ES2406360A1 - Method of measuring the permeability of a material to a gas (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Method of measuring the permeability of a material to a gas, comprising the steps of: - preparing a test piece (12) of a material whose permeability to a gas is to be measured; - placing said specimen (12) in a device (17) configured to keep its side faces sealed; - connecting at least one gas storage medium (11) to the end of the specimen (12) through which the gas enters; - connecting a flowmeter (15, 25, 35) to the end of the specimen (12) through which the gas exits; - connecting the output of a mass flow detector (22) included in the flow meter (15, 25, 35) to data conversion means (23) connected to a computer; - selecting at least three values of inlet pressure in a manometer-regulator (14); - for each inlet pressure, perform with the flow meter (15, 25, 35) at least one measure of the flow through the test piece (12), and obtain the permeability coefficient k, substituting the average flow value in the equation of darcy; - obtain the coefficient of permeability of the specimen (12) from the average value of the permeability coefficients k. (Machine-translation by Google Translate, not legally binding)

Description

METHOD OF MEASUREMENT OF THE PERMEABILITY OF A MATERIAL TO A GAS   

5

FIELD OF THE INVENTION The present invention belongs to the field of construction and, more specifically, to methods of controlling the permeability of a material.

10 15

BACKGROUND OF THE INVENTION There are standards that regulate the measurement of permeability of certain materials against gases. For example, Spanish regulations regulate the oxygen permeability test method through the UNE 83966: 2008 standards: Concrete durability. Test methods. Conditioning of concrete specimens for gas permeability and capillarity tests and UNE 83981: 2008: Concrete durability. Test methods. Determination of the oxygen permeability of hardened concrete.      

20 ~ 5

The basis of the test is to apply a constant pressure of gas, on one of the faces of a concrete specimen (or sample) and, after a sufficient time in which the gas has passed through the entire specimen and reached its opposite face, Record the gas flow at the outlet, that is, the volume of gas that passes through the specimen per unit of time. For this, it is necessary that the lateral faces of the specimen are perfectly sealed, in order that no gas escapes through them and in this way, all the gas that is applied on one of the faces, is collected in the opposite face

30

The gas flow inlet is controlled with a pressure gauge-regulator, and the flow rate at the outlet is measured, according to the referenced standard, by moving a soap bubble displaced by the outgoing gas, inside one of the N pipettes

5

graduates who fund the essay. To this end, a rubber knob is placed at the bottom of each pipette of the N pipette assembly. Pressing the knob of the selected pipette by means of a wrench, a soap bubble is generated which, pushed by oxygen, runs through the pipette. It is important to close the keys of the pipettes that are not being used.

10

The flow through the honnigon specimen is the result of dividing the volume that runs through the soap bubble measured as the final and initial difference in values on the graduated scale of the pipette, between the time it takes for the bubble to travel through that space.

1 "5;?: O

Each of the N test pipettes has a different diameter. The greater the penneability of the concrete specimen, the greater the flow through said honnigon specimen, and the higher the rate of rise of the bubble inside the pipette, for which a larger pipette diameter is required. Therefore, depending on the pressure and penneabi1ity of the concrete material, a pipette is selected from the set of N pipettes, in such a way that during the duration of the measurement the bubble moves upwards within said pipette and always without going out at its upper end. If the bubble does not move, the applied oxygen pressure is increased.

With a time measuring device, the time it takes for the soap bubble to pass through the graduated volume on the surface of the pipette is measured. If the measured time of the passage of the bubble is less than 30 seconds, the pipette used must be replaced with another one with greater capacity, being careful to close the keys of the pipettes that are not being used.

30

At the beginning of each measurement, and to avoid an overpressure in the system, the key between the test tube and the pipette assembly is kept open. To perform the test, five oxygen pressure values are selected using the nanometer pressure regulator. The pressures between 0.5 bar and

3.5 bar You can start with 0.1 bar, in the case that the concrete is very permeable, and reach a maximum of 5 bar, in the case that the concrete is not very permeable.

5 To ensure a stable rate of oxygen flow, prior readings of the flow of this flow are made in 5 minute intervals until the difference between successive readings is less than 3%. This stabilization procedure must be repeated for each pressure applied, and is generally achieved in the time between 5 minutes and 30 minutes, depending on the permeability of the concrete tested. Upon reaching the

10 flow stability the value of the flow through the specimen for each pressure applied is recorded. The average value of the flows obtained in each of the pressures for the same test tube is considered in the test.

