Special high-compressive-strength retaining type air entraining agent for machine-made sand and preparation method thereof

Abstract

The invention discloses a special high-compressive-strength retaining type air entraining agent for machine-made sand and a preparation method of the special high-compressive-strength retaining type air entraining agent and relates to the technical field of concrete admixtures. The air entraining agent is prepared from a composite exciting agent, a micro-powder adsorption inhibitor, a calcium ion chelating agent, a hyperbranched polymer, a defoaming control agent, a surfactant and an auxiliary additive. Through the synergistic effect of the composite exciting agent and the micro-powder adsorption inhibitor, the bottleneck that the strength is reduced due to the air entraining agent is broken through, on one hand, calcium sulphoaluminate and gypsum can activate a silicon-aluminum phase in the machine-made sandstone powder, so that the silicon-aluminum phase participates in a pozzolanic reaction to generate calcium silicate hydrate and ettringite, and the structural defect caused by air bubbles introduced by the air entraining agent is overcome; on the other hand, the micro-powder adsorption inhibitor formed by condensation of the modified sodium lignin sulfonate and the polyether amine significantly reduces the adsorption amount of the stone powder to the surfactant through steric hindrance and electrostatic repulsion, and ensures the utilization rate of the effective components of the air entraining agent.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete admixtures, in particular to a high compressive strength retaining air entraining agent specially used for machine-made sand and a preparation method thereof. Background Art

[0002] With the increasing scarcity of natural sand resources, machine-made sand has become the main aggregate substitute in the concrete industry. However, machine-made sand inevitably produces a large amount of fine powder (the stone powder content is usually 10%-20%) during the production process. Its particle morphology is sharp and the gradation is poor, which leads to an increase in the water demand of the concrete and a decrease in fluidity. In addition, stone powder has a significant adsorption effect on air-entraining agents. Traditional air-entraining agents are prone to low air entrainment efficiency and unstable bubble structure in machine-made sand concrete, which in turn affects the frost resistance, durability and strength development of the concrete. Therefore, the development of high-compressive strength-retaining air-entraining agents that are adapted to the characteristics of machine-made sand has become a key technical requirement for improving the comprehensive performance of machine-made sand concrete.

[0003] At present, the stone powder of existing air-entraining agents in machine-made sand concrete has a large specific surface area and high surface energy, which easily adsorbs the surfactant components in the air-entraining agent, resulting in a decrease in the effective concentration of the air-entraining agent, insufficient number of bubbles and uneven distribution. At the same time, the active CaO contained in the machine-made sand and stone powder and the calcium ions released by cement hydration will undergo ion exchange reactions with the air-entraining agent, resulting in a decrease in the strength of the bubble membrane, merging and rupture, making it difficult to form a uniformly closed microbubble system.

[0004] In summary, existing air-entraining agents are difficult to adapt to the high stone powder content and high-activity ion environment of manufactured sand and the high-strength requirements. It is urgent to develop a new type of air-entraining agent that can inhibit stone powder adsorption and stabilize the bubble system while stimulating stone powder activity or optimizing the pore structure to compensate for strength loss, thereby achieving a synergistic improvement in the frost resistance and compressive strength of manufactured sand concrete. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a high-compressive-strength-retaining air-entraining agent for machine-made sand and a preparation method thereof. The air-entraining agent can break through the bottleneck of strength reduction caused by air-entraining agents through the synergistic effect of a composite activator and a micropowder adsorption inhibitor. On the one hand, calcium sulfoaluminate and gypsum can activate the silicon-aluminum phase in the machine-made sand and stone powder, causing it to participate in the pozzolanic reaction to form hydrated calcium silicate and ettringite, thereby filling the structural defects caused by the introduction of bubbles into the air-entraining agent and compensating for the strength loss. On the other hand, the micropowder adsorption inhibitor synthesized by condensing modified sodium lignin sulfonate and polyetheramine significantly reduces the adsorption of surfactants by stone powder through steric hindrance and electrostatic repulsion, thereby ensuring the utilization rate of the effective ingredients of the air-entraining agent and forming closed bubbles with uniform pore size, fully meeting the application requirements of machine-made sand in cold regions and high-grade concrete.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: On the one hand, a high compressive strength retaining air entraining agent for machine-made sand is provided, wherein the air entraining agent comprises: a composite activator, a micropowder adsorption inhibitor, a calcium ion chelating agent, a hyperbranched polymer, a defoaming control agent, a surfactant, and an auxiliary additive, wherein:

[0007] The composite activator is composed of calcium sulfoaluminate and gypsum in a mass ratio of 3:1, and is used to activate the pozzolanic activity of residual stone powder in machine-made sand;

[0008] The micropowder adsorption inhibitor is formed by condensing modified sodium lignin sulfonate and polyetheramine in a molar ratio of 3:1;

[0009] The calcium ion chelating agent adopts disodium ethylenediaminetetraacetic acid to chelate the calcium ions released by cement hydration to adjust the calcium ion concentration in the cement paste;

[0010] The hyperbranched polymer is a polyamine hyperbranched polymer to adjust the pore structure of the concrete;

[0011] The defoaming control agent is nano polytetrafluoroethylene emulsion;

[0012] The surfactant is a surfactant prepared by compounding sodium dodecylbenzene sulfonate and branched alkyl polyether sodium sulfate in a mass ratio of 1:1;

[0013] The auxiliary agents are deionized water and a pH regulator.

