Rapid determination method for MB (methylene blue) value of fine aggregate

Abstract

The invention belongs to the technical field of constructional engineering material detection, and particularly relates to a rapid determination method for a methylene blue MB value of fine aggregate. When the method is used for measuring the MB value of the methylene blue, a sample to be measured only needs to be dissolved in a saturated azure I solution, the absorbance value of the sample to be measured is directly measured by using a spectrophotometer, and the corresponding MB value of the methylene blue of the sample to be measured can be calculated by substituting the absorbance value into an obtained absorbance-methylene blue MB value linear regression equation. The operation steps of the method are simple and standardized, error superposition caused by many repetitive manual operations and determination differences is avoided, the determination of the methylene blue MB value can be completed within 10 min in total, and the detection is faster, more efficient and more accurate.

Description

Technical Field

[0001] The present invention belongs to the technical field of building engineering material testing, and specifically relates to a rapid determination method for the methylene blue MB value of fine aggregates. Background Art

[0002] The methylene blue MB value method can roughly determine the content of silt powder in particles with a particle size < 0.075 mm, and truly reflect the cleanliness of fine aggregates to a certain extent. The methylene blue MB value method utilizes the adsorption between methylene blue and clay minerals, and judges the cleanliness of fine aggregates by the amount of methylene blue solution adsorbed.

[0003] The specific operation of the methylene blue MB value method as specified in GB / T 14684-2022 is as follows:

[0004] (1) Quarter the sample to about 400 g, dry it to a constant weight in an oven at (105 ± 5)°C, and after cooling to room temperature, reserve the particles larger than 2.36 mm.

[0005] (2) Weigh 200 g of the sample accurately to 0.1 g, denoted as m 0 . Pour the sample into a beaker containing (500 ± 5) mL of distilled water, and stir it with an impeller stirrer at a speed of (600 ± 60) r / min for 5 min to form a suspension, and then continue to stir at a speed of (400 ± 40) r / min until the end of the test.

[0006] (3) Add 5 mL of methylene blue solution to the suspension, stir at a speed of (400 ± 40) r / min for at least 1 min, and then dip a drop of the suspension with a glass rod. The diameter of the precipitate of the taken suspension drop should be within 8 mm - 12 mm, and drop it on the filter paper. At the same time, the filter paper should be placed in an empty beaker or other support so that the surface of the filter paper does not contact any solid or liquid. If no color halo appears around the precipitate, add another 5 mL of methylene blue solution, continue to stir for 1 min, and then dip a drop of the suspension with a glass rod and drop it on the filter paper. If no color halo still appears around the precipitate, repeat the above steps until a stable light blue color halo of about 1 mm appears around the precipitate. At this time, continue to stir without adding methylene blue solution, and conduct a staining test every 1 min. If the color halo disappears within 4 min, add another 5 mL of methylene blue solution; if the color halo disappears at the 5th min, add another 2 mL of methylene blue solution. In both cases, continue to stir and conduct the staining test until the color halo can last for 5 min.

[0007] (4) Record the total volume (V) of the methylene blue solution added when the color halo lasts for 5 min, accurate to 1 mL.

[0008] (5) Calculate the methylene blue value: MB = V / m 0 ×10;

[0009] In the formula, MB is the methylene blue value, g / kg; V is the total amount of methylene blue solution added, mL; m 0 ——Sample mass, g; 10——The volume of methylene blue solution consumed per kilogram of sample converted into the mass of methylene blue.

[0010] It can be seen from the above operation steps that the MB value method of methylene blue has at least the following defects: First, the MB value method of methylene blue uses the change in solution color as the endpoint of the titration, and the judgment of the endpoint depends on experience. Different operators may have deviations in the judgment of the endpoint due to visual differences and different experiences. For example, for the slight difference in color change, some operators may think that the endpoint has been reached, while other operators may think that titration needs to continue, which will lead to inconsistency in the measurement results and seriously affect the accuracy of the MB value determination of methylene blue. Second, the operation process of this method is quite complicated, which not only takes a long time, but also has harsh operating conditions, and cannot meet the urgent need to improve the detection efficiency in actual engineering. Third, there are many repetitive manual operations, and the differences in these manual operations will have a greater impact on the measurement results. For example, if the titration speed is too fast, the local concentration of methylene blue may be too high, so that the adsorption sites on the surface of some clay minerals are over-occupied, thereby making the MB value high; and if the stirring speed is uneven or insufficient, it may cause insufficient contact between methylene blue and clay minerals, incomplete adsorption, and low MB value. It can be seen that the operation is difficult to be fully standardized, and the various human differences increase the uncertainty of the results.

