A low-shrinkage high-airtightness concrete special binding material and a preparation method thereof

Abstract

The application discloses a low-shrinkage high-airtightness concrete special cementing material and a preparation method thereof. The special cementing material comprises 48-63wt% low-heat Portland cement clinker, 6-14wt% sulphoaluminate cement clinker, 3-5wt% light-burned magnesia, 7-10wt% sub-micron silica fume, 9-18wt% fly ash, 6-12wt% glass powder, 2-3wt% gypsum, 0.03wt% diethanol mono-isopropanol amine and 0.1wt% pre-dispersed carbon nanotubes. The special cementing material has reasonable particle size distribution, and the components produce interactive superposition effects, complement each other and promote each other, so that the cementing material after hydration is continuously compacted, and the airtight concrete prepared by the special cementing material can maintain excellent airtight performance and volume stability at each stage.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a low-shrinkage, high-airtightness concrete-specific cementitious material and its preparation method. Background Technology

[0002] As the most widely used building material, concrete's durability has always been a key research focus in concrete materials science and technology. Concrete durability not only effectively reflects the safety, reliability, and service life of concrete structures under various environmental conditions, but its evaluation and enhancement can also ensure the stability and sustainability of concrete in various application scenarios.

[0003] The durability process of concrete is complex, but it is essentially related to the pore structure of the concrete and the mass transfer within that pore structure. Therefore, the durability of concrete mainly depends on its permeability. Gas permeability is a direct physical characterization of the ability of a gaseous medium to migrate through cement-based porous materials under pressure. It is an ideal physical parameter for measuring the durability and density of concrete. As a durability performance indicator, it has been widely used in many engineering structures in the field of building materials, such as tunnel lining structures containing methane gas, vacuum pipelines, concrete containment structures in nuclear power plants, radiation-resistant concrete, reinforced concrete structures, and other buildings requiring high airtightness. Researchers have also conducted related studies on the airtightness of concrete. Patent document CN114573288A discloses a high airtightness concrete, which optimizes the concrete composition and micropore structure by adding special components and pre-treated superabsorbent resin to the concrete components, thereby maintaining high airtightness and stability in a long-term low vacuum environment. Patent document CN114133190A discloses an airtight concrete, which increases the airtightness and impermeability of concrete by using manufactured sand with appropriate proportions, combined with airtight agents and expansion agents, to meet the requirements of tunnel construction. Patent document CN110698137A improves the microstructure of concrete and introduces stable elastic air bubbles by adding mineral admixtures and special air-entraining agents, thereby improving the ability to resist gas penetration and pressurized water penetration.

[0004] The aforementioned technical methods for preparing airtight concrete mainly improve its airtightness by adding characteristic components, mineral admixtures, internal curing materials, controlling concrete material quality, and optimizing the concrete mix proportion. However, the most important cementitious material remains unchanged, using ordinary silicate-based cementitious materials. But with the development of modern construction and the needs of specialized engineering projects, more stringent construction and service environments, higher functional requirements, and greater resistance to gas penetration pose new challenges to airtight concrete. Cementitious materials, as a major component of concrete, play a significant role in improving the pore structure through their hydration products, providing strong structural support, promoting concrete durability, and enabling diverse design structures. Conventional ordinary silicate-based cementitious materials lack specific engineering application characteristics, cannot meet the complex and changing service environments, and have poor durability and short service life. Therefore, there is an urgent need to design a low-shrinkage, high-airtightness concrete-specific cementitious material from the perspectives of cementitious material composition, structure, and performance to improve the airtightness of concrete and adapt to more complex engineering environments. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-shrinkage, high-airtightness concrete-specific cementitious material and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] On one hand, the present invention provides a cementitious material for low-shrinkage, high-airtightness concrete, comprising the following raw materials by mass percentage:

[0008]

[0009] And including 2-3 wt% gypsum, 0.03 wt% diethanol monoisopropanolamine and 0.1 wt% predispersed carbon nanotubes, which are the total mass percentages of the above raw materials.

