Preparation method of multifunctional concrete admixture

Abstract

The invention discloses a preparation method of a multifunctional concrete admixture. The preparation method of the concrete multifunctional admixture comprises the following steps: firstly, mixing an oil phase system A formed by PVC and an organic solvent, Span-80, ettringite and calcium carbonate to obtain a solution B, and then emulsifying the solution B with a sodium thiosulfate solution to obtain an emulsion D; secondly, dropwise adding the emulsion D into a PVA emulsion, stirring to form a double emulsion E, stirring, centrifuging, washing, precipitating and drying to obtain microspheres F; and finally, mixing the microspheres F with a sodium sulfate solution, PVA and nano ferroferric oxide to obtain a turbid liquid I, mixing PVC with a plasticizer, a solvent and Span-80 to obtain an oil phase system G, dropwise adding an emulsion J emulsified by I and G into a PVA emulsion, and carrying out after-treatment to obtain the multifunctional concrete admixture. The admixture prepared by the method disclosed by the invention is a microsphere-in-microsphere structure body, so that the integration of concrete early strength and crack repair functions is realized, and the problem of concrete shrinkage cracks caused by early strength can be quickly solved.

Description

Technical Field

[0001] This invention belongs to the field of admixture technology, specifically relating to a method for preparing a multifunctional concrete admixture. Background Technology

[0002] With the rapid development of modern civil engineering, large-volume concrete is widely used in large-scale engineering structures such as high-rise building foundations, bridge piers, and water conservancy dams. This type of concrete is characterized by large pouring volume, large amount of cementitious materials, and concentrated heat release during hydration. It faces two major technical challenges during construction and service: first, the contradiction between early strength improvement and hydration temperature rise control; and second, insufficient self-healing ability after cracks appear during service. These two problems directly affect the safety, durability, and service life of the engineering structure. In terms of early strength enhancement, if the early strength growth of large-volume concrete is slow after pouring, it is susceptible to plastic cracks caused by construction loads, environmental disturbances, and other factors. Therefore, early strength agents are often added in engineering to accelerate the cement hydration process and shorten the curing period. Currently, commonly used early strength agents mainly include chloride salts, sulfates, and organic amines. Among them, sulfate-based early strength agents (such as sodium sulfate) are widely used due to their significant effects and low cost. However, they have obvious drawbacks: on the one hand, the rapid reaction of sulfates leads to a concentrated release of cement hydration heat, which accelerates the internal temperature rise rate and increases the peak temperature rise of the concrete, causing temperature stress cracks and weakening the overall structural integrity; on the other hand, traditional early strength agents have a single function, only improving early strength, and cannot take into account the controllability of hydration temperature rise, and have no repair effect on cracks in the concrete during its service life. Regarding self-healing cracks, large-volume concrete is highly susceptible to microcracks during service due to factors such as hydration heat shrinkage, drying shrinkage, and temperature stress. If these cracks are not repaired in time, external moisture and corrosive media can seep into the interior, corroding the reinforcing steel and deteriorating the cementitious materials, leading to a gradual decline in structural performance. Existing self-healing technologies for concrete mainly include microbial repair, crystalline repair, and capsule repair. Microbial repair technology is greatly affected by environmental pH and temperature, resulting in insufficient stability; the repair effect of crystalline repair materials depends on the long-term presence of moisture at the crack, and the repair strength is limited; capsule repair materials are mostly single-core encapsulation structures, which can only achieve single-use repair and cannot work synergistically with early-strength functions, making it difficult to meet the integrated requirements of "early strength-temperature control-self-healing" for large-volume concrete. To address these issues, the industry has attempted to develop multifunctional composite admixtures, hoping to achieve compatibility of early strength, temperature control, and self-healing functions. However, existing composite technologies are mostly simple blends, and antagonistic effects easily occur between different functional components, resulting in poor synergistic effects. For example, when combining early strength agents with retarders to control temperature rise, some early strength effect is often sacrificed; when self-healing components are mixed with early strength components, the self-healing components are prone to premature failure during early hydration, failing to function when cracks appear. Furthermore, traditional admixtures lack targeting; the release rate of early strength components is difficult to match with the cement hydration process, and self-healing components cannot accurately act on crack sites, resulting in overall performance that fails to meet the stringent requirements of large-volume concrete. Meanwhile, the structural design of existing capsule-type or microsphere-type admixtures has limitations. Most are single-layer encapsulation structures, which cannot achieve multi-component, staged release. Single-layer structures are susceptible to shear force damage during concrete mixing, leading to premature leakage of the core material. Furthermore, they cannot achieve orderly release of the core material according to the needs of different stages of concrete (early strength and temperature control in the early hydration stage, and crack repair in the service stage), making it difficult to meet the performance requirements of each stage. In addition, the preparation process of existing microsphere materials is complex, the encapsulation stability is poor, and they lack the ability to respond to external environmental stimuli (such as magnetic fields and temperature), making it impossible to achieve precise control of the early strength effect. Summary of the Invention

[0003] To address the problems existing in the above-mentioned background technology, the present invention provides a method for preparing a multifunctional concrete admixture. By preparing a microsphere-within-a-microsphere structure, the method integrates the functions of early strength and crack repair in concrete, which can quickly solve the problem of shrinkage cracks in concrete caused by early strength. It is suitable for improving the early strength and controlling cracks in large-volume concrete.

