A method for quickly judging whether the methylene blue value of machine-made sand is qualified

Abstract

The invention discloses a method for quickly judging whether the methylene blue value of machine-made sand is qualified. The principle is to utilize the different effects of stone powder and mud powder on the fluidity of cement paste. Compared with mud powder, stone powder is more conducive to increasing the fluidity of cement paste. Therefore, the method of the invention designs a ratio K of the cement paste fluidity of machine-made sand powder to be tested to the cement paste of powder with a methylene blue value of 1.4 as a benchmark fluidity as a judgment standard. If the K value is greater than or equal to 1, the judgment result is qualified, and if the K value is less than 1, the judgment result is unqualified.

Description

Technical Field

[0001] The invention relates to the technical field of machine-made sand for concrete, and in particular to a method for quickly determining whether a methylene blue value of the machine-made sand is qualified. Background Art

[0002] Artificial sand is made by crushing rocks. Generally, the artificial sand for engineering and the crushed stone for concrete are produced from the same parent rock, and are obtained after crushing, screening and powder removal. The production of artificial sand generally uses rod mills, impact sand making machines or impact sand making machines. After crushing, a large amount of powder below 0.075mm will be brought in, including stone powder produced by the crushing of parent rock and mud powder mixed in during the crushing process. Since artificial sand was first included in the national standard in 2001, its powder content has always been an important indicator for judging the quality of artificial sand. In the standard, particles below 0.075mm are directly called "stone powder", and its content is the "stone powder content". The national standard divides the limit of powder content of machine-made sand into different categories (Class I, Class II, Class II) according to the MB value of machine-made sand (classified by MB value of 1.4g / kg); the relevant regulations in 2006 stipulate that when the MB value is <1.4, it is judged to be mainly stone powder; when the MB value is ≥1.4, it is judged to be stone powder mainly composed of mud powder; as of 2011, the relevant regulations have updated the provisions on relevant quality indicators of machine-made sand. The state stipulates that when the MB value is ≤1.4g / kg, the limit of powder content of each category of machine-made sand is relaxed to 10%, and when the MB value is >1.4g / kg, the limit of machine-made sand does not change.

[0003] At present, whether it is the national standard or the construction standard, the traditional method for testing the MB value of machine-made sand is the methylene blue method, which is used to determine the index of the adsorption performance of machine-made sand. The principle is to continuously add methylene blue solution to the suspension of machine-made sand. After each addition of methylene blue solution, the filter paper contamination test is used to test the appearance of free dye to check the adsorption of the dye solution by the sample. When the appearance of free dye is confirmed, the MB value can be calculated, which is expressed as the number of grams of dye adsorbed per kilogram of test particle size.

[0004] The invention patent application with application number CN202111474536.6 discloses a detection method for distinguishing the stone powder content and mud powder content in machine-made sand, comprising the following steps; S1, a preparation of machine-made sand: uniformly sample the machine-made sand material field, dry it and use the quartering method, and sieve out particles ≤0.75mm for later use; b preparation of pure stone powder: rinse the pebbles, basalt and limestone, crush them and grind them, sieve out particles ≤0.75mm and dry them for later use; c preparation of methylene blue solution: prepare according to the GB / T14684-2001 method; d pure stone powder methylene blue detection method: test according to the JGJ / T318-2014 method; S2, this test is mainly based on pebble stone powder, and the machine-made sand produced and crushed with pebbles is taken; a comparison sample pebble stone powder methylene blue MB value, weigh 50g of pebble stone powder ≤0.75mm. It can supplement and improve the detection and determination methods of the mud content and "stone powder" content of machine-made sand, effectively control the mud content, make full use of the "stone powder" content, improve the application level of machine-made sand quality control, and improve the technical, economic and social benefits of machine-made sand. This technical solution still uses the methylene blue method to test the stone powder content of machine-made sand. The methylene blue method involves many instruments and equipment. The methylene blue solution needed for measurement needs to be configured on-site, has a short validity period, and a long inspection cycle, which affects the inspection efficiency. Summary of the invention

