## 4 Discussion
Thermal stabilization transforms expansive soils by altering their mineralogy and structure through heat, reducing plasticity and swelling, and improving strength. While the technique faces practical implementation challenges, its scientific basis in fundamentally modifying clay properties positions it as a valuable approach for managing problematic soils. The materials used in sustainable enhancement techniques improve the geotechnical properties of expansive soil, such as increasing UCS and the CBR and reducing swell-shrink potential and plasticity. These sustainable waste-based techniques offer economic and environmental advantages, reducing costs and CO\({}_{2}\) emissions. However, research is needed on their long-term durability and other impacts. Unlike traditional chemical methods, biological approaches are often more economical and contribute to sustainability using renewable resources and byproducts. Although laboratory research has provided a fundamental understanding of their mechanisms and demonstrated significant improvements, large-scale implementation and evaluation of their long-term durability under diverse field conditions are crucial for their widespread adoption in sustainable geotechnical engineering. Based on the working hypothesis that sustainable improvement techniques can offer viable solutions with lower environmental impact compared to traditional ones (lime and cement), the results fully support this premise, as observed in Figure 6 (comparative graph of the number of publications by mechanism of action and type of technique) and Tables 4-6 (sustainable techniques by mechanism of action). It was shown that alternative materials such as rice husk ash, bagasse ash, sugarcane straw ash, banana leaves, rice husks, bamboo leaves, peat and coconut fiber, jute fibers, banana fibers, crushed ceramics, wool and banana fibers, molasses, and vinasse residues, have high stabilizing potential and applicability on the Ecuadorian coast, both in their natural and chemically activated forms, significantly improving properties such as plasticity, free swelling, moisture retention and mechanical strength. These observations are consistent with recent research by the authors referenced in Tables 4-6, who demonstrated the positive impact of these agro-industrial residues on expansive clay soils. The inclusion of industrial byproducts (granulated blast furnace slag, lignosulfonate, lime, and calcined clay) in stabilization also coincides with global trends toward waste vaporization, showing that their application not only improves geotechnical properties but also reduces the carbon footprint associated with traditional methods (Table 4). The mineralogical composition of expansive soils has been studied in depth (Table 7). Thus, the high-plasticity clay of Ecuador presents a composition with a high content of kaolinite (30%) and minerals such as quartz, plagioclase, and diopside, in contrast to the soils of Saudi Arabia, which are dominated by montmorillonite (34.7%) and quartz (46.1%). This difference is significant since montmorillonite is the main mineral responsible for extremely expansive behavior. Table 7 shows that although Ecuadorian soils have high plasticity, their swelling potential is likely lower than that of soils with more montmorillonite, directly influencing the choice of stabilization techniques. Furthermore, Ecuadorian soil's more diverse mineral content suggests greater geological heterogeneity, which may open up the possibility of using more versatile techniques. That reinforces the need to adopt sustainable solutions, especially those considering mineralogical type and proportion as key variables. Compared to countries like Saudi Arabia, where minerals with greater swelling activity predominate, Ecuador could benefit from less aggressive and more environmentally friendly treatments. Table 8 shows that Ecuadorian clay contains 57.13% SiO\({}_{2}\), similar to Indian soil (56%) and slightly lower than Saudi Arabian clay (59.34%).