Carbon dioxide injection process for low-carbon ready-mix concrete

Abstract

The present invention discloses a carbon dioxide injection process for low-carbon ready-mixed concrete, and relates to the technical field of low-carbon ready-mixed concrete. The process comprises the following steps: respectively weighing coarse aggregate, fine aggregate, cement, admixture, water and admixture; first pre-carbonizing the fine aggregate, cement, admixture, water and admixture in a closed space A to obtain a ready-mixed mortar; then mixing with the coarse aggregate and continuing to stir in the closed space A, when the mass concentration of CO2 in the closed environment A is ≤10%, transporting the material to the closed space B, continuing carbonization, and obtaining low-carbon ready-mixed concrete. The present application adopts gaseous CO2 for carbonization in a closed environment, which helps to improve the controllability of the low-carbon ready-mixed concrete production process, improve carbonization efficiency and carbon fixation, and also helps to reduce production costs.

Description

Technical Field

[0001] The present invention relates to the technical field of low-carbon ready-mixed concrete, and in particular to a carbon dioxide injection process for low-carbon ready-mixed concrete. Background Art

[0002] Most existing carbon sequestration methods focus on carbon sequestration in raw materials and product curing processes, and there is little research on carbon sequestration in the concrete mixing process.

[0003] The prior art discloses the following process for carbon sequestration technology in the mixing stage: a process for producing low-carbon ready-mixed concrete doped with CO2, comprising the following steps: S1, decompressing and separating the low-temperature liquid CO2; S2, uniformly mixing aggregate, cement, auxiliary cementitious materials and carbonation aids according to a certain water-binder ratio to obtain ready-mixed mortar; S3, introducing the separated CO2 into the ready-mixed mortar and continuously stirring for a certain period of time to obtain low-carbon ready-mixed concrete.

[0004] The above technology uses cryogenic liquid CO2 to mix directly with ready-mixed mortar. However, cryogenic liquid CO2 is not only expensive, but also needs to be transported from a cryogenic liquid CO2 liquefaction plant to a ready-mixed mortar production plant. Due to the liquefaction and transportation processes, the supply is unstable, affecting the timely production of low-carbon ready-mixed concrete. Moreover, the use of cryogenic liquid CO2 makes the CO2 concentration, total CO2 injection volume, and reaction pressure uncontrollable during the carbonization process of the ready-mixed mortar due to factors such as evaporation and escape of the cryogenic liquid CO2. Therefore, it is necessary to develop a more economical and controllable carbon dioxide injection process for low-carbon ready-mixed concrete. Summary of the Invention

[0005] In order to improve the controllability of the production process of low-carbon ready-mixed concrete and reduce production costs, the present application provides a carbon dioxide injection process for low-carbon ready-mixed concrete.

[0006] This application provides a carbon dioxide injection process for low-carbon ready-mixed concrete, which adopts the following technical solutions:

[0007] A carbon dioxide injection process for low-carbon ready-mixed concrete comprises the following steps:

[0008] Weighing materials: weigh coarse aggregate, fine aggregate, cement, admixtures, water and admixtures separately;

[0009] Mixing: Mixing fine aggregate, cement, admixtures, water and additives to obtain a mixture;

[0010] Pre-carbonization: Place the mixture in a closed environment A, stir the mixture, and inject carbonization gas containing CO2 and inert gas into the closed environment A at the same time. When the total mass of injected CO2 reaches 0.25-0.35% of the mass of cement, stop injecting carbonization gas containing CO2. When the air pressure in the closed environment A reaches 0.1-0.2MPa, premixed mortar is obtained.

[0011] Continue carbonization: mix the coarse aggregate with the ready-mixed mortar and continue stirring. When the mass concentration of CO2 in the closed environment A is ≤10%, stop stirring, discharge the gas in the closed environment A, and transport the materials in the closed environment A to the closed environment B. Under stirring, inject carbonized gas and inert gas containing CO2 into the closed environment B. When the total mass of the injected CO2 reaches 0.45-0.55% of the mass of cement, stop injecting carbonized gas containing CO2. When the air pressure in the closed environment B reaches 0.1-0.15MPa, keep the air pressure constant and continue stirring. When the mass concentration of CO2 in the closed environment B is ≤12%, stop stirring, discharge the gas in the closed environment B, and obtain low-carbon ready-mixed concrete.

