A concrete admixture and its preparation method

Abstract

The present invention belongs to the technical field of concrete admixtures, and provides a concrete admixture and a preparation method thereof. The concrete admixture comprises the following raw materials in parts by weight: 15-25 parts of water reducing agent, 20-35 parts of redispersible latex powder, 5-10 parts of modified silicon carbide fiber, 0.5-2 parts of expansive agent, 1-3 parts of retarder, 0.5-1 part of early strength agent, and 30-45 parts of water. The preparation method is as follows: weighing according to parts by weight, mixing the water reducing agent, redispersible latex powder, modified silicon carbide fiber, expansive agent, retarder, early strength agent and water, and stirring evenly to obtain the concrete admixture. The concrete admixture provided by the present invention can improve the workability and durability of concrete, increase the compressive and crack resistance strengths of concrete, greatly extend the service life of concrete, and has a simple preparation method and an economical cost, being suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete admixtures, and particularly relates to a concrete admixture and a preparation method thereof. Background Art

[0002] Concrete is one of the most indispensable building materials in the current construction field and is ubiquitous in our lives. Therefore, the requirements for concrete are getting higher and higher. In order to improve and adjust the performance of concrete, admixtures are added. Concrete admixtures refer to substances added before or during the mixing of concrete to improve the performance of concrete. Concrete admixtures have an important impact on the performance of concrete.

[0003] At present, there are many types of concrete admixtures with different functions. Using various types of admixtures can achieve different effects, such as improving the corrosion resistance of concrete, improving the brittleness of concrete, enhancing the frost resistance of hardened concrete, significantly reducing the water consumption of concrete, increasing the strength of concrete, compensating for the dry shrinkage of concrete, reducing the shrinkage cracks of concrete, extending the service life of concrete, and improving durability. The Chinese patent application document with the patent application number CN106186795A discloses a special admixture for permeable concrete and its application. The special admixture for permeable concrete includes the following components by mass percentage: polycarboxylate water reducer 10 - 20%, polycarboxylate slump retainer 5 - 25%, water retaining agent 0.5 - 3%, thickening agent 0.5 - 5%, retarder 1 - 5%, and water 52 - 75%. The components of the special admixture for permeable cement concrete described in the present invention have good synergistic effects, and on the basis of ensuring its water permeability, the workability of permeable concrete can be well maintained for 2 hours or more. However, the water retaining agent used in this invention has poor chemical stability and is greatly affected by temperature. The heat released during the mixing process of concrete will affect the working performance of the water retaining agent, making it unable to solve the problem of rapid water loss in concrete. The Chinese patent application document with the patent application number CN106477962A discloses an admixture for cement-based permeable concrete, which includes the following components by mass: early strength and high water reducing polycarboxylate mother liquor 5 - 6 parts, super slow release polycarboxylate mother liquor 2 - 3 parts, early strength agent 0.5 - 1 part, organic retarder 0.5 - 1.5 parts, inorganic retarder 0.1 - 0.5 parts, viscosity modifier 3 - 10 parts, air-entraining agent 0.1 - 0.5 parts, defoaming agent 0.1 - 3 parts, internal water regulator 0.1 - 0.5 parts, surface water regulator 0.3 - 0.5 parts, and water 70 - 90 parts. This admixture can effectively improve the early strength and low slump retention ability of cement-based permeable concrete, reduce the air content and water sensitivity of fresh slurry, and increase its water retention and moisture retention. The present invention uses a viscosity modifier to make the slurry have good adhesion to coarse aggregates, but the slurry will still sink to the bottom during long-distance transportation, and the cost of the admixture is relatively high. Summary of the Invention

[0004] In order to improve the problems in the prior art that concrete is prone to poor early strength and easy to shrink and crack, the present invention provides a concrete admixture and a preparation method thereof.

