Concrete internal curing agent as well as preparation method and application thereof

Abstract

The invention discloses a concrete internal curing agent as well as a preparation method and application thereof, and belongs to the technical field of concrete curing. The preparation method of the concrete internal curing agent comprises the following steps: adding acrylic acid into an alkaline aqueous solution, and uniformly mixing to obtain an acrylic acid solution; adding acrylamide into an acrylic acid solution, uniformly stirring, adding the modified vermiculite, continuously stirring, adding a cross-linking agent and an initiator, and uniformly mixing to obtain a mixed solution; mixing and heating an organic solvent and Span60, adding the mixed solution, uniformly stirring, heating to a reaction temperature, and carrying out polymerization reaction to obtain the concrete internal curing agent. The concrete internal curing agent provided by the invention can effectively reduce the shrinkage of concrete, and also can reduce the adverse effect on the strength of the concrete.

Description

Technical Field

[0001] The invention relates to the technical field of concrete curing, and in particular to a concrete internal curing agent and a preparation method and application thereof. Background Art

[0002] Due to the demand for rapid construction of concrete projects and the excessive use of high early strength concrete and new high-efficiency water reducing agents, the problem of early cracking of modern concrete is becoming increasingly common, and will cause the concrete structure to fail during a service life far shorter than the design life, consuming huge amounts of money for repair and reconstruction, leading to large economic losses. Structural damage will also lead to overall structural failure, which has become a common problem affecting the structural safety and service life of modern concrete projects.

[0003] At present, external and internal curing are mainly used to reduce the shrinkage and cracking of concrete materials, thereby ensuring the good performance of concrete. External curing methods mainly include surface spraying and covering curing, such as surface watering curing, surface film covering, covering with wet straw bags, chemical curing, etc., which prevent excessive loss of surface moisture to achieve the purpose of limiting structural shrinkage. However, due to the dense structure of high-strength concrete, the penetration depth of external curing water will be limited to the near-surface area, and it is difficult to truly solve the problems of self-shrinkage and self-drying shrinkage caused by insufficient internal humidity of concrete. Internal curing has its own advantages, and there are obvious differences between it and external curing in terms of moisture distribution state, moisture diffusion direction and moisture carrier. From the perspective of moisture distribution state, during internal curing, the pre-absorbent material is evenly distributed inside the concrete in advance. The uniform distribution increases the probability of contact between the pre-absorbent material and the unhydrated cementitious material, and realizes "nearby curing" and "timely curing" to the greatest extent. However, the humidity control materials (concrete internal curing agents) currently used for internal curing have problems such as low humidity control capacity and poor moisture release performance. Summary of the invention

[0004] The purpose of the present invention is to provide a concrete curing agent and a preparation method and application thereof, so as to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: a method for preparing a concrete internal curing agent, comprising the following steps:

[0007] Adding acrylic acid into the alkaline aqueous solution and mixing them evenly to obtain an acrylic acid solution;

[0008] Add acrylamide to the acrylic acid solution, stir evenly, then add modified vermiculite, continue stirring, add a crosslinking agent and an initiator, mix evenly, and obtain a mixed solution;

[0009] The organic solvent and the dispersant are mixed and heated, and then added to the mixed solution, stirred evenly, and then heated to the reaction temperature for polymerization reaction, and after the reaction is completed, dried, crushed, and sieved to obtain the concrete curing agent (vermiculite / polyacrylic acid-acrylamide composite material);

[0010] The mesh number of the sieve used in the sieving is 400 mesh;

[0011] Furthermore, the neutralization degree of the acrylic acid solution is 70-100%.

[0012] Furthermore, the mass ratio of acrylic acid to acrylamide is (1-10):1;

[0013] The amount of the modified vermiculite is 1-10% of the total mass of acrylic acid, acrylamide and the modified vermiculite.

[0014] Further, the organic solvent includes cyclohexane; the dispersant includes Span60;

[0015] The cross-linking agent includes N-N'methylenebisacrylamide; the amount of the cross-linking agent is 0.5wt.% of the total mass of acrylic acid, acrylamide and modified vermiculite;

[0016] The initiator includes potassium persulfate; the amount of the initiator is 0.3wt.% of the total mass of acrylic acid, acrylamide and modified vermiculite;

[0017] The polymerization reaction was carried out at a temperature of 70° C. and for 3 hours.

[0018] Furthermore, the preparation method of the modified vermiculite comprises the following steps:

[0019] Adding vermiculite into the acid solution, heating and stirring to react to obtain acid-modified vermiculite;

[0020] The acid-modified vermiculite is added into the surface modifier solution and heated to react to obtain the modified vermiculite (organic modified vermiculite).

[0021] Furthermore, the acid solution includes a nitric acid solution with a concentration of 2 to 4 mol / L; the ratio of the acid solution to vermiculite is 10 mL:1 g; the temperature of the heating and stirring reaction is 70 to 99° C., the time is 2 to 8 hours, and the stirring speed is 500 r / min;

[0022] The concentration of the surface modifier solution is 0.5wt.%; the surface modifier solution is hexadecyltrimethylammonium bromide solution; the mass ratio of the acid-modified vermiculite to the surface modifier in the surface modifier solution is 1:10; the temperature of the heating reaction is 80°C and the time is 3h.

[0023] Acid-modified vermiculite has excellent moisture-regulating properties. At the same time, after organic modification, the lipophilicity of vermiculite is improved, and it can be combined with organic materials.

[0024] The second technical solution of the present invention: a concrete curing agent prepared by the above preparation method.

[0025] The third technical solution of the present invention: an application of the above-mentioned concrete curing agent in the preparation of concrete materials.

[0026] The fourth technical solution of the present invention: a concrete material, the raw materials include: basic components of concrete, the above-mentioned concrete curing agent, and additional water (the additional water is the water required by the concrete curing agent);

[0027] The amount of the concrete curing agent is 0.1-0.3% of the mass of the cementitious material in the basic components;

[0028] The amount of additional water used is 20 times the mass of the curing agent in the concrete.

[0029] A fifth technical solution of the present invention is a method for preparing the above concrete material, comprising the following steps:

[0030] The concrete curing agent and the additional water are mixed to pre-absorb water, and then mixed with the basic components of the concrete, and after being stirred evenly, formed and cured to obtain the concrete material.

[0031] The present invention discloses the following technical effects:

[0032] (1) The concrete curing agent of the present invention can effectively reduce the shrinkage of concrete and reduce the adverse effects on the strength of concrete.

[0033] (2) The present invention adopts the reverse suspension polymerization method to prepare the vermiculite / polyacrylic acid-acrylamide composite material (i.e., concrete curing agent), which combines the characteristics of fast moisture absorption and release rate and large specific surface area of ​​vermiculite with the high moisture regulating capacity of polyacrylic acid-acrylamide, and has excellent composite moisture regulating performance.

[0034] (3) The present invention prepares a composite humidity-controlling material (vermiculite / polyacrylic acid-acrylamide composite material) from the perspective of regulating air humidity and environmental protection. The composite humidity-controlling material combines the characteristics of fast moisture absorption and desorption rate of inorganic humidity-controlling materials and strong moisture absorption and high humidity-controlling capacity of organic materials, thereby overcoming the defects of single humidity-controlling materials (low humidity-controlling capacity of inorganic humidity-controlling materials and poor humidity-controlling performance of organic humidity-controlling materials).

[0035] (4) Since the water-cement ratio of high-performance concrete is low and the water content in the capillaries is insufficient, the relative humidity in the pores gradually decreases, which easily leads to self-drying in the hardened cement paste, thereby causing self-shrinkage and affecting the performance (safety and service life) of the concrete material. The composite material prepared by the present invention has good water absorption capacity and humidity regulating performance. When added to concrete, the humidity inside the concrete can be balanced, thereby improving the self-shrinkage of the concrete and enhancing the performance of the concrete material. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 The moisture absorption rate and moisture release rate of the acid-modified vermiculite prepared at different temperatures in Example 2 of the present invention;

[0038] Figure 2 The moisture absorption rate and moisture release rate of the acid-modified vermiculite prepared at different reaction times in Example 3 of the present invention;

[0039] Figure 3 The moisture absorption rate and moisture release rate of the acid-modified vermiculite prepared by using nitric acid solutions of different concentrations in Example 4 of the present invention;

[0040] Figure 4 The surface morphology of the acid-modified vermiculite prepared in Example 4 of the present invention, wherein (a) is a control, (b) is an acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 2 mol / L, (c) is an acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 4 mol / L, (d) is an acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 6 mol / L, and (e) is an acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 8 mol / L;

[0041] Figure 5 The XRD pattern of the acid-modified vermiculite prepared in Example 4 of the present invention;

[0042] Figure 6 This is a physical picture of the acid-modified vermiculite prepared in Example 5 of the present invention;

[0043] Figure 7 This is a physical picture of the organically modified vermiculite prepared in Example 5 of the present invention;

[0044] Figure 8 XRD patterns of acid-modified vermiculite and organic-modified vermiculite prepared in Example 5 of the present invention;

[0045] Fig. 9 FTIR images of the acid-modified vermiculite and the organic-modified vermiculite prepared in Example 5 of the present invention;

[0046] Fig.10 This is a schematic diagram of the preparation process of the concrete curing agent in Example 6 of the present invention;

