Low-shrinkage low-heat mass concrete and preparation method thereof

Abstract

The low-shrinkage low-heat mass concrete is prepared from the following raw materials in parts by weight: 200 to 300 parts of cement, 5 to 10 parts of modified carbide slag, 100 to 180 parts of modified lithium slag powder, 600 to 900 parts of machine-made sand, 950 to 1100 parts of gravel, 140 to 170 parts of water and 6 to 11 parts of a water reducing agent, the specific surface area of the modified carbide slag is 400-600m < 2 > / kg, and the specific surface area of the modified lithium slag powder is 300-500m < 2 > / kg. Under the synergistic effect of doping a large amount of modified lithium slag powder and a small amount of modified carbide slag, the performance requirements of shrinkage-compensating concrete used for structures such as beams and slabs can still be met without using a concrete expanding agent; compared with a method for reducing the temperature rise in the concrete hydration process by using an admixture with a large mixing amount, such as coal ash mixing, the method has the advantages that the adiabatic temperature rise of the concrete is obviously reduced, favorable conditions are provided for controlling the temperature crack of the mass concrete, and the 28-day compressive strength is improved.

Description

A low-shrinkage, low-heat mass concrete and its preparation method Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a low-shrinkage, low-heat mass concrete and its preparation method. Background Technology

[0002] With the rapid development of my country's economy, investment in infrastructure and construction engineering has gradually increased, leading to a surge in large-scale and super-large-scale construction projects and large-area, large-volume concrete foundation projects. Mass concrete, as an important structural form in modern engineering construction, has been widely used in high-rise buildings, water conservancy and hydropower projects, bridges, and port structures. Mass concrete refers to large-volume concrete structures with a minimum solid dimension of 1 meter, or concrete that is expected to develop harmful cracks due to temperature changes and shrinkage caused by the hydration of cementitious materials. When mass concrete is poured, the hydration reaction of the cement releases a large amount of heat, causing a rapid rise in the internal temperature of the structure. Simultaneously, due to the poor thermal conductivity of mass concrete, this heat is difficult to dissipate in time, resulting in an imbalance in the internal and external temperature distribution of the concrete, forming temperature stress, and subsequently inducing temperature cracks within the concrete, severely affecting the service performance and durability of the concrete structure.

[0003] Currently, the main solutions to the problem of harmful cracking in large-volume concrete are to add calcium or magnesium expansive agents to reduce concrete shrinkage and to use low-heat cement or high-volume admixtures to reduce temperature rise during hydration and prevent temperature cracks. However, expansive agents are energy-intensive additives, leading to high concrete costs and energy consumption. Adding other admixtures in large quantities can compromise the concrete's compressive strength and other properties. Therefore, there is an urgent need to find a low-shrinkage, low-heat large-volume concrete to address the problems of harmful cracking, high cost, and high energy consumption during the solidification process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a low-shrinkage and low-heat large-volume concrete, thereby solving the problems of harmful cracks, high cost and high energy consumption in the solidification and molding process of large-volume concrete.

[0005] The technical solution adopted by this invention to solve its technical problem is: a low-shrinkage, low-heat, large-volume concrete, the raw materials comprising, by weight: 200-300 parts cement, 5-10 parts modified calcium carbide slag, 100-180 parts modified lithium slag powder, 600-900 parts manufactured sand, 950-1100 parts crushed stone, 140-170 parts water, and 6-11 parts water-reducing agent; the specific surface area of ​​the modified calcium carbide slag is 400-600 m².2 / kg, the specific surface area of ​​the modified lithium slag powder is 300-500m². 2 / kg.

[0006] Furthermore, the modified calcium carbide slag is obtained by drying calcium carbide slag and then grinding it to a specific surface area of ​​400-600 m². 2 / kg.

[0007] Furthermore, the modified lithium slag powder is prepared by pre-impregnating, acid washing, water washing, solid-liquid separation, drying, and grinding raw lithium slag to a specific surface area of ​​300-500 m². 2 / kg was obtained.

[0008] Furthermore, the pre-soaking is performed by soaking in a dilute sulfuric acid solution or water with a mass concentration of ≤5% for 4 to 8 hours at room temperature, with the mass ratio of the dilute sulfuric acid solution or water to the undisturbed lithium slag being 2 to 3:1.

