Quick-setting admixture and spray concrete

Abstract

To provide a quick-setting admixture which ensures good quick-setting performance and mixability of materials and is excellent in strength developability, and to provide spray concrete.SOLUTION: A quick-setting admixture comprising calcium aluminate having a molar ratio of the contents of CaO and Al2O3 as chemical components (CaO / Al2O3) of from 1.8 to 2.7, sulfates of alkali metals, sulfates of alkaline earth metals and aluminum sulfate, wherein the content of the calcium aluminate is from 55 to 79 mass% based on the total mass of the quick-setting admixture, in the particle size of the sulfate of the alkaline earth metal, the mass ratio of particles of ≤1.5 μm is 33-52 mass% and the mass ratio of particles of ≥10.5 μm and ≤100 μm is 10-29 mass% based on the total amount of the sulfate of the alkali metal.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a quick-setting admixture and a shotcrete. [Background technology]

[0002] Shotcrete is used in tunnels, mine shafts, underground spaces, and other areas to prevent excavation surface collapse and reinforce the ground during or after excavation. Shotcrete's rapid setting ensures adhesion to the target surface. To achieve rapid setting, an accelerator is added to the concrete. For example, powder accelerators containing calcium aluminate or sodium aluminate as active ingredients can impart strong rapid setting properties and tend to produce concrete with higher strength than liquid accelerators. In the wet spraying method, a common method for spraying concrete, for example, base concrete is prepared by weighing and mixing at least cement, water, and aggregate. This base concrete is then pumped into a spraying device via an agitator truck or other device during construction. Separately, powdered or liquid accelerator is added to the base concrete during pumping, and the mixture is mixed in the spraying nozzle of the device to form the shotcrete, which is then sprayed through the nozzle end. Another construction method, dry shotcrete, involves weighing and mixing at least cement, aggregate, and powdered accelerator (other than water and liquids) to prepare dry-mix concrete, which is then pneumatically pumped from a storage tank to a spraying device during construction. Water is added to the pumped dry-mix concrete within the spraying device, and mixing continues until the concrete is pumped to the spraying nozzle, forming the shotcrete, which is then sprayed. In both methods, mixing occurs as the accelerated-setting components within the spraying device travel from the point where they come into contact with water (the water contact point) to the discharge hole at the end of the spraying nozzle, forming the shotcrete. The distance required for mixing is typically several tens of centimeters to several meters, and the travel time is the mixing time. Generally, the longer this distance, the more mixing progresses, the better the mixability, and the easier it is to obtain a more uniform shotcrete in terms of both structure and properties.

[0003] The powdered quick-setting admixtures used to obtain such sprayed concrete generally contain the aforementioned quick-setting components plus additives to adjust various properties. For example, typical conventional powdered quick-setting admixtures (see, for example, Patent Documents 1 and 2) are highly alkalized, combining calcium aluminate, which contains a high CaO content as a chemical component, with gypsum to accelerate hardening, and adding sodium aluminate to enhance early strength development and sodium carbonate to accelerate setting. These admixtures have the primary purpose of providing high quick-setting properties and early strength development. For this reason, setting occurs in an extremely short time after the quick-setting admixture comes into contact with water. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-121763 [Patent Document 2] Patent No. 5129955 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because conventional powder quick-setting admixtures set in a very short time, increasing the mixing distance can cause the concrete to harden during that time, potentially resulting in serious spraying problems such as clogging or blockage of the spray nozzle. On the other hand, shortening the mixing distance can result in insufficient mixing, and an uneven mix can easily cause minute irregularities in the reaction of the constituent components. As a result, it is difficult to obtain a hardened concrete body with uniform properties and stable quality, and hardening properties such as strength are also inferior. Therefore, powder quick-setting admixtures are required not only to have high quick-setting performance, but also to have high mixability so as to prevent clogging of the spray nozzle.

[0006] Therefore, an object of the present invention is to provide a quick-setting admixture and a shotcrete that ensure good quick-setting performance and material mixability, and also have excellent strength development. [Means for solving the problem]

[0007] As a result of intensive research into the above-mentioned problems, the inventors have discovered that by using an alkaline earth metal sulfate having a specific particle size (mass proportion of particles having particle sizes within a specific range), it is possible to obtain a quick-setting admixture and a sprayed concrete that have excellent material mixability and can achieve both high quick-setting performance and high strength development.

