A preparation method of a core-shell structure tackifier suitable for reducing the rebound rate of shotcrete

Abstract

This invention discloses a method for preparing a core-shell structured tackifier suitable for reducing the rebound rate of shotcrete, belonging to the field of concrete admixture technology. The preparation method of the core-shell structured tackifier of this invention includes the following steps: dissolving the tackifier in water to obtain a core material solution; dissolving a silane coupling agent in an organic solvent, then adjusting the pH to acidic to obtain a modified liquid; mixing the modified liquid with nano-silica, reacting to obtain surface-modified nano-silica, then mixing it with the core material solution and shearing it to obtain the core-shell structured tackifier. The core-shell structured tackifier designed in this invention ensures basic adhesion by using the tackifier as a core, while the surface-modified nano-silica imparts sufficient softness and viscoelasticity to the material. When it comes into contact with the surface to be sprayed, the soft shell can instantly deform, spread, and rupture due to the impact of the spraying pressure, thereby releasing the core material and immediately enhancing the adhesion between the shotcrete and the surface to be sprayed.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures, and in particular to a method for preparing a core-shell structure thickener suitable for reducing the rebound rate of shotcrete. Background Technology

[0002] Currently, the field of underground engineering is characterized by its diversity and large scale. Among them, shotcrete is widely used in the reinforcement of underground engineering structures due to its advantages such as rapid setting and high density. However, due to factors such as the long operating cycle of underground engineering, complex and variable geological environment, and material aging, the structures of underground engineering projects in service are prone to problems such as leakage and cracking. This places higher demands on the construction and reinforcement of underground engineering projects, requiring enhanced durability and reduced cracking and rebound to effectively address potential risks. However, the problem of high rebound rate during shotcrete construction remains unresolved, easily leading to economic losses and material waste. Therefore, reducing the rebound rate is of great value for improving construction efficiency, reducing losses, and ensuring construction safety.

[0003] Currently, methods to reduce the rebound rate of shotcrete mainly include adding high-performance admixtures (such as thickeners and accelerators), adding admixtures (such as toughening fibers, fly ash, and steel slag), adjusting the shotcrete mix proportion, and adjusting on-site construction parameters. These methods all achieve the goal of reducing rebound by increasing the viscosity of the concrete slurry itself. However, thickening the slurry during mixing can easily lead to adhesion and blockage of the shotcrete in the wet spraying machine, shortening the machine's lifespan. Furthermore, there is currently no effective method for "instant thickening upon spraying" to reduce the rebound rate of shotcrete. With the increasing scale of underground engineering projects, to meet the requirements of high-performance shotcrete, increasing the dosage of water-reducing agents to improve concrete workability without changing the concrete mix proportion is one improvement direction. However, this approach easily leads to problems such as bleeding, segregation, and decreased cohesiveness in the shotcrete. To effectively improve the cohesiveness and water retention of shotcrete, adding viscosity modifiers to improve its overall workability is an effective method. However, viscosity modifiers added during concrete mixing will initially compete with water-reducing agent molecules for adsorption, and their poor compatibility can easily lead to segregation, significantly reducing the utilization efficiency of building materials. Therefore, developing a novel viscosity-enhancing scheme that can achieve instant viscosity enhancement by utilizing the spraying pressure impact of shotcrete is of great research value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a core-shell structured tackifier suitable for reducing the rebound rate of shotcrete, thereby solving the aforementioned problems in the background art. The core-shell structured tackifier designed in this invention ensures basic adhesion by using the tackifier as a core. Surface-modified nano-silica imparts sufficient softness and viscoelasticity to the material. When it comes into contact with the surface to be sprayed, the soft shell can instantly deform, spread, and rupture due to the impact of the spraying pressure, thereby releasing the core material and immediately enhancing the adhesion between the shotcrete and the surface to be sprayed.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of this invention is to provide a method for preparing a core-shell structure thickener suitable for reducing the rebound rate of shotcrete, comprising the following steps:

[0007] The tackifier is dissolved in water to obtain a core material solution;

[0008] A silane coupling agent is dissolved in an organic solvent, and the pH value is adjusted to acidic to obtain a modified solution. The modified solution is mixed with nano-silica and reacted to obtain surface-modified nano-silica.

