Magnesium oxide-aerogel composite additive, self-repairing low-carbon concrete and preparation method of self-repairing low-carbon concrete

Abstract

The invention discloses a magnesium oxide-aerogel composite additive, self-repairing low-carbon concrete and a preparation method. The magnesium oxide-aerogel composite additive is mainly prepared from light calcined magnesium oxide, a dispersing agent, a sodium silicate solution, a silane coupling agent and a saturated alkali solution. The self-repairing low-carbon concrete is mainly prepared from cement, the magnesium oxide-aerogel composite additive, sand, gravel, water and a water reducing agent, or fly ash. The invention further discloses a preparation method of the magnesium oxide-aerogel composite additive and the self-repairing low-carbon concrete. The magnesium oxide-aerogel composite additive disclosed by the invention can synergistically exert the carbonization reaction of light calcined magnesium oxide and the micropore adsorption effect of silicon dioxide aerogel. The self-repairing low-carbon concrete has active efficient carbon reduction and crack dynamic self-repairing functions, and is high in erosion resistance. The method disclosed by the invention meets a low-concentration CO2 introduction process, carbon capture, mineralization reaction and crack repair are synchronously completed in the hardening stage of the concrete, and the method is simple in process, low in cost and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to an aerogel composite additive, concrete and a preparation method, and in particular to a magnesium oxide-aerogel composite additive, self-repairing low-carbon concrete and a preparation method. Background Art

[0002] During cement production, 0.6 to 0.9 tons of CO2 are emitted per ton of cement. Existing mineral admixture alternative technologies (such as fly ash and slag) typically have a carbon reduction rate of less than 30% and are unable to directly fix CO2. Therefore, the carbon emission problem of traditional concrete has become a global challenge.

[0003] Magnesium oxide has been explored for use in the concrete field due to its carbonization reaction ability. However, existing technologies (such as CN119118167A, which uses a secondary calcination process to increase the activity of magnesium oxide to a CAA value of 10-185s) still have bottlenecks such as uneven dispersion (coefficient of variation > 0.2) and low carbon fixation efficiency (CO2 conversion rate < 35%).

[0004] Although solid waste-based cementitious materials (such as CN117735916A using recycled aggregates and activators) can reduce cement consumption, their carbon reduction potential is limited (CO2 conversion rate <40%) and they lack crack repair capabilities.

[0005] Existing crack self-repair technologies generally rely on external grouting or complex catalysts (such as CN117024074A uses composite admixtures that require the addition of dopamine), have a long repair cycle (≥28 days), and are costly.

[0006] In addition, CO2 mineralization technology often requires a high-purity environment (>90% CO2 concentration) or additional energy consumption, making it difficult to adapt to conventional concrete production lines.

[0007] In summary, existing technologies have failed to collaboratively solve problems such as large cement consumption, high carbon emissions from concrete, high energy consumption of carbon capture technology, low crack repair efficiency, and high cost, resulting in limited carbon reduction rate and durability improvement. It is urgent to optimize the dispersion of magnesium oxide, the low-concentration CO2 injection process and the integration of crack repair functions. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a magnesium oxide-aerogel composite additive that can synergistically exert the carbonization reaction of light-burned magnesium oxide and the microporous adsorption effect of silicon dioxide aerogel.

[0009] The present invention further aims to solve the technical problem of overcoming the above-mentioned defects of the prior art and providing a method for preparing a magnesium oxide-aerogel composite additive with simple process, low cost and suitable for industrial production.

[0010] A further technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a self-repairing low-carbon concrete that has both active and efficient carbon reduction and dynamic self-repair of cracks and strong anti-erosion performance.

[0011] A further technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing self-repairing low-carbon concrete that meets the requirements of low-concentration CO2 introduction process, and simultaneously completes carbon capture, mineralization reaction and crack repair in the concrete hardening stage. The process is simple, the cost is low, and it is suitable for industrial production.

[0012] The present invention solves the technical problem by employing the following technical solution: a magnesium oxide-aerogel composite additive, primarily composed of light-burned magnesium oxide, a dispersant, a sodium silicate solution, a silane coupling agent, and a saturated alkaline solution. Light-burned magnesium oxide, as the core active component, provides active sites for carbonization reactions, reacting with CO2 to form magnesium carbonate minerals (such as magnesite), achieving carbon capture and microcrack repair in concrete. Its high specific surface area and controlled particle size help ensure high reactivity. The dispersant improves the dispersibility of the light-burned magnesium oxide particles, preventing agglomeration and ensuring uniform distribution of the composite additive in the concrete. The sodium silicate solution, serving as a precursor for the bio-based silica aerogel, forms a three-dimensional porous network structure through a sol-gel process, capable of adsorbing CO2 and transferring it to the magnesium oxide surface. The silane coupling agent strengthens the interfacial bonding between the aerogel and magnesium oxide through chemical bonding (Si-O-Mg bonds), preventing the mineralized product from delaminating from the matrix.

[0013] Preferably, the weight proportions of the components of the magnesium oxide-aerogel composite additive are: 100 parts of light-burned magnesium oxide, 1 to 5 parts of dispersant, 200 to 350 parts of sodium silicate solution, 3 to 5 parts of silane coupling agent, and 100 to 200 parts of saturated alkaline solution. If the amount of light-burned magnesium oxide is too much, the proportion of aerogel will be too low and the carbon fixation efficiency will decrease. If the amount of light-burned magnesium oxide is too little, the aerogel network will be difficult to effectively support the mineralization reaction. If the amount of dispersant is too much, too many organic impurities will be introduced, reducing the high-temperature stability of the composite additive. If the amount of dispersant is too little, magnesium oxide will agglomerate and the reaction activity will decrease. If the amount of sodium silicate solution is too much, the gelation time will be prolonged and the aerogel strength will be reduced. If the amount of sodium silicate solution is too little, the silicon source will be insufficient and the porosity will be insufficient. If the amount of silane coupling agent used is too much, it will cause the aerogel to become hydrophobic, affect the modulus stability, and inhibit CO2 adsorption; if the amount of silane coupling agent used is too little, the interface bonding will be weak and the repair efficiency will be low. The amount of silane coupling agent added directly affects the interface bonding between aerogel and magnesium oxide, that is, the mechanical strength and self-repair efficiency of the composite additive.

[0014] Preferably, the light-burned magnesium oxide has a purity of ≥95%, a particle size of ≤50 μm (more preferably D90 ≤30 μm), and a specific surface area of 20 to 50 m 2 / g.