[0008] That is, the present invention includes the following [1] to [5]. [1] A quick-setting admixture containing calcium aluminate having a molar ratio (CaO / Al2O3) of CaO to Al2O3 of 1.8 to 2.7 as chemical components, an alkali metal sulfate, an alkaline earth metal sulfate, and aluminum sulfate, The content of the calcium aluminate is 55 to 79 mass% based on the total mass of the quick-setting admixture, A quick-setting admixture, wherein the particle size of the alkaline earth metal sulfate is such that the mass ratio of particles having a size of 1.5 μm or less is 33 to 52 mass% and the mass ratio of particles having a size of 10.5 μm or more and 100 μm or less is 10 to 29 mass% relative to the total amount of the alkaline earth metal sulfate. [2] The quick-setting admixture according to [1], wherein the content of the alkaline earth metal sulfate is greater than the total content of the alkali metal sulfate and the aluminum sulfate. [3] The quick-setting admixture according to [1] or [2], further containing an alkali metal carbonate. [4] It contains cement, aggregate, water, and any of the quick-setting admixtures of claims [1] to [3], A sprayed concrete in which the content of the quick-setting admixture is 5 to 15 parts by mass per 100 parts by mass of the cement. [5] At 20°C, the test was conducted in accordance with the Japan Society of Civil Engineers' Standard Specifications for Concrete, "Quality Standards for Accelerator for Shotcrete," Appendix "Method for Measuring Instantaneous Setting Time by Penetration Resistance of Mortar with Accelerator Added," and was carried out on a 0.125cm cross-sectional area specimen. 2The penetration resistance measured using a Proctor needle was 0.15 N / mm 25 seconds after adding the quick-setting admixture. 2 The sprayed concrete described in [4] above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a quick-setting admixture and a shotcrete that ensure good quick-setting performance and material mixability, and also exhibit excellent strength development. DETAILED DESCRIPTION OF THE INVENTION

[0010] A preferred embodiment of the present invention will be described in detail below. In this specification, all contents and the like are expressed in terms of solid content and anhydrous content.

[0011] The quick-setting admixture of this embodiment contains, as chemical components, calcium aluminate having a molar ratio of CaO to Al2O3 (CaO / Al2O3) of 1.8 to 2.7, an alkali metal sulfate, an alkaline earth metal sulfate, and aluminum sulfate.

[0012] Calcium aluminate is an inorganic hydration active substance whose main chemical components are CaO and Al2O3, and the molar ratio of CaO to Al2O3 (CaO / Al2O3) is 1.8 to 2.7. If the molar ratio of CaO to Al2O3 is outside the above range, it becomes difficult to achieve both rapid setting and workability. From the viewpoint of easily achieving better rapid setting properties, the molar ratio of CaO to Al2O3 is preferably 1.9 to 2.65, and more preferably 2.0 to 2.6. Calcium aluminate may also contain other components, such as impurities other than CaO and Al2O3 derived from the raw materials, regardless of their form, as long as they do not impair the effects of the present invention.

[0013] Calcium aluminate may be crystalline, amorphous, or a mixture thereof. From the viewpoint of easily obtaining superior quick-setting properties, 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 appropriate reactivity when used as a quick-setting admixture for concrete, it is preferable that the fineness is the same as or greater than that of cement in the hydraulic composition to be mixed, and for example, a Blaine specific surface area of ​​3000 to 6500 cm 2 The particle size is 1 / g.

[0014] The calcium aluminate content is 55 to 79 mass% based on the total mass of the quick-setting admixture. If the calcium aluminate content is outside this range, it becomes difficult to achieve both quick-setting properties and mixability, and strength development is also poor. From the viewpoint of easily achieving excellent quick-setting properties, mixability, and strength development, the calcium aluminate content is preferably 58 to 77 mass% based on the total mass of the quick-setting admixture, more preferably 60 to 75 mass%, and even more preferably 62 to 72 mass%.

[0015] Calcium aluminate can be obtained, for example, by blending a raw material mixture of a CaO source and an Al2O3 source so as to obtain the desired molar ratio of CaO and Al2O3 as chemical components, and heating the blend until it melts. Since differences in the cooling process after heating during production result in various differences in the structural state of calcium aluminate after cooling, the vitrification rate, which is the degree of amorphization, can be adjusted by adjusting cooling conditions such as the cooling rate.

