High-toughness high-ductility low-resilience sprayed concrete and construction method thereof

Abstract

The invention discloses high-toughness, high-ductility and low-resilience shotcrete and a construction method thereof, and relates to the technical field of shotcrete. The invention provides high-toughness, high-ductility and low-resilience sprayed concrete. The high-toughness, high-ductility and low-resilience sprayed concrete is prepared from the following raw materials in parts by mass: 430 to 450 parts of cement, 20 to 30 parts of admixture, 15 to 20 parts of composite fiber, 870 to 890 parts of fine aggregate, 870 to 890 parts of coarse aggregate, 0.5 to 1 part of reinforcing agent, 5 to 7 parts of water reducing agent, 20 to 30 parts of accelerator and 170 to 185 parts of water. The invention provides a tunnel wet spraying process of the sprayed concrete, the sprayed concrete prepared by the invention has lower requirements on the coagulation accelerating effect of the liquid accelerator, has better cohesiveness with a surrounding rock matrix, can improve the single-time spraying thickness of the concrete during construction, shortens the spraying cycle times, and improves the construction efficiency. The problem of aggregate and fiber scattering caused by overlong spraying distance of the aggregate is solved, the construction progress can be accelerated, and the rebound rate of the concrete is reduced. The high toughness and high ductility of the concrete can effectively reduce early deformation of the surrounding rock, and the construction quality and the construction safety are ensured.

Description

Technical Field

[0001] This invention relates to the field of shotcrete technology, and particularly to high-toughness, high-ductility, low-rebound shotcrete and its construction method. Background Technology

[0002] With the continuous increase in the total number of tunnel projects in my country, various types of tunnels are gradually coming into the view of engineers. Shotcrete is one of the most commonly used materials in the initial support process of tunnels. Compared with the traditional concrete pouring method, shotcrete is rapidly delivered to the sprayed surface under the high pressure of compressed air, and achieves the purpose of rapid support without formwork through the rapid setting effect of liquid quick-setting agent.

[0003] Depending on the construction method, shotcrete is divided into wet spraying and dry spraying. Wet spraying has advantages such as controllable concrete rebound, less construction dust, and stable concrete quality; therefore, it has gradually replaced dry spraying and become the mainstream construction method. However, due to the uncertainty of the surrounding rock conditions of tunnels in my country and the volatility of drill-and-blast excavation, shotcrete still experiences excessive rebound in actual use. The fallen concrete cannot be reused, resulting in significant waste. After spraying, the concrete must not only bear the loads from the early convergence and deformation of the surrounding rock in a short period of time, but also resist the disturbance of the matrix caused by subsequent construction processes.

[0004] Therefore, designing a high-toughness, high-ductility, low-rebound shotcrete with good construction performance, reduced concrete rebound before construction, and good surrounding rock bearing capacity after construction is essential. This would not only effectively reduce construction costs, improve construction efficiency and quality, but also effectively reduce construction risks, thus having significant promotion and application value. Summary of the Invention

[0005] This invention provides a high-toughness, high-ductility, low-rebound shotcrete and its construction method. The prepared high-toughness, high-ductility, low-rebound shotcrete exhibits good workability and can effectively reduce the problem of excessive concrete rebound rate caused by factors such as weak surrounding rock and over-excavation during actual construction. Simultaneously, this shotcrete possesses good flexural toughness and tensile ductility, which can effectively improve the load-bearing capacity and deformation resistance of the shotcrete to the surrounding rock matrix, extending the service life of the tunnel. Specifically, this is achieved through the following technologies.

[0006] This invention provides a high-toughness, high-ductility, low-rebound shotcrete, the raw materials of which include, by weight, 430-450 parts cement, 20-30 parts admixture, 15-20 parts composite fiber, 870-890 parts fine aggregate, 870-890 parts coarse aggregate, 0.5-1 part reinforcing agent, 5-7 parts water-reducing agent, 20-30 parts quick-setting agent, and 170-185 parts water;

[0007] The admixture is composed of silica fume, microsphere powder and nano silica;

[0008] The composite fiber is prepared by ultrasonically treating steel fiber, polypropylene fiber and polyvinyl alcohol fiber in a silane coupling agent ethanol solution, a nano-SiO2 aqueous solution and a tetraethyl orthosilicate ethanol solution in sequence.

[0009] Furthermore, the mass ratio of the steel fiber, polypropylene fiber, and polyvinyl alcohol fiber is (6-8):(1-3):1.

[0010] Furthermore, the mass ratio of the steel fiber, polypropylene fiber, and polyvinyl alcohol fiber is 7:2:1.

[0011] Furthermore, in the admixture, the mass ratio of silica fume, microsphere powder and nano silica is (15-17):(3-5):1.

[0012] Furthermore, in the admixture, the mass ratio of silica fume, microsphere powder, and nano silica is 15:4:1.

