A device for measuring the permeability coefficient of permeable concrete and a measuring method thereof

Abstract

The present invention provides a device for measuring the permeability coefficient of permeable concrete and a measuring method thereof. The measuring device includes a workbench, on which there is a bracket, and on the bracket there is an overflow bucket. A water supply pipe is connected to a water source to supply water to the overflow bucket. An overflow pipe is provided on the side wall of the overflow bucket. The bottom of the overflow bucket is connected to the water inlet of a specimen fixing box through a seepage water supply pipe. The water outlet of the specimen fixing box is connected to a seepage drainage pipe, and the height of the water outlet is higher than the height of the permeable concrete specimen. The test port of a Pitot tube velocity measuring device is connected to the pipe wall of the seepage drainage pipe. The measuring device and the measuring method are convenient to operate, eliminate the experimental error caused by manually reading the mass of the seepage water at the end of the time, and make the experimental results more accurate.

Description

Technical Field

[0001] The present invention relates to the field of pervious concrete measurement, and particularly to a device for measuring the permeability coefficient of pervious concrete and a measurement method thereof. Background Art

[0002] The application of concrete materials has turned the large-area naturally pervious ground surface into an impervious hardened ground. The highly dense hardened ground causes a large amount of rainwater resources to flow into rivers, lakes and seas in vain, and the groundwater cannot be replenished, exacerbating the water resource crisis. The emergence of "pervious concrete" is one of the effective measures to alleviate this problem. Its water permeability and air permeability can make rainwater infiltrate and supplement groundwater resources; it can also collect, purify and reuse rainwater, saving water resources to the greatest extent. Therefore, promoting the research and application of pervious concrete is of great significance to the social and economic development of our country.

[0003] Pervious concrete is a two-phase material composed of aggregates and cement paste, and the water permeability is one of the main parameters for evaluating its performance. At present, most of the test methods for the permeability coefficient of pervious concrete obtain the mass of the infiltrated water volume within a certain time by the weighing method, and then convert it into flow rate, and then calculate the infiltration flow rate of the cross-section of the pervious concrete. The problems of these methods are as follows: If the mass of the infiltrated water volume is measured within a relatively short time, there will inevitably be errors in manually reading the water mass at the beginning and end of the test time, further resulting in a certain gap between the measured value and the true value of the permeability coefficient. If the time is extended, a larger water tank is required to accommodate the infiltrated water. Taking a 100mm*100mm*100mm cubic pervious concrete specimen (permeability coefficient k = 10mm / s) with a head difference of 30cm within 60 seconds as an example, the water tank for accommodating the infiltrated water volume within 60 seconds requires a volume of at least 18L, which brings certain troubles to the measurement of the permeability coefficient of pervious concrete. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a device for measuring the permeability coefficient of pervious concrete and a measurement method thereof, which are convenient to operate, eliminate the experimental error caused by manually reading the mass of the infiltrated water at the end of the time, and make the experimental results more accurate.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: A device for measuring the permeability coefficient of pervious concrete, including a workbench, a bracket is provided on the workbench, an overflow bucket is provided on the bracket, a water supply pipe is connected to a water source to supply water to the overflow bucket, an overflow pipe is provided on the side wall of the overflow bucket, the bottom of the overflow bucket is connected to the water inlet of a specimen fixing box through a seepage water supply pipe, the water outlet of the specimen fixing box is connected to a seepage water drain pipe, the height of the water outlet is higher than the height of the pervious concrete specimen, and the test port of a pitot tube velocity measuring device is connected to the pipe wall of the seepage water drain pipe.

[0006] In a preferred embodiment, a plurality of support columns are provided in the specimen fixing box, and the permeable concrete specimen is placed on the support columns.

[0007] In a preferred embodiment, the Pitot tube velocity measuring device includes a Pitot tube. The total pressure intake port and the static pressure intake port of the Pitot tube are located in the seepage drain pipe. The total pressure intake port is located at the central position of the seepage drain pipe. A through hole for the Pitot tube to pass through is provided on the pipe wall of the seepage drain pipe. The total pressure outlet of the Pitot tube is connected to the first pressure measuring tube through a connecting pipe, and the static pressure outlet of the Pitot tube is connected to the second pressure measuring tube through a connecting pipe.

