1. A mechanical property prediction method of ultra-high performance concrete is characterized by comprising the following steps:

(1) establishing a hydration microstructure evolution model of a cement-fly ash-silica fume ternary gelling system based on a CEMHYD3D hydration model, establishing a microscale finite element model by using ls-prepost pretreatment software according to the hydration microstructure evolution model, obtaining a microscale UHPC stress-strain relation according to the established finite element model, and obtaining microscale UHPC mechanical parameters according to the microscale UHPC stress-strain relation;

(2) establishing an aggregate three-dimensional space random accumulation model, establishing a mesoscale mortar finite element model according to the aggregate three-dimensional space random accumulation model, substituting the mechanical properties of the aggregate and the microscale UHPC mechanical parameters obtained in the step (1) into the mortar finite element model for calculation to obtain a mesoscale mortar stress-strain relationship, and obtaining mesoscale mortar mechanical parameters according to the mesoscale mortar stress-strain relationship;

(3) and (3) establishing a fiber three-dimensional space random accumulation model, establishing a UHPC finite element model according to the fiber three-dimensional space random accumulation model, substituting the fiber mechanical characteristics and the mesoscale mortar mechanical parameters obtained in the step (2) into the UHPC finite element model for calculation, and obtaining the stress-strain relation of the macroscale UHPC.

2. The method for predicting the mechanical property of the ultra-high performance concrete according to claim 1, wherein in the step (1), a cubic space is divided into voxel points, the UHPC cementing material is converted into an electronic ball consisting of the voxel points according to an actual mixing proportion and thrown into the cube, a hydration microstructure evolution model is obtained through phase separation and hydration steps, then a finite element model is built by adopting ls-prepost according to the microstructure, and the micro-scale UHPC mechanical parameters can be further calculated according to different physical mechanical parameters.

3. The method for predicting the mechanical properties of the ultrahigh-performance concrete according to claim 1, wherein in the step (2), according to the actual grading of the river sand, a three-dimensional stacking model of convex particles is established by using Visual Studio C + +, namely, a three-dimensional space random stacking model of the aggregates, the model is a cube, the space is divided into cubic grids, based on which a finite element model of the mortar is established by using ls-prepost, and the mechanical parameters of the mesoscale mortar can be further calculated according to the micro-scale clean mortar and the mechanical parameters of the aggregates.

4. The method for predicting the mechanical property of the high-performance concrete according to claim 1, wherein in the step (3), a fiber three-dimensional space random stacking model is established by using Visual Studio C + + according to the actual size of the steel fiber, the model is a cube, a UHPC finite element model is established by using ls-prepost, and a macroscopic scale UHPC stress-strain relation is obtained according to mortar and fiber mechanical parameters.

5. The method for predicting the mechanical property of the high-performance concrete according to claim 1, wherein the step (1) of establishing the evolution model of the hydration microstructure of the cement-fly ash-silica fume ternary gelation system is carried out under the condition that the water-to-gel ratio is less than or equal to 0.2.

Background

The ultra-high performance concrete generally refers to concrete with the compressive strength of more than 150MP, has the performances of ultra-high strength, high toughness, high durability, high anti-explosion performance and the like, and has wide application prospect. At present, regarding the mix proportion of UHPC, a design method is mainly the tightest packing theory, although the method is widely applied, the physical characteristics of a cementing material are only considered in a model, the chemical characteristics of the material are not designed, different powder materials with consistent particle size and distribution are not designed, the chemical reaction activity is different, and the difference of the effect on the internal microstructure of concrete is larger, so that the problems that the UHPC is lack of working performance or the difference of actual strength and working strength is larger are often caused, the accuracy of the existing method for predicting the performance is poor, and effective guidance is difficult to be provided for the design of the mix proportion of the UHPC.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a mechanical property prediction method of ultra-high performance concrete, and solves the problem that the existing method does not consider the chemical characteristics of components and has inaccurate prediction result.