[0009] Furthermore, the acid washing refers to adding the pre-impregnated lithium slag to a 10%–25% dilute sulfuric acid solution and stirring at 40–80°C for 6–10 hours, with the mass ratio of the dilute sulfuric acid solution to the pre-impregnated lithium slag being 2–3:1.

[0010] Furthermore, the water washing involves filtering the acid-washed lithium slag, washing it with clean water at room temperature with stirring 2-4 times, and then obtaining solid residue by suction filtration, pressure filtration, or centrifugation. After drying, this residue is ground in a ball mill with powdered polycarboxylate superplasticizer as a grinding aid to a specific surface area of ​​300-500 m². 2 / kg, thus obtaining modified lithium slag.

[0011] Furthermore, the cement is ordinary Portland cement P·O42.5R.

[0012] Furthermore, the water-reducing agent is a high-performance polycarboxylate water-reducing agent with a water reduction rate of ≥25%.

[0013] Furthermore, the manufactured sand is medium sand from Zone II, with a fineness modulus of 2.7, an MB value of 0.6, and a powder content of 5.3%; the crushed stone is 5-25mm continuously graded crushed stone with a crushing index value of 6.2%.

[0014] A method for preparing low-shrinkage, low-heat mass concrete as described in any of the above claims includes the following steps:

[0015] S1. After drying, the carbide slag is ground to a specific surface area of ​​400-600 m². 2 / kg, to obtain modified carbide slag;

[0016] S2. The raw lithium slag is pre-soaked, acid-washed, water-washed, solid-liquid separated, dried, and ground to a specific surface area of ​​300-500 m². 2 / kg yielded modified lithium slag;

[0017] S3. Add cement, modified calcium carbide slag, modified lithium slag powder, manufactured sand, and crushed stone to the concrete mixer according to the proportions, and mix evenly.

[0018] S4. Add the water-reducing agent to the water, mix well, and then pour it into the concrete mixer. Mix well to obtain low-shrinkage, low-heat, large-volume concrete.

[0019] The beneficial effects of this invention are as follows: The low-shrinkage and low-heat mass concrete of this invention, through the synergistic effect of adding a large amount of modified lithium slag powder and a small amount of modified carbide slag, can still meet the performance requirements of shrinkage-compensating concrete for beams and slabs without the use of concrete expansion agents; it significantly reduces the adiabatic temperature rise of concrete, providing favorable conditions for controlling temperature cracks in mass concrete; compared with the method of using large amounts of admixtures to reduce the temperature rise during the hydration process of concrete, such as adding fly ash, it improves the 28-day compressive strength.

[0020] This invention solves the problem of temperature cracks inside large-volume concrete by simply using a suitable ratio of modified carbide slag and modified lithium slag powder, reducing the use of other high-energy-consuming additives and cement, significantly reducing production costs, and contributing to the green development of the concrete and related industries. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments.

[0022] The raw material proportions for the examples and comparative examples are shown in Table 1. Mass concrete was prepared according to the following steps.

[0023] A method for preparing low-shrinkage, low-heat, large-volume concrete includes the following steps:

[0024] S1. The wet-process calcium carbide slag produced in the acetylene industry is dried to constant weight at 105℃, and then ground to a specific surface area of ​​480 m². 2 / kg, to obtain modified carbide slag;

[0025] S2. Take 100 parts of the raw lithium slag (dry weight), a byproduct of lithium battery production using the sulfuric acid process after high-temperature roasting of spodumene, and add it to 300 parts of a 3% dilute sulfuric acid solution. Pre-soak at room temperature for 6 hours to obtain a pre-soaked lithium slag slurry. Then, pour the pre-soaked lithium slag slurry into 900 parts of a 15% dilute sulfuric acid solution, heat to 60°C and stir for 8 hours. Subsequently, obtain acid-washed lithium slag by vacuum filtration. Wash the acid-washed lithium slag three times with water, stirring, and filter to obtain modified wet lithium slag. Dry the modified wet lithium slag at 105°C to constant weight, and then grind it using a ball mill to achieve a specific surface area of ​​410 m². 2 / kg, to obtain modified lithium slag powder;

[0026] S3. According to the proportion, add cement, modified carbide slag, modified lithium slag powder, manufactured sand, and crushed stone to a concrete mixer and mix evenly; the cement is ordinary Portland cement P·O42.5R, with a 3-day compressive strength of 28.9 MPa and a 28-day compressive strength of 50.2 MPa; the manufactured sand is Zone II medium sand with a fineness modulus of 2.7, an MB value of 0.6, and a powder content of 5.3%; the crushed stone is 5-25mm continuously graded crushed stone with a crushing index value of 6.2%; the water-reducing agent is a high-performance polycarboxylate water-reducing agent with a water reduction rate of ≥25% and a solid content of 13%;

[0027] S4. Add the water-reducing agent to the water, mix well, and then pour it into the concrete mixer. Mix for 2 minutes to obtain low-shrinkage, low-heat, large-volume concrete.