[0047] Fig.11 The moisture absorption rate and moisture release rate of the vermiculite / polyacrylic acid-acrylamide composite materials prepared in Examples 7 to 9 of the present invention, wherein (a) is a vermiculite / polyacrylic acid-acrylamide composite material prepared at different modified vermiculite contents, (b) is a vermiculite / polyacrylic acid-acrylamide composite material prepared at different neutralization degrees, and (c) is a vermiculite / polyacrylic acid-acrylamide composite material prepared at different monomer ratios;

[0048] Fig.12 The SEM images and EDS images of the organically modified vermiculite used in Example 10 of the present invention, the vermiculite / polyacrylic acid-acrylamide composite material prepared in Example 10, and the polyacrylic acid-acrylamide prepared in Comparative Example 1, wherein (a) is a SEM image of the organically modified vermiculite, (b) is an EDS image of the organically modified vermiculite, (c) is a SEM image of the vermiculite / polyacrylic acid-acrylamide composite material, (d) is an EDS image of the vermiculite / polyacrylic acid-acrylamide composite material, (e) is a SEM image of polyacrylic acid-acrylamide, and (f) is an EDS image of polyacrylic acid-acrylamide;

[0049] Fig.13 XRD patterns of expanded vermiculite (vermiculite) used in the present invention, the vermiculite / polyacrylic acid-acrylamide composite material prepared in Example 10, and the polyacrylic acid-acrylamide prepared in Comparative Example 1;

[0050] Fig.14 FTIR graphs of the expanded vermiculite (vermiculite) used in the present invention, the vermiculite / polyacrylic acid-acrylamide composite material prepared in Example 10, and the polyacrylic acid-acrylamide prepared in Comparative Example 1;

[0051] Fig.15 This is a physical picture of the vermiculite / polyacrylic acid-acrylamide composite material prepared in Example 10 of the present invention after moisture absorption equilibrium;

[0052] Fig.16 The figures are physical pictures of BASF internal curing agent and concrete internal curing agent prepared in Example 10 of the present invention, wherein (a) is the concrete internal curing agent prepared in Example 10, and (b) is the BASF internal curing agent;

[0053] Fig.17The actual pictures of the humidity control test specimen and the humidity sensor used in Example 12 of the present invention, wherein (a) is the humidity sensor and (b) is the humidity control test specimen;

[0054] Fig.18 The internal relative humidity of the humidity-controlled test specimen prepared in Example 12 of the present invention, wherein (a) is the internal relative humidity of C01, C02, C03, and C04 concrete, (b) is the internal relative humidity of C03, C05, and C06 concrete, (c) is the internal relative humidity of C03, C03-01, and C03-02 concrete, and (d) is the internal relative humidity of C03 and D03 concrete;

[0055] Fig.19 are the autogenous shrinkage values ​​of different concretes prepared in Example 12 of the present invention, wherein (a) is the autogenous shrinkage value of C01, C02, C03, and C04 concretes, (b) is the autogenous shrinkage value of C03, C05, and C06 concretes, (c) is the autogenous shrinkage value of C03, C03-01, and C03-02 concretes, and (d) is the autogenous shrinkage value of C03 and D03 concretes;

[0056] Fig. 20 These are the drying shrinkage values ​​of different concretes prepared in Example 12 of the present invention, wherein (a) is the drying shrinkage value of C01, C02, C03, and C04 concretes, (b) is the drying shrinkage value of C03, C05, and C06 concretes, (c) is the drying shrinkage value of C03, C03-01, and C03-02 concretes, and (d) is the drying shrinkage value of C03 and D03 concretes. DETAILED DESCRIPTION

[0057] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0058] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0059] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0060] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0061] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0062] The “parts” described in the following examples are all “parts by weight”.

[0063] The expanded vermiculite used in the present invention is purchased from Xinnuo Mineral Products Processing Factory in Lingshou County, Hebei Province.

[0064] The present invention observes the surface morphology of the sample by scanning electron microscope (S-4800 of Hitachi, Japan) at an accelerating voltage of 5kV. The sample is sputter-plated with gold palladium using tin foil as a backing.

[0065] The present invention uses XRD (D8 Advanced of Bruker, Germany) to perform structural analysis, with a scanning speed of 8° per minute, a scanning range of 2θ=5-70°, a target material of Cu, and a wavelength of 0.154 nm.

[0066] The present invention uses the infrared absorption spectrum of the sample using FTIR-850 Fourier transform infrared spectrometer, with a scanning range from 400cm -1 Up to 4000cm -1 , average of 32 scans, resolution 8cm -1 .

[0067] The sample was subjected to a humidity test in a desiccator, the temperature was maintained at 25°C, and the moisture absorption test and moisture release test were performed at 90% RH and 30% RH respectively. An electronic analytical balance (ACCULAB, ALB-224) was used to record the change in sample mass over time within 48 hours, and the value at the moisture absorption or moisture release equilibrium was used to calculate the moisture absorption rate or moisture release rate. The calculation formula for moisture absorption rate (g / g) and moisture release rate (g / g) is:

[0068]

[0069] Where m a is the moisture absorption rate, m b is the moisture release rate, m0 is the initial weight of the dry sample, m1 is the weight of the composite material at the moisture absorption equilibrium state, and m2 is the weight of the composite sample at the moisture release equilibrium state.

[0070] Example 1

[0071] A method for preparing acid-modified vermiculite:

[0072] Add 20 g of expanded vermiculite to 200 mL of nitric acid solution, heat in a water bath, set the stirring temperature to 500 r / min, and heat to react. After the reaction is completed, filter and wash with distilled water until the pH is greater than 6, dry at 80°C for 24 hours, and pass through a 200-mesh sieve to obtain acid-modified vermiculite.

[0073] Among them, the concentration of nitric acid solution is 2mol / L, 4mol / L, 6mol / L or 8mol / L; the heating temperature is 70℃, 80℃, 90℃ or 99℃; the heating reaction time is 2h, 4h, 6h or 8h. Under this condition, a three-factor four-level orthogonal experiment is carried out to test the moisture absorption rate and moisture release rate of the product at 48h. The values ​​at moisture absorption or moisture release equilibrium are used to calculate the moisture absorption rate (absorption ratio) or moisture release rate (desorption ratio). The results of the orthogonal experiment are shown in Table 1.

[0074] The orthogonal experimental results were analyzed and the results are shown in Table 2.

[0075] In Table 2, K1, K2, K3, and K4 represent the first, second, third, and fourth values ​​of the relevant factors, respectively. For example, if it is concentration, K1 represents 2mol / L, K2 represents 4mol / L, K3 represents 6mol / L, and K4 represents 8mol / L. The moisture absorption rate K1 concentration column value is the average of the moisture absorption data of four rows of sample numbers 1, 2, 3, and 4, that is, 0.2254=(0.1837+0.2286+0.2254+0.2638) / 4. The R value is the range value of a single factor, that is, the maximum value minus the minimum value in a single column, from which we can see the impact of a single factor on the overall result.

[0076] Table 1 Orthogonal factors and humidity control performance of acid-modified vermiculite

[0077]

[0078] No. 0 in Table 1 is expanded vermiculite that has not been acidified.

[0079] Table 2 Range analysis of humidity control performance of acid-modified vermiculite

[0080]

[0081]

[0082] It can be seen from Table 1 that the moisture absorption rate of the 16 groups of acid-modified vermiculite is always greater than the moisture release rate, which indicates that moisture release is always incomplete. In addition, the moisture-regulating performance of the vermiculite after acid treatment is generally higher than that of the untreated vermiculite.

[0083] It can be seen from Table 1 and Table 2 that with the increase of nitric acid concentration, heating reaction time and heating temperature, the moisture absorption and desorption performance of acid-modified vermiculite showed a trend of first increasing and then decreasing. The heating reaction time and temperature have little effect on the moisture absorption rate and desorption rate, and the nitric acid concentration has the greatest influence on the moisture absorption and desorption function.

[0084] Through orthogonal experimental analysis and comparison with unacidified vermiculite, it was found that when the concentration was 4 mol / L, the heating reaction time was 4 h, and the temperature was 90°C, the moisture absorption rate and moisture release rate reached the best, which were 34.13% and 23.79% respectively.

[0085] Example 2

[0086] A preparation method of acid-modified vermiculite (single factor experiment):

[0087] Add 20 g of expanded vermiculite to 200 mL of 4 mol / L nitric acid solution, heat to 70°C, 80°C, 90°C, and 99°C in a water bath, set the stirring temperature to 500 r / min, and heat to react for 4 h. After the reaction, filter and wash with distilled water until pH>6, dry at 80°C for 24 h, and pass through a 200-mesh sieve to obtain acid-modified vermiculite.

[0088] The moisture absorption and moisture release rates of the acid-modified vermiculite prepared in this example were measured. Figure 1 .

[0089] from Figure 1 It can be seen that the moisture absorption rate and moisture release rate have the same change pattern, which increases first and then decreases with the increase of temperature, reaching the highest value at 90°C. However, the overall change is small, which shows that temperature has little effect on humidity control.

[0090] Example 3

[0091] A preparation method of acid-modified vermiculite (single factor experiment):

[0092] Add 20 g of expanded vermiculite to 200 mL of 4 mol / L nitric acid solution, heat to 90°C in a water bath, set the stirring temperature to 500 r / min, and heat to react for 2 h, 4 h, 6 h, and 8 h, respectively. After the reaction, filter and wash with distilled water until pH>6, dry at 80°C for 24 h, and pass through a 200-mesh sieve to obtain acid-modified vermiculite.

[0093] The moisture absorption and moisture release rates of the acid-modified vermiculite prepared in this example were measured. Figure 2 .

