RU192382U1 - Laboratory device for simulating the effects of drifting ice on concrete structures - Google Patents

Abstract

The utility model relates to testing equipment, namely, devices for studying the wear resistance of structural materials, in particular concrete, used for the construction of hydraulic structures in the Arctic seas when exposed to drifting ice. The laboratory device contains a rigid platform for fastening the entire device design, a hydraulic cylinder located on the same axis, which generates a force sufficient to break the ice, a guide tube with an extruder at the outlet end and a strain gauge that measures the force of interaction of ice with the test surface, and a holder located on the rigid platform sample, providing an adjustable angle of ice flow to the surface, and the device is configured to be installed in a thermally insulated refrigeration the camera. Effect: providing the possibility of studying abrasive friction pairs such as concrete and ice with the destruction of the latter when interacting with concrete. 1 ill.

Description

Laboratory device for simulating the effects of drifting ice on concrete structures

The utility model relates to testing equipment, namely, devices for studying the wear resistance of structural materials, in particular concrete, used for the construction of hydraulic structures in the Arctic seas when exposed to drifting ice.

The reliability of stationary offshore structures such as lighthouses, mooring walls, etc., operating at low temperatures and the impact of drifting ice on them, is largely determined by the wear resistance of structural materials, in particular concrete, used for the manufacture of such structures.

The relevance of the research topic is determined by the need to develop hydrocarbon reserves on the shelf of the oceans as a result of the gradual depletion of deposits on land and the growing demand of industry for energy. In turn, the development of oil and gas deposits on the continental shelf of the arctic seas is the most important economic problem that determines the development of the fuel and energy complex of Russia.

A significant part of the Russian shelf is located in the cold Arctic and Far Eastern seas, which are characterized by severe climatic conditions and the presence of drifting ice cover. Under these conditions, the main factor affecting the reliability of offshore ice-resistant platforms is the ice regime of the water area in the construction area and, as a result, ice loads and impacts on the structure. One of such effects in water areas with a dynamic regime of ice drift is the abrasive effect of ice due to the interaction of ice formations with the surface of hydraulic structures, especially in the area of variable sea level.

When ice moves relative to the structure, surface erosion and abrasive destruction of the body material occur. The reason for the destruction of the surface of reinforced concrete structures from the abrasive effects of ice formations is associated with the occurrence of significant pulsating pressures in the zone of contact of concrete with drifting ice cover.

Ice crystals are a good abrasive, which helps to gradually reduce the cross section of the structure. Due to high contact pressures, the destruction of the cement stone occurs, which leads to an increase in porosity, loss of aggregate and a decrease in the strength of concrete, and the environmental effect caused by freeze-thaw cycles contributes to the gradual weakening of binders and aggregates of the surface layer and leads to its destruction.

Known equipment for determining the wear resistance of concrete with ice at low temperatures.

For example, an installation for the study of ice abrasion of materials was developed and manufactured in the LLC NPO Gidroteks company under the guidance of prof. A.T. Becker, http://www.vniig.rushydro.ru/upload/iblock/48c/Dissertatsiya_Uvarova_15.12.14.pdf, Thesis by Uvarova T.E. “The abrasive effect of drifting ice cover on offshore hydraulic structures”, p. 90.

The installation is located in a thermally insulated chamber in which a low temperature is maintained (up to -20 ° C), and allows you to press a sample of the test concrete to the surface of the ice block with a force of up to 1000 kg and tell it reciprocating motion at a speed of 1 m / s.

After performing a given number of cycles of reciprocating movement, the concrete sample under study is extracted outside and its degree of wear is assessed.

The disadvantage of this technical solution, in which the studied concrete and ice move parallel to each other, is the significant difference between the dynamics of the interaction of concrete and ice from the real dynamics of the interaction of a moving ice field with concrete structures, in which the movement of ice and concrete occurs at an angle sometimes even at right angles, and at the moment of interaction with the concrete barrier, the ice is destroyed, subjecting the concrete to a pulsed load.

Known GOST 13087-81. Concrete Methods for determining abrasion. This GOST recommends certain types of testing equipment for determining the abrasion of concrete, which, in principle, can also be used for testing the abrasion of concrete with ice. The standard applies to all types of concrete used in all areas of construction. The standard establishes methods for determining the abrasion of concrete with an abrasive on the abrasion circle (for concrete of road structures, floors, stairs and other structures.

Also known patent No. 2542612 "Installation for the study of a sample of material for ice abrasion"

The invention relates to techniques for mechanical testing of materials for abrasion resistance and can be used for ice abrasion testing.

The design of the apparatus for researching a sample of material for ice abrasion contains a base on which a horizontal platform is placed, configured to move an ice sample relative to a sample of abradable material fixed in a means for holding it, and means for pressing them against each other. The device further comprises a knife configured to profile the surface of the ice sample in contact with the abradable sample. The knife contains a vertical guide through which, with the possibility of reciprocating motion, a rod is passed, at the end of which a cutting plate is fixed, the cutting edge of which, facing the ice sample, is made U-shaped. The rod is equipped with a protrusion on which a rod is fixed parallel to the longitudinal axis of the rod, the lower end of which is pivotally attached to the supporting ski. The rod is spaced from the rod relative to the direction of movement of the sample, while the cutting insert is configured to adjust the position of its edge relative to the supporting surface of the supporting ski. The upper end of the rod is made with the possibility of placing additional load on it.

