Low-density corrosion-resistant air-entraining marine concrete and preparation method thereof

Abstract

The present application relates to the technical field of building materials, and particularly relates to a low-volume-density corrosion-resistant air-entraining marine concrete and a preparation method thereof.The components of the low-volume-density corrosion-resistant air-entraining marine concrete include cement, admixture, modified fly ash microbeads, water, air-entraining agent, aggregate, water reducing agent and thickening agent.The present application adopts a high-air-entraining method to reduce the volume density of the concrete, avoids the instability of performance and high cost caused by the use of light aggregate, and innovatively uses a foaming machine to optimize the size and distribution of air bubbles introduced by the air-entraining agent, and then uses nano-bubble water to introduce small closed air bubbles, and pre-treats the added fly ash microbeads to solve the problems of floating and low activity of the fly ash microbeads, and through the addition of the thickening agent, the defects of the hardened concrete are reduced, so that the present application provides a high-air-entraining low-volume-density concrete at a low cost, the strength of the concrete is maintained at a high level, and the concrete has good durability and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a low-density, corrosion-resistant, air-entrained marine concrete and its preparation method. Background Technology

[0002] Currently, reducing the density of concrete mainly relies on adding lightweight aggregates. However, the strength of hardened concrete depends primarily on the most easily damaged phase within the concrete, necessitating that the added lightweight aggregates possess high compressive strength. Selecting high-quality lightweight aggregates can improve strength, but their high price significantly increases construction costs. Most existing technologies do not prioritize cost reduction, demonstrating that current methods for achieving low concrete density using lightweight aggregates require sacrificing cost for improved performance.

[0003] Another direction for reducing concrete density is the development of high-air-entrained concrete. However, the relevant technologies for high-air-entrained concrete are constrained by the research and development of high-performance air-entraining agents. The highest air content is about 7.0%. Generally speaking, the air content is strongly correlated with the concrete density. When the air content is 7.0%, it is still difficult for the concrete density to reach the required lower level. Moreover, existing technologies focus more on exploring the impact of introducing air bubbles on concrete strength, while there are fewer technologies for improving durability.

[0004] Current research on air-entrained concrete technology focuses on the development of high-performance air-entraining agents, primarily aiming to improve concrete strength. Evaluation of air-entraining agent performance is concentrated on the performance of concrete with a 5% air content. Existing technologies lack mix design and production methods for high-air-entrained concrete with an air content exceeding 10%, i.e., concrete with lower density levels, and also lack technologies to improve the durability of high-air-entrained concrete.

[0005] To improve the durability of concrete, adding fly ash microspheres is one of the existing methods. The ball bearing effect of its glassy body is beneficial to improving the workability of high air-entrained concrete. Its filling effect and ability to bind chloride ions help to improve its erosion resistance. However, due to reasons such as floating, insufficient activity, and uneven mixing after actual addition, it cannot fully play its role and has a poor effect on improving the durability of concrete.

[0006] In summary, existing technologies for achieving low-density concrete have the following problems:

[0007] Using lightweight aggregates makes it easier to achieve lightweight and high strength, but the technology in this area depends on the quality of the lightweight aggregate materials. High-quality lightweight aggregates can effectively improve the performance of concrete, but the cost cannot be effectively controlled.

[0008] Current technologies lack research on improving the durability of high-air-entrained concrete, forcing most technologies to focus on the development of air-entraining agents. Furthermore, the characteristics of the bubbles introduced by air-entraining agents (bubble content, bubble movement state) are affected by various factors. Different bubble characteristics affect the workability of the concrete mixture, as well as the strength and durability of the resulting concrete. Therefore, the introduction of air-entraining agents not only affects the density but also has various impacts on its application performance. Currently, in the technical solutions of introducing existing air-entraining agents to achieve high air content and reduce density, the resulting concrete cannot simultaneously maintain both strength and durability; that is, it cannot guarantee that the strength remains at a high level while improving the durability of the concrete.

[0009] Therefore, how to design a scientific and reasonable concrete formula and preparation process to optimize the pore structure of hardened concrete, thereby developing a concrete with comprehensive performance of low cost, high air entrainment, low density and good durability, is precisely the problem that this field is committed to solving. Summary of the Invention

[0010] To address the problems mentioned in the background section, this invention provides a low-density, corrosion-resistant air-entrained marine concrete and its preparation method, the technical solution of which is as follows:

[0011] This low-density, corrosion-resistant, air-entraining marine concrete comprises cement, admixtures, modified fly ash microspheres, water, air-entraining agent, aggregates, water-reducing agent, and thickener.

[0012] The ball milled material is obtained by ball milling the mixture M. The ball milled material is then mixed and stirred with a first portion of water and polyvinyl alcohol dispersant to obtain the modified fly ash microspheres. The mixture M is a mixture of fly ash microspheres, anhydrous sodium silicate, and anhydrous sodium carbonate.

[0013] The diluted air-entraining agent is foamed in a foaming machine and then injected into mixture N for further foaming to obtain a foamed cementitious material. The foamed cementitious material is then mixed uniformly with aggregate, water-reducing agent, and thickener to obtain the concrete. The mixture N is a mixture of cement, admixtures, modified fly ash microspheres, and water (the third part). The diluted air-entraining agent is a mixture of air-entraining agent and water (the second part).

[0014] The total amount of water used is the sum of the amounts of the first part, the second part, and the third part, and the third part is nano-bubble water.

[0015] In some embodiments, the admixture is composed of mineral powder, fly ash, and silica fume; the aggregate is composed of sand and stone.

