Early-strength water-reducing agent for water-rich area early-strength anti-permeability shotcrete, and preparation method and application thereof

Abstract

The application discloses a kind of early-strength anti-permeability shotcrete for water-rich area, including early-strength component, setting component, adjusting component and filling material;Wherein, early-strength component is nano composite early-strength viscosity material, mass ratio 40~60%;Setting component is composed of one or several of triisopropyl alcohol amine, calcium formate, sodium sulfate, lithium sulfate, mass ratio 30~50%;Adjusting component is composed of one or several of powder water reducing agent, boric acid, sodium gluconate, sodium tripolyphosphate, citric acid, mass ratio is 1~5%, the rest is filling material.The application also discloses a kind of early-strength anti-permeability shotcrete for water-rich area and preparation method and application.The application can improve the strength of shotcrete in early age, reduce the rebound amount of shotcrete, improve the compactness and strength of concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures in building materials. More specifically, this invention relates to a spring-load reducer for early-strength, impermeable shotcrete in water-rich areas, its preparation method, and its application. Background Technology

[0002] Shotcrete is a special type of concrete that uses compressed air to spray concrete at high speed onto a target surface, allowing it to set and develop strength rapidly. Compared to cast-in-place concrete, machine-applied shotcrete offers advantages such as shorter setting time, easier construction, shorter construction period, and lower costs, making it widely used for shotcrete reinforcement in coal mine shafts, tunnels, and culverts. However, when using shotcrete in tunnel projects in water-rich areas, the high humidity and presence of standing water on the tunnel walls reduce the bond between the shotcrete and the wall, resulting in a high rebound rate. Simultaneously, the poor cohesiveness of the concrete leads to poor compaction after spraying, resulting in poor water permeability resistance. Often, large-area seepage occurs immediately after spraying, affecting the safety of the support structure.

[0003] Adding thickeners to concrete can improve its cohesiveness, thereby reducing rebound rate. Existing thickeners are of two types: inorganic and organic. Inorganic thickeners do not significantly improve the bonding viscosity between particles and aggregates; organic thickeners, after water evaporation or hydration, can cause enlarged pores, forming harmful pores and leading to reduced concrete strength. Both types of thickeners have their own drawbacks. Furthermore, in water-rich areas, the presence of surface water on the rock strata weakens the initial bonding force under continuous water infiltration, causing spalling. Water seeps into the incompletely hydrated concrete, forming water channels and affecting its durability. Simply increasing the bond strength with the rock strata cannot significantly improve the rebound rate and durability of shotcrete. It is necessary to improve the early-age strength of shotcrete on the basis of thickening, shorten the early strength development time, and reduce the influence of external water on the hydration process. This can effectively improve the concrete's bonding strength and density. However, the addition of traditional early-strength agents often affects the workability of the concrete before spraying, seriously impacting construction safety and quality. Summary of the Invention

[0004] One objective of this invention is to provide a spring-load reducer for early-strength, seepage-resistant shotcrete in water-rich areas, along with its preparation method and application. The spring-load reducer is designed to improve the early-age strength of shotcrete, reduce rebound rate, increase density and strength, without affecting slump retention. It enhances the cohesiveness and hydration rate of shotcrete through early-strength thickening components, improving the slurry encapsulation, post-spray adhesion, and rapid hardening properties, thereby reducing rebound rate and increasing single-shot thickness. Simultaneously, the rapid hydration of aluminum-containing nanoparticles loaded on hydrogel within the pores, along with directional hydration through graphene nucleation, effectively fills harmful pores, thereby improving the density and early-age strength of the shotcrete material. This achieves early strength, low rebound, and high density in shotcrete, solving the problems of high rebound and severe seepage in water-rich areas.

