High density low rebound shotcrete and method of making same

Abstract

The application discloses a kind of high density low rebound shotcrete and preparation method thereof, it is related to shotcrete field, and preparation method includes: (1), respectively to cementitious material, fine aggregate, coarse aggregate is using MAA model to be packed and the design ratio of each raw material in interior is obtained;(2), cementitious material, fine aggregate, coarse aggregate and the rebounding agent of design ratio obtained according to step (1) are fully mixed, water, water reducing agent is mixed, then by the way of mixing with pressurized air, incorporate accelerator, obtain high density low rebound shotcrete.The application uses early strength rebounding agent, improves the pumpability of shotcrete, accelerates the early hydration of concrete, under the joint action of alkali-free accelerator, rapidly improves the early mechanical properties of shotcrete, improves shotcrete construction efficiency.Multiple close packing is used, and cementitious material, fine aggregate, coarse aggregate respectively form close packing structure, effectively improve the plastic viscosity of paste and the compactness of concrete.

Description

Technical Field

[0001] This invention relates to the field of shotcrete, specifically to a high-density, low-rebound shotcrete and its preparation method. Background Technology

[0002] Shotcrete is a type of concrete that is sprayed at high speed onto a target surface and instantly compacted under air pressure through an inflatable hose or pipe. Shotcrete is widely used in railway, highway, water conservancy, and mining projects due to its short final setting time, rapid hydration and hardening, high early-age strength, and simple construction process.

[0003] As one of the main forms of support for tunnels and underground engineering, the amount of shotcrete used has increased dramatically with the further development of infrastructure construction. At the same time, in the current shotcrete construction in my country, due to unreasonable mix proportions and poor slurry cohesion, the slurry and aggregate separate during the spraying process, resulting in an excessive rebound rate during the spraying process, causing a large amount of material waste, seriously affecting the quality of shotcrete and posing certain safety hazards to operators.

[0004] The material composition design of shotcrete still primarily follows the mix design specifications for ordinary concrete, employing a combination of empirical formulas and construction technical specifications to determine specific mix proportions. However, it lacks a systematic and scientific mix design process. For example, patent CN114853419A still uses ordinary concrete design methods for preparing low-rebound shotcrete, merely limiting aggregate particle size and ultimately achieving low-rebound performance by adding thickening materials. Furthermore, patent CN116768563A uses Fuller's maximum density theory to design the gradation of sand and gravel aggregates for low-rebound wet shotcrete, but neglects the proportioning design of the cementitious material system in shotcrete. This makes the shotcrete mix design method incomplete and its guidance for shotcrete preparation limited.

[0005] Existing elasticity-reducing agents can easily lead to increased concrete porosity or prolonged hardening time, which degrades the mechanical or durability properties of concrete. In the face of complex tunnel construction environments in plateau and mountainous areas, existing traditional alkaline quick-setting agents and conventional alkali-free liquid quick-setting agents are difficult to meet the actual construction requirements in shotcrete and have poor compatibility with elasticity-reducing agents.

[0006] Therefore, it is necessary to develop a high-density, low-rebound shotcrete and its preparation method to solve the problems of poor cohesion and high rebound rate of current shotcrete. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a method for preparing high-density, low-rebound shotcrete. By employing multi-stage dense packing to separately pack cementitious materials, sand, and gravel into particles, a graded, zoned, tightly filled system is formed, improving the slurry's encapsulation and enhancing the concrete's density, thereby reducing the concrete's rebound rate and enhancing its mechanical properties. Furthermore, by adding specially formulated anti-rebound agents and accelerators, the pumpability and early strength of the shotcrete are optimized, improving the shotcrete's spraying efficiency.

[0008] The technical solution of this invention is: a method for preparing high-density, low-rebound shotcrete, characterized by comprising the following steps:

[0009] (1) The design proportions of each raw material are obtained by stacking the powder, fine aggregate and coarse aggregate using the MAA model. The powder includes cement and mineral admixtures. The mineral admixtures include one or more of silica fume I, fly ash, mineral powder and ultrafine stone powder. The fine aggregate is sand with a particle size not exceeding 4.75 mm and the particle size is divided into at least 2 grades. The coarse aggregate is gravel with a particle size of 5-15 mm and the particle size is divided into at least 2 grades.

[0010] (2) Mix the cementitious material, fine aggregate, coarse aggregate and elasticity reducer obtained according to the design ratio in step (1), add water and water-reducing agent and mix, and then add accelerator by mixing with pressurized air to obtain high density low rebound shotcrete.

[0011] Preferably, in step (1), the design proportions of each raw material inside are obtained by using the MAA model for packing, specifically including:

[0012] a. The MAA model is used for stacking to form a graded, zoned, tightly packed system;

[0013] b. Based on the particle size of each raw material and the cumulative proportion of the corresponding particle size, obtain the target curve of the mixture;

[0014] c. Based on the target curve of the mixture and the least squares method, the optimal particle size distribution of the mixture is calculated, and the proportion of each raw material corresponding to the optimal particle size distribution is the design proportion.

[0015] The MAA model in this invention is an improved version of the Andreasen and Andersen model, which is one of the classic continuous particle packing models in the field. This invention employs multi-stage close packing to separately pack cementitious materials, sand, and gravel into particles, forming a graded, zoned, tightly packed system.

[0016] In step b, the target curve of the mixture is obtained according to the MAA model of equation (1).

[0017]

[0018] In equation (1) above, D is the currently set particle size; P1(D) is the proportion of particles smaller than D in the mixture, which belongs to the target curve of the mixture. M1 D represents the maximum particle size of the mixture. L1 q1 is the minimum particle size of the mixture, and q1 is the distribution modulus of the mixture, which is between 0.17 and 0.35 depending on the particle size.

