Concrete composite expanding agent and preparation method thereof

Abstract

The invention provides a concrete composite expanding agent and a preparation method thereof, and belongs to the field of concrete admixtures. The concrete composite expanding agent comprises modified phosphogypsum, fly ash, bauxite, a modified oxide and an auxiliary agent, and is obtained by uniformly mixing the modified phosphogypsum, the fly ash, the bauxite, the modified oxide and the auxiliary agent which have different specific surface areas. According to the composite expanding agent, the modified ardealite and the fly ash synergistically provide an early-stage expansion source, early-stage shrinkage of concrete is compensated through calcium sulphoaluminate hydration products, meanwhile, modified magnesium oxide serves as a later-stage expansion source, magnesium hydroxide is generated through slow hydration, and long-term expansion compensation is achieved; the device has the advantages of good strength, compensation capability and the like; a large amount of industrial waste residues such as ardealite and fly ash are utilized, high-added-value utilization of the industrial waste residues is achieved, and remarkable economic benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the field of concrete admixtures, and particularly to a concrete composite expansive agent and a preparation method thereof. Background Art

[0002] During the initial setting or hardening process of concrete, due to factors such as the hydration or water loss of cement itself and temperature changes, the concrete structure shows phenomena such as dry shrinkage, cold shrinkage, and autogenous volume shrinkage, which affect the durability and safety of the structure. As a new type of concrete admixture, a concrete expansive agent generates crystals with an increased volume through the reaction of its own components with cement hydration, causing the concrete volume to expand and generating a certain prestress, which helps to compensate for the shrinkage cracking of the concrete and protect the concrete structure. Currently, the more commonly used expansive agents mainly include types such as calcium sulfoaluminate expansive agent, calcium oxide expansive agent, magnesium oxide expansive agent, and calcium oxide-calcium sulfoaluminate composite expansive agent, etc.

[0003] The calcium sulfoaluminate series of expansive agents generate an expansive effect by forming ettringite. However, its hydration and expansion rates are relatively fast, the expansion amount is large, and it is concentrated within 3 - 14 days. After 28 days, shrinkage will occur. It is suitable for scenarios where rapid shrinkage compensation is required. However, the expansion performance of this type of expansive agent is extremely sensitive to curing humidity and temperature. If early curing is insufficient or the later environment is dry, the formation amount of ettringite is limited and it is prone to decomposition, resulting in increased shrinkage in the later stage and even secondary cracking.

[0004] The composite expansive agent is obtained by co-grinding calcareous clinker, alunite, and gypsum in a certain proportion. The composite expansive agent will generate easily soluble Ca(OH)2, reducing the durability of the concrete, and its application in hydraulic engineering, marine engineering, or concrete projects with erosive media (sulfates) is restricted.

[0005] Magnesium oxide-based expansive agents have the advantages of a long expansion duration and stable later expansion, and are particularly suitable for mass concrete and structures in a humid environment for a long time. However, the hydration rate of magnesium oxide is greatly affected by the calcination temperature, mineral composition, and particle morphology: Magnesium oxide with low-temperature calcination has high activity but too fast hydration, which is prone to cause out-of-control early expansion; Magnesium oxide with high-temperature calcination has low activity, and the hydration process lags, and it may continue to expand for several years after the concrete hardens, leading to delayed cracking.

[0006] The above single-component expansive agents often have difficulty taking into account the expansion requirements and strength development at different ages, resulting in insufficient shrinkage compensation ability. Therefore, it is of great significance to develop a composite expansive agent with high strength and stable expansion performance. Summary of the Invention

[0007] To address the deficiencies of the prior art, the main objective of the present invention is to provide a concrete composite expansive agent and its preparation method. The composite expansive agent of the present invention can not only consume a large amount of industrial solid waste, but also balance early expansion and late compensatory shrinkage, solving the technical problems of the strength, compensatory ability, and overly rapid hydration reaction of concrete expansive agents.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A concrete composite expansive agent, comprising the following components in parts by weight: 30 - 50 parts of modified phosphogypsum, 20 - 30 parts of fly ash, 10 - 20 parts of bauxite, 20 - 35 parts of modified oxide, 3 - 5 parts of quicklime, and 1 - 3 parts of auxiliary agent.

[0009] Preferably, the modified phosphogypsum is prepared by crushing, high-temperature calcination, and reaction with a modifier.

[0010] More preferably, the preparation of the modified phosphogypsum is as follows: First, crush the phosphogypsum to a particle size less than 2 mm, then perform high-temperature calcination to obtain calcined phosphogypsum, and finally grind the calcined phosphogypsum with a modifier in a ball mill to obtain the modified phosphogypsum.

