JP6002425B2 - How to place concrete - Google Patents

Description

  The present invention relates to a concrete placement method, and more specifically, reduces the variation in the quality of the concrete in the height direction when concrete quality is improved by using a water-permeable sheet, and provides a good quality improvement effect. The present invention relates to a concrete placing method that can be obtained.

  In recent years, various measures have been taken to improve the quality of the concrete. As one of them, a permeable mold method using a permeable sheet is known (see, for example, Patent Document 1). In this construction method, concrete is placed by attaching a water-permeable sheet combined with a nonwoven fabric or the like to the inside of a mold. Air bubbles and surplus water contained in the concrete are discharged to the outside through the water-permeable sheet due to the side pressure acting on the mold as the concrete is launched and compaction by the internal vibrator. Thereby, the surface bubbles of the concrete can be reduced and the surface layer portion of the concrete can be densified, so that the quality of the concrete is improved.

  However, in this method, since the action of the side pressure accompanying the concrete launch is utilized, the degree of quality improvement varies in the concrete launch height direction. That is, there is a variation in the density of concrete in the height direction, and in particular, there is a problem that a sufficient quality improvement effect cannot be obtained in the upper portion of the concrete where the side pressure is reduced.

JP-A-6-317011

  An object of the present invention is to provide a concrete placement method capable of reducing the quality variation in the height direction of the concrete when the quality of the surface layer is improved by using a water-permeable sheet and obtaining a good quality improvement effect. Is to provide.

In order to achieve the above object, a concrete placement method according to the present invention is a concrete placement method in which concrete is placed in a mold having a water sheet attached inside, and the concrete is placed in the mold. 30 minutes to 90 minutes after the placement is completed, an internal vibrator is inserted into at least the upper part of the concrete to vibrate, and the internal vibrator at each inserted place is vibrated. It is characterized in that the time to be set is 5 seconds to 15 seconds .

According to the present invention, since concrete is placed in a mold having a water-permeable sheet attached inside, the surface bubbles of the concrete can be reduced and the surface layer portion can be densified. Further, between 30 minutes and 90 minutes after completion of the concrete placement, an internal vibrator is inserted into at least the upper part of the concrete to vibrate, and the internal vibrator at each inserted place is vibrated. Since the time is 5 seconds to 15 seconds, it is possible to effectively discharge further bubbles and surplus water from the vibrated portion. Thereby, also about the upper part of the concrete where the side pressure which acts on a formwork becomes small, reduction of surface bubbles and densification of a surface layer part can be promoted. Therefore, it is possible to obtain a good quality improvement effect by reducing the variation in quality in the concrete height direction.

  Here, it is preferable that the concrete to be placed is within 2 hours from the kneading. If concrete is used for more than 2 hours after kneading, it will be difficult to discharge further bubbles and excess water even if it is vibrated.

  When placing concrete into a plurality of layers in the formwork, the concrete layers are laminated one after another, and after the completion of the placement of the uppermost single layer of concrete, It is also possible to vibrate by inserting an internal vibrator into the upper layer of concrete. As a result, even when the concrete is placed in a plurality of layers on the upper portion of the concrete where the side pressure acting on the mold is reduced, the reduction of surface bubbles and the densification of the surface layer can be promoted. .

  Alternatively, each time a single layer of concrete is placed on the upper side, an internal vibrator can be inserted into the single layer of concrete and vibrated 30 to 90 minutes after completion of the placement.

It is explanatory drawing which illustrates the process of revibrating concrete after completion of placement. It is explanatory drawing which illustrates the process of FIG. 1 on a plane. It is explanatory drawing which illustrates the process re-vibrated after completion of concrete placement of the 2nd layer. It is explanatory drawing which illustrates the process re-vibrated after completion of concrete placement of the 5th layer (uppermost layer). It is a graph which shows the relationship between the timing to re-oscillate, and the amount of drainage. It is a graph which shows the relationship between the up-and-down position of concrete and the air permeability coefficient which varied the timing to revibrate. It is a graph which shows the relationship between the time from concrete kneading to the start of pouring, and the amount of drainage. It is a graph which shows the relationship between the up-and-down position of the concrete and the air permeability coefficient which varied the time from kneading to placement start. It is a graph which shows pore diameter distribution of the concrete lower part. It is a graph which shows pore diameter distribution of the concrete upper part. It is a graph which shows the neutralization depth of concrete.

