With the ongoing rise in global infrastructural development, the scarcity of river sand for concrete production has become pronounced, particularly in coastal regions. To address this issue, scientists and researchers are exploring the viability of using sea sand as an alternative. This paper presents the impact of sea sand and fly ash on the compressive strength of concrete. Three parameters were controlled: river sand, sea sand, and fly ash. Initially, river sand was substituted with sea sand at varying proportions: 0%, 25%, 50%, 75%, and 100%. Results revealed that sea sand and fly ash decrease the workability of fresh concrete. Without fly ash, a 50% substitution of sea sand resulted in the highest compressive strength compared to other compositions. When using fly ash in the mixture, the highest strength was observed by incorporating 20% fly ash as a cement replacement, irrespective of using sea or river sands. The results obtained were expected to address the shortage of river sand and promote the utilization of fly ash as a sustainable material for non-steel concrete structures.