JP7691302B2 - Spraying method and equipment - Google Patents

Description

The present invention relates to a spraying method and a spraying device.

In tunnels, mining pits, underground spaces, etc., sprayed concrete is used to prevent the excavation surface from collapsing and to reinforce the ground during or after excavation. The quick-setting properties of sprayed concrete ensure adhesion to the construction target, contributing to the reinforcement of the construction target.

Sprayed concrete is mixed with quick-setting components to give it quick-setting properties. Among them, powder quick-setting agents whose active ingredients are calcium aluminate, sodium aluminate, etc., can give it strong quick-setting properties and can also obtain high strength. In the wet spraying method, which is a common application method for sprayed concrete, for example, at least cement, water, and aggregate are weighed and mixed to prepare base concrete, which is then pumped to a spraying device via an agitator vehicle or the like during application. In the spraying device, a separate powder or liquid quick-setting agent is added to the base concrete being pumped, and mixing is carried out in the spraying nozzle of the spraying device to form sprayed concrete, which is then sprayed from the nozzle end hole. Mixing is carried out while the quick-setting components in the spraying device move from the point where they come into contact with water (water contact point) to the discharge hole at the end of the spraying nozzle, forming the sprayed concrete. The distance used for mixing is usually several tens of centimeters to several meters, and the travel time is the mixing time. Generally, the longer this distance, the more mixing will take place, the better the mixability will be, and the easier it will be to obtain a more uniform concrete in terms of structure and properties.

To obtain this type of sprayed concrete, the powdered quick-setting admixture mixed into the base concrete generally contains the above-mentioned quick-setting components plus various other components for adjusting the properties. For example, a typical conventional powdered quick-setting admixture contains calcium aluminate with a high CaO content as a chemical component, mixed with gypsum to promote hardening, and sodium aluminate to increase early strength development and sodium carbonate to promote setting (see, for example, Patent Documents 1 to 4). In addition to the above-mentioned cement, water, and aggregate, gypsum to increase long-term strength and water-reducing agents to reduce the amount of water that can lead to a decrease in strength are also added to the base concrete as necessary (see, for example, Patent Document 4).

JP 2012-121763 A JP 2003-012356 A Patent No. 5129955 JP 2020-11891 A

In recent years, depending on the location where sprayed concrete is applied, there is an increasing demand for initial strength development within about three hours of spraying. For this reason, if it is possible to increase strength development not only through powder quick-setting additives that exhibit high strength development, but also through application procedures and equipment, it is believed that a synergistic effect can be achieved between the quick-setting additives and the application procedures and equipment.

Therefore, the present invention aims to provide a spraying method and spraying device that can perform spraying work with high initial strength development.

As a result of extensive research into the above-mentioned problems, the present inventors discovered that adding a quick-setting aid containing gypsum to the base concrete before adding the quick-setting material to the base concrete, separately from the gypsum contained as necessary in the base concrete or the quick-setting material, results in a spraying method with excellent initial strength development, and furthermore, by adjusting the position in the spraying device where the quick-setting aid is added, a spraying device suitable for the method can be obtained.

The present invention provides a spraying method in which a quick-setting material is added and mixed with base concrete containing cement, and then the concrete is sprayed onto the construction object, in which a quick-setting aid containing gypsum is added to the base concrete before the quick-setting material is added.

The present invention also provides a pressure pipe (1) for pressure-feeding base concrete containing cement,
An air supply section (2) and a quick-setting material supply section (3) for supplying a quick-setting material are arranged in this order on the side of the pressure pipe (1) in the pressure-feeding direction;
A spraying device (10) having a spray nozzle (4) at an end of the pressure pipe (1),
At least one quick-setting aid adding section (5) for adding a quick-setting aid containing gypsum is provided on a side of the air supply section (2) and/or on a side of the pressure pipe (1) between the air supply section (2) and the quick-setting material supply section (3).
A spraying device is provided.