The gas flow rates to be measured in the oxygen permeability test on concrete specimens are remarkably small, of the order of 0.1 to 0.5 cm3 / s; due to this, it is not possible to use conventional flowmeters and the soap bubble method is usually used. However, this method has a series of limitations and shortcomings, such as:

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The measurement of the permeability with the device that applies the soap bubble method is a slow and laborious procedure because for each pressure measurement, it is necessary to find the appropriate pipette at the corresponding flow rate, being necessary for this, to perform an important number of measurements with different pipettes until the appropriate pipette is found. In addition, once said pipette is located, the

Complete flow stabilization is achieved after a time of 5 to 30 minutes, it being understood that this is achieved when measurements made at 5 minute intervals do not differ by more than 3% of the measured flow value. That is, in a test in which the stabilization time is 30 minutes, after locating the most suitable pipette, 6 flow measurements must be made every 5 minutes to confirm the stabilization at the corresponding pressure.

-There is no possibility of electronically recording permeability values continuously. It is only possible to make discrete measurements both in the stabilization process and in the measurements once stabilized.

5 10

-The device that applies the soap bubble method requires increasing the inlet pressure when the bubble does not move as a result of low flow and low concrete permeability. The use of high pressures may involve changes in the viscosity of oxygen, thereby altering the values obtained from permeability. In addition, the use of high pressures can lead to the breakdown of the structure of young concrete cement paste, creating new capillaries and voids through which oxygen would pass. This also alters the value obtained from permeability.

SUMMARY OF THE INVENTION

TS

The present invention tries to solve the aforementioned drawbacks by means of a method of measuring the permeability of a material to a gas that allows to measure flow rates of the order of hundredths of cm3 / s, preferably from 0.02 cm3 / s, and obtain Real time flow evolution graphs with time.

~ 5

Specifically, in a first aspect of the present invention, a method of measuring the permeability of a material to a gas is provided, comprising the steps of: -preparation of a specimen of a material whose gas permeability is to be measured ;

30

- placing said specimen in a device configured to keep the side faces of the specimen sealed, ensuring its tightness and allowing gas to enter through one end of said specimen and exit through the opposite end;

-

connect at least one gas storage medium in charge of storing the gas inside it, to the end of the test tube through which the gas enters, where between said at least one storage medium and the test piece is located a pressure gauge-regulator configured to measure and regulate the pressure of the gas flowing from the at least one

5 gas storage means to the end of the test tube through which the gas enters;

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connecting a flow meter to the end of the test tube through which the gas flows, where said flow meter comprises a mass flow detector configured to convert the

10 amount of gas flow through the specimen in a given parameter;

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connect the output of the mass flow detector to data conversion means configured to measure the parameter that comes out of said mass flow detector and convert it into a flow value expressed in cm3 / s;

-

'1.5

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connect the data conversion means to a computer, where said computer allows real-time graphs of evolution of the flow over time to be obtained;

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select at least three inlet pressure values on the pressure gauge-regulator;

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for each selected inlet pressure, perform with the flowmeter at least one measurement of the flow through the specimen, expressed in cm3 / s;

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in the case that in the previous step the number of flow measurements is greater than ~ 5 two, obtain for each selected inlet pressure an average flow value.

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for each selected inlet pressure, obtain the permeability coefficient K, substituting the flow value or the average flow value that passes through the specimen in the Darcy equation;

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obtain the permeability coefficient of the specimen from the average value of the permeability coefficients obtained with the Darcy equation, corresponding to each selected input pressure value.

5 In a possible embodiment, the parameter obtained with the mass flow detector is a continuous electrical voltage. Alternatively, said parameter is an electric current.

In a possible embodiment, the number of inlet pressure values selected in the pressure gauge-regulator is five.

10 In a possible embodiment, the number of flow measurements performed with the quadalmeter for each selected inlet pressure is three.

In a possible embodiment, the manometer-regulator is implemented by two differentiated devices: a manometer and a regulator, the manometer being configured to measure the pressure of gas flowing from the at least one gas storage means to one of the ends of the test tube, and the regulator being configured to regulate said gas pressure.

In a possible embodiment, the material from which its permeability is to be measured is concrete.

