JP2015068771A - Sensor for neutralization environmental evaluation of concrete, and neutralization environmental evaluation method of concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor or the like capable of easily and rapidly evaluating a neutralization environment of concrete.SOLUTION: In the sensor for neutralization environment evaluation of concrete, a hardened body of a cement composition that is produced by molding, into a tabular or block shape, a cement composition 11 having a water/cement ratio (mass ratio) of 35-200% and a water/powder ratio (mass ratio) of 25-70% is used as an infiltration component 11. Furthermore, one surface of the infiltration component 11 is an exposure surface exposed to the atmospheric air, a neutralization detection member 12 for detecting the neutralization using an electrical characteristic is installed on the rear surface facing the exposure surface, and the surface other than the exposure surface is a blocked surface blocked from the atmospheric air by a blocking material 13.

Description

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

  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.

By the way, the conventional evaluation method of neutralization is generally a method of spraying a phenolphthalein solution (red purple) on the split surface of a core collected from concrete and measuring the depth of the neutralized portion that has been colorlessly faded. It was the target. 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.

However, the conventional methods and the methods described in the patent literature have the following problems (1) to (3).
(1) Since core collection and drilling involve damage to concrete, there is a concern that the durability may be lowered.
(2) Since the neutralization of concrete proceeds gradually year by year, the evaluation usually takes several years or more.
(3) The above method is to grasp the neutralization of concrete after the fact or at the same time, and is not suitable for the prior evaluation of the neutralization environment at the new construction site of the concrete structure.
Incidentally, places that require prior assessment include hot springs and chemical industries where there are relatively many acidic substances. In such a place, in order to ensure the durability of the concrete, it is necessary to fully examine the cover thickness of the reinforcing bars, and for that purpose, prior evaluation of the neutralization environment is important.

Japanese Patent Laid-Open No. 2002-40013 Japanese Patent Laid-Open No. 2007-240481

  Therefore, an object of the present invention is to provide a sensor that can easily and quickly evaluate a neutralization environment in which concrete is placed, and a neutralization environment evaluation method using the sensor.

The inventors of the present invention have examined a sensor that meets the above-mentioned purpose. As shown in FIG. 1 to be described later, (i) a mortar neutralization rate constant (ease of neutralization), water / cement The ratio is approximately the same linear relationship regardless of the dry (air exposure) period,
(Ii) The ease of neutralization is primarily determined by the water / cement ratio, and
(Iii) The following sensor created based on this new knowledge was found to achieve the above object, and the present invention was completed. Specifically, the present invention has the following configuration.
[1] Cement formed by molding a cement composition having a water / cement ratio (mass ratio) of 35 to 200% and a water / powder ratio (mass ratio) of 25 to 70% into a plate shape or a block shape. A cured body of the composition is used as a penetrating member, and one surface of the penetrating member is an exposed surface exposed to the atmosphere, and neutralization is detected on the back surface facing the exposed surface using electrical characteristics. A sensor for evaluating the neutralization environment of concrete, wherein a neutralization detection member is installed, and a surface other than the exposed surface is a shield surface that is shielded from the atmosphere by a shielding material.
[2] One side of the hardened body of the cement composition and the back side opposite to the one side are exposed surfaces exposed to the atmosphere, and a neutralization detection member is installed between the two exposed surfaces. A sensor for evaluating the neutralization environment of concrete, wherein the surface other than the exposed surface is a shielding surface shielded from the atmosphere by a shielding material.
[3] The [1] or [1], wherein the neutralization detection member is a member that detects neutralization by a change in electrical resistance, a change in potential, or a change in current density due to a corrosion reaction caused by neutralization. The sensor for evaluating the neutralization environment of concrete according to [2].
[4] The penetrating part of the sensor includes a hardened body of two or more cement compositions having different water / cement ratios connected on the exposed surface and a surface other than the back surface facing the exposed surface, and the connected surface is The sensor for evaluating the neutralization environment of concrete according to any one of [1] to [3], wherein movement of the acidic substance is blocked.
[5] The back surface is formed in a stepped shape so that the distance (thickness) to the exposed surface varies stepwise, and a neutralization detection member is installed on each back surface. ] The neutralization environment evaluation sensor for concrete according to any one of [3] and [4].

