Method for efficiently measuring sand equivalent of fine aggregate

Abstract

The invention belongs to the technical field of constructional engineering material detection, and particularly relates to a method for efficiently measuring the sand equivalent of fine aggregate. According to the method, a saturated azure I solution is innovatively adopted as a solvent for dissolving the fine aggregate, and the sand equivalent of the fine aggregate is measured in combination with an absorbance method. When the sand equivalent is measured, a sample to be measured only needs to be dissolved in the saturated azure I solution, the spectrophotometer is directly used for measuring the absorbance value of the sample, the absorbance value is substituted into the obtained absorbance-sand equivalent linear regression equation, and the sand equivalent corresponding to the sample to be measured can be calculated. The determination method has the advantages of standardized operation steps, simple operation and high efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of building engineering material testing, and particularly relates to a method for efficiently determining the sand equivalent of fine aggregate. Background Art

[0002] The sand equivalent (SE) of fine aggregate is an index used to evaluate the cleanliness of aggregate. The sand equivalent is to determine the content of clay or impurities contained in various fine aggregates such as natural sand, manufactured sand, and stone chips. The sand equivalent is represented by SE and is applicable to aggregates with a nominal maximum particle size not exceeding 4.75 mm.

[0003] Currently, in the sand equivalent test, 120 g of fine aggregate passing through a 4.75 mm sieve is poured into a test cylinder. After mechanical oscillation and flushing with a flushing liquid, it is left to stand. Finally, the height h of the precipitate in the test cylinder is measured. 2 and the height h from the bottom of the test cylinder to the liquid level of the flocculent condensate 1 , with h 2 / h 1 ×100 as the sand equivalent value SE of the fine aggregate. According to the current sand equivalent test, if a relatively accurate sand equivalent value of fine aggregate is to be measured, the following conditions need to be met: (1) The requirements for sample preparation are relatively high. It is required that the moisture content of the test sample be controlled at about 3%. Too dry or too wet will cause the fine aggregate particles to suspend in the flushing liquid and cannot be fully separated. (2) The test takes a long time. In the sand equivalent test, the test sample needs to be left to stand for 10 min after being added to the test cylinder, then mechanically oscillated, and finally left to stand for 20 min before measuring the height. Completing one test takes at least 30 min. And the number of test cylinders equipped with the sand equivalent tester is limited, and the test cylinders of each manufacturer are not universal. After completing one test, the test cylinder needs to be manually rinsed and the water in the cylinder needs to be drained. Moreover, the time limit for the sand equivalent test is strict. If the standing time is exceeded, the test needs to be redone, which seriously interferes with the detection process and manpower allocation. If a large number of tests of the same batch are commissioned, it will be very time-consuming and consume the energy of the detection personnel. (3) If the height of the liquid level of the flocculent condensate is to be accurately measured, the liquid level needs to be parallel to the bottom of the test cylinder, otherwise it will affect the measurement of the final height. In this way, it is quite a test of the flushing skills of the detection personnel and requires a certain amount of operation experience. It can be seen that the operation differences of the operators will have a significant impact on the final measurement result, and the human operation error is relatively large.

[0004] Therefore, there is an urgent need for a method that can quickly, simply and accurately determine the sand equivalent in fine aggregate. Summary of the Invention

[0005] The object of the present invention is to provide a method for quickly, simply and accurately determining the sand equivalent of fine aggregates in view of the above-mentioned defects. This method innovatively proposes to use a saturated Azure I solution as the solvent for dissolving fine aggregates, and combines the absorbance method to determine the sand equivalent of fine aggregates. When determining the sand equivalent, only need to dissolve the sample to be tested in the saturated Azure I solution, directly use a spectrophotometer to measure its absorbance value, and substitute this absorbance value into the obtained absorbance-sand equivalent linear regression equation, then the sand equivalent corresponding to the sample to be tested can be calculated. The operation steps of this determination method are standardized, simple and efficient.

[0006] Azure I, with the CAS number 531-55-5, has the molecular formula 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:

[0007]

[0008] It is found that when using a saturated Azure I solution as the solvent to dissolve fine aggregates and determining the sand equivalent of fine aggregates according to the method described in the present invention, the change range of its absorbance is large, so that the absorbance can have a good linear fitting with the sand equivalent, and the absolute value of the linear correlation coefficient > 0.98.

