JPH0450266B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a precast composite structure comprising a hardened carbon fiber reinforced concrete matrix and at least one ferrous metal component at least partially embedded within the matrix. The inherent brittle nature of cementitious matrices can be significantly improved by dispersing them with appropriate amounts of suitable fibrous materials, such as carbon fibers. Thanks to the development of inexpensive pitch-based carbon fibers, carbon fiber-reinforced concrete is being put into practical use, creating new structures with strength, deformation, and elasticity properties that were not possible with conventional cement concrete. There are great expectations for it as a material. The present inventors have been involved in the development of this carbon fiber reinforced concrete for many years, but it has been discovered that there are fundamental problems that are not found in ordinary concrete when implementing this material. . This is a phenomenon in which when metal comes into contact with this carbon fiber reinforced concrete, metal corrosion (metal oxidation) progresses significantly during the hardening process of this concrete. More specifically, if this carbon fiber reinforced concrete is cured while in contact with reinforcing bars, mesh, steel formwork, binding wire, anchor fasteners, spacers, and other ferrous metal members, these metals will be cured during curing. On the surface where the steel comes into contact with the carbon fiber-reinforced concrete, corrosion progresses at a rate unimaginable with ordinary concrete. The aim of the invention is to solve this problem. The present inventors have discovered that carbon fibers are extremely conductive and have a noble potential comparable to noble metals, so when these carbon fibers come into contact with base metals (ferrous metals), local batteries are formed here. Make sure that
This local cell effect was found to be the main cause of metal corrosion, and reinforced concrete with carbon fibers dispersed at 0.2 to 10% by volume in a cementitious matrix was hardened at the contact surface with the metal. If the electrical resistance between the carbon fiber reinforced concrete and the metal is at least approx.
It was found that if an insulating layer with an electrical resistance of 100 ohms is formed on the surface of the ferrous metal and the concrete is hardened, the problem of metal corrosion peculiar to carbon fiber reinforced concrete can be almost completely solved. Thus, the present invention provides a precast composite structure of carbon fiber reinforced concrete consisting of a hardened carbon fiber reinforced concrete matrix and at least one ferrous metal component at least partially embedded in the matrix. To do this, an insulating layer with an electrical resistance of at least 100 ohms is formed on the surface of the ferrous metal component that would otherwise come into contact with the concrete mix, and the ferrous metal component with the insulating layer formed is molded. Place it in a predetermined position within the frame, and pour a carbon fiber reinforced concrete mixture consisting of hydraulic cement, water, aggregate, and 0.2 to 10% by volume of carbon fiber into the form. partially curing the formed composite structure in a formwork until it is self-supporting, with the metal components being at least partially embedded in the concrete mix; is released from the formwork, and the released composite structure is autoclaved for 100~
Provided is a method for manufacturing a precast composite structure of carbon fiber reinforced concrete, which is characterized by being sufficiently cured at a temperature of 215°C. The invention further comprises: a hardened carbon fiber reinforced concrete matrix containing 0.2 to 10% by volume of carbon fiber; at least one ferrous metal component at least partially embedded in the matrix; and an insulating layer on the surface of the ferrous metal member for preventing contact between the carbon fiber and the ferrous metal member, and the insulating layer is characterized in that it has an electrical resistance of at least about 100 ohms. A precast composite structure made of carbon fiber reinforced concrete is provided. The composite structure according to the present invention has excellent strength, deformation, and elastic properties unique to carbon fiber reinforced concrete, and has little change in dimensions over time.
It is extremely useful as a building material for exterior wall materials, interior wall materials, and flooring materials, especially for rooms housing computers and OA equipment, as well as flooring materials for clean rooms and operating rooms. According to the present invention, by forming an insulating layer on the surface of the metal member in contact with concrete mixes, the formation of local batteries due to contact between the carbon fibers and the metal member is prevented or Current flow generated by the battery is prevented.
To achieve this prevention, in the case of carbon fiber reinforced concrete with 0.2 to 10 volume % carbon fiber dispersed, this insulating layer must have a resistance of at least approximately 100 ohms,
It has been found that preferably it should have an electrical resistance of at least about 500 ohms. at least about 100 ohms, preferably on the surface of the ferrous metal component.
