JPS5949166B2 - Manufacturing method of steel fiber reinforced cementitious pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing centrifugally formed cementitious tubes reinforced with steel fibers.

Conventionally, centrifugally formed cementitious pipes have been reinforced by using a rotating formwork and embedding a knitted reinforcing bar cage inside the cementum, or by embedding steel fibers without using a reinforcing bar cage. This was especially true.

The latter has the following advantages over the former: 1) It does not require rebar cage formation, 2) It has high toughness, high impact resistance, and high cracking strength.The steel fibers used generally have a diameter of 0. .2 to 0.5 Wm, length 25 to 3C)+m.

When reinforcing a cementitious pipe with steel fibers using the latter method, it is desirable to decide where to embed the steel fibers in consideration of the effects of internal and external pressure on the pipe.

In other words, when internal pressure is applied to a cementitious tube, tensile stress is generated uniformly in the direction perpendicular to the cross section passing through the axis of the tube, so the steel fibers cannot be mixed uniformly as shown in Figure 1. Desirably, even when external pressure is applied, tensile stress is generated in a direction perpendicular to the cross section passing through the axis of the tube, but its magnitude is large at the inner and outer peripheral surfaces of the tube, so as shown in Figure 2. As shown in FIG. 3, a laminated pipe in which these parts are reinforced with steel fibers and the middle part is made of cementitious material is preferable because the amount of steel fibers required for the same external pressure strength is smaller.

As a method for manufacturing such a cementitious pipe reinforced with steel fibers, a method is known in which steel fibers and cementitious material are kneaded in a mixer and then molded (hereinafter referred to as a premix method).

However, when reinforcing the hardened material by uniformly dispersing and mixing steel fibers into the cementitious material, the mixing ratio of steel fibers (hereinafter referred to as "steel fiber mixing ratio" refers to the total volume of the cementitious pipe or cementitious molding) However, in the premix method, if the mixing ratio is increased, the steel fibers become entangled with each other during kneading in a mixer, making it difficult to disperse them uniformly. However, when concrete is used as the cementitious material, the limit of the steel fiber content is about 2.5 Vo1%.

Furthermore, even when the cementitious material is mortar, the mixing rate of steel fibers is limited to 3Vo1% as shown in Patent Application Publication No. 1984-41284, and if it exceeds this, it is difficult to disperse it in the mortar. It is said that it takes a long time and that there is a risk of uneven distribution and mixture of air bubbles.

In addition to the premix method, a method of mixing steel fibers into a cementitious material in a larger amount and more uniformly is a method in which steel fibers and cementitious materials are charged separately and simultaneously into a rotating formwork (hereinafter referred to as the "simultaneous charging method"). ) has been proposed.

The true nature of the method is that there is no need to knead the steel fibers and the cementitious material in a mixer, and by appropriately selecting the blend of the cementitious material, it is possible to mix in a larger amount of steel fibers than in the premix method.

However, since steel fibers are generally cut to a predetermined length and supplied to the user, they become intertwined with each other, and as they are unraveled and introduced into the formwork, the amount of steel fibers fed is always constant. Therefore, it is practically impossible to maintain a constant mixing ratio of steel fibers and cementitious material using the simultaneous injection method.

A method has also been proposed in which steel fibers and mortar are charged into the formwork separately and alternately (hereinafter referred to as the simultaneous injection method).In this method, the mortar is first poured into the formwork while rotating the formwork. After putting the steel fibers into the formwork and compacting them, the steel fibers are put into the formwork and spread on the surface of the compacted mortar.After that, the mortar and steel fibers are alternately put in and the mortar is made into a steel fiber deposit layer. For example, a patent application filed in 1970-
No. 71455 (Japanese Unexamined Patent Publication No. 51-116917) describes the weight ratio of fine aggregate (sand) to cement (hereinafter referred to as S/C).
A method of manufacturing a steel fiber reinforced cementitious pipe using a mortar with a ratio of 3 or 6 is exemplified.

Figure 4 shows the manufacturing process of the laminated pipe made of the steel fiber reinforced layer and mortar layer shown in Figure 2 using the alternating injection method, and the manufacturing process of the laminated pipe made of the steel fiber reinforced layer and concrete layer shown in Figure 3. The manufacturing process is shown in Figure 5.

However, the alternating addition method has the following drawbacks.

(1) Since mortar and steel fibers must be added alternately, the process is complicated, the molding time is long, and the production volume is inevitably reduced.

