A processing device and method for testing a small-diameter steel bar and concrete bonding slip performance test piece

Abstract

This invention discloses a processing device and method for testing the bond-slip performance of small-diameter steel bars with concrete. The device includes a mold mounted on a support platform. The mold has a base plate, and side plates are detachably fixed around the base plate. Both the left and right side plates have pre-drilled holes. PVC pipes are installed within these pre-drilled holes, through which small-diameter ribbed steel bars can pass. Steel blocks are positioned at both ends of the support platform corresponding to the mold. Each steel block has a through hole, through which the small-diameter ribbed steel bar can pass. A fixing anchor for clamping one end of the small-diameter ribbed steel bar is installed in the through hole of the right steel block. A hydraulic jack, coaxially aligned with the through hole on the left steel block, is used to pull the other end of the small-diameter ribbed steel bar and generate tensile prestress. This invention overcomes the problems of poor fluidity of dry-hard concrete and steel bar drift and eccentricity during casting, resulting in dry-hard concrete specimens that are dense and of high quality.

Description

Technical Field

[0001] This invention relates to the field of processing technology for steel bar-concrete bond specimens, specifically to a processing device for testing the bond slip performance of small-diameter steel bars with concrete. Background Technology

[0002] In the field of specimen fabrication for testing the bond-slip properties of reinforcing steel bars and concrete, current methods for fabricating specimens of large-diameter ribbed steel bars and ordinary fluid concrete typically involve using monolithic casting molds to fix the steel bars and ensuring concrete density through conventional vibration. The principle is to utilize the good fluidity of ordinary fluid concrete to fully encapsulate the large-diameter steel bars; this method is widely used in practical testing. For specimen fabrication of small-diameter ribbed steel bars and dry-hard concrete; However, since dry-hard concrete usually has poor fluidity and high cohesion, and small-diameter ribbed steel bars usually have low stiffness, if the vibration process of ordinary concrete is continued, there are problems such as the steel bars being prone to eccentricity and tilting due to the lateral pressure of concrete or external vibration force during the concrete pouring process, poor concrete compaction, and affecting the accuracy of subsequent pull-out tests of the specimens. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the existing defects and provide a processing device and method for testing the bond-slip performance of small-diameter steel bars with concrete. This invention overcomes the problems of poor fluidity of dry-hard concrete and drift and eccentricity of steel bars during the pouring process. The processed dry-hard concrete specimens have high overall density and uniformity. This invention realizes the processing of specimens for testing the bond-slip performance between small-diameter ribbed steel bars and dry-hard concrete. The invention has good performance and high accuracy in subsequent pull-out tests of the specimens. This invention can effectively solve the problems in the background technology.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a processing device for testing the bond-slip performance of small-diameter reinforcing bars with concrete, comprising a mold on a support platform, the mold being used to fix small-diameter ribbed reinforcing bars and pour concrete, the mold comprising a base plate, side plates being detachably fixed on all four sides of the base plate, and pre-drilled holes being provided on the left and right side plates; PVC pipes are provided in the pre-drilled holes, through which the small-diameter ribbed reinforcing bars can pass, and the small-diameter ribbed reinforcing bars can be fixed to the mold through the PVC pipes and filler; steel blocks are provided on the support platform at the left and right ends corresponding to the mold, each steel block having a through hole, and the through holes on the left and right sides being coaxially arranged with the pre-drilled holes on the left and right sides, and the small-diameter ribbed reinforcing bars can pass through the through holes on both sides; a fixing anchor for clamping one end of the small-diameter ribbed reinforcing bar is provided in the through hole of the right steel block, and a hydraulic jack coaxially arranged with its through hole is provided on the left steel block, and the hydraulic jack is used to pull the other end of the small-diameter ribbed reinforcing bar and generate tensile prestress; and a compaction block for compacting the concrete in the mold is also included.

[0005] Furthermore, each of the side plates has multiple lugs on its vertical end face. The lugs of adjacent side plates are staggered and fitted together, and a connecting screw is vertically provided between the lugs of adjacent side plates. Each end of the connecting screw is provided with a locking nut. Axial shallow grooves are formed along the axial direction on the outer circumference of the connecting screw. Fiber gratings are fitted in each axial shallow groove. The fiber gratings are used to detect the transverse shear strain experienced by the connecting screw during the pouring and compaction of concrete in the mold. The axial shallow grooves are helical grooves with a helix angle of 45°, and the fiber gratings are helically wound around the connecting screw along the axial shallow grooves.

