## 4 Technological Developments of Sulfur in Construction
### Modified Sulfur Cake Concrete
Cold-mix processes have the potential to use recycled material, like polluted soil or industrial waste [96], thereby aligning with sustainable construction practices. Casting and molding are essential stages in both techniques. Hot-mix sulfur concrete requires molds capable of withstanding thermal shock and maintaining dimensional stability during rapid cooling [97]. Molds produced of metallic or thermally resistant polymer are desirable. Cold-mix concrete, conversely, can be poured into conventional molds, as  
Figure 5: Hot-mix and cold-mix sulfur concrete production routes, process steps, and curing stages, with emphasis on operational differences in temperature and processing conditions. applied in Portland cement. In both cures, the method of curing is not similar to the one used in conventional cement concrete. Sulfur concrete does not need water in the curing process; it will solidify through a physical cooling process. This removes any waiting times associated with curing as well as any risks of cracking due to moisture. Recent advancements, such as automated contour crafting with sulfur concrete, have demonstrated the possibility of 3D printing large-scale structures in extraterrestrial environments, where water is scarce and rapid deployment is crucial [51,98]. Overall, hot-mix remains the most effective technique for producing high-performance sulfur concrete, while cold-mix is emerging as a sustainable alternative, with further research needed to optimize mechanical behavior and scalability [92,93]. Sulfur concrete exhibits distinct mechanical and durability advantages over traditional Portland cement concrete, especially in environments where water, chemicals, and temperature fluctuations are major concerns. Its thermoplastic nature allows rapid setting and curing, while modified sulfur formulations enhance mechanical integrity and long-term performance. Compressive strength is one of the most notable attributes of sulfur concrete. Values typically range from 40 to 55 MPa for properly mixed hot-sulfur concrete, which is comparable to or even exceeds that of standard concrete mixes. Studies show that sulfur concrete with optimized aggregate gradation and modified sulfur binder can achieve a compressive strength of up to 60 MPa after just 24 h of curing [71]. Compared to traditional water-cured concrete, this represents a significant time and energy efficiency advantage [68]. Its tensile and flexural strengths, although lower than compressive strength as expected, can also be improved with the inclusion of additives such as fly ash, rubber crumb, or recycled aggregates. For instance, the addition of 10% waste tire crumb rubber resulted in an increase in tensile strength by 20% and flexural strength by 15% due to improved stress distribution and elasticity [73]. [PERSON] et al. [72] also demonstrated that fly ash addition led to enhanced bond strength and reduced brittleness, increasing the flexural capacity of sulfur concrete up to 8.5 MPa. Durability performance is where sulfur concrete outperforms conventional systems. Its water resistance is exceptionally high due to the hydrophobic nature of sulfur. Water absorption rates are typically below 0.05%, significantly lower than Portland cement concrete, which may absorb up to 5-10% water by mass [99]. This property directly contributes to improved freeze-thaw stability, as minimal internal water reduces cracking and scaling under cyclic freezing conditions [71]. Sulfur concrete also demonstrates superior acid and alkali resistance. In immersion tests in 5% sulfuric acid for 90 days, sulfur concrete showed less than 2% mass loss, compared to over 15% for ordinary concrete [72]. Modified sulfur concrete retained more than 90% of its compressive strength, even after a long-time exposure to both acidic and alkaline conditions, making it suitable for use in industrial floors, sewage, and marine infrastructure applications [69,100]. The material is also of superior chemical stability as well as aging resistance.