Multi-layer slow-release additive for negative-temperature emergency repair concrete, preparation method and usage method

Abstract

The present invention relates to the technical field of building materials, and particularly to a multi-layer slow-release additive for negative-temperature emergency repair concrete, a preparation method and a usage method. The multi-layer slow-release additive sequentially comprises a hydration regulation layer, a setting regulation layer, a pore regulation layer and a temperature regulation layer from outside to inside; the mass ratio of the hydration regulation layer, the setting regulation layer, the pore regulation layer and the temperature regulation layer is 1-2:1-2:1-2:5; the multi-layer slow-release additive realizes targeted regulation of the mixing, curing and service processes of negative-temperature emergency repair concrete through a differential encapsulation technology: the hydration regulation layer is released after being dissolved in hot water; after the water-soluble film swells, the setting regulation layer is slowly released; the isolation layer is dissolved in an alkaline environment to cause the pore regulation layer to be released; the temperature regulation layer is a cement layer permanently encapsulating a phase change material. The preparation process of the multi-layer slow-release additive is simple, the operation for emergency repair and reinforcement is convenient, and the workability and durability of negative-temperature emergency repair concrete can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly to a multi-layer slow-release additive for negative-temperature emergency repair concrete, a preparation method and a use method thereof. Background Art

[0002] Under negative-temperature conditions, the demand for emergency repair and reinforcement of infrastructure is extensive. In engineering, rapid-hardening concrete is usually used. However, negative temperature can cause slow setting and hardening of concrete. At the same time, conventional interface treatment methods result in poor bonding effect between new and old concrete interfaces, and microscopic pores lead to poor erosion resistance of materials, which affects the durability of emergency repair and reinforcement materials.

[0003] Currently, industrial salts are used to lower the freezing point of mixing water to meet the requirements of negative-temperature concrete construction. At the same time, retarders and early-strength agents are introduced to adjust the setting and hardening rate of cement to ensure the constructible time and rapid development of strength. The simultaneous addition of the above-mentioned various additives will restrict each other, resulting in performance attenuation. The batch-by-batch addition process is cumbersome and not suitable for emergency repair and reinforcement scenarios. Phase change materials are used for low-temperature construction, and the released heat can delay the freezing of liquid water, but there are still problems such as easy leakage of materials. Sandblasting, chiseling and applying interface agents have limited improvement in the bonding performance of the repair and reinforcement interfaces. Dense fillers such as emulsions and paraffins in concrete can reduce the porosity, but direct addition seriously affects the workability of construction.

[0004] There is an urgent need for an additive with multiple functions for negative-temperature emergency repair concrete to achieve hierarchical regulation of the mixing, solidification and service processes of negative-temperature emergency repair concrete, and to meet the requirements of negative-temperature construction, interface bonding and durability improvement.

[0005] The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] The first object of the present invention is to provide a multi-layer slow-release additive for negative-temperature emergency repair concrete, which realizes targeted regulation of the mixing, curing and service processes of negative-temperature emergency repair concrete through differential encapsulation technology, and different layers of materials can be gradually released from the outside to the inside under different conditions during use.

[0007] The above technical object of the present invention is achieved by the following technical solutions:

[0008] A multi-layer slow-release additive for negative-temperature emergency repair concrete, characterized in that the multi-layer slow-release additive comprises a hydration regulation layer, a setting regulation layer, a pore regulation layer and a temperature regulation layer from outside to inside, and the mass ratio between layers is 1-2:1-2:1-2:5. Among them, the hydration regulation layer is released after being dissolved in hot water; after the water-soluble film swells, the setting regulation layer is slowly released; the isolation layer is dissolved in an alkaline environment to release the pore regulation layer; the temperature regulation layer is a phase change material permanently encapsulated by a cement layer.

[0009] Add this multi-layer slow-release additive to concrete and mix it with quick-setting cement. Mix with hot water to gradually dissolve the freezing point regulator and retarder in the hydration regulation layer; the freezing point regulator dissolves to form a low-freezing-point mixing medium; the retarder delays the hydration rate of the quick-setting cement to ensure that the negative-temperature concrete can be mixed and poured; during this process, after pouring the negative-temperature emergency repair concrete, vibrate it densely to form a pavement layer to be cured, which is the mixing regulation for negative-temperature emergency repair concrete; as the hydration regulation layer dissolves, the water-soluble film material in the setting regulation layer becomes unstable under the action of free water in the concrete, causing the internal early-strength agent to be slowly released; to achieve hydration curing, the pH of the concrete gradually rises during the hydration process. The carboxylate groups in the isolation film material in the pore regulation layer are protonated in an alkaline environment, the intermolecular repulsive force increases, resulting in swelling of the structure, and then the internal sealant is slowly released; the sealant acts on the admixture to generate polysialate, sealing the microscopic pores; this is the curing regulation for negative-temperature emergency repair concrete; the cement-encapsulated phase change material in the temperature regulation layer uses the energy storage and heat release of the phase change material to provide curing heat and reduce the freeze-thaw cycle during service. This is the service regulation for negative-temperature emergency repair concrete; the present invention realizes targeted regulation of the mixing, curing and service processes of negative-temperature emergency repair concrete through differential encapsulation technology, reducing the attenuation of concrete performance caused by simultaneous addition.

[0010] Preferably, the hydration regulation layer is composed of a freezing point regulator and a retarder. The hydration regulation layer is dissolved in hot water at 50-60°C, and the layer thickness is 0.2-0.5 mm; setting the thickness range ensures the content of the freezing point regulator and retarder in the additive and controls the final size of the additive.

[0011] The freezing point regulator is one or more of sodium nitrite or ethylene glycol, and the particle size range is 30-50 mesh; setting the particle size range ensures the dispersion and migration of the freezing point regulator in the concrete. The freezing point of sodium nitrite is -30°C, and the freezing point of ethylene glycol is -11.5°C. Multi-temperature regulation of -10 to 0°C, -20 to 0°C, and -30 to 0°C is achieved by adjusting the ratio. The type and ratio of the freezing point regulator are determined according to the environment; specifically, after mixing the multi-layer slow-release additive with water, the freezing point is lowered by changing the vapor pressure of the water, providing a low-point mixing medium for the concrete.

