A solid air-entraining agent suitable for plateau low-pressure areas, and its preparation method and application

Abstract

The present invention provides a solid air-entraining agent suitable for plateau low-pressure areas, and its preparation method and application. The preparation method of the solid air-entraining agent suitable for plateau low-pressure areas of the present invention comprises the following steps: (1) cleaning rubber powder aggregate; (2) uniformly mixing the rubber powder aggregate with carbon nanotubes and nano zinc oxide to obtain a solid mixture; (3) mixing the solid mixture with a modified solution to obtain a mixture; (4) ultrasonically treating the mixture, and mechanically stirring, solid-liquid separation, and drying after the ultrasonic treatment to obtain a modified rubber powder aggregate; (5) heat-treating the modified rubber powder aggregate to obtain the solid air-entraining agent suitable for plateau low-pressure areas. The solid air-entraining agent suitable for plateau low-pressure areas of the present invention is applied to concrete, which can make the concrete have excellent frost resistance, significantly improve the service life of concrete structures in plateau low-pressure areas, and reduce maintenance costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and in particular relates to a solid air-entraining agent suitable for plateau low-pressure areas, and a preparation method and application thereof. Background Art

[0002] Typically, air-entraining agents are added to concrete to introduce an appropriate amount of tiny bubbles to improve concrete workability and durability. However, the low air pressure in plateau regions significantly affects the formation and stability of bubbles within concrete, making it difficult to predict the characteristic parameters of pores. Conventional air-entraining methods may not effectively improve the workability and frost resistance of concrete in the low-pressure environment of the plateau.

[0003] Crumb rubber aggregate exhibits large deformation and energy absorption during freeze-thaw cycles, reducing frost heave pressure during cooling and inhibiting external moisture intrusion during warming. Therefore, it is an effective strategy for improving concrete's frost resistance. However, the inventors discovered that the interfacial adhesion between crumb rubber aggregate and the cement matrix is weak, limiting its application in the low atmospheric pressure of the plateau.

[0004] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0005] The purpose of the present invention is to provide a solid air-entraining agent suitable for plateau low-pressure areas, and its preparation method and application, so as to help solve or improve the problem of limited application of rubber powder aggregate in plateau low-pressure environments.

[0006] In order to achieve the above-mentioned object, the present invention provides the following technical solution: a method for preparing a solid air-entraining agent suitable for plateau low-pressure areas, comprising the following steps: (1) cleaning rubber powder aggregate; (2) uniformly mixing the rubber powder aggregate obtained by the treatment in step (1) with carbon nanotubes and nano zinc oxide to obtain a solid mixture; (3) mixing the solid mixture with a modified solution to obtain a mixture; the modified solution contains a silane coupling agent, a titanate coupling agent and an ionic liquid; (4) ultrasonically treating the mixture, and mechanically stirring it after the ultrasonic treatment, separating the solid and the liquid, and drying it to obtain a modified rubber powder aggregate; (5) heat-treating the modified rubber powder aggregate to obtain the solid air-entraining agent suitable for plateau low-pressure areas; the heat treatment temperature is 100-120°C, and the heat treatment time is 1.8-2.1h.

[0007] Preferably, in step (1), when the rubber powder aggregate is cleaned, NaOH solution and HCl solution are used to clean the rubber powder aggregate in sequence; after the HCl solution cleaning is completed, the step of plasma treating the rubber powder aggregate is also included; the particle size of the rubber powder aggregate is at least one of 60-80 mesh, 40-60 mesh and 20-40 mesh.

[0008] Preferably, in step (2), the mass ratio of the rubber powder aggregate, carbon nanotubes and nano zinc oxide is (1-2):(1-2):(0.1-0.5).

[0009] Preferably, in step (3), the ionic liquid is 1-allyl-3-methylimidazole chloride-modified graphene oxide; in the modified solution, the mass ratio of the silane coupling agent, the titanate coupling agent and the ionic liquid is (1-2):(1-2):(0.1-0.5); the mass of the modified solution is 1%-5% of the solid mixture.

[0010] Preferably, in step (4), the ultrasonic treatment time is 20-40 min, and the mechanical stirring time is 10-30 min.

[0011] The present invention also provides a solid air-entraining agent suitable for plateau low-pressure areas, which adopts the following technical solution: a solid air-entraining agent suitable for plateau low-pressure areas, wherein the solid air-entraining agent suitable for plateau low-pressure areas is prepared by the method described above.

[0012] The present invention also provides an antifreeze concrete, which adopts the following technical solution: an antifreeze concrete, the components of which include the solid air entraining agent suitable for plateau low-pressure areas as described above.

[0013] Preferably, the frost-resistant concrete comprises, by weight: 300-500 parts of cement, 1-150 parts of stone powder, 900-1100 parts of coarse aggregate, 600-800 parts of fine aggregate, 4-6 parts of water reducer, 10-70 parts of the solid air entraining agent suitable for plateau low-pressure areas as claimed in claim 6, and 150-200 parts of water.

[0014] Preferably, the cement is ordinary Portland cement; the stone powder is dolomite slag stone powder with a specific surface area of 500-700m 2 / kg; the coarse aggregate is a 5-31.5mm continuously graded crushed stone aggregate made from dolomite slag; the fine aggregate is machine-made sand with a fineness modulus between 2.3 and 2.7 made from dolomite slag; the water reducer is a polycarboxylate water reducer with a water reduction rate greater than 20%.

