1. A device for detecting freezing resistance of a material by adopting a gas freezing and gas melting method is characterized by comprising the following steps: the system comprises a box body, a circulating main pipeline, a high-temperature antifreezing solution buffer tank, a low-temperature antifreezing solution buffer tank, heating equipment, cooling equipment, a first pump, a second pump, a third pump, a fourth pump and an antifreezing solution;

the high-temperature antifreezing solution buffer tank is connected with the circulating main pipeline, the heating equipment and the first pump to form a first circulating system;

the circulating main pipeline is connected with the heating equipment and the second pump to form a second circulating system;

the low-temperature antifreezing solution buffer tank is connected with the circulating main pipeline, the cooling equipment and a third pump to form a third circulating system;

the circulating main pipeline is connected with the cooling equipment and a fourth pump to form a fourth circulating system;

the system comprises a circulating main pipeline, a first-stage distributor, a second-stage distributor and a control device, wherein an antifreezing solution is arranged in the circulating main pipeline, the circulating main pipeline is provided with the first-stage distributor, and the first-stage distributor is connected with a first circulating pipeline and a second circulating pipeline;

the box body is a closed space formed by a top surface, a bottom surface and four side surfaces, wherein one side surface is provided with a box door which can be opened and closed, a rubber ring is arranged in the box door, and the box door plays a role in sealing when closed; the top surface, the bottom surface and the four side surfaces of the box body are respectively provided with a box body pipeline system which is connected with the first circulating pipeline;

a plurality of layers of storage racks are arranged in the box body at intervals and used for placing samples to be detected; each layer of shelf is provided with a shelf pipeline system which is connected with the second circulating pipeline.

2. The device for detecting the freezing resistance of a material by using the air freezing and air melting method according to claim 1,

the first circulation pipeline is also provided with a second-stage distributor, the second-stage distributor is connected with a first sub-circulation pipeline, and the first sub-circulation pipeline is respectively connected with the tank body pipeline systems and used for enabling the antifreeze in the first sub-circulation pipeline to enter the tank body pipeline systems on all sides;

the second circulating pipeline is also provided with a second-stage distributor, the second-stage distributor is connected with second sub-circulating pipelines, and the second sub-circulating pipelines are respectively connected with the commodity shelf pipeline systems of all layers and used for enabling the anti-freezing liquid in the second sub-circulating pipelines to enter the commodity shelf pipeline systems of all layers.

3. The device for detecting the freezing resistance of a material by using the air freezing and air melting method according to claim 2,

the box body pipeline systems on all sides are respectively composed of a plurality of parallel transverse pipelines;

each layer of the commodity shelf pipeline system is respectively composed of a plurality of parallel transverse pipelines; in each pipeline system, the number of transverse pipelines is 4, 6, 8 or 10;

the antifreeze liquid inlet and the antifreeze liquid outlet of the transverse pipeline are respectively arranged at two ends, and the antifreeze liquid inlet and the antifreeze liquid outlet of two adjacent transverse pipelines are arranged at different ends;

the first sub-circulation pipeline is provided with two paths, wherein one path is connected with a transverse pipeline of the antifreeze solution inlet on the left end of each surface of the box body, and the other path is connected with a transverse pipeline of the antifreeze solution inlet on the right end of each surface of the box body;

the second sub-circulation pipeline is provided with two paths, wherein one path is connected with the transverse pipeline at the left end of the inlet of the anti-freezing solution in each layer of the commodity shelf, and the other path is connected with the transverse pipeline at the right end of the inlet of the anti-freezing solution in each layer of the commodity shelf.

4. The apparatus for detecting freezing resistance of material by using the air freezing and air melting method according to claim 1, further comprising:

the upper air outlet pipe is arranged at the upper end of the box body, and the end part of the upper air outlet pipe is provided with an openable mechanism;

the lower air outlet pipe is arranged at the lower end of the box body, and the end part of the lower air outlet pipe is provided with an openable mechanism;

the external fan is arranged outside the box body; when the device is heated or subjected to normal-temperature heat preservation, the external fan is communicated with the upper air outlet pipe; when the device is cooled or kept warm at negative temperature, the lower fan is communicated with the lower air outlet pipe.

5. The device for detecting the freezing resistance of a material by using the air freezing and air melting method according to claim 1,

the commodity shelf is of a hollow structure and comprises a framework part and a hollow part, and the pipeline systems of the commodity shelf of each layer are respectively placed on the framework parts of each layer.

6. The apparatus for detecting freezing resistance of material by using the air freezing and air melting method according to claim 1, further comprising:

the heat insulation layer is made of polyurethane ultra-light plastic and is arranged on the outer side of the box body;

the box body temperature sensor is arranged in the box body and used for monitoring the temperature change in the box body in real time;

the low-temperature antifreezing solution temperature sensor is arranged in the low-temperature antifreezing solution buffer tank and is used for monitoring the temperature of the antifreezing solution in the low-temperature antifreezing solution buffer tank in real time;

the high-temperature antifreezing solution temperature sensor is arranged in the high-temperature antifreezing solution buffer tank and is used for monitoring the temperature of the antifreezing solution in the high-temperature antifreezing solution buffer tank in real time;

the antifreeze temperature test sensor is arranged in the high-temperature antifreeze buffer tank and is used for monitoring the temperature of the antifreeze in the circulating pipeline in real time;

the control equipment comprises a parameter control module, a freezing and thawing module and a control module, wherein the parameter control module is used for adjusting each freezing and thawing parameter and automatically completing the freezing and thawing process of the test piece;

the freeze-thaw parameters comprise: temperature rise rate, temperature drop rate, upper and lower temperature limits, single freeze-thaw cycle time and freeze-thaw cycle times.

7. The device for detecting the freezing resistance of the material by the air freezing and air melting method according to claim 1, wherein the anti-freezing solution is 60% by mass of glycol aqueous solution.

8. A method for detecting freezing resistance of a material by adopting an air freezing and air melting method is characterized by comprising the following steps:

(1) preparing a test piece from the material;

(2) soaking the test piece in water to enable the test piece to reach a saturated state, and controlling the water content of the test piece by adjusting the draining time of the test piece;

(3) wrapping and sealing the test piece obtained in the step (2) in an environment with the temperature of (20 +/-5) DEG C and the relative humidity of more than or equal to 90%, placing the test piece in a closed box body, and controlling the relative humidity in the box body to be more than 90%;

(4) the freeze-thaw test was performed in an air-freeze and air-thaw environment:

setting the heating rate, the cooling rate, the upper and lower temperature limits, the single freeze-thaw cycle time and the freeze-thaw cycle times of the freeze-thaw test according to the test requirements; the temperature rise rate and the temperature reduction rate are respectively controlled within the range of 10 ℃/h to 30 ℃/h, and the control precision is +/-0.5 ℃; the upper and lower temperature limits are controlled within the range of-30 ℃ to 30 ℃; the single freeze-thaw cycle time is controlled within the range of 4-24 h;

when the temperature of the temperature control point reaches a set upper limit, placing a test piece;

reducing the test temperature from the upper temperature limit to the lower temperature limit, and then increasing the test temperature from the lower temperature limit to the upper temperature limit to be used as a freeze-thaw cycle;

after the set freezing and thawing cycle times, taking out the test piece, testing related freezing and thawing damage characterization parameters of the test piece until the test piece cracks, stopping the freezing and thawing test, taking out the test piece, recording the freezing and thawing cycle times, and characterizing the freezing resistance of the material;

the related freeze thaw damage characterization parameters of the test piece comprise: intensity changes before and after freeze-thawing, changes in micro-topography, surface and internal damage.

9. The method for detecting the freezing resistance of a material by using the air freezing and air melting method according to claim 8,

the method comprises the following steps of immersing a test piece to enable the test piece to reach a saturated state, and controlling the water content of the test piece by adjusting the draining time of the test piece, and specifically comprises the following steps:

immersing the test piece in water for 40-50h, keeping the water surface to be 20-40mm higher than the upper surface of the test piece, and turning the test piece once after immersing for 20-30 h; then, taking out the test piece and placing the test piece on a draining rack for draining under the environment of (20 +/-5) DEG C and the relative humidity of more than or equal to 90 percent, turning the test piece up and down once every 30min in the draining process until the set draining time is reached, and determining the water content of the test piece.

10. The method for detecting the freezing resistance of a material by using the air freezing and air melting method according to claim 9,

the material is ultra-light concrete, and the dry density of the material is less than or equal to 150 kg.m^-3；

When the test piece is made of ultra-light concrete, the set draining time is 5-7 h;

when the number of the test pieces is two or more, the distance between any two test pieces is not less than 20 mm.

Background

Freezing resistance refers to the property that the material can withstand multiple freeze-thaw cycles without being damaged and without significant reduction in strength in a hydrated state. The freezing resistance of a material is often expressed in terms of a freezing resistance rating (denoted as F).

In order to detect the frost resistance of the concrete test piece, the temperature change of the natural environment needs to be simulated, and the test of the concrete test piece is called as a freeze-thaw test.

