JP3437060B2 - Ultralight prestressed concrete - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-lightweight prestressed concrete in which prestress is introduced into a superlightweight concrete by using a cable-like tension material mainly composed of a bundle of aramid fibers or the like. Used for construction of piers, precast seismic walls, etc.

[0002]

2. Description of the Related Art Since ordinary concrete is strong against compression but weak against tension, reinforced concrete with reinforcing bars embedded in concrete and prestressed concrete in which prestress is introduced using PC steel are extremely It is commonly used.

Further, fiber-reinforced concrete in which carbon fibers (short fibers, long fibers), aramid fibers, etc. are mixed into the concrete to reinforce it, the tensile strength of the concrete member is improved and the concrete is prevented from being partially chipped. It is known to be very effective in doing this.

On the other hand, since concrete has a large weight and is difficult to handle, especially in the case of precast products and the like, various lightweight concrete using lightweight aggregate, super lightweight concrete, lightweight cellular concrete, etc. have been developed. ing. In addition, lightweight concrete is also reinforced with reinforcing bars and fibers.

Further, for example, in Japanese Unexamined Patent Publication No. 5-331959, a fiber reinforced concrete using a lightweight aggregate, a carbon fiber having a fiber length of several mm to several cm as a reinforcing fiber,
A fiber-reinforced concrete having a low specific gravity in which short fibers such as aramid fibers are mixed is described, and further, such a fiber-reinforced concrete is provided with an FRP reinforcing bar having a carbon fiber as a core material, or the FRP reinforcing bar. There is a statement that pre-stress can be introduced.

[0006]

Conventionally, regarding prestressed concrete, the pretensioning method and the posttensioning method which are general prestressing methods are
All of them are simple methods, and it is possible to improve the tensile strength of the product by introducing prestressing to ultra-lightweight concrete by these methods, as in the case of ordinary concrete. It is possible.

However, in reality, effective prestressing has not been introduced into super lightweight concrete made of PC steel or the like, which is common in ordinary concrete.

The reason for this is that ultra-lightweight concrete having an air-dry specific gravity of 1.5 or less has lower strength than ordinary concrete, and it is often difficult to introduce a large prestress, and the Young's modulus is also the same. Even if an attempt is made to introduce prestress with PC steel having a Young's modulus of about 200 × 10 ³ N / mm ² , which is about 40 to 60% that of ordinary concrete having a level of strength, the super lightweight concrete itself shrinks easily. Therefore, it is difficult to introduce the prestress in the form of residual stress.

The carbon fiber has a Young's modulus E of about (140 to 150) × 10 ³ N / mm ² and, like the case of PC steel, an ultra-lightweight concrete having an air-dry specific gravity of 1.5 or less. It is difficult to introduce prestress into the.

The present invention has been made under the background as described above, and the super-precious concrete of air-dry specific gravity of 1.5 or less and the compressive strength of 30 N / mm ² or more can be manufactured by the conventional pre-casting method. It is an object of the present invention to provide an ultralight prestressed concrete in which effective prestress is introduced by the tension method or the post tension method.

[0011]

SUMMARY OF THE INVENTION In the present invention, ultra-lightweight concrete having an air-dry specific gravity of 1.5 or less and a compressive strength of 30 N / mm ² or more has a Young's modulus (30 to
70) Introduce prestress using a cable-like tendon mainly composed of a bundle of fibers of 10 ³ N / mm ² .

The compressive strength of ultra-lightweight concrete is 30 N /
If it is less than mm ² , the Young's modulus of the ultralight concrete becomes small, and the Young's modulus is (30 to 70) × 10 ³ N / m.
Even if a cable having a fiber bundle of m ² as a main component is used, prestress loss is large, which is not preferable.

If the air-dry specific gravity of the ultra-lightweight concrete exceeds 1.5, the weight of the precast product and the like becomes heavy, the effect of weight reduction is low, and the handling becomes difficult, which is not preferable.

If the air-dry specific gravity of the ultra-lightweight concrete is less than 1.0, it is difficult to increase the compressive strength to 30 N / mm ² or more. Therefore, the air-dry specific gravity of the ultra- lightweight concrete is 1.0 or more. Preferably.

The tendon material in the present invention is a cable mainly composed of a bundle of fibers having a Young's modulus of (30 to 70) × 10 ³ N / mm ^2, that is, a fiber of the Young's modulus is knitted in a braided shape and is made of resin. Use a cable that has been impregnated and cured.

Young's modulus of the fiber is 70 × 10 ³ N / mm
^When it exceeds ² , super-lightweight concrete is easily shrunk, which makes it difficult to introduce prestress in the form of residual stress, which is not preferable. Young's modulus of fiber is 30 × 10
^If it is less than ³ N / mm ^2, it is difficult to introduce prestress to the super lightweight concrete, which is not preferable.

