Study On The Effect Of Structure And Mechanical Properties Of Interfacial Transition Zone On The Strength Of Concrete

The macroscopic mechanical properties of concrete are determined by its meso composition, as an important mechanical parameters of concrete the strength has always been the key of researchers` studied. As the bridge of coarse aggregate and mortar matrix, the looser structure and lower mechanical characteristics of interfacial transition zone(ITZ) have a significant influence on the strength of concrete. Considered these characteristics, this thesis has studied the influence of ITZ on the strength of concrete based on the meso numerical simulation method. The main contents and conclusions include:(1) A program of the distribution of random defects elements in ITZ has been written based on the Secondary Development of ANSYS program. The random locations of defect elements in ITZ are determined by the method of generating random numbers, when building the models. And the problem of the locations of defect elements in ITZ is solved effectively.(2) The influences of initial defects in mortar on the strength of mortar are analyzed based on the finite element simulation technology. And a relationship formula between the strength of mortar and its defects content has been proposed. In this paper the initial defects are represented by circle pore, and we simulate the strength of mortar when the content of defects is from 0 to 10%. The results show that: the simulation results are in good agreement with the formula, when the defect content is less than 7%.(3) A two-dimensional model of concrete in meso-scale is developed with concrete regarded as a four-phase composite consisting of coarse aggregates, mortar, ITZ and initial defects. We simulate the fracture failure process of concrete, and make a comparison between the simulation results and the macroscopic experiments results. The results show that the model can simulate the tensile strength of concrete well.(4) The influences of structure and mechanical properties of ITZ on the strength of concrete are made. In terms of interface structure, we mainly study the influence of thickness、the distribution and content of initial defect of ITZ on the tensile strength of concrete; in terms of the mechanical properties of ITZ, we mainly study the influence of tensile strength and elastic modulus of ITZ on the tensile strength of concrete. The results show that: the content of ITZ initial defect and tensile strength of ITZ have significant effects on the tensile strength of concrete, the tensile strength of concrete fall by 35% when the initial defect content ranging from 10% to 50% and the tensile strength of concrete increased with the strength of ITZ by 62% when the ITZ tensile strength of mortar matrix multiplication 0.5 to 0.9 times of the mortar matrix; the thickness of ITZ has a little influence on the tensile strength of ITZ; the distribution of ITZ initial defects and the elastic modulus of ITZ almost have no effects on the tensile strength of concrete.