[0016] The alkali metal sulfate is not particularly limited and any can be used, but anhydrous alkali metal sulfates are preferred because of their excellent reactivity. Examples of alkali metals include lithium, sodium, and potassium, with sodium being preferred. The alkali metal sulfates may be used alone or in combination of two or more.

[0017] The content of the alkali metal sulfate, calculated as an anhydride, 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, relative to 100 parts by mass of calcium aluminate. When the content of the alkali metal sulfate is within the above range, the quick-setting property and strength development are likely to be excellent.

[0018] The type of alkaline earth metal sulfate is not particularly limited and any can be used, but anhydrous alkaline earth metal sulfates are preferred because of their excellent reactivity. Examples of alkaline earth metal sulfates include magnesium and calcium, and calcium is particularly preferred. One type of alkaline earth metal sulfate may be used alone, or two or more types may be used in combination.

[0019] Regarding the particle size of the alkaline earth metal sulfate, the mass ratio of particles of 1.5 μm or less (hereinafter sometimes referred to as sulfate particles X) to the total amount of alkaline earth metal sulfate is 33 to 52 mass%, and the mass ratio of particles of 10.5 μm to 100 μm (hereinafter sometimes referred to as sulfate particles Y) to the total amount of alkaline earth metal sulfate is 10 to 29 mass%. If the particle size of the alkaline earth metal sulfate is outside the above range, it may be difficult to achieve excellent pumpability and both initial and long-term strength development, so care must be taken. Furthermore, it is preferable that the maximum particle size of the alkaline earth metal sulfate particles is 100 μm or less. With regard to the particle size of the alkaline earth metal sulfate, the mass ratio of the sulfate particles X to the total amount of the alkaline earth metal sulfate is preferably 35 to 50 mass %, more preferably 37 to 48 mass %. With regard to the particle size of the alkaline earth metal sulfate, the mass ratio of the sulfate particles Y to the total amount of the alkaline earth metal sulfate is preferably 12 to 27 mass %, more preferably 13 to 25 mass %. With regard to the particle size of the alkaline earth metal sulfate, the mass proportion of particles having a size of more than 1.5 μm and less than 10.5 μm (hereinafter sometimes referred to as sulfate particles Z) relative to the total amount of alkaline earth metal sulfate is preferably 19 to 57 mass%, more preferably 30 to 55 mass%, and even more preferably 35 to 50 mass%. Regarding the particle size of the alkaline earth metal sulfate, the total mass ratio of the sulfate particles X and the sulfate particles Y to the total amount of the alkaline earth metal sulfate is preferably 40 to 80 mass%, more preferably 50 to 70 mass%, and even more preferably 55 to 65 mass%. Furthermore, with regard to the particle size of the alkaline earth metal sulfate, the ratio x / y of the mass of sulfate particles X to the mass of sulfate particles Y is preferably 1.2 to 6, more preferably 1.4 to 5, even more preferably 1.5 to 4, and particularly preferably 1.6 to 3.5. If the particle size of the alkaline earth metal sulfate is within the above range, better pumpability can be obtained, and the initial and long-term strength development can be further improved.

[0020] The median diameter (d50) of the alkaline earth metal sulfate is preferably 1.5 to 2.9 μm, more preferably 1.55 to 2.5 μm, and even more preferably 1.6 to 2.3 μm. When the median diameter of the alkaline earth metal sulfate is within the above range, better pumpability can be obtained, and the initial and long-term strength development can be further improved.

[0021] The particle size, median diameter, maximum particle size, etc. of the alkaline earth metal sulfate can be estimated from the cumulative distribution of particle size distribution measured using a laser diffraction particle size distribution analyzer, etc. The particle size of the alkaline earth metal sulfate can be adjusted by a method of crushing the alkaline earth metal sulfate as a raw material using a mill or the like and classifying the crushed material, or by a method of mixing multiple alkaline earth metal sulfates with different median diameters or particle sizes.

[0022] The content of the alkaline earth metal sulfate is preferably 10 to 55 parts by mass, more preferably 15 to 50 parts by mass, still more preferably 18 to 48 parts by mass, and particularly preferably 20 to 46 parts by mass, based on 100 parts by mass of calcium aluminate in anhydrous equivalent. When the content of the alkaline earth metal sulfate is within the above range, excellent strength development is likely to occur.

