CN107247010B9 - Method and device for measuring oxygen diffusion coefficient in cement-based material under different humidity - Google Patents
Method and device for measuring oxygen diffusion coefficient in cement-based material under different humidity Download PDFInfo
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- 239000001301 oxygen Substances 0.000 title claims abstract description 205
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 205
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 201
- 239000000463 material Substances 0.000 title claims abstract description 85
- 239000004568 cement Substances 0.000 title claims abstract description 83
- 238000009792 diffusion process Methods 0.000 title claims abstract description 81
- 238000000034 method Methods 0.000 title claims abstract description 28
- 238000012360 testing method Methods 0.000 claims abstract description 136
- 239000007789 gas Substances 0.000 claims abstract description 51
- 239000000243 solution Substances 0.000 claims abstract description 25
- 239000012266 salt solution Substances 0.000 claims abstract description 17
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 32
- 238000007789 sealing Methods 0.000 claims description 17
- 229910052757 nitrogen Inorganic materials 0.000 claims description 16
- 229920006395 saturated elastomer Polymers 0.000 claims description 16
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical class [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 7
- 239000003822 epoxy resin Substances 0.000 claims description 7
- 229920000647 polyepoxide Polymers 0.000 claims description 7
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- 238000012545 processing Methods 0.000 claims description 5
- 238000004364 calculation method Methods 0.000 claims description 4
- 230000008859 change Effects 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- 238000002360 preparation method Methods 0.000 claims description 3
- 229920000459 Nitrile rubber Polymers 0.000 claims description 2
- 239000011521 glass Substances 0.000 claims description 2
- 230000008569 process Effects 0.000 abstract description 11
- 229910000831 Steel Inorganic materials 0.000 abstract description 6
- 239000010959 steel Substances 0.000 abstract description 6
- 238000005259 measurement Methods 0.000 abstract description 4
- 230000007797 corrosion Effects 0.000 abstract description 3
- 238000005260 corrosion Methods 0.000 abstract description 3
- 230000005540 biological transmission Effects 0.000 abstract description 2
- 239000004567 concrete Substances 0.000 description 12
- 239000004570 mortar (masonry) Substances 0.000 description 9
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- 230000035699 permeability Effects 0.000 description 6
- 229940099259 vaseline Drugs 0.000 description 6
- 206010021143 Hypoxia Diseases 0.000 description 5
- 229920001971 elastomer Polymers 0.000 description 5
- SCVFZCLFOSHCOH-UHFFFAOYSA-M potassium acetate Chemical class [K+].CC([O-])=O SCVFZCLFOSHCOH-UHFFFAOYSA-M 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 230000001146 hypoxic effect Effects 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 239000004576 sand Substances 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- 239000010687 lubricating oil Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 239000011150 reinforced concrete Substances 0.000 description 2
- 239000011435 rock Substances 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 239000011398 Portland cement Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000013480 data collection Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000003989 dielectric material Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000007954 hypoxia Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
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- 239000000126 substance Substances 0.000 description 1
- 239000008399 tap water Substances 0.000 description 1
- 235000020679 tap water Nutrition 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
Abstract
A method for determining the oxygen diffusion coefficient in a cement-based material at different humidities, comprising the steps of: 1) Preparing a cement-based material test piece to be tested; 2) The connection of the whole device; 3) Oxygen diffusion coefficient D of cement-based material under different humidity f Is measured. And a test device for determining the oxygen diffusion coefficient in the cement-based material under different humidity is provided, and comprises a gas supply system, a test piece, a left gas chamber, a right gas chamber and a sensing test system. The power of oxygen diffusion in the whole process is only concentration gradient, and the solution tanks are arranged in the two chambers of the device so as to ensure that the whole test process is carried out under constant humidity, the humidity can be changed by changing different salt solutions, the measurement is simple, and the data is accurate and reliable. The transmission rule of oxygen in the cement-based material under different humidity can provide a data base for further researching the corrosion process of oxygen to steel bars in the cement-based material under different humidity.
Description
Technical Field
The invention relates to a method and a test device for measuring oxygen diffusion coefficient in cement-based materials under different humidity, and belongs to the technical field of civil engineering material performance measurement.
Background
Rust on steel bars in concrete structures is the most important factor causing the reduction of the service performance of the structures. After the surface of the steel bar is dulled, oxygen in the air is diffused to the surface of the steel bar through the concrete, and the corrosion rate of the steel bar is directly determined by the oxygen diffusion coefficient in the concrete under different humidity. Therefore, as one of the necessary conditions for the corrosion of the steel bars in the concrete, the determination of the diffusion coefficient of oxygen in the concrete under different humidity has definite scientific and engineering application values. However, because the porosity of the concrete is low, the gas diffusion coefficient is small, and no test device for effectively measuring the oxygen diffusion coefficient in the concrete is available at home and abroad.
