Early-strength, high-durability and low-resilience sprayed concrete and preparation method thereof

Abstract

The invention discloses early-strength, low-resilience and high-durability sprayed concrete and a preparation method thereof. The sprayed concrete is prepared from the following components: cement, an early-strength hardening auxiliary cementing material, coarse aggregate, fine aggregate, water, an additive, a fluoride-free alkali-free high-concentration accelerator, a rheology modifier, fibers and the like. The preparation method of the sprayed concrete mainly comprises two aspects. The method comprises the following steps: (1) proportioning optimization; and (2) functional materials are applied. By optimizing the glue material amount, the water-glue ratio and the sand ratio and adopting the small-particle-size coarse aggregate, the concrete has good workability and homogeneity, the risk of pipe blocking in the pumping and spraying process is reduced, aggregate rebound in the jet flow process is reduced, and the spraying operation effect is optimized. By applying the high-concentration fluoride-free alkali-free accelerator and the early-strength hardening auxiliary cementing material, the early strength of the concrete can be effectively improved, the volume deformation is reduced, and the long-term mechanical property and durability are improved. The fiber and the rheological modifier are added, so that the rheological property of the sprayed concrete can be further effectively improved, and the rebound rate is reduced. Rapid setting of the sprayed concrete and cooperative improvement of mechanical properties and long-term performance are achieved by optimizing the mixing ratio and applying novel functional materials.

Description

Technical Field

[0002] The present invention belongs to building materials and relates to an early high-strength, highly durable, and low-rebound shotcrete and a preparation method thereof. Background Art

[0004] Shotcrete has been widely used in many fields such as tunnel support, slope protection, and structural repair due to its unique construction technology and rapid hardening characteristics. With the extension of China's engineering construction to the western region, more and more tunnel projects have characteristics such as ultra-large burial depth, high altitude, large temperature difference, etc. In addition, they are also affected by adverse geological environments such as high ground stress, high geothermal heat, rich water, and rock burst. Therefore, higher requirements are put forward for the shotcrete used for primary support.

[0005] The application of traditional shotcrete faces many problems, such as high rebound rate, low early strength, poor workability, later strength regression, and insufficient durability. And the liquid accelerating agents used are mostly fluorine-containing and alkali-containing types. On the one hand, they have weak low-temperature setting promotion and insufficient heat resistance of the products. On the other hand, the contained hydrofluoric acid, fluorosilicic acid, etc. are highly corrosive and easily cause environmental pollution. Therefore, it is urgent to develop an early high-strength, highly durable, and low-rebound shotcrete suitable for complex geological environments, so as to improve the construction and use performance of shotcrete and realize the high performance of shotcrete.

[0006] Patent CN114671644A discloses a high-early-strength and low-rebound high-performance shotcrete and a preparation method thereof. By using an alkali-free and fluorine-free accelerating agent and admixtures, the early strength of the concrete is improved and the rebound rate of the side wall and arch top is reduced, but the long-term durability and stability of strength growth of the concrete are not further considered. Patent CN117886575A discloses a low-rebound and high-strength shotcrete material and a preparation method thereof. The shotcrete prepared by using a modified polyacrylamide additive and linear or branched starch reduces the rebound rate and improves the age strength at 7d and 28d, but does not mention the early age strength such as 8h and 1d, and cannot meet the requirements for early high strength of shotcrete. Summary of the Invention

[0008] The purpose of the present invention is to solve the above problems, provide an early high-strength, highly durable, and low-rebound shotcrete, and provide its preparation method and application method.

[0009] The early-strength, high-durability and low-elasticity shotcrete of the present invention comprises the following raw materials in parts by weight: 420-500 parts of cement, 800-900 parts of coarse aggregate, 800-900 parts of fine aggregate, 120-170 parts of water, 3.8-5.5 parts of admixture, 4-10 parts of early-strength and compaction-augmenting supplementary cementitious material, 2.5-4 parts of fluorine-free and alkali-free high-concentration accelerating agent. The early-strength and compaction-augmenting supplementary cementitious material includes two types: early-strength and compaction-augmenting supplementary cementitious material (powder) and early-strength and compaction-augmenting supplementary cementitious material (liquid), and the two can be used alone or synergistically.

