Rapid-setting admixtures and sprayed concrete

Abstract

To provide a rapid-setting admixture and sprayed concrete that exhibit good adhesion and rapid setting properties even in low-temperature environments, and also have excellent strength development. [Solution] A rapid-setting admixture comprising calcium aluminate and at least one metal sulfate, wherein the calcium aluminate has a molar ratio of CaO to Al2O3 (CaO / Al2O3) of 1.6 to 2.7 and a molar ratio of SiO2 to MgO (SiO2 / MgO) of 1.1 to 6.

Description

[Technical Field]

[0001] This invention relates to a rapid-setting admixture and sprayed concrete. [Background technology]

[0002] In tunnels, mining shafts, and underground spaces, shotcrete is applied to prevent collapse of the excavation surface and to reinforce the ground during or after excavation. Shotcrete ensures adhesion to the target object through its rapid setting properties. To impart rapid setting properties, rapid setting components are mixed into the concrete. For example, powdered rapid setting agents containing calcium aluminate or sodium aluminate as active ingredients can impart strong rapid setting properties, and concrete with higher strength is more likely to be obtained compared to liquid rapid setting agents. In the wet shotcrete method, which is a common method of applying shotcrete, for example, base concrete is prepared by weighing and mixing at least cement, water, and aggregate, and this base concrete is pumped to the shotcrete device via an agitator truck or the like during construction. Inside the shotcrete device, a separately delivered powdered or liquid rapid setting agent is added to the base concrete being pumped, and mixing proceeds in the spray nozzle of the shotcrete device to form shotcrete, which is then sprayed from the nozzle end hole. Another construction method, the dry spraying method, involves weighing and mixing water and at least cement, aggregate, and powdered rapid-setting agent to create dry-mix concrete, which is then air-pressurized from a storage tank or similar container to the spraying device during construction. Inside the spraying device, water is added to the dry-mix concrete as it is being pumped, and mixing continues until it reaches the spraying nozzle to form sprayed concrete, which is then sprayed in the same manner. In both methods, mixing occurs as the rapid-setting components in the spraying device travel 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 constitutes the mixing time. Generally, the longer this distance, the more the mixing progresses, the higher the mixability, and the easier it is to obtain sprayed concrete that is more uniform in terms of structure and properties.

[0003] To obtain such sprayed concrete, the powdered rapid-setting agent mixed in is generally a mixture of the aforementioned rapid-setting components with auxiliary agents to adjust various properties. For example, a typical conventional powdered rapid-setting agent (see, for example, Patent Documents 1 and 2) that is highly alkalinized, is made by combining calcium aluminate with a high CaO content as a chemical component, gypsum to accelerate hardening, and sodium aluminate to enhance initial strength development, and sodium carbonate to accelerate setting, etc. The primary objective is to provide high rapid-setting properties and early strength development. As a result, setting occurs in a very short time after the rapid-setting agent comes into contact with water. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-121763 [Patent Document 2] Patent No. 5129955 [Overview of the project] [Problems that the invention aims to solve]

[0005] While sprayed concrete mixed with powdered rapid-setting agents is used at construction sites throughout the year, its adhesion and rapid-setting properties generally decrease in low-temperature environments such as winter. A decrease in the adhesion and rapid-setting properties of sprayed concrete can lead to spalling of the concrete, causing accidents and reducing construction efficiency.

[0006] Therefore, the present invention aims to provide a rapid-setting admixture and sprayed concrete that have good adhesion and rapid setting properties even in low-temperature environments, and also exhibit excellent strength development. [Means for solving the problem]

[0007] As a result of diligent research into the above-mentioned problems, the inventors have found that by using calcium aluminate having specific chemical components, a rapid-setting admixture that exhibits high rapid-setting properties even in low-temperature environments can be obtained.