[0009] The technical solution of the present invention is: a method for efficiently determining the sand equivalent of fine aggregates, which includes the following steps:

[0010] (1) Prepare standard sample solutions:

[0011] First, add an excessive amount of solid Azure I to distilled water at room temperature, stir evenly, and let it stand for at least 24 h to obtain a saturated Azure I solution; take the supernatant as the solvent for the sample solution. A large amount of powdery solid Azure I sinks to the bottom of the solution, which represents that the solution is saturated.

[0012] Then, weigh a series of fine aggregate standard samples with the same mass and dryness, and add them to solvents with the same volume. After stirring evenly, let it stand for 3-5 min to obtain each standard sample solution. The drying of the fine aggregate standard samples 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.

[0013] Among them, 35.0-70.0 mL of solvent is used per gram of fine aggregate standard sample.

[0014] After repeated research, it is found that when measuring the sand equivalent of fine aggregates according to the method steps of the present invention, the fine aggregate standard sample and the saturated Azure I solution need to meet the described ratio standard to ensure that the absolute value of the correlation coefficient of the absorbance-sand equivalent standard curve drawn is greater than 0.98, thereby ensuring the accuracy of the final measurement result.

[0015] (2) Draw the standard curve:

[0016] Use a spectrophotometer to measure the absorbance value of each standard sample solution and record the data; use the absorbance value as the abscissa and the sand equivalent as the ordinate to draw the standard curve.

[0017] And obtain the linear regression equation of the sand equivalent and the absorbance value through data fitting, and the absolute value of the correlation coefficient > 0.98.

[0018] (3) Prepare the sample solution to be measured:

[0019] 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 solvent saturated Azure I solution, stir evenly and let it stand for 3 - 5 minutes to obtain the sample solution to be measured;

[0020] Among them,

[0021] (4) Measure the sand equivalent of the sample to be measured:

[0022] Use a spectrophotometer to measure the absorbance value of the sample solution to be measured; among them, the measurement wavelength of the spectrophotometer is the same as that in step (2);

[0023] Substitute the measured absorbance value of the sample solution to be measured into the linear regression equation obtained in step (2) to calculate the sand equivalent of the sample to be measured.

[0024] 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.

[0025] The sand equivalent determination method described in the present invention can first classify fine aggregates according to their rock types and origins, 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 determination 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.

[0026] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregates, the sand equivalent of the series of standard samples of fine aggregates in step (1) is 45%-95%.

[0027] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregates, the temperature of distilled water in step (1) is 15-25°C. The solubility of Azure I changes little at a temperature of 15-25°C, and the deviation of the saturated solution within this temperature range will not affect the test results.

[0028] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregates, the stirring speed in step (1) is 450-500 r / min, and the stirring time is 3-5 min. An impeller stirrer can be used for stirring. If the stirring speed is too fast, coarse particles will also be suspended in the solution, and some coarse particles will also adsorb a small amount of Azure I, resulting in a smaller sand equivalent 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 causing a larger sand equivalent value measured.

[0029] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregates, at least three parallel standard samples are prepared for each sand equivalent in step (1). When drawing the standard curve, the average value of the absorbance values measured by the parallel standard samples with the same sand equivalent is taken as the absorbance value corresponding to the sand equivalent.

[0030] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregates, the stirring speed in step (3) is 450-500 r / min, and the stirring time is 3-5 min.

[0031] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregates, 50 mL of solvent is used for each gram of the standard sample of fine aggregates in step (1).

[0032] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregates, the wavelength for measuring the absorbance value by the spectrophotometer in steps (2) and (4) is 430-460 nm. Within this measurement wavelength range, the absorbance value is negatively correlated with the sand equivalent value.

[0033] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregate, the wavelength for measuring the absorbance value by the spectrophotometer in step (2) and step (4) is 620 - 700 nm. Within this measurement wavelength range, the absorbance value is positively correlated with the sand equivalent value.

