Method for measuring gas permeation resistance of cement concrete

Abstract

The invention discloses a method for measuring gas permeation resistance of cement concrete, and belongs to the technical field of highway bridge construction detection. The method comprises the following steps: sealing a cement concrete test piece, forming a vent hole in the upper part of the sealed test piece as a gas inlet, forming a vent hole in the lower part of the sealed test piece as a gas outlet, introducing gas into the gas inlet, and measuring and calculating the average mass flow rate of the gas at the gas outlet, the average gas pressure of the gas inlet and the average gas pressure of the gas outlet; calculating an average volume flow rate of the gas in a standard state based on the average mass flow rate of the gas; calculating the actual flow rate of the gas based on the average volume flow rate of the gas in the standard state, the average pressure of the gas at the gas inlet and the average pressure of the gas at the gas outlet; and calculating the gas equivalent permeability based on the actual flow velocity of the gas. According to the method, the gas permeability of the concrete can be quantitatively detected, the detection of tiny gas flow can be realized, and the detection method is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of highway bridge construction detection, in particular to a method for measuring the gas permeability resistance of cement concrete. Background Art

[0002] The impermeability of cement concrete is an important basis for concrete components to resist external forces and environmental damage. Concrete with good impermeability can greatly improve the durability of the structure. However, the traditional test method for impermeability is mainly based on the water permeability grade test. The test method is based on the "Test Method for Impermeability of Cement Concrete" (T 0568-2005) test method given in the "Test Procedure for Cement and Cement Concrete in Highway Engineering" (JTG 3420-2020). This method evaluates the quality of concrete based on water permeability, and this method gives a qualitative conclusion, and does not provide a quantitative evaluation method. On the other hand, when concrete is in an exposed environment, not only water penetration is harmful to the concrete itself, but gas penetration is also harmful. Most concrete immersion damage involves gas, so evaluating the gas permeability of concrete is an important part of evaluating the impermeability of concrete. The existing gas permeability test method uses the gas permeability coefficient to describe gas permeability. This method provides a quantitative description of permeability to a certain extent. However, the specimen size of this method is small, and the measurement results have large deviations. In addition to the problem of small specimen size, a soap film flowmeter is used to measure the flow rate, which cannot detect tiny flow rates. In addition, the test conclusion is only the gas permeability coefficient, not the gas permeability. Summary of the Invention

[0003] The present invention aims to provide a method for measuring the gas permeability resistance of cement concrete to address the aforementioned problems with the prior art. To assess concrete's permeability resistance, the present invention employs a constant pressure differential concrete permeability test method. It also innovatively uses equivalent gas permeability as a permeability evaluation metric, integrating traditional permeability coefficient evaluation methods.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is a method for measuring the gas permeability resistance of cement concrete, comprising the following steps: sealing a cement concrete specimen, providing an air vent on the upper portion of the sealed specimen as an air inlet, and providing an air vent on the lower portion as an air outlet, introducing gas into the air inlet, and measuring and calculating the average mass flow rate of the gas at the air outlet, the average pressure of the gas at the air inlet, and the average pressure of the gas at the air outlet;

[0006] Calculate the average volume flow rate of the gas under standard conditions based on the average mass flow rate of the gas;

[0007] The actual flow rate of the gas is calculated based on the average volume flow rate of the gas under standard conditions, the average pressure of the gas at the gas inlet, and the average pressure of the gas at the gas outlet;

[0008] The gas equivalent permeability is calculated based on the actual flow rate of the gas.

[0009] Furthermore, the calculation method of the average volume flow rate of the gas under the standard state is shown in formula (1):

[0010]

[0011] in, is the average mass flow rate of the gas, in kg / s;

[0012] ρ b is the density of the gas at standard temperature and standard atmospheric pressure, in kg / m 3 ;

[0013] q b is the average volume flow rate of the gas under standard conditions, in m 3 / s.

[0014] Furthermore, the actual flow rate of the gas is calculated as shown in formula (2):

[0015]

[0016] Among them, P b is the standard atmospheric pressure, the unit is Pa;

[0017] P1 is the average pressure of gas at the air inlet, in Pa;

[0018] P 2 is the average gas pressure at the outlet, in Pa;

[0019] q is the actual flow rate of the gas, in m 3 / s.

