Preparation and application of pH-responsive slow-release hydration heat inhibitor

Abstract

The invention discloses preparation and application of a pH-responsive slow-release hydration heat inhibitor, and belongs to the technical field of concrete admixtures. The inhibitor is slowly released in a cement paste alkaline environment, cement hydration is continuously slowed down, and the temperature cracking risk of concrete caused by hydration heat is reduced. The core component is a pH sustained release microsphere, and the pH sustained release microsphere is composed of octadecyl acrylate, Span 80, Tween 60, white oil, acrylic acid, allyl polyoxyethylene ether 500, N, N-methylene bisacrylamide, deionized water, tert-butyl hydroperoxide, sodium pyrosulfite and the like. The preparation method comprises the steps of mixing an oil phase and a water phase, emulsifying, reacting and the like. The inhibitor further comprises sorbitol and methanol, and is prepared through the steps of stirring, filtering, drying and the like. The inhibitor can effectively reduce the hydration heat of cement, delay the setting time and improve the compressive strength of concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete admixtures, and in particular relates to the preparation and application of a pH-responsive slow-release hydration heat inhibitor. Background Art

[0002] With the progress and development of society, modern construction projects are gradually shifting towards larger-scale structures. This has led to the widespread application of large-volume concrete in fields such as water conservancy and hydropower, bridge abutments, and port construction. However, during the pouring process, the cement in the concrete releases heat as it hydrates, causing the internal temperature to rise sharply. Depending on the size of the concrete structure, the internal temperature can reach as high as 70°C to 80°C. After a period of time, the internal temperature of the concrete reaches a peak and gradually cools down. During this period, the external surface heat exchange rate is faster, lower than the internal temperature, and the temperature drop between the inside and the outside increases. This leads to a large temperature difference in the component, causing cracks and damaging the entire structure.

[0003] There are currently two main methods to solve temperature cracking. One is to improve the construction process and adjust the structural design to improve the heat dissipation effect, including: (1) using pre-cooled aggregates and mixing water to reduce the pouring temperature of concrete; (2) using cooling water pipes and surface coatings to reduce the temperature difference between the inside and outside of the concrete after pouring. However, these methods increase the difficulty and cost of construction and have the risk of reducing the strength of concrete. The other is to reduce the cement hydration rate from the material perspective, including: (1) changing the material to reduce the heat release of cement in concrete, such as using medium-heat or low-heat cement or adding mineral admixtures such as fly ash; (2) adding hydration heat inhibitors, such as sugars and their derivatives, starch dextrins, etc. However, changing the material or adding phase change materials is prone to problems such as slow strength development and insufficient strength in the later stage.

[0004] Hydration heat inhibitory materials can reduce the hydration heat exothermic peak, alleviate the risk of temperature cracking in structures, and are economical and convenient. Sugars and their derivatives, starch dextrins, sorbitol, etc. In the early stage of cement hydration, cement is mixed with water to produce calcium hydroxide. The hydroxyl groups in the polysaccharides complex with calcium ions and adsorb to the surface of cement particles to prevent cement hydration. This type of hydration heat inhibitory material can maintain the plasticity of concrete for a long time, facilitate pouring, delay the occurrence time of the cement hydration exothermic peak, and alleviate the formation of temperature differences between the inside and outside of the matrix. However, delayed hydration will affect the setting time of cement, and thus affect the strength. High-dosage sucrose retarders may even cause a "delayed acceleration" phenomenon, so this type of admixture cannot effectively solve the problem of concrete temperature cracking caused by concentrated heat release during cement hydration.

