Low-carbon special concrete for geopolymer base and preparation method thereof

Abstract

The invention relates to the field of concrete manufacturing, and particularly discloses geopolymer-based low-carbon special concrete and a preparation method thereof. The low-carbon special concrete for the geopolymer base is composed of a porous carbon-fixed geopolymer base body and a magnesium oxysulfate cement-based coating. The porous carbon sequestration geopolymer matrix comprises the following raw materials in parts by mass: 400-800 parts of a cementing material, 200-800 parts of porous aggregate, 50-150 parts of a composite carbon sequestration agent, 100-300 parts of an alkaline activator, 0.5-5 parts of a bio-based foaming agent and 5-30 parts of toughening fibers, and the cementing material comprises at least two of fly ash, slag, metakaolin and biomass ash; the surface of the porous carbon sequestration geopolymer matrix is coated with the magnesium oxysulfate cement-based coating. The low-carbon special concrete for geopolymer base has the advantages of low carbon, carbon sequestration and good mechanical property.

Description

Technical Field

[0001] The present application relates to the field of concrete manufacturing, and more particularly, to a low-carbon special concrete for geopolymer base and a preparation method thereof. Background Art

[0002] As global climate change becomes increasingly severe, reducing carbon emissions and achieving sustainable development have become critical tasks across all industries. As the world's most widely used building material, conventional concrete plays a central role in infrastructure construction, real estate, and other fields. However, its production and application come with significant environmental costs.

[0003] Data shows that during the cement production process, about 0.9 tons of CO2 are emitted for every ton of cement produced. Its CO2 emissions account for about 12% of the country's total carbon emissions and more than 60% of industrial process carbon emissions. It is a typical high-energy-consuming, high-emission industry. This emission intensity far exceeds that of other building materials such as steel and glass: calculated per unit volume, the carbon emission coefficient of ordinary concrete is about 1 / 3 of that of low-carbon steel, but because its global annual consumption exceeds 5 billion tons, the overall carbon footprint is still very prominent. More importantly, the internal pore structure of ordinary concrete is relatively dense after hardening, with an average porosity of only 5%-15%, and the pore diameter is mostly concentrated in the harmful pore range of 10-100 nanometers, which makes it difficult for CO2 gas to effectively penetrate and react with the cementitious material to undergo carbonation, and the carbon fixation efficiency is only 3%-5%. Therefore, due to its high carbon emissions and relatively dense internal pores, the carbon sequestration potential of conventional concrete is significantly limited, making it unable to meet the demand for low-carbon, environmentally friendly materials in future green buildings. The development of new concrete materials with higher carbon sequestration capacity and lower carbon emissions is crucial for the concrete industry to achieve a green and low-carbon transformation. Summary of the Invention

[0004] In order to provide a new type of concrete with low carbon emissions and high carbon sequestration capacity, the present application provides a low-carbon special concrete for geopolymer base and a preparation method thereof.

[0005] The present application provides a low-carbon special concrete for geopolymer base using the following technical solutions: A low-carbon special concrete for geopolymer base, consisting of a porous carbon-fixing geopolymer matrix and a magnesium oxysulfate cement-based coating; the porous carbon-fixing geopolymer matrix contains the following raw materials in parts by mass: 400-800 parts of cementitious material, 200-800 parts of porous aggregate, 50-150 parts of composite carbon-fixing agent, 100-300 parts of alkaline activator, 0.5-5 parts of bio-based foaming agent, and 5-30 parts of toughening fiber; the cementitious material includes at least two of fly ash, slag, metakaolin, and biomass ash; and the magnesium oxysulfate cement-based coating is coated on the surface of the porous carbon-fixing geopolymer matrix.

[0006] By adopting the above technical solution, the porous carbon-fixing geopolymer matrix uses fly ash, slag and other industrial waste residues as the main cementitious materials, avoiding the high energy consumption process of high-temperature calcination of traditional cement, reducing carbon emissions from the raw material end, and at the same time, the large-scale utilization of industrial waste residues reduces solid waste landfill pollution. The synergistic effect of the bio-based foaming agent and the porous aggregate enables the matrix to form a multi-level pore structure, providing a channel for CO2 diffusion. The composite carbon fixer generates a gel rich in active sites under the action of an alkaline activator, which promotes the fixation of CO2 through physical adsorption and chemical mineralization reactions. Magnesium oxysulfate cement-based coating uses MgO as the main cementitious component, and its production energy consumption is lower than that of silicate cement, and the coating itself can be fixed by Mg 2+ It reacts with CO2 to generate magnesium carbonate crystals, forming a secondary carbon fixation layer; on the other hand, the dense structure of the coating effectively blocks the corrosion of harmful external ions, improves the durability of the substrate, and at the same time retains micron-level breathable channels to ensure that CO2 continues to penetrate the interior to cause mineralization reaction.

