Method for evaluating influence of admixture on hydration of cement minerals based on molecular dynamics

Abstract

The invention discloses a method for evaluating the influence of an admixture on cement mineral hydration based on molecular dynamics. The method comprises the steps of molecular dynamics model construction, computational simulation and cement mineral hydration system influence evaluation. The molecular dynamics model is composed of a mineral phase, water and an additive. The method can simulate the hydration process of the cement mineral phase when the admixture is doped, quantify the influence of the admixture dosage on the hydration behavior of the cement mineral phase, and calculate the influence of the admixture on a hydrogen bond network in the hydration system of the cement mineral phase, thereby providing a basis for evaluating the influence of the admixture on the hydration of the cement mineral phase.

Description

Technical Field

[0001] The invention relates to a method for evaluating the influence of an admixture on cement mineral hydration based on molecular dynamics, and belongs to the field of building materials. Background Art

[0002] A large amount of concrete is often used in large infrastructure construction. For projects such as high-rise buildings, bridges, dams and roads, the amount of cement used can reach hundreds of tons or even more. When the amount and volume of concrete are large, on the one hand, the heat release of cement hydration will cause temperature rise cracking, and on the other hand, the controllability of fluidity and setting time will decrease. In the process of forming concrete, problems such as large internal stress, uneven slurry, and high construction difficulty are prone to occur. Therefore, how to balance the relationship between cement dosage, controlling hydration heat, improving fluidity and regulating setting time determines the reliability and safety of large-volume concrete applications.

[0003] Admixtures are widely used in concrete because they affect the hydration process of cement, improve workability, regulate setting time, reduce hydration heat, and increase strength. However, due to the complexity of the hydration reaction process inside concrete and the limitations of existing observation methods, the mechanism of the influence of admixtures on concrete performance is not yet fully understood. Currently, admixture design relies more on experience and experiments, and application development still faces certain technical bottlenecks, making it difficult to achieve a breakthrough in essence.

[0004] During cement hydration, mineral phases (such as C3S, C3A, etc.) will have complex interactions with admixtures. However, due to the fast hydration reaction rate and the reaction process occurring at the microscopic scale, traditional experimental methods are difficult to accurately capture the initial changes in cement hydration, especially the subtle interactions between cement minerals and admixtures. Molecular dynamics methods can study material interactions at the atomic scale, so this tool can be used to reveal the interactions between admixture molecules and cement minerals. This method can quantify the effect of admixtures on the hydration reaction of cement mineral phases, which can not only achieve the design of admixture molecules and the evaluation of admixture effects for cement performance, but also understand the effect of admixture dosage on the hydration of cement mineral phases in actual engineering at the molecular scale, which has important engineering application significance. Summary of the invention

[0005] Purpose of the present invention: The purpose of the present invention is to provide a method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics, so as to solve the problem that the effect of admixtures on regulating cement mineral hydration is unclear.

[0006] Technical solution: The method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics of the present invention comprises the following steps: Step 1: Establish a molecular dynamics model of cement mineral phase, water molecules and admixtures, construct mineral phase molecules, water molecules and admixture molecules, and relax them under the NVT ensemble until the system as a whole reaches a stable state; Step 2: Apply force to each atom in the molecular dynamics model established above. The force field is in the form of the following formula: ; In the formula, represents the total potential energy, represents the bonding energy terms, including bond stretching, bond angle, dihedral angle, and higher-order cross terms, represents the non-bonded energy terms, including van der Waals forces and electrostatic interactions; Step 3: In the calculation software, the system temperature and periodic boundary parameters are controlled by setting commands in the established molecular dynamics model to initialize the molecular dynamics model calculation, set the calculation time to simulate the cement mineral hydration process, and adjust the system stability by the Nose-Hoover command; Step 4: According to the calculation results of the molecular dynamics model, the atomic motion coordinate trajectory and the system thermodynamic information are obtained, and the position and conformation information of the mineral phase molecules, water molecules and admixture molecules in the system at different times during the hydration process of the cement mineral phase are obtained, as well as the total adsorption energy of the admixture-mineral system at different dosages; Step 5: Based on the bonding judgment principle and the water molecule conformation information obtained in the previous steps, the initial and final hydrogen bond networks of the dissolved state under different admixture dosages are calculated.

[0007] Preferably, in step one, when establishing a molecular dynamics model, the mineral phase molecules are placed on the upper and lower sides, the water molecules fill the entire system, and the admixture molecules are placed in the middle channels of the mineral phase molecules in a randomly distributed form, wherein the number of admixture molecules added is calculated based on the addition concentration in actual concrete engineering.

[0008] Preferably, in step 2, the force field parameters of the mineral phase, water and admixture are all obtained from the InterfacePCFF force field.