[0008] In other words, the present invention is as follows. [1] A rapid-setting admixture comprising calcium aluminate and at least one metal sulfate, wherein the calcium aluminate has a molar ratio of CaO to Al2O3 (CaO / Al2O3) of 1.6 to 2.7 and a molar ratio of SiO2 to MgO (SiO2 / MgO) of 1.1 to 6. [2] The rapid-setting admixture described in [1], wherein the calcium aluminate content is 55 to 80% by mass based on the total mass of the rapid-setting admixture. [3] The rapid-setting admixture according to [1] or [2], further comprising an alkali metal carbonate. [4] A sprayed concrete comprising cement, aggregate, water, and the rapid-setting admixture described in [1] or [2], wherein the content of the rapid-setting admixture is 3 to 20 parts by mass per 100 parts by mass of cement. [5] During hardening, the compressive strength at 4 hours of age is measured at 10°C in accordance with the Japan Society of Civil Engineers standard JSCE-G561:2010 "Initial strength test method for sprayed concrete by tensile method" and is 0.5 N / mm². 2 The above is the sprayed concrete described in [4]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a rapid-setting admixture and sprayed concrete that have good adhesion and rapid setting properties even in low-temperature environments, and also exhibit excellent strength development. [Modes for carrying out the invention]

[0010] A preferred embodiment of the present invention will be described in detail below. In this specification, all content and other figures are expressed on a solid content basis and anhydrous basis.

[0011] The rapid-setting admixture of this embodiment comprises calcium aluminate and at least one metal sulfate.

[0012] Calcium aluminate is an inorganic hydraulic active substance containing CaO and Al₂O₃ as main chemical components. The calcium aluminate according to the present embodiment has a content molar ratio of CaO to Al₂O₃ (CaO / Al₂O₃) of 1.6 to 2.7, and a content molar ratio of SiO₂ to MgO (SiO₂ / MgO) of 1.1 to 6. When the content molar ratio of CaO to Al₂O₃ and the content molar ratio of SiO₂ to MgO are outside the above ranges, the quick-setting property and adhesion property in a low-temperature environment are reduced. The content molar ratio of CaO to Al₂O₃ is preferably 1.7 to 2.6, more preferably 1.8 to 2.5, and even more preferably 1.9 to 2.3, from the viewpoint that more excellent quick-setting property is easily obtained. The content molar ratio of SiO₂ to MgO is preferably 1.3 to 5, more preferably 1.5 to 4, and even more preferably 1.7 to 3, from the viewpoint that the quick-setting property and adhesion property in a low-temperature environment are further excellent, and the strength development property is also easily improved. The calcium aluminate may also contain different components such as impurities other than CaO, Al₂O₃, SiO₂, and MgO derived from raw materials, regardless of their existing forms, within a range that does not impair the effects of the present invention.

[0013] As the calcium aluminate, any of crystalline, amorphous, or a mixture thereof can be used. From the viewpoint that more excellent quick-setting property is easily obtained, the calcium aluminate preferably has a vitrification rate, which is the degree of amorphization, of 60 mass% or more, more preferably 80 mass% or more, and even more preferably 95 mass% or more. The fineness of the calcium aluminate powder is not particularly limited, but since appropriate reaction activity is easily obtained when used as a quick-setting admixture for concrete, the fineness is preferably equal to or higher than that of the cement in the hydraulic composition to be admixed, and examples thereof include a Blaine specific surface area of 3000 to 6500 cm 2 / g.

[0014] The content of calcium aluminate is preferably 55 to 80 mass%, more preferably 58 to 77 mass%, further preferably 60 to 75 mass%, and particularly preferably 62 to 72 mass%, based on the total mass of the quick-setting admixture. When the content of calcium aluminate is within the above range, good quick-setting property is easily obtained, and clogging during spraying operation is less likely to occur.

[0015] Calcium aluminate can be obtained, for example, by heating a raw material mixture prepared by blending a raw material serving as a CaO source, a raw material serving as an Al₂O₃ source, a raw material serving as a SiO₂ source, and a raw material serving as a MgO source so as to obtain the target molar ratios of CaO and Al₂O₃, and the target molar ratios of SiO₂ and MgO as chemical components, until the mixture is melted. In addition, various differences occur in the structural state of the calcium aluminate after cooling due to the difference in the cooling process after heating during production, so that the vitrification rate, which is the degree of amorphization, can be adjusted according to the cooling conditions such as the cooling rate. The chemical components and vitrification rate of calcium aluminate can be measured by a calibration curve method, a Rietveld method or the like using an X-ray diffractometer.

[0016] The quick-setting admixture of the present embodiment contains at least one metal sulfate. Examples of the metal include alkali metals, alkaline earth metals, transition metals, post-transition metals and the like. Preferred metal sulfates include alkali metal sulfates, alkaline earth metal sulfates, and aluminum sulfate. The quick-setting admixture preferably contains at least two types of metal sulfates.

