LU500946B1

LU500946B1 - A Concrete Permeability Test Device and Test Method for Eliminating Horizontal Circumferential Pressure

Info

Publication number: LU500946B1
Application number: LU500946A
Authority: LU
Inventors: Zheng Liu; Tianyu Cao; Hongyu Zhang; Yi Xia; Chengfeng Wei; Yitian Qiu; Jianmin Du; Meng Wang
Original assignee: Univ China Mining
Priority date: 2021-12-02
Filing date: 2021-12-02
Publication date: 2022-06-02

Abstract

A concrete impermeability test device and test method for eliminating horizontal circumferential pressure, it has a device in which the upper section of the outer side wall of the steel mold is provided with an external threaded section, a limit adjustment mechanism includes a rotating steel sleeve, a connecting rod and a steel washer, the rotating steel sleeve includes an upper top plate and a cylindrical enclosure, the inner wall of the enclosure is provided with an internal threaded section, the steel washer is coaxially set inside the steel mold, a plurality of connecting rods are fixed on the steel washer, and the other end of the connecting rod is fixedly connected to the lower end surface of the upper top plate, it is the method of fixing the steel washer set in the upper part of the center of the mold cavity with the same axis of the steel mold, the steel washer is used to limit the height of the upper end surface of the specimen, the surface of the specimen is coated to form a sealing layer and loaded into the steel mold, the steel mold is connected to the impermeability device, the pressure is set and the test is carried out, after the test is finished, the specimen is cut open and the water seepage is observed, which can effectively eliminate the action of horizontal circumferential pressure and objectively accurately obtain the actual impermeability of concrete, improve the efficiency and accuracy of the test, make the stress and water seepage distribution of the specimen more uniform during the test, and make the test closer to the actual working conditions.

Description

A Concrete Permeability Test Device and Test Method for Eliminating Horizontal ~~ LU500946 Circumferential Pressure

FIELD OF THE INVENTION

[0001] The present invention relates to a concrete impermeability test apparatus and test method for eliminating horizontal circumferential pressure in the technical field of concrete experiments.

BACKGROUND OF THE RELATED ART

[0002] The impermeability of concrete is a fundamental property of concrete, which is particularly important in underground works or other engineering structures with impermeability requirements. This performance is tested using impermeability testing equipment through impermeability testing. Commonly used impermeability testing equipment for HP-4.0 type concrete impermeability device, mainly by the rack test mold, separator, water pump, water storage tank and electrical control device, using the principle of equal pressure at each place of the sealed container and its connected piping system, the pump pressure, and through the intelligent CNC table to maintain the pressure within the specified range to test.

[0003] The frame test mold (steel mold) is a cone-shaped sleeve structure without top cover, and its inner diameter gradually becomes smaller from the bottom to the top, and during the concrete impermeability test with the existing frame test mold, the water pressure is applied from the bottom to the top along the axis of the test piece, and in the vertical direction according to the force balance condition, the vertical downward component of the pressure between the concrete test piece and the steel mold is balanced with the upward water pressure. Angle is very small, so to balance the upward water pressure will require a great pressure between the concrete and the steel mold, and the horizontal component of this pressure will be applied to the concrete impermeable test block in the circular direction, resulting in a large horizontal compressive stress on the impermeable concrete test block.

[0004] Due to the presence of the horizontal annular pressure effect, the vertical pores and voids of concrete are compressed, resulting in a great increase in the impermeability of the concrete of the impermeable test block, which in turn will overestimate the impermeability of the concrete, while the concrete in the actual project does not have this horizontal annular pressure, the actual impermeability of the concrete is much less than the experimentally derived impermeability, so there is a large safety hazard in engineering applications, and water seepage in concrete structures is common.

SUMMARY OF THE INVENTION

[0005] In view of the above problems of the prior art, the present invention provides a concrete 1 impermeability test device and test method that eliminates horizontal circumferential pressure, LU500946 the device and method can significantly eliminate horizontal circumferential pressure, improve test efficiency and accuracy, make the stress and water seepage of the specimen in the test process more uniformly distributed, objectively and accurately obtain the actual impermeability of concrete, and the test results obtained are more reliable.