[0005] The object of the present invention is to provide a method for quickly determining whether the methylene blue value of machine-made sand is qualified in view of the above-mentioned problems. The principle is to utilize the different effects of stone powder and mud powder on the fluidity of cement paste. Stone powder is more conducive to increasing the fluidity of cement paste than mud powder. Therefore, the method of the present invention designs the ratio K of the cement paste fluidity of the machine-made sand powder to be tested to the benchmark fluidity of the powder cement paste with an MB value of 1.4 as the judgment standard. If the K value is greater than or equal to 1, it is qualified, otherwise it is unqualified.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The invention discloses a method for quickly judging whether the methylene blue value of machine-made sand is qualified. According to the technical principle of the invention, firstly, machine-made sand with an MB value of 1.4 is prepared according to test experience, and then the dosage of machine-made sand powder in cement paste is determined by stone powder test, and the fluidity of cement paste with the dosage of powder less than 75 μm in the screening of machine-made sand with an MB value of 1.4 determined by the test is taken as the reference fluidity M0, and then, the powder less than 75 μm in the screening of the machine-made sand to be tested is added to the cement paste according to the dosage determined by the test, to obtain the test fluidity M1, calculate the flow ratio K value, and finally judge whether the MB value of the machine-made sand sample is qualified;

[0008] The technical features of the above technical solution can be used to quickly determine whether the MB value of the machine-made sand is qualified. The entire inspection process is fast, and there is no need to use chemical compound tests. The different characteristics of the stone powder and mud powder in the machine-made sand less than 75μm in powder on the fluidity of cement slurry are fully utilized to complete the entire technical process.

[0009] The technical effects of the present invention are as follows:

[0010] The present invention provides a method for quickly determining whether the methylene blue value of machine-made sand is qualified. The existing technical method uses chemical reagents, the inspection time is too long, the color halo determination in the contamination test is uncertain, and the result processing and analysis are difficult. Therefore, it is different from the existing technical method. By comparing with the technical features of this patent, it can be found that the present application has greatly improved the efficiency and saved a lot of inspection costs. It is very simple to understand, make, operate, control and use. The whole process is harmless to the human body and the environment compared with the existing technical method, and the final result processing and analysis are easier to understand than the existing technical method. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a specific implementation flow chart of the present invention;

[0012] Figure 2 It is the result determination table of the methylene blue method of the prior art;

[0013] Figure 3 It is the dosage test result table of the present invention;

[0014] Figure 4 is a table of results of a benchmark fluidity test of the present invention;

[0015] Figure 5 It is the test group number table of the present invention;

[0016] Figure 6 This is a cement paste fluidity test result table of the present invention;

[0017] Figure 7 is a flow ratio calculation result table of the present invention;

[0018] Figure 8 This is the test result table of artificial sand and gravel powder content;

[0019] Fig. 9 This is the Methylene Blue MB value verification table. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0022] The existing technology uses the test method for the content and MB value of artificial sand and gravel in "Sand for Construction" (GB / T 14684-2011).

[0023] The determination method of the prior art is as follows:

[0024] 1. Materials and instruments required for stone powder content and MB value:

[0025] 1.1 Methylene blue: (C16H18CIN3S·3H2O) content ≥ 95%;

[0026] 1.2 Quantitative filter paper (fast).

[0027] 1.3 Blast drying oven: can control the temperature at (105±5)℃;

[0028] 1.4 Balance: one for weighing 1000g and sensitivity 0.1g and one for weighing 100g and sensitivity 0.01g;

[0029] 1.5 Square hole sieve: one sieve with a hole diameter of 75μm, 1.18mm and 2.36mm;

[0030] 1.6 Container: When washing the sample, the sample must not splash out (depth greater than 250mm);

[0031] 1.7 Pipette: one 5mL and one 2mL pipette;

[0032] 1.8 Three-blade or four-blade impeller agitator: adjustable speed [up to (600±60)r / min], diameter (75±10)mm;

[0033] 1.9 Timing device: accuracy 1s;

[0034] 1.10 Glass volumetric flask: 1L;

[0035] 1.11 Thermometer: accuracy 1C;

[0036] 1.12 Glass rods: 2 pieces (8mm in diameter, 300mm in length);

[0037] 1.13 Enamel tray, brush, 1000mL beaker, etc.

[0038] 2. Inspection steps:

[0039] 2.1 Stone powder content test

[0040] Take samples according to regulations and reduce the sample to about 1100g. Place it in a drying oven at (105±5)℃ and dry it to constant weight. After cooling to room temperature, divide it into two approximately equal portions for later use.

[0041] Weigh 500g of the sample, accurate to 0.1g. Pour the sample into a washing container and add clean water to make the water level about 150mm higher than the sample surface. After fully stirring, soak for 2h, then wash the sample in the water by hand to separate dust, silt and clay from sand particles. Slowly pour the muddy water onto the 1.18mm and 75μm sieves (1.18mm sieve is placed on the 75μm sieve) to filter out particles smaller than 75μm.

[0042] Both sides of the sieve should be moistened with water before the test, and care should be taken to prevent sand loss during the entire process.

[0043] Then pour clean water into the container and repeat the above steps until the water in the container is visually clear.

