Permeable concrete permeability coefficient and heat conductivity coefficient testing device and method

Abstract

The invention is suitable for the technical field of concrete tests, and provides a device and a method for testing the permeability coefficient and the heat conductivity coefficient of pervious concrete, the testing method is based on the testing device, and the testing device comprises a water inlet, a water inlet channel, a valve, a rubber pad, a fixing frame, a hot wire sensor, a water outlet channel and a water outlet. According to the testing device and method provided by the invention, the unidirectional horizontal permeability and heat conductivity coefficient and the vertical permeability and heat conductivity coefficient of the pervious concrete test piece to be tested can be tested, and the comprehensive permeability and heat conductivity coefficient of the pervious concrete test piece to be tested can also be tested; and a more real and reliable reference value is provided for deeply understanding the permeation and heat conduction process of the pervious concrete. Besides, the test device has the advantages of flexible size design, simple structure, low manufacturing cost, simplicity in operation and accurate test result, and is suitable for large-scale popularization so as to meet the urgent requirements in the research and engineering practice of pervious concrete materials.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete testing, and in particular relates to a device and method for testing permeability coefficient and thermal conductivity coefficient of permeable concrete. Background Art

[0002] Permeable concrete, also known as porous concrete, is an innovative and environmentally friendly building material, which is made of coarse aggregate, cement and an appropriate amount of water. It is lightweight and porous. Due to its excellent permeability, this material has shown wide application potential and development prospects in municipal garden landscape design, rainwater drainage management of urban roads, hardening and transformation of urban areas, transportation infrastructure construction and various water conservancy projects.

[0003] Permeability is a key indicator for evaluating the drainage performance of permeable concrete. It directly reflects the connectivity and permeability efficiency of the internal pore structure of the material, and is of great significance to material selection, structural design, and the safety and stable operation of the project. At the same time, the thermal conductivity of permeable concrete determines its heat exchange capacity with the surrounding environment, which is crucial for optimizing the design of rainwater management systems, promoting groundwater recharge and ecological environment restoration. Therefore, in the production and application of permeable concrete, it is particularly necessary to conduct rigorous permeability and thermal conductivity testing. At present, the permeability test methods of permeable concrete are mainly divided into two categories: laboratory measurement and field testing. Laboratory measurement mainly relies on concrete permeameter, which can accurately determine the permeability of concrete samples under specific water pressure and temperature under controlled conditions. On the other hand, field testing focuses more on the simulation of actual working conditions, such as evaluating the permeability of materials through fixed head permeability test, pore water pressure gauge test and pumping test. The test of thermal conductivity mainly adopts two methods: steady-state and transient. The steady-state method usually measures by establishing a temperature gradient. The transient method applies heat in a short period of time and measures the thermal conductivity based on the temperature change. The transient method includes two methods: using a hot wire to heat the inside of the material and using a planar heat source to heat the surface of the material.

[0004] However, the current test experiments of permeability coefficient and thermal conductivity of permeable concrete still have some shortcomings. Most of the permeability coefficient tests focus on the measurement of unidirectional permeability coefficient, that is, only the permeability in the vertical or horizontal direction is tested, which cannot fully evaluate the anisotropic permeability characteristics of permeable concrete. Studies have shown that there are significant differences in the permeability performance of permeable concrete in the vertical and horizontal directions, which is affected by many factors such as material ratio, aggregate shape and pore distribution. Therefore, in order to accurately obtain the permeability coefficient of permeable concrete in two directions, the traditional method usually requires two independent tests, which is not only time-consuming and labor-intensive, but also increases the test cost. At the same time, the use of different specimens for testing may reduce the comparability of the results and affect the accuracy of engineering design. In the thermal conductivity test, many instruments may have some limitations in design and manufacturing. For example, some equipment is not sensitive enough to temperature changes, which may lead to errors in the measurement results. In addition, the preparation process of the test sample is relatively complicated, and the uneven surface of the sample or insufficient sealing will directly affect the reliability of the measurement. The thermal conductivity is also easily affected by environmental conditions, especially in high temperature or high humidity environments, the measurement results may become unstable. At the same time, the porosity of pervious concrete changes with the changes in moisture content and external environment. This change will directly affect its thermal conductivity, resulting in the possibility that the results under different test conditions may not be comparable. Although the traditional steady-state method is a classic test method, it lacks flexibility in some cases; although the transient method is faster, it has high requirements on equipment and requires precise control of experimental conditions. In addition, some advanced methods (such as the laser pulse method) have high measurement accuracy, but have strict requirements on the shape and size of the sample and are not suitable for all types of pervious concrete.

