阅读说明：本技术 细集料亚甲蓝值测试方法 (Fine aggregate methylene blue value testing method ) 是由 范倩 吴传海 李善强 许新权 严超 陈楚鹏 刘锋 刘新海 谢兼亮 于 2021-07-20 设计创作，主要内容包括：本发明公开了细集料亚甲蓝值测试方法,配制浓度为1g/L的标准亚甲蓝溶液；确定亚甲蓝溶液的特征峰；建立亚甲蓝溶液浓度与吸光度的标准曲线；称取待测样品,将待测样品与亚甲蓝溶液混合,混合后静置获得混合溶液,取混合溶液的上层清液并稀释,获得待测溶液；通过标准曲线计算待测溶液的亚甲蓝浓度,最终计算细集料吸附的亚甲蓝质量,并确定细集料亚甲蓝值。本方法是基于分光光度法,以分光光度计测得的吸光度来进行细集料对亚甲蓝吸附情况的表征,有效减少了人为因素对试验结果的影响,确保了试验的可重复性；本申请的测试方法,测得的试验数据更准确可信,可操作性强,对不同细集料的区分度更显著,可实现快速、准确、定量评价。(The invention discloses a fine aggregate methylene blue value testing method, which comprises the steps of preparing a standard methylene blue solution with the concentration of 1 g/L; determining a characteristic peak of a methylene blue solution; establishing a standard curve of the concentration and the absorbance of the methylene blue solution; weighing a sample to be detected, mixing the sample to be detected with a methylene blue solution, standing the mixture to obtain a mixed solution, and taking and diluting a supernatant of the mixed solution to obtain a solution to be detected; and calculating the methylene blue concentration of the solution to be detected through a standard curve, finally calculating the methylene blue mass adsorbed by the fine aggregate, and determining the methylene blue value of the fine aggregate. The method is based on a spectrophotometry, and the characterization of the methylene blue adsorption condition of the fine aggregate is carried out by using the absorbance measured by a spectrophotometer, so that the influence of human factors on the test result is effectively reduced, and the repeatability of the test is ensured; according to the test method, the measured test data is more accurate and credible, the operability is strong, the discrimination of different fine aggregates is more obvious, and quick, accurate and quantitative evaluation can be realized.)

1. The fine aggregate methylene blue value test method is characterized by comprising the following steps: the specific operation steps are as follows:

firstly, preparing a standard methylene blue solution with the concentration of 1 g/L;

secondly, determining a characteristic peak of the methylene blue solution;

thirdly, establishing a standard curve of the concentration and the absorbance of the methylene blue solution;

step four, weighing a sample to be detected, mixing the sample to be detected with a methylene blue solution, standing the mixture to obtain a mixed solution, and taking and diluting supernatant of the mixed solution to obtain a solution to be detected;

and fifthly, calculating the methylene blue concentration of the solution to be detected through a standard curve, finally calculating the methylene blue mass adsorbed by the fine aggregate, and determining the methylene blue value of the fine aggregate.

2. The fine aggregate methylene blue value test method according to claim 1, characterized in that: the first step specifically comprises the following operations: weighing 1g of dried methylene blue powder, adding the methylene blue powder into 1L of clean water while stirring, fully stirring until the methylene blue powder is completely dissolved, and cooling to room temperature;

the second step comprises the following specific operations: performing absorbance full-wavelength scanning on the prepared standard methylene blue solution by using a spectrophotometer to obtain characteristic peaks of absorption spectrum curves of 610nm and 664nm, wherein the maximum absorption wavelength is 664 nm;

the third step specifically comprises the following operations: diluting the standard methylene blue solution to solutions with the concentrations of 10mg/L, 20mg/L, 30mg/L, 40mg/L and 50mg/L, testing the absorbance of the methylene blue solution with different concentrations and clean water at the position with the wavelength of 664nm by adopting a spectrophotometer, and establishing a standard curve of the concentration of the methylene blue solution and the absorbance by taking the concentration of the methylene blue solution as an abscissa and the absorbance as an ordinate.

