Micro-Mechanical Behavior of Nanosilica-Treated High-Sulfate Soils

The addition of calcium-based stabilizers to sulfate-rich expansive soils is associated with the formation of ettringite, a deleterious reactant that can cause moderate-to-severe swell-related damage to overlying lightweight infrastructures. This research study was conducted to understand the effects of combining nanosilica admixtures with a traditional Ca-based stabilizer to treat high-sulfate soils with the intent to suppress ettringite formation. Engineering and microstructural studies were thus performed to gain a comprehensive understanding of the behavior of sulfate-bearing soils treated with lime in the presence of amorphous nanosilica. Engineering studies included strength tests before and after capillary soaking, free swell strain, and resilient moduli to study and understand the macrostructural behavior of these soils at different curing periods. Supplemental studies using scanning electron microscope and energy dispersive X-ray spectroscopy, thermal analyses using differential scanning calorimetry, and X-ray diffraction studies were also conducted to determine the microstructural changes that occur within these sulfate-rich soils. The results showed that additional silica phases furnished from nanosilica suppressed the precipitation of ettringite and correspondingly increased the formation of cementitious phases. This study also provided ample evidence that the application of siliceous nanomaterials positively impacts chemical treatments and reduces the precipitation of ettringite, thus enhancing their engineering performance.