A UHPC-NC specimen, processing mold, processing method and application

Abstract

The present invention relates to a UHPC-NC specimen, a processing mold, a processing method and an application, belonging to the technical field of building material performance testing. Aiming at the problems of the current research on the static mechanical properties of the UHPC-NC interface bonding performance and the influence of the interface morphology on the repair effect, the mold of the present invention includes a base, a assembled cylindrical barrel, an upper cover and an interface partition. A circular boss is arranged in the middle of the base, the assembled cylindrical barrel is arranged on the outer periphery of the circular boss, the interface partition is vertically inserted into the middle of the assembled cylindrical barrel, and the upper cover is buckled on the top of the assembled cylindrical barrel. By using this mold to fabricate UHPC-NC specimens with different interface morphologies, then conducting freeze-thaw cycle erosion tests on the UHPC-NC specimens with different interface morphologies, testing their dynamic mechanical properties under freeze-thaw damage, calculating their dynamic splitting tensile strength, and providing a theoretical basis and technical support for the application of UHPC-NC composite structures in practical engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of performance testing of building materials, and particularly relates to a UHPC-NC specimen, a processing mold, a processing method and an application. Background Art

[0002] In civil engineering applications, the durability and safety of concrete structures are crucial. Due to its excellent mechanical properties and durability, UHPC has the potential to become a repair material and is widely used in the field of repair and reinforcement of damaged engineering materials. By combining ultra-high performance concrete (UHPC) with normal concrete (NC) to form a new UHPC-NC material, the original damaged material can be repaired. However, after the repair and reinforcement of the concrete structure, the bonding interface between UHPC and NC is often a weak area, which is a key index for evaluating the bonding quality of new and old concretes.

[0003] In the western region, freeze-thaw cycle is one of the important factors affecting the bonding strength of the interface between new and old concretes. The concrete structures in cold regions are vulnerable to the action of freeze-thaw cycles, resulting in cracks inside the concrete, degrading its mechanical properties and affecting the bonding effect of the interface between new and old concretes. The degree of influence of freeze-thaw cycles on the concrete performance is related to multiple factors such as low temperature and concrete water content. Therefore, during construction in cold regions, the influence of freeze-thaw cycles on the concrete performance and interface bonding strength should be fully considered, and corresponding measures should be taken to improve the frost resistance and bonding strength of the concrete.

[0004] Therefore, it is very necessary to actively carry out the mechanical property test of UHPC-NC after combination under the action of freeze-thaw cycles, which can serve as the theoretical basis for later application in the freeze-thaw cycle environment. However, the existing research on the bonding performance of the UHPC-NC interface mainly focuses on static mechanical properties, and there is still a lack of dynamic performance test methods for the bonding performance of the UHPC-NC interface. The concrete structures in alpine regions will be subjected to dynamic loads such as explosion and impact during service. After the concrete structure is damaged, high-performance materials are usually used to repair the damaged parts. At present, the static mechanical property research method cannot evaluate the dynamic splitting tensile strength of the interface after damage repair in the freeze-thaw environment, and there is no research showing which type of interface morphology has better mechanical repair effect. Summary of the Invention

[0005] Aiming at the deficiencies existing in the above-mentioned prior art, the purpose of the present invention is to provide a UHPC-NC specimen, a processing mold, a processing method and an application. Based on the requirements of the Brazilian disc splitting test, UHPC-NC specimens with different interface morphologies and circular cross-sections are fabricated by the processing mold of the present invention. After the UHPC-NC specimens are eroded in a set freeze-thaw cycle environment, the dynamic splitting tensile strength is tested to solve the problems in the background art.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention discloses a processing mold for a UHPC-NC specimen. The mold includes a base, a assembled cylindrical barrel, an upper cover and an interface partition. A circular boss is provided in the middle of the base, and the assembled cylindrical barrel is arranged on the outer periphery of the circular boss. The interface partition is vertically inserted into the middle of the assembled cylindrical barrel, and the upper cover is buckled on the top of the assembled cylindrical barrel.

[0008] A further preferred solution of the above technical solution is that the assembled cylindrical barrel is formed by splicing a plurality of arc-shaped plates. A disassembly and assembly component is provided on the outer wall of each arc-shaped plate. The disassembly and assembly component includes a positioning plate, a limiting shaft and a regulator. The positioning plate is fixedly connected to the base, and the limiting shaft and the regulator are respectively connected to the arc-shaped plate and penetrate through the positioning plate. The regulator is located above the limiting shaft, and the opening and closing state of the assembled cylindrical barrel is adjusted by screwing the regulator.

[0009] As a further preferred embodiment, the regulator includes a rotating handle, a threaded rod and a connecting disc. The threaded rod is movably inserted through the positioning plate, the rotating handle and the connecting disc are respectively connected to both ends of the threaded rod, and the connecting disc is located inside a first mounting disc on the outer wall of the arc-shaped plate.

