A concrete aggregate spatial positioning method, a concrete test piece manufacturing device, and a concrete test piece pouring method

Abstract

This invention provides a method for spatial positioning of concrete aggregates, a device for making concrete specimens, and a method for casting concrete specimens, belonging to the field of specimen preparation technology. The positioning method establishes a three-dimensional space by collecting and building an aggregate model library. Aggregate models are automatically arranged in the space according to a preset aggregate gradation ratio and quantity. Using a preset height as a stratification benchmark, the space is divided into several layers from bottom to top, and a corresponding layer number is generated for each aggregate model based on the height of its lowest point. The outer contour of the aggregate to be positioned is projected upwards as a defined range, with the positioning point located within this range and intersecting the outer surface of the aggregate. The centroid projection line of the aggregate to be positioned passes through the positioning point or is located within the connection range of the positioning point. This yields the layer number and positioning point coordinates of the aggregate to be positioned in the specimen making device during subsequent specimen casting. This method achieves precise placement and stable positioning of the aggregates, improving the consistency of the specimen structure and the reliability of experimental data.

Description

Technical Field

[0001] This invention belongs to the field of specimen preparation technology, specifically relating to a method for spatial positioning of concrete aggregates, a device for making concrete specimens, and a method for pouring concrete specimens. Background Technology

[0002] Fully graded concrete is a core structural material in large-scale water conservancy projects, especially high arch dam structures, and its mechanical properties directly affect the stability and safety of the engineering structure. Compared with ordinary concrete, fully graded concrete uses coarse aggregates with a maximum particle size of up to 150 mm, which places higher demands on the molding size and internal structure control of concrete specimens. In the field of concrete experimental research, especially for the analysis of fracture mechanisms, crack propagation paths, and micromechanical behavior, the spatial distribution of large aggregates in the specimen has a crucial impact on the accuracy and repeatability of experimental results. Currently, commonly used concrete preparation methods employ free placement, where the spatial position and arrangement of aggregates in the specimen are uncontrollable and highly randomized. The aggregate distribution varies considerably between each test specimen. Since concrete testing is a destructive test, the variability between specimens affects crack propagation paths, stress concentration areas, and the repeatability and stability of experimental results, increasing the uncertainty in structural design and analysis, and making it difficult to use for establishing clear numerical models or conducting repeatable experimental comparisons. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for spatial positioning of concrete aggregates, a device for making concrete specimens, and a method for casting concrete specimens, which can realize the precise placement and stable positioning of large-diameter aggregates in large-size concrete specimens, improve the stress consistency of the specimen structure and the reliability of experimental data, and meet the engineering needs of simulating the seismic resistance and failure process of complex structures.

[0004] This invention discloses a method for spatial positioning of concrete aggregates, comprising the following steps: Collect and establish an aggregate model library; Establish a space of a preset size, wherein the space is a three-dimensional space in which the X, Y and Z directions are perpendicular to each other; According to the preset aggregate gradation ratio and quantity, aggregate models are selected from the aggregate model library, and the selected aggregate models are automatically arranged in the space using a spatial collision detection algorithm. Using a preset height as the stratification benchmark, the space is divided into several layers from bottom to top along the Z direction. A corresponding layer number is generated for each aggregate model based on the height of the lowest point of each aggregate model in the space. The positioning points of the aggregate models in the same layer are determined one by one. The determination process includes the following steps: the outer contour of the aggregate to be positioned is projected upward as a limited range, the positioning point is located within the limited range and intersects with the outer surface of the aggregate to be positioned, and the center of gravity projection line of the aggregate to be positioned passes through the positioning point or is located within the connection range of the positioning point. Output the layer number N of the aggregate to be positioned and the spatial coordinates (x, y, z) of the positioning point.

[0005] Furthermore, the aggregate includes three-grade aggregate and four-grade aggregate, and the preset height range is 25mm-35mm.

[0006] The minimum particle size of the three-grade aggregate is about 40mm. A layer height of 25mm-35mm ensures that the steel wire does not penetrate into the mortar layer during subsequent aggregate suspension and positioning, and does not cause disturbance or embedding. At the same time, it can provide sufficient vertical arrangement accuracy, so that each layer of aggregate has an independent and controllable positioning height during the pouring process, and facilitates layer-by-layer consolidation.

