Method for testing the pore solution ph of concrete

Abstract

This invention discloses a method for testing the pH value of a concrete pore solution, belonging to the field of building materials technology. It includes the following steps: S1. Drill a hole in the surface of a concrete specimen, add deionized water into the hole, seal it, and cure it under standard conditions until the pH value of the solution in the hole no longer increases. The pH value measured at this point is recorded as X1; S2. Remove all the solution from the hole, add the same volume of deionized water as in step S1 back into the hole, seal it, and then perform standard curing for the same number of days as in step S1. Then test the pH value of the pore solution and record it as X2; S3. Calculate the pH value of the concrete pore solution according to the following formula: OH⁻ in the pore solution from step S1 = (OH⁻ in step S1) / ... ‑ Concentration Y1 = 10 (X1‑14) mol / L; Step S2 solution OH ‑ Concentration Y2 = 10 (X2‑14) mol / L; Actual OH in the solution of concrete pores ‑ Concentration Y = Y1 * Y1 / Y2 mol / L; pH of the concrete pore solution = 14 + lgY. This invention calculates the actual OH- ions in the concrete pore solution based on two pH values. ‑ Concentration can eliminate the dilution effect caused by large pore size, and obtain a pore solution pH value close to the true value.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a method for testing the pH value of a concrete pore solution. Background Technology

[0002] Alkali-aggregate reaction (AAR) in concrete refers to the chemical reaction between alkali in concrete and alkali-reactive aggregates, causing volume expansion and cracking of the concrete, reducing its durability, and shortening the service life of the concrete structure. Three conditions are required for AAR to occur: a humid environment, alkali-reactive aggregates, and a certain alkali content limit in the concrete. Specifically, when the alkali content is below a certain value, even if alkali-reactive aggregates are used, the alkali-aggregate reaction expansion rate of the concrete does not change significantly with increasing alkali content, and the concrete structure remains safe. However, when this value is exceeded, the alkali-aggregate reaction expansion rate increases sharply with increasing alkali content. Similarly, the safe alkali content limit varies for aggregates with different levels of reactivity. Therefore, the pH value of the concrete pore solution is closely related to AAR and can be used to qualitatively analyze whether AAR has occurred, the risk of residual reaction, and other long-term safety issues after using alkali-reactive aggregates. Therefore, accurate testing of the pH value in concrete is necessary. Domestic and international studies have conducted research on the pH value of concrete pore solutions using methods such as in-situ leaching and pressure filtration. Results obtained from pressure filtration are often used as a reference benchmark for results from other methods; therefore, the demand for pressure filtration is increasing. However, it is difficult to obtain pressure-filtered pore solutions from long-aged concrete, low water-cement (binder) ratio concrete, and fully graded concrete. When using the pressing method to prepare pore solutions for testing concrete pH, only a small amount of pore solution can be obtained, which cannot represent the true pore solution. Furthermore, pressure filtration requires complex equipment and has high operating costs.

[0003] Existing technologies include methods that involve drilling holes in the concrete surface, adding neutral water, and then testing the pH value of the pore solution. For example, Chinese patent CN109870492A discloses a method for testing the pH of concrete pore fluid, comprising two parts: specimen preparation and testing. Specimen preparation involves cutting the concrete to be tested into specimens, drilling holes in the specimens, sealing perforated plexiglass over the holes, adding distilled water into the holes and sealing the specimens, and then storing the treated specimens in an environmental test chamber at 100% humidity and 22–25°C. Testing involves placing a glass pH microelectrode and an Ag-AgCl microreference electrode into the holes of the specimens after 14 and 28 days of storage to test the pH value of the pore fluid. However, testing the limiting pH value of the pore solution by drilling holes in the concrete and adding neutral water presents the following problems: if the pore size is too small, too little water is added, resulting in insufficient ion exchange in the concrete; if the pore size is too large, too much water is added, leading to dilution issues; both of these methods result in low accuracy of the test results.

