Anti-crack and high-cold-resistant concrete and preparation method thereof

Abstract

The invention discloses anti-crack and anti-alpine concrete and a preparation method thereof, and relates to the technical field of concrete.The anti-crack and anti-alpine concrete is prepared from, by mass, 300-500 parts of low-heat Portland cement, 50-100 parts of carbon sequestration composite superfine powder and 10-20 parts of nano calcium carbonate; the magnesium oxide is calcined at the temperature of 500 to 600 DEG C, is compounded with the calcium sulphoaluminate, and is modified by a silane coupling agent; the phase change microcapsule is formed by packaging paraffin in a silicon dioxide shell layer, and the phase change temperature ranges from-30 DEG C to 10 DEG C; the microbial self-repairing capsule is characterized in that bacillus pasteurii is coated in a sodium alginate-montmorillonite composite carrier; according to the invention, the multi-dimensional performance breakthrough of the high-cold concrete is realized through gradient expanding agent compounding, fiber synergistic enhancement, phase change microcapsule temperature control and microbial self-repairing technologies. The drying shrinkage is reduced to 1.2 * 10 <-4 > by compounding magnesium oxide / calcium sulphoaluminate, the crack propagation is inhibited by a fiber network, and the initial crack threshold value is less than 0.15 mm.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, in particular to crack-resistant and high-cold-resistant concrete and a preparation method thereof. Background Art

[0002] With the rapid development of infrastructure construction in high-altitude and frigid regions, concrete's crack resistance and durability in extreme low temperatures, freeze-thaw cycles, and large temperature swings are becoming increasingly prominent. Traditional concrete is susceptible to cracking in these conditions due to shrinkage stress, frost heave damage, and internal temperature swings. This can lead to safety hazards such as structural leakage and strength loss.

[0003] Specifically, conventional concrete relies on a single expansive agent to compensate for shrinkage, which struggles to match the gradient shrinkage characteristics of high-altitude cold environments, often resulting in limited crack control effectiveness. Furthermore, the hydration rate of conventional magnesium oxide expansive agents decreases significantly at low temperatures, making them unable to compensate for shrinkage in a timely manner. While existing technologies improve crack resistance by adding fibers or nanomaterials, problems such as poor fiber dispersion and weak interfacial bonding still limit their application.

[0004] Freeze-thaw cycles often cause pore water within concrete to freeze and expand. While traditional antifreeze agents can mitigate freezing damage, long-term use weakens mechanical properties and fails to repair existing microcracks. While research is underway to improve frost resistance using bio-glue and stearic acid, these complex components can interfere with hydration reactions, resulting in slow early strength development.

[0005] Therefore, we propose a crack-resistant and high-cold-resistant concrete and a preparation method thereof in order to solve the problems raised above.

[0006] The above information disclosed in this background technology is only for enhancing understanding of the background technology of the present invention and therefore it may contain information that does not constitute the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0007] The object of the present invention is to provide a crack-resistant and high-cold-resistant concrete and a preparation method thereof, so as to solve one of the problems raised in the above background technology, such as insufficient crack resistance and poor low-temperature durability.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A crack-resistant and high-cold-resistant concrete comprises the following components in parts by weight:

[0010] 300-500 parts of low-heat Portland cement, 50-100 parts of carbon-fixed steel slag powder, and 10-20 parts of nano-calcium carbonate;

[0011] 5%-8% magnesium oxide and 3%-5% calcium sulfoaluminate, wherein the magnesium oxide is calcined at 500-600°C and then compounded with calcium sulfoaluminate and modified with a silane coupling agent;

[0012] Phase-change microcapsules 3%-6%, microbial self-repair capsules 1%-3%, where the phase-change microcapsules are paraffin encapsulated in a silica shell with a phase change temperature of -30°C to 10°C; the microbial self-repair capsules are Bacillus pasteurianus encapsulated in a sodium alginate-montmorillonite composite carrier;

[0013] Basalt fiber 0.5%-1.5%, polyester fiber 0.3%-0.8%;

[0014] Carbon nanotubes 0.05%-0.1%, polycarboxylic acid water reducer 1%-2%.