The present invention provides a spraying method and spraying device that allows spraying construction with high initial strength development.

1(a) and (b) are schematic diagrams showing one embodiment of a spraying device of the present invention.

[Spraying material]
The sprayed material (sprayed concrete) includes base concrete, a quick-setting material, and a quick-setting aid.

Base concrete The base concrete contains cement. The cement is preferably Portland cement, and any type of Portland cement may be used, for example, various types of Portland cement such as normal, early strength, super early strength, moderate heat, low heat, and sulfate resistant Portland cement. As the cement, for example, a mixed cement containing Portland cement such as blast furnace cement or fly ash cement may be used. One type of cement may be used alone, or two or more types may be used in combination. When using Portland cement, the particle size is not particularly limited, and for example, Portland cement having a particle size of 2500 cm ² /g or more according to the JIS standard (JIS R 5210:2019) may be used.

The base concrete may contain aggregates such as fine aggregate and coarse aggregate. The fine aggregate is not particularly limited as long as it is a fine aggregate that can be used in mortar or concrete. The coarse aggregate is not particularly limited as long as it is a coarse aggregate that can be used in concrete. For both fine aggregate and coarse aggregate, it is preferable to use aggregates with a surface dry density of 2.3 to 2.9 g/cm ³ , from the viewpoint that a predetermined aggregate strength is easily ensured, and the specific gravity difference with other contained components is small and material separation is unlikely to occur. Specific examples of such aggregates include natural aggregates such as silica sand and limestone sand, and crushed sand such as andesite, sandstone, and basalt, for fine aggregates, and crushed stone and gravel such as silica stone, limestone, andesite, sandstone, and basalt, for coarse aggregates. One type of aggregate may be used alone, or two or more types may be used in combination.

The amount of aggregate in the base concrete is not particularly limited, but from the viewpoint of excellent pumpability of the concrete during construction, the total amount of fine aggregate and coarse aggregate is preferably 300 to 570 parts by mass, more preferably 380 to 550 parts by mass, and even more preferably 420 to 520 parts by mass per 100 parts by mass of cement. When fine aggregate and coarse aggregate are used in combination, the mass proportion of fine aggregate (mass proportion of fine aggregate in total aggregate) is preferably 54 to 69% by mass, more preferably 55 to 65% by mass, and even more preferably 56 to 63% by mass.

The base concrete may contain a water-reducing agent. The water-reducing agent includes a dispersant, a high-performance water-reducing agent, a high-performance AE water-reducing agent, an AE water-reducing agent, and a fluidizing agent. Examples of such water-reducing agents include those specified in JIS A 6204:2011 "Chemical admixtures for concrete". Examples of water-reducing agents include polycarboxylic acid water-reducing agents, naphthalene sulfonic acid water-reducing agents, lignin sulfonic acid water-reducing agents, melamine water-reducing agents, and acrylic water-reducing agents. Among these, polycarboxylic acid water-reducing agents are preferred. One type of water-reducing agent may be used alone, or two or more types may be used in combination. The content of the water-reducing agent is, for example, preferably 0.01 to 1 part by mass, more preferably 0.05 to 0.5 parts by mass, and even more preferably 0.1 to 0.3 parts by mass, in terms of solid content, relative to 100 parts by mass of cement, from the viewpoint of easily ensuring fluidity while suppressing the amount of water.

The base concrete may contain other components than those mentioned above, provided that they do not impair the effects of the present invention. Examples of components that may be contained include gypsum, thickeners, short fibers, and pozzolanic reactive substances.

The amount of water in the base concrete can be adjusted as appropriate depending on factors such as the purpose and location of use. The water content is preferably 52 to 68 parts by mass, more preferably 53 to 67 parts by mass, and even more preferably 55 to 65 parts by mass, per 100 parts by mass of cement. If the water content is within the above range, the concrete tends to have excellent strength development.

