A high-strength shotcrete for tunnels and its preparation method

Abstract

This application relates to the field of high-strength concrete, and specifically discloses a high-strength shotcrete for tunnels and its preparation method. The raw materials thereof include the following parts by weight: 100-180 parts of cement, 60-90 parts of water, 260-500 parts of aggregate, 0.1-0.35 parts of coupling agent, 20-35 parts of setting-adjusting particles, and 30-50 parts of reinforcing particles; the reinforcing particles include cyclodextrin and composite admixture. The preparation method of the shotcrete includes the following steps: S1 Preparation of reinforcing particles: Dissolve cyclodextrin in water to form a saturated aqueous solution, add the composite admixture and stir for inclusion, and obtain the reinforcing particles after drying; S2, Premix the setting-adjusting particles, reinforcing particles and coupling agent evenly, add them into the cement and aggregate, and finally add water and stir evenly to obtain the shotcrete. The obtained shotcrete not only has good compressive strength and can meet the performance requirements of high strength, but also has excellent fluidity and good pumpability.

Description

Technical Field

[0001] This application relates to the field of high-strength concrete, and more specifically, it relates to a high-strength shotcrete for tunnels and a preparation method thereof. Background Art

[0002] Concrete has the advantages of high strength, good durability, simple process, and rich raw materials. It is an essential building material nowadays. Concrete is generally prepared by mixing cement, auxiliary materials, admixtures, mineral materials, and water according to requirements. With the continuous investment in the construction of railway infrastructure in China, the number of tunnels is increasing, and the research on concrete dedicated to tunnels has further become a hot topic.

[0003] For example, the patent application with the publication number CN110590258A discloses a tunnel shotcrete. Based on the volume of the tunnel shotcrete, it includes the following components: cement 360 - 500 kg / m 3 、coarse sand 818 - 890 kg / m 3 、crushed stone 789 - 817 kg / m 3 、basalt fiber 1.5 - 4.5 kg / m 3 、fly ash 90 - 98 kg / m 3 、accelerator 8 - 20 kg / m 3 、water reducer 5 - 10 kg / m 3 。

[0004] In tunnel construction, concrete is usually formed according to the mix ratio, and a shotcrete machine is used to pump it to the nozzle for spraying construction. However, the above concrete can only meet the requirements of ordinary C30 or C40. To meet higher mechanical strength, the fluidity of the concrete will decrease, and the pumpability will become poor, unable to meet the performance requirements of both high strength and high fluidity. Summary of the Invention

[0005] This application provides a high-strength shotcrete for tunnels and a preparation method thereof. The obtained shotcrete not only has good compressive strength and can meet the performance requirements of high strength, but also has excellent fluidity and good pumpability.

[0006] In the first aspect, a high-strength shotcrete for tunnels provided by this application adopts the following technical solution:

[0007] A high-strength shotcrete for tunnels includes the following raw materials in parts by weight: 100 - 180 parts of cement, 60 - 90 parts of water, 260 - 500 parts of aggregate, 0.1 - 0.35 parts of coupling agent, 20 - 35 parts of setting-adjusting particles, and 30 - 50 parts of strengthening particles; the strengthening particles include cyclodextrin and composite admixture;

[0008] The setting-adjusting particles are prepared through the following steps: mixing lignosulfonate, organic carboxylate and chitosan solution, heating the mixture, and reacting under the action of a catalyst to obtain modified chitosan; mixing the modified chitosan with microbeads and keeping warm to obtain the setting-adjusting particles.

[0009] Further, during the preparation of the setting-adjusting particles, the mixture is heated to 50-60°C and reacts under the action of a catalyst. After the modified chitosan is mixed with the microbeads, it is generally kept warm at a temperature of 30-40°C for 0.35-0.55 h.

[0010] Further, the cement is generally selected as P.O52.5 cement.

[0011] Further, the chitosan solution is specifically: dissolving chitosan in an acidic solution to form a chitosan solution. Chitosan with a degree of deacetylation of 70-90% is preferably used to ensure excellent solubility of chitosan.

