Recycled aggregate concrete mesoscopic modeling method considering partial wrapping of non-uniform old mortar

Abstract

The invention discloses a recycled aggregate concrete mesoscopic modeling method considering partial wrapping of non-uniform old mortar, and adopts the following technical scheme: based on input macroscopic, mesoscopic and old mortar wrapping parameters, calculating an aggregate volume proportion and a target number according to fullerene gradation; according to the statistical fitting distribution function of the old mortar wrapping rate, the weight of each equivalent wrapping rate interval is determined, and the aggregate quantity of the corresponding interval is distributed; an improved grid mapping method is adopted, and layered collision and boundary collision detection are combined, so that the rationality of aggregate distribution is ensured; after mesh generation, node material attributes are determined according to a node material attribute judgment rule, and unit material attributes are distributed according to a priority rule of the node material attributes in units; and finally, an INP file compatible with the ABAQUS finite element software is output.

Description

Technical Field

[0001] This invention relates to the field of numerical simulation technology for recycled concrete, specifically to a microscopic modeling method for recycled aggregate concrete that considers partial encapsulation of non-uniform old mortar. Background Technology

[0002] Recycled concrete, as a core product of construction waste resource utilization, is widely used in construction engineering. However, due to the partial encapsulation and uneven thickness of the old mortar adhering to the surface of recycled aggregates, its microstructure is complex, and its macroscopic properties differ significantly from those of natural aggregate concrete. Numerical simulation is an effective means to study the micromechanical behavior of recycled concrete. Existing modeling methods mainly include solid modeling methods, traditional mesh mapping methods, and image scanning reconstruction methods, but all have obvious limitations.

[0003] Traditional mesh mapping method is oversimplified: The traditional mesh mapping method assumes that the old mortar is a uniform coating layer with a constant thickness, which cannot reflect the characteristics of the actual recycled aggregate partial coating and uneven thickness of the old mortar, resulting in significant deviations in damage distribution and mechanical response prediction.

[0004] Image reconstruction methods are not practical enough: Although reconstruction methods based on CT scanning and digital microscopy can capture the true shape of old mortar, the equipment costs are high, the scanning resolution is limited, and it is difficult to achieve large-scale simulation with adjustable wrapping features, making them unsuitable for engineering parameterization research.

[0005] Solid modeling methods are computationally inefficient: although polygonal models and idealized sphere models can describe some enclosed features, they are difficult to generate high-quality structured meshes and cannot support large-scale mesomechanical analysis.

[0006] Lack of statistical equivalence: Existing methods do not incorporate the statistical distribution of old mortar encapsulation characteristics (surface encapsulation rate, old mortar thickness) into the modeling process, resulting in the generated recycled aggregate population not matching the statistical characteristics of the actual samples, further exacerbating performance prediction errors.

[0007] Therefore, it is necessary to propose a microscopic modeling method for recycled aggregate concrete that takes into account geometric realism, statistical equivalence, and computational efficiency, so as to overcome the limitations of traditional methods and provide reliable technical support for the microscopic numerical simulation and engineering application of recycled aggregate concrete. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention is implemented through the following technical solution: a method for microscopic modeling of recycled aggregate concrete considering partially encapsulated non-uniform old mortar, comprising the following steps:

[0009] Step 1: Input modeling parameters;

[0010] Macroscopic parameters: specimen length L, width W, height H (unit: m), aggregate volume fraction V f Recycled aggregate replacement rate RAR (0-1), aggregate gradation (1-4).

[0011] Detailed parameters: Thickness t of the transition zone (OM-RC-ITZ) between old mortar and recycled aggregate core interface ITZ,old Thickness t of the new mortar-natural interface transition zone (OM-NA-ITZ) ITZ,new Thickness t of the transition zone (NM-OM-ITZ) between new and old mortar ITZ,new-old Thickness t of the transition zone (NM-RC-ITZ) between new mortar and recycled aggregate core interface ITZ,new-core and cell grid step size ;

[0012] Statistical parameters for old mortar: Surface coating rate (Rs) equivalent interval [0, 10%), [10%, 35%), [35%, 65%), [65%, 90%), [90%, 100%], corresponding to equivalent coating rates of 0, 0.25, 0.5, 0.75, and 1.0; peak thickness t of old mortar. max Edge thickness t min .

