High performance air-entrained concrete and method of making same

Abstract

This invention discloses a high-performance airtight concrete and its preparation method, wherein the concrete comprises 444-461 kg / m³ of mixed cement. 3 Fly ash microspheres: 121-126 kg / m³ 3 Mineral powder 162~168kg / m³ 3 Silica fume 81~84kg / m³ 3 Fine aggregate 774~806kg / m³ 3 Coarse aggregate 1114~1160kg / m³ 3 Water 178~184kg / m 3 Water-reducing agent 2.02~2.1kg / m³ 3 Defoamer 1.62~1.68kg / m³ 3 Nano-SiO2 8.08~16.76kg / m 3 This invention uses low-heat cement combined with sulfoaluminate cement, pre-dispersed nano-SiO2, and admixtures to improve the hydration and hardening process, which is beneficial to the early and late-stage development of compressive strength and the refinement of pore structure in concrete, thereby improving the density and crack resistance of concrete in a vacuum environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete materials, in particular to a high-performance air-tight concrete and a preparation method thereof. BACKGROUND

[0002] With the vigorous development of high-speed railways, people have put forward higher and higher requirements for the speediness and convenience of traffic. As a new type of transportation system, the super-high-speed low-vacuum maglev tube system (referred to as the vacuum tube system) can effectively solve the problems of resistance and noise generated during the operation of vehicles in an open air environment and improve the operating speed. In order to achieve the design operating speed, the vacuum tube system needs to meet the establishment and maintenance of low-vacuum conditions inside, and the sealing performance of the tube structure itself and the connecting parts is required to be high. At present, the vacuum tube system adopts a un-tube beam concrete structure wrapped in a steel structure, that is, the upper n-shaped steel pipe and the lower u-shaped concrete wrapped in a steel plate are directly connected through welding to form a closed section to meet the low-vacuum sealing performance; however, there are problems such as complicated construction process, large amount of steel structure welding work, and difficulty in realizing high sealing performance of the tube beam, and therefore it is necessary to explore a new type of high sealing performance material.

[0003] As the most economical and practical material, if the concrete is used as part of the vacuum tube system to replace the wrapped steel shell to realize the sealing of the tube beam, the economic cost can be well saved. Related research shows that the air-tightness of concrete is synonymous with the gas permeability resistance, and is also a basic parameter describing the durability process related to the migration of concrete and gas medium. At present, scholars' research on air-tight concrete is usually in the aspect of ordinary concrete, which is mainly applied in tunnel construction containing gas. In addition, the internal water loss of the concrete material will be aggravated in the low-vacuum environment, which will affect the hydration of the concrete to a certain extent and change the pore structure, which puts forward higher requirements for the air-tightness of the concrete. Therefore, the conventional concrete material is difficult to meet the high sealing requirement of the vacuum tube system. SUMMARY

[0004] The present application aims to provide a high-performance air-tight concrete and a preparation method thereof, which effectively reduces the internal pore diameter of the mixture by designing high-degree particle packing density of the dense reinforcing powder and the aggregate and the aggregate, minimizes the internal pore and micro-crack defects, uses low-heat cement with low hydration heat, small water demand, good volume stability, and higher long-term strength, and matches with sulphoaluminate cement, pre-dispersed nano-SiO2 and special admixtures to improve the hydration and hardening process of the cement, which is beneficial to the development of early and late compressive strength of the concrete and the refinement of the pore structure, improves the density and crack resistance of the concrete in the vacuum environment, and thus meets the low-vacuum sealing performance of the tube.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] The application discloses high-performance air-tight concrete, which comprises the following raw materials per cubic meter of concrete: 444-461 kg / m 3 of mixed cement 3 , 121-126 kg / m of fly ash microbeads 3 , 162-168 kg / m of mineral powder 3 , 81-84 kg / m of silica ash 3 , 774-806 kg / m of fine aggregate 3 , 1114-1160 kg / m of coarse aggregate 3 , 178-184 kg / m of water 3 , 2.02-2.1 kg / m of water reducing agent 3 , 1.62-1.68 kg / m of defoaming agent 3 , 8.08-16.76 kg / m of nano-SiO2.

[0007] In some embodiments of the application, the mixed cement is obtained by mixing 42.5-grade low-heat cement and 42.5-grade sulphoaluminate cement at a mass ratio of 6-10:0.5-1.2, preferably at a mass ratio of 9.2:0.8.

[0008] In some embodiments of the application, the fly ash microbeads have a particle size distribution of 0.5-4 microns, the particles are in the shape of round glass bodies, and the water demand ratio is 88%.

