Low carbon cement, low carbon cement specimen, and preparation method and application thereof

Abstract

The present invention discloses a low-carbon cement, a low-carbon cement specimen, and a preparation method and application thereof, and belongs to the field of cement technology. The present invention obtains a premix by mixing biochar after saturated carbon dioxide adsorption with a cement-based material; mixing the premix with water to obtain a slurry, casting and molding, and curing to obtain a cement specimen; and using power plant flue gas to perform external carbonization curing on the cement specimen to obtain low-carbon cement. The present invention adopts low-cost, negative carbon emission biochar as a carbonization internal curing material, which solves the problem of high cost and high carbon emission of existing carbonization internal curing materials, while improving the CO2 adsorption efficiency and significantly reducing the overall cost of producing low-carbon cement. The present invention reduces the dependence on harsh conditions such as high pressure and high concentration of CO2 in the carbonization curing process by combining industrial flue gas as an external carbonization source, simplifies the curing process, and enhances its industrial application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of cement, and in particular relates to a low-carbon cement, a low-carbon cement test piece, and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Using CO2 adsorption materials for carbonation curing of cement-based materials releases CO2 within the cement, enabling deep, in-situ carbonation curing and effectively improving the carbonization depth and efficiency of the material. However, while existing carbonation curing materials, such as zeolites and MOFs, have a certain adsorption capacity, their high cost, long saturation adsorption times (typically 12 to 24 hours), and high carbon emissions during production limit their widespread application in actual production.

[0004] Furthermore, when using traditional adsorption materials for carbonization internal curing, the adsorption materials have developed pores. This developed pore will absorb a large amount of water when used as a carbonization internal curing material, and the density of the cement specimen will increase. As the carbonization internal curing products fill the pores, the entry of CO2 during the carbonization external curing process is further restricted, hindering the diffusion of CO2, causing the carbonization reaction to occur only on the surface of the material, affecting the carbonization depth and degree of carbonization. Therefore, it is necessary to use high-pressure carbonization curing equipment to perform carbonization external curing on cement specimens. The use of high-pressure carbonization curing equipment has limited the application scenarios of carbonization external curing technology, making it difficult to promote it on a large scale. Summary of the Invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a low-carbon cement, a low-carbon cement specimen, and a preparation method and application thereof. The preparation method provided by the present invention uses biochar to efficiently adsorb CO2 as a carbonized internal curing material, and combines industrial flue gas as an external carbonization source to further increase the CO2 absorption amount, thereby achieving an overall CO2 fixation amount of the material close to or greater than the CO2 emission amount during the material production process, and realizing internal and external coordinated carbonization to prepare low-carbon cement.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A first aspect of the present invention provides a low-carbon cement comprising, by weight, 1-25 parts of biochar that absorbs carbon dioxide and 75-99 parts of cement powder.

[0008] In some embodiments of the present invention, the low-carbon cement comprises, by weight, 1-20 parts of biochar that absorbs carbon dioxide and 80-99 parts of cement powder.

[0009] In some embodiments of the present invention, the low-carbon cement comprises, by weight, 10-20 parts of biochar saturated with carbon dioxide adsorption and 80-90 parts of cement powder.

[0010] In some embodiments of the present invention, the low-carbon cement comprises, by weight, 10 parts of biochar saturated with carbon dioxide adsorption and 90 parts of cement powder.

[0011] In some embodiments of the present invention, the low-carbon cement comprises, by weight, 20 parts of biochar saturated with carbon dioxide adsorption and 80 parts of cement powder.

[0012] A second aspect of the present invention provides a low-carbon cement specimen comprising, by weight, 1-25 parts of biochar that absorbs carbon dioxide, 75-99 parts of cement powder, and 30-50 parts of water;

[0013] After the raw materials are mixed and formed, the obtained cement specimens are subjected to external carbonization curing to obtain low-carbon cement specimens.

[0014] In some embodiments of the present invention, the low-carbon cement specimen comprises, by weight, 1-20 parts of biochar that absorbs carbon dioxide, 80-99 parts of cement powder, and 30-50 parts of water.

[0015] In some embodiments of the present invention, the low-carbon cement specimen comprises, by weight, 1-20 parts of biochar saturated with carbon dioxide adsorption, 80-99 parts of cement powder, and 30-50 parts of water.

[0016] In some embodiments of the present invention, the low-carbon cement specimen comprises, by weight, 10-20 parts of biochar saturated with carbon dioxide adsorption, 80-90 parts of cement powder, and 30-50 parts of water.

[0017] In some embodiments of the present invention, the low-carbon cement specimen comprises, by weight, 10-20 parts of biochar saturated with carbon dioxide adsorption, 80-90 parts of cement powder, and 40 parts of water.

[0018] In some embodiments of the present invention, the low-carbon cement specimen comprises, by weight, 10 parts of biochar saturated with carbon dioxide adsorption, 90 parts of cement powder, and 40 parts of water.

