Method for rapidly determining silt content in fine aggregate by using azure I

Abstract

The invention belongs to the technical field of constructional engineering material detection, and particularly relates to a method for rapidly determining the silt content in fine aggregate by using azure I. The method comprises the following steps: firstly, preparing a series of standard fine aggregate samples with known silt content, adding the standard fine aggregate samples into each saturated azure I solution, stirring and standing, measuring the absorbance value of the standard fine aggregate samples at the wavelength of 460-470nm or 620-760nm by using a spectrophotometer, drawing a standard curve and obtaining a linear regression equation of the silt content and the absorbance value, and calculating the content of the silt content in the standard fine aggregate samples according to the linear regression equation. The absorbance value is highly linearly related to the silt content. And after measuring the absorbance value, substituting the absorbance value into the obtained linear regression equation to calculate the silt content of the fine aggregate sample to be measured. Compared with an existing determination method, the detection time of the determination method is only 2%-3% of the detection time of the existing method, 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 particularly relates to a method for rapidly determining the mud content in fine aggregate by using Azure I. Background Technique

[0002] In building materials such as concrete and mortar, fine aggregate refers to particulate materials with a particle size less than 4.75 mm, usually including natural sand, artificial sand, etc. In asphalt mixture, fine aggregate refers to natural sand, artificial sand and stone chips with a particle size less than 2.36 mm. Fine aggregate plays a key role in concrete and asphalt mixture, such as filling the voids between coarse aggregates, enhancing the compactness and strength of materials, etc. It is an indispensable part of building materials, and its quality and performance directly affect the quality of the final product. One of the main requirements for the quality of fine aggregate is to control the mud content of fine aggregate. The mud content of fine aggregate refers to the content of particles with a particle size less than 0.075 mm in fine aggregate, usually expressed as a mass percentage. Excessive mud content will affect the performance of concrete and mortar, so it needs to be strictly controlled. Different projects have different requirements for the mud content of fine aggregate. For example, the mud content of fine aggregate for concrete generally does not exceed 3%; the mud content of fine aggregate for mortar generally does not exceed 5%.

[0003] Thus, in order to control the mud content of fine aggregate to meet the different requirements of each project, how to accurately determine the mud content of fine aggregate has become an indispensable and important link in engineering construction. By measuring the mud content of fine aggregate, the selection and use of fine aggregate during construction can be guided, thus ensuring the quality and safety of the project.

[0004] Currently, the specific operation for mud content determination specified in GB / T14684-2022 is as follows: (1) Sampling, and reducing the sample to about 1100 g, drying it to constant weight in an oven at (105±5)°C, and after cooling to room temperature, dividing it into two equal parts for standby. (2) Weigh 500 g of the sample, accurate to 0.1 g, and record it as m s0Pour the test sample into the elutriation container, inject clear water so that the water surface is about 150 mm higher than the sample surface. After stirring evenly, soak for 2 h, and then wash the sample by hand in the water to separate the dust, silt and clay from the sand grains. Place the 1.18 mm sieve on top of the 75 μm sieve, and slowly pour the turbid water into the set to filter out the particles smaller than 75 μm. The two sides of the sieve should be wetted with water before the test, and the loss of sand grains should be prevented throughout the process. (3) Inject clear water into the container again and repeat the above operation until the water in the container is visually clear. (4) Wash the remaining fine particles with water, place the 75 μm sieve in the water so that the water surface is higher than the upper surface of the sand grains in the sieve, and shake back and forth to thoroughly wash off the particles smaller than 75 μm. Then pour the sieve residues of the two sieves and the washed test sample in the cleaning container into a shallow pan, dry it to a constant weight in an oven at (105 ± 5) °C, and after cooling to room temperature, weigh its mass (m), accurate to 0.1 g.

[0005] It can be seen that according to the requirements of the above-mentioned existing mud content test method, the test sample needs to be immersed in water for 2 h first, then washed, and finally dried to a constant weight (generally, the drying time is not less than 4 h). It takes at least more than 6 h to complete the mud content detection, which is time-consuming and does not meet the requirements of rapid and efficient engineering detection at present. Especially when a large number of fine aggregate samples to be tested are entrusted at one time, repeating the above method will take even longer, which will greatly reduce the timeliness of issuing the test results of the samples. If the timeliness is to be ensured, a large amount of manpower needs to be occupied and consumed to jointly participate in the mud content detection test, and the labor cost of detection is too high.