The quick-setting material may be either a powder or a liquid. Examples of the powder quick-setting material include those containing calcium aluminate, sulfates of alkali metals, sulfates of alkaline earth metals, and aluminum sulfate. Examples of the liquid quick-setting material include those containing aluminum sulfate as the main component, and commercially available liquid quick-setting materials can also be used.

Calcium aluminate is an inorganic hydration active material whose main chemical components are CaO and Al ₂ O ₃ , and the molar ratio of CaO to Al ₂ O ₃ (CaO/Al ₂ O ₃ ) is preferably 1.8 to 2.7, more preferably 1.9 to 2.65, and more preferably 2.0 to 2.6. If the molar ratio of CaO to Al ₂ O ₃ is within the above range, it becomes easier to achieve both quick setting and workability. Calcium aluminate may also contain other components such as impurities other than CaO and Al ₂ O ₃ derived from the raw materials, regardless of their form of existence, as long as they do not impair the effects of the present invention.

Calcium aluminate may be crystalline, amorphous, or a mixture thereof. From the viewpoint of obtaining a better quick-setting property, calcium aluminate preferably has a vitrification rate, which is the degree of amorphization, of 60% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more. The fineness of calcium aluminate is not particularly limited, but since it is easy to obtain a suitable reaction activity when used as a quick-setting material for concrete, it is preferable that the fineness is the same as or higher than that of the cement in the base concrete to be mixed, for example, a fineness of 3000 to 6500 cm ² /g of Blaine specific surface area.

Calcium aluminate _can be obtained, for example, by heating a mixture of raw materials, which are a CaO source and an _Al2O3 source, so as to obtain the desired molar ratio of CaO _{and Al2O3} as chemical components, until it melts. In addition, since the structural state of calcium aluminate after cooling varies depending on the cooling process after heating during production, the vitrification rate, which is the degree of amorphization, can be adjusted depending on the cooling conditions such as the cooling rate.

The calcium aluminate content is preferably 60-80 mass%, more preferably 65-78 mass%, and even more preferably 66-77 mass%, based on the total mass of the quick-setting material. If the calcium aluminate content is within the above range, it is easy to achieve both quick-setting properties and mixability.

The alkali metal sulfate is not particularly limited and any can be used, with anhydrous being preferred due to its excellent reactivity. Examples of alkali metals include lithium, sodium, potassium, etc., with sodium being preferred. The alkali metal sulfate may be used alone or in combination of two or more. The content of the alkali metal sulfate is preferably 4 to 16 parts by mass, more preferably 5 to 15 parts by mass, and even more preferably 6 to 14 parts by mass, calculated as an anhydrous salt, per 100 parts by mass of calcium aluminate. If the content of the alkali metal sulfate is within the above range, it is likely to have excellent quick-setting properties and strength development.

The alkaline earth metal sulfate is not particularly limited and any of them can be used, and anhydrides are preferred because of their excellent reactivity. Examples of alkaline earth metals include magnesium and calcium, and calcium is preferred. The alkaline earth metal sulfate may be used alone or in combination of two or more. The particle size and grain size of the alkaline earth metal sulfate are also not particularly limited, and examples include those having a Blaine specific surface area of about 4000 to 8500 cm ² /g. The content of the alkaline earth metal sulfate is preferably 5 to 45 parts by mass, more preferably 7 to 40 parts by mass, and even more preferably 10 to 35 parts by mass, calculated as an anhydride, relative to 100 parts by mass of calcium aluminate. If the content of the alkaline earth metal sulfate is within the above range, it is likely to have excellent long-term strength development.

The mass ratio of the alkali metal sulfate to the alkaline earth metal sulfate in the quick-setting material ([mass of alkaline earth metal sulfate]/[mass of alkali metal sulfate]) is preferably 0.5 to 7, more preferably 0.8 to 4, and even more preferably 1 to 4, calculated on anhydrous basis. If the mass ratio of the alkali metal sulfate to the alkaline earth metal sulfate is within the above range, quick-setting properties, mixability, and long-term strength development are easily achieved.

