Pumpability improver, cement concrete, sprayed cement concrete

Abstract

A pumpability improver comprising a poly(ethylene oxide), characterized by the following dynamic viscoelasticity. (1) An aqueous solution of the poly(ethylene oxide), in a dynamic viscoelasticity measurement at an angular frequency of 0.1 rad / s, has a storage modulus G' of 0.01 Pa or greater and a loss modulus G" of 0.01 Pa or greater. (2) The aqueous solution of the poly(ethylene oxide), at an angular frequency of 0.1 rad / s, has a tanδ of 1-30.

Description

Technical Field

[0001] The present invention relates to a pumpability improver, cement concrete, and sprayed cement concrete.

Background Art

[0002] In tunnel excavation work, concrete spraying is carried out to reinforce the ground and stabilize the excavation face. As a spraying method, compressed air sent from a compressor is supplied into a transport pipe that transports concrete sent by a piston pump or the like, and the concrete is pneumatically transported. At the same time, a powdered quick-setting agent pneumatically transported from a quick-setting agent supply facility is supplied to a branch pipe of a confluence pipe, and after mixing the concrete and the quick-setting agent, the concrete is sprayed from a nozzle. There is a wet method, or a dry method in which water is added while dry-mixed concrete is pneumatically transported, a powdered quick-setting agent pneumatically transported from a quick-setting agent supply facility is supplied to a branch pipe of a confluence pipe, and after mixing the concrete and the quick-setting agent, the concrete is sprayed from a nozzle.

[0003] In these spraying methods, since a large amount of dust may be generated when spraying pneumatically transported concrete, a method of adding a powdery dust reducing agent such as water-soluble cellulose and polyethylene oxide to the concrete before mixing has been proposed.

[0004] Also, a method has been proposed in which compressed air sent from a compressor is supplied into a transport pipe that transports concrete sent by a piston pump or the like, the concrete is pneumatically transported, a powdered quick-setting agent pneumatically transported from a quick-setting agent supply facility is supplied to a branch pipe of a confluence pipe, and after mixing the concrete and the quick-setting agent, the concrete is sprayed from a nozzle to reduce dust (see, for example, Patent Document 1 and Patent Document 2).

[0005] Furthermore, a method has been proposed in which a cement composition using coated fine aggregate in which fine aggregate is coated with cement is sprayed to reduce dust (see, for example, Patent Document 3).

[0006] However, in recent years, when excavating tunnels, further improvement of the working environment has been demanded from the viewpoints of the safety and health of workers, and reduction of dust generated in the tunnel has been demanded more than ever.

[0007] Dust generated during the application of shotcrete is no exception, and further improvement of the above dust reduction technology is urgently needed.

[0008] Therefore, as a technology for reducing dust in shotcrete, a powdery dust inhibitor containing an inorganic fine powder composed of polyethylene oxide, talc and / or pyrophyllite is added to impart viscosity to the concrete, strengthen the connection between materials, and reduce dust. A technology has been proposed (Patent Document 4).

[0009] However, the powdery dust reducer has a large viscosity change with temperature change, the slump value is likely to vary, and the substantial water-cement ratio of the shotcrete increases due to adding water or the like, resulting in insufficient strength in some cases.

[0010] Furthermore, cement concrete containing polyethylene oxide has the drawback that the amount of air entrained during mixing increases due to the increased viscosity of the fresh concrete, resulting in a decrease in the viscosity of the concrete and further a decrease in pumpability.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0012] From the above, an object of the present invention is to provide a pumpability improver that can improve pumpability by mixing it with cement concrete or sprayed concrete.