  Hereinafter, the concrete placement method of the present invention will be described based on the embodiments shown in the drawings. In addition, in order to avoid that the content of drawing becomes indefinite, the reinforcing bar arrange | positioned in concrete is abbreviate | omitted and does not show in figure.

  As illustrated in FIG. 1 and FIG. 2, in the present invention, a mold 1 having a water-permeable sheet 2 attached to the inside is used. As the water permeable sheet 2, a known water permeable sheet such as a non-woven sheet or a sheet formed by combining a non-woven fabric or other materials can be used.

  A predetermined amount of concrete C is driven into the mold 1. At this time, the internal vibrator 3 is inserted into an appropriate position of the concrete C into which the internal vibrator 3 is driven, and is vibrated and compacted. In the case of ordinary concrete, compaction by the internal vibrator 3 is necessary, but in the case of highly fluid concrete, such compaction work is unnecessary.

  The frequency of vibration may be a frequency generally used when the concrete C is compacted. The vibration time is, for example, about 10 seconds (5 to 15 seconds) per place. In this way, the concrete C placing is completed. In this embodiment, the concrete C is cast at a launch height H.

  Next, the internal vibrator 3 is inserted into the upper portion h of the placed concrete C 30 to 90 minutes after the completion of placing the concrete C, and is revibrated. In this embodiment, the term “re-vibration” is used because the concrete C is vibrated once in the compacting operation when placing the concrete C. When high fluidized concrete is vibrated at the time of placing and is not compacted, it is “vibrated” instead of “revibrated”.

  The upper portion h of the concrete C is, for example, a portion within about 20 cm to 30 cm from the upper end of the concrete C. As illustrated in the plan view of FIG. 2, the internal vibrator 3 is inserted and revibrated at necessary positions (a plurality of positions) so that the revibration extends over the entire plane.

  The frequency of re-vibration may be a frequency generally used when the concrete C is compacted. The re-vibration time is, for example, about 10 seconds (5 to 15 seconds) per place. In this embodiment, only the upper part h of the placed concrete C is revibrated, but in the present invention, at least the upper part h of the concrete C is revibrated.

  In the present invention, the concrete C in the mold 1 with the water permeable sheet 2 attached to the inside is compacted and placed using the internal vibrator 3, so that the concrete C can be compared with a normal placement method. More bubbles A and excess water W can be discharged. Therefore, the surface bubbles of the concrete C can be reduced and the surface layer portion can be densified.

  Furthermore, since the internal vibrator 3 is inserted into the upper portion h of the concrete C and re-vibrated 30 minutes to 90 minutes after the completion of placing the concrete C, further bubbles are generated from the re-vibrated portion. A and excess water W can be discharged effectively. Thereby, also about the upper part h of the concrete C where the side pressure which acts on the formwork 1 becomes small, reduction of surface bubbles and densification of the surface layer part can be promoted. Therefore, it is possible to obtain a good quality improvement effect by reducing the variation in quality of the concrete C in the height direction.

  In less than 30 minutes after the completion of placing concrete C, depending on the temperature conditions, so much bleeding water is not generated, so even if it is revibrated, the surface layer cannot be highly densified. Since more than 90 minutes after the placement is completed, the hardening of the concrete C proceeds, so even if the internal vibrator 3 is used, it becomes difficult to discharge further bubbles A and excess water W. Therefore, it is effective to revibrate 30 to 90 minutes after the completion of placing concrete C.

  As the concrete C to be cast, it is preferable to use concrete within 2 hours from kneading to the start of casting. This is because, when the concrete is used for more than 2 hours after kneading, since the curing is advanced, it is difficult to discharge further bubbles A and surplus water W even if the vibration is revibrated.

