A Generic Procedure for the Assessment of the Effect of Concrete Admixtures on the Sorption of Radionuclides on Cement:
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$*HQHULF3URFHGXUHIRUWKH$VVHVVPHQWRIWKH(IIHFWRI&RQFUHWH$GPL[WXUHVRQWKH 6RUSWLRQRI5DGLRQXFOLGHVRQ&HPHQW &RQFHSWDQG6HOHFWHG5HVXOWV M.A. Glaus, A. Laube, L.R. Van Loon Waste Management Laboratory, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland. $%675$&7 A VFUHHQLQJSURFHGXUH is proposed for the assessment of the effect of concrete admixtures on the sorption of radionuclides on cement. The VFUHHQLQJSURFHGXUH focuses on a broad and generic assessment and can thus be used as a tool for the assessment of concrete admixtures possibly used in the future. The experimental feasibility of the VFUHHQLQJSURFHGXUH and the relevance of the results obtained are tested using a selection of superplasticisers and set modifiers. Selected results obtained for these admixtures are presented in this contribution. INTRODUCTION Concrete admixtures (abbreviated as BZM) are used for improving the workability of concrete, to influence its physical properties, and to confer beneficial effects to the material. In the context of the safety of a repository for low- and intermediate level radioactive waste planned in Switzerland, which will be mainly built from cementitious materials, BZM are of concern like other organic materials. Sorption of radionuclides on the solid repository matrix is a key factor governing the possible release of radionuclides from the repository [1]. Organic substances contained in the repository may positively or negatively influence this sorption. Therefore the role of organics needs to be addressed in the performance assessment for a radioactive waste repository. The need for detailed investigations in BZM is based on the following reasoning: • BZM are unavoidable components of concretes used in the construction of a cementitious deep underground repository for radioactive waste. • BZM are currently used in the process of waste conditioning with the aim of obtaining low porosity concretes. Concretes with less and smaller pores, are more resistant to chemical attack, they have low permeability and thus lead to lower leaching rates of the radionuclides contained in the waste [2,3,4]. • After hydration of the concrete, BZM are found dissolved in the pore water and chemically bound to the solid [5]. With regard to their chemical structures it can be expected that several types of BZM may form soluble complexes with radionuclides under the alkaline conditions of cement pore water [6]. In addition, the sorption of BZM on the cement surface may possibly alter the sorption properties of cement for radionuclides. From these reasons it is possible that BZM have an adverse impact on the sorption or solubility of the radionuclides. The assessment of BZM is complicated by a series of special circumstances: (i) BZM comprise a variety of completely different chemical structures, and (ii) a single type of BZM is in turn composed of a variety of different compounds. This composition is in many cases illdefined or kept under the pledge of secrecy for proprietary reasons. (iii) It is not known, which BZM wi
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