Any organic or inorganic material capable of forming an insulating layer having an electrical resistance of at least about 500 ohms can be used in the practice of the present invention. Suitable organic materials for forming such an insulating layer include, for example, epoxy resins, acrylonitrile-butadiene rubber, acrylonitrile-styrene-butadiene rubber, silicone resins, and Teflon (polytetrafluoroethylene) dispersions. . Also, suitable inorganic substances include:
For example cement mortars or pastes and ceramic dispersions (e.g. SiO ₂ ,
ZrO ₂ SiO ₂ or SiC + ZrO ₂ SiO ₂ alcohol dispersion). It is recommended to use epoxy resin, cement mortar or paste from the viewpoint of ease of manufacture and economy. The epoxy resin is a mixture of bisphenol A type epoxy with an appropriate curing agent (phenol or aromatic amine), which is normally powdered at 200°C.
Commercially available resins having a gel time of 5 to 25 seconds can be conveniently used. To form the insulating layer, the part of the ferrous metal component where the insulating layer is to be formed is cleaned by shot blasting, the component is preheated, and powdered epoxy resin is applied by electrostatic coating. , and, if necessary, bake to fully harden the resin. In addition, when using multiple iron-based metal parts in combination, after cleaning those parts by shot blasting, assembling them in the desired positional relationship, preheating this assembly, and using powdered epoxy resin. An insulating layer can also be formed on the entire surface of the ferrous metal member assembly by exposing the resin to a fluidized bed to melt and harden the resin, and then baking it in a separate furnace. The epoxy resin layer cured in this way is preferably a continuous layer and at least approximately
Must have an electrical resistance of 100 ohms. By setting the thickness of this cured epoxy resin layer to about 100 μm or more, a preferred electrical resistance value of 500 ohms or more can be safely achieved. The upper limit for the thickness of the epoxy resin layer is not critical, and in most cases thicknesses greater than about 500 μm are not required. The cement mortar or paste mix that can be used to form an insulating layer on a ferrous metal component according to the invention can consist of hydraulic cement, water, a fine aggregate such as silica sand, and a polymer. The water-cement ratio is 20-40, the fine aggregate-cement ratio is 0-2, and the polymer-cement ratio is 0.
It can be ~30%. However, in the case of a cement paste mix that does not contain fine aggregate, it is preferable to mix the polymer in an amount such that the polymer-cement ratio is at least 2%, and if no polymer is used, fine aggregate It is preferable to form the insulating layer using cement mortar mixes containing fine aggregate in an amount such that the cement ratio is at least 0.5. The polymer is incorporated into the cementum in the form of a latex or emulsion. Suitable latexes or emulsions include natural rubber latex, acrylonitrile-butadiene rubber latex, vinyl chloride-vinylidene chloride copolymer emulsion, acrylate polymer emulsion and polyvinyl acetate emulsion. When forming the insulating layer, the part of the ferrous metal member where the insulating layer is to be formed is cleaned by shot blasting, the cement mortar or paste mix as described above is applied, and at least partially Let it harden. Preferred electrical resistance values of 500 ohms or more can be safely achieved by using a hardened cement mortar or paste layer with a thickness of about 1 mm or more. The upper limit for the thickness of the hardened cement mortar or paste layer is not critical, and in most cases no thickness greater than about 5 mm is required. The ferrous metal component thus treated with an insulating material is then brought into contact with carbon fiber reinforced concrete mix and allowed to harden. More specifically, in the case of ferrous metal components, such as steel reinforcing bars and mesh, and tie wires, which are to be fully embedded in the hardened carbon fiber reinforced concrete matrix of the precast composite structure. on all surfaces of the component, and to a lesser extent in the case of ferrous metal components, such as steel inserts or anchor fasteners, to be partially embedded in the hardened carbon fiber reinforced concrete matrix of the precast composite structure. An insulating layer is formed as described above on the surfaces of both components that would otherwise come into contact with the concrete mix, and the components are then placed in position within the formwork. It goes without saying that appropriate spacers may be used in addition to the formwork depending on the shape of the intended structure. The surface of the spacer and the inner surface of the mold have been applied with a suitable mold release agent, such as mineral oil. When using formwork and spacers made of ferrous metals, it is preferable to preform such an insulating layer on the surfaces of these parts that would otherwise come into contact with the concrete mix. . After assembling the formwork and spacer to which a mold release agent has been applied and the ferrous metal components to be at least partially embedded in the desired precast composite structure, carbon fiber reinforced concrete is placed inside the formwork. Pour the tomicus. Carbon fiber reinforced concrete mixes that can be used in the practice of this invention include hydraulic cement, water, aggregates and 0.2 to 10% by volume per concrete mix;
Preferably, it contains at least 1 to 5% by volume of carbon fiber. The length of the carbon fibers can vary from about 1 mm to about 50 mm. It was found that as long as the length of the carbon fiber was within this range, the corrosion characteristics were not affected by the length of the carbon fiber. Corrosion accelerates as the carbon fiber content increases.
