End peeling of mineral based CFRP strengthened concrete structures -: A parametric study

The advantages of FRP-strengthening have been shown time and again during the last decade. All over the world several thousand structures retrofitted with FRPs exist. The most common way to bond the FRP composite to the structure is by the use of epoxy. Epoxy has many advantages; adhere well to concrete and to the FRP material, it has low shrinkage and has in comparison low moisture uptake when set. It is also easy to apply on surfaces of the adherents. However, it also contain some drawbacks; do not adhere well to wet surfaces, are sensitive to low temperature, in particular during curing and it cannot stand high temperatures after curing. It is normally not diffusion open and it might be harmful to men if not handled properly during the application phase. It would therefore be advantageously if the epoxy could be replaced with a more environmental friendly bonding material, which is diffusion open and has the possibility to be applied in wet areas and at low temperature and still function as a shear transfer medium. Here mineral based bonding agents might be a solution. A test program at Lulea University of Technology (LTU) shows that this might be possible and preformed tests have shown very promising results. To increase the understanding of the bonding properties a theoretical study to investigate the shear stress at the cut-off end of concrete beams strengthened for flexure has been carried out. The theoretical study will later be followed by laboratory tests - unfortunately no laboratory tests with MBC (Mineral Based Composite) was ready at time for this paper. In this theoretical study the shear stress at the cut off-end of a concrete beam strengthen in flexural with traditional CFRP plate bonding is calculated and compared with a beam strengthened with MBC (Mineral Based Composite) bonding. The parametric study reveals that the shear stress is considerably smaller for the MBC system used compared to a CFRP epoxy based system at the same load level and loading conditions.