A carbon dioxide-cured concrete and its preparation method

Abstract

This invention discloses a CO2-cured concrete and its preparation method, belonging to the field of building materials technology. The concrete comprises the following raw materials: cement 350-380 kg / m³. 3 Coarse aggregate 1000-1100 kg / m³ 3 Water 100-110 kg / m³ 3 Fine aggregate 850-880 kg / m³ 3 Water-reducing agent 4-6 kg / m³ 3 The method involves incorporating a specially formulated CO2 adsorbent as a functional component into concrete raw materials. This adsorbent is pre-loaded with CO2. During the concrete forming and curing stage, the CO2 inside the adsorbent is slowly released, promoting carbonation from within. This synergistic internal and external curing mechanism overcomes the shortcomings of traditional single external carbonation, which easily leads to surface densification and hinders internal reactions, achieving uniform action and deep sequestration of CO2 within the concrete.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a CO2-cured concrete and its preparation method. Background Technology

[0002] As one of the most important building materials, concrete's production and curing processes have a significant impact on the environment. Cement production is one of the main sources of CO2 greenhouse gas emissions, and traditional concrete curing processes typically consume large amounts of water and heat energy.

[0003] In recent years, CO2 curing of concrete (i.e., carbonation curing) has attracted attention as a potential technological approach. This technology aims to encapsulate industrially emitted CO2 within concrete products while simultaneously promoting the hydration and carbonation reactions of cementitious materials. Theoretically, this could improve the early strength of concrete and achieve carbon emission reduction. Traditional CO2 curing methods typically involve placing molded concrete specimens in a specialized carbonation chamber. By controlling the temperature, humidity, and CO2 concentration within the chamber, CO2 diffuses from the surface of the specimen inwards, reacting with cement hydration products to form calcium carbonate.

[0004] However, this traditional outside-in curing method has inherent drawbacks. High concentrations of CO2 react rapidly with calcium ions in the concrete pore solution at the surface, forming a dense calcium carbonate layer. This dense layer, in turn, hinders the diffusion of subsequent CO2 and moisture into the deeper parts of the concrete, causing the carbonation process to remain mainly on the surface of the specimen, failing to effectively and uniformly cure the internal structure. This can lead to uneven development of the internal and external properties of the concrete product, insufficient activation of internal strength, limited overall performance improvement, and low carbon sequestration efficiency. Therefore, how to achieve uniform and slow release of CO2 within the concrete to realize synergistic strengthening from the inside out is the key issue in improving the effectiveness of CO2 curing technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of traditional CO2 carbonation curing methods in the prior art, such as dense carbonation layer, obstruction of internal curing, and uneven internal and external properties of concrete. The invention provides a CO2-cured concrete and its preparation method that can realize the slow release of CO2 from the inside and synergistic external carbonation curing, thereby comprehensively improving the mechanical properties of concrete.

[0006] To solve the above-mentioned technical problems, the technical solution proposed in this application is as follows:

[0007] This invention provides a CO2-cured concrete, comprising the following raw materials: cement 350-380 kg / m³ 3 Coarse aggregate 1000-1100 kg / m³ 3 Water 100-110kg / m 3Fine aggregate 850-880 kg / m³ 3 Water-reducing agent 4-6 kg / m³ 3 And CO2 adsorbent; the amount of CO2 adsorbent is 1-5% of the cement mass.

[0008] Furthermore, the fine aggregate is river sand with a fineness modulus of 2.8; the coarse aggregate is continuously graded crushed stone with a particle size of 5-30mm, and its surface is in a dry state after being washed with water and naturally air-dried.

[0009] Furthermore, the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 25%, and its dosage is 1%-2% of the cement mass; the cement is P·O42.5 silicate cement.

[0010] Furthermore, the CO2 adsorbent is prepared by the following method:

[0011] SS1: Weigh activated carbon and stir and wash it in a weak alkaline cleaning solvent containing 1-3wt% NaOH to remove stains. After drying, it is crushed into powder to obtain pretreated activated carbon powder C1.

[0012] SS2: The pretreated activated carbon powder C1 is soaked in an active solvent and stirred for 2 hours, and then dried in a vacuum drying oven at 60±5℃ for 1 hour to obtain activated carbon C2 loaded with active substances. The active solvent is a mixture of polyethyleneimine (PEI) and ethanol in a mass ratio of 1:4.

[0013] SS3: Place the activated carbon C2 loaded with active material into a sealed pressure chamber, and continuously introduce CO2 gas with a concentration greater than 95% for 3-4 hours at 15±2℃ and 1±0.1 bar, and then let it stand for 1 hour to obtain activated carbon C3 with adsorption saturation.

