JP2017181171A - Concrete neutralization environment evaluating composition, sensor using the composition, and concrete neutralization condition evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutralization environment evaluating composition which can evaluate a neutralization environment in which a concrete is put easily and accurately, a sensor using the composition, and a concrete neutralization condition evaluation method.SOLUTION: The present invention relates to: a neutralization environment evaluating composition of a concrete made of an olivine-type silicate compound expressed by LiMSiO(in which M denotes at least one selected from Fe, Ni, Co, and Mn), a conductive agent, and a molding agent; a sensor using the composition; and a method for evaluating a neutralization condition of a concrete.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a neutralization environment evaluation composition used in an environment where concrete is installed, a concrete neutralization environment evaluation sensor using the same, and a method for evaluating the neutralization status of concrete. In the present invention, concrete includes not only concrete but also hardened cement such as mortar.

  Normally, the reinforcing bars in concrete are protected by an alkaline substance such as calcium hydroxide generated by hydration of cement to avoid corrosion. However, when an acidic substance such as carbon dioxide gas or sulfurous acid gas in the air enters the concrete and reacts with the alkaline substance to neutralize the reinforcing bar, the rust prevention function of the reinforcing bar is lost. As a result, the expansion of rust caused by corrosion of the reinforcing bars causes cracks in the concrete, and the durability of the concrete is significantly reduced. Therefore, the evaluation of neutralization is extremely important as an index for maintaining and managing the durability of concrete. In particular, in hot spring areas and chemical industrial areas where a relatively large amount of acidic substances are present, it is necessary to fully examine the cover thickness of the reinforcing bars in order to ensure the durability of the concrete. Is required.

By the way, the neutralization evaluation method is generally a method in which a phenolphthalein solution (red purple) is sprayed on the split surface of the core taken from the concrete, and the depth of the neutralized portion that is colorlessly faded is measured. is there. Several other methods for evaluating the neutralization of concrete have been proposed.
For example, Patent Document 1 proposes a method of measuring the neutralization depth of concrete by detecting the alkalinity of concrete powder discharged when drilling concrete. Patent Document 2 proposes a method for predicting corrosion of reinforcing bars using information collected by monitoring and collecting at arbitrary intervals in a concrete in which reinforcing bars are embedded.

  Further, Patent Document 3 and Patent Document 4 propose a method of creating mortar compositions having different compositions and measuring the neutralization depth in order to evaluate the neutralization environment of concrete.

Japanese Patent Laid-Open No. 2002-40013 Japanese Patent Laid-Open No. 2007-240481 JP 2014-199237 A Japanese Patent Laying-Open No. 2015-68771

However, in the method described in Patent Document 1, core collection and drilling are accompanied by damage to the concrete, so there is a concern that the durability may be lowered. In the method of Patent Document 2, the core is not collected or drilled, but the neutralization of the concrete is grasped later or simultaneously, and the neutralization environment in the new construction site of the concrete structure is determined in advance. Not suitable for evaluation.
In the methods of Patent Document 3 and Patent Document 4, it is a measurement of whether or not neutralization of the mortar that is a sensor has occurred, and the progress and degree of neutralization cannot be numerically evaluated. Moreover, since it is manufactured with mortar, a sensor becomes large and it is necessary to secure an installation place.

  Therefore, the present invention provides a neutralization environment evaluation composition that can easily and accurately evaluate a neutralization environment in which concrete is placed, a sensor using the composition, and a method for evaluating the neutralization state of concrete. The purpose is to do.

