Test method for measuring bonding strength of straight-pulling spraying ultrahigh concrete

Abstract

The invention discloses a test method for determining the bonding strength of straight-pull spraying ultrahigh concrete, which comprises the following steps of: simulating a straight-pull bonding state of a formed spraying ultrahigh-performance concrete test block and an existing concrete / rock test block by arranging a test mold, and then arranging an upper clamp and a lower clamp, respectively clamping and connecting corresponding spraying ultra-high performance concrete test blocks or existing concrete / rock test blocks, and loading and directly pulling the stretching rods of the upper clamp and the lower clamp on the two sides by using a universal testing machine to obtain the maximum stretching force when a bonding interface is damaged; the direct-pulling bonding strength of the sprayed ultra-high-performance concrete and concrete / rock can be directly measured, the problems that the test block cutting process is complex, the early bonding strength cannot be measured, the requirement for the strength of the bonding glue is high, and the test result is unreliable are effectively solved, the test process is stable, and the test result is reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of performance testing of sprayed ultra-high performance concrete, and more particularly to a test method for measuring the bond strength of direct-pull sprayed ultra-high performance concrete. Background Art

[0002] Sprayed ultra-high performance concrete combines fast construction and ultra-high performance, and has great application prospects in projects such as support structures, reinforcement of existing structures, and protection of marine structures. The bond strength between sprayed ultra-high performance concrete and existing concrete and rock directly affects its application effect, but there is currently no fast, effective, and convenient test device and method. The "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T 50081) provides a concrete bond strength test method, but this method measures the splitting bond strength between new and old concrete, and cannot directly reflect the direct pull bond strength. In addition, some researchers have used oblique shear, direct shear and other means to measure the bonding performance, and the same problem also exists. The currently commonly used direct pull bond strength test steps for sprayed concrete and existing concrete / rock are as follows: 1) Form a half-thick concrete test block in the slab mold or place a rock with the same size as the slab mold, and spray concrete on the concrete / rock surface; 2) After demoulding, the shotcrete + concrete test block / rock is cut into cubic test blocks at the stone processing plant; 3) Apply adhesive to the shotcrete surface and concrete test block / rock surface respectively, and bond the steel plate with pull-out bolts to the concrete; 4) After the adhesive is cured, measure the breaking strength on a universal testing machine.

[0003] The above method has the following problems: 1) The test piece needs to be cut and the process is complicated, making it difficult to measure the early bond strength; 2) Adhesives with high bond strength need to be selected, and during the test, adhesives often fall off rather than the sprayed concrete and concrete / rock are damaged, which makes the test results invalid; 3) The adhesive takes a long time to cure, making it difficult to measure the early bond strength. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0005] Another object of the present invention is to provide a test method for measuring the bond strength of direct-pull sprayed ultra-high concrete, so as to solve the technical problem that the existing technology is difficult to effectively measure the true bond strength.

[0006] In order to achieve these objects and other advantages according to the present invention, a test method for measuring the bond strength of direct-pull shotcrete ultra-high concrete is provided, comprising the following steps: S1. Set up a test mold and a test fixture. The test mold is an inverted convex regular structure with an upper opening. The lower layer of the test mold is used to set the existing structure test block, and the upper layer of the test mold is used to form the sprayed ultra-high performance concrete test block. The test fixture includes a lower fixture and an upper fixture. The upper fixture is used to temporarily sleeve the ultra-high performance concrete test block, and the lower fixture is used to temporarily connect the existing structure test block. Tensile rods are connected to the back centers of the upper and lower fixtures along the same axis. S2. Place an existing structure test block in the lower layer of the test mold, with the top surface of the existing structure test block not lower than the upper surface of the test mold, and record the top surface area S of the existing structure test block; S3. Roughen the upper surface of the existing structure test block, then vertically spray-form an ultra-high performance concrete test block on the upper layer of the test mold toward the roughened interface. After the ultra-high performance concrete test block solidifies and hardens, flip the test mold over and demould it, forming a bonding interface with an area of S between the sprayed ultra-high performance concrete test block and the existing structure test block. S4. Sleeve the upper fixture onto the ultra-high performance concrete test block and the lower fixture onto the existing structure test block. Level the upper and lower fixtures separately so that the tensile rods on both sides are coaxial and perpendicular to the bonding interface. S5. Measure the direct-pull bond strength by clamping the tensile rods of the upper and lower fixtures on a universal testing machine, setting the tensile speed, and starting the universal testing machine until the test block fails. Record the maximum tensile force F. The direct-pull bond strength between the sprayed ultra-high performance concrete and the existing structure is P=F / S.