[0012] By adopting the above technical solution, the present application adopts carbonized gas containing CO2 as a carbon source, which is not only easy to transport but also cheaper than low-temperature liquid CO2, which helps to reduce raw material costs and transportation costs and improve the controllability of raw material supply. Moreover, in the pre-carbonization step, fine aggregate, cement, admixtures, water and admixtures are first stirred and carbonized, which helps to reduce the total mass of the material during stirring and reduce the resistance to the stirring device during the stirring process, thereby reducing the energy consumption of the mixer and production costs. Carbon dioxide can form a mineralization reaction with the gelling components and other alkaline calcium and magnesium components in the concrete after early hydration and forming, forming carbonate products in the internal pores and interface structures of the concrete, thereby permanently sealing the carbon dioxide in the concrete.

[0013] The present application is carried out in a closed environment throughout the carbonization process, which can ensure that the injected CO2 and other gases will not escape, and help to regulate the total amount and gas pressure of the injected CO2. Moreover, in the pre-carbonization step, the mixture and coarse aggregate are placed in the same closed environment, which can prevent the leakage of CO2 and inert gas when the mixture and aggregate are mixed.

[0014] This method controls the gas pressure within the above-mentioned range, which helps improve carbonization efficiency. Monitoring the mass concentration of CO₂ in the gas helps monitor the amount of carbonized CO₂, thereby controlling the carbon sequestration in ready-mixed mortar and low-carbon ready-mixed concrete within a desired range. Therefore, this method helps improve the controllability of the low-carbon ready-mixed concrete production process, thereby producing low-carbon ready-mixed concrete with superior performance and reducing production costs. The above-mentioned process condition range helps improve carbonization efficiency and carbon sequestration.

[0015] In a specific embodiment, in the pre-carbonization step, the carbon fixation amount of the premixed mortar is 0.22-0.33%.

[0016] By adopting the above-mentioned technical solution and the above-mentioned process conditions, a carbon fixation amount of 0.22-0.33% can be achieved within a shorter mixing time. Moreover, at this carbon fixation amount, the premixed mortar not only has higher fluidity and is easy to transport, but also can quickly reach the required carbon fixation amount in the subsequent carbonization step, thereby helping to improve the efficiency of the method.

[0017] In a specific embodiment, in the pre-carbonization step, the total stirring time in the closed environment A is 30-120 seconds.

[0018] By adopting the above technical solution and under the above process conditions, a premixed mortar with a carbon fixation content of 0.22-0.33% can be obtained by stirring for 30-120 seconds.

[0019] In a specific embodiment, in the continued carbonization step, the carbon sequestration amount of the low-carbon ready-mixed concrete is 0.41-0.52%.

[0020] By adopting the above technical solution, under the above-mentioned carbon fixation amount of premixed mortar and continued carbonization process conditions, low-carbon premixed concrete with a carbon fixation amount of 0.41-0.52% can be quickly obtained. Moreover, the premixed mortar within this carbon fixation amount range has excellent working performance and can improve the compressive strength after curing. After curing, the carbon dioxide is permanently sealed in the concrete, which helps to reduce carbon dioxide emissions and improve the environment and climate.

[0021] In a specific embodiment, in the continued carbonization step, the total stirring time in the closed environment B is 9-12 minutes.

[0022] By adopting the above technical solution, under the above process conditions, low-carbon ready-mixed concrete with a carbon fixation content of 0.41-0.52% can be obtained by stirring for 9-12 minutes.

[0023] In a specific embodiment, in the pre-carbonization step, the admixture includes fly ash and mineral powder, and the weight ratio of the fly ash, mineral powder and cement is (2-5):(2-5):10.

[0024] By adopting this technical solution and using the aforementioned component ratios, it helps increase the carbon sequestration capacity of ready-mixed mortar and low-carbon ready-mixed concrete, thereby permanently storing more carbon dioxide and further reducing carbon dioxide emissions. Furthermore, this component ratio helps further improve the workability and compressive strength of the ready-mixed mortar.

[0025] In a specific embodiment, in the pre-carbonization and continued carbonization steps, the gases in the closed environment A and the closed environment B are discharged into the lime water.

