Spraying UHPC material heated by microwave, preparation method and spraying method

Abstract

The invention discloses a spraying UHPC material heated through microwaves, a preparation method and a spraying method, and relates to the technical field of spraying UHPC, and the preparation method of the spraying UHPC material comprises the steps that a microwave response rheological capsule is prepared from a wrapping material, a microwave response medium and a rheological material serving as a core material; the microwave response early strength capsule is prepared from a wrapping material, a microwave response medium and an early strength material serving as a core material. The spraying ultra-high performance concrete is obtained by mixing and stirring the following raw materials in parts by mass: cement, fly ash floating beads, silica fume, superfine limestone powder, quartz sand, microfilament steel fibers, mixing water, a water reducing agent, a microwave response rheological capsule and a microwave response early strength capsule. In the jetting process, after the rheological capsule is dissolved and released, the static yield stress of the jetted UHPC can be rapidly improved, and after the early strength capsule is dissolved and released, cement hydration can be rapidly promoted, and the early strength of the jetted UHPC is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sprayed UHPC, in particular to a sprayed UHPC material preparation method using microwave heating, a spraying device and a spraying method. BACKGROUND

[0002] Sprayed Ultra-High Performance Concrete (UHPC) is an important research direction in the field of civil engineering materials and construction technology in recent years. Its research background stems from the limitations of traditional concrete in complex engineering environments, such as high load, severe corrosion conditions or special structural forms (such as thin-walled, curved surfaces) application challenges. UHPC, with its ultra-high strength (compressive strength ≥ 120 MPa), excellent durability (low permeability, chemical corrosion resistance) and outstanding toughness (with steel fibers), has become an ideal material to solve such problems. However, the traditional pouring process is difficult to adapt to the construction needs of narrow spaces, rapid repair or complex geometric shapes, so combining spraying process with UHPC becomes the key to breaking through the technical bottleneck.

[0003] Currently, sprayed UHPC is mainly divided into two systems: one is a quick-setting spraying system that adds a quick-setting agent to the air inlet. The quick-setting system has the advantages of high pumping efficiency and fast setting time, but the addition of quick-setting agents can easily lead to slurry powdering, causing a large amount of spraying rebound and strength degradation; the second is a thixotropic spraying system that adds thixotropic materials to the slurry during mixing. The thixotropic system has the advantages of low spraying rebound rate and high strength retention rate, but the addition of thixotropic agents increases the static yield stress of the slurry, and the low discharge speed significantly reduces the pumping efficiency. More importantly, whether it is a quick-setting system or a thixotropic system, the 6h compressive strength can only reach 1-3MPa, which is difficult to meet the application scenarios of short air window period such as subway, high-speed rail research and marine structure tide repair.

[0004] There are few applications of spraying guns with microwave heating function combined with sprayed UHPC materials in the prior art, therefore, it is necessary to develop a sprayed UHPC material preparation method using microwave heating with high pumping efficiency, low rebound rate, fast strength development and no reverse shrinkage, as well as a spraying device and a spraying method. SUMMARY

[0005] The present application aims to solve the problems in the prior art and provides a method for preparing a sprayed UHPC material using microwave heating, a spraying device and a spraying method. The pumping performance of the UHPC is ensured by incorporating rheological materials and early strength materials in the form of capsules, and the microwave heating method dissolves the capsules at the nozzle to ensure the stability of the sprayed UHPC on the wall and shorten the setting time of the sprayed concrete. This not only ensures the pumping efficiency of the UHPC and reduces the rebound rate of the sprayed concrete, but also quickly improves the early strength and provides stable late strength.

[0006] The technical solution of the present application is a method for preparing a sprayed UHPC material using microwave heating, comprising the following steps: Microwave-responsive rheological capsules are prepared using a wrapping material, a microwave-responsive medium and a rheological material as a core material, and the rheological material is polyacrylamide and / or cellulose ether; microwave-responsive early strength capsules are prepared using a wrapping material, a microwave-responsive medium and an early strength material as a core material, and the early strength material is sodium sulfate and / or nano-silicon dioxide; The raw materials include cement 300-400 parts by mass, fly ash floating beads 50-100 parts, silica fume 50-100 parts, ultra-fine limestone powder 40-70 parts, quartz sand 400-500 parts, micro-fiber steel fiber 30-70 parts, mixing water 90-120 parts, water reducing agent 5-15 parts, microwave-responsive rheological capsules 2-5 parts and microwave-responsive early strength capsules 5-15 parts, which are mixed and stirred to obtain the sprayed ultra-high performance concrete.

[0007] Preferably, in the method for preparing a sprayed UHPC material using microwave heating, the wrapping material is polyethylene glycol with a molecular weight of 1000-2000; the microwave-responsive medium is nano-oxidized graphene with a size of 100-2000 nm; the molecular weight of the polyacrylamide is 500,000-1,000,000, and the molecular weight of the fiber ether is 10,000-100,000.

[0008] Preferably, in the method for preparing a sprayed UHPC material using microwave heating, the preparation processes of the microwave-responsive early strength capsules and the microwave-responsive rheological capsules both include: The wrapping material polyethylene glycol is melted in a water bath, the core material is added, the microwave-responsive medium nano-oxidized graphene is added, and the mixture is uniformly mixed to obtain a suspension, the suspension is dropped into a liquid paraffin condensate liquid to form a ball, the ball is taken out, the surface liquid paraffin is washed away with liquid alkanes, and then the ball is immersed in a liquid alkanes solution of polydimethylsiloxane for 30 minutes to 1 hour for hydrophobic treatment, and then vacuum dried to obtain the capsules.

