Forming method of 3D printed concrete interface tensile strength test specimen

Abstract

The present invention belongs to the field of intelligent manufacturing technology. Specifically, it relates to a method for forming a 3D printed concrete interface tensile strength test specimen, including the assembly process of the bottom mold component, the production process of the lower end of the specimen, the assembly process of the sleeve mold component, the assembly process of the bottom mold component and the sleeve mold component, the production process of the upper end of the specimen, and the maintenance and demolding process. The present application adopts an I-shaped specimen to obtain an interface layer that can test the tensile performance of the 3D printed concrete interface. The geometric configuration of the specimen is easy to implement tensile testing. A reasonable specimen configuration can increase the probability of damage in the interface layer, ensuring the test effect and the success rate of the test. The present application simulates the extrusion force of the 3D printer nozzle, the interval time of the interface layer and other parameters to produce the specimen. It can prepare the casting specimen without using 3D printing equipment, and also avoids problems such as damage to the interface layer, processing difficulties and large test errors caused by cutting and trimming the specimen.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent manufacturing technology, and in particular relates to a method for forming a 3D printed concrete interface tensile strength test specimen. Background Art

[0002] 3D-printed concrete technology uses an intelligent control system to carry out layered construction according to a pre-set program. Therefore, during the construction process, interlayer interfaces will be generated due to differences in the degree of concrete setting and hardening. The bonding performance of the interlayer interfaces is directly related to the overall quality of the concrete structure. Therefore, to ensure project quality and structural safety, a method for scientifically evaluating the interlayer interface performance of 3D-printed concrete must be selected.

[0003] Concrete inherently has a low tensile strength. For example, the tensile strength of ordinary concrete is only one-twentieth to one-tenth of its compressive strength. Due to the presence of interfaces between 3D-printed concrete layers, the tensile strength perpendicular to the printing path is even lower. Sufficient interfacial tensile strength is a key indicator for ensuring that 3D-printed concrete meets its overall service performance. Currently, conventional concrete tensile strength testing methods exist, including specimen configurations, molding tools, and testing methods. However, these molding tools and testing methods cannot be directly applied to the tensile testing and evaluation of the interfacial bond properties of 3D-printed concrete. In particular, specimen preparation cannot be performed using the same methods as direct tensile testing of ordinary concrete. Furthermore, it is difficult to produce tensile specimens that meet the requirements of traditional testing methods from 3D-printed structures through core drilling or other methods. Even if specimens meeting the tensile requirements can be produced by cutting out sections of the concrete, the complex cutting and grinding process is not only inefficient and difficult to ensure dimensional accuracy and surface smoothness, but also prone to damage to the specimen interface, resulting in significant errors in the test results.

[0004] Therefore, in order to make a reasonable evaluation of the interfacial bonding performance of 3D printed concrete and thus provide a scientific basis for the research and development of new 3D printed concrete materials and engineering construction, it is necessary to develop a complete set of specimen forming and preparation methods with a reasonable specimen structure, a simple forming mold structure, and the ability to accurately test and evaluate the interfacial bonding performance of 3D printed concrete. Summary of the Invention

[0005] The purpose of the present invention is to address the above-mentioned problems and shortcomings and provide a method for forming 3D printed concrete interface tensile strength test specimens. This application can prepare casting specimens without using 3D printing equipment, and also avoid problems such as interface layer damage, processing difficulties and large test errors caused by cutting and trimming specimens.

[0006] In order to achieve the above purpose, the technical solutions adopted are:

[0007] A method for forming a 3D-printed concrete interface tensile strength test specimen, comprising: using a 3D-printed concrete interface tensile strength test specimen forming mold to produce the test specimen, wherein the test specimen includes an upper specimen end and a lower specimen end, the upper specimen end and the lower specimen end being arranged relative to each other in an upper and lower direction; an interface layer is formed between the upper specimen end and the lower specimen end; the upper specimen end, the interface layer, and the lower specimen end are integrally formed into an I-shaped structure; and the 3D-printed concrete interface tensile strength test specimen forming mold includes a bottom mold assembly and a sleeve mold assembly, the bottom mold assembly and the sleeve mold assembly being arranged relative to each other in an upper and lower direction and connected by a first connecting unit;

[0008] The bottom mold assembly includes:

[0009] base plate;

[0010] A bottom mold front plate and a bottom mold rear plate are correspondingly arranged on both sides of the bottom plate, the inner side shapes of the bottom mold front plate and the bottom mold rear plate correspond to the side shape of the lower end of the test piece, the bottom mold front plate and the bottom mold rear plate are provided with plugging slots, and the bottom plate is provided with plugging bosses corresponding to the plugging slots;

[0011] A bottom mold partition, wherein at least two groups of corresponding first partition slots are provided on the bottom mold front plate and the bottom mold rear plate, the bottom mold partition is matched and clamped in the corresponding two first partition slots, and the lower end of the bottom mold partition is in contact with the bottom plate; and

[0012] a second connecting unit, the second connecting unit being arranged between the bottom mold front plate and the bottom mold rear plate, the second connecting unit being used for fixing the bottom mold front plate, the bottom mold partition plate and the bottom mold rear plate;

[0013] The mold assembly includes:

[0014] Front plate of die set;