[0007] Optionally, the invention further comprises 60-80 parts of a carbon channel regulator, wherein the carbon channel regulator is a mixture of graphene aerogel microspheres and zeolite imidazolate framework material in a ratio of (3-5):1.

[0008] By employing this technical solution, graphene aerogel microspheres possess a three-dimensional porous network structure. Their abundant pores and high specific surface area provide efficient pathways for carbon dioxide transport. The zeolite imidazolate framework, with its regular pore structure and large pore volume, creates a more efficient, interconnected carbon transport channel system within the porous carbon-binding geopolymer matrix. This allows carbon dioxide to diffuse more quickly and evenly throughout the matrix, significantly increasing its reaction rate with the composite carbon-binding agent and cementitious materials, thereby enhancing the carbon sequestration efficiency of concrete. The addition of a carbon channel regulator creates favorable conditions for carbon dioxide transport and adsorption, allowing more carbon dioxide to fully contact the active ingredients in the composite carbon-binding agent and cementitious materials. Under the action of an alkaline activator, this carbon dioxide can more smoothly participate in chemical mineralization reactions, generating more stable carbonate minerals such as calcium carbonate and magnesium carbonate. The formation of these carbonate minerals not only fixes carbon dioxide but also further enhances the strength and stability of concrete, achieving the dual benefits of carbon sequestration and improved material properties.

[0009] Optionally, the porous aggregate is recycled ceramsite, the porosity of the recycled ceramsite is ≥30%, and the particle size is 0.1-5 mm.

[0010] By adopting the above technical solution, the high porosity of the recycled ceramsite itself provides a rich initial pore structure. Its internal through-holes and surface open pores form CO2 transmission channels, which together with the pores introduced by the bio-based foaming agent and the nano-scale pores of the carbon channel regulator constitute a "micron-nano" multi-level pore system, which significantly enhances the contact area and reaction depth between the matrix and the external CO2, and creates physical conditions for carbon fixation reactions. Recycled ceramsite is made by burning construction waste, industrial tailings, etc. as raw materials. Its use directly reduces the mining of natural sand and gravel, and reduces energy consumption and carbon emissions in the concrete aggregate production stage. At the same time, the porous structure of ceramsite can absorb Ca generated during the hydration process of cementitious materials. 2+ Mg 2+ Plasma, in conjunction with the composite carbon fixer, promotes CO2 mineralization. The alkaline ion solution adsorbed on the ceramsite pore walls creates a localized high-concentration reaction environment, accelerating the dissolution of CO2 and its conversion to carbonates, achieving a circular economy effect of "using waste to fix carbon."

[0011] Optionally, the composite carbon-fixing agent includes nano-calcium carbonate, modified steel slag powder, and carbonized active silicon fume in a mass ratio of 1:(2-4):(0.5-1.5).

[0012] By adopting the above technical solution, nano calcium carbonate provides a large number of initial nucleation sites with its ultra-high specific surface area, adsorbs CO2 molecules and catalyzes the generation of bicarbonate ions, accelerating the carbon fixation reaction at the gas-liquid interface; after the modified steel slag powder is mechanically activated and acid-base modified, the CaO and MgO active components exposed on the surface dissolve under the action of the alkaline activator, forming a high concentration of Ca 2+ Mg 2+ Ionic solution, build a local strong alkaline environment, promote the rapid dissolution of CO2 and convert it into carbonate precursor; carbonized active silica fume is rich in amorphous SiO2, and its surface silanols react with CO2 to generate H + The reaction forms a silica gel network, providing a growth support for calcium carbonate and magnesium carbonate crystals. When the three are compounded in a ratio of 1:(2-4):(0.5-1.5), the nanoscale nucleation sites, micron-sized alkaline ion sources, and submicron-sized gel framework form a cross-scale synergy, accelerating the CO2 mineralization reaction rate and increasing carbon sequestration per unit volume compared to single-component systems. Furthermore, nano-calcium carbonate fills the micro-interface between the porous aggregate and the cementitious matrix, reducing stress concentration and enhancing interfacial bonding strength, thereby increasing the matrix's flexural strength.

