Durable Concrete for a Waste Repository - Measurement of Ionic Ingress
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DURABLE CONCRETE FOR A WASTE REPOSITORY MEASUREMENT OF IONIC INGRESS
R.F. FELDMAN*, J.J. BEAUDOIN* AND K.E. PHILIPOSE** * Institute for Research in Construction, National Research Council, Ottawa, Canada ** Waste Management Systems, Atomic Energy of Canada Limited, Chalk River, Canada
ABSTRACT A waste repository for the below ground disposal of low level radioactive waste is planned at Chalk River Nuclear Laboratories. It relies greatly on the durability of concrete for the required 500 year service life. A research program to design durable concrete and predict its service life is in progress. The degradation of the concrete depends to a large extent on the rate of ingress of corrosive agents. Penetration of chloride and sulphate ions are particularly relevant. Twenty mix formulations were developed to create various types and qualities of concrete, and to study their behaviour in different site environmental conditions. A total of 1000 concrete specimens are being exposed at 20'C and 45'C to 25 different combinations of the corrosive agents including C02. Procedures to measure the ionic profiles and to determine the factors controlling diffusion of the ions in the various concretes have been developed. Results of selected concrete systems exposed to chloride and sulphate solutions for 1 year are presented and discussed in terms of pore structure and permeability parameters of the concrete. INTRODUCTION A joint research program designed to predict the durability and service life of concrete required for the construction of low level radioactive waste repositories was initiated by Atomic Energy of Canada Ltd. and the National Research Council [1]. The primary objective was to obtain data needed to design concrete to perform in a known aggressive environment for a predetermined period of time. Different approaches have been considered [2]. The focus in this study was not on the development of a single highly durable concrete but a methodology which would assess the durability aspects of a wide variety of concrete types and quality subjected to different exposure conditions. Environmental factors considered included sulphate and chloride ion concentration in the groundwater, carbonation effects, long term phase changes of hydrated cement components, leaching of concrete constituents, freeze-thaw resistance and susceptability of aggregates to alkaliaggregate reaction. Interactions between concrete and both chloride and sulphate ion, singly and in combination, were considered of major importance and this paper will concentrate on their effect. It was also deemed necessary to explore the possibility of synergistic effects due to combined action of these ions. Durability prediction generally involves the appropriate selection of a suitable rate determining parameter. This will be achieved by determining the time dependent depth of penetration of chloride and sulphate ion into test Mat. Res. Soc. Symp. Proc. Vol. 176. @1990 Materials Research Society
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concretes exposed to chloride and sulphate solutions having a r
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