[0012] The retarder is one or several of sucrose, glucose, and borax, with a particle size range of 80 - 100 mesh; the set particle size range ensures the dispersion and migration of the retarder in concrete. The molecular structure of the retarder contains a large number of polyhydroxy groups, which can adsorb on the surface of the rapid-hardening cement, extend the contact between cement particles and water, delay the cement hydration reaction and rate, and reduce the heat release of the cement.

[0013] Preferably, the setting control layer is successively from outside to inside a water-soluble film and an early strength agent; the water-soluble film contacts the free water in the concrete after the hydration control layer dissolves, and releases the early strength agent after gradually dissolving.

[0014] More preferably, the interlayer thickness of the setting control layer is 0.2 - 0.5 mm, and the thickness of the water-soluble film is 0.2 - 0.5 μm. The set range ensures the content of the early strength agent in the additive and controls the final size of the additive.

[0015] The water-soluble film is one or several of cellulose, plant gum, or animal gum, with a particle size range of 50 - 100 mesh; its structure contains a large number of hydrophilic groups and has water solubility. The set particle size range ensures that the water-soluble film material is conducive to spraying preparation. The water-soluble film contacts the free water in the concrete after the hydration control layer dissolves, and the polar side groups in its molecular structure form hydrogen bonds with water, causing the structure of the water-soluble film to become unstable and gradually dissolve.

[0016] The early strength agent is one or several of sodium carbonate, calcium carbonate, and C-S-H crystal nuclei, with a particle size range of 200 - 500 mesh and a content ≥ 90%; the set particle size range can ensure the dispersion and migration of the early strength agent in concrete. Too small or too large particle size is not conducive to spraying preparation; the content range ensures the content of the early strength agent in the additive and the interfacial bonding effect. There are a large number of broken bonds and structural defects on the surface of the C-S-H crystal nuclei, and the Zeta potential of calcium carbonate and sodium carbonate particles is relatively high, which has a strong adsorption ability for Ca 2+ and reduces the migration rate of Ca 2+ , promotes the growth of "stable nuclei", can serve as the nucleation site of hydration products, and promotes the increase of cement strength.

[0017] Preferably, the pore control layer is successively from outside to inside a separation film and a sealant; during the hydration process, the pH in the concrete changes from 7 to 13, and the separation film gradually swells in the alkaline environment, causing the sealant to be slowly released.

[0018] More preferably, the thickness of the pore control layer is 0.2 - 0.5 mm; the thickness of the separation film is 0.2 - 0.5 μm. The set range ensures the content of the sealant in the additive and at the same time controls the final size of the additive.

[0019] The isolation film is one or several of sodium alginate and potassium alginate. The molecular formula of sodium alginate is (NaC6H7O6)n, and the molecular formula of potassium alginate is (C6H7O6K)n, where n is 1 - 20; the setting range of n controls the dissolution rate. In a neutral environment, the isolation film materials are connected by intermolecular forces. In an alkaline environment, a large number of carboxylate groups in the molecular structure are protonated, the intermolecular repulsion is enhanced, the molecular structure swelling is accelerated, and the isolation film dissolves.

[0020] The sealing agent is one or several of sodium silicate and sodium metasilicate, and the particle size range is 80 - 100 mesh. The molecular formula of sodium silicate is Na2O·nSiO2, the soluble solid ≥ 99%, and the modulus n: 2.0 - 3.6; the molecular formula of sodium metasilicate is Na2SiO3, and the soluble solid ≥ 99%. Both of their molecular structures contain Si - O - Si, react with water to decompose a large amount of OH- acting on the admixture, accelerate the dissolution of [SiO4] and [AlO4] tetrahedrons in the admixture, and generate polysialate through re - bonding by Si - O connection reaction, which can seal micro - pores; at the same time, it can bond hydration products and aggregates. The setting of the modulus, soluble solid content and particle size range ensures the hydrolysis reaction rate and process, and then controls the formation of polysialate.

[0021] Preferably, the temperature control layer is composed of cement and a phase - change material; it is permanently encapsulated by a cement layer, reducing the leakage risk of the phase - change material and the existence of the interfacial transition zone.

[0022] The cement is Portland cement. The specific surface area ≥ 300m 2 / kg, and the 28 - day compressive strength ≥ 42.5MPa; it is sprayed simultaneously with water, wraps the phase - change material, and forms a cement layer after hardening.

[0023] The temperature control layer is in particles, with a diameter of 0.2 - 1.18mm, and the thickness of the cement layer is 10 - 50μm; the size settings of the temperature control layer and the cement layer ensure the encapsulation amount of the phase - change material in the additive, and at the same time control the final size of the additive to be 0.8 - 2.68mm.

[0024] The phase - change material is one or several of n - dodecane and n - tetradecane, with melting points of - 12°C and - 2.2°C respectively, and endothermic enthalpies of 802kJ / kg and 920kJ / kg respectively. By setting two phase - change materials with different melting points, multi - temperature control of - 10 - 0°C, - 20 - 0°C, - 30 - 0°C can be achieved by adjusting the ratio, and the type and ratio of the phase - change material are determined according to the environment.

[0025] The second object of the present invention is to provide a preparation method of a multi - layer slow - release additive for negative - temperature emergency repair concrete. The preparation method includes the following operation steps:

[0026] S1: Temperature control layer: The cement layer wraps the phase - change material;

[0027] S2: Pore regulation layer: A sealing agent and an isolation film material are sequentially sprayed on the surface of S1 particles.

[0028] S3: Setting regulation layer: An early strength agent and a water-soluble film material are sequentially sprayed on the surface of S2 particles.

[0029] S4: Hydration regulation layer: A retarder and a freezing point regulator are simultaneously sprayed on the surface of S3 particles.

