Rapid reinforcement high performance shotcrete for existing tunnel lining and method for preparing the same

Abstract

The application relates to the technical field of concrete materials, and discloses a kind of rapid reinforcement high-performance shotcrete for existing tunnel lining and a preparation method thereof.The shotcrete comprises the following raw materials by weight: 300-350 parts of low-calcium high-Belitite sulphoaluminate cement, 80-100 parts of superfine slag powder, 3-8 parts of trigger-type activator, 5-15 parts of slow-release particles, 2-5 parts of nanogel, 800-900 parts of fine aggregate, 800-900 parts of coarse aggregate, 30-50 parts of copper-plated steel fiber, 0.8-1.2 parts of polypropylene fiber, 30-40 parts of viscosity-adjusting quick-setting agent, 10-20 parts of water-reducing agent, and 160-180 parts of water.The shotcrete has high compressive strength and good durability, can solve the double threats of chemical corrosion and chloride ion permeation / steel bar corrosion, and meets the demand for rapid reinforcement of tunnels and underground projects.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete materials, in particular to a kind of rapid reinforcement high-performance shotcrete for existing tunnel lining and a preparation method thereof. BACKGROUND

[0002] The existing tunnel lining is a permanent supporting structure composed of concrete or reinforced concrete, which has been built and put into use.

[0003] The tunnel projects built before the 1990s have low construction quality due to the limited construction technology at that time.

[0004] In addition, after decades of operation, the existing tunnel lining often has durability problems in harsh environments, mainly including: chemical corrosion, such as sulfate attack and acid attack in groundwater; chloride ion penetration, which leads to internal steel (or steel fiber) corrosion, and further causes concrete cracking and spalling; carbonation, which reduces the alkalinity of concrete and damages the steel passivation film; physical damage caused by increased pressure from groundwater and surrounding rock, such as structure cracking, spalling, and strength reduction, which leads to prominent lining water leakage problems and seriously affects the operation safety.

[0005] When a new tunnel is constructed nearby, the blasting vibration and excavation unloading of the new tunnel will further deteriorate the health status of the existing tunnel lining structure.

[0006] To ensure the safety of the existing tunnel operation, it is necessary to reinforce the tunnel lining during the time window when the operation is stopped, so it is necessary to develop a rapid reinforcement technology for the tunnel lining.

[0007] For the damage caused by the above problems, shotcrete has become the mainstream rapid repair technology due to its convenient construction and strong adhesion to the base.

[0008] To improve the durability of shotcrete, the skilled person in the art usually takes the following technical paths: one is to use high-sulfate-resistant cement, high-dosage mineral admixtures such as slag, fly ash, and silica fume to reduce the content of calcium hydroxide, which is easily corroded in concrete, and to refine the pore structure, thereby improving the chemical corrosion resistance.

[0009] The second is to mix high-quality air entraining agents, high-efficiency water reducers, and organic rust inhibitors to improve the impermeability of concrete or directly protect the steel.

[0010] However, research has found that on the one hand, one of the most effective measures to resist chemical corrosion is to actively reduce the alkalinity of concrete and consume a large amount of calcium hydroxide.

[0011] Because sulfate attack and acid attack are mainly targeted at calcium hydroxide.

[0012] Using large amounts of mineral admixtures or special low-alkali cement is a common means to achieve this goal. However, on the other hand, to effectively prevent chloride-induced steel or steel fiber corrosion, it is necessary to maintain a high alkaline environment (pH > 12.5) inside the concrete.

[0013] Because the passivation film on the surface of the steel bar can only exist stably in this high alkaline environment, once the alkalinity is reduced, the passivation film is destroyed, and the chloride ion will cause corrosion.

[0014] If the alkalinity is reduced in order to prioritize chemical corrosion resistance, the repair layer is easily damaged from the inside due to steel corrosion; if the high alkalinity is maintained in order to prioritize steel protection, the repair layer is easily pulverized and peeled off from the outside due to chemical erosion. The existing technology often has to choose one and lose the other, and it is difficult to achieve long-term durability in harsh chemical and chloride coupling corrosion environments.