[0026] By adopting the above technical solution, lime water can absorb CO2 in the exhausted gas and generate calcium carbonate with economic value. Therefore, it can not only further reduce CO2 emissions but also help to further reduce production costs.

[0027] In a specific embodiment, the carbonized gas containing CO2 is recycled waste gas containing CO2.

[0028] By adopting the above technical solution, recycled waste gas containing CO2 is used as the carbon source. Not only can it be transported nearby from factories around the concrete production plant, but the price is lower than that of pure CO2 gas. The working performance and compressive resistance of the low-carbon ready-mixed concrete are also relatively excellent. Therefore, it helps to further improve the raw material controllability and economy of this method.

[0029] In a specific embodiment, during the pre-carbonization and continued carbonization steps, the O2 content in the external environment of the closed environment A and the closed environment B is monitored in real time to maintain the O2 content within a range of ≥19.5%.

[0030] By adopting the above technical solution, the O2 content in the external environment can be maintained above 19.5%, which helps prevent workers from hypoxia, suffocation, etc. and is safer.

[0031] In a specific embodiment, during the pre-carbonization and continued carbonization steps, the internal temperature of the sealed environment A and the sealed environment B is maintained at 5-35°C.

[0032] By adopting the above technical solution, within the above temperature range, it helps to maintain a good flow state of the material, which is convenient for stirring. Moreover, the present applicant has found through experiments that the carbon fixation amount can be further increased.

[0033] In summary, this application includes at least one of the following beneficial technical effects:

[0034] 1. This application uses gaseous CO2 for carbonization in a closed environment, which helps improve the controllability of the low-carbon ready-mixed concrete production process, increase carbonization efficiency and carbon sequestration, and also helps reduce production costs;

[0035] 2. This application helps to further improve carbonization efficiency and carbon sequestration by optimizing process conditions;

[0036] 3. This application uses recycled waste gas containing CO2 for carbonization, which helps to improve the controllability and economy of this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a process flow chart of the carbon dioxide injection process for low-carbon ready-mixed concrete in Example 1 of the present application. DETAILED DESCRIPTION

[0038] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application were purchased from the market.

[0039] The present application is further described in detail below with reference to the following examples and comparative examples.

[0040] Example

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete, which adopts the following steps:

[0043] A weighing hopper was used to weigh 2277 kg of sand, 1260 kg of gravel with a particle size of 5-16 mm, 1887 kg of gravel with a particle size of 5-31.5 mm, 654 kg of cement, 534 kg of water, 219 kg of fly ash, 219 kg of mineral powder, and 13.08 kg of a water reducer. The water reducer can be any existing medium-effect carboxylic acid water reducer. In this example, PCA-10 water reducer was used.

[0044] Sand, cement, fly ash, mineral powder, water, and a water reducer are mixed to obtain a mixture, which is then added to a mixer (JS3000, nominal capacity 3000L). Stone is added to the aggregate hopper. The channels of the mixer and the aggregate hopper are sealed, leaving only the mixer and the aggregate hopper connected. The space connecting the mixer and the aggregate hopper forms a closed space A, and the mixer is then started. Pure CO2 gas and nitrogen are injected into closed space A at 25°C and 21r / min stirring conditions. When the total mass of the injected CO2 reaches 1.962kg, the injection of pure CO2 gas is stopped. When the air pressure in closed space A reaches 0.15MPa, a premixed mortar is obtained.

[0045] Then, gravel is added to the mixer and stirring is continued. When the CO2 mass concentration in confined space A drops to 10%, stirring is stopped and the gas in confined space A is discharged into saturated clear lime water. During the stirring process, the O2 content in the environment outside the mixer and aggregate hopper is monitored in real time and maintained within a range of ≥19.5%.

[0046] Operate the mixer to transport the material in the mixer to the relay bin (capacity: 9000L). After the relay bin is sealed, the internal space of the relay bin forms a closed space B. Stir the premixed mortar at 25°C and 21r / min stirring conditions, and inject pure CO2 gas and nitrogen into the closed space B at the same time. When the total mass of the injected CO2 reaches 3.27kg, stop injecting pure CO2 gas. When the air pressure in the closed space B reaches 0.125MPa, adjust the injection flow rate of nitrogen to maintain the air pressure in the closed space B at 0.125±0.01MPa. Continue stirring. When the mass concentration of CO2 in the closed space B drops to 12%, stop stirring and discharge the gas in the closed space B into saturated clear lime water to obtain low-carbon ready-mixed concrete. During the mixing process, monitor the O2 content in the external environment of the relay bin in real time throughout the process, and maintain the O2 content within the range of ≥19.5%.