3. The fine aggregate methylene blue value test method according to claim 1, characterized in that: in the fourth step, the sample to be detected is fine aggregate;

when the particle size of the fine aggregate is 0-0.075mm or 0-0.15 mm, weighing 3.0g of dry fine aggregate, adding the dry fine aggregate into a conical flask, pouring 30mL of a standard methylene blue solution with the concentration of 1g/L, shaking the mixture in the conical flask for at least 90s, and standing for 5 min;

when the particle size of the fine aggregate is 0-2.36 mm, weighing 20g of dry fine aggregate, adding the dry fine aggregate into a conical flask, pouring 30mL of a standard methylene blue solution with the concentration of 1g/L, shaking the mixture in the conical flask for at least 120s, and standing for 8 min;

and (3) sucking 5mL of supernatant of the mixed solution in the conical flask by using a straw, adding water to dilute by 10 times to obtain a solution to be detected, and testing the absorbance of the solution to be detected at the position of 664nm of wavelength by using a spectrophotometer.

4. The fine aggregate methylene blue value test method according to claim 3, characterized in that: the fifth step is specifically calculated as follows: when the methylene blue concentration in the solution to be tested is calculated to be A mg/L through the standard curve, the methylene blue concentration B in the supernatant of the mixed solution is 10A mg/L, the methylene blue mass C absorbed by the fine aggregate is (1000-B) multiplied by 30/1000mg,

wherein m is the weight of the fine aggregate in g.

5. The fine aggregate methylene blue value test method according to claim 1, characterized in that: the temperature of the clean water in the first step is controlled to be 35-40 ℃.

6. The fine aggregate methylene blue value test method according to claim 3, characterized in that: and in the fourth step, 5mL of supernatant of the mixed solution is taken, and is diluted by 10 times by adding water, and then the mixed solution is shaken in a conical flask for at least 30s to obtain the solution to be detected.

7. The fine aggregate methylene blue value test method according to claim 4, characterized in that: in the fourth step, the solution to be measured is filtered through quantitative filter paper to obtain a filtered solution, when the methylene blue concentration in the filtered solution is calculated to be A 'mg/L through a standard curve by the calculation method of the fifth step, the methylene blue concentration B' in the supernatant of the mixed solution is 10A 'mg/L, the methylene blue mass C' absorbed by the fine aggregate is (1000-B '). times. 30/1000mg, and the methylene blue mass C' measured after the filtering treatment is

8. The fine aggregate methylene blue value test method of claim 7, characterized in that: obtaining the supernatant of the mixed solution by preparing the solution to be tested and filtering the solution to be testedRespectively testing the filtered solutions, comprehensively calculating the methylene blue concentrations measured twice, and correcting

Wherein K₁As correction factor for the solution to be measured, K₂Is the correction factor for the filtered solution; wherein K₁+K₂Equal to 1.

9. The fine aggregate methylene blue value test method of claim 8, characterized in that: selecting a sample to be tested, which is tested to have a methylene blue value of 0.5 +/-0.2 g/kg by a spectrophotometer method, determining the methylene blue value of the fine aggregate by adopting a traditional method specified in JTG-E42 of Highway engineering aggregate test regulation, adding 0.5ml of methylene blue solution each time in the whole test process, stirring for 1min, carrying out primary color halo test until the color halo can be continued for 5min, and obtaining the MBV of the sample to be tested₀；

MBV and MBV of the sample to be detected₀Substituting MBV' into the calculation formula of the corrected methylene blue value of the fine aggregate to obtain the correction coefficient K of the solution to be measured₁And correction factor K of the filtered solution₂。

Technical Field

The invention relates to the field of road engineering tests, in particular to a fine aggregate methylene blue value test method.

