Ultrahigh-water-reducing type polycarboxylic acid water reducing agent as well as preparation method and application thereof

Abstract

The invention provides an ultrahigh water reducing type polycarboxylate superplasticizer as well as a preparation method and application thereof, the preparation method is basically consistent with a synthesis method of a conventional polycarboxylate superplasticizer in an initial stage, but when the polyether conversion rate reaches 60-75%, the reaction is temporarily frozen through a stopping liquid, then a polyether monomer is supplemented, the polyether monomer conversion rate is actually reduced, and the reaction time is shortened. Restarting the polymerization reaction by adjusting the inorganic acid and continuously dropwise adding the reducing agent; the obtained water reducer product effectively reduces the proportion of products with ultrahigh acid-ether ratio generated in the early stage and the final stage of general polycarboxylic acid synthesis, obviously improves the water-reducing rate of polycarboxylic acid, improves the water-reducing rate by 10-20% compared with the water-reducing rate of existing products, and also has relatively outstanding clay tolerance and ground material adaptability and wide market application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete admixtures, and particularly relates to a super high water-reducing polycarboxylate water reducer, a preparation method thereof and an application thereof. Background Art

[0002] Water reducers are a type of concrete admixture that is currently the most widely studied and applied. When the workability of concrete remains unchanged, adding water reducers can effectively save cement consumption, reduce water consumption, and improve the strength of concrete. As the latest generation of high-performance concrete water reducers, polycarboxylates have outstanding advantages such as low dosage, good slump retention, strong molecular structure controllability, and green and environmentally friendly production processes. Chemically speaking, polycarboxylate is a comb-shaped polymer, which consists of a main chain rich in carboxylic acid groups and polyether side chains. The carboxylic acid groups on the main chain can be adsorbed on the surface of positively charged cement or cement hydrates, and the polyether side chains extend in the solution to form a hydration layer to provide steric repulsion to prevent cement agglomeration. Therefore, this structure endows polycarboxylate with a powerful ability to disperse cement particles.

[0003] With the increasing shortage of high-quality natural concrete materials in China, the application ratios of some low-quality aggregates, mineral admixtures, and industrial waste residues have been increasing year by year, further squeezing the water reduction rate of polycarboxylate water reducers, resulting in a significant increase in the dosage of polycarboxylate water reducers. This not only increases the production cost of concrete enterprises, but also easily causes problems such as non-setting and insufficient strength of concrete. Therefore, the development of super high water-reducing polycarboxylate water reducers has always been the core issue in the research field of admixtures.

[0004] Researchers have found in long-term practice that during the synthesis of polycarboxylic acid, the monomer composition of each stage product is significantly different, so the water-reducing performance of each stage product also varies significantly. In the conventional synthesis of polycarboxylic acid water-reducing agents, two monomers, polyether and acrylic acid, are used. Since the polyether adopts a bottoming process, as the reaction progresses, the concentration of the polyether monomer gradually decreases. For acrylic acid, due to the dropping process, in the initial stage of the reaction, that is, the polymerization induction period, acrylic acid accumulates. After the reaction starts, the concentration of acrylic acid will be rapidly consumed and then maintained at a relatively constant concentration until the end of the reaction. Therefore, during the synthesis of polycarboxylic acid, the instantaneous monomer concentration ratio of acrylic acid and polyether will change from high to low and then gradually increase. According to the principle of polymer polymerization, the monomer composition of the polymerization product is affected by the instantaneous monomer ratio in the polymerization system. Therefore, for a synthesis system with a feed ratio of acrylic acid to polyether of 4, the polymerization product in the early stage (conversion rate < 25%) will be much greater than 4, and the acid-ether ratio of the product in the middle stage (conversion rate 25 - 75%) is generally between 2 and 4. It is found that the product in the middle stage plays a decisive role in the water reduction rate. In the later stage of the reaction (conversion rate > 75%), as the polyether is gradually consumed, its acid-ether ratio soars rapidly. In the initial and final stages of polymerization, the acid-ether ratio of its product will even be greater than 10, which will result in insufficient polyether side chain density and insufficient steric hindrance. It can be said that the products in the early and later stages are "impurities" and cannot make a significant contribution to water reduction.