[0006] Therefore, there is an urgent need for a method that can quickly, efficiently and accurately determine the mud content in fine aggregates. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for quickly determining the mud content in fine aggregates by using Azure I in view of the above-mentioned existing defects. This method innovatively proposes to use Azure I to determine the mud content of aggregates. By using the method of the present invention, the mud content detection can be completed in 10 minutes to obtain the test results. Compared with the traditional method, it only requires 2%-3% of the detection time of the current method, and the detection is faster, more efficient and accurate.

[0008] The technical solution of the present invention is as follows:

[0009] A method for quickly determining the mud content in fine aggregates by using Azure I, which includes the following steps:

[0010] (1) Draw a standard curve:

[0011] Prepare a standard fine aggregate sample:

[0012] First, prepare a series of dried standard fine aggregate samples with known mud contents, and for each mud content, at least three parallel samples should be prepared;

[0013] Then, weigh out the same mass of each standard fine aggregate sample for standby.

[0014] Prepare a saturated Azure I solution:

[0015] Add an excessive amount of Azure I solid to distilled water at 15 - 25°C, stir well, and let it stand for at least 24 h. Then take the supernatant to obtain a saturated Azure I solution for standby. Letting it stand for at least 24 h can ensure the full dissolution of the Azure I solid. A large amount of powdered Azure I solid settling at the bottom of the solution indicates that the solution is saturated, and then the supernatant can be taken.

[0016] Azure I, 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:

[0017]

[0018] When the temperature is controlled within the range of 15 - 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.

[0019] Prepare a suspension of standard fine aggregate samples:

[0020] Add the weighed standard fine aggregate samples to the saturated Azure I solution respectively, stir for 4 - 5 min and then let it stand for 4 - 5 min; among them, 33.5 - 66.5 mL of saturated Azure I solution is used for each gram of standard fine aggregate sample.

[0021] Through research, it is found that when using Azure I to determine the mud content of fine aggregates, the absorbance range of the obtained sample solution is large, so that the absorbance can have a good linear fitting relationship with the mud content, and the linear correlation coefficient is high.

[0022] During the research process, it is found that the ratio relationship between the sample and the saturated Azure I solution directly affects the correlation coefficient of the standard curve. Considering the mud content range of the manufactured sand used in engineering practice and whether the change in absorbance is significant, it is found that when 33.5 - 66.5 mL of saturated Azure I solution is used for each gram of standard fine aggregate sample, regardless of whether it is fine aggregate with a large mud content and strong adsorption ability or fine aggregate with a small mud content and weak adsorption ability, the absolute value of the correlation coefficient of the drawn standard curve can be guaranteed to be > 0.98. Moreover, on the premise of ensuring the measurement accuracy, it can also make the mud content range measured by the method of the present invention larger.

[0023] Adjust within the range of 33.5 - 66.5 mL of the dosage of the saturated Azure I solution according to the correlation coefficient of the standard curve. If the absolute value of the correlation coefficient < 0.98 and the adsorption capacity of the tested sample is strong, it can be adjusted to 66.5 mL of the saturated Azure I solution per gram of the standard fine aggregate sample; otherwise, it can be adjusted to 33.5 mL of the saturated Azure I solution per gram of the standard fine aggregate sample; until the absolute value of the correlation coefficient of the fitted equation > 0.98.

[0024] Draw the standard curve:

[0025] Use a spectrophotometer to measure the absorbance value of each standard fine aggregate sample suspension, and record the data; use the absorbance value as the abscissa and the mud content as the ordinate to draw the standard curve; when drawing the standard curve, the average value of the measured absorbance values of the parallel samples with the same mud content is taken as the corresponding absorbance value of the mud content.

[0026] And obtain the linear regression equation of the mud content and the absorbance value through data fitting, and the absolute value of the correlation coefficient > 0.98.

