A shotcrete and a method for producing the same

Abstract

This invention relates to the field of tunnel engineering technology, specifically to a shotcrete and its preparation method. The shotcrete comprises the following components by weight: 90-120 parts cement, 0-5 parts admixture, 90-600 parts sand, 140-300 parts water, 0-60 parts sodium hydroxide, 0.5-4 parts water-reducing agent, 5-12 parts quick-setting agent, 0-10 parts mixed fiber, and 12-150 parts sawdust. This invention improves the porosity of the mortar by replacing sand with recycled sawdust, reducing its weight and cost. The admixture enhances the bonding properties of the mortar, and the addition of mixed fiber delays cracking and reduces rebound rate. The prepared shotcrete enables tight bonding between the primary support, waterproof layer, and secondary lining, and possesses advantages such as light weight, low rebound rate, high porosity, good permeability, energy saving, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and more specifically, to a sprayed mortar and its preparation method. Background Technology

[0002] In tunnel lining structures, when using sprayed membrane waterproofing technology, a waterproof layer is typically sprayed directly onto the initial shotcrete support surface before constructing the secondary lining, forming a composite structure of the initial support, sprayed membrane waterproofing layer, and secondary lining. However, the initial shotcrete support surface is often uneven, leading to waste of sprayed membrane material and negatively impacting the stress on the waterproofing layer. Therefore, during on-site construction, a non-woven fabric layer is usually placed on the initial support surface for isolation and leveling. Due to the high porosity of the non-woven fabric, it also has a certain drainage capacity, effectively removing seepage water from the initial support surface and relieving water pressure. While this structural design solves the leveling and isolation problems, the non-woven fabric layer is laid in a hanging manner and located between the initial support and the waterproofing layer, resulting in insufficient bonding between the initial support, the sprayed membrane waterproofing layer, and the secondary lining, affecting their combined load-bearing capacity. In some projects, mortar leveling layers are used instead of non-woven fabric layers for leveling. However, replacing non-woven fabric with mortar completely eliminates its water seepage and pressure relief capabilities, increases structural stress, and requires more river sand, making it neither economical nor environmentally friendly. Therefore, current tunnel engineering sprayed membrane waterproof lining structures have not yet been able to simultaneously address issues such as leveling, joint stress distribution, water seepage and pressure relief, and economic and environmental benefits.

[0003] Therefore, there is an urgent need to develop a material for quickly leveling the initial support surface of shotcrete in tunnel engineering, so that the initial support, the waterproof membrane, and the secondary lining are tightly bonded together. At the same time, it should have high porosity and good permeability to allow water to seep through, while also meeting environmental protection requirements.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a sprayed mortar for tunnel lining structures. This sprayed mortar can quickly level the initial support of a tunnel, save on the amount of sprayed membrane material used in a sprayed waterproof lining structure, and ensure a tight bond between the initial support, the waterproof layer, and the secondary lining. This improves the synergistic stress performance of the sprayed waterproof lining in tunnel engineering. Furthermore, compared with ordinary mortar, this sprayed mortar has advantages such as being lightweight, environmentally friendly, having low rebound, high porosity, and strong permeability.

[0006] The second objective of this invention is to provide a method for preparing the aforementioned sprayed mortar, wherein the sprayed mortar prepared by this method can level the initial support, reduce the amount of sprayed film material used, reduce rebound loss, and is simple to operate.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] A first aspect of the present invention provides a sprayed mortar comprising the following components in parts by weight:

[0009] 90-120 parts cement, 0-5 parts admixture, 90-600 parts sand, 140-300 parts water, 0-60 parts sodium hydroxide, 0.5-4 parts water-reducing agent, 5-12 parts quick-setting agent, 0-10 parts mixed fiber and 12-150 parts sawdust.

[0010] This invention introduces sawdust instead of sand into mortar, introducing a large number of pores. Sawdust itself has a distinct porous structure, and its main components are cellulose, hemicellulose, and lignin. In the alkaline environment of the mortar, these components gradually react, corroding and decomposing the sawdust structure, further increasing the porosity. Furthermore, the reaction products of the sawdust can combine with cement hydration products, preventing the cement hydration products from reaching saturation and crystallizing. Additionally, the lignin in the sawdust adheres to the surface of cement particles, giving them the same charge. Due to the repulsion of like charges, further hydration of the cement particles is affected, thus further increasing the porosity of the mortar. Based on these principles, the bulk density of the mortar sample decreases, and its permeability is enhanced. By incorporating admixtures and mixed fibers, the admixtures can improve the bonding performance, and the mixed fibers can act as a "bridge" inside the mortar, delaying cracking and reducing rebound, thus effectively improving the durability of the mortar and enhancing its mechanical properties. This results in the production of lightweight, environmentally friendly, low-rebound, high-porosity, and highly permeable sprayed mortar.

[0011] Preferably, the sprayed mortar comprises the following components in parts by weight:

[0012] 100-120 parts cement, 2-3 parts admixture, 90-500 parts sand, 150-300 parts water, 19-50 parts sodium hydroxide, 0.5-2.5 parts water-reducing agent, 6-10 parts quick-setting agent, 2-5 parts mixed fiber and 24-100 parts sawdust.

