A carbonated cement board based on high-magnesium and low-carbon cement and its preparation method

Abstract

The present invention discloses a carbonized cement board based on high-magnesium low-carbon cement. The raw materials and their weight percentages include: 100 parts of high-magnesium low-carbon cement, 0-3 parts of lightweight aggregate, 0-4 parts of wollastonite powder, 0-4 parts of mica, 4-10 parts of pulp fiber, 0.05-2 parts of reinforcing fiber, 0.3-1.0 parts of improver, 0.1-0.3 parts of dispersant, and 0.1-0.4 parts of water-retaining agent; the high-magnesium low-carbon cement uses C2MS2 as the main mineral. The present invention further introduces a improver and a gradient carbonization curing system based on high-magnesium low-carbon cement obtained by using low-grade limestone and aggregate waste in large amounts, which can effectively enhance the mechanical properties of the obtained carbonized cement board and improve its waterproof performance, etc.; and the preparation cost involved is low, the energy consumption is low, the curing time is short, and there are significant economic and environmental benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a carbonized cement board based on high-magnesium low-carbon cement and a preparation method thereof. Background Art

[0002] Traditional fiber cement boards are typically made from Portland cement using either autoclaved or non-autoclaved curing processes, which often suffer from high energy consumption and long curing cycles. Autoclaved curing typically involves a temperature of 180°C, an air pressure of 1.0-1.2 MPa, and a curing time of 24 hours, resulting in high energy consumption and high-temperature autoclaving equipment costs. Non-autoclaved curing, which uses heat curing below 100°C or natural curing at atmospheric pressure, reduces energy consumption but requires a curing time of 3-28 days. Furthermore, it requires higher cement content and exhibits greater shrinkage and expansion.

[0003] Low-carbon cement clinker primarily consists of the low-calcium minerals C3S2, CS, β-C2S, and γ-C2S. Compared to C3S-based Portland cement clinker, it requires less limestone, calcines at lower temperatures, and absorbs significant amounts of CO2, significantly reducing carbon emissions from the cement industry. It can also be used to produce building materials with superior physical properties. Furthermore, carbonization curing requires a shorter time, at lower temperatures and pressures than autoclave curing. Therefore, the use of low-carbon cement in the production of carbonized cement boards is a significant area of research and application.

[0004] Low-grade limestone has a low CaO content and high MgO and SiO2 contents, making it difficult to combine with other conventional raw materials to form high-KH Portland cement clinker. Furthermore, the high calcination temperature and low eutectic point of the clinker can cause severe melt scaling in equipment, resulting in a narrow range of applications and limited effective utilization. Aggregate plants inevitably discharge large amounts of waste slag containing stone dust during sand and gravel production. The stone dust in this aggregate slag is primarily calcite and dolomite, with an MgO content generally ranging from 5-15%. It also contains clay minerals, resulting in a complex composition and making it difficult to utilize. It is of great significance to effectively recycle this low-grade limestone and aggregate slag with low CaO and high MgO content into resources.

[0005] Using low-grade limestone and aggregate waste with low CaO and high MgO content, and increasing the MgO content in the mix, high-magnesium, low-carbon cement clinker, with C2MS2 (calcium magnesium feldspar) as the primary mineral, can be produced. Compared to low-carbon cement clinker, this high-magnesium, low-carbon cement clinker offers lower calcination temperatures and improved grindability, significantly reducing production costs and energy consumption. However, its carbon fixation rate and carbonation strength are lower, reaching approximately 70-80% of the strength of low-carbon cement clinker with C3S2 as the primary mineral. Therefore, further exploration of the efficient application of high-magnesium, low-carbon cement in cement board production is of great research and application significance. Summary of the Invention

[0006] The main purpose of the present invention is to address the problems and shortcomings of the existing technology and provide a carbonized cement board based on high-magnesium low-carbon cement. On the basis of realizing the large-scale application of high-magnesium low-carbon cement (with low-grade limestone and aggregate waste as the main raw materials), the strength of the obtained carbonized cement board is effectively improved; and the preparation method involved has a short cycle and is suitable for promotion and application.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A carbonized cement board based on high-magnesium low-carbon cement comprises the following raw materials and their weight proportions: 100 parts of high-magnesium low-carbon cement, 0-3 parts of lightweight aggregate, 0-4 parts of wollastonite powder, 0-4 parts of mica, 4-10 parts of pulp fiber, 0.05-2 parts of reinforcing fiber, 0.3-1.0 parts of improver, 0.1-0.3 parts of dispersant, and 0.1-0.4 parts of water-retaining agent.