[0019] In step c, the optimal particle size distribution of the mixture is calculated by continuously adjusting the volume ratio of each raw material in the mixture, calculating the variance RSS between each grade distribution curve and the target curve, and the smallest variance RSS is the optimal particle size distribution.

[0020] The variance RSS of the mixture is calculated using the following formula (2).

[0021]

[0022] In equation (2) above, P tar1 The target curve of the mixture calculated from equation (1), i(m) refers to the raw materials of the mixture (the mixture contains m kinds of raw materials), P mix It is a mixture curve.

[0023] Preferably, the raw materials for the high-density, low-rebound shotcrete include, by weight, 300-350 parts of cement, 120-150 parts of mineral admixtures, 800-900 parts of fine aggregate, 850-1000 parts of coarse aggregate, 20-30 parts of elasticity-reducing material, 15-30 parts of quick-setting agent, 150-200 parts of water, and 4-8 parts of water-reducing agent.

[0024] Preferably, in step (1), the fine aggregate particle size can be divided into four grades: 0.15-0.6mm, 0.6-1.25mm, 1.25-2.36mm, and 2.36-4.75mm, or into two grades: 0.15-1.25mm and 1.25-4.75mm; the coarse aggregate particle size can be divided into two grades: 5-10mm and 10-15mm.

[0025] Preferably, the quick-setting agent comprises, by mass percentage, 35-40% polyaluminum sulfate, 5-8% modified aluminum hydroxide, 2-5% modified alkanolamine, 0.2-0.5% lithium sulfate, 0.1-0.3% nano silica solution, 0.8-1.0% modified hydrated magnesium silicate, and the remainder being water.

[0026] Furthermore, the modified aluminum hydroxide is prepared by a method comprising the following steps: holding aluminum hydroxide at 350-400℃ for 1.5-2h, then raising the temperature to 700-750℃ and holding for 0.8-1h, and finally grinding for 20-30min and passing through a 200-mesh sieve to obtain modified aluminum hydroxide.

[0027] The modified alkanolamine is prepared by a method comprising the following steps: adding a 0.5-1.0 mol / L citric acid solution to a 15-20% triethanolamine solution and stirring to neutralize, wherein the molar ratio of citric acid to triethanolamine is 1:3-4; mixing the neutralized solution with a 10-15% maleic anhydride solution at a volume ratio of 2-3:1; adding a catalyst at 3% by mass of the mixed solution at 50-55°C; and stirring and refluxing for 1-2 hours to obtain the modified alkanolamine.

[0028] Furthermore, the modified hydrated magnesium silicate is prepared by a method comprising the following steps: hydrated magnesium silicate is kept at 500℃-600℃ for 3-4 hours and then milled. During the milling process, 0.3% silane coupling agent, 0.5% citric acid and 0.3% tartaric acid are added according to the mass of hydrated magnesium silicate. After milling for 20-30 minutes, the modified hydrated magnesium silicate is obtained.

[0029] The concentration of the nano-silica solution is 2-4%.

[0030] Preferably, the elasticity reducer comprises, by mass percentage, 53-73% rheological component, 15-25% thickening component, 10-18% early strength component, and 0.5-4% setting regulator component, wherein the sum of the mass percentages of the above components is 100%.

[0031] The rheological component comprises manganese slag powder and silica fume II mixed in a 3:1 mass ratio; the thickening component is tailings powder loaded with nano-modified cellulose ether; the early strength component includes one or more of calcium formate, sodium sulfate, polyaluminum sulfate, lithium sulfate, aluminate cement, and sulfoaluminate cement; and the setting regulator component is one or more of sodium gluconate, sodium tripolyphosphate, boric acid, and citric acid. The specific surface area of ​​the manganese slag powder is 600-800 m². 2 / kg, the specific surface area of ​​the silica fume II is 15000-20000 m² / kg. 2 / kg.

[0032] Furthermore, the tailings powder loaded with nano-modified cellulose ether is prepared by a method comprising the following steps:

[0033] S1. Prepare aqueous solutions of calcium nitrate and sodium metasilicate nonahydrate to obtain solutions A and B, respectively. Disperse the polyether macromonomer in water to form dispersion C. Dissolve the nonionic water-soluble cellulose ether in water to form solution D. The mass ratio of calcium nitrate: sodium metasilicate nonahydrate: polyether macromonomer: cellulose ether is 100:100-150:96-288:1.2-5.0. Slowly and simultaneously add solutions A and B to dispersion C while stirring at a speed of 300-500 rpm. When half of solutions A and B have been added, add solution D to dispersion C. Then stir at a high speed of 1200-2000 rpm until solutions A and B have been added simultaneously, thus obtaining a nano-modified cellulose ether solution. The entire process of simultaneous addition of solutions A and B takes 2-4 hours.

[0034] S2. The tailings sand with a porous structure is crushed into tailings particles with a particle size of 0.5-2mm and a pore size of 100-500nm, wherein the tailings sand comes from one or more of copper tailings sand and iron tailings sand.

[0035] S3. Immerse the tailings particles obtained in step S2 in the nano-modified cellulose ether solution obtained in step S1 for 30-60 minutes. After immersion, dry at 95-105℃ for 3-5 hours, cool, and grind to a specific surface area of ​​50-150 m². 2 / g, yielding tailings powder loaded with nano-modified cellulose ether.

[0036] Furthermore, in step S1, the concentration of calcium nitrate in solution A is 20-30%, the concentration of sodium metasilicate nonahydrate aqueous solution is 20-30%, the mass concentration of polyether macromonomer in dispersion C is 5-15%, and the mass concentration of cellulose ether in solution D is 0.1-0.5%.