[0009] The surface-modified nano-silica is mixed with the core material solution and sheared to obtain the core-shell structure adhesive.

[0010] Unmodified silica has a large number of hydroxyl groups on its surface, which makes it prone to aggregation and has poor compatibility with organic core materials and subsequent substrates. After modification, its surface incorporates organophilic groups, which can reduce the interfacial tension between the core material and the shell, making the core-shell structure more uniform. At the same time, it can also improve the bonding ability of the tackifier with the surfaces of different substrates, reduce delamination and debonding problems, and enhance the stability of the bonding effect.

[0011] Preferably, the tackifier is one or more of hydroxypropyl methylcellulose ether, polysaccharide bio-adhesive, and polyethylene oxide; the mass ratio of the tackifier to water is 1:10-100.

[0012] Preferably, the silane coupling agent is one or more of methyltrimethoxysilane, vinyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane; the pH value of the modified solution is 3-5; the mass ratio of the silane coupling agent to the organic solvent is 1:5-20; and the mass ratio of the modified solution to nano-silica is 1:3-10.

[0013] Preferably, the reaction temperature is 60-100℃ and the reaction time is 2-3 hours.

[0014] Preferably, the mass ratio of the surface-modified nano-silica to the core material solution is 1-2:20.

[0015] Preferably, the shearing process is performed at a rotation speed of 1000-1500 rpm / min for 5-10 min.

[0016] Preferably, after the shearing process, a drying step is further included; the drying temperature is 40-60℃ and the time is 1-2 hours.

[0017] The second technical solution of the present invention provides a core-shell structure thickener suitable for reducing the rebound rate of shotcrete, prepared according to the above preparation method.

[0018] The third technical solution of the present invention provides an application of the above-mentioned core-shell structure thickener in the field of shotcrete modifier.

[0019] The fourth technical solution of the present invention provides a method for reducing the rebound rate of shotcrete by adding the above-mentioned core-shell structure thickener to the shotcrete slurry before spraying.

[0020] The technical principle of this invention is as follows:

[0021] This invention relates to a method for preparing a core-shell structured tackifier suitable for reducing the rebound rate of shotcrete. Through step-by-step preparation and assembly, the functional synergy of the core and shell is achieved. The tackifier solution is uniformly dispersed with hydrophobic Nano-SiO2 (surface-modified nano-silica). Due to the cohesiveness of the polymeric tackifier solution, Nano-SiO2 particles gradually adsorb and coat the surface of the polymeric tackifier solution droplets, initially forming a core-shell structured material. The hydrophobic Nano-SiO2 outer shell network surrounds the polymeric tackifier liquid, thus preventing droplet aggregation. Furthermore, van der Waals forces exist between molecules, enhancing the cohesive force of the Nano-SiO2 shell through particle entanglement, further strengthening the tendency for core-shell structure formation. Under continuous high-speed shearing, the initial core-shell structured particles are sheared at high speed and frequency, thus reducing the size of the core-shell tackifier. Finally, a core-shell material composed of a cohesive tackifier polymer core and a nanoparticle shell is obtained, appearing as a free-flowing, non-adhesive, fluffy powder. The preparation process of this core-shell structure thickener is simple, requiring no high temperature, high pressure, or complicated equipment, and the process is green and low-carbon, showing significant application prospects and promotional value.

[0022] This method mainly uses polymeric thickeners and Nano-SiO2 as raw materials. The core material solution and the modified shell material are sheared under high speed to obtain a fluidized powder, namely the core-shell structure thickener. This invention is based on the core-shell structure preparation concept. This core-shell structured thickener offers significant advantages over traditional thickeners. It is no longer limited to a single thickening function, but uses a polymeric thickener as the core to ensure basic viscosity while employing Nano-SiO2 as the shell. Furthermore, the Nano-SiO2 shell possesses excellent chemical stability and environmental resistance, protecting the core polymeric thickener and reducing its susceptibility to external factors such as temperature, humidity, and chemical media, thus extending the material's effective service life and avoiding the viscosity decay problems common in traditional thickeners due to changes in external conditions. Simultaneously, the Nano-SiO2 shell effectively improves the interfacial bonding between the material and other systems, reducing phenomena such as layering and precipitation caused by poor compatibility between the polymeric thickener and other components, enhancing the overall system stability. This overcomes the shortcomings of thickeners such as hydroxypropyl methylcellulose ether, polysaccharide bio-adhesives, and polyethylene oxide, which are difficult to adapt to complex systems due to their structural limitations, thus meeting the personalized needs of different scenarios.