Currently, the existing test methods mainly aim at the determination of the permeability of concrete water and gas, namely, the test is carried out under the action of pressurized water or gas. For example, chinese patent grant publication No. CN1111737C, the grant publication day is 18/6/2003, named as "method for rapidly evaluating concrete permeability", discloses a method for evaluating concrete permeability by using the values of chloride ion diffusion coefficient and concrete conductivity; chinese patent grant publication No. CN102735592B, grant publication No. 2014, month 4, day 2, entitled "a device for measuring diffusion coefficient of carbon dioxide in rock", which measures diffusion coefficient of carbon dioxide in rock by measuring changes in carbon dioxide pressure; chinese patent grant publication No. CN204924869U, grant publication No. 2015, 12 month and 30 day, named "cement-based material permeability coefficient measuring device", provides an introduction of a device for permeability testing of cement-based materials with different porosities under the action of constant water pressure. However, the water and air permeability coefficients of the concrete, rather than the diffusion coefficients, are measured by the test method. The oxygen is transmitted from the surface of the reinforced concrete to the surface of the reinforced concrete under different humidity under natural conditions, and the mechanism is the diffusion effect of the oxygen. Therefore, developing an oxygen diffusion coefficient measuring method and a testing device for cement-based porous materials under different humidity has great significance for scientific research and engineering application.
Disclosure of Invention
In order to overcome the defects of the oxygen diffusion coefficient measuring device in the existing cement-based structure, the invention takes cement-based materials as test objects, and designs a set of method and test device capable of measuring the diffusion coefficients of oxygen in different humidity.
In order to solve the technical problems, the invention provides the following technical scheme:
a method for determining the oxygen diffusion coefficient in a cement-based material at different humidities, comprising the steps of:
1) Preparation of cement-based material test piece to be tested
Pouring and forming a cement-based material test piece to be tested, cutting the tested cement-based material into cylinders with set thickness, and placing the cylinders in a series of different saturated saline solution closed containers until the internal humidity balance is achieved; and coating the side surface of the test piece with epoxy resin to isolate the influence of external atmosphere;
2) Connection of integral devices
The end surfaces of the cement-based material test piece obtained in the step 1) are respectively connected with the two gas chambers to form a sealed whole; injecting the saturated salt solution which is the same as that in the step 1) into solution tanks at the bottoms of the two chambers, and ensuring that the humidity inside the chambers is balanced with the humidity of a test piece; the air inlet valve of the air chamber is respectively connected with two air supply bottles; the movable piston is respectively connected with the two oxygen sensors; the two oxygen sensors are connected with an oxygen data demodulator; the two oxygen data demodulators are connected with the data recorder; the data recorder is connected with the computer; after the whole device is connected, the good air tightness of the connection is ensured, and the whole device is placed in a constant temperature chamber;
3) Oxygen diffusion coefficient D of cement-based material under different humidity f Is (are) determined by
Opening a gas supply bottle, respectively filling a certain amount of oxygen and nitrogen into the two gas chambers, and obtaining a calculation formula of an oxygen diffusion coefficient under the humidity by utilizing the oxygen concentration change in the two gas chambers under different moments monitored by an oxygen data demodulator and a data recorder and combining an ideal gas state equation and Fick first law:
wherein: d (D) f Is oxygen diffusion coefficient, unit m 2 /s；Oxygen concentration gradient of the left chamber and the right chamber is expressed in mol/m 4 Obtaining a functional relation between the oxygen concentration values and time according to the recorded oxygen concentration values of the two chambers at different moments; t is the test time, unit s; n is the amount of material of the hypoxic chamber increasing total oxygen from t=0 to the end of the test, in mol; s is the effective diffusion area of oxygen, unit m 2 。/>
Further, the cement-based material test piece is cast and molded according to a preset mixing ratio and is subjected to standard curing for 28d, then is cut into cylinders with set thickness, and is placed in a series of different saturated saline solution closed containers until the internal humidity balance is achieved.
