Alkali-free chloride-free powdery master batch soluble accelerator as well as preparation method and use method thereof

Abstract

The invention discloses an alkali-free chloride-free powdery master batch soluble accelerator as well as a preparation method and a use method thereof, and belongs to the technical field of building material admixtures. According to the invention, sulfate and a fluorine-aluminum compound are used as base materials, and the water-based cutting fluid specifically comprises 45-60 wt.% of the base materials, 5-10 wt.% of a stabilizer, 3-5 wt.% of polycarboxylic acid, 5-10 wt.% of lignosulfonate, 1-1.5 wt.% of a pH regulator, 5-8 wt.% of an antifoaming agent, 10-12 wt.% of calcium formate and the balance of water. The preparation method comprises the following steps: pretreating the base material, dissolving and mixing, feeding, adjusting the pH value, decolorizing, concentrating and drying. The prepared accelerator has an efficient coagulation accelerating effect, good crack resistance and impermeability, is environmentally friendly and efficient, and can be widely applied to various cement-based materials; the liquid setting accelerator can be prepared by adding water to dissolve the powdery master batch, and is applied to tunnel spraying construction, so that a powerful guarantee is provided for the safety and stability of a tunnel.

Description

Technical Field

[0001] The invention relates to the technical field of building material admixtures, and in particular to an alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent, a preparation method and a use method thereof. Background Art

[0002] With the rapid development of the modern construction industry, concrete, as the main building material, has become the focus of attention in the industry for its performance and construction efficiency. Especially in some special engineering projects, such as tunnels, slope protection, mines, etc., there are extremely high requirements for the rapid setting and hardening performance of concrete. During the use of traditional quick-setting agents, although they can meet the construction needs to a certain extent, they are often accompanied by the presence of alkalinity and chloride ions, which may not only cause long-term stability problems of concrete structures, but also have adverse effects on the environment and construction personnel.

[0003] Publication No. CN103553406A is a Chinese patent that discloses an alkali-free and chlorine-free liquid accelerator based on industrial polyaluminium sulfate. However, the patent application for the alkali-free liquid accelerator has many problems in terms of stability, economy and product radiation range. In other words, in terms of practicality, the liquid accelerator product still has great limitations in terms of application field and transportation.

[0004] The Chinese patent with publication number CN110204238A discloses a water-soluble powdered alkali-free quick-setting agent and its preparation method. The quick-setting agent raw materials and the mass percentage of each component of the invention are: aluminum sulfate, lithium silicate, manganese fluorosilicate, pH adjuster, suspension stabilizer, and the balance is water, and the total amount is 100%. The invention has the following advantages: (1) It meets the alkali-free standard of GB / T35159-2017 "Accelerator for Shotcrete"; (2) It is a solid powder raw material in normal state, which is convenient for long-distance transportation; (3) It has very good water solubility when used; (4) It has ultra-high stability after use. However, the invention does not disclose the type of pH adjuster, and there is controversy that the pH adjuster is not environmentally friendly.

[0005] In order to solve the above problems, the present invention has deeply studied and developed an alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent. The quick-setting agent uses sulfate and fluoroaluminum compound as main raw materials, and through scientific proportioning and fine preparation process, it achieves the rapid setting and hardening effect of the quick-setting agent, while avoiding the introduction of alkalinity and chloride ions.

[0006] The disclosure of the above background technology content is only used to assist in understanding the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above content has been disclosed on the filing date of this patent application, the above background technology should not be used to evaluate the novelty and creativity of the present application. Summary of the invention

[0007] The purpose of the present invention is to provide an alkali-free and chlorine-free powdered masterbatch soluble accelerating agent, a preparation method and a use method thereof, so as to solve the technical problems of the above-mentioned prior art that the accelerating agent is not environmentally friendly, has limited application fields and has high storage and transportation costs.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0009] An alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent, wherein the base material is composed of sulfate and fluoroaluminum compound, and other modified components are added; the mass percentages of the base material and the components are: 45-60wt.%, 5-10wt.%, 5-10wt.%, 3-5wt.%, 5-10wt.%, lignin sulfonate, 1-1.5wt.%, 1-1.5wt.%, 5-8wt.%, 10-12wt.%, and the balance is water.

