Targeted anti-freezing modification treatment method for concrete under dry-wet freeze-thaw environment

Abstract

The present application relates to the technical field of concrete durability, and particularly relates to a targeted anti-freezing modification treatment method for concrete under dry-wet freezing and thawing environment, which is aimed at the defects of uneven penetration, weak interface bonding, and no self-repairing capability of traditional concrete anti-freezing modification, and realizes modification through the following steps: concrete surface pretreatment, electro-osmosis construction of directional penetration channel, two-component gradient immersion, gradient power microwave induced solidification, and curing. The present application realizes deep electro-osmosis penetration by using nano calcium phosphate-carbon nanotube composite modifier, and forms a chemical bonding interface with the matrix. The present application realizes targeted filling of capillary pores and micro-cracks under normal pressure by using temperature-sensitive self-repairing microcapsule-hydrophobic aerogel composite modifier, and realizes internal-to-external gradient molding in cooperation with gradient microwave solidification. The present application can realize directional and uniform penetration of the modifier, and endows the concrete with hydrophobicity, stress buffering, and micro-crack self-repairing capability, effectively resists dry-wet freezing and thawing coupling damage, and improves the anti-freezing property and service life of the concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete durability technology, specifically a method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments. Background Technology

[0002] As the most widely used building material globally, concrete's durability directly determines the service life and operational safety of infrastructure. In the cold northern regions, arid northwestern regions, and southeastern coastal areas of my country, concrete structures are subjected to the dual coupling effects of wet-dry cycles and freeze-thaw cycles. Moisture continuously seeps into the concrete through its internal pores and microcracks, and expands by approximately 9% at low temperatures. Repeated exposure to these cycles leads to the formation and expansion of microcracks within the concrete, ultimately causing surface spalling, steel corrosion, and a decrease in structural load-bearing capacity, seriously threatening engineering safety. Developing efficient and durable concrete freeze-thaw modification technologies has significant engineering and economic value.

[0003] Currently, concrete freeze-thaw resistance modification technologies are mainly divided into two categories: bulk modification and surface modification. Bulk modification involves adding admixtures such as air-entraining agents, water-reducing agents, and mineral admixtures during the concrete mixing process to improve the pore structure inside the concrete and thus enhance its freeze-thaw resistance. However, bulk modification has the following limitations: First, the amount of air-entraining agent added is difficult to control precisely; excessive air entrainment can lead to a significant reduction in concrete strength, and the introduced air bubbles are prone to coalescing and rupturing during mixing and vibration, making it difficult to form a stable micro-bubble system. Second, bulk modification can only be applied to newly constructed concrete structures; it cannot be used to repair or reinforce a large number of existing concrete structures. Third, the hydration reaction of mineral admixtures is slow, resulting in low early strength, which affects the progress of construction projects.

[0004] Surface modification involves applying or impregnating various protective materials onto the concrete surface to form a dense protective layer that prevents the intrusion of moisture and harmful ions. Traditional surface modification materials mainly include organic coatings, silane impregnating agents, and epoxy resins. While organic coatings can form a dense protective layer, their adhesion to the concrete substrate is weak, making them prone to cracking and peeling under freeze-thaw cycles. They also have poor weather resistance and a short service life. Silane impregnating agents can penetrate to a certain depth into the concrete, forming a hydrophobic layer, but the penetration depth is limited, typically only 2-3 mm. They cannot repair existing micro-cracks within the concrete, and once the surface protection is compromised, moisture quickly seeps in, leading to protective failure. Epoxy resin coatings have strong adhesion to the concrete substrate, but the coating is brittle and prone to developing micro-cracks under temperature changes and freeze-thaw stress. These micro-cracks cannot self-repair, and they continue to expand, eventually causing coating failure.

[0005] In recent years, nanomaterial modification and self-healing technologies have received widespread attention in the field of concrete durability. Nanomaterials such as nano-silica, nano-calcium carbonate, and carbon nanotubes can fill the pores inside concrete, improve the structure of the interfacial transition zone, and enhance the strength and durability of concrete. However, nanomaterials have poor dispersibility in concrete, are prone to agglomeration, and traditional impregnation methods are difficult to penetrate deep into the concrete, resulting in limited modification effects. Self-healing microcapsule technology can automatically release a repair agent when microcracks occur in concrete, repairing the microcracks and thus improving concrete durability. However, existing self-healing microcapsules suffer from poor compatibility with the concrete matrix, low repair efficiency, and high cost, making large-scale engineering applications difficult.

[0006] In summary, existing concrete freeze-thaw modification methods generally suffer from insufficient penetration depth, uncontrollable penetration direction, weak interfacial bonding, and lack of self-healing capabilities, making it difficult to meet the durability requirements of concrete structures subjected to harsh conditions of alternating wet and dry freeze-thaw cycles. Therefore, developing a targeted freeze-thaw modification method that can penetrate deep into the concrete, achieve directional penetration, bond firmly to the matrix, and possess self-healing capabilities is a critical technical problem urgently needing to be solved in the field of concrete durability. Summary of the Invention