[0028] Table 1 (Unit: kg)

[0029] Water-modified carbide slag, original carbide slag, modified lithium slag powder, original lithium slag powder, fly ash, manufactured sand, crushed stone, water-reducing agent. Example 1: 170 206 100 1440 0 82 3 1040 7.2. Example 2: 165 23 280 1600 0 77 7 1060 8.4. Example 3: 160 265 50 1800 0 720 1080 9.9. Comparative Example 1: 170 3600 000 0 82 3 1040 7.2. Comparative Example 2: 170 21600 0 1448 23 1040 7.2. Comparative Example 3: 170 21600 Comparative Example 4: 1440082310407.2; Comparative Example 5: 17035010000082310407.2; Comparative Example 6: 1702060101440082310407.2; Comparative Example 7: 1702061000144082310407.2; Comparative Example 8: 170266100840082310407.2; Comparative Example 9: 1701962001440082310407.2 surface

[0030] The fly ash is Class II fly ash, with a water requirement ratio of 102%, a 28-day activity of 73%, a fineness of 20%, and a loss on ignition of 4.2%.

[0031] The performance of the large-volume concrete obtained in the examples and comparative examples was tested and specimens were prepared. The sample preparation and performance testing were carried out in accordance with the standards GB / T 50080, GB / T 50081 and GB 50119. The 7-day and 28-day compressive strength tests were conducted under standard curing conditions. The results are shown in Tables 2 and 3.

[0032] Table 2

[0033]

[0034]

[0035] Table 3

[0036]

[0037] By comparing Example 1 and Comparative Example 1 (using net cement), the present invention can ensure that the 28-day compressive strength of concrete remains basically unchanged while significantly reducing the amount of cement used, and at the same time significantly reduce the adiabatic temperature rise and shrinkage rate.

[0038] By comparing Example 1 and Comparative Example 2 (using a large amount of fly ash), the present invention has the advantages of high 28-day compressive strength and low shrinkage compared with the mix proportion technology (using a large amount of fly ash) commonly used in current engineering to control the thermal temperature rise of concrete.

[0039] By comparing Example 1 and Comparative Example 3 (without modified calcium carbide slag), modified calcium carbide slag is beneficial to the activation of modified lithium slag. At the same time, the synergistic effect of modified calcium carbide slag and modified lithium slag can significantly reduce shrinkage.

[0040] By comparing Example 1 with Comparative Examples 2 and 4 (using an equal amount of fly ash instead of modified lithium slag powder), it was found that modified carbide slag is beneficial for activating fly ash activity, but the improvement is less than that of modified lithium slag powder. Modified carbide slag and fly ash did not show a synergistic effect similar to that of modified carbide slag and modified lithium slag.

[0041] By comparing Example 1 with Comparative Examples 1 and 5 (which used the same amount of cement instead of modified lithium slag powder), it was found that modified carbide slag did not have an activating and enhancing effect in the clean cement system.

[0042] By comparing Example 1 and Comparative Example 6 (modified calcium carbide slag was replaced with undisturbed calcium carbide slag), the modification of undisturbed calcium carbide slag is beneficial to the workability of concrete, which can improve the fluidity and fluidity retention of concrete. It is also beneficial to the activation efficiency of modified lithium slag powder by calcium carbide slag.

[0043] By comparing Example 1 and Comparative Example 7 (modified lithium slag powder was replaced with undisturbed lithium slag), the modification of undisturbed lithium slag is beneficial to the workability of concrete and can significantly improve the fluidity and fluidity retention of concrete.

[0044] Compared with Example 1 and Comparative Example 8 (reduced amount of modified lithium slag), as the amount of lithium slag decreased and the amount of cement increased, the adiabatic temperature rise of concrete increased significantly, which is not conducive to temperature control of large-volume concrete.