[0005] Patent CN107722194B adopts a technical solution of concentrating the adsorption groups on the side chain to increase the water reduction rate of the existing polycarboxylic acid products by more than 30%; Patent CN109970921B enhances the steric hindrance effect of the polycarboxylic acid water-reducing agent molecule by introducing a benzene ring and a carboxyl structure at the end of the branched chain of the polycarboxylic acid water-reducing agent molecule, and the prepared polycarboxylic acid water-reducing agent has a higher water reduction rate.

[0006] Patent 201910015191.1 discloses a preparation method of a novel polyether for synthesizing a super high water-reducing polycarboxylic acid water-reducing agent, which uses a novel polycarboxylic acid water-reducing agent macromonomer ethylene glycol mono vinyl polyethylene glycol ether (EPEG) as the reaction macromonomer. It has the advantages of high reaction activity, higher adaptability of the synthesized polycarboxylic acid water-reducing agent; short reaction time required, easy control of the reaction process; low reaction temperature required, and the reaction can be carried out at room temperature above 5°C, etc. The initiator of the used ethylene glycol mono vinyl polyethylene glycol ether (EPEG) macromonomer is directly generated by the reaction of acetylene and ethylene glycol, without generating by-products, and the unreacted acetylene can be recycled, with the advantages of environmental protection, low carbon, and sustainable development. Summary of the Invention

[0007] In view of the problems in the prior art during the synthesis of polycarboxylic acids, such as impurities that cannot effectively contribute to water reduction in the early and later stages due to the acid-ether ratio, etc., this application provides a super high water-reducing polycarboxylic acid water reducer, its preparation method and application. The obtained water reducer product effectively reduces the proportion of super high acid-ether ratio products generated in the early and final stages of general polycarboxylic acid synthesis, significantly improves the water reduction rate of polycarboxylic acids, with the water reduction rate increased by 10 - 20% compared to existing products. It also has relatively prominent clay tolerance and adaptability to local materials, and has broad market application prospects.

[0008] A preparation method of a super high water-reducing polycarboxylic acid water reducer, comprising the following steps:

[0009] (1) Mix the polyether monomer and water evenly to prepare solution A; mix the acrylic acid monomer, co-monomer, reducing agent, chain transfer agent and water evenly to prepare solution B; mix the free radical inhibitor, alkaline substance and water evenly to prepare the termination solution;

[0010] (2) Use part of solution A as the base, control the temperature at 10 - 50 °C, add the oxidizing agent, and add part of solution B dropwise to the reaction system, with the dropping reaction time being 0.3 - 2 h;

[0011] (3) Add part of the termination solution to raise the pH of the system to 6.5 - 7.5, terminate the reaction, then replenish part of solution A again, add part of the inorganic acid to adjust the pH value of the reaction system to 3.5 - 5.0, and continue to dropwise add part of solution B, with the dropping reaction for 0.3 - 2 h;

[0012] (4) Repeat the above step (3) cyclically, with the number of cycles being 2 - 5 times;

[0013] (5) After the last cycle of dropping solution B, keep the reaction at a certain temperature for 1 - 2 h to make the monomers react completely, and then add the alkaline substance to neutralize the pH of the final product to 6 - 7, and then it can be discharged;

[0014] The mass ratio of the above polyether monomer, acrylic acid monomer, and co-monomer is 100:(5 - 18):(0.5 - 2).

[0015] The structural formula of the above polyether monomer is shown as the following general formula (I):

[0016] R1 is -H or -CH3, R2 is -OCH2CH2-, -OCH2CH2CH2CH2-, -CH2-, -CH2CH2-; n is an integer from 45 to 90.

[0017] The structural formula of the above co-monomer is shown as the following general formula (II):

[0018] R3 is -H or -CH3, R4 is -CH2CH2-, -CH2CH2CH2-, -CH2CHOHCH2-, phenyl or benzyl, and X is -O- or -NH-. The comonomer is a vinyl monomer containing a tertiary amine structure, and its functions are: (1) The tertiary amine structure has reducibility and can generate free radicals, which can help the initiation system generate free radicals quickly and restart the reaction after adding an inorganic acid to adjust the pH; (2) The free radicals generated by the tertiary amine structure can introduce a certain degree of branching structure into the polymer, increase the steric hindrance of the polycarboxylic acid molecule, and improve the water-reducing performance; (3) The tertiary amine structure has alkalinity and can assist the termination solution to quickly terminate the reaction.