[0006] Furthermore, the bottom plate has latches on all four sides, and the bottom of the inner side of the side plate has grooves that match the latches.

[0007] Furthermore, the support platform also includes a pad block, on which the mold is placed. The upper surface of the pad block has an annular groove adapted to the structure of the mold. The width of the annular groove is adapted to the thickness of the side plate. The bottom of each side plate of the mold is fitted into the annular groove, and the bottom plate of the mold abuts against the upper surface of the pad block. The pad block is located between the steel blocks on the left and right sides and is fixedly connected to each other.

[0008] Furthermore, at least two through holes 1 are horizontally opened on the left end face of the pad, and through holes 2 are opened on the steel block at the positions corresponding to the through holes 1. The pad and the steel block are connected by a long screw passing through the through holes 1 and 2 and locked and fixed by a locking nut 2. At least two through holes 3 are horizontally opened on the upper end of the steel block, and the upper ends of the steel blocks are fixed to each other by a short screw and a locking nut 3.

[0009] Furthermore, the steel block has a square box structure, and through holes one, two, and three are provided on the left and right sides of the steel block.

[0010] To achieve the above objectives, the present invention also provides the following technical solution: a method for processing specimens for testing the bond-slip performance of small-diameter steel bars with concrete, comprising the processing apparatus described above, and including the following steps:

[0011] S1. Pass the small-diameter ribbed steel bars through the pre-drilled holes at both ends of the mold, and fix the small-diameter ribbed steel bars to both ends of the mold using filler and PVC pipe;

[0012] S2. Place the mold with the small-diameter ribbed steel bar fixed on the pad, and fix the steel block to both ends of the pad using long screws and short screws;

[0013] S3. Pass the small-diameter ribbed steel bar through the through hole of the steel block, and clamp one end of the small-diameter ribbed steel bar with the fixed anchor. Tension the other end of the small-diameter ribbed steel bar with the hydraulic jack, and slowly and evenly apply the preset tensile prestress to the small-diameter ribbed steel bar according to the reading on the hydraulic jack.

[0014] S4. While maintaining the prestressed state of the small-diameter ribbed steel bars, the dry-hard concrete prepared in advance according to the design requirements is poured into the mold in layers, and the dry-hard concrete is compacted with a briquette during the pouring process. Fiber Bragg grating data is collected simultaneously during the pouring and compaction of the dry-hard concrete, and the axial strain curve of the distributed fiber Bragg grating during the pouring and compaction process is recorded. The transverse shear strain of the connecting screw is calculated according to the calibration relationship, thereby obtaining and evaluating the degree of compaction of the dry-hard concrete in the mold.

[0015] S5. After the concrete is poured, the hydraulic jack slowly and evenly releases the tensile prestress applied to the small-diameter ribbed steel bars, and then cuts the small-diameter ribbed steel bars at both ends of the specimen to the preset length.

[0016] S6. After the tensile prestress is released, the specimen is demolded after a period of curing, and then immediately subjected to standard curing to ensure the normal development of concrete strength and performance.

[0017] Furthermore, in step S4, before pouring the dry-hard concrete, the support platform and the mold are placed on a vibrating table as a whole, and the dry-hard concrete in the mold is vibrated and compacted during pouring.

[0018] Furthermore, during the layered pouring process in step S4, the initial pouring height needs to be controlled to exceed the pre-set position of the small-diameter ribbed steel bars in the mold by approximately 20mm to ensure dense filling of the concrete below the small-diameter ribbed steel bars. After the concrete pouring is completed, a compactor block is placed on the concrete surface, and a vibrating table is immediately started for vibration compaction, with the vibration compaction time controlled between 30s and 60s. After the first layer of concrete is compacted, the second pouring is immediately carried out to make the filling height in the mold reach two-thirds of the total height, and then vibration compaction continues through the vibrating table and compactor block. Finally, the third pouring is carried out to fill the mold with concrete with a slight surplus, and vibration compaction is carried out again until the top surface is flat and there is no obvious subsidence.

[0019] Furthermore, in step S3, the hydraulic jack applies a tensile prestress of 4KN to the small-diameter ribbed steel bar; in step S4, the reading of the hydraulic jack is controlled to fluctuate within the range of 3KN-6KN during the process of vibrating and compacting dry-hard concrete.