[0017] The alkali metal sulfate is not particularly limited, and any of them can be used, and it is preferably an anhydride because of excellent reactivity. Examples of the alkali metal include lithium, sodium, potassium and the like, and among them, sodium is preferred. The alkali metal sulfates may be used alone or in combination of two or more.

[0018] The alkali metal sulfate content 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, on an anhydrous basis, per 100 parts by mass of calcium aluminate. When the alkali metal sulfate content is within the above range, the material tends to exhibit excellent rapid setting properties and strength development.

[0019] The type of alkaline earth metal sulfate is not particularly limited and any can be used, but anhydrous sulfates are preferred due to their excellent reactivity. Examples of alkaline earth metals include magnesium and calcium, with calcium being the most preferred. Alkaline earth metal sulfates may be used individually or in combination of two or more types.

[0020] The content of alkaline earth metal sulfates is preferably 10 to 55 parts by mass, more preferably 15 to 50 parts by mass, even more preferably 18 to 48 parts by mass, and particularly preferably 20 to 46 parts by mass, on an anhydrous basis, per 100 parts by mass of calcium aluminate. When the content of alkaline earth metal sulfates is within the above range, the material tends to exhibit excellent strength development.

[0021] Aluminum sulfate may be in any form, including 16-hydrate and anhydrous forms, with 16-hydrate being preferred. The aluminum sulfate content is preferably 20 parts by mass or less on an anhydrous basis per 100 parts by mass of calcium aluminate, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. If aluminum sulfate is included, its content may be 0.5 parts by mass or more per 100 parts by mass of calcium aluminate. If the aluminum sulfate content is within the above range, it is easier to ensure strength development even when rapid setting is enhanced in a low-temperature environment. Aluminum sulfate may not be substantially included, meaning that the aluminum sulfate content is 0.5 parts by mass or less on an anhydrous basis per 100 parts by mass of calcium aluminate, and preferably 0.1 parts by mass or less.

[0022] Alkali metal carbonates may be used individually or in combination of two or more. The particle size of the alkali metal carbonates is not particularly limited; for example, a Blaine specific surface area of ​​approximately 3000 to 6500 cm² is acceptable. 2 Powders of / g can be used. The alkali metal carbonate content is preferably 10 parts by mass or less on an anhydrous basis, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of calcium aluminate. If alkali metal carbonate is included, its content may be 0.5 parts by mass or more per 100 parts by mass of calcium aluminate. If the alkali metal carbonate content is within the above range, the initial strength development will be further improved. Alkali metal carbonate may not be substantially included, and substantially not included means that the alkali metal carbonate content is 0.5 parts by mass or less on an anhydrous basis per 100 parts by mass of calcium aluminate, and preferably 0.1 parts by mass or less.

[0023] The rapid-setting admixture of this embodiment may contain various admixtures (materials) to the extent that the effects of the present invention are not impaired. Examples of admixtures (materials) include various pozzolanic powders such as fly ash, silica fume, and slag powder, as well as thickeners and surfactants.

[0024] The rapid-setting admixture according to this embodiment is manufactured by mixing the above-mentioned components. The mixing method is not particularly limited, and a general-purpose mixer such as a tilt mixer, pan mixer, twin-screw mixer, grout mixer, Hobart mixer, or omni mixer can be used.

[0025] The rapid-setting admixture of this embodiment can be prepared as sprayed concrete by mixing it with cement, aggregate, and water. The content of the rapid-setting admixture is preferably 3 to 20 parts by mass, more preferably 5 to 18 parts by mass, and even more preferably 6 to 16 parts by mass per 100 parts by mass of cement. If the content of the rapid-setting admixture is within the above range, good rapid-setting properties are easily obtained, and clogging during spraying work is less likely to occur.

[0026] Portland cement is preferred, and any type of Portland cement may be used, such as ordinary, rapid-hardening, very rapid-hardening, moderate-heat, low-heat, and sulfate-resistant Portland cements. As cement, blended cements such as blast furnace cement or fly ash cement containing Portland cement can also be used. One type of cement may be used alone, or two or more types may be used in combination. The particle size when using Portland cement is not particularly limited, for example, 2500 cm² as per JIS standard (JIS R 5210:2019). 2 Examples include those exceeding / g.