[0013] As a result of intensive studies, the present inventors have found that the above problems can be solved by using polyethylene oxide having specific dynamic viscoelasticity, and have completed the present invention. That is, the present invention is as follows. [Means for Solving the Problems]

[0014] [1] A pumpability improver containing polyethylene oxide having characteristics in the following dynamic viscoelasticity. (1) The storage elastic modulus G' and the loss elastic modulus G'' in the measurement of the dynamic viscoelasticity of the aqueous solution of the polyethylene oxide at an angular frequency of 0.1 rad / s are each 0.01 Pa or more. (2) tanδ = 1 to 30 at an angular frequency of 0.1 rad / s in the aqueous solution of the polyethylene oxide. [2] The pumpability improver according to [1], wherein the polyethylene oxide is further polyethylene oxide having characteristics in the following dynamic viscoelasticity. (3) The storage elastic modulus G' and the loss elastic modulus G'' in the measurement of the dynamic viscoelasticity of the aqueous solution of the polyethylene oxide at an angular frequency of 1000 rad / s are each 2000 Pa or less. [3] Cement concrete containing the pumpability improver according to [1] or [2], wherein the polyethylene oxide in the pumpability improver is contained in an amount of 0.05 to 10 parts by mass with respect to 100 parts by mass of the unit water amount. [4] In the cement concrete according to [3], an antifoaming agent, fly ash, and a Blaine specific surface area of 3000 to 8000 cm 2Sprayed concrete obtained by mixing at least any one of powder accelerators containing calcium aluminate of / g. [5] The sprayed concrete according to [4], further obtained by mixing a liquid accelerator having a pH of 1 to 4 and containing aluminum and sulfur.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a pumpability modifier that can improve pumpability by mixing it into cement concrete or sprayed concrete.

Modes for Carrying Out the Invention

[0016] In this specification, paste, mortar, and concrete are collectively referred to as cement concrete.

[0017] [Pumpability Modifier] The pumpability modifier of the present invention contains polyethylene oxide characterized by the following dynamic viscoelasticity. Here, pumpability refers to the ease of concrete pumping work (high pumpability), and a pumpability modifier refers to one that can improve pumpability by mixing it into concrete rather than without mixing.

[0018] (1) When measuring the dynamic viscoelasticity of an aqueous solution of the above polyethylene oxide at an angular frequency of 0.1 rad / s, the storage elastic modulus G' and the loss elastic modulus G'' are each 0.01 Pa or more. (2) At an angular frequency of 0.1 rad / s of the above polyethylene oxide, tanδ = 1 to 30.

[0019] If the dynamic viscoelasticity of (1) is not satisfied, the dust reduction effect will be impaired. The storage elastic modulus G' is preferably 0.01 to 1000 Pa, more preferably 0.01 to 900 Pa. The loss elastic modulus G'' is preferably 0.01 to 1000 Pa, more preferably 0.01 to 900 Pa.

[0020] Also, if the dynamic viscoelasticity of (2) is not satisfied, the pumpability of the concrete will be impaired. tanδ is preferably from 1 to 25, more preferably from 1 to 20.

[0021] The polyethylene oxide preferably further has characteristics in the dynamic viscoelasticity shown below. (3) When measuring the dynamic viscoelasticity of the aqueous solution of polyethylene oxide described above at an angular frequency of 1000 rad / s, the storage elastic modulus G' and the loss elastic modulus G'' are each 2000 Pa or less.

[0022] (3) By satisfying the dynamic viscoelasticity, good pumpability can be imparted. In (3), the storage elastic modulus G' is preferably from 100 to 2000 Pa, more preferably from 100 to 1000 Pa. The loss elastic modulus G'' is preferably from 100 to 2000 Pa, more preferably from 100 to 1000 Pa.

[0023] The above (1) to (3) can be measured by the method described in the examples. Further, to be in the range of (1) to (3), several kinds of polyethylene oxides with known storage elastic modulus G' and loss elastic modulus G'' are mixed, and the dynamic viscoelasticity of the mixture is measured by the method described in the examples and adjusted to be within the range of (1) to (3).

[0024] Even outside the above (1) to (3), it is preferable that tanδ ≦ 5 when the angular frequency is 10 rad / s, and 0.6 ≦ tanδ ≦ 1.8 when the angular frequency is 100 rad / s. In these cases, the pumpability of the concrete is good.

[0025] In the pumpability improver, the content of the polyethylene oxide according to the present invention is preferably 10% by mass or more, more preferably 50% by mass or more, and still more preferably 100% by mass. By having a content of polyethylene oxide of 50% by mass or more, appropriate viscosity can be imparted to the dust reduction effect. In addition, when the content of polyethylene oxide is not 100% by mass, inorganic fine powders such as talc and pyrophyllite may be contained.