Aluminum sulfate may be in any form, such as the 16-hydrate or anhydrous form, with the 16-hydrate being preferred. The content of aluminum sulfate, calculated as an anhydrous form, is preferably 0.5 to 15 parts by mass, more preferably 0.7 to 13 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of calcium aluminate. If the content of aluminum sulfate is within the above range, it is easy to ensure long-term strength expression even when the rapid setting property is increased in a low-temperature environment.

The mass ratio of the alkali metal sulfate to aluminum sulfate in the quick-setting material ([mass of aluminum sulfate]/[mass of alkali metal sulfate]) is preferably 0.05 to 2, more preferably 0.1 to 1.8, and even more preferably 0.2 to 1.5, calculated on anhydrous basis. If the mass ratio of the alkali metal sulfate to aluminum sulfate is within the above range, quick-setting properties, mixability, and strength development are easily achieved.

The quick-setting material may contain an alkali metal carbonate. The alkali metal carbonate is not particularly limited, and any of them may be used, and anhydrous carbonate is preferable because of its excellent reactivity. Examples of the alkali metal include lithium, sodium, potassium, and the like, and sodium is preferable. The alkali metal carbonate may be used alone or in combination of two or more. The particle size of the alkali metal carbonate is not particularly limited, and for example, a powder having a Blaine specific surface area of about 3000 to 6500 cm ² /g and a maximum particle size of 1 mm or less may be used. The content of the alkali metal carbonate is preferably 1 to 10 parts by mass, more preferably 1.5 to 9 parts by mass, and even more preferably 2 to 8 parts by mass, in terms of anhydrous, per 100 parts by mass of calcium aluminate. If the content of the alkali metal carbonate is within the above range, the initial strength development is further improved.

The quick-setting material is produced by mixing the above-mentioned components. There are no particular limitations on the mixing method, and general-purpose mixers such as tilting mixers, pan mixers, twin-shaft mixers, grout mixers, Hobart mixers, and omni mixers can be used.

The amount of quick-setting material added to the base concrete is preferably 5 to 15 parts by mass, more preferably 6 to 14 parts by mass, and even more preferably 7 to 13 parts by mass, per 100 parts by mass of cement. If the amount of quick-setting material added is within the above range, it is easy to achieve both quick-setting properties and mixability.

-Quick-setting aid The quick-setting aid used in the present invention contains gypsum. Examples of gypsum include anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum, etc., and from the viewpoint of further improving the strength development, anhydrous gypsum is preferred. One type of gypsum may be used alone, or two or more types may be used in combination. From the viewpoint of further improving the initial strength development, the fineness of the gypsum is preferably 3500 to 18000 cm ² /g in terms of Blaine specific surface area, more preferably 5000 to 15000 ^{cm 2} /g, even more preferably 5500 to 14000 cm ² /g, and particularly preferably 7000 to 12000 cm ² /g.

The quick-setting aid may contain components other than gypsum, provided that the effects of the present invention are not impaired. Examples of components that may be contained include alkali metal carbonates, water, and the like. Examples of alkali metal carbonates include those mentioned above, with sodium carbonate being preferred. When the quick-setting aid contains components other than gypsum, the amount of gypsum is preferably 55 to 98 parts by mass, more preferably 65 to 90 parts by mass, and even more preferably 75 to 85 parts by mass, per 100 parts by mass of the solid content of the quick-setting aid.

The amount of quick-setting aid added to the base concrete is preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass, and even more preferably 3 to 8 parts by mass, in terms of solids, per 100 parts by mass of cement. If the amount of quick-setting aid added is within the above range, it is possible to further improve the strength development from the early stages to the long term.

