JPH10317682A - Recycling method of prestressed concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recycle and repair the deterioration of a neutralized prestressed concrete structure, a prestressed concrete structure containing chlorine ions or a prestressed concrete structure comprising aggregate having the possibility of the causing of an alkali aggregate reaction. SOLUTION: In a method, in which a current is flowed, a steel material installed to prestressed concrete is used as a cathode, an anode is mounted on the surface section of concrete and/or a part of concrete, and voltage of hydrygen generating voltage or more is applied between both electrodes and a DC current is flowed. Effective tensile force working to the PC steel material set up to concrete is set in 80% or less of the tensile strength of the PC steel material at that time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating concrete of a prestressed concrete structure using reinforcing steel or PC steel as a reinforcing material, in particular, a concrete structure neutralized by lowering the alkalinity of concrete, and
The present invention relates to a concrete structure containing chlorine ions and a method for regenerating a concrete structure containing aggregate that may cause an alkali-aggregate reaction in concrete.

[0002]

2. Description of the Related Art A prestressed concrete structure is a structure in which a compressive strength and a tensile strength are well balanced by combining a concrete having a high compressive strength and a PC steel having a strong tensile strength. Therefore, it is widely used for various important structures, especially for bridges and long structures such as roads, railways, and warehouses. In addition, concrete generally has high resistance to the environment such as water, fire, and sunlight. In addition, since the alkalinity of concrete is 11 to 13 in alkaline, the PC steel inside it is protected from corrosion by forming a passivation film on the surface of the steel, so that the prestressed concrete structure is It has been considered a durable permanent structure.

However, the durability of the prestressed concrete structure, which has been considered as a permanent structure, has been lowered due to various causes, and the life of the structure has been questioned.

[0004] One of the causes of deterioration of a prestressed concrete structure is a neutralization of concrete and a phenomenon called salt damage.

[0005] Neutralization is a phenomenon in which calcium hydroxide produced by a hydration reaction of cement reacts with carbon dioxide in the atmosphere to form calcium carbonate. Lower than pH 11-13. When the pH drops to about 10, PC
The immovable body coating of steel is destroyed, corrosion of PC steel starts, and the strength balance as a concrete structure is lost,
Its durability will be greatly reduced.

[0006] Such deterioration of the prestressed concrete structure causes a phenomenon of rust of the PC steel inside the concrete, and furthermore, breakage of the PC steel, and is a serious problem both structurally and outwardly.

[0007] In a prestressed concrete structure located on a shore or the like, seawater splashes and adheres to the concrete surface. Furthermore, when the salt contained in the seawater penetrates into the concrete through the voids in the concrete and reaches the position of the PC steel, chlorine ions destroy the immovable body coating of the PC steel and cause corrosion. Occur.

Further, when sea sand is used as fine aggregate used as a concrete material, if the salt is not sufficiently removed, a large amount of chloride will be contained from the time when concrete is produced. As a result, the passive body film formation of the PC steel becomes insufficient, and corrosion occurs.

[0009] Due to the above reasons, cracks occur in the concrete and corrosion occurs in the PC steel, and the durability of the prestressed concrete structure is greatly reduced.

The method for repairing such deteriorated prestressed concrete structures is to remove the surrounding concrete for steel rust, and to remove the concrete at the cracked or missing portion of the concrete, and then remove the concrete. Filling with new concrete or mortar, so-called section restoration, was mainly performed.

In this cross-section repair, repair is performed only for visible deterioration phenomena such as rust of PC steel and cracking or chipping of concrete. Although the concrete was deteriorated, no treatment could be performed on the dangerous part where the deterioration was not apparent on the surface.

Further, as a method of removing a root cause of a reinforced concrete structure for neutralization and salt damage, a repair method using an electrochemical method has been disclosed (JP-A-1-176287, JP-A-2-176287). No. 302384).

One of these methods is to apply a direct current between a steel material in a neutralized concrete portion and an electrode on a concrete surface or in a concrete portion in an alkaline atmosphere having an alkalinity of pH 11 or more. Thereby, an alkaline substance in the alkaline atmosphere, for example, a hydroxide of sodium or potassium moves, and the concrete portion degraded by the neutralization becomes pH 10 or more and is re-alkalized.

