JP2000143322A - Explosion-resistant concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-strength explosion-resistant concrete having high economic efficiency capable of effectively controlling explosion without reducing fluidity. SOLUTION: This explosion-resistant concrete comprises 0.01-0.2 vol.% of an organic fiber which is composed of an organic material having <=30% weight residual ratio when heated at 500 deg.C and has 5-100 μm diameter and 5-40 mm length. The concrete has <=35% water binder ratio. The organic fiber is preferably a polypropylene fiber, a polyvinyl alcohol-based fiber, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to concrete having excellent fire explosion resistance for use in structures such as buildings and tunnels that may be subject to fire.

[0002]

2. Description of the Related Art A high-strength concrete can be obtained by reducing the ratio of water in a concrete and a binder, that is, a material that undergoes a hydration reaction in the concrete, such as cement, slag, fly ash, silica fume and the like. By increasing the strength of the concrete, various benefits can be obtained, such as reducing the cross-sectional dimensions of the columns of the building and increasing the height of the building. However, when the content of water is reduced to increase the strength of the concrete, the concrete on the surface tends to explode due to steam pressure, thermal stress, and the like in a high-temperature environment such as a fire, which may cause various problems. It is known. The following technology is known to suppress the explosion of a building using such high-strength concrete. Japanese Patent Application Laid-Open No. Hei 9-13531 discloses the use of low-strength concrete in the vicinity of pillars and in the vicinity of a surface directly receiving a fire to suppress explosion, while using high-strength concrete in the center to prevent external forces and fire. Structures are described that retain high resistance to them.

[0003] Further, although it is not concrete itself used for a structure, as a high-strength extruded plate used for panels for interior and exterior of buildings, for example, Japanese Patent Publication No. Sho 57-2
No. 0126 describes an extruded plate in which acetate or rayon fiber having a length of 5 to 20 mm and a thickness of 1 to 25 denier is mixed with 0.5 to 2.0% of the weight of cement asbestos. There is a disclosure that pores are formed in such a way that water vapor escapes from this portion to prevent explosion. JP-A-59-1284 discloses a method of preventing explosion by mixing hollow polypropylene fibers and letting steam escape from the holes of the fibers. A method is described in which a mixture of pulp and pulp secures pores of 1 to 5 μm in asbestos cement having a porosity of 30 to 60% to 10% or more of the voids to prevent explosion. They are,
Each of them has a certain effect on the explosion resistance of concrete, but the method of using low-strength concrete on the surface of a high-strength concrete member, as disclosed in Japanese Patent Application Laid-Open No. 9-13531, requires that Inevitably, the effect of using high-strength concrete must be increased, and the use of at least two types of concrete results in a complicated construction method and significantly increases costs. There was a problem.

A method of mixing a filler such as fiber into concrete as disclosed in JP-B-57-20126 and JP-A-59-1284 is applicable to high-strength concrete. If an effective amount having a suppressing effect is mixed, the fluidity of the concrete is reduced, and it is difficult to place the concrete in a formwork at a construction site. Tokiko 62-1219
When technology to secure voids in asbestos cement as in No. 7 is applied to high-strength concrete, strength is inevitably reduced by forming a large amount of voids, and the essential purpose of high-strength concrete is Cannot be achieved.

[0005] Originally, high-strength concrete achieves high strength by reducing the ratio of the amount of water to binder such as cement. However, as the ratio of water binder decreases, the plastic viscosity increases and the workability increases. Therefore, the required fluidity is ensured by the development of a surfactant as a dispersant for high-strength cement and the use of silica fume which is ultrafine particles of vitreous silica. Therefore, in order to ensure resistance to explosion, it is not preferable in practice to mix a large amount of fiber to lower the fluidity, and even if fiber incorporation is effective in preventing explosion, high-strength concrete It must be able to minimize the decrease in liquidity.

[0006]

The current techniques for preventing explosion of high-strength concrete as described above have some effects, but have various problems when applied to high-strength concrete. Have. The present invention has been made in view of such a current situation, and aims to provide a highly economical high-strength concrete that can suppress explosion without lowering fluidity.