[00086] In order to achieve the above purpose, the present invention provides a concrete impermeability test device for eliminating horizontal circumferential pressure, comprising a steel mold and a limit adjustment mechanism, the steel mold has an inner cavity having the same taper as the test piece, upper section of the outer side wall of the steel mold is a straight wall section, and an external threaded section is provided on the straight wall section;

[0007] The limit adjustment mechanism comprising a rotating steel sleeve, a connecting rod and a steel washer, rotating steel sleeve comprising an upper top plate and a cylindrical enclosure plate enclosing the outer circumference of the upper top plate and extending downwardly, the inner wall of the enclosure plate being provided with an inner threaded segment that fits into the outer threaded segment.

[0008] The steel washer is coaxially set inside the steel mold, and a plurality of connecting rods are fixed on the steel washer, and the plurality of connecting rods are arranged circularly and equidistantly with the axis of the steel mold as the center; the other end of the connecting rod is fixedly connected to the lower end surface of the upper top plate.

[0009] A through-hole is provided at the center of the upper top plate.

[0010] The connecting rods are provided with 6.

[0011] Compared with the prior art, this test device can make the lower end surface of the steel washer closely contact with the upper end surface of the specimen during the test by setting a height-adjustable steel washer inside the steel mold, so that the test specimen can be jacked up during the impermeability test to play a limiting role, greatly reduce and eliminate the horizontal circumferential pressure effect, can make the stress and seepage water distribution of the specimen during the test more uniform, can accelerate the speed of the seepage water so that the seepage surface is horizontally distributed, thus objectively and accurately obtaining the actual impermeability of concrete and improving the test validity and accuracy.

[0012] A method for testing concrete impermeability by eliminating horizontal circumferential pressure, comprising the following steps:

[0013] S1: The test solution is injected into the water tank of the impermeability device to remove excess air from the impermeability device.

[0014] S2: A steel washer fixed in the upper part of the center of the cavity of the steel mold on the same axis as the steel mold, the steel washer being used to define the height of the upper end face of the specimen.

2

[0015] S3: The outer circumference of the formed and maintained specimen is uniformly LU500946 coated with a sealing material to form a sealing layer and is loaded into a steel mold, and then weighed for an initial total weight T1.

[0016] S4: The steel mold containing the specimen is fixedly attached to the test platform of the impermeability device.

[0017] S5: The water pressure for loading is set, and the pressure is pressurized at once to reach the set pressure, and the valve of the corresponding test piece is opened for the impermeability test.

[0018] S6: After a period of time, the valve corresponding to the test piece is closed, the steel mold containing the test piece is removed, a subsequent weighing of the total weight T2 is performed, and the total percolation weight T3 is calculated from T2-T1 and recorded.

[0019] S7: The specimen is removed from the steel mold, and the specimen is dissected with a pressure tester to form a cross-section, and the water penetration height is measured and recorded.

[0020] The test solution is either water or one of various salt solutions.

[0021] In this test method, by adding a steel washer to the steel mold to limit the rise height of the specimen and keeping the loaded water pressure constant during the test, analytical data are provided for the water penetration of concrete at different pressurization durations under the same pressure conditions, and since the use of the steel mold with this limiting device eliminates the horizontal circumferential pressure to which the concrete impermeable specimen is subjected, it can objectively and accurately obtain the actual seepage performance of the concrete, and it can play a key role in improving the test validity and accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic diagram of a three-dimensional structure of the present invention.

[0023] FIG. 2 is a longitudinal section of FIG. 1.

[0024] FIG. 3 is a schematic diagram of water penetration in longitudinal sections of specimen | after testing using an existing steel mold at 1.2 MPa pressure.

[0025] FIG. 4 is a schematic diagram of water penetration in longitudinal sections of specimen II after testing using an existing steel mold at 1.2 MPa pressure.

[0026] FIG. 5 is a schematic diagram of water penetration in longitudinal sections of specimen II! after testing at 1.2 MPa pressure using an existing steel mold.

