An organic-inorganic composite admixture, its preparation method and its application in a calcined clay-limestone low-carbon cement system

Abstract

An organic-inorganic composite admixture, its preparation method and its application in a calcined clay-limestone low-carbon cement system. The organic-inorganic composite admixture is prepared by free radical copolymerization of unsaturated carboxylic acid, 2-acrylamido-2-methylpropanesulfonic acid, methacryloylpropyltrimethylammonium chloride or acryloylpropyltrimethylammonium chloride, maleic anhydride grafted β-cyclodextrin, an oxidizing agent and a reducing agent, and then by electrostatic assembly reaction with POM polyoxometalate. In the present invention, a spatial cross-linked double network structure is formed through the characteristics of the β-cyclodextrin and polyoxometalate POM structures, resulting in a large steric hindrance and forming a sufficiently thick adsorption layer, which hinders the competitive adsorption of the clay on the admixture; double adsorption sites are formed through the carboxyl and sulfonic acid groups on the main chain and side chains, further enhancing the dispersion ability of the admixture in the LC 3 system, and finally achieving the characteristics of low dosage, high water reduction rate and excellent slump retention performance.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly relates to an organic-inorganic composite admixture, a preparation method thereof, and an application thereof in a calcined clay-limestone low-carbon cement system. Background Art

[0002] In recent years, with the rapid growth of the population and the improvement of the urbanization level, the demand for relevant urban infrastructure has been increasing continuously. At the same time, it has driven the growth of cement production. However, the manufacturing process of traditional cement not only consumes a large amount of natural raw materials, but its CO 2 emissions have long ranked among the top in global carbon emissions. Therefore, in order to reduce the impact of cement production on natural resources and the environment and reduce the CO 2 emissions of the cement industry, the development and application of high-performance supplementary cementitious materials to largely replace cement and clinker are internationally recognized as one of the most important technical ways for the low-carbon development of the cement and concrete industries.

[0003] Scholars at home and abroad have been researching new low-carbon cementitious systems for a long time. Among them, Limestone Calcined Clay Cement (LC 3 ) originated from the research of the Swiss Federal Institute of Technology (Lausanne) and is a kind of cement composed of limestone, calcined clay, gypsum and clinker. In LC 3 , limestone and calcined clay will react to form calcium carboaluminate hydrate, which promotes cement hydration, and the hydration products increase with the increase of the content of calcined clay. Therefore, LC 3 still has high mechanical properties at a relatively high cement clinker replacement rate. The X in LC 3 -X represents the proportion of the mass of clinker in the total mass of cement. The most typical LC 3 -50 formulation contains 50% Portland cement clinker, 30% calcined clay, 15% limestone powder and 5% gypsum. Since calcined clay does not produce carbon emissions during the heating process and its calcination temperature is lower than that of cement clinker, compared with traditional cement, LC 3 replaces half of the clinker and can reduce carbon dioxide emissions by about 40%.

[0004] However, some studies have shown that LC 3The workability of the system concrete is worse than that of ordinary Portland cement concrete, which is caused by the layered structure and surface electrical properties of clay. At present, the traditional comb-shaped polycarboxylate superplasticizer PCE is particularly sensitive to the amount of clay and has poor adaptability, especially in terms of problems such as initial fluidity and fluidity loss over time. This is because the side chains of PCE are easily inserted into the layered structure of clay, resulting in a sharp decrease in its dispersibility and poor water-reducing workability. Secondly, although the surface of calcined clay particles is negatively charged, in the cement paste, through the complexation of Ca 2+ it will also cause the negatively charged PCE to be anchored on the clay surface and thus unable to continuously play a dispersing role. Therefore, the traditional comb-shaped polycarboxylate superplasticizer cannot be well applied to LC 3 system concrete. Therefore, modifying the molecular structure of the superplasticizer to solve the workability problem of the LC 3 system has attracted extensive attention from relevant concrete technology researchers.

