Abstract: 79% granulated high furnace slag and 15% steel slag and 5% flue gas desulphurization ( FGD ) gypsum was mixed with 1% cement clinker to produce a cementitious material.The ordinary portland cement can be totally substituted by such a mixed cementitious material with iron and steel slags as its major components in preparing the concrete for building high-strength artificial reefs.A concrete with a compressive strengh of 61 MPa can be prepared by using such a mixture as a cementitious material and steel slag grains as its fine and coarse aggregats which have been stubilized by a hot-simmering method. The cement clinker content of the concrete was 0.16%, and solid waste ratio reached over 99%. Hydration processes of net slurry were analysized by XRD and SEM methods.The results show that the early hydration products in the system are mainly AFt and C-S-H gel.The strength growth is mainly contributed by these two phases.

Key words: Steel slags, Cementitious material, Artifical reefs concrete