JPH11180743A - Shot concrete admixture and shot concrete using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a shot concrete having excellent workability such as pump forcible feeding property, sticking property and dust reducing and excellent strength exhibiting property by blending fine powder of a fly ash discharged in a coal combustion and classified as it is without being pulverized. SOLUTION: The fly ash discharged in the coal combustion is classified as it is without being pulverized to obtain the fine powder having particle diameter of <=20 μm and having a smooth and nearly spherical shape as a shot concrete admixture. The shot concrete is obtained by replacing <=30% of cement or a fine aggregate in a shot concrete for spraying a kneaded material composed of at least cement, a fine aggregate and a coarse aggregate with a spray machine by the admixture of the fly ash fine powder. A commercial accelerating agent can be used in the shot concrete and also a commercial high performance water reducing agent or high performance AE water reducing agent can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spraying concrete admixture to be added to at least a material comprising cement, fine aggregate and coarse aggregate, and a spraying concrete using the admixture. For details, pump pumpability suitable for the spraying method using a spraying machine,
The present invention relates to a concrete admixture for spraying and a concrete for spraying, which are excellent in workability such as adhesion and dust reduction and in developing strength.

[0002]

2. Description of the Related Art Conventionally, shotcrete has been used for the protection of walls and slopes of tunnels and slopes, as well as for fire-resistant coatings of concrete structures such as chimneys, etc., to prevent dripping and falling off of concrete. In order to do this, we add a quick-setting agent to the ready-mixed concrete just before spraying and spray it, or add water to a dry-mix concrete material to which a quick-setting agent has been added before spraying. The dry spray concrete method is used.
These shotcrete construction methods have problems such as a large amount of dust generated during spraying, which deteriorates the working environment, and rebounds and spalls, resulting in reduced workability and economy.

In order to solve the above-mentioned problems, Japanese Patent Laid-Open No.
57147 discloses a technique for improving the adhesion of shotcrete to a spring spray face from the material side to reduce rebound, reduce the amount of quick-setting agent added, and improve pumpability. 10-2 of fine aggregate in shotcrete
A concrete in which 0% by volume is replaced with fly ash has been proposed.

Further, Japanese Patent Application Laid-Open No. 8-295550 discloses a technique for obtaining high-performance shotcrete excellent in pumping property, adhesion, dust reduction property and short and long-term strength. Concrete has been proposed in which 3 to 20 parts by weight of calcium carbonate, fly ash, stone powder, granulated blast furnace slag, etc. are added to the parts by weight.

[0005]

However, in the former case,
The quality of fly ash discharged from coal-fired power plants, such as the particle size, fineness, and unburned carbon, varies depending on the place of origin, combustion temperature, and combustion equipment. In the case of mixing, the unit water amount, air entrainment, adhesion, dust generation amount, strength development, and the like fluctuate, and it is necessary to take countermeasures.

[0006] In the latter case, calcium carbonate, stone powder, granulated blast furnace slag, and the like have a poor particle shape.
The unit water volume is greatly increased, and the setting time is delayed or the strength development is reduced.

Therefore, these means can improve the workability such as pumping property, adhesion, dust reduction property and the like of the shotcrete to some extent and the strength development, but cannot obtain a sufficiently satisfactory effect. Can not.

Accordingly, the present invention provides a sprayable concrete admixture and a sprayable concrete which improve the workability and the strength development of the sprayable concrete, such as pumpability, adhesion and dust reduction. I am aiming.

[0009]

In order to achieve this object, an object of the present invention is to provide a spraying concrete which is a fine powder mixed at least in a material consisting of cement, fine aggregate and coarse aggregate. The admixture, wherein the fine powder is a fly ash discharged at the time of coal combustion, is classified as it is without crushing, and is obtained by this classification, and is a concrete admixture for spraying, which is obtained by the classification. .

[0010] Further, in the invention of claim 2, according to claim 1, the fine powder is a concrete admixture for spraying, characterized in that the fine powder has a particle diameter of 20 µ or less.

[0011] The invention of claim 3 is a spray concrete for kneading at least a material consisting of cement, fine aggregate and coarse aggregate and performing spraying using a spraying machine. The fly ash discharged during coal combustion is classified without pulverization as it is, and a fine powder obtained by the classification is blended into the spray concrete.

The invention of claim 4 is the spraying concrete according to claim 3, wherein the fine powder is replaced with at least one of the cement and the fine aggregate.