[0009] In some embodiments of the application, the mineral powder has a specific surface area of 678 m 2 / kg and a 28-day activity index of 105%.

[0010] In some embodiments of the application, the silica ash has a SiO2 content of more than 93% and a specific surface area of 23000 m 2 / kg.

[0011] In some embodiments of the application, the fine aggregate is well-graded II-zone sand obtained by mixing river sand with a particle size of 0-1.18 mm and machine-made sand with a particle size of 0-4.75 mm, and the river sand and the machine-made sand are mixed at a mass ratio of 2:8; the fine aggregate has an apparent density of 2525 kg / m 3 , a bulk density of 1710 kg / m 3 , a fineness modulus of 2.5 and a clay content of 2.1%.

[0012] In some embodiments of the application, the coarse aggregate is continuous graded gravel with hard texture and rough surface; the coarse aggregate has a particle size distribution of 5-10 mm, a clay content of 0.7%, a crushing value of 5.2% and an apparent density of 2782 kg / m 3The bulk density is 1605 kg / m³. 3 .

[0013] In some embodiments of the present invention, the water-reducing agent is a polycarboxylate high-performance water-reducing agent, a white powder with a water reduction rate greater than 30%; the defoamer is a polyether defoamer, a pale yellow powder with a viscosity of 800-1500 mPa·s and a molecular weight of 3000-5000; and the nano-SiO2 has a particle size of 30 nm and a solid content ≥99%.

[0014] This invention discloses a method for preparing high-performance airtight concrete, comprising the following steps:

[0015] Step 1: Preparation of modified fly ash microspheres: Add HCl solution to fly ash microspheres, stir and seal, ultrasonically disperse for 5-15 min, then place under magnetic stirring for 3-4 h. After stirring, quickly centrifuge and wash until the pH of the supernatant is neutral, then place in a 70℃ oven to dry for 1.5-3 days to obtain modified fly ash microspheres.

[0016] Preferably, the mass percentage of fly ash microspheres to HCl solution is 15-20:80-85, and the concentration of HCl solution is 3 mol / L;

[0017] Modified fly ash microspheres can increase the surface roughness of fly ash and improve its adsorption capacity;

[0018] Step 2: Preparation of nano-SiO2-fly ash microsphere suspension: Weigh nano-SiO2 according to the mass ratio for later use, then weigh modified fly ash microspheres at 1.5 to 2 times the mass of nano-SiO2 and water at 8 to 8.5 times the mass of nano-SiO2. Add nano-SiO2 to water and ultrasonically disperse for 3 to 8 minutes, then add modified fly ash microspheres and ultrasonically disperse for 3 to 8 minutes to obtain nano-SiO2-fly ash microsphere suspension;

[0019] Step 2 resulted in the formation of pre-dispersed nano-SiO2 from fly ash microspheres;

[0020] Step 3: Weigh out the mixed cement, fly ash microspheres, mineral powder, silica fume, fine aggregate, coarse aggregate, water, water-reducing agent, and defoamer according to the mass ratio for later use. The mass of fly ash microspheres is the total mass of fly ash microspheres minus the mass of fly ash microspheres used to prepare the nano-SiO2-fly ash microsphere suspension in Step 2. The mass of water is the total mass of water minus the mass of water used to prepare the nano-SiO2-fly ash microsphere suspension in Step 2.

[0021] Step 4: Mix the weighed cement, fly ash microspheres, mineral powder, silica fume and defoamer from Step 3 evenly; then add the weighed coarse aggregate and fine aggregate and continue mixing to obtain the mixed dry material;

[0022] Step 5: After thoroughly mixing the water-reducing agent and water weighed in Step 3, stir. Then add the nano-SiO2-fly ash microsphere suspension prepared in Step 2 and continue stirring until uniform to obtain the mixture.

[0023] Step 6: Pour the mixture into a mold, vibrate to compact it, and then cover it with a film for curing in an environment of 18℃~22℃. After the mixture has hardened, high-performance airtight concrete is obtained.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) In this invention, nano-SiO2 is pre-dispersed so that it is adsorbed on the surface of carrier particles (fly ash microspheres) and uniformly dispersed in the concrete matrix, reducing its encapsulation effect on cement particles. It can give full play to its nano-filling effect, chemical activity and crystal nucleation effect, promote the cement hydration process and optimize the structure of the interface transition zone. In synergy with the defoaming component, it also reduces the channels available for gas transmission and significantly reduces the gas permeability coefficient.

