Role of Nano- and Crystalline Silica to Accelerate Chemical Treatment of Problematic Soil

Abstract

A research study was conducted to accelerate engineering property improvements by using novel silica-based coadditives along with a traditional calcium (Ca)-based stabilizer. Silica-based compounds, crystalline-silica (CS) rich waste product, and laboratory-grade nanosilica (NS) were used as coadditives with dolomitic hydrated lime to treat problematic expansive soil to study their efficacy in accelerating improvements in various engineering characteristics. The optimum dosages of the CS and NS additives with dolomitic hydrated lime were first determined based on unconfined compressive strength property, before and after capillary soaking. These dosages were subsequently corroborated by performing one-parameter and multiparameter statistical analyses. Using these optimized dosages, various engineering tests were performed on the treated soils. These tests included free-swell and linear shrinkage strains, unconfined strength with and without capillary soaking, and resilient modulus studies at curing periods of 0 (6 h), three, and seven days. Supplemental microstructural analyses were performed to gain insights into the factors responsible for the observed improvements in engineering properties. Test results indicated that treatment with hydrated lime and both silica-based coadditives is effective in stabilizing problematics soil as compared with lime treatment alone. Among the two silica-based coadditives, NS treatment provided comparatively higher accelerated improvements in the soil properties after seven days of curing than CS treatment. Mineralogical studies revealed that NS is more reactive than CS as a coadditive; hence, NS has been effective in providing equivalent long-term engineering strength gains while reducing swelling- and shrinkage-related volume-change properties in a relatively short time period.