[0015] The mold sleeve rear plate, the mold sleeve front plate and the mold sleeve rear plate are arranged opposite to each other, the inner side shapes of the mold sleeve front plate and the mold sleeve rear plate correspond to the side shapes of the upper end of the test piece, and at least two groups of corresponding second partition plate slots are provided on the mold sleeve front plate and the mold sleeve rear plate;

[0016] The mold sleeve partition is matched and clamped in the corresponding two second partition slots, and the bottom mold partition and the mold sleeve partition are correspondingly fitted one by one up and down; and

[0017] A third connecting unit is provided between the sleeve mold front plate and the sleeve mold rear plate, and is used for fixing the sleeve mold front plate, the sleeve mold partition plate and the sleeve mold rear plate;

[0018] The method for forming a 3D printed concrete interface tensile strength test specimen comprises the following steps:

[0019] Step a: Assembly of base mold components

[0020] Align and insert the plugging bosses of the bottom plate with the plugging slots of the bottom mold front plate, align and insert each bottom mold partition into the first partition slot of the bottom mold front plate, align and assemble the plugging slots and the first partition slots on the bottom mold rear plate with the bottom plate and the bottom mold partition respectively, and fasten the bottom mold front plate and the bottom mold rear plate through the second connecting unit to complete the assembly of the bottom mold assembly;

[0021] Step b: Preparation of the lower end of the specimen:

[0022] Squeeze the mixed 3D printing concrete into the base mold through the 3D printer nozzle or fill it into the base mold manually until the 3D printing concrete is filled and higher than the base mold assembly. Use a spatula to simulate the 3D printer nozzle to compact and scrape off the excess 3D printing concrete.

[0023] Step c: Assembling the mold components

[0024] Insert each mold sleeve partition into the second partition slot of the mold sleeve front plate, align the second partition slot of the mold sleeve rear plate with each mold sleeve partition, and connect and tighten the mold sleeve front plate and the mold sleeve rear plate through the third connecting unit to complete the assembly of the mold sleeve assembly;

[0025] Step d: Assembling the bottom mold assembly and the sleeve mold assembly

[0026] The sleeve mold assembly and the bottom mold assembly are connected and fixed by a first connecting unit to form a molding mold for the entire 3D printed concrete interface tensile strength test specimen;

[0027] Step e: Preparation of the upper end of the specimen

[0028] Based on the test results of the buildability of the printing material of 3D printed concrete, after the designed printing time interval has elapsed for the upper interface formed at the lower end of the specimen, 3D printed concrete is squeezed into the sleeve mold assembly using a 3D printer nozzle or manually filled until the sleeve mold assembly is completely filled with 3D printed concrete. The upper surface of the sleeve mold assembly is trimmed with a spatula and covered with plastic film to complete the production of the upper end of the specimen.

[0029] Step f: Curing and demoulding

[0030] After the concrete reaches the demoulding strength, the demoulding process is carried out and the test specimens are continued to be cured until the set curing age requirement is reached, and the production of the test specimens is completed.

[0031] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, in step c, after the sleeve mold assembly is assembled, the sleeve mold assembly is placed as a whole above the bottom mold assembly; or

[0032] In step c, during the assembly of the sleeve mold assembly, the sleeve mold front plate and the bottom mold front plate are first placed in an aligned position up and down, and then the sleeve mold partition plate and the sleeve mold rear plate are assembled.

[0033] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, docking limit bosses are provided on the outer sides of the bottoms of the sleeve mold front plate and the sleeve mold rear plate, the inner side surfaces of the docking limit bosses are inclined surfaces inclined outward, and the bottom mold front plate and the bottom mold rear plate are provided with side limit blocks corresponding to the side portions of the docking limit bosses; in step c, the sleeve mold front plate and the sleeve mold rear plate are both positioned with the bottom mold assembly through the docking limit bosses.

[0034] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, at least two groups of second connection units are provided between the bottom mold front plate and the bottom mold rear plate; in the bottom mold front plate and the bottom mold rear plate, both ends of one of them are provided with second connection slots, and the other is hingedly provided with a second connection screw corresponding to the second connection slot, and the movable end of the second connection screw is correspondingly clamped in the second connection slot and fastened by a second connection nut;

[0035] In step a, after the bottom mold rear plate is assembled, each second connecting screw is rotated into the corresponding second connecting slot in sequence, and each second connecting nut is pre-tightened and then tightened to complete the assembly of the bottom mold assembly.

[0036] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, at least two sets of third connection units are provided between the sleeve mold front plate and the sleeve mold rear plate; in the sleeve mold front plate and the sleeve mold rear plate, one of them is provided with third connection slots at both ends, and the other is hingedly provided with a third connection screw corresponding to the third connection slot, and the movable end of the third connection screw is correspondingly clamped in the third connection slot and fastened by a third connection nut;

[0037] In step c, after the assembly of the rear plate of the die sleeve is completed, each third connecting screw is rotated into the corresponding third connecting slot in sequence, and each third connecting nut is pre-tightened and then tightened to complete the assembly of the die sleeve assembly.

[0038] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, at least two groups of first connection units are provided between the sleeve mold front plate and the bottom mold front plate, and between the sleeve mold rear plate and the bottom mold rear plate, the sleeve mold front plate and the sleeve mold rear plate are provided with a plurality of U-shaped first connection slots, the bottom mold front plate and the bottom mold rear plate are hingedly provided with first connection screws corresponding to the first connection slots, and the movable ends of the first connection screws are correspondingly clamped in the first connection slots and fastened by first connection nuts;

[0039] In step d, after the sleeve mold assembly is assembled and aligned with the base mold assembly, each first connecting screw is rotated into the corresponding first connecting slot in turn, and each first connecting nut is pre-tightened and then tightened to complete the production of the 3D printed concrete interface tensile strength test specimen forming mold.

