Composite admixture, its preparation method and application, and tunnel shotcrete

Abstract

The present invention discloses a composite admixture, a preparation method and application thereof, and tunnel shotcrete. The composite admixture comprises the following components by weight: silica fume: 5-8 parts; nano-silica: 0.1-1 part; nano-alumina: 2-5 parts; nano-zirconia: 0.1-2 parts; glass powder: 5-15 parts; silicate powder: 0.5-3 parts; and amino carboxylate: 1-3 parts. Through the coordinated cooperation of multiple components in a specific ratio, the composite admixture can better balance the workability of the concrete mixture and the requirement of resisting calcium ion corrosion. While reducing the rebound rate of the shotcrete, it participates in and promotes the hydration of cement at different stages in the shotcrete, can better solidify the free calcium ions in the cement hydration products, and reduces the performance of calcium ion crystallization precipitation in the shotcrete under the condition of water-rich strata.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel engineering. Specifically, it relates to a composite admixture, a preparation method and application thereof, and tunnel shotcrete. Background Art

[0002] During the construction of mountain tunnels, it is necessary to spray about 25 cm thick concrete on the surface of the surrounding rock excavated, and add a rapid setting agent to make the cement hydrate quickly to form a relatively high early strength of the concrete, which is used to seal the excavation free face and stabilize the surrounding rock. At present, in addition to the problem of excessive rebound rate commonly existing in the tunnel shotcrete construction, in the condition of water-rich karst strata, the seepage water on the excavation face will carry out a large amount of calcium carbonate crystals from the shotcrete, resulting in the blockage of the tunnel drainage pipeline and the increase of the water pressure borne by the lining, leading to the aggravation of leakage and structural safety problems.

[0003] To address this problem, its root cause lies in minimizing the calcium hydroxide in the cement hydration products of the shotcrete as much as possible, and solidifying the calcium hydroxide in the hydration products as much as possible to reduce the crystallization products carried out by the groundwater seeping through the concrete. At present, there are some liquid concrete admixtures with polymer components. By adding and dispersing them during the concrete mixing process, they wrap the cement clinker particles and use the charge of the polymer micelles to adsorb calcium ions in the cement hydration products to reduce the precipitation of calcium ion crystallization. However, such admixtures currently have problems such as changing the water-cement ratio of the concrete and the workability of the concrete mixture, delaying the hydration rate of the cement, reducing the early strength of the concrete, and having poor compatibility with other types of admixtures. In addition, there may also be limitations such as high storage conditions requirements, short storage period, and difficult component inspection. Therefore, some technical measures need to be added in actual use to ensure their use effects. And some powder-type concrete additive materials, although avoiding some problems existing in the above-mentioned liquid admixtures, such as nano-silica particles, although having a fast reaction rate with the concrete hydration products and good effects on improving the concrete performance, also have problems such as difficult mixing and dispersion and the need to adopt pre-dispersion measures, increasing their use difficulty; various common powder mineral admixtures, such as silica fume, fly ash, etc., although simple in storage, addition and dispersion, have a greater impact on the workability of the concrete mixture, which may cause an increase in the rebound rate of the concrete, and either have a long gel state time or a slow reaction rate with the products of cement hydration, and have limited effects on reducing the precipitation of calcium ions in the tunnel shotcrete under water-rich conditions in actual projects.

[0004] Therefore, there is an urgent need to propose a concrete admixture based on powder materials, which can take into account the workability of the concrete mixture to reduce the rebound rate, and can also participate in the main process of cement hydration in the concrete to effectively solidify the free calcium ions in the hydration products and reduce the precipitation of calcium carbonate crystals carried out by groundwater seepage.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a composite admixture and a preparation method and application thereof, as well as tunnel shotcrete, so as to improve the above technical problems.

[0007] The present invention is achieved in that:

[0008] In the first aspect, the present invention provides a composite admixture, which includes the following components, measured by weight: silica fume: 5 to 8 parts; nano silicon dioxide: 0.1 to 1 part; nano aluminum oxide: 2 to 5 parts; nano zirconium oxide: 0.1 to 2 parts; glass powder: 5 to 15 parts; silicate powder: 0.5 to 3 parts; and aminocarboxylate powder: 1 to 3 parts.