[0030] More preferably, the preparation method of the multi-layer slow-release additive comprises the following operation steps:

[0031] S1: Temperature regulation layer: The phase change material is placed in a film coating machine, and cement powder and water are simultaneously sprayed. The machine is rotated at a constant speed to wrap the cement layer around the phase change material to obtain spherical particles, and then left standing for 24 h until the cement layer gains strength.

[0032] S2: Pore regulation layer: The particles in S1 are sieved, and the particles with a diameter of 0.2 - 1.18 mm are placed in a film coating machine. A sealing agent and an isolation film material are sequentially sprayed, and after granulation by wrapping, they are left standing for more than 2 h.

[0033] S3: Setting regulation layer: The particles in S2 are sieved, and the particles with a diameter of 0.4 - 1.68 mm are placed in a film coating machine. An early strength agent and a water-soluble film material are sequentially sprayed, and after granulation by wrapping, they are left standing for more than 2 h.

[0034] S4: Hydration regulation layer: The particles in S3 are sieved, and the particles with a diameter of 0.6 - 2.18 mm are placed in a film coating machine. A retarder and a freezing point regulator are simultaneously sprayed, and the final size of the additive is controlled to be 0.8 - 2.68 mm, and then left standing for more than 2 h.

[0035] The third object of the present invention is to provide a method for using a multi-layer slow-release additive for negative temperature emergency repair concrete, comprising the following operation steps:

[0036] (1) Slurry preparation: The multi-layer slow-release additive, rapid hardening cement, and admixture are mixed in proportion, and water at 50 - 60 °C is added and stirred to obtain a uniform fluid mixture.

[0037] (2) Concrete preparation: Aggregate is added in step (1) and stirred to prepare negative temperature emergency repair concrete.

[0038] (3) Spraying interface agent: An organic interface agent is sprayed on the interface for emergency repair and reinforcement.

[0039] (4) Pouring: After the spraying of the interface agent is completed, the negative temperature emergency repair concrete prepared in step (2) is poured and vibrated densely.

[0040] (5) Curing: The working surface is treated and cured under natural conditions.

[0041] Preferably, the method for using the multi-layer slow-release additive includes the following steps:

[0042] (1) Slurry preparation: Mix the multi-layer slow-release additive, rapid hardening cement, and admixture in proportions of 5-10 parts, 70-80 parts, and 10-25 parts by mass, dry mix for 3-5 min, and spray and add 30-40 parts by mass of water at 50-60 °C, and stir until a uniform fluid mixture is obtained;

[0043] (2) Concrete preparation: Within 5 min after the mixture in step (1) becomes fluid, add 20-30 parts of fine aggregate and 20-30 parts of coarse aggregate in proportion, and stir for 3-5 min to prepare negative temperature emergency repair concrete;

[0044] (3) Spraying the interface agent: While adding the aggregate in step (2), spray an organic interface agent on the interface to be repaired and reinforced, and the coating amount is 0.1-0.2 kg / m 2 ;

[0045] (4) Pouring: Pour the negative temperature emergency repair concrete within 5 min after the spraying of the interface agent is completed, and vibrate it densely;

[0046] (5) Curing: Treat the working surface and cure it under natural conditions.

[0047] Preferably, the rapid hardening cement is sulfoaluminate cement, with an initial setting time ≤ 25 min, a final setting time ≥ 180 min, and a 24-hour compressive strength ≥ 32 MPa. The selection of the range of setting time and strength ensures the rapid development of strength and the requirements for emergency repair.

[0048] Preferably, the admixture is one or more of slag, fly ash, and steel slag, and the content of SiO2 ≥ 15%, and the content of Al2O3 ≥ 25%. The setting of the component content ensures that sufficient [SiO4] and [AlO4] can be continuously dissolved after the sealant acts on the admixture until a three-dimensional network structure of Si-O bonding is formed.

[0049] Preferably, the interface agent is one or more of acrylic emulsion, VAE emulsion, and styrene-acrylate emulsion, with a viscosity range of 1000-4000 mPa·S and a solid content ≥ 47 wt%. The set viscosity range ensures good wettability and permeability of the interface agent at the concrete repair and reinforcement interface, and the set solid content ensures that the interface agent can meet the effects of wetting and bonding hydration products and aggregates within the spraying amount range.

[0050] In summary, the present invention has the following beneficial effects:

[0051] (1) The present invention provides a differential encapsulation technology: hot water mixing causes the freezing point regulator and retarder in the hydration regulation layer to gradually dissolve; a low-freezing-point mixing medium can be formed to regulate the hydration rate, enabling the mixing and pouring of negative-temperature emergency repair concrete; in the setting regulation layer, the polar side groups of the water-soluble film material form hydrogen bonds with free water, resulting in structural instability and slow release of the setting regulation layer; the early strength agent can serve as a nucleation site for hydration products, accelerating strength development and enhancing interfacial adhesion; during the hydration process, the pH of the concrete gradually rises from 7 to 13, and the carboxylate groups in the isolation film material in the pore regulation layer are protonated in the alkaline environment, increasing the intermolecular repulsive force and causing the structure to swell, resulting in slow release of the sealant; it can act on admixtures to generate polysialates and seal micro-pores; in the temperature regulation layer, the cement encapsulates the phase change material, preventing performance degradation caused by material leakage, using the energy storage and heat release of the phase change material to provide curing heat and reducing freeze-thaw cycles during service. The present invention uses a homogeneous cement layer to reduce the interfacial transition zone. Differential encapsulation and multi-layered graded slow release can achieve targeted regulation of the mixing, curing, and service processes of negative-temperature emergency repair concrete, reducing the performance degradation caused by simultaneous addition.