[0040] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, the plug-in boss is a stepped strip-type plug-in boss arranged on both sides of the base plate, and the plug-in slot is a strip-type plug-in groove arranged on the front plate and the rear plate of the base mold and corresponding to the strip-type plug-in boss.

[0041] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, the tops of the sleeve mold front plate and the sleeve mold rear plate are both provided with anti-slip baffles corresponding to the sleeve mold partitions; or

[0042] The top of each second partition slot does not penetrate to the top end surface of the corresponding sleeve mold front plate or sleeve mold rear plate, and anti-slip notches are provided on both sides of the upper end of the sleeve mold partition.

[0043] According to the 3D printing concrete interface tensile strength test specimen forming method of the present invention, preferably, the number of the bottom mold partitions and the sleeve mold partitions is 3 to 8, so that multiple test specimens can be formed in a single time.

[0044] The beneficial effects achieved by adopting the above technical solution are:

[0045] (1) The present invention can prepare casting specimens without using 3D printing equipment, and also avoids problems such as interface layer damage, processing difficulties and large test errors caused by cutting and trimming the specimens. The present application produces the specimens by simulating parameters such as the extrusion force of the 3D printer nozzle and the interval time through the interface layer; the present application uses an I-shaped specimen to obtain an interface layer that can test the tensile performance of the 3D printed concrete interface. The specimen geometric configuration is easy to implement tensile testing. A reasonable specimen configuration can increase the probability of damage in the interface layer, thereby ensuring the test effect and test success rate.

[0046] (2) The present invention adopts layered production of 3D printed concrete specimens. The formation of the interface layer is based on the test results of constructibility, which can better simulate the 3D printing construction conditions and truly reflect the interface tensile properties of 3D printed concrete. The structure of the test specimen can better ensure that the interface layer is consistent with the actual situation. When the interface layer is damaged, the performance parameters can be truly obtained.

[0047] (3) The specimen forming mold of the present invention adopts an assembly method, which can greatly reduce the impact on the integrity of the specimen during demoulding, and at the same time facilitate the cleaning of the mold and maintain the dimensional accuracy of the test mold. The batch production of the present application can produce test specimens with consistent structural performance in a single batch, thereby obtaining batch data based on multiple tests in a single batch, thereby reducing test errors and being able to more truly and effectively reflect interface performance data; in the process of producing test specimens, the present application can effectively control the forming time of the interface layer, thereby simulating the structure of the interface layer of real 3D printed concrete, and because the forming strength of the upper end and the lower end of the specimen is greater than that of the interface layer, the probability of preferential destruction of the interface layer can be greatly increased, thereby ensuring the reliability of the test.

[0048] (4) The setting of the limiting boss and the inclined surface of the specimen forming mold of the present invention ensures that the sizes of the bottom mold and the sleeve mold correspond accurately, the alignment is convenient, and there is no need for frequent position adjustment, which avoids damage to the lower end of the formed specimen during the production process, and ensures the dimensional accuracy of the prepared specimen, avoiding dimensional errors in the interface layer position; the present application will not affect the side of the specimen during the entire specimen production process, and does not require cutting, and reduces the risk and difficulty of demolding during the demolding process, greatly improving the quality and effect of molding.

[0049] (5) The specimen forming mold of the present invention has a simple structure, and the connection method of the screw and butterfly nut makes the assembly operation more convenient, which can reduce the test cost, improve the assembly efficiency of the mold and the specimen production efficiency, and can more accurately control the time of specimen production.

[0050] (6) The present invention can make feasible and convenient 3D printing concrete interface bonding performance tensile test specimens based on the forming mold, thereby facilitating scientific evaluation of the interface bonding performance of 3D printing concrete, providing a basic reference for the research and development of new 3D printing concrete materials and printing construction, and solving new problems faced by new 3D printing technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention. The drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0052] Figure 1 Schematic diagram of the structure of a 3D printed concrete interface tensile strength test specimen according to an embodiment of the present invention.

[0053] Figure 2 This is a schematic structural diagram of a 3D printed concrete interface tensioning specimen forming mold according to an embodiment of the present invention.

[0054] Figure 3This is a top view of the forming mold for the 3D printed concrete interface tensioning specimen according to an embodiment of the present invention.

[0055] Figure 4 This is a front view of the forming mold for the 3D printed concrete interface tensioning specimen according to an embodiment of the present invention.

[0056] Figure 5 This is a side view of a forming mold for a 3D printed concrete interface tensioning specimen according to an embodiment of the present invention.

[0057] Figure 6 2. A top view of a bottom mold assembly according to an embodiment of the present invention.

[0058] Figure 7 It is a front view of the bottom mold assembly according to an embodiment of the present invention.

[0059] Figure 8 A side view of a bottom mold assembly according to an embodiment of the present invention.

[0060] Figure 9 2. It is a top view of the sleeve mold assembly according to an embodiment of the present invention.

[0061] Figure 10 This is a front view of the sleeve mold assembly according to an embodiment of the present invention.

[0062] Figure 11 2 is a side view of a sleeve mold assembly according to an embodiment of the present invention.