Examples of the fiber having the Young's modulus include aramid fiber and glass fiber. Among them, aramid fiber is preferable from the viewpoint of heat resistance.

The diameter of the cable used in the present invention is 13
It is preferably about 20 mm. As the aramid fiber, a commercially available fiber can be used, and examples thereof include FA13 and FA15 manufactured by Fivex Co., Ltd.

Ultralight concrete has an air-dry specific gravity of 1.5.
As long as the compressive strength is 30 N / mm ² or more, any material may be used and the air amount is 10
Approximately 25% of aerated lightweight concrete (see Examples 1 and 4 described below) may be used. For example, a lightweight fine aggregate having an absolute dry specific gravity of 1.2 or less and an absolute dry specific gravity of approximately 0.8 may be used. It is also possible to use ultra-light concrete (see Examples 2, 3, 5, 6 described later) in which lightweight coarse aggregate is combined.

The super lightweight concrete material will be described below.

Examples of the lightweight coarse aggregates include commercially available lightweight coarse aggregates such as Asanolite (manufactured by Nippon Cement Co., Ltd.), Mesalite (manufactured by Mesalite Co., Ltd.) and FA Light (manufactured by Kyuden Sangyo Co., Ltd.). Alternatively, a lightweight coarse aggregate obtained by firing a raw material granulated product of a glassy raw material, a foaming agent, and an adhesive material to obtain the foam is obtained.

The lightweight coarse aggregate has a water absorption of 5.
When a lightweight coarse aggregate having a content of 0% or less is used, the freeze-thaw resistance of ultra-lightweight concrete becomes good, which is preferable.

The lightweight coarse aggregate having a water absorption rate of 5.0% or less is, for example, 100 parts by weight of a glassy raw material, a foaming agent of 0.
It is obtained by firing and foaming a raw material granulated product in a ratio of 1 to 2.0 parts by weight and an adhesive material of 0.1 to 10.0 parts by weight.

From the viewpoint of the strength of the aggregate, rhyolitic glassy powder and waste glass powder are preferable as the above glassy raw material. Specific examples of rhyolite glassy powder include pearlite,
Obsidian, malecanite, minestone, shirasu, etc.
Examples of waste glass include waste materials of glass products such as glass bottles and window glass.

As the foaming agent, SiC, Si ₃ N ₄ , AlN and SiAlON are preferable from the viewpoint of combination with a glassy raw material, and SiC is particularly preferable from the viewpoint of easy handling and cost.

As the adhesive material, dextrin, polyvinyl alcohol, methyl cellulose, acrylic resin, bentonite and water glass are preferable, and bentonite is particularly preferable from the viewpoint of easy handling and cost. Granulation and calcination of the raw material mixture may be carried out using a conventional means.

The firing temperature is 900 to 1300 when rhyolitic vitreous powder is used as the vitreous raw material.
C. is preferably set to 700.degree. C., when waste glass powder is used.

Examples of the lightweight fine aggregates include commercially available lightweight fine aggregates such as Asanolite (manufactured by Nippon Cement Co., Ltd.), Perlite KP1 (manufactured by Asano Pearlite Co., Ltd.), and G-light (manufactured by Sunlight Industry Co., Ltd.). There are materials.

As the cement, there is usually mentioned Portland cement such as early strength Portland cement.

Examples of the water reducing agent include melamine type, naphthalene sulfonic acid type and polycarboxylic acid type water reducing agents (including high performance water reducing agents and high performance AE water reducing agents).

Examples of the kneading water include tap water.

Further, when air bubbles are mixed in the ultra-lightweight concrete, a protein-based or alkyl sulfate-based AE agent may be used.

In the present invention, a part of the cement is replaced with a fine powder admixture such as blast furnace slag fine powder having a Blaine specific surface area of 5000 cm ² / g or more and silica fume.
It is preferable because the strength of the super lightweight concrete is improved.

A conventional mixer such as a twin-screw forced kneading mixer, a pan-type mixer, or an omni mixer can be used for kneading the ultralight concrete.

The kneading method and kneading time of ultra-lightweight concrete are not particularly limited.

Molding of ultralight concrete is carried out by casting,
It can be carried out by a conventional means such as vibration molding.

Curing of ultra-lightweight concrete is also carried out by air-drying, moist air, water, steam curing, or a conventional means that uses them in combination.

After curing, the prestress is introduced into the super lightweight concrete by the pretensioning method or the posttensioning method.

The fiber used in the present invention has a tensile strength substantially the same as that of carbon fiber, but has a Young's modulus of (30 to 30).
70) × 10 ³ N / mm ^2, which is sufficiently smaller than PC steel, so even when used in ultralight concrete with a Young's modulus smaller than ordinary concrete, pre-tension or post-tension It becomes possible to introduce effective pre-stress.