[0005] In view of the above problems, the present invention proposes a device and method for testing the permeability coefficient and thermal conductivity coefficient of permeable concrete. Summary of the invention

[0006] The purpose of the present invention is to provide a device and method for testing the permeability coefficient and thermal conductivity coefficient of permeable concrete, aiming to solve the problems raised in the above background technology.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for testing the permeability coefficient and thermal conductivity coefficient of permeable concrete, the testing method is based on a testing device, the testing device includes a water inlet, a water inlet channel, a valve, a fixing frame, a hot wire sensor, a water outlet channel and a water outlet; the water inlet is used to supply water to the permeable concrete specimen to be tested; a pair of adjacent faces or a group of two adjacent faces of the specimen are the water inlet face and the water outlet face, and the remaining faces of the specimen are wrapped with a plastic film; the water inlet channel is connected to the water inlet and connected to the water outlet face of the specimen, and is used to guide water into the water inlet face of the specimen; each water inlet channel and water outlet channel is provided with a valve; the fixing frame is located around the center of the testing device and is used to fix the specimen; the hot wire sensor is arranged on the inner side of the pipe wall of the water inlet channel and the water outlet channel, and is used to measure the heat change of the liquid in the water inlet channel and the water outlet channel to calculate the thermal conductivity; the water outlet channel is connected to the water outlet and connected to the water outlet face of the specimen, and is used to guide water out of the water outlet face of the specimen; the water outlet is used to discharge the water in the specimen;

[0009] The water inlet is provided with a water supply part, a water inlet pipe and a first flow meter; one end of the water inlet pipe is connected to the water supply part, and the other end is connected to the water inlet; the first flow meter is provided on the water inlet pipe, and is used to measure the water flow in the water inlet pipe;

[0010] The water outlet is provided with a water outlet pipe, a second flow meter and a water storage member; one end of the water outlet pipe is connected to the water outlet of the device, and the other end is connected to the water storage member; the water in the test piece is discharged into the water storage member through the water outlet pipe; the second flow meter is provided on the water outlet pipe, and is used to measure the water flow rate in the water outlet pipe;

[0011] The test method comprises the following steps:

[0012] Step S1: Place the test piece in the center of the test device and fix it;

[0013] Step S2: Select the direction of the coefficient to be measured according to the type of the permeability coefficient and thermal conductivity coefficient to be measured, and wrap the sides of the test piece in other directions with plastic film; select the corresponding water inlet channel and water outlet channel according to the direction of the coefficient to be measured, and place the hot wire sensor on the inner side of the pipe wall; turn on the switch of the hot wire sensor to make it work normally and display the reading; open the valves of the selected water inlet channel and water outlet channel, and keep other valves closed;

[0014] Step S3: adding water from the water inlet and slowly supplying water into the test piece through the selected water inlet channel;

[0015] Step S4: testing the permeability coefficient of the specimen;

[0016] Step S5: testing the thermal conductivity of the test piece.

[0017] Furthermore, before step S4, the testing method further includes:

[0018] The first flow meter at the water inlet is used to measure the water inlet flow rate Q1 of the test piece at time t1, and the hot wire sensor of the water inlet channel is used to record the liquid temperature T1 at the corresponding time; the second flow meter at the water outlet is used to measure the water outlet flow rate Q2 of the test piece at time t2, and the hot wire sensor of the water outlet channel is used to record the liquid temperature T2 at the corresponding time.

[0019] Furthermore, the specific process of step S4 is as follows:

[0020] When the inlet flow rate is equal to the outlet flow rate, record the initial head difference, the final head difference and the time required to pass through the test piece; calculate the permeability coefficient according to the permeability coefficient calculation formula of permeable concrete. The permeability coefficient calculation formula of permeable concrete is as follows:

[0021]

[0022] Among them, K is the permeability coefficient of permeable concrete; Q is the amount of water passing through the specimen within the specified time t, Q = Q1-Q2, t = t2-t1; L is the height of the specimen; A is the cross-sectional area of ​​the specimen; H is the head height acting on the specimen; t is the time required to pass through the specimen.

[0023] Furthermore, the specific process of step S5 is as follows:

[0024] After the hot wire sensor is inserted into the liquid to be tested, current is applied to heat it up and the temperature change is recorded. The thermal conductivity is calculated according to the thermal conductivity calculation formula of permeable concrete. The thermal conductivity calculation formula of permeable concrete is as follows:

[0025]

[0026] Among them, λ is the thermal conductivity of the specimen; q is the heat flux; t1 and t2 are the measurement times; T1 and T2 are the temperatures at the corresponding times.