[0005] Chinese patent application with publication number CN 117105595 A discloses a low-carbon engineering cement-based composite material and its preparation method, which is prepared from the following components in parts by weight: 240-370 parts of cement, 550-650 parts of calcined clay, 140-330 parts of lightly burned dolomite powder, 340-370 parts of quartz sand, 26 parts of PVA fiber, 425 parts of water, and 3-4.5 parts of high-range water reducer. Compared with traditional high-ductility cement-based composites, it has significantly improved mechanical properties, greatly reduced shrinkage, and obvious strain hardening and multi-crack cracking characteristics. However, this patent application does not give the specific structure of the high-range water reducer and does not report its influence on workability.

[0006] Chinese patent application with publication number CN115959870 A discloses a crack-resistant low-carbon high-performance concrete and its preparation method. The raw materials and their dosages include: LC 3 cementitious material 390-410 kg / m 3 sand 640-660 kg / m 3 stone 1000-1100 kg / m 3 water 150-170 kg / m 3 water reducer 8.0-8.5 kg / m 3 activated carbon fiber 0.1-0.3 kg / m 3 graphene oxide 0.1-0.3 kg / m 3 ; where LC 3The gelling material mainly consists of cement, calcined clay, limestone powder and gypsum; the water is composed of the mixing plant wastewater and fresh water. The water reducing agent is a polycarboxylate-based water reducing agent with a solid content of 20% and a water reducing rate of 19%. Whether the PCE structure mentioned above contains anti-clay groups is not mentioned, resulting in no obvious advantages in the slump and spread of this system. Summary of the Invention

[0007] Technical problems to be solved: Aiming at the problems in the prior art that the adaptability of traditional comb-shaped cement dispersants and clay-containing materials is poor, such as insufficient initial water reducing rate and large slump loss, etc., the present invention provides an organic-inorganic composite admixture, its preparation method and its application in the calcined clay-limestone low-carbon cement system. From the perspective of changing the molecular solution conformation of the polycarboxylate admixture, by introducing bifunctional groups, the interaction with clay particles is avoided, and no intercalation structure is formed with clay; monomers with significant steric effects are introduced to further avoid intercalation adsorption while improving the dispersion performance by the steric hindrance generated by the side chains; an admixture with a side chain without -CH 2 -CH 2 -O- structure is synthesized to improve the anti-clay property of the polycarboxylate admixture.

[0008] Technical solution: An organic-inorganic composite admixture, the raw materials of which include the following components: monomer A, monomer B, monomer C, monomer D, polyoxometalate POM, oxidant and reductant, wherein monomer A is an unsaturated carboxylic acid, monomer B is 2-acrylamido-2-methylpropanesulfonic acid (AMPS), monomer C is methylacryloylpropyltrimethylammonium chloride (MAPTAC) or acryloylpropyltrimethylammonium chloride (APTAC), monomer D is maleic anhydride grafted β-cyclodextrin (MAH-β-CD), and the mass ratio of monomer A, monomer B, monomer C, monomer D is 70: (15 - 25) :10 : (0.5 - 1.5), the addition amount of the polyoxometalate and the mass ratio of monomer C is 1:1.1 - 1.4, the dosage of the oxidant is 0.1 - 0.5 wt% of the total mass of the monomers, and the mass ratio of the reductant to the oxidant is 1:2.

[0009] Preferably, the polyoxometalate POM is phosphomolybdic acid H 3 [PMo 12 O 40 or silicomolybdic acid H 4 [SiMo 12 O 40 , both of these two polyoxometalates are commercially available, wherein [SiMo 12 O 40 4- and [PMo 12 O 40 3- ​​The anionic group can perform charge assembly with the cationic tertiary amine group of MAPTAC or APTAC.

[0010] Preferably, the oxidant is a water-soluble azo oxidant, ammonium persulfate, sodium persulfate or potassium persulfate.