[Spraying method]
The spraying method of the present invention is characterized in that a quick-setting aid containing gypsum is added to a base concrete containing cement, and then a quick-setting material is added and mixed, and sprayed onto the construction object. That is, a quick-setting aid containing gypsum is added to the base concrete before adding the quick-setting material, in addition to the gypsum that has been conventionally contained in the base concrete or the quick-setting material as necessary. According to the spraying method of the present invention, spraying construction with excellent initial strength development can be performed. Therefore, it can be suitably applied not only to normal tunnel walls and slopes, but also to construction in environments where adhesion is poor and rapid setting is required, such as places with a lot of water.

[Spraying device]
Hereinafter, an embodiment of the spraying device of the present invention will be described with reference to the drawings. Each drawing is a schematic diagram, and the size of each component is not limited to those shown in the drawings.

Figures 1(a) and (b) are schematic diagrams showing one embodiment of the spraying device of the present invention. The spraying device 10 of this embodiment is equipped with a pressure pipe 1 for pressure-feeding base concrete containing cement, an air supply unit 2, a quick-setting material supply unit 3 for supplying quick-setting material, and a spray nozzle 4. The air supply unit 2 and the quick-setting material supply unit 3 are arranged on the side of the pressure pipe 1 in order in the pressure-feeding direction, and at least one quick-setting aid addition unit 5 for adding a quick-setting aid is provided on the side of the air supply unit 2 and/or on the side of the pressure pipe 1 between the air supply unit 2 and the quick-setting material supply unit 3.

The pressure pipe 1 is not particularly limited as long as it is a pressure-resistant pipe, and may be a metallic pressure-resistant pipe, a pressure-resistant hose, or a composite of these. The length of the pressure pipe 1 can be adjusted appropriately depending on the distance to the construction site. The inner diameter of the pressure pipe 1 is not particularly limited, and may be, for example, 5 to 13 cm. The pressure pipe 1 receives base concrete containing cement from a concrete material supplying machine such as an agitator vehicle or a mortar mixer, and pressure-transports the base concrete using air supplied from the air supply unit 2.

The air supply unit 2 may be any device capable of compressing and delivering air, such as an air compressor. The discharge pressure of the spraying material can be controlled by adjusting the amount of air supplied by the air supply unit. The spraying material includes base concrete, quick-setting material, and quick-setting aid. From the viewpoint of further improving workability during spraying, the installation position of the air supply unit 2 is preferably 6 to 18 m, and more preferably 8 to 15 m, from the tip of the spray nozzle 4.

The quick-setting material supply unit 3 pumps the quick-setting material, and a suitable one can be selected depending on the shape of the quick-setting material. If the quick-setting material is in powder or slurry form, an air compressor or the like can be used, and if it is liquid, a ring-shaped member that supplies liquid toward the center of a ring called a shower ring, water ring, O-ring, or the like can be used. The quick-setting material supply unit 3 is preferably installed 0.5 to 5 m, more preferably 0.8 to 4.5 m, and even more preferably 1 to 3 m from the tip of the spray nozzle, from the viewpoint of making it easy to thoroughly mix the base concrete, quick-setting material, and quick-setting aid.

The spray nozzle 4 is not particularly limited as long as it is one that is normally used for spraying, etc. The length of the spray nozzle 4 is preferably 10 to 50 cm, more preferably 15 to 40 cm, and even more preferably 20 to 35 cm. If the length of the spray nozzle 4 is within the above range, the discharge range is easier to control, and the amount of dust generated can be further reduced.

The quick-setting aid supply unit 5 is for pressure-feeding the quick-setting aid with an air compressor or the like. The quick-setting aid may be in powder form or in slurry form. The quick-setting aid supply unit 5 may be connected to the air supply unit 2 as shown in FIG. 1(a), or may be connected to the pressure pipe 1 between the air supply unit 2 and the quick-setting aid supply unit 3 as shown in FIG. 1(b), or may be connected to both the air supply unit 2 and the pressure pipe 1 by combining the configurations of FIG. 1(a) and (b). By using such a spraying device, the quick-setting aid is added during the spraying process without being added to the base concrete in advance, improving the initial strength development, and since it does not affect the fresh properties of the base concrete, the use of a water-reducing agent can be reduced.