[0063] Figure 12 It is a front view of the bottom mold partition according to an embodiment of the present invention.

[0064] Figure 13 This is a front view of the sleeve mold partition according to an embodiment of the present invention.

[0065] Figure 14 Schematic diagram of the structure of the base plate of an embodiment of the present invention.

[0066] Serial number in the picture:

[0067] 110 is the upper end of the specimen, 111 is the first section, 112 is the second section, 113 is the transition section, 120 is the lower end of the specimen, and 130 is the interface layer;

[0068] 200 is the first connecting unit, 201 is the first connecting screw, 202 is the first connecting slot, 203 is the first connecting nut, 204 is the first pin shaft, and 205 is the first hinge seat;

[0069] 300 is the bottom mold assembly, 310 is the bottom plate, 311 is the plug-in boss, 320 is the bottom mold front plate, 321 is the first partition plate slot, 322 is the plug-in slot, 330 is the bottom mold rear plate, 340 is the bottom mold partition, 350 is the second connecting unit, 351 is the second connecting screw, 352 is the second connecting slot, 353 is the second connecting nut, 354 is the second pin shaft, and 355 is the second hinge seat;

[0070] 400 is the mold assembly, 410 is the mold front plate, 411 is the second partition card slot, 412 is the docking limit boss, 413 is the inclined surface, 414 is the limit platform, 415 is the side limit block, 420 is the mold rear plate, 430 is the mold partition, 431 is the anti-slip recess, 440 is the third connecting unit, 441 is the third connecting screw, 442 is the third connecting card slot, 443 is the third connecting nut, 444 is the third pin shaft, and 445 is the third hinge seat. DETAILED DESCRIPTION

[0071] The following will be combined with the accompanying drawings of specific embodiments of the present invention to clearly and completely describe the exemplary embodiments of the present invention. Unless otherwise defined, technical or scientific terms used in the present invention should be given the common meanings understood by people with ordinary skills in the relevant field.

[0072] In the description of the present invention, it should be understood that the expressions “first” and “second” are used to describe the various elements of the present invention and do not represent any limitation on order, quantity or importance, but are only used to distinguish one component from another.

[0073] It should be noted that when one element is expressed as “connected”, “coupled” or “connected” to another element, it may mean that they are directly connected, coupled or connected, but it should be understood that there may be intermediate elements between the two; that is, the positional relationship of direct connection and indirect connection is covered.

[0074] It should be noted that the use of "a" or "an" and similar words does not necessarily indicate a limitation of quantity. "Include" or "comprising" and similar words mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects.

[0075] It should be noted that terms such as "up", "down", "left" and "right" that indicate orientation or positional relationships are only used to indicate relative positional relationships. This is for the convenience of describing the present invention, and does not mean that the device or element must have a specific orientation, be constructed and operated in a specific orientation. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0076] like Figures 1-13As shown, this application discloses a method for forming a 3D-printed concrete interface tensile strength test specimen, which uses a 3D-printed concrete interface tensile strength test specimen forming mold to produce the test specimen. Specifically, the method includes assembling the bottom mold assembly, making the lower end of the specimen, assembling the sleeve mold assembly, assembling the bottom mold assembly and sleeve mold assembly, making the upper end of the specimen, and curing and demolding steps.

[0077] The structure of the test specimen:

[0078] Since the test specimen needs to ensure that the interface layer is damaged during the stretching process, and then the strength test of the interface layer position is achieved, how to effectively control the damage position and how to make the corresponding test specimens need to be reasonably designed. Under the premise of ensuring the overall integrity and batch production of the test specimens, it is also necessary to be able to truly reflect the interface layer structure of 3D printed concrete. Therefore, the test specimen structure required to be made in this application is: the test specimen includes an upper end 110 and a lower end 120 of the specimen, and the upper end 110 and the lower end 120 of the specimen are arranged relative to each other in the upper and lower directions; an interface layer 130 is formed between the upper end 110 and the lower end 120 of the specimen; the upper end 110, the interface layer 130 and the lower end 120 of the specimen are in an I-shaped structure as a whole. Furthermore, the upper end 110 and the lower end 120 of the specimen each include a first section 111, a second section 112, and a transition section 113 disposed between the first section 111 and the second section 112. The transverse width of the first section 111 is greater than the transverse width of the second section 112. The transition section 113 is trapezoidal, and the transition section 113 smoothly transitions to the second section 112 in an arc shape. Through the design of the above structure, the rectangular columnar structure design of the first section and the second section can, on the one hand, facilitate the clamping of the first section by the stretching device, thereby providing sufficient stretching force. On the other hand, force is applied through the interface layer between the lower end and the upper end of the specimen and the second section. Under sufficient stretching force, the failure position of the specimen can be located at the designed interface layer. The design of the overall structure can provide sufficient stretching force for the destruction of the interface layer. With respect to the formation of the interface layer, this application is achieved through a forming mold and a forming method, so that the failure position can be accurately controlled to achieve a realistic simulation.

[0079] Structure of the molding die for 3D printed concrete interface tensile strength test specimens:

[0080] In order to obtain a specimen that can reflect the actual tensile strength of the 3D printed concrete interface, the present application provides a new assembled forming mold. Specifically, the 3D printed concrete interface tensile strength test specimen forming mold includes a bottom mold assembly 300 and a sleeve mold assembly 400. The bottom mold assembly 300 and the sleeve mold assembly 400 are arranged opposite to each other in the upper and lower parts and are connected by a first connecting unit 200.

