Concrete admixture and preparation method thereof

Abstract

The 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 by weight: 15-25 parts of a water reducer, 20-35 parts of redispersible latex powder, 5-10 parts of modified silicon carbide fiber, 0.5-2 parts of an expanding agent, 1-3 parts of a retarder, 0.5-1 part of an early strength agent, and 30-45 parts of water. The preparation method comprises the following steps: weighing the water reducing agent, the redispersible latex powder, the modified silicon carbide fiber, the expanding agent, the retarder, the early strength agent and the water in parts by weight, mixing, and uniformly stirring to obtain the concrete admixture. The concrete admixture provided by the invention can improve the working performance and durability of concrete, improve the compressive strength and crack strength of the concrete and greatly prolong the service life of the concrete, and the preparation method is simple, economical in cost and suitable for large-scale production.

Description

Technical Field

[0001] The 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 today's construction field. It is everywhere in our lives, so 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 varieties of concrete admixtures with different functions. Using various varieties of admixtures can achieve different effects, such as improving the corrosion resistance of concrete, improving the brittleness of concrete, improving the freeze-thaw resistance of hardened concrete, greatly reducing the water consumption of concrete, improving the strength of concrete, compensating for the shrinkage of concrete, reducing the shrinkage cracks of concrete, extending the service life of concrete, and improving durability. The Chinese patent application document with patent application number CN106186795A discloses a special admixture for permeable concrete and its application, wherein the special admixture for permeable concrete includes the following mass percentage composition: polycarboxylic acid water reducer 10-20%, polycarboxylic acid slump retainer 5-25%, water retainer 0.5-3%, thickener 0.5-5%, retarder 1-5%, water 52-75%, the special admixture for permeable cement concrete described in the invention has good synergistic effect between the components, and on the basis of ensuring its permeability, the workability of permeable concrete can be better maintained to 2 hours or more. However, the water retaining agent used in the invention has poor chemical stability and is greatly affected by temperature. The heat released by concrete during mixing 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 patent application number CN106477962A discloses an admixture for cement-based permeable concrete, comprising the following components by weight: 5-6 parts of early-strength high-water-reducing polycarboxylic acid mother liquor, 2-3 parts of super-slow-release polycarboxylic acid mother liquor, 0.5-1 parts of early-strengthening agent, 0.5-1.5 parts of organic retarder, 0.1-0.5 parts of inorganic retarder, 3-10 parts of viscosity modifier, 0.1-0.5 parts of air entraining agent, 0.1-3 parts of defoamer, 0.1-0.5 parts of internal moisture regulator, 0.3-0.5 parts of surface moisture regulator, and 70-90 parts of water. The admixture can effectively improve the early strength and low slump retention capacity of cement-based permeable concrete, reduce the air content and water sensitivity of the fresh slurry, and increase its water retention and moisture retention. The invention uses a viscosity modifier to give the slurry good adhesion to the coarse aggregate, but it still causes the slurry to sink to the bottom during long-term transportation, and the admixture cost is relatively high. Summary of the invention

[0004] In order to improve the problem of poor early strength and shrinkage cracking of concrete in the prior art, the present invention provides a concrete admixture and a preparation method thereof.

[0005] The purpose 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] Expanding 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 2-3h, add silicon carbide fiber and soak for 3-5h, 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 greatly improve the strength and durability of concrete, but it has poor compatibility with other raw materials and is difficult to disperse evenly in the raw materials, resulting in a significant reduction in the effect of the admixture. In the above technical solution, dopamine is used to modify its surface coating, thereby improving the dispersibility and compatibility of silicon carbide in the raw materials.

[0016] As a preferred embodiment of the present invention, the usage 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 embodiment of the present invention, the modified dopamine is prepared by the following steps:

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

[0019] As a preferred embodiment of the present invention, the usage ratio of aldehyded 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 reducer is one of a polycarboxylic acid water reducer, a naphthalene-based water reducer and an aliphatic water reducer.

