Understanding water vapor sorption hysteresis and scanning behaviors of hardened cement pastes: Experiments and modeling

The water vapor sorption is a potent characterizing technique for the hygro-properties and nano -structures of cement -based materials. However, limited attention has been paid to the scanning curves cutting across the hysteresis region. This paper investigates comprehensively the hysteretic and scanning behaviors of water vapor sorption for hardened cement pastes with usual binders including Portland cement, fly ash, and slag. The reversibility of sorption paths is fully explored and the total hysteresis is attributed to the substrate deformation, the cavitation and the pore blocking. The lowest relative humidity (RH) at which the samples have ever been put into equilibrium is decisive for the subsequent scanning behaviors. This moisture -history dependence is mainly due to the emptying of the confined macropores which cannot be refilled through vapor condensation at 98%RH. Based on these findings, an improved yet concise model of sorption hysteresis and scanning curves is proposed and validated.