[0020] Furthermore, the calculation method of the gas equivalent permeability is shown in formula (3):

[0021]

[0022] Wherein, t is the time that the gas flows in the cement concrete specimen, in seconds;

[0023] A is the surface area of ​​the cement concrete specimen in direct contact with the air inlet, in m 2 ;

[0024] △P is the difference between the average gas pressure at the inlet and the average gas pressure at the outlet (i.e. P1-P2), in Pa;

[0025] μ is the dynamic viscosity of the gas, in Pa·s;

[0026] H is the height of the cement concrete specimen, in m;

[0027] Z avg is the compressibility factor of the gas.

[0028] When gas passes through dense cement concrete specimens, its viscosity has a significant impact on the flow rate. The resistance of gas in cement concrete is closely related to the flow rate per unit time. The flow rate of gas per unit time is directly proportional to the distance it flows and the dynamic viscosity of the gas, and inversely proportional to the cross-sectional area of ​​the gas flow path. In other words, when gas flows through the interconnected gaps inside cement concrete, the dynamic viscosity of the gas is one of the factors affecting the flow rate. And because gas is different from liquid, the volume of gas will be significantly compressed under pressure. Therefore, its flow rate cannot be based on the volume at normal pressure, and the compression state should be considered.

[0029] In order to reduce the error of permeability test, the present invention provides the concept of gas equivalent permeability K, which takes into account both the gas permeability coefficient and the resistance effects such as the dynamic viscosity and compressibility factor of the gas (because there is resistance when the gas penetrates in the concrete, and the resistance mainly comes from the compressibility and dynamic viscosity of the gas itself), forming an improved relationship between the gas permeability coefficient and the gas flow rate, which can better reflect the anti-permeability ability of cement concrete. The unit of K is m 2 (m 3 / m), its physical meaning is the difficulty of gas passing through concrete under a certain pressure gradient. Specifically, it reflects the volume flow rate of gas through unit length of concrete per unit time and unit pressure difference. Therefore, this unit is a composite unit, which comprehensively considers multiple factors such as time, pressure difference, area, gas compressibility, dynamic viscosity and volume flow rate (that is, the gas equivalent permeability of cement concrete is the equivalent volume of gas passing through all gaps or channels in cement concrete per unit time on the unit contact area between gas and cement concrete, under the unit pressure difference gradient at both ends of the aerated cement concrete).

[0030] A second technical solution of the present invention is a gas permeability measuring device for implementing the above-mentioned method for measuring the gas permeability resistance of cement concrete, the gas permeability measuring device comprising a gas cylinder, a first pressure gauge, a gas booster pump, a second pressure gauge, a testing unit, a third pressure gauge, a gas mass flow meter, and a vacuum pump connected in sequence by a pipeline;

[0031] The first barometer or the second barometer is used to measure the pressure of the gas entering the test unit;

[0032] The third pressure gauge is used to measure the pressure of the gas output from the test unit;

[0033] The test unit is used to bear cement concrete.

[0034] A third technical solution of the present invention is a method for measuring the gas permeability resistance of cement concrete using the above-mentioned gas permeability measuring device, comprising the following steps:

[0035] The cement concrete specimen was placed in the test unit and sealed. The valve of the gas cylinder was opened to allow gas to enter the test unit from the air inlet. The gas in the test unit was then pumped out from the air outlet of the test unit by a vacuum pump. The pressure of the outflowing gas was detected by a third barometer, and the mass flow rate of the outflowing gas was detected by a gas mass flow meter. When the mass flow rate of the outflowing gas was lower than 6×10 -8 g / s, the gas output from the gas cylinder is pressurized by a gas booster pump so that the mass flow rate of the outflowing gas is greater than 6×10 -8 g / s;

[0036] When the pressure is not increased, the pressure of the gas entering the test unit is measured by the first barometer or the second barometer; when the pressure is increased, the pressure of the gas entering the test unit is measured by the second barometer; and the average pressure P1 of the gas at the air inlet is calculated;

[0037] The pressure of the outflowing gas is measured by a third barometer, and the average pressure P2 of the gas at the gas outlet is calculated;

[0038] The mass flow rate of the gas flowing out of the test unit is measured by a gas mass flow meter, and the average mass flow rate of the gas is obtained by calculation.