[0009] In a second aspect, the present invention also provides a method for preparing the above-mentioned composite admixture, which comprises: mixing the silica ash, the nano silicon dioxide, the nano alumina, the nano zirconium oxide, the glass powder, the silicate powder and the aminocarboxylate powder in parts by weight.

[0010] In a third aspect, the present invention also provides application of the above-mentioned composite admixture in tunnel shotcrete.

[0011] In a fourth aspect, the present invention further provides a tunnel shotcrete, the raw materials of which include a concrete base material and the above-mentioned composite admixture, wherein the mass ratio of the composite admixture to the cement in the concrete base material is (20-35): (80-65).

[0012] The present invention has the following beneficial effects: through the coordinated cooperation of multiple components in specific proportions, the composite admixture can better take into account the working performance of the concrete mixture and the requirements for resistance to calcium ion dissolution, while reducing the rebound rate of the shotcrete, participating in and promoting different stages of cement hydration in the shotcrete, and can better solidify the free calcium ions in the cement hydration products, reducing the performance of calcium ion crystallization precipitation in the shotcrete under water-rich formation conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0014] Figure 1 This is a physical picture of the composite admixture of Example 1 of the present invention;

[0015] Figure 2 It is a field picture of shotcrete at the tunnel site;

[0016] Figure 3 It is a field picture of rebound rate test by shotcrete on large panels;

[0017] Figure 4 It is a field picture of compressive strength test in the laboratory. Detailed implementation manners

[0018] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained by purchasing in the market.

[0019] Some embodiments of the present invention provide a composite admixture, which includes the following components by weight: silica fume: 5 - 8 parts; nano-silica: 0.1 - 1 part; nano-alumina: 2 - 5 parts; nano-zirconia: 0.1 - 2 parts; glass powder: 5 - 15 parts; silicate powder: 0.5 - 3 parts; and amino carboxylate powder: 1 - 3 parts.

[0020] In some embodiments, the product ratio of the above composite admixture is optimized to further improve its performance. It includes the following components by weight: silica fume: 5 - 8 parts; nano-silica: 0.1 - 0.5 part; nano-alumina: 2 - 3 parts; nano-zirconia: 0.1 - 1 part; glass powder: 5 - 15 parts; silicate powder: 1 - 3 parts; and amino carboxylate powder: 1 - 3 parts.

[0021] In some embodiments, the product ratio of the above composite admixture is further optimized. It includes the following components by weight: silica fume: 8 parts; nano-silica: 0.5 part; nano-alumina: 2 parts; nano-zirconia: 0.1 part; glass powder: 15 parts; silicate powder: 3 parts; and amino carboxylate powder: 3 parts.

[0022] By using silica fume as the main component of the composite admixture, the fluidity, stability and cohesiveness of the concrete mixture can be improved, the rebound rate during shotcrete construction, especially at the arch part of the tunnel, can be reduced, and the concrete consumption can be saved; at the same time, silica fume can quickly combine with the free calcium ions in the hydration products at the early stage of cement hydration to form C-S-H gel with a low calcium-silica ratio, which better inhibits the precipitation of free calcium ions in the initial stage of cement hydration.

[0023] Specifically, in some embodiments, silica fume is an industrial waste recovered by the dry discharge method during the high-temperature smelting process of industrial silicon and ferrosilicon alloys. The average particle size of silica fume is 0.1 μm to 0.2 μm, and the mass content of SiO2 is above 85%, for example, the mass content of SiO2 is above 95%.

[0024] By using nano-silica as one of the components of the composite admixture and adding it in the preparation process of the concrete mixture, a plasticizing effect can be produced, further enhancing the cohesiveness of the concrete mixture and reducing the rebound rate during shotcrete construction. Due to its ultra-fine particle size, it can physically fill the voids of the concrete hydration product gel, improve its compactness, and facilitate the improvement of the concrete performance in cooperation with silica fume. Moreover, due to its large specific surface area, it can more effectively contact and capture the free calcium ions in the cement hydration products, quickly convert them into C-S-H gel, and can also enhance the cement hydration rate and improve the early strength of the concrete. It should be noted that the dosage of nano-silica in the embodiments of the present invention is relatively small, and a larger dosage is likely to cause agglomeration and affect the concrete performance.

