JPS60186447A - Carbon fiber reinforced concrete - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to improvements in carbon fiber reinforced concrete.

The inherent disadvantage of the brittle nature of cementitious matrices can be significantly improved by dispersing them with appropriate amounts of suitable fibrous materials, such as carbon fibres. Thanks to the development of inexpensive pitch-based carbon fiber, carbon fiber-containing reinforced concrete is being put into practical use, and has strength and deformation properties that were not possible with conventional cement concrete2.
There are great expectations for it as a new structural material with elastic properties.

The present inventors have been involved in the development of this carbon fiber-reinforced concrete for many years, and have found that there are fundamental problems in construction using this material that are not found in ordinary concrete. That is, when metal is in contact with this carbon fiber reinforced concrete, metal corrosion (
This is a phenomenon in which metal oxidation progresses significantly. For example, in the construction of this carbon fiber reinforced concrete.

When using reinforcing bars, steel frame 2wi formwork binding, anchor fasteners, spacers, and other hardware, on the surface where these metals come into contact with carbon fiber reinforced concrete,
Corrosion progresses at a rate unimaginable for ordinary concrete.

The present invention aims to solve this problem. For this purpose, the present inventors have conducted intensive research to elucidate the corrosion behavior described above, and have found that various causes interact with each other, but the basic principle is that carbon fiber is extremely conductive. When this carbon fiber comes into contact with a baser metal (usually iron or iron alloy), a local battery is formed, and this local It can be determined that battery action is the main cause of metal corrosion, and when reinforced concrete with carbon fibers dispersed at 0.2 to 10% by volume in a cementitious matrix is cured at the contact surface with metal, If this carbon fiber reinforced concrete is cured after forming an insulating layer made of an inorganic material with an electrical resistance of at least 100Ω or more on the surface of this metal, the problem of metal corrosion peculiar to this carbon fiber reinforced concrete can be solved. It turns out that the above can be almost completely solved in our favor.

The present invention interposes an inorganic insulating layer between the contact surfaces of carbon fiber reinforced concrete and metal, thereby cutting off direct contact between the carbon fibers in the cement matrix and the metal. It is characterized by preventing the local battery effect caused by the carbon fibers formed. In other words, when a carbon fiber-reinforced concrete mixture that has not hardened yet is cured while in contact with reinforcing bars, steel frames, metal formwork, binding wires, anchor fasteners, spacers, and other metal objects, the surface of these metals baser than carbon An electrically insulating layer is formed so that the carbon fibers in the cement matrix do not come into direct contact with each other, and an inorganic material with high insulation resistance is used to form this electrically insulating layer.

There are various types of inorganic materials with high insulation resistance, and basically any inorganic material other than metals or carbon-based materials exhibiting insulation properties can be applied to the present invention. However, in actual construction, things such as reinforcement, bone arrangement, and anchors that require high adhesion resistance with concrete, and items that do not require as much adhesion resistance such as formwork and spacers, and metal parts that are used, Depending on the relationship, it is necessary to consider the type and form of the inorganic material used. In order to form this inorganic insulating layer, if the adhesion resistance between the concrete and the metal member is not required, a sheet-like inorganic material layer may be wrapped or covered on the surface of the metal member, but in practice teeth,
From a construction standpoint, it is convenient to apply a treatment in advance to deposit an insulating layer of a predetermined thickness on the metal surface before contacting it with the carbon fiber reinforced concrete. More specifically, it is most convenient to form an electrically insulating layer by applying cement mortar or cement paste to the metal surface and curing it, and in this case, the material must have sufficient adhesion resistance to concrete. is obtained. Furthermore, instead of this type of cement-based material, a glass-based material or a metal oxide-based material may be used.

In this way, the present invention prevents local battery action due to contact with carbon fibers by interposing a highly insulating inorganic layer on the contact surface with a metal less base than carbon fibers. The layer must be sufficiently insulative to interrupt the flow of current generated by the local cell, ie, sufficiently functional to break contact between the metal and the carbon fibers. The insulation resistance value varies depending on the type of inorganic material used.

According to tests conducted by the present inventors, in the case of reinforced concrete in which carbon fibers are dispersed at 0.2 to 10% by volume in a cement matrix, if an insulating layer of at least 100Ω or more is formed, the metal and carbon fibers can be It turns out that it is possible to break off contact.

