A water reducing agent for pressed concrete and its preparation method and application

Abstract

The present invention proposes a water reducer for pressing concrete and its preparation method and application, which belongs to the technical field of additives for concrete. The raw materials of the water reducer for concrete of the present invention include modified polycarboxylic acid water reducer, acrylic acid, crosslinking agent and initiator, which are mainly prepared by compounding a slow-release water reducer and a hydrogel material. In the preparation process, the hydrogel prepared by using acrylic acid and hyaluronic acid monomers and the slow-release water reducer work together. While the hydrogel absorbs water, the ester group of the slow-release water reducer begins to hydrolyze and participate in the reaction. When the hydrogel is saturated with water, the water reducer works. In the process of preparing concrete using the above-mentioned concrete water reducer, the hydrogel structure is crushed by the pressing method, and the internal free water is squeezed out, so that the whole is kept in a relatively dry state. The demoulding concrete can be used to press small components, such as overhead floors, cement-based pavements, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete additives, and in particular relates to a water reducing agent for pressed concrete and a preparation method and application thereof. Background Art

[0002] Pressed concrete is a concrete forming method carried out under high pressure, mainly used to prepare small components, such as cement floors. Its process is realized through a production line, including weighing, feeding (accuracy within 2%), mixing in a mixer, placing the mixed material on a distributor, and then using a hydraulic press (pressure ≥ 10MPa). During the pressing process, the cement components are pressed, vented, drained (pressed out the water in the slurry and evenly dispersed), pressure-maintaining and aging, mold opening, and product ejection are completed.

[0003] There are many types of water reducers for concrete. For example, according to the composition materials, they are divided into: (1) lignin sulfonates; (2) polycyclic aromatic salts; (3) water-soluble resin sulfonates. According to the chemical composition, they are usually divided into: lignin sulfonate water reducers, naphthalene-based high-efficiency water reducers, melamine-based high-efficiency water reducers, aminosulfonate-based high-efficiency water reducers, fatty acid-based high-efficiency water reducers, and polycarboxylate-based high-efficiency water reducers. Different types of concrete are suitable for different types of water reducers. At present, polycarboxylate water reducers are commonly used in pressed concrete, but their water reduction effect is not ideal. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a water reducing agent for pressed concrete and a preparation method and application thereof.

[0005] To achieve the above object, the present invention provides a method for preparing a modified polycarboxylic acid water-reducing agent, comprising the following steps:

[0006] (1) mixing hyaluronic acid, thionyl chloride and a catalyst, stirring and reacting, and then distilling under reduced pressure and drying to obtain modified hyaluronic acid;

[0007] (2) mixing acrylic acid, the modified hyaluronic acid obtained in step (1) and a solvent, adding a catalyst and a coupling agent during the mixing process, then adding water for extraction and drying to obtain an esterification product;

[0008] (3) adding water to the esterification product obtained in step (2) to obtain an esterification product aqueous solution, and adding a sodium bicarbonate aqueous solution to adjust the pH value to obtain a hydrolyzed product;

[0009] (4) stirring the macromonomer and heating it, adding the hydrolyzate obtained in step (3), acrylic acid, ester compounds, sodium methacrylsulfonate aqueous solution and ammonium persulfate aqueous solution during the stirring process, and keeping the temperature after the reaction is completed to obtain the modified polycarboxylic acid water-reducing agent.

[0010] Furthermore, in step (1), the mass ratio of thionyl chloride to hyaluronic acid is (0.01-0.03):1, and the mass ratio of the catalyst to hyaluronic acid is (0.01-0.05):1;

[0011] The temperature of the mixing and stirring reaction is 40-60° C., and the reaction time is 8-10 hours.

[0012] Furthermore, in step (2), the molar ratio of the acrylic acid to the hyaluronic acid in step (1) is (1-1.2):1, the molar ratio of the catalyst to the hyaluronic acid in step (1) is (0.01-0.03):1, and the molar ratio of the coupling agent to the modified hyaluronic acid obtained in step (1) is (0.005-0.01):1;

[0013] The stirring and mixing temperature is 20-40°C, and the stirring time is 4-6h.

