Sprayed concrete

Abstract

To provide spray concrete which is excellent in mixing properties of materials and can achieve both high quick-setting properties and strength development properties at an initial stage.SOLUTION: Spray concrete comprising a concrete composition, a quick-setting admixture and water, wherein the quick-setting admixture comprises calcium aluminate, a sulfate of an alkali metal, a sulfate of an alkaline earth metal and aluminum sulfate, the content of the calcium aluminate is from 55 to 86 mass% based on the total mass of the quick-setting admixture, and with respect to the particle size of the sulfate of an alkaline earth metal, the mass proportion of particles of at most 1.5 μm is from 33 to 52 mass%, and the mass proportion of particles of at least 10.5 μm and at most 100 μm is from 10 to 29 mass%, to the total amount of the sulfate of an alkaline earth metal.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to sprayed concrete. [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 accelerators set in a very short time, increasing the mixing distance can lead to the concrete hardening during this time, potentially causing serious spraying problems such as clogging and blockage of the spray nozzle. On the other hand, shortening the mixing distance can lead to insufficient mixing, and an uneven mix can easily cause minute variations in the reaction of the components. As a result, it is difficult to obtain uniform and stable hardened concrete, and hardened properties such as strength are also poor. Furthermore, conventional high-strength sprayed concrete has had difficulties in maintaining long-term strength when attempting to increase initial strength development, or in controlling various performance characteristics due to excessive reactivity, which can lead to poor workability due to setting during the construction process. Therefore, there is a demand for a concrete that has excellent initial strength development, high mixability to prevent clogging of the spray nozzle, and long-term strength maintenance.

[0006] Therefore, an object of the present invention is to provide a quick-setting admixture and a shotcrete that ensure good mixing of materials and also exhibit excellent quick-setting properties and strength development in an early stage. [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 sprayed concrete that has excellent material mixability and can simultaneously achieve high rapid setting and strength development in an early stage.

[0008] That is, the present invention includes the following [1] to [4]. [1] A concrete composition including cement, aggregate, and gypsum, a quick-setting admixture, and water, the rapid-setting admixture comprises calcium aluminate, an alkali metal sulfate, an alkaline earth metal sulfate, and aluminum sulfate; The content of the calcium aluminate is 55 to 86 mass% based on the total mass of the quick-setting admixture, The particle size of the alkaline earth metal sulfate is such that the mass ratio of particles of 1.5 μm or less is 33 to 52 mass% and the mass ratio of particles 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 sprayed concrete described in [1], which is for wet spraying. [3] The sprayed concrete according to [1] or [2], wherein the quick-setting admixture further contains an alkali metal carbonate. [4] The sprayed concrete according to any one of [1] to [3], wherein the ratio of fine aggregate to the volume of the total aggregate of the aggregate is 45 to 70% by volume. [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 mixing of materials and also exhibit excellent quick-setting properties and strength development in an early stage. 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 sprayed concrete of this embodiment includes a concrete composition containing cement, aggregate, and gypsum, a quick-setting admixture, and water.

[0012] [Concrete composition] The concrete composition includes cement, aggregate, and gypsum. Various cements can be used, for example, various portland cements such as normal, early strength, ultra-early strength, low heat and medium heat, ecocement, ultra-rapid hardening cement, fly ash cement, etc. One type of cement may be used alone, or two or more types may be used in combination. Portland cement is preferred. 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) is used. 2 / g or more.

[0013] The unit mass of cement is 300 to 500 kg / m 3 is preferably 330 to 480 kg / m 3 More preferably, it is 350 to 450 kg / m 3 If the unit volume mass of the cement is within the above range, the initial and long-term strength development is further improved, and the adhesiveness is also likely to be improved.

[0014] 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 suitable for use in concrete because they can easily ensure a predetermined aggregate strength and are less likely to cause material separation due to their small difference in specific gravity with other contained components, and therefore have a surface dry density of 2.3 to 2.9 g / cm. 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.

[0015] The unit volume mass of fine aggregate is 700 to 1300 kg / m 3 It is preferable that the density is 800 to 1200 kg / m 3 More preferably, it is 900 to 1100 kg / m 3 When the unit volume mass of the fine aggregate is within the above range, the initial and long-term strength development is further improved. The unit volume mass of coarse aggregate is 400 to 900 kg / m 3 is preferably 500 to 850 kg / m 3 More preferably, it is 600 to 800 kg / m 3 When the unit volume mass of the coarse aggregate is within the above range, the initial and long-term strength development is further improved.