However, the maximum permissible content of carbon fiber (i.e. 10
Even in the case of (capacity%), the problem of corrosion can be solved by forming an insulating layer on the surface of the metal member with an electrical resistance of at least about 100 ohms, preferably at least about 500 ohms. The present inventors confirmed this. Therefore, in carrying out the present invention, the length of carbon fibers used and the carbon fiber content in the concrete mix should be determined within the above-mentioned range depending on the mechanical properties of the intended carbon fiber reinforced concrete. good. Other conditions for carbon fiber reinforced concrete mixes that have not set yet, such as the type of hydraulic cement,
The use or non-use of polymer, water-cement ratio, aggregate-cement ratio, polymer-cement ratio, etc. do not constitute the gist of the present invention, and the conditions regarding these commonly used in carbon fiber reinforced concrete mixes are included in the present invention. Applicable to implementation.
That is, the water-cement ratio of carbon fiber reinforced concrete mixes is 20~70, and the aggregate-cement ratio is 0.5~
10, and the polymer cement ratio can be 0-20%. As the aggregate, fine aggregate such as silica sand is preferable, but in some cases coarse aggregate may be used in place of a part of it. When using polymers, latexes or emulsions such as those described above for cement mixes for forming the insulation layer can be used. It goes without saying that additives commonly used in concrete mixes, such as water reducers and thickeners, can be used in the carbon fiber reinforced concrete mix of the present invention, if necessary. The molded composite structure is partially cured in a mold until it is self-supporting. This partial curing in the mold is usually carried out under atmospheric pressure, and optionally can be carried out in a warm steam atmosphere. Once the composite structure in the formwork is self-supporting,
After releasing this from the mold, it is sufficiently cured in saturated steam in an autoclave at a temperature of 100 to 215°C, preferably 150 to 200°C. Autoclave curing in saturated steam at such high temperatures (100-215°C) and correspondingly overpressure (0-20 bar gauge) is necessary to obtain a dimensionally stable precast structure. be. It should be noted that it is not necessarily necessary to remove all elements constituting the formwork from the partially cured composite structure prior to autoclaving. In some cases, the composite structure may be prepared by subjecting the latter to the autoclave curing of the invention without removing some or all of the elements constituting the formwork from the composite structure, after which the formwork elements have been sufficiently cured. It can also be removed from the body. 1 and 2, the illustrated precast composite structure according to the present invention comprises a hardened carbon fiber reinforced concrete matrix containing 0.2 to 10% by volume, preferably 1 to 5% by volume, of carbon fibers. 1, reinforcing reinforcing bars 2 and 2' completely embedded in the matrix 1, anchor bolts 3 partially embedded in the matrix 1, and L-shaped reinforcing bars 3 completely embedded in the matrix 1. A steel reinforcing rod 4, a steel reinforcing mesh 5, 5' completely embedded in the matrix 1, and one side embedded in the matrix 1, with an anchor bolt 3 passing through the center. It consists of a rectangular steel plate 6. On the entire surface of reinforcing bars 2, 2', reinforcing rods 4 and reinforcing meshes 5, 5', and anchor bolts 3
And at least on the surface of the steel plate 6 which would otherwise be in contact with the matrix 1, an insulating layer (not shown) with an electrical resistance of at least 100 ohms is formed according to the invention. Next, the test results forming the basis of the present invention will be described. Corrosion Potential and Polarization Curve A test piece was inserted into a cement mortar placed in a wooden frame, and the corrosion potential of the test piece in the cement mortar was measured (reference electrode: saturated calomel electrode). The cement mortar used was as shown in Table 4, except that no carbon fiber was blended, and the test materials were carbon fiber, steel pieces, and stainless steel mesh bars alone or in combination. Table 1 shows the measurement results of each corrosion potential.