[0013] Preferably, the admixture includes silica fume.

[0014] Preferably, the mixed fibers include natural fibers and synthetic fibers.

[0015] Preferably, the mass ratio of the natural fiber to the synthetic fiber is 1:(0.5-5).

[0016] More preferably, the mass ratio of the natural fiber to the synthetic fiber is 1:(0.5-2).

[0017] Preferably, the natural fiber includes cotton fiber, which is made from natural cotton and has a moisture content of less than 1%.

[0018] More preferably, the cotton fibers have a diameter of 5–20 μm and a length of 2–6 mm.

[0019] Preferably, the synthetic fiber comprises polypropylene fiber.

[0020] More preferably, the polypropylene fiber has a diameter of 15–30 μm and a length of 3–6 mm.

[0021] Preferably, the sawdust comprises natural pine sawdust with a moisture content of less than 10%.

[0022] Preferably, the sawdust is of continuously graded size.

[0023] Preferably, the sawdust gradation ratio is as follows: sawdust with a length of 3-4 mm accounts for 5%-15% by mass; sawdust with a length of 4-5 mm accounts for 10%-30% by mass; sawdust with a length of 5-6 mm accounts for 10%-60% by mass; sawdust with a length of 6-7 mm accounts for 15%-25% by mass; and sawdust with a length of 7-8 mm accounts for 10%-20% by mass.

[0024] More preferably, sawdust with a length of 3-4 mm accounts for 5%-10% of the mass, sawdust with a length of 4-5 mm accounts for 10%-25% of the mass, sawdust with a length of 5-6 mm accounts for 40%-60% of the mass, sawdust with a length of 6-7 mm accounts for 15%-20% of the mass, and sawdust with a length of 7-8 mm accounts for 10%-15% of the mass.

[0025] A second aspect of the present invention provides a method for preparing the sprayed mortar, comprising the following steps:

[0026] (a) Weigh out each raw material according to the specified quantity and set aside;

[0027] (b) The cement, sand and admixtures are initially mixed to obtain the first mixture;

[0028] (c) Add sodium hydroxide to the first mixture and continue stirring. Then add sawdust and stir with the mixture of cement, sand, admixture and sodium hydroxide. After stirring evenly, add mixed fiber and continue stirring to obtain the second mixture.

[0029] (d) Add water and water-reducing agent to the second mixture and stir evenly to obtain the third mixture;

[0030] (e) Add the third mixture to the spraying machine, check the instrument, set the spraying pressure, add the quick-setting agent, and spray the initial support base surface;

[0031] (f) After spraying, the sprayed mortar is cured.

[0032] Preferably, in step (d), the water and the water-reducing agent are added simultaneously after being mixed evenly, while stirring.

[0033] Preferably, in step (e), the spraying process follows a segmented spraying process, and after the spraying is completed, it should be checked immediately and resprayed or re-sprayed.

[0034] Preferably, in step (f), maintenance is carried out by spraying a maintenance solution.

[0035] More preferably, the maintenance solution is an alkaline solution.

[0036] Preferably, the temperature of the alkaline solution is 40–50°C.

[0037] More preferably, the alkaline solution includes a sodium hydroxide solution.

[0038] More preferably, the concentration of the sodium hydroxide solution is 1 mol / L to 5 mol / L.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The sprayed mortar provided by the present invention can quickly level the initial support of tunnel engineering, save the amount of sprayed membrane material in the sprayed membrane waterproof lining structure, protect the sprayed membrane waterproof layer, improve its durability and ensure waterproof quality, and enhance the applicability of sprayed membrane waterproof technology in tunnel engineering; at the same time, it ensures that the initial support, waterproof layer and secondary lining are tightly bonded, and improves the synergistic stress performance of the sprayed membrane waterproof lining in tunnel engineering.

[0041] (2) The sprayed mortar provided by the present invention has the advantages of light weight, low rebound rate, large porosity and good permeability, which can remove seepage water from the initial support surface and meet the requirements of various aspects of the sprayed waterproof lining structure of tunnel engineering.

[0042] (3) The sprayed mortar provided by the present invention saves sand by replacing fine aggregate with recycled sawdust and reduces the burden on the tunnel structure, which is beneficial to environmental protection and energy conservation. Detailed Implementation

[0043] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0044] A first aspect of the present invention provides a sprayed mortar comprising the following components in parts by weight:

[0045] 90-120 parts cement, 0-5 parts admixture, 90-600 parts sand, 140-300 parts water, 0-60 parts sodium hydroxide, 0.5-4 parts water-reducing agent, 5-12 parts quick-setting agent, 0-10 parts mixed fiber and 12-150 parts sawdust.

[0046] The cement used is ordinary Portland cement produced by Zhucheng Yangchun Cement Co., Ltd., with a grade of P·O42.5 and a mass fraction of 90 to 120 parts, for example, any one value or a range of any two values ​​from 90, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, and 120 parts.

[0047] The admixture is used to enhance the adhesion of the sprayed mortar. The mass fraction is 0 to 5 parts, specifically, for example, any one value or a range of any two values ​​from 0 parts, 0.5 parts, 1.0 parts, 1.5 parts, 2.0 parts, 2.5 parts, 3.0 parts, 4.0 parts, and 5.0 parts.