[0004] Therefore, providing an accurate method for testing the pH value of the pore solution in concrete is of great significance for the AAR evaluation of concrete samples. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, the purpose of this invention is to provide a method for testing the pH value of a concrete pore solution. This method is simple to operate, requires no complex equipment, and has high accuracy; it can solve the technical problems of complex operation and low accuracy of test results in the existing technologies.

[0006] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0007] A method for testing the pH value of a concrete pore solution includes the following steps:

[0008] S1. Drill holes in the surface of the concrete specimen, add deionized water into the holes and seal them. Standard curing is carried out until the pH value of the solution in the holes no longer increases. The pH value measured at this time is recorded as X1.

[0009] S2. Remove all the solution from the well, add the same volume of deionized water as in step S1 back into the well and seal it, then perform standard curing for the same number of days as in step S1, and then test the pH value of the solution in the well and record it as X2.

[0010] S3. Calculate the pH value of the solution in the concrete pores using the following formula:

[0011] OH in the solution in step S1 - Concentration Y1 = 10 (X1-14) mol / L;

[0012] Step S2 solution OH - Concentration Y2 = 10 (X2-14) mol / L;

[0013] Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L;

[0014] The pH of the solution in the concrete pore is 14 + lgY.

[0015] The testing method of this invention involves drilling holes in the surface of a concrete specimen, adding deionized water, sealing the specimen, and then standard curing it until the pH value of the solution inside the hole no longer increases; the pH value measured at this point is recorded as X1. Then, all the solution inside the hole is removed, and the same volume of deionized water is added back into the hole. After sealing and standard curing for the same number of days, the pH value of the solution in the hole is measured as X2. The actual OH- ions in the concrete hole solution are then calculated based on the two pH values. -Concentration. By adopting the above technical solution, the dilution effect caused by the large pore size can be eliminated, and a pore solution pH value close to the true value can be obtained.

[0016] Preferably, a method for testing the pH value of a concrete pore solution includes the following steps:

[0017] S1. Drill holes in the surface of the concrete specimen, add deionized water into the holes and seal them, cure under standard conditions for 28 days, take out the solution in the holes and record it as hole solution a, use a pH meter to test the pH value of hole solution a and record it as X1;

[0018] S2. Add the same volume of deionized water as in step S1 back into the pore and seal it. Then, cure it under standard conditions for 28 days. Take out the solution in the pore and record it as pore solution b. Use a pH meter to test the pH value of pore solution b and record it as X2.

[0019] S3. Calculate the pH value of the solution in the concrete pores using the following formula:

[0020] OH in pore solution a - Concentration Y1 = 10 (X1-14) mol / L;

[0021] OH in solution b - Concentration Y2 = 10 (X2-14) mol / L;

[0022] Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L;

[0023] The pH of the solution in the concrete pore is 14 + lgY.

[0024] Preferably, the concrete specimen has a size of not less than Ф100mm*150mm, the hole has a diameter of 20mm and a depth of not less than 100mm.

[0025] Preferably, the concrete specimen has a size of not less than 150mm*150mm*150mm, the hole has a diameter of 20mm and a depth of not less than 100mm.

[0026] Preferably, in step S1, after drilling, the hole is cleaned, and then the concrete specimen is cured for 48 hours according to standard, and then deionized water is added into the hole.

[0027] Preferably, the pH meter is calibrated using buffer solutions with pH=9.18 and pH=12 before testing.

[0028] Preferably, the standard maintenance conditions in steps S1 and S2 are the same.

[0029] The preferred standard maintenance conditions are as follows: temperature 20±3℃, relative humidity not less than 95%.

[0030] Preferably, the hole is located at the center of the surface of the concrete specimen.