The test device for measuring the oxygen diffusion coefficient in the cement-based material under different humidity comprises a gas supply system, a test piece, a left gas chamber, a right gas chamber and a sensing test system, wherein the test piece is a cement-based material test piece, the left gas chamber and the right gas chamber are connected to two end surfaces of the cement-based material test piece, the left gas chamber and the right gas chamber respectively comprise a gas inlet valve, a chamber pipe wall, a movable piston, a piston sealing ring and a solution pool, the gas inlet valve is arranged on the chamber pipe wall, the movable piston is movably sleeved in the chamber pipe wall, the piston sealing ring is arranged between the movable piston and the inner wall of the chamber pipe wall, and the bottom of the chamber is provided with the solution pool for guaranteeing that the humidity inside the chamber is balanced with the humidity of the test piece;
the air inlet valve is connected with the air supply system, the air supply system consists of an air supply cylinder, an air outlet valve and air delivery pipes, the air supply cylinder is provided with an oxygen cylinder and a nitrogen cylinder, two air delivery pipes are respectively connected with the air outlet valve of the air supply cylinder, and the other ends of the two air delivery pipes are connected with the air inlet valve;
the sensing test system comprises an oxygen sensor and an oxygen data demodulator, and is used for measuring the oxygen concentration in the left and right chambers of the cement-based material, and the oxygen sensor is arranged on the side, close to the test piece, of the movable piston; the oxygen sensor is connected with the oxygen data demodulator.
Further, the test device also comprises a data acquisition system, wherein the data acquisition system comprises a data recorder and a computer, and is used for recording and subsequent processing of oxygen concentration data in the left and right chambers of the cement-based material, and the oxygen data demodulator is connected with the data recorder.
Still further, the air supply system, the test piece, the left and right air chambers and the sensing test system are all located in the constant temperature chamber.
Further, a small hole is reserved in the middle of the movable piston, and the oxygen sensor is arranged in the small hole.
The chamber walls are marked with scales for calculating the volumes of the two chambers.
The movable piston main bodies of the two chambers are made of transparent organic glass, the piston sealing rings are made of nitrile rubber, and each piston sealing ring is provided with a small hole of 20mm and is used for being connected with the sensing test system.
A method of operating a device for determining the oxygen diffusion coefficient in a cementitious material at different humidities, comprising the steps of:
1) Cutting the molded and standard cured cement-based material test piece into a cylindrical test piece with the diameter of 50-100mm and the thickness of 10-20mm, placing the cylindrical test piece into a saturated saline solution closed container, and coating a non-diffusion surface (the side surface of the cylinder) by using epoxy resin to isolate the influence of external air after the time reaches the internal humidity balance;
2) After the treated cement-based material test piece and the left and right chambers are filled with rubber sealing gaskets, the left and right chambers are connected with the cement-based material test piece by using stud bolts, and after the connection is finished, proper amount of vaseline is coated at the connection positions such as the periphery of the gaskets so as to ensure the air tightness of the connection positions of the test piece and the chambers;
3) Filling sufficient saturated salt solution which is the same as that in the step 1) into solution tanks of the left and right chambers;
4) Opening air inlet valves at the upper parts of the two chambers, coating a proper amount of lubricating oil on the outer parts of the piston sealing rings, pushing the movable piston into the manufactured chamber wall to remove the original gas in the chambers, and keeping the mobility of the piston while ensuring the air tightness at the piston positions;
5) Placing the oxygen sensor at the small hole reserved by the left and right cavity moving pistons, and smearing vaseline after fixing to ensure air tightness;
6) The other end of the oxygen sensor is connected with an oxygen data demodulator for testing the oxygen concentration in the two chambers, the oxygen data demodulator is connected with a data recorder for data recording, and the recorder is connected with a computer for recording output and subsequent processing;
7) The air inlet valve above the cavity wall is connected with the air supply bottle through the air delivery conduit, the oxygen chamber is connected with the oxygen bottle, the nitrogen chamber is connected with the nitrogen bottle, and the whole device is connected;
8) Checking the air tightness of the device;
9) Starting a test, opening an air outlet valve of an air supply bottle and an air inlet valve at the upper part of a cavity wall, respectively inflating the two cavities, enabling a movable piston to slowly move outwards at a constant speed until the tail part of the cavity, and reading the distance between the piston and the end face of a test piece by using scales on the cavity wall so as to calculate the volume of the cavity;
10 Opening a calibrated oxygen data demodulator connected with the two chambers, recording the moment as t=0, and recording and transmitting the oxygen concentration in the two chambers into a computer by using a data recorder;
11 Due to the difference of oxygen concentration in the left and right chambers, oxygen gradually diffuses from the high-oxygen concentration chamber to the low-oxygen chamber through the cement-based material test piece, and in the process, the humidity in the whole device is kept constant due to the effect of saturated salt solution in the solution tanks of the left and right chambers. Recording the oxygen concentration in the two chambers at different moments by using a recorder;
12 When the oxygen concentration of the two chambers is close, the concentration gradient of the two chambers is small, the diffusion amount of oxygen passing through the cement-based material test piece is small, the test is stopped, and the time t is recorded;
13 According to the above data, under the humidity condition controlled by the saturated salt solution, oxygen diffuses in the cement-based material test piece under the power of the oxygen concentration gradient due to the difference of the oxygen concentrations of the two chambers, and the oxygen diffusion coefficient of the cement-based material test piece can be obtained according to the following formula:
wherein: d (D) f Is the oxygen diffusion coefficient (m 2 /s)；Oxygen concentration gradient (mol/m) for left and right chambers 4 ) The functional relation between the oxygen concentration values and time can be obtained according to the recorded oxygen concentration values of the two chambers at different moments; t is the test time(s); n is the amount of material (mol) of total oxygen that the hypoxic chamber increases from t=0 to the end of the test; s is the effective diffusion area (m 2 )。/>
14 Changing saturated salt solution in the solution tank, and repeating the steps 1) to 13), thereby obtaining the diffusion coefficient of oxygen in the cement-based material under different humidity.