[0037] Furthermore, in step S1, the nonionic water-soluble cellulose ether is one or more of methylcellulose ether, hydroxypropyl methylcellulose ether, hydroxymethylcellulose ether, and hydroxyethylcellulose ether, with a molecular weight of 20,000-100,000. Too low a molecular weight results in poor thickening effect, while too high a molecular weight will cause excessive entanglement and coating of cement particles, reducing the strength of the concrete. Specifically, the polyether macromonomer is isobutylene polyethylene glycol ether (HPEG) or isopentenyl polyethylene glycol ether (TPEG).

[0038] Preferably, the cement is silicate cement with a strength of not less than 42.5 and an apparent density of 3000-3200 kg / m³. 3 ;

[0039] The fly ash has an average particle size of 1-5 μm and a specific surface area greater than 800 m². 2 / kg, apparent density is 2200-2400 kg / m³ 3 ;

[0040] The silica fume I has a SiO2 content greater than 90%, an average particle size of 0.1-0.3 μm, and a specific surface area greater than 20,000 m². 2 / kg, apparent density is 2100-2400 kg / m³ 3 ;

[0041] The mineral powder has an average particle size of 5-10 μm and a specific surface area greater than 90 m². 2 / kg, apparent density is 2500-2700 kg / m³ 3 ;

[0042] The ultrafine stone powder has a calcium carbonate content greater than 98%, an average particle size of 0.5-3 μm, and a specific surface area greater than 1800 m². 2 / kg, apparent density is 2700-2800 kg / m³ 3 .

[0043] Preferably, the water-reducing agent is a liquid polycarboxylate water-reducing agent with a solid content of not less than 15% and a water reduction rate of not less than 20%.

[0044] Preferably, the mineral admixture is a mixture of silica fume I, fly ash, mineral powder, and ultrafine stone powder.

[0045] The present invention also provides a high-density, low-rebound shotcrete, which is prepared by any of the above methods for preparing high-density, low-rebound shotcrete.

[0046] Preferably, the high-density, low-rebound shotcrete has a 1-day strength > 20 MPa, a 28-day strength > 40 MPa, a wet packing density > 0.74, a plastic viscosity > 185 Pa·s, a slump time > 5.5 s, a spread < 450 mm, and a rebound rate < 6.5%. The concrete is in a continuous fluid state when it is poured.

[0047] The beneficial effects of this invention are:

[0048] (1) By adopting multi-stage compact stacking, a compact filling structure is formed in the three particle size stages of cementitious materials, fine aggregates and coarse aggregates, which can effectively improve the plastic viscosity of the paste and the density of concrete, reduce the impact rebound of aggregates and the slurry flow, and enhance the mechanical properties of shotcrete.

[0049] (2) The use of a large amount of mineral admixtures in the mix design significantly reduces the amount of cement used in shotcrete, effectively reducing the energy consumption and cost of shotcrete, which helps to reduce carbon emissions during the shotcrete construction process and improves the economy and ecology of shotcrete.

[0050] (3) The use of early strength reducing agent improves the pumpability of shotcrete, accelerates the early hydration of concrete, and, together with alkali-free quick-setting agent, rapidly improves the early mechanical properties of shotcrete, greatly increases the thickness of a single spraying, and improves the construction efficiency of shotcrete.

[0051] (4) The toughening agent uses porous tailings sand as an inorganic material. The porous structure of the particles enhances the rheological properties of the toughening agent by absorbing and storing water, thereby improving the initial pumping efficiency of concrete and the anti-sagging performance after spraying. By loading nano-modified cellulose ether onto porous tailings sand, the toughening agent can be efficiently dispersed in the powder. At the same time, the nano-modified cellulose ether in the pores gradually dissolves and is released, reducing the concentration of toughening agent molecules in the liquid phase and their entanglement with cement particles. This helps to remove air bubbles during concrete mixing and improves the hydration efficiency of cement particles, thereby increasing the early-age concrete strength.

[0052] (5) In the quick-setting agent: the role of polyaluminum sulfate is to provide sulfate ions and aluminum ions for the formation of ettringite, thereby accelerating the setting of concrete; the role of modified aluminum hydroxide is to provide aluminum ions for the formation of ettringite; the role of modified alkanolamine is to stabilize aluminum ions in supersaturated aluminum sulfate solution as a stabilizer; the role of lithium sulfate is to promote the formation of ettringite in concrete as an early strength agent; the role of nano silica is to promote cement hydration, accelerate the development of early strength and improve the later strength of concrete; the role of modified hydrated magnesium silicate is to stabilize supersaturated aluminum sulfate and aluminum ions in solution as a stabilizer. The synergistic effect of the above components gives the quick-setting agent excellent performance of accelerating setting, early strength and long-term stable performance.

[0053] (6) The wet packing density of the prepared sprayed concrete is >0.74 and the rebound rate is <6.5%, which has the characteristics of high density and low rebound. Moreover, the plastic viscosity is >185Pa·s, the collapse time is >5.5s and the spread is <450mm, which has excellent pumpability and can improve the efficiency of concrete spraying. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of particle classification and stacking of cementitious materials, fine aggregates, and coarse aggregates in Example 1. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is further described below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Unless otherwise specified, the pharmaceuticals used in the following embodiments are commercially available products, and the methods used are conventional methods in the art.

[0056] Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Unless otherwise specified, concentrations expressed as percentages in the following embodiments are mass concentrations.