[0010] A further preferred solution of the above technical solution is that the interface partition includes a base mother board, an adjusting sub-board and a pushing member. The base mother board is connected to the circular boss, and both ends of the base mother board are in contact with the inner wall of the assembled cylindrical barrel. The adjusting sub-board and the pushing member are cooperatively installed on the base mother board. A plurality of elastic rubber columns are connected to the adjusting sub-board, and the pushing member is in contact with the elastic rubber columns. One side of the base mother board is used to form a predetermined specimen interface form, and one side of the adjusting sub-board is used to form a variable specimen interface form.

[0011] As a further preferred embodiment, a plurality of rectangular protrusions are provided on one side of the base mother board, a plurality of limiting columns are evenly distributed on the other side, and a gap is provided between the rectangular protrusions and the limiting columns. Each limiting column includes two L-shaped baffles arranged at intervals and symmetrically to each other, and a space is provided between the two L-shaped baffles.

[0012] As a further preferred embodiment, the adjusting sub-board includes a T-shaped column and an elastic arc-shaped panel. A plurality of T-shaped columns are provided and distributed on one side of the elastic arc-shaped panel. The T-shaped columns are clamped in the space between the two L-shaped baffles. The elastic arc-shaped panel is located outside the base mother board. The pushing member is inserted into the gap and passes through the gap between adjacent limiting columns to abut against the elastic arc-shaped panel.

[0013] As a further preferred embodiment, the mold further includes an interface adjustment member. When it is necessary to change the interface form of the adjustment sub-plate, the interface adjustment member is movably inserted into the base mother plate, and the push member is pushed by the interface adjustment member to move towards the elastic arc panel, so as to push the elastic arc panel to change from an arc shape to a serrated shape.

[0014] In a second aspect, the present invention also discloses a processing method for UHPC-NC specimens. The above processing mold is used to manufacture UHPC-NC specimens, including the following steps:

[0015] The arc-shaped plates are combined to form an assembled cylindrical barrel, and an interface partition is installed in the assembled cylindrical barrel;

[0016] According to the design interface form requirements of the UHPC-NC specimen, NC is added to one side of the interface partition. After curing is completed, the interface partition is taken out, and then UHPC is added to fill the assembled cylindrical barrel, and curing continues;

[0017] If it is necessary to manufacture a UHPC-NC specimen with a serrated interface, the push member is pushed by the interface adjustment member to make the elastic arc panel change from an arc shape to a serrated shape. Then, NC is added to one side of the elastic arc panel. After curing is completed, the interface partition is taken out, and then UHPC is added to fill the assembled cylindrical barrel, and curing continues;

[0018] After curing is completed, by rotating the rotating handle, the arc-shaped plates are driven by the threaded rod to move away from each other to open the assembled cylindrical barrel, and the UHPC-NC specimen can be taken out.

[0019] In a third aspect, the present invention also discloses a UHPC-NC specimen, which is prepared by the above processing method for a UHPC-NC specimen.

[0020] In a fourth aspect, the present invention also discloses a test method for the interfacial dynamic splitting tensile strength of a UHPC-NC specimen under freeze-thaw damage, including the following steps:

[0021] S1: For UHPC-NC specimens with different interface forms, determine the number of freeze-thaw cycles according to the freeze-thaw deterioration ratio coefficient, and conduct freeze-thaw cycle erosion on the UHPC-NC specimens for a set number of times;

[0022] S2: Place the UHPC-NC specimen after freeze-thaw cycle erosion on the SHPB test bench, make the bonding interface of the UHPC-NC specimen and the center of the incident bar in the same horizontal plane, clamp the UHPC-NC specimen with the incident bar and the transmission bar, and set different impact air pressure levels to conduct impact tests on the UHPC-NC specimen;

[0023] S3: Calculate the dynamic splitting tensile strength of the UHPC-NC specimen according to the load received by the UHPC-NC specimen.

[0024] Preferably, in step S1, the freeze-thaw degradation proportional coefficient is determined by the ratio of the number of indoor freeze-thaw cycles to the number of natural freeze-thaw cycles when the UHPC-NC specimen reaches the same freeze-thaw damage degree, and its value range is 10-15, and the number of freeze-thaw cycles is 0-200 times.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention bonds UHPC and NC to form a cylindrical specimen through a processing mold, and the position of the partition is the bonding interface between UHPC and NC. The processing mold is composed of three circumferentially distributed arc plates, and the position of the arc plates is adjusted by disassembling and assembling components to open the assembled cylindrical barrel composed of three arc plates, which is conducive to rapid demolding of the UHPC-NC specimen after processing, avoiding the existing mold from causing a large disturbance to the UHPC-NC specimen due to demolding, and ensuring the accuracy of the subsequent test results of the splitting tensile strength of the bonding interface of the UHPC-NC specimen.