[0005] To address the aforementioned technical problems, this invention provides a spring-reducing agent for early-strength, impermeable shotcrete in water-rich areas, comprising a thickening and early-strength component, a setting-accelerating component, a regulating component, and filler materials; wherein, the thickening and early-strength component is a nano-composite early-strength thickening material, accounting for 40-60% by mass; the setting-accelerating component is composed of one or more of triisopropanolamine, calcium formate, sodium sulfate, and lithium sulfate, accounting for 30-50% by mass; the regulating component is composed of one or more of powder water-reducing agent, boric acid, sodium gluconate, sodium tripolyphosphate, and citric acid, accounting for 1-5% by mass, and the remainder is filler materials.

[0006] Preferably, the nanocomposite early strength thickening material is prepared by hydrogel-modified cationic polyacrylamide followed by adsorption of CASH nanocrystal nuclei, and the preparation method includes the following steps: S1. Mix 100 parts of monomers AMPS (2-acrylamido-2-methylpropanesulfonic acid) and DMAA (N,N-dimethylacrylamide) at a mass ratio of 1:1 to 1:5, and prepare P(AMPS-co-DMAA) hydrogel by blending polymerization. Simultaneously, during the mixing process, add 100 parts of a 0.01-0.05% cationic polyacrylamide aqueous solution to the blend solution dropwise to obtain a modified amide intermediate. S2. Simultaneously and slowly add 50 mL of sodium silicate solution and 50 mL of a mixed solution of calcium nitrate and aluminum nitrate to 100 mL of PCE (polycarboxylate superplasticizer) aqueous solution at a dropping rate of 2.0 mL / min. During the addition, monitor the pH value of the system in real time, and adjust the pH value of the system to 12 with NaOH solution and nitric acid solution. After all the reactants have been added, continue stirring the reactants at 30-35℃ for 24 h to obtain a milky white CASH nanocrystal suspension. S3. After filtering the prepared modified amide intermediate, dry it at 50-60℃ for 2 days. After drying, soak it in a 10-25% concentration of CASH nanocrystal nucleus solution for 10-12 hours. After filtration, obtain a saturated hydrogel, dry it at 50-60℃ for 2 days, add 5-10g of graphene powder, mix and pulverize to prepare a nanocomposite early strength thickening material.

[0007] Preferably, the sodium silicate modulus is 2.2-2.6; the mass concentration of calcium nitrate in the mixed solution of calcium nitrate and aluminum nitrate is 10-15%, and the mass concentration of aluminum nitrate is 20-30%; PCE is a polycarboxylate superplasticizer with a mass concentration of 5-10%.

[0008] Preferably, the cationic polyacrylamide has a molecular weight of 600,000 to 1,000,000.

[0009] Preferably, the graphene is industrial-grade graphene with a density of 10–50 g / cm³.

[0010] Preferably, the filler material is composed of one or more of stone powder, silica fume, and tailings powder.

[0011] This invention also provides a method for preparing a de-elasticity agent for early-strength, impermeable shotcrete in water-rich areas. The method involves mixing a thickening and early-strength component, a setting accelerator, a regulating component, and a filler material according to a designed mass ratio to obtain the de-elasticity agent for early-strength, impermeable shotcrete in water-rich areas.

[0012] Preferably, a nanocomposite early-strength and tackifying material is prepared by modifying cationic polyacrylamide with hydrogel and then adsorbing CASH nanocrystal nuclei, which serves as the tackifying and early-strength component.

[0013] The present invention also provides an application of a de-elasticity agent for early-strength, impermeable shotcrete in water-rich areas, wherein the de-elasticity agent is added to the shotcrete by means of internal admixture, i.e., replacing cement, and the amount of the de-elasticity agent is 1 to 3% of the mass of cementitious materials in the shotcrete.

