A concrete viscosity-enhancing water reducing agent and a preparation method thereof

Abstract

The application provides a concrete viscosity-increasing water reducing agent and a preparation method thereof. The viscosity-increasing water reducing agent is composed of a water reducing agent component and a water-retention viscosity-increasing agent, the inner core of the viscosity-increasing agent is wrapped in a protective shell, and the viscosity-increasing water reducing agent can enhance the cohesiveness and long-term working performance of concrete when segregation, bleeding and bottom stripping of concrete occur. The nano-bentonite is used as a main raw material to provide the protective shell for the viscosity-increasing agent. Under the premise of ensuring the fluidity of the concrete, the bleeding rate of the concrete is reduced. The steps are simple, the cost is low, the whole preparation process is safe and reliable, no organic solvent is used, and the application is non-toxic, non-polluting and environment-friendly. According to the bleeding rate of the applicable concrete, the working environment and other factors, the core-shell ratio and the coating ratio of the water-retention viscosity-increasing agent are properly adjusted, so that the final water reducing agent product has better adaptability, and good slump retention performance is ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of concrete admixtures, and particularly relates to a concrete viscosity-increasing water reducing agent and a preparation method thereof. BACKGROUND

[0002] As a kind of concrete admixtures, polycarboxylate superplasticizer not only has a high water-reducing rate and plasticity retention, but also has a strong adaptability to cement, high strength of molded concrete, and small dry shrinkage in later period, energy saving and environmental protection, which are incomparable to other types of water reducing agents. Polycarboxylate superplasticizer with water-retaining and viscosity-increasing properties is a new type of concrete admixture, which has good effects in inhibiting concrete bleeding and segregation, improving the anti-segregation property of underwater concrete, and ensuring the loss of concrete slump in several hours. In addition, in winter concrete construction, early strength agent needs to be added to accelerate the cement hydration speed, promote the development of early strength of concrete, and improve the efficiency of concrete construction. However, the use of early strength agent cannot control the workability of concrete for a long time, and is not conducive to the development of later strength.

[0003] At present, the viscosity-increasing polycarboxylate superplasticizer mainly used in the market can increase the viscosity of low-grade concrete, but can reduce the fluidity of fresh concrete. In addition, the viscosity of concrete is not durable enough, and in hot summer environment, the water in the concrete is easy to evaporate and lose. In order to maintain the same fluidity, the amount of water reducing agent needs to be increased, or the water-binder ratio needs to be increased. However, increasing the water-binder ratio often destroys the continuity of the slurry and reduces the hardened strength of concrete; and adding more water reducing agent often leads to dosage sensitivity, especially when the day and night temperature difference is large, which is more likely to cause segregation and bleeding. In addition, the viscosity-increasing polycarboxylate superplasticizer on the market often has poor compatibility, serious retardation or air entraining phenomenon, and insufficient viscosity at low shear rate when compounded with other admixtures.

[0004] A viscosity-increasing functional polycarboxylate superplasticizer and a preparation method thereof are disclosed in Chinese patent (CN201611205962.6, publication date: September 10, 2019). Microcrystalline cellulose is added to unsaturated carboxylic acid and concentrated sulfuric acid to undergo acidolysis and esterification reaction; cellulose nanocrystals and esterification derivatives generated in the reaction are copolymerized with polyether macromonomer and other small monomers to form a micro-crosslinked chain structure, and the viscosity-increasing functional polycarboxylate superplasticizer is obtained. However, this method also has some defects: concentrated sulfuric acid is used to esterify microcrystalline cellulose with unsaturated carboxylic acid, which has a high process cost, and the production tailings are difficult to handle, which is not suitable for large-scale industrial application.

[0005] Chinese patent (CN201010586450.5, publication date: March 12, 2014) discloses a tackifier, drilling fluid containing the tackifier and its reserve liquid, the tackifier has the characteristics of being passivated and activated, the reserve liquid of the drilling fluid provided by the invention is composed of water, bentonite, polyanionic cellulose, xanthan gum, tackifier and passivator. Under the action of the activator, the passivated tackifier is activated to play a tackifying role. However, the passivation and activation process provided by the patent is not completely controllable, and the tackifier is easy to complete the activation and take effect in a short time, which can easily affect the construction performance of the concrete. SUMMARY

[0006] To solve the problem that the tackifying water reducing agent in the prior art can increase the viscosity and improve the wrapping property of the initial state of the concrete, but cannot guarantee the stability of the water in the concrete, and is prone to excessive loss of fluidity, the technical scheme provided by the present application is:

[0007] A concrete tackifying water reducing agent, comprising a water reducing agent component and a water-retaining tackifier. The water reducing agent component comprises the following raw materials: 55-75 parts of unsaturated polyether macromonomer, 160-200 parts of unsaturated carboxylic acid / anhydride small monomer, and 0.4-0.8 parts of initiator. The water-retaining tackifier comprises a protective shell composed of the following components: 1-5 parts of octafluoropentyl methacrylate, 5-12 parts of amino silicone oil, 1-2 parts of acrylamide, 100 parts of nano-bentonite, and 800-1200 parts of deionized water; and a tackifier inner core composed of the following components: 25-28 parts of acrylamide, 85-95 parts of acrylic acid, 1-2 parts of N,N'-methylenebisacrylamide, 1-2 parts of azobisisobutyronitrile, and 500-800 parts of deionized water. The above parts are all mass parts.

