Calculation method for the bonding force of a cement-based material matrix

Abstract

The present invention provides a method for calculating the bonding force of a cement-based material matrix. The method includes: determining force field parameters; establishing a molecular dynamics coarse-grained model of cement hydration gel clusters; and using the coarse-grained model to change the force field parameters to simulate and calculate the bonding force of the cement hydration gel clusters. By using the solution of the present invention, quantitative analysis of the bonding property of the cement hydration gel clusters can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of gel mass mechanics, and particularly relates to a method for calculating the bonding force of a cement-based material matrix. Background Art

[0002] Cement hydration gel mass is the main product of cement hydration, playing an important role in bonding non-gel phases such as crystals and aggregates in cement concrete together. Whether the bonding is firm determines the strength and durability of cement concrete.

[0003] Currently, the research on cement hydration gel mass mainly focuses on some specific environments and uses the coarse-graining method, which has the following deficiencies:

[0004] (1) There is a lack of basis for obtaining force field parameters. For example, the value of ε in the LJ (Lennard-Jones) potential energy function lacks a theoretical basis and is assigned empirically, blindly substituting molecular-scale mechanical indexes into the LJ potential energy function.

[0005] (2) The calculation method of microstructure parameters is inaccurate. For example, the calculation of the gel volume directly uses the small ball radius specified in the LJ potential energy function.

[0006] Moreover, there is currently no relevant technical solution for the performance research of cement hydration gel mass under some complex environments (such as conventional phenomena like gel mass dissolution and gel mass bonding force decline). Summary of the Invention

[0007] The present invention provides a method for calculating the bonding force of a cement-based material matrix to effectively solve the quantification problem of the bonding property of cement hydration gel mass.

[0008] For this purpose, the present invention provides the following technical solutions:

[0009] A method for calculating the bonding force of a cement-based material matrix, the method comprising:

[0010] Determine the force field parameters;

[0011] Based on the force field parameters, establish a molecular dynamics coarse-graining model of cement hydration gel mass;

[0012] Use the coarse-graining model to change the force field parameters and simulate and calculate the bonding force of cement hydration gel mass.

[0013] Optionally, the determining the force field parameters includes: calculating the potential energy field between the particles inside the cement hydration gel mass according to the distance and well depth between the particles inside the cement hydration gel mass.

[0014] Optionally, the establishing a molecular dynamics coarse-graining model of cement hydration gel mass includes:

[0015] Establish an initial model;

[0016] Relax the initial model under a force field to obtain a molecular dynamics coarse-grained model of the cement hydration gel cluster.

[0017] Optionally, establishing the initial model according to the force field parameters includes:

[0018] Establish a simulation box;

[0019] Place hydrated gel particles into the simulation box to simulate the precipitation growth process of the hydrated gel cluster and obtain an initial packing model of the gel cluster.

[0020] Optionally, placing the hydrated gel particles into the simulation box includes: using the Monte Carlo method based on the Poisson-Boltzmann distribution to place the hydrated gel particles into the simulation box.

[0021] Optionally, placing the hydrated gel particles into the simulation box includes: under the canonical NVT ensemble, periodically place the hydrated gel particles at a set step size until the change in the number of particles is less than a set value.

[0022] Optionally, relaxing the initial model under a force field includes: placing the initial model under the isobaric-isothermal ensemble for relaxation.

[0023] Optionally, using the coarse-grained model to simulate and calculate the cohesive force of the cement hydration gel cluster includes: by changing the force field parameters in the coarse-grained model, simulating and calculating the performance parameters of the cohesive force of the cement hydration gel cluster.

[0024] Optionally, simulating and calculating the performance parameters of the cohesive force of the cement hydration gel cluster by changing the force field parameters in the coarse-grained model includes any one or more of the following:

[0025] Reduce the particle diameter to simulate the reduction of particles caused by dissolution, shrinkage, or chemical corrosion, which ultimately leads to a decrease in the packing density η;

[0026] Change the elastic modulus to reduce the well depth and simulate the attenuation of the interaction between hydrated gel particles caused by decalcification or chemical corrosion.