[0009] According to the above solution, the raw material of the carbonized cement board based on high-magnesium low-carbon cement also includes water, and the amount of water is configured according to the requirement of slurry moisture content of 35-42%.

[0010] According to the above scheme, the lightweight aggregate is one or two of open-pore expanded perlite and closed-pore vitrified microspheres, with a bulk density of 80-120 kg / m 3 , particle size is less than 0.6mm.

[0011] According to the above scheme, the aspect ratio of the wollastonite powder is (15-20):1, and the fineness is 100-400 mesh.

[0012] According to the above solution, the mica is one or more of muscovite, biotite, phlogopite, etc., and the fineness is 20-100 mesh.

[0013] According to the above solution, the pulp fiber is one or more of wood pulp, bamboo pulp, straw pulp fiber, etc., with a length of 1-3 mm and a diameter of 20-60 μm.

[0014] According to the above solution, the reinforcing fiber is one or more of carbon fiber, alkali-free glass fiber, basalt fiber, etc., with a diameter of 6-20 μm and a length of 10-20 mm.

[0015] According to the above scheme, the dispersant is one or more of acrylamide, polyethylene oxide, etc.

[0016] According to the above solution, the water-retaining agent is one or more of hydroxyethyl methyl cellulose ether, hydroxypropyl methyl cellulose ether, starch ether, etc.

[0017] According to the above solution, the mineral composition of the high-magnesium low-carbon cement includes, by percentage, C2MS2 (calcium magnesium feldspar) 40-80%, C3S2 20-40%, and CS+C2S 0-20%.

[0018] According to the above scheme, the high-magnesium low-carbon cement is obtained by using low-grade limestone, aggregate waste slag and coal gangue as main raw materials, which are proportioned, mixed, ground and calcined.

[0019] According to the above scheme, the mass ratio of the low-grade limestone, aggregate waste slag and coal gangue is 50-70:0-20:20-30.

[0020] Furthermore, the main chemical components and contents of the low-grade limestone include: CaO 40-48%; MgO 3-10%; SiO2 4-10%; Al2O3 0-3%; Fe2O3 0-2%; and loss on ignition 35-42%; the main chemical components and contents of aggregate waste include: CaO 20-40%; MgO 5-15%; SiO2 15-25%; Al2O3 3-6%; Fe2O3 2-5%; and loss on ignition 25-40%; the main chemical components and contents of coal gangue include: CaO 0-5%; MgO 0-5%; SiO2 60-90%; Al2O3 0-8%; Fe2O3 0-5%; and loss on ignition 0-8%.

[0021] According to the above scheme, further control indicators in the batching process include: MgO 6-8wt%, KH 0.3-0.4, SM 4-7, and a total CaO to total SiO2 mass ratio of 1.1-1.3.

[0022] According to the above scheme, the calcination temperature is 1200-1250°C.

[0023] According to the above scheme, the 80μm sieve residue rate of the high-magnesium low-carbon cement is ≤10%.

[0024] According to the above scheme, the improver is one or more of alginic acid, citric acid, fatty acid, polyacrylic acid and soluble salts thereof.

[0025] Furthermore, the soluble salt is one or more of alginate soluble salt, citric acid soluble salt, fatty acid soluble salt, and polyacrylic acid soluble salt.

[0026] The above-mentioned method for preparing a carbonized cement board based on high-magnesium low-carbon cement comprises the following steps:

[0027] (1) Weigh the raw materials according to the ratio and weigh the water according to the requirements of the slurry moisture content;

[0028] (2) Add the weighed lightweight aggregate, pulp fiber and water into a mixer, then add reinforcing fiber, dispersant and water retaining agent, stir evenly, add high magnesium low carbon cement and modifier, stir evenly, add mica and wollastonite powder, continue stirring evenly to obtain slurry;

[0029] (3) The obtained slurry is formed by a mold pressing and water filtration method, and the mold is removed to obtain a slab;

[0030] (4) Pre-curing is performed to adjust the moisture content of the slab to 10-20%;

[0031] (5) The pre-cured slab is subjected to gradient step-by-step carbonization curing to obtain the carbonized cement board based on high-magnesium low-carbon cement.

[0032] According to the above scheme, the pressure used in the molding by the water-drainage molding method is 5-15 MPa, and the pressure holding time is 3-15 minutes.

[0033] According to the above scheme, the gradient step carbonization curing adopts a CO2 concentration of 20-100%, an air pressure of 0.1-0.3 MPa, a temperature of 25-55°C, and a total carbonization time of 12-24 hours.