[0013] Furthermore, the reinforcing agent is composed of EVA latex powder, 1788 type PVA and xanthan gum; the mass ratio of EVA latex powder, 1788 type PVA and xanthan gum is (3.2-3.6):(0.5-1):1.

[0014] Furthermore, the mass ratio of the EVA latex powder, type 1788 PVA, and xanthan gum is 3.5:0.5:1.

[0015] Furthermore, its raw materials, by weight, include 440 parts cement, 25 parts admixture, 20 parts composite fiber, 880 parts fine aggregate, 875 parts coarse aggregate, 0.8 parts reinforcing agent, 5.6 parts water-reducing agent, 24 parts quick-setting agent, and 180 parts water.

[0016] Optionally, in preparing high-toughness, high-ductility, and low-rebound shotcrete, the specific parameters of each raw material can be selected as follows:

[0017] (1) Cement can be any brand and grade of cement available on the market; specifically, P·O 42.5 ordinary Portland cement can be selected;

[0018] (2) In the admixture, the silica fume is in spherical form with a bulk density ≥700 kg / m³. 3 The microsphere powder consists of hollow glass microspheres; the nano-silica particles have a diameter of 20-50 nm.

[0019] (3) Among the raw materials of composite fibers, steel fibers are hooked at the ends and can be selected in length 30 mm; polypropylene fibers are mesh-like and can be selected in length 30 mm; and polyvinyl alcohol fibers can be selected in length 12 mm.

[0020] (4) In the preparation method of composite fiber, the concentration of silane coupling agent-ethanol solution is 5 wt%, the concentration of nano SiO2 aqueous solution is 5 g / L, and the concentration of tetraethyl orthosilicate-ethanol solution is 5 wt%; silane coupling agent can be commercially available types, such as KH-550, KH-560, KH-570, etc.

[0021] (5) Any commercially available fine aggregate can be selected (e.g., river sand, manufactured sand, etc.). For example, medium sand from Zone II with a fineness modulus of 2.6-2.8 and a mud content of ≤2.0% can be selected.

[0022] (6) Any commercially available coarse aggregate can be selected, specifically crushed stone with a particle size of 5-10 mm;

[0023] (7) Any commercially available water-reducing agent can be selected, specifically a high-performance polycarboxylate water-reducing agent with a water reduction rate of 20%;

[0024] (8) An alkali-free liquid accelerator can be selected as the accelerator; when it accounts for 6% of the total cementitious material content, its performance can meet the requirements of GB / T35159-2017 "Accelerator for Shotcrete";

[0025] (9) The mixing water meets the requirements of JGJ 63-2006 "Standard for Water Used in Concrete".

[0026] The final high-toughness, high-ductility, and low-rebound shotcrete has a slump of 210-240 mm, a spread of 420-480 mm, and an emptying time of ≤12 s in an inverted slump bucket, with no bleeding or bottoming issues.

[0027] The present invention also provides a construction method for the above-mentioned high-toughness, high-ductility, low-rebound shotcrete, which uses the high-toughness, high-ductility, low-rebound shotcrete to spray the side or wall of a tunnel, including the following steps:

[0028] The raw materials of the high-toughness, high-ductility, low-resilience shotcrete, excluding the aforementioned quick-setting agent, are formulated into a slurry.

[0029] A colored tarpaulin is laid under the tunnel face to be constructed, ensuring that the tarpaulin is evenly and completely positioned below the sprayed surface.

[0030] Add the quick-setting agent and the slurry, adjust the air pressure to 0.7-0.9 MPa, and perform spraying operation on the sprayed surface.

[0031] Furthermore, during the spraying operation:

[0032] The angle between the nozzle and the surface to be sprayed is 80°-90°, and the spraying distance is 0.3-0.6 m;

[0033] The spraying method is from top to bottom, with a single spray thickness of 25-40 cm and a spraying frequency of 2 times;

[0034] After the first sprayed high-toughness, high-ductility, low-rebound shotcrete has set, the second spraying will be carried out.

[0035] Compared with the prior art, the advantages of the present invention are:

[0036] 1. This invention introduces adhesive modifiers such as silica fume, microsphere powder, and nano-silica into shotcrete, which significantly improves the cohesiveness and thixotropic properties of the concrete while ensuring good workability, thereby enhancing the bond strength between the concrete itself and the surrounding rock matrix. The admixtures can also fill the voids within the shotcrete, improving its density and impermeability to a certain extent.

[0037] 2. The composite fiber selected in this invention improves its adhesion to the concrete matrix at the interface. While ensuring that the shotcrete has good bending toughness and ductility, it greatly reduces the impact of single steel fiber on the concrete state and the wear of the shotcrete hose.

[0038] 3. The reinforcing agent selected in this invention, in combination with the use of composite fibers, plays a synergistic role in improving the toughness and ductility of concrete, thereby ensuring better overall performance of sprayed concrete.