The installation position of the quick-setting aid supply section 5 is such that the length from the quick-setting aid addition section to the quick-setting material supply section is preferably 3 to 18 m, more preferably 4 to 15 m, and even more preferably 4 to 12 m, from the viewpoint of making it easy to thoroughly mix the base concrete and the quick-setting aid.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. The examples were carried out in an environment of 20±1°C unless otherwise specified.

Examples 1 to 6, Comparative Example 1
[material]
Calcium aluminate: CaO/Al ₂ O ₃ 2.5, Blaine specific surface area 5400 cm ² /g, vitrification rate 95 mass%
Sodium sulfate reagent (anhydrous sodium sulfate)
Calcium sulfate reagent (anhydrite)
Aluminum sulfate reagent (16-hydrate)
Quick-setting aid: anhydrous gypsum, Blaine specific surface area 11,000 cm ² /g. When added as a slurry, adjust with water to make a slurry of 75 mass% solids. Cement: ordinary Portland cement, Blaine specific surface area 3,200 cm ² /g, density 3.15 g/cm ³
Fine aggregate: Limestone fine aggregate (surface dry density: 2.65g/cm ³ , center particle size: 0.6mm)
Coarse aggregate: crushed stone (surface dry density: 2.74g/cm ³ , particle size: 5-15mm)

[Preparation of base concrete]
Base concrete was prepared by mixing 100 parts by mass of cement, 300 parts by mass of fine aggregate, 200 parts by mass of coarse aggregate, and 60 parts by mass of water in a concrete mixer for 2 minutes. When a slurry-like quick-setting agent was used, the water contained in the slurry was also adjusted to 60 parts by mass.

[Preparation of quick-setting material]
The mixture was designed so that 100 parts by mass of calcium aluminate contained 5.7 parts by mass of aluminum sulfate, 12.8 parts by mass of sodium sulfate, and 26 parts by mass of calcium sulfate, and was mixed in a Henschel mixer to produce a quick-setting material.

[Preparation of sprayed concrete]
The base concrete was put into a supply tank immediately after mixing, and was pumped from there to the spraying device via a resin hose about 10 m long and 6 cm in inner diameter. The spraying device is a commercially available product whose basic components are a 2-inch inner diameter pressure pipe through which the base concrete is pumped, a cylindrical side pipe (air supply section) that is connected to the side of the pressure pipe at an inclination angle of about 30 degrees to supply air to the base concrete, a cylindrical side pipe (quick-setting material supply section) that is connected to the side of the pressure pipe at an inclination angle of about 30 degrees to supply additives (quick-setting materials) to the base concrete, and a 2-inch inner diameter (tip hole diameter) spraying nozzle for spraying the sprayed concrete.
The side pipe, which is the quick-setting material supply section, was formed by placing a steel T-shaped pipe (three-way pipe) between the main pressure pipe and the injection nozzle. The main pressure pipe and the injection nozzle were connected to the two pipe openings located on a straight line of the T-shaped pipe, respectively, and the supply pipe of the quick-setting material sent separately was connected to the remaining pipe opening. The base concrete and the quick-setting material were mixed in the distance from the addition position of the quick-setting material to the base concrete in the T-shaped pipe (the joining point of the base concrete and the quick-setting material) to the end of the injection nozzle hole, and the distance (hereinafter referred to as the mixing distance) was 2 m. In addition, the quick-setting auxiliary supply section was connected to the air supply section via the T-shaped pipe. The length from the quick-setting auxiliary supply section to the quick-setting material supply section was 6 m.
A predetermined amount of the quick-setting material is added to the base concrete being pumped inside the spraying device by pneumatically pumping it with compressed air. The added concrete is mixed as it travels a predetermined mixing distance to produce the sprayed concrete. The amount of the quick-setting material added is as shown in Table 1. Here, for Examples 1 to 6, the quick-setting aid was added from the quick-setting aid supply unit in the proportions shown in Table 1.