[0057] In the following embodiments, the cementitious materials, fine aggregates, and coarse aggregates are all designed according to the MAA particle packing model. The specific steps are as follows:

[0058] a. The MAA model is used for stacking to form a graded, zoned, tightly packed system;

[0059] b. Based on the particle size of each raw material and the corresponding cumulative proportion of particle size, the target curve of the mixture is obtained. The target curve of the mixture is obtained according to equation (1).

[0060]

[0061] In equation (1) above, D is the currently set particle size; P1(D) is the proportion of particles smaller than D in the mixture, which belongs to the target curve of the mixture. M1 D represents the maximum particle size of the mixture. L1 q1 is the minimum particle size of the mixture, and q1 is the distribution modulus of the mixture, which is between 0.17 and 0.35 depending on the particle size.

[0062] c. Based on the target curve of the mixture and the least squares method, calculate the optimal particle size distribution of the mixture. The proportions of each raw material corresponding to the optimal particle size distribution are the design proportions. That is, continuously adjust the volume ratios of each raw material in the mixture, calculate the variance (RSS) between each proportion curve and the target curve, and the one with the smallest RSS is the optimal particle size distribution.

[0063] The variance RSS of the mixture is calculated using the following formula (4).

[0064]

[0065] In equation (2) above, P tar1 The target curve of the mixture calculated from equation (1), i(m) refers to the raw materials of the mixture (the mixture contains m kinds of raw materials), P mix It is a mixture curve.

[0066] The present invention also specifies the specific amounts of the above-mentioned high-density, low-rebound shotcrete raw materials, including 300-350 parts of cement, 120-150 parts of mineral admixtures, 800-900 parts of fine aggregate, 850-1000 parts of coarse aggregate, 20-30 parts of elasticity-reducing material, 15-30 parts of quick-setting agent, 150-200 parts of water, and 4-8 parts of water-reducing agent by weight.

[0067] The specifications of each raw material for the cementitious material in the following examples are as follows:

[0068] The cement is silicate cement with a strength of not less than 42.5 and an apparent density of 3000-3200 kg / m³. 3 .

[0069] The average particle size of fly ash is 1-5 μm, and its specific surface area is greater than 800 m². 2 / kg, apparent density is 2200-2400 kg / m³ 3 .

[0070] Silica fume I has a SiO2 content greater than 90%, an average particle size of 0.1-0.3 μm, and a specific surface area greater than 20,000 m². 2 / kg, apparent density is 2100-2400 kg / m³ 3 .

[0071] The average particle size of the mineral powder is 5-10 μm, and the specific surface area is greater than 90 m². 2 / kg, apparent density is 2500-2700 kg / m³ 3 ;

[0072] The ultrafine stone powder has a calcium carbonate content greater than 98%, an average particle size of 0.5-3 μm, and a specific surface area greater than 1800 m². 2 / kg, apparent density is 2700-2800 kg / m³ 3 .

[0073] Example 1

[0074] This embodiment provides a method for preparing shotcrete, the steps of which are as follows:

[0075] (1) The design proportions of each raw material were obtained by stacking the cementitious materials, fine aggregates and coarse aggregates using the MAA model. The cementitious materials include cement and mineral admixtures. The mineral admixtures include silica fume I, fly ash, mineral powder and ultrafine stone powder. The fine aggregate is sand with a particle size of less than 4.75 mm and the particle size is divided into four grades: 0.15-0.6 mm, 0.6-1.25 mm, 1.25-2.36 mm and 2.36-4.75 mm. The coarse aggregate is gravel with a particle size of 5-15 mm and the particle size is divided into two grades: 5-10 mm and 10-15 mm.

[0076] To ensure the strength of the concrete, the initial range of the proportion of cement and other powders is set. Cement accounts for 60%-70% of the powder mass, and mineral admixtures such as silica fume and mineral powder account for 30%-40% of the powder. The proportion of each admixture is determined entirely according to the packing curve, and the proportion of different fine aggregates and coarse aggregates is determined entirely according to the packing curve. Then, based on the target curves for powder and aggregate, the volume ratio of each raw material in the mixture was continuously adjusted using the least squares method (LSM) until the optimal match between the designed mixture and the target curve was achieved within a set range. Finally, the close-packed volume ratio of cement:fly ash:mineral powder:silica fume:ultrafine stone powder was obtained as 325:25:25:59:66, which is converted to a mass ratio of 312:20:24:40:55. The mass ratio of 0.15-0.60mm fine aggregate: 0.60-1.25mm fine aggregate: 1.25-2.36mm fine aggregate: 2.36-4.75mm fine aggregate was 149:66:35:189. The mass ratio of 5-10mm coarse aggregate: 10-15mm aggregate was 692:245.

[0077] Figure 1 The results obtained from Example 1 are shown below. The gray-green dashed line on the left, "powder accumulation curve", represents the optimal particle size distribution of the cementitious material. The light blue dashed line in the middle, "fine aggregate accumulation curve", represents the optimal particle size distribution of the fine aggregate. The brown dashed line on the right, "coarse aggregate accumulation curve", represents the optimal particle size distribution of the coarse aggregate.

[0078] (2) The cementitious materials (312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume I, 55 parts ultrafine stone powder), fine aggregates (298 parts 0.15-0.6mm fine aggregates, 132 parts 0.6-1.25mm fine aggregates, 70 parts 1.25-2.36mm fine aggregates, 378 parts 2.36-4.75mm), coarse aggregates (692 parts 5-10mm coarse aggregates, 245 parts 10-15mm coarse aggregates) and 20 parts of elasticity-reducing materials obtained according to the design proportions in step S1 are thoroughly mixed. 180 parts of water and 4 parts of water-reducing agent are added and mixed. Then, 25 parts of quick-setting agent are added by mixing with pressurized air to obtain high-density low-rebound shotcrete.