According to a fifth aspect of the present invention, in the fourth aspect, the fine powder is a powder of the cement or the fine aggregate.
This is a shotcrete characterized by being replaced with 0% by weight or less.

Further, in the invention of claim 6, according to claim 3, the fine powder has a particle diameter of 20 μm or less, which is a concrete for spraying.

[0015]

[Function] Fly ash that has been classified without being crushed contains a large number of particles having a desired size and a curved surface instead of an angular shape, so that when the kneaded concrete is sprayed by a spraying machine. However, compared to fine aggregate, the particle size is smaller, and it is smoother and closer to a sphere, so the fluidity increases even if the viscosity increases, it can be sprayed easily, it is hard to drop even after spraying and it solidifies quickly Can be achieved.

Hereinafter, the present invention will be described in detail.

Concrete is made of at least cement, fine aggregate and coarse aggregate, and additives and the like are added depending on the use. When spraying concrete, it is necessary to ensure fluidity in the spraying system during spraying, but after spraying, the fluidity is reduced, so that the initial strength comes out as soon as it is hardened. The admixture, which is a fine powder, is added in order to prevent the concrete from coming off.

This spray concrete admixture focused on fly ash discharged during coal combustion. The fly ash has a smooth curved surface without any sharpness as if the fine powder was crushed in production. Therefore, the fly ash used can be reduced to a desired size of 20 microns, 10 microns or 5 microns without being crushed.
Classified by micron.

The shotcrete of the present invention is obtained by substituting 30% by weight or less of the fine aggregate mixed in the concrete with fly ash, which is the above-mentioned fine powder. %, Preferably 10 to 20%
% Is most preferred. If the replacement ratio of the fine powder is less than 3% by weight, the adhesion of the spraying concrete and the effect of reducing the dust are not sufficiently exhibited, and if it exceeds 30% by weight, the unit water amount and the viscosity of the concrete increase, and the pumping property and strength are increased. Expression may be reduced. Further, the replacement ratio of the fine powder to the fine aggregate is in the range of 3 to 30% by weight.
An optimum value can be selected according to the quality such as the particle size and the fine particle content.

Further, the shotcrete of the present invention has a content of 30% by weight of cement mixed in the concrete.
The following are substituted by the fine powder described above, preferably 20% by weight or less, particularly preferably 15% by weight or less. If the replacement ratio of the fine powder exceeds 30% by weight, the short-term strength development of the sprayed concrete tends to decrease. Further, the replacement ratio of the fine powder with respect to the cement can be selected from an optimum value according to a desired strength within a range of 30% by weight or less.

The spray concrete admixture of the present invention has a particle size of 20 μm without crushing fly ash.
Is a fine powder classified below. Fine powder can be obtained by pulverizing fly ash discharged during coal firing, by means of air classification, stepwise collection in an electrostatic precipitator, electrostatic separation, or the like, by 20μ, 10μ, or 5μ.
It is a fine powder containing a large amount of spherical particles obtained by classification by the method described above, and there is no particular limitation on the classification point and the lower limit of the particle diameter, and specifically, those described in Japanese Patent Publication No. 2-49264. Can be exemplified.

The concrete admixture for spraying according to the present invention is used as a part of fine aggregate and / or cement mixed with the concrete for spraying.

The spraying concrete used in the present invention is a concrete containing at least cement, fine aggregate and coarse aggregate, and if necessary, concrete containing water, a high-performance water reducing agent and a cement concrete admixture. The quick-setting agent is not necessarily added when spraying the slope.

Examples of the cement used in the present invention include, but are not particularly limited to, various types of Portland cement, such as ordinary and early strength, and various types of mixed cement obtained by mixing fly ash, blast furnace slag, and silica.

Examples of the fine aggregate used in the present invention include river sand, crushed sand, mountain sand, land sand, sea sand, and the like. The amount of the fine aggregate is not particularly limited, and is appropriately selected by a test. . In addition, coarse aggregate is generally 15 m in maximum size in consideration of adhesion and rebound of spraying concrete.
m or less are preferably used, but there is no particular limitation.

The shotcrete of the present invention may use a quick setting agent generally commercially available as calcium aluminate, calcium sulfoaluminate, calcined bright bun, alkali aluminate and the like. it can. The amount of the quick setting agent varies depending on the type. In the case of the calcium aluminate type and the calcium sulfoaluminate type quick setting agent, 3 to 10% based on the weight of the cement.
In the case of the calcined light bang type and the alkali aluminate type, the content is preferably 3 to 8% based on the weight of cement.