[0015] The present invention also provides a method for preparing the antifreeze concrete as described above, which adopts the following technical solution: the method for preparing the antifreeze concrete as described above comprises the following steps: S1. weighing each raw material according to a proportion, wherein the solid air-entraining agent suitable for plateau low-pressure areas is added by an internal mixing method, and is added to the base concrete according to the principle of a fixed percentage of fine aggregate volume, and the corresponding fine aggregate is replaced by an equal volume; S2. cement, stone powder, fine aggregate, coarse aggregate and the solid air-entraining agent suitable for plateau low-pressure areas are mixed, dry-mixed, and then water and a water reducer are added and stirred to obtain the antifreeze concrete.

[0016] Beneficial effects:

[0017] The present invention proposes a method for preparing a solid air-entraining agent suitable for use in plateau low-pressure areas. By using the method of the present invention to treat rubber powder aggregate, the interfacial adhesion between the rubber powder aggregate and the cement matrix is improved, the possibility of interfacial damage is reduced, and the density of concrete is increased when the air-entraining agent is used in concrete, thereby reducing the generation of connected pores.

[0018] The solid air entraining agent suitable for plateau low-pressure areas of the present invention is applied to concrete, which can make the concrete have excellent frost resistance, significantly increase the service life of concrete structures in plateau low-pressure areas and reduce maintenance costs. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0020] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0021] The present invention aims to solve the problem that the application of rubber powder aggregate in plateau low-pressure environment is limited, and provides a preparation method of a solid air-entraining agent suitable for plateau low-pressure areas.

[0022] The preparation method of a solid air-entraining agent suitable for plateau low-pressure areas according to an embodiment of the present invention comprises the following steps: (1) cleaning rubber powder aggregate; (2) uniformly mixing the rubber powder aggregate obtained by the treatment in step (1) with carbon nanotubes and nano zinc oxide to obtain a solid mixture; (3) mixing the solid mixture with a modified solution to obtain a mixture; the modified solution contains a silane coupling agent, a titanate coupling agent and an ionic liquid; (4) ultrasonically treating the mixture, and mechanically stirring, solid-liquid separation, and drying after the ultrasonic treatment to obtain a modified rubber powder aggregate; (5) heat-treating the modified rubber powder aggregate to obtain a solid air-entraining agent suitable for plateau low-pressure areas; the heat treatment temperature is 100-120°C (for example, 100°C, 105°C, 110°C, 115°C or 120°C), and the heat treatment time is 1.8-2.1h. Among them, in step (1), by washing the rubber powder aggregate, it is at least helpful to clean up the inorganic impurities and organic impurities on the surface of the rubber powder aggregate; in step (4), ultrasonic treatment helps to ensure the uniform distribution of the components contained in the modified solution on the surface of the rubber powder particles; mechanical stirring after ultrasonic treatment helps to further improve the uniform distribution of the modified solution and the dispersibility of carbon nanotubes and nano zinc oxide; and the heat treatment in step (5) helps to enhance the binding force between the components of the modified solution and the rubber aggregate.

[0023] Freeze-thaw cycles are the main cause of common damage to concrete in cold regions. In extremely cold environments, temperature changes cause hydrostatic pressure on concrete, leading to the expansion of microcracks and pores, and ultimately forming macrocracks and causing surface peeling. The rationality of the bubble structure is an important factor affecting the frost resistance of aerated concrete. However, the formation and stability of bubbles inside concrete in plateau low-pressure areas are greatly affected, making it impossible to predict the characteristic parameters of its internal pores. The atmospheric pressure air entrainment method may not be able to effectively improve the working performance and frost resistance of concrete in plateau low-pressure environments. The solid air-entraining agent suitable for plateau low-pressure areas prepared by the method of the present invention helps to solve the above-mentioned technical problems. Specifically, the solid air-entraining agent prepared by the method of the present invention helps to improve the interfacial adhesion between rubber powder aggregate and cement matrix, reduce the possibility of interfacial damage, and thus help to improve the density of concrete when it is used in concrete, and reduce the generation of connected pores; in addition, the solid air-entraining agent suitable for plateau low-pressure areas prepared by the method of the present invention can significantly improve the freeze-thaw resistance of concrete, meet the demand for frost resistance of concrete structures in plateau low-pressure areas, effectively solve the cracking problem caused by freeze-thaw cycles, greatly extend the service life of buildings, and have important practical application value.

[0024] In a preferred embodiment of the method for preparing a solid air-entraining agent suitable for use in plateau low-pressure areas, in step (1), when cleaning the rubber powder aggregate, the rubber powder aggregate is sequentially cleaned with a NaOH solution and an HCl solution; after the HCl solution cleaning is completed, the rubber powder aggregate is further subjected to a plasma treatment step; the particle size of the rubber powder aggregate is at least one of 60-80 mesh, 40-60 mesh, and 20-40 mesh. First, the surface of the rubber powder aggregate is cleaned with a NaOH solution (e.g., a 5% NaOH solution) to remove inorganic and organic impurities on the surface; then, the rubber powder aggregate is pickled with dilute hydrochloric acid to further remove surface impurities and increase the surface activity and specific surface area of the rubber powder; finally, plasma treatment (plasma is the fourth state of matter, consisting of charged particles (such as electrons and ions), which is usually formed under high temperature or strong electric field conditions; plasma treatment refers to the use of a plasma torch or reactor to bombard the surface of a material with high-energy particles to change the chemical and physical properties of the material) helps to further improve the activity of the rubber powder aggregate surface and enhance the adhesion of the subsequent modified material.

