A method for detecting water resistance of gypsum using an acidity meter

Abstract

The invention specifically discloses a method for detecting the water resistance of gypsum by using an acidometer, comprising the following steps: S1, aging gypsum; S2, preparing a gypsum test block; S3, measuring the strength and pH value of the absolutely dry gypsum test block; S4, calculating the saturated strength and the gypsum softening coefficient of the gypsum test block to be tested; the technical scheme of the invention uses a simple laboratory acidometer as an online monitoring tool, detects the water resistance of gypsum by the change of pH value of a gypsum immersion water solution, has a simple operation method and a fast detection speed, and is suitable for online monitoring of building mortar production enterprises, construction units and quality inspection institutions.

Description

Technical Field

[0001] The invention relates to the field of detection and inspection methods for the water resistance of gypsum and its products, and in particular to a method for detecting the water resistance of gypsum by using an acidity meter. Background Art

[0002] Building gypsum is mainly composed of semi-hydrated gypsum, which has a low calcination temperature (usually below 200°C) and low production energy consumption, about 1 / 2 of lime and 1 / 3 of cement; gypsum products have good thermal insulation, small heat loss and low energy consumption. During use, since gypsum materials are neutral, have no harmful emissions, and have good compatibility with other materials, they generally do not corrode other materials. Gypsum products can be recycled after dismantling, such as being used as a cement retarder or being fried and reused.

[0003] The main problem of gypsum-based materials is their poor water resistance, which makes them inapplicable to damp areas. In order to improve the water resistance of gypsum, various technical measures have been taken at home and abroad, and various composite gypsum-based cementitious materials with different formulas, processes, water resistance indicators and different scopes of use have been studied, such as moisture-proof gypsum slag decorative panels, gypsum blocks, dihydrate gypsum slag boards, gypsum marble interior and exterior wall decorative panels and gypsum-based exterior wall painting materials. Since various composite gypsum-based cementitious materials vary greatly in terms of waterproof mechanism, hydration products, hardening laws and usage requirements, if the water resistance indicators and test methods of air-hardening gypsum are still used, there will be large differences in the accuracy of test data, the timeliness of quality control and the pertinence of water resistance indicators, making the comparability of gypsum-based material water resistance tests and research poor.

[0004] Therefore, shortening the detection time of water resistance test of gypsum-based materials and improving data accuracy are issues that still need to be solved. Summary of the invention

[0005] Based on this, the present invention provides a method for detecting the water resistance of gypsum using an acidity meter. The method solves the problems of the current gypsum water resistance detection method, such as long detection time, poor comparability, and multiple factors affecting test block molding, which lead to inconvenience in detecting the water resistance data of gypsum-based cementitious materials.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for detecting the water resistance of gypsum by using an acidity meter, comprising the following steps:

[0008] S1. Gypsum aging: weigh 5kg±0.01kg of building gypsum or mixed phase gypsum and place it on the test bench for 20h~24h for aging;

[0009] S2. Preparation of gypsum test blocks: prepare several plastic concrete molds, and brush the inner wall of the plastic molds with release oil; weigh 150-200g of aged gypsum, add distilled water with a pH of 6-7 according to 60%-70% of the mass of gypsum, stir evenly, pour into the plastic concrete mold, heat in a water bath, dry and polish to obtain gypsum test blocks;

[0010] S3. Determine the strength and pH value of the absolute dry gypsum test block: Take out a gypsum test block and place it on the fully automatic testing machine to measure the maximum breaking load M0, i.e. the strength of the absolute dry gypsum test block; take out another one and place it in distilled water at a temperature of 19-20°C, with the water surface covering the test block by more than 20mm, add 1.5g-2g NaHS, insert the detection electrode of the calibrated acidometer PHS-25 into the solution, and read the pH value C0;

[0011] S4. Calculate the saturated strength and softening coefficient of the gypsum test block to be tested: After the gypsum test block or gypsum-based product to be tested is prepared and formed according to steps S1 to S2, it is placed in distilled water and the pH value of the solution is detected to be C1; calculate the strength and softening coefficient of the gypsum test block to be tested:

[0012]

[0013]

[0014] Wherein, M1 is the strength of the gypsum block to be tested, MPa; M0 is the strength of the absolute dry gypsum specimen, MPa; η is the softening coefficient of the gypsum specimen; C0 is the pH value of the absolute dry gypsum specimen; C1 is the pH value of the gypsum block to be tested.