[0034] In the present invention, for the method for efficiently determining the sand equivalent of fine aggregate, after the standard sample solution and the sample solution to be measured are prepared, the absorbance value of the sample solution is measured by the spectrophotometer within 30 minutes.

[0035] During the process of the sample solution obtained by dissolving the fine aggregate with the saturated Azure I solution decreasing with the sand equivalent, the color of the solution can achieve a large span from blue to pink (as Figure 1 shown), thereby enabling a large change range of the corresponding absorbance. This allows for a wide range of wavelength selection applicable to the measurement method of the present invention. Under the wavelength conditions of 430 - 460 nm (blue light wavelength) or 620 - 700 nm (red light wavelength), the sand equivalent of the corresponding fine aggregate sample to be measured can be obtained from the measured absorbance. The large change range of the absorbance reduces the influence of the absorbance measurement error on the sand equivalent measurement result, and the standard curve of absorbance - sand equivalent drawn is more accurate.

[0036] The beneficial effects of the present invention are as follows: The method for efficiently determining the sand equivalent of fine aggregate in the present invention innovatively proposes to use the saturated Azure I solution as the solvent for dissolving the fine aggregate, and combines the absorbance method to determine the sand equivalent of the fine aggregate. When measuring the sand equivalent, only need to dissolve the sample to be measured in the saturated Azure I solution, directly use the spectrophotometer to measure its absorbance value, and substitute this absorbance value into the obtained linear regression equation of absorbance - sand equivalent, then the sand equivalent corresponding to the sample to be measured can be calculated.

[0037] The operation steps of the measurement method are standardized, rather than relying on the experience and skills of the operator, reducing the human experimental error caused by different operation experiences.

[0038] The duration of the traditional sand equivalent test requires at least 30 minutes, and the time limit is strict during the operation process. It is necessary to strictly control the standing time, and the same tester cannot batch - process the measurement samples simultaneously due to the need to count time. However, the measurement method of the present invention only requires less than 10 minutes and can batch - process a large number of measurement samples simultaneously, with more efficient measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a diagram showing the color change of the solution of the present invention from blue to pink with the increase of the sand equivalent.

[0040] Figure 2 It is the standard curve diagram of absorbance - sand equivalent in Example 1.

[0041] Figure 3 It is the absorbance-sand equivalent standard curve graph in Example 2.

[0042] Figure 4 It is the absorbance-sand equivalent standard curve graph in Comparative Example 1.

[0043] Figure 5 It is the absorbance-sand equivalent standard curve graph in Comparative Example 2.

[0044] Figure 6 It is the sand equivalent-absorbance fitting graph in Comparative Example 3.

[0045] Figure 7 It is the absorbance-sand equivalent fitting graph in Comparative Example 4. Specific embodiments

[0046] The present invention will be described in detail below with reference to the accompanying drawings.

[0047] The detection reagent Azure I used in the following examples was purchased from PHYGENE, REF: PH9288-10g.

[0048] Example 1

[0049] The method for efficiently determining the sand equivalent of fine aggregate includes the following steps:

[0050] (1) Prepare a standard sample solution:

[0051] First, add an excessive amount of solid Azure I to distilled water at 25°C, stir evenly, and let it stand for 24 hours to obtain a saturated Azure I solution; take the supernatant as the solvent of the sample solution.

[0052] Then, weigh 20 g of each fine aggregate standard sample with sand equivalents of 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95% respectively, add them to solvents with volumes of 1000 mL each, stir with an impeller stirrer at 500 r / min for 4 minutes, and let it stand for 4 minutes to obtain each standard sample solution.

[0053] (2) Plot a standard curve:

[0054] 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 430 nm, record the data; use the absorbance value as the abscissa and the sand equivalent as the ordinate to plot a standard curve. As Figure 2 shown.

[0055] The linear regression equation between the sand equivalent and the absorbance value was obtained by data fitting: y = -57.45x + 96.61, where x is the absorbance value and y is the sand equivalent; the absolute value of the correlation coefficient is 0.99.