[0027] Furthermore, when it is necessary to test the permeability coefficient and thermal conductivity coefficient in other directions of the same specimen, the testing method includes the following steps:

[0028] Empty the water inside the test device, test pieces, water supply parts and water storage parts;

[0029] All through holes are controlled to be closed, and then the test is repeated according to step S2 to step S5.

[0030] Furthermore, the testing device also includes a rubber pad, which is used to fix the test piece. The rubber pad is provided with a through hole, and the screws of the fixing frame are fixed to the test piece through the through hole.

[0031] Furthermore, the water supply component is a faucet, which supplies water to the water inlet through a water inlet pipe.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The testing device and method provided by the present invention can not only test the unidirectional horizontal permeability and thermal conductivity, vertical permeability and thermal conductivity of the permeable concrete specimen to be tested, but also can test the comprehensive permeability and thermal conductivity of the permeable concrete specimen to be tested, which makes up for the deficiency that the existing testing device cannot test the comprehensive permeability and thermal conductivity of the permeable concrete specimen to be tested, and provides a more real and reliable reference value for in-depth understanding of the permeability and thermal conduction process of permeable concrete. In addition, the testing device has the advantages of flexible size design, simple structure, low manufacturing cost, simple operation and accurate test results, and is suitable for large-scale promotion to meet the urgent needs in permeable concrete material research and engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the testing device in the present invention.

[0035] Figure 2 Flow chart of the testing method in the present invention.

[0036] In the figure: water inlet 1, water inlet channel 2, valve 3, fixing bracket 4, rubber pad 5, hot wire sensor 6, water outlet channel 7, water outlet 8, test piece 9. DETAILED DESCRIPTION

[0037] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0038] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0039] like Figure 1 As shown, an embodiment of the present invention provides a permeability coefficient and thermal conductivity testing device for permeable concrete, comprising a water inlet 1, a water inlet channel 2, a valve 3, a fixing frame 4, a rubber pad 5, a hot wire sensor 6, a water outlet channel 7 and a water outlet 8;

[0040] The water inlet 1 is used to supply water to the permeable concrete specimen 9 to be tested.

[0041] A pair of adjacent faces or a group of two adjacent faces of the test piece 9 is a water inlet face and a water outlet face, and the remaining faces of the test piece 9 are wrapped with a plastic film. After water is added to the device, the opening and closing of the valve 3 is determined according to the direction of the permeability coefficient to be measured, and water passes through the direction of the valve 3 and flows out from the water outlet 8.

[0042] The water inlet channel 2 is communicated with the water inlet 1 and connected to the water outlet surface of the test piece 9 , and is used to introduce water into the test piece 9 .

[0043] Each water inlet channel 2 and water outlet channel 7 is provided with a valve 3 .

[0044] The fixing frame 4 is located around the center of the test device and is used to fix the test piece 9.

[0045] The rubber pad 5 is connected to the fixing frame 4 by bolts. The rubber pad 5 is used to fix the test piece 9. A through hole is provided on the rubber pad 5. The screws of the fixing frame 4 are fixed to the test piece 9 through the through hole.

[0046] The hot wire sensor 6 is arranged on the inner side of the pipe wall of the water inlet channel 2 and the water outlet channel 7, and is used to measure the heat change of the liquid in the water inlet channel 2 and the water outlet channel 7. After the hot wire sensor 6 is inserted into the liquid to be measured, current is applied to heat it up and the temperature change is recorded, and the thermal conductivity is measured by calculation.

[0047] The water outlet channel 7 is communicated with the water outlet 8 and connected to the water outlet surface of the test piece 9 , and is used for draining the water in the test piece 9 .

[0048] The water outlet 8 is used to discharge the water in the test piece 9 .

[0049] like Figure 1 As shown, as a preferred embodiment of the present invention, a water supply component, a water inlet pipe and a first flow meter are provided at the water inlet 1; one end of the water inlet pipe is connected to the water supply component, and the other end is connected to the water inlet 1; the water supply component supplies water to the water inlet 1 through the water inlet pipe; the first flow meter is provided on the water inlet pipe, and is used to measure the water inlet flow in the water inlet pipe (the water supply component refers to a faucet, which, the water inlet pipe and the first flow meter are not drawn in the figure).

[0050] The water outlet 8 is provided with a water outlet pipe, a second flow meter and a water storage member (the water storage member refers to a container for receiving the outgoing water, which, the water outlet pipe and the second flow meter are not drawn in the figure); one end of the water outlet pipe is connected to the water outlet 8 of the device, and the other end is connected to the water storage member; the water in the test piece 9 is discharged into the water storage member through the water outlet pipe; the second flow meter is arranged on the water outlet pipe, and is used to measure the outgoing water flow in the water outlet pipe.