When the frost resistance of the ultra-lightweight concrete is researched in a laboratory, a freeze-thaw test is usually performed in an air-freeze air-thawing mode. Although the air freezing and air melting test method can simulate the freezing and thawing damage process of the ultra-light concrete in the non-water-saturated state. However, when the frost resistance of the material is tested by adopting the existing freezing and air-melting mode, the heating rate and the cooling rate are difficult to control accurately, the freezing temperature and the melting temperature are not easy to control accurately during the test, and the freezing-thawing damage process of the ultra-lightweight concrete in the service environment is difficult to test accurately.

Disclosure of Invention

The invention mainly aims to provide a device and a method for detecting freezing resistance of a material by adopting an air freezing and air melting method, and aims to solve the technical problem of accurately controlling the heating rate and the cooling rate in an air freezing and air melting test so as to more accurately simulate the freezing and thawing damage process of the material in a service environment.

The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. According to the invention, the device for detecting the freezing resistance of the material by adopting the air freezing and air melting method comprises the following steps: the system comprises a box body, a circulating main pipeline, a high-temperature antifreezing solution buffer tank, a low-temperature antifreezing solution buffer tank, heating equipment, cooling equipment, a first pump, a second pump, a third pump, a fourth pump and an antifreezing solution;

the high-temperature antifreezing solution buffer tank is connected with the circulating main pipeline, the heating equipment and the first pump to form a first circulating system;

the circulating main pipeline is connected with the heating equipment and the second pump to form a second circulating system;

the low-temperature antifreezing solution buffer tank is connected with the circulating main pipeline, the cooling equipment and a third pump to form a third circulating system;

the circulating main pipeline is connected with the cooling equipment and a fourth pump to form a fourth circulating system;

the system comprises a circulating main pipeline, a first-stage distributor, a second-stage distributor and a control device, wherein an antifreezing solution is arranged in the circulating main pipeline, the circulating main pipeline is provided with the first-stage distributor, and the first-stage distributor is connected with a first circulating pipeline and a second circulating pipeline;

the box body is a closed space formed by a top surface, a bottom surface and four side surfaces, wherein one side surface is provided with a box door which can be opened and closed, a rubber ring is arranged in the box door, and the box door plays a role in sealing when closed; the top surface, the bottom surface and the four side surfaces of the box body are respectively provided with a pipeline system which is connected with the first circulating pipeline;

a plurality of layers of storage racks are arranged in the box body at intervals and used for placing samples to be detected; and each layer of shelf is provided with a pipeline system which is connected with the second circulating pipeline.

The object of the present invention and the technical problems solved thereby can be further achieved by the following technical measures.

Preferably, the device for detecting the freezing resistance of the material by using a gas freezing and melting method is adopted, wherein

The first circulation pipeline is also provided with a second-stage distributor, the second-stage distributor is connected with a first sub-circulation pipeline, and the first sub-circulation pipeline is respectively connected with the tank body pipeline systems and used for enabling the antifreeze in the first sub-circulation pipeline to enter the tank body pipeline systems on all sides;

the second circulating pipeline is also provided with a second-stage distributor, the second-stage distributor is connected with second sub-circulating pipelines, and the second sub-circulating pipelines are respectively connected with the commodity shelf pipeline systems of all layers and used for enabling the anti-freezing liquid in the second sub-circulating pipelines to enter the commodity shelf pipeline systems of all layers. Preferably, in the device for detecting the freezing resistance of the material by using the gas freezing fusion method, the box pipeline systems on all sides are respectively composed of a plurality of parallel transverse pipelines;

each layer of the commodity shelf pipeline system is respectively composed of a plurality of parallel transverse pipelines;

in each pipeline system, the number of transverse pipelines is 4, 6, 8 or 10;

the antifreeze liquid inlet and the antifreeze liquid outlet of the transverse pipeline are respectively arranged at two ends, and the antifreeze liquid inlet and the antifreeze liquid outlet of two adjacent transverse pipelines are arranged at different ends;

the first sub-circulation pipeline is provided with two paths, wherein one path is connected with a transverse pipeline of the antifreeze solution inlet on the left end of each surface of the box body, and the other path is connected with a transverse pipeline of the antifreeze solution inlet on the right end of each surface of the box body;

the second sub-circulation pipeline is provided with two paths, wherein one path is connected with the transverse pipeline at the left end of the inlet of the anti-freezing solution in each layer of the commodity shelf, and the other path is connected with the transverse pipeline at the right end of the inlet of the anti-freezing solution in each layer of the commodity shelf.

Preferably, the device for detecting the freezing resistance of the material by using a freezing gas melting method further comprises:

the upper air outlet pipe is arranged at the upper end of the box body, and the end part of the upper air outlet pipe is provided with an openable mechanism;

the lower air outlet pipe is arranged at the lower end of the box body, and the end part of the lower air outlet pipe is provided with an openable mechanism;

the external fan is arranged outside the box body; when the device is heated or subjected to normal temperature heat preservation, the upper fan is communicated with the upper air outlet pipe; when the device is cooled or kept warm at negative temperature, the lower fan is communicated with the lower air outlet pipe.

Preferably, in the device for detecting freezing resistance of a material by using a freezing gas melting method, the shelf is of a hollow structure and comprises a framework part and a hollow part, and the circulating main pipeline is placed on the framework part.

Preferably, the device for detecting the freezing resistance of the material by using a freezing gas melting method further comprises:

the heat insulation layer is made of polyurethane ultra-light plastic and is arranged on the outer side of the box body.

The box body temperature sensor is arranged in the box body and used for monitoring the temperature change in the box body in real time;

the low-temperature antifreezing solution temperature sensor is arranged in the low-temperature antifreezing solution buffer tank and is used for monitoring the temperature of the antifreezing solution in the low-temperature antifreezing solution buffer tank in real time;

the high-temperature antifreezing solution temperature sensor is arranged in the high-temperature antifreezing solution buffer tank and is used for monitoring the temperature of the antifreezing solution in the high-temperature antifreezing solution buffer tank in real time;

the antifreeze temperature test sensor is arranged in the high-temperature antifreeze buffer tank and is used for monitoring the temperature of the antifreeze in the circulating pipeline in real time;

the control equipment comprises a parameter control module, a freezing and thawing module and a control module, wherein the parameter control module is used for adjusting each freezing and thawing parameter and automatically completing the freezing and thawing process of the test piece;

the freeze-thaw parameters comprise: temperature rise rate, temperature drop rate, upper and lower temperature limits, single freeze-thaw cycle time and freeze-thaw cycle times.

Preferably, the device for detecting the freezing resistance of the material by using a freezing gas melting method is adopted, wherein the freezing prevention liquid is a glycol aqueous solution with the mass concentration of 60%.

The object of the present invention and the technical problem to be solved are also achieved by the following technical means. The invention provides a method for detecting freezing resistance of a material by adopting an air freezing and air melting method, which comprises the following steps:

(1) preparing a test piece from the material;

(2) soaking the test piece in water to enable the test piece to reach a saturated state, and controlling the water content of the test piece by adjusting the draining time of the test piece;

(3) wrapping and sealing the test piece obtained in the step (2) in an environment with the temperature of (20 +/-5) DEG C and the relative humidity of more than or equal to 90%, placing the test piece in a closed box body, and controlling the relative humidity in the box body to be more than 90%;

(4) the freeze-thaw test was performed in an air-freeze and air-thaw environment:

setting the heating rate, the cooling rate, the upper and lower temperature limits, the single freeze-thaw cycle time and the freeze-thaw cycle times of the freeze-thaw test according to the test requirements; the temperature rise rate and the temperature reduction rate are respectively controlled within the range of 10 ℃/h to 30 ℃/h, and the control precision is +/-0.5 ℃; the upper and lower temperature limits are controlled within the range of-30 ℃ to 30 ℃; the single freeze-thaw cycle time is controlled within the range of 4-24 h;

when the temperature of the temperature control point reaches a set upper limit, placing a test piece;

reducing the test temperature from the upper temperature limit to the lower temperature limit, and then increasing the test temperature from the lower temperature limit to the upper temperature limit to be used as a freeze-thaw cycle;

after the set freezing and thawing cycle times, taking out the test piece, testing related freezing and thawing damage characterization parameters of the test piece until the test piece cracks, stopping the freezing and thawing test, taking out the test piece, recording the freezing and thawing cycle times, and characterizing the freezing resistance of the material;

the related freeze thaw damage characterization parameters of the test piece comprise: intensity changes before and after freeze-thawing, changes in micro-topography, surface and internal damage.

The object of the present invention and the technical problems solved thereby can be further achieved by the following technical measures.

Preferably, the method for detecting the freezing resistance of the material by using the freezing gas-melting method includes the steps of immersing the test piece in water to make the test piece reach a water saturation state, and controlling the water content of the test piece by adjusting the draining time of the test piece, and specifically includes:

immersing the test piece in water for 40-50h, keeping the water surface to be 20-40mm higher than the upper surface of the test piece, and turning the test piece once after immersing for 20-30 h; then, taking out the test piece and placing the test piece on a draining rack for draining under the environment of (20 +/-5) DEG C and the relative humidity of more than or equal to 90 percent, turning the test piece up and down once every 30min in the draining process until the set draining time is reached, and determining the water content of the test piece.

