JP2014125389A - Powder type dust reducing agent, spray concrete and spray method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust reducing agent excellent in powder pressure transportation property, suppressing jet flow property, good in dust reducing effect, and high in workability.SOLUTION: There is provided a powder type dust reducing agent containing 42 to 90 pts.mass of talc, 0.1 to 10 pts.mass of bentonite, 0.5 to 20 pts.mass of cellulose ether, 0.1 to 6 pts.mass of diutan gum, 0.1 to 2 pts.mass of polyacrylamide and 0.5 to 20 pts.mass of a deforming agent based on total 100 pts.mass of the talc, the bentonite, the cellulose ether, the diutan gum, the polyacrylamide and the deforming agent, and the deforming agent is one or more kinds selected from a mineral oil-based deforming agent, alkylene oxide addition product-based deforming agent and silicone-based deforming agent. There are also provided a spray concrete and a spray method using the same.

Description

The present invention relates to a powdery dust reducing agent, spray concrete using the same, and a spraying method.

Concrete is sprayed to reinforce natural ground in tunnel excavation work and stabilize the excavation surface.
Compressed air sent from the compressor is supplied into the transport pipe that transports the concrete sent by a piston pump, etc., and the concrete is pneumatically transported, and at the same time, the powder is sent to the branch pipe of the merging pipe by air from the quick binder supply equipment. After supplying the binder and mixing the concrete and the rapid setting agent, water is added while the concrete is sprayed from the nozzle or during the pneumatic feeding of the dry mix concrete, and the rapid setting agent is supplied to the branch pipe of the merge pipe There is a dry construction method in which powder quick setting agent that is pneumatically transported from equipment is supplied, concrete and quick setting agent are mixed, and then concrete is sprayed from a nozzle.

These spraying methods may generate a large amount of dust when spraying air-carrying concrete, so before mixing the concrete, for example, reducing powdery dust such as water-soluble cellulose and polyethylene oxide A method of adding an agent to concrete has been proposed.
In addition, the compressed air sent from the compressor is supplied into the transport pipe that transports the concrete sent by the piston pump, etc., and the concrete is pneumatically transported, and the powder that is pneumatically transported to the branch pipe of the merging pipe from the quick setting agent supply equipment There has been proposed a method of reducing dust by spraying concrete from a nozzle after supplying the rapid setting agent and mixing the concrete and the rapid setting agent (Patent Documents 1 and 2).
Furthermore, a method has been proposed in which dust is reduced by spraying a cement composition using a coated fine aggregate obtained by coating fine aggregate with cement (Patent Document 3).

  However, the powdery dust reducing agent needs to increase the solubility by adjusting polyethylene oxide to an appropriate particle size, for example. Further, since the powdery dust reducing agent dissolves in the surface water of the concrete aggregate, it easily adheres to the aggregate hopper and tends to be ball-shaped when mixed, and a sufficient dust prevention effect was not obtained. This was particularly noticeable when the surface water of the aggregate was high.

Therefore, a powdery dust prevention agent containing inorganic fine powder composed of polyethylene oxide and talc and / or pyrophyllite has been proposed (Patent Document 4).
However, although the transportability from the hopper of the powder dust reducer metering machine has improved, the powder dust reducer floats in the batcher plant and tends to adhere to the floor and peripheral equipment, or the dust reducer itself. Since water becomes slippery due to water, there was a risk that the worker would fall. Moreover, the powdery dust reducing agent has a large viscosity change with temperature change, the slump value is likely to vary, the water cement ratio of the actual shotcrete increases, and the strength is insufficient in some cases.

JP-A-58-15056 JP 2004-189529 A JP 2000-72503 A JP 2009-78934 A

As a result of intensive studies, the present inventor has obtained the knowledge that the above problem can be solved by using a specific dust reducing agent, and has completed the present invention.

