Carbon-sequestration low-calcium cement concrete and preparation method thereof

Abstract

The invention discloses carbon-sequestration low-calcium cement concrete and a preparation method thereof, and belongs to the field of building materials. The carbon-sequestration low-calcium cement concrete is prepared from the following components in parts by weight: 18 to 50 parts of low-calcium cement, 24.8 to 72 parts of carbon-sequestration aggregate, 9.9 to 25 parts of water and 0.1 to 0.5 part of additive, the sum of the parts of the components is 100. Through reasonable design of raw material composition and process optimization, on the basis of pouring molding, the rapid demolding requirement of the carbon-sequestration low-calcium cement concrete is met, all-component efficient carbon sequestration of the carbon-sequestration low-calcium cement concrete is achieved, and internal homogeneous carbonation of the carbon-sequestration low-calcium cement concrete is achieved. The carbon-sequestration low-calcium cement concrete disclosed by the invention has the characteristics of excellent carbonation performance, simple preparation process and long-term stable development of product strength.

Description

Technical Field

[0001] The invention belongs to the field of building materials and relates to a carbon-fixing low-calcium cement concrete hardened by CO2 carbonation curing and a preparation method thereof. Background Art

[0002] Concrete is the main engineering construction material with huge consumption. my country consumes nearly 10 billion tons of concrete every year. However, existing concrete mainly uses silicate cement as a cementing material. In order to obtain excellent mechanical strength and early hydration activity, there are a large number of high-calcium minerals such as C3S and C3A in the silicate cement clinker minerals, and a large amount of limestone resources are required to burn such minerals. On the other hand, in order to ensure the formation of a high proportion of C3S and C3A high-calcium mineral phases in silicate cement clinker, the burning temperature of the clinker usually needs to reach about 1450°C. The high proportion of calcium raw material consumption and decomposition and high burning temperature will cause a large amount of CO2 to be emitted from cement clinker production. Therefore, the design of high-calcium mineral (C3S and C3A) components in cement clinker is the fundamental reason for the high energy consumption and carbon emissions in the formation process of traditional silicate cement clinker. The use of a large amount of silicate cement in existing concrete has brought great challenges to my country's carbon peak and carbon neutrality work. Many researchers and scholars at home and abroad have been committed to reducing carbon emissions from traditional concrete. Among them, low-calcium cement with carbonatable low-calcium silicate minerals such as C3S2, C2S, and CS as the main components has been widely proposed. The technical method of carbon-fixing low-calcium cement concrete using CO2 carbonation curing and hardening has become a future development trend due to its advantages such as low carbon emissions from low-calcium cement clinker burning and CO2 absorption during the hardening process.

[0003] Patent CN115557755B discloses a carbon-fixing low-calcium regenerated permeable concrete. Although low-calcium cement is used to reduce carbon emissions, it uses a pressing molding process. Patent CN116477881A, Patent CN110818356B and Patent CN114873979A disclose three types of carbonized concrete and their preparation methods. Although casting molding process and low-calcium cement are used, it is still necessary to use materials with high hydration activity in the raw materials, such as silicate cement, sulfoaluminate cement, C3S and C3A and other high-carbon emission clinker minerals, and the preparation process is complicated. Patent CN116835931A discloses a carbonized lightweight aggregate concrete and its preparation method. Although casting molding process and low-calcium cement are used, demolding of the product is not achieved, and the aggregate uses high-temperature fired ceramsite and natural aggregate. The existing carbon-fixing low-calcium cement concrete has the following problems:

[0004] (1) In order to quickly demould and facilitate carbonation curing, carbon-fixing low-calcium cement concrete products are mostly pressed and formed. The molding pressure is high, and the size and shape of the products are difficult to guarantee. This is because the low-calcium clinker minerals in the existing low-calcium cement are mostly γ-C2S, C3S2, CS, and the hydration activity of these minerals is very weak or even non-existent. If the casting molding process is used, high-carbon emission and high-hydration activity raw materials are used in addition for rapid demoulding, which increases the carbon emission of raw materials and the production process.

[0005] (2) Most existing carbon-fixing low-calcium cement concretes use natural aggregates such as river sand and quartz sand. Natural aggregates not only require mining costs, but also bring pressure on environmental protection.

[0006] (3) During the production process of carbon-fixing low-calcium cement concrete, as the carbonation time increases, the outer concrete gradually becomes denser, making it difficult for CO2 to continuously enter the matrix. The carbonation degree and carbon fixation capacity of carbon-fixing low-calcium concrete are limited.

