Decarbonising Construction: Understanding the Chemistry and Engineering of Low-Carbon Alkali-Activated Cements

工业和经济脱碳对于改善我们的生态足迹和地球可再生资源之间的平衡至关重要。这将为人类减轻气候变化的影响提供尽可能好的机会。因此，我们需要重新思考我们建设城市的方式。要做到这一点，我们需要谈谈水泥。水泥，混凝土中的“胶水”，是现代文明赖以建立的耐用，防水和无处不在的材料。混凝土是仅次于水的第二大商品，世界每年生产超过100亿吨。仅水泥生产（不包括建筑的其他方面）就占全球二氧化碳排放量的8%左右，其中约一半来自生产过程中固有的化学反应。随着能源和农业等其他行业减少排放量，到2050年，水泥生产可能占所有人为二氧化碳排放量的近四分之一。与波特兰水泥相比，现代碱激发水泥（AAC）可增强物理性能，并将相关的CO2排放量减少80%以上。此外，这些水泥主要由辅助胶凝材料（SCM）生产，这些辅助胶凝材料通常是工业副产品，如冶金炉渣或天然丰富的矿物质，如粘土，进一步提高了其可持续性。这些水泥需要碱性“活化剂”，以在新鲜水泥浆中提供高pH值，并驱动反应、凝固和硬化。然而，浓碱溶液表现出高粘度和复杂的结晶行为，这极大地影响了反应机理和动力学，以及所得水泥的物理性质，即使在混合配方中只有微小的变化。对于这些下一代低碳水泥，迫切需要详细了解结晶过程，流体-颗粒和颗粒-颗粒相互作用，以实现质量控制并使其适用于大规模建筑。该博士使用原位表面特异性技术，光谱和微观结构表征来检查使用一套碱溶液和SCM生产的AAC中的这些相互作用。对目前未充分利用的SCM（例如，碱性氧气炉、传统炉渣）进行了研究，并与使用高炉炉渣生产的AAC（工业标准）进行了基准测试。所获得的知识将用于设计具有增强性能的新型AAC配方。这将推动实施，并有助于水泥生产脱碳。我们将研究结晶过程，流体-颗粒和颗粒-颗粒相互作用如何影响（i）新水泥浆体的分散，流化和流变性，（ii）反应和凝固，以及（iii）低碳AAC的物理性能发展。我们将利用这些信息来设计和测试新的AAC配方，以提高性能和质量控制。具体而言，它将通过实验评估对结晶过程，流体-颗粒和颗粒-颗粒相互作用的机械理解：活化溶液和新鲜水泥浆的表面化学。水泥的反应和凝固，以及水泥的新态物理特性。水泥结构演化、相组合与耐久性。这将显示原材料的性质如何影响：1）分散，流化和流变，2）反应和凝固，以及3）物理性能的发展。这将有助于优化水泥配方，提高可持续性、性能和耐久性，从而推动工业创新。

Decarbonising industry and the economy is essential to improve the balance between our ecological footprint and the planet's renewable resources. This would provide the best possible chance for humanity to mitigate the effects of climate change. Consequently, we need to rethink the way we build our cities. And to do this, we need to talk about cement. Cement, the 'glue' in concrete, is the durable, waterproof and ubiquitous material upon which modern civilisation is built. Concrete is second only to water in terms of commodity use, and the world produces more than 10 billion tonnes of it each year. Cement production alone (excluding other aspects of construction) accounts for around 8% of global CO2 emissions, about half of which results from chemical reactions inherent in the production process. As other industries such as energy and agriculture reduce their share of emissions, cement production may account for nearly a quarter of all human-driven CO2 emissions by 2050. Modern alkali-activated cements (AAC) can enhance physical properties, and reduce associated CO2 emissions by >80%, compared to Portland cement. Additionally, these cements are produced primarily from supplementary cementitious materials (SCM) which are typically industrial by-products such as metallurgical slags, or naturally abundant minerals such as clays, further enhancing their sustainability. These cements require an alkali 'activator' to provide a high pH in the fresh cement paste and drive reaction, setting and hardening. However, concentrated alkali solutions exhibit high viscosities and complex crystallisation behaviour, which dramatically affects the reaction mechanisms and kinetics, and physical properties of the resultant cements, even with only minor changes in mix formulation. A detailed understanding of crystallisation processes, fluid-particle and particle-particle interactions is urgently required for these next-generation low-carbon cements, to enable quality control and make them practical for use in large-scale construction. This PhD uses in-situ surface-specific techniques, spectroscopic and microstructural characterisation to examine these interactions in AAC produced using a suite of alkali solutions and SCMs. Currently underutilised SCMs (e.g. basic oxygen furnace, legacy slags) are investigated, and benchmarked against AAC produced using blast furnace slag (industry standard). The knowledge obtained will be used to design novel AAC formulations with enhanced performance. This will drive implementation, and help decarbonise cement production. We will examine how crystallisation processes, fluid-particle and particle-particle interactions affect (i) dispersion, fluidisation, and rheology of the fresh cement paste, (ii) reaction and setting, and (iii) physical property development of low-carbon AAC. We will use this information to design and test new AAC formulations for enhanced performance and quality control. Specifically, it will develop a mechanistic understanding of crystallisation processes, fluid-particle and particle-particle interactions, by experimentally assessing: Surface chemistry of the activating solution and fresh cement paste. Reaction and setting, and fresh-state physical characteristics of the cements. Evolution of cement structure, phase assemblage and durability. This will show how the nature of the raw materials affect: 1) dispersion, fluidisation, and rheology, 2) reaction and setting, and 3) physical property development. This will enable optimisation of cement formulations for enhanced sustainability, performance and durability, and hence drive industrial innovation.