A method for improving the frost resistance of concrete by multi-stage pressure reduction

Abstract

The application discloses a method for improving the frost resistance of concrete by multi-stage pressure reduction, and belongs to the technical field of improving the frost resistance of concrete materials. The method specifically comprises the following steps: immediately performing multi-stage pressure reduction on the concrete after the concrete is poured, taking out the concrete after initial setting and normally maintaining the concrete, and spontaneously and uniformly generating a large number of micro-nano bubbles in the concrete, wherein the average diameter of the bubbles is less than 50 microns, and different diameters of the micro-nano bubbles can be controlled by setting different air pressures. The application skillfully utilizes the characteristics that the solubility of the gas in the fresh concrete decreases with the decrease of the air pressure, realizes the generation and control of the micro-nano bubbles in the concrete, and improves the frost resistance of the concrete. The micro-nano bubbles introduced in the application have high stability and are easy to control, can efficiently and durably play a role in the concrete, and are especially suitable for the working conditions in special environments such as high altitudes, which cannot be realized by chemical admixtures, and can improve the frost resistance of the concrete in special environments.

Description

Technical Field

[0001] This invention belongs to the field of concrete material freeze-thaw resistance improvement technology, specifically relating to a multi-stage pressure reduction method for improving the freeze-thaw resistance of concrete. Background Technology

[0002] my country's construction industry is experiencing rapid development, with infrastructure construction becoming the main battleground. In some regions of my country, such as cold-region areas, harsh environments characterized by low air pressure, large temperature differences, extreme cold, and high intensity of heat pose significant durability challenges to concrete structures, particularly in high-altitude areas. These conditions result in widespread freeze-thaw spalling, with frequent and extensive deterioration, sometimes even jeopardizing structural safety. Improving concrete forming quality is an effective way to address the deterioration problem of concrete structures in cold regions.

[0003] Currently, for concrete structures requiring high frost resistance, chemical air-entraining agents are often added during construction to introduce beneficial air bubbles into the concrete, optimizing the internal pore size and improving its frost resistance. It is worth noting that in some regions of my country, especially in high-altitude environments, low air pressure and low temperatures can increase the surface tension of air bubbles, reducing their stability and significantly decreasing or even eliminating the air-entraining effect of the air-entraining agent. Furthermore, the addition of air-entraining agents can introduce other substances, altering the hydration characteristics of the concrete itself. Excessive air-entraining agents can lead to a loss of concrete strength, affecting the service life of the concrete structure.

[0004] Recently, the application of micro- and nanomaterials in concrete, as a method to improve concrete performance and save energy, has brought many opportunities and challenges to the construction industry. Micro- and nanobubbles, as a type of micro- and nanomaterial, refer to ultra-small bubbles with diameters between 10 nm and 50 μm. They possess physical and chemical properties not found in conventional bubbles, attracting widespread attention in the concrete field. Research has shown that replacing tap water with micro- and nanobubble water can accelerate the cement hydration process of cement-based materials and effectively improve the mechanical properties of concrete. Simultaneously, the introduction of micro- and nanobubbles reduces the water absorption rate and water penetration depth of concrete, decreases the pore size of concrete, and strengthens the connection between cement paste and aggregate, significantly enhancing the frost resistance of concrete.

[0005] Methods for manufacturing micro / nanobubbles include pressurized dissolution, microporous aeration, hydraulic cavitation, and electrode electrolysis. Currently, the main method for introducing micro / nanobubbles into concrete construction is to replace tap water used for mixing with micro / nanobubble water. It is worth noting that during concrete mixing, the micro / nanobubbles introduced undergo large-scale collisions due to intense movement, leading to the collapse and failure of a large number of micro / nanobubbles. This hinders their efficient functioning in the later stages, and the improvement in concrete's freeze-thaw resistance cannot be effectively controlled or predicted. Furthermore, the micro / nanobubble water introduced into the concrete mixture contains some large-diameter micro / nanobubbles (generally 50μm-100μm). These large-diameter bubbles significantly reduce the effectiveness of improving concrete performance and are prone to floating and bursting after being added to concrete. The stability and efficiency of micro / nanobubbles in concrete need further improvement.