[Table] The results in Table 1 show that the corrosion potentials in cement mortar are ranked in the following order. CF＞SS＞(CF+St)＞＞(SS+St)＞St This shows that when steel comes into contact with carbon fiber, there is an extremely high possibility that galvanic corrosion will occur. In this specification, "ferrous metals" refer to iron and iron alloys whose corrosion potential in cement mortar is substantially less base than that of carbon fibers, as well as those metals coated with Al or
Refers to materials coated with Zn plating. FIG. 3 shows the change over time in the corrosion potential of steel in plain cement mortar containing no carbon fibers, which was obtained through the above test. The corrosion potential of the same steel specimen in the cement mortar listed in Table 4 containing 2.5% by volume of carbon fiber was measured in the same manner as described above. The results are also shown in FIG. As can be seen in FIG. 3, the corrosion potential of steel shifts to the less noble side with the passage of time, 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 gradually consumed and slowly replenished, resulting in depletion. Therefore,
It is understood that the steel in contact with the noble carbon fibers in the mortar is in the active region and galvanic corrosion will be significant. Figure 4 shows the polarization behavior of steel in a cement mortar containing 2.5% by volume of carbon fibers and the corresponding cement mortar without carbon fibers. From FIG. 4, it can be seen that the cathode current of the steel in the cement mortar increases significantly (approximately 10 times or more) by adding carbon fiber to the cement mortar. This is thought to be because the carbon fibers in the cement came into contact with the steel, and the following oxidation-reduction reaction took place on the carbon fibers. O ₂ + 2H ₂ O + 4e = 4OH ^- pH and redox potential of cement mix The water-cement ratio and sand-cement ratio of the plain cement mix and the cement mix containing 2.5% by volume of carbon fiber used in the above tests are unchanged. Then, only the type of aggregate, the type of water reducing agent, the presence or absence of antifoaming agent, and the presence or absence of thickener were changed as shown in Table 2, and the pH and redox potential of each mix with the pt electrode as the counter electrode were measured. did. The results are shown in Table 3.

【table】

[Table] pH of cement mix as shown in Table 3
The value is approximately constant over the range of variation tested;
It is in a narrow range of 13.4 to 13.7. In addition, the oxidation-reduction potential varies to some extent depending on the cement composition, and is about -0.15 to -0.22V immediately after mortar is placed, but it can be seen that it shifts slightly to the base side 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 oxygen, the upper limit of that potential is determined by the redox equilibrium potential of oxygen, and the equilibrium potential is expressed by the following equation. E. =1.23−0.06pH+0.015 log _Po2
(VvsSHE) = 0.99−0.06pH＋0.015 log Po ₂
(VvsSCE) However, Po ₂ ; partial pressure of oxygen in the environment, i.e.