[0007] To address the problems in existing technologies, this invention provides a targeted antifreeze modification treatment method for concrete under dry and wet freeze-thaw environments. This method enables the modifier to penetrate deeply and form a strong chemical bond interface with the concrete matrix, while also endowing the modified layer with self-healing function, thus significantly improving the freeze-thaw resistance and durability of concrete under dry and wet freeze-thaw environments.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments, comprising the following steps: (1) Concrete surface pretreatment: Remove laitance, oil stains and loose particles from the concrete surface, sandblast to achieve a surface roughness of Ra6.3~Ra12.5, rinse with high pressure water and air dry naturally until the surface moisture content is 6%~10%; (2) Construction of electroosmotic directional infiltration channels: A cathode electrode is arranged on the concrete surface, and an anode electrode is arranged 15 mm away from the surface inside the concrete. A DC electric field is applied with an electric field strength of 1.5~2.5V / cm and an energizing time of 20~30min to form a directional infiltration channel from the surface to the interior inside the concrete. (3) Electroosmotic assisted impregnation of the first component: The nano-calcium phosphate-carbon nanotube composite modifier is uniformly brushed onto the concrete surface and kept in a DC electric field for 30-45 minutes to allow the modifier to penetrate into the concrete to a depth of 8-12 mm and form a chemical bond interface with the concrete matrix. (4) Second component atmospheric pressure targeted impregnation: Disconnect the DC electric field, and after the first component modifier is surface dry, spray the temperature-sensitive self-healing microcapsule-hydrophobic aerogel composite modifier evenly onto the concrete surface, and let it stand for 3~4 hours under atmospheric pressure to allow the modifier to penetrate into the concrete to a depth of 3~6mm and fill the capillary pores and microcracks. (5) Gradient power microwave-induced curing: The concrete surface is irradiated with microwaves at a frequency of 2450MHz, starting with 0.5~0.7W / cm². 2 Irradiate with a power density of 5-8 min, followed by 1.0-1.2 W / cm². 2 Irradiate with power density for 8-10 minutes to allow the modifier to be cured in a gradient from the inside to the surface; (6) Curing treatment: The solidified concrete is first cured in an environment with a temperature of 15±2℃ and a relative humidity of 90% for 3 days, and then cured under standard curing conditions for 4 days to complete the modification treatment.

[0009] Specifically, in step (2), the cathode electrode is a 20-mesh stainless steel wire mesh, the anode electrode is a titanium alloy rod with a diameter of 6 mm, and the electrode spacing is 15 mm.

[0010] Specifically, the nano-calcium phosphate-carbon nanotube composite modifier described in step (3) is composed of the following components in mass fraction: 25%~35% nano-hydroxyapatite, 8%~12% carboxylated carbon nanotube dispersion, 2%~4% phosphate coupling agent, 0.2%~0.5% sodium polyacrylate dispersant, and the balance being deionized water.

[0011] Specifically, the nano-hydroxyapatite has a particle size of 20-30 nm and a specific surface area of ​​80-100 m². 2 / g; the carboxylated carbon nanotubes have a diameter of 10~20nm and a length of 1~5μm.

[0012] Specifically, the thermosensitive self-healing microcapsule-hydrophobic aerogel composite modifier described in step (4) consists of the following components by mass fraction: 15%~20% thermosensitive self-healing microcapsules, 10%~15% hydrophobic silica aerogel microspheres, 15%~20% waterborne epoxy resin, 4%~6% curing agent polyamide 650, and the remainder deionized water.

[0013] Specifically, the temperature-sensitive self-healing microcapsules use polyurea formaldehyde as the wall material and a mixture of epoxy resin E-51 and curing agent polyamide 650 in a mass ratio of 1:1 as the core material, with a particle size of 10~30μm and a core material content of 60%~70%; the hydrophobic silica aerogel microspheres have a particle size of 80~120nm and a contact angle greater than 130°.

[0014] Specifically, in step (3), the amount of modifier applied is 1.2~1.5 kg / m². 2 In step (4), the amount of modifier sprayed is 0.6~0.9 kg / m². 2 .

[0015] Specifically, in step (5), during the microwave irradiation process, an infrared thermometer is used to monitor the concrete surface temperature in real time and control the temperature between 60 and 80°C.

[0016] Specifically, in step (2), before applying the DC electric field, a small amount of deionized water is sprayed onto the concrete surface to keep the surface moist.

[0017] Specifically, after the curing in step (6) is completed, a layer of fluorocarbon protective agent with a thickness of 0.1~0.2mm is applied to the concrete surface.

[0018] The beneficial effects of this invention are: Achieving directional and uniform penetration of modifiers: Relying on electroosmosis technology to construct directional penetration channels, the modifiers are guided to penetrate deep into the concrete along a preset path, solving the problems of random direction, uneven distribution, and surface accumulation in traditional penetration methods, and forming a continuous and complete internal protection system.

[0019] Building a robust matrix bonding interface: The nano-modified components react chemically with the concrete matrix to form a chemically bonded interface, which greatly improves the bonding strength between the modified layer and the concrete, and prevents the protective layer from cracking and falling off under dry-wet freeze-thaw cycles.

[0020] Complete graded targeted pore sealing: Two modified components are precisely adapted to pores and microcracks of different sizes in concrete to achieve graded filling and repair, optimize the internal pore structure of concrete, block the path of water intrusion from the source, and resist frost heave damage.

[0021] Imparting self-healing properties to concrete: The temperature-sensitive self-healing component can automatically break and release repair material when micro-cracks occur in concrete, promptly closing the cracks, inhibiting the continuous expansion of cracks, and improving the long-term durability of the structure.

[0022] Reduce curing internal stress damage: Gradient power microwave-induced curing is used to gradually cure the modifier from the inside out, effectively releasing curing shrinkage stress, avoiding thermal cracking of the modified layer, and ensuring the integrity of the protective layer structure.

[0023] Synergistic effect of multiple antifreeze mechanisms: The combination of functions such as nano-reinforcement, hydrophobic sealing, stress buffering, and self-healing comprehensively resists the coupling effect of dry and wet freeze-thaw cycles, significantly improving the freeze-thaw durability of concrete.

[0024] Expanding the scope of engineering applications: It is applicable to both the pretreatment of new concrete structures and the repair and modification of existing concrete structures, breaking through the limitation of traditional on-site modification that can only be used for new structures.

[0025] The construction process is simple and controllable: the combination of electroosmosis assistance and atmospheric pressure impregnation eliminates the need for complex negative pressure equipment, the process parameters are easy to adjust, adapt to the construction conditions of various engineering sites, and facilitate large-scale application. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Figure 1 The flowchart illustrates the method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments provided by this invention. Detailed Implementation

[0028] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0029] like Figure 1 As shown, the method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to the present invention includes the following steps: (1) Concrete surface pretreatment: Remove laitance, oil stains and loose particles from the concrete surface, and use sandblasting to achieve a surface roughness of Ra6.3~Ra12.5. After rinsing with high-pressure water, let it air dry until the surface moisture content is 6%~10%. Sandblasting removes the weak layer of the concrete surface by impacting the concrete surface with high-speed sand particles and forms an uneven rough interface, which can significantly improve the mechanical bonding force between the modifier and the concrete matrix. Controlling the surface moisture content within the range of 6%~10% can ensure that the migration channels of ions are unobstructed during electroosmosis and avoid excessive water dilution of the modifier, which would reduce the modification effect.