[0016] In some embodiments, the preparation process of modified fly ash microspheres is as follows: dried fly ash microspheres are mixed with anhydrous sodium silicate and anhydrous sodium carbonate to obtain mixture M. Mixture M is placed in a ball mill jar for ball milling to obtain a ball-milled product. The mass ratio of fly ash microspheres, anhydrous sodium silicate, and anhydrous sodium carbonate is (180-200):(3.0-4.0):(1.0-1.5). The ball-to-material ratio during the ball milling process is 10-15, and the ball milling time is 1-2 hours. The ball-milled product is dispersed in a first portion of water, and then polyvinyl alcohol dispersant is added and stirred evenly to obtain modified fly ash microspheres. The first portion of water accounts for (8-10)% of the total mass of the water, and the amount of polyvinyl alcohol dispersant is 2%-5% of the mass of the fly ash microspheres.

[0017] In some embodiments, the modified fly ash microspheres are mixed with the admixture to obtain a mixture; a second portion of water is added to the air-entraining agent to dilute it to a mass fraction of (10-15)%, and the mixture is stirred to obtain the diluted air-entraining agent solution; the diluted air-entraining agent solution is added to a cement foaming machine, and the mixture N formed by the diluted air-entraining agent solution, cement, the admixture, and the third portion of water is foamed for (1-2) min to obtain the foamed cementitious material.

[0018] In some embodiments, the third part of the water is nanobubble water obtained by foaming with a nanobubble machine. The preparation process is as follows: place the inlet and outlet pipes of the nanobubble machine in a water container, start the nanobubble machine, start timing after the air in the pipes of the nanobubble machine is purged, the jetting time is 2 to 3 minutes, then turn off the nanobubble machine and wait for the milky white bubbles to dissipate to obtain the nanobubble water.

[0019] In some embodiments, the raw material components of concrete, by weight, include: 350-400 parts cement, 60-90 parts mineral powder, 50-80 parts fly ash, 10-15 parts silica fume, 10-15 parts modified fly ash microspheres, 130-160 parts water, 680-780 parts sand, 1000-1100 parts aggregate, 0.6-1.0 parts air-entraining agent, 4-6 parts water-reducing agent, and 0.4-0.6 parts thickener.

[0020] In some embodiments, the cement is one of P·O 42.5 and P·O 52.5 cement; the mineral powder is S95 grade mineral powder; the fly ash is Class F, Grade I fly ash; the silica fume is SF94 grade silica fume with an activity index ≥105%; the fly ash microspheres meet the requirements of Grade I fly ash, with a fineness ≤12%, loss on ignition ≤3.0wt%, and 28-day activity ≥70%.

[0021] In some embodiments, the sand is manufactured sand with a fineness modulus of 1.6 to 2.2, a particle size range of 0.3 to 2.36 mm, a crushing value of <20%, and stone powder content and mud content that comply with the requirements of the "Standard for Construction Sand" (GB / T14684-2011); the stone is crushed stone, which is composed of crushed stone with a particle size of 5 mm to 10 mm and crushed stone with a particle size of 10 to 20 mm mixed in a mass ratio of 3:7, with a crushing index of less than 7% and an apparent density greater than 2600 kg / m³. 3 Furthermore, the content of needle-like and flaky gravel in it is less than 10%.

[0022] In some embodiments, the air-entraining agent has a solid content of 20% and is composed of anionic surfactant and nonionic surfactant in a mass ratio of 4:1; wherein the main component of the anionic surfactant is sodium α-alkenyl sulfonate with a solid content of 20%; the main component of the nonionic surfactant is sodium fatty alcohol polyoxyethylene ether sulfate with a solid content of 20%; the water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of 30% and a solid content of 20%; and the thickener is a cellulose ether with a viscosity of 100,000 Pa·s.

[0023] The present invention also provides a method for preparing the low-density, corrosion-resistant, air-entrained marine concrete as described above, which includes the following preparation steps:

[0024] The dried fly ash microspheres are mixed with anhydrous sodium silicate and anhydrous sodium carbonate to obtain mixture M. Mixture M is then placed in a ball mill jar for ball milling to obtain the ball-milled product. The ball-to-material ratio during the ball milling process is 10-15, and the ball milling time is 1-2 hours.

[0025] The ball-milled material was dispersed in the first part of water, and then polyvinyl alcohol dispersant was added and stirred evenly to obtain modified fly ash microspheres.

[0026] The modified fly ash microspheres are mixed with the admixture to obtain a mixture;

[0027] Add a second portion of water to the air-entraining agent to dilute it to a mass fraction of (10-15)%, stir to mix it thoroughly, and obtain the diluted air-entraining agent solution;

[0028] Place the inlet and outlet pipes of the nanobubble generator into a water container, start the nanobubble generator, and start timing after the air in the pipes of the nanobubble generator is purged. After the jetting time is 2 to 3 minutes, turn off the nanobubble generator and wait for the milky white bubbles to dissipate to obtain the nanobubble water.

[0029] Add the diluted air-entraining agent to the cement foaming machine, and perform foaming treatment (1-2) min on the mixture N formed by mixing the diluted air-entraining agent with cement, admixture, and water (part 3) to obtain the foamed cementitious material.

[0030] After the foamed cementitious material is mixed with the aggregate, water-reducing agent and thickener are added and stirred for (3-4) minutes to obtain the concrete.

[0031] Compared with existing technologies, the present invention has the following advantages:

[0032] Compared with conventional low-density marine concrete preparation processes, the present invention takes a different approach by using a high air entrainment method to reduce the density of concrete, thus avoiding the disadvantages of unstable performance and high cost caused by the use of lightweight aggregates.