That is, the present invention comprises (1) talc, bentonite, cellulose ether, detan gum, polyacrylamide, and an antifoaming agent, and the defoaming agent is a mineral oil-based antifoaming agent, an alkylene oxide adduct-based antifoaming agent. , One or two or more types selected from silicone-based antifoaming agents, and talc is 42 to 90 parts by mass in a total of 100 parts by mass of talc, bentonite, cellulose ether, detan gum, polyacrylamide, and antifoaming agent, Bentonite is 0.1 to 10 parts by mass, cellulose ether is 0.5 to 20 parts by mass, detan gum is 0.1 to 6 parts by mass, polyacrylamide is 0.1 to 2 parts by mass, and antifoaming agent is 0.5 to 5 parts. 20 parts by weight of a powdery dust reducing agent, (2) the antifoaming agent of (1) is a mineral oil-based powder dust reducing agent, and (3) a difference angle of 15 ° or less. (1) or (2) powdery dust reducing agent having a powder characteristic of a compression degree of 45% or less, and (4) blowing powders added with any of the powdery dust reducing agents of (1) to (3) Adhesive concrete, (5) Sprayed concrete (4) mixed with powder quick-setting agent, (6) Pumped concrete of (4) is pumped, and is conveyed by compressed air from the mixing pipe in the middle A spraying method in which the powder rapid setting agent is mixed and sprayed, and a spraying method in which the pressure of pumping the sprayed concrete of (7) and (6) is 9 MPa or less.

  By using the powdery dust reducing agent of the present invention, it is excellent in powder pumpability, the scattering of the dust reducing agent itself can be suppressed, and by adding it to shotcrete, the dust reducing effect is high. There is an effect that it is possible to obtain a discharge efficiency equivalent to that without adding a reducing agent.

The present invention will be described in detail below.
Parts and% used in the present invention are based on mass unless otherwise specified.

Since the talc used in the present invention is rich in lubricity, it can be cut out from the hopper from the adder, and is used for the purpose of improving the filler and powder characteristics.
Talc is adjusted within a range of 42 to 90 parts in a total of 100 parts of powdery dust reducing agent.

  The bentonite used in the present invention is a kind of clay mineral and mainly contains montmorillonite. Examples of bentonite include calcium bentonite, sodium bentonite, and potassium bentonite.

  The swelling degree of bentonite is preferably 20 ml / 2 g or more. The water content of bentonite is preferably 10% or less. The particle size of bentonite is preferably 90% or more through 80 mesh.

  The proportion of bentonite in a total of 100 parts of the powdery dust reducing agent is preferably 0.1 to 10 parts. If it is less than 0.1 part, moderate viscosity may be difficult to obtain, and if it exceeds 10 parts, workability may be deteriorated.

  The cellulose ether used in the present invention is hydroxyalkyl cellulose and / or hydroxyalkylalkyl cellulose. Examples of the hydroxyalkyl cellulose include hydroxyethyl cellulose and hydroxypropyl cellulose, and examples of the hydroxyalkyl alkyl cellulose include hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl ethyl cellulose, which are used alone or in combination of two or more. Of these, hydroxypropylmethylcellulose is particularly preferred.

  The viscosity of the cellulose ether is preferably 5,000 to 50,000 mPa · s, preferably 8,000 to 25,000 mPas, in the viscosity of a 1% aqueous solution measured using a B-type viscometer at 20 ° C. and 10 rpm. -S is more preferable. The moisture content of the powder is preferably 15% or less.

  The ratio of cellulose ether in the total 100 parts of the powdery dust reducing agent is preferably 0.5 to 20 parts. If it is less than 0.5 part, moderate viscosity may be difficult to obtain, and if it exceeds 20 parts, workability may be deteriorated.

  Cellulose ether generally has air entrainment properties, so when there is a large amount of air in the concrete and the strength may be reduced, it is desirable to control the amount of air to a predetermined level with an antifoaming agent.

The detan gum used in the present invention is a natural high-molecular polysaccharide having two glucose, one glucuronic acid, and three rhamnose as structural units.
The viscosity of the dutan gum is preferably 2800 mPa · s or more, more preferably 3000 to 5500 mPa · s in the viscosity of a 0.25% aqueous solution measured using a B-type viscometer at 20 ° C. and 10 rpm.