[0020] Compared with the prior art, the beneficial effects of this invention are as follows: The processing device and method for testing the bond slip performance of small-diameter steel bars with concrete apply a preset tensile prestress to the small-diameter ribbed steel bars using a hydraulic jack, preventing drift and eccentricity of the small-diameter ribbed steel bars during pouring and vibration compaction, which would affect the testing accuracy of the specimens; the compaction of the dry-hard concrete in the mold using a pressure block improves the density of the concrete pouring; the axial strain curve of the fiber optic grating is simultaneously acquired during the pouring and compaction of the dry-hard concrete, and the transverse shear strain of the connecting screw is calculated based on the calibration relationship. This method allows for the acquisition and evaluation of the compaction degree of dry-hard concrete within the mold, preventing issues such as poor density of the dry-hard concrete or excessive density leading to eccentricity or tilting of small-diameter ribbed steel bars. The specimens exhibit good processing quality; the molds and support platforms are easy to assemble and disassemble, resulting in good performance. By employing a "three-layer casting" process to apply vibration and pressure layer by layer, the method effectively eliminates pores and air bubbles generated within the dry-hard concrete due to the aggregate bridging effect, preventing the formation of weak interfaces. This significantly improves the overall density and uniformity of the dry-hard concrete specimens, enhancing the testing accuracy. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the processing device of the present invention;

[0022] Figure 2 This is an isometric view of the processing device of the present invention;

[0023] Figure 3 This is a top view of the processing device of the present invention;

[0024] Figure 4 This is a schematic diagram of the mold structure of the present invention;

[0025] Figure 5 This is a schematic diagram of the side plate structure of the present invention;

[0026] Figure 6 This is a top view of the bottom of the present invention;

[0027] Figure 7 for Figure 4 Enlarged view of a specific area;

[0028] Figure 8 This is a schematic diagram of the fiber grating spirally wound on the connecting screw according to the present invention;

[0029] Figure 9 This is a schematic diagram of the steel block structure of the present invention;

[0030] Figure 10 This is a schematic diagram of the pad structure of the present invention;

[0031] Figure 11 This is a schematic diagram of the pressing block structure of the present invention.

[0032] In the diagram: 1. Support platform; 11. Pad block; 111. Through hole one; 112. Annular groove; 12. Steel block; 121. Through hole; 122. Through hole two; 123. Through hole three; 13. Long screw rod; 14. Short screw rod; 2. Mold; 21. Base plate; 211. Tongue; 22. Side plate; 221. Ear block; 23. Connecting screw rod; 24. Locking nut one; 25. Reserved hole; 3. Hydraulic jack; 4. Fixed anchor; 5. Pressure block; 6. PVC pipe; 7. Fiber optic grating; 800. Small diameter ribbed steel bar. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0034] Please see Figure 1-11 The present invention provides a technical solution: a processing device for testing the bond slip performance of small diameter steel bars with concrete, including a mold 2 provided on a support platform 1, the mold 2 being used to fix small diameter ribbed steel bars 800 and to pour concrete. The mold 2 includes a base plate 21, and side plates 22 are detachably fixed to the base plate 21 on all four sides. Each of the four end faces of the base plate 21 has a latch 211, and the bottom of the inner side of each side plate 22 has a groove that matches the latch 211. The base plate 21 is fixedly engaged with the side plate 22 through the latch 211 and the groove. Each vertical end face of the side plate 22 has multiple lugs 221, which are staggered and fitted together. A connecting screw 23 is vertically positioned between the lugs 221 of adjacent side plates 22, and both ends of the connecting screw 23 have locking nuts 24. The circumference of the connecting screw 23... Axial shallow grooves are formed along the axial direction on the outer wall, and fiber optic gratings 7 are fitted inside each axial shallow groove. The fiber optic gratings 7 are used to detect the transverse shear strain of the connecting screw 23 when the concrete is poured and compacted in the mold 2. In this embodiment, the axial shallow groove is a spiral groove with a helix angle of 45°, and the fiber optic gratings 7 are spirally wound around the connecting screw 23 along the axial shallow groove. Reserved holes 25 are formed on the left and right side plates 22. PVC pipes 6 are provided in each reserved hole 25. Small-diameter ribbed steel bars 800 can pass through the PVC pipes 6, and the small-diameter ribbed steel bars 800 can be fixed on the mold 2 through the PVC pipes 6 and the filler. The support platform 1 is provided with steel blocks 12 at both ends of the corresponding mold 2. Each steel block 12 has a through hole 121, and the through holes 121 on the left and right sides are coaxially arranged with the reserved holes 25 on the left and right sides. The small-diameter ribbed steel bar 800 can pass through the through holes 121 on both sides. The through hole 121 of the right steel block 12 is provided with a fixing anchor 4 for clamping one end of the small-diameter ribbed steel bar 800. The left steel block 12 is provided with a hydraulic jack 3 coaxially arranged with its through hole 121. The telescopic end of the hydraulic jack 3 is fixedly provided with the fixing anchor 4, and the telescopic end of the hydraulic jack 3 is connected to the other end of the small-diameter ribbed steel bar 800 through the fixing anchor 4. The hydraulic jack 3 is used to pull the small-diameter ribbed steel bar 800 and generate tensile prestress. The fixing anchor 4 in this embodiment is a clamping anchor. It also includes a compaction block 5 for compacting the concrete in the mold 2. The support platform 1 also includes a pad 11, on which the mold 2 is placed. The upper surface of the pad 11 has an annular groove 112 adapted to the structure of the mold 2. The width of the annular groove 112 is adapted to the thickness of the side plate 22. The bottom of each side plate 22 of the mold 2 is fitted into the annular groove 112. The bottom plate 21 of the mold 2 abuts against the upper surface of the pad 11 to prevent the hydraulic jack 3 from applying tensile prestress to the small-diameter ribbed steel bar 800 and causing the mold 2 to shift. The pad 11 is located between the steel blocks 12 on the left and right sides and is fixedly connected to each other. The pad 11 has at least two through holes 111 horizontally opened on its left end face. The steel block 12 has through holes 122 at the positions corresponding to the through holes 111. The pad 11 and the steel block 12 are connected by a long screw 13 passing through the through holes 111 and the through holes 122 and locked by a locking nut 2. The upper end of the steel block 12 has at least two through holes 123 horizontally opened. The upper ends of the steel block 12 are fixed to each other by a short screw 14 and a locking nut 3. The steel block 12 has a square box structure, and through holes 111, 121, 122 and 123 are provided on the left and right sides of the steel block 12.

