A concrete setting accelerator and early strength agent and its preparation method and application

Abstract

The invention discloses a concrete setting and early strength agent, a preparation method and application thereof, and belongs to the technical field of concrete admixtures. The concrete setting and early strength agent comprises the following components in parts by weight: 5 to 10 parts of ultrafine mineral powder A, 0.5 to 5 parts of polyvinyl alcohol, 10 to 20 parts of modified ultrafine mineral powder B, 5 to 12 parts of modified white carbon black, and 40 to 80 parts of water; the preparation method of the modified ultrafine mineral powder B is as follows: the modifier is dissolved in water to prepare a modified liquid, and then a calcium hydroxide solution is added to adjust the pH value to greater than 12, and then the ultrafine mineral powder B is added, heated to 50 to 80°C, reacted for 1 to 3 hours, filtered, dried, and ground to obtain the modified ultrafine mineral powder B. The setting and early strength agent of the invention is based on ultrafine mineral powder A, and modified ultrafine mineral powder B, polyvinyl alcohol and modified white carbon black are added. The components work together to significantly improve the early strength of concrete, and also have a significant enhancement effect on the later strength, and can significantly shorten the demoulding time of concrete.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete admixtures, and particularly relates to a concrete coagulation accelerating and early strength agent, a preparation method and application thereof. Background Art

[0002] In the construction of large-volume concrete buildings such as large bridges and high-rise buildings, as well as winter construction and special emergency repair projects, not only is the concrete required to have high strength and performance, but it is also hoped that the early strength of the concrete will develop quickly to shorten the demolding time, increase the turnover rate of the formwork, and facilitate the construction of the next process, thereby shortening the construction period and improving the project progress.

[0003] Adding early strength agents to concrete is the most common method to improve the early strength of concrete. Currently, the more commonly used early strength agents for concrete mainly include: (1) Chloride early strength agents: mainly calcium chloride, sodium chloride, potassium chloride, amine oxide, iron oxide, aluminum oxide, etc. Chloride early strength agents all have good early strength effects, among which calcium chloride has good early strength effect and low cost, and is the most widely used. (2) Sulfate early strength agents: mainly sodium sulfate, sodium thiosulfate, calcium sulfate, aluminum sulfate, potassium aluminum sulfate, etc., among which sodium sulfate is more commonly used. (3) Organic early strength agents: organic amine early strength agents mainly include triethanolamine, triisopropanolamine, diethanolamine, etc., among which triethanolamine has the best early strength effect. The above types of early strength agents can be added alone or in combination in engineering. However, the above-mentioned early strength agents all have some shortcomings. For example, chloride-based early strength agents have an obvious corrosion effect on steel bars, sulfate-based early strength agents also cause concrete "frosting" and pose a risk of alkali-aggregate reaction hazards, and amine-based early strength agents are extremely sensitive to the dosage, and over-dosage can easily cause super-retarded setting, so their application is greatly restricted.

[0004] In recent years, the use of artificially synthesized calcium silicate hydrate nanocrystalline cores to improve the early strength of concrete has become a new and efficient early strength means. The calcium silicate hydrate nanocrystalline core can be used as a seed to accelerate the hydration of cement, thereby improving the early strength. For example, Chinese patent CN107555829A discloses a crystal core type coagulation accelerator and early strength agent for concrete and its preparation method. The early strength agent is a CSH crystal core, which is made of 1.55 parts of calcium nitrate, 1.24 parts of sodium silicate, and 1 part of 18# early strength polycarboxylate water reducer. It can effectively reduce the nucleation barrier in the cement hydration process, thereby achieving the effect of accelerating coagulation and improving strength. The early strength increase is better than that of traditional early strength agents; however, the crystal core has a large particle size and poor dispersion stability. When used as a crystal core material, the effect of improving the early strength of cement-based materials is not significant.

