CAREER: Realizing Alternative Cements with Chemical Kinetics: Tuned Mechanical–Chemical Properties of Cementitious Magnesium Silicate Hydrates by Multi-Scale Synthetic Control

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。建筑行业的高能源需求和环境负担促使人们努力发现新的胶凝材料。基于镁和硅之间结合的水泥，如硅酸镁水合物（MSH），是开发较少的替代品之一。控制其胶凝性质的特性，即沉淀速率、强化的结构机制和相关环境中的稳定性，尚不清楚，这阻碍了它们的广泛使用。这个教师早期职业发展（Career）项目将揭示胶凝MSH的化学合成和化学控制其随后的形态，机械和化学性质的新途径。有意义的本科研究经验，针对妇女和代表性不足的少数民族学生在家庭和邻近机构，包括社区学院，将改善STEM和转学生的成果，丰富研究生培训，并创建一个对材料科学和工程感兴趣的学生管道，培养国家未来的劳动力。为了增强体验，学生们将制作展示“水泥和混凝土材料科学”的教育视频，这些视频将分发给达拉斯-沃斯堡的小型建筑企业，以提高建筑工人的工作意识和技能，通过基础设施发展支持该地区快速增长的人口。本研究将强调一种综合方法，包括动态高分辨率方法来探测、驱动和操纵MSH的合成、结构和性质，从成核到体生长，重点关注MSH -流体界面发生的现象。这将通过以下步骤完成。首先，定量描述MSH生长动力学的沉淀率、形态和成分将使用原位和非原位表面敏感分析方法的组合进行研究，并使用应用于硅酸盐片的机理模型进行解释。其次，将在双电层理论框架内理解MSH的介晶组织，并利用聚电解质和电化学力来操纵。第三，将量化MSH粘合剂的局部力学和表面性能，并将其与宏观力学性能联系起来，并研究MSH降解的速率和机制。使用的主要分析方法包括原子力显微镜、动力学地球化学模型、红外光谱、电子显微镜、电化学方法和同步加速器x射线散射。这项研究将最终揭示MSH水泥的加工-结构-性能关系，确定其作为建筑用途粘结材料和普通波特兰水泥替代品的可行性。所获得的基础科学和发现将扩大我们对低温矿物结晶过程和随后跨越空间和时间尺度的属性发展的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).The high energy needs and environmental burden of the construction industry have driven efforts to discover new cementitious materials. Cements based on the bonding between magnesium and silicon, such as magnesium silicate hydrates (MSH), are among the less explored alternatives. The characteristics that control their cementitious nature, i.e., the rates of precipitation, structural mechanisms for strengthening, and stability in relevant environments, are not known and this hinders their widespread use. This Faculty Early Career Development (CAREER) project will reveal new pathways for the chemical synthesis of cementitious MSH and the chemical control of their consequent morphological, mechanical, and chemical properties. Meaningful undergraduate research experiences targeting women and underrepresented minority students at the home and neighboring institutions including a community college will improve STEM and transfer student outcomes, enrich graduate student training, and create a pipeline of students interested in materials science and engineering, cultivating the nation’s future workforce. To enhance the experience, the students will create educational videos that showcase the “Materials Science of Cements and Concrete” that will be distributed to small construction businesses in Dallas–Fort Worth to improve job appreciation and skill in the construction workforce that supports the area’s rapidly growing population through infrastructure development. This research will emphasize an integrated approach involving dynamic high-resolution methods to probe, drive, and manipulate MSH synthesis, structures, and properties from nucleation to bulk growth with a focus on the phenomena that occur at the MSH–fluid interface. This will be accomplished through the following steps. First, precipitation rates, morphologies, and compositions that quantitatively describe MSH growth kinetics will be investigated using a combination of in situ and ex situ surface-sensitive analytical methods and interpreted using mechanistic models applied to sheet silicates. Second, MSH mesocrystalline organization will be understood within the electric double layer theoretical framework and manipulated using polyelectrolytes and electrochemical forcing. Third, local mechanical and surface properties will be quantified and related to macroscale mechanical properties of MSH binders, and the rates and mechanisms of MSH degradation will be investigated. Key analytical methods used include atomic force microscopy, kinetic geochemical modeling, infrared spectroscopy, electron microscopy, electrochemical methods, and synchrotron X-ray scattering. This research will ultimately reveal processing–structure–property relationships in MSH cements, establishing their viability as a binder material for construction purposes and an alternative to ordinary Portland cement. The fundamental science and discovery gained will expand our understanding of low-temperature mineral crystallization processes and the subsequent property development across spatial and temporal scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.