The inventors of the present invention have studied a sensor that meets the above-mentioned object, and have found that lithium metal silicate reacts with carbon dioxide gas to change electrical characteristics, thereby completing the present invention. Specifically, the present invention has the following configuration.
[1] An olivine-type silicate compound represented by Li ₂ MSiO ₄ (wherein M represents one or more selected from Fe, Ni, Co, or Mn), a conductive aid, and a molding agent. Composition for evaluating the neutralization environment of concrete.
[2] A solid detection unit comprising the composition for evaluating the neutralization environment of concrete according to [1],
A first energization unit connected to an end of the detection unit;
A neutralization environment evaluation sensor for concrete, comprising: a second energization unit connected to the other end opposite to the end of the detection unit.
[3] The sensor according to [2] is installed at a place to be evaluated, and a period from when the exposure of the sensor starts until the neutralization detection member detects neutralization is compared, and the period is compared. Then, the neutralization environment evaluation method for concrete, which evaluates the neutralization environment of concrete.
[4] The neutrality of the concrete in which the sensor according to [2] is installed in a concrete structure, and the neutralization state of the concrete is evaluated based on the change in the electrical characteristic value of the detection part of the sensor. Evaluation method

  According to the neutralization environment evaluation composition, neutralization environment evaluation sensor, and neutralization environment evaluation method of the present invention, the neutralization environment of concrete and the progress of neutralization of concrete can be easily and accurately performed. Can be evaluated.

It is a perspective view of the sensor for neutralization environment evaluation (an example) of a block shape. It is sectional drawing (a) and a top view (b) of the sensor for neutralization environment evaluation (an example) of a block shape. It is sectional drawing of the sensor for neutralization environment evaluation (an example) of a block shape. It is a figure which shows transition of the electrical resistance of a sensor from the exposure start time of a sensor. It is the XRD pattern before carbonation of the composition for neutralization environment evaluation, and the XRD pattern after carbonation.

Hereinafter, the neutralization environment evaluation composition, neutralization environment evaluation sensor, concrete neutralization environment evaluation method, and neutralization state evaluation method of the present invention will be described.
1. Neutralizing environment evaluation composition

  The composition for evaluating the neutralization environment of the present invention is lithium metal silicate with conductivity imparted to the particle surface, and the conductivity changes when the metal lithium silicate reacts with an acidic gas such as carbon dioxide gas. It is.

Lithium metal silicate which is a raw material for the composition for evaluating neutralization environment is represented by Li ₂ MSiO ₄ (wherein M represents one or more selected from Fe, Ni, Co or Mn). It is an olivine type silicate compound type mineral. Specific examples of the olivine type silicate compound include Li ₂ FeSiO ₄ , Li ₂ NiSiO ₄ , Li ₂ CoSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ (Fe) m (Mn) 1 -mSiO ₄ (0 <m <1 And the like. Among these, Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , and Li ₂ (Fe) m (Mn) 1 -mSiO ₄ are preferable from the viewpoint of manufacturability and raw material cost.
The lithium metal silicate can be produced by a known method such as a low temperature spray pyrolysis method or a hydrothermal synthesis method.
The particle size is 1 to 20 μm, preferably 3 to 15 μm, from the viewpoint of material synthesis and paste moldability.

The conductive auxiliary agent that is a raw material for the neutralized environment evaluation composition only needs to be a substance that can increase the electron conduction area (electron conduction path) of lithium metal silicate and ensure sufficient electron conductivity. Examples thereof include carbon black-based conductive assistants, scaly graphite, fibrous carbon, and activated carbon. Of these, carbon black-based conductive assistants are preferable, and specific examples include furnace black, ketjen black, acetylene black, and thermal black. The specific surface area of the conductive auxiliary agent is preferably 50 to 2000 m ² / g from the viewpoint of preventing decrease in conductivity and coating properties.
From the point which ensures electroconductivity with respect to 100 mass parts of metal silicate lithium, 0.1-20 mass parts is preferable at a carbon atom conversion amount with respect to 100 mass parts of metal silicate, and also 1-10. Part by mass is preferred.