[0008] In a preferred embodiment, a support plate is provided on the workbench, and the Pitot tube, the first pressure measuring tube and the second pressure measuring tube are fixed on the support plate.

[0009] In a preferred embodiment, scale lines are provided on the support plate.

[0010] In a preferred embodiment, the water source is a water tank, a water pump is provided on the water supply pipe, and the overflow pipe and the seepage drain pipe are connected to the water tank.

[0011] The present invention also provides a measuring method for a permeable concrete permeability coefficient measuring device, including the following steps:

[0012] Step 1: After the preparation of the permeable concrete specimen is completed, measure the cross-sectional area Apc of the specimen. After the measurement device is built, measure the cross-sectional area A of the water pipe and the calibration coefficient μ of the Pitot tube;

[0013] Step 2: Load the permeable concrete specimen to be measured into the specimen fixing box, turn on the water pump, deliver water to the overflow bucket, and flow into the specimen fixing box through the seepage water supply pipe. When the water seeps through the permeable concrete specimen due to the pressure difference, it flows out from the seepage drain pipe, and a stable water level is formed above the specimen fixing box. After the seepage state is stable, the excess water in the overflow bucket flows out from the overflow pipe, and a stable water level is formed in the overflow bucket;

[0014] Step 3: Measure the height Z1 from the water surface in the overflow bucket to the workbench, the height Z2 from the water surface in the specimen fixing box to the workbench, read the reading H1 of the first pressure measuring tube and the reading H2 of the second pressure measuring tube;

[0015] Step 4: Calculate the permeability coefficient according to the measurement data in Step 1 and Step 4.

[0016] In a preferred embodiment, in Step 4, according to the Bernoulli equation, the flow velocity u at the center of the pipe can be obtained:

[0017]

[0018] According to the flow velocity u at the center of the pipe, calculate the average flow velocity u of the pipe avg :

[0019]

[0020] The pipeline flow rate Q1 is:

[0021]

[0022] According to Darcy's law, the seepage flow rate Q2 of the permeable concrete specimen can be obtained as:

[0023]

[0024] From the continuity equation, Q1 = Q2 can be obtained, and thus the calculation formula for the permeability coefficient k of the permeable concrete specimen is:

[0025]

[0026] Among them, μ is the correction coefficient of the pitot tube, g is the acceleration due to gravity, H is the seepage head difference, and L is the seepage path.

[0027] In the preferred solution, in the second step, before loading the permeable concrete specimen to be tested into the specimen fixing box, first wrap the periphery of the permeable concrete specimen to be tested with pvc tape and then apply a layer of vaseline.

[0028] A device and method for measuring the permeability coefficient of permeable concrete provided by the present invention can obtain the permeability coefficient of permeable concrete by measuring with the measuring device and substituting it into the formula for calculation, which simplifies the step of calculating the seepage time in the previous conventional test method and eliminates the experimental error caused by manually reading the mass of the seepage water body at the end of the time, making the experimental results more accurate. This test device has the characteristics of convenient operation, high precision and high practical application value compared with the previous permeability coefficient test devices. Brief Description of the Drawings

[0029] The following further describes the present invention in conjunction with the drawings and embodiments:

[0030] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0031] Figure 2 It is a schematic diagram of the structure of the pitot tube velocity measuring device;

[0032] Figure 3 It is an external view of the specimen fixing box;

[0033] Figure 4 It is an internal schematic diagram of the specimen fixing box;

[0034] Figure 5 It is a schematic diagram of the structure of the overflow bucket;

[0035] In the figure: workbench 1, support 2, overflow bucket 3, water supply pipe 4, overflow pipe 5, seepage water supply pipe 6, sample fixing box 7, seepage drain pipe 8, pitot tube 9, first piezometric tube 10, second piezometric tube 11, support plate 12, water tank 13, water pump 14, water inlet 701, water outlet 702, support column 703, total pressure air inlet 901, total pressure air outlet 902, static pressure air outlet 903, scale line 1201. Detailed implementation mode