[0044] Rinse the fine particles remaining on the sieve with water, and place the 75μm sieve in water (make the water surface slightly higher than the upper surface of the sand particles in the sieve) and shake it back and forth to fully wash away the particles smaller than 75μm. Then pour the remaining particles from the two sieves and the cleaned sample in the cleaning container into an enamel tray, place it in a drying oven at (105±5)℃ and dry it to a constant weight. After cooling to room temperature, weigh its mass to an accuracy of 0.1g.

[0045] 2.1 Methylene blue MB value test

[0046] Take samples according to regulations and reduce the sample to about 400g. Place it in a drying oven and dry it at (105±5)℃ to a constant weight. After cooling to room temperature, screen out particles larger than 2.36mm and set aside for later use.

[0047] Weigh 200 g of the sample, accurate to 0.1 g. Pour the sample into a beaker containing (500 ± 5) mL of distilled water, stir with an impeller stirrer at (600 ± 60) r / min for 5 min to form a suspension, and then continue stirring at (400 ± 40) r / min until the end of the test.

[0048] Add 5mL of methylene blue solution to the suspension, stir at (400±40)r / min for at least 1min, then use a glass rod to pick up a drop of suspension (the drop of suspension should make the diameter of the precipitate within 8mm~12mm), and drop it on the filter paper (placed on an empty beaker or other suitable support so that the surface of the filter paper does not contact any solid or liquid). If no color halo appears around the precipitate, add another 5mL of methylene blue solution, continue stirring for 1min, and then use a glass rod to pick up a drop of suspension and drop it on the filter paper. If no color halo appears around the precipitate, repeat the above steps until a stable light blue halo of about 1mm appears around the precipitate. At this time, continue stirring without adding methylene blue solution, and perform a staining test every 1min. If the color halo disappears within 4min, add another 5mL of methylene blue solution; if the color halo disappears in the 5th minute, add another 2mL of methylene blue solution. In both cases, continue stirring and staining test until the color halo can last for 5min.

[0049] Record the total volume of methylene blue solution added when the color halo lasts for 5 minutes, accurate to 1 mL.

[0050] 3. Result calculation

[0051] 3.1 Calculation of stone powder content

[0052] Calculate according to the following formula, accurate to 0.1%:

[0053] Q=(G0-G1 / G0)×100

[0054] In the formula: Q--stone powder content, %;

[0055] G. --The mass of the dried sample before the test, in grams (g);

[0056] G1 - the mass of the dried sample after the test, in grams (g).

[0057] The stone powder content is determined by taking the arithmetic mean of the test results of the two samples as the measured value, and the rounded value comparison method is used for evaluation.

[0058] 3.2 Calculation of Methylene Blue MB Value

[0059] Calculate according to the following formula, accurate to 0.1:

[0060] MB=(V / G)×10

[0061] Where:

[0062] MB--methylene blue value, in grams per kilogram (g / kg), indicating the mass of methylene blue consumed per kilogram of 0mm-2.36mm particle size sample; G--sample mass, in grams (g); V--the total amount of methylene blue solution added, in milliliters (mL); 10--the volume of methylene blue solution consumed per kilogram of sample converted into the mass of methylene blue.

[0063] The rounded value comparison method is used for evaluation, such as Figure 2 As shown, the MB values ​​of Class I / II / III machine-made sands are compared to determine whether they are qualified.

[0064] That is, the standard stone powder content and MB value test method for determining the quality of machine-made sand has the following problems:

[0065] 1. It involves a large number of instruments and equipment, and the span of disciplines is also wide, including multiple disciplines such as thermodynamics and chemistry, and the process is complicated and tedious.

[0066] 2. The methylene blue solution needed for the measurement needs to be prepared on-site, has a short shelf life, and the remaining solution is easily wasted. In addition, improper disposal of chemical waste liquid can easily cause environmental pollution.

[0067] 3. The inspection cycle is long. The entire process takes at least 8 hours, which seriously affects the inspection efficiency.

[0068] This embodiment effectively solves the above problems, and the theory and method steps are simple and easy to understand, and is more practical for on-site inspection of engineering construction. This embodiment is for machine-made sand with the same source and the same lithology parent material, and the principle is the same for other types of machine-made sand.