[0014] SS4: The adsorbed saturated activated carbon C3 is placed in a 5-10% silica sol solution and gently stirred for 3-5 minutes to form a SiO2 coating on its surface. Then it is taken out, filtered, and placed in a vacuum drying oven to dry, thus obtaining the CO2 adsorbate.

[0015] On the other hand, this application also claims protection for a method for preparing CO2-cured concrete, comprising the following steps:

[0016] S1: Add cement, fine aggregate, and coarse aggregate to a mixer and dry mix for 1 minute to obtain mixed dry material W1;

[0017] S2: Pour most of the mixing water into the dry mixture W1 and stir for 50 seconds to obtain a pre-wetted mixture;

[0018] S3: After pre-mixing the CO2 adsorbent with the water-reducing agent, add it to the pre-wetted mixture and continue stirring for 30 seconds to obtain the preliminary mixture W2;

[0019] S4: Pour all the remaining mixing water into the preliminary mixture W2, stir evenly, and obtain fresh concrete paste W3;

[0020] S5: The freshly mixed concrete paste W3 is poured into a mold, vibrated to compact it, and the surface is smoothed. After being sealed and covered with plastic film, it is left to cure under natural indoor conditions for 1 day to obtain the initial set specimen W4.

[0021] S6: After demolding the initial set specimen W4, place it in a carbonation chamber for curing for 28-32 days. The curing conditions are: temperature 25±2℃, relative humidity >95%, and CO2 volume concentration 20±3%, to obtain the CO2-cured concrete.

[0022] Furthermore, in step S2, the amount of the majority of the mixing water is 70%-85% of the total mass of the mixing water.

[0023] Furthermore, the amount of CO2 adsorbent is 2%-3% of the cement mass.

[0024] Furthermore, in step S5, the temperature of the indoor natural conditions is 18-25℃.

[0025] Furthermore, in step S6, the CO2 gas in the carbonization box is an industrial by-product or recycled CO2 gas.

[0026] Furthermore, in step S3, the CO2 adsorbent and the water-reducing agent are manually mixed evenly in a small container before being added to the mixer.

[0027] Compared with the prior art, the present invention achieves the following beneficial technical effects:

[0028] This invention embeds a CO2-loadable functional adsorbent within concrete, enabling the slow release and reaction of CO2 from the inside out during curing. This synergistic internal and external curing mechanism effectively overcomes the shortcomings of traditional external carbonation, which leads to surface densification and hinders internal penetration. It promotes the uniform formation of calcium carbonate within the concrete, significantly refining the microstructure and thus comprehensively improving the mechanical properties and overall uniformity of the concrete. Simultaneously, this method directly encapsulates industrial CO2 within the concrete product, achieving carbon emission reduction during building material production, while simultaneously providing excellent mechanical strengthening effects and significant environmental benefits. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides an innovative CO2-cured concrete and its preparation method. The core of the invention lies in the introduction of an adsorbent that can be pre-loaded with CO2. This adsorbent, as a component of the concrete, is uniformly dispersed throughout the system during mixing. During the concrete hardening process, the CO2 within the adsorbent is slowly released, promoting carbonation reactions within the internal space. This, combined with the CO2 curing environment provided by the external carbonation chamber, creates a synergistic effect, jointly improving the microstructural density and macroscopic mechanical properties of the concrete.

[0031] The technical solution and effects of the present invention will be described in detail below with reference to specific embodiments and comparative examples. Experimental methods not specified with particular conditions in the embodiments are generally performed under conventional conditions in the art.

[0032] First, the main raw materials used in the examples and comparative examples will be described:

[0033] Cement: P·O 42.5 grade ordinary Portland cement is used, and its performance meets the national standard GB 175-2007.

[0034] Fine aggregate: Natural river sand with a fineness modulus of 2.8 and an apparent density of 2650 kg / m³. 3 .

[0035] Coarse aggregate: Continuously graded crushed stone with a particle size of 5-20mm is used. Before use, it is washed with water and naturally air-dried until surface dry, with an apparent density of 2700 kg / m³. 3 .

[0036] Water-reducing agent: Use a high-performance polycarboxylate-based water-reducing agent with a solid content of 40%. The recommended dosage is 1.0%-2.0% of the mass of the cementitious material, and the water reduction rate can reach more than 25%.

[0037] CO2 adsorbent: Prepared according to the method described in this invention, the specific preparation steps are as follows:

[0038] a) Pretreatment: Weigh a certain amount of granular activated carbon and put it into a container containing 2wt% NaOH solution. Stir and wash to remove surface stains and impurities. After taking it out, rinse it with water until neutral, dry it, and then crush it with a grinding device and sieve it to obtain activated carbon powder with uniform particle size, which is denoted as C1.

