Diaz Caselles, Laura, Laboratoire Matériaux et Durabilité des constructions (LMDC), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées, Université Paul Sabatier - Toulouse III, Martin Cyr, Julie Hot, Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)
Excavation operations produce several tons of soil generally contaminated by the presence of pollutants. Excavated soil is considered as waste and it can be either sent to landfill or destined for reuse depending on the level of pollution. In any case, soil should be properly treated in order to: (i) decrease the release of pollutants into the environment, and (ii) minimize the problems involved in civil engineering applications due to the reactions between cementitious phases and pollutants. In the context of this thesis, we focused on sulfates and molybdenum (Mo). Concerning sulfates, we considered two main issues: (i) external sulfate attack of concrete structures, which are in direct contact with sulfate-rich soil (e.g. dams, foundations), and (ii) the release of sulfates into solution in addition to the swelling and mechanical strength loss in sulfate-rich soil intended for valorization (e.g. reuse in road construction). In the case of Mo, its release into solution is also a serious concern as it can lead to significant risks for the environment. Therefore, in this thesis, we investigated the reaction of concrete in contact with sulfates, and the stabilization of sulfates by using alternative binders for pollution reduction and for reuse of soil. Additionally, we studied the interaction of Mo with alternative binders and their capacity to stabilize Mo. First, we studied the capacity of seven different concretes to resist external sulfate attack under similar experimental conditions. It was found that ordinary Portland cement had high expansions (>0.1%) due to the formation of ettringite in excess caused by the reaction between aluminates and sulfates. Portland cement without C_3A presented lower expansions but gypsum was found to be responsible of cracking at later ages. Meanwhile, alternative binders had low expansions in the range of 0.01-0.03% explained by the absence of C3A and portlandite, in addition to the formation of ettringite during hydration (case of ettringite binders) and the absence of calcium (case of the geopolymer-based metakaolin). Second, we compared the capacity of four different binders to stabilize sulfates in a sulfate-spiked soil. Binders having high C_3A content led to high volume expansions (>5%) caused by the formation of ettringite in excess. These binders also released heavy metals into solution due to their high clinker content. In contrast, binders containing ground granulated blast furnace slag (GGBS) led to low expansions (0,1%) en raison de la formation d'ettringite en excès provoquée par la réaction entre les aluminates et les sulfates. Pour le ciment Portland sans C_3A, des expansions plus faibles ont été mesurées, mais l'apparition de fissures à plus long terme a été attribuée à la formation de gypse. Par ailleurs, les liants alternatifs ont présenté de faibles expansions, de l'ordre de 0,01 à 0,03%, expliquées par l'absence de C_3A et de portlandite, en plus de la formation d'ettringite lors de l'hydratation (cas des liants ettringitiques) et de l'absence de calcium (cas du géopolymère à base de métakaolin). Dans un deuxième temps, nous avons comparé la capacité de quatre liants à stabiliser les sulfates dans des sols sulfatés. Les liants ayant une teneur élevée en C_3A ont entrainé des expansions élevées (>5%) à cause de la formation d'ettringite en excès. Ces liants ont également rélargué des métaux lourds en solution du fait de leur teneur élevée en clinker. En revanche, les liants contenant du laitier ont conduit à de faibles expansions (