[0027] (2) Rapidly determine the mud content of the fine aggregate sample to be tested:

[0028] First, weigh the dry fine aggregate sample to be tested; the fine aggregate sample to be tested and the standard fine aggregate sample are from the same origin and of the same rock type.

[0029] Then, add the weighed fine aggregate sample to be tested into the saturated Azure I solution, stir for 4 - 5 minutes and then stand for 4 - 5 minutes to obtain the fine aggregate sample suspension to be tested;

[0030] Among them,

[0031] Finally, use a spectrophotometer to measure the absorbance value of the fine aggregate sample suspension to be tested under the same wavelength condition as measuring the absorbance value of the standard fine aggregate sample suspension in step (1);

[0032] Substitute the measured absorbance value of the fine aggregate sample suspension to be tested into the linear regression equation obtained in step (1) to calculate the mud content of the fine aggregate sample to be tested.

[0033] Combined with the characteristics of the fine aggregate and a large number of experimental studies, it shows that as long as the fine aggregate sample to be tested is from the same origin and of the same rock type as the standard fine aggregate sample, the same standard curve can be used, and each time the measurement only needs to measure the absorbance of the fine aggregate sample to be tested according to the above steps, without redrawing the standard curve.

[0034] The mud content determination method described in the present invention can first classify according to the rock type and origin of the fine aggregate, and establish a standard curve library for different types of fine aggregates according to step (1) in the method. At that time, according to the origin and rock type of the entrusted sample to be tested, find the standard curve of the same origin and rock type as it, and then only need to measure the absorbance value of the solution of the sample to be tested according to the described operation steps, and substitute it into the linear regression equation of the corresponding standard curve to directly obtain the result, without having to draw a standard curve every time, avoiding the additional consumption of measurement time. It can be seen that the determination method described in the present invention can be widely applied to fine aggregates of different origins and different rock types.

[0035] In the present invention, for the method of rapidly determining the mud content in fine aggregates using Azure I, the mud content of the series of standard fine aggregate samples in step (1) is continuously increasing by X 1 、X 2 、X 3 ……X n ; where X 1 ≥0%, X n ≤20%. This mud content range covers the values that may appear in actual applications. In the actual detection process, it can be determined according to the mud content range of the fine aggregates that are often detected locally. The mud content of the manufactured sand and natural sand used in actual engineering is basically all between 0% and 18%. It can be seen that this method has met the engineering requirements.

[0036] Furthermore, the incremental increase in the mud content of the series of standard fine aggregate samples is 1%.

[0037] In the present invention, for the method of rapidly determining the mud content in fine aggregates using Azure I, the standard fine aggregate samples with known mud content in step (1) are air-dried or dried at a low temperature of 35 - 45 °C. Drying within this temperature range can avoid the problem of interfering with the measurement accuracy due to the destruction of the adsorption property of the mud powder at high temperatures.

[0038] In the present invention, for the method of rapidly determining the mud content in fine aggregates using Azure I, when preparing the suspension of the standard fine aggregate sample and the suspension of the fine aggregate sample to be tested in step (1), the stirring speed is 450 - 550 r / 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 measured mud content 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 measured mud content.

[0039] In the present invention, in the method for rapidly determining the mud content in fine aggregate by using Azure I, when preparing the standard fine aggregate sample suspension in step (1), it is in accordance with the standard of 40 mL of saturated Azure I solution per gram of the standard fine aggregate sample. For example, 20 g of the standard fine aggregate sample is paired with 800 mL of saturated Azure I solution.

[0040] Similarly, when preparing the fine aggregate sample suspension to be measured in step (1), it is in accordance with the standard of 40 mL of saturated Azure I solution per gram of the fine aggregate sample to be measured. For example, 20 g of the fine aggregate sample to be measured is paired with 800 mL of saturated Azure I solution.

[0041] In the present invention, in the method for rapidly determining the mud content in fine aggregate by using Azure I, the wavelength for measuring the absorbance value by the spectrophotometer in steps (1) and (2) is 460 - 470 nm. In this measurement wavelength range, the absorbance value is positively correlated with the mud content.

[0042] In the present invention, in the method for rapidly determining the mud content in fine aggregate by using Azure I, the wavelength for measuring the absorbance value by the spectrophotometer in steps (1) and (2) is 620 - 760 nm. In this measurement wavelength range, the absorbance value is negatively correlated with the mud content.