[0013] Optionally, the alkaline activator comprises water glass with a modulus of 1.2-1.8 and 8-12 mol / L NaOH solution mixed in a ratio of 1:(0.3-0.6).

[0014] By adopting the above technical solution, the main component of water glass is Na2O·nSiO2, which provides the silicon source and alkaline environment required for the polymerization reaction. The modulus of 1.2-1.8 puts the aluminosilicate polymerization reaction in the optimal kinetic range. Too low a modulus leads to insufficient silicon content and low gel production; too high a modulus increases viscosity and poor dispersibility. 8-12 mol / L NaOH solution provides a strong alkaline starting environment, which can quickly destroy the glassy structure of industrial waste such as fly ash and slag, promote the rupture of Al-O-Si bonds, and release active Al 3+ 、Si 4+ When the two are mixed at a ratio of 1: (0.3-0.6), the strong alkalinity of NaOH accelerates the depolymerization of waste residue, and the silicon source supplement of water glass promotes the rapid formation of polysilicate gel, thereby improving the compressive strength of the matrix.

[0015] Optionally, the bio-based foaming agent is a mixture of saponin extract and lignin sulfonate in a ratio of (1-2):1.

[0016] By employing this technical solution, saponin extract, with its highly active hydrophilic and hydrophobic groups, rapidly reduces surface tension in an alkaline activator solution, generating an initial foam with a diameter of 50-200μm. The long-chain aromatic structure of lignin sulfonate adsorbs onto the surface of the foam film, forming an elastic protective film that reduces bubble breakage and merging. When these two components are combined in a specific ratio, they form a closed-pore structure with a pore size distribution concentrated between 50-300μm. This, combined with the primary pores of the regenerated ceramsite and the nanopores of the carbon channel regulator, creates a three-level interconnected pore network, shortening the effective CO2 diffusion path by 30%-40% and increasing the gas-solid reaction area per unit volume by 50%-60%, providing ample physical space for carbon fixation reactions.

[0017] Optionally, the components of the magnesium oxysulfate cement-based coating include 15-30wt% tetrapod-shaped zinc oxide whiskers, 5-10wt% MOF@TiO2 particles, 3-5wt% poly (N-isopropylacrylamide) hydrogel microspheres, and the rest is magnesium oxysulfate cement.

[0018] By adopting the above technical solution, 15-30wt% of four-needle zinc oxide whiskers form a three-dimensional network support skeleton inside the coating with their unique four-legged three-dimensional structure. The four-legged ends of the whiskers are embedded in the magnesium oxysulfate cement matrix, which significantly improves the flexural strength and crack resistance of the coating and reduces the risk of matrix exposure caused by cracking of the coating during service. 2+ The active sites form coordination bonds with CO2 molecules, reducing the activation energy of the mineralization reaction and promoting the Mg 2+It is easier to form magnesium carbonate crystals with CO2, which increases the carbon fixation rate of the coating itself. The porous framework of 5-10wt% MOF@TiO2 particles preferentially enriches external CO2 and transports it into the coating. The TiO2 shell generates photogenerated electron-hole pairs under natural light excitation, catalyzing the photo-promoted mineralization reaction between CO2 and the hydration products of magnesium oxysulfide cement to form stable magnesium carbonate salts. 3-5wt% thermosensitive hydrogel microspheres regulate the porosity of the coating through volume phase change. When the ambient temperature is less than 32°C, the microspheres swell and absorb water, the pore size shrinks, slowing water loss and keeping the interior of the coating moist, promoting CO2 dissolution and mineralization. When the temperature is greater than 32°C, the microspheres shrink and release water, the pore size expands, and accelerates the diffusion of CO2 into the matrix, forming a response mechanism of "low temperature water retention promotes reaction, high temperature pore expansion increases transmission", improving carbon fixation efficiency under different climatic environments.

