A low-alkali quick-setting agent and its preparation method

Abstract

The present invention provides a low-alkali accelerating agent and a preparation method thereof, which relates to the technical field of concrete processing. The preparation method of the low-alkali accelerating agent comprises the following steps: S1, preparing a sodium metaaluminate solution; S2, adding water to the sodium metaaluminate solution, stirring evenly, and then adding aluminum sulfate, and reacting at 50-80 °C for 0.5-1 h under stirring conditions; S3, adding a regulator within 10-30 min after the complete reaction of aluminum sulfate to adjust the pH value to neutral; S4, mixing a strong base weak acid salt and a silica gel evenly, and then adding them to a fluoride salt, and obtaining a modified fluoride salt after mixing evenly; adding the modified fluoride salt to the neutral solution in S3, and carrying out a heat preservation reaction at 50-80 °C for 1-1.5 h; S5, adding an organic alkanolamine and stirring for 0.5-1 h to obtain the low-alkali accelerating agent. The preparation method is simple, and the prepared low-alkali accelerating agent has good storage stability.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete processing, and particularly relates to a low-alkali accelerating agent and a preparation method thereof. Background Art

[0002] An accelerating agent is one of the essential raw materials in the preparation of concrete, which can improve the early strength of concrete and also increase the shrinkage of mortar and cement. The types of commonly used accelerating agents for cement concrete can be classified into alkali-containing accelerating agents or low-alkali accelerating agents according to their alkali content. Alkali-containing accelerating agents have strong corrosiveness due to their high alkali content, corrode construction tools during production and construction, and may also endanger human health. Therefore, they are being replaced by low-alkali accelerating agents.

[0003] However, it is found in the actual use process that the storage stability of low-alkali accelerating agents is poor, which affects the popularization and use of low-alkali accelerating agents. Summary of the Invention

[0004] (I) Technical Problems to be Solved

[0005] In view of the deficiencies of the prior art, the present invention provides a low-alkali accelerating agent and a preparation method thereof, which solve the technical problem of poor storage stability of existing low-alkali accelerating agents.

[0006] (II) Technical Solutions

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0008] A preparation method of a low-alkali accelerating agent includes the following steps:

[0009] S1. Prepare a sodium aluminate solution;

[0010] S2. Add water to the sodium aluminate solution, stir evenly, then add aluminum sulfate, and react at 50 - 80°C for 0.5 - 1 h under stirring conditions;

[0011] S3. Within 10 - 30 min after the complete reaction of aluminum sulfate, add a regulator to adjust the pH value to neutral;

[0012] S4. Mix a strong base weak acid salt and silica gel evenly, then add a fluoride salt, and obtain a modified fluoride salt after mixing evenly; add the modified fluoride salt to the neutral solution in S3, and keep it warm and react at 50 - 80°C for 1 - 1.5 h;

[0013] S5. Add organic alkanolamine and stir for 0.5 - 1 h to obtain the low-alkali accelerating agent.

[0014] Preferably, the silica gel is a hydrophilic type.

[0015] Preferably, the specific surface area of the silica gel is 600-800 m² / g.

[0016] Preferably, the sodium aluminate solution includes sodium hydroxide and aluminum hydroxide, and the mass ratio of sodium hydroxide to aluminum hydroxide is 1:2.5-3.5.

[0017] On the other hand, a low-alkali accelerating agent prepared by the preparation method, and the weight percentages of the low-alkali accelerating agent are as follows:

[0018]

[0019] The sum of each component is 100%;

[0020] The modifier includes: a strong base weak acid salt and silica gel, and the mass ratio of the strong base weak acid salt to silica gel is 2-4:1.

[0021] Preferably, the strong base weak acid salt includes at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, sodium sulfite, sodium acetate, sodium sulfide, and sodium phosphate.

[0022] Preferably, the fluoride salt includes at least one of sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate.

[0023] Preferably, the fluoride salt includes sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate.

[0024] Preferably, the mass ratio of sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate is (1-2):(5-7):(2-3).

[0025] Preferably, the mass ratio of sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate is 1.5:6:2.5.