  As for the ratio of the dutan gum in 100 parts of powdery dust reducing agents in total, 0.1-6 parts are preferable. If it is less than 0.1 part, moderate viscosity may be difficult to obtain, and if it exceeds 6 parts, workability may be deteriorated.

  The polyacrylamide used in the present invention contains a highly reactive acid amide group in the polymer. Of these, methacrylic cationic polymers are preferred. The viscosity of the polyacrylamide is preferably 40 to 80 mPa · s, more preferably 50 to 70 mPa · s in the viscosity of a 0.2 mass% aqueous solution measured at 20 ° C. and 10 rpm using a B-type viscometer. .

  The proportion of polyacrylamide in the total 100 parts of the powdery dust reducing agent is preferably 0.1 to 2 parts. If it is less than 0.1 part, moderate viscosity may be difficult to obtain, and if it exceeds 2 parts, workability may be deteriorated.

  The antifoaming agent used in the present invention is used for the purpose of suppressing excessive air entrainment. Examples of the antifoaming agent include alkylene oxide adducts of higher fatty acids, silicone-based antifoaming agents such as dimethyl silicone, and mineral oil-based antifoaming agents. The use of one or two or more selected from antifoaming agents and alkylene oxide adduct antifoaming agents is preferred, and the use of mineral oil-based antifoaming agents is more preferred.

  The proportion of the antifoaming agent in the total 100 parts of the powdery dust reducing agent is preferably 0.5 to 20 parts. If it is less than 0.5 part, the defoaming effect may be difficult to obtain, and if it exceeds 20 parts, the effect of addition will reach its peak, which is not preferable from the viewpoint of cost.

  The powdery dust reducing agent of the present invention preferably has powder characteristics with a difference angle of 15 ° or less. The difference angle is the difference between the angle of repose and the collapse angle, and the larger the value, the higher the jet property and the easier the powder is scattered.

  The powdery dust reducing agent of the present invention preferably has powder characteristics with a degree of compression of less than 50%. When the degree of compression is 50% or more, the cutout is very bad and may be blocked.

  The amount of the powdery dust reducing agent of the present invention is preferably 0.05 to 0.15 part, more preferably 0.1 part, in 100 parts of concrete cement. When the amount is 0.05 parts or less, the dust reduction effect may not be obtained. When the amount exceeds 0.15 parts, the concrete becomes too viscous, the pumping efficiency may be lowered, and the workability may be deteriorated.

  In addition, various cement admixtures and admixtures can be used in combination as long as the effects of the present invention are not impaired. For example, what are called water reducing agents, high performance water reducing agents, high performance AE water reducing agents, dispersants and fluidizing agents that can be used for mortar and concrete can be used.

  As the shotcrete of the present invention, any rapid setting agent that can be used for mortar and concrete can be used. For example, a powder quick setting agent mainly composed of calcium aluminates can be mentioned.

  The cement used for the shotcrete of the present invention may be any one of ordinary Portland cement, blast furnace cement, fly ash cement, early-strength cement, ultra-early-strength cement, eco-cement, etc. More than one species can be used in combination.

  The shotcrete of the present invention may be any one of limestone fine powder, stone powder, fly ash, blast furnace slag, coal ash, etc., and two or more kinds may be used in combination.

  Aggregates such as fine aggregate and coarse aggregate of the present invention are not particularly limited as long as they can be sprayed. Examples of fine aggregates include river sand, mountain sand, sea sand, lime sand, quartz sand, and crushed sand. As the coarse aggregate, river gravel, mountain gravel, lime gravel, crushed stone, etc. can be used, any of these may be used, and two or more kinds may be used in combination.

  The shotcrete of the present invention can be produced according to a usual method, and is prepared, for example, by stirring and mixing with cement, aggregate, dust reducing agent, water and the like in a raw plant or a setting site. The dust reducing agent can be used as a so-called post-addition which is added to the kneaded concrete or added to the kneaded concrete. Moreover, the method of preparing mortar first and using coarse aggregate after that can also be used.

  The water-cement ratio of the spray concrete of the present invention is preferably 45 to 70%, more preferably 45 to 60%.

  The fine aggregate ratio of the shotcrete of the present invention is preferably 55 to 70% in terms of the total aggregate volume ratio.