[6] One or more sensors according to any one of the above [1] to [5] are installed in a place (two or more places) to be evaluated, and the neutralization detection member is installed from the start of sensor exposure. A method for evaluating the neutralization environment of concrete, which obtains a period until neutralization is detected, and evaluates the neutralization environment by comparing the periods.
[7] One or more sensors according to any one of [1] to [5] are installed in a location to be evaluated, and the neutralization detection member detects neutralization from the start of exposure of the sensor. The neutralization rate constant is calculated using the following formula (A) based on the period and the distance from the exposed surface to the neutralization detection member, and the neutralization environment is evaluated using the constant. A method for evaluating the neutralization environment of concrete.
D = C · t ^1/2 (A)
However, in the formula (A), D represents the distance from the exposed surface to the neutralization detection member, C represents the neutralization rate constant, and t represents the neutralization detection member from the start of exposure of the sensor. Indicates the period until detection.

  According to the neutralization environment evaluation sensor and the neutralization environment evaluation method of the present invention, the neutralization environment of concrete can be easily and quickly evaluated.

Figure 2 is a graph showing a linear relationship between water / cement ratio and neutralization rate constant. It is sectional drawing and a top view of a sensor for neutralization environment evaluation (an example) of a block shape. It is a perspective view of the sensor for neutralization environment evaluation (an example) of a block shape. It is a perspective view of the sensor for neutralization environment evaluation (an example) of disk shape. It is a top view of the sensor for neutralization environment evaluation (an example) by which the hardening body of the cement composition from which water / cement ratio differs is connected. 1 is a perspective view of a neutralization environment evaluation sensor (one example) in which hardened bodies of cement compositions having different water / cement ratios are connected. FIG. It is sectional drawing and a top view of the sensor for neutralization environment evaluation in which the neutralization detection member was installed in steps (2 examples of (a) and (b) are shown). It is a perspective view of the sensor for neutralization environment evaluation (example of the above-mentioned (a)) in which the neutralization detection member was installed in steps. It is a figure which shows an example of a neutralization detection member. It is a figure which shows an example of the neutralization detection member of a radio | wireless system. It is a flowchart which shows an example of the manufacturing method of a neutralization detection member. It is a figure which shows the relationship between an exposure period and the electrical resistance of a neutralization detection member. It is a graph which shows the neutralization depth (experimental value) of the sensor for neutralization environment evaluation of this invention, and its regression curve. It is a graph which shows the neutralization depth (experimental value) of the sensor for neutralization environment evaluation of this invention, and its prediction curve.

Hereinafter, the neutralization environment evaluation sensor and the neutralization environment evaluation method of the present invention will be described.
1. Neutralization environment evaluation sensor The neutralization environment evaluation sensor of the present invention is, as described above, a cement composition formed by molding a cement composition having a specific water / cement ratio or the like into a plate shape or a block shape. The surface of the infiltrating part is an exposed surface exposed to the atmosphere, and the back surface opposite to the exposed surface is neutralized by detecting the neutralization using electrical characteristics. A sensor having a blocking surface in which a chemical detection member is installed and the surface other than the exposed surface is blocked from the atmosphere by a blocking material. And the penetration part which comprises the sensor of this invention is formed with the hardening body of a cement composition, and functions as a member which acidic substances, such as a carbon dioxide gas and a sulfurous acid gas, osmose | permeate.
Hereinafter, (1) the water / cement ratio of the cement composition, (2) the form of the sensor, and (3) the manufacturing method of the sensor will be described in detail.

(1) Water / cement ratio and water / powder ratio of cement composition The water / cement ratio is 35 to 200% by mass. If the ratio is less than 35%, the cured body is dense and the progress of neutralization is slow, so the evaluation period may be long. If it exceeds 200%, there are many voids in the cured body and the progress of neutralization is uneven. As a result, the evaluation accuracy may be reduced. The ratio is preferably 55 to 180%, more preferably 60 to 160%, and still more preferably 60 to 150%.
The water / powder ratio is 25 to 70% by mass. If the ratio is less than 25%, the fluidity of the cement composition may be low and molding may be difficult, and if it exceeds 70%, material separation may occur during molding of the cement composition. The ratio is preferably 30 to 60%, more preferably 30 to 50%.