[0011] In view of this, it is urgent to develop a method that can quickly and accurately obtain the methylene blue MB value of fine aggregate. Summary of the invention

[0012] The purpose of the present invention is to provide a method for quickly determining the methylene blue MB value of fine aggregate in view of the above-mentioned defects. The method innovatively proposes to use Azure I in combination with the absorbance method to determine the methylene blue MB value of fine aggregate. When determining the methylene blue MB value, it is only necessary to dissolve the sample to be tested in a saturated Azure I solution, directly use a spectrophotometer to determine its absorbance value, substitute the absorbance value into the obtained absorbance-methylene blue MB value linear regression equation, and the methylene blue MB value corresponding to the sample to be tested can be calculated.

[0013] The method has simple and standardized operation steps, avoids the error superposition caused by many repetitive human operation differences, does not need to rely on the subjective experience of the operator throughout the operation, and the measurement results are more accurate and stable. In addition, the method of the present invention can achieve the determination of the methylene blue MB value in 10 minutes, and the determination is more efficient.

[0014] AzureⅠ, with a CAS number of 531-55-5, has a molecular formula of C 15 H 16 ClN 3 S, with a molecular weight of 305.83, is a phenothiazine dye. Its molecular structural formula is as follows:

[0015]

[0016] Through research, it is found that when using AzureⅠ to measure the methylene blue MB value of fine aggregates, the change range of its absorbance is large, so that the absorbance can have a good linear fitting with the methylene blue MB value, and the linear correlation coefficient is high.

[0017] The technical solution of the present invention is as follows:

[0018] A rapid determination method for the methylene blue MB value of fine aggregates, which includes the following steps:

[0019] (1) Prepare standard sample solutions:

[0020] Weigh a series of fine aggregate standard samples with the same mass and dry and known methylene blue MB values, and add them to saturated AzureⅠ solutions with the same volume. After stirring evenly, let it stand for 4-5 minutes to obtain each standard sample solution. The drying of the fine aggregate standard sample can be carried out by air drying or low-temperature drying at 35-45°C. Drying within this temperature range can avoid the problem of interfering with the measurement accuracy caused by the destruction of the adsorption of clay powder due to high temperature.

[0021] Among them, 40.0-75.0 mL of saturated AzureⅠ solution is used per gram of fine aggregate standard sample. Through repeated research, it is found that when measuring the methylene blue MB value of fine aggregates according to the method steps of the present invention, the fine aggregate standard sample and the saturated AzureⅠ solution need to meet the above-mentioned ratio standard to ensure that the absolute value of the correlation coefficient of the absorbance-methylene blue MB value standard curve is greater than 0.96, thereby ensuring the accuracy of the final measurement result.

[0022] The current methylene blue method requires that the particle size of the fine aggregate sample ≤ 2.36 mm and the mass of the sample is 200 g. The measurement method of the present invention is applicable to fine aggregates of all particle sizes, that is, as long as the particle size < 4.75 mm according to the definition of fine aggregates, this measurement method can be used.

[0023] (2) Plot the standard curve:

[0024] The absorbance values of each standard sample solution were measured using a spectrophotometer, and the data were recorded. A standard curve was plotted with the absorbance values on the abscissa and the methylene blue MB values on the ordinate. When plotting the standard curve, the average of the absorbance values measured for the parallel standard samples with the same methylene blue MB value was taken as the absorbance value corresponding to that methylene blue MB value.

[0025] And a linear regression equation between the methylene blue MB value and the absorbance value was obtained by data fitting, and the absolute value of the correlation coefficient > 0.96.