[0014] Furthermore, in step (3), the mass concentration of the sodium bicarbonate aqueous solution is 20-40%, the sodium bicarbonate aqueous solution is added to adjust the pH value to 6-7, and the mass concentration of the esterification product aqueous solution is 20-30%.

[0015] Furthermore, in step (3), the reaction temperature is room temperature and the reaction time is 1 h.

[0016] Furthermore, in step (4), the macromonomer includes isopentanol polyoxyethylene ether (molecular weight of 1200-2400) and / or methyl allyl polyoxyethylene ether (molecular weight of 1200-2400); and the ester compound includes one or more of methyl acrylate, ethyl acrylate and butyl acrylate.

[0017] Further, in step (4), the molar ratio of the macromonomer to the hyaluronic acid in step (1) is (1-1.2):1, the molar ratio of the acrylic acid to the hyaluronic acid in step (1) is (2-3):1, the molar ratio of the ester compound to the hyaluronic acid in step (1) is (0.6-1):1, the molar ratio of the sodium methacrylic sulfonate in the sodium methacrylic sulfonate aqueous solution to the hyaluronic acid in step (1) is (0.08-0.12):1, the molar ratio of the ammonium persulfate in the ammonium persulfate aqueous solution to the acrylic acid in step (4) is (0.0030-0.0033):1, and the mass ratio of the ammonium persulfate in the ammonium persulfate aqueous solution to the hyaluronic acid in step (1) is (0.01-0.03):1;

[0018] In step (4), the temperature is raised to 40-60° C. with stirring, and the stirring time is 1-2 h.

[0019] Furthermore, in step (4), the mass concentrations of the ammonium persulfate aqueous solution and the sodium methyl acrylate sulfonate aqueous solution are both 20-40%.

[0020] The present invention also provides a modified polycarboxylic acid water-reducing agent prepared by the above preparation method.

[0021] The present invention also provides a water reducer for pressed concrete, the raw materials of which include the modified polycarboxylic acid water reducer, acrylic acid, a crosslinking agent and an initiator, the molar ratio of the acrylic acid to the modified polycarboxylic acid water reducer is (1-1.5):1, the molar ratio of the crosslinking agent to the acrylic acid is (0.004-0.01):1, and the molar ratio of the initiator to the acrylic acid is (0.01-0.035):1; the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate and / or potassium persulfate.

[0022] Furthermore, the cross-linking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate and / or potassium persulfate.

[0023] The structural formula of the water reducing agent for pressed concrete provided by the present invention is as follows:

[0024]

[0025] Wherein, R1 is methoxy or ethoxy, R2 is methyl, ethyl or butyl, m is 27-54, n is 200-500, and both m and n are natural numbers.

[0026] The present invention also proposes a method for preparing the water reducing agent for pressed concrete, comprising the following steps:

[0027] The modified polycarboxylic acid water-reducing agent, sodium hydroxide aqueous solution and acrylic acid are mixed, the pH is adjusted to be neutral, the temperature is increased, and a cross-linking agent and an initiator are added under stirring conditions. After the reaction is completed, the mixture is washed and dried to obtain the water-reducing agent for concrete.

[0028] Further, the modified polycarboxylic acid water-reducing agent, sodium hydroxide aqueous solution and acrylic acid were mixed, and the pH was adjusted to 7, the temperature was raised to 50° C., and the cross-linking agent and initiator were added within 1 hour under stirring.

