Saline soils are highly aggressive and pose significant challenges to concrete foundations, affecting their durability and service life. The increasing demand for sustainable construction materials has led to the use of rice husk ash (RHA), an inexpensive byproduct of rice mills rich in silica and possessing pozzolanic properties. This study investigates the optimal use of RHA as a partial replacement for cement in concrete to enhance its mechanical properties and resistance to chloride and sulfate attacks in saline environments. Concrete mixtures with RHA replacements of 5, 10, 15, and 20% were prepared and tested for compressive strength. The results indicate that RHA significantly improves the microstructure by reducing porosity and increasing resistance to chloride and sulfate, thereby enhancing durability. The optimum replacement level was found to be 5%, as it balanced mechanical strength and durability, particularly under varying salinity levels of 3, 6, and 9%. This replacement level showed a marked improvement in compressive strength and a substantial reduction in chloride permeability compared to the control mix. The study highlights RHA as a viable supplementary cementing material that not only improves concrete’s performance in saline environments but also promotes sustainability by reducing agricultural waste. However, further research and field studies are recommended to validate the long-term performance of RHA-blended concrete in diverse saline soil conditions. These findings suggest that RHA offers a sustainable solution for enhancing the durability and longevity of concrete foundations in aggressive saline environments.