The derivation process of formula (1) is as follows:
assuming that the steady-state diffusion of oxygen accords with Fick's first law, and under the test method, assuming that the oxygen diffusion mode is one-dimensional diffusion, there are:
dN is the oxygen amount passing through the cement-based material test piece in dt time, D f Is the oxygen diffusion coefficient;is the concentration gradient of oxygen in the x direction; s is the effective diffusion area of oxygen. />
In fact, cement-based materials act as a porous dielectric material in which oxygen diffuses only through the pores. Therefore, the actual path of the oxygen diffusion is tortuous and far greater than the vertical distance between the two surfaces, and the size of the diffusion section cannot be known exactly, so that the oxygen diffusion coefficient in the formula is actually an "equivalent diffusion coefficient", i.e. calculated based on the total area perpendicular to the diffusion direction and the thickness of the cement-based material specimen.
According to the law of gas diffusion: at the same temperature and pressure, the diffusion rate of a gas is inversely proportional to the square root of its density or molecular weight. Therefore, the square root of the molecular weight of both oxygen and nitrogen is very close (5.65 and 5.29), so the diffusion rate of oxygen can be approximately considered to be approximately equal to the diffusion rate of nitrogen. Thus, the pressures of the left and right chambers are equal at all times and the chamber volume is substantially unchanged during diffusion.
From (i), the total oxygen diffusion amount at the time of stopping the experiment was:
therefore, the effective diffusion coefficient of the cement-based material test piece is:
according to the percentage content of oxygen and the volume of the chambers recorded by the left chamber and the right chamber at different moments, the oxygen concentration values of the two chambers at different moments can be obtained according to an ideal gas state equation, the oxygen concentration is assumed to be linearly distributed in the cement-based material, and the oxygen diffusion is one-dimensional diffusion, so that the oxygen-free cement-based material can be obtained
Wherein: c (C) 2 C is the oxygen concentration (mol/m 3) in the high oxygen chamber at a certain moment 1 And X is the thickness (m) of the cement-based material test piece, wherein the oxygen concentration value (mol/m 3) in the hypoxia chamber at the same moment is shown.
As is clear from the formula (5),is a function related to time, and the oxygen concentration gradients of the left chamber and the right chamber of the cement-based material test piece at different moments are different. But->The function with time can be obtained by data fitting by using origin Pro software according to the data recorded by the test, and thus the oxygen diffusion coefficient of the tested cement-based material test piece can be obtained by calculation according to the formula (4). />
The beneficial effects of the invention are as follows: because the driving force of oxygen in the transmission process is only concentration gradient, and the device adopts an oxygen sensor with higher precision and a data recorder, and effectively combines the oxygen sensor with the data recorder, the diffusion coefficient of oxygen in the cement-based material can be conveniently calculated according to test data. On the other hand, the invention uses the saturated salt solution to control the environmental humidity, and the device designs the solution tank to place different saturated salt solutions, so that the humidity stability in the whole test process is controlled, and the purpose of measuring the oxygen diffusion coefficient in the cement-based material under different humidity can be achieved by changing different saturated salt solutions. The whole process is simple in measurement and accurate and reliable in data.
Drawings
FIG. 1 is an overall schematic of the apparatus of the present invention;
FIG. 2 is a schematic view of a gas chamber according to the present invention, wherein (a) is a front view and (b) is a top view;
FIG. 3 is a three-view of a moving piston of the present invention;
FIG. 4 is a graph showing the relationship between oxygen concentration gradient and time obtained from the oxygen concentration values of the left and right chambers of the cement-based material test piece at different moments.
