Determination method of chloride ion

Abstract

To efficiently acquire a plurality of chloride ion indicators for diagnosing deterioration of strength of hardened concrete.SOLUTION: A determination method of chloride ions includes the steps of: preparing powder sample of hardened concrete (S11); preparing a sample solution by adding room temperature water to the powder sample and stirring them (S12); inserting a salinity sensor and a reference electrode into the sample solution to measure a first potential difference (S13); further adding neutralization solution to acidic solution having been adjusted by adding organic acid to the sample solution and stirring them, to prepare a neutralized solution (S14); inserting the salinity sensor and the reference electrode into the neutralized solution to measure a second potential difference (S15); calculating an amount of water-soluble chloride ions contained in the hardened concrete on the basis of the first potential difference (S16); and calculating an amount of acid solution-soluble chloride ions contained in the hardened concrete on the basis of the second potential difference (S17).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for quantifying chloride ions contained in hardened concrete. [Background technology]

[0002] The rebars that make up concrete structures corrode due to salt damage, reducing the strength of the hardened concrete. When a concrete structure is first constructed, the rebars are kept in a highly alkaline state due to the large amount of calcium hydroxide supplied by the cement, which causes them to be covered by a passive film of oxide compounds. However, when chloride ions are present in the hardened concrete, the passive film is destroyed and the rebars begin to rust. This is the mechanism of corrosion due to salt damage.

[0003] In order to diagnose the deterioration of the strength of hardened concrete, it is desirable to periodically measure the amount or concentration of chloride ions contained in hardened concrete. Regarding this measurement, Patent Document 1 discloses a salt sensor that detects salt in hardened concrete. The salt sensor in Patent Document 1 is composed of an anode wire inserted into a hole formed in a concrete structure, and by applying a DC voltage between these electrodes, with the rebar of the concrete structure as the cathode, the salt content is directly detected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6618212 Summary of the Invention [Problem to be solved by the invention]

[0005] The chloride ions contained in hardened concrete include total chloride ions and hot water-extractable chloride ions, as specified in JIS A 1154:2020 (hereinafter simply referred to as the "JIS standard"). Total chloride ions are chloride ions extracted from hardened concrete with nitric acid solution. Hot water-extractable chloride ions are chloride ions extracted from hardened concrete with 50°C hot water. Roughly speaking, the former are chloride ions that are soluble in acid solution, and the latter are chloride ions that are soluble in water.

[0006] It is desirable to have multiple chloride ion indicators to determine corrosion due to salt damage. In this regard, the total chloride ion amount and the hot water extractable chloride ion amount are strong candidates for chloride ion indicators. However, the method for quantifying total chloride ions specified in the JIS standard is naturally different from that for hot water extractable chloride ions. Therefore, quantifying these chloride ions requires preparing two different treatment solutions using separate procedures using specimens obtained from concrete structures or hardened concrete samples prepared in a laboratory, and performing measurements using each method, which is time-consuming.

[0007] An object of the present invention is to provide a technique capable of efficiently obtaining multiple chloride ion indicators for diagnosing the deterioration of strength of hardened concrete. [Means for solving the problem]

[0008] The present invention is a method for quantifying chloride ions contained in hardened concrete, and has the following features. The method comprises: preparing a powder sample of the hardened concrete; adding room temperature water to the powder sample and stirring the mixture to prepare a sample solution in which water-soluble components contained in the powder sample are dissolved; inserting a salinity sensor and a reference electrode connected to a voltmeter into the sample solution and measuring a first potential difference; adding an organic acid to the sample solution and stirring the mixture to prepare an acidic solution in which the water-soluble components and acid-soluble components contained in the powder sample are dissolved, and then adding a neutralizing agent to prepare a neutralized solution; inserting the salinity sensor and reference electrode into the neutralization solution and measuring a second potential difference; Calculating the amount of water-soluble chloride ions contained in the hardened concrete based on a mathematical formula showing the relationship between the potential difference and the amount of chloride ions in solution and the first potential difference; calculating an amount of acid solution soluble chloride ions contained in the hardened concrete based on the formula and the second potential difference; Includes:

[0009] In the present invention, the step of preparing the neutralization solution may be carried out after the step of measuring the first potential difference.

[0010] In the present invention, after the step of preparing the sample solution, a step of measuring the first potential difference using a portion of the sample solution may be performed, and a step of preparing the neutralization solution using the remainder of the sample solution may be performed.