[0019] In some embodiments of the present invention, the low-carbon cement specimen comprises, by weight, 20 parts of biochar saturated with carbon dioxide adsorption, 80 parts of cement powder, and 40 parts of water.

[0020] A third aspect of the present invention provides a method for preparing the above-mentioned low-carbon cement specimen, comprising:

[0021] The biochar after carbon dioxide adsorption is used as a carbonized internal curing material and mixed with cement powder to obtain a premix;

[0022] The premix is ​​mixed with water to obtain a slurry, which is then cast into shape and cured to obtain a cement specimen;

[0023] Carbon dioxide was used to carry out external carbonization curing on cement specimens, and low-carbon cement specimens were obtained under the coordinated internal and external carbonization curing.

[0024] In some embodiments of the present invention, the biochar is obtained by pyrolysis, drying, grinding, and sieving biomass;

[0025] The pyrolysis temperature is 300-900°C, and the pyrolysis atmosphere is an inert atmosphere or an atmosphere with an oxygen content of less than 5%;

[0026] The drying temperature is 100-120°C;

[0027] The sieving is performed through a 120-200 mesh sieve.

[0028] In some embodiments of the present invention, biochar that has adsorbed carbon dioxide to a saturated state is mixed with cement powder to obtain a premix.

[0029] In some embodiments of the present invention, the external carbonization curing is performed at a pressure of 1-5 atmospheres, a curing temperature of 50-90° C., and a curing time of 12-48 hours.

[0030] In some embodiments of the present invention, industrial flue gas is used to perform external carbonization curing on cement specimens, and the carbon dioxide concentration in the industrial flue gas is 10%-30%.

[0031] A fourth aspect of the present invention provides a use of the above-mentioned low-carbon cement or the above-mentioned low-carbon cement specimen in carbon capture engineering and / or engineering construction.

[0032] The beneficial effects of the present invention are:

[0033] The present invention provides a low-carbon cement comprising biochar that absorbs carbon dioxide. Biochar has low cost and a low carbon emission factor, making it very environmentally friendly. The present invention uses biochar that absorbs carbon dioxide as a carbonized internal curing material, thereby improving the carbon dioxide adsorption efficiency of the carbonized internal curing material and reducing production costs and carbon emissions. The biochar that absorbs carbon dioxide is used as an admixture to replace part of the cement in the hydration reaction and is formed. The biochar releases carbon dioxide within the low-carbon cement and fixes the carbon dioxide in the form of carbonates, thereby increasing the diffusion depth of carbon dioxide in the cement-based material and the uniformity of the distribution of carbonization products, improving the carbon fixation amount and carbonization degree of the cement material, and reducing carbon emissions. The porous structure of the biochar itself can optimize the pore distribution of the cement material, providing more CO2 transmission channels for external carbonization curing during the low-carbon cement forming process, and strengthening the external carbonization curing of the material. The formed cement material is externally carbonized and cured in a carbon dioxide atmosphere. The internal and external synergistic effects further improve the carbonization degree and carbon fixation amount, and significantly enhance the early compressive strength of the cement-based material within a shorter curing cycle.

[0034] This method uses biochar as a carbonization internal curing material. Its inherently low carbon emission factor reduces stringent requirements for the carbonization curing environment and parameters, enabling sustainable development of the entire process and enhancing its potential for industrialization. Furthermore, its cost and carbon emissions are lower than those of materials such as zeolite and MOFs. To further enhance the effectiveness of carbonization internal curing, a method of synergistic carbonization curing, using biochar saturated with carbon dioxide, can be employed. This effectively increases the carbon sequestration and mechanical properties of cement materials while reducing their carbon emissions.

[0035] The present invention also provides a low-carbon cement specimen and its preparation method. This method utilizes biochar, which is low-cost, has a low carbon emission factor, and is saturated with carbon dioxide, as a carbonization internal curing material. This improves the adsorption efficiency of the carbonization internal curing material and reduces costs and production carbon emissions. Subsequently, the saturated carbon dioxide biochar is used as an admixture to replace a portion of the cement in the hydration reaction and is formed. The biochar releases CO2 within the cement material and fixes it as carbonates, increasing the diffusion depth of CO2 within the cement-based material and the uniformity of the carbonization product distribution, thereby enhancing the carbonization degree of the material. The porous structure of the biochar optimizes the pore distribution of the material, providing more CO2 transmission channels for external carbonization curing, strengthening the external carbonization curing process, and reducing the pressure of external carbonization curing. The formed cement material is then subjected to external carbonization curing in a carbon dioxide atmosphere. This synergistic effect further enhances the carbonization degree and carbon fixation, significantly increasing the early compressive strength of the cement material within a short curing cycle. This method effectively improves the carbonization degree and carbon fixation of the cement material at a low production cost, while significantly improving the early compressive strength and reducing carbon emissions.

[0036] The present invention uses biochar as the carbonization internal curing material, which is low in cost and shortens the carbon dioxide saturation adsorption time to 1.5-3 hours, which is much lower than the carbon dioxide adsorption time of existing carbonization internal curing materials (12-24 hours), greatly improving production efficiency.

