The confinement of reinforced concrete (RC) columns with fiber reinforced polymer (FRP) jackets is an effective measure for the strengthening and retrofitting of existing structures. The jacket withstands the increasing lateral strains of the axially loaded column causing a three-dimensional stress state inside the concrete. In the result, a higher concrete compressive strength can be achieved. So far, extensive international research on FRP-confined concrete has been conducted, but there are still some open issues regarding the influence of different parameters on the load-bearing behavior. This paper is focusing on the effect of the substrate preparation on the maximum concrete strength and stress-strain behavior. Therefore, an experimental study of carbon fiber reinforced polymer (CFRP) confined concrete cylinders with various substrate conditions and preparation methods is presented. The results are compared with previous investigations and assessed accordingly. Furthermore, recommendations regarding the substrate preparation by current national codes and guidelines are specified and considered critically.
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