Axial compressive behaviour of corroded steel reinforced concrete columns retrofitted with a basalt fibre reinforced polymer-ultrahigh performance concrete jacket

Steel reinforced concrete (RC) members suffer from severe corrosion in some scenarios. New techniques and materials are required for the timely rehabilitation of the deficient structures. To address this challenge, an accelerated retrofit approach using a basalt fibre reinforced polymer (BFRP) sheet combined with ultrahigh performance concrete (UHPC) jacket has been developed. The BFRP sheet was internally embedded within the UHPC matrix to enhance its durability under marine environmental conditions. The treatment of corroded steel stirrups in RC columns replaced with fiber reinforced polymer (FRP) composites is also considered in the retrofit approach. The axial compressive behaviour of a series of corroded RC columns retrofitted with BFRP–UHPC jacket or UHPC jacket is investigated. Specifically, 16 RC columns (six control specimens and 10 retrofitted specimens) were prepared and tested under monotonic axial compression. The test variables were the sectional geometry (i.e. circular or square cross-section), transverse steel reinforcement ratio (i.e. two different stirrup spacings), and retrofitting method (i.e. BFRP–UHPC jacket or UHPC jacket). The test results showed that the maximum increase in the peak load after retrofitting was as large as 145.9%. A simple model for retrofitted RC columns that can provide reasonably accurate but relatively conservative predictions is developed.