  3 and 4, the present invention is applied, and concrete C is placed in a plurality of layers (first layer C1 to fifth layer C5) in a mold 1 in which a water-permeable sheet 2 is bonded to the inside. The case where it does is illustrated. That is, this is an embodiment when the launch height H is high.

  First, an amount of concrete C corresponding to the first layer C1 is driven into the mold 1. At this time, the internal vibrator 3 is inserted into the driven first layer C1 and vibrated and compacted to complete the placement of the first layer C1. The launch height of each of the first layer C1 to the fifth layer is about 40 cm to 100 cm.

  Next, an amount of concrete C corresponding to the second layer C2 is driven into the mold 1. At this time, the internal vibrator 3 is inserted into the driven second layer C2, vibrated and compacted to complete the placement of the second layer C2. Between 30 minutes and 90 minutes after the completion of the placement, as illustrated in FIG. 3, the internal vibrator 3 is inserted into the second layer C2 and revibrated. The re-vibration procedure is the same as in the previous embodiment.

  Next, concrete C is placed in the same manner for the third layer C3, the fourth layer C4, and the fifth layer C5 in order, and re-vibrated 30 to 90 minutes after the placement is completed. The fifth layer C5 will be described. The amount of concrete C corresponding to the fifth layer C5 is driven into the mold 1 and the internal vibrator 3 is inserted into the driven fifth layer C5 to vibrate and compact. This completes the placement of the fifth layer C5. Between 30 minutes and 90 minutes after the placement is completed, as illustrated in FIG. 4, the internal vibrator 3 is inserted into the fifth layer C5 and revibrated. That is, every time one layer of concrete C is placed on the upper side, the internal vibrator 3 is inserted into the one layer of concrete C 30 to 90 minutes after the placement is completed, and is vibrated again.

  As a result, even when the concrete C is placed in a plurality of layers on the upper portion h of the concrete C where the side pressure acting on the mold 1 is reduced, the air bubbles A are further removed from the revibrated portion. And the excess water W can be discharged effectively. Therefore, it is possible to promote reduction of surface bubbles of the concrete C and densification of the surface layer portion.

  In addition, when placing concrete C into a plurality of layers in the mold 1 with the water-permeable sheet 2 attached to the inside, it is not always necessary to vibrate each time each layer is placed. In this case, the concrete C is placed by compaction using the internal vibrator 3 for each layer, the layers of the concrete C are sequentially stacked, and the top layer (C5) of concrete is placed. Between 30 minutes and 90 minutes after completion, as illustrated in FIG. 4, the internal vibrator 3 is inserted into the uppermost layer of concrete (C5) and revibrated.

  Test specimens (200 mm in length, 200 mm in width, 500 mm in height) were made of concrete with the composition shown in Table 1 using a wooden formwork as shown in Table 2, and the measurement of water discharge and air permeability test. Was done.

This concrete was ordinary concrete with a slump of 10 cm. Cement is ordinary Portland cement (density 3.16 g / cm ³ ), S1 is Kimitsu land sand (surface dry density 2.62 g / cm ³ , coarse grain ratio 2.58), S2 is Kodama mountain sand (surface dry density 2 .59 g / cm ³ , coarse particle ratio 2.74), G1 is crushed stone from Ome City (surface dry density 2.68 g / cm ³ , coarse particle ratio 6.97), G2 is crushed stone from Ome City (surface dry density 2 .67 g / cm ³ , coarse particle ratio 6.11), and a lignin sulfonic acid AE water reducing agent was used as an admixture.

The test body was prepared by laminating two layers having a height of 250 mm using concrete for 30 minutes after kneading. Each layer was placed by compaction using an internal vibrator. When re-vibrating, the internal vibrator was inserted to a depth of 400 mm and a vibration of 10 seconds per place was given (total of 5 places). After curing the concrete, the top end face was sealed and the side formwork was kept until the age of 5 days, and then the room was cured in the air.
[Measurement of amount of drainage] The mass of water discharged from the lowermost surface of the mold after the concrete was placed was measured.
[Air permeability test] The Trent method was used. The measurement positions are 100 mm and 400 mm from the bottom surface of the test body.