[0015] As a further optimization solution of the present invention, the mass ratio of magnesium oxide to calcium sulfoaluminate is 1.5:1-2:1;

[0016] The particle size of the phase change microcapsules is 50-200 μm, and the thickness of the silica shell is 1-5 μm.

[0017] As a further optimization scheme of the present invention, the coating carrier of the microbial self-repair capsule is composited by sodium alginate and montmorillonite in a mass ratio of 2:1-3:1, and the capsule particle size is 100-500 μm.

[0018] As a further optimization solution of the present invention, the specific surface area of ​​the carbon-fixed steel slag powder is 400-600m 2 / kg, and contains 40%-60% CaO;

[0019] The particle size of nano calcium carbonate is 20-100 nm, and the surface is modified by stearic acid.

[0020] A method for preparing crack-resistant and high-cold-resistant concrete comprises the following steps:

[0021] Step 1: Dry mix low-heat Portland cement, carbon-fixed steel slag powder, and nano-calcium carbonate for 3-5 minutes, then add basalt fiber and polyester fiber and continue mixing for 8-12 minutes;

[0022] Step 2: calcine magnesium oxide at 500-600℃ for 1-2h, cool it and mix it with calcium sulfoaluminate in proportion, add silane coupling agent in an amount of 0.5%-1% of the mass of the mixed powder, and ball mill for 20-30min;

[0023] Step 3: Stir the premix, gradient expansion agent, crushed stone aggregate with a particle size of 20-25 mm, polycarboxylate water reducer, and water for 3-5 minutes at 0-10°C, then add phase change microcapsules, microbial self-repairing capsules, carbon nanotubes, and antifreeze protein, and continue stirring for 5-8 minutes;

[0024] Step 4: After pouring, cover with phase change insulation film, the phase change temperature is -20℃ to 0℃, and introduce CO2 gas with a concentration of 20%-30% and a pressure of 0.1-0.3MPa for 3-5 days; remove the insulation film and naturally cure for 14 days.

[0025] As a further optimization solution of the present invention, in step 3, the sand ratio of the aggregate is 35%-40%, and the crushed stone is pre-frozen at below -20°C for 12-24 hours;

[0026] In step S4, the CO2 gas introduction rate is 0.5-1.0 L / (m 3 ·min), and the humidity of the curing environment is 90-95%.

[0027] As a further optimization solution of the present invention, the phase change thermal insulation film is a polyethylene-paraffin composite film with a thickness of 0.5-2 mm and a paraffin content of 30%-50%;

[0028] The microbial self-repairing capsules are added to the concrete mixture at a temperature of 10-15°C during stirring.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] In this invention, a multi-dimensional performance breakthrough of cold concrete is achieved through the combination of gradient expansion agent, fiber synergistic reinforcement, phase change microcapsule temperature control and microbial self-repair technology. The magnesium oxide / calcium sulfoaluminate compound reduces the drying shrinkage to 1.2×10 -4 The fiber network inhibits crack expansion, the initial crack threshold is less than 0.15mm, the phase change microcapsules regulate the temperature difference to less than 8℃, and the microbial repair crack healing rate is greater than 90% in 7 days. And by replacing 30% of cement with solid carbon steel slag, combined with CO2 curing, it absorbs 8.5-10.1kg / m 3 , carbon emissions are reduced by 35%, antifreeze protein and nano-modification can achieve construction at -50℃, the strength is increased by 35% and the construction period is shortened by 40%.

[0031] The above summary is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present invention will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a flowchart of the method for preparing the crack-resistant and cold-resistant concrete. DETAILED DESCRIPTION

[0033] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] Example 1

[0035] A crack-resistant and high-cold-resistant concrete comprises the following components in parts by weight:

[0036] 300 parts of low-heat Portland cement, 50 parts of carbon-fixed steel slag powder, and 10 parts of nano-calcium carbonate;

[0037] 5% magnesium oxide and 3% calcium sulfoaluminate, wherein the magnesium oxide is calcined at 500°C and then compounded with calcium sulfoaluminate and modified with a silane coupling agent;

[0038] Phase-change microcapsules 3% and microbial self-repair capsules 1%. The phase-change microcapsules are paraffin encapsulated in a silica shell with a phase change temperature of -30°C. The microbial self-repair capsules are Bacillus pasteurianus encapsulated in a sodium alginate-montmorillonite composite carrier.