[0039] And use the average mass flow rate of the gas The equivalent gas permeability K is calculated based on the average gas pressure P1 at the gas inlet and the average gas pressure P2 at the gas outlet.

[0040] Furthermore, the shape of the cement concrete specimen is cylindrical, with an upper diameter of 217 mm, a lower diameter of 197 mm, and a height of 200 mm.

[0041] Furthermore, the test unit includes a test die and a fixed pressing plate;

[0042] The height of the test mold is the same as that of the cement concrete specimen, and its diameter is 3 mm larger than that of the cement concrete specimen.

[0043] The upper and lower top surfaces of the test mold are provided with flash pressing plates;

[0044] The outer diameter of the flash pressing plate on the top surface of the test mold is 1mm smaller than the diameter of the groove of the fixed pressing plate set on it;

[0045] The outer diameter of the flash pressing plate on the lower top surface of the test mold is 1 mm smaller than the diameter of the groove of the fixed pressing plate arranged thereunder.

[0046] Furthermore, before placing the cement concrete specimen in the test unit, the side surfaces of the cement concrete specimen are coated with a waterproof sealing liquid material (note: the upper and lower surfaces should not be coated) at least three times to ensure that the outside of the cement concrete specimen is airtight; and at least three rubber rings with different inner diameters are inserted into the cement concrete specimen to seal the small gap between the cement concrete specimen and the test mold to ensure that the side gap is airtight.

[0047] Rubber disc rings are used to seal the upper and lower flash pressure plates and the upper and lower fixed pressure plates.

[0048] Furthermore, the width of the flash pressing plate is 40 mm.

[0049] Furthermore, the depth of the groove is 17 mm, and a step with a width of 41 mm and a height of 2 mm is provided in the groove.

[0050] Furthermore, a vent hole is provided at the center of the groove as an air inlet or an air outlet, and the hole diameter is 3 mm.

[0051] Furthermore, the total detection time is ≥24h, and the interval between each detection is 30min.

[0052] The present invention discloses the following technical effects:

[0053] The method of the present invention can quantitatively detect the gas permeability of concrete and can realize the detection of tiny airflows, and the detection method is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 A schematic structural diagram of a molding test mold used in the embodiment;

[0056] Figure 2 A schematic structural diagram of a test mold used in the embodiment;

[0057] Figure 3A schematic structural diagram of a fixed pressure plate used in an embodiment;

[0058] Figure 4 Schematic diagram of the structure of the test device used in the embodiment, wherein 1 is a gas cylinder, 2 is a pressure gauge, 3 is a gas booster pump, 4 is a pressure gauge, 5 is a gas mass flow meter, 6 is a test unit, 7 is a pressure gauge, 8 is a gas analyzer, 9 is a gas mass flow meter, 10 is a vacuum pump, and 11 is a gas filter water cup. DETAILED DESCRIPTION

[0059] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0060] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0061] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0062] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0063] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0064] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0065] The device modules used in the specific implementation of the present invention are as follows:

[0066] (1) The gas cylinder is a steel cylinder, and the gas inlet pressure is accurately controlled by a pressure reducing valve. The pressure should be controlled within 0.2 to 2.0 MPa. The pressure and flow rate should be stable. The pressure fluctuation range should be between ±0.05 MPa, and the flow rate fluctuation should not exceed ±5%. Helium is used as the gas in the present invention mainly because helium molecules are small and can easily pass through the tiny pores inside the concrete. The purity of helium is 99.999%, and the water dew point is ≤-50°C.

[0067] (2) The gas booster pump is a STA gas booster pump, which is in standby mode. When the pressure in the helium cylinder does not meet the requirement, the booster pump is turned on. If the pressure in the helium cylinder meets the requirement, the booster pump is not turned on.

[0068] The driving air pressure is 0.2~1.0MPa, the inlet pressure is 0.15MPa, and the maximum outlet pressure is 150MPa (adjustable).