[0005] The object of the present invention can be achieved by the following technical solutions:

[0006] The first aspect of the present invention provides a concrete admixture, comprising the following raw materials in parts by weight:

[0007] Water reducing agent: 15 - 25 parts;

[0008] Redispersible latex powder: 20 - 35 parts;

[0009] Modified silicon carbide fiber: 5 - 10 parts;

[0010] Expansive agent: 0.5 - 2 parts;

[0011] Retarder: 1 - 3 parts;

[0012] Early strength agent: 0.5 - 1 part;

[0013] Water: 30 - 45 parts;

[0014] The modified silicon carbide fiber is prepared by the following steps:

[0015] Add tris(hydroxymethyl)aminomethane (Tris) to deionized water and stir, adjust the pH to 8 - 8.5, add modified dopamine, stir at room temperature for 2 - 3 h, add silicon carbide fiber and impregnate for 3 - 5 h, filter, wash, and dry to obtain modified silicon carbide fiber. Silicon carbide fiber has high strength, high modulus and excellent chemical resistance. Adding it to concrete can well improve the strength and durability of concrete. However, its compatibility with other raw materials is poor and it is difficult to be evenly dispersed in the raw materials, resulting in a great reduction in the effect of the admixture. In the above technical solution, dopamine is used to coat and modify its surface, thereby improving the dispersibility and compatibility of silicon carbide in the raw materials.

[0016] As a preferred scheme of the present invention, the dosage ratio of tris(hydroxymethyl)aminomethane, deionized water, modified dopamine and silicon carbide fiber is 1.0 - 1.5 g: 100 mL: 0.2 - 0.3 g: 0.6 - 0.8 g.

[0017] As a preferred scheme of the present invention, the modified dopamine is prepared by the following steps:

[0018] Add aldehyde cellulose and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride into the phosphate buffer solution. After stirring and reacting for 0.5 - 1 h, add N-hydroxysuccinimide, continue stirring for 0.5 - 1 h, add dopamine hydrochloride, and stir for 12 - 14 h under nitrogen protection. After the reaction is completed, wash and dry to obtain modified dopamine. Cellulose contains a large amount of hydrophilic polyhydroxy compounds, has the characteristics of capillarity and large specific surface area, so it has high water retention. After grafting reaction with dopamine, dopamine has a certain water absorption ability, good hydrophilicity, and at the same time, a large number of hydrogen bonds formed by hydroxyl groups can form a hydrogen bond network system, which is coated on the silicon carbide fiber, endowing silicon carbide with excellent water retention performance. When added to concrete, it has excellent water retention effect.

[0019] As a preferred embodiment of the present invention, the dosage ratio of aldehyde cellulose, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride, phosphate buffer solution, N-hydroxysuccinimide and dopamine hydrochloride is 2.0 - 2.5 g : 3.36 - 3.40 g : 200 mL : 2.0 - 2.05 g : 0.53 - 0.55 g.

[0020] As a preferred embodiment of the present invention, the water reducing agent is one of polycarboxylate water reducing agent, naphthalene series water reducing agent and aliphatic water reducing agent.

[0021] As a preferred embodiment of the present invention, the expansive agent is one of magnesium oxide and gypsum. During the hardening process of concrete, the expansive agent can use its own volume expansion to compensate for the appropriate shrinkage of concrete, thereby reducing the early cracking phenomenon of concrete.

[0022] As a preferred embodiment of the present invention, the retarder is one of organic retarders and inorganic retarders. The addition of the retarder can effectively reduce the heat of hydration and prolong the setting time of concrete.

[0023] As a preferred embodiment of the present invention, the organic retarder is at least one of sodium gluconate, sucrose and citric acid; the inorganic retarder is at least one of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate.

[0024] As a preferred embodiment of the present invention, the early strength agent is at least one of nitrates, thiocyanates, nitrites, organic alkanolamines, thiosulfates and carboxylates. The addition of the early strength agent can improve the early strength of concrete, shorten the curing time, reduce the cement consumption and economic cost.

[0025] The second aspect of the present invention provides a preparation method of a concrete admixture, comprising the following steps:

[0026] Weigh by parts by weight. Mix water reducer, redispersible latex powder, modified silicon carbide fiber, expansive agent, retarder, early strength agent and water, and stir evenly to obtain a concrete admixture.