(2) Sensor configuration The sensor of [1] includes a penetrating member, a neutralization detecting member, and a blocking material, and is necessary for reinforcing the strength of the sensor, downsizing, avoiding an error factor, and the like. Accordingly, an exterior material is included as an optional member. The penetrating member is a hardened body of a three-dimensional cement composition, and is preferably a hardened body of a plate-like or block-like cement composition as shown in FIGS. .
And, one surface of the sensor of [1] is exposed to the atmosphere so that an acidic substance can enter the penetrating member, and a neutralization detecting member is installed on the back surface facing the exposed surface, Surfaces other than the exposed surface are shielded from the atmosphere by a shielding material to prevent intrusion of acidic substances. The blocking material is not particularly limited as long as it can prevent intrusion of an acidic substance, and examples thereof include one or more selected from films, sheets, coating films, plates, and the like. The blocking material can be fixed to the cured body surface by a known method such as a pressure-sensitive adhesive, an adhesive, and a screw. In addition, when the said exterior material has a function as a shielding material, an exterior material shall be included in a shielding material.

The neutralization detection member detects neutralization based on a change in electrical resistance, a change in potential, a change in current density, and the like due to a corrosion reaction of a metal caused by an acidic substance (a substance causing neutralization). The member is a member formed by forming a conductor pattern portion whose electrical characteristics change due to a corrosion reaction on a base material using a metal thin film.
The shape of the conductor pattern portion is preferably a shape that has a high probability of contact with an acidic substance and that easily undergoes a corrosion reaction, and examples thereof include a zigzag shape as shown in FIG.
Further, the metal constituting the conductor pattern portion is not particularly limited as long as the electrical characteristics change due to a corrosion reaction with an acidic substance such as carbon dioxide gas or sulfurous acid gas. For example, iron having a large ionization tendency, Iron alloys, zinc and the like are preferred.
Furthermore, the base material is not particularly limited as long as it is a material having high electrical insulation, does not react with an alkali component contained in the cured body of the cement composition, and has high weather resistance and water resistance. Examples thereof include glass composite materials such as glass epoxy, phenol resins, polyimides, polyethylene, polypropylene, vinyl chloride resins, fluororesins, and polycarbonates such as PET.

Next, the neutralization detection member will be described based on FIG.
The neutralization detection member 100 includes a conductive pattern portion 101 formed of a metal thin film (for example, an iron foil material produced by rolling iron), a base material 102 that holds the conductive pattern portion 101, and the conductive pattern portion 101. And a thin film portion 103 formed of a noble metal (for example, gold) provided in part. A measuring terminal 101 a is provided at the end of the conductive pattern portion 101. The electrical characteristics of the conductive pattern portion 101 change due to corrosion by an acidic substance.
The mechanism for detecting corrosion by electrical characteristics is as follows.
A cell in which a battery in which a metal anode part and a cathode part can be clearly distinguished is formed is called a macro cell, and a current flowing between both electrodes is called a corrosion current (macro cell current). A reaction in which the metal thin film is ionized due to corrosion (anode reaction) and a reaction in which oxygen is reduced on the surface of the metal thin film (cathode reaction) proceed simultaneously, and the anode part has a base potential and the cathode part has a noble potential. As a result, a potential difference is generated, and a corrosion current flows from the anode portion to the cathode portion, and the corrosion of the metal thin film proceeds. By utilizing this principle and providing the thin film portion 103 (cathode portion) formed of a noble metal, the corrosion of the conductor pattern portion 101 proceeds and the corrosion can be grasped more quickly.
The neutralization detection member is directly connected to a device for detecting neutralization, and measures an electrical signal associated with the corrosion reaction of the conductive pattern portion, or a wireless device having a measurement circuit as shown in FIG. It is also possible to measure wirelessly by connecting in advance.