[0039] b) Active material loading: Prepare an active solvent in which polyethyleneimine (PEI) and anhydrous ethanol are mixed uniformly at a mass ratio of 1:4. Immerse the activated carbon powder C1 obtained in step a in this active solvent and stir continuously for 2 hours to allow PEI to be fully loaded into the porous structure of the activated carbon. Then, transfer the mixture to a vacuum drying oven and dry it at 60°C for 1 hour to obtain PEI-loaded activated carbon, denoted as C2.

[0040] c) CO2 Adsorption: PEI-loaded activated carbon C2 is evenly spread in the loading tray of a sealed pressure vessel. CO2 gas with a purity >95% is continuously introduced into the vessel, maintaining the ambient temperature at 15°C and the pressure at 1 bar (standard atmospheric pressure) for 4 hours to allow the activated carbon to fully adsorb CO2. After the aeration process ends, the vessel is kept sealed and allowed to stand for 1 hour to allow adsorption equilibrium, yielding a saturated CO2 adsorbate precursor, denoted as C3.

[0041] d) Coating and Encapsulation: Prepare an 8% silica sol aqueous solution. Slowly add the C3 obtained in step c to the silica sol solution and stir very gently with a glass rod for about 4 minutes to ensure a thin, uniform silica sol coating on the surface of the C3 particles. Then, use a filter to remove the particles and drain off excess solution. Finally, place the wet particles back into a vacuum drying oven to dry and solidify the SiO2 coating on the surface, obtaining the final CO2 adsorbent product. This adsorbent is stable when dry. When exposed to the alkaline water environment of concrete, the SiO2 coating on its surface gradually dissolves, releasing the internally loaded CO2.

[0042] Comparative Example 1: Ordinary Concrete NC

[0043] This example is a comparative example, showing the preparation of a baseline ordinary concrete (NC) without the addition of CO2 adsorbents.

[0044] The raw material ratio (per cubic meter of concrete) is as follows: 360 kg of cement, 855 kg of fine aggregate (river sand), 1034.63 kg of coarse aggregate (crushed stone), 108.88 kg of water, and 5.12 kg of water-reducing agent (1.42% of the cement mass).

[0045] The preparation method is as follows:

[0046] Pour the weighed cement, river sand, and gravel into a forced single-shaft concrete mixer, turn on the mixer and dry mix for 60 seconds to ensure the dry materials are evenly mixed, thus obtaining W1.

[0047] Add about 80% of the mixing water (about 87.1 kg) to W1 and continue stirring for 50 seconds to obtain a preliminarily moistened mixture.

[0048] The water-reducing agent is premixed with the remaining approximately 20% of the mixing water (approximately 21.78 kg) until homogeneous. Then, the mixture is poured into a mixer and stirred until the concrete mixture is homogeneous and the slump meets the requirements, thus obtaining fresh concrete paste W3.

[0049] W3 was poured into a cubic mold with dimensions of 100mm×100mm×100mm, compacted on a vibrating table, and the surface was smoothed with a trowel.

[0050] Cover the surface of the test mold tightly with plastic film and place it indoors at a temperature of 20±2℃ for 24 hours for static curing.

[0051] After 24 hours, the specimen was demolded and immediately transferred to a standard curing room (temperature 20±2℃, relative humidity ≥95%) for curing until 28 days of age. This specimen is designated as NC.

[0052] Example 2: CO2-cured concrete CNC1

[0053] This embodiment prepares CO2-cured concrete (CNC1) with a CO2 adsorbent content of 1% of the cement mass.

[0054] The raw material ratio (per cubic meter of concrete) is as follows: cement 360 kg, fine aggregate (river sand) 812.25 kg, coarse aggregate (crushed stone) 1034.63 kg, water 108.88 kg, water-reducing agent 5.12 kg, and CO2 adsorbent 3.6 kg (1% of the cement mass). Due to the addition of CO2 adsorbent, the amount of fine aggregate (river sand) was reduced accordingly to maintain the total volume of concrete.

[0055] The preparation method is as follows:

[0056] The weighed cement, river sand, and gravel are poured into a forced single-shaft concrete mixer, and the mixer is turned on to dry mix for 60 seconds to obtain mixed dry material W1.

[0057] Add approximately 80% of the mixing water (approximately 87.1 kg) to W1 and continue stirring for 50 seconds.

[0058] The CO2 adsorbent (3.6 kg) and water-reducing agent (5.12 kg) were manually mixed evenly in a small container before being added to a mixer and stirred for 30 seconds to initially disperse the adsorbent.