[0009] Further, in the method for preparing a sprayed UHPC material using microwave heating, the polyethylene glycol is melted in a water bath at 85-95°C, the liquid alkanes are n-pentane, and the concentration of the liquid alkanes solution of polydimethylsiloxane is 1.5-2.5 wt%.

[0010] The preparation method of the jet UHPC material using microwave heating, the microwave response rheological capsule rheological material, the microwave response medium, the total mass of the wrapping material, the proportion of each component is 40% to 60% of the rheological material, 5 to 10% of the microwave response medium, 30% to 50% of the wrapping material; The early strength material of the microwave response early strength capsule, the microwave response medium, the total mass of the wrapping material, the proportion of each component is 40% to 60% of the early strength material, 5 to 10% of the microwave response medium, 30% to 50% of the wrapping material, the early strength material is formed by sodium sulfate and nano silicon dioxide, the mass content of sodium sulfate in the early strength material is 85% to 95%, and the rest is nano silicon dioxide.

[0011] The preparation method of the jet UHPC material using microwave heating, the microwave response rheological capsule rheological material, the microwave response medium, the total mass of the wrapping material, the proportion of each component is 40% to 60% of the rheological material, 5 to 10% of the microwave response medium, 30% to 50% of the wrapping material; The early strength material of the microwave response early strength capsule, the microwave response medium, the total mass of the wrapping material, the proportion of each component is 40% to 60% of the early strength material, 5 to 10% of the microwave response medium, 30% to 50% of the wrapping material, the early strength material is formed by sodium sulfate and nano silicon dioxide, the mass content of sodium sulfate in the early strength material is 85% to 95%, and the rest is nano silicon dioxide.

[0012] The preparation method of the jet UHPC material using microwave heating, the microwave response rheological capsule rheological material, the microwave response medium, the total mass of the wrapping material, the proportion of each component is 40% to 60% of the rheological material, 5 to 10% of the microwave response medium, 30% to 50% of the wrapping material; 2 The SiO2 content of the silica fume is greater than 90%, and the specific surface area is greater than 20000 m 2 The CaCO3 content of the ultra-fine limestone powder is greater than 95%, and the average particle size is not greater than 80 nm; the particle size interval of the quartz sand is 20-70 mesh, and the silicon dioxide content is more than 80%; the diameter of the micro-fiber steel fiber is 0.1-0.2 mm, and the length is 6-22 mm.

[0013] The preparation method of the jet UHPC material using microwave heating, the microwave response rheological capsule rheological material, the microwave response medium, the total mass of the wrapping material, the proportion of each component is 40% to 60% of the rheological material, 5 to 10% of the microwave response medium, 30% to 50% of the wrapping material; The microwave response rheological capsule raw material wrapping material, microwave response medium, rheological material, the proportion of each component in the total mass of the three is 30% to 50% of the wrapping material, 5% to 10% of the microwave response medium, and 40% to 60% of the rheological material. The microwave response early strength capsule raw material includes a wrapping material, a microwave response medium, and an early strength material, and the proportion of each component in the total mass of the three is 30% to 50% of the wrapping material, 5% to 10% of the microwave response medium, and 40% to 60% of the early strength material.

[0014] The application also provides a spraying method of the sprayed UHPC material using microwave heating, which adopts a spraying device with a microwave heating function, and the sprayed UHPC material using microwave heating is used for spraying operation under the condition that the microwave frequency is 2 GHz-3 GHz and the power is 5 kw-10 kw; the microwave response rheological capsule and the microwave response early strength capsule absorb microwave energy to release the rheological material and the early strength capsule, respectively, during the spraying process. The power of the microwave generator is 5 kw-10 kw, because the time of the ultra-high performance concrete in the spraying process in the spraying pipe is only a few seconds, and a microwave with a large power is needed to heat it quickly; the microwave frequency is 2 GHz-3 GHz, because the higher the microwave frequency, the higher the thermal efficiency, but too high a frequency will result in a decrease in the penetration of the microwave.

[0015] Preferably, the spraying device comprises a spraying pipe shell, a microwave reflection inner pipe layer, a waveguide pipe, a microwave generator, a spraying gun head, and an air pipe, the spraying pipe shell is connected to the front end of the spraying gun head, the inner wall of the spraying pipe shell is provided with the microwave reflection inner pipe layer, the microwave generator is in communication with the microwave reflection inner pipe layer through the waveguide pipe, and is used for conducting the microwave to the sprayed UHPC material, and the air pipe is connected to the rear end of the spraying gun head and is used for air supply.

[0016] Preferably, the spraying pipe shell is made of wear-resistant rubber pipe, and has a length of 0.8-1.2 m. Preferably, the microwave reflection inner pipe layer is made of 316 stainless steel material, and has a thickness of 1 mm-2 mm; and the wall thickness of the waveguide pipe is 1.5 mm-3 mm.

[0017] Preferably, the microwave generator is one or more, when there are multiple microwave generators, each microwave generator is in one-to-one correspondence with a waveguide pipe in communication with the microwave reflection inner pipe layer, and the multiple waveguide pipes are circumferentially and equally spaced at the connection positions with the microwave reflection inner pipe layer.