[0014] The present invention has at least the following beneficial effects: This invention provides a shotcrete de-rebound agent that can improve the early-age strength of shotcrete, reduce the rebound rate of shotcrete, and improve the density and strength of concrete. It aims to enhance the cohesiveness and hydration rate of shotcrete by increasing the viscosity and early strength components, thereby improving the slurry encapsulation, adhesion to the walls after spraying, and rapid hardening performance, thus reducing the rebound rate and increasing the thickness of a single spraying. Furthermore, aluminum ion-containing nanoparticles loaded on hydrogel rapidly hydrate in the pores, directionally filling harmful pores, effectively improving the density and early strength of shotcrete, and achieving early strength, low rebound, and high density of shotcrete.

[0015] ① This rebound reducer is designed for the characteristics of shotcrete in water-rich areas (poor adhesion to rock strata, low early strength and easy spalling, poor water seepage resistance). It improves the construction quality of shotcrete from three aspects: pre-spraying slump protection, post-spraying adhesion enhancement and early strength, and post-spraying compaction and seepage resistance. It makes the rebound rate in water-rich areas less than 6%, increases the compressive strength by 500% in 1 hour, and reduces the penetration height ratio to less than 10%.

[0016] ② In this elasticity reducer, the CASH nanocrystal nuclei are encapsulated by hydrogel and are slowly released during mixing and transportation. This does not affect the slump retention performance of concrete before spraying. When the quick-setting agent is added, a large number of needle-shaped ettringite are generated, which destroys the surface structure of the hydrogel. The CASH nanocrystal nuclei are rapidly dissolved and released. The CASH nanocrystal nuclei provide nucleation sites, and the aluminum glue promotes rapid hydration, quickly filling the ettringite voids to form a dense structure and generate early strength.

[0017] ③ This elasticity reducer uses low molecular weight cationic polyacrylamide. Cationic polyacrylamide is a linear polymer compound with a low molecular weight, which can effectively reduce the pores formed by water adsorption and aggregation. The nanocrystal nuclei and graphene will simultaneously induce cement hydration during the evaporation of water around the polymer chain to form a large amount of gel to fill the structural pores, thereby achieving the directional filling of harmful pores and improving the density and strength of the hydration products.

[0018] Other advantages, objectives and features of the present invention will be apparent in part from the following description, and in part from what those skilled in the art will understand through study and practice of the invention. Detailed Implementation

[0019] To better understand the purpose, structure, and function of this invention, the following detailed description is provided in conjunction with embodiments, so that those skilled in the art can implement it based on the description.

[0020] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0021] Unless otherwise specified, all components in this application are commercially available products.

[0022] The 2-acrylamido-2-methylpropanesulfonate, N,N-dimethylacrylamide, and cationic polyacrylamide are commercially available products. The triisopropanolamine, calcium formate, sodium sulfate, and lithium sulfate mentioned are all commercially available products; The powder water-reducing agent, boric acid, sodium gluconate, sodium tripolyphosphate, and citric acid mentioned are commercially available products; The filler material is composed of one or more of stone powder, silica fume, and tailings powder, all of which are commercially available products.

[0023] The elasticity-reducing agent of this invention is composed of a thickening and early-strength component, a setting-accelerating component, and a regulating component, and is used at a rate of 1-3% of the mass of the cementitious material in the shotcrete. The thickening and early-strength component is a nano-composite early-strength thickening material, accounting for 40-60% by mass; the setting-accelerating component is composed of one or more of triisopropanolamine, calcium formate, sodium sulfate, and lithium sulfate, accounting for 30-50% by mass; the regulating component is composed of one or more of powder water-reducing agent, boric acid, sodium gluconate, sodium tripolyphosphate, and citric acid, accounting for 1-5% by mass; the remainder is filler material, which is composed of one or more of stone powder, silica fume, and tailings powder.

