Abstract: “Fly ash and bottom ash are two of the most common waste materials produced in the Philippines. Due to the potential environmental problems posed by these by-products, proper waste disposal is a major concern. Asa solution in the local setting, coal ashes were incorporated in concrete mixing as partial replacement for cement and fine aggregates. Furthermore, in efforts to produce sustainable concrete, seawater was introduced as a replacement for freshwater. This research focused on investigating the various influences of replacement materials with respect to the compressive strength development of concrete. The experiment tested the compressive strength of the modified mix containing alternative materials, with varying fly ash ratio of 0, 10, 20, 30, and 40%, respectively, and a constant 20% bottom ash replacement. The results show that fly ash replacement, curing days, and the interaction between the medium and the fly ash content significantly affect compressive strength development,”

Keywords: fly ash, bottom ash, seawater, compressive strength, optimization