[0033] Furthermore, this invention innovatively employs a foaming machine to optimize the size and distribution of air-entraining bubbles introduced by the air-entraining agent; it then uses nano-bubble water to introduce tiny, closed air bubbles; the added fly ash microspheres undergo pre-activation and dispersion pretreatment to solve problems such as fly ash microspheres floating and low activity; and through the addition of a thickener, defects after concrete hardening are reduced. This invention provides a high-air-entraining, low-density concrete at low cost, which maintains a high strength while exhibiting good durability and corrosion resistance. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The present invention also provides formulations (unit: parts by weight) for the embodiments and comparative examples shown in Table 1:

[0036] Table 1

[0037]

[0038]

[0039] Specifically, the embodiments and comparative examples and their preparation processes provided by this invention are as follows:

[0040] Example 1

[0041] The raw materials required in this embodiment are, by weight, as follows:

[0042] 350 parts cement, 90 parts mineral powder, 75 parts fly ash, 15 parts silica fume, 15 parts modified fly ash microspheres, 130 parts water, 780 parts sand, 1000 parts stone, 0.6 parts air-entraining agent, 6 parts water-reducing agent, and 0.4 parts thickener.

[0043] In this embodiment, the mechanochemical activation of fly ash microspheres was achieved by ball milling with a ball-to-material ratio of 10 and a milling time of 1 hour; the amount of polyvinyl alcohol dispersant was 2% of the fly ash microsphere content.

[0044] The method for preparing low-density, corrosion-resistant, air-entrained marine concrete in this embodiment is as follows:

[0045] (1) Preparation of modified fly ash microspheres: activation and dispersion pretreatment:

[0046] After drying the required fly ash microspheres in an oven at 100℃, they are taken out and mixed with anhydrous sodium silicate and anhydrous sodium carbonate (both industrial grade, with a sodium silicate modulus of 1.5). The mass ratio of fly ash microspheres, anhydrous sodium silicate, and anhydrous sodium carbonate is 200:4:1. The mixture is placed in a ball mill jar and activated using a ball-to-material ratio of 10 and a milling time of 1 hour. After milling, the mixture is removed.

[0047] Next, 10% of the water mass in the formula is used as pretreatment water for dispersion (i.e., 10% of the water mass in the formula, this part of water is the first part of water). Activated fly ash microspheres are added to the water, followed by polyvinyl alcohol dispersant. The amount of polyvinyl alcohol is 2% of the mass of activated fly ash microspheres. After stirring together for 1 minute, it is mixed with cement and other admixtures (mineral powder, fly ash, silica fume) to obtain the mixture.

[0048] (2) The air-entraining agent is diluted with water in the second part to a 10% mass fraction of the air-entraining agent dilution solution;

[0049] (3) Weigh the remaining third portion of water into a container. Place the inlet and outlet pipes of the nanobubble generator into the water container. Start the instrument and, after the air in the instrument's pipes is purged, start timing. Adjust the equipment's running time according to the amount of water weighed, with a jetting time of 2-3 minutes. After turning off the equipment, wait for the milky white bubbles to dissipate, then remove the nanobubble water for later use. The total amount of water used is the sum of the amounts of the first, second, and third portions of water, and the third portion of water is nanobubble water.

[0050] (4) Add the diluted air-entraining agent to the foaming machine, turn on the foaming machine, and let the diluted air-entraining agent, the mixture, and the third part of water (i.e., the nano bubble water obtained in step 3) foam the gelling material together for 1 minute. Discharge the foamed gelling material and set it aside.

[0051] (5) Add aggregates (sand and stone) to the mixer and mix for 10 seconds to disperse the sand and stone evenly. Add foaming cementitious material to the mixer, then add water-reducing agent and thickener, and mix together for 3 minutes. After the mixing is completed, low density corrosion-resistant marine concrete can be obtained.

[0052] In this embodiment, the specific selection of each raw material is as follows:

[0053] The cement in question is Runfeng P·O 42.5 grade ordinary Portland cement produced by China Resources Cement Co., Ltd.

[0054] The mineral powder is S95 grade mineral powder;

[0055] The fly ash is Class F, Grade I fly ash;

[0056] The silica fume is SF94 grade silica fume;

[0057] The fly ash microspheres meet the requirements of Class I fly ash, with a fineness of 12%, a loss on ignition of 3.0 wt%, and an activity of 75% after 28 days.

[0058] The sand is manufactured sand with a fineness modulus of 2.2, a particle size range of 0.3 to 2.36 mm, a crushing value of 20%, and stone powder content and mud content that meet the requirements of the "Standard for Construction Sand" (GB / T14684-2011).

[0059] The stone is crushed stone, which is composed of crushed stone with a particle size of 5mm to 10mm and crushed stone with a particle size of 10mm to 20mm mixed in a mass ratio of 3:7. Its crushing index is 6%, and its apparent density is 2630kg / m³. 3 Furthermore, the content of needle-like and flaky gravel in it is 9%.

[0060] The air-entraining agent has a solid content of 20% and is composed of anionic surfactant and nonionic surfactant in a mass ratio of 4:1. The anionic surfactant is mainly sodium α-alkenyl sulfonate with a solid content of 20%; the nonionic surfactant is mainly sodium fatty alcohol polyoxyethylene ether sulfate with a solid content of 20%. The water-reducing agent is Point-400S polycarboxylate-based high-performance water-reducing agent produced by Kezhijie New Materials Group Co., Ltd., with a water reduction rate of 30% and a solid content of 20%. The thickener is cellulose ether with a viscosity of 100,000 Pa·s.

[0061] Example 2

[0062] The raw materials required in this embodiment are, by weight, as follows:

[0063] 370 parts cement, 80 parts mineral powder, 70 parts fly ash, 13 parts silica fume, 13 parts fly ash microspheres, 145 parts water, 740 parts sand, 1045 parts stone, 0.8 parts air-entraining agent, 5 parts water-reducing agent, and 0.5 parts thickener.

[0064] In this embodiment, the mechanochemical activation of fly ash microspheres was achieved by ball milling with a ball-to-material ratio of 12 and a milling time of 1.5 hours; the amount of polyvinyl alcohol dispersant was 3% of the amount of activated fly ash microspheres.