[0004] PVC, due to its excellent chemical stability, mechanical strength, and processing performance, is often used as a microsphere encapsulation material. However, its softening temperature can be controlled by plasticizers, making it possible to achieve temperature-responsive core material release. Nano-ferric oxide possesses excellent magnetic response characteristics and can be targeted through external magnetic field stimulation. Sodium thiosulfate and sodium sulfate, as core materials, not only provide early strength but also allow for the control of hydration temperature rise due to the thermal effect of their dissolution-crystallization process. Eettsonite and calcium carbonate provide the material basis for crack self-healing. Based on these material properties, designing a multi-structured, multi-responsive, and multi-functional synergistic microsphere-encapsulated concrete admixture to solve the technical challenges of improving early strength, controlling hydration temperature rise, and achieving crack self-healing in large-volume concrete has become a direction urgently needed by those skilled in the art.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing a multifunctional concrete admixture includes the following steps: (1) In a stirrer, PVC is added to an organic solvent and stirred until completely dissolved to form an oil phase system A; then oil-soluble emulsifier Span-80, ettringite and calcium carbonate are added to the oil phase system A, ultrasonically dispersed and stirred until completely uniform, and the stirrer is placed in a constant temperature water bath of 65~70℃ to obtain solution B. The mass ratio of PVC to organic solvent is 12~15:100; The organic solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:0.8~1.2; The softening temperature of the PVC base is 75~80℃; The amount of the oil-soluble emulsifier Span-80 added is 2% to 3% of the mass of oil phase system A; The maximum particle size of the ettringite is no greater than 1 μm, and its addition amount is 3-5% of the mass of oil phase system A. The maximum particle size of the calcium carbonate is no greater than 0.5 μm, and its addition amount is 1~2% of the mass of oil phase system A; The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 3~5 min; (2) Add excess sodium thiosulfate to water at 65~70℃ to make it supersaturated, add sodium hydroxide solution to control the pH to 12~13, filter to obtain the supernatant C; then mix the supernatant C with the solution B obtained in step (1) slowly in a stirrer. The mixing process is to slowly add the supernatant C to the solution B at a uniform rate. Before adding, start the high shear emulsifier. After the addition is completed, continue emulsification for 20~30 minutes, and then use an ultrasonic breaker to ultrasonically treat to obtain the W / O emulsion D with micron-sized sodium thiosulfate droplets dispersed. In step (2), the stirrer is placed in a constant temperature water bath at 65~70℃. The temperature of the reaction process is always controlled between 65~70℃ to ensure that the sodium thiosulfate solution is always at high solubility at high temperature. The pH is controlled to ensure the stability of the ettringite particles during subsequent mixing. The purpose of the solution drop emulsification process in step (2) is to ensure the formation of a stable W / O system. The volume ratio of the supernatant C to solution B is 1:8~10, and the dropping time of the supernatant C into solution B is controlled at 8~10 min; The high-shear emulsifier speed is adjusted to 6000~10000 r / min; The ultrasonic processing parameters of the ultrasonic disruptor are: power 200~300W, processing time 3~5min; (3) After adding PVA to water, add sodium hydroxide solution to control the pH between 12 and 13, and disperse it by ultrasonication to obtain PVA emulsion; in a stirrer placed under constant temperature water bath conditions of 65-70℃, slowly add the emulsion D obtained in step (2) into the PVA emulsion. Start the low speed stirrer before adding, and continue stirring after adding to form a stable W / O / W double emulsion E. At this time, the sodium thiosulfate droplets are wrapped by the PVC oil phase film. The mass ratio of PVA to water in the PVA emulsion is 3~5:100; The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 20~30 min; The volume ratio of emulsion D to PVA emulsion is 1:8~10; The speed of the stirrer is adjusted to 180~300r / min. After the dripping is completed, stirring continues for 60~120s. The entire stirring process takes 25~30min. (4) Place the double emulsion E obtained in step (3) in a constant temperature water bath at 65~70℃, adjust the speed of the stirrer and stir continuously to allow the organic solvent, water and other substances to evaporate slowly. During this process, PVC will gradually precipitate, form a film and solidify on the surface of sodium thiosulfate droplets to form core-shell microspheres. After the reaction is completed, pour all the product into a centrifuge and discard the supernatant. Then, use deionized water to repeatedly wash the centrifuged product to remove residual PVA and Span-80. Transfer the washed microspheres to a vacuum drying oven and dry them to constant weight to obtain dried micron-sized core-shell microspheres F. The speed of the stirrer is adjusted to 100~120 r / min, and the continuous stirring time is every 1m. 3 Emulsion E is stirred for 8-10 hours; The centrifugation speed is 4000~6000 r / min, and the centrifugation time is 8~10 min; The washing and settling process is repeated 3 to 5 times. The temperature of the vacuum drying oven is set not to exceed 60°C to ensure that the PVC microspheres do not deform. (5) Place the stirrer in a constant temperature water bath at 32~35℃. Add excess sodium sulfate to the water at 32~35℃ in the stirrer to make it supersaturated. Add sodium hydroxide dropwise to control the pH between 12 and 13. Filter to obtain the supernatant H. During this process, the temperature is always controlled between 32~35℃ to ensure that the sodium sulfate is in a high solubility state. The pH is controlled to ensure the stability of the ettringite particles. Then, mix the micron-sized core-shell microspheres F obtained in step (4) with the supernatant H and add... After adding PVA and nano-Fe3O4, a stable suspension I is formed by ultrasonic dispersion, with the temperature controlled between 32 and 35°C. PVC and plasticizer are mixed and added to a solvent, stirred until completely dissolved, and then Span-80 is added and mixed to form an oil phase system G. Suspension I is slowly and uniformly added to the oil phase system G. A high-shear emulsifier is started before the addition. After the addition is complete, emulsification is continued for 20 to 30 minutes, and then ultrasonic treatment is used to obtain a dispersed W / O emulsion J. The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 20~30 min; The mass ratio of the micron-sized core-shell microspheres F to the supernatant H is 1:20~30; The amount of PVA added is 1-2% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The nano-ferric oxide has a particle size of 10-20 nm, and its addition amount is 0.01-0.03% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The mass ratio of the PVC and plasticizer mixture to the solvent is 12~15:100, the mass ratio of PVC to plasticizer is 100:32~38, and the solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:0.8~1.2. The Span-80 is added at a rate of 2-3% of the total mass of PVC. The volume ratio of the suspension I to the oil phase system G is 1:8~10; The suspension I is slowly added dropwise to the oil phase system G, with the addition time controlled at 8-10 min; the high-shear emulsifier is added by adjusting the rotation speed to 6000-10000 r / min. The ultrasonic processing parameters of the ultrasonic disruptor are: power 200~300W, ultrasonic processing time 3~5min; In this step, the softening temperature of PVC is controlled by adjusting the amount of plasticizer added. This ratio can stably control the softening temperature of the formed PVC between 55 and 62°C. This temperature setting is mainly based on the actual peak temperature rise of large-volume concrete and can also be adjusted according to the actual project conditions. That is, when the actual peak temperature rise is lower than 55-62°C, the softening temperature of PVC can be further reduced to ensure that it softens and liquefies when the peak temperature rise is reached. (6) Prepare PVA emulsion. In a constant temperature water bath at 32~35℃, slowly drip the emulsion J obtained in step (5) into the PVA emulsion in a stirrer. Before dripping, start the low-speed stirrer and adjust the speed to 180~300 r / min. After the dripping is completed, continue stirring for 60~120 s. The stirring time for the entire process is 25~30 min. At this time, the emulsion J is coated by the PVC oil phase film to form a suspension K. Place the suspension K in a constant temperature water bath at 32~35℃ and adjust the speed to 100~120 r / min. Every 1 m 3 Suspension K is continuously stirred for 8-10 hours to allow organic solvents to slowly evaporate. During this process, PVC gradually precipitates, forms a film, and solidifies on the surface of sodium sulfate droplets, forming core-shell structured microspheres. After the reaction is complete, all the product is poured into a centrifuge to centrifuge and the supernatant is discarded. Then, the centrifuged product is repeatedly washed with deionized water to remove the precipitate. Finally, the washed microspheres are transferred to a vacuum drying oven and dried to constant weight to obtain dried core-shell microspheres L, which is the multifunctional concrete admixture described in this invention. The PVA emulsion has a mass concentration of 3% to 5%, and is obtained by ultrasonically dispersing PVA in water for 20 to 30 minutes. The volume ratio of emulsion J to PVA emulsion is 1:8~10; The centrifugation speed is 1000~1500 r / min, and the centrifugation time is 10~15 min; The washing and settling process is repeated 3 to 5 times. The temperature of the vacuum drying oven is set not higher than 50°C.

[0006] Furthermore, the degree of polymerization of the PVC resin described in this invention is 900~1000 (basic softening temperature 75~80℃). Furthermore, the plasticizer described in this invention is dioctyl phthalate (DOP) or tributyl acetyl citrate (ATBC).

[0007] Furthermore, the polyvinyl alcohol (PVA) of the present invention has a degree of alcoholysis of 88% and is water-soluble.

[0008] Furthermore, the present invention also provides a multifunctional concrete admixture prepared by the above method. The multifunctional concrete admixture has a core-shell structure of microspheres within microspheres. The core of the structure is a micron-sized core-shell microsphere F, the outer shell is PVC, and the middle contains a saturated sodium sulfate solution at 32~35℃ and nano-iron oxide particles. The micron-sized core-shell microsphere F contains a saturated sodium thiosulfate, calcium carbonate and ettringite mixture at 60~70℃.

[0009] Furthermore, this invention also provides a method for applying the above-mentioned multifunctional concrete admixture. When used in concrete, the dosage is 0.5% to 5% of the mass of the cementitious material, and it can be widely used to improve the early strength and self-healing ability of mass concrete. The operation after application is as follows: after the concrete with the multifunctional concrete admixture is poured, a magnet is quickly moved across the concrete surface at a speed of 0.5m to 2m / s.

[0010] When the admixture microsphere structure obtained by the preparation method of this invention is added to concrete, it can exert a good microsphere effect in the early stage, improving the performance of the concrete mixture. After pouring, when rapid hardening of the slurry is required, a magnet is quickly swept across the concrete surface, causing strong polarization of the nano-ferric oxide inside the microspheres. This rapid, instantaneous directional movement stimulates the precipitation and crystallization of supersaturated sodium sulfate (because the solubility of sodium sulfate at 32-35℃ is much higher than at room temperature). The precipitation and crystallization process is exothermic, further stimulating the rapid hydration of cement in the concrete and accelerating the early strength improvement. When the cement in the concrete begins to hydrate, an exothermic reaction occurs, while the sodium sulfate and sodium thiosulfate inside the microspheres absorb heat during this process, effectively controlling the temperature rise and achieving controllability of the temperature rise during the concrete hydration process. When the temperature rise during the hydration process in the concrete exceeds the softening temperature of the outer microsphere PVC, the outer microsphere softens and gradually liquefies, releasing the internal sodium sulfate. Sodium sulfate crystals seep out, and magnetic fluid seeps out, further accelerating the strength improvement. During the heating process, the sodium thiosulfate inside dissolves and absorbs heat, preventing a rapid temperature rise and effectively controlling the peak temperature and rate of temperature increase. When the temperature drops below 70°C, the sodium thiosulfate inside the microspheres crystallizes and precipitates, releasing heat to maintain a higher temperature and ensure a rapid reaction.