[0029] The invention also proposes an application of the water reducing agent for pressed concrete in preparing pressed concrete.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] (1) The water reducer prepared by the present invention is a compressed water reducer, which is mainly prepared by compounding a slow-release water reducer and a hydrogel material. During the preparation process, the hydrogel prepared by using acrylic acid and hyaluronic acid monomers first temporarily absorbs a part of the water required for preparing concrete, and at the same time, the slow-release water reducer takes effect. When the hydrogel absorbs water, the ester group of the slow-release water reducer begins to hydrolyze and participate in the reaction. When the hydrogel is saturated with water, the water reducer takes effect.

[0032] (2) When the water reducing agent for pressed concrete of the present invention is used to prepare compacted concrete, the hydrogel structure is crushed by the pressing method, and the free water inside is squeezed out, so that the whole is kept in a relatively dry state, and then demolded, formed and cured, so that the prepared concrete has excellent compressive strength.

[0033] (3) The concrete prepared by using the water reducing agent for pressed concrete of the present invention can be used to press small components, such as elevated floors, cement-based pavements, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0035] Figure 1 This is the infrared spectrum of the modified polycarboxylate water-reducing agent prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 those skilled in the art. The present invention description and examples are exemplary only.

[0040] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0041] The present invention provides a method for preparing a modified polycarboxylate water-reducing agent, comprising the following steps:

[0042] (1) mixing hyaluronic acid, thionyl chloride and a catalyst, stirring and reacting, and then distilling under reduced pressure and drying to obtain modified hyaluronic acid;

[0043] (2) mixing acrylic acid, the modified hyaluronic acid obtained in step (1) and a solvent, adding a catalyst and a coupling agent during the mixing process, then adding water for extraction and drying to obtain an esterification product;

[0044] (3) adding water to the esterification product obtained in step (2) to obtain an esterification product aqueous solution, and adding a sodium bicarbonate aqueous solution to adjust the pH value to obtain a hydrolyzed product;

[0045] (4) stirring the macromonomer and heating it, adding the hydrolyzate obtained in step (3), acrylic acid, ester compounds, sodium methacrylsulfonate aqueous solution and ammonium persulfate aqueous solution during the stirring process, and keeping the temperature after the reaction is completed to obtain the modified polycarboxylic acid water-reducing agent.

[0046] In a preferred embodiment of the present invention, in step (1), the mass ratio of thionyl chloride to hyaluronic acid is (0.01-0.03):1, and the mass ratio of the catalyst to hyaluronic acid is (0.01-0.05):1;

[0047] The temperature of the mixing and stirring reaction is 40-60° C., and the reaction time is 8-10 hours.

[0048] In a preferred embodiment of the present invention, in step (1), the catalyst is pyridine or N,N-dimethylformamide.

[0049] In a preferred embodiment of the present invention, in step (2), the molar ratio of the acrylic acid to the hyaluronic acid in step (1) is (1-1.2):1, the molar ratio of the catalyst to the hyaluronic acid in step (1) is (0.01-0.03):1, and the molar ratio of the coupling agent to the modified hyaluronic acid obtained in step (1) is (0.005-0.01):1;

[0050] The stirring and mixing temperature is 20-40°C, and the stirring time is 4-6h.

[0051] In a preferred embodiment of the present invention, in step (2), the solvent is dichloromethane; the catalyst is 4-dimethylaminopyridine or N,N-dimethylformamide; and the coupling agent is 1,3-dicyclohexylcarbodiimide or 1-ethyl-(3-dimethylaminopropyl)carbodiimide.

[0052] In a preferred embodiment of the present invention, in step (3), the mass concentration of the sodium bicarbonate aqueous solution is 20-40%, the sodium bicarbonate aqueous solution is added to adjust the pH value to 6-7, and the mass concentration of the esterification product aqueous solution is 20-30%.

[0053] In a preferred embodiment of the present invention, in step (3), the reaction temperature is room temperature and the reaction time is 1 h.

[0054] In a preferred embodiment of the present invention, in step (4), the macromonomer includes isopentanol polyoxyethylene ether (molecular weight of 1200-2400) and / or methyl allyl polyoxyethylene ether (molecular weight of 1200-2400); the ester compound includes one or more of methyl acrylate, ethyl acrylate and butyl acrylate.