As electrical characteristics that can detect corrosion, (i) a change in electrical resistance, (ii) a change in potential, and (iii) a change in current density are known. Hereinafter, the electrical characteristics will be described.
(I) Change in electrical resistance As the conductor pattern portion 101 of the neutralization detecting member 100 corrodes, the cross-sectional area of the metal decreases, and as a result, the electrical resistance increases as shown in FIG. Therefore, corrosion (neutralization) can be detected by a change in electrical resistance.
(Ii) Change in potential When the metal of the neutralization detecting member 101 corrodes, when the metal is ionized, electrons at the corrosion occurrence site (anode) move to an uncorroded site (cathode), resulting in a potential difference. Since corrosion current is continuously generated using this as a driving force, and corrosion proceeds, for example, by measuring the potential difference between metals using electrodes, from the change in potential before and after the occurrence of the corrosion phenomenon, The occurrence of corrosion can be determined.
(Iii) Change in current density Corrosion is a phenomenon that occurs due to the generation of a corrosion circuit, and the corrosion phenomenon can be captured by measuring the change in the current density of the corrosion site that occurs with the corrosion current.

FIG. 11 shows a flowchart of a method for manufacturing a neutralization detection member. Specifically, the manufacturing method of the neutralization detection member is as described in the following (i) to (v).
(I) The metal thin film (iron foil material in FIG. 11) and the base material 102 are integrated to produce a metal thin film sheet. As an integration method, for example, an adhesive is applied to a resin film (for example, a resin film such as PET or polyimide material) as a base material, and an iron foil material and the base material 102 are bonded using a roller or the like. Paste together.
(Ii) On the metal thin film of the produced metal thin film sheet, a conductive pattern portion 101 and a resist film having a circuit shape are formed by screen printing or photo printing. At the same time, a guide or the like for individually separating the neutralization detecting member 100 by cutting with a punching die after completion is also printed.
(Iii) The metal thin film sheet on which the resist film is formed is etched in an etching tank. As a result, the exposed metal thin film not coated with the resist film is dissolved in the etching solution (for example, ferric chloride solution), and after the etching is finished, the metal thin film sheet is taken out from the etching tank and the adhering solution is washed. To do.
(Vi) The resist film is removed with a solvent or the like to form the conductor pattern portion 101 and the outer shape of the circuit.
(V) The metal thin film sheet is divided, the masking is peeled off, the conductor pattern portion 101 is completed, and then the sensors subjected to the protection treatment are individually cut and separated using a punching die, and a cord is attached.

(3) Sensor manufacturing method The penetrating part of the sensor of the present invention is composed of a hardened body of a cement composition, and functions as a penetrating member for an acidic substance, preferably mortar or hardened cement body (hardened cement paste) ).
The cement in the cement composition is not particularly limited, and is usually Portland cement, early-strength Portland cement, ultra-early-strength Portland cement, medium heat Portland cement, low heat Portland cement, sulfate-resistant Portland cement, blast furnace cement, fly ash cement. , One or more selected from coal ash-containing cement, silica cement, white cement, eco-cement and the like.
The kneaded water of the cement composition can be used as long as it does not adversely affect the neutralization environment evaluation, and is, for example, tap water or reclaimed water.

When the hardened body is mortar, the fine aggregate to be used includes at least one selected from river sand, land sand, silica sand, lightweight aggregate, and the like. The fine aggregate may be natural aggregate or recycled aggregate.
In order to limit the lower limit of the sensor thickness depending on the particle size of the fine aggregate and to prevent the uneven distribution of the aggregate, the fine aggregate preferably passes through a JIS standard sieve having a nominal size of 2.5 mm. More preferably, it passes through a JIS standard sieve having a nominal size of 850 μm.
The blending amount of the fine aggregate is preferably 3 or less as a fine aggregate / powder ratio (mass ratio). When the value exceeds 3, since the amount of the powder paste is small, the moldability may be reduced and coarse voids may be generated. The unit volume ratio of the fine aggregate is preferably 60% or less.