[0014] Furthermore, the composite activator accounts for 15%-25% of the total mass of the air-entraining agent, which can activate the volcanic ash activity of the residual stone powder in the machine-made sand, generate ettringite crystals to fill the pores around the bubbles, thereby compensating for the loss of concrete strength caused by air entrainment.

[0015] Furthermore, the micro powder adsorption inhibitor accounts for 10%-20% of the total mass of the air entraining agent, which can reduce the adsorption of machine-made sand micro powder on the air entraining agent and ensure the effectiveness of the air entraining agent.

[0016] Furthermore, the calcium ion chelating agent accounts for 0.1%-0.5% of the total mass of the air-entraining agent, and disodium ethylenediaminetetraacetic acid is used to chelate calcium ions released by cement hydration, thereby reducing the negative impact of calcium ions on surfactants, stabilizing bubbles, and extending the action time of the air-entraining agent.

[0017] Furthermore, the hyperbranched polymer accounts for 0.2%-0.8% of the total mass of the air-entraining agent. The use of polyamine hyperbranched polymers can adjust the pore structure of concrete, fill tiny pores, optimize pore size distribution, prevent bubble migration or aggregation, and further improve the compressive strength and durability of concrete.

[0018] Furthermore, the defoaming control agent accounts for 0.3-1% of the total mass of the air-entraining agent, which can eliminate excessive bubbles during the mixing process of machine-made sand concrete, retain small and uniform beneficial bubbles, and optimize the bubble structure of the concrete;

[0019] The surfactant accounts for 30%-40% of the total mass of the air-entraining agent and can be quickly adsorbed on the gas-liquid interface to form tiny bubbles, thereby enhancing bubble stability and preventing bubble merging or bursting.

[0020] Furthermore, the auxiliary agent is the remainder of the air-entraining agent, and the pH regulator in the auxiliary agent is sodium hydroxide, which adjusts the pH value of the air-entraining agent solution to 8-9.

[0021] On the other hand, a method for preparing a high compressive strength retaining air-entraining agent for machine-made sand is provided, wherein the specific steps of the method are as follows:

[0022] S100, synthesis of micropowder adsorption inhibitor: modified sodium lignin sulfonate and polyetheramine were added to a reactor at a molar ratio of 3:1, and stirred for condensation reaction at 70-90°C under nitrogen protection for 4-6 hours to obtain a micropowder adsorption inhibitor;

[0023] S200, composite activator pretreatment: crush calcium sulfoaluminate mineral and hemihydrate gypsum separately, and mix them evenly in a mass ratio of 3:1;

[0024] S300, defoaming control agent dispersion: add nano-PTFE emulsion into deionized water and ultrasonically disperse for 10-15 minutes to form a stable emulsion;

[0025] S400, component compounding: at 50-60°C, add the micropowder adsorption inhibitor, composite activator, calcium ion chelating agent, hyperbranched polymer and defoaming control agent emulsion in sequence, and stir and disperse at 200-400 rpm for 30-40 minutes;

[0026] S500, pH adjustment and finished product preparation: adjust the system pH to 8-9 with sodium hydroxide solution, filter to remove impurities, and prepare the air-entraining agent finished product.

[0027] Compared with the existing technology, this high compressive strength retaining air-entraining agent for machine-made sand and its preparation method have the following beneficial effects:

[0028] 1. The present invention overcomes the bottleneck of strength loss caused by air-entraining agents through the synergistic effect of a composite activator and a micropowder adsorption inhibitor. On the one hand, calcium sulfoaluminate and gypsum can activate the silicon-aluminum phase in the machine-made sand and stone powder, causing it to participate in the pozzolanic reaction to form hydrated calcium silicate and ettringite, filling the structural defects caused by the introduction of bubbles by the air-entraining agent and compensating for the strength loss. On the other hand, the micropowder adsorption inhibitor, which is condensed from modified sodium lignin sulfonate and polyetheramine, significantly reduces the amount of surfactant adsorbed by the stone powder through steric hindrance and electrostatic repulsion, ensuring the utilization rate of the effective ingredients of the air-entraining agent and forming closed bubbles with uniform pore size, fully meeting the application requirements of machine-made sand in cold regions and high-grade concrete.