[0052] (2) The multi-layered slow-release additive of the present invention contains a setting regulation layer that can slowly release an early strength agent; after the water-soluble film dissolves in the hydration regulation layer and contacts the free water in the concrete, the polar side groups in its molecular structure form hydrogen bonds with water, causing the structure of the water-soluble film to become unstable, gradually dissolve, and release the early strength agent. Driven by osmotic pressure, the early strength agent migrates to the repair and reinforcement interface. Due to the presence of a large number of broken bonds and structural defects on the surface of the early strength agent, the Zeta potential is relatively high, and it has a strong ability to adsorb ions. It can serve as a nucleation site for hydration products at the interface, improving the interfacial density; the interfacial agent forms chemical bonds with hydration products and aggregates to form an organic-inorganic three-dimensional interlocking structure, further enhancing the interfacial adhesion performance. 2+ It has a strong ability to adsorb ions, can serve as a nucleation site for hydration products at the interface, and improve the interfacial density; the interfacial agent forms chemical bonds with hydration products and aggregates to form an organic-inorganic three-dimensional interlocking structure, further enhancing the interfacial adhesion performance.

[0053] (3) The multi-layered slow-release additive of the present invention contains a pore regulation layer that can slowly release a sealant; during the hydration process, the pH in the concrete changes from 7 to 13. In the alkaline environment, a large number of carboxylate groups in the molecular structure of the isolation film are protonated, increasing the intermolecular repulsive force and accelerating the swelling of the molecular structure, resulting in slow release of the sealant. Driven by capillary action, it migrates outward along the internal pore structure. The OH- after hydrolysis of the sealant acts on the admixture, accelerating the dissolution of its [SiO4] and [AlO4] tetrahedrons. Through sharing oxygen and alternating bonding, a polysialate with a three-dimensional network structure is formed, which can seal micro-pores and also bond hydration products and aggregates; supplemented by a well-encapsulated phase change material, it reduces the freeze-thaw damage and ion erosion of the concrete, achieving an improvement in the durability of the emergency repair and reinforcement material. Description of the Drawings

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0055] Figure 1 It is a particle model diagram of the composite additive adopted by the present invention.

[0056] Reference numerals: 1, hydration regulation layer; 2, water-soluble film in the setting retardation regulation layer; 3, early strength agent in the setting retardation regulation layer; 4, isolation film in the pore regulation layer; 5, sealant in the pore regulation layer; 6, cement layer in the temperature regulation layer; 7, phase change material in the temperature regulation layer. Specific embodiments

[0057] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, a multi-layer slow-release additive for negative-temperature emergency repair concrete, its preparation and use methods, their specific embodiments, features and effects are described in detail as follows.

[0058] Sources of raw materials used in the embodiments:

[0059] Freezing point regulator: sodium nitrite, ethylene glycol, purchased from Beijing Kangpu Huiwei Technology Co., Ltd., white crystalline powder, 30 - 50 mesh, content ≥ 90%; the freezing points of sodium nitrite and ethylene glycol are -30°C and -11.5°C respectively.

[0060] Setting retarder: sucrose, CAS: 57 - 50 - 1, glucose, CAS: 50 - 99 - 7, anhydrous borax, CAS: 1330 - 43 - 4, purchased from Macklin Reagent, particle size range 80 - 100 mesh.

[0061] Early strength agent: sodium carbonate, CAS: 497 - 19 - 8, calcium carbonate, CAS: 471 - 34 - 1, purchased from Guangzhou Qiangda New Materials; C-S-H crystal seeds purchased from Jiangsu Aolait; particle size range 200 - 500 mesh, content ≥ 90%.

[0062] Water-soluble film: cellulose, molecular formula (C6HO5)n, CAS: 9004 - 34 - 6, purchased from Macklin Reagent; plant gum selects sesame gum, CAS: 38821 - 53 - 3, animal gum selects bone glue, purchased from Chongqing Tianrun Biological Products Co., Ltd. Particle size range is 50 - 100 mesh.

[0063] Sealing agent: Sodium silicate with the molecular formula Na2O·nSiO2, where n ranges from 2.0 to 3.6; Sodium metasilicate with the molecular formula Na2SiO3, CAS: 6834-92-0, solid powder, sourced from Tongxiang Chemical Industry in Zhejiang. Particle size range is 80 - 100 mesh, soluble solids ≥ 99%.

[0064] Separator membrane: Sodium alginate with the molecular formula C6H7NaO6, CAS: 9005-38-3, purity ≥ 90%; Potassium alginate with CAS: 9005-36-1, molecular formula C 12 H 16 K2O 13 , purity ≥ 90%, sourced from Macklin Reagent.

[0065] Phase change material: n-Dodecane with CAS: 112-40-3, n-Tetradecane with CAS: 629-59-4; Melting points are -12°C and -2.2°C respectively, heat absorption enthalpies are 802 kJ / kg and 920 kJ / kg, sourced from Macklin Reagent.

[0066] Cement: P·O42.5 ordinary Portland cement, sourced from Conch Cement Factory, specific surface area is 328 m 2 / kg, 28-day compressive strength is 47 MPa.

[0067] Quick-setting cement: R·SAC42.5 cement, specific surface area ≥ 350 m 2 / kg, initial setting ≤ 25 min, final setting ≥ 180 min, 24-hour compressive strength ≥ 32 MPa, sourced from Dengfeng Dengdian Cement Factory.

[0068] Admixture: Fly ash sourced from the secondary ash of Jurong Power Plant, specific surface area 287 m 2 / kg, SiO2 content is 36%, Al2O3 content is 35%; Slag powder is S95 slag powder produced by Huailong Slag Powder Factory, specific surface area is 385 m 2 / kg, SiO2 content is 36%, Al2O3 content is 35%; Steel slag is sourced from Nanjing Chenghong Building Materials, 200 mesh, density is 3.3 g / cm 3 , CaO content is 40%, SiO2 content is 22%.

[0069] Fine aggregate: River sand and lake sand, Nanjing Kangsisheng Building Materials, particle size 0.1 - 3 mm, continuous grading.

[0070] Coarse aggregate: Basalt gravel, Hebei Yueshan Environmental Protection Technology Co., Ltd., particle size range 10 - 25 mm.

[0071] Interface agent: acrylic emulsion, styrene-acrylate emulsion, milky white viscous liquid, viscosity 2000 - 4000 mPa·S, solid content 49 - 51 wt%, sourced from Weifang Ruiguang Chemical Co., Ltd.; VAE emulsion, Wacker VINNAPAS EP707K from Germany, viscosity 1000 - 2500 mPa·S, solid content 50 wt%.