[0026] (2) The cement used in this invention is low-heat cement and sulfoaluminate cement. Low-heat cement possesses characteristics such as low water demand, low heat of hydration, low shrinkage, high durability, and excellent long-term mechanical properties. Using it as a cement material for airtight concrete can effectively improve the density and crack resistance of the concrete matrix while ensuring the workability of the mixture, thus enhancing the sealing performance of the concrete. When used in combination with sulfoaluminate cement, the early strength and micro-expansion characteristics of sulfoaluminate cement can effectively compensate for the lower early strength of low-heat cement, further optimizing the pore structure. When anhydrous calcium sulfoaluminate (CaA3S) in sulfoaluminate cement undergoes hydrolysis, nano-SiO2, with its strong specific surface area and adsorption capacity, can preferentially adsorb Ca. 2+ Promote Ca 2+ and SO4 2- Diffusion accelerates the hydrolysis of CaA3S, providing more nucleation sites for the development of ettringite (AFt), making AFt more likely to accumulate on the surface of cement particles, promoting early hydration, improving the interfacial transition zone, and making the internal structure of concrete more compact.

[0027] (2) The high-performance airtight concrete of the present invention has good mechanical properties and gas permeability resistance, which can effectively alleviate the chemical shrinkage caused by the loss of internal moisture of concrete in a vacuum environment, so that the concrete can maintain excellent airtightness and volume stability after curing in a low vacuum environment, and can provide a reference for the track structure design of vacuum pipeline system. Detailed Implementation

[0028] 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.

[0029] In this embodiment of the invention, the mixed cement is a mixture of 42.5 grade low-heat cement and 42.5 grade sulfoaluminate cement in a mass ratio of 9.2:0.8.

[0030] In this embodiment of the invention, the particle size of the fly ash microspheres is distributed between 0.5 and 4 μm, and the water requirement ratio is 88%.

[0031] In this embodiment of the invention, the specific surface area of ​​the mineral powder is 678 m². 2 / kg, with an activity index of 105% after 28 days.

[0032] In this embodiment of the invention, the SiO2 content in the silica fume is greater than 93%, and the specific surface area is 23000 m². 2 / kg.

[0033] In this embodiment of the invention, the fine aggregate 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 0-4.75 mm at a mass ratio of 2:8; the apparent density of the fine aggregate is 2525 kg / m³. 3 The bulk density is 1710 kg / m³. 3 It has a fineness modulus of 2.5 and a mud content of 2.1%.

[0034] In this embodiment of the invention, the coarse aggregate is continuously graded crushed stone; the particle size of the coarse aggregate is distributed between 5 and 10 mm, the mud content is 0.7%, the crushing value is 5.2%, and the apparent density is 2782 kg / m³. 3 The bulk density is 1605 kg / m³. 3 .

[0035] In this embodiment of the invention, the water-reducing agent is a polycarboxylate high-performance water-reducing agent with a water reduction rate greater than 30%; the defoamer is a polyether defoamer with a viscosity of 800-1500 mPa·s and a molecular weight of 3000-5000; the nano-SiO2 has a particle size of 30 nm and a solid content ≥99%.

[0036] Example 1

[0037] As a preferred embodiment of the present invention, the high-performance airtight concrete disclosed in this embodiment has the specific composition shown in Table 1.

[0038] Table 1 Concrete mix design table for Example 1

[0039] Raw material name mass ratio kg / m 3 ]] Cement 461 Fly ash microbead 126 Mineral powder 168 Silica fume 84 Fine aggregate 774 Coarse aggregate 1114 Water 184 Water reducing agent 2.1 Defoaming agent 1.68 nano-SiO2 8.38

[0040] The high-performance airtight concrete of this embodiment is prepared according to the mass ratio of each raw material in Table 1, including the following steps:

[0041] Step 1: Preparation of modified fly ash microspheres: Fly ash microspheres (15.084 kg / m³) 3 HCl solution was added to the mixture, with a mass percentage of fly ash microspheres to HCl solution of 16:84 and a concentration of HCl solution of 3 mol / L. After stirring with a glass rod, the mixture was sealed and placed in an ultrasonic disperser for ultrasonic dispersion for 10 min. Then, it was placed in a magnetic stirrer for magnetic stirring for 4 h. After stirring, the mixture was quickly centrifuged and washed until the pH of the supernatant was neutral. Subsequently, it was placed in a 70℃ oven and dried for 2 days to obtain modified fly ash microspheres.

