Detection method of residual anionic polyacrylamide concentration and molecular weight in machine-made sand

Abstract

The present disclosure provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in manufactured sand, comprising: establishing a database of double-threshold values ​​of anionic polyacrylamide standard aqueous solutions at different concentrations and molecular weights based on the I-V relationship curve of a standard sample, and fitting the double-threshold value database of anionic polyacrylamide standard aqueous solutions into a nonlinear surface formula; obtaining characteristic points V1 and V2 from the I-V relationship curve of the sample to be tested, substituting V1 and V2 into the nonlinear surface formula fitted by the double-threshold value database of anionic polyacrylamide standard aqueous solutions to obtain the molecular weight Mr and concentration Φ of the anionic polyacrylamide in the sample to be tested; and calculating the concentration Φ0 of the anionic polyacrylamide attached to the manufactured sand based on the mass ratio of manufactured sand to deionized water. The present disclosure effectively addresses the current limitation of the unknown molecular weight of anionic polyacrylamide in the field of manufactured sand testing.

Description

Technical Field

[0001] The present disclosure relates to the technical field of civil engineering materials, and more particularly to a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand. Background Art

[0002] In concrete, various types of sand with reasonable gradation are used as fine aggregate to fill the gaps between stones. On the one hand, they ensure the fluidity of freshly mixed concrete, and on the other hand, they provide support for the strength of hardened concrete. They are one of the important raw materials for concrete.

[0003] In recent years, due to national resource and environmental protection requirements, the mining of natural river sand, a high-quality fine aggregate, has been restricted. Consequently, an increasing number of manufactured sands are being used as fine aggregate in concrete. However, as an artificial sand, the biggest difference between manufactured sand and natural river sand is that, after the raw stone is crushed and screened, manufactured sand typically undergoes a washing process to meet national or industry standards for low mud and stone dust content in fine aggregate. Furthermore, washing processes typically pursue non-standardization and high efficiency, often using anionic polyacrylamide as a flocculant to accelerate the sedimentation of mud and stone dust. This results in the attachment of anionic polyacrylamide flocculants of unknown molecular weight to the manufactured sand, effectively altering its properties, which in turn significantly impacts the performance of concrete and leads to poorer quality in concrete projects.

[0004] Research clearly demonstrates that the presence of anionic polyacrylamide flocculants on manufactured sand significantly impacts the slump and slump loss of concrete. Specifically, for an 18 million molecular weight anionic polyacrylamide, every 0.001% increase in its attachment to the manufactured sand reduces the mortar expansion by 5.36 mm. When the anionic polyacrylamide content reaches 0.009% of the sand's mass, the mortar expansion is reduced by over 25%. At 0.015% of the sand's mass, the optimal water-reducing agent is rendered ineffective. Furthermore, anionic polyacrylamide exhibits different molecular weights, with larger molecular weights exhibiting superior flocculation. Therefore, when using anionic polyacrylamide with a molecular weight of 20 million, the two thresholds can be reduced to 0.006% and 0.012%, respectively.

[0005] Existing tests for anionic polyacrylamide, such as turbidity, absorbance, or viscosity, can only detect anionic polyacrylamide of a specific molecular weight and are not suitable for detecting anionic polyacrylamide of unknown molecular weight attached to manufactured sand. Furthermore, manufactured sand also contains other interfering impurities, such as fine mud particles and pigment particles that cause the sand washing water to appear yellowish-brown. In fact, the engineering community has very strict regulations on the fluidity of concrete under certain mix ratios, which determines whether fresh concrete can be successfully pumped and poured. Therefore, testing only for anionic polyacrylamide of a specific molecular weight is of limited significance. A method is needed that can simultaneously detect the concentration and molecular weight of flocculants attached to manufactured sand to more comprehensively determine the performance of manufactured sand and ensure that the fluidity of concrete meets on-site requirements.

[0006] Therefore, a rapid, low-cost, and accurate method for detecting different concentrations and molecular weights of anionic polyacrylamide in machine-made sand is needed. Summary of the Invention

[0007] (1) Technical issues to be resolved

[0008] In view of this, the present disclosure provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand to solve the current limitation problem of the lack of anionic polyacrylamide molecular weight in the field of machine-made sand detection.

[0009] (2) Technical solution

[0010] The present disclosure provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand, the method comprising:

[0011] S1: Prepare the samples to be tested, standard samples and test reagents, connect the test components and configure the test equipment;

[0012] S2: Testing the standard sample to obtain an IV relationship curve between the ammeter output current value I of the standard sample and the volume V of the added anionic polyacrylamide standard aqueous solution;

[0013] S3: establishing a double-threshold database of anionic polyacrylamide standard aqueous solutions under different concentrations and different molecular weights based on the IV relationship curve of the standard sample, and fitting the double-threshold database of anionic polyacrylamide standard aqueous solutions into a nonlinear surface formula;

[0014] S4: testing the sample to be tested, and obtaining an IV relationship curve between the output current value I of the ammeter of the sample to be tested and the volume V of the added anionic polyacrylamide aqueous solution;

[0015] S5: Obtain characteristic points V1 and V2 from the IV relationship curve of the sample to be tested, substitute V1 and V2 into the nonlinear surface formula fitted by the double threshold database of anionic polyacrylamide standard aqueous solution, and obtain the molecular weight Mr and concentration Φ of the anionic polyacrylamide in the sample to be tested by solving the nonlinear equation system;

[0016] S6: Based on the mass ratio of machine-made sand to deionized water in S1, the concentration Φ0 of anionic polyacrylamide attached to the machine-made sand is calculated.

