Fire high-temperature lining internal water vapor migration barrier model and experimental method thereof

Abstract

The application discloses a lining internal water vapor migration barrier model under high temperature of fire and an experimental method thereof. The model is composed of a test block, a control and data collection device and a high-temperature combustion furnace. The test block is a concrete cubic component, three groups of steam pressure test tubes are arranged in the center of the test block, vertical thin steel plates are arranged in the inner side of each side wall at a distance of 10 cm, and the distance between the bottom of the steel plate and the bottom surface of the test block is 2 cm. The test method obtains the relationship curve of the pressure in the test block, the time and the temperature change by preparing and simulating the combustion process. The thin steel plate with high temperature resistance and water resistance is arranged in the concrete test block, the horizontal migration of the water vapor in the test block is blocked, the water vapor can only seep out along the thickness direction of the concrete, the migration condition of the water vapor in the actual tunnel when the fire occurs is simulated, and the rationality and accuracy of the measurement result are ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tunnel fire research, and particularly relates to a lining internal water vapor migration barrier model under high temperature fire and an experimental method thereof. BACKGROUND

[0002] A significant feature of tunnel fire is that the smoke generated is large, the visibility in the tunnel is low, and the fire spreads rapidly, and in a short time it can even reach above 1000℃, and then the highest temperature lasts for a long time.

[0003] In the initial stage of tunnel fire, the surface of the concrete lining subjected to fire will suddenly burst, causing the steel embedded in the concrete to be exposed, resulting in an instantaneous reduction in the load-bearing capacity of the concrete structure. At present, understanding the performance changes of concrete in high-temperature fire environment is an important part of the research on the fire resistance of concrete in tunnel concrete construction.

[0004] The steam pressure burst mechanism believes that the heat generated by the fire will be transferred from the heated surface of the lining to the interior of the concrete, forming a temperature gradient in the concrete. When the temperature rises to 100℃, free water, adsorbed water, and crystalline water begin to evaporate and form water vapor. On the one hand, the water vapor on the surface of the concrete subjected to fire volatilizes into the air, and on the other hand, due to the low permeability of concrete, the water vapor in the concrete is not easy to release, and thus accumulates in the pore space to form a pressure gradient, causing the water vapor to move along the thickness direction of the concrete and the secondary lining in the ring direction. However, concrete is a thermal inert material, the internal temperature rises slowly and the transfer speed is slow, and in the initial stage of fire, the concrete lining can be regarded as being locally heated. The moving water vapor will condense again when it encounters cold, and will be saturated in a certain cold area, forming a water vapor impermeable area (saturated plug), thus causing the water vapor to migrate along the thickness direction of the lining.

[0005] Full-scale tests can truly and intuitively reflect the burst performance of concrete in actual fires, but due to the limitations of actual site and economic conditions, it is often difficult to carry out full-scale test research, so some scholars start from concrete test blocks to try to master the distribution law of steam pressure in the test blocks. A part of the test adopts open fire heating, and the lower surface of the concrete test block on the inner side of the furnace is heated by the open fire. After being subjected to high temperature, the water vapor formed inside the test block moves towards the outside of the concrete, and finally seeps out from the side and top of the test block, resulting in a smaller or even zero value of the steam pressure measured along the thickness direction of the concrete. In the actual tunnel, the concrete far from the fire surface may not reach the temperature condition for the decomposition of free water and bound water in the concrete, or a saturated plug has been formed, so that the water vapor can only move along the thickness direction of the lining. Therefore, if the four sides of the test block are not water-proofed, it is impossible to simulate the situation that the water vapor migrates along the ring direction of the lining in the actual tunnel.

[0006] The side of the test block is wrapped with waterproof materials commonly used in tunnels to prevent water vapor from escaping from the side of the test block, however, part of the steam pressure will still diffuse to the side of the test block, making the steam pressure in the thickness direction smaller, if the waterproof material is embedded in the concrete test block, due to the low melting point of the existing waterproof material, the internal temperature of the concrete is relatively high during the test, part of the waterproof material will be decomposed due to high temperature, thereby unable to effectively block the horizontal migration of water vapor in the concrete, resulting in a certain deviation in the measurement result. SUMMARY

[0007] In view of the above problems, the present application provides a lining internal water vapor migration blocking model under fire high temperature and an experimental method thereof.

