Slurry infiltrated fiber concrete (SIFCON) is an advanced generation of fiber-reinforced concrete (FRC) with higher fiber content. SIFCON offers excellent potential for use in areas that require high ductility and impact resistance, particularly when designing seismic retrofits and repairing or strengthening structural reinforced concrete members. This study investigated the behavior of square normal strength concrete (NSC) columns of grade M35 strengthened with SIFCON shell and compared them with unstrengthen NSC. The effect of different SIFCON shell thicknesses (2 and 3) cm, fiber type and volume fraction (4 and 6%), and tie spacing (8 and 16) cm were studied. The fiber types employed were polypropylene and hooked-end steel fiber. Eleven columns were cast and tested for the current investigation in two groups, where the first group (control specimens) consists of two unstrengthen NSC columns and one square NSC column strengthened with a 2 cm SIFCON shell with a 6% steel fiber ratio. The second group comprises eight NSC columns strengthened with a hybrid fiber SIFCON shell. The NSC square columns had dimensions of (8x8x80) cm. 3 cm SIFCON shell thickness was observed to evolve the strengthen columns' load-carrying capacity and energy absorption. The maximum load achieved is about 223% as compared with unstrengthened NSC columns. The energy absorption was about 16 times that of the control. At the same time, the stiffness of strengthened columns is less than that of NSC columns