Preferably, the method for detecting the frost resistance of the material by using the gas freezing melting method is adopted, wherein the material is ultra-light concrete, and the dry density of the material is less than or equal to 150 kg.m^-3；

When the test piece is made of ultra-light concrete, the set draining time is 5-7 h;

when the number of the test pieces is two or more, the distance between any two test pieces is not less than 20 mm.

By the technical scheme, the device and the method for detecting the freezing resistance of the material by adopting the air freezing and air melting method provided by the invention at least have the following advantages:

1. the device for detecting the freezing resistance of the material by adopting the air freezing and air melting method comprises a box body, a circulating main pipeline, a high-temperature anti-freezing solution buffer pool, a low-temperature anti-freezing solution buffer pool, a heating device, a cooling device, a first pump, a second pump, a third pump, a fourth pump and anti-freezing solution, wherein a double-buffer pool four-circulation system is arranged, pipeline systems are respectively arranged on each surface of the box body and a plurality of layers of storage racks in the box body to form a full-framework pipeline system of the box body, a first distributor is arranged on the circulating main pipeline to enable the anti-freezing solution to respectively enter the pipeline systems of the box body and the storage racks at the same time, the flow rate and the flow rate of the anti-freezing solution entering the pipeline systems can be adjusted by adjusting the distribution proportion of the distributor, the temperature rising and falling processes in the box body can be controlled quickly and accurately to reach the preset temperature, and the temperature uniformity in the box body can be ensured, realize the accurate control of box temperature to realize can accomplishing the process of gas freezing gas thawing in a box.

2. The device can flexibly adjust the upper and lower limits of temperature, the heating rate, the cooling rate and the time required by single thawing cycle of the thawing test according to the actual requirements of research and work, and meets the test requirements of materials under different freezing and thawing conditions.

3. The device has the characteristics of good sealing performance and good heat preservation performance, can effectively prevent the temperature exchange between the inside of the box body and the outside, and avoids unnecessary energy consumption. Meanwhile, the device of the invention is further provided with an upper air outlet pipe and a lower air outlet pipe at the upper end and the lower end of the box body respectively, and the upper air outlet pipe and the lower air outlet pipe are adopted to work alternately in the melting and freezing processes, so that the uniformity and the uniformity of the temperature in the box body are greatly improved, and the test accuracy and the test reliability are improved.

4. According to the method, the temperature in the box body is accurately controlled by controlling the temperature rise rate and the temperature drop rate in the box body, the water content of the test piece after water saturation is controlled by adjusting the draining time of the test piece, and a freeze-thaw test is performed in an air-freeze air-thawing mode, so that the freeze-thaw damage process of the material in a service environment, particularly the frost resistance of ultra-light concrete, is more accurately simulated.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.

Drawings

FIG. 1 is a schematic structural diagram of an apparatus for detecting freezing resistance of a material by using an air-freezing and air-melting method according to an embodiment of the present invention;

FIG. 2 illustrates a front view of FIG. 1 in accordance with an embodiment of the present invention;

FIG. 3 illustrates a side view of FIG. 1 in accordance with an embodiment of the present invention;

FIG. 4 illustrates a front view of the internal structure of FIG. 1 in accordance with an embodiment of the present invention;

FIG. 5 illustrates a rear view of FIG. 1 in accordance with an embodiment of the present invention;

FIG. 6 is a schematic view of a single layer shelf in a housing according to an embodiment of the present invention;

FIG. 7 shows a schematic view of the distribution structure of the antifreeze according to an embodiment of the present invention;

FIG. 8 shows a schematic view of the distribution structure of the antifreeze according to another embodiment of the present invention;

FIG. 9 is a view showing how a test piece according to an embodiment of the present invention is placed when draining water;

FIG. 10 is a diagram illustrating the specimen drilling location and sensor placement in accordance with an embodiment of the present invention;

FIG. 11 shows the cooling profile of the apparatus and refrigerator of the present invention during freezing;

FIG. 12 shows the temperature profile of a single freeze-thaw cycle at the upper, middle and lower three points inside the cabinet of the apparatus of the present invention;

FIG. 13 shows the variation of the water content of the ultra lightweight concrete at different draining times;

FIG. 14 shows temperature variation curves of freeze-thaw process of ultra-lightweight concrete with two dry densities for draining 6 h;

FIG. 15a shows 150kg/m after 5 freeze-thawing³Apparent appearance of the dry density ultra-light concrete;

FIG. 15b shows 150kg/m after 10 freeze-thawing³Apparent appearance of the dry density ultra-light concrete;

FIG. 15c shows 150kg/m after 20 freeze-thawing³Apparent appearance of the dry density ultra-light concrete;

FIG. 15d shows 150kg/m after 30 freeze-thaw cycles³Apparent appearance of the dry density ultra-light concrete;

FIG. 16a shows a dry density of 150kg/m³The frost resistance test results of the ultra-light concrete under different draining times;

FIG. 16b shows a dry density of 350kg/m³The frost resistance test results of the ultra-light concrete under different draining times;

FIG. 17 shows 150kg/m³After the freeze-thaw cycle of the dry-density ultra-lightweight concrete is carried out for 10 times, penetrating cracks appear;

FIG. 18a shows the melting temperature vs. 150kg/m³Influence of the freeze resistance test result of the dry density ultra-light concrete;

FIG. 18b shows the melting temperature vs. 350kg/m³Influence of the freeze resistance test result of the dry density ultra-light concrete;

FIG. 19a shows 150kg/m with dimensions 70mm by 70mm³Apparent appearance of freeze thawing of a dry density test piece for 20 times;

FIG. 19b shows 150kg/m with dimensions 100mm by 100mm³Apparent appearance of freeze thawing of a dry density test piece for 20 times;

FIG. 19c shows 150kg/m with dimensions 150mm by 150mm³Apparent appearance of freeze thawing of a dry density test piece for 20 times;

FIG. 20a shows the test piece size vs. 150kg/m³Influence of the freeze resistance test result of the dry density ultra-light concrete;

FIG. 20b shows the test piece size vs. 350kg/m³Influence of the freeze resistance test result of the dry density ultra-light concrete;

FIG. 21 shows 150kg/m³Temperature change curves of freeze-thaw process of test pieces with three dimensions of dry density.

Detailed Description

To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be given to the specific embodiments, structures, features and effects of the apparatus and method for detecting freezing resistance of a material by using an air-freezing melting method according to the present invention with reference to the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "an embodiment" refers to not necessarily the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

As shown in fig. 1, an embodiment of the present invention provides an apparatus for detecting freezing resistance of a material by using an air-freezing and air-melting method, including: the system comprises a box body 1, a circulating main pipeline 10, a high-temperature antifreezing solution buffer tank 11, a low-temperature antifreezing solution buffer tank 12, heating equipment 14, cooling equipment 15, a first pump machine 18, a second pump machine 17, a third pump machine 16, a fourth pump machine 19 and antifreezing solution;

the high-temperature antifreeze solution buffer tank 11, the circulating main pipeline 10, the heating device 14 and the first pump 18 form a first circulating system (temperature rising process);

the circulation main pipeline 10, the heating device 14 and the second pump 17 form a second circulation system (high-temperature heat preservation process);

the low-temperature antifreeze solution buffer tank 12, the circulating main pipeline 10, the cooling equipment 15 and the third pump 16 form a third circulating system (cooling process);

the circulation main pipe 10, the cooling device 15 and the fourth pump 19 form a fourth circulation system (low-temperature heat preservation process).

In the embodiment, the heating equipment is preferably a high-power heater, so that the maximum set temperature upper limit temperature reached by the box body in a short time is ensured; the cooling device preferably selects a high-power compressor, and the maximum set temperature lower limit temperature reached by the box body in a short time is ensured.

The temperature of the antifreeze in the high-temperature antifreeze buffer tank 11 is higher than that of the antifreeze in the circulating main pipeline 10, the temperature value of the antifreeze in the high-temperature antifreeze buffer tank 11 can be controlled to be higher than that of the antifreeze in the circulating main pipeline 10 by the touch screen type parameter control module 2, and the adjustment range is 0-20 ℃.

The temperature of the antifreeze in the low-temperature antifreeze buffer tank 12 is lower than that of the antifreeze in the circulating main pipeline 10, and the temperature value of the antifreeze in the low-temperature antifreeze buffer tank 12 can be controlled to be lower than that of the antifreeze in the circulating main pipeline 10 by the touch screen type parameter control module 2, wherein the adjustment range is-20-0 ℃.

As shown in fig. 2, 3 and 7, an anti-freezing solution is provided in the circulation main pipe 10, a first-stage distributor 101 is provided on the circulation main pipe 10, and a first circulation pipe 102 and a second circulation pipe 103 are connected to the first-stage distributor 101;

the box body 1 is a closed space formed by a top surface, a bottom surface and four side surfaces, wherein one side surface is provided with a box door 3 which can be opened and closed, a rubber ring is arranged in the box door 3, when the box door 3 is closed, the rubber ring is in an extrusion state, a sealing effect is achieved, and heat exchange between the box body 1 and the outside can be effectively avoided; the top surface, the bottom surface and four side surfaces of the box body 1 are respectively provided with a box body pipeline system 1023 which is connected with the first circulating pipeline 102;

a plurality of layers of storage racks 20 are arranged in the box body 1, and the plurality of layers of storage racks 20 are arranged at intervals and used for placing samples to be tested; each shelf is provided with a shelf pipeline system 1033 connected with the second circulation pipeline 103.