[0027] 2. The processing mold of the present invention is provided with an interface partition, and the interface partition is composed of a side with a fixed shape and a side with a variable shape. The test piece with a rectangular interface shape can be processed through the fixed shape side of the interface partition, and the test piece with an arc interface shape can be produced through the variable shape side without deformation. In addition, it can also cooperate with an interface adjustment component. During the process of inserting the interface adjustment component into the interface partition, the adjustment sub-plate is pushed and deformed into a sawtooth shape through the insertion rod, and the sawtooth interface shape is produced by using the deformed interface partition. In general, the mold can realize the processing of UHPC-NC test pieces with three different interface shapes, which is conducive to the later testing of the splitting tensile strength of UHPC-NC test pieces under different interface shapes, and obtaining more comprehensive UHPC-NC test piece performance analysis results.

[0028] 3. Based on the freeze-thaw degradation proportional coefficient, the present invention converts the number of freeze-thaw cycles under the test conditions into the corresponding number in the actual engineering scenario, determines the number of freeze-thaw cycles required for the test, and then uses the Brazilian disc splitting test method as a basis to test the dynamic splitting tensile strength of the bonding interface of the UHPC-NC specimen using the Brazilian splitting test combined with the SHPB device. This method can more accurately simulate the tensile failure form of the UHPC-NC composite structure in actual engineering, and the obtained dynamic splitting tensile strength test results are basically consistent with the actual mechanical properties.

[0029] 4. The method of the present invention is scientific and reasonable, and the test results are accurate and reliable. The dynamic splitting tensile strength of different interfaces can be measured, and the interface type that can improve the interface bonding strength can be obtained, which can be extended to the dynamic tensile strength of different types of concrete bonding interfaces, providing a theoretical basis for the later application of UHPC to the repair and reinforcement of concrete structures in different environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0031] Figure 1 It is a schematic diagram of the overall structure of a processing mold for a UHPC-NC specimen of the present invention;

[0032] Figure 2 It is a schematic diagram of the structure of the disassembly and assembly component of the present invention;

[0033] Figure 3 It is a coordination relationship diagram of the disassembly and assembly component and the arc plate of the present invention;

[0034] Figure 4 It is a position relationship diagram of the assembled cylindrical barrel and the interface partition plate of the present invention;

[0035] Figure 5 It is a schematic diagram of the structure of the interface partition plate of the present invention;

[0036] Figure 6 It is a schematic diagram of the structure of the basic mother board of the present invention;

[0037] Figure 7 It is a schematic diagram of the structure of the top push member of the present invention;

[0038] Figure 8 It is an original state diagram of the elastic arc panel of the present invention;

[0039] Figure 9 It is a schematic diagram of the elastic arc panel changing from an arc shape to a zigzag shape of the present invention;

[0040] Figure 10 It is a coordination relationship diagram of the top push member and the elastic arc panel of the present invention;

[0041] Figure 11 It is a coordination relationship diagram of the interface adjustment member and the interface partition plate of the present invention;

[0042] Figure 12 It is a temperature rise and fall mechanism and high and low temperature duration diagram of the present invention;

[0043] Figure 13 It is a clamping schematic diagram of the UHPC-NC specimen of the present invention on the SHPB test bench;

[0044] Figure 14 It is a partially enlarged schematic diagram of the loading method of the UHPC-NC specimen of the present invention;

[0045] Figure 15 It is a dot line graph of the dynamic splitting tensile strength corresponding to an impact air pressure of 0.1 MPa for the UHPC-NC specimens with three interface forms of the present invention under different freeze-thaw cycle numbers;

[0046] Figure 16 It is a dot line graph of the dynamic splitting tensile strength corresponding to an impact air pressure of 0.125 MPa for the UHPC-NC specimens with three interface forms of the present invention under different freeze-thaw cycle numbers;

[0047] Figure 17 It is a dot line graph of the dynamic splitting tensile strength corresponding to an impact air pressure of 0.15 MPa for the UHPC-NC specimens with three interface forms of the present invention under different freeze-thaw cycle numbers;

[0048] In the figure: 1. Base; 11. Circular boss; 2. Assembled cylindrical barrel; 21. Arc plate; 3. Upper cover; 4. Interface partition; 41. Basic mother board; 411. Rectangular protrusion; 412. Limit column; 413. Gap; 42. Adjusting sub-board; 421. T-shaped column; 422. Elastic arc panel; 43. Thrust member; 431. Flat plate; 432. Push plate; 5. Disassembly and assembly component; 51. Positioning plate; 52. Limit shaft; 53. Regulator; 531. Rotating handle; 532. Threaded rod; 533. Connecting plate; 6. Interface adjustment member; 61. Cover plate; 62. Insert rod; 621. Cone; 622. First cylinder; 623. Second cylinder; 7. Elastic rubber column; 8. Incident rod; 9. Transmitting rod; 10. Rigid cushion strip; 20. Strain gauge. Detailed implementation manners