[0005] On the other hand, when mineral powder is added to concrete, the mineral powder replaces a part of the cement clinker, resulting in a decrease in the relative content of cement clinker participating in the early hydration, which greatly reduces the early strength of the concrete. In addition, since the activity of the mineral powder is too low, it takes a long time for its activity to be stimulated and for it to participate in hydration and generate hydration products with strength. Therefore, the cement hydration rate is greatly slowed down after the addition of mineral powder, so that the early strength requirements cannot be met, which is manifested as low 1d and 3d strengths, and the demoulding time of its prefabricated components is long, which limits its use.

[0006] Therefore, it is of great significance to provide a concrete early strength agent prepared by using mineral powder, which can significantly improve the early strength of concrete without reducing the later strength of concrete. Summary of the invention

[0007] In view of the above deficiencies in the prior art, one of the objects of the present invention is to provide a concrete setting accelerator and early strength agent, which can accelerate the cement hydration process, shorten the demoulding time of prefabricated parts, significantly improve the early strength of concrete, and do not reduce the later strength of concrete.

[0008] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0009] A concrete setting accelerator and early strength agent, comprising the following components in parts by weight: 5-10 parts of ultrafine mineral powder A, 0.5-5 parts of polyvinyl alcohol, 10-20 parts of modified ultrafine mineral powder B, 5-12 parts of modified white carbon black, and 40-80 parts of water;

[0010] The preparation method of the modified ultrafine mineral powder B is as follows: dissolving the modifier in water to prepare a modified solution, then adding calcium hydroxide solution to adjust the pH value to greater than 12, then adding the ultrafine mineral powder B, heating to 50-80° C., reacting for 1-3 hours, filtering, drying, and grinding to obtain the modified ultrafine mineral powder B;

[0011] The modifier is prepared by compounding powdered polycarboxylic acid water-reducing agent and polymethylsiloxane in a mass ratio of 1: (1-1.5).

[0012] Preferably, the preparation method of the modified white carbon black is as follows: white carbon black is mixed with a sodium hydroxide solution, reacted at 60 to 100° C. for 1 to 3 hours, cooled to room temperature, and then washed and dried to obtain the modified white carbon black. Modification of white carbon black with sodium hydroxide can significantly improve the early strength effect of the early strength agent.

[0013] Preferably, the specific surface area of ​​the ultrafine mineral powder A is ≥850m 2 / kg, activity index ≥130%.

[0014] Further preferably, the content of the ultrafine mineral powder A with a particle size less than 13 μm reaches more than 97%.

[0015] Preferably, the specific surface area of ​​the ultrafine mineral powder B is ≥850m 2 / kg, activity index ≥130%.

[0016] Another object of the present invention is to provide a method for preparing the concrete setting accelerator and early strength agent, the steps of which are as follows:

[0017] S1. Weigh each component in parts by weight, first add water to polyvinyl alcohol to prepare a polyvinyl alcohol solution, then add ultrafine ore powder A, ultrasonically disperse, to obtain a mixed solution;

[0018] S2. Add modified ultrafine mineral powder B to the mixed solution obtained in step S1, stir evenly, then add modified white carbon black, and continue stirring for 2 to 3 hours to obtain the concrete setting accelerator.

[0019] Another object of the present invention is to provide the use of the concrete accelerating setting and early strength agent in concrete, wherein the dosage of the concrete accelerating setting and early strength agent in concrete is 3-10% of the cementitious material.

[0020] Compared with the prior art, the present invention is beneficial in that:

[0021] (1) Ultrafine mineral powder A has a significant reinforcing effect. Its reinforcing effect lies not only in its filling effect in tiny gaps, but also in its ultra-high pozzolanic activity. In the early stage of hydration, the ultrafine mineral powder reacts with free calcium oxide in cement and the early hydration product of cement Ca(OH)2 to produce more hydration products, thereby increasing the early strength.

[0022] (2) The modified ultrafine mineral powder B can effectively reduce the barrier to the formation of CSH gel and induce hydration, so that a large amount of CSH gel is generated in the early stage of hydration, thereby significantly improving the early hydration process of cement and the early strength of concrete.