The concrete for spraying of the present invention is intended to reduce the unit water content and to improve the quality and the initial and long-term strength development properties of the salt of formalin condensate of naphthalenesulfonic acid and formalin melaminesulfonic acid. A commercially available high performance water reducing agent or a high performance AE water reducing agent containing a polycarboxylate as a main component can be used. There is almost no decrease in slump (value for measuring the softness of concrete) during transportation, which is preferable. The shotcrete of the present invention can also be used together with cement concrete admixture materials such as calcium carbonate, stone powder, blast furnace slag powder, and silica fume, if necessary.

[0028]

Embodiments will be described below.

1. Mortar test 1) Materials used Table 1 shows the materials used for the mortar test.

[0030]

[Table 1] 2) Mixing and kneading of mortar The mixing of mortar used in the test is as shown in Test No. 1 shown in Table 2.
The S (fine aggregate) / C (cement) of ~ 16 is constant at 3.0, and the W (water) / C of test No. 1 is 50.0%,
The W / C of Test Nos. 2 to 16 was changed so that the flow obtained in Test No. 1 was within the range of ± 5 mm. The amount of quick-setting agent (QP) used is 6% based on cement weight in the case of fine aggregate replacement, 6% based on (cement + fine powder) in the case of cement replacement, and the test NO. .1-14 are
A high performance water reducing agent (NT) was used at 0.7% based on the weight of cement or (cement + fine powder). The mortar kneading temperature was 19.0 to 19.5 ° C.

The mortar is mixed according to JIS R520
1 Using a mixer specified in “Physical test method of cement”, after charging all the materials except for the quick setting agent, continuously for 3 minutes at low speed, then knead (statically) for 15 minutes, then quick set. The agent (QP) was added and kneaded for 20 seconds.

3) Test method (1) Flow JIS R 5201 “Physical test method of cement” 1
0.7 Depends on how the flow value is measured.

(2) Setting time According to JIS A 6204 "Chemical admixture for concrete" Appendix 1 Concrete setting time test method.

(3) Compressive strength The test specimen for compressive strength was a prism of 4 × 4 × 16 cm, and was vibrated on a shaking table, tamped with a ram, and finished smoothly with a trowel. Test material age is 3 and 24 hours,
The test specimen was cured in a curing room at 20 ° C. and 80% RH until a predetermined time.

The compressive strength is in accordance with JIS A 1114 “Test method for compressive strength of concrete using beam sections”.

4) Test results The test results with the mortar are shown in Table 2. In the table, Test No. 1 (Comparative Example), No. 2 to 6 (Example), and NO.
13-14 (comparative example), NO.15 (comparative example), NO.16
(Example) is a case where FA5, FA10 and FA20 of the present invention were replaced with fine aggregate, and Test Nos. 7 to 12 were a case where cement was replaced. Test Nos. 1 to 14 are cases where a high-performance water reducing agent was used.
Is not used. Test No.1, NO.13 and N
O.14 is a comparative example not using FA5, FA10 and FA20, and test No.13 was fly ash (JFA)
No. 14 is the case where limestone powder (CCA) was used. As a result of the test, the following findings were obtained.

(1) Flow (W / C) When FA5, FA10 and FA20 of the present invention are replaced with fine aggregate, W / C (unit water amount) at a replacement rate of 15% is as follows.
There was almost no difference due to the difference between the types, and the test NO.
Test No. 13 was slightly larger than Comparative Example 1.
(JFA) and Test No. 14 (CCA) increase significantly. In addition, the ratio of W / C tends to increase as the replacement ratio increases.

When FA5, FA10 and FA20 of the present invention were replaced with cement, W / C at a replacement ratio of 10% was used.
Is smaller in the order of FA5>FA10> FA20, and is equal to or smaller than that of Test No.1. In addition, W / C decreases as the replacement ratio increases.

(2) Setting time In the case where FA5, FA10, and FA20 of the present invention were replaced with fine aggregate, the setting time at a replacement rate of 15% did not show any remarkable difference due to the difference in type. Test No. 13 (JFA) and Test No. 14 (CCA) are significantly delayed compared to the comparative examples. Further, when the replacement ratio is 30%, there is a tendency to be delayed.

When FA5, FA10, and FA20 of the present invention were replaced with cement, the setting time at a replacement ratio of 10% was promoted in the order of FA20>FA10> FA5, and the test was conducted.
Equivalent or promoted compared to NO.1. In addition, the setting time is accelerated as the substitution rate increases.