[0023] The beneficial technical effects of the present invention are as follows:

[0024] The core-shell structured tackifier designed in this invention ensures basic adhesion by using a polymeric tackifier as the core, while the modified Nano-SiO2 shell imparts sufficient softness and viscoelasticity. When the core-shell particles come into contact with the surface to be sprayed, the soft shell can instantly deform, spread, and rupture due to the impact of the spraying pressure, maximizing the contact area and releasing the core material, thereby immediately enhancing the adhesion between the sprayed concrete and the surface. This allows it to be adapted to more scenarios without the need for additional functional additives.

[0025] In engineering applications, the instant viscosity-enhancing properties achieved through jetting pressure allow concrete to undergo core-shell rupture upon contact with the sprayed surface, rapidly forming a viscous structure. This reduces material flow and sagging due to its own weight, and significantly lowers the rebound rate of shotcrete by controlling the interfacial bonding properties, rheological characteristics, and structural stability of the concrete slurry. This eliminates the need for frequent work interruptions to wait for the concrete to initially set when constructing complex facades such as vertical walls, ceilings, and tunnel arches, enabling continuous and efficient spraying and significantly shortening the construction cycle. Furthermore, for engineering projects with complex terrain and confined spaces, such as underground caverns and foundation pit supports, this feature ensures rapid adhesion and formation of concrete under high-pressure jetting, reducing rework and material waste, and improving the adaptability and convenience of construction.

[0026] The method for preparing the core-shell material designed in this invention is simple, convenient, low-cost, green, and low-carbon, and has broad development prospects and application value. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The images show a comparison of scanning electron microscope (SEM) images of the core-shell structure adhesive of Example 1 before and after fracture under stress. In the images, (a) shows the image before fracture and (b) shows the image after fracture. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0030] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0032] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0033] Patent CN117567068A discloses a water-resistant rebound inhibitor thickener, its preparation and application method, and its application. This method improves the cohesiveness and water erosion resistance of shotcrete to damp rock surfaces, enhances the self-cohesiveness of shotcrete, and increases its early strength without reducing the fluidity of shotcrete or prolonging its setting time, thereby reducing the rebound rate of shotcrete. However, the thickener in this patent contains numerous components, which is not conducive to cost control and limits its application scope.

[0034] Patent CN110760295A discloses a high-temperature thickener for oil well cement slurry and its preparation method. This method improves the thickening effect of oil well cement at temperatures between 50-160℃ and is applicable to a wide range of oil well cementing projects. However, this patent uses too many raw materials and has stringent application scenarios, making it unsuitable for all shotcrete projects, especially for achieving rebound reduction.

[0035] While the thickeners mentioned in the aforementioned patents have made some progress in the performance of shotcrete, improvements are still needed in terms of raw material types, preparation methods, and applications. Currently, researchers pursuing better rebound reduction effects face cumbersome procedures, hindering large-scale application. Furthermore, existing research focuses primarily on adjusting component ratios or introducing other thickening agents, with insufficient research on thickener structural design. Regarding innovation in rebound reduction mechanisms, researchers mostly incorporate admixtures into shotcrete by adding fibers, stabilizers, reinforcing agents, and accelerators to adjust the fluidity, plasticity, and cohesiveness of the concrete paste, altering the hydration process of cement particles, influencing the structure of cement hydration products, and enhancing the bonding between cement particles. Currently, commonly used admixtures for reducing shotcrete rebound rates are mainly accelerators and viscosity modifiers (VMA), which achieve rapid setting and hardening by regulating the hydration process of cement particles and interparticle interactions, thereby strengthening the shotcrete system and reducing rebound rates. Accelerators can shorten the setting time of shotcrete, accelerate hydration, promote rapid crystal nucleation, increase the internal adhesion of the shotcrete, and form a three-dimensional network with organic polymers and hydration products, enabling the concrete adhering to the sprayed surface to maintain a certain degree of adhesion under subsequent spraying impact, thus reducing rebound rate. Tackifiers can improve the initial adhesion and adhesion retention of shotcrete, and improve the adhesion between the shotcrete material and the sprayed surface through surface or internal diffusion to reduce rebound.