In actual construction, some oxide film (black scale) is formed on the surface of iron-based metal materials, although the amount and thickness are not uniform, and black scale is actively generated. Since it is common to use reinforced reinforcing bars, this oxide film layer may also function as an insulating layer.However, this oxide film may peel off in places during transportation or construction, exposing the metal surface, or causing damage to the metal surface. Since the thickness also varies, it cannot be expected to completely prevent local battery formation with this alone.Also, if the oxide film peels off and an exposed metal surface is formed, the gap between the oxide film and the Local batteries are formed on the surface of the steel, which can lead to accelerated corrosion.Furthermore, if the scale layer is too thick, it can reduce the adhesion strength between the concrete and the steel surface.Therefore, in carrying out the present invention, inorganic insulation It is important to have a separate layer. 9 In the present invention, an insulating layer with an electrical resistance of at least 100 Ω means an inorganic material alone with an electrical resistance of 100 Ω excluding this oxide film.
This means that it is an insulating layer that has a higher electrical resistance.

To most conveniently carry out the invention, a cement mortar or cement paste having a cementitious composition similar to that of carbon fiber-reinforced concrete is applied to the metal surface and the applied layer is cured (this is a fully cured layer). (Although it may be in a semi-cured state, there is virtually no problem)
Therefore, it is best to bring it into contact with carbon fiber reinforced concrete that has not yet hardened. In this case, it is possible to enjoy the advantage that there is no problem of a decrease in the adhesion resistance between the carbon fiber reinforced concrete and the metal, and the construction is easy.

Assuming that one of the carbon fibers uniformly dispersed in the cement matrix is in contact with the exposed surface of the iron at its tip in the presence of water, the magnitude of the current flowing from the carbon fiber to the iron is , increases as the surface area of the carbon fiber increases. Therefore.

A large current will flow through long fibers. However, when carbon fibers are dispersed in the same amount, corrosion may actually progress more quickly if short fibers are used. This is probably because the number of contact points at which the m-fiber tips come into contact with the metal surface increases. The results of experiments conducted by the present inventors show that when carbon fibers are dispersed in a cement matrix in an amount of 0.2 to 10% by volume, which is the usual amount of carbon fibers for carbon fiber reinforced concrete, the length of the carbon fibers is No matter how strong the material is, if an insulating layer of at least 100Ω or more is formed between it and the surface of the ferrous metal, the contact between the metal and the carbon fiber will be cut off and corrosion will occur, forming a galvanic cell. We confirmed that the current can be completely cut off.

1. According to the present invention, carbon fiber-reinforced concrete with an insulating layer interposed between it and the metal is one in which carbon fibers are dispersed in a cement matrix, and the presence or absence of aggregate such as sand or gravel and its amount are not required. .

In addition, regardless of the presence or absence of various additives and admixtures, and regardless of their amount, and regardless of the type of cement, it exhibits the effect of preventing metal corrosion due to the formation of local batteries due to contact with carbon fibers. be.

The content of the present invention will be explained in more detail below based on the test results.

[Corrosion potential and polarization curve]

Place a cement mortar in a wooden frame, insert a carbon fiber specimen, a steel specimen, a stainless steel mesh muscle, or a couple of these into the mortar, and install an oxidation-reduction potential measuring device (using a saturated MCI solution with one counter electrode). ; platinum) and potentiostat (using saturated Amagi electrode as reference electrode,
The corrosion potential and polarization curve of each test material in cement were measured using a potential sweep rate of 40 mV/min + counter electrode (platinum).

The measurement results of each corrosion potential are shown in Table 1 on the next page.

0 As is clear from the results in Table 1, the ranking of corrosion potential in cement mortar is:

CF>SS> (CF10 St) >> (SS+St)
>St, indicating that there is an extremely high possibility that galvanic corrosion will occur when steel comes into contact with CF.

11 Figure 1 shows the corrosion potential of steel inserted in each mortar, when CF is dispersed in cement mortar (CF addition amount: 2.5% by volume) and when ordinary mortar is used without CF. This shows changes over time. As seen in Figure 1, the corrosion potential of steel moves toward the shore as time passes, moving from the so-called passive region to the active region.

If the cathode reaction is an oxygen reduction reaction, this would indicate that oxygen in the cement is being gradually consumed and being slowly replenished, leading to depletion. Therefore, since the steel in contact with the CF in the mortar is in the active region, galvanic corrosion becomes significant.

Figure 2 shows the cathodic polarization behavior of steel inserted into each mortar, when CF is dispersed in cement mortar (CF addition amount: 2.5% by volume) and when ordinary mortar is used without CP. show. C into cement mortar
It can be seen that the addition of F significantly increases the cathode current, approximately 10 times or more, compared to the case without addition. This is because CF in cement comes into contact with steel,
This is thought to be due to the addition of the following redox reaction amount on CF.

02 +2 out 0 +4e ” 40H- [pH and oxidation-reduction potential of cement mixture] p of cement mixture using the blending materials shown in Table 2.

The redox potential was measured and the results shown in Table 3 were obtained.

