JP5437044B2 - Corrosion prevention method for reinforcing steel inside reinforced concrete - Google Patents

Description

  The present invention mainly relates to improvement of durability of a concrete structure in a marine environment, that is, seawater resistance and corrosion resistance.

  In recent years, there has been an increasing demand for improving the durability of concrete structures in the civil engineering and construction fields.

As one of the deterioration factors of concrete structures, there is salt damage in which reinforcing bars corrode by chloride ions. In offshore structures, salt infiltrates into reinforced concrete due to incoming salt, and the steel rusts. On roads in cold regions, salt damage occurs due to the application of anti-freezing agents such as sodium chloride and calcium chloride. Also, in concrete containing sea sand containing chloride ions and admixtures, salt damage occurs due to the internal salt content.
As a method of suppressing the penetration of chloride ions from the outside, there is a method of imparting chloride ion penetration resistance to a concrete structure.

  As a method for suppressing chloride ion penetration into the hardened concrete and imparting chloride ion penetration resistance, a method of reducing the water / cement ratio is known (see Non-Patent Document 1).

Also, for the purpose of imparting early strength to cement concrete and preventing corrosion of reinforcing bars, it contains CaO.2Al ₂ O ₃ and gypsum as the main component and contains fine powder with a Blaine specific surface area value of 8000 cm ² / g. Chloride ion permeation resistance using a cement admixture containing a calcium aluminate having a CaO / Al ₂ O ₃ molar ratio of 0.3 to 0.7 (see Patent Document 1) A method for improving the performance (see Patent Document 2) has been proposed.

  Methods for adding nitrite and nitrite hydrocalumite have been proposed for the purpose of rust prevention of reinforcing steel (see Patent Documents 3 to 5). Nitrite shows rust prevention effect, but does not show blocking effect of chloride ions entering from the outside, and nitrite type hydrocalumite shows rust prevention effect, but this is not mixed The cemented hardened body is likely to be porous, but rather to allow permeation of chloride ions from the outside.

  On the other hand, as a method for preventing corrosion of reinforcing bars, a sacrificial anode material type cathodic protection method using a difference in standard electrode potential of metal is known. There are features such as no need for external electrodes, easy maintenance, and excellent long-term corrosion resistance (see Patent Document 6).

  However, when the sacrificial anode material is used in combination with a specific calcium aluminate, it has not been known at all about enhancing salt damage resistance.

  The present inventors have found that excellent salt damage resistance can be obtained by installing a sacrificial anode material inside a hardened concrete body containing a specific calcium aluminate.

Koichi Kishitani, Noriaki Nishizawa et al., “Durability series of concrete, salt damage (I)”, Gihodo Publishing, pp. 59-63, May 1986

JP 47-035020 A JP 2005-104828 A JP-A-53-003423 Japanese Patent Laid-Open No. 01-103970 Japanese Patent Laid-Open No. 04-154648 Japanese Patent No. 3099830

  The present invention provides a method for improving the durability of a reinforced concrete structure in a salt damage environment.

In the present invention, (1) a calcium aluminate compound having a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and a brain surface area value of 2000 to 7000 cm ² / g, cement, and water are mixed. A sacrificial anode material is installed inside the hardened concrete, and a porous material containing an electrolyte solution having a pH of 12 or more is attached around the sacrificial anode material in order to avoid the formation of a non-conductive state of the anode. , the sacrificial anode material and concrete interior rebar Ri Na electrically connected, the metal of the sacrificial anode material, zinc, aluminum, and a metal or an alloy including the selected one or two or more from the group consisting of magnesium there, reinforced concrete inside the steel reinforcement corrosion method, (2) a porous material anticorrosive method of reinforced concrete internal reinforcement of which comprises an alkali silica reaction inhibitor (1), (3) alk The reinforced concrete internal rebar corrosion method silica reaction inhibitor comprising lithium ions (2), is.

  The present invention has an effect of imparting an excellent rust prevention effect to reinforced concrete and suppressing the corrosion of the reinforcing bars to improve the salt damage resistance.

