JP7765946B2 - Neutralization depth determination method - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Published in the CD-ROM summary of the 48th Technical Presentation of the Kanto Branch of the Japan Society of Civil Engineers, published on February 18, 2021.

Patent Act Article 30, Paragraph 2 applied. Presented at the 48th Technical Presentation of the Kanto Branch of the Japan Society of Civil Engineers held on March 2, 2021.

Article 30, Paragraph 2 of the Patent Act applies. Published on the website of the proceedings of the 76th Annual Academic Lecture Meeting of the Japan Society of Civil Engineers, 2021, posted on August 1, 2021.

Application of Article 30, Paragraph 2 of the Patent Act. Presented at the 76th Annual Academic Lecture Meeting of the 2021 Japan Society of Civil Engineers National Convention held on September 9, 2021.

The present invention relates to a technology for determining the depth of carbonation in concrete.

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.

As mentioned above, from the perspective of understanding the deterioration of concrete structures, it is important to understand the carbonation depth, which indicates the point in the concrete depth direction where carbonation has reached.

Patent Document 1 and Patent Document 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 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.

JP 2010-230383 A JP 2018-36278 A

However, the technology in Patent Document 1 requires drilling holes in the concrete to be evaluated, which is time-consuming. Similarly, the technology in Patent Document 2 requires determining the diffusion coefficient using concrete specimens taken from the concrete structure to be evaluated, which is time-consuming. Taking these circumstances into consideration, the present invention aims to identify the carbonation depth using a simple method.

To solve the above problem, the carbonation depth determination method 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, where the specific element is at least one of Si, S, K, and Al.

The method for determining the carbonation depth according to a preferred embodiment of the present invention makes it possible to determine the carbonation depth in a simple manner.

FIG. 2 is a schematic diagram showing the position of a region to be measured in concrete of a concrete structure. FIG. 2 is a schematic diagram showing measurement points in a region to be measured for concrete of a concrete structure. 1 is a graph showing the relationship between the abundance ratio of specific elements (Si, S, K) and the neutralization depth for each region that was the subject of measurement.

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 concrete surface of a concrete structure that is the target for determining the carbonation depth will be referred to as the "target area."

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 specific elements changes (increases or decreases).

Based on the above findings, the neutralization depth determination method 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.

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

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 detect X-rays (fluorescent X-rays) specific to each element.

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

The size of the symmetric region is arbitrary, but is, for example, approximately 200 mm x 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 using 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 positioned at a predetermined interval.

It is not necessary to use the average value across multiple measurement points within a target region as the abundance ratio of a specific element in that 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 that 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.

The type of concrete whose carbonation depth is determined using the carbonation depth determination method according to this embodiment can be any type, but examples include concrete containing Portland cement or blended cement as the cement. From the perspective of determining the carbonation depth with high accuracy, concrete containing Portland cement as the cement is preferred.

In this embodiment, the neutralization depth is determined based on the relationship between a predetermined reference value and the abundance ratio of a specific element (hereinafter referred to as the "detection value") identified in the target area by X-ray fluorescence analysis.

The reference values are described in detail below. For example, one of the following reference values 1 to 4 may be used as the reference value.

<Reference value 1>
As described above, the abundance ratio of a specific element changes (increases or decreases) as carbonation progresses (i.e., as 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.

An example of a point in time before concrete neutralization has progressed is when a concrete structure is newly constructed. When newly constructed, specific elements have not yet migrated within the concrete, so the specific elements are present 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 new construction (i.e., reference value 1) can be calculated based on the concrete mix and blending. For example, reference value 1 may be determined using a distribution curve that correlates the relationship between the concrete mix and blending and the abundance of the specific element (or neutralization depth). The distribution curve is created using any known logical analysis (for example, a logical analysis that simulates element diffusion within concrete).

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 aggregate such as sand, coarse aggregate such as crushed stone, water, and any other materials. Specific elements are contained in each material mixed and blended into concrete. Specifically, the reference value 1 is calculated from the mix and proportion of concrete and the component composition of each material mixed and blended into concrete.