[0006] Among the existing micro-nano bubble generation processes, the pressurized dissolved air method has received more attention and research due to the small size and large number of microbubbles generated. The pressurized dissolved air method involves dissolving air in water under high pressure to form supersaturated dissolved air water. Subsequently, the pressure is reduced, causing the solubility of air in water to decrease and precipitate in the form of microbubbles. In the field of concrete, the application of this method still faces many challenges. For example, there are two problems in the pressurization stage: (1) If the mixing water is pressurized directly, the treated mixing water is in a state of external stirring and dissolution during the mixing process, generating extremely unstable microbubbles, which expand, gather, merge and break in large quantities; (2) If the fresh concrete is pressurized directly, the concrete strength is subjected to strong external extrusion while developing, which easily generates microcracks and endangers the quality of concrete. It is worth mentioning that because there is a large pressure difference between the pressurization process and the depressurization process, the larger the pressure difference, the larger the diameter of the micro-nano bubbles generated. Therefore, the bubble size generated by the conventional dissolved air release method is 50μm-200μm. The effect of bubbles of this size on improving the durability of concrete is limited, and if they are too large, it may even be detrimental.

[0007] Therefore, in order to reduce the loss and failure behavior during the introduction of micro- and nano-bubbles into concrete, it is urgent to design a convenient, effective, economical and reliable process for introducing micro- and nano-bubbles into concrete to stably and efficiently improve the freeze-thaw resistance of concrete. Summary of the Invention

[0008] To address the aforementioned shortcomings of existing technologies, this invention provides a multi-stage decompression method for improving the freeze-thaw resistance of concrete. This invention cleverly utilizes the decompression and leaching characteristics of dissolved gases within fresh concrete and innovatively employs a two-stage decompression process to effectively optimize the internal pore size of the concrete and improve its freeze-thaw resistance. The micro-nano bubbles introduced in this invention exhibit high stability, are easily controlled, and can function efficiently and persistently within the concrete.

[0009] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows:

[0010] A method for improving the freeze-thaw resistance of concrete through multi-stage pressure reduction includes the following steps:

[0011] Before pouring, the mixing water is exposed to a designed gaseous environment for 24 hours. This gas has a solubility of 30 mL / L-1000 mL / L, does not react violently with the concrete components, and its impact on the final result is controllable. This gas includes, but is not limited to, CO2, C2H2, O2, and air. The specific process is as follows:

[0012] (1) Preparation of concrete mixture;

[0013] (2) Perform segmented pressure reduction treatment on it.

[0014] Furthermore, the segmented depressurization process is carried out in a closed environment and includes at least two depressurization processes.

[0015] Furthermore, the constructed low-pressure treatment system (which includes, but is not limited to, a sealable environment, an E8080 temperature controller, a TX012-MFR humidity controller, and a 2BV6161 water ring vacuum device) has good sealing performance and can maintain the set low-pressure conditions within 24 hours without significant fluctuations.

[0016] Furthermore, the system should have a wide range of pressure regulation with high precision. It should also include temperature and humidity control devices to maintain consistent temperature and humidity inside and outside the system.

[0017] Furthermore, ordinary concrete was poured according to the mix proportions in the article "Compressive Dynamic Properties of Ordinary Concrete and Lightweight Aggregate Concrete," but not limited to those in the article "Compressive Dynamic Properties of Ordinary Concrete and Lightweight Aggregate Concrete," with an appropriate amount of concrete thickener added. The concrete mixture underwent a two-stage decompression treatment. The purpose of using the concrete thickener was to increase the plastic viscosity of the fresh concrete, thereby constraining the expansion and enlargement of the large air bubbles during the decompression process and limiting the diameter changes of the large air bubbles.