[0026] (III) Beneficial Effects

[0027] The present invention provides a low-alkali accelerating agent and a preparation method thereof. Compared with the prior art, the following beneficial effects are achieved:

[0028] The preparation method of the low-alkali accelerating agent provided by the present invention first adds sodium aluminate solution and aluminum sulfate, adjusts the pH value to neutral, and then adds a modified fluoride salt. The modifier includes a strong base weak acid salt. Under neutral conditions, the strong base weak acid salt hydrolyzes, and the hydrolysis of the strong base weak acid salt further promotes the hydrolysis of the fluoride salt. The hydrolysis of the fluoride salt generates fluoride ions and silica gel. In the prepared low-alkali accelerating agent system, the generated silica gel encapsulates the fluoride ions and aluminum ions in the system, weakening the combination probability of the fluoride ions and aluminum ions, thereby avoiding the formation of aluminum fluoride crystals and slow agglomeration into large particles during storage. Therefore, the prepared low-alkali accelerating agent does not generate crystals during storage and has good storage stability. The modifier also includes silica gel, and this silica gel further encapsulates fluoride ions and chloride ions, improving the storage stability of the low-alkali accelerating agent during storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 It is a state diagram of the low-alkali accelerating agent prepared in Example 1 after 90 days of storage;

[0031] Figure 2 It is a state diagram of the low-alkali accelerating agent prepared in Comparative Example 1 after 3 days of storage;

[0032] Figure 3 It is a state diagram of the low-alkali accelerating agent prepared in Comparative Example 2 after 5 days of storage;

[0033] Figure 4 It is a state diagram of the low-alkali accelerating agent prepared in Comparative Example 3 after 5 days of storage. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] The embodiments of the present application provide a low-alkali accelerating agent and its preparation method, solving the technical problem of poor storage stability of existing low-alkali accelerating agents.

[0036] The technical solutions in the embodiments of the present application for solving the above technical problems generally have the following ideas:

[0037] In the preparation process of the low-alkali quick-setting agent, first, a strong base weak acid salt and silica gel are used to modify the fluoride salt, and then the modified fluoride salt is used to prepare the low-alkali quick-setting agent system. When using the modified fluoride salt to prepare the low-alkali quick-setting agent, the strong base weak acid salt promotes the hydrolysis of sodium fluorosilicate to generate silica gel. Both the newly generated silica gel and the silica gel in the modifier can respectively wrap the fluoride ions and chloride ions in the low-alkali quick-setting agent system, weakening the combination probability of fluoride ions and aluminum ions. Furthermore, it avoids the slow agglomeration of small aluminum fluoride particles into large particles during storage, thereby improving the storage stability of the low-alkali quick-setting agent.

[0038] The modifier also includes silica gel, which further wraps the fluoride ions and chloride ions, improving the storage stability during the storage process of the low-alkali quick-setting agent. Especially in the initial stage of the hydrolysis of the fluoride salt, less silica gel is produced by hydrolysis. This silica gel can better play the role of wrapping the fluoride ions produced by hydrolysis, blocking the contact between fluoride ions and chloride ions, and ensuring that no small aluminum fluoride particles are generated during the preparation process.

[0039] In the initial stage of the hydrolysis of the fluoride salt, the silica gel in the modifier can also inhibit the hydrolysis of the fluoride salt, reducing its hydrolysis rate, so as to avoid the rapid hydrolysis rate generating a large amount of fluoride ions and aluminum ions combining to form small aluminum fluoride particles, which would cause particulate matter to be generated during the preparation of the low-alkali quick-setting agent.

[0040] To better understand the above technical solution, the following will combine the accompanying drawings of the specification and specific implementation manners to elaborate on the above technical solution in detail.

[0041] Example 1:

[0042] This example provides a preparation method of a low-alkali quick-setting agent, including the following steps:

[0043] S1. Take an appropriate amount of water and make a sodium aluminate solution with sodium hydroxide and aluminum hydroxide in a mass ratio of 1:2.5;

[0044] S2. Add an appropriate amount of water to the sodium aluminate solution. After stirring evenly, add aluminum sulfate to the above system at one time, start stirring and heating, set the reaction temperature at 60 °C and keep the reaction for 0.5 h;

[0045] S3. After the aluminum sulfate reaction is complete, add a regulator to the above system within 10 min to adjust the pH value to neutral;

[0046] S4. Use a stirring device to mix sodium carbonate and hydrophilic silica gel with a mass ratio of 2:1 evenly to obtain a modifier, and then add it to sodium fluorosilicate. After mixing evenly, obtain modified sodium fluorosilicate;

[0047] The specific surface area of the silica gel is 600 ㎡ / g;

[0048] Add the modified sodium fluorosilicate to the neutral solution of S3, and keep it at 60 °C for reaction for 1 h;

[0049] S5. Turn off the heating, add organic alkanolamine, and stir for 0.5 h to obtain the low-alkali quick-setting agent.

[0050] No particulate matter is generated during the preparation of the low-alkali quick-setting agent.