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0050] Example 1: Refer to Figures 1-11, the present invention provides a processing mold for UHPC-NC specimens. The mold includes a base 1, a split cylindrical barrel 2, an upper cover 3 and an interface partition 4. A circular boss 11 is provided in the middle of the base 1, and a card slot is opened in the middle of the circular boss 11. The split cylindrical barrel 2 is composed of a plurality of arc-shaped plates 21 spliced together, and the split cylindrical barrel 2 is arranged on the outer periphery of the circular boss 11. The interface partition 4 is vertically inserted into the middle of the split cylindrical barrel 2 and cooperates with the card slot. The upper cover 3 is buckled on the top of the split cylindrical barrel 2. The upper cover 3 is in a conical structure, and an exhaust hole is opened at its top. When making specimens, it needs to be placed on a vibrating table for vibration. Through the upper cover 3, it can prevent the materials in the split cylindrical barrel 2 from overflowing outward due to vibration.

[0051] As Figures 2-4 shown, each arc-shaped plate 21 is connected to the base 1 through a disassembly and assembly component 5. Among them, the disassembly and assembly component 5 includes a positioning plate 51, a limiting shaft 52 and a regulator 53. The positioning plate 51 is fixedly connected to the base 1. The limiting shaft 52 and the regulator 53 are respectively connected to the arc-shaped plate 21 and penetrate through the positioning plate 51. The regulator 53 is located above the limiting shaft 52. By screwing the regulator 53, the opening and closing state of the split cylindrical barrel 2 is adjusted; in this embodiment, three positioning plates 51 are provided and are circumferentially and evenly arranged at the edge of the base 1. The limiting shaft 52 is connected through the positioning plate 51 and is threadedly connected to the second mounting plate on the outer wall of the arc-shaped plate 21.

[0052] Specifically, the regulator 53 includes a rotating handle 531, a threaded rod 532 and a connecting disk 533. The threaded rod 532 is movably inserted through the positioning plate 51, and the threaded rod 532 is in threaded cooperation with the positioning plate 51. The rotating handle 531 and the connecting disk 533 are respectively connected to both ends of the threaded rod 532, and the connecting disk 533 is located inside the first mounting plate on the outer wall of the arc-shaped plate 21. When the rotating handle 531 is screwed, the rotating handle 531 drives the threaded rod 532 to rotate, and simultaneously makes the connecting disk 533 rotate inside the first mounting plate. Through the cooperation of the threaded rod 532 and the positioning plate 51, the three arc-shaped plates 21 are close to each other and spliced together to form the split cylindrical barrel 2, or the three arc-shaped plates 21 are far away from each other to open the split cylindrical barrel 2 to demold the processed specimens.

[0053] As Figures 5-11 shown, the interface partition 4 is a strip-shaped plate with different interface forms that can be formed on both sides. The interface partition 4 is installed in the card slot. The contact surfaces of the interface partition 4 with the split cylindrical barrel 2 are all arc-shaped surfaces. Thus, when the interface partition 4 is installed in the split cylindrical barrel 2, the interface partition 4 can be completely fitted with the split cylindrical barrel 2. During the process of making specimens, the interface partition 4 can be drawn out from the split cylindrical barrel 2.

[0054] Specifically, the interface partition 4 includes a base mother board 41, an adjustment daughter board 42, and a pushing member 43. The base mother board 41 is connected to the circular boss 11, and both ends of the base mother board 41 are abutted against the assembled cylindrical barrel 2. The adjustment daughter board 42 and the pushing member 43 are both connected to the base mother board 41. One side of the base mother board 41 is used to form a predetermined specimen interface form, and one side of the adjustment daughter board 42 is used to form a variable specimen interface form. A number of elastic rubber columns 7 are connected to the adjustment daughter board 42 (such as Figure 11 in). The pushing member 43 is in contact with the elastic rubber column 7.

[0055] Such as Figure 6 shown, a number of rectangular protrusions 411 are provided on one side of the base mother board 41, a number of limit columns 412 are evenly distributed on the other side thereof, and a gap 413 is provided between the rectangular protrusions 411 and the limit columns 412. Each limit column 412 includes two L-shaped baffles arranged at intervals and symmetrically to each other. The adjustment daughter board 42 is connected to the base mother board 41 through a number of limit columns 412. The pushing member 43 is installed in the gap 413 and extends to cooperate with the adjustment daughter board 42. The pushing member 43 and the adjustment daughter board 42 are connected through the elastic rubber column 7.

