JP2006327910A - Method for electrochemical salt removal from concrete structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a salt removal method which enables salt removal from an objective concrete structure in a manner suited for the situation of the concrete structure and is capable of attaining the maximum economical salt removal effect. <P>SOLUTION: The electrochemical salt removal method for the concrete structure comprises performing simulated salt removal from a concrete sample 45 sampled from the concrete structure to analyze the relationship between current passing conditions and a salt removal effect, and removing salts from the concrete structure under the current passing conditions set according to the results of the analysis. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for electrochemical desalination of a concrete structure containing steel.

  When a large amount of chloride is present in the vicinity of steel materials such as concrete reinforcing bars and PC steel materials, the passive film on the surface of the steel material is destroyed, corrosion of the steel material begins, and the durability of the concrete structure decreases. The phenomenon that the steel material in the concrete is rusted by the chloride ions existing inside the concrete and the durability is lowered is called salt damage of the concrete.

  The electrochemical desalination method is a method in which chloride ions that cause salt damage to concrete are discharged out of the concrete by direct current. This is an extremely effective method for suppressing the decrease in durability of the resulting concrete structure.

For example, Non-Patent Document 1 describes a design / construction method in an electrochemical desalination method, and shows that current is supplied for 2 months at a current density of 1 A / m ² as a standard energization treatment condition.

Japan Society of Civil Engineers "Electrochemical anticorrosion method design and construction guidelines (draft)"

  Although the desalination design construction manual of Non-Patent Document 1 indicates that the investigation of the structure must be carried out in designing, the current density, the energization processing period, and the conditions of the electric circuit must be determined. The design and construction management method is not shown.

  For this reason, the design and construction management of the conventional desalination method are based on the experience of the installer, and are not necessarily in accordance with the situation of the structure to be constructed. In addition, since a concrete design and construction management method has not been established, the construction period has become provisional, and the effects and economics of the construction method have not been sufficiently evaluated.

  The object of the present invention is to solve such problems, to enable desalting according to the situation of the concrete structure to be desalted, and to obtain the maximum desalting effect economically. Is.

  As a result of intensive studies, the inventor collected a concrete sample from the target structure, performs simulated desalination, and grasps the characteristic values related to desalination of the target structure, thereby determining the chloride content at the time of construction. The present invention has been completed by obtaining knowledge that it is possible to predict movement over time, and that specific design and construction management such as a required accumulated current amount are possible.

That is, the present invention analyzes the relationship between the energization condition and the desalting effect in advance by performing simulated desalting on a concrete sample taken from the concrete structure when performing electrochemical desalting of the concrete structure. The concrete structure is desalted according to the energization conditions set based on the analysis result.
The analysis is performed by obtaining a relationship between a chloride ion concentration of the concrete sample and a chloride ion decrease amount per unit integrated current amount.
Further, the setting of the energization condition based on the analysis result is characterized in that at least an integrated current amount is set.
Further, the concrete structure is desalted under the energization conditions set based on the analysis result, and during the desalting, the chloride ions extracted from the concrete structure are measured, and the measurement result is Based on this, the current-carrying condition is corrected.

  According to the electrochemical desalting method of the present invention, a concrete sample collected from a concrete structure is subjected to simulated desalting, for example, the relationship between the chloride ion concentration and the amount of chloride ion reduction per unit integrated current is determined, Analyzing the relationship between energization conditions and the effect of desalination in advance, based on the results of this analysis, we designed concrete changes over time in the chloride concentration distribution during energization inside the concrete structure. Energization conditions (current density, energization period, energization method (including surface treatment method for energization)) are set, and the concrete structure is desalted according to the set energization conditions. Thereby, desalting according to the situation of the concrete structure to be desalted is possible, and the maximum desalting effect can be obtained economically.

  Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to such embodiments, and appropriate modifications can be made within the scope of the gist of the present invention.

In the electrochemical desalting method of the present invention, the following steps are performed as a pre-step of actual desalting.
(1) Step of collecting concrete sample (2) Step of analyzing the relationship between energization condition of target concrete structure and effect of desalination by simulating desalination of concrete sample (3) Analysis result by simulated desalination Thus, the process of designing the temporal change of the chloride concentration distribution during energization inside the concrete structure and setting the energization conditions during construction will be described in detail below.

(1) Collection of concrete samples Concrete samples are collected from the concrete structure to be desalted. Usually, the concrete sample uses a concrete core cut from the concrete structure. Although there is no restriction | limiting in particular in the diameter of a concrete core, In order to acquire sufficient data, it is desirable that a diameter is 50 mm or more. In addition, the concrete sample does not necessarily need to be a concrete core, and may be cut by another method. The sampling depth of the sample is preferably equal to or greater than the depth corresponding to the reinforcing bar inside the concrete structure from the concrete surface.