BRIEF DESCRIPTION OF THE FIGURES

In order to help a better understanding of the features of the invention, in accordance with a preferred example of practical realization thereof, and to complement this description, a set of drawings is attached as an integral part thereof, whose character is Illustrative and not limiting. In these drawings:

30 Figure 1 shows a scheme of a system on which the method of implementation is implemented

the invention.

5

Figure 2 shows a diagram of the inside of a flowmeter comprised in the system on which the method of the invention is implemented. Figure 3 shows a diagram of the front view of the flowmeter comprised in the system on which the method of the invention is implemented.

10

Figure 4 shows a graph of the evolution of the flow that leaves the specimen as a function of time, and that is measured by the flow meter, for five different inlet pressures.

DETAILED DESCRIPTION OF THE INVENTION

In this text, the term "comprises" and its variants should not be understood in an exclusive sense, that is, these terms are not intended to exclude other technical characteristics, additives, components or steps.

,twenty

In addition, the terms "approximately", "substantially", "around", "ones", etc. they should be understood as indicating values close to which these terms accompany, since due to calculation or measurement errors, it is impossible to achieve those values with total accuracy.

25

In addition, a sample is understood as a sample of a material on which to measure its permeability.

30

The characteristics of the method of the invention, as well as the advantages derived therefrom, may be better understood with the following description, made with reference to the drawings listed above.

The following preferred embodiments are provided by way of illustration, and are not

5

It is intended to be limiting of the present invention. In addition, the present invention covers all possible combinations of particular and preferred embodiments indicated herein. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention.

10

The following describes a minimum configuration of a system on which the method of the invention for measuring the permeability to a gas of a material is implemented, in accordance with the scheme thereof of Figure 1. The material under measurement must be permeable Non-limiting examples of materials whose permeability can be measured by the system described are: concrete, ceramic or natural stone.

1.5

The system of Figure 1 comprises at least one gas storage means 11, responsible for storing the gas inside. Said at least one gas storage means 11 must contain the gas at a pressure greater than the pressure necessary to perform the measurement. In a particular embodiment, this storage means 11 is a gas bottle.

2: 5

The gas storage means 11 is attached to one of the ends of a test tube 12 whose permeability to a gas is to be measured, by means of a transport means 13 configured so that the gas circulates inside it from the storage means 11 to the corresponding end of the specimen 12. Preferably, the pressure at which the gas circulates inside the transport means 13 is regulated and controlled by a pressure gauge-regulator 14. Alternatively, the pressure gauge-regulator device 14 is It implements by means of two differentiated devices: a manometer and a regulator.

30

The transport means 13 can be of any material capable of withstanding pressures of approximately 10 bars, and with a diameter not greater than approximately 20 mm. Non-limiting examples of materials are steel, rubber or latex tubes,

rigid or flexible Preferably, and for security reasons, the means of

Transport 13 connected to the storage medium 11 is a rigid steel tube.

5

In a possible embodiment, in the case that the pressure gauge-regulator 14 is a single device, it is located between the storage means 11 and the test tube 12. In this case, the transport means 13 can be formed by two different elements , consecutively, joined by the pressure gauge-regulator 14. Alternatively, the pressure gauge 14 is placed in the storage medium 11 itself.

10 tS

In another possible embodiment, in the case that the pressure gauge and regulator are two differentiated devices, both are located between the storage means 11 and the test tube 12. In this case, the transport means 13 can be formed by three different, consecutive elements . Alternatively, the manometer and the regulator are located in the storage medium 11. Alternatively, one of the devices (manometer or regulator) is located in the storage medium 11, and the other device (regulator or manometer, respectively) is located between the storage means 11 and the test tube 12. In this case, the transport means 13 can be formed by two different, consecutive elements.

Prior to carrying out the test, the test tube 12 is conditioned, so that it has a constant moisture content such that it makes the results comparable.

Next, the specimen 12 is located inside a device 17 configured to keep the side faces of the specimen 12 sealed, ensuring its tightness and allowing the entry of gas through one of the ends of the specimen 12 and the exit through the opposite end. The materials from which the device 17 is formed are sealing materials, such as rubber or latex.

30

Therefore, during the use of the system, the gas from the storage medium 11 circulates inside the transport means 13 with a certain pressure,

selected in pressure gauge-regulator 14 (or in the regulator in the case where two independent devices are used). The gas enters one end of the test tube 12 and passes through it until it reaches its opposite end.