[0072] After the preparation of negative-temperature concrete, its performance is evaluated according to the following test methods:

[0073] (1) Spread: Refer to the "Standard Test Method for Properties of Fresh Concrete" GB / T 50080-2016, and test the spread at the time of discharge after mixing and the spread after standing for 10 minutes respectively. The measurement should be accurate to 1 mm; the negative-temperature environment is set at -5°C, -20°C, -30°C, and cured in an ultra-low temperature refrigerator.

[0074] (2) Setting time: According to the setting time determination method in the "Standard Test Method for Properties of Fresh Concrete" GB / T 50080-2016, the measurement is accurate to 1 MPa; the negative temperature is set at -5°C, -20°C, -30°C, and the mixture is placed in an ultra-low temperature refrigerator; the experimental conditions are set at a low temperature of 0 - 5°C to reduce heat exchange.

[0075] (3) Compressive strength: Refer to the "Test Method for Mechanical Properties of Concrete" GB / T 50081-2019, the size of the formed specimen is 100*100*100 mm, and the measurement is accurate to 1 MPa; the low-temperature curing of concrete is -5°C and -20°C respectively; according to the requirements of emergency repair and reinforcement, the 24-hour strength needs to be determined.

[0076] (4) Interface bond strength: Refer to the "Repair Mortar" JCT 2381-2016 standard, the size of the bonded cube specimen is 150 mm 3 , and for new and old concrete, each is (150 mm × 150 mm × 75 mm). It is tested using a splitting tensile test mold and calculated as follows:

[0077]

[0078] f ft,s — Splitting tensile strength of the bonded specimen, MPa;

[0079] F max — Maximum load, N;

[0080] A — Bonded surface area of the specimen, mm 2 , approximately taken as 150 mm × 150 mm in the test.

[0081] (5) Freeze-thaw cycle resistance: In accordance with the "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082), the specimen size is 100×100×400 mm, the mass loss is measured, and the unit is %, with 100 cycles as a period. The specimen size is 100×100×100 mm, the compressive strength is measured, the unit is MPa, and 200 cycles are used as a period.

[0082] (6) 28d impermeability pressure: The test refers to the "Standard Test Method for Basic Properties of Building Mortar" JGJ / T 70-2009. Concrete specimens are formed, and the maximum pressure when 4 specimens out of 6 specimens in each group do not show water seepage is calculated, and the unit is recorded as MPa.

[0083] Example 1

[0084] A multi-layer slow-release additive for negative-temperature emergency repair concrete, the composition of which from the outside to the inside is a hydration regulation layer, a setting regulation layer, a pore regulation layer and a temperature regulation layer in turn, and the mass ratio is 1.5:1.5:1.5:5.

[0085] Hydration regulation layer: It includes a freezing point regulator and a retarder combined in a mass ratio of 1:1. Among them, the freezing point regulator is a combination of sodium nitrite and ethylene glycol in a mass ratio of 1:1; the retarder is a combination of sucrose, glucose and borax in a mass ratio of 2:2:1.

[0086] Setting regulation layer: The early strength agent is a combination of sodium carbonate, calcium carbonate and C-S-H crystal nuclei in a mass ratio of 1:2:2; the water-soluble film is a combination of bone glue, sesame glue and cellulose in a mass ratio of 1:2:2.

[0087] Pore regulation layer: The sealant is a combination of sodium silicate and sodium metasilicate in a mass ratio of 4:1; the isolation film is a combination of sodium alginate and potassium alginate in a mass ratio of 3:2;

[0088] Temperature regulation layer: Cement, P·O42.5 ordinary Portland cement, and the phase change materials are a combination of n-dodecane and n-tetradecane in a mass ratio of 4:1; it is applicable to the range of -20°C to 0°C.

[0089] A preparation method of a multi-layer slow-release additive for negative-temperature emergency repair concrete, including the following operation steps:

[0090] S1: Temperature regulation layer: Place the phase change material in a film coating machine, and at the same time spray cement and water, rotate the machine at a constant speed to make the cement layer wrap around the phase change material to obtain spherical particles, and let it stand for 24 h until the cement layer gains strength.

[0091] S2: Pore regulation layer: Sieve the particles in S1, select the particles with a diameter of 0.2 - 1.18 mm and place them in a film coating machine, and spray the sealant and the isolation film material in turn, wrap and granulate, and let it stand for more than 2 h;

[0092] S3: Coagulation regulation layer: Sieving the particles in S2, selecting particles with a diameter of 0.4 - 1.68 mm and placing them in a film coating machine. Sequentially spray early strength agent and water-soluble film material, agglomerate by coating, and let stand for more than 2 h.

[0093] S4: Hydration regulation layer: Sieving the particles in S3, selecting particles with a diameter of 0.6 - 2.18 mm and placing them in a film coating machine. Simultaneously spray a retarding agent and a freezing point regulator, and simultaneously control the final size of the additive to be 0.8 - 2.68 mm, and let stand for more than 2 h.

[0094] A method for using a multi-layer slow-release additive for negative-temperature emergency repair concrete, comprising the following operation steps:

[0095] (1) Slurry preparation: Mix the multi-layer slow-release additive, rapid hardening cement, and admixture in a ratio of 10:80:10 by mass, dry mix for 5 min; spray and add 30 parts by mass of water at 60 °C, and stir until a uniform fluid mixture is obtained; the admixture is composed of slag, fly ash, and steel slag in a mass ratio of 1:2:2.

[0096] (2) Concrete preparation: Within 5 min after the mixture in step (1) becomes fluid, add 20 parts of fine aggregate and 30 parts of coarse aggregate in proportion, and stir for 5 min to prepare negative-temperature emergency repair concrete;

[0097] (3) Spraying interface agent: While adding the aggregate in step (2), spray an organic interface agent on the interface of a 150×150×75 mm specimen, with a coating amount of 0.2 kg / m 2 , and the interface agent is composed of acrylic emulsion, VAE emulsion, and styrene-acrylate emulsion in a mass ratio of 1:2:2.