[0013] Step 2: Statistical quantification of old mortar wrapping characteristics; 2.1 Thickness Distribution Model: Establishing a Gaussian Attenuation Model: ;

[0014] Among them, the The top corner of the area covered by old mortar. The attenuation coefficient is obtained by... Lower limit of the constraint thickness.

[0015] 2.2 Randomization of the Wrapped Region: Generating Random Axis Unit Vectors By using a rotation matrix to rotate the spherical crown to a random direction, the randomness of the wrapping position is achieved.

[0016] Step 3: Aggregate generation and stratification collision detection;

[0017] 3.1 Aggregate gradation calculation: Based on the Fuller gradation curve Determine the volume ratio of each particle size range and calculate the target number of aggregates for each aggregate size range (recycled aggregates and natural aggregates are allocated according to the replacement rate RAR).

[0018] The determination of aggregate targets specifically includes the following sub-steps:

[0019] Step 3.11: Calculate the volume ratio of each grade of gradation based on the Fuller gradation curve, and then allocate the volume of each grade of gradation after normalization;

[0020] Step 3.12: Calculate the volume of a single aggregate based on the volume of the sphere, determine the total target number for each grade, and allocate the target number of recycled aggregate and the target number of natural aggregate according to RAR;

[0021] Step 3.13: Calculate the weight of each equivalent wrapping rate interval by fitting the statistical distribution function of the old mortar wrapping characteristics.

[0022] 3.2 Aggregate coordinate generation: Based on the principle of prioritizing large particle size, the core coordinates of the aggregate are randomly generated in the specimen space to ensure that the coordinates meet the boundary constraints;

[0023] 3.3 Layered Collision Detection:

[0024] Coarse detection: Define an AABB bounding box for each aggregate; define the AABB of the i-th aggregate:

[0025] AABB i =[x i -R i ,x i +R i ]×[y i -R i ,y i +R i ]×[z i -R i ,z i +R i ];

[0026] Among them, the characteristic radius of recycled aggregate Characteristic radius of natural aggregate ; Let the radius of the i-th recycled aggregate core be denoted as . Let be the peak thickness of the i-th recycled aggregate non-uniform old mortar; Let be the radius of the i-th natural aggregate. If aggregate i and aggregate j have no intersection in their AABB (Aspect-Advanced Boundary Components), they are directly determined to be non-collision; otherwise, they are considered to be collisions. Fine-tuning: Calculate the angle θ between the vector connecting the centers of the two aggregates and the axis of the recycled aggregate. Based on the thickness model in step 2.2, obtain the thickness of the old mortar. Collision threshold Calculated according to the following rules: Both aggregates are recycled aggregates and the line connecting them is located within the encapsulated area. ): ;

[0027] Both aggregates are recycled aggregates, and only one aggregate's line of connection is located within the enclosed area. ),

[0028] If it is recycled and natural aggregate and :

[0029] ;

[0030] The two aggregates are recycled and natural aggregates, respectively. :

[0031] .

[0032] Both aggregates are natural aggregates:

[0033] If the center distance between the two aggregates ≤ + A collision was detected, and the coordinates were regenerated.

[0034] Boundary collision detection requires ensuring that the aggregate and mortar layer are completely within the specimen, meeting the following requirements.

[0035]

[0036]

[0037] Where L is the side length of the specimen.

[0038] Step 4: Mesh generation and material determination;

[0039] 4.1 Mesh Generation: The specimen was globally meshed using 8-node hexahedral elements (C3D8R), with a mesh size of [mesh size missing]. step ;

[0040] 4.2 Determination of Node Material Phase: Traverse all nodes in the model and determine the node material phase according to the rules based on the distance d from the node to the aggregate core and the angle θ between the node and the old mortar wrapping axis.