[0017] In the above solution, step S1 includes:

[0018] S11: Fully mix the machine-made sand sample to be tested and deionized water in a mass ratio of 1:1 to 1:3 to prepare the sample to be tested;

[0019] S12: preparing anionic polyacrylamide solid samples of different molecular weights, with molecular weights ranging from 12 million to 20 million, with a molecular weight step of 2 million; using deionized water to prepare anionic polyacrylamide standard aqueous solutions with concentrations of 0.003% to 0.021% as standard samples;

[0020] S13: preparing type A and type B reagents as detection reagents, wherein the type A reagent can react with anionic polyacrylamide and has a relatively obvious reaction phenomenon, and the type B reagent does not react with anionic polyacrylamide but has good conductivity;

[0021] S14: Prepare a 24-36V AC power supply, connect the solution pools numbered 1, 2, 3, and 4 in series with copper wires, connect the positive electrode of solution pool No. 1 to the positive electrode of the power supply, connect the negative electrode of solution pool No. 4 to the negative electrode of the power supply, and connect an ammeter between the negative electrode of solution pool No. 1 and the positive electrode of solution pool No. 4; use a hose to connect solution pools No. 1, 2, 3, and 4 to solution pool No. 5, set up a peristaltic pump in the middle, and adjust the peristaltic pump flow rate to 2-5ml / min; prepare a 4-channel synchronous electromagnetic stirrer with a speed of 100r / min-500r / min.

[0022] In the above scheme, the Class A reagents described in step S13 include: copper sulfate, ferric sulfate, copper chloride, ferric chloride, ferrous sulfate, ferrous chloride, nickel chloride, potassium chromate, potassium dichromate or potassium permanganate; the concentration of the Class A reagents is 0.005 mol / L to 0.01 mol / L; the Class B reagents described in step S13 include: sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, calcium chloride, magnesium chloride or magnesium sulfate; the Class B reagents have two concentrations: the higher concentration is 0.005 mol / L to 0.01 mol / L, and the lower concentration is 0.001 mol / L to 0.003 mol / L.

[0023] In the above solution, step S2 includes:

[0024] S21: Take 200mL~300mL of Class A reagent and inject it into the No. 1 solution tank of the detection equipment, take an equal volume of lower concentration Class B reagent and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of higher concentration Class B reagent and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL~1000mL of standard sample and add it into the No. 5 solution tank;

[0025] S22: Turn on the power supply, and the single chip computer immediately records the initial output current value I0 of the ammeter; turn on the peristaltic pump, and add the anionic polyacrylamide standard aqueous solution in the No. 5 solution pool to the No. 1 and No. 3 solution pools. After each addition of 5ml to 10ml, the output current value I of the ammeter is recorded. x ; The current value I0 and I x Normalize it:

[0026] I=I x -I0

[0027] The IV relationship curve between the output current value I of the ammeter and the volume V of the added anionic polyacrylamide standard aqueous solution was drawn using a single-chip microcomputer, with the starting point being point 0.

[0028] In the above solution, step S3 includes:

[0029] S31: for each molecular weight of anionic polyacrylamide standard aqueous solution with different concentrations, obtain the range of characteristic points on the curve under different concentrations and different molecular weight conditions, record it as a double threshold value represented by the volume V of the added anionic polyacrylamide standard aqueous solution, and establish a database of double threshold values ​​of anionic polyacrylamide standard aqueous solutions under different concentrations and different molecular weight conditions;

[0030] S32: Fitting the double threshold database of the anionic polyacrylamide standard aqueous solution into a nonlinear surface formula.

[0031] In the above scheme, in the dual threshold value represented by the volume V of the added anionic polyacrylamide standard aqueous solution in step S31, the maximum value of the current value I on the curve corresponding to threshold 1 is the corresponding volume V1 of the anionic polyacrylamide standard aqueous solution, and the volume V2 of the anionic polyacrylamide standard aqueous solution corresponding to the intersection of the curve and the x-axis is corresponding to threshold 2. The nonlinear surface formula for fitting the database of the dual threshold value of the anionic polyacrylamide standard aqueous solution in step S32 is as follows:

[0032] V1=A1×Φ+B1×Mr+C1×Φ 2 +D1×Mr 2 +E1×Φ×Mr+F1

[0033] V2=A2×Φ+B2×Mr+C2×Φ2 +d2×Mr 2 +E2×Φ×Mr+F2

[0034] Among them, the horizontal axis x and the vertical axis y correspond to the concentration Φ and molecular weight Mr of the anionic polyacrylamide standard sample, respectively. Except for V1, V2, Φ and Mr, other parameters are constant coefficients.

