Neutralization depth determination method

Abstract

To specify a neutralization depth by a simple method.SOLUTION: A neutralization depth specification method is the method for specifying a neutralization depth of concrete in an existing concrete structure. The neutralization depth is specified in accordance with an existence ratio of a specified element measured by an X-ray fluorescence analysis with respect to an object area on a front surface of the concrete. The specified element is one of at least Si, S, K, and Al.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for identifying the carbonation depth in concrete. [Background technology]

[0002] It is known that the pH of concrete in structures made of concrete (hereinafter referred to as "concrete structures") drops and becomes neutralized when carbon dioxide from the atmosphere penetrates into the interior. The neutralization of concrete progresses over time from the surface of the wall toward the interior. When the neutralization reaches the location of the steel materials embedded in the concrete structure, the corrosion-resistant oxide film (passive film) on the surface of the steel materials is destroyed. When the oxide film is destroyed, the steel materials corrode. When the steel materials corrode, cracks and peeling occur in the concrete, causing problems such as deterioration.

[0003] As described above, from the perspective of understanding the deterioration of concrete structures, it is important to understand the carbonation depth, which indicates the position in the depth direction of the concrete where carbonation has reached.

[0004] Therefore, Patent Documents 1 and 2 disclose techniques for measuring the carbonation depth of concrete. Specifically, Patent Document 1 involves drilling a hole in concrete, applying a phenolphthalein solution to the inner surface of the drilled hole, and identifying the position of the boundary between the colored and non-colored areas as the carbonation depth. Patent Document 2 also discloses a technique for estimating carbonation based on the concentration of chlorine or sodium. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-230383 [Patent Document 2] Japanese Patent Application Publication No. 2018-36278 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technique of Patent Document 1 requires drilling holes in the concrete to be evaluated, which is time-consuming. Similarly, the technique of Patent Document 2 also requires determining the diffusion coefficient using concrete specimens taken from the concrete body to be evaluated, which is time-consuming. In consideration of the above circumstances, the present invention aims to identify the carbonation depth using a simple method. [Means for solving the problem]

[0007] In order to solve the above problems, the method for determining the carbonation depth of the present invention is a method for determining the carbonation depth of concrete in an existing concrete structure, and determines the carbonation depth based on the abundance ratio of a specific element measured by X-ray fluorescence analysis for a target area on the surface of the concrete, wherein the specific element is at least one of Si, S, K, and Al. [Effects of the Invention]

[0008] According to the method for determining the neutralization depth according to a preferred embodiment of the present invention, it is possible to determine the neutralization depth in a simple manner. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram showing the position of a region to be measured in concrete of a concrete structure. [Figure 2] FIG. 2 is a schematic diagram showing measurement points in a region to be measured for concrete of a concrete structure. [Figure 3] 1 is a graph showing the relationship between the abundance ratio of specific elements (Si, S, K) and the neutralization depth for each measurement region. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention is a method for determining the carbonation depth of concrete in an existing concrete structure (hereinafter referred to as the "carbonation depth determination method"). Note that concrete structures include various structures constructed primarily using concrete as a material. In the following description, the area of ​​the surface of the concrete in the concrete structure that is the target for determining the carbonation depth will be referred to as the "target area."

[0011] Here, the neutralization of concrete progresses over time from the surface toward the interior. It is known that chloride ions migrate (concentrate) in areas where neutralization has occurred. However, it was not known that the abundance ratio of specific elements (hereinafter referred to as "specific elements") present on the surface of concrete changes as neutralization progresses. As described in the examples below, the inventors of the present invention have newly discovered that there is a correlation between the abundance ratio (abundance rate) of specific elements on the surface of concrete and the depth of neutralization. Specifically, the more neutralization progresses (i.e., the deeper the neutralization depth), the more the abundance ratio of the specific elements changes (increases or decreases).

[0012] Based on the above findings, the method for determining neutralization depth according to the present invention determines the neutralization depth according to the abundance ratio of a specific element present in a target region. The abundance ratio of the specific element is determined by X-ray fluorescence analysis (XRF) of the target region.

[0013] In the present invention, the specific element is an element contained in the concrete material, and is any one of Si, S, K, and Al. From the viewpoint of being able to determine the carbonation depth with high accuracy, among these elements, Si, S, and K are preferred, and Si is more preferred. Note that the carbonation depth may be determined by combining the abundance ratios of two or more elements.

