<p>Crushing waste coral concrete into recycled aggregates to create recycled coral aggregate concrete (RCAC) contributes to sustainable construction development on offshore islands and reefs. To investigate the impact of recycled coral aggregate on concrete properties, this study performed a comprehensive analysis of the physical properties of recycled coral aggregate and the basic mechanical properties and microstructure of RCAC. The test results indicate that, compared to coral debris, the crushing index of recycled coral aggregate was reduced by 9.4%, while porosity decreased by 33.5%. Furthermore, RCAC retained the early strength characteristics of coral concrete, with compressive strength and flexural strength exhibiting a notable increase as the water-cement ratio decreased. Under identical conditions, the compressive strength and flexural strength of RCAC were 12.7% and 2.5% higher than coral concrete’s, respectively, with porosity correspondingly reduced from 3.13% to 5.11%. This enhancement could be attributed to the new mortar filling the recycled coral aggregate. Scanning electron microscopy (SEM) analysis revealed three distinct interface transition zones within RCAC, with the ‘new mortar-old mortar’ interface identified as the weakest. The above findings provided a reference for the sustainable use of coral concrete in constructing offshore islands.</p>