[0069] In this embodiment, the data used are preferred solutions, but are not used to limit the present invention;

[0070] In this embodiment, the MB value is the methylene blue value of machine-made sand;

[0071] In this embodiment, the test room temperature is 20℃±2℃, and the relative humidity should not be less than 50%; the temperature of all materials, instruments and appliances should be consistent with that of the test room;

[0072] like Figure 1 As shown, this embodiment discloses a method for quickly determining whether the methylene blue value of machine-made sand is qualified, including a blast drying box, a shaking screen machine, a cement slurry mixer and a weighing tool electronic balance, including the following steps:

[0073] S1: Determine the powder content in cement paste, weigh 300g cement, adopt internal mixing method, add stone powder at 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35% for comparative test, add 105g distilled water respectively for comparative test, stir in cement paste mixer; mix and stir to produce cement paste, stir at low speed for 120s, stop for 15s, and finally stir at high speed for 60s, stirring for a total of 180s; inject cement paste into truncated cone circular mold, scrape it flat with a scraper, lift the truncated cone circular mold in the vertical direction, start the stopwatch at the same time, and time the cement paste flowing on the glass plate for 30s, measure the flowing part of cement mortar on the glass plate with a vernier caliper, and take the average value as the cement paste fluidity;

[0074] like Figure 3 As shown, when the dosage is between 15% and 20%, the fluidity does not change much, so the dosage of artificial sand powder is determined to be 15%.

[0075] S2: Determination of the benchmark fluidity, prepare benchmark machine-made sand, weigh 500g of the prepared benchmark machine-made sand sample with an electronic balance, and be accurate to 1g; pour the sample into a set of sieves assembled from top to bottom according to the aperture size for screening, the set of sieves includes a sieve bottom, place the set of sieves on a shaking sieve machine, shake the sieve for 10 minutes, take out the sieve bottom and pour it into a porcelain plate, repeat the above steps until 500g of the benchmark machine-made sand powder is collected; weigh 45g of the benchmark machine-made sand powder, and determine the cement paste fluidity according to step S1 to obtain the benchmark fluidity M0;

[0076] like Figure 4 As shown, the cement paste fluidity is measured according to step S1, and the test is performed ten times, and the calculated average value is taken as the final reference fluidity M0=163mm.

[0077] S4: Preparation of bottom material for flow samples. Samples are taken from the on-site machine-made sand silo. The bottom, middle and top parts are grouped into one group. Five samples are taken from each group, for a total of 15 samples. They are numbered separately, and each sample weighs 20 kg.

[0078] like Figure 5 As shown, the bottom groups are numbered A1-A5, the middle groups are numbered B1-B5, and the top groups are numbered C1-C5;

[0079] S5: Determination of the fluidity of the machine-made sand sample. Dry the machine-made sand sample under laboratory conditions and collect the powder according to step S2. Weigh 45g of the machine-made sand powder sample and determine the fluidity M1 of the cement paste according to step S1. The test results are as follows: Figure 6 shown.

[0080] S6: Calculation of fluidity ratio: according to step S2 and step S5, the reference fluidity M0 and the cement paste fluidity M1 are obtained, and the fluidity ratio is calculated according to the formula K=M1 / M0;

[0081] S7: Determination of the results: for each machine-made sand sample, if the flow ratio is less than 1, it is considered unqualified; for the remaining samples, if the flow ratio is greater than or equal to 1, it is considered qualified. Figure 7 As shown, the flow ratios of A1, A3, and A4 are less than 1, which are judged as unqualified, while the remaining samples are qualified.

[0082] In this embodiment, the temperature of the blast drying oven is controlled at (105±5)°C; the weighing tool electronic balance includes two units, one weighing 1000g, with a sensitivity of 1g; the other weighing 1000g, with a graduation value of 1g; the set of sieves is a square hole sieve, and square hole sieves of specifications of 150μm, 300μm, 600μm, 1.18mm, 2.36mm, 4.75mm and 9.50mm are selected, and each square hole sieve is provided with a sieve bottom and a sieve cover.

[0083] In this embodiment, the truncated cone circular mold has an upper diameter of 36 mm, a lower diameter of 60 mm, a height of 60 mm, and a smooth inner wall without joints. The size of the glass plate is 400 mm × 400 mm × 5 mm. P.042.5 low-alkali cement is used, stone powder is <75 μm, and homemade MB value 1.4 benchmark sand and distilled water are used.