[0037] The present invention uses industrial flue gas to perform external carbonization curing on cement specimens, which reduces the dependence on harsh conditions such as high pressure and high concentration of CO2 in the carbonization curing process, simplifies the curing process, and enhances its industrial application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0039] Figure 1 This is a graph showing the carbon dioxide adsorption capacity of various biochars in Example 1 of the present invention; wherein, ①→②: drying at elevated temperature in N2 atmosphere; ②→③: drying at 110°C in N2 atmosphere for 2 hours; ③→④: cooling to room temperature in N2 atmosphere; ④→⑤: adsorption at room temperature and pressure in CO2 atmosphere;

[0040] Figure 2 The XRD patterns of the low carbon cement specimens prepared in Examples 4 and 6 of the present invention and Comparative Examples 3, 4, 5, and 7 on the third day are shown;

[0041] Figure 3 The thermogravimetric spectra of the low carbon cement specimens prepared in Examples 4 and 6 of the present invention and Comparative Examples 3, 4, 5, and 7 on the third day. DETAILED DESCRIPTION

[0042] In view of the problems of high carbon emission factor and long carbon dioxide adsorption time of existing carbonization internal curing materials, as well as the fact that external carbonization curing needs to be carried out under high pressure and high carbon dioxide concentration conditions and has low efficiency, the present invention proposes a low-carbon cement, a low-carbon cement specimen, and its preparation method and application.

[0043] In a first typical embodiment of the present invention, a low-carbon cement is provided, comprising, by weight, 1-25 parts of biochar that absorbs carbon dioxide and 75-99 parts of cement powder.

[0044] Biochar is a low-cost, carbon-negative material. It is produced by pyrolyzing biomass feedstocks such as agricultural solid waste (such as corn stalks and rice husks), municipal organic waste (such as sludge and kitchen waste), and animal manure at high temperatures (300-900°C) under low-oxygen or anaerobic conditions, forming a stable solid structure with high porosity and a large specific surface area. Its abundant pores and high specific surface area impart excellent CO2 adsorption properties, reaching saturation within 1.5-3 hours at room temperature and pressure, combining high adsorption efficiency with stability. When used as a carbonization internal curing material, biochar exhibits low water absorption in cement and maintains high porosity, facilitating CO2 incorporation, enabling the integration of carbonization internal curing with carbonization external curing.

[0045] The inventors have discovered that biochar is not only a low-cost, carbon-negative material, but its high specific surface area and porous structure enable efficient adsorption of large amounts of CO2 in a relatively short period of time (1.5-3 hours), significantly reducing the cost of carbonization and internal curing while improving efficiency. Furthermore, the biochar's inherent porous structure strengthens the material's pore distribution after incorporation into cement, providing more CO2 transmission channels for external carbonization and curing. This results in a low-carbon cement using biochar that absorbs carbon dioxide as a carbonization and internal oxidation material. This, combined with external carbonization and curing, further enhances CO2 absorption, achieving an overall CO2 fixation level close to or exceeding the CO2 emissions during production, achieving synergistic internal and external carbonization.

[0046] Table 1 shows the differences between various carbonized internal curing materials.

[0047] Table 1 Comparison of carbonized internal curing materials

[0048]

[0049] As shown in Table 1, biochar has a lower carbon emission factor than molecular sieves and MOFs. This invention uses low-cost, low-carbon-emission-factor biochar as a carbonized internal curing material, addressing the high cost and high carbon emissions of existing carbonized internal curing materials and significantly reducing the overall cost of low-carbon cement.

[0050] The amount of carbonized internal oxidation material affects the mechanical properties of low carbon cement. In order to further improve the mechanical properties of low carbon cement and increase the carbon fixation amount, the low carbon cement preferably includes 1-20 parts of biochar that absorbs carbon dioxide and 80-99 parts of cement powder by mass.

[0051] As can be understood, the CO2 content in CO2-adsorbed biochar affects the carbonation-curing effectiveness of low-carbon cement. A high CO2 content results in a higher carbon fixation capacity and a higher degree of carbonation-curing in the cement material, while reducing carbon emissions. Therefore, biochar saturated with CO2 is preferred as the carbonation-curing material. The low-carbon cement comprises, by weight, 1-20 parts of biochar saturated with CO2 and 80-99 parts of cement powder.

[0052] As the amount of carbonized biochar saturated with carbon dioxide increases, the degree of carbonized internal curing of low-carbon cement increases. However, using biochar as a carbonized internal curing material to replace part of the cement will affect the strength of the cement specimens. As the biochar content increases, the compressive strength of the cement specimens gradually decreases. When the carbonized internal curing material content reaches 25%, the compressive strength of the cement specimens is too low. Therefore, the content of carbonized internal curing material should be controlled within a reasonable range to avoid excessively low specimen strength. To avoid low mechanical properties of low-carbon cement, the low-carbon cement preferably includes 10-20 parts by mass of biochar saturated with carbon dioxide and 80-90 parts by mass of cement powder.