[0015] Preferably, the dispersant includes polycarboxylates and / or lignin sulfonates. Polycarboxylates have a comb-like molecular structure, with the main chain adsorbed on the surface of magnesium oxide particles, while the side chains create steric hindrance, preventing particle agglomeration. This structure effectively improves the dispersion uniformity of light-burned magnesium oxide and reduces the loss of activity caused by agglomeration. Its water reduction rate can reach over 30%, reducing the total water consumption of concrete and indirectly reducing cement usage, thus meeting low-carbon goals and achieving a balance between dispersion performance and interface optimization. Lignosulfonates, as anionic dispersants, stabilize particles through electrostatic repulsion and are particularly suitable for dispersing inorganic materials. The sulfonic acid groups in their molecules bind to the hydroxyl groups on the magnesium oxide surface, enhancing wettability. Their low cost makes them suitable for large-scale production. As an industrial byproduct (e.g., extracted from papermaking wastewater), their cost is only one-third to one-half that of polycarboxylates, further reducing carbon emissions. Although the source of lignin sulfonates may introduce impurities (e.g., sugars), copolymerization modification with silane coupling agents can reduce the impact of impurities on interfacial bonding. The combination of polycarboxylic acid and lignin sulfonate avoids the drawbacks of single dispersants, such as the tendency for pure polycarboxylic acid to cause concrete segregation and the low dispersion efficiency of pure lignin sulfonate. This achieves a complementary effect between the efficient dispersion of the polycarboxylic acid and the retarding and air-entraining effects of the lignin sulfonate, as well as the synergistic effect of the uniform distribution of magnesium oxide particles and the microporous structure of the aerogel. The water reduction rate of the polycarboxylic acid system is ≥25%.

[0016] More preferably, the polycarboxylic acid series includes Sika ViscoCrete-530P, JSJ03 and the like, and the lignin sulfonate includes DP-2015 and the like.

[0017] Preferably, the mass concentration of the sodium silicate solution is 5-32% (more preferably 15-31%), and the modulus is 3.0-3.8. The modulus of sodium silicate = n(SiO2) / n(Na2O).

[0018] Preferably, the silane coupling agent includes one or more of epoxy silane (more preferably KH-560), bisamino silane (more preferably KH-792) or methyltrimethoxysilane (MTMS for short).

[0019] Preferably, the saturated alkaline solution includes calcium hydroxide solution or the like.

[0020] Preferably, the sodium silicate solution is prepared by adding wood ash to an acidic aqueous solution for acid washing, filtering, rinsing to neutrality, ball milling, and calcining. The resulting silicon oxide powder is then added to an alkaline aqueous solution and subjected to a hydrothermal reaction in a sealed hydrothermal reactor. The acid washing process primarily removes impurities. The wood ash (primarily containing K2CO3, SiO2, and metal oxides) reacts with hydrochloric acid (HCl) to dissolve metal impurities (such as Fe2O3, Al2O3, and CaO), generating soluble chlorides that are then removed by filtration. This improves the purity of the subsequent sodium silicate and prevents metal ions from interfering with the aerogel structure. Calcination activates the solution. After acid washing, the calcined wood ash decomposes organic matter and promotes the transformation of amorphous SiO2 into a more active crystalline state. Simultaneously, carbonates (such as K2CO3) decompose into K2O and CO2, optimizing the reactivity of SiO2 and providing a high-purity silicon source for the subsequent hydrothermal reaction. The role of the hydrothermal reaction is synthesis. The calcined SiO2 reacts with the NaOH solution under high temperature and high pressure to generate sodium silicate with a modulus (SiO2 / Na2O molar ratio) of 3.0 to 3.4, forming a high modulus sodium silicate solution, which provides a precursor for aerogel, and its microporous structure and specific surface area can be controlled by the reaction conditions.

[0021] Preferably, the initial particle size of the wood ash is 100 to 300 μm.

[0022] Preferably, the plant ash includes one or more of rice husk ash, straw ash or wood ash, etc. The present invention uses agricultural waste plant ash to replace high-purity quartz sand, which can reduce raw material costs by more than 40% and realize solid waste resource utilization.

[0023] The invention purifies the wood ash by acid washing and calcining, so that the purity of SiO2 in the wood ash is ≥90%, reaching the standard of industrial-grade quartz sand.

[0024] Preferably, the mass volume ratio of the wood ash to the acid aqueous solution is g / mL 1:4-6.

[0025] Preferably, the concentration of the acid aqueous solution is 0.8 to 1.2 mol / L. More preferably, the acid aqueous solution includes hydrochloric acid or the like.

[0026] Preferably, the pickling temperature is 70-90° C., and the pickling time is 1.5-2.5 h.

[0027] Pretreatment under the above pickling conditions can not only remove impurities (such as metal oxides), but also improve the purity of SiO2, indirectly improve the modulus, and avoid excessive acid corrosion of equipment by balancing the metal removal rate and acid consumption.

[0028] Preferably, the ball milling is performed to a particle size of 50 to 150 μm.

[0029] Preferably, calcination is performed under oxygen-rich conditions at a temperature of 550-650°C for 3-5 hours. Oxygen-rich conditions ensure sufficient calcination. This calcination temperature is significantly lower than the conventional dry process temperature of ≥1400°C, reducing energy consumption by over 35% while also preventing excessive sintering of the SiO2.

[0030] Preferably, the mass volume ratio of the silicon oxide powder to the alkaline aqueous solution is g / mL 1:2 to 4. The concentration and modulus of the sodium silicate solution can be adjusted by controlling the amount of plant ash and alkali.

[0031] Preferably, the concentration of the aqueous alkali solution is 3 to 6 mol / L. At this concentration, the modulus can be precisely controlled, resolving the issue of unstable modulus observed in conventional wet processes. When the concentration of the aqueous alkali solution is lower than 4 mol / L, the hydrothermal reaction time must be extended to ≥ 8 hours to ensure that the modulus meets the required standard. More preferably, the aqueous alkali solution comprises an aqueous sodium hydroxide solution, for example.

[0032] Preferably, the hydrothermal reaction temperature is 140-180°C, the pressure is 0.3-1.0 MPa, and the reaction time is 5-12 hours. The product modulus obtained under normal pressure is too high (e.g., 2.9). Pressurized reaction can not only shorten the reaction time but also achieve a moderate modulus by adjusting the temperature, pressure, and time.

[0033] The present invention further solves the technical problem by adopting the following technical solution: a method for preparing a magnesium oxide-aerogel composite additive, comprising the following steps: (1) Magnesium oxide pretreatment: Grind the light-burned magnesium oxide and then mix it with a dispersant to obtain premixed magnesium oxide; (2) Curing and drying of magnesium oxide-aerogel: First, the premixed magnesium oxide obtained in step (1) is added to the sodium silicate solution, mixed, and the pH value is adjusted. After adding the silane coupling agent and mixing, the mixture is allowed to stand for gelation. The mixture is then poured into a saturated alkaline solution, aged, gradient dried, dry-mixed and ball-milled, and sieved to obtain a magnesium oxide-aerogel composite additive.

[0034] The inventive concept of the method of the present invention is: using light-burned magnesium oxide as the core component, optimizing dispersibility by a dispersant + aerogel-magnesium oxide interface bonding + low-energy gradient drying; the dispersant is mainly used for the primary dispersion of light-burned magnesium oxide particles, and agglomeration is prevented by electrostatic repulsion or steric hindrance; at the same time, bio-based silica aerogel is introduced using sodium silicate solution as a precursor, and a porous network with a high specific surface area is formed through a normal pressure gradient drying process, and chemical bonding modification with magnesium oxide is carried out by a silane coupling agent to form a Si-O-Mg chemical bonding interface.