[0043] In the determination method of the present invention, the saturated Azure I solution is used to dissolve the fine aggregate. The prepared suspension, with the increase of the mud content, its solution color can achieve a large span from blue to pink (as Figure 8 shown), thereby enabling a large change range of the corresponding absorbance. This brings the following advantages: First, the wavelength selection range applicable to the determination method of the present invention is wide, and the mud content of the corresponding fine aggregate sample to be measured can be obtained through the measured absorbance under the wavelength conditions of 460 - 470 nm (blue light wavelength) or 620 - 760 nm (red light wavelength). Second, the absorbance change range is large, reducing the influence of the absorbance measurement error on the mud content determination result, and the standard curve of absorbance - mud content drawn is more accurate.

[0044] In addition, through a large number of experimental explorations, the shelf life of the saturated Azure I solution used in the determination method is 14 d. If 0.01 - 0.02 g of antioxidant is added to each liter of saturated Azure I solution, the shelf life of the saturated Azure I solution can be extended to 28 d. The antioxidant can be selected from at least one of tert - butylhydroquinone (TBHQ), ascorbic acid, butylated hydroxyanisole (BHA) or dibutylhydroxytoluene (BHT).

[0045] The beneficial effects of the present invention are as follows: the method of the present invention first prepares a series of standard fine aggregate samples with known mud content, adds them to each saturated Azure I solution, stirs and allows to stand, and then uses a spectrophotometer to measure the absorbance value at a wavelength of 460-470nm or 620-760nm, draws a standard curve and obtains a linear regression equation between the mud content and the absorbance value, and there is a high linear correlation between the absorbance value and the mud content. When the mud content of the fine aggregate sample to be measured is measured, it is only necessary to adopt the same detection steps, measure its absorbance value, and substitute it into the linear regression equation obtained above, so as to quickly calculate the mud content of the fine aggregate sample to be measured.

[0046] The determination method of the present invention improves the accuracy and reliability of the determination results by drawing a standard curve and using a spectrophotometer for precise measurement, and can meet the precision requirements of aggregate mud content detection in roads and construction projects. In addition, after completing sample preparation, this method only needs to stir for about 5 minutes, let it stand for about 5 minutes, and the spectrophotometer detection takes about 1 minute. The mud content detection can be completed in less than 15 minutes in total. The absorbance of the measured fine aggregate sample to be tested is brought into the linear regression equation to calculate the mud content of the sample to be tested. Compared with the traditional detection method that requires at least 6 hours of detection time, the detection time of the determination method of the present invention is only 2%-3% of the detection time of the current method, and the detection is faster, more efficient and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the absorbance-mud content standard curve in Example 1.

[0048] Figure 2 This is the absorbance-mud content standard curve in Example 2.

[0049] Figure 3 This is the standard curve of absorbance-mud content in Comparative Example 1.

[0050] Figure 4 This is the standard curve of absorbance-mud content in Comparative Example 2.

[0051] Figure 5 This is the mud content-absorbance fitting diagram in Comparative Example 3.

[0052] Figure 6 This is the absorbance-mud content fitting diagram in Comparative Example 4.

[0053] Figure 7 This is a color comparison chart of sample solutions with different mud contents in Comparative Example 4.

[0054] Figure 8 This is a graph showing the color change from blue to pink of the solution of the present invention as the sand equivalent increases. DETAILED DESCRIPTION

[0055] The present invention will be described in detail below with reference to the accompanying drawings.

[0056] The detection reagent Azure I used in the examples was purchased from PHYGENE, REF: PH9288-10g.

[0057] Example 1

[0058] The method for rapidly determining the mud content in fine aggregate using Azure I is as follows in specific operation steps:

[0059] The first step: Draw a standard curve

[0060] (1) Prepare standard fine aggregate samples:

[0061] First, prepare a series of standard fine aggregate samples with mud contents of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15% respectively, and at least three parallel samples should be prepared for each mud content. Each standard fine aggregate sample is air-dried or dried at a low temperature of 35-45 °C.