[0007]

Means for Solving the Problems In view of the above problems, the present inventors have focused on the point that the technique of mixing fibers made of an organic material is effective in preventing explosion and is highly economical.
The present invention was completed after various studies on effective means for suppressing a decrease in fluidity and applying to high-strength concrete. That is, in order to suppress a decrease in fluidity when fibers are mixed, explosion is prevented with a small amount of fibers. That is, it is effective to use a fiber having a high explosion prevention effect. The present inventors have studied conventionally known organic fiber materials,
Based on the finding that there is a large difference in the explosion prevention effect due to the difference in the amount of evaporation when heated to 00 ° C., the above object is achieved by using a specific material that can efficiently form voids under high temperature conditions. It has been found that it can be achieved.

That is, the explosion-resistant concrete of the present invention comprises:
Made of an organic material having a weight retention rate of 30% or less when heated to 500 ° C., having a diameter of 5 to 100 μm and a length of 5 to 40.
It is characterized by containing 0.02 to 0.2% by volume of organic fibers having a water binder ratio of 35% or less. By using an organic fiber made of an organic material having a small weight residual ratio (non-evaporation amount) of 30% or less when heated to 500 ° C., even if the amount of the added fiber is small, Since an effective pore can be formed by rapidly reducing the volume, an effective explosion-proof property can be achieved even with the added amount of the organic fiber which does not decrease the fluidity of the concrete.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, as an organic fiber to be added to concrete, a fiber formed of an organic material having a residual weight ratio of 30% or less when heated to 500 ° C. is used. Normally, as a material for forming pores for preventing explosion by releasing steam when heated to explosion-resistant concrete, an organic material having a low melting point is preferable, but as a result of a study by the present inventors, Simply having a low melting point does not necessarily develop excellent explosion resistance.
It was found to be related to the residual weight when heated to ° C.

When various types of organic fibers are heated to 500 ° C., there are various types of the residual weight from 10 to 20% to about 80%. In the event of a fire, the holes for water vapor in the concrete for preventing explosion formed by evaporation of the fiber are not sufficiently formed, and the effect of the fiber on explosion prevention is greatly impaired. On the other hand, the fibers having a small weight retention rate when heated to 500 ° C. evaporate well in the event of a fire, can effectively form a water vapor escape hole, and can effectively prevent explosion with a small number of fibers. Become. 500
If the residual weight ratio at the time of heating to 30 ° C. exceeds 30%, the formation of water vapor escape holes due to the evaporation of the fiber is insufficient, and the explosion resistance is reduced. Large pores with a volume comparable to the fiber volume before evaporation are formed, and the pores function well as water vapor release holes,
It develops favorable explosion resistance.

As described above, since each fiber present in the concrete matrix quickly forms effective pores after heating, the amount of fibers used can be reduced, and the mixing of fibers affects the fluidity of concrete. The influence is reduced, and high-strength concrete with good workability can be economically realized. As an organic material constituting these organic fibers, a natural, semi-synthetic or synthetic organic material which is decomposed or melted by heating in a fire to cause a sharp decrease in volume is used.

Next, a method for measuring the weight residual ratio when heated to 500 ° C. will be described. First, the air-dried mass of the organic fiber is measured, 6 to 7 mg is weighed, and the measurement is performed by differential scanning calorimetry. As specific measurement conditions, a differential scanning calorimeter (TAS200, manufactured by Rigaku Denki Co., Ltd.) was used, and the temperature rise rate was 5.0 ° C. in an alumina sample holder.
/ Min, measurement time interval: 0.6 seconds.

In relation to organic materials, fibers having relatively low melting temperatures, such as polypropylene and polyvinyl chloride,
When vinylon, acrylic fiber and the like were measured under the above conditions, the residual weight ratio of polypropylene and vinylon was 14
% And 18%, which satisfies the requirements of the present invention. However, polyvinyl chloride and acrylic fibers are not suitable as the fibers of the present invention because the residual weight ratio exceeds 30%. As a natural, semi-synthetic or synthetic organic material constituting the organic fiber of the present invention, the volume is rapidly reduced by melting or evaporating by heating, and particularly, the weight residual ratio when heated to 500 ° C. is 30%.
%, It is necessary to select from known synthetic resins, natural fibers, synthetic fibers, semi-synthetic fibers and the like in consideration of the above conditions. For example, polypropylene-based, vinylon-based, vinylidene-based and the like The following materials are preferred.