[0035] Preferably, in step (1), the grinding is performed to a D90 of less than 15 μm. The particle size of the light-burned magnesium oxide directly affects its specific surface area and reactivity. At this particle size, the particles can be fully dispersed, thereby improving the subsequent interfacial bonding efficiency with the aerogel. If the grinding is insufficient, the particles will agglomerate, resulting in a decrease in specific surface area and a decrease in CO2 adsorption capacity. If the grinding is excessive, the crystal structure may be destroyed, reducing the mechanical strength.

[0036] Preferably, in step (1), the mixing time is ≥30 min. Adding the dispersant first can ensure that it is fully coated on the surface of the magnesium oxide particles, inhibiting agglomeration through electrostatic repulsion and steric hindrance, optimizing particle distribution, and laying the foundation for the subsequent uniform infiltration of the sodium silicate solution. If the mixing time is too short, it will lead to uneven coating and cause local reaction activity differences. If the mixing time is too long, it may introduce mechanical energy overload and destroy the chemical bonds on the particle surface.

[0037] Preferably, in step (2), the pH value is adjusted to 10-11. The pH value is the optimal condition for the silane coupling agent (such as KH-560) to form Si-O-Mg bonds. More preferably, the pH value is adjusted with sodium carbonate. Sodium carbonate, as a weak alkaline regulator, can not only avoid the destruction of the aerogel pore structure by strong bases (such as NaOH), but also provide CO3 2- Ions promote the bonding between sodium silicate and magnesium oxide; if the pH value is too low, the coupling reaction is incomplete and the interfacial bonding force is weak; if the pH value is too high, it may cause the aerogel network to hydrolyze and collapse.

[0038] Preferably, in step (2), the temperature of the standing gelation is 70-90°C and the time is 10-14 hours. The sodium silicate solution forms a three-dimensional porous network through sol-gel transformation at high temperature. At the temperature, the polycondensation reaction can be accelerated and the gelation time can be appropriately extended to ensure the integrity of the network structure. If the temperature is too low, the gelation time will be too long. If the temperature is too high, it will induce local rapid polycondensation, forming a macroporous structure and reducing the adsorption performance.

[0039] Preferably, in step (2), the aging reaction temperature is 60-80°C and the time is 18-30h. The aging reaction is carried out in a saturated Ca(OH)2 solution. The aerogel skeleton and magnesium oxide enhance the interface stability through ion exchange and chemical bonding. Calcium hydroxide plays a key role in interface bonding and pore regulation. Appropriate aging temperature can promote Mg 2+ With SiO3 2- The ions penetrate into the aerogel to form a dense composite structure. If the temperature is too high, it may cause thermal decomposition of the aerogel skeleton; if the aging time is too short, the bonding is insufficient and the interface bonding strength is low.

[0040] Preferably, in step (2), the gradient drying refers to: first drying at 50-70°C for 10-14h, then drying at 70-90°C for 10-14h, and finally drying at 90-110°C for 4-8h. The temperature of the latter gradient drying is higher than that of the previous one. Staged atmospheric pressure gradient drying (such as 50°C → 70°C → 90°C → 110°C) replaces supercritical drying, and can avoid pore collapse caused by capillary stress by gradually removing free water, bound water and residual solvent. Compared with supercritical drying, gradient drying reduces energy consumption by more than 35%, and the porosity is maintained at ≥80%, and the specific surface area is ≥600 m 2 / g; the purpose of the first stage of drying is mainly to gently remove free water to prevent micropore collapse; the purpose of the second stage of drying is mainly to remove bound water to maintain skeleton stability; the purpose of the third stage of drying is mainly to completely remove residual solvents to avoid long-term high temperature causing magnesium oxide lattice distortion.

[0041] Preferably, in step (2), the dry-mix ball milling process is performed at a rotational speed of 200 to 400 rpm for a time of 0.5 to 1.5 hours. Dry-mix ball milling can mechanically break up soft aggregates in the composite powder, thereby improving the contact efficiency between the water-reducing agent and the aerogel-magnesium oxide interface during the concrete stage. If the rotational speed is too slow, dispersion is insufficient, resulting in gaps between particles. If the rotational speed is too high, excessive pulverization may occur, destroying the porous structure of the aerogel.

[0042] Preferably, in step (2), the concrete admixture is sieved through a 200-mesh sieve. Sieving can ensure the fluidity and filling properties of the concrete admixture.

[0043] The present invention further solves its technical problems by adopting the following technical solution: self-repairing low-carbon concrete is mainly made of cement, the magnesium oxide-aerogel composite additive, sand, gravel, water, and a water reducer, or fly ash. The water reducer optimizes the fluidity of the magnesium oxide-aerogel composite additive through adsorption-lubrication effects, ensuring its uniform mixing with the other concrete components (cement, sand, and gravel). At the same time, during the drying and curing stage, the molecular chains of the water reducer can partially fill the micropores of the aerogel, forming a "temporary support" to prevent pore collapse and maintain a specific surface area of ≥600 m 2 / g open structure to achieve pore structure protection; in addition, the polar groups in the water reducer (such as the carboxylate of polycarboxylic acid) react with the epoxy group of the silane coupling agent (KH-560) to form a "water reducer-coupling agent" composite interface layer, which enhances the interfacial compatibility and strengthens the bonding stability between magnesium oxide and aerogel (the breaking energy of Si-O-Mg bond is improved).

[0044] Preferably, the self-repairing low-carbon concrete comprises the following components by weight: 200-400 parts cement, 20-120 parts magnesium oxide-aerogel composite additive, 600-900 parts sand, 800-1200 parts gravel, 150-200 parts water, 0.5-3.0 parts water reducer, and 0-100 parts fly ash. Excessive water reducer usage can cause concrete segregation and reduce compressive strength, while insufficient water reducer usage can lead to poor fluidity and uneven aerogel distribution.

[0045] More preferably, the weight proportions of the components of the self-repairing low-carbon concrete are: 250-350 parts of cement, 60-120 parts of the magnesium oxide-aerogel composite additive, 700-800 parts of sand, 1000-1200 parts of gravel, 160-190 parts of water, 0.5-3.0 parts of water reducer, and 0-80 parts of fly ash.

[0046] Preferably, the mass fraction of magnesium oxide in the magnesium oxide-aerogel composite additive is 40.0-70.0% (more preferably 44.0-64.0%), and the specific surface area is ≥600 m 2 / g, the volume fraction of micropores is ≥80%.

[0047] Preferably, the specific surface area of the cement is 200 to 400 m 2 / kg.

[0048] Preferably, the cement includes general-purpose Portland cement or composite cement, etc. The general-purpose Portland cement includes P·O 42.5 cement or P·II 52.5 cement, etc.

[0049] Preferably, the sand is medium sand with a fineness modulus of 2 to 3.

[0050] Preferably, the particle size of the gravel is 5 to 20 mm.