The molding agent is added to maintain the neutralized environment evaluation composition in a solid state, and examples thereof include a resin-based binder, a rubber-based binder, and a cellulose-based binder. Examples of the resin binder include polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyvinyl alcohol (PVA), polyethylene oxide, polyvinyl pyrrolidone, polyester resin, acrylic resin, phenol resin, and epoxy resin. It is done. Examples of the rubber binder include ethylene-propylene-diene copolymer resin, styrene butadiene rubber (SBR), polybutadiene, and fluorine rubber. Examples of the cellulose binder include hydroxypropyl cellulose and carboxymethyl cellulose (CMC). These binders may be used individually by 1 type, and may use 2 or more types together. Among these, PVDF is particularly preferable.
The molding agent is 0.1 to 20 parts by mass, preferably 1 to 15 parts by mass with respect to 100 parts by mass of the total amount of lithium metal silicate and the conductive auxiliary, from the viewpoint of adhesion to lithium metal silicate and the conductive auxiliary. And

2. Neutralization environment evaluation sensor The neutralization environment evaluation sensor of the present invention is a solid material obtained by molding the above-described lithium metal silicate and a conductive additive, and further, if necessary, a molding agent into a plate shape or a block shape. And at least one surface of the detection unit is an exposed surface exposed to the atmosphere or an acidic gas such as carbon dioxide such as concrete, and one end and the other end opposite to the end are exposed. An energizing part is provided, and the neutralization environment is evaluated by utilizing the fact that the lithium metal silicate reacts with the acidic gas and the electrical characteristics of the detecting part change.
Hereinafter, it will be described in detail by dividing into (1) sensor form and (2) sensor manufacturing method.

(1) Sensor form As shown in FIG. 1, the sensor 10 is a sensor 11 for measuring the neutralization environment evaluation composition and the electrical characteristics that change due to the neutralization of the sensor. The two lead wires 12. Moreover, as shown in FIG. 2, in order to protect the detection part 11 and to limit the exposure surface with acidic gas, the exterior part which covers the surface except at least one surface of the detection part 11 as an arbitrary member as needed 13 is included.
The shape of the sensor 10 is not limited, but is preferably a columnar shape, a plate shape, or a block shape from the viewpoint of ease of molding.
Although the shape of the detection part 11 is not ask | required, when used in concrete, the exposure surface to the concrete of the detection part 11 shall be larger than the largest dimension of an aggregate.
The exterior part 13 consists of a film, a sheet | seat, a coating film, mortar, ceramics, resin, etc. When embedding in concrete, use a material with strength equal to or higher than that of concrete so as to prevent damage due to impact during placement and not to be a weak point in the strength of the concrete structure. Use. When it is not necessary to protect the detection unit 11 and it is desired to limit the exposed surface of the carbon dioxide gas, the exterior member 13 may be a film, a sheet, a coating film, a plate, or the like.
Two lead wires 12 are embedded so as to be electrically connected to the detection unit 11 so that electric characteristics such as electrical resistance, potential change, and current density of the detection unit can be measured by a measuring instrument such as a tester. .

  Furthermore, as shown in FIG. 3, when the exposed surface of the detection unit 11 such as an impact at the time of placing concrete may also be damaged, the covering unit 14 may be provided as an arbitrary member on the exposed surface. The coated part 14 may be made of cement paste or mortar that is alkaline and becomes porous after solidification. The water-cement ratio of the cement paste or mortar is equal to or higher than that of reinforced concrete structures so that it is as close to the environment as possible and does not prevent the passage of corrosion factors from the concrete surface to the reinforcement. A water cement ratio is preferred. The covering portion 14 preferably has a thickness of 2 to 15 mm so as not to break.

(2) Sensor Manufacturing Method One example of the sensor manufacturing method of the present invention is shown in the following (A) to (F).
(A) Lithium hydroxide and sodium silicate are mixed in water containing an organic solvent such as glycerin. To this solution, a metal sulfate metal salt such as iron sulfate is added and mixed. The mixed solution is put into an autoclave, a hydrothermal reaction is performed at 120 to 200 ° C., and the reaction solution is filtered and dried. Lithium metal silicate can be obtained by adding an organic solvent such as glucose and water to the dried product and firing at 500 to 800 ° C. in a reducing atmosphere.
(B) Next, a conductive additive and a molding agent are mixed with the obtained lithium metal silicate, and an organic solvent is added thereto. The amount of the organic solvent is preferably 30 to 60% by mass, more preferably 45 to 55% by mass, as the content (slurry concentration) of lithium metal silicate and the conductive additive in the slurry.
The mixing means may be a planetary mixer, a twin screw extruder, a single screw extruder, a centrifugal disk mixer, a double arm kneader, a ball mill, a planetary mill, or a Henschel mixer, with a planetary mixer being more preferred.

