A method for efficiently activating and regenerating micropowder assisted by silicone carbide

Abstract

The present invention discloses a method for efficiently activating and regenerating micro powder assisted by silicone carbide. The silicone is dispersed in the regenerated micro powder to obtain modified regenerated micro powder. The modified regenerated micro powder is used as an auxiliary cementitious material and replaces cement according to a conventional proportion to prepare a cement concrete specimen. A gas containing carbon dioxide is continuously introduced into the closed space for curing the specimen. During this process, the silicone synergistically carbonizes and activates the regenerated micro powder, and simultaneously fixes the carbon dioxide in the gas. The present invention significantly improves the activity of the regenerated micro powder by assisting the carbonization of the silicone carbide, absorbs the carbon dioxide in the gas, and promotes the resource utilization of solid waste and carbon sequestration.

Description

Technical Field

[0001] The present invention belongs to the field of activation application and carbon sequestration of recycled fine powder of waste concrete, and specifically relates to a method for efficiently activating recycled fine powder with the assistance of silicone for carbonization. Background Art

[0002] Recycled coarse aggregate and recycled fine aggregate that can be prepared by crushing and sorting waste concrete can already be applied to low-strength concrete projects, but 10-20% of the finer powder particles in the production process have not been effectively utilized.

[0003] The activity of the recycled fine powder generated during the crushing of waste concrete is generally low, and efficient activation technology is urgently needed to improve its utilization rate. Many studies have been carried out at home and abroad on carbonization activation of recycled fine powder. After carbonization, the recycled fine powder can generate substances such as calcium carbonate and silica gel. Calcium carbonate can fill the pores of the system to increase the density, and silica gel can promote the formation of more hydration products. Chinese Patent CN112125541B discloses a method for wet carbonization activation of recycled fine powder of waste concrete and the application of the recycled fine powder. In this method, the recycled fine powder and water are formed into a mixed slurry, and industrial waste gas containing carbon dioxide is continuously introduced into the mixed slurry, and highly active recycled fine powder is obtained through mineralization. In this patent, a large amount of water is required to form the convection of carbon dioxide and water, and continuous stirring needs to be maintained, resulting in excessive energy consumption, cumbersome operation, and low improvement in the activity of the recycled fine powder. Summary of the Invention

[0004] The object of the present invention is to address the technical problems such as low activity of recycled fine powder in the prior art, and propose a method for efficiently activating recycled fine powder with the assistance of silicone for carbonization, which modifies the recycled fine powder with silicone and uses carbonization to assist in stimulating the activity of the recycled fine powder.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In the method for efficiently activating recycled fine powder with the assistance of silicone for carbonization of the present invention, silicone is dispersed in the recycled fine powder generated during the crushing of waste concrete to obtain modified recycled fine powder. The modified recycled fine powder is used as an auxiliary cementitious material and replaces cement according to the conventional proportion to prepare cement concrete specimens. In the closed space for curing the specimens, a gas containing carbon dioxide and water vapor is continuously introduced. During this process, the silicone synergistically carbonizes and activates the recycled fine powder, and at the same time fixes the carbon dioxide in the gas.

[0007] The recycled fine powder is particles with a particle size less than 150 microns generated during the crushing of waste concrete.

[0008] The silicone is one or more of alkyl silicate, alkyl siloxane silane, and polyalkyl hydroxy siloxane.

[0009] The mass ratio of the silicone to the recycled fine powder is 0.0001~0.01:1.

[0010] The stirring and mixing time of the silicone and the recycled fine powder is 0.1~1.5 h.

[0011] In the environment containing carbon dioxide and water vapor, the volume fraction of carbon dioxide ≥5%, and the volume fraction of water vapor ≥10%.

[0012] During the curing process, the environmental temperature is controlled at 5~50 °C.

