Characterisation of capillary hysteresis in porous building materials by single-sided nuclear magnetic resonance

We propose a model for moisture redistribution in porous building materials, considering capillary hysteresis. The proposed model relies on a newly defined moisture transfer potential, the active moisture content, which replaces the commonly used capillary pressure. While calibration of available hysteresis models requires very time-consuming experiments to assess local capillary pressure during adsorption and desorption processes, the new approach employs a faster procedure based on determination of the local moisture content by single-sided nuclear magnetic resonance (NMR). As a proof of concept, the proposed approach is applied to investigate water uptake and capillary hysteresis in the moisture redistribution process of three exemplary building materials, i.e., autoclaved aerated concrete, calcium silicate and ceramic brick. In a first stage, water uptake without capillary hysteresis is assessed, compared with gravimetric water uptake tests and data from the literature. In a second stage, the effect of capillary hysteresis on the moisture redistribution process is investigated, finding a fair agreement between experimental and numerical results. As future potential applications, the method can be used for predicting important moisture transfer processes affecting durability and sustainability of the built environment, such as driving rain adsorption in a building facade or rising damp.