JPH0469524B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for forming a centrifugally formed body using centrifugal force, and more specifically, a method for centrifugally forming concrete to which a high performance water reducing agent has been added. - Concerning forming methods for pole/hium pipes, steel pipe lined steel pipe composite piles, etc. still,
Concrete as used in the present invention is a general term for mortar and concrete. [Conventional technology and its problems] Conventionally, concrete to which high-performance water reducing agents have been added has a high viscosity and the concrete does not harden even when centrifugally formed, causing sagging and waving on the inner surface of the centrifugally formed body. Problems included the generation of a large amount of slag, and the formation of slag (so-called "nests") due to water remaining between the inner slag layer and the concrete layer due to water not being completely dehydrated. It is known that this tendency becomes extremely large as the amount of high performance water reducing agent added increases. Therefore, when manufacturing molded bodies such as humid pipes and steel pipe linings where the inner finish is the lifeblood, it is a general rule not to use not only high performance water reducers but also general water reducers. However, if the purpose is to increase the strength of the propulsion tube and to increase the external pressure by increasing the strength, it is necessary to increase the amount of cement per unit and at the same time limit the amount of high-performance water reducer to about 0.4% (based on the weight of cement). is taken. However, increasing the amount of cement per unit impairs economic efficiency, causes thermal cracking, and is inefficient due to longer pipe manufacturing time. Problems include the formation of jitters between the slag layer and the concrete layer due to insufficient dehydration, which causes internal surface lifting and increases the defective rate. For piles and the like where internal finishing is not important, the slag treatment that occurs is a pollution problem due to its strong alkaline nature, and at the same time, the number of slag treatments has increased in recent years with the development of auger construction methods. Piles installed using the auger method are increasingly required to have a finished inner surface. Further, in the same way as described above, when a jitter layer is formed, it also causes a decrease in strength. Furthermore, when considering centrifugal force molded bodies, the use of high performance water reducing agents, expansion agents, high strength admixtures, or a combination of the three is becoming more sophisticated and is beginning to be standardized. However, as mentioned above, the use of high-performance water reducing agents may result in the separation of the expanding agent and high-strength admixture as slag, resulting in a significant loss of the expected effects based on the amount of these additives added. many. In order to prevent these, for example,
Publication No. 53-31888, JP-A-56-
As shown in Japanese Patent No. 160358, a method of further adding a third component has been proposed. Furthermore, Japanese Patent Application Laid-Open No. 59-81116 proposes a method in which the G No. and rotation time at the maximum speed of rotation are determined by the outer diameter of the molded body without using any third component. However, the method of adding a third component is not only economically disadvantageous, but also requires complicated management. Furthermore, by attempting to improve centrifugal force formability by specifying the G No. and rotation time at the maximum rotation speed, it is not possible to eliminate the numerous drawbacks and adverse effects of concrete to which high-performance water reducing agents have been added. The conventional centrifugal compaction method, as shown in Japanese Patent Application Laid-Open No. 59-81116, involves centrifugal compaction at low and medium speeds when and after concrete is poured into the formwork. The method shown in Table 1 is generally adopted and has become a habit. However, as mentioned above, concrete containing high-performance water reducers has many problems, such as weak compaction of the inner surface of the molded body and the generation of large amounts of slag.
Therefore, even if admixtures and the like are added, they do not work effectively, and there is also an economical problem.

[Means for solving problems]

