Method for rapidly detecting content of calcium oxide and magnesium oxide in cement for roads, bridges and tunnels

Abstract

The invention provides a method for rapidly detecting the content of calcium oxide and magnesium oxide in cement for roads, bridges and tunnels, and relates to the technical field of content detection of calcium oxide and magnesium oxide. The detection method comprises the following steps: adding a digestion solution and a proper amount of purified water into cement to prepare a turbid liquid, adding a proper amount of cobalt chloride into the turbid liquid until the turbid liquid becomes pink, putting a filter bag into the turbid liquid, and adding a proper amount of strong-acid cation exchange resin into the filter bag until the pink disappears; taking out the filter bag filled with the strong-acid cation exchange resin, treating the filter bag in an aluminum sulfate solution, filtering the aluminum sulfate solution, drying and weighing precipitates generated in the solution, carrying out EDTA titration on the original turbid liquid, and calculating the content of calcium oxide and magnesium oxide. According to the method, the defects in the prior art are overcome, the calcium ions and the magnesium ions are separated and detected, the content of calcium oxide and the content of magnesium oxide can be detected only through one test, and meanwhile the detection speed, the detection precision and the operation safety are effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of calcium oxide and magnesium oxide content detection, and in particular to a method for quickly detecting the calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels. Background Art

[0002] Cement for roads, bridges and tunnels is a material commonly used in road, bridge and tunnel construction projects. It is hardened in air or water to firmly bond sand, stone and other materials together to form a concrete structure with a certain strength, such as bridge load-bearing structure, road pavement and tunnel lining structure. The production of cement for roads, bridges and tunnels must comply with relevant national standards, among which the stability and strength of cement are particularly important. The stability of cement reflects the uniformity of the volume change of cement during the coagulation and hardening process, and the strength of cement reflects the ability of the cement mortar hardening specimen to withstand external force damage. The content of calcium oxide and magnesium oxide in cement determines the stability and strength of cement. The right amount of calcium oxide content is the key to high strength of cement, but if the calcium oxide content is too high, it will affect the stability of cement, and if the calcium oxide content is too low, it will affect the strength of cement; the right amount of magnesium oxide can improve the volume stability of cement, improve the fire resistance of cement, improve the durability of cement and improve the sulfate resistance of cement. However, if the magnesium oxide content in cement is too high, it will reduce the quality of the building and even cause accidents. Therefore, the detection of calcium oxide and magnesium oxide content in cement is of great significance.

[0003] At present, the method for detecting the content of magnesium oxide and calcium oxide in cement is to detect it by the method provided in the national standard GB / T176-2008 for cement chemical analysis, wherein the detection of calcium oxide content requires the method of high-temperature alkali fusion to treat the sample, and high-temperature burning is required. There is a certain danger in the test process. In addition, the alkaline reagent added during the high-temperature burning process will affect the result; in the detection of magnesium oxide content, the cement sample is treated with a hydrofluoric acid-perchloric acid system and then tested. The hydrofluoric acid introduced during the treatment process may cause certain damage to the instrument. The detection method of calcium oxide and magnesium oxide content in a silicate cement provided by Publication No. CN108279274A detects the calcium oxide and magnesium oxide content by an ion chromatograph, but the retention time of magnesium ions and calcium ions in the ion chromatogram is relatively close. If the chromatographic conditions are not ideal, it may be difficult to achieve effective separation of the two. This will cause peak overlap or tailing, thereby affecting the accuracy of quantitative analysis. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for rapid detection of calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels. By separating calcium ions and magnesium ions and performing detection, the content of calcium oxide and magnesium oxide in cement can be detected in one test while effectively improving detection accuracy and operational safety.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented through the following technical solutions:

[0006] A rapid detection method for calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels, the detection method comprising the following steps:

[0007] S1. Add y ml of digestion solution to a container containing m grams of cement sample and stir thoroughly. After the reaction is complete, add d ml of pure water to obtain a suspension sample; where y>8.87m, d=500-y;

