## 4 Technological Developments of Sulfur in Construction
### Modified Sulfur Cake Concrete
Furthermore, due to its recyclability, sulfur concrete can be re-melted and reused without significant loss of properties, contributing to circular construction practices [88,90]. The integration of modified sulfur cake into sulfur concrete technologies provides a balanced approach to improving matrix structure, mechanical performance, and environmental durability positioning it as a highly viable construction material for critical and corrosive environments. The production of sulfur concrete involves distinct techniques that significantly affect its mechanical properties, durability, and application scope. Both hot-mix and cold-mix sulfur concrete production techniques are commonly used, each with specific casting, molding, \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Concrete** & **Additive(s)** & **Additive** & **Compressive** & **Tensile/Flexural** & **Durability** & **Ref.** \\
**Type** & **Additive(s)** & **Content** & **Strength MPa** & **Strength MPs** & **Durability** & **Ref.** \\ \hline Silica fume & Amorphous & 5–15\% & & & Ultra-low & \\ concrete & \(\mathrm{SiO_{2}}\) & cement & 60–90 & 5–8 (tensile), & permeability; & \\  & & replacement & & 9–14 (flexural) & enhanced early & \\  & & replacement & & & strength; ASR & \\  & & & & & mitigation & \\ \hline \multirow{3}{*}{Geopolymer} & Fly ash/GGBS & \multirow{3}{*}{-100\%} & \multirow{3}{*}{40–80} & \multirow{3}{*}{4–6 tensile; 6–10 flexural} & Excellent acid & \\  & & & & & & resistance, thermal & \\ \cline{1-1} \cline{4-5}  & \(\mathrm{NaOH/Na_{2}SiO_{3}}\) & & & & stability \textgreater{}400 \({}^{\circ}\)C, & 82 \\ \cline{1-1} \cline{4-5}  & & & & & 80\% CO\({}_{2}\) reduction & \\ \hline \end{tabular}
\end{table} 
Table 7: _Cont._and curing protocols that influence final performance characteristics. Figure 5 provides the sequential steps involved in both hot-mix and cold-mix sulfur concrete production, highlighting differences in processing temperatures, mixing conditions, and curing methods. The most commonly used method is noted to be hot-mix sulfur concrete, in which the element sulfur is pre-heated to 120-140 \({}^{\circ}\)C in order to obtain the molten phase and then mixed with the dry aggregates. In comparison, the dry mixing process is operationally simple and well-suited for field or precast applications; however, it may face limitations in terms of uniformity, especially if the sulfur is not adequately modified or pre-reacted. Alternatively, wet blending, where modified sulfur is pre-processed with organic stabilizers before mixing with aggregates, can improve homogeneity and long-term stability, but requires more controlled production conditions. Sulfur which is modified by the addition of stabilizers, such as dicyclopentadiene (DCPD) or sulfur cake, has been employed to minimize recrystallization and increase durability. After the hot sulfur concrete has been mixed well it is placed in molds. It also sets rapidly by cooling down without water-based curing, taking only 30 min to reach initial set, with full strength being reached in less than 24 h [91]. This makes it suitable for quick construction applications and is especially favorable for precast building parts and emergency subsidizing [92]. Optimally designed mixes and aggregate gradations enhance hot-mix sulfur concrete's compressive strength to more than 50 MPa [93]. Cold-mix sulfur concrete, in contrast, uses lower manufacturing temperatures, typically below 60 \({}^{\circ}\)C, and uses pre-polymerized or emulsified sulfur. The technique is in the development stages and is not widely used because of the problems in obtaining the total polymerization and the homogeneity. The cold-mix method usually involves the utilization of chemical substances or mechanical agitation to mix sulfur-based binders with aggregates. Cold mixing consumes less energy and has fewer emissions but may have decreased compressive strength (usually <30 MPa) and setting time compared to hot-mix versions [94,95].