JP2876514B2 - Carbon fiber reinforced concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

[0001] The present invention relates to an improved carbon fiber reinforced concrete.

[0002]

2. Description of the Related Art Cement-based matrices used as materials for construction and civil engineering have brittle properties, and as such, lack reliability as a structural material alone.
Reinforcing bars have been used for the purpose of complementing. recent years,
Further improvement of the properties (mainly strength) of the structural material by the reinforcing fiber has been studied. For example, by mixing an appropriate amount of carbon fiber into a cement matrix, strength properties, deformation properties, elastic properties, etc., that could not be exhibited by conventional cement concrete, can be imparted. I have.

[0003] However, by the application of carbon fiber,
It turned out that there was a basic problem that could not be considered in ordinary concrete work. That is, when a metal comes into contact with carbon fiber reinforced concrete, the corrosion (oxidation) of the metal proceeds significantly. That is, in the implementation of carbon fiber reinforced concrete, when using reinforcing bars, steel frames, formwork, binding wires, anchor fasteners, spacers and other hardware, these metals are usually in contact with the carbon fiber reinforced concrete, Rapid corrosion, which is unthinkable in concrete, progresses.

It is thought that various factors are acting on this, and the basic factors are the conductivity and oxidation-reduction potential of carbon fibers. That is, the carbon fiber has extremely good conductivity and the potential has a noble potential comparable to a noble metal, and when the carbon fiber comes into contact with a metal such as base iron, a local battery is formed there. This local battery action is the main cause of the metal corrosion. Therefore, in order to prevent metal corrosion in carbon fiber reinforced concrete, it is conceivable to lower the conductivity of carbon fiber, set the oxidation-reduction potential to a lower potential, or cut off the contact between the carbon fiber and the lower metal. Can be

Conventionally, various attempts have been made to prevent corrosion of metal as follows. (1) Resin between carbon fiber reinforced concrete and metal,
A method of forming an electrical insulating layer made of any of ceramic and rubber components and curing reinforced concrete
(JP-A-184810) (2) A method of using an insulating resin for the electric insulating layer
(3) A method in which an inorganic material is used for an electric insulating layer (Japanese Patent Application Laid-Open No. 60-1985)
And (4) a method of using an epoxy resin for the electric insulating layer (Japanese Patent Laid-Open No. 62-21744). These methods mainly cut off the contact between the carbon fiber and the base metal. That's what the method is trying.

[0006]

In any of the above-mentioned prior arts, the metal fibers are coated with an electrically insulating material to prevent direct contact between the carbon fibers and the metal in the reinforced concrete. Insulation is attempted, but this insulation method has the following problems.

[0007] One problem is that when a large area such as a mold is to be insulated and coated with a metal material that comes into contact with the carbon fiber reinforced concrete, thickness unevenness is apt to occur. Direct contact with the metal, causing metal corrosion due to the formation of local cells. In addition, the uneven thickness may form fine irregularities on the surface of the obtained carbon fiber reinforced concrete, which may adversely affect the finish of the coating.

In addition, for example, in the case of a reinforcing bar or a steel frame, adhesion to concrete must be taken into consideration, and the insulating layer is likely to peel off when these are transported, moved or constructed. , Etc. are mentioned as problems.
Therefore, when obtaining carbon fiber reinforced concrete,
There is a need for a reinforced concrete that does not suffer from the limitations described above.

[0009]

The present inventors have conducted intensive studies to develop a carbon fiber reinforced concrete which is not restricted by these conventional methods and has excellent resistance to metal corrosion, and as a result, has a high specific resistance. The present inventors have found that the use of carbon fiber reinforced concrete suppresses metal corrosion at a portion where concrete and a metal material come into contact, and reached the present invention.

The gist of the present invention is to provide a reinforcing concrete comprising a cement component and 0.3% by volume or more of carbon fiber.
1 day in a humidity chamber at 20 ° C and 90% or more humidity
The carbon fiber reinforced concrete is characterized in that the reinforced concrete that has been cured, removed from the mold, and cured in water for 7 days has a specific resistance of 500 Ω · cm or more.

Hereinafter, the present invention will be described in detail. The specific resistance of the carbon fiber reinforced concrete of the present invention is 100Ω · cm.
It is necessary that the above is satisfied, whereby the corrosion of the metal material in contact with the carbon fiber reinforced concrete can be suppressed. To more completely prevent metal corrosion, a specific resistance of 50
It is preferably 0 Ω · cm or more.

In order to achieve the above specific resistance of the carbon fiber reinforced concrete of the present invention, a carbon fiber having a specific resistance of 1.0 × 10 ⁻² Ω · cm or more is used. Furthermore, the specific resistance of the carbon fiber is more preferably 0.5 × 10 ⁻¹ Ω · cm or more. In addition, even if the carbon fibers in the carbon fiber reinforced concrete have a high volume fraction, in order to keep the specific resistance of the carbon fiber reinforced concrete sufficiently high, the specific resistance of the carbon fibers must be 1.0 × 10 ⁻¹ Ω · cm or more. It is even more preferred. If the specific resistance is less than 500 Ω · cm, galvanic corrosion due to contact between the metal and the carbon fiber is likely to proceed. That is, it is considered that the presence of the highly conductive carbon fiber in the cement matrix increases the cathode area of the galvanic corrosion battery, and forms so-called small and large anodes to promote corrosion.