[0024] The aforementioned nanocomposite early-strength thickening material is a multifunctional thickening material with early strength, slow release, and directional pore filling capabilities. It is prepared by modifying cationic polyacrylamide with hydrogel and then adsorbing CASH nanocrystal nuclei. The modified polyacrylamide exhibits good thickening effects in concrete. The CASH nanoparticles in the hydrogel move with the polyacrylamide molecules and, during hydration, are released into the liquid phase surrounding the polymer chains. The nanoparticles provide nuclei, and highly active aluminum ions promote rapid hydration. Nucleation occurs rapidly where water is encapsulated by polyacrylamide molecules, promoting the generation of hydration products. This material works synergistically with graphene to fill pores after water hydration and evaporation, preventing the formation of harmful pores. Simultaneously, it works synergistically with a quick-setting agent to accelerate concrete hydration. The preparation process is as follows: S1. Mix 100 parts of monomers AMPS (2-acrylamido-2-methylpropanesulfonic acid) and DMAA (N,N-dimethylacrylamide) at a mass ratio of 1:1 to 1:5, and prepare P(AMPS-co-DMAA) hydrogel by blend polymerization. Simultaneously, during the mixing process, add 100 parts of a 0.01-0.05% cationic polyacrylamide aqueous solution dropwise to the blend solution to obtain a modified amide intermediate. The cationic polyacrylamide is of low molecular weight, ranging from 600,000 to 1,000,000. Too low a molecular weight results in poor thickening effect, while too high a molecular weight will cause excessive entanglement and coating of cement particles, reducing the strength of the concrete.

[0025] S2. Simultaneously and slowly add 50 mL of sodium silicate solution and 50 mL of a mixed solution of calcium nitrate and aluminum nitrate to 100 mL of PCE aqueous solution at a dropping rate of 2.0 mL / min. During the addition, monitor the pH value of the system in real time with a high-precision pH meter, and adjust the pH value of the system to around 12 with NaOH solution and nitric acid solution. After all the reactants have been added, continue stirring the reactants at 30-35℃ for 24 h to obtain a milky white CASH nanocrystal suspension with a high active aluminum content. The sodium silicate modulus is between 2.2 and 2.6, the mass concentration of calcium nitrate in the mixed solution of calcium nitrate and aluminum nitrate is 10-15%, the mass concentration of aluminum nitrate is 20-30%, and PCE is a polycarboxylate superplasticizer with a mass concentration of 5-10%.

[0026] S3. The prepared modified amide intermediate is filtered and dried at 50-60℃ for 2 days. After drying, it is soaked in a 10-25% concentration CASH nanocrystal nucleus solution for 10-12 hours. After filtration, a saturated hydrogel is obtained and dried at 50-60℃ for 2 days. After drying, 5-10g of graphene powder is added, mixed, and then pulverized to prepare a nanocomposite early-strength tackifier. The graphene is industrial-grade graphene with a density of 10-50g / cm3. After drying, the saturated hydrogel is prone to agglomeration during pulverization. The inclusion of graphene can effectively separate the pulverized fragments from the powder, thus playing a dispersing role. During hydration, the graphene provides nuclei, which further promotes the hydration of cement particles around the tackifier, fills the pores, and improves the impermeability and compressive strength of the shotcrete.

[0027] Example 1 This embodiment provides a spring-loaded agent for early-strength, impermeable shotcrete in water-rich areas, comprising the following components by weight: 40 parts of thickening and early-strength component, 50 parts of setting accelerator component, 5 parts of conditioning component, and 5 parts of filler material.

[0028] The coagulant components include 20 parts of triisopropanolamine and 30 parts of lithium sulfate; The adjusting components include 2 parts powder water-reducing agent, 1 part boric acid and 2 parts sodium gluconate; The filling material includes 5 parts of tailings powder.

[0029] In this embodiment, the early-strength thickening component is a nanocomposite early-strength thickening material, and its preparation method is as follows: S1. 100 parts of monomers AMPS (2-acrylamido-2-methylpropanesulfonic acid) and DMAA (N,N-dimethylacrylamide) were mixed at a mass ratio of 1:1 and a P(AMPS-co-DMAA) hydrogel was prepared by blend polymerization. Simultaneously, 100 parts of a 0.05% cationic polyacrylamide aqueous solution were added dropwise to the blend solution during the mixing process to obtain a modified amide intermediate. The cationic polyacrylamide was of low molecular weight, ranging from 600,000 to 1,000,000.