[0035] In the above solution, step S4 includes:

[0036] S41: Take 200mL to 300mL of Class A reagent and inject it into the No. 1 solution tank of the detection equipment, take an equal volume of a lower concentration Class B reagent and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of a higher concentration Class B reagent and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL to 1000mL of the sample to be tested and add it to the No. 5 solution tank;

[0037] S42: Turn on the power supply, and the single chip computer immediately records the initial output current value I0 of the ammeter; turn on the peristaltic pump, and add the sample to be tested in the No. 5 solution pool to the No. 1 and No. 3 solution pools. After each 5ml to 10ml of water is added, the output current value I of the ammeter is recorded. x ; The current value I0 and I x Normalize it:

[0038] I=I x -I0

[0039] The single chip microcomputer is used to draw the IV relationship curve between the output current value I of the ammeter and the volume V of the sample to be tested, with the starting point being point 0.

[0040] In the above solution, the characteristic point V1 in step S5 is the volume V1 of the sample to be detected, corresponding to the maximum value of the current value I; the characteristic point V2 in step S5 is the volume V2 of the sample to be detected, corresponding to the intersection of the curve and the x-axis.

[0041] In the above scheme, the calculation method used in step S6 to obtain the concentration Φ0 of anionic polyacrylamide attached to the machine-made sand is:

[0042] Φ0=Φ×m2 / m1

[0043] Wherein, m1 is the mass of machine-made sand in step S1, and m2 is the mass of deionized water in step S1.

[0044] In the above scheme, the method further includes: judging whether the machine-made sand raw material from which the machine-made sand sample is obtained can be used for concrete preparation based on the calculated anionic polyacrylamide concentration Φ0 and the anionic polyacrylamide molecular weight Mr attached to the machine-made sand, wherein:

[0045] When the test result shows anionic polyacrylamide with a molecular weight of 18 million, when the concentration of anionic polyacrylamide Φ0≤0.009%, its effect on the slump and slump loss of concrete is small, and it can be used to prepare concrete; when the concentration of anionic polyacrylamide is 0.009%<Φ0≤0.015%, its effect on the slump and slump loss of concrete is significant, and the concrete mix ratio needs to be adjusted, and the amount of water reducer needs to be appropriately increased to meet the slump requirements; when the concentration of anionic polyacrylamide Φ0>0.015%, its effect on the slump and slump loss of concrete can no longer be compensated by using water reducer, and the machine-made sand needs to be cleaned twice with clean water before retesting;

[0046] When the test result is anionic polyacrylamide with a molecular weight of 20 million, when the anionic polyacrylamide concentration Φ0≤0.006%, its effect on the slump and slump loss of concrete is small, and it can be used to prepare concrete; when the anionic polyacrylamide concentration is 0.006%<Φ0≤0.009%, its effect on the slump and slump loss of concrete is significant, and the concrete mix ratio needs to be adjusted, and the amount of water reducer needs to be appropriately increased to meet the slump requirements; when the anionic polyacrylamide concentration Φ0>0.009%, its effect on the slump and slump loss of concrete can no longer be compensated by using water reducer, and the machine-made sand needs to be cleaned twice with clean water before retesting.

[0047] (3) Beneficial effects

[0048] A method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand to address the current limitation of the unknown molecular weight of anionic polyacrylamide in the field of machine-made sand detection.

[0049] It can be seen from the above technical solution that the method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand provided by the present disclosure has at least the following beneficial effects:

[0050] 1. The present disclosure provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand. Through a one-time detection method, the molecular weight of the anionic polyacrylamide flocculant attached to the machine-made sand and the corresponding concentration value are directly, quickly and accurately tested, which effectively solves the current limitation of the lack of anionic polyacrylamide molecular weight in the field of machine-made sand detection, and ensures the reasonable evaluation of the quality of machine-made sand. This has not been mentioned in the prior art, and this is also the biggest difference and the most important innovation of the present disclosure from the prior art. This is because the prior art is mostly focused on developing a concentration test or characterization method for an anionic polyacrylamide flocculant of a specific molecular weight (existing turbidity method, absorbance method, viscosity method and TOC method, etc.), which is not conducive to detecting its concentration under the condition of the presence of multiple molecular weight flocculants. It will result in a larger measured concentration of a lower molecular weight flocculant or a smaller measured concentration of a higher molecular weight anionic polyacrylamide flocculant, which is not conducive to the reasonable evaluation of the quality of machine-made sand.

[0051] 2. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand provided by the present disclosure fully considers the soluble impurities other than the anionic polyacrylamide flocculant attached to the machine-made sand and the fine particles that change the color of the aqueous solution, and adopts the constant voltage conductivity test method to avoid the interference of the above impurities on the test results. The detection of anionic polyacrylamide aqueous solution is expanded to the detection of the concentration of other flocculants attached to the machine-made sand. This is completely different from the existing technology, and also solves the problems that have not been solved by the existing technology (turbidity method, absorbance method, viscosity method and TOC method, etc.), highlighting the innovativeness of the present disclosure.

[0052] 3. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand provided by the present invention realizes the judgment of molecular weight and concentration by establishing a dual threshold value and a dual threshold value database of the IV curve of the anionic polyacrylamide standard aqueous solution. Compared with the existing technology that only uses a single slope and a single inflection point, it is more accurate and can achieve accurate judgment of anionic polyacrylamide attached to machine-made sand of different molecular weights at the same concentration. The operation method is simple and has strong universality, and can simply and effectively judge the quality of machine-made sand.

