Sulfur Mortar Goes to Infinity: Mechanical Performance and Characterization of Sulfur Mortar Composed of Different Aggregates During Heating Cycles, Exploring Potential Sustainability, Recyclability, and Circularity

Sulfur mortar hardens quickly, shows a high chemical resistance, and can be recycled, making it ideal for construction and rehabilitation in extreme environments. Despite its potential for sustainability, current research lacks sufficient characterization of sulfur mortar’s performance during recycling, particularly regarding the physical and chemical changes when iron oxide is introduced. This study investigates the replacement of conventional siliceous sand with high-iron-content sand in sulfur mortar, through a series of five break–recast cycles. The results demonstrate an 11% increase in compressive strength and a 26% increase in flexural strength after five recasting cycles. Optical microscopy and scanning electron microscopy (SEM) revealed that recasting improved the distribution of the sulfur binder, while the formation of iron sulfates filled the gaps between aggregates and the binder. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the presence of iron sulfates, and differential scanning calorimetry (DSC) showed that high-iron-content sulfur mortar narrowed the phase change temperature range, preventing uneven solidification within the samples. This study sheds light on the strengthening mechanisms that occur during the recycling process, enhancing the material’s durability and recyclability. This aligns with circular economy principles, contributes to resource efficiency, and supports sustainable construction practices.