[0018] Furthermore, the specific process of the two-stage pressure reduction treatment is as follows:

[0019] S1, First stage of voltage reduction processing

[0020] The system pressure was reduced to 0.7–0.8P0, where P0 is the ambient air pressure during concrete pouring, and maintained for 30–50 minutes. The gas solubility formula was used: C = K × P, where C represents solubility; K represents the Henry's constant, which depends on the characteristics of the system and temperature (K decreases with increasing temperature); and P represents the partial pressure of the gas. It is noteworthy that the size of the dissolved micro / nano bubbles increases with increasing pressure difference. Within the 0–0.2P range, the rate of pressure change is relatively small, and the bubble size remains below 50 μm. When the pressure difference is greater than 0.2P, the increase in pressure difference leads to a rapid increase in bubble size, reaching over 100 μm.

[0021] Therefore, when the ambient air pressure is reduced to 0.7–0.8 P, the decrease in gas solubility causes some gas to spontaneously precipitate as micro-nano bubbles with a diameter of less than 50 μm and distribute evenly inside the concrete. The temperature and humidity within the closed system are set according to curing requirements to ensure the initial formation of concrete properties. After 30 minutes of concrete hydration, the viscous resistance increases, which can initially form a restraining effect, preventing the size of the dissolved micro-nano bubbles from continuing to expand due to further decreases in air pressure.

[0022] S2, Second Stage Voltage Reduction Process

[0023] After 30 minutes of hydration, the viscous resistance formed in the concrete is sufficient to constrain the size change of the dissolved micro- and nano-bubbles. As the gas pressure continues to decrease, the bubbles continue to dissolve due to the viscous force, and their size remains below 30 μm. Based on the above principle, the gas pressure in the system can be adjusted according to the requirements of frost resistance to control the number and size of dissolved micro- and nano-bubbles in the concrete.

[0024] Furthermore, the system pressure in the first stage of depressurization was 0.8P0 and maintained for 30 minutes.

[0025] Furthermore, the pressure in the second stage of depressurization is 0.1–0.65P0.

[0026] Furthermore, it also includes step (3): after the concrete has initially set, it is removed and then routinely cured.

[0027] The beneficial effects of this invention are:

[0028] This invention utilizes the depressurization leaching characteristics of dissolved gases within fresh concrete to generate and uniformly distribute micro- and nano-bubbles within the concrete, optimizing the internal pore size and improving its freeze-thaw resistance. The depressurization leaching method offers advantages over directly adding microbubble water in the following four aspects:

[0029] 1. This process is simple to operate, and micro-nano bubbles are spontaneously generated in situ in the concrete, avoiding the problems of micro-nano bubble merging, loss and failure caused by long-distance transportation and collisions during the mixing process. It is economical and reliable.

[0030] 2. The micro-nano bubbles generated by this process are uniformly distributed inside the concrete, with a maximum pore size of less than 50μm.

[0031] 3. The presence of surfactants and ions within the concrete provides dual stabilizing effects, enhancing the stability of micro- and nano-bubbles and ensuring their efficient and sustained performance.

[0032] 4. By setting up a two-stage pressure reduction process, the amount and size of micro-nano bubbles introduced into the concrete can be controlled more accurately, thereby quantitatively improving the performance of the concrete. Attached Figure Description

[0033] Figure 1 This is a flowchart of the technical solution of this application;

[0034] Figure 2 The effects of different treatment methods on the pore size and pore spacing of micro-nano bubbles in concrete.

[0035] Figure 3 The effects of different treatment methods on the content of micro-nano bubbles in concrete;

[0036] Figure 4 The effects of micro-nano bubbles generated by different treatment methods on the freeze-thaw resistance of concrete;

[0037] Figure 5 The dispersion uniformity coefficient of micro-nano bubbles generated by different processing methods;

[0038] Figure 6 The pore distribution of micro- and nano-bubbles generated by different processing methods. Detailed Implementation

[0039] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0040] Example 1

[0041] A method for improving the freeze-thaw resistance of concrete through multi-stage pressure reduction includes the following steps:

[0042] (1) Construct a closed low-pressure treatment system. The system consists of a closed environment, an E8080 temperature controller, a TX012-MFR humidity controller and a 2BV6161 water ring vacuum device. The pressure control range is 1kPa to 101kPa. Within 4 hours, the internal pressure fluctuates by ±1kPa, the temperature fluctuates by ±1℃, and the humidity fluctuates by ±1%.