Background

In the road engineering aggregate test procedure (JTG E42-2005), the fine aggregate methylene blue test is used to determine whether swelling clay minerals are present in the fine aggregate and to determine its content. The specific operation steps can be summarized as follows: "prepare 10g/L methylene blue solution"; stirring for 5min to prepare fine aggregate suspension; "Add 5mL methylene blue solution and stir for 1 min"; "halo test (if halo appears, proceed to the next step; if not, return to the previous step)"; continuously stirring the suspension, and carrying out the color halo test every 1 min; if the color halo disappears within 4min, then 5mL of methylene blue solution is added; if the halo disappears in 5min, then 2mL of methylene blue solution is added; "continue stirring and color halo test until color halo can last for 5 min"; "calculating the methylene blue value MBV as V/m × 10g/kg according to the total volume V of the added methylene blue solution".

Analysis of the fine aggregate methylene blue test procedure has several major drawbacks: 1. the test operation process is complicated, and in order to ensure that suspended dropping liquid taken in a color halo test is representative, the fine aggregate should be in a relatively uniform suspension state as much as possible, so that the stirring state is required to be kept all the time in the test process until the test is finished; 2. the test result has low precision and is greatly influenced by human, which is mainly characterized in that 5mL of methylene blue solution is added into suspension each time in the test process, and a stable light blue halo with about 1mm of emission around a precipitate is taken as a titration end point; 3. the test process is long in time consumption, the fine aggregate suspension is prepared for 5min, methylene blue solution is added for at least 1min, the color halo is detected for at least 5min, the total time is at least 11min, and if the fine aggregate sample contains more expansive clay minerals, the time consumption is longer; 4. the waste liquid generated in the test process is more, the volume of the prepared fine aggregate suspension is more than 500mL, and the prepared fine aggregate suspension is changed into the waste liquid to be treated after methylene blue solution is added, and special treatment is needed (the methylene blue can generate double salt with most inorganic salts, the aqueous solution is alkaline, and the toxicity is low, so that the contact between the skin and eyes is avoided).

Disclosure of Invention

Aiming at the problems, the invention aims to provide a method for testing the methylene blue value of the fine aggregate, which is safe, environment-friendly and easy to repeatedly operate.

In order to realize the technical purpose, the scheme of the invention is as follows: the fine aggregate methylene blue value testing method comprises the following specific operation steps:

firstly, preparing a standard methylene blue solution with the concentration of 1 g/L;

secondly, determining a characteristic peak of the methylene blue solution;

thirdly, establishing a standard curve of the concentration and the absorbance of the methylene blue solution;

step four, weighing a sample to be detected, mixing the sample to be detected with a methylene blue solution, standing the mixture to obtain a mixed solution, and taking and diluting supernatant of the mixed solution to obtain a solution to be detected;

and fifthly, calculating the methylene blue concentration of the solution to be detected through a standard curve, finally calculating the methylene blue mass adsorbed by the fine aggregate, and determining the methylene blue value of the fine aggregate.

Preferably, the specific operations in the first step are as follows: weighing 1g of dried methylene blue powder, adding the methylene blue powder into 1L of clean water while stirring, fully stirring until the methylene blue powder is completely dissolved, and cooling to room temperature;

the second step comprises the following specific operations: performing absorbance full-wavelength scanning on the prepared standard methylene blue solution by using a spectrophotometer to obtain characteristic peaks of absorption spectrum curves of 610nm and 664nm, wherein the maximum absorption wavelength is 664 nm;

the third step specifically comprises the following operations: diluting the standard methylene blue solution to solutions with the concentrations of 10mg/L, 20mg/L, 30mg/L, 40mg/L and 50mg/L, testing the absorbance of the methylene blue solution with different concentrations and clean water at the position with the wavelength of 664nm by adopting a spectrophotometer, and establishing a standard curve of the concentration of the methylene blue solution and the absorbance by taking the concentration of the methylene blue solution as an abscissa and the absorbance as an ordinate.