[0042] Step 2: Preparation of nano-SiO2-fly ash microsphere suspension: Weigh out 8.38 kg / m³ of the suspension. 3 The nano-SiO2 was prepared for later use, and then 1.8 times the mass of the modified fly ash microspheres (15.084 kg / m³) were weighed out. 3 ) and water (69.554 kg / m³) which is 8.3 times the mass of nano-SiO2. 3 Nano-SiO2 was added to water and ultrasonically dispersed for 5 min, then modified fly ash microspheres were added and ultrasonically dispersed for 5 min to obtain a nano-SiO2-fly ash microsphere suspension.

[0043] Step 3: Weigh out cement (461 kg / m³) 3 ), fly ash microspheres ((126-15.084=110.916)kg / m 3 ), mineral powder (168kg / m 3 ), silica fume (84kg / m 3 ), fine aggregate (774kg / m³) 3 ), coarse aggregate (1114kg / m³) 3 ), water ((184-69.554=114.446)kg / m 3 ), water-reducing agent (2.1kg / m³) 3 ) and defoamer (1.68kg / m 3 )spare;

[0044] Step 4: Mix the weighed cement, fly ash microspheres, mineral powder, silica fume and defoamer from Step 3 evenly; then add the weighed coarse aggregate and fine aggregate and continue mixing to obtain the mixed dry material;

[0045] Step 5: After thoroughly mixing the water-reducing agent and water weighed in Step 3, stir. Then add the nano-SiO2-fly ash microsphere suspension prepared in Step 2 and continue stirring until uniform to obtain the mixture.

[0046] Step 6: Pour the mixture into a mold, vibrate to compact it, and then cover it with a film for curing in an environment of 18℃~22℃. After the mixture has hardened, high-performance airtight concrete is obtained.

[0047] Example 2

[0048] As a preferred embodiment of the present invention, the high-performance airtight concrete disclosed in this embodiment has the specific composition shown in Table 2.

[0049] Table 2 Concrete mix design table for Example 2

[0050]

[0051]

[0052] The high-performance airtight concrete of this embodiment is prepared according to the mass ratio of each raw material in Table 2, including the following steps:

[0053] Step 1: Preparation of modified fly ash microspheres: Fly ash microspheres (30.168 kg / m³) 3 HCl solution was added to the mixture, with a mass percentage of fly ash microspheres to HCl solution of 16:84 and a concentration of HCl solution of 3 mol / L. After stirring with a glass rod, the mixture was sealed and placed in an ultrasonic disperser for ultrasonic dispersion for 10 min. Then, it was placed in a magnetic stirrer for magnetic stirring for 4 h. After stirring, the mixture was quickly centrifuged and washed until the pH of the supernatant was neutral. Subsequently, it was placed in a 70℃ oven and dried for 2 days to obtain modified fly ash microspheres.

[0054] Step 2: Preparation of nano-SiO2-fly ash microsphere suspension: Weigh out 16.76 kg / m³ of the suspension. 3 The nano-SiO2 was prepared for later use, and then 1.8 times the mass of the nano-SiO2 was weighed out, along with 30.168 kg / m³ of modified fly ash microspheres. 3 ) and water (139.108 kg / m³) which is 8.3 times the mass of nano-SiO2. 3 Nano-SiO2 was added to water and ultrasonically dispersed for 5 min, then modified fly ash microspheres were added and ultrasonically dispersed for 5 min to obtain a nano-SiO2-fly ash microsphere suspension.

[0055] Step 3: Weigh out cement (461 kg / m³) 3 ), fly ash microspheres ((126-30.168=95.832)kg / m³ 3 ), mineral powder (168kg / m 3), silica fume (84kg / m 3 ), fine aggregate (774kg / m³) 3 ), coarse aggregate (1114kg / m³) 3 ), water ((184-139.108=44.892)kg / m 3 ), water-reducing agent (2.1kg / m³) 3 ) and defoamer (1.68kg / m 3 )spare;

[0056] Step 4: Mix the weighed cement, fly ash microspheres, mineral powder, silica fume and defoamer from Step 3 evenly; then add the weighed coarse aggregate and fine aggregate and continue mixing to obtain the mixed dry material;

[0057] Step 5: After thoroughly mixing the water-reducing agent and water weighed in Step 3, stir, then add the nano-SiO2-fly ash microsphere suspension prepared in Step 2 and continue stirring until uniform to obtain the mixture.

[0058] Step 6: Pour the mixture into a mold, vibrate to compact it, and then cover it with a film for curing in an environment of 18℃~22℃. After the mixture has hardened, high-performance airtight concrete is obtained.

[0059] Example 3

[0060] As a preferred embodiment of the present invention, the high-performance airtight concrete disclosed in this embodiment has the specific composition shown in Table 3.