[0018] The principle of the present application is to incorporate rheological material and early strength material in the form of capsules to eliminate the influence of rheological material and early strength material on the workability of UHPC, to ensure that the UHPC slurry has good pumpability, and to design a microwave generating jet gun head that can emit microwaves inside the jet pipe. When the prepared slurry is pumped to the jet head, the capsule containing the responsive medium (such as water, nano graphene oxide which can quickly absorb microwave energy to heat up) is then stimulated by applying microwaves at the gun mouth, causing the capsule to heat up and dissolve from the inside and release the internal rheological material and early strength material, enhancing the static yield stress of UHPC and accelerating the early hydration reaction of UHPC for improving the adhesion of sprayed UHPC on the sprayed surface and accelerating the strength development of sprayed UHPC. In addition, microwaves can also quickly raise the temperature of the slurry (water in the slurry can absorb microwave energy to heat up), and the nucleation effect of nano graphene oxide promotes the nucleation of C-S-H reaction, further accelerating the early strength hydration reaction rate. Therefore, this technology not only ensures the pumping efficiency of UHPC and reduces the rebound rate of spraying, but also quickly improves the early strength of UHPC.

[0019] The beneficial effects of the present application are: (1) The prepared rheological capsule and early strength capsule are used to mix UHPC slurry, which can make UHPC maintain good pumpability and good slump retention performance. During the spraying process, after the rheological capsule dissolves and releases, the static yield stress of the sprayed UHPC can be quickly improved, and after the early strength capsule dissolves and releases, the early strength of the sprayed UHPC can be quickly promoted. In addition, the air entraining effect of rheological material during UHPC mixing can be avoided, and the influence of rheological material on the later strength of UHPC can be reduced.

[0020] (2) Nano graphene oxide is used as the responsive medium of microwaves. After nano graphene oxide absorbs microwaves, the capsule starts to heat up and melt from the inside, which quickly raises the temperature of the capsule and the UHPC slurry, causing the capsule to quickly dissolve in a very short time. In addition, nano graphene oxide can also act as a nucleation site for cement hydration, thereby promoting the hydration of UHPC and improving the mechanical properties of sprayed UHPC.

[0021] (3) Microwave heating is used as the excitation method for capsule dissolution, which has high energy utilization efficiency and fast temperature rise, can quickly raise the temperature of the capsule to the dissolution temperature in a short time, and can make the rheological material and early strength material dissolve before being applied to the wall. In addition, microwave heating can also raise the temperature of the UHPC slurry and accelerate the early hydration of the sprayed UHPC.

[0022] (4) When the spraying operation, the microwave in stainless steel microwave reflection inner tube layer constantly reflected, rheological capsule and early strength capsule due to response medium nano graphene oxide and water began to absorb microwave energy and heating, when the temperature rises to 40 degrees Celsius gradually release core rheological material and core early strength material, the release of core rheological material can enhance the thixotropic properties and sag resistance of the paste, reduce the rebound rate of spraying. Early strength material release can promote the rapid hydration of cement particles in the paste, improve the early strength. In addition, as the capsule shell microwave response medium graphene is released, which can also be used as nucleation sites to promote the generation of C-S-H gel. Finally, under the multiple effects of rheological material, early strength material, nano graphene oxide and microwave heating, the rapid forming and curing of sprayed ultra-high performance concrete is realized. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The preparation process of the microwave response capsule; Figure 2 The spraying device with microwave heating function; Figure 3 The spraying gun head sectional view (left) and the spray pipe sectional view (right) Among them, 101 is the spray pipe shell, 102 is the microwave reflection inner tube layer; 201 is the No. 1 waveguide tube, 202 is the No. 2 waveguide tube, 203 is the No. 1 microwave generator, and 204 is the No. 2 microwave generator; 3 is the spraying gun head; 401 is the air pipe No. 1, and 402 is the air pipe No. 2. DETAILED DESCRIPTION

[0024] The concept and technical effects of the present application will be described below in conjunction with examples for a clear and complete description, so as to fully understand the purpose, features and effects of the present application. Obviously, the described examples are only part of the examples of the present application, not all examples, and other examples obtained by those skilled in the art without creative labor based on the examples of the present application are within the scope of protection of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are conventional products that can be purchased on the market. The following component percentages are mass percentages.

[0025] The present application will be further described in detail in the following specific examples. The amount of each material and the spraying method in the examples and comparative examples are shown in Table 1 below.

[0026] Table 1 Formulation amount and spraying method The specifications of the raw materials used are as follows: The wrapping material is polyethylene glycol with a molecular weight of 1000-2000; The microwave-responsive medium is nano-oxidized graphene with a size of 100-2000 nm; The molecular weight of polyacrylamide is 500-1000; The molecular weight of the fiber ether is 10-100; The cement is a Portland cement with a strength of not less than 42.5; The average particle size of fly ash floating beads is 1-5 μm, and the specific surface area is greater than 2500 m 2 / kg; The SiO2 content of silica fume is greater than 90%, and the specific surface area is greater than 20000 m 2 / kg; The CaCO3 content of ultra-fine limestone powder is greater than 95%, and the average particle size is not greater than 80 nm; The particle size of quartz sand is 20-70 mesh, and the silicon dioxide content is more than 80%; The diameter of the micro-fiber steel fiber is 0.2 mm, and the length is 13 mm.

[0027] Example 1 The preparation method of the spray UHPC material using microwave heating is as follows: S1: As Figure 1 shown, microwave-responsive rheological capsules and microwave-responsive early strength capsules are prepared, and the microwave-responsive rheological capsules are prepared as follows: S1-1: Melt polyethylene glycol in a water bath at 85-95 °C, then add rheological material (cellulose ether), and finally add nano-oxidized graphene. The mass ratio of each component in the rheological material + polyethylene glycol + nano-oxidized graphene is cellulose ether 50%, polyethylene glycol 45%, and nano-oxidized graphene 5%. Stir the mixture for 5-10 minutes until a uniform suspension is obtained.