(2) Simulated desalination of concrete sample One concrete sample is cut at an appropriate interval for each depth, and the amount of chloride ions is measured for each cut sample. The amount of chloride ions is usually determined by crushing the sample at each depth into powder, dissolving with nitric acid, etc., and then determining the chloride ion amount per unit volume of the concrete from the chloride concentration measured by potentiometric titration. The value converted into is used. The chloride concentration measurement method is not necessarily required by potentiometric titration as long as the exact chloride concentration in a solution dissolved in nitric acid can be measured. It may be a different method.

  Next, electrochemical desalting (simulated desalting) is performed for an arbitrary period on another concrete sample (preferably taken from a portion as close as possible to the previous sample). During simulated desalination, the resistance value of concrete should be obtained as preliminary data from the relationship between voltage and current. The concrete sample after simulated desalting is analyzed, and the amount of chloride ions left in the concrete sample after desalting is measured. This measurement method may be the same as the measurement method described above.

  Based on the results of simulated desalting on concrete samples, the relationship between the energization conditions of the target concrete structure and the effect of desalting is analyzed. Specifically, the relationship between the chloride ion concentration and the amount of chloride ion decrease per unit integrated current is determined as the characteristic value of the target concrete structure. The accumulated current amount is an integrated value of the flowed current and the period.

(3) Setting energization conditions at the time of construction work From the analysis results by simulated desalination, by designing the temporal change of the chloride concentration distribution during energization inside the concrete structure to be desalted, Set energization conditions. Specifically, the cross section of the desalting target concrete structure is modeled as an electric circuit capable of evaluating the movement amount of chloride ions by an appropriate method. By substituting the characteristic value obtained from simulated desalting for the concrete sample into the model and performing analysis, the amount of chloride ion at a certain position on the cross-sectional area to be examined is calculated to obtain an integrated current amount. The electric current and energization period required for electrochemical desalination of the structure are required.

The actual electrochemical desalting of the concrete structure to be desalted is carried out according to the energization conditions set through the preceding steps. As a result, it is possible to make the construction of electrochemical desalination, which has been uniquely determined as a current density of 1 A / m ² energization period of 2 months per concrete surface area, suitable for the concrete structure, The maximum desalting effect can be obtained economically.

  Further, in the present invention, the concrete structure is desalted under the energization condition set based on the analysis result, and the temporal change of chloride ions extracted from the concrete structure is measured during the desalting. It is preferable to correct the energization condition based on the measurement result. Specifically, if the measurement result of chloride ions extracted from the concrete structure is different from the result of simulated desalination, if the characteristic values used in the design are corrected to match the actual values, Thus, the construction plan can be corrected at a relatively early stage of construction without waiting for two months.

  Hereinafter, specific examples of the present invention will be described.

(1) Collection of concrete samples Three concrete samples (specimens A, B, and C) of φ50 mm x 100 mm from the concrete structure to be desalted (preferably larger as long as the target structure is not adversely affected). ). Specifically, as shown in FIG. 1, a core sample drill 12 is used to collect from the target structure 11.

  Specimen A measures the amount of chloride ions at each depth for the purpose of grasping the amount of chloride ions before desalting. For this reason, the specimen A is divided in the depth direction with a concrete cutter or the like. The number of divisions is determined based on the amount necessary for analysis, but is not particularly limited as the amount of chloride ions can be measured by the amount of one division plane. In this example, as shown in FIG. 2, the sample was divided into five parts, the sample at each depth was crushed into powder, dissolved in nitric acid, and then the chloride concentration was measured by potentiometric titration.

(2) Analysis of relationship between energization condition and desalting effect by simulated desalting of concrete samples Specimens B and C are used for simulated desalting. In the simulated desalination, a current is passed through two opposing surfaces, and the amount of current in the concrete sample, the energization time, and the change properties of the chloride ion concentration are grasped. If only one sample can be collected, the sample is divided to create a plurality of samples. FIG. 3 shows an example of dividing into two.

  The simulated desalination situation is shown in FIG. 4 (perspective view) and FIG. 5 (schematic cross-sectional view). In the simulated desalting, a specimen 45 having a cathode 44 placed on the upper surface is placed in a container 43 containing an anode 41 and an electrolyte solution 42, and a current flows between the anode and the cathode. The other surface (side surface) is subjected to an insulation treatment using a coating material or the like so that a current flows between the two opposing surfaces of the specimen for simulated desalting. Further, the specimen 45 and the anode 41 in the electrolyte solution are held by the spacer 46 so that they do not come into contact with each other. The specimen 45 is oriented according to the target structure, and is placed so that the concrete surface side of the target structure is the anode side and the concrete inner side is the cathode side.