[0094] from Figure 2 It can be seen that the moisture absorption rate is generally higher than the moisture release rate. Both the moisture absorption rate and the moisture release rate first increase and then decrease with time, reaching the highest value at 4 hours.

[0095] Example 4

[0096] A preparation method of acid-modified vermiculite (single factor experiment):

[0097] 20 g of expanded vermiculite was added to 200 mL of nitric acid solutions with concentrations of 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 6 mol / L and 8 mol / L, respectively, and the mixture was heated to 90°C in a water bath, the stirring temperature was set to 500 r / min, and the reaction was heated for 4 hours. After the reaction, the mixture was filtered and washed with distilled water until the pH was greater than 6, dried at 80°C for 24 hours, and passed through a 200-mesh sieve to obtain acid-modified vermiculite. The expanded vermiculite without any treatment was used as a control (recorded as 0 mol / L nitric acid solution).

[0098] The moisture absorption and moisture release rates of the acid-modified vermiculite prepared in this example were measured. Figure 3 .

[0099] from Figure 3 It can be seen that the moisture absorption rate is generally higher than the moisture release rate. Both the moisture absorption rate and the moisture release rate first increase and then decrease with the increase of concentration, reaching the highest value at 4 mol / L.

[0100] It can be seen from the results of Examples 1 to 4 that the conclusions of the single-factor experiment are consistent with those of the three-variable four-level orthogonal experiment.

[0101] The surface morphology of the acid-modified vermiculite prepared in this example was measured. Figure 4 ; Figure 4 (a) is the control, (b) is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 2 mol / L, (c) is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 4 mol / L, (d) is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 6 mol / L, and (e) is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 8 mol / L.

[0102] from Figure 4It can be seen that expanded vermiculite has a lamellar structure. Before nitric acid treatment, vermiculite is in large granular form with a relatively flat surface and a relatively complete lamellar structure. After acid treatment, the lamellar structure of vermiculite is destroyed. The lamellar structure of vermiculite first decomposes from the edge of the particle to form fine flaky particles, which reduces the overall size of the vermiculite. As the acid treatment concentration increases, the edge of the vermiculite gradually decomposes, the overall size of the vermiculite continues to decrease, and the specific surface area increases.

[0103] The XRD pattern of the acid-modified vermiculite prepared in this example is shown in Figure 5 ; Figure 5 In the table, 0-0-0 is the control, 1-4-90 is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 1 mol / L, 2-4-90 is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 2 mol / L, 3-4-90 is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 3 mol / L, 4-4-90 is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 4 mol / L, 6-4-90 is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 6 mol / L, and 8-4-90 is the acid-modified vermiculite prepared by using a nitric acid solution with a concentration of 8 mol / L.

[0104] from Figure 5 It can be seen that the structure of expanded vermiculite changes after being treated with nitric acid of different concentrations. Expanded vermiculite is mainly phlogopite structure, while retaining some incompletely expanded vermiculite and hydrobiotite structures. After acid treatment, the peak of vermiculite disappears first, indicating that acid treatment first destroys the vermiculite structure. When the nitric acid concentration is not greater than 2 mol / L, the characteristic peak of phlogopite is still retained; but when the nitric acid concentration is greater than or equal to 4 mol / L, the characteristic peak of phlogopite basically disappears, indicating that the vermiculite structure is transformed into an amorphous structure and cannot continue the subsequent organic intercalation synthesis.

[0105] The BET data of the acid-modified vermiculite prepared in this example are shown in Table 3.

[0106] Table 3 BET data of acid-modified vermiculite

[0107]

[0108]

[0109] It can be seen from Table 3 that after the vermiculite was treated with acid, the specific surface area, pore volume and average pore size of the vermiculite were greatly increased, and the humidity control performance of the vermiculite was improved, which is consistent with the results of the orthogonal experiment and the single factor experiment. With the increase of nitric acid concentration, the specific surface area of ​​the vermiculite first increased and then decreased, reaching the highest value of 466.136 m when the nitric acid concentration was 3 mol / L. 2 / g; the total pore volume and average pore diameter of vermiculite first increased and then decreased, reaching the highest value when the nitric acid concentration was 2 mol / L.

[0110] In summary, the concentration of nitric acid has an effect on the morphology and structure of vermiculite. When the concentration of nitric acid is greater than 2 mol / L, the vermiculite is transformed into an amorphous structure, and the total pore volume and average pore size of the vermiculite are reduced, which has an adverse effect on the organic modification and moisture absorption and desorption rate of the vermiculite. Therefore, the acid-modified vermiculite prepared by 2 mol / L nitric acid solution is subsequently subjected to organic modification (using a nitric acid solution with a concentration of 2 mol / L, a heating reaction time of 4 h, and a temperature of 90 ° C to organically modify the acid-modified vermiculite).

[0111] Example 5

[0112] A preparation method of organic modified vermiculite:

[0113] (1) Add 20 g of expanded vermiculite to 200 mL of 2 mol / L nitric acid solution, heat to 90° C. in a water bath, set the stirring temperature to 500 r / min, and heat to react for 4 h. After the reaction, filter and wash with distilled water until the pH is greater than 6, dry at 80° C. for 24 h, and pass through a 200-mesh sieve to obtain acid-modified vermiculite. The actual picture of acid-modified vermiculite is shown in FIG. Figure 6 .

[0114] (2) The acid-modified vermiculite was added to a 0.5 wt.% cetyltrimethylammonium bromide solution (the mass ratio of the acid-modified vermiculite to the cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide solution was 1:10), heated to 80° C., stirred for 3 h, washed with distilled water and anhydrous ethanol until no bromide ions were present, dried, and ground through a 200-mesh sieve to obtain an organically modified vermiculite. The actual picture of the organically modified vermiculite is shown in FIG. Figure 7 .

[0115] The XRD patterns of the acid-modified vermiculite (nitric acid-modified vermiculite) and the organic-modified vermiculite prepared in this example are shown in FIG. Figure 8 .

[0116] from Figure 8 It can be seen that the characteristic diffraction peak of acid-modified vermiculite is at 2-Theta = 7.53°, while after organic modification, this peak moves to 2-Theta = 6.98°, which corresponds to the (002) crystal plane. From the Bragg equation λ = 2dsinθ, it can be obtained that the interplanar spacing of acid-modified vermiculite is 11.74nm, while the spacing after modification is 12.65nm. The larger interplanar spacing indicates that the organic matter has been attached and intercalated, and the modification is successful.

[0117] The FTIR images of the acid-modified vermiculite (nitric acid-modified vermiculite) and the organic-modified vermiculite prepared in this example are shown in Fig. 9 .

[0118] from Fig. 9It can be seen that the infrared absorption spectrum of acid-modified vermiculite mainly shows the vibration of Si(Al)-O bond [including the stretching vibration of Si(Al)-O bond and the bending vibration of O-Si(Al)-O, Si-O-Si(Al)] and the vibration of silicon (aluminum) oxygen tetrahedron skeleton; after organic modification, the infrared absorption spectrum of acid-modified vermiculite is mainly characterized by ... -1 With 790cm -1 The peak at 952 cm represents the characteristic absorption peak of Si-O stretching vibration in acid-modified vermiculite. -1 The peak at 457 cm represents the characteristic absorption peak of Si-O-Si stretching vibration in acid-modified vermiculite. -1 represents the characteristic absorption peak of Si-O bending vibration in acid-modified vermiculite, while 3490 cm -1 With 1637cm -1 The peak at 2923cm represents the vibration absorption peak of the interlayer water molecules in the acid-modified vermiculite. -1 The peak at 2852 cm represents the asymmetric stretching vibration peak of CH2 in CTAB. -1 The peak at 1630 cm represents the symmetrical stretching vibration peak of CH2 in CTAB. -1 The red shift at is the stretching vibration peak of C=C, indicating that CTAB has been attached to the surface of the sample and the inorganic substance has been successfully modified.

[0119] The acid-modified vermiculite and organic-modified vermiculite prepared in this example were subjected to BET analysis. The results are shown in Table 4.

[0120] Table 4 shows the data of acid-modified vermiculite and BET organic-modified vermiculite

[0121] <![CDATA[Specific surface area (m 2 / g)]]> Total pore volume (mL / g) Average pore size (nm) Acid modified vermiculite 402.617 0.413 4.105 Organic modified vermiculite 338.495 0.274 3.239

[0122] It can be seen from Table 4 that compared with acid-modified vermiculite, the specific surface area, pore volume and pore size of vermiculite are reduced after organic modification, which indicates that hexadecyltrimethylammonium bromide is inserted into the interlayers and pores of vermiculite. The humidity regulating performance of vermiculite after organic modification is lower than that of acid-modified vermiculite, but after organic modification, the lipophilicity of vermiculite is improved, and it can be combined with organic materials.

[0123] Example 6

[0124] A preparation method of a concrete curing agent (vermiculite / polyacrylic acid-acrylamide composite material):

[0125] (1) Add 20 mL of distilled water to a 50 mL beaker, add NaOH according to the degree of neutralization (the degree of neutralization is the degree to which acrylic acid is neutralized by NaOH), then slowly dropwise add acrylic acid (AA), then add acrylamide (AM), and stir at below 30° C. for 30 min to obtain a mixed solution 1; add the organically modified vermiculite (modified vermiculite) prepared in Example 5 to the mixed solution 1, and stir for 30 min to obtain a mixed solution 2; add N-N'methylenebisacrylamide (the amount is 0.5 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) and potassium persulfate (the amount is 0.3 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 2, mix well, and form a mixed solution 3.