[0025] Specifically, in some embodiments, nano-silica is a high-purity ultra-fine SiO2 powder with an average particle size of 30 nm to 50 nm produced by chemical precipitation method, gas-phase method, etc., and the mass content of SiO2 is above 99.5%.

[0026] By using nano-alumina as one of the components of the composite admixture and adding the above-mentioned dosage of nano-alumina in the preparation process of the concrete mixture, due to its good dispersibility, it can be uniformly mixed into the concrete. Through the "ball bearing" effect, the fluidity and pumpability of the concrete mixture can be improved. At the same time, due to its ultra-fine particle size and large specific surface area, it can play a role similar to that of nano-silica, that is, physically fill the voids of the concrete hydration product gel and effectively capture free calcium ions. However, the product formed by its combination with free calcium ions is calcium aluminate hydrate with better stability than C-S-H gel, and the effect of solidifying free calcium ions and the effect of enhancing the early strength of the concrete can be further strengthened, which can supplement and enhance the role of nano-silica.

[0027] Specifically, in some embodiments, nano-alumina is a high-purity ultra-fine Al2O3 powder with an average particle size of 20 nm to 50 nm produced by solid-phase method, gas-phase method or liquid-phase method, etc., and the mass content of Al2O3 is above 99.5%.

[0028] By using nano-zirconia as one of the components of the composite admixture and adding the nano-zirconia in the amount as described during the preparation of the concrete mixture, it can play a role similar to that of nano-alumina, improving the fluidity and pumpability of the concrete mixture; due to its ultra-fine particle size, it can physically fill the voids of the concrete hydration product gel; however, the difference between it and nano-alumina is that it cannot participate in the early hydration of cement. In the early stage, it mainly makes the concrete denser through the filling effect, thereby reducing the growth space of calcium hydroxide inside the matrix, reducing the preferred orientation of calcium hydroxide crystals, contributing to the 28d strength of the concrete, and being beneficial to improving the long-term performance and durability of shotcrete.

[0029] Specifically, in some embodiments, the nano-zirconia is a high-purity ultra-fine ZrO2 powder with an average particle size of 20nm to 40nm prepared by gel precipitation method or the like, and the mass content of ZrO2 is above 99.5%.

[0030] By using glass powder as one of the components of the composite admixture, after the glass powder is incorporated into the concrete, it can fill the tiny voids in the concrete and improve the compactness of the concrete. In addition, when the glass powder is incorporated into the concrete, it usually starts to gradually exhibit pozzolanic activity and participate in the cement hydration process after 10 to 14 days. Therefore, it can play a complementary role with other powders provided by the embodiments of the present invention, play a role in different main stages of concrete hydration, continuously capture the free calcium ions precipitated by cement hydration in a longer period, and improve the durability of the concrete. In some embodiments, the particle size of the glass powder is 1μm to 20μm, and the glass powder is ground glass powder; grinding the glass to the described particle size can avoid or inhibit the alkali-silicate reaction caused by the incorporation of glass powder into the concrete. Since the surface of the ground glass powder particles is smooth, it can play a role in physical water reduction, improve the workability of the concrete mixture, and partially offset the negative effects of the increased water demand and increased late shrinkage of the concrete caused by components such as silica fume and nano-powders. The ground glass powder of the embodiments of the present invention is obtained by grinding common soda-lime glass, and its common main components and contents are approximately 70% SiO2, 13% Na2O, and 10% CaO.

[0031] By using sodium silicate powder as one of the components of the composite admixture, the main use of the sodium silicate powder in the amount as described is as an activator to accelerate the hydration process of the cement clinker components, and it can also make the concrete pore solution quickly become alkaline, further promoting the reaction of other powder admixtures added synchronously with the cement hydration products. At the same time, sodium silicate undergoes a displacement and precipitation reaction with free calcium ions to form calcium silicate gel to solidify the calcium ions. In some embodiments, the sodium silicate powder is an amorphous white powder prepared by a dry method through melting, cooling, dissolving, clarifying, concentrating to a certain concentration, and then spray drying, and its soluble silicate content is about 80% to 82%.

