## 4 Technological Developments of Sulfur in Construction
### Modified Sulfur Cake Bitumen Technologies  
Modified sulfur cake has become a prospective additive in bitumen technology, having economic and performance-based benefits. Modified sulfur cake, which contains elemental sulfur combined with calcium compounds and other components, has proven to be rather promising as an alternative to the traditional way of using pure sulfur in the process of improving the properties of asphalt binders. Specifically, its addition to bitumen alters the chemical properties and rheology of the binder, enhancing binder performance with regard to softening point, viscosity, and age resistance [102]. Modified sulfur cake might be an affordable and effective method of enhancing the performance of asphalt binder. It has a better thermal resistance, higher mechanical stability and aging character, and a reasonable compatibility with blending compatibilities when employed in optimal proportions. This enhancement makes it a strategic additive to high-performance and sustainable asphalt pavement systems [102]. The SEM and DSC analyses in Figure 6a-d offer a critical understanding of the microstructural and thermal behavior of pure sulfur (Figure 6a,c) and modified sulfur (Figure 6b,d), the latter synthesized through a controlled oil bath procedure. This modification process involved blending 90 wt% molten sulfur with 10 wt% of a hydrocarbon mixture comprising 7% residual olefinic hydrocarbons and 3% bituminous residue at 145 \({}^{\circ}\)C for 3 h, followed by controlled cooling. These alterations are intended to improve the compatibility and performance of sulfur binders in construction materials. The SEM image of a sample of pure sulfur (Figure 6a) displays a rough and crystalline structure and tightly fitted angularly shaped particles are observed, possessing clear and  
Figure 6: SEM and DSC analysis of sulfur-based materials: (**a**) SEM image of pure sulfur; (**b**) SEM image of modified sulfur cake; (**c**) DSC curve of pure sulfur; (**d**) DSC curve of modified sulfur cake. All images are reproduced from [PERSON] et al., 2015 [50], in their original form under the terms of the Creative Commons Attribution–NonCommercial–NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). sharp boundaries and having observable micro-pores. This morphology is characteristic of pure elemental sulfur which crystallizes when cooled, and is itself brittle. All these microstructural characteristics are associated with low flexibility and mechanical integrations when sulfur is applied in concrete or bitumen directly [50]. Conversely, Figure 6b shows that the morphological surface pattern is significantly much smoother and more homogeneous in the altered sulfur. The particles are denser and smoother; their number of voids is smaller. This means that the increase in intermolecular contacts and the inhibition of the recrystallization of the sulfur are chemically stabilized under the effect of the olefinic hydrocarbons and the bitumen modification. Such an enhanced microstructure provides superior dispersion and bonding in concrete or asphalt matrices and finally, the resulting mechanical strength and durability are improved as well [14]. The DSC thermograms also explain the thermal transitions resulting from the modification process. In Figure 6c, pure sulfur shows the characteristic endothermic transitions around 119.2 \({}^{\circ}\)C and 165.8 \({}^{\circ}\)C, associated with the melting of orthorhombic S\({}_{8}\) and a lower-intensity transition, possibly due to some polymerization or allotropic transformation of sulfur. This narrow thermal range highlights sulfur's low thermal stability and its tendency toward recrystallization upon cooling [62].