[0055] In a preferred embodiment of the present invention, in step (4), the molar ratio of the macromonomer to the hyaluronic acid in step (1) is (1-1.2):1, the molar ratio of the acrylic acid to the hyaluronic acid in step (1) is (2-3):1, the molar ratio of the ester compound to the hyaluronic acid in step (1) is (0.6-1):1, the molar ratio of the sodium methacrylic sulfonate in the sodium methacrylic sulfonate aqueous solution to the hyaluronic acid in step (1) is (0.08-0.12):1, the molar ratio of the ammonium persulfate in the ammonium persulfate aqueous solution to the acrylic acid in step (4) is (0.0030-0.0033):1, and the mass ratio of the ammonium persulfate in the ammonium persulfate aqueous solution to the hyaluronic acid in step (1) is (0.01-0.03):1;

[0056] In step (4), the temperature is raised to 40-60° C. with stirring, and the stirring time is 1-2 h.

[0057] In a preferred embodiment of the present invention, in step (4), the mass concentrations of the aqueous ammonium persulfate solution and the aqueous sodium methyl acrylate sulfonate solution are both 20-40%.

[0058] The embodiment of the present invention also provides a modified polycarboxylic acid water-reducing agent obtained by the above preparation method.

[0059] The embodiment of the present invention also provides a water reducer for pressed concrete, the raw materials include the modified polycarboxylic acid water reducer, acrylic acid, a crosslinking agent and an initiator, the molar ratio of the acrylic acid to the modified polycarboxylic acid water reducer is (1-1.5):1, the molar ratio of the crosslinking agent to the acrylic acid is (0.004-0.01):1, and the molar ratio of the initiator to the acrylic acid is (0.01-0.035):1; the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate and / or potassium persulfate.

[0060] In a preferred embodiment of the present invention, the cross-linking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate and / or potassium persulfate.

[0061] The water reducing agent for pressed concrete proposed in the embodiment of the present invention has the structural formula:

[0062]

[0063] Wherein, R1 is methoxy or ethoxy, R2 is methyl, ethyl or butyl, m is 27-54, n is 200-500, and both m and n are natural numbers.

[0064] The embodiment of the present invention also provides a method for preparing the water reducing agent for pressed concrete, comprising the following steps:

[0065] The modified polycarboxylic acid water-reducing agent, sodium hydroxide aqueous solution and acrylic acid are mixed, the pH is adjusted to be neutral, the temperature is increased, and a cross-linking agent and an initiator are added under stirring conditions. After the reaction is completed, the mixture is washed and dried to obtain the water-reducing agent for pressed concrete.

[0066] In a preferred embodiment of the present invention, the modified polycarboxylic acid water-reducing agent, sodium hydroxide aqueous solution and acrylic acid are mixed, and the pH is adjusted to 7. The temperature is raised to 50° C., and the crosslinking agent and initiator are added within 1 hour under stirring.

[0067] The room temperature in the embodiments of the present invention refers to "25±3° C.", and the raw materials used in the embodiments are all commercially available.

[0068] The technical solution of the present invention is further illustrated by the following embodiments.

[0069] Example 1

[0070] A method for preparing a water reducing agent for pressed concrete comprises the following steps:

[0071] (1) 37.9 g (0.1 mol) of hyaluronic acid, 0.38 g of thionyl chloride and 0.76 g of catalyst (pyridine) were added to a reactor, stirred and heated to 40° C., nitrogen was continuously introduced, and after reacting for 8 h, the mixture was distilled under reduced pressure and dried to obtain modified hyaluronic acid;

[0072] (2) 7.2 g (0.1 mol) of acrylic acid, the modified hyaluronic acid obtained in step (1) and 78 g of solvent (dichloromethane) were added to a reactor, the temperature was adjusted to 20° C., and the mixture was reacted for 4 h under stirring. Within 4 h, 0.39 g of a catalyst (4-dimethylaminopyridine, 0.003 mol) and 0.2 g of a coupling agent (1,3-dicyclohexylcarbodiimide, 0.001 mol) were added dropwise to the reactor. After the reaction was completed, water was added, the mixture was extracted and dried to obtain an esterified product.