[0015] Furthermore, in step S2, the specific steps of water bath heating and drying and polishing are:

[0016] S21, placing the plastic mold in a constant temperature water bath at a temperature of 35°C to 40°C and heating for 2 hours;

[0017] S22, then soak the gypsum test block in a 90% to 95% ethanol solution for 1 to 2 hours, then take it out and place it in a constant temperature drying oven at 40°C to 45°C for 10 to 30 minutes;

[0018] S23, take out the test block and place it on the test bench for 30min to 40min, open the plastic mold, and take out the two paste test blocks;

[0019] S24. Use 300-400 mesh emery sandpaper to grind the plaster test block in contact with the mold for 10-15 times on each side, and wipe off the dust on the surface with a dry cloth.

[0020] Furthermore, in the steps S1 and S2, the temperature of the test bench is 20° C. to 25° C., and the humidity is 50% to 55%.

[0021] Furthermore, in step S2, the size of the plastic mold is 100 mm×100 mm×100 mm, and the plastic mold consists of three cubic boxes of the same volume.

[0022] Furthermore, in step S3, the method for determining the strength M0 of the absolute dry gypsum specimen is as follows: the precision of the press is adjusted to level I, so that the axis of the specimen coincides with the pressure center of the test machine pressure plate, and the load is applied at a speed of 0.05 MPa / s to 0.10 MPa / s until the specimen is destroyed, and the maximum load M0 at destruction is recorded.

[0023] Furthermore, the technical solution of the present invention can be optionally that when the gypsum test block / gypsum-based product used is phosphogypsum / phosphogypsum-based product, a masking agent needs to be added when the gypsum test block is placed in distilled water to measure the pH value of the solution in steps S3 and S4, and then 1.5g to 2g of NaHS is added, and then the pH value of the solution is measured.

[0024] Furthermore, the masking agent is EDTA sodium ethylenediaminetetraacetate and NaF, the weight ratio is 1:1, and the amount of addition is 5% to 8% of the mass of NaHS.

[0025] Based on the above technical solution, the embodiments of the present invention can at least produce the following technical effects:

[0026] (1) The present invention provides a method for detecting the water resistance of gypsum by using an acidity meter. By changing the pH value of a gypsum immersion solution, a simple laboratory acidity meter is used as an online monitoring tool to detect the water resistance of gypsum. The operation method is simple and convenient, and provides a new idea for the study of the water resistance of gypsum.

[0027] (2) The method provided by the present invention for detecting the water resistance of gypsum by using an acidometer is not only suitable for the detection of natural gypsum and its products, but also for the detection of industrial by-product gypsum such as desulfurized gypsum and phosphogypsum, and can also detect modified composite cementitious materials such as cement, fly ash and slag, and has wide applicability.

[0028] (3) The present invention provides a method for detecting the water resistance of gypsum using an acidity meter, which has a fast detection speed, high data accuracy, and no hysteresis, and is particularly suitable for online monitoring of building mortar production enterprises, construction units and quality inspection agencies. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with examples, which are intended to illustrate the present invention rather than to limit the scope of the present invention. Those skilled in the art can determine the essential features of the present invention, and can make various modifications and changes to the present invention without departing from the spirit and scope of the present invention to enable it to use various purposes and conditions.

[0030] Example 1: Water resistance test of ordinary building gypsum

[0031] This embodiment provides a method for detecting the water resistance of common building gypsum, comprising the following steps:

[0032] S1. Gypsum aging:

[0033] Weigh 5kg±0.01kg of building gypsum, place the gypsum on a test bench at a temperature of 20℃~25℃ and a humidity of 50%~55% for 20h~24h for aging;

[0034] S2. Preparation of gypsum test blocks:

[0035] Prepare several plastic concrete molds, and brush the inner wall of the plastic mold with demoulding oil made of waste oil; weigh 150-200g of aged gypsum, add distilled water with a pH of 6-7 according to 60%-70% of the mass of gypsum, stir evenly, pour into a 100mm×100mm×100mm plastic concrete mold, and pour 2 boxes simultaneously each time stirring;

[0036] S21, water bath heating: place the plastic mold in a constant temperature water bath at 35℃~40℃ and heat for 2h;

[0037] S22, constant temperature drying: then the gypsum test block is placed in a 90% to 95% ethanol solution and soaked for 1h to 2h, then taken out and placed in a constant temperature drying oven at 40℃ to 45℃ for 10min to 30min;

[0038] S23, demoulding: take out the test block and place it on the test bench for 30min to 40min, open the plastic mold and take out the gypsum test block;

[0039] S24. Test block polishing: Use 300-400 mesh emery sandpaper to polish each side of the gypsum test block that contacts the mold for 10-15 times, and wipe off the dust on the surface with a dry cloth.