[0027] A computer-readable storage medium stores a computer program thereon, and when the computer program is run by a processor, it executes the steps of the method for calculating the cohesive force of the cement-based material matrix.

[0028] The cement-based material matrix adhesion calculation method provided by the present invention determines force field parameters, establishes a molecular dynamics coarse-grained model of cement hydration gel clusters based on the determined force field parameters, and uses the coarse-grained model to change the force field parameters to simulate and calculate the adhesion of cement hydration gel clusters. Using the solution of the present invention, quantitative analysis of the adhesion of cement hydration gel clusters can be achieved. For example, the development of strength and durability during the hydration curing process of cement concrete can be quantified, providing quantitative indicators for performance regulation. For another example, the degradation of the performance of cement concrete during service can be quantified, providing accurate early warning data for material deterioration and failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 is a flowchart of a cement-based material matrix adhesion calculation method provided by the present invention;

[0031] Figure 2 is a flowchart of establishing a molecular dynamics coarse-grained model of cement hydration gel clusters in the cement-based material matrix adhesion calculation method provided by the present invention;

[0032] Figure 3 is a schematic diagram of the changes in the packing structure and free energy of the initial model during the structural relaxation process in an embodiment of the present invention;

[0033] Figure 4 is a schematic diagram of the physical meaning of the coarse-grained model in an embodiment of the present invention;

[0034] Figure 5 is a schematic diagram of the relationship between the small ball amplification factor and the specific surface area and porosity obtained through experiments in an embodiment of the present invention;

[0035] Figure 6 is a schematic diagram of the stress-strain relationship curve of the hydration gel clusters calculated based on the coarse-grained model in an embodiment of the present invention;

[0036] Figure 7 is for Figure 6 The schematic diagram of the packing density and elastic modulus obtained from the stress-strain relationship shown;

[0037] Figure 8 is for Figure 6 The schematic diagram of the packing density and tensile strength obtained from the stress-strain relationship shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0039] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0040] In view of the deficiencies in the existing research on the bonding performance of cement hydration gel clusters, the present invention provides a method for calculating the bonding force of a cement-based material matrix. A molecular dynamics coarse-grained model of cement hydration gel clusters is established according to force field parameters, and the bonding force of cement hydration gel clusters is simulated and calculated by using the coarse-grained model to realize the quantitative calculation of the bonding property of cement hydration gel clusters.

[0041] As Figure 1 shown, it is a flowchart of a method for calculating the bonding force of a cement-based material matrix provided by the present invention, including the following steps:

[0042] Step 101, determine the force field parameters.

[0043] The LJ potential energy function is a mathematical model for describing the intermolecular interaction force, which consists of two parts: an attractive term and a repulsive term. The attractive term represents the van der Waals force between molecules, and the repulsive term represents the Pauli repulsive force between molecules.

[0044] The LJ force field parameters include: the strength parameter ε of the attractive term and the scale parameter σ of the repulsive term. The selection of these two parameters has an important impact on the accuracy and reliability of the simulation results.

[0045] In the embodiment of the present invention, the potential energy field between the particles inside the hydration gel cluster is described by the potential energy function U ij (r ij ). The potential energy function U ij (r ij ) is calculated using the following generalized Lennard-Jones, as shown in formula (1) below.

[0046]

[0047] Among them, r ij is the distance between two particles i and j. When reaching the equilibrium state, the distance between the two particles is r 0 , r 0 = 2 1 / γ×σ ij ,σ ij =(σ i +σ j ) / 2; γ = 12.

[0048] ε ij is the well depth between two particles with diameters of σ i and σ j . Among them, ε ii is the well depth between two particles with a diameter of σ i , and ε jj is the well depth between two particles with a diameter of σ j .

[0049] Under the standard unit (i.e., LJ unit) defined by LAMMPS (Large-scale Atomic / Molecular Massively Parallel Simulator), the temperature T = 0.15 and the chemical potential μ = -1.