[0048] The sand can be river sand or manufactured sand. In some preferred embodiments of the present invention, the sand is natural dredged river sand with a bulk density of 1450 kg / m³. 3 The particle size is medium sand, fineness modulus is 2.31, moisture content is 0.2%, mud content is <5%, and mass fraction is 90 to 600 parts, for example, any one value or any two values ​​from 90, 94, 159, 224, 289, 354, 419, 484, 549, and 600 parts.

[0049] The water is tap water, and the mass fraction is 140 to 300 parts, for example, any one value or a range of any two values ​​from 140, 150, 160, 170, 180, 190, 200, 210, 220, 240, 260, 280, to 300 parts.

[0050] The sodium hydroxide is a test chemical reagent produced by Aladdin Reagents (Shanghai) Co., Ltd., in powder form, AR analytical grade, 95%. The sodium hydroxide is in powder or granular form to facilitate stirring and prevent clumping upon contact with water, which would make it difficult to dissolve and affect subsequent construction. The mass fraction is 0 to 60 parts, for example, any one value or a range of any two values ​​from 10, 14, 19, 20, 21, 22, 23, 24, 25, 26, 30, 34, 38, 42, 46, 50, and 60 parts.

[0051] The water-reducing agent used is a polycarboxylate-based high-performance water-reducing agent, manufactured by Tianjin Weihe Technology Development Co., Ltd., model HLX, with a density of 1040 kg / m³. 3 It has a solid content of 38.5%, a pH value of 6, and a mass fraction of 0.5 to 4 parts, for example, any one value or a range of any two points from 0.5, 1, 1.5, 2, 3, to 4 parts.

[0052] The accelerator used is FSA alkali-free accelerator, produced by Tianjin Weihe Technology Development Co., Ltd., with a density of 1510 kg / m³. 3 It has a solid content of 49.67%, a pH of 3.2, and a mass fraction of 5 to 12 parts, for example, any one value or a range of any two points from 5, 6, 7, 8, 9, 10, 11, or 12 parts.

[0053] The mixed fibers can act as a "bridging" agent inside the mortar, delaying mortar cracking and reducing rebound, effectively improving the durability of the mortar, and improving the mechanical properties of the mortar. The mass fraction is 0 to 10 parts, for example, any one value or any two values ​​in the range of 1 part, 2 parts, 3 parts, 4 parts, 6 parts, 8 parts, and 10 parts.

[0054] The sawdust is used to increase the porosity of the mortar, reduce its bulk density, reduce its weight, and save sand. This results in a mortar that is lightweight, has high porosity, good permeability, and is energy-saving and environmentally friendly. The sawdust is used in quantities ranging from 12 to 150 parts by weight, for example, any one value or a range of any two values ​​from 12, 24, 36, 48, 60, 72, 84, 96, 110, 130, to 150 parts.

[0055] The sprayed mortar provided by this invention is environmentally friendly and energy-saving, low in cost, and has the advantages of light weight, high porosity, low rebound rate, and good permeability. It can play a role in leveling, water seepage prevention, and buffering in tunnel sprayed waterproof lining structures, and therefore can be used for the initial support leveling of tunnel sprayed waterproof lining structures.

[0056] In some preferred embodiments of the present invention, the composition of the sprayed mortar is further optimized to produce a lighter mortar with higher porosity, lower resilience, better permeability, and better overall performance, including the following components by weight:

[0057] 100-120 parts cement, 2-3 parts admixture, 90-500 parts sand, 150-300 parts water, 19-50 parts sodium hydroxide, 0.5-2.5 parts water-reducing agent, 6-10 parts quick-setting agent, 2-5 parts mixed fiber and 24-100 parts sawdust.

[0058] In some preferred embodiments of the present invention, the admixture is silica fume, which is beneficial to enhance the adhesion of the sprayed mortar; it is produced by Sichuan Evande New Material Co., Ltd., with an average particle size of 0.1μm, a light gray powder, and a model number of 950U GL.

[0059] In some preferred embodiments of the present invention, the mixed fibers include natural fibers and synthetic fibers.

[0060] In some preferred embodiments of the present invention, the mass ratio of the natural fiber to the synthetic fiber is 1:(0.5 to 5).

[0061] Preferably, the mass ratio of the natural fiber to the synthetic fiber is 1:(0.5 to 2), for example, any ratio or a range of any two ratios from 1:0.5, 1:1, 1:1.5, 1:2.

[0062] In some preferred embodiments of the present invention, the natural fiber includes cotton fiber with a density of 150 kg / m³. 3 It has a tensile strength of 50 MPa and a moisture content of less than 1%.

[0063] The cotton fiber can be obtained by purchasing or prepared from natural cotton. In some preferred embodiments of the present invention, the cotton fiber is prepared from natural cotton, and the cotton used is produced in Chengdu, Sichuan Province.

[0064] In some preferred embodiments of the present invention, the size of the cotton fiber is 5 to 20 μm in diameter, for example, any one value or any two values ​​of 5 μm, 10 μm, 15 μm, and 20 μm, and the length is 2 to 6 mm, for example, any one value or any two values ​​of 2 mm, 4 mm, and 6 mm.