The technical result is the provision of a stable contact area of rubbing materials and an increase in the bearing capacity of ice due to its cutting with a knife on both sides.

All of the above technical solutions are suitable only for the study of wear in the conditions of shockless interaction of concrete and ice (or any other abrasive pair), such as, for example, the impact of car tires on the roadway, or the wear of the stairs of a railway station with a large flow of passengers, etc. .

A significant difference between the mechanism of interaction of concrete and ice with the help of all the above devices, in which ice and concrete move parallel to each other, in which the ice does not break down, but gradually wears out, from the dynamics of the interaction of a real moving ice field with concrete structures, at which at the moment of interaction at an angle with an obstacle, ice always breaks up, subjecting concrete to a pulsed load, is a common drawback of all the technical solutions mentioned above without exception.

According to the applicant, in order to simulate in laboratory conditions the interaction of drifting ice on an obstacle in the zone of interaction of concrete and ice, the forces should be directed at an angle or even normal and sufficient to break the ice with squeezing the products of its destruction along the surface of the concrete with the following portions of ice.

As a prototype, the device selected from the application for invention No. 94021945 "Method for cleaning the hull and device for its implementation." In this method, the hull is cleaned by feeding (at an angle or normal) to the surface of the hull of the working medium under pressure, and ice crumb obtained by pre-cooling the water jet with subsequent throttling in an expanding nozzle is used as the working medium. The proposed device has a water supply installation, including a high-pressure unit and a feeding apparatus, connected by a pipeline with valves, while the installation is mounted on a movable base. The difference is that the water additionally enters a cooler connected in parallel with the pipeline with valves, and the supply device has the form of a supersonic expanding nozzle.

The disadvantage of this device is that ice crumb is delivered to the treated surface, and not ice monolith, which is destroyed only when interacting with the treated surface, which, as in the above technical solutions, does not correspond to the real dynamics of the interaction of crumbling ice with a hard surface.

The proposed utility model provides the following technical result - providing the opportunity to study abrasive friction pairs such as concrete and ice, with the destruction of the latter when interacting with concrete, using a device to simulate the effects of drifting ice on concrete structures.

The technical result is achieved by the fact that in the device for the influence of water ice supplied under pressure on the treated surface, as proposed in application No. 94021945, ice at an arbitrary angle to the treated surface of the test sample using a mechanism comprising a hydraulic cylinder located on the same axis, which creates a force sufficient to break the ice, a guide tube with an extruder at the outlet end and a strain gauge are continuously supplied in the form of a monolith cut from previously frozen ice, which, when contact with the test concrete sample is destroyed, and the destroyed ice along with the erosion products on the surface of the concrete is pushed out of the sample under the pressure of the following portions of ice, the force with which ice is forced through the guide tube with the extruder and interacts with the test surface is measured using a tensometer, moreover, the test sample is fixed in a holder that provides an adjustable angle of ice flow to the surface, and the whole process is carried out in a heat-insulated chamber with a reduced temperature atura.

A laboratory device for simulating the effects of drifting ice on concrete structures, including a device for applying water ice supplied under pressure on the surface to be treated, characterized in that the ice is at an arbitrary angle to the surface of the test sample using a mechanism including a hydraulic cylinder located on one axis, creating a force sufficient to break the ice, guiding the pipe with an extruder at the output end and a strain gauge, is continuously supplied in the form of a monolith, cut out o from pre-frozen ice, which, when contacted with the concrete sample being tested, is destroyed, and the destroyed ice along with erosion products on the surface of the concrete is pushed out of the sample under the pressure of the following portions of ice, the force with which ice is forced through the guide tube with the extruder and interacts with the investigated surface, it is measured using a tensometer, and the test sample is fixed in the holder, providing an adjustable angle of ice flow to the surface, and the whole process is carried out in a thermally insulated chamber with a temperature lower than zero degrees.

The design of the proposed device is shown in figure 1.

In Fig. 1, an ice monolith 1 by a rod 2 of a hydraulic cylinder 3 (the oil station with which the hydraulic cylinder is set in motion, not shown in the diagram) is sent through the guide pipe 4 to the test sample 5, mounted in the holder 6 with the possibility of adjusting the angle and distance from the cut guide pipe using fasteners and thrust elements 7. The output part 8 of the guide pipe is a removable part - an extruder, which can be attached to any configuration. The whole structure is attached to a rigid platform 9. The load cell 10 controls the force with which ice is forced through the guide tube and interacts with the test sample. In the zone of interaction of ice 11 with the sample, ice is destroyed and expelled to the sides outside the sample. The entire device is located in a thermally insulated refrigerating chamber 11, in which a low temperature is maintained using a refrigeration unit (not shown in the diagram). When the ice in the guide cylinder ends, the hydraulic cylinder rod is pushed back, the hydraulic cylinder leans up, a new ice monolith is inserted into the guide pipe, and the test continues.