[0036] As Figures 1 to 5 shown, a device for measuring the permeability coefficient of permeable concrete includes a workbench 1. A support 2 is provided on the workbench 1, and an overflow bucket 3 is provided on the support 2. The overflow bucket 3 is fixed at a certain height. In this embodiment, a steel wire rope is connected to the upper end of the overflow bucket 3 and is hung on the support 2 through the steel wire rope. The water supply pipe 4 is communicated with a water source to supply water to the overflow bucket 3. An overflow pipe 5 is provided on the side wall of the overflow bucket 3. The bottom of the overflow bucket 3 is communicated with the water inlet 701 of the sample fixing box 7 through a seepage water supply pipe 6. The water outlet 702 of the sample fixing box 7 is connected to the seepage drain pipe 8. The height of the water outlet 702 is higher than the height of the permeable concrete sample. The total pressure air inlet 901 and the static pressure air inlet 904 of the pitot tube 9 are located in the seepage drain pipe 8. The total pressure air inlet 901 is located at the central position of the seepage drain pipe 8. A through hole for the pitot tube 9 to pass through is provided on the pipe wall of the seepage drain pipe 8.

[0037] Preferably, as Figure 3 shown, a plurality of support columns 703 are provided in the sample fixing box 7, and the permeable concrete sample is placed on the support columns 703. The height of the bottom of the permeable concrete sample is higher than the height of the water inlet 701.

[0038] The water in the overflow bucket 3 enters the sample fixing box 7 through the seepage water supply pipe 6, the water level rises, the water penetrates upward from the bottom of the permeable concrete sample, and then is discharged from the water outlet 702.

[0039] During specific use, before loading the permeable concrete sample to be measured into the sample fixing box 7, first wrap the periphery of the permeable concrete sample to be measured with pvc tape and then apply a layer of vaseline. It can make the sample closely arranged against the inner wall of the sample fixing box 7 and prevent water from seeping between the sample and the inner wall of the sample fixing box 7 during the penetration test.

[0040] As Figure 2 shown, the pitot tube speed measuring device includes a pitot tube 9. The total pressure air inlet 901 and the static pressure air inlet 904 of the pitot tube 9 are located in the seepage drain pipe 8. The total pressure air inlet 901 is located at the central position of the seepage drain pipe 8. A through hole for the pitot tube 9 to pass through is provided on the pipe wall of the seepage drain pipe 8. The total pressure air outlet 902 of the pitot tube 9 is connected to the first piezometric tube 10 through a connecting pipe, and the static pressure air outlet 903 of the pitot tube 9 is connected to the second piezometric tube 11 through a connecting pipe. The connecting pipe is selected as a rubber tube.

[0041] The liquid level height measured by the first piezometer tube 10 represents the piezometric head at which the kinetic energy of the water body at the center of the pipeline is converted into pressure energy. The liquid level height measured by the second piezometer tube 11 represents the hydrodynamic pressure head of the water body at the center of the pipeline.

[0042] Preferably, a support plate 12 is provided on the workbench 1, and the pitot tube 9, the first piezometer tube 10, and the second piezometer tube 11 are fixed on the support plate 12.

[0043] By providing the support plate 12, it is convenient to fix the pitot tube 9, the first piezometer tube 10, and the second piezometer tube 11, and keep them in a vertical state.

[0044] Preferably, scale lines 1201 are provided on the support plate 12. By providing the scale lines 1201, it is convenient to read the liquid level heights of the first piezometer tube 10 and the second piezometer tube 11.

[0045] Preferably, the water source is a water tank 13, a water pump 14 is provided on the water supply pipe 4, and the overflow pipe 5 and the seepage drain pipe 8 are connected to the water tank 13.

[0046] By providing the water tank 13, the test water can circulate, saving water.

[0047] A measuring method for a permeable concrete permeability coefficient measuring device includes the following steps:

[0048] Step 1: After the preparation of the permeable concrete specimen is completed, measure the cross-sectional area Apc of the specimen. After the measuring device is set up, measure the cross-sectional area A of the water pipe and the calibration coefficient μ of the pitot tube.