[0065] In some preferred embodiments of the present invention, the synthetic fiber comprises polypropylene fiber, produced by Changzhou New Material Technology Co., Ltd., with a density of 800 kg / m³. 3 It has a tensile strength of 600 MPa and a moisture content of less than 1%.

[0066] In some preferred embodiments of the present invention, the polypropylene fiber has a diameter of 15 to 30 μm, for example, any one value or any two values ​​of 15 μm, 20 μm, 25 μm, and 30 μm, and a length of 3 to 6 mm, for example, any one value or any two values ​​of 3 mm, 4 mm, 5 mm, and 6 mm.

[0067] In some preferred embodiments of the present invention, the sawdust comprises natural pine sawdust, produced in Mianyang City, Sichuan Province, with a density of 450 kg / m³. 3 The moisture content is less than 10%.

[0068] In some preferred embodiments of the present invention, the sawdust is of continuously graded size.

[0069] In some preferred embodiments of the present invention, the sawdust has a length of 3-8 mm. Specifically, the gradation ratio is as follows: sawdust with a length of 3-4 mm accounts for 5%-15% of the mass, for example, any one value or any two values ​​from 5%, 10%, and 15%; sawdust with a length of 4-5 mm accounts for 10%-30% of the mass, for example, any one value or any two values ​​from 10%, 15%, 20%, 25%, and 30%; and sawdust with a length of 5-6 mm... The mass percentage is 10% to 60%, for example, any one value or any two values ​​from 10%, 20%, 30%, 40%, 50%, and 60%. The sawdust length is 6 to 7 mm. The mass percentage is 15% to 25%, for example, any one value or any two values ​​from 15%, 20%, and 25%. The sawdust length is 7 to 8 mm. The mass percentage is 10% to 20%, for example, any one value or any two values ​​from 10%, 15%, and 20%.

[0070] Preferably, the sawdust length of 3-4 mm accounts for 5%-10% of the mass, the sawdust length of 4-5 mm accounts for 10%-25% of the mass, the sawdust length of 5-6 mm accounts for 40%-60% of the mass, the sawdust length of 6-7 mm accounts for 15%-20% of the mass, and the sawdust length of 7-8 mm accounts for 10%-15% of the mass.

[0071] A second aspect of the present invention provides a method for preparing the sprayed mortar, comprising the following steps:

[0072] (a) Weigh out the cement, admixture, sand, sodium hydroxide, water, water-reducing agent, mixed fiber and sawdust according to the corresponding proportions, and set aside;

[0073] (b) Mix cement and sand for 1 to 3 minutes, then add admixtures and mix evenly for 1 to 3 minutes to obtain the first mixture;

[0074] (c) Add sodium hydroxide to the first mixture and stir for 0.5 to 1 min, then add sawdust and stir for 1 to 2 min, then add mixed fibers and continue stirring for 2 to 5 min to obtain the second mixture;

[0075] (d) Add water and water-reducing agent to the second mixture and stir for 1-3 minutes to obtain the third mixture;

[0076] (e) Add the third mixture to the spraying machine all at once. After checking the initial support base, set the spraying pressure to 0.2 to 0.5 MPa, for example, any one value or any two values ​​of 0.2 MPa, 0.3 MPa, 0.4 MPa, or 0.5 MPa. Set the pumping speed of the accelerator according to the amount of accelerator used and spray. During spraying, the accelerator is mixed with the mortar at the spray nozzle.

[0077] (f) Inspect the sprayed mortar base surface, manually treat the mortar in local areas, re-spray or level it, and start curing the mortar after the initial setting of the mortar.

[0078] In some preferred embodiments of the present invention, in step (d), the water and the water-reducing agent need to be pre-mixed before being added, and the mixed water-reducing agent and water are slowly added to the second mixture in batches while stirring, so that the water-reducing agent is more evenly dispersed in the material.

[0079] In some preferred embodiments of the present invention, in step (e), the spraying process follows a segmented, bottom-up spraying process, while maintaining a spraying distance of 1 to 2 m and a spraying angle of 80° to 90° to ensure spraying quality and reduce rebound loss. After spraying is completed, it should be checked immediately and resprayed or re-sprayed.

[0080] In some preferred embodiments of the present invention, in step (f), maintenance is carried out by spraying a maintenance solution.

[0081] In some preferred embodiments of the present invention, the maintenance solution is an alkaline solution.

[0082] In some preferred embodiments of the present invention, the temperature of the alkaline solution is 40-50°C to ensure the reaction efficiency of the sawdust, for example, any one value or a range of any two values ​​among 40°C, 45°C, and 50°C.

[0083] In some preferred embodiments of the present invention, the alkaline solution includes a sodium hydroxide solution.

[0084] In some preferred embodiments of the present invention, the sodium hydroxide solution is prepared from sodium hydroxide and water, and the concentration is 1 mol / L to 5 mol / L, for example, any one value or a range of any two values ​​among 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, and 5 mol / L.

[0085] The following detailed description of some embodiments of the present invention is provided in conjunction with specific application examples. Unless otherwise specified, all raw materials used in the embodiments are commercially available.