[0019] In a second aspect, the present application provides a method for preparing geopolymer-based low-carbon special concrete, which adopts the following technical solution: A method for preparing geopolymer-based low-carbon special concrete comprises the following steps: The cementitious material, porous aggregate, composite carbon fixer and toughening fiber are dry-mixed for 3-5 minutes, an alkaline activator is added and stirred to form a slurry, and then a bio-based foaming agent is added and stirred to foam; Inject the foamed slurry into the mold and steam cure it at 60-80℃ and humidity ≥90% for 24-48 hours before demoulding; A magnesium oxysulfate cement-based coating is coated on the demoulding concrete surface with a coating thickness of 1-2 mm. After the magnesium oxysulfate cement-based coating is initially set, it is carbonized for 6-12 hours in an environment with a CO2 concentration of 20-30% and a pressure of 0.2-0.5 MPa to obtain a low-carbon special concrete for geopolymer base.

[0020] By adopting the above technical solution, steam curing conditions at 60-80°C and humidity ≥90% increase the polymerization reaction rate of the geopolymer cementitious material, causing the aluminosilicate glass to quickly depolymerize under alkaline stimulation, generating C-(N-)ASH gel to wrap the regenerated ceramsite and fiber, rapidly improving the compressive strength, while fixing the pore structure formed by the bio-based foaming agent to avoid pore collapse caused by later shrinkage. The high humidity environment inhibits water evaporation, ensuring that the modified steel slag powder in the composite carbon fixer continuously releases Ca 2+ Mg 2+ ions, creating an early, highly alkaline carbon-fixing environment and laying the foundation for sustained mineralization after demolding. A 1-2mm thick magnesium oxysulfate cement-based coating evenly covers the substrate surface, providing a dense structure that blocks external erosion while retaining micron-sized through-pores that allow CO2 to penetrate. A subsequent carbonization treatment at a 20-30% CO2 concentration and 0.2-0.5MPa pressure for 6-12 hours synergistically fixes carbon.

[0021] Optionally, a carbon channel regulator is also added during the dry mixing.

[0022] In summary, this application has the following beneficial effects: 1. This application replaces traditional cement with industrial waste residues such as fly ash, slag, and biomass ash, reducing carbon emissions at the root of production. It also incorporates solid wastes such as recycled ceramsite, modified steel slag powder, and lignin sulfonate, creating a "waste-to-solid waste" recycling system. Bio-based foaming agents avoid chemical pollution, further enhancing the green nature of the concrete. This significantly reduces carbon emissions during the concrete production phase compared to conventional concrete, aligning with the "low carbon, carbon sequestration" goals and the requirements of a circular economy.

[0023] 2. In this application, it is preferred to use the primary pores of regenerated expanded clay, bio-based foaming pores and carbon channel regulator nanopores to construct a three-level through-pore network, which improves the CO2 diffusion efficiency and expands the contact area; the composite carbon fixer provides cross-scale active sites and increases the catalytic mineralization reaction rate.

[0024] 3. This application preferably uses toughened fibers and recycled ceramsite skeletons to compensate for the strength loss of the porous structure, so that the concrete matrix can obtain good mechanical properties while maintaining efficient carbon fixation, meeting actual engineering needs. DETAILED DESCRIPTION

[0025] The present application is further described in detail below with reference to the examples. It is particularly noted that if no specific conditions are specified in the following examples, the reactions are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources. Example

[0026] Example 1 A method for preparing geopolymer-based low-carbon special concrete: (1) Raw material preparation: Cementitious materials: fly ash and slag are mixed in a mass ratio of 2:1, with a total amount of 600kg; the fly ash is Class I fly ash, with a 45μm sieve residue ≤12%, ignition loss ≤5%, and SiO2+Al2O3+Fe2O3 content ≥85%; S95 grade granulated blast furnace slag, with a specific surface area ≥450m 2 / kg, 7-day activity index ≥75%, 28-day activity index ≥95%; Porous aggregate: 500kg shale ceramsite, porosity 35%-45% (determined by mercury intrusion), particle size distribution 0.1-5mm continuous grading (D10=0.3mm, D50=2.1mm, D90=4.5mm), bulk density 800-1000kg / m 3 ; Composite carbon fixer: nano calcium carbonate, modified steel slag powder, and carbonized activated silica fume are mixed in a ratio of 1:1:1, with a total weight of 100 kg. Nano calcium carbonate is a cubic crystal with an average particle size of 30-50 nm and a specific surface area of ≥25 m 2 / g, purity ≥98%; modified steel slag powder is ground from electric furnace steel slag (D90 ≤ 10μm), activated with 5% citric acid, f-CaO content ≤ 3%, CaO ≥ 40%; carbonized active silica fume is non-densified silica fume, SiO2 ≥ 92%, average particle size 0.1-0.3μm, activity index (7d) ≥ 120%; Alkaline activator: 200 kg of water glass with a modulus of 1.5 and 10 mol / L NaOH solution in a ratio of 1:0.45; the water glass is sodium water glass (Na2O·nSiO2), with a Baume degree of 40-42° and a solid content of ≥36%; Bio-based foaming agent: saponin extract and calcium lignin sulfonate are mixed in a ratio of 1.5:1, with a total weight of 3 kg. The saponin content of the saponin extract is ≥60%, the pH is 6.5-7.5, and the foaming multiple is 8 times (0.5% aqueous solution). The lignin sulfonate is calcium-based lignin sulfonate, with a water reduction rate of 12%, a pH of 8-9, and a sulfate content of ≤3%. Toughening fiber: polyvinyl alcohol fiber (length 12 mm, diameter 20-40 μm) 15 kg.