[0028] S1-2: Add the mixed suspension droplets to the liquid paraffin condensate. Since the paraffin condensate is not miscible with polyethylene glycol and has low surface energy, each droplet will form a regular spherical capsule and solidify.

[0029] S1-3: Filter and wash the liquid paraffin attached to the surface of the capsule with liquid alkane (n-pentane), which is miscible with paraffin and insoluble in polyethylene glycol, to obtain a capsule precursor. Due to the water solubility of polyethylene glycol, it is easily released in water or fresh cement.

[0030] S1-4: Hydrophobic treatment in a 2 wt% polydimethylsiloxane solution in liquid alkane for 45 min. After vacuum drying, the controlled release capsules are finally obtained.

[0031] The preparation of the microwave response early strength capsule, except that the early strength material is sodium sulfate and nano silicon dioxide, the respective mass proportions of the early strength material + polyethylene glycol + nano graphene oxide are 50% sodium sulfate, 5% nano silicon dioxide, 40% polyethylene glycol, and 5% nano graphene oxide, and the rest are the same as the preparation mode of the microwave response rheological capsule.

[0032] S2: The jet UHPC directly mixed with the capsule-wrapped rheological material and the early strength material is composed of the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of ultra-fine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 4 parts of microwave response rheological capsule (50% cellulose ether, 45% polyethylene glycol, and 5% nano graphene oxide), and 10 parts of microwave response early strength capsule (50% sodium sulfate, 5% nano silicon dioxide, 40% polyethylene glycol, and 5% nano graphene oxide).

[0033] The preparation process includes the following steps: 1) The Portland cement, fly ash, silica fume, ultra-fine limestone powder, and quartz sand are thoroughly mixed and stirred for 1-2 minutes. 2) The mixing water and the water reducing agent are added and mixed for 3-5 minutes. 3) The steel fiber, the microwave response rheological capsule, and the microwave response early strength capsule are added and stirred for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0034] S3: The jet UHPC is placed in a pumping device, a jet UHPC large plate is formed by using a microwave heating jet method with a frequency of 2.45 GHz and a power of 8 kw, a rebound rate test is performed, and the test specimen of the jet UHPC is placed in a standard curing room for curing.

[0035] The jet device used in the present application is shown in Figures 2-3 The jet device includes a jet pipe shell 101, a microwave reflection inner pipe layer 102, a waveguide, a microwave generator, a jet gun head 3, and an air pipe. The jet pipe shell 101 is connected to the front end of the jet gun head 3, and the inner wall of the jet pipe shell 101 is provided with the microwave reflection inner pipe layer 102. The microwave generator is in communication with the microwave reflection inner pipe layer 201 through the waveguide, for conducting microwaves to the jet UHPC material. The air pipe is connected to the rear end of the jet gun head 3 for air supply. The flow direction in the jet device is from back to front, and Figure 2 the direction is from right to left in the same

[0036] The material of the jet pipe shell 101 is a wear-resistant rubber pipe with a length of 0.8-1.2 m.

[0037] The microwave reflector inner tube layer 102 is made of 316 stainless steel with a thickness of 1mm-2mm. The waveguide wall thickness is 1.5mm-3mm. There may be one or more microwave generators; when there are multiple generators, each generator is connected to the microwave reflector inner tube layer 102 via a corresponding waveguide. In some preferred embodiments, there may be two generators, referred to as microwave generator 1 203 and microwave generator 204, which are symmetrically arranged at the rear end of the spray gun head 3. Microwave generator 1 203 is connected to the microwave reflector inner tube layer 102 via waveguide 1 201, and microwave generator 204 is connected to the microwave reflector inner tube layer 102 via waveguide 2 202. The connections between waveguide 1 201, waveguide 2 202, and the microwave reflector inner tube layer 102 are circumferentially spaced.

[0038] When spraying ultra-high performance concrete is performed using the spray gun head 3, a microwave generator is simultaneously activated to emit microwaves. These microwaves are continuously reflected within the stainless steel microwave reflector inner tube layer 102. As the ultra-high performance concrete slurry passes through the stainless steel microwave reflector inner tube layer 102, it is subjected to the microwaves emitted by waveguides 1 and 2. The microwave-responsive rheological capsules and microwave-responsive early-strength capsules heat up as the response medium, nano-graphene oxide, and water absorb microwave energy. Once the temperature reaches 40 degrees Celsius, the core rheological material and core early-strength material are gradually released. The release of the core rheological material enhances the thixotropic properties and anti-sagging properties of the slurry, reducing the spray rebound rate. The release of the early-strength material promotes rapid hydration of cement particles in the slurry, increasing early strength. Furthermore, the released graphene, serving as the microwave-responsive medium in the capsule shell, can also act as nucleation sites for cement particles, promoting the formation of CSH gel. Ultimately, through the combined effects of the rheological material, the early-strength material, nano-graphene oxide, and microwave heating, rapid molding and curing of sprayed ultra-high performance concrete is achieved.

[0039] Example 2 This embodiment provides a method for preparing UHPC material by microwave heating, with the following steps: S1: As Figure 1 As shown, microwave-responsive rheological capsules and microwave-responsive early-strength capsules were prepared. Preparation of microwave-responsive rheological capsules: S1-1: Melt polyethylene glycol in a water bath at 85~95 °C, then add rheology material (cellulose ether), and finally add nano-graphene oxide. The mass ratio of each component in the rheology material + polyethylene glycol + nano-graphene oxide is 50% cellulose ether, 40% polyethylene glycol, and 10% nano-graphene oxide. Stir the mixture for 5~10 minutes until a uniform suspension is obtained.