[0081] The bottom mold assembly 300 includes a bottom plate 310, a bottom mold front plate 320 and a bottom mold rear plate 330 correspondingly arranged on both sides of the bottom plate 310, a bottom mold partition 340 and a second connecting unit 350, the inner side surface shapes of the bottom mold front plate 320 and the bottom mold rear plate 330 correspond to the side surface shape of the lower end head 120 of the specimen, the bottom mold front plate 320 and the bottom mold rear plate 330 are provided with plug-in slots, and the bottom plate 310 is provided with plug-in bosses 311 corresponding to the plug-in slots, the plug-in bosses are stepped strip-type plug-in bosses arranged on both sides of the bottom plate 310, and the plug-in slots are strip-type plug-in grooves arranged on the bottom mold front plate 320 and the bottom mold rear plate corresponding to the strip-type plug-in bosses. At least two groups of corresponding first partition slots 321 are provided on the bottom mold front plate 320 and the bottom mold rear plate 330, and the bottom mold partition 340 is matched and clamped in the corresponding two first partition slots 321, and the lower end of the bottom mold partition 340 is in contact with the bottom plate 310; the second connecting unit 350 is provided between the bottom mold front plate 320 and the bottom mold rear plate 330, and the second connecting unit 350 is used to fix the bottom mold front plate 320, the bottom mold partition 340 and the bottom mold rear plate 330.

[0082] Preferably, in this embodiment, at least two sets of second connecting units 350 are disposed between the bottom mold front plate 320 and the bottom mold rear plate 330. Second connecting slots 352 are provided at both ends of one of the bottom mold front plate 320 and the bottom mold rear plate 330, and a second connecting screw 351 corresponding to the second connecting slot 352 is hingedly provided on the other. The movable ends of the second connecting screws 351 are correspondingly engaged in the second connecting slots 352 and secured by second connecting nuts 353. To install the second connecting screws, in this embodiment, the second connecting screws are hingedly connected to second hinged seats 355 on the bottom mold front plate or the bottom mold rear plate via second pins 354.

[0083] The mold assembly 400 includes a mold front plate 410, a mold rear plate 420, a mold partition 430 and a third connecting unit 440. The mold front plate 410 and the mold rear plate 420 are arranged relative to each other, and the inner side shapes of the mold front plate 410 and the mold rear plate 420 correspond to the side shapes of the upper end 110 of the specimen. At least two groups of corresponding second partition card slots 411 are provided on the mold front plate 410 and the mold rear plate 420; the mold partition 430 is matched and carded in the corresponding two second partition card slots 411, and the bottom mold partition 340 and the mold partition 430 are correspondingly fitted one by one up and down; the third connecting unit 440 is provided on the Between the front and rear mold plates 410 and 420, the third connecting units 440 are used to secure the front and rear mold plates 410, 430, and 420. In this embodiment, at least two sets of third connecting units 440 are provided between the front and rear mold plates 410 and 420. One of the front and rear mold plates 410 and 420 has third connecting slots 442 at both ends, and the other is hingedly provided with a third connecting screw 441 corresponding to the third connecting slot 442. The movable end of the third connecting screw 441 is correspondingly retained in the third connecting slot 442 and secured by a third connecting nut 443. In this embodiment, the third connecting screw is hingedly connected to a third hinge seat 445 on the front or rear mold plate via a third pin 444.

[0084] In order to ensure the effective positioning of the sleeve mold assembly and the bottom mold assembly and avoid damage to the test piece surface due to frequent adjustments during the positioning process, the present application provides docking limit bosses 412 on the bottom outer sides of the sleeve mold front plate 410 and the sleeve mold rear plate 420. The inner side surface of the docking limit boss 412 is an outwardly inclined inclined surface 413. The bottom mold front plate and the bottom mold rear plate are provided with side limit blocks corresponding to the side portions of the docking limit bosses. Through the eight-shaped inclined surface structure on the two groups of left and right docking limit bosses, effective alignment can be achieved, which greatly reduces the difficulty of alignment of the sleeve mold and the bottom mold and improves the convenience and practicality of operation.

[0085] In this embodiment, at least two groups of first connecting units 200 are provided between the sleeve mold front plate 410 and the bottom mold front plate 320, and between the sleeve mold rear plate 420 and the bottom mold rear plate 330. The sleeve mold front plate 410 and the sleeve mold rear plate 420 are provided with a plurality of U-shaped first connecting slots 202. The bottom mold front plate 320 and the bottom mold rear plate 330 are hingedly provided with first connecting screws 201 corresponding to the first connecting slots 202. The movable ends of the first connecting screws are correspondingly clamped in the first connecting slots 202 and are connected by first connecting nuts 201. 03 Tightening, for the installation of the first connecting screw, in this embodiment, the first connecting screw is hinged to the first hinge seat 205 on the front plate or the rear plate of the sleeve mold through the first pin shaft 204; when the bottom mold assembly and the sleeve mold assembly are aligned and assembled, the side limit block and the docking limit boss can respectively play a lateral and longitudinal limiting role in one direction, and the first connecting screw can be aligned and engaged with the first connecting slot, and can also play the same lateral limiting role, and cooperate with the inclined surface of the docking limit boss to achieve circumferential positioning, thereby ensuring its alignment accuracy.