Further, the cured body may contain an admixture in order to adjust the solidity of the cured body. The admixture is preferably a fine mineral powder not having latent hydraulic properties or pozzolanic activity, such as fine limestone powder or silica powder. Fineness of該混sum material is a Blaine specific surface area, preferably 2500~10000cm ² / g, more preferably 3000~8000cm ² / g. If the value is less than 2500 cm ² / g, water retention and material separation resistance may be reduced, resulting in sensor quality fluctuations. If it exceeds 10,000 cm ² / g, viscosity may increase and molding may be difficult. . The substitution rate of the admixture is preferably 10 to 85% by mass. In addition, the said substitution rate is content rate (mass%) of an admixture when the sum total of the mass of an admixture and cement is set to 100. As shown in FIG.

In addition, the cured body contains organic fibers such as vinylon fiber, polyethylene fiber, and polypropylene fiber, inorganic fibers such as steel fiber and glass fiber, shrinkage reducing agents, moisturizing agents, and the like in order to prevent cracks due to drying shrinkage. May be included. The amount of the fiber added is preferably 0.02 or less by mass ratio with respect to the amount of powder in the cement composition.
Moreover, in order to improve the fluidity | liquidity of a cement composition, you may add water reducing agents, such as a water reducing agent, AE water reducing agent, and a high performance AE water reducing agent. The addition rate of the water reducing agent is preferably 0.05 or less in terms of mass ratio with respect to the amount of powder in the cement composition.
Further, the cement composition may adjust the amount of air using an air amount adjusting agent in order to keep fresh properties such as fluidity. The amount of air is preferably 5 to 30%. If the value is less than 5%, the fluidity and surface finish of the cement composition are low, and if it exceeds 30%, the amount of air may fluctuate easily. The value is more preferably 5 to 25%, still more preferably 10 to 25%. The fluidity of the cement composition is preferably 105 to 250 mm in terms of a flow value of 15 strokes (JIS R 5201-1997).
In addition, from the viewpoint of evaluation accuracy, the constituent material of the sensor of the present invention is preferably the same as the material used for the concrete when the evaluation target concrete is determined.

  The penetrating member constituting the sensor of the present invention can be manufactured by casting into a mold, extrusion molding, press molding, vibration pressure molding or the like. For example, the neutralization detection member is installed on the bottom side of an acrylic or high-strength mortar formwork (exterior material), and the cement composition is placed on the exposed surface side. And after shaping | molding, a molded object may perform wet curing, underwater curing, steam curing, autoclave curing, etc.

Next, the sensors described in [2], [4] and [5] will be described.
The sensor according to [2] is formed of the cement composition as a penetrating member, and one surface of the cured body of the cement composition and a back surface facing the one surface are exposed surfaces exposed to the atmosphere. The neutralization detection member is installed between the two exposed surfaces, and the surface other than the exposed surface has a blocking surface blocked from the atmosphere by a blocking material. And since the sensor of [2] can measure the period from the start of exposure of the sensor from two surfaces until the neutralization detection member detects neutralization, unlike the sensor of [1], 1 Double data is obtained in each test, and the reliability of environmental evaluation is increased accordingly.

  In the sensor described in [4], as shown in FIGS. 5 and 6, cured bodies of two or more cement compositions having different water / cement ratios are connected on the exposed surface and the surface other than the back surface. The connecting surface is formed by blocking the movement of the acidic substance. If this sensor is used, the neutralization environment can be evaluated all at once in consideration of the difference in the water / cement ratio of the concrete, which is efficient and the number of acquired data increases. The accuracy of evaluation is also improved.

Further, as shown in FIGS. 7 and 8, the sensor of [5] has a back surface formed in a step shape so that the distance (thickness) between the back surface and the exposed surface varies stepwise. In addition, a neutralization detection member is provided on each step-like back surface. As another form of the sensor, instead of forming the back surface in a stepped shape, the sensor can be formed in a stepped shape so that the thickness of the penetrating member is different on the exposed surface. The shielding material is provided with a shielding material on the surface other than the exposed surface in order to shield surfaces other than the exposed surface from the atmosphere. According to this shape, it is economical because a plurality of sensors of the same material (water / cement ratio, etc.) can determine the period from the start of exposure until the neutralization detection member detects neutralization. .
Although the thickness of the hardened body (penetrating member) of the cement composition is not particularly limited, it is preferably 2 to 100 mm, more preferably 5 to 60 mm in consideration of the neutralization speed and the like. If the value is less than 2 mm, the sensor may crack, and if it exceeds 100 mm, the evaluation period becomes too long.

