Organic cross-linking material and application thereof in sprayed concrete

Abstract

The invention provides an organic cross-linking material. The organic cross-linking material comprises a polymeric monomer, an initiator and a cross-linking agent, the use amount of the initiator is 1-6% of the use amount of the polymeric monomer; the dosage of the cross-linking agent is 0.02%-0.10% of the dosage of the polymeric monomer, and the cross-linking agent is one or a combination of more of triethyl boron propylene diamine, triethyl lithium boride, triphenyl n-butyl lithium borate and sodium borate. According to the high-strength and low-rebound-rate sprayed concrete based on organic and inorganic crosslinking, after spraying, the organic crosslinking material is polymerized to form a three-dimensional network structure, and a concrete hydration product is filled in the three-dimensional network structure and is mutually crosslinked and tightly combined. Through connection of the net-shaped structure, all parts of the sprayed concrete are connected more tightly, the rebound rate is reduced, meanwhile, cracks in a concrete matrix are reduced, the compactness is increased, and the compressive strength of the sprayed concrete can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly relates to an organic cross-linked material and its application in shotcrete. Background Art

[0002] With the continuous development of infrastructure construction in China, transportation facilities such as subways, railways, and highways are also developing rapidly. China has a vast territory and complex terrain. During the construction process, when encountering mountain and rock obstacles, tunnels are often excavated as internal passages to cross complex terrains. During the tunnel excavation process, it is necessary to spray a layer of concrete on the surface of the surrounding rock as the initial support to achieve the purpose of supporting the surrounding rock and enhancing the structural stability. Among them, shotcrete is a kind of concrete formed by using a spraying machine to spray a mixture of materials mixed in a certain proportion onto the sprayed surface at high speed under pressure. Compared with ordinary concrete, shotcrete has the advantages of not requiring formwork and rapid forming, effectively accelerating the project progress, and has been widely used in tunnel engineering, foundation pit slope protection, and underground engineering.

[0003] However, shotcrete also has problems such as low strength and high rebound rate. Generally, the strength of shotcrete is about C25 - C35, and the rebound rate is related to the quality of the concrete and the spraying process, and generally can reach about 20%. The low strength of shotcrete will lead to unsatisfactory initial support effect, and in severe cases, problems such as tunnel collapse may occur; the high rebound rate will result in waste of concrete. The rebounded concrete can only be disposed of and cannot be reused, and the disposal is time-consuming and laborious.

[0004] Patent 202210856126.3 discloses a high-strength and ultra-fine admixture for shotcrete, which includes the following components in parts by weight: 47 - 57 parts of ultra-fine silica, 32 - 42 parts of ground granulated blast-furnace slag powder, 0 - 5 parts of aluminum sulfate, 0 - 5 parts of calcium sulfate, 2 - 3 parts of calcium hydroxide, 2 - 3 parts of sodium hydroxide, 0.3 - 0.7 parts of polyacrylamide, 0 - 0.8 parts of hydroxypropyl methylcellulose, and 0.05 - 0.15 parts of polyvinyl alcohol. Through the synergistic cooperation of the above specific components and their weight ratios, the early strength of shotcrete can be significantly improved, the adhesion between the cement paste and the aggregate can be enhanced, the rebound rate and dust content during the construction of shotcrete can be reduced, and at the same time, the shotcrete has better strength and durability. However, the incorporation of a large amount of powder materials, especially ultra-fine silica, will affect the workability of the concrete, resulting in a greater spraying pressure required during the spraying process of shotcrete, and at the same time, the spraying efficiency will also be affected.