When centrifugally forming concrete in which 0.2% by weight or more of a high-performance water reducing agent is added in terms of solid content to cement, the first step is to centrifugally form the concrete using G No. L that satisfies the following formula. minutes, and then as a first step, G that satisfies Eq.
This is a method for forming a centrifugally formed body, which is characterized by performing centrifugal force forming using No.M. ．． :(a-4)≦L<a. :(a+3)<M However, a is the G No. when dehydration starts. The present invention will be explained in detail below. In centrifugal force molding, the G number, that is, the centrifugal force is a multiple of the gravitational acceleration g, and is usually expressed as 9G, for example, as shown in the following equation. G No. = 4π ² rv ² /g where r = radius of rotation (radius to center of pipe thickness) (cm) v = rotational speed (rps) g = gravitational acceleration (980cm/sec ² ) In centrifugal force forming, usually According to experiments conducted by the present inventors, the G No. when concrete begins to dehydrate is within a relatively narrow range of about 9 G, and if a high performance water reducer is mixed in concrete above a certain level, the unit cement amount Although it is hardly affected by concrete conditions such as fine aggregate ratio, water/cement ratio, and slump, it is affected by concrete temperature, and the higher the temperature, the lower the G No. when dewatering starts. The lower the temperature, the higher the G No. High performance water reducer compared to cement in terms of solid content
The method for forming concrete containing 0.2% by weight or more involves, as a first step, centrifugal force forming at a GNo.L that is less than the GNo.a at which the concrete begins to dehydrate and is at least (a-4). Normally, the G No.L in the first stage is about 5G or more and less than 12G. The higher the GNo.L, the greater the dehydration effect, slag generation prevention effect, and compaction effect, but the higher the concrete temperature, the better a lower GNo. In this case, a higher G No. is preferable. At this time, it is even more important to take sufficient rotation time. If GNo.L is less than (a-4), the effect will be extremely poor even at high temperatures, and if it is more than a, cement will separate with water even if the temperature is low, which is not preferable. Normally, when the concrete temperature is high (about 15℃ or higher), about 5 to 9G is sufficient, but if the temperature is 15℃ or higher,
At temperatures below about 0.degree. C., about 9 to 12 G is preferable. It is preferable that the rotation time is sufficient in terms of physical properties, but it may be shorter if the G No. is increased, and in the present invention, which is carried out in two stages, the rotation time in the second stage is 4 to 10 minutes.
It's a minute. Next, GNo.M in the first stage is larger than GNo.a at the time when dehydration starts, and is larger than (a+3). GNo.m in the first stage is usually 15G or more, preferably 20G or more. At 20G or more, the dehydration effect does not become particularly large, but it becomes advantageous in terms of strength. That is, the molding is performed by raising the G No. 15G or more, preferably 20G or more at once, and the rotation time at this time is less important than that in the first stage, and about half of it is sufficient. In addition, when the slump is hard for a long object such as a concrete pile, it is more preferable to stretch the concrete sufficiently at about 3G and perform centrifugal force forming in stages. Furthermore, the high-performance water reducing agent referred to in the present invention is a water reducing agent that exhibits high dispersibility with little excessive setting delay or air entrainment effect even when added in a relatively large amount. According to the "High Strength Concrete Design and Construction Guidelines (Draft)," it is broadly classified into two types based on the chemical structure of its main components: A. polyalkylaryl sulfonate systems and B. high condensate systems of triazine derivatives. Those belonging to A have a formalin high condensate of naphthalene sulfonic acid or its derivatives or related substances as a main component, and those belonging to B have a melamine formalin resin sulfonate as a main component. Although commercially available products are mainly those belonging to A, both A and B can be used in the present invention. Table 2 shows typical commercially available products.
become that way. The amount of the high-performance water reducing agent added is at least 0.2% by weight or more, preferably 0.4% by weight or more in terms of solid content, based on the weight of cement in the concrete. If it is less than 0.2% by weight, the G No. when dehydration starts,
It is difficult to grasp this clearly, and centrifugal formability is not improved by the method of the present invention. In addition to high-performance water reducing agents, ordinary water reducing agents whose main ingredients are ligninsulfonic acid and oxycarboxylic acid can also be used.In addition, gypsum, high-strength admixtures mainly composed of gypsum, Inorganic powders such as silica hume, expansive materials, slag, fly ash, silica substances, etc. may also be added.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 Using the concrete composition shown in Table 3, centrifugal force forming properties were investigated by varying the conditions of centrifugal force forming. The concrete temperature is 30℃. A test tube of 20φcm x 30lcm x 5tcm was used as the centrifugal force molded body, and the amount of concrete was kept constant at 18Kg. The results are shown in Table 4.