[0039] 4. The concrete prepared and sprayed using the raw materials and preparation method of the present invention has a compressive strength of more than 10 MPa at 8 hours, more than 20 MPa at 1 day, and more than 45 MPa at 28 days. The overall rebound rate of the concrete is less than 8%, and the sprayed concrete does not exhibit problems such as cracking, falling off, or water seepage during subsequent curing.

[0040] 5. High-toughness, high-elongation, and low-rebound shotcrete uses readily available raw materials, has a simple production process, and a mature wet-spraying construction process, making it suitable for the increasingly complex construction conditions in the initial support of tunnels today. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] In some embodiments of the present invention, the raw materials of the high-toughness, high-ductility, low-rebound shotcrete provided include, by weight, 430-450 parts of cement, 20-30 parts of admixture, 15-20 parts of composite fiber, 870-890 parts of fine aggregate, 870-890 parts of coarse aggregate, 0.5-1 part of reinforcing agent, 5-7 parts of water-reducing agent, 20-30 parts of quick-setting agent, and 170-185 parts of water;

[0043] The admixture is composed of silica fume, microsphere powder and nano silica;

[0044] The composite fiber is prepared by ultrasonically treating steel fiber, polypropylene fiber and polyvinyl alcohol fiber in a silane coupling agent ethanol solution, a nano-SiO2 aqueous solution and a tetraethyl orthosilicate ethanol solution in sequence.

[0045] Optionally, the mass ratio of the steel fiber, polypropylene fiber and polyvinyl alcohol fiber is (6-8):(1-3):1.

[0046] Specifically, the mass ratio of the steel fiber, polypropylene fiber, and polyvinyl alcohol fiber is 7:2:1.

[0047] Specifically, the method for preparing the composite fiber used in this invention is as follows:

[0048] (1) Add steel fiber, polypropylene fiber and polyvinyl alcohol fiber to a 5% silane coupling agent-ethanol solution at a mass ratio of 70:20:10 and sonicate for 30 min; filter out the filtrate, wash the fibers with anhydrous ethanol and let them stand and dry for 24 h.

[0049] (2) The preliminarily modified fibers were ultrasonically treated in a 5 g / L nano-SiO2 aqueous solution for 3 h;

[0050] (3) The fiber is then placed in a 5 wt% tetraethyl orthosilicate ethanol solution and sonicated for 3 h; filtered, washed with anhydrous ethanol, and dried to obtain the modified composite fiber product.

[0051] Optionally, the mass ratio of silica fume, microsphere powder and nano silica in the admixture is (15-17):(3-5):1.

[0052] Specifically, in the admixture, the mass ratio of silica fume, microsphere powder and nano silica is 15:4:1.

[0053] Optionally, the reinforcing agent is composed of EVA latex powder, type 1788 PVA and xanthan gum; the mass ratio of EVA latex powder, type 1788 PVA and xanthan gum is (3.2-3.6):(0.5-1):1.

[0054] Optionally, the mass ratio of the EVA latex powder, type 1788 PVA and xanthan gum is 3.5:0.5:1.

[0055] Optionally, the raw materials include, by weight, 440 parts cement, 25 parts admixture, 20 parts composite fiber, 880 parts fine aggregate, 875 parts coarse aggregate, 0.8 parts reinforcing agent, 5.6 parts water-reducing agent, 24 parts quick-setting agent, and 180 parts water.

[0056] Optionally, in preparing high-toughness, high-ductility, and low-rebound shotcrete, the specific parameters of each raw material can be selected as follows:

[0057] (1) Cement can be any brand and grade of cement available on the market; specifically, Yangfang brand P·O 42.5 ordinary Portland cement can be selected;

[0058] (2) In the admixture, the silica fume is in spherical form with a bulk density ≥700 kg / m³. 3 The microsphere powder consists of hollow glass microspheres; the nano-silica particles have a diameter of 20-50 nm.

[0059] (3) Among the raw materials of composite fibers, steel fibers are hooked at the end and can be selected in length 30 mm; polypropylene fibers are mesh-like and can be selected in length 30 mm; and polyvinyl alcohol fibers can be selected in length 12 mm.

[0060] (4) In the preparation method of composite fiber, the concentration of silane coupling agent-ethanol solution is 5 wt%, the concentration of nano SiO2 aqueous solution is 5 g / L, and the concentration of tetraethyl orthosilicate-ethanol solution is 5 wt%; silane coupling agent can be commercially available types, such as KH-550, KH-560, KH-570, etc.

[0061] (5) Any commercially available fine aggregate can be selected (e.g., river sand, manufactured sand, etc.). For example, medium sand from Zone II with a fineness modulus of 2.6-2.8 and a mud content of ≤2.0% can be selected.