[0040] S1-2: The mixed suspension liquid drops are added into the liquid paraffin condensate liquid. Since the paraffin condensate is not miscible with polyethylene glycol and has low surface energy, each liquid drop will form a regular spherical capsule and solidify.

[0041] S1-3: The liquid alkane (n-pentane) is filtered and washed to remove the liquid paraffin attached to the surface of the capsule. The liquid alkane is miscible with paraffin and insoluble in polyethylene glycol, so that the capsule precursor is obtained. Since polyethylene glycol is water-soluble, it is easy to release in water or fresh cement.

[0042] S1-4: Hydrophobic treatment is carried out by immersing in a liquid alkane solution of 2 wt% polydimethylsiloxane for 45 min. After vacuum drying, the controlled release capsule is finally obtained.

[0043] The preparation of microwave-responsive early strength capsules, except that the early strength material is sodium sulfate and nano-silicon dioxide, the mass ratio of each in the early strength material + polyethylene glycol + nano-oxidized graphene is 50% sodium sulfate, 5% nano-silicon dioxide, 35% polyethylene glycol, and 10% nano-oxidized graphene, and the rest is the same as the preparation method of rheological capsules.

[0044] S2: The rheological material and early strength material wrapped by the capsule are directly mixed into the sprayed UHPC by the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of ultra-fine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 4 parts of microwave-responsive rheological capsules (50% cellulose ether, 40% polyethylene glycol, 10% nano-oxidized graphene), and 10 parts of microwave-responsive early strength capsules (50% sodium sulfate, 5% nano-silicon dioxide, 35% polyethylene glycol, 10% nano-oxidized graphene).

[0045] The preparation process includes the following steps: 1) Mix the Portland cement, fly ash, silica fume, ultra-fine limestone powder, and quartz sand thoroughly, and dry stir for 1-2 minutes; 2) Add water for mixing and water reducing agent, and mix for 3-5 minutes; 3) Add steel fiber, microwave-responsive rheological capsules, and microwave-responsive early strength capsules, and continue to stir for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0046] S3: Put into the pumping device, use the frequency of 2.45 GHz and the power of 8 kw microwave heating to spray the UHPC large plate, and test the rebound rate. Put the test piece of the sprayed UHPC into the standard curing room for curing.

[0047] Comparative Example 1 The spray UHPC directly mixing rheological material and early strength material without being encapsulated by capsules is composed of the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of ultra-fine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 2 parts of rheological material (cellulose ether), and 5 parts of early strength material (90% sodium sulfate and 10% nano silicon dioxide).

[0048] The preparation process comprises the following steps: 1) The Portland cement, fly ash floating bead, silica fume, ultra-fine limestone powder, and quartz sand are fully mixed and dry stirred for 1-2 minutes; 2) The mixing water and water reducing agent are added and mixed for 3-5 minutes; 3) The steel fiber, rheological material, and early strength material are continuously stirred for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0049] 4) The obtained material is placed into a pumping device, and a conventional spray method is used to spray the UHPC large plate, and the rebound rate test is performed to obtain the UHPC test piece which is placed into a standard curing room for curing.

[0050] Comparative Example 2: The spray UHPC directly mixing rheological material and early strength material without being encapsulated by capsules is composed of the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of ultra-fine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 2 parts of rheological material (cellulose ether), and 5 parts of early strength material (90% sodium sulfate and 10% nano silicon dioxide).

[0051] The preparation process comprises the following steps: 1) The Portland cement, fly ash floating bead, silica fume, ultra-fine limestone powder, and quartz sand are fully mixed and dry stirred for 1-2 minutes; 2) The mixing water and water reducing agent are added and mixed for 3-5 minutes; 3) The steel fiber, rheological material, and early strength material are continuously stirred for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0052] 4) The obtained material is placed into a pumping device, and a conventional spray method is used to spray the UHPC large plate, and the rebound rate test is performed to obtain the UHPC test piece which is placed into a standard curing room for curing.

[0053] Comparative Example 3: The rheological material directly wrapped with capsules and the early strength material without being wrapped with capsules are mixed into the sprayed UHPC of the slurry, which is composed of the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of superfine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 4 parts of microwave responsive rheological capsules (cellulose ether 50%, polyethylene glycol 45%, nano graphene oxide 5%, the rheological capsules are prepared according to the preparation method in the reference example 1), and 5 parts of early strength material (90% sodium sulfate, 10% nano silicon dioxide).

[0054] The preparation process comprises the following steps: 1) The Portland cement, fly ash floating beads, silica fume, superfine limestone powder and quartz sand are fully mixed and dry stirred for 1-2 minutes; 2) The mixing water and water reducing agent are added and mixed for 3-5 minutes; 3) The steel fiber, microwave responsive rheological capsules and early strength material are continuously stirred for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0055] 4) The obtained material is placed into a pumping device, and a sprayed UHPC large plate is formed by using a spraying method of microwave heating with a frequency of 2.45 GHz and a power of 8 kw, and a rebound rate test is performed, and the test sample of the sprayed UHPC is placed into a standard curing room for curing.

[0056] Comparative example 4: The rheological material without being wrapped with capsules and the early strength material wrapped with capsules are directly mixed into the sprayed UHPC of the slurry, which is composed of the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of superfine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 2 parts of rheological material (cellulose ether), and 10 parts of microwave responsive early strength capsules (50% sodium sulfate, 5% nano silicon dioxide, polyethylene glycol 40%, nano graphene oxide 5%, the early strength capsules are prepared according to the preparation method in the reference example 1).

