Thermodynamic Evaluation of Smectite Treated with Hydrogen Ion Stabilizer

Abstract

Smectite-bearing, expansive clayey soils are common in many areas of Texas, causing damage to pavements and building foundations by cyclic shrinking and swelling. The mechanism of shrinking and swelling has been widely studied, but there is limited research on geochemical modeling of the impact of chemical modifiers on shrink-swell soils. Two thermodynamic equilibrium models (Visual MINTEQ and Geochemist’s Workbench) based on Gibbs free energy minimization were used to model the interaction of a hydrogen ion stabilizer (HIS) with a smectite clay. The models describe the release of Al3+ ions from the octahedral layer of smectite and molecular structural changes by dissolution. X-ray diffraction and Fourier transform infrared spectroscopy were used to validate structural changes indicated by both models. Smectite was treated with concentrated HIS (no added water) and chemical stabilizer HIS (diluted with 20 parts water to 1 part stabilizer). Partial dissolution of smectite layers was observed when the clay was treated with the 20-to-1 dilution. Reduced d-spacing of 2 Å was recorded at 95% relative humidity for the sample treated with 20-to-1 diluted chemical stabilizer. One-dimensional cyclic swell testing indicated a reduction in swelling of up to 46% following the third swell cycle for smectite treated with 20-to-1 diluted HIS compared to untreated smectite.