[0026] (3) Preparation of the sample solution to be measured:

[0027] Weigh the dry fine aggregate sample to be measured. The fine aggregate sample to be measured and the fine aggregate standard sample are from the same origin and of the same rock type. Add it to the saturated Azure I solution, stir evenly and let it stand for 5 - 7 min to obtain the sample solution to be measured.

[0028] Among them,

[0029] (4) Determination of the methylene blue MB value of the sample to be measured:

[0030] The absorbance value of the sample solution to be measured was measured using a spectrophotometer. Among them, the measurement wavelength of the spectrophotometer was the same as that in step (2).

[0031] Substitute the measured absorbance value of the sample solution to be measured into the linear regression equation obtained in step (2) to calculate the methylene blue MB value of the sample to be measured.

[0032] Combined with the characteristics of fine aggregates and a large number of experimental studies, it shows that as long as the fine aggregate sample to be measured is from the same origin and of the same rock type as the fine aggregate standard sample, the same standard curve can be used. Each time of measurement only needs to measure the absorbance of the fine aggregate sample to be measured according to the described steps, and there is no need to redraw the standard curve.

[0033] The method for determining the methylene blue MB value described in the present invention can first classify according to the rock type and origin of the fine aggregates, establish a standard curve library for different types of fine aggregates according to step (1) in the method. Then, according to the origin and rock type of the sample to be measured entrusted, find the standard curve that is from the same origin and of the same rock type as it. Then, only need to measure the absorbance value of the sample solution to be measured according to the described operation steps, substitute it into the linear regression equation of the corresponding standard curve to directly obtain the result, without having to draw the standard curve every time of measurement, avoiding the extra consumption of measurement time. It can be seen that the determination method described in the present invention can be widely applied to fine aggregates from different origins and different rock types.

[0034] In the present invention, for the rapid determination method of the methylene blue MB value of the fine aggregates, the methylene blue MB values of the series of fine aggregate standard samples in step (1) are in the range of 0.0 - 3.5.

[0035] In the present invention, for the rapid determination method of the methylene blue MB value of fine aggregate, the known series of methylene blue MB values in step (1) are consecutive arithmetic progressions.

[0036] In the present invention, for the rapid determination method of the methylene blue MB value of fine aggregate, the saturated Azure I solution is prepared through the following steps: Add an excessive amount of Azure I solid to distilled water at 20 - 25°C, stir well, let it stand for at least 24 h, and take the supernatant to obtain the saturated Azure I solution. A large amount of powdered Azure I solid settling at the bottom of the solution indicates that the solution is saturated, and the supernatant can be taken. When the temperature is controlled within the range of 20 - 25°C, the solubility of Azure I changes little, and the deviation of the saturated solution within this temperature range will not affect the test results.

[0037] In the present invention, for the rapid determination method of the methylene blue MB value of fine aggregate, at least three parallel standard samples are prepared for each methylene blue MB value in step (1).

[0038] In the present invention, for the rapid determination method of the methylene blue MB value of fine aggregate, the stirring speed in steps (1) and (3) is 400 - 500 r / min, and the stirring time is 5 - 7 min. Stirring can be carried out using an impeller stirrer to fully disperse the soil particles in water. This stirring speed range can ensure that the finer particles in the fine aggregate are completely suspended in the solution, while the coarser particles still sink to the bottom, so that the fine powder can better fully adsorb Azure I, and the coarser particles sinking to the bottom reduce the influence on the test. If the stirring speed is too fast, the coarser particles will also be suspended in the solution, and some coarser particles will also adsorb a certain amount of Azure I, resulting in a larger methylene blue MB value measured in the test; if it is too slow, the stirring ability is insufficient, and some fine powder will also sink to the bottom, resulting in insufficient participation in the adsorption process and a smaller methylene blue MB value measured.

[0039] In the present invention, for the rapid determination method of the methylene blue MB value of fine aggregate, 60 mL of saturated Azure I solution is used for each gram of the fine aggregate standard sample in step (1). For example, 20 g of the standard fine aggregate sample is paired with 1200 mL of saturated Azure I solution.