[0007] Preferably, when setting the existing structure test block, threaded steel bars are pre-embedded in a direction perpendicular to the bonding interface, and one end of the threaded steel bar facing away from the bonding interface extends out of the existing structure test block, and the threaded steel bars are symmetrically arranged along the center of the bonding interface. Prefabricated holes are opened at the bottom of the test mold corresponding to the threaded steel bars for temporarily positioning and fixing the threaded steel bars. The lower fixture includes a connecting steel plate, and connecting holes are opened on the connecting steel plate corresponding to all the threaded steel bars. When installing the lower fixture, the outer end of the threaded steel bar extends out of the corresponding connecting hole and is screwed onto the outer end of the threaded steel bar by a tightening nut for tightening and leveling.

[0008] Preferably, the existing structure test block is made of ordinary concrete or rock. When ordinary concrete is set in the lower layer of the test mold, the threaded steel bar is set using the prefabricated hole, and then ordinary concrete is poured to form the existing structure test block made of ordinary concrete. When rock is set in the lower layer of the test mold, a rebar hole is pre-drilled upward from the lower end of the rock, and the upper end of the threaded steel bar is inserted into the rebar hole and fixed with rebar glue. The curing time of the rebar glue is 3~24h, and the pull-out strength with the threaded steel bar is ≥18MPa.

[0009] Preferably, the upper clamp as a whole is a C-shaped structure with an opening at the bottom, and is sleeved on the outside of the sprayed ultra-high performance concrete test block. The inner cavity height of the upper clamp is slightly larger than the thickness of the sprayed ultra-high performance concrete test block, and the opening is slightly larger than the cross-sectional size of the existing structure test block. The inner side of the bottom of the upper clamp is set as the abutment surface with the sprayed ultra-high performance concrete test block, and a leveling structure is provided on the abutment surface for adjusting the verticality of the stretching rod of the upper clamp relative to the bonding interface.

[0010] Preferably, corresponding to the vertical direction of the stretching rod relative to the bonding interface, the upper clamp and the lower clamp are respectively provided with horizontal vials at the centers of one quarter on the end faces connected to the corresponding outriggers, and the upper clamp is provided with a vertical vial at the center of one of its sides. The vertical and horizontal vials are used to ensure that the corresponding upper clamp or the lower clamp is vertical and horizontal.

[0011] Preferably, the lower layer of the test mold is a cubic or cylindrical structure, and the upper layer of the test mold is a cubic structure, and the projected area of the upper layer is 2 to 4 times that of the lower layer.

[0012] Preferably, the upper layer and the lower layer of the test mold have the same height, and the height of the lower layer is 1 / 3 to 1 / 2 of the side length or diameter of the lower layer.

[0013] Preferably, the side length of the lower inner cavity of the test mold is 75~100 mm, the surface flatness of the sprayed ultra-high performance concrete test block is ±5 mm, the diameter of the threaded steel bar is 8~12 mm, the upper end of the threaded steel bar is 5~10 mm away from the upper surface of the existing structure test block, and the upper end of the threaded steel bar extends 30~40 mm from the lower surface of the existing structure test block.

[0014] Preferably, when setting up the test fixture, the upper fixture and the lower fixture are pre-aligned along a coaxial line with the stretching rods on both sides thereof, a plurality of distance measuring sensors are symmetrically arranged outwardly at the lateral edge ends of the lower fixture, a reflective target is respectively arranged at the lateral edge ends of the upper fixture corresponding to each distance measuring sensor, a remote control terminal is provided to communicatively connect all the distance measuring sensors, distance data during pre-alignment is obtained through the distance measuring sensors, data from one of the distance measuring sensors is used as a comparison origin, and the difference in distance data obtained by the remaining distance measuring sensors is calculated as a comparison parameter; After the upper clamp and the lower clamp are respectively connected to the corresponding sprayed ultra-high performance concrete test block and the existing structure test block, the axis angles of the stretching rods on both sides are adjusted in combination with the vertical vial and the horizontal vial. The new distance measurement data obtained by the distance measurement sensor is compared with the corresponding comparison parameters to adjust the positions of the stretching rods on both sides relative to the bonding interface to achieve precise alignment of the axes of the stretching rods on both sides.