[0008] To achieve the above object, the technical scheme adopted by the present application is:

[0009] A lining internal water vapor migration blocking model under fire high temperature, comprising a test block, a control and data collection device, and a high-temperature combustion furnace.

[0010] The test block is a cubic member formed by pouring concrete, and the composition of the concrete of the test block is determined by the composition parameters of the test concrete lining.

[0011] The high-temperature combustion furnace is used to heat the bottom surface of the test block, and the maximum heating temperature is greater than 1100℃.

[0012] The control and data collection device includes a temperature sensor, a pressure sensor, and a recorder.

[0013] The high-temperature combustion furnace is built into a cubic structure with refractory bricks and refractory cement, with an open top, a combustion port and a smoke exhaust port on the side.

[0014] The distance between the three groups of steam pressure test pipes is 5cm.

[0015] The steam pressure test pipe is composed of a M20*1.5 nut joint and a stainless steel pipe with an outer diameter of 4 mm, an inner diameter of 2 mm and a length of 50 cm.

[0016] The application also discloses a model experiment method for water vapor migration barrier in a lining under high temperature fire.

[0017] Step one, determine the concrete strength grade, and calculate the concrete mixing ratio: determine the size of the test block as a cube with a length of 80 cm, a width of 80 cm and a height of 30 cm, and convert the required amount of various materials according to the size of the test block;

[0018] Step two, make the mold of the concrete test block, place four thin steel plates with a length of 60 cm, a width of 28 cm and a thickness of 2 mm vertically on the bottom of the mold and parallel to the side of the mold, the outer side of the thin steel plate is 10 cm away from the side of the test block, and a gap of 2 cm is reserved between the bottom of the thin steel plate and the bottom of the concrete, mark the position where the thin steel plate needs to be placed and point weld together;

[0019] Step three, embed three groups of steam pressure test pipes with an outer diameter of 4 mm, an inner diameter of 2 mm and a length of 50 cm at the center of the test block; the distance between adjacent steam pressure test pipes is 5 cm, and the distance between the bottom of the steam pressure test pipe and the bottom surface of the test block is 2 cm, 3 cm and 5 cm respectively, for measuring the steam pressure along the thickness direction of the concrete;

[0020] Step four, pour the concrete and insert the vibration rod for vibration, so that the concrete is densely combined, the honeycomb and pitted surface of the concrete is eliminated, and the strength is improved;

[0021] Step five, standard curing is performed on the poured concrete test block;

[0022] Step six, build a high-temperature combustion furnace with firebricks and refractory cement, and reserve holes for placing burners and smoke outlets on the bottom and side of the hearth respectively, and the size of the upper opening of the hearth is 60 cm in length, 60 cm in width and 80 cm in height.

[0023] Step seven, place the test block on the upper opening of the high-temperature combustion furnace; inject 1000 cps silicone oil from the steam pressure test pipe port by using a syringe and iron wire tools, stir the silicone oil with a hard thin iron wire while slowly injecting the silicone oil, so as to ensure that no bubbles are generated during the injection process, and make the silicone oil flow down along the test pipe slowly until the entire steam pressure test pipe is filled; the pressure sensor is connected to the nut of the steam pressure test pipe through the threaded joint at the end, and the positive and negative electrodes at the tail end of the sensor are connected to the positive electrode 24V+ and the negative electrode C end of the paperless recorder respectively; after the paperless recorder is connected to the power supply, data can be automatically collected, the data display unit of the paperless recorder is adjusted to MPa, and whether the values of each pressure channel are normal is checked;

[0024] Step eight, install a thermocouple with a range of 0-1200℃ inside the furnace to measure and record the temperature rising rate; open the control valve of the burner to heat the concrete test block, pay attention to the temperature inside the furnace displayed by the testing instrument during the heating process, adjust the size of the control valve to make the temperature rising curve inside the furnace fit the temperature rising curve of the target combustion characteristics, test the combustion for 30 minutes, and heat to 1100℃, then close the control valve of the burner to stop heating after 30 minutes, and end the test after waiting for the temperature of the test block and the furnace to reduce to the ambient temperature;

[0025] Step nine, record and analyze the obtained pressure-time and temperature change curve.

