A low-carbon gelling material prepared using supercritical carbon dioxide and a preparation method thereof

Abstract

The present invention discloses a low-carbon cementitious material prepared by using supercritical carbon dioxide and a preparation method, which belongs to the field of building materials technology. The low-carbon cementitious material is obtained by impregnating recycled micropowder with an activation solution and then placing it in a supercritical carbon dioxide environment for carbonization to obtain an auxiliary cementitious material. The auxiliary cementitious material is compounded with cement to obtain a low-carbon cementitious material; the activation solution includes a surfactant and a calcium ion complexing agent; the surfactant is one or more of phosphoric acid, a soluble phosphate and a soluble aluminum salt; the calcium ion complexing agent is one of ethylenediaminetetraacetic acid, trisodium nitrilotriacetate, and triethanolamine. Using waste concrete recycled micropowder as the object, a strengthened product is obtained by supercritical carbon dioxide mineralization, which replaces a certain proportion of cement clinker. While solving the problem of efficient resource utilization of construction solid waste, it also achieves the sequestration of carbon dioxide, providing a new low-carbon cementitious material.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to a low-carbon gelling material prepared by utilizing supercritical carbon dioxide and a preparation method thereof. Background Art

[0002] Reducing and minimizing emissions and energy consumption throughout the entire lifecycle of cement concrete is a key research focus in the cement production industry, encompassing three main areas. First, optimizing cement production processes and identifying alternatives to fossil fuels; second, reducing cement clinker usage, such as partially replacing cement with solid waste and developing new cementitious materials; and third, developing durability-enhancing technologies to produce long-life concrete. Carbon reduction focuses on the development and utilization of industrial solid waste, achieving the goal of "less cement in concrete, less clinker in cement, and less alite in clinker." After crushing construction waste, the larger particles can be used as aggregate to replace natural sand and gravel, while recycled fine powder (less than 0.075mm) can be used as a mineral admixture to partially replace cement. Recycled fine powder primarily consists of sand and gravel fragments, along with small amounts of hydration products such as CSH gel and calcium hydroxide. It has low chemical activity and essentially does not participate in cement hydration. Instead, it relies on the nucleation effect of its fine particles to promote cement hydration. However, since it also contains a small amount of hardened cement stone and a small amount of unhydrated cement particles, and a large number of microcracks are introduced during the crushing process, its water demand is greater than that of cement, affecting the working performance of cement-based materials.

[0003] In existing research, the activity of regenerated micropowder is improved by mechanical grinding and heat treatment, but there is a problem of high energy consumption. Carbonization treatment, which has emerged in recent years, achieves carbon neutrality while improving the activity of regenerated micropowder. However, the efficiency of conventional carbonization treatment is too low to achieve large-scale application. For example, CN112125541B discloses a method for wet carbonization of waste concrete regenerated micropowder and the application of regenerated micropowder. By controlling the ratio of regenerated micropowder to water, ventilation rate, carbon dioxide concentration, water temperature, carbonization reaction time and other parameters, carbonation reaction of carbon dioxide and regenerated micropowder is used to generate highly active calcium carbonate and silica gel, which is used as an auxiliary cementitious material. This method utilizes the convection of carbon dioxide and water, and then enhances the rapid carbonization reaction of regenerated micropowder by stirring.

[0004] To sum up, the preparation of low-carbon cementitious materials using construction solid waste is an effective treatment method. Therefore, seeking more efficient and low-carbon treatment methods, further improving production efficiency, and reducing new energy consumption generated in the process of solid waste resource utilization are important development directions for realizing the application of solid waste in the field of low-carbon cementitious materials. Summary of the Invention

[0005] To address the low efficiency of conventional carbonization treatments, which hinder large-scale application, the present invention provides a low-carbon cementitious material prepared using supercritical carbon dioxide and a preparation method. Using recycled concrete fine powder as the raw material, the supercritical carbon dioxide mineralization yields a fortified product, which replaces a certain proportion of cement clinker to create the low-carbon cementitious material. This approach not only effectively utilizes construction solid waste as a resource, but also achieves carbon dioxide sequestration, providing a novel low-carbon cementitious material.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A low-carbon cementitious material prepared using supercritical carbon dioxide is obtained by impregnating recycled micropowder with an activation solution and then carbonizing it in a supercritical carbon dioxide environment to obtain an auxiliary cementitious material. The auxiliary cementitious material is compounded with cement to obtain a low-carbon cementitious material.