[0027] Advantages of the present invention:

[0028] A concrete admixture provided in the present invention is composed of a water reducer, redispersible latex powder, modified silicon carbide fiber, expansive agent, retarder, early strength agent and water. The obtained admixture can greatly reduce the water consumption of concrete and improve the early strength of concrete. The incorporation of the modified silicon carbide fiber can not only improve the microscopic structure of concrete, but also play a bridging role, absorb energy and enhance the strength when the concrete cracks under load. The redispersible latex powder has a certain air-entraining effect, and can introduce an appropriate amount of tiny closed bubbles into the concrete. On the one hand, it can cut off the capillary passage in the concrete, block the water evaporation channel and reduce the loss of internal water in the concrete; on the other hand, it enhances the plasticity of the concrete and plays a certain role in relieving the plastic shrinkage pressure, thus preventing the early shrinkage cracking of the concrete to a certain extent.

[0029] A concrete admixture and its preparation method provided in the present invention, through reasonable proportioning, optimizes the types and dosages of admixtures suitable for concrete. At the same time, the preparation process is simple, the cost is low, and it is suitable for large-scale production. The provided admixture can improve the workability and durability of concrete, increase the compressive and crack-resistant strengths of concrete, and greatly extend the service life of concrete. Specific embodiments

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0031] The aldehyde-grouped cellulose used in the examples and comparative examples of the present invention is prepared through the following steps:

[0032] Mix 100 g of cellulose (mass fraction 2.0%) with 1.0 g of sodium periodate, adjust the pH value to 5.0 with HCl, and then carry out an oxidation reaction under the conditions of a temperature of 50°C and nitrogen protection, with light avoidance and stirring. After a certain period of time, add 2 mL of ethylene glycol to the system to terminate the reaction, and wash 3 times with deionized water to obtain aldehyde-grouped cellulose, which is freeze-dried for standby.

[0033] Example 1

[0034] This example provides a concrete admixture, which, by weight, comprises the following components:

[0035] Polycarboxylate water reducer: 15 parts, redispersible latex powder: 25 parts, modified silicon carbide fiber: 5 parts, magnesium oxide: 0.5 part, sodium gluconate: 1.5 parts, sodium nitrate: 0.6 part, water: 35 parts.

[0036] Among them, the preparation steps of the modified silicon carbide fiber are as follows:

[0037] S1. Add 2.0 g of aldehyde group-modified cellulose and 3.36 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to 200 mL of phosphate buffer solution (pH value = 5.7), stir and react for 0.5 h, then add 2.0 g of N-hydroxysuccinimide, continue to stir for 0.5 h, add 0.53 g of dopamine hydrochloride, and stir for 12 h under nitrogen protection. After the reaction, wash with deionized water three times, dry, and obtain modified dopamine;

[0038] S2. Add 1.0 g of tris(hydroxymethyl)aminomethane (Tris) to 100 mL of deionized water and stir, adjust the pH to 8.5, add 0.2 g of modified dopamine, stir at room temperature for 2 h, add 0.6 g of silicon carbide fiber and impregnate for 3 h, filter, wash, and place in an oven at 105 °C for drying for 8 h to obtain modified silicon carbide fiber.

[0039] Among them, the preparation method of the concrete admixture is as follows:

[0040] Weigh by weight, mix the polycarboxylate water reducer, redispersible latex powder, modified silicon carbide fiber, magnesium oxide, sodium gluconate, sodium nitrate and water, and stir evenly to obtain the concrete admixture.

[0041] Example 2

[0042] Compared with Example 1, the difference is only that:

[0043] The preparation steps of the modified silicon carbide fiber are as follows:

[0044] S1. Add 2.5 g of aldehyde group-modified cellulose and 3.40 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to 200 mL of phosphate buffer solution (pH value = 5.7), stir and react for 0.5 h, then add 2.05 g of N-hydroxysuccinimide, continue to stir for 0.5 h, add 0.55 g of dopamine hydrochloride, and stir for 12 - 14 h under nitrogen protection. After the reaction, wash with deionized water three times, dry, and obtain modified dopamine.

[0045] Example 3

[0046] Compared with Example 1, the difference is only that:

[0047] The preparation steps of the modified silicon carbide fibers are as follows:

[0048] S2. Add 1.5 g of tris (hydroxymethyl) aminomethane (Tris) to 100 mL of deionized water, stir, adjust the pH to 8.5, add 0.3 g of modified dopamine, stir at room temperature for 2 h, add 0.8 g of silicon carbide fibers, impregnate for 3 h, filter, wash, and dry in an oven at 105 °C for 8 h to obtain the modified silicon carbide fibers.