[0057] The preparation process comprises the following steps: 1) The Portland cement, fly ash floating beads, silica fume, superfine limestone powder and quartz sand are fully mixed and dry stirred for 1-2 minutes; 2) The mixing water and water reducing agent are added and mixed for 3-5 minutes; 3) The steel fiber, rheological material and microwave responsive early strength capsules are continuously stirred for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0058] 4) The obtained material is placed into a pumping device, and a sprayed UHPC large plate is formed by using a spraying method of microwave heating with a frequency of 2.45 GHz and a power of 8 kw, and a rebound rate test is performed, and the test sample of the sprayed UHPC is placed into a standard curing room for curing.

[0059] Comparative Example 5 The spray UHPC directly incorporating the rheological material and early strength material encapsulated by capsules was composed of the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of ultra-fine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 4 parts of microwave responsive rheological capsules (50% cellulose ether, 50% polyethylene glycol, prepared according to the rheological capsules of Example 1, the only difference being that no nano-oxidized graphene was added), 10 parts of microwave responsive early strength capsules (50% sodium sulfate, 5% nano-silicon dioxide, 40% polyethylene glycol, 5% nano-oxidized graphene, prepared according to the early strength capsules of Example 1).

[0060] The preparation process included the following steps: 1) The Portland cement, fly ash, silica fume, ultra-fine limestone powder, and quartz sand were thoroughly mixed and dry stirred for 1-2 minutes; 2) The mixing water and water reducing agent were added and mixed for 3-5 minutes; 3) The steel fiber, microwave responsive rheological capsules, and early strength capsules were added and stirred for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0061] 4) The material was placed into a pumping device, and a spray UHPC large plate was formed by using a microwave heating spray method with a frequency of 2.45 GHz and a power of 8 kW. The rebound rate was tested, and the test specimen of the spray UHPC was placed in a standard curing room for curing.

[0062] Comparative Example 6 The spray UHPC directly incorporating the rheological material and early strength material encapsulated by capsules was composed of the following mass components: 360 parts of ordinary Portland cement, 50 parts of fly ash, 90 parts of silica fume, 70 parts of ultra-fine limestone powder, 450 parts of quartz sand, 100 parts of water, 10 parts of water reducing agent, 50 parts of steel fiber, 4 parts of microwave responsive rheological capsules (50% cellulose ether, 50% polyethylene glycol, prepared according to the rheological capsules of Example 1, the only difference being that no nano-oxidized graphene was added), 10 parts of microwave responsive early strength capsules (50% sodium sulfate, 5% nano-silicon dioxide, 40% polyethylene glycol, 5% nano-oxidized graphene, prepared according to the early strength capsules of Example 1).

[0063] The preparation process included the following steps: 1) The Portland cement, fly ash, silica fume, ultra-fine limestone powder, and quartz sand were thoroughly mixed and dry stirred for 1-2 minutes; 2) The mixing water and water reducing agent were added and mixed for 3-5 minutes; 3) The steel fiber, microwave responsive rheological capsules, and early strength capsules were added and stirred for 2-4 minutes to obtain the ultra-high performance cement-based material.

[0064] 4) Place the UHPC large-format sheet into a pumping device and use a microwave heating method with a frequency of 2.45 GHz and a power of 8 kW to perform spraying and springback testing. Then, place the sprayed UHPC specimens into a standard curing room for curing.

[0065] Comparative Example 7 The sprayed UHPC, in which the rheological material and early-strength material encapsulated in capsules are directly incorporated into the slurry, consists of the following components by weight: 360 parts ordinary silicate cement, 50 parts fly ash, 90 parts silica fume, 70 parts ultrafine limestone powder, 450 parts quartz sand, 100 parts water, 10 parts water-reducing agent, 50 parts steel fiber, 4 parts microwave-responsive rheological capsules (50% cellulose ether, 45% polyethylene glycol, and 5% nano-graphene oxide, prepared according to Example 1), and 10 parts microwave-responsive early-strength capsules (50% sodium sulfate, 5% nano-silica, 40% polyethylene glycol, and 5% nano-graphene oxide, prepared according to Example 1).

[0066] The preparation process includes the following steps: 1) Thoroughly mix silicate cement, fly ash cenospheres, silica fume, ultrafine limestone powder, and quartz sand, and dry mix for 1-2 minutes; 2) Add mixing water and water-reducing agent, and mix for 3-5 minutes; 3) Add steel fiber, microwave-responsive rheological capsules, and microwave-responsive early strength capsules and continue stirring for 2-4 minutes to obtain ultra-high performance cement-based material.

[0067] 4) Place the UHPC large-format sheet into a pumping device and use a microwave heating method with a frequency of 2.45 GHz and a power of 3 kW to perform spraying and springback testing. Then, place the sprayed UHPC specimens into a standard curing room for curing.

[0068] Comparative Example 8 The sprayed UHPC, in which the rheological material and early strength material encapsulated in capsules are directly incorporated into the slurry, consists of the following components by weight: 360 parts ordinary silicate cement, 50 parts fly ash, 90 parts silica fume, 70 parts ultrafine limestone powder, 450 parts quartz sand, 100 parts water, 10 parts water-reducing agent, 50 parts steel fiber, 4 parts microwave-responsive rheological capsule A (50% cellulose ether, 45% polyethylene glycol, 5% nano-graphene oxide, prepared according to Example 1), and 10 parts microwave-responsive early strength capsule B (50% sodium sulfate, 5% nano-silica, 40% polyethylene glycol, 5% nano-graphene oxide, prepared according to Example 1).