[0008] The activation solution includes a surfactant and a calcium ion complexing agent; the surfactant is one or more of phosphoric acid, a soluble phosphate, and a soluble aluminum salt; the calcium ion complexing agent is one of ethylenediaminetetraacetic acid, trisodium nitrilotriacetate, and triethanolamine; the concentration of the surfactant in the activation solution is 0.01 mol / L to 1 mol / L, and the calcium ion complexing agent accounts for 0.01% to 1% of the mass of the activation solution.

[0009] The mass ratio of the regenerated micropowder to the activation solution is 1:5~20;

[0010] The recycled micropowder is made from waste concrete, waste mortar or waste cement paste generated during the demolition of old buildings and the production of commercial concrete mixing plants, and is produced after crushing, grinding, screening and drying. The recycled micropowder contains cement hydration products CSH, CH, AFt and unhydrated minerals C2S, C3S and C4AF, and has carbonization ability. The particle size of the recycled micropowder is less than 0.075 mm, and the specific surface area is greater than 350 m 2 / kg.

[0011] The cement is one of cement clinker, Portland cement, ordinary Portland cement, sulphoaluminate cement, high belite cement and belite sulphoaluminate cement; the mass ratio of the auxiliary cementitious material to the cement is 1:1-1:9.

[0012] On the other hand, the present invention also provides a method for preparing a low-carbon gelling material using supercritical carbon dioxide, which specifically comprises the following steps:

[0013] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0014] (2) placing the impregnation mixture in a reaction device, and introducing carbon dioxide gas into the reaction device, setting the temperature to 35-60°C and the pressure to 7.5-10 MPa to obtain supercritical carbon dioxide, and carbonizing the impregnation mixture in a supercritical carbon dioxide environment;

[0015] (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement to obtain a low-carbon cementitious material.

[0016] Furthermore, the carbon dioxide gas in step 2 is industrial tail gas or commercial gas with a concentration of not less than 90%, and the industrial tail gas comes from the steel industry, cement industry, electric power industry, chemical industry and other industries or any combination of tail gas.

[0017] Furthermore, in step (2), the flow rate of carbon dioxide gas is 20-50 L / min.

[0018] Furthermore, the carbonization reaction time in step (2) is 1-3 hours.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention utilizes supercritical carbon dioxide to cure the regenerated micropowder. Supercritical carbon dioxide has the dual characteristics of gas and liquid in terms of physical properties. Its density is several hundred times that of gas, close to that of liquid. This also gives supercritical carbon dioxide a strong solvating ability and a relatively high diffusion coefficient of gas. These properties can improve the mass transfer efficiency of supercritical carbon dioxide into the microporous structure of the regenerated micropowder, effectively accelerating the carbonization of the substance. After supercritical carbon dioxide curing, the time required for conventional carbon dioxide curing can be greatly shortened, the reaction temperature and energy consumption during the treatment process can be reduced. At the same time, because supercritical carbon dioxide has strong transmission properties, it can fully carbonize on the surface of the regenerated micropowder and can fully enter the internal pores of the regenerated micropowder, making carbonization more complete. This solves the problem of conventional carbon dioxide curing in which dense hydration products are quickly generated on the surface of the regenerated micropowder, which hinders the gas from further entering the internal pores of the regenerated micropowder and makes it difficult to achieve complete carbonization. The porosity of the regenerated micropowder after full carbonization decreases, weakening the impact of the decline in the working performance of the cement-based material caused by its incorporation, while improving the mechanical properties of the cement-based material.

