agent synthesized in Example 3 is as Figure 1 shown, indicating that the corresponding polymer-inorganic nano-composite early-strength agent was successfully synthesized.

[0048] Comparative examples

[0049] The differences between Comparative Examples 1-3 and Examples 1-8 are as follows: the raw materials and preparation process conditions of the early-strength agent are different. Specifically, see Table 3 and Table 4 below. Among them, the feeding ratio is the molar ratio of monomer A, monomer B, and monomer C, and the dosage of the oxidant is a percentage of the total mass of the monomers:

[0050] Table 3 Raw material ratios of Comparative Examples 1-3

[0051] ,

[0052] Table 4 Process parameter tables of Comparative Examples 1-3

[0053]

[0054] Application examples

[0055] The polymer-inorganic nano-composite early-strength agents synthesized in Examples 1-11 and Comparative Examples 1-3 of the present invention were used to prepare corresponding cement-based materials. The differences in Application Examples 1-11 are that the sources and dosages of the early-strength agent are different. Specifically, see Table 5 below:

[0056] Table 5 Sources and Dosages of Organic-Inorganic Composite Admixtures in Application Examples 1-11

[0057]

[0058] Comparative Application Examples

[0059] The differences between the comparative application examples and the application examples lie in the sources and dosages of the early-strength agents. See the following Table 6 for details:

[0060] Table 6 Sources and Dosage Tables of Early-Strength Agents in Comparative Application Examples 1-3

[0061]

[0062] Performance Testing:

[0063] The test method for the strength of cement mortar is referred to the test method in GB / T 17671-2021 (ISO method) to evaluate the early-strength agents in the application examples and the comparative application examples. The basic mix ratios of the test mortar are shown in the following Table 7. The cement used in the test is P.Ⅱ 52.5 cement, and the sand used in the test is ISO standard sand. The performance test results of the control group, the examples and the comparative examples are shown in the following Table 8, and its dosage (in terms of solid content) is 0.2% - 0.5% of the dosage of the cementitious material. In addition, a control group is set up. The admixture in the control group is the commercially available Sika 530P early-strength water reducer. Among them, the dosage of the early-strength agent in Control Group 1 is 0.3%, and the dosage of the early-strength agent in Control Group 2 is 0.5%.

[0064] Table 7 Experimental Mix Ratios of the Control Group, Examples and Comparative Examples

[0065] ,

[0066] Table 8 Performance Test Results of Samples in the Control Group, Examples and Comparative Examples (under Standard Curing Conditions)

[0067] ,

[0068] It can be seen from the test results in Table 8 that according to the performance comparison between Application Examples 1-8 and Control Group 1, when the dosage of the early-strength agent is the same at 0.3%, Examples 1-8 can significantly promote the significant growth of the early strength of the cement-based material. The 12 h compressive strength and 1 d compressive strength of the prepared cement-based material are significantly improved, and are higher than the performance of Control Group 1. When the dosage of the early-strength agent in Control Group 2 is increased to 0.5%, the 12 h compressive strength working performance of the prepared cement-based material is still lower than that of Examples 1-8. Therefore, compared with the traditional early-strength agent, the polymer-inorganic nano composite early-strength agent of the present invention has the characteristics of low dosage and excellent early-strength efficiency.

[0069] In addition, under the same dosage conditions, the dispersion effects of the early strength agent in application examples 1 to 4 are also different, that is, the performance of application example 3 is better than that of other application examples. This is because the long chain of polyether and the nanostructure of nano-attapulgite will form a spatial cross double network structure. In order to form a sufficiently thick adsorption layer, the molecular weight of the early strength agent and the mass fraction of nano-attapulgite play an important role, and the quantity of the two should not be too high or too low. The reason is that when the molecular weight of the early strength agent is too high, the main chain structure will cause a cage effect on the carboxylic acid group. When the molecular weight is too low, the low content of the carboxylic acid group will cause the early strength agent to be unable to fix on the surface of the cement particles and too few NAT components cannot exert their nanocrystalline core effect and volcanic ash effect, making it difficult to improve the early strength of concrete.

[0070] In addition, it can be seen from the working performance of Application Examples 5 to 6 that when the number of repeating units of Monomer A is small, the adsorption sites in the early strength agent, i.e., the carboxylic acid groups, will be too few and the dispersion performance will be too low, so the working performance of Application Example 5 is better than that of Application Example 6; it can be seen from Application Examples 7 to 8 that the working performance of Application Example 7 is better than that of Application Example 8, because the number of monomer B structures, i.e., the number of polyether units, should not be too high. If it is too high, the early strength agent itself will be entangled and agglomerated, and it will not be able to effectively disperse the cement-based material system.

[0071] At the same time, it is not difficult to find from application examples 3, 9~11 that when the dosage of the early strength agent increases (0.2%→0.5%), the working strength of the test sample will slowly increase, but if the dosage continues to increase, the working strength of the test sample shows an obvious downward trend, which confirms that when the dosage of the polymer-inorganic nanocomposite early strength agent is too much, it may enter an adsorption supersaturation state. At this time, NAT may undergo secondary agglomeration due to the adsorption bridge effect caused by the adsorption groups on the early strength agent, which may cause the polymer chains in the early strength agent to entangle with each other, reducing the dispersion performance of the cement, and ultimately resulting in a lower working strength of the obtained cement-based material.