[0039] Basalt fiber 0.5%, polyester fiber 0.3%;

[0040] Carbon nanotubes 0.05%, polycarboxylic acid water reducer 1%.

[0041] As attached Figure 1 As shown, a method for preparing crack-resistant and high-cold-resistant concrete includes the following steps:

[0042] Step 1: Dry mix low-heat Portland cement, carbon-fixed steel slag powder, and nano-calcium carbonate for 3 minutes, then add basalt fiber and polyester fiber and continue mixing for 8 minutes;

[0043] Step 2: calcine magnesium oxide at 500°C for 1 hour, cool it down and mix it with calcium sulfoaluminate in proportion, add silane coupling agent (the amount is 0.5 of the mass of the mixed powder), and ball mill for 20 minutes;

[0044] Step 3: At 0°C, stir the premix, gradient expansion agent, crushed stone aggregate with a particle size of 20 mm, polycarboxylate water reducer, and water for 3 minutes, then add phase change microcapsules, microbial self-repairing capsules, carbon nanotubes, and antifreeze protein, and continue stirring for 5 minutes; the sand ratio of the aggregate is 35%, and the microbial self-repairing capsules are added to the concrete mixture at a temperature of 10°C during stirring.

[0045] Step 4: After pouring, cover with a phase-change insulation film at a phase-change temperature of -20°C. A 20% concentration of CO2 gas at a pressure of 0.1 MPa is introduced for 3 days. After removing the insulation film, naturally cure for up to 14 days. The phase-change insulation film is a polyethylene-paraffin composite film with a thickness of 0.5 mm and a paraffin content of 30%.

[0046] Example 2

[0047] A crack-resistant and high-cold-resistant concrete comprises the following components in parts by weight:

[0048] 500 parts of low-heat Portland cement, 100 parts of carbon-fixed steel slag powder, and 20 parts of nano-calcium carbonate;

[0049] 8% magnesium oxide and 5% calcium sulfoaluminate, wherein the magnesium oxide is calcined at 600°C and then compounded with calcium sulfoaluminate and modified with a silane coupling agent;

[0050] Phase-change microcapsules (6%) and microbial self-repair capsules (3%). The phase-change microcapsules are paraffin encapsulated in a silica shell with a phase transition temperature of 10°C. The microbial self-repair capsules are Bacillus pasteurianus encapsulated in a sodium alginate-montmorillonite composite carrier.

[0051] Basalt fiber 1.5%, polyester fiber 0.8%;

[0052] Carbon nanotubes 0.1%, polycarboxylic acid water reducer 2%.

[0053] A method for preparing crack-resistant and high-cold-resistant concrete comprises the following steps:

[0054] Step 1: Dry mix low-heat Portland cement, carbon-fixed steel slag powder, and nano-calcium carbonate for 5 minutes, then add basalt fiber and polyester fiber and continue mixing for 12 minutes;

[0055] Step 2: calcining magnesium oxide at 600°C for 2 hours, cooling and mixing with calcium sulfoaluminate in proportion, adding silane coupling agent in an amount of 1% of the mixed powder mass, and ball milling for 30 minutes;

[0056] Step 3: Stir the premix, gradient expansion agent, crushed stone aggregate with a particle size of 25 mm, polycarboxylate water reducer, and water at 10°C for 5 minutes, then add phase change microcapsules, microbial self-repairing capsules, carbon nanotubes, and antifreeze protein, and continue stirring for 5-8 minutes; the sand ratio of the aggregate is 40%, and the microbial self-repairing capsules are added to the concrete mixture at a temperature of 15°C during stirring.

[0057] Step 4: After pouring, cover with a phase-change insulation film at a phase-change temperature of 0°C and introduce 30% CO2 gas at a pressure of 0.3 MPa for 5 days. Remove the insulation film and allow to naturally cure for up to 14 days. The phase-change insulation film is a polyethylene-paraffin composite film with a thickness of 2mm and a paraffin content of 50%.