[0056] (3) Prepare the test sample solution:

[0057] Weigh 20 g of the dry fine aggregate test sample and add it to 1000 mL of the solvent saturated Azure I solution. Use an impeller stirrer to stir at 500 r / min for 4 min, and then let it stand for 4 min to obtain the test sample solution.

[0058] (4) Determine the sand equivalent of the test sample:

[0059] Using a spectrophotometer at a wavelength of 430 nm, the absorbance value of the test sample solution was measured to be 0.43.

[0060] Substitute this absorbance value into the linear regression equation obtained in step (2) to calculate that the sand equivalent of the test sample is 72%.

[0061] To verify the accuracy, the sample was tested according to the sand equivalent test method in the standard JTG 3432-2024 "Test Regulations for Aggregates in Highway Engineering". The measured sand equivalent was 73%, with a difference of only 1%, meeting the requirement that the allowable error in sand equivalent determination should not be greater than 4%, proving that the sand equivalent measured by this method is very accurate.

[0062] The fine aggregate measured by this method is the limestone manufactured sand from Yishui Zhengda Stone Factory. The main production areas of the limestone manufactured sand in this stone factory are quarry sites in southwestern Shandong such as Linzi and Linyi. After establishing the above standard curve, when detecting the sand equivalent of fine aggregates in this area and of this rock type, the linear regression equation y = -57.45x + 96.61 can be directly used.

[0063] Example 2

[0064] The method for efficiently determining the sand equivalent of fine aggregates includes the following steps:

[0065] (1) Prepare the standard sample solution:

[0066] First, add an excessive amount of Azure I solid to distilled water at 25°C, stir evenly, and let it stand for 24 h to obtain a saturated Azure I solution; take the supernatant as the solvent for the sample solution.

[0067] Then, weigh 20 g each of standard samples of fine aggregates with sand equivalents of 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95% respectively, add them to solvents with a volume of 1000 mL each, use an impeller stirrer to stir at 500 r / min for 4 min, and let stand for 4 min to obtain standard sample solutions.

[0068] (2) Plot the standard curve:

[0069] Within 30 minutes after preparing the standard sample solutions, use a spectrophotometer to measure the absorbance values of each standard sample solution at a wavelength of 630 nm, and record the data; use the absorbance values as the abscissa and the sand equivalent as the ordinate to plot the standard curve. As Figure 3 shown.

[0070] Obtain the linear regression equation of the sand equivalent and the absorbance value through data fitting: y = 56.72x + 44.35, where x is the absorbance value and y is the sand equivalent; the absolute value of the correlation coefficient is 0.99.

[0071] (3) Prepare the sample solution to be measured:

[0072] Weigh 20 g of the dry fine aggregate sample to be measured and add it to 1000 mL of the solvent saturated Azure I solution. Use an impeller stirrer to stir at 500 r / min for 4 min and let stand for 4 min to obtain the sample solution to be measured.

[0073] (4) Determine the sand equivalent of the sample to be measured:

[0074] Use a spectrophotometer to measure the absorbance value of the sample solution to be measured at a wavelength of 630 nm, and the measured absorbance value is 0.29.

[0075] Substitute this absorbance value into the linear regression equation obtained in step (2) to calculate that the sand equivalent of the sample to be measured is 61%.

[0076] To verify the accuracy, detect the sample according to the sand equivalent test method in the standard of JTG 3432 - 2024 "Test Regulations for Aggregates in Highway Engineering". The measured sand equivalent is 63%, and the difference between the two is only 2%, meeting the requirement that the allowable error of sand equivalent measurement should not be greater than 4%, proving that the sand equivalent measured by this method is very accurate.

[0077] The fine aggregate measured by this method is the limestone manufactured sand from Yishui Zhengda Stone Factory. The main production areas of the limestone manufactured sand in this stone factory are quarry sites in southwestern Shandong such as Linzi and Linyi. After establishing the above standard curve, when detecting the sand equivalent of fine aggregates in this area and of this rock type, the linear regression equation y = 56.72x + 44.35 can be directly used.

[0078] It can also be seen from the combination of Example 1 and Example 2 that for the measurement method described in the present invention, as the sand equivalent of the obtained sample solution decreases, the change range of the absorbance is relatively large. Under the wavelength conditions of 430 - 460 nm (blue light wavelength) or 620 - 700 nm (red light wavelength), the sand equivalent of the corresponding sample to be measured can be measured through the absorbance. Thus, 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.

