JP2020012710A - Method for obtaining prediction formula for predicting neutralization depth of concrete in existing building, method for predicting neutralization depth of concrete in existing building, and method for predicting remaining life of existing building - Google Patents

Abstract

To provide a new prediction formula capable of being applied to the neutralization depth of concrete in existing buildings, regardless of the type of finishing and whether it is finished.SOLUTION: Specific values of a, b, c, e and f constituting the following equation (1) are determined by applying the least-squares method between the actual measured values of the neutralization depth of concrete and the estimated value of the neutralization depth of concrete according to the following equation (1). The determined concrete values are substituted into the following expression (1) to obtain an expression (1') which is a relational expression between x and t, C, dand d. Here, x: depth of carbonation of concrete, t: age of concrete, C: COconcentration of air in the environment where concrete is placed, d: thickness of mortar on concrete, d: thickness of decorative building materials on concrete.SELECTED DRAWING: None

Description

  The present invention relates to a method for obtaining a prediction formula for predicting the neutralization depth of concrete in an existing building, a method for predicting the neutralization depth of concrete in an existing building, and a method for predicting the remaining life of the existing building.

  "Building construction standard specifications and commentary JASS5 Reinforced concrete construction 2015" (Architectural Institute of Japan) includes a formula (A): C = A @ t (here, C : Neutralization depth, A: neutralization rate coefficient of concrete, t: years elapsed). By substituting the measured value of the neutralization depth C obtained by the neutralization survey and the age t of the existing building into the equation (A), the neutralization rate coefficient A can be obtained.

Then, by substituting the obtained neutralization rate coefficient A and the cover thickness C (actually measured value by investigation) into the equation (A ′): t = (C ÷ A) ² obtained by modifying the equation (A). Further, the time t required for the neutralization of the concrete to progress to the reinforcing bar position is obtained, and the remaining life of the existing building can be predicted.

  "Building construction standard specification and commentary JASS5 Reinforced concrete construction 2015" (Architectural Institute of Japan) has a formula (a): C = A '@ t, A' = Axb ( Here, C: neutralization depth, A ′ = carbonization rate coefficient considering finishing, A: carbonation rate coefficient of concrete without finishing, b: carbonation rate of finishing material (finishing , T: elapsed years).

  In "Durability Design Construction Guidelines and Remarks for Reinforced Concrete Buildings" (2016, Architectural Institute of Japan), the following formula (c) is shown as a more accurate prediction formula when finishing is performed.

Here, x: neutralization depth, A: neutralization rate coefficient of concrete without finishing, R: neutralizing resistance of finishing, t: elapsed years, Tc: finishing layer is all neutralized. period.

  In addition, Patent Literatures 1 and 2 disclose a prediction formula and a prediction method of a neutralization depth when there is a finish.

  Non-Patent Document 1 discloses an equation for predicting the progress of neutralization when finish mortar is applied to concrete.

Patent No. 4949336 Patent No. 4039992

Lee Ei-Lan and Yoshihiro Masuda, "Analytical Study on Quality and Carbonation of Surface Concrete", Journal of Structural Engineering, Architectural Institute of Japan, 75, 649, 499-504, March 2010

  The prediction equation disclosed in the above-mentioned equation (a), equation (c) or Patent Literature 1 includes a neutralization rate coefficient A of concrete in the equation. A sex investigation is performed and the value is determined according to the formula (A). The estimation of the neutralization rate coefficient A increases in accuracy as the number of survey points increases. In general buildings, various finishes (for example, mortar painting, tile application, etc.) are applied on concrete, and the exposed walls are few. . Therefore, the places to be examined for the exposed concrete are limited, and it is difficult to obtain the neutralization rate coefficient A with high accuracy. If it is attempted to accurately predict the depth of neutralization by using the equations (a), (c), or the prediction equation disclosed in Patent Document 1, the target building is limited to a building having many exposed walls. Would be done.

  The prediction method disclosed in Patent Literature 2 prepares concrete specimens subjected to various types of finishing, gives deterioration equivalent to the age, and applies a medium equivalent to the age to each of the deteriorated specimens. This is a time-consuming and time-consuming prediction method of conducting a sex promotion test. It is desirable that the method of predicting the neutralization depth of concrete be a simple method based on survey data of existing buildings.

  Non-Patent Document 1 does not discuss the case where a decorative building material such as a tile is stuck on concrete.

  The present disclosure has been made under the above circumstances.

An object of the present disclosure is to provide a new prediction formula that can be applied irrespective of the presence or absence and type of finishing as a prediction formula of the neutralization depth of concrete of an existing building.
Further, the present disclosure aims to predict the neutralization depth of concrete regardless of the presence or absence and type of finishing, and has an object to solve the problem.
Further, the present disclosure aims at estimating the remaining life of an existing building even when the investigation points of concrete are limited, and aims to solve the problem.
Further, the present disclosure aims to predict the remaining life of an existing building when an existing finish is removed, and has an object to solve the problem.

  The concrete means for solving the above-mentioned problem is based on the assumption that the following equation (1), which is a theoretical equation of the depth of carbonation of concrete, is satisfied.

Here, x: neutralization depth of concrete, t: age of concrete, C ₀ : CO ₂ concentration of air in the environment where concrete is placed, d _m : thickness of mortar on concrete, d _t : Thickness of decorative building materials on concrete.

  Specific means for solving the above problems include the following aspects.

[1] A method for obtaining a prediction formula for predicting the neutralization depth of concrete in an existing building, including the following steps (1) to (3), wherein the prediction formula is the following formula (1 ′) How to get.
Step (1): a step of investigating the neutralization depth of the concrete of the existing building and the thickness of the finish applied on the concrete. However, the number of survey points is five or more, and two or more of the survey points are concrete with a decorative building material finish in which a decorative building material exists on concrete via mortar. Investigate the neutralization depth of concrete, mortar thickness and decorative building material thickness.
Step (2): The least squares method is applied between the measured value of the carbonation depth of the concrete obtained in the above step (1) and the estimated value of the carbonation depth of the concrete according to the equation (1). And determining specific values of a, b, c, e, and f that constitute the formula (1).
Step (3): a determined by the step (2), b, c, the specific value of e and f is substituted into the equation (1), the relationship between x and _t, C 0, _{d m} and _{d t} A step of obtaining equation (1 ′), which is an equation.

[2] A method for predicting the neutralization depth of concrete in an existing building, the method including the following step (4) using the equation (1 ′) obtained by the method according to [1].
Step (4): t in the formula (1 '), the C _0, d _m and d _t, substituting a specific value for the concrete to know the neutralization depth, neutral calculated x of the concrete The process of predicting the depth of development.

[3] A method for predicting the remaining life of an existing building, the method including the following step (5) using the equation (1 ′) obtained by the method according to [1].
Step (5): 'to _C 0, _{d m} and _{d t} of, by substituting the specific value for the focused concrete, and the formula (1 Formula (1)' to x) of, for concrete to the noted Substituting the depth of the reinforcing steel corrosion start position of the above, the number of years t required for the concrete of interest to neutralize to the reinforcing steel corrosion start position was obtained, and the elapsed years t ₀ of the concrete of interest was subtracted from the number of years t. process to predict the number of years (t-t ₀₎ and the remaining life of the existing building.

[4] The prediction method according to [3], wherein the step (5) is performed on concrete at a plurality of locations, and the method further includes the following step (6).
Step (6): step of predicting the remaining life of existing buildings the minimum value among the lives of the respective concrete at a plurality of locations (t-t _0).

[5] A method for predicting the remaining life of an existing building when removing an existing finish from concrete, the following step (7) based on the formula (1 ′) obtained by the method according to [1]: A method for predicting the remaining life of existing buildings, including
Step (7): Substituting the specific value of a contained in the above formula (1 ′) into a of the following formula (3), and replacing C ₀ , x ₀ and x of the following formula (3) with: Substituting specific values for concrete from which existing finishes are to be removed, and predicting the calculated t 'as the remaining life of the existing building.

Here, t ′: remaining life of the existing building, C ₀ : CO ₂ concentration of air at the finished surface to be removed, x ₀ : neutralization depth of concrete at the time of removing the finish, x: start of corrosion of reinforcing steel Depth of position, a: a that constitutes equation (1), and is a coefficient included in equation (1 ′).