[0027] (2) Matrix preparation: The cementitious material, ceramsite, composite carbon fixer and fiber were dry-mixed for 4 minutes, an alkaline activator was added and stirred for 3 minutes to form a uniform slurry, and a foaming agent was added and stirred at a high speed of 1500 rpm for 2 minutes.

[0028] (3) Molding and curing: The foamed slurry was injected into a mold, steam-cured at 75° C. and 95% humidity for 36 hours, and then demoulded to obtain a porous carbon-fixing geopolymer matrix.

[0029] (4) Coating construction: Magnesium oxysulfate cement slurry with a water-cement ratio of 0.4 was coated on the substrate surface twice with a total thickness of 2 mm, and glass fiber mesh cloth with a pore size of 2.5 mm was embedded between the layers.

[0030] (5) Carbonization strengthening: The carbonization treatment was carried out in a closed reactor with a CO2 concentration of 25% and a pressure of 0.3 MPa for 9 hours, and then the product was cured at room temperature of 25°C for 7 days to obtain a low-carbon special concrete product.

[0031] Example 2 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that the raw materials of the porous carbon-fixing geopolymer matrix are: 400 kg of cementitious material, 200 kg of porous aggregate, 50 kg of composite carbon-fixing agent, 100 kg of alkaline activator, 0.5 kg of bio-based foaming agent, and 5 kg of toughening fiber.

[0032] Example 3 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that the raw materials of the porous carbon-fixing geopolymer matrix are: 800 kg of cementitious material, 800 kg of porous aggregate, 150 kg of composite carbon-fixing agent, 300 kg of alkaline activator, 5 kg of bio-based foaming agent, and 30 kg of toughening fiber.

[0033] Example 4 A method for preparing low-carbon special concrete for geopolymer base: The difference from Example 1 is that the cementitious material is fly ash, slag, metakaolin, and biomass ash mixed in a mass ratio of 4:2:1:1. The metakaolin is calcined kaolin with D50 = 2-5 μm, Al2O3 ≥ 35%, whiteness ≥ 85%, and pozzolanic activity ≥ 110%; the biomass ash is rice husk ash with SiO2 ≥ 90%, C content ≤ 5%, and specific surface area ≥ 15m 2 / g.

[0034] Example 5 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that 70 kg of carbon channel regulator is added during dry mixing, and the carbon channel regulator is a mixture of graphene aerogel microspheres and zeolite imidazolate skeleton material in a mass ratio of 4:1. The graphene aerogel microspheres have a diameter of 0.5-2 mm, a porosity of ≥95%, a pore size distribution of 50-200 nm, and a conductivity of ≥10 S / m. The zeolite imidazolate skeleton material is ZIF-8 type, with a particle size of 100-300 nm and a specific surface area of ≥1300 m 2 / g.

[0035] Example 6 A method for preparing geopolymer-based low-carbon special concrete: The difference from Example 1 is that 60 kg of carbon channel regulator is added during dry mixing.

[0036] Example 7 A method for preparing geopolymer-based low-carbon special concrete: The method differs from Example 1 in that 80 kg of a carbon channel regulator is added during dry mixing.

[0037] Example 8 A method for preparing geopolymer-based low-carbon special concrete: The difference from Example 1 is that the carbon channel regulator is a mixture of graphene aerogel microspheres and zeolite imidazolate skeleton material in a mass ratio of 3:1.

[0038] Example 9 A method for preparing geopolymer-based low-carbon special concrete: The difference from Example 1 is that the carbon channel regulator is a mixture of graphene aerogel microspheres and zeolite imidazolate skeleton material in a mass ratio of 5:1.