[0025] Preferably, during plasma treatment, the rubber powder aggregate is plasma treated using a plasma device in an argon atmosphere for a treatment time of 5-10 minutes (for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes) to further improve the activity of the rubber powder surface and enhance the adhesion of subsequent modified materials.

[0026] In a preferred embodiment of the method for preparing a solid air-entraining agent suitable for plateau low-pressure areas of the present invention, in step (2), the mass ratio of rubber powder aggregate, carbon nanotubes and nano-zinc oxide is (1-2):(1-2):(0.1-0.5) (for example, 1:1:0.1, 1:1:0.5, 1:1:0.3, 1:2:0.1, 1:2:0.5, 2:1.5:0.1, 2:1:0.3 or 1.5:1.5:0.3, etc.).

[0027] In a preferred embodiment of the method for preparing a solid air-entraining agent suitable for plateau low-pressure areas of the present invention, in step (3), the ionic liquid is 1-allyl-3-methylimidazole chloride-modified graphene oxide; in the modified solution, the mass ratio of the silane coupling agent, the titanate coupling agent and the ionic liquid is (1-2):(1-2):(0.1-0.5) (for example, 1:1:0.1, 1:1:0.5, 1:1:0.3, 1:2:0.1, 1:2:0.5, 2:1.5:0.1, 2:1:0.3, 1.5:1:0.5 or 1.5:2:0.3, etc.); the mass of the modified solution is 1%-5% of the solid mixture (for example, 1%, 2%, 3%, 4% or 5%).

[0028] In a preferred embodiment of the method for preparing a solid air-entraining agent suitable for plateau low-pressure areas of the present invention, in step (4), the ultrasonic treatment time is 20-40 min (for example, 20 min, 25 min, 30 min, 35 min or 40 min), and the mechanical stirring time is 10-30 min (for example, 10 min, 15 min, 20 min, 25 min or 30 min).

[0029] The present invention further proposes a solid air-entraining agent suitable for plateau low-pressure areas. The solid air-entraining agent suitable for plateau low-pressure areas in the embodiment of the present invention is prepared by the method described above.

[0030] The present invention further provides an antifreeze concrete. The components of the antifreeze concrete in the embodiment of the present invention include the solid air entraining agent suitable for plateau low-pressure areas as described above.

[0031] In a preferred embodiment of the frost-resistant concrete of the embodiment of the present invention, the frost-resistant concrete comprises, by weight, 300-500 parts of cement (for example, 300 parts, 350 parts, 400 parts, 450 parts or 500 parts), 1-150 parts of stone powder (for example, 1 part, 10 parts, 40 parts, 70 parts, 110 parts or 150 parts), 900-1100 parts of coarse aggregate (for example, 900 parts, 950 parts, 1000 parts, 1050 parts or 1100 parts), and fine aggregate. 600-800 parts (for example, 600 parts, 650 parts, 700 parts, 750 parts or 800 parts), 4-6 parts (for example, 4 parts, 5 parts or 6 parts) of water reducer, 10-70 parts (for example, 10 parts, 20 parts, 30 parts, 40 parts, 50 parts, 60 parts or 70 parts) of solid air entraining agent suitable for plateau low pressure areas as described above, and 150-200 parts (for example, 150 parts, 160 parts, 170 parts, 180 parts, 190 parts or 200 parts) of water.

[0032] The present invention develops frost-resistant concrete suitable for plateau low-pressure areas by using stone powder, fine aggregate, and coarse aggregate prepared from slag and incorporating the solid air-entraining agent of the present invention, which is suitable for plateau low-pressure areas. The introduction of nanomaterials in the solid air-entraining agent enhances the concrete's crack resistance, wear resistance, and UV resistance, extending the service life of the structure. The solid air-entraining agent exhibits excellent stability and adaptability in the plateau low-pressure environment; the deformation and energy absorption characteristics of the solid air-entraining agent can be utilized to ensure the reliability of frost-resistant concrete in the plateau low-pressure environment, providing a longer service life for bridge construction in plateau low-pressure areas.

[0033] In a preferred embodiment of the frost-resistant concrete of the present invention, the cement is ordinary Portland cement; the stone powder is dolomite slag stone powder with a specific surface area of 500-700m 2 / kg (e.g., 500m2 / kg、550m 2 / kg、600m 2 / kg、650m 2 / kg or 700m 2 / kg); the coarse aggregate is a 5-31.5 mm continuously graded crushed stone aggregate made from dolomite slag; the fine aggregate is machine-made sand with a fineness modulus of 2.3-2.7 made from dolomite slag; and the water reducer is a polycarboxylate water reducer with a water reduction rate greater than 20%.

[0034] The present invention also provides a method for preparing the concrete described above. The method for preparing frost-resistant concrete according to an embodiment of the present invention comprises the following steps: S1. Weighing the raw materials according to the proportions, wherein a solid air-entraining agent suitable for use in plateaus and low-pressure areas is added by internal mixing, in which a fixed percentage of fine aggregate volume is added to the base concrete, replacing the corresponding fine aggregate by equal volume; S2. Mixing cement, stone powder, fine aggregate, coarse aggregate, and the solid air-entraining agent, dry-mixing (mixing uniformly), then adding water and a water reducer, and stirring (stirring uniformly) to obtain frost-resistant concrete. The dry-mixing time for mixing the cement, stone powder, fine aggregate, coarse aggregate, and solid air-entraining agent can be 3-4 minutes; after adding the water and water reducer, the stirring time can be 4-6 minutes.