[0079] In this embodiment, the solid content of the water-reducing agent is 15%, and the water reduction rate is 20%.

[0080] Based on the same inventive concept, this embodiment also provides a shotcrete comprising 312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume, 55 parts ultrafine stone powder, 298 parts 0.15-0.6mm fine aggregate, 132 parts 0.6-1.25mm fine aggregate, 70 parts 1.25-2.36mm fine aggregate, 378 parts 2.36-4.75mm, 692 parts 5-10mm coarse aggregate, 245 parts 10-15mm coarse aggregate, 20 parts elasticity-reducing material, 25 parts quick-setting agent, 180 parts water, and 4 parts water-reducing agent. The proportions of cementitious materials (including five raw materials: ordinary Portland cement, silica fume I, fly ash, mineral powder, and ultrafine stone powder), fine aggregates (including four specifications of raw materials: 0-0.6mm, 0.6-1.25mm, 1.25-2.36mm, and 2.36-4.75mm), and coarse aggregates (including two specifications of raw materials: 5-10mm and 10-15mm) were all designed using the close packing theory.

[0081] The elasticity reducer in this embodiment is prepared according to the following steps: Prepare 53 parts by weight of rheological component, 25 parts by thickening component, 18 parts by weight of early strength component, and 4 parts by weight of setting regulator component. Mix the rheological component, thickening component, early strength component, and setting regulator component to obtain the elasticity reducer. The rheological component is a mixture of manganese slag powder and silica fume II at a mass ratio of 3:1. The thickening component is tailings powder loaded with nano-modified cellulose ether. The early strength component is calcium formate, and the setting regulator component is sodium tripolyphosphate. The preparation steps of the nano-modified cellulose ether tailings powder are as follows:

[0082] S1. Preparation of nano-modified cellulose ether: Calcium nitrate and sodium metasilicate nonahydrate were dissolved in distilled water to obtain a 20% calcium nitrate aqueous solution A and a 30% sodium metasilicate nonahydrate aqueous solution B. The polyether macromonomer (specifically HPEG in this example) was dispersed in water to prepare a dispersion C (5% by mass). Hydroxypropyl methylcellulose ether was dissolved in water to form a solution D (0.2% by mass). Then, 12g of solution A and 12g of solution B were slowly added to 46g of dispersion C by simultaneous dropwise addition over 2 hours (stirring at a low speed of 500 rpm for the first hour). After 1 hour of dropwise addition, 30g of cellulose ether aqueous solution D was added. After another hour of high-speed stirring (1500 rpm), solutions A and B were added simultaneously, and the nano-modified cellulose ether solution was obtained. Based on the specific dosages above, in this embodiment, the mass ratio of calcium nitrate: sodium metasilicate nonahydrate: polyether macromonomer: cellulose ether is 100:150:96:2.5.

[0083] S2. Porous copper tailings sand is crushed into particles with a pore size of 100-500nm and a particle size of 0.5-2mm.

[0084] S3. After soaking the tailings particles in a nano-modified cellulose ether solution for 30 minutes, remove them, dry them at 105℃ for 3 hours, cool them, and then grind them into powder using a ball mill with a specific surface area of ​​50-150 m². 2 / g, tailings powder loaded with nano-modified cellulose ether was obtained.

[0085] The quick-setting agent in the example is prepared as follows: the raw materials are 40% polyaluminum sulfate, 8% modified aluminum hydroxide, 5% modified alkanolamine, 0.5% lithium sulfate, 0.3% nano silica solution with a concentration of 4%, 0.8% modified hydrated magnesium silicate, and the remainder is water. The quick-setting agent is obtained by mixing polyaluminum sulfate, modified aluminum hydroxide, modified alkanolamine, lithium sulfate, nano silica solution, modified hydrated magnesium silicate, and water.

[0086] The method for preparing modified aluminum hydroxide in quick-setting agent is as follows: aluminum hydroxide is kept at 400℃ for 2 hours, then the temperature is raised to 750℃ and kept at 1 hour, and finally it is ground for 20-30 minutes and passed through a 200-mesh sieve to obtain modified aluminum hydroxide.

[0087] The method for preparing modified alkanolamines in quick-setting agents is as follows: 0.5 mol / L citric acid solution is added to 15% triethanolamine solution and stirred to neutralize, with a molar ratio of citric acid to triethanolamine of 1:3; the neutralized solution is mixed with 10% maleic anhydride at a volume ratio of 2:1, and 3% by mass of catalyst (5% acrylic acid solution) is added to the mixed solution at 50°C. The mixture is stirred and refluxed for 1-2 hours to obtain modified alkanolamines.

[0088] The modified hydrated magnesium silicate is prepared by placing the hydrated magnesium silicate at 600℃ for 4 hours and then grinding it. During the grinding process, 0.3% silane coupling agent, 0.5% citric acid and 0.3% tartaric acid are added based on the mass of the hydrated magnesium silicate. After grinding for 20-30 minutes, the modified hydrated magnesium silicate is obtained.

[0089] Example 2

[0090] This embodiment provides a method for preparing shotcrete, the steps of which are as follows:

[0091] (1) The design proportions of each raw material were obtained by stacking the cementitious materials, fine aggregates and coarse aggregates using the MAA model. The cementitious materials include cement and mineral admixtures. The mineral admixtures include silica fume I, fly ash, mineral powder and ultrafine stone powder. The fine aggregate is sand with a particle size not exceeding 4.75 mm and two particle size grades, namely 0.15-1.25 mm and 1.25-4.75 mm. The coarse aggregate is gravel with a particle size of 5-15 mm and two particle size grades, namely 5-10 mm and 10-15 mm.