[0031] Preferably, the amount of deionized water added in both steps S1 and S2 is 20 mL.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] The method for determining the pH value of concrete pore solution of the present invention has the advantages of simple equipment, convenient operation, low cost and high accuracy, and is suitable for carrying out durability test research such as evaluation of concrete alkali-aggregate reaction and determination of concrete carbonation. Attached Figure Description

[0034] Figure 1 This is a picture of a pH meter.

[0035] Figure 2 A schematic diagram of the concrete specimen and the hole;

[0036] Figure 3 This is a photograph of a concrete specimen being drilled using a vertical rock drill. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In the following examples and comparative examples, the pH meter is a Leici PHS-3C pH meter, and the electrode is a pH composite electrode with a diameter of 10 mm, which is composed of a glass electrode and a reference electrode. When the electrode is not in use, the glass bulb at the end of the electrode needs to be immersed in a 3.3 mol / L potassium chloride protective solution.

[0039] In the following embodiments, the method for testing the pH value of the well solution is performed according to the following steps: the composite electrode is connected to the main unit of the pH meter, and the glass bulb at the end of the composite electrode is immersed in buffer solutions with pH=9.18 and pH=12 respectively for calibration; then the calibrated glass bulb at the end of the electrode is immersed in the well solution, and the reading is recorded after it stabilizes to obtain the pH value of the well solution.

[0040] Unless otherwise specified, the curing conditions in the following examples are a temperature of 20±3℃ and a relative humidity of not less than 95%.

[0041] Example 1

[0042] This embodiment provides a method for testing the pH value of a solution in a concrete pore, including the following steps:

[0043] S1. A neat cement paste specimen with a molding size of 150*150*150mm was prepared. The cement used was 42.5 grade medium-heat silicate cement with an alkali content of 0.58% and a water-cement ratio of 0.3. After curing for 3 days, a hole with a diameter of 20mm and a depth of 100mm was drilled in the specimen. The hole was cleaned, and the specimen was cured for 48 hours. After removal, 20mL of deionized water was added to the hole to seal it. The specimen was then placed in a curing chamber for further curing. The pH value of the solution in the hole was tested directly after curing for 7, 14, 28, and 56 days. The results are as follows:

[0044] Maintenance days 7d 14d 28d 56d pH 13.02 13.09 13.11 13.12

[0045] The results in the table show that the pH value of the pore solution stabilized after 28 days and no longer increased, indicating that the OH- ions in the paste decreased after 28 days of curing. - Sufficient exchanges have been completed.

[0046] S2. Form a neat pulp specimen in the same manner as in step S1. After curing for 3 days, drill a hole with a diameter of 20 mm and a depth of 100 mm in the specimen. Clean the hole and then cure the specimen for 48 hours. After removing the specimen, add 20 mL of deionized water into the hole to seal it. Place the specimen in a curing chamber and cure for 28 days. Then, remove all the solution from the hole to obtain hole solution a. Use a pH meter to test the pH value of hole solution a and obtain X1 = 13.11.

[0047] S3. Add 20 mL of deionized water back into the well, seal the well, and place the specimen in the curing chamber again for 28 days. Then, remove all the solution from the well to obtain well solution b. Test the pH value of well solution b and obtain X2 = 12.88.

[0048] S4. Calculate the pH value of the solution in the concrete pores using the following formula:

[0049] OH in pore solution a - Concentration Y1 = 10 (X1-14) mol / L;

[0050] OH in solution b - Concentration Y2 = 10 (X2-14) mol / L;

[0051] Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L;

[0052] The pH of the solution in the concrete pore is 14 + lgY.

[0053] Substituting the pH value of pore solution a (X1 = 13.11) obtained in step S2 and the pH value of pore solution b (X2 = 12.88) obtained in step S3 into the formula in step S4, we can obtain the pH value of the concrete pore solution as 13.34.