[0053] In some examples of this embodiment, the low-carbon cement comprises, by weight, 10 parts of biochar saturated with carbon dioxide adsorption and 90 parts of cement powder. With this ratio, the resulting low-carbon cement specimens exhibit high compressive strength and high carbon sequestration.

[0054] In some examples of this embodiment, the low-carbon cement comprises, by weight, 20 parts of biochar saturated with carbon dioxide adsorption and 80 parts of cement powder. With this ratio, the resulting low-carbon cement specimens exhibit high compressive strength and maximum carbon sequestration.

[0055] A second typical embodiment of the present invention provides a low-carbon cement specimen comprising, by weight, 1-25 parts of biochar that absorbs carbon dioxide, 75-99 parts of cement powder, and 30-50 parts of water;

[0056] After the raw materials are mixed and formed, the obtained cement specimens are subjected to external carbonization curing to obtain low-carbon cement specimens.

[0057] The low-carbon cement specimen provided by the present invention contains carbonized internal curing material, biochar that absorbs carbon dioxide as carbonized internal oxidation material, and combined with external carbonization curing, which increases the specimen's absorption of CO2, realizes internal and external coordinated carbonization, and achieves an overall CO2 fixation amount of the material that is close to or greater than the CO2 emissions during the material production process.

[0058] In some examples of this embodiment, the low-carbon cement specimen comprises, by weight, 1-20 parts of carbon dioxide-adsorbed biochar, 80-99 parts of cement powder, and 30-50 parts of water. The amount of carbonized internal oxidation material affects the mechanical properties of the low-carbon cement specimen. Within the above range, the resulting low-carbon cement specimen exhibits excellent mechanical properties and high carbon sequestration.

[0059] In some examples of this embodiment, the low-carbon cement specimen comprises, by weight, 1-20 parts of biochar saturated with carbon dioxide adsorption, 80-99 parts of cement powder, and 30-50 parts of water. It is understood that the carbon dioxide content in the carbon dioxide-adsorbed biochar affects the carbonation-curing effect of the low-carbon cement. A high carbon dioxide content results in a higher carbon fixation capacity and a higher degree of carbonation-curing in the cement material, while reducing carbon emissions. Therefore, biochar saturated with carbon dioxide adsorption is preferably used as the carbonation-curing material.

[0060] In some examples of this embodiment, the low-carbon cement specimen comprises, by weight, 10-20 parts of biochar saturated with carbon dioxide adsorption, 80-90 parts of cement powder, and 30-50 parts of water. As the amount of biochar saturated with carbon dioxide adsorption increases, the degree of carbonization and internal curing of the low-carbon water specimen increases. However, replacing part of the cement with biochar as a carbonization and internal curing material will affect the strength of the cement specimen, and as the biochar content increases, the compressive strength of the cement specimen gradually decreases. When the content of the carbonization and internal curing material reaches 25%, the compressive strength of the cement specimen is too low. Therefore, the content of the carbonization and internal curing material should be controlled within the above-mentioned reasonable range to avoid excessively low material strength.

[0061] In some examples of this embodiment, the low-carbon cement specimen comprises, by weight, 10-20 parts of biochar saturated with carbon dioxide adsorption, 80-90 parts of cement powder, and 40 parts of water. The water-to-cement ratio affects the mechanical properties of the low-carbon cement specimen. At a water-to-cement ratio of 0.4, the resulting low-carbon cement specimen exhibits excellent mechanical properties.

[0062] In some examples of this embodiment, the low-carbon cement sample comprises, by weight, 10 parts of biochar saturated with carbon dioxide adsorption, 90 parts of cement powder, and 40 parts of water. With this ratio, the resulting low-carbon cement exhibits high compressive strength and high carbon sequestration.

[0063] In some examples of this embodiment, the low-carbon cement specimen comprises, by weight, 20 parts of biochar saturated with carbon dioxide adsorption, 80 parts of cement powder, and 40 parts of water. With this ratio, the resulting low-carbon cement specimen exhibits high compressive strength and maximum carbon sequestration.

[0064] A third typical embodiment of the present invention provides a method for preparing the above-mentioned low-carbon cement specimen, comprising:

[0065] The biochar after carbon dioxide adsorption is used as a carbonized internal curing material and mixed with cement powder to obtain a premix;

[0066] The premix is ​​mixed with water to obtain a slurry, which is then cast into shape and cured to obtain a cement specimen;

[0067] Carbon dioxide was used to carry out external carbonization curing on cement specimens, and low-carbon cement specimens were obtained under the coordinated internal and external carbonization curing.