[0015] The present invention includes at least the following beneficial effects: the test method for measuring the bond strength of direct-pull sprayed ultra-high performance concrete of the present invention simulates the direct-pull bonding state of a formed sprayed ultra-high performance concrete test block and an existing concrete / rock test block by setting a test mold, and then setting an upper clamp and a lower clamp to respectively clamp and connect the corresponding sprayed ultra-high performance concrete test block or the existing concrete / rock test block, and using a universal testing machine to load the tensile rods of the upper clamp and the lower clamp on both sides of the direct pull to obtain the maximum tensile force when the bonding interface is destroyed. The direct-pull bond strength of the sprayed ultra-high performance concrete and concrete / rock can be directly measured, effectively solving the problems of complex test block cutting process, inability to measure early bonding strength, high bonding glue strength requirements, unreliable test results, etc., and the test process is stable and the test results are reliable.

[0016] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a main structural diagram of the test fixture of the present invention when performing a direct pull bond strength test on a sprayed ultra-high performance concrete test block; Figure 2 A top view of the upper fixture of the present invention; Figure 3 This is a main structural diagram of the test mold of the present invention; Figure 4 This is a front structural diagram of the C-shaped stand of the present invention; Description Figure Numbers: 1. Upper fixture, 101. Tensile rod of upper fixture, 102. Vertical level bubble of upper fixture, 103. C-shaped structure, 104. Leveling structure, 105. Horizontal level bubble of upper fixture; 2. Lower fixture, 201. Connecting steel plate, 202. Fastening nut, 203. Horizontal level bubble of lower fixture, 204. Tensile rod of lower fixture; 3. Test mold, 301. Threaded steel bar, 302. Upper layer of test mold, 303. Lower layer of test mold, 304. Prefabricated hole; 4. Sprayed ultra-high performance concrete test block, 5. Existing structure test block, 6. Bonding interface, 7. Distance measuring sensor, 8. Reflection target, 9. C-shaped stand. DETAILED DESCRIPTION

[0018] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0019] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified; in the description of the present invention, the terms "horizontal", "longitudinal", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0020] like Figure 1-4 As shown, the present invention provides a test method for measuring the bond strength of direct-pull shotcrete ultra-high concrete, comprising the following steps: S1. Set up a test mold 3 and a test fixture. The test mold 3 is an inverted convex regular structure with an upper opening. The lower layer of the test mold 3 is used to set the existing structure test block 5, and the upper layer of the test mold 3 is used to form the sprayed ultra-high performance concrete test block 4. The test fixture includes a lower fixture 2 and an upper fixture 1. The upper fixture 1 is used to temporarily fit the ultra-high performance concrete test block, and the lower fixture 2 is used to temporarily connect the existing structure test block 5. Tensile rods 101 and 204 are connected coaxially at the back centers of the upper fixture 1 and lower fixture 2, respectively. A steel tensile rod integrally connected to the upper fixture 1 is provided at the center of the upper surface of the upper fixture 1, and a steel tensile rod integrally connected to the lower fixture 2 is provided at the center of the upper surface of the lower fixture 2 to ensure that the test fixtures are clamped on the universal testing machine.

[0021] Preferably, the test mold 3 can be optimized to have a trumpet-shaped structure, wherein the lower layer 303 of the test mold 3 is a cube or cylindrical structure, and the upper layer 302 of the test mold 3 is a cube structure and the projected area of the upper layer is 2 to 4 times that of the lower layer, which is used to form sprayed ultra-high performance concrete while ensuring the stability of the clamping of the fixture. For example, the projected shape of the lower layer is a square with a side length of 75 mm or 100 mm, or a circle with a diameter of 75 mm or 100 mm, which is used to form existing concrete or rock test blocks.

[0022] Preferably, the upper layer and the lower layer of the test mold 3 have the same height, and the height of the lower layer is 1 / 3 to 1 / 2 of the side length or diameter of the lower layer, to prevent the test block from being too large to be operated by one person.