[0032] By using amino carboxylate powder as one of the components of the composite admixture, under the condition of an alkaline solution, the amino carboxylate can undergo a complexation reaction with metal ions, especially calcium and magnesium ions, to form a soluble and relatively stable metal complex with only coordination bonds and no covalent bonds. The undissociated complex can stably exist in the internal pores of the concrete; for the dissociated complex, if it is free in the region with a high concentration of silicate ions, the active groups are replaced by silicate ions to form calcium crystallites, and the detached active groups continue to complex with the free calcium ions generated by hydration. The amino carboxylate in the stated dosage can complex with the calcium ions in the cement hydration products and be distributed in the concrete pore solution, promoting the process of cement hydration. At the same time, this part of the complex carrying calcium ions continuously combines with the silicate ions in the concrete pore solution to form calcium silicate gel, further solidifying the free calcium ions in the cement hydration products.

[0033] In some embodiments, the amino carboxylate powder is selected as sodium nitrilotriacetate powder, which is a white crystalline powder.

[0034] After the multiple powders of the composite admixture in the above embodiments of the present invention are compounded, an excellent "superposition" effect can be produced, overall improving the performance of shotcrete. When the weight part of cement in the basic mix proportion of shotcrete is 100, by the internal admixture method (replacing the same mass of cement), the above composite admixture is incorporated into the concrete mixture, and the following effects can be achieved: Through the "ball bearing" effect of the composite admixture, the workability of the concrete mixture can be improved, the pumping fluidity can be increased, and the shotcrete rebound rate can be reduced; within 0 - 7 days of cement hydration, silica fume, nano-silica, nano-alumina, and sodium silicate powder can rapidly solidify the free calcium ions precipitated during cement hydration, increasing the formation amount of C-S-H gel and calcium aluminate hydrate; within 7 - 14 days of cement hydration, the glass powder gradually starts to participate in the process of cement hydration, capturing the free calcium ions generated by the continuous hydration of the cement to form C-S-H and C-N-S-H gels, and this reaction process can last for more than 56 days; due to the specific surface effect and small size effect of the nano-materials, nano-zirconia can induce the hydration of cement, making the cement hydration generate more calcium silicate gel and ettringite, improving the cement interface and enhancing the densification degree of the matrix; the amino carboxylate powder participates in the whole process of cement hydration, continuously complexing with the calcium ions in the cement hydration products, promoting the combination of calcium ions with the silicate ions in the concrete pore solution, and generating precipitation products for solidification.

[0035] It should be noted that in the embodiments provided by the present invention, the raw materials used are all in powder form. Generally, after being uniformly mixed in a dispersion device according to a given mass fraction ratio, they are bagged or canned and transported to the tunnel construction site. During the concrete mixing process, they are added to the mixing device synchronously with raw materials such as cement, sand, and gravel to prepare a concrete mixture, and then transported to the construction site for wet spraying or semi-dry spraying to construct shotcrete.

[0036] Some embodiments of the present invention also provide a method for preparing the above composite admixture, which includes: mixing silica fume, nano-silica, nano-alumina, nano-zirconia, glass powder, silicate powder, and amino carboxylate powder according to a weight ratio.

[0037] It should be noted that the above components of the composite admixture can be directly added to the concrete mixture for mixing, or can be mixed evenly first and then added to the concrete mixture for mixing.

[0038] Some embodiments of the present invention also provide the application of the composite admixture in any of the above embodiments in tunnel shotcrete.

[0039] Some embodiments of the present invention also provide a tunnel shotcrete, the raw materials of which include a concrete base material and the composite admixture in the above embodiments. The mass ratio of the composite admixture to the cement in the concrete base material is (20 - 35):(80 - 65). For example, the mass ratio of the composite admixture to the cement is 20:80, 23:77, 25:75, 28:72, 30:70, 33:67, or 35:65, etc. It should be noted that the concrete base material is a commonly used composition mixture for tunnel shotcrete.