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

[0022] As a preferred embodiment of the present invention, the retarder is one of an organic retarder and an inorganic retarder. The addition of the retarder can effectively reduce the hydration heat and prolong the setting time of the 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 nitrate, thiocyanate, nitrite, organic alcohol amine, thiosulfate and carboxylate. The addition of early strength agent can improve the early strength of concrete, shorten the curing time, reduce cement dosage and economic cost.

[0025] A second aspect of the present invention provides a method for preparing a concrete admixture, comprising the following steps:

[0026] The water reducing agent, redispersible latex powder, modified silicon carbide fiber, expansion agent, retarder, early strength agent and water are weighed in parts by weight, mixed, and stirred evenly to obtain a concrete admixture.

[0027] Beneficial effects of the present invention:

[0028] A concrete admixture provided in the present invention is a mixture of a water reducing agent, a redispersible latex powder, a modified silicon carbide fiber, an expansion agent, a retarder, an early strength agent and water. The obtained admixture can greatly reduce the water consumption of concrete and improve the early strength of concrete. The addition of modified silicon carbide fiber can not only improve the microstructure of concrete, but also play a bridging role, absorb energy and play a reinforcing role when concrete cracks under load. Redispersible latex powder has a certain air entraining effect, and can introduce an appropriate amount of tiny closed bubbles into concrete. On the one hand, it can cut off the capillary passage in concrete, block the water evaporation channel, and reduce the water loss inside the concrete; on the other hand, it enhances the plasticity of concrete and relieves the plastic shrinkage pressure to a certain extent, thereby preventing early shrinkage and cracking of concrete to a certain extent.

[0029] The present invention provides a concrete admixture and a preparation method thereof. Through reasonable proportioning, the type and amount of the admixture suitable for concrete are optimized. Meanwhile, the preparation process is simple, the cost is low, and it is suitable for large-scale production. The provided admixture can improve the working performance and durability of concrete, increase the compressive strength and crack resistance of concrete, and greatly extend the service life of concrete. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

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

[0032] 100 g of cellulose (mass fraction 2.0%) was mixed with 1.0 g of sodium periodate, and the pH value was adjusted to 5.0 with HCl. Then, an oxidation reaction was carried out at a temperature of 50° C. under nitrogen protection with stirring in the dark. After a certain period of time, 2 mL of ethylene glycol was added dropwise to the system to terminate the reaction. The mixture was washed three times with deionized water to obtain aldehyded cellulose, which was freeze-dried for later use.

[0033] Example 1

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

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

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

[0037] S1. Add 2.0 g of formaldehyded cellulose and 3.36 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to 200 mL of phosphate buffer solution (pH = 5.7), stir and react for 0.5 h, then add 2.0 g of N-hydroxysuccinimide, continue stirring for 0.5 h, add 0.53 g of dopamine hydrochloride, and stir under nitrogen protection for 12 h. After the reaction is completed, wash with deionized water 3 times and dry to 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 soak for 3 h, filter, wash, and dry in an oven at 105 ° C for 8 h to obtain modified silicon carbide fiber.

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

[0040] The polycarboxylate water-reducing agent, redispersible latex powder, modified silicon carbide fiber, magnesium oxide, sodium gluconate, sodium nitrate and water are weighed in parts by weight, mixed, and stirred evenly to obtain a concrete admixture.

[0041] Example 2

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

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

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

[0045] Example 3

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

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

[0048] S2. Add 1.5 g of tris(hydroxymethyl)aminomethane (Tris) to 100 mL of deionized water and 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 fiber and soak for 3 h, filter, wash, and dry in an oven at 105 ° C for 8 h to obtain modified silicon carbide fiber.

[0049] Example 4

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

[0051] 5 parts of modified silicon carbide fibers were replaced with 7 parts of modified silicon carbide fibers.

[0052] Example 5

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

[0054] 5 parts of modified silicon carbide fibers were replaced with 10 parts of modified silicon carbide fibers.