[0011] In the present invention, the first potential difference substituted into the variable of the formula in the step of calculating the amount of water-soluble chloride ions may be a measurement value after 20 to 240 minutes have elapsed since the end of the step of preparing the sample solution and the insertion of the salinity sensor and reference electrode, or may be a measurement value after 20 to 60 minutes have elapsed since the end of the step of preparing the sample solution.

[0012] In the present invention, the second potential difference substituted into the variable of the formula in the step of calculating the amount of chloride ions soluble in the acid solution may be a value measured 0 to 10 minutes after the insertion of the salinity sensor and the reference electrode. [Effects of the Invention]

[0013] According to the present invention, the amount of water-soluble chloride ions is calculated using a first potential difference measured using a sample solution and a mathematical formula showing the relationship between the potential difference and the amount of chloride ions in the solution. Furthermore, the amount of acid-soluble chloride ions is calculated using the above mathematical formula and a second potential difference measured using a neutralized solution prepared from the same sample solution as the sample solution used to measure the first potential difference. Therefore, according to the present invention, it is possible to efficiently obtain two types of chloride ion indicators: the amount of water-soluble chloride ions and the amount of acid-soluble chloride ions.

[0014] Furthermore, as will be understood from the experimental examples described later, the amount of water-soluble chloride ions calculated by the present invention generally coincides with the amount of hot-water-extractable chloride ions according to the JIS standard, and the amount of acid-solution-soluble chloride ions calculated by the present invention also generally coincides with the amount of total chloride ions according to the JIS standard. Therefore, the present invention can be said to be useful as a method for quantifying two types of chloride ions equivalent to the total chloride ions and hot-water-extractable chloride ions specified in the JIS standard. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart illustrating an example of a method according to an embodiment. [Figure 2] FIG. 1 is a diagram showing an example of the relationship between the potential difference and the chloride ion concentration in a solution. [Figure 3] 10 is a flowchart illustrating another example of a method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a method for quantifying chloride ions according to an embodiment of the present invention (hereinafter also simply referred to as "the method according to the embodiment") will be described with reference to the drawings. In this specification, when a numerical range is expressed using "to", the range is intended to include both end values.

[0017] 1.Quantitative method 1-1. Example 1 Fig. 1 is a flowchart showing an example of a method according to an embodiment. In the example shown in Fig. 1, the method according to an embodiment includes producing a powder sample (S11), preparing a sample solution (S12), measuring the potential difference E1 (S13), preparing a neutralization solution (S14), measuring the potential difference E2 (S15), calculating the amount of water-soluble chloride ions (S16), and calculating the amount of acid solution-soluble chloride ions (S17).

[0018] In the powder sample preparation step (S11), a powder sample is prepared. In the preparation step (S11), a sample of chloride ions to be quantified is collected, and the collected concrete powder is adjusted and weighed. Examples of samples to be quantified include concrete structures and hardened concrete samples prepared in a testing laboratory. The sample is collected by drilling holes using a drill, crushing a core specimen or a cylindrical specimen, or the like. When drilling holes using a drill, drill-bored powder is obtained. When crushing a core specimen or a cylindrical specimen, the specimen is cut to the required length, and then coarsely crushed using a jaw crusher or the like, and finely crushed using a fine crusher or a mortar (e.g., made of agate or iron). This results in crushed powder.

[0019] To prepare the concrete powder, the drilled or crushed powder is put into a sieve to remove large particles of concrete powder. The mesh size of the sieve is, for example, 100 to 1000 μm. To measure the concrete powder, a predetermined amount (for example, 2.0 to 10.0 g) of concrete powder that passes through the sieve is accurately weighed into a sample bottle. This produces a powder sample.

[0020] In the sample solution preparation step (S12), the powder sample obtained in the production step (S11) is used to prepare a sample solution in which the water-soluble components contained in the powder sample are dissolved. In the preparation step (S12), a predetermined amount (e.g., 10.0 to 40.0 g) of purified water at room temperature (15 to 25°C) is first accurately measured and placed in a sample bottle. This purified water is then added to the sample bottle containing the powder sample, gently stirred, and then allowed to stand for a predetermined time (e.g., 1 to 2 minutes). This prepares the sample solution.