[0049] Example 4

[0050] Compared with Example 1, the difference is only that:

[0051] Replace 5 parts of the modified silicon carbide fibers with 7 parts of the modified silicon carbide fibers.

[0052] Example 5

[0053] Compared with Example 1, the difference is only that:

[0054] Replace 5 parts of the modified silicon carbide fibers with 10 parts of the modified silicon carbide fibers.

[0055] Example 6

[0056] Compared with Example 1, the difference is only that:

[0057] A concrete admixture, by weight, comprises the following components:

[0058] Polycarboxylate water reducer: 24 parts, redispersible latex powder: 30 parts, modified silicon carbide fibers: 8 parts, magnesium oxide: 1.8 parts, sodium gluconate: 2.5 parts, sodium nitrate: 0.8 parts, water: 40 parts.

[0059] Example 7

[0060] Compared with Example 1, the difference is only that:

[0061] A concrete admixture, by weight, comprises the following components:

[0062] Polycarboxylate water reducer: 20 parts, redispersible latex powder: 25 parts, modified silicon carbide fibers: 6 parts, gypsum: 1.2 parts, citric acid: 2 parts, sodium nitrate: 0.6 parts, water: 35 parts.

[0063] Comparative Example 1

[0064] This comparative example provides a concrete admixture, by weight, comprising the following components:

[0065] Polycarboxylate water reducer: 15 parts, redispersible latex powder: 25 parts, magnesium oxide: 0.5 part, sodium gluconate: 1.5 parts, sodium nitrate: 0.6 part, water: 35 parts.

[0066] Among them, the preparation method of the concrete admixture is as follows:

[0067] Weigh according to parts by weight. After mixing polycarboxylate water reducer, redispersible latex powder, magnesium oxide, sodium gluconate, sodium nitrate and water, stir evenly to obtain the concrete admixture.

[0068] Comparative Example 2

[0069] Compared with Example 1, the only difference is:

[0070] A concrete admixture, by weight, includes the following components:

[0071] Polycarboxylate water reducer: 15 parts, redispersible latex powder: 25 parts, silicon carbide fiber: 5 parts, magnesium oxide: 0.5 part, sodium gluconate: 1.5 parts, sodium nitrate: 0.6 part, water: 35 parts.

[0072] Comparative Example 3

[0073] Compared with Example 1, the only difference is:

[0074] Replace 5 parts of modified silicon carbide fiber with 3.5 parts of modified silicon carbide fiber.

[0075] Comparative Example 4

[0076] Compared with Example 1, the only difference is:

[0077] Replace 5 parts of modified silicon carbide fiber with 11.5 parts of modified silicon carbide fiber.

[0078] Comparative Example 5

[0079] Compared with Example 1, the only difference is:

[0080] A concrete admixture, by weight, includes the following components:

[0081] Polycarboxylate water reducer: 10 parts, redispersible latex powder: 25 parts, modified silicon carbide fiber: 5 parts, magnesium oxide: 0.5 part, sodium gluconate: 1.5 parts, sodium nitrate: 0.35 part, water: 35 parts.

[0082] Comparative Example 6

[0083] Compared with Example 1, the only difference is:

[0084] A concrete admixture, by weight, includes the following components:

[0085] Polycarboxylate superplasticizer: 15 parts, redispersible latex powder: 25 parts, modified silicon carbide fiber: 5 parts, sodium gluconate: 1.5 parts, sodium nitrate: 0.6 parts, water: 35 parts.

[0086] The concrete admixtures prepared in Examples 1 - 7 and Comparative Examples 1 - 6 were subjected to application tests:

[0087] The obtained admixtures of Examples 1 - 7 and Comparative Examples 1 - 6 were mixed with concrete raw materials and water to form concrete slurries. After 28 days of standard curing, concrete specimen blocks were made, and their compressive strengths were tested. After placing the concrete specimen blocks in a high - salt service environment for 6 months, their compressive strengths were tested again: (1) The compressive strength test was carried out according to the method specified in GB / T50081 - 2019 "Standard Test Method for Physical and Mechanical Properties of Concrete"; (2) The cracking test was carried out according to the method specified in GB / T 50082 - 2009 "Standard Test Method for Long - Term Performance and Durability of Ordinary Concrete"; (3) The slump test was carried out according to the method specified in GB / T 50080 - 2016 "Standard Test Method for Properties of Fresh Ordinary Concrete".