[0054] In step S4, the actual OH in the concrete pore solution - Basis for concentration calculation formula: As can be seen from the results of step S1, the OH in the pulp in this embodiment... - After exchanging with 20 mL of deionized water and curing for 28 days, the OH- in the pulp... - It can be completely diluted; therefore, steps S2 and S3, under the same conditions as step S1, require 28 days of curing to reduce the OH content in the pulp. - It can also be completely diluted, and the volume of deionized water added in steps S2 and S3 is the same; therefore, steps S2 and S3 participate in OH... - The volumes V1 and V2 of the diluted pore solution are theoretically equal. That is:

[0055] (20+V1)*Y1=V1*Y, after conversion V1=20*Y1 / (Y-Y1);

[0056] (20+V2)*Y2=V2*Y1, after conversion V2=20*Y2 / (Y1-Y2);

[0057] Assuming V1 = V2, that is, 20 * Y1 / (Y - Y1) = V2 = 20 * Y2 / (Y1 - Y2), after conversion, Y = Y1 * Y1 / Y2.

[0058] Example 2

[0059] This embodiment provides a method for testing the pH value of a solution in a concrete pore, including the following steps:

[0060] S1. Mortar specimens with a molding size of 150*150*150mm were prepared using 42.5 grade medium-heat silicate cement with an alkali content of 0.58%, a water-cement ratio of 0.3, a cement-sand ratio of 1:2, and limestone sand with a fineness modulus of 2.7. After curing for 3 days, a hole with a diameter of 20mm and a depth of 100mm was drilled in the specimen. The hole was cleaned, and the specimen was cured for 48 hours. After removal, 20mL of deionized water was added to the hole to seal it, and the specimen was placed in a curing chamber for further curing. The pH value of the solution in the hole was tested directly after curing for 7, 14, 28, and 56 days. The results are as follows:

[0061] Maintenance days 7d 14d 28d 56d pH 12.73 12.88 12.90 12.91

[0062] The results in the table show that the pH value of the pore solution stabilized after 28 days and no longer increased, indicating that the OH- ions in the mortar decreased after 28 days of curing.- Sufficient exchanges have been completed.

[0063] S2. Form a mortar specimen in the same manner as in step S1. After curing for 3 days, drill a hole with a diameter of 20 mm and a depth of 100 mm in the specimen. Clean the hole and then cure the specimen for 48 hours. After removing the specimen, add 20 mL of deionized water to the hole to seal it. Place the specimen in a curing chamber and cure for 28 days. Then, remove all the solution from the hole to obtain hole solution a. Use a pH meter to test the pH value of hole solution a and obtain X1 = 12.90.

[0064] S3. Add 20 mL of deionized water back into the well to seal it. Then place the specimen in the curing chamber again for 28 days. Then remove all the solution from the well to obtain well solution b. Test the pH value of well solution b and obtain X2 = 12.61.

[0065] S4. Calculate the pH value of the solution in the concrete pores using the following formula:

[0066] OH in pore solution a - Concentration Y1 = 10 (X1-14) mol / L;

[0067] OH in solution b - Concentration Y2 = 10 (X2-14) mol / L;

[0068] Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L;

[0069] The pH of the solution in the concrete pore is 14 + lgY.

[0070] Substituting the pH value of pore solution a (X1 = 12.90) obtained in step S2 and the pH value of pore solution b (X2 = 12.61) obtained in step S3 into the formula in step S4, we can obtain the pH value of the concrete pore solution as 13.19.

[0071] In step S4, the actual OH in the concrete pore solution - Basis for concentration calculation formula: As can be seen from the results of step S1, the OH in the mortar of this embodiment... - After exchanging with 20 mL of deionized water and curing for 28 days, the OH- in the mortar... - It can be completely diluted; therefore, steps S2 and S3, under the same curing conditions as step S1, for 28 days, will reduce the OH content in the mortar. - It can also be completely diluted, and the volume of deionized water added in steps S2 and S3 is the same; therefore, steps S2 and S3 participate in OH... - The volumes V1 and V2 of the diluted pore solution are theoretically equal. That is:

[0072] (20+V1)*Y1=V1*Y, after conversion V1=20*Y1 / (Y-Y1);

[0073] (20+V2)*Y2=V2*Y1, after conversion V2=20*Y2 / (Y1-Y2);

[0074] Assuming V1 = V2, that is, 20 * Y1 / (Y - Y1) = V2 = 20 * Y2 / (Y1 - Y2), after conversion, Y = Y1 * Y1 / Y2.