[0092] The final mass ratio of cement:fly ash:mineral powder:silica fume:ultrafine stone powder is 312:20:24:40:55. The mass ratio of 0.15-1.25mm fine aggregate to 1.25-4.75mm fine aggregate is 417:463. The mass ratio of 5-10mm coarse aggregate to 10-15mm aggregate is 692:245.

[0093] (2) The cementitious materials (312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume I, 55 parts stone powder), fine aggregates (417 parts 0.15-1.25mm fine aggregates, 463 parts 1.25mm-4.25mm fine aggregates), coarse aggregates (692 parts 5-10mm coarse aggregates, 245 parts 10-15mm coarse aggregates), and 20 parts of elasticity-reducing materials obtained according to the design proportions in step (1) are thoroughly mixed. 180 parts of water and 4 parts of water-reducing agent are added and mixed. Then, 25 parts of quick-setting agent are added by mixing with pressurized air to obtain high-density, low-rebound shotcrete.

[0094] Based on the same inventive concept, this embodiment also provides a shotcrete comprising 312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume, 55 parts ultrafine stone powder, 417 parts 0.15-1.25mm fine aggregate, 463 parts 1.25mm-4.25mm fine aggregate, 692 parts 5-10mm coarse aggregate, 245 parts 10-15mm coarse aggregate, 20 parts elasticity-reducing material, 25 parts accelerator, 180 parts water, and 4 parts water-reducing agent. The proportions of the cementitious materials (including ordinary Portland cement, silica fume I, fly ash, mineral powder, and ultrafine stone powder), the fine aggregate (including two specifications: 0.15-1.25mm and 1.25mm-4.25mm), and the coarse aggregate (including two specifications: 5-10mm and 10-15mm) are all designed using close-packing theory.

[0095] The quick-setting agent and the elasticity-reducing material used are the same as in Example 1.

[0096] Comparative Example 1:

[0097] This comparative example provides a shotcrete composed of the following components by weight: 370 parts ordinary Portland cement, 70 parts fly ash, 850 parts 0.15-4.75mm single-grade fine aggregate, 930 parts 5-15mm coarse aggregate, 20 parts elasticity-reducing material, 25 parts accelerator, 160 parts water, and 4 parts water-reducing agent. (The elasticity-reducing material and accelerator are the same as in Example 1.)

[0098] The preparation process includes the following steps:

[0099] 1) Thoroughly mix silicate cement, fly ash, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0100] Comparative Example 2:

[0101] This comparative example provides a shotcrete composed of the following components by weight: 340 parts ordinary Portland cement, 90 parts mineral powder, 870 parts 0.15-4.75mm single-grade fine aggregate, 920 parts 5-15mm coarse aggregate, 25 parts elasticity-reducing material, 20 parts quick-setting agent, 160 parts water, and 4 parts water-reducing agent.

[0102] The preparation process includes the following steps:

[0103] 1) Thoroughly mix silicate cement, mineral powder, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0104] Comparative Example 3:

[0105] This comparative example provides a shotcrete composed of the following components by weight: 380 parts ordinary Portland cement, 60 parts silica fume, 850 parts 0.15-4.75mm single-grade fine aggregate, 930 parts 5-15mm coarse aggregate, 25 parts elasticity-reducing material, 25 parts quick-setting agent, 170 parts water, and 4 parts water-reducing agent.

[0106] The preparation process includes the following steps:

[0107] 1) Thoroughly mix silicate cement, silica fume, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0108] Comparative Example 4:

[0109] This comparative example provides a shotcrete composed of the following components by weight: 420 parts ordinary Portland cement, 30 parts ultrafine stone powder, 850 parts 0.15-4.75mm single-grade fine aggregate, 930 parts 5-15mm coarse aggregate, 20 parts elasticity-reducing material, 25 parts quick-setting agent, 180 parts water, and 4 parts water-reducing agent.

[0110] The preparation process includes the following steps:

[0111] 1) Thoroughly mix silicate cement, ultrafine stone powder, fine aggregate, and coarse aggregate, and dry stir for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0112] Comparative Example 5:

[0113] This comparative example provides a shotcrete composed of the following components by weight: 340 parts ordinary Portland cement, 30 parts fly ash, 20 parts mineral powder, 30 parts silica fume, 40 parts ultrafine stone powder, 50 parts 0.15-4.75mm single-grade fine aggregate, 930 parts 5-15mm coarse aggregate, 20 parts elasticity-reducing material, 25 parts quick-setting agent, 160 parts water, and 4 parts water-reducing agent.

[0114] The preparation process includes the following steps:

[0115] 1) Thoroughly mix silicate cement, fly ash, mineral powder, silica fume, ultrafine stone powder, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0116] Comparative Example 6:

[0117] This comparative example provides a shotcrete composed of the following components by weight: 312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume, 55 parts stone powder, 298 parts 0.15-0.6mm fine aggregate, 132 parts 0.6-1.25mm fine aggregate, 70 parts 1.25-2.36mm fine aggregate, 378 parts 2.36-4.75mm and 692 parts 5-10mm coarse aggregate, 245 parts 10-15mm coarse aggregate, 25 parts commercially available SA160 BASF early-strength alkali-free quick-setting agent, 180 parts water, and 4 parts water-reducing agent.

[0118] The preparation process includes the following steps:

[0119] 1) Thoroughly mix silicate cement, fly ash, mineral powder, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0120] Comparative Example 7:

[0121] This comparative example provides a shotcrete composed of the following components by weight: 312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume, 55 parts stone powder, 298 parts 0.15-0.6mm fine aggregate, 132 parts 0.6-1.25mm fine aggregate, 70 parts 1.25-2.36mm fine aggregate, 378 parts 2.36-4.75mm coarse aggregate, 692 parts 5-10mm coarse aggregate, 245 parts 10-15mm coarse aggregate, and commercially available... - 20 parts VM1005 long-lasting concrete thickener, 25 parts commercially available SA160 BASF early-strength alkali-free quick-setting agent, 180 parts water, and 4 parts water-reducing agent.

