Abstract
The Interfacial Transition Zone (ITZ) between two basic materials having differentiations in their mechanical properties has always been intriguing. The stiffness disparities between the two will result in a very distinctive area, the interface. Cement based components such as mortar and concrete consist of the cement paste and aggregates, with the ITZ at the perimeter. When compared to the cement paste, this ITZ has a higher porosity with a dissimilar crystal formation. The resulting area therefore becomes the weak link in concrete. A Finite Element Model (FEM) was developed to construct the load-displacement behavior of a single inclusion specimen and to study the crack propagation within the ITZ. The ITZ was modeled as a linkage element having a double spring, perpendicular and parallel to the ITZ surface. The individual stiffness behavior of these springs was obtained from laboratory-tested specimens. Non-linearity was generated by evaluating the principal stresses and strains at Gauss points, while the CEB-FIB 2010 code was used for the constitutive material behavior of the mortar. Iteration is conducted by the arc-length method developed by Riks-Wempners. The load-displacement curves resulting from the FEM were validated with laboratory tested specimens to compare its effectiveness and assess the correctness of the model.
Highlights
The Interfacial Transition Zone (ITZ) in concrete is the weak link within the material
It was clearly shown that the presence of the ITZ in the analysis of concrete could not be neglected
The modeling of the ITZ as a double spring was proven to be an excellent representation of the behavior of the interface
Summary
The first spring was perpendicular to the aggregate surface, representing the ITZ in tension, and the second parallel, illustrating the shear response In meshing, this ITZ was constructed by assigning two nodes having identical coordinates. The behavior of the ITZ was expressed by the two spring constants, kη in tension and kξ in shear The behavior of these constants were conveyed in their load-displacement responses, obtained through uniquely developed laboratory tests [1,3,4]. The tangent modulus in the anisotropic axes system was obtained from the corresponding stress-strain relationship, while the material stiffness matrix as proposed by Chen and Chen and Saleeb [7, 8] was chosen for the finite element algorithms. To accommodate the non-linearity of the model, the arch-length iteration technique was applied
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