Biologically-Inspired Silicification of Fine-Grained Soils

许多生物将组织矿化，以产生具有多种功能的结构，如骨骼支撑和保护性复合层。这些结构是通过对生物体具有较低代谢成本的生物矿化过程形成的。特别令人感兴趣的是生物硅化过程--生物引导机械效率高的二氧化硅骨架材料成核和生长的能力。生物硅化研究的进展为生物矿化和岩土工程这两个看似不同的学科之间提供了相互促进的机会，以促进地基加固技术的发展。该项目的目标是：1)发现细粒土壤中二氧化硅聚合的新途径，2)利用生物硅化研究的见解，开发使用环境友好的化学材料在自然pH值水平下形成无定形二氧化硅水泥的新工艺，以及3)减少与地基改善相关的生命周期影响。为了实现项目目标，将进行室内试验，模拟湿土和干土混合加固路基的岩土施工实践。石灰和水泥稳定的样品将作为对照处理。由纯粘土矿物、粘土矿物混合物、尾矿和天然土壤组成的土壤材料将用聚阳离子和硅酸钠进行硅化。吸附和硅化引起的土壤地球化学性质的变化将通过X射线衍射、Zeta电位、表面积、阳离子交换量和pH来评估。将确定由于处理而引起的岩土指标特性的变化，并用于优化试验。硅化土的强度将通过无侧限压缩、固结不排水三轴压缩试验来测量。将使用固结和蠕变试验来评估强度和压缩性的变化。硅化过程减少与膨胀土有关的体积变化的潜力将被确定。试点规模的现场试验将指导现场实施方法的发展，并提高治疗效果。该项目的成果将通过减少岩土施工对环境的生命周期影响以及培训下一代岩土工程师而造福社会。目前的地面处理过程可能具有相对较高的体现能量，并且它们依赖于在人类时间尺度上无法更新的资源。这也可能对土壤和地下水造成影响，并向大气释放大量二氧化碳。硅化过程提供了使用更少的环境友好投入材料的潜力，以实现与当前技术相当或更好的工程性能。通过减少对环境的影响，这一新工艺有可能降低基础设施项目的成本。这些发现还有可能使资源回收行业在管理细粒尾矿方面受益。研究生将接受跨学科培训，并将有独特的机会在快速增长的应用生物地球化学和生物启发材料领域发展专业知识。

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.