Na-smectite soils, owing to their high swelling potential, strength loss, and reduced durability under aggressive environments, have been recognized as one of the major challenges in geotechnical engineering. In this study, the soil was stabilized with a lime–silica fume (LSF) binder to improve its engineering performance, control swelling, and enhance chemical durability. The novelty of this study lies in the integrated evaluation of mechanical performance, swelling behavior, chemical durability, and microstructural characteristics, together with elucidating their relationships with the calculated Ca/Si and Si/Al molar ratios in different stabilizer mixtures. To this end, specimens containing 4–16 wt.% stabilizer and 40–90% silica fume replacement were prepared and subjected to unconfined compressive strength (UCS) and free swelling tests after curing periods of 7, 28, and 56 days. In addition, the chemical durability of the 28-day specimens was evaluated under acidic, sulfate, saline, and alkaline environments, and their microstructures were examined using scanning electron microscopy (SEM). The results showed that the mixture containing 10 wt.% stabilizer with 50% silica fume replacement achieved a UCS of 3.06 MPa after 28 days and 3.36 MPa after 56 days, while reducing the free swelling from 73% to approximately 3%. Increasing the silica fume replacement beyond 60% resulted in an approximately 30% reduction in strength, whereas the greatest strength loss (approximately 67%) occurred under acidic conditions. Microstructural observations revealed the development of a denser soil matrix, while analysis of the calculated Ca/Si and Si/Al molar ratios, used as complementary indicators of changes in the chemical composition of the mixtures, provided additional insight into the observed changes in strength, swelling control, and chemical durability.