[0062] Then, weigh each standard fine aggregate sample, with a mass of 20 g each; reserve for use.

[0063] (2) Prepare a saturated Azure I solution:

[0064] Add an excessive amount of Azure I solid to distilled water at 25 °C, stir well, let it stand for 24 h, and take the supernatant to obtain a saturated Azure I solution, reserve for use.

[0065] (3) Prepare a suspension of standard fine aggregate samples:

[0066] Add the weighed 20 g standard fine aggregate samples to the saturated Azure I solutions with a volume of 800 mL each, stir with an impeller stirrer at 500 r / min for 5 min, and let it stand for 5 min to obtain suspensions of standard fine aggregate samples.

[0067] (4) Draw a standard curve:

[0068] Within 30 minutes after preparing the suspensions of standard fine aggregate samples, use a spectrophotometer to measure the absorbance values of each suspension of standard fine aggregate samples at a wavelength of 460 nm, record the data; use the absorbance values as the abscissa and the mud content as the ordinate to draw a standard curve, as Figure 1 shown.

[0069] Obtain the linear regression equation of the mud content and the absorbance value by data fitting: y = 12.97x + 4.44, where x is the absorbance value and y is the mud content; the absolute value of the correlation coefficient is 0.99.

[0070] Step 2: Rapidly determine the mud content of the fine aggregate sample to be tested:

[0071] (1) Weigh 20 g of the representative dry fine aggregate sample to be tested;

[0072] (2) Add the weighed 20 g of the fine aggregate sample to be tested into 800 mL of saturated Azure I solution, stir with an impeller stirrer at 500 r / min for 5 min, and let it stand for 5 min to obtain a suspension of the fine aggregate sample to be tested.

[0073] The absorbance value of the suspension of the fine aggregate sample to be tested at 460 nm measured by a spectrophotometer is 0.412. Substitute this absorbance value into the linear regression equation obtained in the first step: y = 12.97x + 4.44, and calculate that the mud content of this fine aggregate to be tested is 9.8%.

[0074] To verify the accuracy, the sample was tested according to the mud content test method in GB / T 14684-2022 "Sand for construction", and the measured mud content was 9.7%.

[0075] It can be seen that the mud content of the sample measured by the measurement method described in the present invention is 9.8%, and the mud content measured by the mud content test in the current specified standard is 9.7%. The difference between the two is only 0.1%, meeting the requirement that the allowable error of mud content measurement should not be greater than 0.5%, which proves that the mud content measured by this method is very accurate.

[0076] The fine aggregate measured by this method is the natural sand from Jinan Xing'an Stone Factory. The main production areas of the natural sand in this stone factory are Jinan and Tai'an. After establishing the above standard curve, when detecting the mud content of the fine aggregate in this area and this rock type, the linear regression equation y = 12.97x + 4.44 can be directly used.

[0077] Example 2

[0078] The method for rapidly determining the mud content in fine aggregate using Azure I is specifically operated as follows:

[0079] First step: Plot the standard curve

[0080] (1) Prepare standard fine aggregate samples:

[0081] First, prepare a series of standard fine aggregate samples with mud contents of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15% respectively. At least three parallel samples should be prepared for each mud content. Each standard fine aggregate sample is air-dried or dried at a low temperature of 35 - 45 °C.

[0082] Then, weigh each standard fine aggregate sample, with a mass of 20 g each; reserve for use.

[0083] (2) Prepare a saturated Azure I solution:

[0084] Add an excessive amount of solid Azure I to distilled water at 25°C. After stirring well, let it stand for 24 h, and then take the supernatant to obtain a saturated Azure I solution for standby.

[0085] (3) Prepare a suspension of standard fine aggregate samples:

[0086] Add 20 g of each weighed standard fine aggregate sample to each 800 mL of the saturated Azure I solution respectively. Use an impeller stirrer to stir at 500 r / min for 5 min, and then let it stand for 5 min to obtain suspensions of each standard fine aggregate sample.

[0087] (5) Plot the standard curve:

[0088] Within 30 minutes after preparing the suspensions of each standard fine aggregate sample, use a spectrophotometer to measure the absorbance value of each suspension at a wavelength of 650 nm, and record the data. Plot the standard curve with the absorbance value as the abscissa and the mud content as the ordinate, as Figure 2 shown.

