The Reconstruction Of The 3D Material Structure Model Of Concrete And Application Based On CT Technology

Physical and mechanical properties of rock or concrete materials as well as their failure mechanism are determined by the material structure and the properties of each constituent. Therefore, it has become a developing trend to consider the actual structure of material as accuracy as possible in numerical methods. It is of theoretical and practical value to research digital reconstruction methods of materials structure combined with numerical methods, which enable us to more deeply understand the mechanical properties and fracture mechanisms. In this paper, taking concrete as an example, computerized tomography (CT) technology is employed to capture a serial of section images of the concrete material structure. Then, aiming at the color characteristic of the CT image, the characterization method for material structure from CT images has bee developed. After that, two reconstruction methods for 3D material structure have been proposed. The data of the 3D material structure mdoels can be imported into FLAC3D and RFPA3D as preliminary applications, respectively, which provides a novel tool and a kind of research idea for studying mechanical properties and failure mechanism of rock, concrete as well as composite materials. The main works are as follows:(1) The characteristics of CT slice images are analyzed. The segmentation method based on annular zonal method and automatically identifying threshold for CT images is proposed to possibly characterize internal mesomaterial (i.e. aggregate, motar and the interfacial transition zone between them) composing concrete accurately and realize thecharacterization of the three phase material in concrete;(2) Based on the vectorization of the BMP image and then considering the vectorized data from each CT image as the framework, the reconstruction method for the 3D digitized solid model of material structure is proposed; Moreover, considering the pixel as an element, the other reconstruction method for the 3D grid model of material structure is proposed by overlapping. A code is also programmed for this purpose and the advantages and disadvantages of two methods are also discussed;(3) The 3D solid material structure model of the concrete specimen is built using the proposed method. The data of the model is input into the commercial software FLAC3D and then the mechanical behaviors of concrete under uniaixal compression are examined on the basis of elastic-plastic theory;(4) The data interface between the 3D grid material structure model and RFPA3D code is developed and the 3D grid material structure model is established, and input into RFPA3D to build the numerical specimen of concrete taking into account the releastic aggregate distribution. Then the uniaxial compression test is simulated using RFPA3D code.By comparison, it is found that the results of the numerical test in which the releastic distribution and geometry of coarse aggregates are taken into account are of comparability with the experimental results. The mechanical parameters and final failure patterns of the specimen from the numerical test approach those from the experimental test. The effect of ITZ on concrete mechanical behaviors is further investigated. It provides a new idea for deeply studying the mechanical behaviors of quasi-brittle materials such as concrete, rock and composite materials.