Why sorption hysteresis in tobermorite is limited

Molecular simulations are performed to decipher the nanoscale processes associated with water sorption in tobermorite, a microporous phase that functions as the binder in autoclaved aerated cement composites. Merlino's cross-linked tobermorite 11 Å is studied. We show that there is no hysteresis in bulk tobermorite at the molecular scale because the zeolitic cavities occupied by water are smaller than the critical pore size for hysteresis disappearance, and upon sorption, tobermorite 11 Å shows virtually no volume change. These effects combined explain why hysteresis under sorption in tobermorite is limited. Similar explanation could also explain absence of significant hysteresis in some layered double hydroxides present in cement systems.