[0034] According to the above scheme, in the gradient step carbonization curing, more than two carbonization curing steps are adopted, and the CO2 concentration and gas pressure used are increased in sequence.

[0035] Furthermore, in the gradient step-by-step carbonization curing, the CO2 concentration used in the first carbonization curing step is 20-30%, the air pressure is 0.1-0.2 MPa, and the time is 5-40% of the total carbonization time; when the temperature is set to 25-40°C, the CO2 concentration used in the last carbonization curing step is 50-100%, the air pressure is 0.2-0.3 MPa, and the time is 30-70% of the total carbonization time; when the temperature is set to 40-55°C, the CO2 concentration used in the last carbonization curing step is 30-100%, the air pressure is 0.1-0.3 MPa, and the time is 30-70% of the total carbonization time.

[0036] Furthermore, between the adjacent carbonization curing steps, the increase in CO2 concentration is 10-40% (absolute value), the increase in gas pressure is 0-0.1 MPa, and the time (carbonization time) changes to 0-30% of the total carbonization time.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1) The present invention uses high-magnesium, low-carbon cement (with calcite as the main mineral) with lower cost and energy consumption to prepare carbonized cement board, which has good economic and environmental benefits;

[0039] 2) The C2MS2 in the high magnesium low carbon cement obtained by the present invention can be compared to C3S2, Mg 2+ The radius of the ion is smaller than that of Ca 2+ Ion, MgO-SiO2 bond strength is stronger than CaO-SiO2, so the carbonization activity of MgO is weaker than that of CaO; the present invention introduces a modifier to make Mg 2+ It is complexed and thus more easily carbonized, which can effectively stimulate the carbonization activity of C2MS2; secondly, the generated MgCO3 further plays the role of filling, connecting, and interface reinforcement between silica gel and traditional carbonization product CaCO3; in addition, the present invention further combines the gradient carbonization curing conditions for the carbonization of C2MS2 minerals to further effectively improve the strength of the carbonized cement board made with high-magnesium low-carbon cement. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] In the following examples, the actual chemical compositions and contents (mass percentages) of the low-grade limestone, aggregate waste, and coal gangue used are shown in Table 1.

[0042] Table 1 Chemical composition (%)

[0043]

[0044] Example 1

[0045] A carbonized cement board based on high-magnesium low-carbon cement, the preparation method of which comprises the following steps:

[0046] (1) Weigh the raw materials and their weight proportions as follows: 100 parts of high magnesium low carbon cement (C2MS2=71.4%, C3S2=20.5%, C2S=6.7%, 80μm sieve residue ≤10%), 2 parts of lightweight aggregate (expanded perlite), 2 parts of wollastonite powder (200 mesh), 2 parts of mica (muscovite 40 mesh), 4 parts of pulp fiber (wood pulp fiber), 2 parts of reinforcing fiber (alkali-free glass fiber), 0.6 parts of improver (alginic acid), 0.1 parts of dispersant (acrylamide), 0.1 parts of water retaining agent (hydroxyethyl methyl cellulose ether), and weigh water according to the requirement of 38% moisture content of slurry;

[0047] The high-magnesium low-carbon cement is prepared by mixing low-grade limestone, aggregate waste, and coal gangue in a mass ratio of 56:20:24, while controlling the MgO content to 7.776%, KH to 0.352, SM to 5.466, and the total CaO to SiO2 mass ratio to 1.195; mixing and grinding the mixed raw materials, and then calcining them at 1210°C.

[0048] (2) Add lightweight aggregate, pulp fiber and water into a mixer, then add reinforcing fiber, dispersant and water retaining agent, stir evenly, add high magnesium low carbon cement and modifier, stir evenly, add mica and wollastonite powder, and continue stirring to obtain slurry;

[0049] (3) Place a porous filter plate in the bottom mold of the porous forming mold, lay a filter screen, add slurry, cover with a filter screen, put in a porous filter plate, cover with the cover mold of the forming mold, and use the mold pressure filtration method with a pressure of 10 MPa and a holding time of 8 minutes to form. Remove the mold to obtain a slab, and the moisture content is measured to be 20.5%;

[0050] (4) Pre-curing at 45°C was used to control the moisture content of the slab to 14%;

[0051] (5) The pre-cured slab was placed in a carbonization kettle and first carbonized for 6 h at a CO2 concentration of 30%, an air pressure of 0.1 MPa, and a temperature of 25 °C; then the CO2 concentration was adjusted to 50%, an air pressure of 0.2 MPa, and a temperature of 25 °C for a further 6 h; finally, the CO2 concentration was adjusted to 70%, an air pressure of 0.3 MPa, and a temperature of 25 °C for a further 12 h; a total of 24 h of carbonization was carried out under this gradient curing to obtain a carbonized cement board based on high magnesium low carbon cement.