[0040] For example, the concrete base material includes, but is not limited to, 65 - 80 parts of cement, 175 - 185 parts of medium sand, 165 - 175 parts of crushed stone, 40 - 50 parts of water, 1 - 1.2 parts of water reducing agent, and 5 - 7 parts of accelerating agent; among them, the total number of parts of cement and the composite admixture is 100 parts.

[0041] In some embodiments, the accelerating agent is FSA alkali-free liquid accelerating agent, produced by Tianjin Weihe Technology Development Co., Ltd., with a density of 1510 kg / m 3 , a solid content of 49.67%, and a pH of 3.2; the water reducing agent is a polycarboxylate water reducing agent, produced by Tianjin Weihe Technology Development Co., Ltd., with a model of HLX type, a density of 1040 kg / m 3 , a solid content of 38.5%, a pH value of 6, and a water reduction rate of not less than 14%.

[0042] The features and properties of the present invention will be further described in detail below in conjunction with examples.

[0043] The silica fume provided in the following embodiments of the present invention has a SiO2 component content of 96% and an average particle size of 0.1 μm.

[0044] The nano-silica provided in the following embodiments of the present invention has a SiO2 component content of 99.5% and an average particle size of 30 nm.

[0045] The nano-aluminum oxide provided in the following embodiments of the present invention has an Al2O3 component content of 99.5% and an average particle size of 30 nm.

[0046] The nano-zirconia provided in the following embodiments of the present invention has a ZrO2 component content of 99.5% and an average particle size of 30 nm.

[0047] The glass powder provided in the following embodiments of the present invention is made by finely grinding soda-lime glass. Its main components and contents are 70% SiO2, 13% Na2O, and 10% CaO, with the remaining component being 7%. The median particle size is 10 μm.

[0048] The sodium silicate powder provided in the following embodiments of the present invention is of analytical purity.

[0049] The sodium nitrilotriacetate powder provided in the following embodiments of the present invention is of industrial purity.

[0050] In the following implementation of the present invention, the basic mix ratio of the tunnel shotcrete by weight is as follows: cement: 100 parts, medium sand: 180 parts, crushed stone: 170 parts, water: 45 parts, water reducer: 1 part; accelerating agent: 6 parts.

[0051] Among them, the cement is ordinary Portland cement, produced by Zhucheng Yangchun Cement Co., Ltd., with a grade of P·O42.5; the river sand is natural dredged river sand, with a bulk density of 1450 kg / m 3 , the particle size grade is medium sand, the fineness modulus is 2.31, the water content is 0.2%, and the mud content < 5%; the water is tap water; the accelerating agent is the FSA alkali-free liquid accelerating agent produced by Tianjin Weihe Technology Development Co., Ltd., and the initial setting time of the cement paste ≤ 5 min, and the final setting time ≤ 10 min. The water reducer is the polycarboxylate-based high-performance water reducer produced by Tianjin Weihe Technology Development Co., Ltd., and the water reduction rate is not less than 14%.

[0052] Example 1

[0053] This example provides a composite admixture, which by weight, comprises the following components: silica fume 5 parts; nano-silica: 0.1 part; nano-aluminum oxide: 2 parts; nano-zirconia: 1 part; glass powder: 10 parts; sodium silicate powder: 1 part; sodium nitrilotriacetate powder: 1 part.

[0054] In this embodiment, the composite admixture in the specified parts by weight is used to replace the cement of the same mass in the basic mix ratio, that is, the internal admixture method is adopted to adjust the mix ratio of shotcrete. At the same time, the water reducer in the basic mix ratio is adjusted to 1.1 parts. After adjustment, the mix ratio of shotcrete becomes: cement: 79.9 parts, medium sand: 180 parts, crushed stone: 170 parts, water: 45 parts, water reducer: 1.1 parts; accelerator: 6 parts; composite admixture: 20.1 parts.