Next, in order to study the shape of the organic fiber, the present inventors evaluated using a concrete model. Although the shape of the organic fibers is directly related to the shape of the pores formed by the evaporation of the organic fibers, the effect of the pores, that is, the water vapor vent holes that provide resistance to explosion upon heating, is considered to be the shape of the fibers considered here. The effect varies depending on the diameter, the amount of fibers mixed in, the strength of the concrete, and the like. When the fibers (diameter d _f ) dispersed in the concrete are modeled as being uniformly covered with the cover concrete portion and distributed in parallel as shown in FIG. 1 (A), the fibers are formed by a single fiber in a fire. Water vapor from a cylindrical concrete portion (referred to as an effective concrete column) approximated by a hexagon as shown in FIG. This movement of water vapor is indicated by an arrow in FIG. In this way, the holes formed by the fibers allow the water vapor from the area of the cover concrete portion to escape from the holes. The diameter of a hexagonal effective concrete column is d _c
(Mm), the diameter of the fiber is d _f (mm), and the mixing amount of the fiber is V _f (cm ³ / m ³ ), and d _c , d _f , and V _r are represented by the following formula (1). It is calculated that there is a relationship.

[0015]

(Equation 1)

The relationship between d _c and V _{f in} the equation (1) is converted from V _f into a mixing ratio (%), and the diameter of the fiber is used as a parameter,
The plot is as shown in FIG. FIG. 2 is a graph showing the relationship between the diameter d _c (mm) of the effective concrete column and the amount V _f (cm ³ / m ³ ) of fiber mixed into the concrete for each fiber diameter. From FIG. 2, it can be seen that the diameter of the effective concrete column decreases as the fiber mixing ratio increases, and that the diameter of the effective concrete column decreases as the fiber diameter decreases. As described with reference to the model diagram in FIG. 1, the smaller the diameter of the effective concrete column, the smaller the area for collecting water vapor at one fiber hole, and thus the greater the explosion prevention effect. That is, it is understood that the larger the fiber mixing ratio and the smaller the fiber diameter, the more effective in preventing explosion.

The diameter of the effective concrete column required for preventing explosion is reduced as the strength increases, because the strength of the concrete, that is, the speed of collecting water vapor in one fiber hole differs depending on the denseness of the structure. According to the loading heating experiment of the reinforced concrete column performed by the present inventors, the amount of fiber required to maintain a force of 1/3 of the strength (the maximum value of a normal long-term load) for 3 hours is determined by the fiber diameter. Was mixed with concrete having different compressive strengths using polypropylene fibers of 20 μm and evaluated. When the compressive strength of concrete was 800 kgf / cm ² , the necessary fiber mixing amount was 0.01 to 0.02% by volume. , 1000kgf / cm ²
In this case, the content was about 0.05% by volume. Figure 2
To consider fitting the graph, the diameter of the effective concrete column required explosion prevention, compressive strength of concrete 2.0~2.5mm about in the case of 800 kgf / cm ^2, in the case of 1000 kgf / cm ² 1 It is estimated to be around 0.0 mm.

In the present invention, from the viewpoint of improving the explosion resistance of high-strength concrete, considering that at least the compressive strength of the concrete is about 800 kgf / cm ² or more, the effective concrete shown in the model diagram in FIG. It can be seen that it is necessary to select a column in a region where the diameter (d _c ) of the column is 2.0 mm or less. If the diameter of the fiber suitable for preventing explosion is selected in consideration of the diameter of the effective concrete column, the diameter of the fiber is preferably 5 to 100 μm. 5μ
If it is less than m, it is difficult to form pores which are preferable as a water vapor passage, and if it is more than 100 μm, it is difficult to exhibit sufficient explosion resistance to high-density concrete.