[0043] (2) Expose the mixing water to a CO2 environment for 24 hours before pouring.

[0044] (3) Take 150 parts of the above-treated mixing water, 360 parts of PO42.5 ordinary Portland cement, 650 parts of fine aggregate with a particle size of 0-5mm, 900 parts of coarse aggregate with a particle size of 10-20mm, 1 part of polycarboxylate superplasticizer, and 2 parts of hydroxypropyl methylcellulose HPMC concrete thickener and mix them thoroughly. Pour the freshly mixed concrete according to the process required by the standard GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" and pour it into a 100mm×100mm×100mm concrete mold. After vibration and smoothing, cover the concrete surface with plastic wrap.

[0045] (4) Place a portion of the freshly mixed concrete into a low-pressure treatment system and seal it. Set the system pressure to 0.8P0 (P0 represents atmospheric pressure 101kPa), temperature to 20℃, humidity to 95%, and maintain this pressure for 30 minutes.

[0046] (5) After the concrete has been hydrated for 30 minutes, the air pressure is reduced to 0.3P0, while other environmental conditions remain unchanged.

[0047] (6) The initial setting time of the concrete under this mix proportion was measured to be 6h. After the fresh concrete was placed in a low-pressure environment for 6-6.5h, it was taken out and placed under the standard curing conditions of 20℃ and 95% humidity. Observe whether there are any fine cracks on the concrete surface. If so, the initial setting time needs to be re-measured.

[0048] (7) Continue curing under standard curing conditions for 24 hours, demold with an air mold gun, and continue curing the demolded concrete sample to the normal age.

[0049] (8) After curing, place it in a rapid freeze-thaw test chamber to evaluate its antifreeze performance and evaluate it by the mass loss rate.

[0050] Example 2

[0051] A method for improving the freeze-thaw resistance of concrete through multi-stage pressure reduction includes the following steps:

[0052] (1) Construct a sealable low-pressure treatment system, which consists of a sealable environment, an E8080 temperature controller, a TX012-MFR humidity controller, and a 2BV6161 water ring vacuum device. The pressure control range is 1 kPa to 101 kPa. Within 24 hours, the internal pressure fluctuates by ±1 kPa, the temperature fluctuates by ±1℃, and the humidity fluctuates by ±1%.

[0053] (2) Expose the mixing water to a CO2 environment for 24 hours before pouring.

[0054] (3) Take 150 parts of the above-treated mixing water, 360 parts of PO42.5 ordinary Portland cement, 650 parts of fine aggregate with a particle size of 0-5mm, 900 parts of coarse aggregate with a particle size of 10-20mm, 1 part of polycarboxylate superplasticizer, and 2 parts of hydroxypropyl methylcellulose HPMC concrete thickener and mix them thoroughly. Pour the freshly mixed concrete according to the process required by the standard GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" and pour it into a 100mm×100mm×100mm concrete mold. After vibration and smoothing, cover the concrete surface with plastic wrap.

[0055] (4) Place a portion of the freshly mixed concrete into the low-pressure treatment system and seal it. Set the system pressure to 0.8P0 (P0 represents atmospheric pressure 101 kPa), temperature to 20°C, and humidity to 95%. Maintain this pressure for 30 minutes.

[0056] (5) After the concrete has been hydrated for 30 minutes, the air pressure is reduced to 0.65P0, while other environmental conditions remain unchanged.

[0057] (6) The initial setting time of the concrete under this mix proportion was measured to be 6h. After the fresh concrete was placed in a low-pressure environment for 6-6.5h, it was taken out and placed under the standard curing conditions of 20℃ and 95% humidity. Observe whether there are any fine cracks on the concrete surface. If so, the initial setting time needs to be re-measured.