[0041]

[Table 2] (3) Compressive strength When FA5, FA10, and FA20 of the present invention were replaced with fine aggregate, the initial stage at a replacement rate of 15% (3,24 hours)
The compressive strength showed no remarkable difference due to the difference in type, and was larger than that of the comparative example of Test No. 1,
Test No. 3 (JFA) and Test No. 14 (CCA)
Is equivalent to Further, when the substitution rate is 30%, it tends to decrease.

When FA5, FA10 and FA20 of the present invention were replaced with cement, the initial (3,24 hours) compressive strength at a replacement ratio of 10% was FA5>FA10> FA.
The number increases in the order of 20 and increases significantly as compared with Test No.1. Further, even when the replacement ratio is increased to 15%, almost no change in the compressive strength is recognized, but when the replacement ratio is increased to 30%, the compression strength decreases.

2. Spray test with concrete 1) Materials used The materials used for the spray test with concrete are shown in Table 3.
Shown in

[0044]

[Table 3] 2) Mixing and production of concrete Table 4 shows the mixing of concrete used in the spraying test. Concrete was produced at a ready mixed concrete factory. The concrete temperature is 22.0 ~
24.5 ° C.

[0045]

[Table 4] 3) Spraying machine and method (1) Spraying machine A pumping-type spreamer (trade name) manufactured by Menadia Co., Ltd. was used at a discharge rate of 8.0 m3 / hr.

(2) Quick-setting agent feeder, manufactured by Nippon Ply Glico Co., Ltd.
An f / cm 2 Q gun (trade name) was used.

(3) Spraying method The concrete pumped by a spreamer is air-conveyed, and the quick-setting agent air-conveyed by a Q gun is mixed with a Y-shaped pipe in front of the spray nozzle and sprayed on the construction surface. .

4) Test method (1) Slump According to JIS A 1101 “Slump test method for concrete”.

(2) Air volume According to JIS A 1128 “Test method for air volume of fresh concrete by pressure”.

(3) Bounce Rate The sheet was laid in the area where the bounce scattered, and after the spraying was completed, the weight of the concrete that bounced on the sheet was measured. From the total sprayed weight, the bounce rate was determined by the following formula.

Bounce rate (%) = bounce weight / total spray weight × 100 (4) Dust concentration The dust concentration is calculated by integrating the dust for one minute with a digital dust meter at a position 5 m away from the spraying point. The value was measured.

(5) Compressive strength The strength at the age of 3 and 24 hours was determined by JSCE-G 561.
Based on the "pull-out test", it was calculated from the shear strength. The strength at the age of 7 days was based on a core specimen prepared according to JIS A 1107 by preparing a panel in accordance with JSCE-G561.

5) Test Results The results of the spraying test using concrete are shown in Table 5. In Table 5, Test No. 17 is a comparative example not using FA20 of the present invention, and Test Nos. 18 to 20 were tested. , FA20
Is replaced with fine aggregate by 4, 9, 14%. As a result of the test, the following findings were obtained.

(1) Unit water amount Test Nos. 18 to 2 in which FA20 of the present invention was replaced with fine aggregate
The unit water amount of the concrete of No. 0 is smaller than that of the comparative example of Test No. 17.

(2) Pumpability The pumpability of Test Nos. 18 to 20 was good, with no pulsation observed.

(3) Bounce Rate The bounce rates of Test Nos. 18 to 20 were all the same as Test No. 1.
7 is smaller than that of Comparative Example 7, and tends to decrease as the replacement ratio increases.

(4) Amount of Dust Generated The amount of dust generated in Test Nos. 18 to 20 was the same as in Test No. 1
7 is smaller than that of Comparative Example 7, and tends to decrease as the replacement ratio increases.

(5) Compressive Strength The compressive strengths of Test Nos. 18 to 20 are greatly increased as compared with the Comparative Example of Test No. 17. At an initial age of 24 hours or less, the strength tends to increase as the replacement rate increases, and no significant difference due to the increase in the replacement rate is observed after 7 days.

[0059]

[Table 5] 3. On-site shotcrete test 1) Materials used Table 6 shows the materials used for the on-site shotcrete test.

[0060]

[Table 6] 2) Mixing and production of concrete Table 7 shows the mixing of concrete used in the on-site spray test.
Shown in The concrete was manufactured in a field plant. The concrete temperature was 24.0 ° C.