The high temperature in the high temperature antifreeze buffer pool is the melting temperature adopted when detecting the frost resistance of the material, which is different from the material, and is generally between about 0 ℃ and 30 ℃, and can also be between 5 ℃ and 25 ℃, 15 ℃ and 20 ℃, and the like.

The low temperature in the low-temperature antifreezing solution buffer tank refers to the freezing temperature adopted when the freezing resistance of the material is detected, which is different from the material, generally between about-30 ℃ and-5 ℃, and also between-25 ℃ and-15 ℃, between-20 ℃ and-18 ℃ and the like.

In some embodiments, such as when testing the frost resistance of ultra lightweight concrete, the freezing temperature is set at-15 ℃ and the melting temperature is set at 15 ℃.

The term "ultra-lightweight concrete" as used in the present example means that the dry density is not more than 400 kg.m^-3The ultra-light low-strength cement-based material. Low strength generally means a strength of 1MPa or less. The setting of one-level distributor can make antifreeze liquid get into in the first circulating line and the second circulating line simultaneously, and through adjusting the velocity of flow and the flow of the coolant liquid that the one-level distributor control got into in the first circulating line and in the second circulating line for the temperature of supporter and the temperature of box can reach synchronous lift, and realize the accurate control of rate of heating and cooling. The first pump 18, the second pump 17, the third pump 16 and the fourth pump 19 are used for driving the circulation of the anti-icing liquid in the respective circulation system.

The device of this embodiment adopts two buffer tank four cycle systems and full skeleton piping system, has increased the circulating surface area of antifreeze, enables the temperature of box to rise rapidly and reduce, realizes that the box is whole to accomplish intensification and cooling process, ensures that the box temperature is even to realize the accurate control of box temperature.

The embodiment of the invention provides a double-buffer-tank four-circulation system and full-skeleton antifreeze liquid circulation, which realize the rapid and controllable temperature rise and reduction process of a test device and specifically comprises the following steps:

the device of the embodiment adopts a double-buffer-tank four-circulation system, in the process of low temperature to high temperature, a high-temperature antifreeze solution buffer tank is connected with a circulation main pipeline, feedback data are collected through a temperature sensor in a box body, the flow speed and flow of antifreeze solution are adjusted, the temperature rise process of the box body is controlled quickly and precisely, after the preset temperature is reached, a valve of the high-temperature antifreeze solution buffer tank is closed, and the circulation main pipeline is directly connected with heating equipment to finish the high-temperature heat preservation process; in the process of converting high temperature into low temperature, the low-temperature antifreezing solution buffer tank is connected with the circulating main pipeline, the flow speed and flow of the antifreezing solution are adjusted by acquiring feedback data through a temperature sensor in the box body, the cooling process of the box body is controlled quickly and precisely, after the preset temperature is reached, a valve of the low-temperature antifreezing solution buffer tank is closed, and the circulating main pipeline is directly connected with cooling equipment (a compressor) to finish the low-temperature heat preservation process.

Further, in some embodiments, as shown in fig. 8, a second-stage distributor 1021 is further disposed on the first circulation pipeline 102, a first sub-circulation pipeline 1022 is connected to the second-stage distributor 1021, and the first sub-circulation pipeline 1022 is respectively connected to the tank pipeline systems 1023, so that the antifreeze in the first sub-circulation pipeline 1022 enters the tank pipeline systems 1023 on each side;

the second circulation pipeline 103 is further provided with a second-stage distributor 1031, the second-stage distributor 1031 is connected with a second sub-circulation pipeline 1032, and the second sub-circulation pipeline 1032 is respectively connected with the shelf pipeline systems 1033 of each layer, so that the antifreeze in the second sub-circulation pipeline 1032 enters the shelf pipeline systems 1033 of each layer.

Furthermore, the box pipeline systems 1023 on each side are respectively composed of a plurality of parallel transverse pipelines;

each layer of the rack pipeline system 1033 is composed of a plurality of parallel transverse pipelines;

in each conduit system 1023, 1033, the number of transverse conduits is 4, 6, 8 or 10;

the antifreeze liquid inlet and the antifreeze liquid outlet of the transverse pipeline are respectively arranged at two ends, and the antifreeze liquid inlet and the antifreeze liquid outlet of two adjacent transverse pipelines are arranged at different ends;

the first sub-circulation pipeline 1022 has two paths, one of which is connected with the transverse pipeline of the antifreeze solution inlet at the left end of each surface, and the other of which is connected with the transverse pipeline of the antifreeze solution inlet at the right end of each surface;

similarly, the second sub-circulation pipeline 1032 has two paths, one path is connected to the transverse pipeline at the left end of the antifreeze solution inlet in each layer, and the other path is connected to the transverse pipeline at the right end of the antifreeze solution inlet in each layer.

The antifreeze in the circulating main pipeline is divided into two paths by a first-stage distributor, the first path enters a pipeline on a box body, the second path enters a pipeline on a commodity shelf, then secondary distribution is carried out respectively, the antifreeze in the first path is distributed into the pipelines on all sides of the box body according to a ratio by a second-stage distributor, the proportional distribution means that the antifreeze passing through the unit area of all sides of the box body is the same, the antifreeze in the second path is uniformly distributed into the pipelines on all layers of the commodity shelf by another second-stage distributor, and all the layers of the commodity shelf are set to be the same size in order to ensure that the temperature rising and falling rates of all the layers are the same.

Through the arrangement mode, the fluid can be uniformly distributed on each surface of the box body and each layer of the storage rack as far as possible, so that the heating rate and the cooling rate of the box body and/or each layer are uniform, the heating rate and the cooling rate are accurately controlled, the accurate control of the freezing temperature and the melting temperature in the test is facilitated, the freezing and thawing damage process of the material in the service environment or the set environment can be accurately tested, and the frost resistance of the material is further obtained.

Further, in some embodiments, as shown in fig. 4 and 5, the apparatus for detecting frost resistance of a material by using an air-freezing method further includes:

the upper air outlet pipe 4 is arranged at the upper end of the box body 1, and the end part of the upper air outlet pipe 4 is provided with an openable mechanism; the openable mechanism is preferably composed of two blades;

the lower air outlet pipe 5 is arranged at the lower end of the box body 1, and the end part of the lower air outlet pipe 5 is provided with an openable mechanism; the openable mechanism is preferably composed of two blades;

the external fan 15 is arranged outside the box body 1; when the device is heated or subjected to normal temperature heat preservation, the external fan 15 is communicated with the upper air outlet pipe 4, two blades on the upper air outlet pipe are in an open state, and two blades on the lower air outlet pipe are in a closed state; when the device is cooling or negative temperature keeps warm, external fan 15 with lower tuber pipe 5 intercommunication, two blades on the lower tuber pipe are in the open mode, go up two blades on the tuber pipe and be in closed mode. When the air conditioner stops working, the two blades on the upper air outlet pipe and the two blades on the lower air outlet pipe are both in a closed state.

The upper air outlet pipe and the lower air outlet pipe share the external fan in the embodiment, so that energy consumption can be saved, and the damage probability of the fan is reduced. The air output is adjusted by controlling the power of the fan, so that the air flow in the box body is promoted, and the temperature in the box body is uniform.

Aiming at the problem that the refrigerator has large temperature difference up and down in the freezing process in the freeze-thaw test, the embodiment of the invention provides an idea that an external fan promotes the air flow of the refrigerator body and the circulation of the full-skeleton antifreeze is taken as an auxiliary idea, so that the uniform temperature in the refrigerator body in the whole freeze-thaw test is realized, and the idea is as follows:

the device is provided with an external fan, the fan is connected with air outlet pipelines at the upper end and the lower end of the box body, cold air sinks when freezing, and the fan is communicated with an air outlet pipe at the bottom end of the box body to promote the cold air to upwelle. When the hot air is melted, the hot air is gathered, and the fan is automatically communicated with the air outlet pipe at the top end of the box body, so that the hot air moves downwards. The air in the box body is in a flowing circulation state in the whole freezing and thawing process, so that the testing device can provide a stable and uniform temperature environment for the freezing and thawing process of the test piece, and an equipment foundation is provided for accurately simulating the freezing and thawing damage process of the material in the actual service environment.

Further, in some embodiments, as shown in fig. 4 and 6, the rack 20 has a hollow structure, and includes a framework portion and a hollow portion, and the rack piping systems of each layer are respectively disposed on the framework portion of each layer. The hollow part is beneficial to the temperature transmission between the test piece and the box body and the air flow in the box body; if a large-mass and large-volume test piece is to be placed, a high-pressure bearing material is selected, or a reinforcing member is added to reinforce the commodity shelf.