[0045] By comparing Example 1 and Comparative Example 9 (increasing the amount of modified carbide slag), the excessive amount of modified carbide slag resulted in decreased workability, increased 7-day strength, and a significant increase in adiabatic temperature rise, which is not conducive to temperature control of large-volume concrete.

[0046] In summary, the workability of carbide slag and lithium slag in concrete can be significantly improved through modification; at the same time, the shrinkage of concrete can be significantly reduced through the synergistic effect of modified carbide slag and modified lithium slag powder; and the concrete strength can be maintained while reducing the adiabatic temperature rise by using a large amount of lithium slag.

Claims

1. A low-shrinkage, low-heat, large-volume concrete, characterized in that, The raw materials, by weight, include: 200-300 parts cement, 5-10 parts modified calcium carbide slag, 100-180 parts modified lithium slag powder, 600-900 parts manufactured sand, 950-1100 parts crushed stone, 140-170 parts water, and 6-11 parts water-reducing agent; the modified calcium carbide slag has a specific surface area of ​​400-600 m². 2 / kg, the specific surface area of ​​the modified lithium slag powder is 300-500m². 2 / kg.

2. The low-shrinkage, low-heat, large-volume concrete according to claim 1, characterized in that: The modified calcium carbide slag is obtained by drying calcium carbide slag and then grinding it to a specific surface area of ​​400-600 m². 2 / kg.

3. The low-shrinkage, low-heat, large-volume concrete according to claim 1, characterized in that: The modified lithium slag powder is produced by pre-soaking, acid washing, water washing, solid-liquid separation, drying, and grinding of undisturbed lithium slag to a specific surface area of ​​300-500 m². 2 / kg was obtained.

4. The low-shrinkage, low-heat, large-volume concrete according to claim 3, characterized in that: The pre-soaking process involves soaking the lithium slag in a dilute sulfuric acid solution or water with a mass concentration of ≤5% for 4–8 hours at room temperature, with the mass ratio of the dilute sulfuric acid solution or water to the undisturbed lithium slag being 2–3:

1.

5. The low-shrinkage, low-heat, large-volume concrete according to claim 3, characterized in that: The acid washing refers to adding the pre-impregnated lithium slag to a 10%–25% dilute sulfuric acid solution and stirring at 40–80°C for 6–10 hours. The mass ratio of the dilute sulfuric acid solution to the pre-impregnated lithium slag is 2–3:

1.

6. The low-shrinkage, low-heat, large-volume concrete according to claim 3, characterized in that: The water washing process involves filtering the acid-washed lithium slag, then washing it 2-4 times with clean water at room temperature with stirring. Solid residue is then obtained by suction filtration, pressure filtration, or centrifugation. After drying, this residue is ground in a ball mill with powdered polycarboxylate superplasticizer as a grinding aid to a specific surface area of ​​300-500 m². 2 / kg, thus obtaining modified lithium slag.

7. The low-shrinkage, low-heat, large-volume concrete according to claim 1, characterized in that: The cement is ordinary Portland cement P·O42.5R.

8. The low-shrinkage, low-heat, large-volume concrete according to claim 1, characterized in that: The water-reducing agent is a high-performance polycarboxylate water-reducing agent with a water reduction rate of ≥25%.

9. The low-shrinkage, low-heat, large-volume concrete according to claim 1, characterized in that: The manufactured sand is medium sand from Zone II, with a fineness modulus of 2.7, an MB value of 0.6, and a powder content of 5.3%; the crushed stone is 5-25mm continuously graded crushed stone with a crushing index value of 6.2%.

10. A method for preparing low-shrinkage, low-heat, large-volume concrete according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. After drying, the carbide slag is ground to a specific surface area of ​​400-600 m². 2 / kg, to obtain modified carbide slag; S2. The raw lithium slag is pre-soaked, acid-washed, water-washed, solid-liquid separated, dried, and ground to a specific surface area of ​​300-500 m². 2 / kg yielded modified lithium slag; S3. Add cement, modified carbide slag, modified lithium slag powder, manufactured sand, and crushed stone to the concrete mixer according to the proportions, and mix evenly; S4. Add water-reducing agent to water, mix evenly, and then pour into the concrete mixer and mix evenly to obtain low-shrinkage, low-heat, large-volume concrete.

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