[0069] The preparation process includes the following steps: 1) Thoroughly mix silicate cement, fly ash cenospheres, silica fume, ultrafine limestone powder, and quartz sand, and dry mix for 1-2 minutes; 2) Add mixing water and water-reducing agent, and mix for 3-5 minutes; 3) Add steel fiber, microwave-responsive rheological capsules, and microwave-responsive early strength capsules and continue stirring for 2-4 minutes to obtain ultra-high performance cement-based material.

[0070] 4) Place the UHPC large-format sheet into a pumping device and use a microwave heating method with a frequency of 2.45GHz and a power of 12kW to perform spraying and springback testing. Then, place the sprayed UHPC specimens into a standard curing room for curing.

[0071] Performance testing The working performance, mechanical properties, and rebound rate of the sprayed UHPC were compared between the examples and the comparative examples, and the results are shown in Table 2 below.

[0072] Table 2. Working performance, mechanical properties, and rebound rate of sprayed UHPC test The experimental results in Table 2 show that: Compared with Comparative Example 1, Comparative Example 2, when sprayed using microwave heating, showed a significant improvement in the early strength of the sprayed UHPC and a reduction in the springback rate. This indicates that microwave heating accelerates the reaction rate of the early-strength material in the slurry and the hydration rate of the slurry itself, thereby improving the early strength of the UHPC and enhancing its resistance to springback.

[0073] Compared with Comparative Examples 1 and 2, the addition of rheological materials in the form of capsules in Comparative Example 3 significantly improved the initial collapse expansion of UHPC, as well as the 6-hour and 28-day strengths, while reducing the rebound rate. This indicates that adding rheological materials in the form of microwave-heated capsules can not only effectively improve the pumping efficiency of jet UHPC, but also enhance its resilience by promoting early strength development of UHPC under the action of graphene and high temperature, and improve the later strength of the matrix by reducing porosity.

[0074] Compared with Comparative Examples 2 and 3, the early strength material in Comparative Example 4 and Example 1 was added in the form of capsules. After addition, the slump retention performance of UHPC was significantly improved, the 6-hour strength and 28-day strength were slightly improved, and the rebound rate was also reduced. This indicates that adding early strength material in the form of microwave-heated capsules can avoid work losses during the transportation of UHPC, maintain its good construction performance, and improve its mechanical properties and anti-rebound ability under the action of graphene and high temperature.

[0075] Compared with Experimental Example 1, Comparative Example 5 did not add nano-graphene oxide to the rheological capsule, and the rebound rate of UHPC shotcrete increased significantly. This indicates that without nano-graphene oxide, the capsule can only be heated by the slurry heated by external microwave absorption, which reduces the capsule dissolution rate and ultimately reduces the anti-sagging performance of the slurry.

[0076] Compared with Experimental Example 1, the early strength capsule in Comparative Example 6 did not contain nano-graphene oxide, and the early strength of UHPC shotcrete was reduced. This indicates that without nano-graphene oxide, the capsule can only be heated by the slurry heated by external microwave absorption, which reduces the capsule's dissolution rate and ultimately leads to a decrease in the early mechanical properties of UHPC.

[0077] Compared with Experiment 1, in Experiment 2, after the content of nano-graphene oxide in the rheological capsule and early strength capsule was increased to 10%, the rebound rate of UHPC shotcrete decreased, while the early strength and later strength were improved. This indicates that increasing the content of nano-graphene oxide can further accelerate the dissolution of the capsule and the development of the early strength of UHPC, as well as further reduce the porosity to improve the later strength of the matrix.

[0078] Compared with Experimental Example 1, Comparative Example 7 reduced the microwave power, resulting in a significant decrease in the mechanical properties of UHPC shotcrete and a significant increase in the rebound rate. This indicates that when the microwave power is insufficient, the heating rate of the slurry and capsule decreases, the degree to which rheological materials and early-strength materials participate in the reaction decreases, ultimately leading to a decrease in the anti-sagging properties of shotcrete UHPC and a reduction in the early hydration reaction rate stage.

[0079] Compared with Experimental Example 1, Comparative Example 8 increased the microwave power, which improved the early mechanical properties of UHPC shotcrete and reduced the shotcrete rebound rate, but deteriorated the later mechanical properties. This indicates that when the microwave power is too high, although the heating rate of the slurry and capsule is high, and the rheological materials and early strength materials can be quickly dissolved and released, improving the anti-sagging performance and early strength of the shotcrete UHPC, the excessively high temperature will cause the slurry to lose water rapidly, resulting in the deterioration of the later strength of the UHPC matrix due to the increase of microcracks.

Claims

1. A method for preparing sprayed UHPC material using microwave heating, characterized in that, Includes the following steps: A microwave-responsive rheological capsule is prepared using a rheological material comprising an encapsulation material, a microwave-responsive medium, and a rheological material as a core material, wherein the rheological material is polyacrylamide and / or cellulose ether; a microwave-responsive early-strength capsule is prepared using an early-strength material comprising an encapsulation material, a microwave-responsive medium, and an early-strength material as a core material, wherein the early-strength material is sodium sulfate and / or nano-silica. The raw materials, including 300-400 parts of cement, 50-100 parts of fly ash cenospheres, 50-100 parts of silica fume, 40-70 parts of ultrafine limestone powder, 400-500 parts of quartz sand, 30-70 parts of microfiber steel fibers, 90-120 parts of mixing water, 5-15 parts of water-reducing agent, 2-5 parts of microwave-responsive rheological capsules, and 5-15 parts of microwave-responsive early-strength capsules, are mixed and stirred to obtain sprayed ultra-high performance concrete.

