Saeed Bozorgmehr Nia - Research and Development Department, Aptus Iran Company, Karaj, Iran.
Reza Jamalpour - Professor of Faculty of civil engineering, Islamic Azad University, Karaj Branch, Karaj, Iran.
Masoud Taheri - Faculty of civil engineering, Islamic Azad University, Karaj Branch, Karaj, Iran.

Coastal High-Performance Concrete (HPC) structures face deterioration challenges from exposure to biodegradables like algae and moss. This study examined the durability of coastal HPC under these biodegradable influences, emphasizing their effects on various transport properties. Conducted over ۲ years in the environmentally rigorous Bandar Anzali Ports, the research evaluated key HPC transport properties such as water absorption, Rapid Chloride Penetration Test (RCPT), Rapid Chloride Migration Test (RCMT), electrical resistivity, and freeze-thaw resistance. Experimental samples, replicating real-world coastal conditions, incorporated diverse algae and moss concentrations.The comprehensive testing indicated that algae and moss presence notably hastened HPC degradation. Samples exposed to these organisms demonstrated increased water absorption, evidenced by weight gain. Enhanced chloride penetration and migration were evident from RCPT and RCMT results, suggesting an elevated corrosion risk in the concrete structures. Moreover, a marked drop in electrical resistivity indicated reduced concrete capacity to impede electrical current, while freeze-thaw tests showed heightened damage vulnerability from cyclic freezing and thawing.In light of these findings, it's crucial to address the biodegradable impact on coastal HPC structures. Implementing strategies like routine cleaning and maintenance to reduce algae and moss, combined with appropriate surface treatments, can extend the lifespan of coastal concrete installations. These insights aid in creating resilient and sustainable concrete mixes specific to coastal applications, ensuring extended structure longevity and integrity.Keywords: Coastal structures, High-Performance Concrete (HPC), algae, moss, durability

Coastal structures, High-Performance Concrete (HPC), Algae, moss, Durability