[0036] This invention discloses a method for preparing a core-shell structure thickener suitable for reducing the rebound rate of shotcrete, comprising the following steps:

[0037] (1) Preparation of core material solution: Mix water and thickener in a container, then stir to dissolve, let stand, and obtain a light yellow transparent core material solution;

[0038] (2) Modification of shell material: Dissolve silane coupling agent in organic solvent, then adjust pH value to 3-5 to obtain modified liquid; add the modified liquid and nano silica into high-speed mixer, turn on stirring, heat to 60-100℃, stir for 2-3h, filter the precipitate to obtain surface modified nano silica (modified Nano-SiO2).

[0039] (3) Preparation of core-shell structure: The core material solution described in step (1) is placed into a beaker, and then the surface-modified nano-silica described in step (2) is added. The solution is sheared at high speed at 1000-1500 rpm / min for 5-10 min to obtain a fluid powder. Then, the powder is dried at 40-60℃ for 1-2 h to obtain a core-shell structured adhesive with a polymeric adhesive core and a modified Nano-SiO2 shell.

[0040] Furthermore, the organic solvent is one or more of ethanol, isopropanol, toluene, benzyl alcohol, and acetone; the step of adjusting the pH value is carried out by adding acetic acid, hydrochloric acid, nitric acid, phosphoric acid, or formic acid.

[0041] The average particle size of the fumed silica nanoparticles used in the following embodiments and comparative examples of the present invention is 20 nm.

[0042] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0043] Example 1

[0044] A method for preparing a core-shell structured thickener, comprising the following steps:

[0045] (1) Preparation of core material solution: Add 10g of hydroxypropyl methylcellulose ether to a container containing 500g of deionized water, dissolve both completely with a high-speed disperser, and let stand until the solution is slightly yellow and transparent to obtain the core material solution.

[0046] (2) Modification of shell material: 8g of methyltrimethoxysilane was selected as silane coupling agent, dissolved in 50mL of ethanol and stirred evenly, hydrochloric acid was added dropwise to adjust the pH value to 4, and then 50g of fumed nano silica was added to a high-speed mixer, stirring was turned on and heated to 80℃, stirring was continued for 2.5h, and filtered to obtain surface-modified nano silica.

[0047] (3) Preparation of core-shell structure: Under continuous high-speed shearing conditions, 200g of core material solution was placed into a beaker, and then 15g of surface-modified nano silica was added. The solution was sheared at a high speed of 1200rpm / min for 8min using a high-speed disperser to obtain a fluidized powder. Finally, the finished product was dried at 50℃ for 1.5h to obtain a core-shell structured thickener with a polymer thickener as the core and modified nano silica as the shell.

[0048] A method for preparing shotcrete:

[0049] The mix proportions of the shotcrete slurry used are as follows: 8 kg cement (PO42.5 ordinary Portland cement), 6% (constitution ratio) accelerator (model L-40), 0.3% (constitution ratio) of the aforementioned core-shell structure thickener, 0.3% (constitution ratio) of polypropylene (PP) fiber, 12 kg standard sand (particle size 0.25-0.65 mm), and 31 kg aggregate (particle size ≤ 5 mm). The water-cement ratio is fixed at 0.45, and the mortar-cement ratio is 2:3. Specifically, the spraying angle is set at 90°, and the spraying distance is 1 meter. The main equipment for spraying includes a mortar screw pump, a three-inlet-one-outlet spray gun, an air compressor, and an accelerator diaphragm pump. First, the mass of materials pumped by the screw pump and diaphragm pump within 1 minute was adjusted to ensure that the mass of the accelerator pumped within a certain time was 6% of the mass of the cementitious material. After debugging, the mass flow rate of the mortar screw pump was 84 kg / min, and the mass flow rate of the accelerator diaphragm pump was 0.74 kg / min.