[0011] During the service life of concrete, when cracks occur, it can act as a self-healing group for cracks. When water seeps into the cracks, a water film will form on the surface of the inner microspheres. Under long-term water immersion conditions, the ettringite AFt attached to the surface of the inner microspheres will rapidly disintegrate to form AFm due to the decrease in pH, and the volume will shrink rapidly, creating pores. This will cause the sodium thiosulfate inside to dissolve rapidly, increasing the sulfate ions in the system. It will then react with AFm, as well as calcium and aluminum ions in the cement, to form an expanded phase of ettringite to block the gaps. AFm and calcium carbonate can also react to form a gel, thus filling and reinforcing the cracks.

[0012] In summary, this invention realizes a preparation method that integrates early strength and crack repair functions. It can improve early strength and achieve self-repair function. Compared with existing single-function early strength agents, it can quickly solve the problem of concrete shrinkage cracks caused by early strength. Its comprehensive utilization effect is better and it is suitable for improving the early strength and controlling cracks in large-volume concrete. It solves the problem that the two functions of large-volume concrete cannot be compatible.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) Structural innovation: Precise layered encapsulation design of double-layer core-shell microspheres In existing technologies, W / O / W emulsion materials for concrete are mostly single-layer dual emulsion structures or single-function microcapsules. However, this invention constructs a nested microsphere structure of "outer (PVC microsphere) system + middle (sodium sulfate / nano iron oxide emulsion) system + inner (PVC microsphere + sodium thiosulfate / ettringite / calcium carbonate) system" through a two-step W / O / W emulsion preparation process. This achieves layered isolation and orderly storage of multiple components. This structure breaks through the limitations of existing single-layer encapsulation or simple compounding, and provides a structural basis for the phased release of functional components. It is an innovative optimization of the microstructure design of concrete admixtures.

[0014] (2) Functional synergistic innovation: early strength-temperature control-self-repair integration In existing technologies, concrete admixtures are mostly single-function or simply composite (e.g., early-strength agents only improve strength, self-healing microcapsules only repair cracks), and there are functional antagonism issues (e.g., early strength and temperature control are incompatible). This invention achieves functional synergy through structural design. The outer layer system relies on the magnetic responsiveness of nano-ferric oxide to trigger the exothermic crystallization of sodium sulfate, accelerating early strength, while simultaneously utilizing the thermal effect of sodium thiosulfate dissolution-crystallization to regulate the hydration temperature rise. After cracks occur, the inner layer system releases repair components through the pH-responsive disintegration of ettringite, achieving crack filling and reinforcement. This invention, through the integrated design of "early-strength temperature control + service-life self-healing," solves the compatibility problem of the two core challenges of large-volume concrete, breaking through the application bottleneck of existing single-function admixtures.

[0015] (3) Response mechanism innovation: precise regulation triggered by synergistic effects of multiple stimuli Existing magnetically responsive concrete microcapsules rely solely on magnetic fields to trigger the wall material to rupture and release the core material, while temperature-responsive materials are mostly triggered by a single temperature threshold. This invention integrates a triple mechanism of magnetic response, temperature response, and pH response: magnetic fields trigger the directional release and exothermic reaction of early-strength components; temperature changes (cement hydration temperature rise / ambient cooling) regulate the softening / curing of the PVC film, achieving phased release of components; and the pH drop caused by moisture infiltration at cracks triggers the disintegration and repair reaction of the inner ettringite layer. The synergistic effect of these multiple response mechanisms achieves precise matching between the admixture's action sequence and the needs of different service stages of concrete, making it more intelligent and adaptable than existing single-response materials.

[0016] (4) Material system innovation: Targeted optimization of PVC-based emulsion templates Existing W / O / W emulsions used in concrete applications mostly employ encapsulation materials such as epoxy resin and chitosan, and rarely incorporate functional mineral components. This invention specifically selects PVC (whose softening temperature can be controlled via plasticizers) as the encapsulation material, combining it with PVA and Span-80 to form a stable emulsion system. Simultaneously, it co-encapsulates mineral components such as ettringite and calcium carbonate with chemical reagents. This material combination ensures both the temperature responsiveness and mechanical stability of the encapsulation wall, while providing a sufficient material basis for self-healing reactions, making it more suitable for the complex hydration and service environment of concrete than existing emulsion-based materials. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments.