[0040] In the present invention, for the rapid determination method of the methylene blue MB value of fine aggregate, the wavelength for measuring the absorbance value by the spectrophotometer in steps (2) and (4) is 420 - 450 nm. Within this measurement wavelength range, the absorbance value is positively correlated with the methylene blue MB value.

[0041] In the present invention, for the rapid determination method of the methylene blue MB value of fine aggregate, the wavelength for measuring the absorbance value by the spectrophotometer in steps (2) and (4) is 620 - 650 nm. Within this measurement wavelength range, the absorbance value is negatively correlated with the methylene blue MB value.

[0042] In this measurement method, as the methylene blue MB value increases in the sample solution obtained by dissolving fine aggregate with saturated Azure I solution, the color of the solution can span from blue to red, and accordingly, the absorbance has a large change range. This enables a wide wavelength selection range applicable to the measurement method of the present invention. Under the wavelength conditions of 420 - 450 nm (blue light wavelength) or 620 - 650 nm (red light wavelength), the methylene blue MB value of the corresponding fine aggregate sample to be measured can be obtained from the measured absorbance. The large change range of absorbance reduces the influence of absorbance measurement error on the determination result of the methylene blue MB value, and the standard curve of absorbance - methylene blue MB value drawn is more accurate.

[0043] In the present invention, for the rapid measurement method of the methylene blue MB value of fine aggregate, after preparing the standard sample solution and the sample solution to be measured, the absorbance value of the sample solution is measured using a spectrophotometer within 30 minutes.

[0044] The beneficial effects of the present invention are as follows: The rapid measurement method of the methylene blue MB value of fine aggregate described in the present invention innovatively proposes to use Azure I and combine with the absorbance method to measure the methylene blue MB value of fine aggregate. When measuring the methylene blue MB value, only need to dissolve the sample to be measured in saturated Azure I solution, directly use a spectrophotometer to measure its absorbance value, and substitute this absorbance value into the obtained linear regression equation of absorbance - methylene blue MB value, then the methylene blue MB value corresponding to the sample to be measured can be calculated.

[0045] The operation steps of the method are simple and standardized, avoiding the error superposition caused by many repetitive manual operations and judgment differences. The whole operation process does not rely on the subjective experience of the operator, and the measurement result is more accurate and stable. In addition, after the sample preparation is completed, this method only needs to stir for about 5 minutes, stand for about 4 minutes, and the spectrophotometer measurement takes less than 1 minute. It can complete the measurement of the methylene blue MB value in less than 10 minutes in total, and the detection is faster, more efficient and accurate. Description of the Drawings

[0046] Figure 1 It is the standard curve graph of absorbance - methylene blue MB value in Example 1.

[0047] Figure 2 It is the standard curve graph of absorbance - methylene blue MB value in Example 2.

[0048] Figure 3 It is the standard curve graph of absorbance - methylene blue MB value in Comparative Example 1.

[0049] Figure 4 It is the standard curve graph of absorbance - methylene blue MB value in Comparative Example 2.

[0050] Figure 5 It is the fitting graph of methylene blue MB value - absorbance in Comparative Example 3.

[0051] Figure 6 It is the fitting graph of absorbance - methylene blue MB value in Comparative Example 4. Specific Embodiments

[0052] The present invention will be described in detail below with reference to the accompanying drawings.

[0053] The detection reagent Azure I used in the examples was purchased from PHYGENE, REF: PH9288 - 10g.

[0054] Example 1

[0055] The rapid determination method of the methylene blue MB value of fine aggregates includes the following steps:

[0056] (1) Preparation of standard sample solutions:

[0057] First, a series of fine aggregate standard samples with methylene blue MB values of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 were prepared. For each methylene blue MB value, at least three parallel samples were prepared, and the absorbance values measured for the standard sample solutions of the three parallel samples were all finally fitted. Each fine aggregate standard sample was air - dried or dried at a low temperature of 35 - 45 °C.