The present disclosure provides a new prediction formula that can be applied regardless of the presence or absence of finishing as a prediction formula for the neutralization depth of concrete in an existing building.
According to this prediction formula, it is possible to predict the neutralization depth of concrete regardless of the presence or absence and the type of finishing.
Further, since the present prediction formula can be applied regardless of the presence or absence and the type of finishing, it is possible to predict the remaining life of the existing building even when the investigation points of the concrete are limited.
In addition, the remaining life of the existing building when the existing finishing is removed can be predicted based on the prediction formula.

It is a schematic diagram showing the relationship between the neutralization and the CO ₂ diffusion mortar in concrete cosmetic building materials finishing. It is a schematic diagram showing the relationship between the neutralization and the CO ₂ diffusion Concrete Concrete cosmetic building materials finishing. It is a schematic diagram showing the relationship between the neutralization and the CO ₂ diffusion concrete Uchihanashi. It is an image figure showing the progress of carbonation of concrete in the case of removing an existing finish. It is a scatter diagram which shows the correlation of the measured value of the neutralization depth of concrete in Example and the estimated value by Formula (1).

  Hereinafter, embodiments of the invention will be described. These descriptions and examples illustrate the embodiments and do not limit the scope of the invention.

  In the present disclosure, the numerical ranges indicated by using “to” include the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  In the present disclosure, the term “step” is included in the term as well as an independent step, even if it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

In the present disclosure, the concentration of carbon dioxide (CO ₂ ) is a volume percentage concentration.

[1] Derivation of theoretical formula for carbonation depth of concrete Each method according to the present disclosure is an invention on the assumption that formula (1), which is a theoretical formula for carbonation depth of concrete, is satisfied. . First, the theory from which Expression (1) is derived and Expression (1) will be described.

  Non-Patent Document 1 (Ei-Ran Lee, Yoshihiro Masuda, "Analytical Study on Quality and Surface Neutralization of Surface Concrete" in Case of Concrete with Mortar Finish on Non-Patent Document 1) , Vol. 75, No. 649, 499-504, March 2010). Based on the prediction model of Non-Patent Document 1, a prediction model of the depth of neutralization of concrete for decorative building material finishing was examined, and a theoretical formula was derived.

The decorative building material finish of the prediction model is a finish in which the decorative building material is pasted on concrete with mortar. It is assumed that the CO ₂ concentration of air on the surface of the decorative building material is constant from the time of building construction to the future.

Cosmetic building material is intended to its components do not or absorb or CO ₂ reacts with CO _2, and the makeup of building materials CO ₂ is gradually spread in accordance with Fick's first law.
Incidentally, amount of components of the decorative building material has abstracted or possibly absorb or CO ₂ reacts with CO _2, the progress of the neutralization is expected to Me severity. In making a judgment on whether or not to continue using an existing building, a stricter prediction is more useful than a sweet prediction.

In the neutralization of mortar or concrete, carbon dioxide (CO ₂ ) diffused into the interior of the building reacts with calcium hydroxide (Ca (OH) ₂ ) in the mortar or concrete to produce calcium carbonate (CaCO ₃ ). It progresses by things. It is assumed that while carbonation of the mortar is progressing, carbonation of the concrete does not progress, and neutralization of the concrete starts after all the mortar is neutralized.

In the mortar, it is assumed that CO ₂ does not diffuse in a non-neutralized region and CO ₂ diffuses in a neutralized region (neutralized region of the mortar) according to Fick's first law.

In the concrete, it is assumed that CO ₂ does not diffuse in a non-neutralized region and CO ₂ diffuses in a neutralized region (neutralized region of concrete) according to Fick's first law.

FIG. 1 and FIG. 2 show schematic diagrams of the progress of carbonation of concrete on which a decorative building material finish has been applied. FIG. 1 is a schematic diagram showing the relationship between mortar neutralization and CO ₂ diffusion during the period in which mortar neutralization is progressing. FIG. it is a schematic diagram showing the relationship between the neutralization and the CO ₂ diffusion concrete in the period in which sexual reduction is in progress.
Hereinafter, the process of deriving the theoretical formula from the prediction model will be described.

[1-1] Period in which mortar is neutralized The coordinates of the horizontal axis (neutralization depth) in FIG. 1 are as follows.
The coordinates of the interface between concrete and mortar are set to 0.
The thickness of the mortar and d _m, the interface between the coordinates of the mortar and the decorative building material and -d _m.
The thickness of the decorative building material and _{d t,} the coordinates of the decorative building material surface and _-d t -d _m.
It is assumed that neutralization of the mortar is progressing up to the coordinate x at the time t.

It is assumed that Ca (OH) ₂ in the mortar is completely consumed at the depth of the coordinate x, and is in a steady state at the depth of the coordinate x. It is assumed that CO _{2 that} has reached the coordinate x instantaneously reacts with Ca (OH) ₂ present there to generate CaCO ₃ .

From the coordinate -d t _-d m _(decorative building material surface), reach through the per area S of the plane orthogonal to the depth direction, the coordinate -d m per Δt time _(the interface between the mortar and the decorative building material) CO ₂ amounts? CO2 ₂ is expressed by the following formula (1-1).
From the coordinate -d m _(the interface between the mortar and the decorative building material), through a per area S of the plane orthogonal to the depth direction, CO ₂ which per Δt time reaches coordinate x (neutralization depth of the mortar) amounts? CO2 ₂ is expressed by the following formula (1-2).
The amount? CO2 ₂ of CO ₂ consumed when CO ₂ that has reached the coordinate x to generate CaCO ₃ reacts with Ca (OH) ₂ is expressed by the following equation (1-3).

here,
x: Neutralization depth of the mortar _{(-d m ≦ x ≦ 0)} ,
Δx: thickness of the boundary region,
t: time,
Δt: minute time,
C ₀ : CO ₂ concentration of air on the surface of the decorative building material,
C _m : CO ₂ concentration at the interface between the mortar and the decorative building material,
D _m : CO ₂ diffusion coefficient of neutralized mortar,
D _t : CO ₂ diffusion coefficient of decorative building material,
d _m : mortar thickness
d _t : thickness of decorative building material,
H _m : the amount of Ca (OH) ₂ per unit volume contained in the mortar,
S: Area of a surface orthogonal to the depth direction.

  Assuming that equation (1-1) is equal to equation (1-2),

  Assuming that equation (1-2) is equal to equation (1-3),

  Substituting equation (1-4) into equation (1-5) and rearranging,

  When Δt is brought close to 0 to the limit in equation (1-6), the following differential equation is obtained.

Integrate both sides of Expression (1-7). The left-hand side, the neutral region of the mortar, i.e., by integrating the coordinate -d m _(the interface between the mortar and the decorative building material) to the coordinates x (neutralization depth of the mortar), the right-hand side, neutralization time of the mortar That is, integration is performed from time 0 to time t.

  Expanding and arranging equation (1-8),

  Solving the above equation for x gives

  Substituting t = 0 into equation (1-9) gives

Equation (1-9) becomes x = -d _m when t = 0 (of the interface between the mortar and the decorative building material coordinates). That is, at time 0, mortar neutralization has not started.

  Solving t with x = 0 in equation (1-9) gives

  Equation (1-10) indicates the time required for mortar neutralization to reach the interface between the concrete and the mortar (coordinate 0), that is, the time required for all mortar to be neutralized.

[1-2] Period during which carbonation of concrete is progressing after all mortar is neutralized The coordinates of the horizontal axis (neutralization depth) in FIG. 2 are as follows.
As in FIG. 1, the coordinates of the interface between concrete and mortar are set to 0.
1 Like, the thickness of the mortar and d _m, the interface between the coordinates of the mortar and the decorative building material and -d _m.
Figure 1 and likewise a thickness of the decorative building material and _{d t,} the coordinates of the decorative building material surface and _-d t -d _m.
It is assumed that the carbonation of the concrete has progressed to the coordinate x at the time t.

It is assumed that Ca (OH) ₂ in the concrete is completely consumed at the depth of the coordinate x, and is in a steady state at the depth of the coordinate x. It is assumed that CO _{2 that} has reached the coordinate x instantaneously reacts with Ca (OH) ₂ present there to generate CaCO ₃ .