[0039] Example 10 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that the porous aggregate is replaced by recycled ceramsite, which is prepared from construction waste.

[0040] Example 11 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that the composite carbon fixer is adjusted to nano-calcium carbonate: modified steel slag powder: carbonized active silica fume = 1:3:1.

[0041] Example 12 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that water glass with a modulus of 1.5 is mixed with 10 mol / L NaOH solution at a ratio of 1:0.3.

[0042] Example 13 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that water glass with a modulus of 1.5 is mixed with 10 mol / L NaOH solution at a ratio of 1:0.6.

[0043] Example 14 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that water glass with a modulus of 1.2 is selected.

[0044] Example 15 A method for preparing low-carbon special concrete based on geopolymer: The method differs from Example 1 in that water glass with a modulus of 1.8 is used.

[0045] Example 16 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that 8 mol / L NaOH solution is selected.

[0046] Example 17 A method for preparing geopolymer-based low-carbon special concrete: The method differs from Example 1 in that a 12 mol / L NaOH solution is used.

[0047] Example 18 A method for preparing geopolymer-based low-carbon special concrete: The difference from Example 1 is that the bio-based foaming agent is a mixture of saponin extract and lignin sulfonate in a mass ratio of 1:1.

[0048] Example 19 A method for preparing geopolymer-based low-carbon special concrete: The difference from Example 1 is that the bio-based foaming agent is a mixture of saponin extract and lignin sulfonate in a mass ratio of 2:1.

[0049] Example 20 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 1 is that the components of the magnesium oxysulfate cement-based coating include 15wt% tetrapod-shaped zinc oxide whiskers, 5wt% MOF@TiO2 particles, 3wt% poly-N-isopropylacrylamide hydrogel microspheres, and the rest is magnesium oxysulfate cement mortar with a water-cement ratio of 0.4. Among them, the tetrapod-shaped zinc oxide whiskers have a needle length of 10-30μm, a diameter of 0.5-1μm, a purity of ≥99.9%, and an aspect ratio of ≥20:1. The MOF@TiO2 particles are MIL-125(Ti)-loaded TiO2 core-shell structure, with a particle size of 200-500nm and a specific surface area of ≥800m 2 / g, pore size 2-3nm, thermosensitive response temperature of poly (N-isopropylacrylamide) microspheres 32-35°C, particle size 50-100μm, swelling ratio ≥5 times (25°C→40°C).

[0050] Example 21 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 20 is that the components of the magnesium oxysulfate cement-based coating include 30wt% tetrapod-shaped zinc oxide whiskers, 10wt% MOF@TiO2 particles, 5wt% poly (N-isopropylacrylamide) hydrogel microspheres, and the rest is magnesium oxysulfate cement mortar with a water-cement ratio of 0.4.

[0051] Example 22 A method for preparing low-carbon special concrete based on geopolymer: The difference from Example 20 is that the components of the magnesium oxysulfate cement-based coating include 22wt% tetrapod-shaped zinc oxide whiskers, 8wt% MOF@TiO2 particles, 4wt% poly (N-isopropylacrylamide) hydrogel microspheres, and the rest is magnesium oxysulfate cement mortar with a water-cement ratio of 0.4.

[0052] Comparative Example Comparative Example 1 A method for preparing geopolymer-based low-carbon special concrete: The method differs from Example 1 in that no composite carbon-fixing agent is added.

[0053] Comparative Example 2 A method for preparing low-carbon special concrete based on geopolymer: The method is different from Example 1 in that water glass is not added to the alkali activator.

[0054] Comparative Example 3 A method for preparing geopolymer-based low-carbon special concrete: The difference from Example 1 is that only lignin sulfonate is used as the bio-based foaming agent.

[0055] Performance testing Detection method Carbon sequestration capacity and efficiency: Under the conditions of CO2 concentration of 20% and pressure of 0.3MPa, the cumulative carbon sequestration amount (kgCO2 / m 3 ).

[0056] Carbonate content: The CO2 binding amount (wt%) was determined by thermogravimetric analysis (TGA).

[0057] Mechanical properties Compressive strength: GB / T50081-2019, 28-day strength (MPa).

[0058] Flexural strength: GB / T50081-2019, 28-day strength (MPa).

[0059] Durability Chloride ion penetration resistance: ASTM C1202, coulometric test (coulomb value).