[0013] To confirm this, the corrosion potential and the polarization curve as shown below were measured in order to examine the metal corrosion reaction occurring in concrete and how the conductive carbon fiber participated in the reaction. went.

The corrosion potential was determined by measuring the specific resistance of 1 × 10 ⁻³ Ω · cm carbon fibers chopped to a length of 3 mm in a resin container at 0.5% by volume (V _f = 0.5%) and 1%. 0.0% by volume
( _Vf = 1.0%) A steel specimen and a reference electrode (Ag-AgCl) through a salt bridge were inserted into a kneaded mixture and a cement paste not kneading carbon fibers (without CF), and Hokuto Denko With the use of a potentiostat (HZ-1A) manufactured by Co., Ltd., the change with time of the potential between the steel specimen and the reference electrode was measured. FIG. 1 shows the results.

As shown in FIG. 1, the corrosion potential of the steel material shifts to the noble side at first, and then shifts to the base side with the passage of time. Normally, the pH of cement is as high as 12 to 13, and iron forms a passivation in this region. It is considered that the change in the initial corrosion potential is due to transient development in which a passivation layer is formed on the surface of the steel material. In addition, the shift of the corrosion potential to the base side is that if the cathodic reaction of corrosion is a reduction reaction of oxygen, oxygen in the cement is gradually consumed and oxygen is deficient because the supply is moderate. It seems to do.

When carbon fibers are dispersed in cement as compared to a cement paste containing no carbon fibers (V _f =
(0.5% and V _f = 1.0%) increased in the noble direction. Also, the value increased in proportion to the amount added. This is because if the corrosion potential is determined by the oxidation-reduction reaction of oxygen on carbon fiber, the carbon fiber in the cement comes into contact with the steel material, the site where the cathode reaction occurs increases, and the corrosion potential increases. Conceivable.

Next, a description will be given of a measurement of a polarization curve performed to grasp the corrosion reaction more quantitatively. The polarization curve was measured with a three-electrode system using a Pt electrode as a counter electrode for a steel material serving as a working electrode in a corrosion potential measurement system. Ag-AgCl and a potentiostat (HZ-1A) manufactured by Hokuto Denko KK were used for the reference electrode as in the measurement of the corrosion potential.

FIG. 2 shows a schematic diagram of the metal corrosion reaction. In the steady state of corrosion, the anodic reaction current and the cathodic reaction current are equal, so the corrosion state is represented by the intersection of two polarization curves. The potential and the current density at the intersection are the corrosion potential and the corrosion current density, respectively.

FIG. 3 shows that a specific resistance of 2.0 × 10
^When 1.0% by volume of ^-3 Ω · cm carbon fiber is dispersed (V _f = 1.0%), no carbon fiber is inserted (no CF)
The case shows the polarization behavior of a steel material inserted into the cement. It can be seen that the corrosion current is significantly increased by adding carbon fiber to the cement, and is increased by about 10 times. From now on, carbon fiber in cement will come into contact with steel,
It can be seen that corrosion is significantly accelerated.

As described above, when contact between cement and carbon fiber is unavoidable, the electrical properties of the carbon fiber itself, particularly the specific resistance and the volume fraction of the carbon fiber in the carbon fiber reinforced concrete, reduce the magnitude of the corrosion rate. Depends. In other words,
It can be seen that the specific resistance of the carbon fiber reinforced concrete itself determines the magnitude of the corrosion rate. Therefore, as a carbon fiber that can be used in the present invention, excellent expression of strength properties,
Polyacrylonitrile-based carbon fibers having characteristics balanced with required performance including specific resistance are preferable.
As the strength characteristics, the strand tensile strength is 100 kg /
mm ² or more is preferable. The form of the carbon fiber may be a long fiber or a short fiber.

The amount of carbon fiber in the concrete of the present invention is in the range of 0.1 to 20% by volume fraction, but considering the strength of the carbon fiber reinforced concrete and the cost performance of the reinforced concrete, 0.3%. Is preferably in the range of 2% to 2%.

The high-resistivity carbon fiber used in the present invention exhibits strong adhesiveness to cement without any particular surface treatment. However, the surface treatment by oxidation of a chemical such as nitric acid or the like, the surface treatment in high-temperature air or ozone. Treatment, surface treatment in plasma of gas such as Ar, O ₂ , CF _3, etc., and surface treatment by electrolytic oxidation in electrolyte such as nitric acid, sulfuric acid, sodium hydroxide, bicarbonate, nitrate, phosphoric acid, etc. The adhesiveness and dispersibility of carbon fiber and cement can be further improved. Also,
Improve adhesion and dispersibility by coating the surface of carbon fiber with immersion treatment of inorganic or organic low molecular or high molecular, chemical vapor deposition (CVD), physical vapor deposition (PVD), electrolytic polymerization, etc. Can be planned. In particular, by treating the carbon fiber surface with an aminosilane coupling agent, the adhesiveness and dispersibility can be further improved.