[0073] (3) At room temperature, 45 g of the esterification product obtained in step (3) was added with water in a reactor to obtain a 30% mass concentration aqueous solution of the esterification product, and then a 20% mass concentration aqueous solution of sodium bicarbonate was added to adjust the pH value to 7, and the reaction was stirred for 1 hour. After the reaction was completed, the hydrolysis was confirmed by measuring with pH test paper to obtain a hydrolyzed product;

[0074] (4) 240 g of a macromonomer (isoprenol polyoxyethylene ether, molecular weight 2400, 0.1 mol) was placed in a reactor, stirred and heated to 50° C., 43.1 g of the hydrolyzate obtained in step (3), 14.4 g of acrylic acid (0.2 mol), 6.9 g of an ester compound (methyl acrylate, 0.0676 mol), a 20% aqueous solution of sodium methyl acrylate sulfonate (containing 1.3 g of sodium methyl acrylate sulfonate, 0.00817 mol) and a 20% aqueous solution of ammonium persulfate (containing 0.15 g of ammonium persulfate, 0.000657 mol) were added to the reactor under stirring, and the reaction was stirred for 3 h. After the reaction was completed, the temperature was kept for 1 h to obtain a modified polycarboxylic acid water reducer;

[0075] (5) 0.1 mol of the modified polycarboxylic acid water-reducing agent obtained in step (4) and 7.2 g of acrylic acid (0.1 mol) were added to a reactor, and a 10 wt % sodium hydroxide aqueous solution was added dropwise to adjust the pH value to 7. The temperature was raised to 40° C. and stirred for 1 h. 0.036 g of a cross-linking agent (N,N′-methylenebisacrylamide, 0.00044 mol) and 0.072 g of an initiator (ammonium persulfate, 0.00032 mol) were added dropwise to the reactor. After the reaction was completed, the mixture was washed with anhydrous ethanol, dried, and powdered to obtain a water-reducing agent for pressed concrete.

[0076] The infrared spectrum of the modified polycarboxylate water-reducing agent prepared in Example 1 of the present invention is shown in Figure 1 ,Depend on Figure 1 It can be seen that 3450cm -1 The hydroxyl group (-OH) of the side chain is 1710 cm -1 There is an obvious carbonyl (C=O) vibration peak at 1100 cm -1 , at 1690cm -1 There is a vibration peak of amide bond (CO-NH) at , indicating that the synthesis is successful and a compressed water reducer is obtained.

[0077] Example 2

[0078] A method for preparing a water reducing agent for pressed concrete comprises the following steps:

[0079] (1) 37.9 g (0.1 mol) of hyaluronic acid, 1.137 g of thionyl chloride and 1.895 g of a catalyst (pyridine) were added to a reactor, stirred and heated to 50° C., nitrogen was continuously introduced, and after reacting for 8 h, the mixture was distilled under reduced pressure and dried to obtain modified hyaluronic acid;

[0080] (2) 7.2 g (0.1 mol) of acrylic acid, the modified hyaluronic acid obtained in step (1) and 78 g of solvent (dichloromethane) were added to a reactor, the temperature was adjusted to 20° C., and the mixture was reacted for 4 h under stirring. Within 4 h, 0.13 g of a catalyst (4-dimethylaminopyridine, 0.001 mol) and 0.2 g of a coupling agent (1,3-dicyclohexylcarbodiimide, 0.001 mol) were added dropwise to the reactor. After the reaction was completed, water was added, the mixture was extracted and dried to obtain an esterification product.