[0061]

[Table 7] 3) Spraying equipment and method (1) Spraying machine A piston type spraying machine with a discharge rate of 12.0 m3 / hr was used.

(2) Quick-setting agent feeder A screw-feeder type quick-setting agent feeder having a discharge pressure of 7.0 kgf / cm 2 was used.

(3) Spraying method The concrete pumped by a spraying machine is conveyed by air, and the quick-setting agent is mixed with a Y-shaped pipe in front of the spraying nozzle, and sprayed on the construction surface by a spraying robot. Was.

4) Test method (1) Slump According to JIS A 1101 “Slump test method for concrete”.

(2) Air volume According to JIS A 1128 “Test method for air volume of fresh concrete by pressure”.

(3) Bounce Rate The sheet was laid in a range where the bounce scattered, and after the spraying was completed, the weight of the concrete bounced on the sheet was measured. From the total spray weight, the bounce rate was determined by the following formula.

Bounce rate (%) = bounce weight / total spray weight × 100 (4) Dust concentration Dust concentration was measured using a digital dust meter. The measurement position is the center position of the tunnel 5 m away from the spraying point, and the measurement is performed immediately before the start of the spraying and every minute after the start, until the end of the spraying 5 minutes, and the average value is calculated. I asked.

(5) Compressive strength The strength at the age of 3 and 24 hours was determined by JSCE-G 561.
Based on the "pull-out test", it was calculated from the shear strength. The strength at the age of 7 days was based on a core specimen prepared according to JIS A 1107 by preparing a panel in accordance with JSCE-G561.

5) Test Results The results of the on-site spray test with concrete are shown in Table 8, in which Test No. 21 was FA20 of the present invention.
Is a comparative example in which fine aggregate is not replaced.
This is a comparative example in which fly ash (JFA) is substituted by 15%, and Test No. 23 is an example in which FA20 is substituted by 15%. As a result of the test, the following findings were obtained.

(1) Unit Water Amount The unit water amount of Test No. 23 in which FA20 of the present invention was replaced was smaller than that of Comparative Example of Test No. 21, but was lower than that of Test No. 2.
2 is larger than Test No. 21.

(2) Pumpability Test No. 21 and Test No. 22 showed slight pulsation, but Test No. 23 showed good pumpability without any pulsation.

(3) Bounce Rate The rebound rate of test No. 23 is smaller than that of the comparative example of test No. 21, but test No. 22 is larger than test No. 23.

(4) Amount of Dust The amount of dust generated in test No. 23 is smaller than that in the comparative example of test No. 21, but that of test No. 22 is larger than that of test No. 23.

(5) Compressive Strength The compressive strength of Test No. 23 is higher than that of Comparative Example of Test No. 21, but Test No. 22 is lower than that of Test No. 23.

[0075]

[Table 8]

[0076]

According to the first aspect of the present invention, by mixing fly ash that has been classified without pulverization, the pumping performance is excellent, the adhesion during spraying is improved, and the rebound rate is greatly reduced. Thus, it is possible to provide a concrete admixture for spraying, which significantly reduces dust generation and exhibits good initial and long-term strength.

The invention of claim 2 shows higher performance in addition to the effect of the invention of claim 1.

According to the third aspect of the present invention, since the admixture of the first aspect is used, a concrete for spraying having the same effect as that of the first aspect can be provided.

The inventions of claims 4 to 6 show higher performance in addition to the effects of the invention of claim 3.

Claims (6)

[Claims] 1. A spraying concrete admixture which is a fine powder mixed at least in a material comprising cement, fine aggregate and coarse aggregate, wherein the fine powder is fly ash discharged during coal combustion Characterized by being classified without pulverization as it is, and obtained by this classification. 2. The concrete admixture for spraying according to claim 1, wherein the fine powder has a particle size of 20 μm or less. 3. A spraying concrete for kneading at least a material consisting of cement, fine aggregate and coarse aggregate and performing spraying using a spraying machine, wherein the concrete is discharged into the material during coal combustion. A shotcrete characterized by classifying fly ash without pulverization as it is, and blending the fine powder obtained by the classification. 4. The shotcrete according to claim 3, wherein the fine powder is replaced with at least one of the cement and the fine aggregate. 5. The shotcrete according to claim 4, wherein the fine powder is replaced by 30% by weight or less of the cement or the fine aggregate. 6. The shotcrete according to claim 3, wherein the fine powder has a particle size of 20 μm or less.