JP4987217B2 - Method for preparing wet spray concrete - Google Patents

Description

  The present invention relates to wet spray concrete using coal ash generated in a coal-fired power plant or the like.

  Conventionally, as spray concrete for lining a wall excavated by a tunnel excavator, concrete obtained by kneading cement, aggregate, and water at a predetermined blending ratio has been used. Aggregate is an expensive material, so coal ash generated in thermal power plants etc. is used in large quantities (1 to 2 times the amount of cement) to reduce the amount of cement and aggregate used. The intended wet spray concrete is employed (see, for example, Patent Document 1).

JP 2000-247715 (pages 2 to 4).

  According to the spray concrete using the above coal ash, when it is sprayed on the wall surface of tunnel excavation, it can secure the same strength as the conventional spray concrete made of cement, aggregate and water, and further rebound. It has the advantage that the amount of dust generated can be reduced, but because the mixing amount of coal ash with respect to the cement amount is as high as 1 to 2 times, the viscosity of the spray concrete becomes high and the fluidity is high There is a problem that pulsation occurs when pumping concrete for spraying or the pipe line is clogged and spraying work cannot be performed smoothly.

  For this reason, chemical admixtures such as polycarboxylic acid and naphthalene sulfonic acid are added as fluidizing agents (water reducing agents) for spray concrete, but such chemical admixtures are more expensive than cement, Therefore, not only is the construction cost high, but in order to obtain a predetermined fluidity, the addition amount of the chemical admixture and the accuracy of the kneading process are required, and the spraying concrete has a stable transportability. There was a problem that it was difficult to obtain.

  The present invention has been made in view of the above problems, and its object is to have the same strength as conventional products without using a chemical admixture and to reduce the amount of rebound and dust generated. It is in providing the concrete for wet spraying which can aim at and can have the stable conveyance property.

In order to achieve the above object, the spray concrete of the present invention, as described in claim 1, is a wet spray concrete obtained by kneading cement, coal ash, fine aggregate, coarse aggregate, water, coal ash the sum of the amount of cement and coal ash per concrete 1 m ³ using a 380~420Kg without classifying those generated by the dust collection in thermal power plants, and, mixing ratio of cement and coal ash the weight ratio of 75: 25 to 65: Yes as 35, further, the amount of the coarse aggregate, along with a concrete 1 m ³ per 0.26～0.28M ^3, the amount of water, the amount of cement and coal ash 45 to 60% by weight with respect to the total of the above, and is characterized by being adjusted to a predetermined slump value by adding water without adding a fluidizing agent .

The total amount of cement and coal ash per 1 m ^{3 of} concrete, that is, the total amount of powder is in the range of 380 to 420 kg, and the blending ratio of cement and coal ash is 75:25 to 65:35 by weight ratio. In addition, since it is adjusted to a predetermined slump value by adding water without adding a fluidizing agent , an inexpensive spraying concrete can be provided, and further, the initial required as a spraying concrete can be provided. In addition to stable strength and long-term strength, when spraying on tunnel excavation walls, etc., with a spraying machine, it exhibits smooth transportability without causing pulsation or blockage of pipelines In addition, uniform spraying of concrete is possible throughout the four seasons, so that the efficiency of spraying work can be improved and an accurate spraying layer can be formed. Moreover, the concrete slump required for spray construction can be obtained without increasing the amount of water added.

  Describing the best mode for carrying out the present invention, the wet spray concrete of the present invention comprises coal ash generated in a coal-fired power plant, cement, fine aggregate, coarse aggregate, and water in predetermined amounts. However, if the blending amount of coal ash is greater than the blending amount of cement, the viscosity of the concrete for spraying will increase, causing pulsation during spraying with a sprayer, While there is a risk of clogging and the strength after spraying decreases, if the blending amount is small, the viscosity of the spray concrete decreases and rebound occurs during spraying, resulting in poor adhesion to the wall. And the blending ratio of coal ash is in the range of 75:25 to 65:35 by weight.

Furthermore, if the total amount of the cement and coal ash per 1 m ^{3 of} concrete (total powder amount) becomes too large, the transport resistance of the spraying concrete in the pipe line of the spraying machine will increase and smooth. While spraying cannot be performed, the strength after spraying decreases if the amount is too small, so the total amount of powder is set to 380 to 420 Kg / m ³ .

  The cement to be used is not particularly limited, and ordinary portland cement, early strength, super early strength portland cement, and the like are used. Further, sand having a maximum particle size of 5 mm or less such as river sand and crushed sand is used as the fine aggregate, and river gravel and crushed stone having a diameter of 5 to 15 mm are used as the coarse aggregate.