[0010] Furthermore, the mineral composition of the low-heat silicate cement clinker includes: 29.9 wt% C3S, 46.3 wt% C2S, 1.8 wt% C3A, and 15.3 wt% C4AF; the specific surface area of ​​the low-heat silicate cement clinker is 350–370 m². 2 / kg, 3d compressive strength ≥14MPa.

[0011] Furthermore, the mineral composition of the sulfoaluminate cement clinker includes: 27.5 wt% C2S, 5.3 wt% C4AF; the specific surface area of ​​the sulfoaluminate cement clinker is 390–420 m². 2 / kg, 3d compressive strength ≥40MPa.

[0012] Furthermore, the lightly calcined magnesium oxide contains ≥85wt% magnesium oxide, ≥65wt% active magnesium oxide, and has a particle size ≤40μm.

[0013] Furthermore, the submicron-sized silica fume contains >93wt% SiO2 and has a specific surface area of ​​23000m². 2 / kg, 7d activity index ≥105%.

[0014] Furthermore, the fly ash is Class I fly ash with a specific surface area of ​​398 m². 2 / kg; the glass powder is waste quartz glass powder with a specific surface area of ​​450m². 2 / kg.

[0015] Furthermore, the gypsum is natural gypsum or mixed gypsum, wherein the anhydrite content in the natural gypsum or mixed gypsum is no more than 50 wt% of the total gypsum, and the specific surface area of ​​the gypsum is 317–421 m². 2 / kg; the solid content of the diethanol monoisopropanolamine is ≥85wt%, and the pH value is 10.24.

[0016] Furthermore, the pre-dispersed carbon nanotubes are carbon nanotubes with a length of 100–200 μm and a diameter of 7–9 nm obtained through pre-dispersion treatment.

[0017] Further, the pre-dispersed carbon nanotubes are prepared as follows: (1) Carbon nanotubes, polyvinylpyrrolidone dispersant and deionized water with a mass ratio of 0.1:0.3:100 are weighed for later use; (2) Carbon nanotubes and polyvinylpyrrolidone dispersant are added to deionized water, stirred, sealed and ultrasonically treated, and then homogenized under high pressure to obtain a pre-dispersed liquid; (3) The pre-dispersed liquid is freeze-dried until all water is removed, and then placed in a high-temperature drying oven to remove polyvinylpyrrolidone dispersant to obtain pre-dispersed carbon nanotubes;

[0018] Preferably, in (2), the ultrasonic treatment is repeated 6 times, and the ultrasonic time is 5 minutes each time;

[0019] Preferably, (3) the temperature of the high-temperature drying oven is 600℃ and the processing time is 3h.

[0020] On the other hand, the present invention provides a method for preparing a low-shrinkage, high-airtightness concrete-specific cementitious material, comprising the following steps:

[0021] S1. Weigh out the following materials by mass percentage: low-heat silicate cement clinker, sulfoaluminate cement clinker, lightly calcined magnesia, submicron silica fume, fly ash, and glass powder. Weigh out the following materials by mass percentage: gypsum, diethanol monoisopropanolamine, and pre-dispersed carbon nanotubes.

[0022] S2. Take out the pre-dispersed carbon nanotubes and weigh 10 times the mass of low-heat silicate cement clinker and 81.6 times the mass of isopropanol, wherein the low-heat silicate cement clinker is weighed from the corresponding raw materials prepared in S1; divide the isopropanol into two parts, add the pre-dispersed carbon nanotubes to one part of the isopropanol, stir to dissolve and ultrasonically disperse to obtain the first mixture, then add the low-heat silicate cement clinker and the other part of the isopropanol to the first mixture, stir to dissolve and ultrasonically disperse to obtain the second mixture; place the second mixture in a high-temperature drying oven to remove the isopropanol, and obtain clinker-CNT dry powder;

[0023] Preferably, when adding the pre-dispersed carbon nanotubes to one part isopropanol, stirring to dissolve and then ultrasonically dispersing, the ultrasonic time is 30 minutes.