[0027] FIG. 6 is a schematic diagram of water penetration in longitudinal sections of specimen IV after testing at 1.2 MPa pressure using an existing steel mold.

[0028] FIG. 7 is a schematic diagram of water penetration in longitudinal sections of specimen V after testing at 3.6 MPa pressure using an existing steel mold. 3

[0029] FIG. 8 is a schematic diagram of water penetration in longitudinal sections of specimen LU500946 VI after testing at 3.6 MPa pressure using an existing steel mold.

[0030] FIG. 9 is a schematic diagram of water penetration in a longitudinal section of a specimen after testing using an existing steel mold.

[0031] FIG. 10 is a schematic diagram of water penetration in a longitudinal section of another specimen after testing using the steel mold in the present invention.

[0032] FIG. 11 is a schematic diagram of a contact extrusion model of an existing steel mold using finite element analysis software.

[0033] FIG. 12 is a cloud of the horizontal compressive stress distribution inside the concrete specimen obtained by numerical simulation in a conventional steel mold under 3.6 MPa water pressure.

[0034] In the figure: 1, steel mold, 2, external thread section, 3, limit adjustment mechanism, 4, rotating steel sleeve, 5, connecting rod, 6, steel washer, 7, upper top plate, 8, enclosure plate, 9, internal thread section, 10, through hole.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention is further described below with examples.

[0036] As shown in FIGS. 1 and 2, a concrete impermeability test device for eliminating horizontal circumferential pressure, comprising a steel mold 1 and a limit adjustment mechanism 3; the steel mold 1 has an internal cavity with the same taper as the test piece, the upper section of the outer side wall of the steel mold 1 is a straight wall section, and an external thread section 2 is provided on the straight wall section.

[0037] The limit adjustment mechanism 3 comprises a rotating steel sleeve 4, a connecting rod 5 and a steel washer 6, rotating steel sleeve 4 comprising an upper top plate 7 and a cylindrical enclosure 8 enclosing the outer circumference of the upper top plate 7 and extending downwardly, the inner wall of the enclosure 8 being provided with an internal thread section 9 cooperating with the external thread section 2.

[0038] The steel washer 6 is coaxially set inside the steel mold 1, and a plurality of connecting rods 5 are fixed on the steel washer 6, and the plurality of connecting rods 5 are arranged at equal intervals in a circular shape centered on the axis of the steel mold 1; the other end of the connecting rod 5 is fixedly connected to the lower end surface of the upper top plate 7.

[0039] To facilitate observation as well as adjustment of the steel washer 6, a through-hole 10 is opened in the center of upper top plate 7, and the diameter of the through-hole 10 can be 20 mm.

[0040] In order to avoid the weakening of the local load-bearing capacity of the steel washer 6 by the centralized setting of the connecting rod 5, the connecting rod 5 is provided with 6 units.

4

[0041] The preferable inner ring radius of the steel washer 6 is 40 mm and the preferable LU500946 outer ring radius is 70 mm. The thickness of the steel washer 10 is preferably 16 mm.

[0042] The present invention also provides a method for testing concrete impermeability by eliminating horizontal circumferential pressure, comprising the following steps:

[0043] S1: The test solution is injected into the water tank of the impermeability device to remove excess air from the impermeability device.

[0044] S2: A steel washer coaxially with the steel mold 1 is fixed in the upper part of the center of the mold cavity of the steel mold 1, and the steel washer 6 is used to define the height of the upper end surface of the specimen.

[0045] S3: The outer circumference of the formed and maintained specimen is uniformly coated with a sealing material to form a sealing layer and is loaded into the steel mold 1, and then weighed for an initial total weight T1.

[0046] S4: The steel mold 1 containing the test specimen is fixedly attached to the test platform of the impermeability device.

[0047] S5: The water pressure for loading is set, the pressure is pressurized at once to reach the set pressure, the valve of the corresponding test piece is opened and the impermeability test is carried out.

[0048] S6: After a period of time, the valve corresponding to the test piece is closed, the steel mold 1 containing the test piece is removed, a subsequent weighing of the total weight T2 is performed, and the total percolation weight T3 is calculated from T2-T1 and recorded.