[0053] 4. The present invention provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand, and establishes a complete set of evaluation methods and post-treatment methods for anionic polyacrylamide flocculants attached to machine-made sand that affect the workability of concrete. This method can prompt on-site staff to pay attention to questionable machine-made sand raw materials in a timely manner, and assist technical personnel in making adjustments to the concrete mix ratio to ensure the quality of concrete projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The above contents and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0055] Figure 1 Flowchart of a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand according to an embodiment of the present disclosure.

[0056] Figure 2a and Figure 2b This is a dual threshold database of anionic polyacrylamide standard aqueous solutions with a concentration of 0.003% to 0.021% and a molecular weight of 16 million to 20 million according to the embodiment of the present disclosure; wherein the abscissa x and the ordinate y correspond to the concentration Φ and the molecular weight Mr of the anionic polyacrylamide standard sample, respectively. Figure 2a The z axis in the middle is the volume V2 of the sample to be tested. Figure 2b The middle z-axis is the volume V1 of the sample to be tested;

[0057] Figure 3 is an IV curve obtained by testing sample 1 according to an embodiment of the present disclosure;

[0058] Figure 4 is an IV curve obtained by testing sample 2 according to an embodiment of the present disclosure;

[0059] Figure 5 1 is an IV curve obtained by testing sample 3 according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0060] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0061] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0062] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0063] To address the current difficulty in quantitatively detecting the residual concentration of anionic polyacrylamide flocculants of varying molecular weights in manufactured sand, while also preventing the impact of soluble impurities and colored particles attached to the manufactured sand that alter water quality on the test results, the present disclosure proposes a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in manufactured sand. This method directly, rapidly, and accurately measures the molecular weight and corresponding concentration of the anionic polyacrylamide flocculant attached to the manufactured sand, ensuring a reasonable assessment of the manufactured sand's quality. This approach, which has not been addressed in the prior art, highlights the innovation of the present disclosure. Furthermore, the present disclosure fully considers soluble impurities other than the anionic polyacrylamide flocculant attached to the manufactured sand, as well as fine particles that alter the color of the aqueous solution, thereby avoiding interference with the test results from such impurities, a significant difference from the prior art. Furthermore, the present disclosure establishes a dual-threshold IV curve and a dual-threshold database for anionic polyacrylamide standard aqueous solution to enable molecular weight and concentration determination. Furthermore, the present disclosure provides an evaluation method and post-treatment method for anionic polyacrylamide flocculants attached to manufactured sand, ensuring the quality of concrete projects.

[0064] like Figure 1 As shown, Figure 1 A flow chart of a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand according to an embodiment of the present disclosure is shown. The method comprises the following steps:

[0065] S1: Prepare the samples to be tested, standard samples and test reagents, connect the test components, and configure the test equipment; specifically include:

[0066] S11: Fully mix the machine-made sand sample to be tested and deionized water in a mass ratio of 1:1 to 1:3 to ensure that the anionic polyacrylamide flocculant molecules attached to the machine-made sand sample can be fully dissolved in the water, thereby obtaining an anionic polyacrylamide flocculant aqueous solution with an unknown molecular weight as the sample to be tested;

[0067] S12: preparing anionic polyacrylamide solid samples of different molecular weights, with molecular weights ranging from 12 million to 20 million, with a molecular weight step of 2 million; using deionized water to prepare anionic polyacrylamide standard aqueous solutions with concentrations of 0.003% to 0.021% as standard samples;

[0068] S13: preparing type A and type B reagents as detection reagents, wherein the type A reagent can react with anionic polyacrylamide and has a relatively obvious reaction phenomenon, and the type B reagent does not react with anionic polyacrylamide but has good conductivity;

[0069] In this step, the Class A reagent includes: copper sulfate, ferric sulfate, copper chloride, ferric chloride, ferrous sulfate, ferrous chloride, nickel chloride, potassium chromate, potassium dichromate or potassium permanganate, etc. The Class A reagent can react with the anionic polyacrylamide flocculant and has a relatively obvious reaction phenomenon; the concentration of the Class A reagent is 0.005 mol / L to 0.01 mol / L. Under this concentration condition, when the concentration of the anionic polyacrylamide flocculant in the sample to be tested is extremely low, it is conducive to the rapid reaction between the two.

[0070] In this step, the Class B reagents include: sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, calcium chloride, magnesium chloride or magnesium sulfate, etc. This type of reagent does not react with the anionic polyacrylamide flocculant but has good conductivity; the Class B reagents have two concentrations: the higher concentration is 0.005mol / L~0.01mol / L, under this concentration condition, the reagent has stable and good conductivity; the lower concentration is 0.001mol / L~0.003mol / L, under this concentration condition, when the concentration of anionic polyacrylamide in the sample to be tested is extremely low, it can ensure that the anionic polyacrylamide has good conductivity.