[0011] Preferably, the reducing agent is at least one of sodium metabisulfite, sodium sulfite, sodium bisulfite, sodium dithionite, sodium thiosulfate and ferrous sulfate.

[0012] Preferably, the structural formula of monomer A, an unsaturated carboxylic acid, is as shown in the following formula (I):

[0013] (I)

[0014] In the formula, R 1 is H or CH 3 , and R 2 is H or an alkali metal ion.

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

[0016] (II).

[0017] Furthermore, the structural formula of monomer C is as shown in the following formula (III):

[0018] (III),

[0019] In formula (III), R 3 is H or CH 3 .

[0020] Furthermore, the structural formula of monomer D is as shown in the following formula (IV):

[0021] (IV),

[0022] In formula (IV), M represents an alkali metal ion.

[0023] Based on the above preparation method of an organic-inorganic composite admixture, the steps are as follows:

[0024] Step 1, copolymerization reaction: Monomers A, B, C, D, and the oxidant and reducing agent undergo a free radical copolymerization reaction, and this free radical copolymerization reaction is a conventional free radical copolymer reaction in an aqueous system;

[0025] Step 2, electrostatic assembly reaction: Add polyoxometalate POM to the copolymer system in Step 1, and the electrostatic assembly reaction can be completed by magnetic stirring at room temperature.

[0026] The weight-average molecular weight of the organic-inorganic composite admixture polymer is 60-100 kDa, and the PDI is 2-3.

[0027] Preferably, in the free radical copolymerization reaction in the first step, the polymerization temperature is 35-55 °C, the reaction time is 4-7 h, and the polymerization concentration is 15-20%.

[0028] Preferably, the conditions for the normal temperature magnetic stirring reaction in the second step are: under normal temperature (25 °C), the stirring rate is 600-1000 r / min, and the reaction time is 3-5 h.

[0029] Based on the above-mentioned organic-inorganic composite admixture in the application as an admixture for the calcined clay-limestone low-carbon cement system (LC 3 ). It can be used to improve the clay tolerance of the polycarboxylic acid admixture to the LC 3 system and can greatly improve the construction performance of concrete.

[0030] Preferably, the dosage of the organic-inorganic composite admixture is 0.1-0.2 wt%.

[0031] The principle of the present invention is as follows:

[0032] Cyclodextrin is a kind of cyclic oligosaccharide maltose formed by connecting D-pyranose glucose units through α-(1-4) glycosidic bonds. According to the number of glucose units, cyclodextrin can be divided into α-, β-, γ-, δ-......θ-cyclodextrin, etc. Among them, β-cyclodextrin (abbreviated as β-CD) has a slightly conical hollow cylindrical three-dimensional ring structure. The inner diameter of the molecular cavity is about 0.61 nm at the smallest and about 0.78 nm at the largest; its height is about 0.78 nm, with a significant steric hindrance effect. A large number of hydroxyl groups are contained in β-CD, and many kinds of cyclodextrin derivatives containing different functional groups can be obtained through modification. Relevant literature has pointed out that since the interlayer exchange ions of clay are cations, only structural units with opposite charges will enter the crystal layer due to electrostatic interaction to form an intercalated structure. Therefore, β-CD groups can be introduced into the polycarboxylic acid molecular structure. Because it has a negative charge, it avoids entering the crystal layer of clay due to electrostatic interaction, thereby preventing the chemical adsorption of the polycarboxylic acid admixture on the clay. In addition, the polymer structure with a large steric hindrance of the β-CD group also has an inhibitory effect on the interlayer intercalation adsorption of the polycarboxylic acid molecule on the clay.