[0008] S2. Add c grams of cobalt chloride hexahydrate to the above suspension sample until the suspension turns pink;

[0009] S3, take the filter bag, immerse the bag body of the filter bag in the pink suspension in step S2 above, and extend the upper opening of the filter bag above the liquid surface of the suspension;

[0010] S4, adding the strongly acidic cation exchange resin into the filter bag in batches from the upper opening of the filter bag until the pink color in the suspension disappears;

[0011] S5, take out the filter bag together with the strongly acidic cation exchange resin therein, wash the residual suspension on the surface thereof with clean water, and pour the solution obtained after washing back into the suspension;

[0012] S6, placing the cleaned filter bag together with the strongly acidic cation exchange resin therein into a container filled with aluminum sulfate, taking out the filter bag after stirring and washing its surface with clean water, and pouring the solution obtained after washing back into the aluminum sulfate solution;

[0013] S7, filter the aluminum sulfate solution after standing, dry and weigh the mass m of the precipitate obtained by filtration p1 gram;

[0014] S8, perform an EDTA titration test on the suspension in S5, and determine the consumption of 1 ml of titrant at the end of the titration based on the change in solution color;

[0015] S9, according to the mass m of the precipitate in S7 p1 g, and the consumption of 1 ml of titration solution in S8, calculate the content of calcium oxide and magnesium oxide in cement, and

[0016] The calculation formula for calcium oxide content is:

[0017] The calculation formula of magnesium oxide content is:

[0018] Where: ω1 is the calcium oxide content in cement; ω2 is the magnesium oxide content in cement, K1 is the ratio of the molar masses of calcium oxide and calcium sulfate; K2 is the ratio of the molar masses of magnesium oxide ETDA-Na2; ω3 is the mass fraction of EDTA-Na2 solution.

[0019] Preferably, the digestion solution is dilute hydrochloric acid with a mass fraction of 10%.

[0020] Preferably, in step S1, y>8.87m, d=500-y, 20≤m<20.5.

[0021] Preferably, in step S2, c=0.002y+0.0014m+9.328.

[0022] Preferably, the method of adding the strongly acidic cation exchange resin in step S4 comprises the following steps:

[0023] S4-1, add α ml of strong acid cation exchange resin into the filter bag and stir;

[0024] Wherein, a=[13.89m+4.67c-13], where [] is the rounding down symbol;

[0025] S4-2. Observe the solution color:

[0026] ① If the solution color does not change, add b ml of strongly acidic cation exchange resin and stir, where:

[0027] ②If the color of the solution disappears, stop adding the strong acid cation exchange resin.

[0028] Preferably, the cleaned filter bag in step S6 is placed in a container filled with aluminum sulfate and stirred for 30 seconds every 5 minutes, and the filter bag is taken out after a total treatment of 30 minutes.

[0029] Preferably, the method of the EDTA titration test in step S8 comprises the following steps:

[0030] S8-1, insert a pH meter into the suspension in S5, and add appropriate amounts of triethanolamine solution and ammonia-ammonium chloride buffer solution until the pH value of the suspension reaches 10;

[0031] S8-2, adding chrome black T indicator to the suspension;

[0032] S8-3, place the suspension under the burette, and use the burette to add an appropriate amount of EDTA-Na2 into the solution;

[0033] S8-4. Observe the color change of the solution:

[0034] ① If the solution color does not change, repeat step S8-3;

[0035] ②If the solution turns blue, record the amount of titrant consumed (1 ml).

[0036] The present invention provides a method for quickly detecting the content of calcium oxide and magnesium oxide in cement for roads, bridges and tunnels, which has the following advantages compared with the prior art:

[0037] (1) Different from the conventional technology for detecting the content of calcium oxide and magnesium oxide in cement, the present invention can detect the content of calcium oxide and magnesium oxide in cement through only one test. The present invention dissolves the calcium oxide and magnesium oxide in lime, separates the calcium ions and magnesium ions, and detects the calcium ions by a precipitation method and the magnesium ions by an EDTA titration method. This avoids the cumbersome steps and operations in conventional technology, is simple to operate, and has no technical requirements for operators. It improves the detection speed of magnesium oxide and calcium oxide in cement while ensuring the detection accuracy.