[0010] The early-strength and compaction-augmenting supplementary cementitious material (liquid) is a suspension with a calcium-silicon ratio of 0.6-2 prepared by a co-precipitation method using calcium salts, silicon salts and a dispersant. The calcium salts are at least one of calcium nitrate, calcium sulfate, calcium hypochlorite, calcium bromide, calcium fluoride, calcium iodate, calcium nitrite, calcium oxalate; the silicon salts are at least one of sodium silicate, aluminum silicate, potassium silicate, sodium metasilicate, potassium metasilicate; and the dispersant is a polycarboxylic acid type.

[0011] The early-strength and compaction-augmenting supplementary cementitious material (powder) is composed of an early-strength component and a compaction-augmenting component, wherein the mass ratio of the early-strength component is 20%-40%, and the mass ratio of the compaction-augmenting component is 60%-80%. The early-strength component is at least one of calcium sulfate, tricalcium aluminate, sodium sulfate, magnesium sulfate, potassium sulfate; and the compaction-augmenting component is at least one of silica fume, fly ash, slag powder, stone powder.

[0012] The fluorine-free and alkali-free high-concentration accelerating agent meets the requirements that the fluoride ion and alkali content < 0.05%, the initial setting time of neat cement paste (5°C) ≤ 5 min, the final setting time of neat cement paste (5°C) ≤ 10 min, the 28-day compressive strength ratio of mortar (80°C) ≥ 90%, and the stability (-10°C) ≤ 5 mL.

[0013] The cement is P·O42.5 ordinary Portland cement; the fine aggregate is river sand or manufactured sand with a fineness modulus of 2.3-3.0; the coarse aggregate is crushed stone with a particle size of 5-8 mm; the rheology regulator is at least one of cellulose ether, redispersible latex powder, xanthan gum, welan gum, guar gum; the admixture is a polycarboxylic acid high-performance water reducer with a water reduction rate ≥ 25%. The rheology regulator is at least one of cellulose ether, redispersible latex powder, xanthan gum, welan gum, guar gum.

[0014] The fiber is at least one of basalt fiber, polypropylene fiber, polyethylene fiber, polyvinyl alcohol fiber.

[0015] The spread of the shotcrete is 400-600 mm, and the air content is 4-6%.

[0016] The preparation method of the shotcrete comprises the following steps:

[0017] (1) Put cement, fine aggregate, coarse aggregate, early-strength and compaction-enhancing supplementary cementitious material (powder), and fiber into a mixer and stir for 30 s to obtain a dry-mixed material;

[0018] (2) Add water, early-strength and compaction-enhancing supplementary cementitious material (liquid), rheology regulator, and admixture to the dry-mixed material and stir for 3 min to obtain a concrete mixture;

[0019] (3) Add the mixture to a wet spraying device, mix it with a quick-setting agent, and spray it onto the sprayed surface to obtain early-high-strength, high-durability, and low-rebound sprayed concrete.

[0020] When the sprayed concrete is sprayed onto the sprayed surface, the spraying angle is 75-90°; the spraying distance is 1.0-1.5 m; the spraying air pressure is 0.3-0.6 MPa; the movement track of the nozzle is linear reciprocating or circular rotating horizontal movement; the one-time spraying thickness of the side wall is 8-15 cm, and the one-time spraying thickness of the arch top is 6-10 cm.

[0021] Application of the described early-high-strength, high-durability, and low-rebound sprayed concrete in tunnel and slope support.

[0022] The positive effects of the early-high-strength, high-durability, and low-rebound sprayed concrete of the present invention are:

[0023] The early-high-strength, high-durability, and low-rebound sprayed concrete prepared in the present invention has good workability and homogeneity by optimizing the mix ratio, adopting a higher air content and medium slump, reducing the risk of pipe blockage during pumping and spraying. In terms of concrete aggregate, the particle size is 5-8 mm, reducing the aggregate rebound phenomenon during the jetting process and improving the spraying effect.

[0024] In addition, the early-high-strength, high-durability, and low-rebound sprayed concrete uses a high-concentration fluorine-free and alkali-free quick-setting agent and an early-strength and compaction-enhancing supplementary cementitious material. The fluorine-free and alkali-free quick-setting agent used meets the requirement that the active aluminum phase content is as high as more than 60%, which can effectively improve the coagulation-accelerating and early-strength performance and stability of the quick-setting agent under harsh environments. The early-strength and compaction-enhancing supplementary cementitious material includes two types: early-strength and compaction-enhancing supplementary cementitious material (powder) and early-strength and compaction-enhancing supplementary cementitious material (liquid). The powder is a sulfoaluminate-based raw material, and after adding, it can promote the rapid hydration of the cement system and generate ettringite-based hydration products with a certain strength at an earlier stage, thereby enhancing the early strength. The liquid contains nano-CSH, and after adding, it can induce the acceleration of the hydration of calcium silicate minerals, thereby enhancing the early strength. When these two early-strength materials are used in combination, the two early-strength mechanisms can simultaneously play the early-strength function and have a certain synergistic effect. Specific embodiments

[0026] The following further describes the present invention in detail with specific embodiments.