[0069] (3) The gas mass flow meter is ACU10FD-LMYS gas mass flow meter, which can meet the low-speed gas flow in 3-8 mm gas pipelines and has a range of 0.02-2 sccm (the mass flow rate can be directly displayed. For helium, the mass flow rate range is 6×10 -8 ~6×10 -6 g / s), measurement and control range 100:1, accuracy ±1% FS, linearity ±0.5% FS, repeatability ±0.2% FS.

[0070] It is used to detect the flow rate of helium in a pipeline in a vacuum environment. The helium penetrates from one end of the concrete and flows from one end of the pipeline to the other end under the extraction of a vacuum pump.

[0071] (4) The gas analyzer is a PLT600-He portable helium gas analyzer. For concentration analysis, the range is 0 to 0.1 ppm, and the helium concentration measurement range is 0 to 100%. It is used to detect helium in a vacuum tube. The linearity is ≤ ±2% FS, and the repeatability error is ≤ ±1% FS. In this invention, the main purpose is to determine whether the helium content is zero in a vacuum environment.

[0072] (5) The vacuum pump is a portable oil-free vacuum pump with a pumping rate of 120 L / min and a vacuum degree of 0.001 to 0.01 MPa.

[0073] (6) Thermohygrometer: used to measure the test environment. The test environment is required to have a temperature of 20℃±5℃ and a humidity of no more than 40%.

[0074] (7) Gas filter cup, with water in it, placed on the gas pipe at the rear end of the vacuum pump to visually detect helium leakage.

[0075] Example 1

[0076] A method for determining the gas permeability resistance of cement concrete:

[0077] (1) Making cement concrete specimen molding mold

[0078] The mold is a cylindrical, upper-large, lower-smaller cylinder with a base. Its upper inner diameter is 217mm, its lower inner diameter is 197mm, and its height is 200mm. The mold is made of 2mm steel plate and consists of two semicircular bodies connected by snaps. The diameter of the base plate is 281mm. The two semicircular bodies and the base plate must fit tightly together to prevent slurry leakage, and the entire cylinder should be free of deformation. The inner surface of the mold should be polished to ensure a smooth finish.

[0079] The structural diagram of the forming test mold is shown in Figure 1 .

[0080] (2) Test piece preparation

[0081] A. Mix ratio of cement concrete

[0082] Cement, fly ash, silica fume, crushed stone, sand, polycarboxylate water reducer, water, and chopped basalt fiber were mixed in a mass ratio of 1:0.11:0.05:3.03:1.04:0.01:0.44:0.007 to obtain a concrete slurry with a water-cement ratio of 0.44 and a water-binder ratio of 0.38.

[0083] The concrete slurry was placed into the molding test mold and vibrated on a vibration table to produce a total of 6 cement concrete specimens.

[0084] After production, the cement concrete specimen was cured for 14 days under standard curing conditions (20℃±2℃) to obtain a compressive strength of 50.8MPa.

[0085] Among them, cement, strength grade is P.O42.5MPa;

[0086] Water, free of impurities;

[0087] Fly ash fineness should meet the requirements of 45μm square hole sieve residue not exceeding 12%, water requirement ratio not exceeding 95%, loss on ignition not exceeding 4.5%, sulfur trioxide content not exceeding 2%, and 7d activity index not less than 75%;

[0088] Silica fume (active mineral admixture), with a silicon dioxide content of more than 95%, a 45μm square mesh sieve residue of no more than 10%, and a 7-day rapid activity index of no less than 105%;

[0089] Crushed stone: adopt 5-25mm continuous grading, mud content not more than 0.5%, needle-like content not more than 10%;

[0090] Sand (medium-coarse sand), fineness modulus 2.7-2.9, mud content not more than 1%;

[0091] Polycarboxylic acid-based water-reducing agent, with a solid content of not less than 45%, an alkali content of not more than 1%, a water-reducing rate of not less than 38%, and a slump loss of not more than 30 mm within 2 hours;

[0092] Chopped basalt fiber, chopped rate ≥ 95%, dispersion rate ≥ 95%.

