Comparative study of methods for estimating liquid diffusivity in earth building materials

Liquid water diffusivity, water retention curve (WRC), and moisture capacity are key material properties for hygrothermal modeling of the building envelope and for building-scale analyses. The extensive and complex nature of existing methods for material properties determination make hygrothermal simulations challenging. This study compares the moisture diffusivity derived from the water retention curve (WRC) with that obtained using the Kießl–Künzel approach. For this purpose, the complete WRC of compressed earthen bricks is experimentally determined using a combination of methods, including the desiccator technique, controlled climate chamber tests, initial saturation conditions, and osmotic methods. The van Genuchten and Kosugi models are then fitted to the retention data. In addition, the saturated hydraulic conductivity is experimentally measured and compared against empirical models commonly used for estimating permeability. This method is compared with the Kießl-Künzel approach, which is based on the water absorption test outlined in the EN ISO 15148 standard. The current study considers two temperature conditions, laboratory temperature (22°C) and high temperature (40°C), to evaluate the influence of temperature on moisture diffusivity. The results indicate that, although the Kießl–Künzel method is generally effective, it shows limitations under both unsaturated and saturated conditions. Liquid diffusivity estimated using the van Genuchten model demonstrated better performance compared to that derived from the Kosugi model, highlighting that the choice of water retention model can significantly influence the shape of the resulting moisture diffusivity curve. The dependency of moisture diffusivity on temperature showed only a minor effect on the estimation of liquid diffusivity. • Moisture diffusivity of compressed earthen brick was estimated using the van Genuchten, Kosugi, and Kießl–Künzel methods. • A complete water retention curve (WRC) was obtained through vapor equilibration and osmotic methods. • The choice of water retention model significantly influenced the shape of the moisture diffusivity profile. • Temperature had only a minor effect on moisture diffusivity.