[0047] Example 2

[0048] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A. When the total mass of the injected CO2 reaches 1.635 kg, the injection of pure CO2 gas is stopped.

[0049] Example 3

[0050] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A. When the total mass of the injected CO2 reaches 2.289 kg, the injection of pure CO2 gas is stopped.

[0051] Example 4

[0052] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that when the air pressure in the enclosed space A reaches 0.1 MPa, gravel is added to the mixer and stirring is continued.

[0053] Example 5

[0054] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that when the air pressure in the enclosed space A reaches 0.2 MPa, gravel is added to the mixer and stirring is continued.

[0055] Example 6

[0056] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space B. When the total mass of the injected CO2 reaches 2.943 kg, the injection of pure CO2 gas is stopped.

[0057] Example 7

[0058] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space B. When the total mass of the injected CO2 reaches 3.597 kg, the injection of pure CO2 gas is stopped.

[0059] Example 8

[0060] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that when the air pressure in the confined space B reaches 0.1 MPa, the nitrogen injection flow rate is adjusted to maintain the air pressure in the confined space B at 0.1±0.01 MPa, and stirring is continued.

[0061] Example 9

[0062] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that when the air pressure in the confined space B reaches 0.15 MPa, the nitrogen injection flow rate is adjusted to maintain the air pressure in the confined space B at 0.15±0.01 MPa, and stirring is continued.

[0063] Example 10

[0064] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A. When the total mass of the injected CO2 reaches 1.635 kg, the injection of pure CO2 gas is stopped; when the air pressure in the confined space A reaches 0.2 MPa, a ready-mixed mortar is obtained; pure CO2 gas and nitrogen are injected into the confined space B. When the total mass of the injected CO2 reaches 2.943 kg, the injection of pure CO2 gas is stopped; when the air pressure in the confined space B reaches 0.15 MPa, the injection flow rate of nitrogen is adjusted to maintain the air pressure in the confined space B at 0.15±0.01 MPa, and stirring is continued.

[0065] Example 11

[0066] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A. When the total mass of the injected CO2 reaches 2.289 kg, the injection of pure CO2 gas is stopped; when the air pressure in the confined space A reaches 0.1 MPa, a ready-mixed mortar is obtained; pure CO2 gas and nitrogen are injected into the confined space B. When the total mass of the injected CO2 reaches 3.597 kg, the injection of pure CO2 gas is stopped; when the air pressure in the confined space B reaches 0.1 MPa, the injection flow rate of nitrogen is adjusted to maintain the air pressure in the confined space B at 0.1±0.01 MPa, and stirring is continued.

[0067] Example 12

[0068] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that a weighing hopper is used to weigh 2277 kg of sand, 1260 kg of gravel with a particle size of 5-16 mm, 1887 kg of gravel with a particle size of 5-31.5 mm, 654 kg of cement, 534 kg of water, 261.6 kg of fly ash, 261.6 kg of mineral powder, and 13.08 kg of water reducer.

[0069] Example 13

[0070] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that a weighing hopper is used to weigh 2277 kg of sand, 1260 kg of gravel with a particle size of 5-16 mm, 1887 kg of gravel with a particle size of 5-31.5 mm, 654 kg of cement, 534 kg of water, 130.8 kg of fly ash, 130.8 kg of mineral powder, and 13.08 kg of water reducer.

[0071] Example 14

[0072] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that a weighing hopper is used to weigh 2277 kg of sand, 1260 kg of gravel with a particle size of 5-16 mm, 1887 kg of gravel with a particle size of 5-31.5 mm, 654 kg of cement, 534 kg of water, 327 kg of fly ash, 327 kg of mineral powder, and 13.08 kg of water reducer.

[0073] Example 15

[0074] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that a weighing hopper is used to weigh 2277 kg of sand, 1260 kg of gravel with a particle size of 5-16 mm, 1887 kg of gravel with a particle size of 5-31.5 mm, 654 kg of cement, 534 kg of water, 117.72 kg of fly ash, 117.72 kg of mineral powder, and 13.08 kg of water reducer.