[0126] The neutralization degree is 70%, 80%, 90% or 100%; the mass ratio of acrylic acid to acrylamide is 1:1, 4:1, 7:1 or 10:1; and the amount of organically modified vermiculite is 1%, 4%, 7% or 10% of the total mass of acrylic acid, acrylamide and organically modified vermiculite.

[0127] (2) In a 250mL three-necked flask equipped with a mechanical stirrer and a condenser, add 100mL of cyclohexane and 5g of Span60, heat to 40°C, stir for 20min, then slowly inject the mixed solution 3 into the three-necked flask, stir for 30min, gradually heat the solution to 70°C and react for 3h to complete the polymerization process. After polymerization, take out the sample from the bottle, wash it with ethanol and methanol three times respectively, and dry it in a vacuum oven at 80°C for 24h. After grinding, filter through a 200-mesh sieve to obtain a vermiculite / polyacrylic acid-acrylamide composite material. See the schematic diagram of the preparation process. Fig.10 .

[0128] A three-factor four-level orthogonal experiment was conducted based on the three conditions of neutralization degree, mass ratio of acrylic acid and acrylamide (monomer ratio), and dosage of organic modified vermiculite (modified vermiculite content, %). The moisture absorption rate and moisture release rate of the test product at 48 hours were tested. The orthogonal experiment results are shown in Table 5.

[0129] The orthogonal experimental results were analyzed and the results are shown in Table 6.

[0130] Table 5 Orthogonal experimental table of humidity control experiment of vermiculite / polyacrylic acid-acrylamide composite materials

[0131]

[0132] Table 6 Range analysis of humidity control performance of vermiculite / polyacrylic acid-acrylamide copolymer composites

[0133]

[0134] It can be seen from Table 6 that the variation patterns of moisture absorption and moisture release properties are consistent. Among the three factors, the monomer ratio has the greatest influence on the composite material, followed by the influence of modified vermiculite content, and the influence of neutralization degree is the smallest. The best levels are A2 (vermiculite content 4%), B3 (neutralization degree 90%), and C2 (mAA:mAM=4:1).

[0135] Table 7 Difference analysis of humidity control properties of vermiculite / polyacrylic acid-acrylamide copolymer composites

[0136]

[0137]

[0138] Table 8 Analysis of variance of humidity control performance of vermiculite / polyacrylic acid-acrylamide copolymer composites

[0139]

[0140] It can be seen from Tables 7 and 8 that both the modified vermiculite content and the monomer ratio have a significant effect on the hygroscopicity and dehumidification (P<0.05), while the effect of the neutralization degree is not significant (P>0.05). The monomer ratio has the highest F value, followed by the modified vermiculite content, and the neutralization degree is the smallest, which is consistent with the results of the range analysis.

[0141] It can be seen from Table 5 that the moisture release rate of the composite materials is lower than the moisture absorption rate under the same test conditions; and with the increase of vermiculite content, neutralization degree and proportion of acrylic acid, the moisture absorption and release rate of the composite materials shows a trend of first increasing and then decreasing.

[0142] It can be seen from Tables 5 to 8 that the most suitable orthogonal test conditions should be A2B3C2, that is, when the content of modified vermiculite is 4%, the degree of neutralization is 90% and mAA:mAM=4:1, the moisture absorption and release performance of the composite material is the best. However, the orthogonal test conditions of A2B3C2 do not appear in the orthogonal test table 5. For this reason, the preparation of the composite material under the conditions of A2B3C2 was carried out separately, and the moisture absorption and release experiments showed that the moisture absorption and release of the composite material reached 1.285g / g and 1.172g / g respectively, which is better than the moisture absorption and release performance of the best sample (sample No. 8) in the orthogonal test table 5.

[0143] Example 7

[0144] A preparation method of a concrete curing agent (vermiculite / polyacrylic acid-acrylamide composite material) (single factor experiment):

[0145] (1) Add 20 mL of distilled water to a 50 mL beaker, add NaOH according to a neutralization degree of 90% (neutralization degree refers to the degree to which acrylic acid is neutralized by NaOH), then slowly dropwise add acrylic acid (AA), then add acrylamide (AM) (the mass ratio of AA to AM is 4:1), and stir for 30 min at below 30° C. to obtain a mixed solution 1; add the organically modified vermiculite prepared in Example 5 to the mixed solution 1 (the amount of modified vermiculite is 1%, 4%, 7% or 10% of the total mass of acrylic acid, acrylamide and organically modified vermiculite, respectively), and stir for 30 min to obtain a mixed solution 2; add N-N'methylenebisacrylamide (the amount is 0.1 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) and potassium persulfate (the amount is 0.3 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 2, mix well, and form a mixed solution 3.

[0146] (2) In a 250 mL three-necked flask equipped with a mechanical stirrer and a condenser, 100 mL of cyclohexane and 5 g of Span60 were added, heated to 40 ° C, stirred for 20 min, and then the mixed solution 3 was slowly injected into the three-necked flask. After stirring for 30 min, the solution was gradually heated to 70 ° C for 3 h to complete the polymerization process. After polymerization, the sample in the bottle was taken out, washed with ethanol and methanol for 3 times, respectively, and dried in a vacuum oven at 80 ° C for 24 h. After grinding, it was filtered through a 200 mesh sieve to obtain a vermiculite / polyacrylic acid-acrylamide composite material.

[0147] Example 8

[0148] A preparation method of a concrete curing agent (vermiculite / polyacrylic acid-acrylamide composite material) (single factor experiment):

[0149] (1) Add 20 mL of distilled water to a 50 mL beaker, add NaOH at a neutralization degree of 70%, 80%, 90% or 100% (neutralization degree is the degree to which acrylic acid is neutralized by NaOH), then slowly dropwise add acrylic acid (AA), then add acrylamide (AM) (the mass ratio of AA to AM is 4:1), and stir for 30 min at below 30° C. to obtain a mixed solution 1; add the organically modified vermiculite prepared in Example 5 (the amount of modified vermiculite is 4% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 1, and stir for 30 min to obtain a mixed solution 2; add N-N'methylenebisacrylamide (the amount is 0.1 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) and potassium persulfate (the amount is 0.3 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 2, mix well, and form a mixed solution 3.

[0150] (2) In a 250 mL three-necked flask equipped with a mechanical stirrer and a condenser, 100 mL of cyclohexane and 5 g of Span60 were added, heated to 40 ° C, stirred for 20 min, and then the mixed solution 3 was slowly injected into the three-necked flask. After stirring for 30 min, the solution was gradually heated to 70 ° C for 3 h to complete the polymerization process. After polymerization, the sample in the bottle was taken out, washed with ethanol and methanol for 3 times, respectively, and dried in a vacuum oven at 80 ° C for 24 h. After grinding, it was filtered through a 200 mesh sieve to obtain a vermiculite / polyacrylic acid-acrylamide composite material.

[0151] Example 9

[0152] A preparation method of a concrete curing agent (vermiculite / polyacrylic acid-acrylamide composite material) (single factor experiment):

[0153] (1) Add 20 mL of distilled water to a 50 mL beaker, add NaOH according to a neutralization degree of 90% (neutralization degree refers to the degree to which acrylic acid is neutralized by NaOH), then slowly dropwise add acrylic acid (AA), then add acrylamide (AM) (the mass ratio of AA to AM is 1:1, 4:1, 7:1 or 10:1, respectively), and stir for 30 min at below 30° C. to obtain a mixed solution 1; add the organically modified vermiculite prepared in Example 5 (the amount of modified vermiculite is 4% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 1, and stir for 30 min to obtain a mixed solution 2; add N-N'methylenebisacrylamide (the amount is 0.1 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) and potassium persulfate (the amount is 0.3 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 2, mix well, and form a mixed solution 3.

[0154] (2) In a 250 mL three-necked flask equipped with a mechanical stirrer and a condenser, 100 mL of cyclohexane and 5 g of Span60 were added, heated to 40 ° C, stirred for 20 min, and then the mixed solution 3 was slowly injected into the three-necked flask. After stirring for 30 min, the solution was gradually heated to 70 ° C for 3 h to complete the polymerization process. After polymerization, the sample in the bottle was taken out, washed with ethanol and methanol for 3 times, respectively, and dried in a vacuum oven at 80 ° C for 24 h. After grinding, it was filtered through a 200 mesh sieve to obtain a vermiculite / polyacrylic acid-acrylamide composite material.

[0155] The moisture absorption rate (absorption ratio) and moisture release rate (desorption ratio) of the vermiculite / polyacrylic acid-acrylamide composite materials prepared in Examples 7 to 9 were tested at 48 hours. The results are shown in Fig.11 .

[0156] Fig.11In the figure, (a) is a vermiculite / polyacrylic acid-acrylamide composite material prepared at different modified vermiculite contents (represented by vermiculite content in the figure), (b) is a vermiculite / polyacrylic acid-acrylamide composite material prepared at different neutralization degrees, and (c) is a vermiculite / polyacrylic acid-acrylamide composite material prepared at different monomer ratios.