[0027] Examples of aggregates include fine aggregate and coarse aggregate. Fine aggregate is not particularly limited as long as it can be used in mortar and concrete. Coarse aggregate is not particularly limited as long as it can be used in concrete. Both fine and coarse aggregates are suitable because they easily ensure the required aggregate strength and have a small difference in specific gravity from other components, making material segregation less likely. Therefore, a surface-dry density of 2.3-2.9 g / cm³ is desirable. 3 It is preferable to use aggregates of the following types. Specific examples of such aggregates include fine aggregates such as natural aggregates like silica sand and limestone sand, and crushed sand such as andesite, sandstone, and basalt, and coarse aggregates such as crushed stone and gravel like silica, limestone, andesite, sandstone, and basalt. Aggregates may be used individually or in combination of two or more types.

[0028] The aggregate content in sprayed concrete is not particularly limited, but from the viewpoint of excellent pumpability of concrete during construction, the total 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 content. When fine aggregate and coarse aggregate are used in combination, the ratio of fine aggregate to the total aggregate volume ([volume of fine aggregate / volume of total aggregate] × 100) is preferably 45 to 70 by volume, more preferably 50 to 68 by volume, and even more preferably 55 to 65 by volume. If the fine aggregate ratio of the aggregate is within the above range, the pumpability during construction will be further improved, and the initial and long-term strength development will also be further improved.

[0029] The sprayed concrete of this embodiment may also contain components other than those mentioned above, as long as they do not hinder the effects of the present invention. Such components can be selected from those commonly used in sprayed concrete, but examples of components that can be included include water-reducing agents, thickeners, short fibers, pozzolanic reactive substances, and so on.

[0030] The amount of water in the sprayed concrete of this embodiment can be appropriately adjusted 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. When the water content is within the above range, the strength development tends to be excellent.

[0031] Shotcrete may be manufactured, for example, by a wet spraying method in which each material except for the rapid-setting admixture is mixed with water to form a base concrete, and the base concrete and rapid-setting admixture are mixed at the tip of a spraying nozzle and sprayed. Alternatively, it may be manufactured by a dry spraying method in which each material including the rapid-setting admixture is mixed to form a base composition, and the base composition and water are mixed at the tip of a spraying nozzle and sprayed. From the viewpoint of reducing dust and rebound, it is preferable to manufacture shotcrete by a wet spraying method.

[0032] The shotcrete of the present embodiment, in an environment of 10°C, complies with the "Standard Specifications for Concrete of the Japan Society of Civil Engineers, 'Quality Standards for Accelerators for Shotcrete' Annex 'Method for Measuring Flash Setting Time by Penetration Resistance of Mortar Added with Accelerator'", with a cross-sectional area of 0.125 cm 2 The penetration resistance value measured using a Proctor needle is preferably 0.25 N / mm at 25 seconds after the addition of the quick-setting admixture 2 or more, more preferably 0.3 N / mm 2 or more, and even more preferably 0.5 N / mm 2 or more. When the penetration resistance value is within the above range, the quick-setting property is favorable even in a low-temperature environment, which facilitates early work after adhesion. In the penetration resistance test, for shotcrete containing coarse aggregate, the total content corresponding to the sum of coarse aggregate and fine aggregate is all converted to the content of fine aggregate, without containing coarse aggregate, and the measurement is performed using a base mortar adjusted to a mortar mix without changing the other components and their contents.

[0033] When hardened, the shotcrete of the present embodiment has a compressive strength at an age of 4 hours measured in a 10°C environment in accordance with JSCE Standard JSCE-G561:2010 "Test Method for Early Strength of Shotcrete by Pullout Method" of 0.5 N / mm 2 or more, preferably 0.6 N / mm 2 or more, more preferably 0.65 N / mm 2 or more. If the compressive strength at an age of 4 hours measured in a 10°C environment is within the above range, sufficient strength can be obtained at an early stage even in a low-temperature environment, so that the construction site is further reinforced.

[0034] The quick-setting admixture and shotcrete of the present embodiment ensure good adhesion and quick-setting properties even in a low-temperature environment, and are also excellent in strength development. Therefore, the quick-setting admixture and shotcrete of the present embodiment can be safely constructed because they firmly adhere to tunnel walls and slopes even in low-temperature environments such as winter, and enable efficient construction with little material loss. [Examples]

[0035] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, the examples were conducted under conditions of 10±1℃. In the examples, all content and other figures are based on solid content and anhydrous weight.