[0079] The following is an example for illustration. Weigh a sample to be measured. According to the operation steps for quickly measuring the sand equivalent of fine aggregate samples to be measured described in the present invention, the absorbance of the sample to be measured at a wavelength of 430 nm is detected to be 0.61. Then, substitute it into the linear regression equation y = -57.45x + 96.61 obtained from the standard curve plotted at a wavelength of 430 nm, and calculate that the sand equivalent of the sample to be measured is 62%. The absorbance of the sample to be measured at a wavelength of 630 nm is detected to be 0.33. Substitute it into the linear regression equation y = 56.72x + 44.35 obtained from the standard curve plotted at a wavelength of 630 nm, and calculate that the sand equivalent of the sample to be measured is 63%. The difference between the two is 1%, meeting the requirement that the allowable error for sand equivalent measurement should not be greater than 4%, which proves the accuracy of the measurement results of the method described in the present invention.

[0080] Comparative Example 1

[0081] The difference between this comparative example and Example 1 is as follows:

[0082] 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 600 mL, that is, 30 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 step (1) of Example 1.

[0083] In step (3), the 20 g of the fine aggregate sample to be measured is added to 600 mL of saturated Azure I solution, and a vane stirrer is used to stir at 500 r / min for 4 min and then left standing 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.

[0084] The standard curve plotted in this comparative example is as Figure 4 shown.

[0085] It can be seen through Figure 4 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 absolute value of the linear correlation coefficient of the relationship equation between the absorbance and the sand equivalent plotted is 0.916, which is lower than 0.98. Thus, it cannot be used as a standard curve for the method described in the present invention.

[0086] To verify that the standard curve drawn for this comparative example cannot be used in the method of the present invention, the following operations are carried out:

[0087] First, weigh the sample to be tested. According to the operation steps for rapidly determining the sand equivalent 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 0.95. Substitute it into the linear regression equation of the above standard curve: y = -44.67x + 101.87; calculate the sand equivalent to be 59%.

[0088] However, when this sample is detected according to the sand equivalent test method in JTG 3432-2024 "Test Regulations for Aggregates in Highway Engineering", the measured sand equivalent is 65%. The difference between the two is 6%, which does not meet the requirement that the allowable error of sand equivalent determination should not be greater than 4%. This proves that this equation cannot be adopted and the drawn standard curve cannot be used in the method of the present invention.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 1 is as follows:

[0091] 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 1500 mL, that is, 75 mL of saturated Azure I solution is allocated to each gram of the standard fine aggregate sample. The other operations are the same as those in step (1) of Example 1.

[0092] In step (3), 20 g of the fine aggregate sample to be tested weighed is added to 75 mL of saturated Azure I solution, and a vane stirrer is used to stir at 500 r / min for 4 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.

[0093] The standard curve drawn in this comparative example is as Figure 5 shown.

[0094] It can be seen through Figure 5 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 absolute value of the linear correlation coefficient of the relationship equation between the drawn absorbance and the sand equivalent is 0.947, which is lower than 0.98. Thus, it cannot be used as a standard curve in the method of the present invention.

[0095] To verify that the standard curve drawn for this comparative example cannot be used in the method of the present invention, the following operations are carried out:

[0096] First, weigh the sample to be tested. According to the operation steps for rapidly determining the sand equivalent 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 0.11. Substitute it into the linear regression equation of the above standard curve: y = -88.14x + 88.24; calculate the sand equivalent to be 79%.

[0097] However, when testing this sample according to the sand equivalent test method in JTG 3432-2024 "Test Regulations for Aggregates in Highway Engineering", the measured sand equivalent is 71%, with a difference of 8% between the two, which does not meet the requirement that the allowable error in sand equivalent determination should not be greater than 4%. This proves that this equation cannot be adopted, and the standard curve drawn cannot be used in the method described in the present invention.

[0098] 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.