[0023] The content of alkaline earth metal sulfate is preferably greater than the total content of alkali metal sulfate and aluminum sulfate. The mass ratio of the alkaline earth metal sulfate to the total content of alkali metal sulfate and aluminum sulfate ([mass of alkaline earth metal sulfate] / ([mass of alkali metal sulfate]+[mass of aluminum sulfate])) is preferably 1.05 to 5, more preferably 1.1 to 4.5, and even more preferably 1.2 to 4, calculated on anhydrous basis. When the mass ratio of the alkaline earth metal sulfate to the total content of alkali metal sulfate and aluminum sulfate is within the above range, the quick-setting property and strength development are further improved.

[0024] Aluminum sulfate may be in any form, including the hexadecahydrate and anhydrous form, with the hexadecahydrate being preferred. The content of aluminum sulfate, calculated as anhydrous form, is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 2 to 12 parts by mass, per 100 parts by mass of calcium aluminate. When the content of aluminum sulfate is within the above range, strength development is easily ensured even when rapid setting is enhanced in a low-temperature environment.

[0025] The quick-setting admixture of this embodiment may contain an alkali metal carbonate. The alkali metal carbonate is not particularly limited and any can be used, but an anhydrous alkali metal carbonate is preferred because of its excellent reactivity. Examples of alkali metals include lithium, sodium, and potassium, and sodium is particularly preferred.

[0026] 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. For example, the particle size may be about 3000 to 6500 cm in terms of Blaine specific surface area. 2 A powder having a maximum particle size of 1 mm or less per 100 parts by mass of calcium aluminate can be used. The content of the alkali metal carbonate is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass, calculated as an 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.

[0027] The quick-setting admixture according to this embodiment is produced by mixing the above-mentioned components. The mixing method is not particularly limited, and a general-purpose mixer such as a tilting mixer, a pan mixer, a twin-shaft mixer, a grout mixer, a Hobart mixer, or an omnimixer can be used.

[0028] The quick-setting admixture of this embodiment can be mixed with cement, aggregate, and water to prepare sprayed concrete. The content of the quick-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 quick-setting admixture is within the above range, it is easy to achieve both quick-setting properties and mixability.

[0029] 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, ultra-early strength, moderate heat, low heat, and sulfate resistant. As the cement, a mixed cement containing Portland cement, such as blast furnace cement or fly ash cement, may also be used. One type of cement may be used alone, or two or more types may be used in combination. When Portland cement is used, the particle size is not particularly limited, and for example, the 2500 cm particle size according to the JIS standard (JIS R 5210:2019) may be used. 2 / g or more.

[0030] Examples of aggregates include 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. Both fine aggregate and coarse aggregate are preferably selected from those having a surface dry density of 2.3 to 2.9 g / cm because they can easily ensure a predetermined aggregate strength and are less likely to cause material separation due to a small difference in specific gravity with other contained components. 3 It is preferable to use aggregates such as those listed above. Specific examples of such aggregates include fine aggregates such as natural aggregates like silica sand and limestone sand, and crushed sands like andesite, sandstone, and basalt, and coarse aggregates such as crushed stone and gravel like silica stone, limestone, andesite, sandstone, and basalt. One type of aggregate may be used alone, or two or more types may be used in combination.

[0031] The content of aggregate in the sprayed concrete is not particularly limited, but from the viewpoint of improving the pumpability of the 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.When fine aggregate and coarse aggregate are used in combination, the fine aggregate ratio (mass ratio of fine aggregate to all aggregate) is preferably 54 to 69% by mass, more preferably 55 to 65% by mass, and even more preferably 56 to 63% by mass.

[0032] The sprayed concrete of this embodiment may contain components other than those described above, provided that the effects of the present invention are not impaired. Such components may be selected from those commonly used in sprayed concrete, and examples of components that may be contained include water-reducing agents, thickeners, short fibers, and pozzolanic reactive substances.

[0033] The amount of water in the sprayed concrete of this embodiment can be adjusted appropriately 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 strength development tends to be excellent.