5 10

The gas outlet from the opposite end of the specimen 12 is measured by means of a flow meter 15 which is connected to that end of the specimen 12 by means of a transport means 16. The transport means 16 can be of any material such as to guarantee the internal pressure and security. Non-limiting examples of materials are steel, rubber or latex tubes, rigid or flexible. The flow meter 25 comprises a mass flow detector 22 responsible for converting the amount of gas flow through the specimen into continuous electrical voltage (or current interchangeably).

1 "5

The mechanism by which the mass flow is converted into an electrical voltage or current depends on the type of detector. A membrane detector quantifies the flow based on its deformation. A laser detector is capable of detecting a mass flow from the amount of particles that stand between a laser emitter and a detector. A temperature detector has an electrical resistance that is cooled by the flow. Preferably the mass flow detector 22 is a membrane or laser mass flow detector.

2: 5

The mass flow detector 22 must be precise enough to detect and convert quantities of gas flow in the range of approximately 0.02 cm3 / s and 5 cm3 / s, at a voltage of ± 5 V. Examples of mass flow detectors with these characteristics are: Honeywell AWM3000 Series, Ornron's manifold or Mass flow of SENSORTECHNICS.

30

Data conversion means 23 measure the continuous electrical voltage (or current interchangeably) that exits the mass flow detector 22 and converts it into a flow value expressed in cm3 / s. For this, it is necessary to perform a previous calibration of the

data conversion means 23, comparing at least five flow rates

measured by the soap bubble method with the voltage measured by the

data conversion means 23, thus obtaining a calibration equation. Bliss

equation is valid for measuring the permeability of any material that

5

require inlet pressure ranges between the minimum and maximum values of

calibration.

The data conversion means 23 is connected through an output interface

Digital to a computer. Thanks to this connection it is possible to obtain in real time

10

graphs of evolution of the flow over time and observe when the system

it stabilizes without the need to take measurements to check it. In addition, the

data conversion means 23 may comprise a screen 21 showing the

gas flow in cm3 / s that passes through the specimen.

'1 "5

In a possible embodiment, the data conversion means 23 is external and is not

are included in the flow meter 25. Preferably, the flow meter 25

it has an output interface 24, preferably an analog BNC type output, which

allows the output of the mass flow detector 22 of the flowmeter 25 to be connected to the

external data conversion means 23. In another possible embodiment, the means of

data conversion 23 are included in the flow meter 25. In another possible

embodiment, the data conversion means 23 are implemented both inside

of the flowmeter 25 as outside it.

An example of the flowmeter front 35 is shown in Figure 3, in which you can

observe the on-off switch 31 connected to the main input of

voltage, the display of the data conversion means 32 included in the

flowmeter 35, flowmeter input 33 and output interface 34 which

provides an analog electrical output of ± 5V corresponding to the measured flow

by the flowmeter 35.

30

To carry out the measurement of the permeability of a test tube 12 to a gas,

select at least three values of inlet pressure in pressure gauge-regulator 14 (or in the regulator in the case where two independent devices are used). Preferably the number of selected inlet pressure values is five.

5 10

For each of the selected inlet pressure values, at least one measure of the flow through the specimen 12, expressed in cm 3 / s, is carried out with the flowmeter 15, 25, 35. Preferably the number of flow measurements that are made for each selected inlet pressure is three. Then, in the event that this number of flow measurements is different from one, an average flow value is obtained for each pressure.

~ 5

The measured flow value for each selected input value (or the average value in case the number of flow measurements is different from one) is replaced in the Darcy equation, thus obtaining the permeability coefficient K:

K = 2P¡RLll A (P / _p¡2)

Where

twenty

K = Permeability coefficient [m2] 1) = Viscosity of the gas used [N * S / m2] L = Length of the test tube [m] R = Gas flow at the outlet of the test tube [m3 / s] A = Area of the cross section of the specimen [m2] PI = Absolute pressure at the outlet of the specimen [N / m2] P2 = Absolute pressure at the inlet of the specimen [N / m2]

30

Finally, the permeability coefficient of the specimen 12 is obtained from the average value of the permeability coefficients obtained with the Darcy equation, corresponding to each selected inlet pressure value.