[0157] from Fig.11 As can be seen in Figure (a), with the increase of the modified vermiculite content, the humidity control performance of the composite material first increases and then decreases, reaching a maximum value at 4%. Since the composite material is mainly composed of polyacrylic acid-acrylamide and the vermiculite content is relatively small (≦10%), the humidity control performance of the composite material is mainly determined by polyacrylic acid-acrylamide. When the vermiculite content is ≦4%, the addition of low-content vermiculite will make the surface of the composite material rougher, reduce the cross-linking density, increase the specific surface area and porosity of the composite material, and improve the humidity control performance of the material. However, with the continued increase of the vermiculite content (≧7%), the content of polyacrylic acid-acrylamide decreases. At the same time, the introduction of a large number of vermiculite particles makes the composite material more likely to agglomerate and form large blocks of gel, and the cross-linking density increases, which in turn reduces the specific surface area of ​​the composite material and reduces the moisture absorption and release performance of the composite material. Therefore, the optimal vermiculite content is 4%.

[0158] from Fig.11 As can be seen in Figure (b), the hygroscopic and dehumidifying properties of the composite material first increase and then decrease with the increase of the neutralization degree, reaching the maximum when the neutralization degree is 90%. The reason is that as the neutralization degree increases, the -COOH in the acrylic acid is converted into a more hydrophilic -COONa, the hydrophilicity of the composite material increases, and the hygroscopicity increases. When the neutralization degree exceeds 90%, the hygroscopic and dehumidifying properties of the material decrease. The reason is that the rigidity of the molecular chain increases, so the optimal neutralization degree of the composite material is 90%.

[0159] from Fig.11As can be seen in Figure (c), the hygroscopic and dehumidifying properties of the composite material first increase and then decrease with the increase of the ratio of mAA:mAM, and reach the maximum when mAA:mAM=4:1. The dehumidifying property of the composite material mainly depends on the high specific surface area and porosity of vermiculite. Under the condition of constant vermiculite content, the humidity control performance of the composite material is mainly determined by PAA-AM. The hygroscopic property mainly depends on the mutual synergistic effect of -COOH, -COONa and -CONH2 groups in PAA-AM resin. The introduction of a small amount of non-ionic hydrophilic group -CONH2 in the ionic lipid diversifies the hydrophilic group and reduces the regularity of the network structure, thereby slightly improving the hygroscopic capacity. However, as the amount of AM further increases -CONH2, the hydrophilicity is not as good as -COONa. The characteristic will be clearly manifested, resulting in a significant decrease in humidity control performance. Therefore, only when AA and AM are polymerized in a suitable ratio can higher humidity control performance be exhibited. In the present invention, the optimal ratio of AA to AM is mAA:mAM=4:1.

[0160] According to the above orthogonal experiment and single factor experiment, the optimal parameters for achieving the highest absorption and desorption ratio were determined and verified, namely, the vermiculite content was 4%, the neutralization degree was 90%, and mAA:mAM=4:1. The moisture absorption and desorption test showed that the moisture absorption and desorption rates of the optimal sample were 1.285g / g and 1.172g / g respectively.

[0161] Example 10

[0162] A preparation method of a concrete curing agent (vermiculite / polyacrylic acid-acrylamide composite material):

[0163] (1) Add 20 mL of distilled water to a 50 mL beaker, add NaOH according to a neutralization degree of 90% (neutralization degree refers to the degree to which acrylic acid is neutralized by NaOH), then slowly dropwise add acrylic acid (AA), then add acrylamide (AM) (the mass ratio of AA to AM is 4:1), and stir for 30 min at below 30° C. to obtain a mixed solution 1; add the organically modified vermiculite prepared in Example 5 (the amount of modified vermiculite is 4% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 1, and stir for 30 min to obtain a mixed solution 2; add N-N'methylenebisacrylamide (the amount is 0.1 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) and potassium persulfate (the amount is 0.3 wt.% of the total mass of acrylic acid, acrylamide and organically modified vermiculite) to the mixed solution 2, mix well, and form a mixed solution 3.

[0164] (2) In a 250 mL three-necked flask equipped with a mechanical stirrer and a condenser, 100 mL of cyclohexane and 5 g of Span60 were added, heated to 40 ° C, stirred for 20 min, and then the mixed solution 3 was slowly injected into the three-necked flask. After stirring for 30 min, the solution was gradually heated to 70 ° C for 3 h to complete the polymerization process. After polymerization, the sample in the bottle was taken out, washed with ethanol and methanol for 3 times, respectively, and dried in a vacuum oven at 80 ° C for 24 h. After grinding, it was filtered through a 200 mesh sieve to obtain a vermiculite / polyacrylic acid-acrylamide composite material.

[0165] Comparative Example 1

[0166] Preparation method of polyacrylic acid-acrylamide:

[0167] Acrylic acid, acrylamide, crosslinking agent N,N-methylenebisacrylamide and initiator K2S2O8 neutralized with a certain amount of NaOH were dissolved in distilled water, and then added to the oil phase composed of 200# solvent oil and Span-60, stirred for about 30 minutes, and heated to 70°C under nitrogen protection. Maintain a certain stirring speed, polymerize for 3 hours, filter the reaction product while hot, wash it with methanol 3 times, and vacuum dry it to obtain white granular resin P (AA-AM).

[0168] The SEM and EDS images of the organically modified vermiculite used in Example 10, the vermiculite / polyacrylic acid-acrylamide composite material prepared in Example 10, and the polyacrylic acid-acrylamide prepared in Comparative Example 1 are shown in FIG. Fig.12 .

[0169] Fig.12 Among them, (a) is the SEM image of organically modified vermiculite, (b) is the EDS image of organically modified vermiculite, (c) is the SEM image of vermiculite / polyacrylic acid-acrylamide composite material, (d) is the EDS image of vermiculite / polyacrylic acid-acrylamide composite material, (e) is the SEM image of polyacrylic acid-acrylamide, and (f) is the EDS image of polyacrylic acid-acrylamide.

[0170] from Fig.12It can be seen that the modified vermiculite (organic modified vermiculite) is a layered particle with a particle size of less than 10μm. After heating expansion and acid treatment, the interlayer spacing increases, some interlayers are broken, and the specific surface area and porosity increase. Polyacrylic acid-acrylamide is a spherical particle with a particle size of about 10μm and a relatively flat surface, so the specific surface area is relatively small. The vermiculite / polyacrylic acid-acrylamide composite material is an irregular particle. The particle size of the composite material is above 10μm, the surface is rough, the specific surface area is increased, and a layered structure can be observed on the surface, which is conducive to the adsorption and release of water. In the EDS element energy spectrum, by comparing the components of the three materials, it can be seen that the modified vermiculite mainly contains C, O, and Si elements; polyacrylic acid-acrylamide contains C, O and Na elements, and does not contain Si elements; after adding 4% of modified vermiculite, C, O, Na and Si elements appear in the composite material, which indicates that the modified vermiculite and polyacrylic acid-acrylamide are successfully synthesized.

[0171] The XRD patterns of expanded vermiculite (vermiculite), the vermiculite / polyacrylic acid-acrylamide composite material (composite material) prepared by organically modified vermiculite used in Example 10, and the polyacrylic acid-acrylamide (PAA-AM copolymer) prepared in Comparative Example 1 are shown in FIG. Fig.13 .

[0172] from Fig.13 It can be seen that vermiculite contains phlogopite phase and hydrobiotite phase structures. The characteristic peak of vermiculite is at 2θ=7.53°, which is the (002) crystal plane of the hydrobiotite phase formed after the expansion of vermiculite. The crystal plane spacing is 1.173nm, and the other characteristic peaks are phlogopite phase structures. The X-ray diffraction spectrum of polyacrylic acid-acrylamide is a diffuse scattering peak, which indicates that polyacrylic acid-acrylamide is an amorphous structure. The diffraction peaks of vermiculite and polyacrylic acid-acrylamide appear simultaneously in the diffraction spectrum of the composite material, and some peaks of vermiculite disappear. The characteristic peak of hydrobiotite at (002) moves to 2θ=6.84°, and the interplanar spacing expands to 1.291nm. In addition, a new diffraction peak appears at 2θ=30.85° of the composite material, which is caused by the expansion of the (131) interplanar spacing in the phlogopite structure of vermiculite. The characteristic peak moves from 2θ=33.97° to 2θ=30.85°, and the interplanar spacing expands from 0.267nm to 0.2896nm. This indicates that during the polymerization process, polyacrylic acid-acrylamide enters the interlayer of vermiculite and increases the interplanar spacing of vermiculite.

[0173] The FTIR spectra of expanded vermiculite (vermiculite), the vermiculite / polyacrylic acid-acrylamide composite material (composite material) prepared by organically modified vermiculite used in Example 10, and the polyacrylic acid-acrylamide (PAA-AM copolymer) prepared in Comparative Example 1 are shown in FIG. Fig.14 .

[0174] from Fig.14It can be seen that in the infrared spectrum of vermiculite, 1072cm -1 and 796cm -1 The Si-O stretching vibration absorption peak is at 952 cm -1 The Si-O-Si stretching vibration absorption peak is at 457 cm -1 The Si-O bending vibration absorption peak is at 3416 cm -1 At 1667cm -1 The absorption peak at 1621 cm is the carbonyl (C=O) stretching vibration absorption peak in the amide group (-CONH2). -1 The bending vibration absorption peak of -NH2 in the amide group (-CONH2) is at 1557cm -1 The carbonyl (C=O) stretching vibration absorption peak in the carboxyl anion (-COO-) is at 1304 cm -1 The CN stretching vibration absorption peak in the amide group (-CONH2) is located at 1.50 nm. In the infrared spectrum of the composite material, the absorption peaks of vermiculite and polyacrylic acid-acrylamide can be found, and the intensity and position of the absorption peaks have changed, which shows that vermiculite is successfully composited with polyacrylic acid-acrylamide.