[0019] The above chain transfer agent is selected from any one or a combination of mercaptoacetic acid, mercaptopropionic acid, and mercaptoethanol; the dosage of the chain transfer agent in step (1) is 0.1-0.6% of the total mass of the polyether monomer, acrylic acid monomer, and comonomer.

[0020] The above reducing agent is selected from any one or a combination of L-ascorbic acid, sodium formaldehyde sulfoxylate, sodium sulfite, sodium bisulfite, and ferrous sulfate; the dosage of the reducing agent in step (1) is 0.15-1% of the total mass of the polyether monomer, acrylic acid monomer, and comonomer.

[0021] The above oxidizing agent is selected from any one or a combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the dosage of the oxidizing agent in step (2) is 0.2-2% of the total mass of the polyether monomer, acrylic acid monomer, and comonomer.

[0022] The above radical inhibitor is selected from any one or a combination of hydroquinone, p-benzoquinone, methylhydroquinone, p-methoxyphenol, and phenothiazine; the dosage of the radical inhibitor in step (1) is 0.01-0.05% of the total mass of the polyether monomer, acrylic acid monomer, and comonomer.

[0023] The above basic substance is selected from any one or a combination of sodium hydroxide, potassium hydroxide, pyridine, ethylenediamine, triethylamine, diethylenetriamine, and sodium acetate; the dosage of the basic substance in step (1) is 35-150% of the total mass of the acrylic acid monomer and comonomer; the inorganic acid is selected from any one or a combination of hydrochloric acid, sulfuric acid, and nitric acid.

[0024] In step (1), the mass fraction of the polyether monomer in solution A is 50-60%. Limited by the solubility and viscosity of the polyether monomer, the concentration cannot be too high or too low, otherwise the reaction will be too slow or will not proceed. Therefore, 50-60% is more appropriate; in step (2), the dosage of the initial solution A is 15-40% (equivalent to less initial polyether, a reduced proportion of polyether passing through the induction period, resulting in fewer impurities, but there is also a certain proportion and cannot be infinitely small, otherwise too much polyether will be added subsequently, equivalent to starting the reaction from the beginning and entering the induction period again), and the dosage of solution A replenished each time in the subsequent steps is 15-40%.

[0025] There is no specific requirement for the amount of water used to prepare Solution B and the termination solution, but the total concentration of the reaction system should be maintained at 40-60%; in each step, the amount of Solution B is based on the ratio A% of the amount of Solution A in this step, and the amount of Solution B is (A%-10%)-(A%+10%). The dropping reaction time (0.3-2h) in steps (2) and (3) is actually determined by the polyether conversion rate. When the polyether conversion rate reaches 60-75%, the termination solution is immediately added to suspend the reaction; due to the differences in the reaction monomers, initiators, and temperatures, the dropping times to reach the target polyether conversion rate are also different.

[0026] The water reducer obtained by the above preparation method has the structural formula shown in the following general formula (III): R1 is -H or -CH3, R2 is -OCH2CH2-, -OCH2CH2CH2CH2-, -CH2-, -CH2CH2-; n is an integer from 45 to 90; R3 is -H or -CH3, R4 is -CH2CH2-, -CH2CH2CH2-, -CH2CHOHCH2-, phenyl or benzyl, X is -O- or -NH-; a = 5-38, b = 1-20, c = 15-140, n = 45-90.

[0027] The above super high water reducing polycarboxylate water reducer has a weight average molecular weight of 20,000-80,000. When the water reducer is applied to the cement concrete system, the dosage of the water reducer is 0.05%-0.3% of the total mass of the cementitious materials. The dosage is the pure solid dosage, and the percentage is the mass percentage. Too low a dosage will deteriorate its performance, and too high a dosage will cause economic waste and the performance cannot be improved.

[0028] The super high water reducing polycarboxylate water reducer described in the present invention can be used in combination with other commercially available water reducers, such as lignosulfonate water reducers, naphthalene sulfonate water reducers, polycarboxylate water reducers, etc., and can also be used after adding air-entraining agents, retarders, early strength agents, expansive agents, thickening agents, shrinkage reducing agents, and defoaming agents.