[0018] A method for preparing a multifunctional concrete admixture includes the following steps: (1) In a stirrer, PVC is added to an organic solvent and stirred until completely dissolved to form an oil phase system A; then oil-soluble emulsifier Span-80, ettringite and calcium carbonate are added to the oil phase system A, ultrasonically dispersed and stirred until completely uniform, and the stirrer is placed in a constant temperature water bath of 65~70℃ to obtain solution B. The mass ratio of PVC to organic solvent is 12~15:100; The organic solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:0.8~1.2; The softening temperature of the PVC base is 75~80℃; The amount of the oil-soluble emulsifier Span-80 added is 2% to 3% of the mass of oil phase system A; The maximum particle size of the ettringite is no greater than 1 μm, and its addition amount is 3-5% of the mass of oil phase system A. The maximum particle size of the calcium carbonate is no greater than 0.5 μm, and its addition amount is 1~2% of the mass of oil phase system A; The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 3~5 min; (2) Add excess sodium thiosulfate to water at 65~70℃ to make it supersaturated, add sodium hydroxide solution to control the pH to 12~13, filter to obtain the supernatant C; then mix the supernatant C with the solution B obtained in step (1) slowly in a stirrer. The mixing process is to slowly add the supernatant C to the solution B at a uniform rate. Before adding, start the high shear emulsifier. After the addition is completed, continue emulsification for 20~30 minutes, and then use an ultrasonic breaker to ultrasonically treat to obtain the W / O emulsion D with micron-sized sodium thiosulfate droplets dispersed. In step (2), the stirrer is placed in a constant temperature water bath at 65~70℃. The temperature of the reaction process is always controlled between 65~70℃ to ensure that the sodium thiosulfate solution is always at high solubility at high temperature. The pH is controlled to ensure the stability of the ettringite particles in the subsequent mixing. The purpose of the solution drop emulsification process in step (2) is to ensure the formation of a stable W / O system. The volume ratio of the supernatant C to solution B is 1:8~10, and the dropping time of the supernatant C into solution B is controlled at 8~10 min; The high-shear emulsifier speed is adjusted to 6000~10000 r / min; The ultrasonic processing parameters of the ultrasonic disruptor are: power 200~300W, processing time 3~5min; (3) After adding PVA to water, add sodium hydroxide solution to control the pH between 12 and 13, and disperse it by ultrasonication to obtain PVA emulsion; in a stirrer placed under constant temperature water bath conditions of 65-70℃, slowly add the emulsion D obtained in step (2) into the PVA emulsion. Start the low speed stirrer before adding, and continue stirring after adding to form a stable W / O / W double emulsion E. At this time, the sodium thiosulfate droplets are wrapped by the PVC oil phase film. The mass ratio of PVA to water in the PVA emulsion is 3~5:100; The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 20~30 min; The volume ratio of emulsion D to PVA emulsion is 1:8~10; The speed of the stirrer is adjusted to 180~300r / min. After the dripping is completed, stirring continues for 60~120s. The entire stirring process takes 25~30min. (4) Place the double emulsion E obtained in step (3) in a constant temperature water bath at 65~70℃, adjust the speed of the stirrer and stir continuously to allow the organic solvent, water and other substances to evaporate slowly. During this process, PVC will gradually precipitate, form a film and solidify on the surface of sodium thiosulfate droplets to form core-shell microspheres. After the reaction is completed, pour all the product into a centrifuge and discard the supernatant. Then, use deionized water to repeatedly wash the centrifuged product to remove residual PVA and Span-80. Transfer the washed microspheres to a vacuum drying oven and dry them to constant weight to obtain dried micron-sized core-shell microspheres F. The speed of the stirrer is adjusted to 100~120 r / min, and the continuous stirring time is every 1m. 3 Emulsion E is stirred for 8-10 hours; The centrifugation speed is 4000~6000 r / min, and the centrifugation time is 8~10 min; The washing and settling process is repeated 3 to 5 times. The temperature of the vacuum drying oven is set not to exceed 60°C to ensure that the PVC microspheres do not deform. (5) Place the stirrer in a constant temperature water bath at 32~35℃. Add excess sodium sulfate to the water at 32~35℃ in the stirrer to make it supersaturated. Add sodium hydroxide dropwise to control the pH between 12 and 13. Filter to obtain the supernatant H. During this process, the temperature is always controlled between 32~35℃ to ensure that the sodium sulfate is in a high solubility state. The pH is controlled to ensure the stability of the ettringite particles. Then, mix the micron-sized core-shell microspheres F obtained in step (4) with the supernatant H and add... After adding PVA and nano-Fe3O4, a stable suspension I is formed by ultrasonic dispersion, with the temperature controlled between 32 and 35°C. PVC and plasticizer are mixed and added to a solvent, stirred until completely dissolved, and then Span-80 is added and mixed to form an oil phase system G. Suspension I is slowly and uniformly added to the oil phase system G. A high-shear emulsifier is started before the addition. After the addition is complete, emulsification is continued for 20 to 30 minutes, and then ultrasonic treatment is used to obtain a dispersed W / O emulsion J. The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 20~30 min; The mass ratio of the micron-sized core-shell microspheres F to the supernatant H is 1:20~30; The amount of PVA added is 1-2% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The nano-ferric oxide has a particle size of 10-20 nm, and its addition amount is 0.01-0.03% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The mass ratio of the PVC and plasticizer mixture to the solvent is 12~15:100, the mass ratio of PVC to plasticizer is 100:32~38, and the solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:0.8~1.2. The Span-80 is added at a rate of 2-3% of the total mass of PVC. The volume ratio of the suspension I to the oil phase system G is 1:8~10; The suspension I is slowly added dropwise to the oil phase system G, with the addition time controlled at 8-10 min; the high-shear emulsifier is added by adjusting the rotation speed to 6000-10000 r / min. The ultrasonic processing parameters of the ultrasonic disruptor are: power 200~300W, ultrasonic processing time 3~5min; In this step, the softening temperature of PVC is controlled by adjusting the amount of plasticizer added. This ratio can stably control the softening temperature of the formed PVC between 55 and 62°C. This temperature setting is mainly based on the actual peak temperature rise of large-volume concrete and can also be adjusted according to the actual project conditions. That is, when the actual peak temperature rise is lower than 55-62°C, the softening temperature of PVC can be further reduced to ensure that it softens and liquefies when the peak temperature rise is reached. (6) Prepare PVA emulsion. In a constant temperature water bath at 32~35℃, slowly drip the emulsion J obtained in step (5) into the PVA emulsion in a stirrer. Before dripping, start the low-speed stirrer and adjust the speed to 180~300 r / min. After the dripping is completed, continue stirring for 60~120 s. The stirring time for the entire process is 25~30 min. At this time, the emulsion J is coated by the PVC oil phase film to form a suspension K. Place the suspension K in a constant temperature water bath at 32~35℃ and adjust the speed to 100~120 r / min. Every 1 m 3 Suspension K is continuously stirred for 8-10 hours to allow organic solvents to slowly evaporate. During this process, PVC gradually precipitates, forms a film, and solidifies on the surface of sodium sulfate droplets, forming core-shell structured microspheres. After the reaction is complete, all the product is poured into a centrifuge to centrifuge and the supernatant is discarded. Then, the centrifuged product is repeatedly washed with deionized water to remove the precipitate. Finally, the washed microspheres are transferred to a vacuum drying oven and dried to constant weight to obtain dried core-shell microspheres L, which is the multifunctional concrete admixture described in this invention. The PVA emulsion has a mass concentration of 3% to 5%, and is obtained by ultrasonically dispersing PVA in water for 20 to 30 minutes. The volume ratio of emulsion J to PVA emulsion is 1:8~10; The centrifugation speed is 1000~1500 r / min, and the centrifugation time is 10~15 min; The washing and settling process is repeated 3 to 5 times. The temperature of the vacuum drying oven is set not higher than 50°C.

[0019] Furthermore, the degree of polymerization of the PVC resin described in this invention is 900~1000 (basic softening temperature 75~80℃). Furthermore, the plasticizer described in this invention is dioctyl phthalate (DOP) or tributyl acetyl citrate (ATBC).

[0020] Furthermore, the polyvinyl alcohol (PVA) of the present invention has a degree of alcoholysis of 88% and is water-soluble.

[0021] Furthermore, the present invention also provides a multifunctional concrete admixture prepared by the above method.

[0022] Furthermore, the present invention also provides a method for applying the above-mentioned multifunctional concrete admixture. When used in concrete, the dosage is 0.5% to 5% of the mass of the cementitious material. The operation after application is as follows: after the concrete with the multifunctional concrete admixture is poured, a magnet is used to quickly move across the concrete surface at a speed of 0.5m to 2m / s.