[0007] Based on the same inventive concept, this invention also provides a concrete specimen preparation device based on the above-mentioned concrete aggregate spatial positioning method. The device includes a base plate, two end plates, two side plate assemblies, and a positioning assembly. The base plate is perpendicular to the Z-direction; The two end plates are perpendicular to the X-direction and are respectively connected to the two ends of the base plate in the X-direction. The two side plate assemblies are perpendicular to the Y direction and are respectively connected to the two ends of the base plate in the Y direction; The cavity formed by the bottom plate, the end plate, and the side plate assembly is a three-dimensional space of a preset size; The positioning assembly includes two fixing plates, a positioning line, and a positioning rod; The fixing plate is opposite to and perpendicular to the Y direction, and is fixed to the outside of the three-dimensional space; The positioning lines are arranged along the Y direction, and the two ends of the positioning lines are detachably connected to the fixing plate. One end of the positioning rod is vertically connected to the positioning line.

[0008] Furthermore, the side panel assembly includes several unit panels, which are detachably connected sequentially along the Z-direction, and the height of each unit panel is a preset height.

[0009] Based on the same inventive concept, the present invention also provides a method for casting concrete specimens, using the above-mentioned concrete specimen preparation apparatus, comprising the following steps: S1. Install positioning blocks at the positioning points of the aggregate; S2. Assemble the base plate, end plate and side plate according to the preset three-dimensional space to form an open top accommodating space; S3. Position the aggregates in the same layer. Based on the coordinates (x, y, z) of the positioning point of the aggregate to be positioned in the bottom layer, thread a positioning line on the fixing plate. The positioning line is located in the plane X=x and the height of the positioning line is greater than z. Hang the positioning rod on the positioning line. The coordinates of the lower end of the positioning rod are (x, y, z). Connect the positioning block on the aggregate to be positioned to the lower end of the positioning rod. Repeat the above operation to suspend and position other aggregates to be positioned in the same layer in turn. S4. Pour mortar into the accommodating space to the preset height and vibrate it. After the mortar has initially set, remove the positioning lines and positioning rods that will affect the layout of the upper aggregate. S5. Repeat S3 and S4, performing positioning, pouring, and unhanging operations on the aggregates to be positioned layer by layer from bottom to top, until the aggregate positioning and pouring of the entire specimen are completed.

[0010] Compared with existing testing techniques for large-volume concrete components, this invention has the following advantages: 1. By using 3D modeling and path planning, interference from other aggregates is eliminated, and the stable positioning point of large-diameter aggregate in the concrete specimen is determined. In the subsequent pouring process, the positioning of the aggregate in the specimen is precisely guided. 2. Compared with the traditional free placement method, the present invention uses a steel wire guide and physical positioning device to achieve precise spatial placement of large-diameter aggregates in large-size specimens, which improves the controllability of the internal structure of the specimen and the repeatability of experimental results. 3. Compared with the indirect method of using small-sized wet-sieve specimens to derive the performance of fully graded concrete, this invention effectively preserves the mechanical characteristics of the original rock aggregate by directly preparing large-volume specimens consistent with the actual engineering conditions, thereby improving the representativeness and accuracy of the test results. 4. The mold adopts a spliced ​​side mold structure and adjustable template unit to adapt to different pouring height requirements. The steel wire positioning component can be disassembled and reused. The overall structure is easy to assemble, convenient to transport, and suitable for batch application. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of aggregate suspension provided by some embodiments of the present invention; Figure 2 This is a schematic diagram of aggregate suspension provided by some embodiments of the present invention; Figure 3 This is a left-side sectional view of the spatial positioning of the concrete specimen preparation device provided in some embodiments of the present invention; Figure 4 This is a three-dimensional schematic diagram of the spatial positioning of the concrete specimen preparation device provided in some embodiments of the present invention; Figure 5 This is a left view of a concrete specimen preparation apparatus provided in some embodiments of the present invention.

[0012] Explanation of reference numerals in the attached figures: 001 Aggregate, 100 Base Plate, 110 Tie Rod, 200 End Plate, 300 Side Plate Assembly, 310 Unit Plate, 400 Positioning Assembly, 410 Fixing Plate, 420 Positioning Line, 430 Positioning Rod, 440 Positioning Block. Detailed Implementation