2. The neutralization environment evaluation method of concrete The neutralization environment evaluation method of concrete of this invention is the method described in said [6] and [7], and, below, this method is demonstrated concretely.
(1) Evaluation method according to [6] In this method, one or more sensors according to any one of [1] to [5] are installed at a location (two or more locations) to be evaluated. This is a method for obtaining a period from the start of exposure of the sensor until the neutralization detection member detects neutralization and comparing the periods to evaluate the neutralization environment.
Here, the term “one or more sensors described in [1] to [5]” means that two or more sensors of the same type selected from the sensors described in [1] to [5] are used. This includes any case where two or more different types of sensors are used.
The number of sensors to be installed is 1 or more, preferably 3 or more, the thickness of the sensor is 1 level or more, preferably 2 levels or more, and the water / cement ratio of the sensor is 1 level or more, preferably Is more than 3 levels. If it is each said preferable level number, the precision of evaluation will improve.
In addition, installing in the environment subject to the evaluation means installing in a place where concrete is planned to be installed, or in a range having the same neutralization environment as the concrete subject to evaluation. It is preferable to install as close to concrete as possible.

  Since the neutralization environment of concrete can be directly evaluated by the neutralization depth and duration, the sensor in the case of a constant distance from the exposed surface to the neutralization detection member is used in the evaluation method [6]. The period from the start of exposure until the neutralization detection member detects neutralization is used as an evaluation index. If this evaluation method is explained using a specific example, one or more sensors having penetrating members of the same thickness are installed at each of the points A and B until the neutralization detection member detects neutralization. Measure the period. If the period at the sensor installed at point A is 100 days and the period at the sensor installed at point B is 70 days, the neutralization environment at point B is a relatively severe neutralization environment compared to point A. It can be evaluated qualitatively and easily.

(2) Evaluation method according to [7] The method is based on a period from the start of exposure of the sensor until the neutralization detection member detects neutralization, and a distance from the exposed surface to the neutralization detection member. The neutralization rate constant is calculated using the formula (A), and the neutralization environment is quantitatively evaluated using the constant, and the following methods are exemplified.
(i) Method Using Ratio of Neutralization Rate Constants The method will be specifically described by applying the specific example given in the above (1) to the above formula (A).
According to the specific example of (1) above, the neutralization rate constant is C _A = 10 (mm) / 100 ^1/2 (day) = 1.0 at point A and C _B = 10 (mm at point B). ) / 80 ^1/2 (day) = 1.2. When the difference in neutralization environment between the two points is expressed by the ratio (K) of the neutralization rate constant between the two points, K = C _B / C _A = 1.2 / 1.0 = 1.2 is obtained. Therefore, it can be quantitatively evaluated that the point B is in an environment that is more easily neutralized by about 20% than the point A.

(Ii) Method of setting and using the standard environment For example, the neutralization environment of the point A is set as the standard environment, and the neutralization rate constant at the point A is obtained as a standard value (standard neutralization rate constant). Then, in the next and subsequent evaluations, the evaluation target location can be evaluated using the ratio between the neutralization rate constant and the standard neutralization rate constant. Measurement of the period until neutralization is detected requires only the location to be evaluated and is economical.
Furthermore, in order to generalize the neutralization evaluation, 20 ° C., which is a general dry environment of concrete, and 60% relative humidity are set as the standard environment, and the standard neutralization rate constant obtained under the environment, You may compare with the neutralization rate constant calculated | required in the environment with the structure of evaluation object.
Specifically, the neutralization environment at the B point is expressed by the following equation (B) using the neutralization rate constant (C _B ) and the standard neutralization rate constant (C _S ) at the B point. Can be quantitatively evaluated.
K = C _B / C _A or K = C _B / C _S (B)
In the formula (B), K represents a neutralization rate constant ratio, C _A and C _B represent a neutralization rate constant at point A and a neutralization rate constant at point _B , respectively, and C _S is standard. Represents the crystallization rate constant.