[0075] Example 16

[0076] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that a weighing hopper is used to weigh 2277 kg of sand, 1260 kg of gravel with a particle size of 5-16 mm, 1887 kg of gravel with a particle size of 5-31.5 mm, 654 kg of cement, 534 kg of water, 359.7 kg of fly ash, 359.7 kg of mineral powder, and 13.08 kg of water reducer.

[0077] Example 17

[0078] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A under stirring conditions of 5°C and 21r / min; pure CO2 gas and nitrogen are injected into the confined space B under stirring conditions of 5°C and 21r / min.

[0079] Example 18

[0080] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A under stirring conditions of 35°C and 21r / min; pure CO2 gas and nitrogen are injected into the confined space B under stirring conditions of 35°C and 21r / min.

[0081] Example 19

[0082] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A under the stirring conditions of 4°C and 21r / min; pure CO2 gas and nitrogen are injected into the confined space B under the stirring conditions of 4°C and 21r / min.

[0083] Example 20

[0084] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas and nitrogen are injected into the confined space A under stirring conditions of 40°C and 21r / min; pure CO2 gas and nitrogen are injected into the confined space B under stirring conditions of 40°C and 21r / min.

[0085] Example 21

[0086] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas is replaced by recycled waste gas with a CO2 concentration of 80%.

[0087] Example 22

[0088] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas is replaced by recycled waste gas with a CO2 concentration of 50%.

[0089] Example 23

[0090] This embodiment provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this embodiment and Example 1 is that pure CO2 gas is replaced by recycled waste gas with a CO2 concentration of 20%.

[0091] Comparative Example

[0092] Comparative Example 1

[0093] This comparative example provides a carbon dioxide injection process for low-carbon ready-mixed concrete, which adopts the following steps:

[0094] A weighing hopper was used to weigh 2277 kg of sand, 1260 kg of gravel with a particle size of 5-16 mm, 1887 kg of gravel with a particle size of 5-31.5 mm, 654 kg of cement, 534 kg of water, 219 kg of fly ash, 219 kg of mineral powder, and 13.08 kg of a water reducer. The water reducer can be any existing medium-effect carboxylic acid water reducer. In this example, PCA-10 water reducer was used.

[0095] Sand, cement, water, fly ash, mineral powder and water reducing agent were mixed to obtain a mixture, which was added to a mixer (JS3000, nominal capacity 3000 L). The mixer was started, and 1.962 kg of low-temperature liquid CO2 was injected into the mixer at 25°C and 21 r / min, and stirred for 55 s to obtain a premixed mortar.

[0096] Then add the gravel into the mixer, continue stirring for 30 seconds, and stop stirring. During the stirring process, the O2 content in the external environment of the mixer is monitored in real time and maintained within the range of ≥19.5%.

[0097] Operate the mixer and transfer the material in the mixer to the relay bin (capacity: 9000L). Under the stirring conditions of 25°C and 21r / min, inject 3.27kg of low-temperature liquid CO2 into the relay bin and continue stirring. When the total stirring time in the relay bin reaches 11.3 minutes, stop stirring and discharge the gas in the closed relay bin into saturated clear lime water to obtain low-carbon ready-mixed concrete. During the stirring process, the O2 content in the external environment of the closed relay bin is monitored in real time throughout the process and the O2 content is maintained within the range of ≥19.5%.

[0098] Comparative Example 2

[0099] This comparative example provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this comparative example and Example 1 is that sand, cement, water, fly ash, mineral powder, and water reducer are mixed to obtain a mixture, the mixture is added to a mixer (JS3000 type, nominal capacity 3000L), gravel is added to the aggregate hopper, the channels of the mixer and the aggregate hopper are sealed, only the mixer and the aggregate hopper are kept connected, and the space connected inside the mixer and the aggregate hopper forms a closed space A, and then the mixer is started. Under stirring conditions of 25°C and 21r / min, pure CO2 gas and nitrogen are injected into the closed space A. When the total mass of the injected CO2 reaches 1.308kg, the injection of pure CO2 gas is stopped. When the air pressure in the closed space A reaches 0.05MPa, a ready-mixed mortar is obtained.