[0029] The synthesis method of the super high water reducing polycarboxylate water reducer described in the present invention is basically the same as that of the conventional polycarboxylate water reducer in the initial stage. However, when the polyether conversion rate reaches 60-75%, the reaction is temporarily frozen by the termination solution, and then the polyether monomer is replenished. In fact, the polyether monomer conversion rate decreases, and then through the adjustment of inorganic acid and the continuous dropping of reducing agent, the polymerization reaction is restarted. This polymerization method of termination and restart has the following advantages compared with the prior art:

[0030] (1) There is an induction period only during the first feeding polymerization, generating "impurities" with a high acid-ether ratio. There will be no long induction period during subsequent cycles, thus effectively reducing the proportion of low-dispersion products in the initial stage. During each feeding polymerization process, due to the accumulation of polymerization inhibitors and salts (produced by the neutralization of the base and inorganic acid in the termination liquid), the difference in the reactivity ratios between acrylic acid and polyether monomers will gradually decrease, thereby reducing the "impurities" with a high acid-ether ratio in the later-stage products and improving their water-reducing ability.

[0031] (2) The super high water-reducing polycarboxylate water reducer of this application has excellent water-reducing and slump-retention capabilities, with a 10 - 20% improvement in water-reducing ability compared to conventional polycarboxylate water reducers.

[0032] (3) The super high water-reducing polycarboxylate water reducer of this application has excellent clay tolerance, and the effect of reducing the dosage and saving costs is more obvious when applied in areas with a high mud content in sand and gravel aggregates.

[0033] (4) The super high water-reducing polycarboxylate water reducer of this application has strong adaptability to various cementitious materials, admixtures, sand and gravel aggregates, and has universality in national applications, without the need to waste excessive manpower for adaptation work.

[0034] (5) The production process is simple. Using the one-pot method, it is simple and efficient, can be continuously produced in the same reaction kettle, has high reaction efficiency and short time, is basically the same as the production conditions of conventional polycarboxylate water reducers, does not require equipment improvement, and is easy to achieve large-scale industrial production. Detailed Embodiments

[0035] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] The polyether monomers (double bond retention value > 98%) used in the embodiments of the present invention are produced by Nanjing Bote New Materials Co., Ltd., and other raw materials are all purchased from TCI Chemical Reagent Co., Ltd.

[0037] The polyether monomers used in the embodiments of the present invention are respectively methallyl polyoxyethylene ether (HPEG), isopentenyl polyoxyethylene ether (TPEG), 4-hydroxybutyl vinyl polyoxyethylene ether (VPEG), and diethylene glycol mono vinyl ether polyoxyethylene ether (EPEG). The numbers following the English abbreviations of the polyethers in the embodiments represent the weight-average molecular weight. For example, TPEG-2400 represents isopentenyl polyoxyethylene ether with a weight-average molecular weight of 2400.

[0038] The structural formulas and corresponding codes of the comonomers used in the embodiments of the present invention are as follows:

[0039]

[0040] In each example and comparative example of this application, the number-average molecular weight of the polymer was measured using a gel permeation chromatograph of Wyatt technology corporation. (Gel column: Two Shodex SB806 + 803 chromatographic columns in series; Eluent: 0.1M NaNO3 solution; Mobile phase velocity: 1.0 ml / min; Detector: Shodex RI-7 differential refractive index detector; Molecular weight standard: Polyethylene glycol GPC standard sample (Sigma-Aldrich, molecular weights 1010000, 478000, 263000, 118000, 44700, 18600, 6690, 1960, 628, 232).

[0041] Example 1

[0042] The preparation steps of the super high water-reducing polycarboxylate water reducer are as follows:

[0043] Mix 100 parts of polyether monomer and 66.7 parts of water evenly to prepare solution A, mix 7.27 parts of acrylic acid monomer, 0.643 parts of co-monomer A-1, 0.271 parts of reducing agent L-ascorbic acid, 0.449 parts of chain transfer agent mercaptoethanol and 26 parts of water evenly to prepare solution B, mix 0.0505 parts of free radical inhibitor hydroquinone, 4.04 parts of sodium hydroxide and 24 parts of water evenly to prepare the termination solution. Subsequently, add 25% of solution A to the flask equipped with a stirrer and a thermometer to prime, heat the reaction system to 50 °C, add 1.163 parts of oxidant hydrogen peroxide, and then slowly drip 20% of solution B into the reaction system through a dropping pump, and carry out the dropping reaction for 2 h;

[0044] Cycle 1: Slowly add the termination solution to increase the pH of the system to 7.1. At this time, 28% of the termination solution is fed, the reaction is terminated, then 30% of solution A is replenished, and then inorganic acid (total amount 4.11 parts) is added to adjust the pH value of the reaction system to 4.2. At this time, 26% of the inorganic acid is fed, and 20% of solution B is continuously added dropwise, and the dropping reaction is carried out for 0.6 h;