[0012] As a further preference for the chitosan solution, the mass concentration of the chitosan solution is 3-8%.

[0013] By reacting lignosulfonate and carboxylate with chitosan solution, the setting-adjusting particles simultaneously have sulfonic acid groups and carboxylic acid hydration groups, and cooperate with the microbead effect to endow the system with excellent fluidity and thixotropy, thereby effectively improving the pumpability of concrete materials. The strengthening particles are obtained by encapsulating composite admixtures with cyclodextrin, which can enable the composite admixtures to participate in the system reaction in the middle and late stages of cement hydration, giving the material a certain pumping time, and at the same time ensuring that after the material is pumped, the mechanical properties of the concrete material can be significantly improved and the compressive strength is good.

[0014] For general C30 or C40 grade concrete materials, in the funnel test, if the concrete materials can all flow out of the funnel within 10-20 s, it means that the fluidity of the materials is appropriate, the viscosity of the materials is suitable, and the materials have good workability; and it is well known in the art that the higher the strength grade of concrete materials, the greater the viscosity of the materials, and the longer the time for the concrete materials to flow out of the funnel. It has always been a difficult problem in the art to make high-strength concrete materials have excellent fluidity. However, it is found in the research experiment that after the setting-adjusting particles and strengthening particles are compounded in the present application and under the action of a coupling agent, they can not only synergistically improve and adjust the fluidity and pumpability of concrete materials, so that the concrete materials have excellent workability in the early stage, but also can significantly improve the density inside the concrete to meet the requirements of the concrete materials having both high strength and excellent pumping performance.

[0015] Preferably, the component dosage of the setting-adjusting particles is as follows, in parts by weight: 1-3 parts of lignosulfonate, 1-2.5 parts of organic carboxylate, 12-20 parts of chitosan solution, 0.2-0.5 parts of catalyst, and 5.8-9 parts of microbeads.

[0016] Furthermore, the lignosulfonate is preferably sodium lignosulfonate.

[0017] By adopting the above technical solution, the dosage relationship of each raw material component in the setting-adjusting particles is optimized, and the comprehensive quality of the setting-adjusting particles is improved, so as to be more conducive to better coordination with the strengthening particles and jointly improve the fluidity and pumpability of the concrete material.

[0018] Preferably, the microbeads are fly ash microbeads and / or vitrified microbeads. The microbeads can be fly ash microbeads, can be vitrified microbeads, or can be a compound of fly ash microbeads and vitrified microbeads.

[0019] As a preferred technical solution of the microbeads, a mixture of fly ash microbeads and vitrified microbeads with a mass ratio of 1:1 - 2 is selected.

[0020] More preferably, the particle size of the microbeads is 50 - 100 μm.

[0021] By adopting the above technical solution, the microbeads are small in particle size and high in activity, which can reduce the viscosity of the concrete system, and both fly ash microbeads and vitrified microbeads can be used as aggregates to fill inside the concrete material, assisting in improving the mechanical properties of the material.

[0022] Preferably, the organic carboxylate is one of sodium benzoate and potassium succinate.

[0023] Preferably, the catalyst is ammonium persulfate.

[0024] By adopting the above technical solution, the selection of the components of the organic carboxylate and the catalyst is further optimized to promote the effectiveness of the setting-adjusting particles.

[0025] Preferably, the mass ratio of the cyclodextrin to the composite admixture is 1:(3.5 - 6).

[0026] Preferably, the composite admixture includes at least two of mineral powder, silica fume and kaolin.

[0027] Furthermore, the mineral powder is preferably S95 grade mineral powder, and the SiO2 content of the silica fume is ≥95%.

[0028] Furthermore, the composite admixture can be a compound of mineral powder and silica fume, can be a compound of silica fume and kaolin, can be a compound of mineral powder and kaolin, or can be a mixture of mineral powder, silica fume and kaolin.