[0023] Preferably, the existing structure test block 5 is made of ordinary concrete or rock. When ordinary concrete is set in the lower layer 303 of the test mold 3, the prefabricated hole 304 is used to set the threaded steel bar 301, and then ordinary concrete is poured to form the existing structure test block 5 made of ordinary concrete. When rock is set in the lower layer of the test mold 3, a rebar hole is pre-drilled upward from the lower end of the rock, and the upper end of the threaded steel bar 301 is inserted into the rebar hole and fixed with rebar glue. The rebar glue is a modified epoxy resin rebar glue or a vinyl ester rebar glue, and the curing time is 3~24h. The pull-out strength with the threaded steel bar 301 is ≥18MPa. On the one hand, fast-curing rebar glue can be selected according to the test age of the bonding strength to measure the early bonding strength. On the other hand, high-strength rebar glue can ensure that the steel bar will not be pulled out first during the pulling process, resulting in invalid test results.

[0024] Preferably, when setting the existing structure test block 5, the threaded steel bar 301 is pre-embedded in a direction perpendicular to the bonding interface 6, and the end of the threaded steel bar 301 facing away from the bonding interface 6 extends out of the existing structure test block 5. The threaded steel bar 301 is symmetrically arranged along the center of the bonding interface 6. The bottom of the test mold 3 is provided with prefabricated holes 304 corresponding to the threaded steel bar 301 for temporarily positioning and fixing the threaded steel bar 301. The lower clamp 2 includes a connecting steel plate 201, and the connecting steel plate 201 is provided with connecting holes corresponding to all the threaded steel bars 301. When installing the lower clamp 2, the outer end of the threaded steel bar 301 extends out of the corresponding connecting hole and is screwed on the outer end of the threaded steel bar 301 by the fastening nut 202 for fastening and leveling. The fastening nut 202 can fix the lower clamp 2 to the threaded steel bar 301 on the one hand, and on the other hand, the horizontal direction of the lower clamp 2 can be adjusted by the fastening nut 202 to ensure that the lower clamp 2 remains horizontal.

[0025] Preferably, the side length of the lower inner cavity of the test mold 3 is 75-100 mm. The surface flatness of the sprayed ultra-high performance concrete test block 4 is ±5 mm to ensure that the upper fixture 1 can be completely inserted into the test block. The diameter of the threaded steel bar 301 is 8-12 mm to ensure that the threaded steel bar 301 is tightly bonded to the concrete or rock. The upper end of the threaded steel bar 301 is 5-10 mm from the upper surface of the existing structure test block 5, that is, the embedment depth is 30-40 mm from the upper surface of the concrete or rock. The upper end of the threaded steel bar 301 protrudes 30-40 mm from the lower surface of the existing structure test block 5 to secure the lower fixture 2. The bottom of the test mold 3 is provided with four or six symmetrical prefabricated holes 304 along the center of the halfway mark. These holes allow the threaded steel bar 301, pre-embedded in the existing concrete / rock, to protrude from the test mold 3 and serve as a connector for the lower fixture 2.

[0026] S2. Set the existing structure test block 5 in the lower layer 303 of the test mold 3. The top surface of the existing structure test block 5 is not lower than the upper surface of the test mold 3. Record the top surface area S of the existing structure test block 5.

[0027] Preferably, the height of the formed existing concrete or rock can be 1-3 mm higher than the lower layer of the test mold 3 to ensure that the sprayed ultra-high performance concrete is tightly bonded to the existing concrete / rock.

[0028] S3. Roughen the upper surface of the existing structure test block 5. Then, vertically spray-form an ultra-high performance concrete test block on the upper layer 302 of the test mold 3 toward the roughened interface. After the ultra-high performance concrete test block solidifies and hardens, flip the test mold 3 over and demold it, forming a bonding interface 6 with an area of S between the sprayed ultra-high performance concrete test block 4 and the existing structure test block 5.

[0029] S4. Sleeve the upper fixture 1 onto the ultra-high performance concrete test block, and sleeve the lower fixture 2 onto the existing structure test block 5. Level the upper fixture 1 and the lower fixture 2 respectively so that the tensile rods on both sides are coaxial and perpendicular to the bonding interface 6.