[0010] Furthermore, the stabilizer includes one or any combination of low-viscosity hydroxypropyl methylcellulose, low-viscosity hydroxypropyl methylcellulose potassium, low-viscosity hydroxypropyl methylcellulose magnesium, and low-viscosity hydroxypropyl methylcellulose calcium.

[0011] Furthermore, the pH regulator is any combination of lithium sulfate and diglycolamine.

[0012] Furthermore, the defoaming agent includes any one of ammonium sulfate, aluminum sulfate, magnesium sulfate and a combination thereof.

[0013] Technical principle of the present invention:

[0014] The present invention adds low-viscosity hydroxypropyl methylcellulose, polycarboxylic acid, lignin sulfonate, lithium sulfate and diglycolamine and other ingredients to further improve the performance of the accelerator. Low-viscosity hydroxypropyl methylcellulose can improve the fluidity of concrete and reduce the resistance during construction; polycarboxylic acid, as another important additive, plays a role of dispersion and stabilization in the accelerator, and can be adsorbed on the surface of concrete particles to form a stable dispersion layer, which effectively prevents the agglomeration and sedimentation of concrete particles, thereby ensuring the uniformity and stability of concrete; lignin sulfonate, as a natural polymer compound, not only has good water solubility and dispersibility, but also the lignin sulfonic acid group can chelate with metal ions in concrete, further enhancing the stability and durability of concrete.

[0015] The addition of lithium sulfate and diglycolamine is to further optimize the setting and hardening effect of the accelerator. Lithium sulfate can enhance the compressive strength and durability of concrete, while diglycolamine can adjust the setting time of concrete to make it more in line with construction requirements.

[0016] The present invention also takes into special consideration the environmental performance of the accelerating setting agent, and selects low-pollution environmentally friendly materials to ensure that the accelerating setting agent will not pollute the environment during use, while minimizing the generation of waste during the construction process.

[0017] In summary, the alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent developed by the present invention not only has excellent setting and hardening performance, but also has good environmental protection performance and construction performance, which will provide strong technical support for the development of the modern construction industry and promote the continuous progress of the industry.

[0018] The present invention also provides a method for preparing an alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent, comprising the following steps:

[0019] (1) Base material pretreatment: grinding sulfate and fluoroaluminum compound;

[0020] (2) Dissolving and mixing: After the water temperature in the reactor rises, add the sulfate and fluoroaluminum compound pretreated in step (1) into the reactor, and then mix and stir for 0.5-1 h until the mixture is completely dissolved;

[0021] (3) Adding materials: The mixed solution in the reaction kettle of step (2) is drained into a vacuum agitator through a special pipe, and stabilizer, polycarboxylic acid, lignin sulfonate, defoamer, and calcium formate are added through the feeding port, and stirring is continued for 1-1.25 hours to obtain a uniform and stable mixed solution;

[0022] (4) Adjusting the pH value: adding a pH adjuster through the feed port to adjust the pH value of the liquid to obtain an accelerator mother solution;

[0023] (5) Decolorization treatment: stop the feeding operation in step (4), and add a decolorizing flocculant to the accelerator mother liquor for decolorization treatment;

[0024] (6) Concentration and drying: A vacuum agitator and a condensing device are used to cool the mother liquor of the accelerator. The mother liquor of the accelerator changes from a liquid to a semi-liquid and semi-solid state, and finally becomes a solid accelerator powder under the action of vacuum stirring and drying. The mother liquor is then dried to reduce the water content to obtain an alkali-free and chlorine-free powdered masterbatch soluble accelerator.

[0025] Furthermore, in the step (1), the sulfate and the fluoroaluminum compound are ground to a particle size of 200-250 mesh.

[0026] Furthermore, the water temperature in step (2) is 60-95°C.