3 As shown in Table 3, the pI (value) of the cement mixture is almost constant regardless of the composition and is in the range of 13.4 to 13.7.The oxidation-reduction potential is -0.15 immediately after mortar is placed.
The voltage is about -0.22V, but it shifts slightly toward the shore during steam curing. This means that the oxidizing nature of the environment decreases over time. If the redox potential of the environment is determined by the redox reaction of oxygen, the upper limit of that potential is determined by the redox equilibrium potential of oxygen, which is expressed by the following equation.

E, =1.23 0.06pH+0.015 log
PO2(VVSSHE)=0.99 0.06pH
+〇, 015 log Po2 (VvsSCE) Substituting Po2 = Q, 2atm, pH-13.5, E = 0.19 (VvsSG[!) This value is the redox potential measured by Pt. considerably higher than the value. Considering that the overpotential of the oxygen reduction reaction is high, it can be assumed that the redox potential of the system is determined by the oxygen reduction reaction unless other effective oxidizing agents (e.g., pe3+) are present in the system. You can think about it.

From the above test results, CF in the cement matrix
It can be seen that the presence of (carbon fibers) has a negative effect on the corrosion of iron (wl) in contact with this cement matrix.

This is because CF has good conductivity and its potential is as high as that of noble metals such as PT.
This is thought to be due to galvanic corrosion due to contact with.

That is, the presence of CF in the cement matrix increases the cathode area of the galvanic corrosion cell, forming what is called a small anode and a large cathode, thereby promoting corrosion.

If this is electrochemically diagrammed, it will be as shown in Figure 3.

That is, initially, steel maintains its corrosion resistance at a potential of ■, but when the oxide film is locally destroyed due to the presence of ions such as Cl-1, the potential shifts to ■ and corrosion occurs. On the other hand, the cathode reaction increases due to the presence of CF, so the potential shifts to ■ and corrosion is accelerated. On the surface of the steel that is the anode of this galvanic cell, the pH drops to a low 15% due to the reaction expressed by the following formula, so a stable film cannot be maintained. For this,
Corrosion will grow.

Fe” 10, 1-10-*Fe (OH) +H (pH
However, in the case of contact between CF and stainless steel, there is no galvanic corrosion because the potentials of both are close and in the passive region.

Examples Various test reinforcing bars 2 were buried in carbon fiber-reinforced concrete 1 having the composition shown in Table 4 as shown in Figure 4, and after being steam-cured at 40°C for 5 hours, In an autoclave at 180°C and 10 atm.

A 5-hour accelerated corrosion test was conducted 1.3.5 times. The test reinforcing bars 2 were ordinary reinforcing bars without black skin, hot-dip galvanized steel, and 5US304 stainless steel.

and cement mortar layer on ordinary reinforcing steel (film thickness approx. 2111 mm)
A coated and cured version of m) was used.

After steam curing or after each autoclave treatment, each test reinforcing bar was taken out of the concrete and its corrosion status was examined. The results are shown in Table 5.

7 However, + No rust occurred + Bi point rust occurred.

C: Several spots of black rust occurred + red rust partially occurred on Di.

E: Red rust occurs on 50% or more of the area.

In addition, a similar corrosion acceleration test was conducted using ordinary concrete with the composition shown in Table 4, except that no carbon fiber was added, but in this case, no rust occurred in any of the sample reinforcing bars. Ta.

8

[Brief explanation of drawings]

Figure 1 shows the change in corrosion potential over time with and without the addition of carbon fiber to cement mortar, Figure 2 shows the polarization curve with and without the addition of carbon fiber to cement mortar, and Figure 3 shows the change in corrosion potential with and without the addition of carbon fiber to cement mortar. Fig. 4 is a diagram showing the dimensions and shape of the test specimen subjected to the accelerated corrosion test of reinforcing bars. l...Carbon fiber reinforced concrete 2...Test reinforcing bar Applicant: Kajima Corporation Ru ← Guichiichi First page continued @ Inventor: Shoji Kamakura Nishi-Nagasu Kunio Technical Research Institute μ ■Inventor: Takashi Mikami Hitoibara City Nishikoo Technical Research Institute 1 0 Author Hideaki Yuki 1-3 Nishi-Nagasu Kazuo Technical Research Institute, Amagasaki City Sumitomo Metal Industries, Ltd. 1-3 Nidori Sumitomo Metal Industries, Ltd. Inside the company

Claims (1)

[Claims] (l) 0.2 carbon fibers in a cementitious matrix
When reinforcing concrete dispersed at ~10% by volume is cured on the contact surface with metal, an insulating layer made of an inorganic material with an electrical resistance of at least 100Ω or more is preformed on the surface of the metal and then cured. Carbon fiber reinforced concrete. (2) The carbon fiber reinforced concrete according to claim 1, wherein the metal is iron or an iron alloy. (3) The carbon fiber reinforced concrete according to claim 1 or 2, wherein the insulating layer made of an inorganic material is a hardened or semi-hardened layer of cement mortar or cement paste.