[0055] In this embodiment, first, each raw material is weighed and prepared according to the parts by weight. Subsequently, the cement, medium sand, crushed stone, and composite admixture are poured into a concrete mixer for dry mixing, and then the water and water reducer in the designed parts by weight are added and stirred evenly. The prepared concrete mixture is transported to the shotcrete construction site, and a wet shotcreting machine is used for shotcreting the concrete. The accelerator is added by the accelerator pump configured by the wet shotcreting machine at the gun head of the spray gun. Among them, the composite admixture is as Figure 1 shown.

[0056] The spraying capacity of the wet shotcreting machine is 25 m 3 / h, its working air pressure is 0.5 MPa, and the metering accuracy error of the accelerator pump is ≤ ±2%. The main parameters of the shotcreting construction operation include the nozzle distance: 1.5 m, the spraying angle: 90°, and the spraying parts include the side wall and arch crown of the tunnel. The operation process is as Figure 2 shown.

[0057] In this embodiment, the test method for the parameters related to shotcrete is as follows: After collecting the fallen concrete on-site and weighing it, dividing by the total consumption of shotcrete, the comprehensive rebound rate of shotcrete can be obtained (as Figure 3 shown); By spraying shotcrete slabs on-site, after curing for 24 h, cutting them into test blocks of 150 mm × 150 mm × 150 mm, and then conducting the compressive strength tests at 1 d and 7 d in the laboratory (as Figure 4 shown); By spraying shotcrete slabs on-site, after curing for 24 h, cutting them into test blocks of 70 mm × 70 mm × 70 mm, soaking them in 1 L of deionized water, changing the water every 24 h and calculating the weight of calcium ions precipitated each time, and calculating the total weight of calcium ions precipitated after continuous soaking for 30 d.

[0058] The relevant test data of the shotcrete obtained in this embodiment are: comprehensive rebound rate: 8%; 1 d compressive strength: 15 MPa; 7 d compressive strength: 40 MPa; 30 d calcium ion precipitation weight: 340 mg.

[0059] Example 2

[0060] This embodiment provides a composite admixture, which, by weight, comprises the following components: 8 parts of silica fume; 0.5 part of nano-silicon dioxide; 2 parts of nano-aluminum oxide; 0.1 part of nano-zirconium oxide; 15 parts of glass powder; 3 parts of sodium silicate powder; 3 parts of nitrilotriacetic acid sodium powder.

[0061] In this embodiment, the composite admixture in the said weight parts is used to replace the cement of the same mass in the basic mix ratio, that is, the internal admixture method is used to adjust the mix ratio of shotcrete. At the same time, the water reducer in the basic mix ratio is adjusted to 1.3 parts. After adjustment, the mix ratio of the shotcrete becomes: cement: 67.4 parts, medium sand: 180 parts, crushed stone: 170 parts, water: 45 parts, water reducer: 1.3 parts; accelerating agent: 6 parts; composite admixture: 32.6 parts.

[0062] In this embodiment, the preparation method of the concrete mixture, the spraying equipment, the requirements for the spraying process, the test items and methods of the concrete parameters are the same as those in Embodiment 1.

[0063] The relevant test data of the shotcrete obtained in this embodiment are: comprehensive rebound rate: 5%; 1-day compressive strength: 18 MPa; 7-day compressive strength: 50 MPa; 30-day calcium ion precipitation weight: 130 mg.

[0064] Comparative Example 1

[0065] The mix ratio of the tunnel shotcrete provided in this comparative example adopts the basic mix ratio by weight, cement: 100 parts, medium sand: 180 parts, crushed stone: 170 parts, water: 45 parts, water reducer: 1 part; accelerating agent: 6 parts. That is, no composite admixture is added.

[0066] In this comparative example, the preparation method of the concrete mixture, the spraying equipment, the requirements for the spraying process, the test items and methods of the concrete parameters are the same as those in Embodiment 1.

[0067] The relevant test data of the shotcrete obtained in this comparative example are: comprehensive rebound rate: 28%; 1-day compressive strength: 10 MPa; 7-day compressive strength: 35 MPa; 30-day calcium ion precipitation weight: 1230 mg.

[0068] Comparative Example 2

[0069] This comparative example provides a composite admixture, which, by weight, comprises the following components: 12 parts of silica fume; 0.5 part of nano-silicon dioxide; 5 parts of nano-aluminum oxide; 0.5 part of nano-zirconium oxide; 15 parts of glass powder; 3 parts of sodium silicate powder; 3 parts of nitrilotriacetic acid sodium powder.

