Strengthening of Reinforced Concrete Columns Using Ultra-High Performance Fiber-Reinforced Concrete Jacket

The use of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) increased in the field of civil engineering throughout the last few decades. UHPFRC is being used considerably on a large scale in megastructure applications. High compressive and tensile strength permits reconstruction and optimization of the structural members. At the same time, its improved durability properties make it easier to extend the life of the design and can be used as thin layers, cladding, repairs, and column coverings. Although UHPC has an extremely high compressive strength, it exhibits very brittle fracture behavior compared to normal strength concrete (NSC). Since the ductility and fracture toughness of UHPC can be enhanced by adding fibers, the addition of fibers to production adds innovative features to UHPFRC structures and opens up new application areas for UHPFRC. The aim of this study is to investigate the axial behavior of square reinforced concrete (RC) columns strengthened with UHPFRC jackets. Nineteen specimens were cast (1000 mm in height and a cross-sectional area of 150 × 150 mm, whose interface treatment methods were prepared through vertical grooving (VG), horizontal grooving (HG), and without grooving (NG), with the jacket thickness (20 mm and 40 mm) and the number of strengthened sides of the column (two, three, and four sides). The results show a brittle failure for all strengthened specimens. The UHPFRC-reinforced RC columns with vertical grooving (VG) showed a higher ultimate load capacity compared to the columns with horizontal grooving (HG) and the columns without grooving (NG). The horizontal grooving (HG) gives a better result than the jacket without grooving (NG) and increases the cohesion area between the jacket and the column for two and three of the RC columns’ strengthened sides. But, in the case of strengthening the columns on four sides, the effect of confining the jacket to the column appears, and the grooving causes weakness in the body of the original column so that the jacket without grooving (NG) gives a better result than the jacket with horizontal grooving (HG).