[0084] In this embodiment, the above results were verified according to the test method for the content of machine-made sand and stone powder and the MB value in "Construction Sand" (GB / T 14684-2011). The test steps were verified according to the methylene blue method test steps in the prior art. The test results are as follows: Figure 8 As shown;

[0085] Further, in this embodiment, the MB value of methylene blue is calculated according to the formula MB=(V / G)*10. The calculation result is as follows: Fig. 9 As shown, according to the MB value results, A1, A3, and A4 are greater than 1.4 and are judged to be unqualified. The MB values ​​of the remaining samples of artificial sand are less than 1.4 and are judged to be qualified, which verifies that the technical solution of this embodiment is correct and feasible.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for quickly determining whether the methylene blue value of machine-made sand is qualified, comprising a blast drying oven, a shaker, a cement slurry mixer and an electronic balance as a weighing tool, characterized in that: The steps include: S1: Determine the powder content in cement paste. Weigh 300g cement and use the internal mixing method to add stone powder at 0%, 5%, 10%, 15%, 20%, 25%, 30%, and 35% for comparative test. Add 105g of distilled water respectively for comparative test and stir in a cement paste mixer. Mix and stir to produce cement paste. Pour the cement paste into a truncated cone mold and scrape it flat with a scraper. Lift the truncated cone mold in a vertical direction and start a stopwatch at the same time. Allow the cement paste to flow on the glass plate for 30s. Use a vernier caliper to measure the maximum diameters of the flowing part in two directions perpendicular to each other, and take the average value as the fluidity of the cement paste. S2: Determination of the benchmark fluidity, preparation of benchmark machine-made sand, weighing 500g of the prepared benchmark machine-made sand sample on an electronic balance, and accurate to 1g; pouring the sample onto a set of sieves assembled from top to bottom according to the aperture size for screening, the set of sieves including a sieve bottom, placing the set of sieves on a shaking sieve machine, shaking the sieve for 10 minutes, taking out the sieve bottom and pouring it into a porcelain plate, repeating the above steps until 500g of the benchmark machine-made sand powder is collected; weighing 45g of the benchmark machine-made sand powder, determining the cement paste fluidity according to step S1, and obtaining the benchmark fluidity M0; and preparing benchmark machine-made sand with an MB value of 1.4 and distilled water; S4: Preparation of the base material for the test machine-made sand. Samples were taken from the machine-made sand silo on site. Each part of the top is a group, and the same number of samples are taken from each group and numbered separately, each weighing 20kg; S5: Determination of the fluidity of the test machine-made sand. After drying the test machine-made sand under laboratory conditions, collect the powder according to step S2, weigh 45g of the test machine-made sand powder, and determine the fluidity M1 of the cement paste according to step S1; S6: Calculation of fluidity ratio: according to step S2 and step S5, the reference fluidity M0 and the cement paste fluidity M1 are obtained, and the fluidity ratio is calculated according to the formula K=M1 / M0; S7: Determination of the results: for each test machine-made sand, if the fluidity ratio is less than 1, it is judged as unqualified; for the rest, if the fluidity ratio is greater than or equal to 1, it is judged as qualified.

2. The method for quickly determining whether the methylene blue value of machine-made sand is qualified according to claim 1, characterized in that: The step S7: determining the result, verifying the determination result by using the methylene blue method, and calculating the MB value according to the formula MB=(V / G)*10.

3. The method for quickly determining whether the methylene blue value of machine-made sand is qualified according to claim 2, characterized in that: According to the formula MB result, the MB value result is greater than 1.4, which is judged to be unqualified. The MB value of the sample artificial sand is less than 1.4, which is judged to be qualified.

4. The method for quickly determining whether the methylene blue value of machine-made sand is qualified according to claim 1, characterized in that: The step S1: the powder content in the cement paste is determined, and when stirring in the cement paste mixer, the cement paste is first stirred at a low speed for 120 seconds, the cement paste mixer is stopped for 15 seconds, and finally stirred at a high speed for 60 seconds, for a total of 180 seconds.

5. The method for quickly determining whether the methylene blue value of machine-made sand is qualified according to claim 1, characterized in that: The step S5: determining the fluidity of the test machine sand, the test room temperature of the test room conditions is 20°C ± 2°C, the relative humidity should be not less than 50%; the temperature of all materials, instruments and appliances is consistent with that of the test room.

6. The method for quickly determining whether the methylene blue value of machine-made sand is qualified according to claim 1, characterized in that: The temperature of the blast drying oven is controlled at 105±5°C.

7. The method for quickly determining whether the methylene blue value of machine-made sand is qualified according to claim 6, characterized in that: The electronic balance comprises two units, one unit has a weighing capacity of 1000g and a sensitivity of 1g; the other unit has a weighing capacity of 1000g and a graduation value of 1g.

8. The method for quickly determining whether the methylene blue value of machine-made sand is qualified according to claim 7, characterized in that: The set of sieves is a square hole sieve, and one square hole sieve with specifications of 150μm, 300μm, 600μm, 1.18 mm, 2.36 mm, 4.75 mm and 9.50 mm is selected, and each square hole sieve is attached with a sieve bottom and a sieve cover.

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