[0015] Therefore, it is urgent to develop a new type of shotcrete material that can simultaneously solve the dual threats of chemical corrosion and chloride penetration / steel corrosion, in order to meet the needs of long-term repair and reinforcement technology for tunnels and underground engineering that can be quickly implemented under time constraints. SUMMARY

[0016] The present application provides a kind of for existing tunnel lining Rapid reinforcement high-performance shotcrete and its preparation method.

[0017] The technical scheme of the present application is: a kind of for existing tunnel lining Rapid reinforcement high-performance shotcrete, including the following weight parts of raw materials:

[0018] 300-350 parts of low calcium type high belite sulphoaluminate cement, 80-100 parts of superfine slag powder, 3-8 parts of trigger type activator, 5-15 parts of slow-release particles, 2-5 parts of nanogel, 800-900 parts of fine aggregate, 800-900 parts of coarse aggregate, 30-50 parts of copper-plated steel fiber, 0.8-1.2 parts of polypropylene fiber, 30-40 parts of viscosity adjusting accelerator, 10-20 parts of water reducing agent, and 160-180 parts of water;

[0019] The trigger-type activator is obtained by uniformly mixing sodium sulfate, triethanolamine and calcium sugar in a mass ratio of (5-8) :(1-2) :1; the slow-release particles have a core-shell structure, the shell is a nano-scale pozzolan material, the core is a saturated alkaline solution, the nano-scale pozzolan material is nano-metakaolin or nano-silica fume, the saturated alkaline solution is a saturated calcium hydroxide or potassium hydroxide solution, and the mass ratio of the shell to the core is 1:(1-2); the nanogel is a polyelectrolyte hydrogel containing carboxyl groups, has a particle size distribution of 50-500 nm, shrinks in an environment with a pH greater than 11.5, and swells in an environment with a pH less than 10.5; and the viscosity-modifying accelerator is obtained by compounding an alkali-free liquid accelerator and a viscosity-increasing agent, the content of the viscosity-increasing agent is 0.5% to 2% based on the mass of the alkali-free liquid accelerator, the alkali-free liquid accelerator is an aluminum sulfate-based accelerator, and the viscosity-increasing agent is hydroxypropyl methyl cellulose or warm rubber.

[0020] In the trigger-type activator, SO4 2- reacts with calcium ions to generate ettringite and destroy the slag glass structure. Triethanolamine complexes calcium ions on the surface of slag, destroying the passivation layer. Calcium sugar is adsorbed on the cement particles, delaying hydration. Together, they promote the early participation of slag in the reaction to generate C-S-H gel and fill pores.

[0021] The nanogel shrinks in a high-pH environment due to the ionization of carboxyl groups. In a low-pH environment, the carboxyl groups are protonated, causing the gel to swell. The swelling process blocks the transport of the medium in the capillary pores and fixes hydrogen ions through ion exchange.

[0022] The core of the slow-release particles stores saturated alkali solution. When the environmental pH value drops to the critical point, the shell structure disintegrates, releasing the alkali solution. The alkali solution acts on the steel fiber interface, causing the local pH value to rise and the passivation film to be rebuilt.

[0023] The cementitious system forms a low-alkalinity dense matrix. The nanogel blocks the migration of the medium by swelling when the pH drops. The slow-release particles release alkali solution when the pH further decreases, protecting the steel fibers. This multi-level mechanism unifies the chemical corrosion resistance of the matrix and the anti-corrosion ability of the steel fibers.

[0024] In one possible implementation, in the low-calcium high-Berlittite sulfoaluminate cement, the content of the Berlittite mineral is not less than 40%, and the content of the aluminum phase mineral is not more than 15%.

[0025] In one possible implementation, the particle size D50 of the superfine slag powder is ≤5 μm;

[0026] And / or, the particle size of the coarse aggregate is 5-10 mm;

[0027] And / or, the length of the copper-plated steel fiber is 25-30 mm, and the aspect ratio is 50-80;

[0028] and / or, the polypropylene fiber length is 12-19mm, and the diameter is 20-50um.