[0026] The polyethylene oxide used in the present invention preferably has a viscosity average molecular weight of 50,000 to 5,000,000, more preferably 50,000 to 2,000,000, from the viewpoints of pumpability and low dust generation.

[0027] The viscosity average molecular weight of polyethylene oxide can be determined in accordance with ASTM D2857 and D4020.

[0028] The average particle size of the polyethylene oxide used in the present invention is preferably 400 to 700 μm, more preferably 500 to 700 μm, from the viewpoint of powder transportability. The average particle size of polyethylene oxide can be measured by the laser diffraction scattering method.

[0029] [Cement Concrete] The cement concrete of the present invention contains the pumpability improver of the present invention, and contains 0.05 to 10 parts by mass of polyethylene oxide in the pumpability improver with respect to 100 parts by mass of the unit water amount.

[0030] When the amount of polyethylene oxide is less than 0.05 part by mass, the dust reduction effect is impaired, and when it exceeds 10 parts by mass, the pumpability is impaired.

[0031] The amount of cement in the cement concrete is preferably 300 to 500 kg / m in terms of the unit amount of cement 3 and more preferably 350 to 450 kg / m 3 The water / cement ratio in the cement concrete with water premixed is preferably 45 to 65% by mass, more preferably 50 to 60% by mass.

[0032] [Shotcrete] The sprayed concrete of the present invention is obtained by mixing at least one of an antifoaming agent, fly ash, and a powdery quick-setting agent containing calcium aluminate with a Blaine specific surface area of 3000 to 8000 cm 2 / g in the cement concrete of the present invention.

[0033] The antifoaming agent is not particularly limited as long as it is an antifoaming agent used in general concrete, and examples thereof include mineral oil-based antifoaming agents, ester-based antifoaming agents, amine-based antifoaming agents, amide-based antifoaming agents, polyether-based antifoaming agents, and silicone-based antifoaming agents.

[0034] From the viewpoint of the defoaming effect, the content of the antifoaming agent in the sprayed concrete is preferably 0.0005 to 0.02 parts by mass, more preferably 0.0008 to 0.015 parts by mass, based on 100 parts by mass of cement.

[0035] The fly ash preferably satisfies the quality specified in JIS A6201 "Fly Ash for Concrete", and type I is more preferable.

[0036] From the viewpoints of imparting viscosity and fluidity, the content of fly ash in the sprayed concrete is preferably 10 to 150 parts by mass, more preferably 30 to 120 parts by mass, based on 100 parts by mass of cement.

[0037] The powdery quick-setting agent contains calcium aluminate, and preferably contains aluminum sulfate, sodium sulfate, calcium sulfate, and alkali carbonate in addition to the calcium aluminate. From the viewpoints of setting property and strength characteristics, the content of the powdery quick-setting agent in the sprayed concrete is preferably 4 to 20 parts by mass, more preferably 4 to 15 parts by mass, based on 100 parts by mass of cement.

[0038] Calcium aluminate is a general term for substances with hydration activity mainly composed of CaO and Al2O3, which are obtained by mixing calcia raw materials and alumina raw materials and performing heat treatment such as firing in a kiln or melting in an electric furnace. If CaO is abbreviated as C and Al2O3 as A, then C3A, C 12 A7, C 11 A7·CaF2, C 11 A7·CaCl2, C2A·SiO2, CA, and C2A, etc. can be mentioned. Furthermore, some of CaO and Al2O3 are replaced by alkali metal oxides, alkaline earth metal oxides, silicon oxide, titanium oxide, iron oxide, alkali metal halides, alkaline earth metal halides, alkali metal sulfates, and alkaline earth metal sulfates, etc. Compounds, or compounds in which these are slightly dissolved in those mainly composed of CaO and Al2O3 are also included.

[0039] As the form of calcium aluminate, either crystalline or amorphous can be used. Among these, from the viewpoint of reaction activity, amorphous calcium aluminates are preferred, and C 12 Amorphous calcium aluminate obtained by rapidly cooling the heat-treated product corresponding to the A7 composition is more preferred.