(2) If the steel fiber layer is thick, it is difficult for the paste in the mortar to enter the steel fiber layer, so there is a risk of creating voids. Therefore, the thickness that can be formed with one injection of steel fiber is 10 m,
If a thicker steel fiber reinforcing layer is required, it is necessary to increase the number of times that steel fibers and mortar are alternately introduced, making the manufacturing process even more complicated.

(3) The paste in the mortar enters the steel fiber layer, and the fine aggregate has a larger particle size than cement, so it is difficult to enter the steel fiber layer. Therefore, the strength of having more fine aggregate inside the steel fiber reinforcement layer forming a low mortar layer and thus also reducing the strength of the formed tube.

(4) When forming a pipe with a desired internal pressure strength by changing the amount of steel fibers mixed in, it is desirable that the steel fibers be mixed uniformly throughout, but in the alternating injection method, the density of steel fibers (hereinafter referred to as Since the mixing density of steel fibers (meaning the volume percentage of steel fibers with respect to the volume of the steel fiber reinforcing layer) is constant, the alternating injection method is not suitable unless the entire pipe is formed with this constant mixing density. It cannot be used.

(5) When forming a laminated pipe with a desired external pressure strength by changing the amount of steel fibers mixed in, there are two methods: changing the density of steel fibers in the steel fiber reinforcement layer and changing the thickness of the steel fiber reinforcement layer. However, in the alternating addition method, the mixed density of steel fibers remains constant, so the external pressure strength can only be changed by changing the thickness of the steel fiber reinforcing layer.

(6) In a laminated pipe consisting of a steel fiber reinforced layer and a cementitious layer, the product quality is better when the cementitious layer is a concrete layer shown in Fig. 3 than when it is a mortar layer shown in Fig. 2. However, if the laminated pipe shown in Fig. 3 is manufactured by the alternating injection method, the manufacturing process is as shown in Fig. 5. It also requires crosstalk, making it even more complicated.

The main object of the present invention is to provide a method for manufacturing steel fiber reinforced cementitious pipes that solves the various drawbacks mentioned above.
Specifically, it provides a method of mixing a large amount of steel fibers, and also provides a method of making the density of steel fibers mixed uniformly and at a required value, and further comprises a steel fiber reinforced layer and a concrete layer. The present invention provides a method for simplifying the manufacturing process of laminated pipes.

In the production of steel fiber-reinforced cementitious pipes by centrifugal force forming, the present invention is performed at a rotational speed at which the centrifugal force acting on the unsolidified cementitious material placed in the formwork and the gravity are equal to or higher than about 9, and
While rotating the formwork at a rotation speed at which the unsolidified cementitious material does not compact and harden (hereinafter referred to as the first rotational speed), the unsolidified cementitious material is poured into the mold and spread over the inner surface of the mold, and then While rotating the formwork at a first rotational speed, steel fibers, unsolidified cementitious material, and coarse aggregate with a high specific gravity are
They were introduced separately and alternately into the formwork to penetrate into the unsolidified cementitious material, and then the rotational speed of the formwork was increased (hereinafter referred to as
A method of compaction forming (referred to as a second rotational speed) is provided.

The cementitious material used in the present invention may be a paste made by mixing cement and water, a mortar made by mixing cement, fine aggregate, and water, or a concrete made by mixing cement, fine aggregate, coarse aggregate, and water. It is also possible to use
Mortar is preferred.

Particularly remarkable effects are exhibited when mortar with an S/C of 0.5 to 2.0 is used.

Mortar can be sufficiently compacted using centrifugal force (usually 50G or less), which is commonly used in cement secondary product factories, but paste cannot be compacted, so the rotation of the formwork is stopped. In order to prevent the paste from peeling off from the inside of the formwork, there is a method of using a fast-setting agent to solidify it while the formwork is rotating, but this method requires a quick-setting agent and the mortar is not sufficient. Since it hardens, it is possible to finish only the inner surface layer of the tube with mortar, but in this case, it is necessary to prepare mortar in addition to the paste, making the process complicated.

In addition, when concrete is used, due to the presence of coarse aggregate, the penetration of coarse aggregate, which forms the concrete layer in steel fibers and laminated pipes, into concrete is limited to S/C of 0.5.
This is more difficult than when using a mortar of ~2.0.

As cement, any hydraulic cement such as ordinary cement, early strength cement, mixed portland cement such as blast furnace cement, fly ash cement, etc. can be used, but the efficiency of use of formwork, price, etc. From this point of view, it is generally preferable to use early-strength cement.