[0058] Example 3

[0059] A crack-resistant and high-cold-resistant concrete comprises the following components in parts by weight:

[0060] 400 parts of low-heat Portland cement, 75 parts of carbon-fixed steel slag powder, and 15 parts of nano-calcium carbonate;

[0061] 5%-8% magnesium oxide and 4% calcium sulfoaluminate, wherein the magnesium oxide is calcined at 550°C and then compounded with calcium sulfoaluminate and modified with a silane coupling agent;

[0062] Phase change microcapsules 5% and microbial self-repair capsules 2%. The phase change microcapsules are paraffin encapsulated in a silica shell with a phase change temperature of 0°C; the microbial self-repair capsules are Bacillus pasteurianus encapsulated in a sodium alginate-montmorillonite composite carrier;

[0063] Basalt fiber 1%, polyester fiber 0.5%;

[0064] 0.08% carbon nanotubes, 1.5% polycarboxylate water reducer.

[0065] A method for preparing crack-resistant and high-cold-resistant concrete comprises the following steps:

[0066] Step 1: Dry mix low-heat Portland cement, carbon-fixed steel slag powder, and nano-calcium carbonate for 4 minutes, then add basalt fiber and polyester fiber and continue mixing for 10 minutes;

[0067] Step 2: calcining magnesium oxide at 550°C for 1.5 hours, cooling and mixing with calcium sulfoaluminate in proportion, adding silane coupling agent in an amount of 0.7% of the mixed powder mass, and ball milling for 25 minutes;

[0068] Step 3: Stir the premix, gradient expansion agent, crushed stone aggregate with a particle size of 23 mm, polycarboxylate superplasticizer, and water at 5°C for 4 minutes, then add phase change microcapsules, microbial self-repairing capsules, carbon nanotubes, and antifreeze protein, and continue stirring for 6 minutes;

[0069] Step 4: After pouring, cover with phase change insulation film, the phase change temperature is -10℃, and introduce 25% CO2 gas with a pressure of 0.2MPa for 4 days; remove the insulation film and naturally cure for 14 days.

[0070] Example 4

[0071] A crack-resistant and high-cold-resistant concrete, comprising the following components in parts by weight: 450 parts of low-heat Portland cement, solid carbon steel slag powder (specific surface area 500m 2 / kg, CaO 52%) 80 parts, nano calcium carbonate (particle size 50nm, stearic acid modified) 15 parts, gradient expansion agent: magnesium oxide (calcined at 600℃ for 1.5h) 6% + calcium sulfoaluminate 4% (mass ratio 1.5:1, KH550 modified), phase change microcapsules (paraffin silica, particle size 100μm, shell 3μm, phase change temperature -20℃-5℃) 5%, microbial self-repairing capsules (sodium alginate: montmorillonite = 2.5:1, particle size 300μm, Bacillus pasteurianus survival rate 95%) 2%, basalt fiber (length 8mm, epoxy resin-nano SiO2 coating) 1.0%, polyester fiber (three-dimensional mesh, monofilament 20μm) 0.5%, carbon nanotubes 0.08%, polycarboxylic acid water reducer 1.5%, and antifreeze protein (molecular weight 5kDa) 0.08%.

[0072] A method for preparing crack-resistant and high-cold-resistant concrete comprises the following steps:

[0073] Step 1: Dry mix cement, steel slag powder, and nano calcium carbonate for 4 minutes, then add basalt fiber and polyester fiber and mix for 10 minutes;

[0074] Step 2: After calcining magnesium oxide, mix it with calcium sulfoaluminate, add 0.8% KH550, and ball mill for 25 minutes to form zirconium oxide balls, with a ball-to-material ratio of 3:1 and a rotation speed of 300 rpm;

[0075] Step 3: Aggregate: crushed stone and sand with a particle size of 20-25mm, frozen at -20℃ for 18 hours, with a sand ratio of 38%;

[0076] Low-temperature mixing was performed at 5°C: premix + aggregate + gradient expansion agent + water reducer + water (water-binder ratio 0.30) was stirred for 4 minutes, and then phase change microcapsules, microbial capsules, carbon nanotubes, and antifreeze protein were added and stirred for 7 minutes. The mixture temperature was 8°C and the slump was 185 mm.

[0077] Step 4: Cover with polyethylene-paraffin composite film with a thickness of 1mm and 40% paraffin, and introduce 25% CO2 with a pressure of 0.2MPa and a rate of 0.8L / (m 3 ·min), humidity 95% for 4 days, and natural curing for 14 days.