[0023] (3) Under the action of polyvinyl alcohol, ultrafine mineral powder A, modified ultrafine mineral powder B, and modified white carbon black can react with free calcium oxide in cement and calcium hydroxide, an early hydration product of cement, in the early stage of hydration to produce more hydration products, further improving the early strength of concrete.

[0024] (4) Compared with the mineral powder and white carbon black in the prior art, the setting and early strength accelerator of the present invention innovatively uses ultrafine mineral powder A, modified ultrafine mineral powder B, polyvinyl alcohol and modified white carbon black. The components work synergistically with each other, significantly improving the early strength of concrete, and also significantly enhancing the later strength, and can significantly shorten the demolding time of concrete. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the following examples and comparative examples, the specific surface area of ​​the ultrafine mineral powder A is ≥850m 2 / kg, activity index ≥130%; the average particle size of ultrafine mineral powder is less than 513μm, and the content of particles less than 13μm reaches more than 97%; the specific surface area of ​​ultrafine mineral powder B is ≥850m 2 / kg, activity index ≥130%; the average particle size of the ultrafine mineral powder is less than 513μm, and the content of particles less than 13μm reaches more than 97%.

[0027] Example 1

[0028] This embodiment provides a concrete setting accelerator, comprising the following components in parts by weight: 8 parts of ultrafine mineral powder A, 3 parts of polyvinyl alcohol, 15 parts of modified ultrafine mineral powder B, 9 parts of modified white carbon black, and 68 parts of water;

[0029] The preparation method of modified ultrafine mineral powder B is as follows: dissolving the modifier in water to prepare a modified liquid with a mass concentration of 10%, then taking 200g of the modified liquid, adding calcium hydroxide solution to adjust the pH value to 12, then adding 12g of ultrafine mineral powder B, heating to 65°C, reacting for 1.5h, filtering, drying, and grinding to a particle size of 20 to 50nm to obtain modified ultrafine mineral powder B;

[0030] The modifier is prepared by mixing polycarboxylate water reducer and polymethylsiloxane in a mass ratio of 1:1;

[0031] The preparation method of modified white carbon black is as follows: white carbon black is mixed with sodium hydroxide solution, reacted at 80° C. for 1.5 hours, cooled to room temperature, and then washed and dried to obtain the modified white carbon black.

[0032] The preparation method of the concrete setting accelerator of the present embodiment comprises the following steps:

[0033] S1. Weigh each component by weight, first add water to polyvinyl alcohol to prepare a polyvinyl alcohol solution with a mass concentration of 20%, then add ultrafine ore powder A, ultrasonically disperse, to obtain a mixed solution;

[0034] S2. Add the modified ultrafine mineral powder B to the mixed solution obtained in step S1, stir evenly, add the modified silica and the remaining water, and continue stirring for 2 to 3 hours to obtain the concrete setting accelerator.

[0035] Example 2

[0036] Example 2 is basically the same as Example 1, except that the concrete setting accelerator of this example comprises the following components in parts by weight: 1 part of ultrafine mineral powder A, 5 parts of polyvinyl alcohol, 10 parts of modified ultrafine mineral powder B, 5 parts of modified white carbon black, and 75 parts of water;

[0037] The preparation method of modified ultrafine mineral powder B is as follows: dissolving the modifier in water to prepare a modified liquid with a mass concentration of 10%, then taking 200g of the modified liquid, adding calcium hydroxide solution to adjust the pH value to 13, then adding 12g of ultrafine mineral powder B, heating to 80°C, reacting for 1h, filtering, drying, and grinding to a particle size of 20 to 50nm to obtain modified ultrafine mineral powder B;

[0038] The modifier is a mixture of polycarboxylate water reducer and polymethylsiloxane in a mass ratio of 1:1.5;

[0039] The preparation method of modified white carbon black is as follows: white carbon black is mixed with sodium hydroxide solution, reacted at 60° C. for 3 hours, cooled to room temperature, and then washed and dried to obtain the modified white carbon black.