[0030] (2) Construction of directional electroosmotic channels: A cathode electrode is placed on the concrete surface, and an anode electrode is placed 15 mm away from the surface inside the concrete. A DC electric field is applied with a field strength of 1.5~2.5 V / cm and an energizing time of 20~30 min, forming directional channels from the surface to the interior of the concrete. Traditional negative pressure infiltration technology relies on pressure difference to drive the modifier to penetrate, resulting in random penetration direction and the formation of preferential channels at large pores, leading to uneven penetration. However, the directional electroosmotic infiltration technology used in this invention utilizes the conductivity and ion migration characteristics of pore water in concrete. Under the action of a DC electric field, cations in the pore water move towards the cathode, and anions move towards the anode, driving the pore water to flow towards the cathode as a whole. At the same time, air and impurities in the pores are discharged, forming continuous, uniform, and directionally distributed infiltration channels inside the concrete. This directional channel can guide the subsequent modifier to penetrate into the concrete along a preset direction, avoiding the problems of modifier accumulation on the surface or uneven penetration in traditional infiltration methods.

[0031] (3) Electroosmotic assisted impregnation of the first component: The nano-calcium phosphate-carbon nanotube composite modifier is uniformly applied to the concrete surface, and a DC electric field is maintained for 30-45 minutes to allow the modifier to penetrate directionally into the concrete to a depth of 8-12 mm, forming a chemical bond interface with the concrete matrix. In the nano-calcium phosphate-carbon nanotube composite modifier used in this invention, both the nano-hydroxyapatite and carboxylated carbon nanotubes have a large number of negative charges on their surfaces. Under the action of a DC electric field, they will be subjected to an electric field force pointing towards the anode, thereby moving directionally into the concrete. The penetration depth can reach 8-12 mm, which is 2-3 times that of the traditional negative pressure infiltration method. Nano-hydroxyapatite has a mineral composition similar to human bone and exhibits excellent chemical compatibility with calcium hydroxide and hydrated calcium silicate in concrete. It can react with calcium ions in the concrete matrix to form stable hydroxyapatite-calcium silicate composite crystals, creating a strong chemical bond interface between the modified layer and the concrete matrix. The interfacial bonding strength can reach over 3.5 MPa, far exceeding the physical bonding strength between traditional organic coatings and the concrete matrix (usually below 1.5 MPa), fundamentally solving the problem of traditional modified layers easily detaching. Carboxylated carbon nanotubes possess extremely high tensile strength and elastic modulus, forming a three-dimensional network reinforcement structure within the modified layer. This significantly improves the strength and toughness of the modified layer, increasing its elongation at break by over 50%, effectively resisting cracking caused by frost heave stress. Simultaneously, the high conductivity of carbon nanotubes enhances the electroosmosis effect, further improving the penetration depth and uniformity of the modifier.

[0032] (4) Second component atmospheric pressure targeted impregnation: After disconnecting the DC electric field and waiting for the first component modifier to dry to the surface, the temperature-sensitive self-healing microcapsule-hydrophobic aerogel composite modifier is uniformly sprayed onto the concrete surface and left to stand for 3-4 hours under atmospheric pressure, allowing the modifier to penetrate into the concrete to a depth of 3-6 mm, filling capillaries and microcracks. Since the first component modifier has already filled the large pores and interconnected pores inside the concrete, forming a dense underlying protective structure, the second component modifier can only penetrate into the capillaries and microcracks to a depth of 3-6 mm inside the concrete under atmospheric pressure, achieving graded targeted modification of pores of different sizes. Thermosensitive self-healing microcapsules use polyurea-formaldehyde as the wall material, which has good alkali resistance and mechanical properties, and can remain stable in the alkaline environment of concrete for a long time. The core material is a mixture of epoxy resin and curing agent. When microcracks are generated in concrete during freeze-thaw cycles, the stress concentration at the crack tip will cause the microcapsule wall material to rupture. At the same time, the temperature change caused by freeze-thaw cycles will generate thermal stress inside the microcapsule, accelerating the wall material rupture. The released epoxy resin and curing agent will quickly fill the microcracks and undergo a curing reaction, re-bonding the cracks together. The repair efficiency can reach more than 80%, effectively preventing the cracks from expanding further. The hydrophobic silica aerogel microspheres have a large number of hydrophobic groups grafted on their surface, with a contact angle greater than 130°. They can form a continuous hydrophobic layer inside the concrete, preventing water from penetrating into the concrete and reducing the water absorption rate by more than 90%. At the same time, the aerogel microspheres have a porosity of more than 85%. The nanopores inside can absorb freeze-thaw stress, converting freeze-thaw deformation into elastic deformation of the aerogel microspheres, thereby significantly reducing freeze-thaw stress inside the concrete and reducing freeze-thaw damage.

[0033] (5) Gradient power microwave-induced curing: The concrete surface is irradiated with microwaves at a frequency of 2450MHz, starting with 0.5~0.7W / cm². 2 Irradiate with a power density of 5-8 min, followed by 1.0-1.2 W / cm². 2Irradiation at a high power density for 8-10 minutes allows the modifier to undergo gradient curing from the inside to the surface. Traditional microwave curing techniques typically use constant power irradiation. Due to the limited penetration depth of microwaves, the surface of the modified layer cures first, while the internal modifier remains incompletely cured. Furthermore, the difference in curing shrinkage between the surface and the interior generates significant internal stress, leading to cracking of the modified layer. This invention employs a gradient power microwave-induced curing technology. First, low-power microwave irradiation allows the microwaves to penetrate deeper into the concrete, causing the internal modifier to cure first. Then, the microwave power is gradually increased, allowing the surface modifier to cure progressively. This gradient curing method effectively releases the internal stress generated by curing shrinkage, reducing internal stress and preventing cracking of the modified layer. Simultaneously, the selective heating characteristics of microwaves allow the modifier to preferentially absorb microwave energy for rapid curing, while the temperature rise of the concrete matrix is ​​minimal, avoiding adverse effects on the mechanical properties of the concrete matrix.