The technical scheme is as follows: the invention discloses a mechanical property prediction method of ultra-high performance concrete, which comprises the following steps:

(1) establishing a hydration microstructure evolution model of a cement-fly ash-silica fume ternary gelling system based on a CEMHYD3D hydration model, establishing a microscale finite element model by using ls-prepost pretreatment software according to the hydration microstructure evolution model, obtaining a microscale UHPC stress-strain relation according to the established finite element model, and obtaining microscale UHPC mechanical parameters according to the microscale UHPC stress-strain relation;

(2) establishing an aggregate three-dimensional space random accumulation model, establishing a mesoscale mortar finite element model according to the aggregate three-dimensional space random accumulation model, substituting the mechanical properties of the aggregate and the microscale UHPC mechanical parameters obtained in the step (1) into the mortar finite element model for calculation to obtain a mesoscale mortar stress-strain relationship, and obtaining mesoscale mortar mechanical parameters according to the mesoscale mortar stress-strain relationship;

(3) and (3) establishing a fiber three-dimensional space random accumulation model, establishing a UHPC finite element model according to the fiber three-dimensional space random accumulation model, substituting the fiber mechanical characteristics and the mesoscale mortar mechanical parameters obtained in the step (2) into the UHPC finite element model for calculation, and obtaining the stress-strain relation of the macroscale UHPC.

In the step (1), firstly, a cubic space is divided into voxel points, then the UHPC cementing material is converted into an electronic ball consisting of the voxel points according to an actual mixing proportion and thrown into the cube, phase splitting and hydration steps are carried out to obtain a hydration microstructure evolution model, then a finite element model is established by adopting ls-prepost according to the microstructure, and the micro-scale UHPC mechanical parameters can be calculated according to different physical mechanical parameters.

In the step (2), according to the actual grading of river sand, a convex particle three-dimensional stacking model is established by using Visual Studio C + +, namely an aggregate three-dimensional space random stacking model, the model is a cube, the space is divided into cube grids, based on the model, an ls-prepost is adopted to establish a mortar finite element model, and according to the micro-scale clean slurry and the aggregate mechanical parameters, the micro-scale mortar mechanical parameters can be further calculated.

And (3) establishing a fiber three-dimensional space random accumulation model by using Visual Studio C + + according to the actual size of the steel fiber, wherein the model is a cube, establishing a UHPC finite element model by using ls-prepost, and further obtaining a macroscopic scale UHPC stress-strain relation according to the mortar and the fiber mechanical parameters.

The step (1) of establishing the hydration microstructure evolution model of the cement-fly ash-silica fume ternary gelation system is carried out under the condition that the water-to-gel ratio is less than or equal to 0.2.

Has the advantages that: the method has accurate calculation and high stability, adopts a multi-scale design method, fully considers the physicochemical characteristics of the raw material components, overcomes the problem of large error of the traditional UHPC mix proportion design method, and can realize accurate prediction of the mechanical property of the UHPC.

Drawings

FIG. 1 is a schematic diagram of a hydration 7d microstructure of a cement-fly ash-silica fume ternary gelling system;

FIG. 2 is a schematic view of a finite element model of a clean slurry;

FIG. 3 is a schematic diagram of a fiber three-dimensional space random packing model;

FIG. 4 is a mortar stress cloud;

FIG. 5 is a schematic view of a fiber model;

FIG. 6 is a diagram showing the comparison of mechanical properties of the test simulation.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