[0065] The method for preparing low-density, corrosion-resistant, air-entrained marine concrete in this embodiment is as follows:

[0066] (1) Preparation of modified fly ash microspheres: activation and dispersion pretreatment:

[0067] After drying the required fly ash microspheres in an oven at 100℃, they are taken out and mixed with anhydrous sodium silicate and anhydrous sodium carbonate (both industrial grade, with a sodium silicate modulus of 1.5). The mass ratio of fly ash microspheres, anhydrous sodium silicate, and anhydrous sodium carbonate is 180:3:1. The mixture is placed in a ball mill jar and activated using a ball-to-material ratio of 12 and a milling time of 1.5 hours. After milling, the mixture is removed.

[0068] Next, 10% of the water mass in the formula is used as pretreatment water for dispersion (i.e., 10% of the water mass in the formula, this part of water is the first part of water). Activated fly ash microspheres are added to the water, followed by polyvinyl alcohol dispersant. The amount of polyvinyl alcohol is 3% of the mass of activated fly ash microspheres. After stirring together for 1 minute, it is mixed with cement and other admixtures (mineral powder, fly ash, silica fume) to obtain the mixture.

[0069] (2) The air-entraining agent is diluted with water in the second part to a 10% mass fraction of the air-entraining agent dilution solution;

[0070] (3) Weigh the remaining third portion of water into a container. Place the inlet and outlet pipes of the nanobubble generator into the water container. Start the instrument and, after the air in the instrument's pipes is purged, start timing. Adjust the equipment's running time according to the amount of water weighed, with a jetting time of 2-3 minutes. After turning off the equipment, wait for the milky white bubbles to dissipate, then remove the nanobubble water for later use. The total amount of water used is the sum of the amounts of the first, second, and third portions of water, and the third portion of water is nanobubble water.

[0071] (4) Add the diluted air-entraining agent to the foaming machine, turn on the foaming machine, and let the diluted air-entraining agent, the mixture, and the third part of water (i.e., the nano bubble water obtained in step 3) foam the gelling material together for 1 minute. Discharge the foamed gelling material and set it aside.

[0072] (5) Add aggregates (sand and stone) to the mixer and mix for 10 seconds to disperse the sand and stone evenly. Add foaming cementitious material to the mixer, then add water-reducing agent and thickener, and mix together for 3 minutes. After the mixing is completed, low density corrosion-resistant marine concrete can be obtained.

[0073] In this embodiment, the specific selection of each raw material is as follows:

[0074] The cement in question is Runfeng P·O 42.5 grade ordinary Portland cement produced by Run Cement Co., Ltd.

[0075] The mineral powder is S95 grade mineral powder;

[0076] The fly ash is Class F, Grade I fly ash;

[0077] The silica fume is SF94 grade silica fume;

[0078] The fly ash microspheres meet the requirements of Class I fly ash, with a fineness of 12%, a loss on ignition of 3.0 wt%, and an activity of 75% after 28 days.

[0079] The sand is manufactured sand with a fineness modulus of 2.2, a particle size range of 0.3 to 2.36 mm, a crushing value of 20%, and stone powder content and mud content that meet the requirements of the "Standard for Construction Sand" (GB / T14684-2011).

[0080] The stone is crushed stone, which is composed of crushed stone with a particle size of 5mm to 10mm and crushed stone with a particle size of 10mm to 20mm mixed in a mass ratio of 3:7. Its crushing index is 6%, and its apparent density is 2630kg / m³. 3 The content of needle-like and flaky gravel is 9%. The air-entraining agent has a solid content of 20% and is composed of anionic surfactant and nonionic surfactant in a mass ratio of 4:1. The main component of the anionic surfactant is sodium α-olefin sulfonate with a solid content of 20%; the main component of the nonionic surfactant is sodium fatty alcohol polyoxyethylene ether sulfate with a solid content of 20%; the water-reducing agent is Point-400S polycarboxylate-based high-performance water-reducing agent produced by Kezhijie New Materials Group Co., Ltd., with a water reduction rate of 30% and a solid content of 20%; the thickener is cellulose ether with a viscosity of 100,000 Pa·s.

[0081] Example 3

[0082] The raw materials required in this embodiment are, by weight, as follows:

[0083] 400 parts cement, 60 parts mineral powder, 80 parts fly ash, 10 parts silica fume, 10 parts fly ash microspheres, 160 parts water, 700 parts sand, 1085 parts stone, 1.0 part air-entraining agent, 4 parts water-reducing agent, and 0.4 parts thickener.

[0084] In this embodiment, the mechanochemical activation of fly ash microspheres was achieved by ball milling with a ball-to-material ratio of 15 and a milling time of 2.0 h; the amount of polyvinyl alcohol dispersant was 5% of the amount of activated fly ash microspheres.

[0085] The method for preparing low-density, corrosion-resistant, air-entrained marine concrete in this embodiment is as follows:

[0086] (1) Preparation of modified fly ash microspheres: activation and dispersion pretreatment:

[0087] After drying the required fly ash microspheres in an oven at 100℃, they are taken out and mixed with anhydrous sodium silicate and anhydrous sodium carbonate (both industrial grade, with a sodium silicate modulus of 1.5). The mass ratio of fly ash microspheres, anhydrous sodium silicate, and anhydrous sodium carbonate is 200:3.5:1.5. The mixture is placed in a ball mill jar and activated using a ball-to-material ratio of 15 and a milling time of 2.0 hours. After the milling is completed, the mixture is removed.

[0088] Next, 10% of the water mass in the formula is used as pretreatment water for dispersion (i.e., 10% of the water mass in the formula, this part of water is the first part of water). Activated fly ash microspheres are added to the water, followed by polyvinyl alcohol dispersant. The amount of polyvinyl alcohol is 5% of the mass of activated fly ash microspheres. After stirring together for 1 minute, it is mixed with cement and other admixtures (mineral powder, fly ash, silica fume) to obtain the mixture.