From the coordinate -d t _-d m _(decorative building material surface), reach through the per area S of the plane orthogonal to the depth direction, the coordinate -d m per Δt time _(the interface between the mortar and the decorative building material) CO ₂ amounts? CO2 ₂ is expressed by the following formula (2-1).
From the coordinate -d m _(the interface between the mortar and the decorative building material), through a per area S of the plane orthogonal to the depth direction, the coordinates 0 per Δt time CO ₂ to reach (the interface between the concrete and mortar) The amount ΔCO ₂ is represented by the following equation (2-2).
The amount of CO ₂ from the coordinate 0 (the interface between the concrete and the mortar), passing around the area S of the surface orthogonal to the depth direction, and reaching the coordinate x (the neutralization depth of the concrete) per Δt time ΔCO ₂ is represented by the following equation (2-3).
The amount ΔCO _{2 of} CO ₂ consumed when the CO ₂ that has reached the coordinate x reacts with Ca (OH) ₂ to generate CaCO ₃ is represented by the following equation (2-4).

here,
x: neutralization depth of concrete (0 ≦ x),
Δx: thickness of the boundary region,
t: time,
Δt: minute time,
C ₀ : CO ₂ concentration of air on the surface of the decorative building material,
C _m : CO ₂ concentration at the interface between the mortar and the decorative building material,
C _c : CO ₂ concentration at the interface between concrete and mortar,
D: CO ₂ diffusion coefficient of neutralized concrete,
D _m : CO ₂ diffusion coefficient of neutralized mortar,
D _t : CO ₂ diffusion coefficient of decorative building material,
d _m : mortar thickness
d _t : thickness of decorative building material,
H: Ca (OH) ₂ amount per unit volume contained in concrete,
S: Area of a surface orthogonal to the depth direction.

  Assuming that equation (2-2) is equal to equation (2-3),

  Assuming that equation (2-1) and equation (2-2) are equal,

  Substituting equation (2-5) into equation (2-6) and rearranging,

  Assuming that equation (2-4) is equal to equation (2-3),

  Substituting equation (2-7) into equation (2-8) and rearranging:

  In the equation (2-9), when Δt approaches 0 to the limit, the following differential equation is obtained.

Integrate both sides of equation (2-10). The left side integrates from the neutralization area of concrete, that is, coordinate 0 (the interface between concrete and mortar) to the coordinate x (concrete neutralization depth), and the right side shows the neutralization time of concrete, that is, integrating from the time t ₁ the neutralization of mortar is completed until time t.

  Expanding and arranging equation (2-11),

Time _{t 1,} since the mortar is all the time required to neutralize, _{t 1} is represented by Formula (1-10). If you organize by substituting the formula (1-10) to _{t 1} of the formula (2-12),

  Solving the above equation for x gives

In the formula (2-13), when the thickness d _t = 0 of the decorative building material is set, the following formula (2-13a) is obtained.

  The formula (2-13a) is described in Non-Patent Document 1 (Ei-Ran Lee, Yoshihiro Masuda, "Analytical Study on Quality and Carbonation Progress of Surface Concrete", Transactions of the Architectural Institute of Japan, Vol. 75, No. 649, 499-504, 2010 This is the same as the prediction formula shown in March) for finishing mortar on concrete.

Of the elements constituting the equation (2-13), decorative building materials surface in CO ₂ concentration in the air _{(C 0)} and a thickness of finishing _(d m, _{d t)} is a relatively easy to learn the site investigation However, it is relatively difficult to know the CO ₂ diffusion coefficient (D, D _m , D _t ) and the amount of Ca (OH) ₂ per unit volume (H, H _m ) by field survey.
Then, regarding D, D _m , D _t , H and H _m , which are relatively difficult to know by field surveys, D / H = a, D / D _m = b, H _m / D _m = c, D / If D _t = e and H _m / D _t = f, equation (2-13) becomes equation (1) below.

Here, x: neutralization depth of concrete (mm), t: age of concrete (years), C ₀ : CO ₂ concentration of air (%) on the surface of decorative building material, d _m : mortar of concrete on concrete Thickness (mm), _dt : Thickness (mm) of decorative building material on concrete.

Equation (1) is the neutralization depth x of the concrete, which can be known by construction recording or site investigation _t, C 0, _{d m} and _{d t} and, unknown coefficients a, b, c, e and and f is a theoretical expression.

In addition, if d _t = 0 in Expression (1), the following Expression (1a) is obtained, and if d _m = 0 and d _t = 0 in Expression (1), the following Expression (1b) is obtained. Equation (1a) is an equation for concrete with a mortar finish, and equation (1b) is an equation for exposed concrete. C 0 _{(CO 2} concentration) in the case of concrete mortar finishing a CO ₂ concentration of the air in the mortar surface, in the case of Uchihanashi concrete is the CO ₂ concentration of the air in the concrete surface.

Equation (1) is a theoretical equation that can be applied to any of concrete with a decorative building material finish, concrete with a mortar finish, and exposed concrete. C ₀ in equation (1) is collectively referred to as the CO ₂ concentration of the air in the environment where the concrete is placed.

Equation (1) includes unknown coefficients a, b, c, e, and f. Coefficients a, b, determines the specific value of c, e and f, and substituting these specific values in equation (1), formula (1), the relationship between x and _t, C 0, _{d m} and _{d t} It becomes an expression. This relational expression is referred to as Expression (1 ′).

  Next, a method of determining the specific values of the coefficients a, b, c, e, and f to obtain the equation (1 ′), that is, a method of obtaining the prediction equation according to the present disclosure will be described.

[2] Method of Obtaining Prediction Formula for Predicting Neutralization Depth of Concrete A method of obtaining a prediction formula for predicting the neutralization depth of concrete according to the present disclosure (also simply referred to as “method of obtaining a prediction formula”). Means a method for obtaining the formula (1 ′).

The method of obtaining the prediction formula according to the present disclosure is based on the minimum two-way between the actual measured value of the carbonation depth of the concrete obtained in the field survey and the estimated value of the carbonation depth of the concrete by the formula (1). by applying a multiplicative determine a, b, c, the specific value of e and f constituting the equation (1), the determined specific values into equation (1), x and _t, C 0, _{d m} This is a method of obtaining Expression (1 ′), which is a relational expression between _dt and _dt .

  A method for obtaining a prediction equation according to the present disclosure includes steps (1) to (3).

  Step (1): a step of investigating the neutralization depth of the concrete of the existing building and the thickness of the finish applied on the concrete. However, the number of survey points is five or more, and two or more of the survey points are concrete with a decorative building material finish in which a decorative building material exists on concrete via mortar. Investigate the neutralization depth of concrete, mortar thickness and decorative building material thickness.

  Step (2): applying a least squares method between the measured value of the neutralization depth of concrete obtained in the step (1) and the estimated value of the carbonation depth of the concrete according to the equation (1), A step of determining specific values of a, b, c, e, and f that constitute Expression (1).

Here, x: depth of neutralization of concrete (mm), t: age of concrete (years), C ₀ : CO ₂ concentration (%) of air in the environment where concrete is placed, d _m : on concrete Mortar thickness (mm), d _t : thickness of decorative building material on concrete (mm).

Step (3): Step (2) a determined by, b, c, the specific value of e and f into Equation (1), x and _t, the relation expression between C 0, _{d m} and _{d t} A step of obtaining a certain formula (1 ′).

  The details of each step will be described below.

[2-1] Step (1)
Step (1) is a step of investigating the neutralization depth of concrete in an existing building and the thickness of the finish applied on the concrete.

  Since the number of coefficients determined in step (2) is five, the number of locations to be examined in step (1) is set to five or more. From the viewpoint of improving the prediction accuracy of the prediction formula, it is preferable that the number of survey points is larger. From the viewpoint of shortening the survey period or the cost of the survey, it is preferable that the number of survey sites is small. The number of survey points is preferably 10 or less.

Examples of the investigation site include exposed concrete, mortar-finished concrete in which mortar is applied on concrete, and decorative building material-finished concrete in which decorative building materials are present on concrete via mortar.
However, two or more survey points shall be made of concrete with decorative building material finish. For concrete with decorative building material finish, the neutralization depth of concrete, mortar thickness and thickness of decorative building material shall be investigated. This is because equation (1) for mortar-finished concrete or bare concrete is equation (1a) or equation (1b). This is because the specific values of the coefficients e and f cannot be determined.
It is preferable that the number of the inspection places of the concrete of the mortar finish and the concrete of the decorative building material finish be four or more in total in order to determine the four coefficients b, c, e and f relating to these finishes.