The method of the invention solves the drawbacks detected in the current state of the art, since it takes the flow measurement in real time. In this way, it is possible to obtain the stabilization curve of the system, specifying the moment in which the data recording can be performed without the need to make measurements

5 spaced in time to confine the stabilization. This reduces the test time and the number of measurements needed to stabilize the system, optimizing the duration of the test. Flow rates are obtained faster than with the method described in the prior art.

10 The pennite method measures the evolution of the penneability of a material to a gas, over wide intervals of time, allowing continuous flow measurement in real time. In this way, it is possible to obtain the stabilization curve of the system, specifying the time at which data can be recorded without the need to make measurements spaced in time to confine the stabilization. This reduces the test time and the number of measurements needed to stabilize the system, optimizing the duration of the test. Flow rates are obtained faster than with the systems described in the prior art.

In addition, the greater sensitivity of the 15.25.35 flowmeter included in the system on which the method is implemented, allows to measure flow rates of the order of hundredths of cm3 / s, preferably from 0.02 cm3 / s, avoiding having to use pressures as high as necessary to obtain measurable flow rates in the device that applies the soap bubble method.

Example

A concrete example of embodiment of the invention and the results obtained are shown below.

30 The gas storage medium used is a gas bottle, which contains the gas at a pressure greater than the minimum necessary in the course of the tests, which is

5

regulates and controls thanks to a pressure gauge-regulator. Said gas bottle is connected to the upper end of a test tube whose permeability to a gas is to be measured, by means of a rigid steel tube that connects the gas bottle with the pressure gauge-regulator and by a flexible rubber gas tube that connects said manometer-regulator with said upper part of the test tube.

10

The specimen is cylindrical of 20% recycled concrete, dimensions 96 mm high and 150 mm in diameter, and is located inside a rubber side coating device, configured to keep the side faces of the specimen sealed, in such a way that the constant pressure of gas that is applied at its upper end, crosses the entire test tube and reaches its opposite end.

Therefore, during the use of the system, the gas coming from the gas bottle circulates inside the rigid steel tube at the pressure of 5 bar. Once said gas reaches the pressure gauge-regulator, it passes through the rubber gas hose, at the pressure selected in the pressure gauge-regulator, until it reaches the upper end of the test tube. The gas enters through said upper end and crosses the entire test tube until it reaches its lower end.

eO

The gas outlet at the opposite end of the specimen is measured by a flowmeter connected to the lower end of the specimen by a latex tube. a

~ 5 30

The flow meter comprises an on-off switch, which must be connected to the main voltage input, a mass membrane flow detector responsible for converting the amount of gas flow through the test tube into continuous electrical voltage (or current interchangeably) and a BNC output that allows the output of the mass flow detector of the flowmeter to be connected to external data conversion means that measure the voltage or electric current that comes out of the mass flow detector and convert it into a flow value expressed in cm3 / s The conversion means are in turn connected to a computer, and thanks to this connection it is possible to obtain real-time graphs of flow evolution over time.

Figure 4 shows a graph obtained with the flowmeter comprised in the system on which the method of the invention is implemented, in which the stabilization curve of the concrete specimen described above for five different pressure values is represented. The ordinate axis represents the flow in cm3 / s and the axis

5 of abscissa represents the time in seconds.

Each of the five peaks seen in the figure, correspond to the five pressure values selected in the pressure gauge-regulator, these pressures being 1 bar, 1.1 bar, 1.2 bar, 1.3 bar and 1.4 bar respectively.

10 The first ascent corresponds to the system connection (start of the test) with an inlet pressure of 1 bar. Then the graph descends smoothly until it reaches the stabilization zone. As can be seen, this stabilization process takes approximately 300 seconds (5 minutes).

Next, a new ascent of the flow corresponding to the disconnection and connection of the pressure gauge-reducer can be observed, in order to modify the inlet pressure in the system. In this case, the inlet pressure is increased to 1 bar, which is why this second peak is higher than the first. The stabilization curve is very similar to that of the first peak and its duration is also approximately 300 seconds. As expected, the asymptote of stabilization and, therefore, the flow at the exit, is greater in the second case.