[0029] In a possible implementation, the fine aggregate is natural sand or machine-made sand, and the particle size range is 0.15-4.75mm.

[0030] In a possible implementation, the water reducing agent is a polycarboxylic acid type high efficiency water reducing agent.

[0031] In a possible implementation, the preparation method of the slow-release particles is as follows:

[0032] S11, slowly adding nano metakaolin into saturated Ca(OH)2 solution to form a suspension;

[0033] S12, adding the suspension drop by drop into a sodium alginate solution to form a mixed solution, and then slowly adding the mixed solution into a calcium chloride solution, and standing for solidification;

[0034] S13, filtering and collecting the particles of the solidification product, then dispersing the particles in deionized water, alternately adding poly diallyl dimethyl ammonium chloride and nano metakaolin suspension, stirring and washing, collecting the product, and then spray drying to obtain the slow-release particles.

[0035] In a possible implementation, the preparation method of the nanogel is as follows:

[0036] S21, adding a methacrylic acid monomer and a crosslinking agent BIS into 90ml deionized water, and introducing nitrogen to remove dissolved oxygen;

[0037] S22, under the protection of nitrogen, adding an aqueous solution of initiator APS, and reacting in a water bath for 6-8h;

[0038] S23, after the reaction is completed, cooling to room temperature, dialyzing with deionized water to obtain a milky white gel liquid, and then freeze-drying to obtain the nanogel.

[0039] The application also provides a method for preparing a rapid reinforcement high-performance sprayed concrete for existing tunnel lining, comprising the following steps:

[0040] S1, weighing each raw material according to the proportion;

[0041] S2, uniformly mixing the low-calcium high-Berlite sulfoaluminate cement, the ultra-fine slag powder, the trigger type activator, the slow-release particles and the nanogel to obtain a composite cementitious material;

[0042] S3, adding the coarse aggregate and the fine aggregate to the composite cementitious material for dry mixing, and then slowly adding the copper-plated steel fiber and the polypropylene fiber in the stirring process, and uniformly stirring to obtain a dry mixture;

[0043] S4, adding water reducing agent into water and stirring to obtain an additive solution;

[0044] S5, adding the additive solution and viscosity adjusting and rapid setting agent into dry mixture and stirring to obtain rapid reinforcement high performance shotcrete for existing tunnel lining.

[0045] The present application has the following advantages:

[0046] 1. The low calcium high belite sulphoaluminate cement and superfine slag powder composite system is used, and through the synergistic excitation of the trigger type activator, a large amount of low alkalinity C-S-H gel and ettringite crystals are generated in the early stage, and a high strength dense matrix with a compressive strength of more than 60 MPa is formed.

[0047] 2. The dual protection is formed by the pH response characteristics of the nanogel and the alkalinity control function of the slow-release particles. The nanogel blocks the penetration by swelling effect when the medium invades; the slow-release particles release alkali under the critical pH condition, and maintain the stability of the steel fiber interface passivation film, so that the material has excellent chemical corrosion resistance and chloride ion penetration resistance.

[0048] 3. The synergistic effect of the viscosity adjusting and rapid setting agent and the superfine powder makes the mixture have suitable cohesiveness, and the rebound rate is controlled to be less than 6%, so that the aggregate and fiber are uniformly distributed and effectively anchored in the spraying process, a reinforcement layer with good integrity is formed, and the technical requirements of rapid construction are met. DETAILED DESCRIPTION

[0049] All the proportions are calculated by weight, and the basic mixture ratio is kept consistent, specifically: low calcium high belite sulphoaluminate cement 330 parts, superfine slag powder 90 parts, fine aggregate 850 parts, coarse aggregate 850 parts, copper-plated steel fiber 32 parts, polypropylene fiber 1.0 parts, water reducing agent 15 parts, and water 170 parts. The changes of each component and the function characterization are as follows.