[0061] Table 3 Concrete mix design table for Example 3

[0062] Raw material name mass ratio kg / m 3 ]] Cement 444 Fly ash microbead 121 Mineral powder 162 Silica fume 81 Fine aggregate 806 Coarse aggregate 1160 Water 178 Water reducing agent 2.02 Defoaming agent 1.62 nano-SiO2 8.08

[0063] The high-performance airtight concrete of this embodiment is prepared according to the mass ratio of each raw material in Table 3, including the following steps:

[0064] Step 1: Preparation of modified fly ash microspheres: Fly ash microspheres (14.544 kg / m³) 3 HCl solution was added to the mixture, with a mass percentage of fly ash microspheres to HCl solution of 16:84 and a concentration of HCl solution of 3 mol / L. After stirring with a glass rod, the mixture was sealed and placed in an ultrasonic disperser for ultrasonic dispersion for 10 min. Then, it was placed in a magnetic stirrer for magnetic stirring for 4 h. After stirring, the mixture was quickly centrifuged and washed until the pH of the supernatant was neutral. Subsequently, it was placed in a 70℃ oven for drying for 2 days to obtain modified fly ash microspheres.

[0065] Step 2: Preparation of nano-SiO2-fly ash microsphere suspension: Weigh out 8.08 kg / m³ of the suspension. 3The nano-SiO2 was prepared for later use, and then 1.8 times the mass of the nano-SiO2 was weighed out, along with 14.544 kg / m³ of modified fly ash microspheres. 3 ) and water (67.064 kg / m³) which is 8.3 times the mass of nano-SiO2. 3 Nano-SiO2 was added to water and ultrasonically dispersed for 5 min, then modified fly ash microspheres were added and ultrasonically dispersed for 5 min to obtain a nano-SiO2-fly ash microsphere suspension.

[0066] Step 3: Weigh out cement (444 kg / m³) separately. 3 ), fly ash microspheres ((121-14.544=106.456)kg / m³ 3 ), mineral powder (162kg / m 3 ), silica fume (81kg / m 3 ), fine aggregate (806kg / m 3 ), coarse aggregate (1160kg / m³) 3 ), water ((178-67.064=110.936)kg / m 3 ), water-reducing agent (2.02kg / m³) 3 ) and defoamer (1.62kg / m 3 )spare;

[0067] Step 4: Mix the weighed cement, fly ash microspheres, mineral powder, silica fume and defoamer from Step 3 evenly; then add the weighed coarse aggregate and fine aggregate and continue mixing to obtain the mixed dry material;

[0068] Step 5: After thoroughly mixing the water-reducing agent and water weighed in Step 3, stir. Then add the nano-SiO2-fly ash microsphere suspension prepared in Step 2 and continue stirring until uniform to obtain the mixture.

[0069] Step 6: Pour the mixture into a mold, vibrate to compact it, and then cover it with a film for curing in an environment of 18℃~22℃. After the mixture has hardened, high-performance airtight concrete is obtained.

[0070] Example 4

[0071] As a preferred embodiment of the present invention, the high-performance airtight concrete disclosed in this embodiment has the specific composition shown in Table 4.

[0072] Table 4 Concrete Batching Table for Example 4

[0073] Raw material name mass ratio kg / m 3 ]] Cement 444 Fly ash microbead 121 Mineral powder 162 Silica fume 81 Fine aggregate 806 Coarse aggregate 1160 Water 178 Water reducing agent 2.02 Defoaming agent 1.62 nano-SiO2 16.16

[0074] The high-performance airtight concrete of this embodiment is prepared according to the mass ratio of each raw material in Table 4, including the following steps:

[0075] Step 1: Preparation of modified fly ash microspheres: Fly ash microspheres (29.088 kg / m³) 3 HCl solution was added to the mixture, with a mass percentage of fly ash microspheres to HCl solution of 16:84 and a concentration of HCl solution of 3 mol / L. After stirring with a glass rod, the mixture was sealed and placed in an ultrasonic disperser for ultrasonic dispersion for 10 min. Then, it was placed in a magnetic stirrer for magnetic stirring for 4 h. After stirring, the mixture was quickly centrifuged and washed until the pH of the supernatant was neutral. Subsequently, it was placed in a 70℃ oven and dried for 2 days to obtain modified fly ash microspheres.

[0076] Step 2: Preparation of nano-SiO2-fly ash microsphere suspension: Weigh 16.16 kg / m³ 3 The nano-SiO2 was prepared for later use, and then 1.8 times the mass of the nano-SiO2 was weighed out, along with 29.088 kg / m³ of modified fly ash microspheres. 3 ) and water (134.128 kg / m³) which is 8.3 times the mass of nano-SiO2. 3 Nano-SiO2 was added to water and ultrasonically dispersed for 5 min, then modified fly ash microspheres were added and ultrasonically dispersed for 5 min to obtain a nano-SiO2-fly ash microsphere suspension.