[0078] Performance tests were conducted on Example 4. The results showed that its 28-day compressive strength was 62.5 MPa, the mass loss was 0.8% after 300 freeze-thaw cycles at -50°C, the relative dynamic elastic modulus was 92%, no visible cracks were found in the 24-hour flat plate crack resistance test (Grade I), the crack self-repair rate was 0.3 mm, the 7-day healing rate was 93%, and the CO2 absorption rate (28 days) was 9.2 kg / m3 .

[0079] The fifth embodiment differs from the fourth embodiment in that:

[0080] The components of the crack-resistant and cold-resistant concrete by mass are: 7% magnesium oxide + 3.5% calcium sulfoaluminate (mass ratio 2:1); 1.2% basalt fiber, 0.6% polyester fiber; 40% aggregate sand ratio, and 0.28 water-binder ratio;

[0081] During the preparation process, the CO2 curing pressure was 0.3 MPa and the rate was 1.0 L / (m 3 ·min).

[0082] The sixth embodiment differs from the fourth and fifth embodiments in that:

[0083] During the preparation process, the construction environment temperature was -40°C, the mold temperature was 8°C, the phase change temperature of the phase change microcapsules was adjusted to -30°C to 0°C, the antifreeze protein content was 0.1%, and the CO2 curing time was extended to 5 days.

[0084] During the implementation process, there was no surface ice within 2 hours after the concrete was put into the mold, and the final setting time was extended to 14 hours; after pre-freezing at -50℃ for 12 hours, it was immediately loaded and the compressive strength loss rate was less than 5%; the bonding strength with the old concrete reached 3.8MPa.

[0085] Experimental comparative example

[0086] Components and proportions: 500 parts of ordinary Portland cement, Grade II fly ash, specific surface area 350m 2 / kg 100 parts. UEA expansion agent 8%, polypropylene fiber 1.0%, calcium nitrite 2.0%, sand rate 35%, water-binder ratio 0.32, crushed stone aggregate particle size 20-25mm.

[0087] Preparation process: Cement, fly ash, and UEA expansion agent were dry-mixed for 5 minutes, followed by the addition of polypropylene fiber and mixing for 5 minutes. Finally, the mixture was stirred with aggregate, water, and water-reducing agent for 5 minutes at a stirring temperature of 20°C.

[0088] The curing method is natural curing, without CO2 accelerated carbonization and phase change insulation film covering. The experimental results are shown in the following table:

[0089]

[0090]

[0091] Traditional concrete's expansive agent, due to its single hydration rate, cannot achieve gradient expansion compensation. The polypropylene fiber has weak adhesion to the matrix, and the absence of phase-change microcapsules leads to sudden temperature fluctuations within the concrete, accelerating freeze-thaw failure after cracks expand to 0.5 mm. Furthermore, the CO2 absorption rate of traditional formulations is only 3%-5% of that of the examples, and the fly ash utilization rate is low. Construction requires heating the aggregate to above 5°C, and the natural curing period is as long as 28 days.

[0092] The experimental conclusion is that Examples 4-6 of the present invention comprehensively surpass traditional concrete in core indicators such as crack resistance, durability, and self-repair ability; steel slag powder is used to replace 30% of cement, reducing material costs by 8%-10%; and each cubic meter of concrete can store 8-10kg of CO2.

[0093] In summary, the combination of magnesium oxide and calcium sulfoaluminate in the appropriate mass ratio provides dual expansion compensation in both the early and late stages, completely suppressing shrinkage cracks. In the flat plate crack resistance test, all examples achieved Level I with no visible cracks, while the comparative example exhibited Level III cracks.

[0094] Basalt fiber and polyester fiber form a three-dimensional network, the fiber-matrix bonding strength is improved, which is significantly higher than the control example, and the initial crack width threshold is reduced to 0.10-0.15mm. After freeze-thaw cycles, the crack expansion rate is less than 0.02mm / time.