[0049] S7: The test specimen is removed from the steel mold 1, and the test specimen is dissected with a pressure tester to form a cross section, and the water penetration height is measured and recorded.

[0050] In S2 the height of the steel washer 6 in the cavity of the steel mold 1 can be adjusted.

[0051] The specific process of S3 is as follows: the shaped specimen is removed from the curing chamber the day before the test and heated to 35°C to 45°C together with the steel mold 1. Atthe same time, the sealing material for sealing is heated until it is completely melted to form a sealing solution, and then the circumferential surface of the specimen is rolled uniformly in the sealing solution to form a uniform sealing layer, and then the specimen is pressed into the steel mold 1.

[0052] The sealing material is preferably paraffin wax, which becomes a liquid when heated and dissolved, and solidifies at room temperature with good sealing performance, in addition the solid paraffin wax is stable and difficult to react with other substances; the sealing material can also be a mixture of paraffin wax and rosin, or a mixture of butter and sodium polyacrylate absorbent resin.

[0053] According to the requirements for the test solution in the impermeability test, the test solution is water or one of various salt solutions, as a preference, 10% sodium sulfate solution 5 is used. LU500946

[0054] Validation analysis:

[0055] Under 1.2 MPa pressure, four specimens with the same water-cement ratio and the same conditions were subjected to the same batch and the same duration of water infiltration experiments using the existing steel mold, and the water infiltration heights of the four specimens are shown in Figures 3 to 6, and the height of water penetration varies under the same pressure. Under the same permeation time, they are roughly distributed in “U” shape. The specimen shown in Fig. 6 shows that there is almost no water penetration in the central part. The water seepage height in the central part of the specimen shown in Figure 5 also reached only 1. 5 to 2 cm. The shape of the water penetration height was found to be related to the height of the specimen being jacked up in the process of impermeability, with the increase of the jacking height, the water penetration height of the specimen decreased, and the U-shaped distribution of the water penetration curve became more and more obvious.

[0056] Under the pressure of 3.6 MPa, two specimens made with the same water-cement ratio and the same conditions were subjected to the same batch of water penetration experiments of equal duration using the existing steel mold, as shown in Figures 7 and 8 of the accompanying drawings of the specification, when the rise height of the specimen reached more than 2 cm, the upper surface of the specimen had protruded from the steel mold and the specimen showed the phenomenon of delamination damage.

[0057] In order to simulate the force process of the test block in the rising process of water pressure, the contact extrusion model shown in Figure 11 can be established with the help of ANSYS finite element analysis software: where the lower boundary of the steel mold is fixed, the surface-to-surface contact is set between the test block and the steel mold, and the water pressure is applied on the bottom surface of the test block. The main model parameters are shown in Table 1.

[0058] Table 1 Fitted parameters for existing steel mold FEA

[0059] on (a Expression ers 25 E, Young's Modulus of Concrete | =| Ci [eee 5 x 10°[Pa] | steel 6

Paramet LU500946 gs ers Poisson’s ratio of structural

[0060] The results obtained by numerical simulation are as follows:

[0061] As shown in Figure 12 ofthe accompanying drawings, the concrete test block produces a large horizontal compressive stress under the action of horizontal circumferential pressure, and it can be seen from Figure 12 that the compressive stress gradually increases from the upper to the lower part of the concrete test block, and the lowermost horizontal compressive stress can reach more than 20 MPa, and the distribution of the compressive stress in the lower part of the concrete test block also shows a compressive stress distribution with a large middle and small periphery. This corresponds to the distribution pattern of water seepage height in Fig. 3 to Fig. 6, because the concrete in the lower part of the concrete test block has a large horizontal compressive stress under the action of horizontal circumferential pressure, and the horizontal compressive stress compresses the vertical pores, voids and microcracks inside the concrete test block, which hinders the infiltration of water or solution to the upper part; while the horizontal compressive stress at the edge of the test block is relatively small, so the water seepage height is larger. Therefore, the obtained seepage height curves are “U” type distribution.