Further, in some embodiments, as shown in fig. 4, the apparatus for detecting frost resistance of a material by using an air-freezing method further includes:

the heat insulation layer is made of polyurethane ultra-light plastic and is arranged on the outer side of the box body 1;

the heat preservation insulating layer distributes in the outside of whole box, and the outside here includes the top surface, the bottom surface and four sides of box, also sets up the heat preservation insulating layer on the chamber door, and the heat preservation insulating layer is preferred to be made with polyurethane ultralight plastics, effectively avoids box and external heat exchange.

The box body temperature sensor 6 is arranged in the box body 1 and used for monitoring the temperature change in the box body 1 in real time, the box body temperature sensor 6 adopts a pt100 temperature sensor, the temperature acquisition range can reach-200 ℃ to +850 ℃, and the box body temperature sensor is used for monitoring the temperature change in the box body in real time; in some preferred embodiments, an auxiliary box temperature sensor 9 is further arranged in the box body 1, a pt100 temperature sensor is adopted, the temperature acquisition range can reach-200 ℃ to +850 ℃, and the auxiliary box temperature sensor is used for verifying the accuracy of the temperature measured by the box body temperature sensor 6 and ensuring the uniform temperature and humidity in the box body;

the low-temperature antifreeze liquid temperature sensor 29 is arranged in the low-temperature antifreeze liquid buffer tank 12 and is used for monitoring the temperature of the antifreeze liquid in the low-temperature antifreeze liquid buffer tank 12 in real time; a pt100 temperature sensor is adopted, the temperature acquisition range can reach-200 ℃ to +850 ℃, the temperature sensor is used for monitoring the temperature of the antifreeze solution in the low-temperature buffer tank, when the measured temperature is lower than the set temperature, 27 is opened, 16 works, and the antifreeze solution is ensured to be in the set temperature value range;

the high-temperature antifreeze temperature sensor 30 is arranged in the high-temperature antifreeze buffer tank 11 and is used for monitoring the temperature of the antifreeze in the high-temperature antifreeze buffer tank 11 in real time; a pt100 temperature sensor is adopted, the temperature acquisition range can reach-200 ℃ to +850 ℃, the temperature sensor is used for monitoring the temperature of the antifreeze solution in the high-temperature buffer tank, and when the measured temperature is lower than the set temperature, 25 is opened, 18 works, and the antifreeze solution is ensured to be in the set temperature value range;

and the antifreeze liquid temperature test sensor (not shown in the figure) is arranged in the circulating main pipeline 10 and is used for monitoring the temperature of the antifreeze liquid in the circulating main pipeline 10 in real time. The temperature acquisition range can reach-200 ℃ to +850 ℃ by adopting a pt100 temperature sensor, and the temperature acquisition sensor is used for monitoring the temperature of the antifreeze in the circulating main pipeline.

In some embodiments, the test device further comprises a test sensor 7 for testing the internal temperature of the test piece, as shown in fig. 10, a pt100 temperature sensor is adopted, the temperature acquisition range can reach-200 ℃ to +850 ℃, and a plurality of sensors can be added according to the test requirements. And monitoring the temperature change of the central temperature of the test piece in real time.

Further, in some embodiments, the apparatus for detecting freezing resistance of a material by using an air-freezing and air-melting method further includes:

the antifreezing solution is glycol water liquid with the mass concentration of 60%, and the freezing point is as follows: -48.3 ℃, boiling point: 110.0 ℃, is arranged in a circulation main pipeline and is pushed to circulate by a pump to finish the temperature exchange with the box body.

Further, in some embodiments, the apparatus for detecting freezing resistance of a material by using an air-freezing and air-melting method further includes: the control equipment comprises a parameter control module, a freezing and thawing module and a control module, wherein the parameter control module is used for adjusting each freezing and thawing parameter and automatically completing the freezing and thawing process of the test piece;

the freeze-thaw parameters comprise: temperature rise rate, temperature drop rate, upper and lower temperature limits, single freeze-thaw cycle time and freeze-thaw cycle times.

Specifically, the control equipment comprises a touch screen type parameter control module 2, which is used for adjusting each freezing and thawing parameter; and according to the real-time measured value of the temperature sensor, the switch of the freezing and melting related device and the distribution proportion of each distributor are controlled so as to ensure that each parameter reaches the preset value.

The test device is provided with a parameter control module, and can be used for freeze-thaw test research under different parameter conditions by adjusting:

adjusting the heating rate and the cooling rate: the temperature rise rate and the temperature drop rate can be adjusted within the range of 10 ℃/h to 30 ℃/h, and the control precision is +/-0.5 ℃;

adjusting the upper and lower temperature limits: adjusting the temperature within the range of-30 ℃ to 30 ℃ according to actual research and working requirements;

single freeze-thaw cycle time adjustment: the freezing resistance of the freezing and melting duration (automatic heat preservation after reaching the set temperature) can be adjusted, and the single freezing and melting cycle time can be adjusted within the range of 4-24 h according to the research and the actual working requirements.

Frost resistance of concrete: refers to the ability of the concrete to withstand the effects of freeze-thaw cycles without failure when hydrated. The freeze-thaw damage of the concrete is caused by volume expansion of water in the concrete after freezing, when the expansion force exceeds the tensile strength of the concrete, the concrete generates tiny cracks, and the repeated freeze-thaw cracks continuously expand, so that the strength of the concrete is reduced until the concrete is damaged. The anti-freezing label is represented by an anti-freezing label, wherein the anti-freezing label is represented by the maximum freezing-thawing cycle frequency which can be borne by stones with age of 28 days after the stones are saturated with water and repeatedly subjected to freezing-thawing cycle at-15 to 200 ℃, and the compression strength is reduced by no more than 25 percent, and the weight loss is no more than 5 percent. The concrete is divided into the following nine frost resistant grades: d10, D15, D25, D50, D100, D150, D200, D250 and D300 respectively show that the concrete can bear the repeated dynamic melting cycle times of not less than 10, 15, 25, 50, 100, 150, 200, 250 and 300.

Further, in some embodiments, the apparatus for detecting freezing resistance of a material by using the air-freezing method further comprises various control valves, including but not limited to the following valves:

as shown in fig. 1, a valve 23 controls the opening and closing of two thick and thin pipelines to realize the adjustment of three flows of antifreeze, namely large, medium and small flows, in the process of converting high temperature to low temperature, the valves 23 and 27 are opened, 16 work to connect 12, 15 and 10, feedback data is collected through temperature sensors 6 and 9 to adjust the flow rate and flow rate of the antifreeze, the temperature rise process of a box body is controlled quickly and precisely, after the preset temperature is reached, the valves 23 and 19 work, and 10 is directly connected with 15 to finish the heat preservation process;

a valve 24, connected to 14 and 10, for controlling the opening and closing of the section of pipe;

a valve 25, connected to 11 and 14, for controlling the opening and closing of the section of pipe;

the valve 26 controls the opening and closing of the thick and thin pipelines to realize the adjustment of the large, medium and small flows of the antifreeze, in the process of converting low temperature into high temperature, the valves 24 and 26 are opened, the valves 18 work to connect the valves 11 and 14 with the valves 10, feedback data is collected through the temperature sensors 6 and 9 to adjust the flow rate and the flow of the antifreeze, the temperature rise process of the box body is controlled quickly and precisely, after the preset temperature is reached, the valves 26 and 17 are closed to work, and the valves 10 are directly connected with the valves 14 to finish the heat preservation process;

a valve 27, connected to 15 and 10, for controlling the opening and closing of the section of pipe;

valve 28, connections 12 and 15, controls the opening and closing of the length of tubing.

According to the real-time measured value of the temperature sensor, the parameter control device controls the on-off of the freezing and melting related devices to complete the conversion of the freezing and melting processes, so that the freezing and melting processes of the test piece can be automatically completed in one device, and the labor force in the test process is reduced.

The device can set the times of freeze-thaw cycles and the temperature of the box body after the freeze-thaw is finished; may be set to a certain positive or negative temperature.

In another embodiment of the present invention, a method for detecting freezing resistance of a material by using an air freezing and air melting method is provided, where the freezing resistance of the material is detected by a freeze-thaw test, and the method specifically includes the following steps:

(1) preparing a test piece from the material;

the method specifically comprises the following steps: the method for manufacturing the test piece by using the material is described by taking the test piece for manufacturing the low-strength cement-based material as an example, and comprises the following steps of: controlling the room temperature to be (25 +/-2) DEG C, accurately weighing the raw materials according to the formula ratio, pouring the raw materials into a stirring pot, fully mixing at the rotating speed of (200 +/-50) rpm, stirring at the rotating speed of (300 +/-50) rpm for 5-8 s, then filling into a mold, and standing; and covering the surface of the test block with a plastic film after 3-5 h, curing for 48h, and then removing the mold. Coating the test piece after the mold is removed with a plastic film, moving to a standard curing room, curing for 28d, and cutting into a cubic test piece with a given size;

the dry density grades prepared by the method are respectively 150kg/m³And 350kg/m³Two kinds of dry density ultra-light concrete test pieces are respectively marked as an LH-150 test piece and an LH-350 test piece.