[0040] Example 3

[0041] Example 3 is basically the same as Example 1, except that the concrete setting accelerator and early strength agent of this example comprises the following components in parts by weight: 5 parts of ultrafine mineral powder A, 1 part of polyvinyl alcohol, 20 parts of modified ultrafine mineral powder B, 12 parts of modified white carbon black, and 60 parts of water;

[0042] The preparation method of modified ultrafine mineral powder B is as follows: dissolving the modifier in water to prepare a modified liquid with a mass concentration of 10%, then taking 200g of the modified liquid, adding calcium hydroxide solution to adjust the pH value to 12, then adding 12g of ultrafine mineral powder B, heating to 50°C, reacting for 3h, filtering, drying, and grinding to a particle size of 20 to 50nm to obtain modified ultrafine mineral powder B;

[0043] The modifier is prepared by mixing polycarboxylate water reducer and polymethylsiloxane in a mass ratio of 1:1;

[0044] The preparation method of modified white carbon black is as follows: white carbon black is mixed with sodium hydroxide solution, reacted at 100° C. for 1 hour, cooled to room temperature, and then washed and dried to obtain the modified white carbon black.

[0045] Comparative Example 1

[0046] Comparative Example 1 is substantially the same as Example 1, except that the modifier is a powdered polycarboxylic acid water-reducing agent and does not contain polymethylsiloxane.

[0047] Comparative Example 2

[0048] Comparative Example 2 is substantially the same as Example 1, except that the setting accelerator and early strength agent of this comparative example comprises the following components in parts by weight: 23 parts of ultrafine mineral powder A, 3 parts of polyvinyl alcohol, 9 parts of modified silica, and 68 parts of water;

[0049] That is, compared with Example 1, the accelerator of setting and early strength agent in this comparative example does not contain the modified ultrafine mineral powder B, and the dosage of the ultrafine mineral powder A is increased accordingly.

[0050] Comparative Example 3

[0051] Comparative Example 3 is substantially the same as Example 1, except that the setting accelerator of this comparative example comprises the following components in parts by weight: 8 parts of ultrafine mineral powder A, 15 parts of modified ultrafine mineral powder B, 9 parts of modified white carbon black, and 71 parts of water;

[0052] That is, compared with Example 1, the accelerating and early-strengthening agent of this comparative example does not contain polyvinyl alcohol.

[0053] Comparative Example 4

[0054] Comparative Example 4 is substantially the same as Example 1, except that the setting accelerator of this comparative example comprises the following components in parts by weight: 8 parts of ultrafine mineral powder A, 3 parts of polyvinyl alcohol, 15 parts of modified ultrafine mineral powder B, 9 parts of white carbon black, and 68 parts of water;

[0055] That is, compared with Example 1, unmodified silica is used instead of modified silica.

[0056] Test example

[0057] The setting and early strength accelerating agents of Examples 1 to 3 and Comparative Examples 1 to 4 were used in concrete. The dosage of the setting and early strength accelerating agents was 6% of the total mass of the cementitious material. The mix ratio of the concrete was as shown in Table 1.

[0058] Table 1 shows the concrete mix ratio (kg / m 3 )

[0059] cement Fly ash sand gravel water Water reducing agent 370 80 726 1025 175 6.75

[0060] The cement is Conch P·I 52.5; the fly ash is Grade II fly ash; the sand is machine-made sand with a fineness modulus of 2.6; the crushed stone is 5-20 mm continuously graded crushed stone; and the water reducing agent is a high-performance polycarboxylic acid powder water reducing agent with a water reducing rate of 28%.

[0061] According to the provisions of GB / T50081-2019 "Standard Test Methods for Mechanical Properties of Ordinary Concrete", the 1d and 28d compressive strengths of concrete were measured; according to the provisions of GB / T50080-2019 "Standard Test Methods for Performance of Ordinary Concrete Mixtures", the setting time of concrete was tested. The test results are shown in Table 2.