In fig. 1, cement-based material test pieces; 2. an epoxy resin; 3. a rubber sealing gasket; 4. the wall of the cavity; 5. an air inlet valve; 6. moving the piston; 7. a piston seal ring; 8. a solution pool; 9. a stud bolt; 10. an oxygen sensor; 11. an oxygen data demodulator; 12. a data recorder; 13. a computer; 14. a gas delivery conduit; 15. a gas supply cylinder; 16. and an air outlet valve.
Detailed Description
The invention will be further described with reference to the accompanying drawings
Referring to fig. 1-4, a method for determining the oxygen diffusion coefficient in a cement-based material at different humidities, comprising the steps of:
1) Preparation of cement-based material test piece to be tested
Pouring and forming a cement-based material test piece to be tested, cutting the tested cement-based material into cylinders with certain thickness, and placing the cylinders in a series of different saturated saline solution closed containers until the internal humidity balance is achieved; and coating the side surface (non-oxygen diffusion surface) of the test piece with epoxy resin to isolate the influence of external atmosphere;
2) Connection of integral devices
The test piece obtained in the step 1) is connected with two gas chambers into a sealed whole by using a stud after being filled with a rubber sealing gasket, and a small amount of vaseline is coated at the contact position to increase the tightness; injecting the saturated salt solution which is the same as the saturated salt solution in the 1) into solution tanks at the bottoms of the two chambers, and ensuring that the humidity inside the chambers is balanced with the humidity of a test piece; the upper air inlet valve of the cavity is respectively connected with two air supply bottles; the movable piston is respectively connected with the two oxygen sensors; the two oxygen sensors are connected with an oxygen data demodulator; the two oxygen data demodulators are connected with the data recorder; the data recorder is connected with a computer. After the whole device is connected, the good air tightness of the connection is ensured, and the whole device is placed in a constant temperature chamber to eliminate the influence of temperature on oxygen diffusion.
3) Oxygen diffusion coefficient D of cement-based material under different humidity f Is (are) determined by
Opening a gas supply bottle, respectively filling a certain amount of oxygen and nitrogen into the two gas chambers, and obtaining a calculation formula of an oxygen diffusion coefficient under the humidity by utilizing the oxygen concentration change in the two gas chambers at different moments monitored by the online oxygen meter and the paperless recorder and combining an ideal gas state equation and Fick first law:
wherein: d (D) f Is the oxygen diffusion coefficient (m 2 /s)；Oxygen concentration gradient (mol/m) for left and right chambers 4 ) The functional relation between the oxygen concentration values and time can be obtained according to the recorded oxygen concentration values of the two chambers at different moments; t is the test time(s); n is the amount of material (mol) of total oxygen that the hypoxic chamber increases from t=0 to the end of the test; s is the effective diffusion area (m 2 )。/>
The test device for measuring the oxygen diffusion coefficient in the cement-based material under different humidity comprises a cement-based material test piece 1, wherein the left side and the right side of the cement-based material test piece are respectively connected with a gas chamber; each of the left and right cavities of the gas cavity is composed of an air inlet valve 5, a cavity pipe wall 4, a movable piston 6 and a solution pool 8; the two air inlet valves 5 are respectively arranged at the upper parts of the left cavity wall 4 and the right cavity wall 4 and are connected with two air delivery pipes 14; a small hole with the diameter of 20mm is reserved in the middle of the movable piston 6 for placing the oxygen sensor probe 10; the solution tanks 8 are positioned at the bottoms of the chambers respectively and used for placing saturated salt solution.
The other ends of the two gas delivery pipes 14 are respectively connected with gas outlet valves 16 of an oxygen cylinder and a nitrogen cylinder, and the gas outlet valves are connected to two gas supply cylinders 15 for controlling the gas flow rates of oxygen and nitrogen. The other end of the oxygen sensor 10 is connected with an oxygen data demodulator 11, and the oxygen data demodulator 11 adopts a KY-2F1 type oxygen analyzer for testing the oxygen concentration in the left and right chambers. The oxygen data demodulator 11 is connected with the data recorder 12, and the data recorder 12 collects test data and inputs the test data into a computer 13 connected with the data recorder to complete data collection in the test process.