[0051] Preferably, the water reducer includes one or more of a polycarboxylate superplasticizer, a sulfamate superplasticizer, or a sulfonated melamine formaldehyde resin (SMF). The polycarboxylate superplasticizer has a water reduction rate of ≥25%, the sulfamate superplasticizer has a solids content of 25-33%, and the sulfonated melamine formaldehyde resin has a water reduction rate of 15-25%. Examples of polycarboxylate superplasticizers include Sika ViscoCrete-530P and JSJ03.

[0052] Preferably, the fly ash includes Class I and / or Class II fly ash that complies with GB / T 1596-2017 standards.

[0053] The present invention further solves its technical problems by adopting the following technical solution: a method for preparing self-repairing low-carbon concrete, first dry-mixing cement, the light-burned magnesium oxide-aerogel composite additive, sand, gravel and a water reducer, or fly ash, then adding water and stirring, while introducing CO2 gas; pouring the obtained concrete slurry into a mold, drying and curing it, and then the concrete slurry is ready.

[0054] The invention idea of the method of the present invention is: low concentration CO2 gas is introduced into the concrete during the water adding and stirring stage, and the high specific surface area (≥600 m2) of the aerogel in the light-burned magnesium oxide-aerogel composite additive of the present invention can be utilized. 2 / g) and microporous structure (pore size ≤ 2 nm, accounting for ≥ 80%) significantly improve the adsorption capacity of CO2, and transfer it to the surface of magnesium oxide to accelerate the mineralization reaction. The dolomite (MgCO3) generated by in-situ mineralization is combined with the aerogel skeleton through chemical bonding (Si-O-Mg bond), and the cracks and pores of the concrete are directionally filled with the expansion filling effect (volume expansion rate 120%). The water reducer can optimize the fluidity of the light-burned magnesium oxide-aerogel composite additive, reduce the amount of water used in concrete mixing, and improve the density. For example, the polycarboxylic acid-based water reducer can reduce the friction resistance between cementitious materials through the adsorption-dispersion mechanism. During the curing stage, The coordinated regulation of excessive humidity and low-concentration CO2 promotes the directional growth of mineralized products and repairs microcracks. The method of the present invention realizes the efficient capture of CO2, in-situ formation of mineral phases and dynamic repair of microcracks in concrete during the hardening stage through the composite structure design of light-burned magnesium oxide and high-specific surface area silica aerogel, combined with the coordinated regulation mechanism of low-concentration CO2 gas activation and humidity, while reducing chloride ion permeability and improving durability. It solves the problems of traditional concrete that are difficult to meet the needs of low-carbon construction and high-durability engineering due to large cement consumption, low carbonization efficiency and difficult crack repair.

[0055] Preferably, the dry mixing time is 2 to 4 minutes.

[0056] Preferably, the stirring speed is 100-200 rpm (more preferably 140-180 rpm), and the stirring time is 5-8 min.

[0057] Preferably, the flow rate is 0.4 to 0.8 m 3 / h·m 3Concrete is injected with CO2 gas at a volume fraction of 4 to 10%. The effects of the injection of the aforementioned volume of CO2 gas are: 1) promoting the carbonization of light-burned magnesium oxide (MgO) to generate magnesium carbonate (MgCO3), filling the pores of concrete and fixing CO2 to improve density; 2) transferring CO2 to the surface of magnesium oxide through the micropores of aerogels to generate an expansive magnesite phase, which can repair 0.25mm cracks within 28 days; 3) optimizing the reaction kinetics. A moderate concentration of CO2 can balance diffusion and reaction activity, ensuring that the CO2 diffusion rate maintains continuous mineralization, avoiding insufficient reaction at too low a concentration (e.g., at a concentration of 3%, the carbon fixation efficiency is only 60% of that at 5%), or exothermic reaction at too high a concentration, leading to the collapse of aerogel micropores (specific surface area from ≥600 m 2 / g dropped to <500 m 2 / g), at the same time, excessive CO2 will destroy the alkaline environment of concrete, causing a sudden drop in local pH value and inhibiting hydration.

[0058] Preferably, the ambient humidity of the drying curing is ≥80%, the volume concentration of CO2 is 4-10%, and the ambient humidity × the volume concentration of CO2 × 10 4 ≥400, for 28 days. High humidity can maintain the pore water liquid phase environment, drive CO2 dissolution to generate carbonic acid to continuously mineralize magnesium oxide, and inhibit drying shrinkage cracks; CO2 concentration can balance carbon fixation efficiency and reaction activity, and its product with humidity comprehensively reflects the reaction driving force, such as in Example 1 of the present invention method (humidity 90% + CO2 5%): ambient humidity × CO2 concentration × 10 4 =450, the mineralization depth was 1.5 mm after 28 days, which verified the balance between the density of the mineralized product and the repair efficiency under this condition; Example 3 of the method of the present invention (humidity 95% + CO24.2%): ambient humidity × CO2 concentration × 10 4 =399, and the mineralization depth after 28 days was 1.6 mm. This demonstrates that even with slightly lower CO2 concentrations, comparable performance can be achieved through humidity compensation, ensuring product density. The 28-day curing period is divided into two phases: the first 20 days complete 80% mineralization, and the last 8 days slowly fill microcracks and strengthen interfacial bonding. This system achieves compatibility between optimized material properties and low-carbon processes through precise control of humidity, concentration, and time. More preferably, the CO2 gas is derived from purified industrial waste gas.

[0059] The beneficial effects of the present invention are as follows: (1) Highly efficient synergy of carbon capture driven by low-concentration CO2 and active crack repair mechanism: Through the synergistic effect of the carbonization reaction of light-burned magnesia and the microporous adsorption of bio-based silica aerogel, the present invention simultaneously achieves high-efficiency capture of CO2 in concrete (fixed amount reaches 60-85 kg / m 3) and dynamic crack self-repair function, breaking through the limitations of traditional single carbon sequestration technology (CO2 conversion rate <35%) or passive repair technology, achieving a deep coupling of carbon reduction efficiency and self-healing ability, and improving the comprehensive carbon reduction rate to 65%. Compared with technologies that rely on external grouting, microbial activity or complex catalysts (repair cycle ≥ 28 days), the repair process of this invention is synchronized with the hardening of concrete, and can repair 0.25mm cracks within 28 days, with a strength recovery rate of ≥ 90%, without the need for additional energy input. (2) Multi-scale durability enhancement: The dense carbonate network formed by the mineralization products works synergistically with the aerogel micropores to significantly improve the corrosion resistance of concrete; 1) Chloride ion barrier: The aerogel nanopores capture Cl by electrostatic adsorption. - , chloride ion permeability reduced to 480 Coulombs (over 80% lower than traditional concrete); 2) Carbonation inhibition: Magnesium oxide continuously releases an alkaline environment (pH ≥ 12.5), delaying the carbonation process, with the carbonation depth ≤ 1.5 mm after 28 days (≥ 2.5 mm in the blank group); 3) Mechanical property optimization: The stress transfer effect of the composite aerogel resulted in a 28-day compressive strength of 48.6 MPa (an 18% increase compared to the pure cement group); (3) Contribution to low-cost resource recycling and carbon neutrality: 1) Process simplification: In the preparation of magnesium oxide-aerogel composite additives, normal pressure gradient drying (60℃→100℃) is used instead of supercritical drying, which reduces energy consumption by 35%; 2) Raw material optimization: Rice husk ash (agricultural waste) is used to extract bio-based aerogel silicon source (the cost is 40% lower than that of industrial TEOS), and economical materials such as lignin sulfonate are used as dispersants; 3) Waste gas utilization: Directly use industrial waste gas to purify CO2 (purity ≥5%) for mineralization reaction, avoiding the additional cost of high-purity gas; 4) Cement replacement Generation: Magnesium oxide-aerogel composite additives can replace 10-30% of cementitious materials in traditional concrete, and the carbon emissions of single cubic meter of concrete can be reduced by 1.2 tons; 5) Low carbon throughout the life cycle: Carbon negative emissions are achieved from raw material extraction to maintenance process, which is in line with the carbon neutrality strategy needs; the present invention adopts conventional concrete production equipment and processes, and achieves cost reduction and efficiency improvement through the above innovations. It has a high degree of industrial adaptability and cost advantages, and promotes green transformation through the "waste treatment" model. It is suitable for high-durability scenarios such as marine engineering and prefabricated components, and is both environmentally friendly and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 is an SEM image of the magnesium oxide additive (a) obtained in Comparative Example 1 of the present invention and the magnesium oxide-aerogel composite additive (b) obtained in Example 1; Figure 2 These are laser scanning microscope images of prefabricated cracks and repaired cracks in Example 1 of the self-repairing low-carbon concrete of the present invention after drying and curing for 28 days (wherein (a) is the prefabricated crack, and (b) is the prefabricated crack after repair). DETAILED DESCRIPTION