[0058] Weighed each fine aggregate standard sample, with a mass of 20 g each; and added them to each saturated Azure I solution with a volume of 1200 mL. Use an impeller stirrer to stir at 500 r / min for 5 min, and then let it stand for 5 min to obtain each standard sample solution.

[0059] (2) Plotting the standard curve:

[0060] Within 30 minutes after preparing the standard sample solutions, use a spectrophotometer to measure the absorbance value of each standard sample solution at a wavelength of 420 nm, and record the data; use the absorbance value as the abscissa and the methylene blue MB value as the ordinate to plot the standard curve. As Figure 1 shown.

[0061] The linear regression equation of methylene blue MB value and absorbance value was obtained by data fitting: y = 3.25x + 0.12, where x is the absorbance value and y is the methylene blue MB value; the absolute value of the correlation coefficient is 0.979.

[0062] (3) Preparation of the sample solution to be measured:

[0063] Weigh 20 g of the dry fine aggregate sample to be tested and add it to 1200 mL of saturated Azure I solution. After stirring evenly, let it stand for 5 minutes to obtain the sample solution to be tested.

[0064] (4) Determine the methylene blue MB value of the sample to be tested:

[0065] Use a spectrophotometer to measure the absorbance value of the sample solution to be tested at a wavelength of 420 nm, which is 0.22.

[0066] Substitute this absorbance value into the linear regression equation obtained in step (2) to calculate that the methylene blue MB value of the sample to be tested is 0.8

[0067] To verify the accuracy, the sample was tested according to the methylene blue value test method in the standard of JTG 3432-2024 "Test Regulations for Aggregates in Highway Engineering", and the measured methylene blue MB value was 1.0.

[0068] According to the methylene blue test calculation method in the current regulations, when the MB value is 0.8, a total of 15 ml of methylene blue solution is added, and when the MB value is 1.0, a total of 20 ml of methylene blue solution is added. According to the formula in the standard: MB = V / m 0 ×10, two results with a difference in the amount of methylene blue added can be calculated. Since the final judgment of the methylene blue MB value depends on the experience of the tester and the subjectivity influence is relatively large, the specification does not stipulate the repeatability experimental error either. A difference in the amount of methylene blue added in the judgment of the color halo at the end point is acceptable. Therefore, the result measured by the method of the present invention is accurate.

[0069] The fine aggregate measured by this method is the basalt manufactured sand of Chayouhouqi Hengyuan Basalt Mining Co., Ltd. The main production area of this quarry is Wulanchabu City, Inner Mongolia. After establishing the above standard curve, when detecting the mud content of the fine aggregate in this area and of this rock type, the linear regression equation y = 3.25x + 0.12 can be directly used.

[0070] Example 2

[0071] The rapid determination method of the methylene blue MB value of the fine aggregate includes the following steps:

[0072] (1) Prepare the standard sample solution:

[0073] First, prepare a series of fine aggregate standard samples with methylene blue MB values of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 respectively. For each methylene blue MB value, at least three parallel samples are prepared. Each fine aggregate standard sample is air-dried or dried at a low temperature of 35 - 45 °C.

[0074] Weigh each standard sample of fine aggregate separately, with a mass of 20 g each; and add them to each saturated Azure I solution with a volume of 1200 mL. Use an impeller stirrer to stir at 500 r / min for 4 min, and let it stand for 5 min to obtain each standard sample solution.

[0075] (2) Plot the standard curve:

[0076] Within 30 minutes after preparing the standard sample solution, use a spectrophotometer to measure the absorbance value of each standard sample solution at a wavelength of 620 nm, and record the data; use the absorbance value as the abscissa and the methylene blue MB value as the ordinate to plot the standard curve. As Figure 1 shown.

[0077] Obtain the linear regression equation between the methylene blue MB value and the absorbance value by data fitting: y = -3.22x + 3.85, where x is the absorbance value and y is the methylene blue MB value; the absolute value of the correlation coefficient is 0.977.

[0078] (3) Prepare the test sample solution:

[0079] Weigh 20 g of the dry fine aggregate test sample and add it to 1200 mL of saturated Azure I solution. After stirring evenly, let it stand for 5 min to obtain the test sample solution.