[0058] (7) Continue curing under standard curing conditions for 24 hours, demold with an air mold gun, and continue curing the demolded concrete sample to the normal age.

[0059] (8) After curing, place it in a rapid freeze-thaw test chamber to evaluate its antifreeze performance and evaluate it by the mass loss rate.

[0060] Example 3

[0061] A method for improving the freeze-thaw resistance of concrete through multi-stage pressure reduction includes the following steps:

[0062] (1) Construct a sealable low-pressure treatment system, which consists of a sealable environment, an E8080 temperature controller, a TX012-MFR humidity controller, and a 2BV6161 water ring vacuum device. The pressure control range is 1 kPa to 101 kPa. Within 24 hours, the internal pressure fluctuates by ±1 kPa, the temperature fluctuates by ±1℃, and the humidity fluctuates by ±1%.

[0063] (2) Expose the mixing water to a CO2 environment for 24 hours before pouring.

[0064] (3) Take 150 parts of the above-treated mixing water, 360 parts of PO42.5 ordinary Portland cement, 650 parts of fine aggregate with a particle size of 0-5mm, 900 parts of coarse aggregate with a particle size of 10-20mm, 1 part of polycarboxylate superplasticizer, and 2 parts of hydroxypropyl methylcellulose HPMC concrete thickener and mix them thoroughly. Pour the freshly mixed concrete according to the process required by the standard GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" and pour it into a 100mm×100mm×100mm concrete mold. After vibration and smoothing, cover the concrete surface with plastic wrap.

[0065] (4) Place a portion of the freshly mixed concrete into a low-pressure treatment system and seal it. Set the system pressure to 0.8P0 (P0 represents atmospheric pressure 101kPa), temperature to 20℃, humidity to 95%, and maintain this pressure for 30 minutes.

[0066] (5) After the concrete has been hydrated for 30 minutes, the air pressure is reduced to 0.65P0, while other environmental conditions remain unchanged.

[0067] (6) After the concrete has been hydrated for 15 minutes, the air pressure is further reduced until it reaches 0.3P0, while other environmental conditions remain unchanged.

[0068] (7) The final and initial setting times of the concrete under this mix proportion were measured to be 6h. After the fresh concrete was placed in a low-pressure environment for 6-6.5h, it was taken out and placed under standard curing conditions of 20℃ and 95% humidity. Observe whether there are any fine cracks on the concrete surface. If so, the final and initial setting times need to be measured again.

[0069] (8) Continue curing under standard curing conditions for 24 hours, demold with an air gun, and continue curing the demolded concrete sample to the normal age.

[0070] (9) After curing, place it in a rapid freeze-thaw test chamber to evaluate its antifreeze performance and evaluate it by the mass loss rate.

[0071] Comparative Example 4

[0072] A concrete treatment method includes the following steps:

[0073] (1) Construct a sealable low-pressure treatment system, which consists of a sealable environment, an E8080 temperature controller, a TX012-MFR humidity controller, and a 2BV6161 water ring vacuum device. The pressure control range is 1 kPa to 101 kPa. Within 24 hours, the internal pressure fluctuates by ±1 kPa, the temperature fluctuates by ±1℃, and the humidity fluctuates by ±1%.

[0074] (2) Expose the mixing water to a CO2 environment for 24 hours before pouring.

[0075] (3) Take 150 parts of the above-treated mixing water, 360 parts of PO42.5 ordinary Portland cement, 650 parts of fine aggregate with a particle size of 0-5mm, 900 parts of coarse aggregate with a particle size of 10-20mm, and 2 parts of hydroxypropyl methylcellulose HPMC concrete thickener and mix them thoroughly. Pour the freshly mixed concrete according to the process required by the standard GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" and pour it into a 100mm×100mm×100mm concrete mold. After vibration and smoothing, cover the concrete surface with plastic wrap.

[0076] (4) No low-pressure treatment is applied to the fresh concrete. The system has a pressure of 1.00P0 (P0 represents atmospheric pressure 101kPa), a temperature of 20℃, and a humidity of 95%.