[0050] Example 2

[0051] A method for preparing a core-shell structured thickener, comprising the following steps:

[0052] (1) Preparation of core material solution: Add 10g of polysaccharide bio-gum to a container containing 500g of deionized water, dissolve both completely with a high-speed disperser, and let stand until the solution is slightly yellow and transparent to obtain the core material solution.

[0053] (2) Modification of shell material: 8g of vinyltriethoxysilane was selected as silane coupling agent, dissolved in 50mL of ethanol and stirred evenly, hydrochloric acid was added dropwise to adjust the pH value to 3, and then 50g of fumed nano silica was added to a high-speed mixer, stirring was turned on and heated to 70℃, stirring was continued for 3h, and filtered to obtain surface-modified nano silica.

[0054] (3) Preparation of core-shell structure: Under continuous high-speed shearing conditions, 200g of core material solution was put into a beaker, and then 15g of surface-modified nano silica was added. The solution was sheared at a high speed of 1300rpm / min for 10min using a high-speed disperser to obtain a fluidized powder. Finally, the finished product was dried at 55℃ for 2h to obtain a core-shell structured thickener with a polymer thickener as the core and modified nano silica as the shell.

[0055] A method for preparing shotcrete:

[0056] The mix proportions of the shotcrete slurry used are as follows: 8 kg cement (PO42.5 ordinary Portland cement), 6% (constitutional weight ratio) accelerator, 0.3% (constitutional weight ratio) of the aforementioned core-shell structure thickener, 0.3% (constitutional weight ratio) of polypropylene (PP) fiber, 12 kg standard sand (particle size 0.25-0.65 mm), and 31 kg aggregate (particle size ≤ 5 mm). The water-cement ratio is fixed at 0.45, and the mortar-cement ratio is 2:3. Specifically, the spraying angle is set at 90°, and the spraying distance is 1 meter. The main equipment for spraying includes a mortar screw pump, a three-inlet-one-outlet spray gun, an air compressor, and an accelerator diaphragm pump. First, the mass of materials pumped by the screw pump and diaphragm pump within 1 minute was adjusted to ensure that the mass of the accelerator pumped within a certain time was 6% of the mass of the cementitious material. After debugging, the mass flow rate of the mortar screw pump was 84 kg / min, and the mass flow rate of the accelerator diaphragm pump was 2.112 kg / min.

[0057] Example 3

[0058] A method for preparing a core-shell structured thickener, comprising the following steps:

[0059] (1) Preparation of core material solution: Add 10g of polyethylene oxide to a container containing 500g of deionized water, dissolve both completely with a high-speed disperser, and let stand until the solution is slightly yellow and transparent to obtain the core material solution.

[0060] (2) Modification of shell material: 8g of γ-mercaptopropyltrimethoxysilane was selected as a silane coupling agent, dissolved in 50mL of ethanol and stirred evenly. Hydrochloric acid was added dropwise to adjust the pH value to 3.5. Then 50g of fumed nano silica was added to a high-speed mixer, stirred and heated to 65℃, stirred continuously for 3h, filtered, and surface-modified nano silica was obtained.

[0061] (3) Preparation of core-shell structure: Under continuous high-speed shearing conditions, 200g of core material solution was placed into a beaker, and then 15g of surface-modified nano silica was added. The solution was sheared at a high speed of 1400rpm / min for 15min using a high-speed disperser to obtain a fluidized powder. Finally, the finished product was dried at 60℃ for 3h to obtain a core-shell structured thickener with a polymer thickener as the core and modified nano silica as the shell.

[0062] A method for preparing shotcrete:

[0063] The mix proportions of the shotcrete slurry used are as follows: 8 kg cement (PO42.5 ordinary Portland cement), 6% (constitutional weight ratio) accelerator, 0.3% (constitutional weight ratio) of the aforementioned core-shell structure thickener, 0.3% (constitutional weight ratio) of polypropylene (PP) fiber, 12 kg standard sand (particle size 0.25-0.65 mm), and 31 kg aggregate (particle size ≤ 5 mm). The water-cement ratio is fixed at 0.45, and the mortar-cement ratio is 2:3. Specifically, the spraying angle is set at 90°, and the spraying distance is 1 meter. The main equipment for spraying includes a mortar screw pump, a three-inlet-one-outlet spray gun, an air compressor, and an accelerator diaphragm pump. First, the mass of materials pumped by the screw pump and diaphragm pump within 1 minute was adjusted to ensure that the mass of the accelerator pumped within a certain time was 6% of the mass of the cementitious material. After debugging, the mass flow rate of the mortar screw pump was 84 kg / min, and the mass flow rate of the accelerator diaphragm pump was 2.112 kg / min.