[0035] The following describes in detail the solid air-entraining agent suitable for plateau low-pressure areas, its preparation method and application through specific examples.

[0036] In the following examples, the cement is P·O 525 ordinary Portland cement; the stone powder is dolomite slag stone powder with a specific surface area of 620m 2 / kg; the coarse aggregate is a 5-31.5mm continuously graded crushed stone aggregate made from dolomite slag; the fine aggregate is machine-made sand with a fineness modulus between 2.3 and 2.7 made from dolomite slag; the water reducer is a polycarboxylic acid high-efficiency water reducer with a water reduction rate greater than 20%; the carbon nanotubes are multi-walled carbon nanotubes (MWCNTs); the particle size of nano-zinc oxide is 20-50nm, and the purity is ≥99%; the silane coupling agent is KH-570; the titanate coupling agent is NDZ-201; and the ionic liquid is 1-allyl-3-methylimidazole chloride-modified graphene oxide.

[0037] Example 1

[0038] The preparation method of the solid air-entraining agent suitable for plateau low-pressure areas in this embodiment includes the following steps:

[0039] (1) First, 5% NaOH solution was used to treat rubber powder aggregate (60-80 mesh, apparent density 1000-1100 kg / m 3) surface to remove inorganic and organic impurities on the surface, and then pickling with dilute hydrochloric acid to further remove surface impurities and increase the surface activity and specific surface area of the rubber powder aggregate. Finally, the rubber powder aggregate is plasma treated with an argon atmosphere plasma device (the gas type is argon, the gas flow rate is 150 ml / min, the vacuum degree is 80 Pa, and the radio frequency power is 120 W) for 7 minutes to further improve the activity of the rubber powder surface and enhance the adhesion of subsequent modified materials.

[0040] (2) Rubber powder aggregate, carbon nanotubes and nano zinc oxide are uniformly mixed in a ratio of 1:1:0.2, and then a modified solution composed of a silane coupling agent, a titanate coupling agent and an ionic liquid with a mass fraction of 2% of the rubber powder aggregate is added (wherein the silane coupling agent is KH570, the ionic liquid is 1-allyl-3-methylimidazole chloride-modified graphene oxide, and the mass ratio of the silane coupling agent, the titanate coupling agent and the ionic liquid is 1:1:0.2).

[0041] (3) The mixture was ultrasonically treated for 30 min to ensure uniform distribution of the modifier on the surface of the rubber powder aggregate.

[0042] (4) After ultrasonic treatment, mechanical stirring was performed for 20 min to further improve the uniform distribution of the modifier and the dispersibility of the nanomaterials.

[0043] (5) The stirred rubber powder aggregate is naturally air-dried, and then the modified rubber powder aggregate is heat-treated at 100° C. for 2 hours to enhance the bonding force between the modifier and the surface of the rubber powder; after the heat treatment, the solid air-entraining agent of this embodiment suitable for plateau low-pressure areas is obtained.

[0044] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 760 parts of fine aggregate, 5 parts of water reducer, 16 parts of solid air-entraining agent suitable for plateau low-pressure areas of this embodiment, and 200 parts of water.

[0045] The method for preparing frost-resistant concrete of this embodiment comprises the following steps: S1. weighing the raw materials according to the proportions, wherein the amount of rubber powder aggregate used to prepare the solid air-entraining agent of this embodiment is determined by the internal admixture method, and the amount of solid air-entraining agent is determined based on the principle of a fixed percentage of fine aggregate volume (replacing the corresponding fine aggregate by equal volume), and the solid air-entraining agent is added to the base concrete; S2. mixing cement, stone powder, fine aggregate, coarse aggregate, and the solid air-entraining agent of this embodiment, dry-mixing for 3-4 minutes, then adding water and a water-reducing agent, and stirring for 5-8 minutes, thereby obtaining the frost-resistant concrete of this embodiment.

[0046] Example 2

[0047] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 720 parts of fine aggregate, 5 parts of water reducer, 33 parts of solid air entraining agent, and 200 parts of water.

[0048] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 10% of the fine aggregate.

[0049] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the particle size of the rubber powder aggregate used to prepare the solid air entraining agent is 60-80 mesh and the apparent density is 1000-1100 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0050] Example 3

[0051] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 680 parts of fine aggregate, 5 parts of water reducer, 50 parts of solid air entraining agent, and 200 parts of water.

[0052] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 15% of the fine aggregate.

[0053] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the particle size of the rubber powder aggregate used to prepare the solid air entraining agent is 60-80 mesh and the apparent density is 1000-1100 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0054] Example 4

[0055] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 640 parts of fine aggregate, 5 parts of water reducer, 66 parts of solid air entraining agent, and 200 parts of water.

[0056] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 20% of the fine aggregate.

[0057] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the particle size of the rubber powder aggregate used to prepare the solid air entraining agent is 60-80 mesh and the apparent density is 1000-1100 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0058] Example 5

[0059] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 760 parts of fine aggregate, 5 parts of water reducer, 15 parts of 40-60 mesh solid air entraining agent, and 200 parts of water.