[0077] (5) Continue curing under standard curing conditions for 24 hours, demold with an air gun, and continue curing the demolded concrete sample to the normal age.

[0078] (6) After curing, place it in a rapid freeze-thaw test chamber to evaluate its antifreeze performance and evaluate it by the mass loss rate.

[0079] Comparative Example 5

[0080] A method for one-stage pressure reduction of concrete includes the following steps:

[0081] (1) Construct a sealable low-pressure treatment system, which consists of a sealable environment, an E8080 temperature controller, a TX012-MFR humidity controller, and a 2BV6161 water ring vacuum device. The pressure control range is 1 kPa to 101 kPa. Within 24 hours, the internal pressure fluctuates by ±1 kPa, the temperature fluctuates by ±1℃, and the humidity fluctuates by ±1%.

[0082] (2) Expose the mixing water to a CO2 environment for 24 hours before pouring.

[0083] (3) Take 150 parts of the above-treated mixing water, 360 parts of PO42.5 ordinary Portland cement, 650 parts of fine aggregate with a particle size of 0-5mm, 900 parts of coarse aggregate with a particle size of 10-20mm, 1 part of polycarboxylate superplasticizer, and 2 parts of hydroxypropyl methylcellulose HPMC concrete thickener and mix them thoroughly. Pour the freshly mixed concrete according to the process required by the standard GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" and pour it into a 100mm×100mm×100mm concrete mold. After vibration and smoothing, cover the concrete surface with plastic wrap.

[0084] (4) Place a portion of the freshly mixed concrete into the low-pressure treatment system and seal it. Set the system pressure to 0.3P0 (P0 represents atmospheric pressure 101kPa), temperature to 20℃, and humidity to 95%.

[0085] (5) The final and initial setting times of the concrete under this mix proportion were measured to be 6 hours. After the fresh concrete was placed in a low-pressure environment for 6-6.5 hours, it was taken out and placed under standard curing conditions of 20°C and 95% humidity. The concrete surface was observed to see if there were any micro-cracks. If so, the final and initial setting times needed to be measured again.

[0086] (6) Continue curing under standard curing conditions for 24 hours, demold with an air gun, and continue curing the demolded concrete sample to the normal age.

[0087] (7) After curing, place it in a rapid freeze-thaw test chamber to evaluate its antifreeze performance and evaluate it by the mass loss rate.

[0088] Experimental Example 1

[0089] The project is located in Shigatse City, Tibet Autonomous Region, a high-altitude and cold region with abundant rainfall and large diurnal temperature variations. In this water-storage environment, the water inside the pores is prone to freezing, causing severe freeze-thaw damage and endangering structural safety. The technical solution described in this invention was applied to this project, and the pore structure was tested using a rapid freeze-thaw test method and a combination of mercury intrusion porosimetry and a porosimetry analyzer. Image analysis was used to evaluate the uniformity of bubble distribution. The effectiveness of the technical solution described in this invention was analyzed, and the specific process is as follows:

[0090] During the experiment, the mass loss rate of concrete under freeze-thaw cycles was monitored, and key indicators affecting the freeze-thaw resistance of concrete—the pore size distribution and the bubble dispersion uniformity coefficient—were tested (using image recognition-binarization method, the number of bubbles was identified and recorded in each 1mm×1mm area, and the result of the maximum / minimum number was taken as the bubble distribution uniformity coefficient; the closer this value is to 1, the better the uniformity). This was to evaluate the improvement effect of different technical solutions on the freeze-thaw resistance of concrete. Concrete with added micro-nano bubble water was used as a control group. The micro-nano bubble water used was ultra-micro-nano bubble water for concrete produced by Sichuan Mykelano Bubble Technology Co., Ltd., transported from Chengdu to the construction site, and prepared according to the micro-nano bubble content in the manufacturer's instructions, so that the micro-nano bubble content introduced into the concrete was consistent with that in Example 2. The test results are shown in […]. Figures 2-4 .