[0029] Second, the present invention introduces disodium EDTA as a calcium ion chelating agent, which synergistically regulates the microenvironment of cement paste with polyamine hyperbranched polymers. Disodium EDTA selectively chelates excess calcium ions released in the early stage of cement hydration, delaying the rapid precipitation of CSH gel and avoiding the rupture of bubble membranes due to excessive local ion concentration. At the same time, the hyperbranched polymer forms a network scaffold in the paste through its three-dimensional branched structure, guiding the directional arrangement of bubbles and refining the pore size, significantly improving the impermeability of concrete and further ensuring the long-term stability of the bubble system.

[0030] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0032] Figure 1 The present invention is a flow chart of a method for preparing a high compressive strength retaining air entraining agent specially used for machine-made sand. DETAILED DESCRIPTION

[0033] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0034] The present invention provides a high compressive strength retaining air entraining agent for machine-made sand, which comprises a composite activator, a micropowder adsorption inhibitor, a calcium ion chelating agent, a hyperbranched polymer, a defoaming control agent, a surfactant and an auxiliary agent, wherein:

[0035] The composite activator is composed of calcium sulfoaluminate and gypsum in a mass ratio of 3:1, accounting for 15%-25% of the total mass, and is used to activate the volcanic ash activity of residual stone powder in machine-made sand;

[0036] The micro powder adsorption inhibitor is made by condensing modified sodium lignin sulfonate and polyetheramine in a 3:1 molar ratio, accounting for 10%-20% of the total mass, and is used to inhibit the adsorption of surfactants by stone powder;

[0037] The calcium ion chelating agent is disodium ethylenediaminetetraacetic acid, accounting for 0.1%-0.5% of the total mass, which is used to chelate the calcium ions released by cement hydration and adjust its concentration;

[0038] The hyperbranched polymer is a polyamine hyperbranched polymer, accounting for 0.2%-0.8% of the total mass, and is used to optimize the pore structure of concrete;

[0039] The defoaming control agent is nano-polytetrafluoroethylene emulsion, accounting for 0.3%-1% of the total mass, which is used to stabilize the bubble system;

[0040] The surfactant is a mixture of sodium dodecylbenzene sulfonate and sodium branched alkyl polyether sulfate in a mass ratio of 1:1, accounting for 30%-40% of the total mass, and is used to reduce the surface tension of the solution and generate uniform bubbles;

[0041] Auxiliary additives are the remaining components, including deionized water and pH regulator sodium hydroxide. The pH of the air entraining agent solution is adjusted to 8-9 to ensure the stability of the system. Figure 1 As shown, the specific steps of the method for preparing a high compressive strength retaining air-entraining agent for machine-made sand are as follows:

[0042] S100, synthesis of micropowder adsorption inhibitor: modified sodium lignin sulfonate and polyetheramine were added to a reactor at a molar ratio of 3:1, and stirred for condensation reaction at 70-90°C under nitrogen protection for 4-6 hours to obtain a micropowder adsorption inhibitor;

[0043] S200, composite activator pretreatment: crush calcium sulfoaluminate mineral and hemihydrate gypsum separately, and mix them evenly in a mass ratio of 3:1;

[0044] S300, defoaming control agent dispersion: add nano-PTFE emulsion into deionized water and ultrasonically disperse for 10-15 minutes to form a stable emulsion;

[0045] S400, component compounding: at 50-60°C, add the micropowder adsorption inhibitor, composite activator, calcium ion chelating agent, hyperbranched polymer and defoaming control agent emulsion in sequence, and stir and disperse at 200-400 rpm for 30-40 minutes;

[0046] S500, pH adjustment and finished product preparation: adjust the system pH to 8-9 with sodium hydroxide solution, filter to remove impurities, and prepare the air-entraining agent finished product.

[0047] Example 1

[0048] Preparation of micropowder adsorption inhibitor: Modified sodium lignin sulfonate accounting for 15% of the total mass of the air-entraining agent and polyetheramine accounting for 5% of the total mass are added to the reactor in a molar ratio of 3:1, and stirred and condensed at 80°C under nitrogen protection for 5 hours. As the reaction proceeds, the modified sodium lignin sulfonate and polyetheramine gradually condense. The generated micropowder adsorption inhibitor can utilize steric hindrance and electrostatic repulsion to reduce the adsorption of the machine-made sand micropowder on the surfactant in the air-entraining agent, thereby ensuring the subsequent air-entraining effect.