[0008] The unsaturated polyether macromonomer used for synthesizing the water reducing agent comprises one or more of vinyl polyoxyethylene ether, allyl polyoxyethylene ether, hydroxybutyl vinyl polyoxyethylene ether, isobutenyl alcohol polyoxyethylene ether, and isoamylenol polyoxyethylene ether, with a molecular weight of 800-3000. The unsaturated carboxylic acid / anhydride comprises one or more of methacrylic acid, acrylic acid, maleic acid, maleic anhydride, itaconic acid, and itaconic anhydride. The initiator is one of ammonium persulfate and potassium persulfate.

[0009] In the water-retaining tackifier, the core-shell ratio of the tackifier inner core to the protective shell is 2:1-5:1, and the coating ratio of the protective shell is 35%-55%. The specific core-shell ratio and coating ratio are determined according to the bleeding rate of the concrete and the use environment of the concrete. For example, if the bleeding rate of a certain formula of concrete is high, or the use environment temperature of the concrete is low, the core-shell ratio and coating ratio of the water-retaining tackifier can be appropriately reduced to control the bleeding problem.

[0010] The preparation method of the concrete tackifying water reducing agent comprises the following steps:

[0011] Step 1: 55-75 parts of unsaturated polyether macromonomer, 160-200 parts of unsaturated carboxylic acid / anhydride small monomer, 0.4-0.8 parts of initiator are uniformly mixed and reacted at 30-40 DEG C for 3-5 h to obtain a polycarboxylic acid water reducer;

[0012] Step 2: 100 parts of nano-bentonite are fully stirred in 800-1200 parts of deionized water to obtain a nano-bentonite aqueous dispersion; 1-5 parts of octafluoropentyl methacrylate, 5-12 parts of amino silicone oil and 1-2 parts of acrylamide are fully mixed and added to the nano-bentonite aqueous dispersion to form a stable white solution after stirring and reacting at 30-40 DEG C for 60-120 min;

[0013] Step 3: 25-28 parts of acrylamide, 85-95 parts of acrylic acid and 1-2 parts of N,N'-methylenebisacrylamide are fully dissolved in 500-800 parts of deionized water, 1-2 parts of azobisisobutyronitrile is added and reacted at 30-50 DEG C for 2-3 h to obtain an internal core of a tackifier;

[0014] Step 4: the white solution obtained in Step 2 and the internal core of the tackifier obtained in Step 3 are fully mixed in a ratio of 1:2-1:5 and reacted at 30-40 DEG C for 1-2 h to obtain a water-retention type tackifier;

[0015] Step 5: the polycarboxylic acid water reducer obtained in Step 1 and the water-retention type tackifier obtained in Step 4 are mixed in a ratio of 100:(8-25) to obtain a concrete tackifying water reducer.

[0016] Compared with the prior art, the concrete tackifying water reducer has the following advantages: 1. The concrete tackifying water reducer is wrapped in a protective shell composed of octafluoropentyl methacrylate, amino silicone oil, acrylamide and nano-bentonite, the tackifier can be released according to the demand, and the working performance of the concrete is ensured; 2. The method uses nano-bentonite as the main raw material to provide a protective shell for the tackifier, reduces the bleeding rate of the concrete under the premise of ensuring the fluidity of the concrete, and has the advantages of simple steps, low cost, safety and reliability in the whole preparation process, no use of organic solvents, no toxicity and no pollution, and environmental friendliness; 3. According to the bleeding rate of the concrete, the working environment and other factors, the core-shell ratio and the coating ratio of the water-retention type tackifier are appropriately adjusted, so that the final water reducer product has better adaptability to ensure good slump retention performance. DETAILED DESCRIPTION

[0017] Hereinafter, the embodiments of the present application will be described.