[0059] Pour the remaining mixing water (approximately 21.78 kg) into the mixer and continue mixing until the concrete mixture is uniform and the slump is similar to that of NC in Example 1, thus obtaining fresh concrete paste W3.

[0060] The steps of pouring, vibrating, smoothing, covering and curing for 24 hours were the same as in Example 1 to obtain the initial set specimen W4.

[0061] After demolding, specimen W4 was placed in a dedicated carbonation chamber for curing. The environmental parameters of the carbonation chamber were set as follows: temperature 25℃, relative humidity >95%, and CO2 concentration 20%. Curing was carried out continuously under these conditions for 28 days. After curing, a CO2-cured concrete specimen was obtained, designated CNC1.

[0062] Example 3: CO2 Curing Concrete CNC2

[0063] This embodiment prepares CO2-cured concrete (CNC2) with a CO2 adsorbent content of 2% of the cement mass.

[0064] Raw material proportions (per cubic meter of concrete): cement 360 kg, fine aggregate 812.25 kg, crushed stone 1034.63 kg, water 108.88 kg, water-reducing agent 5.12 kg, CO2 adsorbent 7.2 kg (2% of cement mass). The preparation method is exactly the same as in Example 2, only the CO2 adsorbent dosage is different. The specimen after curing is designated CNC2.

[0065] Example 4: CO2 Curing Concrete CNC3

[0066] This embodiment prepares CO2-cured concrete (CNC3) with a CO2 adsorbent content of 3% of the cement mass.

[0067] Raw material proportions (per cubic meter of concrete): cement 360 kg, fine aggregate 812.25 kg, crushed stone 1034.63 kg, water 108.88 kg, water-reducing agent 5.12 kg, CO2 adsorbent 10.8 kg (3% of cement mass). The preparation method is exactly the same as in Example 2, only the CO2 adsorbent dosage is different. The specimen after curing is designated CNC3.

[0068] Example 5: CO2 Curing Concrete CNC4

[0069] This embodiment prepares CO2-cured concrete (CNC4) with a CO2 adsorbent content of 4% of the cement mass.

[0070] Raw material proportions (per cubic meter of concrete): cement 360 kg, fine aggregate 812.25 kg, crushed stone 1034.63 kg, water 108.88 kg, water-reducing agent 5.12 kg, CO2 adsorbent 14.4 kg (4% of cement mass). The preparation method is exactly the same as in Example 2, only the CO2 adsorbent dosage is different. The specimen after curing is designated CNC4.

[0071] Example 6: CO2 Curing Concrete CNC5

[0072] This embodiment prepares CO2-cured concrete (CNC5) with a CO2 adsorbent content of 5% of the cement mass.

[0073] Raw material proportions (per cubic meter of concrete): cement 360 kg, fine aggregate 812.25 kg, crushed stone 1034.63 kg, water 108.88 kg, water-reducing agent 5.12 kg, CO2 adsorbent 18 kg (5% of cement mass). The preparation method is exactly the same as in Example 2, only the CO2 adsorbent dosage is different. The specimen after curing is designated CNC5.

[0074] Performance testing

[0075] For all concrete specimens from examples (NC, CNC1-CNC5) cured to the specified age (28 days), mechanical properties were tested according to the national standard GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The main tests included cubic compressive strength, splitting tensile strength, and flexural strength. The average value of three specimens was used as the result for each test item. The test results are summarized in the table below:

[0076]

[0077] Results analysis:

[0078] The test data in the table above shows that:

[0079] Compared to ordinary concrete (NC) without added CO2 adsorbents, concrete (CNC1-CNC5) with added CO2 adsorbents and cured in a carbonation chamber showed varying degrees of improvement in compressive strength, splitting tensile strength, and flexural strength at most admixture dosages. This demonstrates the effectiveness of the synergistic technology of "built-in CO2 adsorbent + external carbonation curing" proposed in this invention.

[0080] There is an optimal range for the CO2 adsorbent dosage to enhance performance. Data shows that the most significant improvements in various mechanical properties of concrete are observed when the adsorption dosage is 1%-3% of the cement mass (CNC1-CNC3). Particularly at a dosage of 3% (CNC3), the compressive strength and splitting tensile strength reach their peak values, increasing by approximately 16% and 17.6% respectively compared to the baseline NC. At a dosage of 2% (CNC2), the flexural strength shows the most significant improvement, reaching 46.1%.