[0089] Obtain the linear regression equation of the mud content and the absorbance value by data fitting: y = -14.71x + 16.10, where x is the absorbance value and y is the mud content; the absolute value of the correlation coefficient is 0.99.

[0090] Second step, quickly determine the mud content of the fine aggregate sample to be tested:

[0091] (1) Weigh 20 g of a representative dry fine aggregate sample to be tested;

[0092] (2) Add the 20 g of the weighed fine aggregate sample to be tested to 800 mL of the saturated Azure I solution. Use an impeller stirrer to stir at 500 r / min for 5 min, and then let it stand for 5 min to obtain a suspension of the fine aggregate sample to be tested.

[0093] The absorbance value of the suspension of the fine aggregate sample to be tested at 650 nm measured by a spectrophotometer is 0.435. Substitute this absorbance value into the linear regression equation obtained in the first step: y = -14.71x + 16.10, and calculate that the mud content of this fine aggregate sample to be tested is 9.7%.

[0094] To verify the accuracy, test the sample according to the mud content test method in GB / T 14684-2022 "Sand for construction", and the measured mud content is 9.7%.

[0095] It can be seen that the mud content of the sample measured by the measurement method described in the present invention is 9.7%, and the mud content measured by the mud content test in the current specified standard is also 9.7%. The results are exactly the same, which proves that the mud content measured by this method is very accurate.

[0096] The fine aggregate measured by this method is the natural sand from Jinan Xing'an Stone Factory. The main production areas of the natural sand in this stone factory are Jinan and Tai'an. 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 = -14.71x + 16.10 can be directly used.

[0097] It can also be seen from combining Example 1 and Example 2 that for the measurement method using Azure I described in the present invention, as the mud content of the obtained fine aggregate sample suspension increases, the change range of the absorbance has a relatively large span. Under the wavelength conditions of 460 - 470 nm (blue light wavelength) or 620 - 760 nm (red light wavelength), the mud content of the corresponding fine aggregate sample to be measured can be obtained through the absorbance. In this way, not only the applicable range of this method is expanded, but also the results measured at two different wavelengths can be mutually verified, further ensuring the accuracy of the results.

[0098] The following is an example for illustration. Weigh a sample to be measured. According to the operation steps for quickly measuring the mud content of the fine aggregate sample to be measured described in the present invention, the absorbance of the sample to be measured at a wavelength of 460 nm is detected to be 0.73. Then, substitute it into the linear regression equation y = 12.97x + 4.44 obtained from the standard curve plotted at a wavelength of 460 nm, and calculate that the mud content of the sample to be measured is 13.9%. The absorbance of the sample to be measured at a wavelength of 650 nm is detected to be 0.16. Substitute it into the linear regression equation y = -14.71x + 16.10 obtained from the standard curve plotted at a wavelength of 650 nm, and calculate that the mud content of the sample to be measured is 13.7%. The difference between the two is 0.2%, meeting the requirement that the allowable error of mud content measurement should not be greater than 0.5%, which proves the accuracy of the measurement result of the method described in the present invention.

[0099] Comparative Example 1

[0100] The difference between this comparative example and Example 1 is as follows:

[0101] In the first-step operation, 20 g of each standard fine aggregate sample weighed is respectively added to each saturated Azure I solution with a volume of 1360 mL, that is, 68 mL of saturated Azure I solution is allocated to each gram of the standard fine aggregate sample. The other operations are the same as the first-step operation of Example 1.

[0102] In the second operation, add the weighed 20 g of the fine aggregate sample to be tested into 1360 mL of saturated Azure I solution, stir with an impeller stirrer at 500 r / min for 5 min, and let it stand for 5 min to obtain a suspension of the fine aggregate sample to be tested. The other operations are the same as those in the second step of Example 1.

[0103] The standard curve drawn in this comparative example is as Figure 3 shown.

[0104] Through Figure 3 It can be seen 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 absorbance and the mud content drawn is 0.95, which is lower than 0.98. Thus, it cannot be used as a standard curve for the method described in the present invention.