(2) Soaking the test piece in water to enable the test piece to reach a saturated state, and controlling the water content of the test piece by adjusting the draining time of the test piece;

the method specifically comprises the following steps: immersing the cut test pieces in water for 48h, wherein the distance between the test pieces is not less than 20mm, keeping the water surface to sink about 30mm above the upper surface of the test piece, and turning over the test pieces once after immersing for 24h to ensure that the test pieces absorb water more uniformly; after 48h, taking out the test piece and placing the test piece on a draining rack for draining under the environment of (20 +/-5) DEG C and the relative humidity of more than or equal to 90 percent, wherein the test piece is placed in a draining mode during draining, as shown in figure 9, 8 is the test piece, and in the draining process, the test piece is placed at intervals of about 30minThe test piece is turned over once, so that the test piece is more uniform in draining, and the moisture content of each test piece is ensured to be uniform. The draining time is 1h, 6h and 12h respectively, and the compressive strength f of the test piece of the test reference group is specified according to JC/T2357₁。

And (3) measuring the water content of the test piece: soaking LH-150 and LH-350 test pieces in water for 48h, taking out, placing on a draining rack according to the requirement of FIG. 9, weighing the two test pieces at a certain interval, and recording as n_iDraining water for 72h, weighing, placing two groups of test pieces in an electrothermal blowing drying oven, drying at 65 + -5 deg.C to constant weight (the drying process is separated by more than 4h, and the difference between the two previous weighing is not more than 0.5% of the test piece mass), and determining the mass of the test piece as n₀。

The water content of the test piece is calculated according to the formula (3) and is accurate to 0.1 percent.

In the formula (3), W represents the mass loss rate,%;

n_imass g of the test piece after draining for a period of time;

n₀the dried mass of the test piece is g.

The water content directly influences the water saturation of the ultralight concrete, and the water content of the test piece can be effectively adjusted by controlling the draining time. The moisture absorbed by the test piece can flow out again during draining, and because the test piece is subjected to sealing treatment during pretreatment by the method, the moisture content of the test piece can be basically kept stable in the freeze-thaw process, so that the moisture content of the test piece in a subsequent freeze-thaw test is directly determined by the draining time. As shown in FIG. 13, the change of the water content of the ultra-lightweight concrete under different draining time is shown, and as can be seen from FIG. 13, the change of the water content of the ultra-lightweight concrete samples with two dry densities is the largest within 1h before draining, because the water in the open pores on the surfaces and the communicating pores inside the test samples can rapidly flow out in the form of water drops or even water columns when the test samples are taken out of the water, and the water drops of the concrete with two dry densities can not drop after the draining time is prolonged, particularly after the draining time is 6h, so that the water content of the test samples is highThe rate reduction speed is obviously slowed down, the water content of two kinds of dry density concrete test pieces is basically unchanged after 12 hours of draining, the draining time is selected to be 1 hour, 6 hours and 12 hours respectively, the test pieces with the thickness of 100mm multiplied by 100mm are adopted, the melting temperature is 25 ℃, and the test is carried out according to the method. As shown in FIG. 14, the temperature change curves of the freeze-thaw process of the ultra-lightweight concrete with two dry densities for 6h, as can be seen from FIG. 14, during the freeze-thaw cycle, 350kg/m³The sensitivity of the dry density concrete to the external temperature change is less than 150kg/m³The freeze-thaw damage degree of the dry density concrete is more serious compared with the higher dry density ultra-light concrete and the low dry density concrete. In addition, the platform section exists in the freezing and melting stages of the test piece, and the temperature range of the platform section is-2-0 ℃, because the freezing and ice-forming water melting processes of the water in the ultra-light concrete macro-pores occur in the temperature range, and the heat release and heat absorption phenomena occur in the two processes respectively, so that the temperature change is slowed down. As shown in FIG. 15a, FIG. 15b, FIG. 15c and FIG. 15d, which are 150kg/m after 5 times of freeze thawing, 10 times of freeze thawing, 20 times of freeze thawing and 30 times of freeze thawing, respectively³The apparent appearance of the dry-density ultra-light concrete can be seen from the figure, along with the increase of the number of freeze-thaw cycles, the surface of the ultra-light concrete is seriously corroded and damaged, because a small part of water is concentrated on the upper bottom surface and the lower bottom surface of the test piece under the action of gravity, and the two bottom surfaces of the test piece are seriously damaged in the freeze-thaw process. As shown in FIG. 16a and FIG. 16b, the dry density was 150kg/m³And 350kg/m³The results of the frost resistance tests of the ultralight concrete under different draining times show that the compressive strength loss rate and the mass loss rate of the ultralight concrete with two dry densities increase along with the increase of the number of freeze-thaw cycles. And 150kg/m under the same number of freeze-thaw cycles³The freeze-thaw damage degree of the ultra-light concrete with dry density is obviously higher than 350kg/m³The loss rate of the dry-density ultra-light concrete after 30 times of freeze-thaw cycle is over 5 percent. Along with the extension of waterlogging caused by excessive rainfall time, the moisture content of test piece reduces, and the downthehole moisture of ultralight concrete reduces, and in the freeze thawing process, the frost heaving pressure that suffers of test piece is less relatively. At the same timeThere are studies showing that: although the draining treatment is carried out, the difference of the moisture content inside and outside the test piece still exists, and the smaller the moisture content outside the test piece is, the smaller the difference of the stress inside and outside the test piece is, the lighter the freeze-thaw damage degree is. The change trends of the mass loss of the test pieces drained for 6h and 12h in the freeze thawing process are basically the same and the difference is not large, and it can be known from fig. 13 that the water contents of the ultra-light concrete with low dry density and high dry density after 6h draining are 44.5% and 23.0% respectively, and the water contents of the concrete with the two dry densities are the closest under the draining time. In combination with the time cost, the preferred draining time for the ultra-light concrete of both dry densities in the subsequent freeze resistance test is 6 hours.

(3) Wrapping and sealing the test piece obtained in the step (2) in an environment with the temperature of (20 +/-5) DEG C and the relative humidity of more than or equal to 90%, placing the test piece in a closed box body, and controlling the relative humidity in the box body to be more than 90%;

specifically, test pieces of the test group are wrapped and sealed by plastic films one by one, holes are formed in the wrapped LW150 test pieces and LW350 test pieces (the test piece punching position and the sensor placement mode are shown in FIG. 10), temperature sensors (the test precision is +/-0.2 ℃) are placed, heat insulation cotton is attached to the punched positions, and the test pieces are used for testing the central temperature curve of the test pieces in the subsequent freeze-thaw cycle. And the rest test pieces are placed in the same sealing bag according to the same group of six test pieces to avoid water loss, and are used for testing the quality loss rate and the strength loss rate of the subsequent freeze-thaw test.

The seal comprises: coating a preservative film on the surface of the test piece, or sealing the test piece in a sealing bag, or sealing the test piece in vacuum at a low air extraction rate (less than or equal to 3L/min) by adopting a micro vacuum pump to prevent water loss in the freeze thawing process;

preferably, the test piece is wrapped by a preservative film, and then the test piece wrapped by the preservative film is sealed in a sealing bag under the environment of (20 +/-5) DEG C and the relative humidity of more than or equal to 90 percent.

In order to ensure the stability of the moisture content of the test piece, when the temperature of the box body is normal temperature, the relative humidity of the box body is ensured to be more than 90% through the humidification of the humidifier.

The wrapped test piece 8 is punched, the punching position of the test piece and the placement mode of the sensors are as shown in fig. 10, a temperature sensor 7 (with the test precision of +/-0.2 ℃) is placed in the hole of the test piece 8, the test piece is connected with the outside through a data line 71, and heat insulation cotton 72 is attached to the punched position for testing the central temperature curve of the test piece in the subsequent freeze-thaw cycle. The punch location is located approximately in the middle of the specimen and in some embodiments, 47mm and 45mm from either side as shown in FIG. 10. Further, the width of the hole is about 6mm, and the temperature sensor 7 is placed in the hole, wherein the distance between the temperature sensor 7 and the wall of the hole is about 0.5mm, and the temperature sensor 7 is connected with a data line, and the distance between the data line and the wall of the hole is about 2 mm.

And the rest test pieces are placed in the same sealing bag according to the same group of six test pieces to avoid water loss, and are used for testing the quality loss rate and the strength loss rate of the subsequent freeze-thaw test.

(4) Performing a freeze-thaw test in an air-freeze and air-thaw environment;

the method specifically comprises the following steps:

setting the heating rate, the cooling rate, the upper and lower temperature limits, the single freeze-thaw cycle time and the freeze-thaw cycle times of the freeze-thaw test according to the test requirements;

the freezing and melting temperature control points can select the air temperature in the box body (the dry density is less than or equal to 1600 kg/m)³) Or the central temperature of the reference test piece (dry density is more than 1600 kg/m)³) Measured by the corresponding temperature sensor.

When the temperature of the temperature control point reaches a set upper limit, putting the test pieces, and when a plurality of test pieces are put into the test pieces, the distance between the test pieces is more than or equal to 20 mm; the distance between the test pieces in the device, and the number of the test pieces to be placed is determined according to the test requirement;

the test temperature is reduced from the upper temperature limit to the lower temperature limit, and then is reduced from the lower temperature limit to the upper temperature limit to be used as a freeze-thaw cycle; in the actual freeze-thaw test, the temperature of the box body or the central temperature of the test piece can be selected as a temperature adjusting reference for testing according to needs, and then unified modification can be performed.