[0071] S14: prepare a 24-36V AC power supply, connect the solution pools numbered 1, 2, 3, and 4 in series with copper wires, connect the positive electrode of the No. 1 solution pool to the positive electrode of the power supply, connect the negative electrode of the No. 4 solution pool to the negative electrode of the power supply, and connect an ammeter between the negative electrode of the No. 1 solution pool and the positive electrode of the No. 4 solution pool (optionally, the ammeter has a range of 100Ma and an accuracy of 10μA); use a hose to connect the solution pools No. 1, 2, 3, and 4 to the No. 5 solution pool, set up a peristaltic pump in the middle, and adjust the peristaltic pump flow rate to 2-5ml / min. This speed can ensure that the anionic polyacrylamide flocculant It can fully react with Class A reagent and ensure stable ammeter output. In addition, a 4-channel synchronous electromagnetic stirrer with a rotation speed of 100r / min to 500r / min is prepared to accelerate the full reaction of anionic polyacrylamide flocculant with Class A reagent, and can also avoid the influence of irregular molecular thermal motion in the solution on conductivity, and ensure stable current output. The reason for using this circuit structure to carry out the test is that it can shield the soluble impurities attached to the machine-made sand (including soluble salts, mud powder, stone powder, etc.) from interfering with the test results, thereby showing the difference from the existing technology.

[0072] S2: Testing the standard sample to obtain an IV curve between the current value I output by the ammeter of the standard sample and the volume V of the added anionic polyacrylamide standard aqueous solution; specifically including:

[0073] S21: Take 200mL~300mL of Class A reagent and inject it into the No. 1 solution tank of the detection equipment, take an equal volume of lower concentration Class B reagent and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of higher concentration Class B reagent and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL~1000mL of standard sample and add it into the No. 5 solution tank;

[0074] S22: Turn on the power supply, and the single chip computer immediately records the initial output current value I0 of the ammeter; turn on the peristaltic pump, and add the anionic polyacrylamide standard sample aqueous solution in the No. 5 solution pool to the No. 1 and No. 3 solution pools. After each addition of 5ml to 10ml, the output current value I of the ammeter is recorded. x ; The current value I0 and I x Normalize it:

[0075] I=I x -I0

[0076] The IV relationship curve between the output current value I of the ammeter and the volume V of the added anionic polyacrylamide standard aqueous solution was drawn using a single-chip microcomputer, with the starting point being point 0.

[0077] S3: establishing a double-threshold database of anionic polyacrylamide standard aqueous solutions under different concentrations and different molecular weights based on the IV relationship curve of the standard sample, and fitting the double-threshold database of anionic polyacrylamide standard aqueous solutions into a nonlinear surface formula; specifically comprising:

[0078] S31: for each molecular weight of anionic polyacrylamide standard aqueous solution with different concentrations, obtain the range of characteristic points on the curve under different concentrations and different molecular weight conditions, record it as a double threshold value represented by the volume V of the added anionic polyacrylamide standard aqueous solution, and establish a database of double threshold values ​​of anionic polyacrylamide standard aqueous solutions under different concentrations and different molecular weight conditions;

[0079] In this step, in the dual threshold represented by the volume V of the added anionic polyacrylamide standard aqueous solution, the maximum value of the current value I on the curve corresponding to threshold 1 is the corresponding volume V1 of the anionic polyacrylamide standard aqueous solution, and the volume V2 of the anionic polyacrylamide standard aqueous solution corresponding to the intersection of the curve and the x-axis is corresponding to threshold 2;

[0080] S32: fitting the double threshold database of the anionic polyacrylamide standard aqueous solution into a nonlinear surface formula;

[0081] In this step, the double threshold database of the anionic polyacrylamide standard aqueous solution (such as Figure 2a 、 Figure 2b )The nonlinear surface formula for fitting is as follows:

[0082] V1=A1×Φ+B1×Mr+C1×Φ 2 +D1×Mr 2 +E1×Φ×Mr+F1

[0083] V2=A2×Φ+B2×Mr+C2×Φ 2 +D2×Mr 2 +E2×Φ×Mr+F2

[0084] Among them, the horizontal axis x and the vertical axis y correspond to the concentration Φ and molecular weight Mr of the anionic polyacrylamide standard sample, respectively. Figure 2a The z axis in the middle is the volume V2 of the sample to be tested. Figure 2b The z-axis is the volume V1 of the sample to be tested. Except for V1, V2, Φ and Mr, other parameters are constant coefficients. The constant coefficient fitting results and fitting goodness are shown in the following table:

[0085] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[C1]]> <![CDATA[D1]]> <![CDATA[E1]]> <![CDATA[F1]]> <![CDATA[R 2 ]]> <![CDATA[-2.05×10 4 ]]> <![CDATA[-1.36×10 -6 ]]> <![CDATA[-1.39×10 6 ]]> <![CDATA[-9.31×10 -26 ]]> <![CDATA[-4.96×10 -3 ]]> 56.24 0.9988 <![CDATA[A2]]> <![CDATA[B2]]> <![CDATA[C2]]> <![CDATA[D2]]> <![CDATA[E2]]> <![CDATA[F2]]> <![CDATA[R 2 ]]> <![CDATA[-1.42×10 5 ]]> <![CDATA[-1.39×10 -5 ]]> <![CDATA[-8.17×10 -7 ]]> <![CDATA[2.78×10 -13 ]]> <![CDATA[-6.67×10 -3 ]]> 231.12 0.9995