[0061] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0062] The light-burned magnesium oxide used in the examples and comparative examples of the present invention has a purity of ≥95%, a particle size of ≤50 μm (D90=12 μm), and a specific surface area of 30 m 2 / g, purchased from Hebei Meishen Technology Co., Ltd.; the rice husk ash and wood ash used had an initial particle size of 100-300 μm and were purchased from Shandong Yitan New Materials Co., Ltd.; the Sika ViscoCrete-530P used had a water reduction rate of ≥25% and was purchased from Chongqing Haiyu Chemical Products Co., Ltd.; the aminosulfonate water reducer had a solid content of 25-33% and was purchased from Qingdao Hongxia Polymer Materials Co., Ltd.; the sulfonated melamine formaldehyde resin had a water reduction rate of 15-25% and was purchased from Henan Botai Chemical Co., Ltd.; the JSJ03 had a water reduction rate of ≥25% and was purchased from Sichuan Hengze Building Materials Co., Ltd.; the cement used was P·O 42.5 with a specific surface area of 315 m 2 / kg; the sand used is medium sand with a fineness modulus of 2.6; the particle size of the crushed stone used is continuously graded from 5 to 20 mm; the water used is tap water with a pH value of 7; the Grade II fly ash used complies with the GB / T 1596-2017 standard and was purchased from the fly ash comprehensive utilization base of Huaneng Power Group; the raw materials or chemical reagents used in the embodiments of the present invention, unless otherwise specified, were obtained through conventional commercial channels.

[0063] Preparation method of sodium silicate solution Reference Example 1 Rice husk ash was added to a 1 mol / L hydrochloric acid solution at a mass-to-volume ratio of g / mL of 1:5, acid-washed at 80°C for 2 h, filtered, rinsed to neutrality, ball-milled to a particle size of 100-150 μm, and calcined at 600°C for 4 h under oxygen-enriched conditions. 144 g of the obtained silicon oxide powder (purity of 90.6%) was then added to 380 mL of a 3.2 mol / L sodium hydroxide aqueous solution (density of 1.13 g / mL). The mixture was hydrothermally reacted in a closed hydrothermal reactor at 180°C and a pressure of 0.8 MPa for 12 h to obtain a sodium silicate solution (mass concentration of 29.32% and modulus of 3.57).

[0064] Reference Example 2 for Preparation of Sodium Silicate Solution Wood ash was added to a 0.8 mol / L hydrochloric acid solution at a mass-to-volume ratio of g / mL of 1:5, acid-washed at 70°C for 1.5 h, filtered, rinsed to neutrality, ball-milled to a particle size of 100-150 μm, and calcined at 550°C for 3 h under oxygen-enriched conditions. 204 g of the obtained silicon oxide powder (purity of 90.1%) was then added to 490 mL of a 3.3 mol / L sodium hydroxide aqueous solution (density of 1.135 g / mL). The mixture was hydrothermally reacted in a closed hydrothermal reactor at 180°C and a pressure of 0.8 MPa for 12 h to obtain a sodium silicate solution (mass concentration of 30.75% and modulus of 3.78).

[0065] Examples 1 to 3 of magnesium oxide-aerogel composite additives Examples 1 to 3 of the magnesium oxide-aerogel composite additive are prepared from the components and weight parts shown in Table 1.

[0066] Table 1 Components and weight percentages in Examples 1 to 3 and Comparative Examples 1 and 2 of magnesium oxide-aerogel composite additives

[0067] Note: “-” in the table means not added.

[0068] Preparation method of magnesium oxide-aerogel composite auxiliary agent Example 1 (1) Magnesium oxide pretreatment: According to the components and weight parts in Table 1, light-burned magnesium oxide was ground to D90 = 12 μm, and then mixed with a dispersant in a double-screw mixer for 40 min to obtain premixed magnesium oxide; (2) Curing and drying of magnesium oxide-aerogel: According to the weight parts of each component in Example 1 in Table 1, the premixed magnesium oxide obtained in step (1) was first added to the sodium silicate solution, mixed, and then the pH value was adjusted to 10.5 with sodium carbonate. After adding the silane coupling agent and mixing, the mixture was allowed to stand at 80°C for 12 hours for gelation, and then poured into a saturated alkaline solution. After aging reaction at 70°C for 24 hours, gradient drying was performed: first at 60°C for 12 hours, then at 80°C for 12 hours, and finally at 100°C for 6 hours. After dry mixing and ball milling at a speed of 300 rpm for 1 hour, the mixture was passed through a 200-mesh sieve to obtain a magnesium oxide-aerogel composite additive (the mass fraction of magnesium oxide was 48.77%) with a specific surface area of 720 m 2 / g, the volume fraction of micropores is 85%, such as Figure 1 (b)).

[0069] Preparation method of magnesium oxide-aerogel composite auxiliary agent Example 2 (1) Magnesium oxide pretreatment: According to the components and weight parts in Example 2 in Table 1, light-burned magnesium oxide was ground to D90 = 12 μm, and then mixed with a dispersant in a double-screw mixer for 45 minutes to obtain premixed magnesium oxide; (2) Curing and drying of magnesium oxide-aerogel: According to the weight parts of each component in Example 2 in Table 1, the premixed magnesium oxide obtained in step (1) was first added to the sodium silicate solution, mixed, and then the pH value was adjusted to 11.0 with sodium carbonate. After adding the silane coupling agent and mixing, the mixture was allowed to stand at 90°C for 14 hours for gelation. The mixture was then poured into a saturated alkaline solution and aged at 80°C for 30 hours. The mixture was then dried in a gradient manner: first at 70°C for 14 hours, then at 90°C for 14 hours, and finally at 110°C for 8 hours. The mixture was dry-mixed and ball-milled at a speed of 400 rpm for 1.5 hours, and then passed through a 200-mesh sieve to obtain a magnesium oxide-aerogel composite additive (the mass fraction of magnesium oxide was 44.46%) with a specific surface area of 680 m 2 / g, the volume fraction of micropores is 80%).