[0040] The Blaine specific surface area of calcium aluminate is preferably 3000 - 8000 cm 2 / g in terms of flash setting property and initial strength development property, and more preferably 5000 - 7000 cm 2 / g.

[0041] Aluminum sulfate is not limited, and it may be an anhydrous salt or a hydrated salt (hydrate). Compared with its anhydrous form, the hydrated aluminum sulfate has a higher dissolution rate and can improve the coagulation characteristics. The hydrated aluminum sulfate includes, for example, hydrates of 4 - 27, preferably 10 - 18, and more preferably 14 - 18. Among these, by including the 14 - 18 hydrate of aluminum sulfate and also including at least the 17 hydrate of aluminum sulfate, the coagulation characteristics can be enhanced.

[0042] As for sodium sulfate, the quick-setting admixture contains sodium sulfate. The strength development property can be improved by sodium sulfate. As alkali metal sulfates other than sodium sulfate, potassium sulfate, lithium sulfate, etc. may be included. These may be used alone or in combination of two or more. Among these, as sodium sulfate, neutral anhydrous sodium nitrate may be used.

[0043] Examples of calcium sulfate include anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum. Also, natural gypsum produced naturally, flue gas desulfurized gypsum obtained as an industrial by-product, fluosilicic acid by-product anhydrous gypsum, etc. may be used. One kind or two or more kinds of these can be used. Among these, from the viewpoint of the expression of adhesion strength, anhydrous gypsum may be used.

[0044] The alkali carbonate refers to an acid alkali metal salt and can significantly improve the setting property and initial strength development property of the powder quick-setting agent. The alkali carbonate is not particularly limited, and examples include lithium carbonate, sodium carbonate, sesquisodium carbonate, potassium carbonate, sodium bicarbonate, sodium hydrogen carbonate, etc. Particularly effective for setting and initial strength development are sodium carbonate, potassium carbonate, sesquisodium carbonate, sodium bicarbonate, and sodium hydrogen carbonate, and it is also possible to combine one or more of these. Preferably, it is at least one selected from the group consisting of sodium carbonate, sesquisodium carbonate, sodium bicarbonate, and potassium carbonate.

[0045] In the powder quick-setting agent, calcium aluminate is preferably 40% by mass or more, more preferably 40 to 90% by mass. Aluminum sulfate is preferably 1 to 30% by mass or more, more preferably 5 to 20% by mass. Sodium sulfate is preferably 5 to 35% by mass or more, more preferably 5 to 30% by mass. Calcium sulfate is preferably 5 to 40% by mass or more, more preferably 10 to 30% by mass. The alkali carbonate is preferably 5 to 20% by mass or more, more preferably 5 to 15% by mass.

[0046] The sprayed concrete of the present invention is preferably further formed by mixing a liquid accelerator having a pH of 1 to 4 and containing aluminum and sulfur. Since the liquid accelerator is acidic, its handleability is improved as compared with an alkaline liquid accelerator.

[0047] As the liquid accelerator, for example, an aqueous solution of aluminum sulfate, or various raw materials appropriately selected from an aqueous solution of aluminum sulfate, alum, aluminum hydroxide, sodium hydroxide, sulfuric acid, natural or synthetic cryolite, sodium fluoride, aluminum fluoride, etc. are mixed in a liquid and heated at 80 to 95 ° C for 30 to 120 minutes to produce it. From the viewpoint of good productivity, it is preferable to use sulfuric acid, aluminum hydroxide, aluminum sulfate or various alums, and natural or synthetic cryolite as the raw materials. Further, it is preferable to use water or the like as the liquid.

[0048] The contents of aluminum, sulfur, and sodium in the liquid accelerator are not particularly limited, but from the viewpoint of rapid setting properties, aluminum is preferably 1 to 20 parts by mass in terms of Al2O3, sulfur is preferably 10 to 30 parts by mass in terms of SO3, and sodium is preferably 0.1 to 3 parts by mass in terms of Na2O. More preferably, aluminum is 5 to 10 parts by mass in terms of Al2O3. More preferably, sulfur is 12 to 25 parts by mass in terms of SO3. More preferably, sodium is 0.1 to 2 parts by mass in terms of Na2O.