[0086] The connecting nuts in the first connecting unit, the second connecting unit and the third connecting unit of the above structure are butterfly nuts, which are convenient for pre-tightening at any time, and the structure of each connecting unit can also adopt other structural forms, such as bolt connection structure or clamps and other relatively commonly used connection and fixing structures in the existing technology, so they will not be repeated.

[0087] The tops of the sleeve mold front plate 410 and the sleeve mold rear plate 420 are both provided with anti-slip baffles corresponding to the sleeve mold partition 430; or the tops of the second partition slots 411 do not penetrate to the top surface of the corresponding sleeve mold front plate 410 or sleeve mold rear plate 420, that is, the tops of the second partition slots form a limit platform 414, and the upper ends of the sleeve mold partitions 430 are provided with anti-slip recesses 431 corresponding to the limit platforms. In order to realize the batch production of test specimens and obtain data more accurately through batch testing, provide sufficient data support, and reduce single measurement errors, the number of bottom mold partitions 340 and sleeve mold partitions 430 in this application is 3 to 8, and then 2-7 or even more test specimens are produced. The number of partitions can be selected according to the actual needs of interface bonding strength evaluation and the difficulty of mold assembly.

[0088] The above-mentioned splicing structure forming mold can more conveniently produce I-shaped test specimens and facilitate demolding, greatly reducing damage to the test specimens and ensuring the integrity of the specimens, thereby truly reflecting the interfacial bonding strength of 3D printed concrete.

[0089] Based on the above test specimens and forming molds, the 3D printing concrete interface tensile strength test specimen forming method of the present application specifically includes the following steps:

[0090] Step a: Assembly of the bottom mold assembly 300

[0091] Align and insert the insertion bosses 311 and insertion slots between the bottom plate 310 and the bottom mold front plate 320. Align and insert each bottom mold partition plate 340 into the first partition plate slots 321 of the bottom mold front plate 320. Align and assemble the insertion slots and first partition plate slots 321 on the bottom mold rear plate 330 with the bottom plate 310 and bottom mold partition plates 340, respectively. Connect and secure the bottom mold front plate 320 and bottom mold rear plate 330 via the second connecting unit 350, completing the assembly of the bottom mold assembly 300. During the assembly process, after the bottom mold rear plate 330 is assembled, each second connecting screw 351 is rotated into the corresponding second connecting slot 352, pre-tightened, and then tightened. This completes the assembly of the bottom mold assembly 300.

[0092] Step b: Manufacturing process of the lower end 120 of the specimen

[0093] The mixed 3D printing concrete is squeezed into the bottom mold through the 3D printer nozzle or manually filled into the bottom mold until the 3D printing concrete is filled and higher than the bottom mold assembly 300. A spatula is used to simulate the 3D printer nozzle to compact and scrape off excess 3D printing concrete.

[0094] Step c: Assembling the mold assembly 400

[0095] Each mold sleeve partition plate 430 is correspondingly inserted into the second partition plate slot 411 of the mold sleeve front plate 410, and then the second partition plate slot 411 of the mold sleeve rear plate 420 is aligned and assembled with each mold sleeve partition plate 430. The mold sleeve front plate 410 and the mold sleeve rear plate 420 are connected and fastened together using the third connecting unit 440 to complete the assembly of the mold sleeve assembly 400. In this process, the specific assembly method of the third connecting unit is as follows: after the mold sleeve rear plate 420 is assembled, each third connecting screw 441 is rotated into the corresponding third connecting slot 442 in sequence, and each third connecting nut 443 is pre-tightened and then tightened to complete the assembly of the mold sleeve assembly 400.

[0096] Step d: Assembling the bottom mold assembly 300 and the sleeve mold assembly 400

[0097] The sleeve mold assembly 400 and the bottom mold assembly 300 are connected and fixed by the first connecting unit 200 to form the entire 3D printed concrete interface tensile strength test specimen forming mold; the specific assembly method of the first connecting unit is: after the sleeve mold assembly 400 is completed and aligned with the bottom mold assembly 300, each first connecting screw 201 is rotated into the corresponding first connecting slot 202 in turn, and each third connecting nut 443 is pre-tightened and then tightened to complete the production of the 3D printed concrete interface tensile strength test specimen forming mold.

[0098] It is also possible to provide docking limit bosses 412 on the outer sides of the bottoms of the sleeve mold front plate 410 and the sleeve mold rear plate 420, wherein the sleeve mold front plate 410 and the sleeve mold rear plate 420 are both positioned with the bottom mold assembly 300 through the docking limit bosses 412. In order to achieve overall precise positioning, during the assembly process, the side limit blocks and the docking limit bosses are limited, the first connecting screws and the first connecting slots are limited, and the inclined surfaces of the docking limit bosses are limited to achieve effective positioning in the horizontal direction, thereby achieving accurate and rapid assembly. Specifically, after the assembly of the sleeve mold assembly is completed, the first connecting screw is clamped in the first connecting groove before the sleeve mold assembly and the bottom mold assembly are aligned. At this time, the cooperation between the first connecting screw and the first connecting groove can play a one-dimensional constraint and limiting role. As the sleeve mold assembly continues to move downward, further limiting can be performed between the docking limit boss and the side limit block, the inclined surface and the bottom mold assembly. During the entire process, the first connecting nut can be continuously pre-tightened to maintain the effective limitation of the first connecting screw, thereby achieving precise positioning and assembly.