[0013] In the present invention, the silicone is adsorbed on the surface of the recycled fine powder particles. The silicone can continuously generate salts that increase the alkalinity of the pore solution of the cement-based material in an environment with low-concentration carbon dioxide, promoting the activation of the recycled fine powder. At the same time, the negative effect of the retardation of the silicone on the strength is eliminated. During the application process, the carbon fixation amount of the recycled fine powder can be significantly increased. The present invention also has the following advantages:

[0014] (1) The activation process of the recycled fine powder proposed by the present invention is simple and low-cost, and can be applied to the production of factory precast components. Compared with the existing chemical activation and carbonation activation of recycled fine powder, the activation technology is more easily promoted to industrial production and use, which helps to solve the problems of difficult utilization and low utilization rate of recycled fine powder at the present stage;

[0015] (2) The present invention significantly improves the activity of the recycled fine powder, reduces the adverse effects of directly mixing the recycled fine powder into cement concrete, broadens its engineering application scope, and the process of the present invention is low-carbon and environmentally friendly, significantly increasing the carbon fixation amount of carbon dioxide in the recycled fine powder, and has broad application prospects. Description of the Drawings

[0016] Figure 1 It is an infrared spectrum analysis diagram of the recycled fine powder and the modified recycled fine powder in Example 1.

[0017] Figure 2 It is a scanning electron microscope diagram of the microstructure of the recycled fine powder composite cement paste prepared in Example 1 and Comparative Examples 1 to 3 after curing. Detailed Embodiments

[0018] The technical solutions of the present invention will be described in detail below with reference to the drawings and in combination with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Without conflict, the features in the embodiments of the present invention can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0019] To illustrate the effects of the efficient utilization of recycled fine powder proposed by the present invention, in the examples and comparative examples, the recycled fine powder before and after modification was used as an auxiliary cementitious material, and carbonation curing and natural curing were carried out. Examples 1 and Comparative Examples 1 to 3, Examples 2 and Comparative Examples 4 to 6 are to illustrate the effect of the improved activity of the modified recycled fine powder when used as an auxiliary cementitious material with carbonation curing; Examples 1 and Comparative Example 3, Examples 2 and Comparative Example 6, Examples 4 and Comparative Examples 8 and 9 are to illustrate the degree of improvement in the carbon sequestration performance of the modified recycled fine powder with carbonation curing; Examples 3 and Comparative Example 7, Examples 4 and Comparative Examples 8 to 9 are to illustrate the effects of the amount of silicone and the carbon dioxide concentration on the activation effect and the improvement of the carbon sequestration performance of the recycled fine powder. Example 5 and Comparative Example 10 are to illustrate the influence of the type of silicone on the activation effect of the recycled fine powder.

[0020] The compressive strength was used to evaluate the effect of activation. The strength test was carried out in accordance with GB / T 17671-1999 "Test Method for Cement Mortar Strength (ISO Method)"; the percentage of mass loss at 500-900 °C was used to illustrate the amount of carbon dioxide sequestered. The specific method was to crush and grind the specimen into powder, weigh 2.00 g of the powder, heat it at 500 °C for 1 h, measure the mass of the residue m1, heat it again at 900 °C for 1 h, and the mass of the residue was called m2. The mass loss at 500-900 °C could be expressed as the amount of carbon dioxide sequestered, and the calculation method was (m1 - m2) / m1.

[0021] Example 1:

[0022] Octyltriethoxysilane and recycled fine powder were stirred at a mass ratio of 0.0005:1 for 1 h to obtain modified recycled fine powder. The modified recycled fine powder was used as an auxiliary cementitious material. The modified recycled fine powder, water and ordinary Portland cement were mixed and stirred evenly at a mass ratio of 1:1:1.5 to prepare a composite cement paste, which was poured into a 4 mm × 4 mm × 4 mm mold for molding. After demolding in 1 day, the specimens were placed in an environment with a temperature of 20 °C, containing 20% carbon dioxide and 50% water vapor for curing for 7 d. The compressive strength of the specimens after curing was measured, and the crushed specimens were ground into powder to measure the amount of carbon dioxide sequestered.