[0081] (3) at room temperature, in a reactor, add water to 45 g of the esterification product obtained in step (3) to obtain a 30% mass concentration aqueous solution of the esterification product, then add a 30% mass concentration aqueous solution of sodium bicarbonate, adjust the pH value to 7, stir and react for 1 hour, and after the reaction is completed, measure with pH paper to confirm that the hydrolysis is complete, and obtain a hydrolyzate;

[0082] (4) 288 g of a macromonomer (isoprenol polyoxyethylene ether, molecular weight 2400, 0.12 mol) was placed in a reactor, stirred and heated to 50° C., 43.1 g of the hydrolyzate obtained in step (3), 14.4 g of acrylic acid (0.2 mol), 12.82 g of an ester compound (butyl acrylate, 0.1 mol), a 20% aqueous solution of sodium methacrylic acid sulfonate (containing 1.3 g of sodium methacrylic acid sulfonate, 0.00817 mol) and a 20% aqueous solution of ammonium persulfate (containing 0.15 g of ammonium persulfate, 0.00063 mol) were added to the reactor under stirring, and the reaction was stirred for 3 h. After the reaction was completed, the temperature was kept for 1 h to obtain a modified polycarboxylic acid water reducer;

[0083] (5) 1 mol of the modified polycarboxylic acid water-reducing agent obtained in step (4) and 7.2 g of acrylic acid (0.1 mol) were added to a reactor, and a 10 wt % sodium hydroxide aqueous solution was added dropwise to adjust the pH value to 7. The temperature was raised to 40° C. and stirred for 1 h. 0.082 g of a cross-linking agent (N,N′-methylenebisacrylamide, 0.001 mol) and 0.228 g of an initiator (ammonium persulfate, 0.001 mol) were added dropwise to the reactor. After the reaction was completed, the mixture was washed with anhydrous ethanol, dried, and powdered to obtain a water-reducing agent for pressed concrete.

[0084] Example 3

[0085] A method for preparing a water reducing agent for pressed concrete comprises the following steps:

[0086] (1) 45.48 g (0.12 mol) of hyaluronic acid, 0.758 g of thionyl chloride and 0.379 g of catalyst (pyridine) were added to a reactor, stirred and heated to 60° C., nitrogen was continuously introduced, and after reacting for 8 h, the mixture was distilled under reduced pressure and dried to obtain modified hyaluronic acid;

[0087] (2) 7.2 g (0.1 mol) of acrylic acid, the modified hyaluronic acid obtained in step (1) and 78 g of solvent (dichloromethane) were added to a reactor, the temperature was adjusted to 20° C., and the mixture was reacted for 4 h under stirring. Within 4 h, 0.26 g of a catalyst (4-dimethylaminopyridine, 0.002 mol) and 0.1 g of a coupling agent (1,3-dicyclohexylcarbodiimide, 0.0005 mol) were added dropwise to the reactor. After the reaction was completed, water was added, the mixture was extracted and dried to obtain an esterification product.

[0088] (3) At room temperature, in a reactor, 45 g of the esterification product obtained in step (3) was added with water to obtain an aqueous solution of the esterification product having a mass concentration of 30%, and then a 40% mass concentration of sodium bicarbonate aqueous solution was added, the pH value was adjusted to 7, and the reaction was stirred for 1 hour. After the reaction was completed, the hydrolysis was confirmed to be complete by measuring with a pH test paper to obtain a hydrolyzed product;

[0089] (4) 264 g of a macromonomer (methallyl polyoxyethylene ether, molecular weight 2400, 0.11 mol) was placed in a reactor, stirred and heated to 50° C., 43.1 g of the hydrolyzate obtained in step (3), 21.6 g of acrylic acid (0.3 mol), 8.0 g of an ester compound (ethyl acrylate, 0.08 mol), a 20% aqueous solution of sodium methacrylic acid sulfonate (containing 1.91 g of sodium methacrylic acid sulfonate, 0.012 mol) and a 20% aqueous solution of ammonium persulfate (containing 0.15 g of ammonium persulfate, 0.00063 mol) were added to the reactor under stirring, and the reaction was stirred for 3 h. After the reaction was completed, the mixture was kept warm for 1 h to obtain a modified polycarboxylic acid water reducer;