[0033] Polyoxometalate (hereinafter referred to as POM) is a molecular cluster formed by the self-assembly of tetrahedral transition metal oxalate precursors in aqueous or organic solutions through common points, edges or faces. It is a special type of anionic metal oxide cluster with various chemical compositions and rich topological structures. With the development of supramolecular chemistry, more and more polyoxometalates and their derivatives have been widely used as inorganic building units to design and construct organic-inorganic hybrid materials with unique functional properties. The synergistic effect between inorganic nanomaterials and polymers endows polymer nanocomposites with the function of synergistic enhancement. One of the main characteristics is that the small size effect of inorganic nanoparticles leads to a sharp increase in the interfacial area between them and the polymer matrix. Introducing POM units into the molecular structure of polycarboxylic acid can further increase the steric hindrance of polycarboxylic acid molecules to ensure their high water-reducing and dispersing ability.

[0034] According to the structural characteristics and activity effects of the currently commonly used anti-clay admixtures, β-CD and POM groups, the present invention attempts to solve the above problems from the idea of synthesizing organic-inorganic composite polymer materials, and then improve the construction performance of calcined clay-limestone low-carbon cement system (LC 3 ) concrete.

[0035] Therefore, the present invention provides an organic-inorganic composite admixture, its preparation method and its application in a calcined clay-limestone low-carbon cement system (LC 3 ) By modifying the molecular structure of the admixture, introducing anti-clay functional monomers for modification, changing the structure of the polycarboxylic acid admixture molecules to improve their anti-clay performance, and at the same time ensuring the working performance of the admixture molecules, thereby realizing and solving the application problems of large-scale promotion of low-carbon cementitious systems in the concrete and construction industries.

[0036] The application to calcined clay-limestone low-carbon cement (LC 3)(In the molecular structure of the organic-inorganic composite admixture of the system, carboxyl groups and sulfonic acid groups (i.e., the adsorption sites with the cement-based material) are distributed on both the main chain and the side chain, forming double adsorption sites, which can effectively improve the adsorption capacity and thus fully realize the high water-reducing function. Secondly, the significant spatial effect of β-CD and the nanostructure of POM existing in the organic-inorganic composite admixture form a spatial cross-linked double network structure, causing a large steric hindrance and forming a sufficiently thick adsorption layer, further enhancing the dispersing ability of the admixture for cement particles. Moreover, there is no long-side-chain polyether monomer in the molecular structure of the organic-inorganic composite admixture as in conventional polycarboxylate admixtures, making it difficult to form an intercalated structure with clay and preventing the admixture from being adsorbed by clay. In addition, the AMPS unit can increase the absolute value of the Zeta potential on the clay surface, thereby further improving the dispersibility of the admixture in the system. Finally, the nanostructure of POM has the small-size effect of inorganic nanoparticles, which will lead to a sharp increase in the interfacial area between it and the polymer matrix, resulting in less adsorption of the admixture on clay and further improving the high-efficiency utilization rate of the admixture in concrete.)

[0037] Beneficial effects:

[0038] (1) The present invention utilizes the structural characteristics of the organic-inorganic composite admixture, that is, through the significant spatial effect of the β-CD unit structure and the nanostructure of the POM unit in the organic-inorganic composite admixture to form a spatial cross-linked double network structure, causing a large steric hindrance and forming a sufficiently thick adsorption layer, which doubly hinders the intercalated adsorption of the admixture between clay layers and significantly improves the adaptability of the admixture.)

[0039] (2) The present invention utilizes the carboxyl groups and sulfonic acid groups on the main chain and side chain in the molecular structure of the organic-inorganic composite admixture to form double adsorption sites and fully exert the water-reducing effect.)

[0040] (3) The present invention utilizes the POM unit in the organic-inorganic composite admixture. The small-size effect of the inorganic nanoparticles it possesses will lead to a sharp increase in the interfacial area between it and the polymer matrix, resulting in less adsorption of the admixture on clay and further improving the high-efficiency utilization rate of the admixture in concrete.) Specific embodiments

[0041] The present invention will be further described below in conjunction with specific embodiments.)

[0042] In the embodiments of this specification, unless otherwise specified, the raw materials used are all from ordinary commercially available products.)