[0045] Cycle 2: Slowly add the termination solution to increase the pH of the system to 6.8. At this time, 34% of the termination solution is fed, the reaction is terminated, then 25% of solution A is replenished, and then inorganic acid is added to adjust the pH value of the reaction system to 3.8. At this time, 30% of the inorganic acid is fed, and 30% of solution B is continuously added dropwise, and the dropping reaction is carried out for 0.6 h;

[0046] Cycle 3: Slowly add the remaining 38% of the termination solution to increase the pH of the system to 6.5, terminating the reaction. Subsequently, add 30% of Solution A, and then add the remaining 44% of the inorganic acid to adjust the pH value of the reaction system to 4.4. Continue to dropwise add 30% of Solution B and react for 1.2 h, and then keep the reaction at a constant temperature for 1 h;

[0047] After Cycle 3 is completed, add 6.31 parts of sodium hydroxide to obtain the super high water-reducing polycarboxylate water reducer. The measured solid content is 49.3%, the molecular weight measured by GPC is 62706, and the conversion rate is 95.12%.

[0048] The synthesis methods of Examples 2 to 10 are the same as that of Example 1, and the specific reaction conditions are listed in the following table. Tables 1-1 and 1-2 are the types and dosages of raw materials in the reaction, Tables 2 and 3 are the usage plans of Solution A and Solution B in the reaction, and Table 4 is the reaction temperature and product characterization data in the examples.

[0049] Table 1-1

[0050]

[0051]

[0052] Table 1-2

[0053]

[0054] Table 2

[0055]

[0056] Table 3

[0057]

[0058]

[0059] Table 4

[0060] Example Reaction temperature (°C) Solid content (%) Molecular weight Conversion rate (%) 1 50 49.3 62706 95.12 2 45 43.6 48338 94.66 3 45 38.5 72953 95.07 4 35 42.7 36137 94.95 5 35 48.6 24860 93.80 6 20 48.5 60107 93.91 7 15 48.3 34607 95.63 8 15 47.6 37889 94.48 9 15 49.2 65318 93.24 10 12 48.2 30960 93.22

[0061] Comparative Examples 1 to 2 represent the performance levels of current conventional polycarboxylate water reducers. Among them, Comparative Example 1 is synthesized in the laboratory, and Comparative Example 2 is purchased externally.

[0062] Comparative Example 1

[0063] Add 100 parts of HPEG-2400, 0.142 parts of hydrogen peroxide and 100 parts of water into a flask equipped with a stirrer and a thermometer. Then stir and heat up to 45°C. At this temperature, dropwise add a mixed solution composed of 14.16 parts of acrylic acid, 0.355 parts of mercaptoethanol, 0.183 parts of L-ascorbic acid and 12.5 parts of water. The dropping time is 3 h. After the dropping is completed, keep the temperature for 1 h. Then add 4.1 g of sodium hydroxide. This is a common polycarboxylate water reducer prepared by a conventional method in the laboratory. The measured solid content is 50.1, the molecular weight measured by GPC is 31692, and the conversion rate is 94.77%.

[0064] Comparative Example 2

[0065] A commercially available high-performance polycarboxylate water reducer, purchased from a certain admixture company in South China. The measured solid content is 34.8, the molecular weight measured by GPC is 40615, and the conversion rate is 93.65%.

[0066] Comparative Example 3

[0067] Add 100 parts of HPEG-2400, 0.37 parts of hydrogen peroxide and 100 parts of water into a flask equipped with a stirrer and a thermometer. Then stir and heat up to 45°C. At this temperature, dropwise add a mixed solution composed of 14.16 parts of acrylic acid, 0.786 parts of co-monomer A-3, 0.328 parts of mercaptoethanol, 0.352 parts of L-ascorbic acid and 13.4 parts of water. The dropping time is 3 h. After the dropping is completed, keep the temperature for 1 h. Then add 4.1 g of sodium hydroxide. This is a common polycarboxylate water reducer prepared by a conventional method in the laboratory. The measured solid content is 49.9, the molecular weight measured by GPC is 40152, and the conversion rate is 93.58%.