The essence and operation of the utility model is illustrated by the example of the device depicted above in figure 1.

A sample of test concrete 5 in the form of a cube 70x70x70 mm (all surfaces of concrete are pre-ground and can be treated with ice alternately) are installed in holder 6, which, in turn, is fixed with the help of embedded stop elements (as a rule, the angle is 45 ° to axis of the structure) at a distance of 25 mm (half the thickness of the ice monolith) from the front plane of the extruder 8.

The extruder 8 is made so that its plane facing the inclined concrete sample is parallel to its surface.

An ice monolith cut from a pre-frozen liquid and processed to the desired size, which may be frozen pure water or a salt solution simulating sea water, and, in particular, may include abrasive additives such as sand, clay, etc., is installed in the guide tube 4. . In our case, the ice monolith has a square section of 50x50 mm and a length of 400 mm.

The ice monolith by the rod 2 of the hydraulic cylinder 3 is brought into contact with the concrete surface at the lower point. All these manipulations are performed directly in the refrigerating chamber 11 at an air temperature in it of -10 ... -15 ° C, since it is important to prevent ice from melting and freezing it to the guide tube during subsequent cooling to operating temperature (up to -40 ° C), otherwise, the frozen ice monolith will be completely destroyed by the rod in the guide tube. After loading another ice sample, the air in the refrigerator is cooled to a predetermined temperature, held for 10-20 minutes, so that all the details of the mechanism, ice and a concrete sample acquire a predetermined temperature, after which the hydraulic cylinder rod is moved at a speed of 2-10 mm / s. The ice monolith begins to collapse upon contact with the surface of the concrete sample, and the products of ice destruction, small crumbs and individual pieces of ice up to 1 cm are squeezed out to the sides, mainly towards the slope of the sample (up in Fig. 1). The load cell detects a random pulsating force at this time with a spread from almost 0 to 1200 kg. A characteristic crisp sound is heard with individual strokes and clicks.

If you reduce the distance from the surface of the concrete sample to the cut of the extruder or reduce the angle of inclination of the sample, the force recorded by the strain gauge increases to the extent that it exceeds the allowable force for this type of strain gauge (3000 kg). When approaching the angle of inclination of the surface of the sample to the perpendicular to the axis of the device to 20 degrees or less, the ice completely stops moving at any effort available for this device. You can choose the right hydraulic cylinder and strain gauge and make the ice still move (at very high pressures of ~ 100 MPa, the ice becomes plastic, due to which the glaciers in the mountains move down), but in real Arctic conditions, to simulate which this device was created, such high pressures do not arise in the interaction zone between ice and concrete structures, since the strength of uniaxial compression of ice does not exceed 1-1.5 MPa. (10-15 kg / cm ² ).

After the full development of the ice monolith, the hydraulic cylinder rod is retracted, the hydraulic cylinder is thrown up, a new monolithic piece of ice is inserted into the guide tube, the destroyed ice that has accumulated on the periphery of the concrete sample is removed, and the whole procedure is repeated up to 10 times. That is, up to 4 meters of an ice monolith passes through the zone of interaction with a concrete sample. The total duration of such processing with stops for loading new portions of ice can reach 2-3 hours.

At the end of 10 cycles, the concrete sample is removed from the holder, cleaned of ice, washed, dried and the degree of wear of the concrete surface is assessed using a micrometer indicator of the clock type IC.

The wear zone is a region of approximately elliptical shape measuring 50x60 mm, elongated along the direction of inclination of the sample. The maximum wear depth in the center of the zone reaches 0.2-0.3 mm (after passing 4 meters of ice monolith). In some cases, the separation of individual grains of the filler was observed. To the edges of the wear zone, the depth decreases to 0. The relief of the wear zone is uneven and is determined by the position of the aggregate granules, whose hardness is higher than the hardness of cement stone.

If the processing depth is insufficient for measuring with a micrometer indicator, the entire procedure of 10 runs of ice monoliths 400 mm long each is repeated.

On one cubic sample of concrete, in which all faces are ground, it is possible to conduct ice tests 6 times.

Using the device, it is possible to study the interaction of ice not only with the flat surface of the sample, but also with cylindrical concrete samples, for which it will be necessary to manufacture an extruder of the appropriate shape.

Comparison of the test results of a flat concrete surface with ice using the above-described devices, providing shockless abrasion with the movement of the contacting pairs parallel to each other, with the results of studies using the proposed device, which exposes the concrete to a pulsed load due to ice breaking, show that in the latter case, wear concrete at times exceeds the wear of a soft impact, up to tearing out grains of the filler.

Claims (1)

A laboratory device for simulating the effects of drifting ice on concrete structures, characterized in that it contains a rigid platform for fastening the entire structure of the device, a hydraulic cylinder located on the same axis, creating a rod sufficient for breaking ice, a guide tube with an extruder at the output end and a strain gauge measuring force ice interaction with the test surface, as well as a sample holder located on a rigid platform, providing an adjustable angle of ice flow to the surface, moreover, the device is configured to be installed in a thermally insulated refrigeration chamber.

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