[0035] When using: After passing the small-diameter ribbed steel bar 800 through the pre-drilled hole 25 in the mold 2, the small-diameter ribbed steel bar 800 is fixed to both ends of the mold 2 using filler and PVC pipe 6. The mold 2 with the small-diameter ribbed steel bar 800 fixed is placed on the pad block 11, and the small-diameter ribbed steel bar 800 is passed through the through hole 121 in the steel block 12. One end of the small-diameter ribbed steel bar 800 is clamped by the fixing anchor 4, and the other end of the small-diameter ribbed steel bar 800 is tensioned by the hydraulic jack 3. According to the reading on the hydraulic jack 3, the small-diameter ribbed steel bar 800 is slowly and evenly tensioned. 00 Apply a preset tensile prestress; place the support platform 1 and the mold 2 as a whole on the vibration table, pour the dry hard concrete prepared in advance according to the design requirements into the mold 2 in layers, and connect the pressure block 5 to the external lifting equipment and place it on the concrete surface during the layered pouring process, and immediately start the vibration table to vibrate and compact; during the pouring and compaction of dry hard concrete, collect the data of the fiber optic grating 7, record the axial strain curve of the distributed fiber optic grating 7 during the pouring and compaction process, and calculate the transverse shear strain of the connecting screw 23 according to the calibration relationship. When the dry-hard concrete inside mold 2 is compressed, the four side plates 22 expand outward due to the Poisson effect; the outward expansion of the side plates 22 causes the connecting bolts 23 to be subjected to transverse shear force. Dry-hard concrete under vertical pressure exhibits the following lateral expansion strain:

[0036] (1)

[0037] in, For the lateral expansion of dry-hard concrete, It is a vertical compressive force. The cross-sectional area of ​​dry-hard concrete under compression; The elastic modulus of dry-hard concrete; The Poisson's ratio for dry, stiff concrete;

[0038] Lateral displacement caused by expansion of side plate 22 for:

[0039] (2)

[0040] in For the lateral displacement of side plate 22, The thickness of side panel 22;

[0041] The transverse shear strain experienced by the connecting screw 23 is:

[0042] (3)

[0043] The transverse shear strain experienced by the connecting screw 23 The shear length of connecting screw 23;

[0044] Since the fiber grating 7 and the connecting screw 23 deform together, the transverse shear strain of the fiber grating 7 and the connecting screw 23 is consistent.