[0014] X-ray fluorescence analysis is a method for identifying the types and abundance (%) of elements contained in an object to be analyzed by irradiating the object with X-rays using an X-ray fluorescence analyzer (XRF analyzer) to excite the inner shell electrons of the elements contained in the object to be analyzed, and then detecting X-rays (fluorescent X-rays) specific to each element.

[0015] In the method for determining carbonation depth according to the present invention, a portable (handy) X-ray fluorescence analyzer is preferably used, since X-ray fluorescence analysis can be performed at the site where the concrete structure is installed. The X-ray fluorescence analyzer can determine the abundance ratio of a specific element within a range of several millimeters from the surface in the depth direction, for example.

[0016] The size of the symmetric region is arbitrary, but is, for example, approximately 200 mm × 150 mm. In this embodiment, the abundance ratio of a specific element is determined at multiple points (hereinafter referred to as "measurement points") within the target region by X-ray fluorescence analysis, and the average value across the multiple measurement points is used as the abundance ratio of the specific element in the target region. The multiple measurement points are located at a predetermined interval.

[0017] It is not essential to use the average value across multiple measurement points within a target region as the abundance ratio of a specific element in the target region. The abundance ratio of a specific element at one measurement point within the target region may also be used as the abundance ratio of the specific element in the target region. However, from the perspective of determining the abundance ratio of a specific element in the target region with high accuracy, it is preferable to use the average value across multiple measurement points.

[0018] The type of concrete for which the carbonation depth is determined by the carbonation depth determining method according to this embodiment is arbitrary, but examples thereof include concrete containing Portland cement or blended cement as cement. From the viewpoint of determining the carbonation depth with high accuracy, concrete containing Portland cement as cement is preferred.

[0019] In this embodiment, the neutralization depth is determined according to the relationship between a predetermined reference value and the abundance ratio of a specific element (hereinafter referred to as the "detection value") determined for the target region by fluorescent X-ray analysis.

[0020] The reference value will be described in detail below. For example, any one of the following reference values ​​1 to 4 is used as the reference value.

[0021] <Reference value 1> As mentioned above, the abundance ratio of a specific element changes (increases or decreases) as carbonation progresses (i.e., the carbonation depth deepens). Therefore, the abundance ratio of a specific element corresponding to the carbonation depth determined from the concrete mix and proportioning is defined as Reference Value 1, and the carbonation depth is determined based on the comparison result (e.g., the difference) between Reference Value 1 and the detected value. The difference between Reference Value 1 and the detected value can also be said to be the amount of change in the abundance ratio of a specific element from the time before carbonation progressed to the time when the detected value was measured. In this invention, "mixture" and "mixing" are synonymous and refer to the proportion (amount) of each material used in concrete. Mixture is the term used by the Japan Society of Civil Engineers and JIS, while mix is ​​the term used by the Architectural Institute of Japan.

[0022] A point in time before concrete neutralization progresses is, for example, when a concrete structure is newly constructed. At the time of construction, the specific element has not yet migrated within the concrete, so the specific element exists at a constant abundance throughout the depth of the concrete. Therefore, the abundance of the specific element in the target area at the time of construction (i.e., Reference Value 1) can be calculated based on the concrete mix and proportion. For example, Reference Value 1 may be determined using a distribution curve that correlates the relationship between the concrete mix and proportion and the abundance of the specific element (or the carbonation depth). The distribution curve is created using any known logical analysis (e.g., a logical analysis that simulates element diffusion within concrete).

[0023] The mix and proportion of concrete refers to the mix and proportions of each material mixed and blended into that concrete. Materials mixed and blended into concrete include, for example, cement, fine aggregates such as sand, coarse aggregates such as crushed stone, water, and any other materials. Specific elements are contained in each material mixed and blended into concrete. Specifically, the standard value 1 is calculated from the mix and proportion of concrete and the component composition of each material mixed and blended into concrete.

[0024] The neutralization depth is then determined based on the comparison result (difference) between the reference value 1 and the detection value. For example, the greater the difference between the reference value 1 and the detection value, the deeper the neutralization depth in the target area is determined to be, and the smaller the difference between the reference value 1 and the detection value, the shallower the neutralization depth in the target area is determined to be. Note that the neutralization depth may be determined by multiplying the comparison result between the reference value 1 and the detection value by a predetermined coefficient. Furthermore, the comparison result between the reference value 1 and the detection value is not limited to a difference, and may be, for example, a ratio between the reference value 1 and the detection value.

