Capillary Forces and Sorption Hysteresis of Cement Pastes with Small Slit Pores

Abstract

Cement-based materials often display an extraordinarily pronounced hysteresis of water sorption isotherms, even at low vapor pressures. This hysteresis is reflected in the volume change of the solid skeleton. To explain these observations, we propose a simple mechanism based on strong capillary forces in slit pores. Condensed water can exert capillary forces that change the volume of pores which are embedded in elastic solids. A macroscopic model predicts a pronounced sorption hysteresis for soft materials with narrow slit-shaped pores. The proposed mechanism can also be the origin of hysteresis in more rigid materials such as hardened cement pastes, which have a large fraction of micropores.