[0016] The fine aggregate ratio to the total aggregate volume ([volume of fine aggregate / volume of total aggregate] × 100) is preferably 45 to 70 volume %, more preferably 50 to 68 volume %, and even more preferably 55 to 65 volume %. If the fine aggregate ratio of the aggregate is within the above range, pumpability during construction will be even better, and initial and long-term strength development will also be further improved.

[0017] Examples of gypsums include anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum. As the gypsums, anhydrous gypsum is preferred from the viewpoint of further improving the strength development. One type of gypsum may be used alone, or two or more types may be used in combination. The fineness of the gypsums is preferably 3200 to 18000 cm in terms of Blaine specific surface area from the viewpoint of further improving the initial strength development. 2 / g, and 5000 to 15000 cm 2 / g, and more preferably 5500 to 14000 cm 2 / g, and more preferably 7000 to 12000 cm 2 / g is particularly preferred.

[0018] The content of gypsum is preferably 1 to 10 parts by mass, more preferably 1.5 to 9 parts by mass, and even more preferably 2 to 7 parts by mass, relative to 100 parts by mass of cement. If the content of gypsum is within the above range, the quick-setting property is further improved, and the initial and long-term strength development is further improved.

[0019] The concrete composition may contain various admixtures (materials) within the range that does not impair the effects of the present invention. Examples of admixtures (materials) include water-reducing agents, expansive agents, antifoaming agents, waterproofing agents, rust inhibitors, shrinkage-reducing agents, thickeners, water-retaining agents, pigments, water-repellents, anti-efflorescence agents, fibers, and pozzolanic substances.

[0020] The concrete composition can be prepared by mixing the above-mentioned components using a commonly used mixing tool, and the tool is not particularly limited. Examples of the mixing tool include a concrete mixer.

[0021] [Quick setting admixture] Rapid setting admixtures include calcium aluminate, alkali metal sulfates, alkaline earth metal sulfates, and aluminum sulfate.

[0022] 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 preferably 1.8 to 2.7, more preferably 1.9 to 2.65, and even more preferably 2.0 to 2.6. When the molar ratio of CaO to Al2O3 is within the above range, both rapid setting and workability are easily achieved. 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.

[0023] Calcium aluminate may be crystalline, amorphous, or a mixture thereof. From the viewpoint of easily achieving 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 be the same as or greater than that of the cement in the base concrete to be mixed, for example, a Blaine specific surface area of ​​3000 to 6500 cm. 2 The particle size is 1 / g.

[0024] 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.

[0025] The calcium aluminate content is 55 to 86% by 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 the initial 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 60 to 84% by mass, more preferably 65 to 82% by mass, and even more preferably 70 to 80% by mass based on the total mass of the quick-setting admixture.

[0026] 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.

[0027] The content of the alkali metal sulfate is preferably 1 to 20 parts by mass, more preferably 4 to 15 parts by mass, and even more preferably 5 to 10 parts by mass, in terms of anhydride relative to 100 parts by mass of calcium aluminate. When the content of the alkali metal sulfate is within the above range, the rapid setting property and the initial and long-term strength development tend to be excellent.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The content of the alkaline earth metal sulfate is preferably 12 to 50 parts by mass, more preferably 13 to 40 parts by mass, still more preferably 13.5 to 30 parts by mass, and particularly preferably 14 to 25 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 from the early stage to the long term.

[0033] 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 3, more preferably 1.1 to 2, and even more preferably 1.2 to 1.6, 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 initial rapid setting property and strength development are even more excellent.

[0034] Aluminum sulfate may be in any form, such as the hexadecahydrate or anhydrous form, with the hexadecahydrate being preferred. The content of aluminum sulfate, calculated as an anhydride, is preferably 0.5 to 10 parts by mass, more preferably 0.8 to 8 parts by mass, and even more preferably 1 to 5 parts by mass, relative to 100 parts by mass of calcium aluminate. When the content of aluminum sulfate is within the above range, it is easy to ensure long-term strength development even when the quick-setting property is increased in a low-temperature environment.