[0025] <Reference value 2> Reference value 2 is the proportion of a specific element measured by X-ray fluorescence analysis on the surface of concrete when the concrete structure is newly constructed (i.e., before the concrete has begun to neutralize). Reference value 2 is measured in advance when the concrete structure is newly constructed.

[0026] As in the case of reference value 1, the neutralization depth is determined based on the comparison result (e.g., difference) between reference value 2 and the detection value. For example, the greater the difference between reference value 2 and the detection value, the deeper the neutralization depth in the target area is determined to be, and the smaller the difference between reference value 2 and the detection value, the shallower the neutralization depth in the target area is determined to be. Note that the neutralization depth may be determined by multiplying the comparison result between reference value 2 and the detection value by a predetermined coefficient. Furthermore, the comparison result between reference value 2 and the detection value is not limited to a difference, and may be, for example, the ratio between reference value 2 and the detection value.

[0027] <Standard value 3> Reference value 3 is the abundance ratio of a specific element measured by X-ray fluorescence analysis in an area of ​​the concrete surface of a concrete structure where neutralization has not progressed (hereinafter referred to as the "reference area"). The reference area is an area formed of the same concrete as the target area, and any method can be used to identify the reference area. For example, an area that has little deterioration as determined by visual inspection by a worker can be identified as the reference area.

[0028] As in the case of reference value 1, the neutralization depth is determined based on the comparison result (e.g., difference) between reference value 3 and the detection value. For example, the greater the difference between reference value 3 and the detection value, the deeper the neutralization depth in the target area is determined to be, and the smaller the difference between reference value 3 and the detection value, the shallower the neutralization depth in the target area is determined to be. Note that the neutralization depth may be determined by multiplying the comparison result between reference value 3 and the detection value by a predetermined coefficient. Furthermore, the comparison result between reference value 3 and the detection value is not limited to a difference, and may be, for example, the ratio between reference value 3 and the detection value.

[0029] <Standard value 4> Reference value 4 is a value that corresponds to the proportion of a specific element measured by X-ray fluorescence analysis in a reference area on the surface of concrete, and the actual measurement value of the carbonation depth determined by destroying the reference area and determining the color reaction of a reagent (e.g., phenolphthalein solution). The reference area is an area formed from the same concrete as the target area, and is any area on the concrete surface.

[0030] The actual measurement value can be determined using any known technique. For example, the core method involves taking a core from the reference area, spraying phenolphthalein onto the fractured surface, and determining the carbonation depth from the color reaction. The chipping method involves chipping the reference area, spraying a reagent onto the chipped surface, and determining the carbonation depth from the color reaction. Finally, the drilling method involves drilling a hole in the reference area, dropping the powder onto filter paper soaked in a reagent, and determining the carbonation depth from the color reaction. The determination of the actual measurement value using a reagent complies with JIS A 1152:2011, "Method for measuring the carbonation depth of concrete."

[0031] For example, the reference value 4 is the ratio of the actual measured value to the abundance ratio of a specific element measured by X-ray fluorescence analysis for the reference region. The neutralization depth in the target region is determined by multiplying the detection value by the reference value 4. Note that the neutralization depth may also be determined by multiplying the reference value 4 by a predetermined coefficient in addition to the detection value.

[0032] When using standard value 4, the carbonation depth is determined by using the area of ​​the concrete surface surrounding the standard area as the target area.

[0033] The reference values ​​used in the method for determining the neutralization depth are not limited to the above examples. For example, a value obtained by multiplying Reference Value 1-Reference Value 4 by a predetermined coefficient may be used as the reference value.

[0034] The use of a reference value is not essential in the carbonation depth determination method of the present invention. For example, the carbonation depth may be determined by inputting the detected value into a trained model (e.g., a neural network) that has trained the relationship between the abundance ratio of a specific element on the surface of concrete and the carbonation depth.

[0035] The carbonation depth can be determined for each area (target area) located at a predetermined interval on the surface of the concrete using the carbonation depth determination method of the present invention, and a distribution map can be created on a drawing corresponding to the surface of the concrete, distributing the carbonation depth determined for each area.