[0060] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 5% of the fine aggregate.

[0061] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 40-60 mesh and an apparent density of 900-1000 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0062] Example 6

[0063] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 720 parts of fine aggregate, 5 parts of water reducer, 30 parts of solid air entraining agent, and 200 parts of water.

[0064] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 10% of the fine aggregate.

[0065] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 40-60 mesh and an apparent density of 900-1000 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0066] Example 7

[0067] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 680 parts of fine aggregate, 5 parts of water reducer, 45 parts of solid air entraining agent, and 200 parts of water.

[0068] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 15% of the fine aggregate.

[0069] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 40-60 mesh and an apparent density of 900-1000 kg / m3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0070] Example 8

[0071] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 640 parts of fine aggregate, 5 parts of water reducer, 60 parts of solid air entraining agent, and 200 parts of water.

[0072] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 20% of the fine aggregate.

[0073] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 40-60 mesh and an apparent density of 900-1000 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0074] Example 9

[0075] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 760 parts of fine aggregate, 5 parts of water reducer, 14 parts of solid air entraining agent, and 200 parts of water.

[0076] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 5% of the fine aggregate.

[0077] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 20-40 mesh and an apparent density of 800-900 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0078] Example 10

[0079] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 720 parts of fine aggregate, 5 parts of water reducer, 27 parts of solid air entraining agent, and 200 parts of water.

[0080] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 10% of the fine aggregate.

[0081] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 20-40 mesh and an apparent density of 800-900 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0082] Example 11

[0083] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 680 parts of fine aggregate, 5 parts of water reducer, 41 parts of solid air entraining agent, and 200 parts of water.

[0084] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 15% of the fine aggregate.

[0085] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 20-40 mesh and an apparent density of 800-900 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0086] Example 12

[0087] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 640 parts of fine aggregate, 5 parts of water reducer, 54 parts of solid air entraining agent, and 200 parts of water.

[0088] The stone powder and solid air entraining agent are both added by internal mixing. In terms of mass percentage, the stone powder replaces 20% of the cement; in terms of volume percentage, the solid air entraining agent replaces 20% of the fine aggregate.

[0089] The solid air entraining agent of this embodiment is suitable for plateau low pressure areas (the rubber powder aggregate used to prepare the solid air entraining agent has a particle size of 20-40 mesh and an apparent density of 800-900 kg / m 3 ) and the preparation method of frost-resistant concrete are the same as those in Example 1.

[0090] Example 13

[0091] The frost-resistant concrete of this embodiment differs from that of Example 1 in that the rubber micro-aggregate used to prepare the solid air-entraining agent includes 60-80 mesh rubber powder aggregate, 40-60 mesh rubber powder aggregate, and 20-40 mesh rubber powder aggregate, with the mass ratio of the three being 1:1:1.

[0092] The frost-resistant concrete of this embodiment includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 680 parts of fine aggregate, 5 parts of water reducer, 16 parts of solid air entraining agent, and 200 parts of water.

[0093] Comparative Example 1

[0094] The only difference between the frost-resistant concrete of this comparative example and Example 1 is that the solid air-entraining agent is replaced by a liquid air-entraining agent.

[0095] The frost-resistant concrete of this comparative example includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 760 parts of fine aggregate, 5 parts of water reducer, 2 parts of liquid air entraining agent, and 200 parts of water.

[0096] The method for preparing the frost-resistant concrete of this comparative example comprises the following steps: S1. weighing the raw materials according to the proportion;

[0097] S2. Mix cement, stone powder, fine aggregate and coarse aggregate, dry mix for 3-4 minutes, then add water, water reducer and liquid air entraining agent, and stir for 5-8 minutes.

[0098] Comparative Example 2

[0099] The frost-resistant concrete of this comparative example is different from that of Example 1 in that the stone powder is replaced by cement of equal mass, and the solid air-entraining agent is replaced by a liquid air-entraining agent.

[0100] The frost-resistant concrete of this comparative example includes the following raw materials in parts by weight: 500 parts of cement, 1000 parts of coarse aggregate, 760 parts of fine aggregate, 5 parts of water reducer, 2 parts of liquid air entraining agent, and 200 parts of water.

[0101] Comparative Example 3

[0102] The frost-resistant concrete of this comparative example is different from that of Example 1 in that the stone powder is replaced with cement of equal mass.

[0103] The frost-resistant concrete of this comparative example includes the following raw materials in parts by weight: 500 parts of cement, 1000 parts of coarse aggregate, 760 parts of fine aggregate, 5 parts of water reducer, 16 parts of solid air entraining agent, and 200 parts of water.

[0104] Comparative Example 4

[0105] The frost-resistant concrete of this comparative example is different from that of Example 1 in that the solid air-entraining agent is unmodified rubber powder aggregate.

[0106] The concrete of this comparative example includes the following raw materials in parts by weight: 500 parts of cement, 1000 parts of coarse aggregate, 760 parts of fine aggregate, 5 parts of water reducer, 16 parts of 60-80 mesh rubber powder aggregate (unmodified), and 200 parts of water.

[0107] Comparative Example 5

[0108] The only difference between the frost-resistant concrete of this comparative example and Example 1 is that the solid air-entraining agent is omitted and the amount of fine aggregate is 780 parts; the rest is consistent with Example 1;

[0109] The frost-resistant concrete of this comparative example includes the following raw materials in parts by weight: 400 parts of cement, 100 parts of stone powder, 1000 parts of coarse aggregate, 780 parts of fine aggregate, 5 parts of water reducer, and 200 parts of water.