[0029] By adopting the above technical solution, the mineral powder, silica fume and kaolin in the composite admixture can all be used as fillers to fill inside the concrete material, exerting excellent filling effects and pozzolanic reactions, making the inside of the concrete more dense, improving the density and strength inside the concrete, and ensuring the mechanical properties of the later-stage forming of the concrete.

[0030] Preferably, the aggregate includes coarse sand, medium sand and quartz sand with a mass ratio of (0.55 - 1):1:(0.15 - 0.4).

[0031] Furthermore, the coarse sand is sand and gravel with an average particle size of 0.5 mm - 1.5 mm; the fineness modulus is 3.1 - 3.7; the medium sand has a fineness modulus of 2.3 - 3.0 and an average particle size of 0.35 - 0.5 mm; the average particle size of quartz is 0.2 - 0.35 mm, and the water content is < 2%.

[0032] By adopting the above technical solution, the present application uses a suitable ratio of coarse sand, medium sand and quartz sand for compounding, so that the inside of the concrete material is filled densely, which helps to improve the strength of the material.

[0033] In a second aspect, the present application provides a method for preparing high-strength shotcrete for tunnels, adopting the following technical solution:

[0034] A method for preparing high-strength shotcrete for tunnels includes the following steps:

[0035] S1 Reinforcing particle preparation: Dissolve cyclodextrin in water to form a saturated aqueous solution, add a composite admixture and stir for inclusion, and obtain reinforcing particles after drying.

[0036] S2 Premix the setting-adjusting particles, reinforcing particles and coupling agent evenly, add them to cement and aggregate, and finally add water and stir evenly to obtain shotcrete.

[0037] By adopting the above technical solution, cyclodextrin is formed into a saturated aqueous solution, and the composite admixture is included by spray drying inclusion technology to form an inclusion compound, which slowly releases the composite admixture after encountering water, improves the fluidity and thixotropy of the material, and significantly improves the mechanical properties of the concrete after shotcrete forming.

[0038] First, premix the coupling agent, setting-adjusting particles and reinforcing particles to improve their surface activity, which helps to disperse better in the subsequent mixing with cement and aggregate, and the dispersibility of the system is better. Finally, add water to obtain shotcrete with excellent fluidity and thixotropy and strong pumpability.

[0039] In summary, in the present application, lignosulfonate and carboxylate are reacted with chitosan colloid solution so that the setting-adjusting particles simultaneously have sulfonic acid groups and carboxylic acid hydration groups, and combined with the microsphere effect, excellent fluidity and thixotropy are imparted to the system, thereby effectively improving the pumpability of concrete materials. The strengthening particles are obtained by encapsulating composite admixtures with cyclodextrin, which can enable the composite admixtures to participate in the system reaction in the middle and late stages of cement hydration, giving the material a certain pumping time. At the same time, it is ensured that after the material is pumped, the mechanical properties of the concrete material can be significantly improved and the compressive strength is good. The setting-adjusting particles and the strengthening particles are compounded, and under the action of the coupling agent, they can not only synergistically improve and regulate the fluidity and pumpability of concrete materials, so that the concrete materials have excellent workability in the early stage, but also can significantly improve the density inside the concrete to meet the requirements of concrete materials with both high strength and excellent pumpability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flowchart of the preparation method of the high-strength shotcrete for tunnels in the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The following will describe the embodiments of the present invention in detail. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. The specific conditions not specified in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0042] Preparation Example of Setting-Adjusting Particles

[0043] Preparation Example 1

[0044] The setting-adjusting particles are prepared through the following steps: 1 part of sodium lignosulfonate, 2.5 parts of potassium succinate and 12 parts of chitosan colloid solution with a mass concentration of 8% are mixed and heated to 50 °C, and reacted with 0.2 part of ammonium persulfate to obtain modified chitosan. The modified chitosan is mixed with 5.8 parts of fly ash microspheres and kept warm at 30 °C for 0.55 h to obtain the setting-adjusting particles;

[0045] Among them: the chitosan colloid solution is: chitosan with a deacetylation degree of 70% is dissolved in an acetic acid solution with a mass concentration of 5%;

[0046] The particle size of the fly ash microspheres is 50 - 70 μm.