[0070] Preparation method of magnesium oxide-aerogel composite auxiliary agent Example 3 (1) Magnesium oxide pretreatment: According to the components and weight parts in Table 1, Example 3, light-burned magnesium oxide was ground to D90 = 12 μm, and then mixed with a dispersant in a double-screw mixer for 30 minutes to obtain premixed magnesium oxide; (2) Curing and drying of magnesium oxide-aerogel: According to the weight parts of each component in Example 3 of Table 1, the premixed magnesium oxide obtained in step (1) was first added to the sodium silicate solution, mixed, and then the pH value was adjusted to 10.0 with sodium carbonate. After adding the silane coupling agent and mixing, the mixture was allowed to stand at 70°C for 10 hours for gelation. The mixture was then poured into a saturated alkaline solution and aged at 60°C for 18 hours. The mixture was then dried in a gradient manner: first at 50°C for 10 hours, then at 70°C for 10 hours, and finally at 90°C for 4 hours. The mixture was dry-mixed and ball-milled at a speed of 200 rpm for 0.5 hours, and then passed through a 200-mesh sieve to obtain a magnesium oxide-aerogel composite additive (the mass fraction of magnesium oxide was 59.40%) with a specific surface area of 750 m 2 / g, and the volume fraction of micropores is 88%).

[0071] Preparation method of magnesium oxide auxiliary agent Comparative Example 1 According to the components and weight parts in Table 1, light-burned magnesium oxide was ground to D90 = 12 μm, and then mixed with the dispersant in a double-screw mixer for 40 min, and then dry-mixed and ball-milled for 1 h at a speed of 300 rpm, and then passed through a 200 mesh sieve to obtain a magnesium oxide additive (such as Figure 1 (as shown in (a)).

[0072] Preparation method of magnesium oxide-aerogel composite additive Comparative Example 2 (1) Magnesium oxide pretreatment: same as step (1) in Example 1; (2) Curing and drying of magnesium oxide aerogel: Omit the silane coupling agent, and the rest is the same as step (2) of Example 1.

[0073] Self-repairing low-carbon concrete examples 1 to 3 Self-repairing low-carbon concrete Examples 1 to 3 are made from the components and weight parts shown in Table 2.

[0074] Table 2 Components and weight percentages in Examples 1 to 3 and Comparative Examples 1 and 2 of self-repairing low-carbon concrete

[0075] Note: “-” in the table means not added.

[0076] Preparation method of self-repairing low-carbon concrete Example 1 According to the components and weight parts in Table 2 Example 1, cement, magnesium oxide-aerogel composite additive, sand, gravel and water reducer were first put into the mixer, dry mixed for 3 minutes, and then water was added at 160 rpm and stirred for 6 minutes. At the same time, the flow rate was 0.7 m 3 / h·m 3 Concrete, introduce 8% volume fraction of CO2 gas (industrial waste gas purification, containing SO2 ≤ 0.1%); pour the obtained concrete slurry into the mold, and in the environment of 90% humidity, CO2 volume concentration of 5% (ambient humidity × CO2 volume concentration × 10 4 =450) and dry-cured for 28 days.

[0077] Preparation method of self-repairing low-carbon concrete Example 2 According to the components and weight parts in Table 2 Example 2, cement, magnesium oxide-aerogel composite additive, sand, gravel, water reducer and Class II fly ash were first put into the mixer, dry mixed for 3 minutes, and then water was added at 150 rpm and stirred for 6 minutes. At the same time, the flow rate was 0.5 m 3 / h·m 3 Concrete, introduce 6% volume fraction of CO2 gas (industrial waste gas purification, containing SO2 ≤ 0.1%); pour the obtained concrete slurry into the mold, and in the environment of 85% humidity and 5% volume concentration of CO2 (ambient humidity × volume concentration of CO2 × 10 4 =425) and dry-cured for 28 days.

[0078] Preparation method of self-repairing low-carbon concrete Example 3 According to the components and weight parts in Table 2 Example 3, cement, magnesium oxide-aerogel composite additive, sand, gravel and water reducer were first put into the mixer, dry mixed for 4 minutes, and then water was added at 180 rpm and stirred for 5 minutes. At the same time, the flow rate was 0.6 m 3 / h·m 3 Concrete, introduce CO2 gas with a volume fraction of 4.2% (industrial waste gas purification, containing SO2 ≤ 0.1%); pour the obtained concrete slurry into the mold, and heat it in an ambient humidity of 95% and a volume concentration of CO2 of 4.2% (ambient humidity × volume concentration of CO2 × 10 4 =399), and then dry and cure for 28 days.

[0079] Comparative Example 1 of Concrete Preparation Method The difference between this comparative example and Example 3 of the method for preparing self-repairing low-carbon concrete is that the magnesium oxide-aerogel composite additive used in Example 3 is replaced by the magnesium oxide additive obtained in Comparative Example 1. The rest is the same as Example 3.

[0080] Comparative Example 2 of Concrete Preparation Method The difference between this comparative example and Example 1 of the method for preparing self-repairing low-carbon concrete is that the magnesium oxide-aerogel composite additive used in Example 1 is replaced by the magnesium oxide-aerogel composite additive obtained in Comparative Example 2. The rest is the same as Example 1.

[0081] In order to evaluate the performance of the self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention and the concrete obtained in Comparative Examples 1 and 2, tests were conducted according to the following standards: The CO2 fixation test was conducted using the hydrochloric acid dissolution-gravimetric method in accordance with GB / T 35153-2017, Determination of CO2 Absorption in Concrete. The 28-day compressive strength was determined in accordance with GB / T 50081-2019, Test Methods for Physical and Mechanical Properties of Concrete. Chloride ion permeability was measured using the ASTM C1202-19 electric flux method on 28-day-old specimens. The 28-day crack repair width was determined using a laser scanning microscope to observe the repair process of 0.3 mm precast cracks. The carbonation depth was determined using the phenolphthalein reagent method in GB / T 50082-2009, Test Methods for Long-term Performance and Durability of Ordinary Concrete. The comprehensive carbon reduction rate was calculated using a full life cycle carbon emission model based on the DB64 / T 1954-2023, Calculation Method and Evaluation Standard for Carbon Emissions of Concrete, comparing the embodied carbon emissions of the new concrete with those of traditional concrete. The results were also analyzed in accordance with GB / T 51366-2019. The data was calibrated according to the Building Carbon Emission Calculation Standard; the results are shown in Table 3.