[0030] S2. Simultaneously and slowly add 50 mL of sodium silicate solution and 50 mL of a mixed solution of calcium nitrate and aluminum nitrate to 100 mL of PCE aqueous solution at a dropping rate of 2.0 mL / min. During the addition, monitor the pH value of the system in real time with a high-precision pH meter, and adjust the pH value of the system to around 12 with NaOH solution and nitric acid solution. After all the reactants have been added, continue stirring the reactants at 35℃ for 24 h to obtain a milky white CASH nanocrystal suspension with a high active aluminum content. The sodium silicate modulus is between 2.2 and 2.6, the mass concentration of calcium nitrate in the mixed solution of calcium nitrate and aluminum nitrate is 15%, the mass concentration of aluminum nitrate is 30%, and PCE is a polycarboxylate superplasticizer with a mass concentration of 10%.

[0031] S3. The modified amide intermediate was filtered and dried at 60℃ for 2 days. After drying, it was soaked in a 25% concentration of CASH nanocrystal core solution for 12 hours. After filtration, a saturated hydrogel was obtained. The hydrogel was dried at 60℃ for 2 days. After drying, 10g of graphene powder was added and mixed and then pulverized to prepare a nanocomposite early strength thickening material.

[0032] A method for preparing a de-elasticity agent for early-strength, impermeable shotcrete in water-rich areas involves mixing the following components by weight: 40 parts of thickening and early-strength component, 50 parts of setting accelerator component, 5 parts of regulating component, and 5 parts of filler material.

[0033] The elasticity reducer prepared in Example 1 was added to the shotcrete by means of internal admixture, i.e., replacing cement. The amount of elasticity reducer was 2% of the mass of cementitious material in the shotcrete.

[0034] Example 2 This embodiment provides a spring-loaded agent for early-strength, impermeable shotcrete in water-rich areas, comprising the following components by weight: 50 parts of thickening and early-strength component, 40 parts of setting accelerator component, 3 parts of conditioning component, and 7 parts of filler material.

[0035] The coagulant components include 20 parts of triisopropanolamine and 20 parts of lithium sulfate; The adjusting components include 1 part powder water-reducing agent, 1 part boric acid and 1 part sodium gluconate; The filling material includes 7 parts of tailings powder.

[0036] Everything else is exactly the same as in Example 1.

[0037] Example 3 This embodiment provides a spring-loaded agent for early-strength, impermeable shotcrete in water-rich areas, comprising the following components by weight: 60 parts of thickening and early-strength component, 30 parts of setting accelerator component, 1 part of regulating component, and 9 parts of filler material.

[0038] The coagulant components include 10 parts of triisopropanolamine and 20 parts of lithium sulfate; The adjusting components include 0.4 parts of powder water-reducing agent, 0.2 parts of boric acid, and 0.4 parts of sodium gluconate; The filling material includes 9 parts of tailings powder.

[0039] Everything else is exactly the same as in Example 1.

[0040] Comparative Example 1 The standard C25 shotcrete was used without any added elasticity reducer.

[0041] Comparative Example 2 Following the formulation of Example 3, the hydrogel and the nano-CASH nucleation early strength agent were added directly without pre-adsorption. Everything else was the same as in Example 3.

[0042] In this embodiment, the early-strength thickening component is a nanocomposite early-strength thickening material, and its preparation method is as follows: S1. Mix monomers AMPS (2-acrylamido-2-methylpropanesulfonic acid) and DMAA (N,N-dimethylacrylamide) at a mass ratio of 1:1, totaling 100 parts, and prepare P(AMPS-co-DMAA) hydrogel by blending polymerization.

