Method for detecting concentration and molecular weight of residual anionic polyacrylamide in machine-made sand

Abstract

The invention provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand, which comprises the following steps: establishing a database of dual thresholds of anionic polyacrylamide standard aqueous solution under the conditions of different concentrations and different molecular weights on the basis of an I-V relation curve of a standard sample, fitting the database of the dual thresholds of the anionic polyacrylamide standard aqueous solution into a nonlinear curved surface formula; the method comprises the following steps: obtaining characteristic points V1 and V2 from an I-V relation curve of a to-be-detected sample, and respectively substituting V1 and V2 into a nonlinear curved surface formula formed by fitting a database of dual thresholds of an anionic polyacrylamide standard aqueous solution to obtain the molecular weight Mr and concentration phi of anionic polyacrylamide in the to-be-detected sample; according to the mass ratio of the machine-made sand to the deionized water, the concentration phi 0 of the anionic polyacrylamide attached to the machine-made sand is obtained through calculation. The problem that the limitation that the molecular weight of anionic polyacrylamide is unknown lacks in the current machine-made sand detection field is effectively solved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of civil engineering materials, and more specifically 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 grading are used as fine aggregate to fill the gaps between stones. On the one hand, it ensures the fluidity of fresh concrete, and on the other hand, it provides support for the strength of hardened concrete. It is one of the important raw materials for concrete.

[0003] In recent years, due to the needs of national resource protection and environmental protection, the mining of natural river sand as high-quality fine aggregate has been restricted, and more and more machine-made sand has been used as fine aggregate in concrete. However, as an artificial sand, the biggest difference between machine-made sand and natural river sand is that machine-made sand usually needs to go through a washing process after the original stone is crushed and screened to meet the national or industry standards for the lower mud powder and stone powder content in fine aggregate. At the same time, the washing process usually pursues non-standardization and high efficiency, and often uses anionic polyacrylamide as a flocculant to accelerate the sedimentation of mud powder and stone powder, which will cause the machine-made sand to be attached with anionic polyacrylamide flocculants of unknown molecular weight, which actually changes the performance of the machine-made sand, and then has a greater impact on the performance of concrete, resulting in poor quality of concrete projects.

[0004] The study clearly stated that when anionic polyacrylamide flocculants are attached to machine-made sand, the slump and slump loss of concrete will be significantly affected. Specifically, for anionic polyacrylamide with a molecular weight of 18 million, for every 0.001% increase in its attachment to machine-made sand, the mortar expansion will be reduced by 5.36 mm. When the anionic polyacrylamide attached to the machine-made sand reaches 0.009% of the mass of the machine-made sand, the mortar expansion can be reduced by more than 25%. When it reaches 0.015% of the mass of the machine-made sand, the water reducer with the optimal dosage will be ineffective. At the same time, anionic polyacrylamide has the characteristics of different molecular weights. The flocculation effect of anionic polyacrylamide with a larger molecular weight is better. Therefore, when anionic polyacrylamide with a molecular weight of 20 million is used for testing, the above two thresholds can be reduced to 0.006% and 0.012% respectively.

[0005] Among the existing tests for anionic polyacrylamide, the turbidity method, absorbance method or viscosity method can only detect anionic polyacrylamide of a certain molecular weight, and cannot detect anionic polyacrylamide of unknown molecular weight attached to machine-made sand. At the same time, other interfering impurities are attached to machine-made sand, such as fine mud powder particles and pigment particles that cause sand washing water to appear yellow-brown. In fact, the engineering industry has very strict regulations on the fluidity of concrete under certain mix conditions, which determines whether the fresh concrete can be pumped and poured smoothly. At this time, the significance of only testing anionic polyacrylamide of a certain molecular weight is very limited. A method that can simultaneously realize the detection of flocculant concentration and molecular weight attached to machine-made sand is needed, so as to more comprehensively determine the performance of machine-made 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 limitation problem of the lack of anionic polyacrylamide and unknown molecular weight in the current machine-made sand detection field.