[0024] Preferably, when the low-heat silicate cement clinker and another part of isopropanol are added to the first mixture, stirred to dissolve, and ultrasonically dispersed, the ultrasonic time is 90 minutes.

[0025] Preferably, the temperature of the high-temperature drying oven is 100±5℃, and the processing time is 24 hours;

[0026] S3. Mix the sulfoaluminate cement clinker, lightly calcined magnesium oxide, submicron silica fume, fly ash, glass powder, gypsum, diethanol monoisopropanolamine, and the remaining low-heat silicate cement clinker, as well as the clinker-CNT dry powder obtained in S2, evenly to obtain the low-shrinkage, high-airtightness concrete-specific cementitious material.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The special cementitious material of this invention is mainly composed of low-heat silicate cement clinker with low water demand, low heat of hydration, high durability, and excellent long-term mechanical properties. It is modified by introducing appropriate amounts of sulfoaluminate cement clinker, lightly calcined magnesia, and diethanol monoisopropanolamine (DEIPA). The micro-expansion effect of sulfoaluminate cement clinker and lightly calcined magnesia effectively compensates for the shrinkage of the low-heat silicate cement clinker, resulting in a lower hydration volume shrinkage in the special cementitious material system. Furthermore, DEIPA is used to reduce the Fe content in the system. 3+ The complexation effect effectively activates the high-content (C4AF) iron phase in low-heat silicate cement clinker. In synergy with gypsum, it further enhances the hydration reaction of the ferrite phase in the paste, accelerates the consumption of DEIPA and the formation of ettringite (AFt) and monosulfoaluminate (AFm) in the hydration products, promotes the dissolution of mineral admixtures, optimizes pore size distribution, densifies the microstructure, and effectively improves early-stage mechanical properties. Simultaneously, the addition of specific proportions of fly ash and glass powder improves the lubricity and dispersibility of the special cementitious material, enhancing the overall later-stage strength.

[0029] 2. This invention controls the particle size of each material. Submicron-sized silica fume and pre-dispersed carbon nanotubes, as fine powders, can fill the pores of other materials, improving the matrix density. Simultaneously, the pre-dispersion treatment of carbon nanotubes effectively reduces the degree of entanglement between them without damaging their structure, resulting in a looser network structure. This dispersion within the low-heat silicate cement clinker particles facilitates uniform dispersion of carbon nanotubes in the cementitious material. This effectively fills the micropores generated after cement hydration and acts as a bridge and filler within the internal pores, enhancing matrix density, effectively inhibiting the development of microcracks, and thus significantly improving the mechanical properties of concrete, as well as its shrinkage resistance and airtightness.

[0030] 3. The special cementitious material of the present invention has a reasonable particle size distribution, and the components generate an interactive superposition effect, complementing and promoting each other, so that the cementitious material after hydration becomes denser, and the airtight concrete prepared can maintain excellent airtight performance and volume stability at all stages. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] In this embodiment of the invention, the mineral composition of the low-heat silicate cement clinker includes: 29.9 wt% C3S, 46.3 wt% C2S, 1.8 wt% C3A, and 15.3 wt% C4AF; the specific surface area of ​​the low-heat silicate cement clinker is 350–370 m². 2 / kg, 3d compressive strength ≥14MPa.

[0033] In this embodiment of the invention, the mineral composition of sulfoaluminate cement clinker includes: 27.5 wt% C2S, 5.3 wt% C4AF; the specific surface area of ​​the sulfoaluminate cement clinker is 390–420 m². 2 / kg, 3d compressive strength ≥40MPa.

[0034] In this embodiment of the invention, the magnesium oxide content in the lightly calcined magnesium oxide is ≥85wt%, the active magnesium oxide content is ≥65wt%, and the particle size is ≤40μm.

[0035] In this embodiment of the invention, the SiO2 content in the submicron-sized silica fume is >93wt%, and the specific surface area is 23000m². 2 / kg, 7d activity index ≥105%.

