Volume Change Behavior of Expansive Clay Stabilized with Bio-based Silica Gel

This document presents the assessment of the swelling behavior of expansive clay stabilized with bio-based silica gel and subjected to wetting and drying cycles. The expansive clay used in this research was obtained from Anthem, Arizona. Rice husk is a rich silica by-product of rice production with commercial uses and applications in the industry. Rice husk ash from two different sources -California (named ASU) and India- were subjected to chemical characterization. Fourier Transform Infra-red Spectroscopy was used to verify the functional groups of the gel formed. Results showed differences between the ashes from different sources and confirmed the presence of silica structure bonds. X-Ray Diffraction (XRF) results showed that the ASU ash contained more amorphous silica than the Indian ash.One dimensional swell and consolidation tests were performed to investigate the volume change behavior of the untreated and silica gel treated remoulded samples. The free swell of the clay decreased from 12.3% (untreated sample) to 7.2% (ASU sample) and 11.4% (Indian sample). The effect of the wet and dry cycles on the swelling and consolidation characteristics of the untreated clay demonstrated that the treatment is irreversible after three cycles. Swelling of clay treated with ASU ash was reduced after the first cycle, while that of the clay treated with Indian ash was reduced after three cycles. This was due to the gelation time difference between treatments. Scanning Electron Microscopy images showed that the structure of the untreated clay was discontinuous, flaky and without aggregations whereas particles in the treated samples were aggregated and new bonds were created, decreasing the surface area. The X-Ray Diffraction (XRF) results showed that the main mineral responsible for expansive behavior of the clay studied was illite. The d-spacing of the illite decreased from 4.47Å for the untreated clay to 3.33Å for the treated clay. This study demonstrates a promising technique for clay swelling reduction and a more sustainable solution than that available to current practicing engineering.