Hereinafter, the present invention will be described in detail.
In the present invention, “parts” and “%” are based on mass unless otherwise specified.
The concrete referred to in the present invention is a general term for cement paste, mortar, and concrete.

  In civil engineering and construction applications, usually, raw concrete is transported from the raw concrete factory to the construction site and placed in large quantities. In such a usage pattern, the pot life needs to be secured for at least 1 hour, and preferably 3 hours or more.

The calcium aluminate compound (hereinafter referred to as CA compound) used in the present invention is a mixture of calcia-containing raw material and alumina-containing raw material, and heat treatment such as firing in a kiln or melting in an electric furnace. This is a general term for compounds obtained mainly from CaO and Al ₂ O ₃ . In the present invention, the chemical composition of the CA compound is in the range of 0.15 to 0.7 in terms of a CaO / Al ₂ O ₃ molar ratio. Even if the CA compound contains, for example, SiO ₂ or R ₂ O (R is an alkali metal), it can be used as long as the object of the present invention is not impaired.
The CaO / Al ₂ O ₃ molar ratio of the CA compound of the present invention is 0.15 to 0.7, and more preferably 0.4 to 0.6. If it is less than 0.15, the chloride ion shielding effect may not be sufficiently obtained. Conversely, if it exceeds 0.7, rapid hardening may appear, and the pot life may not be secured.

Fineness of CA compound, Blaine specific surface area value (hereinafter, referred to as Blaine value) is preferably 2000~7000cm ² / g in, 3000~6000cm ² / g is more preferable. If the brane value is less than 2000 cm ² / g, a sufficient chloride ion shielding effect may not be obtained, and if it exceeds 7000 cm ² / g, rapid hardening appears and the pot life is shortened.

  As the cement, various portland cements such as normal, early strength, super early strength, low heat, and moderate heat, various mixed cements in which blast furnace slag, fly ash, or silica is mixed with these portland cements, limestone powder and blast furnace slow Portland cement such as filler cement mixed with fine powder of cold slag, etc., and environmentally friendly cement (eco-cement) manufactured using municipal waste incineration ash and sewage sludge incineration ash as raw materials are listed. Or 2 or more types can be used.

  The amount of the CA compound used in the present invention is preferably 1 to 30 parts, more preferably 5 to 15 parts, per 100 parts of cement. If it is less than 1 part, there is little sufficient rust prevention effect and chloride ion shielding effect, and if it exceeds 30 parts, rapid hardening will appear and the pot life will be shortened.

  The water / binder ratio of the present invention is preferably 25 to 70%, more preferably 30 to 65%. Here, the binder means the total of cement and CA compound. When the water / binder ratio is less than 25%, pumpability and workability are lowered, cracking due to self-shrinkage is likely to occur, and salt damage resistance may be lowered. On the other hand, if it exceeds 70%, the amount of voids in the cured body increases, and salt damage resistance may decrease.

  In the present invention, the respective materials may be mixed at the time of construction, or a part or all of them may be mixed in advance.

  As the mixing device, any existing device can be used, and for example, a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer can be used.

  In the present invention, in addition to cement and CA compound, fine aggregate such as sand, coarse aggregate such as gravel, expansion material, water reducing agent, AE water reducing agent, high performance water reducing agent, high performance AE water reducing agent, antifoaming agent , Thickeners, conventional rust inhibitors, antifreeze agents, shrinkage reducers, polymer emulsions, setting modifiers, clay minerals such as bentonite, anion exchangers such as hydrotalcite, granulated blast furnace slag fine powder and blast furnace gradual It is possible to use together 1 type or 2 types or more of the group which consists of admixture materials, such as slag and limestone fine powder, such as cold slag fine powder, in the range which does not inhibit the objective of this invention substantially.

  In the present invention, the salt damage resistance of the concrete is further improved by installing the sacrificial anode material inside the hardened concrete body which is prepared by mixing and kneading the CA compound, cement, and water.

  The effect of the hardened concrete blended with the CA compound and the effect of installing the sacrificial anode material inside the hardened concrete body are synergistically higher when combined with the effect obtained in each case. Is obtained.