[0086] Examples 1-8

[0087] The mortars provided in Examples 1-8 for tunnel lining structures include cement, sand, sodium hydroxide, water, water-reducing agent, quick-setting agent, and sawdust, with specific proportions shown in Table 1.

[0088] In Examples 1-8, no admixtures or mixed fibers were added. The cement used was ordinary Portland cement produced by Zhucheng Yangchun Cement Co., Ltd., with a grade of P·O42.5. The sand used was natural dredged river sand with a bulk density of 1450 kg / m³. 3 The particle size distribution is medium sand, with a fineness modulus of 2.31, a moisture content of 0.2%, and a mud content of <5%. Sodium hydroxide is from Aladdin Reagents (Shanghai) Co., Ltd., in powder form, AR analytical grade, 95%. The water is tap water. The water-reducing agent is a polycarboxylate-based high-performance water-reducing agent from Tianjin Weihe Technology Development Co., Ltd., model HLX, with a density of 1040 kg / m³. 3 It has a solids content of 38.5% and a pH value of 6; the accelerator used is FSA alkali-free accelerator, produced by Tianjin Weihe Technology Development Co., Ltd., with a density of 1510 kg / m³. 3 It has a solids content of 49.67% and a pH of 3.2; the sawdust is made from natural pine sawdust, produced in Mianyang City, Sichuan Province, with a density of 450 kg / m³. 3 The moisture content is less than 10%, and the sawdust content is increased by 12 parts per group.

[0089] Specifically, the sawdust gradation is as follows: sawdust with a length of 3-4mm accounts for 5% of the mass, sawdust with a length of 4-5mm accounts for 20% of the mass, sawdust with a length of 5-6mm accounts for 50% of the mass, sawdust with a length of 6-7mm accounts for 15% of the mass, and sawdust with a length of 7-8mm accounts for 10% of the mass.

[0090] The sprayed mortar in Examples 1-8 above is prepared through the following steps:

[0091] (a) Weigh out the corresponding amounts of cement, sand, sodium hydroxide, water, water-reducing agent, and sawdust;

[0092] (b) Add all the cement and sand to the mixing container and dry mix for 2 minutes to obtain the first mixture;

[0093] (c) Add sodium hydroxide to the first mixture and continue to dry stir for 1 minute. Then add all the sawdust in two batches into the mixing container and stir for 1 minute to obtain the second mixture.

[0094] (d) Mix the water-reducing agent and water and add the mixture to the second mixture in three portions, stirring continuously for 2 minutes to obtain the third mixture;

[0095] (e) Check the working condition of the spraying machine, wet the pipe wall, add the third mixture into the spraying machine at one time through the filter screen, set the spraying pressure to 0.2MPa, set the pumping speed of the accelerator according to the amount of accelerator, and spray. The accelerator is mixed with the mortar at the spraying nozzle. When spraying, select the section and segment, spray from bottom to top, the spraying distance is 1m, and the spraying angle should be kept as close to 90° as possible.

[0096] (f) Inspect the sprayed base surface, repair any uneven areas, and spray with a 40℃, 1mol / L sodium hydroxide solution for curing after the mortar has initially set.

[0097] Table 1. Components and their weights (g) in Examples 1-8

[0098]

[0099] Examples 9-16

[0100] The shotcrete for tunnel lining structures provided in Examples 9-16 includes cement, admixtures, sand, sodium hydroxide, water, water-reducing agent, quick-setting agent, mixed fiber, and sawdust, with specific proportions shown in Table 2.

[0101] Unlike Examples 1-8, Examples 9-16 added admixtures and mixed fibers. Except for the admixtures and mixed fibers, the sources of the other raw materials were the same as those in Examples 1-8.

[0102] Specifically, the admixture is silica fume, produced by Sichuan Evande New Material Co., Ltd., with an average particle size of 0.1μm, a light gray powder, and a model number of 950U GL.

[0103] Specifically, the mixed fiber is made by mixing cotton fiber and polypropylene fiber in a mass ratio of 1:1.

[0104] The cotton fiber is made from natural cotton, and the density of the prepared cotton fiber is 150 kg / m³. 3The tensile strength is 50 MPa, the moisture content is less than 1%, and the cotton used is produced in Chengdu, Sichuan Province.

[0105] Specifically, the cotton fiber preparation steps are as follows: cotton is soaked in an alkaline sodium hydroxide solution with a concentration of 3 mol / L and a temperature of 50°C for 24 hours to perform alkaline pretreatment on the cotton, and then dried at 50°C for 10 hours. The alkaline pretreated cotton fibers are then cut into cotton fibers with a diameter of 15 μm and a length of 4 mm.

[0106] The polypropylene fiber is produced by Changzhou New Material Technology Co., Ltd., with a density of 800 kg / m³. 3 It has a tensile strength of 600MPa, a moisture content of less than 1%, and dimensions of 20μm in diameter and 4mm in length.

[0107] The sawdust gradation is the same as in Examples 1-8.

