The role of the fly ash pozzolanic activity in simulated sulphate radioactive liquid waste

Effects of the very concentrated sulphated salts that accompanied the low ( LLW) and medium level wastes (MLW), on the cementitious characteristics of materials employed in the Spanish disposal are discussed. The study was car ried out according to the Koch-Steinegger test, at the temperature of 40 de grees C during a period of 365 days. Samples of a specific backfilling fly ash-pozzolanic-cement mortar. were immersed in a simulated radioactive liqu id waste very rich in sulphate (2.05 M) and sodium (4.1 M) ions. In additio n to the mechanical behavior, the changes of the microstructure characteris tics of the mortar were evaluated by X-ray diffraction (XRD), mercury intru sion porosimetry (MIP) and extracted pore solution analyses. The results sh owed the important role played by the fly ash pozzolanic reactivity which i s activated markedly by the ingress of sulphate and sodium ions towards the porous microstructure. Accordingly, the porosity is strongly refined and t he mechanical properties enhanced. (C) 2000 Elsevier Science Ltd. All right s reserved.