[0049] Step 2: Before loading the permeable concrete specimen to be tested into the specimen fixing box 7, first wrap the periphery of the permeable concrete specimen to be tested with pvc tape and then apply a layer of vaseline. Load the permeable concrete specimen to be tested into the specimen fixing box 7, turn on the water pump 14, deliver water to the overflow bucket 3, and flow into the specimen fixing box 7 through the seepage water supply pipe 6. When the water flows through the permeable concrete specimen due to the pressure difference and then flows out from the seepage drain pipe 8, a stable water level is formed above the specimen fixing box 7. After the seepage state is stable, the excess water in the overflow bucket 3 flows out from the overflow pipe 5, and a stable water level is formed in the overflow bucket 3. Thus, the seepage state under a constant head is generated. Then, the water in the water tank enters the water circulation device and repeats continuously.

[0050] Step 3: Measure the height Z1 from the water surface in the overflow bucket 3 to the workbench 1, the height Z2 from the water surface in the specimen fixing box 7 to the workbench 1, read the reading H1 of the first piezometer tube 10, and the reading H2 of the second piezometer tube 11.

[0051] Step 4: Calculate the permeability coefficient based on the measurement data in Step 1 and Step 4.

[0052] According to Bernoulli's equation, the flow velocity u at the center of the pipe can be obtained:

[0053]

[0054] Considering that the flow velocity measured by the Pitot tube is the flow velocity at the center of the pipe, in order to obtain the average flow velocity of the pipe, it is necessary to determine whether the flow regime of the water body in the pipe is laminar or turbulent, so the Reynolds number needs to be calculated. Now, the cases where the Reynolds number changes due to common influencing factors are grouped and calculated as shown in Table 1.

[0055] Table 1 Influence of different factors on the Reynolds number of the water body in the pipe

[0056]

[0057] It can be found from Table 1 that under normal circumstances, the flow regimes of each group of water bodies are in the turbulent state. According to existing research and experimental verification, when the fluid flows in a circular pipe, if it is in the turbulent state, the average flow velocity is 0.8 times the flow velocity at the center of the pipe. Therefore, the average flow velocity u of the pipe can be obtained as: avg For:

[0058]

[0059] Therefore, the pipe flow rate Q1 is:

[0060]

[0061] The seepage flow rate Q2 of the permeable concrete specimen can be obtained according to Darcy's theorem:

[0062]

[0063] From the continuity equation, Q1 = Q2, and thus the calculation formula for the permeability coefficient k of the permeable concrete specimen is:

[0064]

[0065] Among them, μ is the calibration coefficient of the Pitot tube, g is the acceleration due to gravity, H is the seepage head difference, and L is the seepage path.

[0066] Substitute the measurement data in Step 1 and Step 4 into formula (5) for calculation, and the accurate permeability coefficient k can be obtained.

[0067] Now, compare the permeability coefficient determined by the present invention with the test results of the traditional method. The traditional method is to measure the mass of the permeated water per unit time to obtain the seepage flow rate, and then convert it to obtain the permeability coefficient k. Five groups of permeable concrete specimens with different mix ratios are taken for the test. The mix ratios of the permeable concrete specimens are shown in Table 2, and the comparison results are shown in Table 3.

[0068] Mix proportion of pervious concrete specimens in Table 2

[0069]

[0070] Comparison of test results in Table 3

[0071]

[0072] Analysis of the data in Table 3 shows that for the traditional method of measuring the permeability coefficient, as the permeability coefficient of the specimen increases, the standard deviation of its permeability coefficient also gradually increases. The reason is that the traditional method obtains the seepage flow by measuring the mass of the seeping water body. When the specimen has a large permeability coefficient, the tester must read the mass of the water body at the end of the test time. The large flow rate will lead to inaccurate reading of the value, resulting in a large error, manifested as the standard deviation increasing with the increase of the specimen's permeability coefficient. In contrast, the standard deviation of the permeability coefficient measured by the determination method proposed in the present invention is basically stable between 0.02 - 0.04 as the permeability coefficient of the specimen increases, remaining within a certain range. The reason is that this method is less affected by the change of the specimen's own permeability coefficient. Secondly, the standard deviation of the measured permeability coefficient obtained by the test method proposed in the present invention is smaller than that measured by the traditional method, indicating that the value measured by this method is more accurate.