[0098] (4) Pouring: Pour into the mold within 5 min after the interface agent spraying is completed, and simultaneously form the specimens required for testing, and vibrate thoroughly;

[0099] (5) Curing: Treat the working surface and cure under natural conditions.

[0100] Table 1 Performance test of negative-temperature emergency repair concrete

[0101] Test Items Unit Example 1 Initial Spread mm 450 10 - minute Spread mm 430 Initial Setting Time (-5°C) min 25 Initial Setting Time (-20°C) min 35 24 - hour Compressive Strength (-5°C) MPa 35 24 - hour Compressive Strength (-20°C) MPa 30 Interface Bonding Strength MPa 2.5 Freeze - Thaw Cycle - Mass Loss (cycles) ％ 1.0(2) Freeze - Thaw Cycle - Compressive Strength (cycles) MPa 45(2) 28 - day Impermeability Pressure MPa 6.7

[0102] Example 2

[0103] A multi-layer slow-release additive for negative-temperature emergency repair concrete, the composition of which from the outside to the inside is sequentially a hydration regulation layer, a coagulation regulation layer, a pore regulation layer, and a temperature regulation layer, and the mass ratio is 1:2:1.5:5.

[0104] Hydration regulation layer: It includes a freezing point regulator and a retarding agent combined in a mass ratio of 1:2. The freezing point regulator is composed of sodium nitrite and ethylene glycol combined in a mass ratio of 1:1; the retarding agent is composed of sucrose, glucose and borax combined in a mass ratio of 2:2:1.

[0105] Setting regulation layer: The early strength agent is composed of sodium carbonate, calcium carbonate and C-S-H crystal nuclei combined in a mass ratio of 1:2:2; the water-soluble film is composed of bone glue, sesame glue and cellulose combined in a mass ratio of 1:2:2.

[0106] Pore regulation layer: The sealer is composed of sodium silicate and sodium metasilicate combined in a mass ratio of 4:1; the isolation film is composed of sodium alginate and potassium alginate combined in a mass ratio of 3:2;

[0107] Temperature regulation layer: Cement, P·O 42.5 ordinary Portland cement, the phase change material is composed of n-dodecane and n-tetradecane combined in a mass ratio of 4:1; applicable to the range of -20°C to 0°C.

[0108] A preparation method of a multi-layer slow-release additive for negative temperature emergency repair concrete includes the following operation steps:

[0109] S1: Temperature regulation layer: Place the phase change material in a film coating machine, and at the same time spray cement and water. Rotate the machine evenly to make the cement layer wrap the phase change material to obtain spherical particles, and let it stand for 24 h until the cement layer gains strength.

[0110] S2: Pore regulation layer: Screen the particles in S1, select particles with a diameter of 0.2 - 1.18 mm and place them in a film coating machine. Spray the sealer and the isolation film material in sequence, wrap and granulate, and let it stand for more than 2 h;

[0111] S3: Setting regulation layer: Screen the particles in S2, select particles with a diameter of 0.4 - 1.68 mm and place them in a film coating machine. Spray the early strength agent and the water-soluble film material in sequence, wrap and granulate, and let it stand for more than 2 h;

[0112] S4: Hydration regulation layer: Screen the particles in S3, select particles with a diameter of 0.6 - 2.18 mm and place them in a film coating machine. Spray the retarding agent and the freezing point regulator at the same time, and at the same time control the final size of the additive to be 0.8 - 2.68 mm, and let it stand for more than 2 h.

[0113] A usage method of a multi-layer slow-release additive for negative temperature emergency repair concrete includes the following operation steps:

[0114] (1) Slurry preparation: Mix the multi-layer slow-release additive, rapid hardening cement and admixture in a ratio of 10:80:10 by mass, and dry mix for 5 min; spray and add 30 parts by mass of water at 60°C, and stir until a uniform fluid mixture is obtained; the admixture is composed of slag, fly ash and steel slag in a mass ratio of 1:2:2.

[0115] (2) Concrete preparation: Within 5 minutes after the mixture reaches the flowing state in step (1), add 20 parts of fine aggregate and 30 parts of coarse aggregate in proportion, and stir for 5 minutes to prepare negative-temperature emergency repair concrete;

[0116] (3) Spraying interface agent: While adding the aggregate in step (2), spray an organic interface agent on the interface of a 150×150×75 mm specimen, with a coating amount of 0.2 kg / m 2 , and the interface agent is composed of acrylic emulsion, VAE emulsion, and styrene-acrylate emulsion in a mass ratio of 1:2:2.

[0117] (4) Pouring: Pour into the mold within 5 minutes after the interface agent spraying is completed, and at the same time form the specimens required for testing, and vibrate until dense;

[0118] (5) Curing: Treat the working surface and cure under natural conditions.

[0119] Table 2 Performance test of negative-temperature emergency repair concrete

[0120] Test Items Unit Example 2 Initial Spread mm 450 10 - minute Spread mm 430 Initial Setting Time (-5°C) min 45 Initial Setting Time (-20°C) min 52 24 - hour Compressive Strength (-5°C) MPa 30 24 - hour Compressive Strength (-20°C) MPa 28 Interface Bonding Strength MPa 2.4 Freeze - Thaw Cycle - Mass Loss (cycles) ％ 1.0(2) Freeze - Thaw Cycle - Compressive Strength (cycles) MPa 47(2) 28 - day Impermeability Pressure MPa 7.2

[0121] Example 3

[0122] A multi-layer slow-release additive for negative-temperature emergency repair concrete, whose composition from the outside to the inside is successively a hydration regulation layer, a setting regulation layer, a pore regulation layer, and a temperature regulation layer, with a mass ratio of 2:1:1:5.

[0123] Hydration regulation layer: The freezing point regulator and the retarder are combined in a mass ratio of 1:1, where the freezing point regulator is composed of sodium nitrite and ethylene glycol in a mass ratio of 1:1; the retarder is composed of sucrose, glucose, and borax in a mass ratio of 2:2:1.