The principle of this will be described below with reference to FIG.

FIG. 1 is a comparison of cases where prestressing is applied to concrete by the pretensioning method, and FIG. 1 (a) is a case where prestressing is applied to ordinary concrete using PC steel (Comparative Example 1). , Fig. 1 (b) shows the case of introducing prestress to the super lightweight concrete by using PC steel (Comparative example 2), and Fig. 1 (c) shows the cable-like tension mainly composed of the bundle of aramid fibers in the super lightweight concrete. The case where the prestress is introduced using the material (the present invention) is shown.

In the figure, E _N represents the Young's modulus of ordinary concrete having a compressive strength of about 35 _N / mm ² , which is 25 × 10 5.
The value is about ³ N / mm ² . Also, E _EL compressive strength indicates the Young's modulus of the ultra lightweight concrete of about 35N / mm ^2, taking ^{(10~15) × 10 3 N /} mm 2 a value of about.

In FIG. 1 (a), δ _P (representing 1/2 elongation of the whole) is applied to the PC steel material as the tension material by the tension force T.
Pre-stress is introduced into ordinary concrete by pouring ordinary concrete in a state where the elongation of the concrete has occurred, and releasing the tension T at the stage where the required strength is developed after curing. δ _N (1/2 of the whole
(Representing the amount of shrinkage of) is in a state where shrinkage has occurred.

On the other hand, in the case of FIG. 1 (b), when attempting to introduce prestressing with PC steel material as well, since the Young's modulus of ultra-lightweight concrete is small, δ _EL (1/1 of the whole)
A large amount of shrinkage (representing the amount of shrinkage of 2) occurs, and along with that, the stress in the super lightweight concrete of PC steel is almost released, so that effective prestressing is not introduced.

On the other hand, FIG. 1 (c) corresponding to the present invention.
Then, when the same tension force T is applied, the elongation δ _A (representing 1/2 elongation of the whole) of the cable mainly composed of the aramid fiber bundle is 3 to 4 times δ _P. Even after the release, sufficient stress remains in the cable mainly composed of aramid fiber bundles, and effective prestress is introduced into the ultralight concrete.

The above is the introduction of pre-stress by the pre-tension method, but the same can be considered for the post-tension method.

[0047]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention together with comparative examples (see Table 1).

(1) The materials used are shown below.

Cement; Early Strength Portland Cement (manufactured by Nippon Cement Co., Ltd.) Admixture: Blast furnace slag fine powder (Fine Cerament 10
A (Blaine specific surface area: 8000 cm ² / g): Daiichi Cement Co., Ltd. Admixture; High-performance AE water reducing agent (Reobuild SP-8H)
E: manufactured by NMB Co., Ltd., AE agent (Micro Air 7)
75S: NMB Co., Ltd. Light weight fine aggregate; A: Asanolite (Nippon Cement Co., Ltd.), absolute dry specific gravity 1.68, water absorption rate 9.8% B: Perlite KP1 (Asano Perlite Co., Ltd.) ),
Absolute dry specific gravity 1.04, water absorption 5.7% C: G light (manufactured by Sunlight Industry Co., Ltd.), absolute dry specific gravity 0.73, water absorption 4.0% Light weight coarse aggregate; A: Asanolite ( Nippon Cement Co., Ltd., absolute dry density 1.25, water absorption 9.7% B: Okushiri pearlite powder (Blaine value 5000 cm ² /
g) 100 parts by weight, SiC (manufactured by Showa Denko KK) 0.5 parts by weight, and bentonite (Toyo Bentonite Co., Ltd.)
(Made in Japan) 10.0 parts by weight of raw materials are mixed, granulated with a pan-type pelletizer, dried, and then fired and foamed at 1150 ° C. to obtain lightweight coarse aggregate, absolute dry weight 0.80, water absorption Rate 2.
4% C: Waste glass powder (Blaine value 5000 cm ² / g) 1
00 parts by weight, SiC (manufactured by Showa Denko KK) 0.1 parts by weight,
And bentonite (manufactured by Hoyo Bentonite Co., Ltd.) in an amount of 3 parts by weight, the raw materials were mixed, granulated with a pan-type pelletizer, dried, and then baked and foamed at 900 ° C. The dry specific gravity is 0.75 and the water absorption rate is 2.3%. In addition, the absolute dry specific gravity and water absorption rate of the lightweight fine aggregate are "JIS A 113".
4 (Specific gravity and water absorption test method for lightweight structural fine aggregates) ”, the absolute dry specific gravity and water absorption of the light weight coarse aggregate are“ JI
S A 1135 (Specific gravity and water absorption test method for lightweight structural aggregate).