[0082] Table 3 Performance comparison of the self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention and the concrete obtained in Comparative Examples 1 and 2

[0083] As shown in Table 3, the self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention achieves the following technical effects by adding a magnesium oxide-aerogel composite additive and combining a humidity and CO2 synergistic curing process: (1) CO2 fixation efficiency and carbon reduction mechanism: The aerogel microporous network in the self-repairing low-carbon concrete obtained in Example 1 of the present invention (such as Figure 1 (b) significantly improved the CO2 adsorption capacity, with a carbon fixation capacity of up to 82.5 kg / m 3 Compared with Comparative Example 2 (no silane coupling agent was added, resulting in poor interface bonding between the aerogel and magnesium oxide (i.e., no Si-O-Mg bond), the interface bonding was loose, and the CO2 fixed capacity was only 58.3 kg / m 3 ) increased by 41.5%, and the comprehensive carbon reduction rate increased to 65% (comparative example 2 was only 48%), verifying the key role of the silane coupling agent in Si-O-Mg interface bonding and the synergistic effect on the carbon fixation efficiency of the composite additive: the coupling agent strengthens the chemical bonding between aerogel and magnesium oxide, optimizes the CO2 transfer path, avoids the loss of adsorption capacity caused by interface stripping, and thus significantly improves the carbon mineralization efficiency and material stability; In Comparative Example 1, no sodium silicate solution was added to form aerogel, and only magnesium oxide dispersion optimization was relied upon, with a carbon fixation capacity of 50.2 kg / m 3 , verified the limitations of single magnesium oxide, compared with traditional mineral admixture technology (≤30 kg / m 3 ) increased by 67.3%, verifying the decisive role of the CO2 introduction process on carbon mineralization, but it was far less than the synergistic effect of magnesium oxide-aerogel composite additive + CO2 introduction on carbon mineralization in the embodiment of the present invention.

[0084] (2) Improved mechanical properties and durability: Compressive Strength: The self-healing low-carbon concrete obtained in Example 1 of the present invention achieved a 28-day compressive strength of 48.6 MPa, an 18% increase over Comparative Example 2 (41.2 MPa) and a 7.3% increase over Comparative Example 1 (45.3 MPa). The lower compressive strength of Comparative Example 2 is attributed to the lack of a silane coupling agent, resulting in a loose interface between the aerogel and magnesium oxide (lacking Si-O-Mg bonds). This inability of the aerogel skeleton to effectively transfer stress results in a loose bond between the mineralized products (such as MgCO3) and the matrix, forming weak areas. Furthermore, interfacial defects increase porosity, further reducing compactness. Furthermore, the composite adjuvant used in Example 1 of the present invention is a composite adjuvant comprising DP-2015 lignin sulfonate and a polycarboxylic acid dispersant, which achieves higher compressive strength than the composite adjuvant using a single DP-2015 lignin sulfonate in Example 2. This is because the "comb-like" molecular structure of the polycarboxylic acid dispersant in the composite adjuvant can provide steric hindrance to prevent particle agglomeration, while the lignin sulfonate enhances wettability through electrostatic repulsion. The synergistic optimization of the two makes the magnesium oxide particles more evenly dispersed and the mechanical properties improved. Chloride ion permeability: The aerogel micropores in the self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention capture Cl by physical adsorption and electrostatic effect. - , the chloride ion permeability dropped to 480 Coulombs, which was 51% lower than that of comparative example 1 (980 Coulombs); comparative example 2 (850 Coulombs) had a loose interface, and the chloride ion permeability was 480 Coulombs, which was 51% lower than that of comparative example 1 (980 Coulombs). - The permeability increased by 77% compared with Example 1. In Comparative Example 2, the aerogel and magnesium oxide were loosely bonded due to the lack of coupling agent (permeability 850 Coulombs), which verified the necessity of coupling agent for durability. Carbonation depth: The carbonation depth of the self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention was 1.5 mm, which was slightly higher than that of Comparative Example 1 (1.2 mm), but significantly lower by 29% than that of Comparative Example 2 (2.1 mm). This result needs to be comprehensively explained in conjunction with the mechanism of action of the material: Comparative Example 1 (containing only magnesium oxide additive): When magnesium oxide is directly exposed to the concrete matrix, it rapidly releases the alkaline substance Mg(OH)2 early on, causing a rapid increase in the surface pH value, which in the short term inhibits surface carbonization. As a result, its carbonization depth is minimal (1.2 mm). However, in the long term, magnesium oxide lacks the CO2 adsorption and transfer function of the aerogel micropores, resulting in incomplete mineralization reactions and the easy consumption of alkaline substances, and the risk of deep carbonization remains high. Examples 1 to 3 (containing magnesium oxide-aerogel composite additive): The microporous structure of the aerogel may initially accelerate the diffusion of CO2 into the interior, resulting in slightly deeper surface carbonization (1.5 mm). However, the aerogel cooperates with magnesium oxide to form a dynamic mineralization-repair mechanism: the CO2 adsorbed by the aerogel is continuously transferred to the surface of the magnesium oxide to form magnesium carbonate. At the same time, magnesium oxide releases alkaline substances for a long time (pH ≥ 12.5), delaying the deep carbonization process. Comparative Example 2 (no silane coupling agent added): The interface between aerogel and magnesium oxide is loose, the CO2 adsorption and transfer efficiency is low, and the ability to maintain an alkaline environment is weak, resulting in the maximum carbonization depth (2.1 mm); Conclusion: Although the short-term carbonization depth of Examples 1 to 3 is slightly higher than that of Comparative Example 1, the synergistic effect of aerogel-magnesium oxide achieves a balance between long-term carbonization inhibition and dynamic repair. Combined with better corrosion resistance (the chloride ion permeability of Example 1 of the present invention is reduced by 51% compared with that of Comparative Example 1) and mechanical properties (the compressive strength of Example 1 of the present invention is increased by 7.3% compared with that of Comparative Example 1), the comprehensive durability of Examples 1 to 3 of the present invention is significantly better than that of Comparative Example 1.

[0085] (3) Crack self-repair performance and mechanism: The coupling agent (such as KH-560) added to the self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention promotes the directional growth of magnesium carbonate minerals and fills cracks by forming a Si-O-Mg bonding interface. A 0.25 mm crack (such as Figure 2 As shown). However, in Comparative Example 2 (without adding coupling agent), due to the lack of Si-O-Mg bonding interface, the mineralized product has weak bonding with the matrix and can only repair 0.18 mm cracks. The compressive strength (41.2 MPa) and CO2 fixation capacity (58.3 kg / m 3 ) are significantly inferior to those of Example 1 of the present invention, further demonstrating that the synergistic effect of the coupling agent and the dispersant in the composite additive is a necessary condition for achieving both efficient repair and improved mechanical properties; Repair mechanism: 1) Chemical bonding-driven repair: Magnesium oxide (MgCO3) generated by magnesium oxide mineralization combines with the aerogel through Si-O-Mg bonds, forming a mineral-aerogel composite network that penetrates the cracks and restores structural integrity; 2) Dynamic repair capability: The magnesium oxide exposed at the cracks continues to react with CO2 in the environment during the curing stage, allowing Example 1 of the present invention to repair 0.25 mm cracks.

