Understanding cement-superplasticiser interactions in blended Portland cement wasteforms

Grantham Scholar Ava M Sjoberg’s project looks at a more sustainable method of encapsulation and decommissioning of nuclear waste using cement. 

The project

Nuclear waste comes in all shapes and sizes. As part of the immobilisation process for safe disposal, the waste is encapsulated in cement to help to prevent transfer of hazardous materials including radionuclides. For this process to be as efficient as possible, the concrete mix must be very fluid to ensure the highest infiltration possible, and the cured product must be highly permeable to create an effective barrier to ensure safe disposal.

It seems obvious to increase the water content of a mix to increase fluidity, however this would compromise the desired permeability characteristics. To overcome this, the mix can be chemically manipulated through steric hindrance and electrostatic repulsion by adding an organic superplasticiser. The addition of a superplasticiser enables a low water-cement ratio mix to be upheld whilst improving the fluidity of the mix. There are many advantages of a low water-cement (w/c) mix with improved flow characteristics, such as an increased early strength of the concrete, higher waste infiltration, and a less permeable cementitious matrix, and therefore less leaching of radionuclides.

In addition to organic SPs, supplementary cementitious materials (SCM) such as ground blast furnace slag (BFS) and pulverised fuel ash (PFA), can be introduced in high quantities to the cement. These SCMs enhance physical properties such as the strength and durability of the concrete whilst reducing embodied CO2 emissions due to the fact that they are by-products of blast furnace processes which would have otherwise been disposed of in landfill. These SCMs are used widely on waste encapsulation plants.

The industry currently faces significant gaps in knowledge surrounding the cement-superplasticiser interactions in blended Portland cement wasteforms, however early studies suggest that it is important to understand the implications of the addition of an SP when dealing with high activity waste. This project will experimentally develop a mechanistic understanding of the interactions between organic superplasticisers and the inorganic cement particles, in PC, PC-BFS, and PC-PFA grouts. This will facilitate a safer, effective and more sustainable method of encapsulation and decommissioning of nuclear waste, ultimately contributing to the UK energy sector’s efforts of shifting towards Net Zero.

Social media

You can find Ava M Sjoberg on Twitter.

And you can connect with her on LinkedIn.



Dr Brant Walkley

Department of Chemical and Biological Engineering


Professor John L Provis

Department of Materials Science and Engineering