[0027] Example 1: A high-early-strength, high impermeability, low rebound high-performance shotcrete, and its preparation process is as follows:

[0028] (1) Place 1 part of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, drop 1 part of the calcium salt solution and 4 parts of the silicon solution into the reaction solution. Control the dropping time to 30 min. After the dropping is completed, continue the reaction for 30 min to obtain the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A1.

[0029] (2) Mix 1 part of the early-strength component with 4 parts of the compaction component to obtain the early-strength and compaction-enhancing auxiliary cementitious material (powder) B1 with the early-strength component accounting for 20% and the compaction component accounting for 80%.

[0030] (3) Add 464 parts of cement, 820 parts of sand, 885 parts of gravel, 0.8 part of fiber, and 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (powder) B1 to the mixer. After stirring for 30 s, add 167 parts of water, 1 part of the rheology regulator, 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A1, and 4.7 parts of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 38 parts of the high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain the shotcrete.

[0031] Example 2: A high-early-strength, high impermeability, low rebound high-performance shotcrete, and its preparation process is as follows:

[0032] (1) Place 1 part of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, drop 1.5 parts of the calcium salt solution and 3 parts of the silicon solution into the reaction solution. Control the dropping time to 30 min. After the dropping is completed, continue the reaction for 30 min to obtain the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A2.

[0033] (2) Mix 1 part of the early-strength component with 3 parts of the compaction component to obtain the early-strength and compaction-enhancing auxiliary cementitious material (powder) B2 with the early-strength component accounting for 25% and the compaction component accounting for 75%.

[0034] (3) Add 470 parts of cement, 830 parts of sand, 888 parts of gravel, 0.8 part of fiber, and 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (powder) B2 to the mixer. After stirring for 30 s, add 171 parts of water, 1 part of the rheology regulator, 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A2, and 4.7 parts of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 38 parts of the high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain the shotcrete.

[0035] Example 3: A high-early-strength, high impermeability, low rebound high-performance shotcrete, and its preparation process is as follows:

[0036] (1) Place 1 part of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, add 1.5 parts of the calcium salt aqueous solution and 1.5 parts of the silicon solution dropwise to the reaction solution. Control the dropping time to 30 min. After the dropping is completed, continue the reaction for 30 min to obtain the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A3.

[0037] (2) Mix 3 parts of the early-strength component and 3 parts of the compaction-enhancing component to obtain the early-strength and compaction-enhancing auxiliary cementitious material (powder) B3 with the early-strength component accounting for 50% and the compaction-enhancing component accounting for 50%.

[0038] (3) Add 480 parts of cement, 840 parts of sand, 840 parts of gravel, 0.8 part of fiber, and 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (powder) B3 to the mixer. After stirring for 30 s, add 168 parts of water, 1 part of the rheology modifier, 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A3, and 4.8 parts of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 33 parts of the high-concentration fluorine-free and alkali-free accelerating agent, and then spray it onto the sprayed surface to obtain the sprayed concrete.

[0039] Example 4: A high-performance sprayed concrete with high early strength, high impermeability, and low rebound. The preparation process is as follows:

[0040] (1) Place 1 part of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, add 1.5 parts of the calcium salt aqueous solution and 2 parts of the silicon solution dropwise to the reaction solution. Control the dropping time to 30 min. After the dropping is completed, continue the reaction for 30 min to obtain the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A4.

[0041] (2) Mix 5 parts of the early-strength component and 3 parts of the compaction-enhancing component to obtain the early-strength and compaction-enhancing auxiliary cementitious material (powder) B4 with the early-strength component accounting for 62.5% and the compaction-enhancing component accounting for 37.5%.

[0042] (3) Add 480 parts of cement, 840 parts of sand, 840 parts of gravel, 0.8 part of fiber, and 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (powder) B4 to the mixer. After stirring for 30 s, add 168 parts of water, 1 part of the rheology modifier, 8 parts of the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A4, and 4.8 parts of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 34 parts of the high-concentration fluorine-free and alkali-free accelerating agent, and then spray it onto the sprayed surface to obtain the sprayed concrete.