[0030] Preferably, the upper fixture 1 as a whole is a C-shaped structure 103 with an opening at the bottom, and the two side opposite to each other are connected so that the sprayed ultra-high performance concrete test block 4 can be inserted from the side. The inner cavity height of the upper fixture 1 is slightly larger than the thickness of the sprayed ultra-high performance concrete test block 4, such as the difference range is 1cm~1.5cm, to ensure that the upper fixture 1 can completely insert the sprayed ultra-high performance concrete test block 4 inside, and the opening is slightly larger than the cross-sectional size of the existing structure test block 5. The inner side of the bottom of the upper fixture 1 is set as the abutment surface with the sprayed ultra-high performance concrete test block 4, and a leveling structure 104 is provided on the abutment surface for adjusting the verticality of the stretching rod of the upper fixture 1 relative to the bonding interface 6. A leveling knob is provided at the bottom of the upper clamp 1. The upper end of the leveling knob is a threaded rod, which is passed through and threadedly connected to the bottom of the upper clamp 1. An abutment piece is provided on the top of the leveling knob, which is used to abut against the bottom of the part of the sprayed ultra-high performance concrete test block 4 that extends beyond the existing structure test block 5. On the one hand, it plays a fixing role, and on the other hand, it plays a role in adjusting the water direction of the sprayed ultra-high performance concrete test block 4.

[0031] Preferably, corresponding to the vertical direction of the stretching rod relative to the bonding interface 6, the upper clamp 1 and the lower clamp 2 are respectively provided with horizontal vials 105 and 203 at the quarter centers on the end faces connected to the corresponding outriggers, and the upper clamp 1 is provided with a vertical vial 102 at the center of one of its sides. The vertical vial 102 and the horizontal vials 105 and 203 are used to ensure that the corresponding upper clamp 1 or the lower clamp 2 is vertical and horizontal.

[0032] S5. Determine the direct-pull bond strength by clamping the tensile rods 101 and 204 of the upper fixture 1 and the lower fixture 2, respectively, on a universal testing machine with a maximum load of 100 kN to 200 kN. Set the tensile speed to a loading rate of 50 N / s to 100 N / s. Start the universal testing machine and test until the test block fails. Record the maximum tensile force F. The direct-pull bond strength between the sprayed ultra-high performance concrete and the existing structure is P = F / S.

[0033] The test method for measuring the bonding strength of direct-pull sprayed ultra-high performance concrete of the present invention simulates the direct-pull bonding state of a formed sprayed ultra-high performance concrete test block 4 and an existing concrete / rock test block by setting a test mold 3, and then setting an upper clamp 1 and a lower clamp 2 to respectively clamp and connect the corresponding sprayed ultra-high performance concrete test block 4 or the existing concrete / rock test block. The tensile rods of the upper clamp 1 and the lower clamp 2 on both sides of the direct-pull are loaded by a universal testing machine to obtain the maximum tensile force when the bonding interface 6 is destroyed. The direct-pull bonding strength of the sprayed ultra-high performance concrete and the concrete / rock can be directly measured, effectively solving the problems of complex test block cutting process, inability to measure early bonding strength, high bonding glue strength requirements, unreliable test results, etc. The test process is stable and the test results are reliable.

[0034] In another technical solution, Figure 4 As shown, when setting up the test fixture, the upper fixture 1 and the lower fixture 2 are pre-aligned along the coaxial line with the stretching rods on both sides. A plurality of distance measuring sensors 7 are symmetrically arranged outwardly at the lateral edge ends of the lower fixture 2. A reflective target 8 is respectively arranged at the lateral edge ends of the upper fixture 1 corresponding to each distance measuring sensor 7. A remote control terminal is provided to communicate with all the distance measuring sensors 7. Distance data during pre-alignment is obtained through the distance measuring sensors 7. The data of one of the distance measuring sensors 7 is used as a comparison origin, and the difference in distance data obtained by the remaining distance measuring sensors 7 is calculated as a comparison parameter. After the upper clamp 1 and the lower clamp 2 are respectively connected to the corresponding sprayed ultra-high performance concrete test block 4 and the existing structure test block 5, the axial angles of the stretching rods on both sides are adjusted in combination with the vertical level bubble and the horizontal level bubble. The new distance measurement data obtained by the distance measurement sensor 7 is compared with the corresponding comparison parameters to adjust the positions of the stretching rods on both sides relative to the bonding interface 6 to achieve precise alignment of the axes of the stretching rods on both sides.