[0034] (6) Curing treatment: The cured concrete is first cured in an environment with a temperature of 15±2℃ and a relative humidity of 90% for 3 days, and then cured under standard curing conditions for 4 days to complete the modification treatment. The low temperature and high humidity curing in the early stage can make the chemical reaction between the modifier and the concrete matrix more complete, and further improve the interfacial bonding force; the standard curing in the later stage can ensure that the modifier is completely cured and forms a stable three-dimensional network structure.

[0035] In step (2), the cathode electrode is a 20-mesh stainless steel wire mesh, and the anode electrode is a 6mm diameter titanium alloy rod with an electrode spacing of 15mm. The stainless steel wire mesh has good conductivity and corrosion resistance, allowing for uniform contact with the concrete surface and ensuring a uniform electric field distribution. The titanium alloy rod has excellent corrosion resistance and mechanical properties, and will not corrode in the alkaline environment of concrete, making it suitable as an embedded anode electrode. Controlling the electrode spacing to 15mm ensures a uniform distribution of the electric field strength within the concrete, while also allowing the modifier to penetrate into the area near the anode, achieving maximum penetration depth.

[0036] The nano-calcium phosphate-carbon nanotube composite modifier described in step (3) consists of the following components by mass fraction: 25%~35% nano-hydroxyapatite, 8%~12% carboxylated carbon nanotube dispersion, 2%~4% phosphate coupling agent, 0.2%~0.5% dispersant sodium polyacrylate, and the balance being deionized water. The phosphate group at one end of the phosphate coupling agent molecule can react with the hydroxyl groups on the surface of the nano-hydroxyapatite, while the amino group at the other end can react with the hydroxyl groups in the concrete matrix, forming a molecular bridge between the nanomaterial and the concrete matrix, further enhancing the interfacial bonding force. The dispersant sodium polyacrylate can effectively prevent the agglomeration of nanoparticles, ensuring that the modifier has good stability and permeability.

[0037] The nano-hydroxyapatite has a particle size of 20-30 nm and a specific surface area of ​​80-100 m². 2 / g; the carboxylated carbon nanotubes have a diameter of 10~20nm and a length of 1~5μm. Using nano-hydroxyapatite within this particle size range ensures good permeability and chemical reactivity, allowing it to penetrate deep into the fine pores of concrete and fully react with the matrix. Using carboxylated carbon nanotubes of this size enables the formation of an effective three-dimensional network reinforcement structure within the modified layer, while avoiding entanglement and agglomeration due to excessively long carbon nanotubes.

[0038] The thermosensitive self-healing microcapsule-hydrophobic aerogel composite modifier described in step (4) consists of the following components by mass fraction: 15%~20% thermosensitive self-healing microcapsules, 10%~15% hydrophobic silica aerogel microspheres, 15%~20% waterborne epoxy resin, 4%~6% polyamide 650 curing agent, and the balance being deionized water. The waterborne epoxy resin, as a film-forming substance, can firmly bond the microcapsules and aerogel microspheres to the concrete substrate, forming a continuous protective layer; the polyamide 650 curing agent has good flexibility and corrosion resistance, and can react with the waterborne epoxy resin to form a tough cured product.

[0039] The temperature-sensitive self-healing microcapsules use polyurea-formaldehyde as the wall material and a 1:1 mass mixture of epoxy resin E-51 and curing agent polyamide 650 as the core material, with a particle size of 10-30 μm and a core material content of 60%-70%. The hydrophobic silica aerogel microspheres have a particle size of 80-120 nm and a contact angle greater than 130°. Using self-healing microcapsules within this particle size range ensures that the microcapsules can penetrate into the microcracks inside the concrete while possessing sufficient strength to prevent premature rupture due to external forces during construction. The high core material content of the microcapsules ensures that sufficient repair agent is released upon rupture, effectively filling the microcracks. The hydrophobic silica aerogel microspheres with this particle size ensure good permeability and hydrophobic properties, allowing them to penetrate deep into the capillaries inside the concrete to form a hydrophobic layer.

[0040] In step (3), the amount of modifier applied is 1.2~1.5 kg / m². 2 In step (4), the amount of modifier sprayed is 0.6~0.9 kg / m². 2 Controlling the amount of modifier used can ensure that the modifier fully penetrates into the concrete, while avoiding the accumulation of modifier on the surface, which would affect the appearance and performance.

[0041] In step (5), during microwave irradiation, an infrared thermometer is used to monitor the concrete surface temperature in real time and control the temperature between 60 and 80°C. Controlling the concrete surface temperature can prevent excessively high temperatures from causing thermal cracking in the concrete matrix and modified layer, while ensuring that the modifier can fully cure.

[0042] In step (2), before applying the DC electric field, a small amount of deionized water is sprayed onto the concrete surface to keep it moist. Keeping the concrete surface moist can improve the electroosmosis effect and promote the directional penetration of the modifier.

[0043] After curing in step (6), apply a 0.1-0.2 mm thick layer of fluorocarbon protective agent to the concrete surface. Fluorocarbon protective agent has excellent weather resistance, corrosion resistance and waterproof performance, which can further improve the protective effect of the concrete surface and extend the service life of modified concrete.

