CN211627273U - Concrete surface humidity transfer coefficient rapid testing device suitable for different wind speeds - Google Patents
Concrete surface humidity transfer coefficient rapid testing device suitable for different wind speeds Download PDFInfo
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- CN211627273U CN211627273U CN201922147856.2U CN201922147856U CN211627273U CN 211627273 U CN211627273 U CN 211627273U CN 201922147856 U CN201922147856 U CN 201922147856U CN 211627273 U CN211627273 U CN 211627273U
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Abstract
The utility model discloses a concrete surface passes wet coefficient quick testing arrangement suitable for different wind speeds, the device include induced air passageway, concrete mould, on-line monitoring electronic balance, frequency conversion fan, electronic computer. The air inducing channel (1) is arranged above the concrete mould (2), and the bottom surface of the air inducing channel and the upper surface of the concrete mould are positioned at the same horizontal position; the concrete mould (2) is placed on the electronic balance (3), the measured concrete is poured into the mould (2), and the upper surface of the concrete and the upper surface of the mould are positioned at the same horizontal position; the electronic balance (3) has a data real-time transmission function and can transmit the mass change data of the concrete test block to the computer (5) for storage; the variable frequency fan (4) is positioned on one side of the induced draft channel (1), has a variable frequency speed regulation function, and can simulate the influence of different wind speeds on the surface moisture transmission coefficient of concrete. By adopting the device, the change process of the mass of the concrete sample along with time can be continuously measured from the concrete pouring moment, and the surface moisture transmission coefficient of the concrete under different wind speed conditions can be calculated.
Description
Technical Field
The invention belongs to the technical field of concrete materials, and particularly relates to a device for quickly testing the surface moisture transmission coefficient of concrete suitable for different wind speeds.
Background
Concrete is one of the most widely applied building materials in the field of civil engineering at present, has the advantages of wide raw material sources, low price, excellent building performance and the like, and is widely applied to the fields of roads, bridges, hydraulic structures, house buildings and the like, however, the surface cracking phenomenon is easy to occur in the using process of the concrete material, which not only influences the apparent quality of the building structure. More importantly, the surface cracks can damage the protective layer of the concrete structure, provide channels for aggressive media to enter the concrete, accelerate the corrosion of the steel bars and further initiate the structural damage. Research results show that the generation and development of concrete surface cracks are closely related to the water dispersion loss of the concrete surface. When the formwork is removed, moisture exchange takes place between the concrete surface and the surrounding environment, so that a portion of the water is lost to the surrounding environment and a drop in humidity is caused. The change of the humidity of the concrete surface directly affects the development of shrinkage deformation, and surface cracking is generated when the shrinkage deformation is restrained. Therefore, to study the development rule of concrete surface shrinkage and reduce the risk of cracking on the concrete surface, the moisture exchange rate between the concrete surface and the environment is first studied. The concrete surface moisture transmission coefficient is the physical quantity that describes the rate of moisture exchange between the dry surface of the concrete and the surrounding environment. The larger the concrete surface moisture transmission coefficient is, the faster the surface humidity is reduced, and the larger the shrinkage strain is; conversely, the smaller the concrete surface moisture transmission coefficient is, the slower the surface humidity decreases, and the smaller the shrinkage strain is. Therefore, the accurate determination of the concrete surface moisture transmission coefficient has important significance for reducing the concrete surface cracking and improving the engineering quality.
At present, researchers at home and abroad have made certain progress on the determination of the surface moisture transmission coefficient of the concrete, but a rapid determination method for the surface moisture transmission coefficient of the concrete under the condition of considering different wind speeds is still rarely reported. Bakhshi of foreign scholars proposes a method for testing the surface moisture transmission coefficient of concrete in a paper Model for Early-Age Rate of evaluation of center-base materials, and the method calculates the surface moisture transmission coefficient of concrete by testing the mass loss Rate of the poured concrete. The principle is that the concrete surface is in direct contact with the environment during the drying process, and because the humidity level of the concrete surface is usually higher than the ambient humidity, the moisture on the concrete surface will diffuse into the surrounding environment under the action of the humidity gradient. The diffusion equation is shown below:
in the formula (I), the compound is shown in the specification,Jthe water loss rate (kg/m) of the concrete under dry conditions2s），D mIs the diffusion coefficient (m) of water vapor in air2/s），Ps is the saturated vapor pressure (Pa) of water at a given temperature,Ris an ideal gas constant (J/mol K),Mis the molar mass of water (kg/mol),Tin order to obtain a temperature (K),Hthe relative humidity of the concrete.