[0036] In this embodiment of the invention, the fly ash is Class I fly ash with a specific surface area of ​​398 m². 2 / kg.

[0037] In this embodiment of the invention, the glass powder is waste quartz glass powder with a specific surface area of ​​450 m². 2 / kg.

[0038] In this embodiment of the invention, the gypsum is natural gypsum or mixed gypsum, wherein the content of anhydrite in the natural gypsum or mixed gypsum is no more than 50 wt% of the total gypsum, and the specific surface area of ​​the gypsum is 317–421 m². 2 / kg; the solid content of the diethanol monoisopropanolamine is ≥85wt%, and the pH value is 10.24.

[0039] In this embodiment of the invention, the pre-dispersed carbon nanotubes are carbon nanotubes with a length of 100-200 μm and a diameter of 7-9 nm obtained by pre-dispersing.

[0040] The pre-dispersed carbon nanotubes were prepared as follows: (1) Carbon nanotubes, polyvinylpyrrolidone dispersant and deionized water with a mass ratio of 0.1:0.3:100 were weighed and set aside; (2) Carbon nanotubes and polyvinylpyrrolidone dispersant were added to deionized water, stirred with a glass rod and sealed, and placed in an ultrasonic disperser for ultrasonic treatment. Each stage of ultrasonic treatment was performed for 5 minutes, and the ultrasonic operation was repeated 6 times for a total ultrasonic time of 30 minutes. Then, the mixture was placed in a high-pressure homogenizer for high-pressure homogenization to obtain a pre-dispersed liquid; (3) The pre-dispersed liquid was freeze-dried until all water was removed, and then placed in a high-temperature drying oven at 600℃ for 3 hours to remove the polyvinylpyrrolidone dispersant and obtain pre-dispersed carbon nanotubes.

[0041] In this embodiment of the invention, the preparation method of a special cementitious material for low-shrinkage and high-airtightness concrete includes the following steps:

[0042] S1. Weigh out the following materials by mass percentage: low-heat silicate cement clinker, sulfoaluminate cement clinker, lightly calcined magnesia, submicron silica fume, fly ash, and glass powder. Weigh out the following materials by mass percentage: gypsum, diethanol monoisopropanolamine, and pre-dispersed carbon nanotubes.

[0043] S2. Take out the pre-dispersed carbon nanotubes and weigh 10 times the mass of low-heat silicate cement clinker and 81.6 times the mass of isopropanol, wherein the low-heat silicate cement clinker is weighed from the corresponding raw materials prepared in S1; divide the isopropanol into two parts, add the pre-dispersed carbon nanotubes to one part of the isopropanol, stir to dissolve and ultrasonically disperse for 30 min to obtain the first mixture, then add the low-heat silicate cement clinker and the other part of the isopropanol to the first mixture, stir to dissolve and ultrasonically disperse for 90 min to obtain the second mixture; place the second mixture in a high-temperature drying oven at 100±5℃ for 24 h to remove the isopropanol, and obtain clinker-CNT dried powder;

[0044] S3. Mix the sulfoaluminate cement clinker, lightly calcined magnesium oxide, submicron silica fume, fly ash, glass powder, gypsum, diethanol monoisopropanolamine, and the remaining low-heat silicate cement clinker, as well as the clinker-CNT dry powder obtained in S2, evenly to obtain a low-shrinkage, high-airtightness concrete-specific cementitious material.

[0045] Example 1

[0046] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete-specific cementitious material disclosed in this embodiment is shown in Table 1 below.

[0047] Table 1

[0048] Low-heat silicate cement clinker 63 Sulfoaluminate cement clinker 7 Lightly calcined magnesium oxide 5 Submicron silica ash 10 fly ash 9 glass powder 6

[0049] In this embodiment, the special cementitious material for low-shrinkage and high-airtightness concrete also includes 3 wt% gypsum, 0.03 wt% diethanol monoisopropanolamine and 0.1 wt% pre-dispersed carbon nanotubes, which are the total mass percentages of the raw materials listed in Table 1.