[0007] (4) The hydration activity of low-calcium clinker minerals in existing carbon-fixing low-calcium cement concrete is very weak or even non-existent, and the performance growth requirements and long-term reliability of carbon-fixing low-calcium cement concrete products during service are not taken into account.

[0008] Therefore, how to make full use of the carbon fixation advantages and carbonation properties of low-calcium cement to prepare castable carbon-fixing low-calcium cement concrete products, break through the limitations of CO2 channels, meet the efficient and homogeneous carbonation reactions inside and outside the carbon-fixing low-calcium cement concrete, achieve efficient carbon fixation of all components of raw materials, and ensure the long-term stability and reliability of product strength is a technical problem that needs to be solved urgently. Summary of the invention

[0009] The purpose of the present invention is to overcome the above-mentioned technical problems and shortcomings of the existing carbon-fixing low-calcium cement concrete, and to propose a new type of carbon-fixing low-calcium cement concrete and its preparation method. On the basis of casting and molding, the carbon emission of the raw materials of the carbon-fixing low-calcium cement concrete is further reduced, the carbon fixation amount of the carbon-fixing low-calcium cement concrete is increased, and the long-term stable development of the strength performance of the carbon-fixing low-calcium cement concrete products is achieved.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A carbon-fixing low-calcium cement concrete, wherein the components and their weight proportions include: 18-50 parts of low-calcium cement, 24.8-72 parts of carbon-fixing aggregate, 9.9-25 parts of water, and 0.1-0.5 parts of admixture. The sum of the above components is 100 parts.

[0012] In the above scheme, the low-calcium cement technical method is disclosed in the patent (application publication number: CN117645420A) applied for by the inventor, and the low-calcium cement is obtained by calcining in a rotary kiln.

[0013] Furthermore, in the low-calcium cement, each mineral phase and its mass percentage include dicalcium silicate (abbreviated as C2S, including β-C2S, α' L -C2S, amorphous C2S, one or more combinations thereof): 10-90%, calcium sulfosilicate (abbreviated as C5S2$): 10-90%, anhydrite (abbreviated as C$): 0-5%, calcium sulfoaluminate (abbreviated as C4A3$): 0-10%, solid solutions containing potassium, sodium, magnesium, iron, titanium and other elements in the above minerals, such as N x K y M z C 2-x-y-z S, N x K y M z C 5-x-y-z S2$、C4F x A 3-x $ and other solid solution minerals, as well as other unavoidable miscellaneous items. The Blaine specific surface area of ​​the low calcium cement is 300 to 600 m 2 / kg.

[0014] In the above scheme, the admixture includes a water reducing agent and a water retaining agent, with a mass ratio of 1:1. The water reducing agent is one or more combinations of water reducing agents such as polycarboxylic acid water reducing agent, naphthalene water reducing agent, and melamine water reducing agent, and the water reducing rate of the water reducing agent is 20-45%. The water retaining agent can be one or more combinations of maltodextrin, hydroxypropyl methylcellulose, etc.

[0015] In the above scheme, the carbon-fixing aggregate is prepared by carbonation hardening of one or more of steel slag, magnesium slag and recycled concrete micro powder raw materials. The particle size of the carbon-fixing aggregate is 0.1 mm to 31.5 mm, with continuous grading.

[0016] The present invention also provides a method for preparing the carbon-fixing low-calcium cement concrete, and the specific steps are as follows:

[0017] (1) Weigh the raw materials of each component according to the proportion. The components and their weight proportions include: 18-50 parts of low-calcium cement, 24.8-72 parts of carbon-fixing aggregate, 9.9-25 parts of water, and 0.1-0.5 parts of admixture. The sum of the above components is 100 parts;

[0018] (2) adding the admixture weighed in step (1) into water and stirring evenly to form an admixture solution, adding low-calcium cement, carbon-fixing aggregate and the admixture solution into a mixer, and stirring evenly to form a low-calcium cement concrete raw material mixture;

[0019] (3) pouring the mixture in step (2) into a product mold to form the product, wherein the maximum thickness of the product is not greater than 300 mm;

[0020] (4) curing the formed concrete product in a dry or natural environment for 6 to 48 hours before removing the mold, and then controlling the water content in the low-calcium cement concrete embryo to a mass ratio of 0.15 to 0.25 to the low-calcium cement by drying or humidifying;

[0021] (5) Carbonating and hardening the low-calcium cement concrete body obtained in step (4) in a carbonation reactor containing CO2 gas. Before introducing CO2, the air in the reactor is first evacuated to -0.05MPa, and then the CO2 gas is introduced. The carbonation conditions include but are not limited to: CO2 gas concentration of 20% to 100%, such as pure CO2 gas, CO2-containing industrial waste gas, etc., CO2 gas partial pressure of 0.05MPa to 2.0MPa, preferably 0.2 to 1.0MPa, and carbonation time of 2 to 24h. After carbonation, a carbon-fixed low-calcium cement concrete product is obtained.