[0052] Example 2

[0053] A carbonized cement board based on high-magnesium low-carbon cement, the preparation method of which comprises the following steps:

[0054] (1) Weigh the raw materials and their weight proportions as follows: 100 parts of high magnesium low carbon cement (C2MS2=71.4%, C3S2=20.5%, C2S=6.7%, 80μm sieve residue ≤10%), 1 part of lightweight aggregate (vitrified microspheres), 2 parts of wollastonite powder (200 mesh), 2 parts of mica (biotite 100 mesh), 6 parts of pulp fiber (bamboo pulp fiber), 2 parts of reinforcing fiber (basalt fiber), 0.8 parts of modifier (citric acid), 0.1 parts of dispersant (polyethylene oxide), 0.2 parts of water retaining agent (starch ether), and weigh water according to the requirement of 36% moisture content of slurry;

[0055] The high-magnesium low-carbon cement is prepared by mixing low-grade limestone, aggregate waste, and coal gangue in a mass ratio of 56:20:24, while controlling the MgO content to 7.776%, KH to 0.352, SM to 5.466, and the total CaO to SiO2 mass ratio to 1.195; mixing and grinding the mixed raw materials, and then calcining them at 1210°C to obtain the cement.

[0056] (2) Add lightweight aggregate, pulp fiber and water into a mixer, then add reinforcing fiber, dispersant and water retaining agent, stir evenly, add high magnesium low carbon cement and modifier, stir evenly, add mica and wollastonite powder, and continue stirring to obtain slurry;

[0057] (3) Place a porous filter plate in the bottom mold of the porous forming mold, lay a filter screen, add slurry, cover with a filter screen, put in a porous filter plate, cover with the cover mold of the forming mold, and use the mold pressure filtration method with a pressure of 10 MPa and a holding time of 8 minutes to form. Remove the mold to obtain a slab, and the moisture content is measured to be 20.3%;

[0058] (4) The moisture content of the slab was regulated to 13.5% by pre-curing at 45°C;

[0059] (5) The pre-cured slab was placed in a carbonization kettle and first carbonized for 8 h at a CO2 concentration of 20%, an air pressure of 0.2 MPa, and a temperature of 25 °C; then the CO2 concentration was adjusted to 50%, an air pressure of 0.2 MPa, and a temperature of 25 °C for a further 8 h; finally, the CO2 concentration was adjusted to 80%, an air pressure of 0.3 MPa, and a temperature of 25 °C for a further 8 h; a total of 24 h of carbonization was carried out under this gradient curing to obtain a carbonized cement board based on high magnesium low carbon cement.

[0060] Comparative Example 1

[0061] A carbonized cement board, the preparation method of which is substantially the same as that of Example 1, except that:

[0062] The high-magnesium low-carbon cement in step (1) is replaced by low-carbon cement whose mineral composition is mainly C3S2 (C3S2=78.6%, CS=19.5%, 80μm sieve residue rate ≤10%);

[0063] No modifier is added in step (2);

[0064] The carbonization curing system in step (5) was changed to carbonization for 24 h at a CO2 concentration of 70%, an air pressure of 0.3 MPa, and a temperature of 25°C.

[0065] Comparative Example 2

[0066] A carbonized cement board, the preparation method of which is substantially the same as that of Example 1, except that:

[0067] No modifier is added in step (2);

[0068] The carbonization curing in step (5) was changed to carbonization for 24 h at a CO2 concentration of 70%, an air pressure of 0.3 MPa, and a temperature of 25°C.

[0069] Comparative Example 3

[0070] A carbonized cement board, the preparation method of which is substantially the same as that of Example 1, except that no modifier is added in step (2).

[0071] Comparative Example 4

[0072] A carbonized cement board, the preparation method of which is substantially the same as that of Example 1, except that the carbonization curing in step (5) is changed to carbonization for 24 hours at a CO2 concentration of 70%, an air pressure of 0.3 MPa, and a temperature of 25°C.

[0073] The physical property test results of the carbonized cement boards obtained in various embodiments and comparative examples are shown in Table 2.