[0041] The rule for determining the phase of the node material is as follows:

[0042] Recycled aggregate node: It is the core phase of recycled aggregate;

[0043] and This is the transitional phase at the core interface between old mortar and recycled aggregate;

[0044] and It is the old mortar phase;

[0045] and This is the transition zone phase between the new mortar and the old mortar interface;

[0046] and This is the transitional phase at the core interface of the new mortar and recycled aggregate;

[0047] Natural aggregate nodes: It is a natural aggregate phase;

[0048] This is the transitional phase at the interface between the new mortar and natural aggregate;

[0049] The remaining nodes are new mortar phase;

[0050] 4.3 Determination of unit material properties:

[0051] Area encased in old mortar ( The recycled aggregate unit is determined by the high-priority material priority rule. According to the priority order of recycled aggregate materials, the unit with high-priority material nodes is classified as that phase.

[0052] For the area outside the old mortar wrapping ( The material type (recycled aggregate or natural aggregate) of a unit is determined based on the statistical quantity of materials in the nodes within the unit, following the principle of prioritizing the most abundant material; if the quantities are equal, the principle of prioritizing the inner layer material is applied.

[0053] Step 5: Model output;

[0054] Generates finite element INP files containing node coordinates, element connection relationships, and material partitions (element sets, node sets), which can be directly imported into software such as ABAQUS for micromechanical simulation.

[0055] This invention provides a method for microstructure modeling of recycled aggregate concrete that considers partial encapsulation of non-uniform old mortar. It has the following beneficial effects:

[0056] Strong geometric realism: Breaking through the assumption of uniform thickness wrapping around the entire circle in traditional methods, it accurately characterizes the partial wrapping and thickness gradient features of old mortar through Beta distribution and Gaussian decay model, making the morphology of recycled aggregate closer to reality.

[0057] Excellent statistical equivalence: The skewed distribution of the wrapping rate and the spatial heterogeneity of the thickness are incorporated into the modeling process to ensure that the statistical characteristics of the recycled aggregate population are consistent with the real samples.

[0058] Accurate collision detection: A layered detection strategy is adopted, combined with orientation-dependent collision threshold calculation, to avoid collision misjudgment caused by non-uniform old mortar.

[0059] Parameters are controllable and flexible: By adjusting statistical parameters, thickness parameters and gradation parameters, recycled concrete from different sources and with different replacement rates can be simulated, making it suitable for parametric studies;

[0060] High computational efficiency: Inheriting the advantages of the mesh mapping method, it directly generates high-quality structured meshes without additional geometric reconstruction, supporting large-scale mesoscopic simulation;

[0061] This method overcomes the limitations of traditional approaches that simplify old mortar into a complete, uniformly thick outer layer of aggregate. By introducing a Gaussian decay model of surface coverage rate and old mortar thickness, combined with a distribution function to describe the distribution characteristics of old mortar coverage rate and thickness, it achieves a geometric representation of the partial coverage and non-uniform thickness gradient characteristics of old mortar. Furthermore, a recycled aggregate population model based on statistical equivalence is constructed. Through equivalent coverage rate levels and weight allocation mechanisms, the model ensures statistical consistency with real samples. A layered collision detection algorithm considering partial coverage characteristics and a unit material priority determination scheme are developed, effectively solving the modeling challenges caused by the non-uniform spatial distribution of partially covered old mortar. This method significantly outperforms traditional modeling approaches in terms of geometric realism and statistical equivalence, providing a reliable tool for simulating the micromechanical properties of recycled concrete. Attached Figure Description

[0062] Figure 1 The overall flowchart of the microstructure modeling method for recycled aggregate concrete with partially encapsulated non-uniform old mortar is shown in the present invention.