[0091] like Figures 2-4As shown, Example 1 uses a two-stage pressure reduction (first stage 0.8P0, second stage 0.3P0), and Example 2 uses a two-stage pressure reduction (first stage 0.8P0, second stage 0.65P0). Compared with the method of adding micro-nano bubble water and Comparative Example 4 without low-pressure treatment, the average pore size and average pore spacing of the concrete are reduced to a certain extent, the pore structure is optimized, and the frost resistance is significantly improved.

[0092] The final pressure values ​​of Examples 1, 3, and Comparative Example 5 were all 0.3P0. The difference was that Example 1 used a two-stage pressure reduction method, Example 3 used a three-stage pressure reduction method, and Comparative Example 5 used a one-stage pressure reduction method. The pore distribution was as follows: Figure 6 As shown, direct single-stage pressure reduction, with its large pressure difference, significantly increases the number of dissolution pores with a size >50μm and decreases the number of dissolution pores with a size <50μm. However, with a multi-stage pressure reduction process, the viscous resistance of the concrete reaches a certain level after 30 minutes of hydration, at which point the micro-nano bubbles are constrained and cannot expand further. The continued reduction in pressure results in the continuous dissolution of small-sized micro-nano bubbles. The three-stage pressure reduction process produces a more ideal micro-nano bubble size distribution and more pores of the target size than the two-stage process. This is because the viscous resistance formed in the concrete after 30 minutes of hydration is insufficient to completely control the expansion of micro-nano pores under excessive pressure differences. Therefore, if the pressure value is low (pressure value <0.4P0), a multi-stage pressure reduction process is recommended for optimal results.

[0093] A comparison of Example 2 and the method of adding micro-nano bubble water shows that the pore diameter introduced by the pressure reduction leaching method is all <50μm, and has basically no effect on pores larger than 50μm. Furthermore, the bubble distribution in the concrete treated by the present application's technical solution is more uniform than that in the group treated with micro-nano bubble water. In contrast, the number of pores with a diameter less than 10μm introduced by adding micro-nano bubble water is far less than in Example 2, and there are clearly large-diameter micro-nano bubbles with a diameter of 50μm-100μm. This is because the violent collisions during the stirring process of the micro-nano bubble water cause the tiny bubbles to aggregate into larger bubbles. These bubbles are prone to rising and breaking, exhibiting poor stability, thus weakening or even eliminating the effect of enhancing the concrete's frost resistance. Therefore, the frost resistance of the concrete group treated with micro-nano bubble water is significantly inferior to that of Examples 1 and 2 treated by the present application's technical solution.

[0094] In summary, through comparison, it can be seen that the technical solution of this application can uniformly generate micro-nano bubbles inside concrete. The bubble pore size is less than 50μm, and the bubble has high stability. It can play a sustainable and efficient role in concrete, effectively improving the long-term performance of concrete structures. Especially in the extreme high-altitude service environment, it can effectively ensure the safety of engineering structures.

[0095] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the freeze-thaw resistance of concrete through multi-stage pressure reduction, characterized in that, Includes the following steps: (1) Preparation of concrete mixture; (2) Perform segmented pressure reduction treatment on it. The segmented pressure reduction treatment is a two-stage pressure reduction treatment, which is carried out in a closed environment. The specific process is as follows: S1, First stage of voltage reduction processing Reduce the system pressure to 0.7~0.8P0 and maintain it for 30~50 minutes; S2, Second Stage Voltage Reduction Process Continue to reduce the system pressure so that the final bubble size is less than 50 μm.

2. The method for improving the frost resistance of concrete through multi-stage pressure reduction according to claim 1, characterized in that, In the first stage of depressurization, the system pressure is 0.8P0 and maintained for 30 minutes.

3. The method for improving the freeze-thaw resistance of concrete through multi-stage pressure reduction according to claim 1, characterized in that, The pressure in the second stage of depressurization is 0.1~0.65P0.

4. The method for improving the frost resistance of concrete through multi-stage decompression according to any one of claims 1 to 3, characterized in that, It also includes step (3): after the concrete has initially set, remove it and then carry out routine curing.

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