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Bentonite and concrete may be found together as backfilling and sealing materials in the reference concepts for the spent fuel and vitrified radioactive waste disposal facilities. The radwaste decay heat and the underground water will influence the equilibrium of the physicochemical properties of the bentonite-concrete system. The Ecoclay project was devised to study the interaction between cement and bentonite, in an attempt to identify cements that will not jeopardise the stability of the bentonite sealing materials. Two types of bentonite were considered: Volclay, a sodic type bentonite, and Febex -a calcicmagnesic type.

From past characterisation work and alkaline water alteration tests on bentonite, it may be stated that pH is the main factor controlling the alteration processes. Below pH 12.6, the mineralogical and retention properties of bentonite do not seem to be altered. A migration of Ca from the cement to the bentonite (and a micro-structural modification in the clay) has been detected.

Accelerated degradation tests were performed to simulate the long-term repository conditions, based on neutralisation of the cement pastes by acid, finding that nitric acid is most suitable for this type of test, though using carbonic acid or sodium bicarbonate reproduces the natural conditions more accurately.

The Kindis and EQ3/6 codes have been used to analyse the results. Some of the mineralogical transformations and the reaction activation factors have been reproduced with these codes.

Nevertheless, the numerical approaches used to model the different experiments need to be refined; it is also necessary to gain insight into the kinetic factors of some of the main reactions.

Additional information

Authors: HUERTAS ET AL, Enresa, Madrid (ES);GRIFFAULT L, ANDRA, Chatenay Malabry (FR);LEGUEY ET AL, UAM, Madrid (ES);ANDRADE ET AL, CSIC-IET, Grenada (ES);PARNEIX ET AL, ERM, Poitiers (FR);MEUNIER ET AL, Hydrasa, Poitiers (FR)
Bibliographic Reference: EUR 19609 EN (2000), 140pp Euro: 22.00
Availability: Available from European Commission, DG XII Communication Unit rue de la Loi/Wetstraat 200, B-1049 Bruxelles (BE) Tel: +32-2-2950001 Fax:+32-2-2958220 email:
ISBN: ISBN 92-828-9774-4
Record Number: 200012880 / Last updated on: 2000-11-29
Original language: en
Available languages: en