[0023] Example 1 A method for preparing a multifunctional concrete admixture includes the following steps: (1) In a stirrer, weigh 12 parts of PVC and add it to 100 parts of organic solvent and stir until completely dissolved to form an oil phase system A; then add oil-soluble emulsifier Span-80, ettringite and calcium carbonate to the oil phase system A, ultrasonically disperse and stir until completely uniform, place the stirrer in a 65℃ constant temperature water bath to obtain solution B. The organic solvent is formed by mixing cyclohexanone and tetrahydrofuran in a mass ratio of 1:1.2; The softening temperature of the PVC base is 75°C; The amount of the oil-soluble emulsifier Span-80 added is 3% of the mass of oil phase system A; The ettringite has a maximum particle size of 1 μm and an average particle size of 0.52 μm, and its addition amount is 3% of the mass of oil phase system A. The calcium carbonate has a maximum particle size of 0.5 μm and an average particle size of 0.3 μm, and its addition amount is 1% of the mass of oil phase system A. The ultrasonic dispersion parameters are: ultrasonic frequency 20 kHz, ultrasonic dispersion time 5 min; (2) Add excess sodium thiosulfate to water at 65℃ to make it supersaturated, add sodium hydroxide solution to control the pH to 12, and filter to obtain the supernatant C; then in a stirrer, slowly mix the supernatant C with the solution B obtained in step (1). The mixing process is to slowly add the supernatant C to the solution B at a uniform rate, and start the high shear emulsifier before adding. After the addition is completed, continue emulsification for 20 minutes, and then use an ultrasonic breaker to ultrasonically treat to obtain the W / O emulsion D with micron-sized sodium thiosulfate droplets dispersed. In step (2), the stirrer is placed in a 65°C constant temperature water bath, and the temperature of the reaction process is always controlled at 65°C to ensure that the sodium thiosulfate solution is always at high temperature and has high solubility. The pH is controlled to ensure the stability of the ettringite particles in the subsequent mixing. The purpose of the solution drop emulsification process in step (2) is to ensure the formation of a stable W / O system. The volume ratio of the supernatant C to solution B is 1:10, and the dropping time of the supernatant C into solution B is controlled at 8 minutes. The high-shear emulsifier speed is adjusted to 10000 r / min; The ultrasonic processing parameters of the ultrasonic disruptor are: power 200W, processing time 5min; (3) After adding PVA to water, sodium hydroxide solution is added dropwise to control the pH between 1 and 3, and PVA emulsion is obtained by ultrasonic dispersion. In a stirrer placed under a constant temperature water bath at 65°C, the emulsion D obtained in step (2) is slowly added dropwise to the PVA emulsion. Before adding, the stirrer is started at a low speed. After the addition is completed, stirring is continued to form a stable W / O / W double emulsion E. At this time, the sodium thiosulfate droplets are wrapped by the PVC oil phase film. The mass ratio of PVA to water in the PVA emulsion is 5:100; The ultrasonic dispersion parameters are: ultrasonic frequency 25 kHz, ultrasonic dispersion time 20 min; The volume ratio of emulsion D to PVA emulsion is 1:10; The speed of the stirrer is adjusted to 180 r / min. After the addition is completed, stirring continues for 120 seconds. The total stirring time is 30 minutes. (4) Place the double emulsion E obtained in step (3) in a constant temperature water bath at 65°C, adjust the speed of the stirrer and stir continuously to allow the organic solvent and water to evaporate slowly. During this process, PVC will gradually precipitate, form a film and solidify on the surface of sodium thiosulfate droplets to form core-shell microspheres. After the reaction is completed, pour all the product into a centrifuge and discard the supernatant. Then, use deionized water to repeatedly wash the centrifuged product to remove residual PVA and Span-80. Transfer the washed microspheres to a vacuum drying oven and dry them to constant weight to obtain dried micron-sized core-shell microspheres F. The speed of the stirrer is adjusted to 100 r / min, and the continuous stirring time is every 1 m. 3 Emulsion E was stirred for 10 hours; The centrifugation speed was 4000 r / min, and the centrifugation time was 10 min; The washing and settling process is repeated three times. The vacuum drying oven is set to a temperature of 60°C to ensure that the PVC microspheres do not deform. (5) Place the stirrer in a 35°C constant temperature water bath, add excess sodium sulfate to the water at 35°C in the stirrer to make it supersaturated, add sodium hydroxide dropwise to control the pH between 1 and 3, filter to obtain the supernatant H, and keep the temperature between 35°C throughout the process to ensure that the sodium sulfate is in a high solubility state. The pH is controlled to ensure the stability of the ettringite particles. Then mix the micron-sized core-shell microspheres F obtained in step (4) with the supernatant H, add PVA and nano iron oxide, and then disperse by ultrasonication to form a stable suspension I, keeping the temperature between 35°C. Mix PVC and plasticizer and add them to the solvent. Stir until completely dissolved, then add Span-80 and mix to form an oil phase system G. This ratio can stably control the softening temperature of the formed PVC at 55°C. Slowly and uniformly drop the suspension I into the oil phase system G. Before dropping, start the high shear emulsifier. After dropping, continue emulsifying for 20 minutes, and then use an ultrasonic crusher to ultrasonically treat to obtain the dispersed W / O emulsion J. The ultrasonic dispersion parameters are: ultrasonic frequency 20 kHz, ultrasonic dispersion time 30 min; The mass ratio of the micron-sized core-shell microspheres F to the supernatant H is 1:20; The amount of PVA added is 2% of the total mass of the micron-sized core-shell microspheres F and the supernatant H. The nano-ferric oxide has a particle size of 10~20nm, and its addition amount is 0.01% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The mass ratio of the PVC and plasticizer mixture to the solvent is 12:100, the mass ratio of PVC to plasticizer is 100:38, and the solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:1.2. The Span-80 is added at 2% of the total mass of PVC; The volume ratio of the suspension I to the oil phase system G is 1:8; The suspension I was slowly added dropwise to the oil phase system G, with the addition time controlled at 10 min; the high-shear emulsifier was added by adjusting the rotation speed to 6000 r / min. The ultrasonic processing parameters of the ultrasonic disruptor are: power 200W, ultrasonic processing time 3min; (6) Prepare PVA emulsion. In a constant temperature water bath at 35℃, slowly drip the emulsion J obtained in step (5) into the PVA emulsion in a stirrer. Before dripping, start the low-speed stirrer and adjust the speed to 180 r / min. After the dripping is completed, continue stirring for 120 s. The total stirring time is 30 min. At this time, the emulsion J is coated by the PVC oil phase film to form a suspension K. Place the suspension K in a constant temperature water bath at 35℃ and adjust the speed to 100 r / min. Every 1 m 3 Suspension K was continuously stirred for 10 hours to allow organic solvents to slowly evaporate. During this process, PVC gradually precipitated, formed a film, and solidified on the surface of sodium sulfate droplets, forming core-shell structured microspheres. After the reaction was completed, all the product was poured into a centrifuge to centrifuge and the supernatant was discarded. Then, the centrifuged product was repeatedly washed with deionized water to remove the precipitate. Finally, the washed microspheres were transferred to a vacuum drying oven and dried to constant weight to obtain dried core-shell microspheres L, which is the multifunctional concrete admixture described in this invention. The PVA emulsion has a mass concentration of 3%, which is obtained by ultrasonically dispersing PVA in water for 20 minutes. The volume ratio of emulsion J to PVA emulsion is 1:10; The centrifugation speed was 1000 r / min, and the centrifugation time was 15 min; The washing and settling process is repeated three times. The vacuum drying oven is set to a temperature of 50°C.

[0024] The PVC resin has a degree of polymerization of 900 (basic softening temperature of 75°C). The plasticizer is dioctyl phthalate (DOP). The polyvinyl alcohol (PVA) has a degree of alcoholysis of 88% and is water-soluble.

