Impact of carbonation on water transport properties of cement-based materials M. Auroy 1,2,* , S. Poyet 1 , P. Le Bescop 1 , J-M. Torrenti² 1 CEA, DEN, DPC, SECR, Laboratoire d’Etude du Comportement des Bétons et des Argiles, F-91191 Gif-sur-Yvette, France. 2 Université Paris-Est, IFSTTAR, Département Matériaux & Structures, 14-52 Boulevard Newton, F-77447 Marne la Vallée Cedex 2, France. * Corresponding author: martin.auroy@cea.fr Abstract: Cement-based materials would be commonly used for nuclear waste management and, particularly for geological disposal vaults as well as containers in France. Under service conditions, the structures would be subjected to simulta- neous drying and carbonation. Carbonation relates to the reaction between CO 2 and the hydrated cement phases (mainly portlandite and C-S-H). It induces miner- alogical and microstructural changes (due to hydrates dissolution and calcium car- bonate precipitation). It results in transport properties modifications, which can have important consequences on the durability of reinforced concrete structures. Concrete durability is greatly influenced by water: water is necessary for chemical reactions to occur and significantly impacts transport. The evaluation of the un- saturated water transport properties in carbonated materials is then an important issue. That is the aim of this study. A program has been established to assess the water transport properties in carbonated materials. In this context, four mature hardened cement pastes (CEM I, CEM III/A, CEM V/A according to European standards and a Low-pH blend) are carbonated. Accelerated carbonation tests are performed in a specific device, controlling environmental conditions: (i) CO 2 con- tent of 3%, to ensure representativeness of the mineralogical evolution compared to natural carbonation and (ii) 25°C and 55% RH, to optimize carbonation rate. After carbonation, the data needed to describe water transport are evaluated in the framework of simplified approach. Three physical parameters are required: (1) the concrete porosity, (2) the water retention curve and, (3) the effective permeability. The obtained results allow creating link between water transport properties of non- carbonated materials to carbonated ones. They also provide a better understanding of the effect of carbonation on water transport in cementitious materials and thus, complement literature data.