Low-shrinkage high-airtightness concrete and preparation method thereof

Abstract

The application discloses a kind of low shrinkage high air-tightness concrete and preparation method thereof, the air-tightness concrete includes the following raw materials by weight preparation: special composite cementitious material: 687~746kg / m 3 ; Sand: 848~893kg / m 3 ; Stone: 1036~1091kg / m 3 ; Water: 165~171kg / m 3 ; Water reducing agent: 3.9~4kg / m 3 ; Pre-dispersed carbon nanotube: 0.687~0.746kg / m 3 ; Diethanol mono-isopropanol amine: 0.206~0.224kg / m 3 The workability and overall later strength of the air-tightness concrete are high, the mechanical performance, shrinkage resistance and air-tightness are good, and the complex and changeable service environment can be met.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a low-shrinkage, high-airtightness concrete 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 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.

[0004] Researchers have conducted 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 uses manufactured sand with appropriate proportions, combined with airtight agents and expanding agents to increase the airtightness and impermeability of the concrete, meeting 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.

[0005] The aforementioned techniques 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 proportions. 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 demanding construction and service environments, higher functional requirements, and stronger 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 from the perspectives of cementitious material composition, structure, and performance to adapt to more complex engineering environments. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a low-shrinkage, high-airtightness concrete and its preparation method, so as to at least solve some of the above-mentioned technical problems.

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

[0008] On the one hand, a low-shrinkage, high-airtightness concrete is provided, comprising the following raw materials prepared by weight:

[0009] Special composite cementitious material: 687~746kg / m 3 ;

[0010] Sand: 848~893kg / m³ 3 ;

[0011] Gravel: 1036~1091kg / m 3 ;

[0012] Water: 165~171kg / m 3 ;

[0013] Water-reducing agent: 3.9~4kg / m³ 3 ;

[0014] Predispersed carbon nanotubes: 0.687~0.746kg / m 3 ;

[0015] Diethanol monoisopropanolamine: 0.206~0.224kg / m 3 .

[0016] Furthermore, the specialized composite cementitious material comprises the following components by weight percentage:

[0017] High-Belly cement clinker: 55-61 wt%;

[0018] Ferroaluminate cement clinker: 6–12 wt%;

[0019] Lightly calcined magnesium oxide: 3-5 wt%;

[0020] Submicron silica fume: 7–10 wt%;

[0021] Fly ash: 9-12 wt%;

[0022] Glass powder: 6-8 wt%;

[0023] Gypsum: 3 wt%.

[0024] Furthermore, the weight percentages of minerals in the high-belite cement clinker are as follows: C2S: 50-60 wt%, C3S: 17-25 wt%, C4AF: 13-19 wt%, C3A: 2-5 wt%; the specific surface area of ​​the high-belite cement clinker is 350-370 m². 2 / kg, 3d compressive strength ≥12MPa.

[0025] Furthermore, the weight percentage of minerals in the aluminoferrite cement clinker is as follows: 35-55 wt%, C2S: 15-35 wt%, C6AF2: 15-30 wt%; the specific surface area of ​​the aluminoferrite cement clinker is 370-390 m². 2 / kg, 3d compressive strength ≥42MPa.

[0026] Furthermore, the lightly calcined magnesium oxide contains ≥85wt% magnesium oxide, ≥65wt% active magnesium oxide, and has a particle size ≤40μm; the submicron-sized silica fume contains >93wt% SiO2 and has a specific surface area of ​​23000m². 2 / kg, 7-day activity index ≥105%; the fly ash is Grade I fly ash with a specific surface area of ​​398m². 2 / kg; the glass powder is waste quartz glass powder with a specific surface area of ​​450m². 2 / kg; the gypsum is natural gypsum or mixed gypsum, wherein the anhydrite content in the natural gypsum or mixed gypsum is not greater than 50wt% of the total gypsum, and the specific surface area of ​​the gypsum is 317-421m². 2 / kg.

[0027] Furthermore, the sand is Zone II sand, which is a mixture of river sand with a particle size of 0–1.18 mm and manufactured sand with a particle size of 0.15–4.75 mm. The river sand and manufactured sand are mixed at a mass ratio of 4:6, and the apparent density is 2573 kg / m³.3 The bulk density is 1769 kg / m³. 3 The fineness modulus is 2.6.

[0028] Furthermore, the gravel is continuously graded crushed stone with a particle size distribution between 5 and 10 mm, a mud content of 0.7 wt%, a crushing value of 5.2%, and an apparent density of 2782 kg / m³. 3 The bulk density is 1605 kg / m³. 3 .

[0029] Furthermore, the water-reducing agent is a polycarboxylate high-performance water-reducing agent with a water reduction rate greater than 30%; the diethanol monoisopropanolamine has a solid content ≥85wt% and a pH value of 10.24.

