JP2554576B2 - Centrifugal molding of concrete - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for centrifugally molding concrete.

[0002]

2. Description of the Related Art Conventionally, many concrete secondary products such as concrete pipes and concrete piles are manufactured by a centrifugal compaction method, and the process varies depending on the actual conditions of each factory. Being manufactured. (1) A step of charging the kneaded concrete material into a mold and rotating it at a low speed (around 4 G) to uniformly fill the concrete material; (2) From the above uniformly filled concrete material, Step of obtaining a concrete compact by rotating the frame at a medium speed (around 20 G); (3) High-speed rotation of the above compact (around 35-40 G)
By compacting the molded body by:

In the above step (3), the classification and dewatering of the concrete material simultaneously proceed due to the centrifugal force, whereby the compact is compacted. At this time, the concrete material is classified in the order of the concrete layer, the mortar layer, and the cement paste layer (neat layer) from the mold toward the inner surface of the molded body.

In the above centrifugal molding method, however,
With the water squeezed out as a result of the high-speed rotation, fine particles and cement particles in the concrete are discharged, and so-called slag is generated. Noro is an industrial waste whose processing is very expensive. Conventionally, as a method for reducing such slag, a method of adding a polymer flocculant or a coagulation accelerator (Japanese Patent Publication No. 53-20525, JP-A No. 61-10480).
No. 4, JP-A-3-80140) have been proposed.

[0005]

[Problems to be Solved by the Invention] However, Japanese Patent Publication No. 53-
In the method of No. 20525, since a polymer flocculant is used, there is a problem that the workability of unsolidified concrete is deteriorated, the inner surface finish is poor, and it becomes difficult to handle. Further, the coagulation accelerator specifically proposed in JP-A-61-104804 is substantially the same as the above-mentioned polymer coagulant, and cannot be said to solve the above problems. Further, Japanese Patent Laid-Open No. 3-80140 discloses centrifugal molding using a water-reducing agent and a water-soluble polymer having a relatively low molecular weight, but the water-soluble polymer is added during concrete kneading. However, the effect of reducing slag is not satisfactory.

By the way, in the method of centrifugally molding concrete, when high-speed centrifugation is performed and then it is allowed to stand, water remaining in the molded article spontaneously settles. Part of the dense layer below the inner surface may be lifted, and a phenomenon may occur in which a void is formed inside, so-called floating. Once such floating occurs, the floating portion must be peeled off, and then the portion must be treated again with mortar or the like, and repairing it requires a great deal of time and manpower.

Therefore, the present invention is intended to solve the above-mentioned problems in the conventional centrifugal molding method by investigating the kind of the polymer to be added in the centrifugal molding method of concrete and the addition timing thereof. By improving the finishability, workability and dehydratability,
An object of the present invention is to provide a method for centrifugally molding concrete that can improve productivity.

[0008]

According to the present invention, a concrete material is kneaded and charged into a mold, and then the concrete material is uniformly filled by rotating the mold at a low speed. By rotating at a high speed, then by rotating at a high speed, the concrete material is molded, and in the centrifugal molding method of concrete including the step of compacting the concrete material, after performing the kneading and before the medium-speed rotation, the concrete material is , The molecular weight is 300,000
The present invention provides a method for centrifugally molding concrete, which comprises adding a polyacrylamide partial hydrolyzate solution having a hydrolysis rate of 5,000,000 to 1,000,000 and a hydrolysis rate of 5 to 35%.

The concrete material is not particularly limited, and various kinds of Portland cement, blast furnace slag,
Examples thereof include silica admixtures.

The above polyacrylamide partial hydrolyzate (hereinafter referred to as the polyacrylamide of the present invention) has a molecular weight of 300,000 to 1,000,000, preferably 400,000 to 800,000, and is hydrolyzed. It is a partial hydrolyzate of polyacrylamide having a ratio of 5 to 35%, preferably 10 to 30%, more preferably 15 to 20%.