[0025] Example 2 A method for preparing a multifunctional concrete admixture includes the following steps: (1) In a stirrer, weigh 15 parts of PVC and add it to 100 parts of organic solvent and stir until completely dissolved to form an oil phase system A; then add oil-soluble emulsifier Span-80, ettringite and calcium carbonate to the oil phase system A, ultrasonically disperse and stir until completely uniform, place the stirrer in a 65℃ constant temperature water bath to obtain solution B. The organic solvent is formed by mixing cyclohexanone and tetrahydrofuran in a mass ratio of 1:0.8; The softening temperature of the PVC base is 80℃; The amount of the oil-soluble emulsifier Span-80 added is 2% of the mass of oil phase system A; The ettringite has a maximum particle size of 0.5 μm and an average particle size of 0.2 μm, and its addition amount is 5% of the mass of oil phase system A; The calcium carbonate has a maximum particle size of 0.2 μm and an average particle size of 0.1 μm, and its addition amount is 1% of the mass of oil phase system A. The ultrasonic dispersion parameters are: ultrasonic frequency 25 kHz, ultrasonic dispersion time 3 min; (2) Add excess sodium thiosulfate to water at 70℃ to make it supersaturated, add sodium hydroxide solution to control the pH to 12, and filter to obtain the supernatant C; then mix the supernatant C with the solution B obtained in step (1) slowly in a stirrer. The mixing process is to slowly add the supernatant C to the solution B at a uniform rate, and start the high shear emulsifier before adding. After the addition is completed, continue emulsification for 30 minutes, and then use an ultrasonic breaker to ultrasonically treat to obtain the W / O emulsion D with micron-sized sodium thiosulfate droplets dispersed. In step (2), the stirrer is placed in a 70°C constant temperature water bath, and the temperature of the reaction process is always controlled at 70°C to ensure that the sodium thiosulfate solution is always at high solubility at high temperature. The pH is controlled to ensure the stability of the ettringite particles in the subsequent mixing. The purpose of the solution drop emulsification process in step (2) is to ensure the formation of a stable W / O system. The volume ratio of the supernatant C to solution B is 1:8, and the dropping time of the supernatant C into solution B is controlled at 10 min. The high-shear emulsifier speed was adjusted to 6000 r / min; The ultrasonic processing parameters of the ultrasonic disruptor are: power 300W, processing time 3min; (3) After adding PVA to water, add sodium hydroxide solution to control the pH between 1 and 2, and then ultrasonically disperse to obtain PVA emulsion; in a stirrer placed under a constant temperature water bath at 70℃, slowly drop the emulsion D obtained in step (2) into the PVA emulsion. Before adding, start the low speed stirrer. After the addition is completed, continue stirring to form a stable W / O / W double emulsion E. At this time, the sodium thiosulfate droplets are wrapped by the PVC oil phase film. The mass ratio of PVA to water in the PVA emulsion is 3:100; The ultrasonic dispersion parameters are: ultrasonic frequency 20 kHz, ultrasonic dispersion time 30 min; The volume ratio of emulsion D to PVA emulsion is 1:8; The speed of the stirrer is adjusted to 300 r / min. After the addition is completed, stirring continues for 60 seconds. The total stirring time is 25 minutes. (4) Place the double emulsion E obtained in step (3) in a constant temperature water bath at 70°C, adjust the speed of the stirrer and stir continuously to allow the organic solvent and water to evaporate slowly. During this process, PVC will gradually precipitate, form a film and solidify on the surface of sodium thiosulfate droplets to form core-shell microspheres. After the reaction is completed, pour all the product into a centrifuge and discard the supernatant. Then, use deionized water to repeatedly wash the centrifuged product to remove residual PVA and Span-80. Transfer the washed microspheres to a vacuum drying oven and dry them to constant weight to obtain dried micron-sized core-shell microspheres F. The speed of the stirrer is adjusted to 120 r / min, and the continuous stirring time is every 1 m. 3 Emulsion E was stirred for 10 hours; The centrifugation speed was 6000 r / min, and the centrifugation time was 8 min; The washing and settling process is repeated 5 times. The vacuum drying oven is set to a temperature of 50°C to ensure that the PVC microspheres do not deform. (5) Place the stirrer in a constant temperature water bath at 32℃. Add excess sodium sulfate to the water at 32℃ in the stirrer to make it supersaturated. Add sodium hydroxide dropwise to control the pH between 1 and 2. Filter to obtain the supernatant H. During this process, the temperature is always controlled between 32℃ to ensure that the sodium sulfate is in a high solubility state. The pH is controlled to ensure the stability of the ettringite particles. Then, mix the micron-sized core-shell microspheres F obtained in step (4) with the supernatant H. Add PVA and nano iron oxide and then disperse by ultrasonication to form a stable suspension I. Control the temperature between 32℃. Mix PVC and plasticizer and add them to the solvent. Stir until completely dissolved. Add Span-80 and mix to form an oil phase system G. This ratio can stably control the softening temperature of the formed PVC between 62℃. Slowly and uniformly drop the suspension I into the oil phase system G. Start the high shear emulsifier before dropping. After dropping, continue emulsification for 20 minutes. Then use an ultrasonic crusher to ultrasonically treat to obtain the dispersed W / O emulsion J. The ultrasonic dispersion parameters are: ultrasonic frequency 20 kHz, ultrasonic dispersion time 30 min; The mass ratio of the micron-sized core-shell microspheres F to the supernatant H is 1:30; The amount of PVA added is 1% of the total mass of the micron-sized core-shell microspheres F and the supernatant H. The nano-ferric oxide has a particle size of 10~20nm, and its addition amount is 0.03% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The mass ratio of the PVC and plasticizer mixture to the solvent is 15:100, the mass ratio of PVC to plasticizer is 100:32, and the solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:0.8. The Span-80 is added at 3% of the total mass of PVC; The volume ratio of the suspension I to the oil phase system G is 1:9; The suspension I was slowly added dropwise to the oil phase system G, with the addition time controlled at 8 min; the high-shear emulsifier was added by adjusting the rotation speed to 10000 r / min. The ultrasonic processing parameters of the ultrasonic disruptor are: power 300W, ultrasonic processing time 5min; (6) Prepare PVA emulsion. In a constant temperature water bath at 32℃, slowly drip the emulsion J obtained in step (5) into the PVA emulsion in a stirrer. Before dripping, start the low-speed stirrer and adjust the speed to 300 r / min. After the dripping is completed, continue stirring for 60 s. The total stirring time is 25 min. At this time, the emulsion J is coated by the PVC oil phase film to form a suspension K. Place the suspension K in a constant temperature water bath at 32℃ and adjust the speed to 120 r / min. Every 1 m 3 Suspension K was continuously stirred for 8 hours to allow organic solvents to slowly evaporate. During this process, PVC gradually precipitated, formed a film, and solidified on the surface of sodium sulfate droplets, forming core-shell structured microspheres. After the reaction was completed, all the product was poured into a centrifuge and the supernatant was discarded. Then, the centrifuged product was repeatedly washed with deionized water to remove the precipitate. Finally, the washed microspheres were transferred to a vacuum drying oven and dried to constant weight to obtain dried core-shell microspheres L, which is the multifunctional concrete admixture described in this invention. The PVA emulsion has a mass concentration of 5%, which is obtained by ultrasonically dispersing PVA in water for 30 minutes. The volume ratio of emulsion J to PVA emulsion is 1:8; The centrifugation speed was 1500 r / min, and the centrifugation time was 10 min; The washing and settling process is repeated 5 times. The vacuum drying oven is set to a temperature of 40°C.

[0026] The PVC resin has a degree of polymerization of 1000 and a basic softening temperature of 80°C.

[0027] The plasticizer is acetylglucosyl tributyl citrate (ATBC).

[0028] The polyvinyl alcohol (PVA) has a degree of alcoholysis of 88% and is water-soluble.

[0029] Example 3 A method for preparing a multifunctional concrete admixture includes the following steps: (1) In a stirrer, weigh 14 parts of PVC and add it to 100 parts of organic solvent and stir until completely dissolved to form an oil phase system A; then add oil-soluble emulsifier Span-80, ettringite and calcium carbonate to the oil phase system A, ultrasonically disperse and stir until completely uniform, place the stirrer in a 68℃ constant temperature water bath to obtain solution B. The organic solvent is formed by mixing cyclohexanone and tetrahydrofuran in a mass ratio of 1:1. The softening temperature of the PVC base is 77°C; The amount of the oil-soluble emulsifier Span-80 added is 2.8% of the mass of oil phase system A; The ettringite has a maximum particle size of 0.6 μm and an average particle size of 0.2 μm, and its addition amount is 4% of the mass of oil phase system A. The calcium carbonate has a maximum particle size of 0.1 μm and an average particle size of 0.06 μm, and its addition amount is 1.5% of the mass of oil phase system A. The ultrasonic dispersion parameters are: ultrasonic frequency 22 kHz, ultrasonic dispersion time 4 min; (2) Add excess sodium thiosulfate to water at 68℃ to make it supersaturated, add sodium hydroxide solution to control the pH to 12.8, filter to obtain the supernatant C; then in a stirrer, slowly mix the supernatant C with the solution B obtained in step (1). The mixing process is to slowly add the supernatant C to the solution B at a uniform rate, and start the high shear emulsifier before adding. After the addition is completed, continue emulsification for 25 minutes, and then use an ultrasonic breaker to ultrasonically treat to obtain the W / O emulsion D with micron-sized sodium thiosulfate droplets dispersed. In step (2), the stirrer is placed in a 68°C constant temperature water bath, and the temperature of the reaction process is always controlled at 68°C to ensure that the sodium thiosulfate solution is always at high solubility at high temperature. The pH is controlled to ensure the stability of the ettringite particles in the subsequent mixing. The purpose of the solution drop emulsification process in step (2) is to ensure the formation of a stable W / O system. The volume ratio of the supernatant C to solution B is 1:9, and the dropping time of the supernatant C into solution B is controlled at 9 minutes. The high-shear emulsifier speed was adjusted to 7000 r / min; The ultrasonic processing parameters of the ultrasonic disruptor are: power 280W, processing time 4min; (3) After adding PVA to water, sodium hydroxide solution is added dropwise to control the pH between 12 and 8, and PVA emulsion is obtained by ultrasonic dispersion. In a stirrer placed under a constant temperature water bath at 68℃, the emulsion D obtained in step (2) is slowly added dropwise to the PVA emulsion. Before adding, the stirrer is started at a low speed. After the addition is completed, stirring is continued to form a stable W / O / W double emulsion E. At this time, the sodium thiosulfate droplets are wrapped by the PVC oil phase film. The mass ratio of PVA to water in the PVA emulsion is 4:100; The ultrasonic dispersion parameters are: ultrasonic frequency 22 kHz, ultrasonic dispersion time 25 min; The volume ratio of emulsion D to PVA emulsion is 1:9; The speed of the stirrer was adjusted to 240 r / min. After the addition was completed, stirring continued for 120 seconds. The total stirring time was 28 minutes. (4) Place the double emulsion E obtained in step (3) in a constant temperature water bath at 68°C, adjust the speed of the stirrer and stir continuously to allow the organic solvent and water to evaporate slowly. During this process, PVC will gradually precipitate, form a film and solidify on the surface of sodium thiosulfate droplets to form core-shell microspheres. After the reaction is completed, pour all the product into a centrifuge and discard the supernatant. Then, use deionized water to repeatedly wash the centrifuged product to remove residual PVA and Span-80. Transfer the washed microspheres to a vacuum drying oven and dry them to constant weight to obtain dried micron-sized core-shell microspheres F. The speed of the stirrer is adjusted to 110 r / min, and the continuous stirring time is every 1 m. 3 Emulsion E was stirred for 9 hours; The centrifugation speed was 5000 r / min, and the centrifugation time was 9 min; The washing and settling process is repeated four times. The vacuum drying oven is set to a temperature of 40°C to ensure that the PVC microspheres do not deform. (5) Place the stirrer in a constant temperature water bath at 32.4℃. Add excess sodium sulfate to the water at 32.4℃ in the stirrer to make it supersaturated. Add sodium hydroxide dropwise to control the pH between 12 and 8. Filter to obtain the supernatant H. During this process, the temperature is always controlled at 32.4℃ to ensure that the sodium sulfate is in a state of high solubility. The pH is controlled to ensure the stability of the ettringite particles. Then, mix the micron-sized core-shell microspheres F obtained in step (4) with the supernatant H, and add PVA and nano-iron oxide. A stable suspension I was formed by ultrasonic dispersion, with the temperature controlled at 32.4℃. PVC and plasticizer were mixed and added to a solvent. After stirring until completely dissolved, Span-80 was added and mixed to form an oil phase system G. This ratio can stably control the softening temperature of the formed PVC at 58℃. Suspension I was slowly and uniformly added dropwise to the oil phase system G. A high-shear emulsifier was started before the dropwise addition. After the dropwise addition was completed, emulsification was continued for 25 minutes. Then, the mixture was ultrasonically treated with an ultrasonic disruptor to obtain a dispersed W / O emulsion J. The ultrasonic dispersion parameters are: ultrasonic frequency 22 kHz, ultrasonic dispersion time 28 min; The mass ratio of the micron-sized core-shell microspheres F to the supernatant H is 1:25; The amount of PVA added is 1.5% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The nano-iron oxide has a particle size of 10~20nm, and its addition amount is 0.02% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The mass ratio of the PVC and plasticizer mixture to the solvent is 14:100, the mass ratio of PVC to plasticizer is 100:36, and the solvent is formed by mixing cyclohexanone and tetrahydrofuran in a mass ratio of 1:1. The Span-80 is added at a rate of 2.8% of the total mass of PVC. The volume ratio of the suspension I to the oil phase system G is 1:10; The suspension I was slowly added dropwise to the oil phase system G, and the addition time was controlled at 9 min; the high shear emulsifier was added by adjusting the rotation speed to 7000 r / min. The ultrasonic processing parameters of the ultrasonic disruptor are: power 280W, ultrasonic processing time 4min; (6) Prepare the PVA emulsion. In a constant temperature water bath at 32.4℃, slowly drip the emulsion J obtained in step (5) into the PVA emulsion in a stirrer. Before dripping, start the low-speed stirrer and adjust the speed to 240 r / min. After the dripping is completed, continue stirring for 120 s. The total stirring time is 28 min. At this time, the emulsion J is coated by the PVC oil phase film to form a suspension K. Place the suspension K in a constant temperature water bath at 32.4℃ and adjust the speed to 110 r / min. Every 1 m 3 Suspension K was continuously stirred for 9 hours to allow the organic solvents to evaporate slowly. During this process, PVC gradually precipitated, formed a film, and solidified on the surface of sodium sulfate droplets, forming core-shell structured microspheres. After the reaction was completed, all the product was poured into a centrifuge and the supernatant was discarded. Then, the centrifuged product was repeatedly washed with deionized water to remove the precipitate. Finally, the washed microspheres were transferred to a vacuum drying oven and dried to constant weight to obtain dried core-shell microspheres L, which is the multifunctional concrete admixture described in this invention. The PVA emulsion has a mass concentration of 4%, which is obtained by ultrasonically dispersing PVA in water for 25 minutes. The volume ratio of emulsion J to PVA emulsion is 1:9; The centrifugation speed was 1200 r / min, and the centrifugation time was 12 min; The washing and settling process is repeated four times. The vacuum drying oven is set to a temperature of 40°C.