  In the present invention, the reinforcing bar in the concrete is used as a cathode, a sacrificial anode material is installed in the concrete, and the two are electrically connected to each other, thereby supplying an anticorrosion current to the reinforcing bar and preventing the reinforcing bar from being corroded. Here, the sacrificial electrode material refers to a material that contains a metal that has a higher ionization tendency than iron and that prevents corrosion of the reinforcing bars by ionization prior to iron.

  Examples of the metal constituting the sacrificial anode material include an alloy containing one or more selected from the group consisting of zinc, aluminum, and magnesium.

  In order to avoid passivation of the sacrificial anode material, it is necessary to keep the surroundings of the metal at a sufficient pH. For example, in the case of a zinc-aluminum alloy, the pH value needs to be 13.3 or more, and the pH value for suppressing passivation is different depending on the metal used, but the pH value is preferably 12 or more.

  Since the pH of the electrolyte solution contained in the porous material attached around the sacrificial anode material is high, there is a concern about the alkali silica reaction in the concrete portion adjacent to the porous material. Therefore, it is preferable that an alkali silica reaction inhibitor is present in the electrolyte solution.

  The alkali silica reaction inhibitor is preferably lithium ions in order to avoid a decrease in pH of the electrolyte solution, and it is preferable to add lithium hydroxide, lithium carbonate, or lithium-type zeolite.

  The method of electrically connecting the reinforcing bar and the sacrificial anode material is not particularly limited as long as the reinforcing bar and the metal constituting the sacrificial anode material are electrically connected to each other. A method of embedding a part of the metal in the metal in the sacrificial anode material and winding it around a reinforcing bar is practically simple.

  In the present invention, after partially filling the concrete structure, the sacrificial anode material is installed and electrically connected to the reinforcing bar, or the sacrificial anode material and the reinforcing bar are electrically connected, and then the concrete is cast. An electrolyte solution having a pH sufficient to avoid the formation of a non-conductive coating on the metal surface, in which a concrete structure is constructed by embedding the sacrificial anode material, or the metal and the reinforcing bar are electrically connected. After covering with a porous material containing, the concrete is placed and the concrete structure is constructed by embedding the sacrificial anode material, so that an anticorrosion current flows between the sacrificial anode material and the reinforcing bar, and the reinforcing bars in the concrete are Corrosion protection.

In the present invention, the anticorrosion effect of the reinforcing bars can be confirmed by measuring the potential.
When a metal having a lower standard electrode potential is electrically connected to the reinforcing bar in the concrete, the potential of the reinforcing bar itself is lowered. Therefore, the effectiveness can be judged from the numerical value by measuring the potential.
The electric potential is measured using the lead verification electrode with the surface where the sacrificial anode material of the reinforcing bar in the concrete is installed as the measurement point. At this time, the sacrificial anode material and the reinforcing bar can be disconnected, and the instant-off potential immediately after the disconnection and the potential after 24 hours (off-potential after 24 hours) are measured and recovered from these differences. Calculate the extreme amount. The greater the amount of depolarization, the greater the effect of preventing corrosion of the reinforcing bars.

  Hereinafter, although an example and a comparative example are given and the contents are explained in detail, the present invention is not limited to these.

"Example 1"
10 parts of the CA compound shown in Table 1 was mixed with 100 parts of cement to prepare a concrete (mortar) having a water / binder ratio of 50%, and a 10 × 10 × 40 cm specimen was prepared. A reinforcing bar was placed in the center of the specimen in the axial direction, and a sacrificial anode material I was installed inside the specimen. Lead wires were connected to the reinforcing bar and sacrificial anode material, respectively, so that the electrical connection could be turned on and off outside the concrete specimen.
On the surface where the sacrificial anode material inside the concrete is installed, the point corresponding to the center of the reinforcing bar is taken as the measurement point, the lead-off reference electrode is used to measure the instant-off potential and the off-potential after 24 hours. The amount was calculated. Except when measuring the amount of depolarization, the rebar and the sacrificial anode material were electrically connected. In addition, the rust prevention effect, compressive strength, and chloride ion penetration depth were investigated. The results are also shown in Table 1.