[0009] (II) 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 samples to be tested, standard samples and test reagents, connect test elements and configure test equipment;

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

[0013] S3: establishing a double threshold database of anionic polyacrylamide standard aqueous solution under different concentrations and different molecular weight conditions based on the IV relationship curve of the standard sample, and fitting the double threshold database of anionic polyacrylamide standard aqueous solution 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 anionic polyacrylamide aqueous solution added;

[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 group;

[0016] S6: According to 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 scheme, 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 obtain a sample to be tested;

[0019] S12: preparing anionic polyacrylamide solid samples with different molecular weights, the molecular weights of which are 12 million to 20 million, and the molecular weight step is 2 million; using deionized water to prepare anionic polyacrylamide standard aqueous solutions with concentrations of 0.003% to 0.021%, respectively, 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 an AC power supply with a voltage of 24 to 36 V, 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 flow rate of the peristaltic pump to 2 to 5 ml / min; prepare a 4-channel synchronous electromagnetic stirrer with a rotation speed of 100 r / min to 500 r / min.

[0022] In the above scheme, the Class A reagent described 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 0.005mol / L~0.01mol / L; the Class B reagent described 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 0.005mol / L~0.01mol / L, and the lower concentration is 0.001mol / L~0.003mol / L.

[0023] In the above scheme, 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 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 Class B reagents but with higher concentrations and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL~1000mL of the standard sample and add it into the No. 5 solution tank;

[0025] S22: Turn on the power supply, and the single-chip microcomputer 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 5ml to 10ml is added, 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 scheme, 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 represented by the volume V of the added anionic polyacrylamide standard aqueous solution, and establish a database of double thresholds of anionic polyacrylamide standard aqueous solution 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 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 intersection of the curve corresponding to threshold 2 and the x-axis corresponds to the volume V2 of the anionic polyacrylamide standard aqueous solution; the nonlinear surface formula for fitting the database of the dual threshold 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 abscissa x and the ordinate 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 scheme, 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 Class B reagent with a lower concentration and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of Class B reagent with a higher concentration 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 into the No. 5 solution tank;

[0037] S42: Turn on the power supply, and the single-chip microcomputer 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 filling, 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 scheme, 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 according to 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 is 18 million molecular weight anionic polyacrylamide, when the concentration of anionic polyacrylamide Φ0≤0.009%, it has little effect on the slump and slump loss of concrete, and can be used to prepare concrete; when the concentration of anionic polyacrylamide is 0.009%<Φ0≤0.015%, it has a significant effect on the slump and slump loss of concrete, 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;

[0046] When the test result is 20 million molecular weight anionic polyacrylamide, 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 water reducer, and the machine-made sand needs to be cleaned twice with clean water and re-tested.

[0047] (III) Beneficial effects

[0048] The detection method of residual anionic polyacrylamide concentration and molecular weight in machine-made sand is used to solve the limitation of the unknown molecular weight of anionic polyacrylamide in the current machine-made sand detection field.

[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 detection method of the concentration and molecular weight of residual anionic polyacrylamide in the machine-made sand provided by the present invention directly, quickly and accurately tests the molecular weight of the anionic polyacrylamide flocculant attached to the machine-made sand and the corresponding concentration value through a one-time detection method, which effectively solves the problem of the limitation of the lack of unknown molecular weight of anionic polyacrylamide in the current machine-made sand detection field, and ensures the reasonable evaluation of the quality of the machine-made sand. This has not been mentioned in the prior art, which is also the biggest difference and the most important innovation point between the present invention and the prior art. 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.), it is not conducive to detecting its concentration under the condition of the presence of multiple molecular weight flocculants, which 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 the machine-made sand.

[0051] 2. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand provided in the present invention 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, which is completely different from the prior art. At the same time, it also solves the problems that have not been solved by the prior art (turbidity method, absorbance method, viscosity method and TOC method, etc.), highlighting the innovativeness of the present invention.

[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 double threshold value and a double threshold value database of the IV curve of the standard aqueous solution of anionic polyacrylamide. Compared with the prior art which only uses a single slope and a single inflection point, it is more accurate and can realize the 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 can prompt on-site staff to pay attention to questionable machine-made sand raw materials in a timely manner to the greatest extent possible, 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 It is 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.

[0056] Figure 2a and Figure 2b It is a dual threshold database of anionic polyacrylamide standard aqueous solution 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 3 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 exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, 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 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 existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0062] All terms (including technical and scientific terms) used herein 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] In order to solve the problem that the residual amount of anionic polyacrylamide flocculants with different molecular weights in the current machine-made sand is difficult to quantitatively detect, and at the same time avoid the influence of soluble impurities attached to the machine-made sand and colored particles that change the water quality on the test results, the present disclosure proposes a detection method for the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand, which directly, quickly and accurately tests the molecular weight and corresponding concentration value of the anionic polyacrylamide flocculant attached to the machine-made sand, ensuring a reasonable evaluation of the quality of the machine-made sand, which has not been mentioned in the prior art, highlighting the innovation of the present disclosure; at the same time, 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, avoiding the interference of the above impurities on the test results, which is completely different from the prior art; in addition, the present disclosure establishes a dual threshold value of the IV curve of the anionic polyacrylamide standard aqueous solution and a dual threshold value database to realize the molecular weight and concentration judgment, and also provides an evaluation method and a post-processing method for anionic polyacrylamide flocculants attached to machine-made sand to ensure the quality of concrete engineering.