[0035] Preferably, when the upper clamp 1 and the lower clamp 2 are pre-aligned, a C-shaped stand 9 is set, the lower part of the C-shaped stand 9 is set as a base, and a lower hole is opened downward on the top surface, and the upper part is set as a top seat, and an upper hole is opened through the top seat, and the upper hole and the lower hole are coaxially arranged. The stretching rod of the upper clamp 1 is aligned with the upper hole and temporarily fixed on the top seat. After the stretching rod passes through the upper hole, it is tightened with an upper nut, and the stretching rod of the lower clamp 2 is aligned with the lower hole and temporarily placed on the base, so that the stretching rods of the upper clamp 1 and the lower clamp 2 are coaxially pre-aligned, and the lateral side of the lower clamp 2 is aligned with the upper hole. A plurality of distance measuring sensors 7 are symmetrically arranged outwardly at the edge end. The connecting steel plate 201 can be set to a size slightly larger than the existing structural test block 5 to facilitate the installation and fixing of the distance measuring sensors 7. A reflective target 8 is respectively provided at the lateral edge end of the upper fixture 1 corresponding to each distance measuring sensor 7. A remote control terminal is provided to communicate with all the distance measuring sensors 7. The distance data during pre-alignment is obtained through the distance measuring sensors 7. The data of one of the distance measuring sensors 7 is used as a comparison origin, and the difference in the distance data obtained by the remaining distance measuring sensors 7 is calculated as a comparison parameter. After the upper clamp 1 and the lower clamp 2 are respectively connected to the corresponding sprayed ultra-high performance concrete test block 4 and the existing structure test block 5, the axial angles of the stretching rods on both sides are adjusted in combination with the vertical level bubble and the horizontal level bubble. The new distance measurement data obtained by the distance sensor 7 is compared with the corresponding comparison parameters, and the positions of the stretching rods on both sides relative to the bonding interface are adjusted to achieve rapid and accurate alignment of the axes of the stretching rods on both sides, improve the test efficiency, and ensure the accuracy of the test results. At the same time, when the data of the distance sensor 7 suddenly increases, it can be used to review the time when the maximum tensile force is generated, thereby reducing the probability of error caused by human participation in the test.

[0036] Example: In the Hangzhou Bay Cross-sea Bridge pier wet joint spraying UHPC protection project, because the project site is located in a tidal area, the spraying operation is immediately exposed to tidal erosion. In addition to measuring the 28-day bond strength between the sprayed UHPC and the concrete structure, it is also necessary to verify its bonding performance after 8 hours. To this end, the test was conducted according to the test method of the present invention and the following data parameters: 1) Ordinary concrete test block molding. The lower layer size of the test mold cavity is 100mm*100mm, and the upper layer size is 180mm*180mm. First, Figure 3 The test mold shown is in accordance with Figure 4 In one form, 10mm diameter threaded steel bars are embedded. The top of the embedded steel bars in the test mold is 8mm away from the upper surface of the lower mold, and the embedded steel bars extend 30mm out of the prefabricated hole. Then, ordinary concrete is poured in the lower layer of the test mold to form an existing structure test block. The casting surface is 2mm higher than the upper surface and moisture maintenance is carried out. The casting surface area S = 10000mm is recorded.2 .

[0037] 2) Spraying ultra-high performance concrete. After the conventional concrete has cured for 7 days, the surface of the existing structural test blocks is roughened to a depth of 1mm to 3mm. The test blocks are then molded and sprayed with ultra-high performance concrete. During spraying, the nozzle should be perpendicular to the upper surface of the mold, and the spray thickness should be level with the upper surface of the mold. After the sprayed ultra-high performance concrete test blocks have solidified, the mold can be flipped over for demolding. The test blocks are divided into two groups. The first group is immediately tested for the bond strength between the sprayed UHPC and concrete, while the second group is tested for bond strength after curing for 28 days.