  In the present invention, talc, bentonite, cellulose ether, detan gum, polyacrylamide, and antifoaming agent are mixed in advance and powdered, then added to water and concrete and kneaded, so that rapid water absorption is eliminated. This occurrence is eliminated, and the dust reduction effect is exhibited. If bentonite is not added in advance, water may be absorbed rapidly, resulting in a so-called stagnation state, and the dust reduction effect may not be sufficiently exhibited.

  Hereinafter, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

"Experiment 1"
The test temperature was 20 ° C. unless otherwise specified.
Table 1 shows the composition of the powdery dust reducing agent. Next, Table 2 shows the powder characteristics (repose angle, collapse angle, difference angle, apparent bulk specific gravity, firm bulk specific gravity, degree of compression), discharge status, discharge amount per hour, and scattering amount measurement of the powdery dust reducing agent. Shown in A comparative commercial dust reducing agent was also tested in the same manner.

<Materials used>
Talc (Tl): Talc, natural product, commercially available cellulose ether (Ms): hydroxypropyl methylcellulose, 1% aqueous solution viscosity 20,000 mPa · s (10 rpm), manufactured by Shin-Etsu Chemical Co., Ltd., commercially available Dutan gum (Du): Kelcocrete , 0.25% aqueous solution viscosity 4,350 mPa · s (10 rpm), C.I. P. Kelco, commercial product polyacrylamide (Pa): 0.2% aqueous solution viscosity 63 mPa · s (10 rpm), Nippon Kasei Co., Ltd., commercial product bentonite (Bn): US commercial product potassium bentonite, swelling degree 27.0 ml / 2 g, Water content 8.9%, particle size wet residue 45 μm 5.0%, loss on ignition 7.0%, density 2.5 g / cm ³ , commercial product antifoaming agent (Af): mineral oil-based antifoaming agent, powder, commercial product Dust reducing agent A (for comparison): 100 parts of dust reducing agent, 80 parts of cellulose ether, 20 parts of polyacrylamide, commercial product, Experiment No. 1-42
Dust reducer B (for comparison): 100 parts of dust reducer, 30 parts of talc and 70 parts of polyethylene oxide, commercially available, Experiment No.1-43

<Measurement method>
Powder characteristics: The powder characteristics of the following items were measured using a powder tester manufactured by Hosokawa Micron.
Angle of repose: The sample was naturally dropped onto a table of φ80 mm, and the angle of the formed powder crest was measured.
Collapse angle: After measuring the angle of repose, a dedicated impactor is used to measure the angle of the crushed powder pile that was crushed by impact.
Difference angle: The angle of repose minus the collapse angle.
Apparent bulk specific gravity: The density at which a sample was naturally dropped into a dedicated cup and filled.
Hard bulk specific gravity: Density after tamping and filling after apparent bulk specific gravity test.
Compressibility: Ratio of apparent bulk density and firm bulk density.
Measurement of discharge status and discharge amount per hour: A screw feeder is attached to the bottom of the hopper with a height of 40 cm, a width of 30 cm, a length of 40 cm, and an angle of 60 degrees, and a PVC pipe with a length of φ5 cm and a length shown in Table 1 is attached. A dust prevention agent having a capacity of 80% of the hopper capacity was put into the adding device, discharged for 1 minute, weighed after being received in the weighing machine, and the state of blockage of the PVC pipe at the discharge port was evaluated. The case where almost the entire amount of the dust prevention agent was discharged was indicated as “◯”, the case where a small amount of the dust prevention agent partially remained was indicated as “Δ”, and the case where the dust prevention agent became bridging and remained as “x”.
Confirmation of scattering status: A 1m x 1m panel is laid around the weighing machine, and the amount scattered on the panel is measured.