[0005] Therefore, it is necessary to prepare a hydration heat inhibition material with adjustable slow release, which can be slowly released according to the hydration process for large-volume concrete, continuously slowing down the cement hydration rate to achieve the purpose of step-by-step regulation. Summary of the Invention

[0006] To address the above technical issues, the present invention proposes the preparation and application of a pH-responsive slow-release hydration heat inhibitor. This material is stimulated to release slowly in the alkaline environment of cement paste, continuously slowing cement hydration, alleviating the formation of temperature differences between the inside and outside of the matrix, and reducing the risk of cracking.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the objects of the present invention is to provide pH sustained-release microspheres, comprising the following components in parts by weight: 0.1-5 parts of octadecyl acrylate, 1-10 parts of Span 80, 1-10 parts of Tween 60, 60-80 parts of white oil, 1-30 parts of acrylic acid, 1-10 parts of allyl polyoxyethylene ether 500, 0.0001-5 parts of N,N-methylenebisacrylamide, 20-40 parts of deionized water, 0.0001-0.1 parts of tert-butyl hydroperoxide and 0.001-0.1 parts of sodium metabisulfite.

[0009] Preferably, the pH sustained-release microspheres comprise the following components in parts by mass: 1-3 parts of octadecyl acrylate (preferably 1 part or 3 parts), 3 parts of Span 80, 2 parts of Tween 60, 60 parts of white oil, 30 parts of acrylic acid, 1-15 parts of allyl polyoxyethylene ether 500, 0.005-0.01 parts of N,N-methylenebisacrylamide, 30 parts of deionized water, 0.001 parts of tert-butyl hydroperoxide and 0.01 parts of sodium metabisulfite.

[0010] A second object of the present invention is to provide a method for preparing pH sustained-release microspheres, comprising the following steps:

[0011] Dissolve octadecyl acrylate, Span 80, and Tween 60 in white oil to obtain an oil phase;

[0012] Dissolve acrylic acid, allyl polyoxyethylene ether 500, and N,N-methylenebisacrylamide in deionized water to obtain an aqueous phase;

[0013] The oil phase and the water phase are mixed, emulsified, and stirred, and then tert-butyl hydroperoxide is added under a nitrogen atmosphere for reaction, and finally sodium metabisulfite is added and stirred for reaction. After the reaction is completed, the mixture is filtered, washed, and dried to obtain a white granular powder, i.e., pH sustained-release microspheres.

[0014] Furthermore, the emulsification conditions are: high-speed emulsification at a rotation speed of 5000 rpm for 20 minutes.

[0015] Further, tert-butyl hydroperoxide was added and reacted for 20 minutes, and then sodium metabisulfite was added, and the reaction was continued with stirring for 2-4 hours.

[0016] The third object of the present invention is to provide a pH-responsive slow-release hydration heat inhibitor, comprising the following components in parts by weight: 10-60 parts of pH slow-release microspheres, 5-20 parts of sorbitol, and 60-100 parts of methanol.

[0017] Furthermore, the pH-responsive slow-release hydration heat inhibitor comprises the following components in parts by mass: 10-20 parts of pH slow-release microspheres (preferably 10 parts or 20 parts), 20 parts of sorbitol, and 60 parts of methanol.

[0018] A fourth object of the present invention is to provide a method for preparing a pH-responsive sustained-release hydration heat inhibitor, comprising the following steps: adding sorbitol and pH-responsive sustained-release microspheres to methanol, stirring, filtering, and drying to obtain a white granular powder, namely, a pH-responsive sustained-release hydration heat inhibitor.

[0019] A fifth object of the present invention is to provide a pH-responsive slow-release hydration heat inhibitor for use as an admixture in concrete materials.

[0020] Furthermore, the dosage of the pH-responsive slow-release hydration heat inhibitor is 0.1-3% of the mass of the gelling material.