[0122] The preparation process includes the following steps:

[0123] 1) Thoroughly mix silicate cement, fly ash, mineral powder, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0124] Comparative Example 8:

[0125] This comparative example provides a shotcrete composed of the following components by weight: 312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume, 55 parts stone powder, 298 parts 0.15-0.6mm fine aggregate, 132 parts 0.6-1.25mm fine aggregate, 70 parts 1.25-2.36mm fine aggregate, 378 parts 2.36-4.75mm and 692 parts 5-10mm coarse aggregate, 245 parts 10-15mm coarse aggregate, 20 parts of elasticity-reducing material (i.e., the elasticity-reducing material in Example 1), 25 parts commercially available SA 160 BASF early-strength alkali-free quick-setting agent, 180 parts water, and 4 parts water-reducing agent.

[0126] The preparation process includes the following steps:

[0127] 1) Thoroughly mix silicate cement, fly ash, mineral powder, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0128] Comparative Example 9:

[0129] This comparative example provides a shotcrete (prepared using a multi-stage close-packing method), composed of the following components by weight: 312 parts ordinary Portland cement, 20 parts fly ash, 24 parts mineral powder, 40 parts silica fume, 55 parts stone powder, 298 parts 0.15-0.6mm fine aggregate, 132 parts 0.6-1.25mm fine aggregate, 70 parts 1.25-2.36mm fine aggregate, 378 parts 2.36-4.75mm coarse aggregate, 692 parts 5-10mm coarse aggregate, 245 parts 10-15mm coarse aggregate, and commercially available... - 20 parts of VM1005 long-lasting concrete thickener and elasticity reducer, 25 parts of self-made quick-setting agent (i.e., the quick-setting agent in Example 1), 180 parts of water, and 4 parts of water-reducing agent.

[0130] The preparation process includes the following steps:

[0131] 1) Thoroughly mix silicate cement, fly ash, mineral powder, fine aggregate, and coarse aggregate, and dry mix for 1-2 minutes; 2) and 3) Same as in Example 1, to obtain a comparative sample.

[0132] Performance testing

[0133] The mechanical properties, bulk density, workability, and rebound rate of the sprayed concrete were tested using the above examples and comparative examples. The particle-filled structure of the concrete was evaluated using wet bulk density. The specific calculation formula for wet bulk density is given in equation (3).

[0134]

[0135] in M represents the wet bulk density of mortar. max ρ represents the maximum mass of concrete measured under different raw material stacking conditions (the average net weight of concrete in three containers, in g), where V represents the volume of the container (taken as 480 mL). w ρ i and ρ j Density of water, powder, and aggregate (g / m³) 3 ), while R w R i and R j These represent the volume fraction of each raw material.

[0136] Compressive strength tests were conducted using 100mm × 100mm × 100mm cubic samples. The test procedure was performed at 1.2 MPa / s (1000 kN). Samples underwent standard curing at 7 days and 28 days, followed by testing. Three samples were tested at each age, and the average compressive strength was calculated.

[0137] The rebound rate of shotcrete was determined using a large-scale shotcrete slab. Concrete was sprayed into a slab with dimensions of 400mm × 400mm × 120mm, and geotextile was placed underneath the slab to catch the rebounding concrete. After the slab was filled with shotcrete, the volume of concrete in the slab and the mass of the rebounding concrete falling onto the geotextile were calculated. Each test group was tested three times, and the average value was taken.

[0138] The test results of Comparative Examples 1-5 and Examples 1-2 are shown in Table 1.

[0139] Table 1 Test Results

[0140]

[0141]

[0142] As shown in Table 1, compared with the comparative example, the concrete packing density, 1-day and 28-day strength of Examples 1 and 2 were improved, indicating that the multi-stage dense packing method can effectively improve the packing density of concrete, optimize the pore structure of concrete, and enhance the compressive strength of concrete. Furthermore, compared with the comparative example, the plastic viscosity of concrete in Examples 1 and 2 was significantly increased, resulting in a slight increase in slump time and a slight decrease in spread, while the rebound rate of concrete during spraying was significantly optimized. These findings demonstrate that the multi-stage dense packing method can not only effectively improve the mechanical properties of sprayed concrete and increase the utilization efficiency of cementitious materials, but also effectively reduce the rebound rate of sprayed concrete.

[0143] The test results for Comparative Examples 6-9 and Example 2 are shown in Table 2.

[0144] Table 2 Test Results

[0145]

[0146] As shown in Table 2, the rebound rates of other test groups were significantly lower than those of Comparative Example 6, which did not contain the rebound-reducing material. Secondly, compared to Comparative Examples 7 and 8, Example 1 showed improved 1-day and 28-day strengths, indicating that the self-made accelerator had a smaller impact on the mechanical properties of concrete compared to the commercially available SA 160 BASF early-strength alkali-free accelerator. Finally, compared to Comparative Examples 7 and 9, Example 1 exhibited a faster slump time and greater spread, resulting in improved shotcrete spraying efficiency. This demonstrates that the self-made rebound-reducing material can optimize the pumpability of shotcrete and improve spraying efficiency.