[0022] (6) The carbon-fixing low-calcium cement concrete product obtained in step (5) can be directly put into service, or placed in water-containing conditions for further water curing to achieve further performance improvement.

[0023] Furthermore, the preparation method of the carbon-fixing aggregate is as follows:

[0024] (1.1) Mix water and one or more of steel slag, magnesium slag and recycled concrete powder evenly at a water-cement ratio of 0.1 to 0.15.

[0025] (1.2) The slurry mixed in step (1.1) is placed in a granulator to form continuously graded aggregate raw material particles with a particle size of 0.1 mm to 31.5 mm.

[0026] (1.3) The particles formed in step (1.2) are placed in a carbonation reactor and CO2 gas is introduced to carbonate and harden the particles to form carbon-fixed aggregate.

[0027] Furthermore, the carbonation conditions involved in step (1.3) include but are not limited to: CO2 gas concentration of 20% to 100%, such as pure CO2 gas, CO2-containing industrial waste gas, etc., CO2 gas partial pressure of 0.05MPa to 1.0MPa, preferably 0.1 to 0.5MPa, carbonation time 1 to 24h.

[0028] The beneficial effects of the carbon-fixing low-calcium cement concrete of the present invention are:

[0029] (1) The concrete of the present invention adopts the technical route of "hydration-carbonation-hydration". First, the concrete product is cast, which is beneficial to production efficiency and a wider range of product shape design.

[0030] (2) The low-calcium cement used in the present invention contains a small amount of C4A3$ clinker minerals, which have rapid hydration activity and can also synergize with C5S2$ to achieve rapid demoulding strength of low-calcium cement concrete products. There is no need to add other high hydration active components, and no clinker minerals with high carbon emissions are used.

[0031] (3) Compared with other carbon-fixing low-calcium cement concretes, the carbonation activity of C5S2$ and C2S minerals in the low-calcium cement used is more significant, and the production carbon emissions of high-proportion C5S2$ clinker minerals are lower. The carbonation process does not require a carbonation environment higher than room temperature, and can quickly make low-calcium cement concrete products reach the required mechanical strength, and the products have a high carbon fixation content.

[0032] (4) Compared with the existing carbon-fixing low-calcium cement concrete, the β-C2S and C5S2$ minerals in the low-calcium cement used have long-term hydration activity. During long-term maintenance or service of concrete products, hydration reactions can further occur to fill pores, achieve long-term performance growth of low-calcium cement concrete products, and are beneficial to the durability and reliability of concrete products.

[0033] (5) The carbon-fixing low-calcium cement concrete of the present invention creatively designs carbon-fixing aggregates, which not only realizes the recycling of solid waste, but also realizes efficient carbon fixation of all components of the carbon-fixing low-calcium cement concrete.

[0034] (6) Compared with traditional sand and gravel aggregates, the carbonation products formed on the surface of the carbonized aggregate and the carbonation products formed during the carbonation and hardening process of low-calcium cement are more likely to bond together to form a whole. During the carbonation process of low-calcium concrete, the carbonized aggregate can still be further carbonated, thereby enhancing the mechanical properties of low-calcium concrete.

[0035] (7) There are a small amount of pores inside the carbonated aggregate. During the carbonation process, a portion of CO2 is stored before the CO2 channel of the outer concrete is sealed by the carbonated product, thus achieving homogeneous carbonation inside the concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 These are representative cross-sectional color photos of concrete products of Examples 1 to 6; Figure 1 (a) is a color development photograph of the cross section of the product of Example 1; Figure 1 (b) is a color development photograph of the cross section of the product of Example 4.

[0037] Figure 2 The color development of a representative cross section of the concrete product of Comparative Example 1; Figure 2 (a) is a color development photograph of the cross section of the product of Comparative Example 1; Figure 2 (b) is a color development photograph of the cross section of the product of Comparative Example 2. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail through the following examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] In the following embodiments, the low-calcium cement used is based on the designed mineral composition requirements, with limestone, stripping soil, and phosphogypsum as raw materials, and is crushed, ground, batched, homogenized, and calcined in a rotary kiln to form clinker, which is then ground to obtain low-calcium cement.