[0021] The pH-responsive slow-release hydration heat inhibitor of the present invention works as follows: as cement hydration proceeds, the pH in the solution continuously rises. Alkaline solution gradually enters the pH-responsive slow-release hydration heat inhibitor, dissolving the crystallized sorbitol. Simultaneously, the carboxyl groups in the cross-linked polyacrylic acid are ionized, causing the molecular chains to stretch, prompting the sorbitol to gradually exit the microspheres. Simultaneously, the polymerized allyl polyoxyethylene ether 500 exerts a certain steric hindrance, controlling the slow-release rate of the sorbitol. As hydration proceeds, the sorbitol is gradually released, and the hydroxyl groups on the sorbitol complex with calcium ions, adsorbing on the surface of the cement particles and preventing hydration. This slow-release method can avoid the inability to achieve sustained hydration inhibition due to the addition of too little sorbitol alone into concrete, while also avoiding excessive hydration inhibition caused by excessive sorbitol addition, which can severely retarded concrete.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] This invention successfully addresses the cracking problem caused by excessive heat of hydration in large-volume concrete through an innovative pH-responsive slow-release mechanism and optimized microsphere design, while also meeting the requirements for setting time and mechanical properties. Its simple and low-cost preparation method offers broad application prospects and significant economic and social benefits. DETAILED DESCRIPTION

[0024] 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 rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0026] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice 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 any conflict with any incorporated document, the contents of this specification shall prevail.

[0027] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0028] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0029] The present invention provides a method for preparing a pH-responsive slow-release hydration heat inhibitor, comprising the following steps:

[0030] (1) Preparation of pH sustained-release microspheres: In terms of mass fractions, the oil phase is prepared by dissolving 0.1-5 parts (as an example, 1 part, 3 parts and any part between 0.1-5 parts) of octadecyl acrylate, 1-10 parts (as an example, 3 parts and any part between 1-10 parts) of Span 80, and 1-10 parts (as an example, 2 parts and any part between 1-10 parts) of Tween 60 in 60-80 parts (white oil is used as a solvent, and its amount increases appropriately with the increase in the amount of solute, as an example, 60 parts and any part between 60-80 parts) of white oil; the water phase is prepared by dissolving 1-30 parts (as an example, 30 parts and any part between 1-30 parts) of acrylic acid, 1-10 parts (as an example, 1 1-10 parts) allyl polyoxyethylene ether 500, 0.0001-5 parts (as an example, 0.005 parts, 1 part and any part between 0.0001-5 parts can be selected) N, N-methylene bisacrylamide are dissolved in 20-40 parts (deionized water is used as the solvent, and its amount increases appropriately with the increase of the solute amount. As an example, 30 parts and any part between 20-40 parts can be selected) deionized water; The phase and the aqueous phase are mixed, and after high-speed emulsification at a speed of 5000 rpm for 20 minutes, the mixture is transferred to a 500 mL three-necked flask, stirred at 20-40°C (as an example, 20°C, 25°C and any temperature between 20-40°C can be selected), nitrogen is introduced for deoxygenation for 10 minutes, and 0.0001-0.1 parts (as an example, 0.001 parts and any number between 0.0001-1 parts) of tert-butyl hydroperoxide are added. After 20 minutes, 0.001-0.1 parts (as an example, 0.01 and any number between 0.001-1 parts can be selected) of sodium metabisulfite are added to the system, and the reaction is stirred for 2-4 hours (the stirring reaction time is appropriately extended as the amount of raw materials increases, as an example, 2 hours, 4 hours and any time between 2-4 hours can be selected); after the reaction is completed, the microspheres are separated from the cyclohexane by filtration, repeatedly washed with ethanol, and finally dried in a vacuum drying oven at 45°C to obtain a white granular powder;

[0031] (2) Preparation of pH-responsive sustained-release hydration heat inhibitor: 5-20 parts (as an example, 20 parts and any part between 5-20 parts can be selected) of sorbitol and 10-60 parts (as an example, 10 parts, 20 parts and any part between 10-60 parts can be selected) of pH sustained-release microspheres are added to 60-100 parts (methanol is used as a solvent, and its mass fraction is appropriately increased with the increase in the amount of raw materials used, as an example, 60 parts and any part between 60-100 parts can be selected) of methanol, stirred for 2-4 hours (as an example, 3 hours can be selected), and then filtered. The obtained filter residue is dried in a vacuum drying oven at 45°C to obtain a white granular powder, which is the final product.