[0045] The relationship between the transverse shear stress and transverse shear strain experienced by fiber grating 7 is as follows:

[0046] (4)

[0047] This represents the transverse shear stress experienced by fiber Bragg grating 7. This represents the transverse shear strain experienced by fiber grating 7. The shear modulus of fiber grating 7;

[0048] To improve sensitivity, the fiber grating 7 is spirally wound around the connecting screw 23, with the wound portion of the fiber grating 7 perpendicular to the axis of the connecting screw 23. The angle converts the transverse shear stress on fiber grating 7 into axial strain:

[0049] (5)

[0050] in The axial strain experienced by fiber grating 7;

[0051] When the winding portion of the fiber grating 7 forms a 45° angle with the axis of the connecting screw 23:

[0052] (6)

[0053] The relationship between the relative wavelength change of fiber Bragg grating 7 and the changes in axial strain and temperature is as follows:

[0054] (7)

[0055] This represents the relative changes in the seven wavelengths of the fiber Bragg grating. This is the initial Bragg wavelength of fiber grating 7. This represents the wavelength change of fiber optic grating 7. The photoelastic coefficient, The thermo-optic coefficient of fiber Bragg grating 7. The temperature change of fiber grating 7 is taken into account; and the influence of temperature can be ignored during the process of vibratory compaction of dry hard concrete. The conversion relationship between the axial stress of fiber grating 7 and the relative change of wavelength of fiber grating 7 can be determined by the demodulator.

[0056] Combining formulas (6) and (7), the relationship between the transverse shear stress of fiber grating 7 and the relative change in wavelength of fiber grating 7 can be obtained as follows:

[0057] (8)

[0058] From the above formulas (1) to (8), it can be seen that the transverse shear strain experienced by the connecting screw 23 is... Lateral expansion of dry-hard concrete The correlation is positive, meaning the transverse shear stress on the connecting screw 23 is positive. The larger the lateral expansion of dry-hard concrete The larger the shear strain, the greater the transverse shear strain of the fiber grating 7, due to the joint deformation of the fiber grating 7 and the connecting screw 23. Transverse shear strain of connecting screw 23 Consistent; its axial strain can be calculated by varying the wavelength of fiber grating 7. and the transverse shear stress it is subjected to Then through the transverse shear stress of fiber grating 7 The transverse shear strain of fiber grating 7 can be calculated. Based on the transverse shear strain of fiber grating 7 It can obtain and evaluate the compaction degree of dry-hard concrete in mold 2, and avoid situations such as low density of dry-hard concrete or excessive density of dry-hard concrete causing eccentricity or tilting of small-diameter ribbed steel bars 800.

[0059] The processing device for testing the bond-slip performance of small-diameter steel bars with concrete disclosed in this embodiment applies a preset tensile prestress to the small-diameter ribbed steel bars 800 using a hydraulic jack 3 before pouring dry-hard concrete. This prevents the small-diameter ribbed steel bars 800 from drifting and becoming eccentric during pouring and vibration compaction, which would affect the test accuracy of the specimen. The dry-hard concrete in the mold 2 is compacted using a pressure block 5 to increase the density of the concrete pouring. The transverse shear strain of the fiber optic grating 7 can be calculated by measuring the wavelength change of the fiber optic grating 7, thereby allowing the acquisition and evaluation of the compaction degree of the dry-hard concrete in the mold 2. The transverse shear strain experienced by the connecting screw 23... The compaction degree of dry-hard concrete in mold 2 is obtained and evaluated by shear strain, avoiding poor compaction of dry-hard concrete or eccentricity and tilting of small-diameter ribbed steel bars 800 due to excessive compaction of dry-hard concrete; the specimen processing quality is good; mold 2 and support platform 1 are easy to disassemble and assemble, and the processing device has good performance; steel block 12 and pad block 11 are fixedly connected to each other by long screw 13 and short screw 14, bottom plate 21 is fixedly engaged with the groove of side plate 22 by latch 211, and ear blocks 221 between adjacent side plates 22 are fixed to each other by connecting screw 23. Mold 2 and support platform 1 are easy to disassemble and assemble, and flexible and convenient to use. Example