[0051] The weight percentages of the obtained low-alkali quick-setting agent are:

[0052]

[0053]

[0054] Example 2

[0055] This example provides a preparation method of a low-alkali quick-setting agent, which includes the following steps:

[0056] S1. Prepare a sodium aluminate solution with sodium hydroxide and aluminum hydroxide in a mass ratio of 1:3;

[0057] S2. Add water to the sodium aluminate solution, stir evenly, then add aluminum sulfate to the above system at one time, start stirring and heating, set the reaction temperature at 70 °C and keep it for reaction for 0.8 h;

[0058] S3. After the reaction of aluminum sulfate is complete, add a regulator to the above system within 20 min to adjust the pH value to neutral;

[0059] S4. Use a stirring device to mix sodium bicarbonate and silica gel with a mass ratio of 3:1 evenly to obtain a modifier, and then add it to magnesium fluorosilicate and mix evenly to obtain modified magnesium fluorosilicate;

[0060] The silica gel is hydrophilic, and its specific surface area is 700 ㎡ / g;

[0061] Add the modified magnesium fluorosilicate to the neutral solution of S3, and keep it at 70 °C for reaction for 1.2 h;

[0062] S5. Turn off the heating, add organic alkanolamine, and stir for 0.8 h to obtain the low-alkali quick-setting agent.

[0063] No particulate matter is generated during the preparation of the low-alkali quick-setting agent.

[0064] The weight percentages of the obtained low-alkali quick-setting agent are:

[0065]

[0066]

[0067] Example 3

[0068] This example provides a preparation method of a low-alkali accelerating agent, which includes the following steps:

[0069] S1. Prepare a sodium aluminate solution by mixing sodium hydroxide and aluminum hydroxide at a mass ratio of 1:3.5;

[0070] S2. Add water to the sodium aluminate solution, stir evenly, then add aluminum sulfate to the above system at one time, start stirring and heating, set the reaction temperature at 80 °C and keep the reaction for 1 h;

[0071] S3. After the reaction of aluminum sulfate is complete, add a regulator to the above system within 30 min to adjust the pH value to neutral;

[0072] S4. Use a stirring device to mix potassium carbonate and silica gel evenly at a mass ratio of 4:1, then add them to the fluoride salt, and obtain a modified fluoride salt after mixing evenly; the fluoride salt includes sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate, and the mass of sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate is 1.5:6:2.5.

[0073] The silica gel is hydrophilic, and its specific surface area is 800 m² / g;

[0074] Add the modified fluoride salt to the neutral solution of S3, and keep the reaction at 80 °C for 1.5 h;

[0075] S5. Turn off the heating, add organic alkanolamine, and stir for 1 h to obtain the low-alkali accelerating agent.

[0076] No particulate matter is generated during the preparation of the low-alkali accelerating agent.

[0077] The weight percentage of the obtained low-alkali accelerating agent is:

[0078]

[0079]

[0080] Comparative Example 1:

[0081] The difference between this comparative example and Example 1 is that sodium fluorosilicate is not modified, that is, sodium fluorosilicate is added to the neutral solution of S3, and the others are the same as in Example 1.

[0082] Particulate matter is generated during the preparation process.

[0083] Comparative Example 2:

[0084] The difference between this comparative example and Example 1 is that only sodium carbonate is used to modify sodium fluorosilicate, and the others are the same as in Example 1.

[0085] The prepared low-alkali quick-setting agent has no particulate matter.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 1 is that only silica gel is used to modify sodium fluorosilicate, and the others are the same as in Example 1.

[0088] The prepared low-alkali quick-setting agent has no particulate matter.

[0089] The storage stabilities of the low-alkali quick-setting agents prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested, and the test results are shown in Table 1.

[0090] Storage stability test method: Store the prepared low-alkali quick-setting agent at normal temperature and pressure. After standing for a certain time, observe whether obvious crystals appear in the low-alkali quick-setting agent system, and record the time. The longest standing time is 90 days. Among them, Figure 1 is the state of the low-alkali quick-setting agent prepared in Example 1 after 90 days of storage, and no obvious crystals appear. Figure 2 is the state of the low-alkali quick-setting agent prepared in Comparative Example 1 after 3 days of storage, and obvious crystals appear. Figure 3 is the state of the low-alkali quick-setting agent prepared in Comparative Example 2 after 5 days of storage, and obvious crystals appear. Figure 4 is the state of the low-alkali quick-setting agent prepared in Comparative Example 3 after 5 days of storage, and obvious crystals appear.