[0026] The beneficial effects of the present application are: the technical scheme of the present application sets a high-temperature-resistant and water-impermeable steel sheet inside the concrete, blocks the horizontal migration of water vapor inside the test block, makes the water vapor only seep out along the thickness direction of the concrete, simulates the migration of water vapor in the actual tunnel fire as much as possible, and ensures the rationality and accuracy of the measurement results. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the elevation view of the lining internal water vapor migration blocking model of the present application under fire high temperature.

[0028] Figure 2 is the A-A sectional view of Figure 1 .

[0029] Figure 3 is the model test elevation view of the present application.

[0030] Figure 4 is the model test furnace elevation view of the present application.

[0031] Figure 5 is the curve diagram of the steam pressure change with time obtained by the embodiment of the present application.

[0032] Explanation of reference numerals in the drawing:

[0033] 1, inner concrete; 2, steel sheet; 3, outer concrete; 4, fire surface; 5, steam pressure measuring pipe; 6, combustion inlet; 7, smoke exhaust hole; 8, test furnace; 9, inside the furnace. DETAILED DESCRIPTION

[0034] The present application will be further described below in conjunction with specific embodiments, which are further descriptions of the principles of the present application and do not limit the present application in any way. The same or similar technology as the present application does not exceed the scope of protection of the present application.

[0035] in conjunction with the drawings.

[0036] As Figures 1-4As shown, the internal water vapor migration barrier model of the lining under high temperature fire of the present application comprises: internal concrete, steel plate, external concrete, steam pressure measuring tube, pressure sensor, recorder, burner, test furnace. The steel plate is embedded in the internal concrete to divide the concrete test block into two internal and external parts, and the concrete test block is once cast and formed, and the bottom is connected as a whole. The steel plate is kept a certain distance from the bottom of the concrete, so that the internal and external concrete still remains as a whole. The steam pressure measuring tube is embedded in the concrete as the steel plate, and the lower part of the pressure measuring tube is used to collect the steam inside the test block, and the upper part is connected to the pressure sensor. The steam pressure inside the test block is transmitted to the pressure sensor through the pressure measuring tube, and the pressure sensor is connected to the recorder to display the measured pressure value in real time. The burner nozzle is placed at the combustion inlet, the gap between the nozzle and the reserved hole is filled with asbestos, and the flame is sprayed into the furnace through the nozzle to make the bottom of the test block be on fire.

[0037] The experimental method of the model of the present application comprises the following steps:

[0038] Step one, determine the concrete strength grade, and calculate the calculated mixing ratio of the concrete; the mixing ratio of this example is water: cement: sand: stone = 1:2:3.75:6.96, and the size of the test block is determined as a cube with a length of 80 cm, a width of 80 cm and a height of 30 cm. According to the size of the test block, the required amount of various materials is calculated: water 33.6 kg, cement 67.2 kg, sand 126 kg, and stone 234 kg;

[0039] Step two, make the mold of the concrete test block, and place four 310S thin steel plates with a length of 60 cm, a width of 28 cm and a thickness of 2 mm vertically on the bottom of the mold and parallel to the side of the mold. The outer side of the steel plate is 10 cm away from the side of the test block, and a gap of 2 cm is reserved between the bottom of the steel plate and the bottom of the concrete. Mark the position where the steel plate needs to be placed and weld it together;