A test device for determining the oxygen diffusion coefficient in cement-based materials at different humidity, the working process comprising the steps of:
1) Cutting the molded and standard cured cement-based material test piece 1 into a cylindrical test piece with the diameter of 50-100mm and the thickness of 10-20mm, placing the cylindrical test piece in a saturated saline solution closed container, and coating a non-diffusion surface (the side surface of the cylinder) by using epoxy resin 2 after the time reaches the internal humidity balance to isolate the influence of external air;
2) After the treated cement-based material test piece 1 and the left and right chambers are filled with rubber sealing gaskets 3, the left and right chambers are connected with the cement-based material test piece 1 by using stud bolts 9, and after the connection is finished, a proper amount of vaseline is coated at the connection positions such as the periphery of the gaskets 3 so as to ensure the air tightness of the connection positions of the test piece and the chambers;
3) A sufficient amount of saturated salt solution which is the same as that in the step 1) is injected into the solution tanks 8 of the left and right chambers;
4) The air inlet valve 5 at the upper parts of the two chambers is opened, after a proper amount of lubricating oil is coated on the outer part of the piston sealing ring 7, the movable piston 6 is pushed into the manufactured chamber wall 4 so as to remove the original gas in the chamber, and the piston position is required to meet the requirement of ensuring the air tightness and simultaneously keeping the mobility of the piston;
5) Placing the oxygen sensor 10 into a small hole reserved in the left and right cavity moving piston 6, and smearing vaseline after fixing to ensure air tightness;
6) The other end of the oxygen sensor 10 is connected with an oxygen data demodulator 11 for testing the oxygen concentration in the two chambers, the oxygen data demodulator 11 is connected with a data recorder 12 for data recording, and the recorder 12 is connected with a computer 13 for recording output and subsequent processing;
7) The air inlet valve 5 above the cavity wall 4 is connected with the air supply bottle 15 through the air delivery conduit 14, the oxygen chamber is connected with the oxygen bottle, the nitrogen chamber is connected with the nitrogen bottle, and the whole device is connected;
8) Checking the air tightness of the device;
9) Starting a test, opening an air supply bottle air outlet valve 16 and an air inlet valve 5 at the upper part of the cavity wall, respectively inflating the two cavities, enabling the movable piston to slowly move outwards at a constant speed until the tail part of the cavity, and reading the distance between the piston and the end surface of the test piece by using scales on the cavity wall so as to calculate the volume of the cavity; .
10 A calibrated oxygen data demodulator 11 connected to the two chambers is turned on, the time is recorded as t=0, and the oxygen concentration in the two chambers is recorded by a data recorder 12 and transmitted to a computer 13;
11 Due to the difference of the oxygen concentration in the left and right chambers, oxygen gradually diffuses from the high-oxygen concentration chamber to the low-oxygen chamber through the cement-based material test piece, and in the process, the humidity in the whole device is kept constant due to the effect of saturated salt solution in the solution tanks 8 of the left and right chambers. Recording the oxygen concentration in the two chambers at different moments by using a recorder;
12 When the oxygen concentration of the two chambers is close, the concentration gradient of the two chambers is small, the diffusion amount of oxygen passing through the cement-based material test piece is small, the test is stopped, and the time t is recorded;
13 According to the above data, under the humidity condition controlled by the saturated salt solution, oxygen diffuses in the cement-based material test piece under the power of the oxygen concentration gradient due to the difference of the oxygen concentrations of the two chambers, and the oxygen diffusion coefficient of the cement-based material test piece can be obtained according to the following formula:
wherein: d (D) f Is the oxygen diffusion coefficient (m 2 /s)；Oxygen concentration gradient (mol/m) for left and right chambers 4 ) The functional relation between the oxygen concentration values and time can be obtained according to the recorded oxygen concentration values of the two chambers at different moments; t is the test time(s); n is the amount of material (mol) of total oxygen that the hypoxic chamber increases from t=0 to the end of the test; s is the effective diffusion area (m 2 )。/>
14 Changing saturated salt solution in the solution tank, and repeating the steps 1) to 13), thereby obtaining the diffusion coefficient of oxygen in the cement-based material under different humidity.
The operation of the present invention will be specifically described by taking the measurement of oxygen diffusion coefficient of a mortar test piece using a saturated potassium acetate solution (at 288K, controllable environment relative humidity rh=23.40±0.32%) with a water-cement ratio of 0.53 and a water-sand ratio of 1:0.53:2.0 as an example.
The raw materials of the mortar for the mixing of the embodiment are as follows: the cement is P.I 525-grade portland cement, the sand adopts river sand with fineness modulus of 2.6, and the water adopts tap water. After standard curing for 28d in a curing room, the mortar test piece is cut into a cylindrical test piece with the diameter of 75mm and the thickness of 10mm, and in this embodiment, after the test piece is placed in a saturated potassium acetate solution closed container for curing until the inside is balanced, the side surface (non-oxygen diffusion surface) of the test piece is coated with epoxy resin to isolate the influence of external atmosphere, and the oxygen diffusion coefficient is tested.