[0055] Example 6

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

[0057] A concrete admixture, comprising the following components in parts by weight:

[0058] Polycarboxylic acid water reducer: 24 parts, redispersible latex powder: 30 parts, modified silicon carbide fiber: 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 only difference is:

[0061] A concrete admixture, comprising the following components in parts by weight:

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

[0063] Comparative Example 1

[0064] This comparison provides a concrete admixture, which includes the following components by weight:

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

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

[0067] The polycarboxylate water-reducing agent, redispersible latex powder, magnesium oxide, sodium gluconate, sodium nitrate and water are weighed in parts by weight, mixed, and stirred evenly to obtain a concrete admixture.

[0068] Comparative Example 2

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

[0070] A concrete admixture, comprising the following components in parts by weight:

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

[0072] Comparative Example 3

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

[0074] 5 parts of modified silicon carbide fibers were replaced with 3.5 parts of modified silicon carbide fibers.

[0075] Comparative Example 4

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

[0077] 5 parts of modified silicon carbide fibers were replaced with 11.5 parts of modified silicon carbide fibers.

[0078] Comparative Example 5

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

[0080] A concrete admixture, comprising the following components in parts by weight:

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

[0082] Comparative Example 6

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

[0084] A concrete admixture, comprising the following components in parts by weight:

[0085] Polycarboxylic acid water reducer: 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 to 7 and Comparative Examples 1 to 6 were subjected to application tests:

[0087] The admixtures obtained in Examples 1-7 and Comparative Examples 1-6 were mixed with concrete raw materials with water to form concrete slurry. After standard curing for 28 days, concrete specimens were prepared and their compressive strength was tested. The concrete specimens were placed in a high-salt service environment for 6 months and their compressive strength was tested again: (1) The compressive strength test was carried out according to the method specified in GB / T50081-2019 "Standard for Test Methods 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 for Test Methods 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 for Test Methods for Performance of Ordinary Concrete Mixtures".

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

[0089] Table 1

[0090]

[0091] It can be seen from Table 1 that, compared with Comparative Examples 1-2, the compressive strength, cracking strength, slump and number of frost resistance cycles of the concrete specimens obtained by adding water to the concrete raw materials of the concrete admixture in Example 1-7 are better than those of the concrete specimens in Comparative Examples 1-2. At the same time, the compressive strength of the concrete specimens in Comparative Examples 1-6 after 6 months is significantly reduced compared to the compressive strength after 28 days. Therefore, it can be seen that the durability of the concrete specimens obtained in Comparative Examples 1-6 is not good. It can be seen from Examples 1-7 and Comparative Examples 3-6 that the different admixture components and dosages have an impact on the durability, compressive strength, cracking strength, slump and number of frost resistance cycles of concrete.

[0092] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0093] 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 admixture, characterized in that: It includes 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; Expanding agent: 0.5-2 parts; Retarder: 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 trihydroxymethylaminomethane to deionized water and stir, adjust the pH to 8-8.5, add modified dopamine, stir at room temperature for 2-3 hours, add silicon carbide fiber and soak for 3-5 hours, filter, wash and dry to obtain modified silicon carbide fiber.

2. A 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. A concrete admixture according to claim 2, characterized in that: The modified dopamine is prepared by the following steps: Add aldehyded cellulose and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to a phosphate buffer solution, stir and react for 0.5-1h, then add N-hydroxysuccinimide, continue stirring for 0.5-1h, add dopamine hydrochloride, and stir under nitrogen protection for 12-14h. After the reaction is completed, wash and dry to obtain modified dopamine.

4. A concrete admixture according to claim 3, characterized in that: The dosage ratio of aldehyded 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.

5. A concrete admixture according to claim 1, characterized in that: The water reducer is one of a polycarboxylic acid water reducer, a naphthalene water reducer and an aliphatic water reducer.

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

7. A concrete admixture according to claim 1, characterized in that: The retarder is one of an organic retarder and an inorganic retarder.

8. A concrete admixture according to claim 7, characterized in that: 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.

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

10. A method for preparing a concrete admixture according to any one of claims 1 to 9, characterized in that: The following steps are involved: The water reducing agent, redispersible latex powder, modified silicon carbide fiber, expansion agent, retarder, early strength agent and water are weighed in parts by weight, mixed, and stirred evenly to obtain a concrete admixture.

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