[0086] S4: Testing the sample to be tested to obtain an IV relationship curve between the output current value I of the ammeter of the sample to be tested and the volume V of the added anionic polyacrylamide aqueous solution; specifically including:

[0087] S41: Take 200mL to 300mL of Class A reagent and inject it into the No. 1 solution tank of the detection equipment, take an equal volume of a lower concentration Class B reagent and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of a higher concentration Class B reagent and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL to 1000mL of the sample to be tested and add it to the No. 5 solution tank;

[0088] S42: Turn on the power supply, and the single chip computer immediately records the initial output current value I0 of the ammeter; turn on the peristaltic pump, and add the sample to be tested in the No. 5 solution pool to the No. 1 and No. 3 solution pools. After each 5ml to 10ml of water is added, the output current value I of the ammeter is recorded. x ; The current value I0 and I x Normalize it:

[0089] I=I x -I0

[0090] The single chip microcomputer is used to draw the IV relationship curve between the output current value I of the ammeter and the volume V of the sample to be tested, with the starting point being point 0.

[0091] S5: Obtain characteristic points V1 and V2 from the IV relationship curve of the sample to be tested, substitute V1 and V2 into the nonlinear surface formula fitted by the double threshold database of anionic polyacrylamide standard aqueous solution, and obtain the molecular weight Mr and concentration Φ of the anionic polyacrylamide in the sample to be tested by solving the nonlinear equation system;

[0092] In this step, the characteristic point V1 is the volume V1 of the sample to be detected, corresponding to the maximum value of the current value I; the characteristic point V2 is the volume V2 of the sample to be detected, corresponding to the intersection of the curve and the x-axis.

[0093] S6: Based on the mass ratio of machine-made sand to deionized water, the concentration of anionic polyacrylamide attached to the machine-made sand is calculated as follows:

[0094] Φ0=Φ×m2 / m1

[0095] Wherein, m1 is the mass of machine-made sand in step S1, and m2 is the mass of deionized water in step S1.

[0096] Thus, the present disclosure provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand, which obtains the concentration Φ0 of anionic polyacrylamide attached to the machine-made sand and the molecular weight Mr of anionic polyacrylamide.

[0097] Furthermore, based on the concentration Φ0 of anionic polyacrylamide attached to the machine-made sand and the molecular weight Mr of anionic polyacrylamide obtained in the present disclosure, it can be further determined whether the machine-made sand raw material from which the machine-made sand sample is obtained can be used for concrete preparation, specifically including:

[0098] When the test result shows anionic polyacrylamide with a molecular weight of 18 million, when the concentration of anionic polyacrylamide Φ0≤0.009%, its effect on the slump and slump loss of concrete is small, and it can be used to prepare concrete; when the concentration of anionic polyacrylamide is 0.009%<Φ0≤0.015%, its effect on the slump and slump loss of concrete is significant, and the concrete mix ratio needs to be adjusted, and the amount of water reducer needs to be appropriately increased to meet the slump requirements; when the concentration of anionic polyacrylamide Φ0>0.015%, its effect on the slump and slump loss of concrete can no longer be compensated by using water reducer, and the machine-made sand needs to be cleaned twice with clean water before retesting;

[0099] When the test result is anionic polyacrylamide with a molecular weight of 20 million, when the anionic polyacrylamide concentration Φ0≤0.006%, its effect on the slump and slump loss of concrete is small, and it can be used to prepare concrete; when the anionic polyacrylamide concentration is 0.006%<Φ0≤0.009%, its effect on the slump and slump loss of concrete is significant, and the concrete mix ratio needs to be adjusted, and the amount of water reducer needs to be appropriately increased to meet the slump requirements; when the anionic polyacrylamide concentration Φ0>0.009%, its effect on the slump and slump loss of concrete can no longer be compensated by using water reducer, and the machine-made sand needs to be cleaned twice with clean water before retesting.

[0100] The following examples further illustrate the method for detecting the molecular weight of a flocculant in manufactured sand, provided by this disclosure. The flocculant is anionic polyacrylamide. This example uses manufactured sand coated with anionic polyacrylamide as the research object. Following the instructions in the specific implementation plan, a dual-threshold database of standard aqueous solutions of anionic polyacrylamide with varying concentrations and molecular weights is generated. These solutions are then thoroughly mixed at a 1:1 mass ratio to obtain an aqueous solution of anionic polyacrylamide with an unknown molecular weight, serving as the test sample. Further testing yields current values ​​and corresponding injection volumes, as shown in Table 1.

[0101]

[0102] Table 1 Test current values ​​and test solution sample filling volumes

[0103] The IV curve drawn according to Table 1 is as follows Figure 3 、 Figure 4 、 Figure 5 shown.

[0104] Figure 3 The middle dual threshold values ​​were V1 = 21.80, V2 = 48.19; Figure 4 V1 = 15.20, V2 = 32.10 for the middle dual threshold; Figure 5 The dual threshold values ​​of V1=18.60 and V2=40.07.