After a rubber sealing gasket is filled on a mortar test piece, the mortar test piece is connected with the two gas chambers into a whole in a sealing way through a stud, and a small amount of vaseline is coated at a contact position to increase the tightness; filling sufficient saturated potassium acetate solution into solution pools at the bottoms of the two chambers, and ensuring that the humidity inside the chambers is balanced with the humidity of a test piece; the upper air inlet valve of the cavity is respectively connected with two air supply bottles; the movable piston is respectively connected with the two oxygen sensors; the two oxygen sensors are connected with an oxygen data demodulator; the two oxygen data demodulators are connected with the data recorder; the data recorder is connected with a computer. After the whole device is connected, the good air tightness of the connection is ensured, and the whole device is placed in a constant temperature chamber to eliminate the influence of temperature on oxygen diffusion.
Opening the gas supply bottle, respectively filling a certain amount of oxygen and nitrogen into the two gas chambers, and then transmitting the oxygen through the cement-based test piece under the action of concentration gradient. In the whole test process, the humidity inside the whole device is kept constant due to the effect of saturated potassium acetate solution in the solution tank. The oxygen concentration in the left and right gas chambers of the mortar test piece at different times in this example was monitored by an oxygen sensor and a data recorder as shown in table 1.
TABLE 1
( Description of data: because the device method only needs the existence of the oxygen concentration gradient of the left chamber and the right chamber, the oxygen concentration in the nitrogen chamber and the oxygen chamber is not 0% and 100% because the two chambers in the embodiment exclude the original gases in the chambers to different degrees. )
The test conditions for this example are as follows:
T＝288K，P＝101000Pa，V＝0.075*0.075*250＝1.40*10 -3 m 3 ，
S＝0.075*0.075＝5.6*10 -3 m 2 ；
according to the ideal gas state equation: pv= nRt; bonding of
In the above formula:the amount (mol) of the substance being oxygen in each of the left and right chambers; c is the oxygen species concentration (mol/m) 3 ) The method comprises the steps of carrying out a first treatment on the surface of the V is the chamber volume (m 3 )；/>Is the concentration gradient (mol/m) of oxygen in the x-direction 4 ) Assuming that the linear distribution of the oxygen concentration in the cement-based material test piece shows that the oxygen concentration gradient is equal to that of the cement-based material test pieceThe oxygen concentration difference Δc is divided by the test piece thickness X. />
Substituting the data in Table 1 to obtainThe diagram is shown in fig. 4./>
According to the experimental result of FIG. 4 after data processing, the data fitting is performed by using OriginPro software to obtainAs a function of time t, as can be seen from fig. 4, the oxygen concentration gradient of the left and right chambers of the cement-based material test piece of the embodiment 3 is as follows: />
According to the data of table 1, the example obtained a total increase in oxygen in the nitrogen chamber n= 0.008775mol from the start to the end of the test.
Thus, combined typet= 97380s, the diffusion coefficient of oxygen in the mortar test piece under the power of the oxygen concentration gradient can be found as follows: />
The example was completed, in which the effective oxygen diffusion coefficient of the mortar test piece was D when the relative humidity of the mortar test piece was 23.40.+ -. 0.32% (saturated potassium acetate solution control) f ＝6.03*10 -8 (m 2 /s)。
Claims (9)
1. A method for determining the oxygen diffusion coefficient in a cement-based material, characterized by: the method comprises the following steps:
1) Preparation of cement-based material test piece to be tested
Pouring and forming a cement-based material test piece to be tested, cutting the tested cement-based material into cylinders with set thickness, and placing the cylinders in a series of different saturated saline solution closed containers until the internal humidity balance is achieved; and coating the side surface of the test piece with epoxy resin to isolate the influence of external atmosphere;
2) Connection of integral devices
The end surfaces of the cement-based material test piece obtained in the step 1) are respectively connected with the two gas chambers to form a sealed whole; injecting the saturated salt solution which is the same as that in the step 1) into solution tanks at the bottoms of the two chambers, and ensuring that the humidity inside the chambers is balanced with the humidity of a test piece; the air inlet valve of the air chamber is respectively connected with two air supply bottles; the movable piston is movably sleeved in the cavity pipe wall, a piston sealing ring is arranged between the movable piston and the inner wall of the cavity pipe wall, and the movable piston is respectively connected with the two oxygen sensors; the two oxygen sensors are connected with an oxygen data demodulator; the two oxygen data demodulators are connected with the data recorder; the data recorder is connected with the computer; after the whole device is connected, the good air tightness of the connection is ensured, and the whole device is placed in a constant temperature chamber;
3) Oxygen diffusion coefficient D of cement-based material under different humidity f Is (are) determined by
Opening a gas supply bottle, respectively filling a certain amount of oxygen and nitrogen into the two gas chambers, and obtaining a calculation formula of an oxygen diffusion coefficient under the humidity by utilizing the oxygen concentration change in the two gas chambers under different moments monitored by an oxygen data demodulator and a data recorder and combining an ideal gas state equation and Fick first law:
wherein: d (D) f Is oxygen diffusion coefficient, unit m 2 /s；
2. The method for determining the oxygen diffusion coefficient in a cement-based material of claim 1, wherein: and after the cement-based material test piece is cast and molded according to a preset mixing ratio and is subjected to standard curing for 28d, cutting the cement-based material test piece into a cylinder with a set thickness, and placing the cylinder into a series of different saturated saline solution closed containers until the humidity balance inside the container is achieved.