Fine aggregate has a coarse grain ratio of about 2 to 3.5, and coarse aggregate has a grain size of about 5 to 3.5.
A general type of about 20 pieces can be used, but because the coarse aggregate that forms the concrete layer in laminated pipes is forced into the unsolidified cementitious material by centrifugal force, its specific gravity is lower than that of unsolidified aggregate. It is necessary that the cement material be larger.

Steel fibers will penetrate into unsolidified cementitious materials if the diameter is 0.1 m or more, but considering the performance of the formed pipe, steel fibers with a diameter of 0.3 to 0.5 m and a length of about 20 to 35 W are recommended. is the most suitable.

Note that the shape of the cross section perpendicular to the long axis of the steel fiber is not limited to a circle, and may be square, rectangular, or the like.

If the S/C in the mortar is less than 0.5, it cannot be compacted like a paste, and if it exceeds 2.0, a large amount of steel fiber cannot be mixed in as shown in FIG.

Therefore, the mortar S/C is preferably 0.5 to 2.0.
It is.

By appropriately selecting the S/C of the mortar within this range, steel fibers having a desired mixed density can be uniformly introduced into the mortar.

The consistency of the mortar needs to be soft to facilitate the penetration of steel fibers, but if it is too soft, the fine aggregate of the mortar will easily separate. The flow time measured by Test Method J (P funnel) (Japan Society of Civil Engineers) is 3.
A suitable time is 0 to 180 seconds.

Consistency also affects the density of steel fibers, but within the above range, the effect is very small.

If the consistency of the mortar is softened, there are concerns about negative effects such as a decrease in the strength of the product and an increase in drying shrinkage, but in centrifugal force forming, excess water is squeezed out by compacting at the second rotational speed. Such effects are small.

Using a water reducer in mortar can reduce the water-cement ratio required to obtain the desired consistency, increasing the viscosity of the mortar, preventing separation of fine aggregate, and improving product quality. preferable.

As the water-reducing agent, a general water-reducing agent for cement products can be used, but a water-reducing agent whose main component is a polyalkylaryl sulfonate or a polycyclic aromatic sulfonate is particularly suitable.

Regarding the rotational speed of the formwork, the rotational speed (first rotational speed) when unsolidified cementitious material is introduced into the formwork and spread, and then steel fibers or coarse aggregate is introduced and enters into the cementitious material is In order to prevent the cementitious material from falling off the inner surface of the formwork, the rotation speed must be at least at a level where the centrifugal force acting on the cementitious material in the formwork and gravity are balanced, but if the rotational speed is too high, the cementitious material will compact and harden. Since the steel fibers or coarse aggregate forming the concrete layer cannot penetrate into the cementitious material, it is necessary to keep the rotation speed to a level that does not compact the cementitious material.

The upper limit of the first rotation speed varies depending on the composition of the cementitious material, but in the mortar of the present invention, a centrifugal force of 15 G or less, about 3 to 7 G is suitable.

On the other hand, the appropriate rotational speed (second rotational speed) during compaction is about 30G in terms of centrifugal force.

Next, the manufacturing process of the steel fiber-reinforced cementitious pipe according to the present invention will be explained.

FIG. 8 shows a process for manufacturing a laminated pipe with a steel fiber reinforced layer and a concrete layer as shown in FIG. 3 using the apparatus shown in FIG. 6 and mortar.

That is, while the drive roller 6 rotates the formwork 1 at the first rotation speed, a predetermined amount of mortar of a predetermined mix based on the dimensions of the pipe is poured into the formwork by the concrete pump 2. The steel fiber reinforced layer F! is spread evenly on the inner surface, and while the formwork is continuously rotated at the first rotation speed, the steel fiber reinforced layer F! Fiber dispenser 3,
The aggregate is sequentially introduced into the formwork by the aggregate feeding machine 5 and the belt conveyor 4 and allowed to enter the mortar, and then the rotational speed of the formwork is increased to the second rotational speed and compacted.

Since mortar, steel fiber and coarse aggregate can be added in predetermined amounts separately, the thickness of the steel fiber reinforcement layer and concrete layer,
In addition, the steel fiber mixing density in the steel fiber reinforcing layer can be correctly maintained at the target value.

In addition, since there is no need to separately mix and pour concrete to form the concrete layer, which contributes to drying shrinkage of the cement pipe and reduction of material costs, the manufacturing process is better than the alternate pouring method shown in Figure 5. The molding process is greatly simplified, and the time required for molding can be reduced by several orders of magnitude.

Furthermore, the consistency of the mortar during molding does not change much, making the work easier, and the steel fiber reinforced layer has a uniform mixture of steel fibers with various thicknesses and steel fiber mixing densities.
Steel fiber reinforced cementitious tubes with concrete layers of various thicknesses can be manufactured economically.