The polyacrylamide of the present invention has a molecular weight of
If it is lower than 300,000, the effect of addition is extremely inferior, and if it exceeds 1,000,000, the property as a polymer flocculant becomes strong and the concrete becomes stiff and compaction itself tends to be poor. Occurs. The hydrolysis rate of the polyacrylamide of the present invention is also limited to the above range, and if it deviates from the range of 5 to 35%, the effect of addition is significantly reduced.

The polyacrylamide of the present invention is prepared in advance as a solution having a concentration of about 1 to 10%, and when used,
It is preferable to add it after diluting it about 2 to 10 times with water.

The polyacrylamide of the present invention, unlike the conventionally used polymer flocculants, is readily soluble in water and has excellent stability. Therefore, as in the past,
It is not necessary to dissolve the powder at the use site using special equipment, and it can be easily added.

The addition of the polyacrylamide of the present invention is carried out after the concrete material is kneaded and before the medium speed rotation of the centrifugal molding of concrete is carried out. That is, by kneading a concrete material was introduced into a mold, concrete is uniformly filled with by low speed, then medium speed rotation, then in the step of compacting the molded body by high-speed rotation, medium speed after kneading Although it is added before the rotation, the addition effect is particularly large when it is added during low-speed rotation.

The addition amount of the polyacrylamide of the present invention is
Although it varies depending on the type of concrete material, etc., it is usually 0.005% by weight or less, preferably 0.0005 to 0.003% by weight, as a pure content, relative to the concrete material.
Particularly preferably, it is in the range of 0.001 to 0.0025% by weight. If the addition amount exceeds 0.005% by weight, the concrete becomes stiff and the compaction property remarkably deteriorates even though a polymer having a relatively low molecular weight is used.

As a method for adding the polyacrylamide of the present invention, a method of showering the liquid containing the polyacrylamide of the present invention from above when the concrete material after kneading is charged into a centrifugal molding form using a conveyor or the like, Examples of the method include spraying with a millet or a pump during low-speed centrifugal molding, but the method is not limited to these.

[0017]

[Operation] When the polyacrylamide of the present invention is added to a concrete material and subjected to high-speed centrifugation, the noro component in the concrete material has a relatively low molecular weight, and the polymer has a hydrophilicity with good reactivity with noro ( It reacts with the polyacrylamide of the invention) to form fine flocs, which are taken up inside the concrete to form a thin layer of fine particles having excellent water permeability on the inner surface. Therefore, the water in the inside is easily discharged to the outside through this layer within a relatively short time. Therefore, according to the centrifugal molding method of the present invention, the amount of slag generated in the obtained concrete product is reduced, the dehydration property is improved, and the smoothness of the inner surface is also maintained extremely well, and so-called floating occurs. Disappear.

[0018]

EXAMPLES The present invention will be described in more detail with reference to examples. Examples 1 to 2 : Centrifugal forming experiments of concrete were conducted using the concrete materials shown in the concrete recipe table of Table 1. The kneading was performed by stirring for 2 minutes with a pan mixer.

[0019]

[Table 1] In the above Table 1, W is water, C is ordinary Portland cement,
a is aggregate, S ₁ is mountain sand (specific gravity 2.43, coarse grain ratio 4.1
9), S ₂ is crushed sand (specific gravity 2.63, coarse grain ratio 3.01),
G means crushed stone (specific gravity 2.70, coarse grain ratio 5.40), and AD means cement dispersant (naphthalenesulfonic acid formalin condensate), respectively.

16 kg of the above concrete material was charged into a standard centrifugal molding mold having an inner diameter of 200 and a length of 300 mm,
Molding was performed by sequentially performing low speed rotation (5 G / 2 minutes), medium speed rotation (15 G / 2 minutes) and high speed rotation (35 G / 5 minutes).