The length of the fiber is preferably 5 to 40 mm. When it is less than 5 mm, the effect of preventing explosion is insufficient, and when the fiber length exceeds 40 mm,
Dispersion of the fibers is poor, making it difficult to obtain uniform concrete.
As long as these organic fibers can be uniformly dispersed without agglomeration in concrete, either monofilaments or strand fibers can be used. The amount of fibers required to prevent explosion of high-strength concrete is 0.02 to 0.2% by volume based on the volume of concrete, that is, 0.2 to 2 liters per m ³ . Like the organic fibers of the present invention, evaporation occurs quickly at high temperatures,
Even when a fiber that easily forms an effective void is used, it is preferable to use a fiber having an effective void.
If it is less than 02% by volume, that is, less than 0.2 l / m ³ , the effect of preventing explosion is insufficient, and 0.2% by volume, ie, 2 l / m 3
Mixing ³ or more is not preferable because the fluidity of the concrete decreases.

As described above, in the explosion-resistant concrete of the present invention, continuous voids are formed by the heat shrinkage and evaporation of the mixed fibers, and the steam is transmitted through the voids one after another to efficiently escape the steam. Explosion can be prevented. The organic fibers according to the present invention are flexible and have little effect on fluidity even when dispersed in concrete. By dispersing this fiber as a filler in concrete, the water vapor in the concrete generated at the time of fire is released to the outside, thereby effectively preventing the explosion of the concrete. % In the case of ordinary concrete in which the effect of explosion occurring in the concrete at the time of a fire is not a problem. The present invention is particularly useful when applied to high-strength concrete having a water binder ratio of 35% or less. It can be said that.

[0021]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. (Examples 1 and 2) (1) Concrete material Cement: ordinary Portland cement Fine aggregate: mountain sand (specific gravity 2.55, water absorption 1.54%) and hard sandstone crushed sand (specific gravity 2.65, water absorption 1) .26%) in a ratio of 6: 4 Coarse aggregate: crushed hard sandstone (specific gravity 2.6, water absorption 1.12%) Admixture: powdered silica fume (specific gravity 2.2, specific surface area 14 m ² / g, SiO) ₍₂ content 94%) Admixture: Polycarboxylate-based high-performance AE water reducing agent (trade name: Tupole HP-11, manufactured by Takemoto Yushi Co., Ltd.) (2) Mixing of concrete An experiment was performed using 25% high-strength concrete as a base material.

[0022]

[Table 1]

(3) Organic fiber A polypropylene fiber having a diameter of 20 μm, a length of 19 mm,
The one having a residual weight ratio of 14% when heated to 500 ° C. was used. (4) Incorporation amount of fiber The organic fiber was added to the concrete prepared above in a quantity of 0.0
5% by volume, 0.10% by volume, 0.20% by volume, 0.30%
It was mixed under the condition of volume%. (5) Production of concrete A 100-liter pan-type forced kneading mixer was used. The amount of one kneading was 60 liters. After sand, cement and silica fume were kneaded for 15 seconds, water and an admixture were added and kneaded for 1 minute, and then coarse aggregate was added. The mixing time after the addition of the coarse aggregate was 2 minutes, and the fibers were mixed during the first 30 seconds. In the obtained concrete, the mixing amount of the organic fiber is 0.05
The one with 0.1% by volume was designated as Example 2, the one with 0.1% by volume was designated as Example 2, the one with 0.2% by volume was designated as Example 3, and the one with 0.3% by volume was designated as Example 4.

(6) Fluidity test of concrete The L-flow rate of concrete having a slump flow of 60 cm was measured by the method described in Japanese Patent No. 2,589,575, and the effect of mixing of fibers on fluidity was examined. L
Those having a high flow rate have low plastic viscosity and good fluidity. The results are shown in Table 2 below. Table 2 also shows the results of the same measurement with the control (Comparative Example 1) in which no organic fiber was mixed. The relationship between the fluidity and the fiber mixing ratio is shown in the graph of FIG. (7) Fire resistance test φ15 cured in a sealed state to prevent evaporation of water vapor
JIS A1304 by unsealing the × 30cm specimen
The specimen was heated according to the standard heating curve defined in the above section, and the weight of the specimen before and after the heating was measured. In this test, the exploded material becomes lighter in weight and the difference in weight before and after heating becomes larger.
Therefore, those having a small weight change (weight loss ratio) were evaluated as having excellent explosion resistance. The results are shown in Table 2 below. The relationship between the weight loss rate and the fiber mixing rate is shown in the graph of FIG.