[0062] Figure 9 shows the water penetration in the longitudinal section of a specimen after a test using an existing steel mold, and it can be seen that the normal water penetration in the middle of the specimen in Figure 9 is seriously affected by the circumferential pressure. And after using the test device of the present invention, the vertical upward water pressure is no longer balanced by the vertical component of the vertical pressure of the steel mold on the concrete specimen, but directly or mostly by the upper limit device, so the horizontal circumferential pressure inside the concrete is eliminated, and the concrete is no longer subjected to compressive stress in the horizontal direction internally, and the vertical pores, voids and microcracks of the concrete maintain their original size and are no longer compressed, so the seepage height curve is basically horizontal (see Figure 10), and the water infiltration rate is also greatly improved compared with the original impermeable device.

[0063] It can be seen that the conventional impermeability test device results in significantly higher measured concrete impermeability due to the presence of horizontal circumferential pressure. It was also found through the research of the inventors that there are few phenomena of unsatisfied impermeability in concrete impermeability testing. In contrast, the problem of water seepage in underground concrete structures abounds in actual projects. This 7 is directly related to the inherent defects of the traditional impermeability test device. With the LU500946 present invention, the actual impermeability of concrete can be obtained only after the influence of horizontal circumferential pressure is eliminated, and the hidden danger of water penetration in the project is eliminated.

8

Claims

1. A concrete impermeability testing device for eliminating horizontal circumferential LU500946 pressure, comprising a steel mold (1) having an inner cavity having the same taper as the test piece, characterized in that it also includes a limit adjustment mechanism (3); called upper section of the outer side wall of the steel mold (1) is a straight wall section, and an external thread section (2) is provided on the straight wall section; the called limit adjustment mechanism (3) includes a rotating steel sleeve (4), a connecting rod (5) and a steel washer (6), called rotating steel sleeve (4) comprising an upper top plate (7) and a cylindrical enclosure (8) enclosing the outer circumference of the upper top plate (7) and extending downward, the inner wall of the enclosure (8) being provided with an internal thread section (9) cooperating with the outer threaded section (2); the steel washer (6) is coaxially set inside the steel mold (1), and a plurality of connecting rods (5) are fixed on the steel washer (6), the plurality of connecting rods (5) being centered on the axis of the steel mold (1). (The other end of the connecting rod (5) is fixedly connected to the lower end surface of the upper top plate (7).

2. A concrete impermeability test device for eliminating horizontal circumferential pressure according to claim 1, characterized in that upper top plate (7) is opened with a through hole (10) at the center.

3. A concrete impermeability test device for eliminating horizontal circumferential pressure according to claim 1 or 2, characterized in that connecting rods (5) are provided with 6 units.

4. A method for testing concrete impermeability by eliminating horizontal circumferential pressure, characterized in that it comprises the following steps: S1: The test solution is injected into the water tank of the impermeability device to remove excess air in the impermeability device; S2: The steel washer is fixed coaxially with the steel mold (1) in the upper part of the center of the mold cavity of the steel mold (1), and the steel washer (6) is used to limit the height of the upper end surface of the test piece; S3: The outer circumference of the formed and maintained specimen is evenly coated with sealing material to form a sealing layer, and is loaded into the steel mold (1), and then the initial total weight T1 is weighed, S4: The steel mold (1) with the specimen is fixedly connected to the test platform of the impermeability device; S5: The water pressure of the load is set, and the pressure is pressurized to the set pressure at once, and the valve of the corresponding specimen is opened for the impermeability test; SE: After a certain period of time, close the valve of the corresponding test piece, remove the steel mold (1) containing the test piece, carry out the subsequent weighing of the 9

CLAIMS total weight T2, calculate the total seepage weight T3 by T2-T1 and record; LU500946 S7: Remove the test piece from the steel mold (1), and use the pressure tester to cut open the test piece to form a section, measure the seepage height and record.

5. A method for testing the permeability of concrete by eliminating horizontal circumferential pressure according to claim 4, characterized in that test solution is one of water or various salt solutions.