[0050] The special cementitious material of this embodiment is used to prepare concrete. The raw material ratio per cubic meter of concrete is as follows: special cementitious material 686.6 kg / m³ 3 Polycarboxylate superplasticizer 4kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0051] Example 2

[0052] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete-specific cementitious material disclosed in this embodiment is shown in Table 2 below.

[0053] Table 2

[0054] Low-heat silicate cement clinker 56 Sulfoaluminate cement clinker 14 Lightly calcined magnesium oxide 3 Submicron silica ash 7 fly ash 12 glass powder 8

[0055] In this embodiment, the special cementitious material for low-shrinkage and high-airtightness concrete also includes 3 wt% gypsum, 0.03 wt% diethanol monoisopropanolamine and 0.1 wt% pre-dispersed carbon nanotubes, which are the total mass percentages of the raw materials listed in Table 2.

[0056] The special cementitious material of this embodiment is used to prepare concrete. The raw material ratio per cubic meter of concrete is as follows: special cementitious material 686.6 kg / m³ 3 Polycarboxylate superplasticizer 4.1kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0057] Example 3

[0058] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete-specific cementitious material disclosed in this embodiment is shown in Table 3 below.

[0059] Table 3

[0060] Low-heat silicate cement clinker 54 Sulfoaluminate cement clinker 6 Lightly calcined magnesium oxide 5 Submicron silica ash 10 fly ash 15 glass powder 10

[0061] In this embodiment, the special cementitious material for low-shrinkage and high-airtightness concrete also includes 2 wt% gypsum, 0.03 wt% diethanol monoisopropanolamine and 0.1 wt% pre-dispersed carbon nanotubes, which are the total mass percentages of the raw materials listed in Table 3.

[0062] The special cementitious material of this embodiment is used to prepare concrete. The raw material ratio per cubic meter of concrete is as follows: special cementitious material 686.6 kg / m³ 3 Polycarboxylate superplasticizer 3.8kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0063] Example 4

[0064] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete-specific cementitious material disclosed in this embodiment is shown in Table 4 below.

[0065] Table 4

[0066] Low-heat silicate cement clinker 48 Sulfoaluminate cement clinker 12 Lightly calcined magnesium oxide 3 Submicron silica ash 7 fly ash 18 glass powder 12

[0067] In this embodiment, the special cementitious material for low-shrinkage and high-airtightness concrete also includes 2 wt% gypsum, 0.03 wt% diethanol monoisopropanolamine and 0.1 wt% pre-dispersed carbon nanotubes, which are the total mass percentages of the raw materials listed in Table 4.

[0068] The special cementitious material of this embodiment is used to prepare concrete. The raw material ratio per cubic meter of concrete is as follows: special cementitious material 686.6 kg / m³ 3 Polycarboxylate superplasticizer 3.9kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0069] Comparative Example 1

[0070] The specific composition of the cementitious material in this comparative example is shown in Table 5 below.

[0071] Table 5

[0072] Ordinary Portland cement (PO42.5) 70 fly ash 20 silica ash 10

[0073] The cementitious material in this comparative example was used to prepare concrete. The raw material proportions per cubic meter of concrete were as follows: 686.6 kg / m³ of special cementitious material. 3 Polycarboxylate superplasticizer 3.7kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0074] Comparative Example 2

[0075] The cementitious materials in this comparative example are the same as those in Example 1, except that low-heat silicate cement clinker is used instead of sulfoaluminate cement clinker and lightly calcined magnesia.

[0076] The cementitious material in this comparative example was used to prepare concrete. The raw material proportions per cubic meter of concrete were as follows: 686.6 kg / m³ of special cementitious material. 3 Polycarboxylate superplasticizer 3.9kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0077] Comparative Example 3

[0078] The cementitious materials used in this comparative example are the same as those in Example 1, except that low-heat silicate cement clinker is used instead of submicron silica fume and no pre-dispersed carbon nanotubes are added.