[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, and the method comprises the following steps:

[0065] S1: Prepare samples to be tested, standard samples and test reagents, connect test elements and configure 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 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 with different molecular weights, the molecular weights of which are 12 million to 20 million, and the molecular weight step is 2 million; using deionized water to prepare anionic polyacrylamide standard aqueous solutions with concentrations of 0.003% to 0.021%, respectively, 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 detected is extremely low, it is conducive to the rapid reaction of the two;

[0070] In this step, the Class B reagent includes: 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 reagent has 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 detected 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~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, ensuring 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 relationship curve between the current value I of the ammeter output of the standard sample and the volume V of the anionic polyacrylamide standard aqueous solution added; 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 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 Class B reagents but with higher concentrations and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL~1000mL of the standard sample and add it into the No. 5 solution tank;

[0074] S22: Turn on the power supply, and the single-chip microcomputer 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 5ml to 10ml is added, 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: Based on the IV relationship curve of the standard sample, a database of double threshold values ​​of anionic polyacrylamide standard aqueous solution under different concentrations and different molecular weight conditions is established, and the database of double threshold values ​​of anionic polyacrylamide standard aqueous solution is fitted into a nonlinear surface formula; specifically including:

[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 represented by the volume V of the added anionic polyacrylamide standard aqueous solution, and establish a database of double thresholds of anionic polyacrylamide standard aqueous solution under different concentrations and different molecular weight conditions;

[0079] In this step, in the double 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 of 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 in the middle 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 anionic polyacrylamide aqueous solution added; 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 Class B reagent with a lower concentration and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of Class B reagent with a higher concentration 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 into the No. 5 solution tank;

[0088] S42: Turn on the power supply, and the single-chip microcomputer 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 filling, 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 group;

[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: According to the mass ratio of machine-made sand to deionized water, the concentration of anionic polyacrylamide attached to the machine-made sand is calculated as Φ0. The calculation method used is:

[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 invention provides a method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand, and 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 obtained in the present disclosure and the molecular weight Mr of anionic polyacrylamide, it can be further judged 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 is 18 million molecular weight anionic polyacrylamide, when the concentration of anionic polyacrylamide Φ0≤0.009%, it has little effect on the slump and slump loss of concrete, and can be used to prepare concrete; when the concentration of anionic polyacrylamide is 0.009%<Φ0≤0.015%, it has a significant effect on the slump and slump loss of concrete, 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;

[0099] When the test result is 20 million molecular weight anionic polyacrylamide, 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 water reducer, and the machine-made sand needs to be cleaned twice with clean water and re-tested.

[0100] The following will further illustrate the molecular weight detection method of flocculant in machine-made sand provided by the present disclosure in combination with an example, wherein the flocculant is anionic polyacrylamide. This example takes machine-made sand attached with anionic polyacrylamide as the research object, and obtains a dual threshold database of anionic polyacrylamide standard aqueous solutions of different concentrations and different molecular weights according to the description in the specific implementation plan; and fully mixes them at a mass ratio of 1:1 to obtain anionic polyacrylamide aqueous solution dissolved with unknown molecular weight as the sample to be tested. Further testing obtains the current value and the corresponding injection solution volume, 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 thresholds were V1 = 21.80, V2 = 48.19; Figure 4 The middle dual thresholds have V1 = 15.20, V2 = 32.10; Figure 5 The dual threshold values ​​of medium are V1=18.60, V2=40.07.

[0105] Substituting the above threshold into the nonlinear surface formula fitted by the double threshold database of anionic polyacrylamide standard aqueous solution shown in Figure 2, it can be learned 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 concentrations of anionic polyacrylamide 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 effect 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;

[0109] Sample 3: Anionic polyacrylamide with a concentration of 0.009% and a molecular weight of 20 million has a significant effect 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] So far, the embodiments of the present disclosure have been described in detail in conjunction with the accompanying drawings. It should be noted that the implementation methods not shown or described in the drawings or the body of the specification are all forms known to ordinary technicians in the relevant technical field and are not described in detail. In addition, the above definitions of each element and method are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and ordinary technicians in the field can simply change or replace them.