[0038] (2) The present invention utilizes a strong acid cation exchange resin material to achieve the effect of separating calcium ions and magnesium ions, thereby detecting the contents of calcium ions and magnesium ions separately; in addition, the strong acid cation exchange resin can be repeatedly recycled. After the test, the strong acid cation exchange resin can be restored to its regeneration capacity and participate in the recycling of the next test through steps such as backwashing with clean water, injection of a strong acid regeneration agent, slow flushing, and fast flushing, which is beneficial to sustainable development.

[0039] (3) The present invention avoids the high-temperature alkali melting step of cement used in the conventional technology, thus ensuring the safety of the test operation and being more energy-efficient. At the same time, the method avoids the introduction of hydrofluoric acid in the conventional detection technology, thus ensuring that the test equipment is not damaged. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flow chart of a method for quickly detecting the content of magnesium oxide and calcium oxide in cement for roads, bridges and tunnels of the present invention;

[0041] Figure 2 This is a schematic diagram of the placement of the filter bag and the container in Example 1 of the present invention;

[0042] In the figure: 1. filter bag; 2. beaker; 3. suspension. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Embodiment 1:

[0045] 1. Instruments and reagents

[0046] Laboratory electronic precision balance; burette; beaker; flask; glass funnel; filter paper; glass rod; filter bag; stainless steel measuring spoon (1 / 2 teaspoon); cobalt chloride hexahydrate (analytical grade); aluminum sulfate 18hydrate (analytical grade); 10% dilute hydrochloric acid (analytical grade); ammonia water (concentration 25-28%); ammonium chloride (analytical grade); EDTA-Na2·2H2O (analytical grade); triethanolamine (analytical grade); strongly acidic cation exchange resin; laboratory water is ultrapure water; the sample used is ordinary Portland cement sample P.O42.5 (produced by Zhucheng Yangchun Cement Co., Ltd.).

[0047] 2. Preparation of aluminum sulfate solution, EDTA-Na2 and ammonia-ammonium chloride buffer:

[0048] Take 400 grams of aluminum sulfate 18hydrate and put it into a conical flask, add 645.9 grams of pure water into the flask and shake it to dissolve it completely, to prepare an aluminum sulfate solution with a mass fraction of 20%;

[0049] Take 40g of EDTA-Na2·2H2O in a conical flask, add 325.6g of pure water and shake to dissolve it completely, to prepare a 10% EDTA-Na2 solution;

[0050] Take 5.4 grams of ammonium chloride in a conical flask, add 800 grams of water into the flask and shake to dissolve it completely, insert a pH meter into the flask, and gradually add ammonia water until the pH of the solution reaches 11.0 to prepare an ammonia-ammonium chloride buffer solution.

[0051] 3. Detection of calcium oxide and magnesium oxide in cement:

[0052] S1. Add 200 ml of 10% dilute hydrochloric acid to a beaker containing 20 g of cement sample and stir. After complete reaction, add 300 ml of pure water to obtain a suspension.

[0053] S2. Add 9.71 g of cobalt chloride hexahydrate to the suspension and stir until the solution turns a distinct pink color;

[0054] S3. Reference Figure 2 Place the filter bag in the suspension, making sure the bag is in full contact with the suspension;

[0055] S4, adding an appropriate amount of strong acid cation exchange resin to the filter bag in batches until the pink color in the suspension disappears, comprising the following steps:

[0056] Add 310 ml of strong acid cation exchange resin to the filter bag and stir; if the color of the solution does not change, continue to add 5 ml of strong acid cation exchange resin and stir;

[0057] S5, take out the filter bag and wash the remaining suspension on its surface with clean water, and pour the solution obtained after washing back into the suspension;