During the above-mentioned molding process, the molecular weight of 50
Polyacrylamide partial hydrolyzate having a hydrolysis rate of 50,000 and a hydrolysis rate of 15% (hereinafter referred to as polyacrylamide A)
Was added to the concrete material in a predetermined amount (pure content) by the method described below, and the amount of slag produced after 9 minutes was examined. Next, the amount of slag produced in the case where Horiacrylamide A was not added was examined, and the slag reduction rate was examined from these comparisons. At the same time, visually and touching
The tightness of the concrete material was examined, and the difference in finishing time between the case where polyacrylamide A was added and the case where polyacrylamide A was not added was also examined. The results are shown below.

Example 1: When the concrete material after kneading was charged into a mold with a scoop, the addition amount of polyacrylamide A was 0.002.
It was added by showering so as to be 5% by weight. The reduction ratio was 83%. High-speed centrifugation time is 40%
Was reduced. Example 2: Polyacrylamide A was 0.0 at the time of low speed rotation.
025 wt% was added. The slag reduction rate was 80%, and the high speed centrifugation time was also reduced by 40%. In each case, the inner surface of the molded product was smooth, and no inconvenience such as floating was observed even when the molded product was left as it was and observed after steam curing.

Comparative Examples 1 and 2 Except that the addition timing of polyacrylamide A was changed, substantially the same experiment as in the above-mentioned Examples was conducted. These are shown as Comparative Examples 1 and 2. Comparative Example 1: Polyacrylamide A was added at a kneading amount of 0.0006% by weight to the concrete material. At this time, the slag reduction rate was 35%, and the high-speed centrifugal dehydration time was almost the same as when polyacrylamide A was not added. Comparative Example 2: Polyacrylamide A was added at 0.0025% by weight with a Hisaku at high speed rotation. Noro reduction rate is 0.1
%, And the high-speed centrifugation time is polyacrylamide A
Was the same as when no was added.

Comparative Examples 3 to 6 In the same manner as in the above Examples except that a polyacrylamide partial hydrolyzate having a molecular weight of 5,000,000 and a hydrolysis rate of 15% (hereinafter referred to as polyacrylamide B) was used. The slag reduction rate was investigated. The results are shown below, but the dehydration property was extremely poor, and in both cases, the amount of dehydration and the amount of discharge of noro were extremely small, and it was impossible to obtain the noro reduction rate on the same scale. Comparative Example 3: Polyacrylamide B was added at the time of kneading, but the concrete became stiff and it was impossible to continue the operation thereafter. Comparative Example 4: When the concrete material was charged into the mold with a scoop, polyacrylamide B was added by showering so as to be 0.0025% by weight. However, some parts were stiff and could not be sufficiently compacted. Comparative Example 5: Polyacrylamide B was 0.0 at the time of low speed rotation.
025 wt% was added. After molding, observing the inner surface,
Adhesion of coarse flocs was observed. Comparative Example 6: Polyacrylamide B was 0.0 at the time of high speed rotation.
025 wt% was added. As in Comparative Example 5 above, many deposits were observed on the inner surface of the molded product. From the results shown in Examples 1 and 2 and Comparative Examples 1 to 6, it can be seen that the centrifugal molding method of the present invention exhibits excellent effects.

Example 3 : A molecular weight of 500,000 and a hydrolysis rate of 0, 10, 1
The slag reduction rate was examined by the same method as in Example 2 except that 5,20,25,35% polyacrylamide partial hydrolyzate was used. Polyacrylamide C: 0% hydrolysis rate Polyacrylamide D: 10% hydrolysis rate Polyacrylamide E: 15% hydrolysis rate Polyacrylamide F: 20% hydrolysis rate Polyacrylamide G: 25% hydrolysis rate Polyacrylamide H: Hydrolysis rate Decomposition rate 35% The result is shown in FIG.

From the results shown in FIG. 1, the hydrolysis rate was 5 to 35.
%, Preferably 10 to 30%, more preferably 15 to
It can be seen that 20% polyacrylamide exhibits a good slag reduction rate.