[0056] Such as Figure 8 shown, the adjustment daughter board 42 includes a T-shaped column 421 and an elastic arc-shaped panel 422. A plurality of T-shaped columns 421 are provided and fixedly connected between the two L-shaped baffles of the same limit column 412. The elastic arc-shaped panel 422 is connected to the T-shaped column 421, and the elastic arc-shaped panel 422 is located outside the base mother board 41. The pushing member 43 includes a flat panel 431 and a pushing plate 432. A plurality of pushing plates 432 are provided and evenly distributed on one side of the flat panel 431. The top of the other side of the flat panel 431 is set as a smooth arc surface. The flat panel 431 is inserted into the gap 413, and the end of the pushing plate 432 abuts against the elastic arc-shaped panel 422 after passing through the gap between two adjacent limit columns 412.

[0057] Using the above-mentioned mold, the production of UHPC-NC specimens in two forms with rectangular and arc-shaped interface forms can be realized. According to the requirements of the experiment for various interface forms of UHPC-NC specimens, an interface adjustment member 6 is also provided in this embodiment. By changing the form of the adjustment daughter board 42 through the interface adjustment member 6, the elastic arc-shaped panel 422 can be transformed into a serrated panel, so as to realize the production of UHPC-NC specimens with a serrated interface form.

[0058] Specifically, such as Figure 11As shown in the figure, the interface adjustment member 6 includes a cover plate 61 and insertion rods 62. There are multiple insertion rods 62 which are evenly connected to the bottom of the cover plate 61. A handle is provided on the top of the cover plate 61 for easy grasping when placing the insertion rods 62 in the gap 413. Each insertion rod 62 is composed of a cone 621, a first cylinder 622 and a second cylinder 623 which are integrally connected from bottom to top. A reduced-diameter transition section is provided between the first cylinder 622 and the second cylinder 623. The diameter of the first cylinder 622 is smaller than that of the second cylinder 623. An arc-shaped long groove is provided on one side of the rectangular protrusion 411 close to the pushing member 43. The diameter of the second cylinder 623 is adapted to the diameter of the arc-shaped long groove. When it is necessary to manufacture a UHPC-NC specimen with a serrated interface shape, the interface adjustment member 6 is movably inserted into the base mother board 41. The pushing member 43 is pushed by the insertion rods 62 to move towards the elastic arc-shaped panel 422. The elastic arc-shaped panel 422 is deformed from an arc-shaped surface to a serrated shape by using the pushing plate 432. When the insertion rods 62 are inserted into the bottom of the gap 413, the second cylinder 623 is used to cooperate with the arc-shaped long groove to tightly press against the pushing member 43.

[0059] Embodiment 2: On the basis of the above Embodiment 1, the present invention further provides a processing method for UHPC-NC specimens, using the processing mold of the present invention to complete the processing and production of UHPC-NC specimens with different interface shapes, specifically as follows:

[0060] First, by adjusting the disassembly and assembly component 5, the three arc-shaped plates 21 are mutually close and tightly assembled to form an assembled cylindrical barrel 2. The interface partition plate 4 is inserted into the assembled cylindrical barrel 2 and clamped in the card slot on the circular boss 11.

[0061] Then, according to the interface shape of the UHPC-NC specimen to be manufactured, NC (ordinary concrete, specific mix ratio is shown in Table 1) prepared in advance is selected to be added to the left area or the right area of the interface partition plate 4. Before adding, a release agent can be applied to the interface partition plate 4 on the determined feeding side. The release agent is vaseline. The mold is placed in a curing room for 28 days. The curing temperature is 20°C ± 2°C, and the relative humidity is 95%. Then the interface partition plate 4 is removed, and the prepared UHPC (ultra-high performance concrete, specific mix ratio is shown in Table 2) is filled into the mold. It is placed in the curing room again for 28 days. The curing temperature is 20°C ± 2°C, and the relative humidity is 95%.

[0062] Table 1 Mix ratio of ordinary concrete (kg / m 3 )

[0063] ;

[0064] Table 2 Mix ratio of UHPC (kg):

[0065] ;

[0066] After curing is completed, the UHPC-NC specimen is formed. By turning the rotating handle 531, the threaded rod 532 rotates to gradually press the UHPC-NC specimen. Since the connecting plate 533 is installed on the arc plate 21, when the connecting plate 533 rotates synchronously with the threaded rod 532, it drives the arc plate 21 to move away from the UHPC-NC specimen, enabling the UHPC-NC specimen to be quickly demolded. After the UHPC-NC specimen is manufactured, both ends of the UHPC-NC specimen are cut off by 1 / 7 of its overall height, so as to eliminate the influence of uneven aggregate distribution and pitted surface at the end face on subsequent tests. Finally, the height of the UHPC-NC specimen is 50 mm.

[0067] As Figure 8 shown, the original form of the interface partition 4 can be used to process UHPC-NC specimens with two interface forms, namely rectangular interface and arc interface. If it is necessary to manufacture a UHPC-NC specimen with a serrated interface, the interface adjustment member 6 needs to be used. The operator grasps the handle and inserts the insertion rod 62 into each arc-shaped long groove correspondingly. During the downward insertion process of the insertion rod 62, the flat plate 431 is pushed by the insertion rod 62 to move, so that the push plate 432 connected to the other side of the flat plate 431 pushes the elastic arc-shaped panel 422, causing the elastic arc-shaped panel 422 to deform from an arc-shaped surface to a serrated shape. As Figure 9 shown, when the insertion rod 62 is inserted into the bottom of the gap 413, the second cylinder 623 is used to cooperate with the arc-shaped long groove to tightly abut against the top push member 43, preventing the deformed serrated panel from automatically restoring under the action of the elastic rubber column 7.