[0040] In the following examples, the chemical compositions of the steel slag and magnesium slag used are shown in Table 1.

[0041] Table 1 Chemical composition of raw materials

[0042] Raw material types loss CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO <![CDATA[Fe2O3]]> MnO <![CDATA[SO3]]> <![CDATA[P2O5]]> other Steel slag 1.76 41.18 14.58 7.59 4.04 21.90 3.66 0.84 1.72 2.73 Magnesium slag 2.13 60.89 28.82 0.81 4.51 2.68 0.04 0.02 0 0.1

[0043] Example 1

[0044] A method for preparing a carbon-fixing low-calcium cement concrete product comprises the following steps:

[0045] (1) To prepare carbon-fixing aggregate, water and steel slag powder are mixed evenly in a ratio of 0.1. The mixed slurry is placed in a granulator to form aggregate raw material particles with continuous grading of 0.1 mm to 31.5 mm. The aggregate raw material particles are placed in a carbonation reactor, and CO2 gas with a gas concentration of 99% is introduced until the relative pressure in the reactor reaches 0.2 MPa. Carbonation hardening is performed for 2 hours to prepare carbon-fixing aggregate.

[0046] (2) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete: 50 parts of low-calcium cement, 24.8 parts of carbon-fixing aggregate, 25 parts of water, and 0.2 parts of admixture;

[0047] The carbon-fixing aggregate is the aggregate prepared in step (1); the mineral phases of the low-calcium cement and their mass percentages include C2S (including β-C2S, α' L -C2S, amorphous C2S, one or more combinations): 36.7%, C5S2$: 48.8%, C$: 1.6%, C4A3$: 8.4%, containing sodium, potassium, magnesium, iron, titanium and other elements in the solid solution of the above minerals. Low calcium cement specific surface area 400m 2 / kg.

[0048] (3) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture. In this embodiment, the admixtures used are polycarboxylic acid high-performance water-reducing agent and hydroxypropyl methylcellulose (water-retaining agent).

[0049] (4) The mixture in step (3) is poured into a product mold to form the product, wherein the thickness of the product is 100 mm.

[0050] (5) The molded concrete product is placed in a natural environment for curing for 24 hours before demolding, and then the mass ratio of water content in the concrete product to low-calcium cement is controlled to be 0.15 by drying;

[0051] (6) The concrete product obtained in step (5) is placed in a carbonation reactor, the air in the reactor is first evacuated to -0.05 MPa, and then CO2 gas with a concentration of 99% is introduced until the pressure in the reactor reaches 0.3 MPa. Carbonation hardening is performed for 2 h and 24 h respectively to obtain a carbon-fixed low-calcium cement concrete product.

[0052] (7) Curing the concrete product obtained in step (6) under standard curing conditions for 1 month to obtain a carbon-fixing low-calcium cement concrete product with enhanced mechanical properties.

[0053] Example 2

[0054] The preparation method of the carbon-fixing low-calcium cement concrete product comprises the following steps:

[0055] (1) To prepare carbon-fixing aggregate, water and magnesium slag powder are mixed evenly in a ratio of 0.15. The mixed slurry is placed in a granulator to form aggregate raw material particles with continuous grading of 0.1 mm to 31.5 mm. The aggregate raw material particles are placed in a carbonation reactor, and CO2 gas with a gas concentration of 99% is introduced until the relative pressure in the reactor reaches 0.2 MPa. Carbonation hardening is performed for 2 hours to obtain carbon-fixing aggregate.

[0056] (2) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete: 30 parts of low-calcium cement, 54.5 parts of carbon-fixing aggregate, 15 parts of water, and 0.5 parts of admixture;

[0057] The carbon-fixing aggregate is the aggregate prepared in step (1); the mineral phases of the low-calcium cement and their mass percentages are the same as those in Example 1.

[0058] (3) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture. In this embodiment, the admixtures used are naphthalene-based high-performance water-reducing agent and maltodextrin (water-retaining agent).

[0059] (4) The mixture in step (3) is poured into a product mold to form the product, wherein the thickness of the product is 150 mm.