[0049] Pretreatment composite activator: Calcium sulfoaluminate mineral accounting for 20% of the total mass of the air-entraining agent and hemihydrate gypsum accounting for about 6.7% of the total mass are crushed separately, and mixed evenly in a mass ratio of 3:1. After crushing and mixing, calcium sulfoaluminate and gypsum are fully in contact. The formed composite activator can better activate the volcanic ash activity of residual stone powder in machine-made sand when subsequently used in concrete, preparing to compensate for the strength of concrete.

[0050] Dispersed defoaming control agent: Add nano-PTFE emulsion accounting for 0.5% of the total mass of the air-entraining agent into an appropriate amount of deionized water and ultrasonically disperse it for 12 minutes. After ultrasonic dispersion, the nano-PTFE emulsion is evenly distributed in the water. During the subsequent concrete mixing, it can effectively eliminate excessive bubbles, making the bubbles inside the concrete smaller and more uniform, thereby improving the frost resistance and durability of the concrete.

[0051] Component compounding: At 55°C, add surfactant (35% of the total mass of the air-entraining agent), prepared micropowder adsorption inhibitor, composite activator, disodium ethylenediaminetetraacetic acid (0.1% of the total mass), polyamine hyperbranched polymer (0.3% of the total mass) and defoaming control agent emulsion in sequence, and stir and disperse at 300 rpm for 35 minutes. The surfactant quickly forms tiny bubbles at the gas-liquid interface, disodium ethylenediaminetetraacetic acid chelates with calcium ions released by cement hydration to stabilize the bubbles, and the polyamine hyperbranched polymer optimizes the pore structure of the concrete. The components are fully mixed during stirring to synergistically improve the performance of the air-entraining agent.

[0052] pH adjustment and finished product preparation: Use sodium hydroxide solution to adjust the system pH to 8.5, filter out impurities, and prepare the air-entraining agent product. Adjusting the pH value to 8.5 can ensure the stability of the air-entraining agent system, filter out impurities, improve the purity of the air-entraining agent, and ensure that it performs the best effect in concrete.

[0053] Implementation Results: When applied to manufactured sand concrete containing 15% stone dust, the air content stabilized at 5.0%, with an average bubble size of 80 μm and uniform distribution. This stabilized the concrete's internal structure, resulting in a 28-day compressive strength of 45 MPa and a strength retention rate of 93.75%. This was attributed to the strength-enhancing effects of the composite activator and hyperbranched polymer.

[0054] Example 2

[0055] Preparation of micropowder adsorption inhibitor: Modified sodium lignin sulfonate accounting for 18% of the total mass of the air-entraining agent and polyetheramine accounting for 6% of the total mass are added to the reactor in a molar ratio of 3:1. The mixture is stirred and condensed at 85°C under nitrogen protection for 5.5 hours. The higher proportion of raw materials and longer reaction time make the generated micropowder adsorption inhibitor more capable of inhibiting stone powder adsorption, providing a guarantee for the stable operation of the air-entraining agent in a high stone powder environment.

[0056] Pretreatment composite activator: Crush the calcium sulfoaluminate mineral, which accounts for 22% of the total mass of the air-entraining agent, and the hemihydrate gypsum, which accounts for about 7.3% of the total mass, separately, and mix them evenly in a mass ratio of 3:1. Increasing the amount of composite activator and through fine crushing and mixing, can more fully activate the activity of stone powder, providing more help to improve the strength of concrete.

[0057] Dispersed defoaming control agent: Add nano-polytetrafluoroethylene emulsion accounting for 0.7% of the total mass of the air-entraining agent into an appropriate amount of deionized water, and ultrasonically disperse it for 13 minutes. Increasing the amount of defoaming control agent and extending the ultrasonic dispersion time can make it more effective in eliminating excessive bubbles, optimizing the bubble structure, and improving the frost resistance and anti-permeability properties of concrete.

[0058] Component compounding: At 58°C, add surfactant (38% of the total mass of the air-entraining agent), micropowder adsorption inhibitor, composite stimulant, disodium ethylenediaminetetraacetic acid (0.15% of the total mass), polyamine hyperbranched polymer (0.4% of the total mass) and defoaming control agent emulsion in sequence, and stir and disperse at 320 rpm for 38 minutes. Adjustment of the proportions of the various components and sufficient stirring make the synergistic effects of surfactant entrainment, disodium ethylenediaminetetraacetic acid stabilization of bubbles, and polyamine hyperbranched polymer optimization of pore structure more significant.

[0059] pH adjustment and finished product preparation: Use sodium hydroxide solution to adjust the system pH to 8.6, filter to remove impurities, and prepare the air-entraining agent finished product. The pH value is adjusted to 8.6 to further optimize the air-entraining agent system environment. Filtration ensures product purity and improves the air-entraining agent performance.

[0060] Implementation Results: In tests on manufactured sand concrete containing 15% stone dust, the air content was 4.8%, the average bubble size was 75 μm, the 28-day compressive strength was 46 MPa, and the strength retention rate reached 95.83%. The air-entraining agent also withstood 420 freeze-thaw cycles, demonstrating excellent performance across all performance areas, demonstrating its suitability for high-stone dust content manufactured sand concrete.