[0100] Then, gravel is added to the mixer and stirring is continued. When the CO2 mass concentration in confined space A drops to 10%, stirring is stopped and the gas in confined space A is discharged into saturated clear lime water. During the stirring process, the O2 content in the environment outside the mixer and aggregate hopper is monitored in real time and maintained within a range of ≥19.5%.

[0101] Operate the mixer to transport the material in the mixer to the relay bin (capacity: 9000L). After the relay bin is sealed, the internal space of the relay bin forms a closed space B. Stir the premixed mortar at 25°C and 21r / min stirring conditions, and inject pure CO2 gas and nitrogen into the closed space B at the same time. When the total mass of the injected CO2 reaches 2.616kg, stop injecting pure CO2 gas. When the air pressure in the closed space B reaches 0.05MPa, adjust the injection flow rate of nitrogen to maintain the air pressure in the closed space B at 0.05±0.01MPa. Continue stirring. When the mass concentration of CO2 in the closed space B drops to 12%, stop stirring and discharge the gas in the closed space B into saturated clear lime water to obtain low-carbon ready-mixed concrete. During the mixing process, monitor the O2 content in the external environment of the relay bin in real time throughout the process, and maintain the O2 content within the range of ≥19.5%.

[0102] Comparative Example 3

[0103] This comparative example provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this comparative example and Example 1 is that sand, cement, water, fly ash, mineral powder, and water reducer are mixed to obtain a mixture, the mixture is added to a mixer (JS3000 type, nominal capacity 3000L), gravel is added to the aggregate hopper, the channels of the mixer and the aggregate hopper are sealed, only the mixer and the aggregate hopper are kept connected, and the space connected inside the mixer and the aggregate hopper forms a closed space A, and then the mixer is started. Under stirring conditions of 25°C and 21r / min, pure CO2 gas and nitrogen are injected into the closed space A. When the total mass of the injected CO2 reaches 2.616kg, the injection of pure CO2 gas is stopped. When the air pressure in the closed space A reaches 0.25MPa, a ready-mixed mortar is obtained.

[0104] Then, gravel is added to the mixer and stirring is continued. When the CO2 mass concentration in confined space A drops to 10%, stirring is stopped and the gas in confined space A is discharged into saturated clear lime water. During the stirring process, the O2 content in the environment outside the mixer and aggregate hopper is monitored in real time and maintained within a range of ≥19.5%.

[0105] Operate the mixer to transport the material in the mixer to the relay bin (capacity: 9000L). After the relay bin is sealed, the internal space of the relay bin forms a closed space B. Stir the premixed mortar at 25°C and 21r / min stirring conditions, and inject pure CO2 gas and nitrogen into the closed space B at the same time. When the total mass of the injected CO2 reaches 3.924kg, stop injecting pure CO2 gas. When the air pressure in the closed space B is maintained at 0.2MPa, adjust the injection flow rate of nitrogen to bring the air pressure in the closed space B to 0.2±0.01MPa, and continue stirring. When the mass concentration of CO2 in the closed space B drops to 12%, stop stirring and discharge the gas in the closed space B into saturated clear lime water to obtain low-carbon ready-mixed concrete. During the mixing process, monitor the O2 content in the external environment of the relay bin in real time throughout the process, and keep the O2 content within the range of ≥19.5%.

[0106] Comparative Example 4

[0107] This comparative example provides a carbon dioxide injection process for low-carbon ready-mixed concrete. The difference between this comparative example and Example 1 is that sand, cement, water, fly ash, mineral powder, and water reducer are mixed to obtain a mixture, the mixture is added to a mixer (JS3000 type, nominal capacity 3000L), gravel is added to the aggregate hopper, the channels of the mixer and the aggregate hopper are sealed, only the mixer and the aggregate hopper are kept connected, and the space connected inside the mixer and the aggregate hopper forms a closed space A, and then the mixer is started. Under stirring conditions of 25°C and 21r / min, pure CO2 gas and nitrogen are injected into the closed space A. When the total mass of the injected CO2 reaches 5.232kg, the injection of pure CO2 gas is stopped. When the air pressure in the closed space A reaches 0.15MPa, a ready-mixed mortar is obtained.