Next, examples of the present invention will be shown, but the present invention is not limited to these unless it exceeds the gist thereof.

Example 1 This example shows the relationship between mortar S/C, steel fiber mixing density, and bending strength.

Note that the steel fibers were mixed uniformly as shown in FIG.

(1) Materials used Steel fiber: Dimensions: 0.25 Xo, 50 Specific gravity 2.58° Water absorption rate 2.1
0%, coarse grain ratio 2.80) (2) When adding centrifugal mortar and steel fiber: 5G When compacting: 30G (3) Specimen dimensions: inner diameter 24cm, tube thickness 3crn, length 30CrrI (4)
Standard curing 28 days (5) Strength test method JIS A3303 r Centrifugal force reinforced concrete pipe
The experimental results of external pressure test (6) are shown in Table 1 and Figure 7.

As shown in Table 1 and FIG. 7, the mixing density of steel fibers can be adjusted by changing the mortar C8/C.

Example 2 This example shows the effect of a water reducing agent.

The experimental conditions were as follows: In addition to the water reducing agent used in Example 1, a polycyclic aromatic sulfonate-based water reducing agent (manufactured by Hozoris Bussan,
The procedure was the same as in Example 1, except that Hozolith NL1440) was also used.

The experimental results are shown in Table 2 along with a comparative example in which no water reducing agent was used.

A... Polyalkylaryl sulfonate system B...
Polycyclic aromatic sulfonate system 1...wt% relative to the amount of cement As shown in Table 2, by using a water reducing agent, the water-to-cement ratio required to obtain the required consistency can be reduced. Therefore, the bending strength can be increased.

Example 3 In this example, a laminated tube shown in FIG. 3 was molded and an external pressure test was conducted.

The experimental conditions were as follows: Crushed stone for Sagami No. 6 (specific gravity 2.74, water absorption rate 1.41%) was used as coarse aggregate to form the concrete layer.
, coarse grain ratio: 6.34°, maximum dimension: 1511 m).

The experimental results are shown in Table 3.

Fl, F2: Steel fiber reinforced layer C: Concrete layer A cement laminated pipe with different thicknesses of steel fiber reinforced layer and concrete layer could be manufactured by a simple process.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are partial views of sections perpendicular to the axis of steel fiber-reinforced cementitious tubes in different embodiments. The figure shows a laminated pipe made up of a steel fiber reinforced layer and a mortar layer, and Figure 3 shows a laminated pipe made up of a steel fiber reinforced layer and a concrete layer. FIGS. 4 and 5 are process diagrams showing different aspects of the alternating injection method. FIG. 6 is a schematic diagram of an example of an apparatus used to carry out the method of the invention. FIG. 7 is a graph showing the relationship between the S/C of the mortar used in the present invention and the steel fiber mixing density. FIG. 8 is a manufacturing process diagram of a laminated pipe including a steel fiber reinforced layer and a concrete layer in the method of the present invention. Explanation of codes of main parts, F1%F2... Steel fiber reinforcement layer, M... Mortar layer, C... Concrete layer, 1... Formwork , 2... Concrete pump, 3... Fiber dispenser, 4... Belt conveyor, 5...
Aggregate feeder, 6... Drive roller, 7...
・Cementum tube being formed

Claims (1)

[Scope of Claims] 1. In the production of steel fiber-reinforced cementitious pipes by centrifugal force forming, the centrifugal force acting on the unsolidified cement material charged into the formwork and the gravity must be at a rotational speed of approximately 9 or higher, and While rotating the formwork at a rotational speed that does not allow the solidified cementitious material to compact and solidify, unsolidified cementitious material is introduced into the formwork and spread over the inner surface of the formwork, and the formwork is continued to be rotated at the same rotational speed. Steel fibers, unsolidified cementitious material and coarse aggregate with a high specific gravity are separately and alternately introduced into the formwork to penetrate into the unsolidified cementitious material, and then the rotational speed of the formwork is increased. A method characterized by forming steel fiber reinforced layers and concrete layers in alternating layers. 2. The method according to claim 1, wherein the cementitious material is mortar. 3. The method according to claim 2, wherein the weight ratio of fine aggregate to cement in the mortar is 0.5 to 2.0. 4. The method according to claim 2, wherein the mortar has a consistency of 30 to 180 seconds. 5. The method according to claim 2, wherein the mortar contains a water reducing agent. 6. The method according to claim 5, wherein the water reducing agent is mainly composed of a polyalkylaryl sulfonate or a polycyclic aroma sulfonate.