[0034] Shotcrete may be produced, for example, by a wet spraying method in which the materials except for the quick-setting admixture are mixed with water to form a base concrete, and the base concrete and the quick-setting admixture are mixed at the tip of a spraying nozzle and sprayed, or by a dry spraying method in which the materials including the quick-setting admixture are mixed to form a base composition, and the base composition and water are mixed at the tip of a spraying nozzle and sprayed. Shotcrete is preferably produced by a wet spraying method, as this method tends to reduce dust and rebound.

[0035] The sprayed concrete of this embodiment is prepared in a 20°C environment in accordance with the "Measurement method for instantaneous setting time by penetration resistance of mortar containing an accelerator added" in the "Quality standard of accelerator for sprayed concrete" appendix of the Japan Society of Civil Engineers' Standard Specifications for Concrete, and has a cross-sectional area of ​​0.125 cm. 2 The penetration resistance measured using a Proctor needle was 0.15 N / mm 25 seconds after adding the quick-setting admixture. 2 It is preferable that the resistance is 0.3N / mm or more. 2 More preferably, it is 0.5N / mm 2 It is even more preferable that the penetration resistance value is equal to or greater than this. If the penetration resistance value is within the above range, the quick setting property is good, making it easy to work with soon after adhesion. In the case of shotcrete containing coarse aggregate, the penetration resistance value test is measured using a base mortar whose mortar formulation has been changed so that the amount equivalent to the total content of coarse aggregate and fine aggregate is entirely the content of fine aggregate, and the other components and their contents remain unchanged.

[0036] The shotcrete of this embodiment has a compressive strength of 0.5 N / mm2 at 4 hours of age when hardened, measured in a 20°C environment in accordance with the Japan Society of Civil Engineers standard JSCE-G561:2010 "Test method for early strength of shotcrete by pull-out method." 2 It is preferable that the resistance is 0.6N / mm or more. 2 More preferably, it is 0.7N / mm 2If the compressive strength measured at 4 hours in an environment of 20°C is within the above range, sufficient strength can be obtained early on, and the construction area can be further reinforced.

[0037] The quick-setting admixture and sprayed concrete of this embodiment ensure good quick-setting performance and material mixability, and also have excellent strength development. Therefore, when sprayed onto tunnel walls or slopes, there is little unevenness in quality due to insufficient mixing, and sufficient strength can be achieved. [Example]

[0038] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The examples were carried out in an environment of 20±1°C unless otherwise specified. In the examples, all contents and the like are expressed in terms of solid content and anhydrous content.

[0039] [Preparation of calcium aluminate] Commercially available industrial chemicals, CaCO3 and Al2O3, were weighed and mixed to obtain calcium aluminates with the molar ratios of CaO and Al2O3 (CaO / Al2O3, C / A ratio) shown below, and raw material mixtures were prepared using a Henschel mixer. These raw material mixtures were heated in an electric furnace at approximately 1600°C ± 50°C for 60 minutes. With the exception of some samples, the heated materials were immediately removed from the furnace after the heating time had elapsed. The surfaces of the removed heated materials were rapidly cooled by spraying nitrogen gas at a maximum flow rate of approximately 30 mL / s, yielding cooled materials. The vitrification rate of the cooled materials was adjusted by spraying nitrogen gas at a flow rate slower than the maximum. Each cooled material was pulverized in an all-steel ball mill and passed through a classifier to obtain a Blaine specific surface area of ​​approximately 5400 cm. 2 The vitrification rate of calcium aluminate was determined by quantifying the mass of each mineral contained in calcium aluminate clinker with a mass of M1 using a powder X-ray diffractometer by an internal standard method or the like, calculating the total mass of the mineral phases that could be quantified, M2, and assuming the remainder to be a pure glass phase, using the following formula: Vitrification rate (mass%)={1-(M2 / M1)}×100

[0040] [material] Calcium aluminate (abbreviated as CA): CaO / Al2O3 ratio is 2.3, and the Blaine specific surface area is 5400 cm 2 / g, vitrification rate 99% or more Calcium sulfate reagent (abbreviated as CS): anhydrous gypsum, particle size adjusted (see Table 1), maximum particle size 100 μm or less Aluminum sulfate reagent (abbreviation AS): Aluminum sulfate hexahydrate Sodium sulfate reagent (abbreviated as NS): anhydrous sodium sulfate Sodium carbonate reagent (abbreviated as NC) Cement: Ordinary Portland cement, Blaine specific surface area 3200 cm 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 / cm 3 , particle size 5~15mm)