[0040] S3. Determine the strength and pH value of the absolutely dry gypsum test block:

[0041] Take out a gypsum test block and place it on the fully automatic testing machine. Adjust the pressure accuracy of the testing machine to level I, so that the central axis of the gypsum test block coincides with the pressure center of the test machine pressure plate, and add load at a speed of 0.05MPa / s to 0.10MPa / s until the gypsum test block is destroyed. Record its maximum destruction load M0, that is, the absolute dry gypsum test block strength;

[0042] Take out another piece and put it into distilled water at a temperature of 19-20℃, so that the water surface submerges the test piece and the liquid level is more than 20mm above the test piece, and add 1.5g-2g NaHS to enhance the conductivity of the solution and reduce the influence of alkaline substances. Insert the detection electrode of the calibrated pH meter PHS-25 into the solution and read the pH value C0;

[0043] S4. Calculate the saturated strength and gypsum softening coefficient of the gypsum specimen to be tested:

[0044] After the gypsum test block or gypsum-based product to be tested is prepared and formed according to steps S1 to S2, it is placed in distilled water, and the detection electrode of the calibrated pH meter PHS-25 is inserted into the solution to read the pH value C1;

[0045] The strength M1 and softening coefficient η of the gypsum specimen to be tested are calculated:

[0046]

[0047]

[0048] Wherein, M1 is the strength of the gypsum block to be tested, MPa; M0 is the strength of the absolute dry gypsum specimen, MPa; η is the softening coefficient of the gypsum specimen; C0 is the pH value of the absolute dry gypsum specimen; C1 is the pH value of the gypsum block to be tested.

[0049] Example 2: Water resistance test of phosphogypsum

[0050] This embodiment provides a method for detecting water resistance of phosphogypsum, comprising the following steps:

[0051] S1. Gypsum aging:

[0052] Weigh 5kg±0.01kg of phosphogypsum, place the phosphogypsum on a test bench at a temperature of 20℃~25℃ and a humidity of 50%~55% for 20h~24h for aging;

[0053] S2. Preparation of gypsum test blocks:

[0054] Prepare several plastic concrete molds, and brush the inner wall of the plastic mold with demoulding oil composed of waste oil; weigh 150-200g of aged phosphogypsum, add distilled water with a pH of 6-7 according to 60%-70% of the mass of the gypsum, stir evenly, pour into a 100mm×100mm×100mm plastic concrete mold, and cast 2 boxes simultaneously each time stirring;

[0055] S21, water bath heating: place the plastic mold in a constant temperature water bath at 35℃~40℃ and heat for 2h;

[0056] S22. Constant temperature drying: then immerse the phosphogypsum test block in a 90% to 95% ethanol solution for 1 to 2 hours, then take it out and place it in a constant temperature drying oven at 40°C to 45°C for 10 to 30 minutes;

[0057] S23, demoulding: take out the test block and place it on the test bench for 30min to 40min, open the plastic mold and take out the phosphogypsum test block;

[0058] S24. Test block polishing: Use 300-400 mesh emery sandpaper to polish the phosphogypsum test block that contacts the mold for 10-15 times on each side, and wipe off the dust on the surface with a dry cloth.

[0059] S3. Determine the strength and pH value of the absolutely dry gypsum test block:

[0060] Take out a phosphogypsum test block and place it on the fully automatic testing machine. Adjust the pressure accuracy of the testing machine to level I, so that the central axis of the phosphogypsum test block coincides with the pressure center of the pressure plate of the testing machine, and add load at a speed of 0.05MPa / s to 0.10MPa / s until the gypsum test block is destroyed. Record its maximum destruction load M0, that is, the absolute dry gypsum test block strength;

[0061] Take out another phosphogypsum test block and put it into distilled water at a temperature of 19-20℃, so that the water surface submerges the phosphogypsum test block and the liquid level is more than 20mm above the phosphogypsum test block, add masking agents sodium ethylenediaminetetraacetate (EDTA) and NaF in a ratio of 1:1, and the amount added is 5% to 8% of the mass of NaHS to reduce the effect of eutectic phosphorus Ca(HPO4)2 on the solubility of CaSO4, then add 1.5g to 2g NaHS, insert the detection electrode of the calibrated acidity meter PHS-25 into the solution, and read the pH value C0;

