Practical Model for Predicting Internal Relative Humidity of Concrete Exposed to Drying

Abstract

This paper presents a finite-element model developed to predict concrete drying behavior and internal relative humidity with very simple inputs that are known to engineers and practitioners (concrete mix design and cement Bogue composition). The model is based on an empirical derivation of the sorption isotherm, which is used to deduce the pore size distribution, as well as a derivation of total porosity and pore tortuosity through previously published formulations. Pore size distribution and total porosity are used to determine vapor and liquid water permeability, which is used to solve for moisture transport due to drying. The model is applicable for concrete that is not exposed to self-desiccation and/or wetting and drying cycles. The model is compared with a wide range of published experimental results and found to provide accurate predictions of internal relative humidity with these simple inputs, even in cases where the Bogue composition is not known. Limitations and uncertainties associated with the model are discussed and room for future improvement is suggested.