The Effect of Particle Size on the Hydration of Blast Furnace Slag Blended Grouts for the Immobilisation of Nuclear Waste

Author(s): Rebecca A. Sanderson, Gavin M. Cann and John L. Provis
Paper category: Proceedings
Book title: 3rd International RILEM Conference on Microstructure Related Durability of Cementitious Composites
Editor(s): Changwen Miao, Wei Sun, Jiaping Liu, Huisu Chen, Guang Ye and Klaas van Breugel
Print-ISBN: 978-2-35158-188-9
e-ISBN: 978-2-35158-189-6
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 252-257
Total Pages : 6
Language : English

Abstract: Currently, the preferred route used in the UK for the disposal of intermediate level radioactive waste (ILW) is encapsulation in a cementitious matrix. The cement grout is formulated by blending Portland cement with a large percentage of blast furnace slag (BFS).
However, the UK cement and iron industries have been, and continue to be, faced by a series of economic challenges, causing an inconsistent supply of BFS to the nuclear sector. The UK nuclear industry have had to change their slag powder supply from a unique specification, with a much coarser grind than the powders now used in the construction industry,
to a commercially available material. A lower surface area than what is used in construction is desirable for nuclear waste applications, as rapid mechanical strength development is less important than fluidity control in such materials. The material now used is a blend of ground granulated blast furnace slag (GGBS) with a much coarser fraction of the same chemical composition, called Calumite. Blending of the two materials is required because the fine GGBS increases reactivity and causes poor fluidity. Therefore, the coarser Calumite fraction is essential when trying to control the performance of the grout. The grout produced has to conform to specific performance requirements in order for it to be suitable for use during encapsulation. The composition and particle characteristics of the cementitious powders have a major impact on the reaction mechanism and thus microstructural and performance properties
of the hardened grout system, which must be designed to retain its integrity for centuries or millennia to retain the ILW in a safe and immobile form. Consequently, it is necessary to control the powder properties within a tight specification.
The focus of the work presented here is the definition of a reliable method for assessing the heat of hydration of candidate grout formulations. Isothermal conduction calorimetry and semiadiabatic calorimetry were carried out to monitor the heat evolution of the cementitious systems, including model systems where Calumite is replaced with inert quartz sand. This study aims to underpin the science and in turn future-proof the supply of cement powder for the UK’s nuclear waste cementation program.

Online publication : 2016
Publication type : full_text
Public price (Euros) : 0.00

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