[0041] [Calcium sulfate adjustment] Commercially available anhydrous gypsum was mixed, crushed, classified, and other processes to adjust the particle size to that shown in Table 1. The particle size of the alkaline earth metal sulfate was measured using a laser diffraction particle size distribution analyzer HELOS (manufactured by Japan Laser Co., Ltd.), and the median diameter (d50), the mass proportion of particles of 1.5 μm or less, and the mass proportion of particles of 10.5 μm to 100 μm were determined from the cumulative distribution. Details of calcium sulfate are shown in Table 1.

[0042] [Table 1]

[0043] [Preparation of quick-setting admixture] The materials were mixed in the proportions shown in Table 2 and mixed for 1 minute in a Henschel mixer.

[0044] [Table 2]

[0045] [Preparing the base concrete] For Examples 1 to 12 and Comparative Examples 1 to 8, 292 parts by mass of fine aggregate and 194 parts by mass of coarse aggregate were mixed with 100 parts by mass of cement, and then 60 parts by mass of water was added and mixed for 2 minutes in a concrete mixer to prepare base concrete.

[0046] [Preparation of sprayed concrete] Immediately after mixing, the base concrete was placed in a supply tank, from which it was pumped to the spraying device via a resin hose approximately 10 m long and 6 cm in inner diameter. The spraying device is a commercially available product, consisting essentially of a 2-inch inner diameter pressure pipe through which the base concrete was pumped, a cylindrical side pipe connected to the side of the pressure pipe at an angle of approximately 30 degrees for supplying and adding additives (quick-setting admixtures) to the base concrete, and a 2-inch inner diameter (tip hole diameter) spraying nozzle for spraying the shotcrete. The side pipe for supplying additives was formed by inserting a T-shaped steel pipe (three-way pipe) between the main pressure pipe and the spraying nozzle. The main pressure pipe and the spraying nozzle were connected to two pipe openings located on a straight line of the T-shaped pipe, respectively, and the remaining pipe opening was connected to a supply pipe for the quick-setting admixture, which was sent separately. The base concrete and quick-setting admixture were mixed over the distance from the point where the quick-setting admixture was added to the base concrete inside the T-shaped pipe (the point where the base concrete and quick-setting admixture meet) to the end of the injection nozzle hole, and this distance (hereinafter referred to as the mixing distance) was 2 m. A specified amount of quick-setting admixture was pumped using compressed air and added to the base concrete being pumped inside the spraying device, and the added concrete was mixed as it traveled the specified mixing distance to produce sprayed concrete. The amounts of quick-setting admixture added are shown in Table 2.

[0047] Each test evaluation was carried out according to the following methods. The test results are shown in Table 3. [Rapid setting evaluation] In the base concrete mix, the amounts equivalent to the total content of coarse aggregate and fine aggregate contained in each component were all changed to fine aggregate, and a base mortar was prepared using the same procedure as the base concrete, with the mortar mix changed to include no coarse aggregate and the other components and their contents unchanged.The quick-setting admixtures shown in Table 1 were added to the obtained base mortar, and the mixture was mixed for 5 seconds in a high-speed mixer to prepare a mortar mixture. The Proctor penetration resistance of the mortar mixture was measured 25, 45, 60, and 180 seconds after the addition of the quick-setting admixture to evaluate its quick-setting properties. The measurement method for Proctor penetration resistance conforms to the Japan Society of Civil Engineers' Standard Specifications for Concrete, "Quality Standards for Accelerator for Shotcrete," Annex "Method for Measuring Instantaneous Setting Time by Penetration Resistance of Mortar with Added Accelerator," and is for a cross-sectional area of ​​0.125 cm. 2 The results of the measurement of the penetration resistance are shown in Table 3. 2 )" indicates that the Proctor needle could be driven in, but it was within the measurement limit of the equipment used this time (maximum 16N / mm 2 ) is exceeded. If the measurement limit of the equipment used is exceeded, no further measurements are taken and the result is indicated as "-".