[0005] Patent 202210294941.5 discloses a high-early-strength and low-rebound high-performance shotcrete and its preparation method. Among the self-made admixtures used in the provided high-performance shotcrete, the content of calcium sulfoaluminate is relatively large. It first reacts rapidly with dihydrate gypsum in the cement hydration system to generate a large amount of ettringite and aluminosilicate gel. The rapid formation of ettringite can provide a framework structure for the cement paste, promote the setting of the paste and increase the early strength. At the same time, by utilizing the synergistic effect of calcium sulfoaluminate and the accelerator, the two are ejected by the high-pressure air of the wet shotcreting machine and can quickly set and harden and generate strength after contacting at the nozzle, which can greatly reduce the shotcrete rebound rate. However, after a large amount of calcium sulfoaluminate is used, it may cause the rapid loss of the early functional properties of the concrete, affecting the subsequent shotcreting process. At the same time, in a salt erosion environment, a large amount of sulfoaluminate may accelerate the sulfate erosion and damage of the concrete, restricting its further application.

[0006] Patent 202310191849.0 discloses a preparation method of a crosslinked monomer for preparing high-early-strength and low-rebound concrete. First, a reducing agent and a crosslinked monomer are added to the water reducer, and the prepared water reducer is added to the concrete. When the concrete reaches the spraying surface, an initiator is added to the accelerator, and the prepared accelerator is added to the concrete for mixed spraying to obtain the ultra-early-strength and low-rebound rate shotcrete. The invention utilizes the crosslinking of monomers with multiple saturated double bonds under the action of an initiator to immediately release heat, and uses the products of the redox reaction as early-strength salts to accelerate the mineral hydration reaction to achieve the purpose of high early strength of the shotcrete. At the same time, a large number of three-dimensional network structures are produced by the crosslinked products, which can improve the cohesion of the concrete and have the ability to resist water scouring. However, this method requires additional treatment of the accelerator, increasing the construction process and affecting the on-site construction progress. Summary of the Invention

[0007] In view of the above deficiencies and other problems in the prior art, the present invention provides an organic crosslinked material and its application in shotcrete. Through the in-situ polymerization of polymer monomers under the action of an initiator and a crosslinking agent, a polymer with a three-dimensional network structure is formed. The polymer network structure formed by in-situ polymerization is bonded to each component of the concrete, reducing the rebound rate during the shotcrete process of the shotcrete and simultaneously improving the compressive strength of the concrete. Through the boron-based material in the crosslinked material, the cement hydration reaction in the concrete is promoted, the hydration process is accelerated, and the compressive strength of the concrete is further improved.

[0008] An organic crosslinked material, comprising polymer monomers, an initiator, and a crosslinking agent; the dosage of the above initiator is 1% - 6% of the dosage of the polymer monomers; the dosage of the above crosslinking agent is 0.02% - 0.10% of the dosage of the polymer monomers, and the crosslinking agent is one or a combination of triethylboron propanediamine, lithium triethylborohydride, lithium phenylbutyl borate, and sodium borate.

[0009] The boron-based material in the cross-linking agent can promote the cement hydration reaction in concrete, accelerate the formation process of C-S-H gel during hydration, improve the internal structure of concrete, make the concrete more dense, reduce the possibility of shrinkage and cracking, and further improve the compressive strength of concrete. The three-dimensional network structure formed by the reaction of the organic boron cross-linking agent can achieve efficient cross-linking in a short time and is more suitable for shotcrete systems.

[0010] The above polymerization monomers are one or a combination of several of acrylamide, acrylate, methacrylate, acrylic acid, and allyl alcohol.

[0011] The above initiators are one or a combination of several of azobisisobutyronitrile, sodium persulfate, potassium persulfate, and sodium bisulfite.

[0012] This organic cross-linking material is applied to shotcrete with high strength and low rebound rate. The shotcrete with high strength and low rebound rate includes the following raw materials: Cement: 300 - 500 kg / m 3 ; Gelatinous material: 0 - 200 kg / m 3 ; Coarse aggregate: 550 - 850 kg / m 3 ; Fine aggregate: 550 - 850 kg / m 3 ; Accelerator: 10 - 50 kg / m 3 ; Water reducing agent: 5 - 20 kg / m 3 ; Water for concrete mixing: 150 - 350 kg / m 3 ; Organic cross-linking material: 10 - 30 kg / m 3 .