[0099] Comparative Example 3

[0100] In this comparative example, the saturated Azure I solution in Example 1 was replaced with 0.1% methyl green, 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 were the same as in Example 1. The obtained sand equivalent-absorbance fitting diagram is as Figure 6 shown.

[0101] Through Figure 6 it can be seen that methyl green, acid fuchsin, and crystal violet have very weak adsorption ability for soil in aqueous solution. As the sand equivalent decreases, the change in the absorbance of the solution is irregular and cannot be applied to the determination method of the sand equivalent described in the present invention.

[0102] 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 the detection reagent hardly changes, indicating that it is not feasible to determine the sand equivalent using redox characteristics.

[0103] Comparative Example 4

[0104] 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.

[0105] Methylene blue, its molecular formula is C 16 H 18 ClN 3 S, and its structural formula is:

[0106]

[0107] Other conditions were the same as in Example 1.

[0108] The obtained absorbance-sand equivalent fitting graph is as Figure 7 shown. By Figure 7 It can be seen that when using methylene blue as the solvent to dissolve the fine aggregate, the absorbance of the obtained sample solution only varies within the range of 0 - 0.5 AU, and the variation range is smaller than that of the saturated azurin I solution (the saturated azurin I solution can vary within the range of 0 - 1 AU).

[0109] From Figure 7 it can be clearly seen that when the absorbance is within 0 - 0.2 AU, the error bars representing the standard deviation of the absorbance are longer. That is to say, when the absorbance is small, the repeatability error of the value 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 for the method described in the present invention, the variation range of its absorbance is around 0 - 0.5 AU, and the absorbance of samples with a basic sand equivalent of more than 80% is concentrated within 0 - 0.1 AU. It can be seen that when measuring samples with a relatively high sand equivalent, if the commonly used methylene blue solution is used as the solvent for the measurement method described in the present invention, the error of the measurement result is larger and the accuracy is poor.

[0110] In addition, from Figure 7 it can also be seen 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 sand equivalent result.

Claims

1. A method for efficiently determining the fine aggregate sand equivalent, characterized in that: The following steps are involved: (1) Preparation of standard sample solution: First, add excess Azure I solid to distilled water at room temperature, stir evenly, and let stand for at least 24 hours to obtain a saturated Azure I solution; take the supernatant as the solvent of the sample solution; Then, a series of fine aggregate standard samples with known sand equivalent of the same mass and dried are weighed and added into each solvent with the same volume, stirred evenly and allowed to stand for 3-5 minutes to obtain each standard sample solution; Among them, 35.0-70.0mL of solvent is added for each gram of fine aggregate standard sample; (2) Draw the standard curve: Use a spectrophotometer to measure the absorbance value of each standard sample solution and record the data; draw a standard curve with the absorbance value as the horizontal axis and the sand equivalent as the vertical axis; The linear regression equation of sand equivalent and absorbance value was obtained by data fitting, and the absolute value of the correlation coefficient was > 0.98; (3) Prepare the sample solution to be tested: Weigh the dry fine aggregate sample to be tested and add it to the solvent saturated Azure I solution, stir evenly and let it stand for 3-5 minutes to obtain the sample solution to be tested; in, (4) Determine the sand equivalent 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 sand equivalent of the sample solution.

2. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: The sand equivalent of the series of standard samples of fine aggregate in step (1) is between 45% and 95%.

3. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: The temperature of the distilled water in step (1) is 15-25°C.

4. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: The stirring speed in step (1) is 450-500 r / min, and the stirring time is 3-5 min.

5. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: In the step (1), at least three parallel standard samples are prepared for each sand equivalent.

6. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: The stirring speed in step (3) is 450-500 r / min, and the stirring time is 3-5 min.

7. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: In the step (1), 50 mL of solvent is added to each gram of the fine aggregate standard sample.

8. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: The wavelength of the absorbance value measured by the spectrophotometer in the steps (2) and (4) is 430-460 nm.

9. The method for efficiently determining fine aggregate sand equivalent according to claim 1, characterized in that: The wavelength of the absorbance value measured by the spectrophotometer in the steps (2) and (4) is 620-700 nm.

10. The method for efficiently determining fine aggregate sand equivalent 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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