[0077] Step 3: Weigh out cement (444 kg / m³) separately. 3 ), fly ash microspheres ((121-29.088=91.912)kg / m 3 ), mineral powder (162kg / m 3 ), silica fume (81kg / m 3 ), fine aggregate (806kg / m 3 ), coarse aggregate (1160kg / m³) 3 ), water ((178-134.128=43.872)kg / m 3 ), water-reducing agent (2.02kg / m³) 3 ) and defoamer (1.62kg / m 3 )spare;

[0078] Step 4: Mix the weighed cement, fly ash microspheres, mineral powder, silica fume and defoamer from Step 3 evenly; then add the weighed coarse aggregate and fine aggregate and continue mixing to obtain the mixed dry material;

[0079] Step 5: After thoroughly mixing the water-reducing agent and water weighed in Step 3, stir. Then add the nano-SiO2-fly ash microsphere suspension prepared in Step 2 and continue stirring until uniform to obtain the mixture.

[0080] Step 6: Pour the mixture into a mold, vibrate to compact it, and then cover it with a film for curing in an environment of 18℃~22℃. After the mixture has hardened, high-performance airtight concrete is obtained.

[0081] Comparative Example 1

[0082] The concrete used in this comparison was the same as in Example 1, except that ordinary Portland cement (PO42.5 cement) was used instead of mixed cement.

[0083] Comparative Example 2

[0084] The concrete used in this comparison was the same as in Example 2, except that ordinary Portland cement (PO42.5 cement) was used instead of mixed cement.

[0085] Comparative Example 3

[0086] The concrete used in this comparison was the same as in Example 3, except that ordinary Portland cement (PO42.5 cement) was used instead of mixed cement.

[0087] Comparative Example 4

[0088] The concrete used in this comparison was the same as in Example 4, except that ordinary Portland cement (PO42.5 cement) was used instead of mixed cement.

[0089] Comparative Example 5

[0090] The concrete used in this comparison was identical to that in Example 1, except that it did not contain nano-SiO2—fly ash microsphere suspension and nano-SiO2.

[0091] Comparative Example 6

[0092] The concrete used in this comparison was identical to that in Example 3, except that it did not contain nano-SiO2—fly ash microsphere suspension and nano-SiO2.

[0093] Comparative Example 7

[0094] The concrete used in this comparison was identical to that in Example 4, except that nano-SiO2 was directly added (i.e., no nano-SiO2-fly ash microsphere suspension was prepared and added).

[0095] Test case

[0096] The concrete samples from Examples 1-4 and Comparative Examples 1-4 were cured using the following method: standard curing was performed for 28 days according to GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". After curing, some specimens were tested; some specimens were further cured for another 28 days before testing; and the remaining specimens were transferred to a vacuum curing chamber and cured for another 28 days at 10000Pa before testing.

[0097] After the test blocks used for the gas permeability test have reached the corresponding curing age, they must be cut, sealed, and dried in accordance with the standard JC / T2758-2023 "Test Method for Gas Permeability Performance of Concrete" before the test is carried out.

[0098] (1) Compressive strength test: The compressive strength of concrete specimens under different curing conditions was tested according to GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0099] (2) Gas permeability test: Gas permeability test was conducted on concrete specimens under different curing conditions according to JC / T2758-2023 "Test Method for Gas Permeability Performance of Concrete". 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.

[0100] The experimental results are shown in Table 5.

[0101] Table 5 Experimental Data

[0102]

[0103]

[0104] (1) As shown in Table 5, by comparing Examples 1-4, it can be seen that concrete in each component range has better mechanical properties and gas penetration resistance under different curing methods; and the overall performance of the specimens after vacuum curing for 28 days is still improving, but is significantly lower than that of concrete specimens after standard curing for 56 days.

[0105] (2) As shown in Table 5, by comparing Examples 1-4 and Comparative Examples 1-4, it can be seen that under different curing methods and ages, the overall performance of concrete using mixed cement is better than that of ordinary Portland cement. In particular, under long-term curing, low-heat cement can significantly improve the compressive strength and air tightness of concrete. After standard curing for 56 days, Example 2 has the best overall performance, with a compressive strength of 133.7 MPa and a gas permeability coefficient of 0.01 × 10⁻⁶. -18 m 2 Because concrete loses moisture under vacuum curing, the hydration rate decreases and the pore structure changes. A comparison showed that the gas permeability coefficient of Comparative Examples 1-4 did not decrease significantly compared to standard curing for 28 days, and even increased in some groups. However, this phenomenon was not observed in the Examples. This indicates that concrete prepared with low-heat cement is more adaptable to the vacuum environment and has better airtightness.

