Influence of Waste Coral Powder on the Properties of Alkali-Activated Slag Cement Prepared with Seawater

In this paper, alkali-activated materials (AAMs) were prepared combining waste coral powder (CP) and blast furnace slag (BFS) as precursors, artificial seawater and deionized water as mixing water, and blends of NaOH and sodium silicate solution as alkaline activators. The effect of CP and seawater on the fluidity, mechanical properties, and hydration was discussed. The experimental results showed that a 15% CP content effectively improved the fluidity of fresh paste while having little effect on compressive strength of the samples. Compared with deionized water, the use of seawater for sample preparation resulted in a reduction of the fluidity and mechanical properties of the samples. The pore structure could be refined by CP and seawater, but gel micropores increased significantly when the CP content reached 25%. The use of CP and seawater did not cause significant changes in the type of hydration products. Although the amount of hydration products in the early stages of the samples prepared with seawater was relatively low compared with those prepared with deionized water, it gradually surpassed that in samples prepared with deionized water with increasing curing time. Increasing the CP content led to a higher reaction degree, and a CP content of 25% resulted in a reaction degree of approximately 30%–50%, which was roughly twice that of a sample containing 5% CP. These findings have important implications for the development of sustainable construction materials for utilization in marine engineering.