[0091] Table 1 Test results of the storage stability of the prepared low-alkali quick-setting agent

[0092] Low-alkali accelerating agent Time when obvious crystals appear Example 1 Did not appear Example 2 Did not appear Example 3 Did not appear Comparative example 1 3 days Comparative example 2 5 days Comparative example 3 5 days

[0093] It can be seen from the results in Table 1 that after the fluorinated salt is modified with a strong base weak acid salt and silica gel and then added to the system, the prepared low-alkali quick-setting agent has good stability and no obvious crystals appear within 90 days; when the fluorinated salt is directly added to the system without modification, obvious crystals appear in the prepared low-alkali quick-setting agent after 3 days. Therefore, modifying the fluorinated salt with a strong base weak acid salt and silica gel can improve the stability of the low-alkali quick-setting agent. However, when only a single component of a strong base weak acid salt or silica gel is used to modify the fluorinated salt, obvious crystals also appear in the prepared low-alkali quick-setting agent after 5 days. This may be because the strong base weak acid salt and silica gel work synergistically to better improve the storage stability of the low-alkali quick-setting agent.

[0094] According to the standard of GB / T 35159-2017 "Quick-setting agent for shotcrete", the low-alkali quick-setting agents prepared in Examples 1 to 3 and Comparative Examples 1 to 3 after 5 days of storage were added to the cement paste in amounts of 4% and 6% of the cement weight respectively, and the setting time of the cement paste and the compressive strength of the cement mortar were tested, as shown in Table 2.

[0095] The mixing ratio for testing the setting time of neat cement paste is: reference cement: water = 400:140.

[0096] The mixing ratio for testing the compressive strength of cement mortar is: reference cement: standard sand: water = 900:1350:450.

[0097] Table 2 Test results of setting time and compressive strength

[0098]

[0099] As can be seen from Table 2, the low-alkali accelerating agents prepared in Examples 1-3 are used in neat cement paste or cement mortar, and their setting times and compressive strengths are superior to those of the low-alkali accelerating agents prepared in Comparative Examples 1-3. This is because after modifying the fluorinated salts with strong base weak acid salts and silica gel and then adding them to the system, the prepared low-alkali accelerating agent has good stability. When this low-alkali accelerating agent is added to neat cement paste or cement mortar, the amount of effective components that can play the accelerating role is large.

[0100] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0101] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A preparation method of a low-alkali accelerating agent, characterized in that, it comprises the following steps: S1. Prepare a sodium metaaluminate solution; S2. Add water to the sodium metaaluminate solution, stir evenly, then add aluminum sulfate, and react at 50 - 80 °C for 0.5 - 1 h under stirring conditions; S3. Adjust the pH value to neutral after the aluminum sulfate is completely dissolved to obtain a neutral solution; S4. Mix a strong base weak acid salt and silica gel evenly, then add a fluoride salt, and obtain a modified fluoride salt after mixing evenly; Add the modified fluoride salt to the neutral solution, and keep the temperature at 50 - 80 °C for heat preservation reaction for 1 - 1.5 h; S5. Add organic alkanolamine and stir for 0.5 - 1 h to prepare the low-alkali accelerating agent; The fluoride salt includes at least one of sodium fluorosilicate and magnesium fluorosilicate, or, The fluoride salt includes at least one of sodium fluorosilicate and magnesium fluorosilicate and sodium fluoride.

2. The preparation method according to claim 1, characterized in that, the silica gel is a hydrophilic type.

3. The preparation method according to claim 1, characterized in that, the specific surface area of the silica gel is 600 - 800 m² / g.

4. The preparation method according to claim 1, characterized in that, the sodium metaaluminate solution includes sodium hydroxide and aluminum hydroxide, and the mass ratio of sodium hydroxide to aluminum hydroxide is 1:2.5 - 3.

5.

5. A low-alkali accelerating agent prepared by the preparation method according to any one of claims 1 - 4, characterized in that, the weight percentages of the low-alkali accelerating agent are as follows: the sum of each component is 100%; the modifier includes: a strong base weak acid salt and silica gel, and the mass ratio of the strong base weak acid salt to silica gel is 2 - 4:

1.

6. The low-alkali accelerating agent according to claim 5, characterized in that, the strong base weak acid salt includes at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, sodium sulfite, sodium acetate, sodium sulfide, and sodium phosphate.

7. The low-alkali accelerating agent according to claim 5, characterized in that, the fluoride salt includes sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate.

8. The low-alkali accelerating agent according to claim 7, characterized in that, the mass ratio of sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate is (1 - 2):(5 - 7):(2 - 3).

9. The low-alkali accelerating agent according to claim 7, characterized in that, the mass ratio of sodium fluoride, sodium fluorosilicate, and magnesium fluorosilicate is 1.5:6:2.5.

Images