[0051] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a method for testing the permeability coefficient and thermal conductivity coefficient of permeable concrete, which is applied to the above-mentioned testing device. The method includes the following steps:

[0052] Step S1: Place the test piece 9 at the center of the test device and fix it with a fixing frame 4 and a rubber pad 5;

[0053] Step S2: Select the direction of the coefficient to be measured according to the type of the permeability coefficient and thermal conductivity coefficient to be measured, and wrap the side surfaces of the test piece 9 in other directions with plastic film; select the corresponding water inlet channel 2 and water outlet channel 7 according to the direction of the coefficient to be measured, and place the hot wire sensor 6 on the inner side of the pipe wall; turn on the switch of the hot wire sensor 6 to make it work normally and display the reading; open the valves 3 of the selected water inlet channel 2 and water outlet channel 7, and keep the other valves 3 closed;

[0054] Step S3: adding water from the water inlet 1 and slowly supplying water to the test piece 9 through the selected water inlet channel 2 to reduce the flow rate, so as to facilitate the first flow meter, the second flow meter and the hot wire sensor 6 to perform measurement;

[0055] Step S4: testing the permeability coefficient of the test piece 9;

[0056] Step S5: testing the thermal conductivity of the test piece 9.

[0057] As a preferred embodiment of the present invention, before step S4, the testing method further includes:

[0058] The first flow meter at the water inlet 1 is used to measure the water inlet flow rate Q1 of the test piece 9 at time t1, and the hot wire sensor 6 of the water inlet channel 2 is used to record the liquid temperature T1 at the corresponding time; the second flow meter at the water outlet 8 is used to measure the water outlet flow rate Q2 of the test piece 9 at time t2, and the hot wire sensor 6 of the water outlet channel 7 is used to record the liquid temperature T2 at the corresponding time.

[0059] As a preferred embodiment of the present invention, the specific process of step S4 is as follows:

[0060] When the inlet flow rate is equal to the outlet flow rate, record the initial head difference, the final head difference and the time required to pass through the test piece 9; calculate the permeability coefficient according to the permeability coefficient calculation formula of permeable concrete. The permeability coefficient calculation formula of permeable concrete is as follows:

[0061]

[0062] Where K is the permeability coefficient of permeable concrete (unit: m / s); Q is the amount of water passing through the test piece 9 within the specified time t (unit: m 3 ), Q = Q1-Q2, t = t2-t1; L is the height of the specimen 9 (unit: m); A is the cross-sectional area of ​​the specimen 9 (unit: m 2 ); H is the height of the water head acting on the specimen 9 (unit: m); t is the time required to pass through the specimen 9 (unit: s).

[0063] As a preferred embodiment of the present invention, the specific process of step S5 is as follows:

[0064] After the hot wire sensor 6 is inserted into the liquid to be tested, current is applied to heat it up and the temperature change is recorded. The thermal conductivity is calculated according to the thermal conductivity calculation formula of permeable concrete. The thermal conductivity calculation formula of permeable concrete is as follows:

[0065]

[0066] Where, λ is the thermal conductivity of specimen 9 (unit: W / m·K); q is the heat flux (unit: W / m 2 ); t1 and t2 are the measurement times (unit: s); T1 and T2 are the temperatures at the corresponding times (unit: K).

[0067] As a preferred embodiment of the present invention, when the permeability coefficient and thermal conductivity coefficient of one type are tested on the same test piece 9, and the permeability coefficient and thermal conductivity coefficient of other directions need to be tested, the testing method includes the following steps:

[0068] Empty the water inside the test device, the test piece 9, the water supply part and the water storage part;

[0069] All through holes are controlled to be closed, and then the test is repeated according to step S2 to step S5.

