Mechanical Test of Mortar with Addition of Fly Ash Using Seawater Immersion

Background: The rapid pace of infrastructure development has increased the demand for more environmentally friendly cement-based binders. One potential approach is the use of fly ash as a supplementary cementitious material in mortar. Objective: To determine the compressive strength of mortar and evaluate the effects of fly ash replacement at proportions of 0%, 5%, 10%, and 15% by weight of cement, using two curing media: seawater and freshwater. Method: This study employed a quantitative experimental approach involving laboratory testing to evaluate the effects of varying fly ash replacement proportions on the compressive strength and water absorption of mortar specimens cured in two different media. Results: The compressive strength of mortar increased with increasing fly ash content and curing age in both curing media. The highest value was obtained with 15% fly ash replacement after 28 days of freshwater curing, reaching 31.53 kN, whereas seawater curing under the same conditions yielded 22.90 kN. Freshwater curing consistently resulted in higher compressive strength than seawater curing across all fly ash replacement proportions. Conversely, the 28-day water absorption test showed that specimens cured in seawater exhibited relatively higher water absorption than those cured in freshwater. Conclusion: Chloride, calcium, magnesium, and sulfate ions in seawater may influence cement hydration. These effects may accelerate early-age strength development but may also increase porosity and compromise long-term durability. These findings provide preliminary insights into the potential benefits and limitations of using seawater as a curing medium for mortar.