[0049] From the viewpoints of setting properties and strength development properties, the content of the liquid accelerator in the sprayed concrete is preferably 5 to 20 parts by mass, more preferably 5 to 15 parts by mass, per 100 parts by mass of cement.

[0050] The sprayed concrete of the present invention is pumped while being mixed with a liquid accelerator as necessary by the expansion and flow of compressed air in a transport pipe, discharged from a nozzle, and sprayed onto a ground surface or the like which is a sprayed surface.

[0051] In the present invention, the total amount of compressed air for pneumatically transporting the shotcrete to the nozzle is 5 to 30 m, calculated as the atmospheric pressure equivalent. 3 / min is preferable, 10-20m 3 / min is more preferable. If the total amount of compressed air is small, the amount of air will be insufficient, resulting in insufficient consolidation of the quick-setting cement concrete against the sprayed surface, making it difficult to obtain strength, and the quick-setting cement concrete will have poor pumpability and may become clogged in the piping. If the total amount of compressed air is large, the amount of pumped air will be excessive, resulting in a large amount of dust.

[0052] In the present invention, the spraying pressure of the shotcrete is preferably 0.2 to 0.5 MPa. The pressure of the compressed air for compressing and feeding the liquid quick-setting admixture is preferably about 0.01 to 0.3 MPa higher than the pumping pressure of the shotcrete, so as not to clog the junction pipe or transport pipe of the shotcrete when it is mixed therein.

[0053] The spraying equipment is not particularly limited as long as it can spray sufficiently. For example, a product named "MKW-25SMT" manufactured by Shintech Co., Ltd. can be used to pump the sprayed cement concrete, and a pumping device for quick-setting agents such as "Nattomcrete" can be used to pump the quick-setting agent.

[0054] According to the present invention, it is possible to improve the pumpability of concrete and also to improve the dust prevention effect. EXAMPLES

[0055] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the present invention. Furthermore, unless otherwise specified, parts and % are based on mass.

[0056] [Experimental Example 1] <Measurement of dynamic viscoelasticity> The following PEO (polyethylene oxide) was mixed in an amount of 5 mass % with distilled water to prepare a measurement sample. ·PEO-a: Density: 1.2g / cm3 Average particle diameter: 600 μm Viscosity average molecular weight: 600,000 - 1,100,000 · PEO-b: Density: 1.1 g / cm 3 Average particle diameter: 590 μm Viscosity average molecular weight: 1,100,000 - 1,500,000 · PEO-c: Density: 1.2 g / cm 3 Average particle diameter: 600 μm Viscosity average molecular weight: 600,000 - 1,000,000 · PEO-d: Density: 1.3 g / cm 3 Average particle diameter: 580 μm Viscosity average molecular weight: 600,000 - 1,000,000 · PEO-e: Density: 1.2 g / cm 3 Average particle diameter: 610 μm Viscosity average molecular weight: 500,000 - 1,000,000 · PEO-f: Density: 1.2 g / cm 3 Average particle diameter: 620 μm Viscosity average molecular weight: 700,000 - 1,000,000

[0057] The prepared samples were measured for dynamic viscoelasticity using a rotational rheometer. The measurement was carried out by setting the measurement sample prepared in a dynamic viscoelasticity measuring device rheometer (manufactured by Anton paar) and measuring the frequency ω (rad / sec) dispersion of the storage modulus G’ (Pa) and the loss modulus G’’ (Pa). A parallel plate with a diameter of 50 mm was used as the sample holder, and the distance between the plates was set to 1 mm. The measurement temperature was 25°C, and the measurements were made at each value of angular frequency ω = 0.1, 1, 10, 100, 1000 rad / sec and under the condition of strain = 0.1% strain. Also, the value of tanδ was calculated from the ratio of G’ and G’’ (G’’ / G’). The measurement results are shown in Table 1.