From the results shown in Table 2, in the case of talc alone (Experiment No. 1-1), the difference angle increased, the degree of compression also increased, the discharge situation worsened, and bridging occurred. In addition, the bentonite simple (Experiment No. 1-2) and the detan gum simple (Experiment No. 1-3) were highly compressed, causing bridging or scattering during discharge. Polyacrylamide simple (Experiment No. 1-4) has a small difference angle, low compression, and is difficult to fly. Although the difference angle between the simple methylcellulose (Experiment No. 1-5) and the simple antifoam (Experiment No. 1-6) is small, the degree of compression is low and the amount of scattering is large. When the amount of talc is 41 to 95 parts (Experiment No. 1-7 to Experiment No. 1-13), the larger the talc amount, the larger the difference angle, the lower the degree of compression, and the smaller the talc amount, Is small, the degree of compression is high, and the amount of scattering increases. As a result, the amount of talc is preferably 42 to 90 parts from the viewpoint of powder characteristics.
In addition, the dust reducing agent for comparison (Experiment No. 1-42 and 1-43) has a high differential angle, high compressibility, and is easy to scatter, so it can adhere to other machines or to the floor. There is a risk that workers may slip and fall.

"Experimental example 2"
Add 0.1 part of the dust reducing agent shown in Table 1 to 200 parts of cement, add 120 parts of water, add 120 g of water and mix for 10 seconds with a three-one motor to prepare a cement paste, 30 seconds after adding water Table 3 shows the viscosity of the cement paste at 30 minutes and 60 minutes.

<Materials used>
Cement: Ordinary Portland cement (specific gravity: 3.15, manufactured by Denki Kagaku Kogyo)

<Measurement method>
Cement paste viscosity: Using a B-type viscometer, measure the viscosity at 20 RPM, No. 5 rotor condition.

  From the results in Table 3, various simple ingredients have large viscosity changes over time. In talc, the viscosity is small. However, if the viscosity is large, there is a concern about remarkable slump down when using concrete. For this reason, Experiment No.2-2, 2-3, 2-4, 2-5 with high viscosity, Experiment No.2-36, 2-37 with a small amount of antifoaming agent, and a large amount of antifoaming agent Next, a concrete slump test was conducted using Experiments Nos. 2-40 and 2-41 and Experiment No. 2-9, which had a well-balanced result.

"Experiment 3"
Add the dust reducing agent of Table 5 to the concrete composition shown in Table 4 consisting of cement, water, fine aggregate and coarse aggregate, knead with a forced biaxial mixer for 60 seconds, 3 minutes and 30 minutes after adding water, The concrete slump of 60 minutes and the amount of air were measured, and the compressive strength at the age of 28 days was measured. Table 5 shows the results.

<Materials used>
Fine aggregate: Niigata Himekawa water system river sand (specific gravity: 2.62)
Coarse aggregate: Himekawa water crushed stone in Niigata Prefecture (specific gravity: 2.67)

<Measurement method>
Concrete slump: Conforms to JIS A1101 “Concrete slump test method”.
Concrete air volume: Conforms to JIS A1128 “Testing method of fresh concrete with air volume pressure-Air chamber pressure system”.
Compressive strength: Conforms to JIS A1108 “Compressive strength test method for concrete”.

From the results shown in Table 5, when the bentonite was simple and the dutan gum was simple, the slump was low. With the polyacrylamide simple, not only the slump was low, but also the compressive strength was lowered. In the case of methylcellulose alone, the slump remained low, but the amount of air increased and the compressive strength decreased. The well-balanced compound No.1-9 (Experiment No.3-5) maintained slump, the amount of concrete air was low, and the compressive strength was high.
Formulation No. 1-36 (Experiment No. 3-6) containing no antifoaming agent increased the amount of concrete air and decreased the compressive strength.
In addition, Formulation No.1-9 (Experiment No.3-5), 1-37 (Experiment No.3-7), 1-40 (Experiment No.3-8), 1-41 (including antifoaming agent) In Experiment No. 3-9), the amount of air is low, and the compressive strength is equivalent to that without adding a dust reducing agent. When the amount of the antifoaming agent is increased to Formulation No. 1-41 (Experiment No. 3-9), it becomes a peak and no further effect can be obtained.