  If the investigation site is mortar-finished concrete, investigate the neutralization depth of the concrete and the thickness of the mortar. If the survey site is bare concrete, investigate the neutralization depth of concrete. Mortar-finished concrete need not necessarily be included in the survey area. Exposed concrete need not necessarily be included in the survey area.

  The neutralization depth of concrete is the actual measurement value at the surveyed location. The neutralization depth of the concrete of the existing building can be determined, for example, by measuring the neutralization depth using a concrete sample extracted from the existing building as a sample (for example, JIS A1152: 2011 “Method of measuring the neutralization depth of concrete”). ”).

  The thickness of the finish applied on the concrete may be an actually measured value or a value recorded in a construction record. The thickness of the finish applied on the concrete is preferably an actually measured value from the viewpoint of increasing the prediction accuracy of the prediction formula.

  In the present disclosure, mortar-finished concrete is not limited to concrete in which mortar is the outermost surface. For mortar-finished concrete, neutralization progresses to the same degree as mortar finish with exposed mortar surface, such as concrete in which paint (paint, etc.) that cannot be expected to have a neutralizing effect is applied directly to the finished mortar. Includes concrete expected.

In the present disclosure, the exposed concrete is not limited to the concrete whose surface is exposed. Exposed concrete includes, for example, concrete in which a paint (such as paint) that cannot be expected to have a neutralization inhibitory effect is directly applied to the concrete surface; Concrete that is directly attached on top; concrete on which plate-like building materials (such as plasterboard) are floated (ie, concrete whose concrete surface is directly exposed to CO ₂ ); Includes concrete that is expected to progress.

In the present disclosure, the decorative building materials include tiles, stones, heat insulating materials, cloths, paints that are regularly repainted, and the like.
Model to derive the formula (1) it is because it is the component of the cosmetic in building materials has abstracted the possibility of absorbing or CO ₂ or react with CO ₂ model, in each process according to the present disclosure, the decorative building materials there If it is decorative building material consisting of a low material likely to or absorbs or CO ₂ reacts with CO _2, it is possible to more accurate prediction.

  At least five survey points in step (1) require that the concrete be the same mix. The fact that the concrete is the same mix can be known from the casting record or can be estimated from the compressive strength of the sample extracted from the building. For example, the concrete strength is estimated by investigating the compressive strength as described below.

Since the general construction to Da設approximately every 100 m ³ 200 m ³ for setting strokes or floors per day, measuring the vent compression strength of the core of the structure concrete by three approximately every 100 m ³ 200 m ³ or floors I do. A one-way analysis of variance is performed on the measured compressive strengths using the area as a factor to check whether there is a difference in the compressive strength for each area. If there is a significant difference between the areas, a one-way analysis of variance is similarly performed on the adjacent areas to determine the compound switching point, and the significant difference between the adjacent areas is determined. Check if there is. As described above, the area of the same combination is specified.

  In many existing buildings, concrete of the same type of structure (eg, walls, columns, beams, etc.) on the same floor can be considered as the same mix.

  From the viewpoint of improving the prediction accuracy of the prediction formula, it is preferable that the mortars have the same mix of the concrete of the decorative building material finish used as the investigation site. The fact that the mortars are of the same formulation can be inferred from the results of the composition analysis. In many existing buildings, mortar can be considered to be the same mix if the same finishing materials are used on the same floor.

  From the viewpoint of improving the prediction accuracy of the prediction formula, it is preferable that the materials of the decorative building materials be the same as the decorative building material finish concrete to be investigated. That the decorative building materials are the same material can be estimated from the result of the composition analysis.

  When the mortar finish concrete is included in the survey location, the mortar finish concrete used as the survey location and the decorative building material finish concrete used as the survey location must have the same mortar mix from the viewpoint of improving the prediction accuracy of the prediction formula. Is preferred. The fact that the mortars are of the same formulation can be inferred from the results of the composition analysis.

  The structure serving as the investigation site may be any of a wall, a column, a beam, a ceiling, a floor, and the like.

[2-2] Step (2)
Step (2) applies a least squares method between at least five measured values and at least five estimated values of the neutralization depth of concrete to form equation (1) a, b , C, e, and f.

  In the following, the number of investigation points is n in total (n is an integer of 5 or more), the number of investigation points of bare concrete is m (m is an integer of 1 or more), and the number of investigation points of mortar-finished concrete is s. -M pieces (sm is an integer of 1 or more) and the number of surveyed points of concrete for decorative building material finishing is ns (ns is an integer of 2 or more) will be described as an example. .

In the above example, y ₁ the measured value of the neutralization depth of concrete _Uchihanashi, ..., y _m Distant, y _{m + 1} the measured value of the neutralization depth of concrete mortar _finishing, ..., y _s Distant, the measured values of neutralization depth of concrete cosmetic building materials finishing y _{s + 1, ...,} put a y _n.
Further, x ₁ the estimate of the neutralization depth of concrete _Uchihanashi, ..., x _m Distant, x _{m + 1} estimates of neutralization depth of concrete mortar _finishing, ..., x _s Distant, decorative building materials Let x _{s + 1} ,..., X _n be the estimated value of the neutralization depth of the finished concrete.

In equation (1), the number of years elapsed concrete for each survey location (t), CO ₂ concentration _(C 0) of the air, (the thickness of the mortar) _{d m} and _{d t} specific value (the thickness of the decorative building material) substituting and coefficients a, b, c, e and the estimated value by substituting the initial value f _x 1, ..., to obtain a _{x n,} Found _y 1, ..., _{y n} and the estimated value _{x 1,} ... , _Xn, and specific values of coefficients a, b, c, e, and f are determined such that the residual sum of squares of the measured value and the predicted value is minimized. The least squares method is represented by the following equation. The coefficients a, b, c, e, and f that minimize the residual sum of squares are obtained while changing a, b, c, e, and f little by little. This calculation can be performed by, for example, a solver function of spreadsheet software Excel.

  In equation (1), t is the age (year) of concrete. The specific value of t to be substituted into equation (1) can be known from the construction record of the existing building under investigation.

In the equation (1), C ₀ is the CO ₂ concentration (%) of the air in the environment where the concrete is placed. For concrete survey point is Uchihanashi a CO ₂ concentration of the air in the concrete surface, if survey points are concrete mortar finishing a CO ₂ concentration of the air in the mortar surface, If the survey point is concrete cosmetic building materials finishing Is the CO ₂ concentration of air on the surface of the decorative building material. Specific values of C ₀ is substituted into equation (1) may be a measured value of the air of the concrete is placed environment, it may be given conditions set in accordance with the concrete is placed environment. The conditions are given in accordance with, for example, guidelines of the Architectural Institute of Japan and the Japan Society of Civil Engineers. As an example of the application condition, 0.10% indoor and 0.05% outdoor.

_{D m} In equation (1) is the thickness of the mortar on the concrete (mm), _{d t} is the thickness of the decorative building material of the concrete (mm). Specific values of d _m and d _t is substituted into equation (1) may be a measured value, it may be marked values construction recording. The specific values of _dm and _dt substituted in the equation (1) are preferably actually measured values from the viewpoint of improving the prediction accuracy of the prediction equation. Mortar finished concrete has d _t = 0, and bare concrete has d _m = 0 and d _t = 0.

[2-3] Step (3)
Step (3), a determined by step (2), b, c, the specific value of e and f into Equation (1), the relationship between the x, _t, and C 0, _{d m} and _{d t} This is the step of obtaining the equation (1 ′). Equation (1 ′) is an equation that expresses the neutralization depth of concrete by the number of years elapsed, the CO ₂ concentration of air, and the thickness of the finish.

  Equation (1 ′) is used for the method for predicting neutralization according to the present disclosure and the method for predicting the remaining life of an existing building according to the present disclosure, which will be described next.