[0080] (4) Determine the methylene blue MB value of the test sample:

[0081] Use a spectrophotometer to measure the absorbance value of the test sample solution at a wavelength of 620 nm to be 0.51.

[0082] Substitute this absorbance value into the linear regression equation obtained in step (2) to calculate that the methylene blue MB value of the test sample is 2.2.

[0083] To verify the accuracy, the sample was tested according to the methylene blue value test method in the standard of JTG 3432-2024 "Test Regulations for Aggregates in Highway Engineering", and the measured methylene blue MB value was 2.2, which is the same as the methylene blue MB value measured by the method of the present invention.

[0084] The fine aggregate measured by this method is the basalt manufactured sand from Chayouhouqi Hengyuan Basalt Mining Co., Ltd. The main production area of this quarry is Wulanchabu City, Inner Mongolia. After establishing the above standard curve, when detecting the mud content of fine aggregates in this area and of this rock type, the linear regression equation y = -3.22x + 3.85 can be directly used.

[0085] It can also be seen from Combining Example 1 and Example 2 that for the measurement method described in the present invention, as the methylene blue MB value of the obtained sample solution increases, the change range of the absorbance is relatively large. Under the wavelength conditions of 420 - 450 nm (blue light wavelength) or 620 - 650 nm (red light wavelength), the methylene blue MB value of the corresponding sample to be measured can be obtained through the absorbance. This not only expands the applicable range of this method, but also the results measured at two different wavelengths can be mutually verified, further ensuring the accuracy of the results.

[0086] The following is an example for illustration. Weigh a sample to be measured. According to the operation steps for rapidly measuring the methylene blue MB value of fine aggregate samples to be measured described in the present invention, it is detected that the absorbance of the sample to be measured at a wavelength of 420 nm is 0.27. Then, substitute it into the linear regression equation y = 3.25x + 0.12 obtained from the standard curve plotted at a wavelength of 420 nm, and calculate to obtain the methylene blue MB value of 1.0; it is detected that the absorbance of the sample to be measured at a wavelength of 620 nm is 0.89, substitute it into the linear regression equation y = -3.22x + 3.85 obtained from the standard curve plotted at a wavelength of 620 nm, and calculate to obtain the methylene blue MB value of 1.0; the two are equal.

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 lies in:

[0089] In step (1), 20 g of each fine aggregate standard sample weighed is respectively added to each saturated Azure I solution with a volume of 700 mL, that is, 35 mL of saturated Azure I solution is used per gram of the standard fine aggregate sample. The other operations are the same as those in step (1) of Example 1.

[0090] In step (3), the 20 g of the fine aggregate sample to be measured is added to 700 mL of saturated Azure I solution, and a vane stirrer is used to stir at 500 r / min for 5 min and then left to stand for 5 min to obtain the sample solution to be measured. The other operations are the same as those in step (3) of Example 1.

[0091] The standard curve plotted in this comparative example is as Figure 3 shown.

[0092] Through Figure 3 it can be seen that when the ratio of the fine aggregate sample to the saturated Azure I solution does not follow the standard described in the present invention, the linear correlation coefficient of the relationship equation between the absorbance and the methylene blue MB value plotted is 0.943, which is lower than 0.96. Thus, it cannot be used as a standard curve for the method described in the present invention.

[0093] To verify that the standard curve plotted in this comparative example cannot be used in the method described in the present invention, the following operations are carried out:

[0094] First, weigh the sample to be tested. According to the operation steps for rapidly determining the methylene blue MB value of the fine aggregate sample to be tested described in the present invention, the absorbance of the sample to be tested is detected to be 0.83. Substituting it into the linear regression equation y = 3.03x - 0.03 obtained from the above standard curve, the methylene blue MB value is calculated to be 2.5.

