Fundamental Investigation of Preferred Orientation Mechanism in Concrete

非技术描述：随着时间的推移，混凝土结构在其支撑的重量下变形，如果不更换，最终导致结构失效。当将混凝土结合在一起的微观颗粒（称为硅酸钙水合物的颗粒）在压缩力的作用下相互移动时，就会导致混凝土变形。然而，导致某些混凝土比其他混凝土变形更大的机制还不清楚。在这个项目中，研究人员正在研究一系列硅酸钙水合物如何响应压缩应力。例如，该团队正在研究添加铝的效果，铝现在被添加到一些水泥中，作为一种环境友好的方式来处理金属废物。研究人员正在使用先进的基于X射线的成像技术来直接可视化颗粒对压缩的反应。该项目的结果可用于深入了解混凝土失效机制，并提出补救措施，以提高对环境负责的基础设施的耐久性。因此，该项目在预测和替换国家方面发挥着至关重要的作用。老化的民用基础设施。该项目培训本科生和研究生，重点是从科学领域代表性不足的群体中招募学生加入团队。技术问题：混凝土的一个潜在的腐蚀机制是应力下的蠕变。主要的粘结相，纳米晶硅酸钙水合物（C-S-H），是牵连在蠕变，但有很少的了解，这些晶粒如何滑过对方。C-S-H颗粒包含许多用二氧化硅四面体装饰的氧化钙片，其中每个片被水分子薄层隔开。取决于硅的量或是否存在金属，C-S-H的性质可以显著变化。该团队正在使用国内同步加速器设备来测量单轴应力下的晶粒排列（纹理），以确定晶粒滑移的机制。C-S-H中的水环境正在用质子核磁共振弛豫测量法进行研究，以确定它是液体还是冰。最后，用单轴应力拉曼光谱研究应力下硅-氧键中的应变，以确定在单轴应力下结构内是否存在滑移面。单轴应力拉曼光谱的发展将有助于理解其他纳米晶陶瓷材料中的类似现象。该项目的成果对水泥基结构的结构完整性的工程模型非常有用。该奖项反映了NSF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。

NON-TECHNICAL DESCRIPTION: Over time, concrete structures deform under the weight they support, which ultimately leads to structural failure if not replaced. The concrete deformation is caused when the microscopic grains that bind the concrete together - grains known as calcium-silicate-hydrate - are compelled by the compressive force to move past each other. However, the mechanism that causes some concretes to deform more than others is not well understood. In this project, researchers are studying how a series of calcium-silicate-hydrates responds to compressive stress. For example, the team is examining the effect of adding aluminum, which is now being added to some cements as an environmentally friendly way to dispose of metal wastes. The researchers are using advanced X-ray-based imaging techniques to directly visualize how the grains respond to compression. The results of this project can be used to provide insights into concrete failure mechanisms and suggest remedies to increase durability towards more environmentally responsible infrastructure. As such, this project plays a crucial role in the forecasting and replacement of the nation?s aging civil infrastructure. The project is training both undergraduate and graduate students; an emphasis is placed on recruiting students from groups typically underrepresented in the sciences to join the team.TECHNICAL DETAILS: An insidious decay mechanism of concrete is its creep under stress. The main binding phase, nanocrystalline calcium-silicate-hydrate (C-S-H), is implicated in the creep, but there is very little understanding of how these grains slide past each other. C-S-H grains comprise a number of calcium oxide sheets decorated with silica tetrahedra, where each sheet is separated by a thin layer of water molecules. Depending on the amount of silicon or if metals are present, the properties of the C-S-H can vary significantly. The team is using domestic synchrotron facilities to measure grain alignment (texturing) under uniaxial stress towards determining the mechanism(s) of grain slippage. The water environment in C-S-H is being studied with proton nuclear magnetic resonance relaxometry to determine how liquid- or ice-like it is. Finally, the strain in silicon - oxygen bonds under stress is being studied with uniaxial-stress Raman spectroscopy to determine if there are slip planes within the structure under uniaxial stress. The development of uniaxial-stress Raman spectroscopy will be useful for understanding similar phenomena in other nanocrystalline ceramic materials. The results of the project are useful for engineering models of structural integrity in cement-based structures.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.