[0124] Setting regulation layer: The early strength agent is composed of sodium carbonate, calcium carbonate, and C-S-H crystal nuclei in a mass ratio of 1:2:2; the water-soluble film is composed of bone glue, linseed gum, and cellulose in a mass ratio of 1:2:2.

[0125] Pore regulation layer: The sealant is composed of sodium silicate and sodium metasilicate in a mass ratio of 4:1; the isolation film is composed of sodium alginate and potassium alginate in a mass ratio of 3:2.

[0126] Temperature regulation layer: Cement, P·O 42.5 ordinary Portland cement, and the phase change material is n-dodecane; applicable to an environment of -30°C to 0°C.

[0127] A preparation method of a multi-layer slow-release additive for negative-temperature emergency repair concrete, including the following operating steps:

[0128] S1: Temperature regulation layer: Place the phase change material in a film coating machine, spray cement and water simultaneously, rotate the machine at a constant speed to coat the cement layer on the phase change material to obtain spherical particles, and let them stand for 24 hours until the cement layer becomes strong.

[0129] S2: Pore regulation layer: Sieve the particles in S1, select particles with a diameter of 0.2 - 1.18 mm and place them in a film coating machine, spray the sealant and the isolation film material in sequence, perform granulation by coating, and let them stand for more than 2 hours;

[0130] S3: Setting regulation layer: Sieve the particles in S2, select particles with a diameter of 0.4 - 1.68 mm and place them in a film coating machine, spray the early strength agent and the water-soluble film material in sequence, perform granulation by coating, and let them stand for more than 2 hours;

[0131] S4: Hydration regulation layer: Sieve the particles in S3, select particles with a diameter of 0.6 - 2.18 mm and place them in a film coating machine, spray the retarder and the freezing point regulator simultaneously, and control the final size of the additive to be 0.8 - 2.68 mm, and let them stand for more than 2 hours.

[0132] A method for using a multi-layer slow-release additive for negative-temperature emergency repair concrete, including the following operation steps:

[0133] (1) Slurry preparation: Mix the multi-layer slow-release additive, rapid hardening cement and admixture in a ratio of 10:80:10 by mass, dry mix for 5 minutes; spray and add 30 parts by mass of water at 60 °C, and stir until a uniform fluid mixture is obtained; the admixture is composed of slag, fly ash and steel slag in a mass ratio of 1:2:2.

[0134] (2) Concrete preparation: Within 5 minutes after the mixture in step (1) becomes fluid, add 20 parts of fine aggregate and 30 parts of coarse aggregate in proportion, and stir for 5 minutes to prepare negative-temperature emergency repair concrete;

[0135] (3) Spraying the interface agent: While adding the aggregate in step (2), spray an organic interface agent on the interface of a 150×150×75 mm specimen, with a coating amount of 0.2 kg / m 2 , and the interface agent is composed of acrylic emulsion, VAE emulsion and styrene-acrylate emulsion in a mass ratio of 1:2:2.

[0136] (4) Pouring: Pour into the mold within 5 minutes after the interface agent spraying is completed, and vibrate thoroughly;

[0137] (5) Curing: Treat the working surface and cure under natural conditions.

[0138] Table 3 Performance test of negative-temperature emergency repair concrete

[0139]

[0140]

[0141] Comparative Example 1

[0142] It is different from Example 1 in that the additive does not have a multi-layer structure, and the freezing point regulator, setting retarder, early strength agent, sealant, etc. are mixed with the cement and admixture in the usage method (1). The steps such as proportion, preparation method, usage method, and performance detection method are exactly the same. The performance of the concrete prepared in Example 1 and Comparative Example 1 was compared.

[0143] Table 4 Performance Test of Negative Temperature Emergency Repair Concrete

[0144] Test Items Unit Example 1 Comparative Example 1 Initial Spread mm 450 400 10 - minute Spread mm 430 100 Initial Setting Time (-5°C) min 25 ＞600 Initial Setting Time (-20°C) min 35 ＞600 24 - hour Compressive Strength (-5°C) MPa 35 5 24 - hour Compressive Strength (-20°C) MPa 30 1 Interface Bonding Strength MPa 2.5 0.1 Freeze - Thaw Cycle - Mass Loss (cycles) ％ 1.0(2) / Freeze - Thaw Cycle - Compressive Strength (cycles) MPa 45(2) / 28 - day Impermeability Pressure MPa 6.7 /

[0145] As can be seen from Table 4, when functional additives such as freezing point regulator and setting retarder are simultaneously added to negative temperature concrete, it seriously affects the workability of construction, and there is basically no slump after 10 minutes; the setting retarder will act on the periphery of the early strength agent and sealant, resulting in a significant prolongation of the setting time. At the same time, the early strength agent cannot function, leading to extremely low early strength.

[0146] Comparative Example 2

[0147] It is different from Example 1 in that the multi-layer slow-release additive does not have the water-soluble layer in the setting control layer, and the preparation, usage method, and performance detection are exactly the same. The performance of the concrete prepared in Example 1 and Comparative Example 2 was compared.

[0148] Table 5 Performance Test of Negative Temperature Emergency Repair Concrete

[0149] Test Items Unit Example 1 Comparative Example 2 Initial Spread mm 450 450 10 - minute Spread mm 430 410 Initial Setting Time (-5°C) min 25 36 Initial Setting Time (-20°C) min 35 42 24 - hour Compressive Strength (-5°C) MPa 35 12 24 - hour Compressive Strength (-20°C) MPa 30 5 Interface Bonding Strength MPa 2.5 0.2 Freeze - Thaw Cycle - Mass Loss (cycles) ％ 1.0(2) 5.5(1) Freeze - Thaw Cycle - Compressive Strength (cycles) MPa 45(2) 10(1) 28 - day Impermeability Pressure MPa 6.7 1.0

[0150] As can be seen from Table 5, when the water-soluble layer is not provided, under the action of the hydration control layer, the slump of the negative temperature emergency repair concrete is close at 10 minutes, ensuring mixability and pourability; however, the early strength agent in the setting control layer is released prematurely and cannot exert its effect after being wrapped by the unreacted setting retarder, resulting in an extended setting time and slow strength development at negative temperature; at the same time, due to the incomplete formation of the concrete structure and limited free early strength agent, it cannot migrate to the interface, affecting the interface bonding performance; the strength develops slowly, the structure is not dense, the porosity is higher, and the durability is poor.