Preferably, the sample to be detected in the fourth step is fine aggregate; when the particle size of the fine aggregate is 0-0.075mm or 0-0.15 mm, weighing 3.0g of dry fine aggregate, adding the dry fine aggregate into a conical flask, pouring 30mL of a standard methylene blue solution with the concentration of 1g/L, shaking the mixture in the conical flask for at least 90s, and standing for 5 min;

when the particle size of the fine aggregate is 0-2.36 mm, weighing 20g of dry fine aggregate, adding the dry fine aggregate into a conical flask, pouring 30mL of a standard methylene blue solution with the concentration of 1g/L, shaking the mixture in the conical flask for at least 120s, and standing for 8 min;

and (3) sucking 5mL of supernatant of the mixed solution in the conical flask by using a straw, adding water to dilute by 10 times to obtain a solution to be detected, and testing the absorbance of the solution to be detected at the position of 664nm of wavelength by using a spectrophotometer.

Preferably, the fifth step specifically includes the following steps: when the methylene blue concentration in the solution to be detected is calculated to be A mg/L through the standard curve, the methylene blue concentration B in the supernatant of the mixed solution is 10A mg/L, the methylene blue mass C absorbed by the fine aggregate is (1000-B) multiplied by 30/1000mg, and the methylene blue value of the fine aggregateWherein m is the weight of the fine aggregate in g.

Preferably, the temperature of the clean water in the first step is controlled to be 35-40 ℃.

Preferably, in the fourth step, 5mL of the supernatant of the mixed solution is taken, diluted 10 times by adding water, and shaken in an erlenmeyer flask for at least 30s to obtain the solution to be tested.

Preferably, in the fourth step, the solution to be measured is filtered through a quantitative filter paper to obtain a filtered solution, and when the methylene blue concentration in the filtered solution is calculated as a ' mg/L by the calculation method of the fifth step through a calibration curve, the methylene blue concentration B ' in the supernatant of the mixed solution is 10A ' mg/L, the methylene blue mass C ' adsorbed to the fine aggregate is (1000-B ') × 30/1000mg, and the methylene blue value of the fine aggregate measured after the filtering treatment is

Preferably, the supernatant of the mixed solution is taken, the solution to be detected is prepared, the solution to be detected is filtered to obtain a filtered solution, the filtered solution is respectively tested, the methylene blue concentration obtained by two times of measurement is comprehensively calculated, and the methylene blue value of the fine aggregate after correction is as follows:

wherein K₁As correction factor for the solution to be measured, K₂Is the correction factor for the filtered solution; wherein K₁+K₂Equal to 1.

Preferably, a sample to be tested with a methylene blue value of 0.5 +/-0.2 g/kg is selected through a spectrophotometer method, the methylene blue value of the fine aggregate is determined by adopting a traditional method specified in road engineering aggregate test regulation JTG-E42, 0.5ml of methylene blue solution is added every time and stirred for 1min in the whole test process, and then one-time vignetting test is carried out until the vignetting can last for 5min, so that the MBV of the sample to be tested is obtained₀；

MBV and MBV of the sample to be detected₀Substituting MBV' into the calculation formula of the corrected methylene blue value of the fine aggregate to obtain the correction coefficient K of the solution to be measured₁And correction factor K of the filtered solution₂。

The method has the beneficial effects that the test method is based on a spectrophotometry, tests the fine aggregate, abandons the test operation of adopting a color halo test to carry out artificial judgment on the methylene blue adsorption condition of the fine aggregate, and carries out characterization on the methylene blue adsorption condition of the fine aggregate by using the absorbance measured by a spectrophotometer, thereby effectively reducing the influence of artificial factors on the test result, being more objective and accurate than the result measured by the original test method, simultaneously reducing the experience requirement on operators and ensuring the repeatability of the test; according to the test method, the measured test data is more accurate and credible, the operability is strong, the discrimination of different fine aggregates is more obvious, and the quick, accurate and quantitative evaluation of the methylene blue value of the fine aggregate can be realized; meanwhile, a filtering solution is obtained by adopting a filtering mode, and the methylene blue value of the mixed solution is corrected, so that the error of the suspended particles brought to the absorbance of the solution tested by the spectrophotometer method is reduced.