<Materials used>
CA compound A: Reagent primary calcium carbonate and reagent primary aluminum oxide were blended at a predetermined ratio, baked at 1650 ° C. in an electric furnace, and then slowly cooled to synthesize. CaO / Al ₂ O ₃ molar ratio 0.1, Blaine value 4000 cm 2 / g
CA compound B: synthesized in the same manner as CA compound A, CaO / Al ₂ O ₃ molar ratio 0.15, Blaine value 4000 cm ² / g
CA compound C: Reagent primary calcium carbonate and reagent primary aluminum oxide were blended in a predetermined ratio, baked at 1550 ° C. in an electric furnace, and then slowly cooled to synthesize. CaO / Al ₂ O ₃ molar ratio 0.4, Blaine value 4000 cm ^{2 /} g
CA compound D: synthesized in the same manner as CA compound C, CaO / Al ₂ O ₃ molar ratio 0.5, Blaine value 4000 cm ² / g
CA compound E: synthesized in the same manner as CA compound C, CaO / Al ₂ O ₃ molar ratio 0.6, Blaine value 4000 cm ² / g
CA compound F: Reagent grade 1 calcium carbonate and reagent grade 1 aluminum oxide are blended at a predetermined ratio, baked at 1450 ° C. in an electric furnace, and then slowly cooled to synthesize. CaO / Al ₂ O ₃ molar ratio 0.7, Blaine value 4000 cm ² / g
CA compound G: synthesized in the same manner as CA compound F, CaO / Al ₂ O ₃ molar ratio 0.9, Blaine value 4000 cm ² / g
Cement: Normal Portland cement, commercially available fine aggregate: river sand, surface dry density 2.62 g / cm ³
Water: Tap water sacrificial anode material I: Zinc block covered with porous mortar containing LiOH as alkali silica reaction inhibitor (pH = 13.5)

<Measurement method>
Rust prevention effect: Sodium chloride was added to the concrete (mortar) as an internal chloride ion so as to be 10 kg / m ^{3 in} terms of chloride ion. The specimen was heated to 40 ° C. to promote the corrosion of the reinforcing bars, and the presence or absence of rusting of the reinforcing bars was confirmed. The case where rust did not occur in the reinforcing bars was good, the case where rust occurred within an area of 1/10 was acceptable, and the case where rust occurred beyond an area of 1/10 was deemed impossible.
Compressive strength: The compressive strength at the age of 28 days was measured according to JIS R 5201.
Chloride ion penetration depth: A test body to which sodium chloride was not added was prepared, and resistance to penetration of chloride ions from the outside was examined. The test specimen was cured in water at 20 ° C. until the age of 28 days, and then immersed in a saline solution having a salt concentration of 3.5% at 30 ° C. for 12 weeks, and the chloride penetration depth was measured. The chloride penetration depth was determined by the fluorescein-silver nitrate method, the portion of the cross section of the mortar specimen where the tea did not change was regarded as the chloride penetration depth, and the average value was obtained by measuring 8 points with calipers.
Depolarization amount: At 6 months of age, using a lead verification electrode, the instant-off potential immediately after disconnecting the electrical connection between the reinforcing steel inside the concrete and the sacrificial anode material, and OFF 24 hours after 24 hours have elapsed after cutting The potential was measured, and the amount of repolarization was calculated by the following equation.
Depolarization amount (mV) = [Eio (mV)] − [Eof (mV)]
Eio: Instant off potential Eof: Off potential after 24 hours

From Table 1, it can be seen that according to the present invention, an excellent rust-preventing effect is imparted to the hardened concrete (mortar) and the salt damage resistance is improved.
From Experiments No. 1-1 and 1-2 to 1-7, the combined use of the CA compound and the sacrificial anode material provides a synergistically higher effect.

"Example 2"
It carried out like Example 1 except having used together the CA compound D of the fineness shown in Table 2. The results are also shown in Table 2.

  From Table 2, it can be seen that according to the present invention, an excellent rust-preventing effect is imparted to the hardened concrete (mortar), and the salt damage resistance is improved.