[0110] Comparative Example 6

[0111] The only difference between this comparative example and Example 1 is that nano zinc oxide is omitted in the preparation of the solid air-entraining agent; the rest are consistent with Example 1.

[0112] Comparative Example 7

[0113] The only difference between this comparative example and Example 1 is that carbon nanotubes are omitted when preparing the solid air-entraining agent; the rest are consistent with Example 1.

[0114] Comparative Example 8

[0115] The only difference between this comparative example and Example 1 is that the silane coupling agent is omitted when preparing the solid air-entraining agent; the rest are consistent with Example 1.

[0116] Comparative Example 9

[0117] The only difference between this comparative example and Example 1 is that the titanate coupling agent is omitted when preparing the solid air-entraining agent; the rest are consistent with Example 1.

[0118] Comparative Example 10

[0119] The only difference between this comparative example and Example 1 is that the ionic liquid is omitted when preparing the modified rubber (the ionic liquid is replaced by an equal amount of ethanol); the rest is consistent with Example 1.

[0120] Comparative Example 11

[0121] The only difference between this comparative example and Example 1 is that the step of heat treatment at 100°C is omitted when preparing the solid air-entraining agent (step (4) is ultrasonic treatment followed by separation to obtain a solid, which is then dried to obtain a solid air-entraining agent); the rest is consistent with Example 1.

[0122] Experimental example

[0123] 1. Mechanical properties test:

[0124] According to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2019), the compressive strength and splitting tensile strength of concrete are tested before freeze-thaw. Specifically:

[0125] Concrete compressive strength test method:

[0126] Specimen preparation: Standard cube (side length 150mm) or cylinder (diameter 150mm, height 300mm) specimens are usually used. The specimens should be cured under standard curing conditions for up to 28 days;

[0127] Place the specimen on the workbench of the pressure testing machine so that the pressure acts evenly on the pressure-bearing surface of the specimen. Start the testing machine and apply vertical pressure at a loading rate that is consistent with the standard (e.g., 0.6 MPa / s) until the specimen fails.

[0128] Concrete splitting tensile strength test method:

[0129] Specimen preparation: Standard cylindrical specimens (150 mm in diameter and 300 mm in height) are usually used, and the specimens are also cured under standard curing conditions for 28 days;

[0130] Start the testing machine and apply vertical pressure. The loading rate should be uniform according to the standard (such as 0.08MPa / s) until the specimen is split and damaged.

[0131] The mechanical properties test results are shown in Table 1 below:

[0132] Table 1

[0133]

[0134] Combining the experimental data from Comparative Example 4 (using crumb rubber aggregate as a solid air-entraining agent) and Comparative Example 5 (no air-entraining agent) in Table 1 shows that the addition of crumb rubber aggregate to concrete reduces the strength of the concrete. However, combining Example 1 and Comparative Example 4 shows that the solid air-entraining agent prepared by treating crumb rubber aggregate according to the present invention, when added to concrete, significantly improves the mechanical properties of the concrete, reaching a level substantially equivalent to that of Comparative Example 5 (the mechanical properties of Example 13 are even significantly better than those of Comparative Example 5). This indicates that the solid air-entraining agent of the present invention can improve the mechanical properties of concrete (e.g., density, interfacial bonding properties, etc.) to a certain extent compared to crumb rubber aggregate.

[0135] 2. Freeze-thaw resistance test:

[0136] The concrete prepared in the Examples and Comparative Examples was tested for freeze-thaw resistance according to ASTM / C666, "Standard Test Method for Rapid Freeze-Thaw Resistance of Concrete." One freeze-thaw cycle lasted approximately 3 hours, with no less than 0.5 hours allowed for thawing. The center temperatures of the specimens during freezing and thawing were (-18±2)°C and (5±2)°C, respectively, and the number of freeze-thaw cycles was 300.

[0137] Special low-pressure simulation equipment is used to adjust the air pressure, temperature and humidity in the test chamber to simulate the actual environmental conditions in the plateau low-pressure area. The air pressure in the test chamber during the low-pressure test is ~70kPa; the air pressure during the normal-pressure test is ~101kPa.

[0138] The mass loss rate and relative elastic modulus test results of the frost-resistant concrete of the embodiment and the comparative example after freeze-thaw cycles are shown in Table 2 below:

[0139] Table 2

[0140]

[0141] It can be seen from Table 1-2 that the solid air-entraining agent prepared by the present invention, which is suitable for plateau low-pressure areas, effectively improves the anti-freeze performance of concrete while ensuring its mechanical properties.

[0142] A comparison of Examples 1 to 12 shows that as the solid air-entraining agent dosage increases, the mass loss of the concrete first decreases and then increases, while the relative dynamic elastic modulus first increases and then decreases. The frost resistance of concrete reaches its peak at a dosage of 15%. Furthermore, the optimization effect of the solid air-entraining agent on the frost resistance of concrete increases with decreasing particle size.