[0011] Preferably, the mass ratio of the calcined phosphogypsum to the modifier is 10:0.5 - 1.

[0012] Among them, the modifier includes at least one of aluminum sulfate and sodium carbonate.

[0013] Preferably, the bauxite is obtained by crushing, high-temperature calcination, and ball milling.

[0014] Preferably, the preparation of the bauxite is as follows: First, crush the bauxite to a particle size less than 2 mm, then perform high-temperature calcination and then ball milling.

[0015] Preferably, the auxiliary agent is a mixture of triethanolamine and polyacrylamide, with a mass ratio of 1:1 - 3.

[0016] Preferably, the specific surface area of the modified phosphogypsum ≥ 280 m 2 / kg, the specific surface area of the bauxite ≥ 350 m 2 / kg, the specific surface area of the fly ash ≥ 290 m 2 / kg, the specific surface area of the quicklime ≥ 350 m 2 / kg.

[0017] Preferably, the modified oxide is magnesium oxide coated with silica, and the preparation method is as follows: a. After high-temperature calcination of magnesite, place it in a ball mill for ball milling to obtain magnesium oxide particles; b. Disperse magnesium oxide particles in ethanol to form a magnesium oxide suspension; c. Add tetraethyl orthosilicate and ammonia water to ethanol to form a silica precursor solution; d. Slowly add the silica precursor solution to the oxide suspension, stir evenly, filter, wash and dry to obtain silica-coated magnesium oxide powder.

[0018] Preferably, the specific surface area of the magnesium oxide particles is greater than 200 m 2 / kg.

[0019] Preferably, the dosage ratio of the magnesium oxide particles to ethanol is 1 g:(1.5 - 2.5) ml; The volume ratio of the tetraethyl orthosilicate, ammonia water and ethanol is 2 - 3:1:5 - 15.

[0020] On the other hand, the present invention provides a preparation method of a concrete composite expansive agent, including: Mix the modified phosphogypsum, fly ash, bauxite, modified magnesium oxide, quicklime and additives evenly by weight to obtain the concrete composite expansive agent.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The composite expansive agent of the present invention uses modified phosphogypsum and fly ash as early expansion sources to compensate for the early shrinkage of concrete, and uses modified magnesium oxide as a late expansion source to compensate for the late shrinkage, which helps to improve the concrete structure; moreover, the preparation process of the expansive agent is simple and easy to implement, and turns waste into treasure, reducing environmental pollution and land occupation.

[0022] 2. The present invention calcines phosphogypsum and grinds it with aluminum sulfate for modification, effectively improving its activity and specific surface area, promoting the early hydration reaction, shortening the setting time and enhancing the gelling performance; using silica-coated magnesium oxide to control the hydration rate of magnesium oxide, avoiding local expansion stress and structural defects caused by too fast hydration of magnesium oxide, enabling the concrete to have a stable and appropriate early expansion rate in water, and effectively reducing shrinkage in air and maintaining long-term volume stability.

[0023] 3. The present invention optimizes the ratio of the specific surface area and dosage of each component of the composite expansive agent to achieve the synergistic cooperation of each component, so that the composite expansive agent has the advantages of controllable setting time, balanced strength development and controllable expansion rate, significantly improving the comprehensive performance of the concrete. Specific embodiments

[0024] Example 1: This embodiment provides a concrete composite expansive agent, which comprises the following components in parts by weight: 40 parts of modified phosphogypsum, 25 parts of fly ash, 15 parts of bauxite, 28 parts of modified magnesium oxide, 4 parts of quicklime, 0.6 part of triethanolamine, and 1.2 parts of polyacrylamide; the preparation of the concrete composite expansive agent is as follows: (1) Calcination of phosphogypsum: After crushing phosphogypsum to a particle size less than 2 mm, it is placed in a high-temperature furnace at 650 °C and kept warm for 1.5 h to obtain calcined phosphogypsum; the calcined phosphogypsum and aluminum sulfate are ground in a ball mill for 30 min to obtain modified phosphogypsum; wherein, the mass ratio of the calcined phosphogypsum to aluminum sulfate is 10:0.8, and the specific surface area of the modified phosphogypsum is 300 m 2 / kg; (2) Calcination of bauxite: Bauxite is crushed to a particle size less than 2 mm, placed in a high-temperature furnace at 700 °C, kept warm for 1.5 h, cooled to room temperature, and then placed in a ball mill and ball-milled to a specific surface area of 380 m 2 / kg to obtain bauxite powder; (3) Preparation of silica-coated magnesium oxide: a. After calcining magnesite at 700 °C for 1.5 h, it is placed in a ball mill to obtain magnesium oxide particles with a specific surface area greater than 200 m 2 / kg; b. Take 10 g of magnesium oxide particles and ultrasonically disperse them in 20 ml of ethanol to form a magnesium oxide suspension; c. Add 5 ml of tetraethyl orthosilicate and 2 ml of ammonia water to 20 ml of ethanol to form a silica precursor solution; d. Slowly add the silica precursor solution to the magnesium oxide suspension, stir evenly, filter and wash, dry at 45 °C for 2 h, cool to room temperature, and then place in a ball mill and ball-mill to a specific surface area of 310 m 2 / kg to obtain silica-coated magnesium oxide powder; (4) Preparation of the concrete composite expansive agent: Mix the modified phosphogypsum, fly ash, bauxite, modified magnesium oxide, quicklime, triethanolamine, and polyacrylamide evenly according to the parts by weight to obtain the concrete composite expansive agent; Among them, the specific surface area of fly ash is 310 m 2 / kg, and the specific surface area of quicklime is 370 m 2 / kg.