[0106] (3) As shown in Table 5, by comparing Examples 1, 2 and Comparative Example 5, and Examples 3, 4 and Comparative Example 6, it can be seen that under different curing methods, the incorporation of nano-SiO2-fly ash microsphere suspension greatly improves the compressive strength and gas permeability resistance of the matrix, and this improvement increases with the increase of the dosage. This is because the adsorption of nano-SiO2 on the surface of fly ash microspheres improves the dispersion of nano-SiO2 in the concrete matrix, allowing nano-SiO2 to better exert its nano-filling effect, chemical activity, crystal nucleation effect, and optimize the structure of the interface transition zone. Under the synergistic effect with the defoaming component, the channels available for gas transmission are reduced, and the gas permeability coefficient is significantly reduced.

[0107] (4) As shown in Table 5, by comparing Example 4 and Comparative Example 7, it can be seen that compared with directly incorporating nano-SiO2 into the concrete matrix, encapsulating nano-SiO2 particles onto the carrier material and acting on the concrete can improve the dispersibility of SiO2, weaken its encapsulation effect on cement, promote the cement hydration process, facilitate the increase of the compressive strength of the matrix in the later stage and the refinement of the pore structure, and improve the gas permeability resistance of concrete.

[0108] In summary, the high-performance airtight concrete prepared by this invention improves the internal pore structure of the concrete, reduces gas permeability, and enhances durability through the synergistic effect of dense reinforcing powder, defoamer, and pre-dispersed nano-SiO2 from fly ash microspheres. Furthermore, the combined use of low-heat cement and sulfoaluminate cement significantly optimizes the workability and stability of the concrete, improves the dispersion stability of mineral admixtures and additives, effectively increases the density and crack resistance of the concrete matrix, and enhances its sealing performance, enabling the concrete to maintain excellent mechanical properties and airtightness even in a vacuum environment.

[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 high-performance airtight concrete, characterized in that, The following raw materials are included per cubic meter of concrete: 444~461 kg / m³ of mixed cement. 3 Fly ash microspheres: 121~126 kg / m³ 3 Mineral powder 162~168kg / m³ 3 Silica fume 81~84kg / m³ 3 Fine aggregate 774~806kg / m³ 3 Coarse aggregate 1114~1160kg / m³ 3 Water 178~184kg / m³ 3 Water-reducing agent 2.02~2.1kg / m³ 3 Defoamer 1.62~1.68kg / m³ 3 Nano-SiO2 8.08~16.76kg / m 3 ; The method for preparing high-performance airtight concrete includes the following steps: Step 1: Preparation of modified fly ash microspheres: Add HCl solution to fly ash microspheres, stir and seal, ultrasonically disperse for 5-15 min, then place under magnetic stirring for 3-4 h. After stirring, quickly centrifuge and wash until the pH of the supernatant is neutral, then place in a 70℃ oven to dry for 1.5-3 days to obtain modified fly ash microspheres. Step 2: Preparation of nano-SiO2-fly ash microsphere suspension: Weigh nano-SiO2 according to the mass ratio for later use. Weigh modified fly ash microspheres at a mass ratio of 1.5 to 2 times that of nano-SiO2 and water at a mass ratio of 8 to 8.5 times that of nano-SiO2. Add nano-SiO2 to water and ultrasonically disperse for 3 to 8 minutes. Then add modified fly ash microspheres and ultrasonically disperse for 3 to 8 minutes to obtain nano-SiO2-fly ash microsphere suspension. Step 3: Weigh out the mixed cement, fly ash microspheres, mineral powder, silica fume, fine aggregate, coarse aggregate, water, water-reducing agent, and defoamer according to the mass ratio for later use. The mass of fly ash microspheres is the total mass of fly ash microspheres minus the mass of fly ash microspheres used to prepare the nano-SiO2-fly ash microsphere suspension in Step 2. The mass of water is the total mass of water minus the mass of water used to prepare the nano-SiO2-fly ash microsphere suspension in Step 2. Step 4: Mix the weighed cement, fly ash microspheres, mineral powder, silica fume and defoamer from Step 3 evenly; then add the weighed coarse aggregate and fine aggregate and continue mixing to obtain the mixed dry material; Step 5: After thoroughly mixing the water-reducing agent and water weighed in Step 3, pour the mixture into the dry material mixture and stir. Then add the nano-SiO2-fly ash microsphere suspension prepared in Step 2 and continue stirring until uniform to obtain the mixture. Step 6: Pour the mixture into the mold, vibrate to compact it, and then cover it with a film for curing in an environment of 18℃~22℃. After the mixture has hardened, high-performance airtight concrete is obtained.