[0038] 3) Insert the upper fixture. Figure 1 The method shown is to first insert the upper clamp along the lower protruding part of the sprayed ultra-high performance concrete test block, and use the leveling knob to adjust the horizontal and vertical directions of the upper clamp. During the leveling process, use the vertical and horizontal vials to determine its direction.

[0039] 4) Insert the lower fixture. Figure 1 Align the connecting steel plate of the lower clamp with the connecting hole and pass the embedded threaded steel bar through it in the manner shown, and tighten and level the lower clamp with the fastening nut. During the leveling process, use the level bubble to determine its direction.

[0040] 5) Direct Tensile Bond Strength Test. After the upper and lower fixtures are secured and leveled, clamp the tensile rods of the upper and lower fixtures onto a universal testing machine. Set the tensile speed to 80 N / s and start the machine until the specimen fails. Record the maximum tensile force, F. The immediate maximum tensile force for the first set of specimens was 3.25 kN, while the 28-day maximum tensile force for the second set was 22.03 kN.

[0041] The direct tension bond strength between sprayed ultra-high performance concrete and ordinary concrete is P=F / S. The immediate bond strength measured by the first group of test blocks and the 28-day bond strength measured by the second group of test blocks are 0.324MPa and 2.194MPa, respectively.

[0042] Comparative Example: Testing the bond strength between UHPC and ordinary concrete using structural adhesive requires cutting the test pieces. The UHPC specimens were sized 100mm*100mm, and the ordinary concrete specimens were sized 100mm*100mm, taking 0.5 days to complete. After cutting, the bond strength between the UHPC and ordinary concrete was measured at one day and 28 days. Because the structural adhesive requires one day to cure, the bond strength was measured at 1.5 days and 28 days. Using the universal testing machine in the example, at the same tensile speed of 80 N / s, the maximum tensile forces at 1.5 days and 28 days were 0.356 MPa and 2.213 MPa, respectively.

[0043] Compared with the test method of the comparative example in which the structural adhesive needs to be cured for at least one day, the embodiment scheme can measure the early bond strength of the sprayed ultra-high performance concrete, and even the bond strength at the age of hours, so as to understand the performance of the sprayed ultra-high performance concrete. The comparison of the test results of the embodiment and the comparative example shows that for the same time of 28d bond strength, the test data are close. The test method for measuring the direct pull bond strength of the sprayed ultra-high performance concrete and the existing concrete / rock of the present invention can quickly and directly measure the direct pull bond strength of the sprayed ultra-high performance concrete and the concrete / rock, and the test process is stable and the test results are reliable.

[0044] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A test method for measuring the bond strength of direct-pull sprayed ultra-high concrete, characterized in that: The steps include: S1. Set up a test mold and a test fixture. The test mold is an inverted convex regular structure with an upper opening. The lower layer of the test mold is used to set the existing structure test block, and the upper layer of the test mold is used to form the sprayed ultra-high performance concrete test block. The test fixture includes a lower fixture and an upper fixture. The upper fixture is used to temporarily sleeve the ultra-high performance concrete test block, and the lower fixture is used to temporarily connect the existing structure test block. Tensile rods are connected to the back centers of the upper and lower fixtures along the same axis. S2. Place an existing structure test block in the lower layer of the test mold, with the top surface of the existing structure test block not lower than the upper surface of the test mold, and record the top surface area S of the existing structure test block; S3. Roughen the upper surface of the existing structure test block, then vertically spray-form an ultra-high performance concrete test block on the upper layer of the test mold toward the roughened interface. After the ultra-high performance concrete test block solidifies and hardens, flip the test mold over and demould it, forming a bonding interface with an area of S between the sprayed ultra-high performance concrete test block and the existing structure test block. S4. Sleeve the upper fixture onto the ultra-high performance concrete test block and the lower fixture onto the existing structure test block. Level the upper and lower fixtures separately so that the tensile rods on both sides are coaxial and perpendicular to the bonding interface. S5. Measure the direct-pull bond strength by clamping the tensile rods of the upper and lower fixtures on a universal testing machine, setting the tensile speed, and starting the universal testing machine until the test block fails. Record the maximum tensile force F. The direct-pull bond strength between the sprayed ultra-high performance concrete and the existing structure is P=F / S.

2. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 1, characterized in that: When setting the existing structure test block, threaded steel bars are pre-embedded in a direction perpendicular to the bonding interface, and one end of the threaded steel bar facing away from the bonding interface extends out of the existing structure test block. The threaded steel bars are symmetrically arranged along the center of the bonding interface. Prefabricated holes are opened at the bottom of the test mold corresponding to the threaded steel bars for temporarily positioning and fixing the threaded steel bars. The lower fixture includes a connecting steel plate, and connecting holes are opened on the connecting steel plate corresponding to all the threaded steel bars. When installing the lower fixture, the outer end of the threaded steel bar extends out of the corresponding connecting hole and is screwed onto the outer end of the threaded steel bar by a tightening nut for tightening and leveling.

3. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 2, characterized in that: The existing structure test block is made of ordinary concrete or rock. When ordinary concrete is set in the lower layer of the test mold, the threaded steel bar is set using the prefabricated hole, and then ordinary concrete is poured to form the existing structure test block made of ordinary concrete. When rock is set in the lower layer of the test mold, a rebar hole is pre-drilled upward from the lower end of the rock, and the upper end of the threaded steel bar is inserted into the rebar hole and fixed with rebar glue. The curing time of the rebar glue is 3~24h, and the pull-out strength with the threaded steel bar is ≥18MPa.

4. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 2, characterized in that: The upper clamp as a whole is a C-shaped structure with an opening at the bottom, and is sleeved on the outside of the sprayed ultra-high performance concrete test block. The inner cavity height of the upper clamp is slightly larger than the thickness of the sprayed ultra-high performance concrete test block, and the opening is slightly larger than the cross-sectional size of the existing structure test block. The inner side of the bottom of the upper clamp is set as the abutment surface with the sprayed ultra-high performance concrete test block, and a leveling structure is provided on the abutment surface for adjusting the verticality of the stretching rod of the upper clamp relative to the bonding interface.

5. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 1, characterized in that: Corresponding to the vertical direction of the stretching rod relative to the bonding interface, the upper clamp and the lower clamp are respectively provided with horizontal vials at the centers of one quarter of the end faces connected to the corresponding outriggers, and the upper clamp is provided with a vertical vial at the center of one of its sides. The vertical and horizontal vials are used to ensure that the corresponding upper clamp or the lower clamp is vertical and horizontal.

6. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 1, characterized in that: The lower layer of the test mold is a cube or cylindrical structure, and the upper layer of the test mold is a cube structure, and the projected area of the upper layer is 2 to 4 times that of the lower layer.

7. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 6, characterized in that: The upper layer and the lower layer of the test mold have the same height, and the height of the lower layer is 1 / 3 to 1 / 2 of the side length or diameter of the lower layer.

8. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 6, characterized in that: The side length of the lower inner cavity of the test mold is 75~100 mm, the surface flatness of the sprayed ultra-high performance concrete test block is ±5 mm, the diameter of the threaded steel bar is 8~12 mm, the upper end of the threaded steel bar is 5~10 mm away from the upper surface of the existing structure test block, and the upper end of the threaded steel bar extends 30~40 mm from the lower surface of the existing structure test block.

9. The test method for measuring the bond strength of direct-pull sprayed ultra-high concrete according to claim 8, characterized in that: When setting up the test fixture, the upper fixture and the lower fixture are pre-aligned along a coaxial line with the stretching rods on both sides, a plurality of distance measuring sensors are symmetrically arranged outwardly at the lateral edge ends of the lower fixture, and a reflective target is respectively arranged at the lateral edge ends of the upper fixture corresponding to each distance measuring sensor, a remote control terminal is provided to communicatively connect all the distance measuring sensors, distance data during pre-alignment is obtained through the distance measuring sensors, data from one of the distance measuring sensors is used as a comparison origin, and the difference in distance data obtained by the remaining distance measuring sensors is calculated as a comparison parameter; After the upper clamp and the lower clamp are respectively connected to the corresponding sprayed ultra-high performance concrete test block and the existing structure test block, the axis angles of the stretching rods on both sides are adjusted in combination with the vertical vial and the horizontal vial. The new distance measurement data obtained by the distance measurement sensor is compared with the corresponding comparison parameters to adjust the positions of the stretching rods on both sides relative to the bonding interface to achieve precise alignment of the axes of the stretching rods on both sides.

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