[0061] Example 3

[0062] Preparation of micropowder adsorption inhibitor: Modified sodium lignin sulfonate accounting for 12% of the total mass of the air-entraining agent and polyetheramine accounting for 4% of the total mass are added to the reactor in a molar ratio of 3:1. The mixture is stirred and condensed at 75°C under nitrogen protection for 4.5 hours. With relatively low proportions of raw materials and mild reaction conditions, the generated micropowder adsorption inhibitor can meet the basic demand for inhibiting stone powder adsorption while reducing production costs.

[0063] Pretreatment composite activator: Crush calcium sulfoaluminate mineral accounting for 15% of the total mass of the air-entraining agent and hemihydrate gypsum accounting for about 5% of the total mass respectively, and mix them evenly in a mass ratio of 3:1. After crushing and mixing, an appropriate amount of composite activator can activate the activity of part of the stone powder and provide certain support for improving the strength of concrete.

[0064] Dispersed defoaming control agent: Add 0.3% of the total mass of the air-entraining agent to a proper amount of deionized water and ultrasonically disperse it for 10 minutes. A small amount of defoaming control agent can remove some of the oversized bubbles after ultrasonic dispersion, thus playing a preliminary role in optimizing the bubble structure of the concrete.

[0065] Component compounding: At 52°C, add surfactant (30% by weight of the total mass of the air-entraining agent), micropowder adsorption inhibitor, composite stimulant, disodium ethylenediaminetetraacetic acid (0.08% by weight of the total mass), polyamine hyperbranched polymer (0.2% by weight of the total mass) and defoaming control agent emulsion in sequence, and stir and disperse at 250 rpm for 32 minutes. Add each component in proportion and stir and mix them together to play the role of entraining air, stabilizing bubbles and optimizing pore structure, thereby ensuring the basic performance of the air-entraining agent.

[0066] pH adjustment and finished product preparation: Use sodium hydroxide solution to adjust the system pH to 8.3, filter to remove impurities, and prepare the air-entraining agent finished product. Adjust the pH value and perform the filtering operation to maintain the stability of the air-entraining agent system and ensure product quality.

[0067] Implementation Results: Applied to manufactured sand concrete with a 15% stone powder content, the results showed an air content of 5.2%, an average bubble size of 85 μm, a 28-day compressive strength of 43 MPa, and a strength retention rate of 91.49%. The product also achieved 380 freeze-thaw cycles and a P8 impermeability rating, meeting the basic performance requirements of manufactured sand concrete. However, the overall performance improvement was relatively weak.

[0068] Example 4

[0069] Preparation of micro-powder adsorption inhibitor: Modified sodium lignin sulfonate accounting for 20% of the total mass of the air-entraining agent and polyetheramine accounting for about 6.7% of the total mass are added to the reactor in a molar ratio of 3:1. The mixture is stirred and condensed at 90°C under nitrogen protection for 6 hours. The high proportion of raw materials and high temperature and long reaction time produce a micro-powder adsorption inhibitor with extremely strong ability to inhibit the adsorption of stone powder, greatly improving the utilization rate of the effective ingredients of the air-entraining agent.

[0070] Pretreatment of composite activator: Calcium sulfoaluminate mineral accounting for 25% of the total mass of the air-entraining agent and hemihydrate gypsum accounting for about 8.3% of the total mass are crushed separately, and mixed evenly in a mass ratio of 3:1. A large amount of composite activator can fully activate the activity of stone powder after fine treatment, providing sufficient material basis for compensating the strength of concrete.

[0071] Dispersed defoaming control agent: Add nano-polytetrafluoroethylene emulsion accounting for 1% of the total mass of the air-entraining agent into an appropriate amount of deionized water and ultrasonically disperse it for 15 minutes. A large amount of defoaming control agent and long-term ultrasonic dispersion can completely eliminate excessive bubbles, deeply optimize the bubble structure, and significantly improve the durability of concrete.

[0072] Component compounding: At 60°C, add surfactant (40% of the total mass of the air-entraining agent), micropowder adsorption inhibitor, composite stimulant, disodium ethylenediaminetetraacetic acid (0.2% of the total mass), polyamine hyperbranched polymer (0.6% of the total mass) and defoaming control agent emulsion in sequence, and stir and disperse at 350 rpm for 40 minutes. Add each component in high proportion and stir thoroughly to maximize the synergistic effect, thereby comprehensively improving the effects of air entrainment, foam stabilization and pore structure optimization.

