ORIGINAL ARTICLE Diffusivity evolution under decalcification: influence of aggregate natures and cement type Ce ´line Perlot • Myriam Carcasse `s • Je ´ro ˆme Verdier Received: 22 September 2011 / Accepted: 17 August 2012 / Published online: 27 September 2012 Ó RILEM 2012 Abstract Since the decalcification of cement paste has been largely reviewed, we focus our studies on the influence of aggregate nature on this phenomenon in relation to the type of cement used, Ordinary Portland Cement or blended cement with fly ash and slag. Some characteristics of similar mortar mixtures where only aggregate nature differs (lime and siliceous sand) are therefore compared for the two types of cement before and after chemical decalcification induced by ammo- nium nitrate attack: mechanical strength, microstruc- ture (porosity observed by mercury intrusion and profiles of oxide content trough degraded and sound zones determined by electronic microprobe analysis), transport properties (chloride ions diffusivity, gas and water permeabilities). The characterization of sound mortars underlines that siliceous aggregates promote less porous cementitious matrix. The duplication of ammonium nitrate attacks on same material allows testing the experimental parameters governing the degradation. The flows of calcium leached, the microstructure and the evolution of transport proper- ties with decalcification suggest that limestone aggre- gates are not inert material. Consequently, for the mortars incorporating siliceous sand, the cementitious matrix is more decalcified and this leads to an amplification of ionic transports, especially through blended cement paste. Keywords Decalcification Á Aggregate natures Á Blended cement Á Microstructure Á Transport properties 1 Introduction The repository in deep geologic formation is a potential issue considered for the storage of nuclear waste in France by the ANDRA (National Radioactive Waste Management Agency). Given the very long life duration of the radio- elements (thousands of years), the engineering barrier system (EBS) has to maintain confinement properties at least over such periods. The exceptional service life of this structure involves taking into account all the interactions between the host formation and the EBS that could affect the durability and more particularly the phenomena of alteration, usually neglected because very slow, such as the leaching induced by contact with underground water. All the design parameters, and especially the concrete’s composi- tion, play a key role in the long term behaviour of the C. Perlot (&) SIAME (EA 4581), Equipe Ge ´omate ´riaux et Structures du Ge ´nie Civil/IPRA FR, Universite ´ de Pau et des Pays de l’Adour, Alle ´e du Parce Montaury, 64600 Anglet, France e-mail: celine.perlot@univ-pau.fr M. Carcasse `s Á J. Verdier Laboratoire Mate ´riaux et Durabilite ´ des Constructions (LMDC, EA 3027), INSA-UPS Ge ´nie Civil Complexe scientifique, 135 avenue de Rangueil, 31077 Toulouse Cedex, France Materials and Structures (2013) 46:787–801 DOI 10.1617/s11527-012-9934-y