The reinforcing bars used in the present invention may be those used for ordinary reinforced concrete, and are not particularly limited. In addition, it is usual to use a reinforcing bar in which black scales are actively generated. In this case, since the oxide film acts as an insulating layer, it is expected that the generation of a local battery is imperfectly suppressed.

The carbon fiber reinforced concrete according to the present invention can be prepared by dispersing carbon fibers in a cement matrix.
Alternatively, regardless of the amount of various additives and admixtures, and irrespective of the type of cement, it exerts an effect of preventing metal corrosion due to local battery formation due to the conductivity of carbon fibers. .

[0025]

EXAMPLES The present invention will be described below more specifically based on examples. [Examples 1 to 3], [Comparative Examples 1 and 2] Using polyacrylonitrile fiber as a raw material, carbonization firing temperatures of 600 ° C. (used in Example 1), 800 ° C. (used in Example 2), 900 ° C. (executed) Table 1 shows the strand strength and the specific resistance of the carbon fibers treated at 1300 ° C. (used in Example 3) and 1300 ° C. (used in Comparative Example 1).

[0026]

[Table 1]

The obtained carbon fiber was kneaded into a cement paste having the composition shown in Table 2 at a volume fraction of 1%.
To 3 and Comparative Example 1. In the carbon fiber reinforced concrete, a black bar-free ordinary rebar polished with sandpaper # 400 and sufficiently degreased with acetone is buried, and the temperature is 40 ° C. ×
After steam curing for 5 hours, 18 hours in an autoclave.
After carrying out a corrosion acceleration test (1st time) at 0 ° C. × 10 atm × 5 hours, and after further treatment in an autoclave under the same conditions (2nd time), the steel was taken out of the concrete, The corrosion occurrence rate of the surface (corrosion area / total surface area × 100%) was examined. Table 3 shows the results. As Comparative Example 2, the state of corrosion of the reinforcing bar was examined in the same manner as in the example without carbon fibers. Table 3 also shows the results.
It was shown to.

[0028]

[Table 2]

[0029]

[Table 3]

Table 4 shows the flexural strength of carbon fiber reinforced concrete and the specific resistance of carbon fiber reinforced concrete obtained by blending the carbon fibers used in each of the examples and comparative example 1 in the concrete shown in Table 2. Comparative Example 2
The concrete is also shown. Curing at that time was carried out by curing in a humidity chamber at 20 ° C. and a humidity of 90% or more for 1 day, followed by removing the mold and curing in water for 7 days. Specimen size is JI
The measurement was performed at 4 cm × 4 cm × 16 cm according to S-R5201. In each of the examples, the development of sufficient strength was confirmed at a low volume fraction.

[0031]

[Table 4]

[0032]

The carbon fiber reinforced concrete of the present invention is
Since carbon fibers having extremely high specific resistance and high strength are used, excellent resistance to corrosion of metals such as reinforcing bars and steel frames in concrete and high bending strength can be achieved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between corrosion potential of steel in cement and time.

FIG. 2 shows a block diagram of a metal corrosion reaction.

FIG. 3 is a graph showing the polarization behavior of a steel material by carbon fibers in cement.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C04B 14:38 24:00) 111: 26 111: 90 (72) Inventor Yoshikazu Takei 191-1 Tobita-Ki 2-chome, Chofu City, Tokyo No. Kashima Construction Co., Ltd.Technical Research Laboratories (72) Inventor Tatsuo Suenaga 2-9-1, Tobita-Ki, Chofu-shi, Tokyo Kashima Construction Co., Ltd. No. 1 Kashima Construction Co., Ltd. Technical Research Institute (56) References JP-A-7-211418 (JP, A) JP-A-7-206502 (JP, A) JP-A-7-81989 (JP, A) JP-A-4-74747 (JP, A) JP-A-3-174342 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 28/02 C04B 14/38 D01F 9/22

Claims (5)

(57) [Claims] 1. A reinforced concrete consisting of cement component and 0.3% by volume or more of carbon fibers, 20 ° C., humidity
After curing for 1 day in a humidity chamber of 90% or more, remove the mold and water for 7 days.
Specific resistance value of reinforced concrete moderately cured is 500 Ω · c
m or more. 2. The method according to claim 1, wherein the carbon fiber content is 0.3 to 2 % by volume.
Item 6. The carbon fiber reinforced concrete according to Item 1 . 3. The method according to claim 1, wherein the specific resistance value is 7 kΩ · cm or more.
Item 6. The carbon fiber reinforced concrete according to Item 1 . 4. A carbon fiber having a specific resistance of 1.0 × 10 ^−2.
3. The carbon fiber reinforced concrete according to claim 1, which has a resistance of not less than Ω · cm. 5. The carbon fiber has a strand strength of 100 kg.
/ Mm ² or more, the carbon fiber reinforced concrete according to any one of claims 1 to 3.