Understanding Cement-Superplasticiser Interactions in Blended Portland Cement Wasteforms

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.

Based in the Departments of Chemical and Biological Engineering, and Materials Science and Engineering, the successful candidate will be joining a team of multidisciplinary researchers at The University of Sheffield to develop research and innovation for decarbonisation. The successful applicant will also benefit from industrial supervision by the Encapsulant Integrated Research Team lead and deputy of the Intermediate Level Waste Packaging Development Centre of Expertise, Sellafield Ltd. They will benefit from being a member of a friendly and collegial group with world-leading expertise and facilities.

The Sustainable Materials at Sheffield group (in the Department of Chemical and Biological Engineering) and the Cements@Sheffield group (in the Department of Materials Science & Engineering) are world-leading research teams, located in highly-rated and very successful departments, building from over 100 years of history in cements research at Sheffield. We investigate interesting and important cements and related materials for applications in nuclear and infrastructure sectors, publish our work in the leading journals and conferences in the field, and take great pride in the fact that alumni have gone on to the highest levels of success in both academia and industry.

Both the Department of Chemical and Biological Engineering and the Department of Materials Science & Engineering rank among the top in the UK, and have among the highest levels of research income.

Start Date of Studentship: 26th September 2022

For more details contact Dr Brant Walkley at [Email Address Removed].

Please see this link for information on how to apply: https://www.sheffield.ac.uk/cbe/postgraduate/phd/how-apply. Please include the name of your proposed supervisor and the title of the PhD project within your application.

This interdisciplinary project spans chemical and materials engineering.

Applicants should have a first or upper second class UK honours degree or equivalent in a related discipline (Chemical/Materials/Environmental/Civil Engineering, Materials/Inorganic Chemistry or Mineralogy/Geochemistry). A strong undergraduate background in chemical/materials engineering, with an interest in driving sustainability is desired. If English is not your first language then you must have an International English Language Testing System (IELTS) average of 6.5 or above with at least 6.0 in each component, or equivalent. Please see this link for further information: https://www.sheffield.ac.uk/postgraduate/phd/apply/english-language.