[3] Method of Predicting the Neutralization Depth of Concrete in Existing Building The neutralization depth of concrete in an existing building can be determined by, for example, measuring the neutralization depth of a concrete sample extracted from an existing building ( For example, it can be known by performing JIS A1152: 2011 “Method of measuring the neutralization depth of concrete”.
However, there are places where concrete samples cannot be obtained in existing buildings.
The method for predicting the neutralization depth of concrete of an existing building according to the present disclosure (also simply referred to as “neutralization prediction method”) is based on the concrete neutralization depth of a place where a concrete sample in an existing building cannot be obtained. It is effective when you want to know the quality.
In other words, select a place where the same mix or similar mix of concrete exists as the place where you want to know the neutralization depth but cannot obtain the concrete sample, and set that place as the investigation point in step (1). If the equation (1 ′) is obtained, the neutralization prediction method according to the present disclosure can be effectively performed.

  Concrete that is a target of the neutralization prediction method according to the present disclosure may be concrete of any structure of an existing building, such as a wall, a column, a beam, a ceiling, and a floor.

  The neutralization prediction method according to the present disclosure is applied to concrete whose finish has not changed since the building was constructed and whose finish is not to be changed in the future.

  The concrete to which the carbonation prediction method according to the present disclosure is applied is the same as the concrete which is the investigation point in the step (1) for obtaining the formula (1 ′) from the viewpoint of accurately predicting the carbonation depth. It is preferred to be a blend.

  The neutralization prediction method according to the present disclosure includes the following step (4) using equation (1 ′) obtained by the method for obtaining the prediction equation according to the present disclosure.

Step (4): t of formula (1 '), the C _0, d _m and d _t, substituting a specific value for the concrete to know the neutralization depth, neutralization of the concrete the calculated x The process of predicting depth.

  In the neutralization prediction method according to the present disclosure, t in Expression (1 ′) is the age (year) of concrete. The specific value of t to be substituted into the equation (1 ') can be known from the construction record of the existing building under investigation.

In the neutralization prediction method according to the present disclosure, C ₀ in Expression (1 ′) is the CO ₂ concentration (%) of the air in the environment where the concrete whose neutralization depth is to be known is placed. Uchihanashi For concrete a CO ₂ concentration of the air in the concrete surface, in the case of concrete mortar finishing a CO ₂ concentration of the air in the mortar surface, decorative building materials when finishing concrete makeup air in building materials surface CO ₂ Concentration. Specific values of C ₀ is substituted into equation (1 ') may be a measured value of the air of the concrete is placed environment, it may be given conditions set in accordance with the concrete is placed environment. The conditions are given in accordance with, for example, guidelines of the Architectural Institute of Japan and the Japan Society of Civil Engineers. As an example of the application condition, 0.10% indoor and 0.05% outdoor.

Wherein the neutralization prediction method according to the present disclosure (1 ') d _m of a thickness of the mortar on the concrete want to know the neutralization depth (mm), the formula (1' d _t) of the It is the thickness (mm) of the decorative building material on concrete for which the neutralization depth is to be known. Specific values of d _m and d _t is substituted into equation (1 ') may be a measured value, it may be marked values construction recording. The specific values of _dm and _dt substituted in the equation (1 ′) are preferably actually measured values from the viewpoint of accurately predicting the neutralization depth of concrete. Mortar finished concrete has d _t = 0, and bare concrete has d _m = 0 and d _t = 0.

  The carbonation prediction method according to the present disclosure can predict the carbonation depth of concrete regardless of the presence or absence of finish and the type. That is, the neutralization prediction method according to the present disclosure is applicable to any of bare concrete, concrete with mortar finish, and concrete with decorative building material finish. As described above, the exposed concrete includes concrete in which the progress of neutralization is expected to be as high as that of the concrete whose surface is exposed. As described above, concrete with mortar finish includes concrete in which the progress of neutralization is expected to be at the same level as in mortar finish in which the mortar surface is exposed.

  When the neutralization prediction method according to the present disclosure is applied to a concrete of a decorative building material finish, the decorative material of the decorative building material finish obtains the formula (1 ′) from the viewpoint of accurately predicting the neutralization depth. It is preferable that the material of the decorative building material finish concrete, which is the investigation point in step (1), and the material of the decorative building material are the same.

  When the neutralization prediction method according to the present disclosure is applied to a concrete of a decorative building material finish, the decorative material of the decorative building material finish obtains the formula (1 ′) from the viewpoint of accurately predicting the neutralization depth. It is preferable that the mortar mix is the same as the concrete of the decorative building material finish, which is the investigation point in step (1).

  When the carbonation prediction method according to the present disclosure is applied to mortar-finished concrete, the mortar-finished concrete is a process for obtaining the formula (1 ′) from the viewpoint of accurately predicting the carbonation depth. It is preferable that the mix of the mortar and the concrete of the decorative building material finish and / or the mortar finish concrete, which is the investigation point of (1), be the same.

[4] Method of predicting the remaining life of an existing building The method of predicting the remaining life of an existing building according to the present disclosure is based on the assumption that the number of years required for concrete to be neutralized from the surface to the position where corrosion of reinforcing steel starts is regarded as the life of the building. Below is a method to predict the remaining life of existing buildings.

  The method for estimating the remaining life of an existing building according to the present disclosure includes the following step (5) using equation (1 ′) obtained by the method for obtaining the prediction equation according to the present disclosure.

Step (5): 'to _C 0, _{d m} and _{d t} of, by substituting the specific values for the concrete of interest, and the formula (1 Formula (1)' to x of) Corrosion of interest to concrete By substituting the depth of the starting position, the number of years t required for the target concrete to neutralize to the reinforcing bar corrosion start position is obtained, and the number of years (tt) obtained by subtracting the elapsed years t ₀ of the target concrete from the above-mentioned years t ₀ ) the process of estimating the remaining life of the existing building.

That step (5) is a step of 'substituting _{C 0,} d m, _{d t} and x in the formula (1 Formula (1)' search of t by solving the) is calculated further _{(t-t 0)} It is.

In the method for predicting the remaining life of an existing building according to the present disclosure, C ₀ in Expression (1 ′) is the CO ₂ concentration (%) of the air in the environment where the target concrete is placed. Uchihanashi For concrete a CO ₂ concentration of the air in the concrete surface, in the case of concrete mortar finishing a CO ₂ concentration of the air in the mortar surface, decorative building materials when finishing concrete makeup air in building materials surface CO ₂ Concentration. Specific values of C ₀ is substituted into equation (1 ') may be a measured value of the air of the concrete is placed environment, it may be given conditions set in accordance with the concrete is placed environment. The conditions are given in accordance with, for example, guidelines of the Architectural Institute of Japan and the Japan Society of Civil Engineers. As an example of the application condition, 0.10% indoor and 0.05% outdoor.

Wherein the residual lifetime prediction method for existing buildings according to the present disclosure (1 ') d _m of a thickness of the mortar on the concrete of interest (mm), the formula (1' d _t) of the attention to the concrete It is the thickness (mm) of the upper decorative building material. Specific values of d _m and d _t is substituted into equation (1 ') may be a measured value, it may be marked values construction recording. It is preferable that the specific values of _dm and _dt substituted into the equation (1 ′) are actually measured values from the viewpoint of accurately predicting the remaining life of the existing building. Mortar finished concrete has d _t = 0, and bare concrete has d _m = 0 and d _t = 0.

  In the method for estimating the remaining life of an existing building according to the present disclosure, x in Expression (1 ′) is the depth (mm) of the reinforcing bar corrosion start position of the focused concrete. The specific value of x to be substituted into the expression (1 ') follows, for example, guidelines of the Architectural Institute of Japan and the Japan Society of Civil Engineers. According to the guidelines of the Architectural Institute of Japan, the depth of the reinforcing bar corrosion start position is the cover thickness +20 mm indoors and the cover thickness outdoors. According to the guidelines of the Japan Society of Civil Engineers, the depth of the reinforcing bar corrosion start position is the cover thickness indoors and the cover thickness −10 mm outdoors. The cover thickness may be an actually measured value or a value described in a construction record. The cover thickness is preferably an actually measured value from the viewpoint of accurately predicting the remaining life of the existing building.

In the method for predicting the remaining life of an existing building according to the present disclosure, t ₀ is the age (year) of the concrete of interest. Specific values of t ₀ is, it is possible to know by the construction record of existing buildings that are surveyed.

  The concrete of interest may be present in any structure of an existing building, such as walls, columns, beams, ceilings, floors, and the like. As the concrete to focus on, select a concrete whose finish has not changed since the construction of the building and whose finish will not be changed in the future.