[0047] Preparation Example 2

[0048] The setting - adjusting particles are prepared through the following steps: Mix 3 parts of sodium lignosulfonate, 1 part of potassium succinate and 20 parts of chitosan gum solution with a mass concentration of 3% and heat to 60°C, react with 0.5 part of ammonium persulfate to obtain modified chitosan, mix the modified chitosan with 9 parts of vitrified microspheres and keep warm at 40°C for 0.3 h to obtain the setting - adjusting particles;

[0049] Among them: The chitosan gum solution is obtained by dissolving chitosan with a deacetylation degree of 90% in an acetic acid solution with a mass concentration of 3%;

[0050] The particle size of the vitrified microspheres is 80 - 100 μm.

[0051] Preparation Example 3

[0052] The setting - adjusting particles are prepared through the following steps: Mix 2.3 parts of sodium lignosulfonate, 1.5 parts of sodium benzoate and 16 parts of chitosan gum solution with a mass concentration of 6% and heat to 55°C, react with 0.3 part of ammonium persulfate to obtain modified chitosan, mix the modified chitosan with 4 parts of fly ash microspheres and 4 parts of vitrified microspheres and keep warm at 35°C for 0.4 h to obtain the setting - adjusting particles;

[0053] Among them: The chitosan gum solution is obtained by dissolving chitosan with a deacetylation degree of 85% in an acetic acid solution with a mass concentration of 3%;

[0054] The particle sizes of the fly ash microspheres and the vitrified microspheres are 60 - 85 μm.

[0055] Preparation Example 4

[0056] The difference from Preparation Example 1 is that the setting - adjusting particles are prepared through the following steps: Mix 4 parts of sodium lignosulfonate, 0.5 part of sodium benzoate and 30 parts of chitosan gum solution with a mass concentration of 6% and heat to 55°C, react with 0.1 part of ammonium persulfate to obtain modified chitosan, mix the modified chitosan with 2 parts of fly ash microspheres and 1 part of vitrified microspheres and keep warm at 35°C for 0.4 h to obtain the setting - adjusting particles.

[0057] Comparative Preparation Example 1

[0058] The difference from Preparation Example 3 is that the setting - adjusting particles are prepared by mixing sodium lignosulfonate, sodium benzoate, chitosan gum solution, fly ash microspheres and vitrified microspheres, and the dosages of each component are the same as those in Preparation Example 3.

[0059] Comparative Preparation Example 2

[0060] The difference from Preparation Example 3 is that sodium lignosulfonate and sodium benzoate are equally replaced by cyclodextrin, and the rest are the same as those in Preparation Example 3.

[0061] Comparative Preparation Example 3

[0062] It is different from Preparation Example 3 in that no microbeads are added, and the rest are the same as Preparation Example 3. Example

[0063] Example 1

[0064] Tunnel high-strength shotcrete, comprising the following raw materials in parts by weight: 100 parts of cement, 60 parts of water, 300 parts of aggregate, 0.1 part of coupling agent, 35 parts of setting-adjusting granules prepared in Preparation Example 1, and 30 parts of reinforcing granules; the reinforcing granules comprise cyclodextrin and a composite admixture with a mass ratio of 1:3.5;

[0065] wherein the composite admixture is blast furnace slag and silica fume with a mass ratio of 2:1;

[0066] The aggregate comprises coarse sand, medium sand and quartz sand with a mass ratio of 0.55:1:0.4; the coarse sand is sand and gravel with an average particle size of 0.5 mm - 1.5 mm; the fineness modulus is 3.1 - 3.7; the medium sand has a fineness modulus of 2.3 - 3.0 and an average particle size of 0.35 - 0.5 mm; the average particle size of quartz is 0.2 - 0.35 mm, and the water content is <2%;

[0067] The preparation method of the tunnel high-strength shotcrete comprises the following steps:

[0068] S1 Reinforcing granule preparation: Dissolve cyclodextrin in water to form a saturated aqueous solution, add the composite admixture and stir for inclusion, and obtain the reinforcing granules after spray drying;

[0069] S2 Premix the setting-adjusting granules, reinforcing granules and coupling agent evenly, add them to the cement and aggregate, and finally add water and stir evenly to obtain the shotcrete.