[0021] In the step (S13) of measuring the potential difference E1, the potential difference E1 is measured using the sample solution obtained in the preparation step (S12) and a voltmeter. The potential difference E1 corresponds to the "first potential difference" of the present invention. In the measurement step (S13), first, a salinity sensor is connected to the positive side of the voltmeter, and a reference electrode is connected to the negative side. The salinity sensor connected to the positive side is, for example, an electrode-type salinity sensor as described in Patent Document 1. However, the salinity sensor applicable to the present invention is not limited to this, and any electrode-type salinity sensor can be used.

[0022] After attaching the fixture to the entrance of the sample bottle containing the sample solution, the salinity sensor and reference electrode are inserted into the sample bottle and brought into contact with the sample solution. At this time, the salinity sensor and reference electrode are prevented from touching each other. Then, a DC voltage measurement is performed to measure the potential difference E1. Because it takes a certain amount of time for the potential difference E1 to stabilize, the potential difference E1 is recorded 20 to 240 minutes (preferably 20 to 60 minutes) after the salinity sensor and reference electrode are inserted. In the measurement step (S13), the temperature T1 of the sample solution is also measured using a thermometer.

[0023] In the neutralization solution preparation step (S14), a neutralization solution is prepared using the sample solution subjected to the measurement step (S13). In the preparation step (S14), a predetermined amount of organic acid (reaction aid) (e.g., 2.0 g per 20.0 g of water) is first added to the sample solution. Examples of organic acids include tartaric acid, malic acid, citric acid, maleic acid, and sulfamic acid. Since carbon dioxide gas may be generated depending on the degree of neutralization of the target to be quantified, the solution is left to stand for a predetermined time (e.g., 1 to 5 minutes) after the addition of the organic acid. The sample bottle is then capped and stirred until the powder sample is completely dissolved. This prepares an acidic solution in which the water-soluble and acid-soluble components contained in the powder sample are dissolved.

[0024] In the preparation step (S14), a neutralizing agent is then added little by little to the acidic solution. Examples of neutralizing agents include calcium carbonate, magnesium carbonate, sodium carbonate, potassium carbonate, and calcium hydroxide. The amount of neutralizing agent added is adjusted appropriately depending on the amount of organic acid added to the sample solution. After adding the neutralizing agent, the solution is gently stirred and then allowed to stand for a predetermined time (e.g., 1 to 2 minutes). This prepares the neutralized solution.

[0025] In the step (S15) of measuring the potential difference E2, the potential difference E2 is measured using the neutralization solution obtained in the preparation step (S14) and a voltmeter. The potential difference E2 corresponds to the "second potential difference" of the present invention. The content of the measurement step (S15) is basically the same as that of the measurement step (S13). That is, in the measurement step (S15), a DC voltage measurement is performed using a voltmeter connected to a salinity sensor and a reference electrode, and the potential difference E2 is measured. However, unlike the potential difference E1, the potential difference E2 takes a short time to stabilize, so the potential difference E2 is recorded 0 to 10 minutes after the insertion of the salinity sensor and the reference electrode. In the measurement step (S15), the temperature T2 of the neutralization solution is also measured using a thermometer.

[0026] In the calculation step (S16) of the amount of water-soluble chloride ions, the potential difference E1 and temperature T1 obtained in the measurement step (S13) are substituted into the variables of the formula showing the relationship between the potential difference and the amount of chloride ions in the solution, and the amount of water-soluble chloride ions is calculated. Figure 2 shows an example of the relationship between the potential difference E and the chloride ion concentration S in the solution. Note that Figure 2 is a semi-logarithmic graph with a logarithmic scale on the x-axis. The relationship shown in Figure 2 is expressed by the following formula (1): S=10^(-5.639×E / T)+0.7111···(1) In equation (1), S is the chloride ion concentration [mol / L], E is the potential difference [V], and T is the temperature of the solution when the potential difference is measured [K].

[0027] By transforming equation (1) based on equation (2), which shows the relationship between the amount of chloride ions C and the chloride ion concentration S, we can derive an equation that shows the relationship between the potential difference E and the amount of chloride ions C in the solution. C=2300×{(Ww×S×35.45) / (Ws×1000)}···(2) In equation (2), C is the amount of chloride ions [kg / m3], Ww is the weighed value of purified water [g], Ws is the weighed value of the powder sample [g], and S is the chloride ion concentration [mol / L].

