Physico-chemical Evolution of Geopolymers in Contact with Aggressive Environments 

Alkali-activated materials (AAMs) have been identified as one of the potential low CO2 alternatives (besides blended system with supplementary cementitious materials) to ordinary Portland cement (OPC) towards sustainable construction materials by conversion of several wastes streams into useful products. AAMs are made by mixing aluminosilicates routing from several precursors (e.g. fly ash, blast furnace slag, metakaolin) and alkaline activators (e.g. NaOH, KOH). Geopolymers are considered a sub-group of AAMs with a low calcium system in which alkali aluminosilicate (N-A-S-H) gels with pseudo-zeolitic structure are the main products. Geopolymers consist of an amorphous network of aluminate and silicate tetrahedra sharing bridging oxygen atoms. Though AAMs in general and geopolymers specifically have many potential industrial applications in the field of civil engineering including nuclear waste management, there is a lack of knowledge on and understanding of the (long-term) durability of AAMs under environmental conditions relating to conditioning and disposing a (radioactive) waste stream. This PhD project aims at performing a comprehensive study (combined both experiment and modelling) to assess the evolution of physical and chemical properties of geopolymers in contact with various aggressive environments (representative for certain waste streams). The experimental program focuses on the development and characterization (nano- and microstructure and mineralogy) of reference geopolymer materials compatible with certain waste streams (mainly nitrate containing waste streams with variation of other species in it, e.g. organics, heavy metals), which are then subjected to internal interaction and interface interaction with a waste stream environments. The modelling part focuses on the simulation of the chemico-physical behaviour of geopolymers in an aggressive environment either at the pore-scale or continuum scale using coupled reactive transport codes. Furthermore, the experimental program is used to develop a conceptual model, to derive parameters and to validate the model. Such a model can then be used to assess the long-term evolution of a geopolymer – waste stream system.