The Effect of Alumina Substitution on Viscoelasticity of Calcium Silicate Hydrate

该项目的目的是将水合硅酸钙（C-S-H）的化学成分和分子结构与材料的粘弹性力学性能联系起来。C-S-H是硅酸盐水泥的主要结合水化产物，对混凝土的性能起决定性作用。如果在C-S-H的生产过程中有氧化铝可用，通常从铝硅酸盐补充胶凝材料中，C-S-H能够将铝作为客体离子结合，产生水合铝硅酸盐钙（C-A-S-H）。氧化铝掺入可以通过增加四面体链长度来改变其分子结构，这种变化可以促进C-S-H层之间的交联。通过应用多尺度静态和动态力学测试，包括动态纳米压痕的新型纳米力学表征技术，该项目将测试的主要假设是确定C-A-S-H是否由于这种增加的聚合而比C-S-H具有更少的粘弹性。为了将化学成分和分子结构与粘弹性特性联系起来，将在实验室中合成具有不同成分的相纯C-S-H和C-A-S-H，并使用先进的技术进行表征，例如核磁共振（NMR）用于局部原子环境，x射线衍射（XRD）用于检测晶体相，x射线荧光（XRF）用于检测整体化学成分。此外，结合力学测试前后的核磁共振表征将表明在粘弹性变形过程中分子结构是否有任何变化，这将是革命性的知识。如果C-S-H中氧化铝取代减少徐变的假设被证明是正确的，本研究将导致一种控制混凝土粘弹性的新方法，最终可以延长混凝土结构的使用寿命。混凝土是世界上使用最广泛的建筑材料，其生产约占全球二氧化碳排放量的5%。因此，混凝土结构寿命的任何增加都意味着混凝土产量和相关温室气体排放的减少。此外，C-S-H中氧化铝的主要来源通常是粉煤灰，这种废料也降低了混凝土中硅酸盐水泥的含量，从而减少了混凝土的温室气体排放。该研究与教育计划很好地结合在一起，包括(a)培养研究生在多尺度上对材料进行高级化学力学表征，(b)将研究成果纳入研究生课程，以及(c)在有才华的中学生中激发对工程和可持续建筑的热情。

The objective of this project is to link the chemical composition and molecular structure of calcium silicate hydrate (C-S-H) to the viscoelastic mechanical properties of the material. C-S-H is the main binding hydration product of portland cement that governs properties of concrete. If alumina is available during the production of C-S-H, typically from alumino-silicate supplementary cementitious materials, C-S-H is able to incorporate aluminum as a guest ion, producing a calcium aluminosilicate hydrate (C-A-S-H). Alumina incorporation is seen to alter its molecular structure by increasing the tetrahedral chain length, a change that is seen to promote crosslinking between C-S-H layers. By applying a multiscale static and dynamic mechanical testing that include a novel nanomechanical characterization technique of dynamic nanoindentation, the main hypothesis that will be tested during this project is to determine whether C-A-S-H is less viscoelastic than C-S-H due to this increased polymerization. To relate chemical composition and molecular structure with viscoelastic properties, phase-pure C-S-H and C-A-S-H will be synthesized in the lab with varying composition and characterized using advanced techniques such as nuclear magnetic resonance (NMR) for local atomic environment, X-ray diffraction (XRD) for detection of crystalline phases, and X-ray fluorescence (XRF) for bulk chemical composition. Furthermore, a combination of NMR characterization before and after mechanical testing will indicate if there are any changes in molecular structure during viscoelastic deformation, knowledge that will be transformative.If the hypothesis that alumina substitution in C-S-H reduces creep is proved right, this research will lead to a new method of controlling the viscoelasticity of concrete that can ultimately lead to longer life of concrete structures. Concrete is the most widely used construction material in the world and production of it is associated with approximately 5% of the global CO2 emissions. Thus, any increase in the longevity of concrete structure will mean reduction in the amount of concrete produced and associated greenhouse gas emission. In addition, the main source of alumina in C-S-H is usually fly ash, a waste material that also reduces the portland cement content in concrete and thereby reduces its greenhouse gas emission. The research is well integrated with educational plans, including (a) training graduate student in advanced chemo-mechanical characterization of materials at multiscale, (b) incorporating research findings into graduate level classes, and (c) generating enthusiasm for engineering and sustainable construction among talented middle school students.