[0062] (6) Any commercially available coarse aggregate can be selected, specifically crushed stone with a particle size of 5-10 mm;

[0063] (7) Any commercially available water-reducing agent can be selected, specifically high-performance polycarboxylate water-reducing agent. The product has a water reduction rate of 20%, and is mainly composed of water-reducing mother liquor, slump-preserving mother liquor and various small materials.

[0064] (8) An alkali-free liquid accelerator can be selected as the accelerator; when it accounts for 6% of the total cementitious material content, its performance can meet the requirements of GB / T35159-2017 "Accelerator for Shotcrete";

[0065] (9) The mixing water meets the requirements of JGJ 63-2006 "Standard for Water Used in Concrete".

[0066] In some embodiments of the present invention, the methods of using other raw materials for high-toughness, high-ductility, and low-rebound shotcrete, besides the accelerator, are as follows:

[0067] S1 Add the weighed fine aggregate, coarse aggregate, composite fiber and reinforcing agent into the mixer, start the mixer and premix for 30 seconds;

[0068] S2. Add cement and admixtures separately, and continue mixing for 30 seconds to obtain dry mix;

[0069] S3. Add water and water-reducing agent to the dry mix separately, and continue stirring for 180 seconds to obtain the sprayed concrete slurry.

[0070] The final high-toughness, high-ductility, low-rebound shotcrete has a total cementitious material content ≥430 kg / m³. 3 The water-cement ratio is 0.36-0.41, the sand ratio is 0.49-0.51, the slump is 210-240 mm, the spread is 420-480 mm, the emptying time of the inverted slump bucket is ≤12 s, and there is no problem of water seepage or bottom scrambling.

[0071] The present invention also provides a construction method for the above-mentioned high-toughness, high-ductility, low-rebound shotcrete, which uses the high-toughness, high-ductility, low-rebound shotcrete to spray the side or wall of a tunnel, including the following steps:

[0072] The raw materials of the high-toughness, high-ductility, low-resilience shotcrete, excluding the aforementioned quick-setting agent, are formulated into a slurry.

[0073] A colored tarpaulin is laid under the tunnel face to be constructed, ensuring that the tarpaulin is evenly and completely positioned below the sprayed surface.

[0074] Add the quick-setting agent and the slurry, adjust the air pressure to 0.7-0.9 MPa, and perform spraying operation on the sprayed surface.

[0075] Furthermore, during the spraying operation:

[0076] The angle between the nozzle and the surface to be sprayed is 80°-90°, and the spraying distance is 0.3-0.6 m;

[0077] The spraying method is from top to bottom, with a single spray thickness of 25-40 cm and no more than 2 sprays.

[0078] After the first sprayed high-toughness, high-ductility, low-rebound shotcrete has set, the second spraying will be carried out.

[0079] Example 1

[0080] The high-toughness, high-ductility, low-rebound shotcrete provided in this embodiment comprises, by weight, 430 parts cement, 20 parts admixture, 20 parts composite fiber, 885 parts fine aggregate, 885 parts coarse aggregate, 0.8 parts reinforcing agent, 5.4 parts water-reducing agent, 22 parts quick-setting agent, and 180 parts water.

[0081] Besides accelerators, the usage methods for other concrete raw materials are as follows:

[0082] S1 Add the weighed fine aggregate, coarse aggregate, composite fiber and reinforcing agent into the mixer, start the mixer and premix for 30 seconds;

[0083] S2. Add cement and admixtures separately, and continue mixing for 30 seconds to obtain dry mix;

[0084] S3. Add water and water-reducing agent to the dry mix separately, and continue stirring for 180 seconds to obtain the sprayed concrete slurry.

[0085] Example 2

[0086] The high-toughness, high-ductility, low-rebound shotcrete provided in this embodiment comprises, by weight, 430 parts cement, 30 parts admixture, 15 parts composite fiber, 885 parts fine aggregate, 880 parts coarse aggregate, 0.5 parts reinforcing agent, 5.5 parts water-reducing agent, 26 parts quick-setting agent, and 180 parts water.

[0087] The preparation method of the high-toughness, high-ductility, low-rebound shotcrete in this embodiment is the same as that in Example 1.

[0088] Example 3

[0089] The high-toughness, high-ductility, low-rebound shotcrete provided in this embodiment comprises, by weight, 440 parts cement, 25 parts admixture, 15 parts composite fiber, 880 parts fine aggregate, 880 parts coarse aggregate, 0.5 parts reinforcing agent, 5.6 parts water-reducing agent, 23 parts quick-setting agent, and 180 parts water.

[0090] The preparation method of the high-toughness, high-ductility, low-rebound shotcrete in this embodiment is the same as that in Example 1.

[0091] Example 4

[0092] The high-toughness, high-ductility, low-rebound shotcrete provided in this embodiment comprises, by weight, 440 parts cement, 25 parts admixture, 20 parts composite fiber, 880 parts fine aggregate, 875 parts coarse aggregate, 0.8 parts reinforcing agent, 5.6 parts water-reducing agent, 24 parts quick-setting agent, and 180 parts water.

