[PO-G2] Poster Session 2

[P2-55] Construction of virtual ITZ specimens using extended stochastic optimization and evaluation of their permeability

^○Se-Yun Kim, Tong-Seok Han (Dept. of Civil and Environmental Engineering, Yonsei Univ., Korea)

The external substance penetrates into an interfacial transition zone (ITZ) that is located between an aggregate and bulk cement paste and has a relatively high porosity than the bulk cement paste. However, it is difficult to confirm the 3-D microstructure of the ITZ with the functionally graded void distribution to evaluate its permeability. In this study, 3-D microstructures of bulk cement pastes with three kinds of porosities and the void gradient of the ITZ obtained from 2-D SEM image are used to construct the virtual 3-D microstructures of the ITZ. Based on the two information, the phase distribution characteristics of the ITZ are generated, and they are used for constructing the virtual ITZ specimen using a stochastic optimization. The stochastic optimization is an appropriate method to construct a random heterogeneous material [1], but the ITZ has the functionally graded void distribution, which depends on the distance from the aggregate. To construct the functionally graded microstructure, an extended stochastic optimization is proposed. In addition, an efficient iteration method for stochastic optimization is proposed and utilized for construction of the virtual ITZ specimens, which improved the computational cost. The permeability of the virtual ITZ specimens are evaluated by a finite element method. The effect of the ITZ from the penetration of the external substances is confirmed by the permeability analysis using the virtual ITZ specimen. This study shows that the proposed extended stochastic optimization process is effective for constructing functionally graded phase distribution, while the real 3-D microstructure is difficult to obtain from experimental techniques. This study also confirms that the virtual experiment procedure can be synergistically used with the real experimental approaches.

[1] S. Torquato, Random Heterogeneous Materials: microstructure and macroscopic properties, vol. 16, Springer Science & Business Media, Berlin, 2013.