[0028] In the calculation step (S17) of the amount of chloride ions soluble in the acid solution, the amount of chloride ions soluble in the acid solution is calculated. The content of the calculation step (S17) is basically the same as that of the calculation step (S16). However, in the calculation step (S17), the potential difference E2 and the temperature T2 obtained in the measurement step (S15) are used as variables to calculate the amount of chloride ions soluble in the acid solution.

[0029] Thus, the example shown in Figure 1 makes it possible to efficiently obtain two types of chloride ion amounts: water-soluble chloride ion amounts and acid-soluble chloride ion amounts. In particular, the example shown in Figure 1 allows room-temperature water to be used in the preparation step (S12). This eliminates the need for 50°C hot water, which is required for the quantification of hot water-extracted chloride ions specified in the JIS standard, thereby improving the work safety of the quantification operator. Furthermore, while the JIS standard requires strict hot water conditions (maintained at 50°C ± 1°C), the example shown in Figure 1 has fewer restrictions on water temperature, and differences in water temperature are compensated for by the temperature T1 measured in the measurement step (S13). This makes it suitable for practical quantification.

[0030] 1, the calculation step (S16) may be performed after the measurement of the potential difference E1, i.e., after the measurement step (S13) and before the preparation step (S14). Alternatively, the calculation step (S16) may be performed after the preparation of the neutralization solution, i.e., after the preparation step (S14) and during the measurement step (S15).

[0031] 1-2. Second example Fig. 3 is a flowchart showing another example of a method according to an embodiment. In the example shown in Fig. 3, the method according to an embodiment includes producing a powder sample (S21), preparing a sample solution (S22), measuring the potential difference E1 (S23), preparing a neutralization solution (S24), measuring the potential difference E2 (S25), calculating the amount of water-soluble chloride ions (S26), and calculating the amount of acid solution-soluble chloride ions (S27).

[0032] Processing steps S21 to S27 shown in Fig. 3 are basically the same as processing steps S11 to S17, respectively, described with reference to Fig. 1. However, in the example shown in Fig. 3, a portion of the sample solution prepared in the preparation step (S22) is provided to the measurement step (S23), and the remaining sample solution is provided to the preparation step (S24). That is, in the example shown in Fig. 3, the sample solution prepared in the preparation step (S22) is divided into a portion for measuring the potential difference E1 and a portion for measuring the potential difference E2.

[0033] In the example shown in Fig. 1, the preparation step (S12), measurement step (S13), and preparation step (S14) are performed in this order. In contrast, in the example shown in Fig. 3, after the preparation step (S22) is performed, the measurement step (S23) and preparation step (S24) are performed in parallel. Therefore, according to the example shown in Fig. 3, the same effect as the example shown in Fig. 1 can be obtained. In addition, it is also possible to complete the quantitative processing in a shorter time than the example shown in Fig. 1.

[0034] 2. Experimental Example Next, the method according to the embodiment will be described in detail with reference to experimental examples.

[0035] 2-1. Calculation using hardened concrete sample specimens Concrete with the component ratios shown in Table 1 was mixed and cylindrical specimens with a diameter of 10 cm and a height of 20 cm were prepared. After the cylindrical specimens were sealed and cured for 28 days, they were all finely pulverized to adjust the particle size to 600 μm or less. The amount of chloride ions (0 to 15 kg / m) added to the finely pulverized concrete was adjusted to 0.015 kg / m. 3 The amount of chloride ions was calculated according to the method according to the embodiment and the method based on the JIS standard. The calculation results of the amount of chloride ions by each method are shown in Table 2.

[0036] The conditions employed in the method according to the embodiment are as follows: Amount of powder sample: 5.0g Amount of purified water: 20.0g Organic acid: 2.0g tartaric acid Neutralizer: 2.0g of calcium carbonate

[0037] [Table 1]

[0038] [Table 2]

[0039] As can be seen from the results in Table 2, the amount of acid solution-soluble chloride ions in Nos. 1 to 6 calculated according to the method of the embodiment and the total amount of chloride ions in Nos. 1 to 6 calculated according to the method based on the JIS standard were almost identical to the amount of chloride ions actually added to each of the pulverized concretes in Nos. 1 to 6.