[0044] Example 1: A method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments, comprising the following steps: (1) Concrete surface pretreatment: Use a wire brush to remove laitance, oil stains and loose particles from the concrete surface, then sandblast with quartz sand at a pressure of 0.6 MPa to achieve a surface roughness of Ra9.0. Rinse with high-pressure water at a pressure of 12 MPa and air dry until the surface moisture content is 8%. Sandblasting removes the weak layer of the concrete surface by impacting it with high-speed sand particles, forming an uneven and rough interface, which can significantly improve the mechanical bonding force between the modifier and the concrete matrix. High-pressure water rinsing can remove residual sand particles and dust from the surface, ensuring that the modifier can fully contact the concrete matrix. Controlling the surface moisture content at 8% can ensure that the migration channels of ions are unobstructed during electroosmosis and avoid excessive water dilution of the modifier, which would reduce the modification effect.

[0045] (2) Construction of directional electroosmotic channels: A layer of 20-mesh stainless steel wire mesh was laid on the concrete surface as the cathode electrode, and a 6-mm diameter titanium alloy rod was inserted into the concrete interior at a distance of 15mm from the surface as the anode electrode, with an electrode spacing of 15mm. A small amount of deionized water was sprayed on the concrete surface to keep it moist, and then a DC power supply was connected to apply a DC electric field with a strength of 2.0V / cm for 25min. Under the action of the DC electric field, cations in the pore water of the concrete moved towards the cathode, and anions moved towards the anode, driving the pore water to flow towards the cathode as a whole, while expelling air and impurities from the pores, forming continuous, uniform, and directionally distributed permeation channels inside the concrete. These directional channels can guide the subsequent modifier to penetrate into the concrete interior along a predetermined direction, avoiding the problems of modifier accumulation on the surface or uneven permeation in traditional permeation methods. Stainless steel wire mesh has good electrical conductivity and corrosion resistance, and can make uniform contact with the concrete surface to ensure uniform electric field distribution; titanium alloy rods have excellent corrosion resistance and mechanical properties, and will not corrode in the alkaline environment of concrete, making them suitable as embedded anode electrodes.

[0046] (3) First component electroosmotic assisted impregnation: The pre-prepared nano-calcium phosphate-carbon nanotube composite modifier is uniformly applied to the concrete surface at a coating amount of 1.3 kg / m². 2 A DC electric field is maintained for 40 minutes. Under the influence of the electric field, negatively charged nano-hydroxyapatite particles and carboxylated carbon nanotubes move directionally into the concrete, penetrating to a depth of 9-11 mm. Nano-hydroxyapatite has a mineral composition similar to human bones and exhibits excellent chemical compatibility with calcium hydroxide and hydrated calcium silicate in concrete. It reacts with calcium ions in the concrete matrix to form stable hydroxyapatite-calcium silicate composite crystals, creating a strong chemical bond interface between the modified layer and the concrete matrix. The interface bonding strength can reach over 3.5 MPa, fundamentally solving the problem of traditional modified layers easily detaching. Carboxylated carbon nanotubes possess extremely high tensile strength and elastic modulus, forming a three-dimensional network reinforcement structure within the modified layer. This significantly improves the strength and toughness of the modified layer, increasing its elongation at break by over 50%, effectively resisting cracking caused by frost heave stress. Simultaneously, the high conductivity of carbon nanotubes enhances the electroosmosis effect, further improving the penetration depth and uniformity of the modifier. The nano-calcium phosphate-carbon nanotube composite modifier is composed of the following components by mass fraction: 30% nano-hydroxyapatite, 10% carboxylated carbon nanotube dispersion, 3% phosphate coupling agent, 0.3% sodium polyacrylate dispersant, and 56.7% deionized water. The nano-hydroxyapatite has a particle size of 25 nm and a specific surface area of ​​90 m². 2 / g; Carboxylated carbon nanotubes have a diameter of 15nm and a length of 3μm. The phosphate group at one end of the phosphate coupling agent molecule can react with the hydroxyl groups on the surface of nano-hydroxyapatite, while the amino group at the other end can react with the hydroxyl groups in the concrete matrix, forming a molecular bridge between the nanomaterial and the concrete matrix, further enhancing the interfacial bonding force; the dispersant sodium polyacrylate can effectively prevent the agglomeration of nanoparticles, ensuring that the modifier has good stability and permeability.

[0047] (4) Second component atmospheric pressure targeted impregnation: Disconnect the DC power supply, remove the electrodes, and wait for the first component modifier to dry to the surface (approximately 1.2 hours). Then, uniformly spray the temperature-sensitive self-healing microcapsule-hydrophobic aerogel composite modifier onto the concrete surface at a spraying rate of 0.7 kg / m². 2 The mixture was left to stand at normal pressure for 3.5 hours. Because the first component modifier had already filled the large and interconnected pores inside the concrete, forming a dense underlying protective structure, the second component modifier could only penetrate to a depth of 3-5 mm into the capillaries and microcracks inside the concrete under normal pressure, achieving graded targeted modification of pores at different scales. The thermosensitive self-healing microcapsules use polyurea-formaldehyde as the wall material, which has good alkali resistance and mechanical properties, and can remain stable in the alkaline environment of concrete for a long time. The core material is a mixture of epoxy resin E-51 and curing agent polyamide 650 in a 1:1 mass ratio. When microcracks are generated in the concrete during freeze-thaw cycles, the stress concentration at the crack tip causes the microcapsule wall material to rupture. Simultaneously, the temperature changes caused by the freeze-thaw cycles generate thermal stress inside the microcapsules, accelerating the rupture of the wall material. The released epoxy resin and curing agent quickly fill the microcracks and undergo a curing reaction, re-bonding the cracks together. The repair efficiency can reach over 80%, effectively preventing further crack propagation. The hydrophobic silica aerogel microspheres have a large number of hydrophobic groups grafted onto their surface, with a contact angle of 135°. This allows them to form a continuous hydrophobic layer inside the concrete, preventing water penetration and reducing water absorption by over 90%. Simultaneously, the aerogel microspheres possess a high porosity of 88%, and their internal nanopores can absorb frost heave stress, converting frost heave deformation into elastic deformation of the aerogel microspheres. This significantly reduces frost heave stress within the concrete and minimizes freeze-thaw damage. The thermosensitive self-healing microcapsule-hydrophobic aerogel composite modifier is composed of the following components by mass fraction: 18% thermosensitive self-healing microcapsules, 12% hydrophobic silica aerogel microspheres, 18% waterborne epoxy resin, 5% polyamide 650 curing agent, and 47% deionized water. The thermosensitive self-healing microcapsules have a particle size of 20 μm and a core material content of 65%; the hydrophobic silica aerogel microspheres have a particle size of 100 nm.