[0068] Example 3: According to the method in Example 2 above, UHPC-NC specimens with three forms, namely rectangular interface (specimen 1), arc interface (specimen 2), and serrated interface (specimen 3), required for the test are manufactured. Based on the freeze-thaw environment in Jiuquan City, Gansu Province, for UHPC-NC specimens with different interface forms, the following method is implemented to test the dynamic splitting tensile strength of the interface under the influence of freeze-thaw damage, specifically as follows:

[0069] First, for the manufactured UHPC-NC specimens, the number of freeze-thaw cycles is determined according to the freeze-thaw deterioration ratio coefficient, and the UHPC-NC specimens are subjected to a set number of freeze-thaw cycle erosions.

[0070] Introduce the freeze-thaw deterioration ratio coefficient K a , with a value of 12. Considering that the local annual freeze-thaw cycle number in Jiuquan area of Gansu Province is 100 - 130 times, 115 times is taken as the annual freeze-thaw number. Therefore, the number of indoor freeze-thaw cycles in one year is N = 115 / K a≈10 times, with a cycle of every 5 years, considering the deterioration of the dynamic splitting tensile strength of the UHPC-NC bonding interface, the number of freeze-thaw cycles is set to 0, 50, 100, 150, and 200 times respectively. Combining with the temperature in the western region, 25°C is selected as the highest temperature to simulate the summer temperature, and -20°C is selected to simulate the lowest winter temperature. In order to allow the water to freeze and melt fully, keep the temperature constant for 2 hours at the lowest temperature and 1 hour at the highest temperature. The temperature rising and falling mechanism and the duration of high and low temperatures are set as shown in Figure 12 and the UHPC-NC specimens are subjected to freeze-thaw cycle erosion. According to the environmental conditions and test requirements in the western region, the temperature rising and falling mechanism and the duration of high and low temperatures are set. The freeze-thaw cycle erosion includes a spraying stage, a cooling stage, a low-temperature constant-temperature stage, a heating stage, and a high-temperature constant-temperature stage, and the duration of each stage is 5 min, 2 h, 2 h, 1 h, and 1 h in sequence, totaling 6 hours and 5 minutes.

[0071] Then, place the UHPC-NC specimens after freeze-thaw cycle erosion on the SHPB test bench, make the bonding interface of the UHPC-NC specimens be on the same horizontal plane as the center of the incident bar, clamp the UHPC-NC specimens using the incident bar and the transmission bar, and set different impact air pressure levels to conduct impact tests on the UHPC-NC specimens;

[0072] After the above treatment of the UHPC-NC specimens, place the UHPC-NC specimens on the SHPB (Split Hopkinson Pressure Bar experimental system) test bench, clamp the UHPC-NC specimens using the incident bar 8 and the transmission bar 9, and a strain gauge 20 is provided on the transmission bar 9. The transmitted wave of the transmission bar 9 is captured through the strain gauge 20. Rigid cushion strips are provided at the contact surfaces of the incident bar 8, the transmission bar 9, and the UHPC-NC specimens, and the radian of the rigid cushion strips is adapted to the outer wall of the UHPC-NC specimens to avoid damage at the stress concentration point of the UHPC-NC specimens due to stress concentration. Then, set different impact air pressure levels to conduct impact tests. The greater the impact air pressure, the higher the dynamic splitting tensile strength of the bonding interface of the UHPC-NC specimens (i.e., the strain rate effect). According to the actual conditions of the laboratory and ensuring that the specimens are damaged under dynamic impact, corresponding gradients are set. Specifically, the value of the impact air pressure in the present invention is 0.1 MPa to 0.15 MPa.

[0073] In this embodiment, as shown in Figure 13 and Figure 14 , a straight cone variable cross-section SHPB test loading device with a diameter of 74 mm is adopted. The elastic modulus of the rigid cushion strip 10 is 210 GPa, the elastic wave velocity in the rigid cushion strip 10 is 5172 m / s, and the density of the rigid cushion strip 10 is 7850 kg / m 3; The length of the incident bar 8 is 3.2 m, and the length of the transmission bar 9 is 1.8 m. Place the UHPC-NC specimen on the SHPB test bench so that the UHPC-NC bonding interface is in the same horizontal plane as the center of the incident bar. Clamp the UHPC-NC specimen using the incident bar 8 and the transmission bar 9. Rigid cushion strips 10 are provided at the contact surfaces of the incident bar 8, the transmission bar 9, and the UHPC-NC specimen, and the curvature of the rigid cushion strips is adapted to the outer wall of the UHPC-NC specimen. The clamping method is as shown in Figure 14 and impact tests are carried out on the UHPC-NC specimen by setting impact air pressures of 0.1 MPa, 0.125 MPa, and 0.15 MPa respectively.

