Degradation behavior and mechanism of marine concrete with crushed waste seashells as complete fine aggregates under sulfate attack

Restricted by insufficient local aggregate resources and the prohibitive transportation cost of conventional aggregates in remote offshore regions, crushed waste seashells (CWS) can be recycled as fine aggregates for marine concrete fabrication. To verify the engineering feasibility of CWS recycling for marine concrete structures, a one-year accelerated sulfate attack test was conducted in this work. CWS concrete, with CWS serving as 100% of the fine aggregate, and a reference mixture using natural river sand with the same mix proportion were prepared for comparative analysis. Sulfate ion distribution, surface morphology, mass change, relative dynamic elastic modulus and damaged layer depth were studied to explore the damage process of CWS concrete, and a damage evolution equation was established accordingly. In addition, mineralogical composition and pore size distribution were analyzed to reveal the underlying damage mechanism. The results showed that the higher porosity and rough texture of CWS fine aggregate enable more sulfate erosion products to be accommodated and raise the cracking threshold. Consequently, CWS concrete exhibited better sulfate resistance than river sand concrete with the same mix proportion and was more suitable for marine engineering structures. This study offers a feasible application pathway and experimental support for the resource utilization of waste seashells in ocean engineering.