[0105] In order to verify that the standard curve drawn in this comparative example cannot be used for the method described in the present invention, the following operations are carried out:

[0106] First, weigh the sample to be tested. According to the operation steps for quickly determining the mud content 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 0.22, and substituting it into the linear regression equation of the above standard curve: y = 10.18x + 6.53; the calculated mud content is 8.8%.

[0107] However, when this sample is tested according to the mud content test method in GB / T 14684-2022 "Sand for construction", the measured mud content is 10.1%, with a difference of 1.3% between the two, which does not meet the requirement that the allowable error of mud content determination should not be greater than 0.5%. This proves that this equation cannot be adopted, and the standard curve drawn cannot be used for the method described in the present invention.

[0108] Comparative Example 2

[0109] The difference between this comparative example and Example 1 is as follows:

[0110] In the first operation, add the weighed 20 g of each standard fine aggregate sample into each saturated Azure I solution with a volume of 630 mL respectively, that is, 31.5 mL of saturated Azure I solution is used for each gram of the standard fine aggregate sample. The other operations are the same as those in the first step of Example 1.

[0111] In the second operation, add the weighed 20 g of the fine aggregate sample to be tested into 630 mL of saturated Azure I solution, stir with an impeller stirrer at 500 r / min for 5 min, and let it stand for 5 min to obtain a suspension of the fine aggregate sample to be tested. The other operations are the same as those in the second step of Example 1.

[0112] The standard curve drawn in this comparative example is as Figure 4 shown.

[0113] By Figure 4 It can be seen 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 absorbance and the mud content drawn is 0.94, which is lower than 0.98. This equation cannot be adopted and cannot be used as a standard curve for the method described in the present invention.

[0114] In order 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:

[0115] First, weigh the sample to be tested. According to the operation steps for rapidly determining the mud content 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 0.73. Substitute it into the linear regression equation of the above standard curve: y = 10.59x + 4.52; the calculated mud content is 12.3%.

[0116] However, when this sample is detected according to the mud content test method in GB / T 14684-2022 "Sand for construction", the measured mud content is 10.5%, with a difference of 1.8% between the two, which does not meet the requirement that the allowable error of mud content determination should not be greater than 0.5%. This proves that this equation cannot be adopted and the standard curve drawn cannot be used in the method described in the present invention.

[0117] 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.

[0118] Comparative Example 3

[0119] In this comparative example, the saturated Azure I solution in Example 1 was respectively replaced with 0.1% methyl orange, 0.1% acid fuchsin, 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 are the same as in Example 1. The obtained fitting diagram of mud content - absorbance is as Figure 5 shown.

[0120] By Figure 5 It can be seen that the adsorption ability of methyl orange, acid fuchsin, and crystal violet to soil in aqueous solution is very weak. As the mud content increases, the change in the absorbance of the solution is irregular and cannot be applied to the method for determining the mud content described in the present invention.

[0121] Potassium permanganate has strong oxidizing properties, while soil is a substance that stably exists in nature after long-term weathering, and most of it does not have reducibility. The absorbance obtained using potassium permanganate as a detection reagent hardly changes, indicating that it is not feasible to determine the mud content using redox properties.

[0122] Comparative Example 4

[0123] 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.

[0124] Methylene blue, whose molecular formula is C 16 H 18 ClN 3 S, and its structural formula is:

[0125]

[0126] Other conditions were the same as in Example 1.

[0127] The obtained fitting graph of absorbance - mud content is as Figure 6 shown. It can be seen from Figure 6 that when methylene blue is used as a solvent to dissolve fine aggregates, the absorbance of the obtained sample solution only varies within the range of 0 - 0.45 AU, and the variation range is smaller than that of the saturated Azure I solution (the saturated Azure I solution can vary within the range of 0 - 1 AU).

[0128] It can be clearly seen from Figure 6 that when the absorbance is within 0 - 0.1 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 value measured by the spectrophotometer is large, indicating that the absorbance at 0 - 0.1 AU is prone to inaccurate measurement. When methylene blue solution is used as a solvent in the method of the present invention, the variation range of its absorbance is around 0 - 0.45 AU, and the absorbance of samples with a basic mud content of less than 8% is concentrated within 0 - 0.1 AU. It can be seen that for samples with a low mud content, if the commonly used methylene blue solution is used as a solvent in the determination method of the present invention, the error of the measurement result is large and the accuracy is poor.