[0023] Comparative Example 1:

[0024] The recycled fine powder was used as an auxiliary cementitious material. The recycled fine powder, water and ordinary Portland cement were mixed and stirred evenly at a mass ratio of 1:1:1.5 to prepare a composite cement paste, which was poured into a 4 mm × 4 mm × 4 mm mold for molding. After demolding in 1 day, the specimens were placed in an environment with a temperature of 20 °C and containing 50% water vapor for curing for 7 d, and the compressive strength after curing was tested.

[0025] Comparative Example 2:

[0026] Octyltriethoxysilane and recycled micropowder were stirred at a mass ratio of 0.0005:1 for 1 h to obtain modified recycled micropowder. The modified recycled micropowder was used as an auxiliary cementitious material. The modified recycled micropowder, water, and ordinary Portland cement were mixed and stirred evenly at a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm × 4 mm × 4 mm mold and forming, it was demolded after 1 day. The specimens were placed in an environment with a temperature of 20°C and 50% water vapor for curing for 7 days, and the compressive strength after curing was tested.

[0027] Comparative Example 3:

[0028] The recycled micropowder was used as an auxiliary cementitious material. The recycled micropowder, water, and ordinary Portland cement were mixed and stirred evenly at a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm × 4 mm × 4 mm mold and forming, it was demolded after 1 day. The specimens were placed in an environment with a temperature of 20°C, 20% carbon dioxide, and 50% water vapor for curing for 7 days, and the compressive strength after curing was tested. The crushed specimens were ground into powder to determine the carbon dioxide fixation amount.

[0029] Example 2:

[0030] Potassium ethyl silicate and recycled micropowder were stirred at a mass ratio of 0.005:1 for 0.3 h to obtain modified recycled micropowder. The modified recycled micropowder was used as an auxiliary cementitious material. The modified recycled micropowder, water, and ordinary Portland cement were mixed and stirred evenly at a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm × 4 mm × 4 mm mold and forming, it was demolded after 1 day. The specimens were placed in an environment with a temperature of 35°C, 70% carbon dioxide, and 20% water vapor for curing for 7 days, and the compressive strength after curing was tested. The crushed specimens were ground into powder to determine the carbon dioxide fixation amount.

[0031] Comparative Example 4:

[0032] The recycled micropowder was used as an auxiliary cementitious material. The recycled micropowder, water, and ordinary Portland cement were mixed and stirred evenly at a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm × 4 mm × 4 mm mold and forming, it was demolded after 1 day. The specimens were placed in an environment with a temperature of 35°C and 20% water vapor for curing for 7 days, and the compressive strength after curing was tested.

[0033] Comparative Example 5:

[0034] Potassium ethyl silicate and recycled fine powder are stirred according to a mass ratio of 0.005:1, and the mixing time is 0.3 h to obtain modified recycled fine powder. The modified recycled fine powder is used as an auxiliary cementitious material. The modified recycled fine powder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm×4 mm×4 mm mold and forming, it is demolded after 1 day. The specimens are placed in an environment with a temperature of 35°C and 20% water vapor for curing for 7 days, and the compressive strength after curing is tested.

[0035] Comparative Example 6:

[0036] The recycled fine powder is used as an auxiliary cementitious material. The recycled fine powder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm×4 mm×4 mm mold and forming, it is demolded after 1 day. The specimens are placed in an environment with a temperature of 35°C, 70% carbon dioxide and 20% water vapor for curing for 7 days, and the compressive strength after curing is tested. The crushed specimens are ground into powder to determine the carbon dioxide storage.

[0037] Example 3:

[0038] Potassium ethyl silicate and recycled fine powder are stirred according to a mass ratio of 0.01:1, and the mixing time is 0.3 h to obtain modified recycled fine powder. The modified recycled fine powder is used as an auxiliary cementitious material. The modified recycled fine powder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm×4 mm×4 mm mold and forming, it is demolded after 1 day. The specimens are placed in an environment with a temperature of 35°C, 10% carbon dioxide and 10% water vapor for curing for 7 days, and the compressive strength after curing is tested. The crushed specimens are ground into powder to determine the carbon dioxide storage.

