Performance evaluation of cement mortars incorporating seawater and calcined marl as sustainable alternatives

This study presents a cement mortar system that combines seawater and calcareous calcined marl to address freshwater scarcity and cement emissions. The marl used in this study is rich in calcium carbonate and has not been previously studied in combination with seawater for cementitious applications. Cement mortars with 0–40% marl replacement were tested for hydration, strength, durability, and microstructure. At 40% marl, seawater accelerated hydration with peak heat flow about 21% higher and the peak arriving 7% earlier than tap water. Compressive strength improved when marl was combined with seawater, reaching 64.7 MPa at 90 days compared with 60.2 MPa for the tap water mix. Seawater further improved transport related properties in the presence of calcined marl. At the 40% replacement level, bulk resistivity at 90 days was 134 Ω·m with seawater versus 96.5 Ω·m for tap water, while permeable voids decreased to 20.7% with seawater compared with 22.3% with tap water with marl. XRD and SEM-EDS confirmed Friedel’s salt, C-A-S-H and ettringite, supporting the improved performance of seawater cement mortars with marl. The results show that seawater and calcareous marl can work together to produce durable, low-carbon cement mortars while reducing freshwater demand.