Axial behavior of circular seawater sea-sand coral concrete columns reinforced with BFRP bars and spirals

For the sake of solving the problem of steel reinforcement corrosion in concrete structures and reducing the transportation cost of concrete raw materials at sea in the development of South China Sea Islands, a new type of coral reef sand concrete columns reinforced with basalt fiber reinforced polymer (BFRP) bars and spirals was proposed. In this study a total of 18 circular seawater sea-sand coral reef concrete columns reinforced with BFRP bars and spirals (B-SSCC) were tested under concentric axial loads. Parameters of nominal longitudinal bar diameters and spiral spacing were investigated to obtain variations on crack propagation, failure modes, load bearing capacity, strain and ductility properties. The results indicated that no obvious cracks were observed until the curves reached up to 0.95 Pmax approximately and the columns experienced more brittle and explosive failure modes with the increase of longitudinal bar diameter and spiral spacing. The load bearing capacity of B-SSCC columns increased with longitudinal reinforcement ratio, however, declined as the spiral spacing narrowed paradoxically. It was owing to the significant discontinuity of coral concrete internally. Compared with B-SSCC square columns, the circular columns with dense stirrups showed pronounced ductile behavior in the post-peak stage, remarked by improved average ductile coefficient β of 22.6%. Finally, a numerical prediction of load bearing capacity was suggested.