[0043] S2. Simultaneously and slowly add 50 mL of sodium silicate solution and 50 mL of a mixed solution of calcium nitrate and aluminum nitrate to 100 mL of PCE aqueous solution at a dropping rate of 2.0 mL / min. During the addition, monitor the pH value of the system in real time with a high-precision pH meter, and adjust the pH value of the system to around 12 with NaOH solution and nitric acid solution. After all the reactants have been added, continue stirring the reactants at 35℃ for 24 h to obtain a milky white CASH nanocrystal suspension with a high active aluminum content. The sodium silicate modulus is between 2.2 and 2.6, the mass concentration of calcium nitrate in the mixed solution of calcium nitrate and aluminum nitrate is 15%, the mass concentration of aluminum nitrate is 30%, and PCE is a polycarboxylate superplasticizer with a mass concentration of 10%.

[0044] S3. P(AMPS-co-DMAA) hydrogel and CASH nanocrystal suspension were mixed to prepare a nanocomposite early strength thickening material.

[0045] Comparative Example 3 Following the formulation of Example 3, without adding graphene, the dried hydrogel was directly pulverized and then the elasticity-reducing agent was added. Everything else was the same as in Example 3.

[0046] In this embodiment, the early-strength thickening component is a nanocomposite early-strength thickening material, and its preparation method is as follows: S1. 100 parts of monomers AMPS (2-acrylamido-2-methylpropanesulfonic acid) and DMAA (N,N-dimethylacrylamide) were mixed at a mass ratio of 1:1 and a P(AMPS-co-DMAA) hydrogel was prepared by blend polymerization. Simultaneously, 100 parts of a 0.05% cationic polyacrylamide aqueous solution were added dropwise to the blend solution during the mixing process to obtain a modified amide intermediate. The cationic polyacrylamide was of low molecular weight, ranging from 600,000 to 1,000,000.

[0047] S2. Simultaneously and slowly add 50 mL of sodium silicate solution and 50 mL of a mixed solution of calcium nitrate and aluminum nitrate to 100 mL of PCE aqueous solution at a dropping rate of 2.0 mL / min. During the addition, monitor the pH value of the system in real time with a high-precision pH meter, and adjust the pH value of the system to around 12 with NaOH solution and nitric acid solution. After all the reactants have been added, continue stirring the reactants at 35℃ for 24 h to obtain a milky white CASH nanocrystal suspension with a high active aluminum content. The sodium silicate modulus is between 2.2 and 2.6, the mass concentration of calcium nitrate in the mixed solution of calcium nitrate and aluminum nitrate is 15%, the mass concentration of aluminum nitrate is 30%, and PCE is a polycarboxylate superplasticizer with a mass concentration of 10%.

[0048] S3. The modified amide intermediate was filtered and dried at 60°C for 2 days. After drying, it was soaked in a 25% concentration of CASH nanocrystal nucleus solution for 12 hours. After filtration, a saturated hydrogel was obtained and dried at 60°C for 2 days to prepare a nanocomposite early strength thickening material.

[0049] Comparative Example 4 The elasticity reducer prepared in Example 3 was added to the shotcrete by means of internal admixture, i.e., replacing cement. The amount of elasticity reducer was 4% of the mass of cementitious materials in the shotcrete.

[0050] Everything else is exactly the same as in Example 3.

[0051] Comparative Example 5 This embodiment provides a spring-loaded agent for early-strength, impermeable shotcrete in water-rich areas, comprising the following components by weight: 70 parts of thickening and early-strength component, 24 parts of setting accelerator component, 1 part of conditioning component, and 5 parts of filler material.

[0052] The coagulant components include 10 parts of triisopropanolamine and 14 parts of lithium sulfate; The adjusting components include 0.4 parts of powder water-reducing agent, 0.2 parts of boric acid, and 0.4 parts of sodium gluconate; The filling material includes 5 parts of tailings powder.

[0053] Everything else is exactly the same as in Example 3.

