EXPERIMENTAL CHARACTERISATION OF CONFINED CONCRETE IN DIRECT COMPRESSION AND FLEXURE

Abstract

The global aging and deterioration of critical civil infrastructure have driven the advancement of retrofitting and strengthening techniques. This study provides an in depth experimental characterisation of confined concrete subjected to direct compression and flexural loading. The primary objective is to evaluate the structural performance improvements of M20 grade concrete specimens externally wrapped with unidirectional Carbon Fiber Reinforced Polymer (CFRP) applied with a high-strength epoxy binder. The experimental program included 18 precisely cast specimens: 6 concrete cubes (150x150x150 mm) for standard compressive strength assessment, 6 concrete cylinders (150x300 mm) for evaluating slenderness and axial compression, and 6 concrete beams (100x100x500 mm) for analyzing flexural strength and displacement ductility. In each geometric category, half of the specimens served as unconfined controls to establish baseline performance, while the other half were wrapped with 200 GSM unidirectional CFRP jackets. This research is highly influenced by the displacement-ductility based design methods and mainly by the analytical models developed by Pantelides et al. (2012). The required thickness of the CFRP jacket was mathematically derived using parameters such as the required stiffness of the FRP jacket, characteristic dimension that targets the ultimate compressive strain to ensure optimal dilation control and to prevent strain softening behavior in the concrete core. The experimental results showed significant improvement in the load-carrying capacity and deformation characteristics of the CFRP confined specimens over all testing regimes. Under direct compressive loading, the CFRP wrapped cubes and cylinders showed significantly higher ultimate peak strengths and prolonged ductility than unconfined cubes and cylinders. The circular cross-sections (cylinders) proved to be highly effective in utilizing hoop stresses arising from FRP confinement. Furthermore, the flexural behavior of the CFRP-strengthened beams showed a significant increase in peak flexural load and considerable energy absorption capacity before ultimate failure, changing the failure mode from brittle catastrophic to ductile and progressive. This extensive thesis details the relation of the experimental data to the existing analytical models of confinement in detail and provides the load deformation paths, failure mode analyses and useful engineering insights for the upgrading of existing elements designed using regular M20 design mix concrete.