Includes bibliographical references

In building infrastructure, engineers and designers heavily rely on concrete, where this standard concrete produces a significant amount of carbon dioxide emissions. Because of these standard procedures, the urgent need for sustainable alternatives are remarkably high. Along with there, there is a massive amount of seafood or marine waste in the Philippines, specifically discarded Green Mussel shells (Perna Viridis, locally known as "Tahong"), which pose considerable environmental and municipal landfill hindrances. This study evaluates the viability of calcined green mussel shell as a supplementary cementitious material (SCM) to mitigate carbon emissions and marine waste in Cavite, Philippines. Following ASTM C311 protocols, 5.6 kg of discarded mussel shells were cleaned, sun-dried for 72 hours, crushed via hammermill, and calcined at for 4 hours to convert calcium carbonate (CaCO3) into reactive calcium oxide (CaO). X-ray fluorescence (XRF) analysis revealed that while the ash was predominantly composed of CaO (65.5%), the primary pozzolanic oxides silicon dioxide (SiOs, 1.1%), aluminum oxide (Al:O, 4.5%), and iron oxide (Fe:Os, 0.1%)-yielded a combined total of only 5.7%. This fails to meet the minimum ASTM C618 standards for Class F/N (70%) or Class C (50%) pozzolans. Sulfur trioxide (SO) content was measured at 0.3%. Physical analysis demonstrated a moisture content of 0.07% (well within the 3% limit) and a Loss on Ignition (LOI) of 7.2%, which slightly exceeds the 6.0% maximum threshold. Consequently, calcined Perna viridis shell ash lacks the necessary reactive silica and alumina to serve as a pozzolanic SCM under ASTM C618. However, its high CaO purity, low moisture content, and eco-friendly attributes position it as a promising limestone filler and raw alternative input for non-structural civil engineering applications and low-carbon architectural elements.