[0108] The sprayed mortar in Examples 9-16 above is prepared through the following steps:

[0109] (a) Weigh out the appropriate amounts of cement, admixtures, sand, sodium hydroxide, water, water-reducing agent, mixed fiber and sawdust;

[0110] (b) Add all the cement and sand to the mixing container and mix for 1 minute. Add the admixture and continue to dry mix for 1 minute to obtain the first mixture.

[0111] (c) Add sodium hydroxide to the first mixture and stir dry for 0.5 min. Then add all the sawdust to the container and stir continuously for 1 min. Premix the cotton fiber and polypropylene fiber for 3 min to obtain mixed fiber. Then add the mixed fiber in two batches and stir continuously for 3 min to obtain the second mixture.

[0112] (d) Mix the water-reducing agent and water and add the mixture to the second mixture in three portions, stirring continuously for 2 minutes to obtain the third mixture;

[0113] (e) Check the working condition of the spraying machine, wet the pipe wall, add the third mixture into the spraying machine at one time through the filter screen, set the spraying pressure to 0.4MPa, set the pumping speed of the accelerator according to the amount of accelerator, and spray the accelerator with the mortar at the spraying nozzle. When spraying, select the section and segment, spray from bottom to top, keep the spraying distance at 1m, and keep the spraying angle as close to 90° as possible.

[0114] (f) Inspect the sprayed base surface, repair any uneven areas, and spray with a 40℃, 2mol / L sodium hydroxide solution for curing after the mortar has initially set.

[0115] Table 2. Components and their weights (g) in Examples 9-16

[0116]

[0117] Examples 17-22

[0118] The shotcrete for tunnel lining structures provided in Examples 17-22 includes cement, admixtures, sand, sodium hydroxide, water, water-reducing agent, quick-setting agent, mixed fiber, and sawdust, with specific proportions shown in Table 3.

[0119] Specifically, Examples 17-22 differ from Examples 11, 12 and 14 in that the mixing ratio of cotton fiber and polypropylene fiber in the mixed fiber is adjusted from 1:1 to 1:2 and 2:1.

[0120] The sources of all raw materials were the same as in Examples 9-16, and the size and sawdust gradation of the cotton and polypropylene fibers were the same as in Examples 9-16.

[0121] The preparation method of the sprayed mortar is the same as that in Examples 9-16.

[0122] Table 3. Components and their weights (g) in Examples 17-22

[0123]

[0124] Examples 23-28

[0125] The shotcrete for tunnel lining structures provided in Examples 23-28 includes cement, admixtures, sand, sodium hydroxide, water, water-reducing agent, quick-setting agent, mixed fiber, and sawdust, with specific proportions shown in Table 4.

[0126] Examples 23-28 differ from Examples 11, 12 and 14 in that the dimensions of the cotton fibers and polypropylene fibers in the mixed fibers are adjusted;

[0127] In Examples 23, 25, and 27, the cotton fibers had a diameter of 5 μm and a length of 2 mm, and the polypropylene fibers had a diameter of 15 μm and a length of 3 mm. In Examples 24, 26, and 28, the cotton fibers had a diameter of 20 μm and a length of 6 mm, and the polypropylene fibers had a diameter of 30 μm and a length of 6 mm.

[0128] The sources of all raw materials are the same as those in Examples 9-16, and the sawdust gradation is also the same as that in Examples 1-16.

[0129] The preparation method of the sprayed mortar is the same as that in Examples 9-16.

[0130] Table 4. Components and their weights (g) in Examples 23-28

[0131]

[0132] Examples 29-34

[0133] The shotcrete for tunnel lining structures provided in Examples 29-34 includes cement, admixtures, sand, sodium hydroxide, water, water-reducing agent, quick-setting agent, mixed fiber, and sawdust, with specific proportions shown in Table 5.

[0134] Examples 29-34 differ from Examples 11, 12, and 14 in that the size distribution of the sawdust is adjusted;

[0135] In Examples 29, 31, and 33, the sawdust size distribution is as follows: sawdust with a length of 3-4 mm accounts for 10% of the mass, sawdust with a length of 4-5 mm accounts for 25% of the mass, sawdust with a length of 5-6 mm accounts for 30% of the mass, sawdust with a length of 6-7 mm accounts for 20% of the mass, and sawdust with a length of 7-8 mm accounts for 15% of the mass. In Examples 30, 32, and 34, the sawdust size distribution is as follows: sawdust with a length of 3-4 mm accounts for 12.5% ​​of the mass, sawdust with a length of 4-5 mm accounts for 27.5% of the mass, sawdust with a length of 5-6 mm accounts for 20% of the mass, sawdust with a length of 6-7 mm accounts for 22.5% of the mass, and sawdust with a length of 7-8 mm accounts for 17.5% of the mass.

[0136] The sources of all raw materials are the same as in Examples 9-16, and the dimensions of the cotton fibers and polypropylene fibers are also the same as in Examples 9-16.

[0137] The preparation method of the sprayed mortar is the same as that in Examples 9-16.

[0138] Table 5. Components and their weights (g) in Examples 29-34

[0139]

[0140] Comparative Example 1

[0141] The shotcrete for tunnel lining provided in Comparative Example 1 includes cement, sand, water, water-reducing agent, and quick-setting agent, and its specific composition is shown in Table 6.