The neutralization depth is then determined based on the comparison result (difference) between reference value 1 and the detection value. For example, the greater the difference between 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 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 also be determined by multiplying the comparison result between reference value 1 and the detection value by a predetermined coefficient. Furthermore, the comparison result between reference value 1 and the detection value is not limited to a difference, and may be, for example, the ratio between reference value 1 and the detection value.

<Reference value 2>
Reference value 2 is the proportion of a specific element present on the surface of concrete measured by X-ray fluorescence analysis at the time of new construction of a concrete structure (i.e., before the concrete has begun to neutralize). Reference value 2 is measured in advance at the time of new construction.

As with 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 also 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.

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

As with 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 also 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.

<Reference value 4>
The 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 the 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 an arbitrary area on the concrete surface.

Actual values can be determined using any known technique. Examples of methods used to determine actual values include the core method, in which a core is taken from a reference area, phenolphthalein solution is sprayed onto the fractured surface, and the carbonation depth is determined from the color reaction; the chipping method, in which the reference area is chipped, a reagent is sprayed onto the chipped surface, and the carbonation depth is determined from the color reaction; and the drilling method, in which powder obtained by drilling a hole in the reference area is dropped onto filter paper that has absorbed a reagent, and the carbonation depth is determined from the color reaction. Note that determination of actual values using reagents complies with the "Method for Measuring Carbonation Depth of Concrete" specified in JIS A 1152:2011.

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

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.

Note that the reference values used in the neutralization depth determination method are not limited to the examples above. For example, a value obtained by multiplying Reference Value 1 - Reference Value 4 by a predetermined coefficient may be used as the reference value.

The use of a reference value is not required 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 learned the relationship between the abundance of a specific element on the surface of concrete and the carbonation depth.

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, showing the carbonation depth determined for each area.

As can be understood from the above explanation, the carbonation depth is determined according to the proportion of a specific element measured by X-ray fluorescence analysis for a target area on the surface of the concrete. This has the advantage of being a simpler method of determining the carbonation depth than methods that destroy the concrete and determine the carbonation depth through a 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 being evaluated (e.g., the technology of Patent Document 2).

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

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

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

The concrete structure in Figure 1 is a wall structure located in an outdoor materials storage yard, and approximately 28 years have passed since it was constructed in 1993. The wall structure consists of a reinforced concrete wall 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.

As shown in Figure 1, the center section of the wall structure was made with ordinary Portland cement, and the two side sections of the wall structure were made with blended cement.

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 abundance ratio of specific elements in the measurement area are average values across the 10 points.

Table 2 shows the measured neutralization depth and the abundance of specific elements for each of the 10 measurement areas.

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, this is as follows:

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

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 particularly significant correlation was observed between carbonation depth and abundance ratio in ordinary Portland cement.

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

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

Claims (8)

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. The method for specifying a neutralization depth according to claim 1 , wherein the specific element is Si. The method for determining the carbonation depth according to claim 1 or 2, wherein the concrete contains Portland cement. The method for determining a neutralization depth according to claim 1 , further comprising: determining a neutralization depth based on a relationship between the abundance ratio measured in the target region and a reference value. The method for determining a neutralization depth according to claim 4 , wherein the reference value is an abundance ratio of the element calculated according to the mix proportion and blending of the concrete. The method for determining a neutralization depth according to claim 4, wherein the reference value is the abundance ratio of the specific element measured by fluorescent X-ray analysis on the surface of the concrete when the concrete structure is newly constructed. The method for determining carbonation depth according to claim 4, wherein the reference value is the abundance ratio of the specific element measured by fluorescent X-ray analysis in a reference region of the surface of the concrete where carbonation has not progressed. A method for determining the carbonation depth according to claim 4, wherein the reference value is a value corresponding to the abundance ratio of the specific element measured by fluorescent X-ray analysis for a reference area on the surface of the concrete, and the actual measured value of the carbonation depth determined by destroying the reference area and a color reaction of a reagent.