[0068] The present invention provides a method for preparing low-carbon cement specimens. This method utilizes biochar, which is low-cost and has a low carbon emission factor and is saturated with carbon dioxide, as a carbonization internal curing material. This improves the adsorption efficiency of the carbonization internal curing material and reduces costs and production carbon emissions. Subsequently, the saturated carbon dioxide biochar is used as an admixture to replace a portion of the cement in the hydration reaction and is formed. The biochar releases CO2 within the cement material and fixes it as carbonates, increasing the diffusion depth of CO2 within the cement-based material and the uniformity of the carbonization product distribution, thereby enhancing the carbonization degree of the material. The porous structure of the biochar optimizes the pore distribution of the material, providing more CO2 transmission channels for external carbonization curing, strengthening the external carbonization curing process while reducing the pressure of the external carbonization curing process. The formed cement material is then subjected to external carbonization curing in a carbon dioxide atmosphere. This synergistic effect further enhances the carbonization degree and carbon fixation, significantly increasing the early compressive strength of the cement material within a short curing cycle. This method can effectively improve the carbonization degree and carbon fixation of the cement material at a low production cost, while significantly improving the early compressive strength and reducing carbon emissions.

[0069] In some examples of this embodiment, the biochar is obtained by pyrolysis, drying, grinding, and screening of biomass. Biochar can be made from various types of waste, urban garbage, animal manure, etc., which have a wide range of raw materials and low production costs.

[0070] The pyrolysis temperature is 300-900°C in an inert atmosphere or one with less than 5% oxygen. The pyrolysis temperature affects the structure and properties of the biochar. Biomass can be fully pyrolyzed at 300-900°C in an oxygen-free or low-oxygen atmosphere.

[0071] The drying temperature is 100-120° C. At this drying temperature, the structure of the biochar does not change, ensuring that the biochar has a porous structure.

[0072] The sieving is performed through a 120-200 mesh screen. After the sieving, the biochar obtained has a moderate particle size and can be fully mixed with cement.

[0073] In some examples of this embodiment, biochar that has reached a saturated state of carbon dioxide adsorption is mixed with cement powder to produce a premix. The high carbon dioxide content in biochar that has reached a saturated state of carbon dioxide adsorption can improve the carbonation internal curing effect of low-carbon cement.

[0074] It can be understood that biochar can be sent into a sealed device for carbon dioxide adsorption. The carbon dioxide atmosphere in the sealed device is at room temperature and pressure, with a concentration of ≥50%. It can also be placed in an industrial flue gas atmosphere. It only takes 1.5-3 hours of adsorption time for the biochar to reach adsorption saturation state, with high production efficiency.

[0075] In some examples of this embodiment, the external carbonization curing is performed at a pressure of 1-5 atmospheres, a curing temperature of 50-90° C., and a curing time of 12-48 hours.

[0076] The present invention uses biochar as the carbonization internal curing material. The porous structure of biochar itself can optimize the pore distribution of the material, provide more CO2 transmission channels for external carbonization curing, avoid external carbonization products filling the pores and hindering CO2 diffusion, affecting the carbonization depth and degree, strengthen the external carbonization curing of the material, and at the same time reduce the pressure of external carbonization curing. External carbonization curing can be achieved under low pressure, reducing curing costs.

[0077] In some embodiments, industrial flue gas is used to perform external carbonization curing on cement specimens, and the carbon dioxide concentration in the industrial flue gas is 10%-30%.

[0078] This invention uses industrial flue gas for external carbonization curing of cement specimens, reducing reliance on the harsh conditions of carbonization curing, such as high pressure and high CO2 concentration, simplifying the curing process and enhancing its potential for industrial application. This invention's use of industrial flue gas for external carbonization curing of cement specimens eliminates the limitations of high-pressure carbonization curing equipment, expands application scenarios, reduces carbonization costs, and enables secondary utilization of industrial waste gas.

[0079] In some embodiments, a specific method for preparing a low-carbon cement specimen is provided, comprising the following steps:

[0080] (1) Select various types of waste, urban garbage, animal feces, etc. as raw materials, pyrolysis temperature 300-900℃, pyrolysis atmosphere is inert atmosphere or low oxygen atmosphere; after pyrolysis, dry at 110℃ for 2 hours, grind, and screen the ground biochar with a 200-mesh sieve; after screening, send the biochar into a sealed device for CO2 adsorption; the CO2 atmosphere in the sealed device is at room temperature and pressure, with a concentration of ≥50%, or in an industrial flue gas atmosphere, and it only takes 1.5 to 3 hours of adsorption time to reach adsorption saturation.

[0081] (2) Take out the saturated adsorbed biochar and use it as a carbonization internal curing agent to mix with cement materials to obtain a premix. Add the premix to water and mix evenly to obtain a slurry. After casting and forming, transfer it to a suitable environment for curing. After prehydration reaches a certain strength, demold the cement specimen to obtain a formed cement specimen. Biochar, as a carbonization internal curing material, slowly and continuously releases CO2 inside the cement specimen, performing carbonization internal curing on the specimen. The addition of biochar can also enhance external carbonization curing. Its porous structure can provide more CO2 diffusion pathways for external carbonization curing. The amount of carbonization internal curing material is ≤20%, and the amount of cement-based material is ≥80%. In terms of mass fraction, the water-cement ratio is controlled at 0.3~0.5, and the precuring time is 24 hours. There are no requirements for the mixing and pouring process, and it is sufficient to meet the national standard requirements.