[0021] The present invention adopts surfactant and calcium ion complexing agent solution to mix with regenerated micropowder, surfactant can improve the dispersibility of regenerated micropowder in water, calcium ion complexing agent can promote the dissolution of calcium ions in regenerated micropowder components, and improve subsequent carbonization efficiency.

[0022] The technical solution provided by the present invention utilizes supercritical carbon dioxide curing to effectively improve the performance of construction solid waste recycled products, provides a new low-carbon cementitious material and CCUS technology, and at the same time reduces carbon emissions throughout the life cycle of cement-based materials, which has important social and environmental significance. DETAILED DESCRIPTION

[0023] In order to better understand the present invention, the content of the present invention is further described below in conjunction with the embodiments, but the content of the present invention is not limited to the scope of the embodiments. On the contrary, these embodiments are provided to explain the principles of the present invention and its practical application, so that other persons skilled in the art can understand the various embodiments of the present invention and various modifications suitable for specific intended applications.

[0024] The recycled micro powder in the examples and comparative examples is a cement slurry with a water-cement ratio of 0.40 prepared in the laboratory, which is crushed and ball-milled for 20 minutes, and then further sieved to obtain a powder with a particle size of less than 0.075 mm and a specific surface area of ​​more than 350 m 2 / kg.

[0025] The activation solution and carbon dioxide in the examples and comparative examples are shown in Table 1 below:

[0026] Table 1 Selection of activation solution and carbon dioxide in Examples and Comparative Examples

[0027]

[0028] Example 1

[0029] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0030] (2) The impregnation mixture was placed in a reaction device, and carbon dioxide gas was introduced into the reaction device. The temperature was set to 35°C and the pressure was set to 7.5 MPa to obtain supercritical carbon dioxide. The carbon dioxide gas flow rate was 25 L / min, and the impregnation mixture was carbonized in a supercritical carbon dioxide environment for 1 hour.

[0031] (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement in a mass ratio of 3:7 to obtain a low-carbon cementitious material. Example 2

[0032] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0033] (2) The impregnation mixture was placed in a reaction device, and carbon dioxide gas was introduced into the reaction device. The temperature was set to 35°C and the pressure was set to 9 MPa to obtain supercritical carbon dioxide. The carbon dioxide gas flow rate was 45 L / min, and the impregnation mixture was carbonized in a supercritical carbon dioxide environment for 2 h.

[0034] (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement in a mass ratio of 1:8 to obtain a low-carbon cementitious material. Example 3

[0035] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0036] (2) The impregnation mixture was placed in a reaction device, and carbon dioxide gas was introduced into the reaction device. The temperature was set to 45°C and the pressure was set to 7.5 MPa to obtain supercritical carbon dioxide. The carbon dioxide gas flow rate was 35 L / min, and the impregnation mixture was carbonized in a supercritical carbon dioxide environment for 3 hours.

[0037] (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement in a mass ratio of 1:5 to obtain a low-carbon cementitious material. Example 4

[0038] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0039] (2) The impregnation mixture was placed in a reaction device, and carbon dioxide gas was introduced into the reaction device. The temperature was set to 60°C and the pressure was set to 7.5 MPa to obtain supercritical carbon dioxide. The carbon dioxide gas flow rate was 25 L / min, and the impregnation mixture was carbonized in a supercritical carbon dioxide environment for 1 hour.

[0040] (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement in a mass ratio of 3:7 to obtain a low-carbon cementitious material. Example 5

[0041] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0042] (2) The impregnation mixture was placed in a reaction device, and carbon dioxide gas was introduced into the reaction device. The temperature was set to 35°C and the pressure was set to 10 MPa to obtain supercritical carbon dioxide. The carbon dioxide gas flow rate was 25 L / min, and the impregnation mixture was carbonized in a supercritical carbon dioxide environment for 1 hour.

[0043] (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement in a mass ratio of 3:7 to obtain a low-carbon cementitious material. Example 6

[0044] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0045] (2) The impregnation mixture was placed in a reaction device, and carbon dioxide gas was introduced into the reaction device. The temperature was set to 35°C and the pressure was set to 7.5 MPa to obtain supercritical carbon dioxide. The carbon dioxide gas flow rate was 25 L / min, and the impregnation mixture was carbonized in a supercritical carbon dioxide environment for 3 hours.