[0062] Table 2 Concrete performance test results

[0063]

[0064]

[0065] It can be seen from the results in Table 2 that, compared with the blank group, the addition of the accelerating setting and early strength agent of the present invention can significantly improve the early mechanical properties (1d strength) of concrete, also has a significant enhancing effect on the later strength of concrete, and can shorten the demoulding time.

[0066] Compared with Example 1, the modifier of Comparative Example 1 does not contain polymethylsiloxane, and Comparative Example 4 uses unmodified white carbon black, and the early strength of the concrete is significantly reduced, the late strength is also significantly reduced, and the demolding time of the concrete precast is prolonged. By comparing Example 1 and Comparative Example 2, it can be found that the early strength of the concrete is significantly reduced by replacing the modified ultrafine mineral powder B with ultrafine mineral powder A in Comparative Example 2, and the demolding time of the concrete precast is also significantly prolonged. It can be seen that the modified ultrafine mineral powder B can not only improve the early and late strength of the concrete, but also cooperate with other components to shorten the demolding time of the concrete precast; by comparing Example 1 and Comparative Example 3, it can be found that Comparative Example 3 does not contain polyvinyl alcohol, not only the demolding time of the concrete precast is significantly prolonged, but also the early and late strength of the concrete is significantly reduced, indicating that polyvinyl alcohol can not only shorten the demolding time of the concrete precast, but also cooperate with other components to improve the early and late strength of the concrete. In summary, changing or replacing any component in the early strength agent of the present invention will greatly reduce the compressive strength of concrete and prolong the demolding time. It can be seen from Example 1 of the present invention and Comparative Examples 1-3 that it is precisely due to the synergistic effect of the modified ultrafine mineral powder B, polyvinyl alcohol and modified white carbon black that the accelerator of the present invention can significantly improve the early strength and late strength of concrete, and at the same time can significantly shorten the demolding time of concrete precast parts.

[0067] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A concrete setting accelerator, characterized in that: The invention comprises the following components in parts by weight: 5-10 parts of ultrafine mineral powder A, 0.5-5 parts of polyvinyl alcohol, 10-20 parts of modified ultrafine mineral powder B, 5-12 parts of modified white carbon black, and 40-80 parts of water; The preparation method of the modified ultrafine mineral powder B is as follows: dissolving the modifier in water to prepare a modified solution, then adding calcium hydroxide solution to adjust the pH value to greater than 12, then adding the ultrafine mineral powder B, heating to 50-80° C., reacting for 1-3 hours, filtering, drying, and grinding to obtain the modified ultrafine mineral powder B; The modifier is prepared by compounding powdered polycarboxylic acid water-reducing agent and polymethylsiloxane in a mass ratio of 1: (1-1.5); The preparation method of the modified white carbon black is as follows: white carbon black is mixed with a sodium hydroxide solution, reacted at 60-100° C. for 1-3 hours, cooled to room temperature, and then washed and dried to obtain the modified white carbon black.

2. A concrete setting accelerator according to claim 1, characterized in that: The specific surface area of ​​the ultrafine mineral powder A is ≥850m 2 / kg, activity index ≥130%.

3. A concrete setting accelerator according to claim 1, characterized in that: The content of the ultrafine mineral powder A with a particle size less than 13 μm reaches more than 97%.

4. A concrete setting accelerator according to claim 1, characterized in that: The specific surface area of ​​the ultrafine mineral powder B is ≥850m 2 / kg, activity index ≥130%.

5. The method for preparing the concrete setting accelerator and early strength agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1 weighed each component in parts by weight, first the polyvinyl alcohol was added with water to prepare a polyvinyl alcohol solution, and then the ultrafine mineral powder A was added, ultrasonically dispersed to obtain a mixed solution; S2. Add the modified ultrafine mineral powder B to the mixed solution obtained in step S1, stir evenly, then add the modified silica, and continue stirring for 2 to 3 hours to obtain the concrete setting accelerator.

6. Use of the concrete setting accelerator and early strength agent according to any one of claims 1 to 4 in concrete, characterized in that: The amount of the accelerating setting and early strength agent in concrete is 3-10% of the cementitious material.

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