CHARACTERIZATION, MODELING AND SIZE EFFECT OF CONCRETE-EPOXY INTERFACES
Open Access
- Author:
- Coronado, Carlos Arturo
- Graduate Program:
- Civil Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 17, 2006
- Committee Members:
- María López De Murphy, Committee Chair/Co-Chair
Charles E Bakis, Committee Member
David John Green, Committee Member
Theodor Krauthammer, Committee Member
Andrew Scanlon, Committee Member - Keywords:
- composites
debonding
concrete-epoxy interface
finite element modeling
damage mechanics
bond
fracture mechanics - Abstract:
- Concrete-epoxy interfaces are formed during the installation of bonded concrete repairs. These repairs are widely used in civil engineering applications such as structural rehabilitation, pavement repair, and concrete overlays. The structural performance of these applications is often governed by the behavior of the concrete-epoxy or concrete-repair interface as found elsewhere (ACI 440 2002, Granju et al. 2004). Therefore, characterizing and predicting the bond behavior of such interfaces is required. This study focuses on the experimental characterization and numerical modeling of concrete-epoxy interfaces typical of concrete members strengthened with FRP laminates. In particular, the fracture properties of two concrete-epoxy interfaces, CEI-1 and CEI-2, are determined. Such interfaces are formed during the installation of two commercially available FRP strengthening systems. During the experimental program, the cohesive crack method (Hillerborg et al. 1976) is used to determine the softening curve of the concrete-epoxy interfaces CEI-1 and CEI-2. Such curve is defined by three material properties, the tensile strength, ft, the size-effect fracture energy, Gf, and the cohesive fracture energy, GF. The sensitivity of these properties to the type of epoxy, specimen geometry, and condition of the concrete surface is also investigated experimentally. From this sensitivity study, test procedures and specimen geometries are recommended in order to properly determine the softening curve of a concrete-epoxy interface. Furthermore, it was found that the size-effect fracture energy is a suitable parameter to compare the behavior of different concrete-epoxy interfaces. The analytical approach is focused on the introduction and application of the concept of damage band for predicting the debonding failure of concrete-epoxy interfaces. In such an innovative approach, all the processes taking place during the debonding failure of a concrete-epoxy interface are smeared in a band of fixed width (damage band). This makes the band concept attractive from a modeling point of view since softening relations can be used in order to characterize the debonding behavior. Analytical predictions, using the concept of damage band, are validated against experimental results obtained from different bond test. In particular, it is explored the capability of the analytical approach to predicting load-strain curves, strain distributions, failure sequences, and failure mechanisms experimentally observed during pull-off and beam-bond tests. The sensitivity of the numerical results is also studied. In particular, it is evaluated the effect of the geometry and discretization of the damage band on the numerical predictions. From this study, it was found that numerical predictions are not affected by changes of the thickness of the damage band within 0.5 and 2.0 the aggregate size.