CT-Technology-based Research On Meso-structure And Fractal Character Of Concrete

As a kind of building material widely used in today's society,concrete plays an indispensable role in the field of civil engineering.Its mechanical properties are closely related to the safety of structure and the economy of construction.At the macro level,concrete is usually regarded as homogeneous and continuous material,and the assumption of linear elasticity is used for structural design.However,at the microscopic level,concrete is a heterogeneous discontinuous material composed of cement mortar,coarse aggregate,interface transition zone and pores.It is precisely because of the heterogeneity at the mesoscopic level that the mechanical behavior of concrete presents the discrete and nonlinear characteristics at the macroscopic level.Therefore,concrete should be studied more deeply from the microscopic level or even the microscopic level to deepen the understanding of the mechanical behavior of concrete.Guided by the mesoscopic theory,this paper uses CT technology and fractal theory to study the mesoscopic structure and fractal characteristics of concrete,mainly including the following aspects:(1)In order to obtain the mechanical indexes of concrete and its components,two mechanical tests were carried out: one was the mechanical test of concrete,including cube compressive strength test and elastic modulus test;the second was the mechanical test of each component of concrete,including the elastic modulus test of cement mortar and rock.The number of specimens for each type of test was 30.(2)CT technology was used to obtain the fault image of the internal structure of concrete.After image enhancement and image segmentation,the image was transformed into a binary image containing cement mortar and coarse aggregate,which was further applied to the three-dimensional reconstruction of concrete cube specimens.MATLAB programming eliminated the adhesion between aggregates and smoothes the edges of aggregates,so as to established a three-dimensional model reflecting the concrete mesoscopic structure.(3)Fractal theory was used to describe the geometric properties of concrete fault images and 3d models,which were quantitatively characterized by fractal dimension.By analyzing the relationship between the fractal dimension of the fault image and the 3d model,it was found that the correlation between the fractal dimension of the fault image and the 3d model is poor.The geometrical properties of concrete are characterized more accurately by fractal dimension of 3d model.(4)By analyzing the correlation between aggregate gradation index and fractal dimension of concrete,the influence of aggregate gradation on the geometric properties of concrete was discussed.Considering the macroscopic mechanical properties of concrete was related to its mesoscopic structure,the influence of fractal dimension of concrete on the compressive strength,elastic modulus and poisson's ratio was analyzed.The causes and internal mechanism of the phenomenon are explained,That is,the macroscopic mechanical properties were determined by the mesoscopic structure,and the macroscopic mechanical properties were the macroscopic manifestations of the mesoscopic structure under the external action.