  In the present invention, the neutralization rate constant is calculated from the exposure period and the neutralization depth using the equation (A). The neutralization detection member detects neutralization from the start of exposure of the sensor. Fit the curve using equation (A) with the period up to the explanatory variable and the neutralization depth as the objective variable, or take the logarithm of equation (A) and convert it to a linear expression of the logarithmic function And the value of the intercept (logC). However, since it is known from the experience that the formula (A) is highly accurate, if the data that can be used is one, the neutralization detection member detects neutralization from the start of exposure of the sensor to the formula (A). The neutralization rate constant may be calculated by directly substituting the value of the period until neutralization and the value of the neutralization depth.

3. Method for Reflecting Evaluation Results of Present Invention to Building Specifications Reinforcing bars in concrete structures are protected from corrosion due to neutralization by cover concrete covering the reinforcing bars. Therefore, the concrete cover thickness is usually set at the design stage, assuming a standard environment (steady dry environment at 20 ° C. and 60% relative humidity), depending on the importance of the structure and the service life. For example, if the neutralization rate constant (Cs) of the standard environment is used with a service life of 50 years, the neutralization depth becomes Cs × (50 years) ^1/2 , and the cover thickness is multiplied by a safety factor. I want.

Further, actually the neutralization rate constant determined at the location where the building is placed and C _R, if C _R /Cs=1.0, it can be determined that may be design specifications. On the other hand, when the ratio exceeds 1.0, the risk of neutralization increases. When the ratio exceeds the safety factor, the structure is expected to be less than the expected service life due to corrosion of reinforcing bars due to neutralization.
Actually, it is difficult to grasp the environmental conditions in the field in advance, and when designing with an excessive safety factor as in the past, the amount of concrete used will increase and the living space in the building will decrease, resulting in a substantial decrease. It is easy to lead to cost increase.

In contrast, using the sensor of the present invention, in advance if to grasp the neutralization rate constant Cs in a standard environment, on the basis of neutralization rate constant C _R in local obtained using the sensor, suitable The cover thickness can be set. Specifically, if C _R / C _S = 1.2, the cover thickness for the set service life is designed with a neutralization depth of 1.2 times and multiplied by a safety factor. It is desirable to decide.

Further, if the concrete water / cement ratio is set low in advance, the same cover thickness can be handled. For example, if C _R / C _S = 1.2 and the slope of the linear relationship between the neutralization rate constant and the water / cement ratio (%) is 0.024, 0.2 / 0.024 = 8.3. Therefore, if the water / cement ratio is set low by about 9%, the initial design can be modified taking into account the risk due to neutralization. The sensor used here may be either a single water / cement ratio sensor or a plurality of water / cement ratio sensors.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
1. Materials used (1) Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement)
(2) Fine aggregate: quartz sand (fine sand), quartz sand that has passed through a JIS standard sieve having a nominal size of 850 μm.
(3) Admixture: fine limestone powder, Blaine specific surface area of 6000 cm ² / g
(4) Water: tap water (5) AE water reducing agent: JIS A 6204 AE water reducing agent-lignin sulfonic acid compound compatible with standard type I (6) Air amount adjusting agent: JIS A 6204 AE agent-compatible with type I Alkyl ether anionic surfactant

2. Neutralization test Four types of mortar were kneaded according to the formulation shown in Table 1 and were 80 mm long, 150 mm wide, and 50 mm thick, and 5 mm, 10 mm, 15 mm, 20 mm, 30 mm, and 40 mm from the exposed surface, respectively. After forming a block-shaped sensor (type (a) in FIG. 7) in which six neutralization detection members (members that can detect corrosion due to changes in electrical resistance) are embedded at remote positions, Sealing curing was performed for 7 days.