Drawings

FIG. 1 is a methylene blue solution absorption spectrum plot;

FIG. 2 is a standard curve of methylene blue solution concentration versus absorbance.

Detailed Description

The invention is described in further detail below with reference to the figures and specific embodiments.

As shown in fig. 1-2, the specific embodiment of the invention is a fine aggregate methylene blue value test method, which comprises the following specific operation steps:

step one, preparing a standard methylene blue solution with the concentration of 1g/L, weighing 1g of dried methylene blue powder, adding the methylene blue powder into 1L of clean water while stirring, fully stirring until the methylene blue powder is completely dissolved, and cooling to room temperature; wherein the temperature of the clean water is controlled to be 35-40 ℃.

Secondly, determining a characteristic peak of a methylene blue solution, and performing absorbance full-wavelength scanning on the prepared standard methylene blue solution by using a spectrophotometer to obtain characteristic peaks of absorption spectrum curves of 610nm and 664nm, wherein the maximum absorption wavelength is 664 nm;

and thirdly, establishing a standard curve of the concentration and the absorbance of the methylene blue solution, diluting the standard methylene blue solution to the solutions with the concentrations of 10mg/L, 20mg/L, 30mg/L, 40mg/L and 50mg/L, testing the absorbance of the methylene blue solution with different concentrations and clean water at the wavelength of 664nm by adopting a spectrophotometer, and establishing the standard curve of the concentration and the absorbance of the methylene blue solution by taking the concentration of the methylene blue solution as a horizontal coordinate and the absorbance as a vertical coordinate.

Step four, weighing a sample to be detected, mixing the sample to be detected with a methylene blue solution, and standing after mixing to obtain a mixed solution, wherein the sample to be detected is fine aggregate;

when the particle size of the fine aggregate is 0-0.075mm or 0-0.15 mm, weighing 3.0g of dry fine aggregate, adding the dry fine aggregate into a conical flask, pouring 30mL of a standard methylene blue solution with the concentration of 1g/L, shaking the mixture in the conical flask for at least 90s, and standing for 5 min;

when the particle size of the fine aggregate is 0-2.36 mm, weighing 20g of dry fine aggregate, adding the dry fine aggregate into a conical flask, pouring 30mL of a standard methylene blue solution with the concentration of 1g/L, shaking the mixture in the conical flask for at least 120s, and standing for 8 min;

sucking 5mL of supernatant of the mixed solution in the conical flask by using a suction pipe, adding water to dilute by 10 times, shaking in the conical flask for at least 30s to obtain a solution to be tested, and testing the absorbance of the solution to be tested at the wavelength of 664nm by using a spectrophotometer;

fifthly, when the methylene blue concentration in the solution to be detected is calculated to be Amg/L through the standard curve, the methylene blue concentration B in the supernatant of the mixed solution is 10A mg/L, the methylene blue mass C absorbed by the fine aggregate is (1000-B) x 30/1000mg,

fine aggregate methylene blue value:

wherein m is the weight of the fine aggregate; when the particle size of the fine aggregate is 0-2.36 mm, 20g of m is taken; when the particle size of the fine aggregate is 0-0.075mm or 0-0.15 mm, m is 3.0 g.

And fourthly, when the mixed solution is obtained, regarding the selection of the optimal mixing time of the fine aggregate and the methylene blue, because the adsorption of the methylene blue by the fine aggregate can be completed within a certain time, in order to ensure that the fine aggregate fully adsorbs the methylene blue, and avoid unnecessary time waste, the optimal mixing time of the fine aggregate sample to be tested and the methylene blue standard solution needs to be determined through tests.