[0063] Figure 2 This is a schematic diagram of the equivalent surface coating rate of the recycled aggregate in this invention;

[0064] Figure 3 This is a schematic diagram of the non-uniform old mortar thickness distribution based on the Gaussian decay model of the present invention;

[0065] Figure 4 Flowchart of aggregate layer collision detection considering partial encapsulation features in this invention;

[0066] Figure 5 This is a schematic diagram of the logic for determining the material properties of unit nodes in this invention;

[0067] Figure 6 This is an example diagram of the microscopic numerical model of recycled concrete of the present invention;

[0068] Figure 7 This is a comparison chart of the stress-strain curves of recycled aggregate concrete obtained by the numerical simulation method of this invention and by experiments. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] This invention provides a technical solution:

[0071] Modeling parameter input:

[0072] Macroscopic parameters: Specimen dimensions (length × width × height) 0.15m × 0.15m × 0.15m, aggregate volume fraction 0.5%, recycled aggregate replacement rate 0.5%; 2-gradation; minimum particle size, maximum particle size, and equivalent particle size corresponding to each gradation: 1: [[0.02, 0.005, 0.015]], 2: [[0.04, 0.02, 0.03], [0.02, 0.005, 0.015]], 3: [[0.08, 0.04, 0.06], [0.04, 0.02, 0.03], [0.02, 0.005, 0.015]], 4: [[0.15, 0.08, 0.12], [0.08, 0.04, 0.06], [0.04, 0.02, [0.03], [0.02, 0.005, 0.015]]

[0073] Detailed parameters: The thickness of the new mortar-natural aggregate interface transition zone, the new mortar-old mortar interface transition zone, the old mortar-recycled aggregate core, and the new mortar-recycled aggregate core are all 0.001m;

[0074] Statistical parameters of old mortar: t max =0.005m, t min =0.001m, mesh step =0.001m.

[0075] Statistical Quantification of Characteristics of Old Mortar Encapsulation:

[0076] In this embodiment, the equivalent surface coating rate of the recycled aggregate is divided into 5 intervals, corresponding to equivalent coating rates of 0, 0.25, 0.5, 0.75, and 1.0, as shown in the appendix to the specification. Figure 2 The equivalent wrapping rate distribution is shown. Based on the statistical results of recycled aggregate, a Beta distribution is used for fitting, with fitting parameters α=2 and β=5. Calculation of the weight of the old mortar wrapping rate intervals: The weights of each interval are obtained by integration as [0.32, 0.41, 0.21, 0.05, 0.01].

[0077] Thickness distribution: ,For example When =0.5, =π / 2, The thickness distribution characteristics are as shown in the attached instruction manual. Figure 3 As shown.

[0078] Aggregate generation and collision detection:

[0079] Gradation calculation: According to the Fuller gradation curve, the volume ratio of the 0.005~0.02m range is 35%, the volume ratio of the 0.02~0.04m range is 65%, and the total target number of aggregates is 120 (60 recycled and 60 natural).

[0080] Coordinate generation: Large-diameter aggregates (0.02-0.04m) are generated first. Within this size range, recycled aggregates are allocated the wrapping rate according to weight (30 wrapping rates for 25%, 13 wrapping rates for 50%, and 17 wrapping rates for the rest).

[0081] Collision detection: as per the instruction manual. Figure 4 The layered collision detection process shown uses AABB coarse detection to screen potential collision pairs, fine detection to calculate the orientation-dependent collision threshold, and finally generates a collision-free aggregate distribution.

[0082] Mesh generation and material determination:

[0083] Mesh generation: Mesh size 0.001m;

[0084] Unit node material determination: as per the instruction manual. Figure 5 The node material property determination logic shown is based on the node location and distance, and divides the material into eight material phases: new mortar (NM), new mortar-natural aggregate interface transition zone (NM-NA-ITZ), natural aggregate (NA), recycled aggregate core (RC), old mortar-recycled aggregate interface transition zone (OM-RC-ITZ), old mortar (OM), old mortar-new mortar interface transition zone (OM-NM-ITZ), and new mortar-recycled aggregate core interface transition zone (NM-RC-ITZ).