[0064] Comparative Example 1

[0065] The only difference from Example 1 is that the core-shell structure thickener was omitted during the preparation of the shotcrete, and an equal mass of hydroxypropyl methylcellulose ether was added.

[0066] Comparative Example 2

[0067] The only difference from Example 2 is that the core-shell structure thickener was omitted during the preparation of the shotcrete, and an equal mass of polysaccharide bio-adhesive was added.

[0068] Comparative Example 3

[0069] The only difference from Example 3 is that the core-shell structure thickener was omitted during the preparation of the sprayed concrete, and an equal mass of polyethylene oxide was added.

[0070] Effect verification

[0071] 1. The effect of core-shell structure thickeners on the mechanical strength of shotcrete

[0072] To investigate the mechanical properties of the core-shell structured thickener for shotcrete of the present invention, the mechanical strength of concrete at 28 days was tested according to GB / T 50081-2019 under the same accelerator dosage and water-cement ratio. The mechanical strength of shotcrete from Examples 1-3 and Comparative Examples 1-3 at 28 days was tested. The test results are shown in Table 1.

[0073] Table 1. Experimental results of concrete compressive strength

[0074] 28-day compressive strength (MPa) Comparative Example 1 70.6 Example 1 84.5 Comparative Example 2 71.2 Example 2 86.6 Comparative Example 3 69.3 Example 3 80.8

[0075] As shown in Table 1, the compressive strength of the shotcrete specimens in Examples 1-3 at 28 days was significantly higher than that of the concrete specimens in Comparative Examples 1-3. This indicates that the shotcrete incorporating the core-shell structured thickener designed in this invention exhibits a significant improvement in later-stage strength, demonstrating that the core-shell structured thickener of this invention can effectively improve the later-stage strength of shotcrete. This is mainly because the pozzolanic reaction in the shotcrete of this invention is continuous, especially in the later stages (28 days and beyond). When the hydration rate of the cement itself slows down, the reaction between nano-SiO2 and calcium hydroxide (CH) continues, constantly generating new CSH gel, thereby further enhancing its later-stage strength.

[0076] 2. The effect of core-shell structure thickeners on the rebound rate of shotcrete

[0077] To investigate the rebound rate of the core-shell structure thickener for shotcrete of the present invention, the rebound of shotcrete from Examples 1-3 and Comparative Examples 1-3 was tested under the same accelerator dosage and water-cement ratio. The test results are shown in Table 2.

[0078] Table 2. Experimental results of shotcrete rebound rate

[0079] Serial Number Rebound rate (%) Comparative Example 1 42.6 Example 1 9.5 Comparative Example 2 45.9 Example 2 8.7 Comparative Example 3 50.7 Example 3 7.3

[0080] As can be seen from Table 2, the rebound rate of the shotcrete in Examples 1-3 was significantly lower than that in Comparative Examples 1-3, indicating that the addition of the core-shell structure thickener of the present invention can effectively reduce the rebound rate of shotcrete.

[0081] 3. The effect of core-shell structure tackifiers on the bond strength of shotcrete

[0082] To investigate the adhesive performance of the core-shell structure tackifier for shotcrete of the present invention, the adhesive strength of the shotcrete in Examples 1-3 and Comparative Examples 1-3 was tested under the same accelerator dosage and water-cement ratio. The test results are shown in Table 3.

[0083] Table 3. Experimental results of adhesive strength of sprayed concrete

[0084]

[0085] As can be seen from Table 3, the bonding strength of the cement paste with core-shell structured tackifier in Examples 1-3 at 2h and 28d is significantly higher than that of the concrete specimens in Comparative Examples 1-3. The bonding strength of the cement paste with core-shell structured tackifier is significantly improved, indicating that the core-shell structured tackifier of the present invention can effectively improve the bonding strength of shotcrete, thereby achieving the effect of rapid bonding.