[0060] Please see Figure 1-11 The present invention also provides a technical solution: a processing method for a specimen for testing the bond slip performance of small-diameter steel bars with concrete, comprising the processing device described above, wherein the mold 2 has dimensions of 150mm×150mm×150mm, the side plate 22 has a thickness of 15mm, the pre-drilled hole 25 has a diameter of 10mm, the base plate 21 has dimensions of 150mm×150mm×10mm, the four side latches 211 of the base plate 21 have dimensions of 150mm×7.5mm×10mm, and the latches 211 are embedded in the grooves of the side plate 22 for positioning and sealing; the connecting screw 23 has a diameter of 8mm, the fiber optic grating 7 has a diameter of 1mm, the small-diameter ribbed steel bar 800 has a diameter of 5mm; the through hole 121 on the steel block 12 has a diameter of 10mm; and the weight of the pressure block 5 is 20kg. The specific processing method includes the following steps: S1. Pass the small-diameter ribbed steel bar 800 through the pre-drilled holes 25 at both ends of the mold 2, and fix the small-diameter ribbed steel bar 800 to both ends of the mold 2 through filler and PVC pipe 6. S2. Place the mold 2 with the small diameter ribbed steel bar 800 fixed on the pad 11, and fix the steel block 12 to both ends of the pad 11 by the long screw 13 and the short screw 14. S3. Pass the small-diameter ribbed steel bar 800 through the through hole 121 of the steel block 12, and clamp one end of the small-diameter ribbed steel bar 800 with the fixed anchor 4. Tension the other end of the small-diameter ribbed steel bar 800 with the hydraulic jack 3, and apply a tensile prestress of 4KN to the small-diameter ribbed steel bar 800 slowly and evenly according to the reading on the hydraulic jack 3. S4. While maintaining the prestressed state of the small-diameter ribbed steel bar 800, place the support platform 1 and the mold 2 as a whole on the vibration table, and pour the dry hard concrete prepared in advance according to the design requirements into the mold 2 in layers. The specific layered pouring process is as follows: the initial pouring height needs to be controlled to exceed the position of the pre-set small-diameter ribbed steel bar 800 in the mold 2 by about 20mm, so as to ensure the dense filling of the concrete below the small-diameter ribbed steel bar 800; after the concrete is poured, the pressure block 5 is placed on the concrete surface, and the vibrating table is immediately started for vibration compaction. The vibration compaction time is controlled in the range of 30s to 60s. Immediately after the first layer of concrete is compacted, the second pouring is carried out to fill the mold 2 to two-thirds of the total height. Then, the concrete is compacted by vibration using a vibrating table and compaction block 5. Finally, a third pour is made to fill the mold 2 with concrete, leaving a little excess. The concrete is then vibrated and compacted again until the top surface is flat and there is no obvious subsidence. During the vibration compaction of the dry-hard concrete, the reading of the hydraulic jack 3 is controlled to fluctuate within the range of 3KN-6KN. During the pouring and compaction of dry-hard concrete, data from the fiber optic grating 7 are collected simultaneously. The axial strain curve of the distributed fiber optic grating 7 during the pouring and compaction process is recorded, and the transverse shear strain of the connecting screw 23 is calculated based on the calibration relationship. This allows for the acquisition and evaluation of the compaction degree of the dry-hard concrete in the mold 2, avoiding situations such as low density of dry-hard concrete or excessive density of dry-hard concrete leading to eccentricity or tilting of small-diameter ribbed steel bars 800. S5. After the concrete is poured, the hydraulic jack 3 slowly and evenly releases the tensile prestress applied to the small diameter ribbed steel bar 800, and then cuts the small diameter ribbed steel bar 800 at both ends of the specimen to the preset length. S6. After relieving the tensile prestress, cover the specimen surface with a layer of plastic wrap. After curing for 24 hours, demold the specimen and conduct a visual inspection and numbering. Then, immediately carry out standard curing to ensure the normal development of concrete strength and performance.

[0061] Comparative Example 1: Compared with the processing method of the specimen for testing the bond slip performance of small diameter steel bars with concrete in this invention, under the premise that the mix proportion of dry hard concrete, the size of mold 2, the frequency amplitude of the vibration table and the curing conditions are completely the same, only the pouring process of dry hard concrete is changed; the dry hard concrete is poured into the top layer of mold 2 in one go, and a 20kg pressure block 5 is placed on the top surface of the concrete and vibrated to compact and level it. Comparative Example 2: Compared with the processing method of the specimen for testing the bond slip performance of small diameter steel bars with concrete in this invention, under the premise that the mix proportion of dry hard concrete, the size of mold 2, the frequency amplitude of the vibration table and the curing conditions are completely the same, only the pouring process of dry hard concrete is changed; the dry hard concrete is poured into the top layer of mold 2 in two stages, and after each layer is poured, a 20kg pressure block 5 is placed on the top surface of the concrete to vibrate and compact it.