[0054] Comparative Example 6 Wuhan Yuanjin Building Materials Technology Co., Ltd.'s HT-01 elasticity reducer product.

[0055] The above-described embodiments and comparative examples were prepared using sprayed concrete according to Table 1 below.

[0056] Table 1. Mix proportions of C25 shotcrete (kg / m³) The various performance tests conducted on the above embodiments and comparative examples are shown in Table 2 below.

[0057] Table 2 Performance Tests As shown in Table 2, the different components of the shotcrete reducer used in Examples 1, 2, and 3, compared with Comparative Example 1, effectively increased the plastic viscosity and 1-hour strength of shotcrete, thereby improving the adhesion and early strength of shotcrete during spraying, reducing the rebound rate, making the concrete denser, increasing the 28-day compressive strength and bond strength, and reducing the impermeability height ratio. Comparing the test results of Examples 1, 2, 3, and 5, it can be seen that with the increase of the viscosity-enhancing and early-strength components, the viscosity of shotcrete further increases, the rebound rate further decreases, and the strength at each age also improves. The effect of increasing strength weakens after the dosage exceeds 60%, and the 28-day strength decreases slightly. Comparing the results of Example 3 and Comparative Example 2, it is clear that without pre-adsorption of the hydrogel and nano-CASH nucleation early-strength agent, the nano-CASH nucleation early-strength agent significantly affects the slump retention of concrete, rendering it unusable during spraying and unsuitable for subsequent testing. Comparing Example 3 and Comparative Example 3, directly pulverizing the dried hydrogel without adding graphene encapsulation leads to powder agglomeration, making it difficult to disperse in concrete, resulting in uneven concrete quality, increased porosity, and reduced strength and impermeability. Comparing Example 3 and Comparative Example 4, increasing the dosage of the elasticity reducer increases the time-dependent loss of concrete, increases rebound, and also increases the impermeability height ratio. Comparing Example 3 and Comparative Example 6, compared to commercially available elasticity reducer products, the dosage of this application's product is lower, yet the spraying effect and concrete strength at all ages are higher than the comparative products.

[0058] This product was successfully applied in the Tianchiya Tunnel of the Shiwu-Nan Expressway. The Tianchiya Tunnel traverses a water-rich fractured zone, with some sections experiencing rock seepage rates reaching 100L / min. The seepage pressure was high, the rock surface was slippery and soft, resulting in poor concrete adhesion. Traditional wet-mix shotcrete exhibited a rebound rate of 50%, and the initial support structure had numerous honeycomb-like voids. The 28-day compressive strength was only 20MPa, failing to meet support requirements. After using this product, the initial setting time was shortened to 3 minutes, meeting the rapid setting requirements of a dynamic water environment. The rebound rate decreased to 7.5%, the 28-day compressive strength increased to 40.5MPa, the bond strength reached 2.2MPa, the sprayed material density reached 95%, and the number of seepage points decreased by 83%. This product successfully solved the technical bottlenecks of poor adhesion of shotcrete in water-rich strata and weak impermeability of the support structure, forming a zero-leakage shotcrete structure for water-rich tunnels.

[0059] Based on the above experimental results, this invention successfully formulated a shotcrete reducer that can reduce the rebound rate of shotcrete in water-rich areas, increase the early-age strength of shotcrete, and improve the density and strength of concrete by using the synergistic effect of thickening and early-strength components, accelerators, and regulators. The thickening and early-strength components enhance the cohesiveness and hydration rate of shotcrete, improve the slurry encapsulation, adhesion to walls after spraying, and rapid hardening performance, thereby reducing the rebound rate and increasing the thickness of a single spraying. The aluminum ion-containing nanoparticles loaded on the hydrogel rapidly hydrate in the pores, directionally filling harmful pores, effectively improving the density and early strength of shotcrete, and achieving early strength, low rebound, and high density of shotcrete.