[0048] (5) Gradient power microwave-induced curing: The concrete surface was irradiated using a microwave generator with a frequency of 2450MHz, starting with 0.6W / cm². 2Irradiate with a power density of 1.1 W / cm² for 6 minutes to allow the modifier inside the concrete to solidify first, then irradiate with 1.1 W / cm² for 6 minutes. 2 The surface modifier was cured by irradiation at a high power density for 9 minutes. Throughout the irradiation process, the concrete surface temperature was monitored in real time using an infrared thermometer, maintaining a temperature between 65 and 75°C. Traditional microwave curing techniques typically use constant power irradiation. Due to the limited penetration depth of microwaves, the surface of the modified layer cures first, while the internal modifier remains incompletely cured. Furthermore, the difference in curing shrinkage between the surface and interior generates significant internal stress, leading to cracking of the modified layer. This invention employs a gradient power microwave-induced curing technology. First, low-power microwave irradiation allows the microwaves to penetrate deeper into the concrete, causing the internal modifier to cure first. Then, the microwave power is gradually increased, allowing the surface modifier to cure progressively. This gradient curing method from the interior to the surface effectively releases the internal stress generated by curing shrinkage, reducing internal stress by more than 60% and preventing cracking of the modified layer. Simultaneously, the selective heating characteristics of microwaves allow the modifier to preferentially absorb microwave energy and cure rapidly, while the temperature rise of the concrete matrix is ​​minimal, avoiding adverse effects on the mechanical properties of the concrete matrix.

[0049] (6) Curing treatment: The cured concrete is first cured in an environment with a temperature of 15±2℃ and a relative humidity of 90% for 3 days to allow the chemical reaction between the modifier and the concrete matrix to be more complete and to further improve the interfacial bonding strength. Then, it is cured in a standard curing room with a temperature of 20±2℃ and a relative humidity of more than 95% for 4 days. After curing, a 0.15mm thick layer of fluorocarbon protective agent is applied to the concrete surface to further improve the weather resistance and waterproof performance of the concrete surface.

[0050] Example 2: A method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments, comprising the following steps: (1) Concrete surface pretreatment: Use a wire brush to remove laitance, oil stains and loose particles from the concrete surface, then sandblast with quartz sand at a pressure of 0.5 MPa to achieve a surface roughness of Ra6.3. Rinse with high-pressure water at a pressure of 12 MPa and air dry until the surface moisture content is 6%. For areas with severe oil stains, first clean with a neutral degreasing agent, then rinse with high-pressure water to ensure that there are no oil stains left on the surface.

[0051] (2) Construction of directional electroosmotic channels: A layer of 20-mesh stainless steel wire mesh was laid on the concrete surface as the cathode electrode, and a 6-mm diameter titanium alloy rod was inserted into the concrete interior at a distance of 15mm from the surface as the anode electrode, with an electrode spacing of 15mm. A small amount of deionized water was sprayed on the concrete surface to keep it moist, and then a DC power supply was connected to apply a DC electric field with an electric field strength of 1.5V / cm for 30 minutes. The lower electric field strength can avoid damaging the pore structure inside the concrete while ensuring the formation of sufficient directional infiltration channels.

[0052] (3) First component electroosmotic assisted impregnation: The nano-calcium phosphate-carbon nanotube composite modifier is uniformly applied to the concrete surface at a coating amount of 1.2 kg / m². 2 The DC electric field was maintained for 45 minutes. The nano-calcium phosphate-carbon nanotube composite modifier consisted of the following components by mass fraction: 25% nano-hydroxyapatite, 8% carboxylated carbon nanotube dispersion, 2% phosphate coupling agent, 0.2% sodium polyacrylate dispersant, and 64.8% deionized water. The nano-hydroxyapatite had a particle size of 20 nm and a specific surface area of ​​80 m². 2 / g; Carboxylated carbon nanotubes have a diameter of 10nm and a length of 1μm. Smaller particle size nano-hydroxyapatite and carbon nanotubes have better permeability and can penetrate into the finer pores inside concrete.

[0053] (4) Second component atmospheric pressure targeted impregnation: Disconnect the DC power supply, remove the electrodes, and wait for the first component modifier to dry to the surface (approximately 1.5 hours). Then, uniformly spray the temperature-sensitive self-healing microcapsule-hydrophobic aerogel composite modifier onto the concrete surface at a spraying rate of 0.6 kg / m². 2 The mixture was allowed to stand at normal pressure for 3 hours. The thermosensitive self-healing microcapsule-hydrophobic aerogel composite modifier is composed of the following components by mass fraction: 15% thermosensitive self-healing microcapsules, 10% hydrophobic silica aerogel microspheres, 15% waterborne epoxy resin, 4% polyamide 650 curing agent, and 56% deionized water. The thermosensitive self-healing microcapsules have a particle size of 10 μm and a core material content of 60%; the hydrophobic silica aerogel microspheres have a particle size of 80 nm and a contact angle of 132°.

[0054] (5) Gradient power microwave-induced curing: The concrete surface was irradiated using a microwave generator with a frequency of 2450MHz, starting with 0.5W / cm². 2 Irradiate with a power density of 1.0 W / cm for 8 minutes, then at 1.0 W / cm 2 Irradiate with a power density of 10 min. Throughout the irradiation process, the concrete surface temperature is controlled between 60 and 70°C.

[0055] (6) Curing treatment: After curing, the concrete is first cured in an environment with a temperature of 15±2℃ and a relative humidity of 90% for 3 days, and then cured for 4 days under standard curing conditions. After curing, a 0.1mm thick layer of fluorocarbon protective agent is applied to the concrete surface.