[0075] Example 3

[0076] This embodiment provides a method for testing the pH value of a solution in a concrete pore, including the following steps:

[0077] S1. Concrete specimens with molding dimensions of 150*150*150mm were prepared using 42.5 grade medium-heat Portland cement with an alkali content of 0.58% and a water-cement ratio of 0.35. The sand used was limestone sand with a fineness modulus of 2.7, and the cement dosage was 400 kg / m³. 3 The coarse aggregate is limestone, the mass ratio of medium stone to fine stone is 6:4, the sand ratio is 40%, and the sand usage is 600 kg / m³. 3 After 3 days of curing, a hole with a diameter of 20 mm and a depth of 100 mm was drilled in the specimen. The hole was cleaned, and the specimen was cured for 48 hours. After removal, 20 mL of deionized water was added to the hole to seal it. The specimen was then placed in a curing chamber for further curing. The pH value of the solution in the hole was measured directly after 7, 14, 28, and 56 days of curing. The results are as follows:

[0078] Maintenance days 7d 14d 28d 56d pH 12.15 12.34 12.39 12.37

[0079] The results in the table show that the pH value of the pore solution stabilized after 28 days and no longer increased, indicating that the OH- ions in the concrete decreased after 28 days of curing. - Sufficient exchanges have been completed.

[0080] S2. Form concrete specimens in the same manner as in step S1. After curing for 3 days, drill a hole with a diameter of 20 mm and a depth of 100 mm in the specimen. Clean the hole and then cure the specimen for 48 hours. After removing the specimen, add 20 mL of deionized water to the hole to seal it. Place the specimen in a curing chamber and cure for 28 days. Then, remove all the solution from the hole to obtain hole solution a. Use a pH meter to test the pH value of hole solution a and obtain X1 = 12.39.

[0081] S3. Add 20 mL of deionized water back into the well, seal the well, and place the specimen in the curing chamber again for 28 days. Then, remove all the solution from the well to obtain well solution b. Test the pH value of well solution b and obtain X2 = 12.03.

[0082] S4. Calculate the pH value of the solution in the concrete pores using the following formula:

[0083] OH in pore solution a - Concentration Y1 = 10 (X1-14) mol / L;

[0084] OH in solution b - Concentration Y2 = 10 (X2-14) mol / L;

[0085] Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L;

[0086] The pH of the solution in the concrete pore is 14 + lgY.

[0087] Substituting the pH value of pore solution a (X1 = 12.39) obtained in step S2 and the pH value of pore solution b (X2 = 12.03) obtained in step S3 into the formula in step S4, we can obtain the pH value of the concrete pore solution as 12.75.

[0088] In step S4, the actual OH in the concrete pore solution - Basis for concentration calculation formula: As can be seen from the results of step S1, the OH in the concrete of this embodiment... - After exchanging with 20 mL of deionized water and curing for 28 days, the OH- in the concrete... - It can be completely diluted; therefore, steps S2 and S3, under the same curing conditions as step S1, for 28 days, will reduce the OH content in the concrete. - It can also be completely diluted, and the volume of deionized water added in steps S2 and S3 is the same; therefore, steps S2 and S3 participate in OH... - The volumes V1 and V2 of the diluted pore solution are theoretically equal. That is:

[0089] (20+V1)*Y1=V1*Y, after conversion V1=20*Y1 / (Y-Y1);

[0090] (20+V2)*Y2=V2*Y1, after conversion V2=20*Y2 / (Y1-Y2);

[0091] Assuming V1 = V2, that is, 20 * Y1 / (Y - Y1) = V2 = 20 * Y2 / (Y1 - Y2), after conversion, Y = Y1 * Y1 / Y2.