[0079] The cementitious material in this comparative example was used to prepare concrete. The raw material proportions per cubic meter of concrete were as follows: 686.6 kg / m³ of special cementitious material. 3 Polycarboxylate superplasticizer 4kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0080] Comparative Example 4

[0081] The cementitious materials in this comparative example are the same as those in Example 1, except that low-heat silicate cement clinker is used instead of fly ash and glass powder.

[0082] The cementitious material in this comparative example was used to prepare concrete. The raw material proportions per cubic meter of concrete were as follows: 686.6 kg / m³ of special cementitious material. 3 Polycarboxylate superplasticizer 4.2kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0083] Comparative Example 5

[0084] The gelling material in this comparative example is the same as that in Example 1, except that diethanol monoisopropanolamine is not added.

[0085] The cementitious material in this comparative example was used to prepare concrete. The raw material proportions per cubic meter of concrete were as follows: 686.6 kg / m³ of special cementitious material. 3 Polycarboxylate superplasticizer 4kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0086] Comparative Example 6

[0087] The cementitious material in this comparative example is the same as that in Example 1, except that carbon nanotubes are used instead of pre-dispersed carbon nanotubes.

[0088] The cementitious material in this comparative example was used to prepare concrete. The raw material proportions per cubic meter of concrete were as follows: 686.6 kg / m³ of special cementitious material. 3 Polycarboxylate superplasticizer 4kg / m3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0089] Comparative Example 7

[0090] The cementitious material in this comparative example is the same as that in Example 1, except that the pre-dispersed carbon nanotubes are not dispersed in the low-heat silicate cement clinker particles but are directly mixed with each raw material.

[0091] The cementitious material in this comparative example was used to prepare concrete. The raw material proportions per cubic meter of concrete were as follows: 686.6 kg / m³ of special cementitious material. 3 Polycarboxylate superplasticizer 4kg / m 3 , sand 892.5kg / m 3 1090.8 kg / m³ of gravel 3 Water 164.8 kg / m 3 .

[0092] Test case

[0093] (1) Testing the physical properties of cementitious materials

[0094] Referring to GB17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)" and GB / T1346-2011 "Test Method for Standard Consistency Water Requirement, Setting Time and Soundness of Cement", the physical properties of the cementitious materials in each embodiment and comparative example were tested, and the test results are shown in Table 6 below.

[0095] Table 6

[0096]

[0097] As can be seen from the data in Table 6, by comparing Examples 1-4 and Comparative Example 1, it can be seen that the special cementitious material obtained by modifying low-heat silicate cement clinker and adding pre-dispersed carbon nanotubes as the main component has a compressive strength at each age that is about 2-6 MPa higher than that of conventional cementitious materials.

[0098] By comparing Example 1 and Comparative Examples 2-7, it can be seen that the incorporation of sulfate cement clinker and lightly calcined magnesium oxide can effectively improve the strength of concrete while alleviating system shrinkage, especially the early strength. The incorporation of silica fume and pre-dispersed carbon nanotubes can effectively fill the internal pores of the matrix, greatly improving its mechanical properties. The addition of DEIPA can promote the formation of hydration products under the synergistic effect of gypsum components, optimize the pore size distribution, effectively improve the early mechanical properties of the matrix, and make the microstructure more compact. Compared with directly incorporating carbon nanotubes into the matrix or without preparing clinker-CNT dry powder, the special cementitious material of this invention can effectively reduce the degree of entanglement between carbon nanotubes, making its network structure loose and uniformly filling the microporous structure, playing a good bridging and filling role, thereby improving the matrix strength.