[0085] Unit material property determination: Determine the material phase of the unit according to the set unit material property determination rules.

[0086] Model output: Generates an INP file. An example of the generated mesoscopic numerical model is shown in the accompanying manual. Figure 6 As shown.

[0087] Simulation verification:

[0088] Import the INP file into Abaqus. The material properties are based on the concrete plastic damage constitutive model. During model setup, create reference points RP-1 and RP-2. Create lower coupling constraints on reference point RP-1 and upper coupling constraints on reference point RP-2 for load application. When applying loads, fix the lower coupling constraint (RP-1), and then apply a uniaxial compressive load to reference point RP-2 to simulate uniaxial compression conditions.

[0089] A simulation analysis was conducted using recycled aggregate concrete with a 50% replacement rate as an example. The analysis results are shown in the appendix to the instruction manual. Figure 7As shown in the figure, the simulation test calculation and analysis is fast and efficient, and the calculation results are accurate and reliable, proving the authenticity and effectiveness of the algorithm of this invention. The damage cloud diagram in the specification shows that it is basically consistent with the damage morphology observed in the experiment, verifying the superiority of the method of this invention in capturing the key damage mechanisms of recycled concrete.

[0090] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0091] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for microstructure modeling of recycled aggregate concrete considering partially encapsulated non-uniform old mortar, characterized in that, Includes the following steps: Step 1: Input modeling parameters, including macroscopic parameters, microscopic parameters, and old mortar statistical parameters; The macroscopic parameters specifically include the specimen dimensions (length L, width W, height H) and aggregate volume fraction (V). f , Recycled aggregate replacement rate (RAR), Aggregate gradation; The specific micro-parameter is the thickness t of the transition zone at the old mortar-recycled aggregate core interface. ITZ,old Thickness t of the transition zone between new mortar and natural interface ITZ,new Thickness t of the transition zone between new and old mortar interfaces ITZ,new-old Thickness t of the transition zone between new mortar and recycled aggregate core interface ITZ,new-core and cell grid size ; The specific statistical parameter for the old mortar is the surface coating rate R. s Equivalent range, peak thickness t of old mortar max and edge thickness t min ; Step 2: Statistical quantification of old mortar wrapping features. By fitting the statistical distribution function of old mortar wrapping features, the weight of each equivalent wrapping rate interval is calculated, and the old mortar thickness distribution function is established. Combined with the random axis generation mechanism, the random distribution of old mortar wrapping area is realized. Step 3: Aggregate generation and stratification collision detection. The volume ratio of each particle size range is determined according to the Fuller gradation curve. The core coordinates of the aggregate are generated by adopting the principle of prioritizing large particle size. A collision detection strategy combining inter-aggregate stratification collision detection and aggregate-specimen boundary detection is adopted. Step 4: Mesh generation and element material property determination. The specimen is meshed into a hexahedron, and the element nodes are traversed. The element material properties are determined based on the node material phase determination rule. The element material properties are determined based on the material properties of the nodes within the element according to the high-priority material priority rule. Step 5: Model output, generating an ABAQUS INP file containing element and node information, which can be directly imported into ABAQUS finite element software for simulation analysis.

2. The method for microstructure modeling of recycled aggregate concrete considering partially encapsulated non-uniform old mortar as described in claim 1, characterized in that: The equivalent package interval mentioned in step 2 is specifically: R s The equivalent division is into five intervals: [0, 10%), [10%, 35%), [35%, 65%), [65%, 90%), and [90%, 100%], corresponding to equivalent parcel rates of 0, 0.25, 0.5, 0.75, and 1.

0.

3. The method for microstructure modeling of recycled aggregate concrete considering partially encapsulated non-uniform old mortar as described in claim 1, characterized in that: The thickness distribution function of the old mortar in step 2 is: Where θ is the angle between the node and the wrapping axis. The semi-apex angle of the line connecting the edge of the old mortar and the center of the aggregate relative to the wrapping axis. The attenuation coefficient is obtained by... Lower limit of the constraint thickness.