[0030] 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, and the preparation method is as follows:

[0031] (1) Weigh carbon nanotubes, polyvinylpyrrolidone dispersant and deionized water in a mass ratio of 0.1:0.3:100 for later use;

[0032] (2) Carbon nanotubes and polyvinylpyrrolidone dispersant were added to deionized water, stirred, sealed and then ultrasonically treated, followed by high-pressure homogenization to obtain a pre-dispersion.

[0033] (3) The pre-dispersed liquid was freeze-dried until deionized water was removed, and then placed in a high-temperature drying oven to remove polyvinylpyrrolidone dispersant, thus obtaining pre-dispersed carbon nanotubes.

[0034] Preferably, in (2), the ultrasonic treatment is repeated 6 times, and the ultrasonic time is 5 minutes each time;

[0035] Preferably, (3) the temperature of the high-temperature drying oven is 600℃ and the processing time is 3h.

[0036] On the other hand, a method for preparing low-shrinkage, high-airtightness concrete is provided, comprising the following steps:

[0037] Step 1: Weigh out the pre-dispersed carbon nanotubes according to the mass ratio, and weigh out 10 times the mass of the special composite cementitious material and 81.6 times the mass of isopropanol. 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 special composite cementitious material 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 the cementitious material - CNT dry powder.

[0038] 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.

[0039] Preferably, when the special composite gelling material and another part of isopropanol are added to the first mixture, stirred to dissolve and ultrasonically dispersed, the ultrasonic time is 90 minutes.

[0040] Preferably, the temperature of the high-temperature drying oven is 100±5℃, and the processing time is 24 hours;

[0041] Step 2: Weigh out sand, gravel, water-reducing agent, diethanol monoisopropanolamine, water, and the remaining special composite cementitious material according to the mass ratio. The mass of the remaining special composite cementitious material is the total mass of the special cementitious material minus the mass of the special composite cementitious material corresponding to the cementitious material-CNT dried powder prepared in Step 1.

[0042] Step 3: Mix the remaining special composite cementitious material from Step 2 with the cementitious material-CNT dry powder prepared in Step 1 until homogeneous; then add the weighed sand and gravel and continue mixing until homogeneous to obtain a mixed dry material;

[0043] Step 4: After thoroughly mixing the water-reducing agent, diethanol monoisopropanolamine and water weighed in Step 2, stir with the dry mixed material to obtain a mixture; pour the mixture into a mold, vibrate to compact it, and then cover and cure it in an environment of 18℃~22℃. After the mixture has hardened, low-shrinkage and high-airtightness concrete is obtained.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. The special composite cementitious material used in this invention is mainly high-belite cement clinker with low heat of hydration, low drying shrinkage, good high-temperature stability, and excellent long-term mechanical properties. It is modified by introducing appropriate amounts of lightly calcined magnesia and aluminoferrite cement clinker. The micro-expansion characteristics of the lightly calcined magnesia and aluminoferrite cement clinker effectively compensate for the shrinkage of the high-belite cement clinker, resulting in a lower hydration volume shrinkage rate in the concrete matrix. The hydration of the ferric phase in the aluminoferrite cement clinker can accelerate the hydration of C2S to a certain extent, resulting in a synergistic hydration reaction with the high-belite cement clinker. This makes the concrete structure denser, promotes strength development, and gives it high strength, high frost resistance, high impermeability, wear resistance, and corrosion resistance. It also further improves the adaptability of the airtight concrete prepared by the special composite cementitious material to complex environments. Simultaneously, by adding a specific proportion of fly ash and glass powder, the lubricity and dispersibility of the special composite cementitious material are improved, enhancing the workability and overall later-stage strength of the concrete.

[0046] 2. This invention controls the particle size of each material. The submicron-sized silica fume and pre-dispersed carbon nanotubes in the special composite cementitious material can act as fine powders, filling the pores of other materials and 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 particles of the special composite cementitious material facilitates uniform dispersion of the carbon nanotubes, effectively filling the micropores generated after cement hydration. Furthermore, the carbon nanotubes act as excellent bridges and fillers within the internal pores, enhancing matrix density and effectively inhibiting the development of microcracks. This significantly improves the mechanical properties of concrete, enhancing its shrinkage resistance and airtightness.

[0047] 3. The special composite cementitious material of this invention has a reasonable particle size distribution, using sand and gravel as fine and coarse aggregates respectively. Furthermore, the components exhibit an interactive and synergistic effect, complementing and promoting each other, resulting in continuous densification of the hydrated cementitious material. It is also used in conjunction with pre-dispersed carbon nanotubes and diethanol monoisopropanolamine (DEIPA), utilizing DEIPA to regulate the Fe content in the system. 3+ The complexation effect effectively activates the iron phase with higher content in the two clinker systems. Under the synergistic effect with gypsum, it can further enhance the hydration reaction of the ferrite phase in the paste, accelerate the consumption of DEIPA and the formation of ettringite (AFt) and monosulfoaluminate (AFm) in the hydration products, promote the dissolution of mineral admixtures, optimize the pore size distribution, make the microstructure of concrete denser, and maintain excellent airtightness and volume stability at all stages. Detailed Implementation

[0048] 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. In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] Example 1

[0050] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete of the present invention is shown in Table 1 below.