[0099] Step e: Manufacturing process of the upper end 110 of the specimen

[0100] Based on the test results of the buildability of the printing material of 3D printed concrete, after the designed printing time interval has passed for the upper interface formed by the lower end 120 of the specimen, 3D printed concrete is squeezed into the sleeve mold assembly 400 using a 3D printer nozzle or manually filled until the 3D printed concrete fills the sleeve mold assembly 400. The upper surface of the sleeve mold assembly 400 is trimmed with a spatula and covered with plastic film to complete the production of the upper end 110 of the specimen.

[0101] Step f: Curing and demoulding process

[0102] After the concrete reaches the demolding strength, it generally needs 24 hours of curing, then the formwork is removed and the test specimens are continued to be cured. The curing cycle is generally about 28 days until the set requirements are met and the molding of the test specimens is completed.

[0103] Finally, a tensile test was carried out on the test specimen using a tensile device to extract the experimental data of the effective failure position, and then obtain the performance parameters such as the tensile strength of the bonding interface of the 3D printed concrete.

[0104] In step c, after the sleeve mold assembly 400 is assembled, the entire sleeve mold assembly 400 is placed above the base mold assembly 300. Alternatively, in step c, during the sleeve mold assembly 400 process, the sleeve mold front plate 410 and the base mold front plate 320 are first aligned vertically, and then the sleeve mold partition plate 430 and the sleeve mold rear plate 420 are assembled. The sleeve mold assembly can be installed by both integral assembly and disassembly.

[0105] During the assembly process of the above-mentioned bottom mold assembly and the sleeve mold assembly, in order to facilitate subsequent demolding, a release agent is applied to the bottom mold front plate, bottom mold rear plate, bottom plate, sleeve mold front plate and sleeve mold rear plate before assembly.

[0106] While preferred embodiments for implementing the present invention have been described in detail above, it should be understood that these embodiments are provided for illustrative purposes only and are not intended to limit the scope, applicability, or configuration of the present invention in any way. The scope of the present invention is defined by the appended claims and their equivalents. Persons skilled in the art may make numerous modifications to the aforementioned embodiments in light of the present invention, and such modifications are intended to fall within the scope of the present invention.

Claims

1. A method for forming a 3D printed concrete interface tensile strength test specimen, characterized in that: A test specimen is produced using a 3D printed concrete interface tensile strength test specimen forming mold, wherein the test specimen includes an upper end and a lower end, which are arranged relative to each other up and down; an interface layer is formed between the upper end and the lower end; the upper end, the interface layer and the lower end of the specimen are in an I-shaped structure as a whole, and the upper end and the lower end of the specimen each include a first section, a second section, and a transition section arranged between the first section and the second section, the transverse width dimension of the first section is greater than the transverse width dimension of the second section, the transition section is trapezoidal, and the transition section and the second section have an arc-shaped smooth transition; the 3D printed concrete interface tensile strength test specimen forming mold includes a bottom mold assembly and a sleeve mold assembly, which are arranged relative to each other up and down and connected by a first connecting unit; The bottom mold assembly includes: base plate; A bottom mold front plate and a bottom mold rear plate are correspondingly arranged on both sides of the bottom plate, the inner side shapes of the bottom mold front plate and the bottom mold rear plate correspond to the side shape of the lower end of the test piece, the bottom mold front plate and the bottom mold rear plate are provided with plugging slots, and the bottom plate is provided with plugging bosses corresponding to the plugging slots; A bottom mold partition, wherein at least two groups of corresponding first partition slots are provided on the bottom mold front plate and the bottom mold rear plate, the bottom mold partition is matched and clamped in the corresponding two first partition slots, and the lower end of the bottom mold partition is in contact with the bottom plate; and a second connecting unit, the second connecting unit being arranged between the bottom mold front plate and the bottom mold rear plate, the second connecting unit being used for fixing the bottom mold front plate, the bottom mold partition plate and the bottom mold rear plate; The mold assembly includes: Front plate of die set; The mold sleeve rear plate, the mold sleeve front plate and the mold sleeve rear plate are arranged opposite to each other, the inner side shapes of the mold sleeve front plate and the mold sleeve rear plate correspond to the side shape of the upper end of the test piece, and at least two groups of corresponding second partition card grooves are provided on the mold sleeve front plate and the mold sleeve rear plate; docking limit bosses are provided on the outer sides of the bottoms of the mold sleeve front plate and the mold sleeve rear plate, the inner side surfaces of the docking limit bosses are outwardly inclined inclined surfaces, and the bottom mold front plate and the bottom mold rear plate are provided with side limit blocks corresponding to the side portions of the docking limit bosses; The mold sleeve partition is matched and clamped in the corresponding two second partition slots, and the bottom mold partition and the mold sleeve partition are correspondingly fitted one by one up and down; and A third connecting unit is provided between the sleeve mold front plate and the sleeve mold rear plate, and is used for fixing the sleeve mold front plate, the sleeve mold partition plate and the sleeve mold rear plate; The method for forming a 3D printed concrete interface tensile strength test specimen comprises the following steps: Step a: Assembly of base mold components Align and insert the plugging bosses and plugging slots between the bottom plate and the bottom mold front plate, align and insert each bottom mold partition into the first partition slot of the bottom mold front plate, align and assemble the plugging slots and first partition slots on the bottom mold rear plate with the bottom plate and the bottom mold partition respectively, and fasten the bottom mold front plate and the bottom mold rear plate through the second connecting unit to complete the assembly of the bottom mold assembly; Step b: Preparation of the lower end of the specimen: Squeeze the mixed 3D printing concrete into the base mold through the 3D printer nozzle or fill it into the base mold manually until the 3D printing concrete is filled and higher than the base mold assembly. Use a spatula to simulate the 3D printer nozzle to compact and scrape off the excess 3D printing concrete. Step c: Assembling the mold components Insert each mold sleeve partition into the second partition slot of the mold sleeve front plate, align the second partition slot of the mold sleeve rear plate with each mold sleeve partition, and connect and tighten the mold sleeve front plate and the mold sleeve rear plate through the third connecting unit to complete the assembly of the mold sleeve assembly; After the sleeve mold assembly is assembled, the sleeve mold assembly is placed as a whole on top of the bottom mold assembly; or During the assembly of the die sleeve components, first align the die sleeve front plate and the bottom die front plate up and down, and then assemble the die sleeve partition plate and the die sleeve rear plate. The front plate and the rear plate of the sleeve mold are both positioned with the bottom mold assembly by docking the limiting bosses; Step d: Assembling the bottom mold assembly and the sleeve mold assembly The sleeve mold assembly and the bottom mold assembly are connected and fixed by a first connecting unit to form a molding mold for the entire 3D printed concrete interface tensile strength test specimen; Step e: Preparation of the upper end of the specimen Based on the test results of the buildability of the printing material of 3D printed concrete, after the designed printing time interval has elapsed for the upper interface formed at the lower end of the specimen, 3D printed concrete is squeezed into the sleeve mold assembly using a 3D printer nozzle or manually filled until the sleeve mold assembly is completely filled with 3D printed concrete. The upper surface of the sleeve mold assembly is trimmed with a spatula and covered with plastic film to complete the production of the upper end of the specimen. Step f: Curing and demoulding After the concrete reaches the demoulding strength, the demoulding process is carried out and the test specimens are continued to be cured until the set curing age requirement is reached, and the production of the test specimens is completed.