[0050] Example 1

[0051] This embodiment provides a complete embodiment of the present application. Among them, component A is a trigger type activator, the dosage is 5 parts, component B is a slow-release particle, the dosage is 10 parts, component C is a nanogel, the dosage is 3 parts, and component D is a viscosity adjusting and rapid setting agent, the dosage is 35 parts.

[0052] Firstly, each functional component is prepared according to the standard preparation steps:

[0053] Component A preparation: sodium sulfate, triethanolamine and calcium sugar are weighed according to the mass ratio of 7:1.5:1, and after preliminary mixing, they are ball milled in a ball mill at 300 r / min for 30 minutes, and then sieved through an 80 μm sieve and sealed for storage.

[0054] Preparation of component B: nano metakaolin was dispersed in saturated calcium hydroxide solution under high shear to form a core suspension; the core suspension was added dropwise into a sodium alginate solution, and then calcium chloride solution was added dropwise to perform ion crosslinking to form primary gel particles; the shell was constructed by alternately adsorbing PDDA and nano metakaolin suspension for 5 times of layer-by-layer self-assembly; finally, the release particles were obtained by spray drying and sieving.

[0055] Preparation of component C: methacrylic acid monomer and crosslinking agent BIS were dissolved in deionized water and deoxygenated by nitrogen; under the protection of nitrogen and stirring at 70°C, initiator APS was added and reacted for 6 hours; the reaction solution was purified by dialysis and freeze-dried, and then sieved to obtain nanogel solids.

[0056] Preparation of component D: 98 parts of aluminum sulfate-based alkali-free liquid accelerator was compounded with 2 parts of HPMC powder under stirring, and the stirring was continued for 60 minutes until a uniform viscous liquid was formed, which was sealed for later use.

[0057] Subsequently, the concrete was prepared: the raw materials were weighed according to the ratio; the low-calcium high-belite sulfoaluminate cement, ultra-fine slag powder, and the above-prepared components A, B, and C were mixed uniformly to obtain a composite cementitious material; coarse and fine aggregates were added to the composite cementitious material for dry mixing, and then copper-plated steel fibers and polypropylene fibers were slowly added and stirred uniformly to obtain a dry mixture; the water reducing agent was added to water and stirred uniformly to obtain an admixture solution; finally, the admixture solution and component D were added to the dry mixture at the same time, and the mixture was stirred uniformly at high speed to obtain the shotcrete.

[0058] Example 2

[0059] This example aims to illustrate the influence of adjusting the content of functional components within the scope of the claims on the performance. The ratio is slightly adjusted based on Example 1: component A is 7 parts, component B is 7 parts, component C is 5 parts, and component D is 32 parts.

[0060] The preparation steps of each functional component (A, B, C, D) are exactly the same as in Example 1. The preparation steps of the concrete are also consistent with Example 1.

[0061] Comparative Example 1

[0062] This comparative example aims to investigate the influence of missing component A. The ratio does not contain component A, and the contents of the other components are exactly the same as in Example 1.

[0063] The preparation steps of components B, C, and D are the same as in Example 1. In the preparation steps of the concrete, only cement, ultra-fine slag powder, components B, and C are mixed without adding component A during the preparation of the composite cementitious material. The subsequent steps are consistent with Example 1.

[0064] Comparative Example 2

[0065] This comparative example aims to investigate the influence of missing component B. It does not contain component B in the proportion, and the rest of the components and contents are the same as Example 1.

[0066] The preparation steps of components A, C, and D are the same as Example 1. In the preparation steps of concrete, component B is not added when preparing composite cementitious materials. The subsequent steps are consistent with Example 1.

[0067] Comparative Example 3

[0068] This comparative example aims to investigate the influence of missing component C. It does not contain component C in the proportion, and the rest of the components and contents are the same as Example 1.

[0069] The preparation steps of components A, B, and D are the same as Example 1. In the preparation steps of concrete, component C is not added when preparing composite cementitious materials. The subsequent steps are consistent with Example 1.