[0093] The preparation method of the high-toughness, high-ductility, low-rebound shotcrete in this embodiment is the same as that in Example 1.

[0094] Example 5

[0095] The high-toughness, high-ductility, low-rebound shotcrete provided in this embodiment comprises, by weight, 450 parts cement, 20 parts admixture, 20 parts composite fiber, 875 parts fine aggregate, 875 parts coarse aggregate, 0.8 parts reinforcing agent, 5.6 parts water-reducing agent, 30 parts quick-setting agent, and 185 parts water.

[0096] The preparation method of the high-toughness, high-ductility, low-rebound shotcrete in this embodiment is the same as that in Example 1.

[0097] Example 6

[0098] The high-toughness, high-ductility, low-rebound shotcrete provided in this embodiment comprises, by weight, 450 parts cement, 30 parts admixture, 15 parts composite fiber, 875 parts fine aggregate, 870 parts coarse aggregate, 0.5 parts reinforcing agent, 5.5 parts water-reducing agent, 30 parts quick-setting agent, and 185 parts water.

[0099] The preparation method of the high-toughness, high-ductility, low-rebound shotcrete in this embodiment is the same as that in Example 1.

[0100] Comparative Example 1

[0101] The sprayed concrete provided in this comparative example contains, by weight, 430 parts cement, 30 parts composite fiber, 885 parts fine aggregate, 880 parts coarse aggregate, 0.5 parts reinforcing agent, 5.5 parts water-reducing agent, 26 parts quick-setting agent, and 180 parts water; that is, the raw materials do not contain admixtures.

[0102] Besides the accelerator, the usage methods for other raw materials in the concrete of this comparative example are as follows:

[0103] S1 Add the weighed fine aggregate, coarse aggregate, composite fiber and reinforcing agent into the mixer, start the mixer and premix for 30 seconds;

[0104] S2. Add cement separately and continue mixing for 30 seconds to obtain dry mix;

[0105] S3. Add water and water-reducing agent to the dry mix separately, and continue stirring for 180 seconds to obtain the sprayed concrete slurry.

[0106] Comparative Example 2

[0107] The sprayed concrete provided in this comparative example contains, by weight, 450 parts cement, 20 parts admixture, 875 parts fine aggregate, 875 parts coarse aggregate, 0.8 parts reinforcing agent, 5.6 parts water-reducing agent, 30 parts quick-setting agent, and 185 parts water; that is, the raw materials do not contain composite fibers.

[0108] Besides the accelerator, the usage methods for other raw materials in the concrete of this comparative example are as follows:

[0109] S1 Add the weighed fine aggregate, coarse aggregate and reinforcing agent into the mixer, start mixing and premix for 30 seconds;

[0110] S2. Add cement and admixtures separately, and continue mixing for 30 seconds to obtain dry mix;

[0111] S3. Add water and water-reducing agent to the dry mix separately, and continue stirring for 180 seconds to obtain the sprayed concrete slurry.

[0112] Comparative Example 3

[0113] The sprayed concrete provided in this comparative example uses the same raw materials as in Example 2 by weight. The admixture is made by mixing silica fume and microsphere powder at a weight ratio of 15:4; that is, the raw materials of the admixture do not contain nano-silica.

[0114] The preparation method and construction method of the high-toughness, high-ductility, low-rebound shotcrete in this comparative example are the same as those in Example 1.

[0115] Comparative Example 4

[0116] The sprayed concrete provided in this comparative example uses the same raw materials as in Example 2 by weight. The admixture is made by mixing silica fume and nano-silica at a weight ratio of 15:1; that is, the raw materials of the admixture do not contain microspheres.

[0117] The preparation method and construction method of the high-toughness, high-ductility, low-rebound shotcrete in this comparative example are the same as those in Example 1.

[0118] Comparative Example 5

[0119] The sprayed concrete provided in this comparative example uses the same raw materials as in Example 2 by weight. The admixture is made by mixing microsphere powder and nano-silica at a weight ratio of 4:1; that is, the raw materials of the admixture do not contain silica fume.

[0120] The preparation method and construction method of the high-toughness, high-ductility, low-rebound shotcrete in this comparative example are the same as those in Example 1.

[0121] Comparative Example 6

[0122] The high-toughness, high-ductility, and low-rebound shotcrete provided in this embodiment uses the same raw materials by weight as in Example 5. The composite fiber is made by directly mixing ordinary steel fibers, polypropylene fibers, and polyvinyl alcohol fibers; that is, the composite fiber has not undergone any treatment.

[0123] The preparation method and construction method of the high-toughness, high-ductility, low-rebound shotcrete in this comparative example are the same as those in Example 1.

[0124] Comparative Example 7

[0125] The sprayed concrete provided in this comparative example uses the same raw materials as those in Example 1 by weight.