[0068] The actual acid-ether ratio of polymer is measured by nuclear magnetic resonance (NMR), and the testing instrument is a Bruker AvanceIII 400MHz NMR spectrometer, uses D2O as solvent, and the ratio of characteristic peak area is taken to calculate the acid-ether ratio. Provide the actual acid-ether ratio of embodiment 1~10 and comparative example 1 sample early stage, mid-term and later stage product below, to verify the effect of the control stage reaction of the method for the present invention. During the test, when the reaction proceeds to conversion efficiency C1 (20~25%), C2 (70~75%) and reaction end terminal C3, take out a small amount of sample, drop into ice-water bath rapidly to stop the reaction, then the sample is put into dialysis bag (molecular weight cut-off 7000), dialyze in deionized water for 7 days to remove unreacted monomer and other impurity, the sample low temperature freeze drying that obtains, removes moisture, and then does the NMR test. The test value of the sample taken out at the conversion rate C1 is the average acid-ether ratio of the product between the conversion rate 0 and C1 (this data represents the acid-ether ratio of the early product), and the test value of the sample taken out at the conversion rate C2 is calculated by removing the data of the product between the conversion rate 0 and C1, and converted to the average acid-ether ratio of the product between the conversion rate C1 and C2 (this data represents the acid-ether ratio of the mid-term product). Similarly, the test value of the sample taken out at the conversion rate C3 is calculated by removing the data of the product between the conversion rate 0 and C2, and converted to the average acid-ether ratio of the product between the conversion rate C2 and C3 (this data represents the acid-ether ratio of the late product). The test results are shown in Table 5.

[0069] Table 5

[0070]

[0071] manual

[0072]

[0073] It can be seen from the data in Table 5 that during the synthesis of Examples 1 to 10 and Comparative Examples 1-3, the acid-ether ratio of the products at each stage has experienced a process from large to small and then increased. The difference is that the maximum acid-ether ratio of the example samples generally does not exceed 5.5, while the maximum acid-ether ratio of the comparative example samples exceeds 9. These samples with excessive acid-ether ratios are obviously by-product impurities with extremely weak dispersibility. From the standard deviation of the acid-ether ratio data of the early, middle and late products, the example samples (0.6 to 1.1) are significantly smaller than the comparative example (2.6 to 2.8), which shows that the acid-ether ratio of the products at each stage of the example samples is more average, and the acid-ether ratio of the products has a larger proportion in the optimal range. In short, the above results show that the ultra-high water-reducing polycarboxylate water-reducing agent described in the present invention has a significant difference in the acid-ether ratio composition of the stage products compared with the conventional polycarboxylate water-reducing agent, which provides a theoretical basis for the continued improvement of the performance of polycarboxylate.

[0074] The cement used in the following test examples is Conch PⅡ42.5, the mineral powder is S95 type mineral powder produced by Jiangnan Grinding Co., Ltd., the fly ash is Class I fly ash produced by Jiangsu Huanneng Electric Power Company, the sand is Yongqiang machine-made sand, and the gravel is basalt with a continuous gradation of 5-20 mm particle size.

[0075] Test Example 1: Determination of mortar fluidity

[0076] According to the regulations in GB / T8077-2000 "Test Methods for Homogeneity of Concrete Admixtures", the mortar fluidity of the super high water-reducing polycarboxylate water reducer synthesized in the examples and comparative examples of the present invention was determined to evaluate the water-reducing and slump retention capabilities of the samples for cement paste. The test mix ratio was: cement 445 g, fly ash 205 g, sand 1300 g, water 240 g, the solid content of the water reducer was 0.14%, and sodium gluconate was 0.03%. The results are shown in Table 6.

[0077] Table 6

[0078]

[0079] Note: -- indicates loss of fluidity

[0080] Comparative Examples 1 and 2 represent the level of conventional polycarboxylate water reducers, and Comparative Example 3 is a sample with the same raw materials as those used in the examples of the present invention but different polymerization methods. Analyzing the data in Table 6, it can be seen that at the same dosage, the initial fluidity of Examples 1-10 is approximately between 270-300 mm, while that of the comparative examples is between 230-250 mm. From the perspective of fluidity over time, the examples still have fluidity at 120 min, while the comparative examples have lost all fluidity. The above results show that the super high water-reducing polycarboxylate water reducer described in the present invention has more excellent water-reducing and slump retention properties compared to conventional polycarboxylate water reducers. The reason for the performance improvement is not the update of raw materials, but the beneficial effects brought by the stop-repolymerization method described in the present invention.