Materials other than the cement and coal ash, that is, the blending ratio and blending amount of fine aggregate and coarse aggregate are not particularly limited, but the amount of fine aggregate used should be reduced according to the blending amount of coal ash. Can do. Furthermore, the blending amount of water causes pulsation and clogging when spraying concrete obtained by kneading this water with the cement, coal ash, fine aggregate, and coarse aggregate is sprayed by a spraying machine. Furthermore, when it sprays on a wall surface, it is set so that it may become a slump value which does not dripping the concrete for spraying along a wall surface. In this case, as described above, the total amount of cement and coal ash per 1 m ³ of concrete is 380 to 420 Kg, and the ratio of cement and coal ash is 75:25 to 65:35 by weight. Therefore, initial strength and long-term strength can be expressed without adding a fluidizing agent as described later.

  When spraying this spraying concrete onto the tunnel excavation wall surface to form a concrete lining, spraying with a constant amount of quick setting material per unit time at the mouth of the nozzle of the spraying machine while spraying Construction is performed. At this time, if the discharge amount per unit time of the spraying concrete from the spraying machine is small, the addition rate of the quick setting material added to the spraying concrete increases and the initial strength becomes too high. However, when the amount of sprayed concrete per unit time from the spraying machine is large, the proportion of the quick setting material added to the spraying concrete decreases. Although the initial strength is insufficient and the concrete sprayed on the wall surface hangs down, in the present invention, the pulsation and clogging of the spray concrete does not occur, and it does not sag when sprayed on the wall surface. An initial strength can be developed.

The amount of quick setting material added to spraying concrete varies depending on the type of quick setting material, so it cannot be determined uniquely. However, when using calcium aluminate type quick setting material, 1 m ^{3 of} spraying concrete is used. It is desirable to add 18 to 30 kg per unit, more preferably 22 to 26 kg. In addition, coal ash generated at a thermal power plant and collected is used without being classified. Next, the present invention will be described in more detail with reference to examples of the present invention and comparative examples.

[Example 1]
Spray concrete was prepared by kneading water 210 Kg / m ³ , cement 271 Kg / m ³ , coal ash 117 Kg / m ³ , fine aggregate 970 Kg / m ³ , and coarse aggregate 737 Kg / m ³ .

[Example 2]
Water 196 Kg / m ^3, the cement 280 Kg / m ^3, coal ash 120 Kg / m ^3, fine aggregates 1004Kg / m ^3, to prepare a spray concrete by kneading coarse aggregate 747 Kg / m ^3.

Example 3
Spray concrete was prepared by kneading 208 Kg / m ^{3 of} water, 288 Kg / m ^{3 of} cement, 124 Kg / m ^{3 of} coal ash, 978 Kg / m ^{3 of} fine aggregate, and 737 Kg / m ^{3 of} coarse aggregate.

[Comparative Example 1]
Spray concrete was prepared by kneading water 241 Kg / m ³ , cement 180 Kg / m ³ , coal ash 180 Kg / m ³ , fine aggregate 883 Kg / m ³ , and coarse aggregate 656 Kg / m ³ .

[Comparative Example 2]
Water 212 Kg / m ^3, the cement 252 Kg / m ^3, coal ash 108 Kg / m ^3, fine aggregates 1043Kg / m ^3, to prepare a spray concrete by kneading coarse aggregate 655 Kg / m ^3.

[Comparative Example 3]
Spray concrete was prepared by kneading water 206 Kg / m ³ , cement 228 Kg / m ³ , coal ash 152 Kg / m ³ , fine aggregate 969 Kg / m ³ , and coarse aggregate 737 Kg / m ³ .

[Comparative Example 4]
Water 218 Kg / m ^3, the cement 336 Kg / m ^3, coal ash 84 kg / m ^3, fine aggregates 922 Kg / m ^3, to prepare a spray concrete by kneading coarse aggregate 745Kg / m ^3.

[Comparative Example 5]
Water 198 Kg / m ^3, the cement 280 Kg / m ^3, coal ash 160 Kg / m ^3, fine aggregates 1015Kg / m ^3, to prepare a spray concrete by kneading coarse aggregate 692 Kg / m ^3.

In Examples 1 to 3 and Comparative Examples 1 to 5 described above, the unit of each material used represents the weight per 1 m ³ of spraying concrete, and further, blending of materials other than cement and coal ash The ratio of coarse aggregate is 0.26-0.28m ³ / m ³ , water / (cement + coal ash) is 45-60% by weight, and the rest is fine aggregate, and the slump value of spray concrete is It was set to be approximately 10 cm. The material used was ordinary Portland cement with a specific gravity of 3.16. The specific gravity of coal ash was 2.20, the specific gravity of fine aggregate was 2.56 to 2.62, and the specific gravity of coarse aggregate was 2.64 to 2.71.

