## 5 Conclusions  
The innovative and sustainable soil improvement techniques that have shown the greatest potential and practical applications in Ecuadorian expansive soils are those based on chemical mechanisms (such as rice husk ash, bagasse ash, sugarcane straw ash, banana leaf ash, rice husk ash, and bamboo leaf ash), physical-mechanical mechanisms (e.g., peat and coconut fiber, jute fibers, banana fibers, crushed ceramics), and biological mechanisms (such as wool and banana fiber, molasses, and vinasse residues). A comparative analysis of sustainable materials used to improve expansive soils on the Ecuadorian coast concludes the following:  
* The mineralogy of Ecuador's highly plastic clay, dominated by kaolinite and with a low montmorillonite content, indicates moderate expansive behavior compared to soils such as those of Saudi Arabia, which are highly rich in montmorillonite. This difference suggests that less intensive improvement techniques could be employed in Ecuador, prioritizing sustainable and local strategies over aggressive chemical stabilization. * The low content of reactive oxides such as CaO and Fe\({}_{2}\)O\({}_{3}\) in Ecuadorian soils limits the effectiveness of conventional stabilizers such as lime or cement, which technically justifies the use of alternative additives with high pozzolanic reactivity, such as rice husk ash or local silica-rich byproducts, aligning with the study's sustainability focus. * Mineralogical analysis reveals a marked difference between the expansive soils of Ecuador (30% kaolinite) and Saudi Arabia (34.7% montmorillonite), which explains their lower expansion potential. Regarding chemical composition, the low CaO content of the Ecuadorian clay (1.73%) compared to 9.31% in the Saudi soil significantly reduces the effectiveness of lime stabilization, highlighting the need for alternative additives. * The evaluation of agricultural byproducts such as rice husk ash (SiO\({}_{2}\) = 97.69%) and sugarcane bagasse showed high pozzolanic potential, while using natural fibers such as jute (85% cellulose) increased tensile strength. Through the comparison index (Ic), it was shown that alternative materials significantly improve the UCS (up to 2.3 times) and the CBR (up to 1.9 times), positioning themselves as viable, sustainable solutions for lime-poor soils such as those of the Ecuadorian coast. * Natural fibers in other countries, such as jute and coconut, have a high proportion of cellulose, improving the soil's mechanical properties. That reinforces the potential use of Ecuadorian plant fibers (such as plantain and abaca) as sustainable reinforcement materials, the experimental exploration of which is still pending at the national level. * Agroindustrial byproducts available in Ecuador, such as rice husk ash and sugarcane bagasse, have chemical concentrations comparable to those used internationally in soil stabilization. That validates their application as sustainable alternatives to conventional additives, with the added value of promoting the circular economy and reducing environmental impacts. * Treating Ecuadorian soil with recycled byproducts such as rice ash and ceramics has demonstrated significant bearing capacity (BBC) improvements, comparable with international studies. However, the lack of complementary data, such as UCS or MDD, highlights the need for additional trials to technically support the widespread adoption of these techniques in road and urban infrastructure projects. Ashes from agricultural and industrial sources significantly improve expansivity in the UCS value of the soils (and the CBR). Furthermore, combinations with alkaline activators or natural fibers maximize these effects. The results support using local waste in Ecuador as a viable, economical, and sustainable technical solution for soil stabilization in road infrastructure. Conceptualization, F.J.T.E., J.G.-R., and M.M.-P.; methodology, O.A.-P., and M.M.-P.; validation, J.G.-R., F.J.T.E., and O.A.-P.; formal analysis, J.G.-R., and F.J.T.E.