[0129] In addition, it can also be seen from Figure 6 that the slope of the fitting equation of the methylene blue solution is relatively high, and a small error in absorbance measurement will have a greater impact on the mud content result.

[0130] As Figure 7 shown, it can be seen that as the mud content increases, if the methylene blue solution is used in the determination method of the present invention, the color of the obtained sample solution can only change from dark blue to light blue. Therefore, when detected by a spectrophotometer, only the blue light wavelength of about 460 nm can be used, and the red light wavelength of 650 nm cannot be used for measurement. Single - wavelength measurement cannot, like the present invention, use the results measured by two wavelengths to verify the accuracy with each other.

Claims

1. A method for rapidly determining the mud content in fine aggregate using Azure I, characterized in that: The following steps are involved: (1) Draw a standard curve: Preparation of standard fine aggregate samples: First, prepare a series of dried standard fine aggregate samples with known mud content, with at least three parallel samples prepared for each mud content; Then, weigh the same mass of each standard fine aggregate sample and set aside; Prepare saturated Azure I solution: Add excess Azure I solid to distilled water at 15-25°C, stir thoroughly, let stand for at least 24 hours, take the supernatant to obtain a saturated Azure I solution for later use; Prepare standard fine aggregate sample suspension: Add the weighed standard fine aggregate samples to the saturated Azure I solution respectively, stir for 4-5 minutes and then let stand for 4-5 minutes; wherein, 33.5-66.5 mL of saturated Azure I solution is added for every gram of standard fine aggregate sample; Draw a standard curve: Use a spectrophotometer to measure the absorbance value of each standard fine aggregate sample suspension and record the data; draw a standard curve with the absorbance value as the horizontal axis and the mud content as the vertical axis; The linear regression equation of mud content and absorbance value was obtained by data fitting, and the absolute value of the correlation coefficient was > 0.98; (2) Rapid determination of mud content in fine aggregate samples: First, weigh the dry fine aggregate sample to be tested; Then, the weighed fine aggregate sample to be tested is added to the saturated Azure I solution, stirred for 4-5 minutes and then allowed to stand for 4-5 minutes to obtain a suspension of the fine aggregate sample to be tested; in, Finally, using a spectrophotometer, the absorbance value of the fine aggregate sample suspension to be tested is measured under the same wavelength conditions as the absorbance value of the standard fine aggregate sample suspension measured in step (1); Substitute the measured absorbance value of the fine aggregate sample suspension to be tested into the linear regression equation obtained in step (1) to calculate the mud content of the fine aggregate to be tested.

2. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: The mud content of the series of standard fine aggregate samples in step (1) is X1, X2, X3...X1 which increases continuously. n ; Where X1≥0%, X n ≤20%.

3. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 2, characterized in that: The mud content of the series of standard fine aggregate samples increases continuously in increments of 1%.

4. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: In the step (1), the standard fine aggregate sample with known mud content is air-dried or low-temperature dried at 35-45°C.

5. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: When preparing the standard fine aggregate sample suspension and the fine aggregate sample suspension to be tested in step (1), the stirring speed is 450-550 r / min.

6. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: When preparing the standard fine aggregate sample suspension in step (1), the standard is to add 40 mL of saturated Azure I solution per gram of standard fine aggregate sample.

7. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: When preparing the suspension of the fine aggregate sample to be tested in step (1), the standard is 40 mL of saturated Azure I solution per gram of the fine aggregate sample to be tested.

8. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: The wavelength of the absorbance value measured by the spectrophotometer in step (1) and step (2) is 460-470nm.

9. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: The wavelength of the absorbance value measured by the spectrophotometer in the steps (1) and (2) is 620-760 nm.

10. The method for rapidly determining the mud content in fine aggregate using Azure I according to claim 1, characterized in that: After preparing the standard fine aggregate sample suspension or the fine aggregate sample suspension to be tested, the absorbance value of the suspension is measured by a spectrophotometer within 30 minutes.

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