[0060] (5) The molded concrete product is placed in a natural environment for curing for 48 hours before demolding, and then the mass ratio of water content in the concrete product to low-calcium cement is controlled to be 0.185 by drying;

[0061] (6) The concrete product obtained in step (5) is placed in a carbonation reaction kettle, the air in the kettle is first evacuated to -0.05 MPa, and then CO2 gas with a concentration of 99% is introduced until the pressure in the reactor reaches 0.5 MPa. Carbonation hardening is performed for 2 h and 24 h respectively to obtain a carbon-fixed low-calcium cement concrete product.

[0062] (7) The concrete product obtained in step (6) is subjected to standard curing for 3 months to obtain a carbon-fixed low-calcium cement concrete product with enhanced mechanical properties.

[0063] Example 3

[0064] The preparation method of the carbon-fixing low-calcium cement concrete product comprises the following steps:

[0065] (1) Prepare carbon-fixing aggregate. The preparation method is the same as that in Example 2.

[0066] (2) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete, including 18 parts of low-calcium cement, 72 parts of carbon-fixing aggregate, 9.9 parts of water, and 0.1 parts of admixture;

[0067] The carbon-fixing aggregate is the aggregate prepared in step (1); the mineral phases of the low-calcium cement and their mass percentages are the same as those in Example 1;

[0068] (3) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture. In this embodiment, the admixtures used are melamine-based water reducer and hydroxypropyl methylcellulose (water retaining agent).

[0069] (4) The mixture in step (3) is poured into a product mold to form the product, wherein the thickness of the product is 200 mm.

[0070] (5) The molded concrete product is placed in a natural environment for curing for 24 hours before demolding, and then the mass ratio of water content in the concrete product to low-calcium cement is controlled to 0.21 by drying;

[0071] (6) The concrete product obtained in step (5) is placed in a carbonation reactor, the air in the reactor is first evacuated to -0.05 MPa, and then CO2 gas with a concentration of 99% is introduced until the pressure in the reactor reaches 0.8 MPa. Carbonation hardening is performed for 2 h and 24 h respectively to obtain a carbon-fixed low-calcium cement concrete product.

[0072] (7) The concrete product obtained in step (6) is subjected to standard curing for 3 months to obtain a carbon-fixed low-calcium cement concrete product with enhanced mechanical properties.

[0073] Example 4

[0074] The preparation method of the carbon-fixing low-calcium cement concrete product comprises the following steps:

[0075] (1) Prepare carbon-fixing aggregate. The preparation method is the same as that in Example 2.

[0076] (2) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete, including 40 parts of low-calcium cement, 39.6 parts of carbon-fixing aggregate, 20 parts of water, and 0.4 parts of admixture;

[0077] The carbon-fixing aggregate is the aggregate prepared in step (1); the mineral phases of the low-calcium cement and their mass percentages include C2S (including β-C2S, α' L -C2S, amorphous C2S, one or more combinations): 12.7%, C5S2$: 72.3%, C$: 2.2%, C4A3$: 9.7%, containing sodium, potassium, magnesium, iron, titanium and other elements in the solid solution of the above minerals, as well as unavoidable miscellaneous items. Low calcium cement specific surface area 450m 2 / kg.

[0078] (3) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture.

[0079] (4) The mixture in step (3) is poured into a product mold to form a product, wherein the thickness of the product is 150 mm. In this embodiment, the admixtures used are polycarboxylic acid-based high-performance water reducing agent and maltodextrin (water retaining agent).

[0080] (5) The molded concrete product is placed in a natural environment for curing for 24 hours before demolding, and then the mass ratio of water content in the concrete product to low-calcium cement is controlled to be 0.175 by drying;

[0081] (6) The concrete product obtained in step (5) is placed in a carbonation reactor, the air in the reactor is first evacuated to -0.05 MPa, and then CO2 gas with a concentration of 99% is introduced until the pressure in the reactor reaches 0.3 MPa. Carbonation hardening is performed for 2h and 24h to obtain a carbon-fixed low-calcium cement concrete product.

[0082] (7) The concrete product obtained in step (6) is subjected to standard curing for 1 month to obtain a carbon-fixed low-calcium cement concrete product with enhanced mechanical properties.

[0083] Example 5

[0084] The preparation method of the carbon-fixing low-calcium cement concrete product comprises the following steps:

[0085] (1) Prepare carbon-fixing aggregate. The preparation method is the same as that in Example 2.