[0175] The actual picture of the vermiculite / polyacrylic acid-acrylamide composite material prepared in Example 10 after moisture absorption equilibrium is shown in Fig.15 .

[0176] Embodiment 11

[0177] Effect of internal curing agent dosage on the fluidity of pure slurry:

[0178] The raw materials, dosage and fluidity of cement paste are shown in Table 9.

[0179] Table 9 Relationship between cement paste fluidity and internal curing agent dosage

[0180]

[0181]

[0182] Wherein, the internal curing agent is the concrete internal curing agent prepared in Example 10 (crushed and passed through a 400-mesh sieve).

[0183] The cement used is P.O42.5R cement produced by Zhucheng Yangchun Cement Plant, which has qualified stability. The initial setting time is >150min, the final setting time is <240min, the 3d flexural strength is >3.5MPa, the 3d compressive strength is >17MPa, the 28d flexural strength is >6.5MPa, and the 28d compressive strength is >42.5MPa.

[0184] W / C is the water-to-cement ratio.

[0185] It can be seen from Table 9 that as the amount of internal curing agent increases, the fluidity of the pure slurry increases slowly, and the slurry gradually transitions from a dry and hard state to a flowable state, which indicates that the internal curing agent still has good stability in mechanical action and alkaline solution, and has no obvious adverse effect on the fluidity of the pure slurry. In cement slurry without internal curing agent, when the water-binder ratio increases from 0.35 to 0.45, the slurry changes from thick to thin, and the fluidity increases significantly.

[0186] Example 12

[0187] A concrete material:

[0188] The raw materials and amounts of concrete materials are shown in Table 10.

[0189] Table 10 Raw materials and dosage

[0190]

[0191] The internal curing agent is the concrete internal curing agent prepared in Example 10 (crushed through 100 mesh, 200 mesh, and 400 mesh sieves, see the actual picture). Fig.16 (a) in the figure) or BASF internal curing agent (crushed through a 400-mesh sieve, see the actual picture Fig.16 (b) Figure 5, BASF 5920F).

[0192] The cement used is P.O42.5R cement produced by Zhucheng Yangchun Cement Plant, which has qualified stability. The initial setting time is >150min, the final setting time is <240min, the 3d flexural strength is >3.5MPa, the 3d compressive strength is >17MPa, the 28d flexural strength is >6.5MPa, and the 28d compressive strength is >42.5MPa.

[0193] The aggregates used are coarse aggregate (stone) and fine aggregate (sand) produced by Tianjin Jinyu Concrete Company. The particle size of the fine aggregate (sand) is <5mm, and the particle size of the coarse aggregate (stone) is 5-25mm.

[0194] The water reducer uses HLX polycarboxylic acid high-performance water reducer produced by Feike New Materials Technology Co., Ltd., which has a light yellow transparent liquid appearance.

[0195] C01, C02, C03, and C04 refer to internal curing agent (400 mesh) as 0%, 0.1%, 0.2%, and 0.3% of cement dosage respectively (the additional water intake is 20 times the mass of the internal curing agent); C03, C03-1, and C03-2 refer to internal curing agent passing through 400 mesh, 200 mesh, and 100 mesh sieves respectively; C05 and C06 refer to water-cement ratios of 0.38 and 0.42 respectively (internal curing agent is 400 mesh); D03 refers to the addition of BASF internal curing agent (400 mesh).

[0196] Prepare concrete materials according to the raw materials and amounts in the table as follows:

[0197] (1) Pre-absorb water from the internal curing agent (the amount of water absorbed (additional water intake) is 20 times the mass of the internal curing agent, and the pre-absorption time is 2 hours) and mix it with cement. Pour it into a mixer and stir for no less than 30 seconds. Then pour fine aggregate and coarse aggregate into the mixer and stir for about 30 seconds. Add base water into the mixer and stir for about 30 seconds. Add water reducer into the mixer and stir for about 1 minute to obtain concrete slurry.

[0198] The slump and expansion of concrete slurry were determined in accordance with GB / T50080-2016. The results are shown in Table 11.

[0199] Table 11 Fluidity of concrete slurry

[0200] serial number Slump(mm) Expansion(mm) C01 160 402 C02 178 445 C03 195 484 C04 203 511 C05 220 522 C06 264 565 C03-01 193 479 C03-02 192 478 D03 185 468

[0201] From the slump and expansion data of C01-C04 concrete, it can be seen that the amount of concrete curing agent has a significant effect on the fluidity of concrete. The greater the amount, the better the fluidity of concrete. The slump of concrete without concrete curing agent and with 0.1% concrete curing agent is less than 180mm, the expansion is less than 450mm, and the fluidity is poor. When the amount is ≥0.2%, the cohesion and water retention of concrete are better, and there is no segregation, and the fluidity is better.

[0202] Comparing C03, C05 and C06 concretes, it can be seen that the water-binder ratio of concrete has a significant effect on the fluidity of concrete. The larger the water-binder ratio, the better the fluidity of the concrete. When the water-binder ratio reaches 0.42, the fluidity increases rapidly, indicating that at a high water-binder ratio, adding curing agents to concrete is not conducive to the mixing performance of concrete.

[0203] Comparing C03, C03-1 and C03-2, it can be seen that the size of the curing agent in concrete has little effect on the working performance of concrete.

[0204] By comparing C03 and D03, it can be seen that the effects of the concrete internal curing agent prepared by the present invention and the BASF internal curing agent on the working performance of concrete are slightly different.

[0205] In summary, the addition of curing agent in concrete has a great influence on the working performance of concrete, the amount of curing agent added in concrete and the water-cement ratio have a significant influence on the working performance of concrete, and the size of the curing agent in concrete has little effect on the working performance of concrete.

[0206] (2) Load the concrete slurry prepared in step (1) into a mold (size 110mm×110mm) and smooth it. Pre-embed a 6×50mm plastic tube in the center of the specimen and insert a steel rod inside to prevent concrete from pouring into the plastic tube and causing blockage. Seal the specimen with a film. After the specimen is formed, remove the mold, pull out the steel rod, and plug the plastic tube with a plug. During the test, quickly pull out the plug and insert the humidity probe into the plastic tube. When the data stabilizes, read the humidity value (test the internal humidity of the concrete for 1 to 7 days, 14 days, 21 days, and 28 days); see Humidity test specimens and humidity sensors. Fig.17 .

[0207] Fig.17 In the figure, (a) is the humidity sensor and (b) is the humidity test specimen. The relative humidity change inside the concrete is shown in Fig.18 ; Fig.18 Among them, (a) is the internal relative humidity of C01, C02, C03, and C04 concrete, (b) is the internal relative humidity of C03, C05, and C06 concrete, (c) is the internal relative humidity of C03, C03-01, and C03-02 concrete, and (d) is the internal relative humidity of C03 and D03 concrete.

[0208] from Fig.18 It can be seen that the internal relative humidity (IRH) of concrete gradually decreases with the extension of age. The reduction of the internal relative humidity of concrete with the addition of concrete curing agent is mainly within 1 to 7 days. The reason is that the hydration reaction of concrete is intense, the water consumption is large, and the IRH drops rapidly; from 7 to 14 days, the hydration reaction slows down and the decline of IRH decreases. The change of IRH is mainly concentrated within 14 days. After 14 days, it enters a stable period with little change; after 14 days, the internal relative humidity of concrete without the addition of concrete curing agent will still decrease, which shows that the addition of concrete curing agent is conducive to inhibiting the reduction of the internal humidity of concrete.

[0209] By comparing C01 to C04, it can be seen that with the increase in the amount of curing agent in concrete, the rate of decrease of relative humidity inside the curing agent in concrete decreases before 14 days, and the internal relative humidity is higher after 14 days; the humidity changes of C03 and C04 are similar, indicating that when the content of curing agent in concrete is less than 0.2%, the increase in the content of curing agent has a more obvious effect on inhibiting the decrease in humidity inside concrete; when it is greater than 0.2%, further increasing the content of curing agent has a limited effect on reducing the humidity inside concrete.

[0210] By comparing C03, C05 and C06, it can be seen that the change patterns of the three are consistent. With the increase of water-binder ratio, the rate of decrease of humidity inside concrete decreases. Under the same conditions, the higher the water-binder ratio, the higher the water content inside concrete.

[0211] By comparing C03, C03-1 and C03-2, it can be seen that the change range and equilibrium humidity of the three groups of concrete are almost the same, indicating that the change in the fineness of the curing agent in the concrete has little effect on the change in the humidity inside the concrete.

[0212] Comparing C03 and D03, compared with BASF's internal curing agent, the concrete internal curing agent prepared by the present invention has a more obvious effect on improving the internal humidity of concrete, which is beneficial to improving the autogenous shrinkage of concrete.

[0213] In summary, the curing agent in concrete is moisture-sensitive and can release moisture in time when the humidity inside the concrete decreases. In addition, the increase in the content of curing agent in concrete is conducive to further improving the internal relative humidity of the concrete.

[0214] (3) The concrete slurry prepared in step (1) was placed in a mold (size: 110 mm × 110 mm). One day after the specimen was formed, the mold was removed and the specimen was moved to a standard curing room for 3 days of curing (calculated from the time of mixing and adding water). Afterwards, the specimen was moved to a cement shrinkage test chamber for testing.

[0215] Before the test, measure the initial length of the specimen and measure the length of the specimen at time intervals.

[0216] Refer to GB / T 50082-2009 to test the autogenous shrinkage value and composite shrinkage value.