[0081] Test Example 2: Clay tolerance test

[0082] Montmorillonite is a typical clay that widely exists in some poor-quality aggregates and can greatly weaken the dispersion performance of polycarboxylate. Therefore, in this experiment, the method of adding montmorillonite to cement was used to imitate the mud content in the actual application environment to detect the clay tolerance of the super high water-reducing polycarboxylate water reducer in the examples. The test method was that the total of cement and montmorillonite was 300 g, the water-cement ratio was fixed at 0.29, the dosage of the water reducer in the examples was fixed at 0.15%, and the dosage of the water reducer in the comparative examples was fixed at 0.17%, so that the fluidity of the samples was similar without montmorillonite, which could clearly show the anti-mud effect of the samples. The results are shown in Table 7.

[0083] Table 7

[0084]

[0085] Note: a = (fluidity without montmorillonite - fluidity with 1% montmorillonite) / fluidity without montmorillonite.

[0086] The data in Table 7 show that after adding 0.5% montmorillonite, the fluidity of the neat cement pastes of both the examples and the comparative examples decreased. After adding 0.5% montmorillonite, the examples still had fluidity, while the comparative examples had lost fluidity. Considering the fluidity loss from when there was no montmorillonite to when there was 0.5% montmorillonite, the loss of the examples was between 20% and 25%, and the loss of the comparative examples reached about 40%. These data clearly show that the super high water-reducing polycarboxylate water reducer described in the present invention has excellent clay tolerance, and this product will have good application prospects in areas where the mud content of sand and gravel aggregates is high.

[0087] Test Example 3: Adaptability Test

[0088] The adaptability of the super high water-reducing polycarboxylate water reducer described in the present invention to materials from different regions was evaluated through neat cement paste tests in different cements. Test method: When testing, the water-cement ratio was fixed at 0.29, and it was still ensured that the admixture dosage of the water reducer in the examples was fixed at 0.15%, and the admixture dosage of the water reducer in the comparative examples was fixed at 0.17%. The test results are shown in Table 8.

[0089] Table 8

[0090]

[0091] The data in Table 8 show that among the 5 different cements, the standard deviation of the fluidity of the neat cement paste of the example samples was basically about 35 mm, while that of the comparative examples was greater than 50 mm. This shows that the super high water-reducing polycarboxylate water reducer described in the present invention has good adaptability to different cement materials, which is of great significance for solving the problems of frequent changes in local materials and large quality differences of commercial concrete users at present.

[0092] Test Example 4: Dispersion Ability Test

[0093] Finally, the dispersion ability of the super high water-reducing polycarboxylate water reducer described in the present invention was evaluated through a concrete fluidity test. In the test, poor quality machine-made sand with a high mud content (mud content of 4.3%) was selected as the fine aggregate to further verify the anti-clay performance of the example samples. Concrete mass mix ratio: cement 235, mineral powder 35, fly ash 35, machine-made sand 945, crushed stone 1000, water 160, sodium gluconate 0.04%. The test results are shown in Table 9.

[0094] Table 9

[0095]

[0096] Note: -- indicates that the slump flow has been lost

[0097] As can be seen from the concrete test results in Table 9, on the premise that the dosage is 20% lower, there is no difference between the examples and the comparative examples in terms of slump / spread at the initial stage and 60 minutes. This shows that the super high water-reducing polycarboxylate water reducer described in the present invention has a greater dosage advantage compared with the conventional polycarboxylate water reducer in practical applications, and can significantly save the costs of customers.

[0098] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a super high water-reducing polycarboxylate water reducer, characterized in that, It includes the following steps: (1) Mix the polyether monomer and water evenly to prepare solution A; mix the acrylic monomer, co-monomer, reducing agent, chain transfer agent and water evenly to prepare solution B; mix the free radical inhibitor, alkaline substance and water evenly to prepare the termination solution; (2) Pour a part of solution A as a base, control the temperature at 10 - 50 °C, add the oxidizing agent, and add part of solution B dropwise to the reaction system, with the dropwise addition reaction time of 0.3 - 2 h; (3) Add part of the termination solution to increase the pH of the system to 6.5 - 7.5, terminate the reaction, then replenish part of solution A again, add part of the inorganic acid to adjust the pH value of the reaction system to 3.5 - 5.0, and continue to add part of solution B dropwise, with the dropwise addition reaction of 0.3 - 2 h; (4) Repeat the above step (3) cyclically, with the number of cycles being 2 - 5 times; (5) After the last cycle of dropwise addition of solution B, keep the temperature for reaction for 1 - 2 h to complete the monomer reaction, and then add the alkaline substance to neutralize the pH of the final product to 6 - 7 for discharging; The mass ratio of the polyether monomer, acrylic monomer and co-monomer is 100:(5 - 18):(0.5 - 2).