[0074] During the impact test, the stress wave is transmitted to the UHPC-NC specimen through the rigid cushion strip 10. The interface crack initiation point occurs at the center of the UHPC-NC specimen, causing a main crack perpendicular to the loading direction to appear at its center. Then the main crack propagates to both sides, splitting the UHPC-NC specimen into two parts.

[0075] To ensure reliable test data, the SHPB impact splitting test needs to meet two basic assumptions: (1) One-dimensional elastic wave assumption: The incident bar 8 and the transmission bar 9 are always within the elastic range during the test, and the stress wave propagation in the incident bar 8 and the transmission bar 9 is approximately regarded as a one-dimensional wave; (2) Uniformity assumption: During the test, the stress and strain in the specimen are uniformly distributed along the specimen length.

[0076] According to the propagation principle of one-dimensional elastic waves, the displacement at the end face of the incident bar 8 is:

[0077] ;

[0078] Since the displacement at the end face of the transmission bar 9 is only related to the transmitted wave, the displacement at the end face of the transmission bar 9 is:

[0079] ;

[0080] Subtract the displacement at the end face of the transmission bar 9 from the displacement at the end face of the incident bar 8 to obtain the overall displacement of the specimen, that is:

[0081] ;

[0082] The loads and at the end face of the incident bar 8 and the end face of the transmission bar 9 are respectively expressed as:

[0083] ;

[0084] ;

[0085] Therefore, the average load borne at both ends of the specimen is:

[0086] ;

[0087] According to the balance hypothesis, that is it can be obtained that:

[0088] ;

[0089] In the above formula: C 0 is the wave velocity, is the incident wave, is the reflected wave, is the transmitted wave, t is the time, is the load borne at the end face of the incident bar 8, is the load borne at the end face of the transmitted bar 9, P ( t ) is the load borne by the UHPC-NC specimen, and respectively represent the cross-sectional area and elastic modulus of the pressure bars (i.e., the incident bar 8 and the transmitted bar 9) of the SHPB test loading device.

[0090] In the present invention, to measure the dynamic splitting tensile strength of the specimen, the data of the transmitted wave needs to be captured. After the strain gauge 20 obtains the electrical signal, the experimental data is collected through a strain gauge, and the transmitted wave is obtained after data processing. The strain gauge in this embodiment is the model SDY2107B ultra-dynamic strain gauge produced by Beidaihe Practical Electronic Technology Research Institute.

[0091] Finally, calculate the dynamic splitting tensile strength of the UHPC-NC specimen according to the load borne by the UHPC-NC specimen;

[0092] For the experimental data analysis of the UHPC-NC specimen after loading the impact air pressure, first, calculate the load borne by the UHPC-NC specimen according to the formula

[0093] Then, according to the load borne by the obtained UHPC-NC specimen, calculate the dynamic splitting tensile strength of the UHPC-NC specimen, and its calculation formula is as follows:

[0094] ;

[0095] In the formula, is the dynamic splitting tensile strength of the UHPC-NC specimen, is the maximum load borne by the UHPC-NC specimen, n is the number of freeze-thaw cycles, ​is the inner diameter of the self-made mold, L is the height of the UHPC-NC specimen.

[0096] In this embodiment, the splitting tensile strength tests after freeze-thaw erosion are respectively carried out on the above-prepared Specimen 1, Specimen 2 and Specimen 3, where: n take the values of 0, 50, 100, 150, 200 respectively, , L = 50 mm. Under the impact air pressures of 0.1 MPa, 0.125 MPa and 0.15 MPa, the splitting tensile strengths of the UHPC-NC specimens with three different interface morphologies are obtained by calculation ， The results are shown in Table 3, Table 4 and Table 5 respectively.

[0097] Table 3 Dynamic splitting tensile strength of the UHPC-NC specimen (Specimen 1) with a rectangular bonding interface:

[0098] ;

[0099] Table 4 Dynamic splitting tensile strength of the UHPC-NC specimen (Specimen 2) with an arc-shaped bonding interface:

[0100] ;

[0101] Table 5 Dynamic splitting tensile strength of the UHPC-NC specimen (Specimen 3) with a serrated bonding interface:

[0102] ;

[0103] The comparison results of the interface dynamic splitting tensile strengths under different interface morphologies are as Figures 15-17 shown. Through analysis, Specimen 3 (i.e., the UHPC-NC specimen with a serrated interface morphology) performs well in terms of dynamic splitting tensile strength, and its performance is significantly higher than that of the UHPC-NC specimens with rectangular and arc-shaped interface morphologies. It can be seen that in practical engineering applications, the interface of the concrete to be repaired can be processed into a serrated shape, which is expected to effectively improve the strength of the repaired structure. This has important practical significance for improving the overall quality of the project and ensuring the long-term stable operation of the project, and can provide valuable reference and guidance for practical engineering practice.

