Alkali-activated materials (AAMs) are a class of sustainable cements with the potential to substantially lower anthropogenic CO2 emissions associated with the Portland cement manufacturing industry. However, the underlying chemical mechanisms controlling formation, stability and long term degradation of AAMs remain largely elusive due to the heterogeneous and disordered nature of the binders. In this talk I will outline how we use atomistic simulations and synchrotron-based X-ray pair distribution function (PDF) analysis to investigate the chemical mechanisms at play in AAMs. To assess gel/binder stability, we have used density functional theory (DFT) to investigate the influence of alkali substitution on the structure and thermodynamics of a model system for calcium-alumino-silicate-hydrate (C-A-S-H) gel, 14Å tobermorite. The results provide important new information on the impact of alkali substitution in this model gel system, and insight on the structural arrangements present in sodium-substituted C-A-S-H gels. Moreover, I will present our recent work on the influence of nano-zinc oxide on the kinetics of AAM formation, where the molecular mechanism responsible for retardation of the alkali-activation reaction has been elucidated using in situ X-ray PDF analysis and isothermal calorimetry. By tracking the evolution of specific atom-atom correlations, the intermediate metastable zinc-containing phase has been identified, revealing that a calcium zincate phase is responsible for retardation of the reaction in a slag-containing AAM. Given that zinc has no effect on a fly ash-containing AAM (i.e., sodium-alumino-silicate-hydrate gel), these results reveal that the type of gel growth can be manipulated using zinc to obtain the desired properties.
Seminars are open to alumni, friends of the Department, and the general public.