[0013] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the invention. It should be noted that the terms "set," "connect," and "install" should be interpreted broadly, for example, referring to direct connection, indirect connection, or integral connection. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0014] Data was collected on the tertiary and quaternary aggregates in the full-graded coarse aggregate used in the dam structure. The data included surface contour and structural image data, mass data, and weight distribution data. For example, in this embodiment, the tertiary aggregate particle size range was 40–80 mm, with approximately 450 particles selected, totaling approximately 155 kg; the quaternary aggregate particle size range was 80–150 mm, with approximately 90 particles selected, totaling approximately 155 kg. Referring to the aggregate shape characterization method proposed by Su Dong et al. in "Characteristics of Aggregate and Recycled Aggregate Particle Shape Based on 3D Scanning and Spherical Harmonic Analysis," 3D models of each aggregate were obtained. A structured light 3D scanner was used to perform a full-angle 3D scan of each aggregate, acquiring its surface contour and structural image data. The image data underwent preprocessing such as noise reduction, stitching, and meshing before being stored to establish an aggregate model library, which was then imported into the modeling software.

[0015] According to the "Test Procedure for Hydraulic Concrete" and general engineering testing experience, the minimum geometric dimension of the specimen must be at least three times the maximum particle size of the coarse aggregate. The maximum aggregate particle size in the fully graded concrete used in the dam structure is 150mm, therefore the minimum cross-sectional side length of the concrete specimen must be at least 450mm. Taking the three-point bending beam test as an example, the loading span and supporting structure design requirements of the three-point bending beam test must ensure sufficient crack development length and pure bending zone length in the effective mid-span area. The specimen length is set at 1550mm, a size that simultaneously satisfies the requirements for demonstrating the true mechanical behavior of the fully graded aggregate and the processing and arrangement conditions of large-scale structural testing equipment. Based on the above requirements, using the specimen fabrication for the three-point bending beam test as a specific example, the specimen dimensions are 1550mm long, 450mm wide, and 450mm high. A space with dimensions of 1550mm × 450mm × 450mm is created in the modeling software, corresponding to the specimen dimensions. This space also corresponds to the specimen casting space. In another embodiment, if the tensile properties of fully graded concrete are studied, the specimen dimensions are 900mm long, 450mm wide, and 450mm high. Correspondingly, a space with dimensions of 900mm×450mm×450mm is created in the modeling software to correspond to the dimensions of the tensile specimen.

[0016] Based on the preset aggregate gradation ratio and quantity, aggregate models are selected from the aggregate model library, referencing the "Boolean cutting intrusion discrimination method" proposed by Wu Yuhang et al. in "Establishment of Three-Dimensional Mesoscopic Random Model of Concrete Based on Python-Abaqus". By introducing geometric Boolean operations during the random aggregate placement process, it is determined whether "interference" occurs between newly generated aggregates and existing aggregates. If geometric overlap is detected, the placement position is abandoned and regenerated; otherwise, the position is accepted, thus ensuring that the aggregates remain non-overlapping in three-dimensional space. The selected aggregate models are automatically arranged in space using the aforementioned spatial collision detection algorithm, ensuring that aggregates of different particle sizes are randomly distributed in three-dimensional space without contact, and controlling the minimum distance between any two aggregates to be greater than 3mm.

[0017] The minimum particle size of the three-grade aggregate is approximately 40mm. A layer height of 25mm-35mm ensures that the steel wire will not penetrate the mortar layer during subsequent aggregate suspension and positioning, preventing disturbance or embedding. Simultaneously, it provides sufficient vertical arrangement accuracy, allowing each layer of aggregate to have an independently controllable positioning height during pouring, and facilitating layer-by-layer consolidation. In this embodiment, the space is discretized using 30mm as the layering benchmark, dividing the space into fifteen layers. A corresponding layer number is generated for each aggregate model based on the height of its lowest point in the spatial coordinate system; this layer number is the pouring layer number for that aggregate.