[0126] The method for preparing the composite fiber used in this comparative example is as follows:

[0127] (1) Add steel fiber, polypropylene fiber and polyvinyl alcohol fiber to a 5% silane coupling agent-ethanol solution at a mass ratio of 70:20:10, and sonicate for 30 min; filter out the filtrate, wash the above fibers with anhydrous ethanol, and let stand and dry for 24 h.

[0128] (2) The preliminarily modified fiber was ultrasonically treated in a 5 g / L nano-SiO2 aqueous solution for 3 h, filtered, washed with anhydrous ethanol, and allowed to stand and dry to obtain the modified composite fiber product. That is, the composite fiber was not ultrasonically treated with tetraethyl orthosilicate ethanol solution.

[0129] The preparation method and construction method of the high-toughness, high-ductility, low-rebound shotcrete in this comparative example are the same as those in Example 1.

[0130] Comparative Example 8

[0131] The sprayed concrete provided in this comparative example uses the same raw materials as those in Example 1 by weight.

[0132] The method for preparing the composite fiber used in this comparative example is as follows:

[0133] (1) Add steel fiber, polypropylene fiber and polyvinyl alcohol fiber to a 5% silane coupling agent-ethanol solution at a mass ratio of 70:20:10, and sonicate for 30 min; filter out the filtrate, wash the above fibers with anhydrous ethanol, and let stand and dry for 24 h.

[0134] (2) The preliminarily modified fiber was ultrasonically treated in 5 wt% tetraethyl orthosilicate for 3 h, filtered, washed with anhydrous ethanol, and allowed to stand and dry to obtain the modified composite fiber product. That is, the composite fiber was not ultrasonically treated with nano-SiO2 aqueous solution.

[0135] The preparation method and construction method of the high-toughness, high-ductility, low-rebound shotcrete in this comparative example are the same as those in Example 1.

[0136] Experimental Example: Construction and Specimen Performance Testing of Shotcrete

[0137] This application example utilizes the shotcrete provided in the above embodiments and comparative examples, employing a wet spraying method for construction. The construction process and specimen performance testing process are as follows:

[0138] 1. Equipment connection and debugging

[0139] Complete the power connection work for the wet spraying machine and air compressor, and confirm the normal extension, retraction and folding of the robotic arm.

[0140] The operation of the air compressor and accelerator pumping system was tested. The equipment's piping was lubricated by spraying tap water to ensure that the overall operation of the equipment was normal.

[0141] After the commissioning is completed, empty the water remaining in the hopper and pipes.

[0142] 2. Production and construction of shotcrete

[0143] Before the actual spraying, the rock strata on the sprayed surface are inspected and treated to ensure the stability of the surrounding rock matrix itself.

[0144] After laying the colored tarpaulin under the tunnel face to be constructed, ensuring that the tarpaulin is evenly and completely positioned below the spraying surface, the robotic arm is extended to the spraying point and the air compressor and accelerator pump are turned on. Once the accelerator is atomized and sprayed from the nozzle, the shotcrete is fed into the hopper of the wet shotcrete machine. Then, the concrete pumping system is turned on, and the shotcrete operation officially begins.

[0145] 3. Construction parameter requirements

[0146] Adjust the air pressure to 0.7-0.9 MPa, and adjust the dosage of the accelerator in real time according to the actual construction location. The application of the accelerator follows the principle of bottom-up, gradually increasing. The minimum dosage is used on the sidewalls, followed by the arch foot, and the maximum dosage is used at the arch crown. The optimal dosage is the minimum amount required to prevent localized concrete spalling.

[0147] During construction, the angle between the nozzle and the surface to be sprayed should be controlled at 80°-90°, and the spraying distance should be controlled at 0.3-0.6 m. Spraying should be carried out from bottom to top, with a single spray thickness of 25-40 cm, and the number of round trips should be 2.

[0148] After the first layer of concrete has set, the second layer of spraying is carried out to ensure adhesion between the concrete layers.

[0149] Finally, the surface sweeping work is completed according to the design requirements. The swept concrete must completely cover the steel arch frame and other steel reinforcement structures. At the same time, the concrete surface should be sprayed to a smooth surface, and there should be no voids between the concrete and the surrounding rock matrix. Excess concrete shoveled off the arch frame after construction is not included in the scope of fallen concrete.

[0150] After construction is completed, the concrete that has fallen off the tarpaulin should be collected, and the excess concrete on the steel arch frame should be removed in a timely manner.

[0151] Generally, the production and mixing time of the above-mentioned shotcrete is controlled at ≥180 s, and the total time from production to completion of construction is ≤120 min.

[0152] 4. Testing the rebound rate of shotcrete

[0153] The rebound rate index test was carried out according to the method mentioned in Appendix G of JGJ / T 372-2016 "Technical Specification for Application of Shotcrete".