[0095] However, when this sample is tested according to the methylene blue MB value test method in JTG 3432-2024 "Code for Aggregate Tests in Highway Engineering", the measured methylene blue MB value is 1.8. According to the formula in the standard: MB = V / m 0 ×10, it can be calculated that the difference between the two is 15 ml of methylene blue solution. Calculated by adding 5 ml of methylene blue solution each time, it is equivalent to adding 3 more times of methylene blue solution in the result of this method than in the standard test method. Those skilled in the art know that this error is already relatively large, proving that this equation cannot be adopted and the drawn standard curve cannot be used in the method described in the present invention.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is as follows:

[0098] In step (1), 20 g of each fine aggregate standard sample weighed is respectively added to each saturated Azure I solution with a volume of 1600 mL, that is, 80 mL of saturated Azure I solution is used for each gram of standard fine aggregate sample. The other operations are the same as those in step (1) of Example 1.

[0099] In step (3), the 20 g of the fine aggregate sample to be tested weighed is added to 1600 mL of saturated Azure I solution, and a vane stirrer is used to stir at 500 r / min for 5 min and then left standing for 5 min to obtain the sample solution to be tested. The other operations are the same as those in step (3) of Example 1.

[0100] The standard curve drawn in this comparative example is as Figure 4 shown.

[0101] It can be seen through Figure 4 that when the ratio of the fine aggregate sample to the saturated Azure I solution does not conform to the standard described in the present invention, the linear correlation coefficient of the relationship equation between the drawn absorbance and the methylene blue MB value is 0.935, which is lower than 0.96. Thus, it cannot be used as a standard curve in the method described in the present invention.

[0102] To verify that the standard curve drawn in this comparative example cannot be used in the method described in the present invention, the following operations are carried out:

[0103] First, weigh the sample to be tested. According to the operation steps for rapidly determining the methylene blue MB value of the fine aggregate sample to be tested described in the present invention, the absorbance of the sample to be tested is detected to be 0.21. Substituting it into the linear regression equation y = 3.70x + 0.73 obtained from the above standard curve, the methylene blue MB value is calculated to be 1.5.

[0104] However, when testing this sample according to the methylene blue MB value test method in JTG 3432 - 2024 "Test Regulations for Aggregates in Highway Engineering", the measured methylene blue MB value is 2.0. According to the formula in the standard: MB = V / m 0 ×10, it can be calculated that the difference between the two is 10 ml of methylene blue solution. Calculated by adding 5 ml of methylene blue solution each time, it is equivalent to adding 2 more times of methylene blue solution in the result of this method compared to the standard test method. Those skilled in the art know that this error is already relatively large, indicating that this equation cannot be adopted, and the drawn standard curve cannot be used in the method described in the present invention.

[0105] In summary, it can be seen that the ratio standard between the fine aggregate sample and the saturated Azure I solution is also one of the key factors for the accuracy of the determination method of the present invention.

[0106] Comparative Example 3

[0107] In this comparative example, the saturated Azure I solution in Example 1 was respectively replaced with 0.1% methyl green, 0.1% methyl orange, and 0.1% crystal violet, which are common in the laboratory and are also organic dyes, and 0.01 mol / L potassium permanganate with strong oxidizing properties was also used. Other conditions were the same as in Example 1. The obtained methylene blue MB value - absorbance fitting diagram is as Figure 5 shown.

[0108] Through Figure 5 it can be seen that methyl green, methyl orange, and crystal violet have very weak adsorption ability to soil in aqueous solution. As the methylene blue MB value decreases, the change in the absorbance of the solution is irregular and cannot be applied to the determination method of the methylene blue MB value described in the present invention.

[0109] Potassium permanganate has strong oxidizing properties, while soil is a stable substance existing in nature after long - term weathering, and most of it does not have reducibility. The absorbance obtained using potassium permanganate as the detection reagent hardly changes, indicating that it is not feasible to determine the methylene blue MB value using redox characteristics.

[0110] Comparative Example 4

[0111] In this comparative example, the saturated Azure I solution was replaced with the commonly used methylene blue solution with a concentration of 0.02 g / L.

[0112] Methylene blue, its molecular formula is C 16 H 18 ClN 3S, with the structural formula:

[0113]

[0114] Others are the same as in Example 1.

