Macro and micro properties of the cement-based material mixed with coral powder and GGBFS under seawater condition

On island, the use of discarded coral reef is a way to resolve the lack of raw material for preparing concrete. Discarded coral reef can not only be used as aggregate, but be ground to powder to replace cement. Since the cement-based material prepared with discarded coral reef is exclusively used on island, the property of the cement-based material exposed to seawater condition should be studied. In this study, discarded coral reef is ground into coral powder (CP). CP is used together with ground granulated blast furnace slag (GGBFS) to replace Portland cement (PC) partially to prepare a mixture with good performance and the minimum use of PC. The compressive strength, solid phase composition and pore structure of the cement-based material exposed to seawater condition are investigated systematically. The results show that the addition of CP decreases the fluidity of the cement mortar since it has a more rough surface than other raw materials. Although the use of CP decreases the compressive strength of cement mortar, the coupled use of GGBFS can largely mitigate the strength loss of the cement mortar by comparing 9 mixtures. When the specimens are exposed to seawater, the strength of cement mortar only decreases slightly, but the pore structure of cement paste is densified. It suggests that the use of CP and GGBFS together in the concrete can meet the construction of island; the compressive strength of the sample made with 25% CP and 25% GGBFS is around 54 MPa after exposed to seawater to 1 year.