[0073] pH adjustment and finished product preparation: Use sodium hydroxide solution to adjust the system pH to 8.8, filter to remove impurities, and prepare the air-entraining agent product. Adjusting the pH value and filtering operations ensure that the air-entraining agent can perform optimally in concrete.

[0074] Implementation effect: In the machine-made sand concrete with a stone powder content of 15%, the air content is 4.6%, the average bubble particle size is 70μm, the 28-day compressive strength is 47MPa, the strength retention rate is 97.92%, and the number of freeze-thaw cycles is 450 times, with excellent comprehensive performance.

[0075] Example 5

[0076] Preparation of micropowder adsorption inhibitor: Modified sodium lignin sulfonate accounting for 9% of the total mass of the air-entraining agent and polyetheramine accounting for 3% of the total mass are added to the reactor in a molar ratio of 3:1. The mixture is stirred and condensed at 70°C under nitrogen protection for 4 hours. The low proportion of raw materials and short reaction time can produce a micropowder adsorption inhibitor that can inhibit stone powder adsorption to a certain extent, making it suitable for cost-sensitive applications.

[0077] Pretreatment composite activator: Crush the calcium sulfoaluminate mineral accounting for 18% of the total mass of the air-entraining agent and the hemihydrate gypsum accounting for about 4% of the total mass separately, and mix them evenly in a mass ratio of 3:1. After treatment with an appropriate amount of composite activator, it can activate the activity of part of the stone powder, which is helpful to improve the strength of concrete.

[0078] Dispersed defoaming control agent: Add nano-polytetrafluoroethylene emulsion accounting for 0.2% of the total mass of the air-entraining agent into an appropriate amount of deionized water and ultrasonically disperse it for 8 minutes. A small amount of defoaming control agent can be ultrasonically dispersed to remove some large bubbles and preliminarily optimize the bubble structure of the concrete.

[0079] Component compounding: At 50°C, add surfactant (25% by weight of the total mass of the air entraining agent), micropowder adsorption inhibitor, composite activator, disodium ethylenediaminetetraacetic acid (0.05% by weight of the total mass), polyamine hyperbranched polymer (0.15% by weight of the total mass) and defoaming control agent emulsion in sequence, and stir and disperse at 200 rpm for 30 minutes. Each component is added in a relatively low proportion and stirred and mixed, which can achieve basic air entraining, foam stabilization and pore structure optimization functions.

[0080] pH adjustment and finished product preparation: Use sodium hydroxide solution to adjust the system pH to 8.0, filter to remove impurities, and prepare the air-entraining agent finished product. Adjust the pH value and filter to maintain the stability of the air-entraining agent system and ensure product quality.

[0081] Implementation effect: It is used for machine-made sand concrete with a stone powder content of 15%, an air content of 5.5%, an average bubble particle size of 90μm, a 28-day compressive strength of 42MPa, a strength retention rate of 90.22%, and an anti-freeze-thaw cycle number of 350 times. It can meet the basic use requirements of machine-made sand concrete, but its comprehensive performance is relatively weak.

[0082] The above examples focus on a high-compressive-strength-retaining air-entraining agent specifically for manufactured sand. To explore the performance of this type of air-entraining agent specifically for manufactured sand, multiple examples were developed to study the effects of different component ratios on the air-entraining agent's performance. As shown in the table below, by comparing these data, we can more intuitively understand the performance of the air-entraining agent in manufactured sand concrete at different component ratios, providing a strong basis for optimizing the air-entraining agent formulation. The changes in component content are shown in the table below:

[0083]

[0084]

[0085] Comparative Example 1

[0086] Pretreatment of composite activator: Calcium sulfoaluminate mineral accounting for 20% of the total mass of the air-entraining agent and hemihydrate gypsum accounting for about 6.7% of the total mass are crushed separately and evenly mixed in a mass ratio of 3:1. After crushing and mixing, the composite activator can activate the activity of the stone powder. However, due to the lack of micropowder adsorption inhibitor, the stone powder will absorb a large amount of surfactant, affecting the air-entraining effect.

[0087] Dispersed defoaming control agent: Add nano-polytetrafluoroethylene emulsion accounting for 0.5% of the total mass of the air-entraining agent into an appropriate amount of deionized water and ultrasonically disperse it for 12 minutes. Although the defoaming control agent can optimize the bubble structure, its role cannot be fully exerted due to insufficient air entrainment. Ultrasonic dispersion only makes the emulsion evenly dispersed, and has limited effect on improving the overall air entrainment effect.

[0088] Component preparation: At 55°C, a surfactant (35% by weight of the total air-entraining agent), a composite activator, 0.1% by weight of disodium EDTA, 0.3% by weight of a hyperbranched polyamine polymer, and a defoaming control agent emulsion were added in sequence, stirring and dispersing at 300 rpm for 35 minutes. Because the surfactant was adsorbed by the stone powder, the components were unable to effectively entrain air. The effectiveness of the disodium EDTA and hyperbranched polyamine polymer in stabilizing bubbles and optimizing pore structure was also significantly reduced, resulting in poor mixing.