[0143] By comparison of Example 1 and Comparative Example 1, it can be seen that the solid air-entraining agent prepared by the present invention has a better effect on improving the antifreeze performance of concrete under low pressure than the existing liquid air-entraining agent. The low pressure environment greatly restricts the formation and stability of bubbles inside the concrete by the liquid air-entraining agent. However, the solid air-entraining agent is not significantly affected by the low pressure during the freeze-thaw process. When the stress of the concrete increases due to the expansion of water freezing, cracks are continuously generated inside and gradually expand into cracks. Because the solid air-entraining agent is an elastomer, it can prevent the continued expansion of internal cracks by buffering the expansion pressure, so that the concrete obtains better antifreeze performance. At the same time, the addition of the solid air-entraining agent can improve the internal pore structure, introduce a large number of bubbles, form many closed pores, and inhibit the development of capillary pores formed by cement hydration inside the specimen, thereby effectively improving the antifreeze performance of the concrete.

[0144] From the comparison of Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that when the stone powder dosage is 20%, the concrete still has excellent frost resistance, and its mass loss rate and relative dynamic elastic modulus under low pressure environment are not significantly different from those of the pure cement system.

[0145] Comparison of Example 1, Comparative Example 1, and Comparative Examples 4-11 shows that the solid air-entraining agent prepared by the present invention has an excellent modification effect on rubber microaggregate. When the rubber microaggregate is unmodified, it is difficult to combine with cement mortar, resulting in poor adhesion between the rubber microaggregate and the substrate, forming a relatively weak bonding surface. However, in this case, the effect of improving the frost resistance of the structure is still better than that of liquid air-entraining agents. The addition of carbon nanotubes improves the interfacial bonding ability between the rubber microaggregate and the substrate, while also increasing the toughness and crack resistance of the concrete and reducing crack propagation caused by freeze-thaw cycles. Nano-zinc oxide fills micropores, reduces water infiltration, reduces freeze-thaw damage, and improves the ultraviolet stability of concrete structures in plateau areas. Silane coupling agents improve interfacial bonding and water resistance, reducing interfacial damage caused by freeze-thaw cycles. Titanate coupling agents reduce interfacial damage and thermal expansion and contraction stress, thereby improving frost resistance. Ionic liquids improve dispersibility and interfacial wettability, enhancing chemical stability. The solid air-entraining agent of the present invention not only increases the density of the concrete structure and reduces the rate of interconnected pore formation, but also improves the interfacial adhesion between the rubber microaggregate and the cement matrix, reducing the likelihood of interfacial failure. Therefore, compared to conventional rubber microaggregates, the solid air-entraining agent of the present invention not only fully utilizes its inherent deformation properties but also improves the weakest interfacial transition zone in the structure composed of the cement matrix and the rubber microaggregate, resulting in significantly improved frost resistance. This conclusion is also verified by the changes in concrete porosity.

[0146] The experimental results of freeze-thaw cycle tests under normal and low pressure conditions, respectively, for Example 1, Comparative Example 1, and Comparative Example 5, show that the solid air-entraining agent prepared by the present invention has a superior effect on regulating the frost resistance of concrete in the low-pressure environment of the plateau. When conventional liquid air-entraining agents are applied from a normal freeze-thaw environment to a low-pressure freeze-thaw environment on the plateau, the mass loss rate increases by more than 3%. However, when solid air-entraining agents are applied from a normal freeze-thaw environment to a low-pressure freeze-thaw environment on the plateau, the mass loss rate increases by less than 1.5%. Furthermore, the solid air-entraining agent significantly improves the frost resistance of concrete under normal freeze-thaw conditions compared to conventional liquid air-entraining agents. Furthermore, a combination of Comparative Examples 1 and 5 shows that while liquid air-entraining agents have a good effect on improving the freeze-thaw resistance of concrete under normal pressure, the freeze-thaw resistance of Comparative Example 1, which incorporates liquid air-entraining agents under low pressure, is even worse than that of Comparative Example 5, which does not incorporate air-entraining agents. This is because the air-entraining agent introduces insufficient bubbles into the concrete under low pressure, and the bubbles are of poor quality (i.e., larger in size).

[0147] A comprehensive analysis of the effects of solid air-entraining agent particle size and dosage on freeze-thaw resistance showed that a mix ratio of 60-80 mesh: 40-60 mesh: 20-40 mesh = 1:1:1 and a dosage of 15% (Example 13) was recommended as the relatively optimal mix ratio. The solid air-entraining agent prepared based on this ratio and the antifreeze concrete containing it can ensure excellent freeze-thaw resistance in plateau low-pressure areas, and can be used to guide the optimization design of mix ratios of similar materials.

[0148] 3. Porosity test before and after freeze-thaw:

[0149] Test method: The water saturation method is a commonly used method to measure the porosity of concrete. The porosity is calculated by completely immersing the concrete specimen in water and measuring its weight change. The following is the specific test method:

[0150] (1) Dry the concrete specimen in an oven, usually at 105°C for 24 hours, to ensure that the specimen is completely dry. Record the mass md after drying;

[0151] (2) Place the dried test piece in water and immerse it completely. The vacuum saturation method is usually used, that is, immersing the test piece in water under vacuum conditions to ensure that all pores are filled with water; the immersion time depends on the specific situation and can be 24 hours or longer, until the weight of the test piece no longer increases;

[0152] (3) Take the test piece out of the water, gently wipe the surface moisture with a cloth, and record the mass ms after water saturation;

[0153] (4) Measure the volume V of the test block by geometric measurement or drainage method.

[0154] The porosity (P) can be calculated by the following formula: P = (ms-md) / ρo·V×100%;

[0155] Where: P is the porosity (%), md is the mass of the dry specimen (g), ms is the mass of the water-saturated specimen (g), and ρo is the density of water, usually 1 g / cm 3 , V is the volume of the test piece (cm 3 ).