[0013] The above cement is portland cement or ordinary portland cement with a strength grade greater than or equal to 42.5; the above gelatinous material is one or a combination of several of fly ash, silica fume, and slag; the above fine aggregate is river sand or manufactured sand; the above coarse aggregate is continuously graded gravel with a particle size below 10 mm; the above water reducing agent is a polycarboxylate water reducing agent; the above accelerator is an alkali-free accelerator.

[0014] The above organic cross-linking material can be applied to shotcrete of various strength grades, directly added during the concrete mixing process, eliminating the process of dissolving the polymerization monomer, initiator, and cross-linking agent in water, and reducing the construction process.

[0015] A preparation method for shotcrete with high strength and low rebound rate includes the following steps:

[0016] (1) Pour the cement, gelatinous material, organic cross-linking material, fine aggregate, and coarse aggregate into a concrete mixer and mix for 30 - 60 s;

[0017] (2) Add water for concrete mixing and water-reducing agent, and stir for 1 - 3 min to prepare a concrete mixture;

[0018] (3) The quick-setting agent is sprayed out through a spray gun and mixed with the concrete mixture sprayed out from the concrete spray gun to obtain shotcrete with high strength and low rebound rate.

[0019] The above organic cross-linking material is directly incorporated into the concrete binder and stirred together with the concrete. The polymerization monomer, initiator, and cross-linking agent dissolve in the concrete mixing water and then undergo an in-situ polymerization reaction. The cross-linking agent cross-links with the polymerization monomer through polar bonds and coordination bonds to form a polymer with a three-dimensional network structure. At the same time, the alkaline environment formed by the hydration of the concrete accelerates the polymerization reaction. The polymer network structure formed in-situ in the cement concrete binds to each component of the concrete, reducing the generation of cracks in the shotcrete and simultaneously reducing the rebound rate.

[0020] For the above shotcrete with high strength and low rebound rate based on organic-inorganic cross-linking, after spraying, the organic cross-linking material polymerizes to form a three-dimensional network structure, and the concrete hydration products fill in the three-dimensional network structure, cross-linking and tightly binding with each other. Through the connection of the network structure, each part of the shotcrete is connected more tightly, the rebound rate is reduced, and at the same time, the generation of cracks in the concrete matrix is reduced and the density is increased, which can significantly improve the compressive strength of the shotcrete.

[0021] This application has the following advantages compared with the prior art:

[0022] (1) Through the in-situ polymerization of the polymerization monomer under the action of the initiator and cross-linking agent, efficient cross-linking is achieved in a short time to form a polymer with a three-dimensional network structure; the polymer network structure formed in-situ binds to each component of the concrete, increasing the stability of the concrete, reducing the rebound rate during the spraying process of the shotcrete, and simultaneously improving the compressive strength of the concrete.

[0023] (2) Through the boron-based material in the cross-linking material, the cement hydration reaction in the concrete is promoted, the hydration process is accelerated, the internal structure of the concrete is improved, and the compressive strength and impermeability of the concrete are further enhanced.

[0024] (3) The high-strength and low-rebound shotcrete based on organic cross-linking technology is added as a powder material during the concrete mixing process. Compared with the traditional organic cross-linking technology, it is exempt from the process of dissolving and mixing in water, reducing the construction procedures, facilitating on-site application, and accelerating the construction progress. Specific embodiments

[0025] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0026] In each embodiment, the manufacturers of the polymerization monomer, initiator, and crosslinking agent are Nanjing Wanqing Chemical Glass Instrument Co., Ltd.; the cement is PII 42.5 portland cement; the water is tap water; the fine aggregate is river sand with a particle size of 0.075 - 4.75 mm continuous gradation; the coarse aggregate is basalt with a particle size of 4.75 - 9.5 mm; the water reducing agent is a polycarboxylate water reducing agent produced by Jiangsu Sobute New Materials Co., Ltd.; the accelerating agent is an alkali-free accelerating agent produced by Jiangsu Sobute New Materials Co., Ltd.