After the set freezing and thawing cycle times, taking out the test piece, testing related freezing and thawing damage characterization parameters of the test piece until the test piece cracks, stopping the freezing and thawing test, taking out the test piece, recording the freezing and thawing cycle times, and characterizing the freezing resistance of the material;

the related freeze thaw damage characterization parameters of the test piece comprise: and testing the strength change, the microscopic morphology change and the surface and internal damage conditions of the material before and after freeze thawing, and comparing the strength change, the microscopic morphology change and the surface and internal damage conditions with corresponding parameters of a test piece before freeze thawing circulation to represent the anti-freezing performance of the material.

And (3) testing the strength: the strength loss rate is calculated by testing the compression strength and the rupture strength of the test piece before and after the test, subtracting the test value before the test from the test value after the test and dividing by the test value before the test so as to represent the frost resistance of the material.

Change of micro-morphology: the shape and the structure of a material (a flat sheet is adopted, and a sample is subjected to gold spraying coating in a vacuum coating machine) are observed in a high vacuum mode through a scanning electron microscope, so that the change of the micro shape of the material before and after freeze thawing damage is researched.

Surface degradation and failure: the state was analyzed by photographing for observation.

Internal destruction and microstructural damage: the strain test can be adopted, strain gauges are pasted on the lateral surface of the test piece in the horizontal direction and the vertical direction, the change of the strain value of the test piece before and after the test is recorded, and the anti-freezing performance of the material is represented.

Further, the heating rate and the cooling rate are respectively controlled within the range of 10 ℃/h to 30 ℃/h, and the control precision is +/-0.5 ℃;

the upper and lower temperature limits are controlled within the range of-30 ℃ to 30 ℃;

the single freeze-thaw cycle time is controlled within the range of 4 h-24 h;

the number of freeze-thaw cycles, which may be suitably increased or decreased according to the freezing resistance of the test material, is 5, 10, 15, 25, and 50 in some embodiments, respectively.

When detecting ultra-light low-strength concrete, the number of freeze-thaw cycles is increased by 5 times of detection times in consideration of the performance of the ultra-light low-strength concrete.

Freeze-thaw test and characterization parameters:

(1) cooling the low-temperature box to-15 ℃ in advance; the relative humidity of the constant temperature and humidity chamber is adjusted to 90 +/-5%, and the temperature is respectively adjusted to 5 ℃, 15 ℃ and 25 ℃. The temperature in the two boxes is kept uniform.

(2) And (3) placing the test piece in the sealing bag into a low-temperature box, freezing at the temperature of minus 15 +/-2 ℃ for 6 +/-0.5 h, taking out the sealing bag, and placing the sealing bag into a constant-temperature and constant-humidity box to melt for 5 +/-0.5 h, wherein the constant-temperature and constant-humidity box is used as a freeze-thaw cycle. The dry density was 150kg/m³The concrete is frozen and thawed for 5 times, 10 times, 20 times and 30 times respectively, and the dry density is 350kg/m³The concrete is frozen and thawed for 5 times, 15 times, 25 times and 50 times respectively. After each freeze-thaw cycle is carried out for 2 times, the test piece is turned over for 1 time from top to bottom, and excessive water accumulation at the bottom of the test piece is prevented.

(3) Every 5 cycles, the test pieces were inspected and recorded for appearance failure during the freeze-thaw process. Once the test piece cracks, falls off the angle and other conditions, the damaged test piece is removed, and the other test pieces continue to be subjected to freeze thawing test.

(4) And a high-precision temperature recorder is adopted to monitor the change of the central temperature of the ultra-light concrete test piece in the previous two freezing-thawing circulation processes of the LW150 and the LW350 in real time.

In the freeze-thaw test, when the set number of freeze-thaw cycles is reached, two groups of test pieces are taken, the plastic films wrapped on the test pieces are removed, and one group of test pieces is used for measuring the compressive strength f according to the JC/T2357 rule₂. Removing the plastic film from the other group of test pieces, putting the test pieces into water, slightly swinging to remove the strippable substances attached to the test pieces, and filtering out the strippable substances; then the test piece and the filtered peeled and fallen objects are placed in an electric heating air blast drying oven, and are dried to constant weight (the drying process interval is more than 4h, the difference between the two previous times and the two subsequent times is not more than 0.5 percent of the mass of the test piece) at the temperature of (65 +/-5), and the mass m of the test piece and the mass m of the peeled and fallen objects are respectively measured₁And m₂To the nearest 0.1 g.

Freeze-thaw strength loss rate: the strength loss rate was calculated to the nearest 0.1% according to equation (1).

In the formula (1), P represents the loss rate of compressive strength,%;

f₁the compressive strength of the test piece before freeze thawing is MPa;

f₂the compressive strength of the test piece after the freeze-thaw cycle is i times, and is MPa.

Freeze-thaw quality loss rate: the mass loss rate was calculated as in equation (2) to the nearest 0.1%.

In the formula (2), M represents mass loss rate,%;

m₁g is the dried mass of the test piece;

m₂the amount of exfoliated material of the test piece, g.

Influence of melting temperature on the results of the ultra-light concrete frost resistance test:

cracking phenomenon appears in the freeze-thaw process of the test piece which drains for 1h and 6h, and is 150kg/m as shown in FIG. 17³The method has the advantages that the penetrating crack appears after the freeze-thaw cycle of the dry-density ultra-light concrete is carried out for 10 times, and besides the influence of the moisture content of the test piece, the preliminary inference that the test piece cracks can also be caused by overlarge temperature difference between the upper limit and the lower limit of the temperature in the freeze-thaw process. The melting temperature was controlled to 5 deg.C, 15 deg.C and 25 deg.C respectively, and test pieces of 100mm × 100mm × 100mm were used for the test.

The selection of the melting temperature determines the temperature span of the freeze-thaw cycle and directly influences the severity of the freeze-thaw mode of the ultra-light concrete. When the test is carried out at the melting temperature of 5 ℃ and 15 ℃, the cracking phenomenon of the test piece does not occur in the whole freezing-thawing cycle process, the melting temperature is reduced, and the problem of large-scale cracking of the test piece is effectively solved. As shown in FIGS. 18a and 18b, the melting temperature is shown for 150kg/m³And 350kg/m³The influence of the test results of the freezing resistance of the two kinds of dry density ultra-light concrete can be seen from the figure, and 350kg/m³The test result of the dry density test piece has obvious regularity, namely, the strength loss rate and the quality loss rate are increased along with the increase of the melting temperature, and 150kg/m³The freeze-thaw test results of the test pieces with dry density at the three thawing temperatures are not very different. The test piece is atAfter the low-temperature box with the melting temperature of 5 ℃ is melted for 5 hours, the surface of the test piece is frozen and not melted. Therefore, the test method is suitable for carrying out subsequent anti-freezing tests by selecting the melting temperature of 15 ℃.

Influence of the size of the test piece on the result of the ultra-light concrete frost resistance test: the strength of the ultra-light concrete is relatively low, the size of a test piece is properly increased, which is beneficial to reducing the measurement error of the characterization parameters, meanwhile, the ultra-light concrete is used as a material such as a heat insulation board in practical application, the thickness of the test piece is mostly about 70mm, the original standard is that the test piece of 100mm multiplied by 100mm is adopted for testing when testing the frost resistance of the ultra-light concrete, in order to research the influence of the size of the test piece on the frost resistance of the ultra-light concrete, the test pieces of 70mm multiplied by 70mm, 100mm multiplied by 100mm and 150mm multiplied by 150mm are respectively adopted for the test, and the test is carried out according to the test method.

In the whole test process, the test pieces with three sizes are not cracked in the freeze thawing process. 150kg/m in three sizes of 70mm × 70mm × 70mm, 100mm × 100mm × 100mm, and 150mm × 150mm × 150mm as shown in FIG. 19a, FIG. 19b, and FIG. 19c, respectively³The apparent morphology of the dry density test piece after being frozen and thawed for 20 times can be seen from the figure, and the degradation damage degree of the surface of the ultra-light concrete is gradually increased along with the increase of the size of the test piece. The larger the size of the test piece is, the larger the temperature difference between the inside and the outside of the test piece is in the freeze-thaw cycle process, so the larger the stress difference is generated, and the more serious the test piece is damaged. As shown in FIGS. 20a and 20b, the test piece size pair of 150kg/m is shown³And 350kg/m³The influence of the results of the freeze resistance test of the two kinds of dry density ultra-light concrete can be seen in the figure, 350kg/m³The mass loss rate of the dry density small-size test piece is greatly different from that of the large-size test piece, the mass loss of the test piece with the thickness of 70mm multiplied by 70mm and the mass loss of the test piece with the thickness of 150mm multiplied by 150mm after 50 times of freeze-thaw cycle are respectively 0.27 percent and 2.0 percent, and the mass loss rate change trends of the test piece with the thickness of 100mm multiplied by 100mm and the test piece with the thickness of 150mm multiplied by 150mm are basically consistent. As shown in FIG. 21, 150kg/m³As can be seen from FIG. 21, the temperature change curves of the freeze-thaw process of the test pieces with three dry densities have the same central temperature curve change trend and are the sameMeanwhile, the central temperature values of the test pieces with two sizes are not greatly different, and the test pieces with 70mm multiplied by 70mm have obviously higher sensitivity to the external temperature change in the freezing and thawing process. In addition, the test piece of 150mm multiplied by 150mm has the defects of inconvenient operation, easy collision, angle falling and the like in the test pretreatment and freeze-thaw test process, so the test piece of 100mm multiplied by 100mm is more reasonable and feasible to test the frost resistance of the ultralight concrete.