[0070] In this embodiment, the composite admixture in the above weight parts is used to replace the cement of the same mass in the basic mix ratio, that is, the internal admixture method is used to adjust the mix ratio of the shotcrete. At the same time, the water reducer in the basic mix ratio is adjusted to 1.3 parts. After adjustment, the mix ratio of the shotcrete becomes: cement: 62 parts, medium sand: 180 parts, crushed stone: 170 parts, water: 45 parts, water reducer: 1.3 parts; accelerator: 6 parts; composite admixture: 38 parts.

[0071] In this embodiment, the preparation method of the concrete mixture, the spraying equipment, the requirements for the spraying process, the test items and methods of the concrete parameters are the same as those in Embodiment 1.

[0072] The relevant test data of the shotcrete obtained in this embodiment are as follows: comprehensive rebound rate: 10%; 1-day compressive strength: 8 MPa; 7-day compressive strength: 30 MPa; 30-day calcium ion precipitation weight: 1350 mg.

[0073] Comparative Example 3

[0074] This comparative example provides a composite admixture, which contains the following components by weight: silica fume 8 parts; nano-silicon dioxide: 0.5 part; nano-aluminum oxide: 2 parts; nano-zirconium oxide: 0.1 part; glass powder: 15 parts; sodium silicate powder: 3 parts.

[0075] In this comparative example, the composite admixture in the above weight parts is used to replace the cement of the same mass in the basic mix ratio, that is, the internal admixture method is used to adjust the mix ratio of the shotcrete. At the same time, the water reducer in the basic mix ratio is adjusted to 1.3 parts. After adjustment, the mix ratio of the shotcrete becomes: cement: 60.4 parts, medium sand: 180 parts, crushed stone: 170 parts, water: 45 parts, water reducer: 1.3 parts; accelerator: 6 parts; composite admixture: 29.6 parts.

[0076] In this comparative example, the preparation method of the concrete mixture, the spraying equipment, the requirements for the spraying process, the test items and methods of the concrete parameters are the same as those in Embodiment 1.

[0077] The relevant test data of the shotcrete obtained in this comparative example are as follows: comprehensive rebound rate: 5%; 1-day compressive strength: 16 MPa; 7-day compressive strength: 45 MPa; 30-day calcium ion precipitation weight: 223 mg.

[0078] Comparative Example 4

[0079] This comparative example provides a composite admixture, which contains the following components by weight: silica fume 8 parts; nano-silicon dioxide: 0.5 part; nano-aluminum oxide: 2 parts; nano-zirconium oxide: 0.1 part; glass powder: 20 parts; sodium silicate powder: 3 parts; nitrilotriacetic acid sodium powder: 3 parts.

[0080] In this comparative example, the composite admixture in the stated parts by weight was used to replace the cement of the same mass in the basic mix ratio, i.e., the internal admixture method was used to adjust the mix ratio of the shotcrete. At the same time, the water reducer in the basic mix ratio was adjusted to 1.1 parts. After adjustment, the mix ratio of the shotcrete became: cement: 63.4 parts, medium sand: 180 parts, crushed stone: 170 parts, water: 45 parts, water reducer: 1.1 parts; accelerator: 6 parts; composite admixture: 36.6 parts.

[0081] In this comparative example, the preparation method of the concrete mixture, the spraying equipment, the requirements for the spraying process, the test items and methods for the concrete parameters were the same as those in Example 1.

[0082] The relevant test data of the shotcrete obtained in this comparative example were: comprehensive rebound rate: 6%; 1-day compressive strength: 12 MPa; 7-day compressive strength: 38 MPa; 30-day calcium ion precipitation weight: 650 mg.

