Papers by Author: Jun Hong

Abstract: Since meso-structure of plain concrete can not be observed directly, numerical simulation is the main approach to obtain the model coincident with the real structure on statistics. By applying the discrete element method, we have developed the 3D dynamic simulation for random aggregate model of plain concrete. According to the real ration of mass, the spatial positions of aggregate have been obtained, which is more close-grained compared with the random-distributed models based on Monte Carlo method. Compared with the geometrical generating algorithm for 2D random polyhedral aggregate, the algorithm for 2D or 3D random polyhedral aggregate is simpler. The results are the foundation for further studying the interface fracture and chloride diffused channels.

Abstract: The complex behavior of concrete is largely related to the mechanical response of calcium silicate hydrate (C-S-H) gel. During the past two decades, a great deal of efforts has been devoted to the structure of C-S-H at the nanoscale level, including both experiment investigation and molecular simulation. The smallest C-S-H unit has a layered crystal structure at atomic scale, with a lamella thickness in the nm range. And moreover, ordered stacks of up to several tens or even hundreds of nano-lamellae have been observed experimentally. The key features of structure and morphology is remarkably the ubiquitous presence of an orientational order. Now we focus on the physical understanding on such orientational ordered C-S-H structures at mesoscale. In respect that there exists a high nematic order in the stacking C-S-H of nano-lamellae, by introducing some physical parameters, such as the magnitude of nematic order of the nano-lamellae, we try to predict the mechanical properties of the crystalline in terms of its micro-structure.

Abstract: A new robust numerical technique was proposed for analyzing chloride transient diffusion in concrete with non-homogenous coefficient. The method was based on a meshless boundary element method which results in an integral equation for explicitly evaluating field chloride quantities. Weighted residual method and Green’s function were adopted to derive domain and boundary integral equations. A radial integration method coupling with radial basis function approximation technology was used to convert domain integral into equivalent boundary integral. With central finite difference method, an explicit time iteration scheme was established for solving transient diffusion equation. Two numerical examples for 2D diffusion problem were given to demonstrate the robustness of the proposed method. Numerical results show that the non-homogenous diffusion coefficient causes the chloride distribution non-uniform, and the diffusion process is nonlinear with respect to time.