2. The method for preparing sprayed UHPC material using microwave heating as described in claim 1, characterized in that, The encapsulation material is polyethylene glycol with a molecular weight of 1,000 to 2,000; the microwave-responsive medium is nano-graphene oxide with a size of 100 to 2,000 nm; the polyacrylamide has a molecular weight of 500,000 to 1,000,000, and the cellulose ether has a molecular weight of 10,000 to 100,000.

3. The method for preparing sprayed UHPC material using microwave heating as described in claim 2, characterized in that, The preparation processes for both the microwave-responsive early-strength capsules and the microwave-responsive rheological capsules include: Polyethylene glycol is used as the encapsulating material in a water bath. The core material is added, followed by the addition of microwave-responsive nano-graphene oxide, which is mixed evenly to obtain a suspension. The suspension is then dropped into a liquid paraffin condensate to form spheres. The spheres are then removed and washed with liquid alkane to remove the surface liquid paraffin. They are then immersed in a liquid alkane solution of polydimethylsiloxane for 30 min to 1 h for hydrophobic treatment, followed by vacuum drying to obtain capsules.

4. The method for preparing sprayed UHPC material using microwave heating as described in claim 3, characterized in that, Polyethylene glycol is melted in a water bath at 85-95°C. The liquid alkane is n-pentane, and the concentration of the liquid alkane solution of polydimethylsiloxane is 1.5-2.5 wt%.

5. The method for preparing sprayed UHPC material using microwave heating as described in claim 1, characterized in that, In the total mass of the rheological material, microwave-responsive medium, and encapsulation material of the microwave-responsive rheological capsule, the proportions of each component are as follows: rheological material 40%~60%, microwave-responsive medium 5%~10%, and encapsulation material 30%~50%. In the total mass of the early-strength material, microwave-responsive medium, and encapsulation material of the microwave-responsive early-strength capsule, the proportions of each component are as follows: early-strength material 40%~60%, microwave-responsive medium 5%~10%, and encapsulation material 30%~50%. The early-strength material is formed by sodium sulfate and nano-silica. The mass content of sodium sulfate in the early-strength material is 85%~95%, and the remainder is nano-silica.

6. The method for preparing sprayed UHPC material using microwave heating as described in claim 5, characterized in that, In the total mass of the microwave-responsive rheological capsule, the components of rheological material, microwave-responsive medium, and encapsulation material are respectively 40-45% encapsulation material, 5-10% microwave-responsive medium, and 50% rheological material. In the total mass of the early strength material, microwave response medium, and encapsulation material of the microwave-responsive early strength capsule, the proportions of each component are as follows: encapsulation material 35-40%, microwave response medium 5-10%, and early strength material 55%.

7. The method for preparing sprayed UHPC material using microwave heating as described in claim 1, characterized in that, The cement is silicate cement with a strength of not less than 42.5; the fly ash cenospheres have an average particle size of 1~5μm and a specific surface area greater than 2500m². 2 / kg; SiO2 content of silica fume is greater than 90%, and specific surface area is greater than 20000 m². 2 / kg; the CaCO3 content of the ultrafine limestone powder is greater than 95%, and the average particle size is not greater than 80nm; the particle size range of the quartz sand is 20~70 mesh, and the silica content is more than 80%; the diameter of the microfiber steel fiber is 0.1~0.2 mm and the length is 6~22 mm.

8. A microwave-heated sprayed UHPC material, characterized in that, The UHPC material prepared by the microwave-heated spraying method according to claims 1-7 is comprising, by weight: 300-400 parts cement, 50-100 parts fly ash cenospheres, 50-100 parts silica fume, 40-70 parts ultrafine limestone powder, 400-500 parts quartz sand, 30-70 parts microfiber steel, 90-120 parts mixing water, 5-15 parts water-reducing agent, 2-5 parts microwave-responsive rheological capsules, and 5-15 parts microwave-responsive early-strength capsules. The raw materials of the microwave-responsive rheological capsule include encapsulation material, microwave-responsive medium, and rheological material, with the proportions of each component in the total mass being 30%~50% for encapsulation material, 5%~10% for microwave-responsive medium, and 40%~60% for rheological material; The raw materials for the microwave-responsive early-strength capsule include encapsulation material, microwave-responsive medium, and early-strength material. The proportions of each component in the total mass of the three are 30% to 50% for encapsulation material, 5% to 10% for microwave-responsive medium, and 40% to 60% for early-strength material.

9. A spraying method for spraying UHPC material using microwave heating as described in claim 8, characterized in that, Using a spraying device with microwave heating function, under the conditions of microwave frequency of 2GHz-3GHz and power of 5kw-10kw, the spraying operation of microwave-heated UHPC material is carried out. During the spraying process, microwave-responsive rheological capsules and microwave-responsive early strength capsules absorb microwave energy and heat up to release rheological material and early strength capsules respectively.

10. The spraying method for spraying UHPC material using microwave heating as described in claim 9, characterized in that, The spraying device includes a nozzle shell (101), a microwave reflective inner tube layer (102), a waveguide, a microwave generator, a spray gun head (3), and a duct. The nozzle shell (101) is connected to the front end of the spray gun head (3), and the inner wall of the nozzle shell (101) is provided with a microwave reflective inner tube layer (102). The microwave generator is connected to the microwave reflective inner tube layer (102) through the waveguide and is used to conduct microwaves to spray UHPC material. The duct is connected to the rear end of the spray gun head (3) for air supply.

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