[0009] Preferably, in step three, in the model calculation file, the NVT ensemble is used, the total calculation time is 250 ns, the temperature is set to 297 K to allow the entire box to relax to equilibrium, and the time step is 1 fs to ensure that the conformational information of the admixture in the mineral phase solution region is fully sampled.

[0010] Preferably, in step 4, the output data specified by the model calculation results include: atomic spatial position information at different times and system thermodynamic parameter information, and Matlab is used for data processing to obtain the total adsorption energy of the admixture-mineral system at different admixture dosages.

[0011] Preferably, in step five, Matlab is used to calculate the time-varying information of the number of hydrogen bonds during the dissolution process and the initial and final hydrogen bond network information based on the spatial position distribution of atoms.

[0012] Compared with the prior art, the present invention has the following significant advantages: The present invention can establish a hydration process model when adding admixtures under different cement mineral phase systems through a molecular dynamics method, can make up for the defect that the nano-micro scale behavior of cement containing admixtures during hydration is difficult to observe through existing experimental conditions, can more vividly characterize the conformational changes of admixtures and cement mineral phases during the hydration process, and quantify the influence of admixtures on the hydration of cement mineral phases by calculating total adsorption energy and hydrogen bond network data. It not only has guiding significance for theoretical research on admixture design on a molecular scale, but also can guide the design of admixture dosage in the actual concrete pouring process by constructing a molecular model of the interaction between admixtures with different dosages and cement mineral phases. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a flow chart of the method of the present invention; Figure 2 It is an overall schematic diagram of the hydration model of cement mineral phase containing admixtures constructed in an embodiment of the present invention; Figure 3 The adsorption energy time-varying curves of different admixture amounts of admixtures calculated using output data in the embodiment of the present invention; Figure 4 A time-varying graph of the number of hydrogen bonds calculated using output data in an embodiment of the present invention; Figure 5 Schematic diagram of hydrogen bond network distribution calculated using output data in an embodiment of the present invention. DETAILED DESCRIPTION

[0014] In order to deepen the understanding of the present invention, embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0015] like Figure 2~Figure 4 As shown, the method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics described in the present invention includes establishing a molecular dynamics model of cement mineral phase, water molecules and admixtures, applying force to each atom in the molecular model, initializing the established model by setting commands in the computing software, obtaining the atomic motion coordinate trajectory, calculating the total adsorption energy of the admixture-mineral system at different admixture dosages, and obtaining the initial and final hydrogen bond networks at the initial dissolution stage at different admixture dosages, thereby realizing the evaluation of the effect of admixtures on the hydration of cement mineral phases. The implementation of the present invention can be carried out according to the following steps.

[0016] Step 1: First, use the molecular dynamics simulation software Materials Studio to establish a molecular dynamics model of cement mineral phase, water molecules and admixtures, and construct mineral phase molecules C3S, water molecules and admixture molecules TRI. The mineral phase molecule C3S model is based on the NI Golovastikov crystal structure. During the modeling process, the Q chain of the model is guaranteed to be consistent with the X-ray diffraction spectrum results of C3S in cement. The unit cell size is 48.74 Å ×56.28 Å×80 Å, and the total C3S model size is 4×8×2 times the unit cell size. C3S is placed above and below in the grid, and the blank position in the middle is used to place TRI. TRI is composed of long-chain sugar structures. The sugar monomer structure is used in the model to study the interaction between C3S, water and TRI. For this purpose, x TRI molecules are randomly placed in the middle channel position. The distribution of water molecules is filled in the model through Monte Carlo water absorption simulation, and the liquid water density is 1g / cm 3 Then re-assign the charge to the singularly charged atoms in the model to maintain the overall charge balance until the system charge is 0, and complete the molecular modeling in Materials Studio. Figure 2 As shown, the model is exported as car, cor files. Then the car, cor files are imported into LAMMPS and InterfacePCFF force fields are assigned to the mineral phase molecules C3S, water molecules and admixture molecules TRI in the model. Interface force field is a molecular force field specially designed to describe organic molecules, inorganic materials and their interactions at the interface. This force field can effectively capture the complex physical and chemical interactions between interfaces and is an ideal tool for studying interface phenomena such as polymer-inorganic composites, adsorption, wetting, mineral dissolution and precipitation.

[0017] Step 2: Initialize the model calculation in the multi-core parallel molecular dynamics simulation software LAMMPS, set the ensemble to NVT, set the system temperature to 297 K to allow the entire box to relax to equilibrium, and set the time step to 1 fs to ensure that the conformational information of the admixture in the mineral phase solution region is fully sampled. The total calculation time field is set to 250 ns to simulate the initial hydration process of C3S. The preset output information during the calculation process includes: the adsorption energy between the mineral phase C3S and the TRI molecular group, and the atomic trajectory of the entire hydration process.