The third, fourth and fifth rise correspond to the disconnection and connection of the

2: 5 pressure gauge-reducer, with the aim of increasing the system inlet pressure to

1.2 bars, 1.3 bars and 1.4 bars respectively, which is why each peak is higher than the previous one. The stabilization curve is very similar in all cases, its duration being approximately 300 seconds. Each stabilization asymptote, and therefore the flow at the exit, is greater the greater the power at the input.

For each inlet pressure, three flow measurements are made once it has stabilized and its average is performed. This average flow value as a function of pressure is shown in Table 1.

Pressure 02

Flow

[kgjcm 2]

[m3js]

1.00

1.25E-06

1.10

1.43E-06

1.20

1.61E-06

1.30

1.79E-06

1.40

1.98E-06

Table 1. Average value of the flow through the specimen based on the inlet pressure.

The average flow value is substituted in the Darcy equation, thus obtaining the permeability coefficient K shown in Table 2:

Pressure 02 [kgfcm2]

Flow rate [m3js] Coef Permeability [m2]

1.00

1.25E-06 9.14E-16

1.10

1.43E-06 9.20E-16

1.20

1.61E-06 9.20E-16

1.30

1.79E-06 9.16E-16

1.40

1.98E-06 9.13E-16

Table 2. Average value of the flow through the specimen and coefficient of permeability depending on the inlet pressure.

Finally, the permeability coefficient of the specimen is the average value of the permeability coefficients obtained with each pressure, being in this case 9.l7E-16

m.

Claims (9)

5

1. Method of measuring the permeability of a material to a gas, characterized in that it comprises the steps of: -preparation of a specimen (12) of a material whose permeability to a gas is to be measured;

10

- placing said test tube (12) in a device (17) configured to keep the side faces of the test tube (12) sealed, ensuring its tightness and allowing gas to enter through one of the ends of said test tube (12) and exit through the opposite end;

: 1 = 5

- connect at least one gas storage medium (11) responsible for storing the gas inside it, to the end of the test tube (12) through which the gas enters, where said at least one storage medium (11) enters Y The test tube (12) is located a pressure gauge-regulator (14) configured to measure and regulate the pressure of the gas flowing from the at least one gas storage medium (11) to the end of the test tube (12) by which the gas enters;

:the

-connecting a flow meter (15, 25, 35) to the end of the test tube (12) through which the gas leaves, where said flow meter (15, 25, 35) comprises a mass flow detector (22) configured to convert the quantity of gas flow through the specimen (12) in a certain parameter;

- connect the output of the mass flow detector (22) to data conversion means (23) configured to measure the parameter that comes out of said mass flow detector (22) and convert it into a flow value expressed in cm3 / s ;

30

-connecting the data conversion means (23) to a computer, where said computer allows real-time graphs of flow evolution over time to be obtained;

-

select at least three values of inlet pressure in the pressure gauge-regulator (14);

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for each selected inlet pressure, perform with the flowmeter (15, 25, 35) at least 5 a measurement of the flow through the test tube (12), expressed in cm3 / s;

-

in the case that in the previous step the number of flow measurements is greater than two, obtain for each selected inlet pressure an average flow value.

10 -for each selected inlet pressure, obtain the permeability coefficient K, substituting the flow value or the average flow value that passes through the specimen (12) in the Darcy equation;

-

obtain the permeability coefficient of the specimen (12) from the average value of the permeability coefficients obtained with the Darcy equation, corresponding to each selected inlet pressure value.

2.

The method of any of the preceding claims, wherein said parameter obtained with the mass flow detector (22) is a continuous electrical voltage.

3.

The method of claim 1, wherein said parameter obtained with the mass flow detector (22) is an electric current.

Four.

The method of any of the preceding claims, wherein the number of inlet pressure values selected in the pressure gauge-regulator (14) is five.

5.

The method of any of the preceding claims, wherein the number of flow measurements made with the flow meter (15, 25, 35) for each selected inlet pressure is three.

6. The method of any of the preceding claims, wherein the manometer regulator (14) is implemented by two differentiated devices: a manometer and a regulator, the manometer being configured to measure the pressure of gas flowing from the at least one gas storage medium (11) to one end of the test tube (12), and the regulator being configured to regulate said gas pressure. 7. The method of any of the preceding claims, wherein the material of which its permeability is to be measured is concrete. 13 13 fifteen 11 16  Figure 1  Figure 2   3.5 ('one') 2.5 AND or 2 1.5 one ! OR 3000 4000 5000