[0070] Comparative Example 4

[0071] This comparative example aims to investigate the influence of missing component D. It does not contain component D in the proportion, and instead of component D, an equal amount of ordinary non-alkali liquid accelerator (i.e. without composite tackifier) is used, and the rest of the components and contents are the same as Example 1.

[0072] The preparation steps of components A, B, and C are the same as Example 1. In the preparation steps of concrete, the water-reducing agent and the ordinary non-alkali liquid accelerator are added together to form an admixture solution in water, and then added to the dry mixture for stirring at one time, instead of being added at the same time as component D.

[0073] The following test methods are used to test the performance of the concrete prepared in Examples 1-2 and Comparative Examples 1-4: rebound rate test standard: JGJ / T 372-2016; compressive strength: GB / T 50081-2019; strength corrosion resistance coefficient: GB / T 50082-2009; and chloride ion penetration resistance (electric flux method): ASTM C1202-22. The test results are shown in Table 1 below.

[0074] Table 1 Performance of concrete prepared in Examples 1-2 and Comparative Examples 1-4

[0075] Group Rebound (%) 1 day compressive strength (MPa) 28 day compressive strength (MPa) Corrosion resistance factor (%) Chloride ion permeability rating (Coulomb value, C) Example 1 5 25 65 >95 very low (< 800) Example 2 6 23 63 93 Very low (< 800) Comparative Example 1 12 12 55 90 Medium (~ 2500) Comparative Example 2 6 24 64 94 High (~ 4500) Comparative Example 3 6 24 62 91 Low (~ 1500) Comparative Example 4 25 8 58 92 Low (~ 1200)

[0076] Data analysis and explanation

[0077] In terms of rebound rate, Examples 1 and 2 show lower rebound rate, mainly due to the synergistic effect of component D and ultra-fine powder to improve the cohesiveness of the paste. Comparative Example 1 lacks component A, resulting in insufficient early paste structure formation and reduced viscosity, leading to increased rebound rate. Comparative Example 4 does not add component D, resulting in a significant decrease in paste cohesiveness, with a rebound rate of 25%, which cannot meet the requirements of spray construction.

[0078] In terms of compressive strength, both early and late strength of examples 1 and 2 are higher, due to component A promoting early synergistic hydration and dense structure. Comparative example 1 lacks component A, and early strength development is slow; comparative example 4 lacks component D, and early structure formation is hindered, with low 1-day strength, affecting the effect of rapid reinforcement.

[0079] The corrosion resistance coefficient results show that each group performs well in the sulfate environment, mainly due to the low-alkali, low-calcium ettringite matrix formed by low-calcium high-belli type sulphoaluminate cement and ultra-fine slag powder, which has excellent resistance to sulfate attack.

[0080] In terms of chloride ion permeability, examples 1 and 2 have very low permeability. Comparative example 2 lacks component B, and cannot maintain a high-alkali environment at the steel fiber interface, losing the ability to protect against chloride ions; comparative examples 1 and 3 respectively lack components A and C, resulting in decreased matrix density and weakened permeability barrier, and the permeability is worse than that of the examples.

[0081] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent substitutions for part of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A rapid reinforcement high performance shotcrete for existing tunnel lining, characterized in that, The raw materials include the following weight parts: low calcium type high belite sulphoaluminate cement 300-350 parts, superfine slag powder 80-100 parts, trigger type activator 3-8 parts, slow-release particles 5-15 parts, nanogel 2-5 parts, fine aggregate 800-900 parts, coarse aggregate 800-900 parts, copper-plated steel fiber 30-50 parts, polypropylene fiber 0.8-1.2 parts, viscosity adjusting accelerator 30-40 parts, water reducing agent 10-20 parts, and water 160-180 parts; The trigger type activator is obtained by uniformly mixing sodium sulfate, triethanolamine and calcium sugar in a mass ratio of (5-8) :(1-2) :1; The slow-release particles have a core-shell structure, the outer shell is a nano-level volcanic ash material, the inner core is a saturated alkaline solution, the nano-level volcanic ash material is nano-metakaolin or nano-silica fume, the saturated alkaline solution is a saturated calcium hydroxide or potassium hydroxide solution, and the mass ratio of the outer shell to the inner core is 1:(1-2); The nanogel is a polyelectrolyte hydrogel containing carboxyl groups, has a particle size distribution of 50-500 nm, shrinks in an environment with pH>11.5, and swells in an environment with pH<10.5; The viscosity adjusting accelerator is obtained by compounding an alkali-free liquid accelerator and a viscosity increasing agent, the content of the viscosity increasing agent is 0.5%-2% based on the mass of the alkali-free liquid accelerator, the alkali-free liquid accelerator is an aluminum sulfate-based accelerator, and the viscosity increasing agent is hydroxypropyl methyl cellulose or warm rubber glue.

