JPH07277798A - Precast concrete frame and its production - Google Patents

Abstract

PURPOSE:To obtain a precast concrete frame having excellent permanence, fire resistance and flexural strength, by blending cement with a fine aggregate, fly ash fibers, alkali-resistant glass fibers and a water reducing agent, molding and curing. CONSTITUTION:Cement is kneaded with a fine aggregate wholly passing through a 10mm sieve, fly ash fibers, alkali-resistant glass fibers and a water reducing agent by a twin-screw forced mixer or Omni-mixer in such a way that the content of the fly ash fibers and the alkali-resistant glass fibers is 3-8vol.% and the water cement ratio is about 27-35vol.% to give fresh concrete. The concrete is cast into a mold, extrusion molded or press molded and cured with steam or by an autoclave at 40-150 deg.C to give a precast concrete frame.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precast concrete formwork and a method for producing the same, and more particularly to a precast concrete formwork which is excellent not only in durability and fire resistance but also in bending strength and the production thereof. Regarding the method.

[0002]

2. Description of the Related Art In recent years, the shortage of skilled workers in the construction industry has become a problem, and in order to rationalize construction, when constructing pillars, beams or walls of structures with concrete, the factory For example, a method of using a precast concrete formwork (hereinafter also referred to as a PC formwork) manufactured from cement and fine aggregate has been developed. In this construction method, the PC form itself is integrated with the concrete cast inside it to form the outer perimeters of columns, beams, walls, etc. Therefore, the work of removing the form can be omitted, and the material of the form can be omitted. As wood is not used as such, forest resources can be protected.

[0003]

Glass fibers, carbon fibers, aramid fibers or vinylon fibers are known as fibers for reinforcing the PC form. Among these fibers, the glass fiber has fire resistance, so the PC formwork reinforced with this has no problem in fire resistance, but since glass fiber originally has poor alkali resistance, the action of cement that is alkaline is effective. As a result, the strength of the PC mold reinforced with glass fiber tends to gradually decrease, and thus the PC mold has poor durability. Therefore, the durability can be improved by using the alkali resistant glass fiber, but it is still insufficient.

On the other hand, the PC formwork reinforced with carbon fiber, aramid fiber or vinylon fiber is durable but poor in fire resistance because these fibers are alkali resistant. Under such circumstances, there has been a demand for development of a PC formwork having high durability and sufficient fire resistance.

[0005]

Means for Solving the Problems The present inventor has conducted various studies on fly ash fibers described below as reinforcing materials for PC formwork, and as a result, fly ash fibers and alkali resistant glass fibers are used as the reinforcing materials. When used together, PC
It has been found that not only is the durability and fire resistance of the formwork improved, but so too is its bending strength.

The present invention has been invented based on the above findings, and not only is excellent in durability and fire resistance,
(1) A precast concrete formwork made of cement, fine aggregate, fly ash fiber and alkali resistant glass fiber, and (2) for the purpose of providing a precast formwork excellent in bending strength and a method for producing the same. Cement, fine aggregate, fly ash fiber, alkali resistant glass fiber and water reducing agent are mixed to make fresh concrete, which is then molded and aged at high temperature, relating to a method for producing a precast concrete formwork Is.

The fly ash fiber used in the present invention produces coal ash produced when coal is burned in a thermal power plant or the like in the range of several thousand and several hundreds, preferably 1100 to 1900.
It can be produced by fiberizing a high-temperature melt obtained by melting at a high temperature of 140 ° C to 1700 ° C.
Although its composition varies depending on the origin of coal, it is mainly composed of silicon dioxide and alumina, and these two minerals account for about 60 to 80% by weight of the whole. In addition, a small amount of ferric oxide, calcium oxide, magnesium oxide, etc. are contained.

The specific gravity of the fly ash fiber used in the present invention is generally 2.2 to 2.6. The fiber length is not particularly limited and is not necessarily uniform, but is 5
It is preferably in the range of -30 mm. Generally, the fiber diameter is preferably 3 to 20 μm. The tensile strength depends on the fiber diameter and is not necessarily uniform.
It is preferably in the range of up to 4000 MPa. The tensile modulus is preferably in the range of 20 to 200 GPa.

Alkali-resistant glass fibers are usually G
Alkali resistant glass fibers used for RC (glass fiber reinforced concrete) can be used,
For example, ARG fiber manufactured by Nippon Electric Glass Co., Ltd. may be mentioned. The specific gravity is 2.7. Fiber length is generally 10
˜50 mm, fiber diameter is generally 12-15 μm, tensile strength is generally 1000-2000 MPa,
The tensile modulus is generally 75000 MPa.

As the cement, a commonly used cement can be used, and examples thereof include ordinary Portland cement or early strength Portland cement, blast furnace cement or fly ash cement. The cement may optionally be mixed with silica fume or blast furnace slag fine powder.

As the fine aggregate, fine aggregate which is usually used for concrete can be used, and preferably, fine aggregate that passes through all 10 mm sieve and 85% or more by weight of 5 mm sieve is used.

As the water reducing agent, any commonly used water reducing agent can be used. For example, lignin sulfonate, naphthalene sulfonate, oxycarboxylate, alkylallyl sulfonate, melamine sulfonate. Although a salt etc. are mentioned, More preferably, a high performance water reducing agent is used. The high-performance water reducing agent can improve the workability of kneaded concrete significantly and increase the strength of hardened concrete in a smaller amount. For example, naphthalene sulfonic acid formalin condensate and alkylnaphthalene sulfonate condensate. , Melamine sulfonate condensates, aromatic amino sulfonic acid-based polymer compounds, and the like.