[0060] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention, and other modifications can be easily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A modifier for reducing elasticity in early-strength, impermeable shotcrete used in water-rich areas, characterized in that, It includes a thickening and early-strength component, a setting accelerator, a regulating component, and filler materials; among which, the thickening and early-strength component is a nano-composite early-strength thickening material, accounting for 40-60% by mass; the setting accelerator is composed of one or more of triisopropanolamine, calcium formate, sodium sulfate, and lithium sulfate, accounting for 30-50% by mass; the regulating component is composed of one or more of powder water-reducing agent, boric acid, sodium gluconate, sodium tripolyphosphate, and citric acid, accounting for 1-5% by mass, and the remainder is filler materials; The nanocomposite early strength thickening material is prepared by modifying cationic polyacrylamide with hydrogel and then adsorbing CASH nanocrystal nuclei. The preparation method includes the following steps: S1. Mix 100 parts of monomers AMPS (2-acrylamido-2-methylpropanesulfonic acid) and DMAA (N,N-dimethylacrylamide) at a mass ratio of 1:1 to 1:5, and prepare P(AMPS-co-DMAA) hydrogel by blending polymerization. Simultaneously, during the mixing process, add 100 parts of a 0.01-0.05% cationic polyacrylamide aqueous solution to the blend solution dropwise to obtain a modified amide intermediate. S2. Simultaneously and slowly add 50 mL of sodium silicate solution and 50 mL of a mixed solution of calcium nitrate and aluminum nitrate to 100 mL of PCE (polycarboxylate superplasticizer) aqueous solution at a dropping rate of 2.0 mL / min. During the addition, monitor the pH value of the system in real time, and adjust the pH value of the system to 12 with NaOH solution and nitric acid solution. After all the reactants have been added, continue stirring the reactants at 30-35℃ for 24 h to obtain a milky white CASH nanocrystal suspension. S3. After filtering the prepared modified amide intermediate, dry it at 50-60℃ for 2 days. After drying, soak it in a 10-25% concentration of CASH nanocrystal nucleus solution for 10-12 hours. After filtration, obtain a saturated hydrogel, dry it at 50-60℃ for 2 days, add 5-10g of graphene powder, mix and pulverize to prepare a nanocomposite early strength thickening material.

2. The elasticity-reducing agent for early-strength, impermeable shotcrete in water-rich areas as described in claim 1, characterized in that, The sodium silicate modulus is 2.2-2.6; the mass concentration of calcium nitrate in the mixed solution of calcium nitrate and aluminum nitrate is 10-15%, and the mass concentration of aluminum nitrate is 20-30%; PCE is a polycarboxylate superplasticizer with a mass concentration of 5-10%.

3. The elasticity-reducing agent for early-strength, impermeable shotcrete in water-rich areas as described in claim 1, characterized in that, The cationic polyacrylamide has a molecular weight of 600,000 to 1,000,000.

4. The elasticity-reducing agent for early-strength, impermeable shotcrete in water-rich areas as described in claim 1, characterized in that, The graphene is industrial-grade graphene with a density of 10–50 g / cm³. 3 .

5. The elasticity-reducing agent for early-strength, impermeable shotcrete in water-rich areas as described in claim 1, characterized in that, The filler material is composed of one or more of stone powder, silica fume, and tailings powder.

6. The method for preparing the elasticity-reducing agent for early-strength, impermeable shotcrete in water-rich areas as described in any one of claims 1 to 5, characterized in that, The thickening and early-strength components, the setting accelerator, the regulating components, and the filler materials are mixed according to the designed mass ratio to obtain the elasticity reducer for early-strength, impermeable shotcrete in water-rich areas.

7. The application of the elasticity-reducing agent for early-strength, impermeable shotcrete in water-rich areas as described in any one of claims 1-5, characterized in that, The elasticity reducer is added to the shotcrete by means of internal admixture, i.e., replacing cement, and the amount of the elasticity reducer is 1 to 3% of the mass of the cementitious material in the shotcrete.

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