[0025] Example 2: This embodiment provides a concrete composite expansive agent, which comprises the following components in parts by weight: 30 parts of modified phosphogypsum, 20 parts of fly ash, 10 parts of bauxite, 20 parts of modified magnesium oxide, 3 parts of quicklime, 0.4 part of triethanolamine, and 0.8 part of polyacrylamide; The preparation of the concrete composite expansive agent is as follows: (1) Calcination of phosphogypsum: After crushing phosphogypsum to a particle size less than 2 mm, it is placed in a high-temperature furnace at 650 °C and kept warm for 1.5 h to obtain calcined phosphogypsum; The calcined phosphogypsum and aluminum sulfate are ground in a ball mill for 30 min to obtain modified phosphogypsum; Among them, the mass ratio of calcined phosphogypsum to aluminum sulfate is 10:0.5, and the specific surface area of the modified phosphogypsum is 280 m 2 / kg; (2) Calcination of bauxite: The bauxite is crushed to a particle size less than 2 mm, placed in a high-temperature furnace at 700 °C, kept warm for 1.5 h, cooled to room temperature, and then placed in a ball mill and ball-milled to a specific surface area of 350 m 2 / kg to obtain bauxite powder; (3) Preparation of magnesium oxide coated with silicon dioxide: a. After calcining magnesite at 700 °C for 1.5 h, it is placed in a ball mill to obtain magnesium oxide particles with a specific surface area greater than 200 m 2 / kg; b. Ultrasonically disperse 10 g of magnesium oxide particles in 20 ml of ethanol to form a magnesium oxide suspension; c. Add 5 ml of tetraethyl orthosilicate and 2 ml of ammonia water to 20 ml of ethanol to form a silicon dioxide precursor solution; d. Slowly add the silicon dioxide precursor solution to the magnesium oxide suspension, stir evenly, filter and wash, dry at 45 °C for 2 h, cool to room temperature, and then place in a ball mill and ball-mill to a specific surface area of 290 m 2 / kg to obtain magnesium oxide powder coated with silicon dioxide; (4) Preparation of concrete composite expansive agent: Mix the modified phosphogypsum, fly ash, bauxite, modified magnesium oxide, quicklime, triethanolamine, and polyacrylamide evenly according to the parts by weight to obtain the concrete composite expansive agent; Among them, the specific surface area of fly ash is 290 m 2 / kg, and the specific surface area of quicklime is 350 m 2 / kg.