[0062] Experimental verification: The specimens processed using the casting methods of Comparative Example 1, Comparative Example 2, and Example 2 were compared and analyzed. The experimental data are shown in Table 1.

[0063] Table 1. Comparative data of specimens processed by different casting methods.

[0064]

[0065] As shown in Table 1, the 28-day compressive strength of the specimens prepared using the casting method of Comparative Example 1 is 25 MPa; the 28-day compressive strength of the specimens prepared using the casting method of Comparative Example 2 is 48 MPa; and the 28-day compressive strength of the specimens prepared using the casting method of Comparative Example 2 is 57 MPa. Therefore, it can be seen that... Single-layer and two-layer casting methods, due to their large material depth, result in a significant decrease in vibration energy from top to bottom, making it difficult to effectively compact the dry, hard material at the bottom. This easily leads to the formation of pores and loose areas in the lower part of the specimen and below the reinforcing bars. In contrast, the "three-layer casting" process proposed in this invention, through the application of vibration and pressure layer by layer, effectively eliminates the pores and air bubbles generated inside the dry, hard concrete due to the aggregate bridging effect, avoids the formation of weak interfaces, and can significantly improve the overall density and uniformity of the dry, hard concrete specimens, thereby improving the testing accuracy of the specimens.

[0066] The method for processing specimens for testing the bond-slip performance of small-diameter steel bars with concrete disclosed in this embodiment involves applying a preset tensile prestress to the small-diameter ribbed steel bars 800 using a hydraulic jack 3 before pouring the dry-hard concrete. This prevents the small-diameter ribbed steel bars 800 from drifting and eccentricity during pouring and vibration compaction. The dry-hard concrete in the mold 2 is vibrated and compacted using a pressure block 5 and a vibration table to improve the density of the concrete pouring. The transverse shear strain of the fiber optic grating 7 can be calculated by measuring the wavelength change of the fiber optic grating 7, thereby obtaining and evaluating the degree of compaction of the dry-hard concrete in the mold 2. To avoid issues such as poor density in dry-hard concrete or eccentricity and tilting of small-diameter ribbed steel bars 800 due to excessive density, this method enables the processing of specimens demonstrating the bond-slip performance between small-diameter ribbed steel bars 800 and dry-hard concrete, resulting in high-quality specimens. By employing a three-layer casting process to apply vibration and pressure layer by layer, the method effectively eliminates pores and air bubbles generated within the dry-hard concrete due to the aggregate bridging effect, preventing the formation of weak interfaces. This significantly improves the overall density and uniformity of the dry-hard concrete specimens, thereby enhancing the testing accuracy.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A processing apparatus for testing the bond-slip performance of small-diameter reinforcing bars with concrete, comprising a mold mounted on a support platform, the mold being used to fix the small-diameter ribbed reinforcing bars and to pour concrete, characterized in that: The mold includes a base plate, with side plates detachably fixed on all four sides. Pre-drilled holes are provided on both the left and right side plates. PVC pipes are installed within these pre-drilled holes, through which small-diameter ribbed steel bars can pass. These small-diameter ribbed steel bars are fixed to the mold using the PVC pipes and filler. Steel blocks are located at both ends of the support platform corresponding to the mold. Each steel block has a through hole, and the through holes on both sides are coaxially aligned with the pre-drilled holes on both sides. Small-diameter ribbed steel bars can pass through the through holes on both sides. A fixing anchor for clamping one end of the small-diameter ribbed steel bar is installed in the through hole of the right steel block. A hydraulic jack is coaxially aligned with the through hole on the left steel block. The jack is used to pull the other end of a small-diameter ribbed steel bar and generate tensile prestress; it also includes a compaction block for compacting concrete in the mold; multiple lugs are provided on the vertical end face of each side plate, the lugs of adjacent side plates are staggered and fitted together, and a connecting screw is provided vertically between the lugs of adjacent side plates, with a locking nut at both ends of the connecting screw; axial shallow grooves are provided along the axial direction on the outer circumference of the connecting screw, and fiber optic gratings are fitted in each of the axial shallow grooves. The fiber optic gratings are used to detect the transverse shear strain of the connecting screw during the pouring and compaction of concrete in the mold; the axial shallow grooves are helical grooves with a helix angle of 45°, and the fiber optic gratings are helically wound around the connecting screw along the axial shallow grooves. The method for fabricating specimens for testing the bond-slip properties of small-diameter steel bars with concrete includes the following steps: S1. Pass the small-diameter ribbed steel bars through the pre-drilled holes at both ends of the mold, and fix the small-diameter ribbed steel bars to both ends of the mold using filler and PVC pipe; S2. Place the mold with the small-diameter ribbed steel bar fixed on the pad, and fix the steel block to both ends of the pad using long screws and short screws; S3. Pass the small-diameter ribbed steel bar through the through hole of the steel block, and clamp one end of the small-diameter ribbed steel bar with the fixed anchor. Tension the other end of the small-diameter ribbed steel bar with the hydraulic jack, and slowly and evenly apply the preset tensile prestress to the small-diameter ribbed steel bar according to the reading on the hydraulic jack. S4. While maintaining the prestressed state of the small-diameter ribbed steel bars, the dry-hard concrete prepared in advance according to the design requirements is poured into the mold in layers, and the dry-hard concrete is compacted with a briquette during the pouring process. Fiber Bragg grating data is collected simultaneously during the pouring and compaction of the dry-hard concrete, and the axial strain curve of the distributed fiber Bragg grating during the pouring and compaction process is recorded. The transverse shear strain of the connecting screw is calculated according to the calibration relationship, so as to obtain and evaluate the degree of compaction of the dry-hard concrete in the mold. S5. After the concrete is poured, the hydraulic jack slowly and evenly releases the tensile prestress applied to the small-diameter ribbed steel bars, and then cuts the small-diameter ribbed steel bars at both ends of the specimen to the preset length. S6. After the tensile prestress is released, the specimen is demolded after a period of curing, and then immediately subjected to standard curing to ensure the normal development of concrete strength and performance. In step S4, before pouring dry-hard concrete, the support platform and the mold are placed on the vibrating table as a whole, and the dry-hard concrete in the mold is vibrated and compacted during pouring. During the layered pouring process in step S4, the initial pouring height needs to be controlled to exceed the position of the pre-set small-diameter ribbed steel bar in the mold by about 20mm to ensure the dense filling of the concrete below the small-diameter ribbed steel bar. After the concrete is poured, a tamping block is placed on the concrete surface, and the vibrating table is immediately started for vibration compaction. The vibration compaction time is controlled in the range of 30s to 60s. After the first layer of concrete is compacted, the second pouring is carried out immediately to make the filling height in the mold reach two-thirds of the total height. Then, vibration compaction is continued through the vibrating table and tamping block. Finally, the third pouring is carried out to fill the mold with concrete with a slight excess, and vibration compaction is carried out again until the top surface is flat and there is no obvious settlement.