[0043] A kind of provided by the present invention can be applied to calcined clay-limestone low-carbon cement (LC 3The organic-inorganic composite admixture of the system is formed by the random copolymerization of monomer A (unsaturated carboxylic acid), monomer B (2-acrylamido-2-methylpropanesulfonic acid (AMPS)), monomer C (methacryloylpropyltrimethylammonium chloride (MAPTAC) or acryloylpropyltrimethylammonium chloride (APTAC)), and monomer D (maleic anhydride grafted β-cyclodextrin (MAH-β-CD)), and then through electrostatic interaction with POM (polyoxometalate).

[0044] In the examples of this specification, the alkali metal ions are sodium and potassium.

[0045] The structural formula of the monomer A is as shown in the following formula (Ⅰ):

[0046] (Ⅰ)

[0047] In formula (Ⅰ), R 1 is H or CH 3 , and R 2 is H or an alkali metal ion.

[0048] The monomer A is specifically acrylic acid, methacrylic acid, sodium acrylate, or potassium acrylate.

[0049] The structural formula of the monomer B is as shown in the following formula (Ⅱ):

[0050] (Ⅱ)

[0051] The structural formula of the monomer C is as shown in the following formula (Ⅲ):

[0052] (Ⅲ)

[0053] In formula (Ⅲ), R 3 is H or CH 3 .

[0054] The structural formula of the monomer D is as shown in the following formula (Ⅳ):

[0055] (Ⅳ)

[0056] In formula (Ⅳ), M represents an alkali metal ion.

[0057] The weight-average molecular weight Mw of the organic-inorganic composite admixture is 60 - 100 kDa, and the PDI is 2 - 3.

[0058] In addition, in the examples, it can be applied to calcined clay-limestone low-carbon cement (LC 3The weight-average molecular weight of the organic-inorganic composite admixture for the system was determined using a Shimadzu LC-20A high-performance gel permeation chromatograph (GPC). The chromatographic column used was the TSK G4000PWXL series, the column temperature was 25 °C, the eluent was 0.1 M aqueous sodium acetate solution, the flow rate was 0.5 ml / min, the injection volume was 15 μl of a 1‰ aqueous solution of the sample, and a dextran standard (Sigma-Aldrich) was used to prepare the standard curve.

[0059] This application example also provides a preparation method for an organic-inorganic composite admixture applied to calcined clay-limestone low-carbon cement (LC 3 ), and the specific steps are as follows:

[0060] (1) Copolymerization reaction:

[0061] Raw materials: monomer A, monomer B, monomer C, and monomer D. Monomer A is an unsaturated carboxylic acid, monomer B is 2-acrylamido-2-methylpropanesulfonic acid (AMPS), monomer C is methylacryloylpropyltrimethylammonium chloride (MAPTAC) or acryloylpropyltrimethylammonium chloride (APTAC), and monomer D is maleic anhydride grafted β-cyclodextrin (MAH-β-CD). The mass ratio of the input of monomers A, B, C, and D is 70: 15~25 :10 :0.5~1.5.

[0062] The oxidant consists of a single oxidant, selected from any one of water-soluble azo oxidants, ammonium persulfate, sodium persulfate, and potassium persulfate. The dosage of the oxidant is 0.1~0.5 wt% of the total mass of the monomers. The reducing agent is one or two of sodium metabisulfite, sodium sulfite, sodium bisulfite, sodium dithionite, sodium thiosulfate, and ferrous sulfate in any proportion combination. The mass ratio of the dosage of the reducing agent to the oxidant is 1:2.

[0063] Preparation steps: Mix monomer A, monomer B, monomer C, and monomer D, as well as the oxidant and the reducing agent, and carry out a free radical copolymerization reaction at a temperature of 35-55 °C for 4-7 hours. Among them, the free radical copolymerization reaction is a water-based free radical copolymerization reaction, and the polymerization concentration of the free radical copolymerization reaction is 15-20%.