Example 4 Partial hydrolyzate of polyacrylamide having a hydrolysis rate of 15% and a molecular weight of 100,000, 300,000, 500,000, 800,000, 10
Example 2 above except that those of 0,000 and 1,200,000 were used
The reduction rate was examined in the same manner as in. Polyacrylamide I: Molecular weight 100,000 Polyacrylamide J: Molecular weight 300,000 Polyacrylamide K: Molecular weight 500,000 Polyacrylamide L: Molecular weight 800,000 Polyacrylamide M: Molecular weight 1 million Polyacrylamide N: Molecular weight 1.2 million The results are shown in FIG. However, in the case of polyacrylamide N having a molecular weight of 1.2 million, it was not stiff and compacted, and thus the slag reduction rate was not obtained.

From the results shown in FIG. 2, the molecular weight was 300,0.
00 to 1,000,000, preferably 400,000
It can be seen that a polyacrylamide of ˜800,000 shows a good reduction rate.

Example 5 : A polyacrylamide partial hydrolyzate having a molecular weight of 500,000 and a hydrolysis rate of 15% (hereinafter referred to as polyacrylamide O) was used, and the addition amount was changed, and the above-mentioned Example 2 was used. The reduction rate was examined in the same manner as in. The results are shown in Fig. 3. However, when the amount of polyacrylamide O added was 0.003%, no slag reduction was obtained because the sample was not stiff and compacted.

From the results shown in FIG. 3, the polyacrylamide of the present invention was added to the concrete material in an amount of 0.001 to 0.001.
It can be seen that when about 0.0025 wt% is added, a good slag reduction rate is exhibited.

Example 6 A molecular weight of 50 was added in the step of charging a concrete material into a mold.
Add a polyacrylamide partial hydrolyzate with a hydrolysis rate of 15% and a showering method to produce a fume tube in the usual way. A comparative study was conducted. The produced fume tube has a nominal diameter of 1,000 to 2,200. As a result, in the case of using the additive-free concrete, the incidence of plow was 18% of the production number ratio, whereas in the case of adding the polyacrylamide partial hydrolyzate, it was 3%.

[0032]

According to the method for centrifugally molding concrete of the present invention, the water permeability of the cement paste layer of the obtained concrete product is good, and dewatering can be carried out in an extremely short time. The amount of glue generated is also extremely reduced. Further, since the dehydration property is improved, the residual water content is also reduced, and as a result, the occurrence of floating is prevented.

[Brief description of drawings]

FIG. 1 is a graph for explaining a correlation between a hydrolysis rate of polyacrylamides C to H and a slag reduction rate in Example 3 .

FIG. 2 is a graph for explaining the correlation between the molecular weight of polyacrylamides I to N and the slag reduction rate in Example 4 .

FIG. 3 is a graph for explaining the correlation between the addition amount of polyacrylamide O and the slag reduction rate in Example 5 .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunihiro Takahashi 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd. (72) Yoshio Ichihashi 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Issue Kurita Industry Co., Ltd. (72) Inventor Michiyo Kubo 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Inside Kurita Industry Co., Ltd. (72) Kazuhisa Fujita 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Issue Kurita Industry Co., Ltd. (72) Inventor Yoshihiro Hadamata 1001-8 Kakinuma, Kumagaya-shi, Saitama Prefecture (72) Inventor Masahiro Asatsuma 1137-6 Mishimashinta, Konan-cho, Osato-gun, Saitama Prefecture (56) References JP-A-3-80140 (JP, A) JP-A-61-183158 (JP, A)

Claims (1)

(57) [Claims] 1. A concrete material is kneaded and charged into a mold, and the mold is rotated at a low speed to uniformly fill the concrete material, and then the mold is rotated at a medium speed and then rotated at a high speed. Thereby, in the method of centrifugally forming concrete, which comprises molding the concrete material and compacting the concrete material, before carrying out the kneading and the medium-speed rotation, the molecular weight of the concrete material is 300, 000 to 1,000,000,
A method for centrifugally molding concrete, characterized in that a solution of a partially hydrolyzed polyacrylamide having a hydrolysis rate of 5 to 35% is added.