[0058] S6. Place the filter bag containing the strongly acidic cation exchange resin into a 500 ml beaker filled with 20% aluminum sulfate by mass, stir for 30 seconds every 5 minutes, take out the filter bag after 30 minutes and wash its surface with clean water, and pour the solution obtained after washing back into the aluminum sulfate solution;

[0059] S7, filtering the aluminum sulfate solution after standing, drying and weighing the mass of the precipitate obtained by filtration to be 30.05 g;

[0060] S8, performing an EDTA titration test on the suspension in S5, and determining that the consumption of the titrant at the end of the titration is 61 ml according to the change in the color of the solution, comprising the following steps:

[0061] S8-1, insert a pH indicator into the suspension in S5, add 5 ml of triethanolamine solution and an appropriate amount of ammonia-ammonium chloride buffer solution until the pH value of the solution is 10;

[0062] S8-2, add 2 drops of chrome black T indicator to the suspension in S5;

[0063] S8-3. Place the suspension in S5 under the burette and add 1 ml of 5% EDTA-Na2 to the solution. If the solution does not change color, repeat S8-2 and S8-3 until it turns blue. Record the consumption of the titrant: 61 ml.

[0064] S9, water According to the following formula, the content of calcium oxide in cement is 61.6%:

[0065]

[0066] The calcium oxide content in cement is calculated to be 61.6%, where: ω1 is the calcium oxide content in cement; m p1 is the mass of calcium sulfate precipitate produced; K1 is the ratio of the molar mass of calcium oxide to calcium sulfate;

[0067] The content of magnesium oxide in cement is calculated as 3.64% according to the following formula:

[0068]

[0069] Wherein, ω2 is the magnesium oxide content in cement; ω3 is the mass fraction of ETDA-Na2 solution; l is the mass of calcium sulfate precipitate produced; K2 is the ratio of the molar mass of calcium oxide to calcium sulfate.

[0070] Embodiment 2:

[0071] Calcium oxide and magnesium oxide content detection and verification:

[0072] (1) Take 14g of calcium oxide and 0.8g of magnesium oxide in a beaker and stir them evenly to prepare the sample to be tested;

[0073] (2) Add 200 ml of 10% dilute hydrochloric acid to the beaker containing the sample to be tested and stir. After the reaction is complete, add 300 ml of pure water to prepare a solution to be tested;

[0074] (3) Add 9.71 g of cobalt chloride hexahydrate to the test solution and stir until the solution turns a distinct pink color;

[0075] (4) Place the filter bag into the pink test solution, making sure the bag is in full contact with the test solution;

[0076] (5) Add 310 mL of strongly acidic cation exchange resin to the filter bag until the pink color disappears in the test solution;

[0077] (6) Take out the filter bag and clean the residual solution on its surface with clean water, and pour the solution obtained after cleaning back into the original solution;

[0078] (7) Place the filter bag containing the strongly acidic cation exchange resin into a 500 ml beaker filled with 20% aluminum sulfate by mass, stir for 30 seconds every 5 minutes, take out the filter bag after 30 minutes and wash its surface with clean water, and pour the solution obtained after washing back into the aluminum sulfate solution;

[0079] (8) filtering the aluminum sulfate solution after standing, drying and weighing the precipitate obtained by filtration, which is 32.47 g;

[0080] (9) Perform an EDTA titration test on the original solution in step (6). According to the change in solution color, determine that the titrant consumption at the end of the titration is 64 ml:

[0081] Insert a pH indicator into the original solution in step (5), add 5 ml of triethanolamine solution and an appropriate amount of ammonia-ammonium chloride buffer solution until the pH value of the solution is 10;

[0082] Add 2 drops of chrome black T indicator to the original solution in S5;

[0083] Place the original solution under the burette and add 1 ml of 5% EDTA-Na2 to the solution; if the solution does not change color, repeat the above steps until it turns blue and record the consumption of the titrant as 64 ml.

[0084] (10) Based on the mass of the precipitate (32.47 g) and the amount of titrant consumed (64 ml), the mass of calcium oxide was calculated to be 13.37 g; the mass of magnesium oxide was calculated to be 0.76 g.