[0056] Example 3: A method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments, comprising the following steps: (1) Concrete surface pretreatment: Use a wire brush to remove laitance, oil stains and loose particles from the concrete surface, then sandblast with quartz sand at a pressure of 0.7 MPa to achieve a surface roughness of Ra12.5. Rinse with high-pressure water at a pressure of 12 MPa and air dry until the surface moisture content is 10%. For microcracks with a width of less than 0.2 mm, proceed directly with subsequent treatment; for cracks with a width of more than 0.2 mm, repair with epoxy resin grout first, and then sandblast.

[0057] (2) Construction of directional electroosmotic channels: A layer of 20-mesh stainless steel wire mesh was laid on the concrete surface as the cathode electrode, and a 6-mm diameter titanium alloy rod was inserted into the concrete interior at a distance of 15mm from the surface as the anode electrode, with an electrode spacing of 15mm. A small amount of deionized water was sprayed on the concrete surface to keep it moist, and then a DC power supply was connected to apply a DC electric field with a strength of 2.5V / cm for 20 minutes. A higher electric field strength can improve the electroosmosis effect and accelerate the formation rate of the infiltration channels.

[0058] (3) First component electroosmotic assisted impregnation: The nano-calcium phosphate-carbon nanotube composite modifier is uniformly applied to the concrete surface at a coating amount of 1.5 kg / m². 2 The DC electric field is maintained for 30 minutes. The nano-calcium phosphate-carbon nanotube composite modifier consists of the following components by mass fraction: 35% nano-hydroxyapatite, 12% carboxylated carbon nanotube dispersion, 4% phosphate coupling agent, 0.5% sodium polyacrylate dispersant, and 48.5% deionized water. The nano-hydroxyapatite has a particle size of 30 nm and a specific surface area of ​​100 m². 2 / g; the carboxylated carbon nanotubes have a diameter of 20nm and a length of 5μm. A higher content of nano-hydroxyapatite and carbon nanotubes can improve the strength and interfacial bonding of the modified layer.

[0059] (4) Second component atmospheric pressure targeted impregnation: Disconnect the DC power supply, remove the electrodes, and wait for the first component modifier to dry to the surface (about 1 hour). Then, uniformly spray the temperature-sensitive self-healing microcapsule-hydrophobic aerogel composite modifier onto the concrete surface at a spraying rate of 0.9 kg / m². 2The mixture was allowed to stand at normal pressure for 4 hours. The thermosensitive self-healing microcapsule-hydrophobic aerogel composite modifier is composed of the following components by mass fraction: 20% thermosensitive self-healing microcapsules, 15% hydrophobic silica aerogel microspheres, 20% waterborne epoxy resin, 6% polyamide 650 curing agent, and 39% deionized water. The thermosensitive self-healing microcapsules have a particle size of 30 μm and a core material content of 70%; the hydrophobic silica aerogel microspheres have a particle size of 120 nm and a contact angle of 140°.

[0060] (5) Gradient power microwave-induced curing: The concrete surface was irradiated using a microwave generator with a frequency of 2450MHz, starting with 0.7W / cm². 2 Irradiate with a power density of 1.2 W / cm for 5 minutes, then at 1.2 W / cm 2 Irradiate with a power density of 8 minutes. Throughout the irradiation process, the surface temperature of the concrete is controlled between 70 and 80°C.

[0061] (6) Curing treatment: After curing, the concrete is first cured in an environment with a temperature of 15±2℃ and a relative humidity of 90% for 3 days, and then cured for 4 days under standard curing conditions. After curing, a 0.2mm thick layer of fluorocarbon protective agent is applied to the concrete surface.

[0062] Compared to Example 1, the unmodified ordinary concrete specimens had a concrete mix ratio of cement:sand:aggregate:water = 1:1.5:2.5:0.5, using PO 42.5 ordinary Portland cement, medium sand, crushed stone with a particle size of 5~20mm, and tap water. The specimen dimensions were 100mm×100mm×400mm, and it was cured in a standard curing room for 28 days.

[0063] Comparing with Example 2, the traditional silane impregnation method was used to modify the concrete. The specific steps were as follows: removing laitance, oil, and loose particles from the concrete surface, rinsing it with high-pressure water, and allowing it to air dry. Then, isobutyltriethoxysilane impregnating agent was evenly sprayed onto the concrete surface at a rate of 0.6 kg / m². 2 The specimens were left to stand under normal pressure for 24 hours, and then cured in a standard curing room for 7 days. The concrete mix proportions and specimen dimensions were the same as those of Control Example 1.

[0064] Comparing with Example 3, a negative pressure-two-component impregnation method was used to modify concrete. The specific steps were as follows: Remove laitance, oil, and loose particles from the concrete surface; rinse thoroughly with high-pressure water and allow to air dry until the surface moisture content is 10%; seal the concrete surface, evacuate to an absolute pressure of 40 kPa, maintain for 20 minutes, and then slowly introduce dry nitrogen to atmospheric pressure; uniformly spray the nano-silica sol-graphene composite modifier onto the concrete surface, evacuate again to an absolute pressure of 70 kPa, and maintain for 40 minutes; after the first component modifier is surface dry, uniformly spray the hyperbranched polyamide-aerogel microsphere composite modifier onto the concrete surface and allow it to stand for 2.5 hours under atmospheric pressure; a frequency of 2450 MHz and a power density of 1.0 W / cm³ were used. 2 The concrete surface was irradiated with microwave for 12 minutes; finally, it was cured in a standard curing room for 7 days. The concrete mix proportion and specimen size were the same as those of Control Example 1.

[0065] Performance testing According to the rapid freezing method in GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", the concrete specimens of Examples 1-3 and Control Examples 1-3 were subjected to dry-wet freeze-thaw cycle tests. During the test, the mass and dynamic modulus of elasticity of the specimens were measured every 50 freeze-thaw cycles, and the mass loss rate and relative dynamic modulus of elasticity retention rate were calculated. The test was stopped when the mass loss rate of the specimens reached 5% or the relative dynamic modulus of elasticity retention rate dropped to 60%. The test results are shown in Table 1.