From the above, the mass loss rate and the strength loss rate of the test piece both show a descending trend along with the prolonging of the draining time; the problem of cracking of a test piece can be effectively solved by reducing the melting temperature in the freeze-thaw test; the larger the test piece size, the more severe the freeze-thaw damage. Accordingly, the appropriate draining time, melting temperature and test piece size are respectively determined to be 6h, 15 ℃ and 100mm multiplied by 100mm, and the frost resistance of the ultra-light concrete can be more accurately tested.

The method is realized by adopting the device provided by the embodiment, and the freezing and thawing process of the material in the service environment, particularly the freezing and thawing process of the ultralight concrete in the service environment can be more accurately simulated.

The test device of the test piece can be used for accurately testing the frost resistance of the ultra-lightweight concrete, adjusting freeze-thaw test parameters according to related test requirements, and testing the frost resistance of other materials, such as: cement board, gypsum board, concrete slab, ceramic tile, and the like. In addition, the test device can also be used for researching the frost resistance of plants, such as the cold resistance research of winter wheat.

The present invention will be further described with reference to the following specific examples, which should not be construed as limiting the scope of the invention, but rather as providing those skilled in the art with certain insubstantial modifications and adaptations of the invention based on the teachings of the invention set forth herein.

In the following examples of the present invention, the components referred to are commercially available and the reagents used are commercially available to those skilled in the art unless otherwise specified, and the methods referred to are conventional unless otherwise specified.

Example 1

The device can realize controllable, rapid and high-precision temperature rise rate and temperature drop rate of the box body, and in order to verify the function, the prior refrigerator and the device are respectively selected as research objects in the embodiment 1, the refrigerator and the device are respectively provided with a temperature sensor, and when the placing number of the test pieces is tested and changed, the temperature drop curves of the refrigerator and the device are tested and changed in the freezing process.

The specific implementation steps are as follows:

step 1, placing test pieces (the test pieces have the same mixing ratio and the sizes of the test pieces are 100mm multiplied by 100mm) in a thermostat, setting the temperature of the thermostat to be 15 ℃, and preserving heat for 24 hours to ensure that the initial temperatures of the test pieces are the same;

step 2, respectively placing a temperature sensor in the middle of the refrigerator body and the middle of the refrigerator body of the device, respectively setting the freezing temperature of the refrigerator and the freezing temperature of the device to-15 ℃, respectively placing 12 test pieces in the two devices after the two devices reach the preset temperature, and taking out the test pieces after the two devices reach the preset temperature again;

step 3, after the two devices reach the preset temperature, respectively putting 24 test pieces into the two devices, and taking out the test pieces after the two devices reach the preset temperature again;

after the test is finished, the temperature data measured in steps 2 and 3 are derived and plotted for analysis, and a graph as shown in fig. 11 is obtained.

As can be seen from fig. 11, the cooling rate curves of 12 test pieces and 24 test pieces placed in the device of the present invention coincide, which indicates that the number of test pieces does not affect the overall cooling rate in the box, while the cooling rate curves of 12 test pieces and 24 test pieces placed in the existing refrigerator are separated, which indicates that the number of test pieces affects the overall cooling rate in the box, and it can be seen from the curves that the cooling rate in the device of the present invention is faster and more stable. Therefore, compared with the existing refrigerator, the device provided by the invention can rapidly reach the preset temperature by the double-buffer-tank four-circulation system and the circulation of the box body full-framework antifreeze solution even if the number of the test pieces is changed, and the cooling rate is stable and controllable in the two cooling processes, so that the device provided by the invention has the advantages of extremely high repeated reproducibility, reliability, stability and practicability, and can more accurately simulate the freezing and thawing damage process of the material in the service environment.

Example 2

The device can provide a stable and uniform positive and negative temperature environment for a test sample, and in order to verify the effect, the temperature sensors are respectively arranged at the upper, middle and lower parts of the box body of the device in the embodiment 2, and the temperature difference of the three parts of the box body is measured in the freezing process and the heat preservation process of the test device.

The specific implementation steps are as follows:

step 1, opening a door of a device box, respectively placing three sensors at the upper, middle and lower parts of a box body, wherein the vertical interval of the three sensors is 60cm, the upper and lower sensors are respectively 10cm away from the upper and lower bottom surfaces of the box body, and simultaneously ensuring that probes of the three sensors are not contacted with the inner wall of the box body or a test piece placing frame so as to prevent the influence on a test result;

step 2, closing the door of the device, respectively adjusting the upper limit and the lower limit of the temperature to 15 ℃ and-15 ℃ through a parameter control device, respectively adjusting the freezing time and the melting time to 6h and 4h, and adjusting the heating rate and the cooling rate to 12 ℃/h;

step 3, turning on a temperature acquisition device, starting the three temperature sensors to acquire temperature, and starting the device;

and 4, after the test is finished, deriving temperature data, and performing plotting analysis to obtain a curve chart shown in FIG. 12.

As can be seen from the graph 12, the device promotes the flow of air in the box body through the full skeleton anti-freezing solution circulation of the box body and the upper and lower air outlet pipes, so that the box body can quickly reach the preset temperature, the temperature difference of the temperatures of the upper, middle and lower three points in the box body during a single freeze-thaw cycle is less than 1 ℃, the freeze-thaw test is performed by using the device, a uniform and stable temperature environment can be provided for a test sample, the accuracy and the reliability of the freeze-thaw test are improved, and the test conditions cannot be changed due to different positions of the test piece, so that the device can complete the freeze-thaw test of a plurality of test pieces under the same condition.

Example 3

The invention mainly aims to provide a freezing and thawing test result obtained by using a test device of an air freezing and air thawing system and a test operation method, which can reflect the actual frost resistance of a material.

In this embodiment 3, the device and the method of the present invention are mainly used to test the freeze-thaw damage condition of the ultra-light concrete sample after different times of freeze thawing.

The specific implementation steps are as follows:

step 1, immersing the cut ultra-light concrete test blocks in water for 48 hours, wherein the water is required to submerge at least 30mm of the test block, and turning all the test blocks for one time after immersing for 24 hours to ensure that the test blocks absorb water more uniformly;

step 2, taking out the test piece from the water, placing the test piece on a hollow frame for draining for different time, turning the test piece once every 30min in the draining process to ensure uniform draining, and controlling the water content of the test piece by adjusting the draining time of the test piece, wherein the water content of the ultra-light concrete under different draining time is shown in table 1;

3, wrapping the test piece drained for 6 hours by using a preservative film, sealing the test piece wrapped by the preservative film into a sealing bag at the temperature of (20 +/-5) DEG C and under the environment that the relative humidity is more than or equal to 90 percent, and adjusting the upper and lower temperature limits of a thawing test and the time required by a single thawing cycle through a central control screen according to the test requirements;

and 4, placing the test piece into a test device which is lowered to the lower limit of the set temperature in advance, wherein the distance is more than or equal to 20mm, and recording that the temperature of the device is lowered to the lower limit of the set temperature again as a cycle. Respectively freezing and thawing for 5 times, 15 times, 25 times and 50 times according to the freezing and thawing mode (checking and recording the appearance damage condition of the test piece in the freezing and thawing process every 5 times in a cycling way, if the test piece cracks, taking out the test piece, stopping the freezing and thawing test and recording the number of freezing and thawing cycles);

and 5, respectively testing the strength loss rate and the quality loss rate of the test piece subjected to the specified freeze-thaw cycle number, and processing the data as shown in Table 2.

TABLE 1 Water content of ultra lightweight concrete at different draining times

As can be seen from table 1, the draining time of the test piece has a certain relationship with the water content of the test piece, and therefore, the water content of the test piece can be controlled by adjusting the draining time of the test piece.

TABLE 2 test results of ultra-light concrete samples after different thawing times

As can be seen from table 2, the compressive strength loss rate of the ultralight concrete increased by 4.2% at the early stage of the freeze-thaw cycle because the strength of the cement-based ultralight concrete increased by more than the strength loss at the time of the freeze-thaw damage. After 5 times of freeze-thaw cycles, along with the increase of the number of freeze-thaw cycles, the compressive strength loss rate and the mass loss rate of the ultra-light concrete are increased, because the pore wall structure is damaged by the repeated freezing pressure generated in the freeze-thaw process, the number of communication pores is increased, the strength of the concrete is rapidly reduced, and the peeling amount is increased.

In the description of the present invention, it should be noted that the terms "upper", "lower", "horizontal", "vertical", and the like indicate orientations or positional relationships based on methods or positional relationships shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.

In addition, in the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "connected" and "connected" should be interpreted broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.