The Macro- And Meso- Mechanical Properties Of Concrete Based On The Multi-Scale Theory

Concrete has been widely used as an important typical multiphase heterogeneous materials in high-rise buildings, underground factories, dams and nuclear power plants and other industrial and civil buildings. Studying the composition of its meso- structure may explain the concept of the nature of the macroscopic mechanical properties of the external load. With the advancement of micromechanics and computer numerical simulation technology, damage and fracture of concrete at the level of meso has become the focus of widespread concern to researcher. There is a close inner link between macroscopic properties and the meso-structure、meso-composition of the material. In order to understand the physical properties of a material and its failure mechanism,fully grasping the concept of composition and analysis of its fine array structure has a key role. This paper relies on the National Natural Science Foundation of China(41430642), funded by the National Natural Science Foundation of Youth Foundation of China(51108207), State Key Laboratory of Frozen Soil Engineering Foundation( SKLFSE201514) and China Postdoctoral Science Foundation(2015M581403). A series of macroscopic mechanical experiments 、micro-numerical simulation experiments and theoretical research work about concrete,which was viewed as a three-phase composite consisting of aggregate, mortar and interface composition from meso-level to macro level, from global to local, have been completed in the paper based on multi-scale theory1. In this paper, the concrete multi-meso mechanics random aggregate numerical model has been established based on the finite element, including random aggregate growth, delivery and aggregate, mortar, three-phase medium interface coordinate positioning pretreatment process. Meanwhile, the scalar damage constitutive relations has been introduced in the explicit solutions process of Finite Element Method.2. According to the existing meso-mechanical model, we proposed a method for efficient delivery of aggregates and the corresponding state matrix to determine the aggregate position method, the pretreatment efficiency by 23%.The nonlinear damage softening relation was introduced in the model of multi-related damage mechanics of concrete.3. We has researched on the concrete mortar at the meso level, and aggregate interface consisting of the mechanical properties study of macro meso,which were based on homogenization theory and multi-scale finite element method. The effects of the size of the cellular equivalent macroscopic mechanical parameters of concrete has been investigated. The results show that the multi-scale method can accurately calculate the equivalent macroscopic mechanical parameters of concrete.4. Through macro-static compression concrete materials tests of C20 and C30, the effects of coarse aggregate content concrete matrix type and particle size of the coarse aggregate concrete macroscopic mechanical equivalent has been discussed, which provides real and effective test data when we will reverse the meso interface equivalent parameters. The results showed that showed that the macroscopic equivalent elastic modulus and compressive strength of concrete coarse aggregate content increases and improved, and the elastic modulus of the growth rate faster than the growth rate of the compressive strength, but when the aggregate when the content is less than 30%, the compressive strength of concrete is lower than the strength of the matrix.5. The elastic modulus of concrete meso transition zone interface has been identified and reversed based on improved homotopy algorithm. The results showed that without considering the impact of mortar and aggregate interface, the high demand of the macro equivalent elastic modulus of concrete; depending on the interface thickness is 0.1mm, ask concrete macroscopic equivalent elastic modulus and the measured test macroscopic elastic modulus error is within 10%. Therefore, when creating aggregate concrete numerical model, the interface is a phase material is necessary.