[0082] (3) The molded and demolded cement specimens are placed in a carbonization curing kettle for external carbonization curing. After curing, they are transferred to a suitable environment and cured to a specified age, ultimately obtaining low-carbon cement products. The external carbonization curing pressure is 1-5 atmospheres, the CO2 concentration of industrial flue gas is generally 10%-30%, the carbonization curing temperature is 50℃-90℃, and the curing time is 12-48 hours.

[0083] Industrial flue gas is used in the carbonization curing kettle to achieve low-cost curing of low-carbon cement. The internal and external synergy further improves the carbonization degree and carbon fixation amount of the material, and significantly enhances the early compressive strength of the low-carbon cement specimens within a shorter curing cycle, realizing the secondary utilization of industrial waste gas, which is conducive to practical application and promotion.

[0084] A fourth typical embodiment of the present invention provides an application of the above-mentioned low-carbon cement or low-carbon cement specimen in carbon capture engineering and / or engineering construction.

[0085] This invention utilizes low-cost, carbon-negative biochar as a carbonization internal curing material, addressing the high cost and high carbon emissions of existing carbonization internal curing materials and significantly reducing the overall cost of producing low-carbon cement. By incorporating industrial flue gas as an external carbonization source, this invention reduces the reliance on demanding carbonization curing conditions, such as high pressure and high CO₂ concentrations, simplifying the curing process and enhancing its potential for industrial application.

[0086] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0087] The materials used in the following examples are all conventional commercially available products and can be purchased.

[0088] The cement powder used in the following examples is P.O42.5 cement (ordinary Portland cement).

[0089] Figure 1The adsorption capacity of different biochars for carbon dioxide is shown in Figure 2. The biochar used in the following examples and comparative examples is plant straw biochar. The preparation method of the plant straw biochar is as follows:

[0090] Forestry waste was pyrolyzed at 650°C in a nitrogen atmosphere for 2 hours to produce biochar (i.e., forestry waste biochar). The resulting biochar was then dried in an oven at 110°C for 2 hours, ground to a fine powder, and screened through a 200-mesh sieve. The screened biochar was then placed in a sealed device for CO2 adsorption. The CO2 concentration in the device was maintained at 99.99%, the temperature was set at 25°C, and the pressure was maintained at atmospheric pressure (0.1 MPa). The adsorption time was 2 hours, resulting in biochar saturated with CO2, which was used as a carbonization internal curing material.

[0091] Examples 1-3

[0092] A low carbon cement, calculated by mass fraction, has a formula as shown in Table 2.

[0093] Table 2 Formula of low carbon cement described in Examples 1-3

[0094]

[0095] Example 4

[0096] A method for preparing low-carbon cement comprises the following steps:

[0097] Calculated by mass, the low-carbon cement includes 10 parts of biochar saturated with carbon dioxide adsorption, 90 parts of cement powder, and 40 parts of water.

[0098] The carbonized internal curing material was uniformly mixed with cement powder to form a premix. The premix was added to water, mixed thoroughly, and then cast into shape. The casting mold used was a standard cubic mold with dimensions of 2 × 2 × 2 cm. The cast shape was transferred to a standard curing room for pre-curing. The temperature in the standard curing room was controlled at 20 ± 1°C and the humidity was maintained at 90 ± 2%. The pre-curing time was 24 hours.

[0099] After pre-curing, the formed cement specimens were placed in a carbonation curing kettle for external carbonation curing. The carbonation curing kettle simulated an industrial flue gas environment, with curing conditions set as follows: atmospheric pressure (0.1 MPa), a CO2 concentration of 15%, a temperature of 70°C, and a curing time of 24 hours. After curing, the samples were transferred to a constant temperature and humidity curing chamber and continued to cure for three days, ultimately producing low-carbon cement products.

[0100] Example 5

[0101] A method for preparing low-carbon cement differs from Example 4 in that:

[0102] Calculated by mass, the low-carbon cement includes 15 parts of biochar saturated with carbon dioxide adsorption, 85 parts of cement powder, and 40 parts of water.

[0103] The remaining steps are exactly the same as those in Example 4.

[0104] Example 6

[0105] A method for preparing low-carbon cement differs from Example 4 in that:

[0106] Calculated by mass, the low-carbon cement includes 20 parts of biochar saturated with carbon dioxide adsorption, 80 parts of cement powder, and 40 parts of water.

[0107] The remaining steps are exactly the same as those in Example 4.

[0108] Comparative Example 1-2

[0109] A low-carbon cement, the formula of which is shown in Table 3.

[0110] Table 3 Formula of low carbon cement described in Comparative Examples 1 and 2

[0111]

[0112] Comparative Example 3

[0113] A method for preparing cement comprises the following steps:

[0114] In parts by mass, the cement includes 100 parts of cement powder and 40 parts of water.