3. A test device for a method of determining the oxygen diffusion coefficient in a cementitious material as defined in claim 1, wherein: the device comprises an air supply system, a test piece, a left air chamber, a right air chamber and a sensing test system, wherein the test piece is a cement-based material test piece, the left air chamber and the right air chamber are connected to two end surfaces of the cement-based material test piece, the left air chamber and the right air chamber respectively comprise an air inlet valve, a chamber pipe wall, a movable piston, a piston sealing ring and a solution tank, the air inlet valve is arranged on the chamber pipe wall, the movable piston is movably sleeved in the chamber pipe wall, the piston sealing ring is arranged between the movable piston and the inner wall of the chamber pipe wall, and the bottom of the chamber is provided with the solution tank for ensuring that the humidity inside the chamber is balanced with the humidity of the test piece;
the air inlet valve is connected with the air supply system, the air supply system consists of an air supply cylinder, an air outlet valve and air delivery pipes, the air supply cylinder is provided with an oxygen cylinder and a nitrogen cylinder, two air delivery pipes are respectively connected with the air outlet valve of the air supply cylinder, and the other ends of the two air delivery pipes are connected with the air inlet valve;
the sensing test system comprises an oxygen sensor and an oxygen data demodulator, and is used for measuring the oxygen concentration in the left and right chambers of the cement-based material, and the oxygen sensor is arranged on the side, close to the test piece, of the movable piston; the oxygen sensor is connected with the oxygen data demodulator.
4. A test device as claimed in claim 3, wherein: the test device further comprises a data acquisition system, the data acquisition system comprises a data recorder and a computer, the data acquisition system is used for recording and subsequent processing of oxygen concentration data in the left and right chambers of the cement-based material, and the oxygen data demodulator is connected with the data recorder.
5. The test device of claim 3 or 4, wherein: the air supply system, the test piece, the left and right air chambers and the sensing test system are all located in the constant temperature chamber.
6. The test device of claim 3 or 4, wherein: and a small hole is reserved in the middle of the movable piston, and the oxygen sensor is arranged in the small hole.
7. The test device of claim 3 or 4, wherein: the chamber walls are marked with scales for calculating the volumes of the two chambers.
8. The test device of claim 3 or 4, wherein: the movable piston main bodies of the two chambers are made of transparent organic glass, the piston sealing rings are made of nitrile rubber, and each piston sealing ring is provided with a small hole of 20mm and is used for being connected with the sensing test system.
9. The test device of claim 3 or 4, wherein: the air pressure of the left and right air chambers is equal to the external air pressure at the moment.
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| CN110865009A (en) * | 2019-11-06 | 2020-03-06 | 长安大学 | Determination device and determination method for oxygen diffusion coefficient and consumption coefficient in asphalt mixture |
| CN111504876B (en) * | 2020-04-30 | 2023-08-15 | 江苏科技大学 | Device for measuring oxygen diffusion coefficient in concrete under continuous tension and compression effect |
| CN113063700A (en) * | 2021-03-12 | 2021-07-02 | 中国石油大学(华东) | Humidity-controllable gas diffusion experimental device and method |
| CN114544717B (en) * | 2022-01-04 | 2023-09-29 | 青岛理工大学 | ECT quantitative monitoring water transmission method |
| CN114414457A (en) * | 2022-01-17 | 2022-04-29 | 四川轻化工大学 | Soil body gas diffusion coefficient measuring device used in environmental rock field |
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