[0048] [Evaluation of strength development of sprayed concrete] The mixed concrete was immediately sprayed into a 30 x 40 x 20 cm mold with a mixing distance of 2 m, filling the mold. The concrete was then placed in a constant-temperature chamber at 20°C (±1°C) for a predetermined time. After the required time, cylindrical specimens measuring 5 cm in diameter and 10 cm in height were extracted from the hardened concrete in the mold using a core drill. These specimens were then aged 28 days. The unconfined compressive strength of these 28-day specimens was measured using a hydraulic compressive strength testing machine. In addition, similarly prepared shotcrete was subjected to a pullout test in accordance with JSCE-G561:2013 using the pullout test formwork and embedding tools specified in the Japan Society of Civil Engineers (JSCE) standard. The compressive strength of the 4-hour and 24-hour-old shotcrete was measured. The strength measurement results for each specimen are shown in Table 3.

[0049] [Evaluation of adhesion of sprayed concrete] The obtained sprayed concrete was immediately sprayed using the above-mentioned spraying device. The sprayed concrete was sprayed onto a 9 mm thick, 3 m square concrete flat surface, which was installed vertically at a point about 100 cm away from the nozzle end of the spraying device. 3 The sprayed concrete was sprayed at a flow rate of 1 / hour. The adhesion of the sprayed concrete was evaluated by visual observation as follows: Concrete sprayed onto the flat surface that remained adhered without dripping or peeling was judged to have "good" adhesion, while any other condition, or any condition where spraying was not actually possible, was judged to have "poor" adhesion. The results are shown in Table 3.

[0050] [Evaluation of the mixability of shotcrete] Under the same conditions as those used for the adhesion evaluation, spraying was carried out for 5 minutes over a mixing distance of 2m, after which the pressure supply of the base concrete was stopped for 30 minutes to interrupt spraying. After that, the pressure supply of the base concrete was resumed and spraying was carried out again. At this time, depending on the mixing distance, if there was a pressure supply problem such as a narrowing or blockage in the pressure route of the T-shaped pipe or spraying device, or a spraying problem such as a decrease in the sprayed volume of the sprayed concrete, it was judged as having clogging or blockage. In addition, if these phenomena were not observed, the concrete was able to be pressured smoothly and there was no fluctuation in the sprayed volume, it was judged as having no clogging or blockage. The results are shown in Table 3. 10m 3 The mixing time was approximately 1.4 seconds when the mixing distance was 2 m and the flow rate was 1 / hour.

[0051] [Table 3]

[0052] The shotcrete using the quick-setting admixture of the Example could be pumped without clogging, had good adhesion, and was excellent in quick-setting and strength development. On the other hand, the shotcrete using the quick-setting admixture of the Comparative Example exhibited clogging and poor adhesion, and was not excellent in quick-setting and strength development.

Claims

1. Chemical components: CaO and Al ２ O ３ The molar ratio of CaO / Al ２ O ３ A quick-setting admixture containing calcium aluminate, an alkali metal sulfate, an alkaline earth metal sulfate, and aluminum sulfate, wherein the saturation temperature is 1.8 to 2.7, The content of the calcium aluminate is 55 to 79% by mass based on the total mass of the quick-setting admixture, In the particle size of the alkaline earth metal sulfate, the mass ratio of particles having a size of 1.5 μm or less is 33 to 52 mass% relative to the total amount of the alkaline earth metal sulfate, and the mass ratio of particles having a size of 10.5 μm or more and 100 μm or less is 10 to 29 mass%.

2. The quick-setting admixture according to claim 1, wherein the content of the alkaline earth metal sulfate is greater than the total content of the alkali metal sulfate and the aluminum sulfate.

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

4. The quick-setting admixture according to claim 1 or 2 is contained in a mixture of cement, aggregate, water, and the quick-setting admixture according to claim 1 or 2. The content of the quick-setting admixture is 5 to 15 parts by mass per 100 parts by mass of the cement,

5. In a 20°C environment, the test was conducted in accordance with the Japan Society of Civil Engineers' Standard Specifications for Concrete, "Quality Standards for Accelerator for Shotcrete," Appendix "Method for Measuring Instantaneous Setting Time by Penetration Resistance of Mortar with Accelerator Added," and was carried out on a 0.125 cm2 cross-sectional area. ２ The penetration resistance measured using a Proctor needle was 0.15 N / mm 25 seconds after the addition of the quick-setting admixture. ２ The sprayed concrete according to claim 4, wherein

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