Evaluating strength, hydration characteristics, microstructure evolution, and sustainability of seawater-sea sand cement-based materials containing iron ore tailings

The use of seawater and sea sand in construction engineering contributes to sustainable development. This study investigates a design method for sustainable cement-based materials composed of seawater and sea sand. Iron ore tailings (IOT) are used as supplementary cementitious materials (SCMs), and the effects of IOT with different particle sizes (raw IOT (IOT-N) and ground IOT (IOT-F)) on the properties-including strength, hydration characteristics, phase changes, microstructure evolution, and sustainability-of seawater-sea sand mortars (SSSMs) were examined. The results show that IOT-N reduces the compressive strength of SSSMs, but the use of IOT-F can slow down this reduction trend. Compared with IOT-N, IOT-F exhibits a pronounced pozzolanic reaction and nucleation effect, accelerated SSSM hydration, and satisfactory workability. IOT-F can interact with the special pore solution environment provided by seawater and sea sand to generate more hydrates (such as C-S-H gel and Friedel's salt), which can refine the microstructure of SSSMs and promote strength development. Moreover, IOT-F can improve the chemical binding and physical adsorption capacity of SSSMs to free chloride ions, thereby reducing the effect of aggressive ions. These findings provide effective experimental support for using low-activity SCMs in seawater-sea sand cement-based materials.