[0083] According to the comparison of the relevant test result data of Example 1, Example 2 and Comparative Example 1, after adding the composite admixture to the concrete, the rebound rate of the shotcrete was significantly reduced, and the cement hydration rate, compactness, compressive strength and calcium ion precipitation resistance of the concrete were all improved well. From the results of Comparative Example 2, it can be seen that inappropriate content configurations of silica fume, nano-aluminum oxide and nano-zirconium oxide would cause low strength and increased calcium ion precipitation. From Comparative Example 3, it can be seen that if NTA-3 sodium is lacking in the components, it has no effect on the comprehensive rebound rate, but compared with Example 2, the strength growth is slow and the calcium ion precipitation increases. From the results of Comparative Example 4, it can be seen that if the content of glass powder is too much, since the glass powder participates in the hydration process slowly, the early strength increases slowly and the effect of controlling calcium ion precipitation is also poor.

[0084] In summary, the composite admixture for tunnel shotcrete provided in the embodiments of the present invention can better balance the workability of the concrete mixture and the requirements of calcium ion corrosion resistance. While reducing the rebound rate of the shotcrete, it has the performance of reducing the crystallization and precipitation of calcium ions in the shotcrete under the conditions of water-rich strata.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A composite admixture, characterized in that, By weight parts, it comprises the following components: Silica fume: 5 - 8 parts; Nano - silica: 0.1 - 1 part; Nano - alumina: 2 - 5 parts; Nano - zirconia: 0.1 - 2 parts; Glass powder: 5 - 15 parts; Silicate powder: 0.5 - 3 parts; And Amino - carboxylate powder: 1 - 3 parts; The average particle size of the silica fume is 0.1μm - 0.2μm, and the mass content of SiO2 is above 85%; And / or, the average particle size of the nano - silica is 30nm - 50nm, and the mass content of SiO2 is above 99.5%; And / or, the average particle size of the nano - alumina is 20nm - 50nm, and the mass content of Al2O3 is above 99.5%; And / or, the average particle size of the nano - zirconia is 20nm - 40nm, and the mass content of ZrO2 is above 99.5%; And / or, the particle size of the glass powder is 1μm - 20μm, and the glass powder is ground glass powder; And / or, the mass content of soluble silicate in the silicate is 80% - 82%.

2. The composite admixture according to claim 1, wherein By weight parts, it comprises the following components: The silica fume: 5 - 8 parts; The nano - silica: 0.1 - 0.5 part; The nano - alumina: 2 - 3 parts; The nano - zirconia: 0.1 - 1 part; The glass powder: 5 - 15 parts; The silicate powder: 1 - 3 parts; and The amino - carboxylate powder: 1 - 3 parts.

3. The composite admixture according to claim 1, characterized in that, By weight parts, it comprises the following components: The silica fume: 8 parts; The nano - silica: 0.5 part; The nano - alumina: 2 parts; The nano - zirconia: 0.1 part; The glass powder: 15 parts; The silicate powder: 3 parts; and The amino - carboxylate powder: 3 parts.

4. The composite admixture according to any one of claims 1 to 3, characterized in that The silicate is sodium silicate; and / or, the amino - carboxylate is nitrilotriacetic acid sodium powder.

5. The preparation method of the composite admixture according to any one of claims 1 to 4, characterized in that, It comprises: Mixing the silica fume, the nano - silica, the nano - alumina, the nano - zirconia, the glass powder, the silicate powder and the amino - carboxylate according to the weight ratio.

6. The application of the composite admixture according to any one of claims 1 - 4 in tunnel shotcrete.

7. A tunnel shotcrete, characterized in that, Its raw materials include a concrete base material and the composite admixture according to any one of claims 1 - 4, and the mass ratio of the composite admixture to the cement in the concrete base material is (20 - 35):(80 - 65).

8. The shotcrete for tunnel according to claim 7, wherein, By weight parts, the concrete base material comprises 65 - 80 parts of cement, 175 - 185 parts of medium sand, 165 - 175 parts of crushed stone, 40 - 50 parts of water, 1 - 1.2 parts of water - reducing agent, 5 - 7 parts of accelerating agent; wherein, the total number of parts of the cement and the composite admixture is 100 parts.

9. The shotcrete for tunnel according to claim 8, wherein, The accelerating agent is FSA non - alkali liquid accelerating agent, and / or, the water - reducing agent is a polycarboxylate - based water - reducing agent with a water - reducing rate of not less than 14%.

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