[0050] The particle diameter σ is randomly distributed between 6 and 9 nanometers.

[0051] For the value of ε, scientific quantification can be carried out according to the latest literature reports. The latest literature research confirms that the bonding performance between the hydrated calcium silicate molecular layers largely determines the bonding between the hydrated gel particles. Therefore, the elastic modulus between the hydrated calcium silicate molecular layers can be taken as the elastic modulus between the hydrated gel particles.

[0052] The elastic modulus refers to the ratio of the stress per unit area to the corresponding strain when the material is stretched or compressed.

[0053] For example, for the case of hydrated curing for 28 days without environmental damage (different values can be taken for other cases), the elastic modulus m s between the hydrated calcium silicate molecular layers is taken as 57.5 GPa.

[0054] Therefore, the following formula (2) can be used, taking m s = 57.5 GPa to calculate the value of ε.

[0055]

[0056] Step 102: Establish a molecular dynamics coarse-grained model of the cement hydrated gel mass based on the force field parameters.

[0057] Specifically, first establish an initial model, and then relax the initial model under the force field to obtain the molecular dynamics coarse-grained model of the cement hydrated gel mass.

[0058] As shown Figure 2 in the figure, it is a flowchart of establishing a molecular dynamics coarse-grained model of cement hydration gel clusters in the method for calculating the bonding force of the cement-based material matrix provided by the present invention, including the following steps:

[0059] Step 201, establish an initial model.

[0060] First, establish a simulation box; then, place hydration gel particles into the simulation box to simulate the precipitation growth process of the hydration gel clusters, and obtain an initial packing model of the gel clusters. During the placement process, the placed hydration gel particles can displace and diffuse, and the driving force for the displacement and diffusion behaviors is the force field (i.e., the LJ potential field).

[0061] An ensemble is a basic concept introduced when using statistical methods to describe the statistical regularity of a thermodynamic system. It is a form of expression of statistical theory, referring to the collection of a large number of systems with exactly the same properties and structures, in various motion states, and independent of each other under certain macroscopic conditions. The NVT (canonical) ensemble refers to a system in which the number of particles, volume, and temperature are all conserved, and it is applicable to studying the mechanical properties of materials, such as elastic modulus and yield strength.

[0062] In the embodiment of the present invention, under the NVT ensemble, the Monte Carlo method based on the Poisson-Boltzmann distribution can be used to place hydration gel particles into the simulation box. For example, the hydration gel particles are placed periodically according to a set step size until the change in the number of particles is less than a set value.

[0063] During the placement process, the hydration gel particles can displace and diffuse. For example, a particle placement is performed every 100 steps (1 step is a time unit, and by defining the time unit, it can be converted into actual time). In this way, under the action of the force field, the number of hydration gel particles in the box continuously increases around several initial placement sites of the hydration gel particles, thereby simulating the nucleation growth process in the actual formation process of the hydration gel clusters.

[0064] For example, when the change in the number of particles is less than 10 within 10,000 steps, it is considered that the packing structure has reached densification (i.e., a high-density hydration gel cluster), which can be used as the structural configuration of the initial hydration gel cluster, that is, the initial model.

[0065] Step 202, relax the initial model under the force field to obtain a molecular dynamics coarse-grained model of the cement hydration gel cluster.

[0066] Specifically, place the initial model under the NVT ensemble for relaxation. For example, set the pressure to 0 and the temperature to room temperature.

[0067] After the structure of the initial hydrated gel cluster is fully relaxed, a thermodynamically stable hydrated gel cluster structure is obtained. The changes in the packing structure and free energy during the structure relaxation process are as Figure 3 shown.

[0068] The colored arrows therein represent displacement vectors, and their magnitudes are represented by different colors. The pore structure changes from small cracks to large pores, and the stacking configuration gradually transforms into an annular structure.

[0069] Step 103, use the coarse-grained model to simulate and calculate the cohesive force of the cement hydrated gel cluster.

