## 4 Technological Developments of Sulfur in Construction
### Modified Sulfur Cake Bitumen Technologies
For example, a 20% sulfur-modified binder exhibited a G value of 7.8 kPa and a phase angle of 62\({}^{\circ}\), compared to 5.2 kPa and 68\({}^{\circ}\) for the neat binder at 64 \({}^{\circ}\)C [106; 107]. These results reflect increased stiffness and reduced viscous deformation, which directly translate to improved rutting resistance under traffic loads. Such DSR-based metrics allow for reliable performance grading (PG) classification and ensure compliance with Superpave specifications, thereby supporting the engineering design of durable sulfur-modified pavements. Sulfur-extended asphalt formulations (SEAF), particularly sulfur-extended hot mix asphalt (SEHMA), are gaining prominence in sustainable road construction due to their cost-effectiveness, improved performance characteristics, and integration of industrial by-products like modified sulfur cake. A step-by-step production procedure of modified sulfur-bitumen is presented in Figure 7. The design of SEHMA involves partially substituting conventional bitumen with elemental sulfur or sulfur-rich wastes such as modified sulfur cake, typically at levels ranging from 15% to 50% by binder weight. This substitution requires careful formulation to maintain optimal workability, moisture resistance, and mechanical integrity. Sulfur-modified mixes often employ compatibility enhancers such as poly-phosphoric acid or warm-mix additives to improve dispersion and interfacial bonding [112]. Field trials and laboratory-scale evaluations have validated the potential use of SEHMA in real-world applications. Pavements constructed with sulfur-extended binders demonstrate significantly enhanced rutting resistance, especially under heavy traffic and high-temperature conditions. For instance, rutting depth reductions of up to 45% have been observed compared to conventional asphalt mixtures, due to the stiffening and crystallization effects of sulfur within the binder matrix [113]. However, one of the key design challenges is managing moisture susceptibility, as sulfur can reduce the adhesive strength between binder and aggregate if not adequately stabilized. This issue has been addressed using lime treatment or blending agents to restore moisture resistance in SEHMA [114]. SEHMA offers compelling advantages. The substitution of expensive petroleum-based binders with low-cost industrial sulfur waste significantly reduces material costs. Field projects reported up to 30% savings in binder-related expenses, especially when sulfur is sourced locally [84]. Additionally, SEHMA supports the valorization of low-quality aggregates that would otherwise be unsuitable for use in standard asphalt, as sulfur helps enhance the load-distribution characteristics of the composite [115]. Overall, sulfur-extended asphalt formulations, particularly those utilizing modified sulfur cake, present a viable, scalable, and sustainable alternative for modern road infrastructure, with continued improvements being achieved through field validation and advanced binder chemistry [90]. The integration of modified sulfur cake into bitumen offers substantial environmental, mechanical and economic benefits, positioning it as a sustainable and high-performance alternative to conventional asphalt binders. The data in Table 8 supports the importance of the modified sulfur cake in construction. One of the most notable environmental advantages is the significant reduction in volatile organic compounds (VOC) emissions. During mixing and paving operations, traditional bitumen emits considerable amounts of harmful VOCs, which contribute to air pollution and health hazards. Modified sulfur cake lowers these emissions due to its partial replacement of petroleum-based constituents and its stabilization of the binder matrix. It has been demonstrated that VOC emissions can be minimized by up to 35% by the use of sulfur-based modifiers over unmodified binders [116; 117].