The Hydration chemistry of blended portland blastfurnace slag cements for radiactive waste encapsulation

Abstract

Blended Portland-blastfumace slag cements provide a suitable matrix for the encapsulation of low and intermediate level waste due to their inherantly low connective porosity and provide a highly alkaline and strongly reduced chemical environment.
The hydration mechanism of these materials is complex and involves several competing chemical reactions. This thesis investigates three main areas:
1) The developing chemical shrinkage of the system shows that the
underlying kinetics are dominantly linear and estimates of the activation energy
of the slag made by this method and by conduction calorimetry show it to be c.53
kJ/mol.
2) Examination of the soUd phase reveals that caldum hydroxide is initially precipitated and subsequently consumed during hydration. The absolute rate of slag hydration is investigated by chemical and thermal methods and an
estimation of the average silicate chain length (3 silicate units) by NMR is
presented.
3) The developing pore solution chemistry shows that the system becomes rapidly alkaline (pH 13 - 13.5) and subsequently strongly reduced. Ion
chromatography shows the presence of reduced sulphur species which are
associated with the onset of reducing conditions.
In the above studies, close control of the hydration temperature was
maintained and the operation of a temperature controlled pore fluid extration
press is reported.

Date of Award	Jul 1991
Original language	English
Supervisor	C.L. Page (Supervisor)