Another method is to apply a direct current between the steel material in the concrete portion and the electrode on the concrete surface to the concrete containing the salt to remove the salt in the concrete outside the concrete surface. It is a method to take out. However, with these methods,
Since the voltage to be used is higher than the hydrogen generation potential, electrolysis of pore water existing in concrete occurs, and there is a side effect that hydrogen gas is generated on the surface of the steel material as the cathode.

In general, a PC steel material, which is a high-tensile steel and is strained by a large force in concrete, causes embrittlement of a metal structure when hydrogen gas is absorbed in the structure, and delays due to hydrogen embrittlement. This causes a fracture phenomenon called destruction. As a result, the prestressed concrete structure does not work mechanically, and the structure is destroyed. Actually, in the past, there is a collapse phenomenon of prestressed concrete which is considered to be due to hydrogen embrittlement of PC steel.

[0016] Therefore, the repair method using an electrochemical method is most suitable for repairing a concrete structure. However, regarding the application to a prestressed concrete structure, the side effect of hydrogen embrittlement is too dangerous. Not applied until.

Further, in order to avoid generation of hydrogen gas at the cathode, a method of applying a DC current while suppressing the voltage applied to the prestressed concrete to a hydrogen generation potential or less, that is, about 1.0 V or less has been attempted. However, in this method, the pre-stressed concrete structure must be permanently energized, and there is a problem in maintenance and durability of the energizing device, and it is practically difficult to apply the method.

In view of such a situation, the present inventors made various studies to solve the above-mentioned problems, and as a result, the ratio of the effective tensile force acting on the PC steel material to the tensile strength of the PC steel material was determined. The hydrogen sensitivity has changed, and as a result, the present inventors have obtained the knowledge that the electrochemical method can be applied to a prestressed concrete structure without causing the worst case of hydrogen embrittlement, and have completed the present invention.

[0019]

That is, the present invention provides (1)
A steel material installed in prestressed concrete is used as a cathode, and an anode is installed on the surface of the concrete and / or a part of the concrete. Flowing the concrete, wherein the effective tensile force acting on the PC steel material installed on the concrete is 80% or less of the tensile strength of the PC steel material,
(2) A direct current having a current density of 0.1 A or more and 10 A or less per 1 m ² of the surface area of concrete is supplied, and a period for supplying the current is 6 months or less.
It is an energization regeneration method for the described concrete.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
Generally, pore water which is an aqueous solution of calcium hydroxide is sufficiently present inside the hardened concrete. Therefore, when a voltage is applied to the concrete, the pore water serves as an electrolyte, and a current flows according to the resistance of the concrete itself and the added voltage.

Further, in order to apply a direct current necessary for regenerating a neutralized prestressed concrete structure or a salt-damage prestressed concrete structure, the voltage applied to the concrete must be at least 5 V or more.
Preferably, 10 V or more is required. In addition, the reaction of the electrolysis of water generated on the surface of the PC steel material serving as the cathode during the energization treatment is as follows:

[0022]

Embedded image

The hydrogen generation potential of the formula (1) is theoretically expressed as

[0024]

(Equation 1)

The following can be derived.

Therefore, the pH value in concrete is pH1
Since it is about 0.0 to 13.6, E = −0.908 to −1.121 [V], and the hydrogen generation potential is about 0.9 to 1.1 V in absolute value. Therefore, the voltage required for the regeneration treatment becomes higher than the hydrogen generation potential, and the generation of hydrogen gas near the cathode cannot be avoided.

According to the present invention, even when a voltage equal to or higher than the hydrogen generation potential is applied, the effect of hydrogen gas on the PC steel material of the prestressed concrete is examined in detail, and as a result of the investigation, the PC installed in the prestressed concrete is If the effective tensile force acting on the steel material is 80% or less of the tensile strength of the PC steel material, there is no effect of the hydrogen gas, and the regeneration treatment can be performed. And found that it recovered very quickly.

The test method conducted to examine the effect of hydrogen gas on PC steel is as follows. After tensioning the PC steel with a metal reaction frame, concrete is poured around the PC steel, and this concrete is sufficiently removed. After curing, a direct current was applied at a predetermined current density. After applying the current for a predetermined period, PC
The steel material was taken out and immediately subjected to a low strain rate tensile test. This test is a test method in which the influence of hydrogen gas clearly appears on the elongation rate until breakage of the PC steel material, particularly on the cross-sectional shrinkage rate of the PC steel material.