[0032] The "parts" described in the present invention, unless otherwise specified, refer to parts by mass.

[0033] The raw materials used in the present invention are all purchased from the market.

[0034] The technical solution of the present invention is further illustrated by the following examples.

[0035] Example 1

[0036] A method for preparing a pH-responsive slow-release hydration heat inhibitor comprises the following steps:

[0037] (1) Preparation of pH sustained-release microspheres: In terms of mass fractions, the oil phase was prepared by dissolving 1 part of octadecyl acrylate, 3 parts of Span 80, and 2 parts of Tween 60 in 60 parts of white oil; the water phase was prepared by dissolving 30 parts of acrylic acid, 1 part of allyl polyoxyethylene ether 500, and 0.005 parts of N,N-methylenebisacrylamide in 30 parts of deionized water; the oil phase and the water phase were mixed, and after high-speed emulsification at 5000 rpm for 20 minutes, the mixture was transferred to a 500 mL three-necked flask, stirred at 20°C, and deoxygenated with nitrogen for 10 minutes. After adding 0.001 parts of tert-butyl hydroperoxide for 20 minutes, 0.01 parts of sodium metabisulfite were added to the system, and the mixture was stirred for 2 hours; after the reaction was completed, the microspheres were separated from the cyclohexane by filtration, washed repeatedly with ethanol, and finally dried in a vacuum drying oven at 45°C to obtain a white granular powder;

[0038] (2) Preparation of pH-responsive sustained-release hydration heat inhibitor: 20 parts of sorbitol and 20 parts of pH sustained-release microspheres were added to 60 parts of methanol, stirred for 3 h, then filtered, and dried in a vacuum drying oven at 45 °C to obtain a white granular powder, which was the final product.

[0039] Example 2

[0040] A method for preparing a pH-responsive slow-release hydration heat inhibitor comprises the following steps:

[0041] (1) Preparation of pH sustained-release microspheres: In terms of mass fractions, the oil phase was prepared by dissolving 3 parts of octadecyl acrylate, 3 parts of Span 80, and 2 parts of Tween 60 in 60 parts of white oil; the water phase was prepared by dissolving 30 parts of acrylic acid, 2 parts of allyl polyoxyethylene ether 500, and 0.005 parts of N,N-methylenebisacrylamide in 30 parts of deionized water; the oil phase and the water phase were mixed, and after high-speed emulsification at 5000 rpm for 20 minutes, the mixture was transferred to a 500 mL three-necked flask, stirred at 25°C, and deoxygenated with nitrogen for 10 minutes. After adding 0.001 parts of tert-butyl hydroperoxide for 20 minutes, 0.01 parts of sodium metabisulfite were added to the system, and the mixture was stirred for 2 hours; after the reaction was completed, the microspheres were separated from the cyclohexane by filtration, washed repeatedly with ethanol, and finally dried in a vacuum drying oven at 45°C to obtain a white granular powder;

[0042] (2) Preparation of pH-responsive sustained-release hydration heat inhibitor: 20 parts of sorbitol and 10 parts of pH sustained-release microspheres were added to 60 parts of methanol, stirred for 3 h, then filtered, and dried in a vacuum drying oven at 45 °C to obtain a white granular powder, which was the final product.

[0043] Example 3

[0044] A method for preparing a pH-responsive slow-release hydration heat inhibitor comprises the following steps:

[0045] (1) Preparation of pH sustained-release microspheres: In terms of mass fractions, the oil phase was prepared by dissolving 3 parts of octadecyl acrylate, 3 parts of Span 80, and 2 parts of Tween 60 in 60 parts of white oil; the water phase was prepared by dissolving 30 parts of acrylic acid, 5 parts of allyl polyoxyethylene ether 500, and 0.01 parts of N,N-methylenebisacrylamide in 30 parts of deionized water; the oil phase and the water phase were mixed, and after high-speed emulsification at 5000 rpm for 20 minutes, the mixture was transferred to a 500 mL three-necked flask, stirred at 25°C, and deoxygenated with nitrogen for 10 minutes. After adding 0.001 parts of tert-butyl hydroperoxide for 20 minutes, 0.01 parts of sodium metabisulfite were added to the system, and the mixture was stirred for 4 hours; after the reaction was completed, the microspheres were separated from the cyclohexane by filtration, washed repeatedly with ethanol, and finally dried in a vacuum drying oven at 45°C to obtain a white granular powder;

[0046] (2) Preparation of pH-responsive sustained-release hydration heat inhibitor: 20 parts of sorbitol and 10 parts of pH sustained-release microspheres were added to 60 parts of methanol, stirred for 3 h, then filtered, and dried in a vacuum drying oven at 45 °C to obtain a white granular powder, which was the final product.

[0047] Comparative Example 1

[0048] The same as Example 1, except that the mass of acrylic acid in the pH slow-release microspheres is replaced by acrylamide to obtain a pH slow-release hydration heat inhibitor without polyacrylic acid.

[0049] Comparative Example 2

[0050] The same as Example 1, except that the mass of allyl polyoxyethylene ether 500 in the pH sustained-release microspheres is replaced by acrylic acid to obtain a pH sustained-release hydration heat inhibitor without allyl polyoxyethylene ether 500.

[0051] Comparative Example 3

[0052] The same method as Example 1 is used, except that sorbitol is replaced by dextrin in equal mass to prepare a pH-responsive hydration heat inhibitor.

[0053] Performance Testing

[0054] The examples and comparative examples were mixed into concrete for experiments. The concrete raw materials are as follows:

[0055] Cement: Esheng PO 42.5 cement; Sand: Machine-made sand, fineness modulus 2.7; Stone: Crushed pebbles with a particle size of 5-25 mm. Water: Ordinary tap water. Water reducer: GK-3000.

[0056] The concrete formula is shown in Table 1.

[0057] Table 1 Concrete mix ratio (kg / m 3 )

[0058] Material water cement fly ash sand Stone water reducer pH-responsive slow-release hydration heat inhibitor Dosage 170 290 70 805 1025 3.6 2.9

[0059] The concrete setting time was tested according to GB / T 50080-2016, "Standard for Test Methods of Performance of Ordinary Concrete Mixtures." The compressive strength ratio was tested according to GB / T 8076-2008, "Concrete Admixtures."

[0060] The adiabatic temperature rise of concrete is tested using an adiabatic temperature rise meter.

[0061] The concrete without pH slow-release hydration heat inhibitor was used as the benchmark group.

[0062] The relevant performance test results are shown in Table 2.

[0063] Table 2 Performance test results

[0064] 1d adiabatic temperature rise peak reduction value (℃) 7d adiabatic temperature rise peak reduction value (℃) Setting time (h) 28d compressive strength ratio (%) Benchmark Group / / 7.5 / Example 1 10 10 9.5 120 Example 2 8 8 9.0 115 Example 3 5 5 8.8 108 Comparative Example 1 / 15 28.0 70 Comparative Example 2 / 12 15.1 93 Comparative Example 3 0 0 7.4 100

[0065] Note: “ / ” in the table means no detected value.

[0066] Combining Examples 1-3 with the benchmark group, it can be seen that the examples begin to inhibit the temperature rise of concrete after 1 day, and the setting time is slightly delayed. The compressive strength at 28 days is increased, indicating that the pH slow-release hydration heat inhibitor of the present invention can effectively reduce the hydration heat of cement and improve the mechanical properties of concrete.