[0090] (5) 1 mol of the modified polycarboxylic acid water-reducing agent obtained in step (4) and 7.2 g of acrylic acid (0.1 mol) were added to a reactor, and a 10 wt % sodium hydroxide aqueous solution was added dropwise to adjust the pH value to 7. The temperature was raised to 40° C. and stirred for 1 h. 0.036 g of a cross-linking agent (N,N′-methylenebisacrylamide, 0.00044 mol) and 0.27 g of an initiator (potassium persulfate, 0.001 mol) were added dropwise to the reactor. After the reaction was completed, the mixture was washed with anhydrous ethanol, dried, and powdered to obtain a water-reducing agent for pressed concrete.

[0091] Comparative Example 1

[0092] Ordinary polycarboxylate water reducer (commercially available).

[0093] The pressed concrete of Examples 1-3 and Comparative Example 1 was prepared using a water reducing agent to obtain pressed concrete, and the preparation method is as follows:

[0094] 1.1 g of water reducer was added to 450 g of cement (PO·42.5 ordinary Portland cement), stirred by a mixer, and then 189 g of water, 90 g of fly ash (first-grade fly ash), 675 g of sand (particle size ≤ 5 mm) and 225 g of gravel (particle size ≤ 5 mm) were added and mixed, and the mixture was placed on a distributor, and then a hydraulic press (pressure ≥ 10 MPa) was used. During the pressing process, the cement components were pressed, vented, drained (the water in the slurry was pressed out and the slurry was evenly dispersed), the pressure was maintained and matured, the mold was opened, and the product was pushed out to obtain pressed concrete.

[0095] Performance test of pressed concrete prepared by the pressed concrete water reducer of Examples 1-3 and Comparative Example 1:

[0096] (1) Determine the compressive strength according to the method in GB / T 50081

[0097] A blank group was set up, i.e., the addition of water reducing agent was omitted during the preparation of pressed concrete. The compressive strength test results of each group of pressed concrete are shown in Table 1.

[0098] Table 1 Compressive strength test results

[0099]

[0100] It can be seen from Table 1 that the compressed water reducer synthesized in the embodiment of the present invention has a significant improvement in compressive strength at 3d and 28d when added to concrete, and has excellent mechanical properties.

[0101] (2) Determination of water yield

[0102] A blank group was set up, i.e., the addition of water reducing agent was omitted during the preparation of pressed concrete. The water yield test results of each group of pressed concrete are shown in Table 2.

[0103] Water output rate (%) = squeezed water output (g) / water used to prepare concrete (g) × 100%

[0104] Table 2 Water yield measurement results

[0105] Water output rate (%) Blank group 21.80 Comparative Example 1 9.15 Example 1 21.65 Example 2 23.04 Example 3 22.60

[0106] According to Table 2, after the compression type water reducer of the present invention is added to concrete, the water output is significantly improved compared with the blank group without water reducer and the comparative group with commercially available polycarboxylate water reducer. This indicates that during the preparation of concrete, the water reducer of the present invention crushes the hydrogel structure by the compression method, and the internal free water is squeezed out, so that the whole is kept in a relatively dry state, and the demolding and curing are performed, so that the prepared concrete has excellent compressive strength, so that it can be used to press small components, such as overhead floors, cement-based pavements, etc.