2. The preparation method of a super high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The structural formula of the polyether monomer is shown as the following general formula (I): R1 is -H or -CH3, R2 is -OCH2CH2-, -OCH2CH2CH2CH2-, -CH2-, -CH2CH2-; n is an integer from 45 to 90.

3. The preparation method of a super high water reducing polycarboxylate water reducer according to claim 1, characterized in that: The structural formula of the co-monomer is shown as the following general formula (II): R3 is -H or -CH3, R4 is -CH2CH2-, -CH2CH2CH2-, -CH2CHOHCH2-, phenyl or benzyl, and X is -O- or -NH-.

4. The preparation method of a super high water reducing polycarboxylate water reducer according to claim 1, characterized in that: The chain transfer agent is selected from any one or a combination of mercaptoacetic acid, mercaptopropionic acid, mercaptoethanol, etc.; the dosage of the chain transfer agent in step (1) is 0.1 - 0.6% of the total mass of the polyether monomer, acrylic monomer and co-monomer.

5. The preparation method of a super high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The reducing agent is selected from any one or a combination of L-ascorbic acid, sodium formaldehyde sulfoxylate, sodium sulfite, sodium bisulfite, ferrous sulfate, etc.; the dosage of the reducing agent in step (1) is 0.15 - 1% of the total mass of the polyether monomer, acrylic monomer and co-monomer.

6. The preparation method of a super high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The oxidizing agent is selected from any one or a combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, etc.; the dosage of the oxidizing agent in step (2) is 0.2 - 2% of the total mass of the polyether monomer, acrylic monomer and co-monomer.

7. The preparation method of a super high water reducing polycarboxylate water reducer according to claim 1, characterized in that: The free radical inhibitor is selected from any one or a combination of hydroquinone, p-benzoquinone, methylhydroquinone, p-methoxyphenol, phenothiazine, etc.; the dosage of the free radical inhibitor in step (1) is 0.01 - 0.05% of the total mass of the polyether monomer, acrylic monomer and co-monomer.

8. The preparation method of a super high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The alkaline substance is selected from any one or a combination of sodium hydroxide, potassium hydroxide, pyridine, ethylenediamine, triethylamine, diethylenetriamine, sodium acetate, etc.; the dosage of the alkaline substance in step (1) is 35 - 150% of the total mass of the acrylic monomer and co-monomer; the inorganic acid is selected from any one or a combination of hydrochloric acid, sulfuric acid, nitric acid, etc.

9. The preparation method of a super high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The mass fraction of the polyether monomer in solution A in step (1) is 50 - 60%; the dosage of the base solution A in step (2) is 15 - 40%, and the dosage of solution A replenished in subsequent steps is 15 - 40% each time.

10. The preparation method of a super high water reducing polycarboxylate water reducer according to claim 1, characterized in that: The dosage of solution B in each step is based on the proportion A% of the dosage of solution A in this step, and the dosage of solution B is (A% - 10%) - (A% + 10%).

11. The super high water reducing polycarboxylate water reducer obtained by the preparation method of the super high water reducing polycarboxylate water reducer according to any one of claims 1-10, characterized in that, The structural formula of the water reducing agent is shown as the following general formula (III): R1 is -H or -CH3, R2 is -OCH2CH2-, -OCH2CH2CH2CH2-, -CH2-, -CH2CH2-; n is an integer from 45 to 90; R3 is -H or -CH3, R4 is -CH2CH2-, -CH2CH2CH2-, -CH2CHOHCH2-, phenyl or benzyl, X is -O- or -NH-; a = 5 to 38, b = 1 to 20, c = 15 to 140, n = 45 to 90.

12. The application method of a super high water reducing polycarboxylate water reducer according to claim 11, characterized in that: When the water reducing agent is applied to the cement concrete system, the dosage of the water reducing agent is 0.05% - 0.3% of the total mass of the cementitious materials.

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