[0217] The autogenous shrinkage test method is basically the same as the composite shrinkage test method. The difference is that the specimen is taken out after being cured in a standard curing room for 3 days, and the specimen is immediately sealed with butyl waterproof tape to expose the metal probe, and the gap between the probe and the specimen is sealed with epoxy resin glue.

[0218] Concrete will shrink in the early stage of setting and during the hardening process, including plastic shrinkage, carbonation shrinkage, temperature shrinkage, autogenous shrinkage, and drying shrinkage. Plastic shrinkage will occur before the mixture is finally set, but its shrinkage is relatively small. Temperature shrinkage is the shrinkage deformation caused by temperature rise and temperature drop, which is usually only concerned in large-volume concrete structures. Carbonation shrinkage develops slowly, only on the surface of concrete, and only in an environment with suitable humidity. Therefore, drying shrinkage and autogenous shrinkage are the main considerations for concrete shrinkage. The so-called concrete shrinkage is actually the result of drying shrinkage and autogenous shrinkage combined. For general high water-cement ratio concrete, autogenous shrinkage is very small, and usually only the effect of drying shrinkage is considered. However, SCC has a small water-cement ratio and a large amount of cementitious materials, so autogenous shrinkage develops earlier and is more obvious. Therefore, drying shrinkage and autogenous shrinkage need to be considered at the same time.

[0219] The drying shrinkage and autogenous shrinkage of concrete always occur simultaneously and exist in the entire process of concrete coagulation and hardening. The shrinkage mechanisms of the two are roughly the same, but there are differences in the shrinkage modes. Autogenous shrinkage is due to the continuous consumption of water by the hydration reaction of the cementitious material, and the continuous decrease in the relative humidity of the concrete, which leads to volume shrinkage. Drying shrinkage is the volume shrinkage caused by the loss of water in the pores of the concrete surface in a dry environment.

[0220] Therefore, composite shrinkage is simplified to the sum of drying shrinkage and autogenous shrinkage. The shrinkage value tested under constant temperature and humidity conditions is the composite shrinkage value, and the shrinkage value tested under a sealed state is the autogenous shrinkage value. The difference between the two is the drying shrinkage value. As shown in the following formula:

[0221] ε T =ε d +ε a

[0222] Where: ε T is the composite shrinkage value; ε d is the drying shrinkage value; ε a is the autogenous shrinkage value.

[0223] The test results are shown in Tables 12 to 14 and Figures 19-20 .

[0224] Table 12 Autogenous shrinkage values ​​of different concretes

[0225]

[0226] Table 13 Composite shrinkage values ​​of different concrete

[0227]

[0228] Table 14 Drying shrinkage values ​​of different concrete

[0229]

[0230] Fig.19 In the figure, (a) is the autogenous shrinkage value of C01, C02, C03, and C04 concrete, (b) is the autogenous shrinkage value of C03, C05, and C06 concrete, (c) is the autogenous shrinkage value of C03, C03-01, and C03-02 concrete, and (d) is the autogenous shrinkage value of C03 and D03 concrete.

[0231] Autogenous shrinkage occurs throughout the entire life cycle of concrete. In the early stage of concrete coagulation, the IRH decreases rapidly and the autogenous shrinkage develops rapidly, and then the autogenous shrinkage develops steadily.

[0232] from Fig.19 It can be seen from Figures (a) to (d) that the autogenous shrinkage of concrete develops extremely rapidly in the first 2 days, continues to grow in 2 to 7 days, and tends to be gentle after 14 days.

[0233] from Fig.19 As can be seen from Figure (a), with the increase in the amount of curing agent in concrete (C01~C04), the autogenous shrinkage of concrete shows a trend of first increasing and then decreasing. When the amount of curing agent in concrete is 0.2% (C03), the autogenous shrinkage value is the smallest. At the same time, when the amount is between 0 and 0.2%, the increase in the amount has a significant effect on inhibiting the autogenous shrinkage. When the amount is greater than 0.2%, the autogenous shrinkage value increases instead of decreases. This shows that within a certain range of amount, the addition of curing agent in concrete can effectively inhibit the development of structural autogenous shrinkage.

[0234] from Fig.19 As can be seen in Figure (b), when the same 0.2% concrete curing agent is added, the difference in the autogenous shrinkage value of concrete with different water-binder ratios is large. The autogenous shrinkage value of the concrete specimen with a water-binder ratio of 0.42 is 35.75% higher than that of the concrete specimen with a water-binder ratio of 0.35 at 28 days. The increase in the autogenous shrinkage value of concrete before 2 days is due to the decrease in volume caused by cement hydration and increased water content; after 2 days, the autogenous shrinkage growth rate of C03, C05 and C06 slows down and tends to be stable after 7 days.

[0235] from Fig.19 It can be seen from Figure (c) that the fineness of the curing agent in concrete has little effect on the autogenous shrinkage value of concrete. Comparing C03, C03-1 and C03-2, when controlling other variables, as the size of the curing agent in concrete increases, the autogenous shrinkage value of concrete increases overall. The change patterns of the three are consistent, indicating that although the increase in the fineness of the curing material in concrete can slightly reduce its absolute shrinkage value, it will not change the trend of concrete shrinkage development.

[0236] from Fig.19 It can be seen from Figure (d) that, compared with BASF's internal curing agent, the concrete internal curing agent prepared by the present invention can more effectively reduce the autogenous shrinkage of concrete.

[0237] Fig. 20 In the figure, (a) is the drying shrinkage value of C01, C02, C03, and C04 concrete, (b) is the drying shrinkage value of C03, C05, and C06 concrete, (c) is the drying shrinkage value of C03, C03-01, and C03-02 concrete, and (d) is the drying shrinkage value of C03 and D03 concrete.

[0238] from Fig. 20 As can be seen from Figures (a) to (d), the drying shrinkage of concrete is relatively large in the first 7 days, accounting for about 90% of the total shrinkage. Among them, the drying shrinkage of concrete develops rapidly within 1 to 2 days, accounting for more than 60% of the drying shrinkage value. After 7 days, the drying shrinkage value tends to be stable and grows slowly.

[0239] from Fig. 20It can be seen from Figure (a) that with the increase of the content of curing agent in concrete, the drying shrinkage value of concrete decreases, and when the content is between 0 and 0.2%, the increase in the content has a significant inhibitory effect on the drying shrinkage. When the content is greater than 0.2%, the decrease in the drying shrinkage value decreases, indicating that the addition of curing agent in concrete has a significant inhibitory effect on the drying shrinkage of concrete.

[0240] from Fig. 20 As can be seen from Figure (b), the effect of water-binder ratio on the drying shrinkage of concrete is not obvious. Comparing C03, C05 and C06, before 2 days, the drying shrinkage values ​​of concrete with water-binder ratios of 0.42 and 0.38 are higher than that of concrete with a water-binder ratio of 0.35. However, after 2 days, the drying shrinkage value of concrete with a water-binder ratio of 0.42 begins to turn around, and the drying shrinkage value at 28 days is relatively lower.

[0241] from Fig. 20 It can be seen from Figures (c) and (d) that the fineness of the concrete curing agent has little effect on the drying shrinkage value of the concrete. Comparing C03, C03-1 and C03-2, as the size of the concrete curing agent increases, the drying shrinkage value of the concrete increases as a whole, and the change rules of the three are consistent, indicating that the increase in the fineness of the concrete curing material can slightly reduce its drying shrinkage value, but will not change the trend of concrete shrinkage development. In addition, compared with the BASF internal curing agent, the concrete curing agent prepared by the present invention has a more obvious effect on inhibiting the drying shrinkage of concrete.

[0242] In summary, the dosage of concrete curing agent, water-cement ratio, fineness of concrete curing agent and type of curing agent all affect the shrinkage of concrete. Among them, the change of the dosage of concrete curing agent has a significant effect on the autogenous shrinkage and drying shrinkage before the dosage of concrete curing agent is 0.2%; the increase of water-cement ratio will promote the autogenous shrinkage of concrete; the increase of the size of concrete curing agent will promote the shrinkage of concrete, and the autogenous shrinkage and drying shrinkage values ​​will increase significantly; compared with the BASF internal curing agent, the concrete curing agent prepared by the present invention can effectively inhibit the shrinkage of concrete.

[0243] (4) The concrete slurry prepared in step (1) was loaded into a mold (size: 110 mm × 110 mm). One day after the specimen was formed, the mold was removed and the specimen was moved to a standard curing room for curing. The compressive strength and flexural strength of concrete at different ages were measured in accordance with GB / T 50081-2019. The compressive strength measurement results are shown in Table 15; the flexural strength measurement results are shown in Table 16.

[0244] Table 15 Compressive strength of different concrete

[0245]

[0246] From the compressive strength data of concrete C01 to C04 in Table 15, it can be seen that after adding the concrete curing agent, the strength of the concrete decreases. With the increase of the amount of the internal curing agent, the strength of the concrete first increases and then decreases. Comparing C01, C02 and C03, it is found that the strength of the sample with 0.2% concrete curing agent added is the highest, but the strength change law of the three groups of samples is consistent, and the strength at 28 days is not much different, which shows that the addition of concrete curing agent has a great influence on the early strength of concrete. The compressive strength of the sample (C03) added with 0.2% concrete curing agent at 3d, 7d and 28d was 39.7MPa, 51.4MPa and 63.9MPa respectively. Compared with the benchmark sample C01, its compressive strength at 3d, 7d and 28d decreased by 8.7%, 6.2% and 2.3%, and the decline rate gradually decreased. This shows that the internal curing agent has not fully released water before 7d, and the space it occupies has not been fully filled by hydration products, which is equivalent to forming large-sized capillaries in the concrete. The more internal curing agent, the more large capillaries. Because high-strength concrete is sensitive to porosity, the early strength of concrete added with concrete curing agent is generally low; after 7d, the amount of water released by the concrete curing agent increases, hydration continues, and the strength of the concrete recovers to a certain extent.