[0111] It will be appreciated by those skilled in the art that the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways, even if such combinations or combinations are not explicitly described in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0112] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of 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 samples to be tested, standard samples and test reagents, connect test elements and configure test equipment; S2: Testing the standard sample to obtain an IV relationship curve between the current value I of the ammeter output of the standard sample and the volume V of the anionic polyacrylamide standard aqueous solution added; S3: establishing a double threshold database of anionic polyacrylamide standard aqueous solution under different concentrations and different molecular weight conditions based on the IV relationship curve of the standard sample, and fitting the double threshold database of anionic polyacrylamide standard aqueous solution 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 anionic polyacrylamide aqueous solution added; 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 group; S6: According to the mass ratio of machine-made sand to deionized water, the concentration Φ0 of anionic polyacrylamide attached to the machine-made sand is calculated.

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 obtain a sample to be tested; S12: preparing anionic polyacrylamide solid samples with different molecular weights, the molecular weights of which are 12 million to 20 million, and the molecular weight step is 2 million; using deionized water to prepare anionic polyacrylamide standard aqueous solutions with concentrations of 0.003% to 0.021%, respectively, as standard samples; 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; S14: Prepare an AC power supply with a voltage of 24 to 36 V, 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 flow rate of the peristaltic pump to 2 to 5 ml / min; prepare a 4-channel synchronous electromagnetic stirrer with a rotation speed of 100 r / min to 500 r / min.

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: 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 to 0.01 mol / L; The type B reagent in step S13 includes: sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, calcium chloride, magnesium chloride or magnesium sulfate; the type B reagent has two concentrations: a higher concentration of 0.005 mol / L to 0.01 mol / L, and a lower concentration of 0.001 mol / L to 0.003 mol / L.

4. 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 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 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 Class B reagents but with higher concentrations and inject them into the No. 2 and No. 4 solution tanks of the detection equipment; take 500mL~1000mL of the standard sample and add it into the No. 5 solution tank; S22: Turn on the power supply, and the single-chip microcomputer 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 5ml to 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 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.

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: Step S3 includes: 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 represented by the volume V of the added anionic polyacrylamide standard aqueous solution, and establish a database of double thresholds of anionic polyacrylamide standard aqueous solution under different concentrations and different molecular weight conditions; S32: Fitting the double threshold database of the anionic polyacrylamide standard aqueous solution into a nonlinear surface formula.

6. The method for detecting the concentration and molecular weight of residual anionic polyacrylamide in machine-made sand according to claim 5, characterized in that: In the double threshold 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 intersection of the curve corresponding to threshold 2 and the x-axis corresponds to the volume V2 of the anionic polyacrylamide standard aqueous solution; The nonlinear surface formula for fitting the double threshold database of the anionic polyacrylamide standard aqueous solution in step S32 is as follows: V1=A1×Φ+B1×Mr+C1×Φ 2 +D1×Mr 2 +E1×Φ×Mr+F1 <h2 style=";text-align:left;direction:ltr">V2 = A2×Φ + B2×Mr + C2×Φ<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +D2×Mr<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +E2×Φ×Mr+F2 Among them, the abscissa x and the ordinate 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.

7. 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 S4 includes: 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 Class B reagent with a lower concentration and inject it into the No. 3 solution tank of the detection equipment, and take two equal volumes of Class B reagent with a higher concentration 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 into the No. 5 solution tank; S42: Turn on the power supply, and the single-chip microcomputer 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 filling, 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.

8. 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 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.

9. 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 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.

10. 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: According to the calculated concentration Φ0 of anionic polyacrylamide attached to the machine-made sand and the molecular weight Mr of anionic polyacrylamide, it is judged whether the machine-made sand raw materials of the machine-made sand sample can be used for concrete preparation, wherein: When the test result is 18 million molecular weight anionic polyacrylamide, when the concentration of anionic polyacrylamide Φ0≤0.009%, it has little effect on the slump and slump loss of concrete, and can be used to prepare concrete; when the concentration of anionic polyacrylamide is 0.009%<Φ0≤0.015%, it has a significant effect on the slump and slump loss of concrete, 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 20 million molecular weight anionic polyacrylamide, 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 water reducer, and the machine-made sand needs to be cleaned twice with clean water and re-tested.

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