[0099] (2) The concrete prepared in each embodiment and Comparative Example 1 was molded as follows: the weighed cementitious material was poured into a mixer and mixed evenly, and then the weighed sand and stone were added and the mixture was stirred to obtain a dry mixture; the water-reducing agent was mixed into water and allowed to dissolve and mix evenly, and then poured into the above dry mixture to obtain a mixture, which was poured into a mold and allowed to stand to form concrete. The physical properties of the concrete were tested according to the following standards:

[0100] ① Compressive strength test: The compressive strength of concrete specimens after standard curing for 28 days was tested in accordance with GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0101] ② Gas permeability test: Following the JC / T2758-2023 standard standard curing method for concrete, the concrete specimens cured for 28 days were treated and then subjected to a gas permeability test. Cylindrical concrete specimens with a diameter of 150 mm and a height of 50 mm were used, and the test gas pressure was 0.9 MPa.

[0102] ③ Shrinkage test: Refer to the contact method in GB / T50082-2009 "Test Methods for Long-term Performance and Durability of Ordinary Concrete" to test the drying shrinkage value of concrete on the 7th day.

[0103] The test results are shown in Table 7 below.

[0104] Table 7

[0105]

[0106] As can be seen from the data in Table 7, the airtight concrete prepared using the special cementitious material of this invention through the closest packing theory and volumetric method exhibits significantly improved strength compared to conventional concrete of the same grade (Comparative Example 1). The 28-day strength is increased by approximately 20%, and the gas permeability coefficient is significantly reduced, ranging from 0.005 to 0.016 × 10⁻⁶. -18 m 2 It has excellent airtightness and its shrinkage rate is much lower than that of conventional concrete.

[0107] Comparative Examples 1 and 2-7 show that, based on the low-heat silicate cement clinker system, the use of modified components (sulfoaluminate cement clinker, lightly calcined magnesia, and DEIPA), submicron-sized materials, and pre-dispersed carbon nanotubes all improve the internal pore structure of concrete to varying degrees, reduce concrete volume shrinkage, and enhance concrete air tightness and durability. Furthermore, the combined use of fly ash and glass powder significantly optimizes the workability and stability of concrete, improves the dispersion stability of mineral admixtures and additives, and effectively increases the density of the concrete matrix. Compared to Comparative Examples 6 and 7, the specially treated carbon nanotubes, uniformly dispersed in the clinker particles, achieve a tighter bond between the carbon nanotubes and the cementitious particles, thereby improving the overall stability and crack resistance of the material and enhancing the sealing performance of the concrete.

[0108] Experimental data demonstrate that the special cementitious material of this invention can be used to prepare airtight concrete, which can effectively improve the matrix density and crack resistance of concrete. It has the advantages of good volume stability, high mechanical properties and airtightness, and can be applied to application scenarios with varying service environments.

[0109] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A low-shrinkage, high-airtightness cementitious material for concrete, characterized in that, Including the following raw materials by weight percentage: Low-heat silicate cement clinker: 48~63wt%; Sulfoaluminate cement clinker: 6~14wt%; Lightly calcined magnesium oxide: 3~5wt%; Submicron silica fume: 7~10 wt%; Fly ash: 9~18wt%; Glass powder: 6~12wt%; And including 2-3 wt% gypsum, 0.03 wt% diethanol monoisopropanolamine and 0.1 wt% predispersed carbon nanotubes, which are the total mass percentages of the above raw materials; The mineral composition of the low-heat silicate cement clinker includes: 29.9 wt% C3S, 46.3 wt% C2S, 1.8 wt% C3A, and 15.3 wt% C4AF; the specific surface area of ​​the low-heat silicate cement clinker is 350~370 m². 2 / kg, 3d compressive strength ≥14 MPa; The mineral composition of the sulfoaluminate cement clinker includes: 62.3 wt%. 27.5wt% C2S, 5.3wt% C4AF; the specific surface area of ​​the sulfoaluminate cement clinker is 390~420m². 2 / kg, 3d compressive strength ≥40Mpa; The predispersed carbon nanotubes were prepared as follows: (1) Carbon nanotubes, polyvinylpyrrolidone dispersant and deionized water with a mass ratio of 0.1:0.3:100 were weighed and set aside; (2) Carbon nanotubes and polyvinylpyrrolidone dispersant were added to deionized water, stirred, sealed and ultrasonically treated, and then homogenized under high pressure to obtain a predispersed liquid; (3) The predispersed liquid was freeze-dried until all water was removed, and then placed in a high-temperature drying oven to remove the polyvinylpyrrolidone dispersant to obtain predispersed carbon nanotubes.