[0035] 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.

[0036] 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.

[0037] The quick-setting admixture 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, an omni mixer, or a Henschel mixer can be used.

[0038] The amount of the quick-setting admixture is preferably 3 to 25 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 7 to 15 parts by mass, relative to 100 parts by mass of cement. If the amount of the quick-setting admixture added is within the above range, it is easy to achieve both quick-setting properties and mixability.

[0039] [Sprayed concrete] Shotcrete may be produced, for example, by a wet spraying method in which the materials excluding the quick-setting admixture and water are mixed in a concrete mixer or the like to form base concrete, and the base concrete and quick-setting admixture are then mixed and sprayed at the tip of a spray nozzle, 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 and sprayed at the tip of a spray nozzle. Shotcrete is preferably produced by a wet spraying method, as this method makes it easier to reduce dust and rebound and allows the materials to be mixed more uniformly.

[0040] The amount of water in sprayed concrete can be adjusted depending on factors such as the purpose and location of use. The unit mass of water is 100 to 350 kg / m 3 is preferably 150 to 300 kg / m 3 More preferably, it is 170 to 250 kg / m 3 It is more preferable that the unit volume mass of water is within the above range. When the unit volume mass of water is within the above range, pumpability during construction is further improved and high strength development is easily ensured. The amount of water can be adjusted within the above range whether using a wet spraying method or a dry spraying method.

[0041] The water-cement ratio of the sprayed concrete ([mass of water / mass of cement] × 100) is preferably 40 to 70 mass%, more preferably 45 to 65 mass%, and even more preferably 50 to 60 mass%. If the water-cement ratio is within the above range, the initial and long-term strength development and adhesion are further improved.

[0042] 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 1N / mm 25 seconds after adding the quick-setting admixture. 2 It is preferable that the resistance is 2N / mm or more. 2 More preferably, it is 2.5N / 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 rapid setting property is good in the early stage, making it easier 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.

[0043] The shotcrete of this embodiment has a compressive strength of 1.5 N / mm2 at 4 hours of hardening, 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 2N / mm or more. 2 More preferably, it is 2.5N / mm 2 If 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.

[0044] The sprayed concrete of this embodiment ensures good quick-setting properties and material mixability, and also has excellent early strength development. Therefore, the sprayed concrete of this embodiment can be suitably used for spraying on tunnel walls, slopes, environments with spring water, environments with soft ground, etc. [Example]

[0045] 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.

[0046] [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

[0047] [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) Gypsum: Anhydrite, Blaine specific surface area 11000cm 2 / g

[0048] [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.

[0049] [Table 1]

[0050] [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.

[0051] [Table 2]

[0052] [Preparing the base concrete] For Examples 1 to 6 and Comparative Examples 1 to 4, 12 parts by mass of gypsum, 265 parts by mass of fine aggregate, and 182 parts by mass of coarse aggregate were mixed with 100 parts by mass of cement, and then 45 parts by mass of water was added and mixed for 2 minutes in a concrete mixer to prepare base concrete.

[0053] [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.

[0054] 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 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 "-".

[0055] [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.

[0056] [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. 3The 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.

[0057] [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 pressure supply was smooth 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.

[0058] [Table 3]

[0059] The shotcrete using the quick-setting admixture of the Example could be pumped without clogging, had good adhesion, and was excellent in initial quick-setting properties 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 initial quick-setting properties and strength development.

Claims

1. A concrete composition including cement, aggregate, and gypsum, a quick-setting admixture, and water, the rapid-setting admixture comprises calcium aluminate, an alkali metal sulfate, an alkaline earth metal sulfate, and aluminum sulfate; The content of the calcium aluminate is 55 to 86% by mass based on the total mass of the quick-setting admixture, The particle size of the alkaline earth metal sulfate is such that the mass ratio of particles of 1.5 μm or less is 33 to 52 mass% and the mass ratio of particles 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. 2. The sprayed concrete according to claim 1, which is for wet spraying.

3. 3. The sprayed concrete according to claim 1, wherein the quick-setting admixture further comprises an alkali metal carbonate.

4. The sprayed concrete according to claim 1 or 2, wherein the ratio of fine aggregate to the volume of the total aggregate of the aggregate is 45 to 70 volume %.

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