  FIG. 5 shows the result of the drainage measurement, and FIG. 6 shows the result of the air permeability test. From this result, it is understood that drainage is promoted and the air permeability coefficient is improved when revibrating between 40 minutes and 90 minutes after completion of the concrete placement. In addition, when re-vibrated 30 minutes after completion of placing concrete, the amount of drainage is increased by about 10%, and the air permeability coefficient is slightly reduced compared to when re-vibrated 40 minutes after completion of placing. I have confirmed that.

  Moreover, with the concrete of the mixing | blending shown in Table 1, using the wooden formwork which stuck the water-permeable sheet | seat inside, as shown in Table 3, the time from a kneading up to start of placement was varied, and a test body (length 200mm, 200 mm in width and 500 mm in height) were prepared, and the amount of drainage and the air permeability test were performed. Re-vibration of the test specimen is 40 minutes after the placement is completed, and other production conditions are the same as described above.

  FIG. 7 shows the result of the drainage measurement, and FIG. 8 shows the result of the air permeability test. From this result, it is understood that if concrete within 2 hours from the kneading is used, drainage is promoted by re-vibration and the air permeability coefficient is improved.

Furthermore, test specimens (200 mm long, 400 mm wide, 500 mm high) were made of concrete having the composition shown in Table 1 using a wooden formwork as shown in Table 4, and pore diameter distribution measurement and An accelerated neutralization test was conducted. The test body was produced by laminating two layers having a height of 250 mm. Each layer was placed by compaction using an internal vibrator. Forty minutes after the completion of the placement, the internal vibrator was inserted to a depth of 400 mm to give a vibration of 10 seconds per place (total of 6 places). The test specimen was made of concrete for 30 minutes after kneading, and the other production conditions were the same as described above.
[Measurement of pore size distribution] Measured by mercury porosimetry.
[Accelerated neutralization test] The test was carried out in accordance with JIS A 1153.

  The results of the pore size distribution measurement are shown in FIGS. From this result, it can be seen that the amount of pores in the range of pore diameters of 0.06 μm to 2 μm is reduced by using the water-permeable sheet regardless of the height position. Moreover, it is thought that the amount of pores has decreased by re-vibration in the upper part of the specimen.

  The results of the accelerated neutralization test are shown in FIG. From this result, it is understood that the neutralization depth of the concrete is reduced by using the water-permeable sheet, and the neutralization depth is further reduced by re-vibration. In particular, it can be seen that the quality improvement effect of the neutralization depth due to re-vibration is large in the upper part of the specimen.

DESCRIPTION OF SYMBOLS 1 Formwork 2 Water-permeable sheet 3 Internal vibrator C, C1, C2, C3, C4, C5 Concrete A Bubble W Excess water

Claims (4)

In a concrete placement method in which concrete is placed in a formwork with a water permeable sheet attached to the inside, the concrete is placed in the formwork, and between 30 minutes to 90 minutes after completion of the placement. The concrete is characterized in that an internal vibrator is inserted into at least the upper part of the concrete to vibrate, and the time for which the internal vibrator is vibrated at each inserted place is set to 5 to 15 seconds. Placement method.   The concrete placement method according to claim 1, wherein the concrete to be placed is concrete within 2 hours after being kneaded.   When placing concrete into a plurality of layers in the formwork, the concrete layers are laminated one after another, and after the completion of the placement of the uppermost single layer of concrete, The method for placing concrete according to claim 1 or 2, wherein an internal vibrator is inserted into the upper layer of concrete to vibrate.   4. The concrete according to claim 3, wherein each time one layer of concrete is placed on the upper side, an internal vibrator is inserted into the first layer of concrete for 30 to 90 minutes after the placement is completed. Placement method.

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