[0027] Furthermore, the pH value of the liquid in step (4) is controlled between 2 and 3.

[0028] Furthermore, the pH value of the decolorizing flocculant in step (5) is 1.9, and the specific gravity is 1.180 g / cm3 .

[0029] The invention also provides a method for using an alkali-free and chlorine-free powdered masterbatch soluble accelerator. The method comprises two methods. The first method comprises: preparing an alkali-free and chlorine-free powdered masterbatch soluble accelerator with water in a mass ratio of 1:0.5-1.4 to prepare an alkali-free and chlorine-free liquid accelerator, which is used in shotcrete construction and the admixture thereof is 6-9% of the mass of cement; the second method comprises: preparing an alkali-free and chlorine-free powdered masterbatch soluble accelerator with aluminum sulfate and water in a mass ratio of 2-5:1-4:4 to prepare an alkali-free and chlorine-free liquid accelerator, which is used in shotcrete construction and the admixture thereof is 6-9% of the mass of cement.

[0030] The beneficial effects of the present invention compared with the prior art include:

[0031] 1. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent of the present invention has the advantages of being alkali-free, chlorine-free and non-corrosive, with a chloride ion content of less than 0.1% and an alkali content of less than 1%, meeting the alkali-free quick-setting agent standard of GB / T35159-2017 "Accelerator for Shotcrete"; in addition, the weakly acidic quick-setting agent will not corrode the human body during the construction process, thereby ensuring the personal safety and health of the construction workers.

[0032] 2. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent of the present invention has a highly efficient accelerating effect of coagulation, good crack resistance and impermeability. The quick-setting agent prepared by the present invention can achieve a maximum strength of 28.1MPa for 1d of mortar, a maximum compressive strength ratio of 123% for 28d of mortar, and a maximum strength retention rate of 115% for 90 days. The liquid quick-setting agent prepared by the present invention can be prepared by dissolving the product in water and applied to the construction of tunnel spraying, providing a strong guarantee for the safety and stability of the tunnel.

[0033] 3. The product of the present invention has excellent stability and is easy to store for a long time. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent of the present invention is solid powder, which avoids the phenomenon that the liquid quick-setting agent finished product is easy to precipitate or even crystallize during transportation and storage; after being stored in the warehouse for one year, its performance is almost not affected when it is used again. The problem that the liquid quick-setting agent product has great limitations in application field and transportation is solved.

[0034] 4. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent of the present invention can be immediately converted into an alkali-free and chlorine-free liquid quick-setting agent by adding water and stirring in proportion under a room temperature field environment.

[0035] 5. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent of the present invention is environmentally friendly and efficient, and adopts environmentally friendly and non-corrosive modified functional additives. The product of the present invention shows strong adaptability to engineering cement at a lower dosage and can meet the construction requirements of shotcrete. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with specific embodiments. It should be emphasized that the following description is only exemplary and is not intended to limit the scope of the present invention and its application.

[0037] In an embodiment of the present invention, an alkali-free and chlorine-free powdered masterbatch soluble accelerating setting agent is provided, wherein the base material is composed of aluminum sulfate and calcium fluoroaluminate, and other modifying components are added; the mass percentages of the base material and the components are: base material 45-60wt.%, stabilizer 5-10wt.%, polycarboxylic acid 3-5wt.%, magnesium lignin sulfonate 5-10wt.%, pH adjuster 1-1.5wt.%, defoamer 5-8wt.%, calcium formate 10-12wt.%, and the remainder is water.