[0060] Freeze-thaw resistance: GB / T50082-2009, mass loss rate (%) Table 1 Test data Combining Example 1 and Comparative Example 1 with Table 1, it can be seen that the carbon fixation efficiency of Example 1 is 45.2 kg / m 3 , while the comparative example 1 is only 8.2kg / m 3 , indicating that the composite carbon fixer is the core driving force of the carbon fixation reaction. The composite carbon fixer provides nucleation sites through nano-calcium carbonate and steel slag powder releases Ca 2+ / Mg 2+ Silica fume builds a gel network, creating a cross-scale synergistic mineralization effect. In Example 1, without the composite carbon-fixing agent, the carbonate content is extremely low, and the compressive and flexural strengths decrease significantly, verifying the dual role of the composite carbon-fixing agent in carbon fixation and mechanical properties.

[0061] Combining Example 1 and Comparative Example 2 and Table 1, it can be seen that Comparative Example 2 does not add water glass, and its compressive strength decreases by 42% compared with Example 1, and the proportion of harmful pores increases significantly. As the core component of the alkaline activator, water glass provides a silicon source and accelerates the glassy depolymerization of fly ash / slag, promoting the formation of geopolymer gel (C-(N-)ASH). In the absence of water glass, the geopolymer network cannot be effectively polymerized, resulting in a loose matrix structure and poor pore connectivity, and the carbon fixation efficiency is only 71.7% of that of Example 1. In addition, the chloride ion permeability value of Comparative Example 2 is extremely high, indicating that water glass is indispensable for improving durability.

[0062] Combining Example 1 and Comparative Example 3 with Table 1 reveals that Comparative Example 3, which utilizes only lignin sulfonate for foaming, exhibits a 41% decrease in carbon sequestration efficiency compared to Example 1, a reduced porosity, and an increased proportion of harmful pores. The combination of saponin extract and lignin sulfonate forms a stable closed-cell structure, whereas a single lignin sulfonate foaming agent exhibits poor foam stability and uneven pore size distribution, resulting in obstructed CO2 diffusion pathways. Furthermore, the freeze-thaw resistance loss rate of Comparative Example 3 is significantly higher than that of Example 1, demonstrating the optimized pore connectivity and durability of the foaming agent.

[0063] It can be seen from Examples 1-3 and Table 1 that within the formulation range of the porous carbon-fixing geopolymer matrix of the present application, good carbon-fixing capacity and mechanical properties can be achieved.

[0064] Combining Examples 1 and 4 with Table 1, it can be seen that Example 4, using a combination of fly ash, slag, metakaolin, and biomass ash, achieves slightly higher carbon sequestration efficiency than Example 1. This is because the Al₂O₃ in the metakaolin and the SiO₂ in the biomass ash complement the aluminosilicate network of the geopolymer gel, enhancing CO₂ adsorption activity. However, the compressive strength is slightly lower than that of Example 1 due to structural micro-defects caused by differences in the reaction rates of the multi-component cementitious materials.

[0065] Combining Examples 1, 5-9 and Table 1, it can be seen that the best combination of 70 parts of carbon channel regulator, graphene aerogel microspheres and zeolite imidazolate framework material in the present application is 4:1 by mass ratio.

[0066] Combining Examples 1 and 10 with Table 1, it can be seen that Example 10 uses recycled ceramsite, which still has good carbon sequestration performance and the compressive strength still meets the C30 standard, proving the feasibility of recycled ceramsite in the "waste carbon sequestration" scenario.

[0067] Combining Examples 1 and 11 with Table 1, it can be seen that the performance of the composite carbon fixer is better when the mass ratio of nano-calcium carbonate, modified steel slag powder, and carbonized activated silicon fume is 1:(2-4):(0.5-1.5).

[0068] Combining Examples 1, 12-17 and Table 1, it can be seen that a modulus of 1.2-1.8 places the aluminosilicate polymerization reaction in the optimal kinetic range. A too low modulus leads to insufficient silicon content and a small amount of gel production; a too high modulus increases viscosity and poor dispersibility. 8-12 mol / L NaOH solution provides a strong alkaline starting environment, which can quickly destroy the glassy structure of industrial waste such as fly ash and slag, promote the rupture of Al-O-Si bonds, and release active Al 3+ 、Si 4+ When the two are mixed at a ratio of 1: (0.3-0.6), the strong alkalinity of NaOH accelerates the depolymerization of waste residue, and the silicon source supplement of water glass promotes the rapid formation of polysilicate gel, thereby improving the compressive strength of the matrix.

