Coral concrete has low cost and convenient materials, making it an excellent raw material for processing. However, its lower strength limits the application of coral concrete. Surface modification is expected to increase the properties of porous coral concrete. In this study, single and compound modification treatments were applied to the surface of a coral aggregate to improve its properties for promoting the mechanical performance of coral concrete. The results showed that the micro-aggregate effect and pozzolanic activity of granulated blast furnace slag (GBFS) and the permeability and polycondensation of sodium silicate (SS) could be mutually promoted. The GBFS and SS could effectively fill the pores of the coral aggregate, enhancing the properties of the aggregate, such as density and load-bearing capacity, and reducing the water absorption and crushing index by more than 50%. GBFS and SS could intensify and accelerate the hydration of cement, and generate a large number of hard hydration products at the interfacial transition zone (ITZ), which could strengthen the bonding between the aggregate and mortar, improving the strength of the ITZ. The compressive strength of the coral concrete was significantly increased.