[0115] Cement powder was added to water, mixed thoroughly, and then cast into shape. A standard cubic mold with dimensions of 2 × 2 × 2 cm was used. The casted material was transferred to a standard curing room for pre-curing. The temperature in the standard curing room was controlled at 20 ± 1°C and the humidity was maintained at 90 ± 2%. The pre-curing time was 24 hours.

[0116] After the pre-curing is completed, the cement is cured in a standard curing room until the third day to obtain a conventional cement product.

[0117] Comparative Example 4

[0118] A method for preparing cement comprises the following steps:

[0119] In parts by mass, the cement includes 100 parts of cement powder and 40 parts of water.

[0120] Cement powder was added to water, mixed thoroughly, and then cast into shape. A standard cubic mold with dimensions of 2 × 2 × 2 cm was used. The casted material was transferred to a standard curing room for pre-curing. The temperature in the standard curing room was controlled at 20 ± 1°C and the humidity was maintained at 90 ± 2%. The pre-curing time was 24 hours.

[0121] After pre-curing, the formed cement specimens were placed in a carbonation curing kettle for external carbonation curing. The carbonation curing kettle simulated an industrial flue gas environment, with curing conditions set as follows: atmospheric pressure (0.1 MPa), a CO2 concentration of 15%, a temperature of 70°C, and a curing time of 24 hours. After curing, the samples were transferred to a constant temperature and humidity curing chamber and continued to cure for three days, ultimately producing low-carbon cement products.

[0122] Comparative Example 5

[0123] A method for preparing low-carbon cement, which differs from Comparative Example 3 in that, by weight, the low-carbon cement comprises 10 parts of biochar saturated with carbon dioxide adsorption, 90 parts of cement powder, and 40 parts of water.

[0124] The remaining steps are exactly the same as those in Comparative Example 3.

[0125] Comparative Example 6

[0126] A method for preparing low-carbon cement, which differs from Comparative Example 3 in that, by weight, the low-carbon cement comprises 15 parts of biochar saturated with carbon dioxide adsorption, 85 parts of cement powder, and 40 parts of water.

[0127] The remaining steps are exactly the same as those in Comparative Example 3.

[0128] Comparative Example 7

[0129] A method for preparing low-carbon cement, which differs from Comparative Example 3 in that, by weight, the low-carbon cement comprises 20 parts of biochar saturated with carbon dioxide adsorption, 80 parts of cement powder, and 40 parts of water.

[0130] The remaining steps are exactly the same as those in Comparative Example 3.

[0131] Comparative Example 8

[0132] A method for preparing low-carbon cement, which differs from Comparative Example 3 in that, by weight, the low-carbon cement comprises 25 parts of biochar saturated with carbon dioxide adsorption, 75 parts of cement powder, and 40 parts of water.

[0133] The remaining steps are exactly the same as those in Comparative Example 3.

[0134] The low carbon cement obtained in the examples and comparative examples was subjected to compressive strength test, XRD analysis, thermogravimetric test and carbon emission calculation. The compressive strength test is shown in Table 4.

[0135] Table 4 Statistics of compressive strength of each embodiment and comparative example on the 3rd day

[0136]

[0137] As can be seen from the data in Table 4, the compressive strength of Examples 4, 5, and 6 is significantly improved compared to that of Comparative Example 3, indicating that the low-carbon cement prepared by the method of the present invention has significant advantages in compressive strength. By comparing Examples 4, 5, and 6 with Comparative Example 4, it is found that replacing part of the cement with biochar as a carbonized internal curing material will affect the strength of the cement, and as the biochar content increases, the compressive strength gradually decreases. When the content of the carbonized internal curing material reaches 25% of the mass of the cement powder, the compressive strength of the cement product is too low. Therefore, the content of the carbonized internal curing material should be controlled within a reasonable range to avoid excessively low material strength. By comparing Examples 4, 5, and 6 with Comparative Examples 5, 6, and 7, it is found that the internal and external coordinated carbonization curing method can effectively compensate for the strength loss caused by a high content of carbonized internal curing material, effectively improving the initial strength of the material. However, when the content of carbonized internal curing material reaches 25% of the mass of cement powder (Comparative Example 8), the internal and external synergistic carbonization curing can no longer compensate for the negative impact of excessive carbonized internal curing material production on the compressive strength of cement products. Therefore, no other tests were performed on Comparative Examples 8 and 9.

[0138] By comparing the examples and comparative examples with the same dosage of carbonized internal curing material, it can be found that with the increase in the dosage of carbonized internal curing material, the compressive strength of the sample increases more after carbonization external curing, indicating that biochar as a carbonized internal curing material can enhance the external carbonization curing effect of cement, thereby further improving the strength of cement.