[0089] (2) The air-entraining agent is diluted with water in the second part to a 10% mass fraction of the air-entraining agent dilution solution;

[0090] (3) Weigh the remaining third portion of water into a container. Place the inlet and outlet pipes of the nanobubble generator into the water container. Start the instrument and, after the air in the instrument's pipes is purged, start timing. Adjust the equipment's running time according to the amount of water weighed, with a jetting time of 2-3 minutes. After turning off the equipment, wait for the milky white bubbles to dissipate, then remove the nanobubble water for later use. The total amount of water used is the sum of the amounts of the first, second, and third portions of water, and the third portion of water is nanobubble water.

[0091] (4) Add the diluted air-entraining agent to the foaming machine, turn on the foaming machine, and let the diluted air-entraining agent, the mixture, and the third part of water (i.e., the nano bubble water obtained in step 3) foam the gelling material together for 1 minute. Discharge the foamed gelling material and set it aside.

[0092] (5) Add aggregates (sand and stone) to the mixer and mix for 10 seconds to disperse the sand and stone evenly. Add foaming cementitious material to the mixer, then add water-reducing agent and thickener, and mix together for 3 minutes. After the mixing is completed, low density corrosion-resistant marine concrete can be obtained.

[0093] In this embodiment, the specific selection of each raw material is as follows:

[0094] The cement in question is Runfeng P·O 42.5 grade ordinary Portland cement produced by China Resources Cement Co., Ltd.

[0095] The mineral powder is S95 grade mineral powder;

[0096] The fly ash is Class F, Grade I fly ash;

[0097] The silica fume is SF94 grade silica fume;

[0098] The fly ash microspheres meet the requirements of Class I fly ash, with a fineness of 12%, a loss on ignition of 3.0 wt%, and an activity of 75% after 28 days.

[0099] The sand is manufactured sand with a fineness modulus of 2.2, a particle size range of 0.3 to 2.36 mm, a crushing value of 20%, and stone powder content and mud content that meet the requirements of the "Standard for Construction Sand" (GB / T14684-2011).

[0100] The stone is crushed stone, which is composed of crushed stone with a particle size of 5mm to 10mm and crushed stone with a particle size of 10mm to 20mm mixed in a mass ratio of 3:7. Its crushing index is 6%, and its apparent density is 2630kg / m³. 3 Furthermore, the content of needle-like and flaky gravel in it is 9%.

[0101] The air-entraining agent has a solid content of 20% and is composed of anionic surfactant and nonionic surfactant in a mass ratio of 4:1. The anionic surfactant is mainly sodium α-alkenyl sulfonate with a solid content of 20%; the nonionic surfactant is mainly sodium fatty alcohol polyoxyethylene ether sulfate with a solid content of 20%. The water-reducing agent is Point-400S polycarboxylate-based high-performance water-reducing agent produced by Kezhijie New Materials Group Co., Ltd., with a water reduction rate of 30% and a solid content of 20%.

[0102] The thickener is a cellulose ether with a viscosity of 100,000 Pa·s.

[0103] Comparative Example 1

[0104] The only difference between this comparative example and Example 1 is that, in preparing low-density corrosion-resistant marine concrete, this comparative example does not perform pretreatment of fly ash microspheres, but directly mixes them with cement and other admixtures (mineral powder, fly ash, silica fume) to obtain the mixture. Other preparation processes and conditions are consistent with those of Example 1.

[0105] Comparative Example 2

[0106] The only difference between this comparative example and Example 1 is that the third part of the water does not use nano-bubble water, but directly uses tap water to prepare the concrete. The other preparation processes and conditions are the same as in Example 1.

[0107] Comparative Example 3

[0108] The only difference between this comparative example and Example 1 is that, after the air-entraining agent is diluted into a diluted solution, a foaming machine is not used to introduce air bubbles (i.e., step 4 of the foaming process is not performed). Instead, the diluted solution is directly added to the mixer along with the other raw materials (mixture and water in the third part). Other preparation processes and conditions remain the same as in Example 1.

[0109] Comparative Example 4

[0110] The only difference between this comparative example and Example 1 is that:

[0111] In the concrete formula, the dosage of air-entraining agent is changed to make the air-entraining agent "over-added" (reflected in the concrete mixture having a bulk density lower than 88.0% of the bulk density of the group without air-entraining agent).

[0112] Other preparation processes and conditions remain the same as in Example 1.

[0113] Comparative Example 5

[0114] The only difference between this comparative example and Example 1 is that:

[0115] No air-entraining agent is added to the concrete formula;

[0116] Other preparation processes and conditions remain the same as in Example 1.

[0117] Comparative Example 6

[0118] The only difference between this comparative example and Example 1 is that:

[0119] The concrete formula does not include modified fly ash microspheres; the modified fly ash microspheres are replaced by cement or other materials by weight.

[0120] Other preparation processes and conditions remain the same as in Example 1.

[0121] Performance testing of products obtained in the examples and comparative examples:

[0122] The concrete prepared in the above embodiments and comparative examples was subjected to relevant performance tests according to the standards: "Standard for Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009) and "Test Procedure for Hydraulic Concrete" (SL / T352-2020). The results are shown in the table below:

[0123] Table 2

[0124]

[0125] Analysis of test results:

[0126] (1) The low-density air-entrained concrete prepared in Examples 1-3 has a density of 2200 kg / m³. 3 The specific gravity of this concrete formula, without air entrainment, is approximately 2440-2450 kg / m³. 3 The proportion of each embodiment decreased by more than 10%;

[0127] The concrete prepared in Examples 1-3 exhibits high impermeability, with chloride ion diffusion coefficients all around 4.0 × 10⁻⁶. -12 m 2 Below / s, Example 1 achieved 2.5 × 10 -12 m 2 / s, its sulfate resistance rating in wet and dry cycles can reach KS90, and its corrosion resistance coefficient is above 90%; according to the test parameters of hardened concrete slices in the "Test Procedure for Hydraulic Concrete" (SL / T352-2020), a bubble size of 2200μm can be obtained. 2 The number of bubbles above the slice area is a maximum of 5 harmful bubbles in the three embodiments, and its compressive strength is above 48.8 MPa, ensuring that the strength is maintained at a high level. While meeting the application requirements, it also meets the properties of low density, high air entrainment, and high corrosion resistance, and its durability is good.