[0074] Table 2 Physical properties

[0075]

[0076] From the above results we can see that:

[0077] In Comparative Examples 2 and 3, the physical properties of the carbonized cement boards prepared using high-magnesium low-carbon cement without the introduction of a modifier were inferior to those of the carbonized cement board prepared using low-carbon cement whose mineral composition was primarily C3S2 as described in Comparative Example 1. The physical properties of the carbonized cement board prepared in Comparative Example 4, which was prepared using high CO2 concentration and pressure conditions throughout the entire process, were still inferior to those of the carbonized cement board prepared in Example 1 of the present invention.

[0078] The present invention is based on the high-magnesium low-carbon cement produced by extensively utilizing low-grade limestone and aggregate waste, and is combined with improvement measures such as modifiers and gradient curing to effectively improve the physical properties of carbonized cement boards. In particular, the present invention can produce carbonized cement boards with performance superior to that of low-carbon cement produced mainly using C3S2 minerals such as Comparative Example 1, providing a new idea for the preparation of high-performance, low-carbon cement boards.

[0079] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A carbonized cement board based on high magnesium low carbon cement, characterized in that: The raw materials and their weight proportions include: 100 parts of high magnesium low carbon cement, 0-3 parts of lightweight aggregate, 0-4 parts of wollastonite powder, 0-4 parts of mica, 4-10 parts of pulp fiber, 0.05-2 parts of reinforcing fiber, 0.3-1.0 parts of improver, 0.1-0.3 parts of dispersant, and 0.1-0.4 parts of water retaining agent; The mineral composition of the high magnesium low carbon cement includes, by percentage, C2MS2 40-80%, C3S2 20-40%, CS+C2S0-20%; The modifier is one or more of alginic acid, citric acid, fatty acid, polyacrylic acid and soluble salts thereof; The high magnesium low carbon cement is prepared by mixing low grade limestone, aggregate waste slag and coal gangue as main raw materials in a certain proportion, grinding and calcining; the calcination temperature is 1200-1250°C; The main chemical components and contents of the low-grade limestone include: CaO 40-48%; MgO 3-10%; SiO2 4-10%; Al2O3 0-3%; Fe2O3 0-2%; loss on ignition 35-42%; The reinforcing fiber is one or more of carbon fiber, alkali-free glass fiber, and basalt fiber; The gradient carbonization curing conditions for the carbonization of C2MS2 minerals are: using more than 2 carbonization curing steps, and the CO2 concentration and gas pressure used are increased in sequence.

2. The carbonized cement board according to claim 1, characterized in that: The lightweight aggregate is one or both of open-pore expanded perlite and closed-pore vitrified microspheres, with a bulk density of 80-120 kg / m 3 , particle size is less than 0.6mm.

3. The carbonized cement board according to claim 1, characterized in that: The aspect ratio of the wollastonite powder is (15-20):1, and the fineness is 100-400 meshes; the mica is one or more of muscovite, biotite, and phlogopite, and the fineness is 20-100 meshes.

4. The carbonized cement board according to claim 1, characterized in that: The pulp fibers are one or more of wood pulp, bamboo pulp, and straw pulp fibers, and have a length of 1-3 mm and a diameter of 20-60 μm; the reinforcing fibers have a diameter of 6-20 μm and a length of 10-20 mm.

5. The carbonized cement board according to claim 1, characterized in that: The dispersant is one or two of acrylamide and polyethylene oxide; the water retaining agent is one or more of hydroxyethyl methyl cellulose ether, hydroxypropyl methyl cellulose ether and starch ether.

6. The method for preparing a carbonized cement board based on high-magnesium low-carbon cement according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Weigh the raw materials according to the ratio and weigh the water according to the requirements of the slurry moisture content; (2) Add the weighed lightweight aggregate, pulp fiber and water into a mixer, then add reinforcing fiber, dispersant and water retaining agent, stir evenly, add high magnesium low carbon cement and modifier, stir evenly, add mica and wollastonite powder, continue stirring evenly to obtain slurry; (3) The obtained slurry is formed by a mold pressing and water filtration method, and the mold is removed to obtain a slab; (4) Pre-curing is performed to adjust the moisture content of the slab to 10-20%; (5) The pre-cured slab is subjected to gradient step-by-step carbonization curing to obtain the carbonized cement board based on high-magnesium low-carbon cement.

7. The preparation method according to claim 6, characterized in that The gradient step carbonization curing adopts a CO2 concentration of 20-100%, an air pressure of 0.1-0.3 MPa, a temperature of 25-55°C, and a total carbonization time of 12-24 hours.

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