[0040] Step three, embed a steam pressure measuring tube with an outer diameter of 4 mm, an inner diameter of 2 mm and a length of 50 cm in the center of the test block, and the transverse spacing of the pressure measuring tube is 5 cm. The bottom of the pressure measuring tube is 2 cm, 3 cm and 5 cm away from the bottom surface of the test block, respectively, for measuring the steam pressure along the thickness direction of the concrete;

[0041] Step four, pour in the concrete and insert the vibration rod for vibration, so that the concrete is densely combined and the phenomena such as honeycomb and pitted surface of the concrete are eliminated, and the strength is improved;

[0042] Step five, standard curing of the poured concrete test block for 28 days;

[0043] Step six, build a combustion furnace with 83cm in length, 83cm in width and 80cm in height by using fire bricks and fire cement, and reserve holes for placing burners and a smoke outlet on the bottom and side of the furnace respectively, and the internal dimensions of the furnace are 60cm in length, 60cm in width and 80cm in height.

[0044] Step seven, place the inside concrete of the test block to be heated on the furnace, and inject 1000cps silicone oil from the pressure tube by using a syringe and an iron wire tool, and stir the silicone oil with a hard thin iron wire to ensure that no bubbles are generated during the injection, and make the silicone oil flow down the test tube until the whole pressure tube is filled. Connect the pressure sensor with the screw joint of the end head and the screw cap of the pressure tube, and connect the positive and negative terminals of the tail end of the sensor to the positive 24V+ and negative C terminals of the paperless recorder respectively. After the paperless recorder is powered on, the data can be automatically collected, and the data display unit of the paperless recorder is adjusted to MPa, and the values of each pressure channel are checked.

[0045] Step eight, install a thermocouple with a measuring range of 0-1200℃ in the furnace to measure the heating rate in the furnace. Open the control valve of the burner to heat the concrete test block, and pay attention to the temperature in the furnace displayed by the test instrument during the heating process, and adjust the size of the control valve to make the temperature rising curve in the furnace fit the temperature rising curve of the test target combustion characteristics, and the test combustion is 30 minutes, and the highest temperature in the furnace is 1100℃, and after 30 minutes, the control valve of the burner is closed to stop heating, and the test is ended after the temperature of the test block and the furnace is reduced to the ambient temperature. The temperature rising curve of the test target combustion characteristics is the temperature rising curve describing the combustion characteristics of small oil fires such as gasoline tanks, gasoline tanks and chemical transport tanks.

[0046] Step nine, after the test is ended, copy the data of the paperless recorder by using a U disk, then disconnect the power supply, disconnect the connection between the pressure sensor and the paperless recorder, and unscrew the pressure sensor; import the data of the U disk into the computer, and use the software matched with the paperless recorder to draw the curve of pressure change with time and view the historical data record. Select the historical table in the software to view the test data, or click the export report and select channels 1-3 to save the data as an Excel file.

[0047] In this embodiment, the measurement point at 5cm is taken as an example, the imported data is processed by using Excel, the time is taken as the abscissa, and the steam pressure is taken as the ordinate to draw the steam pressure change curve with time, as shown in Figure 5As shown, in the early stage of the experiment, due to the lower temperature in the furnace, the evaporation of the water in the concrete needs a certain time, so the steam pressure measurement value in the first 6 minutes rises slowly, and with the continuous heating of the furnace and the limitation of the water vapor migration by the steel plate, the steam pressure in the concrete rapidly accumulates, and the steam pressure has a rapid rising trend from 6 to 10 minutes of the experiment. It can be seen from this that the measurement results obtained by the model have certain rationality and accuracy.