[0039] Comparative Example 7:

[0040] Potassium ethyl silicate and recycled fine powder are stirred according to a mass ratio of 0.01:1, and the mixing time is 0.3 h to obtain modified recycled fine powder. The modified recycled fine powder is used as an auxiliary cementitious material. The modified recycled fine powder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste. After casting into a 4 mm×4 mm×4 mm mold and forming, it is demolded after 1 day. The specimens are placed in an environment with a temperature of 35°C, 70% carbon dioxide and 20% water vapor for curing for 7 days, and the compressive strength after curing is tested. The crushed specimens are ground into powder to determine the carbon dioxide storage.

[0041] Example 4:

[0042] Potassium ethyl silicate and recycled micropowder are stirred according to a mass ratio of 0.0003:1, and the mixing time is 0.3 h to obtain modified recycled micropowder. The modified recycled micropowder is used as an auxiliary cementitious material. The modified recycled micropowder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste, which is poured into a 4 mm×4 mm×4 mm mold for molding. After demolding in 1 day, the specimens are placed in an environment with a temperature of 35 °C, containing 70% carbon dioxide and 20% water vapor for curing until 7 d, and the compressive strength after curing is tested.

[0043] Comparative Example 8:

[0044] Potassium ethyl silicate and recycled micropowder are stirred according to a mass ratio of 0.006:1, and the mixing time is 0.3 h to obtain modified recycled micropowder. The modified recycled micropowder is used as an auxiliary cementitious material. The modified recycled micropowder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste, which is poured into a 4 mm×4 mm×4 mm mold for molding. After demolding in 1 day, the specimens are placed in an environment with a temperature of 35 °C, containing 70% carbon dioxide and 20% water vapor for curing until 7 d, and the compressive strength after curing is tested.

[0045] Comparative Example 9:

[0046] Potassium ethyl silicate and recycled micropowder are stirred according to a mass ratio of 0.009:1, and the mixing time is 0.3 h to obtain modified recycled micropowder. The modified recycled micropowder is used as an auxiliary cementitious material. The modified recycled micropowder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste, which is poured into a 4 mm×4 mm×4 mm mold for molding. After demolding in 1 day, the specimens are placed in an environment with a temperature of 35 °C, containing 70% carbon dioxide and 20% water vapor for curing until 7 d, and the compressive strength after curing is tested.

[0047] Example 5:

[0048] Potassium ethyl silicate and recycled micropowder are stirred according to a mass ratio of 0.008:1, and the mixing time is 0.3 h to obtain modified recycled micropowder. The modified recycled micropowder is used as an auxiliary cementitious material. The modified recycled micropowder, water and ordinary Portland cement are mixed and stirred evenly according to a mass ratio of 1:1:1.5 to prepare a composite cement paste, which is poured into a 4 mm×4 mm×4 mm mold for molding. After demolding in 1 day, the specimens are placed in an environment with a temperature of 35 °C, containing 70% carbon dioxide and 20% water vapor for curing until 7 d, and the compressive strength after curing is tested.

[0049] Comparative Example 10:

[0050] Stir dimethyldiethoxysilane and recycled micro powder in a mass ratio of 0.008:1 for 0.3 h to obtain modified recycled micro powder. Use the modified recycled micro powder as an auxiliary cementitious material. Mix the modified recycled micro powder, water and ordinary Portland cement in a mass ratio of 1:1:1.5 and stir evenly to prepare a composite cement paste. Pour it into a mold of 4 mm×4 mm×4 mm for molding. Demold after 1 day. Place the specimens in an environment with a temperature of 35°C, containing 70% carbon dioxide and 20% water vapor for curing until 7 d, and test their compressive strength after curing.