[0086] (2) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete, including 40 parts of low-calcium cement, 39.5 parts of carbon-fixing aggregate, 20 parts of water, and 0.5 parts of admixture;

[0087] The carbon-fixing aggregate is the aggregate prepared in step (1); the mineral phases of the low-calcium cement and their mass percentages are the same as those in Example 4;

[0088] (3) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture. In this embodiment, the admixtures used are melamine-based high-performance water-reducing agent and hydroxypropyl methylcellulose (water-retaining agent).

[0089] (4) The mixture in step (3) is poured into a product mold to form the product, wherein the thickness of the product is 200 mm.

[0090] (5) The molded concrete product is placed in a natural environment for curing for 24 hours before demolding, and then the mass ratio of water content in the concrete product to low-calcium cement is controlled to be 0.175 by drying;

[0091] (6) The concrete product obtained in step (5) is placed in a carbonation reactor, the air in the reactor is first evacuated to -0.05 MPa, and then industrial gas with a CO2 concentration of about 30% is introduced until the pressure in the reactor reaches 1.0 MPa. Carbonation hardening is performed for 2 hours and 24 hours respectively to obtain a carbon-fixed low-calcium cement concrete product.

[0092] (7) The concrete product obtained in step (6) is subjected to standard curing for 3 months to obtain a carbon-fixed low-calcium cement concrete product with enhanced mechanical properties.

[0093] Example 6

[0094] The preparation method of the carbon-fixing low-calcium cement concrete product comprises the following steps:

[0095] (1) Prepare carbon-fixing aggregate. The preparation method is the same as that in Example 2.

[0096] (2) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete: 30 parts of low-calcium cement, 54.9 parts of carbon-fixing aggregate, 15 parts of water, and 0.1 parts of admixture;

[0097] The carbon-fixing aggregate is the aggregate prepared in step (1); the mineral phases of the low-calcium cement and their mass percentages are the same as those in Example 4;

[0098] (3) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture. In this embodiment, the admixtures used are polycarboxylic acid high-performance water-reducing agent and hydroxypropyl methylcellulose (water-retaining agent).

[0099] (4) The mixture in step (3) is poured into a product mold to form the product, wherein the thickness of the product is 150 mm.

[0100] (5) The molded concrete product is placed in a natural environment for curing for 24 hours before demolding, and then the water content in the concrete product is controlled by drying to a mass ratio of 0.25 to the low-calcium cement;

[0101] (6) The concrete product obtained in step (5) is placed in a carbonation reaction kettle, the air in the kettle is first evacuated to -0.05 MPa, and then CO2 gas with a concentration of 99% is introduced until the pressure in the reactor reaches 0.05 MPa. Carbonation hardening is performed for 2 h and 24 h respectively to obtain a carbon-fixed low-calcium cement concrete product.

[0102] (7) The concrete product obtained in step (6) is subjected to standard curing for 3 months to obtain a carbon-fixed low-calcium cement concrete product with enhanced mechanical properties.

[0103] Comparative Example 1

[0104] The preparation method of the carbon-fixing low-calcium cement concrete product comprises the following steps:

[0105] (1) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete, including 50 parts of low-calcium cement, 24.8 parts of aggregate, 25 parts of water, and 0.2 parts of admixture;

[0106] The aggregate is standard sand; the mineral phases of the low-calcium cement and their mass percentages are the same as those in Example 1;

[0107] (2) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture.

[0108] (3) The mixture in step (2) is poured into a product mold to form a product, wherein the thickness of the product is 100 mm.

[0109] (4) The molded concrete product is placed in a natural environment for curing for 24 hours before demolding, and then the mass ratio of water content in the concrete product to low-calcium cement is controlled to be 0.15 by drying;

[0110] (5) The concrete product obtained in step (4) is placed in a carbonation reactor, the air in the reactor is first evacuated to -0.05 MPa, and then CO2 gas with a concentration of 99% is introduced until the pressure in the reactor reaches 0.3 MPa. Carbonation hardening is performed for 2 h and 24 h respectively to obtain a carbon-fixed low-calcium cement concrete product.

[0111] (6) The concrete product obtained in step (5) is subjected to standard curing for 3 months to obtain a carbon-fixing low-calcium cement concrete product with enhanced mechanical properties.

[0112] Comparative Example 1 is compared with Example 1. Under the same mix ratio and carbonation conditions, Comparative Example 1 uses natural sandstone aggregate, and Example 1 uses the carbon-fixing aggregate made of steel slag as raw material in the present invention.