[0062] S4. Calculate the saturated strength and gypsum softening coefficient of the gypsum specimen to be tested:

[0063] After the phosphogypsum test block or gypsum-based product to be tested is prepared and formed according to steps S1 to S2, it is placed in distilled water, and the detection electrode of the calibrated acidity meter PHS-25 is inserted into the solution to read the pH value C1;

[0064] The strength M1 and softening coefficient η of the gypsum specimen to be tested are calculated:

[0065]

[0066]

[0067] Wherein, M1 is the strength of the gypsum block to be tested, MPa; M0 is the strength of the absolute dry gypsum specimen, MPa; η is the softening coefficient of the gypsum specimen; C0 is the pH value of the absolute dry gypsum specimen; C1 is the pH value of the gypsum block to be tested.

[0068] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for detecting the water resistance of gypsum using an acidity meter, comprising the following steps: S1. Gypsum aging: weigh 5kg±0.01kg of building gypsum or mixed phase gypsum and place it on the test bench for 20h~24h for aging; S2. Preparation of gypsum test blocks: prepare several plastic concrete molds, and brush the inner wall of the plastic molds with release oil; weigh 150-200g of aged gypsum, add distilled water with a pH of 6-7 according to 60%-70% of the mass of the gypsum, stir evenly, pour into the plastic concrete mold, heat in a water bath, dry and polish to obtain gypsum test blocks; S3. Determine the strength and pH value of the absolute dry gypsum test block: Take out a gypsum test block and place it on the fully automatic testing machine to measure the maximum breaking load M0, i.e. the strength of the absolute dry gypsum test block; take out another one and place it in distilled water at a temperature of 19-20°C, with the water surface covering the test block by more than 20mm, add 1.5g-2g NaHS, insert the detection electrode of the calibrated acidometer PHS-25 into the solution, and read the pH value C0; S4. Calculate the saturated strength and softening coefficient of the gypsum test block to be tested: After the gypsum test block or gypsum-based product to be tested is prepared and formed according to steps S1 to S2, it is placed in distilled water and the pH value of the solution is detected to be C1; calculate the strength and softening coefficient of the gypsum test block to be tested: ； ； Wherein, M1 is the strength of the gypsum block to be tested, MPa; M0 is the strength of the absolute dry gypsum test block, MPa; η is the softening coefficient of the gypsum specimen; C0 is the pH value of the absolutely dry gypsum specimen; C1 is the pH value of the gypsum specimen to be tested; In step S2, the specific steps of water bath heating and drying and polishing are as follows: S21, placing the plastic mold in a constant temperature water bath at a temperature of 35°C to 40°C and heating for 2 hours; S22, then soak the gypsum test block in 90% to 95% ethanol solution for 1 h to 2 h, then take it out and place it in a constant temperature drying oven at 40°C to 45°C for 10 min to 30 min; S23, take out the test block and place it on the test bench for 30min to 40min, open the plastic mold, and take out the two paste test blocks; S24. Use 300-400 mesh emery sandpaper to grind the gypsum test block that contacts the mold for 10-15 times on each side, and wipe off the dust on the surface with a dry cloth; In step S3, the method for determining the strength M0 of the absolute dry gypsum test block is: Adjust the press accuracy to Level I, make the axis of the specimen coincide with the pressure center of the test machine platen, apply load at a speed of 0.05MPa / s to 0.10MPa / s until the specimen is destroyed, and record the maximum load M0 at destruction.

2. The method for detecting the water resistance of gypsum using an acidity meter according to claim 1, characterized in that: In the steps S1 and S2, the temperature of the test bench is 20° C. to 25° C., and the humidity is 50% to 55%.

3. The method for detecting water resistance of gypsum using an acidity meter according to claim 1, characterized in that: The size of the plastic mold in step S2 is 100 mm×100 mm×100 mm, and the plastic mold consists of three cubic boxes of the same volume.

4. The method for detecting the water resistance of gypsum using an acidity meter according to claim 1, characterized in that: When the gypsum test block / gypsum-based product is phosphogypsum / phosphogypsum-based product, a masking agent needs to be added when the gypsum test block is placed in distilled water to measure the pH value of the solution in steps S3 and S4, and then 1.5 g to 2 g of NaHS is added, and then the pH value of the solution is measured.

5. The method for detecting water resistance of gypsum using an acidity meter according to claim 4, characterized in that: The masking agent is sodium EDTA and NaF, the weight ratio is 1:1, and the added amount is 5% to 8% of the mass of NaHS.

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