[0043] Example 5: A high-performance sprayed concrete with high early strength, high impermeability, and low rebound. The preparation process is as follows:

[0044] (1) Place 1 portion of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, add 3 portions of the calcium salt solution and 1.5 portions of the silicon solution dropwise to the reaction solution. Control the dropping time to 30 min. After the dropping is complete, continue the reaction for 30 min to obtain the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A5.

[0045] (2) Mix 1 portion of the early-strength component with 3 portions of the compaction-enhancing component to obtain the early-strength and compaction-enhancing auxiliary cementitious material (powder) B5 with the early-strength component accounting for 25% and the compaction-enhancing component accounting for 75%.

[0046] (3) Add 480 portions of cement, 843 portions of sand, 848 portions of gravel, 0.7 portion of fiber, and 6 portions of the early-strength and compaction-enhancing auxiliary cementitious material (powder) B5 to the mixer. After stirring for 30 s, add 170 portions of water, 1 portion of the rheology modifier, 6 portions of the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A5, and 4.6 portions of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 36 portions of the high-concentration fluorine-free and alkali-free accelerating agent, and then spray it onto the sprayed surface to obtain the sprayed concrete.

[0047] Example 6: Sprayed concrete containing the early-strength and compaction-enhancing auxiliary cementitious material (liquid)

[0048] (1) Place 1 portion of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, add 2 portions of the calcium salt solution and 1.5 portions of the silicon solution dropwise to the reaction solution. Control the dropping time to 30 min. After the dropping is complete, continue the reaction for 30 min to obtain the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A6.

[0049] (2) Add 480 portions of cement, 850 portions of sand, 850 portions of gravel, 0.8 portion of fiber to the mixer. After stirring for 30 s, add 168 portions of water, 1 portion of the rheology modifier, 8 portions of the early-strength and compaction-enhancing auxiliary cementitious material (liquid) A6, and 4.7 portions of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 36 portions of the high-concentration fluorine-free and alkali-free accelerating agent, and then spray it onto the sprayed surface to obtain the sprayed concrete.

[0050] Example 7: Sprayed concrete containing the early-strength and compaction-enhancing auxiliary cementitious material (powder)

[0051] (1) Mix 3 portions of the early-strength component with 3 portions of the compaction-enhancing component to obtain the early-strength and compaction-enhancing auxiliary cementitious material (powder) B6 with the early-strength component accounting for 66% and the compaction-enhancing component accounting for 33%.

[0052] (2) Add 490 parts of cement, 850 parts of sand, 850 parts of gravel, 0.8 part of fiber, and 7 parts of early-strength and compaction-enhancing supplementary cementitious material (powder) B6 to the mixer. After stirring for 30 s, add 173 parts of water, 1 part of rheology modifier, and 4.7 parts of water reducer, and then stir for 3 min to obtain a concrete mixture. Add the mixture to the wet spraying equipment, mix it with 36 parts of high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain sprayed concrete.

[0053] Control Example 1: Ordinary sprayed concrete

[0054] Add 480 parts of cement, 820 parts of sand, 885 parts of gravel, and 0.8 part of fiber to the mixer. After stirring for 30 s, add 168 parts of water, 1 part of rheology modifier, and 4.8 parts of water reducer, and then stir for 3 min to obtain a concrete mixture. Add the mixture to the wet spraying equipment, mix it with 38 parts of ordinary accelerator, and then spray it onto the sprayed surface to obtain sprayed concrete.

[0055] Control Example 2: High-performance sprayed concrete without working condition adjustment. The preparation process is as follows:

[0056] (1) Place 1 part of dispersant solution in a three-necked flask, stir at 300 rpm, and heat up to 40 °C. Then, add 3.5 parts of calcium salt solution and 1.5 parts of silicon solution dropwise to the reaction solution, control the dropping time to 30 min, and continue to react for 30 min after dropping to obtain early-strength and compaction-enhancing supplementary cementitious material (liquid) A7.

[0057] (2) Mix 1 part of early-strength component with 3 parts of compaction component to obtain early-strength and compaction-enhancing supplementary cementitious material (powder) B7 with an early-strength component ratio of 25% and a compaction component ratio of 75%.