A moisture transition layer is present between the dry surface of the concrete and the surrounding environment during the diffusion process, the thickness of the moisture transition layer is usedTo express, assuming that the relative humidity satisfies a linear distribution in the transition layer, the diffusion equation can be expressed as:
in the formulaH 1AndH erespectively the relative humidity of the concrete surface and the environment,a mi.e. the surface moisture transmission coefficient. At ambient humidityH eConstant and concrete surface in moisture saturation state: (H 1= 1.0), the concrete surface moisture transmission coefficient can be expressed as：
In the formulaJThe water loss rate (kg/m) of the concrete under dry conditions2s），H eIn order to be the ambient humidity, the temperature of the atmosphere,a mnamely the surface moisture transmission coefficient (kg/m)2s). From the above formula, the water loss rate of the concrete in the humidity saturation period can be obtained by experimental tests under the condition of constant ambient humidityJThe surface moisture transmission coefficient of the concrete can be calculated by adopting a formula. Based on the principle, Bakhshi and the like adopt a method for manually testing the concrete quality loss rate to test the concrete surface moisture transmission coefficient. However, the above method has two problems: (1) the quality of the concrete test block is tested once by testing the concrete quality loss rate manually by a tester at regular intervals, so that the working strength of the tester is increased, and the quality change is easily caused by concrete block falling or collision in the test process, so that the calculation error is generated; (2) the method can only test the surface moisture transmission coefficient of the concrete under the condition of the wind speed of the laboratory environment, and cannot test the surface moisture transmission coefficient of the concrete under the condition of different wind speeds. And the loss process of manually carrying and testing the concrete quality can cause the gas flow state on the dry surface of the concrete to change, thereby bringing testing errors.
In order to solve the problems, the invention provides a device for quickly testing the surface moisture transmission coefficient of concrete suitable for different wind speeds. The device collects the change rule of the concrete quality along with time in real time through the on-line testing technology of the concrete quality, and thoroughly eliminates the interference of human factors in the testing process. By arranging the variable frequency fan and the induced air channel, the accurate determination of the concrete surface moisture transmission coefficient under different wind speed conditions is tested.
Disclosure of Invention
The utility model aims at providing a concrete surface passes wet coefficient quick testing arrangement who is applicable to different wind speeds to the problem that exists among the current test method.
In order to achieve the above purpose, the utility model adopts the following technical scheme.
A device for rapidly testing the moisture transmission coefficient of the concrete surface suitable for different wind speeds comprises an air inducing channel, a concrete mould, an online monitoring electronic balance, a variable frequency fan and an electronic computer. The air inducing channel is arranged above the concrete mould, and the bottom surface of the air inducing channel is provided with a hole at the corresponding position of the concrete mould, so that the upper surface of the concrete mould and the bottom surface of the air inducing channel are positioned at the same horizontal position. The concrete mould is placed on the online monitoring electronic balance, the measured concrete is poured into the mould, and the upper surface of the concrete and the upper surface of the mould are located at the same horizontal position. The on-line monitoring electronic balance is connected with an electronic computer, and the change condition of the concrete quality along with time is recorded in real time through the electronic computer. The variable frequency fan is positioned on one side of the induced draft channel, has a variable frequency speed regulation function, and can simulate the influence of different wind speeds on the surface moisture transmission coefficient of the concrete.
Furthermore, polymer sealant is adopted between the inner edge of the opening on the lower surface of the air inducing channel and the outer edge of the concrete mould for sealing treatment, so that smooth circulation of gas in the air inducing channel is ensured.
Furthermore, the concrete mould can be processed by organic glass and can also be processed by other moulds.
Furthermore, the online monitoring electronic balance should have real-time quality measurement and data transmission functions, and the electronic computer should have quality monitoring data recording and storing functions.
Furthermore, the variable frequency fan has a wind speed adjusting function, and can accurately adjust the wind speed in the induced draft channel according to the experiment requirement.
Compared with the prior art, the utility model discloses there are following two aspects effects.
1. The device realizes continuous automatic determination of the quality change of the concrete from the beginning of pouring by using an online monitoring electronic scale and an electronic computer, and thoroughly eliminates the influence of human factors. Therefore, the testing precision of the concrete surface moisture transmission coefficient is effectively improved, the testing process is simplified, and the workload of testing personnel is reduced.
2. The device realizes the measurement of the surface moisture transmission coefficient of the concrete under different wind speed conditions by arranging the air inducing channel and the variable frequency fan, thereby simulating the actual state of the concrete under different working conditions and widening the applicability of the testing device.
Drawings
Fig. 1 is the utility model relates to a concrete surface passes wet coefficient quick testing arrangement schematic structure view suitable for different wind speeds.
In the figure: 1. an induced draft channel; 2. a concrete mold; 3. monitoring an electronic balance on line; 4. a variable frequency fan; 5. an electronic computer.
Fig. 2 shows the change of the water loss of the C30 concrete with time when the wind speed V =0.1 m/s.
Fig. 3 is the change of the water loss rate of the C30 concrete with time at the wind speed V =0.1 m/s.
Fig. 4 shows the change of the water loss of the C30 concrete with time at a wind speed V =1.0 m/s.