[0018] Within the modeling space, positioning points are determined for each aggregate model on the same layer. During subsequent specimen casting, suspended positioning rods 430 are connected to these positioning points to locate the aggregate at that point, thus positioning the corresponding aggregate in a predetermined position within the specimen. In one embodiment, a positioning point is selected on the outer surface of the aggregate 001 to be determined in the 3D model as its suspension positioning point. This point does not geometrically overlap with surrounding aggregates in the upward viewing direction. The centroid projection line of the aggregate model to be determined passes through this positioning point, and the 3D coordinate data of this point and its corresponding layer number are output. Figure 1 As shown, a hole is subsequently drilled at this positioning point, and a positioning bolt or other connecting component is used as a positioning block 440 to suspend the aggregate, thus positioning the aggregate in the casting space. The perforation area at the positioning point is located in the upper middle part of the aggregate. In the three-point bending beam test, the stress area of ​​the aggregate is mainly located on the lower side of the aggregate. The perforation at the positioning point avoids the main stress area, and the small hole diameter will not cause significant damage to the aggregate, preserving the original mechanical properties and shape boundary of the aggregate. In another embodiment, as... Figure 2 As shown, in the 3D model, two positioning points are selected on the outer surface of the aggregate 001 to be determined as preset positions for positioning patches 441. These two positioning points do not geometrically overlap with the surrounding aggregates in the upward viewing direction. The projection line of the center of gravity of the aggregate model to be determined passes through the connecting line of the positioning points. The local surface curvature of the aggregate surface where the positioning points are located is moderate, and the distance between the two points is reasonable. The 3D coordinate data of these two points and their corresponding layer numbers are output. Subsequently, hooks are attached to these two points as positioning blocks 440, and positioning rods 430 suspend the hooks at the aggregate positioning points for physical positioning of the aggregate during subsequent pouring. In another embodiment, three positioning points are selected on the outer surface of the aggregate 001 to be determined as preset positions for positioning patches 441 in the 3D model. The projection line of the center of gravity of the aggregate model to be determined passes through the area enclosed by the connecting line of the three positioning points.

[0019] Please refer to Figure 3 and Figure 4This invention provides an embodiment illustrating the specific positioning process: The height of the specimen casting space is set to 450mm. The casting space is discretized using 30mm as the stratification benchmark, resulting in 15 casting layers. Five typical aggregates are selected for illustration, including two graded aggregates (4-grade) and three graded aggregates (3-grade). The graded aggregates have a particle size of 80-150mm, and the graded aggregates have a particle size of 40-80mm, denoted as aggregates A1, A2, B1, B2, and B3, respectively. After performing a 3D scan of the aggregates and importing them into the modeling space, the casting layer is determined based on the height of the lowest point in the spatial coordinate system. In this embodiment, for ease of explanation, the stratification relationship is set as follows: First layer (0-30mm): Aggregates A1, B1, B2; Second layer (30-60mm): Aggregates A2, B3. After determining the casting layer to which the aggregates belong, areas on the aggregate surface suitable for attaching positioning patches are further selected in the 3D model. The coordinate pairs of each aggregate patch point, i.e., the positioning point, are recorded according to the corresponding three-dimensional coordinates (x, y, z). These coordinates guide the actual pasting position of the positioning block 440—the hook patch—and the spatial arrangement of the positioning rod 430, thereby achieving accurate physical reproduction of the positions of the three- and four-grade aggregates during the pouring process. Selection principles include: the point is not obscured by surrounding aggregates in the upward viewing direction; the surface curvature is moderate, facilitating patch adhesion to the aggregate surface; for example, when the side length of the patch pasted on the aggregate surface is approximately 10mm, the local radius of curvature R of the aggregate surface at the preset position of the patch is not less than 15mm, preferably not less than 20mm, to ensure that the patch can fully adhere to the aggregate surface and obtain sufficient bonding strength. The distance between the two positioning points is appropriate, enabling the formation of a stable suspension torque. Taking aggregate A1 as an example, its lowest point is located in the first layer. Two points P1 and P2 are selected on its upper surface as the preset positions of the hook patch, i.e., positioning points. The coordinates of the positioning points of aggregate A1 are: P1: (x=80mm, y=320mm, z=102mm), P2: (x=115mm, y=305mm, z=93mm). The distance between the two points is moderate, which meets the requirements of positioning distance and stability. Similarly, the lowest point of aggregate A2 is located in the second layer. Two points Q1 and Q2 are selected as preset positions for patching. The coordinates of the positioning point of A2 are Q1: (x=195mm, y=280mm, z=120mm) and Q2: (x=265mm, y=295mm, z=133mm). Record and output the data of each layer and the three-dimensional coordinates of the positioning point. Aggregates A1 and A2 form the following structured data: A1: layer number=1, patch point=(P1, P2); A2: layer number=2, patch point=(Q1, Q2); Similarly, the layer numbers of aggregates B1, B2 and B3 are the first layer, the first layer and the second layer, respectively. The positioning points (R1, R2), (S1, S2) and (T1, T2) are selected respectively. Output the layer numbers 1, 1, and 2 corresponding to aggregates B1, B2, and B3, as well as the three-dimensional coordinates of the positioning points R1, R2, S1, S2, T1, and T2.