(C) A cylindrical plastic container is prepared, and aluminum foil or the like is bonded to one end as a bottom plate. The lead wire is passed through aluminum foil in advance, the insertion point is closed with an adhesive or the like, and the slurry prepared in a plastic container is filled. Insert the other lead into the slurry from the other end (top). When using an exterior material, the exterior material made of mortar may be filled instead of the plastic container.

(D) The slurry is dried to make the detection part solid. Any drying method can be used as long as it can volatilize and remove the organic solvent such as vacuum drying and high temperature drying. The dried detector removes the plastic container and the aluminum foil as necessary.
Note that, instead of (B), (C), and (D), the metallic lithium silicate obtained in (A) may be pressed and molded to form a detection unit.

(E) When the exterior material is provided, the aforementioned plastic container, aluminum foil, mortar, or the like may be used as it is. However, in the above-described plastic container and aluminum foil, carbon dioxide gas may enter from the joint or the like, so that an epoxy resin or the like may be newly applied, or an exterior material may be prepared to fit the detector.

(F) When providing a coating part, apply mortar or paste kneaded to the exposed surface of the detection part and perform curing.

  The completed sensor is sealed or stored until used in a gas free of acid gases.

  It should be noted that the manufacturing method and the manufacturing order may be changed within the range of the target function of the present sensor, for example, pressurizing and molding lithium metal silicate and bonding the lead wires later.

3. Method for evaluating the neutralization environment of concrete In the method for evaluating the neutralization environment of concrete, the sensor of the present invention is installed in a place to be evaluated for a certain period of time, and its electrical characteristics are measured. The neutralization environment of concrete is evaluated by comparing the electrical characteristic values of the sensors installed in the target location. The number of sensors installed in one place is preferably 3 or more from the viewpoint of evaluation accuracy.
The place to be evaluated is the place where the concrete is planned to be installed, or within the range that has the same neutralization environment as the concrete to be evaluated. Install as close to the concrete as possible. It is preferable to do this.
In addition, if a neutralized environment standard point is set, the neutralized environment is set as the standard environment, and the transition of the electrical characteristic value is obtained, the evaluation of the evaluation target location will be evaluated in the standard environment in the next and subsequent evaluations. This can be done by comparison with the transition of electrical characteristics. For example, you may set 20 degreeC and 60% of relative humidity which are the general dry environment of concrete as a standard environment.

4). Concrete neutralization status evaluation method Concrete neutralization status evaluation method is a method of embedding the sensor of the present invention in concrete and measuring the penetration depth of acid gas such as carbon dioxide and the degree of neutralization by the penetration of acid gas. taking measurement. Concrete structures have reinforcing bars in the horizontal and vertical directions. A sensor is embedded at a position closer to the surface than these reinforcing bars. Since the neutralization area in concrete reaches the sensor before the reinforcing bar, the sensor detects the neutralization early before the neutralization reaches the reinforcing bar, and measures are taken if necessary. Can be taken. Furthermore, since the sensor continues to react with the acidic gas after the arrival of the acidic gas and the electrical characteristics change, the progress of neutralization of the concrete can also be evaluated.
In addition, by installing a plurality of sensors at different depths from the concrete surface, it is possible to evaluate the depth of acid gas reaching the concrete and the degree of neutralization of the concrete. At this time, each sensor is installed so as not to overlap the concrete surface so that the sensor itself does not hinder the penetration of acid gas.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

