Ettringite hysteresis under sorption from molecular simulations

The response of ettringite under sorption is critical for the utilization of this mineral as an energy storage material and to understand the concrete durability problems associated with ettringite formation. We report molecular simulations directly sampling the osmotic ensemble to understand the sorption processes and structural changes in ettringite-metaettringite transition. Desorption branch and sorption-induced volume changes from simulations agree with the experiments. The structural changes at low relative humidity are analyzed, revealing for the first time details of metaettringite structure. The reversibility under sorption observed experimentally is captured by simulation in the ettringite domain. The reversibility in the conversion of metaettringite into ettringite is not captured by the direct simulations in the osmotic ensemble due to the large volume changes associated with ettringite desorption. Finally, we discuss the role of hydrogen bonds on the hysteresis in ettringite.

Automated summary

The study examines the sorption response of ettringite and metaettringite through molecular simulations and experimental results to understand their structural changes and phase transition processes. Details of the metaettringite structure are revealed for the first time at low relative humidity. The simulations show that the conversion of metaettringite into ettringite exhibits reversibility, while the large volume changes associated with ettringite desorption are not captured in the direct simulations in the osmotic ensemble.