[0142] The sources of all raw materials are the same as those in Examples 1-8.

[0143] The sprayed mortar in Comparative Example 1 above was prepared through the following steps:

[0144] (a) Weigh out the appropriate amounts of cement, sand, water, and water-reducing agent;

[0145] (b) Add all the cement and sand to the mixing container and dry mix for 2 minutes;

[0146] (c) Mix the water-reducing agent and water and add the mixture into the mixing container in 3 portions, stirring while adding, and continue stirring for 2 minutes.

[0147] (d) Check the working condition of the spraying machine, wet the pipe wall, and add the mixture obtained in step (c) into the spraying machine all at once through the filter screen. Set the spraying pressure to 0.2MPa, set the pumping speed of the accelerator according to the amount of accelerator, and spray. The accelerator is mixed with the mortar at the spraying nozzle. When spraying, select sections and segments and spray from bottom to top. Keep the spraying distance at 1m and keep the spraying angle at 90° as much as possible.

[0148] (e) Inspect the sprayed base surface, repair any uneven areas, and spray with room temperature tap water for curing after the mortar has initially set.

[0149] Table 6 shows the components and their weights (g) in Comparative Example 1.

[0150]

[0151] Performance testing

[0152] Performance tests included seven indicators: bulk density, water absorption, open porosity, permeability coefficient, resilience, compressive strength, and splitting tensile strength. Except for the permeability coefficient, all test indicators were conducted according to the "Standard for Basic Performance Test Methods of Building Mortar" (JGJ / T 70—2009) and the "Technical Specification for Application of Shotcrete" (JGJ / T 372—2016). All mortar specimens from Comparative Example 1 and Examples 1-34 were tested at an age of 56 days. The permeability coefficient was tested according to the "Standard for Geotechnical Testing Methods" (GB / T50123—2019), with mortar specimens from Comparative Example 1 and Examples 1-34 also tested at an age of 56 days. The test results are shown in Tables 7, 8, 9, 10, 11, and 12.

[0153] Table 7 Performance test results for Comparative Example 1

[0154]

[0155] Table 8 Performance test results of Examples 1-8

[0156]

[0157] Table 9 Performance test results of Examples 9-16

[0158]

[0159] Table 10 Performance test results of Examples 17-22

[0160]

[0161] Table 11 Performance test results of Examples 23-28

[0162]

[0163] Table 12 Performance test results of Examples 29-34

[0164]

[0165] As shown in Tables 7 and 8, after incorporating sawdust to replace sand in the mortar, the bulk density of the sprayed mortar prepared in each embodiment was significantly lower than that in Comparative Example 1, without the addition of admixtures and mixed fibers. The density decreased continuously with increasing sawdust content, reaching a minimum of only 721 kg / m³. 3 Compared to 1910 kg / m² in Comparative Example 1 3 The amount of sand used was reduced by 63%, reaching the range of lightweight mortar. Simultaneously, the amount of sand used decreased continuously with increasing sawdust content, significantly saving sand and exhibiting energy-saving and environmentally friendly characteristics. Furthermore, the water absorption rate and open porosity of the sprayed mortar were significantly improved, reaching a maximum of 96.2% and 66.7%, respectively, a substantial increase compared to 11.2% and 16.3% in Comparative Example 1. The permeability was also greatly enhanced, from 1.3 × 10⁻⁶ in Comparative Example 1. -6 The speed increased to 6.5 × 10 cm / s. -4 cm / s. Therefore, the sprayed mortars prepared in Examples 1-8 have the advantages of being lightweight, environmentally friendly, having high porosity, and high permeability. However, the mechanical properties of the sprayed mortars will be reduced. The compressive strength of the sprayed mortars in Examples 1-8 is the lowest, only 0.5 MPa, and the splitting tensile strength is less than 0.1 MPa, which is significantly lower than that of Comparative Example 1. At the same time, the rebound amount is also increased compared with Comparative Example 1.

[0166] As shown in Tables 7, 8, and 9, after incorporating admixtures and mixed fibers, the shotcrete prepared in each example not only possesses the advantages of being lightweight, environmentally friendly, having high porosity, and good permeability, but also exhibits better mechanical properties and low resilience, resulting in improved overall performance. Specifically, the shotcrete prepared in Examples 9-16 shows a higher bulk density compared to the shotcrete prepared in Examples 1-8, with an increase ranging from 0 to 100 kg / m³. 3The water absorption rate and open porosity decreased by 0-10%; the permeability coefficient decreased slightly; however, the addition of admixtures and mixed fibers significantly improved the compressive strength of the prepared shotcrete, by about 1 MPa, and the splitting tensile strength by about 0.2 MPa. At the same time, the resilience rate was significantly reduced by more than 10%, indicating that the admixtures and mixed fibers improved the adhesion of the shotcrete and significantly improved the overall performance of the shotcrete.

[0167] As shown in Tables 9 and 10, the performance of the shotcrete changed when the mixing ratio of cotton fiber and polypropylene fiber in the mixed fiber composition was altered. Specifically, as the proportion of polypropylene fiber increased and the proportion of cotton fiber decreased, the bulk density, compressive strength, and splitting tensile strength of the shotcrete increased, but the water absorption, open porosity, permeability coefficient, and resilience decreased. This indicates that the fiber composition of the shotcrete can affect its performance. To balance the mechanical strength and permeability of the shotcrete, it is necessary to rationally control the composition ratio of the mixed fibers.