(2) Mixing of concrete and mixing The above materials were put into a biaxial forced mixing mixer (1 m ³ ) at a ratio shown in Table 1 and mixed for 1.5 minutes to prepare an ultralight concrete.

[0051]

[Table 1]

(3) Introduction of molding, curing, and prestressing Each of the above concretes was made into a predetermined form (80 × 65 × 750).
cm) and vibration molded. After that, the temperature was raised to 60 ° C. at a temperature rising rate of 15 ° C./hr for 2 hours before being placed,
After holding for 6 hours, it was aged under the condition of natural cooling.

After curing, prestress was introduced. The introduction of prestress was performed using a simultaneous tensioner in the pretension system. In the post-tension system, the pulling jack was used.

The effective prestress was 11 ton / piece.

As the tension material, a cable mainly composed of a bundle of aramid fibers (FA15 manufactured by FIVEX Co., Ltd.,
Young's modulus 60 × 10 ³ N / mm ² ) or PC steel wire (Sumitomo Electric Co., Ltd., T15.2B, Young's modulus 200)
× 10 ³ N / mm ² ) was used.

(4) Air-Dry Specific Gravity of Evaluated Concrete After each concrete was put into a mold of φ10 × 20 cm, vibration molding (frequency of 4000 vpm) was performed for 30 seconds on a table vibrator. Then, after curing under the above conditions, the mold was removed, the weight and volume of the specimen were measured, and the specific gravity was calculated. The air-dry specific gravity was measured for three test pieces, and the average value was used as the air-dry specific gravity.

Compressive Strength of Concrete Regarding the above three specimens, "JIS A 1108
(Compressive strength test method for concrete) ”, and the average value was calculated.

Pre-stress loss amount A strain gauge and a displacement gauge are installed at predetermined positions of the tension member and the concrete molded body, and a load cell is installed in the tension member fixing portion, and the displacement amount at the time of introducing the pre-stress is measured. The amount of stress loss was calculated.

The results are shown in the lower part of Table 1.

[0060]

INDUSTRIAL APPLICABILITY According to the present invention, a fiber having a Young's modulus sufficiently smaller than that of PC steel or carbon fiber (Young's modulus is (30
~ 70) × 10 ³ N / mm ² ) A cable-like tension material mainly composed of a bundle of fibers is used to introduce prestress to the super lightweight concrete. , It becomes possible to introduce effective prestress.

As a result, it is possible to expand the applications to structural members and the like of ultra-lightweight concrete, which has a great advantage of lightweight.

[Brief description of drawings]

FIG. 1 is a conceptual diagram comparing the cases of prestressing concrete with a pretension method,
Is a case where prestress is introduced into ordinary concrete using PC steel (Comparative example 1), (b) is a case where prestress is introduced into super lightweight concrete using PC steel (Comparative example 2), and (c) is The case where the prestress is introduced into the ultra-lightweight concrete by using a cable-like tension material mainly composed of a bundle of aramid fibers (the present invention) is shown.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Tamura               1-16-6 Kitaotsuka, Toshima-ku, Tokyo Dopi               -In Construction Industry Co., Ltd. (72) Inventor Hiromi Fujiwara               1-2-23 Kiyosumi, Koto-ku, Tokyo Japan Semé               Central Research Institute (72) Inventor Tatsumasa Shibata               1-2-23 Kiyosumi, Koto-ku, Tokyo Japan Semé               Central Research Institute                (56) References JP-A-3-219911 (JP, A)                 JP 61-270280 (JP, A)                 JP-A-9-57087 (JP, A)                 JP-A-8-158315 (JP, A)

Claims (5)

(57) [Claims] 1. A bundle of fibers having a Young's modulus of (30 to 70) × 10 ³ N / mm ² in ultra-lightweight concrete having an air-dry specific gravity of 1.5 or less and a compressive strength of 30 N / mm ² or more. An ultra-lightweight prestressed concrete characterized by introducing prestressing using a cable-shaped tension material mainly composed of. 2. The fiber is an aramid fiber.
Ultralight prestressed concrete as described. 3. The super lightweight prestressed concrete according to claim 1 or 2, wherein a lightweight coarse aggregate having a water absorption rate of 5.0% or less is used. 4. 100 parts by weight of vitreous raw material, 0.
The lightweight coarse aggregate foamed by firing a raw material granulated product in a ratio of 1 to 2.0 parts by weight and an adhesive material of 0.1 to 10.0 parts by weight is used. Lightweight prestressed concrete. 5. The vitreous raw material is rhyolite glassy powder or waste glass powder; the foaming agent is SiC, Si ₃ N
_4, AlN, be either SiAlON; and, dextrin adhesive, polyvinyl alcohol, methyl cellulose, acrylic resins, bentonite, either or ultralight prestressed concrete according to claim 4, wherein a combination of these water glasses.