[0085] The above overall calculated results of calcium oxide and magnesium oxide have small errors and high accuracy.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for rapid detection of calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels, characterized in that: The detection method comprises the following steps: S1. Add y ml of digestion solution to a container containing m grams of cement sample and stir thoroughly. After the reaction is complete, add d ml of pure water to obtain a suspension sample; where y>8.87m, d=500-y; S2. Add c grams of cobalt chloride hexahydrate to the above suspension sample until the suspension turns pink; S3, take the filter bag, immerse the bag body of the filter bag in the pink suspension in step S2 above, and extend the upper opening of the filter bag above the liquid surface of the suspension; S4, adding the strongly acidic cation exchange resin into the filter bag in batches from the upper opening of the filter bag until the pink color in the suspension disappears; S5, take out the filter bag together with the strongly acidic cation exchange resin therein, wash the residual suspension on the surface thereof with clean water, and pour the solution obtained after washing back into the suspension; S6, placing the cleaned filter bag together with the strongly acidic cation exchange resin therein into a container filled with aluminum sulfate, taking out the filter bag after stirring and washing its surface with clean water, and pouring the solution obtained after washing back into the aluminum sulfate solution; S7, filter the aluminum sulfate solution after standing, dry and weigh the mass m of the precipitate obtained by filtration p1 gram; S8, perform an EDTA titration test on the suspension in S5, and determine the consumption of 1 ml of titrant at the end of the titration based on the change in solution color; S9, according to the mass m of the precipitate in S7 p1 g, and the consumption of 1 ml of titration solution in S8, calculate the content of calcium oxide and magnesium oxide in cement, and The calculation formula for calcium oxide content is: The calculation formula of magnesium oxide content is: Where: ω1 is the calcium oxide content in cement; ω2 is the magnesium oxide content in cement, K1 is the ratio of the molar masses of calcium oxide and calcium sulfate; K2 is the ratio of the molar masses of magnesium oxide ETDA-Na2; ω3 is the mass fraction of EDTA-Na2 solution.

2. The method for rapid detection of calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels according to claim 1, characterized in that: The digestion solution is dilute hydrochloric acid with a mass fraction of 10%.

3. The method for rapid detection of calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels according to claim 1, characterized in that: In the step S1, y>8.87m, d=500-y, 20≤m<20.

5.

4. The method for rapid detection of calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels according to claim 1, characterized in that: In the step S2, c=0.002y+0.0014m+9.

328.

5. The method for rapid detection of calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels according to claim 1, characterized in that: The method of adding the strongly acidic cation exchange resin in step S4 comprises the following steps: S4-1, add α ml of strong acid cation exchange resin into the filter bag and stir; Wherein, a=[13.89m+4.67c-13], where [] is the rounding down symbol; S4-2. Observe the solution color: ① If the solution color does not change, add b ml of strongly acidic cation exchange resin and stir, where: ②If the color of the solution disappears, stop adding the strong acid cation exchange resin.

6. The method for rapid detection of calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels according to claim 1, characterized in that: The cleaned filter bag in step S6 is placed in a container filled with aluminum sulfate and stirred for 30 seconds every 5 minutes, and the filter bag is taken out after a total treatment of 30 minutes.

7. A rapid detection method for calcium oxide and magnesium oxide content in cement for roads, bridges and tunnels according to claim 1, characterized in that: The method of EDTA titration test in step S8 comprises the following steps: S8-1, insert a pH meter into the suspension in S5, and add appropriate amounts of triethanolamine solution and ammonia-ammonium chloride buffer solution until the pH value of the suspension reaches 10; S8-2, adding chrome black T indicator to the suspension; S8-3, place the suspension under the burette, and use the burette to add an appropriate amount of EDTA-Na2 into the solution; S8-4. Observe the color change of the solution: ① If the solution color does not change, repeat step S8-3; ②If the solution turns blue, record the amount of titrant consumed (1 ml).

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