Towards enhancing the durability of seawater coral aggregate concrete under drying-wetting cycles with slag-based geopolymers

The utilization of marine resources (e.g. seawater, coral sand or sea sand, and coral coarse aggregate) for the preparation of seawater coral aggregate concrete (CAC) in reef or island areas contributes to the decreased construction periods and costs for offshore projects. Nevertheless, the high porosity and brittleness of coral aggregates affect the mechanical characteristics and durability of CAC and its structures. In this study, slag-based geopolymers were utilized as substitutes for ordinary Portland cement for preparing geopolymer-based seawater coral aggregate concrete (GPCAC). The mechanical properties of GPCAC and CAC under seawater drying-wetting cycles were explored, and their degradation mechanisms in terms of mechanical characteristics were estimated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results pointed out that GPCAC exhibited better resistance to seawater attack than CAC after being subjected to seawater drying-wetting cycle environments. When subjected to 60 °C seawater corrosion in drying-wetting cycles for 12 months, the cubic compressive strength, elastic modulus, and axial compressive strength of CAC degraded by 14.4%, 13.0%, and 16.9%, respectively, while those of GPCAC only reduced by 5.4%, 11.8%, and 3.1%, respectively. It is concluded that the excellent pore structure, dense microstructure, and stabilized hydration products of geopolymers are responsible for their superior resistance to seawater attack compared to cement-based materials.