Biologically-Inspired Silicification of Fine-Grained Soils

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Many organisms mineralize tissues to produce structures that serve diverse functions such as skeletal support and protective composite layers. These structures are formed through biomineralization processes that have low metabolic cost to the organism. Of particular interest is the process of biosilicification -- the ability of organisms to direct the nucleation and growth of mechanically efficient silica skeletal materials. Advances in biosilicification research present an opportunity for cross-fertilization between the seemingly disparate disciplines of biomineralization and geotechnical engineering to advance ground improvement technology. The goals of this project are to: 1) Uncover new pathways for silica polymerization in fine-grained soil, 2) Use insights from biosilicification research to develop new processes for forming amorphous silica cements at natural pH levels using environmentally benign chemical materials, and 3) Reduce the life cycle impacts associated with ground improvement. To achieve the project goals, laboratory experiments will be conducted to model the geotechnical construction practices of subgrade stabilization using wet and dry soil mixing. Lime and cement stabilized samples will be used as control treatments. Soil materials that consist of pure clay minerals, mixtures of the clay minerals, mine tailings, and natural soils will be silicified with a polycation and sodium silicate. Adsorption and silicification-caused changes in soil geochemical properties will be assessed by x-ray diffraction, zeta potential, surface area, cation exchange capacity and pH. Changes in geotechnical index properties due to treatment will be determined and used to optimize the experiments. Strength of silicified soil will be measured by unconfined compression, consolidated undrained triaxial compression tests. Consolidation and creep tests will be used to evaluate strength and compressibility changes. The potential for the silicification process to reduce the volume changes associated with expansive soil will be determined. Pilot scale field tests will guide development of field implementation methods and to improve treatment effectiveness. Findings from this project will benefit society by reducing the life cycle environmental impacts of geotechnical construction, and training of the next generation of geotechnical engineers. Current ground treatment processes can possess relatively high embodied energy, and they rely on resources that cannot be renewed on human time scales. There can also be impacts to soil and groundwater and significant releases of CO2 to the atmosphere. The silicification process offers the potential for using reduced amounts of environmentally friendly input materials to achieve engineering performance that is comparable to or better than current technologies. By reducing the environmental impact, this new process has the potential to lower the cost of infrastructure projects. The findings also have the potential to benefit the resource recovery industries in managing fine-grained tailings. Graduate students will receive interdisciplinary training and will have the unique opportunity to develop expertise in the rapidly growing areas of applied biogeochemistry and biologically inspired materials.