[0058] (3) Add 490 parts of cement, 850 parts of sand, 850 parts of gravel, 0.8 part of fiber, and 7 parts of early-strength and compaction-enhancing supplementary cementitious material (powder) B7 to the mixer. After stirring for 30 s, add 168 parts of water, 1 part of rheology modifier, 7 parts of early-strength and compaction-enhancing supplementary cementitious material (liquid) A7, and 1 part of water reducer, and then stir for 3 min to obtain a concrete mixture. Add the mixture to the wet spraying equipment, mix it with 36 parts of high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain sprayed concrete.

[0059] Control Example 3: High-performance sprayed concrete with a large water-binder ratio and air content. The preparation process is as follows:

[0060] (4) Place 1 part of dispersant solution in a three-necked flask, stir at 300 rpm, and heat up to 40 °C. Then, add 2 parts of calcium salt solution and 1.5 parts of silicon solution dropwise to the reaction solution, control the dropping time to 30 min, and continue to react for 30 min after dropping to obtain early-strength and compaction-enhancing supplementary cementitious material (liquid) A8.

[0061] (5) Mix 1 part of the early-strength component with 3 parts of the compaction-increasing component to obtain the early-strength and compaction-increasing type supplementary cementitious material (powder) B8 with the early-strength component accounting for 25% and the compaction-increasing component accounting for 75%.

[0062] (6) Add 485 parts of cement, 840 parts of sand, 850 parts of gravel, 0.8 part of fiber, and 7 parts of the early-strength and compaction-increasing type supplementary cementitious material (powder) B8 to the mixer. After stirring for 30 s, add 210 parts of water, 1 part of the rheology regulator, 7 parts of the early-strength and compaction-increasing type supplementary cementitious material (liquid) A8, and 3 parts of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 36 parts of the high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain the shotcrete.

[0063] Comparative Example 4: Shotcrete incorporated with a low dosage of the early-strength and compaction-increasing type supplementary cementitious material

[0064] (1) Place 1 part of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, add 3 parts of the calcium salt aqueous solution and 1.5 parts of the silicon solution dropwise to the reaction solution. Control the dropping time to be 30 min. After the dropping is completed, continue to react for 30 min to obtain the early-strength and compaction-increasing type supplementary cementitious material (liquid) A9.

[0065] (2) Mix 1 part of the early-strength component with 3 parts of the compaction-increasing component to obtain the early-strength and compaction-increasing type supplementary cementitious material (powder) B9 with the early-strength component accounting for 25% and the compaction-increasing component accounting for 75%.

[0066] (3) Add 480 parts of cement, 843 parts of sand, 848 parts of gravel, 0.7 part of fiber, and 2 parts of the early-strength and compaction-increasing type supplementary cementitious material (powder) B9 to the mixer. After stirring for 30 s, add 170 parts of water, 1 part of the rheology regulator, 2 parts of the early-strength and compaction-increasing type supplementary cementitious material (liquid) A9, and 4.6 parts of the water reducer, and then stir for 3 min to obtain the concrete mixture. Add the mixture to the wet spraying equipment and mix it with 36 parts of the high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain the shotcrete.

[0067] Comparative Example 5: Shotcrete incorporated with a high early-strength component functional material

[0068] (1) Place 1 part of the dispersant solution in a three-necked flask, stir at 300 rpm, and after heating to 40 °C, add 3 parts of the calcium salt aqueous solution and 1.5 parts of the silicon solution dropwise to the reaction solution. Control the dropping time to be 30 min. After the dropping is completed, continue to react for 30 min to obtain the early-strength and compaction-increasing type supplementary cementitious material (liquid) A10.

[0069] (2) Mix 8 parts of early strength components with 2 parts of compaction enhancing components to obtain an early strength and compaction enhancing type supplementary cementitious material (powder) B10 with 80% of early strength components and 20% of compaction enhancing components.

[0070] (3) Add 470 parts of cement, 843 parts of sand, 848 parts of gravel, 0.7 part of fiber, and 8 parts of early strength and compaction enhancing type supplementary cementitious material (powder) B10 to a mixer. After stirring for 30 s, add 169 parts of water, 1 part of rheology regulator, 8 parts of early strength and compaction enhancing type supplementary cementitious material (liquid) A10, and 4.6 parts of water reducer, and then stir for 3 min to obtain a concrete mixture. Add the mixture to a wet spraying device, mix it with 36 parts of high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain sprayed concrete.

