A model for elucidating the contributions of meso- and macropores to water sorption and strain in cementitious materials

Abstract

Hardened cement paste and concrete have a wide pore size distribution. Micro-, meso- and macropores can contribute to water sorption isotherms. Modifying a model for Vycor glass, we describe the impact of meso- and macropores in cementitious materials on sorption, swelling and shrinkage by varying relative humidity. Swelling and shrinkage isotherms can be compared with experimental data for autoclaved aerated concrete (AAC). Apart from delayed capillary condensation due to metastable adsorbed films, trapped water in the pore network promotes the appearance of enlarged hysteresis loops in plots of linear strain versus relative humidity. The model is potentially capable of predicting the contributions of meso- and macropores to the humidity-dependent strain in ordinary Portland cement paste (OPC). But in this case a comparison with experimental results turns out to be more difficult, because sorption in slit-like micropores associated with low pressure hysteresis is the main source of the observed strain in OPC.