As the lithium metal silicate, lithium iron manganese silicate (Li ₂ FeMnSiO ₄ ) was used. _{LiOH · H 2 O 4.20g (100mol} ), the Na 4 SiO 4 · nH 2 O 13.98 (50mmol), in a solvent (solvent containing ultrapure water 27.5cm ³ and glycerin 10.0 cm ³ Glycerin content: 27% by mass) was added and mixed (pH at this time was about 13). To this mixture was added FeSO ₄ · 7H ₂ O 3.92 g (14.1 mmol), MnSO ₄ · 5H ₂ O 7.93 g (32.9 mmol) and ZrSO ₄ · 4H ₂ O 0.53 g (1.5 mmol). , Mixed. The obtained liquid mixture was thrown into the autoclave and hydrothermal reaction was performed at 150 degreeC for 12 hours. The reaction solution was filtered and lyophilized for 12 hours. Glucose (carbon concentration: 10%) and ultrapure water (10 cm ³⁾ were added to 8.4 g of the powder obtained by freeze-drying, and calcined in a reducing atmosphere at 650 ° C. for 1 hour to obtain lithium manganese manganese silicate.
Next, acetylene black (manufactured by Denka) as a conductive additive and polyvinylidene fluoride (manufactured by Kureha Co., KF9305) as a molding agent were mixed with the obtained lithium iron silicate lithium in a mixing ratio of 98: 1: 1. Then, N-methyl-2-pyrrolidone was added thereto and kneaded sufficiently to obtain a paste containing a neutralizing environment evaluation composition.

  The exterior material was made of rubber and used was a semi-cylindrical shape having a diameter of 5 mm and a length of 30 mm shown in FIG. Lead wires were connected to both ends, and a paste containing a neutralizing environment evaluation composition was poured. This paste was vacuum-dried at 80 ° C. for 12 hours to obtain a neutralization environment evaluation sensor.

2. Neutralization test The manufactured sensor was exposed to a carbon dioxide concentration of 5%, a temperature of 20 ° C, and a humidity of 60%, and the electrical resistance was measured with a tester for a certain period immediately after the manufacture.

  FIG. 4 shows changes in the electrical resistance of the sensor from the exposure start time of the sensor. Moreover, as shown in FIG. 5, the detection part before the start of neutralization and the detection part in the 8th day progress were extract | collected, and the composition was confirmed by XRD. Before the start of neutralization, only the diffraction peaks of lithium iron manganese silicate and carbon were observed, but after 8 days, the diffraction peak of lithium manganese manganese silicate decreased, and a new diffraction peak of lithium carbonate was confirmed. Of lithium iron silicate was decomposed by carbonation. Therefore, it can be seen that the resistance value of the sensor of the present invention increases when lithium metal silicate is decomposed by carbonation or the like.

  Thus, the sensor of the present invention can detect the presence or absence of carbon dioxide gas, and can evaluate the difference in the neutralization environment of weak concrete by absorbing the carbonation gas. Moreover, also in concrete, the start of neutralization by the penetration | invasion of a carbon dioxide gas or acidic gas, and the progress degree of neutralization can be evaluated.

DESCRIPTION OF SYMBOLS 10 Sensor 11 Detection part 12 Lead wire 13 Exterior part 14 Clothing part

Claims (4)

In concrete composed of an olivine-type silicate compound represented by Li ₂ MSiO ₄ (wherein M represents one or more selected from Fe, Ni, Co, or Mn), a conductive aid, and a molding agent Composition for evaluating oxidative environment. A solid detector comprising the composition for evaluating the neutralization environment of concrete according to claim 1,
A first energization unit connected to an end of the detection unit;
A neutralization environment evaluation sensor for concrete, comprising: a second energization unit connected to the other end opposite to the end of the detection unit.   The sensor according to claim 2 is installed in a place to be evaluated, a period from when the exposure of the sensor is started until the neutralization detection member detects neutralization, the period is compared, and the concrete is A neutralization environment evaluation method for concrete that evaluates the neutralization environment.   A method for evaluating the neutralization status of concrete, wherein the sensor according to claim 2 is installed in a concrete structure, and the neutralization status of the concrete is evaluated on the basis of a change in an electrical characteristic value of a detection part of the sensor. .