This study analyzed the effect of blood clamshell substitution (Anadara granosa) on the mechanical properties of concrete, namely compressive strength and flexural strength, using clamshell material originating from the Bungkutoko island region, Abeli District and Toronipa coastal area Soropia District, Konawe Regency, Southeast Sulawesi Province. In this study, the concrete was made using blood clamshell (Anadara granosa) waste as a substitute for coarse aggregates. As a control, normal

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... e was made using natural materials, namely the Moramo split and Pohara sand. The results show that partial substitution of coarse aggregates using blood clamshell concentrations of 15%, 25%, and 50% reduced the compressive strength of concrete by 11.00%, 16.20%, and 30.62% when compared to the control, respectively. Meanwhile, the respective concrete bending strength also decreased by 7.33%, 13.83%, and 32.53%. The compressive strength testing of 28 days-concrete with the shellfish compositions of 15% and 25% showed the values of 25.35 MPa and 23.87 MPa, respectively, which can be categorized as a medium-quality concrete (structural concrete). Meanwhile, the 50% shell composition had a compressive strength of 19.895 MPa, which can be categorized as a lowquality concrete (non-structural concrete).