Sorption hysteresis in hardened cement paste

In hardened cement paste (C-S-H gel), water intercalated between the C-S-H layers can be adsorbed and desorbed by varying relative humidity. Sorption in the interlayer space between the C-S-H sheets is supposed to be responsible for low pressure hysteresis of water sorption isotherms. Additionally, large hysteresis loops also appear in diagrams that depict the humidity-dependent volume change of the paste.

Hysteresis in sorption and volume change diagrams

In contrast to most other porous solids, the volume of the C-S-H gel is larger along the desorption branch (drying) than along the adsorption branch (rewetting). Based on a macroscopic approach, the researchers use a simple model to describe hysteresis in sorption and volume change diagrams. Computed hysteresis loops, which depend on the lateral extension of the interlayer spaces, are similar to loops observed experimentally.

The study is published in: Cement and Concrete Research Volume 123, September 2019, 105760.