Sulfate Attack Mechanisms in Geopolymers: Measurements and Modeling at the Nanoscale

人为二氧化碳排放的主要贡献者之一是普通波特兰水泥生产，约占总排放量的8%。鉴于波特兰水泥产量预计将在未来30年翻一番，低碳替代品在工业中成功实施是当务之急。地聚合物水泥已成为波特兰水泥基系统的可行替代品，然而，为了在建筑环境中成功实施，显然需要能够准确预测这些水泥的长期耐久性能。然而，与传统水泥系统的情况一样，控制耐久性的确切化学和物理过程并不完全清楚。暴露在硫酸盐中的混凝土的退化是传统混凝土和可持续替代混凝土的一个严重的耐久性问题。因此，抗硫酸盐混凝土的开发对于包括下水道、雨水排水系统、沿海结构和基础在内的广泛基础设施应用是极其重要的。该项目的成果将是创造出具有优异的抗硫酸盐侵蚀能力的可持续水泥，这将通过降低与硫酸盐暴露的混凝土结构的维修和维护相关的成本而造福社会。该项目将研究可持续地聚水泥的原子结构和形态，以加深我们对(I)水泥形成机理和(Ii)硫酸盐侵蚀引起的化学降解过程的理解。本研究的目标是首先利用量子化学和分子动力学建立特定于地聚合物的原子模拟方法，以发现在形成飞灰-矿渣-偏高岭土地聚合物水泥混合料过程中发生的原子过程。将采用关键的表征技术来确保模型的实验有效性，特别是同步加速器和中子用户设施的原位原子分析技术，以及傅里叶变换红外光谱。这些结构模型将被用来确定控制地聚合物水泥形成的关键化学机制，以及前体化学对这些机制的影响。该项目的第二个目标是发现和控制暴露在硫酸盐溶液中的原子降解机制。通过利用对硫酸盐侵蚀最具弹性的原子结构的稳定性，混合料设计将在原子水平上改进抗硫酸盐特性。在项目第一部分开发的建模方法将得到扩展，以便能够模拟不同的硫酸盐暴露在地质聚合物水泥表面时发生的化学过程。将进行现场降解实验，以提供模型的实验验证。

One of the main contributors to anthropogenic carbon dioxide emissions is ordinary Portland cement production, accounting for approximately 8 percent of total emissions. With Portland cement production forecast to double in the next 30 years it is imperative that low-carbon alternatives are successfully implemented in industry. Geopolymer cements have emerged as viable alternatives to Portland cement-based systems, however, there is the explicit need to be able to accurately predict the long-term durability performance of these cements for the successful implementation in the built environment. Nevertheless, as is the case for conventional cement systems, the exact chemical and physical processes controlling durability are not fully understood. Degradation of concrete exposed to sulfates is a serious durability concern for both conventional concrete and sustainable alternatives. Hence, the development of sulfate resistant concrete is extremely important for a wide range of infrastructure applications including sewer pipes, storm-water drainage systems, coastal structures and foundations. The outcome of this project will be the creation of sustainable cements with superior resistance to sulfate attack, which will benefit society by reducing costs associated with repair and maintenance of concrete structures exposed to sulfates.This project will investigate the atomic structure and morphology of sustainable geopolymer cements to improve our understanding of (i) cement formation mechanisms and (ii) chemical degradation processes caused by sulfate attack. The objective is firstly to discover the atomic processes that occur during formation of fly ash-slag-metakaolin geopolymer cement mixes by creating a geopolymer-specific atomistic modeling methodology utilizing quantum chemistry and molecular dynamics. Key characterization techniques will be employed to ensure experimental validity of the model, specifically in situ atomic analysis techniques at synchrotron and neutron user facilities, and Fourier-transform infrared spectroscopy. The structural models will be used to identify the key chemical mechanisms controlling geopolymer cement formation together with the influence of precursor chemistry on these mechanisms. The second objective of this project is to uncover and control the atomistic degradation mechanisms that occur during exposure to sulfate solutions. By exploiting the stability of the atomic structures most resilient to sulfate attack, mix designs will be engineered with improved sulfate resistance characteristics at the atomic level. The modeling methodology developed during the first part of the project will be extended to enable simulation of the chemical processes that occur when different sulfate salts are exposed to the geopolymer cement surfaces. In situ degradation experiments will be conducted to provide experimental validation of the models.