[0069] From Examples 1, 18-19 and Table 1, it can be seen that the bio-based foaming agent, which is a mixture of saponin extract and lignin sulfonate in a ratio of (1-2):1, can achieve good carbon fixation effect and mechanical properties.

[0070] Combining Examples 1, 20-22 and Table 1, it can be seen that the magnesium oxysulfate cement-based coating enhances crack resistance by constructing a three-dimensional network skeleton through four-needle zinc oxide whiskers. 2+ Active sites reduce the energy barrier for CO2 mineralization; MOF@TiO2 particles enrich CO2 in a porous framework and accelerate the generation of magnesium carbonate through photocatalysis; thermosensitive hydrogel microspheres (3-5wt%) dynamically adjust the porosity through temperature response: at low temperatures, water retention promotes dissolution mineralization, and at high temperatures, pore expansion accelerates CO2 penetration, forming a climate-adaptive "carbon fixation-protection" smart coating that takes into account both durability and carbon sequestration efficiency.

[0071] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A low-carbon special concrete for geopolymer base, characterized in that: The invention is composed of a porous carbon-fixing geopolymer matrix and a magnesium oxysulfate cement-based coating; the porous carbon-fixing geopolymer matrix contains the following raw materials in parts by mass: 400-800 parts of cementitious material, 200-800 parts of porous aggregate, 50-150 parts of composite carbon-fixing agent, 100-300 parts of alkaline activator, 0.5-5 parts of bio-based foaming agent, and 5-30 parts of toughening fiber; the cementitious material includes at least two of fly ash, slag, metakaolin, and biomass ash; and the magnesium oxysulfate cement-based coating is coated on the surface of the porous carbon-fixing geopolymer matrix.

2. The low-carbon special concrete for geopolymer base according to claim 1, characterized in that: It also includes 60-80 parts of a carbon channel regulator, which is a compound of graphene aerogel microspheres and zeolite imidazolate framework material in a mass ratio of (3-5):

1.

3. The low-carbon special concrete for geopolymer base according to claim 1, characterized in that: The porous aggregate is recycled ceramsite, the porosity of the recycled ceramsite is ≥30%, and the particle size is 0.1-5 mm.

4. The low-carbon special concrete for geopolymer base according to claim 1, characterized in that: The composite carbon fixer comprises nano calcium carbonate, modified steel slag powder and carbonized active silicon fume in a mass ratio of 1:(2-4):(0.5-1.5).

5. The low-carbon special concrete for geopolymer base according to claim 1, characterized in that: The alkaline activator comprises water glass with a modulus of 1.2-1.8 and a NaOH solution with a concentration of 8-12 mol / L, which are mixed in a mass ratio of 1:(0.3-0.6).

6. The low-carbon special concrete for geopolymer base according to claim 1, characterized in that: The bio-based foaming agent is a mixture of saponin extract and lignin sulfonate in a mass ratio of (1-2):

1.

7. The low-carbon special concrete for geopolymer base according to claim 1, characterized in that: The components of the magnesium oxysulfate cement-based coating include 15-30wt% of tetrapod-shaped zinc oxide whiskers, 5-10wt% of MOF@TiO2 particles, 3-5wt% of poly (N-isopropylacrylamide) hydrogel microspheres, and the rest is magnesium oxysulfate cement.

8. A method for preparing geopolymer-based low-carbon special concrete according to any one of claims 1 to 7, characterized in that: The following steps are involved: The cementitious material, porous aggregate, composite carbon fixer and toughening fiber are dry-mixed for 3-5 minutes, an alkaline activator is added and stirred to form a slurry, and then a bio-based foaming agent is added and stirred to foam; Inject the foamed slurry into the mold and steam cure it at 60-80℃ and humidity ≥90% for 24-48 hours before demoulding; A magnesium oxysulfate cement-based coating is coated on the concrete surface after demoulding, with a coating thickness of 1-2 mm. After the magnesium oxysulfate cement-based coating is initially set, it is carbonized for 6-12 hours in an environment with a CO2 concentration of 20-30% and a pressure of 0.2-0.5 MPa to obtain a low-carbon special concrete for geopolymer base.

9. The method for preparing geopolymer-based low-carbon special concrete according to claim 8, characterized in that: A carbon channel regulator is also added during the dry mixing.

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