  In this example, a titanium mesh was used as the anode material, a steel plate as the cathode material, lithium borate as the electrolyte solution, and a mortar block as the spacer. In addition, each of these materials is used according to the purpose of the simulated desalting and the construction work, and is not particularly limited.

  In this example, the specimens B and C were energized for B time and C time (C> B), respectively, and after energization, the specimens B and C were divided into 5 as in the specimen A, and the amount of chloride ions in each layer Was measured. The number of divisions of the specimens B and C is not particularly limited as the amount of each ion is more than the measurable quantity by the quantity of one division plane, but it is preferable to combine with the specimen A analyzed before desalting.

FIG. 6 shows the amount of chloride ions before (desired specimen A) and after simulated desalting (samples B and C) in this example. In FIG. 6, A _{1 to} A _{5 are shown} from the surface side of the specimen A divided into five parts, and B _{1 to} B ₅ and C _{1 to} C ₅ are shown from the surface side of the specimens B and C divided into five parts, respectively. .

From the change in chloride ion amount and accumulated current amount in Fig. 6, the relationship between chloride ion decrease (kg / m ³ · A · h) and chloride ion amount (kg / m ³ ) per unit accumulated current amount Asked. The result is shown in FIG.

In FIG. 7, Y _BN and Y _CN (N is an integer of 1 to 5) are chloride ion reduction amounts per unit integrated current amount obtained by the following equations, respectively.
Y _BN = (A _N −B _N ) / A _B
Y _CN = (B _N -C _N ) / A _C
Here, A _B is the integrated current amount of the specimen B, A _C is obtained by subtracting the integrated current amount of the specimen B from the integrated current amount of specimen C.

As shown in FIG. 7, in this embodiment, the chloride ion decrease amount y and the chloride ion amount x per unit integrated current amount can be expressed by a relational expression of y = ^0.000111 × ^2.988 . understood. In this example, simulated desalting was performed with two specimens B and C, but the number of specimens subjected to simulated desalting was the amount of chloride ion reduction y and the amount of chloride ions per unit integrated current amount. Since the purpose is to obtain the relationship of x with the required accuracy, the number is not limited.

(3) Setting energization conditions at the time of construction The purpose of electrochemical desalination is to discharge chloride ions that cause corrosion of steel in concrete to the outside of the concrete, so it currently exists in concrete It is necessary to estimate how much chloride ions are discharged and how much current is discharged. On the other hand, if the above relational expression is obtained, a concrete design such as the temporal change of chloride concentration distribution inside the target structure can be performed, and energization conditions (current density, energization period, Method) can be set and construction management related to the transition of desalination amount is possible. One specific example will be described below.

  The target structure is handled as a discrete model as shown in FIG. The range to be modeled and the number of blocks to be divided are not limited. It is known that concrete can be regarded as an electrical resistor and can be handled as a model of the electrical circuit shown in FIG.

  The modeled resistance R is

で示され、コンクリート中の塩化イオン濃度により変化する。ここで、α、βは、模擬脱塩時に予備データとして測定したコンクリートの抵抗値に基づく定数（もしくはコンクリートの種類に応じて経験的に求めた定数）であり、本実施例ではα＝５５０、β＝１．０、を採用した。Ｓはモデル化した各ブロックの断面積（ｍ²）、Ｌはモデル化した各ブロック間の距離（ｍ）である。

It changes with the chloride ion concentration in concrete. Here, α and β are constants based on the resistance value of concrete measured as preliminary data at the time of simulated desalination (or constants obtained empirically depending on the type of concrete), and in this example α = 550, β = 1.0 was adopted. S is the cross-sectional area (m ² ) of each modeled block, and L is the distance (m) between each modeled block.

The amount of decrease in the chloride ion of the concrete that is energized with the current of I (A) during the time Δt is represented by the relational expression of FIG.
ΔCl ⁻ (x) = 0.0011 × [Cl ⁻ ] ^2.988 × I × Δt
Indicated by Here, ΔCl ⁻ (x) represents the amount of chloride ion that decreases during the Δt time. [Cl ⁻ ] represents a chloride ion amount before energization for Δt time.

From the law of conservation of mass, the amount of chloride ions at any node other than the reinforcing bar position shown in FIG.
Cl ⁻ (x) = [Cl ⁻ ] (x) + ΔCl ⁻ (y) −ΔCl ⁻ (x)
It becomes. here,
Cl ⁻ (x): Chloride ion amount of the element of interest ΔCl ⁻ (y): Chloride ion amount flowing from the adjacent element ΔCl ⁻ (x): Chloride ion amount flowing out to the adjacent element

In desalting, since a constant current is normally passed between the reinforcing bar and the external electrode, the sum of the currents flowing in the circuit of FIG. 9 is I ₁₃ + I ₁₄ + I ₁₅ .