"Example 3"
As shown in Table 3, the same procedure as in Example 1 was performed except that the amount of CA compound used was changed with respect to 100 parts of cement. For comparison, a conventional rust preventive material was used in the same manner. The results are also shown in Table 3.

<Materials used>
Commercially available rust preventive material A: Lithium nitrite Commercially available rust preventive material B: Nitrite type hydrocalumite

  From Table 3, it can be seen that according to the present invention, an excellent rust-preventing effect is imparted to the hardened concrete (mortar), and the salt damage resistance is improved.

Example 4
Use the concrete (mortar) used in Experiment No.1-5, install the sacrificial anode material shown in Table 4 inside the concrete, mix the alkali silica reactive aggregate, and have the effect of suppressing the alkali silica reaction The same procedure as in Example 1 was conducted except that the above was investigated. For comparison, a case where no sacrificial anode material was installed or a case where an alkali silica reaction inhibitor was not included in the porous material around the metal was examined. The results are also shown in Table 4.

<Measurement method>
Alkali-silica reaction suppression effect: Curing the specimen at 40 ° C., measuring the rate of change in length. If the rate of change in length at 6 months of age is less than 0.1%, “Yes”, 0.1% When it exceeded, it was set as “None”.

<Materials used>
Sacrificial anode material II: zinc aluminum alloy (pH = 13.5) covered with porous mortar containing LiOH as an alkali silica reaction inhibitor and having a zinc / aluminum ratio of 1/1
Sacrificial anode material III: Aluminum lump (pH = 13.5) covered with porous mortar containing LiOH as an alkali silica reaction inhibitor
Sacrificial anode material IV: Magnesium lump (pH = 12.0) covered with porous mortar containing LiOH as an alkali silica reaction inhibitor
Sacrificial anode material V: Zinc magnesium alloy (pH = 13.5) covered with porous mortar containing LiOH as an alkali silica reaction inhibitor and having a zinc / magnesium ratio of 1/1
Sacrificial anode material VI: Aluminum magnesium alloy (pH = 13.5) covered with porous mortar containing LiOH as an alkali silica reaction inhibitor and having an aluminum / magnesium ratio of 1/1
Sacrificial anode material VII: Zinc-aluminum-magnesium alloy (pH = 13.8) covered with porous mortar containing LiOH as an alkaline silica reaction inhibitor and having a zinc / aluminum / magnesium ratio of 1/1/1
Sacrificial anode material VIII: zinc block covered with porous mortar containing no alkali silica reaction inhibitor (pH = 12.5)

From Table 4, it can be seen that according to the present invention, the hardened concrete (mortar) is imparted with an excellent rust prevention effect, and the salt damage resistance is improved. From Experiment Nos. 4-7 and 4-1 to 4-6, the combined use of the CA compound and the sacrificial anode material provides a synergistically higher effect.
Also, from Experiment No. 4-8, when the porous material around the metal does not contain an alkali silica reaction inhibitor, the metal is passivated, so the amount of depolarization is reduced and the alkali silica reaction is suppressed. The effect is not seen.

  The present invention is suitable for applications such as offshore structures and road slabs in cold regions because it imparts an excellent rust prevention effect to reinforced concrete and improves salt damage resistance.

Claims (3)

In CaO / _Al 2 _{O 3} molar ratio of 0.15 to 0.7, the internal Blaine specific surface area of the calcium aluminate compounds of 2000~7000cm ² / g, cement, and water was allowed to cure kneading concrete A sacrificial anode material is placed on the inside of the sacrificial anode material, and a porous material containing an electrolyte solution having a pH of 12 or more is attached around the sacrificial anode material to avoid the formation of anode conduction. rebar Ri Na electrically connecting the metal of the sacrificial anode material, zinc, aluminum, and a metal or an alloy including one or two or more selected from the group consisting of magnesium, internal reinforced concrete rebar Anticorrosion method. The anticorrosion method for reinforcing bars in reinforced concrete according to claim 1, wherein the porous material contains an alkali silica reaction inhibitor. The anticorrosion method for reinforcing bars in reinforced concrete according to claim 2, wherein the alkali silica reaction inhibitor contains lithium ions.