[0018] Example 1:

[0019] A polycarboxylic acid water reducer was obtained by reacting 55 parts of allyl polyoxyethylene ether, 190 parts of itaconic acid, and 0.8 parts of potassium persulfate at 35°C for 4 hours. A nano-bentonite water dispersion was obtained by dispersing 100 parts of nano-bentonite in 1000 parts of deionized water. A stable white solution was formed by mixing 3.8 parts of octafluoropentyl methacrylate, 9 parts of amino silicone oil, and 1.6 parts of acrylamide in the nano-bentonite water dispersion and stirring at 40°C for 90 minutes. An internal core of a viscosity increasing agent was obtained by dissolving 25 parts of acrylamide, 88 parts of acrylic acid, and 1.2 parts of N,N'-methylenebisacrylamide in 700 parts of deionized water, adding 1 part of azobisisobutyronitrile, and reacting at 37°C for 2.5 hours. The bentonite dispersion and the internal core of the viscosity increasing agent were mixed in a ratio of 3:1 and reacted at 40°C for 1 hour to obtain a water-retention type viscosity increasing agent. The water reducer and the water-retention type viscosity increasing agent were mixed in a ratio of 100:17 to obtain a concrete viscosity-increasing type water reducer S1.

[0020] Example 2:

[0021] A polycarboxylic acid water reducer was obtained by reacting 68 parts of hydroxybutyl vinyl polyoxyethylene ether, 160 parts of maleic anhydride, and 0.6 parts of ammonium persulfate at 40°C for 3 hours. A nano-bentonite water dispersion was obtained by dispersing 100 parts of nano-bentonite in 1200 parts of deionized water. A stable white solution was formed by mixing 4 parts of octafluoropentyl methacrylate, 10 parts of amino silicone oil, and 1.8 parts of acrylamide in the nano-bentonite water dispersion and stirring at 35°C for 110 minutes. An internal core of a viscosity increasing agent was obtained by dissolving 26 parts of acrylamide, 90 parts of acrylic acid, and 1.5 parts of N,N'-methylenebisacrylamide in 800 parts of deionized water, adding 1 part of azobisisobutyronitrile, and reacting at 39°C for 2 hours. The bentonite dispersion and the internal core of the viscosity increasing agent were mixed in a ratio of 4:1 and reacted at 40°C for 1 hour to obtain a water-retention type viscosity increasing agent. The water reducer and the water-retention type viscosity increasing agent were mixed in a ratio of 100:12 to obtain a concrete viscosity-increasing type water reducer S2.

[0022] Example 3:

[0023] A polycarboxylic acid water reducer was obtained by reacting 60 parts of isopentenyl polyoxyethylene ether, 175 parts of acrylic acid, and 0.8 parts of potassium persulfate at 40°C for 4 hours. A nanobentonite water dispersion was obtained by dispersing 100 parts of nanobentonite in 1100 parts of deionized water. A stable white solution was formed by adding 4.5 parts of octafluoropentyl methacrylate, 12 parts of amino silicone oil, and 1.8 parts of acrylamide to the nanobentonite water dispersion and stirring at 40°C for 100 minutes. An internal core of a viscosity increasing agent was obtained by dissolving 28 parts of acrylamide, 90 parts of acrylic acid, and 1.5 parts of N,N'-methylenebisacrylamide in 800 parts of deionized water, adding 1.5 parts of azobisisobutyronitrile, and reacting at 45°C for 2.5 hours. The bentonite dispersion and the internal core of the viscosity increasing agent were mixed in a ratio of 4:1 and reacted at 40°C for 1 hour to obtain a water-retention type viscosity increasing agent. The water reducer and the water-retention type viscosity increasing agent were mixed in a ratio of 100:22 to obtain a concrete viscosity increasing type water reducer S3.

[0024] Comparative Example

[0025] A water reducer product was obtained by uniformly mixing 65 parts of allyl polyoxyethylene ether, 170 parts of methacrylic acid, and 0.5 parts of potassium persulfate and stirring at 35°C for 5 hours as Comparative Example D1.

[0026] A commercially available brand of viscosity increasing type polycarboxylic acid water reducer was purchased as Comparative Example D2.

[0027] The concrete viscosity increasing type water reducers and the intermediate products in the preparation process were analyzed and characterized as follows:

[0028] 1. Scanning electron microscope characterization

[0029] Each water-retention type viscosity increasing agent prepared in Examples S1 to S3 was centrifuged, diluted with deionized water to a suitable concentration (the solution was nearly transparent), and one drop of the solution was dropped on a clean silicon wafer and dried at room temperature. The silicon wafer was attached to the electron microscope stage with conductive glue and observed.

[0030] 2. Thermogravimetric analysis test

[0031] The coating area of the shell on the internal core of the viscosity increasing agent was defined as the coating rate, which was calculated according to the following formula:

[0032]

[0033] wherein Er is the coating rate of the water-retention type viscosity increasing agent.

[0034] W M800℃ Residual rate of the reference product at 800℃;

[0035] W C800℃ Residual rate of the example product at 800℃.

[0036] Characterization results:

[0037] Further through scanning electron microscopy, it is found that the example products S1-S3 are regular spheres with a diameter of about 20-50 μm. When observing a single particle, the particle surface is relatively rough, and the surface has a layer of dense nanoparticles with a particle size of about 25 nm.