[0089] pH adjustment and finished product preparation: The pH of the system is adjusted to 8.5 with sodium hydroxide solution, and impurities are filtered out to obtain the finished air-entraining agent. Although the pH adjustment and filtration operations can ensure the basic stability and purity of the air-entraining agent system, they cannot make up for the performance defects caused by the lack of micropowder adsorption inhibitor.

[0090] Implementation Results: In a machine-made sand concrete containing 15% stone dust, due to the absence of a micropowder adsorption inhibitor, the air content fluctuated widely, reaching only around 3.5%. The average bubble size reached 120 μm and was unevenly distributed. The 28-day compressive strength was 38 MPa, the strength retention rate was 79.17%, and the freeze-thaw cycle resistance was 280. These performance indicators were significantly lower than those in the previous example, highlighting the importance of the micropowder adsorption inhibitor.

[0091] Comparative Example 2

[0092] Preparation of micro-powder adsorption inhibitor: Modified sodium lignin sulfonate accounting for 15% of the total mass of the air-entraining agent and polyetheramine accounting for 5% of the total mass are added to the reactor in a molar ratio of 3:1. The mixture is stirred and condensed at 80°C under nitrogen protection for 5 hours. The micro-powder adsorption inhibitor is normally generated, which can inhibit the adsorption of stone powder on surfactant and ensure the air entrainment of the air-entraining agent, but cannot compensate for the loss of concrete strength.

[0093] Dispersing the defoaming agent: Add 0.5% of the total mass of the air-entraining agent to a nano-PTFE emulsion in deionized water and ultrasonically disperse for 12 minutes. This uniform dispersion of the defoaming agent optimizes the bubble structure, but the lack of a composite activator limits the concrete's strength gains.

[0094] Component preparation: At 55°C, add 35% of the total weight of the air-entraining agent to the surfactant, a micropowder adsorption inhibitor, 0.1% of disodium ethylenediaminetetraacetic acid, 0.3% of the total weight of the polyamine hyperbranched polymer, and a defoaming control agent emulsion in that order. Stir and disperse at 300 rpm for 35 minutes. While these ingredients can entrain air, stabilize foam, and optimize pore structure, they cannot compensate for the lack of a composite activator, resulting in insufficient strength. While mixing is acceptable, overall performance is compromised.

[0095] pH adjustment and finished product preparation: Use sodium hydroxide solution to adjust the system pH to 8.5, filter to remove impurities, and prepare the air-entraining agent product. Adjusting the pH value and filtering ensure the stability and purity of the air-entraining agent system, but cannot improve the concrete strength that is reduced due to the lack of composite activator.

[0096] Implementation effect: It is used for machine-made sand concrete with a stone powder content of 15% and an air content of 4.8%. Due to the lack of a composite activator, the bubble stability is slightly poor. The average bubble particle size is about 110 μm, and the bubbles vary in size and are relatively discretely distributed. The 28-day compressive strength is 36 MPa, the strength retention rate is 75%, and the number of freeze-thaw cycles is 300 times. Compared with the embodiment, the strength is significantly reduced, indicating that the composite activator is crucial to compensating for strength loss and improving concrete performance.

[0097] In summary, to comprehensively evaluate the performance of the high-compressive-strength-retaining air-entraining agent for machine-made sand of the present invention, several examples were compared with comparative examples. The air-entraining effect, strength performance, and durability of each example were monitored and recorded in machine-made sand concrete with the same stone powder content of 15%. The following table details the implementation results of each example and comparative example. By comparing these data, the influence of different formulations on the performance of the air-entraining agent can be clearly seen, providing strong support for the optimization and practical application of the air-entraining agent. The specific data are shown in the following table:

[0098]

[0099] As can be seen from the above table, the high compressive strength retaining air-entraining agent for machine-made sand of the present invention clearly shows the significant effects of each component on the performance of concrete through comparative tests of the examples and comparative examples, specifically:

[0100] From the perspective of gas content and average bubble particle size, the gas content of Examples 1 to 5 is stable between 4.6% and 5.5%, and the average bubble particle size is in the range of 70-90 μm and is evenly distributed, which shows that the components work synergistically to effectively entrain gas and optimize the bubble structure. In contrast, due to the lack of micropowder adsorption inhibitor, the gas content of Comparative Example 1 is only about 3.5%, and the average bubble particle size is 120 μm; Comparative Example 2 does not contain a composite stimulant, the average bubble particle size is 110 μm and the stability is poor, indicating that these two components are crucial to maintaining a reasonable gas content and refining bubbles.