[0168] As shown in Tables 9 and 11, changes in the size of cotton and polypropylene fibers in the mixed fiber blend significantly affect the performance of the shotcrete. Specifically, excessively large or small diameters and lengths of the cotton and polypropylene fibers lead to decreased bulk density, compressive strength, and splitting tensile strength of the shotcrete, while increasing water absorption, open porosity, permeability coefficient, and resilience. This indicates that when using mixed fibers in shotcrete, their size must be adapted to the spraying conditions; unsuitable dimensions can significantly alter the performance of the shotcrete.

[0169] As shown in Tables 9 and 12, changing the sawdust size distribution significantly alters the overall performance of the shotcrete. Specifically, as the sawdust gradation becomes more uniform and the sawdust content within each size range becomes closer, the bulk density, compressive strength, and splitting tensile strength of the shotcrete increase, while water absorption, open porosity, permeability coefficient, and resilience decrease. This indicates that a more concentrated sawdust size distribution results in larger pores and better permeability in the shotcrete, but lower mechanical properties compared to a more uniform sawdust size distribution.

[0170] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A type of sprayed mortar, characterized in that, Includes the following components by parts by mass: 90-120 parts cement, 2-5 parts admixture, 90-600 parts sand, 140-300 parts water, 19-60 parts sodium hydroxide, 0.5-4 parts water-reducing agent, 5-12 parts quick-setting agent, 2-10 parts mixed fiber and 12-150 parts sawdust; The sawdust is continuously graded in size; The sawdust gradation ratio is as follows: sawdust with a length of 3-4mm accounts for 5%-10% of the mass, sawdust with a length of 4-5mm accounts for 10%-25% of the mass, sawdust with a length of 5-6mm accounts for 40%-60% of the mass, sawdust with a length of 6-7mm accounts for 15%-20% of the mass, and sawdust with a length of 7-8mm accounts for 10%-15% of the mass.

2. The sprayed mortar according to claim 1, characterized in that, Includes the following components by parts by mass: 100-120 parts cement, 2-3 parts admixture, 90-500 parts sand, 150-300 parts water, 19-50 parts sodium hydroxide, 0.5-2.5 parts water-reducing agent, 6-10 parts quick-setting agent, 2-5 parts mixed fiber and 24-100 parts sawdust.

3. The sprayed mortar according to claim 1 or 2, characterized in that, The admixture includes silica fume.

4. The sprayed mortar according to claim 1 or 2, characterized in that, The blended fibers include natural fibers and synthetic fibers.

5. The sprayed mortar according to claim 4, characterized in that, The mass ratio of the natural fiber to the synthetic fiber is 1:(0.5~5).

6. The sprayed mortar according to claim 4, characterized in that, The natural fibers include cotton fibers.

7. The sprayed mortar according to claim 6, characterized in that, The cotton fibers have a diameter of 5~20μm and a length of 2~6mm.

8. The sprayed mortar according to claim 4, characterized in that, The synthetic fiber includes polypropylene fiber.

9. The sprayed mortar according to claim 8, characterized in that, The polypropylene fibers have a diameter of 15~30μm and a length of 3~6mm.

10. The sprayed mortar according to claim 1 or 2, characterized in that, The sawdust includes natural pine sawdust.

11. The method for preparing sprayed mortar according to any one of claims 1-10, characterized in that, Includes the following steps: (a) Weigh out each raw material according to the specified quantity and set aside; (b) The cement, sand and admixtures are mixed to obtain the first mixture; (c) Add sodium hydroxide to the first mixture and continue stirring, then add sawdust and stir. After stirring evenly, add mixed fibers and continue stirring to obtain the second mixture. (d) Add water and water-reducing agent to the second mixture and stir evenly to obtain the third mixture; (e) Add the third mixture to the spraying machine, check the instrument, set the spraying pressure, add the quick-setting agent, and spray the base surface; (f) After spraying, the sprayed mortar is cured.

12. The method for preparing sprayed mortar according to claim 11, characterized in that, In step (d), the water and the water-reducing agent are mixed evenly and then added simultaneously while stirring.

13. The method for preparing sprayed mortar according to claim 11, characterized in that, In step (e), the spraying process is carried out in sections and segments. After the spraying is completed, it should be checked immediately and resprayed or re-sprayed.

14. The method for preparing sprayed mortar according to claim 11, characterized in that, In step (f), maintenance is carried out by spraying maintenance solution.

15. The method for preparing sprayed mortar according to claim 14, characterized in that, The maintenance solution is an alkaline solution.

16. The method for preparing sprayed mortar according to claim 15, characterized in that, The temperature of the alkaline solution is 40~50℃.

17. The method for preparing sprayed mortar according to claim 15 or 16, characterized in that, The alkaline solution includes a sodium hydroxide solution.

18. The method for preparing sprayed mortar according to claim 17, characterized in that, The concentration of the sodium hydroxide solution is 1 mol / L to 5 mol / L.

Images