[0038] A method for preparing an alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent comprises the following steps:

[0039] (1) Base material pretreatment: grinding aluminum sulfate and calcium fluoroaluminate to a particle size of 200-250 mesh, wherein the aluminum sulfate and calcium fluoroaluminate are composed in a mass ratio of 3:1;

[0040] (2) Dissolving and mixing: After the water temperature in the reaction kettle rises to 60-95° C., the aluminum sulfate and calcium fluoroaluminate pretreated in step (1) are added to the reaction kettle, and then mixed and stirred for 0.5-1 h until they are completely dissolved to obtain a mixed solution;

[0041] (3) Adding materials: The mixed solution in the reaction kettle of step (2) is drained into a vacuum agitator through a special pipe, and stabilizer, polycarboxylic acid, magnesium lignin sulfonate, defoamer, and calcium formate are added through the feeding port, and stirring is continued for 1-1.25 hours to obtain a uniform and stable mixed solution;

[0042] (4) adjusting the pH value: adding a pH adjuster through the feed port to adjust the liquid pH value to 2-3 to obtain an accelerator mother solution, wherein the pH adjuster is composed of lithium sulfate and diglycolamine in a mass ratio of 2:1;

[0043] (5) Decolorization treatment: Stop the feeding operation in step (4) and add a decolorizing flocculant to the accelerator mother liquor for decolorization treatment. The decolorizing flocculant has a pH value of 1.9 and a specific gravity of 1.180 g / cm 3 ;

[0044] (6) Concentration and drying: A vacuum agitator and a condensing device are used to cool the mother liquor of the accelerator, and the mother liquor of the accelerator changes from a liquid state to a semi-liquid and semi-solid state, and finally becomes a solid accelerator powder under the action of vacuum stirring and drying, and then dried to reduce the water content to obtain an alkali-free and chlorine-free powdered masterbatch soluble accelerator. There are two methods for using the prepared alkali-free and chlorine-free powdered masterbatch soluble accelerator. The first method is to prepare an alkali-free and chlorine-free liquid accelerator by mixing the alkali-free and chlorine-free powdered masterbatch soluble accelerator with water in a mass ratio of 1:0.5-1.4, and use it in the construction of shotcrete, and its dosage is 6-9% of the mass of cement; the second method is to prepare an alkali-free and chlorine-free liquid accelerator by mixing the alkali-free and chlorine-free powdered masterbatch soluble accelerator with aluminum sulfate and water in a mass ratio of 2-5:1-4:4, and use it in the construction of shotcrete, and its dosage is 6-9% of the mass of cement.

[0045] In order to make the disclosure of the present invention more complete, it is described below through more specific embodiments.

[0046] The raw material formula (excluding water) of the alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent of Example 1-5 is shown in Table 1, and its preparation process parameters are shown in Table 2.

[0047] Table 1 Raw material formula of alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent (balance is water)

[0048]

[0049] Table 2 Preparation process parameters of alkali-free and chlorine-free powdered masterbatch soluble accelerator

[0050]

[0051] The comparative example is a water-soluble powdered alkali-free quick-setting agent prepared by Example 3 of the method of application publication number CN 110204238 A.

[0052] The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent prepared in Examples 1-5 was mixed with water at a mass ratio of 1:0.5-1.4 to prepare a conventional alkali-free and chlorine-free liquid quick-setting agent, and added to a cement paste or cement mortar sample in an amount of 6-9% of the weight of cement, and the setting time and compressive strength were tested according to the standard of GB / T35159-2017 "Accelerator for Shotcrete", and the performance indicators required by the standard are shown in Table 3. The comparative example was used as a control, and the blank was used without any quick-setting agent.

[0053] Table 3 Performance requirements of pure paste and mortar with accelerating setting agent

[0054]

[0055] Table 4 Related performance test results

[0056]

[0057]