[0067] Compared with Example 1, Comparative Example 1 is a product that does not contain polyacrylic acid and does not have a pH-responsive sustained-release effect. That is, sorbitol dissolved in the solution is also dissolved and released. No adiabatic temperature rise peak appears on the 1st day, but a peak appears on the 7th day, indicating that its slow-setting effect is too strong and the compressive strength ratio is also reduced. Comparative Example 2 is a product that does not contain allyl polyoxyethylene ether 500. No adiabatic temperature rise peak appears on the 1st day, but a peak appears on the 7th day, indicating that its release rate is faster than that of Example 1, the setting time is too long, and the strength is also reduced. Comparative Example 3 is a microsphere with sorbitol replaced by dextrin as the sole carrier. Since dextrin is insoluble in methanol and is not loaded, there is no hydration heat inhibition effect, the setting time is basically the same as the benchmark, and the strength does not change.

[0068] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A pH sustained-release microsphere, characterized in that: The invention comprises the following components in parts by weight: 0.1-5 parts of octadecyl acrylate, 1-10 parts of Span 80, 1-10 parts of Tween 60, 60-80 parts of white oil, 1-30 parts of acrylic acid, 1-10 parts of allyl polyoxyethylene ether 500, 0.0001-5 parts of N,N-methylenebisacrylamide, 20-40 parts of deionized water, 0.0001-0.1 parts of tert-butyl hydroperoxide and 0.001-0.1 parts of sodium metabisulfite.

2. The pH sustained-release microspheres according to claim 1, characterized in that The pH sustained-release microspheres include the following components in parts by weight: 1-3 parts of octadecyl acrylate, 3 parts of Span 80, 2 parts of Tween 60, 60 parts of white oil, 30 parts of acrylic acid, 1-5 parts of allyl polyoxyethylene ether 500, 0.005-0.01 parts of N,N-methylenebisacrylamide, 30 parts of deionized water, 0.001 parts of tert-butyl hydroperoxide, and 0.01 parts of sodium metabisulfite.

3. A method for preparing pH sustained-release microspheres according to claim 1 or 2, characterized in that: The following steps are involved: Dissolve octadecyl acrylate, Span 80, and Tween 60 in white oil to obtain an oil phase; Dissolve acrylic acid, allyl polyoxyethylene ether 500, and N,N-methylenebisacrylamide in deionized water to obtain an aqueous phase; The oil phase and the water phase are mixed, emulsified, and stirred, and then tert-butyl hydroperoxide is added under a nitrogen atmosphere for reaction, and finally sodium metabisulfite is added and stirred for reaction. After the reaction is completed, the mixture is filtered, washed, and dried to obtain a white granular powder, i.e., pH sustained-release microspheres.

4. The method for preparing pH sustained-release microspheres according to claim 3, characterized in that: The emulsification conditions are: emulsification at 5000 rpm for 20 min.

5. The method for preparing pH sustained-release microspheres according to claim 3, characterized in that: After adding tert-butyl hydroperoxide and reacting for 20 minutes, sodium metabisulfite was added and the reaction was continued with stirring for 2-4 hours.

6. A pH-responsive slow-release hydration heat inhibitor, characterized in that: The invention comprises the following components in parts by mass: 10-60 parts of the pH sustained-release microspheres according to claim 1 or 2, 5-20 parts of sorbitol and 60-100 parts of methanol.

7. The pH-responsive slow-release hydration heat inhibitor according to claim 6, characterized in that: The pH-responsive slow-release hydration heat inhibitor comprises the following components in parts by mass: 10-20 parts of pH slow-release microspheres, 20 parts of sorbitol and 60 parts of methanol.

8. A method for preparing the pH-responsive slow-release hydration heat inhibitor according to claim 6 or 7, characterized in that: The following steps are involved: Sorbitol and pH sustained-release microspheres are added to methanol, stirred, filtered, and dried to obtain white granular powder, namely, pH-responsive sustained-release hydration heat inhibitor.

9. Use of the pH-responsive slow-release hydration heat inhibitor according to claim 6 or 7 as an admixture in concrete materials.

10. The use according to claim 9, characterized in that The dosage of the pH-responsive slow-release hydration heat inhibitor is 0.1-3% of the mass of the gelling material.