[0139] Figure 2 The X-ray diffraction analysis (XRD analysis) of the cement products obtained in Examples 4 and 5 of the present invention and Comparative Examples 3, 4, 5, and 7 is shown in FIG. Figure 2 It can be seen that the diffraction peak intensity of CaCO3 in Examples 4, 6 and Comparative Example 4 is significantly higher than that in Comparative Examples 3, 5 and 7, while the diffraction peak intensity of Ca(OH)2 is lower than that in the Comparative Example. This shows that the use of the preparation method of the present invention for internal and external coordinated carbonization curing can effectively promote the combination of more CO2 and Ca(OH)2 and be sealed, thereby significantly increasing the content of CaCO3 in the material. With the increase in the amount of carbonized internal curing material, the diffraction peak intensity of CaCO3 in Examples 4 and 6 is further enhanced, while the diffraction peak intensity of Ca(OH)2 is significantly weakened, indicating that biochar as a carbonized internal curing material can effectively enhance the carbonized external curing effect of cement.

[0140] Table 5 is a statistical table of carbon sequestration and material carbon emission calculations of the cement products prepared in Examples 4 and 6 and Comparative Examples 3, 4, 5, and 7 on the third day. Figure 3 Thermogravimetric spectra of the cement products prepared in Examples 4, 6 and Comparative Examples 3, 4, 5, and 7 on the third day. Figure 3 As shown, increasing the amount of carbonized internal curing material increases the carbon sequestration of cement products and significantly reduces carbon emissions throughout the product lifecycle. Using the preparation method provided by this invention for synergistic internal and external carbonization curing significantly increases the carbon sequestration of cement products, resulting in significant carbon emission reduction benefits. At a carbonized internal curing material content of 20% of the cement powder mass, CO2 emissions were reduced by 145 kg, achieving a negative carbon effect. Considering the negative impact of high carbonized internal curing material content on the compressive strength of cement products, it is concluded that the content of carbonized internal curing material should be ≤ 20% of the cement powder mass.

[0141] Table 5 Statistics of carbon sequestration and carbon emission of cement products prepared in Examples and Comparative Examples on the third day

[0142]

[0143] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A low carbon cement specimen, characterized in that: Calculated by mass, it includes 10-20 parts of biochar saturated with carbon dioxide adsorption, 80-90 parts of cement powder, and 30-50 parts of water; After the raw materials are mixed and formed, the obtained cement specimens are subjected to external carbonization curing to obtain low-carbon cement specimens; The preparation method of the low carbon cement specimen comprises: The biochar that has adsorbed carbon dioxide to a saturated state is mixed with cement powder to obtain a premix; The premix is ​​mixed with water to obtain a slurry, which is then cast into shape and cured to obtain a cement specimen; The cement specimens are subjected to external carbonization curing using industrial flue gas, wherein the carbon dioxide concentration in the industrial flue gas is 10%-30%, and low-carbon cement specimens are obtained under the coordinated internal and external carbonization curing; the external carbonization curing has a pressure of 1 atmosphere, a curing temperature of 50-90°C, and a curing time of 12-48 hours; The method for preparing the biochar saturated with carbon dioxide adsorption comprises: Forestry waste was pyrolyzed at 650°C in a nitrogen atmosphere for 2 hours to obtain biochar; the obtained biochar was dried in an oven at 110°C for 2 hours to dry it, then ground into a fine powder and screened through a 200-mesh sieve; the screened biochar was sent to a sealed device for CO2 adsorption. The CO2 concentration in the device was 99.99%, the temperature was set at 25°C, the pressure was maintained at 0.1 MPa, and the adsorption time was 2 hours to obtain biochar saturated with carbon dioxide adsorption.

2. The low carbon cement specimen according to claim 1, characterized in that: The low-carbon cement test piece comprises, by weight, 10-20 parts of biochar saturated with carbon dioxide adsorption, 80-90 parts of cement powder, and 40 parts of water.

3. The low carbon cement specimen according to claim 1, characterized in that: The low-carbon cement specimen comprises, by weight, 10 parts of biochar saturated with carbon dioxide adsorption, 90 parts of cement powder, and 40 parts of water.

4. The low carbon cement specimen according to claim 1, characterized in that: The low-carbon cement specimen comprises, by weight, 20 parts of biochar saturated with carbon dioxide adsorption, 80 parts of cement powder, and 40 parts of water.

5. A method for preparing a low carbon cement specimen according to any one of claims 1 to 4, characterized in that: include: The biochar that has adsorbed carbon dioxide to a saturated state is mixed with cement powder to obtain a premix; The premix is ​​mixed with water to obtain a slurry, which is then cast into shape and cured to obtain a cement specimen; The cement specimens were subjected to external carbonization curing using industrial flue gas, wherein the carbon dioxide concentration in the industrial flue gas was 10%-30%, and low-carbon cement specimens were obtained under the coordinated internal and external carbonization curing. The external carbonization curing had a pressure of 1 atmosphere, a curing temperature of 50-90°C, and a curing time of 12-48 h.

6. Use of the low-carbon cement specimen according to any one of claims 1 to 4 in carbon capture engineering and / or engineering construction.

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