[0058]

Table 1

[0059] [Experimental Example 2] The actual discharge amount was measured from the pump operation time from the start to the end of spraying the sprayed concrete using PEO-a~f. The results are shown in Table 2 below. · Actual discharge amount: Concrete usage amount (m 3) ÷ Pump operation time (minutes) ÷ 60 minutes ·S 0.15下 : Fine aggregate with a sieve size of 0.15 mm or less · Sprayed concrete mix · Construction conditions: Cement 360 kg, water (W) 216 kg, fine aggregate 1049 kg, coarse aggregate (crushed stone from the Himekawa River system No. 6 in Niigata Prefecture, density 2.67 g / cm 3 ) 716 kg of concrete was prepared and the PEO shown in the following table was added. The concrete was pumped at a setting of 15 m 3 / h using a concrete pump from Shintec Co., Ltd., model MKW-25SMT. In Tables 2 to 6 below, the amount of water is denoted as "W" and the amount of cement as "C".

[0060]

Table 2

[0061] [Experimental Example 3] Using PEO-a to f, 360 kg of cement, 216 kg of water, 1049 kg of fine aggregate, and coarse aggregate (crushed stone from the Himekawa River system No. 6 in Niigata Prefecture, density 2.67 g / cm 3 ) 716 kg of concrete was prepared and the PEO and defoaming agent (commercially available: polyether type) shown in the following table were added. The concrete was pumped at a setting of 15 m 3 / h using a concrete pump from Shintec Co., Ltd., model MKW-25SMT, and was mixed and merged with compressed air from another line during pumping to conduct air transportation and made into sprayed concrete. The slump value, air content, actual discharge volume, and dust concentration were measured. The results are shown in Table 3 below. · Slump value: A slump test was conducted in accordance with JIS A 1101. · Air content: The air content was calculated by the air chamber pressure method in accordance with JIS A 1128. · Dust concentration: Measured at a position 5 m from the spraying point. The measuring device used was a digital dust meter LD-5R manufactured by Shibata Scientific Co., Ltd.

[0062]

Table 3

[0063] [Experimental Example 4] Using PEO-a~f, 360 kg of cement, 216 kg of water, 1049 kg of fine aggregate, and 716 kg of coarse aggregate (crushed stone from the Himekawa River system No. 6 in Niigata Prefecture, density 2.67 g / cm 3 ) were used to prepare concrete, and the PEO and defoaming agent (commercial product: polyether type) shown in the following table were added. The concrete was pumped at a set discharge rate of 15 m 3 / h using a concrete pump of Shintec MKW-25SMT. Immediately before spraying, the following powder accelerator was pneumatically conveyed by a conveyor device Dencal NATM Cleat so that it was 4 parts per 100 parts of cement, and mixed and merged with the pneumatically conveyed concrete to form sprayed concrete.

[0064] (Powder accelerator) · CA1: Calcium aluminate (vitrification rate 90%, Blaine 2000 cm 2 / g) · CA2: Calcium aluminate (vitrification rate 90%, Blaine 3000 cm 2 / g) · CA3: Calcium aluminate (vitrification rate 90%, Blaine 7000 cm 2 / g) · CA4: Calcium aluminate (vitrification rate 90%, Blaine 9000 cm 2 / g)

[0065] The initial strength and long-term strength were measured as follows. The results are shown in Table 4 below. · Initial strength: Sprayed onto a formwork according to JSCE-G561, and the initial strength was measured by converting the pull-out strength at the ages of 10 minutes, 3 hours, and 1 day into compressive strength. · Long-term strength: Sprayed onto a formwork according to JSCE-F561 and JISA1107, and the core was taken at the age of 28 days to measure the compressive strength.

[0066]

Table 4

[0067] [Experimental Example 5] Using PEO-d~f, concrete was prepared with 360 kg of cement, 216 kg of water, 1049 kg of fine aggregate, 716 kg of coarse aggregate (No. 6 crushed stone from the Himekawa River system in Niigata Prefecture, density 2.67 g / cm 3 ), and 80 kg of fly ash. The PEO and defoaming agent (commercial product: polyether type) shown in the following table were added. Using a concrete pump of Shintec MKW-25SMT, the concrete was pumped at a set discharge rate of 15 m 3 / h. Immediately before spraying, the powdered quick-setting agent CA2 or CA3 was pneumatically conveyed by a Dencor NATMcrete conveying device so that it was 4 parts per 100 parts of cement, and was mixed and merged with the pneumatically conveyed concrete to form sprayed concrete. Similar to Experimental Example 4, the initial strength and long-term strength were measured. The results are shown in Table 5 below.