(Comparative Examples 1 to 4)
The fiber to be mixed is replaced with the organic fiber, and the diameter is 17 μm.
Length of 20 mm, weight residual ratio when heated to 500 ° C is 7
Concrete was manufactured in the same manner as in Example 1 except that 6% of acrylic fiber was used, and the mixing amounts were 0.05% by volume, 0.1% by volume, 0.2% by volume, and 0.3% by volume. And Comparative Examples 1 to 4, respectively. Similarly to Example 1, the concretes of Comparative Examples 1 to 4 were subjected to the (6) fluidity test of the concrete and (7) the fire resistance test. The results are shown in Table 2.

[0026]

[Table 2]

From the graphs in Table 2 and FIG. 3, in Examples 1 to 4, there is little decrease in fluidity as compared with concrete in which no fiber is mixed (in FIG. 3, the amount of fiber mixed = 0), which is a practical problem. It can be seen that there is no level. Table 2
4 and in the graph of FIG. 4, in the fire resistance test, the weight change of Examples 1 to 4 was remarkably reduced as compared with concrete without fiber mixing (fiber mixing amount = 0 in FIG. 4). With the mixing amount of 0.05% by volume of organic fiber,
It can be seen that there is a sufficient effect of preventing explosion. on the other hand,
In Comparative Examples 1 to 4 in which organic fibers outside the scope of the present invention were mixed, the change in weight in the fire resistance test was not different from that in the case of no mixing, and no explosion preventing effect was observed.

[0028]

According to the present invention, since the present invention has the above-described structure, it is possible to effectively suppress explosion without lowering the fluidity, and to provide an economical high-strength explosion-resistant concrete. Play.

[Brief description of the drawings]

1 (A) to 1 (C) are model diagrams showing effective concrete columns and fiber holes for explosion resistance studies.

FIG. 2 is a graph showing the relationship between the diameter of an effective concrete column and the amount of fiber mixed into concrete for each fiber diameter.

FIG. 3 is a graph showing the relationship between the mixing ratio of fibers and the fluidity of explosion-resistant concrete mixed with organic fibers.

FIG. 4 is a graph showing the relationship between the weight loss rate of explosion-resistant concrete mixed with organic fibers and the mixing rate of fibers.

[Explanation of symbols]

 10 Effective concrete columns 12 Fiber holes (voids)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C04B 16:06) 111: 28 (72) Inventor Akio Kohira 1-5-1, Otsuka, Inzai-shi, Chiba Pref. Takenaka Corporation In-store Technology Research Institute (72) Inventor Hideo Fujinaka 1-5-1, Otsuka, Inzai City, Chiba Prefecture Co., Ltd. In-store Takenaka Corporation Technical Research Institute (72) Inventor Kenro Mitsui 1-5-1, Otsuka 1, Inzai City, Chiba Prefecture Stock Company (72) Inventor: Yasuyuki Yamazaki, 3-4-1-17 Ecchujima, Koto-ku, Tokyo Shimizu Construction Co., Ltd. (72) Akira Nishida, 3-4-1-17 Ecchujima, Koto-ku, Tokyo Shimizu Construction Co., Ltd. Technical Research Institute (72) Inventor Takeshi Morita 3-4-17 Etchujima, Koto-ku, Tokyo Shimizu Construction Co., Ltd. Technical Research Laboratory F-term (reference) 2E001 DE01 EA01 HA04 JD04 4G012 PA04 PA24 PB04 PB32 PC02 PC11 PC12 4G056 AA08 AA11 CB23 CC04

Claims (2)

[Claims] 1. The method according to claim 1, wherein the weight residual ratio when heated to 500 ° C. is 3
5-100 μm in diameter made of an organic material that is 0% or less
m, containing 0.02 to 0.2% by volume of organic fibers having a length of 5 to 40 mm and a water binder ratio of 35% or less. 2. The explosion-resistant concrete according to claim 1, wherein the organic material constituting the organic fibers is at least one selected from the group consisting of polypropylene and vinylon.