[0020] To prepare the aforementioned concrete specimens capable of spatially positioning aggregates, such as... Figure 4 and Figure 5 As shown, the present invention also provides a concrete specimen preparation device, including a splicing mold and a positioning assembly. The splicing mold includes: two end plates 200, a bottom plate 100, two sets of side plate assemblies 300 composed of multiple unit plates 310, a sealing strip, tie rods 110 and fixing bolts provided at the bottom and top of the splicing mold. The positioning assembly 400 includes two fixing plates 410, positioning lines 420 and positioning rods 430. In this embodiment, after the end plates 200, the bottom plate 100 and the side plate assemblies 300 are spliced, each component is fastened to the tie rods 110 by bolts, and a sealing strip is provided at the joint, forming a semi-closed structure with an open top. The side panel assembly 300 includes multiple unit panels 310 spliced ​​vertically, and the unit panels 310 are connected by mortise and tenon structure. The side panel assembly 300 consists of fifteen unit panels 310 in total. The height of the uppermost and lowermost unit panels is 50mm, and each has a reserved height of 20mm for connection with the bottom plate 100 and the tie rod 100, respectively. The height of the thirteen unit panels in the middle is 30mm. The unit panels 310 increase in height layer by layer to form the side panel assembly 300.

[0021] The cavity formed by the end plate 200, the bottom plate 100, and the side plate assembly 300 is the pouring space for the concrete specimen. The internal dimensions of the cavity are the effective dimensions of the pouring space. Correspondingly, the effective dimensions of the end plate 200 are 450mm × 450mm, the effective dimensions of the bottom plate 100 are 450mm × 1550mm, and the effective dimensions of the side plate assembly 300 are 1550mm × 450mm.

[0022] The positioning component 400 is disposed outside the mold and is used to achieve spatial positioning of the aggregate. The positioning component 400 includes a symmetrically arranged fixing plate 410, a positioning line 420, and a thick steel wire that acts as a positioning rod 430. Specifically, in this embodiment, the fixing plate 410 is a wire-passing perforated plate fixedly installed on the external positioning frame. The positioning frame is made of steel, with dimensions of 1800mm × 600mm, and has graduations on the edges. Fixing bolts are provided at the top, middle, and bottom. The positioning line 420 is a steel wire, which is fixedly arranged at the corresponding anchor points of the wire-passing perforated plate by a steel wire fixing device for guiding and locking the positioning line 420. The wire-passing perforated plate is processed from a single piece of steel plate. The anchor points are an array of holes equidistantly arranged in the horizontal and vertical directions on the surface of the steel plate. The arrangement density of the hole array is not less than the distribution density of the wiring coordinates of the positioning line 420. In one embodiment, the hole spacing is approximately 10mm, which can meet the precise matching of the coordinates of different aggregate hanging points. The high-density hole array design ensures that, during actual installation, regardless of how the aggregate is pasted, a threading hole position that matches or approximates the coordinates of the patch can be found, thereby enabling the precise lowering and positioning of the positioning rod 430.

[0023] The steel wire fixing device is located at each anchor point, allowing the steel wire to connect to anchor points at relative coordinate positions on two positioning frames, maintaining the stability of the steel wire positioning. The steel wire is a high-strength steel wire with a diameter of not less than 4mm, possessing high tensile strength and bending resistance. Its bottom end is fixed with a square hook for engaging with the positioning block 440 on the surface of aggregate 001 for positioning.

[0024] The method for preparing concrete specimens using the above-mentioned concrete specimen preparation device includes the following steps: Based on the 3D simulation results, hook patches are attached to the positioning points on each aggregate surface.

[0025] Assemble the base plate, end plate, and bottom unit plate, and install sealing strips and bolts to form a mold space that can accommodate 30mm thick mortar.

[0026] According to the wire routing coordinates, the wire is passed through the wire guide plate, and the hanging position and suspension height of the wire are adjusted so that the hook end is positioned in conjunction with the patch at the positioning point on the aggregate. The aggregate with the hook patch is then suspended onto the corresponding wire by the positioning rod, and the position and orientation of the aggregate are finely adjusted according to the 3D model.

[0027] Pour mortar to a thickness of 30mm and vibrate it; after the mortar has reached the initial setting state and can keep the aggregate stable and no longer sink, remove the positioning rod and gently remove the hook from the patch.

[0028] Install and fix the second layer of unit panels; repeat the steps of steel wire laying, aggregate suspension, mortar pouring, positioning rod removal, steel wire removal and hook removal, and construct layer by layer in the order of layering.

[0029] After the specimen reaches the designed height, the tie rods are reinforced and standard curing is carried out to obtain a concrete specimen for spatial positioning of the aggregate.