The PC mold of the present invention can be manufactured, for example, as follows. Only fly ash fibers and alkali resistant glass fibers or fly ash fibers are mixed into the cement to evenly disperse these fibers in the cement. At this time, it is important that the fibers are well dispersed in the cement. Otherwise, a so-called fiber ball is formed in the subsequent kneading step, which causes a decrease in strength of the PC mold. Then, fine aggregate, water and a water-reducing agent, or fine aggregate, water, a water-reducing agent and alkali resistant glass fibers are added and mixed to obtain fresh concrete. At this time, any mixer can be used as long as it can be sufficiently kneaded and mixed, and preferably a biaxial forced mixer or an omni mixer is used. The water cement ratio is preferably 27-35% by volume, especially about 30%
Is. If it is less than 27% by volume, the consistency of the obtained fresh concrete is poor and it cannot be put to practical use.
This is because if it is higher than 35% by volume, the desired bending strength of the PC form cannot be obtained.

The slump value of the obtained fresh concrete is not particularly limited, but it is preferably 10 to 18 cm. The fresh concrete is then shaped into the desired mold. As the molding method, any method known as a molding method can be used. For example, U
A method of pouring into a mold such as a groove, a U-shape, or a flat plate, and applying vibration to the mold to compact it, or extrusion molding or press molding may be used.

After molding the fresh concrete, it is cured. As a curing method, any method known as a curing method can be used. However, in order to accelerate the removal time of the mold and to secure the bending strength required for the PC mold, 40 A high temperature curing which is a curing at a temperature of up to 150 ° C. is preferable, and a steam curing or an autoclave curing which is curing using steam is particularly preferable.

In the present invention, the content of fly ash fibers and alkali resistant glass fibers is preferably 3-8% by volume. If this content is less than 3% by volume, sufficient bending strength of the concrete form cannot be obtained. On the other hand, if it exceeds 8% by volume, fiber balls are likely to be formed in the kneading step, and the strength is rather reduced. Because. The mixing ratio of fly ash fiber and alkali resistant glass fiber is not particularly limited.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 Using a special mixer in which 10 parts by weight of fly ash fiber and 90 parts by weight of early-strength Portland cement were mixed in advance, the cement was mixed to have the composition shown in Table 1,
Silica fume, fly ash fiber, alkali-resistant glass fiber and fine aggregate were put into an omni mixer and kneaded for 45 seconds. After kneading for 1 minute, fresh concretes 1 to 4 were obtained.

[0018]

[Table 1] These fresh concrete 1-4, respectively,
It is poured into a mold, compacted by applying vibration to the mold, molded into a flat plate with a thickness of 20 mm, steam-cured at 60 ° C. for 6 hours, and sealed at 20 ° C. for 28 days, and then the concrete plate of the present invention. 1 and comparative concrete 1-3 plates were obtained.

The fire resistance and durability of these concrete boards were investigated. It was found that the concrete plate 1 of the present invention has excellent fire resistance and durability as compared with the comparative concrete plates 1 to 3.

Further, the compressive strength, the bending strength and the bending proportional limit strength of the concrete obtained by using the fresh concretes 1 to 4 having the compositions shown in Table 1 were measured. The compressive strength is measured according to JIS R5201, and the dimensions of the specimen are 40 mm in length × 40 mm in width × 4 in height.
It was set to 0 mm. Bending strength was measured according to the GRC test method, and the dimensions of the specimen were 400 mm in length × 100 mm in width × 20 mm in thickness. The loading method was the central concentrated loading method, 300 mm span, and loading. A condition of speed 2 mm / min was adopted.

The results are shown in Table 2. From Table 2, the bending strength of the concrete plate 1 of the present invention is not only greater than the bending strength and the bending proportional limit strength of the comparative concrete plate 1 containing no fibers, but also the comparative concrete plate containing only fly ash fibers. 2 or the bending strength and bending proportional limit strength of the comparative concrete plate 3 containing only the alkali resistant glass fiber, the combined use of the fly ash fiber and the alkali resistant glass fiber shows the bending strength and the bending proportion. It can be seen that the reinforcing effect on the limit strength is high. In particular, when fly ash fiber is used in combination with alkali resistant glass fiber, it is a remarkable effect that the bending proportional limit strength increases.

[0022]

As is apparent from the above description, according to the present invention, the precast formwork is excellent not only in durability and fire resistance but also in bending strength and bending proportional limit strength. And a method for manufacturing the same are provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C04B 24:00) 103: 32 111: 20 111: 28 (72) Inventor Shohei Hoshino Minato-ku, Tokyo Akasaka 4-9 9 Japan National Land Development Co., Ltd. (72) Inventor Kenichi Iso Akasaka 4, 9-9 Minato-ku, Tokyo Japan National Land Development Co., Ltd. (72) Inventor Takuya Akinaga 4 Akasaka, Minato-ku Tokyo 9th-9th Japan National Land Development Co., Ltd.

Claims (2)

[Claims] 1. A precast concrete formwork comprising cement, fine aggregate, fly ash fiber, alkali resistant glass fiber and a water reducing agent. 2. A precast concrete formwork characterized by mixing cement, fine aggregate, fly ash fiber, alkali resistant glass fiber and water reducing agent to make fresh concrete, which is then molded and aged at high temperature. Production method.