2. The method for forming a 3D printed concrete interface tensile strength test specimen according to claim 1, characterized in that: At least two sets of second connection units are provided between the bottom mold front plate and the bottom mold rear plate; in the bottom mold front plate and the bottom mold rear plate, both ends of one of them are provided with second connection slots, and the other is hingedly provided with a second connection screw corresponding to the second connection slot, and the movable end of the second connection screw is correspondingly clamped in the second connection slot and fastened by a second connection nut; In step a, after the bottom mold rear plate is assembled, each second connecting screw is rotated into the corresponding second connecting slot in sequence, and each second connecting nut is pre-tightened and then tightened to complete the assembly of the bottom mold assembly.

3. The method for forming a 3D printed concrete interface tensile strength test specimen according to claim 1, characterized in that: At least two sets of third connection units are provided between the sleeve mold front plate and the sleeve mold rear plate; in the sleeve mold front plate and the sleeve mold rear plate, one of them is provided with third connection slots at both ends, and the other is hingedly provided with a third connection screw corresponding to the third connection slot, and the movable end of the third connection screw is correspondingly clamped in the third connection slot and fastened by a third connection nut; In step c, after the assembly of the rear plate of the die sleeve is completed, each third connecting screw is rotated into the corresponding third connecting slot in sequence, and each third connecting nut is pre-tightened and then tightened to complete the assembly of the die sleeve assembly.

4. The method for forming a 3D printed concrete interface tensile strength test specimen according to claim 1, characterized in that: At least two groups of first connection units are provided between the sleeve mold front plate and the bottom mold front plate, and between the sleeve mold rear plate and the bottom mold rear plate. The sleeve mold front plate and the sleeve mold rear plate are provided with a plurality of U-shaped first connection slots. The bottom mold front plate and the bottom mold rear plate are hingedly provided with first connection screws corresponding to the first connection slots. The movable ends of the first connection screws are correspondingly clamped in the first connection slots and fastened by first connection nuts. In step d, after the sleeve mold assembly is assembled and aligned with the base mold assembly, each first connecting screw is rotated into the corresponding first connecting slot in turn, and each first connecting nut is pre-tightened and then tightened to complete the production of the 3D printed concrete interface tensile strength test specimen forming mold.

5. The method for forming a 3D printed concrete interface tensile strength test specimen according to claim 1, characterized in that: The plug-in bosses are stepped strip-type plug-in bosses arranged on both sides of the base plate, and the plug-in slots are strip-type plug-in recesses arranged on the front plate and the rear plate of the base mold and corresponding to the strip-type plug-in bosses.

6. The method for forming a 3D printed concrete interface tensile strength test specimen according to claim 1, characterized in that: The tops of the sleeve mold front plate and the sleeve mold rear plate are both provided with anti-slip baffles corresponding to the sleeve mold partitions; or The top of each second partition slot does not penetrate to the top end surface of the corresponding sleeve mold front plate or sleeve mold rear plate, and anti-slip notches are provided on both sides of the upper end of the sleeve mold partition.

7. The method for forming a 3D printed concrete interface tensile strength test specimen according to claim 1, characterized in that: The number of the bottom mold partitions and the sleeve mold partitions is 3 to 8, so that multiple test specimens can be formed at a single time.

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