[0064] (2) Electrostatic assembly reaction:

[0065] Add POM to the copolymer system prepared in the copolymerization reaction (1). The mass ratio of POM to the mass of monomer C is 1:1.1~1.4, and carry out a conventional magnetic stirring reaction at room temperature for 3-5 h, and the stirring rate is 600~1000 r / min.

[0066] The following is illustrated by specific examples.

[0067] Example

[0068] Table 1 Raw material ratio table of the examples (the feeding ratio is the feeding mass ratio of monomer A, monomer B, monomer C, and monomer D)

[0069]

[0070] Table 2 Process parameter table of the examples (the dosages of the oxidant and the reductant are percentages of the total mass of the monomers)

[0071]

[0072] Comparative example

[0073] The differences between Comparative Examples 1-6 and the examples lie in the different preparation process conditions of the admixture, as shown in Tables 3 and 4 specifically.

[0074] Table 3 Raw material ratio table of the comparative examples (the feeding ratio is the mass ratio of monomer A, monomer B, monomer C, and monomer D)

[0075]

[0076] Table 4 Process parameter table of the comparative examples (the dosages of the oxidant and the reductant are percentages of the total mass of the monomers)

[0077]

[0078] Application example

[0079] The application example of this application provides a calcined clay-limestone low-carbon cement system (LC 3 ).

[0080] The calcined clay-limestone low-carbon cement system is composed of the following substances mixed together:

[0081] (1) 30 parts by mass of calcined clay (CC)

[0082] (2) 15 parts by mass of limestone (L)

[0083] (3) 55 parts by mass of Portland cement (P)

[0084] In this application example, the analysis tables of the composition, particle size, and loss on ignition of the calcined clay-limestone low-carbon cement system are shown in Tables 5 to 7. The composition is determined by a Thermo Fisher Scientific ADVANT·XP type X-ray fluorescence spectrometer, and the particle size composition is determined by an Anton Paar PSA 1190LD type laser particle size analyzer. Among them, the calcined clay, limestone, and Portland cement are all commercially available products.

[0085] Table 5 Calcined clay-limestone low-carbon cement system (LC 3)Raw material composition table

[0086]

[0087] Table 6 Raw material particle size analysis table

[0088]

[0089] Table 7 Raw material loss on ignition data table

[0090]

[0091] Add the organic-inorganic composite admixture prepared in Examples 1-8 to the calcined clay-limestone low-carbon cement system to obtain Application Examples 1-12.

[0092] The differences between Application Examples 1-12 lie in the source and dosage of the organic-inorganic composite admixture. See Table 8 for details.

[0093] Table 8 Source and dosage table of the organic-inorganic composite admixture for Application Examples 1-12

[0094]

[0095] Comparative application examples

[0096] The differences between the comparative application examples and the application examples lie in the source and dosage of the organic-inorganic composite admixture. See Table 9 for details.

[0097] Table 9 Source and dosage table of the organic-inorganic composite admixture for Comparative Application Examples 1-6

[0098]

[0099] Performance testing:

[0100] Refer to the test method in GB / T 8077-2012 "Test Methods for the Homogeneity of Concrete Admixtures". Evaluate the influence of the admixtures in Application Examples 1-12 and Comparative Application Examples 1-6 on the net slurry fluidity and its time-dependent loss of the fresh calcined clay-limestone low-carbon cement system (LC 3 ) paste, and fix the water-cement ratio at 0.30. In addition, a control group is set up, and the admixture in the control group is the commercially available Kelong KL-1389 polyether-type anti-sludge agent. The dosage of the admixture in Control Group 1 is 0.14 wt%, and the dosage of the admixture in Control Group 2 is 0.17 wt%. The experimental results are shown in Table 10.

[0101] Table 10 Performance test result table

[0102]

[0103] Note: The percentages in the table are mass fractions.