[0107] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A water reducing agent for pressed concrete, characterized in that: The raw materials include modified polycarboxylic acid water-reducing agent, acrylic acid, a crosslinking agent and an initiator, wherein the molar ratio of the acrylic acid to the modified polycarboxylic acid water-reducing agent is (1-1.5):1, the molar ratio of the crosslinking agent to the acrylic acid is (0.004-0.01):1, and the molar ratio of the initiator to the acrylic acid is (0.01-0.035):1; the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate and / or potassium persulfate; The preparation method of the modified polycarboxylate water-reducing agent comprises the following steps: (1) mixing hyaluronic acid, thionyl chloride and a catalyst, stirring and reacting, and then distilling under reduced pressure and drying to obtain modified hyaluronic acid; (2) mixing acrylic acid, the modified hyaluronic acid obtained in step (1) and a solvent, adding a catalyst and a coupling agent during the mixing process, then adding water for extraction and drying to obtain an esterification product; (3) adding water to the esterification product obtained in step (2) to obtain an esterification product aqueous solution, and adding a sodium bicarbonate aqueous solution to adjust the pH value to obtain a hydrolyzed product; (4) stirring the macromonomer and heating it, adding the hydrolyzate obtained in step (3), acrylic acid, ester compounds, sodium methacrylsulfonate aqueous solution and ammonium persulfate aqueous solution during the stirring process, and keeping the temperature after the reaction is completed to obtain the modified polycarboxylic acid water reducer; In step (1), the mass ratio of thionyl chloride to hyaluronic acid is (0.01-0.03):1, and the mass ratio of the catalyst to hyaluronic acid is (0.01-0.05):1; the temperature of the mixing and stirring reaction is 40-60°C, and the reaction time is 8-10h; In step (2), the molar ratio of the acrylic acid to the hyaluronic acid in step (1) is (1-1.2):1, the molar ratio of the catalyst to the hyaluronic acid in step (1) is (0.01-0.03):1, and the molar ratio of the coupling agent to the modified hyaluronic acid obtained in step (1) is (0.005-0.01):1; the stirring and mixing temperature is 20-40°C, and the stirring time is 4-6h; In step (4), the molar ratio of the macromonomer to the hyaluronic acid in step (1) is (1-1.2):1, the molar ratio of the acrylic acid to the hyaluronic acid in step (1) is (2-3):1, the molar ratio of the ester compound to the hyaluronic acid in step (1) is (0.6-1):1, the molar ratio of the sodium methacrylic sulfonate in the sodium methacrylic sulfonate aqueous solution to the hyaluronic acid in step (1) is (0.08-0.12):1, the molar ratio of the ammonium persulfate in the ammonium persulfate aqueous solution to the acrylic acid in step (4) is (0.0030-0.0033):1, and the mass ratio of the ammonium persulfate in the ammonium persulfate aqueous solution to the hyaluronic acid in step (1) is (0.01-0.03):1; In step (4), the temperature is raised to 40-60° C. with stirring, and the stirring time is 1-2 h.

2. The water reducing agent for pressed concrete according to claim 1, characterized in that: In step (3), the mass concentration of the sodium bicarbonate aqueous solution is 20-40%, the sodium bicarbonate aqueous solution is added to adjust the pH value to 6-7, and the mass concentration of the esterification product aqueous solution is 20-30%.

3. The water reducing agent for pressed concrete according to claim 1, characterized in that: In step (4), the macromonomer includes isopentanol polyoxyethylene ether and / or methyl allyl polyoxyethylene ether; the molecular weight of the macromonomer is 1200-2400, and the ester compound includes one or more of methyl acrylate, ethyl acrylate and butyl acrylate.

4. A method for preparing a water reducing agent for pressed concrete according to any one of claims 1 to 3, characterized in that: The following steps are involved: The modified polycarboxylic acid water-reducing agent, sodium hydroxide aqueous solution and acrylic acid are mixed, the pH is adjusted to be neutral, the temperature is increased, a cross-linking agent and an initiator are added under stirring conditions, and after the reaction is completed, washing and drying are performed to obtain the water-reducing agent for pressed concrete; The stirring reaction temperature was 50°C and the time was 1 h.

5. Use of the water reducing agent for pressed concrete according to any one of claims 1 to 3 in the preparation of pressed concrete.

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