2. The rapid-reinforcing high-performance shotcrete for existing tunnel linings according to claim 1, characterized in that, In the low calcium type high belite sulphoaluminate cement, the content of belite minerals is not less than 40%, and the content of aluminum phase minerals is not more than 15%.

3. The rapid-reinforcing high-performance shotcrete for existing tunnel linings according to claim 1, characterized in that, The particle size D50 of the superfine slag powder is ≤5 μm. The particle size of the coarse aggregate is 5-10 mm. The length of the copper-plated steel fiber is 25-30 mm, and the length-diameter ratio is 50-80. The length of the polypropylene fiber is 12-19 mm, and the diameter is 20-50 μm.

4. The rapid-reinforcing high-performance shotcrete for existing tunnel linings according to claim 1, characterized by, The fine aggregate is natural sand or machine-made sand, and the particle size range is 0.15-4.75 mm.

5. The rapid-reinforcement high-performance shotcrete for existing tunnel linings according to claim 1, characterized in that, The water reducing agent is a polycarboxylic acid type high efficiency water reducing agent.

6. The rapid-reinforcement high-performance shotcrete for existing tunnel linings according to claim 1, characterized in that, The preparation method of the slow-release particles is as follows: S11, nano-metakaolin is slowly added into a saturated Ca(OH)2 solution to form a suspension; S12, the suspension is added dropwise into a sodium alginate solution to form a mixed solution, and then the mixed solution is slowly added into a calcium chloride solution, and the mixture is left to solidify; S13, the solidified product is filtered to collect particles, the particles are dispersed in deionized water, polydimethyl diallyl ammonium chloride and nano-metakaolin suspension are alternately added, the mixture is stirred and washed, the product is collected, and then the product is spray dried to obtain the slow-release particles.

7. The rapid-reinforcement high-performance shotcrete for existing tunnel linings according to claim 1, characterized in that, The preparation method of the nanogel is as follows: S21, methacrylic monomer and crosslinking agent BIS are added into 90 ml of deionized water, and nitrogen is introduced to remove dissolved oxygen; S22, under the protection of nitrogen, an aqueous solution of initiator APS is added, and the mixture is reacted in a water bath for 6-8 h; S23, after the reaction is completed, the mixture is cooled to room temperature, and then the mixture is dialyzed with deionized water to obtain a milky white gel solution, and then the gel solution is freeze-dried to obtain the nanogel.

8. A method of producing the rapid-reinforcement high-performance shotcrete for existing tunnel linings according to any one of claims 1 to 7, characterized in that, The method includes the following steps: S1, the raw materials are weighed according to the proportions. S2, the low calcium type high bellite sulphoaluminate cement, superfine slag powder, trigger type activator, slow-release particles and nanogel are mixed uniformly to obtain a composite cementitious material; S3, coarse aggregate and fine aggregate are added to the composite cementitious material for dry mixing, and then copper-plated steel fibers and polypropylene fibers are slowly added during the stirring process, and the mixture is stirred uniformly to obtain a dry mixture; S4, the water reducing agent is added to water and stirred uniformly to obtain an admixture solution; S5, the admixture solution and the viscosity adjusting and rapid setting agent are simultaneously added to the dry mixture, and the mixture is stirred uniformly at high speed to obtain a rapid reinforcement high-performance sprayed concrete for existing tunnel lining.