Claims

1. A model for blocking the migration of water vapor inside a lining under high temperature during a fire, characterized in that: It consists of a test block, a control and data collection device, and a high-temperature combustion furnace; The test block is a cubic component formed by concrete pouring. The concrete composition of the test block is determined by the composition parameters of the test concrete lining. The length, width, and height of the test block are 80cm×80cm×30cm. Three sets of steam pressure test tubes are pre-embedded at intervals in the center of the test block. The bottom of the three sets of steam pressure test tubes are 2cm, 3cm, and 5cm away from the bottom surface of the test block, respectively. Vertical thin steel plates are pre-embedded 10cm inside each side wall of the test block. The four steel plates are connected by spot welding. The bottom of each steel plate is 2cm away from the bottom surface of the test block. The high-temperature combustion furnace is used to heat the bottom surface of the test block, with a maximum heating temperature exceeding 1100℃; The control and data collection device includes a temperature sensor, a pressure sensor, and a recorder; the temperature sensor is installed in the high-temperature combustion furnace and connected to the recorder signal; multiple pressure sensors are installed in the steam pressure test tube and connected to the recorder signal.

2. The water vapor migration barrier model inside the lining under high temperature during a fire, as described in claim 1, is characterized in that: The high-temperature combustion furnace is constructed of refractory bricks and refractory cement into a cubic structure with an opening at the top and combustion and exhaust ports on the sides; the area of ​​the opening at the top is 60cm x 60cm.

3. The water vapor migration barrier model inside the lining under high temperature during a fire, as described in claim 1, is characterized in that: The distance between the three sets of steam pressure test tubes is 5cm.

4. The water vapor migration barrier model inside the lining under high temperature during a fire, as described in claim 1, is characterized in that: The steam pressure test tube consists of an M20*1.5 nut connector and a stainless steel tube with an outer diameter of 4mm, an inner diameter of 2mm, and a length of 50cm.

5. An experimental method for a model of water vapor migration barrier inside a fire lining under high temperature, characterized in that... Includes the following steps: Step 1: Determine the concrete strength grade and calculate the concrete mix proportion: Determine the size of the test block as a cube with a length of 80cm, a width of 80cm, and a height of 30cm, and calculate the required amount of various materials based on the size of the test block. Step 2: Make a mold for the concrete test block. Place four thin steel plates, each 60cm long, 28cm wide, and 2mm thick, perpendicular to the bottom of the mold and parallel to the sides of the mold. The outer edge of the thin steel plates should be 10cm away from the side of the test block. Leave a 2cm gap between the bottom of the thin steel plates and the bottom of the concrete. Mark the positions where the thin steel plates need to be placed and spot weld them together. Step 3: Pre-embed three sets of steam pressure test tubes with an outer diameter of 4mm, an inner diameter of 2mm, and a length of 50cm at the center of the test block; the spacing between adjacent steam pressure test tubes is 5cm, and the bottom of the steam pressure test tubes is 2cm, 3cm, and 5cm away from the bottom surface of the test block, respectively, to measure the steam pressure along the thickness direction of the concrete; Step four: Inject concrete and insert a vibrator to vibrate it, so that the concrete is compacted and bonded, eliminating honeycomb and pitted surfaces and improving strength. Step 5: Perform standard curing on the poured concrete test blocks; Step 6: Construct a high-temperature combustion furnace using refractory bricks and refractory cement, and reserve holes for placing the burners and exhaust ports at the bottom and sides of the furnace chamber. The internal dimensions of the furnace chamber are 60cm long, 60cm wide, and 80cm high. Step 7: Place the test block on the top of the high-temperature combustion furnace and fix it in place; pour silicone oil into the steam pressure test tube and connect the pressure sensor to the nut of the steam pressure test tube through the threaded connector at the end. Connect the other end of the sensor to the paperless recorder to collect data. Adjust the paperless recorder to display the data in MPa and check whether the values ​​of each pressure channel are normal. Step 8: Install thermocouples with a range of 0-1200℃ inside the furnace to measure and record the heating rate inside the furnace; turn on the control valve of the burner to heat the concrete test block, adjust the size of the control valve so that the heating curve inside the furnace fits the heating curve of the combustion characteristics of the test target, heat to 1100℃, turn off the burner control valve to stop heating after 30 minutes, and wait for the temperature of the test block and the furnace to drop to the ambient temperature before ending the test. Step nine: Record and analyze the obtained curves showing the relationship between pressure and time and temperature changes.

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