[0071] Comparative Example 6: Sprayed concrete incorporating an early strength and compaction enhancing type supplementary cementitious material without using a dispersant

[0072] (1) Stir in a three-necked flask at 300 rpm. After heating to 40 °C, add 3 parts of calcium salt aqueous solution and 1.5 parts of silicon solution dropwise to the reaction solution, control the dropping time to 30 min, and continue to react for 30 min after dropping to obtain an early strength and compaction enhancing type supplementary cementitious material (liquid) A11.

[0073] (2) Mix 1 part of early strength components with 3 parts of compaction enhancing components to obtain an early strength and compaction enhancing type supplementary cementitious material (powder) B11 with 25% of early strength components and 75% of compaction enhancing components.

[0074] (3) Add 470 parts of cement, 843 parts of sand, 848 parts of gravel, 0.7 part of fiber, and 8 parts of early strength and compaction enhancing type supplementary cementitious material (powder) B11 to a mixer. After stirring for 30 s, add 169 parts of water, 1 part of rheology regulator, 8 parts of early strength and compaction enhancing type supplementary cementitious material (liquid) A11, and 4.6 parts of water reducer, and then stir for 3 min to obtain a concrete mixture. Add the mixture to a wet spraying device, mix it with 36 parts of high-concentration fluorine-free and alkali-free accelerator, and then spray it onto the sprayed surface to obtain sprayed concrete.

[0075] Comparative Example 7: High-performance sprayed concrete without incorporating a rheology regulator

[0076] (1) Stir in a three-necked flask at 300 rpm. After heating to 40 °C, add 3 parts of calcium salt aqueous solution and 1.5 parts of silicon solution dropwise to the reaction solution, control the dropping time to 30 min, and continue to react for 30 min after dropping to obtain an early strength and compaction enhancing type supplementary cementitious material (liquid) A12.

[0077] (2) Mix 1 part of early strength components with 3 parts of compaction enhancing components to obtain an early strength and compaction enhancing type supplementary cementitious material (powder) B12 with 25% of early strength components and 75% of compaction enhancing components.

[0078] (3) Add 470 parts of cement, 843 parts of sand, 848 parts of gravel, 0.7 part of fiber, 8 parts of early-strength and compaction-increasing auxiliary cementitious material (powder) B12 to the mixer. After stirring for 30 s, add 169 parts of water, 8 parts of early-strength and compaction-increasing auxiliary cementitious material (liquid) A12, and 4.6 parts of water reducer, and then stir for 3 min to obtain a concrete mixture. Add the mixture to the wet spraying equipment, mix it with 36 parts of high-concentration fluorine-free and alkali-free accelerating agent, and then spray it onto the sprayed surface to obtain sprayed concrete.

[0079] Effect description:

[0080] In the present invention, the slump flow, air content, and rebound rate of the high-performance sprayed concrete prepared in Examples 1-7 and the comparative sprayed concrete in Comparative Examples 1-7 are measured on-site. After cutting the remaining indicators to the required test size, they are placed in a standard curing room. After curing to a fixed age, corresponding observations and tests are carried out.

[0081] Table 1 Test results of sprayed concrete in examples and comparative examples

[0082] Number Slump Spread / mm Air Content / % 8h Strength / MPa 1d Strength / MPa 7d Strength / MPa 28d Strength / MPa Impermeability Grade Rebound Rate / % Implementation Status Example 1 500 5.0 14.3 18.5 28.8 38.6 ＞P20 7.2 No Cracking and No Pipe Blockage Example 2 480 5.5 14.4 19.6 28.5 39.4 ＞P20 6.4 No Cracking and No Pipe Blockage Example 3 490 4.8 15.5 20.2 28.9 40.1 ＞P20 8.3 No Cracking and No Pipe Blockage Example 4 510 5.2 15.5 20.4 30.1 40.2 ＞P20 8.1 No Cracking and No Pipe Blockage Example 5 490 5.4 16.3 20.7 29.7 41.5 ＞P20 6.5 No Cracking and No Pipe Blockage Example 6 510 5.7 11.1 16.5 26.9 38.7 P10 9.5 No Cracking and No Pipe Blockage Example 7 470 5.4 10.2 15.7 26.8 39.5 P10 8.9 No Cracking and No Pipe Blockage Comparative Example 1 500 4.6 8.3 13.2 24.5 34.3 P6 20.1 No Cracking and No Pipe Blockage Comparative Example 2 300 2.8 13.5 20.6 26.7 41.1 ＞P20 9.3 No Cracking but Pipe Blockage Comparative Example 3 650 6.7 6.2 12.7 20.5 30.1 P6 16.5 No Cracking and No Pipe Blockage Comparative Example 4 480 5.3 9.5 15.5 25.8 39.8 P16 11.2 No Cracking and No Pipe Blockage Comparative Example 5 490 5.0 / / / / / / Cracking but No Pipe Blockage Comparative Example 6 495 5.8 11.1 18.5 26.5 38.1 P16 9.8 No Cracking and No Pipe Blockage Comparative Example 7 485 5.8 12.7 19.3 27.5 40.1 P20 15.3 No Cracking and No Pipe Blockage

