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 either encapsulating it in cement, or another method, to prevent release to the biosphere.

Superplasticisers are of significant interest for the encapsulation of radioactive waste, as they improve fluidity characteristics during cement (grout) production, at a given water content, and may reduce the requirement for tight specifications on cement powders needed at encapsulation plants. This in turn provides security in opening up the range of cement powder supplies available to the plants.

Portland cement (PC) blended with ground granulated blast furnace slag (GGBFS) and pulverised fly ash (PFA) are also of interest as they can provide low viscosity of preparation but also potentially offer benefits with regards to tolerance to problematic waste components (for typical grout formulations), chemical similarity to cement and the ability to produce cement wasteforms from a range of readily available raw materials. However, there is little information on what parameters of raw materials are critical to reliable application, particularly when formulated with superplasticisers, under the conditions required in nuclear encapsulation plants.

This project investigates the mechanisms of superplasticiser interactions with common Portland cement powders, as reference and to increase understanding, and then assessing their effects on PC/GGBFS and PC/PFA grouts. Through investigating fundamental particle interactions more robust specifications can be developed for precursor powders and superplasticisers.

The project aims to use surface-specific techniques, spectroscopic and microstructural characterisation to investigate mechanisms, kinetics and effects of powder-superplasticiser interactions in PC, PC-BFS, and PC-PFA grouts. This will help to reveal fundamental processes controlling dispersion, fluidisation and reaction of PC/PC-BFS/PC-PFA grouts, providing better understanding of key parameters for robust specification.

The project aims to link the physical/chemical powder characteristics (particle size/distribution, morphology, surface area/chemistry) with chemistry, nano/microstructure, fresh-state rheology, chemical resistance and leaching rates, providing information essential for encapsulant specification.

Specifically, it will develop a mechanistic understanding of the interactions between the organic superplasticiser and the inorganic cement particles, in in PC, PC-BFS, and PC-PFA grouts, by experimentally assessing:

1)    Surface chemistry at the cement – superplasticiser interface

2)    Fresh state physical characteristics of the grouts

3)    Evolution of cement structure, phase assemblage and durability

Check out this Grantham Centre to learn more: 

https://www.sheffield.ac.uk/energy/news/exciting-phd-projects underway-thanks-energy-institute-studentships