[0128] (2) Compared with Example 1, the low density air-entrained concrete prepared in Comparative Example 1 has a slightly lower density. This is related to the pretreatment of fly ash microspheres. In the example, the fly ash microspheres were pretreated, which made the fly ash microspheres more evenly distributed in the concrete, achieving a better filling effect. In addition, after activation, their specific surface area increased, and the contact surface with other materials increased, which is conducive to filling large pores and increasing the density. To a certain extent, this will also slightly increase the density.

[0129] The 28-day chloride ion diffusion coefficient of Comparative Example 1 was increased compared to Examples 1-3, while its resistance to chloride ion erosion decreased. This is related to the significant morphological, activity, and filling effects of fly ash microspheres in cement-based materials. In the examples, the fly ash microspheres were activated, allowing them to better participate in the chloride ion curing reaction. The fly ash microspheres had a high Al2O3 content, and when appropriately incorporated into cementitious materials with high calcium content, they were beneficial for combining with chloride ions to form the AFm phase, thereby improving the chloride ion binding force of the slurry. The high aluminum content also facilitated the formation of semi-aluminate, which has low density and high filling rate, promoting slurry densification and significantly inhibiting chloride ion diffusion.

[0130] Compared with Examples 1-3, Comparative Example 1 showed a decrease in its resistance to sulfate attack. This can be explained by the increase in the number of harmful pores: with the increase in harmful pores, when sulfate attacks and expands, the harmful pores cannot withstand the stress generated by the expansion and begin to crack and break.

[0131] (3) The concrete density of Comparative Example 2 is close to that of Example 1. Under the condition of similar total density, Comparative Example 2 has more harmful pores, resulting in its various properties being lower than those of Examples 1-3. Examples introduce more tiny air bubbles, which will block the liquid phase transport inside the concrete and greatly improve its corrosion resistance.

[0132] (4) Compared with Examples 1-3, the concrete performance of Comparative Example 3 is worse, with an increased number of harmful pores. This is because the air-entraining agent mainly acts as a surface-active agent. In the examples, the air bubbles are "injected" into the cementitious material by a foaming machine, so that they mainly act on the cement-water interface. After mixing with the aggregate, the air bubbles are prevented from acting on the aggregate-water interface, thus expanding the interface transition zone, reducing the strength of the hardened concrete, reducing the channels for liquid phase transport in the interface transition zone, and improving the corrosion resistance of the concrete. In addition, the average bubble area and the bubble spacing coefficient of Examples 1-3 are smaller, resulting in lower connectivity between bubbles. The present invention's embodiments scientifically control the parameters such as the number, size, and stability of introduced bubbles, which is beneficial to improving the corrosion resistance of concrete.

[0133] (5) Compared to Example 1, the amount of air-entraining agent in Comparative Example 4 was increased, resulting in a bulk density of 2190 kg / m³. 3 Reduced to 2140 kg / m 3 The bulk density of Comparative Example 4 was 87.6% of that of concrete without air-entraining agent (such as Comparative Example 5). At this point, the bulk density reduction was too large, resulting in increased internal defects and harmful air bubbles in the concrete, which reduced its resistance to chloride ion attack. The strength, impermeability, and sulfate attack resistance also decreased significantly. This indicates that under high air-entraining conditions, there is a maximum limit to the dosage of air-entraining agent. Taking bulk density as a reference, when the bulk density drops below 87% of that of concrete without air-entraining agent, the various properties of the concrete are significantly reduced.

[0134] (6) Compared with Example 1, Comparative Example 5, which does not involve air entrainment, has significantly improved strength, but its resistance to chloride ion attack, impermeability, and sulfate attack is reduced. Furthermore, although the non-air-entrained concrete in the comparative example has a denser internal structure and can withstand greater pressure damage, its density is also insufficient.

[0135] The air bubbles introduced by the air-entraining agent affect the path of chloride ion transport in concrete. Introducing air bubbles can block the transport of chloride ions inside the concrete to a certain extent, thereby improving the resistance to chloride ion erosion. This application introduces small, continuous, and stable air bubbles through the air-entraining agent, which can provide space for the concrete to release stress when it expands and fails after being eroded by sulfate, preventing cracks from continuing to expand, thereby improving its resistance to sulfate erosion. Therefore, the impermeability, chloride ion erosion resistance, and sulfate erosion resistance of Comparative Example 5 (non-air-entrained concrete) are lower than those of Example 1 (high air-entrained concrete).

[0136] (7) Compared with Example 1, the bulk density of Comparative Example 6 did not change much. After the modified fly ash microspheres were replaced by cement and other materials, the compressive strength of the concrete was improved, which further demonstrated the role of activated and dispersed fly ash microspheres in concrete strength.

[0137] The impermeability of Comparative Example 6 decreased, while the resistance to sulfate attack in the corrosion resistance remained largely unchanged. In contrast, the 28-day chloride ion diffusion coefficient of Comparative Example 6 increased significantly. The activated and dispersed fly ash microspheres, when used as admixtures, can replace part of the cement in equal amounts, thereby enhancing the chloride ion binding capacity of the paste, including chemical binding capacity and physical adsorption capacity, and thus improving the chloride ion attack resistance of the concrete.