[0072] Compared with Examples 1 to 8, the working performance of Comparative Application Example 1 is significantly lower than that of the early strength agent of the present invention, which proves that the lack of carboxylic acid groups cannot effectively disperse the cement-based materials, thereby affecting the water-reducing performance of the early strength agent; the reason why the working performance of Comparative Application Example 2 is poor is that the lack of corresponding polyether units, that is, the inability to achieve a spatial network structure, will make it difficult to improve the early strength of cement-based materials; and the working performance of Comparative Application Example 3 is the worst among all the application examples, which proves that the lack of corresponding NAT structure will make it impossible to exert the activity of NAT, and the degree of cement hydration reaction cannot be increased, and it is difficult to achieve the purpose of improving the compressive strength.

[0073] The present invention utilizes the structural characteristics of the composite early-strength agent, improves the dispersibility of nano-attapulgite clay through the charge adsorption and dispersion effect, and significantly enhances the active release of nano-attapulgite clay; grafts the nano-attapulgite clay onto the molecular chain of the composite early-strength agent through the modification polymerization reaction of the polymer coupling agent, thereby further exerting its nano-activity, and jointly forming a spatial cross-linked double network structure with the long-chain polyether unit, significantly improving problems such as low early strength of the cement-based material, and ultimately achieving the purpose of shortening the construction period and improving the environment.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A polymer-inorganic nano-composite early strength agent, characterized in that: It includes monomer A, monomer B, monomer C and a modified nano unit. The weight-average molecular weight of the polymer-inorganic nano composite early strength agent is 60 - 110 kDa, and the PDI is 2 - 3; The structural formula of the monomer A is shown as the following formula (Ⅰ): ， In formula (Ⅰ), R1 is H or CH3, and R2 is H or an alkali metal ion; The structural formula of the monomer B is shown as the following formula (Ⅱ): ， In formula (Ⅱ), the value of n is an integer from 45 to 95; The structural formula of the monomer C is shown as the following formula (Ⅲ): ， In formula (Ⅲ), R3 is H or CH3; The modified nano unit is modified nano attapulgite. The preparation process of the modified nano attapulgite is as follows: First, at room temperature, the nano attapulgite powder is added to deionized water and stirred to obtain suspension Ⅰ with a mass fraction of 3% - 6%. The temperature of suspension Ⅰ is adjusted to 60 - 80 °C, and monomer C is added to obtain suspension Ⅱ. The reaction temperature is maintained unchanged, and stirring is carried out again. Then γ-methacryloxypropyltrimethoxysilane is added, and stirring is continued. The stirring rate, temperature and time in each stage of the reaction remain unchanged. The stirring speed is 600 - 1000 r / min, and the stirring time is 2 - 4 h to obtain the modified nano attapulgite, where the added mass of monomer C is 3% of suspension Ⅰ, and the added mass of γ-methacryloxypropyltrimethoxysilane is 5% of suspension Ⅱ.

2. The polymer-inorganic nano composite early strength agent according to claim 1, characterized in that: The monomer A is an unsaturated carboxylic acid.

3. A polymer-inorganic nano-composite early strength agent according to claim 1, characterized in that: The monomer B is isopentenol polyoxyethylene ether.

4. A polymer-inorganic nano-composite early strength agent according to claim 1, characterized in that: The monomer C is methylacryloylpropyltrimethylammonium chloride or acryloylpropyltrimethylammonium chloride.

5. A method for preparing the polymer-inorganic nano composite early strength agent according to any one of claims 1-4, characterized in that, It includes the following steps: When the system temperature of the modified nano attapulgite drops to 35 - 55 °C and becomes constant, monomer A, monomer B and monomer C, as well as an oxidant and a reductant, are mixed and added, and a free radical copolymerization reaction is carried out at a temperature of 35 - 55 °C for 3 - 6 hours. Among them, the free radical copolymerization reaction is a free radical copolymerization reaction in an aqueous system, and the polymerization concentration of the free radical copolymerization reaction is 25% - 30%.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the total material input of monomer A, monomer B and monomer C is 15 - 25:1 - 3:

2.

7. The preparation method according to claim 5, characterized in that: The oxidant is water-soluble ammonium persulfate, sodium persulfate or potassium persulfate, and the dosage of the oxidant is 0.12% - 0.6% of the total mass of monomer A, monomer B and monomer C.

8. The preparation method according to claim 5, characterized in that: The reductant is one or two of sodium metabisulfite, sodium sulfite, sodium bisulfite, sodium dithionite, sodium thiosulfate, ferrous sulfate. The mass ratio of the dosage of the reductant to the oxidant is 1:

2.

9. Application of the polymer-inorganic nano composite early strength agent according to any one of claims 1 - 4 in the preparation of cement-based materials.

10. The application according to claim 9, characterized in that, The dosage of the polymer-inorganic nano composite early strength agent is 0.2% - 0.5% of the dosage of the cementitious material in the cement-based material.

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