[0038] The residual rates of the example products S1-S3 and the reference product after decomposition are measured by a thermal gravimetric analyzer, and the coating rates of the example product S1, the example product S2, and the example product S3 are calculated to be 41%, 48%, and 53%, respectively.

[0039] Concrete sample analysis and characterization: concrete application performance test

[0040] The five water reducing agent products, the example products S1-S3, the comparative product D1, and a commercially available adhesion-increasing polycarboxylate superplasticizer D2, are prepared into concrete according to a mixing amount of 0.2%. The mechanical properties of the C30 concrete samples are tested according to the GB / T50081-2019 “Standard for Testing Methods for Mechanical Properties of Ordinary Concrete”. According to the test data, the samples mixed with the example products S1-S3 have good air content, and the initial fluidity and cohesiveness of the concrete are significantly higher than those of the sample mixed with the comparative product D1. However, the concrete slump flow retention time and compressive strength are significantly better than those of the sample mixed with the comparative product D1 and the sample mixed with the commercially available product D2. The test temperature is room temperature 26℃.

[0041] The specific concrete sample test data is shown in Table 1 below:

[0042] Table 1: Concrete performance test data

[0043]

[0044]

[0045] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A concrete thickening and water-reducing agent, characterized in that, It includes a water-reducing agent component and a water-retaining tackifier, wherein the water-retaining tackifier includes: The protective shell is composed of the following components: 1-5 parts octafluoroamyl methacrylate, 5-12 parts amino silicone oil, 1-2 parts acrylamide, 100 parts nano-bentonite, and 800-1200 parts deionized water. The tackifier core consists of the following components: 25-28 parts acrylamide, 85-95 parts acrylic acid, 1-2 parts N,N'-methylenebisacrylamide, 1-2 parts azobisisobutyronitrile, and 500-800 parts deionized water. All the numbers mentioned above are by weight.

2. The concrete thickening and water-reducing agent as described in claim 1, characterized in that, The water-reducing agent comprises the following raw materials: 55-75 parts of unsaturated polyether macromonomer, 160-200 parts of unsaturated carboxylic acid / anhydride small monomer, and 0.4-0.8 parts of initiator.

3. The concrete thickening and water-reducing agent according to claim 2, characterized in that, The unsaturated polyether macromonomer includes one or more of the following: vinyl polyoxyethylene ether, allyl polyoxyethylene ether, hydroxybutyl vinyl polyoxyethylene ether, isobutylenol polyoxyethylene ether, and isopentenol polyoxyethylene ether, with a molecular weight of 800 to 3000.

4. A concrete thickening and water-reducing agent according to claim 2, characterized in that, The unsaturated carboxylic acids / anhydrides include one or more of methacrylic acid, acrylic acid, maleic acid, maleic anhydride, itaconic acid, and itaconic anhydride.

5. A concrete thickening and water-reducing agent according to claim 2, characterized in that, The initiator is one of ammonium persulfate and potassium persulfate.

6. A concrete thickening and water-reducing agent as described in claim 1, characterized in that, In the water-retaining tackifier, the core-to-shell ratio of the tackifier core to the protective shell is 2:1 to 5:

1.

7. A concrete thickening and water-reducing agent as described in claim 1, characterized in that, The preparation method of the concrete thickening and water-reducing agent includes the following steps: Step 1: Mix 55-75 parts of unsaturated polyether macromonomer, 160-200 parts of unsaturated carboxylic acid / anhydride small monomer, and 0.4-0.8 parts of initiator evenly, and react at 30-40℃ for 3-5 hours to obtain the water-reducing agent component; Step 2: Thoroughly stir 100 parts of nano-bentonite in 800-1200 parts of deionized water to obtain a nano-bentonite aqueous dispersion; separately, thoroughly mix 1-5 parts of octafluoroamyl methacrylate, 5-12 parts of amino silicone oil, and 1-2 parts of acrylamide, add them to the nano-bentonite aqueous dispersion, and stir and react at 30-40℃ for 60-120 min to form a stable white solution; Step 3: Dissolve 25-28 parts acrylamide, 85-95 parts acrylic acid, and 1-2 parts N,N'-methylenebisacrylamide in 500-800 parts deionized water, add 1-2 parts azobisisobutyronitrile, and react at 30-50℃ for 2-3 hours to obtain the tackifier core. Step 4: Mix the white solution obtained in Step 2 with the tackifier core obtained in Step 3 at a ratio of 1:2 to 1:5, and react at 30-40℃ for 1-2 hours to obtain a water-retaining tackifier; Step 5: Mix the water-reducing agent component obtained in Step 1 with the water-retaining thickener obtained in Step 4 at a ratio of 100:(8~25) to obtain a concrete thickening water-reducing agent. All the numbers mentioned above are by weight.

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