This research paper explores using marine shells as coarse aggregates in producing seawater sea sand UHPC-CA. The study examined factors such as coarse aggregates (granite, oyster shell, and cone shell), fine aggregates (sea sand and river sand), fiber types, and content. The research findings indicate that different coarse aggregates and fibers influence the flow performance of UHPC-SCA. The study identified the cone shell as the best coarse shell aggregate and 1.5% steel fiber as the optimal fiber and inclusion amount. The compressive strength of this combination reached 106 MPa, which is comparable to the granite stone UHPC-CA of the same particle size.