Advancing liquid diffusivity characterization in porous building materials: A novel single-sided NMR approach

Moisture ingress significantly affects the long-term durability and structural integrity of building materials, with consequential implications for hygrothermal behavior, energy efficiency, and indoor air quality. Understanding moisture transport within porous materials is crucial for accurately predicting these associated performance outcomes, wherein liquid diffusivity, a fundamental parameter, plays a vital role in modeling and simulating such transport phenomena. While various techniques exist for determining liquid diffusivity, accurate characterization of liquid diffusivity remains challenging due to methodological limitations like a lack of resolution and size limitations. The single-sided Nuclear Magnetic Resonance (SS-NMR) overcomes these limitations, enabling high-resolution, non-invasive profiling for accurate liquid diffusivity determination. The current work introduces a novel experimental protocol for determining the liquid diffusivity in porous materials using SS-NMR methodology. Leveraging the high resolution of NMR MOUSE (200 μm), this method captures detailed moisture profiles, which are subsequently used to determine liquid diffusivity as a function of water content through Boltzmann transformation. The optimal moisture profiles were modeled using linear regressions with two fitting parameters. Six types of materials were tested, comprising three wood species (fir, spruce, and pine) and three sheathing boards (two glass-mat sheathings and oriented strand board (OSB). Comparative analysis revealed significant differences between the liquid diffusivity values obtained by using the proposed SS-NMR-based methodology and the conventional Künzel empirical approach, which relies on the water absorption coefficient for liquid diffusivity estimation. These findings indicate that the choice of characterization method for liquid diffusivity can profoundly influence subsequent hygrothermal modeling outcomes and post-analysis macro-scale building performance assessments.