[0051] Table 1

[0052] Special composite cementitious materials 687 sand 893 pebbles 1091 water 165 Water reducing agent 3.9 Predispersed carbon nanotubes 0.687 Diethanolmonoisopropanolamine 0.206

[0053] In this implementation, the specific composition of the special composite cementitious material is shown in Table 2 below.

[0054] Table 2

[0055] High Bellite Cement Clinker 61 Ferroaluminate cement clinker 6 Lightly calcined magnesium oxide 5 Submicron silica ash 10 fly ash 9 glass powder 6 plaster 3

[0056] Example 2

[0057] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete of the present invention is shown in Table 3 below.

[0058] Table 3

[0059] Special composite cementitious materials 746 sand 848 pebbles 1036 water 171 Water reducing agent 4 Predispersed carbon nanotubes 0.746 Diethanolmonoisopropanolamine 0.224

[0060] In this implementation, the specific composition of the special composite cementitious material is shown in Table 4 below.

[0061] Table 4

[0062] High Bellite Cement Clinker 61 Ferroaluminate cement clinker 6 Lightly calcined magnesium oxide 5 Submicron silica ash 10 fly ash 9 glass powder 6 plaster 3

[0063] Example 3

[0064] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete of the present invention is shown in Table 5 below.

[0065] Table 5

[0066] Special composite cementitious materials 687 sand 893 pebbles 1091 water 165 Water reducing agent 3.9 Predispersed carbon nanotubes 0.687 Diethanolmonoisopropanolamine 0.206

[0067] In this implementation, the specific composition of the special composite cementitious material is shown in Table 6 below.

[0068] Table 6

[0069] High Bellite Cement Clinker 55 Ferroaluminate cement clinker 12 Lightly calcined magnesium oxide 3 Submicron silica ash 7 fly ash 12 glass powder 8 plaster 3

[0070] Example 4

[0071] As a preferred embodiment of the present invention, the specific composition of the low-shrinkage, high-airtightness concrete of the present invention is shown in Table 7 below.

[0072] Table 7

[0073]

[0074]

[0075] In this implementation, the specific composition of the special composite cementitious material is shown in Table 8 below.

[0076] Table 8

[0077] High Bellite Cement Clinker 55 Ferroaluminate cement clinker 12 Lightly calcined magnesium oxide 3 Submicron silica ash 7 fly ash 12 glass powder 8 plaster 3

[0078] Comparative Example 1

[0079] The specific composition of the concrete in this comparative example is shown in Table 9 below.

[0080] Table 9

[0081] cementing materials 687 sand 893 stone 1091 water 165 Water reducing agent 3.7

[0082] In this comparative example, the specific composition of the cementitious material is shown in Table 10 below.

[0083] Table 10

[0084] Ordinary Portland cement (PO42.5) 70 fly ash 20 silica ash 10

[0085] Comparative Example 2

[0086] The specific composition of the concrete in this comparative example is shown in Table 11 below.

[0087] Table 11

[0088]

[0089]

[0090] In this comparative example, the specific composition of the cementitious material is shown in Table 12 below.

[0091] Table 12

[0092] Ordinary Portland cement (PO42.5) 70 fly ash 20 silica ash 10

[0093] Test case

[0094] After the concrete prepared in Examples 1 to 4 and Comparative Examples 1 and 2 was molded, the physical properties of each concrete were tested according to the following standards:

[0095] 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".

[0096] ② Gas permeability test: Following the JC / T2758-2023 standard standard curing method for concrete, concrete specimens cured for 28 days were treated and subjected to gas permeability testing. Cylindrical concrete specimens with a diameter of 150 mm and a height of 50 mm were used, and the test gas pressure was 0.8 MPa.

[0097] 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.

[0098] The test results are shown in Table 13 below.