[0108] The gravel was then added to the mixer and stirring continued. When the CO2 mass concentration in confined space A dropped to 10%, stirring was stopped and the gas in confined space A was discharged into saturated clarified lime water to obtain premixed mortar. During the stirring process, the O2 content in the environment outside the mixer and aggregate hopper was monitored in real time and maintained within a range of ≥19.5%.

[0109] Operate the mixer and transport the materials in the mixer to the relay bin (capacity: 9000L). After the relay bin is sealed, the internal space of the relay bin forms a closed space B. Stir the premixed mortar at 25°C and 21r / min stirring conditions, and inject nitrogen into the closed space B at the same time. When the air pressure in the closed space B reaches 0.125MPa, maintain the air pressure in the closed relay bin at 0.125±0.01MPa and continue stirring. When the total stirring time in the closed space B reaches 11.3min, stop stirring and discharge the gas in the closed space B into saturated clear lime water to obtain low-carbon ready-mixed concrete. During the stirring process, monitor the O2 content in the external environment of the relay bin in real time throughout the entire process, and maintain the O2 content in the range of ≥19.5%.

[0110] Comparative Example 5

[0111] This comparative example provides a carbon dioxide injection process for low-carbon ready-mixed concrete. This comparative example differs from Example 1 in that sand, cement, water, fly ash, mineral powder, and a water reducer are mixed to obtain a mixture, which is then added to a mixer (JS3000, nominal capacity 3000L). Stone is added to an aggregate hopper. The channels of the mixer and the aggregate hopper are sealed, leaving only the mixer and the aggregate hopper connected. The space connecting the mixer and the aggregate hopper forms a closed space A, and the mixer is then started. Nitrogen is injected into the closed space A under stirring conditions of 25°C and 21 r / min. When the air pressure in the closed space A reaches 0.15 MPa, a ready-mixed mortar is obtained.

[0112] The gravel was then added to the mixer and mixing continued. When the total mixing time in confined space A reached 85 seconds, mixing was stopped and the gas in confined space A was discharged into saturated clarified lime water to obtain premixed mortar. During the mixing process, the O2 content in the environment outside the mixer and aggregate hopper was monitored in real time and maintained within a range of ≥19.5%.

[0113] Operate the mixer to transport the material in the mixer to the relay bin (capacity: 9000L). After the relay bin is sealed, the internal space of the relay bin forms a closed space B. Stir the premixed mortar at 25°C and 21r / min stirring conditions, and inject pure CO2 gas and nitrogen into the closed space B at the same time. When the total mass of the injected CO2 reaches 5.232kg, stop injecting pure CO2 gas. When the air pressure in the closed space B reaches 0.125MPa, adjust the injection flow rate of nitrogen to maintain the air pressure in the closed space B at 0.125±0.01MPa. Continue stirring. When the mass concentration of CO2 in the closed space B drops to 12%, stop stirring and discharge the gas in the closed space B into saturated clear lime water to obtain low-carbon ready-mixed concrete. During the mixing process, monitor the O2 content in the external environment of the relay bin in real time throughout the process, and maintain the O2 content within the range of ≥19.5%.

[0114] Performance testing

[0115] Performance tests were performed on the ready-mixed mortars and low-carbon ready-mixed concretes prepared in Examples 1-23 and Comparative Examples 1-5.

[0116] The total mixing time of the mixer and the intermediate storage bin in each embodiment and comparative example was recorded. The carbon sequestration amount of the premixed mortar and low-carbon ready-mixed concrete in each embodiment and comparative example was tested according to GB / T 14902-2012 "Ready-mixed Mortar". The compressive strength of the low-carbon ready-mixed concrete after 28 days was tested. The results are shown in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] Combining Example 1 with Comparative Examples 1-5 and Table 1, it can be seen that compared to Example 1, the compressive strength of the low-carbon ready-mixed concrete in Comparative Examples 1-5 is lower, and the total mixing time in Comparative Examples 3-5 is longer. This shows that under the method of Example 1, the predetermined carbon sequestration amount can be achieved, with high controllability, which helps to simultaneously improve the carbonation efficiency and compressive strength of the low-carbon ready-mixed concrete.