[0092] Example 4

[0093] This embodiment provides a method for testing the pH value of a solution in a concrete pore, including the following steps:

[0094] S1. Concrete specimens with molding dimensions of 150*150*150mm were prepared using 42.5 grade medium-heat Portland cement with an alkali content of 1.50% and a water-cement ratio of 0.4. The sand used was limestone sand with a fineness modulus of 2.7, and the cement dosage was 400kg / m³. 3 The coarse aggregate is limestone, the mass ratio of medium stone to fine stone is 6:4, the sand ratio is 40%, and the sand usage is 600 kg / m³. 3 After 3 days of curing, a hole with a diameter of 20 mm and a depth of 100 mm was drilled in the specimen. The hole was cleaned, and the specimen was cured for 48 hours. After removal, 20 mL of deionized water was added to the hole to seal it. The specimen was then placed in a curing chamber for further curing. The pH value of the solution in the hole was measured directly after 7, 14, 28, and 56 days of curing. The results are as follows:

[0095] Maintenance days 7d 14d 28d 56d pH 12.36 12.55 12.60 12.59

[0096] The results in the table show that the pH value of the pore solution stabilized after 28 days and no longer increased, indicating that the OH- ions in the concrete decreased after 28 days of curing. - Sufficient exchanges have been completed.

[0097] S2. Form concrete specimens in the same manner as in step S1. After curing for 3 days, drill a hole with a diameter of 20 mm and a depth of 100 mm in the specimen. Clean the hole and then cure the specimen for 48 hours. After removing the specimen, add 20 mL of deionized water to the hole to seal it. Place the specimen in a curing chamber and cure for 28 days. Then, remove all the solution from the hole to obtain hole solution a. Use a pH meter to test the pH value of hole solution a and obtain X1 = 12.60.

[0098] S3. Add 20 mL of deionized water back into the well, seal the well, and place the specimen in the curing chamber again for 28 days. Then, remove all the solution from the well to obtain well solution b. Test the pH value of well solution b and obtain X2 = 12.34.

[0099] S4. Calculate the pH value of the solution in the concrete pores using the following formula:

[0100] OH in pore solution a - Concentration Y1 = 10 (X1-14) mol / L;

[0101] OH in solution b - Concentration Y2 = 10 (X2-14) mol / L;

[0102] Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L;

[0103] The pH of the solution in the concrete pore is 14 + lgY.

[0104] Substituting the pH value of pore solution a (X1 = 12.60) obtained in step S2 and the pH value of pore solution b (X2 = 12.34) obtained in step S3 into the formula in step S4, we can obtain the pH value of the concrete pore solution as 12.86.

[0105] In step S4, the actual OH in the concrete pore solution - Basis for concentration calculation formula: As can be seen from the results of step S1, the OH in the concrete of this embodiment... - After exchanging with 20 mL of deionized water and curing for 28 days, the OH- in the concrete... - It can be completely diluted; therefore, steps S2 and S3, under the same curing conditions as step S1, for 28 days, will reduce the OH content in the concrete. - It can also be completely diluted, and the volume of deionized water added in steps S2 and S3 is the same; therefore, steps S2 and S3 participate in OH... - The volumes V1 and V2 of the diluted pore solution are theoretically equal. That is:

[0106] (20+V1)*Y1=V1*Y, after conversion V1=20*Y1 / (Y-Y1);

[0107] (20+V2)*Y2=V2*Y1, after conversion V2=20*Y2 / (Y1-Y2);

[0108] Assuming V1 = V2, that is, 20 * Y1 / (Y - Y1) = V2 = 20 * Y2 / (Y1 - Y2), after conversion, Y = Y1 * Y1 / Y2.