[0115] The obtained absorbance - methylene blue MB value fitting graph is as Figure 6 shown. By Figure 6 It can be seen that when using methylene blue as the solvent to dissolve fine aggregate, the absorbance of the obtained sample solution only varies within the range of 0 - 0.55 AU, and the variation range is smaller than that of saturated Azure I solution (the saturated Azure I solution can vary within the range of 0 - 1 AU).

[0116] From Figure 6 it can be clearly seen that when the absorbance is within 0 - 0.2 AU, the error bars representing the standard deviation of absorbance are longer. That is to say, when the absorbance is small, the repeatability error of the values measured by the spectrophotometer is larger, indicating that the absorbance at 0 - 0.2 AU is prone to inaccurate measurement. When using methylene blue solution as the solvent in the method of the present invention, the variation range of its absorbance is around 0 - 0.55 AU, and for samples with a basic MB value below 1.5, the absorbance is concentrated within 0 - 0.2 AU. It can be seen that when measuring samples with a low MB value, if the commonly used methylene blue solution is used as the solvent in the measurement method of the present invention, the measurement result has a large error and poor accuracy.

[0117] In addition, from Figure 6 it can also be seen that the slope of the fitting equation of methylene blue solution is relatively high, and a small error in absorbance measurement will have a greater impact on the result of methylene blue MB value.

Claims

1. A method for rapidly determining the methylene blue MB value of fine aggregate, characterized in that: The following steps are involved: (1) Preparation of standard sample solution: Weigh a series of fine aggregate standard samples with known methylene blue MB values ​​of the same mass and dry them, add them to the same volume of saturated azure I solution, stir evenly and let stand for 4-5 minutes to obtain standard sample solutions; Among them, each gram of fine aggregate standard sample is prepared with 40.0-75.0mL of saturated Azure I solution; (2) Draw the standard curve: The absorbance value of each standard sample solution was measured by a spectrophotometer, and the data were recorded; a standard curve was drawn with the absorbance value as the horizontal axis and the methylene blue MB value as the vertical axis; The linear regression equation of methylene blue MB value and absorbance value was obtained by data fitting, and the absolute value of the correlation coefficient was >0.96; (3) Prepare the sample solution to be tested: Weigh the dry fine aggregate sample to be tested and add it to the saturated Azure I solution, stir evenly and let it stand for 4-5 minutes to obtain the sample solution to be tested; in, (4) Determine the methylene blue MB value of the sample to be tested: The absorbance value of the sample solution to be tested is measured by a spectrophotometer; wherein the measuring wavelength of the spectrophotometer is the same as the measuring wavelength of step (2); Substitute the measured absorbance value of the sample solution into the linear regression equation obtained in step (2) to calculate the methylene blue MB value of the sample solution.

2. The method for rapid determination of methylene blue MB value of fine aggregate according to claim 1, characterized in that: The methylene blue MB value of the series of fine aggregate standard samples in step (1) is between 0.0 and 3.

5.

3. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: The series of methylene blue MB values ​​known in step (1) is a continuous arithmetic progression.

4. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: The saturated Azure I solution is prepared by the following steps: adding an excess of Azure I solid to distilled water at 20-25° C., stirring thoroughly, standing for at least 24 hours, and taking the supernatant to obtain a saturated Azure I solution.

5. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: In the step (1), at least three parallel standard samples are prepared for each methylene blue MB value.

6. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: The stirring speed in step (1) and step (3) is 400-500 r / min, and the stirring time is 5-7 min.

7. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: In the step (1), 60 mL of saturated Azure I solution is added to each gram of the fine aggregate standard sample.

8. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: The wavelength of the absorbance value measured by the spectrophotometer in the steps (2) and (4) is 420-450nm.

9. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: The wavelength of the absorbance value measured by the spectrophotometer in the steps (2) and (4) is 620-650nm.

10. The method for rapid determination of methylene blue (MB) value of fine aggregate according to claim 1, characterized in that: After the standard sample solution and the sample solution to be tested are prepared, the absorbance value of the sample solution is measured by a spectrophotometer within 30 minutes.

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