[0093] (3) Make a test mold

[0094] The test mold is made of 2mm steel plate. It is cylindrical, 200mm high, with a larger top and smaller bottom. It has 40mm wide flash platens on the top and bottom. The inner diameter of the upper opening is 220mm, and the diameter of the upper opening and flash platen is 304mm. The inner diameter of the lower opening is 200mm, and the diameter of the lower opening and flash platen is 284mm. The inner surface of the test mold should be polished to ensure a smooth finish.

[0095] The structural diagram of the test mold is shown in Figure 2 .

[0096] (4) Making a fixed pressure plate

[0097] The fixed pressure plate is a device used to fix the test mold and press and seal the upper and lower parts. It consists of two upper and lower steel plates with circular grooves.

[0098] The size of the fixed pressure plate is 50cm×50cm. There are four circular holes at the four corners of the fixed pressure plate as bolt holes. The hole diameter is 12mm. The vertical distance from the edge of the hole to the edge of the pressure plate is 40mm. The bolt holes of the upper and lower pressure plates should be concentrically arranged to facilitate the bolts to fix the upper and lower pressure plates stably and evenly.

[0099] The thickness of the steel plate used to make the fixed pressure plate is 20mm, the depth of the circular groove is 17mm, and a step 41mm wide and 2mm high is set in the groove. The groove should be flat and smooth.

[0100] A small ventilation hole is set in the center of the circular groove as an air inlet or outlet. The hole diameter is 3mm. The ventilation holes of the upper and lower pressure plates are concentrically symmetrical. A ventilation iron pipe with a corresponding inner diameter is welded to the outside of the ventilation hole. There should be screws on the outside of the iron pipe end to facilitate connection with the inlet and outlet pipes.

[0101] The inner diameter of the upper platen groove is 305mm, and the inner diameter of the lower platen groove is 285mm, which should ensure that the upper and lower parts of the test mold can be properly embedded in them.

[0102] The structural diagram of the fixed pressure plate is shown in Figure 3 .

[0103] (5) Prepare the test piece

[0104] ① Use waterproof sealing liquid material to seal the side surface of the cement concrete specimen (note, do not apply to the upper and lower surfaces). Ensure that the application is even and apply at least 3 times. Each application can be applied after it has dried.

[0105] ② After the sealing material is air-dried, the rubber ring is inserted into the cement concrete specimen. Five rubber rings are inserted into each cement concrete specimen (the rubber ring strip is a rubber strip with a diameter of 3mm), one in the middle, and two in total are inserted side by side close to the top and bottom surfaces. The purpose is to seal the tiny gap between the side of the cement concrete specimen and the test mold to ensure that the side gap is airtight.

[0106] The cement concrete specimen is in the shape of a truncated cone (i.e., cylindrical) with an upper diameter of 220 mm and a lower diameter of 200 mm. The inner diameter of the rubber ring in its natural state can be the median of the upper and lower diameters of the concrete specimen, which is 210 mm.

[0107] The sealed cement concrete specimen is pressed into the test mold using a press for testing.

[0108] (6) Instrument connection

[0109] ① Place the lower fixed plate on a flat surface, install the four corner bolts, secure the bottom of the bolts, put the lower circular rubber gasket (7mm thick, 201mm inner diameter, 285mm outer diameter) into the groove of the fixed plate, and make it flat;

[0110] ② Place the prepared test mold and cement concrete specimen on the lower fixed platen, and place a round rubber gasket (7mm thick, 221mm inner diameter, 305mm outer diameter) on the top of the test mold to make it flat;

[0111] ③ Place the upper fixed platen on the top of the test mold, making sure the upper and lower fixed platens are aligned;

[0112] ④ After confirming that the upper and lower fixed pressure plates are in close contact with the top and bottom of the cement concrete specimen, tighten the four corner bolts on the upper and lower fixed pressure plates to form test unit 6.

[0113] ⑤ Connect the gas cylinder 1 (i.e. helium tank), pressure gauge 2, gas booster pump 3, pressure gauge 4, gas mass flow meter 5, test unit 6, pressure gauge 7, gas analyzer 8, gas mass flow meter 9, vacuum pump 10 and gas filter cup 11 in sequence using a vent pipe (see Figure 4 ).

[0114] The test die and the fixed pressing plate constitute the test unit 6 .