[0109] Example 5

[0110] This embodiment provides a method for testing the pH value of a solution in a concrete pore, including the following steps:

[0111] S1. Concrete specimens with dimensions Ф200*200mm were drilled on-site using 42.5 grade medium-heat silicate cement, grade C35, with a small three-grade mix. After curing for 3 days, a hole with a diameter of 20mm and a depth of 100mm was drilled in the specimen. The hole was cleaned, and the specimen was cured for 48 hours. After removal, 20mL of deionized water was added to the hole to seal it. The specimen was then placed in a curing chamber for further curing. The pH value of the solution in the hole was tested directly after 7, 14, 28, and 56 days of curing. The results are as follows:

[0112] Maintenance days 7d 14d 28d 56d pH 11.72 11.88 11.92 11.93

[0113] The results in the table show that the pH value of the pore solution stabilized after 28 days and no longer increased, indicating that the OH- ions in the concrete decreased after 28 days of curing.- Sufficient exchanges have been completed.

[0114] S2. Form concrete specimens in the same manner as in step S1. After curing for 3 days, drill a hole with a diameter of 20 mm and a depth of 100 mm in the specimen. Clean the hole and then cure the specimen for 48 hours. After removing the specimen, add 20 mL of deionized water to the hole to seal it. Place the specimen in a curing chamber and cure for 28 days. Then, remove all the solution from the hole to obtain hole solution a. Use a pH meter to test the pH value of hole solution a and obtain X1 = 11.92.

[0115] S3. Add 20 mL of deionized water back into the well, seal the well, and place the specimen in the curing chamber again for 28 days. Then, remove all the solution from the well to obtain well solution b. Test the pH value of well solution b and obtain X2 = 11.52.

[0116] S4. Calculate the pH value of the solution in the concrete pores using the following formula:

[0117] OH in pore solution a - Concentration Y1 = 10 (X1-14) mol / L;

[0118] OH in solution b - Concentration Y2 = 10 (X2-14) mol / L;

[0119] Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L;

[0120] The pH of the solution in the concrete pore is 14 + lgY.

[0121] Substituting the pH value of pore solution a (X1 = 11.92) obtained in step S2 and the pH value of pore solution b (X2 = 11.52) obtained in step S3 into the formula in step S4, we can obtain the pH value of the concrete pore solution as 12.32.

[0122] In step S4, the actual OH in the concrete pore solution - Basis for concentration calculation formula: As can be seen from the results of step S1, the OH in the concrete of this embodiment... - After exchanging with 20 mL of deionized water and curing for 28 days, the OH- in the concrete... - It can be completely diluted; therefore, steps S2 and S3, under the same curing conditions as step S1, for 28 days, will reduce the OH content in the concrete. - It can also be completely diluted, and the volume of deionized water added in steps S2 and S3 is the same; therefore, steps S2 and S3 participate in OH... - The volumes V1 and V2 of the diluted pore solution are theoretically equal. That is:

[0123] (20+V1)*Y1=V1*Y, after conversion V1=20*Y1 / (Y-Y1);

[0124] (20+V2)*Y2=V2*Y1, after conversion V2=20*Y2 / (Y1-Y2);

[0125] Assuming V1 = V2, that is, 20 * Y1 / (Y - Y1) = V2 = 20 * Y2 / (Y1 - Y2), after conversion, Y = Y1 * Y1 / Y2.

[0126] The pH values ​​of the solutions with a pore size of 20 mm in step S1 of Examples 1 to 5 are shown in Table 1.

[0127] Table 1. pH values ​​of solutions with a pore size of 20 mm

[0128]

[0129] As shown in Table 1, the OH content in the specimens of Examples 1-5 is... - After exchanging the solution with 20 mL of deionized water in the well and curing for 28 days, the OH- in the specimen... - It can be diluted completely.