[0086] (4) Process economy and environmental benefits: Cost comparison: Example 2 of the present invention (low-cost formula): By replacing part of the magnesium oxide-aerogel composite additive with lignin sulfonate and Class II fly ash, the overall cost can be reduced by 20% (¥450 / m 3 →¥360 / m 3), CO2 fixation can still reach 68.4 kg / m 3 Compared with traditional mineral admixture technology (≤30 kg / m 3 ) increased by 128%. The self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention uses bio-based aerogel raw materials (wood ash), which reduces costs by 40% compared to industrial silicon sources, reduces energy consumption in the atmospheric pressure drying process by 35%, and increases the total cost per cubic meter of concrete by ≤15%, significantly lower than similar nanocomposite materials (cost increases of ≥50%). Contribution to carbon emission reduction: The self-repairing low-carbon concrete obtained in Examples 1 to 3 of the present invention replaces 28.6% of the cementitious materials (120 kg / m 3 ) and can fix carbon 82.5 kg / m 3 The net carbon footprint of one cubic meter of concrete is -0.8 tons of CO2 (traditional concrete is +0.4 tons), achieving negative carbon emissions throughout its life cycle.

Claims

1. A magnesium oxide-aerogel composite additive, characterized in that: It is mainly made of light-burned magnesium oxide, dispersant, sodium silicate solution, silane coupling agent and saturated alkali solution.

2. The magnesium oxide-aerogel composite auxiliary agent according to claim 1, characterized in that The weight proportions of the components are: 100 parts of light-burned magnesium oxide, 1 to 5 parts of dispersant, 200 to 350 parts of sodium silicate solution, 3 to 5 parts of silane coupling agent, and 100 to 200 parts of saturated alkaline solution; the purity of the light-burned magnesium oxide is ≥95%, the particle size is ≤50 μm, and the specific surface area is 20 to 50 m 2 / g; the dispersant includes polycarboxylic acid and / or lignin sulfonate; the mass concentration of the sodium silicate solution is 5 to 32%, and the modulus is 3.0 to 3.8; the silane coupling agent includes one or more of epoxy silane, bisaminosilane or methyltrimethoxysilane; and the saturated alkaline solution includes calcium hydroxide solution.

3. The magnesium oxide-aerogel composite auxiliary agent according to claim 1 or 2, characterized in that The preparation method of the sodium silicate solution comprises the following steps: adding plant ash to an acid aqueous solution, performing acid washing, filtering and rinsing to neutrality, ball milling, calcining, and then adding the obtained silicon oxide powder to an alkaline aqueous solution, and performing a hydrothermal reaction in a closed hydrothermal reactor to obtain the solution; the initial particle size of the plant ash is 100 to 300 μm; the plant ash includes one or more of rice husk ash, straw ash or wood ash; the mass volume ratio of the plant ash to the acid aqueous solution is g / mL 1:4 to 6; the concentration of the acid aqueous solution is 0.8 to 1.2 mol / L; the acid washing temperature is 70 to 90° C., and the time is 1.5 to 2.5 h; the ball milling is performed to a particle size of 50 to 150 μm; the calcination is performed under oxygen-rich conditions, and the calcination temperature is 550 to 650° C., and the time is 3 to 5 h; the mass volume ratio of the silicon oxide powder to the alkaline aqueous solution is 1:2 to 4 g / mL; the concentration of the alkaline aqueous solution is 3 to 6 mol / L; the hydrothermal reaction temperature is 140 to 180° C., the pressure is 0.3 to 1.0 MPa, and the time is 5 to 12 h.

4. A method for preparing the magnesium oxide-aerogel composite additive according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Magnesium oxide pretreatment: Grind the light-burned magnesium oxide and then mix it with a dispersant to obtain premixed magnesium oxide; (2) Curing and drying of magnesium oxide-aerogel: First, the premixed magnesium oxide obtained in step (1) is added to the sodium silicate solution, mixed, and the pH value is adjusted. After adding the silane coupling agent and mixing, the mixture is allowed to stand for gelation. The mixture is then poured into a saturated alkaline solution, aged, gradient dried, dry-mixed and ball-milled, and sieved to obtain a magnesium oxide-aerogel composite additive.

5. The method for preparing the magnesium oxide-aerogel composite auxiliary agent according to claim 4, characterized in that: In step (1), the grinding is performed until D90 is less than 15 μm; the mixing time is ≥30 min; in step (2), the pH value is adjusted to 10-11; the temperature of the static gelation is 70-90° C. and the time is 10-14 h; the temperature of the aging reaction is 60-80° C. and the time is 18-30 h; the gradient drying refers to: first drying at 50-70° C. for 10-14 h, then drying at 70-90° C. for 10-14 h, and finally drying at 90-110° C. for 4-8 h; the rotation speed of the dry mixing ball mill is 200-400 rpm and the time is 0.5-1.5 h; and the sieve is sieved with a 200-mesh sieve.

6. A self-repairing low-carbon concrete, characterized by: The composite material is mainly made of cement, the magnesium oxide-aerogel composite additive according to any one of claims 1 to 3, sand, crushed stone, water and a water reducing agent, or fly ash.

7. The self-repairing low-carbon concrete according to claim 6, characterized in that: The weight proportions of the components are: 200-400 parts of cement, 20-120 parts of the magnesium oxide-aerogel composite additive according to any one of claims 1 to 3, 600-900 parts of sand, 800-1200 parts of crushed stone, 150-200 parts of water, 0.5-3.0 parts of water reducer, and 0-100 parts of fly ash; the mass fraction of magnesium oxide in the magnesium oxide-aerogel composite additive is 40.0-70.0%, and the specific surface area is ≥600 m 2 / g, the volume fraction of micropores is ≥80%; the specific surface area of the cement is 200 to 400m 2 / kg; the cement includes general-purpose Portland cement or composite cement; the sand is medium sand with a fineness modulus of 2 to 3; the particle size of the crushed stone is 5 to 20 mm; the water reducer includes one or more of a polycarboxylate water reducer, an aminosulfonate water reducer or a sulfonated melamine formaldehyde resin; and the fly ash includes Class I and / or Class II fly ash that complies with GB / T 1596-2017.

8. A method for preparing the self-repairing low-carbon concrete according to claim 6 or 7, characterized in that: First, cement, the light-burned magnesium oxide-aerogel composite additive according to any one of claims 1 to 3, sand, crushed stone and a water reducer, or fly ash are dry-mixed, and then water is added and stirred while introducing CO2 gas; the resulting concrete slurry is poured into a mold and dried and cured to obtain the product.

9. The method for preparing the self-repairing low-carbon concrete according to claim 8, characterized in that: The dry mixing time is 2 to 4 minutes; the stirring speed is 100 to 200 rpm, and the time is 5 to 8 minutes; the flow rate is 0.4 to 0.8 m 3 / h·m 3 Concrete, passing CO2 gas with a volume fraction of 4 to 10%; the ambient humidity of the drying curing is ≥80%, the volume concentration of CO2 is 4 to 10%, and the ambient humidity × the volume concentration of CO2 × 10 4 ≥400, duration is 28 days.

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