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, intermediate level waste is encapsulated in a cement grout to help to make the waste safer to transport, handle and to store in interim storage before it is placed in a geological disposal facility. For this process to be as efficient as possible, the grout must be very fluid to ensure the highest level of infiltration, and the cured product must be relatively permeable to create an effective barrier.

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 (GGBS) can be introduced to the grout in relatively high quantities. 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. GGBS is widely used on waste encapsulation plants and for construction processes.

The industry currently faces significant gaps in knowledge surrounding the chemistry within cement-superplasticiser interactions in blended Portland cement wasteforms which increases supply chain risk. This project will experimentally develop a mechanistic understanding of the interactions between organic superplasticisers and the inorganic cement particles, in blended PC/GGBS grouts. This will facilitate a more effective and sustainable method of encapsulation of nuclear waste, whilst increasing supply chain security, 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