[0130] The pH values ​​of the pore solutions calculated in step S4 of Examples 1-5 are shown in Table 2.

[0131] Table 2

[0132] Example pH value of solution a pH value of solution b Calculated value Example 1 13.11 12.88 13.34 Example 2 12.90 12.61 13.19 Example 3 12.39 12.03 12.75 Example 4 12.60 12.34 12.86 Example 5 11.92 11.52 12.32

[0133] As shown in Table 2, the pH values ​​of the pore solutions obtained by the test method of this invention are all lower than the pH value (OH) of pore solution a. - The high pH value at which OH- exchange is complete indicates that the existing technology uses OH- - Using the pH value obtained after sufficient exchange as the pH value of the concrete pore solution will lead to an underestimation of the actual pH value due to dilution. This method, however, eliminates the dilution effect, yielding a pore solution pH value close to the true value with high accuracy.

[0134] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for testing the pH value of a concrete pore solution, characterized in that, Includes the following steps: S1. Drill holes in the surface of the concrete specimen, add deionized water into the holes and seal them. Standard curing is carried out until the pH value of the solution in the holes no longer increases. The pH value measured at this time is recorded as X1. S2. Remove all the solution from the well, add the same volume of deionized water as in step S1 back into the well and seal it, then perform standard curing for the same number of days as in step S1, and then test the pH value of the solution in the well and record it as X2. S3. Calculate the pH value of the solution in the concrete pores using the following formula: OH in the solution in step S1 - Concentration Y1=10 (X1-14) mol / L; Step S2 solution OH - Concentration Y2=10 (X2-14) mol / L; Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L; The pH of the solution in the concrete pore is 14 + lgY.

2. The method for testing the pH value of a concrete pore solution according to claim 1, characterized in that, The concrete specimen shall be no smaller than Ф100mm*150mm in size, and the hole shall have a diameter of 20mm and a depth of no less than 100mm.

3. The method for testing the pH value of a concrete pore solution according to claim 1, characterized in that, The concrete specimen is no less than 150mm*150mm*150mm in size, and the hole has a diameter of 20mm and a depth of no less than 100mm.

4. The method for testing the pH value of a concrete pore solution according to claim 1, characterized in that, The standard maintenance conditions are the same in steps S1 and S2.

5. The method for testing the pH value of a concrete pore solution according to claim 4, characterized in that, The standard maintenance conditions are as follows: temperature 20±3℃, relative humidity not less than 95%.

6. The method for testing the pH value of a concrete pore solution according to claim 1, characterized in that, The hole is located at the center of the surface of the concrete specimen.

7. The method for testing the pH value of a concrete pore solution according to claim 1, characterized in that, The amount of deionized water added in both steps S1 and S2 is 20 mL.

8. A method for testing the pH value of a concrete pore solution, characterized in that, Includes the following steps: S1. Drill holes in the surface of the concrete specimen, add deionized water into the holes and seal them, cure under standard conditions for 28 days, take out the solution in the holes and record it as hole solution a, use a pH meter to test the pH value of hole solution a and record it as X1; S2. Add the same volume of deionized water as in step S1 back into the well and seal it. Then, cure it under standard conditions for 28 days. Take out the solution in the well and record it as well solution b. Use a pH meter to test the pH value of well solution b and record it as X2. S3. Calculate the pH value of the solution in the concrete pores using the following formula: OH in pore solution a - Concentration Y1=10 (X1-14) mol / L; OH in solution b - Concentration Y2=10 (X2-14) mol / L; Actual OH in concrete pore solution - Concentration Y = Y1 * Y1 / Y2 mol / L; The pH of the solution in the concrete pore is 14 + lgY.

9. The method for testing the pH value of a concrete pore solution according to claim 8, characterized in that, The pH meter was calibrated using buffer solutions with pH=9.18 and pH=12 before testing.

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