[0027] The dosage ratios of the components in the organic crosslinking materials used in each embodiment are as shown in Table 1 below:

[0028] Table 1

[0029]

[0030]

[0031] The concrete mix ratios used in each embodiment are as shown in Table 2 below (where the types of organic crosslinking materials are shown in Table 1), in kg / m 3 :

[0032] Table 2

[0033]

[0034] According to the data ratios in Tables 1 and 2, pour the cement, gelling material, organic crosslinking material, fine aggregate, and coarse aggregate into a concrete mixer and mix for 50 s; then add the concrete mixing water and water reducing agent and stir for 3 min to obtain a concrete mixture; finally, mix the accelerating agent with the concrete mixture and spray it out through a spray gun to obtain high-strength and low-rebound shotcrete.

[0035] Test Example 1: Compressive strength and rebound rate test

[0036] Shotcrete Compressive Strength Test: The production of concrete test blocks refers to the reference standard JGJ / T 372-2016 "Technical Specification for Shotcrete Application". For the formwork of 450*450*120mm, after curing for 1 day, demold it and place it in the standard curing room for curing. At 7 days, cut it into cube test blocks of 100*100*100mm and continue to cure in the standard curing room until 28 days to test its compressive strength. The method for testing compressive strength refers to the national standard of the People's Republic of China GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0037] Shotcrete Rebound Rate: The test of shotcrete rebound rate refers to the reference standard JGJ / T 372-2016 "Technical Specification for Shotcrete Application", which mainly includes the following three steps: (1) Cover an area of 40-50m on the ground below the surface to be sprayed with plastic film; (2) Mix no less than 1m of concrete mixture, send it into the spraying equipment, and start testing after the sprayed material is stable. The nozzle should be at a 90° angle to the sprayed surface. The total spraying thickness is 80-120mm, sprayed in two layers, and the thickness of each layer is 40-60mm. The spraying process needs to be continuous without interruption, and the concrete in the hopper should be uniform at the start and end of the test; (3) After spraying, collect the rebound material from the plastic film and weigh it. The mass percentage of the rebound material to the total sprayed mixture is the shotcrete rebound rate. 2 of the area; (2) Mix no less than 1m 3 of concrete mixture, send it into the spraying equipment, and start testing after the sprayed material is stable. The nozzle should be at a 90° angle to the sprayed surface. The total spraying thickness is 80-120mm, sprayed in two layers, and the thickness of each layer is 40-60mm. The spraying process needs to be continuous without interruption, and the concrete in the hopper should be uniform at the start and end of the test; (3) After spraying, collect the rebound material from the plastic film and weigh it. The mass percentage of the rebound material to the total sprayed mixture is the shotcrete rebound rate.

[0038] The test results are shown in Table 3 as follows:

[0039] Table 3

[0040]

[0041]

[0042] It can be found from the above results that the compressive strength of the concrete in the examples is generally greater than 36MPa, and the compressive strength of the concrete is increased by more than 25% compared with that of the reference group. This is because the organic cross-linking technology described in this application can increase the cohesion of the shotcrete, thereby reducing the cracks generated during spraying and service of the shotcrete. At the same time, due to the early strength improvement effect of the boron-based material, the compressive strength of the concrete is improved, which proves the effectiveness of the present invention. Although the compressive strength of the concrete in the comparative example is also improved to some extent, its improvement effect is not as good as that of the concrete in the examples, which proves the synergistic effect and necessity of each component in the present invention.

[0043] The rebound rate of the shotcrete can be reduced to within 10%, which is significantly lower than that of the reference group. The reduction of the shotcrete rebound rate is due to the interaction of various materials, which builds a three-dimensional network structure in the shotcrete. The hydration products of cement overlap and fill in the three-dimensional network structure, thus achieving the effect of mutual connection. Under the condition of missing some components, the improvement effect on the concrete rebound rate is not obvious, which proves the effectiveness of this application and the necessity of each component in the invention.