[0070] By changing the force field parameters in the coarse-grained model, simulate and calculate the performance parameters of the cohesive force of the cement hydrated gel cluster.

[0071] Figure 4 (a) to (c) therein describe the physical meaning of the coarse-grained model.

[0072] The essence of the coarse-grained model is to represent the continuous matrix with several rigid spheres, and the interaction between the spheres constitutes a whole. Therefore, for the above-mentioned packing structure, the microstructural calculations such as porosity and pore size distribution cannot directly use the sphere radius in the coarse-grained parameters.

[0073] For this reason, in the embodiments of the present invention, the hydrated gel particle size can be set in the coarse-grained model for microstructure quantification. Specifically, the sphere magnification coefficient ψ can be determined according to the test results of specific surface area and porosity to make the calculation results consistent with the actual values. The specific surface area refers to the total area per unit mass of the material.

[0074] According to the test results, the relationship between the sphere magnification coefficient and the specific surface area and porosity is as Figure 5 shown. The green and yellow shaded areas therein are the suitable ranges of porosity and specific surface area respectively, and the blue area corresponds to the appropriate magnification coefficient ψ.

[0075] Therefore, according to the experimental results, the structure characteristic calculation can be carried out with the magnification coefficient ψ = 0.37.

[0076] The calculation of the mechanical properties of the hydrated gel cluster can be carried out by a uniaxial tensile test in LAMMPS (Large-scale Atomic / Molecular Massively Parallel Simulator). For example, under the NVT ensemble, the whole box is stretched along the a-axis direction (this structure is an isotropic structure) at a strain rate of 0.08 / ps. Record the deformation strain of the box and the stress it receives, and plot the results as a stress-strain diagram.

[0077] Furthermore, by changing the force field parameters, it is possible to simulate, but not limited to, any one or more of the following situations:

[0078] (1) The particle diameter σ decreases, simulating the particle reduction caused by dissolution, shrinkage, or chemical corrosion, ultimately leading to a decrease in the packing density η;

[0079] (2) By changing the elastic modulus m s to reduce the well depth, simulating the attenuation of the interaction between hydrated gel particles caused by decalcification or chemical corrosion.

[0080] Through a series of changes in the above force field parameters, it is possible to obtain Figure 6 the stress-strain relationship curve shown, where the horizontal axis is strain and the vertical axis is stress. The tensile stress-strain relationship reflects the tensile bonding performance of the hydrated gel mass.

[0081] For Figure 6 the stress-strain curve shown, quantification can obtain the elastic modulus and tensile strength, thereby realizing the evaluation of the comprehensive performance of the cement-based material.

[0082] Figure 7 And Figure 8 respectively show the schematic diagrams of the packing density versus the elastic modulus and the packing density versus the tensile strength.

[0083] Among them, the calculation of the packing density η can be refined through experiments, that is, the small ball magnification coefficient ψ is assumed according to the test results of the specific surface area and porosity as described above, so that the calculation result is consistent with the actual value.

[0084] Using the method for calculating the matrix bonding force of the cement-based material provided by the present invention, it is possible to realize the quantitative analysis of the bonding property of the cement hydrated gel mass. For example, it can quantify the development of strength and durability during the hydration curing process of cement concrete, providing quantitative indicators for performance regulation; for another example, it can quantify the performance degradation of cement concrete during service, providing accurate early warning data for material deterioration and failure.

[0085] It should be noted that for the foregoing method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0086] In the above embodiments, the descriptions of the respective embodiments each have their own emphasis. For parts not elaborated in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0087] In several embodiments provided by the present invention, it should be understood that the disclosed device can be implemented in other ways.

[0088] The present invention also provides a storage medium, which is a computer-readable storage medium, on which a computer program is stored. When the computer program runs, it can execute Figure 1 or Figure 2 some or all of the steps of the method shown in

[0089] The above embodiments can be implemented in whole or in part by software, hardware, firmware or any other combination. When implemented using software, the above embodiments can be implemented in the form of a computer program product in whole or in part. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, the processes or functions described in the embodiments of the present application are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center in a wired or wireless manner.

