Isothermal Adsorption Model of Cyclic Water Vapor Adsorption and Desorption for the Whole Range of Relative Humidity for Concrete Material

The water vapor adsorption isothermal model for concrete materials enables the analysis of microstructural characteristics and an understanding of the material’s hygroscopic performance. In this study, the cyclic water vapor adsorption characteristics of concrete materials were investigated under normal temperature and pressure conditions at ambient humidity levels of 11.7%, 40.3%, 59.5%, 76.6%, and 100%. By monitoring the cyclic water vapor adsorption process, it is found that water vapor concentration difference in ambient humidity is the primary driving force for water content exchange and transmission between concrete materials and the external environment. Different from microporous materials, the critical relative humidity for capillary condensation of concrete materials is approximately at 60%. Based on the whole range relative humidity of water vapor adsorption experimental data, a modified model is proposed of the whole range of relative humidity for concrete material.