[0030] The PVC resin has a degree of polymerization of 1000 and a basic softening temperature of 80°C. The plasticizer is dioctyl phthalate (DOP).

[0031] The polyvinyl alcohol (PVA) has a degree of alcoholysis of 88% and is water-soluble.

[0032] Comparative Example 1 Compared with Example 3, equal amounts of sodium thiosulfate, sodium sulfate, ettringite, sodium carbonate, and nano-ferric oxide were mixed evenly to form an admixture, which was then added to the concrete in equal amounts.

[0033] Comparative Example 2 Compared with Example 3, steps (5) and (6) are omitted, and the microspheres F obtained in step (4) are directly added to the concrete in equal amounts.

[0034] Comparative Example 3 Compared to Example 3, no nano-iron oxide was added.

[0035] Comparative Example 4 Compared to Example 3, no calcium carbonate was added.

[0036] Comparative Example 5 Compared to Example 3, no ettringite was added.

[0037] Based on the baseline concrete mix proportions in Table 1, admixtures from Examples 1-3 and Comparative Examples 1-5 of this invention were added, and the concrete slump was adjusted to 180±10mm. The mix proportions were the experimental concrete mix proportions in Table 1. After the concrete with the added multifunctional admixture was poured, a magnet was quickly moved across the concrete surface at a speed of 1m / s. The slump, 1-day compressive strength, 7-day compressive strength, and 28-day compressive strength were then measured. Simultaneously, cracks were pre-introduced in the 28-day cured concrete using a pressure testing machine, with crack widths selected between 0.10 and 0.15mm. The test blocks were then immersed in an aqueous solution for 28 days, and changes in crack width and strength were observed. The results are shown in Table 2. Furthermore, large-volume concrete was prepared based on the above mix proportions, and the peak temperature rise results are shown in Table 2.

[0038] Table 1 Concrete mix proportions / Kg / m 3

[0039] Table 2 Concrete Properties

[0040] The data in Table 2 shows that: Comparing Examples 1-3 with the baseline example, it can be seen that the admixture prepared in this invention significantly increases the 1-day and 3-day compressive strength of concrete, and the 28-day compressive strength is not lower than that of the baseline concrete. Pre-cracks were formed at 28 days. Analysis of the concrete strength at 56 days without pre-cracks and the concrete strength after 28 days of self-healing shows that its strength is basically equivalent to that without pre-cracks, indicating that it has a good self-healing effect. In addition, comparing the peak temperature rise shows that its peak temperature rise is significantly lower than that of the baseline concrete.

[0041] Comparing Comparative Example 1 and Example 3, it can be seen that the 1-day and 3-day compressive strength of concrete significantly increased, but the 28-day compressive strength decreased, and the 56-day compressive strength was relatively lower. The strength after soaking was also not high, and the peak temperature rise was significantly increased. This is because directly adding the agent is equivalent to simultaneously adding a large amount of sulfate accelerator. Although it can improve the early strength of concrete, it causes a decline in strength in the later stages, and the explosive generation of instantaneous hydration products leads to an increase in the peak temperature rise.

[0042] Comparing Comparative Example 2 and Example 3, it can be seen that the 1-day and 3-day compressive strength of the concrete did not decrease, but the 28-day compressive strength decreased slightly, although not significantly different from the reference concrete. Comparing the crack repair, the crack repair rate was also significantly improved. However, comparing the temperature rise, the peak temperature rise was significantly higher, though not significantly different from the reference concrete. This indicates that preparing concrete using the method in Comparative Example 2 helps improve the early strength of the concrete and repair later cracks, but the control over the peak temperature rise is limited.

[0043] Comparing Comparative Example 3 with the baseline group and Example 3, it can be seen that the early strength improvement of the concrete is not significant compared with the baseline concrete, and it is lower than that of Example 3. However, it has obvious self-healing effect and temperature rise control effect. This indicates that without nano-ferric oxide, the exothermic crystallization precipitation effect of the calcium sulfate saturated solution cannot play a positive role, thus affecting the early strength improvement. However, it can still play a good role when the temperature rises.

[0044] A comparison of Comparative Example 4 and Example 3 shows that the self-repairing effect of cracks in the later stages is limited. This is mainly because calcium carbonate primarily reacts with AFm transformed from ettringite to form dense hydration products. When calcium carbonate is lacking, these hydration products cannot be formed, thus weakening the crack repair performance. A comparison of Comparative Example 5 and Example 3 shows that the later crack repair effect is limited. This is mainly because the lack of AFt prevents the formation of pores in the PVC microspheres, thus preventing sodium thiosulfate from seeping out and failing to provide a significant reinforcing effect.