[0068] (Fly ash) · FA: Fly ash (JIS Class II product, density 2.40 g / cm 3 Blaine 4500 cm 2 / g)

[0069] [Table 5]

[0070] [Experimental Example 6] Using PEO-d~f, concrete was prepared with 360 kg of cement, 216 kg of water, 1049 kg of fine aggregate, 716 kg of coarse aggregate (No. 6 crushed stone from the Himekawa River system in Niigata Prefecture, density 2.67 g / cm 3 ), and 80 kg of fly ash. The PEO and defoaming agent (commercial product: polyether type) shown in the following table were added. Using a concrete pump of Shintec MKW-25SMT, the concrete was pumped at 15 m 3 / h. Immediately before spraying, the powdered quick-setting agent CA2 or CA3 was 4 parts per 100 parts of cement by a Dencor NATMcrete conveying device, and the liquid quick-setting agent was pneumatically conveyed from the tank so that it was 8 parts, and was mixed and merged with the concrete by a Y-tube to produce sprayed concrete. In the same manner as in Experimental Example 3, the actual discharge amount and the dust concentration were measured, and in the same manner as in Experimental Example 4, the initial strength and the long-term strength were measured. The results are shown in Table 6 below.

[0071] (Liquid quick-setting agent) · LS: Liquid quick-setting agent (aqueous aluminum sulfate solution, product of Daimyo Chemical Co., Ltd., commercially available product)

[0072] [Table 6]

Industrial Applicability

[0073] The present invention is suitable as an additive when concrete is pumped for the reinforcement of the ground in tunnel excavation work and the stabilization of the excavation face.

Claims

**Claim 1**: A pumpability improver containing 50% by mass or more of polyethylene oxide having an average particle diameter of 400 to 700 μm and characterized by the following dynamic viscoelasticity, and showing higher pumpability when mixed with concrete than when not mixed. (1) The storage elastic modulus G' and the loss elastic modulus G'' during the measurement of the dynamic viscoelasticity of the aqueous solution of the polyethylene oxide at an angular frequency of 0.1 rad / s are 0.01 Pa to 1000 Pa, respectively. (2) tanδ (G'' / G') = 1 to 30 at an angular frequency of 0.1 rad / s for the aqueous solution of the polyethylene oxide. The storage elastic modulus G' and the loss elastic modulus G'' in (1) are measured using a rotational rheometer at a measurement temperature of 25°C for a measurement sample prepared by mixing 5% by mass in distilled water. **Claim 2** The pumpability improver according to claim 1, wherein the polyethylene oxide is further polyethylene oxide characterized by the following dynamic viscoelasticity. (3) The storage elastic modulus G' and the loss elastic modulus G'' during the measurement of the dynamic viscoelasticity of the aqueous solution of the polyethylene oxide at an angular frequency of 1000 rad / s are 2000 Pa or less, respectively. The storage elastic modulus G' and the loss elastic modulus G'' in (3) are measured using a rotational rheometer at a measurement temperature of 25°C for a measurement sample prepared by mixing 5% by mass in distilled water. **Claim 3** Cement concrete containing the pumpability improver according to claim 1 or 2, wherein the polyethylene oxide in the pumpability improver is contained in an amount of 0.05 to 10 parts by mass per 100 parts by mass of the unit water amount. **Claim 4** The sprayed concrete obtained by mixing at least any one of an antifoaming agent, fly ash, and a powder quick-setting agent containing calcium aluminate having a Blaine specific surface area of 3000 to 8000 cm ２ / g in the cement concrete according to claim 3. **Claim 5** Furthermore, it contains aluminum and sulfur. In the liquid accelerator, the aluminum is Al ２ O ３ in terms of 1 to 20 parts by mass, and the sulfur is SO ３ in terms of 10 to 30 parts by mass, and the sprayed concrete according to claim 4, which is obtained by mixing a liquid accelerator having a pH of 1 to 4.

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