2. The low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 1, characterized in that, The lightly calcined magnesium oxide contains ≥85wt% magnesium oxide, ≥65wt% active magnesium oxide, and has a particle size ≤40μm.

3. The low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 1, characterized in that, The submicron-sized silica fume contains >93 wt% SiO2 and has a specific surface area of ​​23,000 m². 2 / kg, 7d activity index ≥105%.

4. The low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 1, characterized in that, The fly ash is Class I fly ash with a specific surface area of ​​398 m². 2 / kg; the glass powder is waste quartz glass powder with a specific surface area of ​​450m². 2 / kg.

5. The low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 1, characterized in that, The gypsum is natural gypsum or mixed gypsum, wherein the content of anhydrite in the natural gypsum or mixed gypsum is no more than 50 wt% of the total gypsum, and the specific surface area of ​​the gypsum is 317~421 m². 2 / kg; the solid content of the diethanol monoisopropanolamine is ≥85wt%, and the pH value is 10.

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6. The low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 1, characterized in that, The pre-dispersed carbon nanotubes are carbon nanotubes with a length of 100~200μm and a diameter of 7~9nm obtained by pre-dispersing.

7. The low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 1, characterized in that, The ultrasonic treatment in (2) was repeated 6 times, with each ultrasonic treatment lasting 5 minutes.

8. The low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 1, characterized in that, The temperature of the high-temperature drying oven in (3) is 600℃ and the processing time is 3h.

9. A method for preparing a low-shrinkage, high-airtightness concrete-specific cementitious material according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Weigh out the following materials by mass percentage: low-heat silicate cement clinker, sulfoaluminate cement clinker, lightly calcined magnesia, submicron silica fume, fly ash, and glass powder. Weigh out the following materials by mass percentage: gypsum, diethanol monoisopropanolamine, and pre-dispersed carbon nanotubes. S2. Take out the pre-dispersed carbon nanotubes and weigh 10 times the mass of low-heat silicate cement clinker and 81.6 times the mass of isopropanol, wherein the low-heat silicate cement clinker is weighed from the corresponding raw materials prepared in S1; divide the isopropanol into two parts, add the pre-dispersed carbon nanotubes to one part of the isopropanol, stir to dissolve and ultrasonically disperse to obtain the first mixture, then add the low-heat silicate cement clinker and the other part of the isopropanol to the first mixture, stir to dissolve and ultrasonically disperse to obtain the second mixture; place the second mixture in a high-temperature drying oven to remove the isopropanol, and obtain clinker-CNT dry powder; S3. Mix the sulfoaluminate cement clinker, lightly calcined magnesium oxide, submicron silica fume, fly ash, glass powder, gypsum, diethanol monoisopropanolamine, and the remaining low-heat silicate cement clinker, as well as the clinker-CNT dry powder obtained in S2, evenly to obtain the low-shrinkage, high-airtightness concrete-specific cementitious material.

10. The method for preparing a low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 9, characterized in that, In step S2, when the pre-dispersed carbon nanotubes are added to one part of isopropanol, stirred to dissolve, and then ultrasonically dispersed, the ultrasonic time is 30 minutes.

11. The method for preparing a low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 9, characterized in that, In step S2, when the low-heat silicate cement clinker and another part of isopropanol are added to the first mixture, stirred to dissolve, and ultrasonically dispersed, the ultrasonic time is 90 minutes.

12. The method for preparing a low-shrinkage, high-airtightness concrete-specific cementitious material according to claim 9, characterized in that, In step S2, the temperature of the high-temperature drying oven is 100±5℃, and the processing time is 24h.

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