[0121] From Examples 1-11 and Table 1, it can be seen that the total mixing time of the mixer in Examples 1-11 is ≤120s, and the total mixing time of the relay bin is ≤12min. Moreover, the carbonization efficiency and compressive strength of the low-carbon ready-mixed concrete are both high. This shows that within the process conditions of Examples 1-11, the predetermined carbon fixation amount can be achieved, the controllability is high, and it is helpful to improve the compressive strength of the low-carbon ready-mixed concrete.

[0122] Combining Example 1, Examples 12-16 and Table 1, it can be seen that Examples 12-16 not only have a shorter total mixing time, but also have a higher compressive strength of the low-carbon ready-mixed concrete. This shows that within the process conditions of Examples 12-16, it is helpful to further improve the carbonization efficiency and compressive strength of the low-carbon ready-mixed concrete.

[0123] Combining Example 1, Examples 17-20 and Table 1, it can be seen that the compressive strength of the low-carbon ready-mixed concrete of Examples 17-18 remains unchanged, while the compressive strength of the low-carbon ready-mixed concrete of Examples 19-20 decreases. This shows that within the temperature range of Examples 1 and 17-20, it is helpful to improve the compressive strength of the low-carbon ready-mixed concrete.

[0124] From Example 1, Examples 21-23 and Table 1, it can be seen that the predetermined carbon fixation amount can also be achieved by using Examples 21-23, and the compressive strength of the low-carbon ready-mixed concrete is also high. This shows that the method of the present application uses waste gas containing CO2 to improve the compressive strength of low-carbon ready-mixed concrete, which helps to reduce raw material costs.

[0125] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A carbon dioxide injection process for low-carbon ready-mixed concrete, characterized in that: The steps include: Weighing materials: weigh coarse aggregate, fine aggregate, cement, admixtures, water and admixtures separately; Mixing: Mixing fine aggregate, cement, admixtures, water and additives to obtain a mixture; Pre-carbonization: Place the mixture in a closed environment A, stir the mixture, and inject carbonization gas containing CO2 and inert gas into the closed environment A at the same time. When the total mass of injected CO2 reaches 0.25-0.35% of the mass of cement, stop injecting carbonization gas containing CO2. When the air pressure in the closed environment A reaches 0.1-0.2MPa, premixed mortar is obtained. Continue carbonization: mix the coarse aggregate with the ready-mixed mortar and continue stirring. When the mass concentration of CO2 in the closed environment A is ≤10%, stop stirring, discharge the gas in the closed environment A, and transport the materials in the closed environment A to the closed environment B. Under stirring, inject carbonized gas and inert gas containing CO2 into the closed environment B. When the total mass of the injected CO2 reaches 0.45-0.55% of the mass of cement, stop injecting carbonized gas containing CO2. When the air pressure in the closed environment B reaches 0.1-0.15MPa, keep the air pressure constant and continue stirring. When the mass concentration of CO2 in the closed environment B is ≤12%, stop stirring, discharge the gas in the closed environment B, and obtain low-carbon ready-mixed concrete.

2. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 1, characterized in that: In the pre-carbonization step, the carbon fixation amount of the premixed mortar is 0.22-0.33%.

3. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 2, characterized in that: In the pre-carbonization step, the total stirring time in the closed environment A is 30-120 seconds.

4. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 2, characterized in that: In the continued carbonization step, the carbon fixation amount of the low-carbon ready-mixed concrete is 0.41-0.52%.

5. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 4, characterized in that: In the continued carbonization step, the total stirring time in the closed environment B is 9-12 minutes.

6. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 1, characterized in that: In the pre-carbonization step, the admixture includes fly ash and mineral powder, and the weight ratio of the fly ash, mineral powder and cement is (2-5):(2-5):

10.

7. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 1, characterized in that: During the pre-carbonization and continued carbonization steps, the gases in the closed environment A and the closed environment B are discharged into the lime water.

8. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 1, characterized in that: The carbonized gas containing CO2 is a recovered waste gas containing CO2.

9. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 1, characterized in that: During the pre-carbonization and continued carbonization steps, the O2 content in the external environment of the closed environment A and the closed environment B is monitored in real time to maintain the O2 content within a range of ≥19.5%.

10. The carbon dioxide injection process for low-carbon ready-mixed concrete according to claim 1, characterized in that: During the pre-carbonization and continued carbonization steps, the internal temperature of the sealed environment A and the sealed environment B is maintained at 5-35°C.

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