[0104] As can be seen from the experimental results in Table 10, when applied to the calcined clay-limestone low-carbon cement system (LC 3 ), according to the performance comparison of Application Examples 1-8 and Comparative Group 1, at the same admixture dosage, the initial net paste fluidity and 1h paste fluidity of the fresh paste in Application Examples 1-8 are higher than those of Comparative Group 1. Therefore, compared with traditional comb-shaped cement dispersants, the organic-inorganic composite admixture of this patent application has the characteristics of low dosage, high water reduction rate and excellent slump retention performance even when applied to the calcined clay-limestone low-carbon cement system with a high clay content.

[0105] In the organic-inorganic composite admixture of this patent application, by using the carboxyl group and sulfonic acid group in its molecular structure to form double adsorption sites, the adsorption capacity can be effectively improved, and then the high water reduction function can be fully realized; secondly, by using the significant spatial effect of the existing β-CD and the nanostructure of POM to form a spatial cross-linked double network structure, a large steric hindrance is caused to form a sufficiently thick adsorption layer, further improving the dispersing ability of the admixture on cement particles; furthermore, there is no long-chain polyether monomer in the molecular structure of this admixture like conventional polycarboxylate admixtures, which makes it difficult to form an intercalation structure with clay and prevents the admixture from being adsorbed by clay, which can greatly reduce the influence of clay on the fluidity of the calcined clay-limestone low-carbon cement system. On the other hand, finally, the small size effect of the POM unit as an inorganic nanoparticle will cause a sharp increase in the interfacial area between it and the polymer matrix, resulting in less adsorption of the admixture on clay and further improving the high-efficiency utilization rate of the admixture in the calcined clay-limestone low-carbon cement system.

[0106] In addition, we also found that under the same dosage condition, the dispersion effects of the admixtures in Application Examples 1-4 are also different. Finally, it was found that the performance of Application Example 3 is better than that of other application examples. This is because too large or too small molecular weight is not conducive to the admixture to exert its working performance. This is because the carboxylic acid and sulfonic acid groups in the admixture structure have a strong affinity for the cementitious material, so the admixture can be fixed on the surface of cement particles, and the nanostructures of β-CD and POM will form a spatial cross-linked double network structure. When the molecular weight of the admixture is too high, the solution conformation of the molecular structure is too large, and the main chain structure will cause a shielding effect on the adsorption sites, namely the carboxylic acid and sulfonic acid groups. When the molecular weight is too low, the content of adsorption sites is too low, resulting in the admixture being unable to be fixed on the surface of cement particles and unable to form an effective network structure, thus unable to effectively hinder the adsorption of the admixture on clay and difficult to improve the initial fluidity and its time-dependent fluidity of the LC 3 system.

[0107] It can be seen from the analysis of Application Examples 5 to 6 that when the number of repeating units of monomer B is small, there will be too few adsorption sites, i.e., sulfonic acid groups, in the admixture, resulting in too low dispersion performance. Therefore, the workability of Application Example 5 is better than that of Application Example 6. It can be seen from Application Examples 7 to 8 that the workability of Application Example 7 is better than that of Application Example 8. This is because the structure of monomer D, i.e., the number of β-CD units, should not be too high. Otherwise, the admixture will entangle and agglomerate itself, and cannot effectively disperse the calcined clay-limestone low-carbon cement system (LC 3 ) system.

[0108] Meanwhile, it is not difficult to find from Application Examples 9 to 12 that when the dosage of the organic-inorganic composite admixture increases (0.1% → 0.2%), the initial fluidity and the fluidity with time of the fresh cement paste of the LC 3 system will first increase slowly and then decrease. Among them, the effect of Application Example 10 is the best. Because when the dosage is too high, the dual adsorption sites of the admixture will cause the bridging effect to easily occur secondary agglomeration phenomenon, and then the segments in the admixture will entangle with each other, thus reducing the initial dispersion performance of the LC 3 system, and ultimately leading to the reduction of the overall workability of the system.