[0070] Example 2

[0071] It is different from Example 1 in that the tunnel high-strength shotcrete comprises the following raw materials in parts by weight: 180 parts of cement, 90 parts of water, 500 parts of aggregate, 0.35 part of coupling agent, 20 parts of setting-adjusting granules prepared in Preparation Example 1, and 50 parts of reinforcing granules; the reinforcing granules comprise cyclodextrin and a composite admixture with a mass ratio of 1:6;

[0072] wherein the composite admixture is kaolin and silica fume with a mass ratio of 2.2:1;

[0073] The aggregate comprises coarse sand, medium sand and quartz sand with a mass ratio of 1:1:0.15;

[0074] The rest are the same as those in Example 1.

[0075] Example 3

[0076] The difference from Example 1 is that the tunnel high-strength shotcrete includes the following raw materials in parts by weight: 155 parts of cement, 73 parts of water, 412 parts of aggregate, 0.25 part of coupling agent, 28 parts of the setting-adjusting particles prepared in Preparation Example 1, and 42 parts of reinforcing particles;

[0077] Among them, the composite admixture is blast furnace slag and silica fume with a mass ratio of 1.2:3.7;

[0078] The aggregate includes coarse sand, medium sand and quartz sand with a mass ratio of 0.81:1:0.36;

[0079] The rest is the same as that of Example 1.

[0080] Example 4

[0081] The difference from Example 3 is that the reinforcing particles include cyclodextrin and composite admixture with a mass ratio of 1:4.9; the composite admixture is blast furnace slag, silica fume and kaolin with a mass ratio of 1.2:3.7:1.

[0082] Example 5

[0083] The difference from Example 4 is that the setting-adjusting particles prepared in Preparation Example 2 are selected, and the rest are the same as those of Example 4.

[0084] Example 6

[0085] The difference from Example 4 is that the setting-adjusting particles prepared in Preparation Example 3 are selected, and the rest are the same as those of Example 4.

[0086] Example 7

[0087] The difference from Example 4 is that the setting-adjusting particles prepared in Preparation Example 4 are selected, and the rest are the same as those of Example 4.

[0088] Comparative Example

[0089] Comparative Example 1

[0090] The difference from Example 6 is that the setting-adjusting particles prepared in Comparative Preparation Example 1 are selected, and the rest are the same as those of Example 6.

[0091] Comparative Example 2

[0092] The difference from Example 6 is that the setting-adjusting particles prepared in Comparative Preparation Example 2 are selected, and the rest are the same as those of Example 6.

[0093] Comparative Example 3

[0094] The difference from Example 6 is that the setting-adjusting particles prepared in Comparative Preparation Example 3 are selected, and the rest are the same as those of Example 6.

[0095] Comparative Example 4

[0096] The difference from Example 6 is that the reinforcing particles are composite admixtures, and the rest are the same as in Example 6.

[0097] Performance detection test

[0098] The specimens prepared in Examples 1-7 and Comparative Examples 1-4 were subjected to 28-day strength and funnel tests according to the "Standard Test Method for Properties of Ordinary Concrete Mixtures" GB / T50080-2016, and the strength data and the time results for the specimens to completely flow out of the funnel were recorded in Table 1.

[0099] Table 1

[0100]

[0101] From Examples 1-7 and in combination with Table 1, it can be seen that the concrete prepared in this application meets the strength requirements of C70 concrete. The time for the concrete material to flow out of the funnel is about 15 s. For high-strength concrete, this fluidity is excellent and can meet the pumping performance of high-strength shotcrete for tunnels. The shotcrete obtained in this application has the advantages of both high strength and excellent pumping performance.