[0036] [Preparation of calcium aluminate] Using commercially available industrial chemicals CaCO3, Al2O3, SiO2, and MgO, the materials were weighed and blended to obtain the calcium aluminate with the following molar ratios of CaO and Al2O3 (CaO / Al2O3, C / A ratio) and SiO2 and MgO (SiO2 / MgO). A Henschel mixer was used to prepare the raw material mixture. This raw material mixture was heated in an electric furnace at approximately 1600°C ± 50°C for 60 minutes. Except for some samples, the heated samples were immediately removed from the furnace after the heating time. The surface of the removed heated samples was rapidly cooled by blowing nitrogen gas at a maximum flow rate of approximately 30 mL / second to obtain cooled samples. The vitrification rate of the cooled samples was adjusted by blowing nitrogen gas at a flow rate lower than the maximum value. Each cooled sample was crushed in an all-steel ball mill and subjected to a classifier to obtain a Blaine specific surface area of ​​approximately 5400 cm². 2 The grains were sized to / g. The vitrification rate of calcium aluminate was determined by using a powder X-ray diffractometer to quantify the mass of each mineral contained in calcium aluminate clinker with mass M1 using the internal standard method, etc., and calculating the total mass of the quantified mineral phases; M2. The remainder was considered to be the pure glass phase, and the vitrification rate was calculated using the following formula. Vitrification rate (mass%)={1-(M2 / M1)}×100

[0037] [material] Calcium aluminate (abbreviations CA1-6): Chemical composition is shown in Table 1, Blaine specific surface area 5400 cm². 2 / g, vitrification rate of 99% or more Calcium sulfate reagent (abbreviation CS): Anhydrous gypsum Aluminum sulfate reagent (abbreviation AS): Aluminum sulfate hecahydrate Sodium sulfate reagent (abbreviation NS): Anhydrous Glauber's salt Sodium carbonate reagent (abbreviation NC) Cement: Ordinary Portland cement, Blaine specific surface area 3200 cm² 2 / g, density 3.15g / cm 3 Fine aggregate: Limestone fine aggregate (surface dry density: 2.65g / cm 3 , center grain size; 0.6mm) Coarse aggregate: Crushed stone (surface dry density: 2.74 g / cm³) 3 , center particle size 5~15mm)

[0038] [Table 1]

[0039] [Preparation of rapid-setting admixture] The rapid-setting admixture was prepared by mixing each material in the proportions shown in Table 2 and mixing them in a Henschel mixer for 1 minute.

[0040] [Table 2]

[0041] [Preparation of base concrete] A base concrete was prepared by mixing 100 parts by mass of cement with 292 parts by mass of fine aggregate and 194 parts by mass of coarse aggregate, then adding 60 parts by mass of water and mixing in a concrete mixer for 2 minutes.

[0042] [Preparation of sprayed concrete] Immediately after mixing the base concrete, it was placed in a supply tank and pumped from there to the spraying device via a resin hose approximately 10m long and 6cm in inner diameter. The spraying device is a commercially available product with a basic configuration consisting of a 2-inch inner diameter supply pipe through which the base concrete is pumped, a cylindrical side pipe connected to the side of the supply pipe at an angle of approximately 30 degrees for supplying additives (rapid-setting admixtures) to the base concrete, and a 2-inch inner diameter (tip hole diameter) spray nozzle for spraying the concrete. The side pipe for supplying additives was formed by connecting a steel T-shaped pipe (three-way pipe) between the main supply pipe and the spray nozzle. The main supply pipe and the spray nozzle were connected to two pipe openings located on a straight line of the T-shaped pipe, and the supply pipe for the separately delivered rapid-setting admixture was connected to the remaining pipe opening. Mixing of the base concrete and the rapid-setting admixture occurred between the point where the rapid-setting admixture was added to the base concrete in the T-shaped pipe (the point where the base concrete and rapid-setting admixture meet) and the end of the spray nozzle hole, with this distance (hereinafter referred to as the mixing distance) being 2m. A predetermined amount of the rapid-setting admixture was air-pressurized by compressed air and added to the base concrete being pumped in the spraying device. The added concrete was mixed as it traveled the predetermined mixing distance, producing sprayed concrete. The amount of rapid-setting admixture added is shown in Table 2.