[0036] As can be understood from the above explanation, the carbonation depth is determined according to the proportion of a specific element measured by fluorescent X-ray analysis for a target area on the surface of the concrete. Therefore, compared to methods that destroy the concrete and determine the carbonation depth by the color reaction of a reagent (e.g., the core method, chipping method, drill method), or methods that determine the carbonation depth using a diffusion coefficient determined from a concrete specimen taken from the concrete to be evaluated (e.g., the technology of Patent Document 2), this has the advantage of being a simple method for determining the carbonation depth. [Example]

[0037] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0038] This paper details the relationship between the carbonation depth actually measured for existing concrete structures and the proportion of specific elements (Si, S, K, Al) on the surface of the concrete.

[0039] FIG. 1 is a schematic diagram (top view) showing the positions of 10 areas (hereinafter referred to as "measurement areas") to be measured in concrete of an existing concrete structure.

[0040] The concrete structure in Figure 1 is a wall structure in an outdoor materials storage yard, and was constructed in 1993, approximately 28 years ago. The wall structure is made up of reinforced concrete walls 1,700 mm high and 200 mm thick. The mix and proportions of the concrete used in the wall structure are shown in Table 1. In Table 1, W is water, C is cement, S is fine aggregate, G is coarse aggregate, and A is a high-performance air-entraining water-reducing agent.

[0041] [Table 1]

[0042] As shown in Figure 1, the central part of the wall structure was made of ordinary Portland cement, and the two side parts of the wall structure were made of blended cement.

[0043] Figure 2 is a schematic diagram of the measurement area. As shown in Figure 2, the carbonation depth and the abundance ratio of specific elements were measured at 10 points (measurement points) in each measurement area. The carbonation depth was measured by spraying a 1% phenolphthalein solution using the chipping method in accordance with JIS A 1152:2011. The abundance ratio of specific elements was measured using a portable X-ray fluorescence analyzer. Note that the carbonation depth and the abundance ratio of specific elements in the measurement area are average values ​​over the 10 points.

[0044] Table 2 shows the measured neutralization depth and the abundance ratio of specific elements for each of the 10 measurement regions.

[0045] [Table 2]

[0046] Figure 3 is a graph showing the abundance ratio of specific elements (Si, S, K, Al) and the carbonation depth for each measurement region. It was confirmed that there is a correlation between the abundance ratio and the carbonation depth for all specific elements. Specifically, it is as follows.

[0047] When the specific element is Si, a correlation was confirmed in which the abundance ratio increases as the carbonation depth increases. A significant correlation was observed for Si in both ordinary Portland cement and blended cement.

[0048] When the specific element is S, a correlation was confirmed in which the greater the carbonation depth, the lower the abundance ratio. For S, a significant correlation was observed between the carbonation depth and abundance ratio, especially in ordinary Portland cement.

[0049] When the specific element is K, a correlation was confirmed in which the greater the carbonation depth, the greater the proportion of K present. A particularly significant correlation was observed between the carbonation depth and the proportion of K present in ordinary Portland cement.

[0050] When the specific element is Al, a correlation was confirmed in which the proportion of Al increases as the carbonation depth increases.A significant correlation was observed between the carbonation depth and the proportion of Al for both ordinary Portland cement and blended cement.

Claims

1. A method for identifying the carbonation depth of concrete in an existing concrete structure, comprising: The carbonation depth, which indicates the extent to which carbonation has progressed from the surface to the interior, is determined based on the abundance ratio of a specific element measured by X-ray fluorescence analysis for a target area on the surface of the concrete; The specific element is at least one of Si, S, K, and Al. Method for determining neutralization depth.

2. The specific element is Si. The method for determining the neutralization depth according to claim 1.

3. The concrete contains Portland cement The method for determining the neutralization depth according to claim 1 or 2.

4. The neutralization depth is determined based on the relationship between the measured abundance ratio and the reference value for the target area. The method for determining the neutralization depth according to any one of claims 1 to 3.

5. The reference value is the abundance ratio of the element calculated according to the mix proportion and mix of the concrete. The method for determining the neutralization depth according to claim 4.

6. The reference value is the abundance ratio of the specific element measured by X-ray fluorescence analysis on the surface of the concrete when the concrete structure is newly constructed. The method for determining the neutralization depth according to claim 4.

7. The reference value is the abundance ratio of the specific element measured by X-ray fluorescence analysis in a reference area of ​​the surface of the concrete where neutralization has not progressed. The method for determining the neutralization depth according to claim 4.

8. The reference value is a value corresponding to the abundance ratio of the specific element measured by X-ray fluorescence analysis in a reference area on the surface of the concrete, and the actual measurement value of the carbonation depth determined by the color reaction of a reagent after destroying the reference area. The method for determining the neutralization depth according to claim 4.

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