0.2atm, SHE means hydrogen electrode, SCE means calomel electrode. By substituting Po ₂ −0.2 atm and pH=13.5 into the latter equation, E=0.19 (V vs SCE) is obtained. This value is considerably higher than the redox potential values measured with Pt shown in Table 3. Considering the high overpotential of the oxygen reduction reaction, unless other effective oxidizing agents (e.g. Fe ³⁺ ) are present in the system,
It can be considered that the redox potential of the system is determined by the reduction reaction of oxygen. From the above test results, it has become clear that the presence of carbon fibers in the cement matrix has an adverse effect on the corrosion of steel in contact with the cement matrix. This is thought to be due to galvanic corrosion due to contact between steel and carbon fiber, since carbon fiber has good electrical conductivity and exhibits a potential as noble as that of a noble metal such as Pt. That is, the presence of carbon fibers 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 simplified, it will be as shown in Figure 5. 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 C1 ^- , the potential shifts to , and corrosion occurs. On the other hand, the presence of carbon fibers increases the cathode reaction, so the potential is transferred and corrosion is accelerated. On the steel surface that is the anode of this galvanic cell, the pH decreases due to the reaction shown by the following equation, so a stable film cannot be maintained. This causes corrosion to grow. Fe ²⁺ H ₂ O→Fe(OH) ⁺ +H ⁺ (pH decrease) Example 1 (1) A wooden formwork suitable for obtaining a test specimen with dimensions of 40 mm x 40 mm x 160 mm was prepared. After applying mineral oil as a mold release agent to the inner wall of the formwork, a steel rod with a diameter of 10 mm was placed in the formwork at a position so that it was embedded approximately along the center line of the resulting rectangular parallelepiped specimen. did. The reinforcing bar tested was JIS G3112 SD30.
It was a steel rod for reinforced concrete that complied with the standards of 1999 (the black crust had been removed by shot blasting). Pour carbon fiber-containing concrete mix with the composition shown in Table 4 into the formwork and heat it at 40°C for 50 minutes.
Steam cured for an hour. After steam curing, the specimen was released from the mold and placed in an autoclave at 180°C for 10
Cured at atmospheric pressure for 5 hours. The obtained test specimen had a structure in which reinforcing bars 12 were embedded in a hardened carbon fiber reinforced concrete matrix 11, and had the dimensions and shape as shown in FIG. 6. . Several such test specimens were created. (2) Instead of a steel rod with a diameter of 10 mm, this is hot-dip galvanized (thickness of the plating layer: 50 μm)
Similar test specimens were prepared using the same procedure except that . (3) A similar test specimen was prepared by repeating the procedure in (1) above, except that instead of a steel rod with a diameter of 10 mm, an epoxy resin coating (film thickness of about 200 μm) was used. The coating was applied as follows. In other words, a steel bar from which mill scale has been removed by shot blasting is preheated at 240°C for 15 minutes, then exposed to a fluidized bed of epoxy resin powder for about 4 seconds, and then heated at 200°C for about 20 minutes to fully harden the resin. I let it happen. (4) A similar test was conducted by repeating the procedure in (1) above, except that instead of a steel rod with a diameter of 10 mm, a cement mortar mix coated and hardened (film thickness of approximately 2 mm) was used. Created a body. The cement mortar mix used was 512 kg of water per 1 ^m3 .
It contains 1082Kg of cement, 274Kg of powdered silica sand, and 10.8Kg of methyl cellulose (water-cement ratio is 47.3%; aggregate-cement ratio is 0.25).
Powdered silica sand has a chemical composition of _SiO2 ; 95.0% by weight,
It contained 2.17% by weight of Al ₂ O ₃ and 1.17% by weight of Fe ₂ O ₃ , had a specific gravity of 2.70, and a specific surface area of 3360 cm ² /g.

[Table] *** Antifoaming agent made by San Nobuco
Each test reinforcing bar was taken out from the test specimen after steam curing and the test specimen after autoclave curing, and the state of corrosion on its surface was examined using an optical microscope. In addition, the test specimen after autoclaving was heated at 180℃.
It was subjected to autoclave treatment (accelerated corrosion test) for 5 hours at 10 atmospheres twice or four times. In our experience, one such autoclaving process roughly equates to four years of exposure to ambient atmosphere. Each of the test reinforcing bars was taken out from the test specimens that had been autoclaved twice and the test specimens that had been autoclaved four times, and the corrosion status of their surfaces was examined in the same manner as described above. The results are shown in Table 5.

[Table] Example 2 A test specimen prepared by the procedure described in Example 1 was exposed to an atmosphere of 80°C and 100% RH for 48 hours.