【table】

【table】

【table】

[Table] According to preliminary tests, the G No. when dehydration starts is
It was 9.0G. In Table 4, Experiment No. 1-1, 2-
2, 1-4, 1-5, 1-10, 1-11, and 1-
No. 16 is a comparative example, and among them, Experiment No. 1-16 is a conventional three-step centrifugal molding method. Also, experiment
In No. 1-11, the slag was particularly separated from the water and the compaction was poor. Example 2 Using the same concrete mix as in Example 1 and at a concrete temperature of 14°C, the molding conditions were investigated in the same manner as in Example 1. The results are shown in Table-5.

[Table] The thickness of the mortar layer is the thickness of the mortar layer that does not harden (mm)
In Table 5, Experiment No. 2-5 is a comparative example and is mostly slag (so-called sludge containing fine particles such as cement), whereas what is dehydrated in the example of the present invention is water with a low solid content. It is in the form of According to preliminary tests, the G No. when dehydration starts is
It was 12G. Example 3 18 kg of concrete with different amounts and types of high-performance water reducing agents was packed into a 20φcm x 30lcm x 5tcm test tube.
The test was conducted in the same manner as in Example 1 at 7G for 4 minutes and 20G for 2 minutes. However, the concrete temperature is 20℃. The concrete composition is shown in Table 6, and the results of centrifugal force forming are shown in Table 7. According to preliminary tests, the G No. when dehydration starts is
It was 9G.

【table】

[Table] <Materials used> High performance water reducing agent E: "Cellflow 110P", powder form,
Main component polyalkylaryl sulfonate type F: "Melment F-10", powder form,
Main component is melamine resin. Materials used other than the above are the same as in Example 1.

[Table] Example of thickness of rutal layer 4 In the concrete mix shown in Table 3, hydrofluoric acid is generated as a by-product instead of sand - 10% by weight of anhydrite based on cement
It was poured into a propulsion tube formwork with a nominal diameter of 1500 mm and a thickness of 140 mm in an unreinforced state, and molded using the conventional method and the method of the present invention. The concrete temperature was 30℃. At the same time as observing the molding condition, the material was cored at 28 days old, cut into a 10 x 10 x 20 cm rectangular column so that the axis direction of the tube was the length direction, and vibration-packed to 10φ x 20 cm without centrifugal force forming. The strength was compared with that of the piece.
In addition, when cutting out the prisms, avoid cutting out the inner surface of the tube as much as possible.
The concrete part of the outer part of the pipe was collected. The molding conditions and results are shown in Table 8.

[Table] According to preliminary tests, the G No. when dehydration starts is
It was 9G. In Table-8, test No. 4-2 is the conventional method,
The uncompacted mortar layer was large, and a large amount of water was dehydrated in the example of the present invention. Example 5 Experiment No. 5 was conducted using the concrete mix shown in Table 3.
The same procedure as in Example 1 was carried out except that after the molding conditions 1-6, a centrifugal force was further applied. The results are shown in Table-9.

〔Effect of the invention〕

The effects of the present invention can be summarized as follows. (1) It is possible to compact the mortar layer on the inner surface of the pipe and reduce or prevent the occurrence of slag. (2) The performance of the admixture can be fully demonstrated. (3) The amount of water removed is large, making it possible to densify the centrifugally formed product and improve its strength. (4) Simplify the centrifugal force molding method and increase production efficiency,
Economical mixing design of unit amount of cement and amount of admixture becomes possible.

Claims (1)

[Claims] 1. When centrifugally forming concrete in which 0.2% by weight or more of a high-performance water reducing agent is added in terms of solid content to cement, first centrifugally forming the concrete with G No. L that satisfies the following formula. A method for forming a centrifugally formed body, characterized in that the first step is carried out for 4 to 10 minutes, and then, as the second step, centrifugal force forming is carried out using G No. M that satisfies the formula. ．． :(a-4)≦L<a. :(a+3)<M However, a is the G No. when dehydration starts.