[0105] Substituting the above threshold values ​​into the nonlinear surface formula fitted by the double threshold database of anionic polyacrylamide standard aqueous solution shown in Figure 2, it can be found that sample 1 contains anionic polyacrylamide with a concentration of 0.009% and a molecular weight of 18 million, sample 2 contains anionic polyacrylamide with a concentration of 0.015% and a molecular weight of 18 million, and sample 3 contains anionic polyacrylamide with a concentration of 0.009% and a molecular weight of 20 million.

[0106] At the same time, since the mass ratio of machine-made sand to water is 1:1 when preparing the samples to be tested, the residual anionic polyacrylamide concentrations in the three machine-made sand samples are:

[0107] Sample 1: Anionic polyacrylamide with a concentration of 0.009% and a molecular weight of 18 million has little effect on the slump and slump loss of concrete and can be used to prepare concrete;

[0108] Sample 2: Anionic polyacrylamide with a concentration of 0.015% and a molecular weight of 18 million has a significant impact on the slump and slump loss of concrete. The concrete mix ratio needs to be adjusted and the amount of water reducer should be appropriately increased to meet the slump requirements.

[0109] Sample 3: Anionic polyacrylamide with a concentration of 0.009% and a molecular weight of 20 million has a significant impact on the slump and slump loss of concrete. It is necessary to adjust the concrete mix ratio and appropriately increase the amount of water reducer to meet the slump requirements.

[0110] The embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that any implementations not depicted or described in the drawings or the main text of the specification are known to those skilled in the art and are not described in detail. Furthermore, the above definitions of the various elements and methods are not limited to the various specific structures, shapes, or methods described in the embodiments, and can be easily modified or replaced by those skilled in the art.

[0111] Those skilled in the art will appreciate that the features described in the various embodiments of the present disclosure may be combined and / or coupled in various ways, even if such combinations or couplings are not explicitly described in the present disclosure. In particular, the features described in the various embodiments of the present disclosure may be combined and / or coupled in various ways without departing from the spirit and teachings of the present disclosure. All such combinations and / or couplings fall within the scope of the present disclosure.

[0112] The above describes the embodiments of the present disclosure. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand, characterized in that: The method includes: S1: Prepare the samples to be tested, standard samples and test reagents, connect the test components and configure the test equipment; S2: Testing the standard sample to obtain an IV relationship curve between the ammeter output current value I of the standard sample and the volume V of the added anionic polyacrylamide standard aqueous solution; S3: establishing a double-threshold database of anionic polyacrylamide standard aqueous solutions under different concentrations and different molecular weights based on the IV relationship curve of the standard sample, and fitting the double-threshold database of anionic polyacrylamide standard aqueous solutions into a nonlinear surface formula; S4: testing the sample to be tested, and obtaining an IV relationship curve between the output current value I of the ammeter of the sample to be tested and the volume V of the added anionic polyacrylamide aqueous solution; S5: Obtain characteristic points V1 and V2 from the IV relationship curve of the sample to be tested, substitute V1 and V2 into a nonlinear surface formula fitted by a double-threshold database of anionic polyacrylamide standard aqueous solutions, and obtain the molecular weight Mr and concentration Φ of the anionic polyacrylamide in the sample to be tested by solving the nonlinear equation system; wherein the characteristic point V1 is the volume V1 of the sample to be tested, corresponding to the maximum value of the current value I; the characteristic point V2 is the volume V2 of the sample to be tested, corresponding to the intersection of the curve and the x-axis; S6: Calculate the concentration of anionic polyacrylamide attached to the machine-made sand based on the mass ratio of machine-made sand to deionized water. Wherein, step S3 includes: S31: For each molecular weight of anionic polyacrylamide standard aqueous solution of different concentrations, obtain the range of characteristic points on the curve under conditions of different concentrations and different molecular weights, record them as a dual threshold represented by the volume V of the added anionic polyacrylamide standard aqueous solution, and establish a database of dual thresholds of anionic polyacrylamide standard aqueous solution under conditions of different concentrations and different molecular weights; in the dual threshold represented by the volume V of the added anionic polyacrylamide standard aqueous solution, threshold 1 corresponds to the maximum value of the current value I on the curve, which is the corresponding volume V1 of the anionic polyacrylamide standard aqueous solution, and threshold 2 corresponds to the volume V2 of the anionic polyacrylamide standard aqueous solution corresponding to the intersection of the curve and the x-axis; S32: Fitting the double threshold value database of the anionic polyacrylamide standard aqueous solution to a nonlinear surface formula is as follows: Among them, the horizontal axis x and the vertical axis y correspond to the concentration Φ and molecular weight Mr of the anionic polyacrylamide standard sample, respectively. Except for V1, V2, Φ and Mr, other parameters are constant coefficients.

2. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand according to claim 1, characterized in that: Step S1 includes: S11: Fully mix the machine-made sand sample to be tested and deionized water in a mass ratio of 1:1 to 1:3 to prepare the sample to be tested; S12: Prepare anionic polyacrylamide solid samples of different molecular weights, ranging from 12 million to 20 million, with a molecular weight step of 2 million; use deionized water to prepare anionic polyacrylamide standard aqueous solutions with concentrations of 0.003% to 0.021% as standard samples; S13: Prepare Class A and Class B reagents as detection reagents, wherein the Class A reagent can react with anionic polyacrylamide and has a relatively obvious reaction phenomenon, and the Class B reagent does not react with anionic polyacrylamide but has good conductivity; wherein the Class A reagent in step S13 includes: copper sulfate, ferric sulfate, copper chloride, ferric chloride, ferrous sulfate, ferrous chloride, nickel chloride, potassium chromate, potassium dichromate or potassium permanganate; the concentration of the Class A reagent is 0.005 mol / L~0.01 mol / L; the Class B reagent in step S13 includes: sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, calcium chloride, magnesium chloride or magnesium sulfate; the Class B reagent has two concentrations: the higher concentration is 0.005 mol / L~0.01 mol / L, and the lower concentration is 0.001 mol / L~0.003 mol / L; S14: Prepare a 24-36V AC power supply, connect the solution pools numbered 1, 2, 3, and 4 in series with copper wires, connect the positive electrode of the solution pool No. 1 to the positive electrode of the power supply, connect the negative electrode of the solution pool No. 4 to the negative electrode of the power supply, and connect an ammeter between the negative electrode of the solution pool No. 1 and the positive electrode of the solution pool No. 4; use a hose to connect the solution pools No. 1, 2, 3, and 4 to the solution pool No. 5, set up a peristaltic pump in the middle, and adjust the peristaltic pump flow rate to 2-5ml / min; prepare a 4-channel synchronous electromagnetic stirrer with a speed of 100r / min-500r / min; The step S2 includes: S21: Take 200mL~300mL of Class A reagent and inject it into the No. 1 solution tank of the detection equipment, take an equal volume of lower concentration Class B reagent and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of higher concentration Class B reagent and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL~1000mL of standard sample and add it into the No. 5 solution tank; S22: Turn on the power supply, and the single chip computer immediately records the initial output current value I0 of the ammeter; turn on the peristaltic pump, and add the anionic polyacrylamide standard aqueous solution in the No. 5 solution pool to the No. 1 and No. 3 solution pools. After each addition of 5ml~10ml, the output current value I of the ammeter is recorded. x ; The current value I0 and I x Normalize it: I=I x - I0 The IV relationship curve between the output current value I of the ammeter and the volume V of the added anionic polyacrylamide standard aqueous solution was drawn using a single-chip microcomputer, with the starting point being point 0.

3. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand according to claim 2, characterized in that: Step S4 includes: S41: Take 200mL~300mL of Class A reagent and inject it into the No. 1 solution tank of the detection equipment, take an equal volume of a lower concentration Class B reagent and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of a higher concentration Class B reagent and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL~1000mL of the sample to be tested and add it to the No. 5 solution tank; S42: Turn on the power supply, and the single chip computer immediately records the initial output current value I0 of the ammeter; turn on the peristaltic pump, and add the sample to be tested in the No. 5 solution pool to the No. 1 and No. 3 solution pools. After each 5ml~10ml is added, the output current value I of the ammeter is recorded. x ; The current value I0 and I x Normalize it: I=I x - I0 The single chip microcomputer is used to draw the IV relationship curve between the output current value I of the ammeter and the volume V of the sample to be tested, with the starting point being point 0.

4. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand according to claim 1, wherein: The calculation method used in step S6 to obtain the concentration Φ0 of anionic polyacrylamide attached to the machine-made sand is: Φ0=Φ×m2 / m1 Wherein, m1 is the mass of machine-made sand in step S1, and m2 is the mass of deionized water in step S1.

5. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand according to claim 1, characterized in that: The method further includes: Based on the calculated anionic polyacrylamide concentration Φ0 and anionic polyacrylamide molecular weight Mr attached to the machine-made sand, it is determined whether the machine-made sand raw materials used to obtain the machine-made sand sample can be used for concrete preparation, where: When the test result shows anionic polyacrylamide with a molecular weight of 18 million, when the concentration of anionic polyacrylamide Φ0≤0.009%, its effect on the slump and slump loss of concrete is small, and it can be used to prepare concrete; when the concentration of anionic polyacrylamide is 0.009%<Φ0≤0.015%, its effect on the slump and slump loss of concrete is significant, and the concrete mix ratio needs to be adjusted, and the amount of water reducer needs to be appropriately increased to meet the slump requirements; when the concentration of anionic polyacrylamide Φ0>0.015%, its effect on the slump and slump loss of concrete can no longer be compensated by water reducer, and the machine-made sand needs to be cleaned twice with clean water before retesting; When the test result is anionic polyacrylamide with a molecular weight of 20 million, when the concentration of anionic polyacrylamide Φ0≤0.006%, its effect on the slump and slump loss of concrete is small, and it can be used to prepare concrete; when the concentration of anionic polyacrylamide is 0.006%<Φ0≤0.009%, its effect on the slump and slump loss of concrete is significant, and the concrete mix ratio needs to be adjusted, and the amount of water reducer needs to be appropriately increased to meet the slump requirements; when the concentration of anionic polyacrylamide Φ0>0.009%, its effect on the slump and slump loss of concrete can no longer be compensated by water reducer, and the manufactured sand needs to be cleaned twice with clean water and then retested.

Images