In this test method, as a result of diligent studies under various conditions and various PC steel materials, if the effective tensile force of the PC steel material is 85% or more of the tensile strength, a clear influence of hydrogen gas is observed. The hydrogen gas is partially affected by 81 to 85%, and has no effect at 80% or less, or
It was found that the effect was very short-lived and that the PC steel material recovered quickly.

The terms used in the present invention are defined as follows. (1) "Steel" refers to metal structural materials such as PC steel, steel bars, steel frames, etc., in concrete or on the concrete surface. (2) “Prestress” is the degree of stress that is applied to concrete in advance or afterwards in order to counteract tensile stress caused by load. (3) “Prestressed concrete” refers to concrete that is prestressed by a tendon material, and generally includes structural materials such as PC steel, steel bars, and steel frames. (4) "PC steel" is a high-strength steel used as a tendon to give prestress. (5) "Effective tensile force" is the tensile force actually acting on the tendon after prestressing the concrete. (6) “Tensile strength” refers to the tensile strength and / or tensile load of PC steel specified in Japanese Industrial Standards. Specifically, “JIS G 3109 (1994) PC steel Stick "," JI
SG 3137 (1994) Small-diameter deformed PC steel bar '', `` JIS G 3536 (1
994) PC steel wire and PC steel strand '', `` JIS G 3538 (1994)
Tensile strength and tensile load described in "PC hard steel wire".

In the present invention, the current density used must be large enough to remove chloride ions from the concrete and to allow an alkaline electrolyte solution to penetrate into the concrete. The value requires the amount of current per concrete surface area. Usually 0.1% per concrete surface area.
1 A / m ² or more, more preferably 0.5 A / m 2
² or more, more preferably 0.75 A / m ² or more. Further, in the present invention, the period during which the current continues to flow is usually about 1 day to 6 months, which is a limited period.
Even though the period during which the current continues to flow is limited, it is dangerous to excessively increase the current density, and the upper limit is necessarily determined. The upper limit is preferably 10 A / m ² or less per concrete surface area, more preferably 7.5 A / m ^2.
/ M ² or less, more preferably 5.0 A / m ² or less.

The external electrodes used in the present invention will be described.
Generally, the electrode on the surface of the concrete is on the positive (+) side, so that an electrical corrosive action acts. In the present invention, since the current is applied for a relatively short period of about 1 day to about 6 months, ordinary reinforcing bars and wire meshes can be used. Those having high resistance are preferred. Specifically, titanium, titanium alloy, platinum, and / or metal plated with them,
Carbon such as carbon fiber and carbon rod, volume electric resistivity is 10 ³ Ω
-An organic polymer having conductivity of not more than cm. Titanium and platinum are stable against electric corrosion, and carbon and organic polymers are almost stable. In addition, since the volume resistivity of ordinary concrete is about 10 ³ to 10 ⁴ Ωcm, as an organic polymer having conductivity,
That is, it is preferably 10 ³ Ωcm or less, more preferably
It is 10 ² Ω · cm or less, more preferably 10 Ω · cm or less.

In the present invention, when electricity is supplied to the concrete, an electrolyte solution may be used.
Aqueous solutions of lithium compounds, aqueous solutions of lithium compounds and other electrolyte materials, aqueous solutions of hydroxides and carbonates such as alkali metals and alkaline earth metals, guanidine carbonate, hydroxylamine, chloramine, and tetrahydroxide Examples thereof include aqueous solutions of amines such as alkylammonium, and examples thereof include an aqueous solution obtained by mixing these and an aqueous solution containing a buffer such as boric acid.

The aqueous solution of a lithium compound is a water-soluble lithium compound, and specifically includes lithium acetate, lithium aluminum hydride, lithium borohydride, lithium bromide, lithium hydroxide, and lithium iodide. Lithium, lithium lactate, lithium nitrate, lithium oxalate, lithium perchlorate, lithium phosphate, lithium pyruvate,
Lithium sulfate, lithium tetraborate, lithium nitrite, lithium carbonate, lithium chloride, lithium citrate, lithium fluoride, lithium hydride, and the like can be used.

[0035]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Example 1 In order to investigate the influence of hydrogen gas on PC steel, concrete was poured around the PC steel in a state where the PC steel was tensioned on a metal reaction force frame, and after the concrete was sufficiently cured, the direct current was increased. A current was applied. After stopping the DC current, the PC steel was taken out and subjected to a low strain rate tensile test. In this test, the presence or absence of hydrogen embrittlement given to PC steel was determined by the PC
It is expressed by the section shrinkage (RA) of the steel material. In addition, the criterion is based on the cross-sectional shrinkage (RA) of the PC steel material at the time of manufacture. If the difference from the reference value exceeds 20, it is “hydrogen embrittlement”. The brittleness is uncertain ”, and if it is 10 or less,“ no hydrogen embrittlement ”. The cross-sectional shrinkage (RA) of the PC steel after fracture is
It is calculated by the following equation.