  From the viewpoint of accurately predicting the remaining life of the existing building, it is preferable that the concrete to be focused has the same mix as the concrete that is the investigation location in the step (1) for obtaining the equation (1 ′).

  Regarding the concrete of interest, it does not matter whether or not the concrete is finished. According to the method for estimating the remaining life of an existing building according to the present disclosure, it is possible to predict the remaining life of an existing building even when the places to be inspected for concrete are limited.

  The concrete of interest may be any of bare concrete, concrete with mortar finish, and concrete with decorative building material finish. As described above, the exposed concrete includes concrete in which the progress of neutralization is expected to be as high as that of the concrete whose surface is exposed. As described above, concrete with mortar finish includes concrete in which the progress of neutralization is expected to be at the same level as in mortar finish in which the mortar surface is exposed.

  In the case where the concrete of interest is a concrete with a decorative building material finish, the concrete with the decorative building material finish should be examined in the step (1) for obtaining the equation (1 ′) from the viewpoint of accurately predicting the remaining life of an existing building. It is preferable that the material of the decorative building material finish and the material of the decorative building material are the same.

  In the case where the concrete of interest is a concrete with a decorative building material finish, the concrete with the decorative building material finish should be examined in the step (1) for obtaining the equation (1 ′) from the viewpoint of accurately predicting the remaining life of an existing building. It is preferable that the mix of the mortar and the decorative building material finish concrete is the same.

  When the concrete of interest is mortar-finished concrete, the mortar-finished concrete is a survey point in the step (1) for obtaining the equation (1 ′) from the viewpoint of accurately predicting the remaining life of an existing building. It is preferable that the mix of the mortar and the concrete of the decorative building material finish and / or the mortar finish concrete is the same.

  As a preferred embodiment of the method for estimating the remaining life of an existing building according to the present disclosure, in Step (1) for obtaining Equation (1 ′), the cover thickness was also measured, and the measured value of the cover thickness was obtained. There is a form in which concrete is used as the concrete in the step (5).

As a preferred embodiment of the method for estimating the remaining life of an existing building according to the present disclosure, there is a form in which the remaining life of an existing building is predicted by focusing on concrete at a plurality of locations and comparing these.
That is, the method for estimating the remaining life of an existing building according to the present disclosure preferably performs the step (5) for concrete at a plurality of locations, and further includes the following step (6).

Step (6): step of predicting the remaining life of existing buildings the minimum value among the lives of the respective concrete at a plurality of locations (t-t _0).

The interior and exterior walls of existing buildings are often finished with various types of designs, and the finished thickness or cover thickness may differ for each design. Therefore, in order to improve the prediction accuracy of the remaining life of the existing building, respectively calculates the number of years (t-t ₀₎ and performed step (5) to the concrete at a plurality of locations of different finishes each other, the minimum value of the It is preferable to estimate the remaining life of the existing building. It is preferable that the concrete at the plurality of places of interest covers as many types of designs as possible.

Hereinafter, a preferred example of an embodiment of a remaining life prediction method of an existing building according to the present disclosure will be described.
In many cases, the concrete on the same floor can be regarded as the same mix, so that the equation (1 ′) is obtained for each floor of the existing building.
The wall surfaces are grouped for each floor and for each type of finish, and the finish thickness and cover thickness at a plurality of locations are investigated for each group. In general, concrete is likely to be neutralized in the order of exposed, mortar finish, and decorative building material finish.Therefore, it can be said that priority should be given to investigating exposed concrete to estimate the remaining life of existing buildings. Since the degree of thickness affects the degree of carbonation and remaining life of concrete, it is preferable to investigate not only bare concrete but also as many types of designs as possible.
After examining a plurality of locations for each group and obtaining the values of the finish thickness and the cover thickness, the minimum values of the finish thickness and the cover thickness in the group are used as specific values to be substituted into equation (1 ′), to calculate the residual life _{(t-t 0)} for each group. By comparing the groups, the minimum remaining life is estimated as the remaining life of the existing building.

[5] Method of predicting remaining life of existing building when existing finish is removed According to the present disclosure, a method of predicting remaining life of existing building when removing existing finish from concrete (hereinafter simply referred to as “after removal of finish”) Residual Life Prediction Method ”) predicts the remaining life of an existing building after finishing removal, based on the assumption that the life of the building is the number of years required for concrete to neutralize from the surface to the position where corrosion of reinforcing steel starts. Is the way.

  The remaining life prediction method after finishing removal according to the present disclosure is an invention on the premise that Expression (3), which is a theoretical expression of the depth of carbonation of concrete, is satisfied. First, the theory from which Expression (3) is derived and Expression (3) will be described.

[5-1] Derivation of Theoretical Formula of Carbonation Depth of Concrete After Finishing Removal FIG. 3 is a schematic diagram showing the relationship between carbonation of exposed concrete and CO ₂ diffusion (see “Reinforced Concrete Structure”). Guidelines for Building Durability Design and Construction of Buildings ”(2016, Architectural Institute of Japan). Carbonation of concrete progresses by carbon dioxide (CO ₂ ) diffused into the interior of the concrete and reacts with calcium hydroxide (Ca (OH) ₂ ) in the concrete to generate calcium carbonate (CaCO ₃ ). It is assumed that CO ₂ diffuses in the neutralized concrete (neutralized region) according to Fick's first law. It is assumed that the CO ₂ concentration of air on the concrete surface is constant from the time of building construction to the future.

The coordinates of the horizontal axis (neutralization depth) in FIG. 3 are as follows.
The coordinates of the concrete surface are set to 0.
It is assumed that the carbonation of the concrete has progressed to the coordinate x at the time t.

It is assumed that Ca (OH) ₂ in the concrete is completely consumed at the depth of the coordinate x, and is in a steady state at the depth of the coordinate x. It is assumed that CO _{2 that} has reached the coordinate x instantaneously reacts with Ca (OH) ₂ present there to generate CaCO ₃ .

The coordinates 0 (concrete surface), through the per area S of the plane orthogonal to the depth direction, the amount? CO2 ₂ of CO ₂ per Δt time reaches coordinate x (neutralization depth of the concrete) is below It is represented by equation (3-1).
The amount ΔCO _{2 of} CO ₂ consumed when the CO ₂ reaching the coordinate x reacts with Ca (OH) ₂ to generate CaCO ₃ is represented by the following equation (3-2).

here,
x: neutralization depth of concrete (0 ≦ x),
Δx: thickness of the boundary region,
t: time,
Δt: minute time,
C ₀ : CO ₂ concentration of air on the concrete surface,
D: CO ₂ diffusion coefficient of neutralized concrete,
H: Ca (OH) ₂ amount per unit volume contained in concrete,
S: Area of a surface orthogonal to the depth direction.

  Assuming that equation (3-1) is equal to equation (3-2),

  In the equation (3-3), when Δt is brought close to 0 to the limit, the following differential equation is obtained.

Removing existing finishes is done with the expectation that the concrete will have a low degree of carbonation at the time the finish is removed and that the concrete will have a significant useful life. When this is illustrated, an image shown in FIG. 4 is obtained. In FIG. 4, t ₀ is the point of time when the finish is removed, x ₀ is the neutralization depth of concrete at the time of removing the finish, x is the depth of the steel bar corrosion start position, and t is x of the concrete neutralization. It is time to reach. t ₀ to the relatively slow progress in neutralization of concrete, neutralization depth of concrete at t ₀ is shallow. Neutralization of concrete progresses relatively quickly from t ₀ and neutralizes to x.
Under the expectation described above, both sides of the equation (3-4) are integrated. The left-hand side is the integral from _{x 0} to x, the right-hand side is integrated from time _{t 0} to time t.

  When formula (3-5) is expanded and arranged,

Among the elements constituting the equation (3-6), the CO ₂ concentration (C ₀ ) of air is relatively easy to know by a site survey, but the CO ₂ diffusion coefficient (D) and the Ca per unit volume (OH) ₂ (H) is relatively difficult to know by field survey.
Then, with respect to D and H, which are relatively difficult to know by a field survey, D / H = a and (t−t ₀ ) = t ′, the equation (3-6) becomes the following equation (3).