Taking 3g of basalt fine aggregates with the particle size of 0-0.075mm as an example, respectively setting the mixing time of a fine aggregate sample to be detected and a methylene blue standard solution to 30s, 60s, 90s and 120s, preparing a mixed solution of the fine aggregates and the methylene blue solution, standing for a sufficient time (20h), taking a supernatant, diluting to a proper concentration, and then carrying out spectrophotometric test.

Difference of supernatant of mixed solution at different mixing time

Mixing time/s	The resolution/A of the 5-fold diluted clear solution	Supernatant concentration/(mg/L)
			30	0.9584	69
60	0.8456	60
			90	0.7324	51
120	0.7467	52

When the mixing time of the fine aggregate sample and the methylene blue solution is 30s-90s, the concentration of the supernatant liquid is gradually reduced along with the increase of the mixing time, and the methylene blue adsorption amount calculated by the calculation is slightly increased. The concentration difference of the supernatant liquid of the suspension liquid with the mixing time of 90s and 120s is not big, so that when the mixed liquid shakes for 90s, the adsorption of the fine aggregate on methylene blue in the mixed liquid reaches a saturated state. Based on the above analysis, in order to achieve rapid testing, the mixing time of the fine aggregate sample with the methylene blue standard solution in the test method of the present application was set to at least 90 s. When the fine aggregate has a particle size of 0 to 2.36mm and a weight of 20g, the mixing time is set to at least 120s due to an increase in the sample amount.

Example 1 is as follows:

absorption spectra curves of different concentrations of methylene blue solutions were tested according to the method of the present application, as shown in figure 1. As can be seen in fig. 1: the shapes and trends of absorption spectrum curves of methylene blue solutions with the concentrations of 25mg/L and 10mg/L are completely the same, and the methylene blue solutions have two absorption peaks which are respectively positioned at the wavelengths of 610nm and 664nm, so that the maximum absorption wavelength of the methylene blue solution is determined to be 664 nm.

The test was performed according to the method of the present application, and a standard curve of the concentration of methylene blue solution and absorbance was established, fig. 2. As can be seen in fig. 2: the concentration of methylene blue solution has good linear positive correlation with the absorbance, and the correlation coefficient can reach more than 0.98. With increasing concentration, the absorbance shows a linear increasing trend, and the fitting relation is as follows: absorbance equals 0.0630 × methylene blue concentration + 0.0904.

Selecting a fine aggregate, screening the fine aggregate according to a method of road engineering aggregate test regulation (JTG E42), cleaning and drying the fine aggregate with various particle sizes for later use, drying the sieve bottom part below 0.075mm for later use, and performing fine aggregate reverse blending according to the target blending ratio of the asphalt mixture, wherein the blending amount of the sieve bottom below 0.075mm is respectively 0g, 1g, 2g, 3g and 4 g.

The test was carried out according to the original test method and the present application, respectively, and the results are as follows.

TABLE 1 Fine aggregate methylene blue test results

The mixing amount of the particles is less than 0.075 mm/g	Original test method	This application
			1	0.5	0.32
2	0.5	0.61
			3	1.0	0.82
4	1.0	1.14

In the original test method, "the addition of the methylene blue solution is stopped, but the suspension is continuously stirred, and the halo test is performed every 1 minute. If the color halo disappears in the first 4 minutes, adding 5mL of methylene blue solution; if the halo disappeared in 5 minutes, 2mL of methylene blue solution was added. In both cases, stirring and the halo test should be continued until the halo can continue for 5 minutes ". Therefore, before the end point is approached, methylene blue which is possibly added may be 5mL or 2mL, so that an error exists between a test value and a true value of an original test method, meanwhile, the chromatic halo is difficult to observe, and the requirement on experience of testers is high.

As can be seen from table 1: when the content of the expansive clay minerals is small or the difference is small, the test result measured by the original test method cannot effectively distinguish the fine aggregates, the method can obviously distinguish the fine aggregates with different screen bottom mixing amounts, the test result is objective and accurate, the interference of human factors is small, and the distinguishing and identifying performance is strong.