[0086] 4. The effect of core-shell structure thickeners on the viscosity of shotcrete

[0087] To verify whether the core-shell structured thickener of the present invention can achieve real-time thickening effect through mechanically triggered crushing, and to investigate the influence of the incorporation method of the core-shell structured thickener on the apparent viscosity of cement-based materials, the apparent viscosity of the sprayed concrete slurry in Examples 1-3 before spraying, the sprayed concrete slurry in Examples 1-3 after spraying, and the sprayed concrete slurry in Comparative Examples 1-3 before spraying were tested. The test results are shown in Tables 4-6.

[0088] Table 4 Apparent viscosity of neat pulp with different incorporation forms of hydroxypropyl methylcellulose ether

[0089] Group Comparative Example 1 Example 1 Before spraying Example 1 After spraying Viscosity (mPa / s) 900 1138 1200

[0090] Table 5 Apparent viscosity of neat pulp with different incorporation forms of polysaccharide bio-adhesive

[0091] Group Comparative Example 2 Example 2 Before spraying Example 2 After spraying Viscosity (mPa / s) 895 969 1300

[0092] Table 6 Apparent viscosity of neat paste with different polyoxyethylene incorporation forms

[0093] Group Comparative Example 3 Example 3 Before spraying Example 3 After spraying Viscosity (mPa / s) 960 1100 1320

[0094] As shown in Tables 4-6, the apparent viscosity of the sprayed concrete slurry in each embodiment is greater than that of the concrete slurry before spraying in the corresponding embodiments and the concrete slurry in each comparative example. This indicates that the core-shell material is broken by the spraying force, releasing the inner core and causing the Nano-SiO2 particles to disperse. This increases the specific surface area and, from the perspective of binding free water molecules, increases the apparent viscosity of the slurry.

[0095] After preparing the core-shell structured adhesive according to the preparation conditions of Example 1, the adhesive was sprayed into a beaker at a spray pressure of 0.5 MPa, collected, and its scanning electron microscope (SEM) image was taken. The test results are shown below. Figure 1 .

[0096] Figure 1 The images show a comparison of scanning electron microscope (SEM) images of the core-shell structure adhesive of Example 1 before and after fracture under stress. In the images, (a) shows the image before fracture and (b) shows the image after fracture.

[0097] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a core-shell structure thickener suitable for reducing the rebound rate of shotcrete, characterized in that, Includes the following steps: The tackifier is dissolved in water to obtain a core material solution; A silane coupling agent is dissolved in an organic solvent, and the pH value is adjusted to acidic to obtain a modified solution. The modified solution is mixed with nano-silica and reacted to obtain surface-modified nano-silica. The surface-modified nano-silica was mixed with the core material solution and sheared to obtain the core-shell structure adhesive. The thickener is one or more of hydroxypropyl methylcellulose ether, polysaccharide bio-glue, and polyethylene oxide; the mass ratio of the thickener to water is 1:10-100. The silane coupling agent is one or more of methyltrimethoxysilane, vinyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane; the pH value of the modified solution is 3-5; the mass ratio of the silane coupling agent to the organic solvent is 1:5-20; and the mass ratio of the modified solution to nano-silica is 1:3-10.

2. The preparation method according to claim 1, characterized in that, The reaction is carried out at a temperature of 60-100℃ for 2-3 hours.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the surface-modified nano-silica to the core material solution is 1-2:

20.

4. The preparation method according to claim 1, characterized in that, The shearing process is performed at a rotation speed of 1000-1500 rpm / min for 5-10 min.

5. The preparation method according to claim 1, characterized in that, The shearing process is followed by a drying step; the drying temperature is 40-60℃ and the time is 1-2 hours.

6. A core-shell structure thickener suitable for reducing the rebound rate of shotcrete, obtained by the preparation method according to any one of claims 1-5.

7. The application of the core-shell structure thickener of claim 6 in the field of shotcrete modifiers.

8. A method for reducing the rebound rate of shotcrete, characterized in that, The core-shell structure thickener of claim 6 is added to the slurry of the shotcrete before it is sprayed.

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