A Bottom-up Approach to Design of Chemical Soil Stabilization Using Thermodynamic Modeling

University Of Connecticut, Storrs CT

Investigators

Abstract

Clay soils are present in large parts of the United States, such as Texas, Oklahoma, Kansas and others. Since clay soils are unsuitable as foundations for construction of highways and other structures, various stabilization techniques are employed to improve their properties. Chemical soil stabilization using lime and Portland cement is among the most widely applied approaches. Typically, design of soil stabilization requires the performance of lab scale treatability studies in order to determine the optimal chemical dosage, and there is still limited ability to predict the long-term behavior of stabilized soils over months and years. Models that describe the chemical reactions within stabilized clays over time are currently lacking and are necessary to improve our predictive ability. Accordingly, the overarching goal of this project is to generate the fundamental kinetic and thermodynamic models that will quantitatively describe the evolution of the chemical reactions between clay minerals and common stabilizers (lime, Portland cement). The long-term vision of the project is to utilize the models to predict long term behavior of stabilized clays and inform the mix design, minimizing the need to conduct treatability studies. In addition, the models will be tools for assessing the behavior of chemically stabilized soils under different scenarios (e.g. increased carbonation or impact of acidification). Model development will be done for eight different combinations (pure kaolinite with different particle sizes, pure Na-bentonite and one soil stabilized with quicklime and Portland cement) that will be provide a) fundamental data for pure minerals; and b) insight into the applicability on a real soil. Three different techniques (quantitative X-ray Diffraction, thermogravimetric and differential thermal analysis and Nuclear Magnetic Resonance) will be employed to monitor the solid phase composition in pure and reactive systems over time, utilizing advanced spectra deconvolution techniques. The generated data will be used to fit kinetic models for the pozzolanic reactions of each clay mineral. In addition, monitoring of pore solution composition will allow to conduct both forward and inverse thermodynamic modeling to predict the system stability and potential evolution. Due to the multi-disciplinary nature of the project, a parallel goal is to provide training opportunities integrating geotechnical engineering, geochemistry and materials science. Specifically designed modules with project-related multi-disciplinary concepts will be designed and integrated in regularly offered teaching and outreach activities at UCONN, providing a sustainable platform for continuous exposure of wide student audiences and expanding existing initiatives, from K-4 soil modules, to an ASCE webinar for professionals, new undergraduate courses and a distance learning Masters of Engineering. Engagement across three professional societies (chemistry, environmental and civil engineering) will result in cross-fertilization and wide dissemination of project results.