[0083] From the data in Table 1, it can be seen that the working performance of the sprayed concrete in the examples is suitable, the early strength develops rapidly, the long-term mechanical properties and durability are excellent, and during the actual spraying operation, the spraying process is smooth and the rebound rate is low.

[0084] Examples 6 and 7 are high-performance sprayed concretes separately added with early-strength and compaction-increasing auxiliary cementitious material (powder) and early-strength and compaction-increasing auxiliary cementitious material (liquid). Adding each early-strength and compaction-increasing auxiliary cementitious material alone can effectively improve the strength and durability. However, compared with Examples 1-5, adding both at the same time is better than the sum of adding them separately in terms of improving the early strength and durability of the sprayed concrete. This is because the early-strength and compaction-increasing auxiliary cementitious material (powder) is a sulfoaluminate-based raw material. After adding, it can react with C 3 A to generate ettringite AFt to accelerate the setting and hardening. During this process, a large amount of calcium hydroxide CH is consumed, thereby promoting the hydration of C 3 S and improving the early strength; the liquid contains nano C-S-H. After adding, it can induce the hydration of calcium silicate minerals to accelerate, thereby improving the early strength. The calcium hydroxide CH generated during the hydration induced by nano C-S-H can be consumed by the sulfoaluminate-based raw material, thereby further promoting the formation of ettringite AFt and the hydration of C 3 S. Therefore, when these two early-strength materials are used together, they can not only play the early-strength function simultaneously, but also have a certain synergistic effect.

[0085] Comparing the comparative examples with the examples, it can be seen that in the comparative examples, the early strength development is relatively slow, the rebound rate is relatively high, the impermeability grade is relatively low, and in some cases, cracking or pipe blockage occurs.

[0086] Comparative Example 1 is conventional concrete. Since no functional materials are added to the conventional concrete, the early strength is low, the rebound rate is high during the spraying process, and at the same time, after adding an ordinary accelerating agent, it is directly sprayed and formed, with poor compactness and low impermeability grade.

[0087] Comparative Example 2 is high-performance sprayed concrete without working condition adjustment. Due to the small slump flow and low air content of the concrete, the pumpability is poor, and pipe blockage occurred during the spraying process.

[0088] Comparative Example 3 is high-performance sprayed concrete with too large water-binder ratio and air content. Due to the large amount of free water in the concrete and the presence of many bubbles inside, the self-compactness is poor, resulting in low strength of the concrete at the age of hardening.

[0089] Comparative Example 4 is sprayed concrete incorporated with low-dosage early-strength and compactness-enhancing supplementary cementitious materials. Since the dosage of the functional materials is low, the accelerating and early-strength effects and the compacting filling effects are relatively weak. Therefore, the strength of the prepared sprayed concrete is lower compared with the examples, but the overall mechanical properties and durability can still be significantly improved compared with the blank group.

[0090] Comparative Example 5 is sprayed concrete incorporated with high-dosage early-strength components. Due to the excessive early-strength components, the early hydration is rapid and the hydration heat is large. Therefore, cracking occurred in the concrete.

[0091] Comparative Example 6 is sprayed concrete incorporated with early-strength and compactness-enhancing supplementary cementitious materials without using a dispersant. Since no dispersant is used, calcium salts and silicate salts are prone to aggregation and precipitation, and the effective components in the liquid are reduced. Therefore, the early-strength effect is relatively poor.

[0092] Comparative Example 7 is high-performance sprayed concrete without incorporating a rheology regulator. The lack of a rheology regulator results in poor bond strength of the sprayed concrete. During the actual spraying process, the adhesion between the concrete and the rock surface is poor, resulting in a high rebound rate of the sprayed concrete.