[0138] In summary, the solution provided by this invention includes the following novelty, mechanism of action and principle, and beneficial effects:

[0139] 1. The research direction of traditional high air-entrained concrete technology, in achieving a comprehensive performance that combines low cost, high air entrainment, low density, and good durability, encounters the following problems and obstacles:

[0140] High dosages of air-entraining agents can reduce the workability of concrete mixtures, especially fluidity. Maintaining good workability while ensuring high air entrainment is a crucial issue. During the preparation of high-air-entrained concrete, introduced air bubbles can migrate and escape, leading to air content loss, bubble aggregation (forming harmful large bubbles), and inter-bubble connectivity. All of these negatively impact the strength and durability of hardened concrete. The characteristics of introduced air bubbles in high-air-entrained concrete preparation are significantly influenced by the air-entraining agent. However, currently available air-entraining agents cannot simultaneously improve strength and durability at high air content. From the perspective of mix design and preparation process, identifying which type of air bubbles can maintain high strength while improving durability, and how to introduce "high-quality" air bubbles, are key issues in this preparation technology. Furthermore, improving the activity of fly ash microspheres and solving the "floating" problem are crucial for improving concrete durability.

[0141] 2. The mechanism by which this invention achieves concrete with comprehensive properties including low cost, high air entrainment, low density, and good durability:

[0142] Currently, existing technologies for achieving lightweight concrete focus on lightweight aggregate research, and patents for air-entrained concrete mostly concentrate on the development of air-entraining agents. However, there are few existing technologies for achieving low density, lightweight, and high durability in air-entrained concrete through mix design and processes. This invention achieves high durability by increasing the number of high-quality air pores, reducing the number of harmful air pores, and reducing the number of interconnected air bubbles.

[0143] Specifically, this invention discloses a low-density, corrosion-resistant air-entrained marine concrete and its preparation method. The concrete comprises the following components: cement, mineral powder, fly ash, silica fume, modified fly ash microspheres, water, sand, aggregate, air-entraining agent, water-reducing agent, and thickener. This formula, combined with specific modified fly ash microsphere preparation and optimized bubble distribution processes, achieves the desired effect.

[0144] (1) The modified fly ash microspheres are added to the mix proportion of the present invention. On the one hand, the "ball bearing" effect of the fly ash microsphere glass can effectively solve the problem of fluidity loss in high-aerated concrete mixtures. On the other hand, its filling effect on concrete and its curing effect on chloride ions can improve its corrosion resistance. However, conventional marine concrete mix proportions cannot effectively solve the problems of microsphere floating and low activity. By activating the fly ash activity through mechanical methods and pretreating the microspheres with dispersants, the problems of fly ash microsphere "floating" and low activity are effectively solved.

[0145] (2) Nano-bubble water is used to introduce tiny, closed bubbles to improve the quality of the introduced bubbles. When the gas content is constant, the more bubbles there are, the less large and harmful bubbles there will be. Tiny, non-connected bubbles can not only hinder the transport of liquid phase inside the concrete, but also provide pressure relief space and prevent the development of cracks during damage. For example, after sulfate erosion for a long time, concrete will expand and crack. Scientifically introducing bubbles can improve its corrosion resistance.

[0146] (3) Using a foaming machine and an air-entraining agent to foam the cementitious material can effectively control the number and size of the introduced air bubbles, resulting in higher air-entraining efficiency. Furthermore, adding aggregates after air-entraining can prevent the air-entraining agent from acting on the aggregate-water interface, expanding the interface transition zone, reducing the strength of the hardened concrete, reducing the channels for liquid phase transport in the interface transition zone, and improving the corrosion resistance of the concrete.

[0147] (4) Thickeners are added to the cementitious materials during mixing with aggregates to thicken the paste, increase viscosity, restrict bubble escape and aggregation, and reduce defects after concrete hardening. When the air content is above 6%, bubbles tend to aggregate before concrete hardening, leading to larger bubbles. Adding cellulose ether thickeners can prevent bubbles from moving when the buoyancy force on them is less than the yield shear stress. When the viscosity is high, the viscous resistance on the bubbles is greater, making it difficult for them to escape. Higher viscosity can also reduce the impact of vibration or external disturbances on the bubbles, acting as a buffer.

[0148] This invention achieves a lower density through a high air-entraining method. Compared to other existing technologies, while adding lightweight aggregates can achieve lightweight and high strength, it is more expensive and its performance is unstable. High air-entrained concrete can achieve a density of 2200 kg / m³. 3 Furthermore, it is less expensive and more durable. A search revealed no identical patents or technologies in China. Therefore, this invention possesses novelty, inventiveness, and practicality.

[0149] In summary, compared with conventional low-density marine concrete preparation processes, the low-density air-entrained corrosion-resistant concrete and its preparation method in this invention take a novel approach by using a high air-entraining method to reduce the concrete density, avoiding the disadvantages of unstable performance and high cost caused by using lightweight aggregates. Furthermore, it innovatively uses a foaming machine to optimize the size and distribution of air bubbles introduced by the air-entraining agent, and then uses nano-bubble water to introduce tiny closed air bubbles, and performs pretreatment for activation and dispersion of fly ash microspheres. Fly ash microspheres are used to improve durability, and a thickener is added to reduce defects after the concrete hardens. Finally, low-density corrosion-resistant air-entrained marine concrete is obtained. This invention provides high-air-entrained, low-density concrete at low cost, which maintains a high level of strength to meet the corresponding application requirements, while the concrete has good durability and corrosion resistance.

[0150] It should be noted that:

[0151] In this article, “~” is used to represent a numerical range, and the range of this expression includes two endpoint values;

[0152] The specific parameters or some commonly used reagents or raw materials in the above embodiments are specific or preferred embodiments under the concept of the present invention, and are not intended to limit it; those skilled in the art can make adaptive adjustments within the concept and protection scope of the present invention.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and 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.

