Understanding Cement-Superplasticiser Interactions in Geopolymer Encapsulants for Safe Disposal of Radioactive Waste

在英国，到目前为止，已经产生了超过15万立方米的放射性废物(足以填满60个奥运大小的游泳池)。大多数放射性废物需要通过将其包裹在水泥中来进行处理，以防止释放到生物圈。与其他密封剂相比，土壤聚合物水泥非常适合这一点，提供低粘度，增加对有问题的废物的耐受性，并降低裂变产物的浸出率。与传统波特兰水泥相比，地聚合物水泥与其生产相关的二氧化碳排放量也显著降低，减少了高达90%的二氧化碳排放量，这是帮助实现2050年净零排放的关键。超塑分散剂可以进一步改善给定水分含量下的流动特性，并降低对胶囊化工厂所需的水泥粉末的严格规格的要求。然而，由于水化学和固体化学在每一种情况下的巨大差异，在土聚合物中的超塑化剂行为与普通波特兰水泥密封剂中的行为有很大的不同。关于哪些参数对可靠应用至关重要的信息很少。土壤聚合物和波特兰水泥包覆剂之间的化学差异导致不同的超塑化剂效应(由于粉末物理/化学特性的不同而加剧)，对于哪些超塑化剂最适合土壤聚合物也知之甚少。我们必须了解水泥-超塑化剂的基本相互作用，以及对土聚密封剂性能的影响，以便制定可靠的规范，并预测密封剂的性能和性能。本博士论文考察了有机超塑化剂与土聚密封剂中无机水泥颗粒之间的相互作用，并与常见的波特兰水泥基密封剂进行了比较。它采用一种新的原位表征方法(包括表面特定技术、光谱和微结构表征)来研究有机-无机相互作用的机理和动力学，以及对性能的影响。我们将阐明控制这些水泥的分散、流态化和反应的基本过程，并设计、生产和测试具有增强性能的新型包覆剂配方。

In the UK, over 150,000m3 of radioactive waste (enough to fill 60 Olympic size swimming pools) has been produced to date. Most of this radioactive waste needs conditioning by encapsulating it in cement to prevent release to the biosphere.Geopolymer cements are ideally suited for this, providing low viscosity, increased tolerance to problematic wastes, and lower leach rates of fission products than other encapsulants. Geopolymer cements also have significantly lower CO2 emissions associated with their production compared to traditional Portland cement, reducing these by as much as 90%, and are critical in helping to reach Net Zero 2050. Superplasticising dispersants can further improve flow characteristics at a given water content, and reduce the requirement for tight specifications on cement powders needed at encapsulation plants. However, superplasticiser behaviour in geopolymers differs significantly from that in common Portland cement encapsulants, due to extensive differences between aqueous and solid-state chemistry in each case. There is little information on what parameters are critical to reliable application.Chemical differences between geopolymers and Portland cement encapsulants lead to different superplasticiser effects (exacerbated by variability in powder physical/chemical characteristics), and little is known about which superplasticisers are most suitable for geopolymers. It is essential that we understand the fundamental cement-superplasticiser interactions, and effect on geopolymer encapsulant performance, so that robust specifications can be developed, and encapsulant properties and performance can be predicted.This PhD examines interactions between organic superplasticisers and inorganic cement particles in geopolymer encapsulants, benchmarked against common Portland cement-based encapsulants. It adopts a new in-situ characterisation approach (including surface-specific techniques, spectroscopic and microstructural characterisation) to investigate mechanisms and kinetics of organic-inorganic interactions, and effects on performance.We will elucidate the fundamental processes controlling dispersion, fluidisation and reaction of these cements, and design, produce and test novel encapsulant formulations with enhanced performance.