[0113] Comparative Example 2

[0114] The preparation method of the carbon-fixing low-calcium cement concrete product comprises the following steps:

[0115] (1) Weigh the raw materials of each component of carbon-fixing low-calcium cement concrete, including 40 parts of low-calcium cement, 39.6 parts of carbon-fixing aggregate, 20 parts of water, and 0.4 parts of admixture;

[0116] The aggregate is standard sand; the mineral phases of the low-calcium cement and their mass percentages are the same as those in Example 4;

[0117] (2) Add the weighed admixture into water and stir evenly to form an admixture solution. Add low-calcium cement, carbon-fixing aggregate and admixture solution into a mixer and mix evenly to form a low-calcium cement concrete raw material mixture.

[0118] (3) The mixture in step (2) is poured into a product mold to form the product, wherein the thickness of the product is 150 mm.

[0119] (4) The molded concrete product is placed in a natural environment for curing for 24 hours before demolding, and then the water content in the concrete product is controlled by drying to a mass ratio of 0.175 to the low-calcium cement;

[0120] (5) The concrete product obtained in step (4) is placed in a carbonation reactor, the air in the reactor is first evacuated to -0.05 MPa, and then CO2 gas with a concentration of 99% is introduced until the pressure in the reactor reaches 0.3 MPa. Carbonation hardening is performed for 2 h and 24 h respectively to obtain a carbon-fixed low-calcium cement concrete product.

[0121] (6) The concrete product obtained in step (5) is subjected to standard curing for 3 months to obtain a carbon-fixing low-calcium cement concrete product with enhanced mechanical properties.

[0122] Comparative Example 2 is compared with Example 4. Under the same mix ratio and carbonation conditions, Comparative Example 2 uses natural sandstone aggregate, and Example 4 uses the carbon-fixing aggregate made of magnesium slag as raw material in the present invention.

[0123] Analysis of the results of Examples 1 to 6 and Comparative Examples 1 to 2:

[0124] For Examples 1 to 6, Comparative Examples 1 and 2, compressive strength tests were performed according to national standards; the carbon fixation amount of the carbon-fixing low-calcium cement concrete products was calculated by weighing method, and the carbon fixation amount refers to the mass ratio of CO2 absorbed by low-calcium concrete to low-calcium cement. The specific test results are shown in Table 2; the carbon-fixing low-calcium cement concrete products of the Examples and Comparative Examples were cut into sections after carbonation and sprayed with phenolphthalein solution for color development to characterize the homogeneity of carbonation. Representative cross-sectional color development photos of the concrete products of Examples 1 to 6 are shown in Table 2. Figure 1 As shown, representative cross-sectional color photos of the concrete products of Comparative Example 1 and Comparative Example 2 are shown in Figure 2 shown.

[0125] Table 2 Mineral composition, compressive strength and carbon fixation of low calcium cement

[0126]

[0127] From the results of the above examples, it can be seen that the raw materials of the carbon-fixing low-calcium cement concrete of the present invention are low in calcium and carbon, and no additional high hydration active materials need to be added. By casting and molding concrete products, the raw materials themselves have minerals with fast hydration activity, and the demoulding strength can be achieved in a short time, which is beneficial to production efficiency and a wider range of product shape design.

[0128] The concrete of the present invention uses carbon-fixing aggregates, which not only realizes the recycling of solid waste, but also realizes efficient carbon fixation of all components of concrete. The carbonation activity of C5S2$ and C2S minerals in low-calcium cement is more significant, and the carbonation process does not require additional reaction conditions higher than room temperature to quickly make the concrete product reach the required mechanical strength.

[0129] According to the test results in Table 2, after the carbonation of the low-calcium cement concrete of the present invention forms strength, the performance can be further enhanced under long-term hydration. The β-C2S and C5S2$ minerals in the low-calcium cement used in the present invention have long-term hydration activity, and can further undergo hydration reaction during long-term water-containing curing or service of concrete products to fill pores, achieve long-term performance growth of concrete products, and are beneficial to the durability and reliability of concrete products.

[0130] According to the attached Figure 1 and attached Figure 2 It can be seen from the comparison photos that the phenolphthalein solution inside the carbon-fixing low-calcium cement concrete of Example 1 and Example 4 of the present invention is almost not colored, indicating that there is efficient and uniform carbonation inside. The phenolphthalein solution inside the carbon-fixing low-calcium cement concrete of Comparative Example 1 and Comparative Example 2 is colored, indicating that there is uneven carbonation inside. This shows that the low-calcium carbon-fixing concrete of the present invention achieves internal homogeneous carbonation. In addition, according to the test results of the carbon fixation amount in Table 2, the carbon fixation amount of Example 1 of the present invention is higher than that of Comparative Example 1, and the carbon fixation amount of Example 4 is higher than that of Comparative Example 2. This also proves the advantage of efficient and homogeneous carbonation of the carbon-fixing low-calcium concrete of the present invention.