[0058] The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent prepared by the present invention has a high-efficiency accelerating setting effect, good crack resistance, impermeability and green environmental protection. This is because the synergistic effect between aluminum sulfate and calcium fluoroaluminate in the composition of the quick-setting agent significantly promotes the rapid hardening and solidification of concrete. Aluminum sulfate can react with cement quickly to generate hydration products such as ettringite due to its excellent activity. These products fill the gaps in concrete particles and enhance the compactness and strength of the concrete. Calcium fluoroaluminate further accelerates this reaction process through its unique chemical properties, thereby greatly shortening the setting time of the concrete. In addition, low-viscosity sodium hydroxypropyl methylcellulose plays a role in reducing viscosity and improving fluidity in the accelerator. It interacts with the moisture and solid particles in the concrete through the hydroxypropyl and methyl groups in its molecular structure, thereby effectively reducing the viscosity of the concrete and improving its fluidity; polycarboxylic acid can be adsorbed on the surface of concrete particles to form a stable dispersion layer, effectively preventing the agglomeration and sedimentation of concrete particles, thereby ensuring the uniformity and stability of the concrete; magnesium lignin sulfonate has good water solubility and dispersibility, and the lignin sulfonic acid group can chelate with the metal ions in the concrete, further enhancing the stability and durability of the concrete; lithium sulfate can effectively adjust the pH value of the concrete, thereby improving the hardening performance and durability of the concrete, and at the same time , it can also react chemically with other components in concrete to generate some new compounds, further enhancing the strength and stability of concrete; diglycolamine plays a buffering and regulating role in the accelerator. It can react with acidic substances in concrete to neutralize, thereby reducing the acidity of concrete and reducing its erosion and damage to the concrete structure. It can also react chemically with other components in concrete to generate some new compounds, further enhancing the stability and durability of concrete; ammonium sulfate mainly plays a role in regulating the performance of concrete in the accelerator. It can react chemically with other components in concrete to change the performance parameters such as the hardening speed and strength of concrete, thereby meeting different engineering requirements; calcium formate can promote the coagulation and hardening process of cement. When calcium formate reacts with cement, it can promote the formation of some cement calcium sulfonate. In addition, calcium formate can also promote the formation of CSH nuclei in cement. These compounds are an important component of cement hardening.

[0059] The test results are shown in Table 4. The chloride ion content of each embodiment is less than 0.1%, and the alkali content is less than 1%, which belongs to the alkali-free and chlorine-free quick-setting agent; according to the standard analysis of GB / T35159-2017 "Accelerator for Shotcrete", the alkali-free quick-setting agent prepared by the present invention can meet the standard requirements at a dosage of 6%. As in Example 3, the 1d compressive strength of the mortar is as high as 28.1MPa, the 28d compressive strength ratio is as high as 123%, and the 90d strength retention rate is as high as 115%. In the comparative example, the setting time of the prepared quick-setting agent is qualified, but the 1d compressive strength is significantly lower than that of the embodiment under the same experimental conditions. In contrast, the alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent prepared by the present invention has a lower dosage and higher compressive strength, indicating that the performance of the alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent prepared by the present invention is significantly better than that of the comparative example product.

[0060] Table 5 Effect of storage time of alkali-free and chlorine-free powdered masterbatch soluble accelerator on the performance of accelerator

[0061]

[0062]

[0063] The experimental results are shown in Table 5, indicating that the alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent of the present invention has almost the same properties as those of the newly produced product, such as setting time and strength, after being stored for one year, which fully demonstrates that the present invention has an ultra-long storage time.

[0064] Table 6 Compatibility of alkali-free accelerator prepared by water-soluble powdered alkali-free accelerator with cement

[0065]

[0066] As can be seen from Table 6, the alkali-free and chlorine-free powdered masterbatch soluble accelerating agent of the present invention can make different brands and types of cement meet the construction requirements of shotcrete at a relatively low dosage, and shows strong adaptability to engineering cement. This is because magnesium lignin sulfonate is a natural polymer compound with excellent dispersibility and stability. In the accelerating agent, it can interact with the charges on the surface of cement particles to form a stable dispersion system, prevent the sedimentation and agglomeration of cement particles, and the lignin sulfonic acid group can chelate with the metal ions in the concrete, further enhancing the stability and durability of the concrete, and further improving the accelerating effect of the accelerating agent.

[0067] The above content cannot be used to determine that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as belonging to the scope of patent protection of the present invention determined by the submitted claims.