Claims

1. A method for preparing high-density, low-rebound shotcrete, characterized in that, Includes the following steps: (1) The design proportions of each raw material are obtained by stacking the cementitious material, fine aggregate and coarse aggregate using the MAA model. The cementitious material includes cement and mineral admixtures. The mineral admixtures include one or more of silica fume I, fly ash, mineral powder and ultrafine stone powder. The fine aggregate is sand with a particle size not exceeding 4.75 mm and the particle size is divided into at least 2 grades. The coarse aggregate is gravel with a particle size of 5-15 mm and the particle size is divided into at least 2 grades. (2) The cementitious materials, fine aggregates, coarse aggregates and elasticity reducers obtained according to the design ratio in step (1) are thoroughly mixed, water and water-reducing agents are added and mixed, and then quick-setting agents are added by mixing with pressurized air to obtain high-density low-rebound shotcrete. The raw materials of the high-density low-rebound shotcrete include 300-350 parts of cement, 120-150 parts of mineral admixtures, 800-900 parts of fine aggregates, 850-1000 parts of coarse aggregates, 20-30 parts of elasticity reducers, 15-30 parts of quick-setting agents, 150-200 parts of water and 4-8 parts of water-reducing agents by weight. The elasticity reducer comprises, by mass percentage, 53-73% rheology component, 15-25% thickening component, 10-18% early strength component, and 0.5-4% setting regulator component, with the sum of the mass percentages of the above components being 100%. The rheology component comprises manganese slag powder and silica fume II mixed in a 3:1 mass ratio. The thickening component is tailings powder loaded with nano-modified cellulose ether. The early strength component comprises one or more of calcium formate, sodium sulfate, polyaluminum sulfate, lithium sulfate, aluminate cement, and sulfoaluminate cement. The setting regulator component comprises one or more of sodium gluconate, sodium tripolyphosphate, boric acid, and citric acid.

2. The method for preparing high-density, low-rebound shotcrete as described in claim 1, characterized in that, In step (1), the design proportions of each raw material are obtained by stacking using the MAA model, specifically including: a. The MAA model is used for stacking to form a graded, zoned, tightly packed system; b. Based on the particle size of each raw material and the cumulative proportion of the corresponding particle size, obtain the target curve of the mixture; c. Based on the target curve of the mixture and the least squares method, the optimal particle size distribution of the mixture is calculated, and the proportion of each raw material corresponding to the optimal particle size distribution is the design proportion.

3. The method for preparing high-density, low-rebound shotcrete as described in claim 1, characterized in that, In step (1), the fine aggregate particle size is divided into four grades: 0.15-0.6mm, 0.6-1.25mm, 1.25-2.36mm, and 2.36-4.75mm, or into two grades: 0.15-1.25mm and 1.25-4.75mm; the coarse aggregate particle size is divided into two grades: 5-10mm and 10-15mm.

4. The method for preparing high-density, low-rebound shotcrete as described in claim 1, characterized in that, The quick-setting agent comprises, by mass percentage, 35-40% polyaluminum sulfate, 5-8% modified aluminum hydroxide, 2-5% modified alkanolamine, 0.2-0.5% lithium sulfate, 0.1-0.3% nano silica solution, 0.8-1.0% modified hydrated magnesium silicate, with the remainder being water.

5. The method for preparing high-density, low-rebound shotcrete as described in claim 4, characterized in that, The modified aluminum hydroxide is prepared by a method comprising the following steps: aluminum hydroxide is kept at 350-400℃ for 1.5-2h, then the temperature is raised to 700-750℃ and kept for 0.8-1h, and finally ground for 20-30min and passed through a 200-mesh sieve to obtain modified aluminum hydroxide. The modified alkanolamine is prepared by a method comprising the following steps: adding a 0.5-1.0 mol / L citric acid solution to a 15-20% triethanolamine solution and stirring to neutralize, wherein the molar ratio of citric acid to triethanolamine is 1:3-4; mixing the neutralized solution with a 10-15% maleic anhydride solution at a volume ratio of 2-3:1; adding a catalyst at 3% by mass of the mixed solution at 50-55°C; and stirring and refluxing for 1-2 hours to obtain the modified alkanolamine.

6. The method for preparing high-density, low-rebound shotcrete as described in claim 4, characterized in that, The modified hydrated magnesium silicate is prepared by a method including the following steps: hydrated magnesium silicate is kept at 500℃-600℃ for 3-4 hours and then ground. During the grinding process, 0.3% silane coupling agent, 0.5% citric acid and 0.3% tartaric acid are added according to the mass of hydrated magnesium silicate. After grinding for 20-30 minutes, the modified hydrated magnesium silicate is obtained. The concentration of the nano-silica solution is 2-4%.

7. The method for preparing high-density, low-rebound shotcrete as described in claim 1, characterized in that, The cement is silicate cement with a strength of not less than 42.5 and an apparent density of 3000-3200 kg / m³. 3 ; The fly ash has an average particle size of 1-5 μm and a specific surface area greater than 800 m². 2 / kg, apparent density is 2200-2400 kg / m³ 3 ; The silica fume I has a SiO2 content greater than 90%, an average particle size of 0.1-0.3 μm, and a specific surface area greater than 20,000 m². 2 / kg, apparent density is 2100-2400 kg / m³ 3 ; The mineral powder has an average particle size of 5-10 μm and a specific surface area greater than 90 m². 2 / kg, apparent density is 2500-2700 kg / m³ 3 ; The ultrafine stone powder has a calcium carbonate content greater than 98%, an average particle size of 0.5-3 μm, and a specific surface area greater than 1800 m². 2 / kg, apparent density is 2700-2800 kg / m³ 3 .

8. A high-density, low-rebound shotcrete, characterized in that, It is prepared by the method for preparing high-density, low-rebound shotcrete according to any one of claims 1-7.

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