Then, it was subjected to an accelerated corrosion test in which the material was exposed to an atmosphere of 80°C and 40% RH for 24 hours, repeated 10 times. A test reinforcing bar was taken out from the treated specimen, and the state of corrosion on its surface was observed using an optical microscope. In the case of the test specimen of Example 1 (1), red rust had occurred on the entire surface of the test reinforcing bar (regular reinforcing bar without black skin). In the case of the test specimen of Example 1 (2), 41 spots of rust with a diameter of about 0.1 to 0.3 were observed on the surface of the test reinforcing bar (hot-dip galvanized reinforcing bar). In the case of the test specimens of Examples 1 (3) and (4), no rust was observed on the surfaces of the test reinforcing bars (epoxy-coated reinforcing bars and cement mortar-coated reinforcing bars). Example 3 0.5 mm ² , 1 mm ² ,
2 scratches each of 2 mm ² and 5 mm ² in size, total of 8
Except for the individual additions, the operations described in Example 1 (3) were carried out,
A test specimen was created. This test specimen was subjected to the autoclave treatment described in Example 1 10 times. A test reinforcing bar was taken out from the treated specimen, and the state of corrosion on its surface was observed using an optical microscope. Of the two ² -mm scratches, one was approximately
Spot rust with a diameter of 0.2 mm had occurred. In addition, spot rust with a diameter of approximately 0.4 mm had occurred in one of the two locations where scratches of 5 mm ² had been made. However, in other places,
No rust was observed at all.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a part of an example of a precast composite structure (exterior wall material) made of carbon fiber reinforced concrete according to the present invention, and FIG. Figure 3 is a graph showing changes over time in the corrosion potential of steel in cement mortar containing carbon fibers and changes over time in the corrosion potential of steel in cement mortar without carbon fibers. Yes, Figure 4 shows the polarization behavior of steel in cement mortar containing carbon fibers,
FIG. 5 is a diagram showing the polarization behavior of steel in cement mortar without carbon fibers; FIG. 5 is a conceptual diagram for electrochemically explaining steel corrosion in carbon fiber-reinforced concrete; FIG. 6 is a diagram showing the dimensions and shape of the test specimen subjected to the accelerated corrosion test. 1... Carbon fiber reinforced concrete matrix, 2, 2'... Reinforcement reinforcing bars completely embedded in matrix 1, 3... Anchor bolts partially embedded in matrix 1, 4... Matrix 1. L-shaped steel reinforcing rod completely embedded in matrix 1, 5, 5'... steel reinforcing mesh completely embedded in matrix 1, 6... one side embedded in matrix 1. A rectangular steel plate with an anchor bolt 3 passing through its center.

Claims (1)

[Scope of Claims] 1. A precast composite structure of carbon fiber reinforced concrete consisting of a hardened carbon fiber reinforced concrete matrix and at least one ferrous metal member at least partially embedded in the matrix. During manufacturing, an insulating layer having an electrical resistance of at least about 100 ohms is formed on the surface of the ferrous metal component that would otherwise come into contact with the concrete mix, and the ferrous metal component on which the insulating layer is formed is formed. A carbon fiber reinforced concrete mixture consisting of hydraulic cement, water, aggregate, and 0.2 to 10% by volume of carbon fiber is poured into the form. The ferrous metal components are at least partially embedded in the concrete mix, the formed composite structure is partially cured in the formwork until it is self-supporting, and the partially cured composite is partially cured. The structure is released from the formwork, and the released composite structure is placed in an autoclave for 100~
A method for producing a precast composite structure of carbon fiber reinforced concrete, characterized in that it fully cures at a temperature of 215°C. 2 The forming is carried out in a formwork made of ferrous metal, and before the concrete mix is poured into the formwork, the surfaces of the formwork which would otherwise come into contact with the concrete mix have an electrical resistance of at least approx. 100
2. The method according to claim 1, further comprising forming an ohmic insulating layer. 3. The method according to claim 1, wherein the insulating layer is formed of epoxy resin. 4. The method according to claim 1, wherein the insulating layer is formed of cement mortar or paste.