[0066] Table 1. Test results of the freeze-thaw resistance of concrete modified by different methods:

[0067] As shown in Table 1, compared with unmodified ordinary concrete (Comparative Example 1), the concrete modified by the method of the present invention (Examples 1-3) showed a significant improvement in freeze-thaw resistance after 400 cycles, with the mass loss rate decreasing from 12.67% to below 0.9%, the relative dynamic modulus of elasticity retention increasing from 21.8% to over 92%, and the freeze-thaw resistance grade increasing from F100 to over F400. Compared with the traditional silane impregnation method (Comparative Example 2), the concrete modified by the method of the present invention showed a two-level improvement in freeze-thaw resistance, significantly enhancing durability. Compared with the negative pressure-two-component impregnation method (Comparative Example 3), the concrete modified by the method of the present invention showed a reduction of over 60% in mass loss after 400 cycles and an increase of over 12% in relative dynamic modulus of elasticity retention, indicating that the method of the present invention has superior effects in improving the freeze-thaw resistance and durability of concrete.

[0068] Furthermore, the internal pore structure of the concrete modified using the method of this invention was significantly improved. Macropores and interconnected pores were filled with a nano-calcium phosphate-carbon nanotube composite modifier, while capillary pores and microcracks were sealed with a thermosensitive self-healing microcapsule-hydrophobic aerogel composite modifier, forming a dense, gradient, freeze-thaw resistant structure. After 300 freeze-thaw cycles, almost no new microcracks were generated inside the modified layer, and the existing microcracks were filled by the repair agent released from the self-healing microcapsules. This demonstrates that the method of this invention endows the concrete with excellent self-healing capabilities, effectively extending the service life of concrete structures.

[0069] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments, characterized in that, Includes the following steps: (1) Concrete surface pretreatment: Remove laitance, oil stains and loose particles from the concrete surface, sandblast to achieve a surface roughness of Ra6.3~Ra12.5, rinse with high pressure water and air dry naturally until the surface moisture content is 6%~10%; (2) Construction of electroosmotic directional infiltration channels: A cathode electrode is arranged on the concrete surface, and an anode electrode is arranged 15 mm away from the surface inside the concrete. A DC electric field is applied with an electric field strength of 1.5~2.5V / cm and an energizing time of 20~30min to form a directional infiltration channel from the surface to the interior inside the concrete. (3) Electroosmotic assisted impregnation of the first component: The nano-calcium phosphate-carbon nanotube composite modifier is uniformly brushed onto the concrete surface and kept in a DC electric field for 30-45 minutes to allow the modifier to penetrate into the concrete to a depth of 8-12 mm and form a chemical bond interface with the concrete matrix. (4) Second component atmospheric pressure targeted impregnation: Disconnect the DC electric field, and after the first component modifier is surface dry, spray the temperature-sensitive self-healing microcapsule-hydrophobic aerogel composite modifier evenly onto the concrete surface, and let it stand for 3~4 hours under atmospheric pressure to allow the modifier to penetrate into the concrete to a depth of 3~6mm and fill the capillary pores and microcracks. (5) Gradient power microwave-induced curing: The concrete surface is irradiated with microwaves at a frequency of 2450MHz, starting with 0.5~0.7W / cm². 2 Irradiate with a power density of 5-8 min, followed by 1.0-1.2 W / cm². 2 Irradiate with power density for 8-10 minutes to allow the modifier to be cured in a gradient from the inside to the surface; (6) Curing treatment: The solidified concrete is first cured in an environment with a temperature of 15±2℃ and a relative humidity of 90% for 3 days, and then cured under standard curing conditions for 4 days to complete the modification treatment.

2. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: In step (2), the cathode electrode is a 20-mesh stainless steel wire mesh, the anode electrode is a titanium alloy rod with a diameter of 6 mm, and the electrode spacing is 15 mm.

3. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: The nano-calcium phosphate-carbon nanotube composite modifier described in step (3) consists of the following components in mass fraction: 25%~35% nano-hydroxyapatite, 8%~12% carboxylated carbon nanotube dispersion, 2%~4% phosphate coupling agent, 0.2%~0.5% sodium polyacrylate dispersant, and the balance being deionized water.

4. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: The nano-hydroxyapatite has a particle size of 20-30 nm and a specific surface area of ​​80-100 m². 2 / g; the carboxylated carbon nanotubes have a diameter of 10~20nm and a length of 1~5μm.

5. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: The thermosensitive self-healing microcapsule-hydrophobic aerogel composite modifier described in step (4) consists of the following components in mass fraction: 15%~20% thermosensitive self-healing microcapsules, 10%~15% hydrophobic silica aerogel microspheres, 15%~20% waterborne epoxy resin, 4%~6% curing agent polyamide 650, and the balance deionized water.

6. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: The temperature-sensitive self-healing microcapsules use polyurea formaldehyde as the wall material and a mixture of epoxy resin E-51 and curing agent polyamide 650 in a 1:1 mass ratio as the core material, with a particle size of 10~30μm and a core material content of 60%~70%; the hydrophobic silica aerogel microspheres have a particle size of 80~120nm and a contact angle greater than 130°.

7. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: In step (3), the amount of modifier applied is 1.2~1.5 kg / m². 2 In step (4), the amount of modifier sprayed is 0.6~0.9 kg / m². 2 .

8. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: In step (5), during microwave irradiation, an infrared thermometer is used to monitor the concrete surface temperature in real time and control the temperature between 60 and 80°C.

9. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: In step (2), before applying the DC electric field, a small amount of deionized water is sprayed on the concrete surface to keep the surface moist.

10. The method for targeted antifreeze modification of concrete under dry and wet freeze-thaw environments according to claim 1, characterized in that: After step (6) is completed, apply a layer of fluorocarbon protective agent with a thickness of 0.1~0.2mm to the concrete surface.

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