Next, one side of the sensor was left and the other five sides were covered with a masking sheet and exposed to the atmosphere.
A period (see FIG. 12, where the threshold is set to 200Ω) from the start of exposure of the sensor until the neutralization detection member embedded at each depth detects neutralization by a change in electrical resistance is obtained. Based on the period and the distance from the exposed surface to the neutralization detection member, the neutralization rate constant was calculated using the equation (A). FIG. 13 shows the neutralization depth (experimental value) of the sensor and its regression curve.

Moreover, the prediction curve calculated using the neutralization rate constant and the formula (A) from the results shown in FIG. 13 and the actual production on the spot at the water / cement ratio of 60% and 70% were installed. The relationship with the verification value of the neutralization depth of concrete is shown in FIG.
As shown in FIG. 14, the prediction curve agrees well with the verification value, and the present invention can be used not only for the evaluation of the neutralization environment but also for the prediction of the neutralization depth of the actual structure. The chemical method described in FIG. 14 is a conventional neutralization test method, in which a concrete specimen exposed to the atmosphere is cut, and a 1% by mass phenolphthalein solution is sprayed on its cross section. This is a method for measuring the length (neutralization depth) of the portion fading colorless. The neutralization depth according to the sensor of the present invention and the chemical method is in good agreement.
From the above, the neutralization environment of concrete can be easily and quickly evaluated by using the neutralization environment evaluation sensor and the neutralization environment evaluation method of the present invention.

10 Sensor 11 Hardened body of cement composition (penetrating member)
12, 100 Neutralization detection member 13 Exterior material (blocking material)
14 Code 101 Conductor pattern portion 101a Measuring terminal 102 Base material 103 Thin film portion

Claims (7)

  A cement composition obtained by molding a cement composition having a water / cement ratio (mass ratio) of 35 to 200% and a water / powder ratio (mass ratio) of 25 to 70% into a plate shape or a block shape. The hardened body is a penetrating member, and one surface of the penetrating member is an exposed surface exposed to the atmosphere, and the back surface facing the exposed surface is neutralized by detecting neutralization using electrical characteristics. A sensor for evaluating the neutralization environment of concrete, in which a detection member is installed, and a surface other than the exposed surface is a shielding surface that is shielded from the atmosphere by a shielding material.   One surface of the hardened body of the cement composition and the back surface facing the one surface are exposed surfaces exposed to the atmosphere, and a neutralization detection member is installed between the two exposed surfaces, and the exposure A sensor for evaluating the neutralization environment of concrete, where the surface other than the surface is a shielding surface shielded from the atmosphere by a shielding material.   The neutralization detection member according to claim 1 or 2, wherein the neutralization detection member is a member that detects neutralization by a change in electrical resistance, a change in potential, or a change in current density due to a corrosion reaction caused by neutralization. Sensor for evaluating the neutralization environment of concrete.   The penetrating part of the sensor includes a hardened body of two or more cement compositions having different water / cement ratios connected to the exposed surface and a surface other than the back surface facing the exposed surface, and the connected surface is made of an acidic substance. The sensor for evaluating the neutralization environment of concrete according to any one of claims 1 to 3, wherein the movement is blocked.   The said back surface is formed in step shape so that distance (thickness) with the said exposed surface may differ in steps, and the neutralization detection member is installed in each back surface, Claim 3 or 3 5. A sensor for evaluating the neutralization environment of concrete according to any one of 4 above.   One or more sensors according to any one of claims 1 to 5 are installed in a place (two or more places) to be evaluated, and the neutralization detection member is neutralized from the start of exposure of the sensor. The neutralization environment evaluation method of concrete which calculates | requires the period until it detects and compares the period and evaluates neutralization environment. One or more sensors according to any one of claims 1 to 5 are installed in a place to be evaluated, and a period from when the exposure of the sensor is detected until the neutralization detection member detects neutralization. The concrete is obtained by calculating a neutralization rate constant using the following equation (A) based on the period and the distance from the exposed surface to the neutralization detection member, and evaluating the neutralization environment using the constant. Neutralization environment evaluation method.
D = C · t ^1/2 (A)
(However, in the formula (A), D represents the distance from the exposed surface to the neutralization detection member, C represents the neutralization rate constant, and t represents the neutralization detection member neutralized from the start of exposure of the sensor. This represents the period until it is detected.)

Images