[0101] In terms of compressive strength, the 28-day compressive strength of the embodiment is between 42-47 MPa, and the strength retention rate reaches 90.22%-97.92%. The composite activator activates the activity of stone powder, and the hyperbranched polymer optimizes the pore structure, which together compensates for the strength loss caused by air entrainment. The strength retention rate of comparative example 1 is 79.17%, and that of comparative example 2 is only 75%, highlighting the key role of these key components in improving strength.

[0102] In terms of durability indicators, the number of freeze-thaw cycles of the embodiment is 350-450 times, while the number of freeze-thaw cycles of the comparative example 1 is 280 times; the number of freeze-thaw cycles of the comparative example 2 is 300 times, and the embodiment performs better, indicating that a reasonable component formula can significantly improve the frost resistance and impermeability of concrete.

[0103] In summary, the various components of the air-entraining agent of the present invention work synergistically to effectively improve the comprehensive performance of machine-made sand concrete. The micropowder adsorption inhibitor and composite activator are key factors affecting air entrainment, strength and durability, providing strong support for the application of machine-made sand in high-performance concrete.

[0104] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A high compressive strength retaining air entraining agent for machine-made sand, characterized in that: The air entraining agent comprises: a composite activator, a micropowder adsorption inhibitor, a calcium ion chelating agent, a hyperbranched polymer, a defoaming control agent, a surfactant, and an auxiliary agent, wherein: The composite activator is composed of calcium sulfoaluminate and gypsum in a mass ratio of 3:1, and is used to activate the pozzolanic activity of residual stone powder in machine-made sand; The micropowder adsorption inhibitor is formed by condensing modified sodium lignin sulfonate and polyetheramine in a molar ratio of 3:1; The calcium ion chelating agent adopts disodium ethylenediaminetetraacetic acid to chelate the calcium ions released by cement hydration to adjust the calcium ion concentration in the cement paste; The hyperbranched polymer is a polyamine hyperbranched polymer to adjust the pore structure of the concrete; The defoaming control agent is nano polytetrafluoroethylene emulsion; The surfactant is a surfactant prepared by compounding sodium dodecylbenzene sulfonate and branched alkyl polyether sodium sulfate in a mass ratio of 1:1; The auxiliary agents are deionized water and a pH regulator.

2. The high compressive strength retaining air entraining agent for machine-made sand according to claim 1, characterized in that: The composite activator accounts for 15%-25% of the total mass of the air entraining agent.

3. The high compressive strength retaining air entraining agent for machine-made sand according to claim 1, characterized in that: The micro powder adsorption inhibitor accounts for 10% to 20% of the total mass of the air entraining agent.

4. The high compressive strength retaining air entraining agent for machine-made sand according to claim 1, characterized in that: The calcium ion chelating agent accounts for 0.1%-0.5% of the total mass of the air entraining agent.

5. The high compressive strength retaining air entraining agent for machine-made sand according to claim 1, characterized in that: The hyperbranched polymer accounts for 0.2% to 0.8% of the total mass of the air entraining agent.

6. The high compressive strength retaining air entraining agent for machine-made sand according to claim 1, characterized in that: The defoaming control agent accounts for 0.3-1% of the total mass of the air entraining agent; The surfactant accounts for 30%-40% of the total mass of the air entraining agent.

7. The high compressive strength retaining air entraining agent for machine-made sand according to claim 1, characterized in that: The auxiliary agent is the remainder of the air entraining agent, and the pH regulator in the auxiliary agent is sodium hydroxide, which adjusts the pH value of the air entraining agent solution to 8-9.

8. A method for preparing a high compressive strength retaining air-entraining agent for machine-made sand, applicable to the high compressive strength retaining air-entraining agent for machine-made sand according to any one of claims 1 to 7, characterized in that: The specific steps of this method are: S100, synthesis of micropowder adsorption inhibitor: modified sodium lignin sulfonate and polyetheramine were added to a reactor at a molar ratio of 3:1, and stirred for condensation reaction at 70-90°C under nitrogen protection for 4-6 hours to obtain a micropowder adsorption inhibitor; S200, composite activator pretreatment: crush calcium sulfoaluminate mineral and hemihydrate gypsum separately, and mix them evenly in a mass ratio of 3:1; S300, defoaming control agent dispersion: add nano-PTFE emulsion into deionized water and ultrasonically disperse for 10-15 minutes to form a stable emulsion; S400, component compounding: at 50-60°C, add the micropowder adsorption inhibitor, composite activator, calcium ion chelating agent, hyperbranched polymer and defoaming control agent emulsion in sequence, and stir and disperse at 200-400 rpm for 30-40 minutes; S500, pH adjustment and finished product preparation: adjust the system pH to 8-9 with sodium hydroxide solution, filter to remove impurities, and prepare the air-entraining agent finished product.

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