[0051] Analyze the performance changes of the recycled micro powder before and after activation in Examples 1 and 2 and Comparative Examples 1 to 6 based on the compressive strength and carbon dioxide carbon sequestration of the examples and comparative examples, and conduct infrared spectroscopy and scanning electron microscopy tests on some samples. As Figure 1 shown, it can be seen that the vibration peak at 1265 cm -1 is the vibration peak of the Si-C group, and the vibration peak at 2851 cm -1 is the vibration peak of the C-H group. Compared with the unmodified recycled micro powder, weak absorption peaks can be seen at 1265 cm -1 and 2851 cm -1 in the infrared spectrum analysis of the modified recycled micro powder, indicating that the organosilicon has been successfully modified by being grafted onto the surface of the recycled micro powder. Conduct scanning electron microscopy tests on the composite cement paste of Example 1 and Comparative Examples 1 to 3. As Figure 2 shown, it can be seen that the composite cement paste of Comparative Examples 1 to 3 contains more pores, while the surface of Example 1 is smooth and the hydration products are dense, with basically no pores, indicating that carbonation assisted by organosilicon activation of recycled micro powder promotes the generation of a large amount of hydration products, optimizes the pore structure, and promotes the development of strength.

[0052] The measured compressive strengths of the composite cement paste of Examples 1 and 2 and Comparative Examples 1 to 6 are shown in Table 1 below:

[0053]

[0054] As can be seen from Table 1, the method proposed by the present invention can significantly improve the activity of recycled fine powder. It can be seen that in natural curing, directly incorporating the recycled fine powder modified by silicone cannot effectively stimulate the activity of the recycled fine powder. However, after carbonation curing, the compressive strength of the composite cement paste prepared with the modified recycled fine powder is much higher than that of the composite cement paste with unmodified recycled fine powder. This shows that the method of using silicone to assist carbonation activation of recycled fine powder proposed by the present invention has a high activation efficiency. The main reason for the increase in the compressive strength of the composite cement paste with modified recycled fine powder after carbonation curing is that in the carbonation curing environment, carbon dioxide and water vapor react fully with silicone, continuously generating soluble carbonates, increasing the alkalinity of the system, stimulating the activity of the recycled fine powder, ultimately accelerating the formation of hydration products, reducing the porosity of the specimens, and thus increasing the strength of the composite cement paste.

[0055] The carbon dioxide fixation amounts of the measured composite cement pastes in Examples 1 and 2 and Comparative Examples 1 to 6 are shown in Table 2 below:

[0056]

[0057] As can be seen from Table 2, the method proposed by the present invention can significantly increase the amount of carbon dioxide absorbed and fixed by recycled fine powder. When silicone activates recycled fine powder, it continuously reacts with carbon dioxide and water vapor, continuously converting carbon dioxide into stable carbonates, achieving the purpose of increasing the carbon fixation of recycled fine powder.

Claims

1. A method for efficiently activating and regenerating fine powder assisted by silicone carbide, characterized in that: Mix silicone with recycled fine powder and stir to obtain modified recycled fine powder. Use the modified recycled fine powder as an auxiliary cementitious material and replace cement in the conventional proportion to prepare cement concrete specimens. Continuously introduce gas containing carbon dioxide into the closed space for curing the specimens. During this process, the silicone synergistically carbonizes and activates the recycled fine powder, and at the same time fixes the carbon dioxide in the gas; The recycled fine powder is particles with a particle size less than 150 microns generated during the crushing of waste concrete; The silicone is one or more of alkyl silicate, alkyl siloxane silane, and polyalkyl hydroxy siloxane; The mass ratio of the silicone to the recycled fine powder is 0.0001~0.01:

1.

2. The method for efficiently activating and regenerating fine powder assisted by silicone carbide according to claim 1, characterized in that: The mixing time of the silicone and the recycled fine powder is 0.1~1.5h.

3. The method for efficiently activating and regenerating fine powder assisted by silicone carbide according to claim 1, characterized in that: The curing environment temperature is 5~50°C and the humidity is 20~90%.

4. The method for efficiently activating and regenerating fine powder assisted by silicone carbide according to claim 1, characterized in that: The volume fraction of carbon dioxide in the curing environment is higher than 5%.

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