Durability of concrete structures in tropical atoll environment

A literature investigation and field surveys were made to explore the durability to destruction of Ordinary Portland cement Concrete (OPC) and Coral Aggregate Concrete (CAC) structures in a tropical atoll environment. The surface free Cl− concentrations (Cs) and apparent chloride diffusion coefficients (Da) were calculated and the calculation method of Da in a one-dimensional half-infinite-body concrete structure was explored. The results show that the complex and severe environment of tropical atolls corrodes concrete structures badly and that the reinforcement corrosion rate is high. For a concrete structure in a tropical atoll, Cs of OPC is generally smaller than that of CAC. At the same time, the Da of concrete calculated by the least squares method is the most reliable according to Fick's second law of diffusion. The calculated results demonstrate that the value of Da is generally smaller in OPC than in CAC. Smaller water-to-binder ratios and higher strengths cause decreases in Da for CAC. When OPC is not available in tropical atoll projects, the water-to-binder ratio should be decreased and the strength should be enhanced in CAC, which should improve the durability of the concrete effectively and decrease the Cs and Da of the concrete structure.