4. The method for microstructural modeling of recycled aggregate concrete considering partially encapsulated non-uniform old mortar as described in claim 1, characterized in that, The determination of aggregate target in step 3 specifically includes the following sub-steps: Step 3.11: Calculate the volume ratio of each grade of gradation based on the Fuller gradation curve, and then allocate the volume of each grade of gradation after normalization; Step 3.12: Calculate the volume of a single aggregate based on the volume of the sphere, determine the total target number for each grade, and allocate the target number of recycled aggregate and the target number of natural aggregate according to RAR; Step 3.13: Combining the weights of each equivalent wrapping rate interval in Step 2, determine the target number of each grade of recycled aggregate in each equivalent wrapping rate interval to ensure statistical equivalence of the recycled aggregate group.

5. The method for microstructure modeling of recycled aggregate concrete considering partially encapsulated non-uniform old mortar as described in claim 1, characterized in that: The collision detection strategy combining inter-aggregate layer collision detection and aggregate-specimen boundary detection in step 3 specifically includes: Step 3.21: Coarse inspection uses axis-aligned bounding boxes (AABBs). Define the AABB of the i-th aggregate: AABB i =[x i -R i ,x i +R i ]×[y i -R i ,y i +R i ]×[z i -R i ,z i +R i ]; Among them, the characteristic radius of recycled aggregate Characteristic radius of natural aggregate ; Let the radius of the i-th recycled aggregate core be denoted as . Let be the peak thickness of the i-th recycled aggregate non-uniform old mortar; Let be the radius of the i-th natural aggregate; if aggregate i and aggregate j have no intersection of AABB, then it is directly determined that there is no collision; otherwise, it is a collision. Step 3.22: Calculate the angle between the line connecting the centers of the two aggregates and the axis of the recycled aggregate wrapping. The thickness of the old mortar in this direction is calculated based on the half-apex angle α of the line connecting the edge of the old mortar and the center of the aggregate relative to the wrapping axis, using the old mortar thickness distribution function of claim 3. Calculate the collision threshold based on aggregate type: Both aggregates are recycled aggregates and the line connecting them is located within the encapsulated area: ； Both aggregates are recycled aggregates, and only one aggregate's line of connection is located within the enclosed area. ): Recycled and natural aggregates : Recycled and natural aggregates : Natural and natural aggregates: ; When the Euclidean distance between two aggregates is greater than the collision threshold, the two aggregates pass the precision test. Step 3.23: Boundary inspection ensures that the aggregate and mortar layer are completely within the specimen, meeting the requirements. and .

6. The method for microstructure modeling of recycled aggregate concrete considering partially encapsulated non-uniform old mortar as described in claim 1, characterized in that: The node material phase determination rule and the high-priority material priority rule in step 4 are as follows: Node material phase determination rules: The Euclidean distance from the node to the aggregate core center is d; the angle between the direction of the line connecting the node and the aggregate center and the enclosing axis is... : Recycled aggregate node: It is the core phase of recycled aggregate; and This is the transitional phase at the core interface between old mortar and recycled aggregate; and It is the old mortar phase; and This is the transition zone phase between the new mortar and the old mortar interface; and This is the transitional phase at the core interface of the new mortar and recycled aggregate; Natural aggregate nodes: It is a natural aggregate phase; This is the transitional phase at the interface between the new mortar and natural aggregate; The remaining nodes are new mortar phase; The recycled aggregate units within the old mortar-wrapped area are determined using a high-priority material priority rule. According to the priority order of recycled aggregate materials, if there are high-priority material nodes within the unit, it is classified as that phase. For units outside the old mortar-wrapped area, the material type is determined based on the statistical quantity of materials at the nodes within the unit, following the principle of prioritizing the most abundant material; if the quantities are equal, the inner layer material takes precedence.

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