[0090] The above embodiments of the present invention have been introduced in detail. In this article, specific implementation manners are used to elaborate on the present invention. The descriptions of the above embodiments are only used to help understand the method and system of the present invention. They are only some of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The content of this specification should not be construed as a limitation on the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the bonding strength of a cement-based material matrix, characterized in that: The method comprises: Determine force field parameters; Based on the force field parameters, a molecular dynamics coarse-grained model of cement hydration gel clusters is established; Using the coarse-grained model to change the force field parameters, the cohesive force of cement hydration gel group is simulated and calculated; The LJ potential energy function is a mathematical model that describes the intermolecular interaction force. It consists of two parts: the attraction term and the repulsion term. The LJ force field parameters include: the strength parameter of the attraction term and the scale parameter of the exclusion term ; The potential energy field between particles in the hydrated gel group is calculated using the potential energy function To describe the potential energy function The following generalized Lennard-Jones is used for calculation, as shown in formula (1): （1） in, For two particles i and j When the equilibrium state is reached, the distance between the two particles is , , ;γ = 12; The diameter is and The depth of the well between the two particles is ;in, εii The diameter is σi The depth of the well between two particles, εjj Diameter σj The depth of the well between the two particles; In the standard units defined by LAMMPS, the temperature T = 0.15 and the chemical potential μ = -1; Particle diameter Randomly distributed between 6 and 9 nanometers; for The elastic modulus between the molecular layers of hydrated calcium silicate is taken as the elastic modulus between the hydrated gel particles; The elastic modulus refers to the ratio of the stress per unit area to the corresponding strain when the material is stretched or compressed.

2. The method for calculating the bonding strength of cement-based materials according to claim 1, characterized in that: The molecular dynamics coarse-grained model for establishing cement hydration gel group comprises: Build an initial model; The initial model is relaxed under a force field to obtain a molecular dynamics coarse-grained model of cement hydration gel clusters.

3. The method for calculating the bonding strength of cement-based materials according to claim 2, characterized in that: The establishing of the initial model according to the force field parameters comprises: Build a simulation box; Hydrated gel particles are placed into the simulation box to simulate the precipitation growth process of the hydrated gel mass and obtain an initial accumulation model of the gel mass.

4. The method for calculating the bonding strength of cement-based materials according to claim 3, characterized in that: The placing of hydrated gel particles into the simulation box comprises: Hydrated gel particles were dropped into the simulation box using a Monte Carlo method based on Poisson-Boltzmann distribution.

5. The method for calculating the bonding strength of cement-based materials according to claim 4, characterized in that: The placing of hydrated gel particles into the simulation box comprises: Under the canonical NVT ensemble, hydrated gel particles are periodically dropped according to the set step size until the change in the number of particles is less than the set value.

6. The method for calculating the bonding strength of cement-based material matrix according to claim 2, characterized in that: The relaxing the initial model under the force field comprises: The initial model was placed in an isobaric-isothermal ensemble and relaxed.

7. The method for calculating the bonding strength of cement-based material matrix according to any one of claims 1 to 6, characterized in that: The method of using the coarse-grained model to simulate and calculate the cohesive force of cement hydration gel groups includes: By changing the force field parameters in the coarse-grained model, the bonding performance parameters of cement hydration gel group are simulated and calculated.

8. The method for calculating the bonding strength of cement-based material matrix according to claim 7, characterized in that: By changing the force field parameters in the coarse-grained model, the simulation calculation of the cement hydration gel group cohesive performance parameters includes any one or more of the following: Reducing the particle diameter, simulating the particle reduction caused by dissolution, shrinkage or chemical corrosion, ultimately leads to a decrease in the packing density η; The elastic modulus was varied to reduce the well depth, simulating the decay of the interaction between the hydrated gel particles caused by decalcification or chemical corrosion.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for calculating the bonding strength of a cement-based material matrix according to any one of claims 1 to 8 are executed.

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