[0247] From the compressive strength data of C03, C05 and C06 concrete in Table 15, it can be seen that when 0.2% of concrete curing agent is added, the 3d, 7d and 28d compressive strength of concrete decreases significantly with the increase of water-binder ratio. The 3d, 7d and 28d compressive strength of the sample (C06) with a water-binder ratio of 0.42 is 27.8MPa, 37.9MPa and 44.9MPa, which are 30.0%, 26.3% and 29.7% lower than that of the C03 sample, respectively. This shows that for the samples added with concrete curing agent, the reference water consumption has a great influence on the strength of concrete. The higher the water-binder ratio, the lower the concrete strength. This is consistent with the strength change law of concrete without concrete curing agent.

[0248] From the compressive strength data of C03, C03-01, and C03-02 concrete in Table 15, it can be seen that the fineness of the curing agent in concrete has a significant effect on the compressive strength of concrete. As the size of the curing agent in concrete increases, the strength of concrete decreases. When the fineness of the curing agent in concrete decreases from 400 mesh to 100 mesh, the 3d, 7d, and 28d compressive strengths of concrete decrease by 6.5%, 6.4%, and 8.9%, respectively. This is because after the size of the curing agent in concrete increases, larger pores are introduced into the concrete. In the early stage of hydration, the water in the gel is not completely released, and at 28 days, the water in the gel is fully released, and large pores are introduced into the concrete, and the strength of the concrete decreases more significantly.

[0249] It can be seen from the compressive strength data of C03 and D03 concretes in Table 15 that, compared with BASF internal curing agent, the compressive strength of concrete prepared using the concrete internal curing agent prepared by the present invention is higher.

[0250] Table 16 28d flexural strength of different concrete

[0251]

[0252] It can be seen from Table 16 that the dosage, fineness, water-cement ratio and type of internal curing agent of concrete will affect the flexural strength of concrete.

[0253] By comparing C01 to C04, it can be seen that with the increase in the amount of curing agent in concrete, the flexural strength of concrete gradually decreases. Compared with C01, the flexural strength of C02, C03 and C04 are 4.5%, 8.75% and 10.1% lower respectively. The higher the amount of curing agent in concrete, the greater the decrease in strength.

[0254] By comparing C03, C05 and C06, it can be seen that when the same amount of concrete curing agent is added, the water-binder ratio has a significant effect on the compressive strength, and the strength of the concrete decreases significantly with the increase of the water-binder ratio.

[0255] By comparing C03, C03-1 and C03-2, it can be seen that under the same conditions, the increase in the size of the curing agent in the concrete will lead to a decrease in the flexural strength of the concrete.

[0256] Comparing C03 and D03, the flexural strength of concrete added with the two internal curing agents is close, which shows that the effect of the concrete internal curing agent prepared by the present invention on the flexural strength of concrete is within a controllable range.

[0257] The present invention synthesized the vermiculite / polyacrylic acid-acrylamide composite material by inverse suspension polymerization and applied it to concrete. The conclusions are as follows:

[0258] Through research, it was found that vermiculite has a flaky structure, and nitric acid treatment will destroy the vermiculite lamellae from the edge; nitric acid modification will change the structure of vermiculite, and with the increase of nitric acid concentration, vermiculite gradually changes into an amorphous structure. Based on the orthogonal experiment, the results of the single factor test and the BET test, it was found that the best acid treatment process was determined from the perspective of humidity control performance, that is, the nitric acid concentration was 2 mol / L, the treatment temperature was 90 ° C, and the heating time was 4 h. Based on the acid modification test, the acid-modified vermiculite was modified with hexadecanetrimethylammonium bromide. The XRD and FTIR spectrum results showed that hexadecanetrimethylammonium bromide was successfully inserted into the interlayer of vermiculite.

[0259] The invention prepares a vermiculite / polyacrylic acid-acrylamide composite material by reverse phase suspension polymerization on the basis of organic modified vermiculite, and studies the morphology, structure and humidity control performance of the composite material, and finds that the composite material presents irregular spherical particles with a rough surface. During the polymerization process, acrylic acid and acrylamide enter the interlayer of vermiculite, undergo polymerization reaction, and form a good combination with the vermiculite. The influence of the organic modified vermiculite content, neutralization degree and the mass ratio of AA to AM on the moisture absorption and release performance of the composite material is analyzed by orthogonal experiment and single factor experiment, and finds that the mass ratio of AA to AM has the greatest influence on the moisture absorption and release performance of the composite material, the influence of the organic vermiculite content is second, and the influence of the neutralization degree is the smallest. The most suitable preparation process is that the mass fraction of organic modified vermiculite is 4%, the neutralization degree is 90% and mAA:mAM=4:1, and the moisture absorption rate and moisture release rate are 1.285g / g and 1.172g / g respectively.

[0260] The present invention uses vermiculite / polyacrylic acid-acrylamide composite humidity-controlling material as concrete internal curing agent, applies it to concrete, systematically studies the influence of concrete internal curing agent dosage, water-cement ratio, concrete internal curing agent fineness and internal curing agent type on concrete performance, and analyzes the influence of adding concrete internal curing agent by testing concrete internal humidity, autogenous shrinkage and drying shrinkage, mechanical properties and working performance.

[0261] The results show that: adding a certain amount of concrete curing agent can improve the working performance of concrete; adding concrete curing agent can improve the internal relative humidity of concrete, the more the amount of concrete curing agent added, the higher the internal relative humidity of concrete, and the increase in water-binder ratio can also improve humidity changes; the change of the amount of concrete curing agent before 0.2% has a significant effect on the autogenous shrinkage and drying shrinkage, the increase in water-binder ratio will inhibit the autogenous shrinkage of concrete, the increase in the size of concrete curing agent will promote the shrinkage of concrete, and the autogenous shrinkage and drying shrinkage values ​​will increase significantly; the addition of concrete curing agent will reduce the compressive and flexural strength of concrete, the increase in water-binder ratio will significantly reduce the strength of concrete, and the increase in the size of concrete curing agent will have an adverse effect on the strength of concrete; compared with the BASF internal curing agent purchased on the market, the concrete internal curing agent prepared by the present invention can effectively reduce the shrinkage of concrete and reduce the adverse effect on the strength of concrete.

[0262] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a concrete internal curing agent, characterized in that: The following steps are involved: Adding acrylic acid into the alkaline aqueous solution and mixing them evenly to obtain an acrylic acid solution; Add acrylamide to the acrylic acid solution, stir evenly, then add modified vermiculite, continue stirring, add a crosslinking agent and an initiator, mix evenly, and obtain a mixed solution; The organic solvent and the dispersant are mixed and heated, and then added to the mixed solution, stirred evenly, and then heated to the reaction temperature for polymerization reaction, and after the reaction is completed, dried, crushed, and sieved to obtain the concrete curing agent; The preparation method of the modified vermiculite comprises the following steps: Add vermiculite to an acid solution, heat and stir to react to obtain acid-modified vermiculite; the acid solution comprises a nitric acid solution with a concentration of 2 to 4 mol / L; the ratio of the acid solution to the vermiculite is 10 mL: 1 g; the temperature of the heating and stirring reaction is 70 to 99° C., the time is 2 to 8 hours, and the stirring speed is 500 r / min; The acid-modified vermiculite is added to the surface modifier solution and heated to react to obtain the modified vermiculite; the mass ratio of the acid-modified vermiculite to the surface modifier in the surface modifier solution is 1:10; the temperature of the heating reaction is 80° C. and the time is 3 hours; The mesh number of the sieve used for the sieving is 400 meshes.

2. The preparation method according to claim 1, characterized in that: The neutralization degree of the acrylic acid solution is 70-100%.

3. The preparation method according to claim 1, characterized in that: The mass ratio of acrylic acid to acrylamide is (1-10):1; The amount of the modified vermiculite is 1-10% of the total mass of acrylic acid, acrylamide and the modified vermiculite.

4. The preparation method according to claim 1, characterized in that: The organic solvent includes cyclohexane; the dispersant includes Span60; The cross-linking agent includes N-N'methylenebisacrylamide; the amount of the cross-linking agent is 0.5wt.% of the total mass of acrylic acid, acrylamide and modified vermiculite; The initiator includes potassium persulfate; the amount of the initiator is 0.3wt.% of the total mass of acrylic acid, acrylamide and modified vermiculite; The polymerization reaction was carried out at a temperature of 70° C. and for 3 hours.

5. A concrete curing agent prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the concrete curing agent according to claim 5 in the preparation of concrete materials.

7. A concrete material, characterized in that: The raw materials include: basic components of concrete, the concrete curing agent according to claim 5, and additional water; The amount of the concrete curing agent is 0.1-0.3% of the mass of the cementitious material in the basic components; The amount of additional water used is 20 times the mass of the curing agent in the concrete.

8. A method for preparing the concrete material according to claim 7, characterized in that: The following steps are involved: The concrete curing agent and the additional water are mixed to pre-absorb water, and then mixed with the basic components of the concrete, and after being stirred evenly, formed and cured to obtain the concrete material.

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