[0043] Each test evaluation was conducted according to the following method. The test results are shown in Table 3. [Assessment of rapid onset] In the base concrete mix design, the amount equivalent to the total content of coarse and fine aggregates in each mix was entirely replaced with fine aggregate, eliminating the coarse aggregate. A base mortar was then prepared using the same procedure as for the base concrete, without changing the other components or their contents. The resulting base mortar was then mixed with rapid-setting admixtures in the proportions shown in Table 1 and mixed in a high-speed mixer for 5 seconds to produce a mortar mixture. The rapid setting properties of the mortar mixture were evaluated by measuring the Proctor penetration resistance values ​​25 seconds, 45 seconds, 60 seconds, and 180 seconds after the addition of the rapid setting admixture. The method for measuring the Proctor penetration resistance was in accordance with the Japan Society of Civil Engineers' Standard Specifications for Concrete, "Quality Standards for Rapid Setting Agents for Sprayed Concrete," Appendix "Method for Measuring Instant Setting Time by Penetration Resistance of Mortar with Rapid Setting Agent Added," using a cross-sectional area of ​​0.125 cm². 2 A Proctor needle was used. The measurement results of the penetration resistance are shown in Table 3. Also, in the table, ">16 (N / mm 2 The description states that the Proctor needle could be driven in, but the measurement limit of the equipment used this time was (maximum 16 N / mm²). 2 This exceeds the specified limit. If the measurement limit of the equipment used is exceeded, further measurements are not performed and it is indicated with "-".

[0044] [Evaluation of Strength Development of Sprayed Concrete] The mixing distance was set to 2m, and the prepared sprayed concrete was immediately sprayed into a molding formwork with inner dimensions of 30 × 40 × 20 cm to fill the formwork. This was placed in a constant temperature chamber at 10°C (±1°C) for a predetermined time, and cylindrical specimens with a diameter of 5 cm and a height of 10 cm were taken from the hardened concrete in the formwork using a core drill to obtain specimens that were 28 days old. The uniaxial compressive strength of these 28-day-old specimens was measured using a hydraulic compressive strength tester. In addition, sprayed concrete prepared in the same manner using the formwork and embeddings specified in the Japan Society of Civil Engineers standard JSCE-G561:2013 was subjected to a pull-out test in accordance with JSCE-G561:2013. The compressive strength of the sprayed concrete at 4 hours and 24 hours was measured by this test. The results of the strength measurements for each specimen are shown in Table 3.

[0045] [Evaluation of the adhesion properties of sprayed concrete] Using the spraying apparatus described above, the obtained sprayed concrete was immediately used for spraying work. The spray was directed 10 meters towards a 3-meter square concrete slab surface with a thickness of 9 mm, which was vertically positioned approximately 100 cm away from the nozzle end of the spraying apparatus. 3The sprayed concrete was applied at a flow rate of [number] hours. The adhesion of the sprayed concrete was evaluated by visual observation as follows: Concrete that remained attached to the flat surface without sagging or spalling was judged to have "good" adhesion, while all other conditions, or cases where spraying was practically impossible, were judged to have "poor" adhesion. The results are shown in Table 3.

[0046] [Table 3]

[0047] The sprayed concrete using the rapid-setting admixture in the example exhibited good adhesion even at low temperatures, as well as excellent rapid-setting properties and strength development. On the other hand, the sprayed concrete using the rapid-setting admixture in the comparative example exhibited poor adhesion and somewhat lower rapid-setting properties.

Claims

1. It comprises calcium aluminate and at least one type of metal sulfate, The aforementioned calcium aluminate contains CaO and Al as chemical components. ２ O ３ The molar ratio of the content (CaO / Al ２ O ３ ) is 1.6 to 2.7, SiO ２ and the molar ratio of MgO content (SiO ２ A rapid-setting admixture with a MgO content of 1.1 to 6.

2. The rapid-setting admixture according to claim 1, wherein the calcium aluminate content is 55 to 80% by mass based on the total mass of the rapid-setting admixture.

3. The rapid-setting admixture according to claim 1 or 2, further comprising an alkali metal carbonate.

4. The mixture comprises cement, aggregate, water, and the rapid-setting admixture described in claim 1 or 2. A sprayed concrete in which the content of the rapid-setting admixture is 3 to 20 parts by mass per 100 parts by mass of cement.

5. During hardening, the compressive strength at 4 hours of age is measured at 10°C in accordance with the Japan Society of Civil Engineers standard JSCE-G561:2010 "Initial strength test method for sprayed concrete by tensile method" and is 0.5 N / mm². ２ The sprayed concrete described in claim 4 is as described above.

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