[0081] When the admixture dosage was further increased to 4% and 5% (CNC4, CNC5), the mechanical properties of the concrete actually showed a downward trend, even falling below the baseline NC. This may be because excessive adsorbent particles introduced too many weak interfaces into the concrete or affected the normal hydration structure of the cement paste, and the negative effects outweighed the positive enhancing effects of CO2 curing.

[0082] In summary, this invention integrates CO2 adsorbents into concrete at an appropriate dosage (preferably 1-3%), enabling the slow release and reaction of CO2 from the inside out during subsequent carbonation curing. This method effectively avoids the drawbacks of traditional external carbonation curing, which tends to form a dense surface layer that hinders internal reactions. It allows CO2 to act more evenly on the entire concrete structure, promoting the conversion of internal hydration products and the uniform precipitation of calcium carbonate, thereby filling micropores, refining the pore structure, and ultimately achieving a comprehensive improvement in the mechanical properties of concrete from the inside out. Furthermore, this method immobilizes industrial CO2, offering environmental benefits.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing CO2-cured concrete, characterized in that, The following raw materials are included in the preparation: cement 350-380 kg / m³ 3 Coarse aggregate 1000-1100 kg / m³ 3 Water 100-110kg / m 3 Fine aggregate 850-880kg / m³ 3 Water-reducing agent 4-6 kg / m³ 3 And CO2 adsorbent; the amount of CO2 adsorbent is 1-5% of the cement mass; The CO2 adsorbate was prepared by the following method: SS1: Weigh activated carbon and stir and wash it in a weak alkaline cleaning solvent containing 1-3wt% NaOH to remove stains. After drying, it is crushed into powder to obtain pretreated activated carbon powder C1. SS2: The pretreated activated carbon powder C1 is soaked in an active solvent and stirred for 2 hours, and then dried in a vacuum drying oven at 60±5℃ for 1 hour to obtain activated carbon C2 loaded with active substances. The active solvent is a mixture of polyethyleneimine (PEI) and ethanol in a mass ratio of 1:

4. SS3: Place the activated carbon C2 loaded with active material into a sealed pressure chamber, and continuously introduce CO2 gas with a concentration greater than 95% for 3-4 hours at 15±2℃ and 1±0.1 bar, and then let it stand for 1 hour to obtain activated carbon C3 with adsorption saturation. SS4: The adsorption-saturated activated carbon C3 is placed in a 5-10% silica sol solution and gently stirred for 3-5 minutes to form a SiO2 coating on its surface. Then it is taken out, filtered, and placed in a vacuum drying oven to dry, thus obtaining the CO2 adsorbent. The preparation method includes the following steps: S1: Add cement, fine aggregate, and coarse aggregate to a mixer and dry mix for 1 minute to obtain mixed dry material W1; S2: Pour most of the mixing water into the dry mixture W1 and stir for 50 seconds to obtain a pre-wetted mixture; S3: After pre-mixing the CO2 adsorbent with the water-reducing agent, add it to the pre-wetted mixture and continue stirring for 30 seconds to obtain the preliminary mixture W2; S4: Pour all the remaining mixing water into the preliminary mixture W2, stir evenly, and obtain fresh concrete paste W3; S5: The freshly mixed concrete paste W3 is poured into a mold, vibrated to compact it, and the surface is smoothed. After being sealed and covered with plastic film, it is left to cure under natural indoor conditions for 1 day to obtain the initial set specimen W4. S6: After demolding the initial set specimen W4, place it in a carbonation chamber for curing for 28-32 days. The curing conditions are: temperature 25±2℃, relative humidity >95%, and CO2 volume concentration 20±3%, to obtain the CO2-cured concrete.

2. The method for preparing CO2-cured concrete according to claim 1, characterized in that, The fine aggregate is river sand with a fineness modulus of 2.8; the coarse aggregate is continuously graded crushed stone with a particle size of 5-30mm, and its surface is in a dry state after being washed with water and naturally air-dried.

3. The method for preparing CO2-cured concrete according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 25%, and its dosage is 1%-2% of the cement mass; the cement is P·O42.5 silicate cement.

4. The preparation method according to claim 1, characterized in that, In step S2, the amount of the majority of the mixing water is 70%-85% of the total mass of the mixing water.

5. The preparation method according to claim 1, characterized in that, The amount of CO2 adsorbent is 2%-3% of the cement mass.

6. The preparation method according to claim 1, characterized in that, In step S5, the indoor natural temperature is 18-25℃.

7. The preparation method according to claim 1, characterized in that, In step S6, the CO2 gas in the carbonization box is an industrial by-product or recycled CO2 gas.

8. The preparation method according to claim 1, characterized in that, In step S3, the CO2 adsorbent and the water-reducing agent are manually mixed evenly in a small container before being added to the mixer.

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