2. The processing device for testing the bond-slip performance of small-diameter steel bars with concrete according to claim 1, characterized in that: The bottom plate has latches on all four sides, and the bottom of the inner side of the side plate has grooves that match the latches.

3. The processing device for testing the bond-slip performance of small-diameter steel bars with concrete according to claim 1, characterized in that: The support platform also includes a pad block, on which the mold is placed. The upper surface of the pad block has an annular groove adapted to the structure of the mold. The width of the annular groove is adapted to the thickness of the side plate. The bottom of each side plate of the mold is fitted into the annular groove, and the bottom plate of the mold abuts against the upper surface of the pad block. The pad block is located between the steel blocks on the left and right sides and is fixedly connected to each other.

4. The processing device for testing the bond-slip performance of small-diameter steel bars with concrete according to claim 1, characterized in that: The pad has at least two through holes 1 horizontally opened on the left end face, and the steel block has through holes 2 at the positions corresponding to the through holes 1. The pad and the steel block are connected by a long screw passing through the through holes 1 and 2 and locked and fixed by a locking nut 2. The upper end of the steel block has at least two through holes 3 horizontally opened, and the upper ends of the steel blocks are fixed to each other by a short screw and a locking nut 3.

5. The processing device for testing the bond-slip performance of small-diameter steel bars with concrete according to claim 4, characterized in that: The steel block has a square box structure, and through holes one, two, and three are provided on the left and right walls of the steel block.

6. The processing device for testing the bond-slip performance of small-diameter steel bars with concrete according to claim 1, characterized in that: In step S3, the hydraulic jack applies a tensile prestress of 4KN to the small-diameter ribbed steel bar; in step S4, the hydraulic jack reading is controlled to fluctuate within the range of 3KN-6KN during the vibration compaction of dry hard concrete.

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