In conclusion, the spectrophotometer is adopted to measure the maximum absorption wavelength of the methylene blue solution and establish the standard curve of the concentration and the absorbance of the methylene blue solution, the methylene blue solution can be used for a long time after being operated once, only comparison and calibration are needed to be carried out periodically, and the test operation is simple, the test accuracy is high, and the artificial influence is small;

according to the method for testing the methylene blue value of the fine aggregate, the test process is short in time consumption, the fine aggregate is mixed with the methylene blue solution and stands for 6.5min, the supernatant is taken and diluted for 1min, and the test is carried out for 1min, namely, only 8.5min is needed for one test, so that the test time is effectively shortened, and the time cost is saved;

according to the fine aggregate methylene blue value testing method, the waste liquid generated in the testing process is less, the methylene blue solution is 30mL, 5mL is taken to dilute by 10 times, and the total amount of the waste liquid generated in one test can be controlled within 100 mL.

Example 2 is as follows:

on the basis of example 1, in order to reduce the error caused by factors such as uneven mixing of the mixed solution and existence of fine suspended particles therein. The test method of the present application makes optimization corrections in example 2:

(1) and (2) adding 30mL of aqueous solution into a conical flask, adding 0-0.075 mm-sized fine aggregate with the mass of 3g, fully mixing uniformly, and standing for 5 min. And (3) sucking 5mL of supernatant of the mixed solution in the conical flask by using a suction pipe, adding water to dilute by 10 times to obtain a solution to be detected, detecting the absorbance of the solution to be detected at a test wavelength of 664nm by using a spectrophotometer, and carrying out comparative analysis on the absorbance of the solution to be detected and the absorbance of a pure water solution.

Effect of finely suspended particles on test results

Solutions of	Aqueous solution	Solution to be tested
			Spectrophotometry (A)	0.0077	0.0393

Therefore, the fine suspended particles in the standing fine aggregate mixed aqueous solution can indeed have certain influence on the test result, and the measured concentration test result of the methylene blue solution is larger.

(2) To eliminate the effect of suspended particles on the assay results, a filtration method may be employed. However, the quantitative filter paper still brings new influence on the test result, and because the quantitative filter paper has a certain adsorption effect on methylene blue, the concentration of the methylene blue solution filtered by the quantitative filter paper may change to a certain extent. In order to study the influence of the test result on the test result, the filtrate obtained by filtering 1g/L of methylene blue original solution through quantitative filter paper and the 1g/L of methylene blue original solution are respectively diluted by 20 times, and then the spectrophotometry is tested and compared.

Effect of Using quantitative Filter paper on test results

Solutions of	Not filtered	Filtration
			Spectrophotometry (A)	3.1266	3.0139

Therefore, the absorbance of the methylene blue solution filtered by the quantitative filter paper is influenced to a certain extent, and the measured concentration test result of the methylene blue solution is smaller.

Based on the analysis of (1) and (2), two groups of parallel tests are considered, in the fourth step, the mixed solution is simultaneously subjected to standing and quantitative filter paper filtration treatment, and the test results measured by the two methods are subjected to weighted integration to serve as a final result, so that the error of the test results measured by the two methods is counteracted, and the test result is ensured to be more accurate.

Filtering the solution to be measured through quantitative filter paper to obtain a filtered solution, calculating through a fifth step, when the methylene blue concentration in the filtered solution is A ' mg/L through a standard curve, the methylene blue concentration B ' in the supernatant of the mixed solution is 10A ' mg/L, the methylene blue mass C ' absorbed by the fine aggregate is (1000-B ') × 30/1000mg, and measuring the methylene blue value of the fine aggregate after filtering treatment

And respectively adopting the method for taking supernatant after filtering and standing by quantitative filter paper in the application to test the methylene blue value of the fine aggregate. By way of comparison, fine aggregate methylene blue values were tested by experiential experimenters according to the conventional method specified in the road engineering aggregate test protocol (JTG E42), with the following differences: in order to ensure that the test result is closer to the true value, 0.5mL of methylene blue solution is added and stirred for 1min each time in the test process, and then the color halo test is carried out until the color halo can last for 5 min.