[0046] (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement in a mass ratio of 3:7 to obtain a low-carbon cementitious material.

[0047] Comparative Example 1

[0048] The cementitious material is prepared by compounding recycled micropowder with P·Ⅱ 52.5 silicate cement, and the mass ratio of recycled micropowder to cement is 3:7.

[0049] Comparative Example 2

[0050] This comparative example is based on Example 1, the difference being that the regenerated micropowder was subjected to conventional carbon dioxide curing.

[0051] (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture;

[0052] (2) The impregnation mixture was placed in a reaction device and carbon dioxide gas was introduced into the reaction device. The temperature was set to 80°C, the pressure was 0.2 MPa, and the carbon dioxide concentration was 25%. The impregnation mixture was carbonized in a carbon dioxide environment for 12 hours.

[0053] (3) After carbonization is completed, the carbonized product is taken out, and after solid-liquid separation, it is dried to obtain an auxiliary cementitious material. The auxiliary cementitious material is compounded with cement in a mass ratio of 3:7 to obtain a low-carbon cementitious material.

[0054] Comparative Example 3

[0055] This comparative example is based on Example 1, except that no activation solution was added.

[0056] (1) Place the regenerated micropowder in a reaction device and introduce carbon dioxide gas into the reaction device. Set the temperature to 35°C and the pressure to 7.5 MPa to obtain supercritical carbon dioxide. The carbon dioxide gas flow rate is 25 L / min. The impregnation mixture is carbonized in a supercritical carbon dioxide environment for 1 hour.

[0057] (2) After carbonization is completed, the pressure is released, the carbonized product is taken out, and dried to obtain an auxiliary cementitious material. The auxiliary cementitious material is compounded with cement in a mass ratio of 3:7 to obtain a low-carbon cementitious material.

[0058] In order to evaluate the improvement effect of the present invention on low-carbon cementitious materials, cement mortar was prepared with low-carbon cementitious materials, and the activity index of the regenerated micropowder before and after supercritical carbonization treatment was evaluated. The compressive strength of the specimens was tested at 3d, 7d, and 28d, respectively, in accordance with the "Test method for strength of cement mortar (ISO method)" GB / T 17671.

[0059] The mass mix ratio of cement mortar is: low-carbon cementitious material: sand: water = 1:3.0:0.5. P·II52.5 cement, standard sand, and tap water are used. Cement mortar is prepared according to standard curing conditions: (20±2)°C, relative humidity not less than 95%.

[0060] Table 2 shows the compressive strength test results of the cement mortar prepared according to the embodiments and comparative examples at 3d, 7d and 28d.

[0061] Table 2 Performance test results of cement mortar

[0062]

[0063] Combined with the results in Table 2, the regenerated micropowder in the cementitious material of Comparative Example 1 has not been carbonized, and its activity index is relatively low. Compared with the data of Example 1, it can be seen that the fluidity and 28d compressive strength of the cement mortar in Comparative Example 1 are much lower than those in Example 1. This is because the activity index of the regenerated micropowder that has not been carbonized is low, while the regenerated micropowder that has been carbonized with supercritical carbon dioxide can convert the calcium hydroxide and hydrated calcium silicate in the regenerated micropowder into calcium carbonate and silica gel, which has a higher hydration activity and can also play a better crystal nucleation role. In addition, calcium carbonate has a denser structure, which can improve the working performance of cement-based materials and enhance the compressive strength after hardening.

[0064] Comparative Example 2, which uses a conventional wet carbonization process to treat regenerated micropowder, exhibits lower fluidity and 28d compressive strength than Example 1. This is because the supercritical carbon dioxide treatment method employed in Example 1 more fully carbonizes the regenerated micropowder than conventional carbonization processes, reducing its porosity and mitigating the degradation of cement-based material performance caused by its incorporation, while also improving the mechanical properties of the cement-based material. Furthermore, the supercritical carbon dioxide treatment method reduces the required reaction time and temperature, shortening the cycle time, increasing the reaction rate, and reducing the energy consumption and carbon emissions associated with high-temperature treatment, further contributing to improved carbon capture efficiency.