Claims

1. A low-density, corrosion-resistant, air-entrained marine concrete, characterized in that: Its components include cement, admixtures, modified fly ash microspheres, water, air-entraining agent, aggregate, water-reducing agent, and thickener; The ball milled material is obtained by ball milling the mixture M. The ball milled material is then mixed and stirred with a first portion of water and polyvinyl alcohol dispersant to obtain the modified fly ash microspheres. The mixture M is a mixture of fly ash microspheres, anhydrous sodium silicate, and anhydrous sodium carbonate. The diluted air-entraining agent is foamed in a foaming machine and then injected into mixture N for further foaming to obtain a foamed cementitious material. The foamed cementitious material is then mixed uniformly with aggregate, water-reducing agent, and thickener to obtain the concrete. The mixture N is a mixture of cement, admixtures, modified fly ash microspheres, and water (the third part). The diluted air-entraining agent is a mixture of air-entraining agent and water (the second part). The total amount of water used is the sum of the amounts of the first part, the second part, and the third part, and the third part is nano-bubble water.

2. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 1, characterized in that: The admixture is composed of mineral powder, fly ash, and silica fume; The aggregate consists of sand and stone.

3. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 1, characterized in that: The preparation process of the modified fly ash microspheres is as follows: Dried fly ash microspheres were mixed with anhydrous sodium silicate and anhydrous sodium carbonate to obtain mixture M. Mixture M was then placed in a ball mill jar for ball milling to obtain a ball-milled product. The mass ratio of fly ash microspheres, anhydrous sodium silicate, and anhydrous sodium carbonate was (180-200):(3.0-4.0):(1.0-1.5). The ball-to-material ratio during the ball milling process was 10-15, and the milling time was 1-2 hours. The ball-milled material is dispersed in the first part of water, and then polyvinyl alcohol dispersant is added and stirred evenly to obtain modified fly ash microspheres; wherein, the first part of water accounts for 8% to 10% of the total water mass, and the amount of polyvinyl alcohol dispersant is 2% to 5% of the mass of the fly ash microspheres.

4. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 1, characterized in that: The modified fly ash microspheres are mixed with the admixture to obtain a mixture; Add a second portion of water to the air-entraining agent to dilute it to a mass fraction of 10% to 15%, and stir to mix it thoroughly to obtain the diluted air-entraining agent solution. The diluted air-entraining agent is added to the cement foaming machine, and the mixture N, which is formed by mixing the diluted air-entraining agent with cement, aggregate, and water (the third part), is foamed for 1-2 minutes to obtain the foamed cementitious material.

5. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 1, characterized in that, The third part of the water is nano-bubble water produced by foaming with a nano-bubble machine. The preparation process is as follows: Place the inlet and outlet pipes of the nanobubble generator into a water container, start the nanobubble generator, and start timing after the air in the pipes of the nanobubble generator is purged. After the jetting time is 2 to 3 minutes, turn off the nanobubble generator and wait for the milky white bubbles to dissipate to obtain the nanobubble water.

6. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 2, characterized in that: By weight, its raw material components include: 350-400 parts cement, 60-90 parts mineral powder, 50-80 parts fly ash, 10-15 parts silica fume, 10-15 parts modified fly ash microspheres, 130-160 parts water, 680-780 parts sand, 1000-1100 parts stone, 0.6-1.0 parts air-entraining agent, 4-6 parts water-reducing agent, and 0.4-0.6 parts thickener.

7. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 2, characterized in that: The cement is one of P·O42.5 and P·O52.5 cement; The mineral powder is S95 grade mineral powder; The fly ash is Class F, Grade I fly ash; The silica fume is SF94 grade silica fume; The performance of the fly ash microspheres meets the requirements of Class I fly ash, with a fineness ≤12%, loss on ignition ≤3.0wt%, and 28-day activity ≥70%.

8. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 2, characterized in that: The sand is manufactured sand with a fineness modulus of 1.6 to 2.2, a particle size range of 0.3 to 2.36 mm, and a crushing value of <20%. The stone is crushed stone, which is made by mixing crushed stone with a particle size of 5mm to 10mm and crushed stone with a particle size of 10 to 20mm in a mass ratio of 3:

7. Its crushing index is below 7%, its apparent density is greater than 2600kg / m³, and the content of needle-shaped and flaky crushed stone is below 10%.

9. The low-density, corrosion-resistant, air-entrained marine concrete according to claim 1, characterized in that: The water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of 30% and a solid content of 20%. The thickener is a cellulose ether with a viscosity of 100,000 Pa·s.

10. A method for preparing low-density, corrosion-resistant, air-entrained marine concrete as described in any one of claims 1-9, characterized in that, The preparation steps include the following: The dried fly ash microspheres are mixed with anhydrous sodium silicate and anhydrous sodium carbonate to obtain mixture M. Mixture M is then placed in a ball mill jar for ball milling to obtain the ball-milled product. The ball-to-material ratio during the ball milling process is 10-15, and the ball milling time is 1-2 hours. The ball-milled material was dispersed in the first part of water, and then polyvinyl alcohol dispersant was added and stirred evenly to obtain modified fly ash microspheres. The modified fly ash microspheres are mixed with the admixture to obtain a mixture; Add a second portion of water to the air-entraining agent to dilute it to a mass fraction of 10% to 15%, and stir to mix it thoroughly to obtain the diluted air-entraining agent solution. Place the inlet and outlet pipes of the nanobubble generator into a water container, start the nanobubble generator, and start timing after the air in the pipes of the nanobubble generator is purged. After the jetting time is 2 to 3 minutes, turn off the nanobubble generator and wait for the milky white bubbles to dissipate to obtain the nanobubble water. The diluted air-entraining agent is added to a cement foaming machine. The mixture N, which is formed by mixing the diluted air-entraining agent with cement, aggregate, and water (the third part), is foamed for 1-2 minutes to obtain the foamed cementitious material. After the foamed cementitious material is mixed with the aggregate, a water-reducing agent and a thickener are added and stirred for 3-4 minutes to obtain the concrete.

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