[0030] In this embodiment, during the layered casting process, aggregates A1, B1, and B2 belonging to the first layer are first placed and positioned using a wire suspension system. Mortar is then poured to the height of the first layer, initially fixing the aggregates in this layer. Once the mortar has reached its initial setting state, some of the wires that would interfere with the placement of the upper aggregate layers are removed; in this embodiment, these are the wires corresponding to B1 and B2, to free up suspension space for the second layer of aggregates. The second layer of aggregates A2 and B3 are then placed, and the wire positioning and mortar pouring steps are repeated. Through layer-by-layer positioning, pouring, and unsustaining operations, the layered molding of the entire specimen is finally completed.

[0031] The present invention has provided a detailed description of a method for spatial positioning of concrete aggregates, a device for making concrete specimens, and a method for casting concrete specimens. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these embodiments are merely for the purpose of helping to understand the core ideas of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for spatial positioning of concrete aggregates, characterized in that, Includes the following steps: Collect and establish an aggregate model library; Establish a space of a preset size, wherein the space is a three-dimensional space in which the X, Y and Z directions are perpendicular to each other; According to the preset aggregate gradation ratio and quantity, aggregate models are selected from the aggregate model library, and the selected aggregate models are automatically arranged in the space using a spatial collision detection algorithm. Using a preset height as the stratification benchmark, the space is divided into several layers from bottom to top along the Z direction. A corresponding layer number is generated for each aggregate model based on the height of the lowest point of each aggregate model in the space. The positioning points of the aggregate models in the same layer are determined one by one. The determination process includes the following steps: the outer contour of the aggregate to be positioned is projected upward as a limited range, the positioning point is located within the limited range and intersects with the outer surface of the aggregate to be positioned, and the center of gravity projection line of the aggregate to be positioned passes through the positioning point or is located within the connection range of the positioning point. Output the layer number N of the aggregate to be positioned and the spatial coordinates (x, y, z) of the positioning point.

2. The method for spatial positioning of concrete aggregates according to claim 1, characterized in that, The aggregate includes three-grade aggregate and four-grade aggregate, and the preset height range is 25mm-35mm.

3. A concrete specimen preparation device, characterized in that, The spatial positioning method for concrete aggregates according to claim 1 or 2 includes a base plate, two end plates, two side plate assemblies, and a positioning assembly. The base plate is perpendicular to the Z-direction; The two end plates are perpendicular to the X-direction and are respectively connected to the two ends of the base plate in the X-direction. The two side plate assemblies are perpendicular to the Y direction and are respectively connected to the two ends of the base plate in the Y direction; The cavity formed by the bottom plate, the end plate, and the side plate assembly is a three-dimensional space of a preset size; The positioning assembly includes two fixing plates, a positioning line, and a positioning rod; The fixing plate is opposite to and perpendicular to the Y direction, and is fixed to the outside of the three-dimensional space; The positioning lines are arranged along the Y direction, and the two ends of the positioning lines are detachably connected to the fixing plate. One end of the positioning rod is vertically connected to the positioning line.

4. The concrete specimen preparation apparatus according to claim 3, characterized in that, The side panel assembly includes several unit panels, which are detachably connected sequentially along the Z-direction, and the height of each unit panel is a preset height.

5. A method for casting concrete specimens, characterized in that, Using the concrete specimen preparation apparatus according to claim 3 or 4 includes the following steps: S1. Install positioning blocks at the positioning points of the aggregate; S2. Assemble the base plate, end plate and side plate according to the preset three-dimensional space to form an open top accommodating space; S3. Position the aggregates in the same layer. Based on the coordinates (x, y, z) of the positioning point of the aggregate to be positioned in the bottom layer, thread a positioning line on the fixing plate. The positioning line is located in the plane X=x and the height of the positioning line is greater than z. Hang the positioning rod on the positioning line. The coordinates of the lower end of the positioning rod are (x, y, z). Connect the positioning block on the aggregate to be positioned to the lower end of the positioning rod. Repeat the above operation to suspend and position other aggregates to be positioned in the same layer in turn. S4. Pour mortar into the accommodating space to the preset height and vibrate it. After the mortar has initially set, remove the positioning lines and positioning rods that will affect the layout of the upper aggregate. S5. Repeat S3 and S4, performing positioning, pouring, and unhanging operations on the aggregates to be positioned layer by layer from bottom to top, until the aggregate positioning and pouring of the entire specimen are completed.

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