[0131] The above-described embodiments merely express the implementation methods of the present invention, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A carbon-fixing low-calcium cement concrete, characterized in that: The components of the carbon-fixing low-calcium cement concrete and their weight proportions include: 18-50 parts of low-calcium cement, 24.8-72 parts of carbon-fixing aggregate, 9.9-25 parts of water, and 0.1-0.5 parts of admixture; the sum of the above components is 100 parts.

2. The carbon-fixing low-calcium cement concrete according to claim 1, characterized in that: In the low-calcium cement, the mineral phases and their mass percentages include: dicalcium silicate (abbreviated as C2S): 10-90%, calcium sulfosilicate C5S2$: 10-90%, anhydrite C$: 0-5%, calcium sulfoaluminate C4A3$: 0-10%, solid solutions of potassium, sodium, magnesium, iron, and titanium elements in the above minerals, and other inevitable miscellaneous items.

3. The carbon-fixing low-calcium cement concrete according to claim 1, characterized in that: The low calcium cement is produced by calcining in a rotary kiln, and the Blaine specific surface area of ​​the low calcium cement is 300 to 600 m 2 / kg.

4. The carbon-fixing low-calcium cement concrete according to claim 1, characterized in that: The admixture comprises a water reducing agent and a water retaining agent in a mass ratio of 1:

1.

5. The carbon-fixing low-calcium cement concrete according to claim 4, characterized in that: The water reducing agent is one or more combinations of polycarboxylic acid water reducing agent, naphthalene water reducing agent and melamine water reducing agent, and the water reducing rate of the water reducing agent is 20-45%; the water retaining agent is one or more combinations of maltodextrin and hydroxypropyl methylcellulose.

6. The carbon-fixing low-calcium cement concrete according to claim 1, characterized in that: The carbon-fixing aggregate is prepared by carbonation hardening of one or more combinations of steel slag, magnesium slag and recycled concrete micro-powder raw materials; the particle size of the carbon-fixing aggregate is 0.1 mm to 31.5 mm, with continuous grading.

7. A method for preparing the carbon-fixing low-calcium cement concrete according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step (1) weighing the raw materials of each component according to the ratio; Step (2) adding the admixture weighed in step (1) into water and stirring evenly to form an admixture solution, adding low-calcium cement, carbon-fixing aggregate and the admixture solution into a mixer, and stirring evenly to form a low-calcium cement concrete raw material mixture; Step (3) pouring the mixture in step (2) into a product mold to form a product; Step (4) curing the formed concrete product and then removing the mold, and controlling the mass ratio of the water content in the low-calcium cement concrete body to the low-calcium cement to be 0.15 to 0.25; Step (5) carbonates the low-calcium cement concrete body obtained in step (4) in a carbonation reactor containing CO2 gas, and obtains a carbon-fixed low-calcium cement concrete product after the carbonation is completed.

8. The method for preparing a carbon-fixing low-calcium cement concrete according to claim 7, characterized in that: The preparation method of the carbon-fixing aggregate is as follows: (1.1) Mix water and one or more of steel slag, magnesium slag and recycled concrete powder evenly at a water-cement ratio of 0.1 to 0.15; (1.2) placing the slurry mixed in step (1.1) into a granulator to form continuously graded aggregate raw material particles with a particle size of 0.1 mm to 31.5 mm; (1.3) The particles formed in step (1.2) are placed in a carbonation reactor and CO2 gas is introduced to carbonate and harden the particles to form carbon-fixed aggregate.

9. The method for preparing a carbon-fixing low-calcium cement concrete according to claim 7, characterized in that: In the step (3), the maximum thickness of the molded product is not greater than 300 mm.

10. The method for preparing a carbon-fixing low-calcium cement concrete according to claim 7, characterized in that: The carbonation process in step (4) is as follows: before introducing CO2, the air in the kettle is first evacuated to -0.05MPa, and then CO2 gas is introduced; the carbonation conditions include but are not limited to: CO2 gas concentration of 20% to 100%, CO2 gas partial pressure of 0.05MPa to 2.0MPa, and carbonation time of 2 to 24h.

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