[0109] Compared with Application Examples 1 to 8, the workability of Comparative Application Example 1 is significantly lower than that of the LC 3 system applied with the organic-inorganic composite admixture of the present invention, which proves that the lack of carboxylic acid groups cannot form dual adsorption sites, and relying only on sulfonic acid groups cannot effectively improve the adsorption capacity, making it difficult to improve the initial fluidity of the LC 3 system. The workability of Comparative Application Example 2 is the worst among all application examples, which proves that the lack of the corresponding β-CD structure will not be able to achieve the spatial cross-linked double network structure, and relying only on the nanostructure of the POM unit cannot form an "isolation zone" between the clay and the cement-based material, thus making it difficult to fully realize the high dispersion function.

[0110] Further analysis of the performance of Comparative Application Examples 3 to 4 shows that too few carboxylic acid groups in the admixture are not conducive to the dispersion performance of the admixture, but too many do not necessarily result in the best workability. This shows that there is a coordination relationship between monomer A, monomer B, monomer C, monomer D and the POM structure in this application. If the number of a certain unit is too large, it will affect the overall structural performance of the admixture. Combining the performance of Comparative Application Example 5 and Comparative Application Example 6, it is found that whether the amount of monomer C and the POM structure is too large or too small, the final application performance is not good, indicating that the number of monomer C and the POM structure will affect the double network structure formed by them and the β-CD unit, and thus affect the overall workability of the admixture.

[0111] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment that do not contribute creatively as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. An organic-inorganic composite admixture, characterized in that: The raw materials include the following components: monomer A, monomer B, monomer C, monomer D, polyoxometalate, oxidant and reductant, wherein monomer A is unsaturated carboxylic acid, monomer B is 2-acrylamido-2-methylpropanesulfonic acid, monomer C is methacryloylpropyltrimethylammonium chloride or acrylylpropyltrimethylammonium chloride, monomer D is maleic anhydride grafted β-cyclodextrin, the mass ratio of monomer A, monomer B, monomer C and monomer D is 70:(15-25):10:(0.5-1.5), the mass ratio of the added amount of polyoxometalate to that of monomer C is 1:1.1-1.4, the amount of oxidant is 0.1-0.5 wt% of the total mass of monomers, and the mass ratio of reductant to oxidant is 1:2; wherein the polyoxometalate is phosphomolybdic acid H3[PMo 12 O 40 ] or silicomolybdic acid H4 [SiMo 12 O 40 ]; The preparation method of the organic-inorganic composite admixture comprises the following steps: Step 1, copolymerization reaction: free radical copolymerization reaction is carried out on monomer A, monomer B, monomer C, monomer D, an oxidant and a reducing agent, and the free radical copolymerization reaction is a conventional water system free radical copolymerization reaction; Step 2: Electrostatic assembly reaction: Add polyoxometalate to the copolymer system in step 1, and perform magnetic stirring reaction at room temperature to complete the electrostatic assembly reaction.

2. An organic-inorganic composite admixture according to claim 1, characterized in that: The oxidant is a water-soluble azo oxidant, ammonium persulfate, sodium persulfate or potassium persulfate.

3. An organic-inorganic composite admixture according to claim 1, characterized in that: The reducing agent is at least one of sodium pyrosulfite, sodium sulfite, sodium bisulfite, sodium dithionite, sodium thiosulfate and ferrous sulfate.

4. The organic-inorganic composite admixture according to claim 1, characterized in that: In the free radical copolymerization reaction in step 1, the polymerization temperature is 35-55° C., the reaction time is 4-7 h, and the polymerization concentration is 15-20%.

5. The organic-inorganic composite admixture according to claim 1, characterized in that: The conditions for the room temperature magnetic stirring reaction in step 2 are: at room temperature, the stirring rate is 600-1000 r / min, and the reaction time is 3-5 h.

6. Use of the organic-inorganic composite admixture according to claim 1 as an admixture for a calcined clay-limestone low-carbon cement system.

7. The use according to claim 6, characterized in that: The dosage of the organic-inorganic composite admixture is 0.1-0.2 wt%.

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