The resistance of the circuit varies depending on the amount of chloride ions, but assuming that it is constant during the time Δt, the resistance of each circuit is obtained from the amount of chloride ions. From the relationship between the resistance of the circuit and the total current, calculating the current I _n flowing. If I _n between the circuits is obtained, Motomari inflow and outflow of chloride ions between elements Δt time, it is possible to calculate the behavior of chloride ion with the above formula for desalination.

  As a specific calculation method, Δt of energization time is 1 hour, and the chloride ion amount of each element before energization is an initial value, and the calculation is repeated. Since the amount of chloride ions changes with each calculation, the resistance of the circuit uses a resistance corresponding to the change.

In order to confirm the validity of the design in this example, the chloride ion content of the target concrete structure was measured before and after desalting. FIG. 10 shows the distribution of chloride ion amount (kg / m ³ ) before desalting. Further, FIG. 11 shows the design values (numbers in parentheses) after 26 days of desalting (624 A · h / m ² ) and 79 days after desalting (1896 A · h / m ² ), and the actually measured chloride ion amount (kg / M ³ ). FIG. 12 shows a comparison between the design value and the actual measurement value at the reinforcing bar position. From these results, it can be seen that, in actual electrochemical desalting, it is possible to set the integrated current amount required to reduce the chloride ion amount to a certain value at a specific position in the examination cross section. .

  Since the relationship between the chloride ion amount and the chloride ion decrease amount and the relationship between the concrete resistance and the chloride ion amount are not linear, the accuracy of the above calculation is affected by the setting of Δt. If Δt is set short, the calculation accuracy is improved, but the calculation time is lengthened. If Δt is set long, the calculation accuracy is lowered, but the calculation time is shortened. In this example, Δt was calculated in one hour, and the calculation results shown in FIGS. 11 and 12 were obtained.

  As described above, according to the present embodiment, the relationship between the chloride ion concentration and the amount of chloride ion reduction per unit integrated current amount is obtained by simulated desalination, and the inside of the concrete structure is determined based on this relationship. Design concrete changes in chloride concentration distribution over time during energization, set energization conditions (cumulative current in this example) in advance, and demineralize the concrete structure according to the energization conditions set. Do. Thereby, desalting according to the situation of the concrete structure to be desalted is possible, and the maximum desalting effect can be obtained economically. In addition, the setting of the energization condition in the implementation work is not limited to the setting of the integrated current amount, and may include an energization method such as a surface treatment method for energization, for example.

It is a schematic diagram for demonstrating the collection method of a concrete sample. It is a figure which shows the mode of the division | segmentation of a concrete sample. It is a figure which shows the mode of the division | segmentation of a concrete sample. It is a perspective view for demonstrating the simulation desalination condition in the Example of this invention. It is a schematic sectional drawing for demonstrating the simulation desalination condition in the Example of this invention. It is a figure which shows the chloride ion amount before and behind the simulation desalting in the Example of this invention. It is a figure which shows the relationship between the chloride ion reduction | decrease amount per unit integrated current amount and the chloride ion amount in the Example of this invention. It is a figure which shows the discretized model of the target structure in the Example of this invention. It is the electric circuit diagram which modeled the target structure in the Example of this invention. It is a figure which shows distribution of the chloride ion amount before the desalting of the target structure in the Example of this invention. It is a figure which shows the design value and measured value of the chloride ion amount after the desalting of the target structure in the Example of this invention. It is a figure which shows the comparison of the design value of the chloride ion amount in the reinforcing bar position of the object structure in the Example of this invention, and a measured value.

Explanation of symbols

11: Concrete structure 12: Core sample drill 41: Anode 42: Electrolyte solution 43: Container 44: Cathode 45: Specimen 46: Spacer

Claims (4)

  When electrochemically desalinating a concrete structure, a concrete sample collected from the concrete structure is simulated and desalted to analyze the relationship between the energization condition and the desalting effect in advance. An electrochemical desalting method characterized in that the concrete structure is desalted according to the energizing conditions set in the above.   2. The electrochemical desalination method according to claim 1, wherein the analysis is performed by obtaining a relationship between a chloride ion concentration of the concrete sample and a chloride ion decrease amount per unit integrated current amount. 3. .   The electrochemical demineralization method according to claim 1 or 2, wherein the setting of the energization condition based on the analysis result is to set at least an integrated current amount.   Desalination of the concrete structure is performed according to the energization conditions set based on the analysis result, and during the desalting, chloride ions extracted from the concrete structure are measured, and based on the measurement result The electrochemical demineralization method according to any one of claims 1 to 3, wherein the energization condition is corrected.

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