Here, t ′: remaining life (years) of the existing building, C ₀ : CO ₂ concentration (%) of air at the finished surface to be removed, x ₀ : neutralization depth of concrete at the time of removing the finishing (Mm), x: Depth (mm) of the reinforcing bar corrosion start position.

  Equation (3), which is a theoretical equation, includes an unknown coefficient a. The specific value of the coefficient a is determined by the above-described method for obtaining the prediction formula according to the present disclosure. That is, in Expression (3), a is a that constitutes Expression (1), and is a coefficient included in Expression (1 ′).

[5-2] Method of Predicting Residual Life After Finish Removal The method of predicting residual life after finish removal according to the present disclosure is not a method of using the entire formula (1 ′) obtained by the method of obtaining the prediction formula according to the present disclosure. , A method using a specific value of the coefficient a included in the equation (1 ′).

  It is significant that the remaining life prediction method after finishing removal according to the present disclosure is performed together with the above-described remaining life prediction method of an existing building according to the present disclosure. In the method for estimating the remaining life of an existing building according to the present disclosure, since the equation (1 ′) is used in its entirety, the specific value of the coefficient a in the equation (1) is naturally determined. Contains specific values. The specific value may be substituted into equation (3) to perform the remaining life prediction method after finishing removal according to the present disclosure.

  The remaining life prediction method after finishing removal according to the present disclosure includes the following step (7) based on the equation (1 ′) obtained by the method for obtaining the prediction equation according to the present disclosure.

Step (7): Substituting the specific value of a included in equation (1 ′) into a in equation (3), and removing the existing finish into C ₀ , x _0, and x in equation (3) Substituting specific values for concrete to be performed and predicting the calculated t ′ as the remaining life of the existing building.

Here, t ′: remaining life (years) of the existing building, C ₀ : CO ₂ concentration (%) of air at the finished surface to be removed, x ₀ : neutralization depth of concrete at the time of removing the finishing (Mm), x: Depth (mm) of the reinforcing-bar corrosion start position, a: a that constitutes equation (1), and a coefficient included in equation (1 ′).

C _{0 in} equation (3) is the CO ₂ concentration (%) of air at the finished surface to be removed. Specific values of C ₀ is substituted into equation (3) may be a measured value of the air at the time of removing the existing finish, it may be given conditions set in accordance with the concrete is placed environment. The conditions are given in accordance with, for example, guidelines of the Architectural Institute of Japan and the Japan Society of Civil Engineers. As an example of the application condition, 0.10% indoor and 0.05% outdoor.

X ₀ of the formula (3) is a neutralization depth of the concrete at the time of removing the existing finish (mm). Specific values of x ₀ is substituted into equation (3) is an actually measured value. x ₀ is, for example, measurement test of the neutralization depth in the concrete that was withdrawn from the existing building to the sample (for example, JIS A1152: 2011 "method of measuring the neutral of the depth of the concrete") is measured carried out.

  Therefore, in order to perform the remaining life prediction method after finishing removal according to the present disclosure, the neutralization depth of concrete is measured in advance at the place where finishing is to be removed. It is preferable that the concrete at the place where finishing is to be removed has the same mix as the concrete which is the place to be investigated in the step (1) for obtaining the formula (1 '). In other words, if formula (1 ') is obtained by setting the scheduled finish removal location as the investigation location in step (1), the method for estimating the remaining life after finish removal according to the present disclosure can be effectively performed.

  X in Expression (3) is the depth (mm) of the reinforcing bar corrosion start position. The specific value of x to be substituted into Expression (3) follows, for example, guidelines of the Architectural Institute of Japan, the Japan Society of Civil Engineers, and the like. According to the guidelines of the Architectural Institute of Japan, the depth of the reinforcing bar corrosion start position is the cover thickness +20 mm indoors and the cover thickness outdoors. According to the guidelines of the Japan Society of Civil Engineers, the depth of the reinforcing bar corrosion start position is the cover thickness indoors and the cover thickness −10 mm outdoors. The cover thickness may be an actually measured value or a value described in a construction record. The cover thickness is preferably an actually measured value from the viewpoint of accurately predicting the remaining life of the existing building.

  The part to be finished and removed may be any structure of an existing building, such as a wall, a pillar, a beam, a ceiling, or a floor.

  As described above, it is meaningful to perform the remaining life prediction method after finishing removal according to the present disclosure together with the remaining life prediction method of the existing building according to the present disclosure. By performing the process (5) and the process (7) for the concrete of interest, it is possible to predict the remaining life of the existing building in the case where the finish is not removed and the case where the finish is removed.

  Hereinafter, the invention according to the present disclosure will be described more specifically with reference to examples.

[6] Example for Actual Existing Building An example in which the neutralization prediction method and the remaining life prediction method according to the present disclosure are applied to a real existing building will be described.

[6-1] Outline of the target building ・ Building location: Shibuya-ku, Tokyo ・ Completion date: August 1984 (1984) ・ Usage: Apartment and building area: Approx. 860m ²
・ Total floor area: about 2,800 m ²
・ Building structure: Reinforced concrete wall structure ・ Basic type: Direct foundation ・ Building scale: 3 floors above ground, 1 basement floor, 1st floor of tower

  Table 1 shows the types of finishing of the target building. Finishes were confirmed by design drawings and field surveys, and there were a total of seven finishes indoors and outdoors.

[6-2] Survey items and survey methods (Table 2)

  The measurement of the neutralization depth was carried out using cores collected from the walls of 6 basements on the first basement, 8 places on the first floor, 8 places on the second floor, 8 places on the third floor, 10 places on the third floor, and 3 places in the tower.

  The measurement of the compressive strength was performed for all floors, and cores collected from three walls at each floor were used as samples. A part of the collected core was also used for the measurement of the neutralization depth.

  Investigation of the cover thickness was performed on the walls of each floor. After removing the finishing material, if any, 6 to 10 locations were measured.

  Tables 3 and 4 show the survey results of the first basement floor (B1) and tower (PH1) in which the types of finishing are exposed, mortar finishing, and tile finishing.

[6-3] Determination of concrete value of coefficient included in prediction formula of carbonation depth of concrete From the survey results shown in Table 3, the following analysis was performed for the first basement (B1) and tower (PH1). Was.

  Since the compressive strength of concrete is different for each floor, it is assumed that the mix of concrete is different or the degree of neutralization is different for each floor. Therefore, the prediction of neutralization was performed for each floor. On the same floor, the concrete on the wall was considered to be the same mix, the mortar finish and the tile finish mortar were the same mix, and the tile finished tiles were considered to be the same material.

  The paint was ignored since it could not be expected to have a neutralization inhibiting effect, and the finish in which paint was applied to the mortar surface was regarded as a mortar finish.

The CO ₂ concentration of air on the wall surface was 0.10% indoors and 0.05% outdoors. However, since the pit on the first basement floor is indoors but no people enter or exit, it is assumed that the CO ₂ concentration is low, and the CO ₂ concentration of air on the wall surface is set to 0.05%, which is the same as outdoors.

For each floor, the least squares method was applied between the measured value (average value) and the estimated value of the neutralization depth to determine the specific value of the coefficient constituting the equation (1). For the first basement floor, only exposed and mortar finished, three coefficients a, b and c were determined based on the six data shown in Table 3. For the tower, five coefficients a, b, c, e, and f were determined based on the five data shown in Table 3. The calculation of the least squares method was performed by a solver function of spreadsheet software Excel.
Table 5 shows specific values of the determined a, b, c, e, and f.

FIG. 5 shows a correlation between the actually measured value and the estimated value obtained by the equation (1). In FIG. 5, the horizontal axis x is an actual measurement value, and the vertical axis y is an estimated value.
As can be seen from FIG. 5, the measured value and the estimated value are well correlated, and it is considered that appropriate specific values of the coefficients a, b, c, e, and f were obtained.

  From the specific values of the coefficients shown in Table 5, the following can be inferred.

  Since the coefficient a of the first basement floor and the coefficient a of the tower are far apart, it is considered appropriate to perform the neutralization prediction for each floor.

The coefficient a (= CO ₂ diffusion coefficient D of neutralized concrete D / Ca (OH) ₂ amount H per unit volume contained in concrete) is smaller on the first basement floor than in the tower house. It is inferred that the CO ₂ diffusion coefficient D of the neutralized concrete is smaller on the first floor than in the tower. This is correlated with the fact that the compressive strength of concrete is higher on the first basement floor than on the tower.