[0115] (7) All interface connections should use pressure-resistant and well-sealed pipes and joints to connect the gas source and gas measuring equipment to ensure that there is no leakage at the connection.

[0116] (8) Testing and recording

[0117] ① Use a thermometer and hygrometer to check the indoor temperature and humidity, turn on the dehumidifier, and ensure that the test temperature is within the range of 20℃±5℃ and the humidity is not more than 40%.

[0118] ②Open the helium tank valve. When the pressure is insufficient to cause gas flow to appear at the outlet, turn on the booster pump to add air pressure to the upper part of the test unit. The pressure (detected by barometer 4) is maintained at 1000000Pa (1MPa).

[0119] ③ Turn on the vacuum pump to extract the gas in the test unit to maintain the vacuum pressure within the range of 0.01MPa to 0.05MPa.

[0120] ④The test duration is 24 hours.

[0121] ⑤ Record the gas pressure at the air inlet, the gas pressure at the air outlet, and the mass flow rate of the gas at the air outlet every 30 minutes and keep records.

[0122] The average gas pressure P1 at the air inlet is calculated based on the gas pressure at the air inlet; the average gas pressure P2 at the air outlet is calculated based on the gas pressure at the air outlet.

[0123] (9) Data calculation

[0124] ① Calculate the average mass flow rate of the gas according to the mass flow rate of the gas at the outlet measured by the gas mass flow meter 9

[0125] ②According to the average mass flow rate of gas Calculate the average volume flow rate q of the gas under standard conditions b , the calculation method is shown in formula (1):

[0126]

[0127] In formula (1), is the average mass flow rate of the gas, in kg / s;

[0128] ρ b is the density of the gas at standard temperature and standard atmospheric pressure (the density of helium is 0.178 kg / m 3 ), unit is kg / m 3 ;

[0129] ③According to the average volume flow rate q of the gas under standard conditions bCalculate the actual flow rate q of the gas. The calculation method is shown in formula (2):

[0130]

[0131] In formula (2), P b is the standard atmospheric pressure (P b =101325Pa), unit is Pa;

[0132] ④ Calculate the gas equivalent permeability K based on the actual gas flow rate q. The calculation method is shown in formula (3):

[0133]

[0134] In formula (3), t is the time that the gas flows in the cement concrete specimen, in seconds;

[0135] A is the surface area of ​​the cement concrete specimen in direct contact with the air inlet, in m 2 ;

[0136] △P is the difference between the average gas pressure at the inlet and the average gas pressure at the outlet (i.e. P1-P2), in Pa;

[0137] μ is the dynamic viscosity of the gas (the dynamic viscosity of helium is 1.89×10 -5 Pa·s), unit is Pa·s;

[0138] H is the height of the cement concrete specimen, in m;

[0139] Z avg is the compressibility factor of the gas (the compressibility factor of helium is 1.0005).

[0140] Table 1 Calculation table of air permeability test of cement concrete specimens

[0141]

[0142]

[0143] It can be seen from Table 1 that the average gas equivalent permeability K of the cement concrete specimens measured by the method of the embodiment is 7.467×10 -18 m 3 / m, this value is extremely small, which means that the equivalent volume of pores and channels inside cement concrete for gas to pass through is very small. When gas penetrates cement concrete, it can only pass through extremely narrow and tiny "paths". And when gas passes through 1m 2 When there is a pressure difference of 1Pa on both sides of the cement concrete area, there will be 7.467×10 -18 m3 The helium gas passes through the cement concrete at a distance of 1m, and the concrete meets the requirements of waterproof and air-proof concrete.

[0144] The results of cement concrete anti-permeability test and gas permeability coefficient test using existing technology are as follows:

[0145] (1) The concrete impermeability grade is P8;

[0146] (2) The gas permeability coefficient of this concrete is 135×10 -18 m 2 .