[0026] Example 3: This embodiment provides a concrete composite expansive agent, which comprises the following components in parts by weight: 50 parts of modified phosphogypsum, 30 parts of fly ash, 20 parts of bauxite, 35 parts of modified magnesium oxide, 5 parts of quicklime, 0.8 part of triethanolamine, and 1.6 parts of polyacrylamide; the preparation of the concrete composite expansive agent is as follows: (1) Calcination of phosphogypsum: After crushing phosphogypsum to a particle size less than 2 mm, it is placed in a high-temperature furnace at 650 °C and kept warm for 1.5 h to obtain calcined phosphogypsum; the calcined phosphogypsum and aluminum sulfate are ground in a ball mill for 30 min to obtain modified phosphogypsum; wherein, the mass ratio of the calcined phosphogypsum to aluminum sulfate is 10:1, and the specific surface area of the modified phosphogypsum is 320 m 2 / kg; (2) Calcination of bauxite: Bauxite is crushed to a particle size less than 2 mm, placed in a high-temperature furnace at 700 °C, kept warm for 1.5 h, cooled to room temperature, and then placed in a ball mill and ground to a specific surface area of 400 m 2 / kg to obtain bauxite powder; (3) Preparation of magnesium oxide coated with silica: a. After calcining magnesite at 700 °C for 1.5 h, it is placed in a ball mill to obtain magnesium oxide particles with a specific surface area greater than 200 m 2 / kg; b. 10 g of magnesium oxide particles are ultrasonically dispersed in 20 ml of ethanol to form a magnesium oxide suspension; c. 5 ml of tetraethyl orthosilicate and 2 ml of ammonia water are added to 20 ml of ethanol to form a silica precursor solution; d. The silica precursor solution is slowly added to the magnesium oxide suspension, stirred evenly, filtered and washed, dried at 45 °C for 2 h, cooled to room temperature, and then placed in a ball mill and ground to a specific surface area of 350 m 2 / kg to obtain magnesium oxide powder coated with silica; (4) Preparation of the concrete composite expansive agent: The modified phosphogypsum, fly ash, bauxite, modified magnesium oxide, quicklime, triethanolamine, and polyacrylamide are mixed evenly according to the parts by weight to obtain the concrete composite expansive agent; Among them, the specific surface area of fly ash is 340 m 2 / kg, and the specific surface area of quicklime is 400 m 2 / kg.

[0027] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is only that the phosphogypsum in Comparative Example 1 is directly used without modification.

[0028] Comparative Example 2: The difference between Comparative Example 1 and Example 2 is only that: the magnesium oxide particles in Comparative Example 2 were not subjected to modification treatment but were directly used.

[0029] According to the GB23439-2009 standard, the concrete composite expansive agents prepared in Examples 1-3 and Comparative Examples 1-3 were tested using the prior art, and the test results are shown in Table 1 below.

[0030] Table 1 Test Results of Concrete Composite Expansive Agents

[0031] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A concrete composite expansion agent, characterized in that, It comprises the following components in parts by weight: 30 - 50 parts of modified phosphogypsum, 20 - 30 parts of fly ash, 10 - 20 parts of bauxite, 20 - 35 parts of modified magnesium oxide, 3 - 5 parts of quicklime, and 1 - 3 parts of additives.

2. A concrete composite expansion agent according to claim 1, characterized in that, The modified phosphogypsum is prepared by crushing, high-temperature calcination, and then reacting with a modifier.

3. A concrete composite expansion agent according to claim 1, characterized in that, The bauxite is obtained by crushing, high-temperature calcination, and ball milling.

4. A concrete composite expansion agent according to claim 1, characterized in that, The additives are a mixture of triethanolamine and polyacrylamide, and the mass ratio is 1:1 - 3.

5. A concrete composite expansion agent according to claim 1, characterized in that, The specific surface area of the modified phosphogypsum ≥ 280 m 2 / kg, the specific surface area of bauxite ≥ 350 m 2 / kg, the specific surface area of the fly ash ≥ 290 m 2 / kg, the specific surface area of quicklime ≥ 350 m 2 / kg.

6. A concrete composite expansion agent according to claim 1, wherein, The modified oxide is metal magnesium oxide coated with silica, and the preparation method is as follows: a. After high-temperature calcination of magnesite, it is placed in a ball mill for ball milling to obtain magnesium oxide particles; b. The magnesium oxide particles are dispersed in ethanol to form a magnesium oxide suspension; c. Tetraethyl orthosilicate and ammonia water are added to ethanol to form a silica precursor solution; d. The silica precursor solution is slowly added to the oxide suspension, stirred evenly, filtered, washed, and dried to obtain silica-coated magnesium oxide powder.

7. A concrete composite expansion agent according to claim 6, characterized in that, The specific surface area of the magnesium oxide particles is ≥ 200 m 2 / kg, and the specific surface area of the silica-coated magnesium oxide metal powder is ≥ 290 m 2 / kg.

8. A concrete composite expansive agent according to claim 6, characterized in that, The dosage ratio of the magnesium oxide particles to ethanol is 1 g:(1.5 - 2.5) ml.

9. A concrete composite expansive agent according to claim 6, characterized in that, The volume ratio of tetraethyl orthosilicate, ammonia water, and ethanol is 2 - 3:1:5 - 15.

10. The preparation method of the concrete composite expansion agent according to any one of claims 1-9, characterized in that, It comprises the following steps: The modified phosphogypsum, fly ash, bauxite, modified magnesium oxide, quicklime, and additives are mixed evenly by weight to obtain the concrete composite expansion agent.

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