[0093] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An early high-strength, high-durability, low-rebound shotcrete, characterized by: The invention comprises the following raw materials in parts by weight: 420-500 parts of cement, 800-900 parts of coarse aggregate, 800-900 parts of fine aggregate, 120-170 parts of water, 3.8-5.5 parts of admixture, 2.5-4 parts of early strength and solidification auxiliary cementitious material, and 2.5-4 parts of fluorine-free and alkali-free high-concentration quick-setting agent; wherein the early strength and solidification auxiliary cementitious material comprises two types: early strength and solidification auxiliary cementitious material (powder) and early strength and solidification auxiliary cementitious material (liquid), and the two can be used alone or together.

2. The early high-strength, high-durability, low-rebound shotcrete according to claim 1, characterized in that The early strength and solidification auxiliary cementitious material (liquid) is a suspension with a calcium-silicon ratio of 0.6 to 2 prepared by a co-precipitation method using calcium salt, silicon salt and a dispersant; the calcium salt is at least one of calcium nitrate, calcium sulfate, calcium hypochlorite, calcium bromide, calcium fluoride, calcium iodate, calcium nitrite and calcium oxalate; the silicon salt is at least one of sodium silicate, aluminum silicate, potassium silicate, sodium metasilicate and potassium metasilicate; and the dispersant is a polycarboxylic acid.

3. The early high-strength, high-durability, low-rebound shotcrete according to claim 1, characterized in that The early strength and solidification type auxiliary cementitious material (powder) is composed of an early strength component and a solidification component, wherein the early strength component accounts for 20% to 40% by weight, and the solidification component accounts for 60% to 80% by weight; the early strength component is at least one of calcium sulfate, tricalcium aluminate, sodium sulfate, magnesium sulfate, and potassium sulfate; the solidification component is at least one of silica fume, fly ash, slag powder, and stone powder.

4. The early high-strength, high-durability, low-rebound shotcrete according to claim 1, characterized in that The fluorine-free and alkali-free high-concentration accelerating setting agent meets the requirements of fluoride ion and alkali content <0.05%, initial setting time of pure slurry (5°C) ≤5min, final setting time of pure slurry (5°C) ≤10min, mortar 28d compressive strength ratio (80°C) ≥90%, and stability (-10°C) ≤5mL.

5. The early high-strength, high-durability, low-rebound shotcrete according to claim 1, characterized in that The cement is P·O42.5 ordinary Portland cement; the fine aggregate is river sand or machine-made sand with a fineness modulus of 2.3-3.0; the coarse aggregate is crushed stone with a particle size of 5-8 mm; the rheology regulator is at least one of cellulose ether, redispersible latex powder, xanthan gum, Wenlun gum, and guar gum; the admixture is a polycarboxylic acid high-performance water-reducing agent with a water reduction rate of ≥25%.

6. The early high-strength, high-durability, low-rebound shotcrete according to claim 1, characterized in that The fiber is at least one of basalt fiber, polypropylene fiber, polyethylene fiber and polyvinyl alcohol fiber.

7. The early high-strength, high-durability, low-rebound shotcrete according to any one of claims 1 to 6, characterized in that The sprayed concrete has an expansion degree of 400-600 mm and an air content of 4-6%.

8. A method for preparing early high-strength, high-durability, low-rebound shotcrete according to any one of claims 1 to 6, characterized in that The following steps are involved: (1) Add cement, fine aggregate, coarse aggregate, early strength enhancing auxiliary cementitious material (powder) into the mixer and stir for 30 seconds to obtain a dry mix; (2) Add water, early strength and solidification type auxiliary cementitious material (liquid), rheology regulator and admixture to the dry mix and stir for 3 minutes to obtain a concrete mixture; (3) Add the mixture into the wet spraying equipment, mix it with the accelerator and then spray it onto the sprayed surface to obtain early high-strength, high-durability and low-rebound sprayed concrete.

9. The method for preparing early high-strength, high-durability, low-rebound shotcrete according to claim 7, characterized in that: In the step (3), the spraying angle when spraying to the sprayed surface is 75-90°; the spraying distance is 1.0-1.5 m; the spraying wind pressure is 0.3-0.6 MPa; the movement trajectory of the nozzle is linear reciprocating or circular rotation horizontal movement; the spraying thickness of the side wall is 8-15 cm, and the spraying thickness of the vault is 6-10 cm.

10. Application of the early high-strength, high-durability, low-rebound shotcrete according to any one of claims 1 to 7 in tunnel and slope support.