[0040] Furthermore, the amounts of chloride ions soluble in acid solution for Nos. 1 to 6 calculated according to the method of the embodiment generally agreed with the total amounts of chloride ions for Nos. 1 to 6 calculated according to the method based on JIS standards. Furthermore, the amounts of water-soluble chloride ions calculated according to the method of the embodiment stabilized for each of Nos. 1 to 6 after 20 minutes had passed since the preparation of the sample solution, and the amounts of water-soluble chloride ions for Nos. 1 to 6 after 20 minutes generally agreed with the amounts of hot water-extractable chloride ions for Nos. 1 to 6 calculated according to JIS standards.

[0041] 2-2. Calculation using concrete structure specimens Three core specimens (Nos. 1 to 3) (3 cm diameter x 10 to 11 cm length) were collected from an actual structure (the beam of a pier) and cut at 1 cm intervals. They were then finely pulverized to a particle size of 600 μm or less to adjust the particle size. Sample numbers were assigned based on the depth from the structural surface of the core specimens, and the chloride ion content was calculated according to both the method of the embodiment and the method based on JIS standards. The pH of each sample was also measured to determine the neutralization depth. The calculation results for the chloride ion content using each method are shown in Table 3, and the pH measurement results are shown in Table 4.

[0042] [Table 3]

[0043] [Table 4]

[0044] As can be seen from the results in Table 3, the amounts of chloride ions soluble in acid solution for Nos. 7 to 17 calculated according to the method of the embodiment generally agreed with the total chloride ion amounts for Nos. 7 to 17 calculated according to the JIS standard. Also, the amounts of chloride ions soluble in aqueous solution for Nos. 7 to 17 calculated according to the method of the embodiment generally agreed with the amounts of chloride ions extracted with hot water for Nos. 7 to 17 calculated according to the JIS standard.

[0045] As can be seen from the results in Table 4, it was confirmed that carbonation had progressed in specimens No. 1 to 3 to a depth of 10 mm or less.

[0046] These experimental results indicate that the water-soluble chloride ions calculated by the method according to the embodiment are equivalent to the hot water-extracted chloride ions according to the JIS standard, and that the acid solution-soluble chloride ions calculated by the method according to the embodiment may be an amount of chloride ions equivalent to the total chloride ions according to the JIS standard.

Claims

1. A method for quantifying chloride ions contained in hardened concrete, comprising: preparing a powder sample of the hardened concrete; adding room temperature water to the powder sample and stirring the mixture to prepare a sample solution in which water-soluble components contained in the powder sample are dissolved; inserting a salinity sensor and a reference electrode connected to a voltmeter into the sample solution to measure a first potential difference; adding an organic acid to the sample solution and stirring the mixture to prepare an acidic solution in which the water-soluble components and acid-soluble components contained in the powder sample are dissolved, and then adding a neutralizing agent to prepare a neutralized solution; inserting the salinity sensor and reference electrode into the neutralization solution to measure a second potential difference; calculating the amount of water-soluble chloride ions contained in the hardened concrete based on a mathematical formula showing the relationship between the potential difference and the amount of chloride ions in solution and the first potential difference; calculating an amount of acid solution soluble chloride ions contained in the hardened concrete based on the formula and the second potential difference; A method for quantifying chloride ions, comprising:

2. 10. The method of claim 1, The step of preparing the neutralization solution occurs after the step of measuring the first potential difference. A method for quantifying chloride ions, comprising:

3. 10. The method of claim 1, After the step of preparing the sample solution, a step of measuring the first potential difference is performed using a portion of the sample solution, and a step of preparing the neutralization solution is performed using the remainder of the sample solution. A method for quantifying chloride ions, comprising:

4. The method according to any one of claims 1 to 3, The first potential difference substituted for the variable of the formula in the step of calculating the amount of water-soluble chloride ions is a measurement value after 20 to 240 minutes have elapsed since the insertion of the salinity sensor and the reference electrode. A method for quantifying chloride ions, comprising:

5. 5. The method of claim 4, The first potential difference substituted for the variable of the formula in the step of calculating the amount of water-soluble chloride ions is a measurement value after 20 to 60 minutes have passed since the insertion of the salinity sensor and the reference electrode. A method for quantifying chloride ions, comprising:

6. The method according to any one of claims 1 to 3, The second potential difference substituted for the variable of the formula in the step of calculating the amount of chloride ions soluble in the acid solution is a measurement value after 0 to 10 minutes have elapsed since the insertion of the salinity sensor and the reference electrode. A method for quantifying chloride ions, comprising:

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