[0099] Table 13

[0100]

[0101] The data in Table 13 show that the airtight concrete prepared by this invention using a special composite cementitious material combined with diethanol monoisopropanolamine and pre-dispersed carbon nanotubes, through the closest packing theory and volumetric method, exhibits significantly improved strength compared to conventional concrete of the same grade (Comparative Examples 1 and 2). The 28-day compressive strength is increased by approximately 20%, and the gas permeability coefficient is significantly reduced. In Example 2, no gas flow was detected at a test pressure of 0.8 MPa, while the gas permeability coefficients for other examples ranged from 0.004 to 0.011 × 10⁻⁶. -18 m 2 It exhibits excellent airtightness and its shrinkage rate is far lower than that of conventional concrete. Therefore, based on the high-belite cement clinker system, the use of modified components (ferroaluminate cement clinker, lightly calcined magnesia), submicron-sized materials (submicron-sized silica fume), diethanol monoisopropanolamine, and pre-dispersed carbon nanotubes all improve the internal pore structure of concrete to varying degrees, reduce concrete volume shrinkage, enhance concrete airtightness and durability, and thus improve the adaptability of airtight concrete to complex environments.

[0102] 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 concrete, characterized in that, Including the following ingredients formulated by weight: Special composite cementitious material: 687~746kg / m 3 ; Sand: 848~893 kg / m³ 3 ; Gravel: 1036~1091 kg / m³ 3 ; Water: 165~171kg / m 3 ; Water-reducing agent: 3.9~4 kg / m³ 3 ; Predispersed carbon nanotubes: 0.687~0.746 kg / m 3 ; Diethanol monoisopropanolamine: 0.206~0.224 kg / m 3 ; The special composite cementitious material comprises the following components by weight percentage: High-Belit cement clinker: 55~61wt%; Ferroaluminate cement clinker: 6~12wt%; Lightly calcined magnesium oxide: 3~5 wt% Submicron silica fume: 7~10 wt% Fly ash: 9~12wt%; Glass powder: 6~8wt% Gypsum: 3 wt%.

2. The low-shrinkage, high-airtightness concrete according to claim 1, characterized in that, The weight percentages of minerals in the high-belite cement clinker are as follows: C2S: 50~60wt%, C3S: 17~25wt%, C4AF: 13~19wt%, C3A: 2~5wt%; the specific surface area of ​​the high-belite cement clinker is 350~370m². 2 / kg, 3d compressive strength ≥12 MPa.

3. The low-shrinkage, high-airtightness concrete according to claim 1, characterized in that, The weight percentage of minerals in the aluminoferrite cement clinker is as follows: The specific surface area of ​​the aluminoferrite cement clinker is 370-390 m², consisting of 35-55 wt% C₂S, 15-35 wt% C₆AF₂, and 15-30 wt% C₂S. 2 / kg, 3d compressive strength ≥42 MPa.

4. The low-shrinkage, high-airtightness concrete 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; the submicron-sized silica fume contains >93wt% SiO2 and has a specific surface area of ​​23000m². 2 / kg, 7-day activity index ≥105%; the fly ash is Class I fly ash with a specific surface area of ​​398m². 2 / kg; the glass powder is waste quartz glass powder with a specific surface area of ​​450m². 2 / kg; the gypsum is natural gypsum or mixed gypsum, wherein the anhydrite content in the natural gypsum or mixed gypsum is not greater than 50wt% of the total gypsum, and the specific surface area of ​​the gypsum is 317~421m². 2 / kg.

5. The low-shrinkage, high-airtightness concrete according to claim 1, characterized in that, The sand is a Zone II sand composed of river sand with a particle size of 0~1.18mm and manufactured sand with a particle size of 0.15~4.75mm, mixed at a mass ratio of 4:6, with an apparent density of 2573kg / m³. 3 The bulk density is 1769 kg / m³. 3 The fineness modulus is 2.

6.

6. The low-shrinkage, high-airtightness concrete according to claim 1, characterized in that, The gravel is continuously graded crushed stone with a particle size distribution between 5 and 10 mm, a mud content of 0.7 wt%, a crushing value of 5.2%, and an apparent density of 2782 kg / m³. 3 The bulk density is 1605 kg / m³. 3 .

7. The low-shrinkage, high-airtightness concrete according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate high-performance water-reducing agent with a water reduction rate greater than 30%; the diethanol monoisopropanolamine has a solid content ≥85wt% and a pH value of 10.

24.

8. The low-shrinkage, high-airtightness concrete according to claim 1, characterized in that, 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 treatment. The preparation method is as follows: (1) Weigh carbon nanotubes, polyvinylpyrrolidone dispersant and deionized water in a mass ratio of 0.1:0.3:100 for later use; (2) Carbon nanotubes and polyvinylpyrrolidone dispersant were added to deionized water, stirred, sealed and then ultrasonically treated, followed by high-pressure homogenization to obtain a pre-dispersion. (3) The pre-dispersed liquid was freeze-dried until deionized water was removed, and then placed in a high-temperature drying oven to remove polyvinylpyrrolidone dispersant, thus obtaining pre-dispersed carbon nanotubes.

9. A low-shrinkage, high-airtightness concrete according to claim 8, characterized in that, (2) Repeat the ultrasonic treatment 6 times, with each ultrasonic treatment lasting 5 minutes.

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

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