[0070] The above are only preferred embodiments of the present invention. It should be pointed out that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These should also be regarded as the protection scope of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A method for testing the permeability coefficient and thermal conductivity of permeable concrete, characterized in that: The test method is based on a test device, which includes a water inlet, a water inlet channel, a valve, a fixing frame, a hot wire sensor, a water outlet channel and a water outlet; the water inlet is used to supply water to the permeable concrete specimen to be tested; a pair of adjacent faces or a group of two adjacent faces of the specimen are the water inlet face and the water outlet face, and the remaining faces of the specimen are wrapped with a plastic film; the water inlet channel is connected to the water inlet and connected to the water outlet face of the specimen, and is used to introduce water into the water inlet face of the specimen; each water inlet channel and water outlet channel is provided with a valve; the fixing frame is located around the center of the test device and is used to fix the specimen; the hot wire sensor is arranged on the inner side of the pipe wall of the water inlet channel and the water outlet channel, and is used to measure the heat change of the liquid in the water inlet channel and the water outlet channel to calculate the thermal conductivity; the water outlet channel is connected to the water outlet and connected to the water outlet face of the specimen, and is used to guide water out of the water outlet face of the specimen; the water outlet is used to discharge the water in the specimen; The water inlet is provided with a water supply part, a water inlet pipe and a first flow meter; one end of the water inlet pipe is connected to the water supply part, and the other end is connected to the water inlet; the first flow meter is provided on the water inlet pipe, and is used to measure the water flow in the water inlet pipe; The water outlet is provided with a water outlet pipe, a second flow meter and a water storage member; one end of the water outlet pipe is connected to the water outlet of the device, and the other end is connected to the water storage member; the water in the test piece is discharged into the water storage member through the water outlet pipe; the second flow meter is provided on the water outlet pipe, and is used to measure the water flow rate in the water outlet pipe; The test method comprises the following steps: Step S1: Place the test piece in the center of the test device and fix it; Step S2: Select the direction of the coefficient to be measured according to the type of the permeability coefficient and thermal conductivity coefficient to be measured, and wrap the sides of the test piece in other directions with plastic film; select the corresponding water inlet channel and water outlet channel according to the direction of the coefficient to be measured, and place the hot wire sensor on the inner side of the pipe wall; turn on the switch of the hot wire sensor to make it work normally and display the reading; open the valves of the selected water inlet channel and water outlet channel, and keep other valves closed; Step S3: adding water from the water inlet and slowly supplying water into the test piece through the selected water inlet channel; Step S4: testing the permeability coefficient of the specimen; Step S5: testing the thermal conductivity of the test piece.

2. The method for testing the permeability coefficient and thermal conductivity of permeable concrete according to claim 1, characterized in that: Before step S4, the testing method further includes: The first flow meter at the water inlet is used to measure the water inlet flow rate Q1 of the test piece at time t1, and the hot wire sensor of the water inlet channel is used to record the liquid temperature T1 at the corresponding time; the second flow meter at the water outlet is used to measure the water outlet flow rate Q2 of the test piece at time t2, and the hot wire sensor of the water outlet channel is used to record the liquid temperature T2 at the corresponding time.

3. The method for testing the permeability coefficient and thermal conductivity of permeable concrete according to claim 2, characterized in that: The specific process of step S4 is as follows: When the inlet flow rate is equal to the outlet flow rate, record the initial head difference, the final head difference and the time required to pass through the test piece; calculate the permeability coefficient according to the permeability coefficient calculation formula of permeable concrete. The permeability coefficient calculation formula of permeable concrete is as follows: Among them, K is the permeability coefficient of permeable concrete; Q is the amount of water passing through the specimen within the specified time t, Q = Q1-Q2, t = t2-t1; L is the height of the specimen; A is the cross-sectional area of ​​the specimen; H is the head height acting on the specimen; t is the time required to pass through the specimen.

4. The method for testing the permeability coefficient and thermal conductivity of permeable concrete according to claim 2, characterized in that: The specific process of step S5 is as follows: After the hot wire sensor is inserted into the liquid to be tested, current is applied to heat it up and the temperature change is recorded. The thermal conductivity is calculated according to the thermal conductivity calculation formula of permeable concrete. The thermal conductivity calculation formula of permeable concrete is as follows: Among them, λ is the thermal conductivity of the specimen; q is the heat flux; t1 and t2 are the measurement times; T1 and T2 are the temperatures at the corresponding times.

5. The method for testing the permeability coefficient and thermal conductivity of permeable concrete according to claim 1, characterized in that: When it is necessary to test the permeability coefficient and thermal conductivity coefficient in other directions of the same specimen, the testing method includes the following steps: Empty the water inside the test device, test pieces, water supply parts and water storage parts; All through holes are controlled to be closed, and then the test is repeated according to step S2 to step S5.

6. The method for testing the permeability coefficient and thermal conductivity of permeable concrete according to claim 1, characterized in that: The testing device also includes a rubber pad, which is used to fix the test piece. The rubber pad is provided with a through hole, and the screws of the fixing frame are fixed to the test piece through the through hole.

7. The method for testing the permeability coefficient and thermal conductivity of permeable concrete according to claim 1, characterized in that: The water supply part is a faucet, which supplies water to the water inlet through a water inlet pipe.

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