The coefficient b (= CO ₂ diffusion coefficient D of neutralized concrete / CO ₂ diffusion coefficient D _{m of} neutralized mortar) is 2.29 for the first basement and 2.32 for the tower, Also exceeded one. This correlates with the fact that mortar is denser than concrete.

The coefficient e of the tower (= CO ₂ diffusion coefficient D of neutralized concrete / CO ₂ diffusion coefficient Dt of tile) is 7.80, and the CO ₂ diffusion coefficient Dt of the tile is It was 1/7 or less of the CO ₂ diffusion coefficient D. Since the tile is a finishing material that suppresses the intrusion of CO ₂ and improves the durability of concrete, it is considered that an appropriate value was obtained as the coefficient e.

It was considered that both the specific values of the coefficient c and the coefficient f were below the number of decimal places that can be calculated by the spreadsheet software. This indicates that Hm (the amount of Ca (OH) ₂ per unit volume contained in the mortar) is close to zero. Mortar was considered.

  At least five data points are required to determine the specific values of the coefficients a, b, c, e, and f. For the tower, two exposed areas and a mortar finish (actually, paint the mortar surface with paint) The specific value of the coefficient was determined based on the data of one place and two places of the tile finish. Since the specific value of the coefficient included in the prediction formula can be determined without unifying the type of finishing to one type, the prediction formula can be obtained even when the investigation location is limited.

For each floor, a shown in Table 5, b, c, the specific value of e and f into Equation (1), the formula (1 a relational expression between x and _t, C 0, _{d m} and _{d t} ') Got. Equation (1 ′) for each floor is shown below.

[6-4] in the formula (1 ') of each prediction floor remaining life of existing buildings, _C 0 shown in Table _6, d m, a specific value of _{d t} and x, are substituted for each type of finishing, The neutralization life t (the number of years required for the concrete to neutralize to the position where corrosion of reinforcing steel starts) was determined. Was calculated residual lifetime (t-t ₀₎ by subtracting the number of years elapsed t ₀ at the time of the survey from neutralization life t.

Here, the minimum values in the same floor and finish group were applied to d _m (mortar thickness) and d _t (tile thickness) to be substituted into equation (1 ′), respectively. That is, the minimum value within the group, which is the data shown in Table 3, was applied.

  X (depth of the reinforcing bar corrosion start position) to be substituted into the expression (1 ') was set to cover thickness +20 (mm) indoors and cover thickness (mm) outdoors. However, the pit on the first basement floor was indoors, but it was assumed that the humidity was high, and the cover thickness (mm) was set similarly to the outdoors.

For the above cover thickness, the minimum value within the same floor and finish group was applied. That is, the minimum value within the group, which is the data shown in Table 4, was applied.
However, as for the mortar finish of the tower, since the cover thickness was not investigated, a legal cover thickness of 30 mm was applied.

The CO ₂ concentration of air on the wall surface was 0.10% indoors and 0.05% outdoors. However, since the pit on the first basement floor is indoors but no people enter or exit, it is assumed that the CO ₂ concentration is low, and the CO ₂ concentration of air on the wall surface is set to 0.05%, which is the same as outdoors.

  Table 6 shows actual measured values and conditions used for predicting the remaining life, and predicted values of the remaining life.

  As shown in Table 6, in the range investigated in this example, the remaining life of the exposed concrete indoors in the tower house was the shortest, but still exceeded 70 years. From this, it is predicted that the existing building of this example can be used for 70 years from the time of the survey.

[6-5] Prediction of residual life after finishing removal For each floor, a shown in Table 5 was substituted into equation (3), and a prediction equation for predicting the remaining life after finishing removal was obtained. The prediction formula for each floor is shown below.

  For the mortar finish on the first basement floor, the mortar finish on the tower, and the tile finish on the tower, the remaining life after finish removal was predicted.

The specific values of C ₀ , x, and x ₀ shown in Table 7 were substituted into the above formula for each floor for each type of finish, and the remaining life t ′ after finish removal was determined.

  X (depth of the reinforcing bar corrosion start position) to be substituted in the above equation was the same as x in Table 6.

For x ₀ (the depth of neutralization of concrete at the time of removing the finish) to be substituted into the above equation, the maximum value within the same floor and finish group was applied. That is, the average value shown in Table 3 and the maximum value in the group was applied.

The CO ₂ concentration of air on the wall surface was 0.10% indoors and 0.05% outdoors. However, since the pit on the first basement floor is indoors but no people enter or exit, it is assumed that the CO ₂ concentration is low, and the CO ₂ concentration of air on the wall surface is set to 0.05%, which is the same as outdoors.

  Table 7 shows measured values and conditions used for predicting the remaining life after finishing removal, and predicted values of the remaining life.

  As shown in Table 7, in the range investigated in this example, the remaining life after finish removal was all over 70 years. From this, it is predicted that the existing building of this example can be used for 70 years from the time of the survey even if the finishing is removed and the building is released.

  As described above, the invention according to the present disclosure has been described with reference to the embodiments. However, the invention according to the present disclosure is not limited to the embodiments.

Claims (5)

A method for obtaining a prediction formula for predicting the neutralization depth of concrete in an existing building,
A method comprising the following steps (1) to (3), and obtaining the following equation (1 ′) as the prediction equation.
Step (1): a step of investigating the neutralization depth of the concrete of the existing building and the thickness of the finish applied on the concrete. However, the number of survey points is five or more, and two or more of the survey points are concrete with a decorative building material finish in which a decorative building material exists on concrete via mortar. Investigate the neutralization depth of concrete, mortar thickness and decorative building material thickness.
Step (2): The least squares method is applied between the measured value of the neutralization depth of concrete obtained in the above step (1) and the estimated value of the neutralization depth of concrete according to the following equation (1). A step of applying and determining specific values of a, b, c, e and f constituting the following equation (1).
Here, x: neutralization depth of concrete, t: age of concrete, C ₀ : CO ₂ concentration of air in the environment where concrete is placed, d _m : thickness of mortar on concrete, d _t : Thickness of decorative building materials on concrete.
Step (3): a determined by the step (2), b, c, the specific value of e and f is substituted into the equation (1), the relationship between x and _t, C 0, _{d m} and _{d t} A step of obtaining equation (1 ′), which is an equation. A method for predicting the neutralization depth of concrete in an existing building, comprising the following step (4) using the equation (1 ′) obtained by the method according to claim 1.
Step (4): t in the formula (1 '), the C _0, d _m and d _t, substituting a specific value for the concrete to know the neutralization depth, neutral calculated x of the concrete The process of predicting the depth of development. A method for predicting the remaining life of an existing building, comprising the following step (5) using the equation (1 ′) obtained by the method according to claim 1.
Step (5): 'to _C 0, _{d m} and _{d t} of, by substituting the specific value for the focused concrete, and the formula (1 Formula (1)' to x) of, for concrete to the noted Substituting the depth of the reinforcing steel corrosion start position of the above, the number of years t required for the concrete of interest to neutralize to the reinforcing steel corrosion start position was obtained, and the elapsed years t ₀ of the concrete of interest was subtracted from the number of years t. process to predict the number of years (t-t ₀₎ and the remaining life of the existing building. The prediction method according to claim 3, wherein the step (5) is performed on concrete at a plurality of locations, and further includes the following step (6).
Step (6): step of predicting the remaining life of existing buildings the minimum value among the lives of the respective concrete at a plurality of locations (t-t _0). A method for predicting the remaining life of an existing building when removing an existing finish from concrete,
A method for predicting the remaining life of an existing building, comprising the following step (7) based on the equation (1 ′) obtained by the method according to claim 1.
Step (7): Substituting the specific value of a contained in the above formula (1 ′) into a of the following formula (3), and replacing C ₀ , x ₀ and x of the following formula (3) with: Substituting specific values for concrete from which existing finishes are to be removed, and predicting the calculated t 'as the remaining life of the existing building.
Here, t ′: remaining life of the existing building, C ₀ : CO ₂ concentration of air at the finished surface to be removed, x ₀ : neutralization depth of concrete at the time of removing the finish, x: start of corrosion of reinforcing steel Depth of position, a: a that constitutes equation (1), and is a coefficient included in equation (1 ′).