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%。随着波特兰水泥产量预计在未来30年内翻一番，在工业中成功实施低碳替代品势在必行。地质聚合物水泥已经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，明确需要能够准确预测这些水泥的长期耐久性性能。然而，与传统水泥系统一样，控制耐久性的确切化学和物理过程尚未完全了解。暴露于硫酸盐的混凝土的退化是传统混凝土和可持续替代品的严重耐久性问题。因此，抗硫酸盐混凝土的发展对于广泛的基础设施应用，包括下水道管道，雨水排水系统，沿海结构和基础，是非常重要的。该项目的成果将是创造具有上级抗硫酸盐侵蚀能力的可持续水泥，该项目将研究可持续地质聚合物水泥的原子结构和形态，以提高我们对（i）水泥形成机制和（ii）由硫酸盐侵蚀引起的化学降解过程。我们的目标是首先发现的原子过程中发生的粉煤灰-矿渣-偏高岭土地质聚合物水泥混合物的形成过程中，通过创建一个地质聚合物特定的原子建模方法，利用量子化学和分子动力学。将采用关键的表征技术，以确保该模型的实验有效性，特别是在同步加速器和中子用户设施的原位原子分析技术，傅里叶变换红外光谱。结构模型将用于确定控制地质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。本项目的第二个目标是揭示和控制暴露于硫酸盐溶液过程中发生的原子降解机制。通过利用对硫酸盐侵蚀最有弹性的原子结构的稳定性，混合物设计将在原子水平上具有改进的抗硫酸盐特性。该项目第一部分开发的建模方法将得到扩展，以模拟不同硫酸盐暴露于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.