[0154] When conducting the rebound rate test, the entire arch frame must be sprayed in one go, and the spraying area should cover the entire cross-section of the tunnel except for the invert arch. The concrete that falls during spraying should be collected, and the rebound rate should be tested using a gravimetric method. The amount of accelerator used is calculated based on the height h (unit: m) of the drop in the liquid level in the ton container on the wet spraying machine, where the surface area of ​​the ton container is 1 m². 2 The following parameters also need to be measured during the testing process: the total mass of concrete weighed on the tarpaulin, m1 (kg), and the total volume of concrete sprayed, f (m³). 3 The unit weight of concrete is ρ1 (kg / m³). 3 The total volume of accelerator consumed by the wet spraying machine is L (m³). 3 The density of the quick-setting agent is ρ2 (Kg / m³). 3 The total volume of accelerator consumed was measured to be L = h × 1 (unit: m³). 3 The formula for calculating the rebound rate HT is:

[0155] .

[0156] 5. Shotcreting, curing, and performance testing of shotcrete specimens

[0157] Adjust the accelerator to the appropriate amount. During the molding process, keep the nozzle perpendicular to the bottom of the mold and complete the spray molding of the corresponding specimen from bottom to top. After molding, remove the excess concrete from the mold, record the molding time, and complete the molding of large slab (450 mm × 350 mm × 120 mm) and round slab (φ800 mm × 90 mm) specimens in the same way.

[0158] Shotcrete needs to be watered for curing approximately 2 hours after final setting, and the concrete surface should be kept moist for 1 day. After that, the frequency of watering should be adjusted to once a day until curing is completed within 14 days. Watering should not be carried out when the temperature is below 5℃.

[0159] The sprayed specimens must not be moved before final setting. After final setting, the specimens should be handled with care to avoid disturbance caused by human factors and should be placed in a standard curing room for curing.

[0160] After curing, the sprayed slab was cut into 100 mm × 100 mm × 100 mm cube specimens. The relevant tests were conducted in accordance with the requirements of GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" and GB / T 50081-2019 "Test Methods of Mechanical Properties of Ordinary Concrete", and the workability and mechanical properties were tested. The flexural toughness was tested in accordance with CECS13:2009 "Standard for Test Methods of Fiber Reinforced Concrete".

[0161] The test results of slump, spread, collapse time, and compressive strength at different ages of shotcrete are shown in Table 1; the test results of splitting tensile strength, flexural toughness, and rebound rate are shown in Table 2.

[0162] Table 1

[0163] As can be seen from the test results in Table 1, the shotcrete in Examples 1-6 all have good workability. After the addition of liquid accelerator, the early strength of the concrete increases significantly, and the concrete can play a bearing role on the surrounding rock matrix at an early age. At the same time, the later strength of the concrete basically reaches the C45 strength grade requirement, which has a positive significance for the subsequent stabilization of the tunnel.

[0164] Further comparison of the data from the examples in Table 1 shows that the addition of admixtures and composite fibers did not cause a loss of concrete fluidity or affect its workability. Further comparison of the data from Examples 2 and 3 in Table 1 shows that the admixtures optimized the fluidity of the concrete to a certain extent. This may be due to the balling effect of spherical silica fume and microsphere powder.

[0165] Comparing the data from Examples 3 and 4 in Table 1, it can be seen that the composite fiber affects the initial state of the concrete to a certain extent, and the effect becomes more pronounced with increasing dosage. However, in actual wet spraying construction, the concrete spraying effect was normal.

[0166] Comparing the data from Example 2 and Comparative Example 1, it can be seen that the concrete without admixtures has lower strength at all ages. Comparing Comparative Examples 3-5, it was found that microspheres can improve the concrete condition, silica fume has a better reinforcing effect, and nano-silica has more balanced properties.

[0167] Comparing the data in Example 5 and Comparative Example 2, it can be seen that the concrete without composite fibers has low cohesion, greater fluidity, and little difference in strength at different ages.

[0168] Compared with Example 5 and Comparative Example 6, the modified fiber's performance in terms of construction and compressive strength is basically the same as that of ordinary fiber.

[0169] Comparative examples 7-8 show that nano-SiO2 and tetraethyl orthosilicate-ethanol solution improve the mechanical strength of composite fibers to some extent.

[0170] In summary, the basic indicators of the shotcrete provided by this invention can meet the requirements for construction and testing.

[0171] Table 2

[0172] As can be seen from the data in Table 2 above, when using this sprayed concrete for wet spraying, except for Comparative Example 1, the concrete rebound rate is controlled within 8%.

[0173] Comparing the rebound rate test data of Examples 2 and 6, Examples 3 and 4, and Examples 1 and 5 in Table 2, it can be seen that within a certain range, the actual rebound rate of shotcrete decreases to some extent as the amount of admixture used increases.

[0174] Comparing Example 2 with Comparative Example 1, Comparative Examples 3-5, it can be seen that the rebound rate of concrete without admixtures is significantly increased. While each component in the admixture has the effect of reducing the rebound rate of concrete, it has little effect on the flexural toughness and splitting strength of concrete.