The invention discloses a mechanical property prediction method of ultra-high performance concrete, which comprises the following specific processes;

based on a CEMHYD3D hydration model and combined with a classical cement chemistry theory, fly ash and silica fume are coupled into CEMHYD3D, a hydration microstructure evolution model of a cement-fly ash-silica fume ternary gelation system is established under the condition that the water-cement ratio is less than or equal to 0.2, the hydration 7d microstructure of the cement-fly ash-silica fume ternary gelation system is shown in figure 1, the microstructure of a cement-based composite material is more complex due to the addition of the fly ash and the silica fume, and the glass phase of the fly ash is mainly active SiO₂And Al₂O₃The active silicon dioxide participating in the reaction generates C-S-H gel, the Ca/Si of the C-S-H gel formed when the active silicon dioxide and the alumina generate the volcanic ash reaction is lower than that of a pure portland cement system because the common CaO content of the fly ash is lower, the chemical reaction formulas of the fly ash and the silica ash mixed in the cement are respectively listed in formulas (1) to (7), and the lower number in the formulas is the stoichiometric number of the chemical volume.

And (3) embedding the established cement stone microstructure model into an LS-DYNA module of general finite element software ANSYS to establish a micro-scale finite element model as shown in figure 2, and performing quasi-static mechanical property simulation to obtain the micro-mechanical property parameters of the UHPC cementing material system. According to the established CEMHYD3D hydration model, the size of the cement stone microstructure model is 100 micrometers multiplied by 100 micrometers, the size of a unit grid is a cube with the side length of 1 micrometer, finite element grid division is carried out according to the unit size, and 100 ten thousand cubic eight-node units are counted. The gel system part has the physical mechanical properties shown in Table 1, and the net slurry size mechanical strength shown in Table 2 can be obtained by calculation to be 62 MPa.

TABLE 1 partial phase mechanical Properties of the gelled System

TABLE 2 Fine calculation parameters for neat paste

Establishing a three-dimensional space random stacking model of the fine aggregate according to the particle size distribution of the aggregate, and then performing grid division by adopting a mapping grid method in a fine mortar mesoscopic numerical model. Modeling a mortar matrix by using a solid unit and a material model CONCRETE _ DAMAGE _ Rel3(MAT _072R3) in LS-DYNA, substituting the mechanical properties and the mechanical strength of the net slurry scale in the table 3 into a mortar finite element model by using a HOLMLIST-JOHNSON-COOK material model (HJC model) to obtain a stress-strain relationship of the mortar in the microscopic scale, wherein the stress-cloud diagram of the mortar is shown in a figure 4(a), the stress-cloud diagram of the aggregate is shown in a figure 4(b), and the mechanical strength of the mortar in the dimensional scale is 130.2MPa through calculation of the stress-strain relationship of the mortar in the microscopic scale.

TABLE 3 Fine-aggregate microscopic calculation parameters

The fiber is used as an important component of UHPC, three-dimensional reconstruction is needed to be carried out on the UHPC, a fine aggregate three-dimensional space random accumulation model is established according to the morphological characteristics of the UHPC, as shown in figure 5, a UHPC microscopic finite element model is established, a UHPC matrix and an end plate adopt three-dimensional eight-node normal stress solid units and adopt hourglass control based on rigidity, and the hourglass coefficient (QM) is taken as 0.02. The steel fiber adopts a beam unit. The maximum equivalent strain criterion is adopted, namely, when the maximum equivalent strain of the unit reaches 0.06, the unit is deleted and does not participate in the calculation. Considering the calculation accuracy and the limitation of the calculation amount, the UHPC mortar unit size is 10mm, and the steel fiber unit size is 3 mm. The fiber adopts an MAT-PLASTIC-KINEMATIC model, for the UHPC mortar material, the material model is selected to be a K & C model, the compression bar adopts an elastic model, namely (MAT _003), model parameters of each component of the UHPC material are shown in table 4, and the mechanical properties of the fiber and the mechanical parameters of the microscale mortar obtained in the step (2) are substituted into the UHPC finite element model for calculation to obtain the stress-strain relation of the macroscale UHPC.

TABLE 4UHPC meso-scale simulation parameters

The mechanical properties of the ultra-high performance concrete calculated by the method are compared with the test results, the results are shown in fig. 6, and the fact that the method has good consistency compared with the test results can be seen from fig. 6.