[0088] The above test results are shown in Table 1:

[0089] Table 1

[0090]

[0091] As can be seen from Table 1, compared with Comparative Examples 1 - 2, the compressive strength, crack - resistance strength, slump, and number of freeze - thaw cycles of the concrete specimen blocks formed by mixing the concrete admixtures with concrete raw materials and water in Examples 1 - 7 are better than those of the concrete specimen blocks in Comparative Examples 1 - 2. At the same time, the compressive strength of the concrete specimen blocks in Comparative Examples 1 - 6 decreased significantly after 6 months compared with that after 28 days. Therefore, it can be seen that the durability of the obtained concrete specimen blocks in Comparative Examples 1 - 6 is poor. From Examples 1 - 7 and Comparative Examples 3 - 6, it can be seen that different admixture components and dosages have an impact on the durability, compressive strength, crack - resistance strength, slump, and number of freeze - thaw cycles of concrete.

[0092] 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 "including", "comprising" 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 explicitly listed, or elements inherent to this process, method, article or device.

[0093] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A concrete admixture, characterized in that, It comprises the following raw materials in parts by weight: Water reducing agent: 15 - 25 parts; Redispersible latex powder: 20 - 35 parts; Modified silicon carbide fiber: 5 - 10 parts; Expansive agent: 0.5 - 2 parts; Retarding agent: 1 - 3 parts; Early strength agent: 0.5 - 1 part; Water: 30 - 45 parts; The modified silicon carbide fiber is prepared by the following steps: Add tris(hydroxymethyl)aminomethane into deionized water and stir, adjust the pH to 8 - 8.5, add modified dopamine, stir at room temperature for 2 - 3 h, add silicon carbide fiber and impregnate for 3 - 5 h, filter, wash, and dry to obtain the modified silicon carbide fiber; The modified dopamine is prepared by the following steps: Add aldehyde - modified cellulose and 1 - ethyl - (3 - dimethylaminopropyl)carbodiimide hydrochloride into phosphate buffer solution, stir and react for 0.5 - 1 h, then add N - hydroxysuccinimide, continue to stir for 0.5 - 1 h, add dopamine hydrochloride, and stir under nitrogen protection for 12 - 14 h. After the reaction is completed, wash and dry to obtain the modified dopamine.

2. The concrete admixture according to claim 1, characterized in that, The dosage ratio of tris(hydroxymethyl)aminomethane, deionized water, modified dopamine and silicon carbide fiber is 1.0 - 1.5 g: 100 mL: 0.2 - 0.3 g: 0.6 - 0.8 g.

3. The concrete admixture according to claim 1, characterized in that, The dosage ratio of aldehyde - modified cellulose, 1 - ethyl - (3 - dimethylaminopropyl)carbodiimide hydrochloride, phosphate buffer solution, N - hydroxysuccinimide and dopamine hydrochloride is 2.0 - 2.5 g: 3.36 - 3.40 g: 200 mL: 2.0 - 2.05 g: 0.53 - 0.55 g.

4. A concrete admixture according to claim 1, characterized in that, The water reducing agent is one of polycarboxylate water reducing agent, naphthalene - based water reducing agent and aliphatic water reducing agent.

5. A concrete admixture according to claim 1, characterized in that, The expansive agent is one of magnesium oxide and gypsum.

6. A concrete admixture according to claim 1, characterized in that, The retarding agent is one of organic retarding agent and inorganic retarding agent.

7. A concrete admixture according to claim 6, characterized in that, The organic retarding agent is at least one of sodium gluconate, sucrose and citric acid; the inorganic retarding agent is at least one of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate.

8. A concrete admixture according to claim 1, characterized in that, The early strength agent is at least one of nitrate, thiocyanate, nitrite, organic alkanolamine, thiosulfate and carboxylate.

9. The preparation method of a concrete admixture according to any one of claims 1-8, characterized in that, It comprises the following steps: Weigh according to parts by weight, mix the water reducing agent, redispersible latex powder, modified silicon carbide fiber, expansive agent, retarding agent, early strength agent and water, and stir evenly to obtain the concrete admixture.

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