[0151] Comparative Example 3

[0152] It is different from Example 1 in that the multi-layer slow-release additive does not have the isolation layer in the pore control layer, and the preparation, usage method, and performance detection method are exactly the same. The performance of the concrete prepared in Example 1 and Comparative Example 3 was compared.

[0153] Table 6 Performance Test of Negative Temperature Emergency Repair Concrete

[0154]

[0155]

[0156] As can be seen from Table 6, without a separation layer, the sealant in the pore regulation layer is released prematurely. At this time, the early strength agent reacts with the cement and is not completely reacted, and the internal pores are not fully formed. Without capillary action, the sealant cannot migrate sufficiently, resulting in a decline in durability.

[0157] Comparative Example 4

[0158] The difference compared with Example 1 is that the components of each layer are swapped, and from the outside to the inside are the pore regulation layer, the setting regulation layer, and the hydration regulation layer in turn. Their preparation, usage methods, and performance detection methods are exactly the same. The performance of the concrete prepared in Example 1 and Comparative Example 4 was compared.

[0159] Table 7 Performance Test of Negative Temperature Emergency Repair Concrete

[0160] Test Items Unit Example 1 Comparative Example 4 Initial Spread mm 450 460 10 - minute Spread mm 430 400 Initial Setting Time (-5°C) min 25 40 Initial Setting Time (-20°C) min 35 49 24 - hour Compressive Strength (-5°C) MPa 35 20 24 - hour Compressive Strength (-20°C) MPa 30 15 Interface Bonding Strength MPa 2.5 0.2 Freeze - Thaw Cycle - Mass Loss (cycles) ％ 1.0(2) 10(1) Freeze - Thaw Cycle - Compressive Strength (cycles) MPa 45(2) 4(1) 28 - day Impermeability Pressure MPa 6.7 1.2

[0161] As can be seen from Table 7, the pore regulation layer is released first. The hydrolysis of the sealant and its participation in the hydration reaction can cause the negative temperature cement to set when mixed with warm water and have a certain strength at the same time. However, as the setting regulation layer is released, the strength is further improved; but due to the premature action of the sealant, it cannot fill the pores of the internal structure, resulting in a decline in durability.

[0162] Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A multi-layer slow-release additive for negative-temperature emergency repair concrete, characterized in that, The multi-layer slow-release additive consists of a hydration regulation layer, a setting regulation layer, a pore regulation layer and a temperature regulation layer from outside to inside in sequence; The mass ratio of the hydration regulation layer, the setting regulation layer, the pore regulation layer and the temperature regulation layer is 1-2:1-2:1-2:5; targeted regulation of the mixing, curing and service processes of the negative-temperature emergency repair concrete is realized through a differential encapsulation technology; The hydration regulation layer is composed of a freezing point regulator and a retarder; the hydration regulation layer dissolves in hot water at 50-60 °C to form a low-freezing-point mixing medium to regulate the hydration rate; the setting regulation layer consists of a water-soluble film and an early strength agent from outside to inside in sequence; the water-soluble film contacts the free water in the concrete after the hydration regulation layer dissolves and releases the early strength agent after gradually dissolving; the pore regulation layer consists of a separation film and a sealant from outside to inside in sequence; the separation film gradually swells in an alkaline environment, enabling the slow release of the sealant, and the temperature regulation layer is composed of a cement layer and a phase change material.

2. The multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 1, characterized in that, The freezing point regulator is one or more of sodium nitrite or ethylene glycol; the retarder is one or more of sucrose, glucose, borax.

3. The multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 1, wherein, The water-soluble film is one or more of cellulose, plant gum or animal gum; the early strength agent is one or more of sodium carbonate, calcium carbonate, C-S-H crystal nucleus.

4. The multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 1, wherein, The separation film is one or more of sodium alginate or potassium alginate; the sealant is one or more of sodium silicate, sodium metasilicate.

5. The multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 1, wherein, The cement layer permanently encapsulates the phase change material.

6. The preparation method of a multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 1, characterized in that, The preparation method includes the following steps: S1: Temperature regulation layer: Wrap the phase change material with a cement layer; S2: Pore regulation layer: Sprinkle a sealant and a separation film material on the surface of the particles in S1 in sequence; S3: Setting regulation layer: Sprinkle an early strength agent and a water-soluble film material on the surface of the particles in S2 in sequence; S4: Hydration regulation layer: Sprinkle a retarder and a freezing point regulator on the surface of the particles in S3 at the same time to obtain the multi-layer slow-release additive.

7. The usage method of a multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 1, characterized in that, The usage method includes the following steps: (1) Slurry preparation: Mix the multi-layer slow-release additive, rapid hardening cement and admixture in proportion, and add water and stir to form a uniform fluid mixture; (2) Concrete preparation: Add aggregate and stir in step (1) to prepare negative-temperature emergency repair concrete; (3) Spray interface agent; Spray an organic interface agent on the interface for emergency repair and reinforcement; (4) Pouring; After the interface agent spraying is completed, pour the negative-temperature emergency repair concrete prepared in step (2) and vibrate it densely; (5) Curing: Treat the working surface and cure it under natural conditions.

8. The method for using the multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 7, characterized in that, The mass ratio of the multi-layer slow-release additive, the rapid hardening cement and the admixture is 5-10:70-80:10-25.

9. The usage method of the multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 7, characterized in that, The rapid hardening cement is sulfoaluminate cement, with an initial setting time ≤ 25 min, a final setting time ≥ 180 min, and a 24-hour compressive strength ≥ 32 MPa.

10. The method for using a multi-layer slow-release additive for negative-temperature emergency repair concrete according to claim 7, characterized in that, The admixture is one or more of slag, fly ash, steel slag.

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