[0036]

(Equation 2)

The test results performed under [Test condition 1]
Type 1 is shown in Table 1 and Type B 1 is shown in Table 2. The low strain rate tensile test was performed twice on the day when the DC current was stopped and one month after the DC current was stopped, and the state of recovery of the PC steel after the DC current was stopped was also examined.

[Test conditions 1]-Low strain rate of tensile test = 1.6 x ^10-5 / sec-Tensile tester: UH-2000kNA manufactured by Shimadzu Corporation-PC steel: "JIS G 3109 (1994) PC steel rod" Class C No. 1 (symbol SBPR 1080/1230) and Class B No. 1 (symbol SBPR 930)
/ 1080), name 13mm. Tensile strength (tensile strength) = 1230 N / mm ² (Class C No. 1) Tensile strength (tensile strength) = 1080 N / mm ² (Class B No. 1) ・ Electrification treatment: current density = 1 A / m ² ( Concrete surface area), energization period = 1 to 180 days-Effective tensile force: 50% to 90% of the tensile strength of PC steel

[0039]

[Table 1]

[0040]

[Table 2]

Example 2 Using the same metal reaction force frame as in Example 1, [Test condition 2]
, A low-strain-rate tensile test was performed. Table 3 shows the results. The low-strain-rate tensile test was performed twice as in Example 1 on the day when the DC current was stopped and one month after the DC current was stopped.
The recovery status of steel materials was investigated.

[Test conditions 2]-Low strain rate in tensile test = 1.6 x ^10-5 / sec-PC steel: deformed PC steel described in "JIS G 3536 (1994) PC steel wire and PC steel stranded wire" Wire (symbol SWPD1L), name 9mm
. Tensile strength (tensile load) = 90.2 kN.・ Electrification treatment: current density = 2 A / m ² (concrete surface area), energization period = 14 to 56 days ・ Effective tensile force: 60% to 85% of the tensile strength of PC steel

[0043]

[Table 3]

Example 3 [Test condition 3] using the same metal reaction force frame as in Example 1.
, A low-strain-rate tensile test was performed. Table 4 shows the results. The low-strain-rate tensile test was performed twice as in Example 1 on the day when the DC current was stopped and one month after the DC current was stopped.
The recovery status of steel materials was investigated.

[Test conditions 3]-Low strain rate in tensile test = 1.6 x ^10-5 / sec-PC steel: Class C No. 1 described in "JIS G 3109 (1994) PC steel rod" (symbol: SBPR 1080) / 1230), 13 mm in name. The tensile strength (tensile strength) = 1230 N / mm ^2.・ Electrification treatment: current density = 0.1 to 10 A / m ² (concrete surface area) ・ Electrification period = 56 days ・ Effective tensile force: 60% to 85% of the tensile strength of PC steel

[0046]

[Table 4]

[0047]

According to the present invention, when an electrochemical regeneration (energization) treatment is carried out on a prestressed concrete structure, there is no influence of hydrogen gas, or even if it is present, it is extremely short. The PC steel recovers within the time. Therefore, the present invention relates to deterioration regeneration, repair and repair of a neutralized prestressed concrete structure, a prestressed concrete structure containing chloride ions, or a prestressed concrete structure containing an aggregate that may cause an alkali aggregate reaction. Useful in fields.
The prestressed concrete structure can be filled and strengthened by electrochemically introducing various substances into the prestressed concrete structure.

Claims (2)

[Claims] 1. A steel material installed in prestressed concrete is used as a cathode, and an anode is installed on a surface portion of the concrete and / or a part of the concrete, and a voltage higher than a hydrogen generation potential is applied between the two electrodes. In the method in which a direct current is applied and applied, the P
An energizing and regenerating method for concrete, wherein the effective tensile force acting on the C steel is 80% or less of the tensile strength of the PC steel. ^2. Per square meter of concrete surface area,
A direct current with a current density of 0.1A or more and 10A or less flows,
2. The method according to claim 1, wherein the current is supplied for a period of 6 months or less.