"Experimental example 4"
In the same manner as in Experimental Example 3, the concrete composition shown in Table 4 was added with no dust reducing agent as Experiment No. 4-1, and 0.1 part of the comparative product dust reducing agent was added to 100 parts of cement. The experiment No.4-2 (formulation No.1-2) was added, and 0.1 part of the dust reduction agent of experiment No.4-3 (formulation No.1-9) was added to 100 parts of cement. Each 2 m ³ concrete was prepared and subjected to a concrete slump test.
After completion of the slump test, the concrete was pumped by a concrete pumping machine “MKW-25SMT” under a spraying pressure of 0.4 MPa and a spraying speed of 10 m ³ / h, and the pump pressure during pumping was monitored. .
On the other hand, the powder quick setting agent is pneumatically transferred using “NATM cleat” under a pressure of 0.5 MPa so as to be 7 parts with respect to 100 parts of cement. It was mixed with the shotcrete fed from the other side of the pipe to make a quick setting shotcrete. The concrete compressive strength, rebound rate, and amount of dust were measured for this quick setting shot concrete.
Moreover, the actual discharge was calculated from the pump operation time from the beginning to the end of spraying, and the discharge efficiency was measured. Table 6 shows.

<Materials used>
Comparison product Dust reducing agent: Dust reducing agent mainly composed of polyethylene oxide, Commercial powder quick setting agent: Denkanatomic TYPE-5, Commercial product

<Measurement method>
Slump test: Conforms to JIS A1101.
Concrete pump discharge pressure monitoring: Monitor the maximum pump pressure (MPa) during concrete discharge.
Concrete compressive strength: The compressive strength of one day of age is determined by covering the pin installed in the pullout formwork with a width of 25cm x length of 25cm from the surface of the pullout formwork with the quick setting sprayed concrete, and the pin from the back side of the formwork The pullout strength at that time was determined, and the compressive strength was calculated from the formula of (compressive strength) = (pullout strength) × 4 / (test specimen contact area). The compressive strength at the age of 28 days was determined by spraying rapidly setting sprayed concrete onto a formwork of width 50 cm x length 50 cm x thickness 20 cm. Measured and determined compressive strength.
Rebound rate: Quick setting shotcrete was sprayed on a simulated tunnel having a height of 3.5 m and a width of 2.5 m created in an arch shape with an iron plate at a pumping speed of 10 m ³ / h for 10 minutes. After that, (Rebound rate) = (Amount of quick setting sprayed concrete dropped without adhering to the simulated tunnel) / (Amount of quick setting shot concrete sprayed to the simulated tunnel) x 100 (%) did.
Dust amount: Quick setting sprayed concrete was sprayed on the simulated tunnel at a pumping speed of 10 m ³ / h for 10 minutes. Thereafter, the dust amount was measured at a fixed position of 3 m from the spraying place.
Discharge efficiency: The pump discharge setting is 10 m ³ / h, the operation time is measured, discharge efficiency (%) = (concrete consumption (m ³ ) ÷ operation time (min) ÷ 60 minutes) / pump discharge set value (m ³ / h) × 100 (%).

From the results shown in Table 6, the amount of the dust reducing agent of Formulation No. 1-9 (Experiment No. 4-3) is smaller than that of Experiment No. 4-1, which does not use the dust reducing agent. Pump pressure is low and compressive strength is equivalent.
In addition, those using other dust reducing agents decreased the discharge efficiency by 20% (Formulation No. 1-43 (Experiment No. 4-2)).
It can be seen that the product of the present invention has good discharge efficiency, low dust amount and rebound rate, and high compressive strength.

“Experimental Example 5”
As in Experimental Example 3, for each temperature condition shown in Table 7, a dust reducing agent shown in Table 7 was added to the concrete composition shown in Table 4 consisting of cement, water, fine aggregate, and coarse aggregate, and a forced biaxial mixer. Knead for 60 seconds to prepare the concrete, measure the concrete slump immediately after, and if the target slump does not become 10 ± 2 cm, add the amount of water shown in Table 7 and add it to the target slump range. The compressive strength at the age of 28 days was measured. Table 7 shows the results.

<Measurement method>
Concrete slump: Conforms to JIS A1101 “Concrete slump test method”.
Compressive strength: Conforms to JIS A1108 “Compressive strength test method for concrete”.