[0095] Carbon-fixed steel slag micropowder replaces 30% of cement. Combined with CO2 gradient curing, each cubic meter of concrete absorbs 8.5-10.1kg of CO2, compared to just 0.3kg for the control, reducing carbon emissions by 35%. Aggregate pre-cooling to -20°C and phase-change insulation film coating eliminate the traditional heating process, reducing construction energy consumption by 60%. Antifreeze protein inhibits ice crystal growth, while nano-calcium carbonate enhances interface density. Accelerated CO2 curing for 4-5 days achieves a 28-day compressive strength of 58.3-65.1 MPa, while shortening construction time by 40%.

[0096] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0097] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A crack-resistant and cold-resistant concrete, characterized in that: The composition comprises the following components in parts by weight: 300-500 parts of low-heat Portland cement, 50-100 parts of carbon-fixing composite ultrafine powder, and 10-20 parts of nano calcium carbonate; 5%-8% magnesium oxide and 3%-5% calcium sulfoaluminate, wherein the magnesium oxide is calcined at 500-600°C and then compounded with calcium sulfoaluminate and modified with a silane coupling agent; Phase-change microcapsules 3%-6%, microbial self-repair capsules 1%-3%, where the phase-change microcapsules are paraffin encapsulated in a silica shell with a phase change temperature of -30°C to 10°C; the microbial self-repair capsules are Bacillus pasteurianus encapsulated in a sodium alginate-montmorillonite composite carrier; Basalt fiber 0.5%-1.5%, polyester fiber 0.3%-0.8%; Carbon nanotubes 0.05%-0.1%, polycarboxylic acid water reducer 1%-2%.

2. The crack-resistant and cold-resistant concrete according to claim 1, characterized in that: The mass ratio of magnesium oxide to calcium sulfoaluminate is 1.5:1-2:1; The particle size of the phase change microcapsules is 50-200 μm, and the thickness of the silica shell is 1-5 μm.

3. The crack-resistant and cold-resistant concrete according to claim 1, characterized in that: The coating carrier of the microbial self-repair capsule is composited by sodium alginate and montmorillonite in a mass ratio of 2:1-3:1, and the capsule particle size is 100-500 μm.

4. The crack-resistant and cold-resistant concrete according to claim 1, characterized in that: The specific surface area of ​​carbon-fixed composite ultrafine powder is 550-650m 2 / kg, and containing not less than 22% CaO; The particle size of nano calcium carbonate is 20-100 nm, and the surface is modified by stearic acid.

5. The method for preparing the crack-resistant and cold-resistant concrete according to claims 1-4, characterized in that: The following steps are involved: Step 1: Dry mix low-heat Portland cement, carbon-fixing composite ultrafine powder, and nano-calcium carbonate for 3-5 minutes, then add basalt fiber and polyester fiber and continue mixing for 8-12 minutes; Step 2: calcine magnesium oxide at 500-600℃ for 1-2h, cool it and mix it with calcium sulfoaluminate in proportion, add silane coupling agent in an amount of 0.5%-1% of the mass of the mixed powder, and ball mill for 20-30min; Step 3: Stir the premix, gradient expansion agent, continuously graded crushed stone aggregate with a particle size of 5-25 mm, polycarboxylate superplasticizer, and water for 3-5 minutes at 0-10°C, then add phase change microcapsules, microbial self-repairing capsules, carbon nanotubes, and antifreeze protein, and continue stirring for 5-8 minutes; Step 4: After pouring, cover with phase change insulation film, the phase change temperature is -20℃ to 0℃, and introduce CO2 gas with a concentration of 20%-30% and a pressure of 0.1-0.3MPa for 3-5 days; remove the insulation film and naturally cure for 14 days.

6. The method for preparing crack-resistant and cold-resistant concrete according to claim 5, characterized in that: In step 3, the sand content of the concrete is 35%-40%, and the crushed stone is pre-frozen at below -20°C for 12-24 hours; In step S4, the CO2 gas introduction rate is 0.5-1.0 L / (m 3 ·min), and the humidity of the curing environment is 90-95%.

7. The method for preparing crack-resistant and cold-resistant concrete according to claim 5, characterized in that: The phase change insulation film is a polyethylene-paraffin composite film with a thickness of 0.5-2mm and a paraffin content of 30%-50%; The microbial self-repairing capsules are added to the concrete mixture at a temperature of 10-15°C during stirring.

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