[0102] From Example 6 and Comparative Examples 1-3 and in combination with Table 1, it can be seen that in Comparative Example 1, the setting-adjusting particles were obtained by simply mixing each raw material component, and each component simply played its own role and could not cooperate with other raw materials; in Comparative Example 2, lignosulfonate and sodium benzoate in the selected setting-adjusting particles were replaced with cyclodextrin; in Comparative Example 3, no microspheres were added to the setting-adjusting particles. The compressive strength and fluidity of the concrete materials obtained in Comparative Examples 1-3 were significantly affected. This is because after lignosulfonate and carboxylate react with the chitosan colloid solution, the resulting setting-adjusting particles simultaneously have sulfonic acid groups and carboxylic acid hydration groups, and with the microsphere effect, they endow the system with excellent fluidity and thixotropy, thereby effectively improving the pumpability of the concrete material. And the microspheres can further act as fillers to fill inside the concrete, increasing the density inside the concrete and further improving the compressive strength of the concrete material. Thus, it can be seen that only the setting-adjusting particles obtained by using the specific components of this application and through specific reactions can, after being compounded with other raw materials, cooperate to improve the comprehensive performance of the concrete material and obtain a concrete material with both high strength and high fluidity.

[0103] It can be seen from Example 6 and Comparative Example 4 in combination with Table 1 that the enhanced particles in Comparative Example 4 adopt a composite admixture, which can effectively participate in the reaction in the early stage of cement hydration, resulting in a significant increase in the viscosity of the material and a significant decrease in fluidity. This is because after the composite admixture is included by cyclodextrin, the composite admixture can participate in the system reaction in the middle and late stages of cement hydration, giving the material a certain pumping time. At the same time, it can significantly improve the mechanical properties of the concrete material after pumping, and thus obtain a concrete material with both high strength and high fluidity.

[0104] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-strength shotcrete for tunnels, characterized in that, It comprises the following raw materials in parts by weight: 100 - 180 parts of cement, 60 - 90 parts of water, 260 - 500 parts of aggregate, 0.1 - 0.35 parts of coupling agent, 20 - 35 parts of setting - regulating particles, and 30 - 50 parts of strengthening particles; the strengthening particles include cyclodextrin and composite admixture; The setting - regulating particles are prepared through the following steps: Mix lignosulfonate, organic carboxylate and chitosan colloid solution and heat them. Under the action of a catalyst, react to obtain modified chitosan. Mix the modified chitosan with micro - beads and keep warm to obtain the setting - regulating particles; The preparation of the high - strength shotcrete for tunnels comprises the following steps: S1 Strengthening particle preparation: Dissolve cyclodextrin in water to form a saturated aqueous solution, add the composite admixture and stir for inclusion, and obtain the strengthening particles after drying; S2 Premix the setting - regulating particles, strengthening particles and coupling agent evenly, add them into the cement and aggregate, and finally add water and stir evenly to obtain the shotcrete.

2. The high-strength shotcrete for tunnels according to claim 1, wherein: The component dosage of the setting - regulating particles is as follows, in parts by weight: 1 - 3 parts of lignosulfonate, 1 - 2.5 parts of organic carboxylate, 12 - 20 parts of chitosan colloid solution, 0.2 - 0.5 parts of catalyst, and 5.8 - 9 parts of micro - beads.

3. The high-strength shotcrete for tunnels according to claim 2, wherein: The micro - beads are fly ash micro - beads and / or vitrified micro - beads.

4. The high-strength shotcrete for tunnels according to claim 2, wherein: The organic carboxylate is one of sodium benzoate and potassium succinate.

5. The high-strength shotcrete for tunnels according to claim 4, characterized in that: The catalyst is ammonium persulfate.

6. The high-strength shotcrete for tunnels according to claim 1, wherein: The mass ratio of the cyclodextrin to the composite admixture is 1:(3.5 - 6).

7. The high-strength shotcrete for tunnels according to claim 6, wherein: The composite admixture includes at least two of mineral powder, silica fume and kaolin.

8. The high-strength shotcrete for tunnels according to claim 1, characterized in that: The aggregate includes coarse sand, medium sand and quartz sand with a mass ratio of (0.55 - 1):1:(0.15 - 0.4).

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