## 5 Challenges and Future Prospects
A more systematic classification based on sulfur cake origin, composition, and thermal reactivity would enhance reproducibility across studies and enable better industrial integration. Future prospects remain promising in spite of these challenges. Innovations in machine learning (ML)-driven formulation optimization, reactive compatibilizers, and encapsulated sulfur additives can enhance dispersion, reduce emissions, and prolong performance life [135,137]. Additionally, techno-economic studies suggest that utilizing waste sulfur cake can reduce binder cost by up to 30%, with CO2 emissions lowered by approximately 40 kg per ton of material compared to conventional Portland cement or asphalt binders [138]. These benefits align well with global climate and circular economy goals, provided that technical barriers and safety protocols are properly addressed. To advance the practical implementation of the modified sulfur cake-based materials on infrastructure, a number of future directions and research needs are proposed. The development of modified sulfur cake technologies as viable and sustainable alternatives to use in contemporary construction will require a blend of material innovation, veracious field testing and backing of the regulatory system. One key source of attention is the use of nano/micro additives to address the shortfalls in performance, increase structural and environmental durability, and benefit both the sulfur concrete and the sulfur-modified bitumen. With the introduction of nano-carbonaceous materials--nano-silica, carbon nanotubes or cellulose nanocrystals--the mechanical strength, thermal stability, and water resistance of composites can be greatly improved. Specifically, cellulose nanocrystals enhanced the fatigue life and rutting resistance of bituminous mixtures by more than 25%, which shows promise in improving pavement life [104]. Similarly, nano-carbon addition increases the binder's elastic recovery and reduces temperature susceptibility, essential characteristics for high-stress applications [139]. The combination of sulfur with polymers or geopolymers represents another transformative direction, for the enhancement of the performance. Sulfur-polymer hybrid binders, such as sulfur-styrene-butadiene or sulfur-polyethylene systems, not only mitigate phase separation but also improve elongation at break and enhance compatibility under dynamic loads. Recent studies reported an increase of 30-50% in tensile strength and improved softening point stability in a field simulation for sulfur-modified polymer binders [140]. Similarly, geopolymer-sulfur blends are being explored as low-carbon, alkali-activated alternatives, promising better early strength and chemical resistance, particularly for marine or industrial environments [141]. Despite these advances, few comparative performance studies have been conducted to rank these sulfur modification approaches under consistent environmental and loading conditions. The authors suggest that future research prioritizes the multi-parameter benchmarking (durability, cost, environmental impact) of polymer-, nano-, and geopolymer-based systems to determine optimal use cases. Long-term durability studies and field trials are critically needed to validate laboratory findings. To date, only limited field-scale evaluations exist for sulfur concrete or sulfur-modified asphalt binders. Nevertheless, preliminary U.S. Department of Transportation trials demonstrated that sulfur-extended asphalt (SEA) can reduce rutting depth by 20-30% over five years while maintaining serviceability in freeze-thaw conditions [142]. Multi-climatic and wide-traffic-load field trials should now be extended to various climates and traffic loads with the aid of multi-year monitoring programs. Also, policy and regulation frameworks need to radically change to accommodate the industrial shift to sulfur-based technologies. The lack of a uniform way of testing systems that are modified with sulfur cake has left contractors and regulators uneasy at the moment.