Concrete lining is carried out by pumping the spray concrete obtained in Examples 1 to 3 and Comparative Examples 1 to 5 with a pump to a spray machine at a predetermined pressure and spraying the spray concrete onto the tunnel excavation wall surface. gave. Conveyability in the pipeline until spraying from the spraying machine at that time, and rebound of the spraying concrete from the wall surface generated at the time of spraying, that is, when there is some rebound and 24 hours have passed after spraying Strength and strength after 4 weeks were measured. The results are shown in Table 1. The addition amount of the rapid setting material to be added to the shotcrete is a concrete and quick-member to adjust the discharge amount so that the spray concrete m ³ per 22～26Kg, about 3m short of the blowing port And mixed with a Y-tube.

In Table 1 above, the total powder amount is the sum of the blending amounts of cement and coal ash, and the coal ash ratio is the ratio of the coal ash blending amount to the total powder amount. Also, the required strength is 5 N / mm ² or more for the purpose of preventing dripping at the 24-hour strength (strength after 24 hours), covering the tunnel wall surface reliably, and preventing the wall from collapsing due to weathering. The week strength (strength after 4 weeks) was set to 18 N / mm ² or more for the purpose of exerting a support function against external pressure (external force).

As is apparent from Table 1, when the total amount of powder is 360 kg / m ³ (Comparative Examples 1 and 2), it is necessary in Comparative Example 2 where the ratio (mixing ratio) of coal ash to cement is 3: 7. Although the strength is reached, the strength is reduced in Comparative Example 1 in which the ratio of coal ash to cement is 5: 5. However, even if the ratio of coal ash to cement is 3: 7 as in Comparative Example 2, the total strength may be just below the required strength when the total amount of powder is 360 kg / m ³ , and it can be said that the required strength is stable and sufficient. I don't get it.

On the other hand, in Examples 1-3, even if the ratio of coal ash and cement is 3: 7, if the total powder amount is increased to the range of 388-412 Kg / m ³ , the variation at the time of spraying on site Considering the above, it is possible to provide a margin for the required strength for both the 24-hour strength and the 4-week strength. However, when the total amount of powder is decreased, the strength is reduced as described above. On the other hand, when the total powder amount is increased, the conveyance resistance in the passage for supplying the spray cement to the spray machine as shown in Comparative Example 5 ( is circulation of spray cement) is increased and can not be performed smoothly spraying construction, to enable smooth spray construction may need to be increased to 18 about the slump value 10 by adding a fluidizing agent Therefore, in the present invention, it is essential to keep the total powder amount within the range of 380 to 420 kg / m ³ .

  Further, when the ratio of coal ash to cement is 2: 8, the rebound amount in spraying increases as is clear from Comparative Example 4, while when the ratio of coal ash to cement is 4: 6, Since the strength is reduced for 24 hours by increasing the amount of ash, in the present invention, it is essential that the ratio (mixing ratio) of coal ash to cement is 75:25 to 65:35 by weight.

Further, looking at the amount of construction materials other than coal ash and cement of Example 1-3, the coarse aggregate 0.26~0.28m ³ / m ^3, ratio of water to Sokonatai weight 49 to 54 wt% Met. This ratio is 45 to 60% by weight in consideration of workability including strength development and transportability.

Next, FIG. 1 to FIG. 4 show the strength results of adopting the spray concrete of Examples 1 and 2 for actual tunnel construction and spraying the excavated wall surface throughout the year according to the tunnel excavation. 1 and 2 show the 24-hour intensity and 4-week intensity in Example 1, respectively, and FIGS. 3 and 4 show the 24-hour intensity and 4-week intensity in Example 2, respectively. In these embodiments, the required strength, i.e., 24 hours strength (strength after 24 hours) in 5N / mm ² or more, a 4-week strength (4 weeks strength after) the 18N / mm ² or more strength Had. The strength varies throughout the year and may slightly exceed the required strength, but the required strength is increased by increasing the total powder amount of cement and coal ash to 380 Kg / m ³ or more. The effect is surpassed.

It is a construction day -24 hour strength result figure in Example 1. FIG. It is a construction day -4 week intensity | strength result figure in Example 1. FIG. It is a construction day-24 hour strength result figure in Example 2. It is a construction day -4 week intensity result figure in Example 2.

Claims (1)

In wet spray concrete made by mixing cement, coal ash, fine aggregate, coarse aggregate, and water, coal ash is generated from a thermal power plant and collected without being classified, per 1 m ^{3 of} concrete. The total blending amount of cement and coal ash is 380 to 420 kg, the blending ratio of cement and coal ash is 75:25 to 65:35 by weight, and the blending amount of coarse aggregate is concrete with 1m is a ³ per 0.26～0.28M ^3, the amount of water is 45 to 60 wt% on the sum of the amount of cement and coal ash, by the addition of water without the addition of fluidizing agents A concrete for wet spraying characterized by being adjusted to a predetermined slump value .

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