[0104] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A processing mold for a UHPC-NC specimen, characterized in that: The mold comprises a base (1), an assembled cylindrical barrel (2), an upper cover (3) and an interface partition (4); a circular boss (11) is arranged in the middle of the base (1); the assembled cylindrical barrel (2) is arranged on the outer periphery of the circular boss (11); the interface partition (4) is vertically inserted in the middle of the assembled cylindrical barrel (2); and the upper cover (3) is buckled on the top of the assembled cylindrical barrel (2); The assembled cylindrical tube (2) is assembled by splicing a plurality of arc-shaped plates (21). The outer wall of each arc-shaped plate (21) is provided with a disassembly assembly (5). The disassembly assembly (5) comprises a positioning plate (51), a limiting shaft (52) and an adjuster (53). The positioning plate (51) is fixedly connected to the base (1). The limiting shaft (52) and the adjuster (53) are respectively connected to the arc-shaped plate (21) and penetrate the positioning plate (51). The opening and closing state of the assembled cylindrical tube (2) is adjusted by screwing the adjuster (53). The interface partition (4) comprises a base mother plate (41), an adjusting sub-plate (42) and a push piece (43); the base mother plate (41) is connected to the circular boss (11), and both ends of the base mother plate (41) are in contact with the inner wall of the assembled cylindrical tube (2); the adjusting sub-plate (42) and the push piece (43) are mounted on the base mother plate (41) in cooperation; one side of the base mother plate (41) is used to form a predetermined specimen interface morphology, and one side of the adjusting sub-plate (42) is used to form a variable specimen interface morphology.

2. A UHPC-NC specimen processing mold according to claim 1, characterized in that: The regulator (53) comprises a rotating handle (531), a threaded rod (532) and a connecting plate (533). The threaded rod (532) is movably inserted into the positioning plate (51). The rotating handle (531) and the connecting plate (533) are respectively connected to two ends of the threaded rod (532). The connecting plate (533) is located inside a No. 1 mounting plate on the outer wall of the arc plate (21).

3. A UHPC-NC specimen processing mold according to claim 2, characterized in that: A plurality of rectangular protrusions (411) are provided on one side of the basic motherboard (41), a plurality of limiting columns (412) are evenly distributed on the other side thereof, and a gap (413) is provided between the rectangular protrusions (411) and the limiting columns (412), and each limiting column (412) includes two mutually symmetrical L-shaped baffles, and a gap is provided between the two L-shaped baffles.

4. A UHPC-NC specimen processing mold according to claim 3, characterized in that: The regulating sub-plate (42) comprises a T-shaped column (421) and an elastic arc panel (422); a plurality of T-shaped columns (421) are provided and distributed on one side of the elastic arc panel (422); the T-shaped column (421) is clamped in the interval between two L-shaped baffles; the elastic arc panel (422) is located outside the base mother plate (41); and the push piece (43) is inserted into the gap (413) and passes through the gap between adjacent limiting columns (412) to abut against the elastic arc panel (422).

5. A UHPC-NC specimen processing mold according to claim 4, characterized in that: The mould further comprises an interface adjustment component (6). When the interface morphology of the adjustment sub-plate (42) needs to be changed, the interface adjustment component (6) is movably inserted into the basic mother plate (41), and the interface adjustment component (6) pushes the push member (43) to move in the direction of the elastic arc panel (422), thereby pushing the elastic arc panel (422) from an arc shape to a sawtooth shape.

6. A method for processing a UHPC-NC specimen, characterized in that: The UHPC-NC specimen is manufactured by using the processing mold of the UHPC-NC specimen according to claim 5, comprising the following steps: Assembling the arc-shaped plates (21) to form an assembled cylindrical tube (2), and installing an interface partition plate (4) in the assembled cylindrical tube (2); According to the design interface morphology requirements of the UHPC-NC specimen, NC is added to one side of the interface partition (4), and after curing, the interface partition (4) is removed, and UHPC is added to fill the assembled cylindrical tube (2), and the curing is continued; If a UHPC-NC specimen with a sawtooth interface is produced, the interface adjustment member (6) is used to push the push member (43) to change the elastic arc panel (422) from an arc shape to a sawtooth shape, and then NC is added to one side of the elastic arc panel (422). After curing is completed, the interface partition (4) is removed, and UHPC is added to fill the assembled cylindrical tube (2), and curing is continued; After the curing is completed, the rotating handle (531) is rotated and the threaded rod (532) is used to drive the arc plates (21) away from each other so that the assembled cylindrical barrel (2) is opened and the UHPC-NC specimen is taken out.

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