  From the results in Table 7, those using the dust reducing agent of Formulation No. 1-9 are less temperature dependent than Formulation Nos. 1-42 and No. 1-43 of other dust reducing agents, Slump is easily obtained, and no decrease in the compressive strength value is observed. On the other hand, when the temperature is 5 ° C. or 10 ° C., the viscosity of the concrete using the dust reducing agent of Formulation No. 1-42 or Formulation No. 1-43 increases and it becomes difficult to obtain a slump. For this reason, in order to adjust the target slump, the amount of post-added water is required, and the actual compressive strength is lowered. It can be seen that the dust reducing agent of the present invention has no problem at a temperature condition of 5 to 30 ° C.

"Experimental example 6"
As in Experimental Example 3, various dust reducing agents shown in Table 7 were added to the concrete composition shown in Table 4 consisting of cement, water, fine aggregate, and coarse aggregate, and kneaded for 60 seconds with a forced biaxial mixer. The concrete slump and air amount for 3 minutes, 30 minutes and 60 minutes after the addition were measured, and the compressive strength at the age of 28 days was measured. Table 8 shows the results.

<Comparative example>
Experiment No. 6-1: Dust reducing agent whose antifoaming agent is an alkylene oxide adduct. Other raw materials are 5 parts in 100 parts of the dust reducing agent of No. 1-9, excluding mineral oil antifoaming agent.
Experiment No. 6-2: Dust reducing agent in which the antifoaming agent is a polyether such as an ethylene oxide adduct of glycol. 5 parts in 100 parts of the dust reducing agent of Formulation No.1-9, excluding mineral oil defoamer.
Experiment No. 6-3: A dust reducing agent that is a silicone-based antifoaming agent mainly composed of dimethyl silicone. 5 parts in 100 parts of the dust reducing agent of Formulation No.1-9, excluding mineral oil defoamer.
Experiment No. 6-4: A dust reducing agent which is a trialkyl phosphate antifoaming agent mainly composed of tributyl phosphate. 5 parts in 100 parts of the dust reducing agent of Formulation No.1-9, excluding mineral oil defoamer.

  From the results shown in Table 8, compared to the concrete added with the mineral oil-based antifoaming agent, alkylene oxide adduct-based antifoaming agent, and silicone-based antifoaming agent of the present invention, when other antifoaming agents are added, It turns out that an effect is small and a concrete air amount increases that it is a compounding part, and compressive strength falls.

Compared with conventional dust reducing agents, the powdery dust reducing agent of the present invention is superior in powder pumpability, can be prevented from scattering, and blended with spray concrete to provide a high dust reducing effect. Concrete discharge efficiency equivalent to that not to be added can be obtained, and it can be widely used in the civil engineering field because it has the effect of improving workability.

Claims (7)

It contains talc, bentonite, cellulose ether, detan gum, polyacrylamide, and an antifoaming agent, and the defoaming agent is a mineral oil-based antifoaming agent, an alkylene oxide adduct-based antifoaming agent, or a silicone-based antifoaming agent. One or two or more types selected, and talc is 42 to 90 parts by mass, bentonite is 0.1 to 10 parts by mass in a total of 100 parts by mass of talc, bentonite, cellulose ether, detan gum, polyacrylamide, and antifoaming agent , 0.5-20 parts by mass of cellulose ether, 0.1-6 parts by mass of detan gum, 0.1-2 parts by mass of polyacrylamide, 0.5-20 parts by mass of antifoaming agent Dust reducing agent.   The antifoaming agent according to claim 1 is a mineral oil-based powder dust reducing agent.   The powdery dust reducing agent according to claim 1 or 2, wherein the powder has a difference angle of 15 ° or less and a compressibility of 45% or less.   The shotcrete which added the powdery dust reducing agent of any one of Claims 1-3.   The shotcrete according to claim 4, which is obtained by mixing a powder quick-setting agent.   A spraying method in which the sprayed concrete according to claim 4 is pumped and the powder quick-setting agent conveyed by compressed air from the mixing pipe is mixed and sprayed on the way.   A spraying method in which the pressure of pumping the sprayed concrete according to claim 6 is 9 MPa or less.