[0156] The specific experimental results are shown in Table 3 below:

[0157] Table 3

[0158] Group Test conditions Porosity before freeze-thaw (%) Porosity after freeze-thaw (%) Example 1 low pressure 5.71 9.52 Normal pressure 4.98 8.36 Example 2 low pressure 5.66 9.2 Example 3 low pressure 5.43 8.42 Example 4 low pressure 5.9 9.87 Example 5 low pressure 6.96 13.86 Example 6 low pressure 7.11 13.21 Example 7 low pressure 7.26 12.93 Example 8 low pressure 7.31 13.79 Example 9 low pressure 8.13 15.66 Example 10 low pressure 8.26 15.21 Example 11 low pressure 8.39 14.92 Example 12 low pressure 8.41 15.57 Example 13 low pressure 5.21 8.68 Comparative Example 1 low pressure 7.21 21.74 Normal pressure 6.18 10.69 Comparative Example 2 low pressure 7.02 18.66 Comparative Example 3 low pressure 6.03 10.22 Comparative Example 4 low pressure 6.65 11.74 Comparative Example 5 low pressure 5.63 18.92 Normal pressure 4.88 16.8 Comparative Example 6 low pressure 6.19 11.28 Comparative Example 7 low pressure 6.27 12.03 Comparative Example 8 low pressure 6.57 14.29 Comparative Example 9 low pressure 6.61 15.01 Comparative Example 10 low pressure 6.29 11.17 Comparative Example 11 low pressure 6.15 10.99

[0159] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a solid air-entraining agent suitable for use in plateau low-pressure areas, characterized in that: The steps include: (1) Cleaning the rubber powder aggregate; (2) uniformly mixing the rubber powder aggregate obtained by the treatment in step (1) with carbon nanotubes and nano zinc oxide to obtain a solid mixture; the mass ratio of the rubber powder aggregate, carbon nanotubes and nano zinc oxide is (1-2):(1-2):(0.1-0.5); (3) mixing the solid mixture with a modified solution to obtain a mixture; the modified solution contains a silane coupling agent, a titanate coupling agent, and an ionic liquid; in the modified solution, the mass ratio of the silane coupling agent, the titanate coupling agent, and the ionic liquid is (1-2):(1-2):(0.1-0.5); the mass of the modified solution is 1%-5% of the solid mixture; (4) subjecting the mixture to ultrasonic treatment, and mechanically stirring after the ultrasonic treatment, separating the solid and liquid, and drying to obtain modified rubber powder aggregate; (5) The modified rubber powder aggregate is heat-treated to obtain the solid air-entraining agent suitable for plateau low-pressure areas; the heat treatment temperature is 100-120°C, and the heat treatment time is 1.8-2.1 h.

2. The method for preparing a solid air-entraining agent suitable for plateau low-pressure areas according to claim 1, characterized in that: In step (1), when the rubber powder aggregate is cleaned, the rubber powder aggregate is cleaned with NaOH solution and HCl solution in sequence; After the HCl solution cleaning is completed, the step of plasma treating the rubber powder aggregate is also included; The particle size of the rubber powder aggregate is at least one of 60-80 mesh, 40-60 mesh and 20-40 mesh.

3. The method for preparing a solid air-entraining agent suitable for use in plateau and low-pressure areas according to claim 1, wherein: In step (4), the ultrasonic treatment time is 20-40 min, and the mechanical stirring time is 10-30 min.

4. A solid air-entraining agent suitable for use in plateau low-pressure areas, characterized in that: The solid air-entraining agent suitable for plateau low-pressure areas is prepared by the method according to any one of claims 1 to 3.

5. A frost-resistant concrete, characterized in that: The components of the antifreeze concrete include the solid air entraining agent suitable for plateau low-pressure areas as described in claim 4.

6. The frost-resistant concrete according to claim 5, characterized in that: The frost-resistant concrete comprises, by weight, 300-500 parts of cement, 1-150 parts of stone powder, 900-1100 parts of coarse aggregate, 600-800 parts of fine aggregate, 4-6 parts of water reducer, 10-70 parts of the solid air entraining agent suitable for plateau low-pressure areas, and 150-200 parts of water.

7. The frost-resistant concrete according to claim 6, characterized in that: The cement is ordinary Portland cement; The stone powder is dolomite slag powder with a specific surface area of 500-700 m 2 / kg; The coarse aggregate is a 5-31.5 mm continuously graded crushed stone aggregate made from dolomite slag; The fine aggregate is machine-made sand made from dolomite slag with a fineness modulus of 2.3-2.7; The water reducer is a polycarboxylic acid water reducer with a water reduction rate greater than 20%.

8. The method for preparing frost-resistant concrete according to claim 6 or 7, wherein: The steps include: S1. Weigh the raw materials according to the ratio, wherein the solid air-entraining agent suitable for plateau low-pressure areas is added by internal mixing method, and the fine aggregate volume is fixed in percentage according to the principle of adding it to the reference concrete, replacing the corresponding fine aggregate by equal volume; S2. Mix cement, stone powder, fine aggregate, coarse aggregate and the solid air-entraining agent suitable for plateau low-pressure areas, dry mix, then add water and a water-reducing agent, and stir to obtain the frost-resistant concrete.

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