Fig. 5 is the change of the water loss rate of the C30 concrete with time at the wind speed V =1.0 m/s.
Detailed Description
The technical solution of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is obvious that the embodiments are only some embodiments, not all embodiments, of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.
Example 1:
the test apparatus shown in fig. 1 was used to test the moisture transmission coefficient of a concrete surface of C30 strength class. In the test, the relative humidity of the environmentH e=30%, concrete surface gas flow rateV aIn the above conditions, the test results show the change of the water loss of the concrete from the casting time to the age of 28 days as a function of time, as shown in fig. 2, and the test is carried out on the concrete at a dry surface size of 400 × 100mm and an ambient temperature of 25 ℃As a result, it can be found that the continuous determination of the development of the concrete water loss amount along with the age shows an obvious two-stage mode, namely a rapid change stage and a slow change stage of the water loss amount. According to theoretical analysis, the water loss amount rapid development stage corresponds to the concrete surface humidity saturation stage, and the slow change stage corresponds to the concrete surface humidity reduction stage. The derivative of the concrete water loss with respect to time is obtained, and the result shown in fig. 3 is obtained. Based on the results of FIG. 3, the surface moisture transmission coefficient of C30 concrete under the test conditions is obtained by simple calculation using the formula (3)a m=J/(1-H e)= 3.711×10-5kg/m2·s。
Example 2:
the test apparatus shown in fig. 1 was used to test the moisture transmission coefficient of a concrete surface of C30 strength class. For comparison with example 1, the wind speed was adjusted to 1.0m/s in this test, and the remaining parameters were the same as in example 1. Under the above conditions, the test results show the change of the water loss of the concrete from the casting time to the 28-day age with time, as shown in fig. 4. The test results show that the change rule of the concrete quality along with time is still compounded with a two-stage rule, which is the same as the test result rule in the figure 2. However, as can be seen from a comparison of the results of FIG. 2, the mass loss rate of the first stage of concrete increases significantly as the wind speed increases from 0.1m/s to 1.0 m/s. The concrete surface moisture transmission coefficient is greatly influenced by the ambient wind speed, and the larger the ambient wind speed is, the larger the concrete surface moisture transmission coefficient is; on the contrary, the smaller the ambient wind speed is, the smaller the moisture transmission coefficient of the concrete surface is. Calculated by the formula (2), when the ambient wind speed is 1.0m/s, the surface moisture transmission coefficient of the concrete isa m=J/(1-H e)= 10.476×10-5kg/m2·s。
According to the above embodiment 1 and embodiment 2, the utility model provides a concrete surface passes wet coefficient quick testing arrangement suitable for different wind speeds can accurately survey the surface of concrete under the different wind speed conditions and pass wet coefficient, and this method has characteristics such as easy and simple to handle, the result is accurate.
Claims (6)
1. A quick testing device for the moisture transmission coefficient of the concrete surface suitable for different wind speeds comprises an air inducing channel, a concrete mould, an online monitoring electronic balance, a variable frequency fan and an electronic computer, and is characterized in that the air inducing channel is arranged above the concrete mould, and the bottom surface of the air inducing channel is provided with a hole at the corresponding position of the concrete mould, so that the upper surface of the concrete mould and the bottom surface of the air inducing channel are positioned at the same horizontal position; the concrete mould is placed on the online monitoring electronic balance, the measured concrete is poured into the mould, and the upper surface of the concrete and the upper surface of the mould are positioned at the same horizontal position; the on-line monitoring electronic balance is connected with an electronic computer, and the change condition of the concrete quality along with time is recorded in real time through the electronic computer; the variable frequency fan is positioned on one side of the induced draft channel, has a variable frequency speed regulation function, and can simulate the influence of different wind speeds on the surface moisture transmission coefficient of the concrete.
2. The device for rapidly testing the surface moisture transmission coefficient of the concrete suitable for different wind speeds as claimed in claim 1, wherein a polymer sealant is used for sealing between the inner edge of the opening on the lower surface of the air inducing channel and the outer edge of the concrete mold so as to ensure smooth circulation of the gas in the air inducing channel.
3. The device for rapidly testing the moisture transmission coefficient of the concrete surface suitable for different wind speeds as claimed in claim 1, wherein the concrete mold comprises but is not limited to a plexiglas mold.
4. The device for rapidly testing the moisture transmission coefficient of the concrete surface suitable for different wind speeds according to claim 1, wherein the on-line monitoring electronic balance has real-time quality measurement and data transmission functions.
5. The device for rapidly testing the moisture transmission coefficient of the concrete surface suitable for different wind speeds as claimed in claim 1, wherein the electronic computer has the functions of recording and storing quality monitoring data.
6. The device for rapidly testing the surface moisture transfer coefficient of the concrete with different wind speeds as claimed in claim 1, wherein the variable frequency fan has a function of adjusting the wind speed, and the wind speed in the induced air channel can be accurately adjusted according to experimental requirements.
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