[0147] Example 2

[0148] 1. Comparison of gas equivalent permeability test results with traditional water seepage test and permeability coefficient test results

[0149] In order to study the correspondence between the gas equivalent permeability of concrete and the impermeability grade and gas permeability coefficient, when conducting the concrete gas equivalent permeability test, concrete specimens were made and the permeability coefficient and impermeability grade tests were conducted according to the test methods of "Test Method for Gas Permeability of Concrete" (JCT 2758-2023) and "Test Method for Impermeability of Cement Concrete" (T 0568-2005) given in "Test Code for Cement and Cement Concrete for Highway Engineering" (JTG 3420-2020). The test conclusions are as follows:

[0150] (1) Anti-seepage grade test results

[0151] The impermeability grade of concrete specimens prepared using the test method of "Test Method for Impermeability of Cement Concrete" (T 0568-2005) given in the "Test Code for Cement and Cement Concrete in Highway Engineering" (JTG 3420-2020) is P8.

[0152] (2) Permeability coefficient test results

[0153] The average gas permeability coefficient of concrete specimens prepared according to the test method of "Test method for gas permeability of concrete" (JCT 2758-2023) is 1.96×10 -16 m 2 .

[0154] 2. Consistency of the three anti-penetration test methods

[0155] The method of the present invention, the "Test Method for Gas Permeability of Concrete" (JCT 2758-2023), and the "Test Method for Impermeability of Cement Concrete" (T 0568-2005) given in the "Test Code for Cement and Cement Concrete in Highway Engineering" (JTG 3420-2020) were used respectively. Five types of concrete, P4, P6, P8, P10, and P12, were configured to produce specimens of the sizes specified by the three test methods. 100 groups of specimens were made for testing, and consistency conclusions were obtained for the three test methods.

[0156] Table 2 Quantity of test specimens for gas permeability test (unit: group)

[0157]

[0158] The details are as follows:

[0159] First, according to the order of magnitude of the gas equivalent permeability, it corresponds to the concrete anti-permeability grade one by one, and is divided into five grades, namely QT1, QT2, QT3, QT4, and QT5. QT represents the gas permeability of concrete, and the numbers 1 to 5 represent the resistance to gas permeability. The larger the value, the greater the concrete's resistance to gas permeability.

[0160] 100 groups of tests were conducted for each method and compared based on the concrete impermeability grade.

[0161] (1) The gas permeability coefficient test was conducted on concrete specimens with various water resistance grades. It was found that the gas permeability coefficient data of concrete specimens with water permeability grades of P4, P6, P8, P10, and P12 correspond to grades V, IV, III, II, and I in the "Test method for gas permeability performance of concrete" (JCT 2758-2023), respectively.

[0162] (2) Gas equivalent permeability tests were carried out on concrete specimens with various water resistance grades. It was found that the gas equivalent permeability data of concrete specimens with water permeability grades of P4, P6, P8, P10, and P12 corresponded to QT1, QT2, QT3, QT4, and QT5 in the present invention, respectively. At the same time, it was found that the gas permeability data of QT1, QT2, QT3, QT4, and QT5 corresponded to grades V, IV, III, II, and I in the "Test Method for Gas Permeability Performance of Concrete" (JCT 2758-2023), respectively.

[0163] Gas equivalent permeability test method: Same as Example 1, except that the composition of the concrete is different.

[0164] The gas equivalent permeability and gas permeability coefficient of concrete with different impermeability grades are shown in Table 3.

[0165] Table 3 Concrete anti-penetration performance and classification table

[0166]

[0167] As can be seen from Table 3, the permeability magnitude obtained by the test method of the present invention corresponds one-to-one with the gas permeability coefficient (method of JCT 2758-2023) and gas impermeability grade (method of T 0568-2005) of the traditional method, indicating that the data of the test method of the present invention is accurate and can be used to evaluate the impermeability performance of concrete.

[0168] However, the traditional method has the following defects:

[0169] (1) The instruments used in the gas permeability coefficient (JCT 2758-2023 method) and gas impermeability grade (T 0568-2005 method) test methods are relatively expensive, and the test detection is not economical.

[0170] (2) The water permeability test can indicate the concrete's permeability level, but it cannot guarantee good gas permeability. Therefore, the gas permeability performance (including the method of CT 2758-2023 and the method of T 0568-2005) can better reflect the concrete's resistance to the penetration of external substances.