[0044] In addition, too much or too little amount of the cross-linking material in the comparative example will lead to the reduction of the mechanical properties of the concrete. This is because when the amount of the cross-linking material in the concrete is too little, enough three-dimensional structures cannot be generated to connect each part of the shotcrete, resulting in the reduction of the density inside the concrete and the decline of the mechanical properties. When the amount of the cross-linking material is too much, a large amount of cross-linking products are generated in a short time, and the hydration products of the concrete cannot be filled in the cross-linking structure in time, thus forming a defect area, affecting the density of the concrete hydration products themselves, and further affecting the mechanical properties of the concrete, resulting in the reduction of the rebound rate. At the same time, after replacing the cross-linking agent in Comparative Example 6, the rebound rate of the shotcrete increased instead. This is because the traditional cross-linking agent itself has a certain negative effect on the concrete hydration process, and the cross-linking reaction rate is slow. Therefore, a network structure cannot be generated in time in the shotcrete system, and the mechanical properties of the shotcrete decline, resulting in the fact that the concrete rebound rate does not decrease or even increases. This proves the effectiveness and necessity of each component in this application, as well as the synergy of the optimal amounts between different components.

[0045] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An organic cross-linked material, characterized in that: It includes polymerization monomers, initiators, and crosslinking agents; the dosage of the initiator is 1% - 6% of the dosage of the polymerization monomers; the dosage of the crosslinking agent is 0.02% - 0.10% of the dosage of the polymerization monomers, and the crosslinking agent is one or a combination of several of triethylboron propanediamine, lithium triethylborohydride, lithium tributylphenyl borate, and sodium borate.

2. An organic crosslinked material according to claim 1, characterized in that: The polymerization monomers are one or a combination of several of acrylamide, acrylate, methacrylate, acrylic acid, and allyl alcohol.

3. An organic crosslinked material according to claim 1, characterized in that: The initiators are one or a combination of several of azobisisobutyronitrile, sodium persulfate, potassium persulfate, and sodium bisulfite.

4. Use of an organic crosslinked material according to any one of claims 1 to 3, characterized in that: This organic crosslinked material is applied to shotcrete with high strength and low rebound rate.

5. A shotcrete with high strength and low rebound rate, characterized in that, It includes the following raw materials: Cement: 300 - 500 kg / m 3 ; Cementitious material: 0 - 200 kg / m 3 ; Coarse aggregate: 550 - 850 kg / m 3 ; Fine aggregate: 550 - 850 kg / m 3 ; Accelerator: 10 - 50 kg / m 3 ; Water reducing agent: 5 - 20 kg / m 3 ; Water for concrete mixing: 150 - 350 kg / m 3 ; Organic cross - linking material: 10 - 30 kg / m 3 ; The organic cross - linking material is the organic cross - linking material described in Claim 1.

6. The shotcrete with high strength and low rebound rate according to claim 5, characterized in that: The cement is portland cement or ordinary portland cement with a strength grade greater than or equal to 42.5; the cementitious materials are one or a combination of several of fly ash, silica fume, and slag.

7. A shotcrete with high strength and low rebound rate according to claim 5, characterized in that: The fine aggregate is river sand or manufactured sand; the coarse aggregate is continuously graded gravel with a particle size below 10 mm.

8. A shotcrete with high strength and low rebound rate according to claim 5, characterized in that: The water reducing agent is a polycarboxylate water reducing agent; the accelerating agent is an alkali-free accelerating agent.

9. A method for preparing a high-strength and low-rebound-rate shotcrete according to any one of claims 5-8, characterized in that, It includes the following steps: (1) Pour the cement, cementitious materials, organic crosslinked materials, fine aggregate, and coarse aggregate into a concrete mixer and mix for 30 - 60 s; (2) Add concrete mixing water and the water reducing agent and stir for 1 - 3 min to prepare a concrete mixture; (3) The accelerating agent is sprayed out through a spray gun and mixed with the concrete mixture sprayed out from the concrete spray gun to obtain shotcrete with high strength and low rebound rate.

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