Claims

1. A method for preparing a multifunctional concrete admixture, characterized in that, Includes the following steps: (1) In a stirrer, PVC is added to an organic solvent and stirred until completely dissolved to form an oil phase system A; then oil-soluble emulsifier Span-80, ettringite and calcium carbonate are added to the oil phase system A, ultrasonically dispersed and stirred until completely uniform, and the stirrer is placed in a constant temperature water bath of 65~70℃ to obtain solution B. (2) Add excess sodium thiosulfate to water at 65~70℃ to make it supersaturated, add sodium hydroxide solution dropwise to control the pH to 12~13, and filter to obtain the supernatant C; Then, in the stirrer, the stirrer is placed in a constant temperature water bath at 65~70℃. The supernatant C is slowly mixed with the solution B obtained in step (1). The mixing process is to slowly add the supernatant C to the solution B at a uniform rate. Before adding the solution, the high shear emulsifier is started. After the addition is completed, the emulsification is continued for 20~30 minutes. Then, the solution is ultrasonically treated with an ultrasonic breaker to obtain a W / O emulsion D with micron-sized sodium thiosulfate droplets dispersed. (3) After adding PVA to water, add sodium hydroxide solution to control the pH between 12 and 13, and then ultrasonically disperse to obtain PVA emulsion; in a stirrer placed under constant temperature water bath conditions of 65-70℃, slowly add the emulsion D obtained in step (2) to the PVA emulsion. Start the low speed stirrer before adding, and continue stirring after adding to form a stable W / O / W double emulsion E; (4) Place the double emulsion E obtained in step (3) in a constant temperature water bath at 65~70℃, adjust the speed of the stirrer and continue stirring to form core-shell structured microspheres; after the reaction is completed, pour all the product into a centrifuge and discard the supernatant. The centrifuged product was then repeatedly washed with deionized water to remove the precipitate. The washed microspheres were then transferred to a vacuum drying oven and dried to constant weight to obtain dried micron-sized core-shell microspheres F. (5) Place the stirrer in a constant temperature water bath at 32~35℃. Add excess sodium sulfate to the water at 32~35℃ in the stirrer to make it supersaturated. Add sodium hydroxide dropwise to control the pH between 12 and 13. Filter to obtain the supernatant H. Then mix the micron-sized core-shell microspheres F obtained in step (4) with the supernatant H. Add PVA and nano iron oxide and then disperse by ultrasonication to form a stable suspension I. Control the temperature between 32~35℃. Mix PVC and plasticizer and add them to the solvent. Stir until completely dissolved. Add Span-80 and mix to form an oil phase system G. Slowly and uniformly drop the suspension I into the oil phase system G. Start the high shear emulsifier before dropping. After dropping, continue emulsifying for 20~30 minutes. Then use an ultrasonic crusher to ultrasonically treat to obtain the dispersed W / O emulsion J. (6) Prepare PVA emulsion. In a constant temperature water bath at 32~35℃, slowly drip the emulsion J obtained in step (5) into the PVA emulsion in a stirrer. Before dripping, start the low-speed stirrer and adjust the speed to 180~300 r / min. After the dripping is completed, continue stirring for 60~120 s. The stirring time for the entire process is 25~30 min. At this time, the emulsion J is coated by the PVC oil phase film to form a suspension K. Place the suspension K in a constant temperature water bath at 32~35℃ and adjust the speed to 100~120 r / min. Every 1 m 3 The suspension K was continuously stirred for 8-10 hours to form core-shell structured microspheres. After the reaction was completed, all the product was poured into a centrifuge and the supernatant was discarded. Then, the centrifuged product was repeatedly washed with deionized water to precipitate. Finally, the washed microspheres were transferred to a vacuum drying oven and dried to constant weight to obtain dried core-shell microspheres L, which is the multifunctional concrete admixture.

2. The preparation method according to claim 1, characterized in that, The mass ratio of PVC to organic solvent in step (1) is 12~15:100; The organic solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:0.8~1.2; The amount of the oil-soluble emulsifier Span-80 added is 2% to 3% of the mass of oil phase system A; The maximum particle size of the ettringite is no greater than 1 μm, and its addition amount is 3-5% of the mass of oil phase system A. The maximum particle size of the calcium carbonate is no greater than 0.5 μm, and its addition amount is 1~2% of the mass of oil phase system A; The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 3~5 min.

3. The preparation method according to claim 1, characterized in that, In step (2), the volume ratio of the supernatant C to the solution B is 1:8~10, and the dripping time of the supernatant C to the solution B is controlled at 8~10 min; The high-shear emulsifier speed is adjusted to 6000~10000 r / min; The ultrasonic processing parameters of the ultrasonic disruptor are: power 200~300W, processing time 3~5min.

4. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of PVA to water in the PVA emulsion is 3~5:100; The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 20~30 min; The volume ratio of emulsion D to PVA emulsion is 1:8~10; The stirring speed is adjusted to 180~300 r / min. After the addition is completed, stirring continues for 60~120s. The entire stirring process takes 25~30min.

5. The preparation method according to claim 1, characterized in that, In step (4), the speed of the stirrer is adjusted to 100~120 r / min, and the stirring time is every 1m. 3 Emulsion E is stirred for 8-10 hours; The centrifugation speed is 4000~6000 r / min, and the centrifugation time is 8~10 min; The washing and settling process is repeated 3 to 5 times. The temperature of the vacuum drying oven is set not higher than 60℃.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the micron-sized core-shell microspheres F to the supernatant H in step (5) is 1:20~30; The amount of PVA added is 1-2% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The nano-ferric oxide has a particle size of 10-20 nm, and its addition amount is 0.01-0.03% of the total mass of the micron-sized core-shell microspheres F and the supernatant H; The mass ratio of the PVC and plasticizer mixture to the solvent is 12-15:100, the mass ratio of PVC to plasticizer is 100:32-38, and the solvent is formed by mixing cyclohexanone and tetrahydrofuran at a mass ratio of 1:0.8-1.2; the amount of Span-80 added is 2-3% of the total mass of PVC. The volume ratio of the suspension I to the oil phase system G is 1:8~10; The ultrasonic dispersion parameters are: ultrasonic frequency 20~25 kHz, ultrasonic dispersion time 20~30 min; The suspension I is slowly added dropwise to the oil phase system G, with the addition time controlled at 8-10 min; the high-shear emulsifier is added by adjusting the rotation speed to 6000-10000 r / min. The ultrasonic processing parameters of the ultrasonic disruptor are: power 200~300W, ultrasonic processing time 3~5min.

7. The preparation method according to claim 1, characterized in that, The PVA emulsion mentioned in step (6) has a mass concentration of 3% to 5%, which is obtained by ultrasonically dispersing PVA in water for 20 to 30 minutes. The volume ratio of emulsion J to PVA emulsion is 1:8~10; The centrifugation speed is 1000~1500 r / min, and the centrifugation time is 10~15 min; The washing and settling process is repeated 3 to 5 times. The temperature of the vacuum drying oven is set not higher than 50°C.

8. The preparation method according to claim 1, characterized in that, The degree of polymerization of the PVC is 900~1000, and its basic softening temperature is 75~80℃; in step (5), the softening temperature of the formed PVC is controlled between 55~62℃ by controlling the amount of plasticizer added. The plasticizer is dioctyl phthalate or tributyl acetylcitrate. The polyvinyl alcohol (PVA) has a degree of alcoholysis of 88% and is water-soluble.

9. A multifunctional concrete admixture prepared by the method according to any one of claims 1 to 8, characterized in that, The multifunctional concrete admixture has a core-shell structure of microspheres within microspheres. The core of the structure is a micron-sized core-shell microsphere F, the outer shell is PVC, and the middle contains a saturated sodium sulfate solution at 32~35℃ and nano-iron oxide particles. The micron-sized core-shell microsphere F contains a saturated sodium thiosulfate, calcium carbonate and ettringite mixture at 60~70℃.

10. A method for applying the multifunctional concrete admixture as described in claim 9, characterized in that, When this multifunctional concrete admixture is used in concrete, its dosage is 0.5% to 5% of the mass of the cementitious material; and after the concrete with this multifunctional concrete admixture is poured, a magnet needs to be used to quickly move across the concrete surface at a speed of 0.5m to 2m / s.

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