[0171] (3) The gas permeability coefficient (JCT 2758-2023 method) is different from the present invention in terms of the accuracy of the test results. The present invention uses a method that can measure 6×10 -8 The method of JCT 2758-2023 cannot achieve the weak gas flow rate of g / s.

[0172] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for determining the gas permeability resistance of cement concrete, characterized in that: The following steps are involved: The cement concrete specimen is sealed, and a vent is set on the upper part of the sealed specimen as an air inlet, and a vent is set on the lower part as an air outlet. Gas is introduced into the air inlet, and the average mass flow rate of the gas at the air outlet, the average pressure of the gas at the air inlet, and the average pressure of the gas at the air outlet are measured and calculated; Calculate the average volume flow rate of the gas under standard conditions based on the average mass flow rate of the gas; The actual flow rate of the gas is calculated based on the average volume flow rate of the gas under standard conditions, the average pressure of the gas at the gas inlet, and the average pressure of the gas at the gas outlet; The gas equivalent permeability is calculated based on the actual flow rate of the gas.

2. The measuring method according to claim 1, wherein The calculation method of the average volume flow rate of the gas under the standard state is shown in formula (1): in, is the average mass flow rate of the gas; ρ b is the density of the gas at standard temperature and standard atmospheric pressure; q b is the average volume flow rate of the gas under standard conditions.

3. The measuring method according to claim 2, wherein The calculation method of the actual flow rate of the gas is shown in formula (2): Among them, P b is standard atmospheric pressure; P1 is the average pressure of gas at the air inlet; P2 is the average gas pressure at the outlet; q is the actual flow rate of the gas.

4. The measuring method according to claim 3, wherein The calculation method of the gas equivalent permeability is shown in formula (3): Wherein, t is the time for gas to flow in the cement concrete specimen; A is the surface area of ​​the cement concrete specimen in direct contact with the air inlet; △P is the difference between the average gas pressure at the inlet and the average gas pressure at the outlet; μ is the dynamic viscosity of the gas; H is the height of the cement concrete specimen; Z avg is the compressibility factor of the gas.

5. A gas permeability measuring device for implementing the method for measuring the gas permeability resistance of cement concrete according to any one of claims 1 to 4, characterized in that: The gas permeability measuring device comprises a gas cylinder, a first pressure gauge, a gas booster pump, a second pressure gauge, a testing unit, a third pressure gauge, a gas mass flow meter and a vacuum pump connected in sequence through a pipeline; The first barometer or the second barometer is used to measure the pressure of the gas entering the test unit; The third pressure gauge is used to measure the pressure of the gas output from the test unit; The test unit is used to bear cement concrete.

6. A method for measuring the gas permeability resistance of cement concrete using the gas permeability measuring device according to claim 5, characterized in that: The following steps are involved: The cement concrete specimen was placed in the test unit and sealed. The valve of the gas cylinder was opened to allow gas to enter the test unit from the air inlet. The gas in the test unit was then pumped out from the air outlet of the test unit by a vacuum pump. The pressure of the outflowing gas was detected by a third barometer, and the mass flow rate of the outflowing gas was detected by a gas mass flow meter. When the mass flow rate of the outflowing gas was lower than 6×10 -8 g / s, the gas output from the cylinder is pressurized by a gas booster pump so that the mass flow rate of the outflowing gas is greater than 6×10 -8 g / s; When the pressure is not increased, the pressure of the gas entering the test unit is measured by the first barometer or the second barometer; when the pressure is increased, the pressure of the gas entering the test unit is measured by the second barometer; and the average pressure P1 of the gas at the air inlet is calculated; The pressure of the outflowing gas is measured by a third barometer, and the average pressure P2 of the gas at the gas outlet is calculated; The mass flow rate of the gas flowing out of the test unit is measured by a gas mass flow meter, and the average mass flow rate of the gas is obtained by calculation. And use the average mass flow rate of the gas The equivalent gas permeability K is calculated based on the average gas pressure P1 at the gas inlet and the average gas pressure P2 at the gas outlet.

7. The method according to claim 6, characterized in that The shape of the cement concrete specimen is cylindrical.

8. The method according to claim 6, characterized in that The total detection time is ≥24h, and the interval between each detection is 30min.

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