2. The high-performance airtight concrete according to claim 1, characterized in that, The mixed cement is a mixture of 42.5 grade low-heat cement and 42.5 grade sulfoaluminate cement in a mass ratio of 6~10:0.5~1.

2.

3. The high-performance airtight concrete according to claim 2, characterized in that, The mixed cement is a mixture of 42.5 grade low-heat cement and 42.5 grade sulfoaluminate cement in a mass ratio of 9.2:0.

8.

4. The high-performance airtight concrete according to claim 1, characterized in that, The fly ash microspheres have a particle size distribution between 0.5 and 4 μm and a water requirement ratio of 88%.

5. The high-performance airtight concrete according to claim 1, characterized in that, The specific surface area of ​​the mineral powder is 678 m². 2 / kg, with an activity index of 105% after 28 days.

6. The high-performance airtight concrete according to claim 1, characterized in that, The silica fume contains more than 93% SiO2 and has a specific surface area of ​​23,000 m². 2 / kg.

7. The high-performance airtight concrete according to claim 1, characterized in that, The fine aggregate is a Zone II sand mixture consisting of river sand with a particle size of 0-1.18 mm and manufactured sand with a particle size of 0-4.75 mm, with the river sand and manufactured sand mixed at a mass ratio of 2:8; the apparent density of the fine aggregate is 2525 kg / m³. 3 The bulk density is 1710 kg / m³. 3 It has a fineness modulus of 2.5 and a mud content of 2.1%.

8. The high-performance airtight concrete according to claim 1, characterized in that, The coarse aggregate is continuously graded crushed stone; the particle size distribution of the coarse aggregate is between 5 and 10 mm, the mud content is 0.7%, the crushing value is 5.2%, and the apparent density is 2782 kg / m³. 3 The bulk density is 1605 kg / m³. 3 .

9. The high-performance airtight 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 defoamer is a polyether defoamer with a viscosity of 800~1500 mPa·s and a molecular weight of 3000~5000.

10. A method for preparing high-performance airtight concrete according to any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1: Preparation of modified fly ash microspheres: Add HCl solution to fly ash microspheres, stir and seal, ultrasonically disperse for 5-15 min, then place under magnetic stirring for 3-4 h. After stirring, quickly centrifuge and wash until the pH of the supernatant is neutral, then place in a 70℃ oven to dry for 1.5-3 days to obtain modified fly ash microspheres. Step 2: Preparation of nano-SiO2-fly ash microsphere suspension: Weigh nano-SiO2 according to the mass ratio for later use. Weigh modified fly ash microspheres at a mass ratio of 1.5 to 2 times that of nano-SiO2 and water at a mass ratio of 8 to 8.5 times that of nano-SiO2. Add nano-SiO2 to water and ultrasonically disperse for 3 to 8 minutes. Then add modified fly ash microspheres and ultrasonically disperse for 3 to 8 minutes to obtain nano-SiO2-fly ash microsphere suspension. Step 3: Weigh out the mixed cement, fly ash microspheres, mineral powder, silica fume, fine aggregate, coarse aggregate, water, water-reducing agent, and defoamer according to the mass ratio for later use. The mass of fly ash microspheres is the total mass of fly ash microspheres minus the mass of fly ash microspheres used to prepare the nano-SiO2-fly ash microsphere suspension in Step 2. The mass of water is the total mass of water minus the mass of water used to prepare the nano-SiO2-fly ash microsphere suspension in Step 2. Step 4: Mix the weighed cement, fly ash microspheres, mineral powder, silica fume and defoamer from Step 3 evenly; then add the weighed coarse aggregate and fine aggregate and continue mixing to obtain the mixed dry material; Step 5: After thoroughly mixing the water-reducing agent and water weighed in Step 3, pour the mixture into the dry material mixture and stir. Then add the nano-SiO2-fly ash microsphere suspension prepared in Step 2 and continue stirring until uniform to obtain the mixture. Step 6: Pour the mixture into the mold, vibrate to compact it, and then cover it with a film for curing in an environment of 18℃~22℃. After the mixture has hardened, high-performance airtight concrete is obtained.

11. The method for preparing high-performance airtight concrete according to claim 10, characterized in that, In step 1, the mass percentage of fly ash microspheres to HCl solution is 15~20:80~85, and the concentration of HCl solution is 3mol / L.

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