Claims

1. An alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent, characterized in that: The base material is composed of sulfate and fluoroaluminum compound, and other modified components are added; the mass percentage of the base material and each component is: base material 45-60wt.%, stabilizer 5-10wt.%, polycarboxylic acid 3-5wt.%, lignin sulfonate 5-10wt.%, pH regulator 1-1.5wt.%, defoamer 5-8wt.%, calcium formate 10-12wt.%, and the balance is water.

2. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent according to claim 1, characterized in that: The stabilizer includes one or any combination of low-viscosity hydroxypropyl methylcellulose, low-viscosity hydroxypropyl methylcellulose potassium, low-viscosity hydroxypropyl methylcellulose magnesium, and low-viscosity hydroxypropyl methylcellulose calcium.

3. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent according to claim 1, characterized in that: The pH regulator is any combination of lithium sulfate and diglycolamine.

4. The alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent according to claim 1, characterized in that: The defoaming agent includes any one of ammonium sulfate, aluminum sulfate, magnesium sulfate and a combination thereof.

5. A method for preparing the alkali-free and chlorine-free powdered masterbatch soluble quick-setting agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Base material pretreatment: grinding sulfate and fluoroaluminum compound; (2) Dissolving and mixing: After the water temperature in the reactor rises, add the sulfate and fluoroaluminum compound pretreated in step (1) into the reactor, and then mix and stir for 0.5-1 h until the mixture is completely dissolved; (3) Adding materials: The mixed solution in the reaction kettle of step (2) is drained into a vacuum agitator through a special pipe, and stabilizer, polycarboxylic acid, lignin sulfonate, defoamer, and calcium formate are added through the feeding port, and stirring is continued for 1-1.25 hours to obtain a uniform and stable mixed solution; (4) Adjusting the pH value: adding a pH adjuster through the feed port to adjust the pH value of the liquid to obtain an accelerator mother solution; (5) Decolorization treatment: stop the feeding operation in step (4), and add a decolorizing flocculant to the accelerator mother liquor for decolorization treatment; (6) Concentration and drying: A vacuum agitator and a condensing device are used to cool the mother liquor of the accelerator. The mother liquor of the accelerator changes from a liquid to a semi-liquid and semi-solid state, and finally becomes a solid accelerator powder under the action of vacuum stirring and drying. The mother liquor is then dried to reduce the water content to obtain an alkali-free and chlorine-free powdered masterbatch soluble accelerator.

6. The method for preparing an alkali-free and chlorine-free powdered masterbatch soluble accelerating setting agent according to claim 5, characterized in that: In the step (1), the sulfate and the fluoroaluminum compound are ground to a particle size of 200-250 mesh.

7. The method for preparing an alkali-free and chlorine-free powdered masterbatch soluble accelerating setting agent according to claim 5, characterized in that: The water temperature in step (2) is 60-95°C.

8. The method for preparing an alkali-free and chlorine-free powdered masterbatch soluble accelerating setting agent according to claim 5, characterized in that: The pH value of the liquid in step (4) is controlled between 2 and 3.

9. The method for preparing an alkali-free and chlorine-free powdered masterbatch soluble accelerating setting agent according to claim 5, characterized in that: The pH value of the decolorizing flocculant is 1.9 and the specific gravity is 1.180 g / cm 3 .

10. A method for using the alkali-free and chlorine-free powdered masterbatch soluble accelerating setting agent prepared according to any one of claims 5 to 9, characterized in that: There are two methods of use. The first method is to prepare an alkali-free and chlorine-free powdered masterbatch soluble accelerator and water in a mass ratio of 1:0.5-1.4 to prepare an alkali-free and chlorine-free liquid accelerator, which is used in shotcrete construction and its dosage is 6-9% of the mass of cement. The second method is to prepare an alkali-free and chlorine-free powdered masterbatch soluble accelerator and aluminum sulfate and water in a mass ratio of 2-5:1-4:4 to prepare an alkali-free and chlorine-free liquid accelerator, which is used in shotcrete construction and its dosage is 6-9% of the mass of cement.

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