[0018] Step 3: First, based on the adsorption energy data between mineral phase C3S and TRI molecular groups calculated and output by LAMMPS, use Matlab to draw the time-varying curve of adsorption energy, and calculate the average value of single and overall TRI and C3S adsorption energy based on the time-varying information of adsorption energy, such as Figure 3As shown; then, according to the atomic trajectory data of the entire hydration process calculated and output by LAMMPS, the atomic bonding is analyzed according to the definition of hydrogen bonding and the geometric and energy standards of hydrogen bonding. The hydrogen bond judgment needs to meet the following requirements: ① The distance between the hydrogen atom and the donor atom should usually be less than 3.5 Å; ② The hydrogen atom should be close to the straight line between the donor and the acceptor atom (that is, the donor-hydrogen-acceptor angle should be close to 180°). Usually, this angle greater than 120° is considered to be a valid hydrogen bond. After obtaining all the hydrogen bond information, Matlab is used to plot the time-varying results of the number of hydrogen bonds in the C3S system and the changes in the hydrogen bond network in the initial and final states of the C3S dissolution, as shown in the figure below: Figure 4 As shown in 5.

[0019] The present invention can establish a hydration process model when adding admixtures under different cement mineral phase systems through a molecular dynamics method, can make up for the defect that the nano-micro scale behavior of cement containing admixtures during hydration is difficult to observe through existing experimental conditions, can more vividly characterize the conformational changes of admixtures and cement mineral phases during the hydration process, and quantify the influence of admixtures on the hydration of cement mineral phases by calculating the total adsorption energy and hydrogen bond network data. It can not only realize the admixture molecular design and admixture effect evaluation oriented to cement performance, but also realize the understanding of the influence of admixture dosage on the hydration of cement mineral phases in actual engineering at the molecular scale, which has important engineering application significance.

[0020] The above descriptions are embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics, characterized in that: The steps include: Step 1: Establish a molecular dynamics model of cement mineral phase, water molecules and admixtures, construct mineral phase molecules, water molecules and admixture molecules, and relax them under the NVT ensemble until the system as a whole reaches a stable state; Step 2: Apply force to each atom in the molecular dynamics model established above. The force field is in the form of the following formula: ; In the formula, represents the total potential energy, represents the bonding energy terms, including bond stretching, bond angle, dihedral angle, and higher-order cross terms, represents the non-bonded energy terms, including van der Waals forces and electrostatic interactions; Step 3: In the calculation software, the system temperature and periodic boundary parameters are controlled by setting commands in the established molecular dynamics model to initialize the molecular dynamics model calculation, set the calculation time to simulate the cement mineral hydration process, and adjust the system stability by the Nose-Hoover command; Step 4: According to the calculation results of the molecular dynamics model, the atomic motion coordinate trajectory and the system thermodynamic information are obtained, and the position and conformation information of the mineral phase molecules, water molecules and admixture molecules in the system at different times during the hydration process of the cement mineral phase are obtained, as well as the total adsorption energy of the admixture-mineral system at different dosages; Step 5: Based on the bonding judgment principle and the water molecule conformation information obtained in the previous steps, the initial and final hydrogen bond networks of the dissolved state under different admixture dosages are calculated.

2. The method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics according to claim 1, characterized in that: In step one, when establishing the molecular dynamics model, the mineral phase molecules are placed on the upper and lower sides, the water molecules fill the entire system, and the admixture molecules are placed in the middle channels of the mineral phase molecules in a randomly distributed form. The number of admixture molecules added is calculated based on the addition concentration in the actual concrete project.

3. The method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics according to claim 1, characterized in that: In step 2, the force field parameters of the mineral phase, water and admixture are obtained from the InterfacePCFF force field.

4. The method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics according to claim 1, characterized in that: In step three, in the model calculation file, the NVT ensemble was used, the total calculation time was 250 ns, the temperature was set to 297 K, and the time step was 1 fs to ensure that the conformational information of the admixture in the mineral phase solution region was fully sampled.

5. The method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics according to claim 1, characterized in that: In step 4, the output data specified by the model calculation results include: atomic spatial position information at different times and system thermodynamic parameter information. Matlab is used to process the data to obtain the total adsorption energy of the admixture-mineral system at different admixture dosages.

6. The method for evaluating the effect of admixtures on cement mineral hydration based on molecular dynamics according to claim 1, characterized in that: In step five, the hydrogen bonding network information of the initial and final states of dissolution is calculated based on the spatial position distribution of atoms.

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