Corrected fine aggregate methylene blue value:wherein K₁As correction factor for the solution to be measured, K₂Is the correction factor for the filtered solution; wherein K₁+K₂Equal to 1. Selecting a sample to be tested, which is subjected to a spectrophotometer method to test the methylene blue value MBV of 0.5 +/-0.2 g/kg, and adopting a traditional method specified in Highway engineering aggregate test regulation JTG-E42 to carry out fine aggregate methylene blue value measurement so as to ensure the accuracy of a test resultAdding 0.5ml methylene blue solution each time, stirring for 1min, performing color halo test until color halo can last for 5min, and obtaining MBV of the sample to be tested₀(ii) a MBV and MBV of the sample to be detected₀Substituting MBV' into the calculation formula of the corrected methylene blue value of the fine aggregate to obtain the correction coefficient K of the solution to be measured₁And correction factor K of the filtered solution₂。

By adding 0.5ml of methylene blue solution each time, the change of the color halo of a sample with the methylene blue value MBV of 0.5 +/-0.2 g/kg can be accurately measured, and the phenomenon that the test result is directly changed from 0.5g/kg to 0.75g/kg is effectively avoided. Since the fine aggregate is a little more fine powder than the fine aggregate, the test results may jump from 0.5g/kg to 0.75g/kg directly, and no more than 0.6g/kg, no more than 0.7g/kg, etc. are measured, since the fine aggregate is a little more fine powder than the fine aggregate. Meanwhile, the required value of the methylene blue value in the specification is not more than 1.5 g/KG.

The results of the fine aggregate methylene blue test by the three methods are as follows:

therefore, compared with the test result which is close to the true value and is measured by the traditional test method, the result which is measured by adopting the quantitative filter paper filtering method is smaller, and the result which is measured by adopting the method of taking supernatant after standing is larger, so the method of taking the weighting coefficient from the results measured by the two methods is considered as the final test result of the methylene blue value of the fine aggregate, and the error of the test result measured by the two methods can be effectively counteracted.

According to the test results, the correction coefficients of the filtered solution and the solution to be tested are respectively K₂Is 0.16, K₁Is 0.84. For a batch of products, the experiment for obtaining the correction coefficient only needs to test for 1-2 times without repeated tests. In general, when the number of samples to be tested is small, values in the specified range can be obtained, for example: k₁Has a value range of 0.1-0.3 and K₂The value range of (A) is 0.7-0.9.

However, due to the difference of aggregate types and dosage, dilution times and the like, the correction coefficient has certain difference, but the influence on the evaluation of the final test result is acceptable.

According to the fine aggregate methylene blue value testing method based on the spectrophotometry, the test operation of manually judging the methylene blue adsorption condition of the fine aggregate by adopting a color halo test is abandoned, the characterization of the methylene blue adsorption condition of the fine aggregate is carried out by using the absorbance in a spectrophotometer, the influence of human factors on the test result is effectively reduced, the result is more objective and accurate than the result obtained by the original test method, meanwhile, the experience requirement on operators is reduced, and the repeatability of the test is ensured; according to the fine aggregate methylene blue value testing method based on the spectrophotometry, the tested test data is more accurate and credible, the operability is strong, the discrimination of different fine aggregates is more obvious, and the quick, accurate and quantitative evaluation of the fine aggregate methylene blue value can be realized; meanwhile, a filtering solution is obtained by adopting a filtering mode, and the methylene blue value of the mixed solution is corrected, so that the error of the suspended particles brought to the absorbance of the solution tested by the spectrophotometer method is reduced.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any minor modifications, equivalent replacements and improvements made to the above embodiment according to the technical spirit of the present invention should be included in the protection scope of the technical solution of the present invention.