Claims

1. A device for measuring the permeability coefficient of permeable concrete, characterized in that, It includes a workbench (1), on which there is a bracket (2), and on the bracket (2) there is an overflow bucket (3). A water supply pipe (4) is connected to a water source to supply water to the overflow bucket (3). An overflow pipe (5) is provided on the side wall of the overflow bucket (3). The bottom of the overflow bucket (3) is connected to the water inlet (701) of a specimen fixing box (7) through a seepage water supply pipe (6). The water outlet (702) of the specimen fixing box (7) is connected to a seepage drain pipe (8). The height of the water outlet (702) is higher than the height of the permeable concrete specimen. The test port of the Pitot tube velocity measuring device is connected to the pipe wall of the seepage drain pipe (8). The Pitot tube velocity measuring device includes a Pitot tube (9). The total pressure air inlet (901) and the static pressure air inlet (904) of the Pitot tube (9) are located inside the seepage drain pipe (8). The total pressure air inlet (901) is located at the central position of the seepage drain pipe (8). A through hole for the Pitot tube (9) to pass through is provided on the pipe wall of the seepage drain pipe (8). The total pressure air outlet (902) of the Pitot tube (9) is connected to a first manometer tube (10) through a connecting pipeline. The static pressure air outlet (903) of the Pitot tube (9) is connected to a second manometer tube (11) through a connecting pipeline.

2. The permeable concrete permeability coefficient measuring device according to claim 1, characterized in that, Several support columns (703) are provided inside the specimen fixing box (7), and the permeable concrete specimen is placed on the support columns (703).

3. The permeable concrete permeability coefficient measuring device according to claim 1, characterized in that, A support plate (12) is provided on the workbench (1), and the Pitot tube (9), the first manometer tube (10) and the second manometer tube (11) are fixed on the support plate (12).

4. The permeable concrete permeability coefficient measuring device according to claim 3, characterized in that, Scale lines (1201) are provided on the support plate (12).

5. The permeable concrete permeability coefficient measuring device according to claim 1, characterized in that, The water source is a water tank (13). A water pump (14) is provided on the water supply pipe (4). The overflow pipe (5) and the seepage drain pipe (8) are connected to the water tank (13).

6. The measuring method of a permeable concrete permeability coefficient measuring device according to any one of claims 1 to 5, characterized in that It includes the following steps: Step 1: After the preparation of the permeable concrete specimen is completed, measure the cross-sectional area A of the specimen pc , after the measurement device is set up, measure the cross-sectional area A of the seepage drain pipe (8) and the calibration coefficient μ of the pitot tube; Step 2: Load the permeable concrete specimen to be tested into the specimen fixing box (7), turn on the water pump (14), convey water into the overflow bucket (3), and let it flow into the specimen fixing box (7) through the seepage water supply pipe (6). When the water seeps through the permeable concrete specimen due to the pressure difference and flows out from the seepage drain pipe (8), a stable water level is formed above the specimen fixing box (7). After the seepage state is stable, the excess water in the overflow bucket (3) flows out from the overflow pipe (5), and a stable water level is formed in the overflow bucket (3). Step 3: Measure the height Z1 from the water surface in the overflow bucket (3) to the workbench (1), the height Z2 from the water surface in the specimen fixing box (7) to the workbench (1), read the reading H1 of the first manometer tube (10) and the reading H2 of the second manometer tube (11). Step 4: Calculate the permeability coefficient according to the measurement data in Step 1 and Step 4.

7. The measuring method of a permeable concrete permeability coefficient measuring device according to claim 6, characterized in that, In the fourth step, according to the Bernoulli equation, the flow velocity at the center of the pipeline can be obtained : ； Based on the flow velocity at the center of the pipeline , calculate the average flow velocity of the pipeline : ； Pipeline flow is as follows: ； Permeation flow of pervious concrete specimens According to Darcy's law, it can be obtained that: ； From the continuity equation, Q1 = Q2 can be obtained, and thus the permeability coefficient k of the permeable concrete specimen is obtained. The calculation formula is: ； Where, μ is the correction coefficient of the Pitot tube, g is the acceleration due to gravity, H is the seepage head difference, and L is the seepage path.

8. The measurement method of a permeable concrete permeability coefficient measuring device according to claim 6, characterized in that, In Step 2, before loading the permeable concrete specimen to be tested into the specimen fixing box (7), first wrap the periphery of the permeable concrete specimen to be tested with pvc tape and then apply a layer of vaseline.

Images