[Evaluation of strength development of sprayed concrete]
Using the spraying device, the sprayed concrete was sprayed into a molding form with inner dimensions of 30 x 40 x 20 cm, filling the form. This was placed in a thermostatic chamber at 20°C (±1°C), and after a specified time had passed, a cylindrical specimen with a diameter of 5 cm and a height of 10 cm was taken from the hardened concrete in the form using a core drill, obtaining a specimen aged 28 days. The uniaxial compressive strength of this 28-day specimen was measured using an Amsler type compressive strength tester.
In addition, using the pull-out test formwork and embedding tools specified in the JSCE-G561 standard, shotcrete prepared in the same manner was subjected to a pull-out test in accordance with JSCE-G561. The compressive strength of the shotcrete at ages of 15 minutes, 3 hours, and 24 hours was measured by this test. The results of the strength measurements of each specimen are shown in Table 1.

Examples 1a to 4a and Comparative Example 1a (Evaluation of quick setting ability)
In the above-mentioned base concrete mix, the amount of the coarse aggregate and fine aggregate contained in each mix was changed to the fine aggregate content, and the base mortar was prepared in the same manner as the base concrete, except that the coarse aggregate was not included and the other components and their contents were not changed. For Examples 1a to 4a, the quick-setting aid was first added and mixed in the ratio shown in Table 2 to the obtained base mortar, and then the quick-setting material was added in the ratio shown in Table 2 and mixed for 5 seconds with a high-speed mixer to prepare a mortar mixture. For Comparative Example 1a, the quick-setting material was added in the ratio shown in Table 2 to the obtained base mortar, and mixed for 5 seconds with a high-speed mixer to prepare a mortar mixture.
The Proctor penetration resistance of the mortar mixture was measured 30 seconds and 60 seconds after the addition of the quick-setting agent to evaluate its quick-setting properties. The method for measuring Proctor penetration resistance complies with the Japan Society of Civil Engineers' Standard Specifications for Concrete, "Quality Standards for Accelerators for Sprayed Concrete," Appendix, "Method for Measuring Instantaneous Setting Time by Penetration Resistance of Mortar with Added Accelerator," and a Proctor needle with a cross-sectional area of 0.125 ^cm2 was used. The results of the measurement of the penetration resistance are shown in Table 2. In addition, the entry "＞16 (N/ ^mm2 )" in the table indicates that the Proctor needle could be driven in, but exceeded the measurement limit of the equipment used (maximum 16 N/ ^mm2 ).

According to the present invention, the sprayed concrete exhibits sufficient quick setting, improves initial strength development at ages of 3 hours and 24 hours, and maintains sufficient strength development over the long term.

REFERENCE SIGNS LIST 1 Pressure pipe 2 Air supply section 3 Quick-setting material supply section 4 Spray nozzle 5 Quick-setting aid adding section
10 Spraying equipment

Claims (4)

A pressure pipe (1) for pumping base concrete containing cement;
An air supply section (2) and a quick-setting material supply section (3) for supplying a quick-setting material are arranged in this order on the side of the pressure pipe (1) in the pressure-feeding direction;
A spraying device (10) having a spray nozzle (4) at an end of the pressure pipe (1),
At least one quick-setting aid adding section (5) for adding a quick-setting aid containing gypsum is provided on a side of the air supply section (2) and/or on a side of the pressure pipe (1) between the air supply section (2) and the quick-setting material supply section (3).
Spraying equipment. 2. The spraying device according to claim 1 , wherein the length from the quick-setting aid adding section (5) to the quick-setting material supply section (3) is 3 to 18 m. 3. The spraying device according to claim 1, wherein the amount of the quick-setting aid added is 1 to 15 parts by mass per 100 parts by mass of the cement. A spraying method for spraying a work object, comprising the steps of: spraying a material onto a work object using the spraying device according to any one of claims 1 to 3 .

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