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

在英国，迄今为止已经产生了超过150，000立方米的放射性废物（足以填满60个奥林匹克游泳池）。大多数放射性废物需要通过将其封装在水泥中进行调节，以防止释放到生物圈中。地聚合物水泥非常适合于此，具有低粘度、对有问题废物的耐受性更高以及比其他封装剂更低的裂变产物浸出率。与传统的波特兰水泥相比，地质聚合物水泥在生产过程中的二氧化碳排放量也显著降低，减少了90%，这对于帮助实现2050年的净零排放至关重要。超塑分散剂可以进一步改善给定含水量下的流动特性，并降低封装厂对水泥粉末严格规格的要求。然而，由于在每种情况下水和固态化学之间的广泛差异，地质聚合物中的超增塑剂行为与普通波特兰水泥澄清剂中的超增塑剂行为显著不同。地质聚合物和波特兰水泥减水剂之间的化学差异导致了不同的超增塑剂效果（由于粉末物理/化学特性的变化而加剧），并且对于哪些超增塑剂最适合地质聚合物知之甚少。这是至关重要的，我们了解基本的水泥超增塑剂的相互作用，以及对地质聚合物密封剂性能的影响，这样就可以制定可靠的规格，密封剂的性能和性能可以预测。这个博士研究有机超增塑剂和无机水泥颗粒之间的相互作用，地质聚合物澄清剂，对常见的波特兰水泥基澄清剂为基准。本课程采用新的原位表征方法（包括表面特异性技术、光谱和微观结构表征）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分散、氟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密封剂配方。

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.