[0175] With the use of composite fibers, shotcrete exhibits better ductility and toughness. Comparing the test data in Examples 1 and 2, 3 and 4, and 5 and 6 in Table 2, it can be seen that increasing the amount of composite fibers has virtually no effect on the concrete rebound rate, but the splitting tensile strength of the specimens increases, and the composite fibers significantly improve the flexural toughness of the specimens. No brittle fracture was observed in the specimens when reaching the ultimate deflection, and they still possessed a certain load-bearing capacity at a deflection of 50 mm.

[0176] Further comparison of Example 5 with Comparative Examples 6-8 shows that, compared with ordinary fibers, modified fibers have better ductility and toughness. Meanwhile, the silane coupling agent plays the main role in reinforcing and modifying, while the reinforcing effects of nano-SiO2 and tetraethyl orthosilicate-ethanol have certain limitations.

[0177] The high-toughness, high-ductility, and low-rebound shotcrete prepared by this invention has good workability and mechanical properties, while making up for the problems of poor ductility and toughness and high rebound of ordinary concrete. Moreover, the construction method of this technical solution is simple and feasible, and it is easy to promote and apply on a large scale.

[0178] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A high-toughness, high-ductility, low-resilience shotcrete, characterized in that, Its raw materials, by weight, include 430-450 parts cement, 20-30 parts admixture, 15-20 parts composite fiber, 870-890 parts fine aggregate, 870-890 parts coarse aggregate, 0.5-1 part reinforcing agent, 5-7 parts water-reducing agent, 20-30 parts quick-setting agent, and 170-185 parts water; The admixture is composed of silica fume, microsphere powder and nano silica; The composite fiber is prepared by ultrasonically treating steel fiber, polypropylene fiber and polyvinyl alcohol fiber in a silane coupling agent ethanol solution, a nano-SiO2 aqueous solution and a tetraethyl orthosilicate ethanol solution in sequence.

2. The high-toughness, high-ductility, low-resilience shotcrete according to claim 1, characterized in that, The mass ratio of the steel fiber, polypropylene fiber and polyvinyl alcohol fiber is (6-8):(1-3):

1.

3. The high-toughness, high-ductility, low-resilience shotcrete according to claim 2, characterized in that, The mass ratio of the steel fiber, polypropylene fiber and polyvinyl alcohol fiber is 7:2:

1.

4. The high-toughness, high-ductility, low-resilience shotcrete according to claim 1, characterized in that, In the admixture, the mass ratio of silica fume, microsphere powder and nano silica is (15-17):(3-5):

1.

5. The high-toughness, high-ductility, low-resilience shotcrete according to claim 4, characterized in that, In the admixture, the mass ratio of silica fume, microsphere powder and nano silica is 15:4:

1.

6. The high-toughness, high-ductility, low-resilience shotcrete according to claim 1, characterized in that, The reinforcing agent is composed of EVA latex powder, 1788 type PVA and xanthan gum; the mass ratio of EVA latex powder, 1788 type PVA and xanthan gum is (3.2-3.6):(0.5-1):

1.

7. The high-toughness, high-ductility, low-resilience shotcrete according to claim 1, characterized in that, The mass ratio of the EVA latex powder, type 1788 PVA and xanthan gum is 3.5:0.5:

1.

8. The high-toughness, high-ductility, low-resilience shotcrete according to claim 1, characterized in that, Its raw materials, by weight, include 440 parts cement, 25 parts admixture, 20 parts composite fiber, 880 parts fine aggregate, 875 parts coarse aggregate, 0.8 parts reinforcing agent, 5.6 parts water-reducing agent, 24 parts quick-setting agent, and 180 parts water.

9. A construction method for high-toughness, high-ductility, low-resilience shotcrete according to any one of claims 1-8, characterized in that, The process of applying the high-toughness, high-ductility, and low-rebound shotcrete to the sides or walls of a tunnel includes the following steps: The raw materials of the high-toughness, high-ductility, low-resilience shotcrete, excluding the aforementioned quick-setting agent, are formulated into a slurry. A colored tarpaulin is laid under the tunnel face to be constructed, ensuring that the tarpaulin is evenly and completely positioned below the sprayed surface. Add the quick-setting agent and the slurry, adjust the air pressure to 0.7-0.9 MPa, and perform spraying operation on the sprayed surface.

10. The construction method of high-toughness, high-ductility, low-rebound shotcrete according to claim 9, characterized in that, During the spraying operation: The angle between the nozzle and the surface to be sprayed is 80°-90°, and the spraying distance is 0.3-0.6 m; The spraying method is from top to bottom, with a single spray thickness of 25-40 cm and a spraying frequency of 2 times; After the first sprayed high-toughness, high-ductility, low-rebound shotcrete has set, the second spraying will be carried out.

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