From fiber to wall: PHYSical approach of hygrothermal transfers in BIO-based construction MATerials

Introduction

Bio-based construction materials are air-fiber systems, such as wood, hemp, cellulose, flax, etc., possibly coated with a mineral paste. They represent a promising solution for carbon emission reduction, due to their low production cost and their partial or full recyclability.

Benefits of Bio-based Materials

Moreover, they bring more comfort to the occupants thanks to their moisture-buffering capacity, and they require less energy for heating or cooling. These qualities are obtained through exchanges between water vapor and “bound water,” i.e., water absorbed in the solid structure, combined with heat transfers.

Importance of Understanding Hygrothermal Transfers

Consequently, understanding and predicting water and heat (hygrothermal) transfers in such materials is essential to:

1. Selecting them appropriately
2. Adjusting their conditions of use
3. Designing innovative materials

However, the current analysis of their performance is generally based on limited evaluations at a global scale or via macroscopic models lacking physical information.

Proposed Approach

My idea is instead to open the black box and start from the fiber scale, to explicitly describe the internal physical processes at this scale, including:

• Sorption dynamics
• Bound water diffusion
• Fiber configuration

Then, I will progressively complete and extend this approach to full-scale materials. This can be used to build for the first time a generic description, understanding, and modeling of hygrothermal phenomena in bio-based construction materials.

Experimental Innovations

This physical description will be supported and enriched by several experimental innovations. Notably, internal measurements of the spatial distribution of moisture content and temperature in time will be obtained from non-invasive time-resolved magnetic resonance imaging (MRI), which can be used to validate the models and determine diffusion properties in an unequivocal way.

Development of Open-source Software

Finally, I will develop an open-source software predicting hygrothermal characteristics and performance based on material characteristics and history of ambient conditions.