SIMULATION OF THE INTERFACIAL TRANSITION ZONE AND AIR VOIDS EFFECTS ON CONCRETE CRACKING USING A MULTISCALE FE APPROACH
Palavras-chave:
Mesoscale approach, Cracking behavior, Interfacial transition zone, Air voidsResumo
Many models successfully consider concrete as a continuous and homogeneous material.
However, mechanical and cracking behavior of concrete can be significantly dictated by its constituents
and interactions between them on a finer scale. This means that considering the different phases of the
mesostructure results in a more accurate modeling of concrete fracturing. Two of the concrete
components that play an essential role in the mechanical response are: air voids and interfacial transition
zone (ITZ), which are acknowledged as the two weakest phases of the material. Therefore, this work
proposes a four-phase mesoscale representation of concrete, which consists of coarse aggregate, cement
matrix, aggregate-matrix interface (ITZ) and air voids. Coarse aggregates and macro air voids are
randomly embedded in the matrix. As a part of the mesh fragmentation technique (MFT) [6], high aspect
ratio elements are placed between regular elements, meaning that the ITZ is explicitly represented and
has its particular properties. An appropriate tension damage model is employed to describe the material
nonlinear behavior. Such approach can also be extended to a multiscale approach, in which a higher
refinement is given only to certain critical regions and the other regions are considered to be elastic with
homogenized properties, resulting in an improved computational performance. The non-matching
meshes are bonded with coupling finite elements (CFE) [8] in their shared boundaries, ensuring
displacement continuity. The analysis of the ITZ and air voids effects on concrete cracking is performed
by comparing the numerical responses for varied ITZ fracture properties and void ratio and size using
the multiscale approach proposed. The study demonstrated that the mechanical response is extremely
sensitive to the air void content, and its increase results in the formation of a very tortuous fracture and
drastic drop of peak load.