[0065] Both Example 1 and Comparative Example 3 use supercritical carbon dioxide for carbonization. The difference between Example 1 and Comparative Example 3 is that an activation solution is added. The activation solution can promote the dissolution of calcium ions in the regenerated micropowder, further improve the carbonization efficiency, and the working performance and mechanical strength of the prepared cement mortar are improved.

[0066] Compared to Example 1, Examples 4, 5, and 6, respectively, employ solutions of increasing temperature and pressure and extending reaction time to further accelerate the carbonization rate of the regenerated micropowder by supercritical carbon dioxide, all of which are beneficial for accelerating carbonization. The amount of regenerated micropowder added significantly affects the properties of cement-based materials. Therefore, in practical applications, the specific process parameters of supercritical carbon dioxide curing can be adjusted based on the desired performance of the regenerated micropowder cement-based material, the required replacement rate of the regenerated micropowder, and the energy consumption requirements.

Claims

1. A low-carbon gelling material prepared using supercritical carbon dioxide, characterized in that: The regenerated micro powder is impregnated with an activation solution and then carbonized in a supercritical carbon dioxide environment to obtain an auxiliary cementitious material. The auxiliary cementitious material is compounded with cement to obtain a low-carbon cementitious material. The activation solution comprises a surfactant and a calcium ion complexing agent; the surfactant is one or more of phosphoric acid, soluble phosphate and soluble aluminum salt; and the calcium ion complexing agent is one of ethylenediaminetetraacetic acid, trisodium nitrilotriacetate and triethanolamine.

2. The low-carbon gelling material prepared by supercritical carbon dioxide according to claim 1, characterized in that: The concentration of the surfactant in the activation solution is 0.01 mol / L to 1 mol / L, and the calcium ion complexing agent accounts for 0.01% to 1% of the mass of the activation solution.

3. The low-carbon gelling material prepared by supercritical carbon dioxide according to claim 1, characterized in that: The mass ratio of the regenerated micropowder to the activation solution is 1:5-20.

4. The low-carbon gelling material prepared by using supercritical carbon dioxide according to claim 1, characterized in that: The particle size of the regenerated micropowder is less than 0.075 mm and the specific surface area is greater than 350 m 2 / kg.

5. The low-carbon gelling material prepared by using supercritical carbon dioxide according to claim 1, characterized in that: The cement is one of Portland cement, ordinary Portland cement, sulphoaluminate cement and Belite sulphoaluminate cement.

6. The low-carbon gelling material prepared by using supercritical carbon dioxide according to claim 1, characterized in that: The mass ratio of the auxiliary cementitious material to cement is 1:1 to 1:

9.

7. The method for preparing a low-carbon gelling material using supercritical carbon dioxide according to any one of claims 1 to 6, characterized in that: The specific steps include: (1) Place the regenerated micropowder in a container, add the activation solution, and mix well to obtain an impregnation mixture; (2) placing the impregnation mixture in a reaction device, and introducing carbon dioxide gas into the reaction device, setting the temperature to 35-60°C and the pressure to 7.5-10 MPa to obtain supercritical carbon dioxide, and carbonizing the impregnation mixture in a supercritical carbon dioxide environment; (3) After carbonization is completed, the pressure is released, the carbonized product is taken out, and the auxiliary cementitious material is obtained by drying after solid-liquid separation. The auxiliary cementitious material is compounded with cement to obtain a low-carbon cementitious material.

8. The preparation method according to claim 7, characterized in that The carbon dioxide gas in step (2) is industrial tail gas or commercial gas with a concentration of not less than 90%.

9. The preparation method according to claim 7, characterized in that The carbon dioxide gas flow rate in step (2) is 20-50 L / min.

10. The preparation method according to claim 7, characterized in that The carbonization reaction time in step (2) is 1-3 hours.

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